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Studies into the application of controlled recirculation ventilation in Canadian underground mines Mchaina, David Mhina 1990

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STUDIES INTO THE APPLICATION QP CONTROLLED RiXJlWJJLATION VENTILATION IN CANADIAN UNDERGROUND MINES By DAVID MHXNA MCHAINA B.Sc., university of Zambia, 1982 M.Sc., University of Zambia, 1986 A THESIS SUBMITTED IN PARTIAL FULFILLMENT CF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY I N THE FACULTY OF GRADUATE STUDIES DEPARTMENT OF MINING AND MINERAL PROCESS ENGINEERING We accept this thesis as conforming to the required standard UNIVERSITY CF BRITISH COLUMBIA SEPTEMBER, 1990 (c) DAVID MHINA MCHAINA, 1990 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference" and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of MMPE The University of British Columbia Vancouver, Canada DE-6 (2/88) i i ABSTRACT Increasing energy costs and the need to conserve energy ccinpounded with low mineral prices have prompted some Canadian mines especially potash producers, to examine their operations and identify potential saving methods. Re-using or recirculating a fraction of ventilating a i r may enable these mines to reduce winter heating costs. Gas and dust concentrations were monitored i n the intake and exhaust airways to assess the potential for recirculating exhaust a i r . The results indicate that the mine pollutant concentrations i n potash mines are low and stable. T r i a l recirculation experiments returning 20 - 47% exhaust a i r into the fresh a i r airway did not cause significant increases i n mixed intake pollutant levels. Two types of recirculation systems - namely variable and fixed quantity - are developed. Detailed designs of recirculation systems for Central Canada Potash of Noranda Minerals Inc. and Rocanville Division, Potash Corporation of Saskatchewan are discussed and recommendations made for the selection and positioning of on-line monitoring, control and telemetry systems. A controlled recirculation system conceptual design for the H-W mine i s given. The economic payback periods for systems proposed for Rocanville Division and CCP are 2 and 3 years respectively. Recirculation percentages of 30%, 64.4% and 23% are feasible for CCP, Rocanville Division and the H-W mine. • a • 1 1 1 The recirculation percentages for the proposed systems were determined using A i r Quality Index c r i t e r i a . Dust deposition studies conducted at CCP i n return airways indicate that 65% of dust by weight i s deposited within a distance of 550 metres from the face. In terms of dust and other contaminant conditions i n the return airways, i t can be concluded that there i s potential for use of recirculation i n the face area. Guidelines for recirculation systems i n gassy and dusty mines are developed. The main features for these recirculation system design guidelines are safety, economic gain, and system performance. The author's a t t r i b u t i o n to ventilation i s i n the use of controlled recirculation to reduce winter heating costs and increase underground airflow, also the guidelines developed for recirculation i n gassy and dusty mines. The overall conclusion i s that controlled recirculation i s a practical method of reducing winter heating cost and/or increasing mine airflows. The financial potential and technology to implement a working system exist. i v TABLE OP CONTENTS j Page ABSTRACT i i LIST OF TABLES x v i i LIST OF ILLUSTRATIONS Xxii> ACKNOWLEDGEMENT xxxii CHAPTER 1. INTRODUCTION 1 1.1 DEFINITION GF CONTROLLED RECIRCULATION . . .. 2 1.2 CONTRIBUTION TO KNOWLEDGE 4 1.3 THE RESEARCH PROPOSAL 4 l . l . l Statement of the Problem 5 1.4 OBJECTIVES OF THE PROJECT 6 1.5 BACKGROUND 7 1.5.1 Winter Heating and Ventilation Costs i n Canadian Mines 8 1.5.2 Ventilation Problems at Rocanville Division and Central Canada Potash Mines 11 1.5.2.1 Rocanville Division of Potash Corporation of Saskatchewan (PCS) 11 1.5.2.2 Central Canada Potash (CCP) 13 V Page CHAPTER 1.5.3 The Regulatory Requirements for Adequate Ventilation 14 1.5.4 Heating Methods 16 1.5.4.1 Advantages and Disadvantages of Heating Methods 17 1.5.5 Heat Recovery Methods 18 1.5.6 General Canadian Ventilation Requirement c r i t e r i a 20 1.5.7 Provision of Adequate Ventilation and Subsequent Development with Increasing Ventilation Requirements 24 1.5.7.1 Main Surface and underground Booster Fans * 26 1.5.7.2 Resistance Reduction .. 29 1.5.7.2.1 Increasing Roadway Sizes 30 1.5.7.2.2 Improved Roadway Lining 31 Page 1.5.7.2.3 Duplication of Major Airways 32 1.5.7.2.4 Construction of Shafts, Raises and Drifts ... 33 1.5.8 controlled Recirculation of Mine Exhaust A i r to Reduce Winter Heating Costs 33 1.5.9 Controlled Recirculation of Mine Exhaust A i r to Increase Underground Airflows .... 35 1.6 SUMMARY 35 CHAPTER 2. A REVIEW OF CONTROLLED RECTJ^CDXATION AND RELATED ISSUES 37 2.1 INI3?ODDCTION 37 2.2 HISTORICAL BACKGROUND OF OUN1W3LLED RECIRCULATION 37 2.3 BENEFITS OF CONIROLLED RECIRCULATION 48 2.3.1 Reduction i n Heating Costs 48 2.3.2 Increased Face Airflows 49 2.3.3 Reduction i n Power Costs 50 2.4 PROBLEMS IN APPLYING CDNTROT.LFT) REOToCULATION SYSTEMS 51 v i i Page 2.5 MINE AIR, ITS CONSTITUENTS AND REGULATIONS CONTROLLING ITS QUALITY 53 2.6 SOURCES OF HARMFULL IMPURITIES IN THE MINE .... 57 2.7 CONTROL METHODS AND REMOVAL OF POLLUTANTS 59 2.7.1 Dilution 59 2.7.2 Emisision Control Hardware 61 2.7.3 Gas and Vapour Removal Processes 64 2.7.3.1 Physical Absorption and Adsorption 64 2.7.3.2 Solubility of Gases 65 2.7.3.3 Oxidation of Gases 66 2.7.3.4 Chemical Reactions 71 2.7.4 Particulate Matter Removal 73 2.7.4.1 Gravity Separation 73 2.7.4.2 Centrifugal Methods 74 2.7.4.3 Filt r a t i o n 75 2.7.4.4 Electrostatic Precipitators ... 76 2.7.4.5 Wet scrubbers 77 2.7.5 Sedimentation 78 2.7.5.1 Gravitational Settling 78 2.7.5.2 Inertial Settling 82 2.7.5.3 Diffusion 82 2.7.5.4 Agglomeration 83 v i i i Page 2.7.6 Dust Ignition Control Methods 85 - CHAPTER 3. REVIEW OF TYPICAL CANADIAN AND SOUTH AFRICAN MINE ENVIRONMENTAL CONDITIONS 86 3.10 INTRODUCTION 86 3.20 PRINCIPLES OF CONTROLLED RECIRCULATION 89 3.2.1 RECIRCULATION FACTOR, F 104 3.2.2 RECIRCULATION FAN SITING 104 3.30 EVALUATION OF CHANGES INDUCED BY THE INTRODUCTION OF RECIRCULATORY VENTILATION SYSTEMS 107 3.3.1 Gaseous Pollutants 107 3.3.2 Particulate Matter 109 3.40 SUMMARY AND INITIAL CONCLUSIONS I l l CHAPTER 4. APPLICATION OF CONTROLLED RECIRCULATION OF MINE EXHAUST AIR IN POTASH MINES AND METAL MINES 112 4.1 UNDERGROUND MINE EXHAUST AIR RECIRCULATION DECISION LOGIC 112 ix Page j / 4.2 FEASIBILITY OF REXIIRCOLATIMG MINE EXHAUST AIR IN POTASH AND METAL MINES 113 4.2.1 Questionnaire Survey 115 4.2.2 Requirement of A i r Quality Survey for Controlled Recirculation 116 4.2.3 Experimental Program and Methods 117 4.2.3.1 Gas Sampling 117 4.2.3.2 Particulate Sampling 120 4.2.3.2.1 Gravimetric Sampling 120 4.2.3.2.2 Instantaneous Sampling 126 4.2.3.2.3 Isokinetic Sampling 126 4.2.3.2.4 Settled Dust 127 4.2.4 Instruments and Materials 128 4.2.4.1 Calibration of Instruments .... 130 4.2.4.1.1 Gas Analyser Calibration 130 4.2.4.1.2 Dust Pumps Calibration 131 4.2.4.1.3 Digital Dust Indicator Calibration 132 4.2.4.1.4 Anemometer Calibration 132 X Page 4.2.5 underground Thermodynamic Survey and Network Analysis 133 4.2.6 Temperature Profiles 134 4.2.7 T r i a l Recirculation Tests 135 4.2.7.1 Central Canada Potash Division 135 4.2.7.2 Rocanville Division of PCS .. 138 4.2.8 Sources of Errors 141 4.3 CONTROL AND MONITORING SYSTEM SELECTION .... 141 4.3.1 Sensors 142 4.3.2 Fire Detection 144 4.3.3 Environmental Monitoring System 145 4.3.4 Telemetry and Control Devices 146 4.3.5 Fire Doors 147 4.3.6 I n i t i a l Designs of Recirculation Systems 148 4.3.7 Detailed Design of Recirculation Systems 149 x i / " • CHAPTER Page 5. EXPERIMENTAL RESULTS AND DISCUSSIONS 150 5.1 INIBCOUCTTON 150 5.2 CENTRAL CANADA POTASH DIVISION OF NORANDA MINERALS INC 151 5.2.1 Dust Sampling 151 5.2.1.1 Respirable Dust Results 151 5.2.1.2 Dust Deposition Studies 153 5.2.1.3 Settled Dust Results 155 5.2.1.4 Dust Size Distribution 156 5.2.2 Discussion 158 5.2.3 Gas Sampling 159 5.2.3.1 Return Station Continuous Gas Sampling 159 5.2.3.2 A i r Conditions With Recirculation 162 5.2.3.2.1 Gas Monitoring ... 162 5.2.3.2.2 Tedlar Bag Sampling 163 5.2.4 Intake, Mixed Intake and Return A i r Quantities 163 5.2.4.1 Intake and Return Airflows Without Recirculation 163 x i i Page 5.2.4.2 Airflows With Recirculation 165 5.2.4.3 Discussion 167 5.2.5 Temperature Profiles 169 5.2.6 Mining Equipment Utilization 172 5.3 ROCANVILLE DIVISION OF POTASH CORPORATION OF SASKATCHEWAN 172 5.3.1 Dust Sampling 172 5.3.2 Dust Deposition Studies 174 5.3.1.3 Dust Size Distribution 175 5.3.2 Gas Sampling 179 5.3.3 A i r Ctonditions With Recirculation ... 179 5.3.4 Mine Wide A i r Quality Survey 184 5.3.5 Mining Equipment Utilization 185 5.3.6 Discussion 185 5.3.6.1 Dust 185 5.3.6.2 Gases 186 5.4 QUESTIONNAIRE SURVEY 187 5.4.1 Potash Mine Ventilation Data 187 5.4.2 Effect of Heating Ssytems on Mine A i r Quality 188 5.5 H-W MINE OF WESTMIN RESOURCES LIMITED 193 5.5.1 Dust Sampling 193 x i i i Page 5.5.2 Gas Sampling 195 5.5.2.1 Return and Intake Gas Conditions 195 5.5.2.2 Sulphur Dioxide Monitoring During Actual Stope Blasting 198 5.6 AIR QUALITY IN CANADIAN UNDERGROUND MINES .. . 202 5.7 CONCLUSIONS 206 CHAPTER 6. DESIGN CXMSIDERATIONS FOR CCBITRQLLED RECIRCULATORY SYSTEMS 206 6.1 INTRODUCTION 207 6.2 RECn^CULATION SYSTEM MODELS TO PREDICT WORKER EXPOSURE 209 6.3 SYSTEM DESIGN 213 6.3.1 F i r e Detection 214 6.3.2 Sensors 216 6.3.3 Recirculation Fan 217 6.3.4 Recirculation System Control Doors .. 218 6.3.5 I n i t i a l Design 218 6.3.5.1 Discussions on Sensing Instrumentation 218 Page 6.3.5.2 Discussions With Mine Inspectorates 219 6.4 DESIGN AND INSTALLATION OF RECIRCULATION SYSTEMS 220 6.4.1 Monitoring System 220 6.4.1.1 Proposed Systems ... 221 CHAPTER 7. T H B DEVELOPMENT CF RECIRCULATION SYSTEMS FOR CENTRAL CANADA POTASH AND ROCANVILLE DIVISIONS AND THE H-W MINE 223 7.1 INTRODUCTION 223 7.2 DEVELOPMENT OF GUIDELINES FOR RECIRCULATION SYSTEMS 223 7.3 RECIRCULATION SYSTEMS 224 7.4 CCP DIVISION CF NORANDA MINERALS INC. 230 7.4.1 Recirculation System - Alternative I .. 236 7.4.1.1 Alternative I with Glycol System 236 7.4.1.2 Alternative II with Direct-Fired Natural Gas Burners 241 X V Page 7.4.2 Recirculation System - Alternative n 245 7.4.2.1 Alternative II with Glycol System 245 7.4.2.2 Alternative II with New Heating System 249 7.5 RCCkNvTLLE DIVISION OF POTASH CORPORATION OF SASKATCHEWAN 252 7.6 H-W MINE OF WESTMIN RESOURCES LIMITED 257 CHAPTER 8. SYSTEM DESIGN 262 8.1 PROPOSED RECIRCULATION SYSTEM CHARACTERISTICS 262 8.1.1 Central Canada Potash Division of Noranda Minerals Inc 262 8.1.2 Rocanville Division of Potash Corporation of Saskatchewan 262 8.1.3 H-W Mine of Westmin Resources T . - i m - i frarl 263 8.2 COMMON FEATURES FOR CCP, ROCANVILLE DIVISION AND THE H-W MINE 268 8.2.1 Doors 268 8.2.2 Monitoring and Control System 269 xvi Page 8.3 COMMISSIONING AND PERFORMANCE EVALUATION OF THE RECIRCULATION SYSTEM 277 8.4 COST ANALYSES FOR CCP AND ROCANVILLE DIVISION SYSTEMS 278 8.4.1 Cost Analysis Example - CCP Recirculation System 279 8.10 TECHNICAL AND SAFETY GUIDELINES 282 CHAPTER 9. CONCLUSIONS AND FURTHER WORK 284 9.1 THE OBJECTIVE OF THIS RESEARCH THESIS 284 9.2 APPLICABILITY CF CONTROLLED RECIRCULATION SYSTEM 284 9.3 BENEFITS OF CONTROLLED RECIRCULATION CF RETURN MINE AIR 287 9.4 SUGGESTIONS FOR FURTHER WORK 289 9.5 CONCLUDING REMARKS 290 REFERENCES ..*.............•...•••••.•••••••.............. 291 APPENDIX 310 x v i i LIST OF TABLES wnmtwr Page 1 Typical Winter Temperatures Representing General Conditions i n Certain Canadian Mining Areas 7 2 Heating and ventilation i n Canadian Mines 8 3 Heating and Ventilation Costs i n Canadian Mines 9 4 Potash Mine Ventilation Data 10 5 Applicable standards and Other Pertinent Limits 15 6 Disadvantages and Advantages of Heating Methods 17 7 Effects of Air Power on the Overall Mine Quantities 28 8 Percentage Reduction i n Resistance With Change i n Cross-Sectional Area 31 9 underground Development Cost Data 34 10 Pollutants at Design Flow Rates Compared to those Before Recirculation 42 11 Environmental Conitions Prior and During Recirculation 43 12 Average Respirable Dust Concentrations Normalized to 1350 Tons/Shift 47 13 Analytical Results of N i t r i c and Carbon Monoxide 47 14 Harmful Gases i n the Underground Mine Atmosphere 55 15 General Air Quality Standards 55 x v i i i Page 16 Gaseous Pollutants of the Underground Mine Atmosphere 58 17 Emission Control Hardware for Diesel Equipment 63 18 NO and NCVj Conversion Values 67 19 Conversion of NO to NOg 68 20 Conversion Rates of N i t r i c Oxide to Nitrogen Dioxide i n A i r Using Dainty and Mogan's Formula 69 21 NO to NC2 Conversion Data 70 22 Particulate A i r Cleaning Devices 74 23 Gravitational Settlement Losses 81 24 Diffusion Losses 84 25 Correction Factor for Temperature 124 26 Correction for Elevation 125 27 Return Air Dust Concentrations - No Recirculation 152 28 Dust Concentration with Recirculation 153 29 Return Concentrations - Miner Cutting 154 30 Dust Levels at Machine 504 155 31 Settled Dust Analytical Results 155 32 Dust Size Distribution 157 33 Normal Return A i r Conditions 161 34 A i r Conditions with Recirculation 162 35 Tedlar Bag Sampling Data 163 36 Normal Intake and Return Airflows 165 Number xtx Number Page 37 Mine Temperatures at Various Locations 170 38 Return and Intake A i r Conditions without Recirculation 171 39 A i r Conditions with Recirculation 171 40 Dust Decay Patterns i n Return Airways 174 41 Dust Size Distribution 178 42 Normal Return A i r Conditions 179 43 A i r Conditions with Recirculation 181 44 A i r Quality Survey with Recirculation 182 45 Mine Wide A i r Quality Conditions 184 46 Mine A i r Heating Data - Rocanville Division 187 47 Heating Systems Used i n Potash Mines 189 48 Winter Average Contaminant Levels 190 49 PCS Allan Division Average Monthly Gas Levels - 1988/89 190 50 Estimated Level of Pollutants i n Mine Ventilation A i r for Various Months 192 51 Estimated Level of Pollutants i n Mine Ventilation A i r for Various Months 192 52 Intake and Return Total Dust Conditions 194 53 Normal Return A i r Conditions - With Pollutants From Production Blasts - 1989 195 54 Effect of Production Blast on the Mine Atmosphere 196 55 Mine Wide Air Conditions 197 Number page 56 Mine Sampling Results 201 57 Gas Sampling Results (K330 stope) 203 58 Canadian Underground Metal Mines Data 204 59 Canadian Underground Mines Ventilation and A i r Heating Data 204 60 A i r Quality i n Canadian Mines 205 61 A i r Conditioning Data for CCP, Rccannville Divisions and the H-W Mine 228 62 Maximum Return Concentration of Pollutants under Various Recirculation Percentages 229 63 Maximum Concentration of Contaminants i n the Airstream from the Collector, Before Mixing With Fresh Air, Cg 231 64 A i r Quality With Various Recirculation Factors - Alternative I 232 65 A i r Quality With Various Recirculation Factors - Alternative II 234 66 Make of Gas and Intake Conditions with Glycol System 236 67 A i r Quality With Various Recirculation Factors - Alternative I 237 68 A i r Quality Indices for Various A i r Passes 240 69 Make of Gas and Intake Conditions - Alternative with Direct Fired Natural Gas Burners 241 • '• . M i i m h o r PaQB 70 A i r Quality With Various Recirculation Factors - Alternative I With Direct Fired Natural Gas Burners 242 71 A i r Quality Indices for Various Air Passes With Direct Fired Natural Gas Burners 243 72 A i r Quality With Various Recirculation Factors - Alternative II - Old System 246 73 A i r Quality Indices for Various A i r Passes - Alternative II With Old Heating System 247 74 A i r Quality With various Recirculation Factors - Alternative II With New Heating System 251 75 A i r Quality Indices for Various Air Passes - Alternative II With New Heating System 252 76 Make of Gas and Intake Conditions 253 77 Rocanville Division A i r Quality Conditions With Various Recirculation Factors 255 78 A i r Quality Indices for Various A i r Passes - Rocanville Division of Potash Corporation of Saskatchewan 256 79 Make of Gas and Intake Conditions - H-W Mine of Westmin Resources Limited 259 80 A i r Quality With various Recirculation Percentages - H-W Mine of Westmin Resources Limited 260 81 Return and Mixed intake A i r Conditions - Recirculation Percentage of 23% 261 82 A i r Quality Indices for various Recirculation Passes - Recirculation Percentage of 23% 261 83 Proposed System's Characteristics for CCP 267 84 Recirculation System Layout Legend 269 85 Recirculation System Sensors 273 86 Conditions for Control Doors Closure 276 87 Ventilation Parameters for CCP and Rocanville Divisions 278 88 Recirculation System Cost Analysis 281 xxxx Page x x i i i LIST QP ILLUSTRATIONS Figure Page 1 Simple Mine-Wide Recirculation System 90 2 Extended D i s t r i c t Recirculation System 91 3 Layout and Definition for Simple D i s t r i c t Recirculation System 93 4 Simple Recirculation Systems 94 5 Wide Scale D i s t r i c t Recirculation System 95 6 D i s t r i c t Recirculation System 96 7 Simple D i s t r i c t Recirculation System 97 8 Mine-Wide Recirculation System - General Configuration for Potash Mines 98 9 Forcing Heading System with Recirculation Overlap 99 10 Exhausting Intake Advance Heading Recirculation System 100 11 Forcing Return Advance Heading Recirculation System 101 12 An Extended Overlap System of Recirculatory Ventilation i n an Intake Adavnce Face 102 13 Normal Ventilation System - Without Recirculation 108 14 Ventilation System with Recirculation 108 15 T r i a l Recirculation Test Location 136 xsriv Figure Page 16 Proposed Recirculation Circuit 137 17 Recirculation System Location 140 18 Proposed Recirculation Circuit - Doors Closed 164 19 Proposed Recirculation Circuit - Doors Open 166 20 Proposed Recirculation c i r c u i t - Doors Open 168 21 PCS Return Airway Dust Deposition Pattern 176 22 PCS Return Airway Dust Deposition Pattern Panel 305 Room 33 177 23 PCS T r i a l Recirculation Location 180 24 Panel 305 A i r Quality Survey (With Recirculation) 183 25 K330 stope Layout - July, 1988 199 26 23-343 Sumps Locality Plan 259 27 Recirculation F e a s i b i l i t y Decision Logic - I n i t i a l Approach 225 28 Design and Assessment of Recirculation Systems 226 29 System Evaluation 227 30 CCP Alternative I - Old System 229 31 CCP Alternative I - New system 244 32 CCP Alternative II - Old System 248 33 CCP Alternative II - New System 250 34 PCS Rocanville Division Recirculation Model 254 35 H-W Mine Recirculation Model 258 36 No. 3 Dr i f t Recirculation System Location 264 37 No. 3 Dr i f t Recirculation System Location 265 Figure XXV Page 38 CCP Recirculation system Layout 270 39 Rocanville Division Recirculation System Layout 271 40 H-W Mine Recirculation System Layout 272 41 CCP Monitoring and Control System 273 42 Rocanville Division Monitoring and Control System 274 43 H-W Mine Monitoring and Control System 275 APPENDIX I 44 CCP Carbon Monoxide Concentration Day Shift - 30/03/88 311 45 CCP Carbon Dioxide Concentration Day Shift - 30/03/88 312 46 CCP N i t r i c Oxide concentration Day Shift 30/03/88 313 47 CCP Nitrogen Dioxide Concentration Day Shift - 30/03/88 314 48 CCP Carbon Monoxide Concentration Night Shift - 30/03/88 315 49 CCP carbon Dioxide Concentration Night Shift - 30/03/88 316 50 CCP N i t r i c Oxide Concentration Night Shift - 30/03/88 317 51 CCP Nitrogen Dioxide Concentration Night Shift - 30/03/88 318 xxvi . f, . CCP Carbon Monoxide Concentration Day Shift - 31/03/88 CCP Carbon Dioxide Concentration Day Shift - 31/03/88 CCP N i t r i c Oxide Concentration Day Shift - 31/03/88 CCP Nitrogen Dioxide Concentration Day Shift - 31/03/88 CCP Carbon Monoxide Concentration Day Shift - 04/04/88 CCP Carbon Dioxide Concentration Day Shift - 04/04/88 CCP N i t r i c Oxide Concentration Day Shift - 04/04/88 CCP Nitrogen Dioxide Concentration Day Shift - 04/04/88 CCP Carbon Monoxide Concentration Night Shift - 04/04/88 CCP Carbon Dioxide Concentration Night Shift - 04/04/88 CCP N i t r i c Oxide Concentration Night Shift - 04/04/88 CCP Nitrogen Dioxide Concentration Night Shift - 04/04/88 • • / X X V 1 1 Figure 64 C9CP Carbon Moncad.de Concentration Day Shift - 06/04/88 65 CCP Carbon Monoxide Concentration Day Shift - 06/04/88 66 CCP Carbon Dioxide Concentration Day Shift - 06/04/88 67 CCP Nitrogen Concentration Day Shift - 06/04/88 68 CCP Carbon Monoxide Concentration Night Shift - 06/04/88 69 CCP Carbon Dioxide Concentration Night Shift - 06/04/88 70 CCP N i t r i c Oxide Concentration Night Shift - 06/04/88 71 CCP Nitrogen Dioxide Concentration Night Shift - 06/04/88 72 CCP Carbon Monoxide Concentration Day Shift - 07/04/88 73 CCP Carbon Dioxide Concentration Day Shift - 07/04/88 74 CCP N i t r i c Oxide Concentration Day Shift - 07/04/88 x x v i i i Figure Page 75 CCP Nitrogen Dioxide Concentration Day Shift - 07/04/88 342 76 CCP Carbon Monoxide Concentration Mixed Intake - 06/04/88 343 77 CCP Carbon Dioxide Concentration Mixed Intake - 06/04/88 344 78 CCP N i t r i c Oxide Concentration Mixed Intake - 06/04/88 345 79 CCP Nitrogen Dioxide Concentration Mixed Intake - 06/04/88 346 80 PCS Carbon Monoxide Concentration Day Shift - 12/04/88 347 81 PCS Carbon Dioxide Concentration Day Shift 12/04/88 348 82 PCS N i t r i c Oxide Concentration Day Shift - 12/04/88 349 83 PCS Nitrogen Dioxide Concentration Day Shift - 12/04/88 350 84 PCS Carbon Monoxide Concentration Night Shift - 12/04/88 351 85 PCS Carbon Dioxide Concentration Night Shift - 12/04/88 352 Figure „ Page 86 PCS N i t r i c Oxide Concentration Night Shift - 12/04/88 353 87 PCS Nitrogen Dioxide Concentration Night Shift - 12/04/88 354 88 Westxnin Carbon Monoxide Concentration Data Day Shift - 24/05/89 255 89 Westmin Carbon Dioxide Concentration Data Day Shift - 24/05/89 256 90 Westmin N i t r i c Oxide Concentration Data Day Shift - 24/05/89 257 91 Westmin Nitrogen Dioxide Concentration Data Day Shift - 24/05/89 258 92 Westmin Sulphur Dioxide Concentration Data Day Shift - 24/05/89 259 93 Westmin Carbon Monoxide Concentration Data Day Shift - 26/05/89 260 94 Westmin Carbon Dioxide Concentration Data Day Shift - 26/05/89 261 95 Westmin N i t r i c Oxide Concentration Data Day Shift - 26/05/89 262 96 Westmin Nitrogen Dioxide Concentration Data Day Shift - 26/05/89 263 Figure XXX P a g e 97 Westmin Sulphur Dioxide Concentration Data Day Shift - 26/05/89 364 98 Westmin Carbon Monoxide Concentration Data Night Shift - 26/05/89 365 99 Westmin Carbon Dioxide Concentration Data Night Shift - 26/05/89 366 100 Westmin N i t r i c Oxide Concentration Data Night Shift - 26/05/89 367 101 Westmin Nitrogen Dioxide Concentration Data Night Shift - 26/05/89 368 102 Westmin Sulphur Dioxide Concentration Data Night Shift - 26/05/89 369 103 Sulphur Dioxide Concentration K330 stope - Panels 7 and 9 - 18/07/88 370 104 Sulphur Dioxide Concentration - 343 Sump Station 371 105 Sulphur Dioxide Concentration 343 Sump - 350 Open Stope - 20/07/88 372 106 Sulphur Dioxide Cencentration K330 Stope, Panel 9 and K337-2C, 21/07/88 373 Figure xxxi Page 107 Sulphur Dioxide Concentration K330 Panel 9 and K337-2C, 21/07/88 374 108 Sulphur Dioxide Concentration K330 Stope - 31/05/88 375 109 Sulphur Dioxide Concentration K330 Stope - 31/05/88 376 x x x i i ACKNOWLEDGEMENTS The author would l i k e t o express h i s a p p r e c i a t i o n t o Management o f the C e n t r a l Canada Potash D i v i s i o n (CCP) o f Noranda M i n e r a l s Inc., Potash C o r p o r a t i o n o f Saskatchewan (PCS) R o c a n v i l l e D i v i s i o n and the H-W Mine o f Westmin Resources f o r p r o v i d i n g a s s i s t a n c e , data and access t o t h e i r mining f a c i l i t i e s . S p e c i a l thanks are extended t o A l a n Coode and Ted Easton o f Mine Department a t CCP and Mike Wooley and J i m Lewis o f PCS f o r p r o v i d i n g guidance and d i r e c t i o n . The author would l i k e t o thank P r o f e s s o r A.E. H a l l f o r p r o v i d i n g the atmosphere o f l e a r n i n g , t h a t he has helped c r e a t e i n the f i e l d s o f underground mine v e n t i l a t i o n and mine s e r v i c e s a t the U n i v e r s i t y o f B r i t i s h Columbia. H i s guidance, encouragement and c o n s t r u c t i v e c r i t i c i s m throughout the study was g r e a t l y a p p r e c i a t e d . The author i s indebted t o h i s Committee Members, Mr. K.E. Mathews, P r o f e s s o r A. Mular, Dr. G. R i c h a r d s , Dr. R. P a k a l n i s and Dr. G. P o l i n g f o r p r o v i d i n g i n v a l u a b l e guidance throughout the study. The f i n a n c i a l support from the Canada Centre f o r M i n e r a l and Energy Technology (CANMET) and the c o o p e r a t i o n of the Mine I n s p e c t o r a t e i n Saskatchewan are g r e a t l y acknowledged. S p e c i a l g r a t i t u d e i s extended t o Washington Musara and B i l l Goldbeck f o r t h e i r a s s i s t a n c e i n r e v i e w i n g p a r t s o f the t e x t . Thanks are extended t o h i s daughter, Menhina and h i s son, H i z a . The author wishes t o acknowledge the devoted support o f h i s w i f e , Grace, throughout the study program. T h i s t h e s i s i s d e d i c a t e d t o Mrs. Grace Mchaina. CHAPTER 1 / INTRODUCTION The majority of the Canadian mines are located i n cold areas with winter temperatures ranging from zero degrees Celsius down to minus 51. Most of these mines, with the exception of a few operations i n permafrost, pre-heat their intake ventilation a i r to prevent freezing of airways and for the comfort of employees. Heating i s expensive despite the relatively low energy costs i n Canada. Hall (1986) indicated that the cost of heating each cubic metre of a i r circulated per second can exceed $ 2,000 per annum, depending cn the heating method employed. In the Canadian potash industry, the average annual heating cost per cubic metre per second of underground ventilating a i r i s $ 1,620 (Hall et a l . , 1988). Increasing energy costs and the need to conserve energy coupled with low mineral prices have prompted the Canadian mining industry to control their costs to remain i n production. Ventilation, heating and a i r conditioning account for a significant part of the production costs i n many Canadian mines. This has resulted i n heating costs and methods being reviewed. Several methods of reducing mine a i r heating costs exist. The caanonly used methods include:- e l e c t r i c heaters, propane or natural gas burners, ice s topes, dual fuel installations, gas heated steam glycol systems and controlled recirculation of used mine a i r . The latter i s a i r which has been circulated through the mine already and i s also called return or exhaust a i r i n mine ventilation literature. 2 1.1 DEFINITION OF CONTROLLED RECIRCULATION Mine a i r recirculation involves a p a r t i a l re-use of warm a i r that i s normally expelled from the mine. A portion of exhaust a i r i s fed back into the fresh a i r supply before i t leaves the underground workings. When a i r i s recirculated, the a i r re-entering a working place carries back; part or a l l of the contaminants that have already been produced i n that place. The concentrations of the contaminants could build up indefinitely i f the recirculation i s i n a self contained cir c u i t . I f the recirculation i s not i n closed c i r c u i t and at the same time the re-entering a i r i s continuously mixed with an adequate fresh a i r flow, the concentration of the contaminant at any point i n the recirculating c i r c u i t doesnot build up indefinitely and stabilizes at a limiting value. Mine ventilation circuits are open and hence recirculation ventilation doesnot lead to contaminant build-up i n the mine environment. The concentration of contaminant depends mainly on the rate of pollutant generation into the area and the volume flow rate of fresh airflow through i t . Under controlled conditions, the quality of fresh a i r i s not compromised by the addition of exhaust a i r . If recirculation i s adopted for reducing heating costs, the result may be a reduction i n intake a i r requiring natural gas heating while maintaining the same quantity of a i r to the working faces. Controlled recirculation of mine a i r provides a means of reducing heating costs. There are three ways of achieving t h i s . The f i r s t approach i s to keep the intake a i r quantity constant and recirculate exhaust a i r through a surface connection. This provides direct heating of the intake a i r by reclaiming exhaust heat. The second approach i s to reduce the intake a i r quantity and to recirculate an equivalent exhaust quantity through an underground connection. The thi r d approach i s to keep the intake a i r quantity constant and to recirculate a portion of the return a i r to increase mine a i r flow. The second and third alternatives, form the basis of this thesis. When mine ventilation systems become complex due to either high mining rates or other mining conditions, i t i s increasingly d i f f i c u l t to supply fresh a i r to the production face. Canadian potash mine ventilation systems are typical examples of mines with such problems. A high percentage of fresh a i r entering the mine does not reach the working face because i t short ci r c u i t s through stoppings, doors and old workings. This a i r i s exhausted without being u t i l i z e d at the workface. Many of these mines have ventilation problems caused by increased leakages which decrease volumetric efficiency and thus increase the power costs. These problems can be offset by reducing the mine resistance, improving the volumetric efficiency of the mine or by installing booster fans to reduce leakage. Installation of a booster fan at the appropriate point i n a c i r c u i t can reduce the difference i n pressure between the intake and return airways, which can significantly reduce leakage. The above' options are often expensive undertakings that many potash producers cannot afford. From these considerations i t i s clear that there i s a need for a new alternative ventilation solution that can be installed i n a relatively short period of time with minimum capital expenditure. Controlled recirculation warrants consideration as a solution to ventilation problems in Canadian mines where exhaust a i r quality i s good enough for the a i r to be re-used. 1.2 CCNTRlBU'riON TO KNOWLEDGE Prior to this project, conditions and quality of exhaust a i r were unknown and amount of diesel operation i n potash mines were uncertain and therefore potential controlled recirculation was not known. This project comprised studies to determine these factors and investigations on dust deposition patterns and temperature profiles. The determination of these factors i s a significant contribution to knowledge. 1.3 THE RESEARCH PROPOSAL The research thesis i s an investigation of the use of controlled recirculation of exhaust mine a i r to the intake, as a means of reducing winter heating costs and/ or increasing airflows i n Canadian underground minpg with particular reference to conditions i n potash mines. The goal i s to reduce winter heating costs, increase face airflows anf l at the same time maintain the a i r quality and safety standards. Two types of recirculation systems are considered, namely variable and fixed quantity recirculation schemes for gassy and non-gassy mines respectively. The fixed quantity recirculation systems are applicable to potash mines while variable quantity schemes are suitable for metal mines. Metal mines blast and have significant transient diesel a c t i v i t y . A i r quality i n potash mines i s relatively constant thhroughout shift s and extra cost of variable quantity system i s not economically j u s t i f i e d . Two recirculation systems are developed for Central Canada Potash Division of Noranda Minerals, Inc., and Rocanville Division of Potash Corporation of Saskatchewan respectively. The recirculation systems for these two mines involved fe a s i b i l t y studies and design considerations. The design for the variable quantity recirculation systems i s based on the a i r quality data obtained at the H-w mine of Westmin Resources Limited. 1.3.1 Statement of the Problem This thesis examines two ventilation problems facing Canadian mines. These are the high ventilation a i r heating costs during winter months and a lack of adequate face airflows. A l l Canadian potash mines are facing these problems. A possible solution to these problems i s the controlled recirculation of a portion of the main exhaust airflow. The method been applied with great success in B r i t i s h coal mines and South African gold mines (Burton et a l . , 1984). In B r i t i s h coal m-in^ controlled recirculation i s used to maintain face a i r velocities while reducing the a i r volumes required to pass through the main airways connecting the shafts. This reduces power requirements and maintains airway velocities at levels which prevent the raising of dust clouds. There i s a need for an alternative ventilation solution that can be installed i n a relatively short period of time with minimal capital expenditure. The principal hypothesis defended i n this thesis i s stated as follows:- " Controlled recirculation has good potential for application i n Canadian mines to reduce winter heating costs and/or to increase a i r flows without ccitpromizing a i r quality and safety standards." 1.4 OBJECTIVES QP THE PROJECT The main objectives of the project are: a) To investigate the f e a s i b i l i t y of introducing controlled recirculation i n Canadian mines with particular reference to potash m-infxa and to assess any cost benefits. b) To develop recirculation systems for Noranda's Central Canada Potash and the Rocanville Division of Potash Corporation of Saskatchewan. c) To develop guidelines for recirculation systems i n gassy and dusty mines. This w i l l include the design of a monitoring system for the control of variable quantity recirculation systems. 1.5 BACKGROUND Typical winter temperatures experienced by some m-i™** i n four Canadian provinces and tne North West Territories (N.W.T.) are shown i n Table 1. Table 1. Typical Winter Temperatures Representing General Conditions i n certain Canadian Mining Areas (After Hall, et a l . , 1988) Province Mine Location Temperature(°C) Number of Mean Lew Winter Days When Heating i s required B r i t i s h Columbia Kimberley - 7 -29 90 Saskatchewan Vanscoy -12 -45 120 Saskatchewan Colcnsay -14 N/A 120 Ontario Sudbury -12 -45 120 Manitoba Thompson -22 -50 120 N.W.T Yellowknife -23 -51 120 Metal mines i n these provinces usually heat their a i r to between l and 2 °C. Potash mine shafts pass through water bearing dolomitic limestone and are lined with steel taibbing to prevent water entering the shaft. These mines heat their a i r to above 10 °C to prevent contraction of the linings, which would allow water ingress into the shaft. Mine heating consumes between 40 and 50 kW of heating per cubic metre circulated i n a typical mine (Hall et a l . , 1988). • /: 8 1.5.1 Winter Heating and Ventilation Costs i n Canadian Mines In Canada, the most significant cost related to ventilation i s that of mine fresh a i r heating. A survey of Canadian underground metal mines investigated the cost of heating and ventilation (Hall, 1985). Hall indicated that the cost can oxcood $ 2,000 per annum for each m3/s of a i r circulated. Tables 2 and 3 set out the operating data for 10 large mines employing a variety of heating methods. Table 2. Heating and Ventilation i n Canadian Mines (After Hall, 1985) ine Quantity Pressure Fan Temp- Heating Gas Heating Power erature Days Quantity Sytems m3/s kPa xw °c L/Day A 165 2.5 750 -20 100 8,300 Propane B 210 1.8 540 -10 160 10,100 Propane C 990 3.1 4,300 -26 120 50,000 Propane D 310 N/A 3,500 - 4 160 14,000 Natural Gas E 250 0.5 180 - 9 140 13,300 Propane F 440 1.5 1,200 -11 160 30,500 Propane 6 2,280 2.5 8,900 -14 120 11,500 Propane H 225 N/A 1,130 - 9 120 6,300 Propane* I 220 N/A 800 -14 140 3,600 Propane J 415 N/A 1340 -30 140 12,800 Propane+ * Propane and E l e c t r i c a l Heaters - 270 kW ** Propane and O i l Heaters (4800 l i t r e s per day) + Propane and E l e c t r i c a l Heaters (4300 kW per Day) Table 3. Heating and Ventilation Costs i n Canadian Mines (After Hall, 1985) Mine Quantity Ventil- Heating Total Cost per m3/s ation Cost Cost Ventil- Heating Total Cost ation m3/s $ $ $ $ $ $ A 165 131,400 259,800 390,800 796 1,572 2,368 B 210 94,600 505,000 599,600 450 2,405 2,855 C 990 753,400 1,875,000 2,628,400 761 1,894 2,655 D 310 613,200 300,000 913,200 1,978 968 2,946 E 250 31,500 581,900 613,400 126 2,328 2,944 P 440 210,200 1,525,000 1,735,200 478 3,466 3,944 6 2,280 1, ,559,300 4,312,500 5,871,800 684 1,891 2,575 H 225 198,000 255,000 453,000 800 1,133 2,013 I 220 140,200 567,000 707,200 637 2,577 3,214 J 415 234,800 1,185,000 1,419,800 566 2,855 3,421 ' ' 10 In the Canadian potash i w i w i w r r industry the cost of heating underground ventilating a i r ranges from $ 27,000 to $ 350,000 per annum. The average annual heating cost per m3/s of underground ventilating a i r exceeds $ 1,600 i n these mines. The potash mines ventilation data i s summarized i n Table 4. Table 4. Potash Mine Ventilation Data Mine A i r Distance Annual Diesel Fewer Exhaust Air -Quantity Between Heating Units Temp- Dust Relative Shafts Cost erature Content Humidity (m3/s) (m) ($) (kW) <°C) (mg/m3) (%) A 118 100 350,000 69 4,605 29.00 4.50 35.00 B 143 152 120,000 95 5,786 15.00 10.00 100.00 C 113 137 270,000 61 4,027 20.00 10.00 80.00 D 118 152 200,000 70 4,041 28.00 5.00 55.00 E 98 300 27,000 110 6,247 20.00 0.80 35.00 P 143 145 194,000 70 3,861 29.00 10.00 35.00 Total 719 986 1, 161,000 475 28,567 141.00 40.30 340.00 Mean 120 164 193,500 79 4,761 23.50 6.70 57.00 Potash mines use direct f i r e d natural gas heaters or steam/glycol heat transfer systems. ' 11 1.5.2 Ventilation Problems at Rocanville Division and Central Canada Potash Mines The t o t a l a i r quantity supplied i n these ™"iri<*g i s based on the t o t a l installed power of the underground diesel machines. The mines are forcedto reduce their intake a i r quantities to the underground workings when the outside a i r temperature drops below minus 40 °C because the heating systems are unable to maintain minimum temperature, which i s required to protect the steel shaft lining. 1.5.2.1 Rocanville Division of Potash Corporation of Saskatchewan Ventilation a i r at Rocanville Division i s circulated through number 2 intake and number 1 exhaust shafts. The intake a i r quantity i s about 143 m3/s. Rocanville Division uses direct f i r e d burners to heat the intake a i r at an annual cost of approximately $ 100,000. Rocanville ventilation d i f f i c u l t i e s during winter cold days may lead to the following conditions: . Freezing of water lines i n No. 2 headframe. . Reduction i n temperature of the fresh airflow to the mine. . Reduction i n a i r quantity supplied from surface i n order to prevent damage to shaft tubbing. In addition, the heating capacities for the direct f i r e d burners are not adequate to heat normal a i r volumes to acceptable temperatures during cold days. The mine a i r heating system i s capable of heating 143 m3/s from -38 to 10 °C. >' ' 12 From past experience, i t has been found that the optimum temperature for maintaining adequate shaft conditions i s between 18.3 and 21 °C (PCS internal memo). These conditions require an increase of a i r heating capacity from the current 28,000 MJ per hour to 40,000 MJ per hour. In order to alleviate cold temperature problems, the following options were available for consideration: a) Installation of higher capacity(40,000 MJ/hour) burners i n the present location. b) Extension of present burners to f u l l width of tunnel and widening of the t»miAi to acccmodate access doors and maintenance area. c) Installation of an additional natural gas li n e and controls. d) Installation of a heat exchanging system with No. 1 exhaust shaft. e) Controlled recirculation system underground with reduced fresh a i r intake. Alternatives a, b and c require large natural gas lines or operation at high pressure. A l l these are major undertakings and costly to i n s t a l l . Alternative d i s feasible but requires special types of heat exchangers because of the corrosive nature of potash dust. The use of plastic heat exchangers (non-metal) i s one possibility of avoiding the corrosion problem. This method was t r i e d at PCS Allan Division and i t proved to be unsuccessful due to a number of operational problems. Controlled recirculation of mine exhaust a i r therefore i s the most attractive alternative for maintaining adequate shaft and underground a i r conditions. 1.5.2.2 > ' 13 Central Canada Potash Ventilation a i r at Central Canada Potash (CCP) i s circulated through number 2 intake and number 1 return shafts respectively. The total intake a i r quantity i s 113 cubic metres per second. The mine uses natural gas to heat steam which i n turn heats glycol which i s pumped to a heating c o i l to heat the intake a i r during the winter at a cost of approximately $ 270,000 per year. CCP has changed i t s heating system to a direct fired burner system. CCP experiences the same problems as those at the Rocanville Division. During very cold days CCP reduces i t s intake a i r quantity. Reducing the a i r quantity to the underground mine workings during cold months i s not recommended since the present total quantity of 113 m3/s i s i n accordance with the Province of Saskatchewan Mines Regulations. This quantity i s based on the installed total power. The mine has 61 diesel units with total capacity of 4027 kW. In addition to winter ventilation and heating, Central Canada Potash and Rocanville Divisions also experience problems i n supplying adequate quantities to the working faces. Both mines have extended ventilation systems divided into d i s t r i c t s supplying individual boring machines. These layouts are similar to longwall coal mine ventilation systems although the potash mines employ room and p i l l a r method. The length of a ventilation d i s t r i c t from the intake shaft to the borer and back to the return shaft can exceed 8000 metres. There are many connections between the intake and return airways in the working d i s t r i c t , resulting i n significant leakage. .. >• ': 14 A number of methods can be considered to overcome these problems. These include: enlargement or duplication of airways, increasing the capacity of the main and booster fans, sinking of s a t e l l i t e shafts and lining of existing airways. The adoption of these solutions may be impractical because of excessive costs. 1.5.3 The Regulatory Requirements for Adequate Ventilation In the design of a recirculation system, one must be concerned with the t$\tm\rsi\ composition and concentration of contaminants i n the a i r . These can be particulates or gases and vapours. Their origin and characteristics w i l l be discussed i n d e t a i l i n the next chapter. nanari-ian mines underground a i r quality requirements are promulgated and enforced by the provincial governments. These regulatory requirements therefore vary from province to province. It i s important therefore to review and to analyse a l l requirements i n terms of these regulations associated with recirculation of mine exhaust a i r . Most m-irving regulations prohibit the re-use of mine exhaust a i r because of the r i s k of uncontrolled recirculation. The mine a i r quality requirements for those Canadian provinces which have potential for recirculation of mine a i r are given i n Table 5 together with limits recommended by the American Conference of Governmental Industrial Hygienists (Anon., 1981; Murray, 1987; Anon., 1978). Most a i r quality standards i n Canada are based to some extent on the American Conference of Governmental Industrial Hygienists (ACGTH) recommended limits (Anon., 1983). 15 Exhaust air quality monitoring in underground mines is not mandate^ in Canada and as a result, there is insufficient literature and data regarding air quality in main return airways. Table 5. Applicable standards and other Pertinent Limits'*' Substance Manitoba Province Ontario Saskatchewan B.C. QUE ACGm CO (ppm) 20 35 25 50 50 50* COj (ppm) 5000 5000 5000 5000 5000 5000 NOg (ppm) 5 3 2 3 - 3 NO (ppm) 25 25 25 25 25 25 SOj (ppm) 5 2 5 5 - 2 Dust (mg/m3) 2 2 10** 2 2 1 Time Weighted Average (TWA) Proposed limit for total dust (Potash mines only) N.W.T. not included in this table because there are no specific concentrations given in the legislation. 16 1.5.4 Heating Methods The commonly used heating methods i n the Canadian mining industry include: e l e c t r i c heaters, propane or natural gas burners, ice stopes, dual fuel installations, gas heated steam - glycol systems and natural heat exchange. Propane or natural gas burners are quite common because of the low fuel and capital cost requirement. Ice stopes use the seasonal temperature variations to reduce heating costs. Ice i s made during winter by spraying water into intake a i r and the latent heat of fusion heats the a i r by 335 kJ per l i t r e of water frozen (Hall et a l . , 1988 and Stachulak, 1989). In spring and summer the higher a i r temperatures melt the ice and the resulting water i s pumped out of the mine. Dual fuel installations (normally electric/natural gas or electric/propane) are used to exploit the low cost e l e c t r i c a l power available i n reduced usage periods between maximum demand loads. Propane or natural gas i s used i n place of the e l e c t r i c a l power at peak el e c t r i c a l demand (Hall, 1988). Gas heated steam - glycol systems use low cost natural gas i n a boiler to produce steam which i s then used to heat glycol circulated through a heating c o i l i n the fresh a i r intake. Natural heat exchange systems consist of a large mass of broken rock (Stachulak, 1989). The broken rock acts as the major heat exchanger, warming the fresh a i r i n winter and cooling the a i r during the summer. / ' 17 1.5.4.1 Advantages and Disadvantages of Heating Methods The advantages and disadvantages of the heating methods are set out i n Table 6. Table 6. Disadvantages and Advantages of Heating Methods Method Advantages Disadvantages E l e c t r i c a l heaters Propane or natural gas heaters Ice stopes Dual fuel Gas heated steam - glycol systems Natural heat exchange systems Clean and easy to control. No CO or COj produced Low fuel and capital cost High energy costs especially during peak demand periods. Increase CO and C 0 2 concentrations i n the mine, have a minimum operating level and are expensive. Have potential f i r e hazard i n the intake. Efficient, l i t t l e Requires large excavations. Mine or no CO or COj pumping capacity may need to be produced. Cost effective for strategic power u t i l i z a t i o n . Avoid e l e c t r i c a l use at peak demand periods. Use low cost gas, does not increase CO and C0_ concentrations i n the intake. Efficient, low cost and l i t t l e or no CO or CO2 produced. increased to cope during spring run-off. Increased CO and 0O2 concentrations i n the mine when propane or natural gas i s used as an alternative. Requires increased capital cost for heat exchanger. Requires large excavations. 1.5.5 Heat Recovery Methods Several methods exist for recovering waste heat i n mi " j u g and the most practical and attractive methods available are: a) Heat recovery from machinery. b) C o i l loop glycol heat exchanger. c) Controlled recirculation. Waste heat from machinery such as compressors and hoisting systems i s being used for heating intake a i r i n Canada. Macassa mine i n Ontario uses underground water to cool the surface mine a i r compressors and the water temperature i s increased to 34 °C. This hot water i s then used to heat the intake a i r to the mine. The system i s limited i n application to mines with a significant quantity of warm water being pumped from underground and pure enough to be used for machinery cooling. This method i s not feasible i n potash mines because the mines are made water tight. Kidd creek mine i n Ontario has a 5 800 kW system that recovers heat from compressor cooling water (Hall, 1988a). Similar systems are used at the Lockerby and Strathcona nickel mines i n Sudbury. Heat transfer from exhaust to intake a i r systems requires the intake and exhaust vents to be close together. Where this i s not possible heat can be transferred to another medium such as brine or glycol, which i s then pumped through insulated pipes to the incoming a i r where the heat i s f i n a l l y transferred to the cold a i r stream. The cost of pipe work and the pipe heat losses determine the economics of the system. Strathcona nickel mine also has a glycol system to recover heat from the exhaust air(McCallum, 1969). The glycol i s pumped through a heat exchanger i n the exhaust a i r and then circulated to a second exchanger i n the intake which heats the a i r entering the mine. The disadvantages of the system are the rapid corrosion of heat exchange c o i l s i n the exhaust a i r and because of the high humidity of the exhaust a i r . Corrosion of heat exchange c o i l s i n potash mines i s a major drawback for use i n these mines. Metal heat exchangers have limited use i n potash and metal mines due to the corrosive nature of potash dust and blasting pollutants. This problem can be overcome to some extent by using plastic or corrosion resistant glass pipes instead of metal heat exchangers. The potash Corporation of Saskatchewan installed p i l o t plastic heat exchangers for a t r i a l system because of corrosion on metal exchangers. The heat exchangers performed below the designed capacity and the project was discontinued. ice forms on the coi l s i f the a i r i s cooled to below 1 °C and this decreases heat transfer. Most mines have intake temperatures down to -30 °C and exhaust a i r temperatures of around 10 °C. i f the intake a i r i s heated to 0 °C, a maximum heat recovery of 25% may be achieved i n these mines. In addition, heat exchangers are limited i n application i n these mines because of low exhaust temperature and high humidity. The system has better economics i n potash mines i f the problem of c o i l corrosion i s eliminated. Inco's Thompson operation calculated a 19 year payback period for a conventional run-round glycol heat recovery system (Hall et a l . , 1987). This long payback curtailed further research efforts. ' 20 Controlled recirculation of exhaust a i r has significant potential for reducing heating costs. I t i s usual to transfer the reclaimed heat directly into the intake a i r without using a heat exchanger. The intake and return airways do not have to be adjacent as long as there i s a suitable existing connection. 1.5.6 General Canadian ventilation Requirement C r i t e r i a The provincial and t e r r i t o r i a l governments are generally responsible for mining legislation and regulations pertaining to the health and safety of the underground worker. The Federal government has jurisdiction over a l l uranium mines and many crown corporations. The certification of m-iT»jTvj equipment and materials employed underground i s provided by the Canadian Explosive Atmosphere Laboratory of the Canadian Centre for Mineral and Energy Technology, CANMET. This laboratory certifies diesel and e l e c t r i c a l equipment intended for use underground i n explosive atmospheres, diesel exhaust emission characteristics and f i r e resistant materials (Dainty and Brown, 1979, 1974). The f i n a l approval, installation, application, specifications and use of the material and equipment i s the responsibilty of the provincial mine inspectors. For those diesel powered units manufactured i n the U.S., the United States Bureau of Mines Schedules 22 and 31 are used for their certification. ' 2 1 Exhaust from diesel engines i s one of the main sources of gaseous pollutants i n underground mines. Diesel engines are the main source of gaseous pollutants i n potash mines. Legislation controlling the use of diesel engines i n operating underground inines varies extensively i n Canada. The most common provision i n a l l regulations, however, i s the specification of an a i r quantity requirement. The required a i r quantity i s expressed i n a number of different ways, namely circulating a i r required i n terms of m3/s per kilowatt (or cfm per brake horsepower) or per vehicle basis. Many Canadian mining provisions require that each vehicle has an engine approved by the Inspectorate. The amount of dilution ventilation required i n some cases i s based on diesel emission data for carbon monoxide, carbon dioxide and oxides of nitrogen (U.S. Federal Regulation, 1976). The formula used to calculate the quantity required to obtain one-half the specified maximum allowable concentration i s : °1 = [ G W /<wa>]/t< ci>/< 0- 5 * ™*i> ~ where, Q_ = volume of dilution a i r for the i - t h contaminant, Mgjjjj = mass flow rate of exhaust, TLV^ = the threshold limit value allowable for the i-th contaminant, C_ = concentration of the i - t h contaminant, and wa = density of a i r at standard conditions. ../'.. ' 22 Values of Q are calculated for each contaminant for each test condition/ and the maximum value of Q among a l l the computed values becomes the minimum a i r requirement for the vehicle. In the case of multiple diesel vehicles i n a working place, the required m-iwiimim a i r quantity formula i s expressed as (MSHA, 1 9 8 1 ) : Qj, = 1 0 0 % Q X + 7 5 % Q 2 . . . + 5 0 % QJJ where, Qj, = t o t a l a i r quantity required, Q 1 = 1 0 0 percent of the permissibility volume rating for the largest rated diesel unit. Q 2 = 7 5 percent of the permissibility volume rating for the next largest rated diesel unit, and Q Q = 5 0 percent of the combined permissibility volume ratings for each additional diesel unit. The method of calculating ventilation level based on a fixed dilution rate per brake horsepower would be satisfactory i f a l l diesel engines had similar emissions. This, however, i s not the case as different engines have emissions that vary up to 4 0 0 percent for a given horsepower (Alcock, 1 9 7 7 ) . It i s for this reason that various Canadian legislations require a comprehensive testing schedule on a l l engines before they are allowed underground. The amount of the various contaminants emitted from a diesel powered unit d i f f e r s depending upon, among other parameters:- engine type and size, amount of engine wear, operating torque and speed, engine maintenance and fuel type, mine layouts, and mining method. ' / 23 The emissions far a particular unit varies significantly during the working s h i f t and the average i s well below the m a x i m u m local cmiaaiem (Morgan and Dainty, 1987). The calculation of ventilation c r i t e r i a using 10O-percent-rated capacity which occurs usually at f u l l load conditions, therefore has a large b u i l t - i n safety factor. The Health Effects Index(HKE) developed by I.W. French and Associates, may be used i n combination with a dilution ratio formula to determine underground ventilation requirements. The index takes into account the combined effects of the mixture of diesel pollutants. The following formula i s proposed for the calculation of the HEI. HEI = (CO) + (NO) + (RCD) + 1.5 rCSCu) + (RCD) 1 * 50 25 2 3 2 + 1.2|-(NQ2 + (RCD) 1 ** 3~ 2 Where, (CO) = Concentration of carbon monoxide i n ppm (NO) = Concentration of n i t r i c oxide i n ppm (RCD) = Concentration of respirable combustion dust i n mg/m3 assumed to include soot plus sulphates - diesel origin (SOj) = Concentration of sulphur dioxide i n ppm (NC^) = Concentration of nitrogen dioxide i n ppm If (*) S O 2 = 0, this term i s omitted I f (**) NOj = 0, this term i s omitted French et a l . i n i t i a l l y considered an index between 3.0 and 4.0 to pose a significant threat to the health of employees. Values i n excess of 4.0 would require more ventilation a i r to be circulated i n order to reduce pollutant levels. An addition of an extra term ([Quartz] / [TLV]) to the equation i s necessary for mines mining ores with a s i l i c a content i n excess of 20 percent. Following review of the original proposal, the HKC i s presented i n a new form called the A i r Quality Index (AQI). The AQI i s now separated into two parts, one for gas concentrations and the other for particulates. A Q I ( G a s ) = (CO) / (TLV-CO) + (NO) / (TLV-NO) + (N0_)/ (TLV-N02) A Q I ( p a r t ) = (RCD) / (TLV-RCD) +[ (SC_) / (TV-SOj) + (RCD) / (TLV-RCD) ] + [(N02)/(TLV-N02) + (RCD) / (TLV-RCD) ] The A Q I s h o u l d not cxcood 1.0 and no individual component should exceed i t s TLV. I t i s recommended that the AQI (particulates) value should not exceed i t s TLV. I f the level of S0 2 or ND2 i s 25% or less of their TLV, they are omitted from the equation. 1.5.7 Provision of Adequate Ventilation and Subsequent Development with Increasing Ventilation Requirements The increasing depth, mining rates, degree of mechanization and distance of working areas from surface connections create an increasing ventilation problem. A l l the factors affect the ventilation system both quantitatively and qualitatively. The use of diesel-powered vehicles uwlerground has increased productivity and lowered operating costs but requires increased quantities of ventilation a i r to be circulated. This i s due to a number of reasons, including: a) Increased number of large openings required by diesel equipment and high mining rates that open up large areas quickly. This i n turn increases overall mine leakage and airway resistances (due to increased airway lengths) which require higher ventilation pressures. b) The mining production requirements to operate several diesel ««f!hiT)pg i n the same m-ira* section significantly increases the ventilation requirements. E l e c t r i c a l l y powered vehicles can reduce heat and pollutant emissions. The use of el e c t r i c a l l y powered vehicles has received attention i n Canada but their reduced mobility has prevented wide-spread adoption of such vehicles. Mine ventilation requirements i n Canadian mines are dictated by occupational health and safety standards at both provincial and federal levels. . /: . 26 The need to provide increased ventilation to improve environmental conditions has led to increasing interest i n searching for economical methods. Dilution ventilation provided by the mine primary ventilation system i s the main protection against the contaminant gases, vapours and particulates i n diesel exhaust. Increasing the fresh a i r quantity to dilute these contaminants to safe limits can be approached i n a number of ways. Possible options to the problem include enlargement or duplication of airways, the use of s a t e l l i t e shafts, use of booster fans and the introduction of controlled recirculation of mine exhaust a i r . 1.5.7.1 Main surface and Underground Booster Fans In a mine system i t i s the available a i r power supplied by the fans, the volumetric efficiency of the network and the resistance that determine the flow characteristics within that system. In order to increase the fresh a i r quantity to the working face, the mine a i r power can be increased by increasing the size and configuration of the main fans. In addition, heavy duty fans, possibly with adequate reserve capacity may be installed. Merely increasing the available a i r power by uprating the existing fans w i l l not necessarily improve the ventilation system's volumetric efficiency. In addition, as mine workings extend, a fan's a b i l i t y to provide adequate ventilation reaches a l i m i t . Increased fan pressure between intake and return can cause increased leakage because of higher pressure differentials and therefore reduce volumetric efficiency below the economic limits. ' . _ / 27 Volumetric Efficiency, = Quantity nf a i r ventilating the working area of a mine system Quantity of a i r circulated by the main fan Mine ventilation costs are proportional to the a i r power. Cost ($ per annum) i s d i r e c t l y proportional to a i r power (RQ3) and hence the ventilation running costs. The a i r power supplied by the main fans i s defined as follows: A i r Power (A.P.) i n Watts = P*Q (Pressure*Quantity) Pressure(P) i n N/m2 = RQ2, R = Resistance = N^/m8 Therefore, A.P. = RQ2*Q = RQ3 TmT«»«i™j the a i r power by 20% and keeping the mine resistance constant w i l l result i n a meager increase i n quantity of about 6%. Doubling the a i r power w i l l increase the quantity by 26%. Table 7 gives quantity values associated with various percentage increases i n a i r power. In a system with main and booster fans, the work load i s shared between the two fans. The pressure produced by the fans w i l l be distributed through the system so reducing leakage and improving the volumetric efficiency. Despite these mentioned benefits booster fans can create control problems, because of power and access requirements to underground remote locations. Table 7. .Effects of A i r Power on the Overall Mine Quantities A i r Power Increase (%) A i r Quantity Increase (%) 10 3.2 20 6.3 30 9.1 40 11.9 50 14.5 60 17.0 70 19.3 80 21.6 90 23.9 100 26.0 1.5.7.2 Resistance Reduction A change of system resistance would affect the available a i r power and the power would not remain constant due to the movement of the operating point on the fan characteristics. The operating point of a wwiw fan i s at the intersection of i t s operating characteristic and the airflow law curve given by: p f = OT *m = p f l&f Where Pm i s the total mine resistance, and P f and Q f are the pressure produced and the quantity passed by the main fan. In order to increase the a i r power available, mine system resistance should be reduced. The following methods of reducing system resistance are commonly used: a) Increase roadway sizes. b) Improve roadway l i n i n g and remove timbering or other obstructions to flow. c) Duplication of major airways to provide p a r a l l e l connections. d) Construction of additional shafts, d r i f t s and raises. 1.5.7.2.1 / increasing Roadway sizes P = RQ2 and R = (K*L*C)/(A3) or R = K*[(C/A 3)]L In order to reduce the resistance, R, for a specific roadway whose length (L) i s defined, either the f r i c t i o n factor K, or the perimeter to area r a t i o must be reduced. 1. K can be reduced by increasing the area. R i s proportional to C/(A3) and i s proportional to (1)/(A 5/ 2) Therefore R i s proportional to (1)/ Increasing the size of a roadway can reduce i t s resistance significantly. But reduction i n resistance of any single roadway has a limited effect on the overall mine resistance i n most cases. Table 8 shows the percentage reduction of resistance i n relation to the increase i n cross-sectional area. Table 8. .Percentage Reduction i n Resistance with Change i n Cross-sectional Area Percentage increase i n Cross-sectional Area Percentage Reduction of Resistance 10 21 20 37 30 48 40 57 50 64 60 69 70 73 80 77 90 80 100 82 1.5.7.2.2 Improve Roadway Lining K can be reduced by l i n i n g the roadway. Lining of roadways may result i n resistance reduction of up to 70% (Hardcastle, 1983). Relining the roadways i s a costly and time consuming task. Removing obstructions, timbering, sudden enlargements or contractions would reduce mine airway resistances. 1.5.7.2.3 / Duplicaticai of Major Airways This can be achieved by creating a number of p a r a l l e l airways, thus s p l i t t i n g the airflow between the two roadways and reducing the pressure drop along them. One of the potential benefits which may be realised by «rig option i s a reduction i n the required a i r power. A parallel airway reduces the t o t a l resistance to airflow between the two points and hence reduces the mine system resistance. Equivalent t o t a l resistance for two parallel c i r c u i t s with equal resistances, Rp i s calculated as follows: [(1)/(Square Root of Rp)] = {[(1)/(Square Root of R_)] + [(1)/(Square Root of R_)]} But R 1 = R_, therefore, [(1)/(Square Root of Rp)] = [(2)/(Square Root of R_)] or The construction of p a r a l l e l roadways throughout the mine i s a major undertaking i n terms of construction time and expenditure. 1.5.7.2.4 / Construction of Shafts, Raises and D r i f t s This may reduce the overall mine resistance especially i f the shafts and roadways are properly planned and incorporated into the existing ventilation system. Sinking new shafts i s costly and requires years of budgeting and planning. The costs of driving various mine openings i n Canadian mines are set out i n Table 9. 1.5.8 Controlled Recirculation of Mine Exhaust A i r to Reduce Winter Heating Costs Controlled recirculation may be used to reduce winter heating costs by reducing the fresh a i r intake. This method does not require high i n i t i a l capital costs provided that the exhaust a i r quality i s good. Before undertaking any mine a i r recirculation project, a systematic approach to evaluate the a i r quality s u i t a b i l i t y for re-use should be conducted. A feasibilty study i s necessary for this application. The f e a s i b i l i t y of a recirculation system and i t s f i n a l design depends on many factors, and requires unique determination for each application. Table 9. / Underground Development Cost Data (From Canadian Mining Journal, 1984) Shaft, Raise and Drift Development Costs Company, Mine Size Length/Depth Cost (m) (m) ($/m) Shaft Development Hudson Bay M&S, Spruce Point 6.9x2.4 655 4412 Noranda Mines Ltd, Lyon Lake 6.9x2.8 914 4921 Westmin Resources Ltd, HW Mine 6.7x4.6 762 5249 Raise Development Hudson Bay M&S, Spruce Point 1.5x2.1 61 164 Noranda Mines Ltd, Lyon Lake 1.8x1.8 Westmin Resources Ltd, HW Mine 1.5X1.5 58 278 D r i f t Development Hudson Bay M&S, Spruce Point*3. 7x3.0 - 328 Noranda Mines Ltd, Lyon Lake 4.3x3.7 - 460 Westmin Resources Ltd,Lynx Mine 2.4x2.4 - 397 Service Ramp 1.5.9 Controlled Recirculation of Mine Exhaust M r to Increase Underground Airflows The introduction of recirculation w i l l reduce fresh a i r leakage and hence increase the fresh a i r flow rates into the workings. In addition/ recirculation of a i r re-introduces a fraction of return a i r back into the intake which w i l l again increase the flow rates throughout the working areas. Before a recirculation decision i s made/ exhaust a i r quality studies should be conducted. Each mine situation should be evaluated individually. Knowledge of contaminant process characteristics and legal requirements are very important parameters to be considered during the i n i t i a l stages of implementation. 1.6 SUMMARY Some Canadian mines experience ventilation problems when outside a i r temperatures drop below minus 40 °C. These problems may include the following: - Reduction i n temperature of the fresh a i r entering the mine; - Reduction i n a i r quantity supplied from surface i n order to maintain normal system intake a i r temperatures - this w i l l prevent damage to shaft lining. In addition/ these mines have insufficient capacities to accomodate the severe winter conditions. A number of methods to solve these problems are proposed. The methods require large amounts of capital investments which are beyond the capabilities of these mines. Because of the cost and problems associated with the above solutions for the above problems, the university of B r i t i s h Columbia, Department of Mining and Mineral Process Engineering i n conjuction with CANMET in i t i a t e d a study to look into a cost effective solution to the above problems. Controlled recirculation ventilation of return mine a i r was examined for application i n Canadian mines. This research project attempts to investigate the f e a s i b i l i t y of using controlled recirculation to reduce winter heating costs and simultaneously increase the mine a i r intake during the winter months. Several methods for recovering waste heat are discussed and these methods require significant capital expenditure and time. This can interfere with mine production a c t i v i t i e s . Controlled recirculation of mine return a i r may be a feasible alternative i n these mines. / CHAPTER 2 • f • A REVIEW CF CONTROLLED RECIRCULATION AND RELATED ISSUES 2.1 INTRODUCTION There are numerous ventilation methods that can be used i n Canadian mines either to reduce heating costs and/ or to increase the face a i r quantities. Controlled recirculation has recently become a popular research topic i n several countries. The attraction of controlled recirculation systems i s that they can reduce heating costs, increase face airflows and reduce overall power costs. These systems have been installed i n British coal mines and South African gold mines ( Lee and Longson, 1987; Middleton et a l . , 1985). In Canada, controlled recirculation i s presently being investigated to reduce heating costs and increase face a i r velocities. This chapter w i l l provide a definition and classification of the different recirculation layouts. The principal variations of recirculation systems w i l l also be discussed. 2.2 HISTORICAL BACKGROUND OF 0C*rab3LLED RECIRCULATION Numerous articles have been published describing the use of controlled recirculation systems i n B r i t i s h coal mines and South African gold mines. Significant papers are reviewed i n the following section. In Canadian mines the objective i s to reduce heating and increase face a i r -velocities. In South Africa the objectives are to increase a i r cooling power at the faces and evaluate the potential benefits of combining controlled recirculation with refrigeration to achieve improved temperatures respectively. In the U.K. controlled recirculation i s used to reduce costs i n undersea coal mines because of high velocities and consequent power costs. Uncontrolled recirculation of mine exhaust a i r , can increase gas and dust concentrations and most legislations prohibit the use of recirculation. Controlled recirculation of mine a i r may be accepted i n the Canadian mining industry provided adequate safety precautions are taken. The use of recirculation i n mines i s not a new practice. I t was f i r s t investigated by Lawton i n 1932 for local cooling i n British coal mines. The objective was to increase a i r cooling power at the faces by increasing a i r velocities. Lawton conducted a number of experiments, but with limited success. During his f i r s t experiment, Lawton installed a fan and a 15 metre length of duct along a longwall coal face and recirculated a i r from the return end of the face. This increased the face a i r velocities by about 77% from 0.152 m/s to 0.27 m/s. The higher temperatures caused by recirculation were offset by the increased velocities and this caused 16.2% and 14.6% improvement i n the dry and wet kata cooling powers respectively. Lawton conducted more experiments and managed to increase the face a - I T -velocity by 110% with a 16% improvement i n the wet kata cooling power. Lawton showed experimentally that local recirculation was feasible but concluded that the results obtained did not j u s t i f y a general recommendation of the method at that stage. The concept of recirculation was abandoned after Lawton's work i n the 1930's u n t i l the early 1960's, probably due to the underground mine explosions and methane layering problems i n the late 1950' s. The behaviour of a methane layer i n an airway depends on the ventilation velocity, the rate of input of methane into the layer, the width of the airway, mode of ventilation, and the slope of the roof of the airway (Bakke and Leach ,1960; 1962). Research work was ini t i a t e d by the Safety i n Mines Research Establishment to investigate the problem of methane layering (Leach, et a l . , 1966), and recirculation was identified as a solution to methane layer dispersal. T r i a l systems were set up and evaluated. As with Lawton's systems, this involved recirculation of a portion of the available ventilation a i r i n order to increase the roadway velocity and thereby achieve more rapid mixing and dispersal of the layer. Bakke, Leach and Slack, (1964) undertook some theoretical and experimental investigations regarding recirculation of m-ino a i r . Their analytical results revealed that when the amount of fresh a i r supplied to an area i s kept constant, the maximum m a * * * ™ * * concentration i n the general body of a i r i s the same with or without recirculation. The local velocity increase due to recirculation increases turbulence and can improve the rate at which methane mixes with a i r . The fear of pollutant build-up within the recirculation zone hindered the application of this concept i n B r i t i s h coal mines u n t i l the 1970's. i n September 1971, the f i r s t exemption was made from the 1956 B r i t i s h Ventilation Regulations of the Mines and Quarries Act which prohibits recirculation by auxiliary fans. This permitted the t r i a l recirculation of exhaust mine a i r at the Seaham Colliery i n the South Durham area. A year after the issue of the permit, a paper covering some of the aspects of the recirculation experiment was presented (Robinson, 1972). The results of the recirculation t r i a l were encouraging and further t r i a l s were authorized i n the Nottingshire and Derbyshire coal f i e l d s . These were a l l i n advance headings (Pickering et a l . , 1977). Since the early 1980' s researchers have shown both by theoretical analysis and actual measurements that the maximum concentration at a face using recirculation i s dependent upon the amount of fresh a i r supplied to the workings and i s independent of the amount of recirculation being conducted. The results of this work i n British coal mines have resulted i n a number of controlled recirculation systems i n the U.K. under Inspectorate exemptions (Hardcastle, 1983). In 1982, there, were 1560 auxiliary ventilation systems i n British mines and 61 of these employed controlled recirculation. These were designed to provide airflows to control firedamp, dust, heat and humidity within legal standards (Pickering and Robinson, 1984). Seme B r i t i s h coal mines have extended undersea ventilation systems and are unable to sink shafts offshore. The main ventilation problem i s that of maintaining adequate airflows at the faces as the volumetric efficiency decreases due to long a i r travel distances. The consequent large pressure differences between intake and exhaust airways result i n increased a i r leakage from intake to return through doors and stoppings. j These mines have started exploiting the benefits offered by controlled recirculation of mine a i r . As a result of the Mine Inspectorate's cooperation, further studies into the application of controlled recirculation to ventilate mine d i s t r i c t s were in i t i a t e d (Pickering and Robinson, 1984). These studies showed that d i s t r i c t recirculation i s feasible and could greatly reduce power costs and improve ventilation at the face without substantially increasing pollutant concentrations i n the return air(Hardcastle, Kolada and Stokes, 1984). The authors reported that recirculation also caused the mixed intake a i r temperature to r i s e , however the associated increased a i r velocities induced by recirculation provided greater heat dilution and cooling of the workers. This resulted i n improved underground conditions. A controlled d i s t r i c t recirculation scheme with a recirculation factor of 33% was installed at the Wearmouth mine, Sunderland (Robinson and Harrison, 1987). The f i r s t 12 months of operating experience f a i l e d to identify any significant contaminant build-up. Power savings of up to can $ 610,000 (305,000 pounds sterling) per annum for t his system were reported by the authors. Mine a i r recirculation was f i r s t suggested i n South Africa i n 1978 by Van Der Walt. The objectives were to reduce the amount of secondary cooling and to provide better control over the distribution of cooling i n South African gold mines. A large-scale f i e l d t r i a l of controlled recirculation was commissioned at Loraine Gold Mines Limited during 1982. The general objective was to assess a l l aspects of recirculation i n a deep gold mine. The specific objective was to evaluate the potential benefits of combining controlled recirculation with refrigeration and dust f i l t r a t i o n to achieve inproved temperature and dust control. A recirculation factor of 70% (15 and 35 m3/s intake and recirculated-air quantities respectively) was achieved. Throughout the recirculation t r i a l , readings were taken of the hourly mean values of gas concentrations within the area. The results are set out i n Table 10. Table 10. Pollutants at Design Flow Rates Compared to those Before Recirculation (From Burton, et a l . , 1984) Pollutant Intake Mixed Intake Return Safe Limits c o g (ppm) 295 425 465 500 c o (ppm) 7 9 10 50 Dust (mg/m3) 0.222 0.231 1.05 2 The mixed; intake wet-bulb temperature dropped from 27.9 to 24 ° c immediately after commissioning of the system. A gradual trend towards about 22 °C was recorded. The return a i r wet-bulb temperature showed a downward trend from 31.5 to a level of 28 °C. Table 11 summarizes the environmental conditions for the recirculation system. Table 11. Environmental Conditions Prior to and During Recirculation Parameter Intake Mixed Intake Return Mean Stope A i r Conditions Intake Return Quantity (m3/s) 16 50 50 - -Wet-bulb (°C) Prior 27.9 27.9 31.5 30.0 31.3 With Recirc. 27.2 22.3 28.4 23.6 28.3 The temperature changes reported here are not only due to the effects of controlled recirculation but also due to heat transfer from equipment and mechanical cooling plants. The Loraine t r i a l recirculation confirmed the fact that recirculation does not lead to any significant increase i n the concentration of contaminants i n the return a i r . I t also does not lead to a gradual build-up of any contaminants. There are three well documented recirculation systems i n South A f r i c a today. These systems are situated at Loraine Gold Mine, President Steyn Mine and Western Holdings Mine. In the recirculation system at Loraine Gold Mine, a i r passing through four working stopes i s boosted by a factor of 3.3. Four Becon combustion par t i c l e detectors are used, one i n the crosscut of each stope and a fourth Becon i s used at the fan to stop the recirculation in the case of a f i r e occurring i n the system. The fan i s not stopped during blasting. At President Steyn Mine, return a i r i s boosted by fans and fed v i a a slotted ventilation door to a development area where i t i s mixed with some fresh a i r . The door i s closed, via telemetry, when blasting i s to take place. The door i s also closed automatically when a f i r e occurs. This i s done using sensors placed upstream from the fans. I f sensors installed fr^nind the door detect smoke, the fans w i l l be stopped. The door w i l l automatically close i n case of a power fa i l u r e . At western Holdings Mine a i r from the main workings was redirected to an area where an internal sub-vertical shaft was being sunk. Sensors are installed near the fans and i n case of f i r e the fans are switched o f f . Prior to blasting from surface the fans are stopped v i a telemetry. Two main fans closer to the surface however, must remain running. The state of these fans i s also monitored i n the control room on surface. Starting the booster fan i s carried out by the banksman's on the sub-bank. F u l l indication of the state of a l l fans i s also available i n the sub-shaft banksman of f i c e . Both the President Steyn and Western Holdings systems, use the f i r e detection cabling. A l l smoke and gas sensors are also monitored by the f i r e detection systems on these shafts. Studies conducted i n the U.S.A. at the TG Soda Ash Inc. to determine the effect of recirculating 25% of the return a i r back into the intake for increased face ventilation showed that controlled recirculation was very effective and safe. The amount of a i r recirculated was 9.63 and 9.20 m3/s providing recirculation fractions (RF) of 26 and 24% respectively. With the recirculation i n operation, there was a s l i g h t increase i n measured respirable dust concentration i n the mixed intake along with a sl i g h t increase i n the mine temperature of 1.67 °C. The increase i n temperature may have been due to a number of different factors i n addition to recirculation. These factors include, heat generated from equipment. The description together with the findings of these studies are reported by Cecala et a l . , 1989. Tables 12 and 13 give summaries of average dust and gas concentration results from the study. These results confirm that controlled recirculation of exhaust a i r i s feasible and safe. Studies into the f e a s i b i l i t y of using controlled recirculation to reduce heating costs were f i r s t initiated at the University of B r i t i s h Columbia i n 1985. CANMET has been funding this project since 1986. Saindon, (1987) developed a computer ventilation model based on a small gold mine with approximately 40 branches. Twelve diesel units with a t o t a l installed power of 1,160 kW were simulated to determine the diesel emissions and the pollutant concentrations i n each branch of the network. The t o t a l ventilation airflow was 103 m3/s. The network was modelled with and without recirculation. The emission values were based on the Deutz F8L714 engine. Saindon found that the increase i n concentration i n the most polluted branch was not proportional to the percentage recirculation. The changes i n contaminant levels with percentage recirculation are given below:-% Recirculation % Increase i n Contaminant 10 5 30 22 50 55 70 125 The simulation assumed that a l l the equipment operated continuously throughout the s h i f t and that leakage i n the mine was minimal. These assumptions are pessimistic for the re a l case because down time of equipment i s significant and leakage often approximates 50% of the t o t a l a i r circulated (Hall et a l . , 1988). The f i r s t underground studies were conducted at Ruttan mine i n Northern Manitoba. The exhaust a i r quality at Ruttan mine i s such that controlled recirculation i s feasible (Hall et a l . , 1988). Further f e a s i b i l i t y studies were conducted at Central Canada Potash Division of Noranda Minerals Inc., and Rocanville Division of Potash Corporation of . Saskatchewan (PCS) to determine the potential for the application of a controlled recirculation system at each mine. 2.3 BENEFITS OF CXWIRDLLED RECIRCULATION Some of the benefits resulting from the use of controlled recirculation of mine a i r include: reduction i n ventilation heating costs, increase i n face a i r velocities, reduction i n power costs and a saving of energy. 2.3.1 Reduction i n Heating Costs Mine a i r heating i s required by mines situated at higher elevations and those located i n cold climates. A primary function of heating mine a i r i s to prevent freezing of ground water and pipes located i n shafts and other i n l e t airways. Ice build - up i n intake shafts i s not only an operational problem, but i t can be extremely hazardous due to ice f a l l s and plugging of primary a i r inlets. Mines which do not heat intake a i r , keep the primary hoisting and service shaft pressures neutral to prevent ice formation during severe winter months. Mine a i r heating i s a common provision i n many hardrock and potash mines i n Canada. These mines may spend over $ 2,000 per m3/s of a i r per annum for heating. In recent years, r i s i n g fuel costs have forced a number of operations to examine alternative sources of energy to heat mine a i r during the winter months. The alternative sources of energy employed i n the Canadian mining industry to supplement the mine a i r heating requirements include, heat recovery from machines and mine return a i r . Controlled recirculation of mine exhaust a i r i s another alternative energy source that can be used to reduce heating costs. This can be achieved by the following approaches: 1) Pre-heating the intake a i r using the recirculated return a i r (direct heat transfer to the intake a i r without using a heat exchanger) while keeping the intake a i r quantities constant. 2) Reduction i n intake a i r quantities and recirculating a fraction of the return a i r quantity i n order to maintain the same intake a i r quantity to the mine. The heating cost reduction i s directly . proportional to the amount of a i r recirculated and hence the recirculation fraction. The allowable recirculation quantity depends on the a i r quality, pollutant fluctuations with time, mine network system and the location of the recirculation connection. 2.3.2 Increased Face Airflows Some have d i f f i c u l t i e s i n supplying adequate a i r quantities to working faces. These problems can be minimized by incorporating l o c a l or d i s t r i c t recirculation of mine return a i r into the ventilation system. Recirculation of mine a i r w i l l increase the amount of a i r supplied to the working faces and hence increase the a i r cooling power and promote pollutant mixing because of the increased a i r velocities. 50 2.3.3 Reduction i n Power Costs B r i t i s h and South African mines experience much higher power costs and have greater fan ventilation pressures. This makes recirculation attractive i n these mines. Canadian mines have the opposite conditions and as a result recirculation i s not usually attractive for ventilation purposes. Few Canadian mines operate at the capacity of a i r supply or at economic airway velocity limits. Power savings of up to $ 610,000 (305,000 pounds sterling) per annum for a system installed at the Wearmouth Colliery of B r i t i s h Coal are reported (Robinson and Harrison, 1987). The annual ventilation power cost at the Wearmouth Colliery i s $ 2 million ( 1 million pounds sterling ) or $ 8,700 per m3/s ( 4350 pounds sterling per m3/s per annum). The t o t a l power saving depends on the amount of a i r recirculated, annual cost to supply 1 m3/s of a i r to the mine and the overall system configuration. The annual ventilation cost to supply 1 m3/s of a i r to a working face i s about Cdn $ 566 (Ball, 1985). Ventilation power cost savings can be calculated i n the following manner. ventilation cost Savings = [(Fan Pressure * Recirculated Quantity * Power Cost * Number of Days/Year * Hours/Year)]/[Fan Efficiency * 1000] Where, Fan Pressure = Total mine fan pressure (Pa) Fan efficiency = Overall system fan efficiency (%) Power Cost = Dollars per kWHr Number of days per year = 365 Number of hours per day = 24 2.4 PROBLEMS IN APPLYING CCflTROLLED RECIRCULATION SYSTEMS Despite the benefits associated with controlled recirculation, most mining regulations prohibit the use of recirculated exhaust mine a i r mainly because uncontrolled recirculation can create excessive dust concentrations, high gas levels and i n the case of a mine f i r e , there i s a p o s s i b i l i t y of products of combustion being carried back into the fresh a i r intake. Controlled recirculation of mine a i r may be accepted i n the m - i n i T v j industry provided adequate safety precautions are taken. These may include automatic a i r cleaning systems, a monitoring system that warns of threshold limit values (TLV's) being exceeded; and safety devices to detect recirculation equipment failure and f i r e . A major problem i n Saskatchewan potash mines i s the high concentrations of coarse dust that occur near the cutting machines. The wetting method for binding dust cannot be used extensively because i t leads to build up of caked ore. Water dissolves s a l t and potash and the use of water sprays could result i n reduced p i l l a r size thus creating ground i n s t a b i l i t y . Improved cutting technology could reduce the dust problem. Dust i s thus a major pollutant to be investigated especially i n the evaluation of the impact of auxiliary and d i s t r i c t recirculation systems i n potash mines. Many Canadian metal mines mining massive sulphide ore bodies can benefit significantly from controlled recirculation. The benefits resulting from the introduction of controlled recirculation of mine a i r d i f f e r from one mine to another depending on their ventilation, heating and a i r conditioning designs. In general, recirculation of a controlled portion of the return a i r around a d i s t r i c t i n underoxound metal mines offers the same economic advantages as those experienced i n potash mines. However, these benefits cannot be exploited f u l l y because of frequent disruptions of the ventilation systems resulting from sulphide dust ignitions. 53 Several underground metal mines i n Canada have potential for recirculation but experience sulphide dust ignition problems. Well documented cases include the Ruttan mine i n Northern Manitoba, Noranda's Geco division, the Fox mine i n Lynn Lake, Manitoba, Heathe Steele Mines i n New Brunswick and minor explosions at the H-W mine i n Campbell River, B r i t i s h Columbia ( Hall, 1989 ). Sulphide dust explosions have also occurred at No. 2 mine of Kidd creek Mines Limited ( Mchaina and Hall, 1987 ). The majority of these mines can employ controlled recirculation of exhaust mine a i r to improve their ventilation efficiency and costs. Presently, most mines mining sulphide ores have modified their mining methods to provide preventative measures against sulphide ignitions. The methods commonly used are inert stemming, water sprays, water bags for stemming, passive and triggered barriers, water atomizers prior to blasting and ventilation ( Mchaina and Hall, 1987; Enright, 1984 ). 2.5 MINE AIR, ITS CONSTITUENTS AND REGULATIONS CONTROLLING Normal atmospheric a i r i s a mixture of nitrogen (and inert gases), oxygen, carbon dioxide and water vapour i n the following proportions by volume: ITS QUALITY Nitrogen 79.04% Oxygen - 20.93% Carbon dioxide 0.03% Other gases (total) < 0.01% In normal atmospheric a i r , moisture i s also always present, from a fraction of 1% up to a maximum of about 6%. As the a i r passes through the mine openings, i t undergoes changes i n i t s composition. The changes involve a reduction i n the amount of oxygen; increase i n C0 2 and addition or extraction of water vapour, addition of particulate pollutants, and the inclusion of small amounts of other pollutants, such as methane, carbon monoxide, nitrous oxides, unburned hydrocarbons, aldehydes, ammonia, hydrogen sulphide and sulphur dioxide. The degree of contamination of the a i r by these pollutants i s controlled by a number of factors. These factors include: the gaseous contents of the strata, the quality of a i r ventilating the mine, the size of the mine workings, the r-hfamirai reactivity of the strata, the degree of mechanization, age of the mine, the mining method, type of ore being mined, and the overall ventilation configuration. Most of these factors tend to remain constant and hence the degree of contamination i s inversely proportional to the quantity of a i r flowing. The principal effects of some of the common harmful gases are given i n Table 14. The respective Threshold Limit Values for these gases are given i n Table 4, section 1.2.3. The underground a i r quality regulations i n Canada vary from province to province. Table 15 gives general Canadian mine a i r quality standards. ['.. K . ' 55 Table 14. Harmful Gases i n the Underground Mine Atmosphere GASES AND THEIR EFFECTS Flammable Toxic Asphyxiant Methane (CH4) Carbon Monoxide (CO) Methane (CH4) Carbon Monoxide (CO) Oxides of Nitrogen (NQ^) Nitrogen (Ng) Hydrogen (Hg) Hydrogen Sulphide (H_S) Carbon dioxide (C02) Hydrogen Sulphide Sulphur dioxide(SOg) Table 15. General A i r Quality Standards GAS TLV TOXICITY RANGE ppm % S = Slight, H = High Carbon Dioxide 5000 0.5 S Carbon Monoxide 50 0.005 H Hydrogen Sulphide 10 0.001 H N i t r i c Oxide 25 0.0025 H Nitrogen Dioxide 3 0.0003 H Sulphur Dioxide 2 0.0002 H In addition to the gaseous emissions to the mine atmosphere, mining operations also produce particulate contamination. These can be divided into two main groups: particulates produced by diesel engines and dust produced during rock breaking processes. These particulates, both diesel and rock dust, are potentially carcinogenic. Since the diesel exhaust particulates are very « m n i n size ( < 1.0 microns) and d i f f i c u l t to control other than by dilution, particulate emissions can be a more severe problem than noxious gases i n Canadian mines. In addition, welding fumes and wood particles are prevalent in underground mines. The effect of size on the action of the particles on the human body i s especially important for particles that are inhaled. The size of the particles that can affect health i s a function of the aerodynamic behaviour of particles i n relation to the characteristics and geometry of the respiratory system. The predominant sizes of inhaled particles which affect health are usually less than 10 microns (Lipkea, Johnson, and Vuk, 1978; Mchaina and Misra, 1986). In addition, small particles remain suspended i n a i r for a very long period of time and this further increases the exposure hazard. The threshold limit value (TLV) for mine a i r particulate matter i s determined by i t s s i l i c a (SiC^) content. For respirable particles containing greater than 1 percent SiOj, the ACGIH reccmmend a TLV given by the relationship: TLV = [( 10 mg/m3)/( % of SiOj +2.0)] A l l Canadian legislation specifies maximum levels of 2 mg/m3 for respirable dust containing s i l i c a and 5 mg/m3 for the t o t a l dust. The potash mine dust i s c l a s s i f i e d as nuisance and because i t has low s i l i c a content i t s l i m i t i s not related to the relationship above. The limi t for the potash dust i s 10 mg/m3, set by Saskatchewan Provincial Regulations. Mine return a i r quality (pollutants) and general ventilation studies are essential pro-requisites for any controlled recirculation system installation. Evaluation of a i r pollutants chemical effects and their possible control methods are c r i t i c a l for any recirculation decision logic tree. 2.6 SOURCES OF HARMFUL IMPURITIES IN THE MINE Table 16 sets out gaseous pollutants found i n underground mine atmospheres. In the case of oxygen i t i s depletion that i s important. Depletion of oxygen levels i n underground mines may be caused by oxidization, combustion, respiration and blasting. Potash mines have limited blasting operations and low diesel equipment u t i l i z a t i o n , hence oxygen depletion due to blasting and diesel equipment i s not a problem. The oxygen level w i l l always support respiration for the limited number of underground workers, except i n the case of a f i r e . The underground mine dustiness depends on a number of operational factors. These include the method used for ore extraction, method of conveyance, and type of ventilation. In metal mines, the main sources of dust are d r i l l i n g , blasting, and transportation operations while ore extraction using continuous miners and mineral conveyance are the main dust generation processes i n potash and coal mines. Table 16. .Gases Cctnnonly found i n Underground Mine Atmospheres GAS SOURCES Oxygen Normal a i r Methane Strata, blasting of strata, and organic decay Oxygen Depletion Oxidization, blasting, respiration and combustion Nitrogen Blasting, strata emissions and organic composition Carbon dioxide Organic deccmposition, strata oxidization and emissions, respiration, spontaneous combustion, diesel engines and blasting. Carbon Monoxide Strata emissions, combustion, f i r e and blasting. Nitrogen r * H ^ o q Combustion, diesel engines, and blasting (NO, NO,) Sulphur Strata emissions, organic decomposition, sulphide (B^S, SO^) dust ignitions, self heating and diesels 2.7 . /: . ' 59 CXWTROL METHODS AND REMOVAL OF POLLUTANTS The underground environment, has a certain a i r cleansing capacity. In other words, through physical and chemical processes, pollutants w i l l be removed from the a i r after a certain residence time. Such processes can improve the quality of mine exhaust a i r and enable a significant percentage of the exhaust a i r to be recirculated safely. There are a number of mechanical methods that can be used to improve the underground a i r quality. These include, dilution ventilation, gas, and particulate removal processes. 2.7.1 Dilution Dilution ventilation i s the most widely employed method for contaminant control i n the mining industry today. Dilution ventilation when used i n conjuction with another control method can produce good results. Dilution ventilation can be achieved through auxiliary ventilation, main ventilation airstream, and diffusers and water sprays. Dilution ventilation i s the only practical approach at present to ensure that adequate quantities for a i r are available to reduce concentrations below the maximum allowable levels (MACS) for the various pollutants i n the mine. Therefore, when considering dieselizing any mining operation, the ventilation should be carefully planned and supply adequate a i r quantities for dilution of the exhaust gases and particulates. The effectiveness of dilirtion ventilation depends on many factors such as volumetric efficiency, age of the mine, mining method and mode of ventilation (ascensional or desoensional systems). In a descensional ventilation system dilution of a i r takes place continuously as the a i r descends i n the mine. Similarly, the exhaust a i r from a highly mechanized stope i s diluted as i t moves to surface due to leakage of fresh a i r from intake to return airways. In f a i r l y large mines, with 10 working levels or more, the total leakage of ventilation a i r may be more than 50%. This implies that, for these mines, the contaminant concentration w i l l have been reduced by 50% once i t reaches the surface exhaust. Recirculation of return a i r can be considered as an alternative ventilation approach for dilution of a i r contaminants i n these mines. Maximum di l u t i o n w i l l be gained by recirculating as close to surface as possible. When considering the use of controlled recirculation for a i r pollutant dilution, a thorough a i r quality survey must be conducted to ascertain that the return a i r i s safe to recirculate to the mine intake airway. ./ 61 2.7.2 fmisflion Contxol Hardware The concentration of diesel exhaust emissions can be lowered either by removing the offensive material from the exhaust or by adding a i r i n quantities sufficient to dilute the contaminants below the maximum allowable concentrations (MAC). Attempts to reduce the emissions of harmful contaminants include the use of a catalyst, recirculation of exhaust gases, injection of water into the intake, and retarding injection taming (Lawscn, 1981). These control techniques are set out i n Table 17. Typical retention of various pollutants i n a water scrubber are as follows: Particulates 30% Hydrocarbons 20 to 25% Aldehydes 50 to 85% Sulphur dioxide 50 to 80% Nitrogen dioxide 7 20% The efficiency of a catalytic p u r i f i e r depends upon how long the exhaust i s within i t and the temperature of the exhaust. To increase the residence time, the p u r i f i e r should be designed i n such a way that i t has a wide cross-section and as large a surface area as possible . For highly e f f i c i e n t oxidation, a high temperature from 260 to 430 °C i s required i n the purifier. The catalytic purifiers convert carbon monoxide to carbon dioxide (50% conversion at 260 °C and 85% conversion at 450 °C) and oxidize most of the hydrocarbons (90%) and aldehydes (85%). They do not significantly alter smoke or nitrogen dioxJ.de concentrations. There could be conversions of nitrogen dioxide to n i t r i c cod.de perhaps by a mechanism of the form: CO + NOj > COg + NO as well as n i t r i c oxide to nitrogen dioxide. 2ND + Oj > 2N02 There i s a serious problem because catalysts convert SO2 to S03 and the TLV of 8O3 i s only 0.25 ppm. Low sulphur diesel fuels are recommended, normally less than 0.25% by mass i n order to reduce the sulphur dioxide emission. During i d l i n g the temperature of the exhaust emission drops appreciably to between 120 °C and 150 °C, hence affecting the purifier performance. More recently, i t has been shown that catalytic converters increase the concentrations of biologically active soluble organic material adsorbed on the particulate as measured by the Ames test ( Hunter et a l . , 1981; Mogan et a l . , 1983 ). The continuing development of diesel engine after-treatment control technology w i l l improve the underground environment and hence f a c i l i t a t e the application of controlled recirculation of mine exhaust a i r . The potash industry uses a minimum of diesel equipment i n their operations and they are used mainly for conveying service materials and men i n almost horizontal roadways. In addition, the average diesel u t i l i z a t i o n i n the potash industry i s significantly lower than that of metal mines. Hence diesel contaminant levels for the potash mines are lower than for metal mines. Table 17. Emission Control Hardware for Diesel Equipment Component Description Performance Evaluation Advantages Disadvantages Catalytic Purifiers High-efficiency CO, unburned hydrocarbons and aldehydes reduction Simple and practical Converts SC_ to HgSOj and some N0_ formation; and high temperatures are required. Conventional Water scrubbers Overall Good flame-unsatisfactory proof device, and good for SOg and cheap and aldehydes Water consumption - 3.4 litres/kW per s h i f t and requires regular servicing. Can contribute to fog formation i n airways. Venturi water High efficiency scrubbers possible for particulate removal possible Flameproof High engine back application pressure. Large water consumption. Can contribute to fog formation i n airways. Exhaust f i l t e r s Excellent for particulate and H_S04 Simple Development of application servicing techniques Exhaust gas Good for NQg recirculation reduction Simple Causes increase i n application particulate emissions emision(80 - 90%), CO unburned hydrocarbons and aldehydes 2.7.3 Gas and Vapour Removal Processes The major removal techniques for gases and vapours i n mines are absorption, adsorption; sol u b i l i t y i n the presence of water; oxidation; and chemical reactions. 2.7.3.1 Physical Absorption and Adsorption Absorption i s a diffusion process i n which molecules are transferred from the exhaust gas to a liquid. The diffusion occurs because there i s a concentration gradient between the exhaust gas and the liquid phase. Water i s the most popular absorber because many contaminants are soluble i n i t and the cost i s low. Physical absorption can be achieved through a spray chamber or through a reactive scrubbing device. Adsorption i s a process i n which a gas or vapour adheres to the surface of a porous solid material. Adsorption i s reversible since no fthgwiirai reaction i s involved. The commonly used adsorbents include, activated carbon, s i l i c a gel, and molecular sieves. Activated carbon produced from wood, nut shells, or petroleum i s most common. To remove vapours such as mercury, the activated carbon can be impregnated with iodine or sulphur. S i l i c a gel, an adsorbent consisting of amorphous s i l i c a , i s useful i n collecting polar cxxpounds such as alcohols. Molecular sieves, generally synthetic calcium or sodium zeolites hydra ted s i l i c a t e s ), have pores with a narrow size range. 2.7.3.2 Solubility of Gases Sulphur dioxide and n i t r i c oxide are highly soluble. Sulphur dioxide has a s o l u b i l i t y i n water of about 18.9% at zero degrees Celsius and 10% at 20 °C. N i t r i c oxide has a solubility of 7.3 cc./lOOg at 0 °C (Calvert, 1984). Metal mines have high relative humidities of up to 100% and they have numerous sources of water. These include seepage; runoff; sump water; and water used for dust suppression during mining and blasting. Water i n these mines i s a major removal mechanism for sulphur dioxide and nitrogen dioxide. The removal of N 0 2 i s increased i n the presence of water vapour. The reaction between NCVj and adsorbed water i s as shown below: 2NC>2 (gas) + HjO(adsorbed) > B N 0 3 (adsorbed) + HNC^ (gas) This reaction forms adsorbed axyacid. The TLV for B N O 3 as set out by AdGH i s 2 ppm, and therefore, i f this reaction were to occur to a significant extent i t could result i n an undesirable acid level i n the atmosphere. In practice t h i s does not happen because dilution of the exhaust gas would reduce the significance of this reaction due to the suppression of the formation of NGj, which dilutes the N O 2 formed i n the atmosphere. Studies conducted at Ruttan mine showed a reduction i n the N O 2 concentration as the exhaust a i r passed through the return system to surface (Hall et a l . , 1987). . . < 66 Moisture i n the return airways dissolved the NQg ax& hence reduced the NO2 ocaicentration. The contaminant decay i n humid mines as the exhaust a i r passes through the return airways can determine the best location for a recirculation crosscut or connection. 2 . 7 . 3 . 3 Oxidation of Gases The thermodynamic properties of some gases are such that they have a strong tendency to react with oxygen i n the a i r (Harkins and Goodwine, 1964). Sulphur dioxide w i l l react i n the manner below: 2 S Q 2 + 0 _ > 2 S 0 3 At p f t T - m a i humidities the S O 3 product of the above reaction w i l l be converted largely to sulphuric acid [H_S0 4 (aq) ]: S O 3 + H_0 > H 2 S 0 4 (aq) The reaction of S O 3 with water i s so fast that any process i n which S O 3 i s formed i n the moist atmosphere can be considered to lead to the formation of sulphuric acid. The oxidizing reaction i s so slow under catalyst-free conditions i n the gas phase that i t can be neglected as a source of S O 3 and consequently as a source of sulphuric acid i n the atmosphere. 67 Most of tne gas-phase chemical reactions of sulphur dioxide involve a variety of excited molecules and free radicals which are generated by photochemical and thermal reactions initiated by sunlight absorption of trace gases i n the atmosphere. The reactions are not li k e l y to take place i n an undergound environment with no sunlight exposure. The oxidation of NO to NOj i n the atmosphere has been documented i n literature. Harkins and Goodwins determined that the rate of conversion of NO to NOj, occuring i n the static atmosphere, could be predicted using the relationship below: Table 18 shows the conversion value which were calculated using Harkins and Goodwine's formula. -[dfNO^/dt] = K(NO)2(02) Table 18. NO to NO2 Conversion Values NO (ppm) NOg Formation (ppm/minute) 1000 210.0000 100 2.1000 10 0.2100 1 0.0021 68 Therefore, at high NO concentrations the rate of conversion i s re l a t i v e l y rapid compared to the rate at lower concentrations. Table 19, an extract from the Matheson Gas Book confirms the above conclusion. Table 19. Conversion of NO to N0_ ( Sources: Matheson Gas Book,1966 ) NO Concentration Time to Convert to N0 2 (ppm) 25% 50% 90% 1000 1.4 min 4 min 3.6 minutes 100 14 min 40 min 6 hours 10 2.3 hrs 7 hrs 63 hours 1 24 hrs 72 hrs 648 hours A formula developed by Dainty and Mogan (1974) at the Canada Centre for Mineral and Energy Technology to calculate the conversion of n i t r i c oxide to nitrogen dioxide i s as follows: N 0 2 = 2.28 X 10" 7 X T X ( N O i T r j ^ a 1 ) 2 X %0_ 2.28 X 10"7 X T X (NO-j^t^i) X ^ + 1 Where, N0 2 = NC_ produced at time T, i n ppm NOjnitial = NO concentration at start T = Time i n seconds % 0 2 = Percent oxygen i n the reacting atmosphere Table 20 gives some of the calculated values from Dainty and Megan's formula. Table 20. Conversion Rates of N i t r i c oxide to Nitrogen dioxide in A i r Using Dainty and Mogan's Formula ( Source: Bossard, et a l . , 1981) Concentration (ppm) Omulative Oxidation N i t r i c Oxide (NO) Nitrogen Dioxide (NO_) Time (minutes) 50 0 0 35.8 14.2 29 24.04 25.96 79 19.24 30.76 117 10.31 39.69 282 5.78 46.75 558 3.25 46.75 1050 1.83 48.17 1925 1.03 48.97 4670 Mogan et a l . (1974) calculated that, at equilibrium, the conversion rate for an atmospheric NO concentration of 14.5 ppm would be 0.044 ppm/minute. At this i n i t i a l concentration, the conversion of NO to NO_ would result i n a f i n a l concentration of 1 TLV equivalent of nitrogen oxides after one-hour residence time. Further experiments to measure the change i n NO/NOj levels upstream and downstream produced by a diesel engine i n a coal mine, were conducted by A.D. L i t t l e . The average data are set out i n Table 21. . /•. <' 70 Table 21. NO to NOj Conversion Data Gas Average Concentration (ppm) Upstream Downstream Nitrogen dioxide (NC^) 0.15 0.15 N i t r i c oxide (NO) 1.70 2.10 Carbon Monoxide (CO) 4.20 4.60 L i t t l e ' s group concluded that i n the mining atmosphere studied, NO was not converting to N O 2 at a hazardous rate. Conversion of NO to N O 2 i s obviously a concern when considering recirculation, because recirculation ventilation increases the residence time of these pollutants. Consider the worst condition of 25 ppm (TLV), as the normal NO working lev e l , and at 50% recirculation, the NO concentration w i l l reduce to 6.25 ppm ( 50% dilution * 50% recirculation * 25 ppm ). I t w i l l take over 5 hours to produce 0.5 TLV nitrogen dioxide ( 25% conversion ). From this, i t can be concluded that the conversion of NO to NOj w i l l be negligible i n a recirculation system. 2.7.3.4 Chemical Reactions During stope or development blasting i n massive sulphide ore deposits, a highly concentrated cloud of sulphide dust i s created and may be ignited, resulting i n a secondary ignition which releases a considerable volume of sulphur dioxide and other sulphur gases. In addition, many other gaseous products are produced during the main production blast, ammonia vapour being amoung the products. Ammonia vapour and sulphur dioxide i n the presence of water vapour or droplets reacts according to the following equations: N H 3 + HgO + SOg > Nfl 4 . H S 0 3 2 N H 3 + HgO + SOj, > (NH4)2S03 m the oxidizing medium of the atmosphere and i n the presence of water vapour or liquid water, formation of the higher oxyacids (sulphuric and n i t r i c acids) from sulphur dioxide and n i t r i c oxides (NQg) i s strongly favoured. sOg (gas) > 2HT + so 4 z °2' ^ ° J . NO(gas), NOu^gas) > BT + N03" Under atmospheric conditions, these reactions are quite slow i n both the gaseous and aqueous (dissolved SOj and NQg i n water) phases despite the strong driving force. Studies conducted by Novakov (1974) cm the effect of carbon i n catalytic acid gas reactions i n the atmosphere revealed that the oxidation of sulphur dioxide i n the presence of carbon i n liq u i d droplets was nearly of zero order type. This means that the reaction rate was nearly independent of the S0_ concentration present. The presence of diesel particulate matter (soot) could therefore be an important catalyst f o r the oxidation of sulphur dioxide. Kirk and Stefanich (1977) determined the sulphuric acid level of particulate i n the Denison uranium mine i n E l l i o t Lake. The data suggested that there were significant amounts of sulphuric acid i n areas of this dieselized mine which had adhered almost entirely to dust particles i n the respirable range (up to 23% by weight of respirable dust). In summary, i t can be said that, CO, 00_ and a l l the hydrocarbons have extremely slow oxidation and solu b i l i t y rates and hence these pollutants are very stable. The understanding of the removal mechanisms for various pollutants i n the mine atmosphere i s essential for recirculation practices. 2.7.4 Particulate Matter Removal The following methods are available, for dust separation: 1. Gravimetric methods 2. Centrifugal methods 3. F i l t r a t i o n 4. Wet scrubbers 5. Electrostatic Precipitators. These methods are l i s t e d i n Table 22 together with the principle of operation and typical particle size for 90% collection efficiency. 2.7.4.1 Gravity Separation Dust i s removed by allowing a horizontal current of dust-laden a i r to enter a rel a t i v e l y stagnant zone of airflow where the dust particles are separated and deposited into the excavated chamber. A large excavation i s required i n order to get high dust deposition rates. This method i s not suitable for fine particles < 100 microns, therefore i t i s not suitable for a recirculation application. • - ' 74 Table 22. / Particulate A i r Cleaning Devices (After McDermott, 1985) Device Cleaning Mechanism Particle Diameter f o r 90% Removal (micrometre) Baghouse F i l t r a t i o n >1 Electrostatic Precipitator Electrostatic Attachment >1 Cyclone - Small Diameter Centrifugal Force >5 Cyclone - Large Diameter Centrifugal Force 25 Scrubber - Spray chamber Tn«*rt"'a1 Impingement 25 Scrubber - Packed bed Inertia1 Impingement 5 Scrubber - High Energy Inertial Impingement and Centrifugal Force >1 2.7.4.2 Centrifugal Methods Centrifugal collectors force the dust-laden a i r to undergo a number of revolutions i n a circular chamber. A typical example of these i s a cyclone. Cyclones impart a circular motion to the exhaust gas that causes particulates to move to the outer part of the airstream where they impact the cyclone walls. 75 Since the a i r velocity i s low at the wall, the particulates drop down the wall into the collection bin at the bottom. Cyclones may be operated as wet collectors i f a water spray with or without a wetting agent i s installed to wet the particles at the in l e t . This increases the effective size of small particles, thus increasing collection efficiency. Small centrifugal collectors have higher efficiency for small particles than do larger cyclones because the tangential force an the particle increases as the radius of the cyclone decreases. Centrifugal collectors have greatest efficiency for particles 5-10 micrometres and larger. The use of centrifugal collectors as the main cleaning devices for recirculation application i s limited due to the above mentioned reasons, however they can be used as the f i r s t stage of a multistage a i r cleaning system. 2.7.4.3 F i l t r a t i o n Airborne dust can be removed from the a i r when i t i s passed through a permeable, porous material which traps particles. This i s achieved through f i l t e r s . The material used i n the f i l t e r s may be woven or felted fabric, i n the form of f l a t envelopes or sleeves. F i l t e r devices f a l l into two major categories: disposable f i l t e r s and reusable f i l t e r elements i n a housing that i s eguiped with a cleaning mechanism for periodic dust removal. \ . /: . 76 F i l t e r s c o l l e c t particles by three mechanisms: impaction/ interception and diffusion (Bethea, 1978). Impaction occurs when dust particles have so much in e r t i a that they collide with f i l t e r fibers rather than flowing around them; interception occurs when particles do not actually h i t the fibers but come so close that they are caught i n the low-velocity a i r layer that surrounds each f i l t e r ; and diffusion results when smaller particles move randomly back and forth within the f i l t e r bed due to Brownian motion (collision with a i r molecules). Impaction and interception are the key collection mechanisms for particles larger than l micron, diffusion predominates for particles below 0.1 micron and between 0.1 to l micron a l l mechanisms contribute to collection efficiency (Bethea, 1978). Impaction and interception are increased with small, closely spaced fibers, t h i s means that high efficiency f i l t e r s exhibit high resistance to airflow. Typical pressure drop i s 250 - 2000 Pa. These f i l t e r s have high efficiencies exceeding 90%. The largest f i l t e r s manufactured can only handle about 450 m3/s(Saindon, 1987) and are too large to i n s t a l l i n mine airways. This limits the application of f i l t e r s to large volumes of a i r i n confined underground spaces. 2.7.4.4 Electrostatic Precipitators In an electrostatic separator, a stream of electrons at right angles to the direction of the airflow passes from a number of negative electrodes, maintained at high voltage (25 - 50 kV), to earthed positive electrode plates. Dust particles acquire a negative charge, are attracted to the positive electrodes and are removed from the e l e c t r i c f i e l d by intermittent mechanical vibration or by water flushing. - / 7 7 These work well i n systems where gas volume i s large and high collection efficiency for small particles i s needed. I f not properly maintained, these devices can gradually lose collection efficiency between cleaning cycles. They are not suitable when the exhaust gas i s flammable or explosive. Precipitators can collect submicron sized particles with high efficiency and with relatively low energy consumption. However, precipitators are susceptible to corrosion and moisture damage. These problems l i m i t their use i n wet atmospheres. 2.7.4.5 Wet scrubbers Wet scrubbers contact particles with water or another liquid and then collect the droplets. There are many types of wet scrubbers and they are the most commonnly used devices i n the mining industry. common types are: flooded bed scrubbers, self-induced scrubbers, venturi scrubbers and simple water sprays i n confined non - venturi flow. The water spray system can be used e f f i c i e n t l y for recirculation application because of the a i r volumes to be handled. The li q u i d flow rate and pressure determine the droplet size. In order to improve collection efficiency a combination of water and compressed a i r i s used to atomize the spray chamber. Scrubbers can remove particles as small as 0.2 micron. Scrubbers are a relatively low-cost method of removing small particles i n cases where adding water to the contaminant does not cause a problem. This technique has a limited use i n potash mines because these mines employ dry m i n i n g techniques. 78 2.7.5 Bed imputation Sedimentation or deposition can take place i n the following ways: a) Gravitational settling; b) Inertia! settling; c) Diffusion; and d) Coagulation. 2.7.5.1 Gravitation Settling Gravitational deposition of dust particles i s characterized by Stoke's Law (Hinds, 1982). The settling behaviour of a particle can be represented by i t s terminal settling velocity, a condition where the drag force of a i r on the particle w i l l be exactly equal and opposite to the force of gravity. Accordingly to Stake's Law the settling velocity i s equal to: Where, VTSV = ( P p d 2 g ) / ( 1 8 I 1 ) V T S v- = Terminal settling velocity of the particle, m/s Pp = Density of particle, kg/m3 d = Particle diameter, micrometre g = Gravitational acceleration, m/s2 n = Viscosity of air, Pa.s From Stake's Law i t can be seen that the terminal settling velocity increases with particle size and i s proportional to the square of the p a r t i c l e diameter. The equation above i s limited to particles > 1.00 micron. An airstream particle < 1.00 micron behaves differently because there i s an interaction between the particle and the gas media. For such particles, a correction factor, which i s a function of particle size must be applied, C c = [1 + (2.52n)/(d)] Cunningham correction factor : Mean free path of the a i r : Particle diameter, micro-metre Applying this correction to Stake's Law gives, VTSV = (P pd 2gC c)/(18n) This equation i s based on spherical particles but i n practice dust i s nonspherical and hence careful consideration must be taken before applying thi« equation to any situation. Theoretical deposition studies i n tunnels under the action of gravity resulted i n the equation below (Fuchs, 1964). c c = n d E = (VrgyL) / (2HD) 80 Where, E = Dust deposition efficiency L = Length of the tamnel or roadway, metres H = Height of the tunnel or roadway, metres U = Mean a i r velocity, m/s Fuchs equation did not take the a i r flew mode (laminar or turbulent) into consideration and hence this equation was rearranged i n order to f i t s pecific a i r conditions (Hardcastle and Knight, 1985). Knight and Hardcastle came up with the following equation, A = Total floor area of the roadway, and Q = Volume of airflow I t i s important to apply a size correction factor before Vrpgy can be used i n the two equations developed by Knight and Hardcastle. The two researchers used the above two equations to compute settling efficiencies of different particle sizes for two hypothetical roadways. Their results are set out i n Table 23. From the data presented i n this Table, i t can be seen that, area to floor ratio plays a very important role i n dust deposition patterns along the roadway. Most coarse dust i s deposited i n the Roadway 1 whereas most of the respirable dust remains suspended. Taminar flow Laminar flow Ejp = 1 - (Exp [(V T S V*A)/(2*Q)] Turbulent flow Where, Also, for turbulent flow there i s a slight decrease i n sedimentation efficiency for coarse dust. Dust deposition study i s an essential pre-reguisite element for any controlled recirculation system application, particularly for local recirculation schemes. Table 23. Gravitational Settlement Losses Particle Aerodynamic Fractional Particle Loss from Settlement Diameter, micrometer Roadway 1, A/Q = 600* Roadway 2 = A/Q = 15 "h'laminar Turbulent Laminar Turbulent 1 0.01 0.01 0.0003 0.0003 2 0.04 0.04 0.0010 0.0010 5 0.24 0.21 0.0060 0.0060 10 0.69 0.06 0.0200 0.0200 15 1.00 0.90 0.0500 0.0500 20 1.00 0.97 0.1000 0.1000 50 1.00 1.00 0.5000 0.4000 100 1.00 1.00 1.0000 0.8500 *Roadway 1 - 3 x 6m cross-section, 1 , 0 0 0 m long, 1 0 m3/s airflow, A/Q = 6 0 0 Roadway 2 - 2 x 3 m cross-section, 1 0 0 m long, 2 0 m3/s airflow, A/Q = 15 ^laminar flow, R Q < 2 0 0 0 ; Turbulent flow, Rg > 2 3 0 0 . '' 82 2.7.5.2 Inertial Settling Inertia 1 settling i s a very important coarse particulate removal mechanism. In this process, particles with sufficient inertia are unable to follow the a i r streamlines when the flow i s deflected, and w i l l impact on the walls of the tunnel. m addition, i n e r t i a l settling i s influenced by wall roughness, and obstacles i n the airways. These obstacles can significantly increase i n e r t i a l impaction. Knight and Harticastle, 1985 reported two studies by Ford, 1976 i n coal mines to investigate the respirable dust deposition within a heading. The results showed considerable deposition over 100 * L/d n; (approximately 300 m). Where, L i s length and ^ = hydraulic diameter. The authors used the terminal settling velocities given by Ford and Reihardt to calculate the sedimentation rate using the same roadways presented i n Table 24. They found that there were considerable discrepancies between theoretical gravitational settling and measured sedimentation (between 10 - 20%) settlement by theoretical calculation and between 30 - 60% settlement with f i e l d data. Knight and Hard castle attributed the discrepancy to ine r t i a l settlement. 2.7.5.3 Diffusion Very fine particles (< 0.1 micron) i n s t i l l a i r w i l l experience a phenomena called Brownian motion. There i s a continuous bombardment between gas molecules and airborne particles. /• 83 This phenomena leads to diffusion of particles from a region of high concentration to a region of lower concentration. As a result of thi? transportation mechanism, particles w i l l be deposited cn the surface walls of the roadways. Knight and Hardcastle, 1985 calculated losses due to diffusion i n two hypothetical roadways using a solution given by Fuchs, 1964. Table 24 shows the calculated losses due to diffusion using three equations, 12, 13 lnd 14 presented i n Knight and Hardcastle, 1985 publication. These results shew that diffusion losses to the walls of the chamber only become significant for very fine particles. 2.7.5.4 Agglomeration Agglomeration i s a process whereby particles c o l l i d e with one another due to a relative motion between them and then adhere to form larger particles. The net result i s a continuous decrease i n number concentration and an increase i n particle size. Dreshler, 1985 investigated the rate at which submicron particles are scavenged by water droplets. His experimental measurements agreed with theoretical work by Wang et a l . , 1978 and showed that agglomeration of particles onto a water droplet decreased rapidly with increasing humidity. For metal mines, with humidity of over 80%, scavenging of submicrometre particles by water droplets w i l l probably be negligible. - ' 84 In potash mines particle agglomeration can be a significant dust removal mechanism due to the low humidity levels (less than 50%). Table 24. Diffusion Losses Particle Fractional Loss to Walls from Diffusion Size Roadway 1 Roadway 2 micron L/Q = 100 B/h = 2 L/Q = 5B/h = 1.5 Eq*: 12 14 13 12 14 13 0.1 _+ - - - -0.01 .001 .003 .0002 - -0.001 .03 .07 .015 .004 .006 .0005 0.0001 .55 .95 .31 .09 .12 .03 Note : Diffusion losses are negligible for particle size above 0.01 microns. In summary, dust i n the a i r can be separated into two fractions, namely mineral dust and diesel particulate matter. Highly dieselised mines w i l l have both dust fractions while non-dieselised mines w i l l have the mineral dust only. A large portion of the respirable dust i s over 1 micron i n size and hence i n e r t i a l and gravitational sedimentation w i l l be most effective i n removing this size fraction from the airstream. ' 85 Most diesel particulates are < 1.00 micron and dilution and f i l t r a t i o n by mechanical means could be effective i n removing particulate i n the airstream. The behaviour of submicxometre particles under the influence of phenomena such as diffusion and agglomeration needs to be investigated further. The selection of a removal mechanism i n a recirculation system requires the Imowledge of the particulate characteristics i n the airstream. 2.7.6 Dust Ignition Control Methods Several underground metal mines i n Canada have potential for recirculation but experience sulphide dust ignition problems. Well documented cases include the Ruttan mine i n Northern Manitoba, Noranda's Geco Division, the Fox mine i n Lynn Lake, Manitoba, Heathe Steele Mines i n New Brunswick and minor explosions at the H-W mine i n Campbell River, B r i t i s h Columbia ( Hall, 1989; Mchaina and Hall, 1987 ). Sulphide dust explosions have also occurred at No. 2 mine of Kidd Creek Mines Limited. The majority of these mines can employ controlled recirculation of exhaust mi™* a i r to improve their ventilation efficiency and costs. These m-infta have modified their methods to provide preventative measures against sulphide dust ignitions. The methods include:-inert stemming, water sprays, water bags for stemming, passive and triggered barriers, water atomizers prior to blasting and ventilation ( Mchaina and Hall, 1987; Hall, 1989; Enright, 1984). The effective use of these methods w i l l enhance the application of controlled recirculation i n mines wining sulphide ores. CHAPTER * T T n ? ' R T : ; REVIEW QF TYPICAL CANADIAN AND SOUTH AFRICAN MINE ENVIRONMENTAL CONDITIONS 3.1 INTRODUCTION Heat i s one of the major environmental hazards i n deep South African gold mines. These mines have problems i n keeping the underground a i r temperatures below 30 °C to prevent heat stroke and heat exhaustion i n their labour intensive workings. Autooompression and heat from rock are the main sources of heat i n these deep gold mines. In order to maintain the underground environment within the legal limits, the majority of these mines are required to refrigerate their ventilation a i r . The amount of a i r circulated through the mine i s restricted by the shaft sizes and the use of underground cooling plants or refrigeration machines presents performance problems/ especially adequate heat rejection. As the depths increase, the heat load necessitates either more frequent re-cooling or an increased airflow at the working faces. The re-cooling of a i r by small coolers i s an expensive method of distributing refrigeration. 87 j '-r .. -I f additional a i r i s to be supplied from surface, fan power requirements w i l l r i s e significantly because an increase of 30% i n airflow requires an increase i n fan power of about 120%. An alternative to the •JTv-rr***?^ supply of a i r from surface i s to increase the sectional flow rate by recirculating return a i r to the face intake. This can be achieved when the return a i r quality i s good. The method i s not suitable for mines containing radon gas because i t increases the residence time of the a i r i n the mine. An intensive research effort into the potential application of controlled recirculation i n gold mines has recently been undertaken. Many researchers concentrated their efforts on the potential benefits of i - y i m V v i n T T v j controlled recirculation with refrigeration and dust f i l t r a t i o n to achieve improved temperature and dust control. Several South African mines have methane problems. Mines i n the Evander and Orange Free State gold f i e l d s experience methane emissions. In order to reduce the r i s k of methane explosion, the South African Authorities have produced guidelines for dealing with methane. The guide c a l l s for regular m A f - n * w A tests and requires a l l the mines to in s t a l explosion proof e l e c t r i c a l equipment and to use flameproof diesel engines. The presence of methane gas i n these mines does not r e s t r i c t the application of controlled recirculation to augument the conventional ventilation system. Some Canadian mines are subject to the presence of radon gas, Radon creates problems i f i t decays to produce the radon daughter products (?°218' E b214 / B*214' a n ^ P o214^ * 1 0 6 r * s k i s minimized by reducing the time that the gas i s resident i n the mine. Good general ventilation supplies adequate oxygen, maintains suitable ambient temperatures, and dilutes and removes the harmful dust, gases, mists, and combustion products. A major problem i s that radon - daughter growth increases the radiation hazard with time. Adequate ventilation W i l l effectively reduce residence time and dilute radon and i t s daughters. Uncontrolled recirculation of mine a i r from the return to the intake i s restricted i n mines with radon gas emission. Radon gas emissions i n these m - i T M * * r e s t r i c t the use of controlled recirculation. Mines m - i n - i i y j massive sulphide ore are subject to ignition depending on the ore composition. Most mines test sulphide ores i n advance of mining to ensure that they are not prone to ignition. Secondary ignitions usually occur after blasting i n ores with high sulphur content. SOj i s one of the by-products of sulphide dust ignition. The sulphur dioxide gas released from the explosion can be then drawn into the intake airways. The majority of the mines experiencing such ignitions withdraw a l l labour from underground during blasting, but this leads to production delays. ' 89 Some precautions taken by the Canadian w r i i v i i v j industry include the use of water or limestone stemming, water foggers and washing down the face area before blasting. The exhaust pollutants emitted from the combustion process of diesel engines represent a principal concern over the use of the equipment i n underground mines. As the number of diesel units and their ratings increase, concern over health effects of the exhaust emissions have N*-*w» more significant than ever before. The issue of proper control of diesel exhaust emissions i s complex because i t involves a number of unrelated parameters such as the equipment operating mode and condition of the engine, the mine environment and the operator's habits. A l l these factors influence the exhaust emission concentrations and composition. Canadian underground mines are highly mechanized, unlike the South African mines which are labour intensive. Hence diesel pollutant characteristics are essential parameters for consideration when carrying out f e a s i b i l i t y studies f o r recirculation. 3.20 PRINCIPLES QF CONTROLLED RECIRCULATION Recirculation of mine a i r means that the same a i r flows more than once past a given point. The basic configurations of recirculation systems are shown in Figures l and 2. With reference to Figure 1, Branch A-B i s referred to as the intake to the recirculation c i r c u i t , or just the intake. 9 0 Heaters Surface Intake Fan B Qi Ci Recirculation Connection v Qr Cr Exhaust Fan Recirculation Fan Mixed Intake Qt Ct Qe Ce Face Emissions Figure 1. Simple Mine-Wide Recirculation System n c ] F ii 11 F R O O Fan Regulator -R-c F o o F R Fan Regulator Figure 2. Ex tended Distr ict Rec i r cu la t i on S y s t e m Flow and pollution concentration of this branch, Qi, and C^, are termed fresh airflow to the system and intake concentrations. Branch B-C i s referred to as the mixed intake flow and pollution concentrations of fcn-jg branch, Qj., and C*., are termed mixed intake airflow to the system and the mixed intake concentrations respectively. Branch E-B i s referred to as the recirculation connection/crosscut to the recirculation c i r c u i t . Flow Qr, and concentration C^., are called recirculation quantity and recirculation concentration respectively. There are three main recirculation system modes: mine wide, face , and d i s t r i c t recirculation systems. Mine wide recirculation systems are not common because they require intensive monitoring of the entire mine ventilation parameters. In the case of monitoring and equipment failure i n a mine wide system, contaminants could be recirculated to a l l parts of the mine. Face and d i s t r i c t recirculation systems are common i n the B r i t i s h coal m-Stiing industry. A d i s t r i c t i s a section of an underground mine, served by i t s own roads and ventilation airways. District recirculation and face systems are easy to monitor i n terms of system volumetric efficiency and other ventilation parameters. Recirculation configurations depicting these systems are shown i n Figures 3 - 12. 9 3 Figure 3. Layout and Definition for Simple District Recirculation System 94 B = C r o s s - c u t S y s t e m F i g u r e 4. S i m p l e R e c i r c u l a t i o n S y s t e m s F i g u r e 5. W i d e S c a l e D i s t r i c t R e c i r c u l a t i o n S y s t e m 9 6 H e a d i n g / F a c e Q 2 Q3 Q 4 Q 1 t Q 5 Figure 6. Distr ict Rec i rcu la t ion S y s t e m c D a: -R-] F F R Fan Regulator o o c 3 -R-F R Fan Regulator Q) O O Figure 7. S imple District Recirculat ion Sys tems 9 8 Heaters Surface Intake Fan B Q2 C2 Q1 C1 Recirculation Connection _ Q4 C4 Exhaust Fan Recirculation Fan Mixed intake Q5 C5 Q3 C3 Face Emissions F = Q4/Q3 or F = Q4/(Q1 +Q4) Figure 8. Mine—Wide Recirculation System General Configuration for Potash Mines 99 H e a d i n g / F a c e Fan Q6 Q7 Q8 Figure 9. Forcing Heading System with Recirculation Overlap Figure 1 0 . Exhausting Intake Advance Heading Recirculation System 101 Figure 11. Forcing Return Advance Heading Recirculation System 102 ure 1 2 . An Ex tended Over lap S y s t e m of Rec i r cu l a to r y Ventilation in an Intake Advance Face 103-Fan position i n recirculation c i r c u i t s i s important i n that i t affects the overall system performance. There are two m a i n alternative sitings, namely with the fan i n the recirculation cross-cut or i n the intake or return roadway (in-line s i t i n g ) . These alternatives are detailed i n Figure 4. In the cross-cut the fan f u l f i l s s t r i c t l y a recirculation role enabling a flow of return a i r to move up pressure gradient from return to intake. In this position the recirculation fan opposes the fans i n the main network and i f this fan i s uprated to increase the flow rate of the recirculation fraction, i t also reduces the fresh a i r flow rate into the recirculation c i r c u i t . In this position only the a i r being recirculated passes through the fan and therefore a lower volume and lower powewed recirculation fan i s necessary than the inl i n e position ( Lee and Longson, 1987 ). S i t i n g the fan i n the recirculation intake or return enables i t to f u l f i l a booster /recirculation duty as i t i s aiding the other fans i n the ventilation network. In this position recirculation i s initiated by creating a short c i r c u i t through the recirculation crosscut. The balance between fresh a i r and recirculated a i r can be conveniently controlled by regulation of this crosscut. At f u l l regulation such as a sealed crosscut, the fan would act entirely as booster fan with the fan power f u l l y directed to pulling fresh a i r into the c i r c u i t . A low resistance recirculation crosscut directs the recirculation fan power to the recirculation zone i t s e l f and consequently results i n the minimum of interaction between the zone and the remainder of the ventilation network (Lee and Longson, 1987 ). 104 3.2.1 RECIRCULATION FACTOR, F j '-s .. . Recirculation factor or fraction i s a term used to define recirculation quantitatively. This factor, theoretically has the range 0 to 1.0, but i t i s norma "My converted to a recirculation percentage. With reference to Figure 1, recirculation factor or fraction, F, i s F = (Qr/Qt) where, Or = the recirculated quantity. Of. = the quantity flowing i n the return directly in-bye of recirculation path, and recirculation percentage i s F*ioo = (Or/Of.) *ioo 3.2.2 RECIRCULATION FAN SITING For recirculation to take place, the pressure difference between the intake and return airways must be reversed to cause a i r to flow from the return airway back into the intake airways (Lee, 1983). There are two types of recirculation, namely, crosscut and in-line recirculation systems (Lee, 1983). The crosscut recirculation configuration requires a recirculation fan to be located i n a crosscut between the intake and return airways. 105 In-line recirculation configuration involves a recirculation fan located - -either i n the recirculation intake or i n the recirculation return (Lee, 1983). Recirculation fan pressures and power requirements for both modes are given below (Anderson and Gostylla, 1988). i) Crosscut recirculation mode: P r f c = Ra*Q2 +R X((F*Q)) 2 APRj, = (Rd + R X*F 2)*F*Q 3 i i ) In-line recirculation mode: p r f i = < R* p 2 + Kd)* 0 2 Anderson and Gostylla developed a more generalized power requirement equation: APR = A*(R Q + R^*!"2)*©3 Where, A = P, for crosscut recirculation A =1, for in-line recirculation Q = d i s t r i c t airflow with recirculation (m3/s) Rg = d i s t r i c t resistance (Ns 2/™ 8) Rg = Resistance of the crosscut (Ns^/m8) 106 Siting the fan i n the recirculation crosscut i s convenient because s '-/ the fan w i l l move only the desired proportion of the return a i r back to the intake. When the fan i s located i n this position i t i s i n opposition to the other fans i n the network. This nay result i n a reduced flew rate of fresh a i r into the recirculation c i r c u i t . S i t i n g the fan i n the intake or return airways, results i n the recirculation fan aiding the main system fans and contributing a boosting effect which increases the fresh a i r flow rate into the recirculation c i r c u i t . The a i r flow rate distribution i n the network i s the same whether an intake or return in-line s i t e i s chosen for the recirculation booster fan. The choice i s usually determined by power av a i l a b i l i t y , fan size, accessibility for inspection, position of doors and airlocks and the conditions existing at the alternative sites for a given recirculation system and individual mine situation for selection. 107 s / 3.30 EVALUATION OF CHANGES INDUCED BY THE INTRODUCTION CF REC1KCULATORY VENTILATION SYSTEMS 3.3.1 Gaseous Pollutants With reference to Figures 13-14, and assuming the ventilation system has reached steady state, the total amount of contaminant arriving at the recirculation junction (position 2) i s given by the relationship: where, Cj. = the return a i r concentration, ppm. C^ = the intake a i r concentration, ppm. C = contaminant emission rate, kg/s. Q.£ = intake quantity, m3/s. Qj. = recirculated quantity, m3/s. Total contaminant flow rate i n the return airway i s (Qi + Or)* Cj. (2) Equating both equations (1 and 2) results i n the following equation. 108 - B -2 Cr - B 1 Qi Ci Working Area Figure 13. Normal Ventilation System — Without Recirculation Qi Ci Qm Cm Figure 14. Ventilation System with Recirculation 109 QiPr = °d ci + c > cr = c i + <c/°d> Cr = C±+ (C/Q±) (3) Sa = {[(QiCi) + (C^n /HQi + Qp)]}.... (4) Recirculation fraction/ R i s R = [(QrH/nQj. + Or)] Therefore/ = c ± + (R^J/CC-) (5) I f there i s no recirculation, the mixed intake concentration w i l l be equal to the intake airway concentration. i 3.3.2 Particulate Matter The concentration of airborne dust i s controlled by deposition and f i l t r a t i o n (with the exception of particles much smaller than 1 micrometre). 110 Theoretically, the a i r flowing i n the recirculation c i r c u i t ^ n be s '-/ - • Shown to be made up of elemental parts that are on their f i r s t , second, third, etc.. pass through the system. Each of these elements i s increasingly smaller as they are repeatedly cut by the recirculation fraction. At steady state these form the components of a geometric series (Hardcastle, 1983), 8 ^ = 8 * * U * * : : : %t&% The return dust flow (g/sec) mass i s also composed of similar elemental parts and i s represented by a geometric composition: = *R± + ^ R i + + ••• + 1 % i ••• ( 1 ) Where, d j ^ = i n i t i a l dust flew (g/sec) i n the return a i r . If a sedimentation term represented by S i s included i n the geometric series, then *ER = *Rx + MRid- 8) + ^ d j ^ d - S ) 2 + F ^ U - S ) 1 1 (2) s The sedimentation of particulate matter can take place under the following mechanisms, gravitational settling, inertia 1 settling, diffusion and coagulation. The details of these processes are described i n the previous sections of this chapter. I l l The sedimentation factor i s assigned constant for every pass the dust makes through the c i r c u i t . Sedimentation i s size selective and i t s efficiency w i l l decrease as the dust becomes depleted of the largest particles and hence the above series (2) becomes, *TR = *RL + ^ R i * 1 - 8 ! ) + F 2d Ri< 1- f il> l1"6!* * — P n d R i ( l - S 1 ) ( l - S 2 ) . . . ( l - S n ) (3) Considering the effect of f i l t r a t i o n i n the system, the series (3) djjj = dj^Cl + P*f (l-S) + i^ f^ ci-s) + ... + F ^ f ^ l - S ) ] In practice S 1 > S 2 > . . . . > S n A detailed modelling of dust behaviour i n a recirculation system i s given elsewhere (Bardcastle, 1985). Bardcastle presented a pioneer study on the prediction of airborne respirable dust concentrations i n mine a i r recirculation systems. 3.40 SUMMARY AND INITIAL CONCLUSIONS Controlled recirculation of mine exhaust a i r i s a practical method of reducing power costs and increasing a i r flows i n underground mines. Preliminary investigations at Ruttan mine have shown that controlled recirculation i s feasible (Hall et a l . , 1988, 1989). Knowledge of contaminant sources, concentration levels and removal mechanisms i s essential i n determining the f e a s i b i l i t y of recirculation systems. CHAPTER FOUR APPLICATION OF GCNIROLLED RECIRCULATION GF MINE EXHAUST AIR IN POTASH MINES AND METAL MINES 4 .1 UNDERGROUND MINE EXHAUST AIR RECIRCULATION DECISION LOGIC In a l l cases tne decision to use exhaust a i r has to be carefully planned. I t i s essential to determine the exhaust a i r quality/ quantity and the overall behaviour of contaminants throughout the system; and the costs and potential savings of the system. I t i s important to establish c r i t e r i a which should be followed when assessing the f e a s i b i l i t y of recirculation for a particular ventilation system. This involves technical f e a s i b i l i t y and economic assessment of recirculation f e a s i b i l i t y . Technical f e a s i b i l i t y of recirculation depends sometimes on the av a i l a b i l i t y of an a i r cleaner with the desired efficiency for each of the contaminants requiring cleaning and the a v a i l a b i l i t y of a technique for detecting failures i n the cleaning system. An economic assessment of a recirculation f e a s i b i l i t y should address the following: i) The ava i l a b i l i t y of energy and i t s cost, i i ) The cost of design studies for a recirculation system, i i i ) The capital cost of scrubbing systems/ monitors/ alarms/ fans, modification of existing f a c i l i t i e s , telemetry system/ data display system/ f i r e doors and the recirculation control package, iv) The operating costs 113 An assessment of the f e a s i b i l i t y of recirculation from an engineering / point of view should take into account the following: i) Estimation of the a i r quality parameters required for system design, i i ) A b i l i t y to maintain tne system especially the monitoring and f i r e detection packages to ensure adequate levels of performance, i i i ) Overall, the most important consideration i n assessing the f e a s i b i l i t y of a recirculation system i s the safety of the underground worker. A decision logic flow sheet i s composed of: i) T n i t i a l approach ( identification of recirculation configuration and a v a i l a b i l i t y of instrumentation). i i ) Decision and system assessment, i i i ) System evaluation. A systematic flowsheet i s developed to give guidelines for the design and evaluation of recirculation systems. The logic flowsheet i s general i n nature and can be used i n a l l aspects of controlled recirculation. 4.2 FEASIBILITY OF RECIRCULATING MINE EXHAUST AIR IN POTASH AND METAL MINES Between September 1987 and May 1989, tests were conducted underground at Central Canada Potash of Noranda Minerals Inc., Rocanville Division of Potash Corporation of Saskatchewan (PCS) and H-W mine of Westmin Resources. These studies were conducted to determine the f e a s i b i l i t y of j / introducing controlled recirculation of mine return a i r i n order to reduce heating costs and to increase face a i r flows. The monitoring strategy was planned to give information on the behaviour of the underground mine contaminants between the intake and exhaust shafts, along roadways and at working faces. Further studies were conducted at the H-W mine of Westmin Resources to quantify sulphur dioxide during blasting i n p y r i t i c ore formations. Westmin Resources mi™* was selected because of i t s proximity to the University. H-W mine i s gassy and dusty as far as underground environment i s concerned due to the sulphide dust ignition incidences, m addition, the following qualifications were also considered i n obtaining an appropriate test mine s i t e : -i) Sulphide dust ignition history for the mine. H-W mine has been experiencing sulphide dust ignitions for the past three years, i i ) Explosion-prone high sulphur ore deposits being mined, i i i ) Management interest. The H-W mine management expressed high interest and commitment to the investigation. The f i r s t series of studies at the H-W mine involved the monitoring of sulphur dioxide before, during, and after blasting. 115 One more test was cxsnriucted on the 2400 level while blasting 350 j  : / longhole stope. A l l sensors were positioned i n the return side of the blast area at about 60 metres from the blast extremities. This was approximately 30 metres behind the water foggers. The second experimental program involved the monitoring of exhaust a i r quality. Continuous monitoring of gaseous pollutants was conducted i n order to determine the f e a s i b i l i t y of introducing controlled recirculation to increase mine a i r flows. The monitoring station was i n 21-337 Drive East, East of 2100 level main diesel shop exhaust ventilation door. Total a i r flow through the d r i f t during the survey was 125 m3/s (253,400 cubic feet per minute (cfm)) or 30% of the t o t a l mine a i r quantity. Questionnaire surveys were done i n order to establish preliminary information required for the selection of potential mines for the study. 4.2.1 Questionnaire Survey A questionnaire survey was designed and circulated to the major potash producers and the Saskatchewan Provincial government. The results were analysed and v i s i t s were made to Central Canada Potash Division of Noranda Minerals Inc., and Rocanville Division of PCS. A decision was made as a result of the v i s i t s to conduct underground investigations at CCP and Rocanville Division to determine the potential for the application of a controlled recirculation system at the mine. 116 Another questionnaire survey vas conducted to determine the a i r J / quality conditions i n Canadian underground mines. Part of this research work involved obtaining underground a i r quality conditions relating to recirculation parameters i n Canadian metal mines. About 32 mining companies and regulatory organizations i n Canada were contacted to provide underground environmental data. The response from the questionnaires was not good. Five replies were received from the companies. 4.2.2 Requirement of A i r Quality Survey for Controlled Recirculation The a i r quality survey program requires a system approach i n order to meet the overall objective of worker safety. The main element that must be evaluated before proceeding with the system design i s the characterization and v a r i a b i l i t y of the airstream and contaminants to be recirculated. These are:-i) Gas properties, i i ) Particulate properties, i i i ) Thermal properties, iv) Mass flow rates, v) Build-up of contaminants. The experimental design for this project addresses the above c r i t i c a l elements which dictate gas and particulate removal mechanisms and equipment selection. 117 4.2.3 Experimental Program and Methods An essential element i n the study of airborne contaminants i s the a b i l i t y to collect representative samples for analysis and evaluation. These samples must accurately reflect the airborne concentration and their characteristics. In the case of particulates the samples must not only r e f l e c t actual particulate concentration but also size distribution. Stationary sampling technique was used tJiroughout the experimental program. This refers to placement of the sampling apparatus at a fixed location i n the workplace f o r the duration of sample collection. Sampling heads containing f i l t e r s and direct reading instruments were used to determine particulate concentrations. Draeger stain tubes and continuous monitoring instruments were used to determine gas concentrations. 4.2.3.1 Gas Sampling Two basic approaches were used i n sampling mine atmospheres: 1) Grab or single samples or short-duration samples. 2) Continuous samples. Sampling using Draeger or similar tubes, relying on visual colour indicators to assess pollutant levels constitutes a grab sample. Sampling using stain tubes i s simple and inexpensive but they have an accuracy of about + 25% (Johnson et a l . , 1977; Bardswich, 1977). 118 • '•• - / Accordingly to Johnson and colleagues the tubes gave higher readings fcnaw for comparable samples measured with more accurate instruments . Since short-duration grab sampling tends to isolate localized activity and i s not indicative of long-term average concentrations on the working section, the major part of the monitoring program i n t h i s thesis was based on continuous sampling technique. Continuous atmospheric sampling or monitoring i s the preferred technique, and permits time - weighted average data to be obtained for a f u l l or p a r t i a l s h i f t . Continuous sampling instruments were used to continuously sample, measure and record the pollutant concentrations. In addition a Draeger polymeter was used for the determination of the mean value of the gas concentrations i n the a i r over the sampling period. Special Draeger long-term detector tubes were used . The volume of a i r drawn i s about 15 cm3 per minute, calculated i n the following manner: V [cm3] = kO^-No) where, k = hose constant = 0.75 cm3/rev, N Q and are i n i t i a l and l a s t counter indications. The detector tube i s located inside the instrument i n such a way that i t i s protected from external flying objects by a cover. This permits i t s use i n areas subject to explosive sulphide ignitions, without damage. Sampling using the Draeger polymeter was limited to the work conducted at the H-W mine only. 119 Continuous sampling was carried out to quantify a i r quality conditions i n terms of SOj, CO, CC^/ NO and NOj concentrations. Tne electrochemical detection method was used for T""nitaring concentrations of a l l gases except COj which used an infrared measuring technique. Grab samples were taken every 30 to 60 mi mites for the following gases: CO, COj, NO, NOg, SOg, and NQg. Time Weighted Average (TWA) data was obtained using a bag sampling technique. A Dupont type P4000 pump, was used to slowly f i l l an 8 l i t r e evacuated Tedlar bag with a continuous sample of a i r . The pump was set at a flow rate of 20 m i l l i l i t r e s per minute. The a i r i n the bag at the end of a sampling period was analysed using Draeger tubes and TWA concentrations were obtained. 120 4.2.3.2 Particulate Sampling Dust sampling experiments were conducted i n order to accurately collect representative samples which r e f l e c t the airborne concentrations. Gravimetric and instantaneous concentration were determined i n the return, intake and mixed intake airways. Further experiments were conducted to determine the particle size distribution of samples. Dust deposition studies were conducted i n the return airways using gravimetric dust pumps, instantaneous d i g i t a l dust indicator, and collector plates. F i l t r a t i o n i s a simple method for determining the mass concentration and for collecting samples for compositional analysis of airborne particles and for compositional examination of collected particles. 4.2.3.2.1 Gravimetric Sampling The most rvmmcm way to determine aerosol mass concentration i s to pass a known volume of the aerosol through a f i l t e r and determine the increase i n mass of the f i l t e r due to the collected aerosol particles. To make such measurements required the accurate weighing of a f i l t e r before and after sampling and accurate measurements of the sampling flow rate and sampling rate. The analytical balance used was a mechanical beam balance that can weigh f i l t e r s to an accuracy of 0.01 mg. The f i l t e r s were 37 mm i n diameter. The airflow rate for a l l samples was set at 2.0 l i t r e s per minute. In order to minimise errors the sampling time allowed was made long enough so that the collected mass was large enough compared to the v a r i a b i l i t y i n f i l t e r weight. 121 The f i l t e r s were allowed to equilibrate for at least 1 hour i n the laboratory environment before each weighing. The relative humidity of the laboratory environment was between 35 and 45 + 5%. Static charge accumulations an the f i l t e r s were neutralized by holding the f i l t e r near an alpha radiation source before weighing. Eight Dupont personal samplers were operated at a flow rate of 2.0 l i t r e s per minute. Airborne dust samples were taken from the return (exhaust) station, main intake airway, and during the recirculation t r i a l . Tn order to minimize experimental errors, for each five sampling f i l t e r s , one f i e l d blank f i l t e r was prepared. Blank samples were treated i n the same fashion as rea l samples, i.e. they were opened at the sampling station and immediately closed and packed with the samples that were collected and given the same analytical treatment. Blanks were used primarily to assess contaminants i n the sampling media, as well as to monitor potential contamination of samples both i n the f i e l d and i n the laboratory. The blank analyses results were subtracted from the analytical results obtained from the real samples. This allowed the data to be adequately corrected for any contamination that may have been present i n the sampling media or that may been added by way of handling the analysis. Isokinetic sampling procedures were observed for each measurement i n order to get representative samples. The samples were weighed and concentrations were computed from the weight of the dust load and t o t a l volume sampled. 122 Instantaneous dust levels were determined using an MDA model P-5L d i g i t a l dust indicator. Cascade impactor samples were collected at a variety of panel return locations. The model 298 Marple cascade impactors manufactured by Andersen/Sierra were borrowed from B.C. Research and Pennyslvania State University, Department of Mineral Engineering for the investigation. In t h i g research project the impactors were used for positional sampling purposes. During collection the dust was divided into fractions which were later weighed separately. The nominal size separations of the stages are 21, 15, 10, 6, 3.5, 2.0, 0.9 and 0.50 microns. The impactor operated at a flow rate of 2 l i t r e s per minute and used the same pump as the personal cassette sampler. Sampling duration was 5 to 8 hours. Dust deposition studies were conducted to determine the extent of dust settlement as the a i r moves from the face to the extremities of the return airway. Throughout the sampling period the barometric and temperature conditions of the sampling s i t e were substantially different from those at the calibration s i t e . Hence, correction factors were applied to the data. World Health Organization (WHO), proposed correction factors as set i n Tables 25 and 26 (WHO, 1983). Another way of calculating correction factors i s as follows: Qs = Q 0*« pc * T s > / < P 8* Tc» 1 / 2 123 Where, Qg = Flow rate at sampling station, l i t r e s per minute. QQ = Flow rate when rotameter i s calibrated, litres/minute. T c = Temperature during calibration, Kelvin. T g = A i r temperature at sampling station, Kelvin. P c and P s are barometric pressures during calibration and at sampling point respectively, Pascals. Concentrations i n mg/m3 can be converted to parts per million (ppm) when sampling i s done at temperatures and pressures different from 25 °C and 760 mm Hg. PPM = mg/m3*24.45*litres/mole In order to apply correction either correct the sampled volume to 25 ° c at 760 mm Hg or change 24.45 l i t r e s per mole to sampling temperature and pressure. The results are the same, regardless of which correction method i s used. v s t p = v ^ v w ^ w w 124 .. • /*. ''' Table 25. Correction Factor for Temperature / . . . . (Source: WHO #80) Temperature Factors to be Applied to Calibrated Flow Rate i f Difference i n Centigrade The Sample Site i s Hotter Sample Site i s Cooler 0 1.000 1.000 5 1.009 0.991 10 1.018 0.983 15 1.027 0.974 20 1.036 0.966 25 1.045 0.958 30 1.054 0.949 35 1.063 0.941 40 1.072 0.933 125 Table 26. Correction f o r Elevation s / .. . (Source: WHO Offset Publication No. 80) Altitude Difference Factor to be Applied to tne i n 1000 Feet Calibration Flow Rate The Sample Site i s Higher The Sample Site i s lower 0.0 1.000 1.000 0.5 1.009 0.991 1.0 1.019 0.982 1.5 1.028 0.973 2.0 1.038 0.964 2.5 i 1.047 0.955 3.0 1.057 0.946 3.5 1.067 0.937 4.0 1.077 0.929 4.5 1.087 0.920 5.0 1.090 0.912 5.5 1.107 0.903 6.0 1.117 0.895 6.5 1.128 0.887 7.0 1.138 0.879 7.5 1.148 0.870 8.0 1.160 0.862 126 • . f. . ' 4.2.3.2.2 Instantaneous Sampling Instantaneous dust levels were measured using the sibata P-5L D i g i t a l Dust Indicator. I t i s an extremely sensitive lig h t scatter detector for the measurement of respirable dusts. The instrument used features both an analog ratemeter and d i g i t a l display, the P-5L provides continuous concentration data and accumulates dust levels over time simultaneously. The measuring range for t h i s model i s 0.01 to 100 mg/m . 4.2.3.2.3 Isokinetic Sampling Isokinetic sampling i s a procedure to ensure that a representative sample of dust (particulate) enters the i n l e t of a sampling probe when sampling from a moving aerosol airstream. This means that the extraction of a particulate sample from a flowing f l u i d i s done at a velocity equal to that of the stream at that point. This ensures that the sample w i l l contain the same size and number range as i n the original stream per unit volume. I f sampling i s isokinetic there i s no particulate loss at the i n l e t regardless of particle size or inertia. A fai l u r e to sample isokinetically (anisokinetic sampling), may result i n a distortion of the size distribution and misrepresentation of the concentration. If isokinetic sampling conditions are not met, there i s no way to determine the true concentration unless the original particle size distribution i s known. 127 For each sampling station, the airstream velocities and quantities were calculated and sampling probes were selected. The sampling probe size, d, was calculated as follows:-(4 * Q p o J / O . U * V ) 1 / 2 = d Where, Qp f r = Pump flow rate. V = Probe i n l e t a i r velocity = airstream velocity. Throughout the experimental program isokinetic conditions were met. 4.2.3.2.4 Settled Dust Settled potash dust samples were collected from various mine locations to determine the relative amounts of soluble dust and insoluble dust. The percentage weights of in solubles were determined using a method established by Professor A.L. Mular and Mr. R. Ellwood of the Department of Mining and Mineral Process Engineering (MMPE), University of B r i t i s h Columbia (UBC). The procedure involved the following steps: i) A 47 mm, 5 micron millipore f i l t e r was weighed and placed i n the millipore f i l t e r holder, i i ) 5 grammes of settled dust sample was washed into the millipore f i l t e r holder mounted on a vacuum system (pump). 128 i i i ) The sides of the f i l t e r holder were rinsed down twice after a l l j -f the water had drained, iv) The vacuum system was turned o f f and the f i l t e r transferred to watch glass and placed i n a drying oven, v) The f i l t e r was then taken from the oven and allowed to cool/ and i t s weight was taken, vi) The weight of the loaded f i l t e r less the f i l t e r weight gives the water insolubles weight of the sample. The percentage weight of solubles was calculated from the sample weight (5 gm) and weight of insolubles. 4.2.4 Instruments and Materials The following instruments and materials were available for the research project. 1) AM 5000 anemometer. 2) Alnor series 6000P anemometer. 3) Sling hygrometer. 4) Draeger pump. 5) Draeger tubes for OO, COj, MO, NOj, NQg, and SC^. 6) Nova gas analyzer for CO, 0-50 ppm; CC^, 0-5000 ppm; NO, 0-10 ppm; N O 2 , 0-10 ppm. 7) City Technology types 3ST and 3SF sensors for SOj monitoring, measuring ranges 0-25 ppm and 0-2000 ppm respectively. 129 8) Nova Textactor I SQg monitor, measuring range 0-50 ppm. 9) Gastach Model 3600 COg monitor, measuring range 0-5000 ppm. 10) Esoom CO sensor type Escom 2T of Dowty automation systems, measuring range 0-40 ppm. 11) 8 l i t r e Tedlar sample bags, complete with colour detector adaptor k i t . 12) Draeger polymeter for Time Weighted Average gas concentrations. Complete with Draeger long duration detector tubes. 13) Gastech four channel data logger, model DL-1007C. 14) Squirrel d i g i t a l data loggers. 15) Hybrid thirty channel, recorder model 3088. 16) Strip chart recorders. 17) Gravimetric dust samplers. - Dupont type P4000 pumps. - Dupont type P2500 pumps. - Complete with f i l t e r holders 37 mm diameter. 18) MDA model P-5L d i g i t a l dust indicator. 19) Marple personal eight stage impactors. 20) Simple f l a t trays. 21) Millipore f i l t e r s . 22) Soap bubble meter (inverted 1 - l i t r e burrete). 23) Certified Matheson zero and span gases. 130 4.2.4.1 Calibration of Instruments Calibration of sampling instruments was done using standard procedures reccmmended by the manufacturers. The instruments calibrated include gas analysers, dust pumps, dust indicator, and anemometers. 4.2.4.1.1 Gas Analyser Calibration The analysers were calibrated before use and checked for deviations daily. Matheson zero gas and Matheson c e r t i f i e d CO, 00^, SC^, NO, and N O 2 gases were used for calibration. The analytical compositions of the span gases were as follows: Gas Output Ranges Calibration Gas Mixture i n Nitrogen (PPm) (ppm) CO 0 - 50 9.71 + 0.50 CO 0 - 100 72.00 + 1.50 °°2 0 - 5000 1041.00 + 21.00 °°2 0 - 5000 967.00 + 19.00 °°2 0 - 5000 2555.00 + 50.00 NO2 0 - 10 6.15 + 0.31 NO 0 - 10 5.39 + 0.27 *h 0 - 50 16.90 + 0.30 SO, 0 - 25 16.90 + 0.30 0 - 2000 1546.00 + 30.00 Zero gasfNj) - 99.90% 131 For the COg sensors, the true zero reading was established on the meters by inserting a COj scrubber i n the i n l e t port prior to span calibration. The instrument deviation was double checked by allowing a flow of nitrogen gas (zero gas) into the instrument. Where necessary, the Azero 7 adjust port was turned u n t i l the reading was zero. Span calibration was achieved by allowing a known calibration gas mixture into the instrument. The xspan' port was adjusted u n t i l the meter reading agreed with the calibration gas analysis. NO, span gas i s considered unstable and there i s a requirement to check i t before a survey ( Gangal, Mogan, and Dainty, 1986 ). In this study this requirement was not considered necessary since the calibration gas was prepared a few days before the surveys. 4.2.4.1.2 Dust Pumps Calibration The dust pumps were calibrated and checked for deviations after every two sampling v i s i t s . An automatic pump flow rate calibrator and a soap bubble-meter were used to determine nominal flow rates. Temperatures and pressures were recorded during calibration and sampling. calibration using the soap - bubble method i s described i n WHO publication No. 80. 132 . >• -4.2.4.1.2 Digital Dust Indicator Calibration Cancentration specifications are given as calibrated on a 1:1 r a t i o with stearic acid, mean particle size 0.3 micron. For i n - f i e l d calibration, the P-5L incorporates an internal light scattering board that i s d i r e c t l y related to the dynamic calibration. With this secondary calibration option, the P-5L was checked and readjusted to original factory specifications regularly. 4.2.4.1.3 Anemometer Calibration 10.2 cm diameter vane anemometers were used throughout the survey. The vane anemometer i s the most commonly used instrument i n the mining industry. The instrument i s practically independent of diminutive a i r density changes encountered i n mines. A l l a i r velocity measuring instruments were sent out to specialized laboratories for calibration i n wind tunnels. The calibrations are i n the form of Tables of plus-or-minus corrections to be made to the observed velocities. The application of these corrections was simplified by plotting the true a i r velocity (VT) against the registered a i r velocity (V_), which approximated a straight l i n e . 133 •. /• The general calibration curve equation for »11 anemometers i s : -V T = A + B*Vr, where, A = Intercept. B = Line slope or V T to V r ratio. 4.2.5 Underground Thermodynamic Survey and Network Analysis This part was not undertaken due to the fact that the f i n a l stage of the project was not implemented. However, i t was planned to investigate the impact of introducing a recirculation system into a mine network on airflow distribution. In order to quantify these effects a general mine network survey should have been conducted i n order to augument the data obtained during the f e a s i b i l i t y study. A cctnputerized ventilation network was important for this task. Continuous monitoring of temperature i n the return and WIVPA intake airways i s necessary i n order to quantify heat build-up due to recirculation. The following are the possible input data forms for the development of a computerized ventilation network model, i) Pressure and quantity survey, i i ) Fan characteristic data. i i i ) Length of the airways, f r i c t i o n factors, equivalent length of shock loss, perimeter and cross-sectional area, iv) Airway resistances. v) Quantity and minimum airway resistance possible (for airflow required through a regulator or booster fan). A number of computer network programs exist on the market today, these include:-i) Ventflow version 1.0 developed by the South African Chamber of Mines. i i ) VnetPC program, developed by Mine Ventilation Services Inc. i i i ) CANMET thermodynamic ventilation network computer program, developed by UBC for CANMET. A l l three were available for the project. 4.2.6 Temperature Profiles The wet and dry bulb temperatures of the a i r were taken at various points i n the mine using a sl i n g psychrcmeter. The data was used to calculate the relative humidity of the a i r . 135 4.2.7 T r i a l Recirculation Tests T r i a l recirculation studies were conducted at CCP and Rocanville Division Mines. At Central Canada Potash of Noranda Minerals Inc., recirculation of a i r through the entry connecting the two shafts i s presently prevented by two doors positioned as shown i n Figures 15 and 16. When the doors were opened, the underground fan pressure was sufficient to cause exhaust airflow into the fresh a i r intake. At Rocanville Division, a t r i a l recirculation of the mine South d i s t r i c t was created by opening roll-up door No. 36716 located between d r i f t s M-l-S and M-O-S, and along panel entry 302-04-00. Intake, mixed intake and exhaust a i r quality conditions were monitored during the t r i a l recirculation, i n terms of dust and gas concentrations, a i r quantities, and temperature profiles. 4.2.7.1 Central Canada Potash Division Ventilation a i r at CCP i s circulated through number 2 intake and number 1 return shafts respectively. The total intake a i r quantity i s 113 m3/s. The ventilation c i r c u i t i s shown i n Figure 15 which also shows the shaft positions and recirculation of a i r f i e l d t r i a l s i t e . CCP mine has several possible sites for a controlled recirculation installation. ~ BRATTICE = MUCK STOPPING m BELT CURTAIN | | DOOR p=« OVERPASS »~. FAN n r> r> "1 ON > IS FUSE STORAGE la 2S POWDER STORAGE 3 S Figure 15. Trial Recirculation Test Location. Underground Exhoust Fon Monitoring Position 2 (Mixed Intake) Monitoring PosMon 3 (Return) To WorWngs/HoooIng* • -B-[] Monitoring Position 1 (Intake) 4^ -B-C] t [] D - D o o r • — Ventilation and monitoring Stations Figure 16. P r o p o s e d Rec i r cu la t i on C i rcu i t 138 One s i t e was selected during an underground v i s i t at CCP as the best potential position for recirculation - the ventilation doors between ON and 2N d r i f t s . The s i t e i s ideal for a recirculation connection because of the following factors:-1) When the two ventilation doors are opened, the underground booster fan pressure was sufficient to cause recirculation of exhaust a i r into the fresh a i r intake. However, the flow direction depends on the skip positions at times. This site i s cost effective and e f f i c i e n t . 2) Its proximity to the shaft affords convenient inspection. 3) High recirculation factor could be realized with a fan. 4.2.7.2 Rocanville Division There are several possible sites for a controlled recirculation installation. Recirculation of a i r through the entry connecting the return and intake airways for each of these sites i s prevented by ventilation doors. Opening the ventilation doors w i l l cause recirculation i n these positions. 139 The following sites were selected during an uxrierground v i s i t at Rocanville Division as potential positions for recirculation;-1) Between Mo. 3 d r i f t and the underground steel storage stopping. 2) The ventilation doors on M-2-N and No. 3 d r i f t intersection. 3) Main ventilation doors along No. 1 d r i f t . 4) Belt transfer N-15 doors, between M-O-N and M-2-N. 5) Belt transfer N-19 doors, between M-O-N and M-2-N. 6) M-O-N doors, between N-25 and N-24. Site No. 1 was ideal for recirculation connection because of the following factors:-i) When the stopping i s opened, the underground booster fan pressure was sufficient to cause recirculation of exhaust a i r into the North mine. This s i t e i s cost effective and eff i c i e n t . i i ) Its proximity to the shaft affords convenient inspection, i i i ) With slight modification a fan i s not required, iv) Recirculation does not affect the shop area, v) High recirculation factor could be realized without a fan. The other sites were not preferred due to a number of disadvantages which include, low recirculation factors (sites No. 5 - 6), retirements for recirculation fans (sites No. 2 - 5 ) , proximity to conveyor transfer point (site No. 6), high f i r e risk (site 6), and recirculation affecting the shop area (site No. 2) and di stance from the shaft (sites 2 - 5). The exact location of s i t e NO. 1 i s shown i n Figure 17. Figure 17. Recirculation System Location 141 / • . . 4.2.8 Sources of Errors In a l l experimental work, there are many sources of error. These include:-i) Observational errors associated with reading the data and scale limitations i n record ing instruments, i i ) Instrument errors associated with the sensors and support equipment such as data loggers used to obtain the pollutant measurements. Observational errors were minimised by rechecking a l l data. These errors were minimised because of minimum data handling - the data from the loggers was transferred directly to a computer. Instrument errors were minimised by calibrating the sensors with a calibration gas before each measurement. 4.3 CONTROL AND MONITORING SYSTEM SELECTION The monitor or sensor i n a recirculating system must be capable of rel i a b l y monitoring the steady-state, normal operation (system equilibrium) of the return airstream continuously and unattended, for an extended period of time. I t must also be able to provide a warning i f a pre-selected level, at which action i s deemed necessary to ensure worker safety, i s reached. Monitors are considered to be the most important components of a recirculation system. 142 . ,: < In order to function properly/ they must be extremely reliable and properly maintained. Any potential monitor malfunctions should be limited i n number, easily detectable, and preventable by following reccmmended procedures and maintenance schedules. The required maintenance should be simple, infrequent, and of short duration. The selection of the best monitor for a given system requires an i n depth knowledge of system contaminants, TLV's, and the monitors available. The f i n a l selection requires considerations of the overall design of the complete recirculation system. 4.3.1 Sensors The recirculation system consists of two recirculation control systems and an environmental sensing package. Two sets - one set with three CO monitors and another set with three products of combustion sensors i s used to detect f i r e s while the environmental, package consist of CO, OOu,, NQg, velocity and temperature sensors. Selection of sensors or detection or detection devices to be installed i n the system i s based on many factors including cost, dependability, a v a i l a b i l i t y and r e l i a b i l i t y . Specified requirements are as follows:-1) Good specific response. 2) Accuracy + 1.00% f u l l scale (maximum). 3) Low maintenance. © 143 4) Linear response. y ; / . 5) Response tine less than 30 seconds. 6) Capable of withstanding severe underground environment. 7) Maximum longterm s t a b i l i t y without recalibration (ininimum 1 month). 8) Tnfomai interfering gas scrubbers (especially for NO and NOg). 9) Power: AC/DC operation, 115 VAC 60 Hz or 12VDC with backup battery power. 10) Output: 0 - 1VDC or 4 - 20 MA isolated and non - isolated optional. A match between signal output and data logger i s required. 11) Alarm: both audio and visual. 12) Enclosure: rugged NEMA and corrosion-resistant. 13) Warranty: Minimum one year unconditional warranty. 14) Installation cable requirements. 15) Cost effective - sensor l i f e and sensor replacement costs. The selected suppliers should conduct mine si t e acceptance tests i n order to demonstrate that the sensors are capable of operating under existing conditions. 144 4.3.2 Fir e Detection Fires i n underground mines present a serious threat to safety of underground miners and property. The products of combustion cannot be allowed to enter the fresh a i r intake. The recirculation zone must be extensively and reli a b l y monitored to achieve this. The most r e l i a b l e approach i s to i n s t a l l an early warning package. The earliest warning of f i r e could be achieved by sensing for trends i n the levels of carbon monoxide/ carbon dioxide/ products of combustion (POC) and temperature. Monitoring of 00 and products of combustion i s considered the most rel i a b l e and least expensive means of detecting an underground f i r e . Such a system should be tied into the emergency alarm system. The POC sensors are required because when n i t r i l e conveyor belts bum, they do not emit significant amounts of CO and use of this conveyor material i s increasing i n underground mines. The monitor i n a recirculating system must be capable of reliably monitoring the steady-state, normal operation (system equilibrium) of the return airstream continuously and unattended, for a period of time. I t must be able to provide a warning i f a preselected lev e l , at which action i s deemed necessary to ensure worker safety, i s reached. There i s a problem when diesel equipment operates close to CO sensors as the equipment may not distinguish between diesel and f i r e . Use of diesel i s limited i n potash mines and sensor positioning was to be such that diesels could not discharge exhaust close to sensors. 145 4.3.3 Environmental Monitoring system In addition to the safety and control systems a continuous mcmitoring system i s required i n the recirculation c i r c u i t . The environmental monitoring unit includes CO, CO2,N0x, velocity and temperature sensors for the three different recirculation systems. In addition to those environmental sensors, a sulphur dioxide sensor i s added i n the environmental monitoring package for H-W mine of Westmin Resources. The range and accuracy for each sensor i s as follows:-Sensor Concentration (ppm) Accuracy (ppm)* Minimum Maximum CO 3.00 50.00 + 1.00 500.00 5000.00 + 20.00 NQg 0.50 10.00 ± 0.50 0.20 10.00 + 0.20 The response to gas concentration within the transducer module range for a 1 - month period. The environmental monitoring package i s to detect levels of pollutants at two sampling positions, the return and mixed intake airways. °°2 * 146 The single gas analyser i s time shared over the two sampling positions by interfacing the detectors with an automatic sampling sequencer. A l l samples are continuously drawn into the sequencer through a set of conduits and only the active point goes to the analyser. The proposed features for the automatic sequencer include:-i) Selectable sample time, i i ) Manual override with sample hold, i i i ) B u i l t i n delay between sample selection, iv) Skip option to allow unwanted samples to be omitted, v) Provision of a common alarm and light indication for sample identification. The system enclosures w i l l be NEMA type 4 (Water, o i l , dust and corrosion resistant), f i t t e d with glands for a l l wires entering enclosure. 4.3.4 Telemetry and Control Devices There are two basic approaches to telemetering: i) Centralized management system, i i ) Distributed system with intelligent outs t a t ions. A distributed system i s the preferred approach. This system i s b u i l t up of intelligent outstations, which are microprocessor based, can be used as programmable controllers and are responsible for monitoring of each bank of sensors. Each sensor's analog output i s read, digitised and sent to the central control station. 147 The control station processes the sensor data and issues ccranands to the J '-/ • • • • ' outstation that controls recirculation doors for example. This approach makes the system components operate independently of the central station i n case of operating problems such as power failure or communication breakdown. The control and data transmission systems were selected based on a number of factors such as sensor r e l i a b i l i t y , data collection parameters, mode of transmission, cost, supply, back-up technical assistance support and software f l e x i b i l i t y . 4.3.5 Fire Doors During an underground mine f i r e , the importance of not recirculating smoke and toxic gases back into the intake airway i s well understood. Suitable ventilation structures which can control the spread of products of combustion (POC's) are essential elements of underground ventilation. In addition, under certain conditions control of propagation of the f i r e i t s e l f i s equally c r i t i c a l for safe mine evacuation of workers. F i r e doors offer the means for accomplishing the above stated objectives. There are f i v e broad categories of f i r e doors currently i n use i n underground mines. These include: i) R o l l doors or roll-down/up doors, i i ) Swing doors with panels opening i n the same direction, i i i ) Swing doors with panels opening i n the opposite direction, iv) Telescoping doors, v) Sliding doors. These doors can be operated manually, mechanically (self closing), e l e c t r i c a l l y , or by compressed a i r . 4.3.6 I n i t i a l Designs of Recirculation Systems The iwi+viai design comprises the following tasks: i) Discussions with sensor manufacturers and representatives, i i ) Discussions with mine management, i i i ) Recirculation schemes. Instrumentation review meetings were held at UBC, Department of MMPE. Attendees participating i n the review were from Environscience Products, Minelec and Levitt Safety. significant issues such as state of the a r t sensing technology, telemetry, control devices, sensor spacing and location were discussed during these meetings. A number of letters were sent out to Canadian sensor suppliers and representatives. More information pertaining to B r i t i s h online monitoring systems was gathered. Literature from three B r i t i s h sensor manufacturing companies - Trolex Limited; Transmitton; and Davis Limited of Derby was reviewed and a system recommended. A number of meetings and s i t e v i s i t s were held. These meetings and v i s i t s resulted i n a refined recirculation designs. various recirculation schemes were considered for each case and an optimum scheme was selected. 4.3.7 Detailed Design of Recirculation Systems Tne design consists of selection of f i r e warning system, environmental monitoring and control systems. Tne monitoring system w i l l consist of three functional components mainly sensors; telemetry; analysis and display equipment. The sensors monitor the environmental parameters and produce an e l e c t r i c a l signal that i s fed into the telemetry system. The telemetry devices receive the signal from the sensors and transmit i t i n form of analog or d i g i t a l output to the analysis and display unit. The transmitted signal i s either stored for later analysis or displayed. CHAPTER FIVE EXPERIMENTAL RESULTS AND DISCUSSIONS 5.1 INTRODUCTION A series of measurements of underground mine a i r quality were made at the main exhaust and intake shafts of three mines i n order to determine the f e a s i b i l i t y of introducing controlled recirculation of exhaust a i r . The monitoring strategy was planned to give information on the behaviour of underground mine pollutants between the main intake and exhaust shafts, along roadways and at the working faces. The environmental survey included, temperature, gas and dust concentrations, dust deposition, velocity, a i r quantity, size distribution and equipment ut i l i z a t i o n . These studies were conducted at Central Canada Potash of Noranda Minerals Inc. (CCP), Rocanville Division of Potash Corporation of Saskatchewan (PCS) and H-W mine of Westmin Resources. In addition, t r i a l recirculation studies were conducted at CCP and Rocanville Division Mines. This chapter details results obtained during the f i e l d tests. / 151 5.2 CENTRAL CANADA POTASH DIVISION CF NORANDA MINERALS INC. 5.2.1 Dust Sampling Figures 15 and 16 snow the experimental section of the mine. During the tests, measurements were made at the return position with no recirculation. The experimental recirculation was then initiated and readings were taken at the intake, return and mixed intake positions shown i n the Figures. 5.2.1.1 Respirable Dust Results Table 27 shows the dust concentrations measured i n the return with no recirculation. The average concentration was found to be 4.64 mg per cubic metre. An average concentration from 6 samples taken during preliminary studies was found to be 3.22 with a standard deviation of 0.49 mg/m3. Table 28 shows the gravimetric and instantaneous dust sampling results for the intake, mixed intake and return sampling positions during recirculation. The average concentrations were 1.64, 2.22 and 5.25 mg per cubic metre respectively. The results obtained from a preliminary underground a i r quality survey indicated the following concentrations: 1.51, 2.24 and 3.46 mg/m3 for intake, mixed intake and return concentrations respectively. Table 27. jteturn A i r Dust Concentrations - No Recirculation Dust Concentration Gravimetric (mg/m3) Counts Per Minute (cpm) 3.88 17 4.49 18 4.20 16 4.54 17 4.40 16 5.69 20 ' 4.67 20 4.00 14 5.72 20 4.37 14 4.87 20 5.16 20 4.70 20 5.02 20 4.80 20 4.53 18 4.45 18 3.90 17 4.70 17 Average 4.64 Standard Deviation 0.51 18.00 2.05 95% Confidence Limits, mean 4.64 + 0.26 18 + 1.23 /' . 153 Table 28. / Dust Concentration with Recirculation Intake Mixed Intake Return mg/m? cpm mg/m? cpm mg/m? cpm 1.96 2 2.14 6 5.66 20 1.96 2 2.30 4 4.84 20 1.80 2 N/A * N/A N/A N/A 1.40 2 II II • i II 1.43 2 II •• II II 1.43 2 II II • i • i 1.63 2 N/A N/A N/A N/A 1.84 2 II II it II 1.69 2 II II II II 1.18 2 • i • i II II 1.78 2 II II II • i Average 1.64 2.00 2.22 5.00 5.25 20.00 Standard Deviation 0.25 0.00 0.11 1.41 0.58 0.00 95% Confidence Limits, Mean 1.64+0.17 2.00 - - - -*N/A = Not Available 5.2.1.2 Dust Deposition Studies Table 29 shows the results of gravimetric and instantaneous dust sampling obtained at the face while a miner was cutting. . /; 154 Table 29. / Return Concentrations - Miner Cutting Approximate Distance From Concentration Location Miner (m) (mg/m3) (cpm) E7S4E 120 192.16 612 110m From E7S4E 230 117.16 500 E12S4 670 68.00 290 41N6E 780 N/A* 135 41N3W 880 N/A 88 *N/A = Not Available Table 30 gives the average dust concentration of samples taken at mining machine 504. . ,• < 155 Table 30. / Dust Levels at Machine 504 Location Average Dust Concentration (mg/m3) Face intake 4.83 Return 70m From Machine 12.07 Return 670m From Machine 6.93 5.2.1.3 Settled Dust Results Table 31 shows the results of the settled dust samples, analysed for water solubles and insolubles. Table 31. Settled Dust Analytical Results Location Water Soluble (%) Water Insoluble (%) No. 502 Borer 94.70 5.30 No. 504 Borer 94.00 6.00 N41 SI W3 95.00 5.00 N50 E20 95.10 4.90 N49 E5 95.50 4.50 No. 1 Shaft 95.60 4.40 Average 94.98 5.02 Standard Deviation 0.53 0.58 95% Confidence Limits, Mean 94.98+0.56 5.02+0.61 5.2.1.4 Dust Size Distribution Four cascade impaotor dust samples were collected at tne main return station and one at a return point 60m from machine 504. These results are set out i n Table 32. The average dust concentration measured i n the main return was 3.35 mg/m3 and the concentration i n the return airway during cutting was 13.59 mg/m3. / 157 Table 32. / Dust Size Distribution Location Size Weight Fraction % Less Stage Concentration (micron) (%) Cut-point (mg/m3) 6.00 0.00 100.00 0.00 3.50 33.33 66.67 1.02 No. 1 2.00 33.33 33.34 1.02 Shaft 0.90 16.67 16.67 0.51 0.50 5.56 11.11 0.17 0.25 11.11 0.00 0.34 Total 3.06 6.00 0.00 100.00 0.00 3.50 29.41 70.59 1.00 No. 1 2.00 23.53 47.06 0.80 Shaft 0.90 17.65 29.41 0.60 0.50 17.65 11.76 0.60 0.25 11.76 0.00 0.40 Total 3.43 6.00 0.00 100.00 0.00 3.50 31.58 68.42 1.11 No. 1 2.00 21.05 47.37 0.74 Shaft 0.90 15.79 31.58 0.56 0.50 15.79 15.79 0.56 0.25 15.79 0.00 0.56 Total 3.53 6.00 0.00 100.00 0.00 3.50 29.41 70.59 1.00 No. 1 2.00 23.53 47.06 0.80 Shaft 0.90 20.60 26.46 0.70 0.50 17.60 8.86 0.60 0.25 8.86 0.00 0.30 Total 3.40 21.00 30.18 69.82 4.10 15.00 20.74 49.08 2.82 10.00 15.09 33.99 2.05 N50E5 6.00 11.32 22.67 1.54 Return 3.50 7.54 15.13 1.03 2.00 5.67 9.46 0.77 0.90 3.78 5.68 0.51 0.50 3.78 1.90 0.51 0.25 1.90 0.00 0.26 Total 13.59 5.2.2 Discussion Average dust concentrations recorded during the f i e l d study were 1.64, 2.22 and 5.25 mg/m3 for fresh a i r , mixed intake and return respectively. The return concentration without recirculation was 4.64+0.26 mg/m3. The average increase i n concentration i n the return airway was therefore 13%, with 23% recirculation. The instantaneous dust concentrations recorded for intake, mixed intake and return positions were 2, 5 and 20 counts per minute (cpm) respectively. The return airway concentration without recirculation was 18+2 cpm. In terms of dust depositions i n the return airways, the measurements taken indicate that 65% of dust by weight was deposited within a distance of 550 metres from the face. The crushing, transport (conveyor belts, transfer points ) operations and vehicle movements i n the exhaust shaft area contribute to the f i n a l dust concentration measured at the return airway monitoring station. Significant dust deposition occurs close to the face as i s clearly shewn i n Table 29. In terms of dust and other contaminant conditions i n the return airways, i t can be assumed that there i s potential for use of recirculation i n the face area to increase the a i r quantity at a particular miner. . r . < 159 However, ground conditions and current mining practices at CCP seem to r e s t r i c t this application. Recirculation i n the face area may be of use to other potash mines with machines at very long distances from their ventilation shafts. Only 5% of the settled dust was found to be insoluble. This indicates that the majority of inhaled dust w i l l be removed from the lungs by body f l u i d s . The dust size distributions, measured at the return station indicated that a l l the dust was less than 6 microns and therefore i n the respirable range. The dust measured near the borer had a concentration of 13.59 mg/m3 and 77.3% was larger than 6 microns. The minus 6 micron concentration was 3.08 mg/m3. This indicates that there i s settlement of respirable dust i n the return airways. No dust was collected i n the 10, 15 and 21 micron stages at No. 1 Shaft. The crushing and transportation ( conveyor belts and transfer points ) operations i n these returns also contribute to the final dust concentration measured at the exhaust shaft. 5.2.3 Gas Sampling 5.2.3.1 Return Station Continuous Gas Sampling Five day and three night shifts were monitored for gaseous pollutants. Normal return conditions with no recirculation for 30/03/88 are shown i n Appendix I ( Figures 44 - 51 ). / 160 Additionalnormal return sampling results with no recirculation for 31/03/88, 04/04/88, 06/04/88 and 07/04/88 are shown i n Appendix I ( Figures 52 - 55, 56 - 63, 64 - 71, and 72 - 75 respectively ). The summarized gas sampling results are set out i n Table 33. Face contaminant concentrations were monitored for five shifts and the average ooncentrations are set out below. Miner Number Contaminant Concentration (ppm) CO NO NOg 501 2.00 700.00 0.50 0.10 502 5.00 900.00 0.50 0.20 503 2.00 800.00 0.50 0.10 504 5.00 1000.00 1.00 0.10 Average 3.50 850.00 0.63 0.13 I / 161 Table 33. , Normal Return A i r Conditions Date Conoentrations (ppm) CO COj NO NOj Day Night Day Night Day Night Day Night 30/03/88 2.25 2.23 845 885 0.76 0.54 0.69 0.58 31/03/88 3.13 N/A 1030 N/A 0.47 N/A 0.54 N/A 04/04/88 2.00 1.54 714 750 0.65 0.58 0.70 0.60 06/04/88 2.76 3.97 770 601 1.29 2.28 0.40 0.13 07/04/88 2.90 N/A 590 N/A 1.77 N/A 0.30 N/A Shift Average 2.61 2.58 790 745 0.99 1.33 0.53 0.44 Standard Deviation 0.47 1.25 163 142 0.53 0.99 0.18 0.27 Day Average 2.60 768 1.16 0.49 . /• ' 1 6 2 5 . 2 . 3 . 2 A i r Conditions With Recirculation 5 . 2 . 3 . 2 . 1 Gas Monitoring The average a i r conditions with recirculation are set out below for the intake, mixed intake and exhaust monitoring stations. These results were obtained by positioning the gas analyser at the mixed intake station and simultaneously measurements were taken at the intake and return positions using Draeger tubes. The results are set out i n Table 3 4 . In Appendix I, Figures 7 6 , 7 7 , 7 8 , and 7 9 show mixed intake concentrations for co, cOg, N O and NOg gases. Table 3 4 . A i r Conditions With Recirculation Parameter Intake Return Mixed Intake Gases (ppm) - CO " ° ° 2 - NO " NOg 0 . 0 0 3 0 0 . 0 0 0 . 0 0 0 . 0 0 1 . 4 8 8 1 4 . 0 0 0 . 8 4 0 . 4 0 Temperature (°C) 1 6 . 5 0 / 1 8 . 5 0 2 2 . 0 0 / 2 9 . 0 0 Humidity (%) 8 2 . 0 0 5 2 . 0 0 Quantity (nr/s) 3 1 . 2 0 1 2 . 8 0 0 . 5 0 5 2 5 . 0 0 0 . 2 5 0 . 0 3 1 6 . 5 0 / 2 0 . 5 0 6 6 . 0 0 4 4 . 0 0 Measured using Draeger tubes 5.2.3.2.2 Tedlar Bag Sampling Table 35 gives tne results obtained from the analysis of the a i r samples collected i n the Tedlar bags. The Time Weighted Average concentrations were determined using Draeger stain tubes. Table 35. Tedlar Bag Sampling Data Location Gas Concentration (ppm) CO °°2 NO, NO* Mixed Intake 0.50 450 0.0 0.50 Return 1.00 700 0.0 0.50 Intake 0.00 300 0.0 0.00 5.2.4 Intake, Mixed Intake and Return A i r Quantities 5.2.4.1 Intake and Return Airflows Without Recirculation Figure 18 gives a i r quantities obtained from monitoring stations 1 and 2; and the Western shaft intake airway. The summarized a i r flow quantities are set out i n Table 36. Underground Exhaust Fan To Workings/Headings Q = 38.76 CM/S [ ] Monitoring Position 2 0 = 36.76 CM/S - B — - « Monitoring Position 3 0 = 0 CM/S 0=6.40 CM/S [ ] Q • D [ ] Monitoring Position 1 Q - 36.50 CM/S 0 = 19.3 CM/S 0 = 61.28 CM/S [ ] 0 = Door • = Ventilation and monitoring Stations CM/S — cubic metres per second Figure 18. Proposed Recirculation Circuit — Doors Closed Table 36. . Normal Intake and Return Airflows Shaft No. 2 Western Intake 80.58 36.50 45.16 5.2.4.2 Airflows With Recirculation Three recirculation tests were conducted during three different s h i f t s . During the f i r s t day of the t r i a l recirculation, there were no skips hoisting ore i n No. 1 shaft. Unexpected flow (4.82 m3/s) from the intake side to the return airway was recorded. These results are set out i n Figure 19. The second recirculation test was attempted and 15.6 m3/s of return a i r was recirculated by opening the two existing doors between the intake and exhaust shafts. This resulted i n a recirculation factor of 0.176 or 17.60%. A i r quality was monitored during the recirculation test and the Time Weighted Average (TWA) concentrations found for 00, COj, NO, ND2 were 1.48, 814, 0.84 and 0.40 ppm respectively. Monitoring of these contaminants was limited to a maximum period of two hours only. A i r Quantities (nr/s) Return Shaft NO. 2 Eastern Intake Underground Exhaust Fan To Workings/Headings 8 Monitoring Position 1 0 = 33.59 CM/S Monitoring Position 3 0 = 4.82 CM/S -B-[] Q • D Monitoring Position 1 Q - 38.36 CM/S 0 = 39.92 CM/S [ ] 0 = 5.85 CM/S [ ] 0 = 19.25 CM/S P><3 • ° 0 = 63.51 CM/S [ ] D = D o o r • = Vontllatlon and monitoring Stations CM/S — cubic metres per second Figure 19. Proposed Recirculation Circuit — Doors Open Skips Stationary 167 The th i r d t r i a l recirculation was attempted when No. 1 shaft was busy (i.e. skips hoisting ore) and the results are shown i n Figure 20. The recirculation of 12.80 cubic metre per second gave a recirculation factor of 0.14 (14%) and reduced the No. 2 shaft eastern intake airway quantity to 31.20 cubic metres per second because of the present ventilation network. This recirculation experiment was conducted during the day s h i f t and the system's contaminants were monitored for 8 hours using Draeger stain tubes. The average values for the mixed intake and exhaust measuring locations together with the required threshold limit values are set out below: CO (ppm) COj (ppm) NOj (ppm) NQg (ppm) TLV (ppm) 25 5000 2 Mixed Intake (ppm) Trace 500 0 0.38 Exhaust (ppm) 0.3 720.0 0.0 0.40 5.2.4.3 Discussion The average normal return gas concentrations for the day shifts were 2.61, 790, 0.99 and 0.53 ppm for CO, COj/ NO and NOg respectively. The average gas concentrations during the night shifts were 2.58, 745, 1.33 and 0.44 ppm for CO, COj, NO and N O 2 respectively. The results indicate 1%, 5.7%, and 17% reduction i n the CO, CCu, and NC^ levels between the day and night shifts. Underground Exhaust Fan To Wcridngs/He actings 00 Q = 42.00 CM/S [ ] Monitoring Position 2 0 = 44.00 CM/S Monitoring Position 3 0 = 1 2.80 CM/S - B -0 = 6.50 CM/S [ ] Q • D Monitoring Position 1 Q - 31.20 CM/S t ^Shoft No^2^ |sh^No^ 0 = 21.10 CM/S 0 = 73.00 CM/S [ ] D = Door • = Ventilation and monitoring Stations CM/S - cubic metres per second Figure 20. Proposed Recirculation Circuit — Doors Open Skips Hoisting 169 •• '.• • ' : The CO, COj, and NOg cxsncentraticai reduction indicate less diesel / a c t i v i t y during the night s h i f t . The trends for these shifts were consistent, either high or low concentration readings and vice versa. These trends could be due to interference of diesesl units i n close proximity to the sampling station. The overall average values recorded during the sampling program for the day and night shifts together with the threshold limit values are set out below: TLV (pan) Exhaust CO (ppm) 25.00 2.60 COj (ppm) 5000.00 768.00 NO (ppm) 25.00 1.16 N O 2 (ppm) 2.00 0.49 5.2.5 Temperature Profiles The average wet and dry bulb temperatures recorded at 12 locations i n the mine are set out i n Table 37. The temperatures ranged from 17.90 to 22.20 °C wet bulb and from 25.70 to 31.10 °C dry bulb. Table 37 gives the measured values at the three measuring stations. Table 37. Mine Temperatures at Various Locations Location Temperature C Wet Bulb Dry Bulb High Bay 18.10 25.70 W4 N2 17.90 26.60 W4 M24 18.90 27.80 W4 M36 19.90 28.90 N41 81 W3 20.00 28.90 N4 N42 20.40 28.90 N41 81 E12 21.00 29.20 N43 E19/E20 21.20 29.80 N48 E5 17.80 24.40 N5 ES 17.80 24.70 N50 E20 21.70 30.40 171 Table 38. Return and Intake Air Conditions Without Recirculation Location Temperature ° C Relative Quantity wet Bulb Dry Bulb Humidity (%) (m3/s) Intake 16.90 21.10 65.20 40.70 Return 20.30 28.90 44.00 92.48 The average air conditions with recirculation are shown in Table 39 for the intake, mixed intake and exhaust measuring stations. Table 39. Air Conditions With Recirculation Location Temperature ° C Relative Quantity Wet Bulb Dry Bulb Humidity (%) (nr/s) Intake 16.10 20.70 62.80 23.89 Return 19.70 28.80 41.30 21.17 Mixed Intake 17.20 23.10 53.60 45.03 The Increase i n the mixed intake temperature as a result of recirculation was small and did not pose a problem. The effect of recirculation i s to reduce the relative humidity of the ventilating a i r . The relative humidity of the mixed intake averaged 53.40% compared to the intake values of 64.00%. This indicates that recirculation systems can used to reduce very high relative humidity values i n potash mines when this i s required. 5.2.6 Mining Equipment Utilization There were 61 diesel units i n use at CCP during the study with t o t a l power capacity of 4027 kW. The average u t i l i z a t i o n time for the 33 diesel units surveyed during the study was found to be 2.5 hours per day s h i f t while the average u t i l i z a t i o n for the night s h i f t was 0.61 hours. Individual values varied from a low of zero to a maximum of 6.6 hours. Total diesel capacity u t i l i z a t i o n was 2661 kW or approximately 66.10% and 662 kW or approximately 16.4% for day and night shif t s respectively. 5.3 ROCANVILLE DIVISION OF POTASH CORPORATION OF SASKATCHEWAN 5.3.1 Dust Sampling The average concentrations for the intake and return conditions were 0.62 and 4.24 mg/m3 respectively. Return dust concentration with no production was 1.75 mg/m3. 173 The detailed results obtained for the intake and return airways are given below:-Intake Return* Return (mg/m3) (mg/m3) (mg/m3) 0.74 1.82 4.95 0.49 2.30 3.30 1.63 3.90 1.26 3.73 4.90 4.80 4.10 Average 0.62 1.75 4.24 TLV 10.00 N/A N/A * Return dust concentrations with no production N/A = Not Applicable , / 174 5.3.2 Dust Deposition Studies Table 40 shows the gravimetric and instantaneous dust deposition sampling results for a variety of return sampling stations while a continuous was cutting. The instantaneous readings were obtained using an MDA Model P-5 l i g h t scattering d i g i t a l dust indicator. Table 40. Dust Decay Patterns i n Return Airways (411-00-10) (Airway Area = 32.70 m2 and Velocity = 1.22 m/s) Distance From Miner (Metres) 150* 580* 730 1524 2300 4200 Concentrations mg/m Counts Per Minute 70.20 290 34.20 250 32.00 197 N/A 110 3.60 73 N/A 10 A dust decay rate of 52% within a proximity of 430 metres was recorded between these two sampling stations. , 1 7 5 . /•. < Figure 21 shows instantaneous dust decay patterns i n panel 305 room 33 return airway. The overall airway cxoss-sectional area and velocity during sampling were 42.7 m2 and 1.00 m/s respectively. Figure 57 shows a dust decay rate of up to 49% within 400 metres from the face and up to 60%, 76% and 84% reduction i n dust concentrations at distances of 500, 700, and 800 metres from the miner respectively. The results indicate that considerable dust settlement occurs along the face airways. A second experiment was conducted while a continuous miner was cutting panel 305 Room 33. The results of this study are summarised i n Figure 22. Overall decay rate of 46% was recorded within a distance of 300 metres from the f i r s t sampling station (366 metres from the miner). 5.3.1.3 Dust Size Distribution Two Cascade impactor dust samples were collected i n the return airway when the miner was cutting panel 305-00-33 - second pass. The results are set out i n Table 41. 1% Table 41. _ Dust Size Distribution Location Size Wt. Fraction % Less Stage Concentration of (microns) (%) Cut - point mg/m3 Xmpactor 21.00 32.60 67.40 39.74 15.00 20.50 46.90 24.99 10.00 15.20 31.70 18.53 6.00 10.10 21.60 12.31 457 Metres 3.50 7.60 14.00 9.26 From Miner 2.00 6.20 7.80 7.56 0.90 5.40 2.40 6.58 0.50 2.20 0.20 2.68 0.25 0.20 0.00 0.25 Total 121.90* 21.00 26.00 74.00 22.54 15.00 16.60 57.40 14.39 10.00 13.70 43.70 11.88 6.00 11.80 31.90 10.23 579 Metres 3.50 10.70 21.20 9.28 From Miner 2.00 9.60 11.60 8.32 0.90 7.80 3.80 6.76 0.50 3.50 0.30 3.03 0.25 0.30 0.00 0.26 Total 86.70+ Gravimetric concentration taken using a dust pump and a f i l t e r averaged 128.70 mg/m3. + Gravimetric concentration taken using a dust pump and a f i l t e r averaged 91.04 mg/m3. These results show that significant dust deposition of coarse dust occurs close to the face. 179 5.3.2 Gas Sampling Two s h i f t s were monitored for gaseous pollutants. Normal return conditions are shown i n Appendix I ( Figures 80 - 87 ). The summarized gas sampling results are set out i n Table 42. Table 42. Normal Return Air Conditions Day and Night Shifts - 12/04/88 Shift Concentrations (ppm) CO °°2 NO N°2 Day 2.21 612.00 0.73 0.49 Night 2.06 451.00 1.32 0.55 Average 2.14 531.50 1.03 0.52 TLV 25.00 5000.00 25.00 2.00 5.3.3 A i r Conditions With Recirculation An experimental t r i a l recirculation of the mine south d i s t r i c t was created by opening r o l l - up door No. 36716 located between d r i f t s M-l-S and M-C—S, and along panel entry 302-04-00. The sampling locations are shown i n Figure 23. Intake Air to Panel 305 Exhaust Air From Panel 305 Mixed Intake Station 1 ^ * Bulkhead A Roll Up Door 0pon<36717) Intake Station >fc • < Fresh Air to Pane) 305 Return Station Roll Up Door Roll Up Door M-2-S Figure 23. PCS Trial Recirculation Location The results were obtained using instantaneous Draeger tubes. Table 43 gives a summary of the average a i r conditions for the intake, exhaust and mixed intake monitoring positions. The recirculation experiment was carried out for a period of five hours. Table 43. A i r Conditions With Recirculation Pollutant Intake Exhaust* Mixed Intake COj (ppm) 450.00 800.00 550.00 CO (ppm) 0.00 Trace - 1.00 0.00 - Trace NOg (ppm) 0.00 0.00 0.00 Dust (mg/m3) 3.60 3.83 3.67 Counts per Minute 6.00 28.00 13.00 Temperature (°C) L6.70/26.70 18.30/28.90 17.50/27.80 Relative Humidity (%) 34.00 35.00 33.50 Quantity (m3/s) 39.52 18.50 — A i r quantity through a recirculation cross-cut. Recirculation of 18.50 m/s or 47% recirculation was achieved by opening ventilation door No. 36716. A slight increase i n temperature (1.00 °C) was recorded between the intake and mixed intake. , 1 8 2 The overall quality of the exhaust a i r was found to be unchanged within the measurement limits despite the high percentage recirculation. Dust concentrations with recirculation were 3.60, 3.83, and 3.67 mg/m3 f o r intake, return and mixed intake respectively. This indicates an average increase i n dustiness of 5% i n the mixed intake compared to the intake airway without recirculation. Figure 24 gives a i r temperatures and dustiness obtained during a recirculation t r i a l . The survey started from a mixed intake station and proceeded to the continuous miner and then through the exhaust airway. A portion of the results along the return airway i s given i n Table 44. Table 44. A i r Quality Survey With Recirculation Distance From Miner Temperature Relative Humidity (m) (WBT/DBT - °C)* (%) 50 21.10/31.67 36 250 19.40/28.30 41 500 19.40/27.80 43 730 18.30/26.90 42 * WBT = Wet Bulb Temperature, DBT = Dry Bulb Temperature 184 5.3.4 Mine Wide A i r Quality Survey A mine wide a i r quality survey was conducted and the results are summarised i n Table 45. The ventilation stations used for regular mine monthly quantity surveys were used for this project. The pollutants monitored were gas and dust concentrations, plus temperature. Draeger tubes were used to monitor CO, COj, and NQg. Zero levels of CO and NOg were recorded for a l l sampling stations except stations 2, 3 and 28 which had NQg concentrations 1.00, 0.30, and 0.30 ppm. Table 45. Mine wide A i r Quality Conditions - 12/04/88 Station Location Type Flow No. of A i r Direction Pollutants , Dust WBT DBT R.H. (PPm) (cpm) <°C) (%) 1 No. 4 D r i f t F"" North (N) 350 5 18.0 27.0 40 2 NO. 3 D r i f t E+ South (S) 900 7 16.7 28.9 28 3 Salvage Bay F West (W) 800 4 16.1 27.2 30 4 X - l l south Mine No. 1 south U/P+ F S 350 3 12.2 22.8 25 6 F W 350 4 13.9 26.7 21 7 M-2-S By IS U/P F S 350 3 13.3 25.6 20 11 No. 2 South U/P W 1000 5 16.7 28.3 27 12 M-l-S By 2S U/P . N 1000 5 18.3 27.8 37 13 M-2-S By 2S U/P N 1000 8 16.7 18.1 29 14 306-01-1250' E 1100 4 17.2 27.2 34 16 Diesel Shop N F N 400 4 14.0 27.0 21 20 M-2-N Bend F N 350 3 18.0 25.0 49 21 M-2-N By 2N U/P F N 350 4 17.5 24.5 47 23 M-l-N (N. End) F N 900 5 18.0 25.0 49 24 No. 3 North U/P F N 350 3 18.0 25.0 49 26 M-2-W By 407 - 01 F N 800 3 17.5 24.5 48 28 410-03 @ M-2-W F N 900 4 18.5 25.5 49 29 NO. 5-411-00-10 3rd Pass F S 1000 6 19.0 26.0 49 31 P.E. 412-04-00 F w 1000 4 20.0 25.0 62 WBT = Wet Bulb Temperature; DBT R.H. = Relative Humidity; F E = Exhaust A i r ; + * U/P = Dry Bulb Temperature = Fresh A i r Underpass 185 5.3.5 Mining Eguipment Utilization Tne mine bad a to t a l diesel capacity of 3974 kW during the study. The average u t i l i z a t i o n time for four miners ( Miner Nos. 50701, 50704, 50705, and 50706 ) surveyed for the month of March, 1988 was found to be 7 hours per day or approximately 30%. 5.3.6 Discussion 5.3.6.1 Dust The overall average gravimetric dust concentrations recorded during the f i e l d study were 0.62, 1.75 and 4.24 mg/m3 for intake, return with no production, and normal return (with production) respectively. Dust concentrations recorded during an experimental t r i a l recirculation of the mine south d i s t r i c t were 3.60, 3.83 and 3.67 mg/m3 for intake, return and mixed intake respectively. The instantaneous dust concentrations recorded for intake, return and mixed intake were 6, 28 and 13 counts per minute respectively. This indicates an average increase i n dustiness of 5% i n the mixed intake compared to the intake airway without recirculation. The dust decay rate was observed to be 14% within 400 metres from the miner and up to 32, 62, 74, and 96% reduction i n dust concentrations at distances of 600, 1400, 2100, and 4000 metres from the i n i t i a l measuring station respectively. The i n i t i a l measuring station was 150 metres from the miner No. 50705. 186 Another deposition test was conclucted i n room 305-00-33 and dust decay rates of up to 49% within 400 metres from the face were measured with 60%, 76% and 84% reduction i n dust concentrations at distances of 500, 700, and 800 metres from the miner respectively. The results indicate that l o c a l recirculation i s feasible as there i s a considerable dust settlement occuring along the face airways. 5.3.6.2 Gases The average normal return gas concentrations were 2.14, 531.5, 1.03 and 0.52 ppm for CO, cOg, MO, and NC^ respectively. The results indicate a reduction i n concentration of 7% for CO and 26% for OC^ between the day and night shifts. NO and NC^ concentrations increased by 81% and 12% between the two shifts. The recirculation experiment resulted i n an average of 18.50 m3/s of exhaust a i r being recirculated and the quality of exhaust a i r was found to be unchanged within the measurement limits despite the high percentage recirculation. The mixed intake a i r quality changed from 450 to 550 ppm or 22% for OO^ . CO, NO, and NO, remained unchanged throughout the recirculation t r i a l . The relative humidity for the entire mine ranged between 20 and 62%. The increase i n mixed intake temperature as a result of recirculation was -small and did not pose a problem. The relative humidity of mixed intake a i r averaged 34% compared to the intake value of 33%. Based on these results, controlled recirculation of mine exhaust a i r i s feasible. 5.4 QUESTIONNAIRE SURVEYS s 187 5.4.1 Potash Mine ventilation Data A survey of Canadian potash mines investigated the cost of heating and ventilation. These costs for 1986 are shown i n Table 4. The average annual heating cost per m3/s of underground ventilating a i r exceeded $ 1,600 i n these mines. Additional information on the annual, heating cost for Rocanville Division i s set i n Table 46. Table 46. Mine A i r Heating Data - Rocanville Division Year Heating Cost Cost per m3 of Natural Gas ($) ( Cents/m3 ) 1988/89 103 107 6.00 1988 92 746 6.50 1987 133 693 10.16 1986 197 427 11.80 1985 173 818 10.40 The data shows a downward trend i n heating costs for Rocanville Division, because of a reducing natural gas cost. This reduced the financial attraction of recirculation and affected the decision to proceed with the construction and installation of a system. 188 - / 5.4.2 Effect of Heating Systems cn Mine A i r Quality / The steam/glycol heat exchanger system at Central Canada Potash Division (CCP) has been changed to a natural gas, direct fired burner system. CCP contracted KS Engineering inc. of Saskatoon to design a system fo r installation. Burners from Advanced Combustion Inc. were selected because of their low generation of pollutants. From the environmental point of view the main difference between the direct and indirect heating systems i s whether the products of combustion enter the mine. Direct f i r e d natural gas burners increase the ambient intake of a i r pollutants. Due to this problem, an intake a i r monitoring progam was recommended before a final design was presented for implementation. The fi n a l design would take into consideration the environmental changes caused by the introduction of direct fired natural gas burners. The thesis design i s based on CCP f i e l d data together with data collected during the 1989/90 winter season. The average a i r conditions taken during the winter months are set out below: -Month Gas Concentrations (ppm) CO °°2 NO N02 November, 1989 2.60 960 N.D. 0.220 December, 1989 3.50 1275 N.D. 0.275 January, 1990 2.40 1060 N.D. 0.160 February, 1990 5.50 1700 0.10 0.350 189 .' - / The average intake gas concentrations recorded during a comprehensive s .. . survey i n February 16, 1990 were 6.00, 1800, 0.1 and 0.42 ppm for CO, CO2, NO and NOj respectively. Because of this new installation at CCP, contacts were made as regards to environmental status of similar systems during the winter months. The mines contacted are l i s t e d i n Table 47. Table 47. Heating Systems Used i n Potash Mines Mine Heating System Main Backup PCS Alla n Natural Gas Fired -PCS Cory Glycol ' -PCS Lanigan Natural Gas Fired Propane PCS Rocanville Natural Gas Fired -Ccminco Natural Gas Fired Glycol IMC Glycol -PGA Natural Gas Fired (when i n use) Table 48 shows average gaseous concentrations during February 1989 for two potash mines. 190 • ^ - ' Table 48. Winter Average Contaminant Levels Mine Concentration (ppm) Temperature CO COj N O J J NOj °C PCS Allan 3.50 2500 N/D* 0.35 -35 Cominco 8.00 2000 0 N/D -35 * N/D = Not Determined Table 49 shows average underground fresh a i r c i r c u i t gas levels at PCS Allan Division. PCS Allan Division uses direct natural gas f i r e d burners to heat the mine intake a i r . Table 49. PCS Allan Division Average Monthly Gas Levels - 1988/89 Year Month Concentrations (ppm) NOj °°2 CO January 0.32 1967 2.70 February 0.35 2500 3.50 1989 March 0.18 1960 2.80 Ap r i l 0.22 1430 2.80 May 0.23 688 2.00 June 0.22 670 1.67 July * 0.15 550 1.00 August 0.10 750 1.00 1988 September 0.29 1125 3.75 October 0.43 1200 3.50 November 0.39 1600 3.70 December 0.35 1600 3.00 • = Heating system not i n use. The average annual gas concentration levels for the two conditions:- furnace on and off i s set out below. Act i v i t y Gas Concentrations (ppm) MO2 OO2 CO Heating System On 0.316 1672 3.22 Heating System Off 0.175 665 1.42 Percentage Increase 80.60 151.40 126.80 Data extracted from a letter to the CCP Mine Superintendent from KS Engineering indicated that for Saskatoon, the lowest temperature ever recorded i s -50 °C, and the highest temperature ever recorded i s +40 °C. The difference between the highest and the lowest temperature recorded i s 90°C. The lowest temperature recorded during th i s period i s -42.80 °C and the highest being 37.80 °C. The temperatures of -40 °C occurred for 18 hours during the 10 year period of 1957 - 1966 ( Company Correspondence). The yearly average temperature for Saskatoon i s +1.8°C. Long range average temperatures for the months of January, February, November and December are: -18.9 °C, -14.10 °C, -5.5 °C and -13.90 °C respectively. KS Engineering Inc. calculated levels of pollutants for the extreme minimum temperature of -50 °C at 5 °C intervals. The calculated levels are presented i n Table 50. 192 Table 50. Estimated Level of Pollutants i n Mine Ventilation ' A i r for various Months Month Mean Change Gas Concentrations (ppm) Ambient Temperature 0^ COj CO January -2.00 67.00 20.69 1238 5.00 0.80 February 6.00 58.40 20.76 1081 4.50 0.73 March 17.10 47.90 20.81 889 4.00 0.58 Ap r i l 38.10 26.90 20.89 501 3.00 0.23 May 52.20 12.80 20.94 239 2.00 0.12 June 60.10 4.90 20.98 92 1.00 0.04 July 65.20 - - - - -August 63.00 2.00 20.99 37 0.50 0.01 Sept. 52.70 12.30 20.95 230 1.90 0.11 October 41.20 23.80 20.90 444 2.80 0.25 November 22.10 42.90 20.83 797 3.70 0.51 December 7.00 58.00 20.77 1074 4.10 0.73 Maximum Allowable Levels 5000 50.00 3.00 Source: Letter From KS Engineering Inc. to CCP Mine Superintendent. * Calculations based on data provided by Western Combustion Services. Table 51 compares pollutant levels from two burner systems. Table 51. Estimated Level of Pollutants i n Mine Ventilation A i r for Various Months Ambient A i r " Temperature WCS"1" ACI* + COj** °C Rise °C CO N C U CO N O . (ppm) (ppm) (PPm) -50 68.30 7.00 1.76 5.50 0.68 2650 -45 63.30 7.00 1.58 5.40 0.62 2489 -40 58.30 7.00 1.40 5.20 0.55 2327 -35 53.30 6.50 1.22 5.00 0.50 2165 -30 48.30 6.00 1.16 5.00 0.45 2002 -25 43.30 6.00 1.07 4.50 0.40 1839 -20 38.30 5.00 0.94 4.50 0.35 1675 -15 33.30 4.80 0.82 4.20 0.30 1510 -10 28.30 4.50 0.70 4.20 0.25 1346 - 5 23.30 4.00 0.60 4.00 0.20 1180 0 18.30 3.00 0.45 3.00 0.16 1014 5 13.50 2.00 0.33 2.00 0.11 878 10 8.30 1.00 0.21 1.00 0.06 681 15 3.30 0.50 0.08 0.50 0.02 512 Source: Letter from KS Engineering Inc. to CCP Mine Superintendent. * -40 °C i s recorded for 18 hours during 10 year period (1957 - 1966). ** 400 ppm i n the outside a i r (background) i s taken into account. + WCS = Western Combustion Services *"*" A d = Advanced Combustion Inc. 5.5 H-W MINE CF WESTMIN RESOURCES LIMITED Environmental conditions were monitored i n 21-337 D r i f t East. About 30% of the whole mine exhaust a i r passes through this d r i f t . Gaseous and dust samples were taken for two day shifts and one night shift. 5.5.1 Dust Sampling Table 52 shows the gravimetric dust sampling results for the intake and return conditions during the study. The average concentrations were 0.27 and 1.23 mg^/s for intake and return airways respectively. Table 52. , Intake and Return Total Dust Conditions Concentrations (mg/m ) intake Return Total Respirable Combustible Dust 0.35 2.08 N/D 0.37 1.25 0.35 0.12 0.64 N/D 0.18 0.83 N/D 0.22 1.35 N/D 0.21 1.43 0.34 0.26 1.47 N/D 0.42 1.27 0.32 1.16 0.26 0.98 N/D 1.36 0.33 1.01 N/D 0.27 1.23 0.32 Average 5.5.2 Gas Sampling 195 5.5.2.1 Return and Intake Gas Conditions Normal return concentrations are shewn in Appendix I ( Figures 88 - 102 ). The summarised gas sampling results are given i n Table 52. Table 53. Normal Return Air Conditions - With Pollutants From Production Blasts - 1989 Date Concentrations (ppm) CO COj NO N02 SOg Day Night Day Night Day Night Day Night Day Night 24/05 5.51 - 983.4 - 4.00 - 1.10 - 1.17 26/05 4.94 6.10 1156.1 1004 5.07 3.90 2.16 1.30 2.11 1.37 Avg. 5.23 6.10 1069.8 1004 4.54 3.90 1.63 1.30 1.64 1.37 The data shown i n Table 53 indicates that there are high concentrations of CO, NOj, NO and SO^ gases. These high concentrations are a result of the main production blasts. Production blast concentration levels are reduced to prior blasting concentrations within a period of 3 hours or 25% of the total s h i f t time. Table 53 shows a summary of gaseous levels before, during and after blasting. 196 . / • • Table 54. Effect of Prediction Blast an tne Mine Atmosphere May, 1989 Date Shift Gas Concentrations (PPm) Decay Time, Hours Before Peak Average To Before Blast Blast Blast Concentration 00 0.60 40.00 5.51 >3.00 CO, 800.00 2800 983.40 2.70 24 Day NO 0.90 26.10 4.00 >2.90 NOj 0.11 8.90 1.10 2.80 SO, 0.12 12.00 1.17 2.90 CO 0.90 39.80 4.94 2.60 °°2 690.00 2500.00 1056.00 2.90 24 Night NO 1.00 20.80 5.07 >2.60 NOg 0.20 10.00 2.16 2.40 SO, 0.14 12.50 2.10 2.60 CO 1.20 36.00 6.10 >2.90 °°2 900.00 3100.00 1004.60 2.60 26 Night NO 1.40 19.00 3.90 3.00 NOg 1.40 10.00 1.30 >3.00 SO, 0.13 17.50 1.37 2.90 In addition to the continuous return a i r condition monitoring, random instantaneous samples were taken at various locations underground together with temperature profiles. Table 54 gives the return and intake conditions f o r the spot samples taken using instantaneous gas detectors. Table 55. Mine Wide A i r Conditions Intake (Fresh Air) Return (Exhaust Air Concentration (ppm) Temperature Concentration (ppm) Temperature CO °°2 (°c)* co °°2 N°2 (°c>* 0.20 500 0.00 9.50/11.0 1.00 800 0.10 10.50/12.0 0.40 550 0.10 9.50/12.0 2.00 750 0.20 10.00/12.5 0.10 480 0.00 9.00/10.0 1.00 950 0.10 10.50/12.5 0.30 500 0.00 10.00/11.0 3.00 900 0.30 13.00/14.0 0.00 400 0.00 9.00/ 9.5 3.00 900 0.20 14.00/15.0 2.00 870 0.10 12.00/13.0 2.00 800 0.20 13.00/14.0 1.50 750 0.20 13.50/14.0 0.20 486 0.00 9.40/10.7 1.94 840 0.18 12.06/13.4 * Wet and Dry Bulb Temperatures + Average values S O 2 = 0 ppm for intake airway and 0.50 ppm for return/face 198 5.5.2.2 Sulphur Dioxide Monitoring During Actual Stope Blasting During blasting of massive sulphide ores, dust clouds can be created and ignited, resulting i n a secondary explosion which releases considerable volumes of sulphur dioxide. High SCj concentrations are a r i s k to people and cause production delays u n t i l they are cleared from the mine. In order to assess the impact of sulphide dust ignition on the stope ventilation, sulphur dioxide was monitored before, during and after the blast. Most of the experimental stations were located on the 2300 level i n K330 stope. There were only three active panels during the investigations, ( 7, 8 and 9 ). One more test was conducted on 2400 level while blasting 350 longhole stope. Figures 25 and 26 show the sampling stations for both experimental locations. Four production blasts were sampled for sulphur dioxide levels. Sample results are shown i n Appendix I ( Figures 103 to 109 ). The summarized gas sampling results are set out i n Tables 55 and 56. Figure 25. K330 Stope Layout - July, 1958 Figure 26. 2 3 - 3 4 3 Sumps Locality Plan ( NTS ) 201 Table 56. Gas Sampling Results - SOu, Date Location Concentration I n i t i a l No. of Control Maximum Minimum Ventilation Holes/ Methods 1988 (ppm) (m3/s) Round 31/05 K330 Stope 232 8 N/A N/A 20/07 343 Sump 10.3 0* 64.52** 23-350 Stope -60 Holes Minimum Concentration = 0 ppm and time taken from maximum concentration to minimum = 30 minutes. ** Airflow through the stope and the 366 ramp. Tables 55 and 56 show gas sampling results. One major sulphide dust explosion occurred on July 18, 1988. The explosion released a sulphur dioxide concentration of 910 ppm with a decaying time of 3.50 hours. The decay time was quite long because the explosion disturbed the stope ventilation system. Two panels were blasted simultaneously and water fogging was the only control method employed for sulphide dust ignition prevention. Four more ignitions were recorded during the experimental period. 202 I t i s thought that, these concentrations are lower than the concentrations at source. This nay be due to the following reasons: 1. Scrubbing effect of water. 2. Reaction with Blasting pollutants. 3. Cross-sensitivity to other gases. 5.6 AIR QUALITY IN CANADIAN UNDERGROUND MINES Part of this research work involved obtaining a i r quality conditions relating to recirculation parameters i n Canadian mines. A total of 32 mining companies and regulatory organizations i n Canada were contacted to provide underground environmental data. Only five m i - n o g replied out of 32 mines and regulatory organizations contacted. The replies received are summarised i n Tables 57, 58 and 59. Exhaust a i r quality monitoring i n underground mines i s not mandated i n Canada and as a result, there i s insufficient data regarding a i r quality i n main return airways. Data extracted from the replies and set out i n Table 59 confirms that the mines are not legislated to monitor exhaust a i r quality. The survey data also indicate that heating costs can exceed $ 2,000 per annum for each m3/s of a i r circulated. The exhaust temperatures and stope a i r concentrations show that recirculation i s feasible i n these mines especially mine C. 25% recirculation w i l l result i n potential heating cost savings of about $ 277,500. 203 Table 57. Gas Sampling Results ( K330 Stope ) Date Concentration Time to Tnitial No of Control July, 1988 Maximum Minimum Minimum Ventilation Holes/ Methods (ppm) (Hrs) (m3/s) Round 18* 910.00 8.00 3.50 5.70 P7 = 75 + Water P9 = 65 Atomizer 21 10.60 0.00 0.50 3.30 P9 = 25 Water 337-2C = 52 Atomizer and Bags 23 ** > 50.00 0.00 1.00 P9 = 57 water Atomizer and Dupont Inert 200 metres of ventilation tubing was damaged and burnt, m addition compressed a i r and water pipes were damaged and two shifts production delays were experienced. Production resumed after restoration of the ventilation, compressed a i r and water supply systems. As measured by long duration and diffusion tubes. P7 = Panel 7 and number of holes blasted = 75 204 Table 58. Canadian Underground Metal Mines Data Mine A i r Distance Annual Cost Diesel Quantity Between Heating Ventilation units Power (m3/s) Shafts (m) ($) (kW) A 330 30 125,000 N/A 58 6636 B 952 700 N/A N/A 88 8272 C 472 800 1,110,000 1,764,000 111 11714 D 240 330 220,000 400,000 19 1413 E 100 1220 210,500 100,000 43 3597 Table 59. Canadian underground Mines ventilation and A i r Heating Data Mine Annual Cost per m/s Pressure Heating Ventilation (Pa) ($) A 378.80 N/A 8000.00 150 N.6. 13 B N/A N/A 12175.00 222 N.6. 15 C* 2351.70 3737.30 11450.00 220 N/A 15 D 916.70 1666.70 10650.00 210 Propane 13 E 2105.00 1000.00 3000.00 180 Propane 17 Heating Exhaust Days System Temperature °c 205, * Reclaim beat from compressors. N/A = Not Available. N.6. = Natural Gas. Table 60. A i r Quality i n Canadian Mines Mine A i r Quality Exhaust Stope 00 CO2 NOvj Dust Temp. CO COj NOg Dust Temp. mg/m3 °C (PPm) mg/m3 °C A _* - - 2.00 13 1.0 500 0.0 1.0 22 B '- - - - Trace 800 - - 15 C 0.0 900 < 0.5 0.50 15 0 500 0.0 0.50 10-25 D - 1.0 150.00+ 18 - - - 18 E — — — — - 7.0 - 0.1 - 18 = Not Available. ppcc = Particles per cubic centimetre, measured by Konimeter. 0 - 300 ppcc = Good/Acceptable 300 - 500 = Fair Range > 500 = Poor 206 5.7 CONCLUSIONS 1. The results indicate that controlled recirculation of wr i™» exhaust a i r i s a practical method of reducing mine winter heating costs and/or increasing the total airflow. 2. T r i a l recirculation circuits returning 20 - 47% of exhaust a i r into the fresh a i r failed to cause significant increases i n mixed intake pollutant levels relative to the conditions without recirculation. 3. Based on these results controlled mine a i r recirculation systems were designed for Rocanville Division of PCS, Central Canada Potash Division of Noranda Minerals Inc., and H-W mine of Westmin Resources Limited. CHAPTER SIX DESIGN CONSIDERATIONS FOR CONTROLLED RECTftCUIATORY SYSTEMS 6.1 INTRODUCTION The development of recirculation systems for Central Canada Potash and PCS Rocanville Division was undertaken, following underground f i e l d studies. These studies indicated that controlled recirculation of mine exhaust a i r has potential application to reduce winter heating costs i n both mines. Environmental studies conducted at Westmin Resources indicated that a variable quantity recirculation system, which would increase face airflows, was feasible. The primary objective of these recirculation systems was to achieve a reduction i n heating costs and an increase i n face airflows without compromizing a i r quality and safety standards. In order to achieve these objectives, emphasis was placed on the development of reliable online monitoring and control systems. The main factors considered i n evaluating the f e a s i b i l i t y of installing a recirculation system i n th i s thesis included the legal, health and safety, technical, and economic issues. The design objectives of the proposed recirculation systems were based on the following c r i t e r i a : i) Protection of employees i i ) A i r containing carcinogens (radon - residue time and decay to radon daughters ) should not be recirculated. / 208 / - • i i i ) Tne system must be economical. The safe and effective operation of a recirculation system d T T r t e on the monitoring equipment. The system must be simple to i n s t a l l , fail-safe-tamper proof and easy to maintain. Selection of the best sensor for a given system requires an in-depth evaluation of system contaminants, threshold levels, and the units available. It cannot be done without considering the overall design of the complete recirculation system. The design of recirculation installation requires a system approach i n order to meet the overall objective of worker safety. These general areas which should be evaluated before proceeding with the system design approach are outlined below: 1. Characterization and v a r i a b i l i t y of a i r contaminants i n the return. 2. Collection of pollutants i n the system (gas and particulate removal). 3. Legal concentrations allowed i n the work area. 4. Equipment capability, limitations, and r e l i a b i l i t y . 5. Costs of purchase, installation and operation. 6. Operation and maintenance requirements. 209 After defining the overall system, detailed specifications can be developed for i t s different components. These include operational, maintenance, r e l i a b i l i t y and performance requirements. 6.2 RECIRCULATION SYSTEM MODELS TO PREDICT WORKER EXPOSURE The employee-projected exposure levels with the recirculating ventilation system operating were estimated using predictive models. These models were used to determine the mavimim allowable return a i r contaminant concentration. A number of mathematical recirculation models have been reported i n literature (Hardcastle, 1983; ACdH, 1982; and Hughes and Amendola, 1982). Hughes and Amendola's model presents the simplest case. Hardcastle's model was developed and tested for underground mine ventilation recirculation systems. The AOdH model defines the permissible concentration of contaminant i n recirculated a i r under equilibrium conditions. The Hughes and Amendola's, and the ACdH models, are general and based on chemical agent mass, or volume balance and an airflow balance. These models are designed for industrial recirculation systems and not mining conditions. The models axe set out below: Hughes and Amendola/s Models °Tr °R = t<l - eJMCj. -kj^nAl - [ ( k R ) * ( i - e)]] .. 6.2.1 CB= {[(Qr/QtJMCg - C M ) * ( l - f)] +[k B*C R]+ + [(1 - k g ) ^ ) ] } 6.2.2 210 Where: C Q = A i r cleaner discharge concentration after recirculation, mg/m3 Cg = Recirculation return concentration, mg/m3 e = Fractional a i r cleaner efficiency, percent. Cg = Local exhaust dust concentration recirculation, mg/m3 kg = Factor which represents the fraction of recirculated exhaust stream that i s composed of recirculation return a i r (0 - l .o ) Cjg = Make-up a i r concentration, mg/m3 C Q = 8 hr. Time-Weighted Average of breathing zone concentration the worker experiences after recirculation, mg/m3 Qp = Total ventilation airflow before recirculation, m3/s Q t = Total ventilation airflow after recirculation, m3/s C Q = 8 hr. Time-Weighted average of breathing zone concentration i n general room areas before recirculation, mg/m3 f = Factor which represents the fraction of time the worker spends i n the influence of a strong exhaust hood (range 0 to 1.0) C ^ = 8 hr. Time-Weighted average of breatning zone concentration i n the general room areas before recirculation, mg/m3 kg = Factor which represents the fraction of the worker's breathing a i r that i s composed of recirculation return a i r (range 0 to 1.0) ACGTH Model Cg = 0.5*{[(TLV - C 0)]*[(Q T/Q R)*(l)/(k)]} ... 6.2.3 i Where: Cg = Concentration of contaminant i n exit a i r from the collector before mixing, any consistent units Qg = Recirculated airflow, m3/s Q/p = Total ventilation flow through affected space, m3/s k = An "effectiveness of mixing" factor, usually varying from 3 to 10, a typical value i s k = 3 and k = 10 implies perfect mixing. TLV = Threshold Limit Value of contaminant C Q = Concentration of contaminant i n worker's breathing zone with local exhaust discharge outside the workplace. NOTE: Conversion from ppm to mg/m3 and vice versa use the following relationship: ppm * molecular weight = mg/m3 * 24.4 Hardcastle's Model P = {[C2 - CJ/HCg - C^]} 6.2.4 Where: F = Recirculation Fraction C 1 = intake concentration to the system, any consistent units Cj = Recirculation intake concentration, fixed by the legislation C3 = Return concentration, any consistent units Robinson and Harrison's Models Robinson and Harrison, (1987) used the following model to predict return gas percentage after recirculation. Cj. = C A + (M/Qi) 6.2.5 Where: Cj. = Concentration of gas i n the return = Concentration of gas of the fresh a i r entering the system Q i = Quantity of fresh a i r entering the system M = Make of gas i n the system, kg/s From t h i s model i t can be noted that the return gas percentage concentration of the system i s not affected by the recirculation factor under steady conditions. Robinson and Harrison (1987) used the following model to predict the gas percentage i n the mixed intake a i r . = {Ci + [(M/Q±)* RF]} 6.2.6 Where: RF = Recirculation factor Qj. = A i r quantity recirculating from the return to the mixed intake. Equations 5.2.3, 5.2.4, 5.2.5 and 5.2.6 were used to evaluate worker's exposure to various contaminants i n the work environment. Hughes and Amendola's models are designed for industrial recirculation systems. They can be used for underground mine ventilation with suitable modification of the models. 213 A i r Quality Model The A i r Quality Index (AQI) can be used to select the optimum recirculation percentage. The AQI i s separated into two parts, one f o r gas levels and the other for particulates, also cancelling the synergistic factors (1.2 and 1.5 i n the Health Effect Index (HEI) assessment model). The AQI i s derived from HEI. A Q I ( G a s ) = (CO) / (TLV-CO) + (NO) / (TLV-NO) + (NO^ / (TLV-NO,) A Q I ( p a r t ) = (RCD) / (TLV-RCD) + [ (SC^)/ (TLV-SOg) + (RCD) / (RCD-TLV) ] + [ (NCgJ/CTLV-NOj) + (RCD) / (TLV-RCD) ] The AQI has not been legislated i n Canada, but the growing interest shown by regulatory bodies suggest that the AQI could become a standard procedure to assess the quality of mine environment. 6.3 SYSTEM DESIGN The design incorporates monitoring, control and safety devices. Safety and control systems, w i l l automatically and remotely step recirculation by closing ventilation doors when any one of the pollutants reaches a predetermined concentration. The predetermined concentrations for each system are set according to the maximum allowable concentration i n the underground ambient a i r for that specific legislation. Doors w i l l also close during prolonged power f a i l u r e to the fans, and the system w i l l have a remotely actuated f i r e alarm. In the event of f i r e , an automatic safety system w i l l detect the CO and other products of combustion produced by the f i r e and stop recirculation. In general, the monitoring system w i l l perform three basic functions: sensing, telemetry (data transmission), and analysis and display of data. 6.3.1 F i r e Detection A set of three 00 sensors located i n the recirculation connection (control system) and three POC sensors are considered adequate to control the performance of the recirculation system. A f a i l u r e or adverse indication from any two sensors i n either set would i n i t i a t e closing of the doors and stop recirculation. Similarly, for the system to continue running, and the ventilation doors to remain open, would require a safe indication from at least two sensors. This implies that a single sensor fa i l u r e would not stop the recirculation system. The effect of diesel exhaust or tobacco smoke on a single sensor would also not stop the recirculation system. Automatic shut-down of the recirculation c i r c u i t initiated by two out of a set of three identical sensors would require microprocessor control. The U.S. Bureau i s developing a novel f i r e detector that can be used to discriminate between smoke produced by a f i r e and smoke produced by a diesel engine. The detector uses a pyrolysis technique whereby a sample of smoke-laden gas passes through a short, heated tube within which f i r e smoke parti c l e s pyrolyse and increase their number concentration and decrease their average size, while diesel smoke particles are unaffected ( Litton, 1988 ). Alarm CO levels for monitors i n the return are set, based on the mayiimm allowable level concentrations i n the ambient a i r stipulated by the Province of Saskatchewan Mines Regulations and the Province of B r i t i s h Columbia Mines Regulations. The alarms are audible (approximately 85 dB at 10 feet (3.05 m)), and visual. The f i r e packages have two alarm level settings, permitting a pre - alarm at a lower CO concentration of 15 ppm and door closure at 25 ppm for Saskatchewan mines. Westmin Resources H-W mine f i r e alarm level settings are 30 ppm and 50 ppm for the lower CO and higher CO concentrations, respectively. The alarm system i s controlled through a data logger or an alarm monitor. The data logger or the alarm monitor together with the remote CO sensor form a complete central alarm monitoring system. The data i s collected from these sensors by a data logger with a modem omnmi cation capability. The recorders directly interface the sensors and store a history of user-programmable data. The data i s then telemetered to a computer over the mine phone system. One sensor i n each set has a d i g i t a l readout for calibration purposes and a user-selectable switch mechanism that allows the readout to be time-shared with the other CO and POC sensors. One telemetry channel i s provided as a backup for other sensors. A delay time of 10 seconds i s allowed between the alarm indication and the actual closure of the door. Calibration of these sensors i s required. . /•. 216 6.3.2 Sensors Cmmercial, sensors are available with adequate accuracy and l i f e to measure 00, COg, NQ^ , airspeed, pressure difference, and temperature, but there i s a need for inexpensive continuous NC^ and dust monitoring sensors ( Hall, Saindon and Mchaina, 1986 ). Existing sensors and instruments for NOj are only suited for s c i e n t i f i c research and are not capable of continuous operation over several years. The only reliable sensor for velocity measurements over extended time i n mines, with minimum maintenance, i s the vortex anemometer. This sensor i s expensive (about $3500), so there i s a need for cheaper a i r velocity sensors. A i r velocity measurements are indirectly used for calculation of the a i r quantity through the recirculation system. Due to high turbulence of a i r i n mine airways, i t i s d i f f i c u l t to get a high degree of accuracy i n calculating a i r quantity, when the a i r velocity i s only measured at one point. The main problem with a i r flow monitoring l i e s with the method of calculating a i r quantity. One-point measurement i s not sufficient to quantify airflow through an airway. Errors of up to +10% are possible for the centre point measurement. 6.3.3 Recirculation Fan 217 Continuous system monitoring must be provided at the recirculation fan to detect and indicate any sign that a f i r e might have occurred at the fan. Monitoring equipment i s required at the recirculation fan to sense and indicate any e l e c t r i c a l or mechanical fault. A Motor Protection unit (MPU) must be installed i n order to provide protection from overload, overcurrent, undercurrent or current-inbalance. i n addition, t r i p and alarm set functions must be incorporated i n the MPU. A vibration indication system monitor must be installed to detect and indicate any developing mechanical fault. A lower fault level gives alarm indication, and the higher fault level automatically stops the fan. To minimize leakage i n the event of the recirculation fan stopping, anti-reversal doors must be installed to ensure closure of the ventilation path between intake and return. These may consist of flaps hinged at the outlet side of the fan casing. The flaps are opened by the pressure generated by the recirculation fan and closed by the pressure difference when the fan stops. For a variable quantity recirculation system, the a i r quantity w i l l be regulated by changing the fan blade angle or fan speed automatically. I t i s possible to get variable speed a-c motors, d-c motors or hydraulic or magnetic coupling between the motor and the fan to get a variable speed potential. The a i r quantity regulation w i l l be i n proportion to the contaminant concentrations. This requires accurate measurement. 6.3.4 Recirculatory System Control Doors Ventilation control doors are required to stop recirculation i n the event of a f i r e or adverse condition. Two sets of class C (3/4 hour or higher) f i r e doors must be installed i n the recirculation crosscut approximately 8 m ( 25 feet) apart. These doors w i l l slide closed i n an emergency. One door w i l l serve as an emergency backup to the other i n the event that one f a i l s to close. Both doors may be opened manually to allow the passage of personnel and w i l l be self-closing. Since the doors are gravity operated, the loss of power w i l l not affect their emergency operation. 6.3.5 I n i t i a l Design The i n i t i a l design was comprised of the following tasks: a) Discussions with sensor manufacturers and representatives. b) Discussions with the mine inspectorates and mine operators. c) Development of recirculation schemes. 6.3.5.1 Discussions on Sensing Instrumentation A number of instrument review meetings were held with representatives from Enviroscience Products, Levitt Safety Limited and Hinelec Limited. / 219 Significant issues such as state-of-the-art sensing technology, telemetry, control devices, sensor spacing and location were discussed during these meetings. Information pertaining to the B r i t i s h online monitoring systems was also obtained from three B r i t i s h companies - Trolex Limited, Transmitton, and Davis Limited of Derby. 6.3.5.2 Discussions With Mine Inspectorates Preliminary discussions were held with the Saskatchewan Inspector of Mines, Mine Safety Unit of the Provincial Ministry of Labour, to obtain his involvement i n the project. The inspectorate has been supporting the project since i t s inception i n 1986. Inputs from the Rocanville Divison's Health and Safety Committe were reviewed and adopted fo r the design. 220 6.4 DESIGN AND INSTALLATION OF RECIRCULATION SYSTEMS 6.4.1 Monitoring System The monitoring system consists of three components: i) Sensors i i ) Telemetry and control devices i i i ) Analysis and display equipment The sensors monitor the environmental parameters and produce an e l e c t r i c a l signal that i s fed into the telemetry system. The telemetry devices receive the signal from the sensors and transmit i t i n the form of analog or d i g i t a l output to the analysis and display unit. The transmitted signal i s either stored for later analysis or displayed. There are two basic approaches to telemetering; i) Centralized management system i i ) Distributed system with intelligent outstations 221 A distributed system i s the preferred approach. This system i s b u i l t up of intelligent outstations, which are microprocessor-based and can be used as programmable controllers, and are responsible for monitoring of each bank of sensors. Each sensor's analog output i s read, digitized and sent to the central control station. The control station processes the sensor data and issues commands to the outstation that controls recirculation doors, for example. The system components operate independently of the central station i n case of operating problems, such as power f a i l u r e or communication breakdown. 6.4.1.1 Proposed Systems The three system proposals and evaluation results are set out i n this section. The projected costs of the three systems are: Transmitton $ 54,100 Davis of Derby $ 68,000 ESC $ 140,700 The detailed cost breakdowns for the proposed monitoring, control and safety systems are given i n a report submitted to PCS - Rocanville Division ( H a l l and Mchaina, 1989 ). 222 The system evaluation results are set out below. Item Transmitton Davis of Derby ESC Sensors Data Collection Transmission Trolex * x X Computer and Data Storage x Cost 1 Supply x Back-up Technical Assistance Good Software Factory * x = Good Trolex x X X 2 X Very Good Can be changed i n f i e l d Nova Tecton x X X 3 X Very Good Factory Transmitton's system i s cheaper than the other two systems but no Canadian representative i s available. In addition/ Transmitton and Davis of Derby systems can be developed to cover control of conveyor systems. In terms of cost, software, and back-up technical assistance, the Davis of Derby system was recommended for installation at Rocanville and Central Canada Potash Divisions. The design for the H-W mine w i l l be based on the same system. CHAPTER SEVEN THE DEVELOPMENT CF RECIRCULATION SYSTEMS FOR CENTRAL CANADA POTASH, PCS RCCANVTLLE DIVISION AND H-W MINE 7.1 INTRODUCTION The recirculation designs developed for CCP and Rocanville are fixed quantity systems. Such systems recirculate a constant airflow quantity from the return to the intake airway at a l l times. The H-W mine recirculation design i s a variable quantity system. The a i r quantity recirculated from the return to the intake airway i s regulated by the pollutant level i n the return, and variable quantity w i l l be achieved by changing the fan blade angle automatically. This chapter sets out the design parameters, guidelines for the development of recirculation systems, economic analysis, system evaluation guidelines and conclusions drawn from the designs. 7.2 DEVELOPMENT OF GUIDELINES FOR RECIRCULATION SYSTEMS Recirculation system guidelines were developed to help mint* ventilation engineers to identify the major system requirements. The ultimate objective i s to ensure that personnel are not exposed to harmful contaminants introduced into the ventilation system. These guidelines are general and they can be used to evaluate various projects i n the areas of both industrial and mine ventilation. Recirculation systems are usually adopted to reduce make-up a i r heating and increase mine airflows, while reducing costs. Figure 27 shows recirculation f e a s i b i l i t y decision logic. This stage i s very important and the engineer considering a recirculation system for a particular application should evaluate the system requirement i n terms of safety and economic savings. After the project i s declared feasible i n terms of safety, then a design and system assessment program i s initiated. The steps to be followed for the program are proposed i n Figure 28. I f the system i s safe and cost effective, then the construction and installation stages of the system are initiated. The steps required for the system evaluation are detailed i n Figure 29. 7.3 RECIRCULATION SYSTEMS In order to use models 6.5.3, 6.5.4, 6.5.5 and 6.5.6 the a i r quality conditions f o r the return and fresh a i r intake concentrations are required. Table 61 shows a i r condition data for the three mines derived from Chapter 5 observations. Using equation 6.2.4 - Hardcastle's model, the maximum allowable return concentrations for CCP, PCS Rocanville Division and H-W mine were calculated and are set out i n Table 61. The values f o r are Threshold Limit Levels for the Provinces of Saskatchewan and British Columbia respectively. REDUCE AIR HEATING COST (1) SET RECIRCULATION OBJECTIVES I INCREASE AIR AIRFLOWS (I) —T— SELECT RECIRCULATION SCHEME I. MINE WIDE HrflSTRICT III. LOCAL EVALUATE MINE INTAKE AND EXHAUST AIR QUALITY (1) + (I) STOP CARCINOGEN/NO SAFE EXPOSUEt LEVELS I STOP' NOT SAFE NOT AVAILABLE J STOP NON-CARCINOGENS/SAFE EXPOSURE LEVELS EVALUATE CRITICAL FAILURE CONDITIONS VS. RECIRCULATION FACTORS #  I SAFE ANQJRACTICALI EVALUATE RECIRCULATION ^sAimMP0NENTS: AVAILABLE, SUITABLE RELIABLE A y i DESIGN AND ASSESS SYSTEM Figure 27 . Reci rcu lat ion Feasibil i ty Decision Logic — Initial Approach DESIGN SYSTEM: - EVALUATE RECIRCULATION FACTORS - EVALUATE SYSTEM COMPONENTS I A S S E S S SYSTEM WILL NOT MEET SAFE EXPOSURE LEVELS STOP HIGH COST STOP SAFE AND PRACTICAL I CONDUCT COST AND ECONOMIC ANALYSIS COST SUITABLE - PAYBACK PERIOD - INTERNAL RATE Cf RETURN i CONSTRUCT AND INSTALL SYSTEM ure 28 . Design and Assessment of Recirculat ion Sys tems C O N S T R U C T AND INSTALL SYSTEM I EVALUATE SYSTEM DEVIATIONS: - SAFETY - DESIGNED OUTPUT PARAMETERS - PERFORMANCE SPECIFICATIONS i U N S A F E E X P O S U R E L E V E L S AND POOR P E R F O R M A N C E i SAFE A N D . P R A C T I C A L SET SAFETY AND OPERATING GUIDELINES C O R R E C T DESIGN COMMISSION SYSTEM i O P E R A T E SYSTEM F igure 2 9 . S y s t e m Eva lua t ion Gu ide l i nes • / 228 The main differences i n the legislations are the exposure levels of CO and NOg as indicated i n Table 5. Table 61. A i r Condition Data for CCP, Rocanville Divisions and the H-W Mine Pollutant Concentrations (ppm) CCP Rocanville H-W Mine Division Return Fresh Return Fresh Return Fresh CO 2.60 0.00 2.14 0.00 5.670 0.0 CCvj 768.00 300.00 531.50 300.00 1036.900 0.0 NO 1.16 0.00 1.03 0.00 4.220 0.0 0.49 0.00 0.52 0.00 1.460 0.0 so2 N/A N/A N/A N/A 1.505 0.0 A i r Quantity m3/s 113 South Mine = 59 North Mine = 83 Total = 142 370 / 229 Table 62. Maximum Return Concentration of Pollutants For various Recirculation Percentages Using Bardcastle's Model Percentage Maximum Allowable Concentrations (ppm) Recirculation i n the Return Airway CCP and Rocanville H-W Mine Divisions CO COj NO NOj CO °°2 NO NO, SCX, 10 250 47300 250 20.0 500 47030 250 30.0 20.0 20 125 23800 125 10.0 250 23680 125 15.0 10.0 25 100 19100 100 8.0 200 19010 100 12.0 8.0 30 83 15967 83 6.7 167 15897 83 10.0 6.7 40 63 12050 63 5.0 125 12005 63 7.5 5.0 50 50 9700 50 4.0 100 9670 50 6.0 4.0 60 43 8133 42 3.3 83 8113 42 5.0 3.3 70 36 7014 36 2.9 71 7001 36 4.3 2.9 80 31 6175 31 2.5 63 6168 31 3.7 2.5 90 28 5522 28 2.2 56 5519 28 3.3 2.2 Actual Measured Concentrations 2. 6 768 1.16 0.4 5.67 1036.9 4.22 1.46 1.505 ,• / 230 The allowable concentrations in the return given by Hardcastle's model are very high. These values are feasible i f the return airway is dedicated solely for that purpose and no personnel are required to work in i t . In Canadian potash and metal mines such concentrations in the return airways would not be allowed because workers are required to enter these airways for inspection and maintenance work. Hardcastle's model therefore cannot be used to design an acceptable system. The reason for this is that Hardcastle's model is based on the individual gaseous components and does not make provision for additive effects of pollutants. There is a strong possibility that AQI will be legislated as a future standard in Canada and the B.C. new legislation requires the cumulative effects of individual gases to be considered. Hardcastle's model cannot therefore be recommended for use in designing Canadian recirculation systems. In view of the possibility of AQI becoming the legislative standard, this relationship has been used to determine the allowable recirculation percentages. 7.4 CENTRAL CANADA POTASH DIVISION OF NORANDA MINERALS INC. Two recirculation schemes were examined for Central Canada Potash Division of Noranda Minerals Inc. Scheme I: 113 m3/s fixed mine quantity inclusive of recirculation. Scheme II: 113 m3/s fixed fresh air intake quantity. The ACGIH Model - equation 6.2.3 was used to predict pollutant levels in return air from the collector before mixing. The mixing ratio for the system was assumed to be 3 throughout the calculations. The predicted results are given in Table 63. 231 Table 63. Maximum Concentration of Contaminants i n the Airstream from the Collector, Before Mixing With Fresh Air, Cg Recirculation Concentrations (PPm) Percentage CO °°2 NO N02 AQI 10 35.80 6916.70 40.00 3.125 4.59 20 17.90 3458.00 20.00 1.563 2.30 25 14.30 2767.00 16.00 1.250 1.84 30 11.90 2306.00 13.30 1.042 1.53 40 9.00 1729.20 10.00 0.780 1.15 50 7.17 1383.00 8.00 0.625 0.92 60 5.97 1153.00 6.70 0.520 0.77 65 5.51 1064.00 6.15 0.480 0.71 70 5.12 988.00 5.70 0.446 0.66 80 4.45 865.00 5.00 0.390 0.57 90 4.00 769.00 4.40 0.347 0.51 100 3.58 692.00 4.00 0.313 0.46 Actual Concentrations Return 2.60 768.00 1.16 0.490 0.395 Face 3.50 850.00 1.00 0.125 0.243 232 In addition, equations 6.2.5 and 6.2.6 vera used to predict return and mixed intake pollutant levels for the schemes. These schemes are detailed i n Tables 64 and 65. I. A year-round whole mine quantity of 113 nr/s (fresh and recirculated air) with various recirculation factors. Table 63 gives the intake, return and mixed intake conditions for CCP. Table 64. A i r Quality With Various Recirculation Factors - Alternative l Fresh A i r Return Mixed Intake Recirculation Quantity CO OOj NO NOj CO COj NO NO2 Percentage (m3/s) (ppm) (ppm) 113.0 2.60 768.0 1.1 0.49 - - - - 0 101.7 2.89 820.0 1.2 0.55 0.289 352 0.13 0.055 10 90.4 3.25 885.0 1.45 0.62 0.65 417 0.29 0.124 20 84.8 3.47 924.0 1.55 0.66 0.87 456 0.39 0.165 25 79.1 3.71 968.6 1.66 0.71 1.11 500 0.50 0.212 30 67.8 4.33 1080.0 1.93 0.83 1.73 612 0.77 0.330 40 56.5 5.20 1236.0 2.33 0.99 2.60 768 1.17 0.496 50 45.2 6.50 1470.0 2.90 1.24 3.90 1002 1.74 0.743 60* 39.6 7.43 1637.0 3.31 1.42 4.83 1169 2.15 0.920 65 33.9 8.67 1860.0 3.86 1.65 6.07 1392 2.71 1.156 70+ 22.6 13.00 2640.0 5.80 2.48 10.40 2171 4.64 1.98 80 11.3 26.00 4980.0 11.59 4.96 23.40 4510 10.43 4.46 90 TLV 'S 25.00 5000 25.00 2.00 At 60%, recirculation return AQI values = 1 and more than 60% recirculation results i n AQI's greater than 1. Fresh a i r concentrations for CO, CQg, NO, NOg are 0.00, 300, 0.00 and 0.00 ppm, respectively. With the various recirculation factors the return a i r quantity remained constant. II. A year round fresh a i r intake of 113 m3/s with various recirculation factors. The a i r quality conditions for the return and mixed intake airways for CCP are given i n Table 65. Using the predicted concentrations set out i n Table 65, compared with the TLV's, i t can be concluded that high recirculation percentages are possible. Even 90% recirculation only results i n an AQI of 0.5 for t h i s The above analyses show that 60% recirculation percentage can provide maximum protection for the CCP workers regardless of the model used to predict the c r i t i c a l concentrations. The AOGXH and Amendola's models do not account for the buildup-up to equilibrium i n successive passes and do not take into account the potential synergistic effects of the numerous pollutants i n the mine. Due to these limitations these models were not used to determine recirculation factors for Rocanville Division and the H-W mine recirculation systems. / 2 3 4 Table 65. A i r Quality With Various Recirculation Factors Alternative n Fresh A i r Return Mixed Intake Recirculation Quantity CO COj NO NOg CO COj NO N O 2 Percentage (m3/s) (ppm) (ppm) 113 2.6 768 113 2.6 768 113 2.6 768 113 2.6 768 113 2.6 768 113 2.6 768 113 2.6 768 113 2.6 768 113 2.6 768 113 2.6 768 113 2.6 768 113 2.6 768 1.16 0.49 -1.16 0.49 0.26 347 1.16 0.49 0.52 394 1.16 0.49 0.65 417 1.16 0.49 0.78 490 1.16 0.49 1.04 487 1.16 0.49 1.30 534 1.16 0.49 1.56 581 1.16 0.49 1.69 602 1.16 0.49 1.82 628 1.16 0.49 2.08 674 1.16 0.49 2.34 721 - - 0 0.116 0.050 10 0.232 0.100 20 0.290 0.124 25 0.348 0.148 30 0.464 0.198 40 0.580 0.248 50 0.700 0.297 60 0.754 0.322 65 0.811 0.347 70 0.927 0.396 80 1.043 0.446 90 TLV's 25.00 5000 25.00 2.00 The method selected for ensuring protection of workers i s to use the A i r Quality Index because of the proposed legislation, a l l designs i n « v f « « thesis were based therefore on the AQI criterion. I t was decided that because the AQI recommended level i s a mayiimim of 2 with no pollutant exceeding i t s TLV, that a safe limit for recirculation i s 50% of this after equilibrium i n the system has been obtained. That i s the mixerl intake and return AQI should not exceed 1.00 and no gas should exceed 50% of i t s allowed TLV i n the mixed intake a i r . This recxmmended lev e l i s conservative but i n the absence of conclusive data and because of lack of experience with recirculation schemes i n Canada i t i s considered that this reccnmendation should be followed u n t i l adequate experience has been gained. At this point relaxation of the limit could be considered. The AQI was used to assess recirculated a i r quality, because i t i s probable that i t w i l l become a legislated standard, as discussed earl i e r i n this chapter. The gas index was used to select recirculation percentages for Central Canada Potash and Rocanville Divisions. Dust samples taken from these mines did not indicate any presence of respirable combustible dust fractions. In the case of the H-W mine gas and particulate indices were used to select recirculation factors. Final selection of a recirculation factor was based on the AQI (gag) • - / 236 The two recirculation alternatives for CCP are analysed using the AQI approach. 7.4.1 Recirculation System - Alternative I The old glycol and the new direct f i r e d natural gas burner a i r heating systems were analysed for recirculation factors with a year-round overall mine quantity of 113 m3/s (fresh and recirculated air) with various recirculation factors. 7.4.1.1 Alternative I with Glycol System Mine-wide make of gas and intake conditions are given i n Table 66. Table 67 gives the mixed intake and recirculation return conditions. Table 66. Make of Gas and Intake Conditions with Glycol Ssytem Parameter Intake Mine-wide Make of Gas Concencentration Concentration CO (ppm) COg (ppm) NO (ppm) NOg (ppm) AQI ( Gag) 0.000 300.000 0.000 0.000 0.000 2.600 468.000 1.160 0.490 0.395 237 Table 67. A i r Quality with Various Recirculation Factors - Alternative I Parameter Recirculation Percentage 0 10 20 30 40 50 60 70 80 90 Mixed Intake Concentrations CO (ppm) 0 0.26 0.52 0.78 1.04 1.30 1.56 1.82 2.08 2.34 COu. (ppm) 300 347 394 440 487 534 581 628 674 721 NO (ppm) 0 0.12 0.23 0.35 0.46 0.58 0.70 0.81 0.93 1.04 NCLg (ppm) 0 0.05 0.10 0.15 0.20 0.24 0.29 0.34 0.39 0.44 Quantity (m3/s) 113 113 113 113 113 113 113 113 113 113 AQI 0 0.04 0.08 0.12 0.16 0.20 0.24 0.28 0.32 0.36 Recirculation Return Airway Concentrations CO (ppm) 2.60 2.86 3.12 3.38 3.64 3.90 4.16 4.42 4.68 4.94 COg (ppm) 768 815 862 908 955 1002 1049 1096 1142 1189 NO (ppm) 1.16 1.28 1.39 1.51 1.62 1.74 1.86 1.97 2.09 2.20 N0 2 (ppm) 0.49 0.54 0.59 0.64 0.69 0.74 0.78 0.83 0.88 0.93 Quantity m3/S 113 11.3 22.6 33.9 45.2 56.5 67.8 79.1 90.4 101.70 AQI 0.395 0.435 0.474 0.51 0.55 0.59 0.63 0.67 0.71 0.75 / 238 In order to establish the recirculation percentage, a i r contaminant i n the return and mixed intake sides were balanced. The following conditions were set for the mixed intake and return airways. 1. AQlg ^ i n the return airway = 1.00 2. COg concentration i n the mixed intake < 2500 ppm or < 0.50 TLV. 3. AQIgas i n the mixed intake < 1.00 4. For H-W mine, A Q I ( T o t a l ) = A Q I ( G a s ) + A Q I ( p a r t ) < 2.50 These conditions were used for setting recirculation fractions for the three mines studied i n this thesis. The recirculation fraction was calculated using the following mathematical expression; Q4*V4 + Qi*V x + Q3* v M Q G = Q *y 3 3 v x = v 4 = v 5 = 1.00; v x = 0.00 + 113*0.395 = 113*1.00 or = 68.40 m3/s Therefore, Recirculated quantity = 68.40 m3/s Fresh a i r quantity = 44.60 m3/s Recirculation percentage = 60.50% The mathematical notations used i n the above analysis are detailed i n Figure 30, where, Q 1 = Fresh a i r intake quantity, m3/s Q 2 = Mixed intake quantity, m3/s Q 3 = Return a i r quantity, m3/s Q 4 = Recirculation quantity, m3/s V 1 to V 5 = Respective AQI's and MOG = Make of Gas The above analysis assumes that face flow quantity i s constant and therefore make of gas i s constant, e Convent ional Venti lat ion n CM Mine Make of Gas V(MOG) = 0.395 01 V1 Fresh Air i i Return Air Downcast Shaft Upcast Shaft Contro l led Recirculat ion Mine Make of Gas V(MOG) = 0.395 Mixed Q2 Intake y2 Q1 V1 Fresh Air r Downcast Shaft Q3 V3 0 5 V5 Return Air Upcast Shaft V1 = 0 R.F. = Recirculation Fan V1 = 0 Figure 3 0 . C C P Al ternat ive I - Old S y s t e m / 240 In addition, Q X and Q^  vary as percentage recirculation changes and Q 3 = Q 1 + Q ^ but Q 3 remains constant. At a recirculation factor of 60.50%, the return AQI w i l l reach equilibrium after 11 passes. The return and mixed intake AQI's for various recirculation passes are given i n Table 68. Table 68. Air Quality Indices for Various A i r Passes Pass A i r Quality Index (AQI) and COj Concentration (ppm) Number Mixed Intake Return AQI (ppm) AQI (Ppm) 1 0.239 581 0.634 1049 2 0.384 753 0.779 1221 3 0.472 857 0.867 1325 4 0.525 920 0.920 1388 5 0.558 958 0.953 1426 6 0.578 981 0.973 1449 7 0.590 995 0.985 1463 8 0.597 1004 0.992 1472 9 0.601 1009 0.996 1477 10 0.604 1012 0.999 1480 11 0.605 1014 1.000 1482 Intake and return a i r concentrations without recirculation are 300 and 768 ppm respectively. . ' 241 7.4.1.2 Alternative I with Direct-Fired Natural Gas Burners Mine-wide make of gas and intake conditions are given i n Table 69. Table 70 gives the mixed intake and recirculation return conditions. Table 69. Make of Gas and Intake Conditions Alternative I with Direct Fired Natural Gas Burners Parameter Intake Mine-wide Make of Gas Concentration Concentration 2.600 468.000 1.160 0.490 0.395 C O (ppm) 6.000 CCv^ (ppm) 1800.000 N O (ppm) 0.100 N O g (ppm) 0.400 AQI 0.444 Table 70. A i r Quality with various Recirculation Factors Alternative I with Direct Fired Natural Gas Burners Parameter Recirculation Percentage 0 10 20 30 40 50 60 70 80 90 Mixed Intake (ppm) 00 6.0 6.26 6.52 6.78 7.04 7.30 7.56 7.82 8.08 8.34 COj 1800 1847 1894 1940 1987 2034 2081 2128 2174 2221 NO 0.10 0.22 0.33 0.45 0.56 0.68 0.80 0.91 1.03 1.14 NOg 0.40 0.45 0.50 0.55 0.60 0.65 0.69 0.74 0.79 0.84 Quantity m3/s 113 113 113 113 113 113 113 113 113 113 AQI 0.44 0.48 0.52 0.56 0.60 0.64 0.68 0.72 0.76 0.80 Recirculation Return (ppm) CO 8.60 8.86 9.12 9.38 9.64 9.90 10.16 10.42 10.68 10.94 COg 2268 2315 2362 2408 2455 2502 2549 2596 2642 2689* NO 1.26 1.38 1.49 1.61 1.72 1.84 1.96 2.07 2.17 2.30 NOj 0.89 0.94 0.99 1.04 1.09 1.14 1.18 1.23 1.28 1.33+ Quantity m3/s 0.00 11.3 22.6 33.9 45.2 56.5 67.8 79.1 90.4 101.7 AQI 0.84 0.88 0.92 0.96 1.0 1.04 1.07 1.11 1.15 1.19*^ * + *+ > 50% recirculation, 00^ level exceeds 50% of TLV > 30% recirculation, NOg level exceeds 50% of TLV > 50% recirculation, AQI exceeds 1.00 Similar conditions used to calculate recirculation fractions i n section 6.4.1.1 were used to compute a recirculation fraction required to maintain AOIg^g equal to 1.00. The recirculation fraction was calculated as follows: Q4*V4 + Q j * ^ + (Q± + Q ^ V ^ = (Q 1 + c ^ ) ^ The above mathematical relationship gives the following values: Q± = 79.10 m3/s, = 33.90 m3/s and Recirculation Percentage = 30% The mathematical variables used i n the above equation are detailed i n Figure 31. At 30% recirculation percentage, system equilibrium w i l l be reached after s i x a i r passes (air changes). The return and mixed intake AQl's for various a i r changes are given i n Table 71. Table 71. A i r Quality Indices for Various A i r Passes with Direct Fired Natural Gas Burners Pass A i r Quality Index (AQI) and COg Oopncentrations (ppm) Number Mixed Intake Return AQI ppm AQI ppm 1 0.427 1940 0.822 2408 2 0.552 1983 0.947 2450 3 0.589 1995 0.984 2463 4 0.600 1999 0.995 2467 5 0.604 2000 0.999 2468 6 0.605 2000 1.000 2468 CM Convent ional Venti lat ion Mine Make of Gas V(MOG) = 0.395 01 V1 Fresh Air A i Return Air Downcast Shaft Upcast Shaft V1 = 0.44 Control led Reci rcu lat ion Mine Make of Gas V(MOG) = 0.395 Mixed Q2 Intake V2 Q1 V1 Fresh Air u Downcast Shaft Upcast Shaft R.F. = Recirculation Fan V1 = 0.44 Figure 3 1 . C C P Al ternat ive I - New S y s t e m 245 7.4.2 Recirculation System - Alternative II Tne old and new heating systems were analysed for recirculation factors, with a year—round fresh a i r intake of 113 m3/s with various recirculation factors. 7.4.2.1 Alternative II with Glycol System Mine-wide make of gas and intake and recirculation are similar to those given i n Table 66. A i r quality with various recirculation factors are given i n Table 72. 246 Table 72. A i r Quality with various Recirculation Factors Alternative H - Old System Parameter Recirculation Percentage 0 10 20 30 40 50 60 70 80 90 Mixed Intake CO (ppm) 0 0.26 0.52 0.78 1.04 1.30 1.56 1.82 2.08 2.34 COg (ppm) 300 347 394 440 487 534 581 628 674 721 NO (ppm) 0 0.17 0.23 0.35 0.46 0.58 0.70 0.81 0.93 1.04 NOj (ppm) 0 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 Quantity m3/s 113 113 113 113 113 113 113 113 113 113 AQI 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Return CO (ppm) 2.6 2.86 3.12 3.38 3.64 3.9 4.16 4.42 4.68 4.94 COj (ppm) 768 815 862 908 955 1002 1049 1096 1142 1189 NO (ppm) 1.16 1.28 1.39 1.51 1.62 1.74 1.86 1.97 2.09 2.20 NC^tppm) 0.49 0.54 0.59 0.64 0.69 0.74 0.79 0.84 0.89 0.94 Quantity m3/s 0.0 12.6 28.3 48.4 75.3 113 169.5 263.7 452 1017 AQI 0 .395 0.44 0.48 0.52 0.55 0.60 0.64 0.68 0.72 0.76 247 The recirculation percentage was calculated using the following mathematical relation: °-l*Vl + Q 4 * V 4 + (Q4 + Ql> *VMOG = 93* V3 V l = 0, V 3 = V 4 = 1, Q3 = Qx+ 04 Therefore, Qi = 173 m3/s, Q± - 113 m3/s and Recirculation Percentage = 60.50% The above variables are detailed i n Figure 32. Table 73 gives the a i r quality indices for various a i r passes. Table 73. A i r Quality Indices for Various Air Passes - Alternative II with Old Heating System Pass A i r Quality Index (AQI) and COg Concentration (ppm) Number Mixed Intake Return AQI ppm AQI ppm 1 0.239 583 0.634 1051 2 0.384 754 0.779 1222 3 0.471 858 0.866 1326 4 0.524 920 0.919 1388 5 0.556 958 0.951 1426 6 0.575 981 0.970 1449 7 0.587 995 0.982 1463 8 0.594 1003 0.989 1471 9 0.598 1008 0.993 1476 10 0.600 1011 0.995 1479 11 0.602 1013 0.997 1481 12 0.602 1014 0.998 1482 13 0.604 1015 0.999 1483 Convent iona l Venti lat ion Mine Make of Gas V(MOG) = 0.395 01 V1 Fresh Air A Return Air Downcast Shaft Upcast Shaft Control led Reci rculat ion Mine Make of Gas V(MOG) = 0.395 Mixed Q2 Intake V2 Q1 V1 Fresh Air Downcast Shaft Upcast Shaft V1 = 0 R.F. = Recirculation Fan vT = 0 Figure 32. CCP Alternat ive II — Old System 7.4.2.2 Alternative n with New Heating System Mine-wide make of gas and intake renditions are given i n Table 69. The mixed intake and recirculation return conditions are given i n Table 74. The recirculation fraction for alternative II was calculated using the following mathematical expression; Ql*v"i + Q4*V 4 + + 0 4 ) * ^ = (Q x + 0 4 ) ^ 3 Substituting the respective values i n the expression above gives the following values: Qx = 113 m3/s , = 47.2 m3/s and Recirculation Percentage = 29.50% The various parameters used i n the above equation are given i n Figure 33. At 29.5% recirculation - NOj level = 50% of T.L.V., th i s i s therefore maximum recommended recirculation for t h i s configuration. At the above recirculation percentage, the return AQI w i l l reach equillibrium after 6 passes. The return and mixed intake AOI's for various recirculation passes are given i n Table 75. Convent iona l Venti lat ion Mine Make of Gas V(MOG) = 0.395 Q1 V1 Fresh Air A I Return Air Downcast Shaft Upcast Shaft Control led Reci rcu lat ion Mine Make of Gas V(MOG) = 0.395 Mixed Q2 Intake v2 Downcast Shaft Upcast Shaft V1 = 0.44 R.F. = Recirculation Fan V1 = 0.44 Figure 33. C C P Al ternat ive II - New S y s t e m Table 74. . , / 251 A i r Quality with Various Recirculation Factors - Alternative II with Mew Heating System Parameter Recirculation Percentage 0 10 20 30 40 50 60 70 80 90 Mixed Intake CO (ppm) 6 6.26 6.52 6.78 7.04 7.30 7.56 7.82 8.12 8.34 COg (ppm) 1800 1847 1894 1940 1987 2034 2081 2128 2174 2221 NO (ppm) 0.1 0.21 0.33 0.45 0.56 0.68 0.80 0.91 1.03 1.14 N0 2 (ppm) 0.4 0.45 0.50 0.55 0.60 0.65 0.69 0.74 0.79 0.84 Quantity m3/s 113 125.6 141.3 161.4 188.3 226.0 282.5 376.7 565.0 1130 AQI 0.44 0.48 0.52 0.56 0.60 0.64 0.68 0.72 0.76 0.8 Recirculation Return CO (ppm) 8.6 8.86 9.12 9.38 9.64 9.90 10.16 10.42 10.72 10.94 COg (ppm) 2268 2315 2362 2408 2455 2502 2549 2596 2642 2689* NO (ppm) 1.26 1.37 1.49 1.61 1.72 1.84 1.96 2.07 2.19 2.30 NO^ppm) 0.89 0.94 0.99 1.04 1.09 1.14 1.18 1.23 1.28 1.33+ Quantity m3/s 0.0 12.6 28.28 48.40 75.3 113 169.5 263.7 452 1017 AQI 0.84 0.88 0.92 0.96 1.00 1.04 1.07 1.11 1.16 1.19*+ * + > 50% recirculation, CCj level exceeds 50% of TLV > 30% recirculation, NOj level oxcooda 50% of TLV * + > 50% recirculation, AQI exceeds 1.00 Table 75. A i r Quality Indices for various A i r Passes - Alternative II with New Heating System Pass A i r Quality Index (AQI) and COj Concentration (ppm) Number Mixed Intake Return AQI ppm AQI ppm 1 0.427 1938 0.822 2406 2 0.553 1979 0.948 2447 3 0.590 1990 0.985 2458 4 0.600 1994 0.995 2462 5 0.604 1995 0.999 2463 6 0.605 1995 1.000 2463 7.5 ROCANVILLE DIVISION OF POTASH CORPORATION OF SASKATCHEWAN One recirculation alternative was proposed for Rocanville Division of PCS, using a year-round overall mine quantity of 83 m3/s ( fresh and recirculated a i r ) with various recirculation factors. The proposed alternative was analysed using the AQI approach and the optimum recirculation percentage was calculated. The mine-wide make of gas and intake conditions are set out i n Table 76. Table 77 gives the mixed intake and recirculation return conditions using various recirculation factors. Table 76. Hake of Gas and Intake Conditions Parameter Intake Mine-wide Make of Gas Concentration Concentration CO (ppm) 0.00 2.140 COg (ppm) 300.00 231.500 NO (ppm) 0.00 1.030 NOj (ppm) 0.00 0.520 Quantity m3/s 83.00 83.000 AQI 0.00 0.387 The recirculation quantity was calculated as detailed follows: Q4*V4 + Q j * ^ + (Q x + Q 4)*V M 0 G = (Q x + Q4)*V3 Substituting the respective values i n the above expression gives the following a i r quantities: Q4 = 51 m3/s Q x = 32 m3/s Recirculation percentage = 64.4%. The mathematical variables used i n the above equation are detailed i n Figure 34. With 64.4% recirculation a i r quality w i l l stabilize after 11 passes. The return and mixed intake AQI's for various recirculation passes are given i n Table 78. Convent ional Venti lat ion North Mine Make of Gas V(MOG) = 0.387 01 V1 Fresh Air A Return Air Downcast Shaft Upcast Shaft Control led Recirculat ion North Mine Make of Gas V(MOG) = 0.387 Mixed Q2 Intake V2 01 V1 Fresh Air Downcast Shaft Upcast Shaft V1 = 0.00 B.F. = Existing Booster Fans vi = 0.00 Figure 34. PCS Rocanville Division Reicirculation Model Table 77. .Rocanville Division A i r Quality Conditions with Various Recirculation Factors Parameter Recirculation Percentage 0 10 20 30 40 50 60 70 80 90 Mixed intake CO (ppm) 0.0 CO2 (ppm) 300 NO (ppm) 0.0 NO2 (ppm) 0.0 Quantity m3/s 83 AQI 0.0 0.21 0.43 0.64 321 346 369 0.10 0.21 0.31 0.05 0.10 0.16 83 83 83 0.40 0.08 0.12 0.86 1.07 1.28 393 416 439 0.41 0.52 0.61 0.21 0.26 0.31 83 83 83 0.16 0.19 0.23 1.50 1.72 1.93 462 485 508 0.72 0.82 0.93 0.36 0.42 0.47 83 83 83 0.27 0.31 0.35 Recirculation Return co (ppm) 2.14 2.35 2.57 2.78 3.00 3.21 3.42 3.64 3.86 4.07 C 0 2 (ppm) 532 553 575 600 625 648 671 694 717 740 NO (ppm) 1.0 1.13 1.24 1.34 1.44 1.55 1.64 1.75 1.85 1.96 NO2 (ppm) 0.52 0.57 0.62 0.68 0.73 0.78 0.83 0.88 0.94 0.99 Quantity m3/s 83 8.3 16.6 24.9 33.2 41.5 49.8 58.1 66.4 74.7 AQI 0.39 0.42 0.46 0.50 0.54 0.58 0.61 0.66 0.70 0.74 Table 78. A i r Quality Indices for Various A i r Passes - Rocanville Division of Potash Corporation of Saskatchewan Pass Number Ai r Quality Index Mixed Intake Return AQI ppm AQI ppm 1 0.240 443 0.627 675 2 0.385 530 0.772 762 3 0.474 584 0.861 816 4 0.529 617 0.916 849 5 0.563 637 0.950 869 6 0.584 650 0.971 882 7 0.597 658 0.984 890 8 0.605 663 0.992 895 9 0.610 666 0.996 898 10 0.612 667 0.999 899 11 0.614 668 1.000 900 The above analyses show that glycol and direct f i r e d natural gas systems can allow up to a maxirmim of 60% and 30% recirculation respectively. . 2 5 7 7.6 H-W MINE OF WESTMIN RESOURCES LIMITED One recirculation alternative was considered f o r H-W mint* of Westmin Resources Limited. A year-round overall mine fresh a i r quantity of 370 m3/s was used with various recirculation factors. The system was analysed for recirculation factors and an optimum recirculation factor was selected, based on the AQI approach. An AQI^ f f was used to compute the recirculation quantity and the maximum recommended AQI (total, gas and particulate) was taken to be 2.5 i n the return side of the system. Threshold Limit Values (TLV's) for CO and N02 i n the Province of B r i t i s h Columbia (B.C.) are 50 and 3 ppm respectively. These TLV's for the Province of B.C. were used i n the computations of the AQI's. The mine-wide make of gas and intake conditions are given i n Table 79. Table 80 gives the mixed intake and recirculation return conditions. The maximum safe recirculation percentage was calculated as follows: Q 4 * V 4 + Qj*^ + (Q4 + Q X ^ V M O Q = (Q4 + Qj)«v3 Substituting the values as given i n Figure 35, gives the following recirculation quantity and percentage. Q 4 = 111.14 m3/s Recirculation Percentage = 23% The above results show that i t would be possible to increase the a i r quantity i n the mine to 480.5 m3/s while maintaining 370 m3/s i n the fresh a i r intake side. Convent ional Venti lat ion Mine Make of Gas V(MOG) = 0.769 0 1 V1 Fresh Air A I Return Air Downcast Shaft Upcast Shaft Control led Reci rcu lat ion Mine Make of Gas V(MOG) = 0.769 Mixed Q2 Intake V2 u Downcast Shaft Upcast Shaft V1 = 0.00 R.F. = Recirculation Fan vi = 0.00 Figure 35. H - W Mine Re ic i rcu la t ion Model Table 79. Make of Gas and intake Conditions - H-W Mine of Westmin Resources Limited Parameter Intake Mine-wide Make of Gas Concentration Concentration CO (ppm) 0.00 5.670 COg (ppm) 330.00 706.900 NO (ppm) 0.00 4.220 NOg (ppm) 0.00 1.460 SOj (ppm) 0.00 1.505 Respirable Combustible Dust (mg/m3) 0.00 0.320 ^ ( G a s ) 0.00 0.769 This rel a t i v e l y small recirculation factor of 23% would result i n mixed intake and return a i r conditions as set out i n Table 81. Table 82 gives the a i r quality indices for various a i r passes. 260 Table 80. A i r Quality with various Recirculation Percentages - H-W Mine of Westmin Resources Limited Parameter Recirculation Percentage 0 10 20 30 40 50 60 70 80 90 Mixed Intake 00 (ppm) 0.0 0.57 1.14 1.70 2.27 2.84 3.40 4.00 4.54 5.1 COg (ppm) 330 400 472 542 613 682 754 825 896 966 NO (ppm) 0.0 0.42 0.85 1.27 1.69 2.11 2.53 2.95 3.38 3.8 N02 (ppm) 0.0 0.15 0.29 0.44 0.58 0.73 0.88 1.02 1.17 1.31 S02 (ppm) 0.0 0.15 0.30 0.45 0.60 0.75 0.90 1.05 1.20 1.35 Quantity m3/s 370 411 463 529 617 740 925 1233 1850 3700 AQIgag 0.0 0.08 0.15 0.23 0.31 0.38 0.46 0.54 0.62 0.69 Recirculation Return CO (ppm) 5.67 6.24 6.81 7.37 7.94 8.51 9.07 9.67 10.21 10.77 C02 (ppm) 1037 1107 1179 1249 1320 1390 1461 1532 1603 1673 NO (ppm) 4.22 4.64 5.07 5.49 5.91 6.33 6.75 7.17 7.60 8.02 NOj (ppm) 1.46 1.61 1.75 1.90 2.04 2.19 2.34 2.48 2.63 2.77* SOj (ppm) 1.51 1.66 1.80 1.96 2.10 2.26 2.40 2.56 2.70 2.86+ Quantity m3/s 0.00 41 93 159 247 370 555 863 1480 3330 AOIU,„) 0.77 0.85 0.92 1.00 1.08 1.15 1.23 1.31 1.38 1.46*' * + *+ > > > 10% recirculation, NC^ level exceeds 50% of TLV 70% recirculation, SC^ level exceeds 50% of TLV 30% recirculation, AQI exceeds 1.00 261 Table 81. Return and Mixed Intake A i r Conditions - Recirculation Percentage of 23% Parameter Mixed intake Recirculation Return CO (ppm) 1.30 6.97 CO, (ppm) 492.60 1199.50 NO (ppm) 0.97 5.19 NOj (ppm) 0.34 1.80 SOj (ppm) 0.35 1.86 Quantity (m3/s) 480.50 110.50 A Q I ( G a s ) 0.18 0.95 AQ 1(Total) 0.44 2.35' * AQ 1 (Total) of 2.35 for tne return i s acceptable. Table 82. A i r Quality Indices for various Recirculation Passes - Recirculation Percentage of 23% Pass Number A i r Quality Index (AQI) and COg Concentration (ppm) Mixed Intake Return AQI ppm AQI ppm 1 0.218 [0.54]* 493.0 0.987 [2.45] 1199.9 2 0.227 [0.56] 530.0 0.996 [2.47] 1236.9 3 0.229 [0.57] 538.6 0.998 [2.48] 1245.5 4 0.229 [0.57] 540.50 0.998 [2.48] 1247.4 * (Total) The A i r Quality Index for the Make of Gas used i n the computation of AQI ( ^tal) w 3 3 1 - 9 1 ' CHAPTER vrrrztrp SYSTEM DESIGN 8.1 PROPOSED RECIRCULATION SYSTEM CHARACTERISTICS The proposed recirculation system characteristics for CCP, PCS Rocanville Divisions and the H-W mine are detailed i n this section. 8.1.1 Central Canada Potash Division of Noranda Minerals Inc. CCP Division downcasts nearly 113 m3/s of fresh a i r to ventilate underground mining operations. The designed recirculation system's characteristics are given i n Table 83. The objectives are to reduce winter heating costs and increase the airflow to the mining d i s t r i c t s by recirculating a fraction of the mine's exhaust a i r into the fresh a i r intake. Recirculation w i l l take place through a series of doors located i n the recirculation cross-cut. Exhaust from the main return airway w i l l be drawn through the doors by a recirculation fan. 8.1.2 Rocanville Division of Potash Corporation of Saskatchewan Rocanville Division supplies 83 m3/s of fresh a i r to ventilate the North mine underground operations. The designed recirculation system for Rocanville Division i s intended to reduce winter heating cost by recirculating a fraction of the exhaust a i r into the fresh a i r intake. The North mine ventilation would be achieved by recirculating 51 m3/s or 64.40% of the t o t a l exhaust a i r (83 m 3/s). Fresh a i r supply to the North mine would be reduced to 32 m3/s. Recirculation w i l l take place through a series of doors located i n the recirculation cross-cut. Exhaust a i r from the return airway w i l l be drawn through the doors by the existing booster fans for the North mine. The booster fans blade angle settings require adjustment to supply the proposed recirculation quantity. Modification of the proposed recirculation connection i s required to meet the designed system's performance. This w i l l include tasks such as wall trimming along the recirculation d r i f t , blocking the existing bulkhead to No. 4 d r i f t and removing the existing stoppings. Figures 36 and 37 show the locations of the existing bulkhead and the proposed f i r e control doors, respectively. When inst a l l i n g the control doors the ve r t i c a l closure (maximum 12.7 mm per year) of the area should be taken into account. 8.1.3 H-W Mine of Westmin Resources T . - i m - i + A r t The H-W mine of Westmin Resources Limited downcasts a total of 370 m3/s of fresh a i r to ventilate underground mining operations. A recirculation design for the H-W mine i s proposed with the objective of increasing the underground airflows. Accounting for a l l legal and a i r quality considerations, Westmin Resources can recirculate up to a ma-sHimmi of 23% of i t s exhaust a i r back to an intake airway. The total and recirculated quantities for the system would be 110.50 m3/s and 480.50 m3/s respectively. This recirculation factor of 23% can be reduced during blasting and increased during ordinary mining ac t i v i t i e s . t Figure 36 . No. 3 Drift Recirculat ion System Location F igu re 37. N o . 3 Drift R e c i r c u l a t i o n S y s t e m L o c a t i o n s 266 A variable quantity recirculation system i s reccaoanded for tne H-W mi-na because of tne overall mine pollutant fluctuations. Peak AQl's of up to 4.86 and durations of decay to pre-blast conditions (AQI = 0.252) of up to 3 hours were recorded during the f i e l d survey. The contaminant peaks result from production blasts. Tnstead of having a variable quantity recirculation system the mine management could consider an on/off system. The system can be switched off just before the main blast and switched on when the miners return underground. Since the H-W mine has a centralized blasting system the recirculation system can be switched on and o f f automatically by means of a timer. Since the H-W mine blasting schedule i s quite consistent 16:00 and 04:00 hours daily/ the use of an electronic timer to switch on and off the recirculation system may be practical and feasible. Exhaust from the main return airway w i l l be drawn through control doors by a recirculation fan. 267 Table 83. Proposed System's Characteristics for CCP Parameter Alternative I Aternative II Heating System Heating System Mew* Old4* New Old Recirculation Quantity (m3/s) 33.70 68.40 47.20 173.00 Fresh A i r Quantity (m3/s) 79.30 44.60 113.00 113.00 Total A i r Quantity (m3/s) 113.00 113.00 160.20 286.00 Recirculation Percentage (%) 30.00 60.50 29.50 60.50 Glycol system and * Direct Fired Burner System 268 8.2 CCMNCN FEATURES FOR CCP, ROCANVILLE DIVISION AND H-W MINE PROPOSED RECIRCULATION SYSTEMS 8.2.1 Doors In these projects, monitoring, control, safety systems and control doors are major installations. Ventilation control doors are required to stop recirculation i n the event of a f i r e or other adverse conditions. Two sets of class C (3/4 hour or better) f i r e doors should be installed i n the recirculation cross-cut. One door w i l l serve as an emergency backup to the other i n the event that one f a i l s to close. Both doors may be opened manually to allow the passage of personnel and w i l l be self closing. The doors w i l l be gravity operated so that the loss of power w i l l not affect their emergency operation. Space between the two doors i s approximately 7.62 metres or 25 feet. Two 2.13 x 3.05 metres or 7' x 10' (height x width) control doors are proposed. When installing the control doors i n the potash mines, the ver t i c a l closure of the area should be taken into account. 269 8.2.2 Monitoring and Control System ventilation conditions within the recirculation c i r c u i t w i l l be continuously monitored by a series of electronic sensors. Information from the sensors w i l l be collected by an on-site microprocessor and transmitted to a surface computer by means of modem-ccmmunication. Figures 38, 39 and 40 show the underground system layouts for CCP, PCS Rocanville and the H-W mine. The description of the various system components i s given i n Table 84. Table 84. Recirculation System Layout Legend Symbol/Abbreviation Description VB Visual Beacon AA Audible Alarm N NOg Sensor C COg Sensor 0 CO Sensor + POC Sensor V Velocity Sensor A Amperage Sensor P Door Proximity Switch Rec. Fan Recirculation Fan i N 4N o CM Local Microprocessor I 1 I 3N X Rec. Fan N,0,T,C,V No. 2 Shaft a Doors No. 1 Shaft Legend [) = Ooor = Fresh Air = Exhau9t Air Figure 38. CCP Recirculation System Layout CM Solvoqe Bay Local Microprocessor + 0 A ^ V B T 4-V 0 D a p + 0 Fire Door (Regulator) HI C Fire Door (Backup) P Warehouse AA VB 4 LEGEND A N N C 0 V i A A North Nine Booster Fans 4 Fresh Air Exhaust Air Mixed Intake Air Figure 39. Rocanville Division Recirculation System Layout CN CN V.AA.VB.P Return 1 t La. Doors -Dust Filter |D N.O.T.C.V • Recirculation Tan 0,0,+ T,V,0,+,+ Intake • Local Microprocessor - j V B M Figure 40. H —W Mine Recirculation System Layout 273 Figures 41, 42 and 43 snow the monitoring and control system schematics for CCP, Rocanville Division and the H-W mine respectively. Table 85 l i s t s a l l sensors and describes their function. Table 85. Recirculation System Sensors Sensor Group Elements Purpose Fire Detection Group 1 Fire Detection Group 2 Recirculation Monitoring Group Environmental Monitoring Group Fan Amperage 3 Carbon Monoxide Sensors 3 Product of Combustion Sensors 1 A i r Temperature 1 Velocity Sensors 1 Oxide of Nitrogen Sensor, 1 Carbon Dioxide Sensor, 1 carbon Monoxide, 1 A i r velocity Sensor, l A i r Temperature Sensor 2 Current Transducers Monitor CO levels i n recirculated exhaust a i r High levels trigger alarms and door closures. Monitors recirculated exhaust for combustion by-products. High levels trigger alarms and door closure. Redundancy with Group 1. Monitors the volume and temperature of recirculated exhaust. Monitors the volume, temperature, and pollutant l e v e l of mixed intake. High levels trigger alarms and door closure. Detects the absence of power or a fan failure. These conditions trigger alarms and door closure. Door Proximity 2 Contact Switches Acknowledges door closure and audible alarms. K . ' 274 F1RE D E T E C T I O N C R O U P 1 FIRE DETECTION CROUP 2 RECRCUIATDN MONITORING CROUP ENVIRONMENTAL MONITORINC CROUP 1 REMOTE ALARM ACTUATION UODEU ODIAAJNCAJTJN PRINTER (REPORTS) FAN AMPERAGE SENSORS DOOR PROXIMITY SWITCHES LOCAL ALARM ACTTVATDN Figure 41. CCP Monitoring and Control System FIRE DETECTION CROUP 1 FIRE DETECTION GROUP 2 RECRCUIATDN MONITORING CROUP ENVIRONMENTAL MONITORING CROUP REWOTT AUkRU JCTr/ATON UDDEU OOUMUNCATON LOCAL UCROPROCESSOR FAN AMPERAGE 5ENSOR5 DOOR PROXIMITY SWITCHES LOCAL ALARM ACTIVATION Figure 42. Rocanville Division Monitoring and Control System FIRE DETECTION GROUP 1 ENVIRONMENTAL MONITORING GROUP FIRE DETECTION GROUP 2 RECIRCULATION MONITORING GROUP MODEM COMMUNICATION SURFACE COMPUTER LOCAL MICROPROCESSOR REMOTE ALARM ACTIVATION i FAN AMPERAGE SENSORS AT MODEM COMMUNICATION DOOR PROXIMITY SWITCHES LOCAL ALARM ACTIVATION DUST FILTER DIFFERENTIAL PRESSURE SENSOR PRINTER (REPORTS) DOOR CLOSE CONTACTS REGULATOR ADJUST AUDIBLE AND H^MS Figure 4 3 . H - W Mine Moni tor ing and Cont ro l S y s t e m / 276 Two f i r e detection groups w i l l be used to increase r e l i a b i l i t y through redundancy. Product of cxxribustion sensors are employed i n Group 2 to detect n i t r i l e conveyor f i r e s which do not produce significant amounts of carbon monoxide. system control outputs w i l l signal door closure and activate the alarms. The primary function of the monitoring and control system i s to stop recirculation from occurring under adverse conditions. Any of the conditions set out i n Table 86 w i l l cause the control doors to close, thereby stopping recirculation: Table 86. Conditions for Control Doors Closure Mo. Conditions 1 Activation of the mine f i r e alarm system from surface or elsewhere. 2 High carbon monoxide readings from f i r e detection group 1 sensors. 3 High product of combustion readings from f i r e detection group 2 sensors. 4 High CO, COg, or NQg readings from environmental monitoring group sensors. 5 Adverse temperature or a i r velocity readings. 6 Failure of the recirculation fan. 7 By instruction from surface computer. 8 Emergency switch at recirculation s i t e . 9 Power fa i l u r e (battery power w i l l be available to signal door closure). 10 Manual release of door latches (no power required). With the exception of item 10, i n Table 86, there w i l l be a 10 second delay between the receipt of a close door signal and the actual closing of the door. During the period, flashing lights and audible a i a m w » w i l l warn of the impending door closure. Once the doors are confirmed closed by proximity switches, the audible alarm w i l l cease. Flashing lights w i l l continue to operate u n t i l manually acknowledged. 8.3 COMMISSIONING AND PERFORMANCE EVALUATION OF THE RECIRCULATION SYSTEM A program to evaluate the installation performance should be undertaken i n order to assess the system's deviation from the planned design efficiency. A long term strategy for maintenance, periodic monitor calibration, and system testing should be developed. There i s a chance for the sensors to give false indications due to the passage of diesel machines, which could result i n the stoppage of recirculation. This would be tested by operating a diesel unit near the CO detectors. The U.S. Bureau of Mines are developing a novel f i r e detector that can discriminate between smoke produced by a f i r e and smoke produced by a diesel engine ( Litton, 1988 ). The control system should be designed to respond only to the exhaust pollutant levels that remain above alarm set points for a short but continuous period. Comprehensive surveys should be conducted to identify the response of personnel to recirculation. This survey would augment results from detailed environmental measurements before and during recirculation and i t would reveal whether recirculation has any unforseen effects cn the miners. 8.4 COST ANALYSES FOR CCP AND ROCANVILLE DIVISION SYSTEMS Cost analyses were performed for the CCP and PCS Rocanville Division systems. The estimated costs for these systems were based on tne following parameters:-Mean daily winter temperature for Rocanville and Colonsay i s -15 °C. Direct f i r e d natural gas burners with 70% efficiency. Number of heating days per year = 120. Natural gas cost per l i t r e = $ 0.00006. i 37.3 kJ can be generated with one l i t r e of natural gas. Intake a i r must be heated to a temperature of 14 °C. A i r flew parameters are set out i n Table 87. Annual ventilation cost for Canadian mines = $ 566.00 per cubic metre per second (Ball, 1985). Table 87. Ventilation Parameters for CCP and Rocanville Divisions Parameter CCP Rocanville Division (Alternative I) Quantity Required (m3/s) Recirculated a i r (m3/s) 113.00 33.70 83.00 51.00 Recirculation Percentage (%) 30.00 64.40 279 8.4.1 Cost Analysis Example - CCP Recirculation System 1. Heat required per hour:-[3600 s/hr * 113 m3/s * (14 - (-15)) * 1.2 kg/m3 * 1.01 kJ/kg °C] / 0.70 = 20426009 kJ/hr 2. Litres required per hour:-[(20426009 kJ/hr)/(37.3 kJ/litre) ] = 547614 l i t r e s per hour. 3. Cost per year:-0.00006 $ / l i t r e * 547614 litres/hr * 24 hrs/day * 120 heating days/year = $ 94628 4. Savings from a i r recirculation = Gain from a i r requirement reduction = $ 94628 * 0.30 = $ 28388 6. Total annual ventilation savings :-= $ 566/m3/s * 33.7 m3/s = $ 19074 7. Total savings from recirculation i f 30% recirculation percentage i s adopted = $ 28388 + 19074 = $ 47462 280 8. Capital Cost Davis of Derby System = $ 68000 Recirculation Fan = $ 16000 Total = $ 84000 9. Labour Costs 250 mannours Q $ 30.00 per hour = $ 7500 10. Total capital cost of system Items (9) + (8) = $ 91500 11. Annual Operating Cost* Miscellaneous $ 4000 - Replacement of sensors - Calibration gas - instrument maintenance Fan power cost $ 10000 Total $ 14000 12. Payback Period = $ (91500) / (47462 - 14000) = 2.734 Years ~ 3 years The payback period for Rocanville Division was determined following the same procedure above. The results for the two systems are summarized i n Table 88. / 281 Table 88. .. Recirculation System Cost Analysis Item Cost $ CCP Rocanville Division I. Annual heating cost 94628 I I . Savings from Recirculation - CCP = 0.300 R.F. 56777 - PCS = 0.644 R.F. III . Total Annual Ventilation Savings - CCP = 33.70 m3/s 19074 - PCS = 51.00 m3/s IV. Total Savings ( II + III) 47462 V. Capital Cost Davis of Derby System 68000 Recirculation Fan 16000 Labour Cost 7500 Total 91500 VI. Annual Operating Cost 14000 VII. Payback Period (Years) [(V) / (IV-VI)] 2.734 3.000 69505 44761 28866 73627 68000 7500 75500 14000 1.27 2.00 282 8.50 TECHNICAL AND SAFETY GUIDELINES To ensure r e l i a b i l i t y of the recirculation system, the following operating practices should be employed: 1. vehicular travel through the recirculation control doors should be allowed only by special permission. This w i l l prevent damage that could cause the doors not to close. 2. Visual inspections for damage to the doors or any of the control systems should be conducted regularly by qualified personnel. 3. The recirculation system should be incorporated into the routine mine a i r ventilation surveys that determine a i r flow, contaminant levels, and relative humidity. 4. A l l underground supervisors should be trained i n the general principles of the systems operation and emergency procedures. 283 j ' / - • 5. Sensors and control system should be calibrated and tested. Key standard procedures, as listed below, should be posted to the respective system location. i) calibration - Procedure - Calibration k i t - Calibration test gas - Calibration duration (at least monthly) i i ) F i e l d Inspection - Transducer parts replacement - Sensor l i f e and replacement date - Documentation (simplified operational and maintenance manual) - Frequency of inspection i i i ) Testing of CO f i r e detection sensors - Shotfiring fumes with CO content above alarm set points - shotfiring of sensors with interferents (in order to check the performance of the scrubber) iv) Maintenance requirements v) Reporting procedures 6. Transient effects should be examined ( Calizaya, et a l . , 1989). CHAPTER NINE COCLUSIONS AND FURTHER WORK 9.1 'itiR OBJECTIVE OF THIS RESEARCH 'nrasTg The objective of this thesis was to investigate the use of controlled recirculation of exhaust a i r to the intake, as a means of reducing winter heating costs and/or increasing airflows i n Canadian underground mines with particular emphasis on conditions i n potash mines. 9.2 APPLICABILITY OF CONTROLLED RECIRCULATION SYSTEM Controlled recirculation of mine a i r can only be used where exhaust a i r quality i s good enough for the a i r to be re-used. The number of environmental pollutants present and their emission levels vary widely between mines, therefore controlled recirculation cannot be used i n a l l mines to reduce the heating costs and increase face or mint* a i r flows. Each mine should be treated differently according to i t s pollutant emission characteristics, levels and other factors affecting the general mine ventilation network. Two types of systems were ""rami-noA i n « v t « thesis. These are variable and fixed quantity recirculation schemes for gassy and non-blasting mines respectively. Fixed quantity recirculation systems were developed for non-blasting mines with minimum pollutant level fluctuations. Potash mines are ideal for fixed quantity schemes. Potash mines have relatively low and stable pollutant concentrations. Mines with unstable and high pollutant concentrations but with definite pollutant emission trends are suited to variable quantity schemes. Mechanized trackless metal mines such as Westmin Resources Limited's H-^W mine and the Ruttan mine of Hudson Bay Mining and Smelting Company Limited are well suited to variable quantity recirculation schemes. The key to controlled recirculation application i s that the a i r quality to be recirculated must be good enough to warrant the practice. Proper understanding of recirculation objectives followed by an adequate evaluation of mine intake and exhaust a i r conditions are important steps i n a recirculation f e a s i b i l i t y study. Fiel d studies were conducted at the three candidate underground m-i™*? to determine the f e a s i b i l i t y of introducing controlled recirculation of exhaust a i r . The monitoring strategy was planned to give information on the behaviour of underground mine pollutants between the main intake and exhaust shafts, along roadways and at working faces. These studies were conduced at CCP, PCS Rocanville Division and the H-W mine of Westmin Resources Limited. In addition, t r i a l recirculation experiments were conducted at Rocanville Division and CCP. The a i r conditions i n these mines are such that significant recirculation percentages are feasible. Monitors are considered to be the most important component of a recirculation system. The monitor or sensor i n a recirculating system must be capable of reliably monitoring the steady-state, normal operation of the return airstream continuously and unattended, for an extended period of time. I t must also be able to provide a warning i f a pre-selected level, at which action i s deemed necessary to ensure worker safety i s maintained. Pre-selected levels are 25 ppm Carbon monoxide concentrations for the two potash mines and 50 ppm for the H-W mine. The monitor should be able to give an early warning of f i r e i n the system. The earliest warning of f i r e could be achieved by the monitoring of CO and products of combustion. The selection of the best monitor was based on the knowledge of system contaminants, TLV's, and the monitor a v a i l a b i l i t y , dependability and r e l i a b i l i t y . A distributed system with intelligent outstations i s the preferred approach for telemetering of the data collected by the monitors. The intelligent outstations selected for these systems are microprocessor based, used as programmable controllers, and are responsible for monitoring each bank of sensors. Each sensor's analog output i s read, digitised and sent to the central control station. The control station processes the sensor data and issues commands to the outstation that controls recirculation doors, etc. The selection of control and data transmission systems was based on sensor r e l i a b i l i t y , data collection parameters, mode of transmission, cost, supply, back-up technical assistance support, and software f l e x i b i l i t y . The Davis of Derby system i s recommended for installation at CCP and Rocanville Division. This system can monitor concentrations of a l l pollutants r e l i a b l y as well as transmit, store and process information. I t can also perform a l l necessary control functions through a surface computer. 9.3 BENEFITS OF CCNIRQLLED RECIRCULATION OF RETURN MINE AIR For many years, recirculation of mine exhaust a i r , has been regarded with suspicion and most legislations prohibit the use of uncontrolled recirculation. Controlled recirculation of mine a i r may be accepted i n the mining industry provided adequate safety precautions are taken. Controlled recirculation of return mine a i r has recently become feasible method of improving existing conventional ventilation systems. Some of the benefits resulting from the use of controlled recirculation of mine a i r include reduction i n ventilation heating costs, increase i n face a i r velocities, reduction i n power costs, and a saving of energy. In this thesis the controlled recirculation of mine a i r concept was used to reduce heating costs by reducing intake a i r quantities and recirculating a fraction of the return a i r to maintain the same intake a i r flow to the mine. 288 The allowable recirculation quantity depends cm the a i r quality, pollutant fluctuations with time, mine network system, and mine make of gas. On the other hand a i r flow to the mine was increased by Tna-i'n+a-in-iTvj the current fresh a i r quantity and at the same time recirculating a fraction of the return mine a i r to the fresh a i r intake. Based cn the present ventilation, underground and intake a i r quality and mine a i r heating systems at CCP and PCS Rocanville Division, these mines can recirculate up to 30% and 64.4% of their t o t a l return airflows respectively. These recirculation levels would not cause any detrimental effect to the health of the workers and the designs do not cxanpromize a i r quality and safety standards. Payback periods for the proposed systems are 3 years for CCP and 2 year for Rocanville Division. The H-W mine of Westmin Resources Limited could recirculate up to a maximum of 23% of i t s exhaust a i r back to the intake airway, and s t i l l maintain a l l gas and dust levels below their respective TLV's. Dust deposition studies i n return airways, indicated that 65% of dust by weight was deposited within a di stance of 550 metres from the face. These results indicate that there i s potential for l o c a l recirculation schemes i n potash mines. 289 9.4 SUGGESTIONS FOR FURTHER WORK 1. There i s a need to establish a test -i^gr-ai Tat-inm as soon as eoonomic at CCP or Rocanville to obtain hands-on experience and to serve as a model for future controlled recirculation systems i n Canada. In order to assess the effect of recirculation on the these mines, the whole mine network should be modeled. 2. Further work i s recommended on the A i r Quality Index as a basis of assessing recirculation systems and underground ventilation i n general. 3. Further studies on dust deposition characteristics i n potash mines are recommended to investigate the f e a s i b i l i t y of local recirculation systems. 4. Studies into improved dust suppression technology i n the potash industry are recommended. 5. The behaviour of a l l pollutants, relative to each other, as they pass through a mine exhaust system should be studied to determine whether a single gas can be used to provide a basis for estimating the other pollutants. 6. Further temperature profi l e and heat pick-up studies are recommended. 7. Diesel discriminating sensor developed by the U.S. Bureau of Mines should be tested to prove the technology. 9.5 CCHCLDDING REMARKS 290 Based on tne results obtained from these studies, controlled recirculation of mine exhaust a i r i s feasible and conditions exist for the successful implementation of the proposed recirculation systems at CCP, PCS Rocanville Division and the H-W mine of westmin Resources. There i s no universal procedure for designing recirculation systems and each mine should be treated individually. This i s due to factors such as contaminant levels, mining method, ventilation parmeters, make of gas, degree of mechanization, mine configuration and dustiness which are not uniform i n underground mines. A l l designs should take safety, economic gains, and system performance into consideration. / Alcock, K./ 1977. Safe Use of Diesel Equipment i n Coal Mines, Mining Congress Journal, Vol. 63, No. 2, February 1977, pp. 53-62. 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Controlled recirculation of mine a i r i n working d i s t r i c t s , Mine Ventilation Society of South Africa, Vol. 40, No. 2. Lipkea, W.H., Johnson, J.H. and vuk, C.T., 1978. The Physical and Chemical Character of Diesel Particulate Emissions - Measurement Techniques and Fundamental Considerations. S.A.E. Paper No. SP430, February, 1978. L i t t l e , Arthur D., Inc., 1977. Effects of Diesel Engine Emissions on Coal Mine A i r Quality. U.S. Bureau of Mines Final Report on Contract NO. J0166009, May, 1977. /' 364 Litton, D.C, et a l . , 1980. The Growth, Structure, and Detectability of Fires i n Mines and Tunnels. Eighteeth Symposium (International) on Combustion, Waterloo, Canada. Proceedings Published by Combustion Institute, 1981, Pittsburgh, PA, pp. 633 - 639. Litton, D.C, 1988. Diesel - Discriminating Fire Sensor, In Recent Developments i n Metal and Non Metal Mines. U.S. Bureau of Mines, Information Circular/1988, pp. 28 - 32. McCallum, V.I., 1969. Design of Mine of A i r Heating Plant at Strathcona Mine, Falconbridge Nickel Mines Limited., Canadian Mining Journal, Oct., 1969, pp. 62-65. McDermott, H.J., 1985. Handbook of Ventilation for Contaminant Control. Second Edition, Butterworth Publishers, An Ann Arbor Science Book. Mchaina, D., and Hall, A.E, 1987. Assessment of Explosibility of Sulphide Dust and the Monitoring of the Sample Trend of Main Blast Pollutants, Proc. of the 3rd Mine Ventilation Symposium, Cushing-Malloy, Inc., Arbor, Michigan. / <• 305 Middleton, J.N., Burton, R.C, and Walker, K., 1985. Monitoring and control i n the recirculation of underground ventilation a i r , IFAC Automation for Mineral Resource Development, IFAC Proceedings Series, Queensland, Australia. Megan, J.P., and Dainty, E.D., 1987. Diesel emission control catalyst friend or foe, In Diesels i n underground Mines, (U.S. Bureau of Mines, Information Circular 9141, U.S. Department of Interior). Mogan, J.P., Westaway, K.C., Horton, A.J. and Dainty, E.D., 1983. Polynuclear Aromatic Hydrocarbons and Mutagens i n the A i r of underground Dieselized Mines. Paper presented at the 10th world Congress on the Prevention of Occupational Accidents and Diseases, Ottawa/Hall, Canada, May 9, 1983. Mogan, P., Stewart, D.B., D'Aoust, A., and Dainty, E.D., 1974. A Gaseous and Particulate Emissions Investigation of an A i r - Cooled, Indirect Injection s i x - Cylinder Diesel Engine Derated to 117 HHP. Fuels Research Centre, Divisional Report, FRC 7418 - CEAL No. 304. Mchaina, D.M., and Misra, G.B., 1986. Incidence of S i l i c o s i s and i t s Relation to Dust Dosage at Mufulira Copper Mine, Zambia. Transactions of the Institution of Mining and Metallurgy, (Section A: Mining Industry ), 95, Ap r i l 1986. ,• / 306 MSHA (Mine Safety and Health Administration), MSHA Policy Memorandum No. 81-19 M, August 1981. MSHA ( Mine Safety and Health Administration ), MSHA Policy Memorandum, No. 81 - 19M, August, 1981. Murray, D.J., 1987. Monitoring and control of diesel engine emissions undergound, 2nd B.C. Industrial Hygiene Symposium, Vancouver, B.C., Canada. Nagy, J., Dorsett, H.6. and Jacobsen, M., 1964. Preventing Ignition of Dust Dispersions by Inerting, Reports of Investigations, No. 6543, U.S. Bureau of Mines. Oberholzer, J.W., 1987. Assessment of co l l i e r y dust levels using a ccoiputerized dust measuring system, 3rd U.S. Mine Ventilation Symposium, (Cushing- Malloy, Inc., Ann Arbor, Michigan ). Pickering, A.J. and Robinson, R., 1984. Application of controlled recirculation to auxiliary ventilation systems and mine d i s t r i c t ventilation c i r c u i t s , 3rd Internat. Mine Ventilation Congress, Harrogate, England, (Inst. Min. Metal 1., London). Pickering, A.J., and Aldred, R., 1977. Controlled Recirculation of Ventilation - A Means of Dust Control i n Face Advance Headings, Mining Engineering, No. 190. Pomroy, W.H., and Helmbrecht, R.E., 1985. Design and operation of four prototype f i r e detection systems i n noncoal underground mines, U.S. Bureau of Mines, Information Circular, 9030, U.S. Department of the Interior. Province of Manitoba, The Mines Act, Manitoba Regulation 254/73, (Queens printer, Manitoba), Jan., 1981. Anon., 1978. Province of Saskatchewan, Mines Regulations, Saskatchewan Department of Labour, Occupational Health and Safety Branch. Robinson, R., and Harrison, T., 1987. Controlled recirculation of a i r at Wearmouth col l i e r y , 3rd Mine Ventilation Symposium, (Cushing-Malloy, Inc., Ann Arbor, Michigan ). Robinson, R., 1972. Tri a l s with a Controlled Recirculation System i n an Advanced Heading. Symposium on Environmental Engineering i n Coal Mines. Saindon, J.P., 1987. Controlled recirculation of exhaust ventilation i n Canadian mines. M.ASc. Thesis, University of B r i t i s h Columbia, Vancouver, Canada. >' 308 Schmidt, H.H., 1978. A Management Scheme for Energy Conservation i n Mine Make-up A i r , Mine Operators Conference, Canadian Institute of Mining and Metallurgy, Porcupine Branch. Thimons, E.D., and Kohler, J.L., 1985. Measurement of Air Velocity i n Mines. Bureau of Mines Report of Investigations, RI 8971. Van Der Walt, J., 1978. Cooling Mines Having High Rock Temperatures - the Case for Recirculation of ventilation a i r . Environmental Engin., Laboratory Project Report, Chamber of Mines, Johannesburg. Vitukuri, V.S., and Lama, R.D., 1986. Mine Explosions and their Control, In Environmental Engineering i n Mines, Cambridge University Press, pp. 264. Wang, P.K., et a l . , 1978. Aerosol Scavenging Rate Model, J. of Atmospheric Science, 35, 1735. Welsh, J.H., Cohen, A.F., and Chilton, J.E., 1987. Suggested m i n i m u m performance specifications for underground coal mine environmental monitoring systems, U.S. Bureau of Mines, Information Circular, 9157, U.S. Department of the Interior. >' 309 Williams, K.L., Chilton, J.E., Tuchman, D.P., and Cohen, A.F., 1987. Measuring gases pollutants from diesel exhaust i n underground mines, i n Diesels i n Underground Mines, (U.S. Bureau of Mines, Information Circular 9141, U.S. Department of the Interior). Williams, R.L., and Timko, R.J., 1984. Performance Evaluation of rea l time aerosol monitor, U.S. Bureau of Mines, Information Circular, 8968, U.S. Department of the Interior. Yang, 6., Calizaya, P., McPherson, and Mousset-Jones, 1989. Mathematical Modelling for Gas Concentration Transients i n Controlled Flow Recirculation. Fourth U.S. Mine Ventilation Symposium, Berkeley, pp. 243 - 252, 1989. 310 APPENDIX I GRAPHICAL REPRESENTATION CLF DATA FOR CENTRAL CANADA POTASH, ROCANVILLE DIVISION AND H-W MINE \ I I I I I 1 I I 1 I I I I I 1 1.4 1.8 2.2 2.6 3 3.4 3.8 Time (Hours) + TWA F i g u r e 44. C C P C a r b o n M o n o x i d e C o n c e n t r a t i o n Day Shift - 30 /03 /88 312 1.2 1.1 1 H •^ g^ 0.9 I s P ^ ~ 2 § f 0.8 c o o 0.7 0.6 H 0.5 Figure 45. Time (Hours) + TWA CCP Carbon Dioxide Concentration Day Shift - 30/03/88 313 o c <J c o o Time (Hours) + TWA Figure 46. CCP Nitric Oxide Concentration Day Shift - 30/03/88 Figure 47. CCP Nitrogen Dioxide Concentration Day Shift - 30/03/88 3 1 5 F i g u r e 48. CCP Carbon Monoxide C o n c e n t r a t i o n Night Shift - 30 /03 /88 316 £ Q . 1.2 1.1 H 1 H §1 OT 0.9 H C . o o o.a H 0.7 0.6 >MMlllMrrilJIMMMIIMIllllMlilMIJIIIIIIitllllJMIJIMiIIilJltlllJinilMIIMIIIIIIIIIirillllllllllMIMIIIIlilJtlMltllllllMlllllllillil i r 2 i 1 1 1 I 1 I I 4 6 8 10 12 Figure 49 . Time (Hours) 4- TWA CCP Carbon Dioxide Concentra t ion Night Shift - 30/03/88 317 Figure 50. CCP Nitric Oxide Concentration Night Shift - 30/03/88 318 F i g u r e 5 1 . C C P N i t r o g e n D i o x i d e C o n c e n t r a t i o n Night Shift - 30/03/88 319 T 1 1 1 1 1 1 1 1 0 1 2 3 4 Time (Hours) + TWA Figure 52. CCP Carbon Monoxide Concentration Day Shift - 31/03/88 . f. 320 Time (Hours) + TWA Figure 53. CCP Carbon Dioxide Concentration Day Shift - 31/03/88 321 Figure 5 4 . CCP Nitric Oxide Concentration Day Shift - 31/03/88 . f. 322 F i g u r e 55. C C P N i t r o g e n D i o x i d e C o n c e n t r a t i o n Day Shift - 31/03/88 323 Figure 56. CCP Carbon Monoxide Concentration Day Sh i f t - 0 4 / 0 4 / 8 8 3 2 4 Time (Hours) + TWA Figure 57. CCP Carbon Dioxide Concentration Day Shift - 04/04/88 325 Figure 58. CCP Nitric Oxide Concentration Day Shift - 04/04/88 Figure 59. CCP Nitrogen Dioxide Concentration Day Shift - 04/04/88 327 Figure 60. CCP Carbon Monoxide Concentration Night Shift - 04/04/88 ' • ' 328 iioiiiiiiiyiiiiiiiiiiiiiiiiiiiiiiiyiiiiiiiiiiiiiiiiipip _1 ! ! ! ! ! ! ! , , 2 4 6 8 10 12 Time (Hours) + TWA Figure 61. CCP Carbon Dioxide Concentration Night Shift - 04/04/88 329 Figure 62. CCP Nitric Oxide Concentration Night Shift - 04/04/88 '•• - ' 330 Figure 63. CCP Nitrogen Dioxide Concentration Night Shift - 04/04/88 Figure 64. CCP Carbon Monoxide Concentration Day Shift - 06/04/88 332 1.2 Figure 65. CCP Carbon Dioxide Concentration Day Shift - 06/04/88 33'3 3 1 9 T i m e ( H o u r s ) + TWA Figure 66. CCP Nitric Oxide Concentration Day Sh i f t - 06/04/88 334 1.2 -j-1.1 -1 -Time (Hours) + TWA Figure 67. CCP Nitrogen Dioxide Concentration Day Shift - 06/04/88 3 3 5 F i g u r e 68 . C C P C a r b o n M o n o x i d e C o n c e n t r a t i o n Night Shift - 06/04/88 336 800 780 -760 -740 -720 -700 680 -660 -640 -620 -600 580 -560 -540 -520 -500 iiuiiiiiiiiiliiiiiniliiiiiiiiiiil iiiiiiiiiiiiiiiiiiiiiiiiiiiniiiii llllllllllllllllllll 2 8 1 10 12 Time (Hours) TWA Figure 69. CCP Carbon Dioxide Concentration Night Shift - 06/04/88 3 3 7 Night Shift - 06/04/88 338 Figure 71. CCP Nitrogen Dioxide Concentration Night shift - 06/04/88 * . ' 339 Figure 72. CCP Carbon Monoxide Concentration Day Shift - 07/04/88 '• - 7 340 1 Figure 73. CCP Carbon Dioxide Concentration Day Shift - 07/04/88 341 1 0.5 H 1 2 Time (Hours) + TWA Figure 7 4 . CCP Nitric Oxide Concentration Day Shift - 07/04/88 342 2 Time (Hours) + TWA Figure 7 5 . CCP Nitrogen Dioxide Concentration Day Shift - 07/04/88 343 10.6 Time (Hours) + TWA Figure 76. CCP Carbon Monoxide Concentration Mixed Intake - 06/04/88 3 4 4 700 -i 650 -600 -c <J § 450 -o 400 H 350 H 84 8.6 8.8 9 9.2 9.4 Time (Hours) + TWA F i g u r e 7 7 . C C P C a r b o n D i o x i d e C o n c e n t r a t i o n Mixed Intake - 06/04/88 3 4 5 0.5 1 1 1 1 1 i r 9.8833 9.9666 10.0499 10.1332 10.2165 10.2998 10.3831 10.4664 10.5497 Time (Hours) + TWA Figure 78. CCP Ni t r i c Oxide Concent ra t ion Mixed Intake - 06/04/88 346 0.5 0.4 H E £ 0.3 0.2 H 0.1 H - B 1 B -10 10.2 10.4 10.6 Time (Hours) + TWA Figure 79. CCP Nitrogen Dioxide Concentration Mixed Intake - Day Shift - 0 6 / 0 4 / 8 8 347 _ j ! ! j , ! ! ! j , j 2 4 6 8 10 12 Time (Hours) + TWA Figure 80. PCS Carbon Monoxide Concentrat ion Day Shift - 12/04/88 • /: . 348 1 0.9 H 0.8 -\ 0.7 .2 a E 3 o 0.6 -J 0.5 1 1 1 11IIIIIIIIIIIIIIIIIIIIIIIIIIIIIII111IIIIII Mil I I IIIIIIIIIIIIIIIIIIIIIIIIIII111111IIII1111IIIIIIIIIIIIIIIII111111111IIIII 1 K. 0.4 H 0.3 4 8 10 12 Time (Hours) + TWA Figure 81. PCS Carbon Dioxide Concentration Day Shift - 12/04/88 349 Time (Hours) + TWA Figure 82. PCS Nitric Oxide Concentration Day Shift - 12/04/88 35D CL. CL C 0.9 H 0.8 H 0.7 H 0.6 H S 0.5 H c o c o o 0.4 H 0.3 H 0.2 0.1 H n i ~—i 1 1 r 4 6 8 Time (Hours) + TWA I 10 WW 12 Figure 83. PCS Nitrogen Dioxide Concentration Day Shift - 12/04/88 <• • ' 351 "i i i i i i i i i i i i i 0 2 4 6 8 10 12 Time (Hours) + TWA Figure 84. PCS Carbon Monoxide Concentration Night Shift - 12/04/88 352 800 700 -BOO -500 -400 -300 Time (Hours) + TWA Figure 85. PCS Carbon Dioxide Concentration Night Shift - 12/04/88 353 Figure 86. PCS Nitric Oxide Concentration Night Shift - 1 2 / 0 4 / 3 8 354 1.5 1.4 liiinilllllliliilM n i r 6 Time ( H o u r s ) + TWA 8 10 12 Figure 87. PCS Nitrogen Dioxide Concent ra t ion Night Sh i f t - 1 2 / 0 4 / 8 8 3 5 5 60 50 -o H \ 1 \ 1 1 1 1 1 \ 2 4 6 8 10 12 Time (Hours) + TWA Figure 88. Westmin Concentration Data Carbon Monoxide - 2 4 / 0 5 / 8 9 - Day Shift 3 5 6 C L •>—' cn I i E? => | | <u i— o — c o o 3.6 3.4 3.2 3 2.8 2.6 2.4 2.2 2 1.8 1.6 1.4 1.2 1 0.8 0.6 0.4 11111111 1 1 1 I I I I I I I l l 4 6 8 10 Time (Hours) + TWA Figure 89. Westmin Concentration Data Carbon Dioxide - 2 4 / 0 5 / 8 9 Day Shift 12 357 Figure 90. W e s t m i n C o n c e n t r a t i o n D a t a Nitric Oxide - 24/05/89 Day Shift 358 £ CL c o a o 15 14 -13 -12 -11 -10 -9 -8 -7 -6 -5 -4 3 -2 -1 -= 0 1111 I I I I I I 11111 u 11 I I I I 111111 I I n I I 11 I I mi I I i I I 11 I I 11 I I ii nun n r 8 Time (Hours) + TWA Figure 91. Westmin Concentration Data Nitrogen Dioxide - 2 4 / 0 5 / 8 9 Day Shift 3 5 9 20 - r 19 -18 -17 -16 -15 -14 -* ? 13 -2 4 6 8 10 12 Time (Hours) + TWA Figure 92. Westmin Concentration Data Sulphur Dioxide - 2 4 / 0 5 / 8 9 - Day Shift 3 6 0 50 2 4 6 8 10 12 Time (Hours) + TWA Figure 93. Westmin Concentration Data Carbon Monoxide - 26 /05/89 - Day Shift 361 Figure 9 4 . Westmin Concentration Data Carbon Dioxide - 26/05/89 - Day Shift 362 40 - r 35 -30 -a. 25 -i 1 1 : 1 1 7 9 11 Time (Hours) + TWA Figure 95. Westmin Concentration Data Nitric Oxide - 2 6 / 0 5 / 8 9 Day Shift 363 Figure 96. Westmin Nitrogen Dioxide Concentration Data Day Shift - 26/05/89 364 - f\ " — . IIIIIIIIIIIIIIIIIIIIKJIIIIII -1 1 1 1 1 1 1 1 1 1 1 1 ' 1 I I 1 ~ l 1 I 1 1 1 2 4 6 8 10 12 Time (Hours) + TWA Figure 97. Westmin Concentration Data Carbon Monoxide - 2 6 / 0 5 / 8 9 Night Shift 36'5 50 40 -E a. 30 c o c V o 20 o o 10 -Time (Hours) + TWA Figure 98. Westmin Concentration Data Carbon Monoxide - 26/05/89 Night Shift 366 F i g u r e 99 . Time (Hours) + TWA Westmin Concentration Data Carbon Dioxide - 2 6 / 0 5 / 8 9 Night Shift 367 Figure 100. Time (Hours) + TWA Westmin Concentration Data Nitric Oxide - 2 6 / 0 5 / 8 9 Night Shift 368 Figure 101. Westmin Nitrogen Dioxide Concentration Data Nitrogen Dioxide - 2 6 / 0 5 / 8 9 Night Shift 369 24 -22 -20 -18 -0 2 4 6 8 10 12 Time (Hours) + TWA Figure 102. Westmin Concentration Data Sulphur Dioxide - 2 6 / 0 5 / 8 9 Night Shift 370 15.167 16.002 16.837 17.672 18.507 19.34220.1 7721.012 Time (Hours) Figure 103. Sulphur dioxide Concentration K330 Stope - Panels 7 and 9 - 1 8 / 0 7 / 8 8 3 7 1 uiiBiuBRiiBBivtiBiiBiiiiigBiiiiiDioonniiniiniBBiiii^ iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiviiiiiiiiiaiBgDpoiiiiiti 14.333 16.0024 17.6724 Time (Hours) F i g u r e 104. S u l p h u r d iox ide C o n c e n t r a t i o n 343 Sump Station - 20/07/88 372 i I i i i i i—i i — i — i — i — i — r 15 15.4 15.8 16.2 16.6 17 17.4 17.8 Time (Hours) Figure 105. Sulphur dioxide Concentration 343 Sump - 350 Open Stope - 2 0 / 0 7 / 8 8 3 7 3 E Q . O . c ID O c o o 15 15.4 15.8 16.2 16.6 Time (Hours) r 17 1 — i — i — r 17.4 17.8 Figure 106. Sulphur dioxide Concentration K330 Stope Panel 9 and K 3 3 7 - 2 C - 2 1 / 0 7 / 8 8 3 7 4 14 F i g u r e 107. 16 18 20 Time (Hours) S u l p h u r dioxide C o n c e n t r a t i o n K330 Panel 9 and K 3 3 7 - 2 C 21 / 0 7 / S 8 3 7 5 260 - r 240 -220 -200 -180 -160 -140 -120 -100 -16 16.2 16.4 16.6 16.8 17 Time (Hours) Figure 1 0 8 . S u l p h u r d iox ide C o n c e n t r a t i o n K330 Stope - 31/05/88 3 7 6 30 28 -26 -24 -22 -20 -18 -16 -14 -12 -10 -8 -6 -4 -2 -0 i i i i i i i i i i i i i i— r 16.08 16.12 16.16 16.2 16.24 16.28 16.32 16.36 16.4 Time (Hours) Figure 1 0 9 . S u l p h u r d iox ide C o n c e n t r a t i o n K330 Stope - 31/05/88 

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