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Controlled recirculation of exhaust ventilation in Canadian mines Saindon, Jean-Paul 1987

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CONTROLLED RECIRCULATION OF EXHAUST VENTILATION IN CANADIAN MINES By JEAN-PAUL SAINDON M.A.Sc The U n i v e r s i t y of B r i t i s h Columbia J A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE i n THE FACULTY OF GRADUATE STUDIES (Mining and M i n e r a l Process Engineering Department) We accept t h i s t h e s i s as conforming to the r e q u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA October 1987 (c) Jean-Paul Saindon, 1987 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 Mining and M i n e r a l Process Engineering February 1987 The University of British Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 Date: 12 February 1987 i i ABSTRACT Un c o n t r o l l e d r e c i r c u l a t i o n of mine a i r i s considered a hazard because i t can r e s u l t i n excessive dust and o b j e c t i o n a l gas l e v e l s . Smoke and gas from a mine f i r e can a l s o be c a r r i e d back i n t o the f r e s h i n t a k e a i r . R e c i r c u l a t i o n i s p r o h i b i t e d by most mining l e g i s l a t i o n s and there i s p r e j u d i c e against i t s use. Recent experiments i n B r i t a i n and South A f r i c a have shown t h a t r e c i r c u l a t i o n of mine a i r can be s a f e l y implemented using s u i t a b l e monitoring instruments. C o n t r o l l e d r e c i r c u l a t i o n of a i r o f f e r s s e v e r a l advantages and shows p o t e n t i a l f o r maintaining the q u a l i t y of the mine a i r i w n i l s t a l s o reducing heating and v e n t i l a t i o n costs i n many Canadian mines. The t h e s i s reviews the work to date and o u t l i n e s proposals f o r f u t u r e a p p l i c a t i o n s of c o n t r o l l e d r e c i r c u l a t i o n i n Canada. P a r t i c u l a r problems of gas p o l l u t a n t s d i l u t i o n , removal mechanisms and dust sedimentation and f i l t r a t i o n are explained. A f i e l d survey a t S h e r r i t t Gordon Ruttan operation to study p o l l u t a n t concentrations and trends i s presented. F i n a l l y , monitoring and instrumentation requirements as w e l l as economics of r e c i r c u l a t i o n are examined. i i i TABLE OF CONTENTS Page Number 1.0 INTRODUCTION 1 2.0 RECIRCULATION - A LITERATURE REVIEW 7 3.0 UNDERGROUND MINE CONTAMINANTS 20 3.1 DIESEL MINE CONTAMINANTS 20 3.1.1 D e s c r i p t i o n of the p o l l u t a n t s 20 3.1.2 Emission c o n t r o l techniques 25 3.2 BLASTING CONTAMINANTS 29 3.3 MINERAL DUST 30 3.4 THRESHOLD LIMIT VALUE 31 3.5 THE HEALTH EFFECTS INDEX 33 4.0 PRINCIPLES OF RECIRCULATION 35 4.1 GAS CONTAMINANTS 35 4.1.1 D i l u t i o n 39 4.1.2 Other s i n k s and removal processes 40 4.2 PARTICULATE MATTER 45 i v TABLE OF CONTENTS (Continued) Page Number 5.0 MATHEMATICAL MODELLING OF DIESEL EXHAUST CONTAMINANTS 56 5.1 CASE STUDY USING THE RECIRCULATION MODEL 58 5.1.1 I n t r o d u c t i o n 58 5.1.2 Pr e s e n t a t i o n of r e s u l t s 61 6.0 FIELD STUDY 64 6.1 SITE OF STUDY 64 6.2 GAS CONCENTRATION STUDY 70 6.2.1 Instrumentation 70 6.2.2 Re s u l t s 71 6.2.3 D i s c u s s i o n 71 6.3 DUST SAMPLING PROCEDURES 75 6.3.1 Mass conc e n t r a t i o n determination 75 6.3.2 I s o k i n e t i c sampling 76 6.3.3 Metrex d i e s e l / m i n e r a l monitor 77 6.3.4 S e t t l e d dust sampling 77 TABLE OF CONTENTS (Continued) Page Number 6.4 DUST SAMPLING RESULTS & DISCUSSIONS 78 6.4.1 Isokinetic sampling 78 6.4.2 Airborne respirable dust concentration 79 6.4.3 Metrex study 81 6.4.4 Settled dust sampling results 81 7.0 EVALUATION OF CONTROL SYSTEMS FOR THE RECIRCULATION j DESIGN AT RUTTAN 84 ! 7.1 CONTROLLED MONITORING IN UNDERGROUND MINES 84 i I 1 7.2 TELEMETRY SYSTEMS 85 ' 7.3 SENSORS AND FINAL CONTROL ELEMENTS 87 7.4 INSTANTANEOUS DUST SENSING INSTRUMENTS 87 7.4.1 Beta attenuation instruments 93 v i TABLE OF CONTENTS (Continued) Page Number 7.4.2 P i e z o e l e c t r i c sensors 93 7.4.3 O p t i c a l sensors 94 7.5 TELEMETRY AND CONTROL SYSTEM 100 7.5.1 Br i s t o l - B a b c o c k system 101 7.5.2 Conspec Controls system 104 7.5.3 Montan-Forschung system 106 7.6 CONCLUSIONS OF INSTRUMENTATION STUDY 109 7.6.1 Dust monitoring 109 7.6.2 Telemetry and processing 110 7.6.3 F i n a l c o n t r o l elements 111 7.6.4 Sensors 111 8.0 DUST FILTRATION 112 9.0 COST ANALYSIS 119 10.0 CONCLUSIONS 122 11.0 BIBLIOGRAPHY 125 APPENDIX 1 135 APPENDIX 2 144 v i i L i s t of I l l u s t r a t i o n s Page Number Figure 1 L o c a l airspeed increase 9 Figure 2 Intake advance heading r e c i r c u l a t i o n 11 Figure 3 Conventional r e t u r n advance headings 12 Figure 4 Return advance heading r e c i r c u l a t i o n 13 Figure 5 Development drivage r e c i r c u l a t i o n 14 Figure 6 D i s t r i c t r e c i r c u l a t i o n schematic 17 Figure 7 Monitoring instrumentation schematic 19 Figure 8 Schematic r e p r e s e n t a t i o n of r e c i r c u l a t i o n 36 Figure 9 Schematic of b l a s t contaminant decay 36 Figure 10 Scavenging r a t e of water drops 54 Figure 11 Lake S h o r t t v e n t i l a t i o n network 59 Figure 12 Ruttan's v e n t i l a t i o n system 65 Figure 13 Monitoring s t a t i o n on 660 mL 67 Figure 14 Monitoring s t a t i o n on 370 mL 68 Figure 15 Schematic of 567 exhaust 69 Figure 16 CO c o n c e n t r a t i o n e q u i l i b r i u m 74 Figure 17 Metrex monitoring r e s u l t s 83 Figure 18 C e n t r a l i z e d c o n t r o l approach 86 Figure 19 D i s t r i b u t e d system 86 Figure 20 Flow system of MMRDM 98 Figure 21 Schematic diagram of O s i r i s sensor 99 Figure 22 B r i s t o l system c o n t r o l c o n f i q u r a t i o n 103 Figure 23 Conspec system c o n t r o l c o n f i g u r a t i o n 105 Figure 24 Montan-Forshung system c o n f i g u r a t i o n 107 Figure 25 Water d r o p l e t s s i z e e f f e c t s 114 Figure 26 Scrubbing e f f i c i e n c i e s of a i r atomizers 116 Figure 27 F i l t r a t i o n vs r e c i r c u l a t i o n curve 118 v i i i LIST OF TABLES Page Number Table 1 Heating and V e n t i l a t i o n i n Canadian Mines 2 Table 2 Annual Heating and V e n t i l a t i o n Costs 3 Table 3 T y p i c a l B l a s t i n g Contaminants Values 29 Table 4 P e r m i s s i b l e Concentrations f o r Airborne Contaminants 32 Table 5 Conversion of NO to NO^ Table 6 G r a v i t a t i o n a l Settlement Losses 50 Table 7 D i f f u s i o n Losses 53 Table 8 Fresh A i r Volumes Required 60 Table 9 Deutz F8L714 Engine Mass-Emissions 61 Table 10 R e s u l t s of Gas-Sampling a t Ruttan 72 Table 11 Concentration Ratios f o r Various P a r t i c l e S i z e s 78 Table 12 Airborne Dust A n a l y t i c a l R e s u l t s 80 Table 13 S e t t l e d Dust A n a l y t i c a l R e s u l t s 82 Table 14 Sensor Summary 88,89,90,91 Table 15 Performance S p e c i f i c a t i o n Chart 92 Table 16 L i g h t S c a t t e r i n g Instrument C h a r a c t e r i s t i c s 96 Table 17 B r i s t o l System Costs 102 Table 18 Conspec System Costs 106 Table 19 Montan-Forschung System Costs 108 i x FOREWORD This t h e s i s was supported by an Energy, Mines and Resources Grant and a Noranda Research F e l l o w s h i p . A major p a r t of the p r o j e c t was performed at Ruttan Mine, Manitoba ( S h e r r i t t Gordon Mines L i m i t e d ) . I would l i k e to thank Mr. Lucien (Buck) Nel and Mr. K. D. B a l l of Ruttan Mine f o r t h e i r continuous support of the p r o j e c t and t h e i r strong b e l i e f i n the p o s s i b i l i t i e s of r e c i r c u l a t i o n . Mr. Nel has been the l i a i s o n w i t h Ruttan and has spent a consi d e r a b l e amount of time sh a r i n g h i s ideas w i t h my sup e r v i s o r and myself as w e l l as making the necessary arrangements f o r the f i e l d survey. I would a l s o l i k e to s i n c e r e l y thank Dr. Mahe Gangal and Dr. Steve Hardcastle from Canmet. Dr. Gangal and Dr. Hardcastle loaned UBC most of the equipment used i n the Ruttan Mine study. Their encouragement and as s i s t a n c e throughout the p r o j e c t was g r e a t l y appreciated. The subject of t h i s t h e s i s was proposed to me by my s u p e r v i s o r , Dr. A l l a n H a l l . Dr. H a l l has been an e x c e l l e n t s u p e r v i s o r . He has supported my work a l l along, provided me w i t h many new ideas and made the important i n i t i a l contacts w i t h Ruttan and EMR. This t h e s i s i s the r e s u l t of a j o i n t e f f o r t by Dr. H a l l and myself. I am a l s o very g r a t e f u l to David Mchaina f o r h i s help on the f i e l d and i n the a n a l y s i s of the samples, and to A n a l i s a Lemieux who had the patience of proofreading the e n t i r e contents of t h i s t h e s i s . 1 .1.0 INTRODUCTION Mine venti lation in Canada is probably the mining sector given the least attention. More often than not, the venti lation networks have been poorly planned and result in very inf lexible and problematic designs. One of the reasons for this is a shortage of sk i l l ed engineers in the mine venti lation f i e l d and the fa i lure , on behalf of the industry, to recognize the fact that the venti lation system must be planned concurrently with the mine design, and not adapted to i t as an afterthought. The problem with venti lation is that most of the benefits are not easily converted to dollars and cents. For example, good ventilation w i l l decrease the re-entry time by increasing the rate of decay of the blasting contaminants; i t w i l l increase the diesel equipment that can operate on a working level and i t w i l l increase productivity through improved environmental conditions. A l l of these benefits are not always appreciated the way they should be because they are not readily apparent. Ventilation has therefore not progressed substantially in Canada. Countries l ike South Afr i ca , France and England have achieved tremendous advancement in the f i e l d of environmental control and venti lation while Canada is s t i l l using the same methods that i t was using some 20 years ago. It is recognized by the Canadian mining industry that a significant contribution towards the improvement of the mining economy can be made through technological advancement. The industry should identify venti lation as being one of the sectors with opportunities for innovation. Significant cost savings can be achieved by the adaptation of existing and proven technologies of other countries. In Canada, the most significant cost related to venti lation is that of mine a i r heating. A study of Canadian underground mines investigated the cost of heating and ventilation (1). Table 1 sets out the operating s tat i s t ics for 10 large mines using a ir heating. 2 TABLE 1 Heating and V e n t i l a t i o n i n Canadian Mines A i r Fan A i r Heat- Propane Heating l i n e Quantity Pressure Power Temp. ing Used Systems M3/S kPa kW °C Days 1/day 1 165 2.5 750 -20 100 8 300 Propane 2 210 1.8 540 -10 160 10 100 Propane 3 990 3.1 4 300 -26 120 50 000 Propane 4 310 3 500 -4 160 •k N a t u r a l Gas (*14 800 1/day) 5 250 0.5 180 -9 140 13 300 Propane 6 440 1.5 1 200 -11 160 30 500 Propane 7 2 280 2.5 8 900 -14 120 115 000 Propane 8 225 1 130 -9 120 6 300 Propane & E l e c . (270 KWelec.) 9 220 — 800 -14 140 3 600 Propane & O i l (4 800 1/day) 10 415 1 340 -30 140 12 800 Propane & E l e c . (4 300 KWelec.) Considerable v a r i a t i o n s i n energy costs were reported by i n d i v i d u a l mines. E l e c t r i c a l costs ranged from 0.5 to 3.0 cents per k i l o w a t t hour and propane costs from 15 to 30 cents per l i t r e . Costs were standardized on the b a s i s of 2 cents per kW hour f o r e l e c t r i c i t y and 25 cents per l i t r e f o r propane, both r e p r e s e n t a t i v e of average c o s t s . Table 2 shows the standardized costs of the heating and v e n t i l a t i o n systems. I t i s c l e a r t h a t the hea t i n g cost i s c o n s i d e r a b l y higher than the v e n t i l a t i o n cost and t h a t these mines are spending an average of $1 M each per year f o r h e a t i n g a t an average cost of $2067 per cubic meter per second c i r c u l a t e d . 3 TABLE 2 Annual Heating and V e n t i l a t i o n Costs A i r V e n t i l a -Quantity t i o n Heating T o t a l Annual Cost per M3/S Mine M3/S Cost Cost Cost V e n t i l a t i o n Heating T o t a l $ $ $ $ $ $ 1 165 131 400 259 800 390 800 796 1 572 2 368 2 210 94 600 505 000 599 600 450 2 405 2 855 3 990 753 400 1 875 000 2 628 400 761 1 894 2 655 4 310 613 200 300 00 913 200 1 978 968 2 946 5 250 31 500 581 900 613 400 126 2 328 2 454 6 440 210 200 1 525 000 1 735 200 478 3 466 3 944 7 2 280 1 559 300 4 312 500 5 871 800 684 1 891 2 575 8 225 198 000 255 000 453 000 -800 1 133 2 013 9 220 140 200 567 000 707 200 637 2 577 3 214 10 415 234 800 1 185 000 1 419 800 566 2 855 3 421 Average 550 396 700 1 136 600 1 533 300 721 2 067 2 788 The author i d e n t i f i e s f i v e research f i e l d s which could have an impact on mine v e n t i l a t i o n and a i r h e a t i n g . They are: (1) Heat Exchangers (2) R e c i r c u l a t i o n (3) Emission C o n t r o l (4) E l e c t r i f i c a t i o n (5) Monitoring and C o n t r o l Instrumentation In the p a s t , heat exchangers have given problems due to i c i n g a t t r a n s f e r surfaces and dust abrasion. Today, w i t h more e f f i c i e n t heat t r a n s f e r methods and more durable m a t e r i a l s , these problems have been p a r t i a l l y solved. However, low temperature g r a d i e n t s , l a r g e d i s t a n c e s between the exhaust and i n t a k e s h a f t s and h i g h i n i t i a l c osts w i l l remain major o b s t a c l e s to the increased implementation of t h i s method. Freyman (2) i n v e s t i g a t e d the p o t e n t i a l f o r recovering heat from exhaust a i r . The survey i n d i c a t e d t h a t 21 % of the t o t a l exhaust a i r has good p o t e n t i a l f o r heat recovery because of i t s temperature and p r o x i m i t y to the i n t a k e s h a f t s . In Canada, only 7 mines re-use the exhaust a i r and only two companies use exhaust a i r to heat i n t a k e a i r . As w i l l be seen i n the next chapter, i n t e r e s t i n r e c i r c u l a t i o n has been motivated by the need to c o n t r o l three major environmental parameters: heat, gases and dust. R e c i r c u l a t i o n could a l s o be used i n c o l d c l i m a t e s to conserve heating. This could r e s u l t i n a major cost saving i n such places as Alaska and Canada. Required d i l u t i o n of d i e s e l contaminants accounts f o r over 60 % of t o t a l v e n t i l a t i o n i n an underground mine. Tremendous advancement i n d i e s e l emission c o n t r o l has taken p l a c e over the l a s t 10 years i n order to reduce d i l u t i o n requirements and provide cleaner a i r f o r workers. I t i s foreseeable t h a t i n the near f u t u r e over 95 % of a l l contaminants w i l l be c o n t r o l l e d a t the source. Mining companies have been very slow at adapting t h i s new technology, as they have not yet been convinced t h a t i t would be cost e f f e c t i v e . While i t i s t r u e t h a t c o n s i d e r a b l e f i e l d and l a b o r a t o r y t e s t i n g i s s t i l l r e q u i r e d , the s t i f f e r v e n t i l a t i o n r e g u l a t i o n s imposed i n Canada w i l l o b l i g e the i n d u s t r y to p a r t i c i p a t e i n the development of b e t t e r emission c o n t r o l methods. The Canadian Mining and Energy Technology Centre has committed i t s e l f to t h i s research and i s c u r r e n t l y t e s t i n g ceramic f i l t e r s i n many Canadian mines. E l e c t r i f i c a t i o n of mining equipment has the p o t e n t i a l of reducing the v e n t i l a t i o n and heating costs s u b s t a n t i a l l y . I f e l e c t r i c equipment was to r e p l a c e d i e s e l equipment, there would s t i l l be a need f o r v e n t i l a t i o n and heating but a i r volumes would be d r a s t i c a l l y reduced. B a s i c needs would be to d i l u t e m i n e r a l dust, provide adequate a i r to the workers, keep pipes from f r e e z i n g , prevent the build-up of i c e i n the s h a f t and provide comfortable working temperatures. Noranda 5 Research and Hydro Quebec are j o i n t l y l o o k i n g at developing a s m a l l Quebec z i n c mine through the e x c l u s i v e use of e l e c t r i c equipment. They are a n t i c i p a t i n g a 60 % r e d u c t i o n i n v e n t i l a t i o n volume. The a c c e s s i b i l i t y of e l e c t r i c power and improved e l e c t r i c a l technology w i l l have an i n f l u e n c e on f u t u r e Canadian mining developments. V e n t i l a t i o n engineers agree t h a t through b e t t e r c o n t r o l of the mine v e n t i l a t i o n network, a r e d u c t i o n of 30 % of r e q u i r e d v e n t i l a t i o n c a p a c i t y could be achieved. The i n i t i a l steps towards e s t a b l i s h i n g b e t t e r c o n t r o l are to conduct a proper v e n t i l a t i o n survey and maintain an up-to-date v e n t i l a t i o n computer model of the mine t h a t can be understood by a l l the engineering personnel. The next step i s to c o n t r o l a l l fans and doors through the use of monitoring and c o n t r o l instrumentation. This w i l l permit the v e n t i l a t i o n system to a d j u s t i t s e l f according to the monitored l e v e l s of contaminants. Instrumentation i n s t a l l a t i o n has increased s i g n i f i c a n t l y i n Canadian mines i n 1986. Brunswick mining i s in v o l v e d i n a three year plan w i t h Canmet to completely automate t h e i r v e n t i l a t i o n system. Although some Canadian mining companies are a l s o i n v o l v e d i n s i m i l a r programs, most of them tend to be r e l u c t a n t to i n v e s t i n i nstrumentation and automation. This i s due to a c o n s e r v a t i v e a t t i t u d e w i t h i n the Canadian mining i n d u s t r y and the very h i g h cost a s s o c i a t e d w i t h c a p i t a l investment and research i n t h i s f i e l d . European c o u n t r i e s such as Germany and France have been quick to adapt the instrumentation technology to mining because government involvement allows f o r the undertaking of i n t e n s i v e research. Such a s t r u c t u r e i n Canada does not e x i s t , but increased c o l l a b o r a t i o n between the companies, through research o r g a n i z a t i o n s such as Hard Rock (a committee funded by Noranda, Falconbridge and Inco to award and supervise s p e c i a l h i - t e c h research programs) w i l l have a b e n e f i c i a l i n f l u e n c e on automation and instrumentation. I t i s p o s s i b l e , t h a t i n the near f u t u r e , by making use of a combination of these new developments, heating and v e n t i l a t i o n costs w i l l be reduced by over 75 %. Falconbridge N i c k e l ' s Strathcona mine r e c i r c u l a t e s 10 % of t o t a l mine a i r and a l s o makes use of a heat exchanger between the i n t a k e and exhaust s h a f t s . This combination has 6 almost e l i m i n a t e d t h e i r cost w h i l s t other Sudbury mines have experienced s i g n i f i c a n t increases i n t h e i r heating costs ( 3 ) . This t h e s i s i n v e s t i g a t e s the use of r e c i r c u l a t i o n i n c o l d c l i m a t e mines. The author has introduced methods t h a t have the p o t e n t i a l of improving v e n t i l a t i o n and reducing heating costs s i n c e t h i s understanding i s necessary i n order to evaluate p r o p e r l y the use of r e c i r c u l a t i o n i n Canadian mines. This r e p o r t was not w r i t t e n to convince the reader t h a t r e c i r c u l a t i o n i s a b s o l u t e l y necessary i n Canada, but to provide the ground work f o r extensive research i n t o t h i s and r e l a t e d f i e l d s . I t w i l l present a unique method of v e n t i l a t i o n and d e s c r i b e the problems that must be solved before i t s f u l l implementation. 7 2.0 RECIRCULATION - A LITERATURE REVIEW R e c i r c u l a t i o n of a i r i s a commonly used technique i n general v e n t i l a t i o n and a i r c o n d i t i o n i n g p r a c t i c e . Through the use of e l e c t r o s t a t i c p r e c i p i t a t o r s and other very e f f i c i e n t f i l t e r types, i n d u s t r i a l v e n t i l a t i o n systems can r e c i r c u l a t e as much as 600 % of the intake a i r , e f f e c t i v e l y reducing heating or c o o l i n g costs ( 4 ) . R e c i r c u l a t i o n of mine a i r , on the other hand, has always been regarded w i t h s u s p i c i o n f o r mining a p p l i c a t i o n s and most l e g i s l a t i o n s p r o h i b i t u n c o n t r o l l e d r e c i r c u l a t i o n . Such r e c i r c u l a t i o n i s un d e s i r a b l e because of the hazardous c o n d i t i o n s which i t can cr e a t e . Probably the f i r s t recorded use of c o n t r o l l e d r e c i r c u l a t i o n was i n the B r i t i s h C o l l i e r i e s as reported by Lawton i n 1933 i n h i s paper e n t i t l e d " L o c a l Cooling Underground by R e c i r c u l a t i o n " ( 5 ) . Lawton conducted s e v e r a l r e c i r c u l a t i o n experiments, but w i t h l i m i t e d success. In h i s f i r s t attempt, he i n s t a l l e d a fan and a 50 f o o t l e n g t h of duct along a l o n g w a l l c o a l face and r e c i r c u l a t e d a i r from the r e t u r n end of the face thus i n c r e a s i n g the a i r v e l o c i t y along the length of the duct. Eleven t e s t s using the r e c i r c u l a t i o n duct were performed and compared w i t h three t e s t s made w i t h conventional v e n t i l a t i o n . Measurements of temperature, dry kata c o o l i n g power and wet kata c o o l i n g power were taken f o r each t e s t and, using the dry kata wind formula, the v e l o c i t i e s of the a i r stream were determined (the v e l o c i t i e s of the a i r flows were too low to measure d i r e c t l y u s i n g a v a i l a b l e instruments). When a i r was r e c i r c u l a t e d , Lawton claimed a 77 % increase i n the v e l o c i t y from 30 ft/ m i n to 53 f t / m i n . The higher temperatures caused by r e c i r c u l a t i o n were o f f s e t by the increased v e l o c i t i e s producing a 16.2 % and 14.6 % improvement i n the dry kata and wet kata c o o l i n g powers r e s p e c t i v e l y . Men working on the face agreed there was an improvement i n the c o o l i n g e f f e c t they experienced, but i t was not as great as they would have wished. Lawton repeated h i s experiment on a second l o n g w a l l face and created a 110 % increase i n the face v e l o c i t y , however, t h i s only caused a 16 % improvement i n the wet kata c o o l i n g power. He concluded t h a t the 8 t e s t s had shown t h a t l o c a l r e c i r c u l a t i o n was u s u a l l y p r a c t i c a l , but t h a t the r e s u l t s obtained d i d not present such advantages t h a t could j u s t i f y a general recommendation of the method. R e c i r c u l a t i o n i n c o a l mines was not considered again u n t i l the e a r l y 1960's a f t e r s e v e r a l s e r i o u s mine explosions i n the l a t e 1950"s revealed an i n c r e a s i n g incidence of methane accumulations i n the c e i l i n g s of roadways. Research work was i n i t i a t e d by the Safety i n Mines Research Establishment i n t o Firedamp Layering ( 6 ) . One proposed method of c o n t r o l l i n g l a y e r i n g i n gate roads was by means of a l o c a l a i r s p e e d increase i n the l e n g t h of roadway i n which l a y e r i n g occurred or was l i k e l y to occur ( 7 ) . As w i t h Lawton's systems, t h i s i n v o l v e d r e c i r c u l a t i o n of a p r o p o r t i o n of the a v a i l a b l e v e n t i l a t i o n a i r i n order to increase the roadway v e l o c i t y and thereby achieve more r a p i d mixing and d i s p e r s a l of the l a y e r ( F i g . l ) . In t h i s p r o j e c t , a much more d e t a i l e d t h e o r e t i c a l treatment and modelling program was i n v o l v e d i n the c o n s i d e r a t i o n of firedamp c o n d i t i o n s r e s u l t i n g both from the a i r r e c i r c u l a t i o n and the pressure changes induced by the presence of the fan (methane r e l e a s e i s i n v e r s e l y p r o p o r t i o n a l to the a i r p r e s s u r e ) . This work was l a t e r extended to t h e o r e t i c a l c o n s i d e r a t i o n s of more general p o t e n t i a l a p p l i c a t i o n s of r e c i r c u l a t i o n . During the 1960's s e v e r a l papers were published (8,9), again p a r t i c u l a r l y r e l a t e d to the behaviour of firedamp. At t h i s time, there were s i g n i f i c a n t improvements i n v e n t i l a t i o n standards, both f o r l o n g w a l l s and headings, so t h a t the need f o r r e c i r c u l a t i o n systems f o r s o l v i n g l a y e r i n g c o n t r o l and firedamp d i l u t i o n problems was l a r g e l y e l i m i n a t e d and no p r a c t i c a l t r i a l s were undertaken. Toward the end of the 1960's the i n c r e a s i n g numbers of advance headings being d r i v e n w i t h l o n g w a l l faces revealed a d d i t i o n a l d u s t - r e l a t e d problems w i t h conventional a u x i l i a r y v e n t i l a t i o n systems and i n t e r e s t i n r e c i r c u l a t i o n r e v i v e d . In 1968, the B r i t i s h Chief Inspector of Mines i n d i c a t e d t h a t he would be w i l l i n g to a u t h o r i z e a l i m i t e d number of t r i a l s where l o c a l i n s p e c t o r s were s t a t i s f i e d t h a t the t r i a l s would be under f u l l y c o n t r o l l e d c o n d i t i o n s . COAL FACE / / / / / / , / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / ACTIVE ZONE FCflCDNG F A N RIPPING t QF + < 3R ROAD F I G U R E 1. L o c a l a i rspeed increase in return gate . 10 In September 1971, the f i r s t exemption was made from the 1956 B r i t i s h V e n t i l a t i o n Regulations of the Mines and Quarries Act p r o h i b i t i n g r e c i r c u l a t i o n by a u x i l i a r y fans. This permitted the underground t r i a l s of an exhausting r e c i r c u l a t i o n system a t the Seaham c o l l i e r y (South Durham ar e a ) . The Area V e n t i l a t i o n Engineer f o r South Durham, Mr. R. Robinson, presented a paper i n the f o l l o w i n g year (10)and s u b s t a n t i a t e d the t h e o r i e s developed f o r gas and dust concentrations from observations made during the t r i a l s . Further t r i a l s were a u t h o r i z e d i n 1974 i n the Nottinghamshire and Derbyshire c o a l f i e l d s , again f o r advance headings, and these were reported by P i c k e r i n g and Ald r e d (11). The f i e l d t r i a l s i n d i c a t e d , p a r t i c u l a r l y i n mechanized headings, that any b e n e f i t s from c o n t r o l l e d r e c i r c u l a t i o n would best be d i r e c t e d toward improved dust c o n t r o l and c l i m a t i c c o n d i t i o n s . Consequently, i t has been the B r i t i s h N a t i o n a l Coal Board's p o l i c y to f u r t h e r the use of r e c i r c u l a t i o n systems f o r improved dust and c l i m a t i c c o n d i t i o n s and not f o r improved firedamp c o n t r o l . I t i s e s s e n t i a l however, to give c a r e f u l c o n s i d e r a t i o n to firedamp c o n d i t i o n s i r r e s p e c t i v e of the reason f o r using the technique. In the l a s t few years, there has been a gradual increase i n the number of i n s t a l l a t i o n s and i n 1982, i n a t o t a l of 1560 a u x i l i a r y v e n t i l a t e d places i n N.C.B. c o l l i e r i e s , 61 were usi n g c o n t r o l l e d r e c i r c u l a t i o n systems. This included 47 i n in t a k e advance headings (30 % of a l l mechanized i n t a k e headings), 10 i n r e t u r n advance headings (11 % of a l l mechanized r e t u r n headings) and 4 i n development drivages. Fig.2 compares an i n t a k e advance heading being v e n t i l a t e d by a conventional system and a r e c i r c u l a t i o n system. Figs.3 and 4 compare conventional and r e c i r c u l a t i o n systems f o r r e t u r n advance headings a p p l i c a t i o n . Fig.5 i l l u s t r a t e s c o nventional and r e c i r c u l a t i o n methods of v e n t i l a t i n g i n development drivages. In 1984, P i c k e r i n g and Robinson (12) presented the f i r s t paper on d i s t r i c t r e c i r c u l a t i o n . They explained t h a t the c o a l f i e l d s had been worked e x t e n s i v e l y f o r hundreds of years and the bulk of the remaining reserves l i e under the North Sea. The dista n c e s t h a t were to be worked 11 FIREDAMP HAKE 10 tl* 2-5 m'A 0-lV.cn 4 FORCING FAN t ,1 ADVANCE HEADING 1 ti F / C / 1 10 m 7s 0-2V.CM 4 7-5m'/». 0-1% CH» INTAKE GATE ROAO lOmJ's 0-1% C H * ( a ) CONVENTIONAL SYSTEM FIREDAMP MAKE 10 rf/s ili_5_ 2TS^0 317- 5 EXHAUSTING FAN 2L ACMANCE /HEADING Quantity mVs 1 2-5 0-2 2 5-0 0-2 3 7-5 0-2 0 / I! C / E / / / 10 m?'* 0-2%a«4 N T A K E \ G A T E R O A O quantity |CMt m*s % 1 12-5 |0-2 2 15-0 10-2 3 17-5 io-2 0-1% CH 4 RECIRCULATION QUANTITIES 1 - 2-S m ¥i 2 - 5-0 m 3 - 7- 5 m /» (b) RECIRCULATION SYSTEM FIGURE 2. Intake advance heading ventilation—recirculation theory. EXHAUST FAN & FILTER n l I 1 (ol EXHAUST Q« EXhAuST FAN t FILTER FQRCNG FAN t FILTE3 ICR FREE-STANONG FILTER I lOr -Q. (bl EXHAUST NG WITH FORCING OVERLAP F A s E J Or (el FULL- LENGTH FORCING FQRCINci FAN/ F I G U R E 3. Return advance headings—conventional ventila (ion systems. FORCNG FAN* FILTER Q. f t 0. FCRCJNG FAN & FILTER I EXHAUST FAN & FILTER 0. Q.-O. (a) FORCNG SYSTEM (bl FORCING WTTH EXHAUST OVERLAP SYSTEM FIGURE 4. Return advance heading—recirculation systems. » Qr * a v — v ^ -« Qr-Qc ) Q i * K EXHAUST F A N S FILTER (a J CONVENTIONAL - MAIN F O R C I N G / O V E R L A P E X H A U S T (Qt < Q r ) E X H A U S T F A N £ F L T E R (b) REC IRCULAT ION — M A I N F O R C I N G / O V E R L A P E X H A U S T (Q» >Qr ) FIGURE 5. Development drivages—ventilation systems. 15 from the s h a f t were expected to be up to 15 k i l o m e t e r s . The main v e n t i l a t i o n problem was t h a t of maintaining adequate a i r q u a n t i t i e s i n the workings as these long distances increased. I n c r e a s i n g the s i z e of airways to reduce r e s i s t a n c e would have been very c o s t l y and time consuming; the very h i g h power c o s t , the problems of high pressures across the doors and s h a f t i n s e t s and increased leakage w i t h reduced v o l u m e t r i c e f f i c i e n c y would a l s o preclude the use of l a r g e r surface fans as a s i n g l e s o l u t i o n . Booster fans had been, f o r a long time, the s o l u t i o n to the problem, but reduced v o l u m e t r i c e f f i c i e n c y as d i s t a n c e and leakage p o i n t s increased and the development of h i g h pressure d i f f e r e n c e s suggested t h a t the t h r e s h o l d l i m i t of t h i s system was not f a r away. Another s o l u t i o n would have been the c o n s t r u c t i o n of a r t i f i c i a l i s l a n d s s e v e r a l k i l o m e t e r s out t o sea, w i t h s h a f t s sunk to the workings, but s a f e t y and cost c o n s i d e r a t i o n s here r e s t r i c t e d i t s a p p l i c a t i o n . The a l t e r n a t i v e was to a l l o w c o n t r o l l e d r e c i r c u l a t i o n of a i r from the r e t u r n a i r stream back i n t o the i n t a k e system. The paper described an underground t r i a l where r e c i r c u l a t i o n of a d i s t r i c t w i t h the help of one booster fan (750 kw) was compared t o the a c t u a l v e n t i l a t i o n system using two (750 kw) booster fans. The d i s t r i c t was composed of four workings and s e v e r a l development headings. The survey, which was c a r r i e d out during a h o l i d a y weekend, demonstrated t h a t the amount of a i r f l o w i n g to the workings w i t h one booster fan was almost as much as when both booster fans were i n o p e r a t i o n under normal c o n d i t i o n s w i t h minimum r e c i r c u l a t i o n . The temperature d i d not increase s i g n i f i c a n t l y a t the headings, and methane concentrations i n the i n t a k e and r e t u r n gates increased by only 0.2 %. In 1984, H a r d c a s t l e , Kolada and Stokes published a paper e n t i t l e d : "Studies i n t o the Wider A p p l i c a t i o n of C o n t r o l l e d R e c i r c u l a t i o n i n Mine V e n t i l a t i o n " (13). The paper presented r e s u l t s of computer models s i m u l a t i n g the e f f e c t s of temperature and methane i n a d i s t r i c t r e c i r c u l a t i o n s i t u a t i o n . The model demonstrated t h a t : when compared w i t h the previous conventional v e n t i l a t i o n , the i n t a k e methane co n c e n t r a t i o n increased but r e c i r c u l a t i o n allowed more f r e s h a i r to reach the working 16 p l a c e s , producing a higher d i l u t i o n of a l l the r e t u r n methane concentrations. R e c i r c u l a t i o n a l s o caused the i n t a k e a i r temperature to r i s e , however higher q u a n t i t y flows and a s s o c i a t e d increased a i r v e l o c i t i e s induced by the r e c i r c u l a t i o n provided greater heat d i l u t i o n and c o o l i n g of the workers. This r e s u l t e d i n an improvement of the c l i m a t i c c o n d i t i o n s on the r e t u r n s i d e of the face. Fig.6 i l l u s t r a t e s the cost savings a s s o c i a t e d w i t h r e c i r c u l a t i o n versus conventional v e n t i l a t i o n . The above authors a l s o suggest c o n t r o l l i n g the r e c i r c u l a t i o n branch w i t h a r e g u l a t o r and a v a r i a b l e p i t c h fan. They mention the need f o r a f a i l - s a f e system which would monitor the methane l e v e l s at c r i t i c a l p o s i t i o n s and s h u t - o f f the r e c i r c u l a t i o n branch i n the case of abnormal methane build-up or a f i r e . Thus f a r the author has described the major developments i n mine r e c i r c u l a t i o n i n England. Mine r e c i r c u l a t i o n i s a l s o popular i n South A f r i c a n metal mines and A u s t r a l i a n c o a l mines. In 1978, Van der Walt (14) suggested r e c i r c u l a t i o n f o r the hot, deep metal mines of South A f r i c a . The o b j e c t i v e s were to reduce the amount of secondary c o o l i n g , to u t i l i z e f u l l y airways ( i n terms of a i r c a p a c i t y ) and to provide b e t t e r c o n t r o l over the d i s t r i b u t i o n of c o o l i n g . A major f i e l d t r i a l a t Loraine gold mine demonstrated t h a t r e c i r c u l a t i o n was a p r a c t i c a l , e f f e c t i v e and safe a i d to normal v e n t i l a t i o n p r a c t i c e (15). Here a t t e n t i o n was given to combining the b e n e f i t s of c o n t r o l l e d r e c i r c u l a t i o n w i t h r e f r i g e r a t i o n and dust c o n t r o l . The r e c i r c u l a t i o n percentage was normally 68 % and a spray chamber was used to remove ai r b o r n e dust from the r e c i r c u l a t e d f r a c t i o n . The f i e l d t r i a l , l a s t i n g over a year, proved s u c c e s s f u l i n using r e c i r c u l a t i o n to c o n t r o l dust and d i s t r i b u t e c o o l i n g . R e c i r c u l a t i o n i t s e l f had l i t t l e e f f e c t on the a i r temperatures and although increased a i r v e l o c i t i e s g i ve higher values of c o o l i n g power, the r e c i r c u l a t i o n mainly provided a means of d i s t r i b u t i n g the a v a i l a b l e r e f r i g e r a t i o n c a p a c i t y , which could not otherwise have been f u l l y u t i l i z e d . An i n t e r e s t i n g aspect of the t r i a l was the very s o p h i s t i c a t e d monitoring and c o n t r o l system i n s t a l l e d underground. They in c l u d e d 7 Becon f i r e d e t e c t o r s ( i o n i z e d p a r t i c l e d e t e c t o r s ) and three sets of the Airflowt obtainable with conventional ventilation 74.1 as.4 V e n t i l a t i o n Cost Main Fan ta.a ts.a £34,k 10 pa £11,228 pa Rec Booster £ 5.130 pa Total £50,768 pa Recirculation F - 18.6 X .1 la.a / d . l a.7 0 zs.a ».a —6 >— _ _ -« ^ . 4 n .a xa. i ia.aj? <Mia> |jj * I . S Control Mechanisms - 1) X-cut Regulator 2) Variable P i t c h Fan # I I . a ,1*7 Alrflowi obtainable wltb controlled recirculation of ventilation NOTE: Ventilation com baud on an arbitrary electricity charge of tO.ll/kWh anion efficiency of 70% FIG. 6 ( After Hardcastle et AL. , 1984) 18 following monitors: a i r temperature, a i r velocity, gas (CO, CO^, CH^, NOx) and dust detectors. Both the methane and ionized part ic le concentration output were capable of tripping the recirculation fans and setting off an alarm i f their respective preset levels were reached. Figure 7 i l lustrates the system schematic and the sensor configuration within the recirculat ion d i s t r i c t . The paper did not provide information on the performance of the sensors and computer configuration. A l l computer operations were centralized in one room. As w i l l be seen in chapter 7, this w i l l not be ideal for Canadian application. Furthermore, the limited use of diesel equipment in South Afr ica results in minimal respirable combustible dust concentrations. Dust sampling w i l l be more c r i t i c a l in Canadian metal mines and more sophisticated dust monitoring w i l l be required. INPUTS I N S T R U M E N T R O O M O U T P U T S f ieu) MONITORS • Becon s y s t e a (7 detect o n ) • Gas s y r t e a ICO COI U l t NOx) a Oust sys tea a A i r temperatures a Water temperatures • A i r ve loc i t ies • Water f low rate EQUIPMENT MONITORS • Recirculation fans ( o n / o f f ?) a Spray chamberpunps I o n / o f f ? ) SIGNAL PANEL PANEL HETER PEN RECORDERS WHWTK SYSTEM EQUIPMENT STATUS • A l l f ie ld nor* tors • A l l equlp-t monitors at Bacons a Methane • F an s •Pumps •Coapu t t r •Scanner •Voltmeter a Computer • S Comprtrs • delay timer r AJT6 STOP FOR MRS J r STANDBY M PRINTER ALARM PANEL COMPUTER COMPARATOR EQUIPMENT • Al l Becorts •AU gases •4Secons • Methane • Fans • Pumps • Computer RECIRCULATION FANS PTOPi 1FORFWS] SIREN REFRIGERATION PLANT REMOTE nan E l . DUPLICATE m mm\ ALARM • ' r PANEL PUMP CHAMBER SIREN D U P L I C A T E S T O P f Wet-bulb temp. Dry-bulb temp. Air velocity CO concentration CO? cencentrat ion CHi concentration NOx concentration Dust concentration Wet-bulb temp. Dry-bulb temp. Air velocity CO concentration CO? concentration CHt concentration NOx concentration Dust concentration -booster fans refrigeration plant instrument room spray chamber raise-bore airway recirculation fans et-Oulb temp. Dry-bulb temp CO concentration CO? concentration CHi concentration NOx concentration Oust concentration Schematic of recirculation installation (After Burton et al., 1984) Fig. 7 20 3.0 UNDERGROUND MINE CONTAMINANTS To design a r e c i r c u l a t i o n system, the engineer must be concerned w i t h the chemical composition of the a i r or, more p r e c i s e l y , the concentration of contaminants i n the a i r . Contaminants are defined as any u n d e s i r a b l e substances not normally present i n a i r or present i n an excessive amount. They can be e i t h e r p a r t i c u l a t e ( l i q u i d s and s o l i d s ) or non p a r t i c u l a t e (gases and vapors). The most common types of a i r contaminants found underground are gases and dust. Their o r i g i n and c h a r a c t e r i s t i c s w i l l be covered i n d e t a i l i n t h i s chapter. 3.1 DIESEL CONTAMINANTS 3.1.1 D e s c r i p t i o n of the P o l l u t a n t s D i e s e l engines are the only i n t e r n a l combustion engines permitted i n Canadian underground mines. A l l d i e s e l engines have the common f e a t u r e of being compression i g n i t i o n , as compared to the spark i g n i t i o n used w i t h g a s o l i n e engines. The power output of a d i e s e l engine i s dependent on the q u a l i t y of f u e l i n j e c t e d i n t o the c y l i n d e r , which can be v a r i e d , w h i l e the amount of a i r e n t e r i n g the c y l i n d e r remains constant. The r a t i o of the amount of f u e l and a i r d e l i v e r e d to the c y l i n d e r a f f e c t s engine performance, as w e l l as the q u a n t i t a t i v e and q u a l i t a t i v e c h a r a c t e r i s t i c s of the emission. The chemic a l l y c o r r e c t f u e l to a i r r a t i o f o r most engines i s around .068. Ge n e r a l l y , f o r d i e s e l s employed underground, the F:A r a t i o i s adjusted to a maximum of .04-.05 so t h a t an excess of a i r to f u e l i s present at a l l times. This adjustment i s commonly r e f e r r e d to as " d e r a t i n g " the engine and r e s u l t s i n lower carbon monoxide and smoke emissions. I f combustion was p e r f e c t , the f o l l o w i n g exhaust products would be produced: Nitrogen - 73% C0 2 and 0 2 - 13% H 20 - 13% 2 1 U n f o r t u n a t e l y , the process i s not p e r f e c t and the f o l l o w i n g p o l l u t a n t s are produced: Hydrocarbon (HC) <1% Carbon monoxide (CO) <1% N i t r i c oxides (NO, N0 2) <1% Carbon or smoke <1% Sulphur d i o x i d e <1% Others -1% Carbon d i o x i d e Carbon d i o x i d e i s one of the end products of the p e r f e c t combustion of d i e s e l f u e l and can only be reduced by reducing the t o t a l d i e s e l consumption or by changing the carbon content of the f u e l . I t i s a c o l o r l e s s , o d o r l e s s , and noncombustible gas t h a t may have an a c i d t a s t e when present i n high c o n c e n t r a t i o n s . Increased concentrations of carbon d i o x i d e r e s u l t i n increased lung v e n t i l a t i o n , and an i n d i v i d u a l exposed to 0.5% carbon d i o x i d e i n otherwise normal a i r w i l l breathe a l i t t l e deeper and a l i t t l e f a s t e r than he would i f breathing normal a i r . A conc e n t r a t i o n of 5% w i l l r e s u l t i n a 300% increase i n the r e s p i r a t o r y r a t e and a co n c e n t r a t i o n of 10% can be t o l e r a t e d f o r only a few minutes. However, even i n h i g h l y mechanized mines making extensive use of d i e s e l equipment, CO^ i s not considered as a contaminant s i n c e the concentration i s w e l l below maximum p e r m i s s i b l e value. I t has been suggested by Hum (16) th a t the C0 2 l e v e l i n mine atmospheres, which i s e a s i l y measured, can be a good i n d i c a t o r of p o l l u t i o n . This important p o i n t w i l l be discussed l a t e r i n the t h e s i s . Carbon Monoxide Carbon monoxide, a r e s u l t of imperfect combustion i s a c o l o r l e s s , o d o r l e s s , t a s t e l e s s , t o x i c , and flammable gas. Carbon monoxide i s poisonous a t low concentrations. I t acts as a type of asphyxiant by d i s p l a c i n g the oxygen normally c a r r i e d by the hemoglobin of the blood. 22 The a f f i n i t y of the blood f o r carbon monoxide i s approximately 300 times t h a t f o r oxygen. Since the h e a l t h e f f e c t i s dependent upon CO i n the blood, oxygen content of a i r breathed, d u r a t i o n of exposure, ambient temperature, oxygen demand i n v o l v e d i n the work being performed, metabolic e f f i c i e n c y , h e a l t h s t a t u s , genotype and c a p a c i t y to stand exposure, i n d i v i d u a l s u s c e p t i b i l i t y to CO shows wide v a r i a t i o n s . At present i t would appear t h a t CO l e v e l s , as seen i n Canadian mines w i t h d i e s e l engines, do not pose a d e f i n i t e h e a l t h hazard, i f v e n t i l a t i o n techniques are p r o p e r l y a p p l i e d . Nitrogen oxide and d i o x i d e The N0 x formation i s r e l a t e d to combustion temperature. More than 95% of the NO produced i s i n the form of NO and the co n c e n t r a t i o n of x r NO w i l l i ncrease w i t h RPM and load. The main e f f e c t of NO r e s u l t s x from i t s combination w i t h hemoglobin to form methemoglobin, which gives r i s e to d e f i c i e n c y i n oxygen t r a n s p o r t by hemoglobin. N0 2 i s an i r r i t a t i n g gas t h a t causes edema, i r r i t a t i o n of the n a s a l mucosa, c o n s t r i c t i o n of the trachea and a m u l t i t u d e of s i d e e f f e c t s , such as headaches, sore t h r o a t , nausea and p o s s i b l e permanent changes i n lung s t r u c t u r e ( h i g h doses). Low ambient l e v e l s of N0 2 may be increased i n t o x i c i t y i f they concentrate on p a r t i c u l a t e s . T h i s , combined w i t h the f a c t t h a t NO^ reduces c i l i a r y a c t i v i t y i n the trachea (a process i n which the lung's l i n i n g move the mucous and the p a r t i c l e s c o l l e c t e d upward a l l the way to the t h r o a t ) and damages the c i l i a , c o u ld, i n the author's o p i n i o n , become a major concern of long-term exposure at low-dose of N0 2 and p a r t i c u l a t e s . Before more i s known on the e f f e c t s of N0 2 (combined w i t h other p o l l u t a n t s , the long term e f f e c t and mechanism of damage), i t w i l l be d i f f i c u l t to s p e c i f y maximum p e r m i s s i b l e exposure l e v e l s f o r underground mines. Sulphur Dioxide The q u a n t i t y of S 0 2 emitted i n d i e s e l exhaust i s d i r e c t l y r e l a t e d to the sulphur content of the f u e l . A p o r t i o n of the S 0 2 emitted i n t o the atmosphere undergoes o x i d a t i o n , l e a d i n g to formation of sulphur 23 t r i o x i d e , s u l p h u r i c a c i d and p a r t i c u l a t e sulphates. Sulphur d i o x i d e has a h i g h s o l u b i l i t y i n water and i s l a r g e l y removed by the surface f l u i d covering the mucosa of the n a s a l passages and l a r g e r upper airways. Sulphur t r i o x i d e a f f e c t s the lower r e s p i r a t o r y t r a c t because i t s p a r t i c u l a t e d r o p l e t form i s c a r r i e d down i n t o the depths of the airways and a l v e o l i (17) and i t i s a p o l l u t a n t of s e r i o u s concern. The t r i o x i d e formation can be d r a m a t i c a l l y increased under heavy load c o n d i t i o n s and when the exhaust i s run through a c a t a l y t i c converter (see s e c t i o n 3.2). Ambient SO^ l e v e l s i n mine a i r may only represent 25-50% of the t o t a l SO^ present due to absorption onto p a r t i c u l a t e and/or d i s s o l u t i o n i n water. There i s a need to d e f i n e these i n t e r a c t i o n s and t h e i r s i g n i f i c a n c e i n terms of p o s s i b l e adverse h e a l t h e f f e c t s . L i k e NO^, SO^ reduces c i l i a r y a c t i v i t y i n the lungs and exposure to SO^ and carbon p a r t i c l e s ( i n the r e s p i r a b l e range) caused development of e f f e c t s non-evident, when e i t h e r of the two p o l l u t a n t s were present s e p a r a t e l y (18). P a r t i c u l a t e s As suggested i n the previous pages, p a r t i c u l a t e emissions are of great concern. P a r t i c u l a t e s can be viewed as a c t i v a t e d carbon because d i e s e l p a r t i c u l a t e s are composed p r i m a r l y of soot or carbon p a r t i c l e s and they provide a tenacious s i t e f o r ad s o r p t i o n of gaseous and non-gaseous environmental c o n s t i t u e n t s . The concern l i e s i n the growing number of s t u d i e s showing adverse lung and body r e a c t i o n s to agglomerates of carbon w i t h adsorbed components such as SO^, a c i d s and p o l y n u c l e a r aromatic hydrocarbons (PNA's). P a r t i c u l a t e s can be defined as di s p e r s e d matter t h a t e x i s t s i n the condensed phase ( l i q u i d or s o l i d ) i n which the s i z e of the i n d i v i d u a l u n i t s range from 0.05 um to about 500 urn (19). The p a r t i c l e s which are able to penetrate the r e s p i r a t o r y system (<5 um) are considered r e s p i r a b l e dust. P a r t i c u l a t e s greater than 2 um are i n h a l e d on the n a s a l passages. P a r t i c l e s 2 um to 0.05 um deposit by g r a v i t a t i o n a l sedimentation at the b r o n c h i a l - b r o n c h i o l a r l e v e l s i n the lung. P a r t i c l e s ranging i n s i z e from 0.01 to 0.05 um are 24 p a r t i c u l a r l y l i k e l y to s e t t l e i n the a l v e o l i (20). I t i s important to note that a great percentage of d i e s e l p a r t i c u l a t e s are " r e s p i r a b l e " . The p o t e n t i a l danger of SO2 and N0 2 combined w i t h p a r t i c u l a t e s has already been mentioned, but researchers are more concerned w i t h long-range e f f e c t s on h e a l t h due to the c a r c i n o g e n i c i t y of some PNA's. Hydrocarbons PNA's are p a r t of a l a r g e r f a m i l y c a l l e d the hydrocarbons. Both unburned and p a r t i a l l y o x i d i z e d hydrocarbons can be found i n d i e s e l exhaust. The mixture of hydrocarbons i s complex and incl u d e s aldehydes, ketones, phenols, as w e l l as alkanes and alkenes ( e t c . ) . A s i g n i f i c a n t p o r t i o n of the PNA's found i n d i e s e l exhaust are as s o c i a t e d w i t h p a r t i c u l a t e matter. This p a r t i c u l a t e matter i n c l u d e s both dust present i n the mine atmosphere ( q u a r t z , carbon, e t c . . ) and d i e s e l exhaust p a r t i c l e s . The q u a n t i t y of PNA's present i n the mine atmosphere i s very d i f f i c u l t to evaluate s i n c e they are present i n the 3 order of nanograms/m and a l a r g e number of r e l a t i v e s i n the f a m i l y are a l s o present and d i f f i c u l t to d i f f e r e n t i a t e . Two f a c t s are c e r t a i n . Numerous s t u d i e s prove t h a t PNA's are p o t e n t i a l l y c a r c i n o g e n i c and research a l s o provided data suggesting t h a t p a r t i c u l a t e s and PNA's are s y n e r g i s t i c (21). 25 3.1.2 Emission C o n t r o l Techniques There are a m u l t i t u d e of ways i n which the noxious contaminants can be reduced. D i e s e l emission i s a f f e c t e d by the f o l l o w i n g parameters: (a) Engine type (b) F u e l (c) F u e l a d d i t i v e s (d) Maintenance (e) D i r e c t exhaust emission c o n t r o l ( f ) I n l e t a i r a) Engine type There are two b a s i c d i e s e l engine designs - d i r e c t i n j e c t i o n ( Dl) and i n d i r e c t i n j e c t i o n (IDI) (23). In d i r e c t i n j e c t i o n , the f u e l i s d i r e c t l y i n j e c t e d i n t o the c y l i n d e r s where i t vaporizes w i t h a i r and burns. In i n d i r e c t i n j e c t i o n , the f u e l and a s m a l l amount of a i r enters the prechamber and begins to burn, then i t enters the main chamber where combustion i s completed. These d i f f e r e n c e s i n engine design and f u n c t i o n r e s u l t i n d i f f e r e n t emission c h a r a c t e r i s t i c s , as w e l l as d i f f e r e n t engine performance. At the NIOSH d i e s e l meeting (22), comparison of two types of engines showed t h a t d i r e c t i n j e c t i o n engines were e m i t t i n g more CO, N0 x and hydrocarbons but had a lower f u e l consumption than the i n d i r e c t i n j e c t i o n . They concluded: "The i n d i r e c t i n j e c t i o n engine has advantages f o r underground mining usage and i s l i k e l y to r e t a i n these advantages f o r at l e a s t the four next years." Mogan presented more recent figures, f o r n a t u r a l l y - a s p i r a t e d heavy-duty d i e s e l engines (24) and showed th a t the RCD ( r e s p i r a b l e combustible p a r t i c u l a t e ) emissions are higher f o r IDI engines and i t i s the RCD t h a t u s u a l l y c o n t r o l v e n t i l a t i o n requirements. In the l i g h t of these new r e s u l t s , i t can be concluded t h a t IDI engines do not have many advantages over DI engines. There are many more 26 d i s c r e p a n c i e s between the d i f f e r e n t engine models than type of i n j e c t i o n s . b) F u e l For underground equipment, most r e g u l a t i o n s r e q u i r e a f u e l c o n t a i n i n g l e s s than 0.5% sulphur. This r e s u l t s i n lower SO^ emission s i n c e the emission q u a n t i t y i s d i r e c t l y r e l a t e d to sulphur content of f u e l . There are three types of f u e l a v a i l a b l e , commonly i n d i c a t e d as l-D, 2-D and 4-D. l-D and 2-D f u e l s are w i d e l y used i n the mining i n d u s t r y ( l - D being more popular i n Canada). The l-D f u e l has a sulphur content by weight of .18% and 2-D, .24-.31%. The optimum would be a s u l p h u r - f r e e f u e l which e l i m i n a t e s SO2 emission and s u l p h u r i c a c i d formation. c) F u e l a d d i t i v e The a p p l i c a t i o n of w a t e r - i n - f u e l emulsions to d i e s e l engines has been a subject of c o n t i n u i n g i n t e r e s t f o r s e v e r a l years. I t was mentioned i n the NIOSH meeting t h a t p o t e n t i a l l a y i n the use of w a t e r / f u e l e m u l s i f i c a t i o n . But i t s main i n t e r e s t l a y i n improved mixing of f u e l and a i r and as a r e s u l t , improved combustion c h a r a c t e r i s t i c s and f u e l savings. In 1980, a paper was presented by CW. Coon from the Southwest Research i n s t i t u t e (25) on u n s t a b i l i z e d w a t e r - i n - f u e l emulsions, used to reduce f u e l consumption of boat operations. The study, showed no improvement f o r any of the contaminants emitted. However, a study by Lawson and Last two years e a r l i e r (26) showed a decrease i n N0 x and p a r t i c u l a t e emissions of n e a r l y 50% f o r an IDI f o u r - s t r o k e engine. Methanol/fuel emulsion has a l s o been t e s t e d but although there was e x c e l l e n t p a r t i c u l a t e matter r e d u c t i o n , N0 x was increased by more than 40%. d) Maintenance Proper maintenance not only assures the lowest emission c h a r a c t e r i s t i c s from an engine, but a l s o the most economic operation 27 of the engine i n terms of down-time, f u e l consumption and engine l i f e . Very good maintenance programs are provided by Hews and Rutherford (27) and by Alcock (28). The r e l a t i o n s h i p of underground d i e s e l engine maintenance to emissions i s covered by R. B r a n s t e t t e r et a l (29). In g e n e r a l , a p o o r l y maintained engine w i l l l e a d to an improper d e r a t i n g r a t i o which w i l l i n t u r n create excessive CO emission. e) D i r e c t exhaust emission c o n t r o l D i r e c t exhaust emission c o n t r o l seems to be the most promising sect o r f o r exhaust contaminant r e d u c t i o n , i n the short term. Most of the d i e s e l s used underground i n Canada are operated w i t h some s o r t of exhaust modifying equipment. At a Canmet symposium i n Vancouver, four papers were presented (31,32,33,34). The f i r s t two d e a l t w i t h the e f f i c i e n c y of water scrubbers and c a t a l y t i c a f t e r b u r n e r s . There i s one important f a c t o r to recognize when d e a l i n g w i t h exhaust modifying equipment and th a t i s backpressure drop. The manufacturers of d i e s e l engines do not accept a pressure drop through the system of more than 75" of H^ O (18.5 Kpa) f o r the warranty on the equipment to be v a l i d f o r a " n a t u r a l l y - a s p i r a t e d " engine. I f a drop of 35" of H^O i s assumed through the system, then the exhaust c o n t r o l device cannot produce a pressure drop of more than 40". The paper on c a t a l y s t s (31) concluded, " c a t a l y t i c a f t e r b u r n e r s are not recommended by us because of t h e i r dubious advantages and obvious disadvantages." Although o x i d a t i o n c a t a l y s t s were very e f f i c i e n t i n reducing aldehyde, CO and odour, the emission of s u l p h u r i c a c i d by o x i d a t i o n and of sulphur d i o x i d e and the impact i t has on PNA's ( n i t r a t i o n and ca r c i n o g e n i c d i n i t r o p y r e n e s ) d i d not make them a t t r a c t i v e . The paper on water scrubbers (32) presented a v e n t u r i type water scubber to r e p l a c e the conventional water scrubbers. Two conventional water scrubbers, a s i n g l e pass b a f f l e d u n i t and a packed bed w i t h t u b u l a r d i s t r i b u t o r were t e s t e d by the Ontario Research Foundation (ORF). They perform q u i t e s i m i l a r l y , c a p t u r i n g 25-30% of the soot and 28 60% and 80% r e s p e c t i v e l y of the sulphur d i o x i d e . The a d d i t i o n of a c a t a l y t i c p u r i f i e r upstream of the scrubber can increase soot capture to 50% at f u l l l o a d , but w i t h an increase i n s u l p h u r i c a c i d (converted by the p u r i f i e r and presumably c a r r i e d through the water bath absorbed on the soot p a r t i c l e s ) . A v e n t u r i scubber has proven to be much more e f f i c i e n t c a p t u r i n g over 50% of the soot without c a t a l y t i c p u r i f i e r , but i t has i t s own problems such as double the amount of water-flow r e q u i r e d f o r c onventional types and considerable back pressure drop. The l a s t two papers d e a l t w i t h the a p p l i c a t i o n of two new emission c o n t r o l devices not yet commercially a v a i l a b l e to heavy-duty engines. C a t a l y t i c t r a p converters (wire mesh u n i t s ) were t e s t e d by the ORF and showed e x c e l l e n t p a r t i c u l a t e r e d u c t i o n (65-85% of t o t a l p a r t i c u l a t e emission) and accompanying PNA's r e d u c t i o n . Sulphur d i o x i d e o x i d a t i o n and excessive backpressure were, however, of some disadvantage. The i n n o v a t i v e design of ceramic w a l l - f l o w f i l t e r s have good p o t e n t i a l f o r the f u t u r e w i t h over 90% r e d u c t i o n i n t o t a l p a r t i c u l a t e and PNA's. A c o s t / b e n e f i t study was performed and the use of the f i l t e r s showed an annual saving of $15M/year f o r the Canadian mining i n d u s t r y (mostly by reduced power and heating c o s t ) . This i s only t r u e f o r h i g h temperature c y c l e LHD s e r v i c e where auto-regeneration of the f i l t e r s i s p o s s i b l e (-25% of underground equipment). The development of an " i n place regeneration system" (not n e c e s s i t a t i n g removal of the f i l t e r from the machine) i s v i t a l f o r the f i l t e r to g a i n wider a p p l i c a t i o n . A recent paper (35) introduced a new chemical process capable of completely removing N0 x from the products of combustion. The process i s based on the a d d i t i o n of I s o c y a n i c a c i d to the exhaust which decomposes N0 x to n i t r o g e n , carbon d i o x i d e , water and carbon monoxide. The paper concludes t h a t t h i s process f o r r a p i d r e d u c t i o n of n i t r o g e n oxides could p l a y a major r o l e i n c o n t r o l l i n g N0 x emissions from most combustion devices. 29 f ) I n l e t a i r Exhaust gas r e c i r c u l a t i o n (EGR) i s a method by which a p o r t i o n of the exhaust i s returned t o the i n l e t and i t i s known to reduce NO by x J as much as 50%. T r i a l s have been made to use i t w i t h Corning f i l t e r s (ceramic w a l l f i l t e r s ) and they were found to be very e f f i c i e n t i n preventing o x i d a t i o n of NO and r e d u c t i o n of NO and NO^ by 42%. Water i n i e c t i o n to the i n l e t a i r i s a l s o e f f e c t i v e f o r the r e d u c t i o n of NO J x emissions (36). 3.2 BLASTING CONTAMINANTS The contaminants t h a t can be r e l e a s e d from an underground e x p l o s i o n are n i t r o g e n oxide, n i t r o g e n d i o x i d e , carbon monoxide, sulphur d i o x i d e , ammonia and mineral dust. Carbon d i o x i d e i s a l s o produced i n l a r g e q u a n t i t i e s . However, as i t was mentioned e a r l i e r , C O 2 i s not considered a p o l l u t a n t i n underground mines. Work by MSA (37) i n d i c a t e d t h a t only i n s i g n i f i c a n t q u a n t i t i e s of NH.j could be found i n the mine-blast environment. A study conducted by Duane et a l (38) provided s i g n i f i c a n t data on the mass of p o l l u t a n t s r e l e a s e d during b l a s t i n g . The e x p l o s i v e s t e s t e d were s e m i - g e l a t i n dynamites, s l u r r i e s and ammonia n i t r a t e e x p l o s i v e s . The range of values measured are shown i n t a b l e 3. TABLE 3 T y p i c a l b l a s t i n g contaminants concentrations Gas Mass conc e n t r a t i o n Peak Concentration P o l l u t a n t ( f t 3 / l b m ) (PPM)  CO 0.08 - 0.3 90 - 550 NO 0.01-0.035 25 - 52 N0 2 0.003 - 0.019 14 - 28 S 0 2 0 - 0 . 0 5 0 - 1 3 30 The c o n c e n t r a t i o n of mineral dust during a b l a s t i s p o o r l y documented and needs to be i n v e s t i g a t e d i n d e t a i l . Sulphide dust explosions have become a growing concern f o r base metal mine operators. A s p e c i a l symposium on the e x p l o s i v i t y of sulphide dust h e l d i n Geco, Ontari o , and attended by the author , has provided an e x c e l l e n t p l a t f o r m f o r the o r g a n i z a t i o n of j o i n t industry-government research i n the f u t u r e (39). Dust explosions occur i n massive sulphide ore bodies because sulphide dust w i l l burn i f there i s a source of i g n i t i o n and dust i s present a t s u f f i c i e n t l y h i g h co n c e n t r a t i o n . When the combustion takes p l a c e i n a confined space, such as i n a mine stope, an e x p l o s i o n can r e s u l t . I n t h i s process, heat i s generated much f a s t e r than i t i s d i s s i p a t e d , and t h i s causes a r a p i d gas expansion, which, combined w i t h the generation of SO^ , leads to the r a p i d i n c r e a s e i n pressure t h a t causes the e x p l o s i v e damage. The e x p l o s i o n can propagate out of the stope s i n c e the compression wave of the b l a s t s can resuspend s u f f i c i e n t dust from the f l o o r and w a l l s of the cro s s - c u t s l e a d i n g to the stope. I t i s important to say tha t current concerns are r e l a t e d to the h i g h l y t o x i c sulphur d i o x i d e concentrations r e l e a s e d from the secondary explosions (and t h e i r e f f e c t on the r e - e n t r y time) and not the m a t e r i a l damage. 3.3 MINERAL DUST The main source of dust i n mining i s the mi n e r a l i t s e l f . I t i s obvious t h a t l a r g e q u a n t i t i e s of dust are produced when the mineral i s broken down and reduced to a s i z e convenient f o r handling. The main mining operations r e s p o n s i b l e f o r the dust i n mine a i r , i . e . a i r b o r n e dust, are: d r i l l i n g , b l a s t i n g , l o a d i n g , conveying and dumping. Free s i l i c a ( q u a r t z , t r i d y m i t e a n d e r i s t o b a l i t e ) i s the most dangerous component of dust a f f e c t i n g the behavior of a l v e o l a r macrophages. When these c e l l s d i e they r e l e a s e a substance which i s f o r e i g n to the body, producing an a l l e r g i c type of r e a c t i o n r e s u l t i n g i n f i b r o s i s . I t has been determined t h a t pneumoconiosis ( f i b r o s i s of the lungs) i s caused by p a r t i c l e s below 5 urn, s i n c e o n ly p a r t i c l e s w i t h i n the 31 s i z e range of about 0.25 to 10 um ( c a l l e d r e s p i r a b l e dust) enter the lung and only the p a r t i c l e s below 5 um may pass i n the s m a l l a l v e o l i . R e s p i r a b l e m i n e r a l dust i n Canadian mines i s measured w i t h a g r a v i m e t r i c dust sampling instrument and the c o n c e n t r a t i o n i s expressed i n mass of dust per u n i t volume of a i r ( i . e . mg/m ). 3.A THRESHOLD LIMIT VALUE Threshold L i m i t Values are e s t a b l i s h e d by the American Conference of Governmental and I n d u s t r i a l H y g i e n i s t s (ACGIH). However, sometimes government and corporate r e g u l a t o r y bodies may set t h e i r own TLV's. These l i m i t s are e s t a b l i s h e d from a dose-response r e l a t i o n s h i p from s c i e n t i f i c s t u d i e s . Most chemicals and drugs have pharmacological or t o x i c o l o g i c a l p r o p e r t i e s and the b i o l o g i c a l e f f e c t s (as measured i n animals) u s u a l l y increase w i t h i n c r e a s i n g dose of the agent. At some dose l e v e l above zero, a p o i n t i s reached where the agent e l i c i t s no response i n the animal, c a l l e d the " t h r e s h o l d dose". In e s t a b l i s h i n g the TLV, a s a f e t y f a c t o r of 10 to 100,000 i s a p p l i e d , which depends on the chemical, the s e v e r i t y or c r i t i c a l nature of the response and the a t t i t u d e of the s c i e n t i s t s conducting the research. Table 4 presents the TLV's f o r the d i f f e r e n t mine p o l l u t a n t s , as e s t a b l i s h e d by the ACGIH and enforced by most of the p r o v i n c i a l mining a c t s . 32 TABLE 4 P e r m i s s i b l e concentrations f o r ai r b o r n e contaminants Contaminant P e r m i s s i b l e Concentrations 8hr. L i m i t PPM mg/nf 15 min. L i m i t PPM mg/m" Black Carbon Carbon Dioxide Carbon Monoxide P a r t i c u l a t e P o l y c y c l i c Aromatic Hydrocarbons (PPAH) Nitrogen Dioxide O i l M i s t S u l f u r d i o x i d e S u l f u r i c A c i d 5,000 20 3.5 9,000 60 9 5 13 1 15,000 30 7 27,000 90 0.2 10 Oxygen - P e r m i s s i b l e a i r not to co n t a i n l e s s than 18% 0^ by volume. Dust - The TLV f o r mine a i r p a r t i c u l a t e matter i s determined by i t s s i l i c a (SIO,,) content. For r e s p i r a b l e p a r t i c l e s c o n t a i n i n g g r e a t e r than 1% S I 0 2 , the TLV i s : TLV = 10mg/m3 %SI0 2+2.0 For r e s p i r a b l e p a r t i c u l a t e matter c o n t a i n i n g l e s s than 1% SI02» the TLV i s 5.0 mg/m3 33 3.5 THE HEALTH EFFECTS INDEX In 1978, Ian W. French & As s o c i a t e s prepared a rep o r t under a co n t r a c t from the department of Energy, Mines and Resources, Canada Center f o r M i n e r a l and Energy Technology (CANMET). This r e p o r t was to review c r i t i c a l l y the r e l e v a n t s c i e n t i f i c l i t e r a t u r e d e s c r i b i n g the occupational environment which underground miners are exposed to and p o t e n t i a l h e a l t h e f f e c t s i n " d i e s e l i z e d " mines (40). The authors suggested a Health E f f e c t s Index to take i n t o account the p o t e n t i a l s y n e r g i s t i c e f f e c t s of the numerous p o l l u t a n t s i n the mine. High emphasis was accorded to the r e s p i r a b l e combustible dust. The H ealth E f f e c t s Index was presented as f o l l o w s : (CO) (NO) AQI = + TLV-CO TLV-CO 1.5 (so2) TLV-SO. (RCD) + TLV-RCD (RCD) TLV-RCD + 1.2 (N0 2) TLV-NO, • + (RCD) TLV-RCD The r e s u l t a n t AQI value should be used to estimate the a c c e p t a b i l i t y of e x i s t i n g v e n t i l a t i o n . V e n t i l a t i o n requirements w i l l be determined, i n most cases, by r e s p i r a b l e combustible p a r t i c u l a t e l e v e l s (of which 75% i s considered to be der i v e d from d i e s e l exhaust on a mechanized l e v e l ) . The 1.5 and 1.2 f a c t o r s are used to provide r e c o g n i t i o n of the synergism e x h i b i t e d between S 0 2 and N0 2 and r e s p i r a b l e p a r t i c u l a t e s . I f the S 0 2 and N0 2 concentrations are 25% or l e s s of t h e i r TLV's, the r e s p e c t i v e r a t i o s are not inc l u d e d i n the c a l c u l a t i o n . I n t e r p r e t a t i o n of the HEI: HEI < 3 ; Acceptable h e a l t h r i s k = 3-4 ; Poses a moderate t h r e a t to h e a l t h HEI > 4 ; Serious h e a l t h t h r e a t r e q u i r i n g increased v e n t i l a t i o n or a re d u c t i o n i n RCD 34 In the l a s t 7 years, t h i s index has been the obje c t of numerous c r i t i c i s m s from the mining i n d u s t r y . The controversy stems from the f a c t t h a t the f a c t o r s (1.2 and 1.5) used were not supported by any experimental s t u d i e s . A new c o n t r a c t by CANMET has permitted Ian W. French & A s s o c i a t e s to update t h e i r 1978 r e p o r t i n the l i g h t of a l l the new s c i e n t i f i c data published. In t h i s r e p o r t , the HEI was r e v i s e d and presented i n a new form c a l l e d the A i r Q u a l i t y Index (AQI). The AQI i s now separated i n t o two p a r t s , one f o r gas l e v e l s and the other f o r p a r t i c u l a t e s , a l s o c a n c e l l i n g the s y n e r g i s t i c f a c t o r s . (CO) (NO) (NO ) AQI (gas) = • • TLV-CO TLV-NO TLV-N0 2 (RCD) AQI ( p a r t ) = TLV-RCD (S0 2) (RCD) j ^ (N0 2) + (RCD) TLV-S0 2 TLV-RCD J |_ TLV-N0 2 TLV-RCD The AQI (gas) should not exceed 1.0 and no i n d i v i d u a l component should exceed i t s TLV. I t i s recommended t h a t the AQI ( p a r t i c u l a t e s ) value should not exceed i t s TLV. I f the l e v e l of S 0 2 or N0 2 i s 25% or l e s s of t h e i r TLV, they are omitted from the equation. This A i r Q u a l i t y Index has not been l e g i s l a t e d i n North America, but the growing i n t e r e s t shown by governmental r e g u l a t o r y bodies i n Canada and the United States suggest t h a t the AQI could become very soon the standard t o assess the q u a l i t y of mine environment. The author s t r o n g l y f e e l s t h a t t h i s index should be used to assess r e c i r c u l a t e d a i r q u a l i t y u n t i l more s c i e n t i f i c research i s a v a i l a b l e to address the concerns of Dr. French on s y n e r g i s t i c e f f e c t s . 35 4.0 PRINCIPLES OF RECIRCULATION In t h i s chapter, the p e r t i n e n t models t h a t have been developed f o r r e c i r c u l a t i o n are presented and t h e i r use f o r a Canadian mine r e c i r c u l a t i o n system are analysed. The chapter i s d i v i d e d i n t o two s e c t i o n s : (1) Gas contaminants and (2) P a r t i c u l a t e matter. For each of the s e c t i o n s , the author a l s o reviews the d i f f e r e n t f a c t o r s which w i l l reduce p o l l u t a n t concentrations as they are r e c i r c u l a t e d through the mine network. 4.1 GAS CONTAMINANTS Burton e t a l (15) have developed a steady s t a t e model t h a t can be used to show the e f f e c t s of r e c i r c u l a t i o n on the r e t u r n and mixed i n t a k e l e v e l s of a gaseous contaminant. A time-dependent model i s a l s o presented to i n d i c a t e the e f f e c t s of r e c i r c u l a t i o n on the decay of gaseous contaminant l e v e l s f o l l o w i n g an instantaneous emission created by a b l a s t . R e c i r c u l a t i o n model f o r gaseous contaminants Nomenclature Q. = q u a n t i t y of in t a k e a i r , m/s 1 3 Q = q u a n t i t y of r e c i r c u l a t e d a i r , m/s C^ = i n t a k e - a i r contaminant c o n c e n t r a t i o n , mg/m^ C = r e t u r n - a i r contaminant c o n c e n t r a t i o n , mg/m,, m J C = contaminant produced i n working area, mg/s A schematic r e p r e s e n t a t i o n of a r e c i r c u l a t i o n system i s shown i n F i g . 8 The model assumes steady-state c o n d i t i o n s w i t h C^ being an unknown value of the r e t u r n - a i r c o n c e n t r a t i o n . The t o t a l amount of contaminant a r r i v i n g a t the r e c i r c u l a t i o n j u n c t i o n (pt.2) w i l l be given by: Q.C. + Q C + C i i r r WORKING AREA Qi ci 1 -*>-a) without' recirculation Qi c Q r 1 1 WORKING A R E A T b) with recirculation Schematic representation of recirculation Fig. 8 Qr I WORKING A R E A volume = V concentration = c n J Schematic of blast-contaminant decay Fig. 9 37 this is also equal to the product of the assumed concentration, C^, and the to ta l flow rate in the return airway: (Q. + Q r ) C r By combining these two equations, the return-air concentration is presented by: G = C. + C/Q. (1) r 1 I If there was no recirculat ion, the return-air concentration, C , r would be given by: C = C. + C/Q. (2) r I x By comparing equations 1 and 2, the important conclusion that the return a ir is not affected by recirculat ion is drawn. The mixed-intake concentration, C^, at point 1 must be given by: Q.C. + Q C m Q. + Q U ; By defining a recirculation fract ion, R, as: Q. R = r Q. + Q i r Combining these two equations with equation 1 above, the mixed intake concentration, C , is given by: m ° J RC Cm " C i + Q- ( 4 ) I If there was no recirculat ion, the mixed-intake concentration would be given by: 38 C = C. m 1 A comparison between equations 3 and A shows t h a t the mixed-intake con c e n t r a t i o n i s dependent on r e c i r c u l a t i o n and t h a t the c o n c e n t r a t i o n increases as the r e c i r c u l a t i o n f r a c t i o n i n c r e a s e s . As the r e c i r c u l a t e d a i r i s increased, the r e c i r c u l a t i o n f r a c t i o n approaches u n i t y and the mixed-intake co n c e n t r a t i o n w i l l approach, but not exceed, the r e t u r n - a i r c o n c e n t r a t i o n . R e c i r c u l a t i o n model f o r b l a s t i n g contaminants 3 Assume t h a t , as a r e s u l t of b l a s t i n g , a stope of volume V (m ) has a 3 uniform instantaneous co n c e n t r a t i o n of a noxious contaminant, C (mg/m ) n (see F i g . 9 ) . The r a t e of decay of noxious contaminant from the working area must equal the r a t e of removal i n the r e t u r n a i r : I t can be seen t h a t r e c i r c u l a t e d q u a n t i t y (Q r) does not appear i n the equation as the amount of contaminant removed by the r e c i r c u l a t e d a i r i s immediately returned to the working area. In t h i s r espect, r e c i r c u l a t i o n w i l l have no e f f e c t on the r a t e of removal of contaminant from the r e c i r c u l a t i o n system. By i n t e g r a t i o n of equation 5, the r e t u r n c o n c e n t r a t i o n i s given by: Gas contaminants behavior under a Canadian r e c i r c u l a t i o n system The a p p l i c a t i o n of r e c i r c u l a t i o n f o r Canadian mines i s q u i t e d i f f e r e n t from the a p p l i c a t i o n i n B r i t i s h c o l l i e r i e s and South A f r i c a n gold mines. In the l a t t e r cases, r e c i r c u l a t i o n i s motivated by the need to c o n t r o l two major enviromental parameters, heat and dust. This i s accomplished through a decrease i n i n t a k e a i r volume which i s replaced by an equal amount of a i r r e c i r c u l a t e d . (5) C r - ( C r - C . ) t = 0 exp(-Q.t/V) +C. (6) 39 The r e c i r c u l a t i o n models presented are s t i l l v a l i d i n t h i s case but they cannot be i n t e r p r e t e d i n the same way. In equations 1 and 2, f o r r e c i r c u l a t i o n i s smaller than without r e c i r c u l a t i o n s i n c e i n a Canadian s i t u a t i o n , the intake a i r w i l l be reduced. Therefore, C w i l l r i n crease as a r e s u l t of r e c i r c u l a t i o n . For the b l a s t model i t must be emphasized t h a t r e c i r c u l a t i o n has no e f f e c t on the r a t e of decay of the contaminants, because of the p r o x i m i t y of the r e c i r c u l a t i o n branch to the workings. I f i t takes the a i r 5 minutes to go through the r e c i r c u l a t i o n c i r c u i t , the r a t e of decay w i l l be increased by 5 minutes. Normal r a t e s of decay are w e l l over 1 hour so th a t the increase i s n e g l i g i b l e . This may not be the case i n e n t i r e mine network r e c i r c u l a t i o n , where the a i r may take up to one hour to complete a network c i r c u i t . Another very important c o n s i d e r a t i o n i s t h a t previous experiments w i t h r e c i r c u l a t i o n were i n d i e s e l f r e e environments. In Canadian mines, where concern f o r d i e s e l contamination i s a major aspect of environmental engineering, an increase of p o l l u t i o n l e v e l i n the mixed-intake w i l l not be t o l e r a t e d . D i s t r i c t r e c i r c u l a t i o n , as p r a c t i c e d i n S o u t h - A f r i c a i s t h e r e f o r e not p o s s i b l e f o r the b e n e f i t s of heating c o n t r o l i n metal mines (Canadian Potash mines could be d i f f e r e n t due to the l i m i t e d d i e s e l mechanization o p e r a t i n g ) . However, r e c i r c u l a t i o n may be acceptable i f i t i s adapted to r e c i r c u l a t e a p o r t i o n of t o t a l mine a i r ( i . e . e n t i r e network r e c i r c u l a t i o n system). The underground environment, much l i k e the earth's atmosphere, has a c e r t a i n c l e a n s i n g or f i l t e r i n g c a p a c i t y . In other words, through p h y s i c a l and chemical processes, p o l l u t a n t s w i l l be removed from the environment a f t e r a c e r t a i n residence time. Such processes could permit a c o n s i d e r a b l e percentage r e c i r c u l a t i o n of a r e l a t i v e l y c l e a n a i r . In the f o l l o w i n g pages, the author w i l l d e f i n e and t r y to q u a n t i f y these f a c t o r s and removal mechanisms f o r some of the gas contaminants. 4.1.1 D i l u t i o n D i l u t i o n w i l l c e r t a i n l y be one of the most important mechanisms i n reducing the contaminants c o n c e n t r a t i o n . AO In a mine, a l l working l e v e l s are connected to the main v e n t i l a t i o n i n t a k e and r e t u r n airways. A i r always flows along the path of l e a s t r e s i s t a n c e . Therefore to prevent the a i r from r e t u r n i n g d i r e c t l y to the surface (by u s i n g the upper working l e v e l routes) v e n t i l a t i o n doors are i n s t a l l e d on the l e v e l s . An opening ( r e g u l a t o r ) i n the door can be adjusted to a l l o w an adequate volume of f r e s h a i r to enter and v e n t i l a t e the l e v e l . This m u l t i t u d e of working l e v e l s c o n t r o l l e d by the use of doors and r e g u l a t o r s i s subject to c o n s i d e r a b l e leakage. The leakage i s even more s i g n i f i c a n t i n the upper l e v e l s . There i s a l s o a p r a c t i c e of o v e r v e n t i l a t i o n i n mines (as opposed to leakage) s i n c e c e r t a i n l e v e l s must be v e n t i l a t e d even i f there i s no equipment operating on the l e v e l i f i t i s expected t h a t equipment could operate there during the s h i f t . F i n a l l y , there i s leakage from the stopes which connect two l e v e l s and from the ore and waste passes. This leakage and o v e r v e n t i l a t i o n i s r e l a t i v e l y c l e a n a i r . I t may c o n t a i n a low l e v e l of mineral dust but p r a c t i c a l l y no gas contaminants. By the time the contaminated a i r from a h i g h l y mechanized s e c t i o n has reached the s u r f a c e , v i a the r e t u r n v e n t i l a t i o n r a i s e , a c o n s i d e r a b l e amount of d i l u t i o n has taken place. In f a i r l y l a r g e Canadian mines, w i t h 10 working l e v e l s or more, the t o t a l volume of a i r v e n t i l a t e d may have an e f f i c i e n c y of l e s s than 50%. In other words, f o r these mines, the contaminant c o n c e n t r a t i o n w i l l have been reduced by 50% once i t reaches the surface exhaust. Maximum d i l u t i o n w i l l be gained by r e c i r c u l a t i n g as c l o s e to the s u r f a c e as p o s s i b l e . Another f a c t o r t h a t must be considered i s the age of the mine; an o l d mine w i l l have more o l d workings and stopes, and t h e r e f o r e more leakage. A.1.2 Other s i n k s and removal processes Toxic gases r e l e a s e d i n t o the mine atmosphere are both p h y s i c a l l y and c h e m i c a l l y a c t i v e . These environmental processes can act as important removal mechanisms f o r c e r t a i n of the gas p o l l u t a n t s . 41 The f o l l o w i n g i s a l i s t of the p o t e n t i a l mechanisms: a) P h y s i c a l adsorption onto p a r t i c u l a t e matter b) S o l u b i l i t y of the gases i n the presence of water c) O x i d a t i o n of the gases d) Chemical r e a c t i o n s w i t h water d r o p l e t s u s i n g p a r t i c u l a t e matter as a c a t a l y s t a) P h y s i c a l adsorption P o t e n t i a l s o l i d adsorbents of gas molecules can be c l a s s i f i e d i n t o three groups (43); nonpolar s o l i d s ( p h y s i c a l a b s o r p t i o n ) , p o l a r s o l i d s (chemical adsorption w i t h no change i n s t r u c t u r e ) and chemical adsorbing surfaces (chemical r e a c t i o n i n v o l v e d ) . The s o l i d s most s u i t e d f o r adsorption are those w i t h l a r g e s u r f a c e to volume r a t i o s , t h a t i s , very porous, such as carbon. Carbon i s a l s o the most important nonpolar adsorbing s o l i d . D i e s e l p a r t i c u l a t e matter (which i s mainly composed of carbon) w i l l t h e r e f o r e be very e f f e c t i v e i n bindi n g nonpolar molecules, such as hydrocarbon gases. This i s why most of the hydrocarbons r e l e a s e d by d i e s e l equipment underground are a s s o c i a t e d w i t h the p a r t i c u l a t e matter. Carbon p a r t i c l e s can a l s o adsorb p o l a r molecules such as s u l f u r d i o x i d e , n i t r o g e n oxides and water. Although the l i t e r a t u r e (44,45) suggests t h a t SO2 and N 0 2 adsorb r e a d i l y on carbon, there was no experimental evidence to support t h i s . b) S o l u b i l i t y of gases S u l f u r d i o x i d e and n i t r i c oxides are h i g h l y s o l u b l e . S u l f u r d i o x i d e has a s o l u b i l i t y i n water of about 18.9% at 0 C e l c i u s (10% at 20 C e l c i u s ) and n i t r i c oxide a s o l u b i l i t y of 7.3 cc./lOOg at 0 C e l c i u s (46). With the h i g h humidity of the mine a i r (up to 100%) and the numerous sources of water a v a i l a b l e such as seepage, runoff and sump water, t h i s could be a major removal mechanism f o r S 0 „ and N 0 „ . 42 c) O x i d a t i o n of gases The thermodynamic p r o p e r t i e s of c e r t a i n gases are such t h a t they have a strong tendency to r e a c t w i t h oxygen i n the a i r under normal atmospheric c o n d i t i o n s (47). Sulphur d i o x i d e w i l l r e a c t i n t h i s way: 2S0 2 + 0 2 -> 2S0 3 Thermodynamics a l s o i n d i c a t e t h a t a t normal h u m i d i t i e s the SO^ product of the r e a c t i o n w i l l be converted l a r g e l y to s u l p h u r i c a c i d [H 2SO A ( a q ) ] : S 0 3 + H 20 H 2S0 A (aq) The r e a c t i o n of SO^ w i t h H 20 i s so f a s t t h a t any process i n which SO^ i s formed i n the moist atmosphere can be considered e q u i v a l e n t to the formation of s u l p h u r i c a c i d . However, the o x i d i z i n g r e a c t i o n i s so slow under c a t a l y s t - f r e e c o n d i t i o n s i n the gas phase t h a t i t can be neglected as a source of s u l p h u r i c a c i d generation i n the normal atmosphere. In f a c t , most of the gas-phase chemical r e a c t i o n s of S 0 2 and NO i n v o l v e a v a r i e t y of e x c i t e d molecules and f r e e r a d i c a l s which are generated by photo chemical and thermal r e a c t i o n s , i n i t i a t e d by s u n l i g h t a b s o r p t i o n of t r a c e gases i n the atmosphere. Obviously, these r e a c t i o n s are not l i k e l y to take p l a c e i n an underground environment w i t h no s u n l i g h t . The o x i d a t i o n of NO to N0 2 i n the atmosphere has been w e l l documented, and Harkins and Goodwine (47) determined t h a t the r a t e of conversion of NO to N0 2» o c c u r r i n g i n the s t a t i c atmosphere, could be p r e d i c t e d u s i n g t h i s equation: 43 Table 5 from the Matheson gas book (45) e x e m p l i f i e s t h i s equation: TABLE 5 CONVERSION OF NO to N0„ NO Time to convert to NO^ Concentrat i o n (PPM) 25% 50% 90% 1000 1-4 min 4 min 3-6 min 100 14 min 40 min 6 hrs 10 2-3 hrs 7 hrs 63 hrs 1 24 hrs 72 hrs 648 hrs Dainty's group (48) c a l c u l a t e d t h a t , at e q u i l i b r i u m , the conversion r a t e f o r an atmospheric NO conc e n t r a t i o n of 14.5 PPM would be 0.044 PPM/minute. At t h i s i n i t i a l c o n c e n t r a t i o n , the conversion of NO to NO^ would r e s u l t i n a f i n a l c o n c e n t r a t i o n of 1.2 PPM (.5 TLV) n i t r o g e n d i o x i d e a f t e r a one-hour residence. This i s o b v i o u s l y a concern of r e c i r c u l a t i o n p r a c t i c e s i n c e residence time f o r the percentage of the a i r r e c i r c u l a t e d w i l l be w e l l over one hour. However, i f d i l u t i o n i s taken i n t o c o n s i d e r a t i o n , a t 50% r e c i r c u l a t i o n under a normal working l e v e l NO con c e n t r a t i o n of 14.5 PPM, the NO con c e n t r a t i o n w i l l be reduced to 3.6 PPM (50% d i l u t i o n * 50% r e c i r c u l a t i o n * 14.5 PPM). I t w i l l take over 10 hours to convert 25% of t h i s amount. So, i t i s safe to say t h a t conversion of NO to NO^ w i l l be n e g l i g i b l e , i n a r e c i r c u l a t i o n system, a t normal d i e s e l exhaust c o n c e n t r a t i o n of 10-15 PPM ( a f t e r d i l u t i o n by the v e n t i l a t i o n a i r ) . d) Chemical r e a c t i o n s i n v o l v i n g c a t a l y s t s I n the o x i d i z i n g medium of the atmosphere and i n the presence of l i q u i d water, formation of the higher oxyacids ( s u l p h u r i c a c i d and n i t r i c a c i d s , r e s p e c t i v e l y ) from s u l f u r d i o x i d e and n i t r o g e n oxides (N0 x) i s s t r o n g l y favored thermochemically: 44 0 ? , H O , S0 2(g) — =-» 2IT + S£ 0 ? , H O NO(g), N0 2(g) — H + NO, However, under atmospheric c o n d i t i o n s , these r e a c t i o n s are q u i t e slow i n both the gaseous and aqueous ( d i s s o l v e d S 0 2 and NO^ i n water) phases d e s p i t e the strong thermodynamic d r i v i n g f o r c e . Dr. Novakov (49) has done a consi d e r a b l e amount of work l o o k i n g at carbon as the c a t a l y t i c f a c t o r i n a c i d gas r e a c t i o n s t h a t take place i n the atmosphere. He found t h a t the o x i d a t i o n of s u l f u r d i o x i d e i n the presence of carbon i n l i q u i d d r o p l e t s was a n e a r l y zero order r e a c t i o n which meant th a t the r e a c t i o n r a t e was n e a r l y independent of the S 0 2 c o n c e n t r a t i o n present. The presence of d i e s e l p a r t i c u l a t e matter could t h e r e f o r e be an important c a t a l y s t f o r the o x i d a t i o n of S 0 2 and p o s s i b l y N0 x« K i r k and S t e f a n i c h (50) determined the s u l p h u r i c a c i d l e v e l of p a r t i c u l a t e i n the Denison uranium mine i n E l l i o t Lake. The data suggested t h a t there were s i g n i f i c a n t amounts of s u l p h u r i c a c i d i n areas of t h i s d i e s e l i z e d mine which had adhered almost e n t i r e l y to dust p a r t i c l e s i n the r e s p i r a b l e range (up t o 23% by weight of r e s p i r a b l e d u s t ) . As a c o n c l u s i o n , i t can be s a i d t h a t , CO, C0 2 and a l l the hydrocarbons are very s t a b l e ( i . e . the o x i d a t i o n r a t e i s extremely slow and the s o l u b i l i t y i s n e g l i g i b l e ) , but some of the other gases can undergo ext e n s i v e chemical and p h y s i c a l changes as has j u s t been demonstrated. The extent of these changes i n the mine atmosphere needs to be assessed i n f u t u r e work, i n order to determine the f a t e of the gases as they pass through the mine workings. The b e n e f i t s of the removal mechanisms f o r r e c i r c u l a t i o n p r a c t i c e could then be determined. 45 4.2 PARTICULATE MATTER U n l i k e gases f o r which c o n c e n t r a t i o n i s c o n t r o l l e d mainly by d i l u t i o n , a d s o r b t i o n and chemical r e a c t i o n s , the con c e n t r a t i o n of airborne dust i s c o n t r o l l e d by d e p o s i t i o n and f i l t r a t i o n ( w i t h the exception of p a r t i c l e s much smaller than 1 um). L i t t l e c o n s i d e r a t i o n has been given to the modelling of dust behaviour i n a r e c i r c u l a t i o n system, except by Hardcastle (1985). Dr. Hardcastle presented an e x c e l l e n t paper (51) on the p r e d i c t i o n of airborne r e s p i r a b l e dust concentrations i n mine a i r r e c i r c u l a t i o n systems. The general equations t h a t were used i n h i s model are presented here: T h e o r e t i c a l l y , the a i r f l o w i n g i n the r e c i r c u l a t i o n c i r c u i t can be shown to be made up of elemental p a r t s t h a t are on t h e i r f i r s t , second, t h i r d , e t c . . .pass through the system. Each of these elements i s i n c r e a s i n g l y s maller as i t i s repeatedly cut by the r e c i r c u l a t i o n f a c t o r . At steady s t a t e these form the components of a geometric s e r i e s , QTR = Q l + F Q 1 + p 2 q l + ' ' ' + f I 1 q 1 = Q i / ( 1 _ F ) where, CL,., = T o t a l r e t u r n a i r q u a n t i t y a t steady s t a t e IK (note t h a t r e t u r n a i r means the a i r e x i t i n g the working place and not the a i r e x i t i n g the mine) Ql = i n t a k e a i r q u a n t i t y F = f r a c t i o n of r e t u r n a i r r e c i r c u l a t e d S i m i l a r l y , the r e t u r n dust flow (gm/sec) mass i s a l s o composed of s i m i l a r elemental p a r t s and t h e r e f o r e can a l s o be represented by a geometric composition, dTR " d R i + F d R i + *Xi +' • -+ F n d R i where, d_. = i n i t i a l dust flow (gm/sec) i n the r e t u r n a i r 46 Sedimentation can be represented by S and a l s o included i n the s e r i e s , dTR " ^ i + F d R i ( 1 " S ) + *\i ( 1 " S ) 2 +- • (1"S>n Here, the sedimentation f a c t o r i s constant f o r every pass the dust makes through the c i r c u i t . In r e a l i t y , sedimentation i s s i z e s e l e c t i v e and i t s e f f i c i e n c y w i l l decrease as the dust becomes depleted of the l a r g e s t p a r t i c l e s . Therefore the c o r r e c t s e r i e s i s , dTR = dRi + FdRiCl-S.) + F ^ R i Q - S - )(1-S„) +. .+FndRi(1-S,)(1-S„)..(1-S ) 1 1 Z 1 Z n or, dTR = d R i [ l + F . f ( l - S ) + F 2 f 2 ( l - S ) + . . + F n . f n ( l - S ) ] w i t h , S, > S„ > . . . > S 1 2 n and, F ( l - S ) = 1-S, F 2 ( l - S ) = ( l - S ^ d - S ^ , e t c . . . Example: I f the decay r a t e of the sedimentation e f f i c i e n c y was constant at 0.5 (50% ) , then would be equal to .5S^ and S^ equal to .5*.5*S 1, (and so on). The gas contaminant models t h a t were presented i n the e a r l i e r s e c t i o n s , were not presented i n the form of a geometrical s e r i e s because the removal processes f o r the gases were not considered. But i f these processes were represented by a f a c t o r such as X (where X could represent the removal processes), then S could be replaced by S i n the previous geometrical s e r i e s . The s e r i e s would represent the maximum gas con c e n t r a t i o n mass flow i n the r e t u r n branch. The mathematical equation was used by Hardcastle to create a r e c i r c u l a t i o n s i m u l a t i o n program which w i l l be considered i n chapter 8 of t h i s t h e s i s . The problem w i t h t h i s equation i s th a t i t does not provide any i n f o r m a t i o n on the t y p i c a l values f o r sedimentation. The sedimentation of p a r t i c u l a t e matter can take p l a c e under the f o l l o w i n g 47 mechanisms: a) g r a v i t a t i o n a l s e t t l i n g b) i n e r t i a l s e t t l i n g c) d i f f u s i o n d) c o a g u l a t i o n a) G r a v i t a t i o n a l S e t t l i n g G r a v i t a t i o n a l d e p o s i t i o n of dust p a r t i c l e s i s c h a r a c t e r i z e d by Stoke's law ( 52 ) . The s e t t l i n g tendency of a p a r t i c l e can be represented by i t s t e r m i n a l s e t t l i n g v e l o c i t y , a c o n d i t i o n where the drag f o r c e of the a i r on the p a r t i c l e w i l l be e x a c t l y equal and opposite to the f o r c e of g r a v i t y . The s e t t l i n g v e l o c i t y i s equal t o : P_ d 2g V = (1) TS 18n v ' where, VTS = Terminal s e t t l i n g v e l o c i t y of the p a r t i c l e P = d e n s i t y of p a r t i c l e d = p a r t i c l e diameter g = f o r c e of g r a v i t y n = v i s c o s i t y of the a i r Terminal s e t t l i n g v e l o c i t y increases r a p i d l y w i t h p a r t i c l e s i z e , being p r o p o r t i o n a l to the square of p a r t i c l e diameter. However, the equation above i s not c o r r e c t f o r p a r t i c l e s s m a l l e r than 1 um where there i s an i n t e r a c t i o n between the p a r t i c l e s and the gas. For such p a r t i c l e s , a c o r r e c t i o n f a c t o r which increases w i t h the s i z e of the p a r t i c l e must be a p p l i e d , 2.52 n C = 1 + — c d (2) 48 where, C = Cunningham c o r r e c t i o n f a c t o r c ° D = mean f r e e path of the a i r d = p a r t i c l e diameter By applying t h i s c o r r e c t i o n to equation 1 we o b t a i n , P d 2gCe VTS= ~£mT (3) Fuchs (53) has considered t h e o r e t i c a l d e p o s i t i o n of dust i n tunnels under the a c t i o n of g r a v i t y and gives the equation, E = V T S L / 2hu (4) where, E = dust p r e c i p i t a t i o n e f f i c i e n c y L = le n g t h of the t u n n e l h = height of the tunne l u = mean a i r v e l o c i t y Knight and Hardcastle (54) rearranged the equation f o r both laminar and t u r b u l e n t f l o w , VTS*A E = 2Q E = 1 - exp VTS A [2Q] laminar flow (5) t u r b u l e n t flow (6) where, A = t o t a l f l o o r area of the roadway Q = volume of a i r flow 49 I t i s important to apply a s i z e c o r r e c t i o n f a c t o r before VTS can be used i n equations 5 and 6. Equation 3 i s based on s p h e r i c a l p a r t i c l e s . However, dust i s n o n s p h e r i c a l and w i l l s e t t l e more s l o w l y . The t e r m i n a l s e t t l i n g v e l o c i t y must be d i v i d e d by a f a c t o r of 1.10 f o r c o a l to 1.36 f o r quartz p a r t i c l e s . Knight and Hardcastle (54) used the above equation to compare s e t t l i n g e f f i c i e n c i e s of d i f f e r e n t p a r t i c l e s i z e s f o r two d i f f e r e n t roadways. The r e s u l t s are presented i n Table 6. I t can be seen t h a t i n the most common type of airway, those w i t h an area to flow r a t i o of about 600, most of the coarse dust i s deposited, whereas most of the r e s p i r a b l e dust remains suspended and can penetrate other p a r t s of the v e n t i l a t i o n system. A l s o , f o r t u r b u l e n t flow (predominant i n a mine network) there i s a s l i g h t decrease i n sedimentation e f f i c i e n c y f o r coarse dust. b) I n e r t i a l S e t t l i n g I n e r t i a l s e t t l i n g i s a very important mechanism f o r coarse p a r t i c l e s . In t h i s process, p a r t i c l e s w i t h s u f f i c i e n t i n e r t i a are unable to f o l l o w the streamlines of the a i r cur r e n t when the flow i s d e f l e c t e d , and w i l l impact on the w a l l s of the t u n n e l . The author could not f i n d any t h e o r e t i c a l s o l u t i o n f o r the i n e r t i a l s e t t l i n g of dust i n tunnels or mine roadways. Hinds (52) presented a t h e o r e t i c a l s o l u t i o n f o r i n e r t i a l impactors which could be a p p l i e d f o r a case where the a i r flow i s d e f l e c t e d by a change i n the d i r e c t i o n of a t u n n e l . The equations, which are very complex, are not presented here and Hinds work i s an e x c e l l e n t reference f o r the i n t e r e s t e d reader. There are other f a c t o r s i n mines, such as w a l l roughness, s t r u c t u r e s and loose r o c k s , which w i l l c r eate o b s t a c l e s t h a t can s i g n i f i c a n t l y i n c r e a s e i n e r t i a l impaction. A t h e o r e c t i c a l a n a l y s i s of such f a c t o r s i s almost impossible. E m p i r i c a l formulas should be de r i v e d from f i e l d i n v e s t i g a t i o n . TABLE 6 GRAVITATIONAL SETTLEMENT LOSSES P a r t i c l e Aerodynamic Diameter jam Fractional P a r t i c l e Loss to Floor from Settlement Roadway 1, A/Q = 600 Roadway 2, A/Q = 15 Laminar Turbulent Laminar Turbulent 1 0.01 0.01 0.0003 0.0003 2 0.04 0.04 0. 001 0.001 5 0. 24 0.21 0.006 0. 006 10 0 . 69 0 . 6 0. 02 0 . 02 15 1 0 . 9 0. 05 0. 05 20 1 0.97 0.1 0.1 50 1 1 0.5 0.4 100 1 1 1 0.85 * Roadway 1 - 3 x 6 m cross-section, 1,000 m long, 10 m 3/sec ai r f l o w A/Q = 6 Roadway 2 - 2 x 3 m cross-section, 100 m long, 20 m 3/sec airlfow A/Q = 15 51 Knight and Hardcastle (54) presented two s t u d i e s by Ford (55) and Reinhardt (56) i n c o a l mines to i n v e s t i g a t e the r e s p i r a b l e s i z e dust d e p o s i t i o n w i t h i n a heading. The r e s u l t s showed considerable d e p o s i t i o n over 100 L/dh (300m); where L i s l e n g t h and dh h y d r a u l i c diameter. The authors used the t e r m i n a l s e t t l i n g v e l o c i t i e s given by Ford and Reinhardt to c a l c u l a t e the sedimentation using the same roadways presented i n Table 6. They found con s i d e r a b l e d i s c r e p a n c i e s between t h e o r e t i c a l g r a v i t a t i o n a l s e t t l i n g and measured sedimentation (between 10-20% settlement by t h e o r e t i c a l c a l c u l a t i o n and between 30-60% settlement w i t h f i e l d d a ta). The authors d i d not say i f the t e r m i n a l s e t t l i n g v e l o c i t i e s were c o r r e c t e d f o r the d i f f e r e n c e i n s i z e c o r r e c t i o n f a c t o r , f o r the c o a l dust used i n the t h e o r e t i c a l study ( f a c t o r 1.10) and i n o r g a n i c m i n e r a l dust monitored i n the f i e l d ( f a c t o r 1.36). However, even t h i s o v e r s i g h t would not j u s t i f y the discrepancy. Knight and Hardcastle e x p l a i n e d t h a t i n e r t i a l settlement was probably r e s p o n s i b l e f o r such d i f f e r e n c e s . c) D i f f u s i o n For very s m a l l p a r t i c l e s (< .1 um), the incessant bombardment of gas molecules w i l l cause the p a r t i c l e s to "wiggle" (52) i n s t i l l a i r . This w i g g l i n g motion of the dust i s c a l l e d Brownian motion. The net t r a n s p o r t (under the e f f e c t of Brownian motion) of these p a r t i c l e s from a r e g i o n of h i g h c o n c e n t r a t i o n to a region of lower c o n c e n t r a t i o n i s c a l l e d d i f f u s i o n . This t r a n s p o r t w i l l cause p a r t i c l e s to deposit on the s u r f a c e w a l l s of the roadway. Hinds (52) c a l c u l a t e d the r a t e at which p a r t i c l e s were removed from the a e r o s o l by d i f f u s i o n onto a surface. He found t h a t a f t e r 16 minutes the c o n c e n t r a t i o n of dust had not been a f f e c t e d beyond 6 mm from the w a l l . He concluded t h a t the process would not r a p i d l y deplete the dust c o n c e n t r a t i o n i n the a i r except where the dimension s c a l e was i n the order of 1 mm or s m a l l e r , or the p a r t i c l e s i z e s i g n i f i c a n t l y l e s s than 0.05 um. 52 Knight and H a r d c a s t l e (54) c a l c u l a t e d l o s s e s due to d i f f u s i o n i n two h y p o t h e t i c a l roadways using the s o l u t i o n given by Fuchs (53). The r e s u l t s (Table 7) show t h a t d i f f u s i o n l o s s e s to the w a l l s of the chamber only become s i g n i f i c a n t f o r very f i n e p a r t i c l e s . A paper by Hahn et a l (57) i n v e s t i g a t e d the t u r b u l e n t d e p o s i t i o n of submicron p a r t i c l e s on rough w a l l s . Their experimental t e s t s proved to be c o n s i s t e n t w i t h the t h e o r e t i c a l a n a l y s i s of Kader and Yaglom (58). They concluded t h a t t u r b u l e n t d e p o s i t i o n of submicron p a r t i c l e s was much greater f o r rough surfaces than f o r smooth surfaces and the a n a l y s i s by Kader and Yaglom should be used to p r e d i c t the r a t e of decay of submicron air b o r n e p a r t i c l e s i n uranium mines. d) Agglomeration Agglomeration i s a process whereby p a r t i c l e s c o l l i d e w i t h one another due to a r e l a t i v e motion between them and adhere to form l a r g e r p a r t i c l e s . The net r e s u l t i s a continuous decrease i n number concentration and an increase i n p a r t i c l e s i z e . Agglomeration of p a r t i c u l a t e i n the concentrated d i e s e l engine exhaust i s s i g n i f i c a n t i n modifying the p a r t i c l e s i z e d i s t r i b u t i o n r e l e a s e d to the atmosphere. Once the dust c o n c e n t r a t i o n has been d i l u t e d w i t h the v e n t i l a t i o n a i r i t i s b e l i e v e d t h a t agglomeration i s i n s i g n i f i c a n t s i n c e p a r t i c l e to p a r t i c l e i n t e r a c t i o n i s g r e a t l y reduced. This should be i n v e s t i g a t e d i n more d e t a i l . Deshler (61) i n v e s t i g a t e d the r a t e at which submicron p a r t i c l e s are scavenged by water d r o p l e t s . His experimental measurements agreed w i t h t h e o r e t i c a l work by Wang et a l (62) and showed th a t the agglomeration of p a r t i c l e s onto a water d r o p l e t decreased r a p i d l y w i t h i n c r e a s i n g humidity ( F i g . 1 0 ) . For metal mines, w i t h humidity of over 80%, scavenging of submicron p a r t i c l e s by water d r o p l e t s w i l l probably be i n s i g n i f i c a n t . Another major dust d e p o s i t i o n mechanism which has been found to occur i s i n ascending airways. Knight and H a r d c a s t l e (55) commented t h a t T A B L E 7 D I F F U S I O N L O S S E S . . Fractional Loss to Walls from D i f f u s i o n P a r t i c l e Roadway 1 Roadway 2 S l Z e L/Q - 100 B/h - 2 L/Q - 5 B/h - 1.5 v t n Eq: 12 14 13 12 14 13 0.1 _1 - - - - -0.01 .001 .003 .0002 - - ' -0.001 .03 .07 .015 .004 .006 .0005 0.0001 .55 .95 .31 .09 .12 .03 Note 1: Diffusion losses are ne g l i g i b l e for p a r t i c l e size above 0.01 um. U> 54 Scavenging rate of water drops for sub-micron aerosols R A D I U S (Mm) Theoretical collection kernels for different humidities compared with measurements of the collection kernel made using a fluorescent aerosol. The letters display the average of two measurements at the humidities indicated, and are centered on the volume mean radius of the aerosol sample. The error bars represent the cumulative effect of uncertainties in the measurement of experimental quantities needed to determine the collection kernel. (After Deshler, 1985) Fig. 10 55 a d i a b a t i c expansion can l e a d to condensation of the moisture i n the a i r which would r e s u l t i n a f i l t r a t i o n of the dust by suspended water d r o p l e t s (much l i k e the water sprays). I n summary i t can be s a i d that dust i n the a i r can be separated i n t o two f r a c t i o n s : mineral dust and d i e s e l p a r t i c u l a t e matter. A l a r g e p o r t i o n of the r e s p i r a b l e dust i s over 1 um i n s i z e . I n e r t i a l and g r a v i t a t i o n a l sedimentation w i l l be very e f f e c t i v e i n removing t h i s f r a c t i o n from the r e c i r c u l a t i o n system. Most of the d i e s e l p a r t i c u l a t e matter i s under 1 um. D i l u t i o n and f i l t r a t i o n (by a mechanical means) coul d be e f f e c t i v e i n removing over 70% of d i e s e l p a r t i c u l a t e i n a r e c i r c u l a t i o n system. The behaviour of submicron p a r t i c l e s under the i n f l u e n c e of phenomena such as d i f f u s i o n and c o a g u l a t i o n needs to be i n v e s t i g a t e d f u r t h e r . 56 5.0 MATHEMATICAL MODELLING OF DIESEL EXHAUST CONTAMINANTS Since v e n t i l a t i o n requirements i n most Canadian mines are set by the amount of d i e s e l equipment being operated, the safe l e v e l s of r e c i r c u l a t i n g a i r q u a n t i t i e s w i l l be a f u n c t i o n of the build-up of d i e s e l contaminants. C u r r e n t l y , there i s i n s u f f i c i e n t f i e l d data showing the r e l a t i o n s h i p between d i e s e l contaminant concentrations produced i n the e n t i r e mine network and d i e s e l contaminant concentrations found i n the exhaust a i r . As a r e s u l t , p r a c t i c a l a n a l y s i s of the i n f l u e n c e of r e c i r c u l a t i o n on p o l l u t a n t l e v e l s i s not p o s s i b l e . I t i s necessary t h e r e f o r e , to use computer modelling i n order to simulate the d i f f e r e n t p o s s i b l e c o n d i t i o n s . The author reviewed the l i t e r a t u r e on d i e s e l contaminant s i m u l a t i o n and found very l i t t l e r e l e v a n t i n f o r m a t i o n . However, a r e p o r t by Stefanko et a l proved to be very i n s p i r i n g . Stefanko e t a l (61) have reported on a model t h a t was developed through a grant from the U.S. Bureau of Mines to simulate d i e s e l exhaust contaminants produced by m u l t i p l e d i e s e l v e h i c l e s i n a network of airways. The main assumptions of the model are: a. Turbulent flow of a i r i n the roadways w i t h a uniform v e l o c i t y d i s t r i b u t i o n , consequently the d i e s e l exhaust i s assumed to be un i f o r m l y mixed across the roadway c r o s s - s e c t i o n . b. The flow of a i r and d i e s e l exhaust i s steady. c. V a r i a t i o n s i n temperature and pressure are not s u f f i c i e n t to cause any d e n s i t y change. The program i s d i v i d e d i n t o two p a r t s : -1) S o l u t i o n of the network f o r q u a n t i t y of a i r i n each branch 2) C a l c u l a t i o n of the contaminant concentrations i n each branch and at each j u n c t i o n . 57 The f i r s t p a r t i s r e s o l v e d w i t h an incompressible a i r v e n t i l a t i o n program developed by Wang and S a p e r s t e i n (62). For the second p a r t , the production l e v e l concentrations are c a l c u l a t e d using time-averaged concentrations of d i e s e l exhaust w h i l e an i t e r a t i o n model i s used to c a l c u l a t e s t e a d y - s t a t e flow throughout the network. A f t e r reviewing the model, the requirements of the computer program th a t would be used f o r the p r o j e c t were determined. They are as f o l l o w s : a. Flow Model The v e n t i l a t i o n program f o r s o l v i n g the flow d i s t r i b u t i o n i n the network should provide a s o l u t i o n f o r compressible a i r problems. b. C y c l i c Model A c y c l i c contaminant production model corresponding to the duty c y c l e would be more appropriate than a time-averaged contaminant conc e n t r a t i o n model. Using t h i s concept, a program generating the upper l i m i t s of each t o x i n , i n s t e a d of an average, could be created. This i n t u r n would provide a b e t t e r f e e l of the a c t u a l behaviour of the d i e s e l by-products i n the network. c. Real-time c a l c u l a t i o n Since r e s u l t s are only as accurate as input data and underground time s t u d i e s are seldom pu b l i s h e d , i t i s impossible to use r e a l - t i m e c a l c u l a t i o n . R e s u l t s would be meaningless and computer time excessive. d. Monte Carlo S i m u l a t i o n I t i s c l e a r t h a t the use of Monte Carlo s i m u l a t i o n would provide the best s o l u t i o n . The model would p r e d i c t c y c l i c exhaust l e v e l s without i n v o l v i n g a time f a c t o r , A convenient way 58 to simulate a c y c l i c p a t t e r n without c o n s i d e r i n g time, i s to use a random number generator that generates emission values from a c y c l i c exhaust c o n c e n t r a t i o n t a b l e (Monte Carlo s i m u l a t i o n ) . In t h i s manner, the network s i m u l a t i o n can show the trend of the r e c i r c u l a t e d contaminants and give the value of the peak waves. The peak value w i l l be an important c o n s i d e r a t i o n i n the case of a v e h i c l e moving i n the same d i r e c t i o n as the a i r c u r r e n t at s i m i l a r v e l o c i t y where the same a i r w i l l be p o l l u t e d s e v e r a l times. A model s a t i s f y i n g these requirements was w r i t t e n . The model i s a subroutine of the Canmet V e n t i l a t i o n Program (63) and uses a Monte Carlo s i m u l a t i o n to generate emission values. 5.1 CASE STUDY USING THE RECIRCULATION MODEL 5.1.1 I n t r o d u c t i o n In order to p r e d i c t the safe r e c i r c u l a t i o n range, s e v e r a l d i f f e r e n t r e c i r c u l a t i o n percentages were simulated. The mine chosen f o r the t e s t was a s m a l l gold mine i n Northern Quebec operated by Falconbridge Copper Lt d . The v e n t i l a t i o n network f o r t h i s mine i s i l l u s t r a t e d i n F i g u r e 11. Table 8 shows the equipment operated by t h i s mine and the volume of a i r recommended by USBM Schedule 24 (64). The p r e d i c t e d volume i n each branch was c a l c u l a t e d by using 100% of the schedule 24 values f o r the most p o l l u t i n g engine i n the branch, 75% f o r the second most p o l l u t i n g and 50% f o r the others. S p e c i a l areas such as the crusher l e v e l and garages were assigned volumes s t i p u l a t e d by the mining act and the network was balanced w i t h Canmet 1s V e n t i l a t i o n Program. * EQUIPMENT LOCATION R REGULATOR 60 TABLE 8 Fresh a i r volumes r e q u i r e d V e h i c l e Motor HP Schedule 24 (USBM) cfm 1 S e r v i c e v e h i c l e : Deutz F6L912W 84 9 000 4 3 Scoop-trams 5 yd : Deutz F8L714 180 4 x 20 000 2 13 ton t r u c k s : Deutz F8L714 180 2 x 20 000 2 jumbo d r i l l s : Deutz F6L912W 78 2 x 9 000 2 u t i l i t y t r u c k s : Deutz F6L912W 78 2 x 9 000 1 grader : Deutz 912W 78 9 000 TOTAL 1 554 173 000 The most d i f f i c u l t p a r t of the s i m u l a t i o n was to produce the c y c l i c exhaust c o n c e n t r a t i o n t a b l e s . Exhaust emission data corresponding to the 6 phases of the operating c y c l e determined by Stewart,Dainty & Mogan (65) f o r the d i f f e r e n t engines used i n Canadian mines are v i r t u a l l y n on-existent. For a l l the equipment used i n the Quebec mine (Table 8 ) , r e l i a b l e data was only a v a i l a b l e f o r the Deutz F8L714 (Table 9). I t was th e r e f o r e decided to use the Deutz data f o r a l l equipment and reduce the value of emissions by the horsepower r a t i o . Example: Emission data f o r the Deutz 912W *(78hp/180hp) = Emission f o r Deutz F8L714 61 TABLE 9 Deutz F8L714 Engine Mass-Emissions For LHP Cycle Phases Exhaust Emissions CO NO P a r t i c u l a t e Phase bhp* rpm g/bhp-hr g/bhp-hr g/bhp-hr 1 121 2 000 1.4 2.5 0.46 2 101 1 625 1.0 2.5 0.60 3 102 2 300 1.1 4.2 0.39 4 129 2 200 1.7 2.8 0.42 5 49 1 500 1.7 6.7 0.23 6 118 2 300 1.1 3.4 0.38 "bhp = torque x rpm 5252 5.1.2 P r e s e n t a t i o n of r e s u l t s A l l the s i m u l a t i o n r e s u l t s are presented i n Appendix 1. The data f o r the most p o l l u t e d branch only (branch 24-25 i n Fig.11) are p l o t t e d . For each s i m u l a t i o n a wave i s r e c i r c u l a t e d through the system 11 times. The gas f i g u r e s , are a i r q u a l i t y index values presented by French and As s o c i a t e s (40). The p a r t i c u l a t e concentrations i n the underground area w i t h the worst c o n d i t i o n s always exceed the TLV value (1.5 mg/M ) w i t h or without r e c i r c u l a t i o n . These hig h concentrations are d i r e c t l y r e l a t e d to the high p a r t i c u l a t e output t h a t was used i n the model f o r a l l equipment and to the f a c t t h a t i n schedule 24, the d i l u t i o n q u a n t i t i e s s t i p u l a t e d are based on gas concentrations at the exhaust pipe. The values w i l l o b v i o u s l y have to be r e v i s e d to take i n t o c o n s i d e r a t i o n the p o t e n t i a l l y more t o x i c p a r t i c u l a t e s . Sulphur d i o x i d e concentrations were a l s o simulated, but s i n c e the r e s u l t s are always lower than the TLV-SO^, they are not presented. 62 The graphed r e s u l t s i n the Appendix are i l l u s t r a t e d such t h a t the l i g h t area represents the c o n c e n t r a t i o n i n the branch w i t h 100% of the a i r being exhausted to the atmosphere and the dark area represents the c o n c e n t r a t i o n reached due to r e c i r c u l a t i o n . Since the generation r a t e f o r a l l d i e s e l engines i s c y c l i c , the e q u i l i b r i u m concentrations are a l s o c y c l i c . As a r e s u l t each wave, even f o r the n o - r e c i r c u l a t i o n c o n d i t i o n s , w i l l vary, but only on an average of 5-10%. R e c i r c u l a t i o n c o n c e n t r a t i o n values build-up r a p i d l y at f i r s t then more s l o w l y u n t i l they reach steady-state (where the dark area i s c o n s i s t e n t from one wave to the n e x t ) . This s t e a d y - s t a t e i s a t t a i n e d sooner at lower r e c i r c u l a t i o n percentages. For both the AQI(gas) and p a r t i c u l a t e s , the i n c r e a s e i n c o n c e n t r a t i o n i s not p r o p o r t i o n a l to the increase i n percentage r e c i r c u l a t e d . The increase i n c o n c e n t r a t i o n i s shown below: % RECIRCULATION % CONTAMINATION BUILD-UP IN BRANCH 24-25 10 5 30 22 50 55 70 125 The gas AQI values at 10% and 30% r e c i r c u l a t i o n are below the l i m i t of 1.0, but at 50% and 70% they are greater than 1.0, exceeding t o l e r a b l e l i m i t s . From the r e s u l t s i t could be argued t h a t i t i s j u s t as good to reduce the i n t a k e by say, 30%, i n s t e a d of r e c i r c u l a t i n g t h a t amount s i n c e the increas e i n contamination (20%) i s about the same. This i s probably t r u e f o r a new mine, l i k e the one simulated, s i n c e the d i l u t i o n i s minimal. But leakage w i l l make q u i t e a d i f f e r e n c e f o r mines t h a t have been i n operation f o r s e v e r a l years. A l s o , the model does not take i n t o c o n s i d e r a t i o n the many s i n k s and removal mechanisms presented i n the preceding chapter. I t was shown th a t f o r dust, n i t r o g e n oxides and s u l f u r d i o x i d e , these f a c t o r s could decrease the r e c i r c u l a t e d concentrations s i g n i f i c a n t l y . I t should be pointed out the s i m u l a t i o n assumes t h a t a l l the equipment i s operating c o n s t a n t l y during the s h i f t . However, underground time s t u d i e s have demonstrated t h a t down time can be 63 s i g n i f i c a n t . This w i l l decrease the t o t a l contaminants being produced simultaneously i n the mine. The model used a Monte-Carlo s i m u l a t i o n , because the author thought i t was important t o d i f f e r e n t i a t e between the v a r i o u s c y c l e modes of the engine. But the sm a l l change i n co n c e n t r a t i o n (5%-10%) between each pass through the r e c i r c u l a t i o n system i n d i c a t e t h a t the model does not need to simulate each mode's emission c h a r a c t e r i s t i c s . Instead, i t should take the average exhaust emission. A more u s e f u l model would simulate the gas and dust removal processes t h a t can take p l a c e i n the r e c i r c u l a t i o n c i r c u i t . This would form, i n the author's view, an e x c e l l e n t t o p i c f o r a d o c t o r a l t h e s i s . 64 6.0 FIELD STUDY 6.1 SITE OF STUDY Over a three-week p e r i o d , i n June 1986, the UBC Mining and M i n e r a l Process Engineering Department conducted a study at S h e r r i t t Gordon's Ruttan o p e r a t i o n . The research was designed to provide i n f o r m a t i o n on the behaviour of p o l l u t a n t s between the mine workings and the surface exhausts i n order to determine the f e a s i b i l i t y of r e c i r c u l a t i o n f o r metal mines. The Ruttan Mine i s an e x c e l l e n t s i t e f o r the survey s i n c e i t s t o t a l 3 v e n t i l a t i o n volume i s approximately 330 m /s and the mining has now been extended to the 1 ower s e c t i o n of the mine (490m l e v e l to the 800m l e v e l ) . D i r e c t f i r e d propane heaters are u t i l i z e d to heat the in t a k e a i r during the w i n t e r at a cost of c l o s e to $lM/year. The primary v e n t i l a t i o n system, shown i n Figure 12, c o n s i s t s of a 7.6m diameter intak e r a i s e i n the f o o t w a l l and two 4.9m diameter exhaust r a i s e s i n the hanging-wall. These r a i s e s , d r i v e n v e r t i c a l l y from 260m l e v e l to s u r f a c e , i n d i v i d u a l l y , form the main a r t e r i a l s f o r the intake and exhaust systems. From 260m l e v e l the intake system conveys some a i r to 430m l e v e l v i a a smaller diameter r a i s e w h i l e the b u l k of the a i r goes down a 3.66m diameter r a i s e to 730 and 800m l e v e l s , the deepest p r o d u c t i o n l e v e l s of the mine. These two l e v e l s s et i n p a r a l l e l connect to the bottom of the east i n t a k e r a i s e , from where a i r i s d i s t r i b u t e d to a l l the remaining working l e v e l s . As i t ascends to surface the a c t u a l a i r flow on the l e v e l s i s from east to west and from f o o t w a l l to hanging-wall i n a l l cases ( F i g . 1 2 ) . The e f f i c i e n c y of the Ruttan v e n t i l a t i o n system i n terms of the u t i l i z a t i o n made of the t o t a l amount of a i r drawn through the mine i s approximately 55%. The lower mine v e n t i l a t i o n system was not e n t i r e l y completed at the time of our survey. The 800-611 (east) in t a k e which i s to convey the a i r 65 562 MAIN INT 4x250 HP SHELDON FANS 546 EX V/R 3X125HP JOY FANS 542 EX. V/R 2X125HP JOY FANS 567 EX. V/R 3x150HP SHELDON FANS RAMP J n n SHAFT SURFACE INTAKE ^EXHAUST EXISTING «— PROPOSED Ruttan Mine Ventilation Circuit for 260.00 m^s Ascensional Pattern }'&g620mL geeomL I -> 14p730mL • J 800mL  860mL Fig. 12 66 on a l l lower l e v e l s and the 660-551 west exhaust r a i s e were not o p e r a t i o n a l . Therefore, the a i r was d i r e c t l y provided on each l e v e l from the main i n t a k e r a i s e and exhausted v i a the 660-586 exhaust. In t h i s system, there was l i m i t e d a i r reaching the lower l e v e l s and the a i r was u t i l i z e d to i t s l i m i t . In choosing s i t e s f o r the monitoring program, the f o l l o w i n g c r i t e r i a were considered: 1. The deepest l e v e l s of the mine must be monitored, as the i n f l u e n c e of sedimentation, humidity, time and d i l u t i o n w i l l be maximized on the contaminants behavior between these l e v e l s and s u r f a c e . 2. One s i t e should be s i t u a t e d i n the most p o l l u t e d area of the mine as i t i s e s s e n t i a l to monitor the extreme c o n d i t i o n s . 3. In a d d i t i o n to t h i s s i t e there should be a s i t e i n the surface exhaust and an intermediate s i t e to e s t a b l i s h the extent of d i l u t i o n and other c o n d i t i o n s a f f e c t i n g the gas and dust c o n c e n t r a t i o n s . The worst c o n d i t i o n s s i t e was e s t a b l i s h e d i n the 586 exhaust on 660 l e v e l ( F i g . 1 3 ) . This area was r e c e i v i n g contaminated a i r from 800 and 660 l e v e l s . On both of these l e v e l s , there were two scooptrams working i n s e r i e s w h i l e the a i r q u a n t i t i e s should have only supported one d i e s e l . As a r e s u l t the a i r was over used. This c o n d i t i o n was r e c t i f i e d s h o r t l y a f t e r the survey, when the new east i n t a k e (800-611) and west exhaust (660-551) became o p e r a t i o n a l . The intermediate s i t e was e s t a b l i s h e d i n the 586 exhaust on 370 l e v e l (Fig.14) and the surface s t a t i o n on 567 exhaust on the exhaust s i d e of the fans. The 567 exhaust i s the upper l e v e l extension of 586 exhaust ( F i g . 1 5 ) . The r e s u l t s f o r the gas and dust survey are presented here i n two d i f f e r e n t s e c t i o n s . Fig. 15 RUTTAN MINE RAISE S C H E M A T I C 567 E X H A U S T 1 0 k — »R~' S U R F A C E 2S0 k -4k 60k » R -5 k — » R -25 k 1 R •* 32k II I 124 k 62 k 5k-57 k-±±1, L E G E N D : R - r e g u l a t o r •* a i r f l o w j. - ven t c u r t a i n OO - f a n • - p o s i t i o n of s a m p l i n g s t a t i o n s 250 320 370 430 490 550 620 660 2 730 o w a s t e M± mm !£i 860 70 6.2 GAS CONCENTRATION STUDY 6.2.1. Instrumentation The f o l l o w i n g instrumentation was provided by the mine and CANMET f o r gas monitoring: 1. ECOLYSER 7000 SERIES f o r monitoring of CO and N0 2 2. ECOLYSER 7000 SERIES f o r monitoring of NO and N0 2 3. ECOLYSER 6000 SERIES f o r monitoring of CO 4. FUJI ZFP5 f o r monitoring of C0 2 5. C a l i b r a t i o n gases (3.5ppm f o r N0 2 > 66ppm f o r CO and 800ppm f o r C0 2) 6. 5 Rustrak s t r i p chart recorders 7. Short term draeger tubes f o r a l l gas contaminants The Ec o l y s e r instruments use an e l e c t r o c h e m i c a l c e l l to measure the gas l e v e l s . Johnson evaluated these instruments (66) under a USBM co n t r a c t . The r e s u l t s showed t h a t mean e r r o r s of over 20% f o r CO and 15% f o r NO and N0 2 were p o s s i b l e . The instruments are a l s o very unstable and i d e a l l y r e q u i r e r e - z e r o i n g and a spanning check every four hours. The advantage of the instruments i s t h a t they are easy to use and are p o r t a b l e . The h u m i d i f i e r i s r e q u i r e d to prevent the c e l l from d r y i n g out, but i s a problem i f i t i s not p r o p e r l y secured as i t can t i p and water can plug the gas l i n e and pump. I t was a l s o discovered e a r l y i n the study t h a t the e l e c t r o c h e m i c a l c e l l s f o r one of the CO and NO sensors were not working p r o p e r l y as i t was not p o s s i b l e to adj u s t the zero and span readings. These sensors were omitted from the survey. The instruments were c a l i b r a t e d every four hours w i t h Matheson c a l i b r a t i o n gases ( c e r t i f i e d standard w i t h 2% accuracy). A recent r e p o r t from CANMET (67) mentions t h a t N0 2 span gas i s unstable and should be checked before a survey. However, t h i s was not considered necessary s i n c e the c a l i b r a t i o n , gas was prepared a week before the survey. The C0 2 F u j i sensor uses an i n f r a r e d technique (NDRl) to measure the co n c e n t r a t i o n . This instrument i s very s t a b l e and does not r e q u i r e 71 frequent c a l i b r a t i o n . Johnson (68) estimates the mean e r r o r to be l e s s than 3%. 6.2.2 R e s u l t s I t would have been i d e a l to measure simultaneously the p o l l u t a n t concentrations i n the surface exhaust and on 370 and 660 l e v e l s i n order to compare the r e s u l t s . Due to the a v a i l a b l e i n s t r u m e n t a t i o n , the d i f f e r e n t s t a t i o n s were monitored one at a time. At every s h i f t a l l the s h i f t boss 1 r e p o r t s were examined to v e r i f y the amount of d i e s e l equipment operating on the l e v e l s connected to the 586 exhaust. At the end of the survey only the f o u r s h i f t s w i t h i d e n t i c a l d i e s e l equipment operating on the c r i t i c a l l e v e l s were used to compare the r e s u l t s of the three s e c t i o n s . The r e g u l a t o r s and doors were not monitored and i t i s c l e a r t h a t i n some cases, d i f f e r e n t a i r q u a n t i t i e s c i r c u l a t e d through the 586 exhaust on d i f f e r e n t s h i f t s . A l l the values recorded were entered manually i n t o computer memory on an IBM Pc-xt and a chart f o r each s h i f t and p o l l u t a n t was generated using a graphic package. A l l the charts are included i n Appendix 2. The r e s u l t s are presented i n a s i m p l i f i e d form i n Table 10. N i t r i c oxide c o n c e n t r a t i o n was not monitored as the e l e c t r o c h e m i c a l c e l l had to be replaced and t h i s was not p o s s i b l e w i t h i n the time p e r i o d r e q u i r e d . 6.2.3 D i s c u s s i o n I t can be seen from the r e s u l t s t h a t the d i l u t i o n of contaminant c o n c e n t r a t i o n , as they r i s e from the lower l e v e l s to s u r f a c e , i s c o n s i d e r a b l e . In a d d i t i o n , the impact of the removal mechanisms covered i n chapter 5 can be appreciated by the amount of the N0 2 removal t h a t occurred. The CO i s reduced by approximately 40-50% (due to d i l u t i o n ) w h i l e N0 2 i s reduced by more than 75%. The C0 2 r e s u l t s confirm the CO values as the concentrations are a l s o reduced by approximately 50%. CO and C0„ are very s t a b l e and do not undergo s i g n i f i c a n t chemical changes 72 as they ascend i n the exhaust r a i s e . The r e s u l t s show t h a t CO i s the p o l l u t a n t t h a t w i l l determine the percentage of r e c i r c u l a t i o n t h a t could be t o l e r a t e d at Ruttan. TABLE 10 Re s u l t s of Gas Sampling a t Ruttan CONCENTRATION (PPM) LEVEL SHIFT MIN MAX AVERAGE DATE CO SAMPLING: 660 afternoon 24 60 41 12/06/86 660 day 16 88 52 12/06/86 660 day 18 84 44 13/06/86 660 n i g h t 20 50 34 13/06/86 Average: 20 70 43 370 day 12 37 27 10/06/86 370 afternoon 11 42 22 10/06/86 370 n i g h t 21 41 29 11/06/86 Average: 15 40 26 Surface afternoon 5 30 15 06/06/86 Surface n i g h t 15 62 27 10/06/86 Average: 10 46 21 :0 2 SAMPLING: 660 afternoon 290 900 610 08/06/86 660 n i g h t 390 1050 690 08/06/86 Surface n i g h t 100 320 220 03/06/86 Surface afternoon 100 450 305 02/06/86 I0 2 SAMPLING: 660 n i g h t 0.8 4.2 2.7 04/06/86 660 afternoon 0 4.1 2.7 03/06/86 370 n i g h t 0 1.4 0.7 11/06/86 370 afternoon 0.1 1.0 0.6 11/06/86 73 A survey of the CO concentration i n the Ruttan mine i n t a k e during w i n t e r heating f o r the l i f e of the mine i n d i c a t e s t h a t normally there i s a t r a c e value downstream of the propane burners w i t h o c c a s i o n a l peaks of 5ppm CO co n c e n t r a t i o n . The exhaust a i r survey i n d i c a t e s t h a t r e t u r n a i r has a time weighted average CO content of approximately 26 ppm on the 370m l e v e l . F i g u r e 16 i l l u s t r a t e s the CO l e v e l s t h a t would be reached i n the 660m Lev e l exhaust and i n the r e s t of the mine (as an average) i f 30% of the a i r was r e c i r c u l a t e d on 370m L e v e l . The increase i n the CO conc e n t r a t i o n i n the mine i s s u b s t a n t i a l and i t s c o n c e n t r a t i o n i n the 660m L e v e l exhaust exceeds the all o w a b l e TLV. However, the CO i n the bottom exhaust i s already i n excess of a l l o w a b l e l i m i t s . These hig h measured l e v e l s of CO were s u r p r i s i n g s i n c e a l l d i e s e l s are equipped w i t h c a t a l y t i c converters which should reduce CO emission. I t i s b e l i e v e d that the operation of two scooptrams i n s e r i e s caused the downstream scooptram to breathe p o l l u t e d and oxygen depleted a i r thus i n c r e a s i n g CO emission. The c o n d i t i o n s of the converters were not checked but they may have been plugged up. In 1985 NO and CO l e v e l s near d i e s e l equipment a t Ruttan, were monitored us i n g an Ec o l y s e r s e r i e s 7000. The NO l e v e l measured was reported to be extremely low which could i n d i c a t e t h a t the f u e l mixture i s too r i c h . I t i s expected t h a t the CO co n c e n t r a t i o n w i l l decrease c o n s i d e r a b l y once the v e n t i l a t i o n system i s completed and the lower mine a i r q u a n t i t y increases. T y p i c a l CO l e v e l s i n Canadian mines range from 2-10 ppm i n workings c o n t r i b u t i n g l e s s than 10% of the t o t a l AQI value (68,69). Such l e v e l s at Ruttan could p o s s i b l y permit 20% r e c i r c u l a t i o n without any added h e a l t h r i s k to the workers. 1 165 k 250 k i 00 ( Intake [ 5 6 2 ] Rec i r cu la t i on b ranch I I E x h a u s t [ 5 6 7 ] 85 k Branches 1 ne twork C O E Q = 3 0 P P M 188k | J " t t t C O p r o d u c e d : 17.4 P P M 660 ml C O E Q = 6 5 P P M 62 k t t t C O p r o d u c e d : 5 2 P P M I I I 165k C O C O N C E N T R A T I O N E Q U I L I B R I U M W I T H 3 0 % R E C I R C U L A T I O N AT P R E S E N T M I N E C O N T A M I N A T I O N L E V E L . Fig. 16 4> 75 6.3 DUST SAMPLING PROCEDURES The c o n c e n t r a t i o n and composition of a i r b o r n e p a r t i c l e s i n the mine has been e s t a b l i s h e d by the technique of f i l t e r t r a p p i n g and subsequent a n a l y s i s by l a b o r a t o r y methods. I n d u s t r i a l hygiene r e g u l a t i o n s r e q u i r e a technique t h a t gives both an instantaneous and a continuous reading, thus monitoring v a r i a t i o n s of dust l e v e l s i n time and space as r e l a t e d to s p e c i f i c a c t i v i t i e s and a l s o g i v i n g an average dust load over 8 hour s h i f t s . Sampling f o r r e c i r c u l a t i o n purposes c a l l s f o r a continuous response technique, i n order to set r e c i r c u l a t i o n schedules based on dust lo a d i n g v a r i a t i o n s i n time. G r a v i m e t r i c SKC - U n i v e r s a l Samplers (model 224-36) and a Metrex-Diesel/Mineral Sensor were used f o r the f i l t e r t r a p p i n g and i n s t a n t response technique r e s p e c t i v e l y . I s o k i n e t i c sampling procedures were observed i n order to ensure t h a t a r e p r e s e n t a t i v e a e r o s o l sample entered the sampling tube s i n c e the e n t i r e sampling was done from a moving a e r o s o l stream. S e t t l e d dust samples from 660 l e v e l exhaust were c o l l e c t e d i n order to determine the composition i n terms of s o l u b l e , combustible and incombustible dust. 6.3.1 Mass co n c e n t r a t i o n determination Four SKC u n i v e r s a l dust samplers w i t h constant flow s e t t i n g s capable of sampling q u a n t i t i e s between 0 and 4 l i t r e s per minute were used. C a l i b r a t i o n of the samplers was done w i t h the help of SKC Model No.302 c a l i b r a t i o n apparatus. The samplers were p o s i t i o n e d i n 660 l e v e l exhaust, the surface exhausts and i n 370 l e v e l v e n t i l a t i o n r a i s e . The sampling tube (probe) was i n s e r t e d d i r e c t l y i n t o the exhaust. Sampled p a r t i c l e s were c o l l e c t e d on s i l v e r and m i l l i p o r e membrane f i l t e r s . M i l l i p o r e f i l t e r s were ashless w i t h 1 micron pore s i z e w h i l e the s i l v e r membranes were of 1.2 pm pore s i z e . Each f i l t e r was weighed and l e f t i n a d e s s i c a t o r 12 hours before being reweighed to 0.01 rag. 76 The mineral compositions of dust samples were assessed i n order to estimate mass concentrations of v a r i o u s c o n s t i t u e n t s such as s o l u b l e , combustible and incombustible f r a c t i o n s . The dust laden f i l t e r s were i n d i v i d u a l l y washed i n 30 ml of cle a n f r e s h Xylene f o r 5 minutes i n order to d i s s o l v e any s o l u b l e hydrocarbons on the f i l t e r . The f i l t e r s were then placed i n c l e a n p e t r i dishes and l e f t to dry f o r an average d u r a t i o n of 5 hours w i t h the help of an e x t r a c t i o n fan. The f i l t e r s were f i n a l l y t r a n s f e r r e d to d e s s i c a t o r s f o r overnight d r y i n g before being weighed. The l o s s of weight i s taken as the weight of the s o l u b l e hydrocarbons i n the sample. In order to q u a n t i f y combustible and incombustible components of the dust samples, the f i l t e r s were ashed i n a furnace. Pre-weighed c l e a n c r u c i b l e s were used and each f i l t e r was ashed i n d i v i d u a l l y . Some Is o p r o p y l a l c o h o l was sprayed onto the f i l t e r and i g n i t e d . A f t e r the f i l t e r had charred, the c r u c i b l e was placed i n d e s s i c a t o r s to c o o l f o r 20 minutes. The c r u c i b l e s were weighed. The l o s s i n weight due to ashing i s taken as the weight of combustibles while the weight of the residue l e f t i n the d i s h i s the weight of the incombustible component. Percentage compositions f o r the three components were c a l c u l a t e d w i t h respect to the f i l t e r dust deposit (airborne r e s p i r a b l e dust d e p o s i t ) . 6.3.2 I s o k i n e t i c sampling In order to o b t a i n r e p r e s e n t a t i v e r e s u l t s of exhaust dust c o n d i t i o n s , the sampling method plays an important r o l e . The measured q u a n t i t i e s should represent t y p i c a l dust concentrations at the measuring p o i n t . This can be achieved by i s o k i n e t i c sampling. Under i s o k i n e t i c sampling c o n d i t i o n s , the c o n c e n t r a t i o n and s i z e d i s t r i b u t i o n of the a e r o s o l e n t e r i n g the sampling tube i s the same as th a t i n the f l o w i n g stream. The sampling tubes of 10 mm. diameter were attached to the SKC instruments and p r o p e r l y a l i g n e d to the f r e e a i r stream of the exhaust ready f o r sampling. C o r r e c t i o n f a c t o r s due to a n i s o k i n e t i c l o s s were 77 c a l c u l a t e d using a formula given by Durham and Lundgren (70). 6.3.3 Metrex d i e s e l / m i n e r a l dust monitor The Metrex d i e s e l / m i n e r a l monitor was developed by Metrex Canada under a Canmet Contract. The p r i n c i p l e i s based on o p t i c a l dust sensing (see S e c t i o n 7.A.3). The source l i g h t s c a t t e r e d by the dust laden a i r i s detected by two sensors w i t h axes centered at 30° and 90° and should represent the c o n c e n t r a t i o n of d i e s e l p a r t i c u l a t e s and m i n e r a l dust r e s p e c t i v e l y . The instrument i s only a prototype, and extensive work w i l l be r e q u i r e d before d i e s e l p a r t i c u l a t e s can be measured a c c u r a t e l y . M i n e r a l dust c o n c e n t r a t i o n has proven to be accurate i n the l a b o r a t o r y i f c a l i b r a t e d p r o p e r l y . As i t was impossible at Ruttan to c a l i b r a t e the sensor f o r the dust composition being monitored i t was decided to use the instrument to study the trend of dust c o n c e n t r a t i o n changes w i t h time and not absolute c o n c e n t r a t i o n values. The Metrex monitor was used at Ruttan as a f i x e d - s t a t i o n instrument. I t s operating mechanism i s based on the u t i l i z a t i o n of n a t u r a l d i f u s i o n and d r a f t s f o r b r i n g i n g the a i r i n t o the sample volume of the instrument. The Metrex monitor has an i n t e r n a l b a t t e r y and low power e l e c t r o n i c s hence i t can monitor dust concentrations at p o i n t s i n a mine w i t h or without power s u p p l i e s . The instrument was used f o r 3 s h i f t s on 660 l e v e l o n l y to study the t r e n d of dust concentrations w i t h time. The instrument then ceased working and i t s use was d i s c o n t i n u e d . 6.3.4 S e t t l e d dust sampling The composition of s e t t l e d dust i n terms of s o l u b l e s , combustibles and incombustibles was determined using the procedures e x p l a i n e d i n the s e c t i o n 6.3.1. The sample was ground and dry screened using screen s i z e s between 38 pm and 212 nm. This sample was c o l l e c t e d randomly from v a r i o u s l o c a t i o n s i n the 660 l e v e l exhaust. 78 6.4 DUST SAMPLING RESULTS AND DISCUSSION 6.4.1 I s o k i n e t i c sampling Concentration r a t i o s f o r a l l p a r t i c l e s i z e s were c l o s e to 1 except f o r p a r t i c l e s w i t h diameters greater than 5 micron. S i m i l a r l y the sampling e r r o r s were below 20% f o r most of the p a r t i c l e s i z e s i n the re q u i r e d s i z e range (0.5 urn - 5 nm) as shown i n Table 11. Dust p a r t i c l e s of diameter l e s s than 5 micron are p a r t i c u l a r l y important as these are the major c o n s t i t u e n t s of r e s p i r a b l e dust. From the r e s u l t s i t can be concluded t h a t sampling was done i s o k i n e t i c a l l y . TABLE 11 Concentration R a t i o s f o r Various P a r t i c l e S i z e s PARTICLE CONCENTRATION SAMPLING ACTUAL DIAMETER RATIO ERROR CONCENTRATION (Lim) C/Co* (%) Co** 0.50 0.998 0.2000 Co=1.002C 1.00 0.995 0.502 Co=1.00502C 2.00 0.980 2.04 Co=1.0204C 3.00 0.957 4.50 Co=1.045C 4.00 0.927 7.87 Co=1.0787C 5.00 0.892 12.11 Co=1.1211C 6.00 0.853 17.23 Co=1.1723C 8.00 0.768 30.20 Co=1.302C * P a r t i c l e Concentration i n the f r e e a i r s t r e a m - Co P a r t i c l e Concentration i n the sampling probe -C **Based on Durham and Lundgren equation (70) 79 6.4.2 Airborne r e s p i r a b l e dust c o n c e n t r a t i o n Table 12 shows the airborne dust concentrations measured by SKC samplers. The f i r s t four samples i n the survey were c o l l e c t e d w i t h s i l v e r membranes and they show very h i g h dust c o n c e n t r a t i o n . These r e s u l t s are not r e l i a b l e as the f i l t e r flow adjustment of 3.5 l i t r e s / m i n was too h i g h and the flow pressure build-up made the e l e c t r i c a l c i r c u i t t r i p a f t e r no more than 3 hours. At t h i s flow l e v e l , the e f f i c i e n c y of the cyclone i s reduced and excessive n o n - r e s p i r a b l e mineral dust i s c o l l e c t e d on the f i l t e r . The low RCD content of the samples i l l u s t r a t e s t h i s very w e l l . The flow, f o r the r e s t of the sampling, was adjusted to 2.0 l i t r e s / m i n and the s i l v e r membrane f i l t e r s were r e p l a c e d by m i l l i p o r e 1.0 /im ashless f i l t e r s . The exhaust on 660 l e v e l had h i g h average mass c o n c e n t r a t i o n w i t h a percentage of RCD over 56% and as h i g h as 87%. The surface exhaust, as expected, had much smaller c o n c e n t r a t i o n due to a combination of d i l u t i o n and sedimentation. I t was expected a l s o that a lower percentage of r e s p i r a b l e combustible dust would be measured as the mineral dust laden d i l u t i o n a i r mixed w i t h the h i g h d i e s e l p a r t i c u l a t e content dust. The r e s u l t s f o r the combustible content shown i n Table 12 i n d i c a t e t h a t t h i s mixing occured between 660 l e v e l and 567 exhaust. The h i g h s o l u b l e organic f r a c t i o n (SOF), 81% i n one case, i s c o n t r a d i c t o r y to expected r e s u l t s and the reason f o r t h i s r e s u l t i s not known. 80 TABLE 12 Airborne R e s p i r a b l e Dust A n a l y t i c a l R e s u l t s 8 Hours Soluble T o t a l Sample No. L o c a t i o n Concentration Combustible Organic Resp. 3 (mg/m ) % % % S i l v e r membrane (1.2pm): 1 660 1. ,67 15. 6 38. 8 54.4 2 660 2. ,47 25. ,0 36. 2 61.2 3 660 2. .87 21. ,3 35. ,5 56.8 4 567 2. .12 22. ,6 17. ,0 39.6 Ashless m i l l i p o r e (1.0pm): 1 660 1. .275 38. .2 49, .0 87.2 2 660 1, .045 38. .8 45, .0 83.8 3 660 1, .255 33. .7 44, .6 78.3 4 660 1. .33 22, .9 45, .3 68.2 5 660 1. .020 26. .7 38. .8 65.5 6 567 0, .32 14. .0 81, .0 95.0 7 567 0, .41 NA NA NA 8 567 0. .86 19. ,4 48. .4 67.8 9 567 0, .55 16, .1 32, .2 48.3 10 370 0, .70 18. ,2 38. .2 56.4 81 6.4.3 Metrex study The Metrex e l e c t r o n i c c i r c u i t r y was a f f e c t e d by the harsh mining environment a f t e r l e s s than 24 hours underground. Some very i n t e r e s t i n g r e s u l t s were c o l l e c t e d during t h i s p e r i o d . F i gure 17 shows the trend of mineral dust c o n c e n t r a t i o n over a p e r i o d of 24 hours. The monitoring s t a r t e d at 10:30am and ended at 10:00am the next day. I t must be emphasized t h a t the r e s u l t s only represent the behaviour of m i n e r a l dust and not d i e s e l dust. M i n e r a l dust c o n c e n t r a t i o n over a s h i f t i s f a i r l y s t a b l e but a b l a s t can increase the c o n c e n t r a t i o n by a s i g n i f i c a n t value. Decay time f o r the dust i s about 2 to 2 1/2 hours. I t i s c l e a r from t h i s data t h a t r e c i r c u l a t i o n should not be permitted during a b l a s t and f o r a p e r i o d f o l l o w i n g the b l a s t , dependent on the dust c o n c e n t r a t i o n decay r a t e . 6.4.4 S e t t l e d dust sampling r e s u l t s S e t t l e d dust percentage composition i n terms of s o l u b l e , combustible and incombustible f r a c t i o n s are given i n Table 13. Combustible percentage shows an i n c r e a s i n g trend from the l a r g e s t s i z e f r a c t i o n to the s m a l l e s t s i z e f r a c t i o n . However, none of the samples were analysed at more than 10% combustible. This r e s u l t was p r e d i c t a b l e s i n c e a l l of the d i e s e l p a r t i c u l a t e s produced are below 3 Micrometers i n s i z e and w i l l t h e r e f o r e remain a i r b o r n e throughout the v e n t i l a t i o n network. TABLE 13 S e t t l e d Dust A n a l y t i c a l R e s u l t s SAMPLE MESH % s o l u b l e s % combustibles %incombustibles ( S i z e /im) A 120 (125) 1 4.14 4.30 91.56 2 3.10 3.70 93.20 3 3.50 3.30 93.20 '4 4.00 4.20 91.80 AVERAGE 3.69 3.88 92.44 S.D. 0.48 0.47 0.88 B 170 (90) 1 5.00 3.43 91.57 2 4.90 2.90 92.20 3 4.70 2.00 93.30 4 4.40 3.00 92.60 AVERAGE 4.75 2.83 92.41 S.D. 0.27 0.60 0.73 C 325 (45) 1 9.91 3.74 86.35 2 6.80 4.10 89.10 3 6.50 3.30 90.20 4 7.00 3.90 89.10 AVERAGE 7.55 3.76 88.69 S.D. 1.59 0.34 1.64 D 270 (53) 1 5.61 4.36 90.03 2 6.00 5.00 89.00 3 5.90 4.10 90.00 4 6.40 5.30 88.30 AVERAGE 5.98 4.69 89.33 S.D. 0.33 0.56 0.84 E 400 (38) 1 20.67 5.25 74.08 2 17.60 5.70 76.70 3 18.90 6.10 75.00 4 17.00 6.00 77.00 AVERAGE 18.54 5.76 75.70 S.D. 1.63 0.38 1.39 F +400 (-38) 1 18.50 6.35 75.15 2 19.80 7.60 72.60 3 16.80 8.30 74.90 4 - 20.20 8.10 71.70 AVERAGE 18.83 7.59 73.59 S.D. 1.53 0.88 1.70 M E T R E X - - C O N T I N U O U S D U S T S A M P L I N G R E S U L T S 6 B O L E V E L T H U R S D A Y , J U N E 0 5 { 1 r i i 1 1 1 1 1 1 1 1 1 1 0 1 4 1 8 2 2 2 6 3 0 3 4 T I M E ( H R S ) 84 7.0 EVALUATION OF CONTROL SYSTEMS FOR THE  RECIRCULATION DESIGN AT RUTTAN 7.1 CONTROLLED MONITORING IN UNDERGROUND MINES Mon i t o r i n g systems can have numerous uses i n a mine. They can a s s i s t i n e f f i c i e n t management by p r o v i d i n g environmental trend data, p r o d u c t i o n and maintenance c o n t r o l and communications. No s i n g l e system w i l l s a t i s f y the t o t a l mine requirement. Some mines may. r e q u i r e simple hard-wired s t a t u s - r e p o r t i n g systems; others, multipurpose computer-based systems that c o l l e c t , analyse and s t o r e data and perhaps c o n t r o l some mine f u n c t i o n s . W h i l s t systems vary i n complexity, they are a l l composed of three f u n c t i o n a l components: a) Sensors b) Telemetry devices c) A n a l y s i s and d i s p l a y equipment. The sensors measure the environmental or production parameters and produce an e l e c t r i c a l s i g n a l t h a t i s fed i n t o the telemetry. The telemetry devices r e c e i v e the s i g n a l from the sensors and transmit i t i n e i t h e r analog or d i g i t a l format to the a n a l y s i s and d i s p l a y equipment. This equipment r e c e i v e s the t r a n s m i t t e d s i g n a l and e i t h e r stores i t f o r l a t e r a n a l y s i s or d i s p l a y s i t . The a n a l y s i s - d i s p l a y equipment ranges from simple s t r i p c h a r t recorders w i t h preset alarms to computers, cathode-ray tubes (CRT's), and l i n e p r i n t e r s . For economic reasons a mining company w i l l give g r e a t e r p r i o r i t y to monitoring f o r production and maintenance than to v e n t i l a t i o n , communication or f i r e monitoring. An i d e a l system of t h i s type should have the c a p a b i l i t y of i n c o r p o r a t i n g a v e n t i l a t i o n subsystem. In the case of Ruttan mine, environmental monitoring w i l l be a c r i t i c a l f a c t o r i f r e c i r c u l a t i o n of mine a i r proves to be f e a s i b l e . 85 7.2 TELEMETRY SYSTEMS There are two b a s i c approaches to telemetering. Figure 18 shows a c e n t r a l i z e d management system which processes a l l acquired i n f o r m a t i o n at a s i n g l e c o n t r o l s t a t i o n . Each sensor has a separate p h y s i c a l connection to the c e n t r a l connection. This s t a t i o n d i g i t i z e s the analog outputs of each sensor and then l i n e a r i z e s i t . This can be very time consuming f o r many sensors. In a d d i t i o n , the c e n t r a l s t a t i o n processes the sensor data and then, based on a computer a l g o r i t h m i t can send out the proper commands to c o n t r o l l e r s underground. The two main disadvantages of such systems are that a very f a s t c e n t r a l s t a t i o n i s required, to implement r e a l time c o n t r o l and i n the event of a communication breakdown between the c e n t r a l s t a t i o n and the network of sensors and c o n t r o l l e r s , monitoring and c o n t r o l c a p a b i l i t i e s are l o s t . F igure 19 shows a d i s t r i b u t e d system which i s a much b e t t e r approach. I n t e l l i g e n t o u t s t a t i o n s , which are microprocessor based and can be used i n some cases as programmable c o n t r o l l e r s , are r e s p o n s i b l e f o r monitoring each bank of sensors. Each sensor's analog output i s read, l i n e a r i z e d i f necessary, d i g i t i z e d and sent to the c e n t r a l c o n t r o l s t a t i o n . Each o u t s t a t i o n can have i t s own p r i v a t e communications l i n k to the c o n t r o l s t a t i o n , or a multidrop c o n f i g u r a t i o n may be used. The c o n t r o l s t a t i o n processes the sensor data and iss u e s commands to other o u t s t a t i o n s t h a t c o n t r o l r e c i r c u l a t i o n fans f o r example. A d i s t r i b u t e d system reduces the number of wires necessary f o r communications between the sensors and c e n t r a l s t a t i o n . A l s o , since the o u t s t a t i o n s handle the sensors and the fans, the c e n t r a l s t a t i o n can be f r e e d to perform other higher l e v e l f u n c t i o n s . I t i s a l s o p o s s i b l e to have a system which can operate independently of the c e n t r a l s t a t i o n i n case of power f a i l u r e or communication breakdown, by usi n g programmable c o n t r o l l e r s to make the o u t s t a t i o n s s u f f i c i e n t l y i n t e l l i g e n t . Sensor Bank Sensor Bank . Sensor Bank Sensor Bank Centralized Monitoring and Control Architecture Fig. 18 Sensor Bank Sensor Bank Sensor Bank Sensor Bank Distributed Monitoring and Control Architecture. Fig. 19 87 7.3 SENSORS AND FINAL CONTROL ELEMENTS The s e l e c t i o n of sensors and f i n a l c o n t r o l elements i s as d i f f i c u l t and important as the s e l e c t i o n of the environmental monitoring system i t s e l f . Gas sensors f o r CO, C0„ and NO are manufactured i n North 2 x America and have been adapted f o r mining environments. D i f f u s i o n based sensor heads would be s u i t a b l e f o r a r e c i r c u l a t i o n monitoring system. Hydrated s o l i d polymer e l e c t r o l y t e sensor c e l l s are p r e f e r a b l e to the el e c t r o c h e m i c a l sensors used. Table 14 summarizes the major sensors a v a i l a b l e i n Canada. The t a b l e was compiled by I n t e r n a t i o n a l Technology Centre (71). Commercially a v a i l a b l e SO^ sensors do not have the r e q u i r e d s e n s i t i v i t y to detect l e v e l s below lppm. In a mine l i k e Ruttan, s u l p h i d e i g n i t i o n s occur f r e q u e n t l y and the consequent l a r g e amount of sulphur d i o x i d e produced must be monitored to avoid r e c i r c u l a t i n g i t . The Spanair System (from the Anglo-American Corporation of South A f r i c a ) appears to merit c o n s i d e r a t i o n , as i t i s an e x c e l l e n t CO^ monitor (non-dispersive i n f r a r e d sensor) and i t i s b e l i e v e d t h a t by changing i t s f i l t e r s i t can a l s o measure S O 2 , t h i s needs t o be i n v e s t i g a t e d . For a r e c i r c u l a t i o n p r o j e c t a l i s t of a l l r e q u i r e d c h a r a c t e r i s t i c s f o r the sensors to be used, should be compiled i n order to choose the best transducers s u i t a b l e f o r the p r o j e c t . S p e c i f i c a t i o n c harts have been generated by the USBM f o r the s e l e c t i o n of methane and carbon monoxide transducers (72) to be used i n a mine-wide environment system. Part of the carbon monoxide l i s t i s shown i n Table 15. 7.4 INSTANTANEOUS DUST SENSING INSTRUMENTS Many techniques are used to measure dust concentrations i n the mining environment, but few can be adapted to remote monitoring. They are: a) o p t i c a l sensing b) p i e z o e l e c t r i c sensing c) beta-attenuation. Table 14 Sensor Summary Type Model Range Cost Outputs Power Comments CO Sensor Sample-Draw Electrochemical Ecolyzer 500I-I'EI :-500 0-500 ppm $1500 8 weeks delivery 4-20 mA or 0-1 V D C (linear) 15-28 V D C 120 mA Sensing head type. CO Sensor Diffusion Electrochemical Ecolyzer 500I-IX'.-50/500 0-500 ppm $865 8 weeks delivery 4-20 mA or 0-1 V D C (linear) 15-28 V D C 30 mA Sensing head type. C O Sensor Diffusion Electrochemical Sieger 911 CO Sensor 0-500 ppm $1077 8 weeks delivery 4-20 mA (linear) 20-35 v i x : Sensing head type. CO Sensor Diffusion Electrochemical MSA flullctin No. 1608-8 0-100 ppm -$800 (Gen Purp) -$1400 (Explosion Proof) 4-20 mA (linear) 6-15 v i x : CO Sensor Diffusion Elcctrivhemical Rcllek I'ireboss 1001) 0-25 ppm or 0-50 ppm $595 (US) Several including 4-20 mA 9-30 V D C 2 mA f loop current Sensing head type. Intrinsically Safe. C02 Sensor Electrochemical Scnsidyne Up lo 10000 ppm $2420 4-20 mA (logarithmic) N/A Sensing head type. C02 Sensor Puji Model / .E I ' lYAZI 0-3000 ppm N/A 0-100 mV N/A Used as an O E M part of Conspcc's Systems. No other info, available. C02 Sensor KentEGMI I N/A N/A N/A 120 V A C Used as an OHM part of Conspcc's Systems. No other info, available. C02 Analyzer NDIK Heck man 864 N/A N/A N/A N/A Analyzer type. More info, requested but not yet received. (continued) Type Model Kunge Cost Outputs Power Commcnis C02 Analyzer NDIK Horiba APBA-200E 0-2000 ppm or 01%or0-5%O2, $2678 8 weeks delivery 4-20 mA 115 VAC Analyzer type. No additional info, has been requested. C02 Analyzer NDIR Andius Analyzer 502 0-5000 ppm N/A 0-5 VDC + 12 VDCreg -12 VDCreg + 14 VDCunreg Analyzer type. NO Sensor Sample-Draw Electrochemical Ecolyzer 5002-PGF-50 0-50 ppm $1865 8 weeks delivery 4-20 mA or 0-1 VDC (linear) 15-28 VDC 120 mA Sensing head type. N02 Sensor Sample-Draw Electrochemical Ecolyzer 5003-PGF-10 0-10 ppm $1865 8 weeks delivery 4-20 mA or 0-1 VDC (linear) 15-28 VDC 120 mA Sensing head type. N02 Sensor Elec trot hemic al Sensidyne 0-10,0-100 ppm $2420 4-20 mA N/A Additional info, has been requested. Noi received yet. S02 Sensor Sample-Draw Electrochemical Ecolyzer 5005-PGF-IO 0-10 ppm $1864 8 weeks delivery 4-20 mA or 0-1 VDC (linear) 15-28 VDC 120 mA Sensing head type. S02 Sensor Diffusion Electrochemical Sieger 911 S02 Sensor 0-100 ppm $1073 8 weeks delivery 4-20 mA (linear) 20-35 VDC Sensing head type. S02 Analyzer InterScan LD-24 S02 0-5 ppm N/A 0.2-1.0 VDC N/A Used as OEM pan of Conspec's Systems. No other info, avail. S02 Analyzer Beck man 864 N/A N/A N/A N/A Additional info, has been requested. Not received yet. (continued) Type Model Rtingc Cost Outputs Power Comments 02 Sensor Electrochemical Sieger 910 02 Sensor 0-25% 0 2 $1902 4-20 mA (linear) 20-35 V D C Sensing head type. 02 Analyzer Control Instruments OXY N/A N/A N/A N/A Analyzer type. 0 2 Monitor MSA 02 Sensing Head 0-25% 0 2 -$800 (Gen Purp) -$1400 (Explosion Proof) 4-20 mA (linear) 6-15 V D C Sensing head type. Radon Gas Daughter Monitor EDA WM-30 Counts/Minute or Mi l l i -working-levels $4950 RS-232 12 V D C Analyzer type. More info, requested. Not received yet. Radon Gas Monitor EDA RGA-40 (Frololype) Counts/Minute or Mi l l i -working-lcvels -$10000 RS-232 12 V D C Analyzer type. More info, requested. Not received yet. Airflow Sensor Kur/. 435DC 0-100, 300, 1250, 2500, or 6000 fps $1242 0-5 V D C 4-20 mA (add $461) 12-15 V D C 200 mA Airflow Sensor (Vortex shedding) J-Tck VA2I6B 50-3000 or 150-1000 fpm $2760 4-20 mA or 0-5 V D C 10-20 V D C 35 mA Sensing head type. Intrinsically Safe. Air Velocity Monitor (Vortex Shedding) Sieger BA.-) 0-2, 10, or 20 nips N/A - 0.4-2 V D C 15 V A C or 12-18 V D C Intrinsically Safe. Aerosol Sensor GCA RAS-I 0.01 mg/m3 -200 nig/m3 $3297 Several including 4-20 mA 12 V D C is an option Analyzer type. (continued) Type Model Range Cost Outputs Power Comments Aerosol Sensor GCA R A M S 3 5|Jg/m -200 mg/rrf $7560 Several including 4-20 mA 115 V A C 10 Walls Analyzer type. Ambient paniculate monitor lloriba APDA-300E 0-1000, 5000 mg/m3 $28,100 4-5 months delivery 0-1 V D C N/A Analyzer type. Smoke/Dust Density Monitor Xobral SD 0-5 Ringelmann or 0-100% smoke $2300 (US) 8-10 weeks delivery 0-1,5-10, 4-20,10-50 mA 115 V A C 75 W Analyzer type. Fire Detector (heat sensitive) Sieger F1RANT N/A N/A 0-2 V D C Low voltage D C Fire Monitor (POCandCO) Sieger F1DESCO N/A N/A 0.4-2 V D C 12 V D C Intrinsically safe. Smoke Sensor FIDES Style Conspcc P1420 N/A N/A N/A N/A Used as an O E M pan of Conspec's system. No other info, available. Smoke Sensor FIDES Style, includes CO Conspec PI 540 N/A N/A N/A N/A Used as an O E M part of Conspec's sytsem. No other info, available. TABLE 15 INTERIM PERFORMANCE SPECIFICATIONS FOR CARBON MONOXIDE TRANSDUCER MODULES Cha r a c t e r i s t i c Interim Performance S p e c i f i c a t i o n s Rationale 2.2 Overall accuracy 2.3 Response-rise time 2.4 Response-recovery t i n The response to CO concentration K i t h the transducer module range for a one-month period s h a l l had an inacuracy including bias and p r e c i s i o n of less than •/- 2 ppm CO at a sample concentration of 5 pp* CO or less and +/1 * ppm CO at a sample concentration of 25 ppm CO. Upon applying a step increase i n CO concentration to a transducer module, the time i n t e r v a l from i n i t i a l response to a response value that i s 90% of f i n a l value s h a l l be less than 2 min. Upon applying a step decrease i n CO concentration to a transducer module, the time i n t e r v a l from i n i t i a l response to a response value 10% greater than the f i n a l value s h a l l be less than 2 min. Accuracy s h a l l include response v a r i a t i o n terms from c a l i b r a t i o n e r r o r , p r e c i s i o n , d r i f t , and temperature changes Q). See rationale of 2.1. False alarms from response inaccuracy must be minimi zed. CO transducer nodules have response times of 2 min. or l e s s . Fast transducer response i s recommended f o r mines with CO sources such as d i e s e l haulage to di s c r i m i n a t e between short and long-term CO concen-t r a t i o n changes to a i d f i r e detection. Fast response w i l l decrease the time required to c a l i b r a t e the transducers. See r a t i o n a l e 2.3. 2.5 Response upon applica-t i o n of power a f t e r power interrupt-recovery time 2.6 S t a b i l i t y - z e r o , re-sponse v a r i a t i o n with time i n pure a i r 2.7 S t a b i l i t y - s p a n , re-sponse v a r i a t i o n i n s e n s i t i v i t y with time Same as 1.4. Response s h a l l meet accuracy s p e c i f i c a t i o n i n less than 20 min. from a p p l i c a t i o n of power. The response d r i f t i n pure a i r s h a l l be less than •/• 1 ppm CO per month. The response d r i f t (change i n s e n s i t i v i t y ) with a CO chal-lenge gas s h a l l be •/• 10% of the gas concentration per month or le s s . Same as r a t i o n a l e 1.4. Response v a r i a t i o n with time for unadjusted conti no CO present should be much less than MSHA-reo monthly c a l i b r a t i o n schedule ( 6 ) . The response v a r i a t i o n i n transducer output from d r i f t i n presence of CO should be less than t o t a l accuracy requirement, and c a l i b r a t i o n should be needed no more frequently than once per month t o maintain accuracy. operation with a l e r t l e v e l f o r 2.8 C a l i b r a t i o n 2.8.1 Procedure 2.8.2 C a l i b r a t i o n test gas A standard c a l i b r a t i o n procedure must be s p e c i f i e d by trans-ducer manufacturer for in-mine c a l i b r a t i o n . A c a l i b r a t i o n k i t s h a l l contain necessary parts for test and reset ( i f necessary) of zero and span s e t t i n g at the mine by means of the measured transducer responses. The test gases s h a l l have an analysis accuracy of +/- 1X or less of stated reading. Uniform procedure f o r c a l i b r a t i o n s h a l l be used to maintain transducer accuracy for intercomparison of measured values w i t h i n mine. Accuracy of transducer must be checked and transducer reset on-site using standard c a l i b r a t i o n gases. 93 Most of the instruments u s i n g these techniques have been thoroughly t e s t e d i n the l a b o r a t o r y , but very l i t t l e i n f o r m a t i o n on t h e i r r e l i a b i l i t y i n the underground mining environment has been published. The a p p l i c a t i o n of the three techniques was i n i t i a t e d i n the 1960's and 70's but i t i s only r e c e n t l y that dependable instruments became a v a i l a b l e . Because these instruments r e q u i r e frequent maintenance and c a l i b r a t i o n , mining companies have been r e l u c t a n t to exchange them f o r the w e l l proven g r a v i m e t r i c method. The need to o b t a i n continuous and instantaneous i n f o r m a t i o n on the q u a l i t y of the mining environment i n d i c a t e s that these r e l a t i v e l y new techniques w i l l become more important i n the near f u t u r e . 7.4.1 Beta a t t e n u a t i o n instruments In beta a t t e n u a t i o n instruments the ae r o s o l i s drawn through an o r i f i c e , and p a r t i c l e s impact on a s u i t a b l e s u r f ace. The impact surface i s p o s i t i o n e d between a beta r a d i a t i o n source and a counter. The amount of beta a d s o r p t i o n recorded by the counter i s p r o p o r t i o n a l to the dust c o n c e n t r a t i o n . The instrument measures the mass c o n c e n t r a t i o n independent of the type of dust and p a r t i c l e s i z e d i s t r i b u t i o n . I t has very l i m i t e d usefulness i n occupational environment measurements. The time r e s o l u t i o n (over 20 minutes f o r low c o n c e n t r a t i o n s ) , absence of an analog output and the poor p r e c i s i o n are major shortcomings. P r e c i s i o n at low c o n c e n t r a t i o n can be l e s s than 40%. 7.4.2 P i e z o e l e c t r i c sensors In p i e z o e l e c t r i c sensing, p a r t i c l e s are drawn through an o r i f i c e and deposited on the face of a quartz c r y s t a l by the use of a corona discharge needle. This c r y s t a l i s a p a r t of an o s c i l l a t o r whose resonant frequency changes l i n e a r l y w i t h small changes i n c r y s t a l t hickness (or mass). As p a r t i c u l a t e mass c o l l e c t s on the c r y s t a l face, the frequency decreases. The r a t e of t h i s frequency change i s p r o p o r t i o n a l to the air b o r n e mass c o n c e n t r a t i o n . The instrument c o n s i s t s of a l a r g e number of s e n s i t i v e components which must operate s a t i s f a c t o r i l y . The corona needle i s a weak p a r t of the instrument. In l a b o r a t o r y t e s t s , as few as 94 5-10 samples could cause the corona current to drop. High humidity and high a e r o s o l concentration can lead to f a i l u r e s . The cost of t h i s instrument i s very h i g h ($35,000) and frequent maintenance i s necessary. I t could be a p r a c t i c a l instrument f o r underground use i n the f u t u r e i f the shortcomings are overcome. 7.4.3 O p t i c a l sensors In o p t i c a l sensing, a beam of l i g h t from e i t h e r an incandescent or l a s e r source i s d i r e c t e d i n t o a chamber c o n t a i n i n g a sample of dust-laden a i r . The i n t e n s i t y of l i g h t s c a t t e r e d over a range of angles produces an e l e c t r i c s i g n a l p r o p o r t i o n a l to the mass concentration of the dust. The dust clouds i n a mine c o n t a i n p a r t i c l e s of many types of m a t e r i a l w i t h d i f f e r e n t r e f r a c t i v e i n d i c e s . The l i g h t - s c a t t e r i n g p r o p e r t i e s of a p a r t i c l e are a f u n c t i o n of i t s s i z e , shape and r e f r a c t i v e index; thus the t o t a l l i g h t s c a t t e r e d by a mixed cloud at any p a r t i c u l a r angle w i l l be a f u n c t i o n of the instantaneous composition of the cloud. The composition of mine dust clouds v a r i e s i n an u n p r e d i c t a b l e way. A d e s i r a b l e f e a t u r e of these instruments i s to have an equal response to p a r t i c l e s of d i f f e r e n t r e f r a c t i v e i n d i c e s i n order to r e l a t e the i n t e n s i t y of s c a t t e r e d l i g h t to the mass conc e n t r a t i o n of the dust cloud. By changing the wavelength of the l i g h t source and the s c a t t e r e d - l i g h t d etector's angle range, i t i s p o s s i b l e to minimize the e f f e c t of the r e f r a c t i v e index of the p a r t i c l e on the s c a t t e r e d l i g h t i n t e n s i t y . Manufacturers use t h e o r e t i c a l l i g h t s c a t t e r i n g a n a l y s i s to d e f i n e these two parameters f o r t h e i r instruments. In order to do the c a l c u l a t i o n , c h a r a c t e r i s t i c s of the p a r t i c l e s found i n underground mines must be known. These c h a r a c t e r i s t i c s are; the r e f r a c t i v e index, the s i z e d i s t r i b u t i o n and the d e n s i t y . The mathematical equations are very complex and v a r i o u s assumptions must be made i n order to a r r i v e at a s o l u t i o n . Since manufacturers use d i f f e r e n t p a r t i c l e s f o r t h e i r a n a l y s i s and d i f f e r e n t assumptions, the parameters of each manufacturer's instrument can vary widely. 95 Table 16 reviews a l l the l i g h t s c a t t e r i n g devices c u r r e n t l y manufactured. In order to evaluate the instruments a v a i l a b l e f o r a p p l i c a t i o n i n a r e c i r c u l a t i o n scheme, a comprehensive review of a l l a v a i l a b l e l i t e r a t u r e on f i e l d and l a b o r a t o r y t e s t i n g of these instruments was undertaken by the author. A l i s t of the most s i g n i f i c a n t a r t i c l e s , reviewed i s given i n the b i b l i o g r a p h y s e c t i o n of t h i s r e p o r t (References 72 to 81). The review i n d i c a t e d t h a t the instruments to be used i n the r e c i r c u l a t i o n monitoring system must meet the f o l l o w i n g c r i t e r i a : (1) Be s u i t a b l y robust f o r sustained use i n a mine environment where the moisture content approaches s a t u r a t i o n . (2) Be equipped w i t h a backup b a t t e r y system capable of s u s t a i n i n g instrument o p e r a t i o n f o r up to 12 hours and s t o r i n g data f o r s e v e r a l hours i n a standby mode. (3) Be equipped w i t h an analog output s i g n a l ( p r e f e r a b l y 4-20 ma) (4) Be equipped w i t h a r e c i r c u l a t i n g c l e a n a i r c i r c u i t to maintain o p t i c a l equipment dust f r e e . (5) Be equipped w i t h a pump i n order to maintain constant flow through the sensing chamber. This i s important i n an exhaust system where a i r v e l o c i t y i s very high. (6) Should be equipped w i t h a pre-sampler. There are two inherent problems w i t h l i g h t s c a t t e r i n g instruments. F i r s t , the response to concentration v a r i a t i o n f o r a l l the instruments i s l i n e a r f o r each type of dust encountered underground. However, the c a l i b r a t i o n f o r each type of dust i s d i f f e r e n t , u s u a l l y v a r y i n g between 10-30%. I t i s t h e r e f o r e necessary to c a l i b r a t e the instrument f o r the mine where i t i s to be used. Readings may s t i l l be u n r e l i a b l e when dust composition changes w i t h i n the mine. The second problem of the instruments i s t h a t they a l l respond to water d r o p l e t s i n the a i r ; t h i s can be overcome by the p r o v i s i o n of a pre-sampler. Two monitors are w e l l s u i t e d to our needs. The f i r s t instrument i s > a modified v e r s i o n of the RAM-1 r e f e r r e d to as the machine-mounted Table 16 INSTRUMENT CHARACTERISTICS Flow I n s t r u m e n t S e n s o r R a n g e 3 (mg/lm ) F r a c t i o n P r e - S a m p l e r Pump H e t e r C a l i b r a t i o n O u t p u t C o s t S i m s l i n I I ( E n g l a n d ) LedA=0.90um 6-16 + 4° 0.1-200 R e s p i r a b l e I l o r i z o n t a l -e l u t r i a t o r 0.625 LPM z e r o , c l e a n a i r d i g i t a l d i s p l a y a n a l o g v o l t a g e d i g i t a l s i g n a l "$12,000 S i b a t a PCD-1 (Japan ) White l i g h t 8=90 + 15" 0.001-10 <10Mm P a r t i c l e Maze 3 LPM t a n z e r o , r e f e r e n c e u n i t a n a l o g d i s p l a y d i g i t a l d i s p l a y a n a l o g v o l t a g e $10,000 MDA PDS-1 (U.S.A) White l i g h t 8=70 + 10° 0.01-100 r e f e r e n c e u n i t d i g i t a l d i s p l a y T M - D i g i t a l (Germany) LedA=0.94um 8=70 + 10° 0.03-100 z e r o , c l e a n a i r r e f e r e n c e u n i t d i g i t a l d i s p l a y d i g i t a l s i g n a l a n a l o g c u r r e n t CGA-RAM-1 (U.S.A) LedA=0.94um 9=70 + 20° 0.001-200 T o t a l r e s p c y c l o n e 2 LPM Membrane pump r o t -ameter z e r o , c l e a n a i r , r e f e r e n c e u n i t d i g i t a l d i s p l a y a n a l o g v o l t a g e $10,000 CGA-PDM (U.S.A.) LedA=0.94um 8=70 + 25° 0.1-100 z e r o , c l e a n a i r r e f e r e n c e u n i t d i g i t a l d i s p l a y a n a l o g v o l t a g e $ A,000 OSIRIS (ENGLAND) LedA=0.90um 8=4-45° 0.1-200 R e s p i r a b l e H o r i z o n t a l e l u t r i a t o r 0.625 LPM vane pump r o t a m e t e r z e r o , c l e a n a i r d i g i t a l d i s p l a y a n a l o g v o l t a g e d i g i t a l s i g n a l METREX LedA=0.94um 0.01-100 D i e s e l 8=30" Mineral8=90° z e r o , c l e a n a i r d i g i t a l d i s p l a y a n a l o g o u t p u t d i g i t a l s i g n a l 97 r e s p i r a b l e dust monitor (MMRDM) (Figur e 20) and the second i s the O s i r i s sensor (Fi g u r e 21). Both instruments have been designed f o r sust a i n e d use i n rugged environments and each has a r e c i r c u l a t i n g clean a i r system to prevent dust d e p o s i t i o n w i t h i n the photometer. In a d d i t i o n , both are equipped w i t h a 37-mm membrane f i l t e r a l l o w i n g the comparison of r e s u l t s w i t h other samplers and f u r t h e r a n a l y s i s of the dust chemical c o n s t i t u e n t s . The two instruments have d i f f e r e n t advantages and drawbacks. Both have a pre-sampler, but l a b o r a t o r y t e s t s showed t h a t the cyclone used i n the MMRDM i s more e f f i c i e n t i n separating water d r o p l e t s than the e l u t r i a t o r i n the O s i r i s . In f a c t the response by the MMRDM to water d r o p l e t s approaches zero. Since the humidity l e v e l at the exhaust of an underground system v a r i e s by 10-35% year around, the change i n humidity should not have a s i g n i f i c a n t impact on the t o t a l dust readings. The O s i r i s sensor has the advantage over a l l other instruments of having a s e l e c t a b l e range of d e t e c t i n g angles between 4-45°. I t provides the p o s s i b i l i t y of tuning the sensor i n order to s u i t a given environment by s e l e c t i o n of the appropriate s c a t t e r i n g angles. The cost of each of these instruments i s i n the range of $12 000 to $14 000. LIGHT SCATTERING SENSING STAGE C L E A N AIR CURTAIN FLOW LINE FLOW RESTRICTOR (HIGH RESISTANCE) CLEAN AIR PURGE LINE 1 FOR ZERO R E F E R E N C E ) fLOWHCTER BACKUP FILTER CARTRIOGC FROM FLOW CONTROLLER CIRCUIT TO FLOW CONTROLLER PRESSURE SENSOR CIRCUIT (FLOW CONTROL) 3-WAY VALVE (GCA O E V E L O P E O ) Flow subsystem of MMRDM. F i g . 2 0 CARRYING HANDLE ELUTRIATOR BATTERY COMPARTMENT ^ C L E A N AIR PHOTOMETER LASER . 1 LENS M E M O R Y HOUSING (OPTIONAL) C L E A N AIR LENSES D A W 1 I ' LASER B E A M A,' 1 1 1 t - —C LIGHT TRAP . v ^ r r r — REFERENCE PHOTODIODE EXHAUST AIR V A L V E FILTER 'UBXiuuieiiiUKEScn P U M P I ACCESS TO FILTER TELEMETRY CONNECTOR CHARGER CONNECTOR Schematic diagram of OSIRIS sensor. Fig. 21 vo 100 7.5 TELEMETRY AND CONTROL SYSTEM S e l e c t i o n of the telemetry and c o n t r o l system i s as d i f f i c u l t and important as the s e l e c t i o n of the sensors and f i n a l c o n t r o l elements. The c o n t r o l instrumentation to be used i n the r e c i r c u l a t i o n design has d i f f e r e n t requirements than most systems used f o r m u l t i l e v e l mining environments and production sensing. The number of areas to be monitored are l i m i t e d and the d i f f e r e n t gases to be monitored at each area are numerous. Not many systems used i n underground mining are capable of handling such requirements. I t i s t h e r e f o r e d i f f i c u l t to configure a system that would s u i t the needs of the p r o j e c t . The c o n t r o l instrumentation developed by the f o l l o w i n g manufacturers has good p o t e n t i a l f o r a p p l i c a t i o n . i ) - B r i s t o l Babcock (U.S.A.) Canadian r e p r e s e n t a t i v e : B r i s t o l of Canada 234 A t w e l l Drive Rexdale, Ontario M9W 5B3 Telex: 06-989176 Phone (416) 675-3820 i i ) - Conspec L t d . (Canada) 44 M a r t i n Ross Avenue Downsview, Ontario M3J 2K8 Phone (416) 661-0500 i i i ) - Montan-Forschung (Germany) Canadian Representative: IMS E l e c t r o n i c s Inc. 811-675 West Hastings S t r e e t Vancouver, B.C. V6B 1N2 Phone (604) 689-1709 101 7.5.1 B r i s t o l / B a b c o c k system B r i s t o l ' s Network 3000 inc l u d e s a h i g h l y f l e x i b l e combination of hardware and software t h a t can be e q u a l l y e f f e c t i v e i n stand-alone and network c o n f i g u r a t i o n . F i gure 22 shows how B r i s t o l products could be used i n the system. The RTU 3320 i s micro-processor based and w i l l monitor most of the sensors used i n the system and do some rudimentary c a l c u l a t i o n s . I t s main f u n c t i o n w i l l be to m u l t i p l e x the data to be processed by the RDC 3350. The RDC 3350 i s a microprocessor based i n t e l l i g e n t c o n t r o l l e r . I t r e c e i v e s analog and d i g i t a l s i g n a l i n p u t s , performs c a l c u l a t i o n s , i s capable of making c o n t r o l d e c i s i o n s and provides c o r r e c t i v e c o n t r o l output s i g n a l s . I t s i n t e l l i g e n c e allows t o t a l l o c a l c o n t r o l without r e q u i r i n g a s u p e r v i s o r y c e n t r a l computer. This i s a very c r i t i c a l f e a t u r e i n the event of a communication breakdown w i t h the surface computer. The 3350 comes w i t h a very s o p h i s t i c a t e d software support (ACCOL I I ) . The ACCOL I I i s a set of 30 preprogrammed software modules t h a t perform the same f u n c t i o n s as hardware devices such as comparators, i n t e g r a t o r s , PID c o n t r o l l e r s , t i m e r s , c a l c u l a t o r s , e t c . . . This w i l l be used to c a l c u l a t e AQI v a l u e s , e f f i c i e n c y of fans, and most important of a l l set the r e c i r c u l a t i o n network to an optimum and safe s t a t e at a l l times. The surface computer, an IBM PC-XT, AT or compatible must be used w i t h the T r o l l t a l k i n t e g r a t e d software package. This combination can then, c o n f i g u r e the RDC 3350, act as a powerful data base and a s u p e r v i s o r y c o n t r o l c e n t r a l , l i m i t access to a u t h o r i z e d personnel o n l y , detect and r e p o r t alarms i n the system, provide instantaneous and p e r i o d i c r e p o r t s on a p r i n t e r . The t o t a l c ost of the system i n c l u d i n g a p r i n t e r , an IBM-XT and c o l o r screen i s given i n Table 17.Total cost i n c l u d e s the p r i c e of two RTU 3320 u n i t s . I t i s p o s s i b l e t h a t the p r o j e c t may r e q u i r e only one (as shown i n ( F i g . 22). The c a p a c i t y of the RDC 3350 i s s u f f i c i e n t to cover the f u n c t i o n s of the e n t i r e network. However, t h i s could prove to be 102 u n d e s i r a b l e , s i n c e long cable lengths between the o u t s t a t i o n and the sensors or c o n t r o l motors could r e s u l t i n hig h voltage l o s s and i n t e r f e r e n c e . These co n s i d e r a t i o n s w i l l have to be assessed i n the second p a r t of the p r o j e c t . The cost t a b l e a l s o includes funding f o r an engineer to be t r a i n e d at B r i s t o l ' s o f f i c e s , i n order to f a m i l i a r i z e himself w i t h the software. I t i s f e l t t h a t t h i s i s a b e t t e r o p t i o n than having a B r i s t o l ' s r e p r e s e n t a t i v e come to Ruttan at $500/day + expenses. TABLE 17 Costs of B r i s t o l System D e s c r i p t i o n Cost $ Software - T r o l l t a l k 2 600 Hardware - T e l e m e t r o l l RDC 3350 9 850 - RTU 3320(2) (@$3 500 each) 7 000 - IBM PC-XT (enhanced v e r s i o n ) 12 600 c o l o r screen, l e t t e r q u a l i t y p r i n t e r , 20 MB hard d i s k , two f l o p p i e s - Telemetry cables 2 000 Other - Shipping - Taxes - Personnel t r a i n i n g / 3 at B r i s t o l Canada i n Toronto 300 2 000 days t r a i n i n g 1 500 Calgary or TOTAL: 37 700 P r i n t e r IBM-XT Network with troHtalk monitor software phone tine E X H A U S T FANS \ ^ INTAKE FANS j RTU 3320.:-f , analog input (Sgrcal output (RECIRCULATION BRANCH) I co L _ T" d u s t veto _ C O _ N O RECIRCULATION F A N P s < r-Z Fig. 22 BRISTOL SYSTEM CONTROL CONFIGURATION 104 7.5.2 Conspec Controls system Conspec's Centurian S e r i e s 180 monitoring and c o n t r o l system i s a Canadian system which could be s a t i s f a c t o r y . F i gure 23 i l l u s t r a t e s how i t would be used i n the p r o j e c t . I t c o n s i s t s of a c e n t r a l computer t h a t has a CRT d i s p l a y keyboard and one p r i n t e r a s s o c i a t e d w i t h i t . The computer i s capable of monitoring two trunk l i n e s of which only one i s req u i r e d f o r r e c i r c u l a t i o n c o n t r o l . At each input or output l o c a t i o n there i s an addressable accessor card which converts the sensor s i g n a l to bina r y or converts a bin a r y command to analog d i g i t a l output. Many types of accessor cards are a v a i l a b l e . One type i s a m u l t i p l e accessor t h a t allows 8 analog i n p u t s . The 8 analog inputs have to be of the same form (such as 4-20 MA or 0-5V). The output of the transducers are not known at t h i s time. I t i s t h e r e f o r e not p o s s i b l e to decide how many m u l t i p l e accessors can be used instead of a s i n g l e accessor f o r each output. Fans and r e g u l a t o r I/O are handled by a B2 accessor plus r e l a y . The trunk l i n e that c a r r i e s a l l the data between underground and surface has a maximum length of 1400 meters. A modem i s required between the master s t a t i o n and the remote trunk l i n e . A software package provided w i t h the system has been developed by Conspec and i s user f r i e n d l y . There i s no l o c a l c o n t r o l or d i s t r i b u t e d a r c h i t e c t u r e w i t h t h i s system, s i n c e the o u t s t a t i o n s are not " i n t e l l i g e n t " . A s p e c i a l f a i l - s a f e device ( b a t t e r y operated) t h a t would shut the r e g u l a t o r i n the r e c i r c u l a t i o n branch i n the e v e n t u a l i t y of a communication breakdown or power shortage, would have to be included. The costs of the u n i t are shown i n Table 18. CENTURIAN SERIES 180 Printer II II, phone line EXHAUST FANS X MODEM 4 A TRUNK ACCESSOR INTAKE FANS 2 * ACCESSOR C A R D (single or multiple input) Fig. 23 CONSPEC SYSTEM CONTROL CONFIGURATION 106 TABLE 18 Conspec System Costs D e s c r i p t i o n Cost $ Hardware and Software - Centurian S e r i e s 180 System 21 200 - S i n g l e accessor c a r d s ( l 2 ) 3 600 - M u l t i p l e acaccessor cards (2) 2 800 - Relays f o r fans & r e g u l a t o r (4) 800 - Telemetry cable ($1.16/foot) 4 000 Other - Shipping - Taxes - Personnel t r a i n i n g / 3 days t r a i n i n g at Conspec's o f f i c e i n Downsview, Ontario TOTAL: 36 700 7.5.3 Montan-Forschung system Montan-Forschung has gained much success i n North America w i t h i t s v o i c e communication system. The Montan-Forshung r a d i o equipment was r e c e n t l y commissioned at Ruttan Mine. The MSE-22/MD Mark I I microprocessor based data t e r m i n a l i s the o u t s t a t i o n that could be used to monitor and c o n t r o l the system ( F i g . 2 4 ) . The o u t s t a t i o n can be adapted w i t h a s p e c i a l input/output p l a t e that w i l l a l l o w the Mark I I to re c e i v e 16 analog input channels and 16 analog output channels. The o u t s t a t i o n does not operate on a stand alone s t a t u s but i t s microprocessor can be programmed to r e t u r n the system to a f a i l - s a f e mode i n the case of communication breakdown. The t e r m i n a l has an i n t e r n a l port which w i l l t a l k to the ra d i o l i n k and the surface i n t e r f a c e computer. The i n t e r f a c e computer, which was purchased by S h e r r i t t Gordon 300 2 500 1 500 I B M - P C - A T Printer phone line INTAKE FANS M O N T A N - F O R S C H U N G SYSTEM C O N T R O L C O N F I G U R A T I O N 108 Mines, under a d i f f e r e n t c o n t r a c t , w i l l p o l l the mobile data s t a t i o n s . The i n t e r f a c e computer w i l l communicate w i t h the master s t a t i o n . The master s t a t i o n p r e s e n t l y used at Ruttan f o r the mobile data equipment i n the mine i s an IBM-PC-AT. Software r e q u i r e d w i l l have to be designed by UBC and IMS e l e c t r o n i c s . I t i s d i f f i c u l t to make an exact quote f o r the cost of t h i s design but estimated c o s t s are shown i n Table 19. TABLE 19 Montan Forschung System Costs D e s c r i p t i o n Hardware - 2 -MSE/22 MD Mark I I ($6,000 each) 2 - I/O Adaptors ($3,000 each) 2 - MSE-22/SE Radio Transceiver ($2,300) Telemetry cables Software - Software f o r IBM-PC-AT 4 000 (This i s only a vague estimate) Other - duty on German equipment 3 000 - Taxes 1 500 - Personnel t r a i n i n g 1 500 Cost $ 12 000 6 000 4 600 2 000 TOTAL: 34 600 109 7.6 CONCLUSIONS OF INSTRUMENTATION STUDY 7.6.1 Dust monitoring There are three methods of dust measurement t h a t can be adapted to an o n - l i n e monitoring system; they are piezobalance, beta a t t e n u a t i o n and l i g h t s c a t t e r i n g . The f i r s t two methods were not considered i n t h i s r eport because they are not s u i t a b l e f o r the purpose of r e c i r c u l a t i o n monitoring. The Piezobalance has not been adapted f o r underground use, and the cost of the equipment i s s i g n i f i c a n t (-$35,000). Beta a t t e n u a t i o n instruments have poor p r e c i s i o n , they cannot detect dust l e v e l s below 0.5 mg/m and time r e s o l u t i o n i s very high. L i g h t s c a t t e r i n g methods t h e r e f o r e remain the only v i a b l e means of measuring instantaneous dust l e v e l s . The dependency of l i g h t s c a t t e r i n g instruments on the o p t i c a l p r o p e r t i e s and surface area of dust p a r t i c l e s makes them s e n s i t i v e to changes i n dust composition. Proper i n t e r n a l c a l i b r a t i o n of the zero and the reference v a l u e s , accurate c a l i b r a t i o n against g r a v i m e t r i c r e s u l t s and a c a r e f u l sampling method could p a r t i a l l y e l i m i n a t e t h i s problem. The l i g h t s c a t t e r i n g instruments t h a t are the most promising f o r r e c i r c u l a t i o n are the MMRDM (modified v e r s i o n of the RAM-1) manufactured by GCA and the O s i r i s (modified v e r s i o n of the S i m s l i n I I ) introduced by the B r i t i s h N a t i o n a l Coal Board. They are very rugged instruments using pre-samplers to measure the r e s p i r a b l e dust. Long-term operation i s a t t a i n e d by r e c i r c u l a t i n g clean a i r through the c a v i t i e s of the l i g h t s c a t t e r i n g sensing stage to prevent the d e p o s i t i o n of p a r t i c l e s on o p t i c a l l y s e n s i t i v e s u r f a c e s . They are a l s o capable of s t o r i n g data f o r over 8 hours and are equipped w i t h analog outputs. The O s i r i s has the advantage of having v a r i a b l e d e t e c t i n g angles which provide the p o s s i b i l i t y of tuning the sensor to best s u i t the s p e c i f i c mine dust composition. The Metrex instrument, designed i n Canada, could have a p p l i c a t i o n i n the f u t u r e , once the company c o r r e c t s the design problems. The 110 p o s s i b i l i t y of measuring the d i e s e l p a r t i c u l a t e l e v e l s underground i s important f o r the use of AQI c r i t e r i a . Most instruments have been t e s t e d and c a l i b r a t e d i n c o a l dust atmospheres. I t i s e s s e n t i a l t h a t t e s t i n g should be conducted f o r dusts t y p i c a l l y found i n metal mines i n c l u d i n g d i e s e l r e l a t e d dusts. 7.6.2 Telemetry and processsing The B r i s t o l System i s very cost e f f i c i e n t and v e r s a t i l e . Each o u t s t a t i o n i s p r o t e c t e d by a f i b e r g l a s s casing which enables i t to withstand environments of 0-100% humidity and 0°-60° temperatures. The o u t s t a t i o n s are " i n t e l l i g e n t " and can operate on t h e i r own, without the surface computer. The p r e d i c t e d cost of $37 000 could be brought down to $27 000 w i t h the purchase of an IBM compatible computer i n s t e a d of a PC-XT and the use of only one RTU-3320 o u t s t a t i o n i f p r a c t i c a l . B r i s t o l i s w e l l e s t a b l i s h e d and has o f f i c e s i n both Western and Eastern Canada. The Conspec system i s not as v e r s a t i l e s i n c e the o u t s t a t i o n s are not " i n t e l l i g e n t " . A l l process c o n t r o l d u t i e s are performed by the s u r f a c e master s t a t i o n . A s p e c i a l f a i l - s a f e system w i l l have to be added. The system i s s t i l l cost e f f i c i e n t and the accessor card i s made to withstand mining environment c o n d i t i o n s . A Conspec system has been r e c e n t l y purchased by Canmet. UBC was asked by Canmet to be i n v o l v e d i n the t e s t i n g of the Conspec sensors i n a mine s i t u a t i o n . This opens up the p o s s i b i l i t y of t e s t i n g the Conspec system without committing money to telemetry instrumentation immediately, by working i n c l o s e r e l a t i o n s h i p w i t h Canmet. The Montan-Forschung system has a l r e a d y been purchased by Ruttan Mine, f o r v o i c e communication and data communication w i t h mobile equipment. In t h i s respect i t would be b e n e f i c i a l to purchase a Montan-Forschung system s i n c e the mine personnel are already f a m i l i a r w i t h the instrumentation and some of the equipment i s already i n p l a c e and does not need to be purchased. The system can be programmed to a l l o w f a i l - s a f e mode f o r an eventual communication breakdown, but i t cannot I l l assume t o t a l l o c a l c o n t r o l u n l i k e the B r i s t o l system. The software needs to be designed and p a r t s supply could be a problem si n c e a l l p a r t s must be shipped from Germany. A l l three systems w i l l have a cost i n the range of $30 000 to $35 000. 7.6.3 F i n a l c o n t r o l elements A frequency c o n t r o l l e r o f f e r s a range of 0.4-1.2 of the nominal fan speed and i s the p r e f e r r e d type of fan q u a n t i t y c o n t r o l . Such d r i v e s cost approximately $20 000 (5 d r i v e s are r e q u i r e d ) . A p o s s i b l e r e g u l a t o r i s a m u l t i p l e vane r e g u l a t o r w i t h a cost i n the range of $4 000 to $5 000. 7.6.4 Sensors S p e c i f i c a t i o n s f o r each sensor to be i n t e g r a t e d i n the design must be d r a f t e d . Dust sensors form a major pa r t of the t o t a l sensor cost. This cost w i l l be i n the range of $40 000 to $45 000. T o t a l cost of the instrumentation system w i l l be i n the range of $150 000 to $200 000. 112 8.0 DUST FILTRATION The study at Ruttan showed t h a t d i l u t i o n and sedimentation played an important r o l e i n reducing the con c e n t r a t i o n of p a r t i c u l a t e matter produced. However, s i n c e these e f f e c t s do not e n t i r e l y e l i m i n a t e the dust, r e c i r c u l a t i o n w i l l increase the l e v e l of dust i n the mine. F i l t r a t i o n of the dust, as the a i r passes through the r e c i r c u l a t i o n branch, could reduce the amount of r e c i r c u l a t e d dust to a l e v e l which would be i n s i g n i f i c a n t i n comparison to the concentrations normally found i n working l e v e l s . The methods a v a i l a b l e f o r dust f i l t r a t i o n are: a) G r a v i t y Methods b) C e n t r i f u g a l Methods c) F a b r i c F i l t e r s d) E l e c t r o s t a t i c P r e c i p i t a t o r s e) Wet scrubbers a) G r a v i t y Methods G r a v i t y c o l l e c t o r s remove dust by a l l o w i n g a h o r i z o n t a l c u r r e n t of dust-laden a i r to enter a r e l a t i v e l y stagnant zone of a i r f l o w where the dust p a r t i c l e s are separated and deposited. However, the r e l a t i v e l y l a r g e s i z e of the apparatus combined w i t h i t s poor e f f i c i e n c y i n d e a l i n g w i t h p a r t i c l e s s m a l l e r than 100 um, render i t i n a p p r o p r i a t e f o r a r e c i r c u l a t i o n a p p l i c a t i o n b) C e n t r i f u g a l Methods C e n t r i f u g a l c o l l e c t o r s f o r c e the dust-laden a i r to undergo a number of r e v o l u t i o n s i n a c i r c u l a r chamber. The dust p a r t i c l e s are c a r r i e d to the w a l l of the chamber and f a l l to the base, where they are withdrawn. C e n t r i f u g a l c o l l e c t o r s or cyclones are very i n e f f i c i e n t i n removing p a r t i c l e s i n the r e s p i r a b l e range (<10 um). 113 c) F a b r i c F i l t e r s A irborne dust can a l s o be removed by passing the dust-laden a i r through a permeable, porous m a t e r i a l which traps the p a r t i c l e s . These f i l t e r s can have very h i g h e f f i c i e n c i e s exceeding 90%. The dust deposit from the f a b r i c can be removed by e i t h e r changing the f i l t e r element, through mechanical rapping or shaking, by reverse a i r j e t , or by pulse j e t . Such f i l t e r s are very popular i n uranium mines to c o n t r o l radon daughters, but the l a r g e s t f i l t e r manufactured can only handle about 450 m / s . Pressure drops across the f i l t e r s can a l s o be s u b s t a n t i a l but are u s u a l l y l e s s than f o r wet scrubbers. d) E l e c t o s t a c t i c P r e c i p i t a t o r s In an e l e c t r o s t a t i c separator (82), a stream of e l e c t r o n s at r i g h t angles to the d i r e c t i o n of the a i r f l o w passes from a number of negative e l e c t r o d e s , maintained at a v o l t a g e , to grounded p o s i t i v e e l e c t r o d e p l a t e s . Dust p a r t i c l e s , having acquired a negative charge, are a t t r a c t e d to the p o s i t i v e e l e c t r o d e s and are then removed from these by i n t e r m i t t e n t mechanical v i b r a t i o n s or by water f l u s h i n g . E l e c t r o s t a t i c separators can remove r e s p i r a b l e s i z e d p a r t i c l e s e f f i c i e n t l y and have r e l a t i v e l y low energy consumption. The a p p l i c a t i o n i s mainly f o r 3 i n d u s t r i a l v e n t i l a t i o n , where the q u a n t i t y of a i r i s below 300 m / s . The e f f i c i e n c y decreases r a d i c a l l y i n h i g h humidity atmosphere (> 80 % ) , making them u n s u i t a b l e f o r a r e c i r c u l a t i o n system. Wet Scrubbers There are many types of wet scrubbers (83) and they are the favoured f i l t r a t i o n devices i n c o a l mines. They c o n s i s t of flooded bed scrubbers, v e n t u r i scrubbers, s e l f - i n d u c e d scrubbers and simple water sprays i n confined non-venturi flow. The only scrubbers t h a t could have an a p p l i c a t i o n i n a r e c i r c u l a t i o n system, because of the l a r g e a i r volume and low c o n c e n t r a t i o n , i s the confined water spray system. The e f f i c i e n c y of such a scrubber i s d i r e c t l y r e l a t e d t o the s i z e of the water d r o p l e t s generated. F i g . 25 demonstrates the importance of s m a l l 114 Airflow around large and small water droplets (after Schowengerdt and Brown, 1976).(86) Fig- 25 115 d r o p l e t s i n the e f f i c i e n c y of the system to capture submicron p a r t i c l e s . A paper by Schroeder et a l (84) s t u d i e d the d r o p l e t s i z e of the d i f f e r e n t n o z z l e types manufactured, and found t h a t s o n i c atomizers, s o n i c mist j e t s and a i r atomizers produced the sm a l l e s t d r o p l e t s . The mean d r o p l e t s i z e f o r these atomizers v a r i e d between 3.8 um and 7.3 um (Table 20). A l l of these sprays r e q u i r e both water and compressed a i r . A spray chamber th a t was used f o r c o o l i n g purposes i n the d i s t r i c t r e c i r c u l a t i o n of a deep gold mine was found to have very b e n e f i c i a l dust-scrubbing q u a l i t i e s . Booth-Jones et a l (85) s t u d i e d the e f f i c i e n c y of t h i s d i r e c t - c o n t a c t spray bulk a i r c o o l e r and showed t h a t such a c o o l e r could e f f i c i e n t l y remove l a r g e p a r t i c l e s (>10 um) but was r e l a t i v e l y i n e f f e c t i v e i n removing dust p a r t i c l e s i n the r e s p i r a b l e s i z e range. A la b o r a t o r y i n v e s t i g a t i o n i n t o the dust-scrubbing c h a r a c t e r i s t i c s of a spray c o o l i n g chamber c o n s i s t i n g of a bank of atomizing n o z z l e s was described i n the paper. The r e s u l t s i n d i c a t e d t h a t by using a s u f f i c i e n t q u a n t i t y of compressed a i r , i t was p o s s i b l e to have a c o l l e c t i o n e f f i c i e n c y of 70 % down to p a r t i c l e s i z e s of .4 um and 60 % f o r p a r t i c l e s as small as .05 um. In Fig.26, the compressed a i r q u a n t i t i e s are 3 represented by kw a d i a b a t i c energy of compression f o r a flow of 3.6 m / s . The only problem w i t h the watersprays (84) i s t h a t i n order to be e f f e c t i v e dust scrubbers, s o n i c a l l y atomized water d r o p l e t s plus captured dust p a r t i c l e s must be removed from the a i r s t r e a m . The use of a coarse counterspray ( n o z z l e producing d r o p l e t s > 20 um) w i l l r e s u l t i n a h i g h l y e f f e c t i v e e l i m i n a t i o n of micron-size d r o p l e t s (75 %) and f u r t h e r increase by i n c o r p o r a t i o n of a mist e l i m i n a t o r (80 % ) . The use of these two methods w i l l c r eate an increase i n pressure drop across the f i l t r a t i o n system. However, no data on pressure drop were a v a i l a b l e . This chapter has b r i e f l y described a l l of the f i l t r a t i o n methods a v a i l a b l e to the v e n t i l a t i o n engineer. I t i s concluded t h a t wet dust-scrubbing and f a b r i c f i l t r a t i o n have the best p o t e n t i a l as f i l t e r s f o r use i n r e c i r c u l a t i o n i n Canadian mines. • Q -• High Energy 15.9kW • Medium Energy 13,0 kW A Low Energy 5,87 kW T T 1 j — — r -0,1 0,2 0,U 0,8 1,6 3,2 Particle size: D (50) microns 0,05 —r— 6A 12,5 i 25 Grade efficiency results for atomizing nozzle scrubber at three levels of energy input: operating parameters (i) high energy: air pressure 400 kPa, water flow rate 1.70 1/s, liquid/gas ratio 0.5 1/m3; (ii) medium energy: air pressure 300 kPa, water flow rate 1.03 1/s, liquid/gas ratio 0.3 l/m J; (iii) low energy: air pressure 170 kPa, water flow rate 0.42 1/s, liquid/gas ratio 0.12 l/m3 (After Booth-Jones et al., 1984) Fig. 26 117 Impact on r e c i r c u l a t i o n ; In the previous chapter, the equation developed by Hardcastle f o r dust sedimentation w i t h a r e c i r c u l a t i o n system was presented. Hardcastle has a l s o developed the equation to take f i l t r a t i o n i n t o account. In f a c t , r e c i r c u l a t i o n and sedimentation can be modelled i n the same way s i n c e they both can be represented by a dust decay f a c t o r : d 3T = d 3 . [ l + F ' ( f ( l - R ) * f ( l - S ) + F 2 * f 2 ( l - R ) * f 2 ( l - S ) + . . . + F n * f n ( l - R ) * f n ( l - S ) ] where R represents the f i l t r a t i o n r a t i o . Hardcastle then wrote a r e c i r c u l a t i o n s i m u l a t i o n program to see the e f f e c t of sedimentation and f i l t r a t i o n at d i f f e r e n t r e c i r c u l a t i o n l e v e l s . The f i e l d work at Ruttan showed t h a t the sedimentation f a c t o r ( i n c l u d i n g the d i l u t i o n f a c t o r ) was at l e a s t 40 %. His model p r e d i c t s t h a t f o r a sedimentation f a c t o r of .4 and a f i l t r a t i o n f a c t o r of .7 f o r r e s p i r a b l e dust (the average f i l t r a t i o n e f f i c i e n c y f o r water s p r a y s ) , i t would be p o s s i b l e to r e c i r c u l a t e up to 18 % w i t h a maximum increase of 5% i n contaminants mass i n the r e t u r n airway and up to 33 % w i t h a maximum increase of 10 % ( F i g 27). 118 Recirculation Factor (%/lOO) 0 Ol 02 03 04 0-5 0€ 07 0-8 0-9 a) Contours of relative change in return side dust flow Dy moss. (After Hardcastle, 1985) F i g . 27 119 9.0 COST ANALYSIS There i s i n s u f f i c i e n t i n f o r m a t i o n a v a i l a b l e a t t h i s time to enable the author to recommend a safe l e v e l of percentage r e c i r c u l a t i o n t h a t may be permitted i n Canadian mines. The Ruttan r e s u l t s show t h a t the maximum percentage should be e s t a b l i s h e d on a case by case b a s i s . However, the author b e l i e v e s t h a t 30 % r e c i r c u l a t i o n could be achieved i n a system combining the use of sound monitoring and c o n t r o l instrumentation w i t h a method of r e c i r c u l a t e d a i r f i l t r a t i o n . I f a 30 % r e c i r c u l a t i o n system i s i n s t a l l e d , the minimum heating cost r e d u c t i o n w i l l be 30 %. The c a p i t a l cost of the system w i l l vary from mine to mine, depending on va r i o u s f a c t o r s such as the a v a i l a b i l i t y of a booster f a n , instrumentation costs and the cost of excavation ( r e c i r c u l a t i o n branch) i f a p p l i c a b l e . The power cost w i l l i n c r e a s e s l i g h t l y , s i n c e the booster fan w i l l work against h i g h pressures but the t o t a l power increase w i l l be r e l a t i v e l y i n s i g n i f i c a n t . The f o l l o w i n g i s an i l l u s t r a t i o n of the e x t r a savings t h a t could be r e a l i z e d f o r a h y p o t h e t i c a l mine: I f a 30 % r e c i r c u l a t i o n system i s i n s t a l l e d i n a mine w i t h the f o l l o w i n g c h a r a c t e r i s t i c s , what annual o p e r a t i o n a l savings ( s t r i c t l y o p e r a t i o n a l ) can be expected ? - 300 m /sec of a i r i s d i s t r i b u t e d to the mine - the a i r exhausts a t a temperature of 10 C - the average w i n t e r temperature i s -15 C - a propane system w i t h 75 % e f f i c i e n c y i s used - there are on the average 130 heating days per year - the propane cost i s 25 c e n t s / l i t r e - 40,000 KJ can be generated w i t h one l i t r e of propane - the in t a k e a i r must be heated to a temperature of 1 C 120 ORIGINAL HEATING COST Heat r e q u i r e d per hour: 3600 s/hr * 300 m3/s * ( l - ( - 1 5 ) ) C * 1.2 kg/m3 * 1.01 KJ/kg C = 20,922,624 KJ/hr L i t r e s r e q u i r e d per hour: 20,922,624 KJ/hr / (40,000 K J / l i t r e * .75) = 697 l i t r e s / h r Cost per year: .25 * 130 * 24 * 697 = $ 543,660.00 per year SAVINGS FROM RECIRCULATION AIR Gain from a i r requirements r e d u c t i o n : $ 543,660 * 30 % = $ 163,098 CAPITAL COST $ 200,000 10,000 25,000 Cost of instrumentation system (see i n strumentation chaper) Cost of booster fan Cost of water spray system TOTAL: 235,000 121 If a water spray system similar to the one in the f i l t r a t i o n chapter is used, the annual energy cost can be outlined as follows: the high 3 3 energy setting of A. A kw/m /s (see f ig 26, 15.9 kw/(3.6 m/ s ) ) w i l l be used to obtain a good respirable dust control efficiency. A power cost of $0.02 per kw-hr is assumed. 3 i 3 Power = A.A kw/m /s * 90 m /sec =396 kw or 3.96 * 10 5 J/s Cost = $ 0.02/1 kw-hr = $ 0.02/3.6 * 106 J Time = 130 days of heating = 11,232,000 seconds TOTAL COST = (3.96 * 105) * (11,232,000) / (3.6 * 10 6) * $ 0.02 = $ 2A,710 / year SUMMARY 1. CAPITAL COST 2. COMPRESSED AIR COST (per 3. SAVINGS (per year) $ 235,000. year) 2A.710. 163,098. This could be an excellent investment with a payback of less than 2 years. 122 10.0 CONCLUSIONS The l i t e r a t u r e survey and environmental monitoring work conducted a t Ruttan provided s u b s t a n t i a l information on the f e a s i b i l i t y of r e c i r c u l a t i n g exhaust mine a i r . The f o l l o w i n g conclusions are the major p o i n t s determined by the survey: 1. D i l u t i o n , sedimentation and moisture have a s i g n i f i c a n t e f f e c t on p o l l u t a n t l e v e l s . I t i s important to r e c i r c u l a t e as c l o s e to the surface as p o s s i b l e i n order to o b t a i n the maximum b e n e f i t from these e f f e c t s . The e f f e c t of d i f f u s i o n and agglomeration on submicron p a r t i c l e s needs to be i n v e s t i g a t e d f u r t h e r , a l s o , the conversion of N O 2 and SO^ to acid s and the t r a n s p o r t of such a c i d s along w i t h the v e n t i l a t i o n a i r must be q u a n t i f i e d . The t o x i c i t y of such a c i d s i s much higher than the gases. 2. Carbon monoxide appears to be the l i m i t i n g f a c t o r i n a r e c i r c u l a t i o n system f o r the present c o n d i t i o n s at Ruttan. However i t i s expected t h a t CO would be reduced to minimum l e v e l s (<10ppm) once the f o l l o w i n g c o n d i t i o n s were met: i ) proper o p e r a t i o n of the new v e n t i l a t i o n network. i i ) accurate d e r a t i n g of the engine. i i i ) proper maintenance of the c a t a l y t i c converters. A study i s underway at Ruttan to t e s t a new p u r i f i e r manufactured by D i e s e l C o n t r o l s Systems L i m i t e d , t h a t could reduce CO l e v e l s by 90%. This could have a major impact on r e c i r c u l a t i o n . 3. A thorough i n v e s t i g a t i o n of dust concentrations i s r e q u i r e d i n order to analyse s t a t i s t i c a l l y the data. Understanding the changes i n the d i f f e r e n t dust c o n s t i t u e n t s as the a i r r i s e s t o the surface i s of p a r t i c u l a r importance. The present r e s u l t s suggest t h a t the l e v e l of dust i n the surface exhaust i s very low. I t i s f e a s i b l e to f i l t e r or suppress p a r t i c u l a t e s i n 123 the r e c i r c u l a t e d a i r i f r e q u i r e d . A. A more extensive study, using r e l i a b l e instrumentation should be c a r r i e d out j o i n t l y by UBC and CANMET. Such study would q u a n t i f y the conce n t r a t i o n of contaminants i n the underground workings and evaluate the f i l t r a t i o n and d i l u t i o n c a p a c i t y of the v e n t i l a t i o n network. The i n t r o d u c t i o n of ceramic p u r i f i e r s i n mines could make r e c i r c u l a t i o n very a t t r a c t i v e . These and other exhaust treatment systems c u r r e n t l y a v a i l a b l e or under development have the p o t e n t i a l to s i g n i f i c a n t l y reduce gaseous p o l l u t a n t emissions. This w i l l have a marked e f f e c t on the AQI values which can be obtained i n exhaust a i r and permit increased r e c i r c u l a t i o n f o r the same environmental q u a l i t y at the workplace. The problem t h a t e x i s t s at present i s i n the monitoring and technology s e c t o r . I t was shown i n t h i s t h e s i s t h a t except f o r o n l i n e dust monitoring, a l l the hardware and software instrumentation r e q u i r e d to monitor adequately and c o n t r o l the network i s p r e s e n t l y manufactured. However, there have been few underground f i e l d t r i a l s i n North America. D u r a b i l i t y of the system i n the harsh mining environment and y e a r l y costs of maintaining such a system are unknown f a c t o r s a t present. The l i m i t a t i o n s could pose a s e r i o u s t h r e a t to r e c i r c u l a t i o n p r a c t i c e . The t e c h n i c a l problem of designing a s u i t a b l e m i neral and d i e s e l p a r t i c l e sensor must a l s o be solved. F i n a l l y i t i s important to devise b e t t e r models which w i l l i n c l u d e the s i m u l a t i o n of a l l the environmental processes t a k i n g place w i t h i n the network. These models w i l l gather more r e l i a b l e i n f o r m a t i o n which w i l l h o p e f u l l y convince governments and companies to provide more funding f o r f i e l d i n v e s t i g a t i o n s . In summary, t h i s p r e l i m i n a r y study to i n v e s t i g a t e the use of r e c i r c u l a t i o n to decrease heating cost of underground v e n t i l a t i o n has proven very s u c c e s s f u l . I t demonstrates t h a t the r a t e of r e t u r n of such 124 an investment i s p o t e n t i a l l y e x c e l l e n t . On the other hand, i t c l e a r l y i n d i c a t e s t h a t there i s a considerable amount of research r e q u i r e d i n t o the f i e l d s of instrumentation and environmental engineering before implementing t h i s new v e n t i l a t i o n p r a c t i c e i n Canada. In the i n t r o d u c t i o n of t h i s t h e s i s , the author mentioned t h a t s u b s t a n t i a l savings could be achieved by c o n t r o l l i n g the speed of the v e n t i l a t i o n fans and a d j u s t i n g the v e n t i l a t i o n t o the needs of the system by monitoring of the contaminants present i n the network. Before i n s t a l l i n g a r e c i r c u l a t i o n system, t h i s goal should f i r s t be achieved. I t would be premature to implement a r e c i r c u l a t i o n c i r c u i t i f a conventional system cannot be c o n t r o l l e d s u c c e s s f u l l y . Another step t h a t must a l s o precede r e c i r c u l a t i o n i s the adequate computer modelling of the v e n t i l a t i n g system. There i s not one mine i n Canada to the author's knowledge t h a t r e l i e s e n t i r e l y on computer modelling to design and troubleshoot the v e n t i l a t i o n network. Mine v e n t i l a t i o n and c o n t r o l of the underground environment o f f e r s a challenge to mining engineers and there i s scope f o r s i g n i f i c a n t improvement i n t h i s f i e l d . The author hopes t h a t t h i s t h e s i s w i l l encourage mine operators, government agencies and f e l l o w mining engineers to i n v e s t i g a t e the p o t e n t i a l f o r c o n t r o l l e d r e c i r c u l a t i o n and improved v e n t i l a t i o n planning i n Canadian mines. 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T., (1976); Colorado School of Mines  Tackles C o n t r o l of R e s p i r a b l e Coal Dust, Coal Age, V o l . 81, Num. 4, A p r i l , 1976, Pages 129-131 . 135 APPENDIX 1 u> -4 AQI(GASES) R E S U L T S 50% RECIRCULATION 2 _. 1 2 3 4 5 6 7 3 3 10 TI [ /\ base contamination (NUMBER OF CYCLES) gg§2 recfrculat. effect AQI(GASES) R E S U L T S 70% RECIRCULATION S J 2 3 4 5 0 7 B 9 J Q J 1 (NUMBER OF CVCLES) | y\ base contamination E§§2 reclrculat. effect PARTICULATES RESULTS 10% RECIRCULATION 4 -2 -3 -fcspzssq / 2 A A Y.A V A 1/ A Y .A I 3 /^j base contamination 8 (NUMBER OF CYCLES) E§53 roclrculat. effect 10 11 PARTICULATES RESULTS 30% RECIRCULATION 7  6 -5 -4 -1 2 3 4 5 6 7 8 9 10 11 [ / H base contamination (NUMBER OF CYCLES) reclrculat. effect 7 PARTICULATES RESULTS 50X RECIRCULATION 6 -5 -1 2 3 4 5 6 7 8 9 10 11 (NUMBER OF CYCLES) CZZj b a s e contaminat ion K£&>2 reclrculot . e f fect P A R T I C U L A T E S R E S U L T S 70% RECIRCULATION 7 . . I /\ base contamination (NUMBER OF CYCLES) ££££3 reclrculat. effect 144 APPENDIX 2 N 0 2 CONCENTRATION ON 660 LEVEL 03/06/86 AFTERNOON 1 ' " • • J j , , 1 , 0 2 4 6 8 TIME (HRS) N 0 2 C O N C E N T R A T I O N O N 6 6 0 L E V E L 04/06/86 NIGHTSHIRT 1 1 1 1 1 1 1 1 1 0 2 4 6 8 TIME (HRS) N 0 2 CONCENTRATION ON 660 LEVEL 0 3 / 0 6 / 8 6 AFTERNOON 1 1 1 I 1 I I I I 0 2 4 6 8 TIME (HRS) N02 CONCENTRATION ON 3 7 0 LEVEL 1 1 / 0 6 / 8 6 NIGHTSHIFT 0 2 4 6 8 TIME (HRS) C O C O N C E N T R A T I O N IN S U R F A C E E X H A U S T MIDNIGHT SHIFT. 1 0 / 0 6 / 8 6 1 1 1 1 1 1 1 1 1 0 2 4 6 8 TIME (HRS) 0. a. z o I r-Z UJ o z o o 90 80 70 H 60 H 50 H 40 H 30 20 H 10 H CO CONCENTRATION ON 3 7 0 LEVEL NIGHT SHIFT. 1 0 / 0 6 / 8 6 TIME (HRS) O 90 CO CONCENTRATION ON 3 7 0 LEVEL DAY SHIFT. 10/06/86 80 -70 -2 60 -Q. Q. 10 H 0 H 1 1 1 1 I 1 1 1 0 2 4 6 8 TIME (HRS) C O C O N C E N T R A T I O N O N 3 7 0 L E V E L AFTERNOON SHIFT, 10/06/86 _j 1 1 1 1 1 1 1 I 0 2 4 6 8 TIME (HRS) Q. a. z o I r -z Ul o z o o 90 80 H 70 H 60 50 H 40 H 30 - i 20 10 H CO CONCENTRATION ON 660 LEVEL NIGHT SHIFT, 1 3 / 0 6 / 8 6 TIME (HRS) CO CONCENTRATION ON 660 LEVEL DAY SHIFT. 13/06/86 90 -1 • • — 10 H o H 1 1 — i 1 1 1 1 1 0 2 4 6 8 TIME (HRS) C O C O N C E N T R A T I O N O N 6 6 0 L E V E L 13/06/86 AFTERNOON 1 1 1 1 1 1 1 1 0 2 4 6 8 TIME ( H R S ) 1 C02 CONCENTRATION ON 660 LEVEL AFTERNOON SHrFT, 03/06/86 2 0. Q_ _ a 5"° O c p o H u O o z O o 8 TIME (HRS) C02 CONCENTRATION IN SURFACE EXHAUST NIGHT SHIFT. 0 3 / 0 6 / 8 6 2 0-c s o JZ K ui. o z o o 0.9 H 0.8 0.7 -0.6 -0.5 -0.4 -0.3 0.2 0.1 0 2 4 TIME (HRS) "T~ 6 8 00 V O O N o C 0 2 CONCENTRATION ON 6 6 0 LEVEL NIGHT SHIFT. 0 4 / 0 6 / 8 6 0.2 -0.1 -0 - | 1 1 I 1 1 1 1 0 2 4 6 8 TIME (HRS) 

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