"Applied Science, Faculty of"@en . "Chemical and Biological Engineering, Department of"@en . "DSpace"@en . "UBCV"@en . "Yu, Ming Ming"@en . "2013-05-02T09:13:22Z"@en . "2013"@en . "Master of Applied Science - MASc"@en . "University of British Columbia"@en . "This thesis project studied the feasibility of co-gasification of biosolids with biomass\nas a means of disposal with energy recovery. The kinetics and gasification\nperformance of biosolids and biomass mixtures were studied with a\nthermogravimetric analyzer and a pilot scale bubbling fluidized bed, respectively.\nFrom the kinetics study, it was found that biomass, such as switchgrass, could\ncatalyze the gasification reactions because the ash of switchgrass contained a high\nproportion of potassium, which is considered as an excellent catalyst for gasification\nprocesses. However, it was found that biosolids could also inhibit gasification. When\nbiosolids were mixed with biomass, the inhibition effect overwhelmed the catalytic\neffect.\nFor the study of gasification performance, the impacts of biosolids proportion in the\nfuel, bed temperature, and steam/fuel ratio on gasification performance were\ninvestigated. As the biosolids proportion increased from 0 to 100%, syngas yield\ndecreased from 1.38 to 0.47 m\u00C2\u00B3/kg, char conversion decreased from 81.7% to 35.5%,\ntar content increased from 10.3 to 200 g/m\u00C2\u00B3, and ammonia concentration increased\nfrom 1660 to 19200 ppmv. A synergistic effect occurred at 25% biosolids. With\nincreasing biosolids proportion in the fuel, H\u00E2\u0082\u0082 and CH\u00E2\u0082\u0084 increased, CO decreased, and\nCO\u00E2\u0082\u0082 remained nearly constant in the syngas. As the steam/fuel ratio increased, the\nconcentrations of H\u00E2\u0082\u0082 and CO\u00E2\u0082\u0082 increased, while that of CO decreased in the syngas.\nDecreasing the bed temperature from 825 to 728\u00E2\u0084\u0083 did not affect syngas composition,\nbut decreased the syngas yield from 0.99 to 0.29 m\u00C2\u00B3/kg"@en . "https://circle.library.ubc.ca/rest/handle/2429/44411?expand=metadata"@en . "Co-gasification of Biosolids with Biomass in a Bubbling Fluidized Bed by Ming Ming Yu B.A.Sc, University of British Columbia, 2011 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE in THE FACULTY OF GRADUATE STUDIES (Chemical and Biological Engineering) THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver) April 2013 \u00C2\u00A9 Ming Ming Yu, 2013 ii\u00C2\u00A0 \u00C2\u00A0 ABSTRACT This thesis project studied the feasibility of co-gasification of biosolids with biomass as a means of disposal with energy recovery. The kinetics and gasification performance of biosolids and biomass mixtures were studied with a thermogravimetric analyzer and a pilot scale bubbling fluidized bed, respectively. From the kinetics study, it was found that biomass, such as switchgrass, could catalyze the gasification reactions because the ash of switchgrass contained a high proportion of potassium, which is considered as an excellent catalyst for gasification processes. However, it was found that biosolids could also inhibit gasification. When biosolids were mixed with biomass, the inhibition effect overwhelmed the catalytic effect. For the study of gasification performance, the impacts of biosolids proportion in the fuel, bed temperature, and steam/fuel ratio on gasification performance were investigated. As the biosolids proportion increased from 0 to 100%, syngas yield decreased from 1.38 to 0.47 m3/kg, char conversion decreased from 81.7% to 35.5%, tar content increased from 10.3 to 200 g/m3, and ammonia concentration increased from 1660 to 19200 ppmv. A synergistic effect occurred at 25% biosolids. With increasing biosolids proportion in the fuel, H2 and CH4 increased, CO decreased, and CO2 remained nearly constant in the syngas. As the steam/fuel ratio increased, the concentrations of H2 and CO2 increased, while that of CO decreased in the syngas. Decreasing the bed temperature from 825 to 728\u00D4\u00A8\u00C2\u00A0did not affect syngas composition, but decreased the syngas yield from 0.99 to 0.29 m3/kg. iii\u00C2\u00A0 \u00C2\u00A0 TABLE OF CONTENTS ABSTRACT\u00C2\u00A0...........................................................................................................\u00C2\u00A0ii\u00C2\u00A0 TABLE OF CONTENTS\u00C2\u00A0......................................................................................\u00C2\u00A0iii\u00C2\u00A0 LIST OF TABLES\u00C2\u00A0.................................................................................................\u00C2\u00A0vi\u00C2\u00A0 LIST OF FIGURES\u00C2\u00A0.............................................................................................\u00C2\u00A0viii\u00C2\u00A0 NOMENCLATURE\u00C2\u00A0..............................................................................................\u00C2\u00A0xii\u00C2\u00A0 ACKNOWLEDGEMENTS\u00C2\u00A0.................................................................................\u00C2\u00A0xiii\u00C2\u00A0 CHAPTER 1: INTRODUCTION\u00C2\u00A0..........................................................................\u00C2\u00A01\u00C2\u00A0 1.1 Introduction to biosolids\u00C2\u00A0.......................................................................................\u00C2\u00A01\u00C2\u00A0 1.1.1 Biosolids treatment technology\u00C2\u00A0......................................................................\u00C2\u00A01\u00C2\u00A0 1.1.2 Biosolids use and disposal\u00C2\u00A0.............................................................................\u00C2\u00A02\u00C2\u00A0 1.2 Introduction to gasification\u00C2\u00A0..................................................................................\u00C2\u00A05\u00C2\u00A0 1.2.1 History of gasification technology\u00C2\u00A0.................................................................\u00C2\u00A06\u00C2\u00A0 1.2.2 Gasification processes\u00C2\u00A0....................................................................................\u00C2\u00A06\u00C2\u00A0 1.2.3 Feedstocks\u00C2\u00A0......................................................................................................\u00C2\u00A07\u00C2\u00A0 1.2.4 Applications\u00C2\u00A0...................................................................................................\u00C2\u00A07\u00C2\u00A0 CHAPTER 2: LITERATURE REVIEW\u00C2\u00A0..............................................................\u00C2\u00A09\u00C2\u00A0 2.1 Biosolids characteristics\u00C2\u00A0.......................................................................................\u00C2\u00A09\u00C2\u00A0 2.1.1 Solid content\u00C2\u00A0..................................................................................................\u00C2\u00A09\u00C2\u00A0 2.1.2 Heating value\u00C2\u00A0...............................................................................................\u00C2\u00A011\u00C2\u00A0 2.1.3 Proximate and ultimate analyses\u00C2\u00A0..................................................................\u00C2\u00A011\u00C2\u00A0 2.1.4 Ash analysis\u00C2\u00A0.................................................................................................\u00C2\u00A015\u00C2\u00A0 2.1.5 Metal content\u00C2\u00A0...............................................................................................\u00C2\u00A018\u00C2\u00A0 2.2 Gasification performance\u00C2\u00A0...................................................................................\u00C2\u00A020\u00C2\u00A0 2.2.1 Catalyst development\u00C2\u00A0...................................................................................\u00C2\u00A020\u00C2\u00A0 iv\u00C2\u00A0 \u00C2\u00A0 2.1.2 Tar removal\u00C2\u00A0..................................................................................................\u00C2\u00A021\u00C2\u00A0 2.1.3 Pollutant byproduct gases: H2S, NH3, and HCl\u00C2\u00A0...........................................\u00C2\u00A021\u00C2\u00A0 2.1.4 Temperature effect\u00C2\u00A0.......................................................................................\u00C2\u00A023\u00C2\u00A0 2.1.5 Steam/fuel ratio effect\u00C2\u00A0..................................................................................\u00C2\u00A024\u00C2\u00A0 2.3 Co-gasification of biosolids with biomass\u00C2\u00A0.........................................................\u00C2\u00A024\u00C2\u00A0 2.3.1 Syngas yield, char conversion and tar concentration\u00C2\u00A0...................................\u00C2\u00A024\u00C2\u00A0 2.3.2 Syngas composition and heating values of syngas\u00C2\u00A0......................................\u00C2\u00A026\u00C2\u00A0 2.3.3 Summary\u00C2\u00A0......................................................................................................\u00C2\u00A027\u00C2\u00A0 2.3.3 Kinetics of co-gasification\u00C2\u00A0...........................................................................\u00C2\u00A027\u00C2\u00A0 2.4 Fluidization flow regime\u00C2\u00A0....................................................................................\u00C2\u00A028\u00C2\u00A0 CHAPTER 3: RESEARCH OBJECTIVES\u00C2\u00A0........................................................\u00C2\u00A030\u00C2\u00A0 CHAPTER 4: MATERIALS\u00C2\u00A0...............................................................................\u00C2\u00A032\u00C2\u00A0 4.1 Biosolids\u00C2\u00A0.............................................................................................................\u00C2\u00A032\u00C2\u00A0 4.2 Biomass\u00C2\u00A0..............................................................................................................\u00C2\u00A034\u00C2\u00A0 CHAPTER 5: KINETIC STUDY IN A TGA\u00C2\u00A0......................................................\u00C2\u00A036\u00C2\u00A0 5.1 Experimental setup\u00C2\u00A0.............................................................................................\u00C2\u00A036\u00C2\u00A0 5.2 Data analysis\u00C2\u00A0.......................................................................................................\u00C2\u00A037\u00C2\u00A0 5.3 Results and discussion\u00C2\u00A0........................................................................................\u00C2\u00A037\u00C2\u00A0 5.3.1 Separate gasification of biosolids, woody pellets and switchgrass\u00C2\u00A0..............\u00C2\u00A037\u00C2\u00A0 5.3.2 Co-gasification of biosolids with biomass\u00C2\u00A0...................................................\u00C2\u00A039\u00C2\u00A0 5.3.3 Catalytic and inhibition effect on gasification rate\u00C2\u00A0......................................\u00C2\u00A042\u00C2\u00A0 CHAPTER 6: GASIFICATION IN HIGHBURY PILOT SCALE BUBBLING FLUIDIZED BED\u00C2\u00A0................................................................................................\u00C2\u00A046\u00C2\u00A0 6.1 Experimental setup (Watkinson et al., 2010)\u00C2\u00A0......................................................\u00C2\u00A046\u00C2\u00A0 6.1.1 Feedstock\u00C2\u00A0.....................................................................................................\u00C2\u00A046\u00C2\u00A0 6.1.2 System\u00C2\u00A0..........................................................................................................\u00C2\u00A047\u00C2\u00A0 v\u00C2\u00A0 \u00C2\u00A0 6.1.3 Operating conditions\u00C2\u00A0....................................................................................\u00C2\u00A052\u00C2\u00A0 6.1.4 Operating procedure adapted from HEI manual\u00C2\u00A0..........................................\u00C2\u00A052\u00C2\u00A0 6.2 Data analysis\u00C2\u00A0.......................................................................................................\u00C2\u00A054\u00C2\u00A0 6.2.1 Syngas composition, LHV and syngas yield\u00C2\u00A0...............................................\u00C2\u00A054\u00C2\u00A0 6.2.2 Tar content in syngas\u00C2\u00A0....................................................................................\u00C2\u00A055\u00C2\u00A0 6.2.3 Ammonia determination\u00C2\u00A0...............................................................................\u00C2\u00A055\u00C2\u00A0 6.2.4 Char conversion\u00C2\u00A0...........................................................................................\u00C2\u00A056\u00C2\u00A0 6.2.5 Carbon balance.............................................................................................\u00C2\u00A056\u00C2\u00A0 6.3 Results and discussion of individual runs\u00C2\u00A0..........................................................\u00C2\u00A057\u00C2\u00A0 6.3.1 10% biosolids with 90% wood pellets by mass\u00C2\u00A0...........................................\u00C2\u00A058\u00C2\u00A0 6.3.2 100% wood pellets\u00C2\u00A0.......................................................................................\u00C2\u00A069\u00C2\u00A0 6.3.3 100% biosolids\u00C2\u00A0.............................................................................................\u00C2\u00A077\u00C2\u00A0 6.3.4 50% biosolids with 50% wood pellets by mass\u00C2\u00A0...........................................\u00C2\u00A084\u00C2\u00A0 6.3.5 25% biosolids with 75% wood pellets by mass\u00C2\u00A0...........................................\u00C2\u00A089\u00C2\u00A0 CHAPTER 7: IMPACTS OF BED TEMPERATURE AND BIOSOLIDS PROPORTION IN FUEL\u00C2\u00A0....................................................................................\u00C2\u00A094\u00C2\u00A0 7.1 Impact of bed temperature on syngas yield and composition\u00C2\u00A0............................\u00C2\u00A094\u00C2\u00A0 7.2 Impact of biosolids proportion in fuel on gasification performance\u00C2\u00A0..................\u00C2\u00A097\u00C2\u00A0 CHAPTER 8: CONCLUSIONS AND RECOMMENDATIONS\u00C2\u00A0.......................105\u00C2\u00A0 REFERENCES\u00C2\u00A0...................................................................................................107\u00C2\u00A0 APPENDIX: SUPPLEMENTAL RESULTS FROM BUBBLING FLUIDIZED BED GASIFICATION\u00C2\u00A0........................................................................................110\u00C2\u00A0 \u00C2\u00A0 \u00C2\u00A0 vi\u00C2\u00A0 \u00C2\u00A0 LIST OF TABLES Table 2-1 Solid content of biosolids from different WWTPs in Vancouver (source: Greater Vancouver Sewerage & Drainage District Quality Control Annual Report, 2011)\u00C2\u00A0....................................................................\u00C2\u00A010\u00C2\u00A0 Table 2-2 Ranges of solid content of biosolids after different dewatering techniques (source: Biosolids Generation, Use, and Disposal in the United States, 1999)\u00C2\u00A0....................................................................................\u00C2\u00A010\u00C2\u00A0 Table 2-3 Typical proximate and ultimate analyses of biosolids\u00C2\u00A0.....................\u00C2\u00A012\u00C2\u00A0 Table 2-4 Typical proximate and ultimate analyses of wood pellets\u00C2\u00A0...............\u00C2\u00A013\u00C2\u00A0 Table 2-5 Typical proximate and ultimate analyses of coal\u00C2\u00A0.............................\u00C2\u00A014\u00C2\u00A0 Table 2-6 Typical ash analyses of biosolids\u00C2\u00A0.......................................................\u00C2\u00A016\u00C2\u00A0 Table 2-7 Typical ash analyses of other gasification feedstocks\u00C2\u00A0......................\u00C2\u00A017\u00C2\u00A0 Table 2-8 Metal content (mg/kg) in biosolids reported by Toronto and Vancouver\u00C2\u00A0....................................................................................................\u00C2\u00A019\u00C2\u00A0 Table 4-1 Proximate and ultimate analyses of biosolids from different sources .......................................................................................................................\u00C2\u00A033\u00C2\u00A0 Table 4-2 Ash fusion analysis of biosolids from Baltimore WWTP\u00C2\u00A0................\u00C2\u00A034\u00C2\u00A0 Table 4-3 Proximate and ultimate analyses of wood pellets and switchgrass\u00C2\u00A035\u00C2\u00A0 Table 5-1 Ash analysis of switchgrass, wood pellets and biosolids\u00C2\u00A0.................\u00C2\u00A039\u00C2\u00A0 Table 6-1 Steady state gas concentrations for the run with 10% biosolids in fuel and for 178-292 min period\u00C2\u00A0................................................................\u00C2\u00A065\u00C2\u00A0 Table 6-2 Characteristics of collected solids in cyclones for run with 10% biosolids with 90% wood pellets\u00C2\u00A0................................................................\u00C2\u00A069\u00C2\u00A0 Table 6-3 Steady state gas concentrations for run with 100% wood pellets and for 130-231 min period\u00C2\u00A0...............................................................................\u00C2\u00A074\u00C2\u00A0 vii\u00C2\u00A0 \u00C2\u00A0 Table 6-4 Characteristics of collected solids in cyclones for run with 100% wood pellets..................................................................................................\u00C2\u00A077\u00C2\u00A0 Table 6-5 Steady state gas concentrations for run with 100% biosolids and for 147-221 min period\u00C2\u00A0.....................................................................................\u00C2\u00A083\u00C2\u00A0 Table 6-6 Characteristics of collected solids in primary cyclone for run with 100% biosolids\u00C2\u00A0.............................................................................................\u00C2\u00A084\u00C2\u00A0 Table 6-7 Steady state gas concentrations for run with 50% biosolids with 50% wood pellets and for 202-254 min period\u00C2\u00A0..................................................\u00C2\u00A088\u00C2\u00A0 Table 6-8 Characteristics of collected solids in primary cyclone for run with 50% biosolids with 50% wood pellets by mass\u00C2\u00A0........................................\u00C2\u00A089\u00C2\u00A0 Table 6-9 Steady state gas concentrations for run with 25% biosolids with 75% wood pellets by mass and for 179-232 min period\u00C2\u00A0...................................\u00C2\u00A091\u00C2\u00A0 Table 6-10 Characteristics of collected solids in cyclones for run with 25% biosolids with 75% wood pellets by mass\u00C2\u00A0.................................................\u00C2\u00A092\u00C2\u00A0 Table 7-1 Operating conditions of the five runs with the bubbling fluidized bed\u00C2\u00A0................................................................................................................\u00C2\u00A098\u00C2\u00A0 Table 7-2 LHV of syngas with various biosolids proportions\u00C2\u00A0.......................\u00C2\u00A0101\u00C2\u00A0 \u00C2\u00A0 \u00C2\u00A0 viii\u00C2\u00A0 \u00C2\u00A0 LIST OF FIGURES Figure 1-1 Estimates of biosolids use and disposal (Source: US EPA 1999)\u00C2\u00A0....\u00C2\u00A03\u00C2\u00A0 Figure 1-2 Applications of syngas from gasification (Higman, 2008)\u00C2\u00A0...............\u00C2\u00A08\u00C2\u00A0 Figure 2-1 Effect of biosolids proportion in fuel mixtures with straw on H2S and NH3 concentration in product gas (Pinto et al., 2008). Operating conditions: bed temperature of 850\u00D4\u00A8,\u00C2\u00A0 feedstock flow rate of 5 g daf/min, ER of 0.21 and steam/fuel ratio of 0.9 g/g daf\u00C2\u00A0..........................................\u00C2\u00A023\u00C2\u00A0 Figure 2-2 Product yield versus biosolids proportion in fuel (Peng et al., 2012). Operating conditions: feedstock flow rate, 1.2 kg/h; reactor temperature, 800\u00D4\u00A8.\u00C2\u00A0............................................................................................................\u00C2\u00A025\u00C2\u00A0 Figure 2-3 Syngas yield, tar concentration and char conversion versus biosolids proportion in fuel (Saw et al., 2011). Operating conditions: reactor temperature 720\u00D4\u00A8; feedstock flow rate, 15.5 kg/h; steam/fuel ratio, 1.1 (kg/kg)\u00C2\u00A0..........................................................................................\u00C2\u00A026\u00C2\u00A0 Figure 2-4 Flow regime diagrams according to Bi and Grace (Bi & Grace, 1995)\u00EF\u00BC\u008Cwith permission from the Elsevier. Ar=Archimedes number; U*=dimensionless gas velocity\u00C2\u00A0...................................................................\u00C2\u00A029\u00C2\u00A0 Figure 5-1 Char conversion of biosolids, wood pellets and switchgrass vs. time. Operating conditions: reactor temperature, 800\u00E2\u0084\u0083; sample size, 300-355 \u00DF\u00A4m; initial mass of sample, 15 mg; CO2 flow rate, 500 mL/min .......................................................................................................................\u00C2\u00A038\u00C2\u00A0 Figure 5-2 Co-gasification of 50:50 biosolids by weight with: a) wood pellets; b) switchgrass. Operating conditions: reactor temperature, 800\u00D4\u00A8; sample size, 300-355 \u00DF\u00A4m; initial mass of sample, 15 mg; CO2 flow rate, 500 mL/min\u00C2\u00A0..................................................................................................\u00C2\u00A040\u00C2\u00A0 Figure 5-3 Repeat of co-gasification experiments: a) co-gasification of biosolids with wood pellets; b) co-gasification of biosolids with switchgrass. Operating conditions: reactor temperature, 800\u00E2\u0084\u0083; sample size, 300-355 \u00DF\u00A4m; initial mass of sample, 15 mg; CO2 flow rate, 500 mL/min\u00C2\u00A0.........................................................................................................\u00C2\u00A042\u00C2\u00A0 Figure 5-4 Co-gasification of 50:50 biosolids with switchgrass ash. Operating conditions: reactor temperature, 800\u00E2\u0084\u0083; sample size, 300-355 \u00DF\u00A4m; initial ix\u00C2\u00A0 \u00C2\u00A0 mass of sample, 15 mg; CO2 flow rate, 500 mL/min\u00C2\u00A0................................\u00C2\u00A043\u00C2\u00A0 Figure 5-5 Co-gasification of 50:50 biosolids ash with: a) wood pellets; b) switchgrass. Operating conditions: reactor temperature, 800\u00E2\u0084\u0083; sample size, 300-355 \u00DF\u00A4m; initial mass of sample, 15 mg; CO2 flow rate, 500 mL/min\u00C2\u00A0.........................................................................................................\u00C2\u00A044\u00C2\u00A0 Figure 6-1 Process flow diagram of the Highbury Energy Inc. bubbling fluidized (Watkinson et al., 2010), with permission from Dr. Watkinson .......................................................................................................................\u00C2\u00A049\u00C2\u00A0 Figure 6-2 Reactor temperature vs. time for run with 10% biosolids with 90% wood pellets by mass\u00C2\u00A0...................................................................................\u00C2\u00A059\u00C2\u00A0 Figure 6-3 Temperature of tar sampling line vs. time for run with 10% biosolids with 90% wood pellets by mass\u00C2\u00A0.................................................\u00C2\u00A060\u00C2\u00A0 Figure 6-4 Pressure drop in reactor for run with 10% biosolids with 90% wood pellets by mass\u00C2\u00A0...................................................................................\u00C2\u00A061\u00C2\u00A0 Figure 6-5 Steam flow rate vs. time for run with 10% biosolids with 90% wood pellets by mass\u00C2\u00A0...................................................................................\u00C2\u00A062\u00C2\u00A0 Figure 6-6 Gas concentrations of dry producer gases for run with 10% biosolids with 90% wood pellets by mass\u00C2\u00A0.................................................\u00C2\u00A063\u00C2\u00A0 Figure 6-7 Nitrogen-free dry syngas composition for run with 10% biosolids with 90% wood pellets by mass\u00C2\u00A0.................................................................\u00C2\u00A064\u00C2\u00A0 Figure 6-8 Bed temperature and dry producer gas concentrations vs. time for run with 10% biosolids with 90% wood pellets by mass\u00C2\u00A0.........................\u00C2\u00A066\u00C2\u00A0 Figure 6-9 Bed temperature and dry syngas composition versus run time for run with 10% biosolids and 90% wood pellets by mass\u00C2\u00A0..........................\u00C2\u00A067\u00C2\u00A0 Figure 6-10 Reactor temperature vs. time for run with 100% wood pellets\u00C2\u00A0.\u00C2\u00A070\u00C2\u00A0 Figure 6-11 Gas concentrations of dry producer gases for run with 100% wood pellets..................................................................................................\u00C2\u00A072\u00C2\u00A0 Figure 6-12 Nitrogen-free dry syngas composition for run with 100% wood pellets\u00C2\u00A0............................................................................................................\u00C2\u00A073\u00C2\u00A0 x\u00C2\u00A0 \u00C2\u00A0 Figure 6-13 Correlation of bed temperature to dry syngas production rate for run with 100% wood pellets\u00C2\u00A0.......................................................................\u00C2\u00A074\u00C2\u00A0 Figure 6-14 Bed temperature and dry syngas composition vs. run time for run with 100% wood pellets\u00C2\u00A0..............................................................................\u00C2\u00A075\u00C2\u00A0 Figure 6-15 Reactor temperature vs. time for run with 100% biosolids\u00C2\u00A0.......\u00C2\u00A079\u00C2\u00A0 Figure 6-16 Gas concentrations of dry producer gases for run with 100% biosolids\u00C2\u00A0........................................................................................................\u00C2\u00A081\u00C2\u00A0 Figure 6-17 Nitrogen-free dry syngas composition for run with 100% biosolids\u00C2\u00A0........................................................................................................\u00C2\u00A082\u00C2\u00A0 Figure 6-18 Reactor temperature (T10) vs. time for run with 50% biosolids with 50% wood pellets by mass\u00C2\u00A0.................................................................\u00C2\u00A086\u00C2\u00A0 Figure 6-19 Gas concentrations of dry producer gases for run with 50% biosolids with 50% wood pellets by mass\u00C2\u00A0.................................................\u00C2\u00A087\u00C2\u00A0 Figure 6-20 Gas concentrations of dry producer gases for run with 25% biosolids with 75% wood pellets by mass\u00C2\u00A0.................................................\u00C2\u00A091\u00C2\u00A0 Figure 7-1 Bed temperature and N2 concentration vs. time for run with 50% biosolids with 50% wood pellets by mass.\u00C2\u00A0................................................\u00C2\u00A094\u00C2\u00A0 Figure 7-2 Syngas yield versus bed temperature. Operating conditions: feedstock, 50% biosolids with 50% wood pellets by mass; steam/fuel mass ratio, 2.73.\u00C2\u00A0...........................................................................................\u00C2\u00A095\u00C2\u00A0 Figure 7-3: Temperature and syngas composition vs. time for run with 50% biosolids with 50% wood pellets by mass.\u00C2\u00A0................................................\u00C2\u00A096\u00C2\u00A0 Figure 7-4 Syngas composition versus bed temperature. Operating conditions: feedstock, 50% biosolids with 50% wood pellets by mass; steam/fuel mass ratio, 2.73.\u00C2\u00A0...........................................................................................\u00C2\u00A097\u00C2\u00A0 Figure 7-5 Syngas composition vs. biosolids proportion in fuel, divided into a) for runs 1, 2, 3 b) for runs 4 and 5\u00C2\u00A0...........................................................\u00C2\u00A0100\u00C2\u00A0 Figure 7-6 Syngas yield and char conversion vs. biosolids proportion in feed .....................................................................................................................\u00C2\u00A0102\u00C2\u00A0 xi\u00C2\u00A0 \u00C2\u00A0 Figure 7-7 Tar content and ammonia concentration vs. biosolids proportion in fuel\u00C2\u00A0..............................................................................................................\u00C2\u00A0103\u00C2\u00A0 \u00C2\u00A0 xii\u00C2\u00A0 \u00C2\u00A0 NOMENCLATURE Ar: Archimedes number C: carbon content in fuel from ultimate analysis, % by weight Ct: carbon proportion by weight in the tar, based on assumption that tar has the composition of toluene, C7H8 Cs: carbon content in solids collected by cyclones, % by weight F: feed rate of fuel, kg/h HEI: Highbury Energy Inc. MWc: molecular weight of carbon, g/mol P: pressure, Pa R: ideal gas law constant, J/K/mol S: weight of solid collected by cyclones, g T: temperature, K TGA: thermogravimetric analyzer Ty: tar content in syngas, g/m3 t: total time of feeding, h U*: dimentionless gas velocity UBC CHBE: Department of Chemical and Biological Engineering at University of British Columbia US EPA : United States Environmental Protection Agency V: total volume of syngas produced, L Wa: weight of ash, taken as final weight of sample in TGA basket, mg Wi: initial weight of sample in TGA basket, mg Wt: weight of sample at time t in TGA basket, mg WWTP : waste water treatment plant X: char conversion at time t, - \u00C2\u00A0 xiii\u00C2\u00A0 \u00C2\u00A0 ACKNOWLEDGEMENTS I want to express my profound gratitude to my supervisors, Drs. John Grace, Jim Lim and Tony Bi, for their continuous guidance, helpful suggestions, and effective supervision. Special thanks are given to Dr. Grace for getting me familiar with the project and accepting me into the Master\u00E2\u0080\u0099s program. I wish to thank Dr. Paul Watkinson for his permission to use their experimental setup for my project. I greatly appreciate Dr. Yonghua Li for his help in many areas, such as teaching me techniques relevant to my project, offering suggestions for my Master\u00E2\u0080\u0099s project and career path, and providing solutions to different kinds of problems. I also want to thank my colleagues for their continuous support. Great thanks are given to Jie Bao for her encouragement all the time. I would like to acknowledge Richard Ryoo for his fast online ordering system. I wish to thank the members of the UBC gasification group for exchanging information about gasification and providing solutions to problems. Sincere thanks are given to Mohammad Masnadi for assisting me in conducting experiments. I would like to thank the Nexterra Systems Corp. for their invitation to participate in their gasification runs and for providing materials for my project. Finally, I would like to thank my family and friends for their unconditional help, caring and support all the time. Great gratitude is given to my mother for taking care of the whole family. 1\u00C2\u00A0 \u00C2\u00A0 CHAPTER 1:\u00C2\u00A0 INTRODUCTION 1.1 Introduction to biosolids Biosolids are treated sewage sludge produced as a by-product of wastewater treatment plants (WWTPs). After flushing the toilet or washing food residues down the drain, the wastewater flows towards WWTPs. During the wastewater treatment process, the solids in wastewater are separated, dewatered, and treated to meet the pollutant and pathogen (bacteria and viruses that cause diseases) requirements of the local environmental protection agency. The solids are called biosolids, composed mainly of water, organic matter and ash. Depending on the level of wastewater treatment process of WWTP, the water content of biosolids ranges from 6 to 70%. The organic content in biosolids also varies significantly, depending on the treatment technology. The ash in biosolids contains inorganic matter and metals. Nevertheless, the major elements in biosolids are carbon, hydrogen, oxygen, nitrogen and sulphur. 1.1.1 Biosolids treatment technology In the WWTP, biosolids go through different treatment processes which affect biosolids properties. Common treatment technologies and their effects on biosolids characteristics are described as follows: Conditioning is the process using chemicals to destroy cell structures in the sludge. This process improves the performance of the following digestion process and increases biosolids dewaterability by coagulation of biosolids sludge. Thickening increases solid concentrations with various simple technologies such as screen thickening, flotation, gravity thickening or membrane thickening. 2\u00C2\u00A0 \u00C2\u00A0 Stabilization/digestion involves alkaline stabilization and biological stabilization of biosolids to reduce pathogens and odours in biosolids and decrease attraction to vectors (disease spread organisms). Composting allows natural micro-organism to digest the pathogens and nutrients in biosolids and to produce fertilizer-grade material. Dewatering removes water from biosolids with energy-intensive technologies such as centrifugation, belt filter press, and vacuum filtration. Water removal reduces the cost of transportation, drying, incineration and gasification. Drying further decreases the water content, usually to a very low level. Heat drying is most effective, but is a very energy-demanding operation commonly used in the WWTP. Drying also has the advantage of killing pathogens in biosolids. 1.1.2 Biosolids use and disposal The US Environmental Protection Agency (EPA, 1999) classified disposal of biosolids into two categories: beneficial use of biosolids and disposal without extracting any value. According to their report, 60% of biosolids were beneficially used in land application, advanced treatment and for other benefits, while 40% of biosolids were incinerated, landfilled, or disposed in other ways; see Figure 1-1. 3\u00C2\u00A0 \u00C2\u00A0 \u00C2\u00A0 Figure 1-1 Estimates of biosolids use and disposal (Source: US EPA 1999) 1.1.2.1 Biosolids Use Since biosolids are rich in nutrient, biosolids can be used as a fertilizer or for soil enrichment. However, local environmental agencies have developed many regulations governing application to land because biosolids contain pathogens and pollutants. For example, the US EPA 40 CFR Part 503 Biosolids Rule sets requirements for biosolids applied to land, and the requirements include the ceiling concentration limits of pathogens, metals and organic contaminants, and limit of vector attractions. These regulations are made to safeguard public health and protect the environment. Beneficial use of biosolids includes application to vegetable crops, lawns, gardens, forests and mine reclamation. In general, the nutrient level of biosolids is lower than that of commercial fertilizers. Also, the public in some area opposes application of biosolids because of the concern of risks and odour. Thus, spreading of biosolids on land has become controversial (Petersen et al. 2005). 41 127 22 17 1 Biosolids\u00C2\u00A0use/disposal\u00C2\u00A0distribution Land\u00C2\u00A0application Advanced\u00C2\u00A0treatment Other\u00C2\u00A0beneficial\u00C2\u00A0use Incineration Landfilled Other\u00C2\u00A0disposal 4\u00C2\u00A0 \u00C2\u00A0 1.1.2.2 Biosolids disposal Incineration and landfill are widely practiced disposal methods, and environmental agencies have also made regulations for these disposal methods. Incineration is the combustion of biosolids at high temperatures, typically from 760 to 870\u00D4\u00A8. After incineration, the volume of biosolids is reduced significantly as virtually all the water, volatile matters, and organic carbon are combusted. Incineration also destroys all the pathogens and toxic organic contaminants. The metal content and other inorganic matter are concentrated in the ash residues from incineration. The US EPA Part 503 Rule limits the metal emission and carbon monoxide emissions from the incineration processes. Incineration is often criticized because it is associated with emission of secondary pollutants (Chun et al., 2011). Landfill or surface disposal spreads biosolids on an area of land. This practice is also regulated by the Part 503 Rule. The water content in biosolids must be less than 80%. In addition, the vector attraction in biosolids must be controlled, and biosolids cannot contain hazardous wastes. The concentration of toxic organics such as polychlorinated biphenyls (PCBs) in biosolids cannot exceed defined ceiling limits. Landfilling requires large area and sealing of the soil, so this method is also problematic (Seggiani et al., 2012). 1.1.2.3 Biosolids gasification The disposal methods mentioned above are therefore far from perfect, and are becoming less and less acceptable. Gasification of biosolids is an alternative disposal method investigated in this project. Gasification is the process that converts carbonaceous substances to syngas, a relatively clean gaseous source of energy and chemical products, at a temperature of about 700-900\u00D4\u00A8. Gasification of biosolids is advantageous in many aspects compared to other disposal methods. Advantages and disadvantages are discussed below. 5\u00C2\u00A0 \u00C2\u00A0 In contrast to land application, gasification does not need to meet the concentration requirements for pathogens and pollutants. Most pathogens and pollutants are gasified or degraded at high temperatures. Also, for land applications, the public is worried about odours and risks, whereas gasification does not appear to worry the public. Compared to incineration, gasification is more efficient in terms of energy and has less gas emission concerns (Saw et al. 2011 & Petersen et al. 2005). Also, incineration extracts energy only in the form of heat, whereas the syngas produced from gasification has wider applications such as being burned in gas engines or converted to other chemicals. In terms of cost, gasification can eliminate treatment processes such as the stabilization, digestion and composting and thus reduces biosolids treatment costs. In future, due to stricter regulations, landfill and land applications will become more costly. Overall, gasification can recover some energy from biosolids and requires less environmental controls and restrictions. Disadvantages of gasification for biosolids include lack of experience and cost of pre-drying the biosolids. Gasification is an emerging technology, and gasification of biosolids is rarely practiced currently. For biosolids to be the feedstock for gasification, its moisture content must be reduced to a satisfactory level depending on the gasification utility, and drying raises the overall cost. 1.2 Introduction to gasification Gasification is an endothermic process that converts carbonaceous fuels to syngas, condensable tars and ash through partial oxidation at high temperatures (typically 700-900\u00D4\u00A8) as in Equation 1-1. Steam, air and pure oxygen are widely used oxidants in gasification process. The product syngas consists mainly of CO, H2, CO2, CH4, N2, and other minor gases. Tars are high molecular weight hydrocarbons formed as byproducts. 6\u00C2\u00A0 \u00C2\u00A0 \u00DC\u00BF\u00DC\u00BD\u00DD\u008E\u00DC\u00BE\u00DD\u008B\u00DD\u008A\u00DC\u00BD\u00DC\u00BF\u00DD\u0081\u00DD\u008B\u00DD\u0091\u00DD\u008F\u00C2\u00A0\u00DD\u0082\u00DD\u0091\u00DD\u0081\u00DD\u0088\u00DD\u008F \u00E0\u00B5\u0085 \u00DD\u0083\u00DC\u00BD\u00DD\u008F\u00DD\u0081\u00DD\u008F\u00C2\u00A0\u00DD\u008B\u00DD\u0094\u00DD\u0085\u00DD\u0080\u00DD\u0081\u00DD\u008A\u00DD\u0090\u00DD\u008F \u00E2\u0086\u0092 \u00DD\u008C\u00DD\u008E\u00DD\u008B\u00DD\u0080\u00DD\u0091\u00DC\u00BF\u00DD\u0090\u00C2\u00A0\u00DD\u008F\u00DD\u0095\u00DD\u008A\u00DD\u0083\u00DC\u00BD\u00DD\u008F \u00E0\u00B5\u0085 \u00DD\u0090\u00DC\u00BD\u00DD\u008E\u00DD\u008F \u00E0\u00B5\u0085 \u00DC\u00BD\u00DD\u008F\u00DD\u0084 (1-1) 1.2.1 History of gasification technology The development of gasification was elaborated by Higman (Higman, 2008). Initial gasification process started in the 1800s, when it was used to produce town gas for lighting, heating, and cooking. However, during that period, gasification technology did not gain much attention or development because of plentiful oil and natural gas. After the 1950s, the world demand for ammonia as a fertilizer increased continuously and exponentially (Slack and James, 1973). The demand for hydrogen, the major reactant for ammonia production increased. Gasification, an effective process for producing hydrogen, addressed this issue and gained importance and research. After the 1970s, gasification entered a fast developing stage. This development results from two main reasons. First, the prices for fuel oil and natural gas have increased dramatically leading scientists and engineers to seek for replaceable or complementary energy sources and energy production methods. Secondly, many governments are encouraging environmentally-friendly processes. Gasification of biomass can also be carbon neutral or carbon negative if CO2 is captured during the process. Also, overall emissions from gasification can be valued compared to other traditional processes like combustion because the impurities and contaminants can be removed during the gasification process. 1.2.2 Gasification processes The most popular gasifiers involve downdraft fixed beds, updraft fixed beds, entrained flow, fluidized beds, and circulating fluidized beds (Higman, et al. 2008). 7\u00C2\u00A0 \u00C2\u00A0 Fixed bed gasifiers are simple in design and operation, but the conversion efficiency and syngas quality are usually lower than for fluidized beds. Also, the exit gases have low temperature, resulting in high tar and methane content. In fluidized beds, the solids and gas contact each other extremely well. Also, due to good mixing, temperature is distributed uniformly, enhancing the gasification performance and helping to prevent unwanted agglomeration, fouling and sintering. 1.2.3 Feedstocks As long as a feedstock is carbonaceous with an appreciable net heating value, it can be gasified. A wide range of materials can be the feedstock for gasification, such as coal, wood pellets, waste bark, switchgrass, biosolids, discarded corn and plastics. Consequently, feedstock characteristics can vary in many aspects: size, density, shape, moisture content, ash content, etc. Among the feedstocks, coal has been the most common feedstock for gasification, and it has been studied thoroughly in the past. In the last decade, because of increased demand for environmental protection, interests have shifted to gasify waste materials like by-products from farms and industries. Many scientists and engineers have shifted their study focus from coal to gasification of biomass such as waste bark, wood pellets and switchgrass. 1.2.4 Applications Syngas produced from gasification can be burnt in gas engines or gas turbines. It can also be converted to other chemicals by Fischer-Tropsch synthesis. There are many other applications as shown in Figure 1-2, 8\u00C2\u00A0 \u00C2\u00A0 Figure 1-2 Applications of syngas from gasification (Higman, 2008) Gasification Ammonia Methanol Carbon\u00C2\u00A0 Monoxide\u00C2\u00A0 Hydrogen OXO\u00C2\u00A0Alcohols Fischer\u00E2\u0080\u0090 Tropsch SNG Town\u00C2\u00A0Gas Reduction\u00C2\u00A0 Gas Gas\u00C2\u00A0Turbines 9\u00C2\u00A0 \u00C2\u00A0 CHAPTER 2: LITERATURE REVIEW 2.1 Biosolids characteristics Knowing the characteristics of the feedstock is critical for successful gasification. Thus, the characteristics of biosolids were researched and compared to the characteristics of other gasification feedstocks like wood pellets and coal. This section only discusses the characteristics which are important for gasification; other characteristics like pathogen content and key parameters for land applications are not included. 2.1.1 Solid content Biosolids after the treatment process still contain some water. The percentage of water, named moisture content, is an important factor for gasification. First, the moisture content can affect the feeding process, High moisture content materials are usually adhesive, causing blockage during feeding. Furthermore, high moisture materials cause problems in fluidization, and this study will use a fluidized bed gasifier. Also, high moisture content feedstock will consume significant amounts of energy to heat and vaporize the water in the gasifier. Metro Vancouver, City of Toronto, and US EPA also reported the solid content of biosolids. The solid content is the weight percentage of total solids in biosolids, i.e. 100% minus the % moisture content. Metro Vancouver summarized the solid content of biosolids from different wastewater treatment plants (WWTP) as reported in Table 2-1. 10\u00C2\u00A0 \u00C2\u00A0 Table 2-1 Solid content of biosolids from different WWTPs in Vancouver (source: Greater Vancouver Sewerage & Drainage District Quality Control Annual Report, 2011) WWTP Annacis Island Iona Island Lions Gate Lulu Island Northwest Langley solid content (%) 28.4 N/A 31.5 24.5 N/A N/A: not available The City of Toronto stated that the solids content of its biosolids depends on the dewatering technology used. If centrifuges are used, solid content can be increased to more than 20% and even to 45%. The City of Toronto described the biosolids after centrifuging as soil-like cake. US EPA estimated solid content of biosolids based on the dewatering/drying process as in Table 2-2. It was reported that solid content could be very high after drying and pelletization by WWTPs in cities like Boston and New York City. Table 2-2 Ranges of solid content of biosolids after different dewatering techniques (source: Biosolids Generation, Use, and Disposal in the United States, 1999) dewatering technology air drying vacuum filter centrifuge belt filter presses plate-and-frame presses heat drying and pelletizing solid content (%) 45-90 12-22 25-35 20-32 35-45 >90 These data show that most biosolids from WWTPs contain high moisture contents compared to other gasification feedstocks. Wood pellets usually have moisture contents <10 wt.%, similar to coal. Biosolids moisture contents are much higher, except when the biosolids are dried by heat or air and pelletized. 11\u00C2\u00A0 \u00C2\u00A0 It is likely to be necessary to reduce the moisture content before feeding the biosolids to gasifiers. Heat drying is effective but very costly. Alternately, mixing biosolids with drier biomass can effectively reduce the average moisture content of the feedstock, and this is inexpensive and operable. 2.1.2 Heating value The heating or calorific value of a material indicates the potential thermal energy it can release due to combustion. Gasification of a material is a way of extracting most of that chemical energy and storing the energy in gaseous form. Thus, the higher the heating value, the more valuable it is for gasification. Biosolids, because they contain a large proportion of organic matter, have a relatively high heating value. The City of Toronto reported the higher heating value of biosolids as 23,000-28,000 kJ/kg on an ash free and dry basis. The US EPA reported the higher heating value of biosolids to range from 15,800 to 23,300 kJ/kg on a dry basis. The higher heating value of biosolids from other sources cover a range from 14,100 to 18,381 kJ/kg on a dry basis (Saw, 2012; Adams, 2011; Nipattummakul, 2010). Wood pellets have similar heating value as biosolids. The heating value of wood does not fluctuate much, between 18,600 and 19,800 kJ/kg (Wilk, 2011; Saw, 2012; Seo, 2010). Coal, as the traditional gasification fuel, has the highest heating value among the feedstock, with heating values usually above 28,000 kJ/kg (Seo, 2010). 2.1.3 Proximate and ultimate analyses Gasification feedstocks such as wood pellets, coal and biosolids, vary greatly with respect to their source, season of extraction and many other factors. Thus, how to identify a feedstock is an issue for researchers. Scientists and engineers often use proximate and ultimate analyses to identify gasification feedstocks. Moreover, 12\u00C2\u00A0 \u00C2\u00A0 proximate and ultimate analyses deliver researchers useful information associated with gasification. The proximate and ultimate analyses of biosolids from several papers are summarized in Table 2-3. For comparison, the proximate and ultimate analyses of typical wood pellets and coal are provided in Table 2-4 and Table 2-5 respectively. Table 2-3 Typical proximate and ultimate analyses of biosolids Material biosolids Water content( %) 8.0 8.0 1.7 19.0 5.2 6.7 80.4 Proximate (wt.% dry) Volatile 47.3 77.2 44.3 57.2 42.6 43.6 N/A Ash content 34.8 13.2 33.9 37.9 52.8 37.8 39.8 Fixed carbon 17.9 9.7 21.8 4.9 4.6 18.6 N/A Ultimate(wt.% dry and ash free) Carbon 56.7 53.9 45.8 53.2 44.7 54.5 51.5 Hydrogen 5.8 7.4 3.0 7.1 7.2 7.7 7.3 Oxygen 27.0 28.3 14.7 30.6 39.0 24.0 30.9 Nitrogen 8.5 9.6 1.5 7.1 6.8 9.9 7.5 Sulfur 2 0.7 1.1 1.9 2.3 1.7 2.7 Location New Zeala nd Las Vegas, USA USA Sweden Bangkok , Thailand Sofia, Bulgaria Kyonggi -Do, Korea Reference Saw et al., 2012 Adams et al., 2011 Nipattum makul et al., 2010 Leckne r et al., 2004 Rirksom boon et al., 2006 Balgaran ova et al., 2003 Rhee et al., 2010 13\u00C2\u00A0 \u00C2\u00A0 Table 2-4 Typical proximate and ultimate analyses of wood pellets Material wood pellets Water content(%) 6.1 8.0 8.1 6.1 2.3 Proximate (dry) Volatile(%) 86.5 84.1 81.7 86.2 78.8 Ash content(%) 0.3 0.4 0.4 0.3 0.8 Fixed carbon(%) 13.3 15.4 17.9 13.5 20.4 Ultimate(dry and ash free) Carbon(%) 50.2 51.5 50.2 50.2 48.9 Hydrogen( %) 6.0 5.9 6.1 6.0 6.4 Oxygen(%) 43.4 42.3 43.6 43.4 44.2 Nitrogen(%) 0.05 <0.2 0.12 0.05 0.1 Sulfur(%) 0.005 <0.1 0.01 0.005 0.3 Location Vienna New Zealand Germany Vienna Korea Reference Wilk et al., 2011 Saw et al., 2012 Leckner et al., 2004 Aigner et al., 2011 Seo et al., 2010 14\u00C2\u00A0 \u00C2\u00A0 Table 2-5 Typical proximate and ultimate analyses of coal Material coal Water content(%) 9.9 3.1 9.0 Proximate (dry) Volatile(%) 32.1 35.7 32.7 Ash content(%) 7.4 11.8 17.5 Fixed carbon(%) 60.5 52.5 49.8 Ultimate(dry and ash free) Carbon(%) 76.5 74.6 84.9 Hydrogen(%) 3.9 4.7 5.0 Oxygen(%) 10.3 19.3 7.7 Nitrogen(%) 1.3 1.1 1.6 Sulfur(%) 0.46 0.3 0.7 Location Vienna Korea Germany Reference Aigner et al., 2011 Seo et al., 2010 Leckner et al., 2004 From Table 2-3, the moisture content of biosolids is not as high as discussed previously. The reason is that low-moisture-content biosolids have often been selectively chosen by researchers for gasification or combustion purposes. These biosolids are already dried by heat, solar energy, or air in the wastewater treatment plant. However, not all researchers have tested dried biosolids. For example, some researchers have received biosolids with moisture content of 80.4% (Rhee, 2010). 15\u00C2\u00A0 \u00C2\u00A0 From the proximate analysis, among the three materials, coal contains the most carbon, wood pellets the most volatiles, and biosolids the most ash. The ash content of biosolids can be very high, e.g. from 13.15 to 52.8% on a dry basis. On the other hand, wood has only 0.29-0.78% ash. High ash content is not desirable for gasification, because ash decreases the energy efficiency, causes disposal problems, and may negatively affect gasification performance. To reduce the overall ash content in feedstock, one solution is to co-gasify biosolids with biomass having low ash content like wood pellets. From the ultimate analysis, biosolids, which can be used as fertilizers, have higher nitrogen content as expected. Nitrogen content of wood is always less than 1%, whereas for coal it is around 1%, but for biosolids it can be as high as 9.88 %. Sulfur content of biosolids is typically around 2%, compared to wood pellets around 0.01%, and coal varying from 0.5% to 8% (higher limit for coal from New Brunswick). Higher nitrogen and sulfur content in biosolids should increase ammonia and hydrogen sulfide production during gasification process, and this is confirmed in a later section of this thesis. 2.1.4 Ash analysis Ash analysis is also important, as ash content can be used to explain catalytic or inhibition effects, if any, in gasification. Ash analysis of biosolids is summarized in Table 2-6, and ash analysis of other feedstocks in Table 2-7 for comparison. \u00C2\u00A0 There have been various studies on the catalytic effects of alkali and alkaline earth metals on gasification (Mitsuoka et al., 2011). Among alkali metals, potassium has been reported to have the greatest catalytic effect on gasification. Among alkaline earth metals, calcium can accelerate gasification reaction catalytically. However, alkali and alkaline earth metals are expensive to use as catalysts in gasification. As a result, researchers have sought substitutes such as co-gasification with biomass 16\u00C2\u00A0 \u00C2\u00A0 containing high potassium and calcium content. Thus, it is important to note the potassium and calcium in the ash content. Table 2-6 Typical ash analyses of biosolids % in ash of biosolids SiO2 27.77 34.78 18.2 20 AlO3/Al2O5 6.82 16.8 9.1 6.5 TiO2 1.34 1.01 0.3 0.5 Fe2O3 3.6 5.43 15.6 20 CaO 14.14 7.26 22.8 22.7 MgO 5.27 3.71 2.3 3.1 K2O 6.27 4.07 0.5 0.6 Na2O 2.86 5.5 4.8 P2O5 30.75 25.9 8.9 21 SO3 1.18 8.2 2 MnO4 0.3 0.1 0.1 NiO 0.05 ZnO 0.33 CuO 0.36 Undertermined 0 0 8.5 0 Location Las Vegas, USA Kyonggi-Do, Korea Basel, Swiss Winterthur, Swiss Reference Adams, 2011 Rhee, 2010 Franz,2008 Franz,2008 \u00C2\u00A0 \u00C2\u00A0 17\u00C2\u00A0 \u00C2\u00A0 Table 2-7 Typical ash analyses of other gasification feedstocks coal sawdust wood chip SiO2 41.4 60.6 13 AlO3/Al2O5 17.79 16.4 2.3 TiO2 0.2 Fe2O3 28.21 5.98 1.5 CaO 6.36 10.93 55.3 MgO 2.9 0 4.9 K2O 2.5 2.93 11 Na2O 0.24 3.99 3.9 P2O5 2.4 SO3 1.62 2.36 1.5 MnO4 1.6 NiO 0.1 ZnO 0.1 CuO 0.1 Undertermined 2.1 Location Korea Korea Vienna Reference Seo,2010 Seo,2010 Kirnbauer, 2011 Table 2-6 shows that biosolids do not contain much potassium, but they do contain relatively high amounts of calcium. Table 2-7 indicates that most coals do not contain much potassium or calcium, whereas wood contains higher proportions of both calcium and potassium. If co-gasifying with wood, a positive catalytic effect is expected (Mitsuoka et al., 2011). 18\u00C2\u00A0 \u00C2\u00A0 2.1.5 Metal content Although metal content may not be directly involved in gasification reactions, it is necessary to know for downstream disposal process. The ash after gasification can be mixed with the ash from incineration plants and transported to disposal area. The metal content in biosolids is reported by Metro Vancouver, the City of Toronto, and limited by the US EPA as shown in Table 2-8. Generally, the metal content in biosolids is higher than in biomass. In Table 2-8 b), the chromium and copper contents of biosolids from the Langley WWTP is much higher than from other WWTPs in Vancouver. The Vancouver annual report only lists these values without explanation. 19\u00C2\u00A0 \u00C2\u00A0 Table 2-8 Metal content (mg/kg) in biosolids reported by Toronto and Vancouver (a) City of Toronto source: Biosolids and Residuals Master Plan City of Toronto, 2003 source US EPA concentration limits Toronto WWTP Canada Fertilizers act typical value from US EPA arsenic 75 4.72 75 4-13 cadmium 85 2.7 20 2.5 chromium 3000 120 ns nd cobalt nd 5.19 150 nd copper 4300 1190 ns 300-470 lead 840 67.9 500 8-46 mercury 57 1.1 5 nd molybdenum 75 16 20 19 nickel 420 27.5 180 16-30 selenium 100 4.24 14 nd zinc 7500 785 1850 560-600 Ns: no standard Nd: no data available 20\u00C2\u00A0 \u00C2\u00A0 (b) Metro Vancouver source: Greater Vancouver Sewerage & Drainage District Quality Control Annual Report, 2011 source Annacis Island WWTP Iona Island WWTP Lions Gate WWTP Lulu Island WWTP Northwest Langley WWTP arsenic 5.9 5.3 <3.3 7.1 <3.6 cadmium 2.6 7 2.1 3.1 3.92 chromium 60 55 38 39 168 cobalt 4.6 5.1 3.6 5.6 5.2 copper 810 600 821 746 1466 lead 92 88 68 34 43 mercury 1.7 1.7 2.1 1.8 0.96 molybdenum 10.8 7.3 10.1 9 12.1 nickel 38 24 30 34 34.7 selenium 7.3 4.3 5.9 5.8 6 zinc 1290 809 1079 1075 1074 2.2 Gasification performance 2.2.1 Catalyst development The catalysts used in gasification are commonly divided into three groups, alkali metals, non-metallic oxides, and metallic oxides (Pfeifer et al., 2011). Alkali metals such as potassium and sodium can greatly enhance gasification reactions. However, these metals are rarely practiced for large scale gasification processes due to their high cost. Common non-metallic oxides include silica sand and olivine sand, and they exist naturally and can be supplied at low cost. Metallic oxides catalyst such as Ni-olivine and Fe-olivine are also of interest. According to Pfeifer et al. (2011)\u00E2\u0080\u0099s investigation, metallic oxides yielded better results than non-metallic oxides in terms of tar removal. 21\u00C2\u00A0 \u00C2\u00A0 2.1.2 Tar removal Tars, containing aromatic ring organic compounds, are high-molecular-weight hydrocarbons formed as by-products during gasification and pyrolysis (Saw et al., 2011). Formation of tars depends on the type of fuel, temperature, steam/carbon ratio, impact of catalysts and many other factors (Pfeifer et al., 2011). The syngas exits from the reactor at a high temperature. Once the syngas temperature drops, the tars can condense, causing problems downstream. Typical tar content in syngas produced by biomass gasification ranges from 1 to 30 g/m3, much higher than the typical limit of 50 mg/m3 for syngas used in gas turbines (Petersen et al., 2005). To reduce cost and operating difficulties, removal or reduction of the tar content in syngas is important or essential. Pfeifer et al. (2011) classified the methods of removal of tars into two categories, primary and secondary. If the tar removal technology is directly applied during gasification, the method is termed a primary method. Primary methods include altering the design of the column, changing the reaction conditions in the bed, or adding a tar cracking catalyst to the bed. Secondary methods remove the tars downstream. Examples of secondary methods include cyclones, filters, electrostatic precipitators and wet scrubbers. Ideally, either type of method should not inhibit or negatively affect the gasification performance. 2.1.3 Pollutant byproduct gases: H2S, NH3, and HCl As noted above, biosolids contain significant percentages of N, S and Cl. Under the reducing conditions of gasification processes, these elements appear mainly in the form of NH3, H2S, and HCl. Pinto et al. (2007) reviewed and studied the formation of these pollutant gases during gasification of biosolids. Temperature can affect the formation of these components, 22\u00C2\u00A0 \u00C2\u00A0 with high temperature usually increasing the production of H2S in the gas phase. For example, Pinto et al. found from his experiments that H2S increased by 30% when the temperature increased from 750 to 850\u00D4\u00A8. On the other hand, high temperature often promotes decomposition of NH3 in the gas phase, because decomposition of NH3 is an endothermic reaction. At temperatures lower than 550\u00D4\u00A8, little HCl is found because chlorine is trapped in alkaline earth metals in the feedstock as a solid phase. According to Pinto\u00E2\u0080\u0099s review, HCl does not vary significantly with temperature. Pinto et al. (2007) also investigated the influence of feedstock composition on the formation of H2S and NH3. The HCl was too low to be detectable for these experiments. Based on the experiments, they concluded that, for gasifying a blend of biosolids with straw, increasing the biosolids proportion in fuel resulted in production of more H2S and NH3 as shown in Figure 2-1. This was expected because the biosolids contained more N and S than the straw. As the biosolids proportion in the biosolids/straw mixture increased from 0 to 100%, the H2S concentration increased from 800 to 1100 ppmv, whereas the NH3 concentration increased from 2000 to 22000 ppmv. 23\u00C2\u00A0 \u00C2\u00A0 Biosolids proportion in fuel (% w/w) 0 20 40 60 80 100 H 2S c on ce nt ra tio n (p pm v) 0 500 1000 1500 2000 N H 3 c on ce nt ra tio n (p pm v) 0 5000 10000 15000 20000 25000 H2S concentration NH3 concentration Figure 2-1 Effect of biosolids proportion in fuel mixtures with straw on H2S and NH3 concentration in product gas (Pinto et al., 2008). Operating conditions: bed temperature of 850\u00D4\u00A8,\u00C2\u00A0 feedstock flow rate of 5 g daf/min, ER of 0.21 and steam/fuel ratio of 0.9 g/g daf \u00C2\u00A0 2.1.4 Temperature effect Many researchers have studied the effect of temperature on gasification performance because temperature has proven to be the most important factor influencing gasification performance. Since the main gasification reactions are endothermic, increasing bed temperature should improve the performance. Several researchers concluded from their experimental results that higher bed temperatures contribute to an increase in syngas yield and H2/CO ratio (Seo et al., 2010, Pfeifer et al., 2011, Peng et al., 2012). However, bed temperature is constrained by the risk of agglomeration and sintering of biosolids (Petersen et al. 2005). On the other hand, CH4 and CO2 concentrations were relatively constant with varying temperature (Peng et al., 2012, Pfeifer et al., 2011, Seo et al., 2010). 24\u00C2\u00A0 \u00C2\u00A0 2.1.5 Steam/fuel ratio effect Steam/fuel ratio is another important factor to study for its impact on gasification. With more steam, the water shift reaction CO \u00E0\u00B5\u0085 H\u00E0\u00AC\u00B6O \u00E0\u00B5\u008C H\u00E0\u00AC\u00B6 \u00E0\u00B5\u0085 CO\u00E0\u00AC\u00B6 shifts to the right to yield more H2 and CO2. Pfeifer et al. (2011) and Seo et al. (2010) studied the impact of steam/fuel ratio on gasification performance. According to Pfeifer et al. (2011), the H2 and CO2 concentrations increased, while that of CO decreased with increasing steam/fuel ratio as expected. The CH4 concentration remained nearly constant with various steam/fuel ratios. Seo et al. (2010) obtained similar results as Pfeifer et al. (2011). 2.3 Co-gasification of biosolids with biomass Researchers are becoming interested in co-gasification of different materials, as this can combine their respective advantages (Peng et al., 2012). Preliminary research indicates that biosolids need to be co-gasified with biomass to reduce the moisture and ash content. Several researchers have investigated the performance of co-gasification of biosolids with biomass (Peng et al., 2012 & Saw et al., 2011). 2.3.1 Syngas yield, char conversion and tar concentration Peng et al. (2012) co-gasified biosolids with forestry wastes. Syngas, tar and char yields versus the biosolids proportion in fuel are plotted in Figure 2-2. This showed that syngas yield started to decrease at 30% biosolids and reached a minimum at 100% biosolids. Figure 2-2 also shows that tar yield increased dramatically with increasing biosolids ratio. Pinto et al. (2007) reported similar behaviour, with biosolids yielding higher tar content than biomass. Moreover, char conversion decreased gradually as the biosolids proportion increased, as seen in Figure 2-2. 25\u00C2\u00A0 \u00C2\u00A0 biosolids proportion in fuel (% w/w) 0 20 40 60 80 100 pr od uc t y ie ld (% ) 0 20 40 60 80 Syngas Tar Char Figure 2-2 Product yield versus biosolids proportion in fuel (Peng et al., 2012). Operating conditions: feedstock flow rate, 1.2 kg/h; reactor temperature, 800\u00D4\u00A8. Saw et al. (2011) performed steam co-gasification of biosolids with wood in a dual fluidized bed gasifier. They plotted syngas yield, tar concentration and char conversion with various biosolids proportion in fuel, as shown in Figure 2-3. It is seen that the syngas yield decreased from 0.7 to 0.3 Nm3/kg as the biosolids proportion increased from 0 to 100%. The maximum syngas yield, 0.8 Nm3/kg, corresponding to 10% biosolids. Figure 2-3 also shows that tar content in syngas increased from 2.7 to 5.8 g/Nm3, with increasing biosolids proportion in the feed from 0 to 100%, except for one point at 60%. It would be interesting to analyze the tar composition in efford to find why gasification of biosolids produced higher yields of tar. Similarly, for char conversion, the point at 60% was unexpected; Other than this point, char conversion decreased from 0.6 to 0.4 as the biosolids proportion increased from 0 to 100%. The author did not explain what caused the unexpected point at 60%. \u00C2\u00A0 26\u00C2\u00A0 \u00C2\u00A0 biosolids proportion in fuel (% w/w) 0 20 40 60 80 100 S yn ga s yi el d (N m 3 /k g) , c ha r c on ve rs io n 0.0 .2 .4 .6 .8 1.0 Ta r c on ce nt ra tio n (g /N m 3 ) 2 3 4 5 6 7 8 syngas yield tar char Figure 2-3 Syngas yield, tar concentration and char conversion versus biosolids proportion in fuel (Saw et al., 2011). Operating conditions: reactor temperature 720\u00D4\u00A8; feedstock flow rate, 15.5 kg/h; steam/fuel ratio, 1.1 (kg/kg) 2.3.2 Syngas composition and heating values of syngas According to Peng et al. (2012), the concentrations of H2 and CO first increased as the biosolids proportion increased from 0 to 50%, and then decreased as the biosolids proportion increased from 50 to 100%. The CH4 concentration was found to remain constant at 8% with varying biosolids proportion. The heating value of the syngas was found to decrease linearly from 14.95 to 11.27 MJ/Nm3 as the biosolids proportion increased from 0 to 100%. Saw et al. (2011) found that, as the biosolids proportion increased from 0 to 100%, the H2 concentration increased linearly, while the CO concentration decreased linearly 27\u00C2\u00A0 \u00C2\u00A0 and the CH4 concentration remained nearly constant. The heating value of syngas was found to be constant at around 15 MJ/Nm3 with varying biosolids proportion. Pinto et al. (2008) studied co-gasification of biosolids with straw. According to their findings, as the biosolids proportion increased, the concentrations of H2 and CO decreased, that of CO2 increased, and CH4 and other hydrocarbons increased gradually. 2.3.3 Summary In summary, previous work shows clearly that syngas yield decreases with increasing biosolids proportion in fuel. This decrease results from lower char conversion of biosolids and higher ash content in the biosolids. Tar concentration in syngas increases with increasing biosolids proportion. The heating value of syngas does not vary much with changing biosolids proportion. In terms of syngas composition, no general conclusion can be drawn because different researchers have reached different conclusions. Synergistic effects seem to often occur when gasifying biosolids with biomass. Peng et al. (2012) concluded that syngas yield and H2 concentration reached maxima at 30% biosolids, whereas Saw et al. (2011) reported that with 10-20% biosolids in fuel, syngas and H2 yield reached maxima. 2.3.3 Kinetics of co-gasification Previous studies have shown that alkali and alkaline earth metals such as potassium and calcium can cause significant catalytic effect on gasification; in particular, potassium is agreed to be an excellent catalyst for gasification. However, addition of alkali or alkaline earth metals as catalysts is costly. As an alternative, researchers have shown interest in investigation of co-gasification with biomass because some types of 28\u00C2\u00A0 \u00C2\u00A0 biomass such as switchgrass have high alkali contents, i.e., potassium-rich (Zhu et al., 2008, Brown et al., 2000, Mitsuoka et al., 2011). 2.4 Fluidization flow regime The pilot scale gasifier used for this study was designed and built by Highbury Energy Inc., as a bubbling fluidized bed gasifier. The fluidization flow regime is mainly determined by the superficial gas velocity and mean particle size. One comprehensive flow regime map was provided by Bi and Grace as shown in Figure 2-4 (Bi & Grace, 1995). Seen from the figure, the bubbling fluidization regime is bounded as in the shaded area. 29\u00C2\u00A0 \u00C2\u00A0 Figure 2-4 Flow regime diagrams according to Bi and Grace (Bi & Grace, 1995)\u00EF\u00BC\u008C with permission from the Elsevier. Ar=Archimedes number; U*=dimensionless gas velocity\u00C2\u00A0 \u00C2\u00A0 t BD b ou nd ar y A p pr ox im at e AB b ou nd ar y Umf U Ty pi ca l A C bo un da ry Uc 1 3 10 30 100 300 0.001 0.01 0.1 1 10 Ar U * 1/3 2 10 10-2 0 10-1 10-3 Bubb ling Use Turb ulen t Pa ck ed B ed s 30\u00C2\u00A0 \u00C2\u00A0 CHAPTER 3: RESEARCH OBJECTIVES As outlined in the previous chapters, gasification of biosolids has potential benefits over landfilling and incineration, and it causes fewer problems than land application. However, major issues of biosolids gasification are the high moisture and ash contents in biosolids. This can be mitigated by co-gasification of biosolids with low ash and moisture content biomass. To investigate the feasibility of biosolids gasification as a disposal method, this study is divided into two parts: (1) kinetic study of co-gasification of biosolids with biomass in a thermogravimetric analyzer; and (2) investigation of gasification performance of co-gasification of biosolids with biomass in a pilot scale bubbling fluidized bed gasifier. For the kinetic study, the main objective is to observe whether any catalytic or inhibition effects are present in co-gasification. In the bubbling fluidized bed gasifier, the co-gasification of biosolids with different proportions (0%, 10%, 25%, 50%, 100% by weight) with biomass is studied. The ultimate goal of this project is to assist with biosolids disposal, so an important objective is to maximize the proportion of biosolids in the mixture without affecting the overall gasification performance. To evaluate the gasification performance, four parameters are investigated. First, syngas composition is monitored because it is an important product quality indicator. Higher H2/CO ratio in syngas is desired. Second, syngas yield is calculated as a measure of the productivity. Third, the tar content in the syngas is determined. Removal of tar from the syngas is a major issue, adding cost to the downstream processing. Because of this, the target is to keep the tar content as low as possible. Finally, ammonia concentration in the syngas is monitored. Ammonia, hydrogen sulphide, hydrogen cyanide, and hydrogen chloride are major contaminants 31\u00C2\u00A0 \u00C2\u00A0 in gasification of biosolids because biosolids have relatively high N, S and Cl contents. In this study, ammonia is determined as a representative contaminant gas. With the bubbling fluidized bed gasifier, the impact of temperature on gasification performance is also studied because temperature is a very important variable in gasification. In one run, temperature is varied from 720 to 830\u00D4\u00A8 in steps of 30\u00D4\u00A8. The effects of temperature on syngas composition and yield are then investigated. 32\u00C2\u00A0 \u00C2\u00A0 CHAPTER 4: MATERIALS Three sources of biosolids and two kinds of biomass were procured and their characteristics were analyzed, before choosing one for the experiments. 4.1 Biosolids Three sources of biosolids were received and compared. In the beginning stage, biosolids sludge from an undisclosed British Columbia (BC) WWTP was obtained. The ultimate analysis of the biosolids was determined by Canadian Micro-analytical Lab. The proximate analysis was performed at UBC CHBE with a thermogravimetric analyzer. The higher heating value of the biosolids was determined at UBC CHBE with a Parr 6100 Calorimeter. Later, the Nexterra Systems Corp. provided biosolids from a WWTP in Washington State and also from a WWTP in Baltimore with analyzed properties, including proximate and ultimate analyses and higher heating value. The properties of all three biosolids are summarized in Table 4-1. By comparing the characteristics of these biosolids with those investigated by previous work in the literature, these properties were typical. The biosolids from the BC WWTP were cake-like materials and contained much water. This would require us to dry the biosolids before use, but drying is energy and time consuming, as well as causing strong smell. In comparison, the biosolids from the Washington State and Baltimore WWTPs were already dried and pelletized. Of these two, the Baltimore biosolids had higher heating value and lower ash content as shown in Table 4-1. Hence, the Baltimore biosolids were tested in this study. 33\u00C2\u00A0 \u00C2\u00A0 Table 4-1 Proximate and ultimate analyses of biosolids from different sources Source BC Washington Baltimore Water content (%) 75.5 4.0 9.2 Proximate (dry) Volatile (%) 50.5 65.7 82.3 Ash content (%) 39.6 25.4 10.9 Fixed carbon (%) 9.9 8.9 6.8 Higher heat value (kJ/kg,dry) 14700 16800 22100 Ultimate(dry and ash free) Carbon (%) 56.0 53.4 55.1 Hydrogen (%) 6.9 8.4 8.6 Oxygen (%) 31.1 28.0 29.0 Nitrogen (%) 4.4 7.8 6.6 Sulfur (%) 1.6 2.4 0.6 The ash fusion temperature of Baltimore biosolids was also provided by the Nexterra Systems Corp. and is reported in Table 4-2. From Table 4-2, the deformation and flow temperatures of biosolids are 1136 and 1290\u00D4\u00A8, much lower than for wood pellets, 1420 and 1450\u00D4\u00A8\u00C2\u00A0respectively (Wilk, et al. 2011). To prevent agglomeration and sintering, it is safe to keep the temperature below 1100\u00D4\u00A8. Our gasification experiments were at around 850\u00D4\u00A8, far below the melting point. 34\u00C2\u00A0 \u00C2\u00A0 Table 4-2 Ash fusion analysis of biosolids from Baltimore WWTP Ash Analysis Unit Analytical Biosolids Fuel Methods Feb-08-2012 *Ash Fusion Temperature (reducing atmosphere): Initial Deformation \u00C2\u00B0C ASTM D1857 1136 Softening (h=W) \u00C2\u00B0C ASTM D1857 1181 Hemispherical \u00C2\u00B0C ASTM D1857 1211 Fluid \u00C2\u00B0C ASTM D1857 1290 4.2 Biomass Two kinds of biomass were received, wood pellets and switchgrass. The wood pellets were provided by Highbury Energy Inc. from a local supplier, whereas the switchgrass from Manitoba was obtained by a fellow graduate student, Mohammad Masnadi. The characteristics of the two materials were analyzed by Highbury Energy Inc. and by Mohammad separately and are summarized in Table 4-3. Wood pellets have been widely used for biomass gasification studies, whereas switchgrass has been reported to have significant catalytic effects (Brown et al. 2000). Hence, both materials were selected to be co-gasified with the biosolids. Also, both biomass materials satisfied the criteria of low moisture and ash contents as shown in Table 4-3. 35\u00C2\u00A0 \u00C2\u00A0 The moisture contents of wood pellets and switchgrass were 5.86 and 9.26% respectively, while their ash contents were 1.09 and 6.29% respectively. Table 4-3 Proximate and ultimate analyses of wood pellets and switchgrass biomass wood pellets switchgrass Water content (%) 5.9 9.3 Proximate (dry) Volatile (%) 83.6 76.9 Ash content (%) 1.1 6.3 Fixed carbon (%) 15.4 16.8 Higher heat value (kJ/kg,dry) 19300 19400 Ultimate(dry and ash free) Carbon (%) 47.9 49.7 Hydrogen (%) 6.4 6.2 Oxygen (%) 44.6 43.1 Nitrogen (%) 0.3 0.9 Sulfur (%) 0.9 0.08 36\u00C2\u00A0 \u00C2\u00A0 CHAPTER 5: KINETIC STUDY IN A TGA \u00C2\u00A0 5.1 Experimental setup A Thermax500 high-pressure TGA was used for the kinetic study. CO2 gasification of the different fuels was performed to compare their gasification rates at atmospheric pressure. The inlet gases were introduced from the bottom of the reactor. The outlet gases went through a tar and moisture removal bucket. The fuels prepared included biosolids, wood pellets, switchgrass and mixtures of biosolids with wood pellets/switchgrass. Fuel samples were sieved to between 300 and 355 \u00DF\u00A4m, and at the beginning of each experiment, sieved samples were put in the TGA basket connected to the balance at the top of the TGA. The initial sample weight was calculated based on the char yield, the weight percentage of chars in fuels. The char yield of biosolids, wood pellets and switchgrass was measured to be 21%, 17% and 17% respectively. In order to have 15 mg of chars after pyrolysis, the weight of the initial sample can be determined, i.e., if pure biosolids was the sample, the initial weight was 15/0.21=71.4 mg. Mass and heat transfer limitations were not investigated. During the experiments, the weight of sample and temperature were monitored. The experiments included two parts, pyrolysis and gasification. For pyrolysis, the reactor was heated from room temperature to 800\u00D4\u00A8 at a heating rate of 25 \u00D4\u00A8/min and then maintained at 800\u00D4\u00A8 for half an hour. During this period, the carrier gas was nitrogen at a flow rate of 500 mL/min. The heating rate and gas flow rate were chosen to maximize the char yield. The purpose of pyrolysis was to yield 15 mg of char for gasification. The selected conditions (gas flow rate, char initial weight, heating rate, 37\u00C2\u00A0 \u00C2\u00A0 etc.) were the same as utilized by Mohammed Masnadi, a PhD student in our group, who is experienced in kinetic studies with TGA. After the pyrolysis, the char samples were subjected to CO2 gasification. Hence, nitrogen was switched to CO2 with the temperature maintained at 800\u00D4\u00A8 throughout the gasification period. The experiments continued until the gasification was complete, i.e. until the weight of sample was no longer decreasing. The impacts of temperature and gas flow rate on gasification were not investigated. 5.2 Data analysis The gasification rate of each run is discussed by plotting the ash-free char conversion versus time during the gasification period. Ash-free char conversion is calculated from the mass of sample, i.e. X\u00E0\u00AD\u00B2 \u00E0\u00B5\u008C \u00E0\u00AD\u009B\u00E0\u00B1\u009F\u00E0\u00AC\u00BF\u00E0\u00AD\u009B\u00E0\u00B1\u00AA\u00E0\u00AD\u009B\u00E0\u00B1\u009F\u00E0\u00AC\u00BF\u00E0\u00AD\u009B\u00E0\u00B1\u0097 (5-1) where Xt: char conversion at time t, - Wi: initial mass of sample, mg Wt: mass of sample at time t, mg Wa: mass of ash, taken as final weight of sample in TGA basket, mg 5.3 Results and discussion Since kinetic study was not the main focus of this project, reproducibility was checked for only two experiments, co-gasification of biosolids with biomass at 50/50 mass proportions, by conducting those experiments twice. 5.3.1 Separate gasification of biosolids, woody pellets and switchgrass Char conversions of biosolids, wood pellets, and switchgrass versus time are plotted in Figure 5-1. \u00C2\u00A0 38\u00C2\u00A0 \u00C2\u00A0 \u00C2\u00A0 Gasification Time (min) 0 200 400 600 C ha r c on ve rs io n, X 0.0 .2 .4 .6 .8 1.0 biosolids wood switchgrass \u00C2\u00A0 Figure 5-1 Char conversion of biosolids, wood pellets and switchgrass vs. time. Operating conditions: reactor temperature, 800\u00D4\u00A8; sample size, 300-355 \u00DF\u00A4m; initial mass of sample, 15 mg; CO2 flow rate, 500 mL/min \u00C2\u00A0 From Figure 5-1, the gasification rate of wood pellets and switchgrass were similar, but the gasification rate of biosolids was obviously slower. It only took 400 min for wood pellets and switchgrass to be completely converted, whereas it took 700 min for biosolids to complete the reaction. For the kinetic study, it is important to know the ash composition of the materials. Ash analysis was performed by Acme Labs in Vancouver, and the results are provided in Table 5-1. From Table 5-1, the ash of switchgrass and wood pellets contained high proportions of potassium and calcium, both of which have been found to catalyze gasification. On the other hand, biosolids ash contained very little alkali and alkaline earth metals, like partially acid washed-biomass. According to Mitsuoka et al. (2010), the gasification rate of acid washed-biomass was significantly slower than that of biomass. In addition, Xu et al. (2009) reported that the continuous ash accumulation near the char surface could also inhibit gasification. Note that biosolids contain higher 39\u00C2\u00A0 \u00C2\u00A0 proportions of ash than wood pellets and switchgrass, 10.9%, vs. 6.3% and 1.1%, respectively. Due to these two reasons, the gasification rate of biosolids was slower than that of wood pellets or switchgrass. Table 5-1 Ash analysis of switchgrass, wood pellets and biosolids switchgrass wood pellets biosolids SiO2 52.1 25.32 23.27 Al2O3 0.5 4.41 10.37 TiO2 0.03 0.22 2.42 Fe2O3 0.96 4.04 16.65 CaO 15.28 21.44 10.36 MgO 5.94 13.63 2.95 K2O 13.11 8.92 1.98 Na2O 0.4 1.36 0.49 P2O5 5.05 1.5 27.05 LOI 6.63 19.16 4.46 *LOI, loss on ignition From Table 5-1, biosolids contains 27.05% P2O5 in ash. The P element should partially evaporate in the form of PO2, PO, and (P2O3)2 during gasification (Bourgel, et al. 2011), and deposit into slag in the form of P-containing glass after gasification (Zhang et al, 2012). 5.3.2 Co-gasification of biosolids with biomass Consider the runs during which biosolids were co-gasified with wood pellets and with switchgrass, both at 50/50 weight proportions. The co-gasification rate is plotted and compared with gasification rate for the pure substances in Figure 5-2. 40\u00C2\u00A0 \u00C2\u00A0 \u00C2\u00A0 (a) Gasification Time (min) 0 200 400 600 C ha r c on ve rs io n, X 0.0 .2 .4 .6 .8 1.0 biosolids alone wood alone biosolids/wood 50/50 mixture expected gasification rate of biosolids/wood 50/50 mixutre \u00C2\u00A0 (b) Gasification Time (min) 0 200 400 600 C ha r c on ve rs io n, X 0.0 .2 .4 .6 .8 1.0 biosolids alone switchgrass alone biosolids/switchgrass 50/50 mixture expected gasification rate of biosolids/switchgrass 50/50 mixutre \u00C2\u00A0 Figure 5-2 Co-gasification of 50:50 biosolids by weight with: a) wood pellets; b) switchgrass. Operating conditions: reactor temperature, 800\u00D4\u00A8; sample size, 300-355 \u00DF\u00A4m; initial mass of sample, 15 mg; CO2 flow rate, 500 mL/min 41\u00C2\u00A0 \u00C2\u00A0 From Figure 5-2, the co-gasification rate of the mixture was much slower than expected. If no catalytic or inhibition occurred, the line for co-gasification would lie between the two lines for gasification of the pure materials as shown in Figure 5-2. Clearly, inhibition must have occurred to slow down the co-gasification reaction. The co-gasification experiments were repeated to confirm the reliability of the results, and the repeated results are plotted in Figure 5-3. (a) Gasification Time (min) 0 100 200 300 400 500 600 700 C ha r c on ve rs io n, X 0.0 .2 .4 .6 .8 1.0 biosolids/wood 50/50 mixture repeat of biosolids/wood 50/50 mixture \u00C2\u00A0 42\u00C2\u00A0 \u00C2\u00A0 (b) Gasification Time (min) 0 100 200 300 400 500 600 700 C ha r c on ve rs io n, X 0.0 .2 .4 .6 .8 1.0 biosolids/switchgrass 50/50 mixture repeat of biosolids/switchgrass 50/50 mixture Figure 5-3 Repeat of co-gasification experiments: a) co-gasification of biosolids with wood pellets; b) co-gasification of biosolids with switchgrass. Operating conditions: reactor temperature, 800\u00D4\u00A8; sample size, 300-355 \u00DF\u00A4m; initial mass of sample, 15 mg; CO2 flow rate, 500 mL/min Figure 5-3 indicates the results of the repeated experiments did not deviate much, so the inhibition effect was confirmed. 5.3.3 Catalytic and inhibition effect on gasification rate Next, co-gasification tests were conducted on biosolids with switchgrass ash with 50/50 proportion. Brown et al. (1999) reported that switchgrass ash contained high K content and should accelerate the reaction. Figure 5-4 plots the co-gasification rate of biosolids with switchgrass ash. \u00C2\u00A0 43\u00C2\u00A0 \u00C2\u00A0 Gasification Time (min) 0 200 400 600 C ha r c on ve rs io n, X 0.0 .2 .4 .6 .8 1.0 biosolids alone switchgrass alone biosolids/switchgrass_ash 50/50 mixture \u00C2\u00A0 Figure 5-4 Co-gasification of 50:50 biosolids with switchgrass ash. Operating conditions: reactor temperature, 800\u00D4\u00A8; sample size, 300-355 \u00DF\u00A4m; initial mass of sample, 15 mg; CO2 flow rate, 500 mL/min Figure 5-4 shows clearly that there is a catalytic effect due to the switchgrass ash. Within 45 minutes, char conversion of the mixture of biosolids with switchgrass ash reached 80%. By comparison, 80% char conversion took switchgrass about 200 minutes and biosolids alone 330 minutes. A key question then is what caused the inhibition? A research was carried out to try to find previous work on the kinetics of biosolids, but few works could be found. To investigate whether the inhibition effect might be due to the biosolids ash, co-gasification of biosolids ash with biomass was performed, with the results plotted in Figure 5-5. 44\u00C2\u00A0 \u00C2\u00A0 \u00C2\u00A0 (a) Gasification Time (min) 0 200 400 600 C ha r c on ve rs io n, X 0.0 .2 .4 .6 .8 1.0 biosolids alone wood alone biosolids_ash/wood 50/50 \u00C2\u00A0 (b) Gasification Time (min) 0 200 400 600 800 C ha r c on ve rs io n, X 0.0 .2 .4 .6 .8 1.0 biosolids alone switchgrass alone biosolids_ash/switchgrass 50/50 mixture \u00C2\u00A0 Figure 5-5 Co-gasification of 50:50 biosolids ash with: a) wood pellets; b) switchgrass. Operating conditions: reactor temperature, 800\u00D4\u00A8; sample size, 300-355 \u00DF\u00A4m; initial mass of sample, 15 mg; CO2 flow rate, 500 mL/min 45\u00C2\u00A0 \u00C2\u00A0 From Figure 5-5, inhibition occurred when co-gasifying biosolids ash with biomass, especially with switchgrass, possibly because of undesired interactions between the ash of biosolids and the ash of switchgrass. It was concluded that the inhibition effect by biosolids ash overcame the positive catalytic effect of the switchgrass ash, with the net result that co-gasification of biosolids with switchgrass was slower than gasification of each individual material. Initially, it was planned to co-gasify switchgrass with biosolids in the Highbury pilot scale bubbling fluidized bed because of its catalytic effect. However, the TGA tests indicated that neither wood pellets or switchgrass could enhance co-gasification. Thus, it was decided to use wood pellets instead of switchgrass because wood pellets are more likely to be used in gasification, at least in British Columbia, and we had ready access to a supply of wood pellets. 46\u00C2\u00A0 \u00C2\u00A0 CHAPTER 6:\u00C2\u00A0 GASIFICATION IN HIGHBURY PILOT SCALE BUBBLING FLUIDIZED BED 6.1 Experimental setup (Watkinson et al., 2010) The pilot scale bubbling fluidized bed process was designed and built by Highbury Energy Inc (HEI). My only contribution to the system was adding the ammonia absorption line. To conduct my experiments, I obtained permission from Dr. Watkinson to use the system for five runs. Before my runs, for safety issues, I was trained by Dr. Yonghua Li to assist in several runs to learn the procedures and safety requirements for operation of the system. Dr. Yonghua Li also taught me data collection and after-experiment data analysis procedures. During my runs, Dr. Yonghua Li supervised and assisted me. Mohammad Masnadi also assisted on some occasions. 6.1.1 Feedstock Based on the current system, the diameter of the feed tube to the gasifier is limited to 11 mm. For successful feeding, the particle size of the feedstock must not exceed 1 mm. Biosolids and wood pellets were therefore crushed and sieved by a 1 mm screen. Biosolids and wood pellets were then pre-mixed in different ratios as fuel for five runs in the bubbling fluidized bed gasifier. The proportions by mass of bioisolids in fuel were 0%, 10%, 25%, 50%, and 100% for the five runs. For each run, the moisture content of the fuel was measured, so that the dry weight could be determined and used for data analysis. All results are expressed on a dry weight basis, for example, syngas yield in m3/kg dry fuel. The feed rate was controlled around 1.4 kg/h for four of the runs. However, in the run with 100% biosolids, the influence of feed rate on 47\u00C2\u00A0 \u00C2\u00A0 gasification performance was studied, with the feed rate varied from 0.7 to 1.9 kg/h. Total feeding time was 2-3 hours for each run. One key issue related to mixing was particle segregation for mixtures of biomass with coal. Segregation may occur in the hopper with the screw feeder used and often occurs in the bubbling fluidized bed, primarily due to the significant difference in density between biomass and coal (Dai et al., 2008). For the mixture of biosolids with wood pellets, the screw feeder was turned on for one hour and segregation was not observed. The possible reason for the segregation effect being negligible was that the densities of biosolids and wood pellets are similar, ~200 and ~300 kg/m3, respectively. 6.1.2 System Process flow diagram The bubbling fluidized bed gasification facility was designed and built by Highbury Energy Inc. The process flow diagram is shown in Figure 6-1.\u00C2\u00A0The hopper (0.22 m3) is filled with prepared feedstock before each run, and during the gasification period, the screw feeder delivered feedstock to the bottom of the gasifier, assisted by conveying nitrogen. The building steam at 85 psig and 160\u00D4\u00A8 was heated by super-heaters (12X240VX1800W, 21.6 kW, 3.7 m long) to about 800\u00D4\u00A8 before entering the gasifier. The steam pipe line was covered by glass fiber insulation. The gasifier was well insulated, and the reactor temperature was controlled by three electrical heaters. Producer gases left from the top of the gasifier and entered two cyclones, main body insulated with ceramic fiber, in series where fly ash was separated and collected from the bottom. Then, producer gases passed through two coolers (double pipe type, 12 m long, heat exchange area of 2 m2), the first one cooled by ambient air, and the second by cooling water. Condensed water and tars were collected at the bottom of the coolers. After passing through the cooler, the producer gases entered a baghouse filter where the remaining ash particles were captured. 48\u00C2\u00A0 \u00C2\u00A0 Finally, producer gases reached the roof top and were burnt with natural gas in a natural gas burner. The data acquisition system used was a PCI-DAS08 card coupled with a signal conditioning board EXP-32. Temperatures and pressures along the path were monitored, recorded, and displayed in Labview 8.6. Location of temperatures and pressures distributions is summarized in Figure A1 of the Appendix for reference. Steam flow rates were also displayed and recorded in Labview 8.6. \u00C2\u00A0 Between the cyclones and coolers, gas samples were withdrawn for tar sampling and ammonia determination. Between the coolers and baghouse, there is another sampling line to extract producer gases for gas concentration analysis. 49\u00C2\u00A0 \u00C2\u00A0 \u00C2\u00A0 Figure 6-1 Process flow diagram of the Highbury Energy Inc. bubbling fluidized (Watkinson et al., 2010), with permission from Dr. Watkinson 50\u00C2\u00A0 \u00C2\u00A0 Gasifier The gasifier is a cylindrical stainless steel pipe (800H/Ht, S40, SMLS) of inside diameter 100 mm, and length 1.2 m. The column is surrounded by ceramic fiber electrical heaters and insulation blankets, two semi-cylindrical heaters (125 mm ID, 225 mm OD, 0.92 m long) at the bottom and one full cylindrical (125 mm ID, 0.15 m long) at the top, with total power of 7.7 kW. At the bottom of the column is a perforated distributor above the steam entrance to distribute inlet steam. The distributor (101.6 mm ID, 24 evenly distributed holes with 3.175 mm diameter) is sandwich-like, with two distributors at bottom and top and filled with packing material in the middle (ceramic packing of size 6.35 mm, 177.8 mm high). Silica sand was chosen as the inert bed material for the process. Olivine sand was also considered, but not chosen. From literature review, lime is also a good catalyst, but the attrition of lime was considered to be excessive. The bed height was about 25-30 cm, and this range of height was thought to be optimal for temperature distribution in the column based on Highbury\u00E2\u0080\u0099s experiments. Unstable fluidization was found when the bed height exceeded 35 cm. The density of silica sand used is 2650 kg/m3. The sand was sieved to particle diameters between 270 and 850 \u00DF\u00A4m, corresponding to Geldart group B particles. An internal cyclone was installed at the top of the column, immediately upstream of where the producer gases exit, to reduce the tar content of the gases. Previous work has shown that the hot surface of the cyclone can thermally crack tars (Pfeifer et al., 2011). Tar and ammonia sampling Tar sampling and ammonia determination are combined in one sampling line in series because they require similar conditions. The tar sampling is HEI\u00E2\u0080\u0099s equipment and protocol, whereas the ammonia determination is my contribution. The Apex Instuments model XC-60 including a sample pump, control valves and dry gas meter 51\u00C2\u00A0 \u00C2\u00A0 is used to extract producer gases through the sampling line. Producer gases first pass through the glass fiber filter, 50 mm in length contained in the pipe, to filter particulates. Then, gases pass through impingement bottles containing solvents kept around 0\u00D4\u00A8\u00C2\u00A0in an ice bath. Before gases enter the impingers, insulation blankets covered the pipe to prevent tar and water condensing half way. A small heater was also installed along this path to maintain the temperature above 300\u00D4\u00A8. The first six impingement bottles containing acetone were used to absorb tar, while the following two contained 1 N sulfuric acid for ammonia absorption. Ammonia was trapped and determined with a modified method CTM-027 of EPA. In method CTM-027, four impingers are used to capture ammonia, two with 0.1 N sulfuric acid and two empty. Due to limited space in our case, two impingers were used to absorb ammonia, one with 1 N sulfuric acid and one empty. After each gasification experiment, tar and ammonia were analyzed separately. Tar was separated by washing, evaporation and drying. First, the solution in the tar- absorbing impingers was poured into a bottle. Then, all impingers were washed with methanol chloride to capture all tar, and the washed liquid is poured into the same bottle. The liquid was then filtered with a 0.22 \u00DF\u00A4m filter to remove fine ash. Next, the liquid was transferred to a spherical flask for distillation. The distillation started at room temperature and atmospheric pressure, rising to 70\u00D4\u00A8\u00C2\u00A0and -25 inch Hg (85 kPa vacuum). After 10 hours of distillation, most of the water, acetone and methanol chloride were evaporated. However, a few water droplets were usually left. The spherical flask was then placed in an oven at 75\u00D4\u00A8 over two nights to remove remaining water. After overnight drying, the leftover should be tars only. The weight of tar collected was then obtained. Then, the tar content of the syngas could be determined by the weight of tar divided by the volume of syngas collected in units of g/m3. After each gasification experiment, the ammonia absorbent (1N sulfuric acid) was poured into a bottle, sealed and delivered to measure ammonia concentration by a 52\u00C2\u00A0 \u00C2\u00A0 back titration method. The volumes of sulfuric acid before and after the gasification experiment were measured to check whether the acid was diluted by absorbing water in the producer gases. The ammonia determination method is explained in detail in the data analysis section. Gas Chromatography To measure gas concentrations of dry and tar free gases, the gas analyzer was placed downstream of the condensers where water and tar in the producer gases have already condensed. Producer gases consisted mainly of CO, CO2, CH4, H2, and N2 all of which were analyzed continuously by online micro gas chromatography (GC) which helium as the carrier gas. It took 4 minutes to analyze the gas concentrations in a gas sample, so every 4 minutes a sample from the producer gases was injected and analyzed. The total time delay for micro GC was ~2 minutes because it took ~2 minutes for gas to flow from the reactor to the gas analysis point. 6.1.3 Operating conditions The feed rate of feedstock was controlled to around 1.4 kg/h. The flow rate of steam was maintained at ~3-4 kg/h, and after calculation, the flow regime fell in the bubbling fluidization flow regime according to the regime map of Bi and Grace (1995). Bed temperature was maintained constant at around 850\u00D4\u00A8\u00C2\u00A0for four runs. In the run with 50% biosolids by mass in the fuel, the temperature effect was studied over the range of 720 to 830\u00D4\u00A8. 6.1.4 Operating procedure adapted from HEI manual Before each run, it is necessary to perform a preparation check. Make sure electrical, steam, water supply, ventilation system, CO monitors, data acquisition system, are working properly. Have adequate compressed N2 and adequate fuel. Ensure that all valves are in correct positions. 53\u00C2\u00A0 \u00C2\u00A0 Start the experiment by turning on the main power and opening cooling-water valve WV0. Then, turn on computer, open Labview 8.6, enter file names, and start data collection for temperatures and pressures. Next, start to introduce fluidization N2 by turning on valves NV0, NV8, and slowly turning on valve NV1 until the reading reaches 3.6 CFM on rotameter NF1. Start conveying N2 by opening valves NV6, NV4, NV5, and slowly open valve NV2 until the NF2 reading reaches 0.9 CFM. When opening valve NV2, note that pressure of P11 increases to ~5 psig and then drops to ~1 psig. After turning on N2, turn on the steam super-heaters and reactor heaters, and set the desired reactor temperature on the reactor heaters. After the reactor temperature reaches the desired temperature, steam and fuel can be fed to the gasifier. Before feeding, start the rooftop after-burner and open the natural gas valves, NGV0 and NGV1. Then, start the feeding steam with the following procedure. Open drain valves, SDV0 and SDV1 to drain condensed steam in the pipe and in the gasifier. After draining, close the drain valves SDV0 and SDV1 and open steam supply valve SV0 and steam control valve SV1. Slowly increase the steam flow rate by adjusting valve SV1 while decreasing the fluidization N2 flow through valve NV1. Fully close valve NV1 once the steam flow rate achieves the desired value. After feeding the steam, start feeding fuel by turning on the feed power switch and setting the screw feeder rotationspeed. During the gasification period, tar and gas sampling are conducted. For the tar sampling line, turn on the sampling heater and open sampling valve SGV4. Turn on the main power of the Apex Instruments model XC-60. Then, turn on the vacuum pump and adjust the gas control valve. For gas sampling, turn on the micro GC and computer, and open sampling valve SGV9. Initiate software Galaxie for gas concentration data logging. Turn on the vacuum pump to draw a gas sample. After finishing tar and gas sampling, close the valves, stop the pumps, and turn off the equipment and computer. 54\u00C2\u00A0 \u00C2\u00A0 After 2-3 hours of gasification, shut-down the system by turning off the main power switch and heaters, stopping data logging, stopping the rooftop burner, and closing valves NV0, NV1, NV2, NV3, NV4, NV5, NV6, NV8, SV1 and SV0. 6.2 Data analysis 6.2.1 Syngas composition, LHV and syngas yield Gas concentrations of the producer gases were analyzed by the online micro GC as mentioned above. The molar concentrations of H2, CO, CO2, CH4, and N2 were measured and recorded throughout the experiments. When averaging the concentration of each gas, steady state had to be considered. Values were only taken which were no longer varying appreciably. Then, the nitrogen-free syngas composition was determined. When calculating syngas composition and yield, nitrogen needs to be excluded because nitrogen is mostly from the conveying nitrogen used to deliver fuel, not part of syngas product. The lower heating value of syngas (LHV) can be estimated from the formula (Peng et al. 2012): LHV\u00E1\u0088\u00BAMJ Nm\u00E0\u00AC\u00B7\u00E2\u0081\u0084 \u00E1\u0088\u00BB \u00E0\u00B5\u008C H\u00E0\u00AC\u00B6% \u00E0\u00B5\u0088 10.798 \u00E0\u00B5\u0085 CO%\u00E0\u00B5\u0088 12.636 \u00E0\u00B5\u0085 CH\u00E0\u00AC\u00B8%\u00E0\u00B5\u0088 35.818 (6-1) where H2, CO and CH4 are the molar concentrations of the nitrogen-free syngas. Syngas yield can also be determined. The flow rate of conveying nitrogen was maintained constant throughout each run, and the concentration of nitrogen in the producer gases was determined by the micro GC. These two values allow us to calculate the flow rate of nitrogen-free syngas, assuming negligible nitrogen release during the gasification. Then, syngas yield was determined from the syngas flow rate divided by the fuel feed rate in units of m3/kg. The fuel feed rate was calibrated before each gasification run. Sometimes, the feed rate was double checked-after the run. 55\u00C2\u00A0 \u00C2\u00A0 6.2.2 Tar content in syngas As mentioned above, after each run, collected tar was weighed after evaporation. The volume of producer gases collected was known from the flow meter. Then, the volume of nitrogen-free syngas could be determined from the N2 concentration in the producer gases. Tar content in the syngas equals the weight of tar divided by the volume of syngas collected, in units of g/m3. 6.2.3 Ammonia determination As noted above, sulfuric acid was used to absorb ammonia according to: 2NH\u00E0\u00AC\u00B7 \u00E0\u00B5\u0085 2H\u00E0\u00AC\u00B6SO\u00E0\u00AC\u00B8 \u00E2\u0086\u0092 \u00E1\u0088\u00BANH\u00E0\u00AC\u00B8\u00E1\u0088\u00BB\u00E0\u00AC\u00B6SO\u00E0\u00AC\u00B8 \u00E0\u00B5\u0085 H\u00E0\u00AC\u00B6SO\u00E0\u00AC\u00B8 (6-2) From Equation 6-2, by knowing the moles of remaining sulfuric acid, the moles of ammonia absorbed could be determined. To determine the moles of sulfuric acid remaining, the back titration technique was applied. A pH indicator, phenolphthalein, was added to the ammonia-absorbing solution, and 0.1N NaOH was added until the solution changed colour. The amount of added NaOH was read and recorded. The back titration reaction was H\u00E0\u00AC\u00B6SO\u00E0\u00AC\u00B8 \u00E0\u00B5\u0085 2NaOH \u00E2\u0086\u0092 Na\u00E0\u00AC\u00B6SO\u00E0\u00AC\u00B8 \u00E0\u00B5\u0085 2H\u00E0\u00AC\u00B6O (6-3) Thus, the moles of NaOH added could be used to back-calculate the moles of remaining sulfuric acid, and then the moles of ammonia absorbed. The moles of ammonia were then converted to volume using the ideal gas law. Since ammonia absorption and tar sampling were connected in series, the volumes of nitrogen-free syngas collected were the same and could be obtained from tar content calculation. The ammonia concentration was the volume of ammonia divided by the volume of collected syngas in units of ppmv. 56\u00C2\u00A0 \u00C2\u00A0 6.2.4 Char conversion Char is defined as the portion of fuel left after the moisture and volatile contents have been removed. Char conversion can be determined from a mass balance on ash. In the mass balance, ignoring ash remaining in the bed, the amount of ash fed into the reactor should equal the amount of ash leaving the reactor because ash is not involved in the gasification reactions as a reactant. The following mass balance equation can be used to calculate the char conversion. M\u00E0\u00AD\u00A7\u00E0\u00AD\u00AC \u00E0\u00B5\u0088 A1% \u00E0\u00B5\u008C M\u00E0\u00AD\u00AD\u00E0\u00AD\u00B3\u00E0\u00AD\u00B2 \u00E0\u00B5\u0088 \u00E1\u0088\u00BA1 \u00E0\u00B5\u0086 X\u00E1\u0088\u00BB \u00E0\u00B5\u0088 A2% (6-4) where Min: mass of chars entering the reactor, kg Mout: mass of chars out of the reactor captured in the cyclone, kg; Min=Mout assuming negligible ash escaped from cyclone. A1: moisture-free and volatile-free ash content in fuel fed to reactor X: char conversion A2: moisture-free and volatile-free ash content in solid from cyclone Proximate analyses of the fuel and solids captured by the cyclones were conducted in a thermogravimetric analyzer, whereas A1 and A2 were determined from the proximate analyses. Then, the char conversion, X, was determined from the above equation. 6.2.5 Carbon balance Carbon balance is performed to check whether the carbon in equals the carbon out for each run. Carbon in and out are calculated from Carbon\u00C2\u00A0in \u00E0\u00B5\u008C F \u00E0\u00B5\u0088 t \u00E0\u00B5\u0088 C% (6-5) 57\u00C2\u00A0 \u00C2\u00A0 where C: carbon content in fuel from ultimate analysis, % by weight F: feed rate of fuel, kg/h t: total time of feeding, h Carbon\u00C2\u00A0out \u00E0\u00B5\u008C carbon\u00C2\u00A0in\u00C2\u00A0syngas \u00E0\u00B5\u0085 carbon\u00C2\u00A0in\u00C2\u00A0cyclone\u00C2\u00A0solids \u00E0\u00B5\u0085 carbon\u00C2\u00A0in\u00C2\u00A0tar \u00E0\u00B5\u008C \u00E0\u00AD\u0094\u00E0\u00AD\u009A\u00E0\u00AD\u0096\u00E0\u00AD\u0098 \u00E0\u00B5\u0088 \u00E1\u0088\u00BACO \u00E0\u00B5\u0085 CO2 \u00E0\u00B5\u0085 CH4\u00E1\u0088\u00BB% \u00E0\u00B5\u0088MW\u00E0\u00AD\u0087 \u00E0\u00B5\u0085 S \u00E0\u00B5\u0088 C\u00E0\u00AD\u00B1% \u00E0\u00B5\u0085 V \u00E0\u00B5\u0088 T\u00E0\u00AD\u00B7 \u00E0\u00B5\u0088 C\u00E0\u00AD\u00B2% (6-6) where Cs: carbon content in solids collected by cyclones, % by weight Ct: carbon proportion by weight in tar, based on assumption that tar has the composition of toluene, C7H8 CH4: CH4 molar concentration in syngas CO: CO molar concentration in syngas CO2: CO2 molar concentration in syngas MWc: molecular weight of carbon, 12 g/mol P: atmosphere pressure, Pa R: ideal gas law constant, J/K/mol S: mass of solid collected by cyclones, g T: room temperature, 298 K Ty: tar content in syngas, g/m3 V: total volume of syngas produced, m3 6.3 Results and discussion of individual runs Five gasification runs were conducted in the Highbury pilot scale bubbling fluidized bed gasifier to study the impact of fuel biosolid mixing ratios on gasification performance. The five runs used mixtures of biosolids with wood pellets as fuel with biosolids proportions of 10%, 0%, 100%, 50%, and 25% in that order. During the run with 100% biosolids, the feed rate was varied to study the impact of the steam/fuel 58\u00C2\u00A0 \u00C2\u00A0 ratio. During the run with 50% biosolids, the reactor temperature was varied to study its effect on gasification. The results from the five runs are discussed in this chapter. The results of each run are first presented in this chapter in brief. In the next chapter, all the results are combined and discussed to assess the impact of biosolids proportions in the feedstock on gasification performance. Also, the temperature effect is discussed in the next chapter. In the following discussion, note that the term \u00E2\u0080\u009Cgasification period\u00E2\u0080\u009D denotes the period when feeding was on and gasification was occurring. It excludes the reactor heating period, when no biomass or biosolids feedstock was entering the reactor. 6.3.1 10% biosolids with 90% wood pellets by mass Operating procedure The first gasification experiment was conducted on August 03, 2012, using a mixture of 10% biosolids and 90% wood pellets as feedstock. The total duration of the experiment was 300 minutes. The reactor was heated to 880\u00D4\u00A8 and maintained at that temperature for half an hour before feeding. At 131 minutes, steam was turned on and fed into the reactor. At t=145 minutes, the micro GC was turned on to measure the producer gas concentration continuously. At 151 minutes, the feeder was turned on to indicate fuel feeding. However, blockage occurred in the feeding system. At 159 minutes, feeding was shut down, and the screw feeder was opened and the blockage removed. At 169 minutes, the feeder was turned on again at a feedrate of 1.27 kg/h. At 183 minutes, the flows in the tar sampling and ammonia absorption line were turned on. At 252 minutes, the flow in the tar sampling and ammonia absorption line was turned off. At 289 minutes, feeder, steam and heater were turned off. The gasification period for this run was considered to be between 169 and 289 minutes. 59\u00C2\u00A0 \u00C2\u00A0 Note that for this initial run, the impingers for ammonia determination had not arrived. Two impingers from the tar sampling setup were borrowed for ammonia determination. In later runs, six impingers were used to capture the tar, but for this initial run, only four impingers were available. Temperature profiles Figures 6-2 and 6-3 show the reactor temperature (T2a in Figure A1 in the Appendix) and the temperature of the tar sampling. Profiles of all other temperatures in the gasifier and downstream for each run are plotted in the Appendix. Run Time(min) 0 50 100 150 200 250 300 Te m pe ra tu re (o C ) 0 200 400 600 800 1000 Bed temperature gasification period \u00C2\u00A0 Figure 6-2 Reactor temperature vs. time for run with 10% biosolids with 90% wood pellets by mass\u00C2\u00A0 \u00C2\u00A0 From Figure 6-2, between 0-80 minutes, the bed temperature increased to the desired temperature of 880\u00D4\u00A8. At 131 minutes, steam was turned on, causing a sharp decrease in bed temperature at 135 minutes. Then, the bed temperature rose with heat supply from the heater. At 160 minutes, the bed temperature decreased again when feeding 60\u00C2\u00A0 \u00C2\u00A0 was turned on. This indicated that the endothermic gasification reaction started, consuming heat. Then, the bed temperature remained steady around 860 \u00D4\u00A8 until the end of the experiment. The steady state bed temperature averaged 857\u00D4\u00A8\u00C2\u00A0during the gasification period. Run Time(min) 0 50 100 150 200 250 300 Te m pe ra tu re (o C ) 0 100 200 300 400 Tar sampling temperature tar sampling period Figure 6-3 Temperature of tar sampling line vs. time for run with 10% biosolids with 90% wood pellets by mass The tar sampling for this run lasted from 183 to 252 minutes. From Figure 6-3, the temperature of tar sampling (T5 in Figure A1 in the Appendix) was above 300\u00D4\u00A8 during this period. Pressure drop The pressure drop in the reactor is plotted in Figure 6-4. It is seen that after feeding started at 169 minutes, the bed pressure drop decreased from 6 to 4 kPa, suggesting that about 5 kg of sand in the bed decreased to about 3.5 kg throughout the 61\u00C2\u00A0 \u00C2\u00A0 experiment. However, the decrease in pressure drop did not appear to affect the results noticeably. Run Time(min) 0 50 100 150 200 250 300 dP 1( kP a) 0 2 4 6 8 10 Figure 6-4 Pressure drop in reactor for run with 10% biosolids with 90% wood pellets by mass Steam flow rate The steam flow rate throughout the run is plotted in Figure 6-5. During the gasification period, the steam flow rate remained stable at 4.04 kg/h. Fuel feed rate was controlled at 1.27 kg/h, so the steam/fuel mass ratio for this run was calculated to be 3.18. 62\u00C2\u00A0 \u00C2\u00A0 Run Time(min) 0 50 100 150 200 250 300 St ea m F lo w R at e (k g/ h) 0 2 4 6 8 10 \u00C2\u00A0 Figure 6-5 Steam flow rate vs. time for run with 10% biosolids with 90% wood pellets by mass Micro GC results Figures 6-6 and 6-7 show the gas concentrations of the producer gases determined by the micro GC and calculated nitrogen-free syngas composition respectively, measured between 137 and 196 minutes. The N2 concentration in the producer gases could be related to the syngas production rate. A higher N2 content in the producer gases signified a lower syngas production rate, given that the flow rate of N2 was maintained constant throughout the run. \u00C2\u00A0 63\u00C2\u00A0 \u00C2\u00A0 Run Time (minutes) 140 160 180 200 220 240 260 280 M ol ar c on ce nt ra tio n (% ) 0 20 40 60 80 100 H2 N2 CO CH4 CO2 total \u00C2\u00A0 Figure 6-6 Gas concentrations of dry producer gases for run with 10% biosolids with 90% wood pellets by mass From Figure 6-6, the steady state for this run extended between 176 and 292 minutes. When averaging the gas concentrations for this run, values were only taken between 176 and 292 minutes. Successful feeding started at 169 minutes, and the gas composition reached steady state at 176 minutes. Hence, for this run, it took only 7 minutes for producer gases to achieve steady state after the system had reached the desired temperature. 64\u00C2\u00A0 \u00C2\u00A0 Run time (minutes) 140 160 180 200 220 240 260 280 M ol ar c on ce nt ra tio n (% ) 0 20 40 60 H2 CO CH4 CO2 Figure 6-7 Nitrogen-free dry syngas composition for run with 10% biosolids with 90% wood pellets by mass As above, when calculating the syngas composition for this run, the average value was taken between 176 and 292 minutes. From Figure 6-7, whenever H2 increased, CO2 increased and CO decreased correspondingly. This is related to the water gas shift reaction: CO \u00E0\u00B5\u0085 H\u00E0\u00AC\u00B6O \u00E2\u0086\u0092 H\u00E0\u00AC\u00B6 \u00E0\u00B5\u0085 CO\u00E0\u00AC\u00B6 As more CO reacted, more H2 and CO2 were produced. The shift of the reaction resulted from increasing the steam/fuel ratio, as discussed in the next section. Table 6-1 presents gas concentrations of the producer gases and the nitrogen-free syngas composition. The heating value of the syngas and the syngas yield were determined to be 12.56 MJ/m3 and 1.10 m3/kg, respectively. 65\u00C2\u00A0 \u00C2\u00A0 Table 6-1 Steady state gas concentrations for the run with 10% biosolids in fuel and for 178-292 min period Total N2 free H2 19.1 42.6 N2 55.0 0 CO 16.0 35.4 CH4 4.4 9.7 CO2 5.5 12.3 \u00C2\u00A0 Feed rate, bed temperature, syngas composition and production rate From this run, it was observed that feed rate variations had a significant effect on the bed temperature, syngas composition and gas production rate. Similar observations were made in later runs. The correlation between feed rate, temperature and gas production rate could be explained with the aid of Figure 6-8, where bed temperature and producer gas concentrations are plotted between 137 and 296 minutes. \u00C2\u00A0 66\u00C2\u00A0 \u00C2\u00A0 Run Time (minutes) 140 160 180 200 220 240 260 280 M ol ar c on ce nt ra tio n (% ) 0 20 40 60 80 100 Te m pe ra tu re (C ) 810 820 830 840 850 860 870 880 890 H2 N2 CO CH4 CO2 total bed temperature \u00C2\u00A0 Figure 6-8 Bed temperature and dry producer gas concentrations vs. time for run with 10% biosolids with 90% wood pellets by mass \u00C2\u00A0 From Figure 6-8, the bed temperature rose during the feeding shut-down period between 159 and 169 minutes. This was expected because the gasification process was endothermic. When there was no feed, gasification ceased, resulting in no heat consumption. When feeding started at 169 minutes, the bed temperature dropped due to heat consumption. Thus, it can be concluded that increasing feed decreased bed temperature. From Figure 6-8, N2 content followed a similar pattern as bed temperature, but with a time lag. Whenever the temperature increased, the N2 concentration increased. As discussed above, increased N2 content led to a decrease in the syngas production rate. Overall, the decreased fuel feed rate caused the temperature and N2 concentration to increase and the syngas production rate to 67\u00C2\u00A0 \u00C2\u00A0 decrease. It was reasonable that a lower feed rate decreased the syngas production rate. From\u00C2\u00A0Figure 6-9, the temperature and syngas composition are plotted between 137 and 296 minutes and are correlated with the feed rate and syngas composition. \u00C2\u00A0 Run time (minutes) 140 160 180 200 220 240 260 280 M ol ar c on ce nt ra tio n (% ) 0 20 40 60 80 100 Te m pe ra tu re (C ) 810 820 830 840 850 860 870 880 890 H2 CO CH4 CO2 bed temperature Figure 6-9 Bed temperature and dry syngas composition versus run time for run with 10% biosolids and 90% wood pellets by mass In Figure 6-9, the H2 content followed a similar pattern as temperature, but with a time lag. Temperature and H2 content in syngas gradually increased throughout the experimental gasification period. The rising temperature was caused by decreased fuel feed rate as discussed above. This decreased fuel feed rate resulted in an increased steam/fuel ratio as steam flow rate remained constant throughout the gasification period. This increase in H2 content should be caused by the rising steam/fuel ratio. 68\u00C2\u00A0 \u00C2\u00A0 Theoretically, with higher steam/fuel ratio, the water shift reaction caused a shift to the right to yield more H2 and CO2. This is consistent with results from the literature (e.g. Seo et al. 2010, Pfeifer et al. 2011). Based on the above discussion, fuel feed rate, temperature, N2, H2, syngas production rate are all inter-related. Also, the gradual increase of H2 content throughout the run implies that the fuel feed rate decreased gradually. To prove this, the fuel feed rates at the beginning and end of the gasification run were measured, giving values of 1.30 and 1.23 kg/h, respectively. This decrease of fuel feed rate possibly resulted from the decrease in the height of fuel in the hopper. Gravitational force from the fuel gradually decreased throughout the run, reducing the feed rate a little. For this run, an average feed rate of 1.27 kg/h was taken as the fuel feed rate for data analysis. Tar and ammonia sampling Tar and ammonia sampling for this run were conducted between 183 and 252 minutes. A total of 267 L of gas was sampled, and the tar amount collected after evaporation was 0.2 g. The average N2 content measured by the online GC during the tar sampling period was 53.3%. The tar content in syngas was determined to be 2.33 g/m3 after N2 correction. According to Dr. Yonghua Li\u00E2\u0080\u0099s experience, this value was too low. The possible reason for the low value might be inadequate impingers for tar absorption for this run. The ammonia concentration in the syngas was determined to be 2690 ppmv. Solids collected in cyclones The total mass of particles collected from the external cyclone during gasification was found to be 543 g from the primary cyclone and 17 g from the secondary cyclone. These totals were greater than expected based on woody biomass gasification (Li, 2012). This may have resulted from higher ash content and lower char conversion of the biosolids. The bulk densities of the solids were measured with a graduated cylinder and balance. The proximate analyses of the two collected materials were determined by a thermogravimetric analyzer. The results of these analyses are summarized in Table 6-2. 69\u00C2\u00A0 \u00C2\u00A0 Table 6-2 Characteristics of collected solids in cyclones for run with 10% biosolids with 90% wood pellets Collected solid Primary cyclone Secondary cyclone Mass g 543 17 Bulk specific gravity 0.37 0.31 Moisture content % 2.7 4.5 Volatiles % 1.2 6.5 Fixed carbon % 60.9 56.0 Ash % 35.3 33.1 Char conversion and carbon balance For this run, the char conversion was determined to be 66.3%. The total carbon masses in and out were determined to be 1.22 and 1.13 kg respectively. The favourable balance on carbon implied that the results were reliable for this run. 6.3.2 100% wood pellets Operating procedure The second bubbling bed gasification experiment was conducted on September 25, 2012, with only wood pellets as feedstock. The total duration of the experiment was 312 minutes. Again, the reactor was heated to 880\u00D4\u00A8 and maintained for half an hour before commencing feeding. At 86 minutes, steam was turned on and fed to the reactor. At 108 minutes, the micro GC was turned on to measure the producer gas concentration continuously. At 112 minutes, the biomass feeder was turned on to feed fuel at 1.27 kg/h. At 134 minutes, the tar sampling and ammonia absorption sampling began. At 231 minutes, flow through the tar sampling and ammonia absorption line was turned off. The gasification run for this study ended at 232 minutes. However, the system was left on for one hour for Giulio Allesina, a visiting Ph.D student, to test his 70\u00C2\u00A0 \u00C2\u00A0 newly designed particle-measurement equipment. At 308 minutes, the system was shut down by turning off the feeder, steam and heater. The gasification period for this run was taken between 112 and 231 minutes. Temperature profiles Figure 6-10 shows the reactor temperature during this run. \u00C2\u00A0 Run Time(min) 0 50 100 150 200 250 300 Te m pe ra tu re (o C ) 0 200 400 600 800 1000 bed temperature gasification period Figure 6-10 Reactor temperature vs. time for run with 100% wood pellets The heater was turned on at the beginning. From Figure 6-10, the bed temperature increased from room temperature to 880 \u00D4\u00A8. At 86 minutes, steam was turned on, causing a slight decrease in temperature for a few minutes. The bed temperature became steady again at 103 minutes. However, at 115 minutes, the bed temperature decreased again when biomass feeding was initiated. This indicated that the endothermic gasification reaction started, thus consuming heat. Then, with heat supplied by the heater, the bed temperature increased to and remained steady at 71\u00C2\u00A0 \u00C2\u00A0 around 860\u00D4\u00A8 until the end of the experimental run. The steady state bed temperature averaged 855\u00D4\u00A8\u00C2\u00A0during the gasification period. The tar sampling for this run was between 134 and 231 minutes, and the tar sampling temperature exceeded 300\u00D4\u00A8 during this entire period. Pressure drop\u00C2\u00A0 The bed pressure drop during the gasification period was about 6 kPa, suggesting that about 5 kg of sand were present in the fluid bed throughout the run. Steam flow rate During the gasification period, the steam flow rate remained stable at 3.48 kg/h. The fuel feed rate was controlled at 1.27 kg/h, so the steam/fuel mass ratio for this run was calculated to be 2.74. Micro GC results Figures 6-11 and 6-12 show the gas concentrations of the producer gases determined by the micro GC and nitrogen-free syngas composition respectively, measured between 110 and 290 minutes. 72\u00C2\u00A0 \u00C2\u00A0 Run Time (minutes) 120 140 160 180 200 220 240 260 280 M ol ar c on ce nt ra tio n (% ) 0 20 40 60 80 100 H2 N2 CO CH4 CO2 total \u00C2\u00A0 Figure 6-11 Gas concentrations of dry producer gases for run with 100% wood pellets From Figure 6-11, the steady state period for this run was considered to extend between 130 and 262 minutes. However, as mentioned above, this study was only interested in the results before 231 minutes. Therefore, when averaging the gas concentrations for this run, only the values between 130 and 231 minutes were included. Feeding started at 112 minutes, and the gas concentrations reached steady state at 124 minutes. It took 12 minutes for the producer gases to reach steady state for this run. \u00C2\u00A0 73\u00C2\u00A0 \u00C2\u00A0 Run time (minutes) 120 140 160 180 200 220 240 260 280 M ol ar c on ce nt ra tio n (% ) 0 20 40 60 H2 CO CH4 CO2 Figure 6-12 Nitrogen-free dry syngas composition for run with 100% wood pellets As above, when calculating the syngas composition for this run, the values were averaged between 130 and 231 minutes. From Figure 6-12, a similar conclusion to that in the previous run could be drawn: whenever the H2 concentration increased, CO2 increased and CO decreased, presumably because of the water shift reaction. Table 6-3 presents the gas concentrations of the producer gases and nitrogen-free syngas composition. The heating value of syngas and syngas yield were determined to be 12.67 MJ/m3 and 1.38 m3/kg, respectively. 74\u00C2\u00A0 \u00C2\u00A0 Table 6-3 Steady state gas concentrations for run with 100% wood pellets and for 130-231 min period Total N2 free H2 22.8 45.7 N2 51.5 0 CO 16.9 34.2 CH4 4.6 9.3 CO2 5.5 10.8 \u00C2\u00A0 Feed rate, bed temperature, syngas composition and production rate From this run, it was proved again that feed rate variations had a significant effect on the bed temperature, syngas composition and syngas production rate. The temperature and syngas production rate could be concluded to be correlated from Figure 6-13, for the bed temperature and nitrogen concentration plotted between 110 and 290 minutes. Run Time (minutes) 120 140 160 180 200 220 240 260 280 M ol ar c on ce nt ra tio n (% ) 30 35 40 45 50 55 60 Te m pe ra tu re (C ) 840 845 850 855 860 865 870 N2 bed temperature \u00C2\u00A0 Figure 6-13 Correlation of bed temperature to dry syngas production rate for run with 100% wood pellets \u00C2\u00A0 75\u00C2\u00A0 \u00C2\u00A0 In Figure 6-13, the N2 content followed a similar pattern as the temperature observed from the peaks. Also, the N2 content was inversely related to syngas production rate. Temperature was inversely related to syngas production rate, as for the previous run. From observation of the previous experiment, the fluctuation in temperature resulted from variations in fuel feed rate. Run time (minutes) 120 140 160 180 200 220 240 260 280 M ol ar c on ce nt ra tio n (% ) 0 20 40 60 80 100 Te m pe ra tu re (C ) 800 820 840 860 880 900 H2 CO CH4 CO2 bed temperature Figure 6-14 Bed temperature and dry syngas composition vs. run time for run with 100% wood pellets From Figure 6-14, as for the previous run, the H2 content followed a similar pattern as temperature with a time lag. The H2 content increased gradually, implying that fuel feed rate decreased gradually in accordance with the observations of the previous run. To prove this, fuel feed rates at the beginning and end of the gasification run were measured, resulting in values of 1.30 and 1.23 kg/h, respectively. The gradual decrease in fuel feed rate likely resulted from the decrease in the height of fuel in the hopper as in the previous run. 76\u00C2\u00A0 \u00C2\u00A0 Tar and ammonia sampling The tar and ammonia sampling for this run was conducted between 134 and 231 minutes. A total of 400 L of gas was sampled, and the tar amount collected after evaporation was 2.02 g. The average N2 content measured by the online GC during the tar sampling period was 50.9%. The tar content of the syngas was determined to be 10.3 g/m3 after N2 correction. The ammonia concentration in the syngas was found to be 1660 ppmv. Solids collected in cyclones The total mass of solids collected by the external cyclone during gasification was found to be 116 g for the primary cyclone and 52 g for the secondary cyclone. Compared to the previous run, the total weight of solid collected was about five times less. However, more solids were captured in the secondary cyclone compared to the mass in the previous run, 17 g. The responsibility of secondary cyclone was to capture finer solids. A greater weight of finer solids indicates that the conversion rate of wood pellets is higher than that of the biosolids. The physical characteristics of collected solids are displayed in Table 6-4. 77\u00C2\u00A0 \u00C2\u00A0 Table 6-4 Characteristics of collected solids in cyclones for run with 100% wood pellets Collected solid Primary cyclone Secondary cyclone Mass g 116 52 Bulk specific gravity 0.2 0.21 Moisture content % 3.5 2.3 Volatiles % 23.1 26.3 Fixed carbon % 43.7 45.5 Ash % 29.8 25.9 Char conversion and carbon balance For this run, the char conversion was determined to be 81.7%. The total carbon masses in and out were determined to be 1.24 and 1.04 kg, respectively. The gap between the amounts of carbon in and out was a little higher than for the previous run. 6.3.3 100% biosolids For this run, the fuel feed rate was varied to study the impact of steam/fuel ratio on syngas yield and composition. The first hour of gasification was used to study the impact of fuel content on the gasification performance, so the operating conditions were the same as for the previous runs, except for the fuel content. The fuel feed rate was then varied every 30 minutes, 10 minutes to reach steady state and 20 minutes for data recording (Note that, although it may take 10 minutes for gas concentrations to reach steady state, the bed material may require much longer time to achieve steady state according to Dr. Jim Lim, one of my supervisors). From the experience of the previous runs, once feeding started, it took about ~10 minutes for the syngas to reach steady state, whereas the temperature quickly reached steady state. However, when analyzing the data later, it was found that the results were not very reliable due to an 78\u00C2\u00A0 \u00C2\u00A0 unstable feed rate. The biosolids had the appearance of a hairy material, were very cohesive and light, and could easily bridge inside the hopper. Once bridging occurred, the feed rate dropped to a very low point. It took almost one month to fix the feeding problem of biosolids. A new design of the screw feeder was implemented to solve the bridging problem. A few long plastic strips were tied all the way along the screw inside the hopper so that the screw could touch and catch more materials while rotating. However, the biosolids feed rate was not very stable. It was found that the feed rate strongly depended on the height of biosolids in the hopper. For example, when the hopper was filled with biosolids and half full, the feed rates were measured to be 2.00 kg/h and 0.879 kg/h, respectively, at the same feed setting. For all data analysis, it has been assumed that the feed rate was that measured when the hopper was full of biosolids. Consequently, the data analysis for the first hour of gasification run was most reliable. As time went on, the biosolids in the hopper were consumed and the height dropped, decreasing the feed rate. Nevertheless, this run still generated valuable results on the impact of fuel composition on gasification from the first hour of gasification period. Results on the effect of varying the fuel feed rate and steam/fuel ratio on gasification are not discussed here, but are summarized in the Appendix. Operating procedure The third gasification experiment was conducted on Oct 12, 2012, with biosolids as the sole feedstock. The total duration of the experiment was 345 minutes. Again, the reactor was heated to 880\u00D4\u00A8 and maintained for half an hour before feeding. At 113 minutes, steam was turned on and fed to the reactor. At 133 minutes, the GC was turned on to measure the producer gas composition continuously. At 139 minutes, the feeder was turned on to feed fuel at 1.50 kg/h. At 169 minutes, the tar sampling and ammonia absorption flow was turned on. At 221 minutes, flow through the tar sampling and ammonia absorption line was turned off, and the fuel feed rate was changed to 0.73 kg/h to study the impact of the steam/fuel ratio. At 249 minutes, the 79\u00C2\u00A0 \u00C2\u00A0 fuel feed rate was changed to 1.50 kg/h. At 283 minutes, the fuel feed rate was changed to 1.91 kg/h. At 310 minutes, the fuel feed rate was changed to 1.22 kg/h. At 338 minutes, the system was shut down by turning off the feeder, steam and heater. In the following discussion, the gasification period for this run is considered to have been between 139 and 221 minutes. Temperature profiles Figure 6-15 shows the reactor temperature during this run. \u00C2\u00A0 Run Time(min) 0 100 200 300 Te m pe ra tu re (o C ) 0 200 400 600 800 1000 bed temperature gasification period Figure 6-15 Reactor temperature vs. time for run with 100% biosolids The heater was turned on at the beginning. From Figure 6-15, the bed temperature increased from room temperature to 880\u00D4\u00A8\u00C2\u00A0in\u00C2\u00A0about\u00C2\u00A0an\u00C2\u00A0hour. At 113 minutes, steam was turned on, causing a slight decrease in temperature at 125 minutes. Unlike the previous runs, the bed temperature was unstable during the gasification period. Attempts were made to maintain the temperature around 850\u00D4\u00A8, but the bed 80\u00C2\u00A0 \u00C2\u00A0 temperature fluctuated, possibly due to unstable fuel feeding. During the experiment, whenever the bed temperature rose, the fuel feed rate should have decreased. Then the operator manually turned the agitation shaft installed on the corner of the hopper to increase the feed rate. In practice with these efforts, the bed temperature usually decreased. The average bed temperature during the gasification period was determined to be 854\u00D4\u00A8. \u00C2\u00A0 The tar sampling for this run was between 169 and 221 minutes, and the temperature of tar sampling was above 300 \u00D4\u00A8 during this period of interest. Pressure drop The bed pressure drop during the gasification period was about 6 kPa, suggesting that about 5 kg of sand were present in the fluidized bed throughout the run. Steam flow rate During the gasification period, the steam flow rate remained stable at 3.43 kg/h. The fuel feed rate was controlled at 1.50 kg/h, so the steam/fuel mass ratio for this run was calculated to be 2.29. Micro GC results Figures 6-16 and 6-17 show the gas concentrations of the producer gases determined by the micro GC and the nitrogen-free syngas composition respectively, measured between 133 and 340 minutes. \u00C2\u00A0 81\u00C2\u00A0 \u00C2\u00A0 Run Time (minutes) 150 200 250 300 M ol ar c on ce nt ra tio n (% ) 0 20 40 60 80 100 H2 N2 CO CH4 CO2 total \u00C2\u00A0 Figure 6-16 Gas concentrations of dry producer gases for run with 100% biosolids As seen from Figure 6-16, the gas concentrations fluctuated, resulting from unstable and manually manipulated fuel feed rate. When calculating the average gas concentrations during the gasification period, the values were averaged between 147 and 221 minutes, during which the gas concentrations were relatively steady. Compared to previous runs, the N2 content was higher, implying that the syngas production rate was lower. 82\u00C2\u00A0 \u00C2\u00A0 Run time (minutes) 150 200 250 300 M ol ar c on ce nt ra tio n (% ) 0 10 20 30 40 50 H2 CO CH4 CO2 Figure 6-17 Nitrogen-free dry syngas composition for run with 100% biosolids As above, when calculating the syngas composition for this run, the values were averaged between 147 and 221 minutes. From Figure 6-17, the same conclusion could be drawn again: Whenever the H2 concentration increased, CO2 increased and CO decreased, because of the water gas shift reaction. Table 6-5 presents the gas concentrations of the producer gases and nitrogen-free syngas composition respectively. The heating value of syngas and syngas yield were determined to be 14.25 MJ/m3 and 0.47 m3/kg, respectively. 83\u00C2\u00A0 \u00C2\u00A0 Table 6-5 Steady state gas concentrations for run with 100% biosolids and for 147-221 min period Total N2 free H2 8.71 33.6 N2 73.3 0 CO 10.1 36.9 CH4 4.7 16.6 CO2 3.3 12.9 Tar and ammonia sampling Tar and ammonia sampling for this run was conducted between 169 and 221 minutes. A total of 197 L of gas was sampled and the tar amount collected after tar evaporation was 10.6 g. The average N2 content measured by the online GC during the tar sampling period was 73.7%. The tar content in the syngas was determined to be 200 g/m3 after N2 correction, whereas the ammonia concentration in the syngas was 19200 ppmv. Solids collected in cyclones The total solids collected from the external cyclone during gasification were found to be 498 g from the primary cyclone and none from the secondary cyclone. Starting from this run, the secondary cyclone no longer worked properly and received no solids. The characteristics of the collected solids are displayed in Table 6-6. 84\u00C2\u00A0 \u00C2\u00A0 Table 6-6 Characteristics of collected solids in primary cyclone for run with 100% biosolids Collected solid Primary cyclone Mass g 498 Bulk specific gravity 0.44 Moisture content % 1.2 Volatiles % 9.6 Fixed carbon % 4.2 Ash % 84.9 Char conversion and carbon balance For this run, the char conversion was determined to be 35.5%. The total carbon masses in and out were found to be 2.56 and 0.867 kg, respectively. The significant gap between the amounts of carbon in and out, resulting in a poor carbon balance, suggests that the fuel feed rate was not very stable and reliable for this run. 6.3.4 50% biosolids with 50% wood pellets by mass For this run, the bed temperature was varied to study the impact of operating temperature on the syngas yield and composition. The first hour of the gasification period was used to study the impact of the fuel content on the gasification performance, so the operating conditions were the same as for the first run except for the fuel content. The reactor temperature was then varied every 30 minutes, the first 10 minutes of which were to reach steady state and the remaining 20 minutes for data recording. Fortunately, this run was successful and generated many valuable results. Note that the thermocouple measuring bed temperature, T2a (refer to Figure A1 in the Appendix), was not working properly since December 18, 2012. To counter this, the 85\u00C2\u00A0 \u00C2\u00A0 freeboard temperature, T10, was used as the bed temperature for the next two runs. Based on results of recent runs by Highbury Energy Inc., T10 was closest to T2a, only 10-20\u00D4\u00A8 below T2a. Operating procedure The fourth gasification experiment, after two months of waiting for the facility, was conducted on Jan 4, 2013, using a mixture of 50% biosolids with 50% wood pellets as feed stock. The total duration of the experiment was 347 minutes. The reactor was again heated to 860 \u00D4\u00A8 and maintained at this condition for half an hour before feeding. At 160 minutes, the GC was turned on to measure the producer gas composition continuously. At 165 minutes, steam was turned on and fed to the reactor. At 202 minutes, the feeder was turned on to feed fuel at 1.50 kg/h. At 222 minutes, the tar sampling and ammonia absorption line was turned on. At 254 minutes, tar sampling and ammonia absorption was stopped, and the heater was turned down to study the temperature effect. At 278 minutes, the heater was turned down further, and at 304 minutes, the heater was turned down again. At 339 minutes, the system was shut down by turning off the feeder, steam and heater. The gasification period for this run was considered to have lasted from 202 to 339 minutes. Temperature profiles Figure 6-18 shows the reactor temperature variation during this run. \u00C2\u00A0 \u00C2\u00A0 86\u00C2\u00A0 \u00C2\u00A0 Run Time(min) 0 100 200 300 Te m pe ra tu re (o C ) 0 200 400 600 800 1000 Bed temperature gasification period Figure 6-18 Reactor temperature (T10) vs. time for run with 50% biosolids with 50% wood pellets by mass From Figure 6-18, the bed temperature increased from room temperature to 860 \u00D4\u00A8\u00C2\u00A0in\u00C2\u00A0 about\u00C2\u00A0an\u00C2\u00A0hour. For this run, addition of steam did not cause the bed temperature to decrease, so the bed heating system seemed more robust. At 202 minutes, the bed temperature decreased when feeding started. Temperature (based on T10) became steady at 222 minutes. At 255, 279, 306 minutes, bed temperature dropped following manual adjustment of the heater. In Figure 6-18, during the gasification period, the bed temperature was nearly steady for four periods at 800, 780, 740, and 690 \u00D4\u00A8, and each steady state period lasted about 20 minutes for data collection. \u00C2\u00A0 The tar sampling for this run lasted from 222 to 254 minutes, and the temperature of tar sampling exceeded 300\u00D4\u00A8 during this period. 87\u00C2\u00A0 \u00C2\u00A0 Pressure drop The bed pressure drop during the gasification period was about 6 kPa, suggesting that about 5 kg of sand remained in the fluid bed throughout the run period. Steam flow rate During the gasification period, the steam flow rate remained stable at 3.49 kg/h. The feed rate was controlled at 1.29 kg/h, so the mass steam/fuel ratio for this run was calculated to be 2.73. Micro GC results Figure 6-19 shows the composition of the producer gases determined by the micro GC, between 200 and 346 minutes. \u00C2\u00A0 Run Time (minutes) 200 220 240 260 280 300 320 340 M ol ar c on ce nt ra tio n (% ) 0 20 40 60 80 100 H2 N2 CO CH4 CO2 total Figure 6-19 Gas concentrations of dry producer gases for run with 50% biosolids with 50% wood pellets by mass 88\u00C2\u00A0 \u00C2\u00A0 For this run, since the bed temperature went through four steady states, the GC results were divided into the four corresponding stages. Within each stage, the gas concentrations were averaged. The impact of temperature on the gas concentrations is discussed in the next chapter. Table 6-7 presents the gas concentrations of the producer gases and nitrogen-free syngas composition during the first hour of the gasification period. The GC results after the first hour are summarized in the next chapter, with attention to the temperature effect on the syngas yield and composition. The heating value of the syngas and the syngas yield for the first hour were determined to be 14.77 MJ/m3 and 0.99 m3/kg, respectively. Table 6-7 Steady state gas concentrations for run with 50% biosolids with 50% wood pellets and for 202-254 min period Total N2 free H2 6.8 22.5 N2 69.5 0 CO 15.7 51.3 CH4 5.0 16.4 CO2 3.0 9.9 Tar and ammonia sampling The tar and ammonia sampling for this run was conducted between 222 and 254 minutes. A total of 122 L of gas was sampled and the tar amount collected after tar evaporation was 2.31 g. The average N2 content measured by the online GC during the tar sampling period was 70.1%. The tar content in syngas was determined to be 63.1 g/m3 after N2 correction. The ammonia concentration in syngas was found to be 6940 ppmv. 89\u00C2\u00A0 \u00C2\u00A0 Solids collected in cyclones The total mass of solids collected from the external cyclone during gasification was found to be 461 g from the primary cyclone and none from the secondary cyclone. The characteristics of collected solids are displayed in Table 6-8. Table 6-8 Characteristics of collected solids in primary cyclone for run with 50% biosolids with 50% wood pellets by mass Collected solid Primary cyclone Mass g 461 Bulk specific gravity 0.66 Moisture content % 0.7 Volatiles % 11.5 Fixed carbon % 11.8 Ash % 76.0 Char conversion and carbon balance For this run, the char conversion was found to be 59.4%. The total carbon masses in and out were determined to be 1.51 and 0.829 kg, respectively. The gap between the amounts of carbon in and out suggested that feed rate was again less stable for this run, but much better than for the previous run. 6.3.5 25% biosolids with 75% wood pellets by mass Operating procedure The final gasification experiment was conducted on Jan 9, 2013, using a mixture of 25% biosolids with 75% crushed wood pellets as feedstock. The total duration of this experiment was 284 minutes. Again, the reactor was heated to 840\u00D4\u00A8 and maintained 90\u00C2\u00A0 \u00C2\u00A0 for half an hour. At 155 minutes, the GC was turned on to measure the producer gas concentration continuously. At 161 minutes, steam was turned on and fed to the reactor. At 166 minutes, feeding was initiated to feed fuel at 1.47 kg/h. At 183 minutes, the tar sampling and ammonia absorption line were turned on. At 232 minutes, tar sampling and ammonia absorption line were terminated. At 254 minutes, the system was shut down by turning off the feeder, steam and heater. The gasification period for this run was considered to be between 166 and 254 minutes. Temperature and pressure drop The bed temperature during the gasification run (again based on T10) was stable, with an average of 828\u00D4\u00A8. The tar sampling for this run lasted between 183 and 232 minutes, and the temperature of tar sampling exceeded 300\u00D4\u00A8 during this period. The bed pressure drop during the gasification period was about 6 kPa, suggesting that about 5 kg of sand remained in the fluid bed throughout the run time. Steam flow rate During the gasification period, the steam flow rate remained stable at 3.28 kg/h. The fuel feed rate was controlled at 1.47 kg/h, so the steam/fuel mass ratio for this run was 2.23. Micro GC results Figure 6-20 shows the gas concentrations of the producer gases determined by the micro GC between 155 and 271 minutes. 91\u00C2\u00A0 \u00C2\u00A0 Run Time (minutes) 160 180 200 220 240 260 M ol ar c on ce nt ra tio n (% ) 0 20 40 60 80 100 H2 N2 CO CH4 CO2 total \u00C2\u00A0 Figure 6-20 Gas concentrations of dry producer gases for run with 25% biosolids with 75% wood pellets by mass From Figure 6-20, the steady state during the gasification period corresponded to the period between 179 and 232 minutes. Table 6-9 presents the gas concentrations of the producer gases and nitrogen-free syngas composition respectively. The heating value of the syngas and syngas yield were determined to be 14.34 MJ/m3 and 1.28 m3/kg, respectively. Table 6-9 Steady state gas concentrations for run with 25% biosolids with 75% wood pellets by mass and for 179-232 min period Total N2 free H2 10.2 25.2 N2 59.4 0 CO 20.4 50.2 CH4 6.0 14.7 CO2 4.0 9.9 92\u00C2\u00A0 \u00C2\u00A0 Tar and ammonia sampling The tar and ammonia sampling for this run was conducted between 183 and 232 minutes. A total of 135 L of gas was sampled, and the tar amount collected after evaporation was 2.01 g. The average N2 content measured by the online GC during the tar sampling period was 56.4%. The tar content in syngas was determined to be 36.5 g/m3 after N2 correction. The ammonia concentration in syngas was determined to be 5010 ppmv. Solids collected in cyclones The total solid amount collected from the external cyclone during gasification was found to be 249 g from the primary cyclone and none from the secondary cyclone. The characteristics of collected solids are displayed in Table 6-10. Table 6-10 Characteristics of collected solids in cyclones for run with 25% biosolids with 75% wood pellets by mass Collected solid Primary cyclone Mass g 249 Bulk specific gravity 0.33 Moisture content % 0.9 Volatiles % 9.7 Fixed carbon % 24.2 Ash % 65.3 Char conversion and carbon balance For this run, the char conversion was determined to be 71.0%. The total carbon masses in and out were determined to be 1.149 and 1.147 kg, respectively. For this 93\u00C2\u00A0 \u00C2\u00A0 run, the gap between the amounts of carbon in and out was very small, giving the best carbon balance. 94\u00C2\u00A0 \u00C2\u00A0 CHAPTER 7: IMPACTS OF BED TEMPERATURE AND BIOSOLIDS PROPORTION IN FUEL 7.1 Impact of bed temperature on syngas yield and composition During the gasification run with 50% biosolids on Jan 4, 2013, the bed temperature effect on syngas yield and composition was studied. Syngas yield versus bed temperature Bed temperature (based on thermocouple T10) and N2 concentration during the gasification period are plotted in Figure 7-1. Run Time (minutes) 200 220 240 260 280 300 320 340 M ol ar c on ce nt ra tio n (% ) 0 20 40 60 80 Te m pe ra tu re (C ) 700 750 800 850 900 N2 bed temperature Figure 7-1 Bed temperature and N2 concentration vs. time for run with 50% biosolids with 50% wood pellets by mass. 95\u00C2\u00A0 \u00C2\u00A0 From Figure 7-1, as temperature decreased, the N2 content increased. This implied that lower bed temperature decreased the syngas production rate. This was expected because steam gasification is endothermic. Also, this was consistent with literature results (e.g. Peng et al. 2012, Pfeifer et al. 2011, Seo et al. 2010). The syngas yield is plotted versus bed temperature in Figure 7-2, showing that the bed temperature significantly affected syngas yield. The syngas yield decreased from 0.99 to 0.29 m3/kg as the bed temperature decreased from 825 to 728\u00D4\u00A8. Temperature (C) 740 760 780 800 820 Sy ng as y ie ld (m 3/ kg ) .2 .4 .6 .8 1.0 1.2 Figure 7-2 Syngas yield versus bed temperature. Operating conditions: feedstock, 50% biosolids with 50% wood pellets by mass; steam/fuel mass ratio, 2.73. Syngas composition versus bed temperature The bed temperature and syngas composition during the gasification period are plotted in Figure 7-3. 96\u00C2\u00A0 \u00C2\u00A0 Run time (minutes) 200 220 240 260 280 300 320 340 M ol ar c on ce nt ra tio n (% ) 0 20 40 60 80 100 Te m pe ra tu re (C ) 700 750 800 850 900 H2 CO CH4 CO2 bed temperature Figure 7-3: Temperature and syngas composition vs. time for run with 50% biosolids with 50% wood pellets by mass. From Figure 7-3, the bed temperature did not significantly affect the syngas composition over the limited range of operation. The syngas composition is plotted versus bed temperature in Figure 7-4. 97\u00C2\u00A0 \u00C2\u00A0 Temperature ( C ) 740 760 780 800 820 G as m ol ar c on ce nt ra tio n (% ) 0 10 20 30 40 50 60 H2 CO CH4 CO2 \u00C2\u00A0 Figure 7-4 Syngas composition versus bed temperature. Operating conditions: feedstock, 50% biosolids with 50% wood pellets by mass; steam/fuel mass ratio, 2.73. From Figure 7-4, H2 and CO did not exhibit obvious dependence on temperature. As temperature increased from 728 to 825\u00D4\u00A8, the CO2 concentration decreased from 15.9 to 9.86%, whereas the CH4 concentration increased from 13.2 to 16.4%. In conclusion, the temperature effect on the syngas composition was relatively weak for the limited temperature range covered in this study. 7.2 Impact of biosolids proportion in fuel on gasification performance During the gasification period for each of the five runs, the first hour was used to study the impact of biosolids proportion in fuel on the gasifier performance. Thus, 98\u00C2\u00A0 \u00C2\u00A0 operating conditions were similar, except for the biosolids proportion in the fuel. The operating conditions are presented in Table 7-1. Table 7-1 Operating conditions of the five runs with the bubbling fluidized bed Run no. 2 1 5 4 3 Biosolids proportion in fuel (%) by mass 0 10 25 50 100 Operating conditions Bed material silica sand silica sand silica sand silica sand silica sand Fuel feed rate (kg/h) 1.27 1.27 1.47 1.29 1.50 Steam flow rate (kg/h) 3.48 4.04 3.28 3.52 3.43 Steam/fuel mass ratio 2.74 3.18 2.23 2.73 2.29 Bed temperature (\u00D4\u00A8) 855 857 828 825 854 As shown from Table 7-1, operating conditions were not identical, but close enough for comparisons to be made, with feed rates around 1.3-1.5 kg/h, but the feed rate was difficult to control. For the steam flow rate, a slight adjustment of the control valve could increase/decrease the flow rate by 3 kg/h. The bed temperatures for runs 1, 2, and 3 were around 855\u00D4\u00A8.\u00C2\u00A0These three experiments were conducted without interruption, with the operating conditions being almost the same. After 2 months, runs 4 and 5 were conducted together, so that their bed temperatures were virtually the same, 827\u00D4\u00A8. During the intervening months, a few experiments had been conducted by Highbury Energy Inc., and a few things had happened. For example, the reactor was opened, lime was used as bed material for one run, and the system was modified slightly. In a complex system like this, a slight change could affect the results. For example, during runs 4 and 5, the reactor temperature could no longer reach 855\u00D4\u00A8 at the temperature setting of the other three runs. Therefore, in the discussion below, some results are discussed as two parallel sets, corresponding to results before and 99\u00C2\u00A0 \u00C2\u00A0 after the system change, corresponding to bed temperature of 855 and 826\u00D4\u00A8, respectively. Influence on syngas composition The syngas composition is plotted versus biosolids proportion in fuel in Figure 7-5, with the results of runs 1, 2, 3 in (a) and results of runs 4, 5 in (b)Error!\u00C2\u00A0Reference\u00C2\u00A0 ource\u00C2\u00A0not\u00C2\u00A0found.. By splitting the plots, the trend of variation of gas concentrations on biosolids proportion can be observed more easily. In runs 1, 2 and 3, the H2 concentration was always higher than CO concentration. A jump in CO concentration and a drop in CH4 and H2 concentration were observed in runs 4 and 5 with 25% and 50% biosolids, and the CO to H2 ratio became higher than 1. At first sight, one might contribute this behaviour to the temperature difference, because the bed temperature in runs 4 and 5 is ~825\u00E2\u0084\u0083, lower than in runs 1 to 3, ~855\u00E2\u0084\u0083. However, from section 7.1, the bed temperature within the limited tested range did not show obvious effect on gas concentrations and, therefore, cannot explain the difference. Second, steam/fuel ratios for different runs are also different. From results in Chapter 6, higher steam/fuel ratio is expected to yield a higher H2/CO ratio. If significant decrease of H2/CO ratio in runs 4, 5 is caused by steam/fuel ratio, then the steam/fuel ratio in runs 4 and 5 should be lower than that in runs 1 to 3, which is not true from Table 7-1. Since the experimental system was slightly modified by HEI after runs 1 to 3, as mentioned above, the difference in the operating system between runs 1 to 3 and runs 4 and 5 appears to have caused the difference in the gas concentrations. 100\u00C2\u00A0 \u00C2\u00A0 (a) Temperature 855 C\u00E3\u0080\u0080 Biosolids proportion (%) in fuel 0 20 40 60 80 100 G as m ol ar c on ce nt ra tio ns (% ) 0 10 20 30 40 50 60 H2 CO CH4 CO2 \u00C2\u00A0 (b) Temperature 826 C Biosolids proportion (%) in fuel 0 20 40 60 80 100 G as m ol ar c on ce nt ra tio ns (% ) 0 10 20 30 40 50 60 H2 CO CH4 CO2 \u00C2\u00A0 Figure 7-5 Syngas composition vs. biosolids proportion in fuel, divided into a) for runs 1, 2, 3 b) for runs 4 and 5 101\u00C2\u00A0 \u00C2\u00A0 In Figure 7-5, the slopes of decrease/increase for the same gas are almost the same for a) and b). The H2 concentration decreased with increasing biosolids proportion, while the CO and CH4 concentrations increased with increasing biosolids fraction. Consequently, the H2/CO ratio decreased with increasing biosolids proportion, while the CO2 concentration remained almost constant. As discussed in Chapter 2, CH4, the simplest hydrocarbon, can be an indicator of the tars and other more complex hydrocarbons (Pfeifer et al., 2011). Therefore, the increase of CH4 concentration at higher biosolids fraction suggests an increase of tar content in the syngas, as verified below in the discussion of tar content and ammonia concentration. The lower heating values (LHV) of syngas with variation of biosolids proportion are summarized in Table 7-2. Table 7-2 LHV of syngas with various biosolids proportions Biosolids proportion in fuel (% by mass) 0 10 25 50 100 Syngas LHV (MJ/Nm3) 12.67 12.56 14.34 14.77 14.25 As shown in this table, the lower heating value of the product syngas was low, 12.6 MJ/Nm3 for 0% and 10% biosolids in the feed. This was mainly because gasification of wood pellets produced low CH4 in the syngas. When the biosolids proportion exceeded 25%, CH4 accounted for a greater proportion of the syngas, and the heating value of the syngas reached about 14.5 MJ/Nm3. Syngas yield and char conversion Syngas yield and char conversion versus biosolids proportion in fuel are plotted in Figure 7-6. 102\u00C2\u00A0 \u00C2\u00A0 Biosolids proportion (%) in fuel 0 20 40 60 80 100 Sy ng as y ie ld (m 3/ kg ) .4 .6 .8 1.0 1.2 1.4 1.6 C ha r c on ve rs io n 0.0 .2 .4 .6 .8 Syngas yield Char conversion Figure 7-6 Syngas yield and char conversion vs. biosolids proportion in feed In Figure 7-6, syngas yield decreased from 1.38 to 0.47 m3/kg as the proportion of biosolids in the fuel increased from 0 to 100%. This decrease resulted from two reasons, higher ash content in the biosolids and lower char conversion in the gasification of biosolids. As shown in Figure 7-6, char conversion decreased from 0.82 to 0.36 as the proportion of biosolids in the fuel increased from 0 to 100 %. This decrease in char conversion is consistent with the conclusion from the kinetic study (see Chapter 6), with biosolids inhibiting co-gasification and slowing down char conversion. The findings are similar to those in the literature discussed in Chapter 2. From Figure 7-6, the maximum syngas yield and char conversion occurred at 0% biosolids. However, since the purpose of this study was for the disposal of biosolids, a blending of up to 25% biosolids to wood pellets would not be expected to cause significant decrease in biochar conversion and syngas yield. This is consistent with 103\u00C2\u00A0 \u00C2\u00A0 the literature where the optimal mixing ratio for co-gasification of biosolids with biomass was reported to be 10-30% (Saw et al., 2011, Peng et al., 2012). Tar content in syngas and ammonia concentration Tar content and ammonia concentration are plotted versus biosolids proportion in Figure 7-7. Biosolids proportion (%) in fuel 0 20 40 60 80 100 Ta r c on te nt in s yn ga s (g /N m 3) 0 50 100 150 200 250 N H 3 co nc en tr at io n (p pm v) 0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000 22000 Tar content in syngas NH3 concentration Figure 7-7 Tar content and ammonia concentration vs. biosolids proportion in fuel This figure indicates that the tar content in the syngas increased from 10.3 to 200 g/m3 as the biosolids proportion in the fuel increased from 0 to 100%. As mentioned in Chapter 6, 10% biosolids proportion in fuel was fed in the first run, and the low tar content of 2.33 g/m3 probably resulted from an inadequate number of impingers for tar absorption. From Figure 7-7, the ammonia concentration also increased with increasing biosolids proportion in the fuel, passing from 1660 to 19200 ppmv as the biosolids proportion increased from 0 to 100%. These trends of tar content and ammonia concentration are consistent with literature results (Peng et al., 2012, Saw et 104\u00C2\u00A0 \u00C2\u00A0 al., 2011, Pinto et al., 2008). Again, there will be only moderate increases in tar content and ammonia concentration if the biosolids content in the feed is controlled to be lower than 25%. \u00C2\u00A0 105\u00C2\u00A0 \u00C2\u00A0 CHAPTER 8: CONCLUSIONS AND RECOMMENDATIONS The kinetic study with the thermogravimetric analyzer proved that ash of switchgrass could catalytically accelerate gasification. However, after mixing switchgrass with biosolids, no obvious catalytic effect occurred because any enhancement was overwhelmed by the inhibition effect of biosolids ash. It can be concluded that biosolids can slow down gasification. From the study on gasification in the pilot scale bubbling fluidized bed gasifier, several conclusions can be drawn: From experience in several gasification runs, it was found that varying the fuel feed can significantly affect bed temperature, syngas yield and syngas composition. Raising the steam/fuel ratio can increase the yields of H2 and CO2 and decrease the CO concentration in the syngas. Carbon balance results were less reliable as the biosolids proportion in the fuel increased. Biosolids are difficult to feed. If the feeding problem could be solved, more reliable results could be generated. Increasing the proportion of biosolids in the fuel feedstock tends to affect gasification performance negatively. Syngas yield and char conversion decreased from 1.38 to 0.47 m3/kg and 82% to 36% respectively as the biosolids proportion in the fuel increased from 0 to 100%. Undesirable products such as tar content and ammonia concentration increased with increasing proportion of biosolids. Tar content increased from 10.3 to 200 g/m3 as the biosolids proportion increased from 0 to 100%. Ammonia concentration increased from 1660 to 19200 ppmv as the biosolids 106\u00C2\u00A0 \u00C2\u00A0 proportion in the fuel increased from 0 to 100%. For the purpose of biosolids disposal, it is recommended that the co-gasification mixing ratio should be chosen to be not more than 25% biosolids in the fuel feed in order to maintain a reasonable biochar conversion, syngas yield and low tar and ammonia contents in the syngas. When discussing the impact of fuel on the syngas composition, the results had to be discussed separately in two sets to have more reasonable explanations compensating for the differences in the system between the two sets of runs. Nevertheless, it is clear that, with a greater proportion of biosolids in the fuel, the concentrations of H2 and CH4 increased, while that of CO decreased and the CO2 concentration remained nearly independent of the biosolids proportion. 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(2008) Catalytic Gasification of Char from Co-pyrolysis of Coal and Biomass, Fuel Processing Technology, 89, 890-896. 110\u00C2\u00A0 \u00C2\u00A0 APPENDIX: SUPPLEMENTAL RESULTS FROM BUBBLING FLUIDIZED BED GASIFICATION \u00C2\u00A0 \u00C2\u00A0 \u00C2\u00A0 \u00C2\u00A0 \u00C2\u00A0 \u00C2\u00A0 \u00C2\u00A0 \u00C2\u00A0 \u00C2\u00A0 \u00C2\u00A0 111\u00C2\u00A0 \u00C2\u00A0 Figure A1: Monitoring temperatures and pressures along the Highbury Energy Inc. gasification process (source: Highbury Energy Inc., Jan 2013) with permission from Dr. Watkinson T0: temperature of the steam entering the bed T1: temperature at the bottom of the bed T2a: bed temperature T3a: temperature of lower freeboard T10: temperature of middle freeboard T2b: temperature of upper freeboard T3b: temperature at reactor top T4: temperature of syngas before entering cyclone T5: temperature of syngas entering tar sampling line T6: temperature of syngas before entering cooler T7: temperature of syngas after first cooler T9: temperature of syngas after second cooler T11: temperature of syngas before entering second cooler 112\u00C2\u00A0 \u00C2\u00A0 T14: temperature of syngas before entering baghouse T13: temperature of freeboard wall T15: temperature of bed wall P2: pressure at bottom of gasifier P3: pressure at top of gasifier dP1: pressure drop across gasifier = P2-P3 113\u00C2\u00A0 \u00C2\u00A0 \u00C2\u00A0 Run Time(min) 0 50 100 150 200 250 300 Te m pe ra tu re (o C ) 0 200 400 600 800 1000 Steam,T0 Reactor Bed,T2a Upper freeboard,T2b Cyclone,T4 Lower freeboard,T3a Middle freeboard,T10 Reactor Top,T3b Freeboard wall,T13 Bed wall,T15 Figure A2: Temperature profiles of gasifier for run with 10% biosolids with 90% wood pellets by mass 114\u00C2\u00A0 \u00C2\u00A0 Run Time(min) 0 50 100 150 200 250 300 Te m pe ra tu re (o C ) 0 100 200 300 400 Tar Sampling,T5 Cooler Inlet,T6 Cooler 1 Oulet,T7 Cooler 2 Outlet,T9 Baghouse,T14 Figure A3: Temperature profiles of the downstream syngas for run with 10% biosolids with 90% wood pellets by mass 115\u00C2\u00A0 \u00C2\u00A0 Run Time (min) 0 50 100 150 200 250 300 P2 a nd P 3 (k Pa ) 0 2 4 6 8 10 P2 P3 Figure A4: Pressure profiles of gasifer for run with 10% biosolids with 90% wood pellets by mass. P2 and P3 are pressures at the bottom and the top of gasifer respectively. 116\u00C2\u00A0 \u00C2\u00A0 Run Time(min) 0 50 100 150 200 250 300 Te m pe ra tu re (o C ) 0 200 400 600 800 1000 Steam,T0 Reactor Bed,T2a Upper freeboard,T2b Cyclone,T4 Lower freeboard,T3a Middle freeboard,T10 Reactor Top,T3b Freeboard wall,T13 Bed wall,T15 Figure A5: Temperature profiles of gasifier for run with 100% wood pellets 117\u00C2\u00A0 \u00C2\u00A0 Run Time(min) 0 50 100 150 200 250 300 Te m pe ra tu re (o C ) 0 100 200 300 400 Tar Sampling,T5 Cooler Inlet,T6 Cooler 1 Oulet,T7 Cooler 2 Outlet,T9 Baghouse,T14 \u00C2\u00A0 Figure A6: Temperature profiles of the downstream syngas for run with 100% wood pellets \u00C2\u00A0 118\u00C2\u00A0 \u00C2\u00A0 Run Time(min) 0 50 100 150 200 250 300 dP 1( kP a) 0 2 4 6 8 10 Figure A7: Pressure drop in reactor for run with 100% wood pellets \u00C2\u00A0 119\u00C2\u00A0 \u00C2\u00A0 Run Time (min) 0 50 100 150 200 250 300 P2 a nd P 3 (k Pa ) 0 2 4 6 8 10 P2 P3 Figure A8: Pressure profiles of gasifer for run with 100% wood pellets. P2 and P3 are pressures at the bottom and the top of gasifer respectively. 120\u00C2\u00A0 \u00C2\u00A0 Run Time(min) 0 50 100 150 200 250 300 St ea m F lo w R at e (k g/ h) 0 2 4 6 8 10 Figure A9: Steam flow rate for run with 100% wood pellets 121\u00C2\u00A0 \u00C2\u00A0 Run Time(min) 0 100 200 300 Te m pe ra tu re (o C ) 0 200 400 600 800 1000 Steam,T0 Reactor Bed,T2a Upper freeboard,T2b Cyclone,T4 Lower freeboard,T3a Middle freeboard,T10 Reactor Top,T3b Freeboard wall,T13 Bed wall,T15 \u00C2\u00A0 Figure A10: Temperature profiles of gasifier for run with 100% biosolids 122\u00C2\u00A0 \u00C2\u00A0 Run Time(min) 0 100 200 300 Te m pe ra tu re (o C ) 0 100 200 300 400 500 Tar Sampling,T5 Cooler Inlet,T6 Cooler 1 Oulet,T7 Cooler 2 Outlet,T9 Baghouse,T14 Figure A11: Temperature profiles of the downstream syngas for run with 100% biosolids 123\u00C2\u00A0 \u00C2\u00A0 Feeding Time(min) 0 50 100 150 200 300 400 500 600 700 800 900 Steam,T0 Reactor Bed,T2a Upper freeboard,T2b Cyclone,T4 Lower freeboard,T3a Middle freeboard,T10 Reactor Top,T3b Freeboard wall,T13 Bed wall,T15 Figure A12: Temperature profiles of gasifier during the gasification period for run with 100% biosolids 124\u00C2\u00A0 \u00C2\u00A0 Run Time (min) 0 100 200 300 dP 1( kP a) 0 2 4 6 8 Figure A13: Pressure drop in reactor for run with 100% biosolids 125\u00C2\u00A0 \u00C2\u00A0 Feed Time (min) 0 100 200 300 P2 a nd P 3 (k Pa ) 0 2 4 6 8 10 P2 P3 Figure A14: Pressure profiles of gasifer for run with 100% biosolids. P2 and P3 are pressures at the bottom and the top of gasifer respectively. 126\u00C2\u00A0 \u00C2\u00A0 Run Time (min) 0 100 200 300 St ea m F lo w R at e (k g/ h) 0 2 4 6 8 10 Figure A15: Steam flow rate for run with 100% biosolids 127\u00C2\u00A0 \u00C2\u00A0 Run Time (minutes) 150 200 250 300 m ol ar c on ce nt ra tio n (% ) 20 40 60 80 Te m pe ra tu re (C ) 800 820 840 860 880 900 N2 bed temperature Figure A16: Bed temperature and N2 concentration vs. time for run with 100% biosolids 128\u00C2\u00A0 \u00C2\u00A0 Run time (minutes) 150 200 250 300 m ol ar c on ce nt ra tio n (% ) 0 20 40 60 80 100 Te m pe ra tu re (C ) 800 820 840 860 880 900 H2 CO CH4 CO2 bed temperature Figure A17: Bed temperature and syngas composition versus run time for run with 100% biosolids 129\u00C2\u00A0 \u00C2\u00A0 Run Time(min) 0 100 200 300 Te m pe ra tu re (o C ) 0 200 400 600 800 1000 Steam,T0 Reactor Bed,T2a Upper freeboard,T2b Cyclone,T4 Lower freeboard,T3a Middle freeboard,T10 Reactor Top,T3b Freeboard wall,T13 Bed wall,T15 \u00C2\u00A0 Figure A18: Temperature profiles of gasifier for run with for run with 50% biosolids with 50% wood pellets by mass 130\u00C2\u00A0 \u00C2\u00A0 Run Time(min) 0 100 200 300 Te m pe ra tu re (o C ) 0 100 200 300 400 Tar Sampling,T5 Cooler Inlet,T6 Cooler 1 Oulet,T7 Cooler 2 Outlet,T9 Baghouse,T14 Figure A19: Temperature profiles of the downstream syngas for run with 50% biosolids with 50% wood pellets by mass 131\u00C2\u00A0 \u00C2\u00A0 Run Time(min) 0 100 200 300 dP 1( kP a) 0 2 4 6 8 10 Figure A20: Pressure drop in reactor for run with 50% biosolids with 50% wood pellets by mass 132\u00C2\u00A0 \u00C2\u00A0 Run Time (min) 0 100 200 300 P2 a nd P 3 (k Pa ) 0 2 4 6 8 10 12 14 P2 P3 Figure A21: Pressure profiles of gasifer for run with 50% biosolids with 50% wood pellets by mass. P2 and P3 are pressures at the bottom and the top of gasifer respectively. 133\u00C2\u00A0 \u00C2\u00A0 Run Time(min) 0 100 200 300 St ea m F lo w R at e (k g/ h) 0 2 4 6 8 10 Figure A22: Steam flow rate for run with 50% biosolids with 50% wood pellets by mass 134\u00C2\u00A0 \u00C2\u00A0 Run time (minutes) 200 220 240 260 280 300 320 340 m ol ar c on ce nt ra tio n (% ) 0 10 20 30 40 50 60 H2 CO CH4 CO2 Figure A23: Nitrogen-free syngas composition for run with 50% biosolids with 50% wood pellets by mass 135\u00C2\u00A0 \u00C2\u00A0 Run Time(min) 0 50 100 150 200 250 300 Te m pe ra tu re (o C ) 0 200 400 600 800 1000 Steam,T0 Reactor Bed,T2a Upper freeboard,T2b Cyclone,T4 Lower freeboard,T3a Middle freeboard,T10 Reactor Top,T3b Freeboard wall,T13 Bed wall,T15 \u00C2\u00A0 Figure A24: Temperature profiles of gasifier for run with 25% biosolids with 75% wood pellets by mass 136\u00C2\u00A0 \u00C2\u00A0 Run Time(min) 0 50 100 150 200 250 Te m pe ra tu re (o C ) 0 50 100 150 200 250 300 350 Tar Sampling,T5 Cooler Inlet,T6 Cooler 1 Oulet,T7 Cooler 2 Outlet,T9 Baghouse,T14 Figure A25: Temperature profiles of the downstream syngas for run with 25% biosolids with 75% wood pellets by mass 137\u00C2\u00A0 \u00C2\u00A0 Run Time(min) 0 50 100 150 200 250 dP 1( kP a) 0 2 4 6 8 10 Figure A26: Pressure drop in reactor for run with 25% biosolids with 75% wood pellets by mass 138\u00C2\u00A0 \u00C2\u00A0 Run Time (min) 0 50 100 150 200 250 P2 a nd P 3 (k Pa ) 0 2 4 6 8 10 12 14 P2 P3 Figure A27: Pressure profiles of gasifer for run with 25% biosolids with 75% wood pellets by mass. P2 and P3 are pressures at the bottom and the top of gasifer respectively. 139\u00C2\u00A0 \u00C2\u00A0 Run Time(min) 0 50 100 150 200 250 St ea m F lo w R at e (k g/ h) 0 2 4 6 8 10 Figure A28: Steam flow rate for run with 25% biosolids with 75% wood pellets by mass 140\u00C2\u00A0 \u00C2\u00A0 Run time (minutes) 180 200 220 240 260 m ol ar c on ce nt ra tio n (% ) 0 10 20 30 40 50 60 H2 CO CH4 CO2 Figure A29: Nitrogen-free dry syngas composition for run with 25% biosolids with 75% wood pellets by mass 141\u00C2\u00A0 \u00C2\u00A0 Run Time (minutes) 160 180 200 220 240 260 m ol ar c on ce nt ra tio n (% ) 20 40 60 80 Te m pe ra tu re (C ) 760 780 800 820 840 860 880 900 N2 bed temperature Figure A30: Bed temperature an N2 concentration vs. time for run with 25% biosolids with 75% wood pellets by mass 142\u00C2\u00A0 \u00C2\u00A0 Run time (minutes) 160 180 200 220 240 260 m ol ar c on ce nt ra tio n (% ) 0 20 40 60 80 100 Te m pe ra tu re (C ) 800 820 840 860 880 900 H2 CO CH4 CO2 bed temperature Figure A31: Bed temperature and syngas composition versus run time for run with 25% biosolids with 75% wood pellets by mass 143\u00C2\u00A0 \u00C2\u00A0 Table A1: Results for run with 10% biosolids with 90% wood pellets by mass a) Gas composition Total N2 free H2 19.1 42.6 N2 55.0 0 CO 16.0 35.4 CH4 4.4 9.7 CO2 5.5 12.3 \u00C2\u00A0 b) Syngas yield Time period N2( m3) N2 concentrati on Total gas(m3) Syngas (m3) Feed rate(kg/h) Time (h) Syngas yield( m3/kg ) 12:30-2: 30pm 3.48 54.98 6.33 2.85 1.27 2.00 1.12 c) Heating value of the syngas Specific heat values(MJ/m3) N2 free molar percentage LHV (MJ/m3) H2 10.798 0.4256 4.60 CO 12.636 0.3544 4.48 CH4 35.818 0.0972 3.48 Total 12.56 d) Tar content in the syngas Total weight of tar(g) Producer gas collected(L) N2 content in producer gas Syngas collected(m3) Tar in syngas(g/m3) 0.29 267.10 53.32 0.12 2.33 e) Ammonia concentration determination Absorption part H2SO4 concentr ation(N) Volume in bottle(m L) Mol H2SO4 in absorbent Volume after absorption (mL) 1 150 0.075 210 144\u00C2\u00A0 \u00C2\u00A0 Titration part Absorbe nt volume( mL) NaOH concentr ation(N) NaOH titrated(mL) Mol NaOH titrated Mol H2SO4 titrated H2SO4 conc in absorbent( M) 4.1 0.1 25.8 0.00258 0.00129 0.315 4.2 0.1 27.6 0.00276 0.00138 0.329 Back titration part H2SO4 conc in absorben t Mol H2SO4 in absorben t Mol H2SO4 reacted with ammonia Mol ammonia captured Volume ammonia captured(m 3) Collected syngas volume(m 3) Ammon ia conc(pp mv) 0.322 0.0676 0.0075 0.0149 0.000335 0.125 2690 f) Char conversion Feedstock Cycloned solids dry volatile free dry volatile free Volatiles (%) 83.4 6.7 Fixed Carbon (%) 14.4 87.4 58.5 62.8 Ash (%) 2.07 12.5 34.6 37.1 Char conversion 0.66 g) Carbon balance Carbon IN Feed rate(kg/h) Time(hours) Carbon content in feedstock Total carbon in(kg) 1.26 2 0.49 1.22 Carbon out Carbon in Syngas Conc(%) Volume of gas(m3) Mol of gas Mol of Carbon in gas Weight of carbon (kg) Syngas produced total(m3) 2.8 114 CO2 12.2 0.343 14.0 14.0 0.168 CO 35.4 0.992 40.4 40.4 0.485 145\u00C2\u00A0 \u00C2\u00A0 Conc(%) Volume of gas(m3) Mol of gas Mol of Carbon in gas Weight of carbon (kg) CH4 9.72 0.272 11.0 11.0 0.133 Total carbon 0.786 Carbon in cyclone Primary cyclone Secondary cyclone Total carbon Solid weight(kg) 0.542 0.0173 Carbon content % 60.8 55.9 Weight of carbon(kg) 0.330 0.00968 0.340 Carbon in tar Tar content in the syngas(g/m3) Syngas produced(m3) Total tar(g) Carbon content in tar (%) Weight of carbon(kg) 2.4 2.8 6.72 0.913 0.00613 Carbon out Total C(kg) 1.13 146\u00C2\u00A0 \u00C2\u00A0 Table A2: Results for run with 100% wood pellets a) Gas composition Total N2 free H2 22.1 45.7 N2 51.6 0 CO 16.7 34.7 CH4 4.5 9.4 CO2 5.1 10.2 b) Syngas yield Time period N2( m3) N2 concentrat ion Total gas(m3) Syngas (m3) Feed rate(kg/h ) Time(h) Syngas yield( m 3/kg) 11:58-1: 58pm 3.72 51.59 7.21 3.49 1.27 2.00 1.37 c) Heating value of the syngas Specific heat values(MJ/m3) N2 free molar percentage LHV (MJ/m3) H2 10.798 0.4569 4.93 CO 12.636 0.3472 4.39 CH4 35.818 0.0936 3.35 Total 12.67 d) Tar content in the syngas Total weight of tar(g) Producer gas collected(L) N2 content in producer gas Syngas collected(m3) Tar in syngas(g/m3) 2.02 400 50.86 0.197 10.3 e) Ammonia concentration determination Absorption part H2SO4 concentr ation(N) Volume in bottle(m L) Mol H2SO4 in absorbent Volume after absorption (mL) 1 110 0.055 155 147\u00C2\u00A0 \u00C2\u00A0 Titration part Absorbe nt volume( mL) NaOH concentr ation(N) NaOH titrated(mL) Mol NaOH titrated Mol H2SO4 titrated H2SO4 conc in absorbent( M) 4.6 0.1 29 0.0029 0.00145 0.315 4.9 0.1 29.6 0.00296 0.00148 0.302 4.6 0.1 28.4 0.00284 0.00142 0.308 4.9 0.1 30 0.003 0.0015 0.306 Back titration part H2SO4 conc in absorben t Mol H2SO4 in absorben t Mol H2SO4 reacted with ammonia Mol ammonia captured Volume ammonia captured(m 3) Collected syngas volume(m 3) Ammon ia conc(pp mv) 0.308 0.047 0.00725 0.0145 0.000326 0.196 1660 f) Char conversion Feedstock Cycloned solids dry volatile free dry volatile free Volatiles (%) 83.5 26.9 Fixed Carbon (%) 15.3 93.3 46.5 63.7 Ash (%) 1.09 6.6 26.5 36.2 Char conversion 0.82 148\u00C2\u00A0 \u00C2\u00A0 g) Carbon balance Carbon IN Feed rate(kg/h) Time(hours) Carbon content in feedstock Total carbon in(kg) 1.3 2 0.48 1.24 Carbon out Carbon in Syngas Conc(%) Volume of gas(m3) Mol of gas Mol of Carbon in gas Weight of carbon (kg) Syngas produced total(m3) 3.5 142 CO2 10.2 0.358 14.5 14.5 0.175 CO 34.7 1.21 49.5 49.5 0.594 CH4 9.36 0.327 13.3 13.3 0.160 total carbon 0.929 Carbon in cyclone Primary cyclone Secondary cyclone Total carbon Solid weight(kg) 0.115 0.0516 Carbon content % 43.7 45.5 Weight of carbon(kg) 0.0506 0.0234 0.074 Carbon in tar Tar content in the syngas(g/m3) Syngas produced(m3) Total tar(g) Carbon content in tar (%) Weight of carbon(kg) 10.4 3.5 36.4 0.913 0.033 Carbon out Total C(kg) 1.03 149\u00C2\u00A0 \u00C2\u00A0 Table A3: Results for run with 100% biosolids a) Gas composition Total N2 free H2 8.71 33.6 N2 73.3 0 CO 10.1 36.9 CH4 4.7 16.6 CO2 3.3 12.9 b) Syngas yield Time p eriod N2( m3) N2 concentrati on Total gas(m3) Syngas (m3) Feed rate(kg/h) Time (h) Syngas yield( m3/kg) 10:56-1 2:16 2.56 73.27 3.49 0.93 1.50 1.33 0.47 12:16-1 2:44 0.91 84.46 1.08 0.17 0.70 0.47 0.51 12:44-1 :18 1.13 80.13 1.41 0.28 1.50 0.57 0.33 1:18-1: 45 0.81 68.88 1.17 0.37 1.90 0.45 0.43 1:45-2: 13 0.87 84.03 1.04 0.17 1.20 0.47 0.30 c) Heating value of the syngas Time period (min) H2 CO CH4 CO2 Total Specific heat values(MJ/m3) 10.798 12.636 35.818 14.1-88.3 N2 free molar % 33.58 36.89 16.63 12.89 91.8-116.5 N2 free molar % 34.94 33.98 12.68 18.32 120-148.2 N2 free molar % 38.96 34.48 12.45 14.05 151.7-176.3 N2 free molar % 31.35 36.97 16.93 14.72 179.9-204.6 N2 free molar % 41.63 29.74 8.40 20.23 14.1-88.3 LHV (MJ/m3) 3.63 4.66 5.96 14.25 91.8-116.5 LHV (MJ/m3) 3.77 4.29 4.54 12.61 120-148.2 LHV (MJ/m3) 4.21 4.36 4.46 13.03 151.7-176.3 LHV (MJ/m3) 3.39 4.67 6.06 14.12 179.9-204.6 LHV (MJ/m3) 4.50 3.76 3.01 11.26 150\u00C2\u00A0 \u00C2\u00A0 d) Tar content in the syngas Total weight of tar(g) Producer gas collected(L) N2 content in producer gas Syngas collected(m3) Tar in syngas(g/m3) 10.6 196.8 73.23 0.053 200 e) Ammonia concentration determination Absorption part H2SO4 concentr ation(N) Volume in bottle(m L) Mol H2SO4 in absorbent Volume after absorption (mL) 1 106 0.053 106 M=N/n Titration part Absorbe nt volume( mL) NaOH concentr ation(N) NaOH titrated(mL) Mol NaOH titrated Mol H2SO4 titrated H2SO4 conc in absorbent( M) 4.2 0.1 24.8 0.00248 0.00124 0.295 4 0.1 23 0.0023 0.00115 0.287 4.2 0.1 24 0.0024 0.0012 0.285 4 0.1 22.6 0.00226 0.00113 0.282 Back titration part H2SO4 conc in absorben t Mol H2SO4 in absorben t Mol H2SO4 reacted with ammonia Mol ammonia captured Volume ammonia captured(m 3) Collected syngas volume(m 3) Ammon ia conc(pp mv) 0.287 0.0305 0.0225 0.045 0.001011 0.0526 19200 151\u00C2\u00A0 \u00C2\u00A0 f) Char conversion Feedstock Cycloned solids dry volatile free dry volatile free Volatiles (%) 82.28 9.75 Fixed Carbon (%) 6.82 38.4 4.23 4.68 Ash (%) 10.9 61.5 86.0 95.3 Char conversion 0.35 g) Carbon balance Carbon IN Feed weight(kg) Carbon content in feedstock Total carbon in(kg) 4.65 0.55 2.56 Carbon out Carbon in Syngas 10:56-12:16 Conc(%) Volume of gas(m3) Mol of gas Mol of Carbon in gas Weight of carbon (kg) Syngas produced total(m3) 0.933 38.0 CO 36.8 0.344 14.0 14.0 0.168 CH4 16.6 0.155 6.33 6.33 0.076 CO2 12.8 0.12 4.90 4.90 0.0589 Total carbon 0.244 12:16-12:44 Conc(%) Volume of gas(m3) Mol of gas Mol of Carbon in gas Weight of carbon (kg) Syngas produced total(m3) 0.168 6.84 CO 33.9 0.05708 2.32 2.32 0.0279 CH4 12.6 0.0213 0.868 0.86 0.0104 CO2 18.3 0.0307 1.25 1.25 0.0150 Total carbon 0.0383 12:44-1:18 Conc(%) Volume of gas(m3) Mol of gas Mol of Carbon in gas Weight of carbon (kg) Syngas produced total(m3) 0.28 11.4 152\u00C2\u00A0 \u00C2\u00A0 Conc(%) Volume of gas(m3) Mol of gas Mol of Carbon in gas Weight of carbon (kg) CO 34.4 0.0965 3.93 3.93 0.0472 CH4 12.4 0.034 1.42 1.42 0.0170 CO2 14.0 0.039 1.604 1.60 0.0192 Total carbon 0.0643 1:18-1:45 Conc(%) Volume of gas(m3) Mol of gas Mol of Carbon in gas Weight of carbon (kg) Syngas produced total(m3) 0.365 14.8 CO 36.9 0.134 5.50 5.50 0.066 CH4 16.9 0.0617 2.51 2.51 0.0302 CO2 14.7 0.0537 2.19 2.19 0.0262 Total carbon 0.0962 1:45-2:13 Conc(%) Volume of gas(m3) Mol of gas Mol of Carbon in gas Weight of carbon (kg) Syngas produced total(m3) 0.165 6.72 CO 29.7 0.0490 2.00 2.00 0.024 CH4 8.40 0.0138 0.565 0.565 0.00678 CO2 20.2 0.0334 1.36 1.36 0.0163 Total carbon 0.0307 Carbon in cyclone Primary cyclone Secondary cyclone Total carbon Solid weight(kg) 0.497 0 Carbon content % 4.18 0 Weight of carbon(kg) 0.0207 0 0.0207 Carbon in tar Tar content in the syngas(g/m3) Syngas produced(m3) Total tar(g) Carbon content in tar (%) Weight of carbon(kg) 200.3 2.03 407 0.9130 0.371 Carbon out Total C(kg) 0.866 153\u00C2\u00A0 \u00C2\u00A0 Table A4: Results for run with 50% biosolids with 50% wood pellets by mass a) Gas composition Total N2 free H2 6.8 22.5 N2 69.5 0 CO 15.7 51.3 CH4 5.0 16.4 CO2 3.0 9.9 b) Syngas yield Time period N2( m3) N2 concentrati on Total gas(m3) Syngas (m3) Feed rate(kg/h) Time (h) Syngas yield( m3/kg) 1:14-2: 00 2.24 69.54 3.22 0.98 1.29 0.77 0.99 2:05-2: 26 1.04 77.48 1.34 0.30 1.29 0.35 0.67 2:32-2: 52 1.01 78.27 1.29 0.28 1.29 0.33 0.65 3:01-3: 27 1.33 89.17 1.49 0.16 1.29 0.43 0.29 c) Heating value of the syngas Time period (min) H2 CO CH4 CO2 Total Specific heat values(MJ/m3) 10.798 12.636 35.818 1:14-2:00 N2 free molar % 22.4 51.2 16.3 9.85 2:05-2:26 N2 free molar % 23.5 49.4 15.2 11.6 2:32-2:52 N2 free molar % 21.1 52.0 15.4 11.3 3:01-3:27 N2 free molar % 23.1 47.7 13.1 15.8 1:14-2:00 LHV (MJ/m3) 2.43 6.48 5.86 14.77 2:05-2:26 LHV (MJ/m3) 2.54 6.25 5.46 14.26 2:32-2:52 LHV (MJ/m3) 2.28 6.57 5.52 14.38 3:01-3:27 LHV (MJ/m3) 2.50 6.03 4.73 13.26 154\u00C2\u00A0 \u00C2\u00A0 d) Tar content in the syngas Total weight of tar(g) Producer gas collected(L) N2 content in producer gas Syngas collected(m3) Tar in syngas(g/m3) 2.31 122 70.1 0.037 63.1 e) Ammonia concentration determination Absorption part H2SO4 concentr ation(N) Volume in bottle(m L) Mol H2SO4 in absorbent Volume after absorption (mL) 1 128 0.064 158 Titration part Absorbe nt volume( mL) NaOH concentr ation(N) NaOH titrated(mL) Mol NaOH titrated Mol H2SO4 titrated H2SO4 conc in absorbent( M) 4.7 0.1 36.4 0.00364 0.00182 0.387 4.8 0.1 35.2 0.00352 0.00176 0.366 4.6 0.1 33.6 0.00336 0.00168 0.365 5 0.1 35.8 0.00358 0.00179 0.358 Back titration part H2SO4 conc in absorben t Mol H2SO4 in absorben t Mol H2SO4 reacted with ammonia Mol ammonia captured Volume ammonia captured(m 3) Collected syngas volume(m 3) Ammon ia conc(pp mv) 0.369 0.0583 0.00565 0.0113 0.000254 0.0366 6940 f) Char conversion Feedstock Cycloned solids dry volatile free dry volatile free Volatiles (%) 82.9 11.6 Fixed Carbon (%) 11.0 64.8 11.8 13.4 Ash (%) 5.99 35.1 76.5 86.5 Char conversion 0.59 155\u00C2\u00A0 \u00C2\u00A0 g) Carbon balance Carbon IN Feed weight(kg) Time (hour) Carbon content in feedstock Total carbon in(kg) 1.28 2.28 0.51 1.51 Carbon out Carbon in Syngas 1:07-1:58 Conc(%) Volume of gas(m3) Mol of gas Mol of Carbon in gas Weight of carbon (kg) Syngas produced total(m3) 1.08 44.3 CO 51.2 0.55 22.7 22.7 0.272 CH4 16.3 0.177 7.25 7.25 0.087 CO2 9.85 0.107 4.36 4.36 0.0524 Total carbon 0.359 1:58-2:23 Conc(%) Volume of gas(m3) Mol of gas Mol of Carbon in gas Weight of carbon (kg) Syngas produced total(m3) 0.359 14.6 CO 49.4 0.177 7.25 7.25 0.0870 CH4 15.2 0.0548 2.23 2.23 0.0268 CO2 11.6 0.0420 1.71 1.71 0.0205 Total carbon 0.114 2:23-2:49 Conc(%) Volume of gas(m3) Mol of gas Mol of Carbon in gas Weight of carbon (kg) Syngas produced total(m3) 0.363 14.8 CO 52.0 0.189 7.70 7.70 0.0924 CH4 15.4 0.0559 2.28 2.28 0.027 CO2 11.3 0.0414 1.68 1.68 0.0202 Total carbon 0.119 2:49-3:24 156\u00C2\u00A0 \u00C2\u00A0 Conc(%) Volume of gas(m3) Mol of gas Mol of Carbon in gas Weight of carbon (kg) Syngas produced total(m3) 0.217 8.86 CO 47.7 0.103 4.23 4.23 0.050 CH4 13.1 0.0287 1.17 1.17 0.0140 CO2 15.8 0.0345 1.40 1.40 0.016 Total carbon 0.064 Carbon in cyclone Primary cyclone Secondary cyclone Total carbon Solid weight(kg) 0.460 Carbon content % 11.8 Weight of carbon(kg) 0.0543 0 0.0543 Carbon in tar Tar content in syngas(g/m3) syngas produced(m3) total tar(g) carbon content in tar weight of carbon(kg) 63.06 2.02 127 0.9130 0.116 Carbon out Total C(kg) 0.829 157\u00C2\u00A0 \u00C2\u00A0 Table A5: Results for run with 25% biosolids with 75% wood pellets by mass a) Gas composition Total N2 free H2 10.2 25.2 N2 59.4 0 CO 20.4 50.2 CH4 6.0 14.7 CO2 4.0 9.9 b) Syngas yield Time period N2( m3) N2 concentrati on Total gas(m3) Syngas (m3) Feed rate(kg/h) Time (h) Syngas yield( m3/kg) 1:20-2: 13 2.42 59.36 4.08 1.66 1.47 0.88 1.28 c) Heating value of the syngas Specific heat values(MJ/m3) N2 free molar % LHV (MJ/m3) H2 10.798 25.18 2.72 CO 12.636 50.20 6.34 CH4 35.818 14.73 5.28 CO2 9.87 Total 14.34 d) Tar content in the syngas Total weight of tar(g) Producer gas collected(L) N2 content in producer gas Syngas collected(m3) Tar in syngas(g/m3) 2.0 135 59.36 0.055 36.5 158\u00C2\u00A0 \u00C2\u00A0 e) Ammonia concentration determination Absorption part H2SO4 concentr ation(N) Volume in bottle(m L) Mol H2SO4 in absorbent Volume after absorption (mL) 1 102 0.051 123 Titration part Absorbe nt volume( mL) NaOH concentr ation(N) NaOH titrated(mL) Mol NaOH titrated Mol H2SO4 titrated H2SO4 conc in absorbent( M) 4.3 0.1 32 0.0032 0.0016 0.372 4.5 0.1 33 0.0033 0.00165 0.366 4.5 0.1 32 0.0032 0.0016 0.355 Back titration part H2SO4 conc in absorben t Mol H2SO4 in absorben t Mol H2SO4 reacted with ammonia Mol ammonia captured Volume ammonia captured(m 3) Collected syngas volume(m 3) Ammon ia conc(pp mv) 0.364 0.0448 0.00613 0.0122 0.000276 0.0550 5010 f) Char conversion Feedstock Cycloned solids dry volatile free dry volatile free Volatiles (%) 83.2 9.7 Fixed Carbon (%) 13.2 78.8 24.3 27.0 Ash (%) 3.54 21.1 65.8 72.9 Char conversion 0.71 g) Carbon balance Carbon IN Feed rate(kg/h) Time(hours) Carbon content in feedstock Total carbon in(kg) 1.47 1.46 0.53 1.14 Carbon out 159\u00C2\u00A0 \u00C2\u00A0 Carbon in Syngas Conc(%) Volume of gas(m3) Mol of gas Mol of Carbon in gas Weight of carbon (kg) Syngas produced total(m3) 3.49 142.3 CO2 10.2 0.357 14.5 14.5 0.174 CO 34.7 1.21 49.4 49.4 0.593 CH4 9.36 0.32 13.3 13.3 0.159 Total carbon 0.927 Carbon in cyclone Primary cyclone Secondary cyclone Total carbon Solid weight(kg) 0.248 Carbon content % 24.1 Weight of carbon(kg) 0.0601 0 0.0601 Carbon in tar Tar content in the syngas(g/m3) Syngas produced(m3) Total tar(g) Carbon content in tar (%) Weight of carbon(kg) 49.95 3.49 174 0.9130 0.159 Carbon out Total C(kg) 1.14 160\u00C2\u00A0 \u00C2\u00A0 Table A6: Results about impact of feed rate on gasification performance in run with 100% biosolid in feed Run No 3 3 3 3 3 Date Oct 12 Oct 12 Oct 12 Oct 12 Oct 12 Feedstock 100%BS 100%BS 100%BS 100%BS 100%BS Bed material silica sand silica sand silica sand silica sand silica sand Biomass feed rate kg(dry)/h 1.50 0.73 1.50 1.91 1.22 Feed time minutes 80 28 34 27 28 Steam rate kg/h 3.43 3.42 3.41 3.42 3.41 Steam/biomass mass ratio 2.29 4.69 2.27 1.79 2.80 Avg bed temperature \u00D4\u00A8 854 837 860 842 854 Free board temperature \u00D4\u00A8 824 814 826 835 841 Syngas H2/CO molar ratio 0.91 1.03 1.13 0.85 1.40 Syngas LHV MJ/m3 14.25 12.61 13.03 14.12 11.26 Syngas yield m3/kg(dry feedstock) 0.47 0.51 0.33 0.43 0.30 Assume syngas yield constant 0.47 0.47 0.47 0.47 0.47 Feed rate based on assumption 1.50 0.77 1.06 1.74 0.76 Steam/biomass ratio based on assumption 2.29 4.44 3.22 1.97 4.49 Tar content in syngas g/m3 200.3 Ammonia concentration ppmv 19200 161\u00C2\u00A0 \u00C2\u00A0 Table A7: Results about impact of temperature on gasification performance in run with 50% biosolids with 50% wood pellets Run time (min) 209-256 261-281 287-307 316-342 Bed Temperature ( \u00D4\u00A8 ) 825.35 803.23 770.70 728.26 Syngas yield (m3/kg) 0.99 0.67 0.65 0.29 Syngas composition (molar %) H2 22.5 23.6 21.1 23.2 CO 51.3 49.5 52.0 47.8 CH4 16.4 15.3 15.4 13.2 CO2 9.9 11.7 11.4 15.9 162\u00C2\u00A0 \u00C2\u00A0 Table A8: Results about impact of feedstock composition on gasification performance Run no. 2 1 5 4 3 Biosolids proportion in fuel (%) 0 10 25 50 100 Operating conditions Bed material silica sand silica sand silica sand silica sand silica sand Feed rate (kg/h) 1.27 1.27 1.47 1.29 1.5 Steam feed rate (kg/h) 3.48 4.04 3.28 3.52 3.43 Steam/fuel mass ratio 2.74 3.18 2.23 2.73 2.29 Bed temperature (\u00E2\u0084\u0083) 855 857 828 825 854 syngas composition (%) H2 45.7 42.6 25.2 22.5 33.6 CO 34.7 35.4 50.2 51.3 36.9 CH4 9.36 9.72 14.7 16.4 16.6 CO2 10.2 12.3 9.87 9.86 12.9 H2/CO ratio 1.32 1.20 0.50 0.44 0.91 Syngas LHV (MJ/Nm3) 12.67 12.56 14.34 14.77 14.25 Syngas yield (m3/kg) 1.38 1.10 1.28 0.99 0.47 Char conversion 0.817 0.663 0.71 0.594 0.355 Tar content (g/m3) 10.3 2.33 36.0 63.1 200.3 Ammonia concentration (ppmv) 1660 2690 5010 6940 19200 "@en . "Thesis/Dissertation"@en . "2013-11"@en . "10.14288/1.0073675"@en . "eng"@en . "Chemical and Biological Engineering"@en . "Vancouver : University of British Columbia Library"@en . "University of British Columbia"@en . "Attribution-NonCommercial-NoDerivatives 4.0 International"@en . "http://creativecommons.org/licenses/by-nc-nd/4.0/"@en . "Graduate"@en . "Co-gasification of biosolids with biomass in a bubbling fluidized bed"@en . "Text"@en . "http://hdl.handle.net/2429/44411"@en .