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Co-gasification of biosolids with biomass in a bubbling fluidized bed Yu, Ming Ming 2013

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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  © Ming Ming Yu, 2013  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  did not affect syngas composition, but decreased the syngas yield from 0.99 to 0.29 m3/kg.  ii     TABLE OF CONTENTS ABSTRACT ........................................................................................................... ii  TABLE OF CONTENTS ...................................................................................... iii  LIST OF TABLES ................................................................................................. vi  LIST OF FIGURES ............................................................................................. viii  NOMENCLATURE .............................................................................................. xii  ACKNOWLEDGEMENTS ................................................................................. xiii  CHAPTER 1: INTRODUCTION .......................................................................... 1  1.1 Introduction to biosolids ....................................................................................... 1  1.1.1 Biosolids treatment technology ...................................................................... 1  1.1.2 Biosolids use and disposal ............................................................................. 2  1.2 Introduction to gasification .................................................................................. 5  1.2.1 History of gasification technology ................................................................. 6  1.2.2 Gasification processes .................................................................................... 6  1.2.3 Feedstocks ...................................................................................................... 7  1.2.4 Applications ................................................................................................... 7  CHAPTER 2: LITERATURE REVIEW .............................................................. 9  2.1 Biosolids characteristics ....................................................................................... 9  2.1.1 Solid content .................................................................................................. 9  2.1.2 Heating value ............................................................................................... 11  2.1.3 Proximate and ultimate analyses .................................................................. 11  2.1.4 Ash analysis ................................................................................................. 15  2.1.5 Metal content ............................................................................................... 18  2.2 Gasification performance ................................................................................... 20  2.2.1 Catalyst development ................................................................................... 20  iii     2.1.2 Tar removal .................................................................................................. 21  2.1.3 Pollutant byproduct gases: H2S, NH3, and HCl ........................................... 21  2.1.4 Temperature effect ....................................................................................... 23  2.1.5 Steam/fuel ratio effect .................................................................................. 24  2.3 Co-gasification of biosolids with biomass ......................................................... 24  2.3.1 Syngas yield, char conversion and tar concentration ................................... 24  2.3.2 Syngas composition and heating values of syngas ...................................... 26  2.3.3 Summary ...................................................................................................... 27  2.3.3 Kinetics of co-gasification ........................................................................... 27  2.4 Fluidization flow regime .................................................................................... 28  CHAPTER 3: RESEARCH OBJECTIVES ........................................................ 30  CHAPTER 4: MATERIALS ............................................................................... 32  4.1 Biosolids ............................................................................................................. 32  4.2 Biomass .............................................................................................................. 34  CHAPTER 5: KINETIC STUDY IN A TGA ...................................................... 36  5.1 Experimental setup ............................................................................................. 36  5.2 Data analysis ....................................................................................................... 37  5.3 Results and discussion ........................................................................................ 37  5.3.1 Separate gasification of biosolids, woody pellets and switchgrass .............. 37  5.3.2 Co-gasification of biosolids with biomass ................................................... 39  5.3.3 Catalytic and inhibition effect on gasification rate ...................................... 42  CHAPTER 6: GASIFICATION IN HIGHBURY PILOT SCALE BUBBLING FLUIDIZED BED ................................................................................................ 46  6.1 Experimental setup (Watkinson et al., 2010) ...................................................... 46  6.1.1 Feedstock ..................................................................................................... 46  6.1.2 System .......................................................................................................... 47  iv     6.1.3 Operating conditions .................................................................................... 52  6.1.4 Operating procedure adapted from HEI manual .......................................... 52  6.2 Data analysis ....................................................................................................... 54  6.2.1 Syngas composition, LHV and syngas yield ............................................... 54  6.2.2 Tar content in syngas .................................................................................... 55  6.2.3 Ammonia determination ............................................................................... 55  6.2.4 Char conversion ........................................................................................... 56  6.2.5 Carbon balance............................................................................................. 56  6.3 Results and discussion of individual runs .......................................................... 57  6.3.1 10% biosolids with 90% wood pellets by mass ........................................... 58  6.3.2 100% wood pellets ....................................................................................... 69  6.3.3 100% biosolids ............................................................................................. 77  6.3.4 50% biosolids with 50% wood pellets by mass ........................................... 84  6.3.5 25% biosolids with 75% wood pellets by mass ........................................... 89  CHAPTER 7: IMPACTS OF BED TEMPERATURE AND BIOSOLIDS PROPORTION IN FUEL .................................................................................... 94  7.1 Impact of bed temperature on syngas yield and composition ............................ 94  7.2 Impact of biosolids proportion in fuel on gasification performance .................. 97  CHAPTER 8: CONCLUSIONS AND RECOMMENDATIONS .......................105  REFERENCES ...................................................................................................107  APPENDIX: SUPPLEMENTAL RESULTS FROM BUBBLING FLUIDIZED BED GASIFICATION ........................................................................................110        v      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) .................................................................... 10  Table 2-2 Ranges of solid content of biosolids after different dewatering techniques (source: Biosolids Generation, Use, and Disposal in the United States, 1999) .................................................................................... 10  Table 2-3 Typical proximate and ultimate analyses of biosolids ..................... 12  Table 2-4 Typical proximate and ultimate analyses of wood pellets ............... 13  Table 2-5 Typical proximate and ultimate analyses of coal ............................. 14  Table 2-6 Typical ash analyses of biosolids ....................................................... 16  Table 2-7 Typical ash analyses of other gasification feedstocks ...................... 17  Table 2-8 Metal content (mg/kg) in biosolids reported by Toronto and Vancouver .................................................................................................... 19  Table 4-1 Proximate and ultimate analyses of biosolids from different sources ....................................................................................................................... 33  Table 4-2 Ash fusion analysis of biosolids from Baltimore WWTP ................ 34  Table 4-3 Proximate and ultimate analyses of wood pellets and switchgrass 35  Table 5-1 Ash analysis of switchgrass, wood pellets and biosolids ................. 39  Table 6-1 Steady state gas concentrations for the run with 10% biosolids in fuel and for 178-292 min period ................................................................ 65  Table 6-2 Characteristics of collected solids in cyclones for run with 10% biosolids with 90% wood pellets ................................................................ 69  Table 6-3 Steady state gas concentrations for run with 100% wood pellets and for 130-231 min period ............................................................................... 74  vi     Table 6-4 Characteristics of collected solids in cyclones for run with 100% wood pellets.................................................................................................. 77  Table 6-5 Steady state gas concentrations for run with 100% biosolids and for 147-221 min period ..................................................................................... 83  Table 6-6 Characteristics of collected solids in primary cyclone for run with 100% biosolids ............................................................................................. 84  Table 6-7 Steady state gas concentrations for run with 50% biosolids with 50% wood pellets and for 202-254 min period .................................................. 88  Table 6-8 Characteristics of collected solids in primary cyclone for run with 50% biosolids with 50% wood pellets by mass ........................................ 89  Table 6-9 Steady state gas concentrations for run with 25% biosolids with 75% wood pellets by mass and for 179-232 min period ................................... 91  Table 6-10 Characteristics of collected solids in cyclones for run with 25% biosolids with 75% wood pellets by mass ................................................. 92  Table 7-1 Operating conditions of the five runs with the bubbling fluidized bed ................................................................................................................ 98  Table 7-2 LHV of syngas with various biosolids proportions ....................... 101         vii     LIST OF FIGURES Figure 1-1 Estimates of biosolids use and disposal (Source: US EPA 1999) .... 3  Figure 1-2 Applications of syngas from gasification (Higman, 2008) ............... 8  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 ,  feedstock flow rate of 5 g daf/min, ER of 0.21 and steam/fuel ratio of 0.9 g/g daf .......................................... 23  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 . ............................................................................................................ 25  Figure 2-3 Syngas yield, tar concentration and char conversion versus biosolids proportion in fuel (Saw et al., 2011). Operating conditions: reactor temperature 720 ; feedstock flow rate, 15.5 kg/h; steam/fuel ratio, 1.1 (kg/kg) .......................................................................................... 26  Figure 2-4 Flow regime diagrams according to Bi and Grace (Bi & Grace, 1995) , with permission from the Elsevier. Ar=Archimedes number; U*=dimensionless gas velocity ................................................................... 29  Figure 5-1 Char conversion of biosolids, wood pellets and switchgrass vs. time. Operating conditions: reactor temperature, 800℃; sample size, 300-355 m; initial mass of sample, 15 mg; CO2 flow rate, 500 mL/min ....................................................................................................................... 38  Figure 5-2 Co-gasification of 50:50 biosolids by weight with: a) wood pellets; b) switchgrass. Operating conditions: reactor temperature, 800 ; sample size, 300-355 m; initial mass of sample, 15 mg; CO2 flow rate, 500 mL/min .................................................................................................. 40  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℃; sample size, 300-355 m; initial mass of sample, 15 mg; CO2 flow rate, 500 mL/min ......................................................................................................... 42  Figure 5-4 Co-gasification of 50:50 biosolids with switchgrass ash. Operating conditions: reactor temperature, 800℃; sample size, 300-355 m; initial viii     mass of sample, 15 mg; CO2 flow rate, 500 mL/min ................................ 43  Figure 5-5 Co-gasification of 50:50 biosolids ash with: a) wood pellets; b) switchgrass. Operating conditions: reactor temperature, 800℃; sample size, 300-355 m; initial mass of sample, 15 mg; CO2 flow rate, 500 mL/min ......................................................................................................... 44  Figure 6-1 Process flow diagram of the Highbury Energy Inc. bubbling fluidized (Watkinson et al., 2010), with permission from Dr. Watkinson ....................................................................................................................... 49  Figure 6-2 Reactor temperature vs. time for run with 10% biosolids with 90% wood pellets by mass ................................................................................... 59  Figure 6-3 Temperature of tar sampling line vs. time for run with 10% biosolids with 90% wood pellets by mass ................................................. 60  Figure 6-4 Pressure drop in reactor for run with 10% biosolids with 90% wood pellets by mass ................................................................................... 61  Figure 6-5 Steam flow rate vs. time for run with 10% biosolids with 90% wood pellets by mass ................................................................................... 62  Figure 6-6 Gas concentrations of dry producer gases for run with 10% biosolids with 90% wood pellets by mass ................................................. 63  Figure 6-7 Nitrogen-free dry syngas composition for run with 10% biosolids with 90% wood pellets by mass ................................................................. 64  Figure 6-8 Bed temperature and dry producer gas concentrations vs. time for run with 10% biosolids with 90% wood pellets by mass ......................... 66  Figure 6-9 Bed temperature and dry syngas composition versus run time for run with 10% biosolids and 90% wood pellets by mass .......................... 67  Figure 6-10 Reactor temperature vs. time for run with 100% wood pellets . 70  Figure 6-11 Gas concentrations of dry producer gases for run with 100% wood pellets.................................................................................................. 72  Figure 6-12 Nitrogen-free dry syngas composition for run with 100% wood pellets ............................................................................................................ 73  ix     Figure 6-13 Correlation of bed temperature to dry syngas production rate for run with 100% wood pellets ....................................................................... 74  Figure 6-14 Bed temperature and dry syngas composition vs. run time for run with 100% wood pellets .............................................................................. 75  Figure 6-15 Reactor temperature vs. time for run with 100% biosolids ....... 79  Figure 6-16 Gas concentrations of dry producer gases for run with 100% biosolids ........................................................................................................ 81  Figure 6-17 Nitrogen-free dry syngas composition for run with 100% biosolids ........................................................................................................ 82  Figure 6-18 Reactor temperature (T10) vs. time for run with 50% biosolids with 50% wood pellets by mass ................................................................. 86  Figure 6-19 Gas concentrations of dry producer gases for run with 50% biosolids with 50% wood pellets by mass ................................................. 87  Figure 6-20 Gas concentrations of dry producer gases for run with 25% biosolids with 75% wood pellets by mass ................................................. 91  Figure 7-1 Bed temperature and N2 concentration vs. time for run with 50% biosolids with 50% wood pellets by mass. ................................................ 94  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. ........................................................................................... 95  Figure 7-3: Temperature and syngas composition vs. time for run with 50% biosolids with 50% wood pellets by mass. ................................................ 96  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. ........................................................................................... 97  Figure 7-5 Syngas composition vs. biosolids proportion in fuel, divided into a) for runs 1, 2, 3 b) for runs 4 and 5 ........................................................... 100  Figure 7-6 Syngas yield and char conversion vs. biosolids proportion in feed ..................................................................................................................... 102  x     Figure 7-7 Tar content and ammonia concentration vs. biosolids proportion in fuel .............................................................................................................. 103     xi     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,   xii     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’s 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’s 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.  xiii     CHAPTER 1:  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. 1     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.  2     Biosolids use/disposal distribution 1 17  Land application 41  Advanced treatment Other beneficial use Incineration  22  Landfilled Other disposal 7  12     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).  3     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 . 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 . Gasification of biosolids is advantageous in many aspects compared to other disposal methods. Advantages and disadvantages are discussed below. 4     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 ) 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.  5           →     (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).  6     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,  7     Ammonia Methanol Carbon  Monoxide  Hydrogen OXO Alcohols  Gasification Fischer‐ Tropsch SNG Town Gas Reduction  Gas Gas Turbines Figure 1-2 Applications of syngas from gasification (Higman, 2008)  8     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.  9     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  Iona  Lions  Lulu  Northwest  Island  Island  Gate  Island  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) belt dewatering  air  vacuum  filter  plate-and-frame heat drying  technology  drying  filter  centrifuge presses presses  45-90  12-22  25-35  and pelletizing  solid content (%)  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. 10     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, 11     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 biosolids  Material Water  8.0  8.0  1.7  19.0  5.2  6.7  80.4  content( %) Proximate (wt.% dry) Volatile  47.3  77.2  44.3  57.2  42.6  43.6  N/A  Ash  34.8  13.2  33.9  37.9  52.8  37.8  39.8  17.9  9.7  21.8  4.9  4.6  18.6  N/A  content Fixed carbon 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  Las  USA Sweden  Bangkok  Sofia,  Kyonggi  Zeala  Vegas,  ,  Bulgaria  -Do,  nd  USA  Thailand  Saw  Adams  Nipattum  Leckne  Rirksom  Balgaran  Rhee et  et al.,  et al.,  makul et  r et al.,  boon et  ova et  al., 2010  2012  2011  al., 2010  2004  al., 2006  al., 2003  Reference  Korea  12     Table 2-4 Typical proximate and ultimate analyses of wood pellets Material  wood pellets 6.1  Water  8.0  8.1  6.1  2.3  86.5  84.1  81.7  86.2  78.8  0.3  0.4  0.4  0.3  0.8  13.3  15.4  17.9  13.5  20.4  content(%) Proximate (dry) Volatile(%) Ash content(%) Fixed carbon(%) 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  0.005  <0.1  0.01  0.005  0.3  Vienna  New  Germany  Vienna  Korea  Leckner et Aigner et al.,  Seo et al.,  %)  Sulfur(%) Location  Zealand Reference  Wilk et al.,  Saw et al.,  2011  2012  al., 2004  2011  2010  13     Table 2-5 Typical proximate and ultimate analyses of coal Material  coal 9.9  Water  3.1  9.0  32.1  35.7  32.7  7.4  11.8  17.5  60.5  52.5  49.8  content(%) Proximate (dry) Volatile(%) Ash content(%) Fixed carbon(%) Ultimate(dry and ash free) 76.5  74.6  84.9  3.9  4.7  5.0  Oxygen(%)  10.3  19.3  7.7  Nitrogen(%)  1.3  1.1  1.6  0.46  0.3  0.7  Vienna  Korea  Germany  Aigner et  Seo et  Leckner et  al., 2011  al.,  al., 2004  Carbon(%) Hydrogen(%)  Sulfur(%) Location Reference  2010  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).  14     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.    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 15     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  8.9  21  SO3  1.18  8.2  2  0.1  0.1  MnO4  0.3  NiO  0.05  ZnO  0.33  CuO  0.36  Undertermined  0  0  8.5  0  Location  Las Vegas,  Kyonggi-Do,  Basel,  Winterthur,  USA  Korea  Swiss  Swiss  Rhee, 2010 Franz,2008  Franz,2008  Reference    25.9  Adams, 2011    16     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 SO3  2.4 1.62  2.36  1.5  MnO4  1.6  NiO  0.1  ZnO  0.1  CuO  0.1  Undertermined  2.1  Location  Korea  Korea  Reference  Vienna Kirnbauer,  Seo,2010 Seo,2010  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).  17     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.  18     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  Toronto  Canada  typical  concentration WWTP  Fertilizers value  limits  act  from US EPA  arsenic  75  4.72  75  4-13  cadmium  85  2.7  20  2.5  3000  120  ns  nd  cobalt  nd  5.19  150  nd  copper  4300  1190  ns  300-470  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  7500  785  1850  560-600  chromium  lead  zinc Ns: no standard Nd: no data available  19     (b) Metro Vancouver source: Greater Vancouver Sewerage & Drainage District Quality Control Annual Report, 2011 source  Annacis  Iona  Lions  Lulu  Northwest  Island  Island  Gate  Island  Langley  WWTP  WWTP  WWTP  WWTP  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  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  1290  809  1079  1075  1074  molybdenum  zinc  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)’s investigation, metallic oxides yielded better results than non-metallic oxides in terms of tar removal.  20     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, 21     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 . 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 , little HCl is found because chlorine is trapped in alkaline earth metals in the feedstock as a solid phase. According to Pinto’s 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.  22     25000  2000  15000 1000 10000  500  H2S concentration  NH3 concentration (ppmv)  H2S concentration (ppmv)  20000 1500  5000  NH3 concentration 0  0 0  20  40  60  80  100  Biosolids proportion in fuel (% w/w)  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 ,  feedstock flow rate of 5 g daf/min, ER of 0.21 and steam/fuel ratio of 0.9 g/g daf    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).  23     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  H O  H  CO 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.  24     80  product yield (%)  60 Syngas Tar Char  40  20  0 0  20  40  60  80  100  biosolids proportion in fuel (% w/w)  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 .  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%.   25     8  syngas yield tar char  7 3  Tar concentration (g/Nm )  .8  6 .6 5  3  Syngas yield (Nm /kg), char conversion  1.0  .4 4 .2  3  0.0  2 0  20  40  60  80  100  biosolids proportion in fuel (% w/w)  Figure 2-3 Syngas yield, tar concentration and char conversion versus biosolids proportion in fuel (Saw et al., 2011). Operating conditions: reactor temperature 720 ; 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  26     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 27     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.  28     10 10  Uc  Use ent l u b Tur  U*  -1 0.1 10  Approximate AB boundary  BD boundary  Ut Typical AC boundary  -2 0.01 10  Umf  Pa ck ed Be ds  ing l b b Bu  11  -3  0.001 10  1 1  3  10 10  Ar  30 1/3  2  100 10  300  Figure 2-4 Flow regime diagrams according to Bi and Grace (Bi & Grace, 1995), with permission from the Elsevier. Ar=Archimedes number; U*=dimensionless gas velocity      29     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  30     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  in steps of 30 . The  effects of temperature on syngas composition and yield are then investigated.  31     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.  32     Table 4-1 Proximate and ultimate analyses of biosolids from different sources Source Water content (%)  BC Washington Baltimore 75.5  4.0  9.2  Volatile (%)  50.5  65.7  82.3  Ash content (%)  39.6  25.4  10.9  Fixed carbon (%)  9.9  8.9  6.8  14700  16800  22100  56.0  53.4  55.1  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  Proximate (dry)  Higher heat value (kJ/kg,dry) Ultimate(dry and ash free) Carbon (%) Hydrogen (%)  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 , much lower than for wood pellets, 1420 and 1450  respectively (Wilk, et al. 2011). To prevent agglomeration and sintering, it is safe to keep the temperature below 1100 . Our gasification experiments were at around 850 , far below the melting point.  33     Table 4-2 Ash fusion analysis of biosolids from Baltimore WWTP Biosolids Ash Analysis  Unit  Analytical  Fuel  Methods  Feb-08-2012  *Ash Fusion Temperature (reducing atmosphere): ASTM Initial Deformation  °C  D1857  1136  ASTM Softening (h=W)  °C  D1857  1181  ASTM Hemispherical  °C  D1857  1211  ASTM Fluid  °C  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.  34     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 wood biomass Water content (%)  pellets  switchgrass  5.9  9.3  83.6  76.9  Ash content (%)  1.1  6.3  Fixed carbon (%)  15.4  16.8  19300  19400  47.9  49.7  6.4  6.2  Oxygen (%)  44.6  43.1  Nitrogen (%)  0.3  0.9  Sulfur (%)  0.9  0.08  Proximate (dry) Volatile (%)  Higher heat value (kJ/kg,dry) Ultimate(dry and ash free) Carbon (%) Hydrogen (%)  35     CHAPTER 5: KINETIC STUDY IN A TGA    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 m, 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 maintained at 800  at a heating rate of 25  /min and then  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, 36     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  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  (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.   37        1.0  Char conversion, X  .8  .6 biosolids wood switchgrass  .4  .2  0.0 0  200  400  600  Gasification Time (min)     Figure 5-1 Char conversion of biosolids, wood pellets and switchgrass vs. time. Operating conditions: reactor temperature, 800 ; sample size, 300-355  m;  initial mass of sample, 15 mg; CO2 flow rate, 500 mL/min    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 38     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 wood switchgrass 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.  39     (a) 1.0  Char conversion, X  .8  .6 biosolids alone wood alone biosolids/wood 50/50 mixture expected gasification rate of biosolids/wood 50/50 mixutre  .4  .2  0.0 0  200  400  600  Gasification Time (min)        (b) 1.0  Char conversion, X  .8  .6 biosolids alone switchgrass alone biosolids/switchgrass 50/50 mixture expected gasification rate of biosolids/switchgrass 50/50 mixutre  .4  .2  0.0 0  200  400  600  Gasification Time (min)     Figure 5-2 Co-gasification of 50:50 biosolids by weight with: a) wood pellets; b) switchgrass. Operating conditions: reactor temperature, 800 ; sample size, 300-355 m; initial mass of sample, 15 mg; CO2 flow rate, 500 mL/min 40     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) 1.0  Char conversion, X  .8  .6 biosolids/wood 50/50 mixture repeat of biosolids/wood 50/50 mixture  .4  .2  0.0 0  100  200  300  400  Gasification Time (min)  500  600  700     41     (b) 1.0  Char conversion, X  .8  .6 biosolids/switchgrass 50/50 mixture repeat of biosolids/switchgrass 50/50 mixture  .4  .2  0.0 0  100  200  300  400  500  600  700  Gasification Time (min)  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 ; sample size, 300-355 m; 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.    42     1.0  Char conversion, X  .8  .6 biosolids alone switchgrass alone biosolids/switchgrass_ash 50/50 mixture  .4  .2  0.0 0  200  400  Gasification Time (min)  600     Figure 5-4 Co-gasification of 50:50 biosolids with switchgrass ash. Operating conditions: reactor temperature, 800 ; sample size, 300-355 m; 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.  43     (a) 1.0  Char conversion, X  .8  .6 biosolids alone wood alone biosolids_ash/wood 50/50  .4  .2  0.0 0  200  400  600  Gasification Time (min)        (b) 1.0  Char conversion, X  .8  .6  biosolids alone switchgrass alone biosolids_ash/switchgrass 50/50 mixture  .4  .2  0.0 0  200  400  600  800  Gasification Time (min)     Figure 5-5 Co-gasification of 50:50 biosolids ash with: a) wood pellets; b) switchgrass. Operating conditions: reactor temperature, 800 ; sample size, 300-355 m; initial mass of sample, 15 mg; CO2 flow rate, 500 mL/min 44     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.  45     CHAPTER 6:  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 46     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. The 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  was heated by  super-heaters (12X240VX1800W, 21.6 kW, 3.7 m long) to about 800  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. 47     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.    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.  48        Figure 6-1 Process flow diagram of the Highbury Energy Inc. bubbling fluidized (Watkinson et al., 2010), with permission from Dr. Watkinson  49     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’s 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 m, 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’s 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 50     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  in 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 . 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 tarabsorbing 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 m 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  and -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  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 51     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  for 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 .  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. 52     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. 53     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 MJ⁄Nm  H %  10.798  CO%  12.636  CH % 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. 54     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  2H SO → NH  SO  H SO  (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 SO  2NaOH → Na SO  2H O  (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. 55     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  A1%  M  1  X  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 in  F  t  C%  (6-5)  56     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 out  carbon in syngas CO  CO2  carbon in cyclone solids  CH4 %  MW  S  C%  carbon in tar V  T  C % (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  57     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 “gasification period” 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  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.  58     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.  1000  Temperature (oC)  800 Bed temperature 600  400 gasification period 200  0 0  50  100  150  200  250  300  Run Time(min)   Figure 6-2 Reactor temperature vs. time for run with 10% biosolids with 90% wood pellets by mass     From Figure 6-2, between 0-80 minutes, the bed temperature increased to the desired temperature of 880 . 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 59     was turned on. This indicated that the endothermic gasification reaction started, consuming heat. Then, the bed temperature remained steady around 860  until the  end of the experiment. The steady state bed temperature averaged 857   during the gasification period.  400  Temperature (oC)  300 Tar sampling temperature  200  tar sampling period 100  0 0  50  100  150  200  250  300  Run Time(min)  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 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 60     experiment. However, the decrease in pressure drop did not appear to affect the results noticeably.  10  dP1(kPa)  8  6  4  2  0 0  50  100  150  200  250  300  Run Time(min)  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.  61     10  Steam Flow Rate (kg/h)  8  6  4  2  0 0  50  100  150  Run Time(min)  200  250  300     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.     62     100  Molar concentration (%)  80  60 H2 N2 CO CH4 CO2 total  40  20  0 140  160  180  200  220  240  260  280  Run Time (minutes)     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.  63     H2 CO CH4 CO2  Molar concentration (%)  60  40  20  0 140  160  180  200  220  240  260  280  Run time (minutes)  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  H O→H  CO  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.  64     Table 6-1 Steady state gas concentrations for the run with 10% biosolids in fuel and for 178-292 min period H2 N2 CO CH4 CO2  Total 19.1 55.0 16.0 4.4 5.5  N2 free 42.6 0 35.4 9.7 12.3     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.     65     100  890 880 870 860  60  850 40  840  Temperature (C)  Molar concentration (%)  80  830 20 820 0  810 140  160  180  200  220  240  Run Time (minutes)  260  280  H2 N2 CO CH4 CO2 total bed temperature     Figure 6-8 Bed temperature and dry producer gas concentrations vs. time for run with 10% biosolids with 90% wood pellets by mass    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 66     decrease. It was reasonable that a lower feed rate decreased the syngas production rate.  From Figure 6-9, the temperature and syngas composition are plotted between 137 and 296 minutes and are correlated with the feed rate and syngas composition.    100  890 H2 CO CH4 CO2 bed temperature  870 860  60  850 40  840  Temperature (C)  Molar concentration (%)  80  880  830 20 820 0  810 140  160  180  200  220  240  260  280  Run time (minutes)  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. 67     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’s 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. 68     Table 6-2 Characteristics of collected solids in cyclones for run with 10% biosolids with 90% wood pellets Primary cyclone Secondary cyclone  Collected solid Mass  g  Bulk specific gravity  543  17  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  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 69     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.    1000  800  Temperature (oC)  bed temperature  600  400 gasification period  200  0 0  50  100  150  200  250  300  Run Time(min) 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  . 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 70     around 860  until the end of the experimental run. The steady state bed temperature  averaged 855  during the gasification period.  The tar sampling for this run was between 134 and 231 minutes, and the tar sampling temperature exceeded 300  during this entire period.  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 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.  71     Molar concentration (%)  100 H2 N2 CO CH4 CO2 total  80  60  40  20  0 120  140  160  180  200  220  240  260  280  Run Time (minutes)     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.     72     H2 CO CH4 CO2  Molar concentration (%)  60  40  20  0 120  140  160  180  200  220  240  260  280  Run time (minutes)  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.  73     Table 6-3 Steady state gas concentrations for run with 100% wood pellets and for 130-231 min period Total 22.8 51.5 16.9 4.6 5.5  H2 N2 CO CH4 CO2  N2 free 45.7 0 34.2 9.3 10.8     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  60  870  55  865  50  860  45  855  40  850 N2 bed temperature  35  Temperature (C)  Molar concentration (%)  and 290 minutes.  845  30  840 120  140  160  180  200  220  240  260  280  Run Time (minutes)     Figure 6-13 Correlation of bed temperature to dry syngas production rate for run with 100% wood pellets    74     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.  900  100 H2 CO CH4 CO2 bed temperature  880  60  860  40  840  20  820  0  800 120  140  160  180  200  220  240  260  Temperature (C)  Molar concentration (%)  80  280  Run time (minutes)  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. 75     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.  76     Table 6-4 Characteristics of collected solids in cyclones for run with 100% wood pellets  Collected solid Mass  g  Primary  Secondary  cyclone  cyclone  116  52  0.2  0.21  Bulk specific gravity 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 77     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  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 78     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.    1000  800  Temperature (oC)  bed temperature  600  400  gasification period 200  0 0  100  200  300  Run Time(min) 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  in about an hour. 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 , but the bed 79     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 .    The tar sampling for this run was between 169 and 221 minutes, and the temperature of tar sampling was above 300  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.    80     100  Molar concentration (%)  80  60  H2 N2 CO CH4 CO2 total  40  20  0 150  200  250  300  Run Time (minutes)     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.  81     50  Molar concentration (%)  40  30  20  10  0 150  200  250  Run time (minutes)  300 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.  82     Table 6-5 Steady state gas concentrations for run with 100% biosolids and for 147-221 min period H2 N2 CO CH4 CO2  Total 8.71 73.3 10.1 4.7 3.3  N2 free 33.6 0 36.9 16.6 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.  83     Table 6-6 Characteristics of collected solids in primary cyclone for run with 100% biosolids Primary cyclone  Collected solid Mass  g  498  Bulk specific 0.44  gravity 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 84     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  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  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.      85     1000  Temperature (oC)  800  Bed temperature  600  400  gasification period  200  0 0  100  200  300  Run Time(min)  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   in   about an hour. 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  , and  each steady state period lasted about 20 minutes for data collection.    The tar sampling for this run lasted from 222 to 254 minutes, and the temperature of tar sampling exceeded 300  during this period. 86      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.    100  Molar concentration (%)  80  60 H2 N2 CO CH4 CO2 total  40  20  0 200  220  240  260  280  300  320  340  Run Time (minutes)  Figure 6-19 Gas concentrations of dry producer gases for run with 50% biosolids with 50% wood pellets by mass 87     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 H2 N2 CO CH4 CO2  Total 6.8 69.5 15.7 5.0 3.0  N2 free 22.5 0 51.3 16.4 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.  88     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 Primary cyclone  Collected solid Mass  g  461  Bulk specific 0.66  gravity 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  and maintained 89      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 . The tar sampling for this run lasted between 183 and 232 minutes, and the temperature of tar sampling exceeded 300  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.  90     100  Molar concentration (%)  80  60  H2 N2 CO CH4 CO2 total  40  20  0 160  180  200  220  240  260  Run Time (minutes)     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 H2 N2 CO CH4 CO2  Total 10.2 59.4 20.4 6.0 4.0  N2 free 25.2 0 50.2 14.7 9.9  91     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 Primary cyclone  Collected solid Mass  g  249  Bulk specific 0.33  gravity 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  92     run, the gap between the amounts of carbon in and out was very small, giving the best carbon balance.  93     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.  900  850 60  800 40  Temperature (C)  Molar concentration (%)  80  750  20 N2 bed temperature 0  700 200  220  240  260  280  300  320  340  Run Time (minutes)  Figure 7-1 Bed temperature and N2 concentration vs. time for run with 50% biosolids with 50% wood pellets by mass. 94     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 .  1.2  Syngas yield (m3/kg)  1.0  .8  .6  .4  .2 740  760  780  800  820  Temperature (C)  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.  95     100  900 H2 CO CH4 CO2 bed temperature  850  60 800 40  Temperature (C)  Molar concentration (%)  80  750 20  0  700 200  220  240  260  280  300  320  340  Run time (minutes)  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.  96     Gas molar concentration (%)  60  50  40  H2 CO CH4 CO2  30  20  10  0 740  760  780  800  820  Temperature ( C )     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 , 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,  97     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 2  1  5  4  3  0  10  25  50  100  silica  silica  silica  silica  silica  Bed material  sand  sand  sand  sand  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 ( )  855  857  828  825  854  Run no. Biosolids proportion in fuel (%) by mass Operating conditions  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 . These 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 . 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  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 98     after the system change, corresponding to bed temperature of 855 and 826 , 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! Reference  ource not found.. 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℃, lower than in runs 1 to 3, ~855℃. 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.  99     60  Gas molar concentrations (%)  (a) Temperature 855 C  50  40 H2 CO CH4 CO2  30  20  10  0 0  20  40  60  80  100  Biosolids proportion (%) in fuel     60  Gas molar concentrations (%)  (b) Temperature 826 C H2 CO CH4 CO2  50  40  30  20  10  0 0  20  40  60  Biosolids proportion (%) in fuel  80  100     Figure 7-5 Syngas composition vs. biosolids proportion in fuel, divided into a) for runs 1, 2, 3 b) for runs 4 and 5  100     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  12.67  12.56  14.34  14.77  14.25  Syngas LHV (MJ/Nm3)  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. 101     1.6 Syngas yield Char conversion  .8  .6  1.2  1.0 .4 .8  Char conversion  Syngas yield (m3/kg)  1.4  .2 .6  .4  0.0 0  20  40  60  80  100  Biosolids proportion (%) in fuel  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  102     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.  22000  250  Tar content in syngas NH3 concentration  200  18000 16000 14000  150 12000 10000 100 8000 6000 50  NH3 concentration (ppmv)  Tar content in syngas (g/Nm3)  20000  4000 2000  0  0 0  20  40  60  80  100  Biosolids proportion (%) in fuel  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 103     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%.     104     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 105     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.  Temperature did not affect syngas composition greatly for the limited range covered, but affected the syngas yield significantly, with syngas yield decreasing from 0.99 to 0.29 m3/kg as the bed temperature decreased from 825 to 728 .  As discussed above, the results may have been influenced by changes in the operating system between two sets of runs. Therefore, it is recommended that a complete set of experiments without any change in the experimental system be carried out in the future to produce more comparable results.  106     REFERENCES 1. Adams, D., Sperl, J., Daniel, J., Cook, T., Chipman, S. (2011) Biosolids Renewable Energy Project - Power Generation with Biosolids Colorado Springs Utilities. 2. Aigner, I., Pfeifer, C., Hofbauer, H. (2011) Co-gasification of Coal and Wood in a Dual fluidized bed Gasifier, Fuel, 90, 2404-2412. 3. Bi, H.T. and Grace, J.R. (1995) Flow Regime Diagrams for Gas-solid Fluidization and Upward Transport, International Journal of Multiphase Flow, 21, 1229-1236. 4. Bourgel, C., Véron, E., Poirier, J., Defoort, F., Seiler, J., Peregrina, C. (2011) Behavior of Phosphorus and Other Inorganics during the Gasification of Sewage Sludge, Energy&Fuel, 25, 5707-5717 5. Brown, R., Liu, Q., Norton, G. (2000) Catalytic Effects Observed During the Co-gasification of Coal and Switchgrass, Biomass & Bioenergy, 18, 499-506. 6. Chun, Y.N., Kim, S.C., Yoshikawa, K. (2011) Pyrolysis Gasification of Dried Sewage Sludge in a Combined Screw and Rotary Kiln Gasifier, Appl. Energy, 88, 1105-1112. 7. Dai, J., Sokhansanj, S., Grace, J.R., Bi, X., Lim, C.J., Melin, S. (2008) Overview and Some Issues Related to Co-firing Biomass and Coal, Canadian Journal of Chemical Engineering, 86, 367-3868. Franz, M. (2008) Phosphate Fertilizer from Sewage Sludge Ash (SSA), Waste Management, 28, 1809-1818. 9. Gomez, A., Zubizarreta, J., Rodrigues,M., Dopazo, C. and Fueyo, N. (2010) Potential and Cost of Electricity Generation from Human and Animal Waste in Spain, Renewable Energy, 35, 498-505. 10. Groß, B., Eder, C., Grziwa, P., Horst, J., Kimmerle, K. (2008) Energy recovery from Sewage Sludge by Means of Fluidized Bed Gasification, Waste Management, 28, 1819-1826 11. Higman, C., Burgt, M. (2008) Gasification, Burlington, MA, the USA, Elsevier Science.  107     12. Kirnbauer, F., Hofbauer, H. (2011), Investigations on Bed Material Changes in a Dual Fluidized Bed Steam Gasification Plant in G€ussing, Austria, Energy Fuels, 25, 3793-3798. 13. Leckner, B., Amanda, L., Luckeb, K., Wertherb, J. (2004) Gaseous Emissions from Co-combustion of Sewage Sludge and Coal/Wood in a Fluidized Bed, Fuel, 83, 477-486. 14. Mitsuoka, K., Hayashi, S., Amano, H., Kayahara, K., Sasaoaka, E., Uddin, M.A. (2011) Gasification of Woody Biomass Char with CO2: The Catalytic Effects of K and Ca Species on Char Gasification Reactivity, Fuel Processing Technology, 92, 26-31. 15. Nipattummakul, N., Ahmed, I., Kerdsuwan, S., Gupta, A. (2010) Hydrogen and Syngas Production from Sewage Sludge via Steam Gasification, International Journal of Hydrogen Energy, 35, 11738-11745. 16. Peng, L., Wang, Y., Lei, Z., Cheng, G. (2012) Co-gasification of Wet Sewage Sludge and Forestry Waste in Situ Steam Agent, Bioresource Technology, 114, 698-702. 17. Petersen, I., Werther, J. (2004) Experimental Investigation and Modeling of Gasification of Sewage Sludge in the Circulating Fluidized Bed, Chemical Engineering and Processing, 44, 717-736. 18. Pfeifer, C., Koppatz, S., Hofbauer, H. (2011) Steam Gasification of Various Feedstocks at a Dual Fluidized Bed Gasifier: Impacts of Operation Conditions and Bed material, Biomass Conv. Bioref., 1, 39-53. 19. Pinto, F., Lopes, H., Andre, R.N., Dias, M., Gulyurtlu, I., Cabrita, I. (2007) Effect of Experimental Conditions on Gas Quality and Solids Produced by Sewage Sludge Cogasification. 1. Sewage Sludge Mixed with Coal, Energy & Fuels, 21, 2737-2745. 20. Pinto, F., Andre, R.N., Lopes, H., Dias, M., Gulyurtlu, I., Cabrita, I. (2008) Effect of Experimental Conditions on Gas Quality and Solids Produced by Sewage Sludge Cogasification. 2. Sewage Sludge Mixed with Biomass, Energy & Fuels, 22, 2314-2325. 21. Rhee, S., Yoo, H. (2010) Evaluation on the Property of Sewage Sludge Cake by Thermal Treatment, Journal of Material Cycles and Waste Management, 12, 240-244. 108     22. Rirksomboon, T., Thipkhunthod, P., Meeyoo, V., Kitiyanan, B., Siemanond, K., Rangsunvigit, P. (2006) Pyrolytic Characteristics of Sewage Sludge, Chemosphere, 64, 955-962. 23. Saw, W., McKinnon, H., Gilmour, I., Pang, S. (2011) Production of Hydrogen-rich Syngas from Steam Gasification of Blend of Biosolids and Wood Using a Dual Fluidised Bed Gasifier, Fuel, 93, 473-478. 24. Seo, M., Goo, J., Kim, S., Lee, S., Choi, Y. (2010) Gasification Characteristics of Coal/Biomass Blend in a Dual Circulating Fluidized Bed Reactor, Energy Fuels, 24, 3108-3118. 25. Simbeck, D. (2007) Gasification opportunities in Alberta, Gasification Technologies, Alberta Government and GTC, Edmonton. 26. Slack, A.V. and James, G.R. (1973 ) Ammonia, Part I, New York : Marcel Decker. 27. Watkinson P., Li, Y., Haligva, J. (2010) IRAP Project 709261 “High Grade synfuels –Phase 1” Report to Accompany Final Claim. 28. Wilk, V., Kitzler, H., Koppatz, S., Pfeifer, C., Hofbauer, H. (2011) Gasification of Waste Wood and Bark in a Dual Fluidized Bed Steam Gasifier, Biomass Conv. Bioref, 1, 91-97. 29. Xu, S., Zhou, Z., Gao, X., Yu, G., Gong, X. (2009) The Gasification Reactivity of Unburned Carbon Present in Gasification Slag from Entrained-Flow Gasifier, Fuel Processing Technology, 90, 1062-1070. 30. Zhang, Q., Liu, H., Li, W., Xu, J., Liang, Q. (2012) Behavior of Phosphorus during Co-gasification of Sewage Sludge and Coal, Energy&Fuel, 26, 2830-2836 31. Zhu, W., Song, W., Lin, W. (2008) Catalytic Gasification of Char from Co-pyrolysis of Coal and Biomass, Fuel Processing Technology, 89, 890-896.  109     APPENDIX: SUPPLEMENTAL RESULTS FROM BUBBLING FLUIDIZED BED GASIFICATION                      110     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 111     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  112        1000  Temperature (oC)  800  600  400  200  0 0  50  100  150  Run Time(min)  200  250  300  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  113     400  Temperature (oC)  300  200  100  0 0  50  100  150  Run Time(min)  200  250  300  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  114     10  P2 and P3 (kPa)  8  6 P2 P3  4  2  0 0  50  100  150  200  250  300  Run Time (min)  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.  115     1000  Temperature (oC)  800  600  400  200  0 0  50  100  150  200  Run Time(min)  250  300  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  116     400  Temperature (oC)  300  200  100  0 0  50  100  150  200  Run Time(min)  250  300  Tar Sampling,T5 Cooler Inlet,T6 Cooler 1 Oulet,T7 Cooler 2 Outlet,T9 Baghouse,T14     Figure A6: Temperature profiles of the downstream syngas for run with 100% wood pellets    117     10  dP1(kPa)  8  6  4  2  0 0  50  100  150  200  250  300  Run Time(min) Figure A7: Pressure drop in reactor for run with 100% wood pellets    118     10  P2 and P3 (kPa)  8  6 P2 P3 4  2  0 0  50  100  150  200  250  300  Run Time (min)  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.  119     10  Steam Flow Rate (kg/h)  8  6  4  2  0 0  50  100  150  200  250  300  Run Time(min) Figure A9: Steam flow rate for run with 100% wood pellets  120     1000  Temperature (oC)  800  600  400  200  0 0  100  200  Run Time(min)  300 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 A10: Temperature profiles of gasifier for run with 100% biosolids  121     500  Temperature (oC)  400  300  200  100  0 0  100  200  Run Time(min)  300 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  122     900  800  700  600  500  400  300 0  50  100  Feeding Time(min)  150  200  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  123     8  dP1(kPa)  6  4  2  0 0  100  200  300  Run Time (min)  Figure A13: Pressure drop in reactor for run with 100% biosolids  124     10  P2 and P3 (kPa)  8  6 P2 P3 4  2  0 0  100  200  300  Feed Time (min) 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.  125     10  Steam Flow Rate (kg/h)  8  6  4  2  0 0  100  200  300  Run Time (min)  Figure A15: Steam flow rate for run with 100% biosolids  126     900  80  860  60  840  Temperature (C)  molar concentration (%)  880  40 820 N2 bed temperature 20  800 150  200  250  300  Run Time (minutes)  Figure A16: Bed temperature and N2 concentration vs. time for run with 100% biosolids  127     100  900 H2 CO CH4 CO2 bed temperature  880  60  860  40  840  20  820  0  Temperature (C)  molar concentration (%)  80  800 150  200  250  300  Run time (minutes)  Figure A17: Bed temperature and syngas composition versus run time for run with 100% biosolids  128     1000  Temperature (oC)  800  600  400  200  0 0  100  200  Run Time(min)  300 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 A18: Temperature profiles of gasifier for run with for run with 50% biosolids with 50% wood pellets by mass  129     400  Temperature (oC)  300  200  100  0 0  100  200  Run Time(min)  300 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  130     10  dP1(kPa)  8  6  4  2  0 0  100  200  300  Run Time(min) Figure A20: Pressure drop in reactor for run with 50% biosolids with 50% wood pellets by mass  131     14  P2 and P3 (kPa)  12 10 8 P2 P3  6 4 2 0 0  100  200  300  Run Time (min)  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.  132     10  Steam Flow Rate (kg/h)  8  6  4  2  0 0  100  200  300  Run Time(min) Figure A22: Steam flow rate for run with 50% biosolids with 50% wood pellets by mass  133     60  molar concentration (%)  50  40  H2 CO CH4 CO2  30  20  10  0 200  220  240  260  280  300  320  340  Run time (minutes) Figure A23: Nitrogen-free syngas composition for run with 50% biosolids with 50% wood pellets by mass  134     1000  Temperature (oC)  800  600  400  200  0 0  50  100  150  200  Run Time(min)  250  300  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 A24: Temperature profiles of gasifier for run with 25% biosolids with 75% wood pellets by mass  135     350  Temperature (oC)  300  250  200  150  100  50  0 0  50  100  150  Run Time(min)  200  250  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  136     10  dP1(kPa)  8  6  4  2  0 0  50  100  150  200  250  Run Time(min) Figure A26: Pressure drop in reactor for run with 25% biosolids with 75% wood pellets by mass  137     14  P2 and P3 (kPa)  12 10 8  P2 P3  6 4 2 0 0  50  100  150  200  250  Run Time (min)  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.  138     10  Steam Flow Rate (kg/h)  8  6  4  2  0 0  50  100  150  200  250  Run Time(min) Figure A28: Steam flow rate for run with 25% biosolids with 75% wood pellets by mass  139     60 H2 CO CH4 CO2  molar concentration (%)  50  40  30  20  10  0 180  200  220  240  260  Run time (minutes)  Figure A29: Nitrogen-free dry syngas composition for run with 25% biosolids with 75% wood pellets by mass  140     900 880 860 840  60  820 800  Temperature (C)  molar concentration (%)  80  40 780 N2 bed temperature  760  20 160  180  200  220  240  260  Run Time (minutes)  Figure A30: Bed temperature an N2 concentration vs. time for run with 25% biosolids with 75% wood pellets by mass  141     100  900 H2 CO CH4 CO2 bed temperature  880  60  860  40  840  20  820  0  800 160  180  200  220  240  Temperature (C)  molar concentration (%)  80  260  Run time (minutes)  Figure A31: Bed temperature and syngas composition versus run time for run with 25% biosolids with 75% wood pellets by mass  142     Table A1: Results for run with 10% biosolids with 90% wood pellets by mass a) Gas composition H2 N2 CO CH4 CO2  Total 19.1 55.0 16.0 4.4 5.5  N2 free 42.6 0 35.4 9.7 12.3     b) Syngas yield Time period 12:30-2: 30pm  N2( m3) 3.48  N2 concentrati Total on gas(m3) 54.98  Syngas (m3)  6.33  2.85  Feed Time rate(kg/h) (h) 1.27  2.00  Syngas yield( m3/kg ) 1.12  c) Heating value of the syngas  H2 CO CH4 Total  Specific heat values(MJ/m3) 10.798 12.636 35.818  N2 free molar LHV percentage (MJ/m3) 0.4256 4.60 0.3544 4.48 0.0972 3.48 12.56  d) Tar content in the syngas N2 content Total Producer in weight gas producer Syngas Tar in of tar(g) collected(L) gas collected(m3) syngas(g/m3) 0.29 267.10 53.32 0.12 2.33  e) Ammonia concentration determination Absorption part Volume Volume H2SO4 in after concentr bottle(m Mol H2SO4 absorption ation(N) L) in absorbent (mL) 1 150 0.075 210 143     Titration part Absorbe nt NaOH Mol Mol volume( concentr NaOH NaOH H2SO4 mL) ation(N) titrated(mL) titrated titrated 4.1 0.1 25.8 0.00258 0.00129 4.2 0.1 27.6 0.00276 0.00138 Back titration part Mol H2SO4 H2SO4 Volume conc in in Mol H2SO4 Mol ammonia absorben absorben reacted with ammonia captured(m t t ammonia captured 3) 0.322 0.0676 0.0075 0.0149 0.000335  H2SO4 conc in absorbent( M) 0.315 0.329  Collected syngas volume(m 3) 0.125  Ammon ia conc(pp mv) 2690  f) Char conversion  Volatiles (%) Fixed Carbon (%) Ash (%) Char conversion  Feedstock dry volatile free 83.4 14.4 2.07  Cycloned solids dry volatile free 6.7  87.4 12.5  58.5 34.6  62.8 37.1  0.66  g) Carbon balance Carbon IN Carbon content in Total carbon Feed rate(kg/h) Time(hours) feedstock in(kg) 1.26 2 0.49 1.22 Carbon out Carbon in Syngas Volume of gas(m3)  Conc(%) Syngas produced total(m3) CO2 CO  12.2 35.4  2.8 0.343 0.992  Mol of gas 114 14.0 40.4  Mol of Carbon in gas  Weight of carbon (kg)  14.0 40.4  0.168 0.485 144      CH4 Total carbon Carbon in cyclone  Mol of Weight of Volume of Carbon in carbon Conc(%) gas(m3) Mol of gas gas (kg) 9.72 0.272 11.0 11.0 0.133 0.786 Primary cyclone  Secondary cyclone Total carbon 0.542 0.0173  Solid weight(kg) Carbon content % 60.8 55.9 Weight of carbon(kg) 0.330 0.00968 0.340 Carbon in tar Tar content in Carbon the Syngas content in tar Weight of syngas(g/m3) produced(m3) Total tar(g) (%) carbon(kg) 2.4 2.8 6.72 0.913 0.00613 Carbon out Total C(kg) 1.13  145     Table A2: Results for run with 100% wood pellets a) Gas composition H2 N2 CO CH4 CO2  Total 22.1 51.6 16.7 4.5 5.1  N2 free 45.7 0 34.7 9.4 10.2  b) Syngas yield Time period 11:58-1: 58pm  N2( m3)  N2 concentrat ion  Total gas(m3)  3.72  51.59  7.21  Syngas (m3)  Feed rate(kg/h )  Time(h)  Syngas yield( m 3/kg)  3.49  1.27  2.00  1.37  c) Heating value of the syngas  H2 CO CH4 Total  Specific heat values(MJ/m3) 10.798 12.636 35.818  N2 free molar LHV percentage (MJ/m3) 0.4569 4.93 0.3472 4.39 0.0936 3.35 12.67  d) Tar content in the syngas N2 content Total Producer in weight gas producer Syngas Tar in of tar(g) collected(L) gas collected(m3) syngas(g/m3) 2.02 400 50.86 0.197 10.3  e) Ammonia concentration determination Absorption part Volume Volume H2SO4 in after concentr bottle(m Mol H2SO4 absorption ation(N) L) in absorbent (mL) 1 110 0.055 155 146     Titration part Absorbe nt NaOH Mol Mol volume( concentr NaOH NaOH H2SO4 mL) ation(N) titrated(mL) titrated titrated 4.6 0.1 29 0.0029 0.00145 4.9 0.1 29.6 0.00296 0.00148 4.6 0.1 28.4 0.00284 0.00142 4.9 0.1 30 0.003 0.0015 Back titration part Mol H2SO4 H2SO4 Volume conc in in Mol H2SO4 Mol ammonia absorben absorben reacted with ammonia captured(m t t ammonia captured 3) 0.308 0.047 0.00725 0.0145 0.000326  H2SO4 conc in absorbent( M) 0.315 0.302 0.308 0.306  Collected syngas volume(m 3) 0.196  Ammon ia conc(pp mv) 1660  f) Char conversion  Volatiles (%) Fixed Carbon (%) Ash (%) Char conversion  Feedstock dry volatile free 83.5 15.3 1.09  93.3 6.6  Cycloned solids dry volatile free 26.9 46.5 26.5  63.7 36.2  0.82  147     g) Carbon balance Carbon IN Carbon content in Total carbon Feed rate(kg/h) Time(hours) feedstock in(kg) 1.3 2 0.48 1.24 Carbon out Carbon in Syngas Volume of gas(m3)  Conc(%) Syngas produced total(m3) CO2 CO CH4 total carbon Carbon in cyclone  10.2 34.7 9.36  Primary cyclone  3.5 0.358 1.21 0.327  Mol of gas 142 14.5 49.5 13.3  Mol of Carbon in gas  Weight of carbon (kg)  14.5 49.5 13.3  0.175 0.594 0.160 0.929  Secondary cyclone Total carbon 0.115 0.0516  Solid weight(kg) Carbon content % 43.7 45.5 Weight of carbon(kg) 0.0506 0.0234 0.074 Carbon in tar Tar content in Carbon the Syngas content in tar Weight of syngas(g/m3) produced(m3) Total tar(g) (%) carbon(kg) 10.4 3.5 36.4 0.913 0.033 Carbon out Total C(kg) 1.03  148     Table A3: Results for run with 100% biosolids a) Gas composition Total 8.71 73.3 10.1 4.7 3.3  H2 N2 CO CH4 CO2  N2 free 33.6 0 36.9 16.6 12.9  b) Syngas yield Time p eriod 10:56-1 2:16 12:16-1 2:44 12:44-1 :18 1:18-1: 45 1:45-2: 13  N2 N2( concentrati m3) on  Total gas(m3)  Syngas Feed Time Syngas (m3) rate(kg/h) (h) yield( m3/kg)  2.56  73.27  3.49  0.93  1.50  1.33  0.47  0.91  84.46  1.08  0.17  0.70  0.47  0.51  1.13  80.13  1.41  0.28  1.50  0.57  0.33  0.81  68.88  1.17  0.37  1.90  0.45  0.43  0.87  84.03  1.04  0.17  1.20  0.47  0.30  c) Heating value of the syngas Time period (min)  14.1-88.3 91.8-116.5 120-148.2 151.7-176.3 179.9-204.6 14.1-88.3 91.8-116.5 120-148.2 151.7-176.3 179.9-204.6  Specific heat values(MJ/m3) N2 free molar % N2 free molar % N2 free molar % N2 free molar % N2 free molar % LHV (MJ/m3) LHV (MJ/m3) LHV (MJ/m3) LHV (MJ/m3) LHV (MJ/m3)  H2  CO  CH4  10.798 33.58 34.94 38.96 31.35 41.63 3.63 3.77 4.21 3.39 4.50  12.636 36.89 33.98 34.48 36.97 29.74 4.66 4.29 4.36 4.67 3.76  35.818 16.63 12.68 12.45 16.93 8.40 5.96 4.54 4.46 6.06 3.01  CO2  Total  12.89 18.32 14.05 14.72 20.23 14.25 12.61 13.03 14.12 11.26 149      d) Tar content in the syngas N2 content Total in weight Producer gas producer Syngas Tar in of tar(g) collected(L) gas collected(m3) syngas(g/m3) 10.6 196.8 73.23 0.053 200  e) Ammonia concentration determination Absorption part Volume Volume H2SO4 in after concentr bottle(m Mol H2SO4 absorption ation(N) L) in absorbent (mL) 1 106 0.053 106 Titration part Absorbe nt NaOH Mol Mol volume( concentr NaOH NaOH H2SO4 mL) ation(N) titrated(mL) titrated titrated 4.2 0.1 24.8 0.00248 0.00124 4 0.1 23 0.0023 0.00115 4.2 0.1 24 0.0024 0.0012 4 0.1 22.6 0.00226 0.00113 Back titration part Mol H2SO4 H2SO4 Volume conc in in Mol H2SO4 Mol ammonia absorben absorben reacted with ammonia captured(m t t ammonia captured 3) 0.287 0.0305 0.0225 0.045 0.001011  M=N/n H2SO4 conc in absorbent( M) 0.295 0.287 0.285 0.282  Collected syngas volume(m 3) 0.0526  Ammon ia conc(pp mv) 19200  150     f) Char conversion  Volatiles (%) Fixed Carbon (%) Ash (%) Char conversion  Feedstock dry volatile free 82.28 6.82 10.9  38.4 61.5  Cycloned solids dry volatile free 9.75 4.23 86.0  4.68 95.3  0.35  g) Carbon balance Carbon IN Carbon Total content in carbon Feed weight(kg) feedstock in(kg) 4.65 0.55 2.56 Carbon out Carbon in Syngas Volume of 10:56-12:16 Conc(%) gas(m3) Mol of gas Syngas produced total(m3) 0.933 38.0 CO 36.8 0.344 14.0 CH4 16.6 0.155 6.33 CO2 12.8 0.12 4.90 Total carbon Volume of 12:16-12:44 Conc(%) gas(m3) Mol of gas Syngas produced total(m3) 0.168 6.84 CO 33.9 0.05708 2.32 CH4 12.6 0.0213 0.868 CO2 18.3 0.0307 1.25 Total carbon Volume of 12:44-1:18 Conc(%) gas(m3) Mol of gas Syngas produced total(m3) 0.28 11.4  Mol of Carbon in gas  14.0 6.33 4.90 Mol of Carbon in gas  2.32 0.86 1.25 Mol of Carbon in gas  Weight of carbon (kg)  0.168 0.076 0.0589 0.244 Weight of carbon (kg)  0.0279 0.0104 0.0150 0.0383 Weight of carbon (kg)  151     CO CH4 CO2 Total carbon  1:18-1:45 Syngas produced total(m3) CO CH4 CO2 Total carbon  Volume Mol of Weight of of Carbon in carbon Conc(%) gas(m3) Mol of gas gas (kg) 34.4 0.0965 3.93 3.93 0.0472 12.4 0.034 1.42 1.42 0.0170 14.0 0.039 1.604 1.60 0.0192 0.0643 Volume Mol of Weight of of Carbon in carbon Conc(%) gas(m3) Mol of gas gas (kg)  36.9 16.9 14.7  1:45-2:13 Conc(%) Syngas produced total(m3) CO 29.7 CH4 8.40 CO2 20.2 Total carbon Carbon in cyclone Primary cyclone Solid weight(kg) 0.497 Carbon content % 4.18 Weight of carbon(kg) 0.0207 Carbon in tar Tar content in the Syngas syngas(g/m3) produced(m3) 200.3 2.03 Carbon out Total C(kg) 0.866  0.365 0.134 0.0617 0.0537 Volume of gas(m3)  14.8 5.50 2.51 2.19  Mol of gas  0.165 0.0490 0.0138 0.0334  6.72 2.00 0.565 1.36  5.50 2.51 2.19 Mol of Carbon in gas  2.00 0.565 1.36  0.066 0.0302 0.0262 0.0962 Weight of carbon (kg)  0.024 0.00678 0.0163 0.0307  Secondary cyclone Total carbon 0 0 0  0.0207  Carbon Total content in tar Weight of tar(g) (%) carbon(kg) 407 0.9130 0.371  152     Table A4: Results for run with 50% biosolids with 50% wood pellets by mass a) Gas composition H2 N2 CO CH4 CO2  Total 6.8 69.5 15.7 5.0 3.0  N2 free 22.5 0 51.3 16.4 9.9  b) Syngas yield Time period 1:14-2: 00 2:05-2: 26 2:32-2: 52 3:01-3: 27  N2 N2( concentrati m3) on  Total gas(m3)  Syngas Feed Time (m3) rate(kg/h) (h)  Syngas yield( m3/kg)  2.24  69.54  3.22  0.98  1.29  0.77  0.99  1.04  77.48  1.34  0.30  1.29  0.35  0.67  1.01  78.27  1.29  0.28  1.29  0.33  0.65  1.33  89.17  1.49  0.16  1.29  0.43  0.29  c) Heating value of the syngas Time period (min)  1:14-2:00 2:05-2:26 2:32-2:52 3:01-3:27 1:14-2:00 2:05-2:26 2:32-2:52 3:01-3:27  Specific heat values(MJ/m3) N2 free molar % N2 free molar % N2 free molar % N2 free molar % LHV (MJ/m3) LHV (MJ/m3) LHV (MJ/m3) LHV (MJ/m3)  H2  CO  CH4  10.798 22.4 23.5 21.1 23.1 2.43 2.54 2.28 2.50  12.636 51.2 49.4 52.0 47.7 6.48 6.25 6.57 6.03  35.818 16.3 15.2 15.4 13.1 5.86 5.46 5.52 4.73  CO2  Total  9.85 11.6 11.3 15.8 14.77 14.26 14.38 13.26  153     d) Tar content in the syngas N2 content Total Producer in weight gas producer Syngas Tar in of tar(g) collected(L) gas collected(m3) syngas(g/m3) 2.31 122 70.1 0.037 63.1  e) Ammonia concentration determination Absorption part Volume Volume H2SO4 in after concentr bottle(m Mol H2SO4 absorption ation(N) L) in absorbent (mL) 1 128 0.064 158 Titration part Absorbe nt NaOH Mol Mol volume( concentr NaOH NaOH H2SO4 mL) ation(N) titrated(mL) titrated titrated 4.7 0.1 36.4 0.00364 0.00182 4.8 0.1 35.2 0.00352 0.00176 4.6 0.1 33.6 0.00336 0.00168 5 0.1 35.8 0.00358 0.00179 Back titration part Mol H2SO4 H2SO4 Volume conc in in Mol H2SO4 Mol ammonia absorben absorben reacted with ammonia captured(m t t ammonia captured 3) 0.369 0.0583 0.00565 0.0113 0.000254  H2SO4 conc in absorbent( M) 0.387 0.366 0.365 0.358  Collected syngas volume(m 3) 0.0366  Ammon ia conc(pp mv) 6940  f) Char conversion  Volatiles (%) Fixed Carbon (%) Ash (%) Char conversion  Feedstock dry 82.9 11.0 5.99 0.59  Cycloned solids volatile free dry volatile free 11.6 64.8 11.8 13.4 35.1 76.5 86.5  154     g) Carbon balance Carbon IN Total Carbon content carbon Time (hour) in feedstock in(kg) 1.28 2.28 0.51 1.51 Carbon out Carbon in Syngas 1:07-1:58 Feed weight(kg)  Volume of gas(m3)  Conc(%) Syngas produced total(m3) CO CH4 CO2 Total carbon 1:58-2:23  51.2 16.3 9.85  Volume of gas(m3)  Conc(%) Syngas produced total(m3) CO CH4 CO2 Total carbon 2:23-2:49  49.4 15.2 11.6  0.359 0.177 0.0548 0.0420  Volume of gas(m3)  Conc(%) Syngas produced total(m3) CO CH4 CO2 Total carbon  1.08 0.55 0.177 0.107  52.0 15.4 11.3  0.363 0.189 0.0559 0.0414  Mol of gas  44.3 22.7 7.25 4.36  Mol of gas  14.6 7.25 2.23 1.71  Mol of gas  14.8 7.70 2.28 1.68  Mol of Carbon in gas  22.7 7.25 4.36  Mol of Carbon in gas  7.25 2.23 1.71  Mol of Carbon in gas  7.70 2.28 1.68  Weight of carbon (kg)  0.272 0.087 0.0524 0.359  Weight of carbon (kg)  0.0870 0.0268 0.0205 0.114  Weight of carbon (kg)  0.0924 0.027 0.0202 0.119  2:49-3:24 155     Conc(%)  Volume of gas(m3)  Mol of gas  Mol of Carbon in gas  Syngas produced total(m3) 0.217 8.86 CO 47.7 0.103 4.23 4.23 CH4 13.1 0.0287 1.17 1.17 CO2 15.8 0.0345 1.40 1.40 Total carbon Carbon in cyclone Primary Secondary Total cyclone cyclone carbon Solid weight(kg) 0.460 Carbon content % 11.8 Weight of carbon(kg) 0.0543 0 0.0543 Carbon in tar carbon Tar content in syngas content in weight of syngas(g/m3) produced(m3) total tar(g) tar carbon(kg) 63.06 2.02 127 0.9130 0.116 Carbon out Total C(kg) 0.829  Weight of carbon (kg)  0.050 0.0140 0.016 0.064  156     Table A5: Results for run with 25% biosolids with 75% wood pellets by mass a) Gas composition H2 N2 CO CH4 CO2  Total 10.2 59.4 20.4 6.0 4.0  N2 free 25.2 0 50.2 14.7 9.9  b) Syngas yield Time period 1:20-2: 13  N2 N2( concentrati m3) on 2.42  Total gas(m3)  59.36  4.08  Syngas Feed Time (m3) rate(kg/h) (h) 1.66  1.47  0.88  Syngas yield( m3/kg) 1.28  c) Heating value of the syngas Specific heat values(MJ/m3) H2 10.798 CO 12.636 CH4 35.818 CO2 Total  N2 free LHV molar % (MJ/m3) 25.18 2.72 50.20 6.34 14.73 5.28 9.87 14.34  d) Tar content in the syngas N2 content Total Producer in weight gas producer Syngas Tar in of tar(g) collected(L) gas collected(m3) syngas(g/m3) 2.0 135 59.36 0.055 36.5  157     e) Ammonia concentration determination Absorption part Volume Volume H2SO4 in after concentr bottle(m Mol H2SO4 absorption ation(N) L) in absorbent (mL) 1 102 0.051 123 Titration part Absorbe nt NaOH Mol Mol volume( concentr NaOH NaOH H2SO4 mL) ation(N) titrated(mL) titrated titrated 4.3 0.1 32 0.0032 0.0016 4.5 0.1 33 0.0033 0.00165 4.5 0.1 32 0.0032 0.0016 Back titration part Mol H2SO4 H2SO4 Volume conc in in Mol H2SO4 Mol ammonia absorben absorben reacted with ammonia captured(m t t ammonia captured 3) 0.364 0.0448 0.00613 0.0122 0.000276  H2SO4 conc in absorbent( M) 0.372 0.366 0.355  Collected syngas volume(m 3) 0.0550  Ammon ia conc(pp mv) 5010  f) Char conversion  Volatiles (%) Fixed Carbon (%) Ash (%) Char conversion  Feedstock dry volatile free 83.2 13.2 3.54  78.8 21.1  Cycloned solids dry volatile free 9.7 24.3 65.8  27.0 72.9  0.71  g) Carbon balance Carbon IN Carbon content in Total carbon Feed rate(kg/h) Time(hours) feedstock in(kg) 1.47 1.46 0.53 1.14 Carbon out 158     Carbon in Syngas Volume of gas(m3)  Conc(%) Syngas produced total(m3) CO2 CO CH4 Total carbon Carbon in cyclone  10.2 34.7 9.36  Primary cyclone  3.49 0.357 1.21 0.32  Secondary cyclone  Mol of gas 142.3 14.5 49.4 13.3  Mol of Carbon in gas  Weight of carbon (kg)  14.5 49.4 13.3  0.174 0.593 0.159 0.927  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 Carbon the Syngas content in tar Weight of syngas(g/m3) produced(m3) Total tar(g) (%) carbon(kg) 49.95 3.49 174 0.9130 0.159 Carbon out Total C(kg) 1.14  159     Table A6: Results about impact of feed rate on gasification performance in run with 100% biosolid in feed Run No Date  3  3  3  3  3  Oct 12  Oct 12  Oct 12  Oct 12  Oct 12  100%BS 100%BS 100%BS 100%BS 100%BS  Feedstock  silica  silica  silica  silica  silica  sand  sand  sand  sand  sand  1.50  0.73  1.50  1.91  1.22  80  28  34  27  28  3.43  3.42  3.41  3.42  3.41  2.29  4.69  2.27  1.79  2.80  Avg bed temperature  854  837  860  842  854  Free board temperature  824  814  826  835  841  0.91  1.03  1.13  0.85  1.40  14.25  12.61  13.03  14.12  11.26  0.47  0.51  0.33  0.43  0.30  0.47  0.47  0.47  0.47  0.47  1.50  0.77  1.06  1.74  0.76  2.29  4.44  3.22  1.97  4.49  Bed material Biomass feed rate  kg(dry)/h  Feed time  minutes  Steam rate  kg/h  Steam/biomass mass ratio  Syngas H2/CO molar ratio Syngas LHV  MJ/m3 m3/kg(dry  Syngas yield  feedstock)  Assume syngas yield constant Feed rate based on assumption Steam/biomass ratio based on assumption Tar content in syngas  g/m3  200.3  Ammonia concentration  ppmv  19200  160     Table A7: Results about impact of temperature on gasification performance in run with 50% biosolids with 50% wood pellets 209-256 Run time (min) Bed Temperature 825.35 ( ) Syngas yield 0.99 (m3/kg) Syngas composition (molar %) 22.5 H2 51.3 CO 16.4 CH4 9.9 CO2  261-281  287-307  316-342  803.23  770.70  728.26  0.67  0.65  0.29  23.6 49.5 15.3 11.7  21.1 52.0 15.4 11.4  23.2 47.8 13.2 15.9  161     Table A8: Results about impact of feedstock composition on gasification performance Run no. Biosolids proportion in fuel (%) Operating conditions Bed material Feed rate (kg/h) Steam feed rate (kg/h) Steam/fuel mass ratio Bed temperature (℃) syngas composition (%) H2 CO CH4 CO2 H2/CO ratio Syngas LHV (MJ/Nm3) Syngas yield (m3/kg) Char conversion Tar content (g/m3) Ammonia concentration (ppmv)  2  1  5  4  3  0  10  25  50  100  silica sand 1.27 3.48 2.74 855  silica sand 1.27 4.04 3.18 857  silica sand 1.47 3.28 2.23 828  silica sand 1.29 3.52 2.73 825  silica sand 1.5 3.43 2.29 854  45.7 34.7 9.36 10.2 1.32 12.67 1.38 0.817 10.3  42.6 35.4 9.72 12.3 1.20 12.56 1.10 0.663 2.33  25.2 50.2 14.7 9.87 0.50 14.34 1.28 0.71 36.0  22.5 51.3 16.4 9.86 0.44 14.77 0.99 0.594 63.1  33.6 36.9 16.6 12.9 0.91 14.25 0.47 0.355 200.3  1660  2690  5010  6940  19200  162     

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