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Handbook of BiomassDowndraft GasifierEngine SystemsSERIISP-271-3022DE88001135March 1988UC Category.' 245This handbook has been prepared by the Solar Energy Research Institute under the U.S.Department of Energy Solar Technical Information Program. It is intended as a guideto the design, testing, operation, and manufacture of small-scale [less than 200 kW(270 hpJ] gasifiers. A great deal of the information will be useful for all levels of biomassgasification.The handbook is meant to be a practical guide to gasifier systems, and a minimumamount of space is devoted to questions of more theoretical interest.We apologize in advance for mixing English and Scientifique Internationale (SI) units.Whenever possible, we have used SI units, with the corresponding English units fol lowing in parentheses. Unfortunately, many of the figures use English units, and itwould have been too difficult to convert all of these figures to both units. We have sup plied a conversion chart in the Appendix to make these conversions easier for thereader.Mr. Bill Nostrand, one of our very helpful reviewers, died in May 1985. Bill was num ber one in the ranks of those who became interested in gasification because of its poten tial for supplying clean, renewable energy. We all will miss him. The improvement ofgasification systems will be noticeably slowed by his death.We dedicate this book to the Bill Nostrands of this world who will bring gasifier systemsto the level of safety, cleanliness, and reliability required to realize their full potential.Thanks, Bill.T B. Reed and A. DasGolden, ColoradoA Product of theSolar Technical Information ProgramSolar Energy Research Institute1 617 Cole Boulevard, Golden, Colorado 80401-3393A Division of Midwest Resea rch InstituteU.S. Department of EnergyOperated for the

AcknowledgmentsSince it is impossible for one or two authors to realistically comprehend a subject from all viewpoints, we havesolicited input from leading workers in the field. Early versions were sent to a number of investigators, and eachwas invited to comment on and supplement our effort. We therefore express our heartfelt thanks to the followingreviewers for greatly enhancing the quality of the final product:Dr. Thomas Milne, Solar Energy Research InstituteDr. Bjorn Kjellstrom, The Beijer Institute, SwedenDr. Thomas McGowan, Georgia Institute of Technology Dr. Hubert Stassen, Twente University, The NetherlandsProf. Ibarra Cruz, University of Manila, The PhilippinesMr. Matthew Mendis, World BankMr. Bill Nostrand, New England Gasification AssociatesWe take final responsibility for the contents and omissions, and extend our apologies to those workers whose workwe may have unknowingly omitted.Organization and UseA gasifier converts solid fuel to gaseous fuel. A gasifier system includes the gasification reactor itself, along withthe auxiliary equipment necessary to handle the solids, gases, and effluents going into or coming from the gasifier.The figure below shows the major components of a gasifier system and the chapters in which they are discussed.FuelCh.3GasmeasurementandcleaningCh. 7, 8GasifierCh.4, 5, 6Engine(or com bustor)Ch. 1 1Whole.systemCh. 9, 1 0--,l.NoticeThis report was prepared as an account of work sponsored by an agency of the United States government. Neither the United States govern ment nor any agency thereof. nor any of their employees, makes any warranties, express or implied. or assumes any legal liability or respon sibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its usewould not infringe privately owned rights. Reference herein to any specific"commercial product, process, or service by trade name, trademark,manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States govern ment or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United Statesgovernment or any agency thereof.Printed in the United States of AmericaAvailable from:Superintendent of DocumentsU.S. Government Printing OfficeWashington, DC 20402National Technical Information ServiceU.S. Department of Commerce5285 Port Royal RoadSpringfield, VA 22161Price: Microfiche A01Printed Copy A07Codes are used for pricing all publications, The code is determined by the number of pages in the publication, Information pertaining to thepricing codes can be found in the current issue of the following publications which are generally available in most libraries: Energy ResearchAbstmcts (ERA); Government Reports Announcements and Index (GRA and I) Scientific and Technical Abstmct Reports (STAR); and publica tion NTIS-PR-360 available from NTIS at the above address.

Contents112333344441 .0 Introduction and Guide to the Literature and Research1.1 Role of Gasification in Biomass Conversion1.2 Biomass Energy Potential . . . .1.3 Guide to Gasification Literature1.3.1 Bibliographies . . . . .1.3.2 Books . . . . . . . . . .1.3.3 Gasification Proceedings1.3.4 Commercial Information1.3.5 Producer Gas Research1.3.6 Producer Gas R&D Funding1.3.7 Federal Emergency Management Agency (FEMA) Gasifier Work6666772.1 Historical Development . . . . . . . . . . .2.1.1 Early Development of Gasification2.1.2 Vehicle Gasifiers . . . .2.2 Current Development Activities2.3 Future Development Directions2.0 H istory, Current Developments, and Future Directions3.0 Gasifier Fuels3.1 Introduction . . . . . .3.2 Biomass Fuel Analysis3.2.1 Proximate and Ultimate Analysis3.2.2 Physical Tests . . . . .3.3 Other Fuel Parameters3.3.1 Particle Size and Shape3.3.2 Charcoal and Char Properties3.3.3 Biomass Ash Content and Effects3.3.4 Biomass Moisture Content and Effects3.3.5 Biomass Heating Value3.4 Beneficiation of Biomass Fuels . .3.4.1 Densifying Biomass Fuels3.4.2 Drying Biomass Fuels3.5 Biomass Fuel Emissions9999. 12. 12. 12. 13. 15. 16. 16. 16. 17. 18. 19. 21. 21. 21. 21. 21. 24. 24. 254.0 Principles of Gasification4.1 Introduction . . . . . .4.2 Biomass Thermal Conversion Processes4.2.1 Introduction . . . . . .4.2.2 Biomass Pyrolysis . . . .4.2.3 Combustion of Biomass . . . .4.2.4 Chemistry of Biomass Gasification4.2.5 Thermodynamics of Gasification .Contentsiii

4.3 Indirect and Direct Gasification Processes4.3.1 Indirect (Pyrolitic) Gasification .4.3.2 Direct Gasification . . . . . . . 25. 25. 254.4 Principles of Operation of Direct Gasifiers4.4.1 Introduction . '. . . . . . . . . .4.4.2 Operation of the Updraft Gasifier4.4.3 Operation of the Downdraft Gasifier4.4.4 Factors Controlling Stability of Gasifier Operation.4.5 Charcoal Gasification. 284.6 Summary. 29.27272728285.0 Gasifier Designs. 305.1 Introduction. 305.2 Basic Gasifier Types. 305.3 Charcoal Gasifiers . . 315.4 Charcoal versus Biomass Fuels. 315.5 The Crossdraft Gasifier . . . . 325.6 The Updraft Gasifier. 32. . . . .5.7 The Imbert Downdraft Gasifier5.7.1 Introduction . . . . .5.7.2 Description of the Downdraft (Imbert) Gasifier5.7.3 Superficial Velocity, Hearth Load, and Gasifier Sizing5.7.4 Turndown Ratio . . . . . . . . . .5.7.5 Disadvantages of the Imbert Design.5.8 The Stratified Downdraft Gasifier . . . . .5.8.1 Introduction . . . . . . . . . . . .5.8.2 Description of the Stratified Downdraft Gasifier5.8.3 Unanswered Questions About the Stratified Downdraft Gasifier5.8.4 Modeling the Stratified Downdraft Gasifier. 38. 38. 38. 40. 425.9 Tar-Cracking Gasifiers5.9.1 Introduction . . . . .5.9.2 Combustion of Tars5.9.3 Thermal Tar Cracking5.9.4 Catalytic Tar Cracking. 42. 42. 43. 45. 465.10 Summary . . . . . . . . . . . 466.0 Gasifier Fabrication and Manufactureiv323233353636. 486.1 Introduction . . . . . . . 486.2 Materials of Construction . . . . 486.3 Methods of Construction . . . . 486.4 Sizing and Laying out the Pipes. 496.5 Instruments and Controls6.5.1 Temperature6.5.2 Pressure6.5.3 Gas Mixture6.5.4 Automatic Controls. 49. 49. 49. 49. 49Handbook of Biomass Downdraft Gasifier Engine Systems

. 517.0 Gas Testing7.1 Introduction . . . . . . . . . . . . . . . . . . . 517.2 Gas-Quality Measurements and Requirements. 517.3 Description of Producer Gas and Its Contaminants7.3.1 The Gas Analysis7.3.2 Particulates7.3.3 Tars . . . . . 51. 51. 51. 557.4 Gas Sampling . . . .7.4.1 Sample Ports7.4.2 Isokinetic Sampling. 55. 55. 567.5 Physical Gas-Composition Testing7.5.1 Raw Gas . . . . .7.5.2 Cleaned Gas. 57. 57. 617.6 Chemical Gas Composition7.6.1 Gas Samples for Chemical Analysis7.6.2 Methods of Analysis .7.6.3 Water Vapor Analysis . . . . . . . . 61. 61. 62. 657.7 Analysis of Test Data . . . . . . . . . . . . .7.7.1 Mass Balances and Energy Balances7.7.2 Flow Rate Characterization . . . . 66. 66. 677.8 Particle-Size Measurement . . . . . . . . .7.8.1 Typical Particle-Size Distributions7.8.2 Sieve Analysis . . . . . . .7.8.3 Microscopic Size Analysis7.8.4 Aerodynamic Size Analysis7.8.5 Graphic Analysis of Size Distribution7.8.6 Physical Size Analysis. 67. 67. 67. 67. 67. 69. 708.0 Gas Cleaning and Conditioning. 718.1 Introduction . . . . . . . . . . 718.2 The Power Theory of Gas Cleanup. 728.3 Gas Cleanup Goals . . . . . . . .8.3.1 Gas Contaminant Characteristics8.3.2 Typical Dirty Gas8.3.3 Gas Cleanup Goals . .8.3.4 Cleanup Design Target. 74. 74. 74. 74. 748.4 Classification of Particles . . . 748.5 Particle Movement and Capture Mechanisms. 748.6 Dry Collectors . . . . . . . . . . .8.6.1 Gravity Settling Chambers8.6.2 Cyclone Separators8.6.3 Baghouse Filter8.6.4 Electrostatic (Cottrell) Precipitators. 75. 75. 75. 80. 838.7 Wet Scrubbers . . . . . . . . . . . .8.7.1 Principles of Wet Scrubbers8.7.2 Scrubber Equipment .8.7.3 Auxiliary Equipment. 84. 84. 86. 88Contentsv

8.8 Disposal of Captured Contaminants8.8.1 Char-Ash .8.8.2 Tar . . . .8.8.3 Condensate. 92. 92. 92. 929.0 Gasifier Systems. 939.1 The Complete Gasifier System. 939.2 Storing, Feeding, and Sealing Solids9.2.1 Characteristics of Solids9.2.2 Storage . . . . . . .9.2.3 Feeding Solids . . . . .9.2.4 Sealing Solid Flows . .9.3 Fans, Blowers, Ejectors, and Compressors9.3.1 Importance of Gas-Moving System Design9.3.2 Fans9.3.3 Blowers9.3.4 Ejectors .9.3.5 Turbochargers and Superchargers. 95. 95. 95. 96. 96. 979.4 Flares and Product-Gas Burners9.4.1 Flares .9.4.2 Burners . . . . . . 97. 97. 981 0.0 Instrumentation and Control. 9910.1 The Need for Instruroentation and Control. 9910.2 Gasifier Instruroents . . . . . . .10.2.1 Pressure Measurement . .10.2.2 Gas Flow Measurement10.2.3 Solid Flow Measurement10.2.4 Temperature Measurements. 99. 9910010310310.3 Controls . . . . . . . . . . .10.3.1 Fuel-Level Controls10.3.2 Pressure Controls . .10.3.3 Temperature Controls10310310310410.4 Computer Data Logging and Control1041 1 .0 Engine Adaptation and Operationvi939393949410511.1 Introduction . . . . . . . . . . .10511.2 Producer Gas for Transportation10511.3 Producer Gas for Electric Power and Irrigation10511.4 Gasifier Types Suitable for Shaft-Power Generation10511.5 Sizing the Gas Producer to the Engine105. . . . . . .11.6 Engine Selection . . . . . . . . . . . . . . . . . . .11.6.1 Large-Vehicle Engines - Truck Engines up to 50 kW11.6.2 Small Engines11.6.3 Natural-Gas Engines11.6.4 Diesel Engines10610610610610611.7 Cogeneration . . . . . . . . .106Handbook of Biomass Downdraft Gasifier Engine Systems

11.8 Spark-Ignition Engine Conversion11.8.1 Engine System11.8.2 Gas Mixers11.8.3 Power Time Lag11.8.4 Engine Startup11.8.5 Ignition Timing11.8.6 Spark Plugs . .11.9 Two-Cycle Engine Conversion. 11011.10 Diesel Engine Conversion . .11.10.1 Diesel Operation with Producer Gas11.10.2 Starting Diesel Engines . . . . . . .11.10.3 Throttling at Partial Load . . . . . .11111111211311.11 Increasing Power from Producer-Gas-Fueled Engines11.11.1 Mechanisms of Power Loss11.11.2 Engine Breathing . . . . .'11.11.3 Efficiency and Power Loss11.11.4 Blowers and Superchargers1 1 . 11.5 Other Methods for Increasing Producer Gas Power.:11311311311411411511.12 Engine Life and Engine Wear11.12.1 Engine Life Expectancy . . . . . . . . . . . . .11.12.2 Sticking Intake Valves11.12.3 Oil Thickening and Contamination11.12.4 Tar/Oil Accumulations1 1 . 12.5 Engine Corrosion11.12.6 Engine Warranty.1151151161161 161161171 1 . 13 Exhaust Emissions. 117. . . .11.14 Other Devices for Producer-Gas Power Generation11.14.1 Gas Turbines . . . . . . . . . .11.14.2 Fuel Cells . . . . . . . . . . .11.14.3 External-Combustion Devices.1 2.0 Safety and Environmental Considerations107107107108109110110117117117118. 119. . . . . . . 11912.2 Toxic Hazards . . . . . .12.2.1 Carbon Monoxide12.2.2 Creosote . . . . 119. 119. 12112.1 Introduction1 2 . 3 Fire Hazards. 122. . . . . . 12312.4 Environmental Hazards13.0 Decision Making . . . . .13.1 Introduction. 124. 124. . . . .13.2 Logistics Assessment13.2.1 Gasifier Application13.2.2 Equipment Selection Factors13.2.3 Feedstock Supply13.2.4 Regulations . . . . . . . . . . . . . . . .13.2.5 Labor Needs13.2.6 Final Logistics Considerations.Contents124124124124124124124vii

13.3 Economics . . . . . . . . . . . .13.3.1 Costs . . . . . . . . . .13.3.2 Calculating Energy Costs13.3.3 Equipment Cost13.3.4 Conversion Efficiency and Fuel Consumption13.3.5 The Cost of Operating Labor13.3.6 Maintenance Costs . . . .12512512512612712712713.4 Cost Benefits . . . . . . . . . . . .13.4.1 Value of Power Produced13.4.2 Cogeneration Possibilities12812812913.5 Financing . . . . . . . . . . . . .13.5.1 Government Subsidies in the Form of Tax Incentives13.5.2 Financial Institutions12912912913.6 Other k of Biomass Downdraft Gasifier Engine Systems139

Chapter 1Introduction andGuide to the Literature and Research1 .1 Role of Gasification in BiomassConversionThis handbook explains how biomass can be convertedto a gas in a downdraft gasifier and gives details f