A Division of Midwest Research Institute

Operated for the U.S. Department of Energy

Handbook of Biomass Downdraft Gasifier Engine Systems

SERIISP-271-3022 DE88001135 March 1988 UC Category.' 245

This 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 guide to 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 biomass gasification.

The handbook is meant to be a practical guide to gasifier systems, and a minimum amount 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 following in parentheses. Unfortunately, many of the figures use English units, and it would have been too difficult to convert all of these figures to both units. We have supplied a conversion chart in the Appendix to make these conversions easier for the reader.

Mr. Bill Nostrand, one of our very helpful reviewers, died in May 1985. Bill was number one in the ranks of those who became interested in gasification because of its potential for supplying clean, renewable energy. We all will miss him. The improvement of gasification systems will be noticeably slowed by his death.

We dedicate this book to the Bill Nostrands of this world who will bring gasifier systems to the level of safety, cleanliness, and reliability required to realize their full potential.

Thanks, Bill.

T_ B. Reed and A. Das Golden, Colorado

A Product of the Solar Technical Information Program Solar Energy Research Institute 1 617 Cole Boulevard, Golden, Colorado 80401-3393

............. _____________ Whole system __________ --,l.

Acknowledgments Since it is impossible for one or two authors to realistically comprehend a subject from all viewpoints, we have solicited input from leading workers in the field. Early versions were sent to a number of investigators, and each was invited to comment on and supplement our effort. We therefore express our heartfelt thanks to the following reviewers for greatly enhancing the quality of the final product:

Dr. Thomas Milne, Solar Energy Research Institute Dr. Bjorn Kjellstrom, The Beijer Institute, Sweden Dr. Thomas McGowan, Georgia Institute of Technology Mr. Matthew Mendis, World Bank

Dr. Hubert Stassen, Twente University, The Netherlands Prof. Ibarra Cruz, University of Manila, The Philippines

Mr. Bill Nostrand, New England Gasification Associates

We take final responsibility for the contents and omissions, and extend our apologies to those workers whose work we may have unknowingly omitted.

Organization and Use A gasifier converts solid fuel to gaseous fuel. A gasifier system includes the gasification reactor itself, along with the 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.

Fuel Ch.3

Gasifier Ch.4, 5, 6

Gas measurement

and cleaning Ch. 7, 8

Engine (or combustor)

Ch. 1 1

Ch. 9, 1 0

Notice

This report was prepared as an account of work sponsored by an agency of the United States government. Neither the United States government nor any agency thereof. nor any of their employees, makes any warranties, express or implied. or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would 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 government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States government or any agency thereof.

Printed in the United States of America Available from:

Superintendent of Documents U.S. Government Printing Office

Washington, DC 20402

National Technical Information Service U.S. Department of Commerce

5285 Port Royal Road Springfield, VA 22161

Price: Microfiche A01 Printed Copy A07

Codes are used for pricing all publications, The code is determined by the number of pages in the publication, Information pertaining to the pricing codes can be found in the current issue of the following publications which are generally available in most libraries: Energy Research Abstmcts (ERA); Government Reports Announcements and Index (GRA and I) Scientific and Technical Abstmct Reports (STAR); and publication NTIS-PR-360 available from NTIS at the above address.

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Contents

1 .0 Introduction and Guide to the Literature and Research 1 1.1 Role of Gasification in Biomass Conversion 1 1.2 Biomass Energy Potential . . . . 2 1.3 Guide to Gasification Literature 3

1.3.1 Bibliographies . . . . . 3 1.3.2 Books . . . . . . . . . . 3 1.3.3 Gasification Proceedings 3 1.3.4 Commercial Information 4 1.3.5 Producer Gas Research 4 1.3.6 Producer Gas R&D Funding 4 1.3.7 Federal Emergency Management Agency (FEMA) Gasifier Work 4

2.0 History, Current Developments, and Future Directions 6 2.1 Historical Development . . . . . . . . . . . 6

2.1.1 Early Development of Gasification 6 2.1.2 Vehicle Gasifiers . . . . 6

2.2 Current Development Activities 7 2.3 Future Development Directions 7

3.0 Gasifier Fuels 9 3.1 Introduction . . . . . . 9 3.2 Biomass Fuel Analysis 9

3.2.1 Proximate and Ultimate Analysis 9 3.2.2 Physical Tests . . . . . . 12

3.3 Other Fuel Parameters . 12 3.3.1 Particle Size and Shape . 12 3.3.2 Charcoal and Char Properties . 13 3.3.3 Biomass Ash Content and Effects . 15 3.3.4 Biomass Moisture Content and Effects . 16

.3.3.5 Biomass Heating Value 16

. 16

. 1

. 18

. 19

3.4 Beneficiation of Biomass Fuels . . 3.4.1 Densifying Biomass Fuels 3.4.2 Drying Biomass Fuels

3.5 Biomass Fuel Emissions 4.0 Principles of Gasification . 21

4.1 Introduction . . . . . . . 21 4.2 Biomass Thermal Conversion Processes . 21

4.2 ..1 Introduction . . . . . . 21 . 21 4.2.2 Biomass Pyrolysis

4.2.3 Combustion of Biomass . . . . . . .

. . . . 4.2.4 Chemistry of Biomass Gasification 4.2.5 Thermodynamics of Gasification . . 25

Contents iii

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4.3 Indirect and Direct Gasification Processes . 25 4.3.1 Indirect (Pyrolitic) Gasification . . 25 4.3.2 Direct Gasification . . . . . . . . . 25

4.4 Principles of Operation of Direct Gasifiers . 27 4.4.1 Introduction . ' . . . . . . . . . . . 27 4.4.2 Operation of the Updraft Gasifier . 27 4.4.3 Operation of the Downdraft Gasifier . 28 4.4.4 Factors Controlling Stability of Gasifier Operation . 28

4.5 Charcoal Gasification . 28 4.6 Summary . . 29

5.0 Gasifier Designs . 30 5.1 Introduction . 30 5.2 Basic Gasifier Types . 30 5.3 Charcoal Gasifiers . . . 31 5.4 Charcoal versus Biomass Fuels . 31 5.5 The Crossdraft Gasifier . . . . . 32 5.6 The Updraft Gasifier . . . . . . 32 5.7 The Imbert Downdraft Gasifier . 32

5.7.1 Introduction . . . . . . 32 5.7.2 Description of the Downdraft (Imbert) Gasifier . 33 5.7.3 Superficial Velocity, Hearth Load, and Gasifier Sizing . 35 5.7.4 Turndown Ratio . . . . . . . . . . . 36 5.7.5 Disadvantages of the Imbert Design . 36

5.8 The Stratified Downdraft Gasifier . . . . . . 38 5.8.1 Introduction . . . . . . . . . . . . . 38 5.8.2 Description of the Stratified Downdraft Gasifier . 38 5.8.3 Unanswered Questions About the Stratified Downdraft Gasifier . 40 5.8.4 Modeling the Stratified Downdraft Gasifier . 42

5.9 Tar-Cracking Gasifiers . 42 5.9.1 Introduction . . . . . . 42 5.9.2 Combustion of Tars . 43 5.9.3 Thermal Tar Cracking . 45 5.9.4 Catalytic Tar Cracking . 46

5.10 Summary . . . . . . . . . . . . 46

6.0 Gasifier Fabrication and Manufacture . 48 6.1 Introduction . . . . . . . . 48 6.2 Materials of Construction . . . . . 48 6.3 Methods of Construction . . . . . 48 6.4 Sizing and Laying out the Pipes . 49 6.5 Instruments and Controls . 49

6.5.1 Temperature . 49 6.5.2 Pressure . 49 6.5.3 Gas Mixture . 49 6.5.4 Automatic Controls . 49

Handbook of Biomass Downdraft Gasifier Engine Systems iv

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7.0 Gas Testing . 51

7.1 Introduction . . . . . . . . . . . . . . . . . . . . 51 7.2 Gas-Quality Measurements and Requirements . 51 7.3 Description of Producer Gas and Its Contaminants . 51

7.3.1 The Gas Analysis . 51 7.3.2 Particulates . 51 7.3.3 Tars . . . . . . 55

7.4 Gas Sampling . . . . . 55 7.4.1 Sample Ports . 55 7.4.2 Isokinetic Sampling . 56

7.5 Physical Gas-Composition Testing . 57 7.5.1 Raw Gas . . . . . . 57 7.5.2 Cleaned Gas . 61

7.6 Chemical Gas Composition . 61 7.6.1 Gas Samples for Chemical Analysis . 61 7.6.2 Methods of Analysis . . 62 7.6.3 Water Vapor Analysis . . . . . . . . . 65

7.7 Analysis of Test Data . . . . . . . . . . . . . . 66 7.7.1 Mass Balances and Energy Balances . 66 7.7.2 Flow Rate Characterization . . . . . 67

7.8 Particle-Size Measurement . . . . . . . . . . 67 7.8.1 Typical Particle-Size Distributions . 67 7.8.2 Sieve Analysis . . . . . . . . 67 7.8.3 Microscop