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Biomass Gasification and Pyrolysis Practical Design and Theory Prabir Basu AMSTERDAM • BOSTON • HEIDELBERG • LONDON NEW YORK • OXFORD • PARIS • SAN DIEGO SAN FRANCISCO • SINGAPORE • SYDNEY • TOKYO Academic Press is an imprint of Elsevier Academic Press is an imprint of Elsevier 30 Corporate Drive, Suite 400 Burlington, MA 01803, USA Elsevier, The Boulevard, Langford Lane Kidlington, Oxford, OX5 1GB, UK © 2010 Prabir Basu. Published by Elsevier Inc. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the Publisher. Details on how to seek permission, further information about the Publisher’s permissions policies, and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency can be found at our website: www.elsevier.com/permissions. This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein). Notices Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary. Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility. To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein. Library of Congress Cataloging-in-Publication Data Basu, Prabir Biomass gasification and pyrolysis : practical design and theory / Prabir Basu. p. cm. Includes bibliographical references and index. ISBN 978-0-12-374988-8 (alk. paper) 1. Biomass gasification. 2. Biomass—Combustion. 3. Pyrolysis. 4. Gas manufacture and works. I. Title. TP339.B355 2010 662′.88—dc22 2010010068 British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library. For information on all Academic Press publications visit our Web site at www.elsevierdirect.com Printed in the United States 10 11 12 13 14 10 9 8 7 6 5 4 3 2 1 Working together to grow libraries in developing countries www.elsevier.com | www.bookaid.org | www.sabre.org To Mother. Preface The art of gasification and pyrolysis of biomass is as old as our natural habitat. Both processes have been at work since the early days of vegetation on this planet. Flame leaping from forest fires is an example of “flaming pyrolysis.” Blue hallow in a swamp is an example of methane gas formation through decomposition of biomass and its subsequent combustion in contact with air. Human beings, however, learned to harness these processes much later. First, large-scale application of gasification for industry and society concen- trated on coal as the fuel. It was primarily for lighting of city streets and affluent people’s houses. Use of gasification, though nearly as ancient as combustion technologies, did not rise with industrialization the same as combustion because of the abundant supply and low prices of oil and natural gas. Only in the recent past has there been an upsurge in interest in gasification, fueled by several factors:  Interest in the reduction in greenhouse gas emissions as a result of energy production  Push for independence from the less reliable supply and fluctuating prices of oil and gas  Interest in renewable and locally available energy sources  Rise in the price of oil and natural gas Several excellent books on coal gasification are available, but a limited few are available about biomass gasification and pyrolysis. A large body of peer- reviewed literature on biomass gasification and pyrolysis is available; some recent books on energy also include brief discussions on biomass gasification. However, there is a dearth of comprehensive publications specifically on gasification and pyrolysis; this is especially true for biomass. Engineers, scientists, and operating personnel of biomass gasification plants clearly need such information from a single easy-to-access source. Better comprehension of the main aspects of gasification technology could help an operator understand the workings of the gasification plant, a design engineer to size the gasifier, and a planner to evaluate different options. The present book was written to fill this important need. It attempts to mold available research results in an easy-to-use design methodology whenever possible. Additionally, it brings into focus new advanced processes such as supercritical water gasification and torrefaction of biomass. This book is comprised of nine chapters and three appendices, which include several tables that could be useful for the design of biomass gasifiers and their vii viii Preface components. Chapter 1 introduces readers to the art of gasification and its present state of art. It also discusses the relevance of gasification to the current energy scenario around the world. Chapter 2 presents the properties of biomass with specific relevance to gasification and pyrolysis of biomass. The basics of pyrolysis are discussed in Chapter 3, which also covers torrefaction. In addition, it introduces readers to the design of a pyrolyzer and elements of the torrefaction process. Chapter 4 deals with an important practical aspect of biomass gasification— the tar issue. This chapter provides information on the limits of tar content in product gas for specific applications. It also discusses several means of reduction in tar in the product gas. Chapter 5 concerns the basics of the gasification of biomass. It explains the gasification process and important chemical reactions that guide pyrolysis and gasification. Chapter 6 discusses design methodologies for gasifiers and presents some worked-out examples on design problems. Chapter 7 introduces the new field of hydrothermal gasification, with specific reference to gasification of biomass in supercritical water. It covers the basics of this relatively new field. One of the common, but often neglected, problems in the design of a gasification plant is the handling of biomass. Chapter 8 discusses issues related to this and provides guidelines for the design and selection of handling equipment. The production of chemicals and synthetic fuels is gaining importance, so Chapter 9 provides a brief outline of how some important chemicals and fuels are produced from biomass through gasification. Production of diesel and bio- gasoline is also discussed briefly here. Appendix A contains definitions of biomass and Appendix B lists physical constants. Appendix C includes several tables containing design data. The Glossary presents definitions of some terms used commonly in the chemical and gasification industries. Acknowledgments The author is greatly indebted to a large number students, professional col- leagues, and institutions who helped revise numerous drafts of this book and provided permission for the use of published materials. Drs. D. Groulux, I. Ugursal, N. Mahinpey, N. Bakshi, A. Dutta, A. M. Leon, and P. Kaushal read parts of the manuscript and provided valuable suggestions. Many students worked tirelessly to support the work on this book. Special efforts were made by M. Greencorn, S. Rao, V. Mettanant, B. Acharya, A. Dhungana, and A. Basu. My hope is that is that what is here will benefit at least some students and/or practicing professionals in making the world around us a little greener and more habitable. Finally, this book would not have materialized without the constant encour- agement of my wife, Rama Basu. About the Author Dr. Prabir Basu is an active researcher and designer of gasifiers with a specific interest in fluidized-bed gasification of biomass. His current research interests include frontier areas, such as supercritical gasification, as well as applied research dealing with biomass co-firing. He is the founder of the prestigious triennial International Conference series on Circulating Fluidized Beds, and founder of Greenfield Research Incorporated, a private research and development company based in Canada that specializes in fluidized-bed boilers and gasification. Professor Basu has been working in the field of energy conversion and the environment for more than 30 years. Prior to joining the engineering faculty at Dalhousie University (formerly known as the Technical University of Nova Scotia), he worked with both a government research laboratory and a private boiler manufacturing company. Dr. Basu’s passion for the transformation of research results into industrial practice is well known, as is his ongoing commitment to spreading advanced knowledge around the world. He has authored more than 200 research papers and six monographs in emerging areas of energy and environment, some of which have been translated into Chinese and Korean. He teaches short courses and seminars in industries and at universities across the globe. Presently, he leads the Circulating Fluidized-Bed Research Laboratory at Dalhousie Univer- sity in Canada. ix Chapter 1 Introduction Gasification is a chemical process that converts carbonaceous materials like biomass into useful convenient gaseous fuels or chemical feedstock. Pyrolysis, partial oxidation, and hydrogenation are related processes. Combustion also converts carbonaceous materials into product gases, but there are some important differences. For example, combustion product gas does not have useful heating value, but product gas from gasification does. Gasification packs energy into chemical bonds while combustion releases it. Gasification takes place in reducing (oxygen-deficient) environments requiring heat; combustion takes place in an oxidizing environment giving off heat. The purpose of gasification or pyrolysis is not just energy conversion; production of chemical feedstock is also an important application. In fact, the first application of pyrolysis of wood into charcoal around 4000 B.C.E. was not for heating but for iron ore reduction. In modern days, gasification is not restricted to solid hydrocarbons. Its feedstock includes liquid or even gases to produce more useful fuels. Partial oxidation of methane gas is widely used in production of synthetic gas, or syngas, which is a mixture of H and CO. 2 Pyrolysis (see Chapter 3), the pioneer in the production of charcoal and the first transportable clean liquid fuel kerosene, produces liquid fuels from biomass. In recent times, gasification of heavy oil residues into syngas has gained popularity for the production of lighter hydrocarbons. Many large gasification plants are now dedicated to production of chemical feedstock from coal or other hydrocarbons. Hydrogenation, or hydrogasification, which involves adding hydrogen to carbon to produce fuel with a higher hydrogen- to-carbon (H/C) ratio, is also gaining popularity. Supercritical gasification (see Chapter 7), a new option for gasification of very wet biomass, is drawing growing interest. This chapter introduces the subject of biomass gasification with a short description of its historical developments, its motivation, and its products. It also gives a brief introduction to the chemical reactions that are involved in gasification. Biomass Gasification and Pyrolysis. DOI: 10.1016/B978-0-12-374988-8.00001-5 Copyright © 2010 Prabir Basu. Published by Elsevier Inc. All rights reserved. 1 2 Chapter | 1 Introduction 1788 1920 1931 1997 Robert Gardner: First Carl von Linde: Lurgi: Pressurized First commercial gasification patent Cryogenic separation moving-bed gasification plant in U.S. of air, fully continuous process gasification process 1659 1974 Thomas Shirley: 1801 1926 Discovered gas Arab oil embargo from coal mine Fourcroy: Water- Winkler fluidized- renewed gas shift reaction bed gasifier gasification interest 1739 1792 1861 1945–1974 2001 Dean Clayton: Murdoc: First use Siemens gasifier: Post-war “oil Advanced Distilled coal in a of coal-gas for First successful unit glut” gasification biomass closed vessel interior lighting renewable energy projects FigurE 1.1 Milestones in gasification development. 1.1 HistoriCal BaCkground The earliest known investigation into gasification was carried out by Thomas Shirley, who in 1659 experimented with “carbureted hydrogen” (now called methane). Figure 1.1 shows some of the important milestones in the progression of gasification. The pyrolysis of biomass to produce charcoal was perhaps the first large- scale application of a gasification-related process. When wood, owing to its overuse, became scarce toward the beginning of the eighteenth century, coke was produced from coal through pyrolysis, but the use of by-product gas from pyrolysis received little attention. Early developments were inspired primarily by the need for town gas for street lighting. The salient features of town gas from coal were demonstrated to the British Royal Society in 1733, but the scientists of the time saw no use for it. In 1798, William Murdoch used coal-gas (also known as town gas) to light the main building of the Soho Foundry, and in 1802 he presented a public display of gas lighting, astonishing the local population. Friedrich Winzer of Germany patented coal-gas lighting in 1804 (www.absoluteastronomy.com/topics/coal gas). By 1823 numerous towns and cities throughout Britain were gas-lit. At the time, the cost of gas light was 75% less than that for oil lamps or candles, and this helped accelerate its development and deployment. By 1859, gas lighting had spread throughout Britain. It came to the United States probably in 1816, with Baltimore the first city to use it. The history of gasification may be divided into four periods, as described in the following: 1.1 Historical Background 3 1850–1940: During this early stage, the gas made from coal was used mainly for lighting homes and streets and for heating. Lighting helped along the Industrial Revolution by extending working hours in factories, especially on short winter days. The invention of the electric bulb circa 1900 reduced the need for gas for lighting, but its use for heating and cooking continued. With the discovery of natural gas, the need for gasification of coal or biomass decreased. All major commercial gasification technologies (Winkler’s fluidized-bed gasifier in 1926, Lurgi’s pressurized moving-bed gasifier in 1931, and Koppers-Totzek’s entrained-flow gasifier) made their debut during this period. 1940–1975: The period 1940–1975 saw gasification enter two fields of application as synthetic fuels: internal combustion and chemical synthesis into oil and other process chemicals. In the Second World War, Allied bombing of Nazi oil refineries and oil supply routes greatly diminished the crude oil supply that fueled Germany’s massive war machinery. This forced Germany to synthesize oil from coal-gas using the Fischer-Tropsch (see Eq. 1.13) and Bergius processes (nC + (n + 1)H → CH ). Chemicals and 2 n 2n+2 aviation fuels were also produced from coal. A large number of cars and trucks in Europe operated on coal or biomass gasified in onboard gasifiers. During this period over a million small gasifiers were built primarily for transportation (see Figure 1.2). The end of the Second World War and the availability of abundant oil from the Middle East eliminated the need for gasification for transportation and chemical production. FigurE 1.2 Bus with an onboard gasifier during the Second World War. (Source: http://www. woodgas.com/history.htm.)