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Wood gas as engine fuel

Mechanical Wood Products Branch Forest Industries Division FAO Forestry Department The designations employed and the presentation of material in this publication do not imply the expression of any opinion whatsoever on the part of the Food and Agriculture Organization of the United Nations concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries. M-38 ISBN 92-5-102436-7 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying or otherwise, without the prior permission of the copyright owner. Applications for such permission, with a statement of the purpose and extent of the reproduction, should be addressed to the Director, Publications Division, Food and Agriculture Organization of the United Nations, Via delle Terme di Caracalla, 00100 Rome, Italy. FAO 1986 This electronic document has been scanned using optical character recognition (OCR) software and careful manual recorrection. Even if the quality of digitalisation is high, the FAO declines all responsibility for any discrepancies that may exist between the present document and its original printed version.

Table of Contents

Preface Chapter 1 - Introduction 1.1 Background 1.2 The present case for wood gasifiers 1.3 Overview of the contents of this publication 1.4 What to expect from a wood gasifier system

Chapter 2 - Small wood and charcoal gasifiers for operation of internal combustion engines 2.1 Fuelling of engines by producer gas 2.1.1 Possibilities of using producer gas with different types of engines 2.1.2 Engine power output using producer gas 2.1.3 Maximizing the power output in producer-gas operation 2.1.4 Resulting power output 2.1.5 Gas quality requirements for trouble-free operation 2.1.6 Use of Stirling engines or gas turbines with producer gas 2.2 Theory of gasification 2.2.1 Prediction of the gas composition 2.2.2 Gasifier efficiency 2.3 Types of gasifiers 2.3.1 Updraught or counter current gasifier 2.3.2 Downdraught or co-current gasifiers 2.3.3. Cross-draught gasifier 2.3.4. Fluidized bed gasifier 2.3.5 Other types of gasifiers 2.4 Gasification fuels 2.4.1 Need for selection of the right gasifier for each fuel 2.4.2 Energy content of the fuel 2.4.3 Moisture content of the fuel 2.4.4 Volatile matter content of the fuel 2.4.5 Ash content and ash chemical composition 2.4.6 Reactivity of the fuel 2.4.7 Particle size and size distribution 2.4.8 Bulk density of the fuel 2.4.9 Charring properties of the fuel 2.4.10 Assessment of the suitability of various types of biomass as gasifier fuel 2.5 Design of downdraught gasifiers 2.5.1 Processes occurring in the down-draught gasifier 2.5.2 Design guidelines for downdraught gasifiers 2.6 Gas cleaning and cooling 2.6.1 Cleaning dust from the gas 2.6.2 Gas cooling 2.7 Applications of biomass gasification 2.7.1 Production of fuel gas 2.7.2 Production of mechanical or electrical power in stationary installations 2.7.3 Mobile applications

2.8 Health and environmental hazards associated with the use of producer gas 2.8.1 Toxic hazards 2.8.2 Fire hazards 2.8.3 Explosion hazards 2.8.4 Environmental hazards Chapter 3 - Recent Swedish experiences with operation of vehicles on wood and charcoal gas 3.1 Overview of development work and testing carried out at the national machinery testing institute 3.1.1 Scope of the work 3.1.2 Gasifier for wood chips 3.1.3 Fibre glass fabric filter system 3.1.4 Conversion of diesel engines to producer gas operation 3.1.5 Tests with different fuels 3.2 Experiences gained from conversion and operation of modern vehicles 3.2.1 The need for continued practical tests 3.2.2 Conversion and operation of a Massey Ferguson 1100 farm tractor 3.2.3 Conversion and operation of a Scania truck 3.2.4 Experiences related to service, maintenance and equipment failures 3.3 Producer gas vehicles recently operated in other countries 3.4 Economic evaluation of operation of vehicles on wood gas 3.4.1 The case for wood gasifiers 3.4.2 Method used for the economic evaluation 3.4.3 Economic baseline assumptions 3.4.4 Marginal costs for the wood gasifier system 3.4.5 Economy of a producer gas tractor 3.4.6 Economy of a producer gas truck 3.5 Feasibility of using the vehicle gasifier technology for stationary applications 3.6 Operating hazards Chapter 4 - A small wood gas power plant at a sawmill in Paraguay 4.1 Description of the wood gas power plant 4.1.1 Fuel supply 4.1.2 The wood gasifier 4.1.3 Wood gas cooling and washing installations 4.1.4 Wood gas filter 4.1.5 Engine and electric generator 4.2 Operating experience

4.2.1 Fuel consumption 4.2.2 Manpower employed and operating procedure 4.2.3 Safety 4.2.4 Environmental impact 4.3 Economic evaluation 4.3.1 Capital investment 4.3.2 Operation and maintenance costs 4.3.3 Fuel costs 4.3.4 Total operating costs 4.3.5 Costs for electricity generation for family homes of sawmill personnel 4.3.6 Comparison with other alternatives for the electricity supply Chapter 5 - A small gasifier power plant in Sri Lanka 5.1 Description of the plant 5.1.1 General system layout 5.1.2 The gasifier 5.1.3 Cyclone 5.1.4 Impingement separator 5.1.5 Glass fibre cloth filter 5.1.6 Cooler 5.1.7 Engine and alternator 5.1.8 Start-up fan and flare 5.1.9 Safety devices 5.1.10 Auxiliaries 5.2 Operational procedures 5.2.1 Start-up 5.2.2 Closing down 5.2.3 System maintenance 5.3 Operational experience 5.3.1 Operating record and observations on the performance 5.3.2 Disturbances of the operation 5.3.3 Desirable modifications 5.4 Economic evaluation of electricity generation costs at Giriulla mill 5.5 Concluding remarks Chapter 6 - A 1.4 MW wood gas fuelled power plant in Paraguay 6.1 Historical background of the gasifier installations 6.2 Wood-fuel supply and preparation 6.3 Description of the down-draught gasifiers 6.4 Electricity production with the gas engine alternator sets 6.5 Operating experiences 6.6 Profitability of using wood gas at Loma Plata

Chapter 7 - The future of wood gas as engine fuel 7.1 Prerequisites for extensive use of wood gasifiers 7.2 Industrialized countries 7.3 Developing countries 7.4 The need for international cooperation Appendix 1 - Calculation of the power output of a producer gas engine Appendix 2 - Design calculation of downdraught gasifier Table of conversion factors and symbols (used in this manual) References

PrefaceWood gasifiers played an important role in the past in the substitution of oil-based fuels in internal combustion engines, but fell into disuse after the Second World War because of their economic and technical disadvantages as compared with relatively inexpensive imported fuels. Since the middle of the 1970's the increase in oil prices has led to a renewed interest in wood gasification technology, especially in countries dependent on oil imports but with adequate supplies of wood or other biomass fuels or, as in the case of Sweden, where the technology is maintained and developed as a matter of policy. Research into the technology of gasifier/engine systems has provided modern designs which work reliably at a level of technical skill appropriate to rural applications in developing countries. Such systems are economic in certain conditions found in many developing countries, but the technology and manufacturing facilities are not widely available and their commercial utilisation is limited. In "Wood Gas as Engine Fuel" FAO presents a summary of modern wood gasification technology and the economics of its application to internal combustion engines. Texts on different aspects of wood gasification, prepared by specialists, are the basis of this publication. FAO gratefully acknowledges the co-operation of B. Kjellstrm of the Beijer Institute, Stockholm; H. Stassen of the Twente University of Technology, Enschede, Netherlands; D. de Silva of the Ceylong Institute of Scientific and Industrial Research; N.E. Caete of the Sociedad Cooperativa Chortitzer Komitee, Paraguay and R. Thun of the Technical Research Centre of Finland.

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1.1 BackgroundCoal, wood and charcoal gasifiers have been used for operation of internal combustion engines in various applications since the beginning of this century. The utilization peaked during the Second World War when almost a million gasifiers were used all over the world, mainly vehicles operating on domestic solid fuels instead of gasoline. It is important to keep in mind that small gasifiers have been used quite extensively in the past and that they have played a very important part in reducing or eliminating the need for fuel imports in some countries. There is no need, however, in this publication to go deeper into the history of the development of small gasifier technology. Those who are interested in the subject are advised to study the reviews made by the Swedish Academy of Engineering Sciences (43) Kaupp and Goss (20) Skov (36) Bailey (3) Earthscan (12) or the National Academy of Sciences in U.S.A. (32). Interest in the technology of gasification has shown a number of ups and downs over the last eighty years, as is strikingly illustrated in Fig. 1.1 which reproduces a histogram that plots the number of wood gasification reports referred to in "Chemical Abstracts" since the year 1900. It appears that interest in gasification research correlates closely with the relative cost and availability of liquid and gaseous fossil fuels. The histogram shows that the number of articles was at an all-time peak in 1979, following a period of low activity in the 1950's and 1960's. There is an important difference between the earlier periods of high interest and the present situation, however. Earlier, the increase in scientific activity corresponded to an increased number of gasifiers in practical use. T

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