Field Document No.44REC|0NAL w000 ENERCY 0EVEL0PHENT PR0CRAHHE |N A8|AC6P|RA8|154|NETFOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONSBangkok, September 1993IMPROVED SOLID BIOMASS BURNING COOKSTOVES:A DEVELOPMENT MANUALIn Collaboration WithAsia Regional Cookstove ProgrammeandEnergy Research Centre of Panjab University, ChandigarhThis publication is printed bythe FAO Regional Wood Energy Development Programme in Asia,Bangkok, ThailandFor copies write to: Regional Wood Energy DevelopmentProgramme in Asia Tel: 66-2-280 2760c/o FAO Regional Offcie for Asia and the Pacific Fax: 66-2-280 0760Maliwan Mansion, Phra Atit Road, E-mail: rwedp@fao.orgBangkok, Thailand Internet: http://www.rwedp.orgThe designations employed and the presentation of material in this publication do not implythe expression of any opinion whatsoever on the part of the Food and Agriculture Organiza-tion of the United nations concerning the legal status of any country, territory, city or area orof its authorities, or concerning the delimitations of its frontiers or boundaries.The opinions expressed in this publication are those of the author(s) alone and do not implyany opinion on the part of the FAO.FOREWORDFor more than 15 years development organizations, research institutes and hundreds of volunteersand specialists have been engaged in the development, testing and dissemination of improved cookstovesthroughoutthedevelopingworldofAsia,AfricaandLatinAmerica.Conceivedasamajorwaytocombatdeforestation, increased efficiency of domestic cooking stoves was the major focus of researchers and hightargetsofdisseminationtheconcernofforestofficials.Unfortunately,notallprogrammesliveduptotheexpectations raised, a major reason being the lack of adequate attention to social, economic and institutionalissues related to introducing improved cookstoves.Basedontheearlierexperiencesanewapproachhasbeenadoptedinmanycountriesinwhichimprovedcookstovesaremoreintegratedintotheoverallobjectivesofruralandurbandevelopment.ThisisreflectedinthebroadrangeofsectorsbecominginvolvedinICSintroduction,e.g.energy,forestryandhealthsectors,womenindevelopmentandruraldevelopment.Onthescientificside,considerableprogresshasbeenmadewithmatchingscientifictheoriesofefficientcombustionwiththeneedsofeasyinstallation,useandmaintenance.Manyreviewsandassessments of ICS programmes have also contributed to a better understanding of the key factors in theirsuccess.Asaresultofalltheseeffortstherearenowthousandsofpublicationsandarticlesonimprovedcookstoves.This large amount of information has been useful for ICS experts, but not always for field staff,who need a comprehensive and informative document that covers all major issues of ICS introduction.TheRegionalWoodEnergyDevelopmentProgrammeinAsia(RWEDP)fromitsverybeginningin1985 has given much attention and resources to the introduction of ICSs in its member countries.Severalworkshops and seminars on various aspects of ICSs have been organized and recently three documents onnational ICSs have been published for China, India and Thailand.DuringthisperiodithasbecomequiteclearthatakeyfactorinthesuccessofICSintroductionisthecommitmentandknowledgeoffieldstaff.OftenthesefieldstafflackbasicinformationonICSdevelopment and dissemination.The present manual provides them an insight into the complexity and thepotentialofICSintroduction.IthasbeenwritteninsuchawaythatitintroducesthefieldworkertoICSswithin a relatively short period.It is hoped that young scientists and students of wood energy conversion willequally benefit from the manual.Theauthorofthismanual,Prof.S.K.Sharma,DirectoroftheEnergyResearchCentreandHonoraryDeanoftheChemicalEngineeringCollegeofPunjabUniversityhastakenupthechallengeofbringing together all relevant information on ICSs in a concise and comprehensive way.RWEDP wishes toexpress its deep appreciation for his contribution to ICS development and his tenacity in (lie preparation ofthis manual.Dr.AroonChoincharn,WoodEnergyConversionSpecialistofRWEDPprovidedthedevelopmentframeworkforthemanualandtechnicalsupportthroughouttheprocessofitspreparation.Mr.AukeKoopmans of Green Fields, Thailand, and Harry Oosterveen of RWEDP assisted with reviewing and editingandMs.MariaNystr6moftheLundCommitteeonHabitatStudiesprovidedhighlyusefulcommentsandinformation for chapter 7, "The kitchen: An integral part of the cooking system".Typing and text layout weredone by Ms. Panpicha Issavasopon and Ms. Navaporn Liangcheevasonthon of RWEDP.I thank them all fortheir commitment and for the high quality of the support provided.The financial contribution and technical comments from the Asia Regional CookstovesProgramme(ARECOP) are also gratefully acknowledged.We hope that the present development manual will stimulate interaction between the many ICS fieldworkersandscientistsfromAsiaandelsewhere.Theircomments,adviceand/oradditionalcontributionsmay become valuable inputs for a revised version which we intend to publish in due course.Egbert PelinckChief Technical AdviseriiTABLE OF CONTENTSPageFOREWORD. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .iLIST OF FIGURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .viLIST OF TABLES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . viiLIST OF SYMBOLS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .viii1TECHNOLOGIES FOR IMPROVED BIOMASS STOVES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11.1 Development Background. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2 Development Approach. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.3 Objectives of the Present Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32HISTORICAL REVIEW OF COOKSTOVE DEVELOPMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42.1 Historical Perspective . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42.2 Earlier Perspective . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52.3 Presen Perspectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53PRINCIPLE FOR IMPROVED COOKSTOVES DESIGN AND DEVELOPMENT. . . . . . . . . . . . . . . . 73.1 Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73.2 ICS Design Perspective . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83.3 Stove Classification. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83.4 Design Criteria. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93.4.1 Social factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113.4.2 Stove power output and other related needs. . . . . . . . . . . . . . . . . . . . . . . . . . 123.4.3 Local resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123.4.4 Economic factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133.4.5 Environmental factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133.5 Design Principle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143.5.1 Combustion process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143.5.2 Heat Tranfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143.5.3 Fluid flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223.5.4 Material science . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234WOOD AND BIOMASS COMPOSITION, PROPERTIES AND COMBUSTION CHARACTERISTICS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244.1 Biomass Composition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244.1.1 Cellulose. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254.1.2 Hemicellulose. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254.1.3 Lignin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254.1.4 Minerals and Ashes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 264.2 Methods for Assessing Biomass. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 264.2.1 Proximate analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 274.2.2 Ultimate analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28iii4.2.3 Calorific value. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 294.2.4 Rate of devolatilization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 294.2.5 Thermo-physical properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 314.3 Wood Combustion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 314.3.1 Stage 1 combustion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 324.3.2 Stage 2 combustion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 334.3.3 Stage 3 combustion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 334.3.4 Combustion of productions of pyrolysis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 334.3.5 Combustion reactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 354.3.6 Effect of moisture on combustion of wood. . . . . . . . . . . . . . . . . . . . . . . . . . . . 354.4 Combustion Controlling Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 364.4.1 Physical and chemical properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 364.4.2 Size and shape of fuel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 364.4.3 Primary and secondary air supplies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 374.4.4 Fuel/air ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 374.4.5 Temperature of flame. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 384.4.6 Fuel supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 384.4.7 Concluding remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 395IMPROVED COOKSTOVE TECHNOLOGIES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 405.1 Combustion in Small Enclosures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 405.1.1 Design considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 425.2 Influence of Sub-system Design on Optimum Efficiency . . . . . . . . . . . . . . . . . . . . . . . 435.2.1 Fire-box/combustion chamber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 435.2.2 Grate. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 475.2.3 Pot hole/rim design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 485.2.4 Chimney . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 495.2.5 Baffle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 505.2.6 Connecting tunnels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 515.2.7 Damper . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 525.3 Cooking Utensils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 535.3.1 Material characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 535.3.2 Geometric factors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 545.3.3 Operating characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 545.4 Stove Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 555.4.1 Criteria for selection of material(s), construction methods and strategies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 555.4.2 Construction problems and prospects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 565.4.3 Construction technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 575.5 Improved Cookstove Testings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 595.5.1 Why test cookstoves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 595.5.2 Criteria for testing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 595.5.3 Indices for testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 595.5.4 Overall thermal efficiency testing methods . . . . . . . . . . . . . . . . . . . . . . . . . . . 605.5.5 Specific task fuel consumption or cooking test . . . . . . . . . . . . . . . . . . . . . . . . 625.5.6 Test selection criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 645.5.7 Concept of efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65iv6ENVIRONMENT AND HEALTH IMPLICATIONS ON BIOMASS BURNING COOKSTOVES. . . . . 696.1 Environmental Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 696.2 Health Effects Related to Domestic Biomass Fuel Burning . . . . . . . . . . . . . . . . . . . . . 696.3 Emission, Characteristics of Biomass Fuels. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 726.4 Strategies for Improvement of Kitchen Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . 756.4.1 Improved stove designs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 756.4.2 Fuel upgradation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 766.4.3 Ventilation improvement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 766.4.4 Switching to other clean fuels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 767KITCHEN, INTEGRAL PART OF THE COOKING SYSTEM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 777.1 Kitchen Stove Nexus. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 777.1.1 Stove functions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 797.1.2 Culinary functions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 797.2 Kitchen Design Considerations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 807.3 Kitchen Indoor Air Quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 827.3.1 Ventilation and building materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 837.3.2 Chimneys and hoods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 838IMPROVED COOKSTOVE AS COMBINED TECHNOLOGY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 858.1 Multipot Hole Stoves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 878.2 Channel/Shielded Fire Stoves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 888.3 Nozzle Type Stoves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 908.4 Chimneyless Stoves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 929FUTURE NEEDS FOR R & D. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 959.1 ICS Monitoring and Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 959.2 Combustion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 959.3 Heat Transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 959.4 Transient Heat Transfer Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 969.5 Environmental Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 979.6 Kitchen Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 979.7 Improved Utensils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 989.8 Improved Culinary Practices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 989.9 Stove Construction Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 989.10 Heat of Chemical Reaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 989.11 Improved Performance of ICS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 999.12 Commercial Stoves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 999.13 Biofuel Upgradation Techniques. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 999.14 Stove Testing, Standardisation and Quality Control . . . . . . . . . . . . . . . . . . . . . . . . . . . 999.15 Final Caveat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99BIBLIOGRAPHY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101APPENDIX 1 CHIMNEYS AND NET POSITIVE SUCTION HEAD. . . . . . . . . . . . . . . . . . . 117viLIST OF FIGURESPageFigure 3.1 Processes in stove design... 8Figure 3.2Design considerations for a stove10Figure 3.3Conduction, convection, radiation and stored heat...15Figure 3.4Total power radiated by a black body as a function of the temperature18Figure 3.5View factor versus the distance to the pot..18Figure 4.1Properties of biomass25Figure 4.2Possible reaction pathways for thermal degradation of cellulose under rapid heatingconditions 30Figure 4.3 The fire triangle32Figure 4.4 Processes and temperatures in a burning piece of wood 32Figure 4.5 Wood combustion34Figure 5.1 Isometric view of an improved cookstove44Figure 5.2 Heat analysis SURBHI-U... 65Figure 6.1 Effect of carbon monoxide concentration in the atmosphere as a function of exposuretime for various conditions of labour70Figure 6.2 Generalised representation of component interactions in a domestic heatingoperation. 75Figure 7.1 Circle diagram illustrating how components of meal preparation are related to eachother and to the general social context at different levels78Figure 7.2 Attributes of operations and independent components 79Figure 7.3 Attributes of dependent components79Figure 7.4 Culinary and related functions of a kitchen. 80Figure 7.5 Supporting equipment and articles also need a place in the kitchen. 81Figure 7.6 Cross ventilated kitchens and the placement of stoves82Figure 7.7 "Miniskirt model" with upper part of bamboo and lower part of concrete blocks.. 83Figure 7.8 The Cooking Window tested in Vietnam. 83Figure 7.9 Hood from a pilot kitchen in Burkina Faso.. 84Figure 8.1 Illustrations showing multipot hole stove, channel type stove and nozzle type stove..86Figure 8.2 The Rohini three-pot stove88Figure 8.3 Channel efficiency as a function of channel length for various channel widths89Figure 8.4 Mai Sauki wood stove.90Figure 8.5 "Sudha", a single-pot pottery ICS. 91Figure 8.6 Thermal efficiencies and combustion characteristics of "Sudha" ICS92Figure 8.7 Priagni, a single pot metal ICS..93viiLIST OF TABLESPageTable 1.1 Sectoral energy consumption as a % of total for some Asian countries1Table 2.1 Survey of importance of objectives for various ICS programmes (%)... 6Table 3.1 Values of the constants C and n for some standard configurations. 21Table 3.2 Values of the constant of the forced convection equation for typical configurations. 21Table 4.1 Properties and characteristics of oven dry biomass... 26Table 4.2 Calorific value of wood at different moisture contents27Table 4.3 Proximate analysis for some fuel types28Table 4.4 Composition of pyrolysis products. 31Table 4.5 Density, conductivity and the thermal diffusivity of different wood species 31Table 5.1 Qualitative effects of different factors on thermal and combustion efficiency. 41Table 5.2 Optimum height of the combustion chamber and vessel mounts 50Table 5.3 Properties of stove construction materials56Table 5.4 Suggested mixtures of soil/sand57Table 5.5 Results of the thermal performance of various stoves66Table 6.1 Mechanisms of principal health effects from major pollutants.. 70Table 6.2 Typical air pollution emissions for fuels and combustion systems... 73Table 6.3 Exposure of women and children to pollutants during cooking. 74Table 6.4 Ambient and occupational air quality standards.. 74Table 8.1 Effect of the wood burning rate on the pot heating rate. 87Table 8.2 Variation of heat gained by individual pots with wood burning rate. 89Table 8.3 Variation of efficiency and CO/CO2 with the pot height from the top plate. 92Table 8.4 Thermal efficiencies and combustion characteristics of "Priagni" ICS.93Table A-1 Density of flue gases.118Table A-2 Effect of elevation on density of air.118viiiLIST OF SYMBOLSA area sizem Greek symbols[a] ash content -cp specific heat J/kg-K " thermal diffusivity m/s[c] carbon content - " resistance coefficient -d diameter m $ thermal expansion coefficient l/KF view factor - ).. difference -f friction factor - , emissivity -Gr Grashoff number - 8 excess air factor -g constant of gravity m/S 0 efficiency %Hf combustion/calorific value J/kg D density kg/mHL latent heat of evaporation J/kg F Stephan-Boltzmann constant W/mKHc chemical heat J/kg > power density kW/mH head inm < volatile fraction -h height m < kinematic viscosity (p/p) m/sh heat transfer coefficient W/mK : viscosity kg/ms[h] hydrogen content - M volume of stoichiometric air m/kgk thermal conductivity W/m -Km mass kg[m] moisture content - Indicesn amount of material molNu Nusselt number - a ambient[o] oxygen content - av averageP power W b boilingPr Prandtl number - c charcoalp pressure kg/m cc combustion chamberQ energy, heat J ch chimneyq heat flux/transfer rate W des designr radial distance, radius m e ends thickness m va evaporationRe Reynolds number - f fuelt time s fb fuelbedT temperature K fl flameV volume m fo foodV volume flow m/s g gasv velocity m/s i initialod oven dryp potrad radiationres resistances simmeringw water1CountryCommercialenergyFuelwood and/orcharcoalResidues,dung, etc.Total traditional energysourcesYear and sourceDomestic OthersDom. Oth. Dom. Oth. Dom. Oth. Tot.Bangladesh 3.8 9.8 11.7 3.4 57.6 13.7 69.3 17.1 86.4 1981/BEPP, 1987Bhutan 1.5 11.3 75.1 11.8 0.6 0.0 75.7 11.8 87.2 1988/FAO, 1991aIndia --- --- --- --- --- --- --- --- 39.1 89/90 Est. 5)Indonesia 12.6 33.1 50.9 3.5 --- --- --- --- 54.3 1979/WB 1980 3)Myanmar0.6 12.0 84.1 --- 2.5 0.8 86.6 0.8 87.4 1990/WB 1990aNepal 1.2 4.4 92.8 1.5 0.0 --- 92.8 1.5 94.4 1982/WB 1983aPakistan 7.1 40.1 41.2 11.6 1)1)41.2 11.6 52.8 1991/Ouerghi'92Philippines 10.1 44.8 32.6 5.3 3.5 3.6 36.1 8.9 45.1 1989/WB 1992bSri Lanka 6.6 21.6 59.0 10.3 2)2.3 59.0 12.6 71.8 1990/CEB 1990Thailand 8.8 60.9 18.9 2.4 1.2 7.6 20.1 10.0 30.3 1988/NEA 4)Vietnam 2.0 24.0 29.6 4.4 34.7 5.2 64.3 9.6 73.9 1988/FAO 1992a Note: "Others" includes Industry, Transport, Agriculture, Commerce, Government as well as Other uses. Conversion losseshave not been accounted for. --denotes "No data available" while 0.0 denotes "Negligible amount"1)Residues are included under fuelwood2)Domestic fuelwood consumption apparently includes residues also3)The Domestic sector includes Government use as well as use by Commerce4)The Domestic use includes use by Commerce as well5)Estimate, based on WRI/UN data for commercial energy and unofficial World Bank data for traditional sources of energy.Table 1.1 Sectoral energy consumption as a % of total for some Asian countries1 INTRODUCTION1.1 Development BackgroundIn the past, traditional sources of energy such as fuelwood, charcoal, dung, etc. were the onlysources of energy used for all types of applications. It is only during the last 250 years that fossil fuels suchas coal, oil and gas and electricity have emerged as major sources of energy in most developed countries.However, nearly 75% of the world's population which lives in the developing countries continues to dependon the traditional sources of energy for most of their energy requirements. This is also evident from table1.1 which shows that in some Asian countries the traditional sources of energy accounted for about 60-90% of the total amount of energy consumed.In particular, the domestic sector relies heavily on traditional sources of energy, mainly for cooking,for which traditional stoves are often used. These stoves are usually thermally as well as environmentallyinefficient and hence create drudgery and problems for the users. Field evidence from many countries inAsia, Africa and Latin America shows that the introduction of improved cookstoves (ICSs) has broughtconsiderablebenefitstoruralandpoorurbanhouseholds(FoleyandMoss1983,Foleyetal1984,FAO/RWEDP 1991, Ramakrishna 1991, Barnes et al 1992, etc.).21.2 Development ApproachWhile recognizing that fuelwood saving and energy conservation are universally accepted asimportant issues, these rarely are the sole reason for users to start using an ICS. In fact, it is increasinglyrecognizedthattheintroductionofICSshasdonelittle,ifanything,toarrestdeforestationand/orenvironmental degradation as these problems are much more complex and, as such, can not be solvedsimply by the introduction of an ICS. Nevertheless, due to the multiple social benefits ICSs bring to theusers, mainly women, many countries have decided to start and/or continue to pursue improved cookstoveprogrammes (ICPs). These benefits of ICSs include:! Savingoffuelsand,directlyorindirectly,savingoftimeduetothestoves' higher thermalefficiency. Cooking can often be done faster while the saving of fuel implies that less time isrequired to acquire it and/or money spent to purchase it. For example, it has been estimated thatin Nepal nearly 200-300 person days (mainly women and children) per year per household arespent in the collection of wood (Singh et al 1984). With the use of an ICS, this period can besubstantially reduced and the time saved can be used productively for other purposes.! More complete combustion and/or the use of a chimney results in less smoke and soot emittedfrom the fire which, in turn, makes the kitchen a healthier place in which to work. Smoke emittedfrom biomass combustion causes serious indoor pollution, which affects the health of the cooks,most of whom are women and children. It has been estimated that the concentration of some ofthe pollutants, emitted due to the combustion of biomass, may exceed 10-100 times the WHOlimits (Smith 1986). Exposure to smoke has emerged as one of the major concerns in the ruralareas of the developing countries (WHO 1992). With more complete combustion less soot isdeveloped and the cooking pots remain cleaner and, as a result, less time is needed to clean thepots.! Additional benefits of ICSs include a reduction in safety hazards such as less exposure to heatresulting in a better work environment, better hygiene due to availability of hot water for washing,protection from burn injuries and fire, etc.Besides the direct and indirect benefits for the users, there are also socio-economic benefits suchas providing job opportunities through the production, sale and maintenance of ICSs, etc. Thus it can beconcluded that ICSs can make a significant contribution in rural development provided that efficient anddurable stoves can be introduced which fulfil all, or most, of the requirements of the users and ultimatelybring with them improved standards of cooking and living for the majority of the people.Studies have shown that the users of ICSs are also concerned about other important features ofcookstovessuchas:lowfuelconsumptionandemissions,lowcost,quickcooking,convenienceofoperation and maintenance, flexibility to use existing kitchen utensils, fuel and cooking practices, ease ofpropagation of fire and control of heat without much supervision and safety of operation. Even thoughcooking is the major requirement of the user, there are other important applications of ICSs such as spaceheating, smoking food items and agriproduce to preserve them, and water heating both in the householdsector as well as in the small scale industrial sector like agro-industries, gur and khandsari establishments,etc. Hence, it is imperative that a unified design-development approach is used in the development ofefficientfuelcombustionsystemstakingsocial,cultural,scientific,economic,ergonomic,andhealthaspects into consideration.31.3 Objectives of the Present StudyA vast amount of literature has appeared in the last 15 to 20 years, covering almost all aspectsof stove development, especially in the areas of hardware development and technologies (e.g. design,testing, stove material, stove production techniques, etc.). Unfortunately, much of it is widely scattered andit is difficult to get a good overview of the status of technological advancement in the stove field. This haslead to duplication of efforts and lack of coverage for certain subjects. In some cases, stove technologyhas become an academic and highly technical subject, far beyond the understanding of the commonresearch worker. Conversely, many stove promoters consider an ICSs to be a very low level intermediatetechnology and hence often introduce crude stove products to the people for use.It is, therefore, considered that a concise but simplified treatise on scientific knowledge relating tobiofuel cookstove technologies, which could facilitate the work of a large number of junior and middle levelstove researchers, is sorely needed. This manual is an attempt to address such a need and endeavoursto provide a challenge to stove experts to improve on the technological developments explored herein.42 HISTORICAL REVIEW OF COOKSTOVE DEVELOPMENT2.1 Early HistoryEvidence, found from archaeological excavations at Chou Kutien in China, indicated that thePeking man (Homo erectus pekingnensis), who lived in caves some 400,000 years ago during the first iceage, knew how to use fire (Bronowski 1973). At that time, fire was presumably used mainly for warmthrather than for cooking. The application of fire to cook food became apparent some 100,000 years ago,in the early part of the Upper Palaeolithic Period. During that period, the aim of cooking perhaps was torender food into a more digestible form. The making and use of refined stone implements and the masteryof fire can be considered important steps towards human civilization whichtook off only about 12,000years ago, when man had begun domestication of some animals and cultivation of plants (Bronowski1973). With the passage of time, human tastes gradually developed and later became sophisticated withmany gastronomic innovations, the use of a wide range of food materials as well as cooking techniques.During the earlier ages, cooking was presumably done over an open-fire with fuel arranged in apyramid configuration. This mode of cooking, primarily for roasting meat, had major drawbacks: dispersionof the flames and heat during windy conditions, a lack of proper control over the fire, exposure to heat andsmoke as well as fire hazards. However, at the same time, heat and smoke had also certain benefits suchas food preservation and/or protection against large animals, insects/rodents and providing warmth duringthe cold seasons.A major step towards the evolution of other cookstoves was the development of pots of variousshapes and sizes. This necessitated the modification of the open-fire to create shielded-fires in order tobalance the pot over the fire. The simplest form of the shielded-fire was a three-stone arrangement inwhich stones were arranged at approximately 120 degrees to one another on level ground. Besides,allowing a cooking pot to rest firmly on it, this arrangement also partly saved the fire from the vagaries ofwind and slightly increased cooking efficiency. However, by and large, the three-stone fire still sufferedsimilar drawbacks as the open-fire.Subsequently, the shielded-fire was changed to a U-shaped mud or mud/stone enclosure with anopening in the front for fuel feeding and combustion air entry. Three small humps (made of the same mudmaterial)werepositionedatthetoprimoftheenclosureandactedasapotrest,inductionpointofsecondary air needed for better combustion of volatile matter and for the exhaust gas exit. In order toconserve heat from the hot flue gases and to enhance cooking productivity, additional pot holes were lateradded. These pot-hole enclosures were connected by a tunnel. All the above mentioned innovations inthe cookstove design were made mainly by the users in light of their own experiences. These innovationsdid increase the efficiency of the stoves to some extent, but health and other hazards remained.Despite human evolution and the developments which have taken place in stoves and fuel, it isamazing, however, to observe that currently most of the estimated 75% of the people who live in thedeveloping world, are still largely employing the three-stone or the shielded-fire for cooking and usingtraditional sources of energy such as fuelwood and other biomass similar to their pre-historic ancestorsseveralthousandyearsago.Inmanycasespeoplehaveactuallymovedbackwardtotheuseofagricultural residues and dung for fuel.52.2 The Recent PastIn the early 1950's in India the first phase of ICS development started with technological attemptsto improve the design of biomass-fired stoves. Because of the appalling smoky working environment ofmany Indian kitchens in which women had to cook, improved multi-pot stoves were introduced (Raju1953). These stoves, which were of the high-mass and shielded-fire type, had a chimney to remove smokefrom the kitchen and had adjustable metal dampers to regulate the fire. Theodorovic (1954) was the firstto conduct controlled laboratory tests on biomass burning ICSs in Egypt, although he did not measure thethermal efficiency of the stoves. Systematic studies on measuring cookstove efficiency was conducted bySinger (1961) in Indonesia on a high-mass mud stove with similar design features to those introduced byRaju.Theoilcrisisofthe1970'sbroughtenergyissuestotheforefrontonceagainandimprovedcookstove programmes (ICPs) were considered as a solution to the fuelwood crisis as well as a meansto arrest deforestation and/or desertification. During this second phase of ICS development, extensiveresearch and development studies were undertaken and a more sound technical base was laid as a resultof detailed thermodynamic, heat transfer and aerodynamic studies. More systematic testing and designprocedures were gradually established. However, the major thrust was on fuel saving while the socio-economicandculturalaspectsofcookingwerelargelymissing.Alargenumberofbiomassburningimproved cookstove (ICS) models began to proliferate, especially from the laboratories in many developingand developed countries. For roughly 10 years, during the early 70's and 80's, various international donorshad a very strong influence on improved cookstove development promotion and assistance all over theworld, particularly in Asia, Africa and Latin America. Unfortunately, the impact of these aid programmesproved to be short lived. This was basically due to the inability of the programmes to meet the expectationsand actual requirements of the users, a lack of long term development objectives, systematic institutionalarrangements and appropriate local manpower development. Many ICPs could not sustain themselvesandassoonasthegovernment/donorfundingstopped,theprogrammesceasedtooperate.Thoseprogrammesthatsurvived,however,managedtogetlocalgovernmentcommitmentsforlongtermsupport.During the third phase, which began as recently as the late 80's, the emphasis shifted towards theneeds of stove users based on lessons learned from the second phase. It was found that, in addition tothe above mentioned criteria, factors such as cooking comfort, smoke free kitchens, convenience andsafety in the use of the stove were considered by the users to be as important as fuel saving.2.3 The PresentA recent global survey (Ramakrishna 1991) conducted by the Energy and Policy Institute of theEast-West Center, Hawaii, for the Energy Sector Management Assistance Programme (ESMAP) of theWorld Bank has shown that the goals for improved cookstove programmes, as shown in table 2.1, havesubstantially expanded and are now rather diverse. The results show that there appears to be a distinctpatternofprioritizingICPobjectivesindifferentgeographicalregions.Forexample,thegreatestimportance (83% of ICS programmes) was placed on smoke reduction in Southeast Asian countries whilethis had a lower priority in Latin America (56% of the ICS programmes). Increased fuel efficiency was ratedvery high in all four regions but very low in Latin America. On the contrary, an increase in the welfare ofthe poor and improvements in the status of women were ranked highest in Latin America. The results ofthis survey provide an interesting overview of the activities of ICPs in different parts of the world. One of6Objective LatinAmericaWest Africa East/CentralAfricaSouth Asia SoutheastAsiaTOTALn = 16 n = 18 n = 48 n = 26 n = 12 n = 120Increase fuel efficiency 44% 72% 79% 65% 75% 70%Reduce smoke emissions 56 67 67 65 83 67Reduce deforestation 56 83 50 46 42 54Save money 37 56 67 23 42 49Improve status of women 56 11 31 42 17 33Increase welfare of the poor 69 17 27 23 25 30Save time 25 44 29 27 25 30Safety 44 11 29 27 8 26Increase environmental awareness 25 39 23 19 17 24Generate income 6 0 31 23 33 22Save fuel in community 31 11 12 23 25 19Skill development 37 6 14 15 17 17Create jobs 6 0 25 15 25 17Community and institutional development 37 neg. 10 27 25 16Prevent soil degradation 19 17 12 19 8 15Others 19 6 2 12 8 8Note: The table shows the frequency with which the objectives were ranked 1 on a scale where 1 = Very important,2 = Important, 3 = Less important, 4 = Not important and 5 = No opinion.Source: Ramakrishna, 1991Table 2.1 Survey of importance of objectives for various ICS programmes (%)the significant findings was that apart from the benefit of fuel and money savings, other benefits such assmokereduction,timesaving,safetyinthekitchen,incomegeneration,improvedstatusofwomen,increased environmental awareness, etc. have also been included as programme objectives.The regional expert consultation on ICS development held in Udaipur, India (FAO/RWEDP 1991),where the status of South Asian ICS programmes was reviewed, common problems and constraintsidentifiedandstrategiesandfuturedirectionsdiscussed,resultedinfourcomprehensivesetsofconclusionsandrecommendationsonissuesrelatedto:researchanddevelopment,programmemanagement, policy and institutions, and involvement of women. The general consensus of the meetingwas that: Future ICP programmes should follow a wider systems approach. Programmes should look atnot only the introduction of ICSs but also at improved kitchens, cooking practices, utensils and fuels. Inaddition,theroleofimprovedstovesinreducingharmfulemissionsandgreenhousegasesthroughcleaner combustion was also highlighted. In short the major concern, in the modern context, has beenfocusedonindoorairquality,thelinkagebetweenthefunctionalityofstovesandkitchens,andtheelimination of cooking drudgery as well as the method of dissemination.73 PRINCIPLESOFIMPROVEDCOOKSTOVEDESIGNANDDEVELOPMENT3.1 DefinitionsInordertoensureaclearunderstandingoftheinformationpresentedinthischapter,thedefinitions of some important terms that will be used in relation to the improved cookstove design and itsprinciples are explained below.The improved cookstove or ICS, in this context pertains to the solid biomass fuel burning systemin which heat is produced, by combustion, for immediate use in domestic cooking. As will be discussedin the next section, ICSs can also perform other tasks, depending on the design purpose arising from theuser'sneeds.Suchastovemayperhapsbetermedanimprovedstove(IS)whichcanbeusedfornumerous applications, namely: cooking, food preservation/drying, domestic heating and other social andcultural activities.Biomass fuel denotes solid biomass either in a raw or processed form. This includes fuelwood,charcoal, agri-residues, briquettes, etc. While fuelwood is generally preferred in domestic cooking, residuefuels in sticks, leaves, straw and granular forms are also increasingly used due to fuelwood scarcity. Aswill be discussed shortly in sections 4.1 and 4.2, each type of biomass fuel has different properties andburning characteristics.Combustionistheprocessthroughwhichthefuelandairchemicallyinteractatsustainableelevated temperatures. The combustion process is dependent on the physico-chemical properties of thefuel, quantity and mode of air supply, and the conditions of the surroundings. All these parameters arediscussed in sections 3.5.1, 4.3, 4-4. and 5.1.Heat transfer is the process by which the heat generated from combustion is transferred (orpurposefully targeted) at a heat absorbing surface. However, it is only possible to transfer a part of the heatreleased on combustion to the food in the cooking vessel, while the rest is dissipated to the surroundingsby different mechanisms of heat transfer, namely: conduction, convection, and radiation. In a normalcookstove design, the losses to the surroundings are suppressed and the transfer of heat to the contentsof the pot is maximized. A detailed discussion is presented in section 3.5.2.Fluid flow is the movement mechanism of fluid, like air, gases and vapours, through a mediumunder normal or artificial pressure. Knowledge of fluid flow principles is essential for understanding the flowof air and flue gases through the stove, flow passages, and chimney. The application of fluid flow principlesarerequiredtounderstandthecombustionprocess,convectiveheattransferandthechimneydraftmechanism.Knowledgeofmaterialscienceplaysanimportantroleintheselectionofmaterialsforstoveconstruction. Properties of materials have an important bearing on durability, cost, method of construction,heat losses, safety, and the scale of the production system. Material issues are discussed in sections3.5.4, 5.4, and 5.5.8+) )