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Reduction of Alkali Release by Two Fuel Additives at Different Bed Temperatures during Grate Combustion of Woody Biomass
Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics. (Anders Rebbling)
Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
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2019 (English)In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 33, no 11, p. 11041-11048Article in journal (Refereed) Published
Abstract [en]

The use of small- and medium-scale combustion of biomass for energy utilization is expected to grow in the coming decades. To meet standards and legislation regarding particle emissions and to reduce corrosion and deposit formation, it is crucial to reduce the release of alkali species from the fuel. This can be achieved by capturing the volatile alkali in the residual bottom ash as more thermally stable compounds. In this work, we investigate the combination of primary measures, i.e., process parameters and fuel additives, for reduction of the release of K and Na from the fuel bed during fixed bed combustion. In addition, the influence of these combined measures on fine particle emissions was explored. The results showed a clear influence of the process parameters, herein bed temperature, and that a significant reduction of the alkali release and PM1 emissions can be achieved by correct settings. Furthermore, the application of additives (kaolin and diammonium sulfate) reduced both K and Na release even further. The observed effects on the release behavior was mainly explained by the formation of KAlSiO4 and K2SO4 during addition of kaolin and diammonium sulfate, respectively. This work therefore emphasizes the importance of good control over the fuel bed conditions, especially temperature, when these additives are applied. To reduce the potential deactivation (for kaolinite) and melting (for K2SO4), the control of bed temperature is vital. Thus, it was concluded that the release of volatile alkali species and related fine particle emissions in small- and medium-scale biomass heat and power plants using wood fuels could be significantly reduced by a correct combination of controlling the combustion parameters and the use of fuel additives.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2019. Vol. 33, no 11, p. 11041-11048
National Category
Chemical Process Engineering Energy Systems
Identifiers
URN: urn:nbn:se:umu:diva-165214DOI: 10.1021/acs.energyfuels.9b02391ISI: 000499741900061OAI: oai:DiVA.org:umu-165214DiVA, id: diva2:1370412
Funder
Swedish Energy AgencyBio4EnergyAvailable from: 2019-11-15 Created: 2019-11-15 Last updated: 2020-01-03Bibliographically approved
In thesis
1. Application of fuel design to mitigate ash-related problemsduring combustion of biomass
Open this publication in new window or tab >>Application of fuel design to mitigate ash-related problemsduring combustion of biomass
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The energy supply of today is, through the use of fossil energy carriers,contributing to increased net emissions of greenhouse gases. This hasseveral negative effects on our environment and our climate. In order toreduce the impact of this, and possibly to reverse some of the effects, allrenewable energy sources must be used. Biomass is the renewable energycarrier that has the greatest potential to reduce net greenhouse gasemissions, but the transition from fossil fuels to biofuels is challenging.The combustion of biomass is associated with various technical andenvironmental problems such as slagging, corrosion, and emissions ofparticles, soot, or harmful chemical compounds. Most of these problemsare linked to ash chemical reactions involving alkali metals. Therefore, toreduce the risk of operational and environmental problems, it is importantto understand and control the ash transformation reactions involvingalkali metals.The research presented in this thesis has focused on the development oftools, such as models and indices, for predicting the behaviour of variousbiofuels during combustion, and on the development of the concept of fueldesign and implementation of the same during industrial combustion ofbiomass. The development of easy-to-use tools for predicting problematicash behaviour is crucial in order to make it possible to increase the use ofbiomass as an alternative to fossil fuels. The tools presented here are basedon theoretical and empirical knowledge and can be used to predictchallenges concerning the fuel ash composition and to propose relevantfuel design measures.The purpose of fuel design, as used here, is to broaden the fuel feedstockand to increase the usability of biomass in the global energy system. Thisis achieved through measures to change the ash chemical composition inorder to enhance beneficial properties, or reduce problematic properties,via the use of additives or blending of two or more different fuels.The present thesis extends the foundation of knowledge regarding fuel ashtransformation reactions and their implications for operational problemsthrough in-depth laboratory studies and analyses. Furthermore, thefeasibility of applying this extended knowledge in the medium and largescaleindustrial combustion of biomass is demonstrated and validated. More specifically, a slagging index has been developed using the results ofseveral years of combustion experiments. Fuel designs based on the indexwas demonstrated during normal operation in local and district heatingplants. Furthermore, a model was developed for predicting slaggingproblems that take into account both the chemical composition of the fueland the burner technology.Several studies have also been performed on different fuel designs basedon the same foundation as the index and the model. Additives to supply forexample calcium and sulphur, as well as the clay kaolin, have been used toreduce both technical and environmental problems.The conclusion is that fuel design, based on ash chemistry, is a possiblepath for increased fuel flexibility and a broader feedstock for bioenergy.

Abstract [sv]

Vår energianvändning bidrar idag genom användandet av fossilaenergibärare till ökade nettoutsläpp av växthusgaser. Detta medför olikaeffekter på vår miljö och vårt klimat. För att minska påverkan, ocheventuellt reversera vissa av effekterna, måste alla förnybara energikälloranvändas. Biomassa är den förnybara energibäraren som har den störstapotentialen att minska nettoutsläppen av växthusgaser, men övergångenfrån fossila bränslen till biobränslen kan vara utmanande.Förbränning av biomassa är förknippad med olika tekniska ochmiljömässiga problem såsom slaggning, korrosion och utsläpp av partiklar,sot eller skadliga kemiska föreningar. De flesta av dessa problem ärkopplade till askkemiska reaktioner som involverar alkalimetaller. För attminska risken för drift- och miljöproblem är det därför viktigt att förståoch kontrollera de asktransformationer som involverar just alkalimetaller.Forskningen som presenteras i denna avhandling har fokuserat påutveckling av verktyg, såsom modeller och index, för att förutsägabeteendet hos olika biobränslen under förbränning, samt på utveckling avkonceptet bränsledesign och implementering av detsamma vid industriellförbränning av biomassa. Utvecklingen av lättanvända verktyg för attförutsäga problematiska askbeteenden är avgörande för att det ska varamöjligt att öka användningen av biomassa som ett alternativ till fossilabränslen. Verktygen som presenteras här är baserade på teoretisk ochempirisk kunskap och kan användas för att förutsäga utmaningarangående bränsleaskans sammansättning och beteende, samt för attföreslå relevanta bränsledesignåtgärder.Syftet med bränsledesign, som det används här, är att bredda råvarubasenför biobränslen samt att öka användbarheten för biomassa i det globalaenergisystemet. Detta uppnås genom åtgärder för att förändra askanskemiska sammansättning, så att gynnsamma egenskaper förstärks ellerproblematiska egenskaper reduceras. Detta möjliggörs genom exempelvisanvändning av additiv eller samförbränning av två eller flera olikabränslen.Den här avhandlingen utvidgar kunskapsbasen för asktransformationerhos biomassa och deras konsekvenser i form av driftproblem genomdjupgående laboratoriestudier och analyser. Dessutom demonstreras och valideras bränsledesign under industriell förbränning av biomassa imedelstor och fullstor skala.Mer specifikt har ett slaggindex utvecklats med hjälp av resultaten frånflera års förbränningsförsök. Bränsledesigner baserade på detta index hardemonstrerats under normal drift i när- och fjärrvärmeanläggningar.Dessutom utvecklades med hjälp av multivariata statistiska metoder enmodell för att förutse slaggningsproblem som tar i beaktande bådebränslets kemiska sammansättning och brännartekniken.Flera delstudier har även genomförts på olika bränsledesigner baserade påsamma grund som indexet och modellen. Sameldning av olika bränslenoch additiv för att tillföra till exempel kalcium och svavel, samtlermaterialet kaolin, har använts för att minska såväl tekniska sommiljömässiga problem.Slutsatsen är att bränsledesign, baserat på askkemiska grunder, är enmöjlig väg för ökad bränsleflexibilitet och breddad råvarubas förbiobränslen.

Place, publisher, year, edition, pages
Umeå: Umeå University, 2019. p. 48
Keywords
Thermochemical energy conversion, biomass, combustion, ash chemistry, fuel design, ash transformation reactions, renewable energy
National Category
Chemical Engineering Bioenergy
Identifiers
urn:nbn:se:umu:diva-165225 (URN)978-91-7855-143-9 (ISBN)
Public defence
2019-12-11, N460, 09:00 (English)
Opponent
Supervisors
Available from: 2019-11-20 Created: 2019-11-15 Last updated: 2019-11-19Bibliographically approved

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Rebbling, AndersFagerström, JonathanSteinvall, ErikCarlborg, MarkusBoman, Christoffer

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