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Application of fuel design to mitigate ash-related problemsduring combustion of biomass
Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
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 [en]
Thermochemical energy conversion, biomass, combustion, ash chemistry, fuel design, ash transformation reactions, renewable energy
National Category
Chemical Engineering Bioenergy
Identifiers
URN: urn:nbn:se:umu:diva-165225ISBN: 978-91-7855-143-9 (print)OAI: oai:DiVA.org:umu-165225DiVA, id: diva2:1370473
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
List of papers
1. Fuel indices for estimation of slagging of phosphorus-poor biomass in fixed bed combustion
Open this publication in new window or tab >>Fuel indices for estimation of slagging of phosphorus-poor biomass in fixed bed combustion
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2017 (English)In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 31, no 1, p. 904-915Article in journal (Refereed) Published
Abstract [en]

The market for solid biofuels will grow rapidly during the coming years, and there will be a great demand for raw materials. This will force the existing fuel base to also cover wooden materials of lower qualities as well as agricultural raw materials and residues, which often show unfavorable ash-melting temperatures. This may lead to combustion-related problems. Thus, for the utilization of lower quality fuels, it is important to be able to predict potential fuel ash-related problems such as slagging. In light of this, the first objective of the present paper was to evaluate the applicability of previously defined indices for slagging of biomass fuels (phosphorus-poor) in fixed bed combustion. The evaluation showed that none of the previously suggested indices in the literature are suitable for qualitative (nor quantitative) prediction of slagging during fixed bed combustion of P-poor biomass fuels. Hence, a second objective was to develop improved novel fuel indices that can be applied to estimate the slagging of phosphorus-poor biomass in fixed bed combustion. The novel fuel indices give a qualitative prediction of the slagging tendency in biomass fixed bed combustion but still needs additional work to further extend the compositional range as well as to fine tune the indices' boundaries.

National Category
Energy Engineering Chemical Sciences
Identifiers
urn:nbn:se:umu:diva-131876 (URN)10.1021/acs.energyfuels.6b02563 (DOI)000392553800094 ()
Projects
Bio4Energy
Available from: 2017-02-24 Created: 2017-02-24 Last updated: 2019-11-15Bibliographically approved
2. Prediction of slag related problems during fixed bed combustion of biomass by application of a multivariate statistical approach on fuel properties and burner technology
Open this publication in new window or tab >>Prediction of slag related problems during fixed bed combustion of biomass by application of a multivariate statistical approach on fuel properties and burner technology
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(English)Manuscript (preprint) (Other academic)
National Category
Chemical Engineering
Identifiers
urn:nbn:se:umu:diva-165223 (URN)
Available from: 2019-11-15 Created: 2019-11-15 Last updated: 2019-11-18Bibliographically approved
3. Demonstrating fuel design to reduce particulate emissions and control slagging in industrial scale grate combustion of woody biomass
Open this publication in new window or tab >>Demonstrating fuel design to reduce particulate emissions and control slagging in industrial scale grate combustion of woody biomass
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(English)Manuscript (preprint) (Other academic)
National Category
Chemical Engineering
Identifiers
urn:nbn:se:umu:diva-165215 (URN)
Available from: 2019-11-15 Created: 2019-11-15 Last updated: 2019-11-18Bibliographically approved
4. Waste gypsum board and ash-related problems during combustion of biomass: 1. Fluidized bed
Open this publication in new window or tab >>Waste gypsum board and ash-related problems during combustion of biomass: 1. Fluidized bed
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2015 (English)In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 29, no 2, p. 877-893Article in journal (Refereed) Published
Abstract [en]

This paper is the first in a series of two describing the use of waste gypsum boards as an additive during combustion of biomass. This paper focuses on experiments performed in a bench-scale bubbling fluidized-bed reactor (5 kW). Three biomass fuels were used, i.e., wheat straw (WS), reed canary grass (RC), and spruce bark (SB), with and without addition of shredded waste gypsum board (SWGB). The objective of this work was to determine the effect of SWGB addition on biomass ash transformation reactions during fluidized bed combustion. The combustion was carried out in a bed of quartz sand at 800 or 700 degrees C for 8 h. After the combustion stage, a controlled fluidizedbed agglomeration test was carried out to determine the defluidization temperature. During combustion experiments, outlet gas composition was continuously measured by means of Fourier transform infrared spectroscopy. At the same place in the flue gas channel, particulate matter was collected with a 13-stage Dekati low-pressure impactor. Bottom and cyclone fly ash samples were collected after the combustion tests. In addition, during the combustion tests a 6-h deposit sample was collected with an air-cooled (430 degrees C) probe. All ash samples were analyzed by means of scanning electron microscopy combined with energy dispersive X-ray spectrometry for elemental composition and with X-ray powder diffraction for the detection of crystalline phases. Decomposition of CaSO4 originating from SWGB was mainly observed during combustion of reed canary grass at 800 degrees C. The decomposition was observed as doubled SO2 emissions. No significant increase of SO2 during combustion of SB and WS was observed. However, the interaction of SWGB particles with WS and SB ash forming matter, mainly potassium containing compounds, led to the formation of K2Ca2(SO4)(3).

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2015
National Category
Chemical Engineering Energy Engineering
Identifiers
urn:nbn:se:umu:diva-101610 (URN)10.1021/ef5024753 (DOI)000349943300049 ()
Available from: 2015-04-10 Created: 2015-04-07 Last updated: 2019-11-15Bibliographically approved
5. Waste Gypsum Board and Ash-Related Problems during Combustion of Biomass. 2. Fixed Bed
Open this publication in new window or tab >>Waste Gypsum Board and Ash-Related Problems during Combustion of Biomass. 2. Fixed Bed
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2016 (English)In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 30, no 12, p. 10705-10713Article in journal (Refereed) Published
Abstract [en]

This paper is the second of two describing the use of shredded waste gypsum board (SWGB) as an additive during combustion of biomass. The focus of this paper is to determine whether SWGB can be used as a fuel additive providing CaO and SO2/SO3 for mitigation of ash-related operational problems during combustion of biomass and waste derived fuels in grate fired fixed bed applications. The former study in this series was performed in a fluidized bed and thus allow for comparison of results. Gypsum may decompose at elevated temperatures and forms solid CaO and gaseous SO2/SO3 which have been shown to reduce problems with slagging on the fixed bed and alkali chloride deposit formation. Three different biomasses, spruce bark (SB), reed canary grass (RG), and wheat straw (WS), were combusted with and without addition of SWGB in a residential pellet burner (20 kWth). Waste derived fuel with and without the addition of SWGB was combusted in a large scale grate-fired boiler (25 MWth). The amount of added SWGB varied between 1 and 4 wt %. Ash, slag, and particulate matter (PM) were sampled and subsequently analyzed with scanning electron microscopy/ energy dispersive spectroscopy and X-ray diffraction. Decomposition of CaSO4 originating from SWGB was observed as elevated SO2 emissions in both the large scale and small scale facilities and significantly higher than was observed in the fluidized bed study. Slag formation was significantly reduced due to formation of calcium-silicates in small scale application, but no conclusive observations regarding calcium reactivity could be made in the large scale application. In the small scale study the formation of K2SO4 was favored over KC1 in PM, while in the large scale study K3Na(SO4)(2) and K2Zn2(SO4)(3) increased. It is concluded that SWGB can be used as a source of CaO and SO2/SO3 to mitigate slag formation on the grate and chloride-induced high temperature corrosion and that fixed bed applications are likely more suitable than bubbling fluidized beds when using SWGB as an additive.

National Category
Chemical Engineering Energy Engineering
Identifiers
urn:nbn:se:umu:diva-130240 (URN)10.1021/acs.energyfuels.6b01521 (DOI)000390072900075 ()
Projects
Bio4Energy
Available from: 2017-01-16 Created: 2017-01-14 Last updated: 2019-11-15Bibliographically approved
6. Combustion characteristics of straw stored with CaCO3 in bubbling fluidized bed using quartz and olivine as bed materials
Open this publication in new window or tab >>Combustion characteristics of straw stored with CaCO3 in bubbling fluidized bed using quartz and olivine as bed materials
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2018 (English)In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 212, p. 1400-1408Article in journal (Refereed) Published
Abstract [en]

The addition of Ca-containing compounds can reduce mass loss from agricultural biomass during storage. The resulting alkaline environment is detrimental to microorganisms present in the material. Theoretical analysis of Ca-containing biomass suggests that combustion properties are improved with respect to slagging. To validate the theoretical calculations, barley straw was utilized as a typical model agricultural biomass and combustion characteristics of straw pre-treated with 2 and 4 w/w% CaCO3 for combined improvement of storage and combustion properties were determined through combustion at 700 degrees C in a bench-scale bubbling fluidized-bed reactor (5 kW) using quartz and olivine sand as bed materials. The combustion characteristics were determined in terms of elemental composition and compound identification in bed ash and bed material including agglomerates, fly ash, particulate matter as well as flue gas measurements. The addition of CaCO3 to straw had both positive and negative effects on its combustion characteristics. Both additive levels raised the total de fluidization temperature for both quartz and olivine, and olivine proved to be less susceptible than quartz to reactions with alkali. With Ca-additives, the composition of deposits and fine particulate matter changed to include higher amounts of KCl potentially leading to higher risk for alkali chloride-induced corrosion. Flue gas composition was heavily influenced by CaCO3 additives by significantly elevated CO concentrations likely related to increased levels of gaseous alkali compounds. The results suggest that it is necessary to reduce gaseous alkali compounds, e.g. through kaolin or sulphur addition, if alkali-rich straw is to be co-combusted with Ca-rich biomass or large amounts of Ca-additives.

Keywords
Agricultural biomass, Barley straw, Calcium additive, Biomass storage, Fluidized bed combustion, Ash emistry
National Category
Energy Engineering
Identifiers
urn:nbn:se:umu:diva-145589 (URN)10.1016/j.apenergy.2017.12.112 (DOI)000425200700103 ()
Projects
Bio4Energy
Available from: 2018-03-20 Created: 2018-03-20 Last updated: 2019-11-15Bibliographically approved
7. Potassium release during time-resolved single pellet combustion of K-rich biomass with kaolin
Open this publication in new window or tab >>Potassium release during time-resolved single pellet combustion of K-rich biomass with kaolin
(English)Manuscript (preprint) (Other academic)
National Category
Chemical Engineering
Identifiers
urn:nbn:se:umu:diva-165221 (URN)
Available from: 2019-11-15 Created: 2019-11-15 Last updated: 2019-11-18Bibliographically approved
8. Reduction of Alkali Release by Two Fuel Additives at Different Bed Temperatures during Grate Combustion of Woody Biomass
Open this publication in new window or tab >>Reduction of Alkali Release by Two Fuel Additives at Different Bed Temperatures during Grate Combustion of Woody Biomass
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2019 (English)In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029Article in journal (Refereed) Epub ahead of print
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.

National Category
Chemical Process Engineering Energy Systems
Identifiers
urn:nbn:se:umu:diva-165214 (URN)10.1021/acs.energyfuels.9b02391 (DOI)
Available from: 2019-11-15 Created: 2019-11-15 Last updated: 2019-11-18
9. Application of kaolin additive for reduction of fine particle emissions during medium-scale fixed bed combustion of woody biomass
Open this publication in new window or tab >>Application of kaolin additive for reduction of fine particle emissions during medium-scale fixed bed combustion of woody biomass
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(English)Manuscript (preprint) (Other academic)
National Category
Chemical Engineering
Identifiers
urn:nbn:se:umu:diva-165222 (URN)
Available from: 2019-11-15 Created: 2019-11-15 Last updated: 2019-11-18Bibliographically approved

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