| 1. |
- Gunarathne, Duleeka, 1984-
(författare)
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Advanced Gasification of Biomass/Waste for Substitution of Fossil Fuels in Steel Industry Heat Treatment Furnaces
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- With the current trend of CO2 mitigation in process industries, the primary goal of this thesis is to promote biomass as an energy and reduction agent source to substitute fossil sources in the steel industry. The criteria for this substitution are that the steel process retains the same function and the integrated energy efficiency is as high as possible.This work focuses on advanced gasification of biomass and waste for substitution of fossil fuels in steel industry heat treatment furnaces. To achieve this, two approaches are included in this work. The first investigates the gasification performance of pretreated biomass and waste experimentally using thermogravimetric analysis (TGA) and a pilot plant gasifier. The second assesses the integration of the advanced gasification system with a steel heat treatment furnace.First, the pyrolysis and char gasification characteristics of several pretreated biomass and waste types (unpretreated biomass, steam-exploded biomass, and hydrothermal carbonized biomass) were analyzed with TGA. The important aspects of pyrolysis and char gasification of pretreated biomass were identified.Then, with the objective of studying the gasification performance of pretreated biomass, unpretreated biomass pellets (gray pellets), steam-exploded biomass pellets (black pellets), and two types of hydrothermal carbonized biomass pellets (spent grain biocoal and horse manure biocoal) were gasified in a fixed bed updraft gasifier with high-temperature air/steam as the gasifying agent. The gasification performance was analyzed in terms of syngas composition, lower heating value (LHV), gas yield, cold gas efficiency (CGE), tar content and composition, and particle content and size distribution. Moreover, the effects on the reactions occurring in the gasifier were identified with the aid of temperature profiles and gas ratios.Further, the interaction between fuel residence time in the bed (bed height), conversion, conversion rate/specific gasification rate, and superficial velocity (hearth load) was revealed. Due to the effect of bed height on the gasification performance, the bed pressure drop is an important parameter related to the operation of a fixed bed gasifier. Considering the limited studies on this relationship, an available pressure drop prediction correlation for turbulent flow in a bed with cylindrical pellets was extended to a gasifier bed with shrinking cylindrical pellets under any flow condition. Moreover, simplified graphical representations based on the developed correlation, which could be used as an effective guide for selecting a suitable pellet size and designing a grate, were introduced.Then, with the identified positive effects of pretreated biomass on the gasification performance, the possibility of fuel switching in a steel industry heat treatment furnace was evaluated by effective integration with a multi-stage gasification system. The performance was evaluated in terms of gasifier system efficiency, furnace efficiency, and overall system efficiency with various heat integration options. The heat integration performance was identified based on pinch analysis. Finally, the efficiency of the co-production of bio-coke and bio-H2 was analyzed to increase the added value of the whole process.It was found that 1) the steam gasification of pretreated biomass is more beneficial in terms of the energy value of the syngas, 2) diluting the gasifying agent and/or lowering the agent temperature compensates for the ash slagging problem in biocoal gasification, 3) the furnace efficiency can be improved by switching the fuel from natural gas (NG) to syngas, 4) the gasifier system efficiency can be improved by recovering the furnace flue gas heat for the pretreatment, and 5) the co-production of bio-coke and bio-H2 significantly improves the system efficiency.
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| 2. |
- Gunarathne, Duleeka, 1984-, et al.
(författare)
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BIOMASS PRETREATMENT FOR LARGE PERCENTAGE BIOMASS CO-FIRING
- 2014
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Konferensbidrag (refereegranskat)abstract
- With the target of reducing net GHG emissions from coal fired power plants, biomass co-firing in such plants is becoming more and more attractive option among other thermal applications of biomass such as combustion, gasification and pyrolysis. Not only CO2, but effective reduction of SOx and NOx emissions can also be expected with this low cost, sustainable and renewable energy option. However, the economic feasibility of such process largely depends on the cost of biomass acquisition and transportation. Therefore, local availability of large quantities of biomass is important for more economic co-firing. Since always this is not the case, pretreatment of biomass to increase energy density is another way to make biomass economical for long distance transportation. Pretreatment also broaden the usage of biomass sources (eg. wet and waste biomass), reduce the moisture content make it hydrophobic reducing drying energy demand, ease to comminute into small particles creating it more economical source for co-firing. Further, as a result of pretreatment, combustion and electricity generation efficiencies will be improved due to increased heating value of pretreated biomass. Therefore, enhancement of biomass properties is advisable not only to improve its inferior characteristics as well as to make it as suitable alternative for fossil fuels. In this paper, the technologies of biomass pretreatment for thermal application, such as physical and thermochemical pretreatments were reviewed. The upgrading processes of biomass including steam explosion, torrefaction and hydrothermal carbonization-HTC were described based on the HHV, adiabatic flame temperature, fouling tendency and emissions. Furthermore, a case study using severely torrified biomass for large percentage co-firing with coal is discussed.
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| 3. |
- Gunarathne, Duleeka, 1984-, et al.
(författare)
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High temperature air/steam gasification of steam exploded biomass
- 2013
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Ingår i: Finnish – Swedish Flame Days 2013.
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Konferensbidrag (refereegranskat)abstract
- Pretreatment of biomass under high pressure steam is called steam explosion. Hydrophobic dark coloured pellets (here referred as Black pellets) produced from this pretreatment technology were used in gasification experiments with both pure air and air-steam mixture as gasifying agents at an updraft High Temperature Air/steam Gasification (HTAG) unit. For comparison purpose, similar experiments were carried out with un-pretreated biomass pellets (referred as Gray pellets). Black pellets show the possibility to co-gasification with peat. Require less volume but, with high height to diameter ratio of the gasifier. High temperature gasification is preferred but decomposes at low temperature resulting around two times higher CO/CO2 ratio. With Black pellets, CO and hydro carbon contents of syngas is higher while H2 contentis higher with Gray pellets. Air gasification gave higher Lower Heating Value (LHV) with Black pellets compared to Gray pellets and was around 7.3 MJ/Nm3. Gas yields were higher with Gray pellets and they were more efficient in air gasification and efficiency was around 79.5% with higher Equivalence Ratio (ER). With steam addition to the feed gas of Black pellets result in syngas with LHV of 10.6MJ/Nm3 compared to 8.2 MJ/Nm3 with Gray pellets. Steam addition has reduced the gas yield of both pellet types. Efficiency was higher with Black pellets around 76.9%.Black pellets gave slightly more tar content in syngas compared to Gray pellets and was composed of mainly secondary tar while Gray pellets gave more tertiary tar. Cases with steam and high ER lowered the tar content. Under the tested conditions, Indene/Naphthalene ratio can be used to predict the tar content even when steam was added. In general, steam gasification of Black pellets is more feasible if syngas with high energy value is desired. But, Gray pellets with high ER was most efficient and contained lowest tar. If higher H2 yield is preferred, unpretreated pellets are more attractive.
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| 4. |
- Gunarathne, Duleeka, 1984-, et al.
(författare)
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Performance of High Temperature Air/Steam Gasification of Hydrothermal Carbonized Biomass
- 2014
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Ingår i: 22nd European Biomass Conference and Exhibition. - 9788889407523 ; , s. 626-631
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Konferensbidrag (refereegranskat)abstract
- In order to effectively use the biomass resources for thermal applications, use of biomass pretreatment technologies like hydrothermal carbonization are emerging. With the aim of studying the gasification performance of hydrothermal carbonized biomass (biocoal) in high temperature air/steam medium, gasification of two types of biocoal pellets produced from spent grain and horse manure, was carried out in a fixed bed updraft gasifier. Steam gasification gave syngas having 10-11 MJ/Nm3 of LHV with both types of biocoal. The syngas yield and thus cold gas efficiency was higher with gasification of spent grain biocoal, but syngas purity in terms of tar and particulates was better with gasification of horse manure biocoal.
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| 5. |
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