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Title
Gasification of alternative biomass feedstock in a dual fluidized bed gasification / von Mónica Martin
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Gasification of alternative biomass feedstock in a dual fluidized bed gasification
AuthorMartin, Mónica
CensorHofbauer, Hermann
PublishedWien, 2017
Description129 Seiten
Institutional NoteTechnische Universität Wien, Diplomarbeit, 2017
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LanguageEnglish
Document typeThesis (Diplom)
Keywords (DE)Biomass / Gasification / Fuel Testing / Economic Evaluation
Keywords (EN)Biomass / Gasification / Fuel Testing / Economic Evaluation
URNurn:nbn:at:at-ubtuw:1-101393 Persistent Identifier (URN)
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 The work is publicly available
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Abstract (English)

Reducing greenhouse gas emissions, cutting the dependency on non-renewable energy sources characterized by fluctuating prices and usually located in countries with a non-stable political situation, as well as promoting the locally available energy sources are objectives that could mean a boost in the development of renewable energy sources. Wind, solar power, or hydropower are nowadays well known and widely implemented with the aim of replacing a significant share of fossil fuels as primary energy; however, seasonality and intermittency characterize these renewable sources, being the biomass the only renewable carbon carrier with the possibility of being stored. Biomass, as produced, is solid and difficult to be used without conversion into gaseous and liquid energy carriers.^ Hence, biomass gasification and specifically the dual fluidized bed (DFB) steam gasification is a promising technology that converts a wide range of feedstocks into a medium calorific product gas to produce electricity, heat, fuels, and chemicals. Even though biomass is considered to be the only alternative to fossil fuels, it is difficult to compete against the plummeting prices of fossil fuels. It is true that harmful long-term effects of fossil fuels are insufficiently included in the economic analysis and for that reason, governments should promote the research and investment in biomass plants by awarding incentives in return for taking risks. This thesis proves the economic disadvantages of using biomass to supply the heat demand of a kiln or boiler instead of using fossil fuels.^ The industrial gasification plant which is chosen to carry out the economic study is Güssing (Austria), as Vienna University of Technology (TU Wien) initially demonstrated there the DFB technology, several researches have been completed at this plant and moreover, the data are of sufficient quality to carry out an economic analysis. This analysis leads to the conclusion that even increasing the capacity of the plant and taking advantages from economies of scale, would not be enough to overthrow fossil fuel prices. However, a glimmer of hope comes linked to the fuel flexibility of the novel DFB steam gasification pilot plant at TU Wien that allows alternative biogenic feedstocks to be gasified. These alternative feedstocks such as chicken manure or exhausted olive pomace mean a waste stream and gasification could be a solution for getting rid of them.^ Three test runs were successfully carried out at TU Wien, which proves the technical feasibility of gasifying alternative feedstocks such as bark and chicken manure with K-feldspar (potassium feldspar) as bed material that has not been used so far at the pilot plant. In particular, the gasification of softwood pellets, a mixture of chicken manure/bark pellets, and pure chicken manure pellets with K-feldspar as bed material represents the core of the experimental part of the present work. Additionally, these tests are compared to the traditional gasification of softwood and olivine. The alternative feedstocks analysed in this thesis are characterized by high ash content with components that can cause fouling, slagging, and bed material agglomeration, causing unscheduled downtimes and damages in downstream equipment. Despite the diversity in fuel composition, the product gas composition is not strongly affected.^ Furthermore, inorganic matter is related not only to the dust content, but also to their catalytic activity allowing tar content in the product gas to be reduced. Therefore, softwood is the biomass feedstock with the lowest ash content among the ones studied but also its product gas is the one with the highest tar content (considering only experiments with K-feldspar). Regarding bed materials, the catalytic activity of olivine, as well as its heat transfer capacity, is higher compared to K-feldspar. It is known that K-feldspar is not characterized as an excellent catalytically active bed material; however, the presence of char and ash content due to the chemical composition of the alternative feedstocks can enhance the catalytic reactions to reduce tar content in the product gas. New biomass feedstocks, and especially the ones that come from waste streams, help operating costs of the gasification process to be lowered.^ According to that, operating costs from the gasification of woody feedstocks can be cut by 40% when using alternative biomass forms.

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