Lignite gasification in gas turbine applications with CO2 capture

Examensarbete för masterexamen

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Type: Examensarbete för masterexamen
Master Thesis
Title: Lignite gasification in gas turbine applications with CO2 capture
Authors: Bondéus, Daniel
Abstract: This thesis work has evaluated the TopCycle technology for power production from lignite, integrated with drying, gasification and CO2-capture. The TopCycle concept is a high pressure, steam injected gas turbine with up to 50% steam in the flue gases. Within the frames of the thesis work the TopCycle concept has been evaluated for oxygen- and air-blown gasification, equipped with pre- and post-combustion CO2-capture, respectively. The results have been benchmarked against a conventional IGCC concept. This thesis has also specifically studied the utilisation of low temperature heat to drive a lignite dryer and the post-combustion CO2 capture unit. The concepts were evaluated by simulations in the heat balance software Ebsilon Professional. The simulations have shown that when using a 100 MW TopCycle unit as a building block, the configuration with an oxygen-blown gasifier and pre-combustion capture has an efficiency of 37% while the configuration with an air blown gasifier and post-combustion capture has an efficiency of 39-49%. The results from the air-blown configurations show a very high potential without CO2 capture, with net electrical efficiencies up to 56% (LHV). With CO2-capture the concepts are able to achieve net electrical efficiencies of up to 49% (LHV), with the assumption that a low pressure CO2-capture unit stripper is able to utilise the large amounts (2.5 MJ/kg CO2) of low temperature heat (<69°C) available in the TopCycle flue gas. If a steam dryer is utilised, instead of a low temperature dryer, the efficiency is reduced to 47 %, but the CO2-capture unit is able to utilize higher grade flue gas (<71°C). The TopCycle works with a high fraction of water as working media. This can be inserted as superheated, pressurised steam prior to combustion, or by humidifying the uncompressed air before entry. The latter case means that lower temperature heat can be used for evaporating water in the uncompressed air, leaving more high temperature heat for the CO2-separation process. It does, however, mean less heat recovery to the power generation process and more compression work, leading to lower efficiencies for the power generation. Depending on the characteristics of the CO2-capture unit, it can be required to humidify the incoming air to achieve an operational system. There are a series of crucial technologies that need to be further developed and validated before the TopCycle concept with post-combustion CO2-capture can be realised: • Operation of a 70 bar air blown gasifier • Cost effectiveness and technical feasibility of a CO2 capture unit driven with low temperature heat and partly operated below atmospheric pressure • An efficient hot gas filter at 500°C • Insensitivity of the gas turbine to SO2 compounds or hot sulphur cleanup in the syngas • A TopCycle gas turbine able to operate with a syngas of low heating value (≈3.8 MJ/kg) Despite many technical uncertainties the conclusion is that the TopCycle unit should be able to reach extraordinary efficiencies together with CO2-capture, showing promise as an important future power production technology. Further work should be focused on optimizing the post-combustion CO2-capture unit to match the heat characteristics of the TopCycle unit, utilizing low temperature heat from the flue gases.
Keywords: Energi;Hållbar utveckling;Kinetik;Kemisk fysik;Termisk energiteknik;Energy;Sustainable Development;Kinetics;Chemical physics;Thermal energy engineering
Issue Date: 2011
Publisher: Chalmers tekniska högskola / Institutionen för energi och miljö
Chalmers University of Technology / Department of Energy and Environment
Series/Report no.: Examensarbete. T - Institutionen för energi och miljö, Avdelningen för energiteknik, Chalmers tekniska högskola
Collection:Examensarbeten för masterexamen // Master Theses

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