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Original title:
CO2 separation by calcium looping from full and partial fuel oxidation processes 
Document type:
Fakultät für Maschinenwesen 
Technische Universität München 
This thesis work deals with the research & development of calcium looping process for CO2 separation from full and partial fuel oxidation based power generation systems. CO2 is the main greenhouse gas and undoubtedly a major contributor to the global warming. It is estimated that more than one third of the total anthropogenic CO2 emissions come from fossil fuel based heat and power generation. Moreover, fossil fuels are unlikely to be phased out rapidly, since developing alternative energy sources not only take time but also require huge investments and infrastructure. An alternative way to reduce emissions in a medium term is to capture the CO2 from fossil fueled power plants and store it away from the atmosphere. This process system combining a bunch of technologies is called carbon capture and storage (CCS). CO2 capture is an important & costly part of CCS and an array of technologies is considered for this. Calcium looping (CaL) is one of such and seems to offer effective and efficient CO2 separation from fuel oxidation processes. CaL process involves separation of CO2 at high temperatures (600-700°C) by calcium sorbents (CaO). CO2 reacts with CaO in a carbonation process and produces CaCO3. In a subsequent thermal regeneration (>850°C) called calcination, the CO2 is released from CaCO3. By alternating carbonations and calcinations over multiple cycles, CO2 is separated from a gas stream. Moreover, the CaL is realised in industrial scale with dual fluidised bed reactors for CO2 capture (the carbonator) and sorbent regeneration (the calciner). As a process in the development, research is still required in many aspects from thermodynamic modeling to experimental studies. Research works have been carried out in process simulations, sorbent reactivity & optimisation studies in a controlled reactor environment and process parametric studies in a semi-pilot scale CaL test facility. ASPEN Plus power plant simulations integrating the CaL based CO2 capture processes were performed and compared with other important competing CO2 capture technologies. The efficiency penalties for CaL looping are less than that of the Amine based process, oxyfuel process and IGCC. Sorbent reactivity studies were the main focus of this work. A wide range of sorbent samples have been studied in several experimental setups. Sorbents decay coefficients and the carbonation and calcination reaction rate coefficients were determined and compared for each of the samples. Experiments have been performed to identify the CaL process parameters that influence the sorbent deactivation. For a given sorbent with a particular number of carbonation and calcination reactions (CCR) cycles, it was found that the calcination temperature is the parameter that directly affects the reactivity. Moreover, the higher the calcination temperature the higher is the sorbent decay. In an effort to minimise the sorbent decay, a calciner design was proposed to lower the calciner temperature. A parametric study has been carried out at a semi pilot scale dual fluidised bed (DFB) CaL test facility that belongs to the Institut für Feuerungs- und Kraftwerkstechnik(IFK), at the Universität Stuttgart. A crucial parameter which defines the CO2 capture efficiency of a particular CaL reactor system was determined by analysing the sorbent samples in a Thermogravimetric Analyser(TGA), collected at steady state operation. A specific TGA experimental procedure was applied for this parametric study. In a separate study, reactivities of DFB samples and fresh ones were analysed in a TGA and compared. A successful method has been tested to substantially restore the lost CO2 capture capacity of spent sorbents from this test facility. Based on the experimental results, a partial hydration of sorbent stream was proposed to sustain the reactivity of the carbonator. Further TGA studies on simultaneous carbonation and sulfation have been performed to optimise the CO2 capture in presence of SO2. Carbonation to sulfation ratio was compared against the residence time and it provided clear indication to minimise the adverse effect of sulfation on CO2 separation. Moreover, pressurised TGA experiments in the context of CaL for partial oxidation processes have been carried out with synthetic syngas. Sorbent behavior under varying temperatures and CO2 concentrations have been studied. Under these conditions, neither the reducing atmosphere nor the presence of H2 and CH4 have a negative influence on the reactivity of CO2 and CaO. In a separate study, sorbent decay due to high temperature sintering have been experimentally determined & discussed. Further on, incomplete(partial) carbonation experiments showed improved sorbent reactivity with number of CCR cycles when compared to that of the same number of complete CCR cycles. 
Translated abstract:
Im Rahmen dieser Doktorarbeit wird die Forschung und Entwicklung von Calcium Looping Verfahren zur CO2-Abtrennung aus vollständigen und teilweise oxidierten Brennstoffen in Kraftwerksprozessen behandelt. CO2 ist das wichtigste Treibhausgas und zweifellos ein wesentlicher Faktor für die globale Erderwärmung. Es wird geschätzt, dass mehr als ein Drittel der gesamten anthropogenen CO2-Emissionen aus auf fossilen Brennstoffen basierender Wärme-und Stromerzeugung kommen. Zudem ist unwahrscheinlich,...    »
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