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Desarrollo de un nuevo proceso de combustión con captura de CO2 empleando óxidos metálicos

AutorAlarcón Rodríguez, Juana María
DirectorAbanades García, Juan Carlos ; Fernández García, José Ramón
Fecha de publicaciónsep-2017
Resumen[EN] Over the last two centuries, the extensive use of fossil fuels to satisfy the world energy demand has been responsible for almost all of the increase in greenhouse gases in the atmosphere, and therefore for the global warming observed over the last few decades. It is for this reason that alternative low-emission energy systems are necessary to counteract these current climate trends. The capture, transport and storage of CO2 is recognized in many climate scenarios as a powerful solution for decoupling CO2 emissions with the use of fossil fuels. This work deals with the capture of CO2 in combustion processes using solid oxygen carriers and the production of H2 with insitu capture of CO2 by combining calcium and copper looping cycles. Studies performed at conceptual and reactor modelling level, with their experimental validation at laboratory scale were carried out. A first process is developed at conceptual level using known principles and design rules in the field of high temperature solid looping cycles using packed bed reactors. It consists in the combustion of methane and CO2 capture in fixed bed reactors using ilmenite as solid oxygen carrier, a low-cost material extensively studied in the literature. The operation at high pressure allows the use of highly efficient power cycles. The use of fixed bed reactors requires specific heat management strategies to control the heat generated and/or consumed in the reaction fronts in order to avoid hot spots. In this work, the use of gas recycles is evaluated to control the progress of the reaction and heat exchange fronts. In order to ensure a continuous cyclic operation, a sequence of four stages is required: reduction, steam reforming, oxidation and heat removal for power generation. A minimum of five reactors working in parallel is necessary to ensure continuous power production and the generation of a high concentrated CO2 stream suitable for transport and storage.
The second process corresponds to the production of H2 with in situ CO2 capture using methane as a fuel and combining CaO/CaCO3 and Cu/CuO chemical loops in fixed bed reactors. This process, which has been patented by CSIC, consists of a sequence of three main stages: the sorption enhanced reforming of methane, the oxidation of copper with air and the exothermic reduction of CuO to promote the simultaneous calcination of CaCO3. The reduction of CuO with a fuel gas (CH4, CO and/or H2) supplies the energy needs for the calcination of CaCO3 (produced in the steam reforming step) which is highly endothermic. A sensitivity analysis was carried out to evaluate the influence of key design variables, such as the CuO/CaCO3 molar ratio, the initial solids temperature and the fuel gas composition. A balanced CuO/CaCO3 ratio ensures a suitable bed performance, allowing the reduction and calcination fronts to advance together, reach moderate maximum temperatures of around 900 ºC and leave behind totally converted solids. The use of CO as fuel gas minimizes the CuO/CaCO3 ratio to 1.3, thereby reducing the energy demand of the process. Experiments to evaluate the reduction of CuO/calcination of CaCO3 and the oxidation of Cu were carried out under different operating conditions. It was confirmed in these experiments that with different fuel gas compositions (using H2 or H2 and CO mixtures) and initial temperatures in the solids bed of more than 650ºC it is possible to achieve the complete calcination of CaCO3. Moreover, an increase in the concentration of CO in the fuel gas reduces the CuO/CaCO3 molar ratio. During the oxidation of Cu, which is a highly exothermic reaction, the effect of diluting the O2 in the inlet gas was evaluated. The recirculation of a large part of the product gas (N2) in order to control the temperature in the reaction front was demonstrated. A good agreement between the experimental data and the results predicted by the model was obtained.
DescripciónTesis doctoral presentada en el Departamento de Energía de la Universidad de Oviedo, 2017. Tutora de la tesis María Belén Folgueras Díaz
Aparece en las colecciones: (INCAR) Tesis
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