Simulation of the sulfur retention in an oxy-fuel 20 MW CFB combustor. M. de las Obras-Loscertales, F. García-Labiano, L. F. de Diego, P. Gayán, A. Abad, J. Adánez Instituto de Carboquímica (ICB-CSIC), Miguel Luesma Castán 4, 50018-Zaragoza, Spain mobras@icb.csic.es Abstract Oxy-fuel combustion is a CO 2 capture technology which consists of burning the fuel with a mix of pure oxygen and recycled flue gas, mainly composed of H 2 O(v) and CO 2 . Therefore, after steam condensation, the CO 2 concentration in the flue gas may be enriched up to 95% (dry basis). Many of current researches are related to oxy-fuel pulverized coal combustion. However, circulating fluidized bed combustors can be a promising technology because in addition to other advantages, they have the possibility of carrying out the in situ desulfurization process via Ca-based sorbent added into the combustor which is highly dependent on the temperature and concentration of CO 2 . Because under oxy-fuel combustion the sorbent can be surrounded by CO 2 concentrations ranging from 60 to 90%, the sulfation of the Ca-based sorbent can be performed at calcining (CaO solid reactant) or non-calcining conditions (CaCO 3 solid reactant). A particle sulfation model has been developed to describe the limestone sulfation reaction which is carried out in two steps. The simplicity of the kinetic model permitted it to be incorporated easily in a 1.5D computational simulation model of an oxy-fuel CFB to predict the sulfur retention reached inside the boiler. The model is capable of giving important information about the oxy-coal combustion process such as longitudinal profiles of the gases (O 2 , CO 2 , H 2 O, SO 2 , etc.), char concentration distribution, combustion efficiency and sulfur retention at different operating conditions. A simulation considering the main operating variables such as temperature, sorbent reactivity, O 2 concentration fed, type of coal and the use of a desulfurization unit in the recycled flue gas was carried out to determine the most influential ones. The model is considered a useful tool to optimize the oxy-fuel combustion process in circulating fluidized bed combustors. Keywords: Modeling, Oxy-fuel, Sulfur retention, Circulating Fluidized Bed 1. Introduction Nowadays, there is a great public awareness about the emissions of pollutant gases into the atmosphere from large power plants. The release of CO 2 and SO 2 gases from coal combustion to generate electric power causes serious environmental problems. The former contributes to the build-up of greenhouse gases and the latter to acid rain formation. According to the IPCC 2005 [1], CO 2 capture and storage technologies could be promising to mitigate CO 2 emissions from large power plants into the atmosphere. The development of CO 2 capture technologies to obtain an outlet gas stream in energy generation processes with high CO 2 concentration seems to be one of the most reliable solutions to slow down the increase of CO 2 in the future. Oxy-fuel combustion is a Carbon Capture technological option which consists of burning the fuel with a mix of pure oxygen and recycled flue gas which is mainly composed of CO 2 . Therefore, the CO 2 concentration in the flue gas may be enriched up to 95% (dry basis) in order to be subsequently transported and stored. Nowadays, oxy-fuel combustion is still under