Modelling of SO 2 retention in oxyfuel circulating fluidized bed combustors (CFBC´s) M. de las Obras-Loscertales, A. Rufas, F. García-Labiano, L.F. de Diego, A. Abad, P. Gayán, J. Adánez Department of Energy and Environment. Instituto de Carboquímica (ICB-CSIC). Miguel Luesma Castán 4. 50018. Zaragoza mobras@icb.csic.es, ldediego@icb.csic.es Abstract Oxy-fuel combustion is a variation of conventional combustion process which belongs to the CO 2 capture technologies for subsequent storage (CCS). It consists in using a mix of pure O 2 and CO 2 recirculated instead of air to perform the combustion. Therefore, an outlet gas stream with high CO 2 concentration is obtained (≈90-95% of CO 2 concentration in dry basis). Among the different options to burn coal, the circulating fluidized bed combustor (CFBC) is a promising technology that allows the CO 2 capture, as well as the in-situ SO 2 retention by means of supplying a calcium-based sorbent into the combustor. The high CO 2 concentration present inside the boiler during oxy-fuel combustion can affect the way to carry out the sulphur retention process with respect to the conventional combustion with air. In fact, depending on the operating conditions existing in the combustor (temperature and CO 2 partial pressure), the sulphation of the sorbent can be carried out at calcining or non-calcining conditions. The aim of this work was to elaborate a mathematical model (1.5 D) of a CFBC operating under oxy-fuel combustion conditions in order to analyse the effect of the main operating variables on the SO 2 retention process. This model considers radial and axial concentration profiles, and integrates the hydrodynamic sub-model with different kinetic sub-models that define the coal combustion and sorbent sulphation processes. The model is used to simulate the effect on the sulphur retention of the main variables related to boiler operation (mainly the temperature to distinguish between calcining and non-calcining conditions) and sorbent materials used. 1. Introduction Global climate change is an issue of major international concern in the present world context. According to the IPCC [1], CO 2 Capture and Storage technologies have a high development potential, and where the costs for mitigating climate change can be decrease compared to strategies where only other mitigation options are considered. The technologies for CO 2 capture have suffered a high development in the last decade and some of them are commercially available today [2]. Among them, oxyfuel is still under development and not yet used commercially for CO 2 capture. However, several pilot plants ranging from 20-40 MW th have been running, and several large-scale demonstration boilers are planned for the next future in 2015-2016. Most of them correspond to pulverized coal (PC) boilers. However,