An efficient way of reducing the effect of coal-fired power plants on greenhouse gases is based on the separation of CO2 from combustion gases with the use of lime as an effective high temperature CO2 sorbent to form the carbonate CaCO3. This work examines the performance and factors affecting the efficiency of the carbonation process with the aid of a 1-D system model. A rapid chemical reaction period takes place initially which then slows down to saturation. The product layer is governed by diffusion inside the particle in the second stage, controlling the speed of reaction. Hydration of CaO in steam is seen to be more effective than dry carbonation but it requires an additional reactor, a steam generation system and a larger temperature range.