System analysis of chemical and carbonate looping processes in IGCC power plants for CO2 separation

Abstract

Chemical and carbonate looping cycles have a strong potential for efficient CO2 capture with limited energy penalty. The main objective of this thesis is to assess the feasibil- ity and to evaluate the potential of these solid looping cycles in integrated gasification combined cycles (IGCC) power plants. Chemical looping combustion (CLC) can replace the combustion chamber of the con- ventional gas turbine cycle. The integration of this process can result in nearly 100% car- bon capture efficiency and around 5% electrical efficiency penalty of the combined cycle. The sensitivity analysis reveals the strong impact of the oxidation reactor temperature and of the pressure ratio. Several configurations of the combined cycles with, for example, CO2-turbine and top firing have thus been proposed and can all achieve close to 100% CO2 -capture. Chemical looping gasification (CLG) does not have the potential of capturing carbon dioxide but eliminates the need for a cryogenic distillation unit and ease the generation of synthesis gas. However, the type of oxygen carrier, the solids flow rate and the oxygen- to-fuel ratios are critical design factors for a successful integration of CLG. Carbonate looping ex situ allows the capture of carbon dioxide by moving the equi- librium of the water-gas shift reaction towards the generation of hydrogen. The capture of carbon dioxide can reach up to 93% and its purity up to 97%. This thesis suggests therefore that both chemical and carbonate looping cycles have a high potential for efficient power generation, with or without carbon dioxide capture. The easiest process to integrate, from a technological aspect, may nevertheless be chemical looping combustion of synthesis gas.