Shift Reactors and Physical Absorption for Low-CO2 Emission IGCCs

Abstract

Integrated Gasification Combined Cycles (IGCC) exhibit conditions particularly favourable to the sequestration of CO2. The concept pursued in this paper is the generation of syngas low in carbon, where most of the heating value of the coal fuel is carried by hydrogen. Catalytic shift reactors convert most of the CO in the syngas into CO2, which is subsequently removed by physical absorption and then compressed to make it suitable for transport and permanent storage. Energy balances, performance and cost of electricity are evaluated for two plants based on a Texaco gasifier and a large, heavy-duty gas turbine giving an overall IGCC power output between 350 and 400 MW. In one plant the raw syngas exiting the gasifier is cooled in a high-temperature, radiative cooler; in the other it is quenched by the injection of liquid water. With respect to “conventional” Texaco IGCCs, the reduction of specific CO2 emissions by 90% reduces LHV efficiency from 5 to 7 percentage points and increases the cost of electricity of about 45%. These penalties can be reduced by accepting lower reductions of CO2 emissions. Compared to the semi-closed cycle considered by other authors, where CO2 is the main component of the gas turbine working fluid, the plants analyzed here exhibit higher efficiency over the whole range of specific CO2 emissions.