Benchmarking of the pre/post-combustion chemical absorption for the CO2 capture

Abstract

The aim of the article was to compare the pre- and post-combustion CO2 capture process employing the chemical absorption technology. The integration of the chemical absorption process before or after the coal combustion has an impact on the power plant efficiency because, in both cases, the thermal energy consumption for solvent regeneration is provided by the steam extracted from the low pressure steam turbine. The solvent used in this study for the CO2 capture was monoethanolamine (MEA) with a weight concentration of 30%. In the case of the pre-combustion integration, the coal gasification was analysed for different ratios air/fuel (A/F) in order to determine its influences on the syngas composition and consequently on the low heating value (LHV). The LHV maximum value (28 MJ/kg) was obtained for an A/F ratio of 0.5 kgair/kgfuel, for which the carbon dioxide concentration in the syngas was the highest (17.26%). But, considering the carbon dioxide capture, the useful energy (the difference between the thermal energy available with the syngas fuel and the thermal energy required for solvent regeneration) was minimal. The maximum value (61.59 MJ) for the useful energy was obtained for an A/F ratio of 4 kgair/kgfuel. Also, in both cases, the chemical absorption pre- and post-combustion process, the power plant efficiency decreases with the growth of the L/G ratio. In the case of the pre-combustion process, considering the CO2 capture efficiency of 90%, the L/G ratio obtained was of 2.55 molsolvent/molsyngas and the heat required for the solvent regeneration was of 2.18 GJ/tCO2. In the case of the post-combustion CO2 capture, for the same value of the CO2 capture efficiency, the L/G ratio obtained was of 1.13 molsolvent/molflue gas and the heat required was of 2.80 GJ/tCO2. However, the integration of the CO2 capture process in the power plant leads to reducing the global efficiency to 30% in the pre-combustion case and to 38% to the post-combustion case.