Thermodynamic Assessment of Cooled and Chilled Ammonia-based CO2 Capture in Air-Blown IGCC Plants

The energy impact of different post-combustion CO2 capture plants integrated in an advanced air-blown IGCC is simulated in this paper. Ammonia scrubbing is considered as the CO2 capture technology and chilled and cooled modes are investigated with reference to operation temperatures at the absorber equal to 7 °C and 20 °C respectively. Ammonia slip is controlled by means of an absorption-desorption cycle just before a final acid wash, where use of the H2S removed from the coal-derived gas at the desulphurization unit of the IGCC is made. Focusing on three levels of CO2 capture, from 80% to 90%, it is possible to appreciate that the cooled mode is promising as far as a reduction of the energy cost related to CO2 capture is concerned. As a matter of fact, the energy saving, possible when adopting an air cooling system instead of a chilling plant, is significant with the specific primary energy consumption for 90% of CO2 avoided which decreases from 2.79 MJ/kgCO2 to 2.54 MJ/kgCO2, when switching from the chilled to the cooled mode, with a difference equal to about 0.7 percentage point in IGCC efficiency.