Combined cycle power plants with post-combustion CO₂ capture: Energy analysis at part load conditions for different HRSG configurations

The part-load behaviour of combined cycle power plants (CCPP) equipped with post-combustion CO₂ capture is analyzed. Different CCPP configurations are compared, including single-, dual- or triple-pressure level steam generators. The gas turbine is a single shaft unit using the variable guide vanes and fuel flow to control the load. The 90% CO₂ capture is achieved using monoethanolamine (MEA 30%wt) as absorbent. In all configurations, the reboiler duty to regenerate the absorbent is partly covered by the hot water of the economizer. This economizer-reboiler loop allows to increase the plant efficiency as the possibility to extract more energy from the economizer results in lowering the steam extraction from the turbine. The dual-pressure level CCPP with CO₂ capture gives the best efficiency at the design operation. As the load is reduced, the efficiency of the single-pressure plant becomes comparable to the efficiency of the dual-pressure plant, due to the effective thermal integration between the heat recovery steam generator and the absorbent regeneration process. Hence, when CCPPs with CO₂ capture operate at part-loads, a further benefit can be achieved with the single-pressure level plant, having it both design simplicity and low efficiency penalties for the CO₂ capture.