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Comparison of Two CO2 Capture Methods for a Natural Gas Combined Cycle Plant

Thermoflex is the perfect tool to analyze the effects of altering cycle parameters. The Natural Gas Combined Cycle (NGCC) plants examined below consist of two GE 7FB gas turbine generators, two 3-pressure single-reheat HRSGs, and one steam turbine generator. The two plants both have post-combustion CO2 capture systems that separate the 90% of the CO2 from the other components of the exhaust stream. Once separated, the CO2 is compressed to 2200 psia (152 bar) for delivery to its final destination.

Both plants use a standard single reheat steam turbine. The high pressure turbine inlet conditions are 2400 psia/1100°F (165 bar/593ºC), the reheat conditions are 420 psia/1050°F (29 bar/566ºC), and the condenser pressure is 0.7 psia (48 mbar). With these steam conditions and the CO2 capturing systems as described above, Plant A has a gross output of 534 MWe, a net output of 480 MWe, and a net LHV efficiency of 48%, while Plant B has a gross output of 559 MWe, a net output of 501 MWe, and a net LHV efficiency of 51%. For comparison, a similar plant without a CO2 capturing system has a net LHV efficiency of 56%.

CO2 Capture System - MEA

CO2 Capture System - CAP

Based on the results above, it is clear that the advanced CO2 capture process imposes less of an energy and efficiency penalty on the power plant than the amine-based process does. This is due to the lower thermal energy consumption of the advanced process (600 vs 1500 Btu/lbCO2, captured [1400 vs 3500 kJ/kgCO2, captured]) and the higher CO2 stream pressure of the advanced process (300 psia/20.7 bar vs 25 psia/1.7 bar) relative to the amine-based process before compression to delivery pressures.