Technologies for increasing CO2 concentration in exhaust gas from natural gas-fired power production with post-combustion, amine-based CO2 capture

Enhanced CO2 concentration in exhaust gas is regarded as a potentially effective method to reduce the high electrical efficiency penalty caused by CO2 chemical absorption in post-combustion capture systems. The present work evaluates the effect of increasing CO2 concentration in the exhaust gas of gas turbine based power plant by four different methods: exhaust gas recirculation (EGR), humidification (EvGT), supplementary firing (SFC) and external firing (EFC). Efforts have been focused on the impacts on cycle efficiency, combustion, gas turbine components, and cost. The results show that the combined cycle with EGR has the capability to change the molar fraction of CO2 with the largest range, from 3.8 mol% to at least 10 mol%, and with the highest electrical efficiency. The EvGT cycle has relatively low additional cost impact as it does not require any bottoming cycle. The externally fired method was found to have the minimum impacts on both combustion and turbomachinery.

Research highlights
► Enhanced CO2 concentration in exhaust gas is a effective method to reduce the high electrical efficiency penalty caused by CO2 chemical absorption.
► Four methods: exhaust gas recirculation (EGR), humidification (EvGT), supplementary firing (SFC) and external firing (EFC) can increase CO2 concentration in the exhaust gas of gas turbine.
► The results show that the combined cycle with EGR has the capability to change the molar fraction of CO2 with the largest range, from 3.8 mol% to at least 10 mol%.
► For electrical efficiency, the system integrated with EGR shows the best performance while the system integrated with air humidification shows the lowest efficiency.
► Regarding investment cost, EvGT cycle has a relatively low cost due to the absence of bottoming cycle, while supplementary firing has a relatively high cost due to its additional burner.