Natural gas combined cycle power plant modified into an O2/CO2 cycle for CO2 capture

Reduction of greenhouse gas emissions is becoming essential for struggling against global warming. Priority has been given to sources where carbon dioxide (CO2) emissions are the largest and the most concentrated. Power plants using fossil fuels offer a great opportunity of applying CO2 recovery processes. The O2/CO2 cycle is an interesting option since CO2 concentration in the flue gas is highly increased. This cycle has been applied to a natural gas combined cycle (NGCC) using an advanced gas turbine (GE9H). The aim of this study is to assess by simulation the energy and environmental performances of this new type of power plant. The oxygen required is produced by an air separation unit (ASU) that can deliver oxygen with a purity ranging between 85 and 97 mol.%. A CO2 recovery process based on a cryogenic separation of carbon dioxide from inert gases has been designed and assessed. The impact of CO2 capture has been calculated with the Aspen plus™ software. With an O2 purity of 90 mol.% and an 85% CO2 recovery rate, the net electrical efficiency reaches 51.3% (based on the low heating value (LHV)). This corresponds to an efficiency loss of 8.1%-points in comparison with the base case. The quantity of avoided CO2 is about 280 g kW−1 h−1. These results have been compared with a conventional amine scrubbing applied to a NGCC. With a lean CO2 loading of 0.16 mol CO2/mol amine, this process leads to a net electrical efficiency of 49.1% (LHV). The conversion into an O2/CO2 cycle seems to be more efficient than amine scrubbing but more difficult to implement because of the specific gas turbine.