Natural gas combined cycle power plant modified into an O 2/CO 2 cycle for CO 2 capture

Abstract

Reduction of greenhouse gas emissions is becoming essential for struggling against global warming. Priority has been given to sources where carbon dioxide (CO 2) emissions are the largest and the most concentrated. Power plants using fossil fuels offer a great opportunity of applying CO 2 recovery processes. The O 2/CO 2 cycle is an interesting option since CO 2 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 CO 2 recovery process based on a cryogenic separation of carbon dioxide from inert gases has been designed and assessed. The impact of CO 2 capture has been calculated with the Aspen plus™ software. With an O 2 purity of 90 mol.% and an 85% CO 2 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 CO 2 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 CO 2 loading of 0.16 mol CO 2/mol amine, this process leads to a net electrical efficiency of 49.1% (LHV). The conversion into an O 2/CO 2 cycle seems to be more efficient than amine scrubbing but more difficult to implement because of the specific gas turbine.