Analysis of Gas-Steam Combined Cycles With Natural Gas Reforming and CO₂ Capture

In the last years greenhouse gas emissions, and in particular carbon dioxide emissions, have become a major concern in the power generation industry and a large amount of research work has been dedicated to this subject. Among the possible technologies to reduce CO₂ emissions from power plants, the pre-treatment of the fossil fuels to separate carbon from hydrogen before the combustion process is one of the least energy consuming way to facilitate CO₂ capture and removal from the power plant. In this paper several power plant schemes with reduced CO₂ emissions were simulated. All the configurations were based on the following characteristics: (1) syngas production via natural gas reforming; (2) two reactors for CO-shift; (3) “pre-combustion” decarbonization of the fuel by CO₂ absorption with amine solutions; (4) combustion of hydrogen rich fuel in a commercially available gas turbine; (5) combined cycle with three pressure levels, to achieve a net power output in the range of 400 MW. The base reactor employed for syngas generation is the ATR (Auto Thermal Reformer). The attention was focused on the optimization of the main parameters of this reactor and its interaction with the power section. In particular the simulation evaluated the benefits deriving from the post-combustion of exhaust gas and from the introduction of a gas-gas heat exchanger. All the components of the plants were simulated using Aspen Plus software, and fixing a reduction of CO₂ emissions of at least 90%. The best configuration showed a thermal efficiency of approximately 48% and CO₂ specific emissions of 0.04 kg/kWh.