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

Abstract

In the last several 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 pretreatment of fossil fuels to separate carbon from hydrogen before the combustion process is one of the least energy-consuming ways 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: (i) syngas production via natural gas reforming; (ii) two reactors for CO-shift; (iii) “precombustion” decarbonization of the fuel by CO2 absorption with amine solutions; (iv) combustion of hydrogen-rich fuel in a commercially available gas turbine; and (v) 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 postcombustion 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.