Comparative Study of Two Low CO2 Emission Power Generation System Options With Natural Gas Reforming

Abstract

Two power plant schemes that reduce CO2 emission and employ natural gas reforming were analyzed and discussed. The first one integrates natural gas reforming technology for efficiency improvement with an oxy-fuel combined power system (OXYF-REF), with water as the main work fluid. The reforming heat is obtained from the available turbine exhaust heat, and the produced syngas is used as fuel with oxygen as the oxidizer. The turbine working fluid can expand down to a vacuum, producing a high-pressure ratio and thus more net work. The second system integrates natural gas reforming in a precombustion decarbonization scheme using chemical absorption technology for the CO2 removal (PCD-REF). The gas turbine is the conventional air-based one with compressor intercooling. Supplementary combustion is employed to elevate the turbine exhaust temperature and thus achieve a much higher methane conversion rate (96.9%). Both systems involve internal heat recuperation from gas turbine exhausts, and particular attention has been paid to the integration of the heat recovery chain to reduce the related exergy destruction. The systems are simulated and their thermal efficiency, overall and component exergy losses, and CO2 removal capacity are compared. The OXYF-REF system has a higher energy efficiency, of 51.4%, and higher CO2 removal, but the product CO2 has lower purity, of 84%. The PCD-REF system has a thermal efficiency of 46%, the captured CO2 is 99% pure, and the CO2 specific emission is 58.5g∕kWh.