Performance analysis of a novel low CO2-emission solar hybrid combined cycle power system

Abstract

This paper is a proposal and analysis of a novel low-CO2 emission solar hybrid combined cycle power system, which is based on solar-driven methane reforming. Nearly full methane conversion is achieved at a mild temperature (∼550 °C) using a methane reforming reactor integrated with a hydrogen separation membrane, enabling the solar thermal energy collected at middle temperature to be applied as the reaction heat in methane reforming, thereby converting the solar heat to chemical energy of the produced syngas. The membrane reactor also offers the advantage of continuously withdrawing hydrogen from the reaction zone, which is then burned at high temperature for power generation in the proposed advanced combined cycle system. The CO2-enriched gas concentrated at the end of the reaction zone is processed through pre-combustion decarbonization. It is shown that system thermal efficiency of 51.6% can be obtained, which is 2.2%-points higher than that of a referenced gas-steam combined cycle system with post-combustion decarbonization (CC-Post) at an equal CO2 removal ratio and no solar assistance. Fossil fuel saving ratio of 31.2% is achieved with a solar thermal share of 28.2%. Exergy analysis indicates that the main contributors for efficiency improvements are the reduced exergy destructions in the combustion and CO2 separation processes. The hybrid system has an exergy efficiency of 58% with 91% CO2 capture, which is 10%-points higher than that of a comparable CC-Post system. A preliminary economic analysis predicts that levelized electricity cost and payback period for the system are found to be 0.062 $/kWh and 10 years, respectively, and cost of CO2 avoided is 81 $/(ton CO2), which is 42.5% lower than that for a CC-Post system. The proposed system hybridization approach simultaneously achieves the dual-purpose of high-efficiency solar heat conversion and low-energy penalty CO2 capture.