Use of Low/Mid-Temperature Solar Heat for Thermochemical Upgrading of Energy, Part II: A Novel Zero-Emissions Design (ZE-SOLRGT) of the Solar Chemically-Recuperated Gas-Turbine Power Generation System (SOLRGT) guided by its Exergy Analysis

Abstract

This paper adds an exergy analysis of the novel SOLRGT solar-assisted power generation system proposed and described in detail in Part I of this study (Zhang and Lior, 2012, “Use of Low/Mid-Temperature Solar Heat for Thermochemical Upgrading of Energy, Part I: Application to a Novel Chemically-Recuperated Gas-Turbine Power Generation (SOLRGT) System,” ASME J. Eng. Gas Turbines Power, Accepted. SOLRGT is an intercooled chemically recuperated gas turbine cycle, in which solar thermal energy collected at about 220 °C is first transformed into the latent heat of water vapor supplied to a reformer, and then via the reforming reactions to the produced syngas chemical exergy. This integration of this concept of indirect thermochemical upgrading of low/mid temperature solar heat has resulted in a high efficiency novel hybrid power generation system. In Part I it was shown that the solar-driven steam production helps improve both the chemical and thermal recuperation in the system, with both processes contributing to the overall efficiency improvement of about 5.6%-points above that of a comparable intercooled CRGT system without solar assist, and nearly 20% reduction of CO2 emissions. An economic analysis of SOLRGT predicted that the generated electricity cost by the system is about 0.06 $/kWh, and the payback period about 10.7 years (including two years of construction). The exergy analysis of SOLRGT in this (Part II) paper identified that the main potentials for efficiency improvement is in the combustion, the turbine and compressors, and in the flue gas due to its large water vapor content. Guided by this, an improved solar-assisted zero-emissions power generation system configuration with oxy-fuel combustion and CO2 capture, ZE-SOLRGT, is hereby proposed, in which the exergy losses associated with combustion and heat dumping to the environment are reduced significantly. The analysis predicts that this novel system with an 18% solar heat input share has a thermal efficiency of 50.7% and exergy efficiency of 53%, with ∼100% CO2 capture.