Integration of in-situ CO2-oxy coal gasification with advanced power generating systems performing in a chemical looping approach of clean combustion

Underground coal gasification (UCG) is a clean coal technology to utilize deep coal resources effectively. In-situ CO2-oxy coal gasification may eliminate the operational difficulty of the steam gasification process and utilize CO2 (greenhouse gas) effectively. Furthermore, it is necessary to convert the clean gasified energy from the UCG into clean combustion energy for an end-use. In order to achieve efficient clean power production, the present work investigates the thermodynamic feasibility of integration of CO2 based UCG with power generating systems operating in a chemical looping combustion (CLC) of product gas. The use of CO enriched syngas from O2/CO2 based UCG reduces the difficulty of the heat balance between a fuel reactor and an air reactor in a nickel oxygen-carrier based CLC system. Thermodynamic analyses have been made for various routes of power generation systems such as subcritical, supercritical and ultra-supercritical boiler based steam turbines and gas turbines for the UCG integrated system. It is shown, based on mass and energy balance analysis, that the integration of CO2 based UCG with the CLC system reduces the energy penalty of carbon capture and storage (CCS) significantly. A net thermal efficiency of 29.42% is estimated for the CCS incorporated system, which operates in a subcritical condition based steam turbine power plant. Furthermore, it is found that the efficiency of the proposed steam turbine system increases to 35.40% for an ultra-supercritical operating condition. The effect of operating temperature of the air reactor and the fuel reactor of the CLC system on the net thermal efficiency of combined cycle power plant is investigated. It is found that a net thermal efficiency of 42.53% can be obtained for the CCS incorporated combined cycle power system operating at an air reactor temperature of 1200 °C.