Thermodynamic analysis of an improved CO2-based enhanced geothermal system integrated with a coal-fired power plant using boiler cold-end heat recovery

CO2-based enhanced geothermal system (EGS) is currently being developed for environmental-friendly power generation and boiler cold-end energy recovery using the low-temperature economizer (LTE) is also aggressively investigated to increase the coal-based power generation efficiency. However, the efficiencies of these two systems are not quite satisfactory due to the limits of the working medium parameters. Here, an improved hybrid system, which highly integrates the CO2-based EGS with the boiler cold-end energy recovery was proposed. In the proposed system, the temperature of the CO2 at the inlet of the CO2 turbine was increased and the parameters of the steam bleed saved by the boiler cold-end energy were also enhanced, leading to a greater system electric power output and a corresponding higher heat utilization efficiency. The mass and energy balance of the proposed integrated system were determined using the developed models and simulation process. Results showed that the net additional power output from the coal-fired power plant was 10.81 MW and the electric output from the CO2-based EGS was 10.11 MW in the proposed system, which are both greater than those of the stand-alone CO2-based EGS and the conventional LTE system, consequently leading to a higher energy utilization efficiency at 36.2%.