Modeling the CO₂-based enhanced geothermal system (EGS) paired with integrated gasification combined cycle (IGCC) for symbiotic integration of carbon dioxide sequestration with geothermal heat utilization

The global warming potential of carbon dioxide (CO₂) emphasizes more the sequestration of CO₂ otherwise emitted from coal-fired power plants in the future. This study is focused on pairing a coal-fired integrated gasification combined cycle (IGCC) plant with enhanced geothermal system (EGS) for simultaneous sequestration of CO₂ and extraction of geothermal heat energy for subsequent electricity generation by an organic Rankine cycle (ORC) in enhanced geothermal systems (EGS). By assuming the reservoir characteristics for two different geothermal source temperatures 200°C and 300°C, heat transfer calculations show that larger reservoir volume (>1km³) is necessary for the sustained extraction of geothermal heat energy over a period of 25 years. The temperature and pressure profiles of CO₂ in the injection well and the production well, the corresponding power output from the ORC for five different working fluids, are simulated by ASPEN Plus Version 7.3. The reservoir conditions and the type of working fluid selected determine the power output in the ORC. The temperature and the pressure of the CO₂ at the outlet of the production well are greater than that at the injection well due to the heating of CO₂ in the reservoir during the extraction of geothermal heat energy. Therefore, a combination of a high pressure turbine and an organic Rankine cycle is beneficial for the conversion of geothermal energy from CO₂ into electricity before its recirculation into the injection well. Among the secondary working fluids used in the modeling of the ORC, the time-averaged net EGS power is highest for isobutane and lowest for isopentane over a period of 25 years. When isobutane is used as a secondary working fluid, the time-averaged power output over a period of 25 years for two geothermal reservoirs at an initial geothermal source temperature of 300°C and 200°C are 46MW_e and 21MW_e, respectively. When neopentane is used as a secondary working fluid, the time-averaged power output for a period of 25 years is 37MW_e for an initial geothermal source temperature of 300°C and 17MW_e for an initial geothermal source temperature of 200°C. Pairing IGCC with EGS can considerably recover some of the energy lost during the sequestration of CO₂ (50MW_e) from a 629MW_e IGCC plant.