Utilization of carbon dioxide from coal-based power plants as a heat transfer fluid for electricity generation in enhanced geothermal systems (EGS)

The feasibility of using carbon dioxide (CO2) as a heat transfer fluid by organic Rankine cycle (ORC) in enhanced geothermal systems (EGS) in arid regions is explored in this paper. As CO2 is available for sequestration at high pressures from an Integrated Gasification Combined Cycle (IGCC) plant, this idea is examined by pairing an IGCC plant with an EGS plant to facilitate both the simultaneous extraction of geothermal heat and sequestration of CO2 as well as power generation from EGS. The ORC portion of EGS was modeled by ASPEN Plus version 7.3. Four different working fluids were chosen for the ORC portion of the EGS to absorb the geothermal energy from the CO2 in a binary heat exchanger. The power generated from the EGS and the lowest possible temperature at which CO2 can be discharged from the binary heat exchanger was evaluated for each working fluid. The addition of a preheater provides an opportunity to add a second cycle so that both CO2 and the working fluid can be discharged at the lowest possible temperature. In all cases, the thermal energy recovered from the EGS reservoir is substantially higher than that required to compress the CO2 stream from the IGCC for sequestration.