Journal
JOURNAL OF CO2 UTILIZATION
Volume 42, Issue -, Pages -Publisher
ELSEVIER SCI LTD
DOI: 10.1016/j.jcou.2020.101323
Keywords
CO2 geothermal; Hybrid geothermal; Auxiliary geothermal heating; Low-temperature geothermal systems; Carbon capture utilization and storage (CCUS)
Funding
- Sustainable Energy Pathways (SEP) grant from the U.S. National Science Foundation (NSF) [SEP-1230691]
- U.S. Department of Energy (DOE) [DE-EE0002764]
- Initiative for Renewable Energy and the Environment (IREE), a signature program of the Institute on the Environment (IonE) at the University of Minnesota (UMN), U.S.A.
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Hybrid geothermal power plants operate by using geothermal fluid to preheat the working fluid of a higher temperature power cycle for electricity generation. This has been shown to yield higher electricity generation than the combination of a stand-alone geothermal power plant and the higher-temperature power cycle. Here, we test both a direct CO2 hybrid geothermal system and an indirect brine hybrid geothermal system. The direct CO2 hybrid geothermal system is a CO2 Plume Geothermal (CPG) system, which uses CO2 as the subsurface working fluid, but with auxiliary heat addition to the geologically produced CO2 at the surface. The indirect brine geothermal system uses the hot geologically produced brine to preheat the secondary working fluid (CO2) within a secondary power cycle. We find that the direct CPG-hybrid system and the indirect brine-hybrid system both can generate 20 % more electric power than the summed power of individual geothermal and auxiliary systems in some cases. Each hybrid system has an optimum turbine inlet temperature which maximizes the electric power generated, and is typically between 100 degrees C and 200 degrees C in the systems examined. The optimum turbine inlet temperature tends to occur where the geothermal heat contribution is between 50 % and 70 % of the total heat addition to the hybrid system. Lastly, the CO2 direct system has lower wellhead temperatures than indirect brine and therefore can utilize lower temperature resources.
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