Exergetic Performance and Power Conversion of a CO2 Thermosiphon

Abstract

Engineered geothermal systems (EGS) supply the potential to produce a significant capacity of base-load renewable electricity. In EGS that are not hydraulically connected to a source of water recharge off the opportunity to use CO2 as a heat extraction fluid instead of H20. CO2 offers the advantages of ease of flow through the subsurface reservoir, an innate buoyancy driving simplifying surface equipment design, and lower dissolution of compounds that lead to fouling in wellbores and surface equipment. These advantages are balanced by higher frictional losses within the wellbores, particularly the production wellbore due to the low density of CO2 in this process component. Here we explore the results of these advantages and disadvantages on the exergy extracted from the geothermal reservoir, and examine the impact of direct use of CO2 in power conversion equipment.