| Abstract |
CO2-EGS for power generation has been extensively modeled over the last few years, most notably by Karsten Preuss et al at Lawrence Berkeley National Laboratory. CO2 has several drawbacks and advantages as compared to water as a geothermal fluid. Overall, however, it is anticipated to be a better geothermal fluid than water with an average heat extraction rate 50% greater than that of water. Despite its operational advantages as a geothermal fluid, there are potential problems with the use of CO2 in stand-alone power generation projects. In particular, the profitability of projects is sensitive to the cost of CO2, the cost of compressing and transporting it, the loss rate (which is unknown) during rapid cycling of CO2 through the system, and the conversion efficiency of heat to power. In the absence of a significant carbon tax, power projects may be restricted to areas with very low cost CO2 (e.g., natural deposits, natural gas processing plants) associated with geothermal resources instead of more costly CO2 from power plants. The highly pressurized CO2 derived from CO2-EGS offers one distinct advantage relative to hot water from water-based geothermal projects: it has great utility as an industrial chemical for a wide range of projects other than power generation. Under certain circumstances, the pressurized CO2 in such projects may have significantly greater economic utility than for power generation. One project utilizing CO2 for a purpose other than power generation may be possible at the St. Johns Dome on the border between Arizona and New Mexico. The energy company that owns 90% of the CO2 leases at the dome intends to transport 10 million tons per year via pipeline to the Permian Basin for enhanced oil recovery beginning in 2016. Using CO2-EGS to pressurize the CO2 to the pipeline standard may cost an order of magnitude less than using conventional technology. Additionally, this project is likely to be far more profitable than a power generation project using an equivalent amount of CO2. There are at least two other uses of CO2 that are large scale and may be highly profitable. These are: ➢ Supercritical fluid extraction. In particular, CO2 could be used for hydrocarbon extraction from oil sands and oil shales. ➢ Desalination of seawater using chemical partitioning. In summary, CO2-EGS offers the potential to use geothermal energy in a wide range of large-scale, profitable industrial processes other than generating power. |