Life cycle analysis of geothermal power generation with supercritical carbon dioxide

Abstract

Life cycle analysis methods were employed to model the greenhouse gas emissions and fossil energy consumption associated with geothermal power production when supercritical carbon dioxide (scCO _2 ) is used instead of saline geofluids to recover heat from below ground. Since a significant amount of scCO _2 is sequestered below ground in the process, a constant supply is required. We therefore combined the scCO _2 geothermal power plant with an upstream coal power plant that captured a portion of its CO _2 emissions, compressed it to scCO _2 , and transported the scCO _2 by pipeline to the geothermal power plant. Emissions and energy consumption from all operations spanning coal mining and plant construction through power production were considered, including increases in coal use to meet steam demand for the carbon capture. The results indicated that the electricity produced by the geothermal plant more than balanced the increase in energy use resulting from carbon capture at the coal power plant. The effective heat rate (BTU coal per total kW h of electricity generated, coal plus geothermal) was comparable to that of traditional coal, but the ratio of life cycle emissions from the combined system to that of traditional coal was 15% when 90% carbon capture efficiency was assumed and when leakage from the surface was neglected. Contributions from surface leakage were estimated with a simple model for several hypothetical surface leakage rates.

Keywords

• 88.05.Hj
• 88.05.Np
• 88.10.H
• geothermal power
• supercritical carbon dioxide
• life cycle analysis