Carbon Dioxide and its potential use for geothermal power generation

Coal plant on the Yangtze River, China - not related to story (source: flickr/ ishmatt, creative commons)
Alexander Richter 6 Nov 2012

A recent study did a life cycle analysis of geothermal power generation with supercritical carbon dioxide, from a nearby coal-fueled power plant, seeing a good opportunity to utilize emissions for a power generation.

Traditionally geothermal power plants utilize hot water derived from geothermal reservoirs for power generation, but instead one could also utilize carbon dioxide as reported here before.

A recent study assesses how waste carbon dioxide could be employed to recover heat for a geothermal power plant and how energy efficient it could be.

The study did a life cycle analysis of geothermal power generation and modeled greenhouse gas emissions and fossile energy consumption associated with geothermal power production when supercritical carbon dioxide is used instead of saline geofluids to recover heat from underground.

The study reports that a significant amout of scCO2 is sequestered below ground in the process and therefore a constant supply of carbon dioxide is required. Therefore the study focused on combining a geothermal power plant with an upstream coal power plant that captured a portion of its CO2 emissions, compressed it to scCO2 and transported the scCO2 by pipeline to the geothermal plan.

“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.”

The full study is available via IOP Science.

While this generally sounds exciting the places that could use this technology are likely limited as there are not many locations that have both a local coal-fired power plant and suitable geological conditions for a supercritical carbon-dioxide geothermal plant. But for suitable sites this could be a great way to cut emissions and actually utilize them for power generation.

Source: Environmental Research Web