Wednesday, 9 December

The CO2 Geothermal Siphon Concept Hotting Up

I reported on 30 October that the DoE awarded $3,000,000 to Symmyx Technologies Inc of Sunnyvale, California, to model the chemical interactions between geothermal rocks, supercritical carbon dioxide and water. Symyx, a combinatorial chemistry firm, will work with the Lawrence Berkeley National Laboratory in collaboration with Idaho National Laboratory. A number of other universities in the U.S. will take part as well. The Geothermal Digest reports on a recent conversation with materials scientist Miroslav Petro of Symyx Technologies about this project. Petro is the Symyx Project manager for this project. Symyx will be studying the interaction between CO2 and the wide variety of minerals likely to be encountered at depth.Petro notes that there is a great deal of fundamental CO2 science and the deep crustal environment that is not as yet understood.

The readers of this blog will know that I am very interested in developments in this area and will report on them as any is achieved. Contrary to some of the more optimistic analyses that come from Berkeley, our research however indicates that the CO2 geothermal siphon concept (this is what we call it) does not offer significant advantages over water as a geothermal heat exchange fluid unless the loop is closed on the surface through a supercritical CO2 turbine. The exergy transfer from the geothermal reservoir to the surface is not superior to water and, in our opinion, does not make it worthwhile (unless there are auxiliary benefits like sequestration, which are difficult to quantify and to validate). However, if we directly expand the CO2 that comes to the surface through a supercritical CO2 turbine, this would eliminate the binary plant heat exchanger, which is the largest source of efficiency loss in a binary power plant. In other words, the system would work just like a dry steam plant but extracting heat from an EGS reservoir. Aleks Atrens et al presented a paper to the AGEG/AGEA conference last month.

Again in the same stimulus package, Wall Street Journal reports on Baker Hughes starting a project to develop drilling and measuring equipment that can operate at 315 ^oC. Careful readers of this blog should remember that the DoE stimulus package had given $5,000,000 to Baker Hughers to develop directional drilling systems that can withstand temperatures up to 300 ^oC. So the WSJ article is probably referring to that same project. But since it appeared on Wall Street Journal, it will probably do a few rounds (as it appears here). Schlumberger (a Baker Hughes competitor) had also been awarded a similar amount to the same purpose as part of the same package. Hopefully one of them, or even better, two of them, will succeed. The EGS sector sure needs it.

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