New Geothermal Extraction

The restraint on the wholesale roll out of geothermal power has always been thermal efficiency. Efficient steam generators need high grade steam. That essentially means pressurized water containing 400 calories per gram, sufficient to instantaneously vaporize when released into a turbine. It occurs naturally at a depth far too deep to penetrate and work with in terms of out drilling technology. Also recall that drilling costs are increasing in a nonlinear fashion as you go to depth. For that reason, our only sources are in active volcanoes in particular for the high grade stuff and in regions of unusual heat for a grade that is at least useable with a lot of engineering help.

In the US we have the entire State of Nevada to work with for the second type of thermal power and it is progressing.

An ability to use a poorer grade of heat naturally expands the supply and possibly opens up new lands to this type of energy. That at least is what is promised here. Technical information is in short supply though, so it is impossible to get excited yet.

The fact is though that mere 100C water can do just fine linked to a reverse Rankin cycle engine. The engine can turn the heat differential of perhaps 70C into 75% brake horsepower and that can be used to power a generator. It has never been properly exploited because it is an additional operating headache to power plants and adds only incremental supply. It has always been too easy to dump the heat into a cooling stack needing no manning.

And let us not forget that most power plants are initially built to robust demand models and usually simply have too much power. It is only as demand matures that this is interesting, at which you are looking at an expensive retrofit.

New Geothermal Heat Extraction Process To Deliver Clean Power Generation

PNNL's introduction of a metal-organic heat carrier, or MOHC, in the biphasic fluid may help improve thermodynamic efficiency of the heat recovery process. This image represents the molecular makeup of one of several MOHCs.

by Staff Writers
Richland WA (SPX) Jul 17, 2009

A new method for capturing significantly more heat from low-temperature geothermal resources holds promise for generating virtually pollution-free electrical energy. Scientists at the Department of Energy's Pacific Northwest National Laboratory will determine if their innovative approach can safely and economically extract and convert heat from vast untapped geothermal resources.

The goal is to enable power generation from low-temperature geothermal resources at an economical cost. In addition to being a clean energy source without any greenhouse gas emissions, geothermal is also a steady and dependable source of power.

"By the end of the calendar year, we plan to have a functioning bench-top prototype generating electricity," predicts PNNL Laboratory Fellow Pete McGrail. "If successful, enhanced geothermal systems like this could become an important energy source." A technical and economic analysis conducted by the Massachusetts Institute of Technology estimates that enhanced geothermal systems could provide 10 percent of the nation's overall electrical generating capacity by 2050.

PNNL's conversion system will take advantage of the rapid expansion and contraction capabilities of a new liquid developed by PNNL researchers called biphasic fluid. When exposed to heat brought to the surface from water circulating in moderately hot, underground rock, the thermal-cycling of the biphasic fluid will power a turbine to generate electricity.

To aid in efficiency, scientists have added nanostructured metal-organic heat carriers, or MOHCs, which boost the power generation capacity to near that of a conventional steam cycle. McGrail cited PNNL's nanotechnology and molecular engineering expertise as an important factor in the development, noting that the advancement was an outgrowth of research already underway at the lab.

"Some novel research on nanomaterials used to capture carbon dioxide from burning fossil fuels actually led us to this discovery," said McGrail. "Scientific breakthroughs can come from some very unintuitive connections."

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