06 August 2006

99% of Earth's Mass is Hotter than Hell--Global Warming from the Inside Out

Yes, you read that correctly, and it has nothing at all to do with climate change or mainstream ideas of global warming. The massive heat is coming from the interior of the earth. To follow up on an earlier Al Fin article on geothermal energy, this report from Engineer Live gives further information:

Roughly 99 per cent of the Earth’s mass is hotter than 1800 E C and, about three miles down, the temperature reaches several hundred degrees. The optimum way of accessing this energy at the moment is Hot Dry Rock (HDR) or Hot Fractured Rock (HFR) technology. These are referred to as Enhanced Geothermal Systems (EGS) because they go beyond the drilling of a simple well.

The HDR system comprises at least two depth drillings and one subterranean heat exchanger. The heat exchanger consists of natural joints in plutonite rock which are fractured and connected to each other with the help of water pressure, known as hydraulic simulation.

This enables the exploration of the Earth’s interior heat outside known geothermal provinces. In contrast to a geothermal field in a volcanic or tectonic anomaly, an EGS depends on the artificial stimulation of otherwise tight formations by hydraulic fracturing to create an underground heat exchanger. Fluid is then circulated in a closed circuit.

It has been suggested that there could be sufficient energy to produce hundreds of megawatts of electricity per network and, at these depths, the technology enables geothermal power production virtually anywhere in the world. It is predicted that plants could work over a reservoir for 30 years without experiencing a significant drop in temperature. And this would be available 24 hours a day because it does not rely on variables such as tides, waves, wind or sun. But drilling is an expensive business.

....The United States continues to produce more geothermal electricity than any other country, comprising some 32 per cent of the world total. But this is being challenged, particularly in the Philippines and Indonesia. HDR technology is also expected to produce hundreds of megawatts in Australia.

....Increasing the efficiency of power generation is the subject of a Siemens Industrial Solutions and Services Group project, which plans a geothermal power plant based on the Kalina Cycle. This uses a binary working fluid of water and ammonia instead of water alone. In contrast to pure media with a constant boiling point such as water or pentane, this mixture boils across a larger temperature range at a given pressure.
Kalina Cycle power plants use less energy to heat the working fluid, allowing more of the energy to go directly to generating power and improving the cost effectiveness of the power plant.

The steam power plant now used to make electricity was invented 150 years ago by Scottish engineer William Rankine. It uses a heat source-coal, oil, natural gas, geothermal heat-to produce high-pressure steam that drives a turbine. The excess steam is condensed into water, which is then pumped back to a boiler. But, in a Rankine cycle, only about 35 to 40 per cent of the heat energy released ever becomes electricity, which means an excess depletion of heating resources.

Mixing the water with ammonia, which evaporates at lower temperatures, can raise efficiency at the heat stage of the cycle. But ammonia also condenses less readily, forcing engineers to use smaller turbines and lowering efficiency. Kalina’s invention solves that problem, using sophisticated thermodynamics to draw off most of the ammonia before the condensation stage. A Kalina cycle can boost efficiency by as much as 40 per cent.

....Geothermal power generation offers many benefits over other renewable sources of energy. It is constantly available and so is ideal for supplying base load requirements, where reliability of supply is paramount. Wells could be operational for 30 years or more before they cool too far, providing plenty of opportunity for recouping the initial investment.

And the technology of obtaining heat from hot dry rock formations can be applied virtually anywhere in the world. It can also draw on the experience of the oil industry in drilling very deep wells to access energy pools that are well below the earth’s surface.

Finally, even modest wells can produce megawatts of electricity, making the technology a very valuable contributor to society’s needs.
There is much more information about European efforts to exploit geothermal energy at the link above.

Geothermal heat is a massive store of energy, far more than humans can ever use--much like solar energy. Kalina cycle heat engines promise to increase efficiencies of heat energy by as much as 20% or more.

As I suggested here, heat is a fairly good method of storing solar energy. With better efficiencies from heat engines, heat is becoming an even more attractive form of storage.

Geothermal heat is not exactly solar energy, but it is energy from the formation of the solar system. All other "renewable energies" are secondary to solar, and not even close in magnitude. Only geothermal stands alongside solar as a virtually inexhaustible source of renewable energy, on time scales that humans can comprehend.

Hat tip, Keelynet.com.

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Blogger Fat_Knowledge said...

Interesting. What do the economics of this look like? How much would it cost per kWh compared with solar or coal? I think it sounds like a good idea, but I wonder why it hasn't been implemented yet if it really is so good.

Also, I think Iceland does a lot of geothermal.

Monday, 07 August, 2006  
Blogger al fin said...

Yes, you are right that this should have been done before now, but the long era of cheap oil caused the postponing of a lot of renewable energy projects that might have been producing by now. Here is one look at relative costs:

It costs 4.5 to seven cents per kWh to produce electricity from hydrothermal systems. In comparison, new coal-fired plants produce electricity at about four cents per kWh.

This particular approach is a different process from conventional geothermal, borrowing from oil drilling technology to create permeable beds of dry hot rock for heating water (and ammonia), then using an advanced heat cycle (Kalina cycle) to extract more energy from the hot water. There are some good background articles on the Kalina cycle linked in the latter part of the posting. Increasing efficiency by 20-30% can make a big difference in the economics of startups.

Monday, 07 August, 2006  
Blogger al fin said...

You might be interested in checking out this link on the hot dry rock geothermal approach. It provides an entertaining little java animation that illustrates the different phases of the drilling and production process.

Monday, 07 August, 2006  

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