Sunday, September 10, 2006

a direct approach to dealing with atmospheric hydrocarbons

According to a study published in Nature, and picked up by the San Jose Mercury News, "methane -- a greenhouse gas 23 times more powerful than carbon dioxide -- is being released from the permafrost at a rate five times faster than thought."

The atmosphere does naturally clean itself of hydrocarbons, but it's a slow process, likely to be overwhelmed by the melting permafrost. Even so, there are some things we can do besides throwing up our hands and declaring that all is lost.

One way of dealing with methane and other atmospheric hydrocarbons would be to build large solar gas turbines with their exhausts pointed skyward. (Note that this is not a reference to the Caterpillar subsidiary Solar Turbines, although there's no reason why they couldn't supply such hardware.)

A jet turbine has three main components:
* a compressor
* a heating (combustion) chamber
* a turbine to power the compressor

The trick to making it work is to add enough energy in the heating chamber to overcome the inefficiency in using the turbine to tap energy from the exhaust to power the compressor. Do that and you get self-sustained operation.

So, arrange the turbine shaft vertically with the turbine at the top, and focus sunlight from a field of heliostats onto the heating chamber.

Preferably mount the turbine assembly on a tower, high enough above the surface to be clear of most aeolian grit.

Install in a desert in the northern hemisphere, where most of the permafrost is located.

With a large enough field of heliostats, you should be able to tap off some energy for the generation of electricity.

Compression would provide some heating and the remainder would have to be added by the heliostats. For the purpose of oxidizing methane and other hydrocarbons, the temperature of the air passing through the heating chamber would have to surpass their ignition temperatures. Most likely this would happen as a matter of course, as the temperature necessary to provide self-sustaining operation would probably be considerably higher than the ignition temperature of any hydrocarbon.

The larger the scale of the installation, the higher into the atmostphere the hot exhaust air would be pushed. Push it high enough and it will tend to spread out above the turbulent lower atmosphere. Short of that, the rising, cooling column of air may produce weather downwind.

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