Crumb Trail: Free Fire Zone

July 07, 2005

Free Fire Zone

Energy John has assembled a brace of unusual energy technology posts that offer possible ways to manage climate. I'd seen them both when posted but they are more interesting when considered together as John has done. The first, from LiveScience considers the engineering issues of the old science fiction idea of using orbital shades to deflect or absorb some solar radiation.

In the newly outlined approach, reflective particles might come from the mining of Earth, the Moon or asteroids. They'd be put into orbit around the equator. Alternately, tiny micro-spacecraft could be deployed with reflective umbrellas.
A ring created by a batch of either "shades the tropics primarily, providing maximum effectiveness in cooling the warmest parts of our planet," the scientists write. An early version of their idea was presented but not widely noticed in 2002.

The rings of Earth? This doesn't seem like an attractive idea to me since space junk is a problem of sorts now and at orbital speeds even tiny pieces of stuff become kinetic weapons in effect. (see ablation cascade)

The second idea is an expansion of the much discussed solar heated thermochemical zinc process which converts zinc oxide to elemental zinc with a catalyzed heat reaction. The catalyst, which lowers the reaction temperatures required, is carbon. At higher temperatures no catalyst is needed. That would be good, a carbon neutral energy system, but since the carbon in the catalyzed system would be captive it might make sense to sequester it.

what if our major energy systems either did not use carbon at all, or were easily and cheaply set up to be carbon negative? That would certainly be a huge accomplishment; it would represent a capability for tuning the CO2 content of the atmosphere to our specifications.
It also appears to be possible. The thermochemical zinc process, which converts carbon and zinc oxide to carbon monoxide and metal, is so far as I know unique in that it accepts biomass as a carbon source and releases it without any contamination from e.g. nitrogen. This pure carbon monoxide can be burned in a gas turbine, but it could also be used to run a solid-oxide fuel cell and kept nitrogen-free. The product stream of pure carbon dioxide would be disposal-ready.

There are some fussy steps in the process to get real world carbon compounds such as biomass into a properly chared state for use in the thermochemical zinc process but if it was all done on a huge scale as the major source of energy used in the world it would be possible to capture enough CO2 to affect the climate.

I'd rather see the biomass used to restore the organic matter lost from the soil due to agriculture. This is sequestration too. It's not permanent storage since it can reenter the atmosphere, but changing the ratio of carbon in the atmosphere to carbon in the soil achieves the same objective. It's the same as growing trees. Though each tree will one day rot and return its carbon to the air, if there are more trees there is less carbon in the air at any time. Plus, soil with more organic matter has several virtues such as better CEC and so lower fertilizer requirements, another aspect of the energy and fossil carbon puzzle.

Still, the uncatalyzed thermochemical zinc process seems very attractive in that it efficiently captures solar heat in a portable form. The system to develop the higher heat required, 1,750ºC, is in development and isn't beyond the capabilities of solar furnaces.

Posted by back40 at 06:53 PM - Energy

For space shielding, you don't want to put the things round the equator, which will mess up meridional heat flow and still leave you with any polar melting you were going to get anyway; you want to put them at the L1 point, where they shield the whole planet equally, and design them so that they can autonomously use the light pressure for station holding. That makes their negative forcing as similar as it can be to GHG forcing (though the fit is far from perfect -- sun shields don't cool you at night).

On zinc, I must admit to an irrational distaste for technologies using molten metal, but I will try to be open minded

On sequestration, what do you think of the charcoal-enrichment ideas that sometimes run under the name Terra Preta?

Posted by: Oliver Morton at July 7, 2005 11:55 PM PERMALINK

There are advantages to an L1 location. But isn't that an unstable equilibrium point? It seems that continuous power for station keeping would be needed. The solar wind would blow objects off station. L4 and L5 are stable, but not in a location to shade the earth. An L1 powered space parasol would be more complex but only one would be needed so perhaps it's workable.

I think the zinc is in gaseous form when pure. Worse than molten perhaps? I was idly speculating about using zinc as the coolant in a high temperature nuclear reactor. Some use lead now though at temperatures far below those needed for the thermochemical zinc process. If some design was possible that could run at such high temperatures there might be some way to benefit. It's not clear that the higher temps wouldn't be more trouble than they are worth though.

Terra Preta do Indio is a mystery still. There seems to be a biological trick there, bacteria or something, in addition to the high carbon. It isn't clear if the Amerinds made it on purpose or not, but many speculate that this is so and that the method is lost, yet to be rediscovered.

But it is fascinating stuff since it not only has very high carbon content it is persistent and would serve for long term sequestration. It also has high phosphorous, CEC, PH and base saturation. Highly fertile and rapidly recovers from cropping. It somehow seems to heal itself after we abuse it in a fraction of the time normal soils require. There are stories about locals mining it to enrich other fields and in time it regenerates itself replacing extracted volume as well as fertility. I don't know how much of all this is true. See the Cornell page, which features a reference to a Science article and a BBC documentary, The Secret of Eldorado. I'll bet you have seen that already.

Terra Preta and glomalin weigh heavy on my mind. The first is a carbon mystery and the second is a fairly recent discovery of huge significance for soil fertility and carbon sequestration. Together they shatter any illusions I might have harbored that we know what we are doing.

Posted by: back40 at July 8, 2005 06:40 AM PERMALINK