During the recent Oil Drum debate on Nuclear EROEI, "Cyril R." a frequent commenter on energy related blogs made a case for "Compressed Air Energy Storage" (CAES).
In a response to a comment concerning the low capacity factor for wind, "Cyril R." stated
"the capacity factor you referenced is very low, good locations in the US get 30-40%, which is close to the average capacity factor in the US. Moreover, consider the correlation with the load to be more indicative than capacity factor. Not good for wind, but with CAES this can be cost-effectively dealt with; the CAES equipment is similar to NG turbines, i.e. they have low materials input so this won't fundamentally increase the materials input for wind."
Cyril R proposed compressed air storage in salt domes and saline aquifers which he argued were adjacent to areas of high-quality wind resources.
My initial response was to observe:
"The last time I checked, the expansion of compressed gasses has a cooling effect. If the gases contain humidity the cooling can produce condensation and even freezing. The Grand Solar Scheme recognized the problem and proposed to burn natural gas in the released air stream to reheat it. There are two problems with this approach. First as we all know natural gas is not a sustainable resource, so it is not a sustainable solution. Secondly, burning natural gas produces CO2, and thus a CAES solution would contribute to global warming."
Cyril R. responded:
". . . using biomass derived fuel for heating in combination with hydrogen. In this instance, the use of hydrogen would be interesting because of the higher thermodynamic efficiency. In adittion, there is the AACAES approach which is hardly rocket science. Just add thermal oil storage (proven industrial technology) to store the heat created during the compression stages and use it later to deal with the cooling effect of expansion."
"Cyril R.'s" burning biomass suggestion is problematic from a number of views. The collection and transportation of large amounts of biomass would be energy intensive, the use of a technology involving the extraction of large amounts of heat from compressed air into mineral oil, and then the discharge of that heat into expanding air would be an added expense to a CAES system.
In addition to "Cyril R.'s" CAES scheme, the January Scientific American, published an article on a "A Grand Solar Plan" that proposed a CAES scheme involving caves.
Following the debate an interesting problem with the CAES system occurred to me. Any CAES project involving the release of compressed air from underground storage in salt domes and saline aquifers would probably transport radon to the surface.
Let us examine the problem. Radon is a colorless, chemically inert, radioactive gas produced by the radioactive decay of thorium and uranium in the earths crust, Because it is a gas radon can be drawn into the lungs. There it produces a radioactive multiple whammy. Radon 222, if it decays in the lungs, produces a long and deadly decay chain. (222Rn (3.82 days) → 218Po (3.1 min) → 218At (1.5 s) → 218Rn (35 ms) → 214Pb (26.8 min) → 214Bi (19.7 min) → 214Po (164 µs) → 210Pb (22.3 yr) → 210Bi (5.01 days) → 210Po (138 days) → 206Pb (stable). Each isotope in the chain releases more radiation into the lungs triggering more and more carsenogenic lung tissue damage. Radon is considered to be next to smoking the second leading cause of Lung cancer for Americans. Radon exposure greatly increases the lung cancer danger for smokers.
While salt domes generally contain virtually no radon, surrounding rock does. Critics of nuclear power have long argued that radioisotopes from "nuclear waste" placed in salt domes can be transported out of them through a variety of mechanisms. Similar mechanisms could transported radon from surrounding rocks into salt dome cavities used to store compressed air. The method of creation of salt dome cavities together with the effect of compressed air on the surrounding salt and rock might tend to open up channels for radon transport from radioactive rocks into the compressed air cavity. These would include the use of water to form the original cavity, the heat and humidity of the compressed air, together with the the effects of highly pressured air on the flaws and imperfections in the salt structure surrounding the cavity. All these forces could tend to open up transport channels between surrounding radioactive rocks, and the salt dome cavity. The fluxuating air pressure, caused by compression and decompression could pump the radon from the surrounding rock into the cavity. The release of compressed air from the cavity would force radon to the surface.
The use of saline aquifers for compressed air storage is even more problematic. A recent Geotimes report, "Rooting Out Radioactive Groundwater" focus on the problem of radon in all aquifers. It states:
"Groundwater from deep aquifers is typically oxygen-depleted and has a very slow flow rate, and marginal water typically has high salinity. These alternative water resources may therefore also have high radium concentrations."
Thus it would appear that significant atmospheric radon release associated with CAES energy storage in saline aquifers is very likely, and in the case of salt dome storage is quite possible.
The presence of radon in geothermal hot water and steam used in the generation of geothermal power has also been ignored, although high concentrations of radon could be expected from molten and hot rocks. Geothermal power techniques involved in the insertion of large amounts of water into hot sub surface rocks, would almost certainly lead to the transport of large amounts of radon to the surface with hot water and steam
In a response to a comment concerning the low capacity factor for wind, "Cyril R." stated
"the capacity factor you referenced is very low, good locations in the US get 30-40%, which is close to the average capacity factor in the US. Moreover, consider the correlation with the load to be more indicative than capacity factor. Not good for wind, but with CAES this can be cost-effectively dealt with; the CAES equipment is similar to NG turbines, i.e. they have low materials input so this won't fundamentally increase the materials input for wind."
Cyril R proposed compressed air storage in salt domes and saline aquifers which he argued were adjacent to areas of high-quality wind resources.
My initial response was to observe:
"The last time I checked, the expansion of compressed gasses has a cooling effect. If the gases contain humidity the cooling can produce condensation and even freezing. The Grand Solar Scheme recognized the problem and proposed to burn natural gas in the released air stream to reheat it. There are two problems with this approach. First as we all know natural gas is not a sustainable resource, so it is not a sustainable solution. Secondly, burning natural gas produces CO2, and thus a CAES solution would contribute to global warming."
Cyril R. responded:
". . . using biomass derived fuel for heating in combination with hydrogen. In this instance, the use of hydrogen would be interesting because of the higher thermodynamic efficiency. In adittion, there is the AACAES approach which is hardly rocket science. Just add thermal oil storage (proven industrial technology) to store the heat created during the compression stages and use it later to deal with the cooling effect of expansion."
"Cyril R.'s" burning biomass suggestion is problematic from a number of views. The collection and transportation of large amounts of biomass would be energy intensive, the use of a technology involving the extraction of large amounts of heat from compressed air into mineral oil, and then the discharge of that heat into expanding air would be an added expense to a CAES system.
In addition to "Cyril R.'s" CAES scheme, the January Scientific American, published an article on a "A Grand Solar Plan" that proposed a CAES scheme involving caves.
Following the debate an interesting problem with the CAES system occurred to me. Any CAES project involving the release of compressed air from underground storage in salt domes and saline aquifers would probably transport radon to the surface.
Let us examine the problem. Radon is a colorless, chemically inert, radioactive gas produced by the radioactive decay of thorium and uranium in the earths crust, Because it is a gas radon can be drawn into the lungs. There it produces a radioactive multiple whammy. Radon 222, if it decays in the lungs, produces a long and deadly decay chain. (222Rn (3.82 days) → 218Po (3.1 min) → 218At (1.5 s) → 218Rn (35 ms) → 214Pb (26.8 min) → 214Bi (19.7 min) → 214Po (164 µs) → 210Pb (22.3 yr) → 210Bi (5.01 days) → 210Po (138 days) → 206Pb (stable). Each isotope in the chain releases more radiation into the lungs triggering more and more carsenogenic lung tissue damage. Radon is considered to be next to smoking the second leading cause of Lung cancer for Americans. Radon exposure greatly increases the lung cancer danger for smokers.
While salt domes generally contain virtually no radon, surrounding rock does. Critics of nuclear power have long argued that radioisotopes from "nuclear waste" placed in salt domes can be transported out of them through a variety of mechanisms. Similar mechanisms could transported radon from surrounding rocks into salt dome cavities used to store compressed air. The method of creation of salt dome cavities together with the effect of compressed air on the surrounding salt and rock might tend to open up channels for radon transport from radioactive rocks into the compressed air cavity. These would include the use of water to form the original cavity, the heat and humidity of the compressed air, together with the the effects of highly pressured air on the flaws and imperfections in the salt structure surrounding the cavity. All these forces could tend to open up transport channels between surrounding radioactive rocks, and the salt dome cavity. The fluxuating air pressure, caused by compression and decompression could pump the radon from the surrounding rock into the cavity. The release of compressed air from the cavity would force radon to the surface.
The use of saline aquifers for compressed air storage is even more problematic. A recent Geotimes report, "Rooting Out Radioactive Groundwater" focus on the problem of radon in all aquifers. It states:
"Groundwater from deep aquifers is typically oxygen-depleted and has a very slow flow rate, and marginal water typically has high salinity. These alternative water resources may therefore also have high radium concentrations."
Thus it would appear that significant atmospheric radon release associated with CAES energy storage in saline aquifers is very likely, and in the case of salt dome storage is quite possible.
The presence of radon in geothermal hot water and steam used in the generation of geothermal power has also been ignored, although high concentrations of radon could be expected from molten and hot rocks. Geothermal power techniques involved in the insertion of large amounts of water into hot sub surface rocks, would almost certainly lead to the transport of large amounts of radon to the surface with hot water and steam
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