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In the next step in the chemical loop, the iron is moved to another chamber. It's exposed to the oxygen in air, forming iron oxide in a chemical reaction that generates heat, which is used to generate electricity. (Alternatively, the iron can be exposed to steam to produce hydrogen for fuel cells or to be made into liquid fuel at a refinery.) The iron oxide then returns to the first chamber to react with more syngas, closing the loop.
Implementing such a system at a full-scale power plant has two main challenges, says David Thimsen, a senior project manager for advanced coal generation at the Electric Power Research Institute. The first challenge is designing mechanisms for moving the iron and iron oxide around inside the plant. The second is ensuring that the materials aren't too expensive. Thimsen says the approach being taken by the Ohio State researchers may not prove to be the best version of chemical looping. The metal oxides can be expensive, for one thing. And gasifying the coal prior to reacting it with the oxides would incur an energy penalty, especially since it involves a process of separating oxygen from air.
Another chemical looping approach is being developed by Alstom Power, under another $5 million DOE project. In that system, Thimsen says, the oxygen-carrying material is derived from limestone, which is cheap. That system has been successful in a small pilot plant, and will be tested in a larger 3,000-kilowatt prototype plant. The Ohio State researchers are also in the early stages of developing an approach that doesn't involve a separate gasification step. That approach could be 10 to 20 percent more efficient than the version for the pilot plant, Li says.
A new process could allow Air Force jets to run exclusively on domestically produced biomass and coal.
CO2 sequestration suffers from the defect that CO2 must eventually escape its container. It is a temporary solution to a permanent problem.
I'm not sure about the OSU proposal recently funded by ARPA-E, but some of the chemical looping technologies use iron redux reactions to convert coal into carbon into carbon monoxide in the same way that a iron foundry operates. So, nitrogen can be avoided through out the process if designed properly.
Though, it should be stated that there does not seem to be a magic bullet for reducing the cost of coal-to-electricity. The cost of all of the different coal systems (if you included Carbon capture & storage) seem to be about the same. The price of PCC-CCS, Oxy-combustion-CCS, Chemical Looping-CCS & IGCC-CCS all seem to be in the same ballpark within the error of cost estimating.
In short term (<25 years), I expect that the norm will be CCS equipment added to existing PCC plants or new IGCC-CCS plants if FutureGen (and ZeroGen overseas) successfully demonstrate the economics of gasification, shift to hydrogen, combustion of hydrogen, and storage of CO2.
Carbon is indeed a macro nutrient, though fertilizer may not be the correct word for CO2. But I see your point; the vast majority of plant species are more productive at elevated CO2 concentrations in the air. The disadvantage is for us, with more violent and unpredictable weather (due to higher energy trapped by more CO2 in the atmosphere) causing increased damages. And possibly some sealevel rises causing near sealevel areas to be inundated (or increasing infrastructure costs such as dykes for those who can afford it...)
Also, increased crop damage due to the storms etc may offset some of the increased yield.
It's a tough call when it comes to future crop productivity...
The article implies that gasification is a common process; however, there have been very few commercially viable coal or other gasification energy generation projects. Capital costs are problematic. The key technology discussed in the article is the iron/rust redox reaction, used to provide an oxidizing reactant for conversion of CO and H2. The process will have to compete with add-on processes for conventional coal plants, where a stream of O2 can be generated from air and introduced before combustion. This also allows production of a waste stream consisting of almost pure CO2 and (easily separated) H2O. The process cited in the article requires capital investment for both gasification AND oxygen/air separation, a conventional plant would only need an add-on air fractionation unit to produce the same result. I suspect this would be less capital intensive. It would have been useful if the article compared the economics of the rust/iron system versus conventional air fractionation as a means for separating O2 from the N2 in air. I would attempt to do a quick calculation but I'm a bit rusty on my thermodynamics!
Perhaps this method can also be a combined ore refining/powerplant. Rust or other iron/metal ore (if possible) is used as oxygen carrier, iron (or other) metal comes out for sale on the market.
It may also be possible to let the flue gas - H20 and CO2 - react with olivine mineral in an autoclave type device. This sequesters the carbon in carbonate mineral, so no compression and storage of CO2 gas is required, and actually gives off energy in the form of reaction heat for self sustaining reaction and even more energy conversion (more heat for electricity).
There could be logistic issues with these schemes though; large amounts of minerals would have to be supplied to the coal plant. However, coal plants already need large delivery systems for the pulverized coal fuel anyway, so perhaps this will be manageable.
On http://www.keshepowercells.com information is given about a new technology to capture in a direct way CO2 and CH4 from the air. From the site a paper can be downloaded with photo's and spectroscopy graphs (of the University of Gent - Belgium).
Remarkable is the discovery of a new state of CO2, namely solid CO2 at room temperature. This CO2 is in nano-state. For the moment only "dry ice" is known as a solid CO2.
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Wolfgang
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Reacting coal with steam to generate carbon monoxide and hydrogen, and then oxidising the gas mixture to carbon dioxide and water, still leaves as the net reaction: carbon and oxygen to carbon dioxide. Coal gasification is not as trivial as being mentioned as an industrial process might suggest. And the difficulties and inefficiencies when combining the two processes are leading to the question whether a more efficient air separation to exclude nitrogen (also an industrial process) or a novel carbon dioxide capturing technology would not be more advantageous...
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