Carbon trap: This laboratory device extracts energy from fossil fuels and produces an easy-to-capture stream of carbon dioxide. A larger version will be tested in a new 250-kilowatt power plant.
Fanxing Li
Process could capture carbon more cheaply.
Researchers at Ohio State University are developing a novel process for generating electricity from coal that also promises to make capturing carbon-dioxide emissions cheaper. The work is being done with the help of a $5 million grant from the U.S. Department of Energy's new Advanced Research Projects Agency-Energy. The technology has been proven in laboratories; researchers will use the new funds to demonstrate it in a 250-kilowatt, pilot-scale power plant.
A coal-fired plant based on the process, which is called chemical looping, would produce a highly concentrated stream of carbon dioxide. Such a stream would be easier to capture and store underground than the standard method of capturing diluted carbon dioxide in the exhaust gas of conventional coal-fired power plants. The new method could make it less expensive for coal plants to meet pending regulations on CO2 emissions.
Chemical looping could be a big improvement over systems for capturing carbon dioxide from conventional power plants. The typical systems reduce the power output of coal plants by as much as 30 percent and, because of the reduced power output and the cost for additional equipment, increase the cost of electricity by 85 percent. With chemical looping, say Fanxing Li, a research scientist at Ohio State, "you don't see that energy penalty," and as a result, "hopefully we can prove that it's cheaper."
Most coal-fired power plants burn pulverized coal in air, and since air is mostly nitrogen, so is the exhaust emissions--only about 14 percent is carbon dioxide. "You have to waste a lot of energy to separate the nitrogen from the carbon dioxide," Li says. With chemical looping, the coal isn't exposed directly to air. Instead, looping involves a series of chemical reactions in which a solid material, acting as an intermediate, first captures oxygen from the air and then transfers it to the fuel--without the nitrogen or other gases in air. The reactions produce heat, which can be used to generate electricity, along with a stream of concentrated CO2 that can easily be captured.
In the version of chemical looping the researchers will use in the pilot plant, the coal is first gasified, a common process that involves converting coal into syngas-- a combination of carbon monoxide and hydrogen gas. The syngas is exposed to particles of iron oxide--that is, rust--which act as an oxygen carrier. As it reacts with the syngas, the iron oxide releases its oxygen, forming metallic iron. The oxygen oxidizes the carbon monoxide, forming carbon dioxide, and the hydrogen, forming steam. At this stage, the steam and carbon dioxide leave the system. The steam can easily be removed by condensing it, leaving behind highly concentrated carbon dioxide that can be captured and stored.
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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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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