For example, designing an IGCC plant to run on Texas lignite, a lower-quality coal, adds 37 percent to the cost of the plant, compared with designing it to run on a high-quality coal called Pittsburgh #8. And the resulting plant is 24 percent less efficient. Designing a conventional plant to run on low-quality coal also costs more, but the increase is only 24 percent–less than the 37 percent with IGCC. The hit to efficiency is also less–10 percent versus 24 percent with IGCC. While the added costs for capturing carbon dioxide are greater for conventional coal plants, these can be largely offset if the plant is being designed for use with lower-quality coal.
As a result, it’s less clear which technology would really make the most economic sense. For some parts of the world, where high-quality coal is easily accessible, IGCC will probably be the clear winner. But areas using low-quality coal could be better served by pulverized coal plants, especially the new ultra-supercritical coal plants that power turbines with very high temperature steam. Such plants are about 13 percent more efficient than IGCC, and higher efficiency translates into less coal needed to generate a certain amount of electricity, and hence less emission of carbon dioxide.
Given so many uncertainties, the MIT report recommends that, rather than picking one technology to support, the government fund large-scale, carbon-dioxide-capturing demonstration plants using various technologies. These plants would be run as commercial projects to reveal the real-world costs.
The report also says that the Department of Energy should increase funding for research on a new generation of technologies for coal power plants. The MIT researchers singled out a process called chemical looping, which Deutch says “offers a completely different process for getting the energy out of coal.” In one version, pulverized coal reacts with particles of metal oxides, such as rust. The reaction converts the oxide into a metal, such as iron, and produces carbon dioxide. The carbon dioxide can be compressed for storage. The iron is then exposed to steam. The reaction between the water and the iron produces heat, converts the iron back into rust, and releases hydrogen gas that can power a fuel cell to make electricity.
“Nobody can tell you what the economics are–it’s just being explored now,” Deutch says. “But it’s an example of a different approach to getting energy out of coal to avoid the emissions of greenhouse gases. We think those kinds of completely different approaches ought to be explored.”
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