Friday, May 05, 2006

Retro-fitting Coal

I've long regarded coal gasification as a key alternative energy technology, enabling us to use our enormous coal reserves in a much cleaner way. More recently, I've focused on the potential of this process to address coal's large impact on climate change. When I attended an energy conference in Washington, DC last fall, practically ever speaker mentioned the technology in glowing terms, including a representative from the Natural Resources Defense Counsel--hardly a traditional friend of coal. There's a major problem with gasification, though, besides its slightly higher capital cost compared to traditional power plant designs; it cannot be retro-fitted to the thousands of existing coal-fired power plants that are responsible for a huge slice of our total global greenhouse gas emissions. A Swedish utility has a possible solution, as described in this article from Technology Review.

Vattenfall's process is simplicity itself. It substitutes pure oxygen for the air consumed by normal power plant combustion, resulting in power plant exhaust that contains essentially only water and carbon dioxide. This is important, because the dilution effect of nitrogen from the air makes separating carbon dioxide from conventional power plant stacks prohibitively costly, and only relatively pure CO2 can be stored, or sequestered, in underground reservoirs and elsewhere, keeping it out of the atmosphere. And the beauty of this approach is that it can potentially be applied to every existing coal power plant.

I don't want to portray this as a free lunch, however. Working with pure oxygen is tricky and potentially dangerous. I have seen steel burning in a pure oxygen atmosphere. Retro-fitting coal plants with Vattenfall's technology will require not just adding a cyrogenic oxygen plant to each power plant, but probably also extensive changes to the metallurgy of some of the plant components. This will be costly and would only pay off in situations in which the power plant owner is required to manage its greenhouse gas emissions.

In the long run, I still think gasification is the better, more flexible process. But Vattenfall's "oxyfuels" concept answers the critical question of what to do about all the conventional coal power plants--more every year--versus the tiny number of coal gasification facilities actually under construction.

By the way, I was quoted in an article on energy trading in today's Stamford Advocate/Greenwich Time.

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