Technologies exist to reduce CO2 emissions from coal power plants

Published: May 19th, 2009
Last revised: July 31st, 2010

In a conventional coal-fired power plant, coal is burned to generate steam, which in turn spins a turbine to generate electricity. The process creates exhaust gases, including water vapor, nitrogen and carbon dioxide, or CO2 — and CO2 is the greenhouse gas primarily responsible for human-caused global warming.

One way to reduce CO2 emissions from a coal plant (or any other fossil-fuel burning plant, but coal is the one experts concentrate on) is to “capture” the CO2, liquefy it and bury it underground, a process known as “Carbon Capture and Storage” (or “Sequestration,” which means the same thing; in either case, the abbreviation is CCS).

A coal plant incorporating CCS, also referred to by many as a “clean coal” plant, is less efficient and requires more equipment than a plant without it. As a result, making electricity with CCS will cost more than making it from conventional plants.The fact that the Environmental Protection Agency has now classified CO2 as a pollutant, however, may ultimately lead to regulations requiring implementation of the technology nevertheless. The individual components of CCS have been demonstrated, and scientists generally agree that much of the country has underground formations suitable for storing CO2 safely; for those areas without good storage sites, pipeline transmission is feasible.

As for exactly where in the combustion process the CO2 is removed, there are many choices. If you simply want to retrofit an existing plant, one method is simply to “scrub” the exhaust before it escapes into the air. Another is to burn the coal in pure oxygen (or oxygen-enriched air) rather than ordinary air. That boosts the concentration of CO2 in the exhaust, which makes it easier to extract; a small-scale plant has been built in Germany to test this approach.

If you are willing to build a new plant, you can also do something called “pre-combustion CO2 capture” or "gasification-based CCS." It works by converting coal into a gas — mostly a mix of carbon monoxide and hydrogen. Then you add steam, which converts the carbon monoxide to CO2 in concentrations that make it easy to extract. What you end up burning to generate electricity is hydrogen. The exhaust in this case is mostly water vapor. As of 2009, over a dozen facilities have been built to generate electricity using gasification technology, including three (soon four) in the US — although none of them are set up to capture the CO2.¹