Coal fired power plants create more pollution and greenhouse gases per unit of energy generated (all other things being equal) than any other power plants, including oil and gas.

Generally they are built in counties with large coal deposits such as China and the United States. Only rarely are they built with the idea of importing coal in mind. Some of the largest Chinese plants have certain economies of scale, but the Chinese appear to having growing concerns about the smog and other pollution. Oddly enough, George W. Bush wants to increase coal use in the United States.