NEW HAVEN, W.Va.--A 100-story smokestack belches a roiling, white cloud of water vapor, carbon dioxide and other leftover gases after burning daily as much as 12,000 tons of coal at theMountaineer Power Plant --a total of 3.5 million tons a year. The facility just outside the town of New Haven boasts a single 65-meter-high boiler capable of generating enough steam to pump out 1,300 megawatts of electricity--enough to power nearly one million average American homes a month--continuously. And now