COAL

About ten miles north of where I live in northern Colorado, a smokestack rises 500 feet in the air alongside a stair-step series of buildings. On a summer day, nothing appears to be coming from the smokestack, as though it is a ghostly relic; in the winter, a white plume rises. On closer approach, a lake teeming with ducks, geese, pelicans, and other waterfowl sits in the foreground. A herd of American bison roam on over 4,000 acres of grasslands surrounding the smokestack. This apparently benign plant called Rawhide Energy Station is actually a 280 MWe coal-fired power plant that provides about one-quarter of the electricity for four nearby communities—Fort Collins, Loveland, Longmont, and Estes Park. It is a public utility owned by the four communities and is near state-of-the-art for a coal-fired power plant, being one of the most efficient in the western United States and among the top ten in lowest emissions (1).

Anatomy of a Coal-Fired Plant

I drove up to the Rawhide Energy Station and called on an intercom box to the security station to identify myself so the guard could open the security gate for me to enter. After driving across the edge of the lake, the armed guard then directed me to the visitor center. I met Jon Little, the knowledgeable and friendly tour guide, and a group of bicyclists from a local environmentally conscious brewery who were taking the tour also. We put on headphones with a radio set and a hard hat for the tour.

The first and largest building houses the boiler and the generators. The coal arrives by train in five — to six-inch lumps, which are broken down into one-inch lumps before being fed by conveyor to grinders that convert it into a powder finer than facial powder. This powder is then mixed with air and blown into the 16-story

boiler from four directions, where it burns efficiently at a hellish temperature of 2,800°F. Three hundred gallons per minute of purified water circulate in tubes through the boiler, which produces steam at 1,000°F and 1,900 pounds per square inch to drive the turbines. The water from the lake is fed through a condenser that turns the steam back to water so it can recirculate through the boiler. Enough heat is absorbed by the water to keep the 5 billion gallon lake at 70°F even in the winter, which the ducks and geese like. The turbines drive the generator, which produces electricity at 24,000 volts (24 kV). The turbine and generator room is extremely noisy, necessitating the headphones and radio set to hear Jon’s explanations. The electricity from the generator then goes through a step-up transformer station to produce electricity at 235 kV that is fed through the transmission lines so people can turn on their lights, air condition their houses, and cook their dinners.

After leaving the clean turbine room, we went to the scrubber room, where the noise level was much more tolerable but there was a lot more coal dust around. The gases and fly ash from the boiler come to this room where the main contami­nants, sulfur oxides, are removed in huge conical scrubber tanks. A mixture of lime and water is injected into the scrubber tanks and mixes with the heated air to chemically react with the sulfur, precipitating out calcium sulfites and sulfates to remove the sulfur. The Rawhide plant is very efficient in this process, produc­ing only about one-tenth of the sulfur dioxide in the exhaust as that of an average coal plant. Finally, the air goes into the bag room, another building filled with huge bag filters where the fly ash is removed, and up the smokestack. The opacity of the exhaust air is continuously monitored and is less than one-tenth of what is allowed by state and federal law. So, when you look at the smokestack you don’t see smoke or anything else coming out, except in the winter—the white plume is the condensed vapor from the water produced when the coal burns.