Coal Supply
Coal is by far America’s most versatile fossil fuel. Sometimes called “Nature’s black diamond,” coal is technically not a mineral, but a combustible sedimentary rock having a rich chemical structure. It is composed primarily of carbon, hydrogen and oxygen, with smaller amounts of sulfur and nitrogen, and traces of other elements ranging from aluminum to zirconium. 
Recoverable U.S. coal reserves are sufficient to last at least 230 years at the current consumption rate. America’s reserves account for 35 percent of the world’s known recoverable coal, the largest total of any single nation. Coal is America’s most important fuel for generating electric power. About 57 percent of the electricity produced by the utility industry is produced with coal.
Coal’s characteristics vary widely from region to region. The various regional coals are broadly classified as anthracite, lignite, sub bituminous and bituminous. Lignite generally has a higher sodium and moisture content and lower heating value (expressed in British thermal units), and anthracite is a low volatility coal. Because of these characteristics, both lignite and anthracite are considered least suitable for coal-fired generation of electricity.
Coal quality has a significant impact on capital costs, operating and maintenance costs, and the design of major electric generating plant systems including:
- Steam generator and auxiliaries
- Particulate collection
- Flue gas desulfurization
- Coal and ash handling
- Solid waste disposal.
Holcomb Station, Sunflower’s coal-fired generation plant, burns in excess of one million 500 thousand tons of coal each year. Sunflower purchases high quality sub bituminous soft coal mined in the Powder River Basin near Gillette, Wyoming. Coal from that area has the lowest sulfur content of any in the nation, but a slightly lower heating value than harder bituminous coal.
Typically, the Wyoming coal contains between .35 and .50 percent sulfur that is converted to sulfur dioxide (SO2) when the coal is burned. Sunflower removes from 70 to 75 percent of this small amount of SO2 from the exhaust gases during the scrubbing process. The amount of SO2 removed by scrubbing averages about 5 percent more than the stringent federal permit requirements.
Sunflower contracts with Western Fuels Association, Inc. for the coal and its delivery. Western Fuels is a cooperatively owned coal supplier for consumer-owner electric utilities. Included in Western, Fuels’ membership are rural electric generation and transmission cooperatives and municipal utilities.
Prior to mining, coal companies are required to obtain an assortment of permits including those related to air and water quality. Following surface mining, the land must be returned to original-or-better conditions suitable for plants and wildlife. Coal companies have to meet strict mining requirements reclaiming the land and protecting the environment.
More than half of Sunflower’s operating expenses under existing contracts are for coal related transportation costs. Coal is delivered about 750 miles from the Wyoming mine to Holcomb Station by the Burlington Northern and Atchison, Topeka & Santa Fe railroads. Burlington Northern transports the coal to Pueblo, Colorado where Santa Fe crews take over operation of the train for the last leg of the trip to Holcomb.
The coal necessary for Sunflower’s operation can only be economically delivered one way — by rail. Because it has access to only one rail route, Sunflower is considered a “captive shipper” and must aggressively pursue coal and rail pricing terms to remain competitive with other regional utilities that have access to alternative transportation suppliers. Negotiating the best possible coal and transportation contracts is an ongoing commitment Sunflower has made to its members.
The environmental effect of coal production and use received widespread attention from the media, government agencies, environmental groups and the president during 1990. Critics claimed it was one of the most serious challenges facing the coal industry. What those same critics fail to recognize is that no other American industry faces as many regulatory controls as coal —from production and delivery, through the process of converting coal to energy, to the restoration of mined land.
Between 1990 and 2000, utility coal consumption increased approximately 400 million tons, yet coal plant emissions of sulfur dioxide (SO2), a combustion by-product linked by some scientists to acid deposition or “acid rain,” decreased by more than a million tons. This decrease was due in part to increased government regulations requiring clean air equipment in newly constructed plants and also to an increased concern for the environment throughout the electric utility industry.
Clean air equipment at Holcomb Station, Sunflower’s 365 megawatt coal-fired generating plant, accounted for about $67 million of the plant’s total cost of $465 million. It costs about $300,000 each year just to operate the clean air equipment.
Holcomb Station utilizes a “dry scrubber” SO2 removal system. An alkaline slurry mixture is sprayed into coal combustion exhaust products. The mixture causes a chemical reaction that forms solid particles of calcium sulfate and calcium sulfide, which are dried in the scrubber and collected in the bag house.
Spray drying is not a new technique. Since the 1920s, powdered milk, detergents and other commercial products have been created using the spray drying process. The spray dryers at Holcomb Station are among the largest in the world.
This complex flue gas desulfurization system (scrubber) is monitored by a computerized Total Distributed Control System that separates the controls into subsystems that can function independently. The control system makes it possible for an operator to monitor and control the clean air equipment from a central location.
Holcomb Station is one of 36 plants built in the United States after 1978 that had to meet more stringent federal clean-air requirements. Sunflower is limited to releasing just under one-half pound SO2 per million British thermal units (Btu) of heat input. Thanks to Holcomb Station’s sophisticated equipment, the plant normally operates at only .10 to .23 pound SO2 per million Btu.
Unlike many of the older plants, located primarily east of the Mississippi, Sunflower emissions are much cleaner than the requirements established by the Clean Air Act Amendments of 1990. Sulfur dioxide removal at Holcomb Station exceeded requirements throughout its 19 year history.