Coal pipelines are pipelines used to transport coal from where it is mined to where it is consumed. For very short distances, large trucks are used to transport coal, but trains and barges are preferred for long distances. In some cases it is more economical to move the coal by pipeline than by train or barge. This can happen when there is no suitable railway or waterway to transport the coal, or when it must be moved very long distances.
There are two types of coal pipelines. Slurry pipelines use a slurry of water and pulverized coal. The ratio of coal to water is about 1 to 1. Coal log pipelines use coal that has been compressed into logs with a diameter 5 to 10% less than the diameter of the pipeline and a length about twice the diameter of the pipeline. The ratio of coal to water is about 3 or 4 to 1.
Coal must be relatively dry before it can be burned efficiently, so the coal must be dried after it arrives at the power plant. Coal transported as slurry requires a lot of drying and electricity generation will be substantially less if it is not dried effectively. Coal logs do not require as much drying because they are packed so tightly that they do not absorb much water, and any water originally in the coal is squeezed out during compression. To dry the coal, the water is evaporated or separated in a centrifuge.
Large coal power plants use a phenomenal amount of coal each day; enough to fill a hundred train coal cars carrying 100 tons each. Water used to transport the coal is likewise significant, particularly in arid regions like the Southwestern United States. Such a power plant would use about 2,400,000 US gallons per day (9,100 m3/d) with a coal slurry pipeline or about 700,000 US gallons per day (2,600 m3/d) with a coal log pipeline. This amounts to about 2,700 or 780 acre feet (3,300,000 or 960,000 m3) per year respectively, which is enough water for a small town.
The 1,580 megawatt Mohave Generating Station in Laughlin, Nevada had the longest coal slurry pipeline in the world at 273 miles (439 km). From 1969 until 2005, the pipeline used 4,500 acre feet (5,600,000 m3) of water per year to carry about 5 million tons of coal to the plant from the Black Mesa Mine in the northeastern corner of Arizona. The plant was shut down on December 31, 2005 because the controversial coal and water supply terms were being renegotiated. The plant also needed a billion dollar upgrade to its pollution control equipment. It was widely criticized by environmental groups for, among other things, its contribution to particulate haze in the Grand Canyon. In 2009, it was announced that the plant would be dismantled, possibly to be replaced by an alternative energy plant. Demolition is to start in December, 2009.