Coal is moved from the mine to its point of end use by a number of transportation modes. The way that coal is transported to where it will be used really depends on the distance to be covered. Because most coal in the world is burned in power plants to generate electricity, the distance between mine and power plant determines the method of transportation.
The unit train is the most common form of long distance coal transportation. A unit train is group of railcars that operate in a dedicated shuttle service between a coal mine and a power plant. A typical unit train consists of 10 to 120 railcars and 3 to 5 locomotives, with each railcar holding about 100 short tons of coal. Carefully coordinated loading and unloading terminals are necessary to minimize costs. A unit train making a round trip from mine to plant has a typical turnaround time of 72 hours, including a 4-hour loading and 10-hour unloading and servicing time per train.
In the 1990s, distributed power (DP) came into widespread use in the western United States. In this system a remotely controlled engine is put into the middle of a train, allowing greater traction and control of train motion. DP trains can consist of 135 cars and are the most efficient method of rail transportation of coal.
Barges on rivers and lakes play an important role in coal transport in the United States and Europe. Coal-carrying barges move in tows of fifteen to forty barges, pulled by a single towboat of 2,000 to 10,000 hp. A "jumbo"-size barge carries 1,800 tons of coal, so a large tow can move 72,000 tons of coal, as much as five unit trains. These large volumes result in significant economies of scale and lower costs. Barge rates can run (on a cost-per-mile or cost-per-kilometer basis) a quarter or less of rail rates. However, waterways often follow circuitous routes, resulting in slow delivery times.
Coal slurry pipelines
Coal slurry pipelines use a slurry of water and pulverized coal. The ratio of coal to water is about 1 to 1. The 1,580 megawatt Mohave Generating Station in Laughlin, Nevada has the longest coal slurry pipeline in the world at 273 miles (439 km). The pipeline carries about 5 million tons of coal annually from the Black Mesa Mine in the northeastern corner of Arizona. The coal removed from the mine is crushed to a diameter of around one millimeter, and is mixed with water in holding tanks with agitators, which keep the coal in suspension in the water. The pipeline consumes around a billion gallons of water annually. After three days the slurry reaches the end of the pipeline, at the Mohave power plant, where it is held in agitated tanks, for immediate use, and in drying ponds, for later use. Heated centrifuges are used to get the water out. As of 2006, the plant is shutdown because the coal and water supply terms are being renegotiated.
The large water and energy requirements for coal slurry pose a significant barrier to further deployment, especially in arid regions of Australia and the western United States.
Coal log pipelines
A new coal log pipeline technology mixes coal that has been mined, cleaned, and crushed, with a binding agent comprised of coal pitch, bitumen, or wax. The coal mixture is then tightly compressed and compacted as coal logs that are 5% to 10% thinner than the transportation pipeline. The logs are injected into a pipeline and pumped along using water. The pipeline can deliver the coal to coal-fired electric power stations or coal storage areas. The coal logs must then be crushed for use in fluidized bed, cyclone, or chain-grate stoker coal-burning boilers or pulverized for use in pulverized-coal combustors.
Proponents of the coal log technology claim that in addition to being more cost effective than coal slurry, the capsule pipeline is also more environmentally sound because the coal logs eliminate coal dust erosion of the pipe interior and erosion of coal fines by rain at the power plant storage site.
Trucks haul coal over relatively short distances, typically at most about 100 miles (160 km) one-way or less. Coal-carrying vehicles are typically end-dump trucks with a carrying capacity of roughly 25 to 50 tons. Truck delivery is used extensively for small power plant sin the eastern United States.
Global trade in coal increased from 498 Mt in 1990 to 917 Mt in 2007. Coal exports are expected to continue to rise and, therefore, the importance of ocean transport will increase. Ocean transport of coal requires a system of (1) transportation from the mine to the port, (2) coal-handling facilities at the export port, (3) ocean carrier networks with adequate number and size of ships, contractual obligations, management of the fleet, and route decisions, (4) coal-handling facilities at the importing port, and (5) transportation from the port to the customer.
Ships are commonly used for international transportation, in sizes ranging from:
- Handysize (40-45,000 dead weight tons (DWT), a term normally taken to mean a vessel of about 10-40,000 DWT.
- Panamax ( about 60-80,000 DWT). Technically, the maximum size vessel that can transit the Panama Canal - restriction of 32.2 M beam.
- Capesize vessels ( 80,000+ DWT). A vessel that is too large to transit the Panama Canal and thus has to sail via Cape of Good Hope from Pacific to Atlantic, and vice versa.
- Liu, H., R. Zuniga, and J. L. Richards. 1993. Economic Analysis of Coal Log Pipeline Transportation of Coal. CPRC Report No. 93-1, University of Missouri, Columbia, Missouri.
- Macmillan Encyclopedia of Energy, Coal, Transportation and Storage Of (Gale Reference Group, 2006)
- Fieldston Company, Inc. (1996). Fieldston Coal Transportation Manual: 1996–97. Washington, DC
- CoalEducation.org, Coal transportation, Accessed 5 January 2009.
- World Coal Institute, Coal Facts 2008. Accessed 5 January 2009.
- Center for Land Use Interpretation, A Long, Strange Trip To Fuel the Grid, Accessed 5 January 2009.
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