As coal technology advances and concern for the environmental impact of coal mining increases, there is a greater push for cleaner burning coal and more environmentally-friendly mining methods. There are 4 main types of mines: shaft mine, drift mine, slope mine, and surface mine.
Alaska's only operable coal mine, Usibelli, is a surface mine, using strip mining for all of its operations. In strip mining, overburden (soil, vegetation, rocks) are removed before coal is mined in open pits.
Because of the difficulty in excavating overburden and coal, Usibelli mine uses blasting to loosen the material before moving it. By using a blasting technique called "cast blasting," they are able to cast a portion of the overburden laterally into an already mined-out pit, reducing the amount that the dragline, bulldozers, shovels, and backhoes must remove from the site.1
Coal as a Fuel
Coal's main use is as a solid fuel to produce electricity and heat during combustion. Alaska has 6 small coal-fired power plants, located at Fort Wainwright, Eielson Air Force Base, Clear Air Force Station in Fairbanks (Aurora Energy LLC), on the University of Alaska Fairbanks campus, and near Usibelli Coal Mine.2
When used for electrical generation, coal is often pulverized before combustion in a furnace with a boiler; the steam from the boiler turns turbines which drive generators to produce electricity. There are other ways to use coal as a fuel, including gasification and liquefaction. The 6 coal-fired plants in Alaska use the pulverization technology.
"Clean Coal" Technology
Clean coal technology addresses atmospheric problems that occur as the result of burning coal on a large scale. Examples of clean coal technology are the use of chemicals to "scrub" impurities from the coal, treating flue gases with steam to remove sulfur dioxides ("SOx," pronounced "socks") and other particulate matter, and the capture and storage of carbon dioxide in the flue gases.
Golden Valley Electric Association has plans to reopen a coal-fired power plant near Healy that was built in the late-1990s. The State Department of Environmental Conservation filed a draft permit which must clear public and federal reviews before the plant can reopen. The 50 MW coal plant sits near the border of Denali National Park and was originally built with experimental technology designed to reduce emissions. GVEA says that the proposed reopening of the plant could save them $2 million a month in costs, allowing them to buy more coal and cut oil consumption.3
Because nitrogen oxides, or "NOx" (pronounced "knocks"), can form during combustion and be released into the air as a pollutant, low-NOx coal burners have been developed to reduce this pollution. Although these low-NOx burners are less effective then the devices that "scrub" the flue gases, they are far less expensive and can cut NOx pollution in half.
Low-NOx coal burners use staged combustion to reduce this pollution, where coal is burned in stages. In this process, Coal is burned in a chamber where there is more fuel than oxygen present, so that the majority of oxygen in the air combines with the fuel rather than with nitrogen. The remaining fuel is then moved to a second combustion chamber where the process is repeated.4
Many "scrubbers" that are used to treat flue gases at coal-fired power plants contain a mixture of crushed limestone and water which is sprayed into the coal combustion gases. The limestone absorbs the nitrogen gases and creates a paste that can be removed from the chamber; there are also "scrubbers" that use a dry power.5