What is Lignite?
A Soft Brown Coal That Provides Low-Cost Energy
Sometimes called “brown coal,” lignite is the lowest quality and most crumbly coal. This softer and geologically “younger” coal sits relatively close to the earth’s surface.
Lignite can be broken down chemically through coal gasification, the process of producing syngas from coal along with water, air and/or oxygen. This creates synthetic natural gas that delivers more power and is easier to operate in commercial-scale electric generations.
According to the Lignite Energy Council, 13.5% of lignite coal is gasified into synthetic natural gas and 7.5% goes into the production of ammonia-based fertilizers. The balance is used to generate electricity, which provides power for more than 2 million consumers and businesses in the Upper Midwest. Because of its high weight relative to its heat content, lignite is expensive to transport and is typically used in pulverized coal or cyclone-fired electric production power plants close to the mine.
North Dakota, in particular, benefits from the power generated by its lignite-based power plants. This affordably produced electricity attracts farmers and businesses to the region, keeping their operational costs low so that they remain competitive locally, nationally, and internationally. Because of the often extreme weather in the area, a low-cost source of electricity is particularly important for North Dakota businesses. The lignite production industry itself also generates about 28,000 jobs, which offer relatively high wages and drive about $100 million in annual state tax revenue.
Characteristics of Lignite Coal
Of all coal types, lignite contains the lowest level of fixed carbon (25-35%) and the highest level of moisture (typically 20-40% by weight, but can go as high as 60-70%). Ash varies by up to 50% by weight. Lignite has low levels of sulfur (less than 1%) and ash (approximately 4%), but it has high levels of volatile matter (32% and higher by weight) and produces high levels of air pollution emissions. Lignite has a heating value of approximately 4,000 to 8,300 Btu per pound.
Availability and Accessibility of Lignite
Lignite is considered moderately available. Approximately 7% of the coal mined in the U.S. is lignite. It's found primarily in North Dakota (McLean, Mercer, and Oliver counties), Texas, Mississippi (Kemper County) and, to a lesser degree, Montana. The Lignite Energy Council notes that brown coal is more accessible than other types of coal. Lignite veins are located relatively near the surface, which means that underground excavation in tunnels isn't necessary and there is no risk of methane or carbon monoxide buildup, a primary safety concern in underground mining.
According to the World Coal Association, the top 10 countries that produce brown coal are (ranked from most to least): Germany, U.S.A., Russia, Poland, Turkey, Australia, Greece, India, Czech Republic, and Bulgaria. In 2014, Germany was by far the largest producer, generating 178.2 million tons of lignite to the U.S.'s 72.1 million tons.
Because of its high moisture content, lignite may be dried to reduce moisture content and increase calorific fuel value. The drying process requires energy but can be used to reduce volatile matter and sulfur as well.
Lignite ranks fourth, or last, in heat and carbon content compared with other types of coal, according to ASTM D388 - 05 Standard Classification of Coals by Rank.