Lignite

With all the news about the oil boom in the Bakken formation in North Dakota we may occasionally need a reminder that North Dakota lignite is a major source of energy in the state as well. Although most North Dakotans are well aware of the coal mines and associated power plants in the Beulah, Center, Stanton, and Underwood areas, I suspect that relatively few among us have a good sense of just what lignite is.

The Lignite Energy Council’s website defines lignite as a “dark brown to black combustible mineral formed over millions of years by the partial decomposition of plant materials subject to increased pressure and temperature in an airless atmosphere.”

Lignite is a form of coal that has not been under enough heat and pressure to make hard, high BTU coal such as anthracite. It is generally considered to be the lowest grade of coal, and is classified as lying between peat and the harder, higher BTU bituminous coal. Lignite is a soft, rather crumbly coal that is brownish-black, and is occasionally referred to as “brown coal.” It has a high water content, which can range from around 35% water to as high as 60%. It also has the reputation of occasionally spontaneously combusting which makes transporting the material problematic, from an economic as well as a safety perspective.

North Dakota lignite formed during the Paleocene from swamp peat about 65-55 MYBP (million years before present). At that time much of western North Dakota had a climate and vegetation that was similar to the forested swamplands of Florida with bald cypress, figs, cycads, and palm trees. As happens today in swampy areas, when the plants died, the material began to accumulate at the bottom of the swamp. However, the decay of that plant material is often incomplete, in part due to the lack of oxygen. So over time the organic material accumulated and was eventually covered over or buried under new mineral sediments. Over the next several million years, with some pressure and heat on the organic material, it was transformed from peat to lignite.

There are currently 4 lignite mines operating in western North Dakota, and the largest lignite producer in the nation is the Freedom Mine northwest of Beulah. Most of the lignite is used to generate electricity in nearby coal fired power plants, with smaller amounts going toward the production of synthetic natural gas.

Chuck Lura

Natural North Dakota is supported by NDSU Central Grasslands Research Extension Center and Minot State University-Bottineau, and by the members of Prairie Public. Thanks to Sunny 101.9 in Bottineau for their recording services.