LIGNITE: THE FORGOTTEN COAL
“There is more appearance of coal today than we have yet seen. The stratas are 6 feet thick in some instances; the earth has been birnt in many places, and always appears in stratas on the same level with stratas of coal.” Journal of Meriwether Lewis, April 29, 1805, Lewis and Clark Expedition.
Little did Lewis realize that the lignite reserves he saw that day were so massive that they might still be providing power 1,000 years later. However, the lignite reserves of North Dakota are estimated to be 25 billion tons – enough to provide an 833 year supply at the current rate of mining. And, that doesn’t include the estimated 325 billion tons of lignite that is thought to exist in the region, but isn’t economical with current technology.
While lignite is usually seen as occupying the bottom of the coal hierarchy because it is softer, contains about 35% water, and has a lower energy value, it is an important power source for America’s electrical grid and a source for the synthetic fuels that we need to decrease our reliance on foreign producers.
The largest lignite mine is the Coteau Properties’ Freedom Mine. It not only provides 15 million tons of lignite a year to the Basin Electric Power Cooperative, it also provides lignite to the Great Plains Synfuels Plant. This plant gasifies lignite to produce over 160 million cubic feet of natural gas, in addition to several agricultural and chemical byproducts.
The Freedom Mine has an aggressive reclamation operation that has won several awards for its reclamation program. Approximately 700-1,000 acres of land are reclaimed each year at the Freedom Mine --the same amount as the acreage disturbed by mining. Most of the land is returned to cropland and rangeland; however, the company, worked with government agencies to design and develop the Harmony Lake Wildlife Management Area. The 45-acre lake, and 637-acre wildlife area was donated to the state of North Dakota, and is recreational destination for the local community.
Although the Lewis and Clark Expedition discovered lignite in the Dakotas, it took several decades before it was exploited. Ironically, coal was being mined in the Dakotas even before the Dakota gold rush. In 1873 several small mines sprung up along the main routes of transportation in western North Dakota. By 1900 there were 73 mines operating in North Dakota. Many of these were small, seasonal mines that removed coal from the face of the outcrop. They were called wagon mines because area farmers and ranchers would often bring their own wagons to the site to be filled with coal. Still, other mines were large operations employing hundreds of men with underground workings extending for thousands of feet. By the early 1920s, there were approximately 250 mines operating in the state, with an equal number of underground and surface strip mines. The advent of the steam shovel increased the profitability of the surface mines and the last underground mine closed in 1966.
Today, lignite continues to be mined in open pit operations. The Freedom Mine works a 13 to 20 foot seam that is between 50 to 150 feet below ground. That requires moving more than 100 million cubic yards of overburden a year to get to the coal. As a result, the mine owns a fleet of massive earth moving equipment like the Bucyrus-Erie Model 2570 walking draglines, which weigh 13 million pounds each and rival the height of the North Dakota Capitol.
Although lignite doesn’t have the energy per pound of some coals, it has many characteristics that make it desirable. Lignite is more accessible than other types of coal because lignite veins are located relatively near the surface, eliminating the need for underground excavation in tunnels. Surface mining also eliminates the risk of methane or carbon monoxide buildup. As a result, lignite powered electricity is much cheaper than other power sources. A cost ranking by Global Energy Decisions ranked four lignite coal power plants in the top 40 low cost power plants in the US. According to them, lignite cost $15.34 per megawatt, while all coal plants cost $22.14. Gas plants coast $74.82 per megawatt.
Modern environmental practices make lignite much more ecologically practical. For instance the Antelope Valley Station, in conjunction with the Freedom Mine tested “Air Jigging.” Air jigging system consists of two processes. One involves pulsating air through the coal stream and the second involves a vibrating slide. In combination, these two processes separate the heavier products in the coal which typically contain the higher percentages of sulfur, mercury, pyrites and clay in the lignite. This not only removes contaminants, it also increases the heat from the lignite.
Although lignite hasn’t received the attention of other coals, it has proven to be a reliable and inexpensive source of energy for over a century. Given the massive reserves in the upper Great Plains of the United States, it’s likely to be a source of energy for many centuries to come.