lignite

Lignite, also known as brown coal, is the lowest rank of coal. It forms from peat through burial and mild metamorphism during geological time, resulting in a material with relatively low carbon content and a high moisture content. Lignite is soft, friable, and ranges in color from yellow-brown to blackish-brown. Its composition varies, but it is characterized by high moisture, moderate-to-low fixed carbon, and relatively high volatile matter and ash. Because of the moisture, its energy density is low and its calorific value typically falls in the low range for coal.

Lignite deposits are found in several regions worldwide, with large resources in Europe (for example Germany, Poland, the Czech Republic), Russia, and North America. It is predominantly mined by surface mining methods from shallow deposits. The principal use of lignite is electricity generation in thermal power plants and, in some areas, district heating. It can also be upgraded by drying or gasified for the production of syngas or refined fuels, though these processes add cost.

Environmental considerations: burning lignite generally yields higher CO2 emissions per unit of energy than higher-rank coals due to its low efficiency and high moisture content; it can also have higher sulfur content and ash. Mining can impact land stability and water quality, and emissions are subject to air-pollution control measures where applicable. Despite its disadvantages, lignite remains an important energy resource in regions where it is abundant and economical.