Before you run away thinking this is another complex compound, let us tell you it’s not! Lignite is simply a kind of coal, usually a brownish-black one. Hence, it is also called brown coal. However, it may also occur in other colored forms like yellow and even black, which is rarely found. So, let’s define lignite. It is soft brownish coal formed from naturally compressed peat at shallow areas having temperatures lower than 100°C. Brown coal is generally combustible in nature and is often formed as a sedimentary rock. Due to its low heat content, lignite is considered the lowest rank of coal and is often found to contain recognizable plant fossils.
Lignite has a carbon content of around 25-35%, which may raise up to 60-70% in an ash-free and dry form. It also has a high moisture content of up to 75% and 6-19% of ash content. The calorific value of lignite is around 17 megajoules per kg.
Some of the water content is even released due to continuous exposure to weather changes, as a result of which, crumbling or disintegration of brown coal may also occur. This, in turn, reduces lignite’s value as a fuel.
Besides, it is geologically younger than other higher-grade coals and generally originates in the Tertiary period.
Brown coal usually has an intermediate density, a wood-like texture, and carbon content between peat and bituminous coal. Peat, lignite, bituminous, and anthracite are all different forms of coal.
There can be numerous uses of lignite coal, and the most commonly seen is the fossil fuel power plant. Since lignite contains high amounts of volatile substances, it can easily be converted into liquid and gas forms, such as petroleum products.
Moreover, due to the abundance of lignite mine reserves worldwide, it is exclusively used as a fuel for generating steam-electric power. The only environmentally beneficial use of brown coal is probably seen in cultivation as well as the distribution of biocontrol microbes, which are used to control harmful disease-causing pests from affecting plants.
The Popular Applications of Lignite Include -
Electricity Generation (79%)
Synthetic Natural Gas Production (13%)
Production of Fertilizers (7%)
Home Heating and Oil Well Drilling Mud (1%)
States like North Dakota benefit tremendously from lignite-based power plants, as they help to generate reliable and affordable amounts of electricity. It especially helps farmers and small businesses as it reduces the overall operational costs. Not only does it help businesses to become competitive on an international level, but it also facilitates the economic and industrial development of the state.
Similarly, the German Democratic Republic became extensively dependent on lignite-based power generation to grow more energy self-sufficient.
Other uses include the conversion of brown coal into coke conducted by East German scientists for metallurgical purposes. Interestingly, much of the Deutsche Reichsbahn railway network relied heavily on lignite-derived energy either through electric lines or steam trains.
However, lignite is inefficient for transportation as it comes with high inherent moisture content and low density. It is, therefore, not traded on the global market compared to other high-grade coals.
Types of Lignite
We can divide lignite into two types - a) Xyloid Lignite, also known as Fossil Wood, and b) Compact Lignite, also referred to as Perfect Lignite.
Xyloid lignite comes with the fibrous structure of wood. This is why this form of lignite may often have the appearance and tenacity of ordinary wood. However, there’s still a lot of visible difference between xyloid lignite and wood, and we can find that the combustible woody tissue in the former has experienced a good deal of modification.
We can reduce xyloid lignite stone into fine powder through the process of trituration. We can also generate a generous quantity of humic acid if we mix it in a weak potash solution.
Further, leonardite is a soft and shiny form of oxidised lignite that comprises humic acid in high levels. Another type of lignite is the jet, a gem-like, hardened substance that is generally used to make different kinds of jewelry.
Did You Know?
Lignite is the most harmful form of coal known to us as it may have serious health hazards. It is because of the high quantities of harmful emissions released into our environment due to combustion, including NOx, SO2, and dust. If we are exposed to air pollution caused by lignite, there can be increased risks of lung cancer, heart disease, and chronic bronchitis.
Besides, the high moisture content present in raw lignite as extracted from the mine can result in dangerous amounts of CO2 emissions. Therefore, we need to address the problem of air pollution due to lignite coal combustion in a more responsible and eco-friendly way.