Lignite in Chemistry Structure Properties and Applications

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 are 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.

Characteristics

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.

Lignite Uses

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%)

Places that Benefit from Lignite-Based Power Plants

• 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 - 

• Xyloid Lignite, also known as Fossil Wood

• Compact Lignite also referred to as Perfect Lignite

Xyloid 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.

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.

Lignite is a flammable dark brown to black mineral generated over millions of years by the incomplete breakdown of plant matter under high pressure and temperature in an airless environment. To put it another way, lignite is coal. Lignite is plentiful and easy to obtain. Electricity generated from lignite is dependable. Electricity generated from lignite is environmentally friendly. Electricity derived from lignite is inexpensive. Power plants use lignite in an environmentally friendly manner.

Characteristics of Lignite

Lignites are brown in colour and have a laminar structure with visible traces of woody fibers. The term lignite is derived from the Latin word lignum, which means "wood." Because they come from plants with a lot of resin, they have a lot of volatile stuff. Freshly mined lignite is rough, but not hard, and breaking the huge lumps needs a hefty blow with a hammer. When exposed to air, however, it quickly loses moisture and disintegrates. Even if it looks to be completely dry, the moisture level might be as high as 30%. Transporting lignite over large distances is not cost-effective because of its high moisture content and low heating value.

Brown coal is another name for unconsolidated lignite.

Lignite is the lowest-ranking coal in the classification system, and it is mostly utilized as a power-plant fuel. Lignite is brown to black in colour and has a heating value of less than 19.306 KJ/Kg . Plant debris may be present in lignite deposits since they are geologically young. The moisture and volatile matter content of lignite are both rather high, at more than 25% and more than 24%, respectively, but the ash level ranges from 3 to 15%. The high moisture content of lignite creates a number of issues for its use, as it reduces the electrical efficiency of thermal power plants and can cause problems during handling, such as spontaneous combustion. Furthermore, the high moisture level affects the fuel's energy density, making long-distance transportation uneconomic. As a result, lignite power stations are frequently built near the mines that provide them.

Uses of Lignite 

The majority of lignite is utilized to produce energy. Small amounts, on the other hand, are utilized in agriculture, manufacturing, and even jewelry as jet. Its historical use as a house heating fuel has steadily dwindled, and its use to generate electricity currently takes precedence.

Heating in the house

Lignite was and is used to heat homes as a substitute for or in conjunction with firewood. For that purpose, it is frequently crushed into briquettes. When compared to higher-value hard coals, lignite was generally considered as a fuel for poor people due to its smell.

Fuel

Lignite is mined all over the world and is virtually solely employed in the manufacture of steam-electric power. Lignite combustion provides less heat per unit of carbon dioxide and sulfur emitted than other coal grades. Emits when burned. 

In the field of Agriculture

Agriculture is an environmentally friendly application of lignite. Lignite may be preferable to commercial K hummates as an environmentally friendly soil supplement, boosting cation exchange and phosphorus availability in soils while minimizing heavy metal availability.  Lignite fly ash, which is created when lignite is burned in power stations, could be used as a soil supplement and fertilizer.  However, there is little comprehensive research on the long-term benefits of lignite products in agriculture. 

Biological control microorganisms that reduce plant pests can also be grown and distributed using lignite. The carbon adds to the organic matter in the soil, while the biological control bacteria act as a natural pesticide alternative. 

Leonardite is a humic acid-rich soil conditioner generated by natural lignite oxidation near the Earth's surface.

Mud for drilling

Amine-treated lignite (ATL) is a result of a quaternary amine reaction that is used in drilling mud to prevent fluid loss during drilling.

As an Adsorbent for Industrial use

Lignite could be used as an industrial adsorbent. Experiments reveal that its methylene blue adsorption falls within the existing range of activated carbons utilized in industry.

In Terms of Jewellery

Jet is a type of lignite that has been used as a gemstone for thousands of years. Jet was widely employed in necklaces and other decorations in Britain from the Neolithic until the end of the Roman period, with the earliest objects dating back to 10,000 BCE. Jet had a brief resurgence in Victorian Britain.

Types of Lignite

Lignite is divided into two categories. The first type is xyloid lignite, also known as fossil wood, and the second is compact lignite, also known as perfect lignite.

Xyloid Lignite

Although xyloid lignite has the tenacity and appearance of conventional wood, it is clear that the flammable woody tissue has undergone significant changes. Trituration reduces it to a fine powder, and it generates a significant amount of humic acid when subjected to the action of a mild solution of potash. Leonardite is a lignite that has been oxidized and includes a lot of humic acids.

Jet Lignite

Another type of lignite is the jet, a gem-like, hardened substance that is generally used to make different kinds of jewelry.

Lignite for Carbonization

For primary tar and liquid fuel production, dry lignite contains less than 20% ash. For the production of briquette lignite for extraction - contains over 12 DM percent bitumen and is used to extract wax and bitumen.

Energetic Lignite

For thermal power plants; energy and ash contents are over 6.5 MJ/kg and less than 40%, respectively.

Briquette Lignite

For the production of briquettes lignite; energy and ash contents over 8.4 MJ/kg and less than 15%, respectively.