Lignite is the lower rank of coal. Vast reserves are available in many parts of the world. The special characteristics of lignite make it different from other coals. Read about this in this article.
Description of Lignite:
Wood and other vegetable matter decayed and transformed under pressure millions of years ago to form coal. Lignite has a Lower Rank in the coalification process, meaning this more recent than bituminous and anthracite coals.
Called Brown Coal, vast reserves of lignite are available in limited areas of the world. Australia, US and China have the major reserve of Lignite. Germany leads the pack with the largest number of power plants burning Lignite. In US, most of the reserves are located in the North Dakota province.
In India, the Lignite reserves are in Naively in the south and in Rajasthan.
Low calorific value and resulting low cost is what makes it attractive. Because of the lower energy density, transportation is not attractive. Lignite power plants are located near to the mines.
Around 17 % of the world’s coal reserves are lignite. As the world’s oil and gas reserves decline, other sources become attractive. That is why there is a sustained interest in the use of Lignite.
Characteristics of Lignite:
Lignite has some special characteristics. These characteristics vary from mine to mine.
- The most important is that the calorific value is low. The CV ranges from 8000 kJ/kg to 15000 kJ/kgs. Compare this to bituminous coal that has calorific value of 12000 to 20000 kJ/kgs.
- Lignite has high moisture content in the range of 45 % to 55 %.
- The Volatile matter content is also high. On an ash and moisture, free basis the Volatile Matter percentage in the range of 45% to 55 %.
- High amounts of Sulphur especially in the form of Ferrous Sulphide FeS2, reduce the ash fusion temperature to low levels like 900 °C. This gives the coal high potential for slagging.
- The lignite is softer than bituminous coal, with a HGI in the range of One Hundred making it easier to pulverize.
These characteristics make Lignite burning different from burning bituminous coals. Germany with large number of Power plants burning Lignite is the forerunner in the technology for Lignite fired boilers.
Applications of Lignite Coal:
According to the Lignite Energy Council, 13.5 percent of lignite coal is gasified into synthetic natural gas and 7.5 percent goes into the production of ammonia-based fertilizers. The balance 79% is used to generate electricity, which provides power for more than 2 million consumers and businesses in the Upper Midwest. Because of its high weight relative to its heat content, lignite is expensive to transport and is typically used in pulverized coal or cyclone-fired electric production power plants.
Because of its high moisture content, lignite may be dried to reduce moisture content and increase calorific fuel value. The drying process requires energy but can be used to reduce volatile matter and sulfur as well.