Lignite, commonly referred to as Brown Coal, is the lowest rank of coal in the coalification process. It is formed from partially decomposed plant material (peat) subjected to relatively low geological pressure and temperature over millions of years.
Due to its limited maturation, lignite retains high moisture content, low carbon concentration, and a soft, friable structure. While it has a lower calorific value than bituminous or anthracite coal, lignite is widely used because it is abundant, economical, easy to ignite, and suitable for continuous large-scale thermal applications.
Coal Rank Comparison
Peat: Carbon < 25%, Very high moisture, very low calorific value
Lignite: Carbon 25–35%, Moisture 30–60%, Calorific value 8–14 MJ/kg
Sub-Bituminous: Carbon 35–45%, Moisture 15–30%, Calorific value 18–25 MJ/kg
Bituminous: Carbon 45–85%, Low moisture, Calorific value 24–35 MJ/kg
Anthracite: Carbon > 85%, Very low moisture, Calorific value 30–36 MJ/kg
Key Characteristics of Lignite
Carbon Content
Typically ranges between 25% and 35%. Although lower than higher-rank coals, this
level is adequate for thermal energy production but not suitable for
high-intensity metallurgical processes.
Moisture Content
High moisture levels of 30%–60% are both inherent and surface-bound. This results
in easier ignition and lower flame temperature but reduces net calorific value
and increases transportation cost.
Heating Value (Calorific Value)
Ranges from 8 to 14 MJ/kg, providing steady and controllable heat ideal for boilers,
steam generation, brick kilns, and lignite-based thermal power plants located near
mines.
Volatile Matter
Typically 35%–45%, enabling fast ignition, stable flame formation, and reduced
dependence on auxiliary fuels.
Ash Content
Generally between 6% and 20%, depending on geological formation and processing.
Lignite ash can be reused in cement manufacturing, brick production, and road
construction.
Color, Texture & Structure
Light to dark brown in color with a soft, crumbly, and porous texture, allowing
easy crushing and high combustion reactivity.
Typical Mechanical & Physical Properties
Density: 0.7 – 1.0 g/cm³
Hardness: Very soft
Compressive Strength: 0.5 – 3 MPa
Moisture Sensitivity: High
Thermal Stability: Low to medium
Grindability: Very high
Typical Chemical Composition
Carbon (C): 25 – 35%
Hydrogen (H): 2 – 5%
Oxygen (O): 20 – 35%
Nitrogen (N): 0.5 – 1.5%
Sulfur (S): 0.3 – 1.5%
Ash: 6 – 20%
Mining & Processing of Lignite
Lignite is predominantly mined using open-cast or surface mining methods, offering high recovery rates and low mining costs. Deposits are typically located near consumption centers due to transportation limitations.
Processing steps include crushing and sizing, screening, optional drying, and value addition through briquetting or pulverizing.
Available Commercial Forms
Raw Lignite (Run-of-Mine)
Used directly in thermal power plants and large industrial boilers.
Lignite Briquettes / Blocks
Compressed for reduced moisture, uniform size, and controlled combustion, suitable
for small industries, hotels, and domestic heating.
Crushed / Pulverized Lignite
Fine particle size for high combustion efficiency, used in brick kilns, cement
plants, and foundries.
Dried Lignite / Lignite Coal Dust
Offers improved calorific value, cleaner combustion, and reduced smoke emissions.
Storage, Handling & Transportation
Lignite must be stored in covered, moisture-controlled yards. Prolonged storage may lead to oxidation and, in rare cases, self-heating. Transportation is typically by truck or rail and is best suited for short distances.
Applications of Lignite
Power Generation
Primary fuel for lignite-based thermal power plants providing reliable baseload
electricity.
Industrial Boilers & Steam Production
Used in cement plants, textile units, food processing, chemical industries, and
paper & pulp mills.
Brick Kilns & Ceramic Industry
Low-cost fuel offering controlled firing temperature and consistent heat output.
Metallurgical & Foundry Applications
Used as a reducing agent and heat source in low-temperature furnaces.
Domestic & Commercial Heating
Briquetted lignite used in rural households, small hotels, and community kitchens.
Agriculture & Soil Improvement
Lignite derivatives improve soil carbon content and moisture retention and are used
in humic acid production.
Environmental Considerations
Advantages include low mining cost, abundant reserves, stable combustion, and support for local energy security. Limitations include lower efficiency, higher CO₂ emissions per unit energy, and the need for emission control systems.
Lignite vs Other Fuels
Compared to bituminous coal and natural gas, lignite offers very low cost and high availability but lower calorific value and higher emissions, making it most suitable where fuel cost is the primary consideration.
Lignite (Brown Coal) remains a cost-effective and reliable energy source for continuous heat generation, particularly in power plants, industrial heating, brick manufacturing, and steam production where affordability and availability are critical.