Coal Classification

Coal classification is based on various factors such as carbon content, moisture content, calorific value, and geological origin. The classification system provides a framework for understanding the properties and suitability of different types of coal for various applications. The most commonly used coal classification system divides coal into four main ranks, or types, based on its carbon content and energy density:

1. Lignite:

   • Lignite, often referred to as brown coal, is the lowest rank of coal.
   • It has a high moisture content (typically 25-35%) and low carbon content (25-35%).
   • Lignite has a relatively low calorific value (around 10-20 MJ/kg) and is considered the least energy-dense type of coal.
   • It is primarily used for electricity generation in power plants located near lignite mines due to its low transportation cost.

2. Sub-bituminous Coal:

   • Sub-bituminous coal has higher carbon content and energy density compared to lignite but lower than bituminous coal.
   • It has a moisture content of around 20-30% and a carbon content of around 35-45%.
   • Sub-bituminous coal has a calorific value ranging from approximately 20-30 MJ/kg.
   • It is used primarily for electricity generation and industrial applications, often in power plants equipped with advanced emissions control technologies.

3. Bituminous Coal:

   • Bituminous coal is the most abundant and widely used type of coal worldwide.
   • It has a higher carbon content (45-86%) and energy density compared to lignite and sub-bituminous coal.
   • Bituminous coal has a moisture content ranging from around 10-20%.
   • It has a calorific value ranging from approximately 24-35 MJ/kg.
   • Bituminous coal is used for electricity generation, steelmaking, cement manufacturing, and other industrial processes.

4. Anthracite:

   • Anthracite is the highest rank of coal and has the highest carbon content and energy density.
   • It has a low moisture content (less than 15%) and a carbon content of over 86%.
   • Anthracite has the highest calorific value among coal types, typically exceeding 35 MJ/kg.
   • It is used primarily for heating purposes, especially in residential and commercial heating systems, as well as in some industrial applications requiring high heat intensity.

In addition to these main ranks, there are also specialty coals such as cannel coal, which has a high oil content and is used for producing oil, and meta-anthracite, which is even higher in carbon content than anthracite.

Coal classification systems may vary by region and application, and additional criteria such as sulfur content, ash content, and volatile matter content may also be used to further classify coal types based on specific requirements.