Coal is

Types of coal

Coal is a combustible black or brownish-black sedimentary rock composed of carbon and formed from the remains of ancient plants. It is classified into several types based on its composition and properties.

• Anthracite Coal:

  This is the highest grade of coal. It has the highest carbon content, around 86% to 97%. It has the highest heating value and the least impurities. It burns cleanest. It has a high luster, almost metallic shine. It is used for residential and commercial space heating and in certain industrial processes.

• Bituminous Coal:

  It is the second highest rank. It has 45% to 86% carbon content. It is the most abundant type, used mainly for electricity generation and steel production (in the form of coke).

• Sub-Bituminous Coal:

  This coal has a lower carbon content than bituminous coal, about 35% to 45%. It has a higher moisture content and lower sulfur content. It is mainly used for electricity generation. It has a lower heating value than bituminous coal.

• Lignite Coal:

  This is the lowest grade of coal. It has the least carbon content, about 25% to 35%. It is often referred to as brown coal. It has a very high moisture content. It is mainly used for generating electricity and for fertilizer production.

• Peat:

  Although not technically coal, peat is the precursor to coal formation. It is an accumulation of partially decayed plant material in waterlogged conditions. It has a high moisture content and is used as a low-grade fuel.

Designs of coal

Although coal is a natural product, it is designed and treated to meet specific requirements. A man-made coal design is called artificial coal. There are many kinds of artificial coals, which can be designed into different shapes according to the needs. Some common designs of coal are as follows:

• Activated coal

  Activated coal is made from coconut shells, wood, and coal. First, high-temperature steam is introduced to activate charcoal. This results in a large number of pores and a huge surface area. The large surface area makes activated coal very effective in adsorbing gases, liquids, and dissolved substances. Therefore, it is widely used in air and water purification, gold extraction, and poison treatment in the medical field.

• Graphitized petroleum coke

  Graphitized petroleum coke is made from petroleum by-products. It is heated to a temperature of 2500-3000 degrees Celsius. At this temperature, the carbon atoms are rearranged into a graphite structure. This structure has a higher electrical conductivity than normal petroleum coke. Therefore, it is used to make batteries and fuel cells.

• Coal briquette

  Coal briquette is made by compressing fine coal dust along with additives. The common additives include lime, starch, and molasses. The process of making coal briquettes involves binding the coal dust under high pressure, followed by shaping it into specific forms. Coal briquettes are used in household stoves, industrial furnaces, and as reducing agents in metallurgy.

• Coal pellets

  Coal pellets are made by mixing fine coal dust with a liquid binding agent and then spraying the mixture in layers on a rotating disc. They are used in fluidized bed combustion systems and gasification reactors.

• Coal tablets

  Coal tablets are made by compressing fine coal dust along with a binder into specific sizes and shapes. They are mainly used as fuel for portable stoves and small-scale power generation.

Scenarios of coal

• Iron Smelting:

  Metallurgical coal is used in making coke, which is a reducing agent to convert iron ore into iron in a blast furnace.

• Cement Production:

  Coal is used as a fuel to heat the kiln to make clinker, the main ingredient of cement.

• Electricity Generation:

  Bituminous and sub-bituminous coals are burned in power plants to generate steam that turns turbines for electricity.

• Coal-to-Liquids (CTL):

  Production of liquid fuels like gasoline and diesel from coal via gasification and synthesis.

• Coal Gasification:

  Conversion of coal into synthesis gas (H2 and CO) for chemicals, fuels, and power using gasifiers.

• Coal Heating:

  Low-grade coals are burned in furnaces for space heating and water heating in homes and buildings.

• Industrial Heating:

  In some industries where other fuels are expensive or unavailable, coal is used to provide process heat.

• Coal Briquettes:

  Coal dust is compacted into briquettes for cooking and heating, especially in rural areas.

• Activated Carbon:

  Coal is processed to make activated carbon for air, water, and gold recovery filtering.

• Carbon Black:

  Coal tar is used to produce carbon black, a pigment and reinforcing agent in rubber products.

• Pharmaceuticals:

  Various coal tar compounds are used as intermediates in making pharmaceutical drugs.

• Pavements and Roofing:

  Coal tar is used to make materials like shingles, sealants, and asphalt for roads and roofs.