Solid fuels are used as a source of energy in various industries such as iron and steel. A few solid fuels are petcoke, anthracite, metallurgical coke, coal, and flexicoke. Coal is the largest source of energy. It is burnt to generate electricity and used for other industrial purposes such as refining metals. Coke is another coal-based fuel that has high carbon content with few impurities. It is formed from the destructive distillation of low-ash, low-sulphur bituminous coal. Cokes made from coal are grey, hard, and porous. Petcoke is a coke type derived from oil refineries or other cracking processes. It has two forms that can be used for different purposes. Green petcoke is used as fuel, and calcinated petcoke is used as feedstock in coatings, paints, and coloring products. Metallurgical coal or metcoke is a grade of coal that is generally used to produce good-quality coke. It is used to reduce iron ore and other bearing materials. It is widely used in steel-making processes. Anthracite, a metamorphosed type of coal, contains a high carbon content that gives smokeless flames when burnt. It is considered environment-friendly coal.