0 to 8 mm coal is a mixture of fine powder, granules, and small chunks. Coal with a size of 8 to 25 mm is burned more slowly and more heat is released. Due to its larger size 25 to 50 mm coal has a slower burning rate compared to smaller coal. This big size 25 to 50 mm coal often has a higher calorific value, leading to more efficient energy production.0 to 50 mm coal divided in sizes ranging from fine powder to 50 mm chank. this coal size is available in 5400 gcv and 3200 gcv at our company.