Coal Cleaning Operations: The Question of Near Gravity Material

Near Gravity Material (NGM) is classically and by BIS defined as the percentage of material occurring within a range of ±0.1 of the relative density at which separation takes place in coal cleaning operations. NGM is said to affect the separation performance of coal cleaning equipment and is believed to be the primary reason or at least an important reason for misplacement between the products. Therefore, coal producers, coal consumers and the technology providers in India are concerned about the effect of NGM on coal cleaning operations. It is true that Indian coal is one of the most difficult to “wash”. The question is, whether this difficulty to “wash” is getting translated or not into a kind of obsession with NGM while keeping other factors apparently out of consideration?