Pore, surface and fillet moisture in centrifuged beds of coarse coal

The moisture content of the coarse coking coal product from the centrifuges of preparation plants was investigated to evaluate the contribution of three types of water: that held internally in pores, that in fillets at points of contacts between the particles, and the moisture covering the surface. A standardised laboratory centrifuge test was used to measure the total non-centrifugable moisture (NCM) content and also the quantity held in internal pores, called NCM i. The fillet moisture NCM f was estimated by means of a formulation which relies on experimentally measured holdup volumes, supplemented by a physical model. The surface moisture NCM s could then be derived by difference. The NCM f, which depends on the body force, the particle size and the surface tension and contact angle of the liquid, ranges from effectively zero for large particles to 10% for fines. The surface moisture NCM s is of the order of 0.5% for high rank coals and increases to 1.5% for lower rank coals.