WATER-ADSORPTION AND DESORPTION BY GOALS AND CHARS

An investigation was carried out on the adsorption and desorption of m oisture in chars of low-rank coal. Equilibrium moisture sorptions of d ry and moist chars were measured at room temperature and at a relative humidity of 30% and 80%. On the basis of these measurements, a simple mathematical model was developed to predict both the rate and the lev el of hydration for coals and chars. The formulation uses a shrinking core model which required only the measurement of the adsorbing materi al's equilibrium moisture content at different temperatures and humidi ties. The model was validated against experimental and literature data . It accurately and reliably predicted both the rate and extent of hyd ration and dehydration for coals and char. Using this model, the effec ts of varying temperatures, relative humidities, and size of the parti cles and coal pile were simulated. The sensitivity study demonstrated that, as expected, relative humidity and temperature had strong effect s on both the rate of hydration and the equilibrium moisture of coal o r char. The particle size dramatically influenced the rate of hydratio n but had no affect on the equilibrium moisture content. This model ca n be used effectively to simulate the impact of moisture on drying, st orage, and spontaneous combustion of coals and coal-derived chars.