Steam-drying of coal. Part 1. Modeling the behavior of a single particle

Steam-drying of coal is an attractive technology that offers, besides reduction of fire and explosion hazards, improved thermal efficiency. In addition, steam-dried coals appear to be less prone to spontaneous combustion. In this paper, a single-particle model has been developed to simulate the drying of granular media in superheated steam. The calculations from the model are compared with experimental data reported in the literature on the steam-drying of ceramic spheres and water droplets. The validated model is then used to investigate, parametrically, the effects of system variables on the drying behavior of coal in steam. The model can be extended with ease to compare results for steam-drying with those for drying of coal in humidified air (or any other inert gas medium). Calculations are presented to illustrate the effects of thermo-physical properties and operating variables on the inversion point temperature; above this temperature, the vaporization rate in steam is greater than that in air. This single-particle model is the first step in the development of a mathematical model, described in an accompanying paper, for the simulation of the operation of a large-scale fluidized bed dryer.