Evaluation of Drying Rates of Lignite Particles in Superheated Steam Using Single-Particle Model

Abstract

Drying rates of lignite particle groups in superheated steam are evaluated using a single-particle model developed for Australian lignite. Size distributions of the particles are assumed to obey the Rosin–Rammler equation with the maximum particle diameters defined as 100, 50, and 6 mm. The results show the drying rate of a lignite group depends strongly on the maximum particle size, and removal of large particles prior to drying is shown to be effective to reduce the drying time. The calculation model is available for simulations of drying behaviors of lignite in various dryers when an appropriate heat transfer coefficient is given. This study simulates the drying of particles smaller than 6 mm using a heat transfer coefficient in a fluidized bed dryer reported elsewhere. The required drying time estimated from the calculation is comparable to the processing time reported in an actual fluidized bed dryer, supporting the validity of the calculation model.