Tetsuya Sawatsubashi

Drying of wet brown coal particles by a steam-fluidized bed dryer

ABSTRACT Although the world has abundant resources of brown coal, its moisture content is often high. Thus, a fluidized bed drying system using superheated steam for fluidizing gas has been developed as large-capacity and low-energy-consumption drying technology. Since brown coal particles have wide particle size distribution and cohesiveness due to high moisture content, it is important to know their fluidization characteristics as well as handling characteristics in storage and transportation facilities. However, their drying characteristics are complicated because brown coal contains water in various forms, namely, free water on a surface, bound water in small pores, and non-freezable water chemically bound to hydrophilic functional groups. In this work, basic experiments were carried out to evaluate drying characteristics of brown coal particles. Drying rate, critical, and equilibrium moisture content were formulated and their relevance to the forms of water was discussed. Also the influence of moisture content on flow properties of pulverized coal was evaluated in relation with forms of water.