This chapter is a systematic summary of the characteristics and applications of spouted beds, called powder–particle spouted beds (PPSBs), consisting of fine powders contacted with coarse particles. The main aspect of conventional spouting that is relevant to PPSBs is the final elutriation of the dried or partially dried fines, often produced by attrition, from a coarse particle bed.

Figure 10.1 shows the operating conditions of several kinds of fluidization for particles of density 2500 kg/m, according to Geldart's classification, indicating also the fine particle size and gas velocity ranges in four reported studies of PPSBs. The two solid lines show the superficial gas velocity at minimum fluidization (Umf) and the terminal velocity of a single particle (Ut). In a PPSB, as one of the operating conditions, the gas velocity is determined by the diameter and density of the coarse particles and is usually greater than Ut of the fine powders, so the fines are elutriated from the coarse particle bed.

Description of powder–particle spouted beds

Conceptual illustrations of a PPSB are shown in Figure 10.2. Group D particles in Geldart's classification usually act as the coarse particles and Group A, B, or C particles as the fine powders. As shown in Figure 10.2a, for a Group C–D particle system, the coarse particles in the bed are first spouted and raw powders (fine particles) in a dry or partially dried state are then continuously fed to the bottom of the spouted bed with spouting gas.