Liquid Vaporization in a Fluidized Bed

Feedstock injection in the riser is a critical step of the fluid catalytic cracking process. However, although a few models have been developed, no experimental study of the vaporization of droplets in a hot fluidized bed has been published. Experimental studies were thus conducted. Agglomeration of wet particles greatly increases the evaporation time. The first step was thus the study of the different agglomeration processes which may occur when liquid droplets are injected into a hot fluidized bed. There are two kinds of agglomeration. Discrete, round agglomerates are formed when droplets are larger than a critical value, which depends on the bed temperature. Large, flat agglomerates are formed when the amount of liquid injected per unit area is larger than a critical value, which is a linear function of the bed temperature. This implies that the height of the bed remains the same when the bed temperature varies. Experiments were then conducted under agglomerate-free conditions in the case of nonpenetrating droplets. In this limiting case, droplets remain within a few millimeters of the bed surface and contact only a restricted number of particles. An estimation of the vaporization time was obtained by deconvolution of the acquisition signal.