Characterization of Fluidization Quality in Fluidized Beds of Wet Particles

Abstract

Monitoring the fluidization quality represents an operating challenge for many processes in which a liquid is sprayed into a gas-fluidized bed, such as fluid coking, fluid catalytic cracking, gas-phase polymerization, agglomeration and drying. Although the presence of liquid will generally have an adverse effect on fluidization, there are often strong incentives in operating with high liquid loadings. For the fluid coking process, for example, operating at lower reactor temperature increases yield and reduces emissions but increases the bed wetness, which may lead to local zones of poor mixing, local defluidization and a reduction in fluidization quality, compromising the reactor performance and stability. The objective of this study is to develop reliable methods to quantify the effects of liquids on fluidized beds.This study examined several methods to evaluate the fluidization quality. Each method was tested in a 3 m tall column, 0.3 m in diameter. Bed wetness was achieved with an atomized spray of various liquids, spanning a wide range of liquid properties.The introduction of liquid in a fluidized bed may result in the formation of wet agglomerates that settle at the bottom of the bed. The liquid may also spread on the particles, increasing their cohesivity and reducing the bed fluidity.Several experimental methods were developed to characterize the effect of liquids on fluidization. Some methods such as the falling ball velocity or the detection of micro-agglomeration from the entrainment of fine particles, are unaffected by agglomerates and detect only the change in bed fluidity. Other methods, such as deaeration or the determination of bubble size from the TDH, are affected by agglomerate formation and changes in bed fluidity.