Dense-phase fluidized beds reactor applications

Dense-phase fluidized beds with bubbles represent the majority of the operating interests although the beds may also be operated without bubbles. The bubbling dense-phase fluidized bed behavior is fluidlike. The analogy between the bubble behavior in gas-solid fluidized beds and that in gas-liquid bubble columns is often applied. Dense-phase fluidized beds generally possess the following characteristics, which promote their use in reactor applications ... 

The initial application of fluidized beds in the petroleum industry was the upflow dilute-phase reactor (M45). The obvious disadvantage of this design is that all of the flowing catalyst passes overhead and must be removed in dust-removal equipment. Later, the basic design which finds widest application is the downflow dense-bed reactor (M2), which has the following major advantages (K26) ... 

We consider here an application to a fluidized bed catalytic chemical reactor whose performance is affected by coalescence between gas bubbles. The problem has been considered in detail by Sweet et al (1987) (based on the earlier work of Shah et al, 1977, which addressed the bubbling process without chemical reaction) and we shall discuss here the formulation aspects of the model. The process of interest consists in blowing a gas containing a reactant A through a bed of catalyst particles at a velocity in excess of the minimum fluidization velocity. The excess gas forms bubbles at the bottom of the bed, which ascend by virtue of their buoyancy up the bed of a dense phase of catalyst particles, and eventually escape from the top surface. The catalyst particles in the dense phase are in vigorous circulatory motion through the bed. The reactant in the gas bubbles has inadequate contact with the catalyst particles so that no reaction takes place. However, the gas in the dense phase does undergo reaction to products. 

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