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A mathematical model based on the concept of an improved bubble assemblage model is developed for calculating the conversion of a reaction system involving a volume change in fluidized beds. The influence of volume change on the hydrodynamic behavior of gas in the bed, such as bubble size variation, superficial gas velocity change, and volume fraction occupied by each phase, is also investigated. It is found that increasing stoichiometric coefficient values results in larger bubble size, higher superficial gas velocities, higher crossflow rate between emulsion phase and bubble phase, and greater volume fraction of bubble phase, but smaller volume fraction occupied by the emulsion phase as well as lower conversions.

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Superficial bubble-phase gas velocity ( u b s ) is an important parameter in the fluidized-bed reactor design, since it influences many other parameters such as volume fractions of each phase and the superficial gas velocities for other phases. The earliest popular postulate of computing u b s , which is known as the two-phase theory of fluidization (Toomey and Johnstone, 1952), suggested that the gas flow rate in the bubble phase is equal to the excess gas flow above what is required for minimum fluidization: u b s = u-Urn? This method presents