Calculation of fluidized bed reactors

Fluidized beds have a number of hydrodynamic and phase-contacting characteristics that make them potentially attractive as sites for gas-solid or heterogeneous catalytic reactions.

Recognized advantages include the ability to operate in either open or closed systems, to handle high solids throughputs, to benefit from excellent solids mixing and, consequently, to have good radial and axial isothermicity and temperature control. Furthermore, the physical characteristics of the catalysts, which have an average size of between 50 and 100 µm and a high specific surface area, remain compatible with acceptable fluidization and contacting conditions. Although the first industrial application of fluidization to a chemical reaction dates back to 1926, with the gasification of coal, it was in 1940, after the launch of the first catalytic cracking reactors, that this technique really took off. There are numerous technical variants to take account of the specific characteristics of a reaction and the constraints of the process. All these factors mean that the design, extrapolation and even transformation of units still rely heavily on experience, and are not without risk.

In the literature, various types of models applicable to fluidized bed reactors can be found, which can be used for sizing. We will present the main models and discuss their applicability to different operating conditions.