(503d) Four Ways to Introduce Structure in Fluidized Bed Reactors

Fluidized-bed reactors couple short intraparticle diffusion lengths and good heat transfer, but suffer from backmixing, catalyst attrition, and scale-up problems. The aim of our research is control by rational reactor design and operation: A higher efficiency is achieved by replacing the classical reaction environment of particles that move in an uncontrolled way by one with an imposed dynamic structure. Structuring reaction environments introduces extra degrees of freedom allowing decoupling of conflicting design objectives, such as high gas flow rate versus small bubble size. In this way, structuring fluidized beds leads to process intensification and more sustainable operation. Structuring can be imposed either (1) via the gas phase or (2) via the particle phase. Moreover, we can modify (a) the geometry or (b) the dynamic behaviour. We will give an example of all four possible combinations.

1.a. By introducing part of the gas via secondary injection (i.e., not via the bottom plate) distributed over the bed, the gas can be optimally dosed to control both hydrodynamics and reactor performance. 1.b. By oscillating the gas flow introduced through the distributor plate of a fluidized bed, regular bubble patterns can be formed and more control over the bubble size and distribution can be obtained. 2.a. By tailoring the particle size distribution, bubble size and distribution can be influenced and mass transfer can be improved. 2.b. By imposing an electric field, particles become polarized and interparticle forces can be introduced. By proper tuning of these forces, bubble size can be significantly reduced.

We will show that these four methods can equip the engineer with practical tools to develop more efficient, better-controlled fluidized-bed processes.