Fluidized Bed Reactors

Abstract

The name “fluidized bed reactors” (FBR) is a generic term and encompasses a variety of engineering systems including chemical reactors, combustors, gasifiers, calcifiers, driers, etc. The common characteristic of the FBR class of engineering systems is the presence of the solid particles that are carried by the fluid and exist in a fluidized state. The carrier fluid effectively lifts the solid particles and carries them to different parts of the FBR, where the fluid velocity is lower, e.g., close to the walls of the FBR. There, the fluid drag is insufficient to keep the particles suspended, and as a consequence, the particles fall to parts of the system where the fluid velocity is high enough to lift them again. This circular particle motion enhances any flow instabilities, such as vortices and turbulence, and results in very high levels of mixing for both the particles and the carrier fluid. Fluid–particle interactions in FBRs typically include momentum exchange, mass exchange (reactions), and energy/heat exchange. The presence and movement of the solid particles in a fluidized state adds to the flow agitation within the FBR and, thus, enhances all fluid–particle interactions as well as the mass, energy, and momentum exchanges. This chapter starts with a short description of the types of FBRs, their parts, and the types of air distributors. The heat and mass transfer processes in FBRs are examined in detail, including the effects of particle sizes and fluidization velocities. A large part of this chapter gives useful details on the flow and heat/mass transfer processes in several industrial types of FBRs, such as catalytic cracking and catalytic synthesis, thermal cracking, coking, combustion and gasification, and other chemical and nonchemical processes. The final part of the chapter includes a short description of the MFIX code, an open-source code, which is currently being developed by the U.S. Department of Energy with the collaboration of several universities and industrial corporations.