Ebullating fluid

In the reactor of Figure 8.3, a stable fluidized bed is maintained by recirculation of the mixed fluid through the bed and a draft tube. An external pump sometimes is used instead of the built-in impeller shown. Such units were developed for the liquefaction of coal and are called ebullating beds.. 

EBULLISM. The formation of buhbles. with particular reference to water vapor bubbles in biological fluids caused by reduced ambient pressure the boiling of body fluids. Sec also Ebulliometer. 

The H-Oil reactor (Fig. 21) is rather unique and is called an ebullated bed catalytic reactor. A recycle pump, located either internally or externally, circulates the reactor fluids down through a central downcomer and then upward through a distributor plate and into the ebullated catalyst bed. The reactor is usually well insulated and operated adiabatically. Frequently, the reactor-mixing pattern is defined as backmixed, but this is not strictly true. A better description of the flow pattern is dispersed plug flow with recycle. Thus, the reactor equations for the axial dispersion model are modified appropriately to account for recycle conditions. 

Another type of reactor is the fluidized-bed reactor, in which the powdered catalyst particles are suspended in a stream of up-flowing liquid or gas (Figure 18.9). Another form of this type of reactor is the ebullating-bed reactor (Figure 18.10). The uniform features of these two types of reactor are the efficient mixing of the solid particles (the catalyst) and the fluid (the reactant) that occurs throughout the whole reactor. 

Catalysts for fluidized-bed reactors have to be spherical as well. The appropriate particle size fraction for gas-solid systems can be estimated after Geldart [1] from the density difference between soKd and gas. Most widely used catalysts for fluidized beds and risers are Geldart-type B powders with particle diameters ranging from 40 to 500 pm or solid densities between 1.4 X 10 and 4 x 10 kg/m, respectively. When fluidization is provided by a Kquid as in ebullated-bed reactors, the particle sizes may be substantially larger because of the higher buoyancy in these systems. However, all types of fluidized-bed catalysts must exhibit high mechanical stability because they are exposed to abrasion on reactor walls and internals, collisions between particles and shear forces exerted by the surrounding fluid. 

Ebullated bed processes are offered for license by Axens (IFF) ABB Lummus. In ebullated bed reactors, hydrogen-rich recycle gas bubbles up through a mixture of oil and catalyst particles to provide three-phase turbulent mixing. The reaction envirorunent can be nearly isothermal, which improves product selectivity. At the top of the reactor, catalyst particles are disengaged from the process fluids, which are separated in downstream flash drums. Most of the catalyst goes back to the reactor. Some is withdrawn and replaced with fresh catalyst. 

Vasalos, I.A. et al., "Study of Ebullated Bed Fluid Dynamics for H-Coal". Final Report, U.S. Dept, of Energy under Contract DE-AC05-10149(1980). 

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