Turbulent-bed reactor

The distinction between bubbling-bed and turbulent-bed reactors is not always clear. Flence, the classification of reactions under these categories is uncertain. 

Turbulent bed reactor East fluidized-bed reactor Transport (or pneumatic) reactor Circulation systems Deactivation control... 

Increasing gas velocity or gas throughput in a reactor eventually leads to a high production rate with transition of flow regimes to turbulent or riser fluidization. Some designs and modifications have been implemented on bubbling bed reactors to operate as turbulent bed reactors ... 

Fig. 24. Elements of a bubbleless turbulent fluid-bed reactor design where the internals create four stages. A represents the shrouded grid B, the first feed ...

The MTO process employs a turbulent fluid-bed reactor system and typical conversions exceed 99.9%. The coked catalyst is continuously withdrawn from the reactor and burned in a regenerator. Coke yield and catalyst circulation are an order of magnitude lower than in fluid catalytic cracking (FCC). The MTO process was first scaled up in a 0.64 m /d (4 bbl/d) pilot plant and a successfiil 15.9 m /d (100 bbl/d) demonstration plant was operated in Germany with U.S. and German government support. 

In comparison, units that are designed with turbulent beds have a lower superficial velocity limit because of soflds entrainment and are unable to independently control the entrained soflds recycle. The soflds loading in the turbulent-bed regenerator configuration are equal to the reactor—regenerator circulation plus the entrained soflds via the cyclone diplegs. 

The models of Chapter 9 contain at least one empirical parameter. This parameter is used to account for complex flow fields that are not deterministic, time-invariant, and calculable. We are specifically concerned with packed-bed reactors, turbulent-flow reactors, and static mixers (also known as motionless mixers). We begin with packed-bed reactors because they are ubiquitous within the petrochemical industry and because their mathematical treatment closely parallels that of the laminar flow reactors in Chapter 8. 

The presence of two phases in the reaction mixture may seem to be a mass-transfer engineering problem, but even moderate stirring of the mixture produces an emulsion, which greatly facilitates the phase transfer steps of the reaction mechanism. In our fixed-bed reactor, the turbulence resulting from the flow rates used seemed to suffice to eliminate external mass transfer hmitations. At MeOH SA of 20 and identical LHSV values, similar acid conversions were observed for two linear flow velocities differing by a factor of two. 

In Chapter 11, we indicated that deviations from plug flow behavior could be quantified in terms of a dispersion parameter that lumped together the effects of molecular diffusion and eddy dif-fusivity. A similar dispersion parameter is usefl to characterize transport in the radial direction, and these two parameters can be used to describe radial and axial transport of matter in packed bed reactors. In packed beds, the dispersion results not only from ordinary molecular diffusion and the turbulence that exists in the absence of packing, but also from lateral deflections and mixing arising from the presence of the catalyst pellets. These effects are the dominant contributors to radial transport at the Reynolds numbers normally employed in commercial reactors. 

Bubble diameter, in foams, 12 2 Bubble-free oxygenation, 15 716 Bubble growth, 11 806 Bubbleless turbulent fluid-bed reactor design, 11 821... 

During recent years experimental work continued actively upon the macroscopic aspects of thermal transfer. Much work has been done with fluidized beds. Jakob (D5, J2) made some progress in an attempt to correlate the thermal transport to fluidized beds with transfer to plane surfaces. This contribution supplements work by Bartholomew (B3) and Wamsley (Wl) upon fluidized beds and by Schuler (S10) upon transport in fixed-bed reactors. The influence of thermal convection upon laminar boundary layers and their transition to turbulent boundary layers was considered by Merk and Prins (M5). Monaghan (M7) made available a useful approach to the estimation of thermal transport associated with the supersonic flow of a compressible fluid. Monaghan s approximation of Crocco s more general solution (C9) of the momentum and thermal transport in laminar compressible boundary flow permits a rather satisfactory evaluation of the transport from supersonic compressible flow without the need for a detailed iterative solution of the boundary transport for each specific situation. None of these references bears directly on the problem of turbulence in thermal transport and for that reason they have not been treated in detail. 

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