Distributor zone

I would like to spend a few minutes over this detail because it leads to a simple and satisfying model for chemical reaction in the distributor zone. When an insoluble gas enters a liquid... 

Sit SP, Grace JR. Hydrodynamics and mass transfer in the distributor zone of fluidized beds. Proc Second World Cong Chem Eng, Montreal, Canada, 1981, pp 81-84. 

Model discrimination was done comparing simulated and 41 experimental data sets. The measure of model accuracy was defined as the sum of squares of relative errors of prediction for Sc2+ and XcH4- The bubble assemblage model assuming plug flow (PF) in the horizontally distributor zone (BAM+PF) was best (for details see [49]). A comparison between results of simulations obtained with the BAM + PF model and experimental data is shown in Figures 25 and 26. C2+ selectivity is very well predicted the conversion of methane is also predicted quite well, however, a tendency to underestimate the conversion was observed. The standard deviations for the prediction of Sc2+ and Xch4 amount to 7 and 8 % respectively. It should be emphasized that the simulations were done without any tuned parameters. 

A generic multipurpose fluidized bed is illustrated in Figure 2 (1). The soHds are contained in a vessel and gas is introduced into the system via a distributor, which is typically a drilled plate at the bottom of the vessel. A plenum chamber is provided below the distributor plate. The height of the soHds level above the distributor is called the bed height, and the vertical space above the bed height is called the freeboard. A splash zone may exist as a transition between the bed and freeboard. Cyclones, located either in the freeboard or external to the vessel, are used to remove soHds from the gas stream. Diplegs can return entrained soHds directly to the bed. 

Fig. 5. Diagram of large Lurgi Spblgas carbonization plant A, coal conveyor B, movable distributor C, coal bunker D, drying zone E, connecting shafts ...

Special attention has to be given to the end compartments of an extraction column, since the phase inlet and outlet points are usually located at different points of the column and are complicated by the presence of phase distributors and at one end by the coalescence zone for the dispersed phase droplets. 

Figure 14-67c shows results of tests in which flows from individual distributor drip points were varied in a gaussian pattern (maxi-mum/mean = 2). When the pattern was randomly assigned, there was no efficiency loss. When the variations above the mean were assigned to a "high zone, and those below the mean to a "low zone, HETP rose by about 20 percent. With structured packing, both random and zonal maldistribution caused about the same loss of efficiency at the same degree of maldistribution. 

Many studies on the flow distribution in random packed beds have been reported in the literature. Mercandelli et al. [8] published a short review of the flow distribution work in random packed trickle bed, which includes the list of various techniques used to determine and quantify the flow distribution. Conventional methods include, for example, collecting liquid at the bottom of the column from different zones while advanced methods include tomographic techniques. Mercandelli et al. [8] used several techniques to quantify liquid distribution in columns of diameters up to 30 cm with three different distributor designs. They used global pressure drop measurements, global residence time distribution (RTD) of the liquid, local heat transfer probes, capacitance tomography and a collector at the bottom of the column. 

At first, the distillation still was charged with methanol—the low-boiling reactant—and heated under total reflux until steady-state conditions were achieved. At that moment, acetic acid—the high-boiling reactant—was fed above the reaction zone to the second distributor. After 30 min the reflux ratio was changed from infinity to 2 and the product withdrawal at the top of the column began. During the... 

The highly agitated condition of the coarse particles serves to disperse the fluidizing medium as it enters the upper zone for the finer solids, thus performing the function of a normal gas distributor ... 

The minimal fluid rate for the existence of the hyperfluidized bed is reached when the fluidized zone has shrunken to zero height, that is, when L reaches the fluid distributor at l0. Under this condition, all solids inventory resides in the fixed bed, and the upper bed level coincides with that for the solids added. 

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