Distributor design

Good gas distribution is necessary for the bed to operate properly, and this requites that the pressure drop over the distributor be sufficient to prevent maldistribution arising from pressure fluctuations in the bed. Because gas issues from the distributor at a high velocity, care must also be taken to minimize particle attrition. Many distributor designs are used in fluidized beds. The most common ones are perforated plates, plates with caps, and pipe distributors. 

Additional definition of the operative mechanisms can obviate the need for the larger unit. It maybe possible to assess limitations in a smaller unit that has only a few injection points on the distributor. The unit could be used to evaluate distributor designs that permit a wide range of acceptable operating conditions. However, if the acceptable range proves smaller than desired, the larger pilot unit would then be needed to estabUsh acceptable performance. 

Dispersed-phase distributor design Which liqmd is dispersed... 

An example of a distributor design is shown in Figure 10. Hole density is low at the top of the pipe and is increased lower on the pipe. The maximum open area density of about 10% assures reasonable bubble formation in this design. The average veloeity out of the top row of holes starts at about 40 m/s and increases as the pressure rises and total flow increases. Total areas of holes plus bottom slot should be equal to at least two times the cross sectional area of the inlet pipe. 

Fnr stripping service, as in a glycol or amine contactor (see Chapt 7 a bubble cap trays are the most common. In recent years, there has b growing movement toward crimped sheet structured packing. Improved vapor and liquid distributor design in conjunction with struc-... 

The summary of HETP values of Vital [142] for various types and sizes of packings are believed to be referenced to typical industrial distributors for the liquid. This variation can influence the value of HETP in any tabulation the effect of distributor design is discussed in an earlier section of this chapter. Porter and Jenkins [143] developed a model to improve the earlier models of Bolles and Fair from about 25% deviation to about a 95% confidence using a 20% factor of safety [139]. 

Moore, F. D., Distributor Design and the Effects on Tower Performance, Norton Chemical Process Products Corp. (1984). 

Two types of air distributors have been used in the past. In some of the original side-by-side units, both the air and the catalyst fltnvcd through the distributor. In virtually all the air distributors designed today, only air flows through the distributor. 

Bauer et al. (1981) measured the influence of bed diameter on the catalytic decomposition of ozone. Figure 6 shows the decrease of the conversion with bed diameter for Bauer s data. This figure also shows the influence of distributor design on conversion. In many small scale experiments, a porous plate is used which will give better performance than the distributors used in large shallow bed commercial designs. 

Figure 8. Distributor design suggested by Werther and Xi (1993) to separate the jet attrition and bubble-induced attrition.

Figure 20. Schematic drawing of the attrition-minimizing distributor design suggested by Parker and Gwyn (1976, 1977).

Of prime importance is the initial distribution of solids at the top of the apparatus. Figure 14 shows the bullet-head solids distributor designed for this purpose. Solids fed from a nearly point source falls on a bullet-shaped target from which they bounce off to land at some distance below, on a fall-breaker baffle which either straightens the particles into essentially vertical paths or simply redistributes them. 

Reactor geometry and distributor design Growth rate... 

Many factors affect gas holdup in three-phase fluidized systems, including bead size and density, liquid physical properties, temperature, sparger type, and fluid superficial velocities (Bly and Worden, 1990). System parameters such as reactor and gas distributor design can have... 

Distributed feedback (DFB) lasers, 22 177 Distributed fiber sensors, 11 152-153 Distribution function, 26 1020 Distributor design, in fluidized beds, 11 810 Distributor grid shroud, 11 813 Distributor jets, 11 812-813 Distributors... 

In all cases the underlying rationale for these hydrodynamic models rests on the observation that beds with identical solids and gas flow rates may develop either large bubbles or small bubbles depending on bed diameter, distributor design, baffle arrangement, etc. thus, bubble size must enter as the primary parameter in the model. A consequence of this argument is that models which do not allow for different bubble sizes at given imposed bed conditions certainly cannot be adequate. 

Bed moisture content Solution type and feed rate Bed temperature Fluidization velocity Aspect ratio Nozzle position and atomization Velocity Air distributor design Jet grinding... 

Suppose that a perforated-pipe distributor made from n on will be used for a feed rate of 428 L/li. The distributor has a length of 1.8 cm (8.5% of the diameter of the bed, D = 21 cm), and length shortly less than the diameter of the bed (20.9 cm). According to the calculations, for the specific feed rate, the distributor will have four round openings with a diameter of 6.6 mm each. The distance between the openings as well as the distance between the terminal openings and the ends of the distributor is 36 mm. However, these calculations can be repeated for various feed rates to choose the optimum distributor design. 

This result indicates the need for an efficient distributor design for this trickle-bed operation at low flow rates (GL< 12). 

From the hydraulics perspective, if scale-up is based on the same superficial velocity, Peh will be higher in a large bed in downflow operation due to the higher bed height, whereas the liquid holdup will be low due to the low velocity, which is frequently used in laboratory beds. This leads to problems and special efforts are required to improve the liquid holdup, for example, a special distributor design. These problems are absent in upflow operation. 

Nozzle position and atomization air velocity Distributor design Jet grinding... 

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