Pipe Distributor

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. 

Figure 13 shows two pipe distributors, one in a branched and one in a ring configuration. These distributors minimize weeping, have good turndown, may requite the lowest pressure drop, and avoid the need for a plenum chamber. They are also well suited to multiple-level fluid injection. The disadvantages of these distributors are that there are defluidized soHds beneath the distributor and the mechanical design is more complex. 

In pipe distributors, the pressure drop requited for good gas distribution is 30% of the bed pressure drop for upward facing holes, but only 10% for downward facing ones. The pressure drop calculation and the recommended hole density are the same as for a perforated plate. To maintain good gas distribution within the header system, it is recommended the relation... 

Further detailed information on pipe distributors may be found in... 

The perforated pipe distributor comprises a central feed sump and pipes that branch out from the sump to provide the liquid discharge. The level in the sump varies with liquid total flow rate, and the size of the lateral pipes and their perforations must be determined carefully to ensure that the ends of the pipes are not starved for hquid. The orifices are typically 4 to 6 mm diameter, and can be subject to phigging if foreign matter is present. The pipes must be leveled carefully, especially for large diameter columns. 

FIG. 14-74 HETP values for Max-Pak structured packing,. 35 kPa (5 psia), two column diameters. Cyclohexane/n-heptane system, total reflux. For 0.4.3 m (1.4 ft) column perforated pipe distributor, 400 streams/m2, 3.05 m (10 ft) bed height. For 1.2 m (4.0 ft) column tubed drip pan distributor, 100 streams/m ,. 3.7 m (12 ft) bed height. Smaller column data. University of Texas/Austin Larger column data. Fractionation Research, Inc. To convert (ft/s)(lb/ft ) to (m/s)(kg/m ) , multiply by 1.2199. (Couiiesy Jaeger Troducts, Inc., Housion, Texas.)... 

Feintuch [221] pre.sents calculations for a pipe distributor with tray and downcomers to disperse the reflux or feed liquid uniformly across the tray (which should not be counted as a working tray, but a distribtuion device) and... 

With a trough distributor it is often more difficult to obtain uniform distribution next to the tower wall than with a PAN or orifice pipe distributor. Bonilla [131] recommends the rule of thumb Any 10% of the outer surface area of packing in the tower should not receive more or less liquid than the average 10% of the surface area. 

The pipe distributor (often called a sparger) differs from the other two distributor types because it consists of pipes with distribution holes in them that are inserted into the bed. This type of distributor will have solids below it that are not fluidized. If this is not acceptable for a process, then this type of distributor cannot be used. However, the pipe distributor has certain advantages. It does not require a large plenum, the holes in the pipe can be positioned at any angle, and it can be used in cases when multiple gas injections are required in a process. A common type of pipe distributor is the multiple-pipe (manifold sparger) grid shown in Fig. 17-12. 

Design of perforated pipe distributors This type of distributor is perhaps the most suitable, especially for beds of small diameter and of simple design. In Figure 3.42, this type of distributor is presented. 

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. 

Figure 1335. Packed column and internals, (a) Example packed column with a variety of internals [Chen, Chem. Eng. 40, (5 Mar. 1984)]. (b) Packing support and redistributor assembly, (c) Trough-type liquid distributor, (d) Perforated pipe distributor, (e) Rosette redistributor for small towers. (0 Hold-down plate, particularly for low density packing.

Perforated-Pipe Distributors The simple perforated pipe or sparger (Fig. 6-34) is a common type of distributor. As shown, the flow... 

Example 9 Pipe Distributor A 3-in schedule 40 (inside diameter 7.793 cm) pipe is to be used as a distributor for a flow of 0.010 m3/s of water (p = 1,000 kg/m3, (1 = 0.001 Pa s). The pipe is 0.7 m long and is to have 10 holes of uniform diameter and spacing along the length of the pipe. The distributor pipe is submerged. Calculate the required hole size to limit maldistribution to 5 percent, and estimate the pressure drop across the distributor. 

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