Perforated pipe distributor

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

For turbulent flow, with roughly uniform distribution, assuming a constant friction factor, the combined effect of friction and inertial (momentum) pressure recovery is given by 

The factor K would be 1 in the case of full momentum recovery, or 0.5 in the case of negligible viscous losses in the portion of flow which remains in the pipe after the flow divides at a takeoff point (Denn, pp. 126-127). Experimental data (Van der Hegge Zijnen, Appl. Sci. Res., A3, 144-162 [1951-1953] and Bailey,/. Mech. Eng. Sci., 17, 338-347 [1975]), while scattered, show that K is probably close to 0.5 for discharge manifolds. For inertially dominated flows, Ap will be negative. For return manifolds the recovery factor K is close to 1.0, ana the pressure drop between the first hole and the exit is given by 

One means to obtain a desired uniform distribution is to make the average pressure drop across the holes Ap large compared to the pressure variation over the length of pipe Ap. Then, the relative variation in pressure drop across the various holes will be small, and so will be the variation in flow. When the area of an individual hole is small compared to the cross-sectional area of the pipe, hole pressure drop may be expressed in terms of the discharge coefficient C and the velocity across the hole VD as 

Provided C0 is the same for all the holes, the percent maldistribution, defined as the percentage variation in flow between the first and last holes, may be estimated reasonably well for small maldistribution by (Senecal, Ind. Eng. Chem., 49, 993-997 [1957]) 

Perforated-pipe distributors are normally of the ladder type (Fig. 3.4a) or the perforated-ring type (Fig. 3.46). Perforations are located on the underside of the pipes. The ladder type is usually easier to fabricate and therefore less expensive thsui the perforated-ring type. A high performance variation of the Fig. 3.4a distributor is shown in Fig. 3.56. 

Prone to uneven levelness N N N Mainly at low rates Mainly at low rates Y Y 

Approximate range of liquid rates for standard design (305), gpm/ft 1-10 1-10 mie 1-30 1.5-70 1-50 1-10 

The perforated-pipe distributor is best suited where vapor mass velocities are high and where an open area in excess of 70 percent is needed to avoid localized flooding (305). Together with the spray type, the perforated-pipe distributor offers the highest vapor flow area. However, the maximum liquid flow recommended for this type of distributor is relatively low and should not exceed 10 gpm/ft of column area (305) with standard designs. 

Another advantage of the perforated-pipe distributor is its low cost. Its construction is simple, it is easy to support, and it generally consumes less vertical space than most other distributors. Guidelines for selection, design, and operation of perforated-pipe distributors are given below. 

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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.)... 

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.

Feed streams are often introduced by means of a perforated pipe distributor (Fig. 15), which directs the... 

The perforated pipe distributor (Fig. 5.8-5) is capable of providing many pour points aad can be... 

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