Sieve plate design areas

The fraction of plate area occupied by disengaging and distributing zones ranges from 5 to 20 percent of the cross section. For most sieve-plate designs, these zones are eliminated completely. 

Liquid-phase back mixing is a serious issue for reactions that have nonzero-order kinetics with respect to the liquid-phase reactant. Sectionalization of bubble column using sieve plates of relatively low free area is an attractive choice in such a case. Although this choice has been mentioned in the literature, its application in solid-catalyzed reactions has not attracted any attention. The sieve plate design must be such that it prevents weeping (Prince 1960). The free area in such sieve plates is... 

Figure 14-25 or Eq. (14-92) may be used for sieve plates, valve plates, or bubble-cap plates. The value of the flooding vapor velocity must be considered as approximate, and prudent designs call for approaches to flooding of 75 to 85 percent. The value of the capacity parameter (ordinate term in Fig. 14-25) may be used to calculate the maximum allowable vapor velocity through the net area of the plate ... 

Reference A3 (Figure 11.28) details the recommended plate configuration for liquid flowrate versus column internal diameter. A reverse flow-type sieve plate is suggested as shown in Figure 9.3. The pitch of the sieve-tray holes is selected so that the total hole area is reduced to 0.07 times the total column area. The other design criteria employed to provide the provisional plate specification are detailed in Table G,3. 

The reciprocating motion of the sieve plate generates vortices in the biosuspension. Each vortex region represents the elementary volume of the bioreactor. When the gas dispersion element moves upwards, the biosuspension is forced to pass through the holes of the sieve plates From each hole, a jet of biosuspension flows downward into the space between two sieve plates. The jet reverses direction as the element reverses direction. Very effective dispersive action is due to the periodic generation of bubbles, which renews the larger interfacial area on each reversal of direction. The important design characteristics of this reactor are summarized in Table XXV. 

For sieve trays, the number of kinetic heads equivalent to the total pressure drop through the plate itself is a function of the ratio of the sieve-hole diameter to the tray thickness and the ratio of the hole area per tray to the active area per tray as shown in Fig. 16-5. This pressure drop for a reasonable sieve-tray design is generally in the range of 1 to 3 kinetic heads, and Fig. 16-12 can be used to choose the most reasonable number to use in preliminary designs Designating the number of kinetic heads obtained from Fig. 16-12 as K.H., the pressure drop due to gas flow through the holes for a sieve tray expressed as liquid head is... 

Since the behavior of packed columns [2,3,4, 5] and bubble cap columns [6] has been previously reported, this research at the National Bureau of Standards was primarily concerned with the characteristics of perforated or sieve plate columns. Such parameters as plate spacing, plate geometry, maximum allowable vapor velocity, weir height and downcomer area were investigated, and the results of these investigations were applied to the design of a pilot plant column. 

Recall that when we designed distillation columns with the graphical McCabe-Thiele method, we specified the relative flow rates of liquid and vapor to obtain the operating lines. What diameter of column is needed to accommodate the absolute flow rates If the column is too narrow le., the sieve plate area is too small), the liquid will pass over the sieve plate too quickly and not equilibrate with the vapor. If the colunm is too wide, the liquid will not cover the tray completely and the vapor will blow through without equilibrating. 

Figure 12-7 Aeration factor and froth density for bubble-cap, sieve, and valve plates, u0 = linear vapor velocity through the active area, ft/s pv = vapor density, lb/ft3. [B. D. Smith, Design of Equilibrium Stage Processes, McGraw-Hill Book Company, New York, 1963, by courtesy McGraw-Hill Book Company.]...

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