Crossflow plate

Fig. 15. Flow pattern in a crossflow plate distillation column.

Three principal vapor—Hquid contacting devices are used in current crossflow plate design the sieve plate, the valve plate, and the bubble cap plate. These devices provide the needed intimate contacting of vapor and Hquid, requisite to maximizing transfer of mass across the interfacial boundary. 

Multiple IJquid-Path Plates. As the Hquid flow rate increases in large diameter crossflow plates (ca 4 m or larger), the crest heads on the overflow weirs and the hydrauHc gradient of the Hquid flowing across the plate become excessive. To obtain improved overall plate performance, multiple Hquid-flow-path plates maybe used, with multiple downcomers. These designs are illustrated and discussed in detail in the Hterature (49). 

FIG. 14-24 Performance of two crossflow plates operating at 0.13 bar pressure and total reflux. Test mixture etbylbenzene/styrene. Spacing between plates is 0.50 m, and outlet weir height is 38 mm. Ut = superficial vapor velocity, pc = vapor density. [Billet, Comad, and Giuhh, I. Chem. E. Symp. Ser. No. 32, 5, 111 (1969).]... 

FIG. 14-25 Flooding correlation for columns with crossflow plates (sieve, valve, bubble-cap). [Fair, Pet/Chem Eng 33(10), 45 (September 1961),]... 

Example 9 Loading/Flooding of a Distillation Plate An available sieve plate column of 2.5-m diameter is being considered for an etbylben-zene/styrene separation. An evaluation of loading at the top plate will be made. Key dimensions of the single-crossflow plate are ... 

Pressure Drop Methods for estimating fluid-dynamic behavior of crossflow plates are analogous, whether the plates be bubble-cap, sieve, or valve. The total pressure drop across a plate is defined by the general equation (see Fig. 14-29)... 

Ejfects of Gas and Liquid Mixing As noted previously, it is necessary in most instances to convert point efficiency E g to Murphree plate efficiency E, ,. This is true because of incomplete mixing only in small laboratoiy or pilot-plant columns, under special conditions, is the assumption E g = E, , likely to be valid. For a crossflow plate with no hquid mixing there is plug flow of hquid. For this condition of liquid flow, Lewis [Ind. Eng. Chem., 28, 399 (1936)] analyzed effects of gas mixing on efficiency. He considered three cases ... 

Cross-file patent searches, 18 243-244 CrossFire Beilstein, 6 19 Cross-flow filtration, 11 383 15 827, 829 in porous pipes, 11 387-388 with rotating elements, 11 383-387 Cross flow model, 21 706 Cross-flow packed scrubber, 26 687-688 Crossflow plates, 6 762-763 Cross-flow screens, 22 282 Cross-flow velocity, 15 725 Crosshead mandrel, in VDC film extrusion, 25 732-733 Cross-lapping, 17 501 Cross-linkable epoxy thermoplastic system (CET), 10 436... 

Crossflow Plate-Pack Coalescer. This unit is simple in design It has no moving pans and is practically maintenance-free. The flow can be cither parallel or perpendicular to the slope of the plates Because the plates arc inclined and the oil panicles rise vertically, they have to move against the flow of water. It was fell that this might reduce the separation efficiency. Also, the plates are closely spaced and this could cause clogging of the passages. 

Because best results are normally obtained with full crossflow plate operation for a sieve tray, units may be designed with a lift valve over the hole in the plate or over a riser from the plate so that the rising gas lifts this valve to allow the vapors to be passed horizontally into the liquid as is illustrated in Fig. 16-1. This liquid cannot easily flow back down the holes in the plate when the gas flow is low because the valve tends to close with the reduced gas flow. 

The heart of a scrubber column is the slurry-gas contact zone, where gases are intimately combined with the absorbent slurry so that the pollutants can be captured by the reactions given previously. There are a number of possible methods for designing the contacting zone, including sprays, crossflow plates, baffle plates, counterflow plates, and packed columns. These all have the purpose of maximizing the interfacial area between the gas phase and the liquid phase, to allow rapid transport of gases across the surface. ... 

FIGURE 13.15 Chart for estimating the height of froth on a crossflow plate. 

FIG. 14-24 Performance of two crossflow plates operating at 0,13 bar pressure and total Test... 

Figure 8.3.5. Crossflow plate in a distillation column (a) gross flow pattern in a cross-sectional view (b) gross flow pattern in a plan view.

Here we have neglected any dispersion/diffusion in the y-direction for phase 2 in crossflow along the plate length. In most analysis of the crossflow plate/stage/device used for distillation, the liquid is assumed to be well-mixed vertically at any axial z-coordinate location. Therefore when one obtains an overall species i balance equation at any location by combining the above two equations. 

On a large plate, there are two stagnant regions (shown in Figure 8.3.5(b)) where there is no liquid replenishment. Ideally therefore, the crossflow plate in a distillation column may be analyzed via the simultaneous solution of equations (8.3.18) and (8.3.20) coupled via appropriate boundary conditions (Porter et at, 1972). 

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