Deentrainment

Liquid Dispersion Spray columns are used with slurries or when the reaction product is a solid. The absorption of SO9 by a hme slurry is an example. In the treatment of phosphate rock with sulfuric acid, offgases contain HF and SiF4. In a spray column with water, solid particles of fluorosilic acid are formed but do not harm the spray operation. The coefficient /cl in spray columns is about the same as in packed columns, but the spray interfacial area is much lower. Considerable backmixing of the gas also takes place, which helps to make the spray volumetri-caUy inefficient. Deentrainment at the outlet usually is needed. 

Superficial vapor velocity, m/sec Vapor linear velocity based on net area for deentrainment usually tower cross-section minus one dovmcomer, ft/sec... 

Kettle reboilers consist of a bundle of tubes in an oversize shell. Submergence of the tubes is assured by an overflow weir, typically 5-15 cm higher than the topmost tubes. An open tube bundle is preferred, with pitch to diameter ratios in the range of 1.5-2. Temperature in the kettle is substantially uniform. Residence time is high so that kettles are not favored for thermally sensitive materials. The large shell diameters make kettles uneconomic for high pressure operation. Deentraining mesh pads often are incorporated. Tube bundles installed directly in the tower bottom are inexpensive but the amount of surface that can be installed is limited. 

Depth of liquid in the vessel should not exceed 10 ft and the vapor velocity should not exceed that given by the equation, u = 0.06Vpz./pg — 1. A wire mesh deentrainer is not feasible because of encrustation. 

Together with the depth of liquid in the dished head, the total depth will be close to the 10 ft specified as the maximum. From Figure 18.5, a free board of 5.5 ft is adequate in the absence of a deentraining pad. Accordingly, the vessel will have a diameter of 12.5 ft, a straight side of 14.5 ft, and dished heads designed for full vacuum. The sketch is to scale. 

Knockout Drum with Wire Mesh Deentrainer 620... 

Gas velocity in gas/liquid separators, V = k lpjpv — 1 ft/sec, with A = 0.35 with mesh deentrainer, k = 0.1 without mesh deentrainer. 

Centrifugal Force Deentrainment These trays use a contact step similar to that in conventional trays, followed by a separation step that disentrains the tray dispersion by using centrifugal force. Separation of entrained liquid before the next tray allows very high gas velocities, as high as 25 percent above the system limit (see System Limit ), to be achieved. The capacity of these trays can be 40 percent above that of conventional trays. The efficiency of these trays can be 10 to 20 percent less than that of conventional trays due to their typical short flow paths (see Efficiency ). 

The only devices capable of debottlenecking a tray system-limit device are those that introduce a new force that helps disentrain the vapor space. Devices that use centrifugal force (see Centrifugal Force Deentrainment ) are beginning to make inroads into commercial distillation and have achieved capacities as high as 25 percent above the system limit. Even the horizontal vapor push (see "Truncated Downcomers/Forward-Push Trays ) can help settle the entrained drops, but to a much lesser extent. It is unknown whether the horizontal push alone can achieve capacities exceeding the system limit. 

Knockout Drum with Wire Mesh Deentrainer For the flow conditions of Example 18.2, design a drum with a standard efficiency stainless steel wire mesh pad. For this condition, k = 0.35, so that... 

Diaphragm pump, 142, 143 Deentrainment commercial equipment, 619 cyclone dimensions, 620 cyclones, 616,620,621 empty drums, 615,617 wire mesh nads. 615.616.618.620 Densities, hulk, data, 677-679 Desalination, 632 performance, 640 Design basis, 12 questionnaire 13, 14 Detergent manufacture, 35 Dewpoint conditions, 376 calculation, 378... 

Wilson equation, activity coefficients, 374 Wilson-Lobb-Hottel eqiration, 214 application, 219 Winkler process 582 Wire mesh deentrainers, 615 calculation example, 620 disengaging space, 616 kev dimensions, 618 k-values, 615 pressure drop, 616 tvnical installations, 616 Work index, size reduction, 342 Wyssmont dryer, 237,251... 

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