Towers bubble cap

Dispersions may be classified into two types, based upon size range of the droplets formed. Turbulence creators (mixing impellers, mixing valves, eductors, orifice plates) will produce fine emulsions of micron-size droplets. Nozzles, perforated plates, bubble caps, tower packings, etc., can form discrete drops of relatively large size which will quickly settle through the continuous phase. 

Gasoline and kerosene rerunning was accomplished primarily in horizontal batch shell stills heated by direct firing or internal steam coils and surmounted by a vertical rectification column with partial condensers to supply reflux. The rectifying column in some installations was packed with iron rings, pipe fittings, earthware crocks, tin cans, or any suitable material readily available. In other units a fairly common type of column was the Heckmann bubble cap tower. 

Extractive Distillation. In extractive distillation a fraction comprising compounds of similar volatility is vaporized and passed countercurrent to a liquid solvent stream in a packed or bubble cap tower. The operating conditions of temperature and pressure are regulated so that one or more of the components of the mixture are dissolved in the entrainer and removed in a liquid phase extract, while the remaining vapor is taken overhead and condensed or discharged as gaseous effluent. 

Cross-sectional view of bubble-cap tower showing effect of excessive liquid gradient. 

Many modifications of the three types of contactors just discussed have been developed in an effort to reduce costs, reduce pressure drop, equalize vapor flow through each contactor, increase plate efficiencies, or, in general, improve the operating performance of the tower. An example of this for modification of bubble-cap towers is the old Uniflux tray originally developed by Socony-Vacuum, which consisted of a series of interlocking S-shaped sections which were assembled in the form of tunnel caps with slot outlets on one side only. Segmental downcomers, similar to the downcomers in conventional bubble-cap columns, were provided. The vapors issued from the Uniflux caps in... 

Cross-sectional view of bubble-cap tower showing flow and nomenclature for pressure-drop calculations. (Units of all symbols are feet of liquid.)... 

Other Types of Wet Scrubbers. Plate towers, like sieve, valve, and bubble cap towers, and packed beds have been used in the past for dust collection but these are all subject to plugging. 

A plant manufacturing dry ice will bum coke in air to produce a flue gas which when cleaned and cooled will contain 15% C02, 6% 02, and 79% N2. The gas will be blown into a bubble-cap tower scrubber at 1.2 atm and 298 K, to be scrubbed countercurrently with a 30 wt% monoethanolamine (C2H ON) aqueous solution entering at 298 K. The scrubbing liquid, which is recycled from a stripper, will contain 0.058 mol C02/mol solution. The gas leaving the scrubber is to contain 2% C02. A liquid-to-gas ratio of 1.2 times the minimum is specified. Assume isothermal operation. At 298 K and 1.2 atm, the equilibrium mole fraction of carbon dioxide over aqueous solutions of monoethanolamine (30 wt%) is given by... 

No. required One Type Bubble cap tower Nomiwd diameter 8 in. 

Figure 10.6-1. Tray contacting devices (a) detail of sieve-tray tower, (b) detail of bubble-cap tower tray.

Figure 13-19. Overall efficiencies for bubble cap towers. (Reproduced with permission from reference 10. Copyright 1946, American Institute of Chemical Engineers.)...

Absorption of nitric oxide takes place in a sieve or bubble-cap tower into which air is added to oxidize the nitric oxide to nitrogen dioxide. The nitrogen dioxide must be absorbed in water to liberate nitric acid and nitric oxide. There are two equilibria, as follows ... 

Nonisothermal Gas Absorption. The computation of nonisothermal gas absorption processes is difficult because of all the interactions involved as described for packed columns. A computer is normally required for the enormous number of plate calculations necessary to estabUsh the correct concentration and temperature profiles through the tower. Suitable algorithms have been developed (46,105) and nonisothermal gas absorption in plate columns has been studied experimentally and the measured profiles compared to the calculated results (47,106). Figure 27 shows a typical Hquid temperature profile observed in an adiabatic bubble plate absorber (107). The close agreement between the calculated and observed profiles was obtained without adjusting parameters. The plate efficiencies required for the calculations were measured independendy on a single exact copy of the bubble cap plates installed in the five-tray absorber. 

The lye boHer is usuaHy steam heated but may be direct-fired. Separation efficiency may be iacreased by adding a tower section with bubble-cap trays. To permit the bicarbonate content of the solution to buHd up, many plants are designed to recirculate the lye over the absorber tower with only 20—25% of the solution flowing over this tower passiag through the boHer. Several absorbers may also be used ia series to iacrease absorptioa efficieacies. 

FIG. 14-79 Cost of trays in plate towers. Price includes tray deck, bubble caps, risers, downcomers, and structural-steel parts. The stainless steel designated is type 410 Peters and Timmerhaus, Plant Design and Economics for Cbemical Engineers, 4th ed., McGraw-Hill, New York, 1.9.91). 

Available in metal only, compared more with tray type performance than other packing materials. About same HETP as Spraypak for available data. Used In towers 24 inches and larger. Shows some performance advantage over bubble cap trays up to 75 psia in fractionation service, but reduced advantages above this pressure or in vacuum service. 

A common type of distillation contacting device used in refinery applications is the sieve tray. In the early 50 s and for many years before, the bubble cap tray was the mainstay of the distillation field. A sieve tray consists of a flat plate with regularly spaced holes, normally 1/2 to 1 inch in diameter. Liquid flows horizontally across the tray and into a channel, called a downcomer, which leads to the tray below. The sieve tray exhibits good capacity, excellent efficiency, low pressure drop, and good flexibility i.e., it will operate quite efficiently at tower loadings which are 1/2 to 1/3 of design values. 

Adsorbers, distillation colunuis, and packed lowers are more complicated vessels and as a result, the potential exists for more serious hazards. These vessels are subject to tlie same potential haz. uds discussed previously in relation to leaks, corrosion, and stress. However, llicse separation columns contain a wide variety of internals or separation devices. Adsorbers or strippers usually contain packing, packing supports, liquid distributors, hold-down plates, and weirs. Depending on tlie physical and chemical properties of the fluids being passed tlirough tlie tower, potential liazards may result if incompatible materials are used for llie internals. Reactivity with llie metals used may cause undesirable reactions, which may lead to elevated temperatures and pressures and, ullinialely, to vessel rupture. Distillation columns may contain internals such as sieve trays, bubble caps, and valve plates, wliicli are also in conlacl with tlie... 

These downcomers are suggested only where liquid flow is relatively small for the required tower diameter, allowing a maximum of space for bubble caps. 

The action on this type of tray seems to produce fewer jets of liquid froth than a bubble cap tray. The entrainment from the surface of the bubbling liquid-froth mixture is less (about K) than a bubble cap tray for the same superficial tower velocity and tray spacing. Generally the trays will flood before capacity reaches a limitation set by entrainment. 

For new towers, the designs will usually develop to utilize the entire tower cross-section. However, for existing towers with perforated trays being installed to replace bubble caps or packing, the optimum active tray area may not utilize the entire cross-section. If the number of holes required is small compared to available area, it is better to group the holes on 2.5 dg to 3.5 do than to exceed these limits. Holes separated by more than 3 in. are not considered effective in tray action so necessary for good efficiency. Blanking strips may be used to cover some holes when more than required have been perforated in the tray. 

Total number of actual trays in tower Number of caps per tray Number of slots per bubble cap Valve density, number of valves per ft or Number of valve units on a valve tray Depth of notches in weir, in or Exponent defined by Equations 8-288 and 327 Dry tray pressure drop for 50% cut baffles, in. liquid per baffle or... 

Maximum allowable mass velocity through column using bubble cap trays, lb/ (hr) (ft tower cross section)... 

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