Bubble cap trays design

Bubble Cap Tray Design and Evaluation Example S-36 Bubble Cap Tray Design... 

Bolles, W.L. Optimum bubble-cap tray design. Pet. Process. 1956, February through May. 

Today the main process application for bubble cap trays is in reactive distillation columns or in chemical absorption columns in either case, it may be necessary to control very carefully the residence time of the liquid to complete a reaction step. For example, bubble-cap trays are used for the methyl acetate column described earlier and published by Agreda et al. An abridged version of the Bolles treatment of bubble-cap tray design is given in the fifth edition of Perry s handbook." ... 

Manufacturers of valve trays, such as Koch-Glitsch, Inc., of Wichita, Kansas (Ballast trays and Flexitrays), and Sulzer-Chemtech (formerly Nutter Engineering Co.), of Tulsa, Oklahoma (Float Valve Trays), have prepared proprietary design manuals. Hence, only limited discussion will be given here. As for bubble-cap trays, design methods follow those for sieve trays. The vapor capacity chart (Figure 12.29) covers valve trays, as does the alternate method of Kister and Haas. Information on liquid entrainment is proprietary, but measurements have been made by Fractionation Research, Inc. Because of the vapor flow reversal, one would not expect entrainment from valve trays to be greater than that from sieve trays. Liquid capacity considerations follow exactly those for sieve trays. 

Bolles, W. L., Optimum Bubble-cap Tray Design, Part II, Pet. Processing, March, 1956, p. 82. 

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. 

Fair s empirical correlation for sieve and bubble-cap trays shown in Fig. 14-26 is similar. Note that Fig. 14-26 incorporates a velocity dependence (velocity) above 90 percent of flood for high-density systems. The correlation implicitly considers the tray design factors such as the open area, tray spacing, and hole diameter through the impact of these factors on percent of flood. 

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. 

Fnr stripping service, as in a glycol or amine contactor (see Chapt 7 a bubble cap trays are the most common. In recent years, there has b growing movement toward crimped sheet structured packing. Improved vapor and liquid distributor design in conjunction with struc-... 

In Table 8-2 Proctor [178] compares efficiencies of sieve and bubble cap trays (plates). He concludes that the sieve design provides a 15% improvement in plate efficiencies. To fully evaluate the actual efficiencies in any particular system, the physical properties, mechanical details of the trays, and flow rates must be considered. See Reference 2 also. 

Capacity Quite similar to sieve tray, as high or higher than bubble cap tray from 50% up to 100% design rate (varies with system and design criteria). Performance at specification quality falls off at lower rates. 

In addition nearly all of the major tray manufacturers can and do design bubble cap trays as well as the other t)pes on request for comparison with competitive types of trays. 

The work of Simkin, Strand, and Olney [64] correlates most of the work of other investigators, and can be used for estimation of probable entrainment from bubble cap trays as shown in Figure 8-116. It is recommended that the liquid entrainment for design be limited to 0.10 mols/mol dry vapor. 

In some sieves the capacity is 1.5 to as much as 3 times that of a bubble cap tray provided careful consideration has been given to all design features. 

Experimental flooding and entrainment data for sieve trays are not plentiful, and measurements are not precise. Accordingly, it has been necessary to relate correlations of flooding and entrainment to those of the well-knowm device, the bubble-cap tray. It appears that the two devices have about the same flooding limits, so long as usual design practice is followed. However, the sieve tray shows entrainment advantages, especially when used in vticuum and atmospheric service. 

Trays are usually designed with F-factor from 0.25 to 2.0 for a turndown of 8 1. Pressure drop per theoretical stage falls between 3 and 8 mm Hg. Note that bubble cap trays are on the high side and sieve trays are on the lower end of the range. Varying tray spacing and system efficiency, the HETP for trays are usually between 24 in. and 48 in. [133]. The C-factor is the familiar Souders and Brown capacity equation. 

The column is designed as an ammonia rectifier-stripper using fundamental design techniques. A 48-in. diameter column will handle at least 500 tons of refrigeration system load for the above temperature range, using 10 bubble cap trays with 32, 4-in. pressed steel caps per tray (slot area = 7.81 in. /cap riser area 4.83 in. /cap 3 ft 0 in. weir length). Tray... 

Bolles, W. L. (1963) Tray hydraulics bubble-cap trays, in Design of Equilibrium Stage Processes, Smith, B. D. (McGraw-Hill). 

The design of the tray fittings and the downcomers influences the column performance. It is convenient to consider this separately for bubble cap trays and sieve trays. In design,... 

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