Sieve holes bubbling

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. 

Vapor bubbles up through the sieve holes, or valve caps, on the tray deck, where the vapor comes into intimate contact with the liquid. More precisely, the fluid on the tray is a froth or foam—that is, a mix-... 

Fig. 3.1. Also note that this nonconventional design has the downcomer outlet area as additional active tray area. This additional active area is the tray deck area under the downcomer having valves, bubble caps, or sieve holes that allow the gas to pass through under the liquid downcomer area of the next tray up. ICPD tray programs dealing with the design and rating of sieve, bubble cap, and valve-type trays allow this active area input. This is an option shown in Table 3.1, which is offered in the three tray design/rating computer programs given in this book.

PRESSURE DROP THROUGH THE CONTACTOR ASSEMBLY. Causes for pressure drop through the contactor assembly are shown in Fig. 16-10 for bubble caps as (1) contraction, (2) friction in riser, (3) reversal of flow direction, and (4) friction in annular space. Similarly, Fig. 16-11 shows for sieve trays that this cause for pressure drop is (1) contraction and (2) friction in the sieve hole. The total pressure drop due to the preceding causes is primarily a function of the kinetic head. The pressure drop as feet of liquid equivalent to one kinetic head is... 

PRESSURE DROP DUE TO LIQUID HEAD ABOVE SLOTS, SIEVE HOLES, OR VALVE OPENINGS. Reference to Fig. 16-10 shows that the total head above bubble-cap slots for an average cap is the sum of static submergence Sm, height of liquid crest above weir ha, and average liquid gradient 0.5hg. The same... 

Vc = linear velocity of gas in riser, reversal area, or annulus of bubble cap (maximum value) or in sieve hole, ft/s = maximum allowable superficial linear velocity of gas (based on net cross-sectional area of tower for vapor flow), ft/s, see Eq. (3)... 

The mass-transfer devices may be sieves (holes), fixed valves, moveable valves, or bubble caps. Fig. 2 shows a selection of mass-transfer devices. The purpose of the device is intimate mixing of the vapor and liquid on the tray deck. An ideal device has high capacity, high flexibility, low leakage, low pressure drop, and low cost. 

This parameter may either be calculated from the droplet diameter or from empirical correlations. Since the droplet diameter can be of many sizes and is usually unknown, C is estimated from correlations based on experimental data. In one such method by Fair (1961), developed specifically for sieve and bubble cap trays, C is correlated as a function of liquid and vapor flow rates and densities, tray spacing, surface tension, foaming properties, and the ratio of the combined hole area in the tray to its active area. In this correlation, is based on the column cross-sectional area available for vapor flow, A -A, where A is the total tray area (or total inside column cross-sectional area) and A is the downcomer cross-sectional area. The parameter C is given as... 

The deentraining device of Fig. 5.7-11 may not be needed if the "contaminated overhead vapor meets distillate specifications. Entrainment data for sieve and bubble-cap trays have been correlated by Fair and coworkers 10 as shown in Fig. 5.7-12. The sieve tray data are for trays with small (less than 7 mm) diameter. Visual dsla of FRI. released as a movie.11 show that uuder distillation conditions 3 mm holes enlmin sigaificantly less than 12.7 mm boles, with hole areas and gross vapor rales being equal,... 

A Pg is the pressure drop which results from the formation of bubbles by the gas. This essentially depends on the surface tension (7 of the liquid and is (for slow bubble growth on a sieve tray, with a sieve hole diameter dj)... 

By repeating this process in successive stages, the deuterium oxide is increased to a concentration of 15%. The ten extraction towers of the plant contain sieve trays. Water flows downward across each tray in successirai. H2S gas is forced upward, bubbling through the sieve holes for contact with the water. This is shown in Fig. 7.9. 

Liquid passes down a slot and spills onto a sieve plate. Vapor bubbles through holes in the sieve plate and creates a froth, which increases the amount of liquid-vapor interface. The amount of frothing can be increased by adding bubble caps to the sieve holes, shown in Figure 5.27. Bubble caps also decrease leakage of preequilibrated... 

Vapor bubbles up through the sieve holes, or valve caps, on the tray deck, where the vapor comes into intimate contact with the liquid. More precisely, the fluid on the tray is a froth or foam—that is, a mixture of vapor and liquid. In this sense, the function of a tray is to mix the vapor and liquid together to form a foam. This foam should separate back into a vapor and a liquid in the downcomer. If the foam caiuiot drain quickly from a downcomer onto the tray below, then the foamy liquid or froth will back up onto the tray above. This is caWed flooding. 

Fig. 4.25 Formation of vapor bubbles from sieve holes in different zones...

The open area for these plates ranges from 15 to 30 percent of the total cross section compared with 5 to 15 percent for sieve plates and 8 to 15 percent for bubble-cap plates. Hole sizes range from 6 to 25 mm (1/4 to 1 in), and slot widths from 6 to 12 mm (14 to V2 in). The Turbogrid and Ripple plates are proprietary devices. 

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. 

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