Spacing of trays

If the pressure in the vapor space of tray j is Pj, then the pressure in the vapor space of tray j -i-1 may be calculated as... 

Develop complete specifications for the distillation column diameter, spacing of trays, type and size of packing, height of contacting zone, and so on, as reported in the present section. 

A major portion of the reaction is found to occur in the vapor space between trays. A unit in which most of the trays are replaced oy empty space is called a. flash roaster its mode of operation is like that of a spray dryer. 

Lieberman gives two rules of thumb for troubleshooting fractionators that could also be used as checks on a design. First, the pressure drops across a section of trays must not exceed 22% of the space between the tray decks, to avoid incipient flood. Mathematical , hold... 

P = Pressure drop in inches of water SG = Specific gravity of the liquid on the tray at the appropriate temperature T = Number of trays T, = Tray spacing, in. 

For a 15-inch spray height, a tray spacing of at least 21 inches is recommended. 

Downcomer Backup Flood. For downcomer backup. Equation 4 can be used. Reference 15 states that if the downcomer backup for valve trays exceeds 40% of tray spacing for high vapor density systems I3.01bs/ft-), 50% for medium vapor densities, and 60% for vapor densities... 

A tray spacing of 0.41 m may be employed. All columns are assumed to have an overall efficiency of 25%. The fixed cost of the column is obtained by multiplying the equipment cost by a factor of 5 to account for installation, instrumentation and other ancillary devices. 

In a trayed absorber the amine falls from one tray to the one below in the same manner as the liquid in a condensate stabilizer (Chapter 6, Figure 6-4). It flows across the tray and over a weir before flowing into the next downcomer. The gas bubbles up through the liquid and creates a froth that must be separated from the gas before it reaches the underside of the next tray. For preliminary design, a tray spacing of 24 in. and a minimum diameter capable of separating 150 to 200 micron droplets (using the equations developed in Volume 1 for gas capacity of a vertical separator) can be assumed. The size of packed towers must be obtained from manufacturer s published literature. 

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. 

Tray spacing can usually be about 6 in. less than for a corresponding bubble tray. Sieve trays are operating on spac-ings of 9 in. and up to 30 in., the latter being necessary for high vacuum service. Spacing of 12-16 in. is common. 

Figure 8-137. Flooding capacity, sieve trays weir height is less than 15% of tray spacing low- to non-foaming system hole area at least 10% hole sizes Ms-in. to M-in. dia. surface tension = 20 dynes/cm. Used by permission, Fair, J. R., Petro/Chem. Engineer, Sept (1961), p. 46, reproduced courtesy of Petroleum Engineer International, Dallas, Texas.

Fair [183] relates sieve trays and includes valve tray remarks to the extensive work done for bubble cap trays. Figure 8-137 and 8-139 show flooding data for 24-in. spacing of bubble cap trays from [81] and represents data well for 36-in. diameter columns, and is conservative for smaller columns. Fair s work has been corrected to 20 dynes/ cm surface tension by ... 

From the residence time in dorvneomers for bubble cap trays, and at the very low tray spacing of 9 inches, select an allowable liquid velocity of 0.1 ft/sec. 

This is spacing of 2.66 do, and is as close as good design would suggest. Use A-in. tray thickness. 

Based on tray spacing of 24 in., assume 50% downcomer full, then ... 

This is satisfactory, because it is less than 50% of the tray spacing of 24-in. Therefore, the tray appears to have adequate liquid handling capacity. No hole blanking strips required. 

The areas of the column trays are 3.14 ft2. If the tray vapor paths are small openings, the worst-case scenario assumes that all the water vapor collects beneath the bottom tray. Assuming a tray spacing of 1 ft, the volume under the first tray is 3.14 ft3. Using an equation of state, we obtain... 

A gas enters the space between trays in an absorber with the component partial pressures shown in column 2 of the table. The rate equation for the reaction, 2N0 + 02 2N02, is... 

---