Flood trays tray spacing

Tray flooding occurs when the liquid height in the downcomer equals or exceeds the height between trays (tray spacing). This is usually due to excessive boilup (vapor rate) but sometimes may be caused by excessive reflux. The control system must keep the column from flooding. Therefore, there are maximum vapor and liquid rates. 

Fig. 18. Flooding correlation for crossflow trays (sieve, valve, bubble-cap) where the numbers represent tray spacing in mm. Also shown are approximate...

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. 

Improper tray spacing at feed location. Premature flooding. Design error. 

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... 

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. 

At lower tray spacing, entrainment flooding may be related to lifting of the froth envelope and to froth rather than spray height. This correlation must not be extended to lower tray spacing. 

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.

Studies of Bubble-Cap Tray Flooding. (24-in. Tray Spacing)... 

Figure 8-140A. Bubble cap tray flooding 24-in. tray spacing.

Figure 8-140B. Sieve tray flooding, 6-in. tray spacing.

Figure 8-140. Studies of sieve tray and bubble cap tray flooding (24-in. tray spacing). (Note that the references listed on the illustrations in Figure 8-140 are from the original source, while Ref. 185 Is from this text.) Used by pennission. Fair, J. R., Petro/Chem Engineer, Sept. (1961) p. 45, reproduced courtesy Petroleum Engineer International Dallas, Texas.

Figure 9-17. Overall comparison of capacity at flood for 24-in. tray spacing with random packing. Reproduced with permission of the American Institute of Chemical Engineers, Kister, H. Z., Larson, K. F., Yanagi, T., Chemical Engineering Progress, V. 90., No. 2 (1994) p. 23 all rights reserved.

In the froth regime, which is between the spray and emulsion ones, flooding may be by either mechanism, depending on the tray spacing and the particular combination of vapour and liquid loads. 

The clear liquid backup is divided by the froth-density to give the froth height if this exceeds the tray spacing plus the outlet weir height, the tray is deemed to be flooded. 

A C3 splitter has 24 in. tray spacing and will operate at 80% of flooding. These data are applicable ... 

Figure 13.34. Chart for finding the diameters of valve trays. Basis of 24 in. tray spacing and 80% of flood for nonfoaming services. Use Figure 13.32(b) for approximate adjustment to other tray spacings, and divide the Vload= V-J——— by the...

The model includes parameters for relative volatility a, vapor velocity v, tray spacing flow constant kv, flooding factor //, vapor py and liquid pL densities, molecular weight MW, and some known upper bound on column flow rates FmaX. 

Downcomer Backup Flooding Aerated liquid backs up in the downcomer because of tray pressure drop, liquid height on the tray, and frictional losses in the downcomer apron (Fig. 14-32). All these increase with increasing liquid rate. Tray pressure drop also increases as the gas rate rises. When the backup of aerated liquid exceeds the tray spacing, liquid accumulates on the tray above, causing downcomer backup flooding. 

Entrainment flooding is predicted by an updated version of the Souders and Brown correlation. The most popular is Fair s (1961) correlation (Fig. 20), which is suitable for sieve, valve, and bubble-cap trays. Fair s correlation gives the maximum gas velocity as a function of the flow parameter (L/G)V(Pg/Pl), tray spacing, physical properties, and fractional hole area. 

Downcomer backup flooding occurs when the backup of aerated liquid in the downcomer exceeds the available tray spacing. Downcomer backup can be calculated by adding the clear liquid height on the tray, the liquid backup caused by the tray pressure drop, and the liquid backup caused by the friction loss at the downcomer outlet. The downcomer backup is then divided by an aeration factor to give the aerated liquid backup. 

Froth entrainment flooding (Fig. 6.7b). At higher liquid flow rates, the dispersion on the tray is in the form of a froth (Figs. 6.25c and 6.27a), When vapor velocity is raised, froth height increases. When tray spacing is small, the froth envelope approaches the tray above, As this surface approaches the tray above, entrainment rapidly increases, causing liquid accumulation on the tray above. 

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