Froth-Spray

Figuf 7 J>ay action in the froth, spray, and emuisian regimes. Horitontal bare Indicate height above tray floor in inches, (a) Froth regime (6) Spray regime. (Ati porta... 

Figure 6.27 (Continued) Tray action in the froth, spray, and emulsion regimes. Horizontal bars indicate height above tray flcor in inches, (c) Emulsion regime. Wall on right is downcomer from tray above. [All parfe courtesy of Fractionation Research Inc. (FR1).]...

Froth-spray. Froth-spray transition has been investigated for sieve trays using a variety of techniques (12,24,88-92,103,108-110). The gradual nature of this transition bred a large number of criteria for defining it, and made its correlation difficult. Excellent overviews of the state of art were given by Lockett (12) and Prado and Fair (103). 

An early study (91) reports that a correlation derived by Barber and Wijn for sieve tray froth-to-spray transition is also applicable to valve trays. A more recent study by Dhulesia (112) disagrees, and reports that valve trays have a stronger tendency to operate in the froth regime than sieve trays. Dhulesia proposed an alternative froth-spray transition correlation for valve trays, but this correlation is based on air-water data from a single type of valve tray, and its extension to other situations has not been tested. 

Solid or fluid particles (bubbles or drops) suspended in another fluid are moving in a large-scale flow. Such a flow can be present in fluidized beds with gas or liquid as continuous phase, for instance dryers, adsorbers, or crystallizers. Fluid particles are moving in bubble or drop columns or in froth (spray or bubble regime) present on coliunn trays. 

Entrainment occurs when spray or froth formed on one tray enters the gas passages in the tray above. In moderate amounts, entrainment will impair the countercurrent action and hence drastically decrease the efficiency. If it happens in excessive amounts, the condition is called priming and will eventually flood the downcomers. 

The product contains 12.6% phosphoms and has an OH number in the 450 mg KOH/g range. Fyrol 6 is used to impart a permanent Class 11 E-84 flame spread rating to rigid foam for insulating walls and roofs. Particular advantages are low viscosity, stabiHty in polyol—catalyst mixtures, and outstanding humid aging resistance. Fyrol 6 is used in both spray foam, froth, pour-in-place, and slab stock. 

The foam forming iagredients are carefully metered to obtain the proper ratio of reactants, thoroughly mixed by either mechanical or impingement means, then appHed as a Hquid, a spray, or a froth with subsequent expansion and cuiing. 

The KEN-FLOTE column (11) is one of several column flotation processes based on a countercurrent principle. The feed slurry containing reagents is iatroduced iato the column just below the froth zone. Air is iujected at the bottom of the column via an air sparger. Wash water is sprayed within the froth zone to reject the entrained impurities from the froth. Test results on this column iadicate that a 6% ash product coal having a combustible-recovery of 75—80% can be obtained. A 70—80% pyrite reduction is also claimed. Figure 2 shows the operation of such a column. 

The term froth in Fig. 14-22 suggests aeration in which the hquid phase is continuous. Under certain conditions there can be an inversion to a gas-continuous regime, or spray. The spray has its phase boundaries equivalent to the boundaries for froth shown in Fig. 14-22. 

As noted, the weir crest is calculated on an equivalent clear-liquid basis. A more realistic approach is to recognize that in general a froth or spray flows over the outlet weir (settling can occur upstream of the weir if a large calming zone with no dispersers is used). Bennett et al. [AIChE J., 29, 434 (1983)] allowed for froth overflow in a comprehensive study of pressure drop across sieve plates their correlation for residual pressure drop /jf in Eq. (14-87) is represented by Eqs. (14-115) through (14-120) ... 

Figure 14-25 also provides a means for estimating whether spray or froth might prevail on the tray. As can be seen, low values of the flow parameter Flg,. s for vacuum fractionators, can lead to the spray regime. 

L = residence time of liquid in the froth or spray zone, s... 

Generally, when spray entrtiinment changes to more froth on the tray or in the tray vapor space, then entrainment has been found to increase with liquid rate [94]. 

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. 

Is believed to be a froth regime (liquid in continuous phase above the tray and gas present as bubbles in the liquid) phenomenon rather than a spray regime (gas in continuous phase above the tray and liquid present... 

Higher open tray areas tend to produce a spray rather than a froth. High vapor rates produce a spray, while the higher liquid rates produce a froth [69]. 

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