Fair S Entrainment Correlation

Low values of FLG indicate vacuum operation, high values indicate operation at higher pressures or at high liquid/vapor loadings. The liquid/gas ratio L/G is based on mass flow rates. For multipass trays, the ratio needs to be divided by the number of passes. The strength of the correlation is at the lower flow parameters. At higher flow parameters (high L/G ratios, high pressures, emulsion flow), Fig. 14-31 gives excessively conservative predictions, with the low values of Csbf to the right likely to result from downcomer flow restrictions rather than excessive entrainment. The curves may be expressed in equation form as [Lygeros and Magoulas, Hydrocarbon Proc. 65(12), 43 (1986)]:

Csbf = 0.0105 + 8.127(10-4)(TS0755)exp[—1.463 FLG842] (14-90)

where TS = plate spacing, mm.

Figure 14-31 or Eq. (14-90) may be used for sieve, valve, or bubble-cap trays. The value of the capacity parameter (ordinate term in Fig. 14-31) may be used to calculate the maximum allowable vapor velocity through the net area of the plate:

where Unf = gas velocity through net area at flood, m/s

Csbf = capacity parameter corrected for surface tension, m/s

Moving Valve Tray

FIG. 14-30 Flood capacity of moving valve trays. (Courtesy of Koch-Glitch LP.)

pv, Vapor Density, Ib/cu ft

FIG. 14-30 Flood capacity of moving valve trays. (Courtesy of Koch-Glitch LP.)

Sieve Tray Flooding Capacity

FIG. 14-31 Fair's entrainment flooding correlation for columns with crossflow trays (sieve, valve, bubble-cap). [Fair, Pet/Chem Eng 33(10), 45 (September 1961).]

Flow parameter = L/G (pV/pL)05

FIG. 14-31 Fair's entrainment flooding correlation for columns with crossflow trays (sieve, valve, bubble-cap). [Fair, Pet/Chem Eng 33(10), 45 (September 1961).]

a = liquid surface tension, mN/m (dyn/cm) pL = liquid density, kg/m3 Pg = gas density, kg/m3

The application of the correlation is subject to the following restrictions:

1. System is low or nonfoaming.

2. Weir height is less than 15 percent of tray spacing.

3. Sieve-tray perforations are 13 mm (V2 in) or less in diameter.

4. Ratio of slot (bubble cap), perforation (sieve), or full valve opening (valve plate) area Ah to active area Aa is 0.1 or greater. Otherwise the value of Unf obtained from Fig. 14-31 should be corrected:

Ah/Aa

Un/UnfFig. 14-31

+1 0

Post a comment