Weeping defined

Weeping capacity is more related to turndown operation. Typically, 80% weep defined by equation (12.52) is used as the weep limit. Valve trays provide better turndown capacity in 3 1 versus sieve trays in 2 1. In other words, valve trays could operate in 30% of normal load with weep rate less than 10%. 

Clw = measured rate of weeping from Equation 8-277 Cv = gas phase loading factor defined in Equation 8-281, ft/.s... 

The weep point is defined as the vapor rate when weeping first becomes noticeable. At that point, little efficiency is lost. As vapor rate is reduced below the weep point, the fraction of tray liquid falling through the holes increases, and the reduction in efficiency becomes more noticeable. When this fraction is sufficiently large to effect a sig-... 

Fair s (31), and Zuiderweg s (17] correlations as those that are generally more reliable. Other design publications (4,18,64) recommended the use of Fair s correlation (31). The author has also had favorable experience with it. According to Fair s model (31), the force balance defining the weep point is... 

Below the dump point (100 percent weep), tray efficiency is a small fraction of its normal value, and mass transfer is extremely poor. Since no liquid enters the downcomers, they lose the liquid seal that prevents vapor from rising through them. Operation below the dump point can be accompanied by severe hydraulic instability due to unsealing of downcomers, as was demonstrated by field experience (76). The startup stability diagram (1), which defines the range of vapor and liquid rates needed for satisfactory startup, has the dump point as the lower limit- The tendency of dumping increases when (77-79)... 

Dimensionless vapor velocity used for correlating weeping rates, defined by Eq, (6.36). 

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