Dump point

Dump Point, Plate Activation Point, or Load Point... 

These trays will dump liquid excessively through the perforations giving exceeding low efficiencies [47] unless a minimum vapor rate is maintained for a given liquid capacity. The smaller the holes the lower the dump point (vapor velocity). 

Tray efficiency is as high as for bubble caps and almost as high as sieve trays. It is higher than bubble caps in some systems. Performance indicates a close similarity to sieve trays, since the mechanism of bubble formation is almost identical. The real point of concern is that the efficiency falls off quickly as the flow rate of vapor through the holes is reduced close to the minimum values represented by the dump point, or point of plate initial activation. Efficiency increases as the tray spacing increases for a given throughput. 

If there is the possibility of apor and liquid rates being reduced to 50% of the indicated values, this would place the trays as selected above at the dumping point, or activation point, which is not a good operating condition. In this situation the number of holes should be reduced in order to maintain a velocity of vapor through the holes greater by at least 15% than the activation velocity. 

The average THg concentration of all tissue samples (n = 285) was 0.2482 0.2546 pg/g, wet weight, ww, ranging from 0.0148 to 0.8052 pg/g. The highest levels were found at the factory site, close to the waste dumping point, followed by the meander, wildlife reserve, and reference sites (Table 1). This fact indicates an important mercury uptake by zebra mussels at the hot spot and redistribution to areas located immediately downstream and near to the river bank opposite the dumping site. 

Dumping As gas velocity is lowered below the weep point, the fraction of liquid weeping increases until all the liquid fed to the tray weeps through the holes and none reaches the downcomer. This is the dump point, or the seal point. The dump point is well below the range of acceptable operation of distillation trays. Below the dump point, tray efficiency is slashed, and mass transfer is extremely poor. Operation below the dump point can be accompanied by severe hydraulic instability due to unsealing of downcomers. 

Above the weep point, W = 0 and fw = 0. At the dump point (Sec. 6.2.14], all liquid weeps from the tray, and fw 1.0. It was stated (50,70) that when weeping across the tray is uniform, the decrease in tray efficiency is usually considered acceptable with a weep fraction of up to 0.1. 

The most extensive studies on dumping were reported by Prince and Chan (77-79). The Chan and Prince dump-point correlation (Fig. 6,20 was recommended by Chase (30), The author has also had favorable experience with the correlation under conditions widely different from those used in its derivation. Alternatively, the dump point can be predicted from a weep rate correlation by setting the weep rate equal to 100 percent of the liquid entering the tray. However, little has been reported by either Lockett and Banik (56) or Hsieh and McNulty <63 about the reliability of dump-point predictions from their correlation. 

Figure 6.20 The Chan and Prince dump point correlation. B K. C Chan, Ph.D. Thesis, University of Sydney, Australia. 1965 courtesy of Professor Prince.)...

Weep point check. If the trays operate above their weep points at turndown conditions, checks of the fractional weep and dump point may not be needed. The weep point check will be performed using Fair s correlation (Sec. 6.2.12). 

Dump point check. This check will be performed using the Prince and Chan correlation (Sec. 6.2.14). 

Comment. Figure 6.20 predicts that at turndown, neither top nor bottom section will dump. However, both sections will operate close to the dump point, and excessive weeping is likely. This is consistent with the prediction from Fair s weep correlation (above), which indicates that at turndown both sections operate well below the weep point. 

Comment. The calculation converged on the first trial to within reasonable accuracy. The calculation showed that the weep fraction is small (<0.07), As per Sec. 6.2.12, a weep fraction of up to 0.1 can be tolerated. This small weep fraction appears inconsistent with what would be expected based on the proximity of the operating point to the predicted dump point and on the large gap between the operating point and the predicted weep point. 

Dump point vapor load, Prince and Chan correlation 119 129 113... 

CW dumping in the White Sea was being carried out for at least 8-9 years. It is a challenge to estimate the amount of CW dumped. They were comprised of obsolete chemical ammunition, i.e. mostly yperite (mustard gas), lewisite and their mixtures. Dumping points indicated officially may not give a true and complete picture. 

Ptgur 6.20 The Chan and Prince dump point correlation. 

Above the weep point, w = 0 while w = 1 at the dumping point. Weeping occurs between the weep point and dumping point. Turn down operation could be still acceptable even if it is below the weep point but the weep ratio w is less than 0.1. This is because tray efficiency is not affected too severely when w is less than 0.1. Increasing vapor load and reducing the clear Uquid height could help to avoid weeping. 

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