Liquid holdup of tray in plate tower
Thread Content
Assuming the plate tower has 100 trays, I believe that under ideal conditions the liquid holdup on each tray from top to bottom is equal; even if it isn’t equal, the difference is minimal； But my colleagues have different opinions. Please ask the experts to provide an answer. Thank you
The liquid layer height on a tray is determined by the pressure drop between adjacent trays; the greater the pressure drop, the higher the liquid layer height on that tray. If the calculated values of the pressure drop between trays are equal, then the liquid layer heights on those trays are also equal, meaning that the holding capacities are equal
The liquid holdup on each tray is likely to be unequal. Since there are feed and discharge points among the 100 trays, the operating load varies, and as a result the open area and liquid holdup also differ.
I also think it’s because they don’t want to wait, as the gas load at the top of the tower is relatively low. But the difference won’t be that great. Besides, what’s the point of discussing this in practice and in theory? For the operation of a distillation column, does a single tray seem to have little significance?
It is designed with equality in mind, but in practice it is not equal
In design, it is generally assumed that they are equal, and this depends on the height of the overflow weir. There is always a difference between reality and theory; theoretical equality means perfect equality, while in actual production, a difference within a certain range is considered acceptable as being equal. I also agree that for distillation towers, especially those with 100 layers, it doesn’t make much sense to discuss each individual layer. You can simply consider them equal – what’s the difference?
Personally, I think they are not equal, because the flow rates of liquid and gas through each tray are different, which in turn affects the liquid holding capacity of the tray.
Strictly speaking, they are different, but the difference is not significant. The volatile components on each tray are different; there is a slight difference, which is normal, but it can be ignored.
Strictly speaking, the liquid-holding capacity of each plate should be different. The cross-section of the liquid level on each tray is trapezoidal, sloping from the liquid inlet pipe toward the overflow weir. From the bottom to the top of the tower, the gas flow rate inside the tower decreases gradually; this means that the support provided by the gas flow to the liquid flow decreases from bottom to top. As a result, the liquid holdup on each tray also decreases from the bottom to the top of the tower.
The pressure differences between the towers are not equal; how could the liquid holdup be the same?
It’s different; although the height of the overflow weir may be the same, the gas-liquid load on each tray is also different.
There are many opinions from those upstairs, but I still don’t understand. I don’t know which one is correct
Theoretically, they are equal. However, the liquid layer height on a tray is determined by the pressure drop between adjacent trays. Assuming that the height of the overflow weir is the same, the entry of new material at the feed tray affects the flow rates of liquid and gas at that tray, which in turn affects the liquid holdup on that tray. Conclusion: In fact, they are not equal. Under normal conditions, it is possible to observe through the sight glass that the liquid layer below the feed inlet is higher than that in the upper part of the tower. If production is abnormal and a gas cushion forms, or if there is a blockage in certain sections of the tray, then the liquid in the upper layers may not be able to flow down, resulting in the upper trays being filled with liquid while the lower trays remain empty... Personal opinion...