Fluctuations in the pressure at the top of the distillation column
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1. Recently, it was found that once the reflux flow at the top of the tower increased, the pressure at the top of the distillation tower began to fluctuate. The distillation tower uses the pressure at its top to control whether liquid is added to or removed from the reflux tank. By comparing the readings on the pressure gauges located at the top of the tower and those on the reflux tank, it was observed that the trends of these readings were actually opposite to each other, with fluctuations that crossed over. When the instruments were sent to be calibrated on-site, it was found that there was liquid in the pressure sensing lines. Has anyone encountered a situation where an isolation tank is necessary for the pressure sensing lines in a distillation tower? 2. The fractionation furnace and the reaction furnace share a common flue. Currently, the negative pressure at the bottom of the furnaces is similar, but the negative pressure at the top is -100 for one furnace and -30 for the other – is this normal?
While ensuring that the product at the top of the tower meets the required standards, the temperature at the top of the tower fluctuates within a very narrow range. Affected by the dry point of the product, the reflux volume remains relatively stable, as does the pressure at the top of the tower. The reflux tank’s pressure is controlled through the addition of air and the removal of air, and it also remains constant. In short, there isn’t much relationship between these two pressures. The tower pressure is related to the depth of the reaction; as the reaction depth increases, the tower pressure rises, while the pressure in the reflux tank stays unchanged even when automatic control is in use
The cause of the tower pressure fluctuations has been identified: it is due to excessive reflux. By increasing the top pressure, the top temperature was adjusted to maintain the dry point of the naphtha. However, it is not clear why excessive reflux leads to tower pressure fluctuations
Excessive reflux results in large heat exchange between the vapor and liquid phases at the tower top, causing the temperature at the tower top to drop