Causes of liquid flooding in distillation columns and their treatment methods?

It’s possible that the heating amount is too high, or that the composition of the feed has changed. You can reduce the heating amount, increase the reflux rate, and check the composition of the feed.

Liquid flooding: During normal operation of the tray, a certain thickness of liquid layer is maintained on the tray to facilitate mass transfer in contact with the gas. If, for some reason, the liquid fills the space between the tray plates, disrupting the normal operation of the tower, this phenomenon is known as flooding. When the liquid flow rate on the tray is high and the velocity of the rising gas is high, the amount of liquid carried by the gas to the upper tray increases significantly, causing the space between the trays to be filled with a gas-liquid mixture. Eventually, the entire tower gets filled with liquid. This type of flooding caused by an excessive amount of liquid entrainment is known as entrained flooding. When the liquid in the downcomer cannot flow downward smoothly, it inevitably accumulates within the tube, causing the liquid level to rise and exceed the top of the overflow weir. The liquid then connects the two plates, leading to an accumulation of liquid on the tray, which rises progressively until the tower is filled with liquid. This phenomenon of flooding caused by a full downcomer is known as downcomer flooding. When flooding occurs during distillation operations, normal operation is disrupted; it is necessary to analyze the causes of flooding and take appropriate actions. If it is caused by a equipment issue, the machine should be stopped for maintenance ； If this is caused by a sudden rise in the reactor temperature due to improper operation, the feed rate should be reduced or stopped, the reactor temperature should be lowered slightly, the extraction at the top of the tower should be halted, and full reflux mode should be adopted so that the poorly volatile components carried to the top of the tower can slowly flow down to the bottom of the tower. When production does not allow the cessation of feed, the reactor temperature can be maintained slightly below the normal operating temperature; the amount taken from the top of the tower can be increased while the reflux ratio is reduced. Once the tower pressure returns to normal levels, the operating conditions can be brought back to normal. This kind of operation can only ensure the quantity of products, but not their quality.

Our plant’s distillation tower is a dimethyl ether distillation tower; if the temperature in the reactor suddenly rises, we should increase the feed rate in order to lower the temperature, rather than reducing the feed as suggested on the third floor.

Steam rising inside the tower prevents the liquid from reaching the next tray, thereby disrupting the normal operation of the tower. If temperatures at various instruments are inconsistent and the pressure inside the tower increases, it indicates flooding. The solution is to reduce the steam supply and decrease the feed rate to the system; if flooding occurs severely, feeding and extraction should be stopped, and operations can resume only after the pressure at the bottom of the tower drops and flooding is eliminated.

It depends on which tower and under what conditions flooding occurs. Generally, there are two possible root causes: either the feed rate is too high, or there is too much heat at the bottom of the tower; another possibility is a problem with the design of the equipment