The downcomer of the bubble column fails to establish an effective liquid seal; seek a solution! ! !

This post was last edited by CHANGBAISHI on 2018-4-17 08:58. If this phenomenon occurs at the beginning of operation on the device, it is likely due to an installation issue. From a process perspective, check whether the design parameters for the reference material distribution meet the production requirements. Such as the resistance values at various sections of the tower, the gas flow rate entering the tower, the liquid flow rate, etc. During operation, it is necessary to first establish a relatively stable flow rate of the liquid flowing downstream, and then gradually increase the appropriate amount of gas flowing upward; fine adjustments can be made by monitoring the resistance parameters as well as the changes in purity after the transformation of the liquid and gas phases. It could also be a regulation issue; did flooding occur? Leaking? ? ? ? If the volume of air flowing in is too high, the optimal operating conditions for the bubble column are lost; there should be an optimal operating condition. By gradually increasing the air volume, the point at which these conditions are disrupted should be set as the upper limit for normal operation. The maximum load operating point is then one that allows the system to operate without being disrupted, and is closest to this limit.

The tower internals were supplied by Sulzer and have been calculated. No problem. The hydraulic calculations are also fine.

Thank you for your reply! Regarding installation: there was on-site supervision during installation with photos taken as evidence, and the access hatch was opened for inspection after installation as well. There is no visible damage to the tower internals. However, one issue is that during the installation of the downcomer in the second tray from the top, interference with the bubbles in the third tray occurred, as a result of which the downcomer was shortened by 50 mm; this meant that the height of the liquid seal tray below the downcomer increased by 50 mm. In terms of the process parameters, both the gas phase volume and the liquid phase volume were at around 70% of full capacity. The process-side gas should also meet the requirements. However, no fine adjustments have been made yet. A tower scan was performed, and it was found that flooding occurred on the second layer; it is uncertain whether this is related to the inability to establish a liquid seal. Previously, the load was stable at around 65%, and after remaining stable for a while, the pressure difference might return to its normal design value. But sometimes it doesn’t work. Therefore, an attempt was made to actively establish a liquid seal: On the first attempt, a large amount of water was added at low load (20%), and then the gas flow rate was increased; the pressure difference dropped suddenly as the load was increased, from 100 mbar to 25 mbar, and the experiment was successful. Second time: A large amount of water was added at low load (20%), and then the gas flow rate was increased; the pressure difference dropped suddenly during the increase in load, falling from 100 mbar to 55 mbar. The pressure difference decreased, but it was different from the first time, remaining at its original level. Third time: At medium load (60%), a large amount of water was added, and then the gas flow rate was slightly increased; it was found that the pressure difference remained high, and liquid was carried downstream. Thus, the load was reduced to 20%, but during this reduction (with no water added to the tray), the pressure difference remained essentially unchanged. As the load is increased, the pressure difference rises; after remaining stable for a considerable period of time, the pressure difference decreases very slowly. After finally stopping the machine, it was found that the pressure difference still remained at 70 mbar. Static pressure difference and liquid layer equilibrium. Only after nitrogen was added to the top of the tower to balance the pressure difference did the liquid level drop suddenly. In the most recent attempt to establish a liquid seal, a large amount of water was added to the top of the tower, after which the gas phase was gradually increased. The pressure drop across the tower remained high, and it hardly decreased even when the load was stable. Strangely enough, when parking later (with no gas flow), the pressure difference could still be maintained at around 70 mbar; it was only by introducing nitrogen at the top of the tower to balance the pressure difference that the liquid phase could flow down. But this time, the liquid should accumulate in large amounts on the very top layer.

Another thing to pay attention to is the measurement sampling point of the instruments; it is also necessary to be aware of whether water enters the negative pressure pipe (the upper measurement point), which could cause measurement issues.

Well, it was proofread multiple times. Confirm there are no issues

It indicates that the operating point corresponding to the normal voltage drop still exists; however, this state point may be unstable and sensitive to certain parameters, making it easy to shift to another state point during startup and shutdown phases.

The problem has been resolved by removing the liquid collection tray below the downcomer and extending the downcomer downward to the tray, with a distance smaller than the height of the overflow weir. The aforementioned problem did not occur again later on.