Please ask for help regarding the abnormal problem of periodic large fluctuations in liquid level, temperature, and pressure in the distillation tower!
Thread Content
Some time ago, during the daily production and operation of a distillation tower in our company, the liquid level in the column tank suddenly rose sharply. At the same time, the temperature in the column tank dropped sharply, by 60 to 70 degrees in a short period of time. In view of the sharp drop in temperature, some adjustments were made, that is, increasing the steam supply to the column tank, but it did not work. The reflux was turned down, and the feed was even briefly closed. After a while, The liquid level began to drop sharply, and the temperature began to rise sharply. Corresponding adjustments were made immediately, but it did not work. After that, the temperature, pressure, liquid level and other parameters of the tower fluctuated greatly periodically. Crucially, the fluctuations in the tower also caused the pressure of the entire steam pipe network to fluctuate periodically. At that time, the company did not analyze the cause internally, so it shut down the operation the next day, until now! The following is a status diagram of each main parameter of the tower when an abnormality occurs (in order, the liquid level of the tower kettle, the kettle temperature, the tower top pressure, and the steam pipe network pressure):
There are three main problems now. First, why did the tower suddenly fluctuate so much? (No adjustments were made to the working conditions before the liquid level suddenly increased and the temperature dropped for the first time.) Second, why did the fluctuation of the tower cause corresponding periodic fluctuations in the pressure of the entire steam pipe network? Third, how should we adjust after this situation occurs? I welcome all the masters to come and give me advice, and I also welcome fellow posters who may be as confused as me after seeing this post to discuss it with me. I am not a chemical professional, so my posts may not be very sophisticated. I hope you will not give up on giving advice or discussion on this issue because my question may not be complete enough, or some details are not explained! If you still need to know about any conditions, please feel free to ask them in Bi. I will reply as soon as possible after seeing them and add more!
The cause of the problem should be the gradually descending trend line in the upper right corner. Only one of these problems can lead to other changes. Check the reason why the trend line in the upper right corner has fallen. In addition, it is best to include a flow chart to facilitate more detailed discussion.
You can check whether the heat source of the reboiler is normal. The next question is whether the PID of the reboiling control valve needs to be reset.
If the operation is correct and the instrument displays normal, it is judged as liquid flooding. The most likely reason is that there is an abnormality in the distillation section. Since the machine is stopped, focus on checking the distillation section to see if the downcomer or tray has fallen off. I hope you can be notified of the maintenance status in time.
At that time, I also considered the direction of liquid flooding, because after the liquid level and temperature of the tower fluctuated, there was a period of time when the upper layer temperature was higher than the lower layer temperature in some temperature points of the tower. However, it was not very consistent. This situation only occurred in some trays. Under normal conditions, the temperature of a distillation tower must gradually decrease with the height of the tower. If there is a problem with the transmitter itself that throws out the instrument, then it is likely that the material from the lower layer of some adjacent trays has poured into the upper tray, which will cause this abnormal temperature situation. But if it was really liquid flooding, it is said that the pressure difference of the tower would fluctuate periodically at that time. However, looking at the pressure difference trend chart of the tower, the time does not correspond to the time, so it feels very contradictory.
There was no increase. Before the temperature started to drop, the working conditions were relatively stable, so no adjustments were made.
Judging from the phenomenon, it is very likely that the feed material contains water.
I don’t know much about this process, but from what you said, there may be a problem with the heat exchange of the equipment. The heat exchange efficiency of the equipment is unstable, sometimes high and sometimes low. It may be caused by the failure to discharge the condensed water in time after steam heat exchange. Check the drainage situation of the on-site distillation tower and see if the trap is working properly.
Agree with the 9th floor, it may be caused by water in the raw materials or steam.
If salt builds up on the tray, causing periodic tower flushing, online water flushing can be considered.