Vacuum drops after removing the reflux ratio controller
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Dear sea friends, I wish you a happy Spring Festival and good health for your whole family! Our plant has an ester recovery tower (vacuum tower). Initially, there was a reflux ratio controller at the top of the tower; however, since the amount of material taken from the top of the tower was relatively small, this reflux ratio controller was removed. Instead, it was decided that the reflux liquid should flow entirely through the feed troughs, and the amount of reflux flowing into the tower was adjusted by controlling the opening degree of the valves in the feed lines. As a result, no material could be taken from the top of the tower anymore. The vacuum level in the tower also decreased, from -99.7°C to -97°C, as the temperature of the reactor increased. After the heating stopped, as the temperature of the reactor decreased, the vacuum level in the system gradually rose to -98.6 KPa. I analyzed the reasons why no material could be extracted from the top of the tower: first, there were already few light components in the raw material, only 0.5%, and second, the vacuum level decreased. But why does the vacuum level at the bottom of the tower decrease after the temperature rises? Does the modification of the reflux ratio controller affect the vacuum level? We have verified that the capacity of the vacuum pump is sufficient, and the vacuum pipes at the top of the tower are not blocked. I hope all experts will kindly share their insights! :handshake
It’s probably related to fine chemicals, I guess: lol. There are very few light-component fractions, but they still need to be extracted; otherwise, the vacuum level will decrease as these light components accumulate. It’s normal for the temperature at the bottom of the tower to rise and the vacuum level to decrease: lol. The higher the temperature, the more heavy components are carried away; it would be strange if the vacuum level didn’t decrease. For the light-component column, if continuous extraction is not feasible, intermittent extraction can be tried (that is, extraction is carried out when the control parameters deviate significantly from normal levels)
I’d like to add that there is actually a small amount of non-condensable gas at the top of the tower as well. (All systems will have it). Normally, it is recovered along with the light components. Now that the light components are no longer extracted, the non-condensable gases can also no longer escape; over time, the vacuum level will decrease as well.
Thank you for your reply! Our tower was also operated intermittently; in fact, not much gas should have risen to the top of the tower, as the temperatures of the primary and secondary condensers at the top were not high when touched. I suspect the vacuum level has dropped; at the same temperature, less liquid evaporates. But on the other hand, if the vacuum level decreases, it shouldn’t be because there is more heavy distillate at the top of the tower, right? I hope you can share your insights~:)
If there is indeed non-condensable gas, shouldn’t it be removed through the vacuum system after the vacuum pump is turned on? We first pour the material into the bottom of the tower, then start to activate the vacuum system. When the vacuum level reaches -99 kPaG, we begin to increase the temperature. At this point, shouldn’t any non-condensable gases be removed? When the temperature of the kettle reaches 200°C, the vacuum level begins to drop. Meanwhile, the temperature at the top of the tower is not very high; the first and second condensers are not hot to the touch, but no product is being collected. When heating is stopped and the temperature drops, the vacuum level gradually increases. Could there be a problem with the tower’s sealing? It can maintain pressure at room temperature, and it can also do so after being heated and then cooled again; so why can’t it maintain pressure at high temperatures? After thermal expansion, the sealing performance should be better, right? I hope you can share your insights~:)
Could you share your PID?