Problems with three-column distillation of methanol

Increase the temperature of the top condenser and the reflux liquid, or use nitrogen to maintain positive pressure

By controlling the pressure in the pressurized tower, air is released from that tower to maintain a positive pressure in the atmospheric pressure tower

May I ask why the original poster requires such strict pressure specifications for the atmospheric tower? Could it explain the problems you are facing in your current operations? In other words, do your products already meet the standards under the current operating conditions?

We didn’t encounter anything special; we’re just in charge of design. Today, while looking at the process, I suddenly wanted to see how other departments manage things. . . As mentioned above, we also use nitrogen or the pressure of gas in the pressurized tower to achieve control

Negative pressure persists in the tower top and the reflux tank; the analyzed reason is the presence of a dead zone between the tower top and the reflux tank. It is recommended that you check the interior of the equipment as well as its connections, to see if there are any low points in the pipes or if the air rise pipes inside the tower are narrow or even blocked. Under normal circumstances, the pipe at the top of the tower is a gooseneck pipe, and the interior of the tower is equipped with floating valve trays (or packing), providing sufficient space for vapor rise. However, if there are issues such as pipe depressions or blockages in the vapor rise pipes of the trays, pressure buildup can occur at the top of the tower, allowing negative pressure to develop. However, this negative pressure is only a slight negative pressure. Then water hammer phenomena will occur in the return pipeline. Of course, there are other reasons for the creation of negative pressure, such as too small a feed rate or even its interruption, as well as a relatively low reboiling amount; these are all factors that lead to the disappearance of atmospheric pressure. In short, controlling tower pressure is the result of comprehensive factors and a relative balance among various parameters.

This question has been answered more than once in this forum; please check there first, and avoid posting the same topic – I don’t want to answer it again either. At the same time, we need to criticize the moderator – they haven’t done their job properly; how is it that the same problem still exists?……

Using a pressurized tower to vent air cannot maintain positive pressure in the atmospheric-pressure tower; it is at most a supplementary measure. The main reliance remains on the pressurized tower to provide sufficient heat, as well as a reflux temperature of around 50–55 degrees. If both the pressure and the top temperature of the pressurized tower are low, then it becomes difficult for the atmospheric-pressure tower to maintain positive pressure.