Why is the non-condensable gas from the pressurized column in triple-column distillation sent to the top of the atmospheric column and then to the atmospheric column cooler?
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In three-column distillation, is there a control valve for the non-condensable gas in the pressurized reflux tank, leading to the top of the atmospheric column and then to the cooler of that atmospheric column? I don’t understand this – why is that? During normal operation, shouldn’t this control valve be at some degree of opening? I think it’s probably to prevent a vacuum from forming at the top of the atmospheric pressure tower, so as to regulate the pressure in that tower. Please provide an answer, thank you!
I think it’s used to regulate the top pressure of the pressure tower. Since the vapor at the top of the pressurized tower is high-quality methanol vapor, it would be a waste to send it to the discharge tank; instead, it is sent to the inlet of the condenser at the top of the atmospheric pressure tower to recover pure methanol. Under normal conditions, this valve does not need to be operated frequently.
Could you be more detailed? I still don’t quite understand.
Functions of this valve: 1. To release nitrogen from the pressurized tower system during startup. 2. In emergency situations (when the pressurized tower is overpressured), to rapidly relieve pressure in the tower by venting it through the atmospheric pressure reflux tank, thereby preventing the use of a flare. During normal operation, this valve should be in the closed position. Furthermore, the vapor phase at the top of the pressurized tower is methanol vapor, with no non-condensable gases present; therefore, the original statement is inappropriate!
One more thing: if this pipe is vented directly, high pressure will cause a large amount of methanol to be released, resulting in a \"methanol rain\" – which is dangerous!
If it’s not discharged directly, but first into a discharge tank, how about discharging from that tank?
The liquid level in the discharge tank is generally kept very low, while the pressure in the pressurized tower is high; therefore, the liquid level in the discharge tank has little impact on the discharge pressure of the pressurized tower.
Methanol has a low boiling point; since the top of the pressure tower contains pure methanol vapor, releasing it directly without cooling will cause it to rapidly condense into liquid methanol, which is dangerous! During normal operation, this valve is not left at an open setting; instead, it is put into self-regulation mode to automatically adjust the pressure at the top of the pressure tower.
It shouldn’t go into the discharge tank. Because ultimately, the venting from the atmospheric tower is either vented directly on-site or sent to the flare.
This is a pressure control valve; theoretically, it is used to regulate the pressure in the pressurized tower. Under normal conditions, it remains fully closed, so there is no risk of methanol vapor being wasted by entering the atmospheric pressure tower for further cooling, as mentioned earlier. Its main function is to control the pressure in the pressurization tower when parking, thereby reducing the pressure.
Generally, the vapor from the reflux tank of the three-column distillation pressurization unit can be combined with the vapor from the top of the atmospheric pressure column to further recover methanol from the non-condensable gases; however, if the valve is kept closed, it should be opened appropriately during shutdown to prevent negative pressure from occurring.