Working principle of the pressure tower

Technical principle and process of the methanol “three-plus-one tower” system: The three-tower process is a distillation system composed of a pre-distillation tower, a pressurized distillation tower, and an atmospheric distillation tower. Among them, the pre-distillation column serves the same purpose as that in the two-column process. The methanol liquid coming from the bottom of the pre-distillation tower is pressurized by a methanol feed pump and then sent to the pressurized distillation tower. The methanol vapor emitted from the top of the tower enters a condensing reboiler; the heat generated by the condensation of this vapor is used as a heat source for the atmospheric pressure distillation tower. The methanol liquid exiting the condensing reboiler then goes into the reflux tank of the pressurized tower. Part of this liquid is pressurized by a pressurized reflux pump and sent back to the pressurized distillation tower as reflux fluid, while the remaining part is cooled to 40°C using a purified methanol cooler, thereby becoming a qualified product. The heat required for the pressure distillation column is provided by the column reboiler. The methanol liquid discharged from the bottom of the pressurized distillation tower is sent to the lower part of the atmospheric distillation tower. The methanol vapor emerging from the top of the atmospheric distillation tower passes through a purified methanol condenser before entering the reflux tank of this tower; part of this vapor is then pressurized by a reflux pump and sent back to the top of the atmospheric distillation tower as reflux, while the remaining portion is sent to the purified methanol tank. The water containing trace amounts of methanol along with other high-boiling-point impurities, which is discharged from the bottom of the atmospheric pressure distillation tower, is cooled in a waste fluid cooler before being sent to a biochemical treatment unit. If a stripping tower or a methanol recovery tower is added after the atmospheric pressure tower to further improve the quality of the wastewater, reduce the wastewater discharge volume, and increase the methanol yield, this is referred to as the three-plus-one tower process. The use of a three-tower or three-plus-one tower process reduces energy consumption (tonnage of methanol vapor per cycle) by about one-third compared to a two-tower process of the same production scale. This post was last edited by zjyang168168 on 2008-1-7 21:55.]

The working principle of the pressure tower is based on the gas-liquid equilibrium principle: by increasing the pressure, the volatility of methanol and water is enhanced, thereby enabling their separation. . . . . . . .

This view is completely wrong; the relative volatility of two substances increases as pressure decreases. The main reason for designing a pressurized tower at the same time is to save steam and reduce costs. Otherwise, if the relative volatility can increase under pressure, wouldn’t it be possible to achieve complete separation of the two substances in a pressurized tower?

Hello from the 5th floor. You said that the main reason for designing a pressurized tower is to reduce costs. ”I then wondered whether more steam is required at normal pressure or under pressure to achieve the same level of evaporation. The main reason for designing a pressurized tower is to achieve better separation, not to save steam, right? This is just my personal opinion; please point out any mistakes if there are any. Thank you

Regarding the issues of pressure and relative volatility, you can refer to the Principles of Chemical Engineering, which provides detailed explanations; I won’t go into further detail here. Regarding energy conservation, the answer is straightforward: as can be seen from the three-tower process, the heat source for the atmospheric pressure tower and the reflux cooling source for the pressurized tower complement each other. By using two extraction towers, it is possible to reduce the height of the extraction towers in the traditional two-tower process, ensure that the residual liquid meets the required standards, and thus cut down on wastewater treatment costs. If you want to learn in detail, you can look up more information on forums; there are many topics on this subject.

:) Hello； Saving steam and equipment is right, but I don’t think it’s comprehensive enough! If the goal is to save steam, wouldn’t it be more cost-effective to keep the pressure in the pressure tower at 2 kilograms? However, in actual production, most operations are carried out at around 5 to 6 kilograms. May I ask why? I think, in any case, the purpose is to increase the opening degree of the light and heavy components, which results in a temperature gradient. In other words, there is a pressure gradient; with it, distillation will yield the desired result. Thank you!

A pressure distillation tower is a distillation tower that operates under certain pressure conditions. However, the operating temperatures at the top and bottom of a pressurized distillation column are different; these temperatures correspond to the boiling or dew point temperatures of the light components and heavy components under that pressure condition, respectively.

I agree with the view from the 5th floor. I believe the reason why the 3-tower process is more energy-efficient than the 2-tower process is that the heat released from the condensation of methanol vapor taken from the top of the pressure tower is used as a heat source for the bottom of the atmospheric pressure tower; this saves both steam and cooling water. But if that is the case, it is necessary for the top temperature of the pressurized tower to be higher than the bottom temperature of the atmospheric pressure tower in order to enable heat transfer; therefore, by increasing the pressure in the pressurized tower, its temperature can be raised, thus facilitating heat transfer. As for the working principle, it is the same as that of ordinary distillation: mass and heat transfer occur, with multiple stages of condensation and vaporization being used to achieve product purification.

The working principle of the pressure tower is based on the gas-liquid equilibrium principle, which is used to distill and separate methanol from water. By simultaneously increasing the distillation pressure, the boiling point of the distillate (i.e., pure methanol) rises, which can be used to heat the bottom liquid in the atmospheric-pressure column. This saves both the steam consumption of the atmospheric tower and the distillate cooling water consumption of the pressurized tower, thereby reducing the energy consumption for distillation.

It only increases the total number of theoretical plates, and pressurization allows energy savings by utilizing temperature differences before and after.

Three-column distillation saves nearly 1/3 of the energy compared to two-column distillation. However, it requires a higher investment in fixed equipment; this increase is one-time only, whereas the energy savings are long-term. In summary, three-column distillation is more energy-efficient than two-column distillation

The pressure control in the pressurized tower is too low, resulting in a low temperature at the top of the tower; this makes it impossible to use heat generation for the atmospheric pressure tower

The main purpose of installing a pressurized column is to achieve double-effect distillation together with an atmospheric column; the methanol vapor exiting from the top of the pressurized column at higher pressure is used to supply heat to the reboiler of the atmospheric column. This helps to **save steam, and this is why three-column distillation saves more steam compared to two-column distillation