Strange problems with methanol distillation?

The pressure in the pressure column bottom rises; there are two possible reasons for this: 1) excessive reflux, or 2) a low feed temperature. It is likely that excessive reflux is the cause, in which case the alcohol content in the feed to the three columns is high. However, in such cases, it is more common for the temperature at the bottom of the atmospheric pressure column to be low while the pressure is high. Then, the high temperature and pressure in the entire retention section cause slight liquid flooding inside the tower, which in turn leads to an increase in the temperature in the distillation section; at this point, one reduces the reflux from towers two and three. The operating conditions will improve. A low pressure in the atmospheric-pressure tower can only be caused by insufficient reflux in tower 2, or by too low an alcohol content in the feed to tower 3; as a result, the pressure throughout tower 3 is low, the temperature is high, and the temperature difference is small. Increasing the reflux in tower 2 or tower 3 will help improve the situation. It is best to increase the diode reflux.

Reply to 1# wyjjhj2008: The first possible cause for this phenomenon is that the temperature of the return fluid is too low. The second possibility is that the methanol content of the material inside the tower is too low, or its specific gravity is too high.

A low reflux temperature has a similar effect to a high reflux flow rate. Moreover, there are basically no means to control the reflux temperature in the other pressure tower, so it can be said that the issue of a low reflux temperature does not apply here

By looking at the curve of the feed temperature at the three towers, you will understand a bit.

The reflux temperature of the two towers is basically uncontrollable; if the temperature at the bottom of these two towers is low, then it is normal for the alcohol content in the feed to the third tower to be high. Furthermore, a low reflux temperature and a high reflux volume can sometimes have similar effects.

It’s likely that the concentration of methanol in the feed solution fluctuates greatly; the content of heavier components is high, which causes these heavier components to rise upward. As a result, the temperature in the distillation section increases, while the pressure at the top of the tower is low. The pressure at the bottom of the tower is also low, but the temperature there is high. The content of heavy components is low, the temperature at the bottom of the tower is low and the pressure is high; the lighter components move down to the stripping section.

Reply to 1# wyjjhj2008: I think the main issue with you is related to the load distribution between your pressurized tower and the atmospheric pressure tower; the amount of steam added to your pressurized tower must be quite high. The amount of steam rising in the pressure tower is large, and essentially all of the methanol is recovered in the pressure tower. This results in a low methanol content in the feed to the atmospheric pressure tower. The moisture content in the atmospheric pressure column is high, so the temperature of the column axe is high, resulting in less methanol being recovered at the top of the column. The pressure column generates more steam to heat the atmospheric column, which requires less heating; as a result, its temperature rises rapidly. A large amount of reflux is needed, but failing to reduce this reflux in time can cause the temperature in the atmospheric column to drop too low. This in turn lowers the reflux temperature of the pressure column as well, resulting in lower temperature and pressure in the pressure column. Try adjusting the load on your two towers, reducing the steam to the pressure tower. First, the pressure at the top of the atmospheric tower will drop, but it will rise again soon.

Hello, I have a question for you. Distillation operations are the most common in the workplace. My biggest takeaway is that distillation is truly unpredictable; there are many phenomena that are utterly baffling, and the more I think about them, the more frustrated I become. In particular, the stripping tower is also sometimes called a recovery tower (4 towers). Let’s start by discussing the design of the stripping tower on our side: The side streams from the three towers (at atmospheric pressure) are sent to between tray levels 34 and 25 of the stripping tower, while the wastewater from the bottom of the atmospheric pressure tower – which may not meet the required standards and has a temperature of 90–103 degrees – is pumped to tray levels 5–7 of the stripping tower. The bottom stream of the stripping tower is sent directly to wastewater treatment or the coal grinding section; methanol oil is extracted from the side stream, and some of the methanol recovered from the tower top is sent to the crude methanol tank. I think there are many factories nowadays whose distillation units are similar to ours. There was a time when the tower was functioning normally; if the temperature at the lower part of the tower (a temperature measurement point above the tower bottom) was low, adding a little steam along with some reflux would help raise that temperature gradually, while the temperature at the methanol oil extraction point in the upper part of the tower remained essentially unchanged. But recently it hasn’t been that easy to use. For example, sometimes when the liquid level in the atmospheric pressure tower rises, it becomes necessary to feed material into the stripping tower. If at that time the distribution within the stripping tower is even, and both the temperature at the bottom of the tower and the temperature at the top of the tower are normal. If feed is supplied to the stripping tower at this time, it will cause the temperature of the bottom layer of the tower to drop. At that point, I’m not sure whether to add steam to the bottom of the tower or reduce the reflux at the top Because sometimes, even though steam is introduced at the bottom, the temperature of the layer above the reactor vessel does not rise but instead drops, while the temperature at the top of the tower gradually increases. As a result, the temperature of the reactor vessel also starts to drop, which leads to the wastewater not meeting the required standards. In the past, there have been cases where, after reducing the reflux at the top of the tower, the temperature at the top of the tower as well as the temperature of the methanol oil obtained (which is the feed point from the side stream of the atmospheric pressure tower) actually decreased. This situation is really hard to understand. Sometimes, the temperature at the top of the tower, as well as the temperature of the methanol oil extracted (which is also the feed point from the side stream of the atmospheric pressure tower), are a bit high. In such cases, reflux is increased, but the temperatures mentioned earlier do not drop; instead, the temperatures at the bottom of the tower and in its lower sections decrease. Please ask an expert to help me explain the above situations, and also teach me exactly how to proceed to get things back to normal. When can distillation operations be performed skillfully?

Hello, I have a question for you. Distillation operations are the most common in the workplace. My biggest takeaway is that distillation is truly unpredictable; there are many phenomena that are utterly baffling, and the more I think about them, the more frustrated I become. In particular, the stripping tower is also sometimes called a recovery tower (4 towers). Let’s start by discussing the design of the stripping tower on our side: The side streams from the three towers (at atmospheric pressure) are sent to between tray levels 34 and 25 of the stripping tower, while the wastewater from the bottom of the atmospheric pressure tower – which may not meet the required standards and has a temperature of 90–103 degrees – is pumped to tray levels 5–7 of the stripping tower. The bottom stream of the stripping tower is sent directly to wastewater treatment or the coal grinding section; methanol oil is extracted from the side stream, and some of the methanol recovered from the tower top is sent to the crude methanol tank. I think there are many factories nowadays whose distillation units are similar to ours. There was a time when the tower was functioning normally; if the temperature at the lower part of the tower (a temperature measurement point above the tower bottom) was low, adding a little steam along with some reflux would help raise that temperature gradually, while the temperature at the methanol oil extraction point in the upper part of the tower remained essentially unchanged. But recently it hasn’t been that easy to use. For example, sometimes when the liquid level in the atmospheric pressure tower rises, it becomes necessary to feed material into the stripping tower. If at that time the distribution within the stripping tower is even, and both the temperature at the bottom of the tower and the temperature at the top of the tower are normal. If feed is supplied to the stripping tower at this time, it will cause the temperature of the bottom layer of the tower to drop. At that point, I’m not sure whether to add steam to the bottom of the tower or reduce the reflux at the top Because sometimes, even though steam is introduced at the bottom, the temperature of the layer above the reactor vessel does not rise but instead drops, while the temperature at the top of the tower gradually increases. As a result, the temperature of the reactor vessel also starts to drop, which leads to the wastewater not meeting the required standards. In the past, there have been cases where, after reducing the reflux at the top of the tower, the temperature at the top of the tower as well as the temperature of the methanol oil obtained (which is the feed point from the side stream of the atmospheric pressure tower) actually decreased. This situation is really hard to understand. Sometimes, the temperature at the top of the tower, as well as the temperature of the methanol oil extracted (which is also the feed point from the side stream of the atmospheric pressure tower), are a bit high. In such cases, reflux is increased, but the temperatures mentioned earlier do not drop; instead, the temperatures at the bottom of the tower and in its lower sections decrease. Please ask an expert to help me explain the above situations, and also teach me exactly how to proceed to get things back to normal. When can distillation operations be performed skillfully? I would also like to ask how to increase the temperature difference across the entire stripping tower Has the pressure difference across the entire tower decreased? Thank you?

Do not arbitrarily increase the feed to the recovery tower due to changes in the liquid level of the atmospheric pressure tower; the recovery tower is essentially used for the stripping of fusel oils. Making such arbitrary changes can cause significant fluctuations in the load on the recovery tower