Three-column distillation of methanol
Thread Content
This is our atmospheric pressure tower. Normally, the higher the pressure, the higher the temperature, and both the top and bottom of the tower tend to rise. However, the temperature at TI-522, located in the middle lower part of the tower bottom, keeps from rising. We don’t dare to reduce the reflux rate too much, as this could result in substandard product quality; on the other hand, if the reflux rate is too high, the alcohol content in the tower bottom becomes too high. Since we haven’t installed a recovery tower, the liquid in the tower bottom ends up being discarded. If this liquid contains alcohol, it represents a waste of resources, and it also causes an unpleasant odor at the site. I have analyzed several reasons; I’d like to ask the experts to check if they are correct. 1. The feed to the atmospheric pressure tower is too large, so the tower cannot handle it all. 2. The pressure in the tower is too high, causing the methanol-volatile components to move downward. 3. Since the amount of water available for circulation is limited and the recirculation flow has been set to its maximum, the temperature of the reflux liquid cannot be reduced. 1. If the large feed volume to the atmospheric pressure tower has an adverse effect, there’s nothing we can do, as in our case the crude methanol produced in the synthesis process is fed directly into the distillation unit. The liquid level in the pressurized tower remains stable, and we also cannot raise the temperature of that tower too much, given that the pressure in the atmospheric pressure tower is already very high. I also don’t dare to set the discharge rate too high, as this affects the liquid level in the pressure tower.
The water cooler of the atmospheric pressure tower is just too inefficient
You can pour some liquid into the feed inlet of the atmospheric tower. Or extract fusel oil.
We just replaced our water cooler with a new one; the old one was clogged up a lot due to internal leaks. The current issue is that the amount of water in circulation is insufficient. The water circulation volume for a set of units was designed at the beginning of plant construction; later, 3 more sets of units were built and still used the same circulating water, with all these units sharing it.
We also collected fusel oils from the side stream, but with no significant effect. Ours is methanol produced from natural gas, so it contains relatively fewer fusel oils.
We also collected fusel oils from the side stream, but with no significant effect. Ours is methanol produced from natural gas, so it contains relatively fewer fusel oils.
The circulating water volume is insufficient, the cooling capacity at the top of the atmospheric pressure tower is inadequate, and the methanol content in the gas phase inside the tower is high; as a result, the methanol content in the liquid at the bottom of the tower is high, which is manifested as a low temperature at the bottom of the tower.
Mm-hm, that’s how I understand it too. Thank you for the guidance.
Do you have a packed tower or a tray tower? Is the heat source for the reboiler in the atmospheric pressure column the gas passing over the top of the pressurized column?
Our atmospheric pressure tower is a double-type tower, with the heat source provided by the vapor from the pressurized tower
From your picture, it shows that the pressure at the bottom of the tower is 21, the pressure in the middle of the tower is 47, and the pressure at the top of the tower is 54. This is the first time I have encountered such a phenomenon. When there is a chance to park, check whether the liquid level in the pressure recovery tank rises. I think it’s possible that there is a leak in the reboiler of the atmospheric pressure tower, which has caused a high methanol level in that tower and led to it operating beyond its capacity.