What to do if no qualified product can be obtained from the atmospheric tower in a three-column distillation system
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The methanol distillation plant has a design capacity of 30,000 tons per year. During recent operations, it was found that no pure methanol could be obtained from the atmospheric pressure tower (this used to work fine before). The analysis of the liquid obtained showed that its specific gravity was fine, but the water content was too high. The temperatures in various sections of the tower were normal. Waxes were found floating on the surface of the residual liquid discharged from the system. Today, it was also discovered that the pipe for collecting fusel oils from the atmospheric pressure tower was blocked. What could be the cause? Is there a leak in the top condenser of the atmospheric pressure tower? Since waxy deposits were found in the residue, it is possible that the internals of the atmospheric pressure tower were blocked by wax. Today, after heating the tower, it was found that the pipeline for extracting fusel oils was blocked. Could it be that the wax melted down after heating the tower, thereby causing the blockage in the pipeline for extracting fusel oils? (The crude alcohol is brought in from another factory for processing on their behalf.) Please help analyze this. Also, I would like to ask whether your factory’s pressure tower and atmospheric tower each have their own product collection tanks This post was last edited by ddfmy on 2009-3-12 22:01]
It’s very likely that there is a leak inside the cooler; another possibility is that severe wax formation in your tower reduces the separation efficiency. In this way, all the indicators appear normal, but the product will still be Unqualified; so what if we examine the temperature at the bottom of the atmospheric pressure tower in more detail?
Find a way to take samples from the vapor pipes at the top of the tower for analysis, to determine whether there is a difference in moisture content before and after the condenser; if such a difference exists, it indicates an internal leak in the condenser!
If sampling and analysis before the product cooler show it to be qualified, then there is a leak in the cooler； If the moisture level is high, it’s due to the tower; during tower cleaning, the moisture remaining inside has not been removed yet. Raising the temperature at the bottom of the tower and increasing the reflux rate will help remove that moisture.
The products are all collected in one storage tank; there’s no need to separate them
Is the amount of reflux too low? That will result in the product not meeting the quality standards. Another issue is that feed to the atmospheric tower is added too early during operation
If all the indicators are normal, it may be caused by a leak inside the condenser; sampling and analysis from both the front and back of the condenser should be carried out to determine this.
Not necessarily; if there is a leak inside the condenser, it cannot explain why the specific gravity remains normal. It’s possible that wax has accumulated in the top condenser of the tower, affecting the condensation process. As a result, although there isn’t a significant change in the reflux rate, the reflux temperature rises, causing the heavier components in the tower to move upward and end up in the product. Even the residue at the bottom of the tower contains wax. It seems that the tower temperature is too low; therefore, it’s necessary to increase the tower temperature appropriately, reduce the tower pressure, and increase the reflux rate. As for the crude alcohol, it is sourced from external manufacturers – whether the quality is consistent across batches could also help identify the reasons for the increase in wax content
After hot washing, the moisture remaining in the tower was not removed; therefore, the reflux rate was increased to maintain an appropriate temperature. Maybe it will get better
A full analysis of the product from the atmospheric tower should be conducted; if paraffin is present, the analysis on the 8th floor will be accurate； If there is no paraffin but other light components are present, it may be due to a slight leak in the cooler; the specific gravity remains within the acceptable range because of the presence of these light components.
The condenser is leaking, or the level of fusel oils is too high
Our unit is also facing such a problem, and it hasn’t been resolved yet! Tomorrow, we’ll discuss it with our leader based on what everyone has said, hehe!
What everyone upstairs has said makes sense; I think, apart from leaks in the water cooler, it’s caused by flooding. First, check whether the pressure difference between the top and bottom of the tower is too large; in other words, determine if the tower top is at near-negative pressure. If so, reduce the reflux and feed rate to adjust the temperature at the tower bottom, and the moisture level will decrease after 2 hours. Also, the small reflux ratio causes water to be carried upward; check that the temperature difference and pressure difference between the top and bottom of the tower are low. The reflux ratio should be increased, but not beyond 3. When increasing the reflux ratio, it must be done gradually, otherwise flooding may occur.
There might be two reasons: 1. The water cooler is leaking, resulting in high moisture content in the product. 2. The water cooler forms wax, resulting in a high reflux temperature, which affects product quality.
The possibility of flooding is very low! It is likely due to poor cooling performance; check whether the heat exchanger is leaking or caked with wax.
In my opinion, this phenomenon occurs when all the process parameters are normal; so there must be no problem with the water cooling temperature, right? The white substance is probably paraffin. Since you are handling processing, you should ensure that high-quality products enter the factory. Then find ways to eliminate the reasons for the product’s non-conformity. By analyzing the product parameters before and after the water cooler, it can be determined whether this is the cause. Assuming it’s paraffin, if it floats on the surface of the liquid, that means the temperature isn’t high enough; the melting point of paraffin is in the low tens of degrees. If the temperature is low, then the reflux will definitely be high. I hope you can upload the data on this aspect for us to take a look
Check whether the density after pre-treatment exceeds 0.88 g/cm3; if it does, reduce the amount of water. If the water level is not high, lower the feed to the atmospheric pressure tower to the lowest level.