The impact of poor heat transfer in the atmospheric pressure tower condenser on the system
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Recently, the atmospheric pressure tower at my facility was not operating properly. Scaling on the condenser at the top of the tower impaired heat exchange, which led to high tower pressure (within the acceptable range) and high reflux temperature. Strangely enough, the moisture level was within normal limits. Methanol could be detected in the bottom product of the atmospheric pressure tower in percentages, and the recovery tower also wasn’t functioning well; the COD levels were often above the acceptable limits. I would like to ask everyone what could be causing these issues. Additionally, the load has decreased, with almost no other adjustments.
It would be great if there were pictures; actually, this is normal – the temperature rises as pressure increases. However, the distillation temperature for methanol remains constant. If the reflux temperature is high, then the amount of reflux should also be significant, so as to keep the moisture under control. If the reflux amount is low, it won’t be possible to control the excess moisture. A high COD level in the recovery tower is related to the condensation process: once moisture is condensed earlier, less will remain later on.
That’s probably due to the high value of my previous feedback control
If the methanol content in the residue at the bottom of the tower is in the percent range, that’s quite high; we usually keep it below 100PPM. I think the main reason for this issue in your case is an insufficient heat load at the bottom of the tower. I’m not sure what temperature is achieved at the bottom of your tower Try to increase the pressure in the pressurized tower
The atmospheric pressure reflux control is way too high
A high pressure at the top of the atmospheric pressure tower leads to poor separation efficiency; as a result, methanol in the bottom of the tower cannot be completely separated, resulting in a high methanol content there. It is normal for the moisture level at the top of the tower not to exceed the specified limits; when the pressure is high and the temperature remains within the normal range, the moisture will not evaporate to the top of the tower. Naturally, the COD level of the wastewater from the recovery tower is above the standard, as it is connected to a column under normal pressure. What specific range does the tower top pressure you mentioned falling within refer to? This indicator is determined based on specific devices, so it may not be the same in all cases. Backflow also has an impact; you can reduce the backflow appropriately and try lowering the temperature at the bottom of the tower.
It’s around 98 degrees when it’s not normal, and usually it’s below 95 degrees
The highest pressure here is 40 KPa. I think this pressure isn’t very high for the system. Why doesn’t the water level rise? After all, the temperature has increased and the amount of methanol returning also decreases; yet the methanol level at the bottom of the tower still goes up
The last edit to this post was made by sdwfsgyykai on 2019-12-18 at 07:57. Do you control the ethanol content in methanol, and if so, at what level?
Generally, control is carried out based on customer requirements; after all, there are no such requirements in national standards. Some customers request compliance with Federal AA standards, which requires the ethanol content to be kept below 10PPm.