Reasons for the persistently high top pressure in the distillation tower

The light component content is even lower than the designed value, indicating incomplete separation; this is likely due to an insufficient number of tray levels or an excessively high opening rate of the trays, resulting in liquid leakage. If it can be confirmed that the number of plates is fine, check whether the pressure at the bottom of the tower is normal; if it is high, reduce the reflux rate and try again.

Can the flow rate of the circulating water entering and leaving the condenser be increased? If so, it can also have a certain effect on reducing pressure. There’s no problem with the condenser itself, such as scaling. From the composition perspective, the separation effect seems to be suboptimal. Is the pressure difference between the top and bottom of the tower (which can reflect the gas velocity) within normal ranges? All of these can be considered.

What are the changes in the temperature and pressure at the bottom of the tower? If the component analyses of the top and bottom of the tower are correct, the pressure difference fluctuations must be significant, indicating that liquid starvation has occurred within the tower, with back-mixing taking place in both the gas phase and the liquid phase. It can simultaneously reduce the consumption of circulating water and steam, allowing for gradual adjustment until the system stabilizes

This tower is new and has just been put into operation; it is currently under commissioning. It’s not possible to increase the pressure at the bottom of the tower, nor is it easy to raise the temperature, unless the pressure at the top of the tower is higher

Could you provide the operating conditions? Based on what you’ve said, it should be a pressure tower; you can analyze it from the following points: 1. First of all, what you need to do is conduct a material balance, which is fundamental in chemical production ； From here, you can determine the amount of venting; if it exceeds the designed value, it indicates a problem with the design of the top condenser or that there is not enough condensing medium ； Also, could it be that too much shielding gas is being used for the tower (if one is used)? 2. The pressure in the tower bottom cannot be increased; the designed pressure difference for this tower is quite low, so there should be no problem with that, which indicates that the tower still has some headroom ； 3. If the temperature at the bottom of the tower cannot be increased, it might be a problem with the reboiler at that location. However, low pressure leads to lower temperatures as well. But you should primarily consider the content of light components at the bottom of the tower in order to determine the appropriate temperature; you shouldn’t rely solely on the temperature value, as it is merely a figure that helps provide an intuitive assessment during operation ； 4. Neither the top nor the bottom of the tower is performing well; could increasing the reflux rate help? Since the pressure difference in this tower is very low, there should be no problem with increasing the reflux rate ； However, whether to use this depends on whether your condenser and reboiler can handle it.

Increasing the height of the plate tower is quite troublesome; the flow rate and pressure of the circulating water have been increased as well, but it seems like everything has already been taken into account. Turn on the manual vent to reduce the pressure, but this isn’t a solution that can be used in the long term. Check the pressure regulation of the reboiler; it might help, but the proper solution is to sue the design firm and the equipment manufacturer.

It seems that the situation described on the 4th floor is more similar. What worries me the most now is the possibility that the openings in the tower plates might be too large, as that would cause problems

Increase the reflux and reduce the steam load, and readjust the draw rates at the top and bottom of the tower according to the composition of the feedstock.