The liquid level at the bottom of the distillation tower in the diesel upgrading unit fluctuates severely

The feed consists of straight wood chips along with accelerated-aging wood chips; at that time, about 6-7 tons of straight wood chips were used. Does this have any impact? Is it a big impact?

The main reason is the feed rate; the PID control for maintaining the bottom temperature is not effective enough and cannot keep up with changes in the feed rate. It’s necessary to properly adjust the PID settings of the control valve.

As you just said, the large fluctuations in the temperature at the bottom of the tower are the main cause of the fluctuations in the liquid level there. The bottom temperature has a significant impact on the liquid level at the bottom of the tower.

Switch the temperature-controlled hydraulic control to manual for a while; once stable, resume automatic operation

I’ve encountered a similar situation: the liquid level remains stable for a while, but after some time it shows a serrated trend. There is a reboiler at the bottom of the tower, and the instability in the liquid level leads to unstable feed to the reboiler. Since the reboiler operates automatically, it cannot keep up, which results in unstable temperature at the bottom of the tower; however, the feed temperature to the distillation column remains stable. I think it has to do with the processing techniques, the different raw materials used, the amount of material processed, as well as the depth of the reaction and the temperature levels. As for the PID parameters of the instrument hydraulic control valve, there are no issues with them; if it operates stably over time, that means there’s no problem. The PID parameters were also adjusted, but that still didn’t solve the issue. I hope the original poster knows the reason and can explain it to me.

Temperature and liquid level influence each other; changes in the feed rate and feed properties cause significant fluctuations in the bottom temperature, which in turn leads to large fluctuations in the liquid level at the bottom of the tower. That’s what it means, right? The temperature at the bottom of the tower and the temperature at the outlet of the reboiler pump experience large fluctuations, while there are no significant fluctuations in the temperatures at the inlet and outlet of the reboiler. So how can we adjust things to reduce the severity of these fluctuations in the bottom temperature? . .

Our reboiler is operated in manual mode; there are no significant fluctuations in the feed to the reboiler, nor in the temperatures at the inlet and outlet. However, there are noticeable fluctuations in the temperature at the bottom of the tower and at the inlet of the reboiler pump, as well as significant variations in the liquid level at the bottom of the tower. We hope that experts can provide some guidance. . .

So, it’s about checking the changes in the feed temperature of the distillation column. We have a stream that goes from the stripping tower to the pre-vaporization tank and then to the distillation column; look back further to examine the trend in the temperature of the reactor bed.

1. Water in the steam at the bottom of the tower; 2. Poor water separation in the cold high-pressure section, which results in excessive water in the feed to the distillation tower.

This is because the temperature at the bottom of the tower might be too low; you can consider raising it appropriately when you have the chance. . .