High liquid level in hydrogenation unit
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The liquid level of the cold high-pressure section fluctuates greatly, while the overall trend of the interface level remains stable. Occasionally, the opening degree of the liquid level control valve reaches zero – what’s causing such severe fluctuations in the liquid level?
1. Try operating the control valve in manual mode; if the liquid level stops fluctuating, it’s a PID issue. 2. If the level still fluctuates, check whether there are any problems with the control valve itself. 3. Compare the liquid level indicated by the instrument with the actual level on site to rule out instrument failure. 4. If none of these issues exist, then examine your operation procedures – take some sulfur-containing wastewater and check whether it contains oil, as well as whether the oil-water separation is adequate. I’m not sure if you’re using a thermal high-pressure process; if so, check the liquid level in that system. Generally, there shouldn’t be any fluctuations in the liquid level in a reaction system
It is a high-temperature high-pressure process, but the liquid level in this system fluctuates steadily. Looking at the overall trend, the fluctuations in the cold high-pressure liquid level are fairly stable. Sometimes, after the control valve is set to its full closed position, this condition can be maintained for an hour; although the liquid level gradually drops, it starts to rise again after a while, and the rate of increase is quite fast.
A too low flow rate of the control valve can also cause this issue. High-pressure control valves are usually pressure-reducing type valves; in some cases, control valves that are chosen to be too large will start to leak over time
It was only during recent operations that I noticed that the liquid level fluctuated unevenly and significantly. The control valve is equipped with interlocks, including a low liquid level interlock. Although the fluctuations in the liquid level are quite severe, it has not dropped below 42%. The liquid level will rise rapidly in a short while
The properties remain largely unchanged, and the temperature stays stable after high-pressure cooling!
If both the system pressure and the cold low-pressure are stable, the properties of the feedstock and the reaction temperature are fine, and the valves are in good condition, it could be caused by PID tuning issues. Last time, it was fluctuations in cold low-pressure that caused fluctuations in cold high-pressure
It could be an issue with PID tuning or the control valve; try using another control valve. If the situation improves, then it’s likely that the control valve is blocked
If it really is a PID issue, then how should it be adjusted?