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[Alaa55]

We are facing an issue in our plant and would appreciate your advice.

Our level control valve is malfunctioning and suspected to be blocked or internally damaged. As a result, it cannot properly handle the liquid in the knock-out drum. To maintain operation, we have been using a manual bypass globe valve to drain the accumulating liquid from the vessel.

However, when we open this bypass valve, we sometimes encounter high pressure in the downstream vessel, leading to PSV lifting. This problem did not occur when the control valve was functioning normally.
 

Key details that may be relevant:​

• We confirmed there is a liquid seal before opening the bypass valve to avoid gas blowby.
• The bypass valve is only opened slightly (small opening).
• The downstream vessel level is typically around 80% due to a pumping issue.
• The pressure increase in the downstream vessel happens almost immediately after opening the bypass valve, leaving no time to close it before PSV lifts.
• The knock-out drum is designed to separate free water from the feed, which is mainly methane.

Since we will need to operate with the bypass valve until the next shutdown to repair the control valve, we are concerned about the risk of repeated high-pressure incidents in the downstream vessel.

 Question: Based on the above, where do you think the problem lies, and how can we avoid this situation?

I have attached a simple schematic of the process for reference.

 

 Untitled Diagram (4).jpg   38.12KB   0 downloads

Edited by Alaa55, Today, 04:43 AM.