TL;DR
High knockout drum level means liquids may carry over to the flare tip. Drain the drum immediately and identify the source of elevated liquid flow.
What you might see
- knockout drum level high alarm active
- liquid carryover visible at flare tip
- flare header liquid dropout increasing
- flare tip noise changing (crackling or pulsing)
Likely causes
Process upset routing excess liquid to the flare header
Knockout drum drain valve stuck closed or blocked preventing normal drainage
Condensation in the flare header from a cold weather event
Relief valve lift event sending a liquid slug to the flare
Required tools
- Level gauge and transmitter
- Gas detector (for drum drain valve area)
- PPE: H2S respirator, chemical splash protection
Safety first
- Flare knockout drum contents are hydrocarbon and potentially sour. Wear H2S monitor and appropriate chemical PPE near the drum drain or pump-out area.
- Liquid carryover to the flare tip is a serious flare system incident. Follow the site emergency response plan if liquid fire at the tip is observed.
- Do not enter the knockout drum for any reason without a full confined space permit and atmospheric testing.
Procedure
- 1
Acknowledge the high level alarm and notify the control room operator immediately.
Warning: Liquid carryover to the flare tip creates a liquid fire event at the tip. Notify operations and establish a watch on the flare tip during high level conditions. - 2
Check the knockout drum drain valve position. Open the drain to the pump-out or blowdown system if the valve is closed.[1]
- 3
Confirm the liquid pump-out pump is running and discharging.[1]
- 4
Identify the source of elevated liquid flow to the flare header. Common sources: process upsets, relief valve leakage, or condensate from a cold header.
- 5
If liquid level is rising despite open drain, verify the pump-out pump flow rate and discharge pressure.
- 6
If liquid level reaches the high-high alarm, notify the plant emergency coordinator. Plant-wide flow to flare may need to be reduced.
- 7
After the level is under control, check the drum level transmitter calibration. A stuck transmitter can delay a genuine high level response.
Sources
John Zink Hamworthy (Koch) John Zink ZTOF / EEF Flare System general technical documentation, John Zink Hamworthy (Koch)
John Zink ZTOF / EEF flare system general knockout drum level control and drain procedures (general)
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