release at a hydrocracker in a refinery plant

The event affected the hydrocracker unit. A sudden release into a cracker compressor flare header destroyed a safety relief valve and damaged a sight glass on a liquid collection pot. As a consequence, release of hydrogen rich vapour to atmosphere occurred, necessitating a shut down of the iso-cracker.

The damage was limited to that previously described, and there were no injuries. The cracker was returned to service four days later.

According to the ICHEME report (see reference), the INITIATING cause was an accumulation of liquid in the flare header. The problem was compounded by undersized header and piping, and triggered by unstable operating conditions.

Considering the recommendations reported by the ICHEME report, it could be concluded that contributing or root causes were inadequacy of related design and of procedures.

hydrocracker compressor and valve

As reported by the ICHEME report, the losses were limited to reduced production and repair costs; however, there was a potential threat to life and major equipment.

The following recommendations are reported (ICHEME) as lesson learnt:
1. Drain drip pots frequently to prevent liquid build-up.
2. Locate source(s) of liquid and remedy now, where possible, or during the shutdown.
3. Ascertain any testing required for individuals exposed to high levels of noise or hazardous vapours.
4. Redesign the liquid removal system to ensure no build-up.
5. Redesign the flare header to reduce velocity and back pressure.
6. Adjust the operating and emergency procedures to reflect the dangers of rapid feed rate changes.
7. Review the maintenance requirements for compressor alarms and trips.
8. Review the refinery quality control procedures for work done in outside workshops.