Release of hydrocarbons and hydrogen in a refinery

The accident occurred on one of the heat exchangers of the hydro-desulphurisation unit.
The role of the exchanger , located between the charge pumps and the furnace, was to heat the charge using the hot products from the reactor. Before the exchanger, pressurised hydrogen is injected into the charge. The exchanger was equipped with interchangeable bundles mounted with deflector plates.

During a shutdown, some beams were mistakenly reassembled upside down. When the installation restarted and the compressor of the hydrogen circuit arrived at 75% of its capacity, one of the deflectors was blown off and obstructed the inlet of the exchanger. Consequently, the safety device of the compressor triggered the compressor stop and the pressure release valves released part of the contents.

The reason for the over-pressurisation of the compressor and the pressure relief activation was the block of part of the gas flow into the heat exchanger tubes bundle.

A ROOT CAUSE component was a human error occurred when re-installing the exchanger's components inverted. However, an additional factor was the failure of the supervision and final inspection procedure to detect the mistake.

heat exchanger

The desulphurisation unit was restarted after a shutdown during which component of the heat exchanger unit were (wrongly) reinstalled

Part of the hydrocarbon load, including hydrogen, was released to the environment.