Explosion and fire at a diesel hydrogenation plant

The incident affected the raw material buffer tank (design pressure 0.38 MPa) of a diesel hydrogenation unit in a refinery. This buffer tank is located between the hydrogenation reactor and the raw material storage tank. During pressure fluctuations in the lubricating oil system of a hydrogen compressor, the operator handled the situation improperly, resulting in an abnormal shutdown of the compressor, causing the hydrogen feed pump to interlock and stop.The outlet valve was not closed in time and two check valves failed. The high-pressure hydrogen gas in the system flowed back into the buffer tank. This caused its overpressurisation, leading to a over-pressure tank rupture and a hydrogen-air explosion followed by a fire, while diesel liquid spilled out to form a liquid pool on the ground.

The INITIATING cause of the explosion was due to the tank being over-pressurised with hydrogen.
According to a preliminary analysis, the sequence of events was the following:
(1) Low lubricating oil pressure on hydrogen circulation compressor.
(2) Compressor automatic shut-down on low oil pressure (unclear if this was an automatic or manual action).
(3) Hydrogenation raw material feed pump stopped automatically because interlocked with the compressor shutdown
(4) Operator’s failure to close pump outlet on time. This valve was not set-up with an emergency shutdown.
(5) Pump check-valve failure.
(6) High-pressure fluid, at a pressure of 5.7MPafrom the reaction system flowed back into the hydrogenation raw material buffer tank through the raw material pump inlet and outlet.
A CONTRIBUTING CASUE was erroneous actions taken by the operator. However, the ROOT CAUSE was an inadequate safety design, which failed to proper interlock al the components critical to properly handling the emergency. A possible additional element could have lack of instruction and training of the operator. .

check-valves
raw material feed pump,
H2 buffer tank,
H2 compressor

The hydrogen compressor was experiencing pressure fluctuations in the lubricating oil system

DESCRIPTION OF THE FACILITY
The plant was producing (600,000 tonnes/year of diesel).

2 fatalities, 1 injured person economic loss of about Euro 0.48 million.