Explosion at the hydrogenation tower of a refinery

The explosion occurred inside the lower hydrogenation tower of a hydrogen peroxide unit, damaging the distribution tray inside the tower. it caused 4 fatalities, 2 injuries and considerabledamage to the installation.

The company was replacing the catalyst, becasue of the decresed catalyst efficiency in the fixed bed of the lower hydrogenation tower.
This is the DETAILED SEQUENCE:
• January 14: the old catalysts was unload of the lower and middle towers;
• February 8: The middle tower was refilled, the upper and lower towers were not refilled;
• March 13: Feeding and start-up was initiated, but only partial flow of the fixed bed in the middle tower and an uneven distribution of working fluid were noted;
• March 16: The leader of the hydrogen peroxide plant replaced the nitrogen inlet pipeline of the middle tower with a pure hydrogen inlet pipeline, but the problems of partial flow of the fixed bed in the middle tower and uneven distribution of working fluid were not resolved;
• March 17: The technician of the new catalyst supplier suggested adding a few more sieve trays to the middle tower distribution tray;
• March 18: from 8:00 am to 9:00 am, the leaders agreed to measure the upper part of the lower tower in order to install the middle tower working fluid inlet facility. At 8:40, workshop director and other 5 employees went to the third-floor platform of the device to check the measurement situation. At 9:26, two employees went to the platform on the fifth floor. At 9:32, one employee entered the lower tower at the same time. At 9:47:40, an explosion occurred inside the lower tower.

The INITIATING cause was the hydrogen inlet line shut-off valve leakage: hydrogen gas leaked internally into the tower and mixed with the air entering from the upper manhole, creating an explosive atmosphere and igniting .

A CONTRIBUTING CAUSE was the fact that the personnel of the enterprise did not take effective isolation measures and entered the lower tower of the hydrogenation tower to work.

ROOT CAUSE was a lack of risk management, of effective maintenance procedures, of risk assessment, of preventive and mitigation measures.
A possible ignition source was sparks from electrostatic frictions produced by the use of non-explosion-proof tools. Operators were not carrying explosion-proof steel socket spanners when accessed the tower.

hydrogenation tower

The event occurred during repalcement of the catalysst i nthe hydrogenation tower.

DESCRIPTION OF THE H2O2 PRODUCTION PROCESS
Hydrogen peroxide (H2O2) is manufactured by the anthraquinone process, originally developed by BASF in 1939.
(1) It begins with the reduction of an anthraquinone to the corresponding anthrahydroquinone, typically by hydrogenation on a palladium catalyst.
(2) The anthrahydroquinone is then brought in contact with oxygen and undergoes autoxidation: the labile hydrogen atoms of the hydroxy groups transfer to the oxygen molecule, to give hydrogen peroxide and regenerating the anthraquinone. Most commercial processes achieve oxidation by passing compressed air through a solution of the anthrahydroquinone, with the hydrogen peroxide then extracted from the solution and the anthraquinone recycled back for successive cycles of hydrogenation and oxidation.

The net reaction for the anthraquinone-catalysed process is: H2 + O2 → H2O2

[https://en.wikipedia.org/wiki/Hydrogen_peroxide]

4 fatalities, two injuries due to burns, a direct economic loss of 0.5 million Euro.

Equipment maintenance and management were not in place. Since the start of the operations, there have been no operation review and regular maintenance.
This, and the absence of proper risk assessment, explains the absence of effective preventive and mitigating measures during the operation of catalyst replacement.