Hydrogen and Diesel Fire at Hydrodesulfurisation Unit Inlet Pipe
The fire, 1 m high fire occurred in a pipe at the inlet of the hydrodesulfurisation unit of a refinery. The fire was caused by the leak of the pipe content, hydrogen and diesel fuel. According to the first elements of observation, a leak on a bolted assembly (flange) at the level of an insulation gasket of the reactor would be at the origin of the incident.The fire was detected visually and was located 25 m above the ground. The personnel was evacuated. The operator did not extinguish the flame in order not to generate a hydrogen cloud, which is highly explosive. The unit was gradually shut down with decompression to a site flare. The gas contained in the unit, feeding the leak, was progressively replaced by nitrogen. A preventive foam mat was put in place under the reactor to protect against a possible ground pool fire.
Event Date
April 25, 2019
Record Quality Indicator
Region / Country
Event Initiating System
Classification of the Physical Effects
Nature of the Consequences
Causes
Cause Comments
During the work of replacing the flanges, the operator observed the good flatness of the flanges but a deformation of the gasket. The operator considers that this deformation would have occurred due to the over-tightening of the flange during the last maintenance shutdown. Moreover, at the time of the event, the desulfurization unit was at the end of its cycle with a replacement of the catalyst initially planned 1 month after the event. According to the operator, the loss of catalytic activity at the end of the cycle is compensated by an increase in the reaction temperature. This temperature increase, combined with the over-tightening of the flange, would be the cause of the leak.
Facility Information
Application Type
Application
Specific Application Supply Chain Stage
Components Involved
hydrodesulfurization unit, pipe
Storage/Process Medium
Location Type
Location description
Industrial Area
Pre-event Summary
At the time of the event, the desulfurization unit was at the end of its cycle with a replacement of the catalyst initially planned 1 month after the event. Due to the loss of catalytic activity at the end of the cycle, the reaction temperature is usually increased.
Consequences
Number of Injured Persons
2
Currency
Lessons Learned
Lessons Learned
As corrective measure, new gaskets and bolts were installed, with a controlled and progressive tightening throughout the start-up of the unit.
Event Nature
Emergency Action
The personnel was evacuated and a emergency operation room was installed.The operator did not extinguish the flame in order not to generate a hydrogen cloud, which is highly explosive. The unit was gradually shut down with decompression to a site flare. The gas contained in the unit, feeding the leak, was progressively replaced by nitrogen. A preventive foam mat was put in place under the reactor to protect against a possible ground pool fire
Release Type
Release Substance
Ignition Source
Detonation
No
Deflagration
No
High Pressure Explosion
No
High Voltage Explosion
No
Flame Type
Source Category
References
References
Event description no. 53363 in the French database ARIA
https://www.aria.developpement-durable.gouv.fr/accident/53363_en/?lang=…
(accessed October 2021)