Fire of a Hydrogen-Rich Gas Mixture in a Fertilizers Plant
The event occurred on vent stack of an ammonia synthesis unit. The release of the gas was more specifically on the water purge line or the hydraulic guard of the vet stack. The process gas consisting in 75% hydrogen, ignited. The fire could be extinguished the by the emergency decompression of the unit and the automatic shutdown of the synthetic gas turbocharger.
Event Date
November 15, 2011
Record Quality Indicator
Region / Country
Event Initiating System
Classification of the Physical Effects
Nature of the Consequences
Causes
Cause Comments
As reported with details the ARIA description (see references), the investigation performed by the plant operator has shown that a series of not-coordinated detection of fluid levels at the exit of the reactor caused an over-pressure in the chimney. This has displaced the liquid content of the hydraulic guard at the bottom of the chimney and some of the syngas passed through the purge line of the guard and ignited. The accidental scenario of syngas emissions from the purge line had not been formally identified by the operator, nevertheless was covered by the general provisions of the emergency plan. The root cause can be identified in some design, such as the incorrect positioning of the 2 low level sensors installed in the separator, and the dimension of the withdrawal valve.
Facility Information
Application Type
Application
Specific Application Supply Chain Stage
Components Involved
vent stack, ammonia reactor
Storage/Process Medium
Location Type
Location description
Industrial Area
Currency
Lessons Learned
Lessons Learned
Although the ARIA report (see references) does not mention any lesson learned, the very accurate and detailed findings from the post-accident investigation (see causes) suggest the following corrective actions:1) to improved sensors location, and the way how their signals are worked out in the safety system of the plant (new HAZOP).20 to better understand the flow dynamics also in accidental cases and adapt the design of the unit.
Event Nature
Emergency Action
The plant operator stated the emergency, the unit is de-pressurised and the plant fire brigade define a safety perimeter till the natural end of the fire.
Release Type
Release Substance
Hydrogen Release Concentration (%)
75.00
Ignition Source
Detonation
No
Deflagration
No
High Pressure Explosion
No
High Voltage Explosion
No
Flame Type
Source Category
References
References
Event description in the French database ARIA
https://www.aria.developpement-durable.gouv.fr/accident/41517/
(accessed October 2020)