Exothermic Runaway Decomposition Causes Ethylene Explosion
During the polymerization of ethylene in a 750 liters pressurized reactor, an exothermic runaway decomposition occurred and ethylene and its decomposition products were released through the two reactor vent stacks and via the dump valves on the supply lines. The released gas (cloud) was ignited apparently by the hot carbon particles obtained by the decomposition of the ethylene and an aerial explosion occurred. The following substances were involved in the accident: Ethylene (60 kg). Ethylene (together with the decomposition products about 60 kg). The decomposition products are normally carbon, hydrogen and methane, but no data are available about their amounts.The explosion caused structural damages to the surrounding plants but no data are available about their cost. The released gas was ignited because the automatic water quenching system operated but failed to prevent the aerial ignition. This was due to a quenching system design not appropriate. The intervention of automatic isolation valves on the reactor were not fast enough to prevent more unused ethylene entering the reactor and therefore to feed the aerial explosion. Automatic dump valves on the feeding line operated 2 seconds to dump residual ethylene to atmosphere resulting also in feeding the aerial explosion.
Event Date
May 25, 1992
Record Quality Indicator
Region / Country
Event Initiating System
Classification of the Physical Effects
Nature of the Consequences
Causes
Cause Comments
The initiating (process-related) cause was an exothermic runaway decomposition which caused a reactor pressure increase with consequent release of ethylene and its decomposition products. The cause of the ignition of the released gas was probably the hot carbon particles obtained by the decomposition of the ethylene). The automatic water quenching system operated but failed to prevent the aerial ignition. The intervention of automatic isolation valves on the reactor were not fast enough to prevent more unused ethylene entering the reactor and therefore to feed the aerial explosion. The root cause could be attributed to inadequate system design (quenching system and valve opening).
Facility Information
Application Type
Application
Specific Application Supply Chain Stage
Components Involved
polymerization reactor, exhaust valves, quenching system
Storage/Process Medium
Location Type
Location description
Industrial Area
Operational Condition
Pre-event Summary
Polymerization of ethylene was carried out in a 750 liters pressurized 19 years old reactor in a polyethylene plant of a petrochemical factory.
Lessons Learned
Lessons Learned
MEASURES TO MITIGATE THE EFFECTS OF THE ACCIDENT: After the accident, the following measures were established: 1- to use new smart sensors to speed up the reactor isolation and, therefore, to reduce the amount of gas released; 2- to vent ethylene to a separate, contained system or increase considerably the delay before the automatic dumping of the lines contents.
Event Nature
Emergency Action
The water quenching system automatically operated but it failed to prevent the aerial ignition of the released gas. The intervention of automatic isolation valves on the reactor were not fast enough to prevent more unused ethylene entering the reactor and therefore to feed the aerial explosion. Automatic dump valves on the feeding line operated 2 seconds to dump residual ethylene to atmosphere resulting also in feeding the aerial explosion.
Emergency Evaluation
The water quenching system automatically operated but it failed to prevent the aerial ignition of the released gas. The intervention of automatic isolation valves on the reactor were not fast enough to prevent more unused ethylene entering the reactor and therefore to feed the aerial explosion.
Release Type
Release Substance
Release Amount (kg)
60.00
Ignition Source
Detonation
No
Deflagration
No
High Pressure Explosion
No
High Voltage Explosion
No
Source Category
References
References
Event description in the European database eMARS
https://emars.jrc.ec.europa.eu/en/emars/accident/view/c1689f9d-1b3a-870…
(accessed September 2020)