Explosion in a Chemical Plant, initiated by Hydrogen Formation
An explosion and fire occurred at a 3000-gallon (approx. 11400 l) reactor, part of the production process of linear alkyl benzene (LAB), Process materials released from the various vessels and piping fuelled a subsequent fire that took approximately 2 hours to extinguish.As reported by Ali Reza (Ali Reza et al., 2007, see References), before the explosion, the bottom of the reactor was plugged with approximately 180 gallons (approx. 800 l) of a sludge-like mixture of coarse aluminum powder, aluminum chloride and various hydrocarbons. The explosion occurred approximately 10 minutes after steam was introduced at the bottom of the reactor in an effort to break up the sludge accumulation.The investigation identified as root cause the direct and sustained contact between the steam and the sludge at the bottom of the reactor, inducing an exothermic hydrolysis of aluminum chloride which produced mainly hydrogen chloride vapour and hydrogen gas. During laboratory tests, this reaction was able to generate pressure up to 45 bar and temperature above 370 degree Celsius (700 Fahrenheit).
Event Date
October 13, 1998
Record Quality Indicator
Region / Country
Event Initiating System
Classification of the Physical Effects
Nature of the Consequences
Causes
Cause Comments
The immediate cause was the decision to use water steam to clean the chemical sludge. The U.S. CSB (see References) identified the root cause in the lack of a Management of Changes system. The plant operator had decided to change of the catalyst use for the reaction few month before.An additional contributing cause was the misunderstanding occurred when the shifts responsible workers communicated with each-others. The injection of steam was not meant to be continuous and prolonged.
Facility Information
Application Type
Application
Specific Application Supply Chain Stage
Components Involved
alkyl benzene production, reactor; steam; chemical sludge;
Location Type
Location description
Industrial Area
Pre-event Summary
About three months prior to the incident, the plant changed its process technology and discontinued the direct addition of aluminum chloride to the reactor.Instead, powdered aluminum was added to the reactor, where it combined with hydrogen chloride to form the necessary aluminum chloride. Shortly after the plantswitched to the new process, the reactor became fouled with a sludge-like catalyst residue (CBS Bulletin, see References).Before the incident, the process plant was shut down for routine maintenance. The need to change pipes to the reactor required its emptying. However, the operators were unable to remove the liquid hydrocarbons from the reactor because the bottom outlet nozzle appeared plugged with a solid, sludge-like material. Initial attempts to clear the solid plug with nitrogen were unsuccessful. The system was flushed for 6 hours with fresh paraffin to reduce the benzene level in the system. A vacuum truck was then used to remove the majority of the liquids from the reactor via a side man-way, but approximately 185 gallons of sludge remained inside the vessel.Having demonstrated that the sludge could be broken with water, a first attempt was done, without results. it was then decided to use pressurized steam (Ali-Razi, 2002).
Lessons Learned
Lessons Learned
The CBS Bulletin 2001-04-SB dedicated to this case identifies as root cause the failure to implement a systematic Management of Changes process. The situation at the plant was not involving emergencies that required rapid decisions. Time was available to look into the circumstances more thoroughly. To maximize the effectiveness of a Management of Changes system, the following activities should be included: 1.Define safe limits for process conditions, variables, and activitiesand train personnel to recognize significant changes. Combined with knowledge of established operating procedures, this additional training will enable personnel to activate the MOC system when appropriate. 2.Apply multidisciplinary and specialized expertise when analysing deviations. 3.Use appropriate hazard analysis techniques. l Authorize changes at a level commensurate with risks and hazards. 4.Communicate the essential elements of new operating procedures in writing. 5.Communicate potential hazards and safe operating limits in writing. 6.Provide training in new procedures commensurate with their complexity.7.Conduct periodic audits to determine if the program is effective.
Event Nature
Emergency Action
Unknown
Detonation
No
Deflagration
No
High Pressure Explosion
No
High Voltage Explosion
No
Source Category
References
References
CBS Safety Bulletin No. 2001-04-SB | August 2001