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Crisis Groups For Disaster Management
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Explosion in reactor for ethyl cellulose manufacturing

In a medium size factory manufacturing ethyl cellulose explosion followed by fire took place on16-3-2002 around 19.30 hours

Incident:
Company was manufacturing ethyl cellulose using caustic flakes, wood pulp, ethyl chloride, air, recovered solvent (crude eather) at 120ºC temp. And 22 to 23 kg./cm2 pressure. This reaction is an exothermic reaction. Once the above-mentioned temperature is achieved, steam supply is stopped. Temp. 145ºC and 28-30kg/cm2 is pressure is maintained for 16-20 hrs. Thereby ethyl cellulose is produced.

Company had changed the process. Instead of air, pure oxygen from cylinder and cobalt chloride was used as a catalyst so as to reduce the time cycle. In addition to this, the reactor, parallel reflux line were fabricated in-house and installed to recover the solvent vapour generated during reflux.
With the above changes in the process and modifications, the process was started. Pressure inside the reactor was suddenly raised. Reflux line from the welding broke. Flange of the bottom valve provided at the reactor bottom also broke and ball inside ball valve was thrown out due to pressure and there was an explosion followed by fire.

Cause of the incident:
Ethyl Chloride is a highly explosive material. It reacts vigorously with oxidizing agent. Pure oxygen from the cylinder and cobalt chloride was used as a catalyst. Because of this, vigorous reaction started and pressure inside the reactor rose suddenly. Stop valve which was installed before the safety valve, was closed, and so the safety valve and rupture disc, which were installed on the reactor, could not function. Valve on the reflux line was opened and due to this, pressure was exerted in the reflux line and it broke from the welding. Flange of the bottom valve broke and ball inside the ball valve was thrown out with pressure. Material inside the reactor came out with pressure and there was an explosion followed by fire.
Area & persons affected: Due to this accident 2 workers died on the spot and 4 workers died during treatment. Plant, building and equipment was also damaged.

Action taken for non-repetition of such incident:

¨ Safety valve of adequate size shall be mounted on the pressure vessel (ethoxylation reactor). The outlet of the safety valve shall be connected to blow down tank. Vent shall be provided on blow down tank and outlet of the vent shall be connected with flame-arrestor.
¨ Reaction vessel shall be isolated with other process by fire – retardant material and explosion proof wall.
¨ Before making any change in the process, process details, its hazards and measure to control the same shall be communicated to CIF before 15 days.
¨ Non-sparking tools shall be used wherever flammable and explosive materials are used in the factory.
¨ Any addition on the pressure vessel/repairing is carried out, it shall be tested by competent person before it is put to use and the testing report in the prescribed form shall be kept.
¨ Sensor with alarm shall be provided for detection of ethyl chloride and other solvent.
¨ Considering the complete safety of the worker, trial/laboratory/pilot experiment shall be carried out before making any change in the process


 

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