Explosion at a acetylene hydrogenation process

The event occurred at an ethylene production plant.
The plant was shutdown at the time as the supply of compressed air to the gauges had inadvertently been switched off. This failure of the air supply was not inititally recognised because of the low pressure alarm was installed before the isolation valve. Shortly after the plant was restarted an unusually high temperature was observed in an acetylene hydrogenation column. Probably the hydrogen supply had not been turned off completely during the shutdown due to a leaking isolation valve and the continued passage of hydrogen through the column led to a gradual increase in temperature. The column thermometers were all located on the outside of the column and registered 120 degrees C when the interior temperature was probably about 400 degrees C. As the plant operator was unaware of this situation, he attempted to reduce the column temperature by passing in additional ethylene. At this high temperature the ethylene was hydrogenated to ethane and the column temperature rose further to about 950 degrees C as the hydrogenation reactions are exothermic. Also the ethylene decomposed into methane, carbon and hydrogen. The hydrogen supply was turned off and the temperature fell to 700 degrees C. The high temperature and pressure generated by the above reactions caused a leakage of flammable gases at a valve flange on a pipe close to the column. An explosion and fire followed.

The INITIATING cause of the incident was i) the restart of the acetylene hydrogenation reactor after the emergency shutdown, ii) ethylene hydrogenation produced excessive heat.

ethylene production, acetylene hydrogenation, air compressor, acetylene reactor

The plant was shutdown

The fire continued to burn for 80 hours. 500 tonnes of hydrocarbons leaked out and burned. The acetylene hydrogenation column and surrounding equipment were totally destroyed. One tenth of the overall plant was burned.

Firefighters took over 5 hours to achieve a measure of control but the fire continued to burn for a further 80 hours because there was no way of preventing 500 tonnes of hydrocarbons leaking out of the plant and feeding the fire.

The series of event which brought to the run-away hydrogenation reaction showed the crucial role of the facility management and of the proper training of personnel.

According to the source (see references), The following measures were taken:
1. alarm systems were installed,
2. Vessels containing liquefied gas were redesigned to allow for a more rapid depressurisation and discharge,
3. Pipes were labelled and made more easy to be distinguished from each other,
4. Sprinkler systems were improved and made more effective,
5. Personnel was properly trained,
6. Operation standards reviewed and improved.