runaway from a propylene hydrogenation reactor

During the start-up of a propylene hydrogenation reactor, very high temperatures were generated in the catalyst bed. At the time, propylene and hydrogen were being fed to the reactor which contained a granular catalyst. The temperature rose rapidly, and the hydrogen supply valve tripped at 176 degrees C. Despite the removal of the reactant supply, the temperature continued to rise to more than 600 degrees C, only stabilizing after the reactor had been isolated and depressurized.

It was concluded that the start of the incident was caused by wrongly setting the propylene/ hydrogen ratio as a result of faulty calibration of the flow instruments. This allowed the temperature to rise to the point where spontaneous exothermic polymerization of propylene occurred.
Investigation of the incident was hampered by the loss of the relevant instrument record charts.

The initial cause of this incident was over-hydrogenation, which in turn generated sufficiently high temperatures to begin polymerisation of propylene.

insulation of a cold box

The reactor was being started

No injury to personnel occurred as a result of this incident and there was no damage to the reactor shell

The following recommendations were made:
1. Stops should be fitted to key controllers/valves to limit flows in the event of a malfunction.
2. Situations where hydrogenation reactors are isolated or have only low flows through them during commissioning, maintenance or other operations should be identified and avoided.
3. The integrity of the trip system should be improved.
4. Good maintenance procedures are required to avoid the possibility of incorrectly calibrated transmitters being returned to process.
5. All records should be retained for a period, and should and incident occur, all relevant records should be impounded immediately (this last recommendation comes from the fact that the Investigation of the incident was hampered by the loss of the relevant instrument record charts).