Published on 11/12/23 593 Views

A styrene monomer and propylene oxide chemical intermediate manufacturing plant was being restarted after a routine catalyst changeout. The hydrogenation reaction section of the plant had been successfully air-freed, leak-tested, flushed with ethyl benzene (EB), placed on circulation with a fresh charge of EB, and allowed to “line out” to ensure the catalyst bed was wetted and heated homogeneously. The next step of the startup procedure was heat up (“reheat”) of the trickle-bed reactors in preparation for reduction of the active metals of the catalyst. The control board operator decided the reheat step was proceeding too slowly and manually increased the heat up rate. An unexpected exothermic (heat-liberating) runaway chemical reaction occurred which generated gases and rapidly increased the reactor pressure. This was not recognised as flows and levels were fluctuating widely and alarms were sounding regularly (as expected from previous restarts). Two explosions occurred in rapid succession and a major fire followed.

Ask yourself and your crew:

How can something like this happen here (e.g. on our site)?
What safety measures (i.e. procedures, controls/barriers) do we have in place to mitigate the risk?
How do we know the risk controls/barriers are working?
What improvements or changes should we make to the procedures, controls/barriers or the way we work?

Original content courtesy of IChemE Safety Centre