In a petrochemical plant, 60 tonnes of unordered ethylene were flared off between 11:15 am and 5:00 pm following the protection of the digester in the steam cracking unit as a result of a lightning strike. Work conducted on one of the plant’s boilers did not allow removing the steam from the flaring operation; a cloud of smoke was visible up to several kilometres away.

The digester converts, using nickel catalysis, hydrogen (H2) and carbon monoxide (CO) into methane (CH4) and water (H2O) at a temperature in the range of 230°C. In this manner, the H2 devoid of CO is able to convert acetylene into ethylene, which is not the case when polluted by CO. Ethylene, which respects a rather strict specification (5 ppm max of acetylene), is then transformed into polyethylene.

On the day of the incident at 11:15 am, the lightning bolt necessitated applying safety precautions to the digester at a high safety temperature; the insufficient H2 production allowed the acetylene to hydrogenate, resulting in a sizeable output of excess ethylene, which in turn had to be flared off due to the absence of a suitable onsite storage system. By noon, the unit was once again operating, but an underestimation of the time required for installation reloading led to excessive ethylene production and hence its transfer to be flared off until 5 pm.