(40c) Lightning Strike Incident at Sabic Europe Plant NAK3;

On Febr-16 2006, a heavy lightning strike occurred on a cooling water cell, which is quit near the control room of Naphtacracker 3 (NAK3). Promptly, the tower flare was ignited heavily, indicating that some disturbance was initiated by the lightning strike. For the ETBE plant, the so-called ?black-screen' scenario was present. ?Black-screen' means that operators do not have control information of the process, although all control valves will remain in the last position. This scenario had been foreseen during the Hazop study, and it was judged to be adequately safe. Real life practice proved to be right. The ETBE plant was shut down in a safe manner, without normal process control. For the cracker, the disturbance was more complex. After 30 min of heavy flaring, a field operator noticed a hydrocarbon leakage, and induced the Gas-alarm system. The plant was shut downed immediately. After some time, 2 major problems were identified:

- Control equipment: all 30 dedicated compressor control devices were defect cq unreliable, caused by over-voltage induced by the lightning strike . Because of this defect, all bypass valves were opened 100 %, and caused excessive high flows over recycle lines and/or chattering of PSV's. This led to a mechanical problem:

- Mechanical: 2 small cracks in 2 different ( D25) weldolets of the flare ventlines of the cracked gas compressor section 4e and 5e stage ; caused by heavy vibration of the PSV's and/or flare-header.

The mechanical problem could be solved within 2 days. Replacing all 30 compressor control devices, for the parallel compressor sections of charge-gas, C2 and C3 refrigeration compressors, was another issue. Only 2 spare controllers were in-house, and it was not clear when 30 controllers could be available on site. Then it was decided to build a simplified control scheme in the DCS, for 1 set of each compressor system. Within 1 day, 1 set of charge-gas, C2 and C3 compressors were equipped with minimum flow and suction pressure control. In a separate Hazop meeting, a judgement on the reliability of the plant ESD system ( Emergency Shutdown System; electronic safeguarding system ) had to be answered. Because some components of the DCS and all dedicated compressor control systems were gone unreliable and/or defect, so what about the electronics of the ESD system? After some discussions, the conclusion was that the ESD system was judged safe for operation, and the plant was started-up. Only 60 hours after the lightning-strike, the NAK3 plant produced on-spec ethylene again.