On Febr-16 2006, a heavy lightning strike occurred on a cooling water cell, which is quit near the control room of Naphthacracker #3 (NAK3). This caused the so-called 'black-screen' scenario for the ETBE unit. 'Black-screen' means that operators do not have control information of the process, although all control valves will remain in the last position. The cracker was shut downed because a small gas leakage near the charge gas compressors. After some time, 2 major problems were identified:Control equipment: all 30 dedicated compressor control devices were defect or unreliable, most certainly caused by over-voltage induced by thelightning strike. Because of this defect, several bypass valves of the cracked-gas compressors were opened 100 %, leading to a mechanical problem:Mechanical: 2 small cracks in 2 different (D25) weldolets of the flare vent lines of the charge gas compressors section 4e and 5e stage; caused by heavy vibration, induced by excessive high recycle flows and/or chattering of PSV's on the flare-header. The mechanical problem could be solved within 2 days. Because of lack of spare dedicated compressor controllers, 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, the reliability of the plant ESD system, and the xnew' compressor DCS controls, was judged to be adequately safe. Only 60 hours after the lightning strike, the NAK3 plant produced on-spec ethylene again.
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