Investigation of an air separation unit explosion

This paper describes the investigation of the cause of a serious explosion in an air separation unit in Bintulu (Malaysia) on 25 December 1997, Since the cause of the explosion was not obvious, a large number of possible scen arios was generated, followed by a systematic process of elimination. Ultim ately, conclusive evidence was obtained that combustible airborne particula tes had passed the main purification section of the air separation unit. Th ese combustible contaminants had accumulated on the aluminium main vaporise rs of the distillation column. Once hydrocarbon combustion was triggered, i t led to aluminium combustion which generated heat and vaporised the cryoge nic liquids. This led to rapid pressure build up and explosive rupture of t he distillation column. The exact ignition mechanism remains unclear, but a low activation energy chemical mechanism, involving radical reactions to p rovide the initiating trigger, has been proposed. However, by designing a p urification system capable of efficiently removing aerosol material and oth er fouling contaminants, and by a proper design of the oxygen reboiler it i s possible to design a plant that can be operated safely in an aerosol poll uted environment. The analysis presented in this paper and the proposed sol utions by the ASU vendors, Shell and independent experts were accepted by p lant insurers and the shareholders of SMDS Malaysia, leading to a subsequen t endorsement of the rebuild investment. (C) 2001 Elsevier Science Ltd. All rights reserved.