Ogle Russell A, Megerle Marcus V, Morrison Delmar R, Carpenter Andrew R
Exponent Failure Analysis Associates, 185 Hansen Court, Suite 100, Wood Dale, IL 60191, USA.
J Hazard Mater. 2004 Nov 11;115(1-3):133-40. doi: 10.1016/j.jhazmat.2004.06.006.
An explosion occurred at a polyvinyl chloride (PVC) resin manufacturing plant. The explosion originated at an atmospheric storage vessel when it received a slurry discharge from a suspension polymerization reactor. The pressure rise caused by the uncontrolled flashing of superheated liquid vinyl chloride resulted in the complete separation of the roof from the tank shell. A cloud of vinyl chloride vapor was released and ignited resulting in a vapor cloud explosion. The accident caused significant property damage but no serious injuries. An investigation was conducted to determine the causes of the accident. It was discovered that the facility had experienced numerous overpressure incidents in the atmospheric storage vessels used as slurry tanks. Many of these incidents resulted in modest structural damage to these slurry tanks. It was determined by Exponent that the rapid flashing of residual liquid monomer present in the product slurry stream caused the earlier overpressure incidents. The facility operator did not adequately investigate or document these prior overpressure events nor did it communicate their findings to the operating personnel. Thus, the hazard of flashing liquid vinyl chloride was not recognized. The overpressure protection for the slurry tanks was based on a combination of a venting system and a safety instrumentation system (SIS). The investigation determined that neither the venting system nor the SIS was adequate to protect the slurry tank from the worst credible overpressure scenario. Fundamentally, this is because the performance objectives of the venting system and SIS were not clearly defined and did not protect against the worst credible overpressure scenario. The lessons learned from this accident include: use prior incident data for recognizing process hazards; identify targets vulnerable to these hazards; explicitly define performance objectives for safeguards to protect against the worst credible overpressure scenario. The ultimate lesson learned here is that a liquid trapped under pressure above its normal boiling point represents an overpressure hazard. To avoid exceeding the design pressure of the receiving vessel, the superheated liquid must be discharged slowly so that the vapor production rate caused by flashing does not exceed the venting rate of the receiving vessel.
一家聚氯乙烯（PVC）树脂制造厂发生了爆炸。爆炸起源于一个常压储存容器，当时该容器接收了悬浮聚合反应器排出的淤浆。过热液态氯乙烯不受控制的闪蒸导致压力上升，致使储罐顶部与罐体完全分离。一团氯乙烯蒸汽被释放并点燃，引发了蒸汽云爆炸。此次事故造成了重大财产损失，但没有人员重伤。开展了一项调查以确定事故原因。发现该设施在用作淤浆罐的常压储存容器中经历过多次超压事件。其中许多事件导致这些淤浆罐出现了适度的结构损坏。由Exponent公司确定，产品淤浆流中存在的残留液态单体的快速闪蒸导致了早期的超压事件。该设施操作人员没有对这些先前的超压事件进行充分调查或记录，也没有将调查结果传达给操作人员。因此，液态氯乙烯闪蒸的危险未被识别。淤浆罐的超压保护基于通风系统和安全仪表系统（SIS）的组合。调查确定，通风系统和SIS都不足以保护淤浆罐免受最严重可信超压情况的影响。从根本上讲，这是因为通风系统和SIS的性能目标没有明确界定，无法防范最严重可信超压情况。从这次事故中吸取的教训包括：利用先前的事故数据识别工艺危害；识别易受这些危害影响的目标；明确界定防护措施的性能目标，以防范最严重可信超压情况。在此学到的最终教训是，被困在高于其正常沸点压力下的液体代表超压危险。为避免超过接收容器的设计压力，过热液体必须缓慢排放，以使闪蒸产生的蒸汽速率不超过接收容器的排气速率。
