Basic Analysis on Severe Accidents for Chemical PCB Detoxification Plant Using the UV/Catalyst Method.

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  • Watanabe Atsuo
    PCB Detoxification Promotion Division, Power Systems and Services Company, Toshiba Corporation
  • Ohara Atsushi
    PCB Detoxification Promotion Division, Power Systems and Services Company, Toshiba Corporation
  • Tajima Naoki
    PCB Detoxification Promotion Division, Power Systems and Services Company, Toshiba Corporation

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Implementation of polychlorinated biphenyls detoxification is being accelerated globally. We have developed an environmentally sound chemical polychlorinated biphenyls detoxification plant (codenamed: HM1), using the Ultraviolet ray (UV)/Catalyst Method. Safety analysis greatly facilitates communication on the subject of risk between the entity wishing to construct and operate the plant and the local residents.<BR>In the UV/Catalyst Method, PCB is mixed with sodium hydroxide (NaOH) and isopropyl alcohol (IPA: solvent) to realize PCB concentration in IPA of 1 wt% and subsequently PCB is dechlorinated by two independent process steps. The first step is the UV irradiating process (UV process), and the second step is the catalyst reaction process. As a result, biphenyl, NaOH, acetone, and water are generated after PCB is dechlorinated. A distilling column is designed in order to separate IPA from the solution, and IPA can be recycled many times as a solvent of PCB. IPA and acetone may form an inflammable mixture after leakage.<BR>Concerning HM1, first, hazardous events which produce severe accidents were identified by Failure Mode and Effect Analysis (FMEA); and secondly, leak of isopropyl alcohol (IPA), that causes fire/explosion, is defined as the most serious event. Based on this result, numerical safety analyses were carried out and the following findings were obtained.<BR>• Thermal runaway experiment of residual liquid in the bottom of a distilling column: It was confirmed experimentally that no possibility of thermal runaway exists.<BR>• Stress analysis of the distilling column after fire/explosion: The strength of the distilling column was proved.<BR>• Impact evaluation concerning the surrounding facilities and residents after fire/explosion: It was confirmed that impact would be slight.<BR>• Impact evaluation concerning exposure of residents to PCB: Exposure of residents to PCB would be negligibly small.<BR>In conclusion, the standardized methodologies for both safety evaluations and procedures concerning PCB plants were proposed and their validity verified.

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