In December 2002 the Lyondell-Citgo Refinery experienced an incident that resulted in tripping one of the Clous Units. Losing the Claus Unit meant higher than normal levels of SO_2 were released from the thermal oxidizers, and that the nearby community was notified of the potential impact. This paper focuses on system analysis and improvement opportunities to reduce the likelihood of a similar incident. The incident had little offsite impact, but did highlight the need for an alternative approach to assess the capabilities of the Sulfur Recovery Complex at the Lyondell-Citgo Refinery. The refinery managers and staff are committed to reducing the likelihood of these types of events in the future. The cause of the release was traced back to a level control failure on a knockout pot in the Coker Unit. This failure resulted in a significant amount of hydrocarbons being carried to the Amine Regeneration Unit. Hydrocarbon in the Amine Unit, if not separated, can result in system upsets in the Claus Units with potential environmental releases. There are several process units that have similar configurations with the potential to result in the same or similar consequences. Because of the complexity of the scenarios, a team of Lyondell-Citgo employees and consultants were tasked with estimating the frequency of the possible scenarios and proposing mitigation options to reduce the frequency. This paper will discuss the methodology used by the team to identify the possible scenarios that have the potential to result in a similar upset to that experienced in December 2002. It will further discuss the benefits of using risk as a basis for decision making for the management team at Lyondell-Citgo.
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