QUANTITATIVE ANALYSIS - A REALISTIC APPROACH TO RELIEF HEADER AND FLARE SYSTEM ANALYSIS

摘要

Most existing pressure relief header and flare systems were originally designed without taking intoaccount any of the multitude of mitigating measures, commonly referred to as safeguards, present in atypical operating facility. However, as plants have increased throughput and added process units, therelief header and flare systems are no longer adequate given the same conservative methods that wereused in the original design. As such, operating companies are faced with the decision of either installingadditional relief header and flare capacity to bring the system into compliance with the original designmethods or evaluating the relief header and flare capacity using more realistic design methods. Tofurther complicate this decision, past experience during flaring events often contradicts the theoreticalcalculations that indicate the system is undersized.Limited budgets have rendered it imperative to distinguish between additions and modifications with anactual safety benefit and those with a theoretical benefit. With this in mind, a more realistic approach tothe analysis of pressure relief header and flare systems that is consistent with recognized and generallyaccepted good engineering practices (RAGAGEP) is required. Quantitative risk analysis (QRA) can beapplied to the problem to better understand the risk profile associated with these systems. Theapplication of QRA renders it possible to evaluate the relief header and flare system, accounting for allsafeguards as well as the frequency of all the relieving scenarios of interest. The QRA methodpresented has been utilized by several major operating companies and is proposed for inclusion in thenext revision of API RP 521.