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 into account any of the multitude of mitigating measures, commonly referred to as safeguards, present in a typical operating facility. However, as plants have increased throughput and added process units, the relief header and flare systems are no longer adequate given the same conservative methods that were used in the original design. As such, operating companies are faced with the decision of either installing additional relief header and flare capacity to bring the system into compliance with the original design methods or evaluating the relief header and flare capacity using more realistic design methods. To further complicate this decision, past experience during flaring events often contradicts the theoretical calculations that indicate the system is undersized. Limited budgets have rendered it imperative to distinguish between additions and modifications with an actual safety benefit and those with a theoretical benefit. With this in mind, a more realistic approach to the analysis of pressure relief header and flare systems that is consistent with recognized and generally accepted good engineering practices (RAGAGEP) is required. Quantitative risk analysis (QRA) can be applied to the problem to better understand the risk profile associated with these systems. The application of QRA renders it possible to evaluate the relief header and flare system, accounting for all safeguards as well as the frequency of all the relieving scenarios of interest. The QRA method presented has been utilized by several major operating companies and is proposed for inclusion in the next revision of API RP 521.