The Integrity Level Design Method and Application of Petrochemical Plant Safety Instrumented System

As a major safety control measure, safety instrumented system (SIS) plays an important role in preventing accidents and reducing the consequences of accidents. However, failure action and spurious trip of SIS, which led to the loss of safety function of SIS, are two problems existing in the running of the SISs.In order to avoid failure action and spurious trip of SIS, SIS information that has been applied in the SISs of the domestic petrochemical plants was summarized in this thesis, and classified information of SIS which contains16kinds of SIS and56categories of SIF was acquired. It can be concluded that failure action and spurious trip of SIS are both caused by the unreasonable design of the SIL. In order to solve the above problems, a new design method for SIL based on the SIS classified information was proposed, including four steps:(1) confirming the high risk deviations by using the HAZOP analysis method (2) designing SIL based on the risk analysis and validating the SIL by using model of fault tree analysis (FTA) and reliability block diagram (RBD); furthermore, bayes method was employed to estimate the failure rate, so as to improve the validation of the SIL reliability (3) designing SIL based on experience, identifying the facility categories, and providing the SIS exercise information for similar facility as the basis of identification and validation of SIL (4) obtaining the final SIL results to finish SIL design by taking into account the results of step (2) and (3).Additionally, based on the above method, this thesis used C#and SQL database to develop a software for SIL design of petrochemical facility (PFSIL). On the basis of traditional risk analysis design, an experience design method for SIL was added into the software. And bayesian estimation was also introduced to SIL validation so as to increase the accuracy of SIL design and avoid failure action and spurious trip of SIS effectively.The whole application process of the design method of SIL for the chemical plants was explained, and the software, PFSIL has been utilized to help SIL design for the wax oil hydrogenation plant. Circulating hydrogen desulfurization tower and circulating hydrogen compressor system were taken as two examples to exhibite the application procedures of the method and software. It was proved that failure action and spurious trip of SIS can be avoided by using this method.