Study On The Spurious Activation And Design Optimization Of Safety Instrumented Systems In Chemical Plants

The petrochemical and chemical industries are the pillar industries of China and play a significant role in the development of the national economy.However,the petrochemical and chemical industries,with a large production scale,have attracted much public attention due to high risk and many accidents happened.The safety instrumented system(SIS)used in chemical plants is acting as an active layer of protection against possible accidents,and it also reduces the frequency and consequence severity of accidents.Nevertheless,spurious activations of the SIS in case of normal operations will result in unwarranted economic losses with unacceptable risks.In view of the current situation of insufficient research on the spurious activation of SIS and the demand of the chemical industry to pursue the balance between safety and economics,this thesis conducted a comprehensive study on the spurious activation analysis and design optimization of SIS in chemical plants.Starting from the concept,definition and triggering cause,spurious activations of the SIS were summarized in three levels including components,safety instrumented functions,and chemical plants.Moreover,general standard regarding the spurious trip rate level was established for chemical plants,and the water supply system was used for the case study to demonstrate the applications.Under the requirement of the spurious trip rate level,the quantitative model of the spurious trip rate for general Koo N voting configurations was developed based on previous studies considering that the combination of safe failure and dangerous detected failure can lead to spurious activations.The model effectively solves the problem that the spurious trip rate of complex voting configurations cannot be quantified,so that it can be integrated into the optimization design of the SIS.In the optimization design part,the impact of three decision variables of component type,redundant structure,and maintenance time interval on the SIS reliability,spurious trip rate,and life-cycle cost was investigated.With the developed model,the SIS appears the optimized redundant structure compared to other configurations.The coke oven gas to methanol process was utilized as the case study to show the design optimization of the SIS by using the NSGA-II genetic algorithm.The results approved the effectiveness and feasibility of the proposed methodology for design optimization of the SIS considering both safety and economic aspects,thus provides an important basis for the safety and long-term operation of chemical plants.