为有效降低在役的化工生产装置过程安全风险，发挥安全仪表系统（SIS）在过程安全风险管控中的作用，选取了某企业石脑油吸附分离装置进行安全完整性（SIL）等级的系统性分析，对该装置预加氢汽提塔重沸炉主燃料气压力低低联锁的回路进行级别认证，通过马尔科夫模型验证确定现有回路满足定级要求，并提出建议措施。

In order to effectively reduce the process safety risk of chemical production plants in service and effectively play the role of safety instrument system (SIS) in the process safety risk management and control,a naphtha adsorption and separation unit of an enterprise is selected to perform systematic analysis of safety integrity level (SIL).The corresponding circuit with low-low pressure interlock of main fuel gas in reboiler of pre hydrogenation stripper in the unit is certified.Through the verification of Markov model,it is determined that the existing circuit meets the grading requirements,and the proposed measures are put forward.