Safety analysis and evaluation of reboiler in nitrobenzene rectification unit

The explosions of the reboiler in the rectifying unit of nitrobenzene processes occurred frequently.For figuring out the general causes and taking effective countermeasures for prevent such damages,ICI'(Imperial Chemical Industries Ltd.) Mond Assessment and Fault Tree Analysis(FTA) are used to carry out hazard analysis.A series of hazard indices are calculated for the process unit on the basis of material factors,process hazards,and toxicities,etc.Offsetting factors for various forms of special protections are then applied and final adjusted values of these indices indicating the overall hazard rating of the unit are calculated.Then the minimal cut and radius sets are calculated by qualitative analysis.Furthermore,the critical importance of the basic events is calculated by quantitative analysis.Finally,the safety measures are put forward.The results of the investigation show that: the rank of the danger of the unit is medium category;air ingress at high temperature,valve failure and flange sealing failure are the most important three causes for such explosion incidents.So relative countermeasures are needed for management enhance on work safety,and controlling heating temperature and avoiding local heat accumulation in the reboiler can also lower the hazard class and ensure work safety.