Design And Rating Of Exothermic Reaction Runaway Relief

Exothermic reaction runaway, one of the main causes of fluid equipment overpressure, is widespread in the petrochemical process, the resulting high temperature and pressure of which would lead to explosive destruction of pressure vessel. Since the 1980s, DIERS (Design Institute of Emergency Relief System) invested a lot in this field, and then a set of vent sizing methodology for exothermic reaction runaway has been gradually established. However, the result of the methodology is often conservative, sometimes even too conservative, resulting in tremendous waste. While the domestic development in the field is relatively slow, little achievements are made, forming a great gap behind the international advanced level. The work and conclusions are summarized as follows:(1) Calorimetry of exothermic reaction runawayUsing the VSP2 adiabatic calorimeter, the combined process of caprolactam synthesis and the cyclohexanone ammoximation process were investigated experimentally, acquiring the essential thermal data for the vent sizing of exothermic reaction runaway, and based upon the experimental data analysis, vent sizing was conducted through hand calculation, getting the following conclusions:For the combined process of caprolactam synthesis, the main reaction in the reactor is an intensive exothermic process. No secondary exothermic reaction is detected when increasing temperature after the first reaction runaway. The failure of cooling device for hexane is screened as the worst case scenario, which is a vapor system, requiring a relief area of 0.090 m2. Since the actual relief area is 0.0912 m2, the existing safety relief devices area can satisfy the safety relief requirements.For the cyclohexanone ammoximation process, the ammoximation reaction is an intensive exothermic process. No secondary exothermic reaction is detected when increasing temperature after the first reaction runaway. High concentration of hydrogen peroxide is screened as the worst case scenario, which is a untempered hybrid system, requiring a relief area of 0.051 m2.(2) Blowdown tests of exothermic reaction runawayThrough the addition of effluent container, rapid response pneumatic valve and orifice, experimental device was improved to track the data during blowdown tests. The impact of heating power, initial fill rate, relief pressure, relief diameter and the material foaming property on the relief capacity and the effluent mass were investigated, getting the following conclusions: The two-phase flow capacity increases with the decrease of vapor generation rate, increases then falls with the rise of fill rate, decreases rapidly then increases slowly with the increase of relief pressure, increases continuously with the increase of relief diameter; while the effluent mass increases with the rise of vapor generation rate, fill rate, relief pressure and relief diameter respectively.Whether the material is foamy or not has significant influence on the final results:the results of foamy material have great difference from that of non-foamy material. As the concentration of the detergent increases, the two-phase flow capacity decreases continuously, while the effluent mass continues to increase.Comparison between the DIERS calculation results and the experiment results shows that, the product of the former and a correction factor 0.69 is still conservative, which can still be able to ensure the safety of relief.(3) Vent sizing program for the exothermic reaction runawayUsing VB, the DIERS methodology for the vent sizing of exothermic reaction runaway is integrated into computer program, including system type determination, vent sizing and effluent handling system selection. For all types of vent sizing, the comparison between the program results and that of hand calculation and the example in handbook shows that, the maximum relative error is 1.8%. Thus it can be concluded that, the calculation of the program is correct and the accuracy can meet the requirements of engineering applications.