Research On Pressure Relief For Exothermic Runaway Reaction

Overpressure caused by runaway reaction is a threat to safe operation of pressure vessels, on condition that the aspects of design and operation could not be changed, a pressure emergency relief system is one of the most economic and effective measures used to protect reactors from exothermic runaway. The purpose of the design for pressure relief is to know the accurate relief area. Due to the complexity of chemical runaway process, the problem has not been solved successfully by now. The research on pressure relief for exothermic runaway was carried out in this paper, in order to understand the reason of the overpressure and determine the relief sizing by applying the corresponding models.The methods for the design of pressure relief system require certain data that are provided by suitable calorimeters. The suitable calorimeters for measuring runaway reaction relief sizing data should be adiabatic and have low thermal inertias. The PHI-TEC II calorimeter has good insulation properties and possesses high detection sensitivity. The VSP2calorimeter equipped with a system of rupture disk could be used to verify the relief design. A development which is offered as a complement to ARSST calorimeter is Flow Regime Detection, it is helpful to classify the relief systems.Based on Phi-TEC II, research on Methanol/acetic anhydride, Dicumyl peroxide in2,2,4-TriMethyl-1,3-pentanediol diisobutyrate and the di-tert-butyl peroxide in Toluene was carried out. The data of temperature rise rate and pressure rise rate changing with temperature were obtained with low thermal inertia, the onset temperature are37℃,145℃and148℃separately. According to the boiling point of reaction mixture and the relationship between temperature and pressure, the three reactive systems can be identified as vapor system, gassy system and hybrid system. Required relief rate and mass flow capacity were calculated by different models and methods, thus the relief sizing of three reactive systems were determined.According to the analysis result, the influences of different condition of venting for relief sizing are discussed, researches show that relief area is proportional to relief pressure, set a low relief pressure yield a smaller relief area. In production, increasing quality of the material calls for increasing relief area. For vapor systems, the reactor volumes have little impact on relief sizing. Whereas for gassy systems, increasing of the reactor volumes and design pressure could reduce the relief areas, when the vent sizing of design is too large for the reactor, it can increase the volume of reactor and the design pressure so as to meet the requirements. By analyzing of the influences, it would be possible to reduce relief area effectively in the design of pressure relief system and achieve the purpose of safety and economy.