Venting Technology And Characteristics Of Chemical Reaction Thermal Runaway

Exothermic reaction is widely present in the chemical industry. Once the thermal reaction runaway occurs, the high temperature and high pressure will result in an explosive damage to the reaction vessel. Statistics demonstrate that chemical accidents caused by thermal reaction runaway accounts for24.1%of the total accidents. However, both the mechanism and characteristics of the exothermic runaway and the runaway prevention and control technology are not fully understood. Especially for the widely used pressure relief technology, when applied to a runaway reaction overpressure situations, there are still some issues, such as determining the starting point of venting, the venting characteristics of two-phase materials.As a consequence, the exothermic runaway discharge characteristics and properties of hydrogen peroxide and an organic peroxide exothermic reaction were examined in the experiments. The main contents and conclusions are as follows:(1)The liquid temperature and vapor pressure of different concentrations of hydrogen peroxide decomposition runaway reaction under alkaline environment were investigated in the experiments. It was concluded that the hydrogen peroxide concentration of10%decomposition runaway reaction leaded to the maximum temperature of90.0℃, the maximum pressure of30.7bar and the maximum temperature rise rate of10.7℃/min. For the higher hydrogen peroxide concentration, the time to enter the runaway process was shorter. The thermal hazards increased. According to the runaway reaction characteristics, four runaway criterions were proposed:limit temperature criterion, limit the rate of temperature rise criterion, temperature rise trend criterion and the average rate of temperature rise criterion. The criterion thresholds and the advantages and disadvantages of the four runaway criterions were detailed discussed.(2) Through changing the discharge pipe diameter, the discharge mode, the discharge pressure and the state of holding tank, discharge characteristics of the runaway reaction of hydrogen peroxide in several different discharge systems were experimentally studied. It was demonstrated that gas venting system was single-phase process, and it could not cool the material. Open vent system was a hybrid non tempered system, while the pressure showed double peak characteristics. Closed and semi-closed vent system just had one peak at stable reaction stage and no vapor was generated. Bottom liquid vent process was divided into two stages, both of these were single-phase process. (3) Through changing the discharge pipe diameter, the discharge mode, the discharge pressure and the state of holding tank, experiments were conducted to study the liquid spurt of hydrogen peroxide runaway reaction in several different venting system. It was concluded that there was an obvious liquid spurt and increase of liquid level during the relief process. When the vent area was large enough, this phenomenon occurred before the second pressure peak. On the contrary, when the vent area was little, the phenomenon occurred after the second pressure peak. Liquid spurt phenomena did not occur in closed or semi-closed system. While in the open system, the large-diameter vent process leaded to a secondary, a small diameter only had one liquid spurt phenomenon(4) The venting characteristics of an organic peroxide under different diameter and venting pressure was experimentally studied. It was concluded that sealed reactor venting process was more prone to leading the secondary peak phenomenon. The initial peak was vapor discharge and the second peak was the gas-liquid two-phase relief. Constant pressure reactor venting process tended to be non-equilibrium process of relief. Liquid relief from the bottom could make emptying of the kettle to ensure reactor safety. Inject Injecting water could effectively inhibit the organic peroxide runaway reaction. For the faster injection rate, the temperature dropped quicklyThe vent diameter was5.0mm for the actual conditions of the experiment organic peroxide safety relief. Some basic data of an organic acid reaction in runaway process was determined using VSP2experiment device. DIERS calculation method was adopted to calculate the safety vent diameter in the5L experimental reactor at4bar pressure safety relief. The calculated safety vent diameter was4.9mm, which was in conformity with the experimental value.