Characteristics Of Thermal Runaway And Relief In Peracetic Acid Production Process

In general,peracetic acid(PAA)is produced by acetic acid oxidation method.Becausethe production process involves the peroxides which are extremely sensitive to heat,it can induce runaway reaction at a low temperature,and cause high temperature and high pressure may develop,resulting in the damage of reactor.Most studies focused on the storage and transport safety of PAA.However,the research on the safety of its production is still lacking.Compared with the storage and transport,the production process contains more complex reactions.There are more factors such as the external heat and the change of production conditions can affect the processes.All influences of these factors on thermal runaway and relief characteristics of PAA production system need to be studied further.Therefore,the PAA production system was studied.And its characteristics of runaway reaction and relief process were researched systemically.The main contents and conclusions are as follows:(1)The influences of heated temperatures on runaway characteristics of reaction system under high temperature were studied.The results showed that the higher heated temperature resulted in higher temperature,pressure,temperature rising rate and pressure rising rate of runaway reaction system.Furthermore,the risk assessment results of runaway systems were given.It was revealed that when the heated temperature was larger or equal to 100?C,the severity and probability grade of runaway reaction were all the highest.Besides,the types of relief system were different under different heated temperatures.When the heated temperature was low,the runaway system was untempered hybrid system.But when the temperature was high,it became tempered hybrid system.Reason for this is that the intense boiling occurred at high heated temperature.Consequently,abundant vapors were produced and the vapor pressure increased,leading to the change of runaway reaction system.(2)The influence of production factors on the runway reaction system's overpressure risk were studied by orthogonal and single factor tests.Regarding the maximum pressure rising rate as evaluation index,it was found that the reactant ratio had obvious impact,the reaction time affected the index but its impact was not very significant.And the catalyst volume fraction and the interaction between these factors had less impact.Specifically,when reactant ratio was low,there were no significant difference in maximum pressure rising rate.But when reactant ratio was high,maximum pressure rising rate became larger with the increase ofhydrogen peroxide ratio.The maximum pressure rising rate increased with the decrease of catalyst dosage when the amount of catalyst was higher than theoretical lower limit.Besides,the PAA synthesis heat was not negligible when reaction time was short.(3)The relief size was determined by using DIERS method under given conditions.Based on this,the venting characteristics of open relief condition and closed relief condition were studied.The results showed that during the relief process,when the collection tank was open,the whole pressure in reactor could be vented rapidly.But when the collection tank was closed,the pressure in reactor could only be vented partially.And as the pressure dropped,the pressure in collection tank increased quickly.These two pressures could achieve the same value in a very short time.Subsequently,the pressures both increased until the reaction completed.(4)Under closed relief condition,the effect of back pressure change on venting characteristics of runaway reaction system was studied by changing the initial back pressure.The results represented that when the initial back pressure was low,there was no second pressure peak in relief process.However,the second pressure peak occurred and exceeded the relief pressure when the initial back pressure was high.For its reason,in the vent area design process using DIERS method,the maximum back pressure rather than initial back pressure should be compared with critical pressure to correct back pressure considering the pressure change.Otherwise,the result may be smaller.A formula of the maximum back pressure was given and the error was less than 5%.