Downside of <i>T</i> _D24 and the Recommended Replacement for Thermal Runaway Hazard Evaluation in an Industrial Chemical Vessel

Thermal runaway from chemical reactions is the result of competition between heat generation and heat dissipation in industrial chemical vessels. However, the worldwide used TD24 (the temperature at which time to maximum rate under adiabatic conditions equals 24 h) focuses solely on heat generation for abnormal conditions of cooling failure, which account for only an insignificant portion of thermal runaway incidents. In contrast, the temperature of no return (TNR), defined by the balance of heat generation and heat dissipation, provides a more relevant threshold for process upsets in industrial chemical vessels. As the operating temperature approaches the TNR, minor thermal disturbances can precipitate thermal runaway. To estimate this threshold, calorimetry is coupled with reactor-scale energy-balance modeling. Kinetic parameters are determined using accelerating rate calorimetry (ARC), with corroborating measurements from differential scanning calorimetry (DSC), vent sizing package (VSP) calorimetry, and micro reaction calorimetry (μRC). In this work, the downside of TD24 for runaway hazard assessment is first analyzed. Guided by the Semenov diagram, a heat-balance model for stirred-tank reactors (STRs) is established, and based on ARC tests on a 20 wt % solution of di-tert-butyl peroxide (DTBP) in toluene under adiabatic conditions, a heat-generation-rate expression and a coolant heat-dissipation-rate expression are derived. A computational procedure is then proposed to determine TNR. Relative to adiabatic TD24, TNR supports optimization of reactor-cooling design, enhancing alarms and interventions under abnormal conditions, and quantitative assessment of reaction hazards.