Screening Tool for Runaway Reaction Characterization

Proper characterization of reactive systems is required to ensure the mechanical integrity of processing equipment and to avoid potential hazards such as fires, explosions, and toxic cloud dispersions. As the temperature of the vessel contents deviates from safe operating limits and becomes too high, the rate of heat production by the chemical reaction (i.e., exponential function of temperature) can exceed the processing equipment rate of heat loss and/or cooling capacity (i.e., linear function of temperature) leading to a runaway reaction. However, not all reactive systems present the same thermal risk level, and accordingly, not all of them require the same level of detail for Emergency Relief System design.

Figure 1: ARC Approach – Temperature History Illustration



The present paper illustrates an easy-to-use screening tool for characterizing any reactive system based on information extracted from basic calorimetric tests. Two parameters have to be estimated for both desired and potential secondary reaction in case of a runaway:

• Adiabatic Temperature Rise
• Time to Maximum Rate under adiabatic conditions

The screening tool is based on the following criteria intended to estimate four (4) key temperature levels which contain the thermodynamic and kinetics information of the runaway reaction:

• Calorimetric Testing; Accelerating Rate Calorimeter:
  Acquiring ΔT_ad and TMR_ad and defining the runaway reaction risk level based on Stoessel criteria.
• Consideration of the so-called “cooling failure scenario” approach developed by Gygax:
  An inherent conservative assumption is taken from Grewer when considering zero reaction orders for estimating basic kinetic parameters of the runaway reaction.
• Consideration of the “Criticality Classes” approach developed by Stoessel:
  Based on the critical classes, the proposed screening tool recommends how to proceed for ensuring a reliable and effective ERS design while optimizing the required time to achieve the final results.