Thermal instability and runaway criteria: The dangers of disregarding dynamics

Two exemplary exothermic processes, synthesis of nitroglycerine in a continuous stirred tank reactor (CSTR) and synthesis of the explosive RDX in a CSTR, are used to demonstrate the dangers of ignoring the system dynamics when defining criteria for thermal criticality or runaway. Stability analyses are necessary to prescribe such criteria, and for these systems prove the presence of dangerous oscillatory thermal instability which cannot be detected using the steady state thermal balances.

► We adjure the use of stability analysis in specifying thermal runaway conditions.
► Two recent works that disregarded stability were re-examined.
► Oscillatory thermal instability was shown to be endemic to these systems.
► It is real, not an artefact, it may occur with violent abruptness, it is dangerous.
► Use of only a steady state enthalpy balance is incorrect and unsafe.