Runaway criteria general

In general, hazard identification criterion represents the deviation of one or more measured variables from specified values. This is the basis upon which a significant percentage of risk analyses are done. For a chemical process, a number of measurable variables, physical properties, and states or positions of various parts of the overall equipment, e.g., pumps, valves, and motors, can be specified for every time or phase of the process. Certain deviations from the "standard" recipe or settings can then be defined in advance as hazardous, and thus can be used for initiation of an alarm at the early stage of a runaway or upset condition. 

Zaldivar, J.M., Cano, J., Alos, M.A., Sempere, J., Nomen, R., Lister, D., Maschio, G., Obertopp, T., Gilles, E.D., Bosch, J. and Strozzi, F. (2003) A general criterion to define runaway limits in chemical reactors. Journal of Loss Prevention in the Process Industries, 16 (3), 187-200. 

A general criterion to define runaway limits in chemical reactors. Journal of Loss Prevention in the Process Industries, 16 (3), 187-200. 

A more recent class of criteria to identify runaway conditions is based on the evidence that, close to runaway boundaries, the system behavior becomes highly sensitive to even small changes of the model parameters. Within this class, the generalized criterion of Morbidelli and Varma [14] makes use of the absolute value of the normalized objective sensitivity s of the temperature maximum 7 max to the generic model parameter 0, defined as... 

The first set of data has been reported by Emig et al. (1980) and refers to the vinyl acetate synthesis reaction catalyzed by zinc acetate supported on activated carbon. A comparison between the boundaries predicted by the generalized criterion and the experimental findings is shown in Figure 6. The open and closed circles refer to safe and runaway operating conditions,... 

Figure 6. Comparison of predicted region of parametric sensitivity with experimental data runaway condition, O nonrunaway condition data of Emig et al. (1980), [from Morbidelli and Varma (1987)]. (a) — Generalized criterion = 0 — Generalized criterion, = 0.1 (b) —...

According to the analysis reported above in the context of thermal explosion theory, we can use the generalized sensitivity criterion to identify the explosion limits of the hydrogen - oxygen mixture. By this we imply that the runaway of such a system actually coincides with its explosion (i.e. a very rapid reaction). 

In all these cases, as in those related to reactor safety discussed above, the generalized criterion provides a useftil tool to determine a priori those operating conditions leading to reactor runaway, which can be avoided in the early stage of reactor design. 

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