Methods For The Investigation Of Upset Operating Conditions

A disturbance affecting a parameter which itself has an influence on the reaction or the cooling power may, as presented in Table 4-9 of Section 4.4.1, in the worst case lead to a runaway (see also Section 4.2). Therefore, it must be the aim of the experimental characterization to simulate the disturbed process situation as well as possible by adiabatic experiments. In order to define the requirements for such experimental devices in a more concrete form, the effects possibly to be observed shall be presented and comprehensively discussed again in a phenomenological way. 

But already at this early stage, surprises may happen if side reactions suddenly become dominant. This possibility is often underestimated. Very easily a side reaction may proceed with quite an insignificant rate at normal operation, but at elevated temperatures the situation reverses completely. 

A first indication of such a situation is obtained if the precalculated adiabatic temperature increase, derived fi om the gross heat of reaction measured imder normal operating conditions, is by far exceeded in the adiabatic experiment. An analytical examination of the final reaction mixture will provide the final proof. 

It should be possible with the help of the same experiment to find out the time after which the secondary processes become perceptible and their character. The latter means, the degree of exothermicity and possibly the strength of an accompanying gas generation. When performing such experiments, it has to be observed whether evaporation prevents a runaway of the reaction. If this turns out to be the case, a closed test system should be available for the measurement. In a closed system the evaporation would be suppressed by the rising internal pressure. 

In summary, the following minimum requirements can be stated which have to be met by a measuring device suitable for the characterization of process deviations  

---