Runaway reactions interpreting data

The maximum temperature which the desired reaction can reach under conditions of cooling failure can be determined from the adiabatic temperature rise, calculated from the remaining heat of reaction and the specific heat of the reactants. If this temperature is high enough to boil the reaction mass or to start a secondary or decomposition reaction under the plant conditions, a hazardous situation may occur. 

Screening tests (see Section 4.3, page 52) can give guidance on when secondary reactions or decompositions may occur. Once this has been established as a possible hazard, adiabatic calorimetry is needed to give a reliable value for the minimum temperature at which self-heating will stan under plant conditions. 

If the tests fully simulate the process conditions and the adiabatic calorimeter is sensitive enough to show accurately what will happen on the plant scale, the experimental data can be used with little if any safety factor. Where the tests are less sensitive, great care is needed in extrapolating the data to the conditions which apply on the plant. 

A worked example for a particular reaction is given in Appendix 2 which illustrates the application in practice of the approaches outlined in this section. 

Where screening tests indicate that the onset temperature of a secondary or decomposition reaction under plant conditions is close to the temperature at which the plant will operate, it is necessary to determine more accurately whether a hazardous situation could occur. The essential factor is to determine whether, on the particular plant, the reaction generates heat faster than it can be lost. The rate of heat loss should ideally be measured for the plant in question, but in the first instance an estimate can be obtained from the literature or calculation. 

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