Cause, Definition, and Prevention of a Runaway

Runaway reactions can be triggered by a number of causes, but, in most cases., their resultant features after initiation are similar [31]. Whenever the heat production rate exceeds the heat removal rate in a reaction system, the temperature begins to rise and can get out of control. The runaway starts slowly but the rate of reaction accelerates, and the rate of heat release is very high at the end. Most runaways occur because of self-heating with the reaction rate (and reaction heat output) increasing exponentially with temperature, while the heat dissipation is increasing only as a linear function of the temperature. 

The effect of a runaway can be neglected only if the amount of heat available in the reaction mass at the point of runaway is low even at high 

Regenass [160] mentions the factors, as listed below, that can lead to a runaway. When any two or more of these factors are present, there is a potential for thermal runaway  

There is a potential thermal runaway upon the combined occurrence of two or more of the above listed factors. For example, an accumulation of reactants in combination with insufficient heat removal leads to a runaway of the desired reaction. The resulting temperature increase (now uncontrolled) may lead to an explosive decomposition if other exothermic reactions, such as decompositions or polymerizations, occur within the range of the temperature increase. 

Heat balances occur at the intersection of the heat generation curve and the heat removal line (points C and D). Stable operation will occur at point C. A reaction temperature lower than point C will result in self-heating up to point C because the heat generation rate exceeds the heat removal rate. At temperature Tb, the heat removal rate exceeds the heat generation rate, so the reaction temperature will fall until point C is reached. Although point D is a heat balance point, no stable operation is possible here a temperature slightly lower than that at point D will result in a decrease in reactor temperature to 

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