Self-heating in a continuous stirred tank reactor

3 SELF-HEATING IN A CONTINUOUS STIRRED TANK REACTOR 

Consider a continuous stirred tank reactor operating at a constant temperature T and to which reactants are fed at a volumetric flow rate F. In the tank, the irreversible first-order exothermic reaction 

For a perfectly insulated reactor, the only heat removed is that carried away in the exit stream from the reactor 

The situation at the upper stable point, when reaction proceeds smoothly to completion at a high temperature without an external source of heat, is described as autothermal or autothermic operation. If the volumetric flow rate of reactants, F, is increased, then the slope of the Ql line is increased and the position of the Qq is also slightly changed the principal effect, however, is that, eventually, an upper intersection of the heat generation and heat loss lines is no longer possible and the autothermic reaction is blown out . 

Inspection of Fig. 24, which represents the behaviour of a reversible exothermic reaction with various cooling rates, shows that autothermal operation is possible (point A), but that a somewhat reduced cooling rate results in a greater Qq, and hence conversion (point B) excessive cooling will, of course, quench the reaction (point C). 

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