Safe Operation of a Semibatch Reactor
Safe Operation of a Semibatch Reactor
This Demonstration illustrates a method to operate a semibatch reactor to avoid thermal runaways.
Consider the following liquid-phase irreversible exothermic reaction taking place in a semibatch reactor equipped with a cooling jacket: , 100 moles of reactant at a concentration of are placed in the reactor vessel, then a stoichiometric amount of is fed at a concentration of and at a constant volumetric flow rate. Thermal runaway is avoided by maintaining the reactor temperature below the temperature trajectory of an ideal case in which all the added species react instantaneously, .
A+BC+D
B
1mol/
3
dL
A
1mol/
3
dL
T
max
For each reacting system and reactor configuration, the reactor performance can be defined with two control variables: the molar feed rate of the added reactant and the coolant temperature . If the cooling system is sufficient to absorb the heat generated due to the reaction, three characteristic reactor behaviors can be distinguished:
T
c
1. If the reactor temperature is always much lower than , a huge accumulation of unreacted reactants occurs. This process is potentially dangerous because in case of a stirring or cooling system failure, the reactor becomes similar to a batch reactor and thermal runaway can occur.
T
max
2. The thermal runaway, where the reactor temperature surpasses the target temperature and approaches much higher temperatures.
3. A case in which the operating temperature is close to the maximum temperature for most of the reacting time. This results in an almost instantaneous conversion and low reactant accumulation and it is the most desirable reactor performance.