A process with controls is shown in Figure Q7.6. The objective is to achieve a d

Question

A process with controls is shown in Figure Q7.6. The objective is to achieve a desired composition of B in the reactor effluent. The process consists of a feed tank of reactant A, which is maintained within a range of temperatures and is fed into the reactor, where the following reactions take place. A rightarrow B A rightarrow C If the reactor level is too high, the pump motor should be shut off to prevent spilling the reactor contents. Identify at least one variable that is controlled by each of the five approaches to control presented in this chapter. Discuss why the approach is (or is not) a good choice. Schematic drawing of process and control design.

Explanation / Answer

In case of the reactor design the output B and C compositions depend on the temperature range and amount of A. That means the mixing pattern in the reactor depends on the internal and external input parameters.Now range of temperatures is mentioned that means the time and rate of reactions determines the output B and C from the same composition of A.

Using mass balance equation total accumulation= input-output+generation. to complete the mass-balance equation

we need to use the stoichiometric coefficient considering the type of reaction and temparture factor. Considering variables like isothermal conditions, steady state and density it is clear that stoichiometric coefficient or the ratio of reactant and product is the variable dependent on all the five approaches. In all these approaches the above mentioned variables, outlet concentration, residence time determine the coefficient.

This approach is good choice as at high reactor content it prevents the spilling maintaining the reactant to product ratio to get accurate stoichiometric coefficient for both resultant content B and C. Finally, the same thing is good for safety measures also.

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