Autorefrigerated Reactor

Why are the CSTRs worth considering at all They are more expensive per unit volume and less efficient as chemical reactors (except for autocatalysis). In fact, CSTRs are useful for some multiphase reactions, but that is not the situation here. Their potential justification in this example is temperature control. BoiUng (autorefrigerated) reactors can be kept precisely at the desired temperature. The shell-and-tube reactors cost less but offer less effective temperature control. Adiabatic reactors have no control at all, except that can be set. 

AUTOREFRIGERATED REACTOR OF LUYBEN DYNAMIC STABILITY ANALYSIS... 

There are many reactors in industry that use evaporative cooling. The liquid in the reactor boils to remove reaction heat. The vapor leaving the reactor is condensed in an external heat exchanger, and the liquid is returned to the reactor. Clearly the vapor phase is important in these autorefrigerated reactors. In addition to chemical kinetics, the vapor-liquid equilibrium properties influence the design of the reactor-condenser system. 

Figure 2.24 Autorefrigerated reactors with (a) 90% conversion and (b) 80% conversion.

Figure 3.45 gives a Matlab program for the nonlinear simulation of the autorefrigerated reactor. The specific case is the 90% conversion with a cooling water temperature in the condenser of 317 K. The reactor volume is 1.68 m3, and the reactor temperature TR is 353 K. The condenser area is 19.9 m2, and the condenser temperature Tc is 331 K. The temperature differential driving force is 331 - 317 = 14 K to transfer 0.237 MW. 

Figure 3.45 Matlab program for autorefrigerated reactor simulation.

Thus the autorefrigerated reactor system provides yet another example of the importance of heat transfer area and the increased difficulty of controlling reactors that do not have high conversion rates. Keep in mind that we are considering exothermic reactions that are irreversible. Control problems are much less severe in reactors with endothermic reactions or with reversible reactions because of the inherent self-regulatory nature of the chemistry. 

Autorefrigerated reactor in sulfuric acid alkylation. In Pet. Technol. Q. Crambeth Allen Publishing Craven Arms, U.K., 1996 27-33. 

For the great majority of reaction schemes, piston flow is optimal. Thus the reactor designer normally wants to build a tubular reactor and to operate it at high Reynolds numbers so that piston flow is closely approximated. This may not be possible. There are many situations where a tubular reactor is infeasible and where CSTRs are used instead. Typical examples are reactions involving suspended solids and autorefrigerated reactors where the reaction mass is held at its boiling point. 

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