The operating curve with recycle
The figure below shows that the liquid recycle from the condenser lowers the high conversion, high temperature portion of the operating curve about 10 C for this system. At the low outlet temperatures, there is almost no solvent boilup so the operating curve is not affected.
The reflux didn't change the unstable temperature range. The loop program, which uses cstr_Q won't obtain solutions in the unstable region so the blue operating curve is in two parts.
This system was chosen to develop and demonstrate the muliphase cstr model. I haven't explored the economic feasibility of this design.
The boiling cstr may be useful for several applications. First, as shown by this example, the operating curve was lowered about 20 C overall by using boilup and cold recycle. The lower temperatures might greatly reduce catalyst decay or product degradation. Biochemical reactions might have temperature limitations for catalyst (yeast, enzyme), reactants, and products. Second, some reaction systems may have a high heat removal/volume requirement. It may not be possible to provide enough heat transfer area/volume for the reactor. The external condenser has no limitation on area. Third, polymerization systems may foul the reactor side heat transfer areas (coils or jackets) with high viscosity fluid or solid on the cold surface. Evaporation and condensation of the monomer avoids that problem.
Farewell to the cstr operating curve
I know you must be getting tired of seeing the cstr operating curve. This post will be the last to use it for awhile, probably until I get to dynamic models. The curve has been a great tool for illustrating the behavior of both real cstr reactors and how their models can be constructed.