System 3
In many continuous-stirred tank reactors, the inlet and outlet pipes
are close together (Figure 13-3). In one operation it was desired to scale up
pilot plant results to a much larger system. It was realized that some short circuiting
occurred, so the tanks were modeled as perfectly mixed CSTRs with a
bypass stream. In addition to short circuiting, stagnant regions (dead zones) are
often encountered. In these regions there is little or no exchange of material
with the well-mixed regions, and, consequently, virtually no reaction occurs there. Experiments were carried out to determine the amount of the material
effectively bypassed and the volume of the dead zone. A simple modification
of an ideal reactor successfully modeled the essential physical characteristics
of the system and the equations were readily solvable.