To keep C _A high throughout a plug-flow reactor, we might, at first glance, believe that we should feed A into the reactor at various points along the reactor, as shown in Figure CD6-1. However, further examination of the situation shows that although the addition of pure A (stream 2) to stream 1 increases the concentration of A in stream 1, stream 2 of pure A is diluted by this addition. Consequently, instead of diluting stream 2 (pure A) by feeding it into the side of the reactor, it is preferable to feed it to the entrance of either another reactor or of the reactor in Figure CD6-1, together with stream 1. The scheme shown in Figure CD6-1 will maintain C _A at a low value.

Figure CD6-1
PFR with feed streams along the length of the reactor.