Feasible designs distributed feed columns

It is apparent that the single feed column is the one limit on the distributed feed column. At the other end of the design spectrum, one may theoretically choose to split the feed stream in infinitely many substreams, resulting in infinitely many CSs. Although this may seem like a purely academic or impractical limit, it does have some use because the feasible region resulting from this will show us all possibilities when deciding on a column. Thus, the profiles of any feed stream division will lie in... 

Before we start searching for feasible designs and interpreting the effects of Xa s and 7 a s, we first have to define our column and break it into a series of CSs. Consider then a two product distillation column terminated at the top by a condenser and at the bottom by a reboiler, as shown in Figure 6.1. We shall define the total feed to the column as Ft, which is to be distributed at multiple points down the length of the column. For the general case where the feed is to be split into N — 1 substreams, at A 1 feed points, the result will be a column consisting of N CSs. 

It is also interesting to note that, from a mathematical point of view, these strange positions of X that may be created through distributed feed addition allow the roots of the DPE to be complex. The profiles are in such cases, of course, still perfectly valid and it is still possible to design a feasible column if the roots of the DPE happen to be complex in a particular CS. 

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