Refluxes and Net Flow

The parameter is particularly difficult to interpret and comprehend in thermally coupled stmctures since there is a transfer of both liquid and vapor streams at the thermally coupled junction. Although the direction of the bulk material is obvious for the product producing CSs, it is not immediately obvious whether CS2, for either structure, is in rectifying or stripping mode. In general, it can be shown that there is only one realizable flow pattern for each structure, such that the structure has to 

FIGURE 6.29 Geometric representation of movement for a th mally coupled side (a) stripper and (b) rectifier colunm. 

Furthermore, a mass balance around the reboiler results in 

Since the feed to the column has to be greater than or equal to any product stream (F B), one finds that 

While the net flows patterns for each structure are now clearer, it still remains difficult to comprehend the effects of changing the reflux in one CS in the rest of the column. The reflux ratio in a specific CS is an important parameter in finding feasible structures and therefore it is necessary to fully understand these effects. As shown in previous chapters, the reflux in a specific CS is a limitless parameter valid anywhere from negative to positive infinity. Notice howev that in the side-stripper configuration, for example, that the liquid stream is split into two parts. 

---

We now have streams in CSk+i written in terms of the stream of CS which allows us to relate their refluxes (and net flows) using the definition of a 7 in Equation 6.1, for 1 ... 

---