All CSs at Infinite Reflux

FIGURE 7.2 CS breakdown for the Petlyuk column operating at infinite reflux. 

For the remaining CSs, the first instinct one may have when specifying that all CSs operate at infinite reflux is that the operating profiles of these CSs will also merely lie on the residue curves as A = 0 (V=L). This is, however, not necessarily the case. Consider expanding the DPE shown in Chapter 3 (Equation 3.9) as follows  

The term 8 = (y —x ) is known as the difference vector. 8 is the difference between vapor and liquid compositions in a CS and remains constant down the length of the CS. For CSs terminated by a reboiler or cond ser (CSi and CS in the Petlyuk), Equation 5.19 reduces to the classic residue curve equation because y = x. 8 can be und stood in much the same way as X a negative value implies that a component is moving downward in the CS, and vice versa. However, unlike it is important to note that 

This implies that the individual elements of 8 caimot all have the same sign if one of the oitries in 8 is positive, then at least one other entry has to be negative to obey 

FIGURE 13 Regions of unique pinch point curve bdiavior the diffmnt placements of 5 (a) S pair 1, (b) 8 pair 2, and (c) 8 pair 3. 

---