Rectification operating line

The McCabe-Thiele method employs the simplifying assumption that the molal overflows in the stripping and the rectification sections are constant. This assumption reduces the rectifying and stripping operating line equations to ... 

Stop 5) Plot the operating line for the rectification section (R.O.L.) ... 

The simplest method is to start with the rectification zone by drawing the corresponding line from the point x = Xp and find the intersection with the g -line. Then the operating line for the stripping zone is simply joining this point with x. ... 

Rectification columns are often operated with several feed streams. At each feed point the internal flow rate of liquid L or vapor G changes. As the slope of the operating line is Z/G, the operating line bends sharply at each feed point, see Fig. 5.2-7. 

From this, the balance, or operating, line of the rectification column is given by... 

The McCabe-Thiele approach for a binary mixture can be described as follows. First, we take the vapor-liquid equilibrium diagram y/x plot). Then we draw the operating lines based on the mass balance for the liquid and the vapor phase. There is one operating line for the stripping section and one for the top (rectification or enriching) section. The assumption of (in each case) constant molar flows of liquid and vapor ensures strictly straight operating lines. 

Figure 3.3.11 Construction of the operating line for the rectification section of a distillation column (x and y refer to lower-bolling feed component A, i.e., to xa and yA In the text).

The McCabe-Thiele method assumes that the liquid on each tray and the vapor above it are in equilibrium, and that between the trays the molar composition of the down-flowing liquid and the up-flowing vapor are related by the operation lines, Eq. (3.3.16) for the rectification section and Eq. (3.3.18) for the stripping section (Figure 3.3.13). 

Finally, in addition to the liquid nitrogen and liquid oxygen - enriched streams from the pressure to the low-pressure column, there is a third liquid air fraction (k) from the pressure to the low-pressure side. This flow is adjusted such that the operating line and the equilibrium curve, as shown in the McCabe-Thiele diagram of the low-pressure column, move closer together. This reduces the irreversibility of the rectification and increases the O2- and Ar-yield. 

The operating lines y =f(x) shown in Figure 16.2 are derived from the respective mass balances of the lighter component in the rectification and stripping sections. The equilibrium line / =f(x), however, is derived from the thermodynamic characteristics of the system in terms of the liquid vapour equilibrium. This equilibrium can be then described by the following relation between the... 

Draw in the rectification section operating line from point on the 45 degree line to point... 

Given the operating lines for both the stripping and the rectification sections, the graphical construction of the steps is applied. In this way, we count the number of steps as shown in the diagram. This particular example shows that the seven theoretical stages are required to achieve the desired... 

Note that if the problem of accurate graphical representation occurs in the rectification end of the diagram, the corresponding relation to use to calculate the balance of the trays, assuming straight line operating and equilibrium lines in the region is [59] ... 

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