McCabe-Thiele diagram rectification

For the design of rectification columns, the equilibrium concentrations of the gas and liquid phases at constant pressure are of decisive importance. The McCabe-Thiele diagram (Figure 2.3.2-4), based on Raoult s law, describes this relationship (Equation 2.3.2-9) ... 

Fig. 1-56. Scliematic of a rectification column for the separation of an ideal binary mixture, and the corresponding McCabe-Thiele diagram.

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 rectification in the crude argon column is almost a pure binary separation between O2 and Ar and can be best visualized and understood in the McCabe-Thiele Diagram, shown in Fig. 2.5. This diagram indicates for each tray the Ar-concentration y of the vapour directed towards the tray and the concentration x... 

For a given rectification problem the minimum reflux ratio v ,jn and the minimum number of separation stages may be determined by the McCabe-Thiele method or calculated by Eqs. (2-74) and (2-77). With these, the required number of theoretical stages for any chosen reflux ratio V is found from the Gilliland diagram. The best economic operating range of rectification columns is... 

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. 

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