It intersects the 45° line at xD and has a slope equal to the ratio of the liquid-to-vapor rates in the rectifying section. Figure 2.23 shows both operating lines together with the y-x vapor-liquid equilibrium curve.
Tray-to-tray calculations involve the solution of vapor—liquid equilibrium relationships and component balances. These tray-to-tray calculations can be solved graphically by stepping back and forth between the operating line (y =-- mx + b) and the VLE curve (y = /(*)), as shown in Figure 2.24.
For example, let us start at the bottom of the column with known values of xB and Ls/Vs. Our VLE relationship gives us yB if we know xB. Graphically,
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