FIG. 14-4 Design diagrams for (a) absorption and (b) stripping.

Once the design recovery for an absorber has been established, the operating line can be constructed by first locating the point x2, y2 on the diagram. The intersection of the horizontal line corresponding to the inlet gas composition y1 with the equilibrium curve y0 = F(x) defines the theoretical minimum liquid-to-gas ratio for systems in which there are no intermediate pinch points. This operating line which connects this point with the point x2, y2 corresponds to the minimum value of Lm/Gm. The actual design value of LM/GM should normally be around 1.2 to 1.5 times this minimum value. Thus, the actual design operating line for a gas absorber will pass through the point x2, y2 and will intersect the line y = y1 to the left of the equilibrium curve.

For stripping one begins by using the design specification to locate the point x1, y1; then the intersection of the vertical line x = x2 with the equilibrium curve y0 = F(x) defines the theoretical minimum gas-to-liquid ratio. The actual value of GM/LM is chosen to be about 20 to 50 percent higher than this minimum, so the actual design operating line will intersect the line x = x2 at a point somewhat below the equilibrium curve.

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