70 1792 1745 from eq 7 3 the curve is computed from

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Unformatted text preview: 5x/(1+0.745x) (3) The McCabe-Thiele diagram on the next page shows the operating lines for determining the minimum reflux ratio. It assumes that the pinch region occurs at the feed stage and not at the sidestream stage. From Eq. (7-18), q for 25 mol% vaporized = 0.75. From Eq. (7-26), the slope of the q-line = q/(q-1) = 0.75/(0.75-1) = -3. The upper section operating line intersects the q-line and equilibrium curve at y=0.823 and x=0.727. Thus, slope of the upper section operating line = L/V = (0.96-0.823)/(0.96-0.727) = 0.588. From Eq. (7-27), Rmin = (L/V)/[1 - (L/V)] = 0.588/(10.588) = 1.427. Therefore, L = 1.427(74.45) = 106.3 kmol/h and V = L + D = 106.3 + 74.45 = 180.75 kmol/h. In the middle section between the feed stage and sidestream stage, for 25 mol% vaporization, L' = L + 0.75(100) = 106.3 + 75 = 181.3 kmol/h and V' = V - 0.25(100) = 180.75 25 = 155.75 kmol/h. Thus, L'/V' = 181.3/155.75 = 1.164. The middle section operating line has this slope and passes through y=0.823 and x=0.7...
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