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Unformatted text preview: ind: Most probable cause for abnormal operation. Recommended further tests. If 90 mol% methanol distillate could be obtained by increasing the reflux ratio for a constant vapor rate. Analysis:
First determine whether the normal operation can be verified by the McCabe-Thiele method. With L/D = R = 1, from Eq. (7-7), the slope of the rectifying operating line = L/V = R/(1 + R) = 1/2 = 0.5. Also, xF = 0.5, xD = 0.90, and xB = 0.05. What is not known is the phase condition of the feed. If a saturated liquid feed is assumed, giving a vertical q-line as shown in the plot below, stepping stages up from the bottom, with the feed stage to plate 3 from the bottom, less than 2 theoretical plates are needed in the rectifying section, while 4 are present. The construction is shown on the next page. Therefore, it appears that the feed is not a saturated liquid, but is partially vaporized. Analysis: Normal Operation (continued) Exercise 7.19 (continued) By trial and error, using q-lines of various slopes, the following McCabe-Thiele diagram is consistent with the given data. It shows a q-line with a slope of -0.34. s...
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