Separation Process Principles- 2n - Seader &amp; Henley - Solutions Manual

# Isothermal can have a large temperature range can not

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Unformatted text preview: cause of the dilute condition, x V′ y V′ y X= ≈x= − Yout = 0.01896 − 0.000095 (3) L′ 1 − y L′ 1− x 1− y which is very close to the given operating line. (b) From Eq. (6-138), N OG = Y = 0.25 dY Y −Y * Y = 0.00503 (4) 1 (Y − Y *) as a function of Y, where for a given value of Y, the value of X is obtained from Eq. (3). Then, x is computed from X. Then, y = y* is computed from the given equilibrium equation, and Y* is 1 then obtained from the equilibrium curve. Below is a plot of versus Y. The area under (Y − Y *) the curve is the value of the integral for NOG . In the table below, the trapezoidal method is used Eq. (4) can be solved graphically or numerically. Both require a table of values of Exercise 6.39 (continued) Analysis: (b) (continued) to break the curve into segments of ∆Y. each, varying in width from 0.0103 to 0.0413. For each segment (width), the average value of 1/(Y-Y*) is used to compute the product = Area = ∆Y times 1/(Y-Y*), which is given in the last column. The sum of these areas is NOG = 5.16. Exercise 7.1 Subject: Comparison of absorption, distillation, and stripping Find: Differences between absorption and distillation, and stripping and distillation Analysis: Absorption Stripping Distillation Feed is gas Feed is liquid Feed is liquid, vapor or a mixture of the two Second phase (absorbent) is added Second phase (stripping agent) Second phase is created by is added heat transfer Operation can be adiabatic Operation can be adiabatic Must have heat transfer at the top and bottom stages Single-section cascade Single-section cascade Two-section cascade Can be almost isothermal Can be almost isothermal Can have a large temperature range Can not separate a closeboiling mixture Can not separate a closeboiling mixture Can separate a close-boiling mixture Tray efficiency can be low Tray efficiency can be moderate Tray efficiency can be high Exercise 7.2 Subject: Emergence of packing to replace trays. Find: Reasons why some existing trayed towers are being retofitted with packing, and some large-diameter columns are being designed for packing. Analysis: New random packings and structured packings have been introduced with higher capacity, lower pressure drop, and higher efficiency than trays. Also for packed columns, liquid distributors have been greatly improved. Channeling of liquid in packed columns is now much less of a problem. Exercise 7.3 Subject: Condenser coolant for distillation of a methane-ethane mixture. Find: Appropriate coolant. Analysis: Assume that the distillate is nearly pure methane, the most volatile of the two components. To use cooling water, the distillate temperature would be approximately 120oF. But the critical temperature of methane is -115oF. Therefore could not condense it. The critical pressure of methane is 673 psia. Using Fig. 7.16, could consider operation at 415 psia because that is safely below the critical pressure (P/Pc = 0.62 and could operate as high as a P/Pc = 0.8). From...
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