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Unformatted text preview: aporization of steam at 273.7 kPa (404 K) = 2,172 kJ/kg Therefore, we need 436,000/2,172 = 200.7 kmol/h or 3,616 kg/h. (f) A rigorous enthalpy balance around the reboiler takes into account the sensible heat effect since the temperature of the liquid entering the reboiler is not the same as the temperatures of the equilibrium liquid and vapor leaving the reboiler. Let N = conditions leaving the reboiler and N-1 be the conditions leaving the stage above the reboiler. Then, QR = VN HVN + LN H LN - LN -1 H LN -1 Note that in the simplified enthalpy balance of part (e), the following equation was applied, QR = VN HVN - H LN Since, VN = LN - LN -1 , this is equivalent to assuming H LN = H LN -1 Exercise 7.28 (continued) Exercise 7.29 Subject: Preliminary design for the distillation of a mixture of ethanol and water at 1 atm. Given: Bubble-point feed containing 20 mol% ethanol in water. Unit consisting of a perforated-tray column, partial reboiler, and total condenser. Distillate to contain 85 mol%...
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