A saturated vapor stream containing 10.9 mole% propane, 75.2% isobutene, and 13.9% n-butane passes from the top

Question:

A saturated vapor stream containing 10.9 mole% propane, 75.2% isobutene, and 13.9% n-butane passes from the top of a distillation column to a total condenser seventy-five percent of the condensate is returned to the column as reflux, and the remainder is removed as the overhead column product at a race of 2500k mol/h. A decision must be made on whether to use a refrigerant or cooling water in the condenser. If the refrigerant is used, it will be fed to the condenser as a liquid and vaporized by the heat released by the condensing column vapor. The refrigerant pressure will be such that the vaporization takes place at ?6?C, at which temperature ?Hv = 151 kJ/kg. The other option calls for cooling water to be taken from a nearby river at its average summer temperature of 25?C. To avoid environmental problems, the temperature of the water returned to the river can be no greater than 34?C. With either system the temperature of the condensate should be 6?C greater than the outlet temperature of the coolant so that if the refrigerant is used the saturated condensate should have a temperature of 0?C, and if cooling water is used the saturated condensate should be at 40?C. The condenser pressure will be set to the minimum value needed to condense all of the vapor, which is to say the condensate will be at its bubble-point temperature at the condenser pressure. Raoult?s law ma? he used for i1 bubble-point and dew-point calculations (see Section 6.4c).

(a) Suppose the refrigerant is used for cooling. Estimate the condenser pressure P (mm Hg): the temperature T_f (?C) of the vapor fed to the condenser, assuming that the vapor is at its de point at pressure P; and the required coolant flow rate (kg/h).

(b) Repeat part (a) assuming that cooling water is fed to the condenser.