Process Calculations GATE-2009

Q 1: Pure water (stream W) is to be obtained from a feed containing 5 wt % salt using a desalination unit as shown below.

If the overall recovery of pure water (through stream W) is 0.75 kg/kg feed, then the recycle ratio (R/F)

A) 0.25
B) 0.5
C) 0.75
D) 1.0

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Common data for Q 2 & 3:

A flash distillation drum (see figure below) is used to separate a methanol-water mixture. The mole fraction of methanol in the feed is 0.5, and the flow rate is 1000 kmol/hr. The feed is preheated in a heater with heat duty Q_h and is subsequently flashed in the drum. The flash drum can be assumed to be an equilibrium stage, operating adiabatically. The equilibrium relation between the mole fractions of methanol in the vapor and liquid phases is y* = 4x. The ratio of distillate to feed flow rate is 0.5.

Q 2: The mole fraction of methanol in the distillate is

A) 0.2
B) 0.7
C) 0.8
D) 0.9

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Q 3: If the enthalpy of the distillate with reference to the feed is 3000 kJ/kmol, and the enthalpy of the bottoms with reference to the feed is -1000 kJ/kmol, the heat duty of the preheater (Q_h in kJ/hr) is

A) -2×10⁶
B) -1×10⁶
C) 1×10⁶
D) 2×10⁶

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