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Process Calculations
Laws of Thermodynamics
GATE 2009
Medium

For the same flash distillation unit (feed 1000 kmol/hr, D/F=0.5, B/F=0.5), 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 (Qh in kJ/hr) is

  • A−2×10⁶
  • B−1×10⁶
  • 1×10⁶
  • D2×10⁶

Explanation

Energy balance (feed enthalpy=0 as reference): Qh=D·HD+B·HB=500×3000+500×(−1000)=1,500,000−500,000=1,000,000 kJ/hr.

Source: GATE CH 2009 (2009)

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