Page 81 - Chemical engineering design

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CHEMICAL ENGINEERING
Distillate (D)
99% Acetone
Feed (F)
1% Water
1000 kg/h 25°C
10% Acetone
90% Water
35°C
All compositions
by weight
reflux ratio 10
Bottoms (W)
< 100 ppm acetone
100°C

Solution

Material balance
It is necessary to make a material balance to determine the top and bottoms product
flow rates.
Balance on acetone, acetone loss in bottoms neglected.
1000 ð 0.1 D D ð 0.99
Distillate,D D 101 kg/h

Bottoms,W D 1000 101 D 899 kg/h

Energy balance
The kinetic and potential energy of the process streams will be small and can be neglected.
Take the first system boundary to include the reboiler and condenser.

H D
Q
C
H
F System
Q
B
H
W
Inputs: reboiler heat input Q B C feed sensible heat H F .
Outputs: condenser cooling Q C C top and bottom product sensible heats H D C H W .
The heat losses from the system will be small if the column and exchangers are properly
lagged (typically less than 5 per cent) and will be neglected.
Ž
Basis 25 C, 1h.