Question

A binary mixture of components A and B are to be separated using a flash drum at a pressure of 1 atm

.

The feed mixture enters the flash vessel at a flowrate of 800 kmol/h, and consists of 50 mol% of component A

.

(a) Determine the compositions of the liquid and vapor stream leaving the flash vessel if the feed is to be 25% vaporized.

(b)Estimate the temperature Tdrum.

(c)Determine the compositions of the liquid and vapor stream leaving the flash vessel , and the temperature T drum when

:(i) 0% of feed is vaporized

(ii) 50% of feed is vaporized

(iii)75% of feed is vaporized

(iv) 100% of feed is vaporized

(d) Plot the operating lines for each of the cases described above

(e) Discuss how the value of the fraction of the feed vaporized affects the operating line obtained

for your flash system

Answer 1

1. PART A

Feed rate - 800 kmol/h

X_A,F = 0.5

For flash distillation,

given only 25% of fead is vaporized

D = 0.25 * F = 200 kmol/h

D = 200 kmol/h

F = D + W...............(1)

W = 600 kmol/h

2. PART B

No temperature of enthalpy data is provided to find Tdrum

3. PART C and D

F z_F = D y_D + W x_W ....................(2)

F H_F + Q = D H_D + W H_W .....................(3)

solving 2 and 3

-W/D = -3

i) 0% feed, W = 800 kmol/h, D = 0, -W/D = 0

ii) 50% feed, W = 400 kmol/h, D = 400 kmol/h, -W/D = 1

iii) 75% feed, W = 200 kmol/h, D = 600 kmol/h, -W/D = 0.5

iii) 100% feed, W = 0 kmol/h, D = 800 kmol/h, -W/D = infinty