Question

​Your plant feeds 100 kmol/h of a mixture that is 46.0 mol% ethanol and 54.0 mol% water to a flash drum. Your boss thinks that results will be better with two flash drums with V₁ = 30.0 kmol/h and V₂ = 30.0 kmol/h.

a.​ Find L1, L2 and x2.

​b.​ Compare x2 to the liquid mole fraction from a single flash drum with V/F = 0.60.

Answer 1

a)from the flash distillation,writing mass balance,

feed(F)=V1+V2+L1+L2

we know F=100,V1=V2=30

L1+L2=40

similarly writing component balance,

Fxf=V1y1+V2y2+L1x1+L2x2

solve the above equation to get the required values

b)for a single flash drum

F=L+V mass/material balance

100=L+60

L=40

now writing the component balance:Fxf=Lx+Vy

whre x,y are the molefractions in liquid and vapor phases

100(0.46)=40x+60(0.6)

46=40x+36

x=0.4

compare this value with the value you got for x2 in double effect drum

hope you understood and comment me if you have any doubt,please up vote

46=40x