Excercise 2.2: kmol A mixture of acetone (1) and water (2)( ) at boiling point w
ID: 702738 • Letter: E
Question
Excercise 2.2: kmol A mixture of acetone (1) and water (2)( ) at boiling point with a mole frac- tion of acetone of xF 0.475 should be cleaned. The distillate stream is preset to be D 4840mO with a purity of xD 0.93. The energy for heating the sump is provided by a steam stream of pure water S which is inserted directly to the sump. Calculate the size of this stream and determine the number of theoretical stages, if the reflux ratio is v 1.0. Use the diagram enclosed for solving this task. Equilibrium diagram for acetone (1)-water (2) at p 1.013 bar 1.0 m 0.9 0.8 0.7 0.6 0.5 E 0.4 0.3 0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0Explanation / Answer
Feed flow rate= 10000 kmol/h
Distillate flow rate= 4840 kmol/h
xF=0.475
xD= 0.93
Overall material balance
F+S = D+W
10000+S = 4840+ W.........(1)
Component balance for acetone
FxF +S(0) =DxD+Wxw
10000* 0.475= W*xW+ 4840*0.93.........(2)
The q value for this question is 1 since the mixture boiling
L'=L+qF..........(3)
where L'= liquid flowrate in the stripping section
and L= Liquid flowrate in the rectification section
also the reflux ratio=R=L/D=1
which implies L=D.......(4)
and in the stripping section
L'=W(since no reboiler).......(5)
Putting the values of (4) and (5) in (3)
W= D+qF
value of q=1
=> W=D+F....(6)
putting the value of W in (1) we get
S= 2D= 2*4840= 9680 kmol/h
W= 14840 kmol/h
xw=0.0167
Plotting the graph:
Plot the points D(0.93,0.93), W(0.02,0) and F(0.475,0.475) on y=x. The y coordinate of W will be zero since there is no reboiler.
The q line will be a line pass through x=0.475 and will be parallel to y axis
Equation of rectifying section: y= 1.532x-0.0256
Joining the point of intersection of rectifying section and q-line with the point W using a straight line we get the stripping section operating line.
The no. of plates can be effectively drawn by The McCabe Thiele Method in which steps are drawn between the operating lines and the equilibrium curve upto point W.
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