1. Binary Multistage Distillation
Condenser
At the top of column, three type of condenser:
Total condenser: takes the overhead vapor from the column and liquefies it completely and split it into two portions:
Distillate which is called overhead product.
Reflux which return back to the top plate.
accumulator D V
Condenser L
Reflux
Overhead
vapour
ChE 334: Separation Processes
Dr Saad Al-Shahrani

2. Binary Multistage Distillation
Partial condenser: takes the over head vapor from the column and liquefies a portion of it to return to the top plate as reflux, while the other portion is vapor product or distillate.
Mixed condenser
Partial condenser V
Condenser L
Vapor overhead
product
accumulator
Reflux
Overhead
vapor
Condenser
Vapor
distillate
Overhead
vapor V
accumulator
liquid
distillate L
Reflux
Mixed condenser
ChE 334: Separation Processes
Dr Saad Al-Shahrani

3. Binary Multistage Distillation
Re-boilers
Kettle type re-boiler
At the bottom of column which heat the bottom liquid to produce vapor partially and return it back to column, while the rest of liquid withdraw as a bottom product.
bottoms
ChE 334: Separation Processes
Dr Saad Al-Shahrani

4. Binary Multistage Distillation
Vertical thermosyphone-type re-boiler.
In this type of re-boilers, re-boiler liquid with drown from the bottom sump.
ChE 334: Separation Processes
Dr Saad Al-Shahrani

5. Binary Multistage Distillation
Vertical thermosyphone-type re-boiler.
In this type of re-boilers, re-boiler liquid with drown from the bottom-tray down comer.
ChE 334: Separation Processes
Dr Saad Al-Shahrani

6. Binary Multistage Distillation
Reflux
It is apart of condensed vapor returned back to stage below. There are two types of reflux:
1. Operating reflux ratio (External Reflux Ratio)
External Reflux Ratio= La/D
Condenser Va ya
accumulator La xa
Top
plate
Reflux D xD
ChE 334: Separation Processes
Dr Saad Al-Shahrani

7. Binary Multistage Distillation
2. Operating reflux ratio (Internal Reflux Ratio)
Internal Reflux Ratio
Vn+2
Ln+3
Plate n+2 or
Vn+1
Ln+2
Plate n+1 or Vn
Ln+1 or
Plate n
Vn-1 Ln
ChE 334: Separation Processes
Dr Saad Al-Shahrani

8. McCabe Thiele Graphical Equilibrium-Stage
Method for trayed tower D xD
accumulator Va ya
water
Stripping Section
Rectifying Section B xB
Condenser
Re-boiler Vb yb
Lb, xb
Bottom
plate
Top La xa
steam
Feed plate
MacCape-Thiele Diagram
Equations for the analysis of continuous flow binary distillation were developed by sorel (1893), but the simplest and most convenient method for analyzing binary distillation column is graphical method by [McCape and Thiele]
Feed
consider the equilibrium-stage distillation column shown in this figure.
Feed is a mixture of two components (A,B)
ya mole fraction of vapor
xa mole fraction of liquid
ChE 334: Separation Processes
Dr Saad Al-Shahrani

9. McCabe Thiele Graphical Equilibrium-Stage
n-1 n
Vn-1
Ln-2 Vn
Ln-1
Vn+1 Ln
We can group values of y and x into 2 groups:
Group 1:
Vapor and liquid leaving each plate
e.g. yn, xn
Group 2:
Vapor and liquid passing each other between two plates n
n-1 Vn yn
Ln-1
xn-1
e.g. yn, xn-1
ChE 334: Separation Processes
Dr Saad Al-Shahrani

10. McCabe Thiele Graphical Equilibrium-Stage
By defining of an ideal plate, the vapor and liquid leaving plate n are in equilibrium, so yn and xn represent equilibrium concentration.
Subcooled liquid
1.0
Superheated Vapor y
Temperature
yn+1 x xn yn
yn-1
xn+1
Saturated liquid line
Saturated vapor line
xn-1
operating
x,y
n-1 n Vn yn
Ln-1
xn-1
Vn+1
yn+1 Ln xn
Vn+2
yn+2
Ln+1
xn+1
Vn-1
yn-1
Ln-2
xn-2
n+1
ChE 334: Separation Processes
Dr Saad Al-Shahrani

11. McCabe Thiele Graphical Equilibrium-Stage
Since the concentration in both phases (vapor, liquid) increases with the hight of the column,
xn-1 > xn > xn+1
yn > yn+1 > yn+2
In spite of xn, yn (streams leaving plate n) are in equilibrium, xn-1, yn+1( streams entering plate n) are not in equilibrium (see the last figure)
ChE 334: Separation Processes
Dr Saad Al-Shahrani

12. McCabe Thiele Graphical Equilibrium-Stage
Condenser Va ya
accumulator La xa I
Overall material balances for Two components systems
Top
plate D xD
Total material balance
Rectifying Section Ln xn
Vn+1
yn+1 F
Component A balance
Feed
n+1
Feed plate
Eliminating B m
Stripping Section Lm xm
Vm+1
ym+1
Eliminating D II
Bottom
plate Vb yb
Re-boiler B xB
ChE 334: Separation Processes
Dr Saad Al-Shahrani
Lb, xb

13. McCabe Thiele Graphical Equilibrium-Stage
Equation (3), (4) are the true for all values of flows of vapor and liquid within the column
Net flow rates
By making a material balance around the condenser and accumulator D xD
accumulator Va ya
Condenser La xa
Top
plate
The difference between the flow rates of vapor and liquid anywhere in the upper section of the column (Rectifying section) = D
ChE 334: Separation Processes
Dr Saad Al-Shahrani

14. McCabe Thiele Graphical Equilibrium-Stage
Total balance around the control surface (I)
Vn+1
yn+1 Ln xn D xD
accumulator Va ya
Condenser
Top
plate La xa I
Then D= net flow in top (rectifying section). Regardless of changes in V and L, their difference is constant and = D
Component balance A
ChE 334: Separation Processes
Dr Saad Al-Shahrani

15. McCabe Thiele Graphical Equilibrium-Stage
By the same manner in the stripping section Total balance around control surface (II)
Vm+1
ym+1 Lm xm B xB
Re-boiler Vb yb
Lb, xb
Bottom
plate II
m is to designate a general plate in the stripping section
B= net flow in the bottom (stripping section)
ChE 334: Separation Processes
Dr Saad Al-Shahrani

16. McCabe Thiele Graphical Equilibrium-Stage
Material balance around the re-boiler B xB Vb yb
Lb, xb
Bottom
plate
Re-boiler
ChE 334: Separation Processes
Dr Saad Al-Shahrani

17. McCabe Thiele Graphical Equilibrium-Stage
Vn+1
yn+1 Ln xn D xD
accumulator Va ya
Condenser
Top
plate La xa I
Operating lines
Because there are two sections in the column,
there are two operating lines
1. For rectifying section (I)
For control surface (I) ( )
Vn+1
yn+1 Ln xn
Operation
relationship n
n+1
ChE 334: Separation Processes
Dr Saad Al-Shahrani

18. McCabe Thiele Graphical Equilibrium-Stage
Vm+1
ym+1 Lm xm B xB
Re-boiler Vb yb
Lb, xb
Bottom
plate II
2. For stripping section (II)
For control surface (II) ( )
Vm+1
ym+1 Lm xm
Operation
relationship m
m+1 Vm ym
Lm-1
xm-1
m-1
ChE 334: Separation Processes
Dr Saad Al-Shahrani

19. McCabe Thiele Graphical Equilibrium-Stage
Number of ideal plates, McCape Thiele Method
When the operating lines represented by:
For rectifying section
For stripping section
are plotted with xy equilibrium diagram, the McCabe Thiele step by step construction can be used to compute the number of ideal plates needed to accomplish a definite concentration difference in either rectifying or the stripping section
ChE 334: Separation Processes
Dr Saad Al-Shahrani

20. McCabe Thiele Graphical Equilibrium-Stage
Constant Molal overflow
For most distillation, the molar flow rates of vapor and liquid are nearly constant in each section of the column (rectifying and stripping) and the operating lines are almost straight. (note: V-L=D, L-V=B)
Reflux Ratio D xD V
Top
plate L
Reflux to overhead product
Reflux to the vapor
ChE 334: Separation Processes
Dr Saad Al-Shahrani

21. McCabe Thiele Graphical Equilibrium-Stage
In both numerator and denominator of the terms on the right hand side of the last two equations are divided by D, the result is for constant molal over flow.
intercept
slope
This equation is the operating line of the rectifying section. The y axis intercept of this line is xD/(RD+1)
ChE 334: Separation Processes
Dr Saad Al-Shahrani

22. McCabe Thiele Graphical Equilibrium-Stage
xD is set by the conditions of design
RD , the reflux ratio, is an operating variable that can be controlled by adjusting the split between reflux and overhead product or by changing the amount of vapor formed in the re-boiler for a given flow rate of the over head product.
Vn+1
yn+1
Put xn= xD
xn=xD L Ln
Reflux
n+1
Top plate
yn+1= xD
So the operating line for rectifying section intersect the diagonal at point (xD,xD). This is true for both partial and total condenser
xD yn+1
ChE 334: Separation Processes
Dr Saad Al-Shahrani

23. McCabe Thiele Graphical Equilibrium-Stage
Condenser and top plate
Vn+2
yn+2
Ln+1
Xn+1
n+1
Vn+1
yn+1
Top
plate
Ln=L =Reflux
Xa=xD
Top plate xn
Concentration of vapor from top plate =yn+1
Concentration of reflux to the top
plate xn= xD =yn+1
ChE 334: Separation Processes
Dr Saad Al-Shahrani

24. McCabe Thiele Graphical Equilibrium-Stage
Total Condenser
Top plate y’
yn+1
n+1
Vn+1
yn+1
yn+2
Equilibrium line
n+2
Top
plate
yn+1
yn+3 Ln xn
n+3
xn=xD
D, xD
n+1
xn+1
yn+2
Reflux
xn+1
n+2
xn+2
yn+3
xn+2
Operating line (rectifying section)
n+3
composition
Equilibrium with
Operating with
xn=xD y’
yn+1
xn+1
yn+2
xn+2
yn+3
ChE 334: Separation Processes
Dr Saad Al-Shahrani

25. McCabe Thiele Graphical Equilibrium-Stage
yn+1
Top
plate Ln
yn+1
xn=xD
n+1
n+1
xn+1
yn+2
yn+2
For total condenser
n+2
n+2
xn+2
yn+3
yn+3
n+3
n+3
xn=xD
xn+1
xn+2
xn+3
Operating line equation for the rectifying section:
45 o line
x = y
ChE 334: Separation Processes
Dr Saad Al-Shahrani

26. McCabe Thiele Graphical Equilibrium-Stage
Partial condenser
Partial Condenser
yD=xD D xD
Top plate
yn+1 V yD
n+1
Vn+1
yn+1
yD=xD
yn+2
Equilibrium line
n+2
Top
plate
yn+1
yn+3 xn Ln xn
n+3
n+1
xn+1
yn+2
Reflux
xn+1
n+2
xn+2
yn+3
xn+2
Operating line (rectifying section)
n+3
composition
Equilibrium with
Operating with xn
xD=yD
yn+1
xn+1
yn+2
xn+2
yn+3
ChE 334: Separation Processes
Dr Saad Al-Shahrani