Page 296 - Process Equipment and Plant Design Principles and Practices by Subhabrata Ray Gargi Das

298 Chapter 11 Distillation

Inputs to and outputs from the McCabeeThiele method for design of a simple binary distillation
column comprising of a single feed and two products are listed in Table 11.4.

Table 11.4 Input and output items for McCabeeThiele method.
Inputs Outputs

· Feed flow rate (F) and composition (z F ) · Distillate and bottoms flow rate (D, B)
· Column pressure (P) (assumed uniform · Minimum number of equilibrium stages (N min )
throughout the column) · Minimum reflux ratio (R min )
· Condition (phase) of feed at column pressure · Boil up rate in reboiler (V)
· V-L-E curve for binary mixture at column · Condenser and reboiler heat load (Q Condenser ,
pressure Q Reboiler )
· Overhead condenser type (total/partial) · Number of equilibrium stages (N)
· Reboiler type · Feed stage location (N F )
· Distillate and bottoms composition (x D and x B ) · Stagewise vapour and liquid composition (y n ,
· Ratio of reflux to minimum reflux (R/R min ) x n )
Flow rates (F,D,B,V) are in mol/hr; Compositions (z F, x D ,x B ,y n ,x n ) are in mole fraction of the more volatile component. N is the
total number of theoretical trays and n denotes the tray number. Conventionally trays are numbered from top to bottom.

The McCabeeThiele construction for design of a benzene-toluene distillation system at near at-
mospheric column pressure is shown in Fig. 11.8.

1.0
0.9 (x D ,y D )
#1
#2
0.8
(x ,y ) #3
e e
#4
0.7
q–line
#6
slope = q
0.6 q–1
#7
0.5 #8 (x ,y )
F F
y
0.4 x D
0, #9
R+1
0.3
#10
0.2
#11
0.1
,y )
(x B
B
0.0
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
x
FIGURE 11.8
McCabeeThiele construction.