Page 276 - Process Equipment and Plant Design Principles and Practices by Subhabrata Ray Gargi Das

10.4 Design illustration 277

Table P10.2b lists the operating line points generated from the above equation, for plotting the
same on the xey axis along with the equilibrium line in Fig. P10.2C.

Table P10.2b Operating line points generated in the range 0.00,553 £ y op £ .1
0 18.339ee5 37.068ee5 56.197ee5 75.74ee5 95.711ee5 116.12ee5 136.99ee5 158.34ee4 180.17ee5
x op
0.00553 0.016027 0.26523 0.03702 0.047517 0.58013 0.06851 0.079007 0.089503 0.1
y op

The tower diameter is estimated based on bottom flow rates that are the highest mass flow rates.
The procedure based on bed flooding given in Section 14.5 is followed using the following values.
3 o
r ¼ð5803:63 = 4000Þ ð273 = 303Þ¼ 1:307; r z 1000 kg=m at 30 C; 1 atm
G L
and m L ¼ 0.0008 Pa.s.
2
The estimated tower cross section for around 70% flooding is: A t ¼ 3.205 m , and
1=2
¼ 2:02 m
d ¼ð3:205 4=pÞ
Finding k a and k a
0
0
x y
Empirical correlations valid for SO 2 (in air)-water system at 20 C with 1 Raschig ring random

00
0:7 1=4 0:82 2
0
0
packing are - k a ¼ 0:0594 m V m L , and k a ¼ 0:152 m L kmol/s.m per
x x
mole fraction.
Correction for operating temperature of 30 C are incorporated by correcting for the change in gas

and liquid phase diffusivities as follows
0:7 1=4 0:7 1=4

1:5
0 ;
k a ¼ 0:0594 m V m L ð303=293Þ ¼ 0:06247 m V m L
x
and
0:82 0:82

k a ¼ 0:152 m V ð303 = 293Þ¼ 0:157 m L
0
x
Due to transfer of solvent, the mass flow rates of the phases vary along the tower. This shall render
the mass transfer coefficients to be calculated for each section of the tower. Considering the system to
be a concentrated system, we include this change in the values of m V and m L . This is again based on
solute balance around the said control volume and appear as
2 3
1 1
4 64 y op þ 29 1 y op 5 ;
m V;op ¼ 160:7
1 y op 3600 3:205