Fix the cold external reflux at 0.8 times the total moles overhead product.
The total number of moles of HC in the overhead vapor is 1.8 Â 805.1 =
1,449.18 mol/h.
Total moles of steam in the overhead vapor is 2,076.
Partial pressure of the hydrocarbons in the overhead vapor is
1, 449:19 Â 29:7
3, 525:18
¼ 12:2 psia
The tower overhead temperature is the dew point of the hydrocarbons at the partial
pressure and is shown in Table 7.
To Calculate Side Stream Stripper Bottom Temperatures
These are calculated by heat balances over the respective side stream strippers. The
following criteria are used in these calculations:
HGO
LGO
KERO
Total stripout % vol
5
8
8
Mol wt of stripout
230
180
120
SG of stripout
0.865
0.820
0.750
Only the heat balance calculation of the HGO stripper is given below (see also
Table 8). The other two stripper calculations will be similar in form (Figs. 20,
21, and 22):
Table 7 Tower overhead composition
Comp
Mol
frac
First
trial K
At 250
F
X = y/K
Mol wt
Weight
factor
SG at 60
Volume
factor
C2
0.008
Neg
Nil
C3
0.054
73.77
0.001
44
0.044
0.508
0.009
iC4
0.021
35.24
0.001
58
0.058
0.563
0.010
nC4
0.084
27.05
0.003
58
0.174
0.584
0.030
C5
0.143
11.80
0.012
72
0.864
0.629
0.137
C6
0.155
4.590
0.034
85
2.89
0.675
0.428
C7
0.175
2.213
0.079
100
7.90
0.721
1.100
Comp 1 0.124
1.066
0.116
114
13.224
0.743
1.780
Comp 2 0.124
0.557
0.223
126
28.098
0.765
3.673
Comp 3 0.075
0.311
0.241
136
32.776
0.776
4.224
Comp 4 0.037
0.135
0.274
152
41.648
0.788
5.285
Total
1.000
0.984
129.7
127.676
0.766
16.675
K2 ¼ K1 Â Sx ¼ 0:135 Â 0:984 ¼ 0:133 ¼> 246
F which will be the tower top temperature.
170
D.S.J. Jones
The total number of moles of HC in the overhead vapor is 1.8 Â 805.1 =
1,449.18 mol/h.
Total moles of steam in the overhead vapor is 2,076.
Partial pressure of the hydrocarbons in the overhead vapor is
1, 449:19 Â 29:7
3, 525:18
¼ 12:2 psia
The tower overhead temperature is the dew point of the hydrocarbons at the partial
pressure and is shown in Table 7.
To Calculate Side Stream Stripper Bottom Temperatures
These are calculated by heat balances over the respective side stream strippers. The
following criteria are used in these calculations:
HGO
LGO
KERO
Total stripout % vol
5
8
8
Mol wt of stripout
230
180
120
SG of stripout
0.865
0.820
0.750
Only the heat balance calculation of the HGO stripper is given below (see also
Table 8). The other two stripper calculations will be similar in form (Figs. 20,
21, and 22):
Table 7 Tower overhead composition
Comp
Mol
frac
First
trial K
At 250
F
X = y/K
Mol wt
Weight
factor
SG at 60
Volume
factor
C2
0.008
Neg
Nil
C3
0.054
73.77
0.001
44
0.044
0.508
0.009
iC4
0.021
35.24
0.001
58
0.058
0.563
0.010
nC4
0.084
27.05
0.003
58
0.174
0.584
0.030
C5
0.143
11.80
0.012
72
0.864
0.629
0.137
C6
0.155
4.590
0.034
85
2.89
0.675
0.428
C7
0.175
2.213
0.079
100
7.90
0.721
1.100
Comp 1 0.124
1.066
0.116
114
13.224
0.743
1.780
Comp 2 0.124
0.557
0.223
126
28.098
0.765
3.673
Comp 3 0.075
0.311
0.241
136
32.776
0.776
4.224
Comp 4 0.037
0.135
0.274
152
41.648
0.788
5.285
Total
1.000
0.984
129.7
127.676
0.766
16.675
K2 ¼ K1 Â Sx ¼ 0:135 Â 0:984 ¼ 0:133 ¼> 246
F which will be the tower top temperature.
170
D.S.J. Jones