overflash) and the mol wt is 305. Then the heat balance can be written as follows
(see also Table 6):
Heat in ¼ Heat out
197, 085x þ 45, 404, 000 ¼ 119, 916, 000
x ¼ 378 Btu=lb
From enthalpy tables, this equates to 704
F.
To Calculate the Side Stream Drawoff Temperatures
The steam rates to be used for side stream stripping will be:
All strippers will have three theoretical trays.
Each gas oil stream stripper will use 0.5 lb/gal.
The Kero stripper will use 0.65 lb/gal of steam.
Steam used is as follows:
Heavy gas oil ¼ 3, 675 Â 0:5 ¼ 1, 838 lb=h
Light gas oil ¼ 6, 300 Â 0:5 ¼ 3, 150 lb=h
Kero ¼ 5, 250 Â 0:65 ¼ 3, 413 lb=h
Tower pressure profile.
There will be 40 fractionating trays in the main tower (trays above the flash
zone) and four residue stripping trays (trays below the flash zone). These trays
will be numbered from the bottom to the top. Thus, the bottom residue stripping
tray will be tray 1. The tower top tray will be tray 45. The pressure profile is
shown in Fig. 19.
Table 6 Flash zone balance
Enthalpy
Stream
V/L
API Wat. K Temp,
F Weight, lb/h Btu/lb
MMBtu/h
In
Residue
L
13
11.5
720
197,085
396
78.046
Stripout
L
25.5
11.5
720
10,868
410
4.456
Steam
V
450
28,980
1,290
37.384
Total in
236,923
119.916
Out
Residue
L
13
11.5
t
197,085
x
197,085x
Stripout
V
25.5
11.5
715
10,868
490
5.325
Steam
V
715
28,980
1,383
a
40.079
Total out
236,933
45.404 +
197,085x
a
At partial pressure of the flash zone = 13.53 psig
Atmospheric and Vacuum Crude Distillation Units in Petroleum Refineries
167