sheet to vendors. Give the crude to overhead vapor heat exchanger a pressure drop
of 2 psi (overhead vapors flow shell side).
Neglect the pressure drop for fittings and piping – this will be quite small for a
properly designed unit.
Then the total tower top pressure is 12 psig.
Assume 40 valve trays in the section of the tower between flash zone and tower
top. Let the pressure drop per tray be 0.25 psi. Then pressure drop in this section of
the tower is 10 psi.
Total flash zone pressure is 12 psig + 10 psi = 22 psig. Call it 25 psig (40 psia)
for design purposes.
Table 1 ASTM distillation conversion to TBP
ASTM,
F
Δt ASTM,
F
Δt TBP,
F
TBP,
F
Naphtha (overhead)
IBP
Not required
10 %
30 %
50 %
300
10
14
305
70 %
310
20
27
319
90 %
330
28
32
346
FBP
358
378
Kero (first side stream)
IBP
345
31
57
287
10 %
124
44
344
30 %
400
19
32
388
50 %
419
17
27
420
70 %
436
24
33
447
90 %
460
35
38
480
FBP
495
518
LGO (second side stream)
IBP
495
25
48
457
10 %
520
12
25
505
30 %
532
11
20
530
50 %
543
16
26
550
70 %
559
13
19
576
90 %
572
23
27
595
FBP
595
622
HGO (third side stream)
IBP
595
20
40
568
10 %
615
11
25
608
30 %
626
7
14
633
50 %
633
7
12
647
70 %
640
18
25
659
90 %
658
17
20
684
FBP
675
704
Atmospheric and Vacuum Crude Distillation Units in Petroleum Refineries
161