Jones D.S.J., Pujado P.R. Handbook of Petroleum Processing
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PETROLEUM PRODUCTS AND A REFINERY CONFIGURATION 89
Table 2.24. FCCU material and sulfur balance
Stream BPCD SG @ 60
◦
F mm lbs/CD S %wt S lbs/CD Routing
Feed
Des HVGO 8,811 0.898 2.757 0.50 13,908 FCCU
Products out
Gas to C
3
714 – 0.13 2.19 2,850 Gas treating
C
3
to C
5
1,736 0.560 0.341 – Neg Alkylation
C
5
to 300
◦
F 3,503 0.7856 0.929 – Neg Gasoline pool
300–420
◦
F 1,695 0.8251 0.489 0.05 262 Gasoline pool
Lt cycle oil 1,366 0.9159 0.438 0.54 2,380 Gas oil blending
Slurry 1,234 0.990 0.428 2.0 8,416 Fuel oil
Total out 10,248 2.757 0.5 13,908
In terms of BPCD:
Gas to C
3
=714
C3 to C
4
’s = 1,736
Naphtha =5,198
Lt Cycle =1,366
Slurry = 1,234
Total =10,248
Overall unit balance (Tables 2.24–2.26).
Lt gas oil hydrotreater. The LGO hydrotreater will operate on two blocked operations
to desulfurize diesel feed and secondly to desulfurize kerosene.
Table 2.25. Diesel hydrotreater material and sulfur balance
Stream BPCD (Scf/D) lbs/gal (MW) mm lbs/CD %wt sulfur lbs/CD sulfur Routing
In
Diesel 8,399 7.0 2.470 1.16 28,652
MU Gas (1,495,000) (11) 0.043 Neg nil
Total in 2.513
Out
Gas to C
5
(42,037) (55) 0.006 69.5 4,168 Gas treating
Naphtha 459 6.55 0.126 0.08 101 Nap Hds
Diesel prod 8,036 6.98 2.356 0.30 7,068 Diesel pool
Vent gas (255,067) (37) 0.025 69.4 17,315 Gas treating
Total out 2.513 28,652
90 CHAPTER 2
Table 2.26. Material balance over the reformer
BPCD SG @ 60
◦
F
Stream (mm Scf/CD) (MW) mm lbs/CD Routing
IN
Hy Nap ex CDU 7,100 0.755 1.863
Hy Nap ex TC 578 0.752 0.152
Hy Nap ex Hds 940 0.793 0.261
Total in 8,618 0.7543 2.276
OUT
Reformer gas (7.33) (11) 0.224 to Naphtha Hds
Light ends 837 0.521 0.152 to Sat Lt Ends
Reformate 6,852 0.7927 1.900 to Gasoline Pool
Total out 7,689 2.276
(i) Diesel operation. The feed in this case will consist of Straight Run diesel from
the CDU and the diesel cut from the thermal cracker. Thus:
BPCD SG @ 60
◦
F #/Gal mm #/CD S %wt S/CD
Straight run 6,915 0.842 7.013 2.04 0.87 17,748
Cracked 1,484 0.825 6.87 0.43 2.55 10,967
Total 8,399 0.841 7.00 2.47 1.16 28,715
The licensor guarantees 75 %wt sulfur removal. Therefore:
Sulfur removed = 21,536 lbs/CD
Sulfur in product =7,179 lbs/CD
Hydrogen consumption for sulfur removal = 157,664 Scf/D for SR Diesel
=97,415 Scf/D for Cracked feed
=673 moles/D
Hydrogen consumption for ring saturation =384,474 Scf/D for Str Run (includes
losses)
=735,322 Scf/D for Cracked feed
=2,954 moles/D
Total hydrogen make up = 1.375 mm Scf/D for Total Feed
Reformer gas make up = 1.495 mmScf/CD
=3,945 moles/D
(ii) Hydrotreater on Kero operation
Kero feed ex CDU = 4,545 BPCD
SG@60ofKero= 0.8048 then mm lbs/CD = 1.280
Sulfur content = 0.21 %wt then Sulfur = 2,685 lbs/CD
PETROLEUM PRODUCTS AND A REFINERY CONFIGURATION 91
Licensor guarantees mid of run sulfur removal as 99 %wt.
Then lbs/CD sulfur removed = 2,631 lbs/CD. This generates 2,795 lbs/CD of H
2
S.
There is no significant amount of naphtha made nor is there significant amount
of hydrogen needed for saturation. Then make up hydrogen required is 82
moles/CD or 82 ÷ 0.92 = 89 moles/CD Reformer gas. This amounts to 33,780
Scf/CD.
(iii) Summary Kero operation
IN
Kero feed 4,545 BPCD 1.280 mm lbs/CD
Hydrogen 89 moles/CD 979lbs/CD of Reformer gas
Total 1,280,979 lbs/CD
OUT
Kero Product 4,539 BPCD 1.277342 mm lbs/CD
Hydrogen sulfide 82 moles/CD 2,788 lbs/CD
Losses from stripper 813
Total 1,280,166 lbs/CD.
Naphtha consolidation and treating. Summary of naphtha and light ends streams to
treating processes.
From Stream BPCD
CDU Gas to C
5
855
Light naphtha to 212
◦
F 5,219.5
Heavy naphtha to 380
◦
F 7,100
Thermal cracker Gas to C
5
852
Light naphtha to 212
◦
F 436.5
Heavy naphtha to 380
◦
F 577.7
The hydrotreaters Gas to C
5
Mostly H
2
S to gas treating
Light naphtha to 212
◦
F 323.5
Heavy naphtha to 380
◦
F 940.5
Unstabilized naphtha feed to naphtha hydrotreater
Gas to C
5
1,707
Light naphtha 5,981
Heavy naphtha 8,618
Total 16,306
92 CHAPTER 2
Light naphtha to gasoline pool
Total 5,970
Heavy naphtha feed to cat reformer
Total 8,618
Catalytic reformer operation. The reformer will operate at a severity of 91 RON and
at a reactor pressure of 350 psig.
Licensor data for these conditions are:
Yield of reformate = 79.5 %LV
Reformate make = 6,851.5 BPCD
Hydrogen made = 5.13 mmScf/CD Purity is 70 mol%
Then reformer gas is 5.13 ÷ 0.7 = 7.33 mmScf/CD
Mol Wt of reformer gas is 12 as given by the Licensor. Then mm lbs/CD of the gas
is 0.237.
C
5
= Reformate = 6,851 BPCD and at an SG of 6.604 lbs/gal lbs/CD of reformate =
1.9 mm lbs/CD.
Light ends leaving the reformer stripper will be in accordance with the following
balance:
lbs per CD of fresh feed = 2.276 mm lbs
lbs per CD of reformate = 1.900 mm lbs
lbs per CD of reformer gas = 0.237 mm lbs
By difference Lt ends = 0.152 mm lbs/CD routed to Reformate Stabilizer.
Analysis of the Lt end stream gave:
%wt lbs/CD BPCD
Gas to C
3
9.8 14,896 122
C
3
33.1 50,312 284
iC
4
22.0 33,440 170
nC
4
35.1 53,352 261
Total 100.0 152,000 837
The associate naphtha hydrotreater receives the fresh reformer feed and desulfurizes
it using the reformer off gas on a once through basis. In this process the hydrotreater
PETROLEUM PRODUCTS AND A REFINERY CONFIGURATION 93
consumes 6 vol% of the hydrogen and absorbs light ends from the reformer gas to
upgrade the off gas to 92 mol% hydrogen.
Hydrogen consumed in the hydrotreater = .308 mmScf/D
Hydrogen leaving in off gas = 5.13−0.308 = 4.822 mmScf/D
Vol of off gas from the hydrotreater = 4.822 ÷ 0.92 = 5.241 mmScf/D
By difference the volume of Lt End gas absorbed into the hydrotreater stabilizer feed
will be 7.33−5.241 = 2.089 mmScf/CD or 5,526 moles/D. This absorbed gas will be
slightly heavier than that for the gas absorbed in the reformate. This will have the
following molar composition:
%mol moles/D lbs/D BPCD
Gas to C
3
8.2 453.1 6,797 56
C
3
37.3 2,061.2 90,693 514
iC
4
20.1 1,110.8 64,422 328
nC
4
34.4 1,900.9 110,255 540
Total 100.0 5,526 272,167 1,438
Saturated light ends consolidation. Although the LEs from the thermal cracker con-
tains a significant amount of unsaturated hydrocarbons, it is usually blended with the
CDU overhead distillate, hydrotreated and then split into its components. Thus the
LEs are considered saturated for the study here.
The isomerization and alkylation processes. The fresh feed to the alkylation reactor
is the C
3
and C
4
streams from the FCCU. The volumetric and mass composition of
this stream is as follows:
Component %vol BPCD #/Gal lbs/CD
C
3
11.7 203 4.22 35,980
C
3−
28.4 493 4.34 89,864
iC
4
14.2 247 4.68 48,550
nC
4
7.1 123 4.86 25,107
C
4−
38.6 670 5.00 140,700
Total 100.0 1,736 4.67 340,201
From licensor data:
Alkylate from propylene = 1.76 × 493 = 868 BPCD
Alkylate from butylene = 1.77 × 670 = 186 BPCD
The volumetric composition of the alkylates is as follows:
94 CHAPTER 2
From butylenes:
%wt #/Gal Vol factor %vol %wt Vol factor %vol
C
5
9.0 5.25 1.71 9.9 4.0 0.8 4.75
C
6
4.0 5.53 0.72 4.16 2.0 0.4 2.37
C
7
68.0 5.73 11.87 68.55 2.0 0.3 1.78
C
8
10.0 5.89 1.69 9.76 80.0 13.58 80.65
C
9+
9.0 6.8 1.32 7.63 12.0 1.76 10.45
Total 100.0 5.78 17.31 100.0 100.0 16.84 100.0 #/Gal = 5.93
Total alkylate = 2,054 BPCD = 50,6101 lbs/CD
iC
4
Consumption =1.34 × propylene + 1.15 × butylene
=1.31 × 493 + 1.15 × 670 = 1,416.3 BPCD
=278,000 lbs/CD.
iC
4
available in FCCU Light Ends = 48,550 lbs/CD. Required from other source =
229,500 lbs/CD or 1,167 BPCD.
A butane isomerizer is included in the process to provide the necessary iso butane
stream. In this process 50 %wt of the normal butane contained in a saturated butane
stream is converted to iso butane.
Thus from Table 2.27 total butanes available from saturate LE is made up as follows:
Iso butane 670 BPCD 131,695 lbs/CD = 29.2 %wt
Normal butane 1,559 BPCD 318,223 lbs/CD = 70.8 %wt
Table 2.27. Material balance over naphtha Hds
BPCD SG @ 60
◦
F
Stream (mm Scf/CD) (MW) mm lbs/CD Routing
IN
Gas to C
5
1,707 0.320 0.313
Lt naphtha 5,970 0.661 1.379
Hy naphtha 8,618 0.756 2.276
Reformer gas (7.33) (11) 0.224
Total in 16,295 4.192
OUT
Deb overheads 2,817 0.436 0.398 To Sats Lt End
Splitter feed 14,588 0.716 3.655 To Nap Splitter
Rich H
2
gas (5.241) (10) 0.139 To H
2
System
Total out 17,296 4.192
PETROLEUM PRODUCTS AND A REFINERY CONFIGURATION 95
Table 2.28. Saturated light ends summary
BPCD
Source Gas to C
3
C
3
iC
4
nC
4
Total
Crude Distillation Unit 51 103 112 590 856
Thermal Cracker 468 156 60 168 852
Cat Reformer 122 284 170 261 837
Naphtha HDS 56 514 328 540 1,438
Total 697 1,057 670 1,559 3,983
50% of the normal butanes are isomerized giving an isomerate 29.2 + 35.4 lbs iso-
butane per 100 lbs feed and 35.4 lbs normal butane (Table 2.29). Feed to the Isomerizer
will be 229, 500 ÷(0.292 + 0.354) = 355, 263 lbs/CD. Or 528 BPCD iC
4
and 1,232
BPCD of nC
4
.
Product blending and properties
(i) Gasoline blending. Both grades of gasoline will be blended to a ‘no give away’
on octane value. These grades and their blending specifications are:
Premium grade Regular grade
Octane research clear 90 82
Ried vapor pressure (Min) 7 psia 7 psia
Volatility ASTM
50 %vol distilled (Min) 275
◦
F 175
◦
F
60 %vol distilled (Max) 300
◦
F 210
◦
F
95 %vol distilled (Max) 400
◦
F 325
◦
F
Table 2.29. Balance over isom/alky plants
Stream lbs/CD lbs/Gal BPCD Routing
In
Unsats ex FCCU 340,201 1,736
Butanes ex Sats 355,263 1,760
Total In 695,464 4.74 3,496
Out
C
3
ex FCCU 35,980 203 LPG pool
nC
4
ex Sats 125,763 616 Gasoline/LPG
nC
4
ex FCCU 25,107 123 Gasoline/LPG
Alkylate 506,101 2,054 Gasoline
Total Out 692,951 5.51 2,996
96 CHAPTER 2
(ii) Premium grade gasoline. The following blend of gasoline precursor streams
meet the Octane specifications and quantity for the Premium Grade Gaso-
line.
BPCD %vol ON(RES) clear Octane factor
Alkylate 2,054 26.7 97 0.26
Heavy cracked naphtha 1,695 22.0 89 0.20
Light cracked naphtha 1,000 13.0 94 0.12
Reformate 1,951 25.3 91 0.23
Light str run naphtha 1,000 13.0 69 0.09
Total 7,700 100.0 90 0.90
The remaining properties of this product are as follows:
(iii) The distillation curves. The TBP curves for each precursor making up the blend
is divided into components of the same boiling range and combined to produce
the composite TBP curve for the blend. Thus:
Lt cracked Hy cracked
LSR Reformate naptha naptha Alkylate
Temp Total
Comp
◦
F %vol BPCD %vol BPCD %vol BPCD %vol BPCD %vol BPCD BPCD
1 45–100 20 200 6 117 5 50 367
2 125 15 150 4 78 5 50 278
3 150 15 150 7 137 19 190 477
4 175 30 300 8 156 14 140 2 41 637
5 200 10 100 8 156 15 150 8 164 570
6 250 10 100 17 331 19 190 2 41 662
7 175 20 390 8 80 30 616 1,086
8 300 12 234 5 50 5 85 45 925 1,294
9 350 12 234 10 100 42 712 13 267 1,313
10 400 3 59 43 728 787
11 475 3 59 10 170 229
Total 100 1,000 100 1,951 100 1,000 100 1,695 100 2,054 7,700
The TBP and the derived ASTM curves are given in Figure 2.7.
The above component breakdown will now be used to determine, the SG of the product
and the quantity of C
4
that will be added to the blend to meet the RVP spec. The RVP
PETROLEUM PRODUCTS AND A REFINERY CONFIGURATION 97
Regular Grade Gasoline
Premium Grade Gasoline
01020304050
% Volume
60 70 80 90 100
ASTM
ASTM
TBP
TBP
600
500
400
300
200
100
0
Temp °F
600
500
400
300
200
100
0
Temp °F
Figure 2.7. Premium and regular grade TBP and ASTM curves.
98 CHAPTER 2
of the finished product is determined by a bubble point calculation in which the C
4
is
an unknown x and the RVP is set at 7 psia and 100
◦
F. Thus:
Comp Mid Bpt #/gal Mol Wt VP @ 100 psia %vol Wt factor Mol factor
1 75 5.96 72 22 4.77 28.43 0.395
2 115 6.03 73 11 3.61 21.77 0.298
3 135 6.09 75 6.2 6.19 37.70 0.503
4 155 6.17 81 5.0 8.27 51.03 0.630
5 185 6.25 90 2.5 7.41 46.31 0.515
6 225 6.39 100 } 8.61 55.02 0.550
7 260 6.49 110 } 14.11 91.57 0.832
8 285 6.56 119 } 1.8 16.79 110.14 1.08
9 315 6.64 128 } 17.06 113.28 0.885
10 375 6.83 148 } 10.22 69.80 0.471
11 420 6.95 162 } 2.96 20.57 0.127
Total 6.45 103 100.00 645.62 6.287
Calculating for butane addition to make 7 psia RVP.
Comp mid Bpt
◦
F VP @ 100
◦
F psia K = VP/7 moles liq moles vap
C
4
60 8.57 x 8.57x
1 75 22 3.14 0.395 1.241
2 115 11 1.57 0.298 0.469
3 135 6.2 0.89 0.503 0.445
4 155 5.0 0.71 0.630 0.450
5 185 2.5 0.36 0.515 0.184
6 225
7 260
8 285 1.8 0.26 3.946 1.015
9 315
10 375
11 420
Total 6.287 + x 3.804 + 8.57x
6.287 + x = 3.804 + 8.57x
x = 0.328
= 0.328 ÷ (6.287 +0.328)
= 0.0495
C
4
will be 4.95 mole% or 4.0 vol% of total product gasoline.