Jones D.S.J., Pujado P.R. Handbook of Petroleum Processing
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PETROLEUM PRODUCTS AND A REFINERY CONFIGURATION 49
60 70 80 90
% Vol
18.55 %
21.33 %
1300
1100
900
700
750 – 930 °F
650 – 750 °F
10.85 %
520 – 650 °F
13.83 %
380 – 520 °F
9.09 %
210 – 380 °F
14.2 %
180-
2.0
3.16 %
C
5
– 180 °F
7.28 %
930 °F +
Temp °F
Temp
°F
1.71
0102030405060
% Vol
700
600
500
400
300
200
100
0
–100
Light Ends
C
3
0.306 % Vol
iC
4
0.224 ''
nC
4
1.180 ''
iC
5
0.954 ''
nC
5
1.201 ''
Figure 2.1. Sassan crude TBP curve and product split.
50 CHAPTER 2
deethanizer with respect to its C
4
content. The fractionation in the de-ethanizer will
be such as to ensure that the C
2
and lighter content of the propane LPG will be such
as to meet that LPG’s Reid Vapor Pressure specification.
The naphthas. There are usually two naphtha cuts produced from most crude. These
are:
r
Light naphtha (sometimes called light gasoline)
r
Heavy naphtha.
Both these streams are the bottom product of the debutanizer unit. They are separated
in a naphtha splitter fractionation tower. The light naphtha contains most of the crude’s
C
5
’s and much of the paraffin portion of the crude’s C
6
’s. The purpose of making such
a division is to produce a satisfactory heavy naphtha which will contain the heavier
naphthenes and will be a suitable feed for a catalytic reformer (see Chapter 14).
The light naphtha has a TBP distillation range of C
5
to around 190
◦
F. The heavy
naphtha as the feed to the catalytic reformer and is a cut on crude of about 190
◦
–360
◦
F.
This cut point of 360
◦
F can vary depending on the severity operation of the catalytic
reformer, the volatility specification of the finished gasoline which the reformate will
be a major precursor, and the refineries production requirements. In this latter case
for example the refinery’s operating plan may call for maximizing kerosene in which
case the atmospheric distillation unit would be operated to decrease the amount of
overhead distillate in order to increase the kerosene (top side stream) fraction. Of
course if the refinery plan is to maximize gasoline the atmospheric tower would be
operated to increase the overhead distillate at the expense of the Kero fraction.
Straight run kerosene. This fraction is usually the first side stream of a conventional
atmospheric distillation unit. It may be cut to meet a burning oil specification or
become a component in Jet Fuel finished product. Its cut range is usually between
360
◦
F and 480
◦
F. Again this cut range may vary with the required heavy end of the
naphtha and the front end of the Gas Oils. In most cases this Kero fraction must meet
a flash point specification after it has been steam stripped, and its end cut point is
usually set to meet a smoke point specification. Usually the sulfur content restriction
is met by hydro-desulfurization, in some cases too the smoke point is reduced by
other processes. These subsequent processes are aimed at removing or converting the
aromatic content of the fraction. It can also be routed to the Gas oil pool as a precursor
for a diesel finished product.
The atmospheric straight run gas oils. Usually there will be two gas oil side streams, a
light gas oil side stream and below this take off a heavy gas oil side stream is withdrawn.
Both these side—streams are steam stripped to meet their respective flash point spec-
ification (usually 150
◦
F minimum). The lighter side stream (cut of about 480–610
◦
F
on crude) is the principle precursor for the automotive diesel grade finished product.
PETROLEUM PRODUCTS AND A REFINERY CONFIGURATION 51
This side stream is desulfurized to meet the diesel sulfur specification in a hydro-
treater (see Chapter 8). The lower gas oil stream is really a guard stream to correct
the diesel distillation end point. This heavy gas oil may also be hydro-desulfurized
and routed to either the fuel oil pool (as a precursor for marine diesel for example) or
to a finished heating oil product from the gas oil pool.
The atmospheric residue. This is the bottom product from the atmospheric distillation
of the crude oil. Most crude oils are distilled in the atmospheric crude oil tower to cut
the atmospheric residue at a +650
◦
Fuptoa+680
◦
F cut point. Cutting the residue
heavier than +680
◦
F risks the possibility of cracking with heavier coke lay down
and discoloring of the distillate products. Those atmospheric crude towers that do
operate at higher cut points minimize the cracking by the recycle of cold quench into
the bottom of the tower (below the bottom stripping tray) and minimizing the residue
hold up time in the tower. The atmospheric residue may be routed to the fuel oil pool
as the precursor to several grades of finished fuel oil products. The other options for
this stream in a modern refinery are as follows:
r
feed to a vacuum distillation unit. (This is the most common option.)
r
feed to a thermal cracker (Visbreaker, or coking unit). See Chapter 11.
r
feed to a deep oil fluid catalytic cracker. See Chapter 11.
r
feed to a hydro-cracker or hydro-treater. See Chapter 11.
The vacuum distillation of atmospheric residue. In modern refinery practice the dis-
tillation of atmospheric residue is accomplished under high vacuum conditions in
a specially designed tower whose internal equipment ensures a very lower pressure
drop. Normally the vacuum conditions in the flash zone of the tower allows about the
same percentage of distillate based on the tower feed to be cut in this tower as the dis-
tillate on whole crude in the atmospheric unit. Again the flash zone temperature in the
vacuum unit is kept below 700
◦
F. Usually there are two or three vacuum distillates
from this tower. In a pure energy related refinery there will be two. The heavier of
the two say to a cut range of 750–930
◦
F will be the feed to a distillate hydro-cracker
(see Chapter 7) or to a fluid catalytic cracker (see Chapter 6). In both these cases
however a small heavier cut is taken off and returned to the tower bottom in order
to correct the bottom distillate condradson carbon content to meet the specification
required for either of the two downstream processes. This distillate product is usually
titled HVGO (Heavy Vacuum Gas Oil).
For those refineries which produce lube oils as non energy products this bottom
distillate may be split into two side streams in order to provide the flexibility required
in the production of the lube oil blending stock specifications (see Chapter 12).
The light vacuum distillate is taken off as a top side stream and is usually routed to a
hydro-desulfurizer to be sent either to the gas oil pool as heating oil stock or routed
52 CHAPTER 2
to the fuel oil pool as blending stock. This side stream is a cut range of 680–750
◦
F
and is usually labeled LVGO (Light Vacuum Gas Oil).
The vacuum residue. This is the bottom product from the vacuum distillation unit. Just
as in the case of the atmospheric residue it has several options for its use in meeting
the refinery’s product slate. In the case of the energy refineries it can be upgraded to
prime distillate products by a recycling thermal cracking process (see Chapter 11),
coking, deep oil fluid catalytic cracking (Chapter 11) or hydro-cracking or indeed a
combination of these processes.
In the case of the production of lube oils it can be processed to remove the heavy
asphaltene portion of the stream. This deasphalted product is excellent lube oil blend-
ing stock, commonly called ‘Bright Stock’, which, when de waxed and subject to
other lube oil processes becomes the precursor for a variety of lube oil products (see
Chapter 12). The asphalt portion of the de asphalting process has a wide spectrum
as precursor to the many grades of bitumen used in building, and road making (see
Chapter 12). The vacuum residue itself also figures in the production of bitumen.
Where non-energy products are significant in the refinery’s product slate, the vacuum
residue as produced is the key component in bitumen production.
Typical properties of some straight run product streams
The cuts and the stream properties are based on Arabian crude, and are shown here
for the light, medium, and heavy Arabian crude oil (Table 2.1).
Product streams from intermediate and finishing processes
Most finished marketable petroleum products are blends of some straight run prod-
uct streams with the products from further processing of some of these streams (see
Part 2 of this chapter). This section deals with the intermediate or finishing product
processes which provide the finished product precursors. Some of these more com-
mon intermediate products together with reference to their respective processes are
described and discussed in the following paragraphs.
The LPG products. These two finished products, Propane LPG and Butane LPG are
products from straight run sources combined with the products from intermediate
processes such as the cracking and the naphtha reforming processes. Their finished
specification except for some mild desulfurization treating are met by the distillation
of the source streams and the central light end units (see Chapter 4). No further
precursors are added, except for injection of odorizing chemicals for the detection of
leaks and thus their safe storage. Finished LPGs are stored in spheres for propane
and, usually, bullets for butane.
PETROLEUM PRODUCTS AND A REFINERY CONFIGURATION 53
Table 2.1. Straight run product streams
Light Medium Heavy
Crude,
◦
API 38.8 30.7 28.2
Sulfur, %wt 1.1 2.51 2.84
Light naphtha
Cut range,
◦
F 68–212 68–212 68–212
Yield, %vol 10.5 9.4 7.9
Gravity,
◦
API 77.4 78.4 80.1
Sulfur, %wt 0.056 0.007 0.0028
RVP, Psig 6.9 7.9 10.2
Paraffins, %vol 87.4 89.7 89.6
Naphthenes, %vol 10.7 8.8 9.5
Aromatics, %vol 1.9 1.5 0.9
RON clear 54.7 48.2 58.7
Heavy naphtha
Cut range,
◦
F 212–302 212–302 212–302
Yield, %vol 9.4 7.4 6.8
Gravity,
◦
API 58.8 59.6 60.6
Sulfur, %wt 0.057 0.019 0.018
Paraffins, %vol 66.3 67.8 70.3
Naphthenes, %vol 20.0 20.8 21.4
Aromatics, %vol 13.7 11.4 8.3
Kerosene
Cut range,
◦
F 302–455 302–455 302–455
Yield, %vol 18.4 13.5 12.5
Gravity,
◦
API 48.0 48.9 48.3
Sulfur, %wt 0.092 0.12 0.19
Paraffins, %vol 58.9 59.9 58.0
Naphthenes, %vol 20.5 21.9 23.7
Aromatics, %vol 20.6 18.2 18.3
Freeze point,
◦
F −67 −72 −84
Smoke point, mm 26 23 26
Luminometer No 57 55 60
Analine point,
◦
F 133 139 138
Kin Cst @ −30
◦
F 5.09 4.63 4.74
Kin Cst @ 100
◦
F 1.13 1.09 1.12
Light gas oil
Cut range,
◦
F 455–650 455–650 455–650
Yield, %vol 21.1 17.4 16.4
Gravity,
◦
API 37.3 37.2 35.8
Sulfur, %wt 0.81 1.09 1.38
Pour point,
◦
F1005
Analine point,
◦
F 166 156 156
Kin Cst @ 100
◦
F 3.34 3.15 3.65
Kin Cst @ 210
◦
F 1.32 1.22 1.4
(Cont.)
54 CHAPTER 2
Table 2.1. (Cont.)
Light Medium Heavy
Heavy gas oil
Cut range,
◦
F 650–1,049 650–1,049 650–1,049
Yield, %vol 30.6 30.5 26.3
Gravity,
◦
API 24.8 22 21.8
Sulfur, %wt 1.79 2.87 2.88
Pour point,
◦
F 100 75 90
Analine point,
◦
F 195 172 172
Kin Cst @ 100
◦
F 49.0 62.2 62.5
Kin Cst @ 210
◦
F 6.65 7.25 7.05
Atmos residue
Cut range,
◦
F +650 +650 +650
Yield, %vol 38.0 50.0 53.1
Gravity,
◦
API 21.7 14.4 12.3
Sulfur, %wt 2.04 4.12 4.35
Pour point,
◦
F 755555
Con carb, %wt 4.5 10.0 13.2
Kin Cst @ 100
◦
F 146 1,570 5,400
Kin Cst @ 210
◦
F 12.4 54.0 106
Vacuum residue
Cut range,
◦
F +1,049 +1,049 +1,049
Yield, %vol 7.4 19.5 26.8
Gravity,
◦
API 11.5 3.8 4.0
Sulfur, %wt 3.0 5.85 5.6
Pour point,
◦
F 80 120 120
Con carb, %wt 19 22.8 24.4
Kin Cst @ 210
◦
F 392 19,335 13,400
Kin Cst @ 275
◦
F 40.1 743 490
Vanadium, ppm 12 249 171
Nickel, ppm 7 55 53
Iron, ppm 36 79 28
Butane LPG is however used extensively as a finished gasoline product precursor to
correct for volatility of the finished gasoline.
Gasoline precursors. Gasoline is a blend of straight run naphtha (usually light
naphtha) and products of intermediary processes. These are usually suitably boil-
ing range products from:
r
Catalytic Reforming Process (see Chapter 5)
r
Fluid Catalytic Cracking Process (see Chapter 6)
Modern refining configurations may also include processes which convert low quality
products to gasoline precursors enhancing the gasoline’s octane rating. These include
the alkylation and Isomerization processes (see Chapter 9). Others which are less
common are the oxygenated precursors (Chapter 1).
PETROLEUM PRODUCTS AND A REFINERY CONFIGURATION 55
Catalytic reforming
This is a process which converts a relatively low octane straight run naphtha into
a high octane liquid reformate which is a major precursor for finished gasoline.
Of equal importance in upgrading naphtha this process also produces a high purity
hydrogen stream. This makes the process a most important one in a modern day
refinery configuration.
Briefly the straight run heavy naphtha is heated and is passed over beds of platinum
catalyst contained in three separate reactor vessels. A recycle hydrogen stream ac-
companies the feed through these reactors and the reaction temperature is controlled
by heaters between each reactor. The reaction of principle importance is the dehy-
drogenation of the naphthenes in the feed to their respective aromatic homologue. In
so doing the excess hydrogen molecule is released as a hydrogen by product. Other
reactions also occur which enhance the octane rating of the debutanized reformate
liquid product. Among these are some isomerization and to some extent some hydro-
cracking. Details of this process are given in Chapter 5.
The properties of the debutanized reformate is given in the following table. The
feed to the catalytic reformer in this case included the straight run naphtha (SRN)
from the crude unit and the naphtha streams from gas oil hydro-treaters and a thermal
cracker. This feedstream was also hydro-treated before entering the catalytic reformer
(Table 2.2).
Table 2.2. Properties of a debutanized reformate
Feed
Crude source Sassan
Heavy naphtha blend
Cut range,
◦
F 212–375
Gravity,
◦
API 56.0
Paraffins, %vol 59.0
Naphthenes, %vol 29.6
Aromatics, %vol 11.4
Octane number (Res) clear 34.5
Reformate
Gravity,
◦
API 47.0
Dist ASTM D86
IBP,
◦
F 124
10 %vol recovered,
◦
F 174
30 %vol recovered,
◦
F 214
50 %vol recovered,
◦
F 255
70 %vol recovered,
◦
F 273
90 %vol recovered,
◦
F 314
FBP,
◦
F 416
Octane number (Res) clear 91.0
56 CHAPTER 2
Table 2.3. Light and heavy cracked naphtha stream properties (Feed is Sasson
HVGO with gravity of 26.1
◦
API)
Light naphtha Heavy naphtha
Gravity,
◦
API 56.1 43.8
ASTM distillation D86
IBP,
◦
F 108 319
10 %vol recovered,
◦
F 158 336
30 %vol recovered,
◦
F 170 348
50 %vol recovered,
◦
F 191 362
70 %vol recovered,
◦
F 223 378
90 %vol recovered,
◦
F 283 388
FBP,
◦
F 330 448
Octane no. (Res) clear 94 89
Cut range,
◦
FC
5
–300 300–420
Naphtha from a fluid catalytic cracking unit
The Naphtha from the FCCU is always a prime precursor for the gasoline blends.
There are usually two naphtha streams which are the debutanized overhead distillate
from the Cracker’s main fractionator. This distillate is fractionated to produce a light
naphtha and the heavy naphtha. As can be seen from Chapter 7 the Fluid Catalytic
Cracker is a very flexible unit with respect to the feedstock that it can process. As a
matter of fact the only real constraints on the process is a high metal and Condradson
carbon content of the feed. And even this is removed with the improved catalysts
now available and some modification to the conventional process (see Chapter 11 on
deep oil cracking). The effect of the feedstock quality however is confined mostly to
the severity of cracking and the resulting yields of the cracked products. The quality
of the streams from the main fractionator can be and usually are constant. Table 2.3
shows the properties of the two naphtha streams from the catalytic cracker which in
this case is operated on Sasson Heavy Vacuum Gas Oil at a 70% severity conversion.
Alkylation plant
The other most common precursor for the gasoline products is the liquid alkalate from
the alkalation process. This process is described in some detail in Chapter 9, and its
part in the gasoline blending pool is shown in Part 2 of this chapter (Table 2.4).
There are other processes that produce precursors for gasoline and diesel motive fuels,
among these are the products from the Olefin Condenser process and other polymer
processes. These are not so common however, but details of the olefin condensing
process are given in Chapter 9.
PETROLEUM PRODUCTS AND A REFINERY CONFIGURATION 57
Table 2.4. Alkylate
Alkylate
Gravity,
◦
API 49.5
ASTM distillation D66
IBP,
◦
F 211
10 %vol recovered,
◦
F 237
30 %vol recovered,
◦
F 266
50 %vol recovered,
◦
F 289
70 %vol recovered,
◦
F 296
90 %vol recovered,
◦
F 304
FBP,
◦
F 394
Octane no. (Res) clear 97
The middle distillate products
Finished products derived from the middle distillate boiling range include:
r
Kerosene for illumination
r
Kerosene as a precursor for Aviation Turbine Gasoline (ATG)
r
Kerosene for Tractor Vaporizing Oil (TVO)
r
Kerosene as a Precursor for Automotive Diesel
r
Kerosene for Asphalt Cut Back
r
Light Gas Oil for Diesel Fuel
r
Heavy Gas Oil for Domestic Heating Oil
r
All Middle Distillates for Fuel Oil Blending
The straight run kerosene products. Most straight run kerosenes are desulfurized and
routed directly to the finished product blending pools. The exception is in the case of
the aviation turbine gasoline (ATG) which will require the kerosene precursor to be
treated for aromatics reduction or removal to meet the strict smoke point specifications
associated with this finished product. In present day refineries this is accomplished
by hydro-treating the kerosene using a nickel catalyst. In older refineries the aro-
matics contained in the cut were removed as an extract in a process using SO
2
as
a solvent. In some cases also the specification for the tractor vaporizing oil (TVO)
requires the kerosene, which is the major component of this finished product, to be
de-aromatized also. Some details of the de-aromatization hydro-treating process are
given in Chapter 8. The straight run kerosene product destined for fuel oil and as-
phalt blending are not usually desulfurized before routing to the respective blending
pools.
Some general specifications for the various finished products containing predomi-
nately kerosene are given in Table 2.5.
58 CHAPTER 2
Table 2.5. General specifications of kerosene finished products
Parameters Reg Kero ATG TVO
Flash point,
◦
F 100 <66 100 D-56
Aromatics, %vol – 20 – D-1319
Temperature @ 20% Max 293
◦
– D-86
Temperature @ 50% Max 374
◦
– D-86
Temperature @ 90% Max 473
◦
540 D-86
Final boiling point 572
◦
F 572
◦
– D-86
Sulfur Max, %wt 0.04 0.04 0.3 D-1266
Smoke point, Min – 25 mm 25 mm D-1322
Freeze point,
◦
C–−47 – D-2386
Straight run light gas oil. This cut is always desulfurized and routed to the automotive
diesel blending pool. It is the major component of this finished product. Its four major
specifications are:
r
Cetane number
r
Pour point
r
Sulfur content
r
Flash point
Other important requirement is its volatility as defined by the ASTM distillation
analysis. Except for the sulfur content these specification are met by the set points
established in the atmospheric crude unit. Some kerosene may be blended to lighten
the front end of the finished product if required, and some heavy gas oil or Light
Vacuum Gas Oil (LVGO) may be added to maximize the finished product yield but
all limited to the product’s ASTM distillation and the other specifications.
Note: Where the refinery configuration contains a thermal cracker, the gas oil cut
from this unit may, depending on the unit’s fractionator cut points, be added to the
light straight run gas oil as feed to the hydro-treater and its subsequent routing to the
diesel blending.
Straight run heavy gas oil. This cut could be a heavy side stream from the atmospheric
crude distillation tower or if there is a vacuum unit in the configuration it could be one
or more of the gas oil distillate cuts from this tower. Most refineries that maximize
motive fuels would almost certainly have a cracking unit of some kind in their config-
uration. More often than not this would be a fluid catalytic process taking as feed the
heavy vacuum gas oil stream. The heavy gas oil from the atmospheric distillation unit
would be hydro-treated before being routed to the heating oil blending pool or partly
to heating oil and partly to fuel oil pool. If there is a catalytic cracker in the refinery
units the cycle oil from this unit would be blended with the straight run heavy gas oil
to be desulfurized and routed as described. This cycle oil as a cracked product will