Note: Descriptions are shown in the official language in which they were submitted.
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THE PRODUCTION OF SUBSTANTIALLY FREE-FLOWING COKE
FROM A DEEPER CUT OF VACUUM RESID IN DELAYED COKING
FIELD OF THE INVENTION
[0001] The invention relates to a modified vacuum distillation and delayed
coking process for making substantially free-flowing coke, preferably free-
flowing
shot coke. A vacuum resid feedstock is used which contains less than 10 wt.%
material boiling between 900 F and 1040 F (482.22 C to 560 C) as determined by
HTSD (Hig11-temperature Simulated Distillation). The use of such a high
boiling
resid favors the formation of shot coke. Use of distillate recycle in the feed
reduces
coker furnace fouling potential of the heavier feedstock.
DESCRIPTION OF RELATED ART
[0002] Delayed coking involves thermal decomposition of hydrocarbonaceous
feedstocks (HFs) including petroleum residua (resids) and deasphalter bottoms
etc.
to produce gas, liquid streams of various boiling ranges, and coke. Delayed
coking
of HFs from heavy and heavy sour (high sulfur) crude oils is carried out
primarily
as a means of disposing of these low value feedstocks by converting part of
the HFs
to more valuable liquid and gas products.
[0003] In the delayed coking process, a resid feedstock is rapidly heated in a
fired heater or tubular furnace at from 480 C to 520 C and pressures of 50 to
550
psig (344.74 to 3792.12 kPa). The heated feedstock is then passed to a coking
drum that is maintained at conditions under which coking occurs, generally at
temperatures above 800 F (425 C), typically between 480 C to 520 C (895 F to
970 F), under super-atmospheric pressures of 15 to 80 psig (103.42 to 551.58
kPa)
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to allow volatiles that form in the coker drum to be removed overhead and
passed
to a fractionator, leaving coke behind. When the coker drum is full of coke,
the
heated feed is switched to another drum and additional hydrocarbon vapors are
purged from the coke drum with steam. The drum is then quenched with water to
lower the temperature to below 300 F (148.89 C) after which the water is
drained.
When the cooling step is complete, the drum is opened and the coke is removed
after drilling andJor cutting using high velocity water jets.
[0004] For example, a high speed, high impact water jet is used to cut the
coke
from the drum. A hole is typically bored in the coke from water jet nozzles
located
on a boring tool. Nozzles oriented horizontally on the head of a cutting tool
then cut
the coke from the drum. The coke removal step adds considerably to the
throughput time of the overall process. Thus, it would be desirable to be able
to
produce a free-flowing coke, in a coker drum, that would not require the
expense
and time associated with conventional coke removal, i.e., it could be drained
out of
the bottom of the drum.
[0005] Even though the coking drum may appear to be completely cooled, some
volumes of the bed may have been bypassed by the cooling water, leaving the
bypassed coke very hot (hotter than the boiling point of water). This
phenomenon,
sometimes referred to as "hot spots" or "hot drums", may be the result of a
combination of morphologies of coke being present in the drum, which may
contain a combination of more than one type of solid coke product, i.e.,
sponge
coke and shot coke. Since unagglomerated shot coke may cool faster than other
coke morphologies, such as large shot coke masses or sponge coke, it would be
desirable to predominantly produce free-flowing shot coke in a delayed coker,
in
order to avoid or minimize hot drums.
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SUMMARY OF THE INVENTION
[00061 In an embodiment, there is provided a delayed coking process
comprising:
a) preparing a vacuum resid that has less than l Owt.% 900 to 1040 F
boiling material as measured by HTSD (High-Temperature Simulated Distillation)
and combining with a distillate recycle stream wherein the distillate recycle
stream
has boiling range within the interval of 450 F to 750 F (232.22 C to 403.89
C);
b) conducting said mixture to a heating zoiie wherein it is heated to an
effective coking temperature; and
c) conducting said heated mixture from said heating zone to a coking zone
wherein vapor products are collected overhead and whereby coke with reduced
incidence of hot drums and of a relatively free-flowing nature is formed.
[0007] In a preferred embodiment, the coking zone is in a delayed coker drum,
and a substantially free-flowing shot coke product is removed from the coker
drum.
[0008] In still another preferred embodiment an additive is introduced into
the
feedstock either prior to heating or just prior to it being introduced in the
coker
vessel, which additive can be a metals-containing or metals-free additive. If
a
metals containing it is preferably an organic soluble, organic insoluble, or
non-
organic miscible metals-containing additive that is effective for the
formation of
substantially free-flowing coke.
[0009] In yet another preferred embodiment of the present invention the metal
of
the additive is selected from the group consisting of sodium, potassium, iron,
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nickel, vanadium, tin, molybdenum, maiiganese, aluminum, cobalt, calcium,
magnesium, and mixtures thereof.
[0010] In another embodiment, the metals-containing additive is a finely
ground
solid with a high surface area, a natural material of high surface area, or a
fine
particle/seed producing additive. Such high surface area materials include
fumed
silica and alumina, catalytic cracker fines, FLEXICOKER cyclone fines,
magnesium sulfate, calcium sulfate, diatomaceous earth, clays, magnesium
silicate,
vanadium-containing fly ash and the like. The additives may be used either
alone
or in combination.
[0011] In another embodiment substantially metals-free additives can be used
in
the practice of the present invention. Non-limiting examples include elemental
sulfur, high surface area substantially metals-free solids, such as rice
hulls, sugars,
cellulose, ground coals, ground auto tires and mineral acids such as sulfuric
acid,
phosphoric acid, and their acid anhydrides. It is to be understood that before
or
after the resid is treated with the additive, a caustic species, preferably in
aqueous
form, may optionally be added. The caustic can be added before, during, or
after
the resid is passed to the coker furnace and heated to coking temperatures.
Spent
caustic obtained from hydrocarbon processing can be used. Such spent caustic
can
contain dissolved hydrocarbons, and salts of organic acids, e.g., carboxylic
acids,
phenols, naphthenic acids and the like.
[0012] In another embodiment, the process is used in conjunction with
automated coke drum bottom deheading valves, and the product coke plus cooling
water mixture is throttled out the bottom of the coke drum through the bottom
valve.
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[00131 If an additive is used, it is desirable to avoid heterogeneous areas of
coke
morphology formation. That is, one does not what locations in the coke drum
where the coke is substantially free flowing and other areas where the coke is
substaiitially non-free flowing. Dispersing of the additive is accomplished by
any
number of ways, preferably by introducing a side stream of the additive into
the
feedstream at the desired location. The additive can be added by
solubilization of
the additive into the vacuum resid, or by reducing the viscosity of the vacuum
resid
prior to mixing in the additive, e.g., by heating, solvent addition, etc. High
energy
mixing or use of static mixing devices may be employed to assist in dispersal
of the
additive agent, especially additive agents that have relatively low solubility
in the
feedstream.
[0014] Preferably, all or substantially all of the coke formed in the process
is
substantially free-flowing coke, more preferably, free-flowing shot coke. It
is also
preferred that at least a portion of volatile species present in the coker
drum during
and after coking be separated and conducted away from the process, preferably
overhead of the coker drum.
BRIEF DESCRIPTION OF THE FIGURES
[0015] Figure 1 is a simplified process flow diagram of one preferred method
of
obtaining a deep cut heavy oil stream for use in the present invention. This
figure
shows the vacuum distillation system modified with a steam side stripper, as
well
as a distillate recycle stream from the coker main fractionator.
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[00161 Figure 2 is another simplified process flow diagram of another
preferred
method for obtaining a deep cut heavy oil stream for use in the present
invention.
This figure is similar to that of Figure 1 hereof except that there is an
intermediate
resid reheating furnace for reheating the stream upstream of the stripper.
[0017] Figure 3 is a cross polarized light optical micrograph showing coke
formed from a transition coke-forming heavy Canadian vacuum resid containing
12
wt.% 1000 F (537.78 C) boiling material as determined by HTSD. The figure
shows small domains ranging in size from 10 to 20 micrometers with some coarse
mosaic ranging from 5 to 10 micrometers (this microstructure is associated
with
bulk coke beds having transition coke morphology).
[0018] Figure 4 shows the effect of further distilling the feed so that it
contains
only 2 wt.% 1000 F (537.78 C) boiling material. The figure is a cross
polarized
light optical micrograph showing coke resid formed from the deeper cut resid
and
shows a medium/coarse mosaic structure ranging in size from 2 to 10
micrometers
(this microstructure is associated with bulk coke beds having shot coke
morphology).
DETAILED DESCRIPTION OF THE INVENTION
[0019] Petroleum vacuum residua ("resid") feedstocks are suitable for delayed
coking. Such petroleum residua are frequently obtained after removal of
distillates
from crude feedstocks under vacuum and are characterized as being comprised of
components of large molecular size and weight, generally containing: (a)
asphaltenes and other high molecular weight aromatic structures that would
inhibit
the rate of hydrotreating/hydrocracking and cause catalyst deactivation; (b)
metal
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contaminants occurring naturally in the crude or resulting from prior
treatment of
the crude, which contaminants would tend to deactivate
hydrotreating/hydrocracking catalysts and interfere with catalyst
regeneration; and
(c) a relatively high content of sulfur and nitrogen compounds that give rise
to
objectionable quantities of SO2, SO3, and NO,t upon combustion of the
petroleum
residuum. Nitrogen compounds present in the resid also have a tendency to
deactivate catalytic cracking catalysts.
[0020] Coke bed morphology is typically described in simplified terms such as
sponge coke, shot coke, transition coke, and needle coke.
[0021] As previously mentioned, there are generally three different types of
solid delayed coker products that have different values, appearances and
properties,
i.e., needle coke, sponge coke, and shot coke. Needle coke is the highest
quality of
the three varieties. Needle coke, upon further thermal treatment, has high
electrical
conductivity (and a low coefficient of thermal expansion) and is used in
electric arc
steel production. It is relatively low in sulfur and metals and is frequently
produced
from some of the higher quality coker feedstocks that include more aromatic
feedstocks such as slurry and decant oils from catalytic crackers and thermal
cracking tars. Typically, it is not formed by delayed coking of resid feeds.
[0022] There are additional descriptors of coke too, although they're less
common. For example, a sandy coke is a coke that after cutting looks to the
naked
eye much like coarse black beach sand.
[0023] In an embodiment, resid feedstocks include but are not limited to
residues from the atmospheric and vacuum distillation of petroleum crudes or
the
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atnlospheric or vacuum distillation of heavy oils, visbroken resids, tars from
deasphalting units, coal liquids, shale oil or combinations of these
materials.
Atmospheric and vacuum topped heavy bitulnens can also be employed.
Feedstocks typically used in delayed coking are high-boiliiig
hydrocarbonaceous
materials with an API gravity of 20 or less, and a Conradson Carbon Residue
content of 0 to 40 weight percent.
[0024] Vacuum resids are characterized by a number of parameters, including
their boiling point distributions. The boiling point distribution can be
obtained by a
physical distillation in a laboratory, but it is costly to perform this type
of analysis.
Another method for determining the boiling point distribution is to use
specialized
gas chromatographic techniques that have been developed for the petroleum
industry. One such GC method is High-temperature Simulated Distillation
(HTSD). This method is described by D.C. Villalanti, et al. In "High-
temperature
Simulated Distillation Applications in Petroleum Characterization" in
Encyclopedia
of Analytical Chemistry, R.A. Meyers (Ed.), pp. 6726-6741 Jobn Wiley, 2000,
and
has been found to be effective for characterizing the boiling point
distributions of
vacuum residua. Boiling point distributions are reported as wt.% off versus
atmospheric equivalent boiling point (AEBP) and are report in increments of 1
wt.%.
[0025] Vacuum distillation is well known in the industry. A number of
variables affect the boiling point distribution of the vacuum distillation
unit
bottoms. As refiners tend to try to push ever more flow through existing
units,
however, the boiling point distributions of the vacuum bottoms tend to pick up
a
higher percentage of the lowest boiling components.
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[0026] It has unexpectedly been found by the inventors hereof that the
components that are contained a virgin resid which boil between 900 F and 1040
F
can have a significant influence on delayed coker coke morphology is they are
present in an abundance in excess of 10 wt.% of the entire virgin feed.
Specifically, it has been found that when a resid that otherwise would make
shot
coke has the 900 F to 1040 F (482.22 C to 560 C) fraction in excess of 10
wt.%, it
will make a transition coke, or a bonded shot, and can have appreciable
percentage
of hot drums when coked under "typical" delayed coker conditions, e.g., DOT =
820 F, DOP = 15 to 35 psig (103.42 to 241.32 kPa), and recycle ratio of under
10%, where DOT is drum outlet temperature and DOP is drum outlet pressure.
[0027] It has been found that by reducing the fraction of 900 F to 1040 F
(482.22 C to 560 C) AEBP material to under 10 wt.% pushes coke morphology
back to a less bonded and less self-supporting coke morphology.
[0028] Such deeper cuts of resids can be obtained by any means available in a
petroleum refinery. One means is represented in Figure 1 hereof wherein
atmospheric resid bottoms is conducted via line 10 through a furnace 1 wherein
it is
heated to a temperature of 700 F to 800 F (371.11 C to 426.67 C) then sent via
line
20 to vacuum distillation tower 2 wherein non-condensable material, such as
steam
and any small amount of remaining light ends are collected overhead via line
30,
preferably by use of an ejector system (not shown). A heavy vacuum gas oil cut
is
removed via line 40. An intermediate cut is removed via line 50 where it is
combined with vacuum bottoms of line 60 and conducted to outboard stripper 3
where a lighter stream, such as one containing at least a fraction of any
remaining
gas oil, is stripped by use of steam injected via line 70 and sent back to the
vacuum
distillation tower via line 80. The stripped vacuum resid bottoms is then
conducted
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via line 90 to a delayed coker where it is typically introduced near the
bottom of the
main fractionator 4, although it can be fed directly to the coker furnace 5.
The
bottoms of the main fractionator line 100 are fed to the coker furnace wherein
recycle distillate is introduced via line 110. Any additives to aid in the
desired
coking reaction can be introduced via line 120. The resid stream is heated in
coker
furnace 5 to coking temperatures then sent via line 130 to one or more coker
drums
(not shown).
[0029] Figure 2 hereof shows another preferred process scheme for obtaining a
deep cut vacuum resid feed for producing substantially free-flowing shot coke
in a
delayed coker. The process scheme is similar to that shown in Figure 1 hereof
except the intermediate cut removed from distillation tower 2 is conducted via
line
50 and combined with vacuum distillation bottoms on line 55 and sent through
outboard stripper furnace 6 for reheating to substantially the same
temperature as
that of furnace 1. The reheated vacuum bottoms/intermediate cut streain is
conducted via line 60 to outboard stripper 3.
[0030] The drawback of the deeper cut resids, however, is that they tend to
foul
the coker furnace more rapidly than less deeply cut resids, and this a
potential
economic debit because this can increase frequency of furnace cleanout, which
in
turn reduces overall throughput of the coker unit. To mitigate the higher
fouling
tendency of the deeper cut vacuum resid, a distillate stream can be added to
the
coker feed. The boiling point distribution of the distillate recycle stream is
such
that it is an effective mitigator of furnace fouling yet its endpoint is low
enough that
it does not affect the coke morphology. An example of this would be a coker
distillate stream with a boiling range of 450 F to 750 F (232.22 C to 403.89
C).
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[0031] The resid feed pumped to a heater at a pressure of 50 to 550 psig
(344.74
to 3792.12 kPa), where it is heated to a teinperature from 480 F (248.89 C) to
520 F (271.11 C). It is then discharged into a coking zone, typically a
vertically-
oriented, insulated coker drum through an inlet at the base of the drum.
Pressure in
the drum is usually relatively low, such as 15 to 80 psig (103.42 to 551.58
kPa) to
allow volatiles to be removed overhead. Typical operating temperatures of the
drum will be between 410 C and 475 C. The hot feedstock thermally cracks over
a
period of time (the "coking time") in the coker drum, liberating volatiles
composed
primarily of hydrocarbon products, that continuously rise through the coke
mass
and are collected overhead. The volatile products are sent to a coker
fractionator for
distillation and recovery of coker gases, gasoline, light gas oil, and heavy
gas oil.
In an embodiment, a portion of the heavy coker gas oil present in the product
stream introduced into the coker fractionator can be captured for recycle and
combined with the fresh feed (coker feed component), thereby forming the coker
heater or coker furnace charge. In addition to the volatile products, delayed
coking
also forms solid coke product.
[0032] Coke bed morphology is typically described in simplified terms such as
sponge coke, shot coke, transition coke, and needle coke. Sponge coke, as the
name suggests, has a sponge-like appearance witll various sized pores and
bubbles
"frozen into" a solid coke matrix. One key attribute of sponge coke produced
by
routine coker operating conditions is that the coke is self-supporting, and
typically
will not fall out of the bottom of an un-headed coker drum, which typically
has a
head diameter of 6 feet. The head of the coker drum can be removed either
manually or by use of a throttled slide valve. Needle coke refers to a
specialty coke
that has a unique anisotropic structure. Preparation of coke whose major
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component is needle coke is known to those skilled in the art and is not the
subject
of this invention.
[0033] Shot coke is a distinctive type of coke. It is comprised of individual
substantially spherical particles that look like BBs. These individual
particles range
from substantially spherical to slightly ellipsoidal with average diameters of
1 mm
to 10 mm. The particles may be aggregated into larger-sized particles, e.g.,
from
tennis-ball size to basketball or larger sizes. The shot coke can sometimes
migrate
through the coke bed and to the bottom drain lines of the coke drum and slow,
or
even block, the quench water drain process. While shot coke has a lower
economic
value that sponge coke, it is the desired product coke for purposes of this
invention
because its ease of removal from the coker drum results in effectively
increasing
the process capacity which more than offsets its reduced economic valve.
[0034] At times there appears to be a binder material present between the
individual shot coke particles, and such a coke is sometimes referred to as
"bonded
shot" coke. Depending upon the degree of bonding in the bed of shot coke, the
bed
may not be self-supporting, and can flow out of the drum when the drum is
opened.
This can be referred to as "fall-out' or "avalanche" and if unexpected it can
be
dangerous to operating personnel and it can also dainage equipment.
[0035] The term "transition coke" refers to coke that has morphology between
that of sponge coke and shot coke. For example, coke that has a mostly sponge-
like physical appearance, but with evidence of small shot spheres that are
just
beginning to form as discrete particles in one type of transition coke.
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[0036] Coke beds are not necessarily comprised of all of one type of coke
morphology. For example, the bottom of a coke drum can contain large
aggregates
of shot, transitioning into a section of loose shot coke, and finally have a
layer of
sponge-rich coke at the top of the bed of coke. There are additional
descriptors for
coke, although less common. Such additional descriptors include: sandy coke
which is a coke that after cutting looks to the naked eye much like coarse
black
beach sand; and needle coke that refers to a specialty coke that has a unique
anisotropic structure. Preparation of coke whose major component is needle
coke
is well known to those having ordinary skill in the art and is not a subject
of this
invention.
[0037] The term "free-flowing" as used herein means that 500 tons (508.02 Mg)
of coke plus its interstitial water in a coker drum can be drained in less
than 30
minutes through a 60-inch (152.4 cm) diameter opening
[0038] It has been discovered that substantially free-flowing shot coke can be
produced by the practice of the present invention by insuring that the resid
feed is
one having a substantially higher initial boiling point than resides
conventionally
used for delay coking. As previously mentioned, conventional delayed coking
resid feeds typically have an initial boiling point from 500 C to 526 C, but
the
resid feeds of the present invention having an initial boiling point from 549
C to
566 C will unexpected produce shot coke over sponge coke.
[0039] Conventional coke processing aids, including an intifoaming agent, can
be employed in the process, for example, delayed coking wherein a resid
feedstock
is air-blown to a target softening point as described in U.S. Patent No.
3,960,704.
While shot coke has been produced by conventional methods it is typically
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agglomerated to such a degree that water-jet technology is needed for its
removal.
Additives are employed to provide for the formation of the desired,
substantially
free-flowing shot coke.
[0040] It is within the scope of this invention to use a suitable additive to
aid in
the formation of shot coke, preferably substantially free-flowing shot coke.
In an
embodiment, the additive is an organic soluble metal, such as a metal
naphthenate
or a metal acetylacetonate, including mixtures thereof. Preferred metals are
potassium, sodium, iron, nickel, vanadium, tin, molybdenum, manganese,
aluminum, cobalt, calcium, magnesium and mixtures thereof. Potassium, sodium,
iron, aluminum and calcium are preferred. Additives in the form of species
naturally present in refinery stream can be used. For such additives, the
refinery
stream may act as a solvent for the additive, which may assist in the
dispersing the
additive in the resid feed. Additives naturally present in refinery streams
include
nickel, vanadium, iron, sodium, and mixtures thereof naturally present in
certain
resid and resid fractions (i.e., certain feed streams). The contacting of the
additive
and the feed can be accomplished by blending a feed fraction containing
additive
species (including feed fractions that naturally contain such species) into
the feed.
[0041] In another embodiment, the metals-containing additive is a finely
ground
solid with a high surface area, a natural material of high surface area, or a
fine
particle/seed producing additive. Such high surface area materials include
fumed
silica and alumina, catalytic cracker fines, FLEXICOKER cyclone fmes,
magnesium sulfate, calcium sulfate, diatomaceous earth, clays, magnesium
silicate,
vanadium-containing fly ash and the like. The additives may be used either
alone
or in combination.
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[0042] It is within the scope of this invention that a metals-free additive be
used.
Non-limiting examples of substantially metals-free additives that can be used
in the
practice of the present invention include elemental sulfur, high surface area
substantially metals-free solids, such as rice hulls, sugars, cellulose,
ground coals,
ground auto tires. Other additives include inorganic oxides such as fumed
silica
and alumina; salts of oxides, such as ammonium silicate and mineral acids such
as
sulfuric acid and phosphoric acid, and their acid anhydrides.
[0043] Preferably, a caustic species is added to the resid coker feedstock.
When
used, the caustic species may be added before, during, or after heating in the
coker
furnace. Addition of caustic will reduce the Total Acid Number (TAN) of the
resid
coker feedstock and also convert naphtllenic acids to metal naphthanates,
e.g.,
sodium naphthenate.
[0044] Uniform dispersal of the additive into the vacuum resid feed is
desirable
to avoid heterogeneous areas of shot coke formation. Dispersing of the
additive is
accomplished by any number of ways, for example, by solubilization of the
additive into the vacuum resid, or by reducing the viscosity of the vacuum
resid
prior to mixing in the additive, e.g., by heating, solvent addition, use of
organometallic agents, etc. High energy mixing or use of static mixing devices
may be employed to assist in dispersal of the additive agent.
[0045] Polarizing light microscopy was used in the examples (illustrated in
Figures 1 and 2) for comparing and contrasting structures of green coke (i.e.,
non-
calcined coke) samples.
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[00461 At the macroscopic scale, i.e., at a scale that is readily evident to
the
naked eye, petroleum sponge and shot green cokes are quite different--sponge
has a
porous sponge-like appearance, and shot coke has a spherical cluster
appearance.
However, under magnification with an optical microscope, or polarized-light
optical microscope, additional differences between different green coke
samples
may be seen, and these are dependent upon amount of magnification.
[0047] For example, utilizing a polarized light microscope, at a low
resolution
where 10-micrometer features are discernable, sponge coke appears highly
anisotropic, the center of a typical shot coke sphere appears much less
anisotropic,
and the surface of a shot coke.sphere appears fairly anisotropic.
[0048] At higher resolutions, e.g., where 0.5-micrometer features are
discemable
(this is near the limit of resolution of optical microscopy), a green sponge
coke
sample still appears highly anisotropic. The center of a shot coke sphere at
this
resolution is now revealed to have some anisotropy, but the anisotropy is much
less
than that seen in the sponge coke sample.
[0049] It should be noted that the optical anisotropy discussed herein is not
the
same as "thermal anisotropy", a term known to those skilled in the art of
coking.
Thermal anisotropy refers to coke bulk thermal properties such as coefficient
of
thermal expansion, which is typically measured on cokes which have been
calcined, and fabricated into electrodes.
[0050] It is within the scope of this invention that a metals-free additive be
used
to encourage the production of free-flowing coke, preferably free-flowing shot
coke. Non-limiting examples of metals-free additives include elemental sulfur,
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high surface area substantially metals-free solids, such as rice hulls,
sugars,
cellulose, ground coals, ground auto tires; inorganic oxides such as fumed
silica
and alumina; salts of oxides, such as ammonium silicate and mineral acids such
as
sulfuric acid, phosphoric acid, and acid anhydrides.
[0051] The present invention will be better understood by reference to the
following non-limiting examples that are presented for illustrative purposes.
EXAMPLE
[0052] A vacuuln resid is produced in a refinery and has had the vacuum
overflash reincorporated into it. The refinery is pushing throughput, and
consequently the resid boiling point distribution is having an increased
amount of
the lightest portion. The vacuum resid has an API gravity of 3.7, contains 5.4
wt.%
S, and 10.0 wt.% hydrogen. The boiling point distribution of the front end as
determined by HTSD is as follows in the column labeled "base case vacuum
resid"
in the table below.
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TABLE
Base Case Vacuum Resid Resid with second stage
vacuum distillation
HTSD Wt.% Off AEBP, Deg. F (Deg. C) AEBP, Deg. F (Deg. C)
IBP 554 (290 910 (487.78)
1 698 (370 954 (512.22)
2 813 433.89 986 530
3 858 (458.89) 1003 (539.44)
4 888 475.56 1016 546.67
911 (488.33) 1027 (552.78)
6 929 498.33 1036 557.78
7 944 506.67 1045 (562.78)
8 957 513.89
9 969 (520.56)
980 526.67
11 990 532.22
12 999 (537.22)
13 1007 (541.67)
14 1016 (546.67)
1024 551.11
16 1032 (555.56)
17 1039 (559.44)
Wt.% 1382 - Deg. F 750 C 79.9 73.6
[0053] The resid contains 12 wt.% 900 F to 1040 F (482.22 C to 560 C)
material. The base case resid is coked in a pilot plant coker with a drum
overhead
temperature of 820 F (437.78 C), drum overhead pressure of 15 psig (103.42
kPa)
and zero recycle. The product coke has a bonded morphology which appears
highly fused throughout the bed. Microscopic examination of the coke under
cross
polarized light reveals mostly small domains (10-20 microns) with coarse
mosaic
(5-10 micron). Percentage shot coke by the micrographic technique is estimate
to
be 25%. By a known relationship with a commercial-scale coker, it is projected
CA 02564048 2006-10-23
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that this coke would yield a bonded shot that would be self-supporting in the
commercial scale coke drum.
[0054] The base case resid then has a second stage vacuum distillation which
removes a portion of the lightest components. The boiling point distribution
of the
resid after distillation is shown in the right colunm of the table, i":'e.,
after the second
stage vacuum distillation, the resid contains 7 wt.% 900 F to 1040 F (482.22 C
to
560 C) material.
[0055] The deeper cut resid is coked in the pilot plant coker with a drum
overhead temperature of 820 F (437.78 C), a drum overhead pressure of 15 psig
(103.42 kPa), and zero recycle. The product coke is 80% shot coke. Microscopic
examination of the coke under cross-polarized light reveals mostly
medium/coarse
mosaic (2-10 microns). Percentage shot coke by the micrographic technique is
estimate to be 75%. By a known relationship with a commercial-scale coker, it
is
projected that this coke would yield a relatively loose shot that would be non-
self
supporting in the commercial scale coke drum.
