U.S. patent application number 15/085200 was filed with the patent office on 2016-10-27 for fluid coking process.
The applicant listed for this patent is ExxonMobil Research and Engineering Company. Invention is credited to Brian A. Knapper, Craig A. McKnight, Jennifer McMillan, Jason S. Wiens, Michael Wormsbecker.
Application Number | 20160312126 15/085200 |
Document ID | / |
Family ID | 55754460 |
Filed Date | 2016-10-27 |
United States Patent
Application |
20160312126 |
Kind Code |
A1 |
Wormsbecker; Michael ; et
al. |
October 27, 2016 |
FLUID COKING PROCESS
Abstract
A fluid coking process is operated in a fluidized bed coking
reactor in which a plurality of heavy oil inlet nozzles are
arranged in a number of rings around the periphery of the dense bed
reaction section at vertically spaced elevations. A heavy oil feed
is injected with atomization steam through the nozzles into the
fluidized. bed, operating at a lower steam-to-oil ratio for the
upper ring or rings of nozzles than for the lower ring or
rings.
Inventors: |
Wormsbecker; Michael;
(Edmonton, CA) ; Wiens; Jason S.; (Edmonton,
CA) ; McMillan; Jennifer; (Edmonton, CA) ;
McKnight; Craig A.; (Sherwood Park, CA) ; Knapper;
Brian A.; (Edmonton, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ExxonMobil Research and Engineering Company |
Annandale |
NJ |
US |
|
|
Family ID: |
55754460 |
Appl. No.: |
15/085200 |
Filed: |
March 30, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62152214 |
Apr 24, 2015 |
|
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|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C10B 55/10 20130101;
C10G 9/005 20130101 |
International
Class: |
C10G 9/00 20060101
C10G009/00 |
Claims
1. In a fluid coking method operated in fluidized bed coking
reactor having (i) a dense bed reaction section of circular
horizontal cross-section about a vertical axis and confined by a
reactor wall and (ii) a plurality of heavy oil inlet nozzles
located in the dense bed reaction section and arranged in rings
around the periphery of the reactor wall in the reaction section at
vertically spaced elevations by means of which a heavy oil feed is
injected into a fluidized bed in the dense bed reaction section to
thermally crack the feed to form solid coke and vaporous cracking
products, the improvement comprising: injecting the heavy oil feed
into the fluidized bed from the upper ring or rings of nozzles at a
lower steam-to-oil ratio than from the lower ring or rings of
nozzles.
2. A fluid coking method according to claim 1 in which the
uppermost rings are operated at the same steam-to-oil ratio and the
lower rings are operated at the same steam to oil ratio, the steam
to oil ratio of the upper rings being lower than that of the lower
rings.
3. A fluid coking method according to claim 1 in which the
fluidized bed coking reactor has six rings of nozzles and the
uppermost two rings are operated at a steam-to-oil ratio lower than
that of the four lower rings.
4. A fluid coking method according to claim 3 in which the four
lower rings are operated at the same steam-to-oil ratio higher than
that of the uppermost two rings.
5. A fluid coking method according to claim 1 in which the
lowermost ring or rings are operated with steam and with or without
oil feed.
6. A fluid coking method according to claim I in which the
uppermost rings are operated at a steam-to-oil ratio from about
0.25 to 0.35% w/w and the lower rings at a steam-to-oil ratio of
about 0.9 to 1.1% w/w.
7. A fluid coking method according to claim 1 in which the
uppermost rings are operated at a steam-to-oil ratio from about 0.4
to 0.6% w/w and the lower rings at a steam-to-oil ratio of about
1.3 to 1.5% w/w.
8. A method for modifying the operation of a fluid bed coking unit
which has (i) a dense bed reaction section of circular horizontal
cross-section about a vertical axis confined by the reactor wall,
and (ii) injection nozzles for injecting a heavy oil feed with the
aid of atomizing steam in at least some of the rings, the nozzles
being arranged in a series of rings at vertically spaced intervals
around the periphery of the upper portion of the dense bed reaction
section; the modification method comprises: operating the unit
after modification at an overall steam/oil ratio for rings in which
oil is injected with atomizing steam at substantially the same rate
or higher as in the unit before modification but with the ratio of
steam-to-oil feed on the uppermost ring or rings lower than for
lower rings,
9. A modification method according to claim 8 in which the
uppermost rings are operated at the same steam-to-oil ratio and the
lower rings are operated at the same steam to oil ratio, the steam
to oil ratio of the upper rings being lower than that of the lower
rings.
10. A modification method according to claim 9 in which the
fluidized bed coking reactor has six rings of nozzles and the
uppermost two rings are operated at a steam-to-oil ratio lower than
that of the four lower rings.
11. A modification method according to claim 9 in which the four
lower rings are operated at the same steam-to-oil ratio higher than
that of the uppermost two rings.
12. A modification method according to claim 8 in which the
lowermost ring or rings are operated with steam and with or without
oil feed.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. Provisional
Application Ser. No. 62/152,214 filed Apr. 24, 2015, which is
herein incorporated by reference in its entirety.
FIELD OF THE INVENTION
[0002] This invention relates to a fluid coker with improved liquid
yield and its method of operation.
BACKGROUND OF THE INVENTION
[0003] Fluidized bed coking is a petroleum refining process in
which heavy petroleum feeds, typically the non-distillable residues
(resids) from fractionation, are converted to lighter, more useful
liquid products by thermal decomposition (coking) at elevated
reaction temperatures, typically about 480 to 590.degree. C.,
(about 900 to 1100.degree. F.). The process is carried out in a
unit with a large reactor vessel containing hot coke particles
which are maintained in the fluidized condition at the required
reaction temperature with steam injected at the bottom of the
vessel with the average direction of movement of the coke particles
being downwards through the bed. The heavy oil feed is heated to a
pumpable temperature, mixed with atomizing steam, and fed through
multiple feed nozzles arranged at several successive levels in the
reactor, usually referred to as "rings" since they are arranged
around the periphery of the reactor at different, vertically spaced
intervals in the upper part of the reactor. Steam is injected into
a stripper section at the bottom of the reactor and passes upwards
through the coke particles in the stripper as they descend from the
main part of the reactor above and promotes fluidization of the
particles in the bed. The feed liquid coats a portion of the coke
particles in the fluidized bed and subsequently decomposes into
layers of solid coke and lighter products which evolve as gas or
vaporized liquid. The light hydrocarbon products of the coking
(thermal cracking) reactions vaporize, mix with the fluidizing
steam and pass upwardly through the fluidized bed into a dilute
phase zone above the dense fluidized bed of coke particles. This
mixture of vaporized hydrocarbon products formed in the coking
reactions continues to flow upwardly through the dilute phase with
the steam at superficial velocities of about 1 to 2 metres per
second (about 3 to 6 feet per second), entraining some fine solid
particles of coke. Most of the entrained solids are separated from
the gas phase by centrifugal force in one or more cyclone
separators, and are returned to the dense fluidized bed by gravity
through the cyclone diplegs. The mixture of steam and hydrocarbon
vapors from the reactor is subsequently discharged from the cyclone
gas outlets into a scrubber section in a plenum located above the
reaction section and separated from it by a partition. It is
quenched in the scrubber section by contact with liquid descending
over scrubber sheds in a scrubber section. A pumparound loop
circulates condensed liquid to an external cooler and back to the
top row of scrubber section to provide cooling for the quench and
condensation of the heaviest fraction of the liquid product. This
heavy fraction is typically recycled to extinction by feeding back
to the fluidized bed reaction zone.
[0004] The solid coke from the reactor, consisting mainly of carbon
with lesser amounts of hydrogen, sulfur, nitrogen, and traces of
vanadium, nickel, iron, and other elements derived from the feed,
passes through the stripper and out of the reactor vessel to a
burner where it is partly burned in a fluidized bed with air to
raise its temperature from about 480 to 700.degree. C. (about
900.degree. to 1300.degree. F.), after which the hot coke particles
are recirculated to the fluidized bed reaction zone to provide the
heat for the coking reactions and to act as nuclei for the coke
formation.
[0005] The Flexicoking.TM. process, also developed by Exxon
Research and Engineering Company, is, in fact, a fluid coking
process that is operated in a unit including a reactor and burner,
often referred to as a heater in this variant of the process, as
described above but also including a gasifier for gasifying the
coke product by reaction with an air/steam mixture to form a low
heating value fuel gas. The heater, in this case, is operated with
an oxygen depleted environment. The gasifier product gas,
containing entrained coke particles, is returned to the heater to
provide a portion of the reactor heat requirement. A return stream
of coke sent from the gasifier to the heater provides the remainder
of the heat requirement. Hot coke gas leaving the heater is used to
generate high-pressure steam before being processed for cleanup.
The coke product is continuously removed from the reactor. In view
of the similarity between the Flexicoking process and the fluid
coking process, the tem "fluid coking" is used in this
specification to refer to and comprehend both fluid coking and
Flexicoking except when a differentiation is required.
[0006] The dense fluid bed behaves generally as a well-mixed
reactor. However, computational fluid dynamics model simulations
and tracer studies have shown that significant amounts of coke
particles coated in heavy petroleum feed can rapidly bypass the
reaction section and descend into the shipper section at the bottom
of the reactor while still coated with a film of liquid which is
then largely lost as a source of potential liquid product.
[0007] Effective mixing of the injected heavy oil feed with the
coke particles is vital to reactor operability and liquid yield. A
major concern in the process is the formation of liquid-rich
agglomerates of coke solids held together by a sticky, adherent
liquid film on the coke particles. These agglomerates, with
particle sizes substantially larger than average bulk solids,
suffer from increased heat and mass transfer limitations and reduce
liquid yields. If the liquid were spread more evenly over the coke
particles, creating thinner films, the heat and mass transfer
limitations could be reduced and subsequently liquid yields would
increase. In addition, when the liquid to solid ratio of the
agglomerates is reduced, the agglomerates are weaker and more
likely to break up so that the steam requirements associated with
attrition of the agglomerates might be reduced. The excess steam
can be removed from the process to reduce sour water make, or be
reemployed in the reactor in an alternative ways such as additional
feed nozzle atomization.
[0008] In order to prolong the average residence time of the wetted
coke particles in the reactor, one method of operation is to inject
the heavy oil feed through the injection nozzles in the upper part
of the reactor but to use the lower rings solely for the injection
of steam. More feed injected higher in the bed increases the
residence time between the feed zone and stripper, affording more
time for the liquid film to dry reducing the fouling in the
stripper region.
[0009] A typical commercial unit with an average feed rate per
nozzle of about 230 m.sup.3/day (about 1450 sbpd) might have, for
example, 96 feed nozzles distributed between 6 feed rings. Rings 1
and 2 at the two highest levels in the reactor might have 20 feed
nozzles each, Ring 3 immediately below Ring 2 might have 19
nozzles, Ring 4 might have 116, Ring 5 might have 14 and Ring 6
might have 7. Rings 5 and 6, however, might not be used for feed
injection but, instead, could be purged with steam to prevent
plugging. Each pair of feed rings (1&2, 3&4, 5&6) could
be connected to a separate feed header line which can be varied
separately, but typically all feed header lines would be controlled
to the same pressure which, in a typical commercial unit, might be
in the range of about 1000 to 2000 kPag (for example, from about
1500 to 1700 kPag), equivalent to about 145 to 290 psig (for
example, from about 220 to 245 psig). The superficial upward
velocity in the reactor might range from about 60 cm/sec at the
level of the lowest ring (Ring 6), increasing to about 1 m/sec at
the level of the highest ring (Ring 1). The average gas to liquid
ratio (GLR or steam-to-oil) ratio at which the nozzles are all
operated (for nozzles feeding oil) might typically be 0.86% w/w
(the GLR is reported as (mass flow rate steam)/(mass flow rate
oil)*100%).
[0010] Studies have shown that increasing the gas to liquid ratio
(GLR) in the feed nozzle enhances the dispersion of the liquid onto
the particles. If this approach is used, the overall steam usage
increases, which is not attractive because of restrictions on the
processing of sour water from the unit and reduced feed throughput
due to reactor top bed velocity restrictions. The objective
therefore is to improve feed dispersion and liquid yield without
increasing the overall steam usage. The majority of these studies
were performed at one fluidization velocity, which was fairly low;
on the order of 15 cm/sec (about 0.5 ft/s). More recently, tests
have reported the benefits of increasing the fluidization
velocities in the region of a feed nozzle: increasing the
fluidization velocity to 90 cm/sec (about 3 ft/sec) provides
similar benefits as increasing GLR to a feed nozzle. Other reports
demonstrated a negligible improvement in jet bed interaction when
the gas/liquid ratio was increased from 1.5% w/w to 2.7% w/w with a
fluidized bed operated at about 40 cm/sec (about 1.3 ft/s).
Increasing the fluidization velocity from 15 cm to about 75 cm/sec
(about 0.5 ft/sec to 2.5 ft/sec) resulted in a significant
improvement in jet bed interaction when using a poorly performing
feed nozzle. When comparing a nozzle operating with and without
atomization, significant differences were observed at the lower
superficial gas velocity, and only a slight decrease in performance
was observed at a higher fluidization velocity when the atomization
gas was removed.
SUMMARY OF THE INVENTION
[0011] Improvement in liquid product yield may be obtained by
reducing the steam supply to the upper feed nozzles in the reactor
while operating the lower nozzles at higher steam/oil ratios, with
no net increase or decrease in atomization steam usage. Operation
in this manner will allow for a greater improvement in feed
dispersion at all feed ring levels since the nozzle operation is
adapted in accordance with the local solids mixing behavior.
[0012] According to the present invention, the fluid coking process
is operated in a fluidized bed coking reactor in which a plurality
of heavy oil inlet nozzles are arranged in a number of rings around
the periphery of the dense bed reaction section at vertically
spaced elevations. A heavy oil feed is injected with atomization
steam through the nozzles into the fluidized bed, operating at a
lower steam-to-oil ratio for the upper ring or rings of nozzles
than for the lower ring or rings.
[0013] The reactor in the unit in which the fluid bed coking is
operated has a dense bed reaction section of circular horizontal
cross-section about a vertical axis confined by the reactor wall.
The reactor has a base region where fluidizing gas is injected to
fluidize a bed of finely-divided solid particles in the reaction
section and an exit at the top through which gas and finely divided
particulate solids exit the reactor. The reactor has injection
nozzles for the heavy oil feed arranged in a series of rings at
vertically spaced intervals around the periphery of the upper
portion of the reactor. The nozzles are fitted for injecting the
oil feed with the aid of atomizing steam and in operation the ratio
of steam to oil feed for the uppermost ring or rings is lower than
for lower rings. Optionally, the lowermost ring or rings may be
operated without oil feed, i.e. only with a steam purge.
[0014] The reactor will be coupled in the unit to a burner/heater
by means of coke lines in the normal way: a cold coke transfer line
takes coke from the bottom of the stripper to the burner/heater and
a hot coke return line brings hot coke from the burner/heater back
to the reactor. In the case of a Flexicoker, the gasifier section
follows the heater vessel as described above.
[0015] The invention may be used as the basis for modifying an
existing fluid coker unit; in that case, the overall steam/oil
ratio would be maintained by distributing the atomizing steam
differently between the successive rings of nozzles: the upper ring
or rings of nozzles will operate at a lower steam-to-oil ratio than
for the lower ring or rings. Thus, the invention provides a method
for modifying the operation of a fluid bed coking unit which has a
dense bed reaction section of circular horizontal cross-section
about a vertical axis confined by the reactor wall, a base region
where fluidizing gas is injected to fluidize a bed of
finely-divided solid particles in the reaction section and an exit
at the top through which gas and finely divided particulate solids
exit the reactor. The reactor has injection nozzles for the heavy
oil feed arranged in a series of rings at vertically spaced
intervals around the periphery of the upper portion of the reactor.
The nozzles are fitted for injecting the oil feed with the aid of
atomizing steam. In the operation of the unit prior to
modification, the steam/oil ratio for each of the rings (at least
for rings in which oil is injected) is substantially the same for
each ring. After modifying the unit, the overall steam-to-oil ratio
(GLR) for all the feed injection rings is maintained at
substantially the same as in the unit before modification but the
GLR of the feed nozzles on the uppermost ring or rings is lower
than for lower rings. Optionally, the lowermost ring or rings may
be operated without oil feed, with only a steam purge.
DRAWINGS
[0016] The single Figure of the accompanying drawings is a
simplified vertical section of a reactor of a fluid coking
unit.
DETAILED DESCRIPTION
[0017] Heavy petroleum feeds which may be treated in the fluid
coking process include heavy hydrocarbonaceous oils, heavy and
reduced petroleum crude oil, petroleum atmospheric distillation
bottoms, petroleum vacuum distillation bottoms, or residuum, pitch,
asphalt, bitumen, other heavy hydrocarbon residues, tar sand oil,
shale oil, coal, coal slurries, liquid products derived from coal
liquefaction processes, including coal liquefaction bottoms, and
mixtures thereof. Such feeds will typically have a Conradson carbon
content (ASTM D 189-06e2) of at least about 5 wt. %, generally from
about 5 to 50 wt. %.
[0018] FIG. 1 is a simplified diagram of the reactor of a fluid
coking unit using frusto-conical staging baffles as shown and
described in U.S. Pat. No. 8,435,452, to which reference is made
for an extended description of the baffles and their functioning.
The reactor coking zone 10 contains a dense phase fluidized bed 11
of heated seed coke particles into which the feedstock, heated to a
temperature sufficient to initiate the coking (thermal cracking)
reactions and deposit a fresh coke layer on the hot fluidized coke
particles circulating in the bed is injected. The coking zone has a
slight frusto-conical form with its major cross-section uppermost
so that the gas flow decelerates towards the top of the reactor
vessel; the upper portion of the vessel is typically cylindrical in
shape. Typically, the feed is preheated by contact with the
cracking vapors passing through the scrubber section atop the
reactor. The feed is injected through multiple nozzles located in
feed rings 12a to 12f, which are positioned so that the feed with
atomizing steam enters directly into the dense fluidized bed of hot
coke particles in coking zone 11. Each feed ring consists of a set
of nozzles (typically 10-20, not designated in FIG. 1) that are
arranged in rings around the circular periphery of the reactor
wall, each ring at a given elevation and with each nozzle in the
ring connected to its own feed line which penetrates the vessel
shell (i.e. 10-20 pipes extending into the fluid bed at the level
of the ring). These feed nozzles are typically arranged
non-symmetrically around the reactor to optimize flow patterns in
the reactor according to simulation studies although symmetrical
disposition of the nozzles is not precluded if the flow patterns in
the reactor can be optimized in this way. There are typically 4-6
feed rings located at different elevations although not all may be
active at any one time while the unit is working; some rings,
usually the lowermost rings, may be used for steam injection only
as noted above.
[0019] Steam is admitted as fluidizing gas in the stripping section
13 at the base of coker reactor 110 through spargers 14 directly
under stripping sheds 15 as well as from lower inlets 16. The steam
passes up into stripping zone 13 of the coking reactor in an amount
sufficient to obtain a superficial fluidizing velocity in the
coking zone, typically in the range of about 0.15 to 1.5 m/sec
(about 0.5 to 5 ft/sec). The coking zone is typically maintained at
temperatures in the range of 450 to 650.degree. C. (about 840 to
1200.degree. F.) and a pressure in the range of about 0 to 1000
kPag (about 0 to 145 psig), preferably about 30 to 300 kPag (about
5 to 45 psig), resulting in the characteristic conversion products
which include a vapor fraction and coke which is deposited on the
surface of the seed coke particles.
[0020] The vaporous products of the cracking reactions with
entrained coke particles pass upwards out of the dense phase
reaction zone 11, through a phase transition zone in the upper
portion 17 of the vessel and finally, a dilute phase reaction zone
at the inlets of cyclones 20 (only two shown, one indicated). The
coke particles separated from the vaporous coking products in the
cyclones are returned to the fluidized bed of coke particles
through cyclone dipleg(s) 21 while the vapors pass out through the
gas outlet(s) 22 of the cyclones into the scrubbing section of the
reactor (not shown). After passing through the scrubbing section
which is fitted with scrubbing sheds in which the ascending vapors
are directly contacted with a flow of fresh feed to condense higher
boiling hydrocarbons in the reactor effluent (typically 525.degree.
C.+/975.degree. F.+) and recycled along with the fresh feed to the
reactor. The vapors leaving the scrubber then pass to a product
fractionator (not shown) in which the conversion products are
fractionated into light streams such as naphtha, intermediate
boiling streams such as light gas oils and heavy streams including
product bottoms which may be recycled to the furnace of the coker
for mixing with fresh feed.
[0021] In the reactor shown in FIG. 1, staging baffles 30 of the
type described in U.S. Pat. No. 8,435,452 extend radially inwards
and downwards from their upper edges which are fixed to the reactor
wall are of generally conical form with a central, circular
aperture to permit downward flow of coke particles and upward flow
of vapors and divide the reactor into an upper feed zone and a
lower drying zone thereby minimizing the bypassing of wet solids to
the stripper zone below. In a reactor having six feed rings, for
example, the baffles may be located below rings 2, 4 and 6 (feed
rings numbered from top down). The lowest baffle is, in any event,
preferably located below the bottommost feed ring as shown in FIG.
1 and successive baffles are located between pairs of feed rings at
higher levels. In one specific embodiment of the reactor, one
baffle is situated below the lowest row of active feed nozzles. A
majority (at least 50% and preferably at least 30%) of the feed is
preferably injected at the intermediate levels of the dense bed,
for example, in the six feed ring reactor in rings 2, 3 and 4 (from
top down). Attrition steam is directed through nozzles 31 below the
bottom baffle 12f and above the top row of stripper sheds in order
to control the mean particle size of the circulating coke.
[0022] A portion of the stripped coke that is not burned in the
heater to satisfy the heat requirements of the coking zone is
recycled to the coking zone through coke return line 26, passing
out of return line 26 through cap 27 to enter the reactor near the
top of the reaction zone; the remaining portion is withdrawn from
the heater as product coke. A variation allows a smaller flow of
hot coke from the heater to be admitted from a second return line
28 higher up in reactor 10 at a point in the dilute phase where it
is entrained into the cyclone inlet(s) as scouring coke to minimize
coking of the reactor cyclones and the associated increase in the
pressure drop. If the unit is a Hexicoking unit, the gasifier
section follows the heater with flow connections for the coke,
return coke and gas flows in the normal way.
[0023] A typical mode would be to operate with a reduced
steam/heavy oil ratio in the uppermost feed ring or rings (Rings 1
and 2) with a consequently lower steam-to-oil ratio for these
nozzles and operating the rest of the feed rings (Rings 3-6) at
higher steam-to-oil ratios. Simple changes in the operation of
existing nozzles will usually allow the necessary changes in steam
rate relative to oil feed rate to be made, for example, by varying
the sizes of the steam inlet orifices in the upstream piping or
imposing some throttling on the steam header(s) to individual
rings. Alternatively, customized feed nozzles with different
steam/oil ratios may be used for the specific feed rings. Either
way, there can be a greater improvement in feed dispersion in all
feed rings since the nozzle is adapted for the localized solids
mixing behavior.
[0024] The improved atomization performance in the lower portion of
the feed zone of the reactor resulting from the higher relative
steam rate(s) in this region will aid the dispersion of the heavy
oil feed from the feed nozzles in a region of the bed that is not
normally as turbulent. The increased dispersion of the jets of
injected oil in this lower region of the reactor result in thinner
oil films on the particles which can be expected to result in
higher liquid yields.
[0025] The GLR operating window for the feed nozzles, i.e. the
nozzles feeding atomized heavy oil feed with atomization steam will
vary according to a
[0026] number of factors including the size of the unit, its
height/diameter ratio, and, particularly, the configuration of the
nozzles. In general terms, the GLR for most nozzles will be in the
range of 0.25 to 1.5% w/w with some nozzles being limited to a
range of about 0.25 to 0.75% w/w while others will allow ranges up
to about 1.5% w/w to be utilized. The extent to which the GLR
values between the upper feed rings and the lower feed rings
(neglecting the rings injecting only steam) will therefore vary
according to the types of nozzle installed in the unit and the safe
operating parameters established for the nozzles and the unit in
which they are operated. In the case, for example of the nozzles
with the lower permissible range of GLR ratios, the upper ring(s)
might be operated with a GLR at the lower end of their operating
range, about 0.25 to 0.35% w/w and the lower rings at a GLR of
about 0.9 to 1.1% w/w. In cases where the nozzles allow higher GLR
ratios, the upper ring(s) might be operated with a GLR at the lower
end of their operating range, about 0.4 to 0.6% w/w and the lower
rings at a GLR of about 1.3 to 1.5% w/w.
[0027] Nozzles of the type shown in US 2012/0063961, for instance,
can typically be operated at a higher GLR than those as shown in
U.S. Pat. No. 6,003,789. A reactor with a total of six rings of
nozzles of the type described in U.S. Pat. No. 6,003,789 could be
operated, for instance, with the top two feed rings at a
steam-to-oil ratio of 0.27% w/w as compared to 0.65% w/w (in
normal, unmodified operation) while remaining within the safe
operating window set for this nozzle in unmodified operation. A
liquid yield increase potential of 0.1% w/w was estimated; further
investigation showed that this relatively small increase resulted
from the narrow operating window of the specific feed nozzle
configuration which did not permit the steam rate to be
significantly reduced in the upper rings as unstable operation
would result. If the nozzle configuration of US 2012/0063961 were
used, the potential liquid yield increase would climb to 0.7% w/w,
excluding benefits accruing from the nozzle configuration
itself.
[0028] A reactor with six rings of nozzles having the configuration
shown in US 2012/0063961 could be operated with the top two feed
rings at a steam-to-oil ratio of 0.45% w/w (vs 0.86% w/w in normal
unmodified operation) and the bottom four feed rings at a
steam-to-oil ratio of 1.37% w/w (vs 0.86% w/w in normal unmodified
operation) while remaining within the safe operating window for
this type of nozzle in the unit. The estimated liquid yield benefit
was 0.4% w/w with no credit for potential reactor temperature
reduction due to improved feed bed contacting.
[0029] For both types of coker feed nozzles, the overall
atomization steam consumption would be comparable to the case in
which the top four rings are operated with oil feed at the same
steam-to-oil ratio; however, this shift in atomization steam usage
would significantly improve interaction between the injected
steam/oil sprays and the bed to increase liquid yields.
[0030] An optimal strategy would utilize customized nozzles for
high solids mixing regions to generate more dispersion from the
nozzle and disperser design to permit the solids mixing process to
control feed dispersion. In regions of lower solids mixing, nozzles
that produce a spray with longer penetrations, higher momentum and
finer droplets could be used to allow the jet to control dispersion
of the feed.
* * * * *