Note: Descriptions are shown in the official language in which they were submitted.
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1 SAFE AND AUTOMATIC METHOD FOR REMOVAL
2 OF COKE FROM A COKE VESSEL
3
4 FIELD OF THE INVENTION
6 The present invention relates to the field of hydrocarbon processing and, in
7 particular, to heavy hydrocarbon processing in coke vessels.
8
9 BACKGROUND OF THE INVENTION
11 Many oil refineries recover valuable products from the heavy residual
12 hydrocarbons (commonly referred to as resid or residuum), which remain
13 following initial refining, by a thermal cracking process known as delayed
14 coking. Generally, the delayed coking process involves heating the heavy
hydrocarbon feed from a fractionation unit, then pumping the heated heavy
16 feed into a large steel vessel commonly known as a coke drum. The
17 unvaporized portion of the heated heavy feed settles out in the coke vessel
18 where the combined effect of retention time and temperature causes the
19 formation of coke. Vapors from the top of the coke vessel, which typically
consist of steam, gas, naphtha and gas oils, are returned to the base of the
21 fractionation unit for further processing into desired light hydrocarbon
22 products. The operating conditions of delayed coking can be quite severe.
23 Normal operating pressures in coke vessels typically range from 25 to about
24 50 pounds per square inch and the heavy feed input temperature may vary
between 900°F and 950°F. The coke drums operate in pairs, with
one drum
26 feeding residuum and the other drum undergoing the "decoking" sequential
27 steps. The drums typically operate on a cycle, switching every 12-30 hours.
28
29 Coke vessels are typically large, cylindrical vessels commonly 19 to 30
feet in
diameter and two to three times as tall having a top head and a funnel shaped
31 bottom portion fitted with a bottom head and are usually present in pairs
so
32 that they can be operated alternately. Coke settles out and accumulates in
33 the vessel until it is filled to a safe margin, at which time the heated
feed is
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1 switched to the empty "sister" coke vessel. Thus, while one coke vessel is
2 being filled with heated residual oil, the other vessel is being cooled and
3 purged of hundreds to thousands of tons of coke formed in the vessel during
4 the previous recovery cycle. The full vessel is isolated, steamed to remove
hydrocarbon vapors, cooled by filling with water, drained, opened, and the
6 coke is removed.
7
8 Coke removal, also known as decoking, begins with a quench step in which
9 steam and then water are introduced into the coke filled vessel to complete
the recovery of volatile, light hydrocarbons and to cool the mass of coke. The
11 vessel is then vented to atmospheric pressure. Decoking is accomplished at
12 most plants using a hydraulic system consisting of a drill stem and drill
bit that
13 direct high pressure water jets into the coke bed. To cut coke in this
manner
14 the top and bottom heads of the vessel must be removed. A rotating
combination drill bit, referred to as the cutting tool, is about 18 inches in
16 diameter with four (4) nozzels and is mounted on the lower end of a long
17 hollow drill rod about 6 inches in diameter. The drill bit is lowered into
the
18 vessel, on the drill stem, through a flanged opening at the top of the
vessel. A
19 "bore hole" is drilled through the coke using the four nozzles angled
approximately 60 degrees down from horizontal. This creates a hole from
21 about 3 to 6 feet in diameter for the coke to fall through. There is
normally a
22 naturally occurring small hole in the coke bed for the initial pass because
the
23 resid flows in from the bottom and out toward the edges of the vessel.
24
When the initial bore hole is complete, the drill bit is then mechanically
26 switched to two (2) horizontal nozzles in preparation for cutting the
"blow"
27 hole, which extends to the full drum diameter. The nozzles shoot jets of
water
28 horizontally outwards, rotating slowly with the drill rod, and those jets
cut the
29 coke into pieces, which fall out the open bottom of the vessel, into a
chute that
directs the coke to a receiving area. At some plants the hydraulic drill is
31 raised slowly up from the bottom the entire vertical height of the coke
mass, at
32 others the drill is lowered from the top through the mass and at still
other
33 plants the coke mass is first cut from the bottom cone of the vessel and
the
34 remainder is cut from the top of the vessel. In any case, the cut coke
falls out
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1 the opening at the bottom of the vessel into the coke chute system. The
drill
2 rod is then withdrawn out the flanged opening at the top of the vessel.
Finally,
3 the top and bottom of the vessel are closed by replacing the head units,
4 flanges or other closure devices employed on the vessel unit. The vessel is
then clean and ready for the next filling cycle with the heavy hydrocarbon
6 feed.
7
8 The process of removing and replacing the removable top head and bottom
9 units of the vessel cover is called heading and unheeding or deheading. It
is
dangerous work, with several risks associated with the procedures. There
11 have been fatalities and many serious injuries. There is significant safety
risk
12 from exposure to steam, hot water, fires and repetitive stress associated
with
13 the manual unbolting work. Accordingly, the industry has devoted
substantial
14 time and investment in developing semi-automatic or fully automatic
unheeding systems, with attention focused on bottom unheeding where the
16 greatest safety hazard is present.
17
18 There are two typical and commonly used methods to move the bottom head
19 out of the way of the falling coke. The first is to completely remove the
head
from the vessel, perhaps carrying it away from the vessel on a cart. This
21 process may be automated as set forth in U.S. Pat. No. 5,336,375. The other
22 way of "removing" the bottom head is to swing it out of the way, as on a
hinge
23 or pivot, while the head is still coupled to the vessel as in U.S. Patent
No.
24 6,264,829. Several U.S. patents disclose various methods and apparatus for
detaching and laterally moving a drum head or swinging away a drum head
26 including: U.S. Pat. No. 6,264,829 (discloses a swing away hydraulically
27 operated drumhead adapted for low headroom situations); U.S. Pat. No.
28 6,254,733 (depicting in the drawings a hydraulically removable drumhead);
29 U.S. Pat. No. 6,066,237 and 5,876,568 (disclosing an apparatus for semi-
automatically clamping and unclamping a drum bottom head); U.S. Pat. No.
31 5,947,674 (a drum head device removed by vertically oriented hydraulic
32 cylinders adapted for lowering the head unit and moving it laterally
aside);
33 U.S. Pat. No. 5,785,843 (claims a process involving a swing away
34 hydraulically operated drumhead adapted for low headroom situations); U.S.
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1 Pat. No. 5,581,864 (a remotely operated carriage mounted drumhead removal
2 system); U.S. Pat. No. 5,500,094 (car mounted drumhead removal system
3 that is horizontally movable); U.S. Pat. No. 5,228,825 (a device and method
4 for deheading a drum comprising, in part, a cradle that holds the drum head
for removal); U.S. Pat. No. 5,221,019 (a remotely operated cart removal
6 system); U.S. Pat. No. 5,098,524 (a pivotally attached unheading device
7 associated with clamps); U.S. Pat. No. 4,726,109 (a platform device lowers
8 the drumhead and moves it laterally away). These systems all use a manual
9 or semi-automatic bolting system that must be uncoupled with every decoking
cycle.
11
12 The above described bottom head removal systems all require that the heated
13 feed enter the coke vessel from the bottom through the center of the bottom
14 head. Although in past years there have been some side entries used, except
for possibly one or two cases, side entry use has been discontinued in coker
16 vessels built and put into operation in the last 20 to 30 or more years.
Thus,
17 in the usual coker operation, to remove the vessel bottom head for decoking
18 the feed line must first be disconnected before the bottom head can be
19 removed. Lastly a coke chute must be manually or hydraulically moved into
place and, typically, safety bolts are manually inserted to secure the chute
to
21 the drum, allowing the chute to receive the falling coke. The chute directs
the
22 coke, as it is drilled out of the vessel, to a receiving area where it is
later
23 removed. These methods still require the feed line to be opened up and the
24 head removed before the bottom chute can be brought up and attached to the
bottom flange of the vessel.
26
27 Considering that there is exposure to personnel and/or equipment when
28 opening the feed line, and considering there is exposure to personnel
and/or
29 equipment when opening the bottom head before the chute comes up and is
attached, and considering there may still be personnel exposure to steam/hot
31 water between the chute and bottom head after the chute is up, improvements
32 in coke vessel bottom unheading system to allow safe removal of coke from
33 the vessel is highly desirable. The object of the present invention is to
34 address this need.
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1
2 SUMMARY OF THE INVENTION
3
4 According to the present invention, a process and apparatus are provided for
repetitively producing and removing coke from a delayed coker vessel without
6 unheeding the vessel bottom, wherein the coker vessel has a bottom portion
7 having an aperture through which coke is released, comprising: (a) sealing
an
8 aperture closure housing to the bottom portion of the coker vessel; (b)
moving
9 a closure member within the closure housing to close the aperture; (c)
feeding
a heavy hydrocarbon feed into the coker vessel through a feed line attached
11 to the coker vessel at a position above the bottom of the coker vessel; (d)
12 coking the heavy hydrocarbon in the coker vessel; (e) moving the closure
13 member within the closure housing to open the aperture to allow coke
14 removal from the coker vessel; (f) releasing coke through the aperture into
a
coke chute, and; repeating steps c through f, successively. In a preferred
16 embodiment of the invention the closure member is power actuated, such as
17 hydraulically, by remote means, thus obviating any need for personnel to be
18 physically present in the vessel bottom area during decoking operations.
19
The delayed coker vessel of the present invention comprises a vessel having
21 a top opening and on the lower portion a side aperture and a bottom
aperture;
22 a feed pipe fitted to said side aperture; a bottom aperture closure housing
23 sealed to the bottom aperture; a closure member moveable within said
24 closure housing; a coke chute sealed to the bottom portion of the closure
housing for directing material from the vessel to a receiving area. The
26 combination of the closure housing and moveable closure member therein is
27 herein termed a closure unit or valve. In one embodiment of the invention
the
28 bottom portion of the coker vessel is designed and fabricated to be
directly
29 sealed to the closure unit, whereas in another embodiment, particularly
useful
for retrofitting existing coker vessels, a bottom transition piece, herein
termed
31 a spool, is interposed between the vessel bottom and the closure unit and
32 pressure-tightly sealed to both. In either of these two embodiments, a
33 preferred feature is that the closure housing is pressure-tightly sealed to
either
34 (a) the coker vessel or (b) the spool piece. Preferably the pressure-tight
seals
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1 will withstand pressures within the range of about 100 psi to 200 psi,
2 preferably within the range of about 125 psi to about 175 psi and most
3 preferably between about 130 psi to about 160 psi and thereby preclude
4 substantial leakage of the coker vessel contents including during operation
thereof at temperature ranges between about 900°F and 1000°F. In
6 embodiment (b) the spool preferably has a side aperture and flanged conduit
7 to which the hydrocarbon feed line is attached and sealed.
8
9 The present invention substantially reduces or eliminates the dangerous and
time consuming procedure of heading and unheeding delayed coker vessels,
11 thus rendering the decoking procedure safer for personnel to perForm by
12 insulating them from exposure to tons of hot, falling coke, high pressure
13 steam, scalding water, mobile heavy equipment and other extreme hazards.
14 Among other factors, the present invention is based on our conception and
finding that coke is safely and efficiently removed from a delayed coker
vessel
16 by the closed system process described herein, sometimes visualized by us
17 as a "closed-pipe" system, which includes side entry for the feed to the
vessel
18 and a pressure-tight seal between a closure housing for a vessel bottom
19 aperture. The vessel bottom aperture, which opens and closes, preferably
includes automatic and remote operation of a closure unit, such as a valve,
21 located at the bottom of the coker vessel rather than unbolting and
removing
22 or swinging away a "head" as in the prior art. One aspect of enabling the
23 process of the present invention is introducing the heated hydrocarbon feed
to
24 the coker vessel at a location above and lateral to the coker vessel bottom
and the closure unit, in combination with the above mentioned pressure-tight
26 seals.
27
28 A preferred embodiment of the present invention is additionally based on
our
29 finding that coke removal in the present process is advantageously carried
out
using a coke chute bolted and pressure-tightly sealed to the bottom of the
31 closure housing. The chute, which preferably remains attached without
32 removal throughout repetitive coking/decoking cycles, assists in directing
coke
33 removed from the coker vessel to a coke receiving area.
34
6
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1 According to a preferred embodiment, the invention further relates to a
2 method and apparatus for automatically opening and closing a vessel bottom
3 aperture by means of a closure unit or valve, in lieu of the removable or
4 partially removable head devices described in the prior art, and without the
associated safety and efficiency drawbacks discussed above. In a preferred
6 embodiment, which takes the place of the prior art removable closure
flanges,
7 spool pieces bolted to stationary vessel flanges, hinged flanges, carts,
8 carriages and the like, powered devices, which may be controlled
9 automatically, move closure a closure member within a closure housing
between open and closed positions. These powered devices may comprise
11 any powered actuators, including motors, solenoids, or the like, but
preferably
12 comprise linear actuators such as hydraulic or pneumatic cylinders with
13 reciprocating piston rods. Such actuators may be mounted on the vessel the
14 closure housing or other stationary location to reversibly and repetitively
move
the closure member from an open to closed position. Preferably the method
16 of the invention does not typically require direct human intervention in
17 proximity to the vessel bottom to actuate the powered devices, which is
18 preferably accomplished by remote instrumentation means such as an
19 electronic relay system or computer controlled system. The entire process
is,
thus, done safely and without significant or dangerous physical effort.
21
22 Although secondary to the significant safety improvements, the present
23 invention also speeds up the procedure so that the coking/decoking cycle
time
24 can be substantially reduced, without compromise in safety or human effort.
The invention also renders the addition of this new closure device onto the
26 hundreds of existing coker vessels to a relatively simple, quick, and
27 inexpensive procedure, as compared to the difficult, expensive, and time
28 consuming requirement of the existing methods and devices of the prior art
29 described above.
31 BRIEF DESCRIPTION OF THE DRAWINGS
32
33 Figure 1 is a schematic diagram of the delayed coking process of the
present
34 invention. Figure 2 is a side view of a typical coke vessel bottom known in
the
7
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1 prior art depicting the typical bottom entry feed, removable vessel bottom
2 head in one of the known arrangements and detachable coke chute
3 arrangement in one of the known arrangements. Figure 3 is a side view
4 depiction of a preferred embodiment of the present invention illustrating a
coker vessel designed and fabricated to be directly attached and sealed to the
6 closure housing and the side entry hydrocarbon feed line. Figure 4 is a side
7 view depiction of another embodiment of the invention, particularly useful
for
8 retrofitting existing coker vessels, showing a spool or flange interposed
9 between the coker vessel bottom and the closure housing. Figures 3 and 4
additionally depict a coke chute affixed and sealed to the closure housing
11 bottom. Figures 5 and 6 depict top and side views of the coke vessel
closure
12 unit with cut-a-way portions showing the movable closure member within the
13 closure housing.
14
DETAILED DESCRIPTION OF THE INVENTION
16
17 The invention relates to an improved method of repetitively coking heavy
18 hydrocarbons in a coker vessel and repetitively decoking the vessel in a
rapid,
19 safe and efficient manner by simply opening and closing a closure member,
such as a valve, within a closure unit, rather than removing or swinging away
21 a bottom head unit, as in the prior art. As generally depicted in Figure 1,
22 delayed coking is accomplished by charging hot, resid oil feed through a
feed
23 line 10 to the fractionator 15 above the bottom vapor zone 20. Lighter
24 hydrocarbon materials such as naphtha, gases, diesel and gas oils are taken
from upper portions of the fractionator vessel 15 by appropriately placed
26 conduits 25, 30, 35 and routed to other facilities for further refining.
27
28 Fresh feed and recycled feed from the bottom of the fractionator 15 are
29 pumped through a coker heater 40 where the combined feed is heated to a
temperature ranging between about 900°F to1000°F, preferably to
between
31 905°F to 950°F and most preferably to between 910°F
and 935°F, partially
32 vaporized and alternatively charged to one of a pair of coker vessels 45,
45a
33 via a feed line 50, 50a laterally attached to the coker vessel 45, 45a. Hot
34 vapors from the top of the coker vessels 45, 45a are recycled to the bottom
of
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1 the fractionator 15 via a feed line 55. In this manner, the hot vapors from
the
2 coke vessel are quenched by the cooler feed liquid, thus preventing any
3 significant amount of coke formation in the fractionator 15 and
simultaneously
4 condensing a portion of the heavy ends which are recycled to the coker
vessels 45, 45a. The unvaporized portion of the coker heater effluent settles
6 out (cokes) in the active coker vessel 45, 45a where the combined effect of
7 temperature and retention time results in coke formation. Coke formation in
8 the coker vessel 45, 45a is continued, typically between about 12 to about
30
9 hours, until the active vessel 45, 45a is full to within a safe margin from
the
vessel top.
11
12 Once the active coke vessel 45, 45a is full, the heated heavy hydrocarbon
13 feed is redirected to the empty coker vessel 45, 45a where the above
14 described process is repeated. Coke is then removed from the full vessel by
first quenching the hot coke with steam and water, then opening a closure unit
16 60 sealed to the vessel bottom, hydraulically drilling the coke from the
top
17 portion of the vessel and directing drilled coke from the vessel through
the
18 open closure unit into a coke chute 65 sealed to the bottom of the closure
unit
19 60 to a coke receiving area 62. Opening of the closure unit is safely
accomplished by a remotely located control unit 70.
21
22 Key features of the coking method and coker vessel of this invention
include
23 the side entry feed line 50a and 50b (see Figures 3 &4), the closure unit
60,
24 with a moveable closure member therein, pressure-tightly sealed to the
vessel
bottom 45, 45a and a coke chute 65 pressure-tightly sealed to the bottom of
26 the closure unit 60. The side entry feed line 50b can be attached to the
27 vessel side from about 6 inches to about 5 feet above the vessel bottom,
28 preferably from 1 foot to about four 4 feet from the vessel bottom and most
29 preferably from 1.5 feet to 2.5 feet from the vessel bottom.
31 Referring to Figures 3 and 4, said pressure-tight seals are accomplished in
32 one preferred embodiment (Figure 3) preferably by means of a gasket 90
33 interposed between facing flanged surfaces of the coke vessel bottom 75,
the
34 closure unit 75a and the coke chute 75b and the closure unit 75c. In
another
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1 preferred embodiment (Figure 4), a spool piece 80 is used to adapt coke
2 vessel bottom apertures and closure unit 60 apertures of different
diameters.
3 In this embodiment said pressure-tight seals are preferably accomplished
4 between facing flanged surfaces of the coke vessel bottom 75, the spool
piece 85, the closure housing 75a, the spool piece 85a and the coke chute
6 75b and the closure unit 75c. To form the pressure tight seals between said
7 flanged surfaces preferably the mating surfaces of the respective flanges
are
8 machined to a desired finish, then pressure-tightly joined together with a
9 plurality of suitable fasteners, such as bolts, clamps or similar means and
with
a carefully selected gasket 90 interposed between said mating surfaces.
11 Similarly, to form the pressure tight seals between the flanged surfaces of
the
12 closure housing bottom 75c and the coke chute 75b preferably the mating
13 surfaces of the respective flanges are machined to a desired finish, then
14 pressure-tightly joined together with a plurality of suitable fasteners,
such as
bolts, clamps or similar means and with a carefully selected gasket 90
16 interposed between said mating surfaces. The method for sealing the coke
17 chute 65 to the closure unit bottom may be different from the method for
18 sealing the vessel or spool to the closure unit top because operating
19 conditions are not a critical factor for seal integrity.
21 According to a more detailed embodiment, preferably, said flanged surfaces
22 are first machined to an RMS (root mean squared) finish ranging from 50 to
23 400, preferably 100 to 300 and most preferably between about 120 to 130.
24 An annular gasket comprised of a metal core, such as stainless steal, and a
flexible material suitable for use as a gasket in combination with metal under
26 temperatures ranging from -50°F to 1000°F and pressures
ranging from 100
27 psi to 200 psi is fitted to one of the flanged surfaces of each of the coke
28 vessel bottom 75, the spool piece 85, 85a and the closure housing 75a. With
29 the gasket interposed between each, the coke vessel bottom 45, and the
closure housing 60 (and in another embodiment the spool piece 80) are
31 pressure-tightly joined together by a plurality of suitable fasteners, such
as
32 bolts, clamps or similar means. The fastening means, such as bolts, clamps
33 or similar means are tightened or torqued such that the pressure placed on
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1 the gaskets 90 ranges between 10,000 PSI to 30,000 PSI, preferably between
2 15,000 and 25,000 PSI and most preferably 20,000 PSI. Preferably, said
3 torque pressure is applied evenly around the gasket circumference.
4
In a preferred embodiment of the present invention the metal gasket is
6 annular and stainless steel ranging in thickness from about .020 " to .140',
7 preferably about .024" to about .035" and most preferably from about .028"
to
8 about .032", and is concentrically corrugated. Said corrugations range in
9 height above the metal surface of the gasket from a minimum of about 0.001
inches to a maximum of about 0.050 inches, preferably from a minimum of
11 about 0.005 inches to a maximum of about 0.030 inches and most preferably
12 from a minimum of about 0.010 inches to a maximum of about 0.020 inches.
13 Once corrugated, the width of the gasket is such that the outside and
inside
14 diameters thereof are respectively coincident with the outside and inside
diameter of the flanged surfaces of the coke vessel bottom, the spool piece,
16 the closure unit and the coke chute. Flexible graphite material, such as
17 Polycarbon flexible graphite Grade B or BP (with antioxidant inhibitor) or
18 Union Carbide flexible graphite grade GTB or GTK (with antioxidant
inhibitor),
19 is bonded to the upper and lower surfaces of the gasket metal core such
that
the gasket is sandwiched between the layers of graphite material. Thickness
21 of the graphite material can range from about 0.005 inches to about 0.030
22 inches, preferably between 0.010 inches to about 0.025 inches and most
23 preferably is about 0.015 inches thick. Preferably the graphite covering
will
24 have the same nominal inside and outside diameter dimensions of the metal
gasket. Upon bonding to the gasket metal core surfaces, the corrugations
26 thereof should be covered by the graphite material. Sealing the flanged
27 surfaces of the coker vessel, the spool piece, the closure unit and,
optionally,
28 the coke chute in the manner described above results in a pressure-tight
seal
29 that tolerates the differential expansion that occurs between the flanges
during the repetitive coking/decoking cycles of the present invention.
31
32 Figures 3 and 4 depict preferred embodiments of the coker vessel. Figure 3
33 depicts the lower portion of a coker vessel 45 which can be 15 to 30 feet
in
34 diameter and 80 to 100 feet tall, which is typically cone or funnel shaped
on
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1 the lower end and which is attached to a lower flange 75 that is typically
60 to
2 72 inches in diameter. A closure unit 60 is pressure-tightly attached or
sealed
3 to the lower flange 75. The closure unit 60 has a flanged lower portion 75c,
4 which is pressure-tightly attached or sealed to a coke chute 65. The closure
unit 60 and coke chute 65 remain sealed in place during repetitive coking and
6 decoking cycles, but can be detached and laterally moved away from the
7 vessel 45 for maintenance via a gantry system, trolley system, rail mounted
8 cart or carriage or other similar system. The number of coking cycle
9 repetitions that can be carried out prior to breakdown of the system for
major
maintenance can vary from 10 to 150 cycles, preferably 20 to 100 cycles and,
11 most preferably, from 30 to 75 cycles per pair of vessels.
12
13 Figure 4 depicts another embodiment of the invention that is particularly
14 suitable for retrofitting existing coker vessels. As in the first
embodiment the
coke vessel 45 is typically cone or funnel shaped on the lower end which is
16 attached to a lower flange unit 75 that is typically 48 to 72 inches in
diameter,
17 preferably 60 to 72 inches in diameter. Interposed between the lower flange
18 75 and the closure housing 60 is a spool piece 80 having a flanged top 85
and
19 bottom 85a and a laterally attached flanged conduit 50b for attachment to
the
heavy hydrocarbon feed line 50a. The spool piece 80, in one embodiment,
21 can be of equal diameter on the top and bottom or, in another embodiment,
22 conical in shape to adapt the coker vessel opening diameter to the closure
23 unit opening diameter, for example a vessel opening of about 72 inches and
a
24 closure unit opening of about 60 inches in diameter.
26 Figures 5 and 6 respectively depict plan and side cut-away views of the
27 closure unit of a preferred embodiment of this invention. The closure unit
60
28 of this invention is a slide, gate, knife, ball, wedge plug or similar type
valve
29 comprising a closure housing 115 defining an interior void wherein a
closure
member 120 is mounted to an actuator or actuators 125, such as hydraulic
31 pistons 130 such that said closure member can be laterally moved to an open
32 or closed position. The closure housing further comprises a first end
section
33 135, a second end section 140 and a middle section 145 which middle section
34 defines an aperture 150 that can range in size from 48 to 72 inches in
12
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1 diameter. When moved laterally within the closure housing 115 the closure
2 member 120 opens and closes said aperture 150.
3
4 To begin the coking cycle described above the closure member 120 is moved
laterally to close the vessel bottom by operating the actuators 125, such as
6 hydraulic cylinders 130 that are, preferably, automatically and remotely
7 operable. When the closure member is moved into the fully closed position
8 the closure housing 115 is purged with nitrogen and/or steam via inlet
valves
9 155 mounted in the closure housing body 115. Coking then begins by the
process described above. During the coking phase of the coking cycle block
11 pressure steam is injected into the closure housing body at a rate
sufficient to
12 maintain pressure at a level to effectively eliminate hydrocarbon leaks at
the
13 closure member/closure housing seat 160. Blocking steam pressure and flow
14 rate are continuously monitored during the coking phase by use of pressure
and flow rate measuring devices 165 installed in the closure housing 115 and
16 connected to a remotely located control unit 70.
17
18 EXAMPLE
19
In a coking vessel used for delayed coking of heavy petroleum hydrocarbon
21 feed stocks, after about 24 hours of operation sufficient coke is
accumulated
22 in the vessel such that removal of the coke is required before coking
23 operations can continue in the vessel. At this point the heated heavy
24 hydrocarbon feed is redirected to an adjoining empty coke vessel. The full
1 coke vessel which is equipped with a lower spool transition piece, a closure
26 unit and attached coke chute operated in accordance with a preferred
27 embodiment of this invention, is shut down, quenched, depressurized and the
28 closure member within the closure housing unit is hydraulically moved
29 laterally to open the coke vessel bottom. Hydraulic movement of the closure
member is actuated by workers from a safe, remotely located control system.
31 Important characteristics of the coker vessel used in preferred embodiments
32 of the present invention that can be repetitively cycled through the coking
and
33 decoking process without removing the closure unit and coke chute, include:
34 A coker lower flange equal to 72 inches in diameter; a flanged spool
transition
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1 piece wherein the top flange of the spool piece is 72 inches in diameter and
2 the bottom flange is 60 inches in diameter; a hydrocarbon feed inlet line
3 installed laterally on the spool piece; a closure housing with a 60 inch
4 diameter opening therein; a closure member laterally moveable by hydraulic
means within the closure housing; a coke chute 60 inches in diameter
6 attached to the bottom opening of the closure housing; and a 60 inch stroke
7 closure member hydraulic actuator powered by a 3000 psi pump.
8
9 Referring again to the coking process steps, upon redirection of the
hydrocarbon feed from the full coker vessel to the empty coker vessel, 4000
11 pounds per hour of steam at 150 psi is injected into the full vessel via
the
12 laterally installed inlet line. The steam strips uncoked hydrocarbon from
the
13 vessel which is routed to the fractionator. After a period of time, usually
about
14 two hours, the vessel is isolated from the fractionator and depressurized
through a relief system. Stripping steam is thereafter continued for an
16 additional hour and thereafter quench water is added to the vessel at a
slow
17 rate to cool the coke bed to approximately 200°F. Upon cooling the
vessel to
18 the desired temperature the water is drained from the vessel via the inlet
line
19 or by, partially or fully, opening the closure member in the closure
housing to
drain water from the vessel into the coke receiving area.
21
22 Once the coke bed is cooled and the water drained, the vessel is prepared
for
23 drilling coke from the vessel with the hydraulic drill system. The closure
24 member within the closure housing is opened hydraulically by remote
actuation thereby allowing the drilled coke to fall into the coke chute which
is
26 attached to the bottom of the closure housing. As the coke is drilled it
falls out
27 of the vessel into the coke chute and is directed into the coke pit. Upon
28 completion of the drilling process the hydraulic drill stem is removed from
the
29 top of the vessel, the vessel top head is replaced and the inlet line and
coke
vessel are visually inspected for plugging. Once the inspection is complete
31 and the removal of coke and absence of plugging is verified, the closure
32 member within the closure housing is hydraulically closed. Then steam is
33 injected into the vessel to purge air and pressure the vessel to test the
34 integrity of the top head seals, inlet line seals, closure
housing/vessel/spool
14
CA 02473105 2004-07-08
WO 03/104353 PCT/US03/05987
1 seals, and the closure member seals within the closure housing. Finally, the
2 vessel is preheated to about 400°F to 600°F skin temperature.
When the
3 desired temperature is reached the resid hydrocarbon feed is switched into
4 this vessel and the adjoining vessel is prepared for decoking in accordance
with the above process.
6
7 Thus, according to a preferred embodiment of the present invention, a
8 delayed coking method and coke vessel have been provided which allow the
9 automatic, safe, quick, and effective opening and closure of coke vessels,
or
the like. While the invention has been herein shown and described in what is
11 presently conceived to be the most practical and preferred embodiment
12 thereof, many other modifications may be made within the scope of the
13 invention, which scope is to be accorded the broadest interpretation of the
14 appended claims so as to encompass all equivalent structures and methods.
For example, the structures of the invention may be reduced in size by a
16 factor of two, thus making it about 36 inches in nominal size, inverted,
and
17 applied in like form but smaller, to provide the highly desired automation
of the
18 flanged closure on the top of the vessel.
