U.S. patent application number 10/043527 was filed with the patent office on 2003-07-10 for safe and automatic method for removal of coke from a coke vessel.
Invention is credited to Bell, Robert V., Blevins, Harry J., Klasnich, Steven, Reeves, David, Riddle, Jeff N..
Application Number | 20030127314 10/043527 |
Document ID | / |
Family ID | 21927605 |
Filed Date | 2003-07-10 |
United States Patent
Application |
20030127314 |
Kind Code |
A1 |
Bell, Robert V. ; et
al. |
July 10, 2003 |
Safe and automatic method for removal of coke from a coke
vessel
Abstract
A closed system that eliminates worker exposure during coker
vessel decoking operations and thereby significantly reduces risks
to workers also increase coking capacity by reducing the coking
cycle time. The closed system preferably comprises a coker vessel
with a side entry feed line attached to the vessel above the vessel
bottom; a closure housing with laterally moveable closure member
therein sealed to the vessel bottom either directly without, or
indirectly with an adapting spool member and; a coke chute sealed
to the bottom of the closure housing. The system can be remotely
and repetitively operated through numerous coking/decoking cycles
without removal of any system element.
Inventors: |
Bell, Robert V.; (Mobile,
AL) ; Blevins, Harry J.; (Pascagoula, MS) ;
Klasnich, Steven; (Martinez, CA) ; Reeves, David;
(Orinda, CA) ; Riddle, Jeff N.; (Woods Cross,
UT) |
Correspondence
Address: |
Steven R. Ellinwood
Chevron Corporation
P. O. Box 6006
San Ramon
CA
94583-0806
US
|
Family ID: |
21927605 |
Appl. No.: |
10/043527 |
Filed: |
January 10, 2002 |
Current U.S.
Class: |
202/262 ;
202/242; 202/244; 202/245 |
Current CPC
Class: |
C10B 1/04 20130101; C10B
25/10 20130101; C10B 55/00 20130101 |
Class at
Publication: |
202/262 ;
202/242; 202/244; 202/245 |
International
Class: |
C10B 025/00; C10B
025/08; C10B 025/16 |
Claims
What is claimed is:
1. A process for repetitively producing and removing coke from a
delayed coker vessel, wherein the coker vessel has a bottom portion
defining an aperture through which coke is released, comprising:
(a) Sealing an aperture closure housing to the bottom portion of
the coker vessel; (b) moving 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 to the coker
vessel at a position above the bottom of the coker vessel; (d)
coking the heavy hydrocarbon in the coker vessel; (e) moving the
closure member within the closure housing to open the aperture to
allow coke removal from the coker vessel; and (f) releasing coke
through the aperture, and; (g) repeating steps c through f
successively.
2. The process in of claim 1 wherein step (c) further comprises
attaching the feed line to the coker vessel at a side entry
position.
3. The process in of claim 1 wherein step (a) further comprises
sealing a transition spool piece to the coker vessel bottom and
attaching the feed line to the spool piece at a side entry
position.
4. The process of claim 1 wherein step (a) further comprises
forming a seal between the aperture closure housing and the bottom
portion of the vessel wherein the seal withstands pressures within
the vessel from atmospheric to 500 psi.
5. The process of claim 4 wherein step (a) further comprises
forming a seal between the aperture closure housing and the bottom
portion of the vessel wherein the seal withstands vessel
temperatures through repetitive coking/decoking cycles ranging from
-50.degree. F. to 1000.degree. F.
6. The process of claim 1 wherein step (a) further comprises
sealing a coke chute to a bottom portion of the aperture closure
housing.
7. The process of claim 1 wherein step (a) further comprises
placing a gasket between the bottom portion of the vessel and
closure unit and pressure-tightly joining the vessel bottom, the
gasket and the closure unit.
8. The process of claim 2 wherein step (a) further comprises
placing a gasket between the bottom of the closure unit and the
coke chute and pressure-tightly joining the closure unit, the
gasket and the coke chute.
9. The process of claim 7 or 8 wherein the gasket comprises an
annular corrugated metal bonded to a graphite material.
10. A process in accordance with claim 6 wherein the process
further comprises using the chute to assist in directing coke
removed from the coker vessel into a coke receiving area.
11. A process in accordance with claim 1 wherein steps (b) and (e)
further comprise moving the closure member by a powered actuator or
a plurality of powered actuators.
12. The process of claim 11 wherein said powered actuators are
remotely actuated.
13. A process in accordance with claim 1 wherein the coking step
(d) is carried out at a temperature between 900.degree. F. and
1100.degree. F., the opening step (e) is done at a temperature
between '50.degree. F. and 110.degree. F., and the valve is
selected to withstand repeated operation at temperature cycling
between step (d) and step (e).
14. A process in accordance with claim 1 wherein the closure member
of steps (b) and (e) is a valve.
15. A process in accordance with claim 14 wherein the valve is
selected from a gate valve, a ball valve, a slide valve, a knife
valve or a wedge plug valve.
16. A process in accordance with claim 1 wherein the aperture opens
to a diameter between 30 and 90 inches.
17. A process in accordance with claim 1 wherein the closure
housing and closure member are mounted to a weight bearing
structure selected from the group consisting of a gantry system and
a trolley system.
18. The process of claim 17 wherein the closure unit is laterally
removable from the coker vessel by means of said weight bearing
structure.
19. A coker vessel comprising: (a) a vessel having a flanged side
aperture and a flanged bottom aperture; (b) a flanged feed pipe
fitted to said flanged side aperture; (c) an aperture closure unit
fitted and sealed to said bottom aperture; (d) a closure member
moveable within said closure unit; (e) A coke chute sealed to the
bottom portion of the closure unit for directing coke from the
vessel to a receiving area.
20. The coker vessel of claim 19 wherein the closure member
comprises a valve.
21. The coker vessel of claim 20 wherein the valve is a gate valve,
a ball valve, a slide valve, a knife valve or a wedge plug
valve.
22. The coker vessel of claim 20 wherein the valve further
comprises a power actuated valve.
23. The coker vessel of claim 20 wherein the bottom aperture is
from 30 to 90 inches.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to the field of hydrocarbon
processing and, in particular, to heavy hydrocarbon processing in
coke vessels.
BACKGROUND OF THE INVENTION
[0002] Many oil refineries recover valuable products from the heavy
residual hydrocarbons (commonly referred to as resid or residuum),
which remain following initial refining, by a thermal cracking
process known as delayed coking. Generally, the delayed coking
process involves heating the heavy hydrocarbon feed from a
fractionation unit, then pumping the heated heavy feed into a large
steel vessel commonly known as a coke drum. The unvaporized portion
of the heated heavy feed settles out in the coke vessel where the
combined effect of retention time and temperature causes the
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 fractionation unit for further processing into
desired light hydrocarbon products. The operating conditions of
delayed coking can be quite severe. Normal operating pressures in
coke vessels typically range from 25 to about 50 pounds per square
inch and the heavy feed input temperature may vary between
900.degree. F. and 950.degree. F. The coke drums operate in pairs,
with one drum feeding residuum and the other drum undergoing the
"decoking" sequential steps. The drums typically operate on a
cycle, switching every 12-30 hours.
[0003] 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 bottom portion fitted with a
bottom head and are usually present in pairs so that they can be
operated alternately. Coke settles out and accumulates in the
vessel until it is filled to a safe margin, at which time the
heated feed is switched to the empty "sister" coke vessel. Thus,
while one coke vessel is being filled with heated residual oil, the
other vessel is being cooled and purged of hundreds to thousands of
tons of coke formed in the vessel during the previous recovery
cycle. The full vessel is isolated, steamed to remove hydrocarbon
vapors, cooled by filling with water, drained, opened, and the coke
is removed.
[0004] Coke removal, also known as decoking, begins with a quench
step in which 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 vessel is then
vented to atmospheric pressure. Decoking is accomplished at most
plants using a hydraulic system consisting of a drill stem and
drill bit that direct high pressure water jets into the coke bed.
To cut coke in this manner 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 diameter with four (4)
nozzels and is mounted on the lower end of a long hollow drill rod
about 6 inches in diameter. The drill bit is lowered into the
vessel, on the drill stem, through a flanged opening at the top of
the vessel. A "bore hole" is drilled through the coke using the
four nozzles angled approximately 60 degrees down from horizontal.
This creates a hole from about 3 to 6 feet in diameter for the coke
to fall through. There is normally a naturally occurring small hole
in the coke bed for the initial pass because the resid flows in
from the bottom and out toward the edges of the vessel.
[0005] When the initial bore hole is complete, the drill bit is
then mechanically switched to two (2) horizontal nozzles in
preparation for cutting the "blow" hole, which extends to the full
drum diameter. The nozzles shoot jets of water horizontally
outwards, rotating slowly with the drill rod, and those jets cut
the 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 raised slowly up from the bottom the
entire vertical height of the coke mass, at others the drill is
lowered from the top through the mass and at still other plants the
coke mass is first cut from the bottom cone of the vessel and the
remainder is cut from the top of the vessel. In any case, the cut
coke falls out the opening at the bottom of the vessel into the
coke chute system. The drill rod is then withdrawn out the flanged
opening at the top of the vessel. Finally, the top and bottom of
the vessel are closed by replacing the head units, 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 feed.
[0006] The process of removing and replacing the removable top head
and bottom units of the vessel cover is called heading and
unheading or deheading. It is dangerous work, with several risks
associated with the procedures. There have been fatalities and many
serious injuries. There is significant safety risk from exposure to
steam, hot water, fires and repetitive stress associated with the
manual unbolting work. Accordingly, the industry has devoted
substantial time and investment in developing semi-automatic or
fully automatic unheading systems, with attention focused on bottom
unheading where the greatest safety hazard is present.
[0007] There are two typical and commonly used methods to move the
bottom head 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 process may be automated as
set forth in U.S. Pat. No. 5,336,375. The other way of "removing"
the bottom head is to swing it out of the way, as on a hinge or
pivot, while the head is still coupled to the vessel as in U.S.
Pat. No. 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 including: U.S. Pat. No. 6,264,829
(discloses a swing away hydraulically operated drumhead adapted for
low headroom situations); U.S. Pat. No. 6,254,733 (depicting in the
drawings a hydraulically removable drumhead); U.S. Pat. Nos.
6,066,237 and 5,876,568 (disclosing an apparatus for
semi-automatically clamping and unclamping a drum bottom head);
U.S. Pat. No. 5,947,674 (a drum head device removed by vertically
oriented hydraulic cylinders adapted for lowering the head unit and
moving it laterally aside); U.S. Pat. No. 5,785,843 (claims a
process involving a swing away hydraulically operated drumhead
adapted for low headroom situations); U.S. Pat. No. 5,581,864 (a
remotely operated carriage mounted drumhead removal system); U.S.
Pat. No. 5,500,094 (car mounted drumhead removal system that is
horizontally movable); U.S. Pat. No. 5,228,825 (a device and method
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 system); U.S. Pat. No. 5,098,524 (a pivotally
attached unheading device associated with clamps); U.S. Pat. No.
4,726,109 (a platform device lowers the drumhead and moves it
laterally away). These systems all use a manual or semi-automatic
bolting system that must be uncoupled with every decoking
cycle.
[0008] The above described bottom head removal systems all require
that the heated feed enter the coke vessel from the bottom through
the center of the bottom 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 vessels built and put
into operation in the last 20 to 30 or more years. Thus, in the
usual coker operation, to remove the vessel bottom head for
decoking the feed line must first be disconnected before the bottom
head can be 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 the drum, allowing the
chute to receive the falling coke. The chute directs the coke, as
it is drilled out of the vessel, to a receiving area where it is
later removed. These methods still require the feed line to be
opened up and the head removed before the bottom chute can be
brought up and attached to the bottom flange of the vessel.
[0009] Considering that there is exposure to personnel and/or
equipment when opening the feed line, and considering there is
exposure to personnel and/or 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 water between the
chute and bottom head after the chute is up, improvements in coke
vessel bottom unheading system to allow safe removal of coke from
the vessel is highly desirable. The object of the present invention
is to address this need.
SUMMARY OF THE INVENTION
[0010] According to the present invention, a process and apparatus
are provided for repetitively producing and removing coke from a
delayed coker vessel without unheading the vessel bottom, wherein
the coker vessel has a bottom portion having an aperture through
which coke is released, comprising: (a) sealing an aperture closure
housing to the bottom portion of the coker vessel; (b) moving 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 to the coker vessel at a position above the
bottom of the coker vessel; (d) coking the heavy hydrocarbon in the
coker vessel; (e) moving the closure member within the closure
housing to open the aperture to allow coke 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
embodiment of the invention the closure member is power actuated,
such as hydraulically, by remote means, thus obviating any need for
personnel to be physically present in the vessel bottom area during
decoking operations.
[0011] The delayed coker vessel of the present invention comprises
a vessel having a top opening and on the lower portion a side
aperture and a bottom aperture; a feed pipe fitted to said side
aperture; a bottom aperture closure housing sealed to the bottom
aperture; a closure member moveable within said 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
combination of the closure housing and moveable closure member
therein is herein termed a closure unit or valve. In one embodiment
of the invention the bottom portion of the coker vessel is designed
and fabricated to be directly sealed to the closure unit, whereas
in another embodiment, particularly useful for retrofitting
existing coker vessels, a bottom transition piece, herein termed a
spool, is interposed between the vessel bottom and the closure unit
and pressure-tightly sealed to both. In either of these two
embodiments, a preferred feature is that the closure housing is
pressure-tightly sealed to either (a) the coker vessel or (b) the
spool piece. Preferably the pressure-tight seals will withstand
pressures within the range of about 100 psi to 200 psi, preferably
within the range of about 125 psi to about 175 psi and most
preferably between about 130 psi to about 160 psi and thereby
preclude substantial leakage of the coker vessel contents including
during operation thereof at temperature ranges between about
900.degree. F. and 1000.degree. F. In embodiment (b) the spool
preferably has a side aperture and flanged conduit to which the
hydrocarbon feed line is attached and sealed.
[0012] The present invention substantially reduces or eliminates
the dangerous and time consuming procedure of heading and unheading
delayed coker vessels, thus rendering the decoking procedure safer
for personnel to perform by insulating them from exposure to tons
of hot, falling coke, high pressure steam, scalding water, mobile
heavy equipment and other extreme hazards. 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 by
the closed system process described herein, sometimes visualized by
us as a "closed-pipe" system, which includes side entry for the
feed to the vessel and a pressure-tight seal between a closure
housing for a vessel bottom aperture. The vessel bottom aperture,
which opens and closes, preferably includes automatic and remote
operation of a closure unit, such as a valve, located at the bottom
of the coker vessel rather than unbolting and removing or swinging
away a "head" as in the prior art. One aspect of enabling the
process of the present invention is introducing the heated
hydrocarbon feed to 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 seals.
[0013] A preferred embodiment of the present invention is
additionally based on our 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 closure housing. The
chute, which preferably remains attached without removal throughout
repetitive coking/decoking cycles, assists in directing coke
removed from the coker vessel to a coke receiving area.
[0014] According to a preferred embodiment, the invention further
relates to a method and apparatus for automatically opening and
closing a vessel bottom aperture by means of a closure unit or
valve, in lieu of the removable or partially removable head devices
described in the prior art, and without the associated safety and
efficiency drawbacks discussed above. In a preferred embodiment,
which takes the place of the prior art removable closure flanges,
spool pieces bolted to stationary vessel flanges, hinged flanges,
carts, carriages and the like, powered devices, which may be
controlled automatically, move closure a closure member within a
closure housing between open and closed positions. These powered
devices may comprise any powered actuators, including motors,
solenoids, or the like, but preferably comprise linear actuators
such as hydraulic or pneumatic cylinders with reciprocating piston
rods. Such actuators may be mounted on the vessel the closure
housing or other stationary location to reversibly and repetitively
move the closure member from an open to closed position. Preferably
the method of the invention does not typically require direct human
intervention in proximity to the vessel bottom to actuate the
powered devices, which is preferably accomplished by remote
instrumentation means such as an electronic relay system or
computer controlled system. The entire process is, thus, done
safely and without significant or dangerous physical effort.
[0015] Although secondary to the significant safety improvements,
the present invention also speeds up the procedure so that the
coking/decoking cycle time can be substantially reduced, without
compromise in safety or human effort. The invention also renders
the addition of this new closure device onto the hundreds of
existing coker vessels to a relatively simple, quick, and
inexpensive procedure, as compared to the difficult, expensive, and
time consuming requirement of the existing methods and devices of
the prior art described above.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a schematic diagram of the delayed coking process
of the present invention. FIG. 2 is a side view of a typical coke
vessel bottom known in the prior art depicting the typical bottom
entry feed, removable vessel bottom head in one of the known
arrangements and detachable coke chute arrangement in one of the
known arrangements. FIG. 3 is a side view depiction of a preferred
embodiment of the present invention illustrating a coker vessel
designed and fabricated to be directly attached and sealed to the
closure housing and the side entry hydrocarbon feed line. FIG. 4 is
a side view depiction of another embodiment of the invention,
particularly useful for retrofitting existing coker vessels,
showing a spool or flange interposed between the coker vessel
bottom and the closure housing. FIGS. 3 and 4 additionally depict a
coke chute affixed and sealed to the closure housing bottom. FIGS.
5 and 6 depict top and side views of the coke vessel closure unit
with cut-a-way portions showing the movable closure member within
the closure housing.
DETAILED DESCRIPTION OF THE INVENTION
[0017] The invention relates to an improved method of repetitively
coking heavy hydrocarbons in a coker vessel and repetitively
decoking the vessel in a rapid, 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 a bottom head
unit, as in the prior art. As generally depicted in FIG. 1, delayed
coking is accomplished by charging hot, resid oil feed through a
feed line 10 to the fractionator 15 above the bottom vapor zone 20.
Lighter hydrocarbon materials such as naphtha, gases, diesel and
gas oils are taken from upper portions of the fractionator vessel
15 by appropriately placed conduits 25, 30, 35 and routed to other
facilities for further refining.
[0018] Fresh feed and recycled feed from the bottom of the
fractionator 15 are pumped through a coker heater 40 where the
combined feed is heated to a temperature ranging between about
900.degree. F. to 1000.degree. F., preferably to between
905.degree. F. to 950.degree. F. and most preferably to between
910.degree. F. and 935.degree. F., partially vaporized and
alternatively charged to one of a pair of coker vessels 45, 45a via
a feed line 50, 50a laterally attached to the coker vessel 45, 45a.
Hot vapors from the top of the coker vessels 45, 45a are recycled
to the bottom of the fractionator 15 via a feed line 55. In this
manner, the hot vapors from the coke vessel are quenched by the
cooler feed liquid, thus preventing any significant amount of coke
formation in the fractionator 15 and simultaneously 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 out (cokes) in the active coker vessel 45, 45a where the
combined effect of temperature and retention time results in coke
formation. Coke formation in the coker vessel 45, 45a is continued,
typically between about 12 to about 30 hours, until the active
vessel 45, 45a is full to within a safe margin from the vessel
top.
[0019] Once the active coke vessel 45, 45a is full, the heated
heavy hydrocarbon feed is redirected to the empty coker vessel 45,
45a where the above 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 60 sealed to the
vessel bottom, hydraulically drilling the coke from the top portion
of the vessel and directing drilled coke from the vessel through
the open closure unit into a coke chute 65 sealed to the bottom of
the closure unit 60 to a coke receiving area 62. Opening of the
closure unit is safely accomplished by a remotely located control
unit 70.
[0020] Key features of the coking method and coker vessel of this
invention include the side entry feed line 50a and 50b (see FIGS. 3
& 4), the closure unit 60, 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 the closure
unit 60. The side entry feed line 50b can be attached to the vessel
side from about 6 inches to about 5 feet above the vessel bottom,
preferably from 1 foot to about four 4 feet from the vessel bottom
and most preferably from 1.5 feet to 2.5 feet from the vessel
bottom.
[0021] Referring to FIGS. 3 and 4, said pressure-tight seals are
accomplished in one preferred embodiment (FIG. 3) preferably by
means of a gasket 90 interposed between facing flanged surfaces of
the coke vessel bottom 75, the closure unit 75a and the coke chute
75b and the closure unit 75c. In another preferred embodiment (FIG.
4), a spool piece 80 is used to adapt coke vessel bottom apertures
and closure unit 60 apertures of different diameters. In this
embodiment said pressure-tight seals are preferably accomplished
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 75b and the closure unit 75c. To form the pressure
tight seals between said flanged surfaces preferably the mating
surfaces of the respective flanges are machined to a desired
finish, then pressure-tightly joined together with a plurality of
suitable fasteners, such as bolts, clamps or similar means and with
a carefully selected gasket 90 interposed between said mating
surfaces. Similarly, to form the pressure tight seals between the
flanged surfaces of the closure housing bottom 75c and the coke
chute 75b preferably the mating surfaces of the respective flanges
are machined to a desired finish, then pressure-tightly joined
together with a plurality of suitable fasteners, such as bolts,
clamps or similar means and with a carefully selected gasket 90
interposed between said mating surfaces. The method for sealing the
coke chute 65 to the closure unit bottom may be different from the
method for sealing the vessel or spool to the closure unit top
because operating conditions are not a critical factor for seal
integrity.
[0022] According to a more detailed embodiment, preferably, said
flanged surfaces are first machined to an RMS (root mean squared)
finish ranging from 50 to 400, preferably 100 to 300 and most
preferably between about 120 to 130. 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
temperatures ranging from -50.degree. F. to 1000.degree. F. and
pressures ranging from 100 psi to 200 psi is fitted to one of the
flanged surfaces of each of the coke vessel bottom 75, the spool
piece 85, 85a and the closure housing 75a. With the gasket
interposed between each, the coke vessel bottom 45, and the closure
housing 60 (and in another embodiment the spool piece 80) are
pressure-tightly joined together by a plurality of suitable
fasteners, such as bolts, clamps or similar means. The fastening
means, such as bolts, clamps or similar means are tightened or
torqued such that the pressure placed on the gaskets 90 ranges
between 10,000 PSI to 30,000 PSI, preferably between 15,000 and
25,000 PSI and most preferably 20,000 PSI. Preferably, said torque
pressure is applied evenly around the gasket circumference.
[0023] In a preferred embodiment of the present invention the metal
gasket is annular and stainless steel ranging in thickness from
about 0.020" to 0.140', preferably about 0.024" to about 0.035" and
most preferably from about 0.028" to about 0.032", and is
concentrically corrugated. Said corrugations range in 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 about 0.005 inches to a maximum of about 0.030 inches
and most preferably from a minimum of about 0.010 inches to a
maximum of about 0.020 inches. Once corrugated, the width of the
gasket is such that the outside and inside diameters thereof are
respectively coincident with the outside and inside diameter of the
flanged surfaces of the coke vessel bottom, the spool piece, the
closure unit and the coke chute. Flexible graphite material, such
as Polycarbon flexible graphite Grade B or BP (with antioxidant
inhibitor) or Union Carbide flexible graphite grade GTB or GTK
(with antioxidant inhibitor), 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 of
the graphite material can range from about 0.005 inches to about
0.030 inches, preferably between 0.010 inches to about 0.025 inches
and most preferably is about 0.015 inches thick. Preferably the
graphite covering will have the same nominal inside and outside
diameter dimensions of the metal gasket. Upon bonding to the gasket
metal core surfaces, the corrugations thereof should be covered by
the graphite material. Sealing the flanged surfaces of the coker
vessel, the spool piece, the closure unit and, optionally, the coke
chute in the manner described above results in a pressure-tight
seal that tolerates the differential expansion that occurs between
the flanges during the repetitive coking/decoking cycles of the
present invention.
[0024] FIGS. 3 and 4 depict preferred embodiments of the coker
vessel. FIG. 3 depicts the lower portion of a coker vessel 45 which
can be 15 to 30 feet in diameter and 80 to 100 feet tall, which is
typically cone or funnel shaped on the lower end and which is
attached to a lower flange 75 that is typically 60 to 72 inches in
diameter. A closure unit 60 is pressure-tightly attached or sealed
to the lower flange 75. The closure unit 60 has a flanged lower
portion 75c, 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 decoking cycles, but can be
detached and laterally moved away from the vessel 45 for
maintenance via a gantry system, trolley system, rail mounted cart
or carriage or other similar system. The number of coking cycle
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, most preferably, from 30 to 75
cycles per pair of vessels.
[0025] FIG. 4 depicts another embodiment of the invention that is
particularly 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 attached to a lower flange
unit 75 that is typically 48 to 72 inches in diameter, preferably
60 to 72 inches in diameter. Interposed between the lower flange 75
and the closure housing 60 is a spool piece 80 having a flanged top
85 and 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, can be of equal diameter on the top and
bottom or, in another embodiment, conical in shape to adapt the
coker vessel opening diameter to the closure unit opening diameter,
for example a vessel opening of about 72 inches and a closure unit
opening of about 60 inches in diameter.
[0026] FIGS. 5 and 6 respectively depict plan and side cut-away
views of the closure unit of a preferred embodiment of this
invention. The closure unit 60 of this invention is a slide, gate,
knife, ball, wedge plug or similar type valve 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
pistons 130 such that said closure member can be laterally moved to
an open or closed position. The closure housing further comprises a
first end section 135, a second end section 140 and a middle
section 145 which middle section defines an aperture 150 that can
range in size from 48 to 72 inches in diameter. When moved
laterally within the closure housing 115 the closure member 120
opens and closes said aperture 150.
[0027] 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 hydraulic cylinders 130 that are,
preferably, automatically and remotely operable. When the closure
member is moved into the fully closed position the closure housing
115 is purged with nitrogen and/or steam via inlet valves 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 pressure steam is injected into the closure housing
body at a rate sufficient to maintain pressure at a level to
effectively eliminate hydrocarbon leaks at the closure
member/closure housing seat 160. Blocking steam pressure and flow
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 connected to a remotely located control
unit 70.
EXAMPLE
[0028] In a coking vessel used for delayed coking of heavy
petroleum hydrocarbon feed stocks, after about 24 hours of
operation sufficient coke is accumulated in the vessel such that
removal of the coke is required before coking operations can
continue in the vessel. At this point the heated heavy hydrocarbon
feed is redirected to an adjoining empty coke vessel. The full coke
vessel which is equipped with a lower spool transition piece, a
closure unit and attached coke chute operated in accordance with a
preferred embodiment of this invention, is shut down, quenched,
depressurized and the closure member within the closure housing
unit is hydraulically moved laterally to open the coke vessel
bottom. Hydraulic movement of the closure member is actuated by
workers from a safe, remotely located control system. Important
characteristics of the coker vessel used in preferred embodiments
of the present invention that can be repetitively cycled through
the coking and decoking process without removing the closure unit
and coke chute, include: A coker lower flange equal to 72 inches in
diameter; a flanged spool transition piece wherein the top flange
of the spool piece is 72 inches in diameter and the bottom flange
is 60 inches in diameter; a hydrocarbon feed inlet line installed
laterally on the spool piece; a closure housing with a 60 inch
diameter opening therein; a closure member laterally moveable by
hydraulic means within the closure housing; a coke chute 60 inches
in diameter attached to the bottom opening of the closure housing;
and a 60 inch stroke closure member hydraulic actuator powered by a
3000 psi pump.
[0029] Referring again to the coking process steps, upon
redirection of the hydrocarbon feed from the full coker vessel to
the empty coker vessel, 4000 pounds per hour of steam at 150 psi is
injected into the full vessel via the laterally installed inlet
line. The steam strips uncoked hydrocarbon from the vessel which is
routed to the fractionator. After a period of time, usually about
two hours, the vessel is isolated from the fractionator and
depressurized through a relief system. Stripping steam is
thereafter continued for an additional hour and thereafter quench
water is added to the vessel at a slow rate to cool the coke bed to
approximately 200.degree. F. Upon cooling the vessel to the desired
temperature the water is drained from the vessel via the inlet line
or by, partially or fully, opening the closure member in the
closure housing to drain water from the vessel into the coke
receiving area.
[0030] Once the coke bed is cooled and the water drained, the
vessel is prepared for drilling coke from the vessel with the
hydraulic drill system. The closure member within the closure
housing is opened hydraulically by remote actuation thereby
allowing the drilled coke to fall into the coke chute which is
attached to the bottom of the closure housing. As the coke is
drilled it falls out of the vessel into the coke chute and is
directed into the coke pit. Upon completion of the drilling process
the hydraulic drill stem is removed from the 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
and the removal of coke and absence of plugging is verified, the
closure member within the closure housing is hydraulically closed.
Then steam is injected into the vessel to purge air and pressure
the vessel to test the integrity of the top head seals, inlet line
seals, closure housing/vessel/spool seals, and the closure member
seals within the closure housing. Finally, the vessel is preheated
to about 400.degree. F. to 600.degree. F. skin temperature. When
the desired temperature is reached the resid hydrocarbon feed is
switched into this vessel and the adjoining vessel is prepared for
decoking in accordance with the above process.
[0031] Thus, according to a preferred embodiment of the present
invention, a delayed coking method and coke vessel have been
provided which allow the 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 presently
conceived to be the most practical and preferred embodiment
thereof, many other modifications may be made within the scope of
the invention, which scope is to be accorded the broadest
interpretation of the 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 factor of two, thus
making it about 36 inches in nominal size, inverted, and applied in
like form but smaller, to provide the highly desired automation of
the flanged closure on the top of the vessel.
* * * * *