U.S. patent application number 14/945771 was filed with the patent office on 2017-05-25 for coke drum with air injection system for skirt junction.
This patent application is currently assigned to INTEVEP, S.A.. The applicant listed for this patent is Intevep, S.A.. Invention is credited to Egler Dubin Araque Vivas, Maria Isabel Specht, Gabriel Arcangel Vivas Chacon.
Application Number | 20170145319 14/945771 |
Document ID | / |
Family ID | 58720060 |
Filed Date | 2017-05-25 |
United States Patent
Application |
20170145319 |
Kind Code |
A1 |
Vivas Chacon; Gabriel Arcangel ;
et al. |
May 25, 2017 |
COKE DRUM WITH AIR INJECTION SYSTEM FOR SKIRT JUNCTION
Abstract
A coke drum includes a coke drum vessel having a substantially
cylindrical wall and a conical bottom portion; a skirt downwardly
depending from a transition of the cylindrical wall into the
conical bottom portion, an inner annular space being defined
between the skirt and the conical bottom portion; and a fluid
injection system communicated with the inner annular space for
injecting fluid at a desired temperature to heat or cool the inner
annular space. The fluid injection system allows the inner annular
space and junction of the skirt with the coke drum vessel to be
heated or cooled to minimize temperature difference between these
areas and a batch of coke to be introduced into the drum.
Inventors: |
Vivas Chacon; Gabriel Arcangel;
(Los Teques Estado. Miranda, VE) ; Specht; Maria
Isabel; (San Antonio de Los Altos, VE) ; Araque
Vivas; Egler Dubin; (Toronto, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Intevep, S.A. |
Caracas |
|
VE |
|
|
Assignee: |
INTEVEP, S.A.
Caracas
VE
|
Family ID: |
58720060 |
Appl. No.: |
14/945771 |
Filed: |
November 19, 2015 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C10B 55/00 20130101;
C10G 9/005 20130101; C10B 1/04 20130101 |
International
Class: |
C10G 9/00 20060101
C10G009/00; C10B 3/02 20060101 C10B003/02; C10B 55/00 20060101
C10B055/00 |
Claims
1. A coke drum, comprising: a coke drum vessel comprising a
substantially cylindrical wall and a conical bottom portion; a
skirt downwardly depending from a transition of the cylindrical
wall into the conical bottom portion, an inner annular space being
defined between the skirt and the conical bottom portion; and a
fluid injection system communicated with the inner annular space
for injecting fluid at a desired temperature to heat or cool the
inner annular space.
2. The coke drum of claim 1, wherein the fluid injection system
comprises a toroid tube in the inner annular space and communicated
with a source of the fluid.
3. The coke drum of claim 1, wherein the fluid injection system has
a fluid inlet and a fluid outlet, and at least one baffle in the
inner annular space between the fluid inlet and the fluid
outlet.
4. The coke drum of claim 1, further comprising a bottom wall
section connected between the skirt and the conical bottom portion
and closing off the inner annular space.
5. The coke drum of claim 1, wherein the fluid injection system
comprises a first toroid tube defining a fluid inlet, a second
toroid tube defining a fluid outlet, and a series of baffles in the
inner annular space between the first toroid tube and the second
toroid tube.
6. The coke drum of claim 5, wherein the series of baffles direct
flow of fluid along the skirt and conical surfaces of the drum.
7. The coke drum of claim 1, wherein the fluid injection system
injects fluid around an entire circumference of the inner annular
space.
8. A process for protecting a coke drum from thermal stresses,
comprising the steps of: determining coke temperature of coke to be
introduced to a coke drum, wherein the coke drum comprises: a coke
drum vessel comprising a substantially cylindrical wall and a
conical bottom portion; a skirt downwardly depending from a
transition of the cylindrical wall into the conical bottom portion,
an inner annular space being defined between the skirt and the
conical bottom portion; and a fluid injection system communicated
with the inner annular space for injecting fluid at a desired
temperature to heat or cool the inner annular space; and
introducing fluid at a temperature substantially similar to the
coke temperature through the fluid injection system and into the
inner annular space, whereby temperature of the inner annular space
and a junction of the skirt with the coke drum vessel is adjusted
to be substantially similar to the coke temperature.
9. The process of claim 8, wherein the fluid injection system
comprises a toroid tube in the inner annular space and communicated
with a source of the fluid.
10. The process of claim 8, wherein the fluid injection system has
a fluid inlet and a fluid outlet, and at least one baffle in the
inner annular space between the fluid inlet and the fluid
outlet.
11. The process of claim 8, further comprising a bottom wall
section connected between the skirt and the conical bottom portion
and closing off the inner annular space.
12. The process of claim 8, wherein the fluid injection system
comprises a first toroid tube defining a fluid inlet, a second
toroid tube defining a fluid outlet, and a series of baffles in the
inner annular space between the first toroid tube and the second
toroid tube.
13. The process of claim 12, wherein the series of baffles direct
flow of fluid along the skirt and conical surfaces of the drum.
14. The process of claim 8, wherein the fluid injection system
injects fluid around an entire circumference of the inner annular
space.
15. A method for adapting an existing coke drum, comprising the
steps of: providing an existing coke drum having a substantially
cylindrical wall transitioning to a conical bottom portion, and
having a skirt downwardly depending from a transition from the
substantially cylindrical wall to the conical bottom portion; and
positioning a fluid injection system relative to an inner annular
space defined between the skirt and conical bottom portion whereby
temperature of a junction of the skirt and the coke drum can be
adjusted by introducing fluid at a desired temperature through the
fluid injection system and into the inner annular space.
Description
BACKGROUND OF THE INVENTION
[0001] The invention relates to coke drums and more particularly to
reducing stresses in the coke drum during heating and cooling of
the coke drum.
[0002] Coke drums and delayed coke drums are vertical thin-walled
pressure vessels that operate under severe conditions by cyclic
heating and quenching operations. In use, a drum is filled with a
hot coker feed and, after a period of time, the drum is emptied and
prepared for the next filling. During filling with hot coker feed,
the drum is exposed to the very high temperature of the hot coker
feed, which can be as high as 900.degree. F. or more. When the drum
is to be emptied, in one step a quench water can be introduced into
the drum, and at this stage, the drum can be much hotter than the
quench water.
[0003] Because of these extreme temperature cycles, coke drums are
one of the pressure vessels that register most failure frequency in
refineries. According to an API survey, skirt cracking was reported
by 73% of companies surveyed who were using coke drums. In order to
repair cracks in the skirt, operational windows are required, which
require interruption of processes and, as a consequence, loss of
opportunities and higher operational costs.
[0004] In addition, incidents have been reported associated with
hydrocarbon leaks and incipient fires, creating certain operational
safety conditions. Studies have recognized that the cracks in coke
drums result from low cycle fatigue induced by cyclic thermal
stress. In order to attempt to address this issue, coke drums have
been provided with a zone called a "hot box" which closes off a
space between the skirt and the conical bottom portion of the coke
drum. This helps to increase the skirt temperature during a heating
stage in order to decrease the thermal effect. This is not enough,
however, to avoid problems with skirt cracking.
[0005] The need remains for a solution to the problem of skirt
cracking.
SUMMARY OF THE INVENTION
[0006] According to the invention, a solution to skirt cracking is
provided. Specifically, a fluid injection system is provided to
inject fluid of an appropriate temperature into the "hot box" and
thereby avoid the severe thermal stresses normally encountered with
coke drum operation.
[0007] According to the invention, a coke drum is provided which
comprises a coke drum vessel comprising a substantially cylindrical
wall and a conical bottom portion; a skirt downwardly depending
from a transition of the cylindrical wall into the conical bottom
portion, an inner annular space being defined between the skirt and
the conical bottom portion; and a fluid injection system
communicated with the inner annular space for injecting fluid at a
desired temperature to heat or cool the inner annular space.
[0008] The fluid injection system can be provided as a toroid tube
in the inner annular space and communicated with a source of the
fluid.
[0009] The fluid injection system can have a fluid inlet and a
fluid outlet, and at least one baffle in the inner annular space
between the fluid inlet and the fluid outlet.
[0010] The coke drum can have a bottom wall section connected
between the skirt and the conical bottom portion and closing off
the inner annular space to define the so-called "hot box".
[0011] The fluid injection system can advantageously have a first
toroid tube defining a fluid inlet, a second toroid tube defining a
fluid outlet, and a series of baffles in the inner annular space
between the first toroid tube and the second toroid tube.
[0012] The series of baffles can be arranged so that they lead the
fluid from the first or inlet toroid tube toward the second or
outlet toroid tube, and positioned to provide that the fluid is
always in contact with the skirt and conical surfaces of the drum.
In one configuration, the baffles can be positioned between the
skirt and conical surfaces with a gap between the baffle and these
surfaces such that flow of fluid is guided along the surface of the
skirt or conical section.
[0013] The fluid injection system can be provided so as to inject
fluid around an entire circumference of the inner annular
space.
[0014] A process for operating the system according to the
invention, and also a method for retrofitting or adapting an
existing coke drum to include the present invention, are also
provided.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] A detailed description of preferred embodiments of the
invention follows, with reference to the attached drawings,
wherein:
[0016] FIG. 1 is a schematic representation of a coke drum;
[0017] FIG. 2 shows an enlarged portion of FIG. 1 showing a "hot
box" portion of the coke drum with a fluid injection system
according to the invention;
[0018] FIG. 3 shows a further enlarged portion of FIG. 2 including
baffles according to a further embodiment of the invention; and
[0019] FIG. 4 shows skirt and cone temperature over time for a coke
drum without the fluid injection system of the present invention
(solid lines) as compared to one with the fluid injection system of
the present invention (dashed lines).
DETAILED DESCRIPTION
[0020] The invention relates to a coke drum having a fluid
injection system for reducing thermal stress and increasing
lifetime of a coke drum and, particularly, increasing lifetime of a
junction between the cone and skirt of a coke drum.
[0021] FIG. 1 illustrates a coke drum 10 which typically has a
substantially vertically oriented cylindrical portion 12 closed off
at a top portion 14 and having a substantially conical bottom
portion 16. Further, a skirt 18 is typically attached to coke drum
10 at a transition point 20 from cylindrical portion 12 to conical
bottom portion 16. Skirt 18 can be attached to coke drum 10, most
typically by welding.
[0022] Skirt 18 is typically used to support a coke drum during
use. In use, coke drum 10 is filled with a hot coker feed and,
after a period of time, the drum is emptied and prepared for the
next filling. At two different stages in the use of a coke drum,
the drum, including the junction of skirt and transition point, are
normally subjected to extreme changes in temperature. As will be
described herein, these changes in temperature are moderated and
controlled so as to reduce thermal stresses through the drum and,
particularly, at the junction of skirt and cone, and thereby extend
the life of the drum.
[0023] FIG. 2 is an enlarged view of the portion indicated in FIG.
1 at A, and shows a portion of a substantially cylindrical wall 22
which extends around axis X to define a coke drum vessel. This wall
thereby defines a substantially closed inner portion into which a
coker feed is introduced for cooling and subsequent treatment.
[0024] As shown, wall 22 transitions at the transition point 20
into an inwardly tapered wall 24 which defines conical bottom
portion 16.
[0025] Skirt 18 is shown connected to the cylindrical drum and
downwardly depending from transition point 20. This connection of
skirt 18 and wall 22/24 is therefore a junction of these
components. At this junction, the components are typically welded,
and it is the protection of this weld that is the focus of the
present invention.
[0026] It should be appreciated that skirt 18 and wall 24 define
between them an enclosed inner annular space 26. A radial wall 28
can also be included, for example extending between skirt 18 and
wall 24 to close off a portion of inner annular space 26. This
portion is referred to as the "hot box" 30.
[0027] FIG. 3 is an enlarged portion of FIG. 2 and shows tubes 32,
34 which define fluid inlet and outlet, respectively, for use in
introducing a fluid to the hot box 30. Tubes 32, 34 can, for
example, be provided as toroid tubes and are preferably disposed
around a circumference of conical bottom portion 16 in the hot box
30 or inner annular space 26 defined between wall 24 and skirt 18.
Tubes 32, 34 are communicated with a source of fluid at a variable
temperature such that fluid can be introduced through tubes 32, 34
to either heat or cool the hot box 30 as desired.
[0028] FIG. 3 shows a further enlarged portion of FIG. 2,
particularly the portion indicated at B. As shown, one tube 32 is
configured as an inlet and the other tube 34 is configured as an
outlet for the fluid flow to be introduced into hot box 30.
Further, as shown in this illustration a series of baffles 36 can
advantageously be positioned in hot box 30 between inlet tube 32
and outlet tube 34 such that fluid introduced through inlet tube 32
must travel a circuitous route to reach outlet tube 34. This
enhances the heat transfer from such fluid through the baffles 36
and into skirt 18 and wall 24 as well as the weld between these
components. As shown, baffles 36 are preferably positioned to
extend between the walls without reaching them, and this
configuration serves to guide flow of fluid along the surfaces of
the conical section and skirt as desired, for example as shown by
the arrows in FIG. 3. Also as shown in FIG. 3, the toroid tubes 32,
34 and baffles 36 define a fluid flow area which extends roughly
the entire height h of hot box 30, and also which advantageously
can extend around an entire circumference c of the hot box
area.
[0029] As set forth above, coke drums in general and the weld at
the junction of skirt 18 and wall 22, 24 are subjected to extreme
changes in temperature in two cycles of typical use of a coke drum.
The first is when a drum is filled with a hot coker feed, which can
have a temperature as high as 900.degree. F. or more. According to
the invention, fluid can be injected into hot box 30 through tube
32 so as to heat the temperature in hot box 30 and adjoining wall
sections and weld to a temperature close to the expected
temperature of incoming hot coker feed. In this way, when the hot
coker feed is introduced into the drum, a AT between components of
the drum and the hot coker feed can be minimized. Still further,
.DELTA.T between the skirt and the cone can be minimized as well,
and this most advantageously reduces thermal stresses in the weld
connection at the junction between these components.
[0030] Thus, in advance of filling a coke drum with hot coker feed,
the expected temperature of the hot coker feed can be determined
using various means well known to the person of ordinary skill in
the art, and hot fluid can then be introduced through tube 32 into
hot box 30 at a temperature sufficient to elevate temperature of
wall 24 and skirt 18 to substantially the same temperature as the
expected incoming hot coker feed. Once the hot coker feed has
rested in the coke drum and it is to be removed, a quench step is
typically conducted where quench water is introduced into the drum.
In advance of this step, fluid can be introduced through inlet tube
32 which is at a temperature suitable to reduce temperature of the
hot box 30 and walls defining same to be substantially the same as
the temperature of the expected quench water. In this way, during
quenching, AT between skirt and cone can also be minimized.
[0031] The fluid to be used in the present invention can be any
type of fluid which would be suitable for delivering the desired
amount of heating and/or cooling to hot box 30. According to one
embodiment of the invention, this fluid is advantageously air.
[0032] In the typical environment of use of the apparatus of the
present invention, air is readily available from a number of
different sources and at a number of different temperatures, and
this therefore advantageously facilitates deployment of systems in
accordance with the present invention. Of course, if desirable for
other reasons different fluids could be used.
[0033] It should also be appreciated that all components defining
the hot box, including tubes 32, 34 and baffles 36, should be
fabricated from materials which are well resistant to any
detrimental effects of being exposed to hot air.
[0034] In order to demonstrate the advantageous results of use of
the present invention, tests were taken using a coker drum without
a fluid injection system according to the present invention, and a
coker drum with the fluid injection system of the present
invention.
[0035] In the course of these tests, temperature of the skirt
section and the cone section were monitored during a full cycle of
use of a coke drum. Results are shown in FIG. 4. In FIG. 4 a solid
line referred to at reference numeral 38 shows cone temperature
over time during the test, for a coke drum without the fluid
injection system of the present invention. As shown, from a
starting point of approximately 65.degree. C., the temperature of
the cone upon filling rapidly climbed, over the period of
approximately 6.5 hours to a temperature of approximately
390.degree. C. Still referring to FIG. 4, the solid line indicated
by reference numeral 40 is the corresponding skirt temperature over
time, and FIG. 4 shows that once the drum is filled, there is a
.DELTA.T between cone 38 and skirt 40 of 30.degree. C. or more.
Further, these large .DELTA.T values are throughout the process,
including times of steep temperature changes, for example during
introduction of a hot coker feed, or at the time of quenching.
[0036] Still referring to FIG. 4, the dashed line indicated at 42
shows cone temperature for a coke drum including a fluid injection
system in accordance with the present invention. Further, the skirt
temperature of this device is shown in FIG. 4 at reference numeral
44. As shown, the spacing between dashed lines 42, 44 or .DELTA.T
when the fluid injection system of the present invention is used,
is significantly smaller than the .DELTA.T in the drum without a
fluid injection system. This advantageously reduces thermal
stresses to which the junction between the skirt and cone is
subjected, and thereby increases the useful life of the coke drum
and, particularly, the welds at this junction.
[0037] It should therefore be appreciated that the system in
accordance with the present invention is advantageously used in a
method wherein temperature of a coker feed to be delivered to the
drum is determined, fluid of a desired temperature is then
introduced through the fluid injection system and inlet tube 32, to
bring the temperature of hot box 30 including both cone and skirt,
to a substantially similar temperature in advance of introduction
of the coker feed into the drum.
[0038] Once the coker feed in the drum has rested a sufficient
period of time, and the drum is to be emptied and cleaned, the
temperature of a quenching water can be determined and additional
fluid injected to the hot box to cool the hot box to substantially
the same temperature as the quenching water. In this way, the
.DELTA.T during quenching can also be minimized in accordance with
the present invention.
[0039] It should also readily be appreciated that the fluid
injection system of the present invention can be easily adapted to
incorporate into an existing coke drum without such a fluid
injection system. This could be done, for example, by introducing
tubes 32, 34 into the inner annular space 26 defined by skirt 18
and wall 24 and further by adding baffles 36 and a radial wall 28
if necessary, such that an existing coke drum could then be
protected with the system of the present invention.
[0040] It is to be understood that the invention is not limited to
the illustrations described and shown herein, which are deemed to
be merely illustrative of the best modes of carrying out the
invention, and which are susceptible of modification of form, size,
arrangement of parts and details of operation. The invention rather
is intended to encompass all such modifications which are within
its spirit and scope as defined by the claims.
* * * * *