U.S. patent application number 16/209245 was filed with the patent office on 2020-06-04 for external floating roof tank shell extension.
This patent application is currently assigned to PHILLIPS 66 COMPANY. The applicant listed for this patent is PHILLIPS 66 COMPANY. Invention is credited to Jeff McBride, Paul J. Rady.
Application Number | 20200172326 16/209245 |
Document ID | / |
Family ID | 70849958 |
Filed Date | 2020-06-04 |
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United States Patent
Application |
20200172326 |
Kind Code |
A1 |
Rady; Paul J. ; et
al. |
June 4, 2020 |
EXTERNAL FLOATING ROOF TANK SHELL EXTENSION
Abstract
The invention relates to an inexpensive technique and procedure
to add storage capacity to existing hydrocarbon storage tanks that
have a double seal floating roof. The additional storage capacity
is obtained by installing an extension that is strong enough to
provide the upper seal of the double seal arrangement to maintain a
sealed vapor space that allows the roof to move higher within the
existing peripheral wall of the storage tank.
Inventors: |
Rady; Paul J.; (Katy,
TX) ; McBride; Jeff; (Houston, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
PHILLIPS 66 COMPANY |
Houston |
TX |
US |
|
|
Assignee: |
PHILLIPS 66 COMPANY
HOUSTON
TX
|
Family ID: |
70849958 |
Appl. No.: |
16/209245 |
Filed: |
December 4, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B65D 90/38 20130101;
B65D 88/42 20130101; B65D 88/005 20130101 |
International
Class: |
B65D 88/42 20060101
B65D088/42; B65D 90/38 20060101 B65D090/38 |
Claims
1. A process for expanding the capacity of a floating roof
cylindrical tank for storing hydrocarbons comprising: providing a
cylindrical tank with a generally circular base having a periphery
extending fully around the circular base and generally cylindrical
peripheral wall extending vertically upward to a top edge and a
floating roof with two spaced apart seals arranged for sealing
contact against the generally cylindrical peripheral wall;
providing a plurality of brackets up to the top of the floating
roof where the brackets include pre-drilled holes for attaching
extension panels; providing a plurality of extension panels that
are each thinner and lighter weight than the generally cylindrical
peripheral wall up to the top of the floating roof where the
extension panels include pre-drilled holes to attach to the
brackets and to attach each panel to others of the plurality of
panels; providing a sealant between each bracket and the generally
cylindrical peripheral wall and attaching each bracket to the
generally cylindrical wall end to end so as to create a sealed
connection between the brackets and the generally peripheral wall
and to provide a structure for which the extension panels may be
attached to the generally cylindrical peripheral wall; providing a
sealant between each of the panels and the bracket and attaching
each of the panels to the bracket and to one another in an
overlapping arrangement where the panels overlap at least part of
the bracket and where at least part of each panel overlaps with
other panels with sealant between where they overlap such that when
the panels are attached to the brackets they form a generally
cylindrical wall extension extending upwardly from the generally
cylindrical wall such that the upper of the two seals on the
floating roof may move vertically with the floating roof and
maintain a sealed vapor space as the seal passes above the top edge
of the generally cylindrical peripheral wall and into contact with
the panel extensions sealed together and to the generally
cylindrical peripheral wall.
2. The process according to claim 1 wherein the top edge includes
an outwardly extending flange and the bracket is secured to the
outwardly extending flange.
3. The process according to claim 1 wherein the panels connect to
one another at overlapping joints and each bracket butts up against
brackets at each edge at butt joints such that the process includes
attaching the panels together such that the overlapping joints are
offset relative to the butt joints so that two such joints do not
coincide to weaken the seal of the floating roof storage tank.
4. The process according to claim 1 wherein the panels are attached
to one another by rivets.
5. The process according to claim 1 where the brackets and panels
are installed while hydrocarbons are stored in the floating roof
storage tank and no drilling or welding would be allowed to occur
that would be hazardous with hydrocarbons in such proximity to the
installation of the panel extension.
6. The process according to claim 1 where the peripheral wall has a
thickness and the panel extensions has a thickness and wherein the
step of providing the panel extensions includes selecting panel
extensions that are less than on fifth of the peripheral wall
thickness.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] None.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] None.
FIELD OF THE INVENTION
[0003] This invention relates to generally cylindrical liquid
hydrocarbon storage tanks and more particularly to large capacity
liquid hydrocarbon storage tanks for storing crude oil and
hydrocarbon products used in refineries and in petrochemical and
fuel transportation and distribution facilities.
BACKGROUND OF THE INVENTION
[0004] Generally cylindrical hydrocarbon storage tanks have been in
use in refineries for many years. These tanks have been used to
store and blend crude oils and intermediate hydrocarbon products
for refining and also to store finished fuels for distribution. One
of the safety advances for such storage tanks is the development of
a floating roof. One of the concerns in storing hydrocarbons is
that hydrocarbon vapors are, in many cases, flammable and, in some
cases, have a toxicity concern. The floating roof development has
reduced these concerns by reducing the volume of vapors in these
large storage tanks.
[0005] Basically, a floating roof comprises a roof that is separate
from the storage tank and floats on the liquid surface using
flotation pontoons or other flotation arrangement. The roof then
rises and falls with the volume of hydrocarbons. The vapor space is
then limited to the volume between the liquid surface and the
underside of the floating roof. To contain the vapors from the
outside atmosphere two or more seals are positioned around the
periphery of the floating roof to be in contact with the inside
wall of the tank to seal the small vapor space from the outside
atmosphere and prevent hydrocarbon releases. Typically, in such
double seal arrangements, a primary seal is located just above the
liquid level and a second seal is positioned above the primary seal
by as much as four feet, but typically between about 18 inches and
up to about 36 inches above the primary seal.
[0006] One of the drawbacks of such double seal arrangements is the
limitation on the maximum capacity of the tank. Each of these large
diameter storage tanks is essentially full when the second seal is
just below the top of the wall. As such, as much as four feet
vertical feet of capacity is unavailable. For a tank having a
100-foot diameter, adding four additional vertical feet of capacity
translates to nearly 235,000 gallons of additional storage capacity
not being available for liquid storage so as to provide vapor
containment for the tank.
[0007] An alternative seal system that would reclaim the storage
capacity or reduce the space committed to vapor containment could
translate into significant dollars, especially for a storage
terminal that is paid to store hydrocarbons. Additional storage
capacity could translate into many dollars of added profit. This
additional capacity would be a welcome addition if capacity could
be incrementally increased without having to invest significantly
in building additional tanks. This may be especially welcome when
there is no available land to install new additional storage
tanks.
BRIEF SUMMARY OF THE DISCLOSURE
[0008] The invention more particularly relates to a process for
expanding the capacity of a floating roof cylindrical tank for
storing hydrocarbons. The process includes starting with a
cylindrical tank having a generally circular base with a periphery
extending fully around the circular base and generally cylindrical
peripheral wall extending vertically upward to a top edge and a
floating roof with two spaced apart seals arranged for sealing
contact against the generally cylindrical peripheral wall. A
plurality of brackets are provided up to the top of the floating
roof where the brackets include pre-drilled holes for attaching
extension panels. A plurality of extension panels are provided that
are each thinner and lighter weight than the generally cylindrical
peripheral wall up to the top of the floating roof where the
extension panels include pre-drilled holes to attach to the
brackets and to attach each panel to others of the plurality of
panels. A sealant is provided between each bracket and the
generally cylindrical peripheral wall and attaching each bracket to
the generally cylindrical wall end to end so as to create a sealed
connection between the brackets and the generally peripheral wall
and to provide a structure for which the extension panels may be
attached to the generally cylindrical peripheral wall. A sealant is
provided between each of the panels and the bracket and attaching
each of the panels to the bracket and to one another in an
overlapping arrangement where the panels overlap at least part of
the bracket and where at least part of each panel overlaps with
other panels with sealant between where they overlap such that when
the panels are attached to the brackets they form a generally
cylindrical wall extension extending upwardly from the generally
cylindrical wall such that the upper of the two seals on the
floating roof may move vertically with the floating roof and
maintain a sealed vapor space as the seal passes above the top edge
of the generally cylindrical peripheral wall and into contact with
the panel extensions sealed together and to the generally
cylindrical peripheral wall.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] A more complete understanding of the present invention and
benefits thereof may be acquired by referring to the follow
description taken in conjunction with the accompanying drawings in
which:
[0010] FIG. 1 is a perspective view of a conventional hydrocarbon
storage tank with a floating top;
[0011] FIG. 2 is a fragmentary cross section elevation view of the
seal of the floating top of a hydrocarbon storage tank shown with
the conventional arrangement with two vertically spaced apart seals
positioned against the interior peripheral wall of the storage
tank; and
[0012] FIG. 3 is a fragmentary elevation view similar to FIG. 2,
but showing a simple and inexpensive extension modification to the
tank according to the present invention that allows the floating
top to rise higher in the tank while containing the liquid
hydrocarbons inside the tank with the spaced apart double seal for
vapor containment;
[0013] FIG. 4 is an exploded fragmentary perspective view of a
hydrocarbon storage tank showing the extension for creating added
storage capacity in a form for being assembled and installed to an
existing hydrocarbon storage tank while in service; and
[0014] FIG. 5 is an enlarged fragmentary cross-sectional view
showing a preferred arrangement for adding a seal extension
according to the present invention.
DETAILED DESCRIPTION
[0015] Turning now to the detailed description of the preferred
arrangement or arrangements of the present invention, it should be
understood that the inventive features and concepts may be
manifested in other arrangements and that the scope of the
invention is not limited to the embodiments described or
illustrated. The scope of the invention is intended only to be
limited by the scope of the claims that follow.
[0016] As shown in FIGS. 1 and 2, a conventional hydrocarbon
storage tank is generally indicated by the number 10 having a
generally circular base, a cylindrical peripheral wall 20 extending
up from the base and having a top comprising a floating roof 12.
The cylindrical peripheral wall 20 is typically made of steel and
is fabricated to hold a very high volume of liquid hydrocarbons L
such as crude oil, gasoline, diesel, naphtha and a host of other
intermediate and finished hydrocarbon liquids. While such tanks may
be made in just about any dimension, it is typical for such storage
tanks to be large with a diameter in the range of 100-foot diameter
and in excess of 30 feet tall or deep.
[0017] The floating roof 12 is arranged to float on the surface of
the liquid contents of the tank 10 using flotation pontoons or the
like while raising and lowering as the liquid level changes. The
reason to have a floating roof 12 is to minimize the vapor space
between the surface level and the bottom of the floating roof 12.
Vapors are hazardous, so minimizing the volume of vapor with in a
hydrocarbon storage tank is safer, preferred and typically required
by environmental regulations.
[0018] Focusing on FIG. 2, the floating roof 12 includes a sealing
system engaged with the cylindrical peripheral wall 20. The sealing
system includes two spaced apart seals where a primary seal 13 is
positioned at the peripheral edge of the floating roof 12 to engage
the peripheral wall 20. A second seal 14 is positioned 18 or more
inches above the primary seal 13 although it is more conventional
that these two seals 13 and 14 are spaced apart by two to three
feet and as much as four feet apart. The second seal 14 is oriented
like the main seal to engage against the inside surface of the
peripheral wall 20 vertically above the primary seal 13 and move
vertically within the cylindrical wall 20. The two seals 13 and 14
seal the vapor space from the open atmosphere preventing
hydrocarbon emissions and together to contain the hydrocarbons. The
primary seal 13 and the second seal 14 are made of flexible
material, typically of a hydrocarbon resistant rubber so that they
slide along and seal against the inside of the cylindrical wall 20
flexing to follow the contour of the cylindrical wall 20 and
accommodate any reasonable shifting of the floating roof due to
unequally distributed weight from workers or equipment on the
floating roof 12. The roof typically has a shape such as with
sloping roof segment 16 to maintain outward pressure of the second
seal 14 against the wall 20
[0019] FIGS. 1 and 2 show the conventional floating roof technology
for liquid hydrocarbon storage tanks in use around the world. The
invention relates to an improvement to such hydrocarbon storage
tanks that simply and very inexpensively increases that available
storage capacity of an existing tank by about the vertical spacing
between the primary seal 13 and the second seal 14. The point that
was observed by the inventors is that both seals need to engage the
peripheral wall making the highest permissible liquid level be
indicated by the dotted line F in FIG. 2 even though the top of the
peripheral wall is indicated by the dotted line T. The difference
between dotted line T and dotted line F represents a significant
difference in capacity within the tank. But, the upper portion of
the cylindrical wall 20, where only the second seal 14 ever
impinges, does not have to be as structurally strong as the rest of
the cylindrical wall 20. The weight of the liquid is never imposed
on that upper portion between the full level L and the top T. While
the dimension and strength of the cylindrical wall of an existing
storage tank is strong top to bottom, it is sufficiently strong to
hold the weight of the liquid right to the top T of the tank 10.
For example, the wall 20 of storage tank 10 is typically at least
1/4 inch thick carbon steel at its top and often thicker and
certainly thicker at lower course heights of storage tanks. Being
strong enough to hold liquid, all that is needed is an extension
that can provide a vapor seal for second seal 14 to engage.
[0020] Turning now to FIG. 3, with an inexpensive extension 21
projecting upwardly from the top of the peripheral wall 20, the
full liquid level or highest permissible level F is much closer to
the top T of the peripheral wall 20 as shown by the new full level
F just below the top T of the tank 10. This creates additional
volume capacity that is roughly equal to the spacing between the
two seals 13 and 14 taking into consideration the area under the
roof 12. This represents a significant gain in storage capacity.
For example, in a storage tank have the spacing between the primary
seal 13 and the second seal 14 of 2 feet with tank diameter of 100
feet, the volume that can be gained by allowing the liquid level to
approach the true top of the tank T would create more than 117,000
gallons of additional capacity. For a facility that does not own
hydrocarbons, but only charges others for storage of their
hydrocarbons, this additional capacity gained in one storage tank
can represent a significant financial opportunity. Once the cost of
installing the extension has been incurred, there is essentially no
further cost for storing additional hydrocarbons and therefore
charging additional storage fees.
[0021] Focusing now on the inventive lightweight extension 21 as
shown in FIGS. 3, 4 and 5 and as envisioned the inventors, the
second seal 14 is allowed to float above the top of the peripheral
wall 20 but still keep the vapors inside the storage tank 10
separated from the atmosphere. The second seal 14 would continue to
function quite satisfactorily while moving vertically up and down
along the light weight sealing extension 21. The extension 21
extends vertically to a level above the top T of the storage tank
10 to a height preferably at least the distance between the two
seals 13 and 14. The extension is preferably made of stainless
steel and is preferably a thin gauge of between 0.010 inches up to
1/8 inch but would more preferably be between 0.020 and 0.050
inches thick. Alternatively, the extension 21 may be plastic,
aluminum or other lightweight metal. The extension 21 would not
need to be permanent, but once installed, it is unlikely to be
removed except for maintenance or repairs.
[0022] Focusing now on an example installation for a lightweight
extension that does not include welding or drilling on the existing
storage tank that is in service (with hydrocarbons stored in the
tank while the extension is being installed). A preferred
attachment method is shown in FIGS. 4 and 5 where the extension
includes a plurality of thin panels 25 that are arc shaped
comparable to the radius of the circular arc of the peripheral wall
20 of the storage tank 10. Each of the panels includes pre-drilled
holes 27 vertically along each end which, when aligned allows the
panels 25 to overlap with one another. The overlapping ends are
arranged to be bolted together or, more preferably, to be riveted
together. An elastomeric sealant is applied between the sections 25
where they overlap to create an effectively continuous
circumferential extension at the top of the peripheral wall 20. The
panels 25 also have a horizontal row of pre-drilled holes 28 along
the lower portion so that they may be mounted to the top of the
peripheral wall 20 by a series of spring brackets 22. The
horizontally arranged pre-drilled holes 28 are arranged to align
with pre-drilled holes 29 in spring brackets 22. More specifically,
as shown in FIG. 5, the spring brackets 22 include a vertical
segment 22A against which the panels 25 may be attached using
rivets 26 through horizontal pre-drilled holes 28 and 29. The
spring brackets 22 include a shape to attach to and extending
around flange 20A at the top of the peripheral wall 20 of the
existing storage tank 10. This flange 20A is conventional at the
top of the peripheral wall 20 where it extends outwardly to
strengthen or reinforce the main body of the peripheral wall 20.
The flange 20A is sufficiently strong to support a modest (4
vertical feet upwardly is not excessive) lightweight extension
comprised of panels 25. The spring brackets 22 are preferably
formed of bent sheet steel to form a channel that slips over the
flange 20A with a compression grip on both top and bottom of the
flange 20A.
[0023] The attachment of the spring bracket 22 is best shown in
FIG. 5 where it can be seen that the vertical segment 22A extends
vertically from the top of the peripheral wall 20 of the storage
tank 10. The vertical segment 22A extends from a top horizontal
segment 22B formed as a bend in a common sheet of thin stainless
steel. The top horizontal segment 22B lies flush on top of the top
surface of the flange 20A while an end segment 22C extends around
the outer periphery of the flange 20A and holds a bottom horizontal
segment generally flush against the bottom of the flange 20A. The
bends formed in the thin sheet of stainless steel are preferably
exaggerated so that the top horizontal segment 22B and bottom
horizontal segment 22D squeeze against the flange 20A. The panels
25 are attached in an overlapping manner with the vertical segment
22A such that the inside face 25A of the panel 25 is nearly flush
with the inside face 20B of the peripheral wall 20 and so that the
second seal 14 may slide from the inside face 20B up to the inside
face 25A of the extension 21 without breaking sealing contact and
maintaining the vapor space closed from the outside
environment.
[0024] While the spring brackets are preferably attached end to end
to extend fully around the peripheral wall 20, preferably they do
not overlap each other as some small space may be left between the
ends for adjustments during the installation process. These small
gaps are preferably bridged by a panel 25 to minimize potential
leaks such that the joints of the panels 25 are offset relative to
the joints in the spring brackets 22. Sealing materials, such as an
elastomeric, paste or putty, is preferably applied with the panels
25 attach flush to the vertical segments 22A.
[0025] In a manner similar to the attachment of the panels 25 end
to end, sealing compound such as elastomeric sealer is preferably
applied before the spring bracket is slipped on to the flange 20A.
The spring bracket includes a vertical segment extending upwardly
to the top of the channel section with a series of pre-formed holes
for attachment of the panels that also have the pre-formed holes.
Elastomeric sealer is also applied to the overlap of the vertical
section with the panels.
[0026] The process of installing the extension 21 begins by
providing spring brackets and extension sections 25 up to the top
of the floating roof. The sections 25 and spring brackets 22 are
preferably light enough to be carried up the stairs by human
personnel and not require heavy lifting equipment, like a crane or
construction forklift, to lift the sections to the top of the tank
10. Sealing compound is applied to the top of the flange 20A and
then spring brackets 22 are slipped over the flange 20A one by one
in an end-to-end arrangement extending fully around the periphery
of the storage tank 10 with the respective vertical segments 22A of
each of the spring brackets 22 being positioned in near alignment
with the inner face 20B of the peripheral wall 20. With the spring
brackets 22 attached, the panels 25 are then attached to the
vertical segments with sealing compound added between each flat
overlying face of the panels 25 and vertical segments 22A until the
extension 21 is fully complete around the peripheral wall 20. After
passing inspections, the liquid level in the storage tank 10 may be
raised such that floating roof 12 may float higher within the
peripheral wall 20 while lifting the second seal 14 above the top T
of the peripheral wall 20 and into contact with the extension
21.
[0027] In closing, it should be noted that the discussion of any
reference is not an admission that it is prior art to the present
invention, especially any reference that may have a publication
date after the priority date of this application. At the same time,
each and every claim below is hereby incorporated into this
detailed description or specification as additional embodiments of
the present invention.
[0028] Although the systems and processes described herein have
been described in detail, it should be understood that various
changes, substitutions, and alterations can be made without
departing from the spirit and scope of the invention as defined by
the following claims. Those skilled in the art may be able to study
the preferred embodiments and identify other ways to practice the
invention that are not exactly as described herein. It is the
intent of the inventors that variations and equivalents of the
invention are within the scope of the claims while the description,
abstract and drawings are not to be used to limit the scope of the
invention. The invention is specifically intended to be as broad as
the claims below and their equivalents.
* * * * *