Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02821287 2013-07-18
Double Walled Tanks with Internal Containment Chambers
Field of Invention
The present invention is directed to double walled storage tanks with internal
containment
chambers.
Background
The storage of materials, including petroleum products and waste materials, in
the
upstream petroleum industry is dependent on primary containment devices, such
as
underground and aboveground storage tanks. Such tanks typically include
secondary
containment measures, which are required in some jurisdictions.
In Alberta, a single-walled above-ground storage tank must have secondary
containment
consisting of a dike with an impervious liner. However, the regulations permit
the use of
double-walled above-ground storage tanks ("DW ASTs") as an alternative to
single-walled
above-ground tanks and a secondary containment system. However, it has been
found that
DW ASTs are typically configured with manways and piping through the walls of
the tanks.
A majority of spills or releases from tanks are the result of operational
issues such as
overfilling, leaks and drips from valves and fittings, and spillage associated
with fluid
transfer. These releases are not being contained by the double-wall
interstitial space.
CA 02821287 2013-07-18
The use of an internal containment chamber within single walled tanks is
known.
Applicant's CA Patent No. 2,196,842 and US Patent No. 5,960,826 disclose the
use of such
containment chambers to contain spills and overflows from various valves used
in these tanks.
Summary Of The Invention
In one aspect, the invention comprises an above-ground storage tank
comprising:
(a) a tank roof, a tank floor, a primary tank and a secondary tank, which
together
define a tank interstitial space therebetween;
(b) a containment chamber formed by a primary chamber wall and a secondary
chamber wall, which together define a chamber interstitial space therebetween,
and an exterior door assembly;
(c) wherein the primary tank, the primary chamber wall and the tank floor
together
define a tank interior volume;
(d) at least one pipe and valve assembly wherein the pipe originates in the
tank
interior volume and the valve is disposed within the chamber;
(e) wherein the at least one pipe and valve assembly does not pass through the
primary tank or the primary chamber wall in a non-freeboard zone.
In one embodiment, the at least one pipe and valve assembly passes into the
chamber
= without passing through the primary tank at all, or passes through the
primary tank in a
freeboard zone and into the containment chamber from the tank interstitial
space, or passes
through the primary and secondary tank in a freeboard zone and into the
chamber through the
exterior door assembly.
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The configuration of the contaimnent chamber and the at least one pipe and
valve
assembly is arranged such that the double-walled protection of the tank is not
compromised by
any pipe or hatch or other opening, except in the freeboard zone.
In another aspect, the invention may comprise a double-walled above-ground
storage tank
comprising:
(a) a tank roof, a tank floor, a primary tank and a secondary tank, which
together
define a tank interstitial space therebetween, wherein the primary tank and
the
tank floor together define a tank interior volume;
(b) a main containment chamber formed by a chamber wall;
(c) an ancillary containment chamber formed by an ancillary chamber wall,
wherein
the ancillary containment chamber is above and contains the main containment
chamber, and both the main and ancillary containment chambers are disposed
within the tank interior volume; and
(d) a high level shutdown pipe which extends between a freeboard portion of
the
tank interior volume and the main containment chamber, passing through the
ancillary containment chamber, and comprising a high level shutdown valve
disposed within the main containment chamber, wherein the high level shutdown
valve comprises a fluid sensor and a switch operative to stop inflow into the
tank, or signal an alarm, or both.
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Brief Description Of The Drawings
In the drawings, like elements are assigned like reference numerals. The
drawings are not
necessarily to scale, with the emphasis instead placed upon the principles of
the present
invention, Additionally, each of the embodiments depicted are but one of a
number of
possible arrangements utilizing the fundamental concepts of the present
invention. The
drawings are briefly described as follows:
Figure 1 shows a vertical cross-section through one embodiment of a tank of
the present
invention.
Figure 2 shows a horizontal cross-section through the embodiment shown in
Figure 1, along
line II-II.
Figure 3 shows a vertical cross-section through an alternative embodiment of a
tank of the
present invention.
Figure 4 shows a horizontal cross-section through the embodiment shown in
Figure 3, along
line IV-IV.
Figure 5 shows a vertical cross-section through an alternative embodiment of a
tank of the
present invention.
Figure 6 shows a horizontal cross-section through the embodiment shown in
Figure 5, along
line VI-VI.
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Figure 7 shows a vertical cross-section through an alternative embodiment of a
tank of the
present invention.
Figure 8 shows a horizontal cross-section through the embodiment shown in
Figure 7, along
line VIII-VIII.
Figure 9 shows one embodiment of the configuration of welds connecting the
primary and
secondary tank walls to the primary and secondary chamber walls.
Figure 10 shows an alternative embodiment of the configuration of welds
connecting the
primary and secondary tank walls to the primary and secondary chamber walls.
Figure 11 shows an alternative embodiment of the configuration of welds
connecting the
primary and secondary tank walls to the primary and secondary chamber walls.
Figure 12 shows a vertical cross-section through an alternative embodiment of
a tank of the
present invention.
Figure 13 shows a horizontal cross-section through the embodiment shown in
Figure 12,
along line XIII.
Figure 14 shows a vertical cross-section through an alternative embodiment of
a tank of the
present invention.
Figure 15 shows a horizontal cross-section through the embodiment shown in
Figure 14,
along line XV.
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Figure 16 shows a vertical cross-section through an alternative embodiment of
a tank of the
present invention.
Figure 17 shows a horizontal cross-section through the embodiment shown in
Figure 9, along
line XVII - XVII.
Detailed Description Of Preferred Embodiments
The invention relates to double-walled aboveground storage tanks. When
describing the
present invention, all terms not defined herein have their common art-
recognized meanings.
To the extent that the following description is of a specific embodiment or a
particular use of
the invention, it is intended to be illustrative only, and not limiting of the
claimed invention.
The following description is intended to cover all alternatives, modifications
and equivalents
that are included in the spirit and scope of the invention, as defined in the
appended claims.
In one embodiment, the invention comprises an above-ground storage tank
defining an
interior volume and having an internal containment chamber. The tank itself is
double-
walled, as is the containment chamber. All pipe and valve assemblies which
penetrate into the
tank are configured so as to not compromise either the interstitial space of
the tank or the
containment chamber. In one embodiment, the interstitial space of the tank is
not
compromised because the primary tank is not penetrated, or is only penetrated
in the freeboard
zone of the tank. As used herein, the term "freeboard" means that area of the
tank above the
highest fluid level of the tank, or an area which is normally not in contact
with fluid in the
tank.
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Therefore, in one embodiment, the invention comprises an above-ground storage
tank
comprising:
(a) a tank roof, a tank floor, a primary tank and a secondary tank, which
together
define a tank interstitial space therebetween;
(b) a containment chamber formed by a primary chamber wall and a secondary
chamber wall, which together define a chamber interstitial space therebetween,
and an exterior door assembly;
(c) wherein the primary tank, the primary chamber wall and the tank floor
together
define a tank interior volume
(d) at least one pipe and valve assembly wherein the pipe originates in the
tank
interior volume and the valve is disposed within the chamber;
(e) wherein the at least one pipe and valve assembly does not pass through the
primary tank or the primary chamber wall in a non-freeboard zone.
In one embodiment, the at least one pipe and valve assembly passes into the
chamber
without passing through the primary tank at all, or passes through the primary
tank in a
freeboard zone and into the containment chamber from the tank interstitial
space, or passes
through the primary and secondary tank in a freeboard zone and into the
chamber through the
exterior door assembly.
As shown in Figures 1 and 2, in one embodiment, a storage tank (10) has an
inner primary
tank (12), and an outer secondary tank (14), which defines a tank interstitial
space (16)
therebetween. As required by regulation in Alberta, the floor (18) is also
double-walled, while
the roof (20) is not as it is considered part of the freeboard zone of the
tank.
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An internal containment chamber (22) is created by a chamber primary wall (24)
and a
chamber secondary wall (26), which together define a chamber interstitial
space (28). The
primary chamber wall (24) is that wall which faces the tank interior volume,
while the
secondary chamber wall (26) is that wall facing inside the chamber (22). The
chamber walls
(24, 26) are attached to the tank walls (12, 14) in a fluid-tight manner, such
as by a suitable
welding process. The attachments between the tank and containment chamber
primary and
secondary walls may be varied, as will be described below. What is essential
is that the tank
interstitial space and chamber interstitial space not be compromised.
Access to the containment chamber (22) is provided by a door assembly (30)
which passes
through the secondary tank wall (14). The door assembly may comprise a box
(32) having a
door (34). The door assembly can either be formed from the tank secondary wall
material, or,
be a completely separate manufactured component that is welded to the exterior
of the tank
secondary wall, over a door opening cut through both secondary and primary
walls. The door
opening must then be framed between the primary and secondary tank walls to re-
seal the
interstitial space. This doorway opening provides access into the containment
chamber.
A tank access hatch (36) may be provided through the tank roof (20). A pipe
access hatch
(38) may be also be provided which provides access the interstitial space,
tank volume or
chamber space which houses pipe and valve assemblies, as described below.
The tank comprises at least one pipe and valve assembly. In one embodiment,
the tank
comprises two pipe and valve assemblies: a suckout pipe (40) and an overflow
pipe (50). The
suckout pipe (40) originates near the tank floor, rises to the freeboard zone
(F), where it passes
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through the primary tank wall (12) and into the tank interstitial space (16).
It then passes
through the containment chamber walls and into the containment chamber, where
it terminates
with a suckout valve (42).
An overflow pipe (50) originates in the freeboard zone, near the fluid line
marking
maximum capacity of the tank, and passes into the tank interstitial space
(16). The overflow
pipe (50) then continues into the containment chamber, and terminates in a
high level
shutdown valve (52). This valve (52) may include sensors and switches
connected to regulate
inflows into the tank, and/or may be connected to transmitters (not shown)
which transmit a
wireless or radio alarm signal, as is well known in the art. If fluid in the
tank exceeds the
maximum capacity, a small amount of fluid will flow into the overflow pipe
(50), and into the
high level shutdown valve (52). Sensors in the valve may detect fluid, and
cause inflows into
the tank to stop. In another embodiment, there may be fluid connections from
either or both
the tank interstitial space or the chamber interstitial space to the high
level shutdown valve.
Accordingly, fluid in either interstitial space, which means that the primary
tank or primary
chamber wall has been breached, will cause an alarm signal or shutdown of
inflows, or both.
As may be seen in Figures 1 and 2, both the suckout pipe (40) and valve (42)
assembly
and the overflow pipe (50) and valve (52) assembly do not compromise the
integrity of the
interstitial space, as they pass into the interstitial space in the freeboard
zone, and then directly
into the containment chamber, which is itself double-walled.
A heater (55) may be provided within the containment chamber to keep the
valves (42, 52)
from freezing in the winter.
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In an alternative embodiment, as shown in Figures 3 and 4, the pipes (40, 50)
pass through
both the primary and secondary tank walls in the freeboard zone. The pipes
then pass along
the exterior of the tank, and enter into the containment chamber through the
door box (32).
Because the pipes are accessible on the exterior of the tank, in this
embodiment, a pipe access
hatch into the tank is not necessary.
In an alternative embodiment, shown in Figures 5 and 6, the tank comprises an
ancillary
containment chamber (60) formed by a single walled enclosure (62). The
ancillary chamber is
formed adjacent to the main containment chamber and has a roof portion (64).
The pipes (40,
50) pass into the ancillary chamber, preferably but not necessarily in the
freeboard zone, and
from there, pass into the main containment chamber. The overflow pipe (50)
simply extends
up through the roof portion (64). Because the single walled enclosure is
ancillary to the
double walled tank and containment chamber, the incursions into the
interstitial spaces are
contained by the ancillary chamber.
In a further alternative embodiment, as shown in Figures 7 and 8, the single
walled
enclosure (62) of the ancillary chamber extends upwards and attaches to the
tank roof (20).
The access hatch (38) through the tank roof (20) provides direct access into
the ancillary
chamber, unlike the embodiment shown in Figures 5 and 6, where the pipe access
hatch (38)
only provides access to the roof portion (64) of the ancillary chamber.
As shown in Figures 9, 10 and 11, various configurations of attachment between
the tank
primary and secondary walls and the chamber primary and secondary walls are
possible. Both
of the primary or secondary chamber walls (24, 26) may attach to the primary
tank wall, as is
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shown in Figure 9. In this case, the tank interstitial space and the chamber
interstitial space
are separated by the primary tank wall. In one embodiment, the attachment is
accomplished
by a full penetration weld (W) which is fluid-tight.
Alternatively, the primary chamber wall (24) may attach to the primary tank
wall (12),
while secondary chamber wall (26) attaches to the secondary tank wall (14). In
one
embodiment, shown in Figure 10, the primary chamber wall is welded to the
primary tank
wall in a fluid tight manner, and the secondary chamber wall is welded to the
secondary tank
wall. As a result, the tank interstitial space (16) is contiguous with the
chamber interstitial
space (Figure 11). Alternatively, there is no sealed connection between the
two (Figure 10),
which means the two interstitial spaces are connected but not contiguous.
In an alternative embodiment, two single walled chambers may be used in place
of a dual-
walled chamber. This implementation may provide more convenient installation
or
retrofitting possibilities in some cases. As shown in Figure 12, a primary
chamber wall (101)
is installed so as to surround a secondary chamber wall (103) and extends all
the way to the
tank roof. The pipes (40, 50) pass through the primary chamber wall (101) and
into an
ancillary chamber (102) and then into the lower containment chamber (104)
through the
secondary chamber wall (103). Preferably, the pipes (40, 50) pass through the
primary
chamber wall (101) in the freeboard zone. Thus, the ancillary chamber (102)
created between
the first and second chamber walls (101, 103) provides the equivalent of an
interstitial space
and may contain any spills or leaks from the tank and from the pipe fittings,
while the lower
chamber (104) corresponds to the containment chamber (22) in the embodiments
described
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above. In one variation, the first single walled chamber (101) does not extend
all the way to
the roof, only to the freeboard zone of the tank. The chamber thus has a roof
section (105)
through which the pipes (40, 50) may pass, as shown in Figure 14 and 15.
Embodiments which provide an ancillary and a lower containment chamber allows
tank
overflow protection into ancillary containment chambers. For example, an
overflow valve
(54) may be provided on the overflow pipe (50), preferably near an upper
section of the pipe.
The overflow valve (54) is normally closed, however, if fluid enters the
overflow pipe up to
the level of the overflow valve (54), then the overflow valve (54) allows the
fluid to enter and
be contained within the ancillary chamber (102). In one embodiment, the
overflow valve (54)
is a simple flapper valve located on the elbow joint of the overflow pipe
(50).
Further redundant overflow protection may be installed. A backup high level
shutdown
sensor and switch (56) installed in the ancillary chamber, for example near
the top or roof of
the ancillary chamber or on the secondary chamber wall (103), may detect fluid
in the
ancillary chamber (104), and operate to stop inflow into the tank by
connection with an intake
valve, or to signal an alarm, or both. Further, in one embodiment, an opening
(58) through the
primary tank wall within the ancillary chamber (104) allows overflow of fluid
into the tank
interstitial space. This overflow protection will only be necessary if all
other high level
shutdown sensors and switches have failed, and the ancillary chamber has
filled to the top,
where the opening (58) exists. Therefore, in one embodiment, the tank
interstitial space
provides the final overflow protection.
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In a further alternative, the primary chamber wall (101) extends up through
the tank roof,
with an access hatch as shown in Figures 16 and 17. Additional features are
shown in this
example, which may also be included with any embodiment of the invention. An
inlet pipe
(110) passes through the chamber door into the chamber, upwards through the
secondary
chamber wall (103), and finally into the tank through the primary chamber wall
(12) in the
freeboard zone. An overflow pipe (50) connects to a high level shut down valve
(52) as
described above.
A suck out pipe (40) and valve (42) may also provided as described above. In
one
embodiment, a siphon break (130) is connected to the suck out pipe (30) and
terminates with a
siphon valve (132) in the containment chamber.
As shown in Figures 13 and 15, the primary chamber wall (101) may be welded to
the
primary tank wall, while the secondary chamber wall (103) may be welded to the
secondary
tank wall. Alternatively, both primary and secondary chamber walls may be
welded to the
primary tank, as shown in Figure 17. The same variations of welding patterns
described
above may apply to these embodiments. As may be appreciated by those skilled
in the art, an
existing double walled tank having a single walled containment chamber may be
easily
retrofitted with a primary chamber wall. The first single walled chamber may
be welded into
the tank in sections to facilitate installation. For example, a lower piece
and an upper piece
may be installed, leaving a middle section open to allow access to the
containment chamber
and tank interior. Once all welds have been finished and all piping installed,
then a middle
piece or pieces may be installed to complete the primary chamber wall.
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In one embodiment, the tank comprises fluid detection sensors (not shown) in
the tank
interstitial space, the chamber interstitial space, or both. If the tank
interstitial space, and the
chamber interstitial space are connected or contiguous, it may possible to
implement only one
fluid detection sensor within either the tank or the chamber interstitial
space. Suitable fluid
detection sensors are well known in the art. In one embodiment, an
interstitial connect (120)
may be provided which provides a fluid connection between either or both of
the tank
interstitial space and the chamber interstitial space and the high level shut
down valve (52).
The interstitial connect (120) may be transparent or translucent to enable
visual confirmation
of fluid in the connect (120). The bottom end of the connect may terminate in
a "Y"
connector (122) to connect both the tank and chamber interstitial spaces. The
interstitial
connect (120) may incorporate one-way valves to prevent fluid the overflow
pipe (50) from
entering the interstitial space.
As will be apparent to those skilled in the art, various modifications,
adaptations and
variations of the foregoing specific disclosure can be made without departing
from the scope
of the invention claimed herein.
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