Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02679790 2009-09-22
Double Walled Tanks with Internal Containment Chambers
Field of the Invention
[0001] The present invention is directed to double walled storage tanks with
internal
containment chambers.
Background
[0002] 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.
[0003] In Alberta, a single-walled aboveground storage tank must have
secondary
containment consisting of a dike with an impervious liner. However, the
regulations permit
the use of double-walled aboveground storage tanks ("DW ASTs") as an
alternative to single-
walled aboveground 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.
[0004] The use of an internal containment chamber within single walled tanks
is known.
Applicant's co-owned CA Patent No. 2,196,842 and US Patent No. 5,960,826
discloses the
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use of such containment chambers to contain spills and overflows from various
valves used in
these tanks.
[0005] There is a need in the art for double-walled tanks with internal
containment chambers,
which comprises an uninterrupted interstitial space.
Summary Of The Invention
[0006] In one aspect, the invention comprises an above-ground storage tank
defining an
interior volume and comprising:
(a) a tank roof, a tank floor, a primary tank and a secondary tank, and an
interstitial
space therebetween;
(b) an containment chamber formed by a primary chamber wall and a secondary
chamber wall, forming a chamber interstitial space therebetween, and an
exterior
door assembly;
(c) at least one pipe and valve assembly wherein the pipe originates in the
tank
interior volume and the valve is disposed within the chamber, in which:
i. the pipe passes into the chamber without passing through the primary tank;
or
ii. the pipe passes through the primary tank in a freeboard zone and into the
containment chamber from the tank interstitial space; or
iii. the pipe passes through the primary and secondary tank in a freeboard
zone
and into the chamber through the exterior door assembly.
[0007] The configuration of the containment 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.
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Brief Description Of The Drawings
[0008] 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:
[0009] Figure 1 shows a vertical cross-section through one embodiment of a
tank of the
present invention.
[0010] Figure 2 shows a horizontal cross-section through the embodiment shown
in Figure 1,
along line II-II.
[0011] Figure 3 shows a vertical cross-section through an alternative
embodiment of a tank of
the present invention.
[0012] Figure 4 shows a horizontal cross-section through the embodiment shown
in Figure 3,
along line N-N.
[0013] Figure 5 shows a vertical cross-section through an alternative
embodiment of a tank of
the present invention.
[0014] Figure 6 shows a horizontal cross-section through the embodiment shown
in Figure 5,
along line VI-VI.
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[0015] Figure 7 shows a vertical cross-section through an alternative
embodiment of a tank of
the present invention.
[0016] Figure 8 shows a horizontal cross-section through the embodiment shown
in Figure 7,
along line VIII-VIII.
[0017] Figure 9 shows one embodiment of the configuration of welds connecting
the primary
and secondary tank walls to the primary and secondary chamber walls.
[0018] 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.
[0019] 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.
Detailed Description Of Preferred Embodiments
[0020] 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.
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[0021] In one embodiment, the invention comprises an above-ground storage tank
defining an
interior volume and comprising:
(a) a tank roof, a tank floor, a primary tank and a secondary tank, and an
interstitial
space therebetween;
(b) an containment chamber formed by a primary chamber wall and a secondary
chamber wall, forming a chamber interstitial space therebetween, and an
exterior
door assembly;
(c) at least one pipe and valve assembly wherein the pipe originates in the
tank
interior volume and the valve is disposed within the chamber;
(d) wherein no part of the at least one pipe and valve assembly passes through
the
secondary tank in a non-freeboard zone.
[0022] The configuration of the chamber and any pipe and valve assembly which
penetrates
into the tank interior volume is such that the tank interstitial space and the
chamber interstitial
space are not compromised, in a non-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.
[0023] As shown in Figures 1 and 2, in one embodiment, a storage tank (10) has
a primary
tank (12), and a 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.
[0024] A containment chamber (22) is created by a chamber primary wall (24)
and a chamber
secondary wall (26), which define a chamber interstitial space (28). The
chamber walls (24,
26) are attached to the tank walls (12, 14) in a fluid-tight manner, such as
by a suitable
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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.
[0025] 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.
[0026] 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.
[0027] 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, where it
passes 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).
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[0028] 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 which regulate
inflows into the
tank, or may be connected to transmitters (not shown) which transmit a
wireless or radio
alarm signal, as is well known in the art.
[0029] As may be seen in Figures 1 and 2, both the suckout pipe and valve
assembly and the
overflow pipe and valve assembly do not compromise the integrity of the
interstitial space, as
they pass directly into the containment chamber, which is itself double-
walled, from the tank
interstitial space.
[0030] A heater (55) may be provided within the containment chamber to keep
the valves, (42,
52) from freezing in the winter.
[0031] 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,
thereby complying
with regulations which allow such intrusions 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 accesible on the exterior of the tank, in this
embodiment, a pipe access
hatch into the tank is not necessary.
[0032] 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).
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The pipes (40, 50) pass into the ancillary chamber, preferably 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 is contained
by the ancillary chamber.
[0033] In an further alternative, as shown in Figure 7 and 8, the single
walled enclosure of the
ancillary chamber extends upwards and attaches to the tank roof (20). The
access hatch (3 8)
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.
[0034] 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 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.
[0035] Alternatively, the primary chamber wall (24) may attach to the primary
tank wall (12),
while secondary chamber wall (26) attachs to the secondary tank wall (14). In
one
embodiment, shown in Figures 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
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space (Figure 11), or there is no sealed connection between the two (Figure
10), which means
the two interstitial spaces are connected but not contiguous.
[0036] 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 continguous, 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.
[0037] 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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