U.S. patent application number 12/903841 was filed with the patent office on 2011-02-03 for lng containment system and method of assembling lng containment system.
Invention is credited to Thomas A. Ballard, Kailash C. Gulati, Alexander V. Krimotat.
Application Number | 20110023404 12/903841 |
Document ID | / |
Family ID | 34956110 |
Filed Date | 2011-02-03 |
United States Patent
Application |
20110023404 |
Kind Code |
A1 |
Gulati; Kailash C. ; et
al. |
February 3, 2011 |
LNG Containment System and Method Of Assembling LNG Containment
System
Abstract
An LNG system generally comprises a primary container, and a
secondary container positioned around the primary container. The
secondary container generally comprises a first end wall, a second
end wall, and at least two side walls. At least one of the walls is
fabricated from a plurality of prefabricated wall panels. Each of
the wall panels is fabricated from a combination of concrete and
steel. The wall panels are preferably prefabricated offsite, and
then transported to the construction site where they are adjoined
together in end-to-end fashion to form walls. A method for
constructing a full containment LNG system is also provided. In one
embodiment, walls and a roof for a secondary container are
assembled, but leaving an end open. At least one primary tank is
brought into the secondary container. A second end wall is then
erected to form the enclosure for the secondary container.
Inventors: |
Gulati; Kailash C.;
(Houston, TX) ; Ballard; Thomas A.; (Campbell,
CA) ; Krimotat; Alexander V.; (Los Gatos,
CA) |
Correspondence
Address: |
EXXONMOBIL UPSTREAM RESEARCH COMPANY
P.O. Box 2189, (CORP-URC-SW 359)
Houston
TX
77252-2189
US
|
Family ID: |
34956110 |
Appl. No.: |
12/903841 |
Filed: |
October 13, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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|
10593457 |
Apr 10, 2007 |
7837055 |
|
|
PCT/US05/17363 |
May 17, 2005 |
|
|
|
12903841 |
|
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|
|
60572736 |
May 20, 2004 |
|
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Current U.S.
Class: |
52/582.1 |
Current CPC
Class: |
F17C 2203/0678 20130101;
F17C 2209/221 20130101; F17C 2223/0161 20130101; F17C 2223/033
20130101; F17C 1/00 20130101; F17C 2203/012 20130101; F17C
2201/0157 20130101; F17C 2203/0341 20130101; F17C 2270/0136
20130101; F17C 2209/22 20130101; F17C 2260/013 20130101; Y10T
29/49826 20150115; F17C 2203/0354 20130101; F17C 2221/033 20130101;
F17C 2203/0629 20130101; F17C 2203/0648 20130101; F17C 2203/0333
20130101; F17C 2201/052 20130101; Y10S 220/901 20130101; F17C
2203/0639 20130101; F17C 2201/035 20130101; F17C 2203/0643
20130101 |
Class at
Publication: |
52/582.1 |
International
Class: |
E04C 2/38 20060101
E04C002/38 |
Claims
1. A wall panel for a secondary container, the secondary container
being employed with a full containment LNG system, the wall panel
comprising: a concrete plate having an inner surface, an outer
surface, and a longitudinal axis; at least one steel beam connected
to the concrete plate along the outer surface of the concrete
plate, and along the longitudinal axis; and wherein the wall panel
is configured so that a plurality of wall panels may be adjoined in
side-to-side fashion so as to form a wall of a secondary container
for the full containment LNG system.
2. The wall panel of claim 1, further comprising: a moisture
barrier disposed on the concrete plate opposite the at least one
steel beam.
3. The wall panel of claim 2, further comprising: an insulation
layer along the moisture barrier opposite the at least one steel
beam; and a liner plate on the insulation layer.
4. A roof panel for a secondary container, the secondary container
being employed with a full containment LNG system, the roof panel
comprising: an elongated steel truss structure; a barrier layer
placed over the steel truss structure; at least one thin concrete
plate placed over the barrier layer along a longitudinal axis of
the concrete plate; and wherein the roof panel is configured so
that a plurality of roof panels may be adjoined in side-to-side
fashion so as to form a roof of a secondary container for the full
containment LNG system.
5. The roof panel of claim 4, wherein the at least one concrete
plate comprises a plurality of concrete plates joined together to
form a grid.
6. The roof panel of claim 4, wherein the barrier layer is
fabricated from a carbon steel.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation application under 35
U.S.C. .sctn.120 of, and claims priority to, U.S. patent
application Ser. No. 10/593,457, entitled LNG CONTAINMENT SYSTEM
AND METHOD OF ASSEMBLING LNG CONTAINMENT SYSTEM, filed on 10 Apr.
2007, which application is the national phase application under 35
U.S.C. .sctn.371 of international application PCT/US05/17363, filed
17 May 2005, which application claims the benefit under 35 U.S.C.
.sctn.119(e) of U.S. Provisional Application 60/572,736, filed 20
May 2004. The entirety of each of these applications is
incorporated herein by reference for all purposes.
BACKGROUND
[0002] 1. Field of the InventionS
[0003] Embodiments of the present invention generally relate to the
storage of large fluid volumes. More particularly, embodiments of
the present invention relate to tank designs for holding
hydrocarbons. In addition, embodiments of the present invention
relate to the manufacture of an LNG containment system.
[0004] 2. Description of Related Art
[0005] Clean burning natural gas has become the fuel of choice in
many commercial and consumer markets around the industrial world.
Such natural gas is oftentimes transported across oceans from the
sites of production to consuming nations. Such transportation of
natural gas typically occurs over long distances using large-volume
marine vessels.
[0006] In order to facilitate transportation the gas is taken
through a liquefaction process. The liquefied natural gas, or
"LNG", is formed by chilling very light hydrocarbons, e.g.,
hydrocarbons comprised primarily of methane, to approximately
-163.degree. C., where it is stored at ambient pressure in special
cryogenic tanks. Due to its low critical temperature, continued
refrigeration is desired for LNG transportation and storage.
[0007] Upon delivery to an import terminal, the LNG is typically
stored for later use and delivery to domestic markets. Experience
shows that bulk storage of liquefied natural gas is most economical
when stored in its fully refrigerated state, and at its bubble
point at or near atmospheric pressure. The boiling point of LNG at
one atmosphere is approximately -163.degree. C. To accommodate this
condition, insulated storage tanks are employed. The LNG storage
tanks typically have a primary container and a surrounding
secondary container.
[0008] For large volume storage of LNG, two distinct types of tank
construction are widely used. The first of these is a
flat-bottomed, cylindrical, self-standing tank that typically uses
a 9% nickel steel for the inner tank and carbon steel, 9% nickel
steel, or reinforced/prestressed concrete for the outer tank. The
second type is a membrane tank wherein a thin (e.g. 1.2 mm thick)
metallic membrane is installed within a cylindrical concrete
structure which, in turn, is built either below or above grade on
land. A layer of insulation is typically interposed between the
metallic membrane, e.g., of stainless steel, and the load bearing
concrete cylindrical walls and flat floor.
[0009] In the context of the cylindrical, self-standing LNG tank,
and from a safety and environmental standpoint, it is preferred
that the tank have "full containment." A "full containment" system
requires that the outer secondary container hold both liquid and
its vapor should the liquid escape from the primary container. The
full containment system should also be configured to permit the
controlled release or withdrawal of these fluid products from the
system. While structurally efficient, cylindrical tanks in their
state-of-practice designs are difficult and time consuming to
build. LNG storage systems using self-standing 9% nickel steel
tanks may require up to 36 months for construction. On many
projects, this causes undesirable escalation of construction costs
and length of construction schedule.
[0010] A need exists for a full containment LNG storage system that
provides liquid and vapor integrity in the event of primary
container leakage, and that can be efficiently fabricated. A need
further exists for an improved method of fabricating a secondary
container, such as an LNG container. A need further exists for
prefabricated wall and roof panels that may be brought to a
construction site for efficient erection of secondary container
walls and roof structure.
SUMMARY
[0011] An LNG full containment system is provided. The LNG system
generally comprises a floor slab, a primary container positioned on
the floor slab, and a secondary container positioned around the
primary container. The secondary container preferably incorporates
the floor slab as part of its structure. The primary container is
insulated in order to maintain a desired temperature within the
primary container. For example, an insulating material such as
pearlite is placed in the annulus between the outer side of the
inner container and the inner side of the outer container.
[0012] The secondary container generally comprises a first end
wall, a second end wall, and at least two side walls. At least one
of the walls is fabricated from a plurality of prefabricated wall
panels. Each of the prefabricated wall panels is fabricated from a
combination of concrete and steel.
[0013] Preferably, each of the prefabricated wall panels includes a
thin concrete plate having a longitudinal axis, and at least one
steel beam connected to the concrete plate along the longitudinal
axis of the concrete plate. In one embodiment, each wall panel
includes a moisture barrier directly attached to the concrete plate
opposite the at least one steel beam. Preferably, each wall panel
is insulated by placing an insulation layer on the concrete plate
or the moisture barrier, if a moisture barrier is installed. The
insulation layer is preferably covered by a liner that is
impervious to LNG and its vapor and that can withstand the
cryogenic temperature of LNG such as thin sheets made of 9% Ni
steel or stainless steel. The wall panels are preferably
prefabricated offsite and then transported to the construction site
where they are adjoined together in side-by-side fashion.
[0014] In another embodiment, a shallow-arch roof is provided that
is also fabricated from a combination of steel and concrete roof
panels. The roof panels also are preferably prefabricated offsite
and then transported to the construction site where they are
adjoined together in side-by-side fashion.
[0015] The present invention also provides a method for assembling
an LNG full containment system. In one embodiment, walls and a roof
as described above are provided. The walls are optionally
constructed from wall panels prefabricated off-site. The
prefabricated panels are then delivered to the tank site where they
are adjoined together in side-to-side fashion according to desired
dimensions.
[0016] In one embodiment of the method, a floor slab is first
poured at the construction site. The slab is fabricated at least in
part from concrete. A first planar end wall is erected on the floor
slab. In addition, first and second planar side walls are erected
on the floor slab, the first and second planar side walls being
connected to the first end wall at opposite ends but being angled
relative to the first end wall to leave an opening for receiving a
second planar end wall so that a polygon having at least four sides
may be formed. A roof structure is also constructed. The roof
structure that covers the polygon formed by the end and side walls
to provide a roof for a secondary container.
[0017] In accordance with the method, a primary container is also
constructed. The opening within the secondary container is used as
a means of access into the secondary container. In one aspect, one
or more substantially completed primary containers is moved into
the secondary container. Finally, a second planar end wall is
erected so as to enclose the primary container within the secondary
container.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 presents a perspective, cutaway view of a containment
structure. In the illustrative drawing of FIG. 1, an external
"secondary container" of the containment structure is seen. In
addition, an inner "primary container" is seen in the cutaway
portion of the drawing.
[0019] FIG. 2 provides an additional perspective view of an
illustrative secondary container. A portion of an upper roof
structure is peeled away to show roof trusses. A plurality of steel
beams can be seen as part of the vertical end and side walls of the
secondary container.
[0020] FIG. 3 shows a series of individual prefabricated panels
that may be used for assembling vertical walls of the secondary
container, in one embodiment. The panels are mated in side-to-side
fashion.
[0021] FIG. 4 provides a top view of a portion of the panels of
FIG. 3.
[0022] FIG. 5 presents a perspective view of a single panel from
FIG. 3. In one embodiment, the single, prefabricated panel
represents the smallest building block of the combination wall
units.
[0023] FIG. 6 is a perspective view of the panels of FIG. 3, seen
from the opposite side. Here, the face or "inner surface" of the
combination panels is seen, with the panels again being mated in
side-to-side fashion.
[0024] FIGS. 7A-7F present sequential steps for assembling a wall
panel as may be used in the construction of walls for the secondary
container, in one embodiment.
[0025] FIG. 7A shows the placement of a steel I-beam in a jig.
[0026] FIG. 7B shows illustrative formwork for the placement of
concrete during fabrication of the wall panels.
[0027] FIG. 7C shows reinforcing cages being laid in the formwork
of FIG. 7B.
[0028] FIG. 7D shows embedded plates and other aids used for the
attachment of a moisture barrier, an insulation layer and the liner
plate being placed alongside the steel reinforcing cages of FIG.
7C.
[0029] FIG. 7E demonstrates the pouring of concrete in the
formworks containing the steel reinforcing cages, embedded plates
and other construction aids of FIG. 7D.
[0030] Finally, FIG. 7F shows the attachment of various layers over
the top surface of the cured concrete plate. Layers may include a
moisture barrier layer, an insulation layer and a liner plate
placed over the concrete plates of FIG. 7E.
[0031] FIG. 8 is an enlarged perspective view of a portion of the
containment system from FIG. 2. Visible in this view are steel
trusses with reinforced concrete roof panels being placed there
over. Vertical side panels in accordance with the panels of FIG. 3
are also visible, supporting the steel roof trusses.
[0032] FIGS. 9A-9F present sequential steps for construction of a
secondary container, in one embodiment.
[0033] FIG. 9A shows the formation of a concrete floor slab. In
this embodiment, the footprint of the slab is rectangular. In
addition, a vertical end wall has been erected over an end of the
floor slab using prefabricated wall panels.
[0034] FIG. 9B presents the placement of a prefabricated roof panel
on the concrete floor slab.
[0035] FIG. 9C is a cutaway view of the secondary container. In
this step, the two opposing side walls have been erected along the
floor slab. In addition, a roof structure has been placed over the
span between the two opposing side walls to define the secondary
container. A substantially complete primary container is being
moved into its position within the secondary container.
[0036] FIG. 9D shows the same construction steps of FIG. 9C, but
shows the secondary container in perspective view without a cutaway
section.
[0037] FIG. 9E demonstrates that the primary container being moved
into the secondary container. Finally, FIG. 9F shows the erection
of the second vertical end wall to form the enclosed secondary
container.
DETAILED DESCRIPTION
Definitions
[0038] The following words and phrases are specifically defined for
purposes of the descriptions and claims herein. To the extent that
a term has not been defined, it should be given its broadest
definition that persons in the pertinent art have given that term
as reflected in printed publications, dictionaries or issued
patents.
[0039] "Primary container" means an inner tank of an LNG
containment system.
[0040] "Secondary container" means a tank that envelopes the
primary container within an LNG containment system.
[0041] "Vertical panel" means a panel of a tank that is
substantially vertical relative to a floor slab on which it is
erected. "Panel" refers to any building block made of a combination
of at least concrete and steel.
[0042] "End panel" means any substantially vertical panel at an end
of a tank.
[0043] "Planar" means substantially planar, and does not exclude a
surface that is slightly concave.
[0044] "Moisture barrier" means any sheet of material resistant to
fluid penetration. A non-limiting example is a 3 mm sheet of carbon
steel.
[0045] "Insulation layer" means any layer of material that provides
thermal insulation to a concrete plate. A non-limiting example is a
sheet of plywood. Another non-limiting example is a layer of
polyurethane foam.
[0046] "Liner plate" means any sheet of material used to line the
inner surface of an LNG container.
DESCRIPTION OF SPECIFIC EMBODIMENTS
[0047] The following provides a description of certain specific
embodiments of the present invention:
[0048] An LNG full containment system is first provided. The system
includes a floor slab; a primary container positioned on the floor
slab, the primary container being insulated to hold liquefied
natural gas; and a secondary container peripherally positioned
around the primary container, the secondary container comprising a
plurality of composite walls attached to the floor slab, with each
of the composite walls being formed from a plurality of
prefabricated wall panels configured to be adjoined in side-to-side
fashion. Each of the prefabricated wall panels includes a concrete
plate having a longitudinal axis and an outer surface, and at least
one steel beam connected to the outer surface of the concrete plate
along the longitudinal axis of the concrete plate. Each of the
plurality of composite walls of the secondary container has a first
end wall, a second end wall, and at least two side walls, with each
of the at least two side walls being disposed on opposing sides of
the first end wall.
[0049] Preferably, each of the prefabricated wall panels further
includes a moisture barrier disposed on the concrete plate opposite
the at least one steel beam. Preferably, each of the prefabricated
wall panels also further includes an insulation layer along the
moisture barrier opposite the at least one steel beam, and a liner
plate on the insulation layer. The moisture barrier may be
fabricated from material selected from the group consisting of: a
metallic material and a polymeric material.
[0050] The LNG full containment system may have a roof structure
that includes a plurality of prefabricated roof panels adjoined in
side-to-side fashion, with each of the roof panels including a
concrete plate an inner surface, and a steel truss structure
connected to the inner surface of the concrete plate.
[0051] A method of assembling an LNG full containment system is
also provided. In one embodiment, the method includes the steps of
pouring a floor slab fabricated at least in part from concrete;
erecting a first end wall on the floor slab; erecting first and
second side walls on the floor slab, the first and second side
walls being connected to the first end wall at opposite ends, but
being angled relative to the first end wall to leave an opening for
receiving a second end wall so that a polygonal enclosure having at
least four sides may be formed; providing a roof structure that is
supported at least in part by the side walls; moving a
substantially assembled primary container into the secondary
container; and erecting the second end wall so as to enclose the
primary container within the secondary container. The step of
moving the substantially assembled primary container into the
secondary container may be accomplished by using the opening for
the second end wall as a means of access into the secondary
container
[0052] In one embodiment, the polygon is a four-sided polygon, and
the first and second end walls and the first and second side walls
connect together to form a rectangle. In another embodiment, the
polygon is a six-sided polygon, the method further comprises the
step of erecting third and fourth side walls on the floor slab, the
third and fourth side walls being connected to the first and second
side walls, respectively, but also being angled to preserve the
opening for receiving the second end wall so that the six-sided
polygon may be formed.
[0053] In one arrangement, the primary container comprises a
plurality of planar, vertical walls, and the method further
comprises the step of fabricating the vertical walls of the primary
container at the same time that at least one of the side walls of
the secondary container is being erected on the concrete floor
slab.
[0054] In addition, a wall panel for a secondary container is
provided. The secondary container is employed with a full
containment LNG system. The wall panel may include a concrete plate
having an inner surface, an outer surface, and a longitudinal axis;
at least one steel beam connected to the concrete plate along the
outer surface of the concrete plate, and along the longitudinal
axis; and wherein the wall panel is configured so that a plurality
of wall panels may be adjoined in side-to-side fashion so as to
form a wall of a secondary container for the full containment LNG
system. The wall panel preferably has an insulation layer disposed
on the concrete plate opposite the at least one steel beam.
Preferably, the wall panel also includes a moisture barrier along
the insulation layer opposite the at least one steel beam, and a
liner plate on the insulation layer.
DESCRIPTION OF EMBODIMENTS SHOWN IN THE DRAWINGS
[0055] The following provides a description of specific embodiments
shown in the drawings:
[0056] FIG. 1 presents a perspective, cutaway view of a containment
structure 100, in one embodiment. The containment structure 100, in
its most general form, comprises an external secondary container
200 and at least one inner primary container 300. A primary
container 300 is seen in the cutaway portion of the secondary
container 200. The primary container 300 is designed to hold
liquefied natural gas ("LNG") at cryogenic temperature and in an
insulated manner. At the same time, the secondary container 200 is
designed to serve as a "back-up" to the primary container 300 in
the event that the primary container 300 loses fluid integrity.
[0057] A secondary container of an LNG storage system fulfills
several functions. During normal operations, the outer, or
"secondary" container holds the insulation in place and provides
protection to the inner, primary tank against the elements of
nature. Under extreme conditions when the inner tank is assumed to
fail and no longer able to hold the cryogenic liquid, the outer
tank is called upon to hold full contents of the inner tank safely
and to permit both controlled withdrawal of the contained liquid
and controlled release of the product vapor. In this event, a
severe set of loads is imposed on the outer tank. Not only is the
outer tank subjected to the hydrostatic loads applied by the liquid
now contained by it, but the outer wall is also subjected to a
`thermal shock` loading due to sudden exposure to the very low
temperatures of the LNG liquid. The inner wall and floor surfaces
of the secondary container experience a sudden and severe drop of
temperature while the outer surfaces of the secondary container
wall remain exposed to ambient temperature. This causes severe
stresses in the secondary container at junctures such as wall-floor
interfaces. Thus, a secondary container 200 is preferably designed
to accomplish one or more of the following: (1) withstand
hydrostatic forces upon fluid leakage from the primary container
300, (2) contain liquids that might escape from the primary
container 300, (3) provide gas tightness from gases that will form
when liquid escapes from the primary container 300, and (4)
withstand thermal shock created if and when extremely cold fluids
from the primary container 300 contact the inner surfaces of the
secondary container 200.
[0058] In the arrangement of FIG. 1, the secondary container 200
defines a polygonal structure having a plurality of walls. More
specifically, the secondary container 200 has a first end wall 212
and a second opposite end wall 214. In addition, the container 200
has at least two opposite side walls disposed intermediate the
first 212 and second 214 end walls. One of the side walls is seen
at 222, while a second side wall is on the back side and not
directly visible, but is nevertheless referenced at 224. The
secondary container 200 further includes a bottom floor slab 250
and a roof structure 260. The end walls 212, 214, the at least two
side walls 222, 224, the floor slab 250 and the roof structure 260
form an enclosure for the primary container 300.
[0059] In the arrangement of FIG. 1, the polygonal form of the
secondary container 200 is a four-sided structure, forming a
rectangle. However, the four-sided structure could also be a
square. Alternatively, the polygonal form of the secondary
container 200 could be formed from more than 4 sides, for example,
a six-sided or an eight-sided structure (not shown). In such an
arrangement, the secondary container 200 would have additional
opposing side walls (not shown) between side walls 222, 224 and end
panel 214, respectively. The various end and side walls may or may
not have the same length, and may or may not be precisely
linear.
[0060] FIG. 2 provides an additional perspective view of an
illustrative secondary container 200'. A rectangular enclosure is
again provided. A plurality of steel beams 232 can be seen as part
of the four vertical walls 212, 214, 222, 224 of the secondary
container 200'. A concrete floor slab 250 is provided under the
walls 212, 214, 222, 224. An upper roof structure 260 is peeled
away to show equidistantly spaced roof trusses 262.
[0061] The secondary container 200 of FIG. 1 employs vertical wall
structures. Preferably, the first and second end walls 212, 214 and
the side walls 222, 224 are erected on-site over the secondary tank
bottom 225. Each wall is substantially vertical and, preferably,
substantially planar.
[0062] To aid in the efficient erection of the various walls 212,
214, 222, 224 prefabricated panels are preferably employed. FIG. 3
shows a series of individual panels 230' that may be used for
assembling vertical walls of the secondary container 200, in one
embodiment. The vertical panels 230' are a combination fabrication,
meaning that they are formed from a combination of steel and
concrete. In the arrangement of FIG. 3, each panel 230 has at least
one I-beam 232 adjoined to a thin concrete plate 234. The steel
beam 232 may be prefabricated, or may be built-up by welding or
otherwise attaching plates to form a beam. In one embodiment, the
panels 230 are adjoined in such a manner that the beams 232 are
spaced at 5 m intervals.
[0063] In one embodiment, the concrete plate 234 is pre-formed by
pouring concrete into a mold, with the cured plate 234 being about
100 mm thick to about 500 mm thick. In another embodiment, the
plate 234 is about 200 to 400 mm thick, or alternatively,
approximately 250 mm to 350 mm thick. The I-beams 232 are attached
to the concrete plates 234 along an outer surface 233 to provide
lateral structural support. The laterally supported thin-wall
arrangement has advantages over the thick, one-meter concrete walls
sometimes seen in modern cylindrical tanks. In this respect,
thicker walls induce large and prolonged through-thickness,
non-linear, thermal gradients, resulting in large,
thermally-induced stresses. The individual wall panels 230 may
optionally be poured as a group of panels 230', such as 2, 3, 4 or
more panels 230 to form a structurally monolithic panel 230'. Thus,
the "smallest building block" may be a panel 230, or a panel
230'.
[0064] FIG. 4 provides a top view of a portion of the panels 230'
of FIG. 3. Visible in FIG. 4 are three spaced-apart I-beams 232
butted against concrete plates 234. Metal plates 236 are optionally
embedded into the concrete plates 234 for receiving additional
layers onto the inner surface of the plates 234, as will be
described below. In one arrangement, the embedded metal plates 236
extend 100 mm into the concrete plates 230. Also visible in FIG. 4
are the ends of steel bars 237. The optional steel bars 237 act as
"rebar," and serve to reinforce the plate 230.
[0065] FIG. 5 presents a single panel 230 from the panels 230' of
FIG. 3, in one embodiment. The panel 230 represents one possible
"smallest building block" of the combination wall units as might be
used in constructing an LNG containment system 100. A plurality of
individual panels 230, e.g., four, may be fabricated as a unit in a
casting yard for delivery to a construction site. The number of
"smallest building blocks," i.e., individual wall panels 230 or
groups of panels 230', that are fabricated as a unit depends on a
number of factors, such as casting yard capabilities and on-site
handling and lifting equipment. In one possible arrangement, for a
95 m long.times.45 m wide.times.35 m high structure with concrete
plate thickness of 350 mm and a steel beam spacing of 5 m, which is
calculated to be a satisfactory secondary container in one
embodiment of a 100,000 m.sup.3 rectangular LNG containment system,
a building unit of four "smallest building blocks" is
preferred.
[0066] FIG. 6 is a perspective view of the panels of FIG. 3, seen
from the opposite side. Here, inner faces 231 of the combination
panels 230' are seen. A group of panels 230' are fabricated as a
single unit. Each inner face 231 may receive additional layers onto
the concrete panel 230. First, a moisture barrier 242 may be placed
onto the inner face 231, i.e., along the concrete panel 230'
opposite the at least one steel beam 232. The moisture barrier 242
is preferably fabricated from either a metallic material or a
polymeric material. Second an insulation layer 244 may be disposed
on the moisture barrier 242. Preferably, the insulation layer 244
is a 5 cm layer of a cryogenic insulation material such as
polyurethane foam. The insulation layer 244 helps to lessen the
severity of initial thermal gradient during a thermal shock event,
and to limit the temperature extremes that the wall is subjected
to. Finally, a liner plate 246 may be placed onto the panel 230',
preferably over the insulation layer 244. The liner plate 246 is
preferably a nickel steel alloy, such as a 5-6 mm thick plate of 9%
Nickel steel. In FIG. 6, layers of a moisture barrier 242, an
insulation layer 244, and a liner plate 246 are shown exploded from
the concrete panels 230'.
[0067] As noted, the various combination panels 230 are joined to
form a wall of any desired length. When assembling walls 212, 214,
222 and 224 for the secondary container 200, the panels 230' are
erected in a vertical orientation over a floor slab, such as a
concrete floor slab. A floor slab is seen at 250 in FIG. 1. The
floor slab 250 provides a fixed base for the containment structure
100. The floor slab 250 preferably has a 9% nickel steel or other
cryogenic material liner 225 on top to cover the foundation slab
250. Additionally, the floor slab may have a moisture barrier and
an insulation layer on top of the foundation slab 250 as previously
discussed for the concrete panels 230'. Such a combination of
liners may also be placed on the end and side walls up to a height
of 3 to 5 meters as corner protection against thermal
expansion.
[0068] The steel beam/concrete combination walls 212, 214, 222, 224
are connected to the floor slab 250. In one embodiment, a "pin"
connection is provided between the panels 230' and the slab 250.
The liner plate 246 on the panels 230 is joined to the liner plate
225 on secondary tank bottom 250 such that a liquid tight secondary
containment is obtained. The steel beams 232 and the exterior
surface 233 of the panels 230' are in some instances coated with
fire proofing materials to enhance their integrity against
fire.
[0069] In practice, the floor slab 250 receives not only the
various end 212, 214 and side 222, 224 walls, but also supports the
primary container 300. Preferably, a bottom insulation layer is
interposed between the concrete floor slab 250 and the steel inner
tank bottom 225 by placing insulation materials (not shown) in the
annular space (also not shown) between the inner 300 and outer 200
tanks.
[0070] The walls 212, 214, 222, 224 of the outer tank 200 of the
present invention are designed to contain the liquid product, i.e.,
LNG, in the event of a large leak from the primary inner container
300. The external vertical steel beams 232 carry a large portion of
the hydrostatic loads of LNG if and when the liquid from the
primary tank 300 leaks out. The concrete sections 234 of the walls
212, 214, 222, 224 induce relatively small thermal stresses due to
the thermal shock at initial contact with LNG. Preferably, the
walls are "thin," having a thickness of about 100 mm to 500 mm. In
one embodiment, the concrete plate 234 is 350 mm to 400 mm in
thickness. The thin walls are capable of surviving the thermal
shock loads without insulation or any other mitigation. A full
height steel liner 246, with a partial or full height insulation
layer 244, assures leak tightness and aids in stress management
during thermal shock. By so splitting the functional duties of
strength provision, liquid containment and liquid and gas leak
tightness, and forbearance of thermal shock induced stresses, the
wall structure achieves efficiency when contrasted with traditional
solutions that ascribe fulfillment of all these requirements to a
thick (e.g., greater than 600 mm), post-tensioned wall installed on
a fixed concrete base.
[0071] FIGS. 7A-7F present sequential steps for assembling a panel
230 as may be used in the construction of walls for the secondary
container 200, in one embodiment. FIG. 7A shows the placement of a
steel I-beam 732. The beam 732 defines an elongated support member.
Preferably, the beam 732 includes one or more small pins 731. The
pins 731 extend along a side of the beam 732, and are generally
enveloped by concrete during panel fabrication. The pins 731 serve
to further secure the beam 732 to the cured concrete plate, seen
FIG. 7F). In FIG. 7A, the beam 732 has been placed in a jig 735.
The jig 735 serves as the bottom formwork for supporting
plate-forming operations.
[0072] FIG. 7B presents a plurality of truss brackets 734
positioned transverse to the single I-beam 732 of FIG. 7A. The
truss brackets 734 provide a support for the wall panel fabrication
operation. In the arrangement of FIG. 7B, form plates 733 have been
laid on opposing sides of the beam 732. Pins 731 extend upward
intermediate the form plates 733. The form plates 733 serve as an
impermeable base over which concrete is later poured. The form
plates 733 may become a permanent inner layer along the concrete
plates 738, though preferably they stay in the jig 735 and are not
a permanent part of a panel 730.
[0073] FIG. 7C shows a next step in the panel-forming operation.
Here, reinforcing cages 736 are being laid. The form plates 733
assist in supporting the cages 736. The cages 736 are preferably
fabricated from steel. The cages 736 receive poured concrete (see
the panel-forming step of FIG. 7E). In this manner, the cages 736
serve as "rebar" to strengthen the formed panel.
[0074] A next step in the panel-forming operation is seen in FIG.
7D. FIG. 7D shows embedded plates 738 being placed over the edges
of the cages 736 of FIG. 7C. Reinforcing cages 736, and embedded
plates 738 are placed in the jig 735 and appropriately connected
together by welding or fastening by other means. FIG. 7E
demonstrates the pouring of concrete in the formwork of FIG. 7D.
The concrete is allowed to cure to form a panel 730.
[0075] Finally, FIG. 7F shows the attachment of various layers 742,
744, 746 over the top surface of the cured concrete panel 730.
Layers may include a moisture barrier layer 742, an insulation
layer 744, and a liner plate 746 placed over the concrete panels of
FIG. 7E. The moisture barrier 742, the insulation layer 744, and
the liner plate 746 are again shown exploded from the concrete
panel 230. Preferably, these fabrication steps would take place in
a concrete casting yard. After assembly, the precast wall sections
230 are moved to the construction site (not shown).
[0076] A roof structure 260 is also provided on the secondary
container 200. The roof structure 260 may be assembled by adjoining
roof panels in side-to-side (including end-to-end) fashion as with
the wall panels described above.
[0077] First, referring again to FIG. 2, this Figure shows an
additional perspective view of an illustrative secondary container
200'. In accordance with the above descriptions, a plurality of
steel beams 232 is provided along vertical end walls 212, 214 and
side 222, 224 walls of the secondary container 200'. In addition,
an upper roof structure 260 is provided. The roof structure 260 is
convex relative to the exterior of the container 200', and in this
embodiment forms a shallow arch. In the view of FIG. 2, the roof
structure 260 is peeled away to show several spaced-apart roof
trusses 262. The roof trusses 262 span the secondary container 200
across the opposing side walls 222 and 224. Concrete panels 266 are
placed over the trusses 262. A carbon steel plate 264 spanning the
entire width and length directions of the secondary container
structure 200 is optionally under the concrete panels 266. As noted
above, the roof structure 260 may be fabricated by adjoining
pre-poured concrete roof panels in side-to-side fashion.
Alternatively, the roof structure 260 may be formed by first
installing the trusses 262, followed by installation of the liner
264, and then pouring a topping layer of concrete on top of the
liner 264. The concrete is poured in place with the liner 264
serving as part of the formwork.
[0078] FIG. 8 provides an enlarged perspective view of a portion of
the containment system 200 from FIG. 2. Visible in this view are
the steel trusses 262 with thin, reinforced concrete roof panels
266 having been placed there over to form the roof structure 260. A
moisture barrier plate 264 is again disposed between the trusses
262 and the concrete plates 266. Vertical side panels 230 in
accordance with the panels 230 of FIG. 3 are also visible,
supporting the steel roof trusses 262 and forming a side wall
224.
[0079] The roof structure 260 of the secondary container 200 is a
steel/concrete combination construction. In the embodiment of FIGS.
2 and 8, the roof structure 260 is shaped to provide a shallow arch
configuration in the width direction of the structure 200.
Uniformly spaced steel trusses 262 spanning the width of the
secondary container 200, with their spacing matching the spacing of
the vertical steel beams 232 of the side walls 222, 224 are
attached to these beams 232 at their upper termini. A carbon steel
plate 264 spanning the entire width and length directions of the
secondary container structure 200 is installed atop and attached to
the upper extremities of the roof trusses 262. The carbon steel
plate 264 serves as the moisture and vapor barrier when the
structure 200 is completed. A layer of reinforced concrete 266 is
installed over the trusses 262 and the carbon steel plate 264.
[0080] The roof structure arrangement 260 of FIGS. 2 and 8 allows
partial prefabrication. In this respect, the steel trusses 262 and
steel plate 264 may be fabricated off-site. A roof "building block"
may be composed of two, three, or more trusses. These
"prefabricated truss panels may be delivered to the tank
construction site to aid in a more efficient secondary tank
construction operation. For example, first the steel truss 262 and
steel plate 264 roof building block may be installed so that the
steel trusses 262, with their spacing matching the spacing of the
vertical steel beams 232 of the side walls 222, 224, are attached
to these wall beams 232 at their upper termini. Then the concrete
plates 266 of the roof structure 260 may be formed by pouring
concrete on top of the steel plate 264 of the roof building block.
Post tensioning of the roof concrete layer 266 may not be necessary
in these arrangements.
[0081] In addition to providing a secondary container for an LNG
containment system 100, a method is also provided herein for
assembling an LNG containment system, such as system 100.
Construction of containment system 100 is expedited by using the
above-described secondary container embodiments 200. The secondary
container 200 is erected over a concrete tank floor (seen at 250 in
FIG. 1). More specifically, individual walls, e.g., end walls 212,
214 and side walls 222, 224 are formed by vertically erecting and
attaching various panels (shown at 230 in FIG. 3) side-by-side.
This is a segmental technique that uses off-site prefabrication of
building blocks that can be assembled into a structural system.
[0082] Known full containment systems typically demand a relatively
long construction schedule. The sequential construction of storage
system elements normally starts with the construction of a
cast-in-place outer tank slab and walls. Only after the domed roof
has been constructed on the outer tank walls is construction on the
internal structures, including the bottom insulation and inner
steel tank, started. This means that the inner steel tank is
constructed in-situ after the secondary container has been at least
substantially completed. A construction schedule of 36 months for a
now typical 160,000 m.sup.3 full containment LNG storage tank is
normal. This long construction schedule is often on the critical
path for an LNG facility construction project, causing a potential
source of delay. Therefore, an improved method for assembling an
LNG containment system is offered.
[0083] FIGS. 9A-9F present sequential steps for construction of a
full containment LNG tank 100, in one embodiment. The full
containment tank 100 will include one or more inner tanks 300 and a
surrounding outer tank 200. First, FIG. 9A shows the formation of a
concrete floor slab 250. In this embodiment, the "footprint" of the
slab 250 is rectangular. In addition, a vertical end wall 212 has
been erected over an end of the floor slab 250. The end wall 212
has been assembled by adjoining prefabricated combination wall
panels (such as those shown at 230 in FIG. 3) in side-to-side
fashion. The wall panels 230' may be individual wall panels 230, or
may be a structurally monolithic collection of wall panels 230'
fabricated in a casting yard to form a single "panel." The wall
panels 230 are tilted up into vertical position using lifting
equipment (not shown). The panels are aligned and braced, and
interconnected to form the end wall 212. Structural connection
between the floor slab 250 and the wall panels 230 forming end wall
212 is then provided.
[0084] In FIG. 9A, scaffolding 310 has been erected. The
scaffolding 310 assists in the lifting, aligning, bracing and
interconnecting of prefabricated wall panels 230'. However, the
methods for constructing an LNG containment system claimed herein
are not limited in scope by the type of equipment used for the
construction.
[0085] Next, panels forming the side walls 222, 224 are installed
similar to the end wall 212. This means that the side walls 222,
224 are lifted up into vertical position. The side panels are
aligned and braced, and interconnected to form the respective side
walls 222, 224. The side walls 222, 224 are then connected to the
floor slab 250 and the adjoining panels of the end wall 212. In
FIG. 9A, a first wall panel 230' is seen being raised for a side
wall.
[0086] Construction of a roof structure 260 follows closely behind
the side wall construction. In one embodiment, prefabricated
combination roof panels (such as those shown at 260' in FIG. 9B)
are erected onto wall panels 230' as the side walls 222, 224 are
being formed. FIG. 9B presents the placement of a prefabricated
roof panel 260' on the concrete floor slab 250. As sufficient
numbers of side wall panels are installed, the roof truss units
with concrete plates (roof panels 260') are brought in, lifted in
place and structurally connected to the walls 222, 224 and
adjoining roof panels 260'. Construction continues until one end
wall 212, two side walls 222, 224 and a roof structure (seen at 260
in FIG. 9C) is completed.
[0087] FIG. 9C is a cutaway view of the secondary container 200. In
this step, the two opposing side walls 222, 224 have been erected
along the floor slab 250. In addition, a roof structure 260 has
been placed over the span between the two opposing side walls 222,
224 to define the secondary container 200. One end of the secondary
container 200 is left open for installation of the inner tank 300.
A substantially complete primary container 300 has been moved into
its position within the secondary container 200. The inner tank may
be insulated by providing a bottom insulation layer interposed
between the concrete floor slab and steel tank bottom.
[0088] FIG. 9D shows another primary container 300 being rolled
into the secondary container 200. In this respect, a secondary
container may hold more than one primary container, in a linear
arrangement.
[0089] FIG. 9E demonstrates that the second primary container 300
has been substantially moved into the secondary container 200.
Additional insulation materials may be placed in an annular space
(not shown) formed between the inner 300 and outer 200 tanks.
[0090] Finally, FIG. 9F shows the erection of the second vertical
end wall 214 to form the enclosed secondary container 200. The two
parallel tracks 11 have been removed. A full containment LNG
container system 100 has been assembled in an efficient manner. The
above procedure permits parallel construction of the inner 300 and
outer 200 tanks, thus reducing the construction schedule
considerably.
[0091] A description of certain embodiments of the inventions has
been presented above. However, the scope of the inventions is
defined by the claims that follow. Each of the appended claims
defines a separate invention, which for infringement purposes is
recognized as including equivalents to the various elements or
limitations specified in the claims.
* * * * *