LIQUEFIED NATURAL GAS TANK

FIELD OF THE INVENTION

This invention relates to a liquefied natural gas tank and method of construction thereof. In particular, the invention relates to construction of the outer wall of the LNG tank.

BACKGROUND TO THE INVENTION

The demand for natural gas throughout the world is increasing due to its "green" classification. Liquefied natural gas (LNG) is a popular form of natural gas used for both transportation and storage purposes. LNG offers an energy density comparable to petrol and diesel fuel but when utilized produces less pollution. However, it is expensive to transport and store due to the need for the cryogenic tanks. Cryogenic tanks must be used in order to maintain the natural gas at approximately -160 ⁰ C in order to keep the natural gas liquefied.

LNG storage tanks are formed from an open top, inner tank which is used to store the LNG, and an outer tank. The outer tank includes a floor on which sits a circular concrete outer wall which is attached to a roof. A vapour barrier extends around the inner surface of the floor, outer wall and roof. In order to erect a LNG tank, construction is commenced with the formation of the outer concrete wall using a typical jump-form insitu method. Once the concrete wall has been formed, the concrete wall vapour barrier is built adjacent the concrete wall. A roof and associated roof vapour barrier is then constructed to complete the outer tank of the LNG tank. Typically the roof is constructed at ground level and then air raised into place. It is only after the roof has been raised and secured that the construction of the inner tank can take place. This method of construction of a LNG tank is time consuming, labour intensive and expensive.

In order to address some of the above problems, a new method of construction of a LNG tank has been developed. This method includes the erection of an outer tank vapour barrier using thicker mild steel. This produces a vapour barrier which is self supporting and of sufficient strength to support a roof of the outer tank. This enables the inner tank construction to begin earlier in the program. However, construction of the structural vapour barrier adds considerable material and labour expense to the construction of the LNG tank even though it reduces project duration. Accordingly, there is only a small cost reduction in the overall production of the LNG tank. Further, additional risk is endured as the structural vapour barrier must be unable to withstand high wind speeds during construction.

OBJECT OF THE INVENTION

It is an object of the invention to overcome or at least alleviate one or more of the above disadvantages and/or provide the consumer with a useful or commercial choice.

SUMMARY OF THE INVENTION

In one form, although not necessarily the only or broadest form, the invention resides in a prefabricated module for construction of an outer wall of a LNG tank, the prefabricated module comprising:

a vapour barrier plate;

at least one support frame connected to the vapour barrier plate; and

a plurality of reinforcement members attached to the at least one support frame.

Normally the vapour barrier plate is curved.

Preferably the support frame is in the form of a body able to provide additional strength to a vapour barrier plate. The body normally includes a plurality of reinforcement locating holes located through the body for positioning of some of the plurality of reinforcement members.

Normally the body is ladder shaped. The body may include a bottom rail and a top rail. The bottom rail and top rail may be interconnected by interconnecting plates. End plates may interconnect the top rail and the bottom rail adjacent their ends.

Typically the reinforcement locating holes are located through the top rail and/or the bottom rail.

Normally there is also a least one stressing ducting locating hole located through the body for positioning of a stressing duct. The at least one stressing duct locating hole may be located adjacent the intersection of the interconnecting plate and the bottom rail.

The plurality of reinforcement members may include horizontal reinforcement members and/or vertical reinforcement members. Typically only the horizontal reinforcement members or the vertical reinforcement members are attached to the support frame.

The horizontal reinforcement members may include inner horizontal reinforcement members and/or outer horizontal reinforcement members. The inner horizontal reinforcement members may be located through the bottom rail of the support frame. The outer horizontal reinforcement members may be located through the top rail of the support frame.

The vertical reinforcement members may include inner vertical reinforcement members and/or outer vertical reinforcement members. The inner vertical reinforcement members may be joined to the inner horizontal vertical members. The outer vertical reinforcement members may be joined to the outer horizontal vertical members.

The prefabricated module may also include stressing ducts. The stressing ducts may include horizontal stressing ducts and/or vertical stressing ducts. The horizontal stressing ducts may be located through the stressing duct locating holes. The vertical stressing ducts may be joined to the horizontal stressing ducts.

In yet another form, the invention resides in a method of producing a prefabricated module for use in the construction of the outer wall of a LNG tank, the method including the steps:

connecting a plurality of support frames to a vapour barrier plate, and;

connecting a plurality of reinforcement members to the plurality of the support frames.

The method may further include one or more of the steps of: locating a plurality of reinforcement members through the support frame; and

locating a plurality of stressing ducts through the support frame.

The method may still further include the step of using a prefabrication jig to place the support frames onto the vapour barrier.

In yet another form, the invention resides in an outer wall of an

LNG tank comprising:

a plurality of prefabricated modules located adjacent one another, each prefabricated module including a vapour barrier plate; at least one support frame connected to the vapour barrier plate; and a plurality of reinforcement members attached to the at least one support frame; and

a settable material located adjacent the vapour barrier plate and covering the support frames and reinforcing members.

The prefabricated module may include the features specified above.

The settable material may be a cementitious material.

Preferably the cementitious material is concrete.

In yet another form, the invention resides in a method of producing an outer wall of a LNG tank, the method including the steps:

locating a plurality of reinforcement modules adjacent each other; each prefabricated module including a vapour barrier plate, at least one support frame connected to the vapour barrier plate; and a plurality of reinforcement members attached to the at least one support frame; and

pouring a settable material between the vapour barrier and a shutter spaced a distance from the vapour barrier.

Normally the settable material settable material is located adjacent the vapour barrier plate and covers the support frames and reinforcing members.

In yet another form, the invention resides in a support frame for a reinforcement module, the support frame including:

a body able to provide additional strength to a vapour barrier plate; and

a plurality of reinforcement locating holes located through the body for positioning of a plurality of reinforcement members.

Normally the body is ladder shaped. The body may include a bottom rail and a top rail. The bottom rail and top rail may be interconnected by interconnecting plates. End plates may interconnect the top rail and the bottom rail adjacent their ends.

Typically the locating holes are located through the top rail and/or the bottom rail.

Normally there is also at least one stressing duct locating hole located through the body for positioning of a stressing duct. The at least one stressing duct locating hole may be located adjacent the intersection of an interconnecting plate and the bottom rail.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment, by way of example only, will be described with reference to the accompanying drawings, wherein:

FIG. 1 is a perspective view of a LNG tank constructed using prefabricated modules;

FIG. 2 is a perspective view of a prefabricated module for use in the construction of an outer wall of the LNG tank shown in FIG. 1 ;

FIG. 3a is a perspective view of a vapour barrier with welded support frames located in a fabrication jig;

FIG. 3b is a top view of a vapour barrier with welded support frames located in a fabrication jig;

FIG. 3c is a side view of a vapour barrier with welded support frames located in a fabrication jig;

FIG. 4a is a perspective view of inner vertical reinforcement being placed on the vapour barrier plate;

FIG. 4b is a top view of inner vertical reinforcement being placed on the vapour barrier plate;

FIG. 4c is a side view of inner vertical reinforcement being placed on the vapour barrier plate;

FIG. 5a is a perspective view of horizontal reinforcement being located through the support frames; FIG. 5b is a top view of horizontal reinforcement being located through the support frames;

FIG. 5c is a side view of horizontal reinforcement being located through the support frames;

FIG. 6a is a perspective view of horizontal stressing ducts being located over the holes on all stressing ducts;

FIG. 6b is a top view of horizontal stressing ducts being located over the holes on all stressing ducts;

FIG. 6c is a side view of horizontal stressing ducts being located over the holes on all stressing ducts;

FIG. 7a is a perspective view of vertical stressing ducts being located over the holes on all stressing ducts;

FIG. 7b is a top view of vertical stressing ducts being located over the holes on all stressing ducts;

FIG. 7c is a side view of vertical stressing ducts being located over the holes on all stressing ducts;

FIG. 8a is a perspective view of outer horizontal reinforcement being located through the support frames;

FIG. 8b is a top view of outer horizontal reinforcement being located through the support frames;

FIG. 8c is a side view of outer horizontal reinforcement being located through the support frames;

FIG. 9a is a perspective view of outer vertical reinforcement being laid on top of the outer horizontal reinforcement;

FIG. 9b is a top view of outer vertical reinforcement being laid on top of the outer horizontal reinforcement;

FIG. 9c is a side view of outer vertical reinforcement being laid on top of the outer horizontal reinforcement;

FIG. 10 is a perspective view of a completed prefabricated module with lifting beam;

FIG. 11a is a perspective view of a partially completed outer wall of a LNG tank; FIG. 11b is a side view of a partially completed outer wall of a LNG tank;

FIG. 12a is a perspective view of a partially completed a LNG tank with additional upper prefabricated modules being added;

FIG. 12b is a side view of a partially completed a LNG tank with additional upper prefabricated modules being added;

FIG. 13a is a perspective view of a partially completed of a LNG tank with shutters added;

FIG. 13b is a side view of a partially completed of a LNG tank with shutters added;

FIG. 14a is a perspective view of a partially completed outer wall of a LNG tank after concrete has been poured to the height of the shutters;

FIG. 14b is a side view of a partially completed outer wall of a LNG tank after concrete has been poured to the height of the shutters;

FIG. 15a is a perspective view of a partially completed outer wall of a LNG tank after concrete has been poured with the shutters at a higher height;

FIG.15b is a side view of a partially completed outer wall of a LNG tank after concrete has been poured with the shutters at a higher height;

FIG. 16a is a perspective view of a partially completed outer wall of a LNG tank after concrete has been poured with the shutters at still a higher height;

FIG.16b is a side view of a partially completed outer wall of a LNG tank after concrete has been poured with the shutters at still a higher height;

FIG. 17a is a perspective view of a partially completed outer wall of a LNG tank after concrete has been poured with the shutters at yet still a higher height;

FIG.17b is a side view of a partially completed outer wall of a

LNG tank after concrete has been poured with the shutters at yet still a higher height; FIG. 18a is a perspective view of a partially completed outer wall of a LNG tank after concrete has been poured with the shutters at a higher height again;

FIG.18b is a side view of a partially completed outer wall of a LNG tank after concrete has been poured with the shutters at a higher height again;

FIG. 19a is a side view of a support frame used in the prefabricated module of FIG. 2;

FIG. 19b is a detail view of a support frame used in the prefabricated module of FIG. 2;

FIG. 19c is a detail view of a two support frames being joined together;

FIG. 20 is a perspective view of a shutter;

FIG. 21a is a perspective view of a prefabricated "pilstar" module for use in the construction of an outer wall of the LNG tank;

FIG. 21b is a side view view of a prefabricated "pilstar" module for use in the construction of an outer wall of the LNG tank; and

FIG. 21c is a top view of a prefabricated "pilstar" module for use in the construction of an outer wall of the LNG tank.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows a perspective view of an LNG tank 10. The perspective view shows a cylindrical outer wall 11 with an attached roof 12 forming an outer tank of the LNG tank. The outer wall is formed from a series of prefabricated modules 100.

FIG. 2 shows a cutaway of part of the outer wall 11 revealing a prefabricated module 100 embedded in concrete 110. The outer wall 11 is formed by several hundred prefabricated modules 100 which are joined together. Each prefabricated module 100 includes a vapour barrier plate 120, support frames 130, inner vertical reinforcement bars 140, inner horizontal reinforcement bars 150, outer vertical reinforcement bars 160, outer horizontal reinforcement bars 170, horizontal stressing ducts 180 and vertical stressing ducts 190. The vapour barrier plate 120 is 6 metres wide by 4 metres high. However, it should be appreciated that the dimensions of the vapour barrier plate 120 may be varied in accordance with design. The thickness of the vapour barrier plate 120 again will be dependent upon design features, such as pour size, expected site temperature, pour rate and mix design. The vapour barrier plate 120 is made from mild steel.

The support frames 130 are connected to the vapour barrier plate 120. The support frames 130, shown in more detail in FIGS. 19a to 19c, include a ladder shaped body 131 having a top rail 132, bottom rail 133, end plates 134 and interconnecting plates 135. The top rail 132 and bottom rail 133 have a series of reinforcement locating holes 136 that extend along the length of the respective top rail 132 and bottom rail 133. A series of stressing duct locating holes 137 are located adjacent the intersection of the interconnecting plates 135 and bottom plates 133. The end plates 135 have joining holes 138 that extend through the end plates 135 to allow adjacent prefabricated modules 100 to be aligned and joined to each other. A series threaded shutter 139 attachment holes are located along the top rail for attachment of shutters.

The inner vertical reinforcement bars 140, inner horizontal reinforcement bars 150, outer vertical reinforcement bars 160 and outer horizontal reinforcement bars 170 are all standard reinforcement bars used in reinforced concrete. The inner vertical reinforcement bars 140 and the outer vertical reinforcement bars 160 are longer than the width of the vapour barrier plate 120 whilst the inner horizontal reinforcement bars 150 and the outer horizontal reinforcement bars 170 are slightly shorter than the length of the vapour barrier plate 120.

The inner horizontal reinforcement bars 150 are located through the reinforcement locating holes 136 located in the bottom rails 133 of the support frames 130 whilst the outer horizontal reinforcement bars 170 are located through the reinforcement locating holes 136 in the top rails 132 of the support frames 130. Both the inner horizontal reinforcement bars 150 and the outer horizontal reinforcement bars 170 are tied to the support frames 130 with some of the outer horizontal reinforcement bars 170 being welded to support frames 130. The inner vertical reinforcement bars 140 are tied to the inner horizontal reinforcement bars 150 whilst the outer vertical reinforcement bars 160 are tied to the outer horizontal reinforcement bars 170.

The horizontal stressing ducts 180 and the vertical stressing ducts 190 are made from hollow galvanized metal tube which has a spiral tread pressed along its length. However, it should be appreciated that other types of stressing duct materials may be used. The horizontal stressing ducts 180 are slightly shorter than the length of the vapour barrier plate 120 whilst the vertical stressing ducts 190 are slightly shorter than the width of the vapour barrier plate 120.

The horizontal stressing ducts 180 are located through the stressing duct locating holes 137 located adjacent the intersection of the interconnecting plates 135 and bottom plate 137. The vertical stressing ducts 190 are tied to the horizontal stressing ducts 180.

In order to produce a prefabricated module 100, the vapour barrier plate 120 is located on a prefabrication jig 20. Once the vapour barrier plate 120 is positioned on the prefabrication jig 20, four support frames 130 are located in predetermined positions across the width of the vapour barrier plate 120 as shown in FIGS. 3a to 3c. The joining holes 138 in the end plates are aligned with associated holes 21 in brackets 22 and the prefabrication jig 20 to ensure that each of the support frames 130 are in their required position. This method of placing the support frames 130 on the vapour barrier plate 120 ensures repeatability for each prefabricated module 100. The support frames 130 are then welded to the vapour barrier plate 120 along the bottom rail 133 of the support frame 130.

The next step is to place inner vertical reinforcement bars 140 atop the vapour barrier plate 120 as shown in FIGS. 4a to 4c. As the length of the vertical reinforcement bars 140 is longer than the length of the vapour barrier plate 120, an end of the inner vertical reinforcement bars 140 extends past an end of the vapour barrier plate 120. The inner vertical reinforcement bars 140 are slightly offset with respect to "true vertical" using guides (not shown). This offsetting of the inner vertical reinforcement bars 140 assists in alignment of adjacent prefabricated modules 100 when positioned on top of each other.

After the inner vertical reinforcement bars 140 are positioned on top of the vapour barrier plate 120, inner horizontal reinforcement bars 150 are installed as shown in FIGS. 5a to 5c. This installation is conducted by locating the inner horizontal reinforcement bars 150 through the reinforcement locating holes 136 located in the bottom rail 133 of the support frames 130. This ensures that the inner horizontal reinforcement bars 150 are located precisely for each prefabricated module 100. The inner horizontal reinforcement bars 150 are then secured to the support frames 130 by tie wire. The inner vertical reinforcement bars 140 are then secured to the inner horizontal reinforcement bars 150 also by tie wire.

FIGS. 6a to 6c show horizontal stressing ducts 180 being located through the horizontal stressing duct locating holes 137 formed within the support frames 130. FIGS. 7a to 7c show vertical stressing ducts 190 located on top of the horizontal stressing ducts 180. Once the vertical stressing ducts 190 are placed on top of the horizontal stressing ducts 180, they are secured in place using metal ties. Alignment guides (not shown) are used for this purpose.

The next step is to locate outer horizontal reinforcement bars 170 through reinforcement locating holes 136 in the top rail 132 of the support frames 130 as shown in FIGS. 8a to 8c. Again, the outer horizontal reinforcement bars 170 are secured to the support frame 130 by tie wire. However, it is envisaged that some of the outer horizontal reinforcement bars 170 may be welded to the support frames 130. This is to assist in preventing distortion of the prefabricated modules 100 during both transport and installation.

Once the outer horizontal reinforcement bar 170 is in place, outer vertical reinforcement bars 160 are placed atop the outer horizontal reinforcement bars 170 and secured with tie wire as shown in FIGS. 9a to 9c. Again, the outer vertical reinforcement bars 160 are offset in a similar manner to the inner vertical reinforcement bars 140 to ensure that each outer vertical reinforcement bar 160 can align with adjacent outer vertical reinforcement bars 160 in a lower prefabricated module 100 without clashing.

The reinforcement module 100 is then completed, as shown in

FIG. 10, and therefore ready for transportation and installation. A lifting beam 195 is used to lift the reinforcement module at this stage. The lifting beam 195 is attached to the end plates of the support frames using fasteners (not shown) which pass through the joining holes 138 and the lifting beam 195.

FIGS. 11a and 11b shows a partially completed partial outer wall 11 of a LNG tank. That is, the lower part of the outer wall 11a has been completed. The lower part of outer wall 11 shown uses two lower prefabricated modulesiOOa which have been embedded in concrete. That is, the support frames 130, inner vertical reinforcement bars 140, inner horizontal reinforcement bars 150, outer vertical reinforcement bars 160, outer horizontal reinforcement bars 170, horizontal stressing ducts 180, and vertical stressing ducts 190 have been covered in concrete. It should be appreciated that the inner vertical reinforcement bars 140, outer vertical reinforcement bars 160, vertical stressing ducts 190 and support frames 130 of the lower prefabricated modules 100a all partially extend out of the concrete 200 to be joined to an upper prefabricated module 100b.

The next step in erecting of the outer wall 11 of the LNG tank is to locate upper prefabricated modules 100b on to the lower prefabricated modules 100a and then join the lower prefabricated modules 100a and upper prefabricate modules 100b together as shown in FIGS. 12a to 12b. The first step is to align the end plates 134 of the support frames 130 of the lower prefabricated modules 100a with end plates 134 of the support frames 130 of the upper prefabricated modules 100b as shown in FIG. 19c. Fasteners are then used to fasten the end plates 134 together.

As the inner vertical reinforcement bars 140 and outer vertical reinforcement bars 160 are offset on each prefabricated module 100a, the inner vertical reinforcement bars 140 and the outer vertical reinforcement bars 160 of the lower prefabricated module 100a are located adjacent the inner vertical reinforcement bars 140 and the outer vertical reinforcement bars 160 of the upper prefabricated module 100b. The inner vertical reinforcement bars 140 and outer vertical reinforcement bars 160 can then easily be tied together using tie wire.

Similarly, as the vertical stressing ducts 190 of both the lower prefabricated modules 100a and the upper prefabricated modules 100b are located adjacent each other, couplers (not shown) and duct tape (not shown) are simply used to join the vertical stressing ducts 190 together.

The next step is to join adjacent upper prefabricated modules 100b together. This involves joining the inner horizontal reinforcement bars 150 and outer horizontal reinforcement bars 170 of adjacent upper prefabricated modules 100b together using lacer bars 220 as shown in FIG. 2. Similarly, as the horizontal stressing ducts 180 of adjacent upper prefabricated modules 100b are located adjacent each other, couplers (not shown) and duct tape (not shown) are simply used to join the horizontal stressing ducts 180 together.

Once the joining of both lower prefabricated modules 100a and the upper prefabricated modules 100b, and adjacent upper prefabricated modules 100b has been completed, external shutters 210 are located over the reinforcement modules 100a and 100b as shown is FIGS. 13a and 13b.

The shutters 210, as shown in more detail in FIG. 20, are relatively short (compared to standard height shutters) and are made of aluminum. This enables a team of 3 men to assemble and disassemble the shutters 210 removing the need for a crane.

The shutters 210 are attached by six threaded wing nuts 211 to the reinforcement module 100. Four wing nuts 211 are attached to the reinforcement module 100 via shutter attachment holes 139 which form part of the support frame 130. These wing nuts 211 are located in the corners of the shutters 210. The other two wind nuts 211 are attached to the outer vertical reinforcement bars using a standard J-bar arrangement. Spacers 212 are used on the ends of each of the wing nuts to ensure the correct outer wall thickness. The shutters are attached to each other using a standard dog and wedge arrangement 213.

After the shutters 210 are in place, concrete is poured between the shutters 210 and the vapour barrier plates 120 as shown in FIGS. 14a to 14b. It should be appreciated that only a section of the outer wall 11 is shown. During a pour, the entire circumference of the outer wall 11 is poured at once. Hence, shutters 210 extend around the entire circumference of the outer wall 11. Accordingly, the height of the pours may only be relatively short but the volume of concrete pour is relatively standard.

Once the concrete is sufficiently cured, the shutters 210 are moved upwardly and the process repeated as shown in FIGS. 15a and 15b through FIGS. 18a to 18b. At each upward movement of each shutter 210, what was the old upper shutter attachment hole is now the new lower shutter attachment hole. This ensures quick and accurate placement of the shutters 210 at each height change. It should also be appreciated that the shutter attachment holes 139 are also used to support the working platforms 230.

Additional prefabricated modules 100 can then be added, as described above, to increase the height of the outer wall 11 until the desired height of the outer wall 11 is achieved.

It should be appreciated that prefabricated modules may be varied depend in requirements. For example, FIGS. 21a to 21c show prefabricated "Pilistar" module 101 which is used for post-stressing the outer wall. It would be appreciated by persons skilled in the art that "pilstars" have been used for post-stressing of outer walls of LNG tanks for some time. The prefabricated "pilistar" module has all of the components of a standard prefabricated module 100 except that the some of the support frames 130 extend further outwardly from the vapour barrier 120, the outer horizontal reinforcement bars 170 are not straight and bend to correspond to the support frames 130, and the horizontal stressing ducts 180 terminate at a front face of the prefabricated "pilistar" module. The prefabricated "pilistar" modules are typically located at 0, 90, 180 and 270 degrees of the outer wall. The method of constructing an outer wall using prefabricated modules provides definite advantages. Firstly, the prefabricated modules can be produce offsite and transported to the site. This allows for saving in both time and labour costs. Further, the duration of the build time for the outer wall can be shortened. The prefabricated modules can be produced at the same time (or ahead of time) as the outer wall is being erected.

It should be appreciated that various other changes and modifications may be made to the embodiment described without departing from the spirit or scope of the invention.