STORAGE TANK CONTAINMENT SYSTEM

Abstract

A storage tank containment system including a cubic-shaped tank having an outer shell having cylindrical walls and an internal cross brace interconnecting the cylindrical walls for the efficient storage and transportation of large quantities of fluid, for example, liquid natural gas.

Description

FIELD OF THE INVENTION

The invention generally pertains to storage tanks and more particularly to storage tanks for fluids including liquids and gases.

BACKGROUND

Industrial storage tanks used to contain liquids or compressed gases are common and are vital to industry. Storage tanks may be used to temporarily or permanently store fluids at an on-site location or may be used to transport the fluids over land or sea. Numerous inventions in the structural configurations of fluid storage tanks have been made over the years. One example of a non-conventional fluid storage tank having a cube-shaped configuration and support structure is found in U.S. Pat. No. 3,944,106 to Thomas Lamb, the entire contents of the patent are incorporated herein by reference.

There has been a progressive demand for the efficient storage and long distance transportation of fluids such as liquid natural gas (LNG), particularly over seas by large ocean-going tankers or carriers. In an effort to transport fluid such as LNG more economically, the holding or storage capacity of such LNG carriers has increased significantly from about 26,000 cubic meters in 1965 to over 200,000 cubic meters in 2005. Naturally, the length, beam and draft of these super carriers have also increased to accommodate the larger cargo capacity. The ability to further increase the size of these super carriers, however, has practical limits in the manufacture and use.

Difficulties have been experienced in the storage and transportation of fluids, particularly in a liquid form, through transportation by ocean carriers. A trend for large LNG carriers has been to use large side-to-side membrane-type tanks and insulation box supported-type tanks. As the volume of transported fluid increases, the loads on the tank containment walls increases significantly. These membrane and insulation type of tanks suffer from disadvantages of managing the “sloshing” movement of the liquid in the tank due to the natural movement of the carrier through the sea. As a result, the effective holding capacity of these types of tanks has been limited to either over 80% full or less than 10% full to avoid damage to the tank lining and insulation. The disadvantages and limitations of these tanks are expected to increase as the size of carriers increase.

The prior U.S. Pat. No. 3,944,106 tank was evaluated for containment of LNG in large capacities, for example, in large LNG ocean carriers against a similar sized geometric cube tank. It was determined that the '106 tank was more rigid using one third the wall thickness of the geometric cube. The '106 tank further significantly reduced the velocity of the fluid, reduced the energy transmitted to the tank and reduced the forces transmitted by the fluid to the tank causing substantially less deformation of the tank compared to the geometric cubic tank.

It was further determined, however, that the '106 configured tank did not prove suitable to handle large capacities of LNG in a large LNG carrier environment.

Therefore, it would advantageous to design and fabricate storage tanks for the efficient storage and transportation of large quantities of fluids such as LNG across land or sea. It is further desirable to provide a storage tank that is capable of being fabricated in ship yards for large tankers that further minimizes the number of components and minimizes the different gages or thickness of materials that are needed for the tank. It is further advantageous to provide a modular-type tank design which facilitates design, fabrication and use in the field.

SUMMARY

The inventive storage tank containment system includes a six-sided generally cube-shaped outer shell and an internal cross-brace interconnecting at least five of the six sides of the storage tank.

In one example, the outer shell of the tank includes twelve substantially identical cylindrical-shaped walls interconnected to one another at opposing edges. The outer shell further includes eight spherical-shaped end caps closing the corners of the cube-shaped tank. The internal cross brace structurally reinforces the cylindrical walls and further distributes the loads due to containment and movement of the fluid contents.

In an alternate example, a different internal cross brace is used which includes a structurally reinforced column, angularly opposed side brackets and end reinforcements.

In another alternate example, cross brace side extensions are used with the internal cross brace along with a base plate to transfer and support the loads of the tank to the fore, aft and transverse bulkheads and tank top of the cargo hold, for example, in a large ocean carrier.

The particular design of the tank base support and extensions provides advantages to support the weight of the tank and its contents and to laterally position the tank center at the same location as the tank thermally contracts, for example, as the low temperature liquid is loaded into it. Above each slot, a locking plate may be provided to prevent the extension from moving out of the mounting slot in a ship due to motion in heavy seas.

Other applications of the present invention will become apparent to those skilled in the art when the following description of the best mode contemplated for practicing the invention is read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The description herein makes reference to the accompanying drawings wherein like reference numerals refer to like parts throughout the several views, and wherein:

FIG. 1 is schematic perspective view of an example of a stand alone tank containment system;

FIG. 2 is partial schematic of the tank in FIG. 1 with the exemplary spherical end caps removed showing part of the internal tank;

FIG. 3 is a perspective view of one cylindrical wall component of the tank in FIG. 2;

FIG. 4 is a partial exploded view of an alternate example of the tank shown in FIG. 2 where the spherical ends caps are deleted;

FIG. 5 is a perspective view of one example of an internal cross brace;

FIG. 6 is a perspective view of an alternate example of an internal cross brace;

FIG. 7 is a schematic perspective view of an alternate storage tank containment system with an alternate cross brace and cross brace side extensions;

FIG. 8 is a schematic perspective view of the bottom side of the tank shown in FIG. 7;

FIG. 9 is a partial cut-away side view of the alternate tank and cross brace shown in FIG. 7;

FIG. 10 is a schematic side view of the tank shown in FIG. 7 installed in a marine vessel cargo hold area;

FIG. 11 is an enlarged view of a portion of FIG. 10;

FIG. 12 is a partial top view of the storage tank shown in FIG. 10 as viewed from direction A in FIG. 11;

FIG. 13 is a schematic side view taken from the view of arrow B in FIG. 12 showing the side extension positioned in a slot in a cargo hold;

FIG. 14 is a perspective view of an alternate example of the side extensions shown in FIG. 7;

FIG. 15 is a schematic perspective view of an alternate internal cross brace; and

FIG. 16 is a schematic side view of an example of an ultra-large LNG carrier with four storage tanks positioned in respective cargo holds.

DETAILED DESCRIPTION

Several examples of the storage tank containment system in explementary uses are shown in FIGS. 1-16. Referring to FIGS. 1 and 2, the containment system includes a storage tank 10 having a generally six-sided cubic configuration. Tank 10 includes twelve independent, substantially identical cylindrical walls 30. The cylindrical walls 30 are arranged to include four vertical cylindrical walls 34 and eight horizontal cylindrical walls 40 generally arranged and configured as shown in FIG. 2. The cylindrical walls 30 form an outer shell of tank 10 having six sides including a top side 14, bottom side 18 and four intermediate sides 20. The combined cylindrical walls define a interior storage chamber 66 for containment of materials or preferably fluids including liquids and/or gases maintained at or above atmospheric pressure.

As best seen in FIG. 3, each cylindrical wall 30 includes a cylindrical-shaped center portion 46 having first ends 50, adjacent edges 52 and second ends 56. As shown in FIG. 2, each cylindrical wall 30 interconnects with four adjacent cylindrical walls through edges 52. In one preferred example of the construction of tank 10, localized regions 80, where the cylindrical walls 30 connect to each other, may be constructed of a higher gage wall thickness. Similarly the remainder of the cylindrical walls 30 may be constructed of lower gage plating. This may be accomplished through tailor-welded blanks or other manufacture or assembly methods known by those skilled in the art.

In one preferred example shown in FIG. 1, eight end caps 60 are used to sealingly close the eight corners of the cubeshaped tank 10. End caps 60 are spherical in shape and complimentary to the shape and orientation of the three adjacent cylindrical walls 30, namely, two horizontal cylindrical walls 46 and a vertical cylindrical wall 34. In this configuration, the cylindrical walls 30 form a tank side opening 64 on each of the six sides of tank 10. One or more entry ports (not shown) to access the interior storage chamber 66 may be used to efficiently fill, extract and monitor the tank contents.

Referring to FIG. 4, an alternate example of the outer shell of tank 10 is shown. In this example, each of the alternate cylindrical walls 70 includes corner portions 74 eliminating the need for end caps 60 shown in FIG. 1.

Referring to FIG. 5, tank 10 includes an internal cross brace 84. Internal cross brace 84 generally includes six brackets 98 angularly orientated with respect to one another for preferable connection to each of the six sides of tank 10 defined by cylindrical walls 30 as more fully described below. The two vertical oriented brackets 98 form a column 100 having an upper end 104 and lower end 108 defining a first axis 110. Brackets 98 forms a first side brace 112 defining a second axis 118 and a second side brace 114 defining a third axis 120. The first, second and third axes meet at a center point (not shown). In a preferred example, the center point is positioned at approximately the center of gravity of the tank 10. Internal cross brace 84 is positioned between the six sides of tank 10 exterior to the internal storage chamber 66 containing the preferred fluid. The internal cross brace 84 can be either tubular or a built up I-beam cross section (not shown).

Internal cross brace 84, and more particularly the four ends 116 on the first side brace 112 and second side brace 114 are connected to cylindrical walls 30 at the side openings 64 on each of the four sides, and top and bottom as best seen in FIG. 5. The rigid structural connections between each cylindrical wall 30 and internal cross brace 84 provide a significantly more robust, structurally reinforced tank 10 over prior tanks.

In a preferred example of materials for exemplary tank 10 shown in FIGS. 1-3 and 5, cylindrical walls 30, end caps 60, and internal cross brace 84 are all manufactured from nickel steel and have varying gage or thickness which is dependent upon the location of the plating, size and anticipated contents of the tank to suit the anticipated stresses in the plating or tank components. The respective components may be connected together through continuous seam welds along all connecting joints for strength and sealability of the tank. It is understood that different materials, gages and methods of connection known by those skilled in the art may be used.

In an exemplary design as generally shown in FIGS. 1 and 2 with an internal cross brace substantially as shown in FIG. 5, a suitable construction of a tank 10 may have the following characteristics. For a very large tank, for example an ultra-large LNG ocean carrier, a tank measuring approximately 36.6 meters each in length, width and height may be used. The tank may be manufactured from nickel steel with a modulus of 210,000 MPa and a poison ratio of 0.3. Other materials may be used to form tank 10 including aluminum or selected steels. The contents may be liquid natural gas (LNG) having a specific gravity of 0.5 occupying approximately 95% of the tank 10 usable volume. In this example, analytical testing indicated areas of higher stress in the tank 10 at the joints of the cylindrical walls 30 and region 80 of the cylindrical walls 34 and 40 due to hydrostatic pressure loads on the tank.

In a preferred alternate example of tank 10, as best seen in FIGS. 2 and 6-13, alternate tank 10 design includes an alternate cross brace 122 and side reinforcements 162. This alternate design discloses exemplary ways for increasing the stress capabilities of the tank and connecting the internal cross brace to an exemplary carrier hull structure. Referring to FIGS. 2 and 6, the alternate tank 10 includes twelve substantially identical cylindrical walls 30 and end caps 60 as previously described. The alternate cross brace 122 comprises of a column 124 including a first wall 126 and second wall 128 positioned approximately perpendicular to one another defining a first axis 110. Cross brace 122 further includes a base 132 and base reinforcements 136 connected to the lower portion of column 124. Internal cross brace 122 further includes an alternate first brace 137 and a alternate second brace 138 defining a second axis 118 and a third axis 120 respectively. The first, second and third axes converge at a center point as previously described.

In the preferred example, each of the first 137 and second 138 braces include top and bottom plate 140 and an inner wall 142 as generally shown. Inner wall 142 may form two separate inner walls as shown.

In a preferred example, each of the first 137 and second 138 braces may include an extension 150 extending axially outward from inner wall 142 along second 118 and third 120 axes. Extensions 150 may each include a pair of side walls 154 and top and bottom plates 155 extending axially outward from inner wall 142 terminating at ends 158. As shown in FIGS. 6 and 9, extension 150 may project slightly beyond tank side 20 for connection of tank 10 to the inner walls of a cargo hold as further described below.

In a preferred examples shown in FIGS. 6, 7 and 9, on each of the four sides 20 of tank 10, four alternate side reinforcements 162 are rigidly attached to extensions 150 and project axially and radially outward from second 118 and third 120 axes to substantially compliment the curved outer surfaces of the cylindrical walls 30 as best seen in FIG. 7. Base 132 of column 124 and reinforcements 136 serve to reinforce the bottom 18 of tank 10.

Referring to FIG. 8, alternate tank 10 may include a base plate 170 used to structurally connect tank 10 to the floor or hull of a cargo hold in a ocean carrier or other transportation device. In the example, cross brace base column 124, base 132 and base reinforcements 136 are rigidly connected to base plate 170. These structures, along with side reinforcements 162 on bottom 18, provide vertical and lateral support of tank bottom 18 and tank 10 in an exemplary cargo hold of a large LNG ocean carrier.

Referring to FIGS. 7, 9-12 an alternate internal cross brace 122 side extension 190 is shown differing from extensions 150 shown in FIG. 6. In the example, alternate side extensions 190 include a bevel 196 preferably facing toward the bottom 18 of the tank 10 and are rigidly connected to end reinforcements 162 as previously described. Alternate side extensions 190 are preferably located in a slot 203 in cargo hold bulkhead 200 defined by bulkhead sides 202, angled support surface 204 and hull side 208. Bulkhead 200, sides 202, and an angled support surface 204, allow the tank lateral extensions 190 to slide down the bulkhead sloped surface 204 (gap shown between 196 and 204 for purposes of illustration only) to accommodate any reduction in tank size due to thermal contraction, for example when cold fluids are loaded in to the tank. A vertical locking plate (not shown) may be positioned above extensions 190 in slot 203 to prevent vertical movement of extension 190 once installed. Alternatively, extensions 190 may be securely attached to the bulkheads or hull.

Referring to FIG. 14, an alternate side extension of internal cross brace 122 is shown. In the example, walls 154, as shown in FIG. 6, are illustrated. In addition, a reinforcement 160 is added axially extending from end 144 to attach to a hull or cargo hold bulkhead as previously described.

Referring to FIG. 15, an alternate internal cross brace 214 is illustrated. Alternate cross brace 214 preferably includes a column 216, a first side brace 220 and a second side brace 222. Similar to FIG. 6, cross brace 214 includes first 120, second 118 and third 120 axes. As generally illustrated, cross brace 214 includes a general I-beam construction and connects to the six sides of the tank 10 (not shown) in a similar method as previously described. Cross brace 214 preferably includes several reinforcement gussets 226 (six shown in FIG. 15) and plates 230 (six shown) to reinforce the I-beam column, side braces and cross brace as generally shown. Cross brace 214 may further connect to the hull or bulkheads of a transportation vehicle in a manner as further described below

Referring to FIGS. 10-13, tank 10 in an exemplary use in a large LNG carrier, may be positioned in a cargo hold or cargo bay area 206 of a carrier vessel 198 or other transportation vehicle. In the preferred example, tank 10 is pre-fabricated and lowered by crane into, or is integrally built into, a cargo hold 206. Tank 10 is vertically supported by base plate 170 which rests on the cargo floor. Cross brace side extensions 190, including preferred beveled 196, are positioned between bulkhead sides 202 and placed in supporting contact with bulkhead surface 204 to lock the tank in a lateral position even as the tank overall dimensions vary with varying cargo temperature. This support and securing design substantially eliminates the need for any mechanical connection. In this position, tank 10 is supported vertically and laterally in cargo hold 206 for receipt and containment of a solid or fluid, for example LNG, for transportation over land or sea. The structural container tank 10 may be filled with, for example, LNG in a range from empty up to about 95 percent of the capacity of internal storage chamber 66.

The tank 10 may be filled with, for example, LNG to a capacity of about 95 percent of the internal storage chamber 66. As shown in the chart below, the volumetric efficiency of a tank 10 design (the CDTS) is compared with prior tank designs and a proposed PRISM membrane tank system (Nobel 2005). Comparing the tanks to a solid cube of 49,108 cubic meters, the respective volumes and efficiencies are shown.

TABLE 1
COMPARISON OF TANK VOLUMETRIC EFFICENCY
	Tank Type	Volume	Efficiency
	Prismatic Self-Standing	46,162	0.94
	Membrane	43,706	0.88
	Membrane PRISM	38,304	0.78
	CDTS	40,000	0.8145
	Sphere	25,713	0.5236

The table shows that the tank 10 (CDTS) is 60% more efficient than a comparable spherical tank and an improvement over the PRISM tank design.

Further, use of a large marine carrier or ship cargo space was also compared. The below table shows the cargo hold space required by each of the below tank designs compared for a 138,000 and 400,000 cubic meter carrier. The numbers in parentheses show the percentage comparison with a membrane tank-type lining system.

TABLE 2
COMPARISON OF HOLD SPACE REQUIRED BY PRISMATIC,
MEMBRANE, SPHEREICAL AND CDTS
			Depth	Space
	Length	Breadth	To Cover	Usage
CAPACITY 138,000 m3
Prismatic Self Standing	176 (95)	44 (100)	35 (103)	0.51 (106)
Membrane Original	186 (100)	44 (100)	34 (100)	0.48 (100)
Spherical	192 (103)	48 (109)	43 (126)	0.35 (73)
CDTS	168 (90)	41 (93)	41 (121)	0.49 (102)
CAPACITY 400,000 m3
Prismatic Self Standing	240 (94)	64 (100)	49 (102)	0.53 (104)
Membrane Original	255 (100)	64 (100)	48 (100)	0.51 (100)
Spherical	285 (138)	67 (105)	57 (119)	0.37 (73)
CDTS	230 (94)	58 (91)	58 (121)	0.52 (102)

The table shows that there are significant size reductions and an increase in percentage of use attainable in a large marine carrier using tank 10 over certain tank systems.

In a preferred example and method of fabrication, the respective components of alternate tank 10 shown in FIGS. 6-13, are preferably fabricated from nickel steel from substantially varying gage suitable for the application and are seam welded as previously described. It is understood that tank 10 maybe fabricated in different sizes, and be fabricated and assembled using alternate material and attachment techniques suitable for the particular contents and application.

The tank 10 includes numerous other advantages over prior tanks. Exemplary advantages of tank 10 include: flexibility on the amount of fluid contained ranging from about 5 to about 95 percent of the tank capacity; there is no need to stage the cargo hold to apply insulation and lining to the cargo hold; there is no need for significant welding of the insulation and lining securing strips and the lining onboard a ship; the tank 10 can be installed in one piece at the most efficient time in the ship production process; tank 10 can be constructed of different materials and is modular in design; tank 10 can be produced at many ship and transportation vehicle build sites using conventional tools; tank 10 can be leak tested before installation in a ship or transportation vehicle; tank 10 is not subject to the level of damage from dropped items as compared to membrane tank containment systems and tank 10 requires a smaller base support “foot print” compared to spherical tanks circumferential skirts. Other advantages known by those skilled in the art may be achieved.

While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiments but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as is permitted under the law.

Claims

1. A storage tank comprising: an outer shell defining six interconnected tank sides defining an interior storage chamber;a cross brace positioned between the six sides and interconnecting at least four of the six sides.

2. The storage tank of claim 1 wherein the outer shell is cubical in shape and comprises twelve substantially identical cylindrically-shaped walls that each connect to the cross brace and four of the adjacent cylindrical walls.

3. The tank of claim 2 further comprising eight spherical end caps, each end cap positioned at one of eight corners of the cubical tank sealingly connecting to three of the adjacent cylindrical side walls.

4. The tank of claim 1 wherein the cross brace further comprises a column connected to two opposing sides of the tank defining a top side and bottom side of the tank, the cross brace further having a first and a second side bracket connected to the column and angularly positioned with respect to one another, the column and the first and second side brackets each connecting to a different of the six sides of the outer shell.

5. The tank of claim 4 further comprising four side extensions, each extension extending axially outward from one of the cross brace side brackets for connection to a bulkhead of a ship or transportation vehicle.

6. An improved cubic storage tank for use in a ship or transportation vehicle, the storage tank including twelve interconnected cylindrical walls and eight spherical end caps defining six sides of the cubic tank and an interior storage chamber, the improved storage tank comprising: a cross brace positioned between the six sides and interconnecting all six sides of the cubic tank.

7. The improved tank of claim 6 wherein the cross brace further comprises a column connecting two of the six sides defining a top side and a bottom side of the tank, and a first and a second side brace angularly positioned relative to one another and connected to the column and adjacent sides of the tank.

8. The improved tank of claim 7 wherein each side brace includes a top plate, a bottom plate and an inner wall.

9. The improved tank of claim 7 further comprising a base plate connecting to a lower portion of the cross brace column for connection of the tank at the bottom side to a bulkhead of a transportation vehicle.

10. The improved tank of claim 7 wherein at least two of the side braces includes a brace extension extending axially outward from the tank side for connection of the tank to an adjacent bulkhead of a transportation vehicle.

11. The improved tank of claim 10 wherein each extension includes four side reinforcements extending axially and radially outward from the side brace and connecting to an adjacent cylindrical wall.

12. The improved tank of claim 9 wherein at least one side brace comprises at least two side extensions on opposing ends, each extension including a beveled surface for lateral supporting connection of the tank to the bulkhead.

13. A method of fabricating a cubic storage tank comprising the steps of: providing twelve substantially identical cylindrical walls interconnecting to one another at their edges defining six sides of the tank and an interior storage chamber; andproviding a cross brace positioned between the six sides and connecting to each of the six sides.

14. The method of claim 13 further comprising the step of providing eight spherically shaped end caps, each end cap attached to three adjacent cylindrical walls to form a sealed tank for the storage of fluids.

15. The method of claim 13 further comprising the step of providing four extensions connected to the cross brace for supporting the tank on bulkheads in a ship or transportation vehicle.

16. The method of claim 15 further comprising the step of providing four side reinforcements extending axially and radially outward from the cross brace and connecting to an adjacent cylindrical wall.

17. The method of claim 13 further comprising the step of filling the tank interior storage chamber with a fluid.