Abstract:
A large volume natural gas storage tank comprises a plurality of rigid tubular walls each having opposing ends and an intermediate segment with a closed tubular cross-section, the plurality of rigid tubular walls arranged in a closely spaced relationship and interconnected at their ends, with each end of a given of the plurality of rigid tubular walls connected with respective ends of two others of the plurality of rigid tubular walls to define a corner of the storage tank, such that the interiors of the plurality of rigid tubular walls define an interior fluid storage chamber.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This continuation application claims priority benefit to U.S. utility patent application Ser. No. 13/660,460 filed Oct. 25, 2012, now U.S. Pat. No. 8,851,320, which is a continuation application claiming priority benefit to U.S. utility patent application Ser. No. 12/823,719 filed Jun. 25, 2010, now U.S. Pat. No. 8,322,551, which is a continuation-in-part application claiming priority benefit to U.S. utility patent application Ser. No. 11/923,787 filed Oct. 25, 2007, now abandoned, which claims priority benefit to U.S. provisional patent application Ser. No. 60/854,593 filed Oct. 26, 2006, all of which are incorporated herein by reference in their entireties. 
    
    
     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 the tank transported fluid increases, the hydrostatic and dynamic loads on the tank containment walls increase 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 &#39;106 tank was more rigid using one third the wall thickness of the geometric cube. The &#39;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 &#39;106 configured tank did not prove suitable to handle large capacities of LNG in a large LNG carrier environment. 
     A further need has developed for the efficient storage and transportation of compressed natural gas (CNG) over land and sea. This includes carriers as well as Floating Oil/CNG Processing and Storage Offshore Platforms (FOCNGPSO) and floating CNG Processing and Storage Offshore Platforms (FCNGPSO). Several systems have been developed including the EnerSea Transport LLC&#39;s VOTRANS (a trademark of EnerSea) system which includes thousands of vertical or horizontal pipes which are individually filled with CNG and arranged in modules, for example on an ocean tanker. Another example is a system by SEA NG Company which involves miles of continuous piping oriented in a horizontal coil or reel called a COSELLE (a trademark of SEA NG). These self-contained coselles can be stacked vertically on one another and positioned in a tanker storage hold. 
     These CNG systems suffer from several disadvantages in managing the high pressure that CNG is typically stored at which can range from 2000-4000 pounds per square inch (psi) and at temperatures between around 0 and minus 30 degrees Centigrade (−30° C.). Some of these disadvantages of prior CNG storage systems include complexity in the storage tanks or systems themselves as well as significant requirements in the carrying vessel&#39;s length, beam, tonnage, propulsion, fuel consumption and the number of storage tank manifolds needed to maintain the desired temperature and pressure of the stored CNG. 
     Therefore, it would be advantageous to design and fabricate storage tanks for the efficient storage and transportation of large quantities of fluids such as LNG or CNG 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 
     Disclosed herein are embodiments of a large volume natural gas storage tank. In one aspect, a large volume natural gas storage tank comprises a plurality of rigid tubular walls each having opposing ends and an intermediate segment with a closed tubular cross-section, the plurality of rigid tubular walls arranged in a closely spaced relationship and interconnected at their ends, with each end of a given of the plurality of rigid tubular walls connected with respective ends of two others of the plurality of rigid tubular walls to define a corner of the storage tank, such that the interiors of the plurality of rigid tubular walls define an interior fluid storage chamber. 
     In another aspect, a large volume natural gas storage tank comprises a plurality of rigid tubular walls each having opposing ends and an intermediate segment with a closed tubular cross-section, the plurality of rigid tubular walls arranged in a closely spaced relationship and interconnected at their ends to form a six-sided storage tank, with each of the six sides of the storage tank defined by four successive of the plurality of rigid tubular walls connected end-to-end, such that the interiors of the plurality of rigid tubular walls define an interior fluid storage chamber. 
     These and other aspects will be described in additional detail below. 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; 
         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; 
         FIG. 17  is a schematic, partially cut-away perspective view of an example of an alternate storage tank with exemplary spherical corners useful for CNG applications; 
         FIG. 18  is a partial perspective view of one portion of the tank illustrated in  FIG. 17 ; 
         FIG. 19  is a partial perspective view of a corner portion of the tank illustrated in  FIG. 18 ; 
         FIG. 20  is an external elevational view of a quarter of the tank shown in  FIG. 17 ; and 
         FIG. 21  is an alternate view of the tank illustrated in  FIG. 18  with the outer tank structure shown in phantom to show an example of an internal bulkhead reinforcing structure. 
         FIG. 22  is an alternate example of the tank shown in  FIG. 18 ; 
         FIG. 23  is an alternate example of the tank configuration shown in  FIG. 17  illustrating different corner structure; 
         FIG. 24  is an perspective view of an example of a bulkhead reinforcement; and 
         FIG. 25  is a schematic of an example of a use of a plurality of CNG tanks in an ocean carrier. 
     
    
    
     DETAILED DESCRIPTION 
     Several examples of the storage tank containment system in exemplary uses are shown in  FIGS. 1-25 . 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 an 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 cube-shaped 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 poisson 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 an 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 m 3                         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 m 3         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. 
     Examples of an alternate storage tank system for exemplary use with compressed natural gas (CNG) are illustrated in  FIGS. 17-25 . Where components, features or functions are substantially the same as the above examples, the same numbers will be used. Referring to  FIGS. 17 ,  18 ,  19  and  23 , an example of an alternate storage tank  300  is shown. In the example illustrated, the tank  300  is substantially cube-shaped with six similarly shaped and dimensioned sides. Tank  300  preferably includes four substantially identical cylindrical walls  314  oriented vertically at the four vertical corners of the tank as best seen in  FIGS. 18 and 23 . In the preferred example, four vertical cylindrical walls  314  connect together to form tank  300  as further described below. Depending in the size of tank  300  one or more substantially horizontal cylindrical portions may be positioned between opposing corner portions  320 . As best seen in  FIGS. 18 ,  21  and  24 , several examples of internal bulkhead reinforcements  330  maybe positioned in an inner chamber  66  adjacent the eight corners  320  used to store the CNG (not shown) more fully described below. 
     As best seen in  FIGS. 17-19 , each cylindrical wall  314  includes two corner portions  320  (eight to form the eight corners of the cube-shaped tank) positioned in a vertical orientation separated by a vertical cylinder member  324  having a peripheral edge  326  and a longitudinal axis  328 . Referring to  FIG. 19 , each corner  320  includes a first tubular member  336  having first end  340 , a second end  346  and a longitudinal axis  328 . Each corner  320  further includes a second tubular member  350  having a first end  354 , a second end  360  and a longitudinal axis  362 . In the example shown, first  336  and second  250  tubular members are geometric cylinders which are positioned in a substantially horizontal orientation. In a one example, corner  320  includes a spherically-shaped end cap  366  generally similar to the end cap  60  described above and illustrated in  FIG. 1 . 
     As best seen in  FIGS. 18 and 19 , first and second tubular walls  336  and  350  are connected to the vertical tubular wall  324  and the other of the first and the second cylinder  350  and  336  at first ends  340  and  354  respectively. Although shown as connecting along straight lines in  FIG. 19 , the connections between the first  336  and second  350 , in a preferred example, are curved areas as generally shown in  FIGS. 17 ,  18  and  20 . As best seen in  FIG. 20 , end cap  366  also is connected about its periphery  370  to the first and second horizontal tubular walls at the respective cylinder first ends as well as vertical cylinder  324 . In one example, end caps  366  are spherically-shaped as described in the alternate example above. 
     Referring to  FIGS. 17 ,  18  and  20 , an example of vertical tubular wall  324  for alternate tank  300  is illustrated. In the example, vertical tubular wall  324  is cylindrically shaped and similar in design to the prior tank  10  vertical cylinder  34  shown in  FIGS. 1 and 3 . In a preferred example, the vertical walls of cylinder  324  more closely resemble straight vertical walls of a traditional cylinder. 
     As best seen in  FIG. 17 , in one example of alternate storage tank  300 , tank  300  uses four of the illustrated cylindrical walls  314  positioned approximately 90 degrees apart from one another to form the cube-shaped tank  310 . In the example shown, and in contrast to the example shown in  FIG. 1 , the first  336  and second  350  horizontal cylindrical walls connect directly to one another at respective second ends  346  and  360  to from the horizontal sidewalls of the tank without using the wrap-around wall  34  or  40  for these horizontal portions of the tank. In the preferred example shown in  FIG. 17 , these horizontal wall portions are substantially tubular with a circular cross section joint where the opposing second ends  346 ,  346  and  360 ,  360  abut and are rigidly connected. The exemplary alternate design in this area for tank  300  has been determined to be superior in handling the high pressure needed for storage of CNG over the design shown in  FIG. 1 . 
     In examples of the alternate tank  300 , the following Table 3 shows several variations for different tank sizes and the approximate thicknesses of the walls/shell. 
     
       
         
               
             
               
               
               
             
               
               
               
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 CDTS Tank Characteristics for Use with Compressed Natural Gas (CNG) 
               
             
          
           
               
                   
                 AMBIENT TEMPERATURE 
                   
               
             
          
           
               
                 125 BAR 
                   
                 CNG 
                   
                   
               
               
                 PRESSURE 
                   
                 Weight 
                 0° C. 
                 −30° C. 
               
             
          
           
               
                 Tank Size 
                 Volume 
                   
                   
                 (Metric  
                 Shell Thickness 
               
               
                 (m) 
                 (m 3 ) 
                 scm 
                 scf 
                 Tons) 
                 (mm) 
               
               
                   
               
             
          
           
               
                 5 
                 102 
                 32886 
                 1160464 
                 21 
                 110 
                 50 
               
               
                 10 
                 813 
                 263088 
                 9283714 
                 171 
                 160 
                 100 
               
               
                 15 
                 2742 
                 887920 
                 31332534 
                 576 
                 211 
                 150 
               
               
                 20 
                 6500 
                 2104700 
                 74269711 
                 1365 
                 259 
                 185 
               
               
                   
               
             
          
         
       
     
     Although particular sizes of tank  300  are described in the above table, different sizes of tanks with commensurate differences in interior capacity, known by those skilled in the art, may be used. Referring to the example shown in  FIG. 18  illustrating a tank with approximate dimensions of 10 meters in length per side, the upper horizontal cylinders  336  and  350  are 40 millimeters (mm) thick and the lower horizontal cylinders  336  and  350  are 90 mm thick. With a 75 mm internal reinforcement, 30 mm doubler plates and a 50 mm base described below, the mass of tank  300  is approximately 594 tons. 
     In an example of material used to construct the shell of alternate tank  300 , high strength, pressure grade steel is used. Other materials and in different thicknesses than those listed in the above table known by those skilled in the art may be used without deviating from the present invention. It is also understood that different components other than those described above and illustrated, as well as in different shapes and orientations, known by those skilled in the art may be used. In preferred example, the above described components are rigidly and continuously seam welded together using known methods to permanently and hermetically seal the components together in a manner to completely contain CNG in the internal chamber  66 . 
     As best seen in  FIGS. 18 ,  21  and  24 , in a preferred example of tank  300  for use in storing CNG, several examples of an internal bulkhead reinforcement  330  are illustrated. Bulkhead  330  is preferably positioned inside chamber  66  inside vertical cylinder wall  314  as generally shown. In one example shown in  FIG. 21 , bulkhead  330  includes a plate  378  and a first web  380 , a second web,  386  and a third web  396  positioned at opposite corners  320  of each vertical wall  314  as best seen in  FIG. 21 . In each corner  320 , first web  380  includes a first edge  382  which spans the internal chamber  66  in the respective corner  320  and connects to the joint where the first horizontal cylinder  336  connects to the end cap  366  and vertical wall  324 . The second web  386  similarly includes a first edge  388  which connects at the joint where the second horizontal cylinder  350  connects to the end cap  366  and the vertical wall  324 . The third web  396  includes a first edge that connects at the joint where the first  336  and second  350  horizontal cylinders connect. All three of the first web  380 , second web  386  and third web  396  include respective second edges  382 ,  390  and  400  which all connect together. In the example of bulkhead  326  shown in  FIG. 21 , plate  378  is removed in the area of the end caps  366  in corners  320 . 
     In alternate examples shown in  FIGS. 18 and 24 , first  380  and second  386  webs extend further into corner  320  and connect to the end cap  366  as generally shown. In this example, apertures  406  are used so as to not block or compartmentalize the CNG in inner chamber  66 . In the example shown in  FIG. 24 , bulkhead  330  includes a reinforcement ring  399  used to connect the bulkhead  330  to the cylinders  330 ,  350  and end cap  366  and provides additional strength to corners  320  through seam welding. In a preferred example, the same material is used for the bulkhead  330  as the tank shell. Other materials, configurations and orientations for bulkhead  330  and other reinforcements known by those skilled in the art may be used. 
     Referring to  FIGS. 18 and 20 , reinforcement plates  410  may be used where needed where separate components are connected together for added structural integrity. These reinforcements may be an additional layer of the shell material or may be of increased or decreased thickness, and may be made from different materials depending on the application. 
     In an alternate example to reinforcement corners  320 , a plurality of gusset plates  421  can be used to further connect bulkhead  330  to adjacent cylinders and end caps as opposed to ring  399 . 
     Referring to  FIG. 17 , closure plates  420  may be used where it is desired to seal off and utilize the interior space, defined as central chamber  408 , between the respective cylindrical walls  324 ,  336  and  350  of tank  300 . Closure plates  420  would be sized and positioned to create an air-tight space between the referenced walls (six total, one for each of the six sides of the cube-shaped tank). One or more outlet ports (not shown) would be provided in the appropriate cylinder walls so the tank interior chamber  66  would be in fluid communication with the central chamber  408  sealed off by plates  420 . Equally, there would be at least one port in the exterior of tank  300  (not shown) for filling or extracting fluid from tank  300  as known by those skilled in the art. There further may be other ports in the exterior and interior of tank  300  for controls, gauges, monitors and other equipment (not shown) known by those skilled in the art to monitor the contents and characteristics of the fluid in tank  300 . 
     Referring to  FIGS. 18 and 21 , a mounting base  440  may be used to provide a controlled support or footprint for tank  300  to rest on the floor or other support surface of a vehicle or vessel for transportation over land, air or sea. In one example, base  440  may be a heavy steel plate connected to one or more of first  336  and second  350  horizontal cylinders at the lower ends of walls  314 . Other bases or support systems described for this invention, for example a pyramidal or trapezoidal shaped base  441  (shown in  FIG. 23 ) may be used as well as variations thereof know by those skilled in the art. 
     In an alternate example of tank  300  shown in  FIG. 23  for use in storage and transportation of CNG, corners  320  do not include spherical end caps  366  as shown in  FIG. 17 . In the example shown, cylinders  324 ,  336  and  350  extend to abut at corner joints  430 ,  434 ,  440 . One or more of the described reinforcements, for example bulkhead  330  may be used to reinforce the joints. 
     In an application of tank  300  to store CNG for transportation on a ocean tanker, it is contemplated that only a few tanks  300 , for example four, could be positioned and secured in cargo holds to store between 1.1 to 1.6 MM scm (millions of standard cubic meters). In larger or super tankers, it is contemplated that between 90 and 108 tanks  300 , positioned on separate vertical decks of a ship as generally shown in  FIG. 25 , could be used to transport between 23.7 to 28.4 MM scm. Due to the modular, self-contained nature of tank  300 , vehicles or vessels could carry quantities of CNG in tanks  300  as well as other cargo, for example LNG in tanks  10 , or other fluids such as crude oil to suit the particular application and specification. In an application for Floating Oil/CNG Processing and Storage Offshore Platforms (FOCNGPSO) or CNG Processing and Storage Offshore Platforms (FCNGPSO), tanks  300  in similar capacities ranging from 1.6 to 28.4 MM scm are contemplated. Other size tanks  300  and configurations may be used to increase or decrease holding capacity to suit the particular application. The combination of tanks  300  as well as tanks for the storage of oil or other fluids may be used to suit the particular application. 
     Through analytical testing of the present invention against the prior VOTRANS and SEA NG designs, the following data was developed. 
     
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 4 
               
             
             
               
                   
               
               
                 Comparison of Known Designs with inventive CDTS Designs for CNG 
               
             
          
           
               
                   
                   
                 VOTRAN 
                   
                 CDTS (present) 
               
               
                   
                   
                 Horizontal OR 
                 SEA NG 
                 Independent 
               
               
                 Containment System 
                   
                 Vertical Pipes 
                 Coselles 
                 Tanks 
               
               
                   
               
             
          
           
               
                 Cargo Capacity 
                 MMscm 
                 22.6 
                 7.7 
                 23.7 Cargo 
               
               
                 Pressure 
                 Bar 
                 125 
                 250 
                 125 
               
               
                 Cargo Temperature 
                 0° C. 
                 −31 
                 0 
                 −31 
               
               
                 Number of Modules/ 
                   
                 74 (1776 pipe tanks, 
                 84 (890 miles 
                 90 
               
               
                 Tanks 
                   
                 200 Kilometers of 
                 of pipe) 
               
               
                   
                   
                 pipe) 
               
               
                 Length between 
                 M 
                 291 
                 204 
                 250 
               
               
                 Perpendiculars 
               
               
                 Beam 
                 M 
                 50 
                 39 
                 50 
               
               
                 Depth at Side 
                 M 
                 27.4 
                 27 
                 28 
               
               
                 Depth of Cover Top 
                 M 
                 35 
                 28 
                 41 
               
               
                 Draft 
                 M 
                 110.36 
                 10.63 
                 11.59 
               
               
                 Speed 
                 Knots 
                 18 
                 20 
                 18 
               
               
                 HP 
                 Kw 
                 22,050 
                 NA 
                 20,820 
               
               
                 Displacement 
                 T 
                 122,500 
                 56,200 
                 115,419 
               
               
                 Cargo Deadweight 
                 T 
                 14,352 
                 5,000 
                 15,096 
               
               
                 Cargo Deadweight 
                   
                 0.12 
                 0.09 
                 0.133 
               
               
                 Coefficient 
               
               
                 Cargo Weight/Module 
                   
                 0.36 
                 0.14 
                 0.285 
               
               
                 Weight Coefficient 
               
               
                 Ship Volumetric 
                   
                 0.09 
                 0.09 
                 0.14 
               
               
                 Efficiency 
               
               
                 Hold Volumetric 
                   
                 0.18 
                 0.14 
                 0.33 
               
               
                 Efficiency 
               
               
                   
               
             
          
         
       
     
     From the data and other advantages of the invention for exemplary use for carriage of CNG in ships and floating production and storage platforms, the present CDTS invention provides benefits of: significant reduction in the required size of tankers (length, displacement and vessel power plant requirements); a significant increase in the ship volumetric efficiency and hold volumetric efficiency; a reduction in the estimated costs of carriers of between 5% and 20%; a reduction in the gross tonnage and therefore many operating costs by 15% to 60%; a significant reduction in surface area and thus heat transfer by a factor of 8 compared to the prior VOTRANS system and a factor of 50 compared to SEA NG system. Other advantages and efficiencies known by those skilled in the art are achievable. 
     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.