Abstract:
A floating platform of vertical axial symmetry which provides processing and/or storage of liquefied hydrocarbon gas. The platform is fixed by mooring or made mobile by added vessel or self-mobilization.  
     The processing and storage being contained in the floating vessel hull, on the deck, or within a center assembly of the floating vessel. The addition of tanks for storage of LNG and liquefied gases conforming to a non-shipshape hull having nonparallel sides, which maximize the volumetric capacity of the structure, yet minimize the stored fluid product mass dynamic effects on the floating vessel.

Description:
[0001]    This application is a continuation-in-part (CIP) of U.S. patent application Ser. No. 09/980,844 filed Oct. 22, 2001. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The invention relates to vertically axial symmetric offshore platforms and buoys with hull-based separator and storage vessels and tanks with features for containment of LNG and liquid forms of gases (liquefied gases).  
           [0004]    2. Description of the Related Art  
           [0005]    The country&#39;s gas supply requirements have increased due to reductions of available gas supplies within the U.S. to meet the energy needs of the country. These requirements have placed new importance on LNG imports to the country. LNG, or Liquefied Natural Gas, is the liquefied state of methane gas maintained at a temperature of minus 260 degrees Fahrenheit at atmospheric pressures.  
           [0006]    LNG supply has high perceived risks due in part to the potential hazards associated with storage before regasification. A distant offshore supply and storage method will remove potential and perceived risks from onshore facilities and the public while simultaneously satisfying the growing demand for clean energy.  
           [0007]    Utilizing economic axisymmetric floating platforms will increase the safety for receipt and storage of LNG and/or liquid gases. As a result, the storage before regasification into normal gas is done safely offshore, thereby eliminating any risks to the public and onshore facilities. This approach is common for storage and shuttling of oil all around the world via storage and offloading vessels termed FSO&#39;s (Floating Storage and Offloading) or FPSO&#39;s (Floating Processing Facilities, Storage and Offloading). However, the implementation of a non-shipshaped or non concrete fixed floating steel platform for storage of LNG/liquefied gas has not been addressed in the prior art. The current storage is performed in conventional ship shapes, which present high risks due to instability in sudden storms. Also proposed are grounded concrete barges, which have limited application due to their practical use only in shallow water. A related need is for an offshore floating platform or facility that permits storage of LNG and other forms of liquefied hydrocarbon gas and which can provide improved motions and safety during offloading independent of water depth, thereby allowing significant offshore placement options. Related issues and embodiments of the present invention are the tank features, which are utilized as follows: to optimize space; to absorb kinematic fluid energy due to the motion of the floating facility; to provide a practical means of connection to the floating facility; to provide a means of thermal/pressure environmental control; and to provide a means of attachment of insulation and a selection of preferred economic materials.  
         SUMMARY OF THE INVENTION  
         [0008]    The present invention provides for an offshore floating facility for storage of LNG and other forms of liquefied hydrocarbon gas such as LPG, or Liquid propane, Butane and other non-hydrocarbon gases in liquid forms under controlled pressure and temperature. By reference to the cited U.S. patent Ser. No. 09/980,844, separation and storage vessels have been proposed within the center column of the structures. It is further proposed that these separation and storage vessels be stored within the hull and on the deck of these and similar offshore moored steel vessels. It is further proposed that the tanks may contain features of form for maximizing available space and features that absorb the contained fluid motion caused by motion of the offshore floating facility in seas. Fluid motion generates heat and boil off of liquid gases. Central to the invention is minimizing the fluid motion to prevent vaporization. This is accommodated by improving the motions of the floating vessel, minimizing the degree of product placed into motion by the floating vessel motion and the strategic use of baffles. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    For further understanding of the nature and objects of the present invention, reference should be had to the following drawings in which like parts are given like reference numerals and wherein:  
         [0010]    [0010]FIG. 1 presents an elevation view of a floating vessel  100  in accordance with the present invention.  
         [0011]    [0011]FIG. 2 presents an elevation view (partially cut-away) of the vessel shown in FIG. 1.  
         [0012]    [0012]FIG. 2 a  presents a storage tank with radial sides and an internal energy dissipating baffle.  
         [0013]    [0013]FIG. 2 b  presents a plan section view of the floating vessel hull filled with storage tanks in a radial configuration.  
         [0014]    [0014]FIG. 3 is a detail view depicting an exemplary temperature control system for a storage vessel in accordance with the present invention.  
         [0015]    [0015]FIG. 4 is a block diagram illustrating steps in an exemplary storage method in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0016]    U.S. patent application Ser. No. 09/980,844, entitled “Satellite Separator Platform” describes as a floating vessel having a floating hull structure with a center column assembly that is non-telescoping extendable and retractable with respect to the hull structure. U.S. patent application Ser. No. 09/980,844, which is owned by the assignee of the present invention, is hereby incorporated herein by reference. That application describes the use of fluid separators within the center column assembly of the platform. In accordance with the present invention, there are provided means within the floating hull and/or atop the hull for storage of LNG/liquefied gas. Additionally, such storage may be provided within the center column assembly.  
         [0017]    [0017]FIG. 1 depicts a floating vessel  100  having a floating hull structure  102  and a center column assembly  104 . The center column assembly  104  is retained within a hollow central section  103  (in FIG. 2) and is axially moveable with respect to the hull  102  SO that the center column assembly  104  is extendable and retractable vertically below the hull  102 . The center column assembly  104  preferably includes a plurality of longitudinal fluid separators  105  for separation of fluid components from a fluid mixture. The hull  102  presents an upper deck  106  for the support of a crane (not shown), a helipad (not shown) and other equipment useful for operation on the platform  100 . Items  200  and  201  are deck-mounted vessels shown in either horizontal or vertical position and supported upon the upper deck  106 .  
         [0018]    The elevation view provided by FIG. 2 reveals storage vessels  202  within the hull  102  for containing LNG or liquefied gas. The storage vessels  202  provide storage and/or separation, or processing of the hydrocarbons. The storage vessels  202  may extend above the deck  106  as shown at  203 .  
         [0019]    The storage vessels  202  containing the LNG or liquefied gas are formed to accommodate a hull  102  which has vertical axial symmetry, thus, curved inner  110  and outer  111  walls. The radial hull  102  shape provides axial symmetry on the vertical axis and thus provides natural structural advantages due to the effective stiffness provided by the general curved geometry, as in the increased strength of a structural arch over a straight beam. The radial sides and baffling of the storage vessels  202  benefit from similar stiffness. Added stiffeners for the storage vessels  202  and  202 ′ would be both internal to resist rotational motion of the fluid and external to provide natural support points for the internal stiffeners of the hull  102 . The storage vessels  202  and  202 ′ may further be provided with an environmental boundary  300 , as shown in FIG. 2, to maintain the volumetric or separation efficiency. The storage tank  202 ′ as shown in FIG. 2A presents certain embodiments of the present invention treating the storage tank features. The sides  206  and  206 ′ are separated by an angle to maximize the radial space of the vessel of axial symmetry. The top  207  and bottom  207 ′ are shown to further deviate from a parallel arrangement. The outer surface  209  and inner surface  209 ′ of the tank are parallel for the case shown but would be configured to maximize the tank volume within the available space of the floating vessel hull. Baffle  210 , within the tank, allows only a small percentage of the fluid cross-sectioned area to pass unrestricted in order to accomplish the degree of energy damping necessary to prevent free surface effects of the fluid and their effects on the floating facility. Stiffeners  208  have many purposes: (a) preventing low frequency response of the storage tank; (b) providing a means of attachment to the floating hull internal stiffeners and (c) providing a means of attachment of external insulation. Other external and internal stiffeners (not shown) may also be incorporated to facilitate fabrication and handling for placing the storage tanks in the floating hull.  
         [0020]    The environmental boundary  300  is provided by a shell or jacket of protective insulation. Within the environmental boundary  300 , the temperature of the content of the vessel  200 ,  201 ,  202 ,  250 ,  202 ′ is controlled within a desired range. Insulation and normal measures for temperature controls are provided. The environmental boundary may be comprised of external insulation on a storage vessel  202 ′ or it may enclose multiple storage vessels  200 ,  201 ,  202 ,  250 ,  202 ′ as a group. This group arrangement for storage vessel  200 ,  201 ,  202 ,  250 ,  202 ′ could, therefore, yield a tank similar to a torus in the plan view FIG. 2 b  and circumferential baffles  211  are used to provide structural stiffness and reduce the fluid motion from affecting the motion of the floating vessel  100 .  
         [0021]    With the full tank radial arrangement, as shown in FIG. 2 b , the fluid elements, which travel most efficiently in a straight direction, are provided a restricted path of ever changing direction through the baffling  210  and  211 , which absorb a great amount of kinetic energy in the fluid contained in the tanks. The efficiency in the system lies in the feature that, as the floating vessel  100  responds to wave motion, the fluid compression pulse transferred, to begin fluid motion by the inner walls  209 ,  209 ′,  207 ,  207 ′ of each tank segment, produces different vector directions of pressure perpendicular to their walls  209 ,  209 ′,  207 ,  207 ′. Since the total mass of the contained fluid in all the tanks is acted on by different pressure pulses in different directions, only a small portion of the fluid is put in motion. The over damping of the baffles  210  and  211  further tends to restrain the fluid from gaining mass velocity. This reduces the amount of fluid mass in motion and decreases the velocity of the reduced fluid mass, thereby greatly reducing the kinetic energy of the fluid that is imparted back onto the opposite vessel walls  209 ′,  209 ,  207 ′,  207 . As a result, the force transferred to floating vessel  100  by contained fluid minimally affects its motion.  
         [0022]    The outer surface of the vessels  200 ,  201 ,  202 ,  202 ′ are designed to include insulation methodology to reduce the transfer of heat to or from the surrounding seawater  204  and hull deck  106  to the contained LNG or liquefied gas. FIG. 3 illustrates, in schematic fashion, an exemplary temperature control system for the storage vessel  202  within the environmental boundary  300 . A cooled space  302  surrounds the storage vessel  202  and an operably associated controller  304 , of a type known in the art, controls the cooled space  302  to maintain the storage vessel  202  and its contents at or near a predetermined temperature. Although FIG. 3 only shows the temperature control arrangement with respect to vessel  202 , it should be understood that it may be used for all such storage vessels of the platform  100 . Temperature control is important in the instance of LNG and other liquefied gases to ensure that they do not vaporize from their liquid state.  
         [0023]    Embodiments of the present invention provide for an offshore floating structure with separators and/or storage vessels and tanks for containment and control of refrigerated liquid forms of gases in either the center column assembly  104 , within the hull  102 , or upon the deck  106  of the hull  102 .  
         [0024]    The systems and methods of the present invention provide for temporary or interim storage of LNG/liquefied gas. In operation, the floating platform, such as platform  100 , is positioned proximate to LNG and/or the liquefied gas production facilities (not shown). It is then moored into place. FIG. 4 illustrates steps for a method of storing LNG/liquefied gas in or upon the platform  100 . Stored LNG and/or liquid gases are transmitted to the platform  100  via hoses or other conduits (not shown) of a type known in the art (step  306 ). The liquid gases are then stored within storage vessels  200 ,  201 ,  202 ,  202 ′ or  250  (step  308 ). Temperature and pressure are controlled for the storage vessels during storage of the liquid gases (step  310 ). Finally, the liquid gases are transferred to either other storage or re-gasification facilities. (step  312 ).  
         [0025]    Additionally, temporary/interim storage of LNG/liquefied gas may be accomplished within the context of the present invention within floating platforms having designs other than that of the floating vessel  100  described above. The solution of effective LNG/liquefied gas storage in a moored vessel for purposes of enabling LNG/liquefied gas transfer offshore is known within the industry, however it is greatly enhanced by use of the tank designs presented herein to minimize vaporization due to damping and wave action of excess fluid motion.  
         [0026]    In addition, the platform  100  may provide for storage of LNG/liquefied gases within the center column assembly  104 . FIG. 2 illustrates storage vessel  250  within the center column assembly  104 .  
         [0027]    The best mode and preferred embodiments of the invention have been described. It is to be understood that the invention is not limited, thereto, but rather is to be measured by the scope and spirit of appended claims.