Patent Publication Number: US-7219682-B2

Title: Liquid displacement shuttle system and method

Description:
FIELD OF THE INVENTION 
   The invention relates generally to the storage and transport of compressed gas and, more particularly, to a fluid displacement shuttle system and method that facilitates loading and unloading compressed gas or other fluids in multiple vessel storage systems. 
   BACKGROUND INFORMATION 
   The gains in storage capacity from increasing levels of pressure under which compressed gasses are held come at the cost of discharging large volumes in a desired short period of time. Many gas storage systems use multiple pressure vessels interconnected to manifolds. Discharging from a high pressure storage vessel (at for example 3500 psig) to a receiving terminal (rated for example at 1200 psig) can be accomplished by pressure equalization in a first stage of evacuation. The gas remaining in the container, which is now at the lower terminal pressure level, undergoes a second stage of evacuation by connection to a drawdown compression or low pressure manifold. As a result, the flow of compressed gas transported in multiple assemblies of pressure vessels at high pressures is frequently subject to a bottleneck of prolonged loading and unloading times. 
   In seeking to improve the evacuation of the contents of these storage vessels, proposed systems, such as that disclosed in Bishop U.S. Pat. No. 6,655,155, seek to displace the gas under full holding pressure using a displacement liquid in a manner similar to that used to move product from underground storage caverns. Given the gross volume of all storage containers, it is possible to purge all interconnected vessels by simultaneous displacement with an equal volume of liquid. However, such an equal volume would require a large shore mounted supply with recycle facilities in the case of marine transportation. Such a volume would be impractical to carry on board a ship and require inordinate amounts of motive power. In response to this problem, Bishop advocates a staged tier displacement system designed into the ship reducing a 200,000 bbls initial on board storage need to 50,000 bbls of on board storage. 
   Accordingly, it would be desirable to provide an improved evacuation system and method that facilitates the reduction of the amount of displacement liquid used for unloading compressed gas from a multi-vessel storage system and to improve evacuation times by displacement of the compressed gas contents in their entirety from the storage vessels. 
   SUMMARY 
   The present invention is directed to a multi-vessel storage and fluid or liquid displacement shuttle system, which utilizes a liquid-piston shuttled to alternate vessels to evacuate stored product such as compressed or high pressure gas or other fluids from the storage vessels. In a preferred embodiment, the gas storage and fluid or liquid displacement shuttle system includes multiple storage vessels or tanks, or banks of vessels or tanks, that are preferably coupled in parallel at one end to a discharge manifold such as a high pressure gas manifold to exhaust the stored product from the vessels and coupled in parallel at another end to separate fluid shuttle circuits. The fluid shuttle circuits include cross-piped fluid fill and drain manifolds that are fluidly linked through interposing reservoirs and pumps. In operation, the stored product is evacuated from the storage vessels by shuttling the volume of displacement liquid between alternating banks of storage tanks and reservoirs with alternating pumps. Alternatively, a single pump and storage (reservoir) system could also be used with a more complex control system when a greater storage volume is required 
   Other systems, methods, features and advantages of the invention will be or will become apparent to one with skill in the art upon examination of the following figures and detailed description. 

   
     BRIEF DESCRIPTION OF THE FIGURES 
     The details of the invention, including fabrication, structure and operation, may be gleaned in part by study of the accompanying figures, in which like reference numerals refer to like parts. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. Moreover, all illustrations are intended to convey concepts, where relative sizes, shapes and other detailed attributes may be illustrated schematically rather than literally or precisely. 
       FIG. 1  depicts a multiple pressure vessel storage and fluid displacement shuttle system in accordance with the present invention prior to the gas evacuation cycle. 
       FIG. 2  depicts the system of the present invention in an initial phase of the gas evacuation cycle. 
       FIG. 3  depicts the system of the present invention in a subsequent phase of the gas evacuation cycle. 
       FIG. 4  depicts the system of the present invention in a subsequent phase of the gas evacuation cycle. 
       FIG. 5  depicts the system of the present invention in a subsequent phase of the gas evacuation cycle. 
       FIG. 6  depicts the system of the present invention in a subsequent phase of the gas evacuation cycle. 
   

   DETAILED DESCRIPTION 
   Turning to the figures, a multi-vessel storage system of the present invention is shown to include a liquid displacement shuttle system. In the liquid displacement shuttle system, use is made of a liquid-piston which is then shuttled to alternate reservoirs for reuse in the next storage vessel or tank in the assembly. In tight spaces, the storage space saved can be used for stored product, and not displacement liquid. Although the liquid displacement shuttle system is depicted and discussed in regard to its use in a compressed or high pressure gas storage system, it is not restricted to use just with compressed gas, and one of skill in the art would understand the liquid displacement shuttle principal being equally suited to moving compatible stored liquids or fluids. 
   The present invention reduces the volume of displacement liquid to a fraction of a storage system&#39;s volume by shuttling the volume of displacement liquid between alternating storage tanks or banks of storage tanks and one or more reservoirs using one or more pumps. Multiple sets of shuttle links along the length of a ship could operate simultaneously, while maintaining a lower level of displacement liquid than advocated by conventional methods (see, e.g., Bishop). As depicted in the figures, the gas storage and liquid displacement shuttle system preferably operates with vertical storage vessels or tanks clustered to a common manifold collector valve, but can operate with horizontally disposed vessels or tanks as well. 
   In a preferred embodiment, as depicted in  FIG. 1 , the gas storage and fluid displacement shuttle system includes multiple pressure storage vessels or tanks  40  arranged in tank banks T 0 , T 1 , T 2 , T 3 , T 4 , . . . Tn preferably comprising the same number of equally sized vessels  40  such that the gross volume of each tank bank is equal. The vessels  40  are preferably coupled in parallel adjacent their vessel tops to a discharge or high pressure gas manifold (HPM)  100  to exhaust stored gas or other fluids from the vessels  40  and coupled in parallel adjacent their vessel bottoms to separate fluid shuttle circuits. The fluid shuttle circuits include cross-piped fluid fill and drain manifolds  30   a ,  30   b ,  32   a  and  32   b  that are fluidly linked through interposing reservoirs  36   a  and  36   b  and pumps  38   a  and  38   b . As depicted, the vessels  40  are coupled through multi-position discharge gas valves  16 ,  17 ,  18 ,  19 ,  20  and  21  to the HPM  100 , which includes a collector valve  102  with a gas delivery outlet  104 . As depicted, the vessels  40  in a first set of the even numbered tank banks T 0 , T 2 , and T 4  are coupled through multi-position shuttle fluid valves  10 ,  12  and  14  to a first fluid drain manifold  30   a  and a first fluid fill manifold  32   a  while the vessels  40  in a second set of the odd numbered tank banks T 1 , T 3 , and Tn are coupled through multi-position shuttle fluid valves  11 ,  13  and  15  to a second fluid drain manifold  30   b  and a second fluid fill manifold  32   b . The first drain manifold  30   a  is coupled to a first reservoir  36   a , which in turn is coupled to a first pump  38   a , which in turn is coupled to the second fill manifold  32   b , thus fluidly linking the first drain manifold  30   a  to the second fill manifold  32   b  and forming the first fluid shuttle circuit. Similarly, the second drain manifold  30   b  is coupled to a second reservoir  36   b , which in turn is coupled to a second pump  38   b , which in turn is coupled to the first fill manifold  32   a , thus fluidly linking the second drain manifold  30   b  to the first fill manifold  32   a  and forming the second fluid shuttle circuit. Interposing the first drain manifold  30   a  and first reservoir  36   a , and the second drain manifold  30   b  and second reservoir  36   b , respectively, are first and second one-way flow check valves  34   a  and  34   b . The multi-position shuttle fluid valves  10 ,  11 ,  12 ,  13 ,  14  and  15 , first and second fluid drain manifolds  30   a  and  30   b , first and second fluid fill manifolds  32   a  and  32   b , first and second reservoirs  36   a  and  36   b , first and second pumps  38   a  and  38   b , first and second flow check valves  34   a  and  34   b  and a low pressure gas displacement system  200  form the liquid displacement shuttle system of the present invention. The low pressure gas displacement system  200  includes a low pressure gas manifold (“LPM”)  201 , which includes a collector valve  204  and is coupled to the vessels  40  through one-way low pressure flow check valves  202 . 
   Preferably, the multi position valves are low pressure gas actuated, control logic valves that may be activated by a stroke count on the pumps or tank level detection depending on physical layout of the system. The actuator exhaust gas is preferably routed to gas expansion heaters. 
   As depicted, the tanks, reservoirs and manifolds are preferably interconnected through small diameter piping, tubing or the like. The one way fluid flow check valves  34   a  and  34   b  permit displacement liquid from the drain manifolds  30   a  and  30   b  to drain into the reservoirs  36   a  and  36   b , but not back into the manifolds  30   a  and  30   b  from the reservoirs  36   a  and  36   b , while the one way gas flow check valves  202  permit low pressure blanket gas to fill and equalize pressure in evacuated spaces within the vessels  40 , but not back into the LPM  201  from the vessels  40 . The blanket gas may be methane, ethane, butane, propane and the like, or mixtures thereof as apropriate to the stored product. 
   The mode of operation is described below in conjunction with  FIGS. 1 through 6 . The valve sequence and activity within each tank bank, as depicted in each figure, are listed in Table 1. 
   Turning to  FIG. 1 , the system is depicted in a state prior to the gas displacement or evacuation cycle to unload the stored gas, with one tank bank, represented by tank T 0 , initially filled with a non reactive displacement liquid such as saturated natural gas liquid (NGL), compatible solvent gas, and the like, or mixtures thereof. The volume of displacement liquid in tank T 0  is preferably substantially equivalent to the volume of gas stored in each individual tank bank. Preferably, the fluid shuttle circuits are also filled displacement liquid. The space above the displacement liquid in tank T 0  is preferably filled with low pressure gas from the LPM  201 . The remaining tanks or vessels  40  in tank banks T 1 , T 2 , T 3 , T 4  . . . Tn are all filled with high pressure gas (“HPG”). (Reference to “tank T 0 , tank T 1 , . . . tank Tn” in the remaining discussion will be understood by one skilled in the art to be referring to the specified tank bank T 0 , T 1 , . . . etc. As would be further understood by one skilled in the art, the tank banks may be configured to include a single vessel or an equal number of a plurality of vessels). 
   As depicted in  FIG. 2 , the unloading process or gas evacuation cycle is initialized by rotating the shuttle valve  10  of tank T 0  to a first opened position coupling tank T 0  to the first drain manifold  30   a  of the first fluid shuttle circuit. The displacement liquid drains from tank T 0  into the first drain manifold  30   a  feeding the first reservoir  36   a , which in turn feeds the first pump  38   a , as low pressure gas from the LPM  201  flows through the check valve  202  into tank T 0  to fill and equalize pressure in the evacuated space above the displacement liquid. The first pump  38 , which is coupled to odd numbered tanks starting with tank T 1 , pumps displacement liquid into the second fill manifold  32   b  and on into tank T 1  which is coupled to the second fill manifold  32   b  with its shuttle fluid valve  11  rotated to a first opened position permitting displacement liquid, which acts as a liquid piston, to push HPG out of tank T 1  through the gas discharge valve  17 . The discharge valve  17  is rotated to an opened position allowing gas to feed into the HPM  100  from where it is delivered through the gas outlet  104  to expansion and heating facilities or to on shore storage. 
   Tank T 2 , which is coupled to the first fill manifold  32   a  of the second fluid shuttle circuit with its shuttle valve  12  rotated to a first opened position, is shown beginning its HPG evacuation cycle being fed displacement liquid from the second pump  38   b  and second reservoir  36   b  through the first fill manifold  32   a  and its open shuttle valve  12 . The HPG is vented to the HPM  100  through the open discharge valve  18 . As depicted in  FIG. 2  and Table 1, the remaining tanks wait in isolated mode. 
     FIG. 3  shows tank T 0  emptied of displacement liquid and filled with low pressure gas. The shuttle fluid valve  10  and gas discharge valve  16  of tank T 0  are closed to isolate tank T 0  from active operations. Tank T 1  has been evacuated of HPG, its gas discharge valve  17  is closed and its shuttle valve  11  has been rotated to a second opened position to couple tank T 1  to the second drain manifold  30   b  of the second fluid shuttle circuit to drain displacement liquid into the second drain manifold  30   b  and on into the second reservoir  36   b  as low pressure gas from the LPM  201  flows through the check valve  202  into tank T 1  to fill and equalize pressure in the evacuated space above the displacement liquid. The second reservoir  36   b  feeds the second pump  38   b  which in turn feeds the first fill manifold  32   a  and tank T 2  which is coupled to the first fill manifold  32   a  with its shuttle  12  open to a first opened position. Displacement liquid fills tank T 2  displacing HPG from tank T 2  through its gas discharge valve  18  which is rotated to an opened position coupling tank T 2  to the HPM  100 . 
   Tank T 3 , which is coupled to the second fill manifold  32   a  with its shuttle valve  13  rotated to a first opened position, is shown beginning its HPG evacuation cycle being fed displacement liquid from the first pump  38   a  and first reservoir  36   a  through the second fill manifold  32   a  and its open shuttle valve  13 . The HPG is vented to the HPM  100  through its open discharge valve  19 . As depicted in  FIG. 3  and Table 1, the remaining tanks wait in isolated mode. 
   In  FIG. 4 , tanks T 0  and T 1  are shown empty of displacement liquid and with their valves  10 ,  11 ,  16  and  17  closed isolating their low pressure gas contents. Tank T 2  is shown nearing drainage completion of its displacement liquid to the first reservoir  36   a  with its gas discharge valve  18  closed and its shuttle valve  12  open to the first drain manifold  30   a . Tank  3  is shown with its shuttle valve  13  open to the second fill manifold  32   b  and being fed displacement liquid from the first pump  38   a , and in the final stage of venting HPG through its gas discharge valve  19  to the HPM  100 . 
   Tank T 4 , which is coupled to the first fill manifold  32   a  with its shuttle valve  14  rotated to a first opened position, is shown beginning its HPG evacuation cycle being fed displacement liquid from the second pump  38   b  and second reservoir  36   b  through the first fill manifold  32   a  and its open shuttle valve  14 . The HPG is vented to the HPM  100  through its open discharge valve  20 . As depicted in  FIG. 4  and Table 1, the remaining tanks wait in isolated mode. 
   Turning to  FIG. 5 , tanks T 0 , T 1  and T 2  are shown in displacement liquid emptied mode with their valves  10 ,  11 ,  12   16 ,  17  and  18  set in isolation positions isolating the low pressure gas contents of T 0 , T 1  and T 2 . Tank T 3 , which has switched to fluid drain mode, is shown with its gas discharge valve  19  closed and its shuttle valve  13  opened to the second drain manifold  30   b  to drain displacement liquid into the second reservoir  36   b . Tank T 4  is shown approaching the final phase of displacing HPG into the HPM  100  through its open gas discharge valve  20  with displacement liquid being fed from the second pump  38   b  to the first fill manifold  32   a  and through its shuttle valve  14  which is opened to the first fill manifold  32   a.    
   A sixth tank bank, tank Tn, which is coupled to the second fill manifold  32   a  with its shuttle valve  15  rotated to a first opened position, is shown beginning its HPG evacuation cycle being fed displacement liquid from the first pump  38   a  and first reservoir  36   a  through the second fill manifold  32   a  and its open shuttle valve  15 . The HPG is vented to the HPM  100  through its open discharge valve  21 . The designation of the fifth tank bank as tank Tn will be understood by one skilled in the art to indicate that the system is expandable beyond the number of tank banks depicted in the figures. 
   In  FIG. 6 , the end phase of this sequence is shown with tanks T 0  through T 3  emptied of displacement liquid and filled with low pressure gas with their valves  10 ,  11 ,  12 ,  13 ,  16 ,  17 ,  18  and  19  set in isolation mode isolating their low pressure gas contents. Tank T 4 , which has switched to fluid drain mode, is shown in final drain mode with its gas discharge valve  20  closed and its shuttle valve  14  opened to the first drain manifold  30   a  to drain displacement liquid into the first reservoir  36   a . The sixth tank bank, tank Tn, is shown approaching the final phase of displacing HPG into the HPM  100  through its open gas discharge valve  21  with displacement liquid being fed from the first pump  38   a  to the second fill manifold  32   b  and through its shuttle valve  15  which is opened to the second fill manifold  32   b . For systems greater in size than that depicted in the figures, the second pump  38   b  would feed displacement liquid to the next tank bank not shown in the figures or Table 1. 
   The above illustrates how through cross piping the initial batch of displacement liquid from tank T 0  can be transferred through all of the tank banks, alternating between different sets of tank banks and shuttling between the reservoirs. The sequence as described above can continue through many more tank banks or vessels within the desired discharge time. The saving in storage space for displacement liquid resulting from this shuttle system is now useable for additional HPG storage. 
   Multi port valving used in the forgoing description can also be replaced by single port valves according to prevailing design codes. 
   
     
       
         
             
           
             
               TABLE 1 
             
           
          
             
                 
             
             
               Sequence of Displacement liquid Shuttle through Pumps &amp; tanks 
             
          
         
         
             
             
             
             
             
             
             
          
             
                 
               tank T0 
               tank T1 
               tank T2 
               tank T3 
               tank T4 
               Tank Tn 
             
             
                 
                 
             
          
         
         
             
             
             
             
             
             
             
          
             
               FIG. 1 
                 
                 
                 
                 
                 
                 
             
             
               Gas Valve 
               Closed 
               Closed 
               Closed 
               Closed 
               Closed 
               Closed 
             
             
               Fluid Valve 
               Closed 
               Closed 
               Closed 
               Closed 
               Closed 
               Closed 
             
             
               Contents/ 
               Disp Fluid 
               HP Gas 
               HP Gas 
               HP Gas 
               HP Gas 
               HP Gas 
             
             
               Status 
               Stored 
               Stored 
               Stored 
               Stored 
               Stored 
               Stored 
             
             
               FIG. 2 
             
             
               Gas Valve 
               Closed 
               Open to HPM 
               Open to HPM 
               Closed 
               Closed 
               Closed 
             
             
               Fluid Valve 
               Open to Res R1 
               Open to 
               Open to 
               Closed 
               Closed 
               Closed 
             
             
                 
                 
               Pump P1 
               Pump P2 
             
             
               Contents/ 
               Disp Fluid 
               30% HP Gas 
               70% HP Gas 
               HP Gas 
               HP Gas 
               HP Gas 
             
             
               Status 
               Emptying to 
               Displacement 
               Displacement 
             
             
                 
               Res R1 
             
             
               FIG. 3 
             
             
               Gas Valve 
               Closed 
               Closed 
               Open to HPM 
               Open to HPM 
               Closed 
               Closed 
             
             
               Fluid Valve 
               Closed 
               Open to 
               Open to 
               Open to 
               Closed 
               Closed 
             
             
                 
                 
               Res R2 
               Pump P2 
               Pump P1 
             
             
               Contents/ 
               LP Gas/ 
               30% Disp Fluid 
               30% HP Gas 
               70% HP Gas 
               HP Gas 
               HP Gas 
             
             
               Status 
               Liq Unloaded 
               Emptying to R2 
               Displacement 
               Displacement 
               Stored 
               Stored 
             
             
               FIG. 4 
             
             
               Gas Valve 
               Closed 
               Closed 
               Closed 
               Open to HPM 
               Open to HPM 
               Closed 
             
             
               Fluid Valve 
               Closed 
               Closed 
               Open to 
               Open to 
               Open to 
               Closed 
             
             
                 
                 
                 
               Res R1 
               Pump P1 
               Pump P2 
             
             
               Contents/ 
               LP Gas/ 
               LP Gas/ 
               Disp Fluid 
               30% HP Gas 
               70% HP Gas 
               HP Gas 
             
             
               Status 
               Liq Unloaded 
               Liq Unloaded 
               Emptying to R1 
               Displacement 
               Displacement 
               Stored 
             
             
               FIG. 5 
             
             
               Gas Valve 
               Closed 
               Closed 
               Closed 
               Closed 
               Open to HPM 
               Open to HPM 
             
             
               Fluid Valve 
               Closed 
               Closed 
               Closed 
               Open to 
               Open to 
               Open to 
             
             
                 
                 
                 
                 
               Res R2 
               Pump P2 
               Pump P1 
             
             
               Contents/ 
               LP Gas/ 
               LP Gas/ 
               LP Gas/ 
               30% Disp Fluid 
               30% HP Gas 
               70% HP Gas 
             
             
               Status 
               Liq Unloaded 
               Liq Unloaded 
               Liq Unloaded 
               Emptying to R2 
               Displacement 
               Displacement 
             
             
               FIG. 6 
             
             
               Gas Valve 
               Closed 
               Closed 
               Closed 
               Closed 
               Closed 
               Open to HPM 
             
             
               Fluid Valve 
               Closed 
               Closed 
               Closed 
               Closed 
               Open to 
               Open to 
             
             
                 
                 
                 
                 
                 
               Res R1 
               Pump P1 
             
             
               Contents/ 
               LP Gas/ 
               LP Gas/ 
               LP Gas/ 
               LP Gas/ 
               30% Disp Fluid 
               30% HP Gas 
             
             
               Status 
               Liq Unloaded 
               Liq Unloaded 
               Liq Unloaded 
               Liq Unloaded 
               Emptying to R1 
               Displacement 
             
             
                 
             
          
         
       
     
   
   In the foregoing specification, the invention has been described with reference to specific embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention. For example, the reader is to understand that the specific ordering and combination of process actions shown in the process flow diagrams described herein is merely illustrative, unless otherwise stated, and the invention can be performed using different or additional process actions, or a different combination or ordering of process actions. As another example, each feature of one embodiment can be mixed and matched with other features shown in other embodiments. Features and processes known to those of ordinary skill may similarly be incorporated as desired. Additionally and obviously, features may be added or subtracted as desired. Accordingly, the invention is not to be restricted except in light of the attached claims and their equivalents.