Abstract:
A system, method, and apparatus for treating ship or barge ballast water. The system includes a ballast tank storing ballast water and one or more nozzles located in the ballast tank. One or more pumps supply a chemical into the ballast tank and water to the nozzles. The nozzles are strategically located in the ballast tank to circulate the ballast water and mix the chemical with the ballast water without removing the ballast water from the ballast tank to a separate mixing and treatment area located outside the tank either onboard or off of the ship or barge.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
       [0001]    This application claims the benefit of the filing date of U.S. Provisional Patent Application Ser. No. 61/661,158, filed Jun. 18, 2012, which is hereby incorporated by reference in its entirety. 
     
    
     STATEMENT OF GOVERNMENT INTEREST 
       [0002]    The invention described herein may be manufactured and used by or for the Government of the United States of America for Governmental purposes without the payment of any royalties thereon or therefor. 
     
    
     FIELD OF THE INVENTION 
       [0003]    The invention relates in general to treating water in the ballast tank of a ship or barge. 
       BACKGROUND 
       [0004]    Ships that transport goods around the world can carry nonindigenous (exotic) species in ballast water. The release of the ballast water from the ships is a major transport mechanism for the nonindigenous aquatic organisms (Carlton, 1985) as recognized by the U.S. National Invasive Species Control Act of 1996 (P.L. 104-332). Approximately 70,000 major cargo ships operating worldwide (Bureau of Transportation Statistics, 2008) pump ballast water on board to ensure stability and balance. Large vessels can carry in excess of 200,000 m 3  of ballast, which is released in varying amounts at or when approaching cargo loading ports. In 1991, U.S. waters alone received approximately 57,000,000 metric tons of ballast water from foreign ports (Carlton et al., 1994). Ship surveys have demonstrated that ballast water is in general a non-selective transfer mechanism—many taxa representing planktonic and nectonic organisms capable of passing through coarse ballast water intake screens are common. These include bacteria, larval fish, zooplankton, and bloom forming dinoflagellates (Chu et al., 1997; Carlton and Geller, 1993). 
         [0005]    The introduction of the nonindigenous (exotic) species has had dramatic negative effects on marine, estuarine, and freshwater ecosystems in the United States and abroad (Elton, 1958; Mooney and Drake, 1986; Chesapeake Bay Commission, 1995; NAS, 1996). Effects include alteration of the structure and dynamics of the ecosystem involved, including extirpation of native species (Office of Technology Assessment Archive, 1993). 
         [0006]    The current state of the art for treating ballast water involves treating the water as it is pumped into or out of the ballast tanks. Methods for treating the water as it is pumped out the tanks are tremendously expensive and time consuming, and it is considered cost prohibitive to treat all water that is pumped into all tanks. The alternative to treating the water as it is pumped into or out of the tanks is to treat it while it resides in the tanks as the ship travels from port to port. To accomplish this, the entire volume of the tanks must be completely mixed in a relatively short time to ensure all the water in the tanks is exposed to the treatment method. This is especially true in emergency situations when a ship is grounded and the water in the ballast tanks must be treated before it is pumped out as part of the response plan to free the grounded vessel. 
         [0007]    Methods for mixing water in tanks as part of a treatment process have been developed to treat waste water from municipal sewage systems, manufacturing, and industry. These treatment methods generally incorporate large circular or square tanks to hold the water during treatment, mixing, and neutralization (if required) before the water is released. These tanks generally lack geometric complexity and are therefore relatively easy to mix using a variety of mechanical methods (i.e. axial mixers, eductors, air, and nozzles). The ballast tanks on ships are quite different. The tanks are engineered to be part of the structure of the ship and are integral to the stability and integrity of the ship. As a result, most ships have multiple ballast tanks (ranging in number from a few to dozens) that are geometrically complex and often have baffles, support structures, web frames, stringers, stations, piping, and rose boxes inside the tanks. Also, there can be different types of ballast tanks with different geometries on a single ship. This complexity makes it difficult to mix the water in the tanks as part of a treatment method. Moreover, there are about 70,000 cargo ships operating worldwide. It would cost the shipping industry billions of dollars to install and maintain permanent mixing systems in all ballast tanks on all ships. 
       SUMMARY 
       [0008]    A system, method, and apparatus for treating ship ballast water is presented herein. The system includes a ballast tank that stores ballast water and one or more nozzles located in the ballast tank. A pump supplies water to the nozzles and a biocide is injected into the water supplied to the nozzles or directly into the tank at alternative locations. The nozzles are strategically located in the ballast tank to circulate the ballast water and mix the chemical with the ballast water without removing the ballast water from the ballast tank. The nozzles may be operated alternately and intermittently to reduce equipment weight and power requirements and to optimize mixing rates. 
         [0009]    The nozzle mixing system can be implemented on an “as needed” basis, is relatively inexpensive to purchase and maintain, is simple to implement, is effective at quickly (a few hours) mixing the contents of the tank, and reduces exotic species introductions and provides improved control of those species introduced in the past. 
         [0010]    The nozzle mixing system and method enhances the mixing of ballast water tanks. Enhanced mixing is needed to 1) ensure all water in the tank is adequately mixed with a biocide for the required exposure time, 2) ensure the biocide is adequately mixed with a neutralizing agent (if required) before the water is released into the environment, 3) improve saltwater exchange efficiency as a means of preventing the spread of exotic species from port to port, and 4) facilitate the suspension of accumulated sediments in the tanks to enhance the efficacy of biocide treatment of exotic species that may be present in the sediment. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    Various aspects and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings. The drawings are not necessarily drawn to scale. In the drawings: 
           [0012]      FIG. 1  is a schematic perspective view of a ship ballast tank with a nozzle mixing system according to an embodiment of the invention; 
           [0013]      FIG. 2A  is a schematic cross-sectional view of a cargo ship illustrating mixing of water in two ballast tanks with double-bottom areas according to an embodiment of the invention; 
           [0014]      FIG. 2B  is a schematic top view of one of the ballast tanks shown in  FIG. 2A  illustrating placement of nozzles according to an embodiment of the invention; 
           [0015]      FIG. 2C  is a schematic perspective view of the ballast tank of  FIG. 2B  according to an embodiment of the invention; 
           [0016]      FIG. 3A  is a schematic, cross-sectional view of a cargo ship with two L-shaped ballast tanks according to an embodiment of the invention; 
           [0017]      FIG. 3B  is a schematic side view of one of the ballast tanks shown in  FIG. 3A  illustrating placement of nozzles and illustrating mixing of water according to an embodiment of the invention; 
           [0018]      FIG. 3C  is a schematic perspective view of the ballast tank of  FIG. 3B  according to an embodiment of the invention; 
           [0019]      FIG. 4A  is a schematic cross-sectional view of a cargo ship having a double-bottom ballast tank with width-to-height ratios that preclude establishment of a sufficient number of rotating fluid cells or vortexes; 
           [0020]      FIG. 4B  is a schematic top view of the double-bottom area of the ballast tank of  FIG. 4A  showing placement of a nozzle at an entrance of a pipe and mixing of water according to an embodiment of the invention; 
           [0021]      FIG. 4C  is a schematic perspective view of a seaward wall section of one of the ballast tanks shown in  FIG. 4A  illustrating placement of nozzles according to an embodiment of the invention; 
           [0022]      FIG. 5  is a schematic perspective view of a portion of a seaward section of the ballast tanks shown in  FIGS. 3C and 4C  according to an embodiment of the invention; 
           [0023]      FIG. 6A  is a diagram showing flow of water from pumps to nozzles according to an embodiment of the invention; 
           [0024]      FIG. 6B  is a graph illustrating determination of establishment of circulation currents in a ballast tank; 
           [0025]      FIG. 7A  is a schematic cross-sectional view of a ballast tank illustrating control of flow of water from a submersible pump to a nozzle according to an embodiment of the invention; 
           [0026]      FIG. 7B  is a schematic top view of the ballast tank shown in  FIG. 7A  according to an embodiment of the invention; 
           [0027]      FIG. 8  is a schematic, cross-sectional view of a ballast tank showing placement of a jet pump on a deck of a ship according to an embodiment of the invention; 
           [0028]      FIG. 9  is a diagram showing a fire suppression pump in an engine room of a ship used to provide water to the nozzle mixing system in a ballast tank according to an embodiment of the invention; 
           [0029]      FIG. 10A  is a diagram illustrating control of flow of water to nozzles using a single valve according to an embodiment of the invention; 
           [0030]      FIG. 10B  is a diagram illustrating control of flow of water to nozzles using multiple valves to achieve intermittent or continuous operation of all nozzles together according to an embodiment of the invention; 
           [0031]      FIGS. 11A and 11B  are schematic diagrams showing alternative nozzle configurations according to embodiments of the invention; 
           [0032]      FIGS. 12A and 12B  are diagrams showing alternative configurations for controlling operation of a valve that supplies water to a nozzle to achieve intermittent or continuous flow through the nozzle according to an embodiment of the invention; 
           [0033]      FIG. 13A  is a schematic top view of a ballast tank illustrating placement of three nozzles according to an example of an embodiment of the invention; 
           [0034]      FIG. 13B  is a schematic side view of the ballast tank of  FIG. 13A ; 
           [0035]      FIG. 14A  is a schematic top view of a ballast tank illustrating placement of two nozzles according to an example of an embodiment of the invention; 
           [0036]      FIG. 14B  is a schematic side view of the ballast tank of  FIG. 14A ; 
           [0037]      FIG. 14C  is a schematic perspective view of the nozzle arrangement shown in  FIG. 14A ; and 
           [0038]      FIG. 14D  is a schematic plan view of the nozzle arrangement shown in  FIG. 14C . 
       
    
    
     DETAILED DESCRIPTION 
       [0039]      FIG. 1  is a schematic perspective view of a nozzle mixing system  100  employed in a typical ballast tank  105  having a seaward wall  110 , a double-bottom area  115 , and a water level  117 . The nozzle mixing system  100  uses one or more nozzles  120  strategically placed inside the ballast tank  105  to deliver jets  125  of water. The type of nozzles  120 , location of the nozzles  120 , and volume and pressure of the water coming from the nozzles  120  create a circulation current  130  inside the tank  105 . The currents  130  developed by the transfer of the energy from the water jets  125  delivered by the nozzles  120  to the water in the ballast tank  105  result in complete mixing of all the water in the ballast tank  105  in a relatively short time (i.e., a few hours). The design of the nozzle mixing system  100  is dependent on the geometry and size of the particular ballast tank that is being mixed. The nozzle type, location of the nozzles in the tanks, and the pressure and volume of water delivered to the nozzles are a function of the environment in which the nozzles will be implemented. 
         [0040]    The nozzles  120  can be permanently installed in the ballast tank  105  when it is empty, or they can be lowered into the tank  105  before filling, during filling, or when it is full of water through inspection/access ports  135  located in the top of the tank  105 . The inspection/access ports  135  are accessible from the deck of the ship or through other hatches or openings in the bulk heads that may separate various components of the ballast tank. This latter type of deployment does not require any modification to the ship. Water is conveyed to the nozzles  120  through pipes/hoses  140 . Water to supply the nozzles  120  can be obtained from 1) an existing firefighting water supply system on the ship, 2) a submersible pump lowered into the ballast tank  105 , 3) a pump drawing water through a bulkhead connection into the lower portion of the ballast tank  105  via access through the maintenance or conveyor tunnels found on most cargo ships, and 4) inline pumps on the deck of the ship, such as jet pumps, diaphragm pumps, axial flow pumps, turbine pumps, gear pumps, piston pumps, centrifugal pumps, etc. Water supply to the nozzles is discussed in greater detail below. 
         [0041]    The double-bottom area  115  is typically only about five feet to six feet in height depending on the construction of the ship. Previous mixing methods have had difficulty mixing the water in double-bottom areas. However, the nozzle mixing system  100  generates hydraulic mixing of all portions of the tank  105 , as explained below. 
         [0042]    The objective of using nozzles for mixing is to impart an impulse force F from a single or multiple set of nozzles to provide the power needed to overcome resistive forces related to fluid drag over tank components by the receiving flow in motion. Multiple versus single nozzles operate at relatively high energy transfer efficiencies, and moderate velocity through the nozzles provides superior transfer efficiencies when compared to very high velocities through the nozzles. Further, establishing a rotary circulation or vortex within the tank is desirable to minimize mixing time rather than creating flow patterns that result in distorted non-circular or rectangular flow cells. Non-circular or rectangular flow cells act to establish bidirectional or opposing flow fields and thus increase power requirements due to fluid shear. Ship ballast tanks are not designed for optimal mixing. Rather, they are designed to add strength to the hull of the ship to withstand roll, pitch, and yaw forces while retaining liquid ballast volumes needed for stability. The nozzle mixing system  100  exploits the structure of ballast tanks, particularly transverse structural web frames, to avoid the drag related to bidirectional flow, as well as to help approximate mixing circulation cells that are stable, predictable, and that require reasonable levels of energy input. 
         [0043]      FIG. 2A  is a schematic cross-sectional view of a cargo ship illustrating two ballast tanks  205   a  and  205   b,  each having a double-bottom area  210   a  and  210   b,  respectively. The tanks  205   a  and  205   b  are structurally isolated from one another, and have dimensions of, for example, about 140 feet in length, 50 feet in width, and 30 feet in depth. Each of the ballast tanks  205   a  and  205   b  illustrates two different nozzle orientations. Nozzle  215  in tank  205   a  is oriented horizontally, and nozzle  220  in tank  205   b  is oriented vertically. Flow from the nozzles  215  and  220  transfers energy either horizontally or vertically, respectively, to establish transverse rolls  225   a  and  225   b  within the tanks  205   a  and  205   b.    
         [0044]      FIG. 2B  is a schematic top view of the tank  205   a.  In the embodiment shown in  FIG. 2B , three nozzles  215   a,    215   b,  and  215   c  divide the tank  205   a  into three mixing cells that impart energy and flow into the hard to mix double-bottom area  210   a.  Water is not jetted directly into the double-bottom area  210   a  because this results in rapid energy dissipation due to the presence of regularly spaced stiffeners and bulk heads (not shown) in the double-bottom area  210   a,  although in some cases this may result in enhanced mixing depending on the geometry of the tank and nozzle orientation. Water moves in and out of the double-bottom area  210   a  and between sections within the double-bottom area via lightening holes  217  in web frames  219 .  FIG. 2C  is a schematic perspective view of tank  205   b  with nozzles  220   a,    220   b,  and  220   c  located near the bottom of the tank. 
         [0045]    The arrows in  FIGS. 2A to 2C  show that the energy transferred from the water delivered by the nozzles, in either orientation, to the water in the tanks  205   a  and  205   b  establishes transverse flow and circulation currents to facilitate complete mixing of all water in the tanks  205   a  and  205   b.    
         [0046]      FIGS. 3A ,  3 B, and  3 C illustrate mixing of L-shaped ballast tanks.  FIG. 3A  is a schematic, cross-sectional view of a cargo ship with two L-shaped ballast tanks  305   a  and  305   b  having seaward sides  310   a  and  310   b  and double-bottom areas  315   a  and  315   b , respectively. Tank  305   b  shows the placement of a nozzle  320  in a vertical orientation.  FIG. 3B  is a schematic side view of the seaward wall of the tank  305   b  and  FIG. 3C  is a schematic perspective view of the tank  305   b,  both illustrating placement of three nozzles  320   a,    320   b , and  320   c.  The nozzles  320   a,    320   b,  and  320   c  operate vertically in this embodiment to induce flow laterally among transverse web frames  325  that are coupled, hydraulically, by lightening holes  330  in the web frames  325 . The surfaces of the web frames  325  prevent drag related to opposing flow streams and hence provide for mixing with relatively low power requirements. 
         [0047]    The arrows in  FIGS. 3A to 3C  show that the energy transferred from the water delivered by the nozzles  320   a,    320   b,  and  320   c  to the water in the tank  305   b  establishes a transverse flow and circulation current to facilitate complete mixing of all water in the tank  305   b.  Water moves in and out of adjacent areas through the lightening holes  330  in the web frames  325  between the tank sections. The circulation currents in the vertical part of the tank  305   b  pull water out of the double-bottom area  315   b  as shown in  FIG. 3A . Mixing of the double-bottom area  315   b  is not depicted in  FIG. 3C . 
         [0048]      FIGS. 4A ,  4 B, and  4 C illustrate mixing of a double-bottom ballast tank  405  that has a width to height ratio that precludes the establishment of a sufficient number of rotating fluid cells or vortexes.  FIG. 4A  is a schematic cross-sectional view of a cargo ship having the ballast tank  405 , a double-bottom area  410 , two seaward wall sections  415   a  and  415   b,  a pipe  420 , and a nozzle  425 .  FIG. 4B  is a schematic top view of the double-bottom area  410  showing a nozzle  430  at an entrance of the pipe  420 , web frames  435  between tank sections, and lightening holes  440 .  FIG. 4C  is a schematic perspective view of the seaward wall section  415   b  illustrating placement of nozzles  425   a,    425   b,  and  425   c.    
         [0049]    Mixing is achieved in this embodiment by using the nozzle  430  to direct water from one end of the tank  405  to the opposite end, which forces water to move through each tank subsection via the lightening holes  440  in the web frames  435  to complete a circulation cell. In the double-bottom area  410 , the nozzle  430  directs water inside the pipe  420  and the energy at the end of the pipe  420  causes water to move between adjacent areas through the lightening holes  440  in the web frames  435 . Mixing in this type of tank occurs due to displacement and dispersion and typically requires two to four complete exchanges to ensure complete mixing of all the water in the tank. There is only one double-bottom ballast tank shown in  FIGS. 4A to 4C . For a ship having two double-bottom tanks that are nearly hydraulically isolated, mixing is achieved by implementing the embodiment shown in  FIG. 4B  in each of the separate tanks. 
         [0050]    The arrows in  FIGS. 4A to 4C  show that the energy transferred from the water delivered by the nozzles  430 ,  425   a,    425   b,  and  425   c  to the water in the tank  405  is sufficient to establish a transverse flow and circulation current to facilitate complete mixing of all water in the tank  405 . 
         [0051]      FIG. 5  is a schematic perspective view of a portion of the seaward section of the ballast tanks shown in  FIGS. 3C and 4C . For purposes of illustration, seaward wall section  415   b  is discussed in relation to  FIG. 5 . The arrows show that the movement of water resulting from the energy transferred from the water delivered by any of the nozzles, for example, the nozzle  425   b,  to the water in the tank section  415   b  establishes a transverse flow and circulation current to facilitate complete mixing of all water in the tank section  415   b . The transfer of energy causes water to move between adjacent areas through the lightening holes  440  in the web frames  435  between the tank sections. 
         [0052]    Ballast tanks are engineered to be part of the structure of the ship and are integral to the stability and integrity of the ship. As a result there are often multiple types of ballast tanks on a ship that are geometrically complex depending on the baffles and support structures inside the tank. Of the approximately 70,000 ships currently engaged in global trade, the variety of tank geometry is vast. 
         [0053]    The nozzle mixing system disclosed herein uses currents developed by the transfer of energy from the water delivered by the nozzles to the water in any tank to completely mix all water in the tank in a relatively short time to facilitate the introduction of biocides and biocide neutralizing agents within the tank so the water can be treated, tested and de-ballasted in accordance with ballast discharge standards. This system does not require the water to be removed from the tank and delivered to a separate mixing and treating system located on or off the ship. Rapid mixing is required since some biocides being considered for killing invasive species have a short half-life. Thorough mixing of the water in the tank requires specifying the type of nozzles used, the locations of the nozzles in the tank, and the pressure and volume of water delivered to the nozzles. All of these specifications are a function of the environment in which the nozzle mixing method is implemented. 
         [0054]    The number of nozzles used is determined by the geometry of the particular ballast tank and the shape and abundance of the internal web frames in the tank. The embodiments shown in  FIGS. 2C ,  3 C, and  4 C show the use of three nozzles to establish the necessary energy to mix the portion of the tank that is adjacent to the seaward wall of the side of the ship. However, if the tanks are longer or contain more internal web frames, more nozzles may be required. Ultimately, the objective is to install the minimum number of nozzles needed to mix the tank in an efficient and timely manner with the minimum energy input into the mixing system. 
         [0055]    The placement of the nozzles is dependent upon the environment in which they will be used. Ultimately, the type, location, and pressure and volume of the water delivered to the nozzles is designed to generate a vertical circulation current in the tank that mixes all the water in the tank in a relatively short time. The currents that are established by the nozzles result in water being pulled out of areas in the tank that are otherwise isolated by the baffles and support structures inside the tank. 
         [0056]    The location of the nozzles is based on the geometry of the tank, the water level in the tank, and the shape and abundance of internal web frames in the tank. Simply placing nozzles on the sides or bottom of a tank will not ensure complete mixing of the water in the tank. The nozzles need to be strategically placed to ensure complete mixing. Also, simply using pumps to draw water from one part of the tank and reintroducing water back into the tank, thereby establishing a circulation loop, results in inconsistent results, extended periods of time to ensure complete mixing, and requires specialized pumps, hoses, pipes, and expensive retrofitting to the ship&#39;s infrastructure. 
         [0057]    Minimizing the amount of energy the nozzle mixing system requires and the weight of the system is a primary objective given (1) the limited energy resources and high cost of energy available on board the ship, and (2) the need to subtract equipment weight from cargo potential of the ship. Equipment weight and power requirements can be reduced by imparting a strategy of intermittent nozzle operation, rather than the standard continuous operation mode, during the treatment period. 
         [0058]    Intermittent operation is achieved by diverting water, for example, from a single submersible pump located in the ballast tank alternately to one or the other of a strategically positioned pair of nozzle assemblies within the same tank. Water routing is achieved through use of powered on/off or 3-way control valves regulated by a time-based control system, such as a programmable logic controller (PLC). Switching frequencies and duration are related to system volume, geometry, and nozzle operating conditions and thus are dependent upon the particular ballast tank. The mixing rate in different regions of the ballast tank is optimized by altering nozzle activation times when one side of the tank has more drag-related structure than the other side. Alternatively, a single nozzle or group of nozzles served by a single dedicated pump can operate intermittently by intermittently powering the pump with a time-based controller that regulates electrical service. 
         [0059]    Energy transfer improves as velocity differentials between the bulk circulating flow and the nozzle velocity increases. Given hydraulic drag effects within the tank will slow bulk fluid velocities after nozzle flow has been terminated, reactivation of the nozzles, intermittently, will result in nozzle flows interacting with bulk flows that are not constant but vary with time and are relatively low, on average. Further, once the bulk circulating flow is established, the kinetic energy of the bulk flow will allow for the continued mixing and blending once nozzle flows have been redirected or terminated. 
         [0060]    The location and number of pumps supplying water to the nozzle(s) can also be optimized to minimize the energy requirements of the mixing system and ensure complete mixing in areas of the tank that are nearly hydraulically isolated. Geometrically complex tanks often result in areas in the tank that are somewhat isolated and difficult to mix. For these tanks, using a single pump could be more efficient than using two pumps located in separate areas of the tank. A single pump located in the area that is difficult to mix would be used to draw water from this area and deliver it to one or more nozzles located elsewhere in the tank. The energy transferred from the nozzles to the water in the tank would result in water circulating back into the area where the pump is located. A pump drawing water from an area that is difficult to mix to supply water to nozzles in other locations combined with the mixing effect of the rotary circulation currents generated by the nozzles is sufficient to thoroughly mix all areas of the tank in an efficient manner with a single pump. 
         [0061]      FIG. 6A  is a diagram showing a Programmable Logic Controller (PLC)  605  used to control the flow of water from one or more pumps  610  to the nozzles, such as nozzles  424   a,    425   b,  and  425   c  illustrated in  FIG. 4C , through valves  615 ,  620 , and  625 . The PLC  605  is a time-based or time-based plus velocity-based controller positioned outside of the ballast tank. A return signal may be used at the PLC  605  to indicate valve positions. Lines  626 ,  627 , and  628  transmit power source/signals respectively to each of the on/off valves  615 ,  620 , and  625  used to control the flow of water from the pump  610  to the nozzles  425   a ,  425   b,  and  425   c.  The number of nozzles used depends upon the application of the mixing technology. 
         [0062]    Also shown in  FIG. 6A  is a flow sensor  630  that can be used in the tank to provide a signal back to the PLC  605 .  FIG. 6B  is a graph illustrating that the flow sensor  630  can be used to determine when circulation currents have been established in the tank (as represented by curve  645 ) and to turn the supply of water on and off as needed (as represented by curves  645 - 650 - 645 - 650 , etc. in succession) to maintain the necessary flow from the nozzles to keep the circulation currents established. Turning the system on and off minimizes energy consumption of the system but maintains the velocities necessary for mixing. The flow sensor  630  in the tank can be used to indicate the condition of the bulk solution velocity and can be used to signal turning the valves  615 ,  620 , and  625  on and off to minimize the energy needs of the mixing system. 
         [0063]      FIG. 7A  is a schematic cross-sectional view of a typical ballast tank  705  showing a power supply  710 , the PLC  605 , and a power line  715  to a submersible pump  717 . Water from the pump  717  moves to a nozzle  720  through pipes/hoses  725 . 
         [0064]      FIG. 7B  is a schematic top view of the ballast tank  705 . The PLC  605  controls valves  730  and  735  and the submersible pump  717 . Water moves from the pump  717 , through the valves  730  and  735 , to the nozzles  720  and  740  through the pipes/hoses  725 . The single pump  717  in this embodiment can supply water to both nozzles  720  and  740  simultaneously or one at a time, alternately, as directed by the PLC  605 . Alternating operation of the nozzles  720  and  740  can reduce the energy demands of the system as discussed above. Alternative locations of the pump, shown as pump  717   a  and  717   b,  can be used to minimize the energy requirements of the mixing system and ensure complete mixing in areas of the tank  705  that are nearly hydraulically isolated. A single pump, such as pump  717   a  or  717   b,  located in an area that is difficult to mix can be used to draw water from this area and deliver it to one or more nozzles located elsewhere in the tank  705 . 
         [0065]      FIG. 8  is a schematic, cross-sectional view of a ballast tank  805  showing placement of a jet pump  810  on the deck of a ship. Using the jet pump  810  eliminates the need to supply electrical power down into the tank  805  that would otherwise be needed if a submersible pump is used. In this embodiment, the power supply  710  supplies power to the PLC  605  that controls operation of the jet pump  810 . Water is drawn from the tank  805  through an inlet  815  containing a check valve. Recirculating flow in two parallel lines  820  and  825  is used to supply water to a nozzle  830  through a pipe/hose  835 . To establish recirculating flow in lines  820  and  825 , line  820  is primed with water from a surface-supplied line such as a hose from the ship&#39;s fire suppression system. 
         [0066]      FIG. 9  is a diagram showing a fire suppression pump  905  in the engine room of the ship used to provide water to the nozzle mixing system in a ballast tank  910 . Water is drawn from the ballast tank  910  by the pump  905  used for the ship&#39;s fire suppression system  915 . A hose/pipe  920  is used to bypass water through a valve  925  that is controlled by the PLC  605 . 
         [0067]      FIGS. 10A and 10B  are diagrams showing alternatives to controlling flow of water to nozzles. In  FIG. 10A , water from a pump  1005  is controlled by a single valve  1010  that is operated by the PLC  605 . Water flows from the valve  1010  through a manifold  1015  to achieve intermittent or continuous operation of all nozzles  1020  together. In  FIG. 10B , additional valves  1025  controlled by the PLC  605  are added between the manifold  1015  and the nozzles  1020  to achieve independent operation of the nozzles intermittently or continuously. 
         [0068]      FIGS. 11A and 11B  are schematic diagrams showing alternative nozzle configurations. In  FIG. 11A , a single nozzle  1105  is used to convey water from a pump  1110  into the ballast tank. In  FIG. 11B , multiple smaller nozzles  1115  are used to convey water from the pump  1110  into the ballast tank. The thrust generated by the nozzles (which can be significant) should be considered when installing them in the ballast tank to ensure that they remain in the desired locations and orientations. Those familiar with fluid mixing will understand that there are various ways to negate nozzle thrust. 
         [0069]      FIGS. 12A and 12B  are diagrams showing alternatives for controlling the operation of a valve  1205  that supplies water to a nozzle  1210  to achieve intermittent or continuous flow through the nozzle  1210 . In  FIG. 12A , the PLC  605  is attached to a submersible pump  1215  and the valve  1205  by a signal/power source cable  1220 . To actuate and control the pump  1215  and the valve  1205 , the PLC  605  sends and receives electricity through the cable  1220 . A configuration that eliminates installation of electrical components underwater in the ballast tank is shown in  FIG. 12B . In this embodiment, water is delivered through the valve  1205  to the nozzle  1210  via a pipe/hose  1225  from a jet pump  1230  located on the deck of the ship. The valve  1205  is operated by a pneumatic controller  1235  on the deck of the ship that is controlled by the PLC  605 . An air line  1240  connects the pneumatic controller  1235  and the valve  1205 . Controlling the operation of the valves to supply water to the nozzles to achieve intermittent or continuous flow through the nozzles can be applied to any of the embodiments described above. 
         [0070]    The advantages of the nozzle mixing system disclosed herein include the following: 
         [0071]    1) the components of the nozzle mixing system are inexpensive; 
         [0072]    2) there are few parts that require maintenance or repair; 
         [0073]    3) the nozzle mixing system needs relatively inexpensive redesign or modification to the ship compared to dedicated pre- or post-treatment systems that are integrated into the infrastructure of the ship; 
         [0074]    4) if permanent installation is desired, the installation and maintenance of the nozzle mixing system as a permanent part of the ship&#39;s infrastructure is inexpensive; 
         [0075]    5) the nozzle mixing system is portable and can be moved from tank to tank as needed so one system can be used to mix multiple tanks onboard a ship, and the portability of the nozzle mixing system facilities its use in emergency situations such as groundings; 
         [0076]    6) the nozzle mixing system can be integrated with the existing firefighting system on board the ship to reduce the amount of equipment needed to implement the system; 
         [0077]    7) the nozzle mixing system can be modified to mix different ballast tank configurations; 
         [0078]    8) the nozzle mixing system can be used to introduce biocides into the ballast tanks by injecting the biocide into the stream used to supply water to the nozzles; 
         [0079]    9) the ballast tank water does not need to be continuously removed, sent through a treatment system, and returned to the tank—complete mixing can be achieved with the nozzles alone; and 
         [0080]    10) the nozzle mixing system can mix and treat the contents of a tank faster than conventional systems can mix a tank. 
         [0081]    Thus, application of the nozzle mixing system can reduce the worldwide spread of aquatic invasive species and the environmental and economic impact they can cause. 
       EXAMPLES 
       [0082]    Examples will now be described in detail below that serve to illustrate embodiments of the nozzle mixing system and method described herein. However, it will be understood that the present invention is in no way limited to the examples set forth below. 
       Example 1 
       [0083]    The nozzle mixing system was tested in a ballast tank having a double-bottom area. Ballast tanks having double-bottom areas are commonly found on many ships. The placement of the nozzles determines the necessary energy to establish circulating currents that result in pulling water out of the double-bottom area. 
         [0084]    Example 1 is illustrated in  FIGS. 13A and 13B .  FIG. 13A  is a schematic top view of a ballast tank  1302  with three nozzles  1305   a,    1305   b,  and  1305   c  and a double-bottom area  1310 .  FIG. 13B  is a schematic side view of the ballast tank  1302 . The nozzle mixing system and method was tested on the ship the Indiana Harbor (American Steamship Company, Williamsville, N.Y.) in ballast tank #4 on the starboard side. The ballast tank had a length L of 144 feet, a width W of 39 feet, and a height H of 45 feet. The double-bottom area  1310  had a height DBH of 31 inches and a width DBW of 9 feet, 9 inches. The tank had 17 web frames that were each 4 feet high and spaced every 8 feet. The depth of water in the tank was 20 feet. 
         [0085]    The nozzles were mounted at a height NH of 88 inches from the bottom of the tank  1302  on the inside of seaward wall  1315  with the nozzles pointing towards mid-ship. To determine the position of the three nozzles  1305   a,    1305   b,  and  1305   c  laterally, the overall length of the tank was divided by three and each of the nozzles was respectively placed at approximately the center of each one-third portion of the length of the tank  1302 . In Example 1, the nozzle  1305   b  was placed at the middle of the length L of the tank, nozzles  1305   a  and  1305   b  were placed at a distance D 1  of 47 feet, respectively, on either side of the nozzle  1305   b,  leaving a distance D 2  of 25 feet at the forward and aft ends of the tank. The height and lateral positions of the nozzles were sufficient to establish the desired mixing and circulation currents in the tank. 
         [0086]    Each nozzle had a ¾-inch diameter nozzle orifice. A 3-inch diameter hose supplied water to each nozzle at a rate of 110 gallons per minute (GPM) at 50 pounds per square inch (PSI) at the nozzle outlet, and 330 GPM total. 
         [0087]    Tank mixing was completed in less than 1.5 hours. 
         [0088]    Example 2 
         [0089]    The Indiana Harbor was also used for the second example, with the same ballast tank dimensions as in Example 1. Example 2 is illustrated in  FIGS. 14A to 14D .  FIG. 14A  is a schematic top view of a ballast tank  1402  with two nozzles  1405   a  and  1405   b  and a double-bottom area  1410 .  FIG. 14B  is a schematic side view of the ballast tank  1402  of  FIG. 14A .  FIG. 14C  is a schematic perspective view of arrangement of the nozzles  1405   a  and  1405   b.    FIG. 14D  is a schematic plan view of the nozzle arrangement shown in  FIG. 14C . 
         [0090]    As shown in  FIG. 14A , the nozzles  1405   a  and  1405   b  are located laterally in the center of the tank  1402  along a seaward wall  1415 . The height of each of the nozzles  1405   a  and  1405   b  from the bottom of the tank  1402  differs, as shown in  FIGS. 14B and 14C . A pipe/hose  1420  conveys water to the nozzles  1405   a  and  1405   b.  The nozzle  1405   a  at the end of the pipe/hose  1420  is located at a height H 1  of 97 inches from the bottom of the tank. Pipe fittings (not shown) that connected the bottom nozzle  1405   a  to the top nozzle  1405   b  resulted in the top nozzle  1405   a  being 13 inches above the bottom nozzle  1405   b,  placing the top nozzle  1405   b  at a height H 2  of 110 inches from the bottom of the tank  1402 . 
         [0091]    The orientation of the nozzles  1405   a  and  1405   b  relative to each other and the seaward wall  1415  of the tank  1402  is shown in  FIG. 14D . The nozzles  1405   a  and  1405   b  were oriented at an angle A 1  of 90° from one another and at an angle A 2  of 45° from the seaward wall  1415  of the tank  1402 . Each nozzle had a ⅞-inch diameter nozzle orifice. A 4-inch diameter hose supplied water to each nozzle at a rate of 150 GPM at 50 PSI at the nozzle outlet, and 300 GPM total. 
         [0092]    Tank mixing was completed in less than 2 hours. 
         [0093]    The type, location, and pressure and volume of the water delivered to the nozzles during the tests are applicable for many ballast tank configurations. However, smaller tanks that are not geometrically complex will require fewer nozzles and lower volume and pressure of water delivered to the nozzles. Likewise, larger tanks that are geometrically complex may require more nozzles and may also require higher volume and pressure delivered to the nozzles. 
         [0094]    Thus, it will be appreciated by those skilled in the art that modifications and variations of the present invention are possible without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents. 
       REFERENCES CITED 
       [0000]    
       
         Bureau of Transportation Statistics 2007 (2008) Washington, D.C. United States Department of Transportation, Research and Innovative Technology Administration http://www.bts.gov/publications/maritime trade and transportation/2007/pdf/entire.pdf. 
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         Carlton, J. T. 1985. Transoceanic and interoceanic dispersal of coastal marine organisms: the biology of ballast water. Oceanogr. Mar. Biol. Ann. Rev. 23: 313-371. 
         Carlton, J. T. and Geller, J. B. 1993. Ecological roulette: the global transport of nonindigenous marine organisms. Science 261: 78-82. 
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         Mooney, H. A. and Drake, J. A. (eds). 1986. Ecology of biological invasions of North America and Hawaii. Springer-Verlag, New York 
         National Academies of Science (NAS) 1996. Stemming the tide: controlling introductions of nonindigigenous species by ships&#39; ballast water. Marine Board Committee on Ships&#39; Ballast Operations. National Academies Press, Wash. D.C., 160 p. ISBN: 0-309-58932-0 
         Office of Technology Assessment Archive, 1993. Harmful Non-Indigenous Species in the United States, September 1993, OTA-F-565,NTIS order #PB94-107679,GPO stock #052-003-01347-9