Abstract:
A method to treat ballast water comprises injecting ozone into water loading into a sea faring vessel prior to charging the water into a ballast tank; and charging the ozone injected water into the ballast tank. A system for treating ballast water comprises a sea faring vessel including at least one ballast tank; an ozone generator that generates ozone, a ballast water conduit that uptakes water through a loading port of a sea faring vessel and conducts the water to load the ballast tank; and an ozone feed line that injects ozone from the generator into water in the conduit at an injection point located upstream to an intersection of the conduit with the ballast tank.

Description:
[0001]    This application claims the benefit of U.S. Provisional Application Serial No. 60/372,806, filed Apr. 17, 2002, the disclosure of which is incorporated herein by reference in its entirety. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    The invention relates to a ballast water ozone injection method and system. More particularly, the invention relates to a system for using ozone to treat ballast water during loading or discharge of ballast water to or from the ballast tanks of a sea faring vessel.  
           [0003]    Ballast water weight is used by sea vessels to compensate for a lack of cargo weight when the cargo load is empty or partially empty. For example in a typical transport operation, a sea vessel docks at a first port where it is loaded with a cargo that the vessel transports to a second port where the cargo is unloaded. The vessel then returns to the first port where it is loaded with another cargo. Typically, the vessel travels empty from the second port back to the first port to pick up another cargo. The vessel is equipped with ballast tanks that can be filled with water to maintain the balance of the vessel on an even keel when it travels empty. Conventional ballast tanks include valves usually mounted over apertures through tank bulkheads. The valves are actuated to move water between and into and out of various ballast tanks to trim the vessel when empty of cargo or when carrying an unevenly distributed cargo.  
           [0004]    The vessel fills its ballast tanks by taking on sea water, usually at its cargo discharge port. The sea water is charged into the ballast tanks at the same time that the vessel off loads its cargo. The vessel then travels to its cargo loading port where it takes on cargo while at the same time it empties at least some and typically all of its ballast tanks by discharging the ballast water into the loading port water environment.  
           [0005]    The ballast water intake is below the water line of a vessel usually at or near the vessel hull bottom. The ballast water contains algae, zooplankton and other organisms that are indigenous to the cargo discharge port. Significant quantities of these indigenous organisms are loaded into the ballast tanks along with the water. The vessel then transports these organisms to the cargo loading port where the organisms are discharged into the water environment along with discharged ballast water. Some of these organisms may be deleterious to and very much unwanted in the loading port environment. They cause damage to the water environment and replace benthic organisms and clear plankton communities that provide food and larvae for resident native species in overlying waters.  
           [0006]    The zebra mussel (Dreissena polymorpha) is an example of an unwanted organism that has been spread by ballast water. The zebra mussel was first found in the mid eighteenth century in the northern Caspian Sea and in the Ural River. Since then, the mussel has spread to other parts of the world by means of ballast water discharge. The mussel was found in the Great Lakes in late 1988. It was first prevalent in Lake Erie. Since then, the mussel has spread into Lake Michigan and into rivers of the Midwest and Northeast.  
           [0007]    The mussel has threadlike tentacles that enable it to adhere to any vertical or horizontal surface. It is particularly adherent to the shell of another mussel. It reproduces quickly and in a brief time can obtain population densities in excess of 30,000 mussels per square meter. Stacks of adhering mussels have been known to completely clog water intake orifices and shut down municipal water treatment plants and industrial water systems.  
           [0008]    In 1996, Congress passed the National Invasive Species Act (P. L. 104-332) to stem the spread of nonindigenous organisms by ballast water discharge. The act reauthorized the Great Lakes ballast management program and expanded applicability to vessels with ballast tanks. The Act requires the Secretary of Transportation to develop national guidelines to prevent the spread of organisms and their introduction into U.S. waters via ballast water of commercial vessels.  
           [0009]    Guidelines developed pursuant to the can require vessels that enter U.S. waters to undertake ballast exchange in the high seas. Ballast water exchange involves replacing coastal water with open-ocean water during a voyage. This process reduces the density of coastal organisms by replacing them with oceanic organisms with a lower probability of survival in near shore waters. However, ballast exchange has two important short-comings. First, the ability to safely conduct ballast water exchange depends upon weather and sea surface conditions, and it is not always possible to perform an exchange. Second, there is still some residual density of coastal organisms in ballast tanks following exchange, so the process is only partly effective.  
           [0010]    There is a need for a safe and effective method and system to treat ballast water for discharge into destination water environments.  
         BRIEF DESCRIPTION OF THE INVENTION  
         [0011]    The invention relates to a safe and effective method and system to treat ballast water. The method comprises injecting ozone into water loading into a sea faring vessel prior to charging the water into a ballast tank; and charging the ozone injected water into the ballast tank. The system comprises a sea faring vessel including at least one ballast tank; an ozone generator that generates ozone, a ballast water conduit that uptakes water through a loading port of the sea faring vessel and conducts the water to load the ballast tank; and an ozone feed line that injects ozone from the generator into water in the conduit at an injection point located upstream to an intersection of the conduit with the ballast tank.  
           [0012]    In an embodiment, the method of treating ballast water comprises pumping ballast water into a sea faring vessel through a flow line; and injecting ozone into the ballast water as it flows through the flow line.  
           [0013]    Another method of ozone treatment comprises injecting ozone into water discharging from a ballast tank at a location downstream from the tank; and unloading the ozone injected water to the sea.  
           [0014]    In another embodiment, a ballast-water treatment system comprises a sea faring vessel including at least one ballast tank; an ozone generator that generates ozone, a ballast water conduit that discharges water from the ballast tank and conducts the water to an unloading port of the sea faring vessel; and an ozone feed line that injects ozone from the generator into water in the conduit at an injection point located downstream to an intersection of the conduit with the ballast tank. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0015]    [0015]FIG. 1 is a schematic perspective view of a double hulled tanker and a prior art ballast water treatment system;  
         [0016]    [0016]FIG. 2 is a schematic top view of a prior art tanker and treatment system;  
         [0017]    [0017]FIG. 3 is a schematic side view of a prior art tanker and treatment system;  
         [0018]    [0018]FIG. 4 is a schematic top view of a tanker and treatment system illustrating an embodiment of the invention;  
         [0019]    [0019]FIG. 5 is a schematic side view of the tanker of FIG. 4;  
         [0020]    FIGS.  6  to  10  are schematic representations of embodiments of ballast water ozone injection methods and systems; and  
         [0021]    [0021]FIG. 11 is a schematic representation of a system to conduct a test ballast water ozone injection. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0022]    Ozone (O 3 ) is an allotropic form of oxygen. It is an unstable blue gas with a pungent odor, a molecular weight of 48 g/mol and a density as a gas of 2.154 g/liter at 0° and 1 atm. It is approximately 13 times more soluble in water than is oxygen. Ozone is highly unstable and is a powerful oxidizing agent. It is 1.5 times better and approximately 3125 times faster than chlorine as an oxidizer. It is non-persistent and has a very short half-life. Its half-life in pure distilled water is approximately 40 min at pH 7.6. Because of the unstable nature of the O 3  molecule, it cannot be stored but must be generated on-site.  
         [0023]    Typically, ozone is produced by passing oxygen, in some concentration, through a highly charged corona field, a technique known as “corona discharge”. The corona may be produced by applying a very high electric potential (20 kV) between two conductors that are separated by an insulating dielectric layer and a small air gap. Under these conditions, molecular oxygen (O 2 ) passing through the gap between the conductors experiences sufficient dissociation energy to partially ionize. A certain fraction of the free oxygen ions will re-associate in the form of O 3 , according to the equilibrium reaction equation: 
         3O 2 +69 kcal⇄2O 3   (I) 
         [0024]    Ozone is currently used as a means for purifying liquids, but most applications for this technology have centered on relatively low liquid volume applications. Ozone has been increasingly suggested as a candidate for very large scale liquid purification projects. For example, ozone has been used to treat ballast water in ballast water tanks. The ozone rapidly converts naturally occurring ballast water iodides and bromides into bromine and iodine, which can be toxic to organisms. The general concept of ballast water treatment with ozone is to use a sea faring vessel&#39;s transit time between ports as an opportunity for treatment. In-transit ozone treatment of ballast water has been found to be cost-effective and environmentally sound. Ozone treatment is viewed as superior to both chemical treatment, which may require the transportation and disposal of hazardous substances over the sea, and separation technology, which is uneconomical because of the large volume of water requiring treatment.  
         [0025]    Commonly assigned Rodden, U.S. Pat. No. 6,125,778 teaches a method to render ballast water free of contaminating organisms. In the Rodden method, a ballast water treatment system includes a source of ozone and a ballast tank connected to the source of ozone. The ozone is provided to a ballast tank through an ozone-transport system. The system may include a pressure generation system to regulate a flow pressure such that the flow pressure is substantially ambient at an exit end of the ozone generator while the ozone is injected under a positive pressure when reaching the ballast tank.  
         [0026]    The Rodden system and method are illustrated in FIGS.  1  to  3 , wherein tanker  2  includes bow  4 , stem  6  and a double hull formed from outer hull  8  and inner hull  10 . Tanker  2  can be a very large carrier designed for transporting crude oil. However, the present invention can be applied to any sea faring ship or vessel that has ballast tanks or bilge water. Tanker  2  is representative of the types of vessels encompassed within the invention and is a conventionally proportioned double hulled oil tanker having cargo compartments within inner hull  10 . The tanker  2  is typical of vessels that transport partly or fully refined or residual petroleum or other bulk liquid products such as seed oil.  
         [0027]    Tank section  12  of tanker  2  is formed by the interior surface of inner hull  10  and includes a port tank section  14  and a starboard tank section  16 , which are separated by longitudinal bulkhead  18 . The longitudinal bulkhead  18  extends the length of tank section  12 . The port tank section  14  and starboard tank section  16  are divided along their lengths by transverse bulkheads  20 . The transverse bulkheads  20  extend into the spacing between outer hull  8  and inner hull  10 . The spacing is also divided by plating  22 , which together with transverse bulkheads  20  divide the double hull spacing into a plurality of ballast tanks  24 .  
         [0028]    The ballast tanks  24  are filled or partially filled with water to maintain the balance of the tanker  2  on an even keel, particularly when it travels empty or partially filled. Tanker  2  typically fills its ballast tanks  24  by taking on water at its cargo discharge port. This water contains species indigenous to the discharge port. As described aforesaid, these species may be harmful to the environment at a cargo loading port where ballast water is discharged to balance added weight of loaded cargo. The tanker  2  may exchange the ballast water in open sea to avoid discharge at the loading port. However, this is a dangerous and labor intensive procedure. According to the present invention, ballast water is treated with ozone while the tanker  2  is in transit between ports to destroy the harmful species. Then, the treated ballast water can be discharged at a loading port without introducing foreign species into the loading port environment.  
         [0029]    The Rodden patent describes an in transit ozone treatment of ballast water by means of a treatment system shown in FIGS.  1  to  3 . The system includes a source of ozone that can be located anywhere on a vessel with ballast water in need of treatment. In FIGS.  1  to  3 , an ozone generator  30  is located on bridge  26  of aft section  28 . Ozone generator  30  can be any apparatus for the generation of ozone. The ozone generator  30  can include a tubular generator or a battery of tubular ozone generators.  
         [0030]    Main ozone feed line  74  runs from ozone generator  30  along top deck  76  parallel to the longitudinal axis of tanker  10 . Off lines  78  intersect feed line  74  at 90 degree angles and connect to feed line  74  via valves  80 . Each off line  74  runs from a respective valve  80  transverse to the feed line  74  and to the longitudinal axis of tanker  10 , thence downwardly through top deck  76  into a ballast tank  24 . As shown in FIGS.  3  to  5 , tanker  2  includes a plurality of ballast tanks  24  arranged in both horizontal and vertical arrays between the tanker outer hull  8  and inner hull  10 . Each vertical array extends transverse to the longitudinal axis of tanker  10  along the side of the tanker and along the tanker bottom as illustrated in FIG. 4. Each horizontal array extends parallel to the longitudinal axis of tanker  10  as shown in FIG. 5. FIG. 4 shows that each off line  78  extends down a vertical array and into an array of ballast tanks along the side of the tanker  2  and along the tanker bottom  82 . A treatment line extends from each off line  78  into a horizontal array of tanks  24 . The treatment line extends into a horizontal array of three tanks  24 . However, a treatment line can extend into a horizontal array of any number of tanks. The tanks  24  are serially connected one after the other, to the ozone generator  30  by means of a treatment line and off line  78  via the feed line  74 . Each off line  78  includes consecutively connected treatment lines from a first treatment line to a final treatment line connected near the termination of the off line  78  near the keel  80  of the tanker  2 . Tanks  24  are serially connected to each consecutively connected off line  78  in a manner as aforesaid.  
         [0031]    A diffuser connects to a treatment line in each serially connected tank  24 . The diffuser is a duct, chamber or section in which a high-velocity, low-pressure stream of ozone is converted into a high-velocity high-pressure flow in the form of small uniform bubbles. A preferred diffuser is a rigid, monolithic, porous gas diffusion element formed of a body of solid particles and comprised of a partially coated, permeable ceramic substrate. The diffuser injects ozone into water within a ballast tank  24  in the form of diffuse, substantially uniform bubbles that form a continuous cascading treatment pattern.  
         [0032]    In operation, ozone is generated by ozone generator  30  and flows along the longitudinal axis of the tanker via main line  74 . If valve  80  is actuated to connect an off line to main line  74 , the ozone will be diffused into ballast water of the tank connected to the off line. The ozone diffusion is continued until the ballast water is substantially treated. During the treatment process, bromine and iodine is consumed in the destruction of the organisms. The bromine and iodine content of the water remains at a stable level until substantially all organisms have been destroyed. Then the bromine and iodine levels of the water begin to increase. Hence, effectiveness of ozone treatment of ballast water within a tank can be monitored by monitoring the ballast water bromine and/or iodine content. Periodic sampling of the water can be conducted. When the bromine and/or iodine content commences to increase to residual levels of about 1 ppm to about 2 ppm or greater then biokill of organisms is assured and ozone treatment can be can be terminated.  
         [0033]    There are a number of complexities that arise in adapting an ozone treatment process to the very large water volumes used in ballast tanks. Further complexities arise from requirements of uniform and substantial dispersal of the ozone into ballast water to achieve adequate biokill. While the FIGS.  1  to  3  system and method are generally effective, they require close, delicate control of both flow rate and time of ozone treatment to provide sufficient biokill. Additionally, the piping, valving and diffuser equipment required to service all the ballast tank water is substantial. The equipment is expensive and subject to failure.  
         [0034]    Another problem with the equipment intensive method and system of FIGS.  1  to  3  is engendered by the chemistry of the ozone generation reaction. Equation (I) is an equilibrium reaction. The reaction is endothermic to produce O 3 , requiring energy, and is exothermic to produce O 2 , giving up energy. Because of its equilibrium nature, the actual efficiency of this ozone formation is relatively low, in the range of 2-8%, depending on the oxygen content of the feed gas and the temperature of the reaction. After being processed in this way, the oxygen-containing feed gas acquires a dilute mixture of ozone. This dilute mixture is then diffused through the treatment liquid. However, the high-energy state of ozone results in very low stability of the gas. The natural tendency is for the ozone to revert back to the more stable, lower-energy allotrope O 2 . While the solubility of ozone in water is approximately 13 times as great as the solubility of O 2 , it has a very short half-life, about 40 minutes in distilled water at a pH of 7.6. Consequently, the storage of ozone is impractical and ozone generation must be performed substantially at the location of use.  
         [0035]    In accordance with the invention, ballast water that is loaded through a port of a sea faring vessel is injected with ozone prior to charging to a ballast tank. The invention can utilize a single point or a small number of ozone injection points prior to charge of the water to the ballast tank to eliminate many of the disadvantages of the prior art ballast tank diffuser method. In another embodiment, ballast water that is discharged from a ballast tank is treated by injection of ozone into the unloading ballast water line prior to unloading to the sea. Surprisingly, despite the short half-life of ozone and the difficulty of charging a flow of water, injection of ozone to loading or discharging ballast water provides a residence time and diffusion for satisfactorily biokill. In an embodiment of the invention, a rate of injection of the ozone into the water is adjusted and the rate of water loading into (or un-loading from) the vessel is adjusted to provide a target biokill of species within the water. In this process, a target biokill is determined, for example by consulting ballast water discharge regulations, and the rate of ozone injection into the water and/or the rate of water flow in the water line is adjusted to obtain the target biokill. For example, the rate of injection can be adjusted and/or the rate of water loading can be adjusted to provide a concentration of ozone of 1.0 to 4.5 mg/l, desirably 1.5 to 4.0 mg/l and preferably 2.0 to 3.0 mg/l. This concentration can be effective to obtain in excess of 95% biokill of all species proscribed by the National Invasive Species Act.  
         [0036]    Features of the invention will become apparent from the drawings and following detailed discussion, which by way of example without limitation describe preferred embodiments of the invention.  
         [0037]    [0037]FIGS. 4 and 5 schematically represent a vessel  110  equipped with a loading water ozone injection system of the invention. Shown in the figures are the vessel “sea chest” stern section  112  with intake/discharge portal  114 . Water conduit  116  connects the intake/discharge port  114  with parallel longitudinal main header pipes  118 ,  120  that traverse the vessel  110  from stern to a bow ballast tank connecting the intake/discharge port  114  with each of respective starboard and port batteries of ballast tanks  122 ,  124 . Ballast water is loaded into the vessel  110  and is then pumped to load each ballast tank through the system of conduit and header pipes  116 ,  118  and  120  shown. At a destination, the process is reversed and water is pumped from each tank  122 ,  124  through the conduit and header pipes  116 ,  118  and  120  for discharge through intake/discharge port  114  to the sea. Or, discharge can be effected through another, separate conduit and port system from the up-take and charge system.  
         [0038]    Ozone generator  126  is illustrated located on the aft deck  124  of the vessel  110 . The generator 126  can generate ozone as described by Rodden U.S. Pat. Nos. 6,125,778; 6,139,809; and 6,270,733. The disclosures of these patents are incorporated herein by reference in their entirety. The generated ozone is pumped through line  128  for injection into water in conduit  116  in accordance with this embodiment of the invention. After injection with ozone, the water is conveyed by one of the main header pipes  118  and  120  that run the entire length of the vessel  110 . As a header pipe  118  or  120  passes through each ballast tank  122  or  124 , a smaller footer pipe (not shown) can be taken off to provide a suction/discharge line. Valving for the footer pipe can be contained in a tunnel or cofferdam area, or actually placed in the tank itself, if space is an issue.  
         [0039]    FIGS.  6  to  9  illustrate embodiments of a system and method to inject ozone into water prior to loading the water into a ballast tank. In each of FIGS.  6  to  9 , like structures are identified with the same number. Each of the figures shows ozone generator  30  located on top deck  76  of a vessel  110  and each figure shows line  128  connecting the ozone generator  30  to a conduit  116  from intake/discharge port  114 . In FIG. 6 ozone is injected into ballast water in conduit  116 ; then conduit  116  divides into conduits  118  and  120 , each of which runs along the longitudinal axis of tanker  2 . In FIG. 6, conduit  118  delivers ozone treated water to each ballast tank of a starboard battery of tanks  122  and conduit  120  delivers ozone treated water to each ballast tank of a port battery of tanks  124 . Water enters through intake/discharge port  114  and is treated and charged into a tank of either the starboard battery or the port battery until each respective tank is sufficiently filled and balanced to compensate for off-loaded cargo.  
         [0040]    [0040]FIG. 7 shows line  128  to inject ozone into ballast water in conduit  116 . In this embodiment, conduit  116  has a recycle conduit  130  that cycles a portion of the injected water from a position down stream from the point of ozone injection to a point upstream. The recycle provides enhance ozone injection to the ballast water. Valve  132  can control ozone injection into conduit  116  and valve  134  can control the proportion of recycle. The valves can be synchronized and tuned to control the degree of ozone treatment in the conduit  116  water. Downstream from the recycle, as in FIG. 6, the conduit  116  divides into conduits  118  and  120 , each of which runs along the longitudinal axis of tanker  2 . As in FIG. 6, conduit  118  delivers ozone treated water to each ballast tank of a starboard battery of tanks  122  and conduit  120  delivers ozone treated water to each ballast tank of a port battery of tanks  124 .  
         [0041]    [0041]FIG. 8 shows a system wherein ozone is injected into single points  136 ,  138 ,  140  in a plurality of conduits  142 ,  144  and  146 , which can deliver ozone treated ballast water to a number of separately connected or serially connected ballast tanks. While FIG. 8 shows three conduits  142 ,  144  and  146 , this depiction is intended to represent any number of a plurality of injection points prior to delivery of ozone to ballast tanks, or indeed, to represent any number of a plurality of injection points in conduits discharging ballast water from tanks.  
         [0042]    [0042]FIG. 9 illustrates the concept of a loading tank  148 . In this embodiment, ozone is injected into ballast water in conduit  116 ; then conduit  116  divides into conduits  118  and  120 , each of which runs along the longitudinal axis of tanker  2 . However, in this embodiment, conduit  115  first fills loading tank  148 . Only after filling loading tank  148  is water allowed to flow into conduits  118  and  120 . After filling loading tank  148 , the flow is continuous into conduits  118  and  120  and is adjusted according to flow into the tank  148  to provide a steady state delivery to the tank and flow from the tank  148 . Residency time in tank  148  enlarges the opportunity to load ballast water with ozone for improved treatment and biokill. The embodiment in FIG. 9 shows a separate loading tank  142 . However, in actuality a first ballast tank can be used as a loading tank with overflow water from the first tank being conveyed to the other ballast tanks for filling one by one. FIG. 9 shows a like loading tank embodiment wherein ozone is charged directly into the tank  142  rather than into conduit  116  at a location upstream from the loading tank  142 .  
         [0043]    The invention advantageously minimizes system hardware particularly piping and control cabling. The invention replaces valves and controls from ballast tank water to extend system life and simplify maintenance and repair compared to an intank ballast water treatment system.  
         [0044]    The following EXAMPLE is illustrative and should not be construed as a limitation on the scope of the claims unless a limitation is specifically recited.  
       EXAMPLE  
       [0045]    [0045]FIG. 11 schematically illustrates a single point injection test system  150 . The system  150  can be used to determine effectiveness of a single point ozone injection treatment , The FIG. 11 shows an ozone differential test module  152  with a sea water source  154  feeding through a 10 inch flexible hose  156  to a 1½ inch main feed line  160 . The module  152  comprises a five gallon spike source  162 , centrifugal pump  164  with 40.0 CPM at 35 PSI capacity and a ¾ inch return line  166 . A ¾ inch flow line  168  comprising 1 to 1000 psi pressure gauge tubing connects an ozone generator  170  to the sea water main line  160  to divert incoming water for cooling purposes. A same gauge flow line  172  returns the sea water to main line  160 . Flow control value  174  is located on main feed line  160  downstream from centrifugal pump  164 . Flow meter  176  measures line flow at a location immediately down stream from the control valve  174 .  
         [0046]    A ¼ inch Teflon tubing feed line  180  conveys ozone from generator  170  to a single point injection to main line  160  at point  182 . The single point  182  represents a location subsequent to sea water inflow into a vessel prior to charge into a vessel&#39;s ballast tanks. However, it should be understood that the experimental system  150  can represent a single point injection into ballast water as the water is expelled from ballast tanks to the sea as well. In the test system  150 , the feed line  180  includes centrifugal pump  182  with upstream gauge  184  and downstream gauge  186 , flow valve  188  and check valve  190 . Ozone generation and injection into incoming or discharging sea water in line  180  is controlled with the series of valves  188 ,  190  and coordinated with flow control valve  174  and pump  164  to provide a target concentration of ozone (and correspondingly a targe biokill) within the water in line  160 . The injected water flows through inline static meter  192  and is then discharged into a battery of 75 gallon test tanks  194  each with a sampling port. Controller  196  controls water flow in line  196  via flow control valve  174  and ozone injection flow valve  188  and receives feed back on rate of injection and biokill from static meter  192  and sampling from the test tanks  194 . In operation, controller  196  controls  198  line  160  water flow in coordination with control  200  of ozone injection to effectively achieve biokill prior to water loading into ballast tanks represented by the tanks  194  or to effectively achieve biokill to discharging ballast water from ballast tanks to the sea. The system is operated until a target 95% biokill is obtained of species that are proscribed by the National Invasive Species Act. A concentration of 2.5 mg/l of ozone in the water is determined to provide target biokill.  
         [0047]    While preferred embodiments of the invention have been described, the present invention is capable of variation and modification and therefore should not be limited to the precise details of the Examples. The invention includes changes and alterations that fall within the purview of the following claims.