NO20170984A1 - Method and system for treating bacterially or organically contaminated water in a tank - Google Patents

Description

Technical Field of the Invention

The present invention relates to a method and a system for circulating ballast water on board a vessel where the ballast water to be circulated passes into a tank as filling water through a filling unit, and discharged as discharging water from a discharging unit, the system comprising a ballast water tank, an inlet pipe system for filling water and an outlet pipe system for discharging water.

Background for the Invention

Vessels depend on ballast water to provide stability and also maneuverability during a voyage. Such ballast water may be tåken on at one port where for example cargo is unloaded and discharged to sea at another port when the vessel is loaded again.

In aqua farming or aquaculture, it is common to use transport vessels for transporting living aquatic biomass, such as salmon, in water filled tanks from production nets, cages or cultivation enclosures for example to an abattoir, either onboard a larger vessel or onshore. To facilitate such transport the living aquatic biomass is pumped from the production nets to tanks onboard the vessel in a pumping and pipe system, using water as transporting medium. Moreover, the fish is correspondingly pumped in the same manner from the tanks onboard to receiving stations at the abattoir. At the same time, such transport vessels are also used to transport for example smolt from hatch to said production nets, cages or cultivation enclosures.

The water used for ballasting and/or pumping living aquatic biomass may be infected with organisms, such as small fish, lice, bacteria, viruses or other micro-organisms. By discharging such infected waters directly to sea, detrimental and undesirable introduction and spread of non-native organisms, called bio-invaders or alien species, will occur. Further, such infested water may also be a source for the spread of detrimental and undesirable diseases or spread of lice or the like to the next generation living biomass.

In a publication named "Marine Bioinvasion facts\Sheet: Ballast water Treatment Options", by Corrina Chase, Christine Reilly and Judith Pederson, it is proposed to heat the ballast water in tanker vessels to between 35 °C and 45 °C by means of the cooling water from the propulsion machinery prior to discharging the ballast water to the sea. Such temperature range is too low to kill all detrimental micro-organisms and bacteria and water temperatures within this range or above will be more prone to cause corrosion in the tank that water stored at a lower temperature.

A method and a system for treating ballast and waste water onboard vessels prior to discharging such water to the sea is described in the Norwegian patent EP 2920118 Al. The water to be treated is pumped through a first heat exchanger where the water is preheated and then through a second heat exchanger where the water is further heated, the second heat exchanger is heated by thermal fluid recovered from various types of heat-generating equipment. This system is treating the ballast water by heating it up to a temperature range enough too to kill all detrimental micro-organisms and bacteria and prone to cause corrosion in the tank.

Today it is approved by the IMO (International Maritime Organization) to replace the ballast water in ballast tanks, by pumping through the tanks three times the tank volume it is assumed that 'all' ballast water is exchanged and can be discharged to the sea. This procedure will shortly be banned because of safety issues and uncertainty about whether all ballast water really has been treated. This uncertainty will in near future lead to the demand that all ballast water must be treated before delivered to onshore base, receiving ships or discharged to the sea.

There is a need for a method and a system which secures that ballast water is treated onboard and not discharged directly to the sea. Moreover, there is a need for a method and a system which secures that all ballast water inside the tank to be circulated, treated and exchanged.

Hence, there is a need for an "in-tank treatment" system of the ballast water when the vessel sails from one port to another. A "full flow treatment" system with in/out pumping to the sea is a larger and more complex system.

Summa ry of the Invention

A main principle of the present invention is to supply of treated, heated

water at the top of a tank and withdraw contaminated water from the bottom of the tank, circulating the contaminated water through a heating source where the temperature of the water is increased to a disinfecting temperature for return to the tank in a stratifying and cooled down manner, the disinfected, heated water being cooled down again to a temperature slightly higher than the temperature of the water before the heat treating stage. The continuous water circulation is continued until the water is freed from disinfecting organisms. If the temperature of the water leaving the tank at the bottom has been increased to

predetermined level, dependent on and decided for the specific plant, it may be tåken as an indication that all water in the tank has been disinfected to the required degree.

Another main principle used is the fact that the specific temperature of cold water is larger than that of the warmer water, i.e. warm water will tend to flow up towards the top of a tank while colder water will tend to sink down towards the tank bottom.

An object of the present invention is to be able to treat the ballast water in the ballast tank by circulating the water through the treatment unit at a minimum number of times/cycles in a controlled manner.

An object of the present invention is to provide an improved method and a system which separates the treated water from the untreated water inside the tank.

Another object of the present invention is to provide a method and system for circulating ballast water onboard in a cost effective way.

Another object of the invention is to provide a system and a method for securing heating of a fluid infested by detrimental organisms in a ballast water tank or a tank or container containing such infested or contaminated water, the water being heated to as high temperature that the organisms in the water is no longer harmful.

Another object of the invention is to provide a system and a method where the infectious or contaminated water is heated prior to be added to the tank and/or that infectious or contaminated water is pumped from the tank to a unit where it is heated and then returned to the tank.

Yet another object of the invention is to provide a system and a method where the heated and treated water is not mixed with the infectious or contaminated water when return to said tank.

Yet another object of the present invention is to provide a method or system where heated and treated water already within the tank and subsequent to supply of such water to the tank, contributes to disinfection or treatment by heat energy to the existing contaminated or infectious water while in the tank by heat transfer within the tank.

Another object of the present invention is to provide a system and a method for obtaining an improved stratification of supplied water in a water containing tank.

A still further object is to obtain a system and a method securing that the water in the tank is at least circulated once through a heating source and cooled partly down again, controlling and identifying the number of circulation and heating cycles.

A still further object of the present invention is to retrieve at least a part of the heat delivered for disinfecting the water in the tank.

Yet another object of the present invention is to provide a system enabling stratification of treated water supplied to the tank.

The object of the present invention is achieved by a method and a system as further defined in the independent claims, while alternative embodiments and variants are defined by the dependent claims.

Another object of the invention is to supply purified water to a tank at a slightly higher temperature than the temperature of the water discharged at the bottom of the tank for circulation through a heating device for return to the tank

According to the present invention, the water to be circulated passes into a tank as treated filling water through a filling unit, and discharged as untreated discharging water from a discharging unit. The filling water when it passes into the tank encounters an obstacle in form of a floating unit located on the water surface enabling the filling water to be distributed at the water surface.

The water to be circulated may for example be ballast water and/or bacterially or organically contaminated water. Further, the treated water contains a higher temperature than the untreated water. Preferably the untreated water inside the tank has a temperature between 0 °C and 32 °C.

According to one embodiment, the filling unit comprises an inlet pipe system extending from the top of the tank to the bottom of the tank, and the discharging unit comprises an outlet pipe system extending from the bottom of the tank to the top of the tank. The inlet pipe is provided with one or more sets of radial perforations along the length of the pipe. The perforations can have different size and location along the length of the pipe.

According to one embodiment, a floating unit is located inside the inlet pipe system, encircling the entire cross sectional area of the pipe and moveable according to the water level in the pipe, which corresponds with the water level at any point in time of the tank.

Further, the circulating water is already treated by the Ballast Water Treatment System onboard and contains a higher temperature than the untreated water inside the tank. When the circulating water passes into the tank as filling water through the inlet pipe, it encounters an obstacle in form of a floating unit. The floating unit is floating on the water surface inside the pipe and prevents the filling water to pass, but to be distributed through the radial perforations on the pipe, and at the water surface. This will ensure that the treated filling water with higher temperature always will be distributed at the water surface of the tank, and as the water gets colder it will gradually sink to the bottom of the tank. It is known that water with temperature between 4 °C and 5 °C has higher weight and will stay at the bottom of the tank. In this way the invention ensures that treated filling water with higher temperature always will be distributed at the top and the colder untreated water will sink to the bottom of the tank. Further, the outlet pipe is located at the bottom of the tank for discharging of the cold water at the bottom, and a circulation pump circulates the water to be treated by the heating system.

According to another embodiment, the filling unit comprises an open water flow into the water tank, like a waterfall. In this embodiment the floating unit is floating and moveable on the water surface positioned below the waterfall, and arranged to dampen the water and redirects the water to be distributed or spread more or less horizontally on to the water surface. In this way the hot water will be separated from the cold water inside the tank.

According to an embodiment of the invention the vessel contains one or more storage tanks onboard equipped with the circulation system according to the invention.

It should be appreciated that the heating process of the water to be cleaned is performed while the vessel sails in a ballast condition.

Further, according to another embodiment, the control of water flow into the tank and out of the tank, are automatically controlled by a control system.

On major advantage with the method and system according to the invention resides in that in general no additional fuel or energy is required or must be provided to ensure the separation of the hot and cold water inside the tank.

Another advantage is that the system can be operated at any water temperature. The temperature may be logged in the control system for documentation upon request from authorities or others.

Short Description of the Drawings

In the following an embodiment of the invention will be described in more detail, referring to the drawings, where: Figure 1 shows schematically a flow diagram of a ballast water treatment system, also indicating the direction of flow through the various pipes and units of the water treatment system, including the tank. Figure 2 shows a cross sectional view of the tank with arrangements according to the invention.

Detailed Description of the Invention

Figure 1 shows schematically a flow diagram of a ballast water treatment system. The system is intended for sterilizing different types of waste water and ballast water, based on a pasteurization method. The water to be treated is discharged from the storage tank 10, after being heated to a specific pasteurizing temperature; it is cooled down again and circled and reentered into the storage tank 10 as filling water with high temperature.

An important feature of the present invention is that it is the contaminated water in a tank that is heated and returned in a disinfected state to the tank, the disinfected, heated water being cooled down again to a temperature of around 6°C above the initial exit temperature of the first water to being drawn from the tank. The contaminated water is drawn from the bottom of the tank, while the treated, heated water when returning to the tank, is supplied to and distributed along the top of the tank. In other words, it is the water in the tank that is circulated a number of times, drawn from the bottom, heated to a des - infecting temperature and cooled down again for return to the tank at the tank top. At the top the disinfected, warmer water is distributed in a manner where the warmer, des-infected water is distributed at the top in a gentle manner in order to avoid mixing or at least substantially reduce mixing with the water below, preferably at the internal water level inside the tank.

Figure 2 shows a water storage tank 10 with the system for circulating water according to the invention. The system comprises an inlet pipe 11 extending from the top of the tank to the bottom, and an outlet pipe 15 extending from the bottom of the tank to the top. The inlet pipe 11 is provided with at least one radial perforation 13 along the length of the pipe 11. A floating unit 12 is arranged inside the inlet pipe 11, floating on the water surface 14, encircles the entire cross sectional area of the pipe 11 and moveable according to the water level. The floating unit 12 is a heat insulating device and/or a heat retention device.

A circulation pump (not shown) is pumping the treated water from the heating system fig.l and into the tank 10 through the inlet pipe 11. Inside the inlet pipe 11 the water will encounter the floating unit 12 floating at the water surface 14. Upon meeting the obstacle in form of the floating unit 12 the water will be redirected horizontally through the radial perforations 13 at the inlet pipe 11 and distributed at the water surface. Heated filling water will stay at the top inside the tank 10 and colder water will sink towards the bottom, and ready to be recycled and treated. The temperature of the water at the bottom is normally between 4 °C and 5 °C. A circulation pump (not shown) is arranged in accordance with the outlet pipe 15 at the bottom of the tank 10 for discharging of the water at the bottom.

As pointed out above, infected water is drawn from the bottom of the tank, passing through a heating source where the water is heated to a temperature high enough for disinfecting the water, i.e. destroying all living organisms in the water. The water may for be heated to a temperature above 70 °C, sufficiently high to kill all the organisms. The water is then cooled down again to a temperature that is slightly higher than the temperature of the corresponding water drawn at the lower end of the tank. Such temperature difference may for example be in the order of 4 °C to 8 °C, typically 6 °C. Since a temperature increase is defined for a plant, for example 6 °C for a specific plant, a temperature increase of the water at the bottom outlet of the tank in the order of 6 °C compared to the original start temperature indicates that all the water in the tank has been treated once. Correspondingly, a temperature difference of 12 °C will indicate that all the water in the tank has been treated twice. For ballast water a temperature of 40 °C. For water in the tank of a well vessel for transport of live stock fish, other maximum temperature may be applicable.

The system according to the present invention is automatically controlled and monitored by a control system (not shown) and can be interfaced to the main computer system (IAS) together with the heating system of figure 1. Safety control system and system for manual control is standard features. The control system is type approved in the major dass society.

For such purposes the system may be provided with temperature and pressure gauges, communicating with the control system allowing automatic control, while the various valves may be remote controlled.

The main circulation pumps may comprise two equal pumps for example mounted on skids, one running and on stand-by. Also the pumps are instrumented both for manual and/or automatic control, so as to enable adjustment of the pumping rate, the pumps preferably being controlled from the remote control system.

It should be appreciated that the system also contains piping, cabling and accessories not shown, such as manually operated valves, temperature and pressure gauges, flow meters, means for time control etc.

Claims (10)

1. Method for treating bacterially or organically contaminated water in a tank (10) on board a vessel where water is circulated through a pipe system with an outlet (15) at the bottom of the tank (10) to a heat source where the water is heated and circulated back to the tank (10), supplied to the tank (10) at its top, where the heated water is distributed in a stratifying layer on top (14) of the existing water in the tank (10) , the temperature of the heated, but cooled down water supplied to the tank top being higher than the temperature of the water drawn from the tank bottom, c h a rete ri zed in that the filling water when it passes through the inlet pipe (11) extending downwards into the tank (10) encounters a floating unit (12) inside the inlet pipe (11), the floating unit (12) redirecting the water to a horizontal direction through at least one radial perforation (13) on the inlet pipe (12).

2. Method according to claim 1, wherein the heated water is supplied to the tank (10) through an inlet pipe (11), extending from the top of the tank (10) to the bottom of the tank (10), the inlet pipe(s) (11) being perforated along its entire length.

3. Method according to claim 1 or 2, wherein the circulating process of the water inside the tank (10) is continued until a temperature increase of the water at the bottom outlet of the tank (10) in the order of 6 °C compared to the original start temperature, indicating that all the water in the tank (10) has been treated once.

4. A system for treating bacterially or organically contaminated water in a water tank (10) on board a vessel, comprising a water tank (10), an inlet pipe (11) for filling heated water into the tank (10) at the top and an outlet pipe (15) for discharging water from an outlet the tank bottom and a heating system with heat exchangers for exposing the water to a temperature high enough for disinfecting the water,characterized in thatinlet pipe (11) extends downwards into the tank (10), the pipe being provided with at least one radial perforation (13) along a length of the pipe (11) and a the floating unit (12) is located inside the inlet pipe (11), encircling the entire cross sectional area of the inlet pipe (11) and moveable according to the water surface (14) inside the tank (10), enabling the heated filling water to be distributed in horizontal direction into the tank (10) at the water surface (14) on top of said floating unit (12).

5. A system according to claim 4, wherein the inlet pipe (11) extends from the top of the tank (10) to the bottom of the tank (10).

6. A system according to claim 4 or 5, wherein the outlet pipe (15) extends from the bottom of the tank (10) to the top of the tank (10).

7. System according to one of the claims 4 to 6, wherein the radial perforations (13) have different size and location.

8. System according to one of the claims 4 to 7, wherein the floating unit (12) is a heat insulating device.

9. System according to one of the claims 4 to 8, wherein the floating unit (12) is a heat retention device.

10. Use of a system as specified in claims 4 to 9, for disinfecting water in a tank (10) of a well vessel used for transport of live stock fish, heating the water to a temperature above 40 °C.