NO314888B1 - Ballast Replacement - Google Patents

Description

The present invention relates to ballast water replacement on vessels, and more specifically to continuous ballast water replacement, preferably while the vessel is in motion, without the ballast water being replaced transferring unwanted biological organisms to foreign areas.

Ballast water is used in ships to maintain stability and safety. In connection with ballast water replacement, a number of alien species have been introduced to places where such species previously did not occur. Some well-known examples are the introduction of the zebra mussel {Dreissena polymofpha) into the North American Great Lakes, the poisonous dinoflagellate Gymnodinium catenatum to Tasmanina, Australia in 1972, and the introduction of the American jellyfish Mnemiopsis leidyi to the Black Sea.

Replacement of ballast water takes place according to two methods, namely by so-called reballasting or by continuous ballast water replacement.

Reballasting takes place by emptying tanks and then refilling them. Reballasting can be carried out without additional investment in the vessel, but can cause major problems with regard to bending moments, shear stresses, stresses in the ship's hull and the vessel's stability. Reballasting entails 90-100% efficient ballast water replacement, so that there may be a risk of transfer of unwanted biological organisms via the remaining ballast water.

During continuous ballast water replacement, seawater is pumped up with ballast water pumps to the ballast water tanks, from which there is an overflow back to sea. The tanks are full at all times, whereby the above-mentioned problems with respect to mechanical stresses and stability are avoided. However, there may be a risk of overpressure on the tanks. The effectiveness of the ballast water replacement mainly depends on the number of tank volumes that have been replaced.

By efficiency in connection with ballast water replacement, it is traditionally meant to what extent the ballast water itself has been replaced. 100% effective ballast water replacement means that all water has been replaced. However, the content of organisms in water can vary greatly from place to place and between different times, and 100% ballast water replacement is not necessarily sufficient. There are both very mobile and very hardy organisms that will entail very strict requirements for ballast water replacement if unwanted transfer to foreign areas is to be avoided.

With the above methods, a varying degree of efficiency is achieved depending on the detailed mechanical design of tanks, pipe arrangement, pumps, the ship's movements and the sea conditions. Many factors come into play, and it seems to be most appropriate to assess what is acceptable ballast water replacement in each individual case, for example for each route with cargo travel. The aim is to avoid the unwanted transfer of biological organisms, which should be a requirement that must be met.

A significantly increased awareness of environmental issues has led to the UN body IMO (International Maritime Organisation) working to introduce regulations to prevent the further spread of organisms. In the near future, it is likely that every vessel that can be thought of carrying unwanted organisms must be able to present an acceptable plan for how the above problems are avoided.

In connection with ballast water replacement, it is known to treat the water with techniques or equipment such as heating, filtration, UV irradiation, ultrasound, electric charging, salinity increase, chemicals, hydrocyclones and other techniques, in order to exclude or kill biological organisms. A thorough review of all known techniques and all known issues can be found in the article "Ballast water management and treatment options", Trans IMarE, Vol 113, part 3, pp. 79-99, by G. Rigby and A. Taylor, made publicly available in March 2001.

According to the above-mentioned article, it is known that heating water to be fed to ballast water tanks, either en route to the ballast water tanks or in a closed loop from a ballast water tank and back (as described in patent publication US 5816181), results in a significant lowering of the content of organisms in the ballast water. Heating to 35 - 40 °C for half an hour will in most cases be sufficient to eliminate unwanted biological organisms.

In connection with a closed loop where the water is heated in a heat exchanger, it is known that ballast water can be pumped from the bottom of the ballast water tanks and returned to the top in the ballast water tanks. It has been claimed that a thermal layering contributes to less mixing of the treated water in the ballast tank. The effectiveness of the watering and the extent of the non-mixing has not yet been further demonstrated and appears somewhat doubtful in the above-mentioned article (see page 87, left column, penultimate and third last paragraph).

In connection with continuous ballast water replacement, it has been found to be known to pump heated water into the bottom of the tanks. In connection with continuous ballast water replacement, it is emphasized as advantageous to achieve good mixing in the ballast water tanks, and the efficiency is held to be greater at sea under sea influence than in port. Good mixing of the tank contents is highlighted as essential to achieve sufficient heating throughout the tank. (See the above article, page 87, left column, third paragraph; page 84, last paragraph, left column to first paragraph, right column; and page 98, right column, last paragraph). In connection with continuous ballast water replacement, no other advice or specific guidance has been found other than to lead heated water into the bottom of ballast water tanks and to achieve good mixing of the entire tank contents, and nothing specific has been indicated beyond heating and the importance of good mixing of the tank contents.

The aim of the present invention is to provide an improved version of continuous ballast water replacement on a vessel, without unwanted transfer of biological organisms with ballast water being replaced, at a competitive cost.

The aim of the present invention is achieved with a plant for continuous ballast water replacement, according to claim 1, and with a method for continuous ballast water replacement, according to claim 7.

Figure 1 illustrates a plant according to the present invention for continuous ballast water replacement.

Reference is made to figure 1, where a facility 1 for continuous ballast water replacement on a vessel is illustrated, without the transfer of biological organisms to foreign areas, which facility includes, in addition to the vessel's already installed cooling water pumps 8 and central coolers 9, a valve arrangement that leads the cooling water on through pipes, via a possible booster pump 1, to a distribution manifold 2,3, 7 and from there on to one or more completely water-filled ballast water tanks 4, from which water can be discharged in the same flow rate as water was brought in, to a collection line 7,2, from which the water carried out from the ballast water tanks can be carried overboard, via a vacuum switch 8 placed at a higher level than the aforementioned tanks. The facility is distinctive in that it includes valves 10, 11, 12 and lines 2, 3, 7 arranged so that water that is led into the ballast water tanks, based on the difference in density between water that is introduced into and water that is already present in the tanks, can is fed in and distributed without a significant switching effect in a layer on the top 16 or in the bottom 17 of the ballast water tanks, while a corresponding flow amount of water is fed out from the bottom or from the top of the ballast water tanks.

Figure 1 shows a t-piece or a three-way valve 10 which is inserted into the seawater cooling system for the machinery, between the heat exchangers 9 and the overboard outlet. This provides a connection to the ballast water tanks, via a possible booster pump 1 which is inserted if it is necessary for circulation. Also illustrated is a possible UV treatment unit that functions by UV irradiation of the water, which can be inserted into the system if desired or needed. Another organism-killing device can possibly be used. A pipe system 2 is mounted on the deck, and in the bottom part 7 of an existing ballast water system is preferably used for distributing the water, and said units have a switchable function depending on how heated water is led to and from the ballast water tanks, with the valves 10 and 12. The valve 12 is arranged so that the water can be led into the top 16 or bottom 17 of the tanks, depending on the density difference between the ballast water in a tank and new water that is led in. In cases where new water is led into the top of the tanks, displaced water is led out via the bottom line 7 and from there further up to deck level, and via a vacuum switch 6 overboard.

The vacuum switch 6 prevents siphoning in the discharge line from the ballast water tanks. The system also includes additional features, such as devices for tank ventilation 5, and a non-return valve 18 on the pressure side of the booster pump 1.

As only heated water is introduced into the ballast water tanks, only water is introduced that is without or with a greatly reduced content of biological organisms.

It is advantageous if the water is heated with waste heat from the vessel's machinery. It is assumed that for most vessels it will be sufficient to exclusively use heat from the vessel's machinery, but additional heating, for example from boilers, may be relevant, particularly if the facility does not contain a UV treatment unit or another unit with a similar effect. In the article mentioned at the outset, there is a thorough review of various conditions regarding heating and removal of specific biological organisms, as well as various devices for heating and additional treatment, also with indications of economic conditions.

The plant according to the invention means that the content of organisms in the ballast water is eliminated or greatly reduced by heating, and that the ballast water is replaced more efficiently by making use of the water's density differences.

With a system according to the invention, it is advantageous if the ballast water is seawater that is pumped up with the vessel's seawater pumps, heated in heat exchange against fluid flows in the machinery's cooling system and led into the top or bottom of ballast water tanks so that heavier water is led into the bottom while lighter water is led into the top of the ballast water tanks.

Supply of water to the top of the ballast water tanks takes place via a line and a nozzle device or a pipe which does not cause swirling or switching in the tanks. By changeover is meant here any mixing of newly introduced water and original water in a ballast water tank. It is therefore advantageous that water is led into or taken out from the top of ballast water tanks through a horizontal pipe or a nozzle device in the form of a horizontally placed sealing plate or sealing disk at the end of a vertically placed pipe, arranged centered at the top of the tanks, through many small horizontal aligned holes in the pipe or around the perimeter of the sealing plate or sealing washer. It is essential to have mainly horizontal inflow spread outwards as much as possible, whereby a very careful mixing of added water is achieved. An alternative design can be in the form of a nozzle or a tube that is bent 90 <0> so that the liquid is only introduced in a horizontal direction and not in a vertical downward direction. A tube with a u-shape at the end is also applicable, possibly a horizontal tube in the upper part of the tank, which tube extends the entire length of the tank and is provided with many horizontally aligned holes for good distribution.

When extracting liquid from the bottom of the tanks, a pipe or a nozzle is used at the end of a pipe that points straight down just above the tank bottom, advantageously in the form of part of an existing ballast water system.

When liquid is fed into the bottom of a tank, liquid is taken out from the top of the same tank. This takes place through the same nozzles or pipes as mentioned above, whereby the first-mentioned liquid flows are turned around.

The plant according to the present invention for continuous ballast water exchange is operated as follows: 1. When introducing water with a lower density than what is already in the tanks, this is fed into the top of the tanks, while original water is fed out from the bottom of the tanks. 2. When introducing water with a greater density than what is already in the tanks, this is fed into the bottom of the tanks, while original water is fed out from the top of the tanks.

When operating the plant according to the above, a sharp stratification is achieved in the completely water-filled tanks due to the difference in density between the water introduced and the original water content in the tanks. The layer of introduced water will mix to a very small extent with the original water, and the introduced water will push out the original water by piston action until the entire tank volume has been replaced, as indicated in an early phase in the drawing with reference numbers 16 and 17. When introduced at the top of the tanks, the layer with introduced water will displace the original water from the top, and vice versa when introduced at the bottom of the tanks. It is important that the tanks are completely full to achieve minimal water changes.

The essential principle is that water with a lower density than the water originally present in a tank is fed into the top of said tank, while water with a higher density is fed into the bottom of said tank. It has been shown that increased salt content has a stronger effect than increased temperature on the change in density in the water. Therefore, seawater will generally be allowed into the bottom of the tanks and settle there as a clear stratified layer at the bottom of the tanks if the water found in the tanks originally has a lower salt content.

In the plant according to the invention, there is advantageously arranged instrumentation for measuring density, either for direct measurement or indirectly by measuring salinity, temperature or conductivity, in heated water 13 to be led to the ballast water tanks, in water in the ballast water tanks 14, and in the outlet line 15 from the ballast water tanks. Thereby, full control over the operation of the plant can be achieved, for example by measuring and recognizing which water is heavier or lighter, and when a tank has been filled can be registered. The above-mentioned instrumentation can in principle be of any known type that can provide the desired measurement results.

It is when relatively salty water with a higher density than the original water is taken in that said water will be fed into the bottom of the tanks. Otherwise, water will enter the top of the tanks. Under conditions without a significant difference in salinity for water taken in, it may be sufficient as a minimum to have arranged a thermometer in the outlet line from the tanks, whereby by means of a resulting temperature rise it can be registered when a tank volume has been filled and the next tank can is connected for ballast water replacement.

All water fed into the tanks is pre-heated by at least one heating unit, whereby biological organisms have been completely or partially eliminated. Most preferred are the vessel's seawater pumps which pump up seawater from the seawater chests for cooling in the engines' heat exchangers, towards the closed cooling system in the engines, and on to the ballast water tanks, instead of directly overboard. The seawater is suitably heated 10 - 40 °C before introduction into the ballast water tanks, for example to 35 - 40 °C, but as it appears from the article mentioned at the outset, what is sufficient heating, and any additional measures, must be assessed in each individual case.

For a typical vessel, 100% ballast water replacement, with regard to volume, can be carried out within approx. 1.5 days.

The invention also provides a method for continuous ballast water replacement on a vessel, without the transfer of biological organisms to foreign areas, using the plant according to the invention. The method comprises pumping up seawater with at least one pump, directing the water through pipes to at least one heating unit where the water is heated, and directing the heated water further through pipes, through a possible booster pump, to a distribution manifold and from there to one or more ballast water tanks completely filled with water, from which water is led out in the same flow rate as water was brought in, to a collection line, from which the water led out from the ballast water tanks is led overboard, via a vacuum switch located at a higher level than the mentioned tanks. The procedure is characterized by the use of valves, lines and instrumentation so that water that is led into the ballast water tanks, if the water is lighter than water already present in the tanks, is introduced and distributed without a significant switching effect in a layer on top of the ballast water tanks, while a corresponding amount of flow water is fed out from the bottom of the ballast water tanks, or vice versa if the water fed in is heavier than water already present in the tanks, whereby water is fed in and distributed without a significant switching effect in a layer at the bottom of the ballast water tanks, while a corresponding flow amount of water is fed out from the top of the ballast water tanks.

More specifically, the method comprises that heated water is fed in and distributed without a significant switching effect in a layer on top of the ballast water tanks, while a corresponding flow amount of water is fed out from the bottom of the ballast water tanks, at approximately the same salinity between water fed into and water present in the tanks, or heated water is fed in and distributed without a significant switching effect in a layer at the bottom of the ballast water tanks, while a corresponding flow amount of water is fed out from the top of the ballast water tanks, if the water that is fed in has a higher salinity than the water present in the tanks beforehand.

The water is advantageously heated 10 to 40 °C in the heating unit, and is, if necessary, advantageously treated in a UV treatment unit or another treatment unit to lower the content of biological organisms. Additional heating is an alternative to a UV treatment unit.

Examples

The basic principle of the invention has been demonstrated through simple experiments. A tank in the form of a vertically standing section of a transparent plastic pipe was used. Water that was brought in was heated 10 °C compared to the original water in the tank. When introduced into the top of the tank, a nozzle with small holes around the circumference of a plate was used. When introducing into the bottom, a vertical pipe pointing straight down just above the tank bottom was used. Introduced water was colored yellow to observe the stratification or mixing. Corresponding flow amount of water that was introduced into the tank was taken out at the opposite end. Table 1 summarizes the results.

The stratification when heated seawater (saltwater) was pumped into the bottom of the tank, in trial no. 3, was significantly better (5 liters of yellow seawater, 16 cm thick layer) than the stratification when heated fresh water was pumped into the top of the tank, trial no. 1 (4.5 liters of yellow fresh water, 30 cm thick layer). Better layering means less mixing with the original water in the tank. Increased salinity or salt content has a clearly stronger effect on the water's density change than warming.

Claims (10)

1. Installation (1) for continuous ballast water replacement on a vessel, without the transfer of biological organisms to foreign areas, which installation comprises at least one pump (8) for pumping up seawater and directing this through pipes to at least one heating unit (9) for heating , and from there on through pipes, via a possible booster pump (1), to a distribution manifold (2,3,7) and from there on to one or more completely water-filled ballast water tanks (4), from which water can be discharged in the same flow rate as water was brought in, rig a collecting duct (7„2), from which the water discharged from the ballast water tanks can be brought overboard, characterized in that the system comprises a valve (10) downstream of the at least one heating unit, with which valve the heated water or part of it can be led through the possible booster pump to a further valve (12) which can be set to either lead the water to the manifold ( 2) or to the manifold (3,7), so that water that is fed into the ballast water tanks, based on the difference in density between water that is fed in and water already present in the tanks, can be fed in and distributed without a significant switching effect in a layer of the top (16) or in the bottom (17) of the ballast water tanks, while a corresponding flow amount of water is led out respectively from the bottom or from the top of the ballast water tanks. 2. Installation according to claim 1, characterized in that the heating unit is a heat exchanger which is connected to transfer heat from the vessel's machinery. 3. Installation according to claim 1 or 2, characterized in that the at least one pump (8) is the vessel's seawater pump(s) which pumps up seawater which is heated in heat exchange against fluid flows in the machinery's cooling system and is led into the top or bottom of ballast water tanks so that heavier water is led into the bottom while lighter water is led into the top of the ballast water tanks. 4. Installation according to claim 1, characterized in that in order to lead water into or take water out from the top of the ballast water tanks, a horizontal pipe or a nozzle device is arranged at the top of each tank in the form of a horizontally placed sealing plate or sealing disc at the end of a vertically placed pipe, arranged centered at the top of the tanks, through many small horizontally aligned holes in the pipe or around the perimeter of the sealing plate or washer. 5. Installation according to claim 1, characterized in that in order to lead water into or take water out from the bottom of the ballast water tanks, a part of a conventional ballast water system is arranged at the bottom of each tank, preferably in the form of a pipe which, centered in the tanks, points straight down just above the tank bottom. 6. Installation according to claim 1, characterized in that instrumentation is provided for measuring density, either for direct measurement or indirectly by measuring salinity, temperature or conductivity, in heated water (13) to be led to the ballast water tanks, in water in the ballast water tanks (14), and in the outlet line (15) from the ballast water tanks. 7. Procedure for continuous ballast water replacement on a vessel, without the transfer of biological organisms to foreign areas, using the facility according to claim 1, by pumping up seawater with at least one pump, directing the water through pipes to at least one heating unit where the water is heated , and to lead the heated water further through pipes, through a possible booster pump, to a distribution manifold and from there on to one or more ballast water tanks completely filled with water, from which water is discharged in the same flow rate as water was admitted, to a collecting pipe, from which the water is discharged from the ballast water tanks is brought overboard, characterized by setting a valve arranged downstream of the heating unit and the possible booster pump to direct heated water either to a distribution manifold connected to the bottom inlet of the ballast water tanks or to a distribution manifold connected to the top inlet of the ballast water tanks, so that water which is lighter than the water already present in the tanks is fed in and distributed without a significant switching effect in a layer on top of the ballast water tanks, while a corresponding flow amount of water is fed out from the bottom of the ballast water tanks, or vice versa if the water fed in is heavier than water already present in the tanks, whereby water is fed in and distributed without substantial switching effect in a layer at the bottom of the ballast water tanks, while a corresponding flow amount of water is carried out from the top of the ballast water tanks. 8. Method according to claim 7, characterized by heated water being fed in and distributed without a significant switching effect in a layer on top of the ballast water tanks, while a corresponding flow amount of water is fed out from the bottom of the ballast water tanks, at approximately the same salinity between water fed into and water present in the tanks, or heated water is fed in and distributed without a significant switching effect in a layer at the bottom of the ballast water tanks, while a corresponding flow amount of water is fed out from the top of the ballast water tanks, if the water fed in has a higher salinity than the water present in the tanks beforehand. 9. Method according to claim 7 or 8, characterized in that the water is heated 10 to 40 °C in the heating unit. 10. Method according to claim 7, 8 or 9, characterized by the fact that the water is, if necessary, treated in a UV treatment unit or another treatment unit to further reduce the content of biological organisms.