Method and arrangement for flushing ballast tanks

Abstract

 The invention relates to a method for flushing a ballast tank (2) of a ship, in the process of which water present in the ballast tank (2) is replaced by surrounding water, present outside the ship. Water from the ballast tank (2) is drained away on a bottom side of the ship via an overflow pipe (8). Preferably, water flowing in is squirted into the direction of the bottom of the ballast tank (2) with the aid of a system of spray nozzles.

Description

[0001] The invention relates to a method for flushing a ballast tank of a ship, in the process of which water in the ballast tank is replaced by surrounding water, available outside the ship. The water which is originally present in the ballast tank may be let in during loading and unloading in a harbour, which means that it may contain contaminants present in the harbour, for example chemical pollutants or polluting micro-organisms. If the water present in the ballast tanks is subsequently discharged in another harbour, then these micro-organisms will be introduced into another ecosystem, which may cause problems. For that reason, some harbour authorities demand that before one puts in on the harbour, all ballast tanks of the ship must be flushed, which means that the water present in the ballast tanks must be replaced by relatively clean surrounding water present for example 200 miles outside the coast. This method is not without any risk; after all the ballast tanks have been filled with some purpose and there is always a possibility that when the ballast tank is pumped out the stability of the ship is reduced or that the tensions in the hull become too high, especially when there is a substantial wave load. According to an improved method which obviates this disadvantage, the surrounding water is supplied to a bottom side of the ballast tank and the water originally present in the ballast tank is discharged via a vent duct placed on top of the ballast tank, across the deck and alongside the ship. Obviously, also this method is not without some risks as the deck may become very slippery, especially if one sails in a low temperature area. Moreover, the vent duct may freeze and block, in which case it will no longer be possible to flush the ballast tanks and there is even a danger that a ballast tank tears if one attempts flushing it.

[0002] The method according to the invention does not have these drawbacks and is characterised in that water is guided outside the ship below the water surface via an overflow pipe which runs at least partly inside the ballast tank.

[0003] A favourable realisation of the inventive method is characterised in that at least part of the surrounding water, flowing into the ballast tank is directed towards the bottom of the ballast tank via a system of discharge openings, preferably in such a direction that surrounding water flowing into the ballast tank will cause turbulence on the bottom, as a result of which sediment that may be present on the bottom will be set free and carried off.

[0004] A further favourable realisation is characterised in that at least part of the surrounding water, flowing into the ballast tank is directed towards the bottom of the ballast tank via a system of spray nozzles. These spray nozzles, which are known as such, are designed such that the surrounding water will pour out in a well directed squirt. The squirts are preferably directed such that a powerful current is obtained near floors, frames, gussets and the like, so that possible sediment is set free and carried out of the ballast tank together with the water via the overflow pipe.

[0005] The invention also relates to an arrangement for replacing water inside a ballast tank of a ship by surrounding water, available outside the ship, comprising a pump, of which a first side is connected to a first pipe ending outside the ship and of which a second side is connected to a second pipe, ending inside the ballast tank. According to the known arrangement, water flows via a vent duct out of the ballast tank. The inventive arrangement is characterised in that the arrangement also comprises an overflow pipe which runs at least partly inside the ballast tank and via which water coming from the ballast tank can be guided outside the ship.

[0006] A favourable embodiment of the inventive arrangement is characterised in that the overflow pipe is provided with a first valve, which means that surrounding water cannot enter the ship on an unexpected moment.

[0007] A further favourable embodiment of the inventive arrangement is characterised in that the overflow pipe exits the ship near a bottom side, which prevents the exit of the overflow pipe from freezing, which means that flushing will always be possible.

[0008] A further favourable embodiment is according to another aspect of the invention characterised in that the arrangement moreover comprises a third pipe, connected to the second side of the pump and ending inside the ballast tank, which third pipe is provided with a number of discharge openings, via which surrounding water can be squirted into a direction of the bottom of the ballast tank, as a result of which a possible sediment present on the bottom will be set free and carried off. Preferably, the discharge openings are provided with spray nozzles, with which a powerful current is obtained near floors, frames, gussets and the like, so that possible sediment is set free and carried out of the ballast tank together with the water via the overflow pipe.

[0009] A further favourable embodiment is characterised in that the second and the third pipe are provided with a second, respectively a third valve. If only the second valve is opened, the ballast tank may be filled, emptied or flushed according to the known method. If only the third valve is opened, the ballast tank may be filled, emptied or flushed according to the inventive method, in the process of which moreover sediment and other pollution may be removed.

[0010] The invention will now be explained in more detail with a reference to the following figures, in which:

Fig. 1

schematically shows a ship provided with ballast tanks according to the state of the art in side view;

Fig. 2

shows a possible embodiment of a ballast tank according to the invention;

Fig. 3

shows an alternative embodiment of a ballast tank according to the invention;

Fig. 4

schematically shows a possible arrangement of the discharge openings or spray nozzles.

[0011] Fig. 1 schematically shows a ship 1 in side view, provided with ballast tanks 2 built into a side wall of ship 1, according to the state of the art, which ballast tank 2 may be filled or emptied according to the state of the art with a pump 3, via a valve 4. On the top, ballast tank 2 is provided with a vent line 5, via which air may escape or flow in when pump 3 is operating. Usually, ballast tank 2 is filled with water in a harbour where cargo is loaded or unloaded. Before ship 1 puts in on a new port, pump 3 is switched on and ballast tank 2 is filled from below with relatively clean surrounding water, in the process of which polluted water originating from the harbour drains away via vent line 5 and via a deck 6.

[0012] Fig. 2 shows a possible embodiment of a ballast tank 2 according to the invention, where ballast tank 2 may be filled or emptied or flushed with a pump 3, via a valve 4 and a pipe 7. For flushing pump 3 is switched on, so that ballast tank 2 is filled from below with surrounding water and water present in ballast tank 2 will drain away via an overflow pipe 8 on the bottom of the ship. The discharge opening of pipe 7 ends near the bottom and is directed such that at the bottom of ballast tank 2 locally a turbulent current will form, which will set free sediment which will be carried along with the water flow via overflow pipe 8. In overflow pipe 8 a valve 9 is placed, which prevents water from entering ballast tank 2 via overflow pipe 8 when closed.

[0013] Fig. 3 shows an alternative embodiment of a ballast tank 2 according to the invention, where ballast tank 2 may be filled or emptied or flushed with a pump 3, via a valve 4a and a pressure pipe 7a. For flushing, pump 3 is switched on, so that ballast tank 2 is filled from below with surrounding water and water present in ballast tank 2 will drain away via an overflow pipe 8 at the bottom of the ship. Ballast tank 2 may also be flushed by opening valve 4b, after which surrounding water will enter ballast tank 2 via pipe 7b and via a number of discharge openings or spray nozzles 10. Discharge openings or spray nozzles 10 are directed such that they will set free any sediment, present on the bottom of ballast tank 2, after which it will be carried along and leave ballast tank 2 via overflow pipe 8.

[0014] Fig. 4 schematically shows a possible arrangement of the discharge openings or spray nozzles 10 in ballast tank 2. Pipe 7b is installed for example ring-shaped and runs along the walls of ballast tank 2. The discharge openings or spray nozzles 10 are placed in such a way that they cause a highly turbulent current near bottom 11 of ballast tank 2. When placing and directing the discharge openings or spray nozzles 10, the inner structure of the ballast tank is taken into account, for example the location of floors 12, frames 13 and gussets 14

Claims

1. Method for flushing a ballast tank of a ship, in the process of which water in the ballast tank is replaced by surrounding water, available outside the ship, characterised in that water is guided outside the ship below the water surface via an overflow pipe which runs at least partly inside the ballast tank.

2. Method according to claim 1, characterised in that at least part of the surrounding water, flowing into the ballast tank is directed towards the bottom of the ballast tank via a system of discharge openings.

3. Method according to claim 1 or 2, characterised in that at least part of the surrounding water, flowing into the ballast tank is directed towards the bottom of the ballast tank via a system of spray nozzles.

4. Arrangement for replacing water inside a ballast tank of a ship by surrounding water, available outside the ship, comprising a pump, of which a first side is connected to a first pipe ending outside the ship and of which a second side is connected to a second pipe, ending inside the ballast tank, characterised in that the arrangement also comprises an overflow pipe which runs at least partly inside the ballast tank and via which water coming from the ballast tank can be guided outside the ship.

5. Arrangement according to one of the previous claims, characterised in that overflow pipe is provided with a first valve.

6. Arrangement according to claim 4 or 5, characterised in that the overflow pipe exits the ship near a bottom side.

7. Arrangement according to one of the claims 4 t/m 6, characterised in that the arrangement moreover comprises a third pipe, connected to the second side of the pump and ending inside the ballast tank, which third pipe is provided with a number of discharge openings, via which surrounding water can be squirted into a direction of the bottom of the ballast tank.

8. Arrangement according to claim 7, characterised in that the discharge openings are provided with spray nozzles.

9. Arrangement according to claim 7 or 8, characterised in that the second and the third pipe are provided with a second, respectively a third valve.

Drawing