GB2469320A

GB2469320A - A marine vessel having a fluid discharge pipe and means for promoting mixing of discharge

Info

Publication number: GB2469320A
Application number: GB0906167A
Authority: GB
Inventors: John David Young
Original assignee: Hamworthy PLC; Kittiwake Developments Ltd; Krystallon Ltd
Current assignee: Wartsila Hamworthy Ltd
Priority date: 2009-04-08
Filing date: 2009-04-08
Publication date: 2010-10-13
Also published as: GB0906167D0

Abstract

A marine vessel comprises a fluid discharge pipe 3 extending through the hull 2 of said vessel for the discharge of fluid into an adjacent body of water 8, wherein means is provided for promoting the mixing of fluid discharged 9 from said pipe with said surrounding body of water. The means for promoting mixing / dispersing may take the form of the shape / curvature 10 of the hull in the region of the discharge pipe outlet. Alternatively, the pipe may comprise a convergence (nozzle) 6 with several apertures possibly defining one substantially annular outlet. Additionally, the pipe may be provided with internal vanes to swirl the fluid. The discharge pipe is ideally connected to an exhaust scrubber of a ship, and the mixing means helps reduce the acidity concentration of the discharged liquid effluent (commonly sea water). An independent claim relates to a pipe possessing features / formations for promoting the mixing of a discharged fluid.

Description

Marine discharge pipe The present invention relates to a pipe for discharging liquid into a marine environment, such as the sea, and a marine vessel comprising said pipe. In particular, it relates to the discharge of a liquid effluent leaving a gas-liquid contacting device, such as scrubbing liquid from the sump of a marine scrubber used for the removal of soluble gases from marine exhaust gases.

In the marine exhaust scrubber system, a liquid, such as seawater, is contacted with exhaust gases to extract soluble gases such as sulphur. dioxide (SO2).

As SO2 is absorbed into the seawater, it causes the pH of the seawater to decrease (i.e. the seawater becomes more acidic). Before discharging the seawater back into the sea, it is often mixed with fresh seawater to raise the pH. With the current levels of dilution, however, the pH of the discharged liquid may still be considerably below the ambient sea levels, such as pH 5.5. The liquid discharged to the sea can therefore have a harmful impact on the marine environment, especially when the ship is moving slowly or is stationary, e.g. in harbour.

When sulphur comes into contact with seawater there is a reaction with the Calcium Carbonate (CaCO3) in the seawater, to form Calcium Sulphate (gypsum) and CO2. The reaction neutralises the acidity of sulphur, and consumes some of the buffering capacity of the seawater. The key environmental benefit of scrubbing is that it short circuits the whole sulphur cycle, and returns the sulphur to the sea in the safest, quickest and least harmful way. This is the core environmental justification for scrubbing.

However, the acidity of the discharged fluid does not change dramatically very close to the point of discharge. The discharge of scrubbing seawater into the sea is the focus of the main environmental objections to seawater scrubbing, and is quoted as an argument against the use of seawater scrubbing.

When discharged, the acidified water will mix with the ambient surrounding water. To prevent environmental harm due to the discharged fluid, the International Maritime Organisation (IMO) and the US Environmental Protection Agency (EPA) have adopted regulations for the mixing of scrubbing effluents with ambient seawater. According to the guidelines, the mixing processes are divided into two defined zones: (i) the acute mixing zone and (ii) the chronic mixing zone. The critical pH limit for the acute mixing zone is 6.5, which should be reached within 4 metres from the point of discharge. The residence time within the chronic mixing zone is longer, and encompasses a dilution at least 1:40,000. The conditions for dilutions of discharge water from a ship will vary depending on travelling speed in open water, or hydro-graphic variations in a dock.

Acidity in discharge water is not believed to be a significant problem in open sea as the high turbulence and alkalinity of seawater acts as a buffer and effectively neutralises the acids. However, scrubber fluids discharged into ports, i.e. when the vessel is moving more slowly or even stationary, are less likely to be neutralised quickly, and thus can cause acidic concentration close to the side of the vessel. This can be harmful to the marine environment and can also be problematic as the acidic liquid could come into contact with the hull of the vessel. This can cause damage to the bull or coatings applied to it..

Prior art discharge pipes do not reliably achieve sufficient mixing to satisfy the standards mentioned above.

The present invention provides an apparatus which address the problems of

the prior art.

According to one aspect of the present invention, there is provided a marine vessel comprising a fluid discharge pipe for the discharge of fluid from the vessel into a body of water adjacent to the vessel and means for promoting the mixing of fluid discharged from the pipe with the adjacent body of water. The pipe extends through a wall of the hull of the vessel.

The references to a body of water adjacent to the vessel' and the adjacent body of water' should be understood to mean the body of water surrounding the vessel, upon which the vessel floats. The body of water can thus be seawater, when the vessel is in an ocean or a sea, or freshwater, when the vessel is on a river or a lake.

The term marine vessel' should be understood to mean any type of marine floating vessel such as a ship, boat, ferry, cruise-liner or yacht etc. The end of the pipe at which the fluid is discharged could be flush with the outer surface of the wall of the vessel. However, preferably, the pipe projects from the wall of the vessel into the adjacent body of water. This results in better mixing and less concentration of the discharged fluid at the wall of the vessel.

The means for promoting the mixing of fluid discharged from the pipe with the adjacent body of water ensures that the discharged fluid mixes quickly and efficiently such that the pH of the discharged fluid is raised to acceptable levels quickly and at a short distance from the discharge end of the pipe. This results in less harm to the marine environment and less damage to the surface of the hull of the vessel in the vicinity of the pipe.

As discussed below, the means for promoting the mixing of fluid discharged from the pipe with the adjacent body of water may be provided by a structural feature of the vessel wall or a structural feature of the pipe.

The pipe may be any shape, but is preferably cylindrical in shape. The pipe is preferably made of a material that is resistant to corrosiorrthrough the action of water or acids. Preferably, the pipe is metallic.

in some embodiments, the means for promoting the mixing of fluid comprises a concave section in said wall of said hull, wherein said fluid discharge pipe extends through and projects from the wall of said vessel at said concave section.

The concave section preferably promotes the mixing of the discharged fluid and the surrounding water by inducing the surrounding water to flow in a circular manner towards the surface of the hull in the area of the concave section. The flow of discharged fluid from the pipe then may educt the flow of surrounding water in the concave section to flow along the direction of the pipe and to mix with the discharged fluid. In other words, the concave section promotes the induction of the surrounding seawater into the discharged stream and therefore increases turbulence and mixing thereof.

Without the concave section, i.e. with the pipe protruding from a substantially planar surface of a hull, there is much less flow of the surrounding water along the pipe. Instead, the surrounding water behind the discharge end of the pipe, i.e. between the discharge end of the pipe and the hull, can remain much more stagnant. This relatively stagnant water can become acidic and damage can be caused to the hull and any coatings applied thereto.

The concave section also facilitates flow of the surrounding water even at distances very close to the hull surface, The layer of liquid in contact with the hull, known as the boundary layer, is much more turbulent and thus less likely to become highly acidic.

In other embodiments, the means for promoting the mixing of fluid comprises a nozzle located at a discharge end of said pipe. The nozzle creates a reduction in the cross-sectional area of the pipe such that fluid flowing through said nozzle is accelerated. The term nozzle' should be understood to mean any narrowing of the internal dimensions of the pipe at its discharge end. Passing fluid through a narrowed portion serves to increase its velocity. Discharging the fluid into the surrounding body of water at a higher velocity facilitates mixing.

Preferably, said nozzle defines a plurality of apertures through which fluid flows in use.

Preferably, the nozzle comprises at least one substantially annular shaped aperture in said discharge end of said pipe. In use, such a nozzle will generate a flow from said discharge end that has a substantially annular cross-section. A flow having an annular cross-section can be considered to be in the shape of a cylinder. Such a flow mixes more easily with surrounding body of water as the flow has a greater surface area in contact with surrounding body of water. If the flow is considered to be cylindrical, the hollow part will be filled with the surrounding water.

Preferably, the nozzle comprises a plurality of concentric substantially annular apertures. This promotes mixing of the resulting discharged fluid flow which has an even greater surface area.

In other embodiments, the means for promoting the mixing of fluid additionally or alternatively comprises means for generating a spiral flow from said discharge end of said pipe. A spiral-shaped flow of discharged fluid promotes mixing as it is a more dynamic, turbulent flow.

Preferably, the means for generating a substantially spiral flow comprises a plurality of circumferentially spaced vanes extending inwardly from an inner surface of said pipe. These vanes serve to spin the fluid flowing along the pipe around the longitudinal axis of the pipe.

Preferably, three vanes are provided.

Preferably, the vanes extend inwardly radially from the inner surface of the pipe.

Preferably, the vanes extend inwardly at an angle to the radius of said pipe.

This may promote the spiral or spinning movement of the fluid flow.

Preferably, the pipe is metallic.

Preferably, the pipe is configured to discharge acidic fluid.

Preferably, the pipe is connected to the outlet of an exhaust gas scrubber and the fluid is a scrubber fluid from said scrubber. The scrubber fluid may be seawater.

A method of discharging fluid into a body of water using the vessel of any preceding claims, comprising the step of passing said fluid through said pipe.

According to another aspect of the present invention, there is provided a fluid discharge pipe for the discharge of fluid from a marine vessel into a body of water adjacent the vessel, wherein said pipe comprises means for promoting the mixing of fluid discharged from the pipe with the adjacent body of water.

This further aspect of the present invention may include any of the features described with respect to the first aspect.

The pipe can be installed in new-build ships as well as retrofitted in existing ships.

Preferably, the means for promoting the mixing of fluid comprises a nozzle located at a discharge end of said pipe, said nozzle creating a reduction in the cross-sectional area of the pipe such that fluid flowing through said nozzle is accelerated.

Preferably, the nozzle defines a plurality of apertures through which fluid flows in use.

Preferably, the nozzle comprises at least one substantially annular shaped aperture in the discharge end of the pipe.

Preferably, the nozzle comprises a plurality of concentric substantially annular apertures in the discharge end of the pipe.

In other embodiments, the means for promoting the mixing of fluid comprises means for generating a substantially spiral flow from a or the discharge end of the pipe.

Preferably, the means for generating a substantially spiral flow comprises a plurality of circumferentially spaced vanes extending inwardly from an inner surface of the pipe.

Preferably, three vanes are provided.

Preferably, the vanes extend inwardly radially.

Preferably, the vanes extend inwardly at an angle to the radius of the pipe.

Preferably, the pipe is metallic.

Preferably, the pipe is configured to discharge acidic fluid.

Preferably, the pipe is connectable to the outlet of a marine exhaust gas scrubber and the fluid is a scrubber fluid from the scrubber. The scrubber fluid may be seawater.

The device and method of this invention are not limited in their application and may be used in any situation where a waste liquid needs to be discharged at high velocity from a ship or similar vessel into the sea, lake or river whilst minimising the harmful effect of low pH stream into the environment.

The present invention in any of the aspects of the present invention may include any of all of the features described in respect of the other aspects and embodiments of the invention to the extent that they are not mutually inconsistent.

Some preferred embodiments of the present invention will now be described, by way of example only, and with reference to the accompanying drawings, of which; Figure 1 is a cross-section through a preferred embodiment of a marine vessel in accordance with the present invention.

Figure 2 is a cross-section through a first preferred embodiment of a pipe in accordance with the present invention.

Figure 3 is a cross-section through a second preferred embodiment of a pipe in accordance with the present invention.

The marine vessel I shown in Figure 1 comprises a hull 2 and a pipe 3 extending from a point 4 on the hull 2. The pipe 3 extends from said point 4 to a discharge end 5. At the discharge end 5, the pipe has a reduction in cross-section, i.e. a nozzle 6. The nozzle serves to accelerate the flow of the fluid 7.

Fluid 7 travels along pipe 3. The fluid may be a scrubber fluid from an onboard marine gas exhaust scrubber. The scrubber fluid may be seawater, which is acidic due to the gases dissolved therein.

The fluid 7 is discharged into surrounding water S (e.g. seawater) in a discharged flow 9. Discharged flow 9 mixes with the surrounding water 8.

The hull 2 has a concave section 10 surrounding the point 4 at which the pipe 3 is connected to the hull 2. While the concave section 10 is shown schematically as rather angular, in practice it is more likely to be less angular and curved smoothly.

The concave section 10 has the effect that the discharged flow 9 inducts a flow 11 in the surrounding water 8. The flow 11 is initially towards the vessel I and then parallel to the pipe 3 and the discharged flow 9. The discharged flow 9 educts the surrounding flow 11 in the manner shown in Figure 1. This creates a more turbulent flow downstream of the discharge end S of the pipe 3 which promotes mixing. It also has the effect or circulating water in the vicinity of the hull surface, which prevents damage caused thereto by the fluid, which may be acidic.

Figure 2 shows a cross-section of the discharge end 5 of a pipe 13 according to a first embodiment. This pipe 13 can be utilised with a vessel either having or not having the construction shown in Figure 1.

Pipe 13 comprises three vanes 15 extending inwardly from its inner surface 14. The vanes 15 extend at an angle a to the radius 17 of pipe 13 having central axis 16. The pipe 13 is substantially cylindrical in shape with a circular cross-section.

The vanes 15 serve to induce a spiral flow 18 of fluid 7 within the pipe 13.

The fluid 7 spirals around central axis 16. The fluid 7 will continue to spiral when it leaves the discharge end 5 of pipe 13 and become discharged flow 9. This creates a more dynamic and turbulent flow which promotes mixing of the flow 9 with the surrounding water 9.

Figure 3 shows a cross-section of the discharge end 5 of a pipe 23 according to a second embodiment. This pipe 23 can be utilised with a vessel either having or not having the construction shown in Figure 1.

Pipe 23 is substantially cylindrical in shape with a circular cross-section. At its discharge end 5, there is provide a nozzle comprising outer annular portion 24 and a central circular portion 26. This creates and annular opening 25 through which fluid 7 can flow. Central circular portion 26 may be connected in some way to annular portion 24 so that it is retained in place. As such, annular opening 25 may be interrupted. However, its overall shape vill be substantially annular. This will provide a discharged fluid flow 9 having a reduced annular cross-section. In other words, the discharged flow 9 will have a cylindrical shape. This creates a higher velocity discharged flow 9 having a higher surface area which will be mixed much more easily with the surrounding water 8.

Claims

CLAIMS: 1. A marine vessel comprising: a fluid discharge pipe for the discharge of fluid from said vessel into a body of water adjacent said vessel, said pipe extending through a wall of the hull of the vessel; and means for promoting the mixing of fluid discharged from said pipe with said adjacent body of water.
2. The marine vessel of claim I, wherein said means for promoting the mixing of fluid comprises a concave section in said wall of said hull, wherein said fluid discharge pipe extends through and projects from the wall of said vessel at said concave section.
3. The marine vessel of claim I or 2, wherein said means for promoting the mixing of fluid comprises a nozzle located at a discharge end of said pipe, said nozzle creating a reduction in the cross-sectional area of the pipe such that fluid flowing through said nozzle is accelerated.
4. The marine vessel of claim 3, wherein said nozzle defines a plurality of apertures through which fluid flows in use.
5. The marine vessel of claim 3 or 4, wherein said nozzle comprises at least one substantially annular shaped aperture.
6. The marine vessel of any of claims 3 to 5, wherein said nozzle comprises a plurality of concentric substantially annular apertures in said discharge end of said pipe.
7. The marine vessel of any preceding claim, wherein said means for promoting the mixing of fluid comprises means for generating a substantially spiral flow from a or said discharge end of said pipe.
8. The marine vessel of claim 7, wherein said means for generating a substantially spiral flow comprises a plurality of circumferentially spaced vanes extending inwardly from an inner surface of said pipe.
9. The marine vessel of claim 8, comprising three vanes.
10. The marine vessel of claim 8 or 9, wherein said vanes extend inwardly radially.
11. The marine vessel of claim 8 or 9, wherein said vanes extend inwardly at an angle to the radius of said pipe.
12. The marine vessel of any preceding claim, wherein said pipe is connected to the outlet of an exhaust gas scrubber and said fluid is a scrubber fluid from said scrubber.
13. A fluid discharge pipe for the discharge of fluid from a marine vessel into a body of water adjacent said vessel; said pipe comprising means for promoting the mixing of fluid discharged from a said pipe with said adjacent body of water.
14. The pipe of claim 13, wherein said means for promoting the mixing of fluid comprises a nozzle located at a discharge end of said pipe, said nozzle creating a reduction in the cross-sectional area of the pipe such that fluid flowing through said nozzle is accelerated.
15. The pipe of claim 14, wherein said nozzle defines a plurality of apertures through which fluid flows in use.
16. The pipe of claim 14 or 15, wherein said nozzle comprises at least one substantially annular shaped aperture in said discharge end of said pipe -11 -
17. The pipe of claim 15 or 16, wherein said nozzle comprises a plurality of concentric substantially annular apertures in said discharge end of said pipe.
18. The pipe of any of claims 13 to 17, wherein said means for promoting the mixing of fluid comprises means for generating a substantially spiral flow from a or said discharge end of said pipe.
19. The pipe of claim 18, wherein said means for generating a substantially spiral flow comprises a plurality of circumferentially spaced vanes extending inwardly from an inner surface of said pipe.
20. The pipe of claim 19, comprising three vanes.
21. The pipe of claim 19 or 20, wherein said vanes extend inwardly radially.
22. The pipe of claim 19 or 20, wherein said vanes extend inwardly at an angle to the radius of said pipe.
23. The marine vessel or pipe of any preceding claim, wherein said pipe is metallic. -
24. The marine vessel or pipe of any preceding claim, wherein said fluid is acidic.
25. The marine vessel or pipe of any preceding claim, wherein said fluid is seawater.
26. A method of discharging fluid into a body of water using the vessel or pipe of any preceding claims, comprising the step of passing said fluid through said pipe.