WO2016130012A1

WO2016130012A1 - Natural vortex overflow system

Info

Publication number: WO2016130012A1
Application number: PCT/NL2016/050104
Authority: WO
Inventors: Adrianus Josephus Petrus Marie KOEVOETS
Original assignee: Ihc Holland Ie B.V.
Priority date: 2015-02-13
Filing date: 2016-02-12
Publication date: 2016-08-18
Also published as: NL2014291B1

Abstract

An overflow system (20) for a hopper dredger (10) includes an inlet portion (22) with an inlet for taking in head water from the hopper (16); an overflow tube (24) extending from the inlet portion (22); and a collector (28) to collect a flow of concentrated solids in the overflow tube (24). The inlet portion (22) and the inlet are shaped and positioned to encourage spiral flow (F).

Description

NATURAL VORTEX OVERFLOW SYSTEM

BACKGROUND

Trailing suction hopper dredgers ("TSHD") are vessels which can be used to dredge from a sea, riverbed or other water body. TSHD' s typically use a suction tube, one end of which can be lowered to the sea or river bed and used to suck up solids such as sand, sludge, silt or sediment, mixed with water. The lower end of this suction tube can be provided with a suction head or a drag head. The solid material mixed with water is pumped through the suction tube into a hopper of the dredging vessel. The mixture is reduced in speed when in the dredger hopper, and this speed reduction allows for the settling of components suspended in the mixture. Excess water is then overflowed out of the hopper through an overflow to allow for more load capacity within the TSHD.

Water from the hopper flows into the overflow through an entry disk or directly into the overflow. This overflow volume is then released via the bottom of the dredging vessel. This mixture may contain fine particles which have not settled, and the interactions between the overflow volume released, the hull, propellers, speed of the vessel and currents; can form a plume in the wake of the dredging process. The settling of this mixture can have an adverse effect on the local environment. Additionally, the suspension of these particles and then release through the overflow can cause a reduction in efficiency of the overall dredging process.

Different industries, such as the processing industry use various types of separating devices for separating solids and particles from a liquid. One such device is shown in DE-A1-3445586, showing a scoop wheel or a sieve to separate sand from water in dredger water mixed with sand. The device also uses a preliminary separating hydro- cyclone and a reconcentrating hydro-cyclone, with a pump for moving liquid through the system. The system requires a drop or free-fall to get sufficient speed. Thus, while the system can be used on dredged water, such a system would not be suitable for use in a hopper, and further may result in a plume if released into a sea from such a fall and increase in speeds.

U.S. Pat. App. Pub. No. 2009/0065417 discloses a solid-liquid separator system for use in a water treatment process. The process uses a separation tub, a froth discharge pipe, a sludge discharge pipe, and a treated water discharge pipe for discharging suspended solids which surface, sludge and treated water. The inflow is provided so that the raw water may rotate as it enters the separation tub. DEI 037418 discloses a sediment separator system for moving sediments to the centre of a vessel with a tapered bottom with an outlet which allows for the settling of sediment when the specific gravity of the suspended matter is greater than that of the liquid. The liquid enters the vessel, and a cylindrical flow is generated throughout the vessel to move the sediment toward the conical centre outlet, and the liquid toward an annular channel for further use. Such systems have not been previously considered for nor would they be suitable for use as an overflow system in a hopper-dredger, as they are used for entire separating systems to separate liquid and different suspensions/sludge/sediment, leading each to their own collection or exit from the systems. They also have specific limitations related to the specific processes and industries to which they are directed as well as the matter which they are aiming to collect which make them unsuitable for use as an overflow system in a hopper dredger.

SUMMARY

According to a first aspect of the invention, an overflow system for a hopper dredger includes an inlet portion with an inlet for taking in head water from the hopper; an overflow tube extending from the inlet portion; and a collector to collect a flow of concentrated solids in the overflow tube. The inlet portion and the inlet are shaped and positioned to encourage spiral flow.

Such an overflow system can encourage spiral flow into and through the overflow system. This spiral flow results in a concentrated flow of solids in the centre of the overflow tube, which can be collected by the collector and returned to the hopper. Thus, the overflow system can result in a cleaner overflow and an overall more efficient dredging process.

According to an embodiment, the inlet portion is substantially cylindrical shaped. A substantially cylindrical shaped inlet portion can help encourage the spiral flow desired through overflow system.

According to an embodiment, the inlet comprises a tangential inlet. A tangential inlet can help to encourage spiral flow into the overflow system.

According to an embodiment, the inlet comprises a flow passage to guide head water from the hopper into a spiral flow path in the overflow system. A flow passage can help to encourage the desired flow into and through the inlet portion of the overflow system.

According to an embodiment, the collector is positioned at a center of the overflow tube. By positioning the collector at the center of the overflow tube, it can collect a portion of the head water which is more concentrated with suspended particles. The spiral flow pattern results in a more concentrated stream of particles in the center of the flow. This concentrated stream at the center is able to be collected by a collector in the center of the overflow tube.

According to an embodiment, the collector is a collection funnel.

According to an embodiment, the overflow system further comprises a plurality of tangential outlets in the overflow tube to allow liquid to exit the overflow tube tangentially.

According to an embodiment, the overflow system further comprises a plurality of radial outlets in the overflow tube for allowing liquid to exit the overflow tube radially.

As the spiral flow pattern forces a more concentrated stream with particles into the center of the overflow tube, a cleaner overflow stream flows around the edges of the overflow tube. Tangential and/or radial outlets can allow for exit of this cleaner overflow stream from the overflow system. After exiting the overflow tube through tangential and/or radial outlets, the stream could be transported to an outside of the vessel by another flow path, for example a pipe surrounding the overflow tube.

According to an embodiment, the overflow system further comprises a straight axial exit from the overflow tube to allow liquid to exit the overflow tube.

According to an embodiment, the overflow system further comprises a collection reservoir connected to the collector for holding a mixture collected by the collector.

According to an embodiment, the overflow system further comprises a flowpath from the collector to the hopper for facilitating flow from the collector to the hopper; and a pump to pump the mixture from the collector to the hopper through the flowpath. By using a collection reservoir and/or a flowpath and pump, the concentrated stream collected by the collector can be returned to the hopper, allowing for settling of particles in the concentrated stream in the hopper.

According to an embodiment, the inlet comprises a plurality of inlets shaped and or positioned to encourage spiral flow in the inlet portion.

According to an embodiment, the overflow system is part of a vessel. According to a second aspect of the invention, a method includes flowing a mixture of water and suspended particles from a hopper through an inlet to an inlet portion of an overflow system; flowing the mixture through the inlet portion, to an overflow tube and through the overflow tube in a spiral flow pattern; and collecting a portion of the mixture in a collector in the overflow tube. Such a flow pattern through the overflow system results in a concentrated flow stream through the center of the overflow tube. The collector is able to collect this concentrated stream, leaving a cleaner mixture for overflowing from the overflow system.

According to an embodiment, the step of flowing a mixture of water and suspended particles from a hopper through a tangential inlet comprises flowing the mixture of water and suspended particles through a flow passage tangential to the inlet portion to encourage a spiral flow in the inlet portion.

According to an embodiment, the method further comprises transporting the collected portion of the mixture from the collector to the hopper. By returning the concentrated portion of the mixture to the hopper, the particles suspended in the concentrated mixture are able to settle in the hopper. This can result in an overall more efficient dredging process.

According to an embodiment, the method further comprises flowing the portion of the mixture not collected in the collector to an outside of the overflow tube through a tangential outlet, radial outlet and/or straight outlet. The spiral flow pattern through the overflow system results in a more concentrated flow through the center of the overflow tube and a cleaner flow around the edges. This cleaner flow can be overflowed through one or more tangential, radial and/or straight axial outlets. This cleaner overflow results in less environmental damages due to overflow liquid and an overall more efficient dredging process.

According to an embodiment, the step of flowing a mixture of water and suspended particles from a hopper through an inlet comprises flowing a mixture of water and suspended particles from a hopper through a tangential inlet. The tangential inlet may have a tangential flow passage. Such an inlet can encourage the desired spiral flow through the overflow system. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a trailing suction hopper dredger during a dredging operation.

Fig. 2a shows a cross-sectional view of a hopper and an overflow system.

Fig. 2b shows an isometric view of the overflow system of Fig. 2a.

Fig. 2c shows a side view of a portion of the overflow system of Fig. 2a.

Fig. 2d shows a top view of the overflow system of Fig. 2a.

Fig. 2e shows a cross-sectional view of tangential outlets of the overflow system of Fig. 2a.

Fig. 2f shows a cross-sectional view of radial outlets of the overflow system of Fig. 2a.

Fig. 3 shows a second embodiment of an overflow system.

DETAILED DESCRIPTION FIG. 1 shows a trailing suction hopper dredger ("TSHD") 10 in water body 11 during a dredging operation. Trailing suction hopper dredger 10 is suctioning a mixture of water and solid particles through suction tube 12. This mixture is then transported to a hopper in THSD 10 (not shown). Excess liquid in the hopper is overflowed, and plume 14 forms due to solids still suspended in the overflow.

Plume 14 can have an adverse impact on local marine biotope, as it reduces the entrance of light into the water body. Additionally, in some cases, the settling particles smother bottom life, and the suspensions can reduce the ability for microorganisms to develop. The suspended particles in the overflow also cause a reduction in efficiency of the overall dredging process. Forming an overflow system which reduces or eliminates suspended particles in the overflow, thereby only overflowing substantially cleaner water, can work to reduce or eliminate the plume 14 exiting vessel 10 and increase efficiency of the dredging process.

Fig. 2a shows a schematic view of a partial cross-sectional of a vessel 10 in water body 11, with view of a hopper 16 and overflow system 20 which works to reduce or eliminate suspended particles in overflow mixture, returning a concentrated mixture with particles back to hopper 16 and overflowing substantially clean liquid. Fig. 2b shows an isometric view of a portion of overflow system 20, Fig. 2c shows a side view of a top portion of overflow system 20, and Fig. 2d shows a top view of overflow system 20. Fig. 2e shows a cross-sectional view of tangential outlets of overflow system 20, and Fig. 2d shows a cross-sectional view of radial outlets.

Overflow system 20 includes inlet portion 22, overflow tube 24, inlets 26 with flow channels 27, collector 28, collection reservoir 29, pump 30, flowpath 31, straight axial outlet 32, tangential outlets 34, radial outlets 36, containment tube 37 and arrows F representing flow through overflow system 20.

Inlet portion 22 of overflow system 20 is cylindrical in shape with inlets 26 to receive head water from hopper 16. Inlets 26 are tangentially shaped with flow channels or paths 27 to encourage spiral flow into and within overflow system 22. In other embodiments, inlets 26 could be differently shaped and/or may not include flow channels 27.

Overflow tube 24 connects to inlet portion 22 and extends from inlet portion 22. Overflow tube 24 is tapered, with a decreasing diameter in the embodiment shown, though in other embodiments overflow tube 24 can have a constant diameter. The connection between inlet portion 22 and overflow tube 24 is curved, and can, for example, have a frequency curve of Y=l/X.

Collector 28 can be a collection funnel, and is located at a central location of overflow tube 24. Collector 28 can be connected to collection reservoir 29, which is connected to hopper 16 through flowpath 31. Pump 30 can be connected to collector 28, collection reservoir 29 and/or flowpath 31 for pumping a mixture from collector 28 or collection reservoir 29 to hopper 16 through flowpath 31. In this embodiment, collection reservoir 29 and pump 30 are located inside vessel 10 but outside hopper 16, though one or both could be located elsewhere in other embodiments.

Overflow system 20 includes straight axial outlet 32, tangential outlets 34 and radial outlets 36. Tangential outlets 34 and/or radial outlets 36 could be located at multiple positions on overflow tube 24, and flow out into containment tube 37. Some overflow systems 20 may only include one or two types of outlets 32, 34, 36. Tangential and/or radial outlets 34, 36 may form a part of overflow tube 24 above collector 28 and/or can be located below collector 28. Straight outlet 32 is typically below collector 28. All outlets 32, 34, 36 are in fluid connection with an outside of vessel 10, either directly or through containment tube 37 or another structure.

In operation, TSUD 10 suctions a mixture of liquid and fractions, and deposits that mixture into dredger hopper 16 (see Fig. 1). The head water in hopper 16 continues to rise as particles within the mixture settle to the bottom of hopper 16. When the head water reaches the level of inlets 26, the head water enters overflow system 20 through inlets 26. Inlets 26 and inlet portion 22 are shaped and positioned to encourage spiral flow F through overflow system 20. Tangential flow passages 27 are shaped and positioned to have head water enter overflow system 20 in a tangential manner, and flow through inlet portion 22 in a spiral flow pattern F. Flow continues in this spiral manner into overflow tube 24 due to the shapes of inlet portion 22, overflow tube 24 and the transition between the two.

The spiral flow pattern of the head water with suspended particles results in an increased density of the core flow toward the centre of the vortex when in the overflow tube 24. This results in a flow of particles suspended in the head water to the centre of the overflow tube 24. This concentrated stream of particles is then collected by collector 28, where it can be transported to collection reservoir 29 and then back to hopper 16 through flow path 31 using pump 30. A cleaner overflow liquid can then be released from overflow system 20 through outlets 32, 34 and/or 36. As the larger particles are forced to the centre of the overflow tube 24 through the spiral flow pattern F, cleaner overflow liquid can be removed from overflow system 20 through tangential outlets 34 and/or radial outlets 36 in overflow tube 24. This cleaner liquid is contained in containment tube 37 after exiting tangential and radial outlets 34, 36, and is transported to an outside of vessel 10. Any liquid not collected in collector 28 (or exited through tangential and radial outlets 34, 36) can then exit overflow system 20 and subsequently vessel 10 through straight axial exit 32.

By forming overflow system 20 with an inlet portion 22 with tangential inlets 26 and a shape to encourage spiral flow to and through overflow tube 24, a more concentrated mixture with suspended particles will be forced to the centre of the overflow tube 24 where it can be collected with collector 28 and returned to hopper 16. Thus, a cleaner overflow liquid can be released from overflow system 20 and vessel 10, thereby reducing any plume and minimizing resulting environmental damage caused by overflow with more suspended particles. Additionally, overflow system 20 can result in an overall more efficient dredging process as fewer suspended particles are overflowed back to the water body being dredged.

Fig. 3 shows a cross-sectional view of a second embodiment of overflow system 20, with parts labelled the same as in Figs. 2a-2f. In this embodiment of overflow system 20, collector 28, collection reservoir 29, pump 30 and a portion of flow path 31 are located within hopper 16. Flow path 31 flows the mixture collected from collector back to hopper 16. Overflow system 20 functions in the same manner as the overflow system of Figs. 2a-2f, and has the same ability to produce a cleaner overflow by encouraging spiral flow through overflow system 20 and collecting a more concentrated flow of particles with collector 28 to flow back to hopper 16. Cleaner overflow exits tangential outlets 34 (located above and below collector 28), radial outlets 36 and/or straight axial outlet 32, where it will then be transported to an outside of vessel. The embodiment of Fig. 3 could be used in situations where it is desirable to contain all of overflow system within hopper 16, for example, when there is not a lot of extra space on vessel 10.

While overflow system 20 is shown with tangential outlets 34, radial outlets 36 and straight outlet 32, some overflow systems could only have one or two types of outlets 32, 34, 36. Additionally, the number and locations of outlets 32, 34, 36 and inlets 26 are shown for example purposes only and can be different in different embodiments. Similarly, the shape of overflow system 20 is shown for example purposes only, and overflow system 20 can be any shape which encourages spiral flow through overflow system 20.

Overflow systems 20 and its components, location(s), and size (particularly the size relative to other components, for example, the ratio of hopper 16 size to vessel 10 and/or overflow system 20 to hopper 16) are shown schematically for example and viewing purposes only. Overflow systems 20 and its components could have different locations, sizes and relative proportions.

While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.

Claims

1. An overflow system for a hopper dredger, the overflow system comprising: an inlet portion with an inlet for taking in head water from the hopper, wherein the inlet portion and the inlet are shaped and positioned to encourage spiral flow; an overflow tube extending from the inlet portion; and

a collector to collect a flow of concentrated solids in the overflow tube.

2. The overflow system of claim 1, wherein the inlet portion is substantially cylindrical shaped.

3. The overflow system of any of the preceding claims, wherein the inlet comprises a tangential inlet.

4. The overflow system of any of the preceding claims, wherein the inlet comprises a flow passage to guide head water from the hopper into a spiral flow path in the overflow system.

5. The overflow system of any of the preceding claims, wherein the collector is positioned at a center of the overflow tube.

6. The overflow system of any of the preceding claims, wherein the collector is a collection funnel.

7. The overflow system of any of the preceding claims, and further comprising: a plurality of tangential outlets in the overflow tube to allow liquid to exit the overflow tube tangentially.

8. The overflow system of any of the preceding claims, and further comprising: a plurality of radial outlets in the overflow tube for allowing liquid to exit the overflow tube radially.

9. The overflow system of any of the preceding claims, and further comprising: a straight axial exit from the overflow tube to allow liquid to exit the overflow tube.

10. The overflow system of any of the preceding claims, and further comprising: a collection reservoir connected to the collector for holding a mixture collected by the collector.

11. The overflow system of any of the preceding claims, and further comprising: a flowpath from the collector to the hopper for facilitating flow from the collector to the hopper; and

a pump to pump the mixture from the collector to the hopper through the flowpath.

12. The overflow system of any of the preceding claims, wherein the inlet comprises a plurality of inlets shaped and/or positioned to encourage spiral flow in the inlet portion.

13. A vessel comprising the overflow system of any of the preceding claims.

14. A method comprising:

flowing a mixture of water and suspended particles from a hopper through an inlet to an inlet portion of an overflow system;

flowing the mixture through the inlet portion, to an overflow tube and through the overflow tube in a spiral flow pattern; and

collecting a portion of the mixture in a collector in the overflow tube.

15. The method of claim 14, wherein the step of flowing a mixture of water and suspended particles from a hopper through a tangential inlet comprises flowing the mixture of water and suspended particles through a flow passage tangential to the inlet portion to encourage a spiral flow in the inlet portion.

16. The method of any of claims 14-15, and further comprising: transporting the collected portion of the mixture from the collector to the hopper.

17. The method of any of claims 14-16, and further comprising:

flowing the portion of the mixture not collected in the collector to an outside of the overflow tube through a tangential outlet, radial outlet and/or straight outlet.

18. The method of any of claims 14-17, wherein the step of flowing a mixture of water and suspended particles from a hopper through an inlet comprises flowing a mixture of water and suspended particles from a hopper through a tangential inlet.