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Title:
SUB-SEA SEDIMENT DIFFUSER
Document Type and Number:
WIPO Patent Application WO/1994/025690
Kind Code:
A1
Abstract:
A diffuser (10) to discharge water containing sediment below water level. The diffuser (10) has a main pipe (14) and a plurality of discharge ports (12) located at spaced intervals along the pipe (14). Relative movement between the water and the diffuser (10) diffuses the sediment within the body of water.

Inventors:
Treloar, Doug
Application Number:
PCT/AU1994/000222
Publication Date:
November 10, 1994
Filing Date:
May 02, 1994
Export Citation:
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Assignee:
Metromix, Pty
LIMITED LAWSON & TRELOAR PTY
LTD
Treloar, Doug
International Classes:
E02F7/02; (IPC1-7): E02F9/00; B65G53/42; B65G53/52; E02F7/10
Foreign References:
FR2545799A11984-11-16
AU7577974A
AU5636369A
AU1911256A
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Claims:
CLAIMS :
1. A method of diffusing sediment below water level, said method including the steps of: providing a diffuser having an inlet and a plurality of spaced outlets; positioning the outlets below water level; causing relative movement between the diffuser and a body of water within which the outlets are submerged; and delivering to said inlet a stream of water containing sediment which leaves said diffuser via said outlets so as to be diffused thereby within the body of water.
2. The method of claim 1 , wherein said diffuser comprises an elongated main pipe with said outlets being positioned at longitudinally spaced positions along said pipe.
3. The method of claim 2. wherein said main pipe is inclined to the horizontal.
4. The method of claim 2 or 3, wherein the transverse internal cross sectional area of said pipe is greater than the cross sectional area of each of the diffusers.
5. A sediment diffuser comprising an elongated main pipe having one end providing an inlet, and a plurality of discharge ports located at spaced locations along said pipe.
6. The diffuser of claim 5, wherein each discharge port has a discharge opening of a predetermined area, and said pipe has an internal transverse cross section greater than each of the discharge areas.
7. The diffuser of claim 6, wherein the pipe has an internal diameter of about 0.65m, and there are about twelve discharge ports.
8. The diffuser of claim 7, wherein each discharge port opening is circular in configuration having a diameter of about 0.15m.
9. The diffuser of claim 8, wherein the discharge ports are spaced by a distance between 0.75m and 4m.
10. A method of diffusing sediment, substantially as hereinbefore described with reference to the accompanying drawings.
11. A diffuser, substantially as hereinbefore described with reference to the accompanying drawings.
Description:
SUB-SEA SEDIMENT DIFFUSER Field of the Invention

The invention pertains to diffusers and more particularly to a diffuser for transporting fine sediment particles from a dredge effluent to a point below the sea surface. The invention may be applied to all suction dredgers where the dredged bed material is extracted and transported via a slurry (solids/water mix), such as stationary suction and cutter suction dredgers or mobile dredgers such as trailing hopper dredgers.

Background of the invention

In the course of a dredging operation, sea bed, river or estuarine bed sediments are extracted and placed in or on a stationary or moving dredge, barge or other site. Excess waste water produced by the dredging process, together with suspended sediments are disposed of by discharging the excess waste with suspended sediments through a pumping system to a pipeline diffuser which penetrates the sea surface to a desired depth. In the past, the mixture of waste water and suspended sediments were discharged through a single port. This had the effect of producing, if only temporarily, undesirable concentrations of sediments (plume) in the water. Even if only temporary, the plume is considered unsightly and may be potentially detrimental to marine life and activities such as professional diving associated with underwater construction, repair or maintenance and even sport diving.

Objects and Summary of the invention

It is an object of the invention to substantially ameliorate some of the disadvantages associated with prior art dredging.

There is disclosed herein a method of diffusing sediment below water level, said method including the steps of: providing a diffuser having an inlet and a plurality of spaced outlets; positioning the outlets below water level; causing relative movement between the diffuser and a body of water within which the outlets are submerged; and delivering to said inlet a stream of water containing sediment which leaves said diffuser via said outlets so as to be diffused thereby within the body of water.

There is further disclosed herein a sediment diffuser comprising an elongated main pipe having one end providing an inlet, and a plurality of discharge ports located at spaced locations along said pipe.

Brief Description of the Drawings

Figure 1 is a side view of a diffuser according to the present invention.

Figure 2 is a front elevation of the diffuser depicted in Figure 1.

Best Mode and Other Embodiments of the Invention

In the example depicted in Figure 1 , the objects of the invention are accomplished by discharging a volume of waste water in which there are suspended solids at a mean

depth of about 15 metres below the sea surface 11. To achieve the desired rapid initial dilution and avoid discharge velocities greater than 10 metres per second a diffuser 10 is provided having a main pipe 14 with an internal diameter of, for example, .65m and eight radial discharge ports 12 each having an internal diameter of .15m. The radial ports may be provided in opposed pairs. An additional axial discharge port 13 may also be provided. Preferably, the discharge port diameters are less than the main pipe diameter. Discharge may be to the port and starboard of a moving vessel to improve dilution from transverse currents, caused in this case by relative motion between the vessel and the sea water. In practicality a minimum port spacing of about .75m would apply. In this- embodiment, port spacing is selected to be 4m, centre to centre, along the diffuser pipeline 14, in order to eliminate plume merging for distance of 20m to 40m behind the diffuser. The main diffuser pipeline 14 is inclined about 45° with respect to the horizontal, but may be inclined from approximately 0-90° depending on the relative vessel speed and drag force on the pipeline.

Increased dilution may be achieved by increasing the number of ports and/or reducing the diameter of the ports. Dilution may also be increased by increasing the length of the diffuser as well as the relative vessel to water speed and the direction of the port openings relative to the vessel. In the case of a stationary dredger, dilution is caused by the exit velocity and transport by ambient currents. Stationary dredgers may then need a swivel connection to allow discharge in the most advantageous directions vis-a-vis the ambient currents. However, in many normal circumstances, there will be practical limits based on pumping requirements, the possibility of oversize particle ingress into the system and drag on the diffuser. Normally, vessel speed will be limited by required control of the suction or cutter/suction dredge head. Further, the ports 12 may be formed of tubing that is tapered or non-tapered. The tubing may also be provided with orifices. It is also envisaged that port spacings and positions relative to each other may be varied. The angle of the diffuser to the horizontal and vertical are also variable in accordance with the discharge requirements. Selection of each of the design parameters is a matter which may require optimization for each particular application. However, it is the provision of a diffuser according to the teachings of the present invention which provides a flexible system which is capable of meeting the requirements of a wide variety of discharge applications.

While the present invention has been disclosed with reference to particular details of construction, these should be understood as having been provided by way of example and not as limitations to the scope or spirit of the invention.