WO2003056107A1

WO2003056107A1 - Suction manifold for dredging

Info

Publication number: WO2003056107A1
Application number: PCT/NO2002/000491
Authority: WO
Inventors: Tom Jacobsen; Terje Fagervold; Gunnar Fagervold; Olav Kvalvaag
Original assignee: Gto Subsea As
Priority date: 2001-12-21
Filing date: 2002-12-20
Publication date: 2003-07-10
Also published as: CN1606649A; NO20016361D0; JP4322679B2; GB2401624A; GB0413933D0; CN100469977C; AU2002351526A1; NO318582B1; JP2005513314A; NO20016361L; CR7376A; GB2401624B; WO2003056107A8

Abstract

Suction manifold for let dredging comprising two inlets or two sets of inlets (1, 2), a first, lower inlet or set of inlets (1) is arranged at or near the lower end of the suction manifold and being adapted to suck up sediments from the bottom together with some amounts of water while the second, upper inlet or set of inlets (2) is arranged at a vertical distance above the first inlet or set of inlets (1) and being adapted to suck in only water. The suction manifold comprises an inner tube (3) adapted to transport water and sediment, the upper end of which is adapted for being connected to a suction hose of approximately the same diameter, the lower part of said inner tube being enveloped by a casing (4) so that a substantially annular void (5) is defined between the lower part of said inner tube (3) an said casing (4). At least one opening forming upper inlet (2) is arranged at the upper end of the casing (4) into the void (5), while inlet (1) is arranged at the lower part of the tube (3) by an at least partly open axial end of tube (3), while also the casing (4) is open in the direction of an axial extension of the tube (3).

Description

Suction manifold for dredging

The present invention concerns a dredge for dredging the sea bottom, in a water magazine or the like. More particularly the invention concerns a dredge of he kind comprising two inlets or .two sets of inlets, the first inlet or set of inlets being arranged at or near the lowest part of the dredge and adapted to suck sediment from the sea bottom together with some water, the second inlet or set of inlets being arranged at a vertical distance from the first inlet or set of inlets, and adapted to such only water.

Background In many situations it is desirable to remove sediment from areas of a sea bottom. It may be in harbours, sailing paths or areas of polluted sediment. It can be desirable to deposit sediment at other locations under water or it may be more convenient to deposit the sediment ashore or to purify the sediment before it is deposited.

Furthermore there are water magazines, primarily in countries where the rivers contain large amounts [ of sediment and where the water magazines are subsequently being filled with sediments to an extent that the water capacity becomes to small. Furthermore sediment may affect the stability, block sluice gates/ doors or the like and lead to undesired wear of turbines, if sediment-containing water is allowed to enter a power plant. The sediment may have the form of large rocks etc. to very fine-grain particles of silt and clay.

When dredging through a suction manifold, the manifold is placed in contact with the sediment at the sea bottom in a defined first location, and will suck up sediment so that a crater is formed at the bottom. Somewhat dependent upon how loose or compact the sediment is at the actual location, sediment around the crater will eventually begin to fall into the crater as the grater becomes deeper and its walls steeper. Occasionally large amounts of sediment will fall into crater without any kind of prewarning, with the result that the suction manifold can be clogged and/ or get stucked.

A particular kind of suction manifold, denoted a saxophone head, has been proposed for dredging. The saxophone head is the first known example of a suction manifold with two inlets or two sets of inlets, the first inlet or set of inlets being arranged at or near the lowest part of the manifold and being adapted to suck up sediment from the bottom together with some amounts of water, while the second inlet or set of inlets being arranged at a vertical distance above said first inlet or set of inlets and being adapted to suck up only water. This suction manifold has the advantage that it to a large extent is self-adjusting with respect to the concentration of sediment being sucked up, and it may therefore to a large extent be left alone with low risk of getting clogged or lose its efficiency. On the other hand it has the disadvantage of being comparatively voluminous and sediment must be transported passed a bend on the manifold with some risk that large particles may get stuck. In addition it is not particularly well suited for spot-dredging.

A particular problem is that the conditions at the sea bottom varies a lot, and that a suction manifold that works well in loose sediment generally does not work as well in more compact sediment. The ability to adjust the suction properties with the conditions of the sea bottom has thus been limited, and is significantly better for the saxophone head than for conventional manifolds. The advantage of this manifold may be summarised as follows: At high concentrations of sediment in manifold and hose/ tube, the velocity within the manifold is reduced and thereby its suction force. Thus in the next period of time comparatively small amounts of sediment are sucked up and comparatively larger amounts of water. Thereby the concentration of sediments in the manifold and tube is reduced, the velocity is increased and the suction force again increased. With suction force in this context is meant the relative underpressure existing at the sediment inlet(s) of the manifold.

If there is a hard crust at the surface, the saxophone head will not be well suited to penetrate this and to access the looser sediment that is more easy to suck up.

Danish patent application No. 120 070 describes a suction apparatus for dredging sediment under water, comprising a manifold with two inlets. A straight inner tubing is surrounded by a substantially closed casing that has two openings at its upper end through which water is injected under pressure from the surface. Close to the lower end of the casing, there is an aperture in to the inner tubing, the length of which is telescopically adjustable. Under operation the manifold is forced into and fluidizes part of the sediment close to the manifold by use of the excess water pressure being supplied, whereafter sediment is being sucked/ pumped up together with some amounts of water. A disadvantage with this apparatus is that it comprises moveable parts that may get stucked and which require maintenance, plus a system for supplying water under pressure. Objective

It is thus an object of the present invention to provide a suction manifold for dredging that is largely selfadjusting with respect to concentration of sediment being sucked up, that is able to handle large particles like rocks of a significant diameter without any risk of blocking the tube.

It is a further objective to provide a suction manifold with said properties that is comparatively compact and is easily controllable by a remote operated vehicle (ROV).

It is a still further objective to provide a suction manifold as defined above that is able to penetrate the upper and commonly compact layer of the sea bottom, so that dredging may be performed from the underlying and looser layers of sediment.

The invention

The mentioned objects are achieved by a suction manifold of the type initially described that is characterized by the features defined by claim 1.

Preferred embodiments of the invention are disclosed by the dependent claims.

A distinction from the known saxophone head is that the suction manifold according to the invention is able to penetrate comparatively compact layers of sediment. At the same time it exhibits the favourable properties common with the saxophone head, that it is largely self-adjusting, so that after a period in which a comparatively large amount of sediment has been sucked up, a period will follow in which relatively small amounts of sediment will be sucked up, resulting in a concentration of sediment within the tubing 3 that fluctuates around a normal level.

Due to its relatively compact design, the suction head according to the invention can be manoeuvred and controlled by an ROV, so that it is simple to control and position with a high degree of accuracy. This is very important for some type of dredging situations, while in other situations there may be no need for precision control. Thus the suction manifold according to the present invention is not generally better than the saxophone head, but it is better in situations where accuracy and manoeuvrability are crucial factors for the dredging operation. One example is dredging that is performed to uncover certain objects or areas being covered by sediments, such as sluice ports, pipes or other equipment used in connection with dam installations or other installations under sea. The detailed design of the suction manifold according to the invention may vary, but it is preferred that the suction manifold is substantially straight and constitutes a mainly straight axial extension of a suction pipe or suction hose when connected to one.

Furthermore it is convenient that the casing surrounding the inner tube and limiting the void around the latter, has such a simple and regular shape, i.e. that its external shape is a substantially cylindrical surface. Internal space elements or support elements that hold the casing in a fixed position relative to the tube, may be designed in many different ways. The same may be said about the means attaching the casing to the tubing, that e.g. may comprise screws, bolts, rivets, adhesion means, welding, brazing or other means. The invention is not limited to any particular way of arranging such fastening means or spacing means for the casing.

It is actually possible to let parts of the casing be substituted by a particular tube or the like that partly is arranged alongside the "inner" tube, and hence does not surround or envelop the inner tube in the entire area from the upper inlet to the lower inlet. Such a solution is equivalent with the solution herein described as long as it is based on the same hydrodynamic principle as the preferred embodiments of the present invention.

At its lower end the casing may deviate somewhat from the simple cylindrical shape, e.g. by being tapered to a cross-section that is close to the size of the cross-section of the inner tube, and possibly reinforced and/ or provided with a wall or with teeth suited to break through compact sediment layers. Furthermore the lower edge of the casing may be provided with an annular flange that comprises nozzles connected to means for supplying water under pressure, so that high pressure flushing is possible where it is difficult to penetrate the sea bottom without it.

Figure la is a length sectional view of an embodiment of the invention in operating modus, Figure lb is an enlarged cross-sectional view of the manifold in Fig. 1, along the line II-II, Figure 2a is a length sectional view of a different embodiment of the manifold according to the invention, Figure 2b is an enlarged cross-sectional view of the manifold of Fig. 2a, along the line II-II. Figure 3 is a length sectional vies of still another embodiment of the invention, Figure 4a is a length sectional vies of yet another embodiment of the invention, Figure 4b is an end view of the embodiment according to Figure 4a. Figure l shows a suction manifold according the invention, comprising an inner tube 3 and an outer casing 4, defining inner and outer boundaries of an annular void 5. At the lower part of the suction manifold is arranged an opening 1 into the tube 3, said opening having the same or approximately the same cross-section as the tube 3. At the upper end of the casing 4 is arranged at least one opening 2 into the void 5. By accommodating the vertical extension of the casing to the relevant use or application one may ensure that opening(s) 2 will always suck in only water, while opening 1 will suck up sediments together with some amounts of water. At the upper end of the manifold the tube 3 is connected to a suction hose 6 through which sediment is transported for further treatment or depositing some other place. Figure lb is a cross-sectional view of the suction manifold at the line I-I in Fig. la. For the shown embodiment there are four inlets 2 into the void 5. The shown embodiment comprises eight attachment members 8 that attach the casing 4 with the tube 3 and delimit the opening 2. The attachment members 8 may have a limited vertical extension, or they may have an extension that corresponds completely or substantially with the extension of the case, so that the void 5 is divided into a corresponding number of separate chambers. It is also an alternative not to arrange support members at the very upper end of the casing, but instead farther down. It is also an option to use more than or fewer than four support members.

Normally the cross-sectional areas of the void 5 and of upper 2 and lower inlet 1 are determined by and designed to determine the relation between the suction force and the amount of water that enters to the upper inlet 2.

Figure 2a and 2b shows an alternative embodiment of the suction manifold according to the invention. The difference is not large, and consists in the upper area between the casing 4 and the tube 3 is partly closed by a "lid" 7 that restricts the opening 2 into the void 5. It is also an alternative to utilize a lid with a valve (not shown) that allows the size of the opening 2 to be varied according to the area of use or even under operation, when the valve is arranged to be remotely controlled. The valve may alternatively be designed as a "safety valve" that opens when the underpressure becomes sufficiently large.

Figure 3 shows an additional optional detail of the suction manifold according to the invention. Here the lower edge of the casing 4 is provided with a particular edge 9 suited to penetrate especially hard layers of sediment. Instead of an even edge, one may use teeth that are replaceable one by one or all as a set when they have become worn. Instead of or in addition to such an egg or such teeth, the same area of the suction manifold can also be provide with nozzles 11 for high pressure flushing of the sediment as illustrated by Fig. 4a and 4b, in order to loosen particularly hard or compact layers of sediment. The nozzles may be arranged on an annular flange 10 around the opening 1, and may be arranged in a way so that the water jets under operation are axially directed relative to the tube 3, as indicated by the arrows in Fig. 4a.

Fig. 4b shows the suction manifold of Fig. 4a in an end view, with an arbitrary number of nozzles 11 distributed around the annular flange 10 surrounding the opening 1. The construction of Fig. 4a and 4b is generally somewhat more complicated than the other shown embodiments, as they comprise means for supply of water under pressure at or near the suction manifold.

Advantages of the device according to the invention are among others that on its simplest form it does not comprise any movable parts, and works solely by means of simple hydrodynamic principles. Neither does it require supply of pressurized water, even if it for some purposes is advantageous to use either water under pressure or a mechanical device to break up compact sediment masses.

Claims

1. Suction manifold for let dredging comprising two inlets or two sets of inlets (1, 2), a first, lower inlet or set of inlets (1) being arranged at or near the lower end of the suction manifold and being adapted to suck up sediments from the bottom together with some amounts of water, the second, upper inlet or set of inlets (2) being arranged at a vertical distance above the first inlet or set of inlets (1) and being adapted to suck in only water, the suction manifold comprising an inner tube (3) adapted to transport water and sediment, the upper end of which is adapted for being connected to a suction hose of approximately the same diameter, the lower part of said inner tube being enveloped by a casing (4) so that a substantially annular void (5) is defined between the lower part of said inner tube (3) an said enveloping casing (4), characterized in that at least one opening forming upper inlet (2) is arranged at the upper end of the casing (4) into the void (5), while inlet (1) is arranged at the lower part of the tube (3) by an at least partly open axial end of tube (3), while also the casing (4) is open in the direction of an axial extension of the tube (3).

2. Suction manifold as claimed by claim 1, characterized in that the suction manifold is substantially straight.

3. Suction manifold as claimed by claim 1 , characterized in that the surrounding casing (4) is substantially cylindrical.

4. Suction manifold as claimed by claim 1 , characterized in that it comprises means (10, 11) for high pressure external flushing at the lower inlet (1) of the suction manifold.

5. Suction manifold as claimed by claim 1, characterized in that it comprises an edge (9) with teeth intended to penetrate compact sediment at its lower end.

6. Suction manifold as claimed by claim 1, characterized in that the upper opening (2) is provided with an adjustable valve.

7. Suction manifold as claimed by claim 1, characterized in that the upper opening (2) is provided with a normally closed valve that is arranged to open when the underpressure reaches a predetermined level.