NO20111113A1 - Device for use in dredging - Google Patents

Abstract

Apparatus for use in dredging in a water reservoir, comprising a suction head (2) with at least one lower opening () adapted to suck in sediments and water, the suction head being coupled to an at least partially flexible outlet line (6) providing the suction power solely at the pressure difference between the water surface (10) in the reservoir and the outlet (9). The device is characterized in that the suction head (2) is suspended in a flexible suspension (3) which is arranged to drop the suction head down to the actual working level and where the sediment rests without prior knowledge of the level, and that the suction head (2) is provided with at least one upper aperture (24) at a vertical distance from the lower aperture (23) to ensure that it cannot be sealed by the settling of sediments towards the lower aperture (23). Furthermore, the suction head (2) and the at least partially flexible outlet line (6) are preferably so balanced that the suction head will maintain an effective working position with or without support of the flexible suspension (3).

Description

Device for use when dredging in water reservoirs, as stated in the preamble to patent claim 1.

Background

In connection with dam facilities, there is often a need to systematically remove sediments that follow the rivers and accumulate in the dams, thereby reducing their capacity and can lead to damage to equipment in the dam if the level becomes too high.

Different techniques have therefore been developed to periodically or continuously remove sediments from the bottom of dams, thereby maintaining water capacity and reducing the risks of problems linked to high levels of sediments.

However, there are many problems associated with the removal of sediments (dredging). Typical problems are that the methods are costly, labor-intensive and sensitive to large particles that can clog the equipment and significantly delay and make the work more expensive.

To make the process more flexible, attempts have been made to use flexible suction hoses and vessels that can easily move the suction nozzle on the hoses from place to place in the pond. However, the use of flexible hoses is not unproblematic either, especially at depths exceeding 10 -15 metres, as the pressure reduction that occurs in the hose during use can easily cause it to collapse, which at least hinders the hose's function, but which also can cause hose breakage.

There is thus still a need to develop methods and equipment that make such removal of sediments easier and more reliable, especially when dredging at great depths.

Many reservoirs are sealed with a thin membrane, for example made of PE or PVC, which is vulnerable to external influences. There will then be a need for equipment that does not damage the membrane even in contact between, for example, the suction head and the membrane.

Dredging is known from a number of publications, and one publication that dredging using a suction head that utilizes the pressure difference between the surface and a level that is lower than the surface is WO 02/057551. However, this publication does not provide any guidance on how to easily dredge from very different areas within a water reservoir.

Purpose

It is thus an aim of the present invention to arrive at equipment for dredging at small and greater depths, which is reliable, simple and affordable and which has the least possible risk of operational failure caused by clogging or hose collapse.

It is a further purpose that the equipment should be easy to reposition.

It is a further purpose that the equipment should be able to be operated without the use of professional personnel and with little supervision. It is a derived purpose that it should have as few moving parts as possible or parts that are exposed to strong wear and tear.

Finally, it is an aim that the equipment should be able to be used in a reservoir with a membrane without the risk of puncturing or otherwise damaging the membrane.

Present invention

The above-mentioned purposes are according to a first aspect achieved through the device according to the present invention as defined in patent claim 1.

Preferred embodiments appear from the non-independent patent claims.

The expression "at least partially flexible outlet line" is understood to mean that at least part of the outlet line near the suction head is sufficiently flexible so that the suction head can be moved and repositioned. In the area closer to the outlet, the outlet opening may be stiff. According to a preferred embodiment, however, flexible joints are placed at regular intervals which connect otherwise rigid sections of the outlet line also in the part of the outlet line which is closer to the outlet than the suction head. Thereby, a desired degree of flexibility is achieved along the entire outlet line, even if it has a certain rigidity at the same time. For example, straight, rigid sections of, for example, 20-40 meters can be spliced together by flexible joints with a length of, for example, 3-6 meters. It is not appropriate to have sharp angle changes between two straight cable elements, therefore the flexible connecting pieces must also have a certain length. In the area near the suction head, however, it is preferred to have a longer, continuous flexible section of the outlet line, such as a section of length 20 to 50 metres.

By "effective working position" is meant a working position where the suction head's lower opening - or set of openings - is in good contact with the sediments. In practice, this means an approximately upright or vertical position for a mainly straight suction head. With an appropriate design of the suction head, a certain tilting of the suction head can be allowed without this being at the expense of the function, e.g. an inclined position of 20 to 30 degrees in relation to a vertical position.

With the present invention, a high degree of flexibility is achieved when it comes to dredging. Use of an - at least partially - flexible outlet line which is led directly out of the water reservoir means that no subsequent step of removing sediments is needed as is the case for WO 02/057551. The use of a soft or flexible suspension in the form of wire or rope means that one does not need to know the depth from which the dredge is to be dredged. The suction head is lowered to the bottom and it is not dangerous or harmful to give out an excess of wire or rope as the suction head is, according to a preferred embodiment, arranged in such a way that it will not tip over. Furthermore, the use of floats attached to the flexible outlet line can ensure that it remains at a vertical level that is acceptable based on the conditions locally, especially with regard to pressure at the suction head, the vertical location of the outlet and the local atmospheric pressure. Furthermore, if necessary, the construction of the suction head can ensure that unexpected pressure pulses in the suction head and outlet line cannot nevertheless bring the pressure conditions into an undesirable area with the potential consequence that dredging stops and possibly that the equipment is damaged. Using a vessel to move the suction head will be preferred in large water reservoirs. When dredging is carried out in smaller reservoirs or at a limited distance from solid ground, a crane standing on land may be used instead of a vessel. During the move, the operator will ensure that the wire or rope is tight, and the suction head will normally be lifted from the bottom, but it is not directly harmful if the suction head drags the bottom when moving. Finally, with the present invention, it is possible to dredge from in principle any depth, as long as the length and nature of the discharge line and wire or rope are adapted to the purpose.

If the distance between the area where dredging is being done and the pond is short, and/or it is not practically possible to route the discharge line through the pond, a siphon can be used over the pond.

Suction head and possible flushing device can be manufactured in soft material such as PE or Polyurethane. As the sediments, if they are cohesive, disintegrate with water flushing, it can be dredged all the way down to/up to vulnerable surfaces and structural parts such as PE or PVC membranes which are normally only 1 - 5 mm thick.

In what follows, the invention will be described in more detail in the form of a non-limiting exemplary embodiment.

Detailed information about the present invention

Figure la shows a preferred embodiment of the device according to the present invention.

Figure 1b shows an enlarged section of a detail from Figure 1b.

Figure 2 shows the principle of the discharge line's pressure line during dredging as shown in Figure 1.

Figures 3a and 3b show further details of preferred embodiments of the device according to the present invention.

A water reservoir 1 is located within a dam or dam wall 5. At the bottom of the reservoir there are sediments 12 which have followed the river and been accumulated. The device comprises a suction head 2 which is carried by a wire 3 or equivalent flexible suspension held by a vessel 4 floating in the reservoir 1. An outlet line 6 is connected to the suction head 2 which has a flexible part 7 which makes it possible to move the suction head. There is nothing to prevent the entire outlet line being flexible, but the most typical thing would be that there is at least one rigid part 8 of the outlet line 6 at a distance from the suction head 2. The mouth 9 of the outlet line is at a point lower than the water level 10 in the reservoir. The pressure of the water column between the two levels 10 and 8 is the driving force for suction of sediments from the reservoir. To regulate the vertical level of the outlet line 6, or at least the flexible part 7 of the outlet line 6 in the reservoir 1, a number of floats 11 are typically used which are attached to the outlet line with lines at certain intervals. The flexible part 7 of the outlet line 6 has a certain structural rigidity, so that it does not collapse at a fairly small pressure difference between the outside and the inside. The pressure difference between the inside and outside of the flexible outlet line will be given by inlet loss, friction loss, the velocity height, pressure difference due to increased specific gravity of the water - sediment mixture as well as pressure pulses due to sudden changes in speed.

Dimensions shown horizontally and vertically are illustrative only and in no way represent any limitation on how deep it can be dredged or how far away from the outlet it can be dredged.

Figure 1b shows the suction head from Figure 1 enlarged, with an inner tube 21 which is open at both ends and connected to the outlet line 6 at the upper end, as well as an outer tube 22 which has an opening 23 at the lower end and which additionally has a preferably adjustable upper opening 24 at a vertical distance from opening 23. The meaning of this is explained in more detail below. Water that is sucked in through the upper opening 24 must first be moved down to the lower opening 23 in the annulus between the outer tube 22 and the inner tube 21, to then pass through the inner tube 21 to the outlet hose 6. On the suction head 2, ballast body 25 is also shown and a buoyancy body 26 which helps to keep the suction head in an upright position. The buoyancy body is shown attached to the suction head 2 via an arm 27 which further contributes to stabilizing the suction head. One opening 24 is shown in figure 1b, but it could just as easily be a set of smaller openings, for example openings distributed around the circumference of the outer tube 22 at a given vertical level near the top of the suction head 2.

Furthermore, there are two specific measures in the present device which are decisive for the outlet line 6 not to collapse. One is that the vertical position of the outlet line 6 is such that the inlet loss, friction loss, velocity height and pressure difference due to increased specific gravity of the water - sediment mixture do not exceed the permitted pressure difference during normal operation.

The second is the presence of said upper opening 24 on the suction head which helps to prevent negative pressure pulses in the outlet line in cases where the suction head is temporarily blocked or has its cross-section significantly reduced by unwanted large amounts of particles simultaneously entering the suction head through the lower opening 23. The sum of these two conditions, seen in relation to the properties of the flexible part 7 of the discharge line 6, seen in relation to the nature of the sediments and seen in relation to the vertical level of the mouth 9 of the discharge line 6, are decisive for whether transport through the discharge line will stop and whether the discharge line 6 may will collapse under operating conditions, such as in the event of sudden, complete or partial clogging of the lower inlet 23 for sediments to the suction head.

It is also of crucial importance that a vacuum does not occur in any part of the outlet line. If the absolute pressure falls towards zero, the outlet pipe will be filled with steam and the flow of water and sediments may be interrupted. It is therefore crucial, so that a vacuum does not occur, that the discharge line is arranged so that it is at any time and in any place lower than the sum of a) its pressure line and b) the local atmospheric pressure measured as the height of the column of water and sediments in the discharge line.

Reference is now made to figure 2. In figure 2, the floats etc. omitted for the sake of clarity, but it should be understood that there will normally be floats attached to the outlet line 6. A first (lowest) pressure line is shown with an alternating dotted line and can be referred to as the outlet line pressure line. It starts with a first or highest pressure at the suction head and ends with a lowest pressure at the outlet. The pressure at the suction head is determined by - the level of the water table in the reservoir, while the pressure at the outlet is equal to the local atmospheric pressure. In general, the pressure line is determined by the inlet loss, any other singular losses and the friction loss in the outlet line. Elements that can cause other singular losses are changes in the cross-section of the wire, breaks in the wire, etc.

In addition to this pressure line, a short dashed line, the vacuum line, is shown, which is higher than the pressure line, and concretely as much higher than this as the corresponding atmospheric pressure calculated as the height (metres) of the column of water and sediments in the outlet line. Figure 2 shows that any point of the discharge line is lower than the vacuum line.

The outlet line can also be routed over, instead of through the pond, provided it is below the vacuum line.

However, one should be aware that the amount of sediments in the outlet line will vary over time, and the higher the concentration of sediments, the higher the density of the mixture will normally be, since sediments generally have a greater density than water. The higher the density of the mixture of water and sediments in the discharge line, the lower the column of the mixture corresponding to atmospheric pressure. It would therefore be appropriate to draw - or calculate - the short dotted line so that it corresponds to the column of water and sediments for one atmosphere of pressure at the highest current or permissible concentration of sediments. Then the challenge remains for the operator to ensure that this highest permissible concentration of sediments is not exceeded in practice at any time under potentially highly varying conditions of use. The present invention also takes care of this. Finally, the height above sea level must be taken into account when the relevant atmospheric pressure is calculated.

Reference is now made to Figures 3a and 3b. The suction head 2 is, by means of the mentioned upper opening 24, designed in such a way that it not only prevents sudden pressure changes from propagating in the outlet line 6, it also ensures that a given maximum density of the mass being sucked in is not exceeded. If the density of the mixture and water and sediments in the suction head 2 exceeds a threshold value, the suction of sediments through the lower opening 23 is reduced and is replaced by an increased suction of clean water through the upper opening 24 instead. According to this embodiment, the suction head thus has a built-in mechanism which ensures that a critical value for the density of water + sediments can never be exceeded in the outlet line. In order to have the possibility of enhancing or regulating this effect, the upper opening 24 can be partially covered by a flap 28 (fig. 3a) which is flexible and allows the opening 24 to have its cross-section temporarily increased if the pressure in the suction head 2 and thereby in the outlet line 6 should fall. Alternatively or in addition, the upper opening can be covered by a regulated damper 28' (Fig. 3b) which can be manually set by the operator to the desired effective cross-section of the opening 24. When using a set of openings 24, some of the openings can be provided with adjustable dampers 28' and some can be provided with flexible flaps 28. . The suction head is preferably arranged in such a way that it will not be able to lie horizontally on the bottom, as its upper part has an effective density lower than water. By "effective" density it is understood that it can be the suction head itself which is made of a light material or there can be buoyancy bodies 26 attached to the upper part of the suction head, to the outlet line near the suction head or to the wire on which the suction head is suspended which contributes to a total buoyancy in the water. As a counterweight to this, the lower part of the suction head is made correspondingly heavier, either by itself or by having at least one ballast body 25 attached to it. The suction head 2 will therefore typically maintain an upright, nearly vertical position, also if there is slack in the wire 3 or when the vessel 4 is used to reposition the suction head by towing it to a new location. With slow movement of the vessel, the suction head will only have a slight "impact side" or tilt during repositioning, even if the lower part of the suction head is in contact with the sediments 12. At the same time, the floats 11 will ensure that a fixed distance is maintained between the surface of the reservoir and the highest part of the outlet line 6 level. The vertical distance between the suction head 2 and the highest level of the discharge line will change slightly as the suction head sucks away sediments. This moderate increase in the vertical distance must be taken into account when the cord length from the floats 11 down to the outlet line 6 is determined.

It is further preferred that the diameter of the outlet line is essentially constant from the suction head 2 to the outlet mouth 9, above all it must not contain cross-sectional reductions, sharp bends or unevenness where sediments can get stuck. According to a particularly preferred embodiment, the diameter of the flexible part of the outlet line near the suction head is somewhat smaller than the diameter of a preferably rigid part of the outlet line near the outlet mouth. In the following, a calculation example is given to illustrate the aspect of the vacuum line in relation to the pressure line.

Calculation example:

At 10% volume concentration and a net specific weight of sediments (beyond the specific weight of water) of 1700 kg/m3, the slurry will have a specific weight of 1170 kg/m3. The height up to the vacuum line at an atmospheric pressure of 1.0 atmospheres -10 mvs - then becomes 10 mvs<*>(1000 kg/m3/ 1170kg/m3) = 8.55 metres.

Under the same conditions but at an altitude of just over 2000 m above sea level, the air pressure will be 0.8 atmospheres, i.e. the height up to the vacuum line will then be

0.8<*>10 mvs<*>(<*>(1000 kg/m3/ 1170kg/m3) = 6. 84 meters.

In summary, the present invention provides unique advantages in that:

• The suction head rests on the bottom with its own weight. It will therefore always be in contact with the sediments, regardless of how quickly these are sucked away, so that a constant high capacity is achieved. • The suction head controls the sediment concentration so that singular loss PLUS friction loss PLUS resistance due to the slurry's own weight always corresponds to the available height difference between water table and outlet.

• The outlet line is always below the "vacuum line" so that the water flow is not interrupted.

• Particles (stones etc) can be sucked up to the diameter of the outlet line

• The technology can be used at unlimited depths

Claims (17)

1. Device for use when dredging in a water reservoir, comprising a suction head (2) with at least one lower opening () adapted to suck in sediments and water, which suction head is connected to an at least partially flexible outlet line (6) as the suction power is provided exclusively by the pressure difference between the water surface (10) in the reservoir and the outlet (9), characterized by the suction head is suspended in a flexible suspension (3) which is designed to release the suction head down to the relevant working level and there rest on the sediments without knowing the level in advance, the suction head is provided with at least one upper opening (24) at a vertical distance from the lower opening (23) to ensure that the suction head cannot be blocked by a landslide of sediments towards the lower opening (23), with the suction head (2) and the at least partially flexible outlet line (6) preferably being like this balanced that the suction head will maintain an effective working position with or without the support of the flexible suspension (3). 2. Device in accordance with patent claim 1, characterized in that the suction head (2) is mainly symmetrical about a longitudinal axis and that its effective working position is when the longitudinal axis is mainly vertical. 3. Device in accordance with patent claim 1, characterized in that the suction head (2) has a low center of gravity with an upper part which has an effective density less than that of the water and a lower part which has an effective density greater than that of the water. 4. Device in accordance with patent claim 3, characterized in that the lower part of the suction head (2) is equipped with a ballast body (25) and possibly the upper part of the suction head is equipped with a buoyancy body (26). 5. Device in accordance with patent claim 1, characterized in that the outlet line (2) is provided with a number of cords attached to floats (11) which partly have the purpose of ensuring correct vertical positioning of the outlet line (6) and partly to ensure that the outlet line does not affect the suction head (2) unwanted large forces. 6. Device in accordance with patent claim 1, characterized in that the outlet line (6) is arranged so that the difference between the external and internal pressure is at all times lower than the pressure difference that the outlet line can maximally tolerate without collapsing 7. Device in accordance with patent claim 1, characterized in that the outlet line (6) is arranged so that it is at any time and in any place lower than the sum of a) its pressure line and b) the local atmospheric pressure measured as the height of the column of water and sediments in the discharge line. 8. Device in accordance with patent claim 1, characterized in that the flexible suspension (3) is selected from among a wire, a chain and a rope. 9. Device in accordance with patent claim 1, characterized in that the outlet pipe is led through the dam wall or over the dam wall so that a siphon is formed. 10. Device in accordance with patent claim 1, characterized in that the flexible suspension (3) is attached to a vessel (4) floating in the water reservoir (1). 11. Device in accordance with patent claim 1, characterized in that the suction head is equipped with nozzles for flushing in front of the suction head to disintegrate sediments. 12. Device in accordance with patent claim 1, characterized in that the suction head (2) is equipped with nozzles for lateral flushing to destabilize sediments to the side of the suction head and provoke a crash towards the suction nozzle. 13. Device in accordance with patent claims 1 and 12, characterized in that the suction head (2) is equipped with a suction nozzle and the flushing device is made of soft material. 14. Device in accordance with patent claim 6, characterized in that the suction head (2) in addition to at least one lower opening (23) for sucking in sediments and water, has at least one upper opening (24) designed to suck in only water in order to reduce rapid pressure variations in the outlet line as a result of varying amounts of sediments through the suction head. 15. Device in accordance with patent claim 1, characterized in that the at least one upper opening (24) is at least partially covered by a self-opening damper (28) which due to increasing negative pressure in the suction head (2) temporarily allows more water to be sucked in per unit of time. 16. Device in accordance with patent claim 1 or 15, characterized in that the at least one upper opening (24) is at least partially covered by a damper (28') which can be adjusted manually according to the conditions with which the suction head is operated. 17. Device in accordance with patent claim 1, characterized in that the cross-section of the flexible part (7) of the outlet line (6) is smaller than the cross-section of the rigid part (8) of the outlet line (6).