NO20220592A1 - Method and device for removing stones from a pond - Google Patents

Description

Method and device for removing stones from a pond

The present invention relates to a method for removing sediments comprising stones as well as fine-grained material deposited by intakes or hatches in an intake dam as stated in the preamble to patent claim 1. According to another aspect, the invention relates to a device for the same purpose as stated in the preamble to patent claim 10.

Background

Water intake in streams and rivers is often established by building a dam that stops the water and raises the water level so that an intake dam is formed. The water is typically led from the intake pond, through an intake grate and into a waterway (tunnel, pipe or channel)

Streams and rivers will often bring with them sand, gravel and stones of variable size (sediments). This happens especially when there is a large flow of water, and the water has enough speed and power to move the sediments. When an intake dam has been established, the speed of the water will be reduced and the sediments will fall to the bottom, and/or the water will be directed at high speed towards the intake.

The result in both cases will be that sediments are directed towards the intake and if there is an intake grate, the sediments will lie against this and block the water intake. The water will then choose the easiest path and flow over the spillway to the dam and flow further down along the watercourse.

Sediments that come with the stream or river (watercourse) can be anything from fine sand and gravel to stones and blocks. Especially in steep streams, it will be possible for stones and blocks to arrive that can be up to a meter or more.

If the intake is a power plant, there will be large losses if the water is not taken in and used for power production. The value of lost production can add up to very large amounts within a short time.

In those cases where there is no separate intake grate, sediments can be transported further with the water and be deposited elsewhere in the waterway where they cause problems or possibly also in the turbine right up to the turbine and cause damage to it.

Intakes in streams and steep rivers are often established without a road connection and in many cases also without a power supply or network. It is therefore difficult or impossible to monitor such intakes, and blockage due to sediments will not be detected until a long time has passed.

If a blockage due to sediments has been discovered, it will still and often takes a long time and requires a lot of planning to remove sediments from intake ponds, transport of equipment and personnel requires a lot of resources and in many cases serviceable weather and/or road conditions to transport personnel and or equipment for the intake pond.

Known technology

Intake ponds are typically cleaned up by digging out sediments with an excavator. Where the intake is roadless, the excavator typically has to be flown in by helicopter, or driven in by all-terrain vehicle.

The second method used is that the bottom hatch is opened, the water is drained down and sediments are flushed out by the water flowing over the sediments and eroding and tearing the sediments away.

In both cases, and if the intake is roadless, planning and sufficiently good weather are required to reach the intake on foot through the terrain or by helicopter.

It is also known that siphon structures can be used to direct water out of reservoirs with the intention of diverting floods.

Purpose

The purpose of the invention is to remove sediments that are deposited in smaller intake ponds. This can be anywhere in the intake pond where you want to remove sediments, but it will typically be in front of intakes to power stations, waterworks, aquaculture facilities and irrigation. It is also a purpose that the sediments are removed only when excess water is available which would otherwise pass over the overflow to the dam and further down the watercourse, and that the invention therefore starts and stops automatically in accordance with this. It is also a purpose that the device starts and the sediments are removed when there is sediment transport in the river. It is also a purpose that the invention has no moving parts and is very operationally reliable, that it is resistant to ice passages and heavy loads during floods. It is also a purpose that it removes all sediments that come with the waterway and that are directed towards and possibly deposited in front of the intake, including also the largest particles (stones) so that the inlet to the invention does not clog up. Such stones can in extreme cases be up to one meter in size or even larger. The invention will therefore also be referred to as a "rock vacuum". Furthermore, it is a purpose that the invention can be produced and in parts with a certain upper weight so that they can be transported in parts, for example by helicopter, and that the parts can then be assembled together at the construction site with hand-held and portable equipment.

Present invention

The purposes stated above are achieved through a method according to the invention as defined in patent claim 1. According to another aspect, the invention relates to a device as stated in patent claim 10. Preferred embodiments appear from independent patent claims.

The invention essentially consists of a pipe structure whose shape is adapted so that the upstream end is placed in front of the intake opening or the intake grate or another place in an intake pond from which sediments, including stones, are to be removed. The pipe will pass over an overflow threshold of the dam or at a similar height.

Although an intake dam will normally be small in extent, it can also be larger. The invention can therefore also be used in a pond or a reservoir of any size. There will normally also be an overflow threshold that diverts excess water, but this is also not a condition.

The outlet of the pipe structure which forms the main element of the device according to the invention is located below the pond and at a lower level than the water level in the intake pond so that the height difference between the water level in the intake pond and the outlet ensures that the water flows through the invention. The flow rate is affected by the vertical location of the outlet. The intended minimum flow rate is ensured by placing the outlet at a level that is sufficiently low for this flow rate through the pipe construction to be achieved. Among other things, this is what is meant by the formulation "dimensioned so that the velocity equals or exceeds the velocity given by Durand's formula for flow velocity". This is sufficient to suck in stones the same size as the pipe, and keep these stones moving up through the pipe and down the downstream side, so that all stones that are sucked in are removed, regardless of size.

The invention will normally be given a rounded shape at the inlet so that singular losses in the inlet are reduced as much as possible. Furthermore, the outlet can be designed with a gradually widened cross-section so that the energy of movement is recovered and the required drop height is reduced.

The outlet of the rock suction will be downstream of a water lock. This is designed so that the outlet is turned sufficiently upwards so that the water trap is completely filled with water at all times when water flows through the rock vacuum.

The inner diameter of the pipe construction will typically be greater than 20 cm, preferably in the range 30-120 cm, more preferably 40-100 cm and most preferably 50-80 cm.

On the upstream side of the rock sucker, and at the level of the overflow threshold, there will be an air hole. This hole is sealed by water when the water level rises above the overflow threshold, so that air flowing out of the rock suction is replaced by water and the flow of water increases.

An essential element is that water flow only starts when the water level in the intake dam reaches such a high level that the water flow over the dam (overflow loss) is as great as the water flow through the rock suction. In this way, you achieve that you do not use water that would otherwise have passed the intake and been used in, for example, power production, to remove sediments. This is achieved by placing the internal lowest point in the rock suction above the overflow at the same level as the mentioned water level. In the same way, the air hole will ensure that the water flow through the rock suction is broken when the water level in the intake pond drops below the mentioned level again.

You then achieve that you remove sediments only with the use of surplus water which would have passed the overflow over the dam anyway, and thus that the removal of sediments has no costs in the form of lost water. (Or other energy supply for that matter)

A small projection or "jump" can be arranged inside the rock vacuum cleaner so that air is mixed in the water, and that this air flows out through the water trap together with the water and contributes to the rock vacuum eventually being completely filled with water and the water flowing through with full capacity.

The invention could be made of several different materials, such as steel or concrete (then as part of the dam), but it would preferably be made of polymer materials that are entirely or largely recyclable, such as polyethylene, or combinations of various polymer materials, with or without fiber reinforcement. Such materials can be made light, durable, robust against external stress, rust-free and easy to transport and easy to assemble together.

It will often be appropriate to produce the device in parts that are easy to transport with an all-terrain vehicle or helicopter. Typically, the device will be produced from polyethylene, which has particularly good properties regarding wear, durability and strength. Polyethylene pipes can be welded together with welding sleeves that can be supplied with power from hand-held equipment.

Although the invention can preferably be started automatically at a certain water level in the pond, for example at an overflow, it can also be started by an operator. This can be done by installing an additional pipe from inside the intake pond that opens into the rock vacuum, so that it pulls air through the water trap and starts the rock vacuum. Such a pipe will typically be opened with a valve if the rock vacuum is to be started by an operator.

If desired, an additional pipe can also be installed with an open inlet that is placed at such a height that it takes in water automatically when the water reaches a certain water level and starts the rock vacuum before the water level has reached the overflow threshold.

The stone cleaner can also be started if you close a tight lid over the outlet and then suck air out of the stone cleaner with a vacuum pump.

It will often be appropriate to design a pit in front of the intake so that sediment can be sucked into the rock vacuum from the bottom of the pit. Since stones slide into the pit along sloping side edges, the pit will ensure that sediments are removed from a larger area in front of the intake.

The stone cleaner can be made with desired angles so that it fits next to existing constructions or into new designs.

More about the invention

Figure 1 shows a typical design of the rock suction placed above an overflow threshold in an intake dam.

Reference is now made to figure 1. This shows the device (also referred to as the rock vacuum) in the form of a pipe structure 1 mounted above an overflow threshold 2b in a dam wall 2. The inlet 3 of the rock vacuum is located in front of the intake 4, which is shown equipped with an intake grate 5. Sediments 6 is deposited in front of the inlet 3 of the rock suction device 1 Sediments are collected in a pit 20 which is designed in such a way that sediments do not settle near the intake. The pit has a sloping bottom with an angle v which can vary, but which is greater than 5 degrees and preferably significantly greater, such as at least 20 degrees and preferably at least 35 degrees.

An opening 7 on the upstream side of the device's highest point, above the overflow threshold of the dam wall, is positioned in such a way that it is covered by water when the water level is so high that the rock vacuum is to start, but which lets in air and breaks the water flow through the rock vacuum when the water level is so low that you want the stone cleaner to stop.

Furthermore, the figure shows that the outlet 8 of the rock vacuum is arranged downstream of a water trap 9. This is designed in that the pipe end which forms the outlet is curved sufficiently upwards so that the water trap, which is filled with water 10 when water flows through the rock vacuum, retains a sealing " pocket" of water even when the water flow ceases. A lid 17 helps ensure that the water does not evaporate, but remains in the water trap over time. Furthermore, the lid 17 provides the opportunity to evacuate air from the upper part of the rock vacuum, i.e. the part that is carried over the overflow threshold 2b, with the help of a vacuum pump 18 and thereby start the rock vacuum regardless of the water level in the pond.

A small projection 11 inside the stone suction will help to mix air into the water, through a sudden change of direction of stones that hit the projection.

The inlet 3 has evenly rounded walls which ensure that water can flow along an evenly curved surface 12 so that there is the least possible singular loss.

At the outlet 8, the rock sucker can be designed with a gradually increasing cross-section which transforms the movement energy in the water into static energy so that the energy loss in the outlet is reduced and the difference in height between the upstream water level and the outlet is utilized as best as possible to give the water speed.

A secondary pipe 14 can be connected between the intake pond and the rock vacuum's downstream side, that is, the side below the overflow threshold in the dam wall 2. The secondary pipe 14 can be opened with a valve 15 so that the rock vacuum can be started by an operator when the inlet opening 16 of the secondary pipe 14 is below the water level in the pond.

If the valve is open at all times, the pipe 14 can serve to automatically start the rock suction when the water level in the pond rises to a level above the inlet opening 16 even if the water is at a lower level than the overflow threshold. For this purpose, in that case, the inlet to the secondary pipe is placed at the height at which the water level is intended to activate the pipe construction (1).

The figure also schematically shows a welding socket 19 which joins two pipe parts together. The primary pipe of the stone suction can of course also be composed of more than two pipe sections.

It is essential for the function of the rock vacuum that the speed in the pipe is sufficient to keep the sediments in suspension so that the pipe does not clog. A recognized way of calculating this speed is to apply Durand's formula for speed in pipes. The pipe construction must therefore be dimensioned so that the velocity equals or exceeds the velocity given by Durand's formula for flow velocity:

where k = a constant 0.8; g = acceleration of gravity 9.81 m/s<2>; D = inside diameter; and SS = relative specific gravity of sediments,

As a calculation example, the following values are used:

k = 0.8

g = 9.81 m/s<2>

D = 1.0 m

Ss = 2.7

Dimensioning speed is then 4.62 m/s.

As can be seen from Durand's formula, the speed is affected by the diameter as well as by the density of the sediments (rocks). With a typical relative density as indicated in the example and with a diameter in the range of approximately 0.5 metres, a flow velocity of 3.5 m/s will be sufficient, while with diameters in excess of 1 metre, the desired minimum flow velocity may be 5 m/s pp.

Claims (14)

Patent claims 1. Procedure for removing sediments comprising fine-grained material as well as stones with a diameter of at least 10 cm deposited at intakes or hatches in an intake pond through a pipe structure (1), characterized by: − said pipe construction (1) is established with an inlet opening (3) in front of said intake or hatch (20) and an outlet opening (8) outside the dam wall at a height lower than the water level in the intake dam, − said pipe construction (1) inside is carried out with a mainly circular cross-section of diameter larger than the largest stones to be removed, − said pipe structure (1) in the area downstream of the high intermediate area is given the form of a water trap (9) − the pipe construction is dimensioned so that the velocity equals or exceeds the velocity given by Durand's formula for flow velocity: � where k = a constant 0.8; g = acceleration of gravity 9.81 m/s<2>; D = inside diameter; and SS = relative specific gravity of sediments, − the pipe structure (1) in a high intermediate area is led over an overflow threshold (2b) in the dam wall (8). − the pipe structure (1) is designed with at least one air hole (7) upstream of the overflow threshold (2b). 2. Method in accordance with patent claim 1, characterized in that the water level that starts and stops the flow of water through the pipe structure is at the same time the water level that causes an overflow over the dam that corresponds to the water flow through the pipe structure. 3. Method in accordance with patent claim 1 or 2, in that a depression (20) is established in the bottom at the place from which the sediments are to be removed, with an inclination of at least 5 degrees, preferably at least 20 degrees and more preferably at least 35 degrees. 4. Method in accordance with any one of the preceding patent claims, the pipe construction (1) being made with a circular cross-section with a diameter greater than 20 cm, preferably with a diameter in the range from 30 to 120 cm, more preferably 40- 100 cm and most preferably 50-80 cm. 5. Method in accordance with any one of the preceding patent claims, the pipe construction being carried out for a minimum flow velocity greater than 3.5 m/s, more preferably greater than 5.0 m/s. 6. Method in accordance with any one of the preceding patent claims, in that the pipe construction (1) at its highest point is equipped with a vacuum pump (18) designed to pump out air from the pipe construction. 7. Method in accordance with any one of the preceding patent claims, in that the pipe construction (1) is equipped with a secondary pipe (14) arranged as a start-up pipe, with an outlet opening inside the pipe construction (1) downstream of the high, intermediate area and an inlet opening (16) placed inside the pond at the height at which the water level is intended to activate the pipe structure (1). 8. Method in accordance with patent claim 7, in that the secondary pipe (14) is equipped with a valve (15). 9. Method according to any one of the preceding claims, the flow rate being affected through the vertical location of the outlet (8). 10. Device comprising a pipe construction (1) for removing sediments comprising fine-grained material as well as stones with a diameter of at least 10 cm deposited at intakes or hatches in an intake dam through said pipe construction (1), characterized in that: − the pipe construction (1) has an inlet opening (3) designed to be placed in front of said intake or hatch (20) and an outlet opening (8) outside the dam wall at a height lower than the water level in the intake dam, − the pipe structure (1) inside has a mainly circular cross-section with a diameter larger than the largest stones to be removed, − the pipe structure (1) in the area downstream of the high intermediate area has the form of a water trap (9) − the pipe construction (1) is dimensioned so that the flow rate equals or exceeds the rate given by Durand's formula for flow rate: � � where k = a constant 0.8 – 1.0; g = acceleration of gravity 9.81 m/s<2>; D = inside diameter; and SS = relative specific gravity of sediments, − the pipe structure (1) in a high intermediate area is arranged to be led over an overflow threshold (2b) on a dam wall (8) − the pipe structure (1) is designed with at least one air hole (7) upstream of the overflow threshold (2b). 11. Device in accordance with patent claim 10, characterized in that the device has a hole upstream of the upper part of the device. 12. Device in accordance with patent claim 10 or 11, characterized in that the device comprises a secondary pipe (14) with an inlet at a defined level in the intake pond and a connection to the pipe structure downstream of its upper part and that the secondary pipe has a valve ( 15), which can be opened and closed. 13. Device according to any one of patent claims 10-12, characterized in that the device is equipped with a vacuum pump (18) designed to evacuate air from the upper part of the device. 14. Device in accordance with any one of patent claims 10-13, characterized in that the pipe construction (1) is mainly made of polymer, fiber-reinforced polymer or composite material, including polyethylene.