SEABED FROM POLLUTION

Technical Field

The invention relates to cleaning of seabeds from pollution, such as cleaning of an inner harbor seabed from pollution. The method, suction head and

arrangement of the invention allow effective cleaning of polluted seabeds without spreading the pollution to non-polluted seabed and water.

Background Art

Pollution of the seabed and water is an increasing problem. Traditional industry has been the main source of the pollution, and still is a major source. Currently, plastics, including microplastics, is an increasing problem. Wear of rubber tires from vehicles and synthetic clothing are major sources of microplastics, detergents and tooth paste are other sources. 90% of the plastic pollution ending in the sea is assumed to sink down on the seabed. Aquaculture, such as salmon farming, results in severe pollution of the seabed under and nearby the cages. Inner harbor seabeds and seabed under marinas are often severely polluted.

A typical problem with the methods and equipment used for cleaning of seabed, is that the pollution is whirled up into the water and spread over large areas, settling on seabed and polluting seawater in large areas. Inner harbor cleaning has resulted in spreading seabed pollution into larger fjord or sea areas. Hg (mercury) and PAH (polycyclic aromatic hydrocarbons) pollution are amongst the most typical of several specific pollution problems. Others are PCB

(polychlorinated biphenyl), TBT (tributyltin), Pb (lead) and Cu (copper). The traditional technique of seabed cleaning is to grab up a piece of the seabed with a grab. However, the result is that only a fraction of the polluted material is captured. The rest, typically a majority of the most dangerous pollution, such as Hg and PAH, is spread around. Often, a large majority of the material grabbed up is non-polluted material, whilst a majority of the most dangerous pollution is spread around.

Another typical method is to cover polluted seabed with non-polluted material. However, the pollution can be spread, particularly when covering the polluted seabed, and diffuse out through the cover over time.

Apparently, no technology is available for simple, reliable cleaning of seabed without causing leakage and spreading of the pollution into surrounding water and seabed. Comprehensive searching has not revealed technology

comparable to the present invention.

The objective of the present invention is to provide a method, a suction head and an arrangement solving or mitigating the spreading of pollution problem described above.

Summary of invention

The invention provides a method for cleaning a seabed from pollution. The method is distinguished by comprising the steps:

a) to place a lower open end of a suction head over a seabed area to be cleaned, thereby confining a suction head volume, preferably whilst operating a suction pump connected to the suction head volume to provide an

underpressure in the suction head volume compared to ambient seawater pressure, thereby avoiding any spreading of whirled up pollution outside the suction head volume,

b) to inject a higher pressure water flow into the suction head volume, by operating an injection pump connected to the suction head volume, while operating the suction pump at higher flow rate than the injection pump, whereby underpressure is maintained in the suction head volume whilst coarser material is flushed and may lift up from the seabed, tumbling against itself, loosening finer polluted material from coarser material while being inside the suction head volume, c) to operate the suction pump, preferably while reducing or stopping the operation of the injection pump, to pump the finer polluted material, including any microplastics, to a cleaning plant or a receiving facility.

The term seabed means in this context the bed of the ocean, the bed of a fjord, the bed of a lake or the bed of a river.

In the method step a), the suction pump flow rate is low, but sufficient to provide a reduced pressure, that is an underpressure or negative pressure, in the suction head volume compared to the surrounding water. The suction flow is preferably applied before the suction head is located on a seabed area to be cleaned, since any swirled up finer polluted material while positioning the suction head on the seabed will be sucked into the suction head volume rather than being spread around. While positioning the suction head on the seabed, injection pumps are preferably at zero flow rate, preferably turned off.

In the method step b), the suction pump or pumps flow rate is higher than the injection pump or injection pumps total flow rate.

In the method step c), the suction pump flow rate is preferably lowered, preferably while the injection pump or pumps total flow rate is reduced, preferably reduced to zero.

Preferably, in step b), the finer polluted material is separated from coarser non- polluted material inside the suction head volume, after which water with the finer polluted material entrained is pumped to a cleaning plant or a receiving facility.

Coarser material means larger and/or heavier material compared to finer material. The pollution is typically found only or in substance in the finer material, typically sedimented or adhering to coarser material.

Preferably, the pollution is cleaned out in a cleaning plant, by sedimentation and filtering, preferably including sand filtering, such as calcareous sand filters, cleaning out solved pollution such as Hg, PAH, and filters for microplastics, and filterbelt pressing. Preferably, floatation and/or UV sterilization is included as cleaning steps.

Underpressure, preferably throughout method steps a) to c), is essential in the suction head volume to eliminate leakage and spreading of pollution. To this end, preferably said underpressure compared to ambient pressure outside the suction head volume, is within the range of 0,1 to 1 bar, more preferably 0, 2 to 0,9 bar, controlled by measuring at least a differential pressure between inside and outside the suction head volume.

Preferably the operation is documented and stored digitally, preferably documenting effective cleaning and documenting that no leakage or spreading of polluted material from the seabed or suction head volume takes place.

Preferably, in method step b), the higher pressure flow of water is injected, by operating at least one connected injection pump, at an injection water overpressure from 10-16 bar, more preferably 12-15 bar relative to ambient seawater pressure, while the underpressure is maintained by pumping out water from the suction head, by the suction pump, at a higher flow rate than the total flow rate of injected higher pressure water flow rate, preferably at least twice the flow rate, more preferably 5-15 times, most preferably about 10 times the flowrate of the higher pressure water flow rate. In method step b), the polluted seabed literally can be a fluidized seabed.

Preferably, the operation is controlled by measuring at least a differential pressure between inside and outside the suction head volume, and/or preferably operating a camera arranged to monitor the lifting of finer polluted material and lifting and tumbling of coarser material within the suction head volume; and preferably a camera arranged to monitor the suction head from the outside. Preferably, the operation is documented and stored digitally, preferably documenting the cleaning, the operation parameters and mapping the area cleaned, preferably documenting that no leakage or spreading of polluted material from the seabed or suction head volume took place. With the suction head placed on seabed to be cleaned, confining a suction head volume, underpressure is ensured if the flow rate Q of the suction pump is larger than the flow rate of all injected and leaked in streams into the suction head volume. The flow rate of the suction pump can be but is not necessarily measured, since the flow rate is directly proportional to the speed in rotations per minute, rpm, which speed can be adjusted according to measured relative reduced pressure in the suction head volume.

In a preferable embodiment the method includes gas lift, for increased suction effect, particularly at depths below 10 m and/or for sucking up large quantities of soft seabed, such as sedimented sewage. With gas lift, it is meant to inject gas, preferably air, in the outlet line from the suction pump to the surface, near the suction pump outlet.

The invention also provides a suction head for operation of the method of the invention, wherein the suction head comprises:

a suction head housing with a downward open lower end to be positioned on the seabed during operation, an outlet, a suction pump operatively arranged to the outlet, wherein the housing as positioned on the seabed to be cleaned confines a suction head volume.

The suction head is distinguished in that it further comprises:

a higher-pressure water injection inlet,

an injection pump operatively arranged to the higher-pressure water injection inlet, and at least one of:

a sensor for measuring a differential pressure between inside and outside the suction head volume, and

a camera arranged to monitor inside the suction head volume; and preferably a camera arranged to monitor outside the suction head volume, and

preferably digital storage media.

The injection pump and higher-pressure water injection inlet preferably direct the injection water to at least one, preferably several, nozzles directed downwards to the seabed, for flushing and/or whirling up seabed and loosening finer polluted material from coarser material.

Preferably, the suction head comprises one or more of the features as follows, in any operative combination:

an outer elastic skirt around and extending downward from the lower end,

openings in at least one of an outer elastic skirt around and extending downward from the lower end and the suction head housing, preferably as one way valve openings opening for inflow of water at under pressure in the suction head volume but closing for outflow of water from the suction head volume, preferably the openings are arranged as overlapping flexible flaps over openings through or seams between elastic lower skirt segments or parts,

a pressure sensor arranged to measure the pressure in the suction head volume,

a positioning device,

a set of thrusters, for moving and positioning the suction head on the seabed,

a larger cross section area in a lower end to be placed on the seabed to be cleaned than the cross-section area in an upper outlet end with a suction pump operatively arranged in an outlet pipe for suction from the suction head volume, facilitating tumbling of material and thereby loosening finer polluted material from coarser material,

several higher-pressure water injection pumps,

several higher-pressure water injection nozzles in the suction head volume, arranged symmetrical about a suction head volume central axis, operatively arranged to one or more higher pressure water injection pumps, preferably the nozzles are arranged inside the periphery of the lower end of the suction cup, directed downwards, slightly inwards and inclined,

a quadratic or rectangular shape of the lower end, of 1 x 1 , or 2 x 2 m, for example, or a round lower end shape,

a suction pump with large cross section flow bore, at least 100 mm, preferably about 150 mm or larger diameter flow bore, preferably an

aquaculture“fish pump”,

a shape of the housing, from the lower end, as a cylindrical square or rectangle or a circle, followed by a pyramid or conical shape narrowing to a central outlet pipe, facilitating tumbling of material and thereby loosening finer polluted material from coarser material,

a rotatable wheel with a rotatable coupling for higher pressure water, with nozzles for injection of higher pressure water, preferably at 10-16 or 12-15 bar overpressure compared to ambient seawater pressure, preferably rotation by inherent water jetting, preferably the nozzles are arranged inside the periphery of the lower end of the suction cup, directed downwards, slightly inwards and inclined,

a little crane or manipulator arm on the suction head, and preferably a basket, for moving and placing larger objects for example in the basket,

a frame, deployable by wirelines, combined with thrusters for moving the suction head within the area encompassed by the frame, the frame can be moved around on the seabed by a crane or manipulator on a ship or barge or another mobile unit,

a set of screens/displays, for footprint, no-leakage and cleaned area documentation, and footage and parameter storage facilities, for documenting the operation.

In a preferable embodiment the suction head includes equipment for gas lift, for increased suction effect, particularly at depths below 10 m and/or for sucking up large quantities of soft seabed, such as sedimented sewage. The equipment for gas lift includes a compressor or another source for supply of gas, preferably air, at controllable pressure, and an injection line for injecting the gas

downstream of the suction pump, near the suction pump in a line from the suction pump to the surface.

The invention also provides an arrangement for cleaning of polluted seabed, distinguished in that the arrangement comprises

a suction head according to the invention, and

a cleaning plant, comprising a sedimentation tank and a filter, and preferably also a filterband press and preferably a sand filter, a floatation unit and/or a UV sterilization unit,

wherein the suction head is operatively arranged to pump polluted seabed material to the plant for cleaning.

Preferably, the plant is arranged on one of, a truck, on a quay, on a barge, on a mobile floating platform or on a ship, preferably comprising an excavator turret and handling arm for positioning the suction head on seabed to be cleaned.

The invention also provides use of the method of the invention, the suction head of the invention and/or the arrangement of the invention, for cleaning of polluted seabed without whirling up the pollution of the seabed outside a suction head volume, thereby avoiding spreading the finely dispersed pollution into seawater and seabed outside the suction head volume.

Brief description of drawings

Figure 1 illustrates an embodiment of a suction head according to the invention, in longitudinal section,

Figure 2 illustrates a further embodiment of a suction head according to the invention in longitudinal section and a detail as seen from below.

Detailed description of the invention

Reference is made to Figure 1 , illustrating an embodiment of the invention of a suction head 1 in longitudinal section, as positioned on a seabed 2 area to be cleaned. The suction head 1 comprises a suction head housing 3 with a downward open lower end to be positioned on the seabed 2 during operation, an outlet 4, a suction pump P operatively arranged to the outlet, wherein the housing as positioned on the seabed to be cleaned confines a suction head volume 6. The suction head 1 further comprises a higher-pressure water injection inlet 7, an injection pump I operatively arranged to the higher-pressure water injection inlet, sensors p for measuring a differential pressure between inside and outside the suction head volume, a camera 8 arranged to monitor inside the suction head volume, cameras 9 arranged to monitor outside the suction head volume, and a digital storage media S. In the illustrated

embodiment, two cameras 9 monitoring outside the suction head volume, and one camera 8 monitoring inside the suction head volume, are coupled (not illustrated, for clarity, but via cable, fibre or wireless communication) to storage medium S, for documenting the operation. In addition, differential pressure as measured by sensors p, and flow rate, speed, power and/or torque of the suction pump P and the injection pump I, are coupled (not illustrated, for clarity) to storage medium S, for documenting the operation. The higher-pressure water injection inlet 7 and the injection pump I are coupled by piping to a rotating coupling 5 which has nozzles 10 for injection of higher-pressure water, with the nozzles symmetrically arranged about the coupling 5. Said nozzles are directed downward, in an inclined and inwards direction, resulting in momentum to rotate the nozzles about the coupling. The arrangement of nozzles may vary and preferably is easy to modify. For example, with much stone to be tumbled up, a more robust arrangement of the nozzles, such as non-rotating nozzles embedded and protected in the suction head housing inner wall, and/or nozzles on a nozzle frame or on nozzle arms, can be preferable. The downward end of the suction head 1 can be a relative flexible skirt, or not. In the illustrated embodiment, the downward skirt 1 1 comprises one-way openings 12, with inner flexible flaps 13 opening for flow of water inwards but not outwards. This ensures a minimum flow rate through suction pump P. An outlet pipe 14 leads the water and finer polluted material pumped by suction pump P to a cleaning plant 15. For underpressure in the suction head volume, the flow rate Q of pump P is larger than, or no larger than in substance equal to, the combined flow rates of injected higher-pressure water q and any leaked in water q2, which means that Q is larger than, or no larger than in substance equal to, the sum of all q, q2,.. added together.

The pump P is preferably a so called“fish pump”, meaning a pump used in aquaculture and fishing industry to pump live fish. This is because larger objects can be pumped without damaging the pump, and opposite, because the pump bore is large. Examples are Karm Fishpumps from Karmoy Winch as of

Norway, and CanaVac fish pumps from Canada.

Figure 2 illustrates a further embodiment of a suction head according to the invention in longitudinal section and the lower end as seen from below. Most features are identical or like the embodiment illustrated in Fig. 1 , but some are different. The suction head housing has a downward open lower end to be positioned on the seabed during operation, with smaller cross section area than at higher elevation. The inlet cross dimension B2 sis mailer than a washing volume dimension B1. This means that the suction head housing expands in horizontal dimension upwards from the lower end, before being cylindrical and/or before being reduced to the pump intake area at the top. This is a preferable feature. In the illustrated embodiment, the lower end is square, with side dimension B2. At higher elevation, over an elevation range corresponding to a washing part, the corresponding side dimension B1 is larger than B2. This improves the washing effect by improved tumbling without lifting coarse material too high, for many seabed structures.

At too low pressure in the suction head volume, one-way valves 15 through the housing at higher elevation than the washing volume dimension B1 open, ensuring that coarse material is not lifted too high, which is controllable by operating the suction pump P and optionally the injection pump or pumps.

In addition, the suction head comprises an outer elastic skirt 16 around and extending downward from the lower end typically about 30 cm and arranged as overlapping flexible rubber cone section flaps 17 with opening between the flaps at the lower end.

A manipulator arm 18 is illustrated, for grabbing larger objects for putting said object in a container for scrap deployed on the seabed or in a basket attached to the suction head (not illustrated).

The illustrated suction head volume is rectangular or square, at least in the lower end, as seen from below. Parallel ribs with higher pressure water injection nozzles 10 are arranged in the suction head volume. The nozzles 10 are rotating nozzles or fixed nozzles. The nozzles 10 nearest to the skirt 16, on the housing lower end but above the flexible skirt, are directed inclined inwards, to avoid leakage of finer polluted material out from the suction head volume. The nozzles are preferably arranged on a nozzle frame 19. The pumped-up water with finer pollution entrained, is pumped to a sorting drum, as the first part of a cleaning plant.

Compared to the traditional grabbing up of seabed by which also non-polluted material is taken up whilst much of the most dangerous pollution is spread around, the suction head, method and arrangement of the invention, typically about 1/9 of the quantity of material from a polluted seabed is taken up, containing in substance only the polluted material in concentrated form, without spreading the pollution. Compared to NO 20000222 A, typically about 1/5 of the quantity of material from a polluted seabed is taken up, containing in substance only the polluted material in concentrated form, without spreading the pollution at all or reduced spreading of the pollution. The suction pump is preferably arranged in the suction head or in the outlet end towards the suction head, providing better control of underpressure in the suction head volume.

The invention provides a method for cleaning a seabed from pollution, with a suction head comprising: a suction head housing with a downward open lower end to be positioned on the seabed during operation; an outlet; a suction pump operatively arranged to the outlet; a higher-pressure water injection inlet; an injection pump operatively arranged to the higher-pressure water injection inlet, and at least one of:

a sensor for measuring a differential pressure between inside and outside the suction head volume, and

a camera arranged to monitor inside the suction head volume, wherein the housing as positioned on the seabed to be cleaned confines a suction head volume,

wherein the method comprises the steps:

a) to place the lower open end of the suction head over a seabed area to be cleaned, thereby confining the suction head volume,

b) to inject a higher pressure water flow into the suction head volume, by operating the injection pump connected to the suction head volume, while operating the suction pump at higher flow rate than the injection pump, for maintaining underpressure in the suction head volume whilst any coarser material is flushed and lifted up from the seabed, tumbling against itself, loosening finer polluted material from coarser material while being inside the suction head volume,

c h a r a c t e r i s e d i n that the method further comprises the step:

c) to operate the suction pump, while reducing flow rate or stopping the operation of the injection pump, to pump the finer polluted material, including any microplastics, as entrained with water, to a cleaning plant or a receiving facility, whilst the coarser material cleaned for finer pollution sinks down to the seabed, controlled by at least one of said sensor and said camera.

The invention provides a suction head (1 ) for operation of the method according to the invention, wherein the housing as positioned on the seabed to be cleaned confines a suction head volume (6), wherein the suction head comprises:

a suction head housing (3) with a downward open lower end to be positioned on the seabed (2) during operation, an outlet (4), a suction pump (P) operatively arranged to the outlet, delivering a higher flow rate than the total flow rate of injected higher pressure water flow rate, a higher-pressure water injection inlet (7), an injection pump (I) operatively arranged to the higher- pressure water injection inlet,

c h a r a c t e r i s e d i n that the injection pump (I) operatively arranged to the higher-pressure water injection inlet, deliver an injection water overpressure from 10-16 bar relative to ambient seawater pressure, wherein the suction head further comprises at least one of:

a sensor (p) for measuring a differential pressure between inside and outside the suction head volume, and

a camera (8) arranged to monitor inside the suction head volume, for pumping the finer polluted material, including any microplastics, as entrained with water, to a cleaning plant or a receiving facility, whilst the coarser material cleaned for finer pollution sinks down to the seabed.

The suction head includes one-way valves around or at the lower end, for inflow of water, through which one way valves all inflow of water into the suction head volume at normal operation takes place. Thereby, water inflow at the seabed into the suction head volume skirt lower end is improved, reducing or eliminating the spreading of pollution. One-way valves further up in the suction head, above the seabed level, open up at further underpressure than at normal operation, for example on clay seabed, to ensure sufficient water inflow to eliminate cavitation and instability of the operation. Compared to covering the polluted seabed, by which the pollution spread or diffuse out through the cover over time, the suction head, method and arrangement of the invention avoids spreading the pollution into the surrounding sea and seabed. The suction head confines the pollution and due to relative reduced pressure inside the suction head volume compared to outside the suction head volume, the pollution will not leak out from the suction head but be separated from coarse typically non-polluted material and pumped up as entrained with water, to the plant for cleaning or a receiving facility, such as a preliminary deposit used before further treatment.