SE537757C2 - Method and system for handling sediments - Google Patents

Abstract

12 ABSTRACT The present invention relates to a method for handling sediment from lake or seabeds, comprising the steps of removing an upper layer of sediment by suction,controlling the suction action such that mainly laminar suction flow is obtained ofsediment and water, separating heavier organic material from said removed layer ofsediment and water, and subsequently separating volatile organic material from thewater, and returning the water to the sea or lake. The present invention also relatesto a system for performing the method, comprising a suction structure (20) forremoving an upper layer of sediment, a control mechanism (22) for providing mainlylaminar flow through said suction structure (20), a first separating unit (38) capable ofseparating heavier organic material, and a second separating unit (40) capable of separating lighter material. (Pig. 1)

Description

METHOD AND SYSTEM FOR HANDLING OF SEDIMENT TECHNICAL AREAThe present invention relates to a method and a system for handling of sediment on lake or sea beds in an efficient yet environmentally friendly way.

BACKGROUND OF INVENTION For a number of years, lakes, sea creeks, and large areas around the costs of thesea, like for instance the Baltic sea, have been supplied with organic sediment,leading to a growth of organic material such that the state of these waters risk to be,or are, altered. Further the adding of organic material raises the sea or lake bed levelsuch that the water disappears or that passages or areas that previously could be passed by boat no longer are accessible.

Another problem with the supply of organic sediment is the addition of nutrients suchas phosphor and the like from the agriculture. The addition increases the growth of different water thriving plants like reed, sea weed, water lilies, just to mention a few.

A conventional approach for handling this problem is to dredge areas that havegrown due to addition of organic material. The dredging may be performed bymechanically digging away the upper layer of the sea or lake bed. With this method itis difficult to remove only the top layer, which is the layer containing the organicmatter, especially since this layer is very light and volatile and spreads easily whendisturbed. Thus, ifan excavator is used, then mostly the lower layers, containingheavier material, which could be contaminated by heavy metals, are removed whilethe upper, light layers that often are the main target for removal, will flow back with the water that leaves the excavator when lifted out of the lake or sea.

Another dredging method for removing material is to use suction pumps for removinglayers of the sea or lake beds. Pipes or hoses are then used to suck up the material.With this method, the lighter top material is removed by the suction action. However, also the lower layers tend to be sucked up because it is very difficult to regulate the suction force with this type of equipment such that only the lighter sediment layer of organic material is removed.

With both the above methods, there is a pronounced problem that also lower layersof the sea or lake beds are removed, because these lower layers may contain environmentally hazardous components, such as heavy metals, as mentioned. Thispotentially hazardous material must be handled in special ways in order to ascertain that the hazardous material cannot spread in other places in the environment.

This in turn means that the hazardous material has to be deposited in specialdedicated sites or that the hazardous material has to be treated in order to reduce the risks of contamination from the material.

BRIEF DESCRIPTION OF INVENTIONThe aim of the present invention is to remedy the drawbacks ofthe state of the art methods and systems for removal of sediment from lake beds and sea beds.

This aim is solved by the features of the independent patent claims. Preferable embodiments of the invention form the subject of the dependent patent claims.

According to a main aspect of the invention, it relates to a method for handlingsediment from lake or sea beds. ln its most basic form, the method comprises anumber of steps, comprising removing an upper layer of sediment by suction. Thesuction action is thereby controlled such that mainly laminar suction flow is obtainedof sediment and water. The laminar flow ensures that a major part ofthe uppermostlayer of sediment is removed, which layer is very light and volatile. Other\Nise,normally, if the flow is turbulent, then the volatile layer is stirred and spreadthroughout the water, while lower, heavier sediment material is removed, which is undesirable.

The removed sediment and water are then preferably treated such that any heavier organic material is separated from said removed layer of sediment and water. ln this manner, any heavier sediment material is firstly separated from the removedwater/sediment mixture. After this the lighter and volatile organic material isseparated from the water in a subsequent step. Finally the sediment free water is returned to the sea or lake. ln order to perform the method according to the invention, it also comprises a system.

The system may comprise a suction structure for removing the upper layer ofsediment. ln order to ascertain a mainly laminar flow through said suction structure,the system may comprise a suction control mechanism for providing mainly laminar flow through said suction structure.

The system further comprises a first separating mechanism capable of separatingheavier organic material. ln this manner, any material that is heavier and that maycontain toxic components and heavy metals is removed before the separation of theuppermost, lighter sediment. This lighter sediment material is then separated by asecond separating mechanism. This separated lighter sediment material may then be collected for subsequent use.

Preferably said suction structure may comprise at least one nozzle that is capable of removing the upper layer of sediment with a laminar flow. ln a favourable embodiment, the suction structure is operably arranged to a removalunit, which removal unit is arranged movable along said sea or lake bed. Theremoval unit is then capable of covering large areas where sediment material needs to be removed. ln one preferable embodiment, the removal unit may be arranged with propellingmeans capable of moving said removal unit over the sea or lake bed. The propellingmeans could be a number of designs that may move the removal unit. lt could eitherbe drive means attached directly on the removal unit, such as electric or hydraulicmotors that are drivably connected to propelling members such as wheels, endlessbands or propellers. The propelling means could also be wires or lines connected to the removal unit, where the wires lead to a winch system arranged on a vessel or on the shore, whereby the removal unit could be pulled by winching in the wires. Further,lines or wires could be directly connected to a vessel, which is capable of movingaround on the surface of the lake or sea, pulling the removal unit with it. Of courseother types and arrangements are feasible within the scope ofthe present invention for propelling the removal unit. ln connection with the propelling means mentioned above, the system may furthercomprise a control system capable of controlling the direction and position of saidremoval unit. ln this way, the removal unit could be manoeuvred such as to covercertain predetermined areas of the sea or lake bed. The control system could have anumber of features to control the position and direction, such as a GPS system,which could be connected to the removal unit directly or to a vessel if the latter ispulling the removal unit. Other types of control systems are feasible within the scopeof the invention. Also the control system could be operably connected to the propelling means to coordinate the removal of sediment material by the removal unit.

According to one preferable feature ofthe invention, the suction control mechanismmay comprise a pump connected to said suction structure, capable of creating mainlylaminar flow. The pump may be of any suitable type that is capable of creating thedesired suction action at the suction structure. ln order to create a controlled suctionaction, the pump may comprise power regulating drivers, whereby for example thespeed of the pump may be controlled and altered such that the desired laminar flowis obtained. ln this respect, the pump may either be placed at the removal unit or on a vessel, or even on the shore. ln order to handle the removed sediment material, preferably the pump is operablyconnected to a transport structure, which in turn is operably connected to said firstseparating mechanism. The transport structure may in that respect be elongatedconduits such as pipes and/or hoses. Further, the first separating mechanism, towhich the transport structure is connected, may preferably be placed above water level on a vessel or on the shore.

According to one preferred aspect of the invention, said first separating mechanism may comprise at least two chambers arranged in flow communication with each other.

The chambers are arranged such that water and sediment from the removal unitenters a first chamber filled with water, where heavier sediment material sinks to thebottom ofthe first chamber, while lighter sediment material stays at the surface ofthefirst chamber. This surface water flows over a dividing wall between the chamberssuch that the water with lighter sediment material enters the second chamber, inwhich a similar process as for the first chamber takes place. ln order to refine the separation process, further chambers may be added.

The last chamber of the first separating mechanism is then arranged in flowcommunication with a second separating mechanism, which is designed to removethe lightest volatile sediment material removed from the sea or lake bed. According toone favourable embodiment of the invention, the second separating mechanismcomprises a centrifuge, capable of removing light organic material. The advantagewith using a centrifuge is that an almost complete removal of sediment material fromthe water is obtained. The remaining water is then so clean from both organicmaterial as well as toxic components or heavy metals that it may be returned to the sea or lake without any restrictions.

The removed light and volatile sediment material is then preferably stored in astorage compartment in communication with said centrifuge. This material is in turnalso so clean that it may be used as a fertilizing component or land fill without any risks of any contamination of toxic material.

These and other aspects of, and advantages with, the present invention will becomeapparent from the following detailed description of the invention and from the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGSln the following detailed description of the invention, reference will be made to the accompanying drawings, of which Fig. 1 shows a schematic example of a system according to the presentinvenüon,andFig. 2 shows a schematic example of a removal structure comprised in the present invention.

DETAILED DESCRIPTION OF THE INVENTION A non-limiting example of a system according to the present invention is shown in Fig. 1. lt comprises a submersible removal unit 10 that is arranged to follow the sea orlake bed 12. ln this respect it could have a number of suitable means for movingalong the bed, such as a number of wheels 14, continuous tracks, runners, or othermechanical structures. The removal unit 10 preferably further comprises flotation orlevel means that are capable of keeping the removal unit submersed during use, butmay be raised to the surface 16 after use. Also the flotation or level means could bedesigned to exert a certain pressure on the sea or lake bed. The flotation or levelmeans could in this respect comprise chambers or compartments that can be filledwith air and/or water, buoyancy material such as expanded cellular plastic. ln thisrespect, the removal unit may also be raised or lowered by other means such as hoists or lifts arranged on a floating vessel 18.

Preferably the removal unit 10 is arranged with a suction structure 20 that is capableof removing predetermined layers of material from the sea or lake bed 12. Thesuction structure 20 may comprise a number of openings of different designscomprising nozzles with different designs and different opening sizes. The nozzlescould be fixedly attached to the removal unit with openings directed downwardstowards the bed. Another embodiment could comprise adjustment mechanisms thatare capable of adjusting the distance between the openings of the suction structureand the sea or lake bed. The suction structure 20 could also comprise a structurethat is moving along, and in contact with, the sea or lake bed, which could be wheel structures or runners, just to mention a few.

The suction structure 20 is operably connected to a pump 22 or the like suctioncreating member capable of creating a suction action at the opening ofthe suction structure 20. One very important aspect in this context is that the suction structure and the suction creating member are capable of creating laminar flow at the openingof the suction structure 20. The laminar flow ensures that the top layer of sedimenton the bed is effectively sucked up and removed. This is important because if there isnot only laminar flow but also, or only, turbulent flow, then the top layer of sediment,that is very light and volatile, tends to move uncontrolled in any direction. Further, thelaminar flow ensures that only small parts ofthe lower layers are removed from the sea or lake bed 12.

According to one favourable embodiment ofthe present invention, the suctionstructure 20 is designed as a rotatable structure, Fig. 2, provided with a number ofopenings 24 or nozzles around its circumference. Thus, when the structure rotateson the sea or lake bed 12, the nozzles 24 will move in contact with the bed. ln orderto control the operation of the nozzles, the structure is designed such and connectedto the pump in such a way that only the nozzles ofthe structure that are in contactwith the bed perform any suction action. ln the embodiment shown there is a fixedconduit 26 that is operably connected to the suction structure 20. The conduit 26 isarranged with a passage 28 that communicates with one nozzle at the time duringrotation of the structure, and always the particular nozzle that has an opening facingthe sea bed, as seen in Fig. 2. ln that particular nozzle a mainly laminar flow 30 of water and sediment material is obtained.

The removal unit 10 is preferably arranged with some type of drive or propellingmechanism 32 that enables it to move along the sea or lake bed. This propellingmechanism could either be suitable drive motors connected to wheels or continuoustracks, when such are used. The propelling mechanism could also include propellers operably connected to suitable drive motors. ln another feasible embodiment, the removal unit may be dragged or pulled along thesea or lake bed by a wire and pulley system having a winch or the like, for examplearranged on a floating vessel on the surface of the lake or sea or arranged on theshore. Further the drive or propelling mechanism or the removal unit itself may be arranged with steering or direction control means that are capable of directing the removal unit in a controlled manner over the sea or lake bed such that it covers a predetermined area. ln this respect, the removal unit may also comprise positioning identification means,such as e.g. GPS, that is capable of accurately locating and monitoring the actualposition of the treatment unit during use. The positioning identification means thenpreferably cooperates with the steering or direction control means such as to facilitate the coverage of a predetermined area of the lake or sea bed.

The removal unit 10 with its suction structure is preferably arranged with a sedimenttransport structure 34 that is operably connected to a sediment treatment unit 36.The sediment transport structure 34 may for example be a hose or pipe system thatis connected to an outlet of the suction creating member or pump 22. The sedimenttreatment unit 36 may in one preferable embodiment comprise a first separation unit38. The first separation unit 38 in turn comprises a number of containers or chambers38 a-c that are separated from each other by walls of certain heights, where the heights are reduced between subsequent chambers.

The incoming water and sediment from the removal unit 10, via the transportstructure 34, is led into a first chamber 38a having the highest wall. There theheaviest material of the incoming water sinks to the bottom while the lighter sedimentmaterial floats on the surface and is passed to an adjacent chamber 38b whereparticles again are filtered off by sinking to the bottom. Preferably at least twochambers are used, more preferably three chambers, for removing material from theincoming water. From the last chamber, the water, with remaining organic material, isled to a second separation unit 40, in the embodiment shown a centrifuge or cyclone,where the last of the organic material is separated from the water. The last organicmaterial is then fed from the centrifuge 40 to a storage compartment 42, while the water is fed back to the lake or sea. ln this respect it is to be understood that also the two first chambers 38a and 38 b areconnected to a third separation unit 44 for handling the sediment and particles that are trapped in those chambers. The third separation unit could either be a separate unit 44 as shown in Fig. 1, such as a centrifuge or cyclone. As an alternative, the second separation unit 40 could be connectable to all the chambers 38a - 38c via asuitable conduit system and valves, whereby one chamber is connected at the time.Further, if the third separation unit is a separate unit, then it is preferably connectedto a suitable storage compartment, either a separate storage compartment 46 or the same storage compartment 42 that the second separation unit 40 is connected to. lt is to be understood that the embodiment described above and shown in thedrawings is to be regarded only as a non-limiting example of the invention and that it may be modified in many ways within the scope of the patent claims.

Claims (13)

1. Method for handling sediment from lake or sea beds, comprising the steps of- removing an upper layer of sediment by suction, - controlling the suction action such that mainly laminar suction flow isobtained of sediment and water, - separating heavier organic material from said removed layer of sediment andwater, and subsequently - separating volatile organic material from the water, and - returning the water to the sea or lake.

2. System for performing the method of claim 1, comprising a - suction structure (20) for removing an upper layer of sediment, - a control mechanism (22) for providing mainly laminar flow through saidsuction structure (20), - a first separating unit (38) capable of separating heavier organic material,and - a second separating unit (40) capable of separating lighter material.

3. System according to claim 2, wherein said suction structure (20) comprises at least one nozzle (24).

4. System according to claim 2 or 3, wherein said suction structure (20) isoperably arranged to a removal unit (10), which removal unit (10) is arranged movable along said sea or lake bed.

5. System according to claim 4, wherein said removal unit (10) is arranged withpropelling means (14, 32) capable of moving said removal unit (10) over the sea or lake bed.

6. System according to claim 5, wherein said suction structure (20) is comprised in the propelling means (14). 11

7. System according to claim 5 or 6, further comprising a control system capable of controlling the direction and position of said removal unit.

8. System according to claim 2, wherein said control mechanism comprises apump (22) connected to said suction structure (20), capable of creating mainly laminar flow.

9. System according to claim 7, wherein said pump is operably connected to atransport structure (34), which in turn is operably connected to said first separating unit (38).

10.System according to claim 8, wherein said first separating unit (38) comprisesat least two chambers (38 a-c) arranged in flow communication with each other.

11.System according to claim 9, wherein said first separating unit (38) is arranged in flow communication with said second separating unit (40).

12.System according to claim 10, wherein said second separating unit (40) comprises a centrifuge, capable of removing light organic material.

13.System according to claim 11, further comprises a storage compartment (42)in communication with said centrifuge (40), for storing said removed light organic material.