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Title:
METHOD AND APPARATUS FOR USE OF GASES IN LIQUIDS
Document Type and Number:
WIPO Patent Application WO/1999/025609
Kind Code:
A1
Abstract:
Methods and apparatus are disclosed based upon dispersing bubbles in a body of liquid so as to modify the mechanical properties of the liquid. In one embodiment, a bubble concentrator (10) is interposed between a gas supply conduit (11) and the body of liquid to produce bubbles (12) of a selected size and at a suitable location to modify natural waves (20) before the waves impact a marine structure (18).

Inventors:
Hall, Roger Arthur Robert (12 Foundry House Kennet Way Hungerford Berks RG17 0YZ, GB)
Application Number:
PCT/GB1998/003425
Publication Date:
May 27, 1999
Filing Date:
November 18, 1998
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
Hall, Roger Arthur Robert (12 Foundry House Kennet Way Hungerford Berks RG17 0YZ, GB)
International Classes:
B01F3/04; B63B1/38; B63B39/10; E02B1/00; B01F13/00; (IPC1-7): B63B39/10; B01F3/04
Foreign References:
US2325937A1943-08-03
US2382393A1945-08-14
GB1538421A1979-01-17
US2492949A1950-01-03
Other References:
PATENT ABSTRACTS OF JAPAN vol. 9, no. 14 22 January 1985 (1985-01-22)
PATENT ABSTRACTS OF JAPAN vol. 10, no. 277 19 September 1986 (1986-09-19)
Attorney, Agent or Firm:
MURGITROYD & COMPANY (373 Scotland Street Glasgow G5 8QA, GB)
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Claims:
CLAIMS
1. A method of altering the mechanical properties of a body of liquid by passing bubbles of one or more gaseous substances therethrough.
2. The method of claim 1, comprising the steps of: i) locating one or more gaseous medium conduit means in a selected location within or adjacent to the body of liquid; and ii) supplying compressed gas via the conduit means so as to disperse bubbles from one or more locations on the conduit means.
3. The method of claim 2, in which the compressed gas emitted from the one or more locations is compressed air.
4. The method of claim 2, in which the compressed gas emitted from the one or more locations is a mixture of one or more gases which may include air.
5. The method of any of claims 2 to 4, in which the step of locating the conduit means includes locating the conduit means on the seabed.
6. The method of claim 5, in which the conduit means includes a number of portions shaped for providing bubbles from one or more locations, thereby reducing the forces upon an object positioned above the conduit means due to varying weather and tide conditions.
7. The method of any of claims 2 to 6, in which the bubbles are provided by means of a bubble concentrator interposed between the conduit and the main body of liquid.
8. The method of any preceding claim, used for one of the following: reducing coastal erosion; decreasing the forces which act upon a mobile marine object due to the impact of one or more surface waves; reducing structural damage to permanent or temporary structures located within a body of liquid; enhancing oil slick dispersion; altering the path of an iceberg; or separating minerals from their gangue.
9. A gaseous medium conduit means consisting of one or more hollow conduits having holes therein for the dispersal of bubbles of one or more gaseous substances therethrough, the conduits being arranged in a structure for supplying bubbles into a body of liquid to alter the mechanical properties of the body of liquid.
10. The structure of claim 9 adapted to be permanently or temporarily retained upon the bed of the body of liquid.
11. The structure of claim 9 or claim 10, in the form of a web consisting of an array of conduits arranged in substantially concentric closed paths and radial supply conduits.
12. The structure of any of claims 9 to 11, in which the conduits are arranged to reduce the coastal erosion due to the motion of a body of liquid and/or due to the impact of one or more waves.
13. The structure of any of claims 9 to 11, in which the conduits are arranged for cooperation with a mobile marine vessel.
14. The structure of claim 13, in which the conduits are arranged in a framework spaced from the hull, submerged or semisubmerged structure of the mobile marine vessel.
15. The structure of claim 14, in which said framework projects forward from the bow of the vessel to decrease the forces due to motion of the body of fluid in which the vessel is travelling and/or the forces due to impact of waves upon the vessel.
16. The structure of claim 15, in which said framework also extends athwart and astern of the vessel.
17. A bubble concentrator for use in a body of liquid, the concentrator comprising a chamber formed by side walls and a lid, the lid comprising one or more sections hinged to the side walls, and means for producing bubbles within the chamber, the arrangement being such that said bubbles are concentrated under the lid until a sufficient buoyancy is established to overcome a closing force of the lid.
18. A bubble concentrator according to claim 17, in which the lid is in the form of two lid sections which are equally weighted to provide a desired closing force.
Description:
Method and Apparatus for use of Gases in Liquids This invention relates to uses generating or introducing gases into a liquid. More particularly, this invention relates to a device for generating or introducing (directly or by concentration and release) bubbles of gas or gases into any liquid or mix of liquids for reducing the density of the liquid or mix of liquids, which has the consequence of reducing one or more of the following: buoyancy forces; forces due to movement of liquid; and forces due to waves or wave trains.

In this field it is already known that the buoyancy force or the dynamic force on an object on, in, or within a liquid can be altered by increasing or decreasing the density of the liquid on a permanent basis. It is also known that the force of, or the effect of, surface waves upon such an object can be reduced by placing a secondary object or objects upstream in order to absorb or dissipate the forces acting upon the object.

The disadvantages in such known methods are that altering the density of a liquid on a permanent basis

is cumbersome, expensive and wasteful and has the potential for causing pollution and destruction of life forms, substrate layers and food chains by the addition of higher or lower density liquids or soluble solids.

There is also the potential for long term, long distance effects upon the environment as a result of such additives, often unconnected with the area where the liquid density has been altered.

In the case of placing secondary objects, such objects are invasive and potentially damaging to the environment. Furthermore, their fabrication, transportation and construction relies heavily upon natural or man made materials, thereby involving the destruction of terrestrial sites and the excessive use of non-renewable energy. Also, the installation of such secondary objects is not an option in remote areas and locations which experience hostile sea and ocean conditions. This may result in the need to suspend or abandon operations such as mineral and oil exploration and production for long, costly periods.

A suitable solution to coastal erosion has not been discovered. This has particular consequences in areas having low population densities, where it is not cost- efficient to prevent or ameliorate erosion, resulting in much valuable land and property being lost to the sea.

Wave action also causes discomfort to crew and passengers aboard marine vessels as fuel consumption and power is. increased to control pitch and roll through high, steep-sided waves.

Scouring around bridge piers, supports and other structural members in marine or brackish waters or in

rivers due to turbulent flow around and downstream of such objects causes problems of instability or over-engineering to counteract the resultant upstream force. Dissipaters and/or reducers placed to combat such effects also suffer scouring, saltation and redistribution of mixed particle sizes of bed load.

This in itself can lead to upstream pressures upon the structures which such dissipaters and/or reducers are supposed to protect.

Oil spillage dispersal often requires spraying an oil slick surface with a suitable detergent.

Emulsification occurs during contact between the dispersing detergent and the oil. This is limited to the area of surface in contact with the atmosphere and consequently, emulsification is delayed. Costly mechanical devices exist which have the purpose of increasing the oil surface area, but such devices can only be applied to spills that have been mechanically contained by boom-type floating structures.

Icebergs have a high mass, in conjunction with a low velocity. The resultant momentum of even relatively low volume icebergs is huge. Consequently little or no attempt is made to divert icebergs from a collision course with other floating marine or seabed fixed structures. Instead, preference is given to moving the structures out of collision course. The downtime for moving such structures has expensive consequences due to the time which is wasted during such operations. It is also well known that floating ice can extend downward to drag along the seabed, and it is possible that such an iceberg base may collide with and cause damage to seabed production fixtures or pipelines with the inevitable loss of valuable oil or gas and resultant pollution.

Mineral separation processes in which minerals are separated from their gangue using a liquid of constant density require combinations of costly mechanical separation and liquid separation techniques which require that the minerals be transported from one apparatus location to another with the associated cost and time losses.

According to a first aspect, the present invention provides a method of altering the mechanical properties of a body of liquid by passing bubbles of one or more gaseous substances therethrough. The method may comprise the steps of: i) locating one or more gaseous medium conduit means in a selected location within or adjacent to the body of liquid; and ii) supplying compressed gas via the conduit means so as to disperse bubbles from one or more locations on the conduit means.

The compressed gas emitted from the one or more locations may be compressed air. Alternatively the compressed gas may be a mixture of one or more gases which may include air.

The step of locating the conduit means may include locating the conduit means on the seabed. The conduit means may be temporarily or permanently retained on the seabed and may include a number of portions shaped for providing bubbles from one or more locations, thereby reducing the forces upon an object positioned above the conduit means due to varying weather and tide conditions.

The bubbles may be provided by means of a bubble concentrator interposed between the conduit and the main body of liquid.

The invention may be used to provide a method of altering the buoyancy forces which act upon an object or series of objects in the body of liquid.

Alternatively, it may provide a method of decreasing the forces which act upon the object or series of objects due to the motion of the body of liquid.

As a further alternative, it may provide a method for decreasing the forces upon the object or series of objects in the body of liquid due to the impact of one or more surface waves upon the object or series of objects.

In another alternative, it may provide a method of reducing coastal erosion.

In yet another alternative, it may provide a method of decreasing the forces which act upon a mobile marine object due to the impact of one or more surface waves.

In still another alternative, it may provide a method of reducing structural damage to permanent or temporary structures located within a body of liquid.

In still another alternative, it may provide a method of enhancing oil slick dispersion.

In still another alternative, it may provide a method of altering the path of an iceberg.

In still another alternative, it may provide a method

of separating minerals from their gangue.

According to a second aspect, the present invention provides a gaseous medium conduit means consisting of one or more hollow conduits having holes therein for the dispersal of bubbles of one or more gaseous substances therethrough.

The conduits may be arranged in a structure for the purpose of supplying bubbles into a body of liquid to alter the mechanical properties of the body of liquid.

The shape and dimensions of the structure may depend upon the shape of the one or more objects located on or in the body of fluid. It may also depend upon the direction of the prevailing current flow or tidal action of the body of liquid. Alternatively, the shape and dimensions may depend upon the requirement to account for current flow or tidal action upon the object from any direction.

The structure may be permanently or temporarily retained upon the bed of the body of liquid.

The structure may be a web consisting of an array of conduits arranged in substantially concentric closed paths and radial supply conduits. The supply conduits may enable a gaseous medium to be transported to one or more sectors of the web structure, the sectors being defined by the concentric conduit and supply conduits.

One or more objects on or in the body of the liquid may be located above the structure such that the buoyancy forces of the object and/or the forces acting upon it due to the motion of the body of liquid and/or due to

the impact of one or more surface waves upon the object may be decreased on passing bubbles of one or more gaseous substances through the conduit means.

The mechanical properties which are altered by passing bubbles into the body of liquid may include the density of the body of liquid and/or the buoyancy force and/or the wave forces acting upon one or more objects on or in the body of liquid.

The conduits may be arranged to reduce the coastal erosion due to the motion of a body of liquid and/or due to the impact of one or more waves.

Alternatively, the conduits may be arranged in a structure capable of co-operating with a mobile marine vessel and may incorporate a framework of conduit pipes spaced from the hull, submerged or semi-submerged structure of the mobile marine vessel. The structure may project forward from the bow of the vessel to decrease the forces due to motion of the body of fluid in which the vessel is travelling and/or the forces due to impact of waves upon the vessel. The structure may also extend athwart and astern of the vessel; this decreases the effect of waves from any direction.

The invention further provides a bubble concentrator for use in a body of liquid, the concentrator comprising a chamber formed by side walls and a lid, the lid comprising one or more sections hinged to the side walls, and means for producing bubbles within the chamber, the arrangement being such that said bubbles are concentrated under the lid until a sufficient buoyancy is established to overcome a closing force of the lid.

The lid may suitably be in the form of two lid sections which are equally weighted to provide a desired closing force.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings of which: Fig 1 is a schematic of an embodiment of the invention; Fig 2a is a plan and Fig. 2b a side view of another embodiment of the invention; Fig 3 is a plan view of a further embodiment of the invention; Figs 4a and 4b are a side view and a plan view, respectively, of another embodiment of the invention; Fig 5a is a schematic side view of a further embodiment; and Fig 5b is a cross-section on B-B of Fig 5a.

In all embodiments of the invention, a supply of compressed gas is conducted to an array of bubble generators. The gas is typically air, but any suitable gas or mixture of gases can be utilised. The gas is delivered into a liquid which may be salt water, fresh water or brackish water, with the purpose of temporarily and locally decreasing the density of the liquid. This has the effect of reducing the forces acting upon an object located within and/or on the liquid. The forces are static forces, such as the buoyancy force acting upon an object in the liquid, or transient forces due to the motion of the body of liquid, or surface waves. The force due to the

expanded, bursting bubble at the surface of the liquid within any wave or waves can be utilised to reduce the momentum of any such wave or waves.

Referring to Fig 1, a device 10 generates or concentrates bubbles 12 at a suitable depth between the atmosphere/water surface 14 and the water/bottom 16 interfaces, at a rate of production and size so that the bubbles rise, expand, and on bursting through any wave or wave/atmosphere interface, cause the waves to collapse or partially collapse, thereby altering the momentum of the wave or waves. This has a resultant effect upon the force on any structure 18 on or in the body of liquid, and can be used to reduce the force of waves upon permanent or semi-submersible structures such as rigs used in oilfield production and/or exploration for sub-seabed oil reservoirs. Typically, air is compressed on site upon such structures, before being conducted to the bubble generators that are situated at a suitable distance away from the structure, and either fully surround or by a movable segment afford protection across the widest dimension of such structures. The original waves and the collapsed waves are shown schematically at 20 and 22, respectively.

By generating a suitable size of bubble, an effect is achieved whereby the bubble expands as it rises and, on approaching the surface, forces water out of the surface into the air space of the bubble to form a relatively flat water surface.

The device 10 permits bubbles 12 of a desired size to be generated. The device 10 comprises a perforated air conduit 11 which forms streams of small bubbles 13 within a housing 15 the top of which is closed by

hinged doors 17 provided with counterweights 19. Thus, the small bubbles 13 are concentrated beneath the doors 17 until they form a sufficient quantity of air to give buoyancy to open the doors 17, releasing the air as one or two large bubbles 12 (as indicated in broken lines in Fig. 1), following which the doors 17 are closed by the counterweights 19.

Referring to Fig 2, a device 24 is placed upstream in a single direction flow stream 26 or uptide and/or downtide of any structure such as a bridge pier 28 or harbour pile to entrain bubbles 30 which reduce the overall density and thus the scouring force and other dynamic forces (for example, pressure on a pile) due to the turbulent and/or laminar flow of liquid upstream, beside and/or downstream of the interface of the flow, and the solid or semi-solid bed and the structure.

The device consists of a series of hollow conduits 32 arranged in a structure which is designed to co-operate with the bridge pier 28, harbour pile or the like and provides a curtain of bubbles to reduce the scouring forces on the structure due to the current and tidal flow of the body of liquid. The conduits 32 are interconnected, having holes 34 therein for the dispersion of the bubbles 30 of a gas, which in this embodiment is compressed air. The compressed air is supplied from the surface via hollow supply conduits 36, from which it is dispersed around the conduits 32 before subsequently passing into the body of fluid.

The device is located on the river bed 38 and surrounds the bridge pier 28 or the like. Some of the conduits 32 are inclined to provide drainage of liquid from within the conduits 32 during use, the conduits 32 having drainage holes 40 for this purposes.

The advantages of the invention and/or the ways in which the disadvantages of previously known arrangements are overcome, include the following. Most if not all existing wave-calming or destroying devices operate only in relatively shallow water. Most involve the interaction with solid or semi-solid, frequently bulky structures often of a permanent nature, such as breakwaters or rock and concrete or alternatively submerged or semi-submerged, captive buoyant or semi-buoyant devices placed within the amplitude of average to above average amplitude waves.

As an alternative to the arrangement shown, the bubble generating device could be positioned separately from the structure, and could be secured on the bed by weights or anchors, or be a floating device tethered to the bed.

No such devices exist in deep water for the protection of oil drilling or production rigs and the like, or converted boats or ships used for floating oil production.

The present invention affords protection to permit offshore oil operations that until now have had to cease due to excessive forces and wave pressure. The present invention also enables a more comfortable and stable work environment to be created.

Referring to Fig 3 the device is located on the seabed, and is used to reduce the forces acting upon a marine installation 42 such as a moored semi-submersible oilfield production rig or the like in a body of liquid. The device consists of a series of conduits which are constructed in rings 44, having connecting radial supply conduits 46. In this embodiment, the

rings 44 are hexagonal, but other polygonal or triangular forms may be used. The conduits forming the hexagonal rings 44 are supplied with a gas, which in this embodiment is compressed air, via the supply conduits 46. The device forms a series of sectors, and it is possible to isolate one or more of such sectors such that compressed air is supplied to one or more of the sectors, individually or in combination. In this way, the forces on the marine installation 42 due to current and tidal motion of the body of liquid, or due to wave forces, can be controlled by supplying compressed air to one or more of the sectors, depending upon the flow direction of the liquid, or the weather conditions causing the surface waves.

The compressed air required for operation of the device is produced on site at the marine installation 42 or on a secondary installation. The device can incorporate bubble concentrators such as that shown in Fig 1 if desired.

The device can also be employed in shallow water where its effects may be used to calm or ameliorate the force of wave erosion to cliffs and coastlines, in a single or multiple linear array generally parallel to the coastline allowing preservation or a possible reclamation of valuable agricultural land adjacent to the sea.

In a modification of the foregoing embodiment, a web- like structure similar to that of Fig 2 but smaller in extent is not secured to the sea bed but is provided with propulsion and buoyancy means (in a manner similar to a remotely operated vehicle) to enable it to be maneouvered to a desired location, which will typically be upstream of a structure to be protected. Shapes and

forms other than web-like structures may be used in a similar way.

Thus far no device has been applied ahead of waterborne vessels, ships, boats etc. Even moderate winds with long fetches (distances over which waves can build unhindered) can and do build the most forceful of wave types known as steep waves with high amplitude that can cause all types of vessels to experience high stresses and strains to their structures causing reduced travel velocities, and sometimes even causing vessels caught in such conditions to make slow, cautionary way or to heave-to, or suffer stresses great enough to induce welds and/or joins to open, finally resulting in failure and sinking. Under such conditions there is serious threat to the safety of the vessel or its deck cargo, or of serious damage to these.

An arrangement of the device may project forward and/or variably athwart of the bows and sides of a mobile marine vessel, being employed up weather or up current.

Injecting bubbles afterward, in the directional sense of from the bows towards the stern, contributes to the forward motion by the jet (action/reaction) effect, and when set to an appropriate bubble size, delivery rate and depth, destroys partially or wholly the steepness and force of any impinging waves.

Referring to Fig 4, the device consists of an articulated framework which is moveable via joints 50, and which is fixed to the hull of a mobile marine vessel such as the ship 52 of Fig 4. The framework incorporates downwardly and forwardly angled conduits 56 with horizontal conduits 58 attached thereto, some of these being provided with holes therein (as

indicated by dashed lines in Fig. 4) for the dispersion of bubbles of a gas, which is intended to be compressed air. The compressed air is supplied to the conduits via one or more suitable supply conduits (not shown).

In this way, bubbles are directed down out of selected angled conduits 56 and horizontal conduits 58, subsequently rising to the surface of the body of liquid to reduce the forces due to current and/or tidal flow of the body of liquid, and the forces due to impact of surface waves upon the marine vessel.

The device also has a second support means in the form of one or more hydrofoils 60, to provide an upthrust force on the device when the liquid flows over the hydrofoil 60. The hydrofoils may be fixed, or may be variable geometry (hinged).

A further advantage of the device is its application to the problem of scouring around solid or semi-solid structures wholly or partly immersed in, on or within flowing liquids downstream of permanent or temporary structures such as river bridge or harbour supports.

In such circumstances, smooth streamline flow often becomes turbulent at certain depths at and near the bed/liquid interface, causing scouring of the bed load, with resultant effects upon such structures.

Thus far nothing has the ability to significantly ameliorate the drag force of the turbulent flow from scouring-where solid or semi-solid upstream structures have been tried they have themselves suffered scouring and often removal from their supposed position of efficacy. Indeed even streamlining of say bridge piers/supports in fast flowing rivers fails to prevent scouring.

By using the device of Fig 2 to partially and temporarily reduce the liquid density by introducing bubbles at a suitable position upstream of the turbulent flow regimes reduces the overall liquid mass and thus reduces the scouring forces.

Current attempts to disperse accidental oil spills upon water take various forms, with a favoured one being detergent spraying and/or containment within a temporary system of oil booms. Dispersal by spraying such superficially homogeneous masses is delayed somewhat since the area of detergent in contact with the oil is limited to the semi-planar upper surface of the oil.

Introducing bubbles into the liquid upon which the oil floats causes break-up of the slick into variably sized masses that present a larger surface area to the detergent, thus increasing the rate of emulsification and eventual dispersal.

Subsea oil exploration and production must enter ever more hostile areas of the earth as the more accessible source regions become depleted. One such area may be the northern North Sea and the adjacent Atlantic regions west of the Shetland Isles, generally in a north to north-west direction as a continuous band across and through the arctic and polar regions to the north west of Canada and Russia.

The device not only has application for wave-calming in these regions of severe and hostile weather, but also has uses in its ability to temporarily reduce liquid density to deal with the very real danger of iceberg collision.

The only way of avoiding inevitable collision between exploration or production rigs has been to design rigs that can within a matter of twelve hours temporarily abandon their position in a collision path with icebergs having a huge momentum.

Steering all but the relatively tiny icebergs out of collision vectors is, where viable, done by powerful vessels, pushing or pulling the icebergs aside through resistant seawater.

The device when used to reduce the seawater density in a suitable position relative to the iceberg will reduce resistance to vector it out of collision course.

In this way the costs due to lost time and the damage risk is significantly reduced as operations can continue uninterrupted.

The present invention may also be used in the field of the separation of mineral ores. It is known, in general, to separate mineral from gangue by flotation methods using liquids or using froth. The present invention contemplates the use of controlled bubble formation to provide a controllably varied density in a liquid and thus to facilitate separation by density.

Such a process is illustrated in outline in Fig 5. A ground mineral ore in a stream of water is introduced to a series of V-shaped troughs 70 each of which has an outlet slot 72 along its bottom and compressed air conduits 74 for forming streams of bubbles in the mixture flowing through the troughs 70. The air pressure to each individual trough 70 and the size of the air outlets from the conduits 74 of each individual trough 70 can be chosen to give a desired alteration in

buoyancy, such that materials of selected density tend to be discharged from the slot 72 of that trough 70.

A similar effect could be achieved in a vessel which combines vortex-inducing vanes, bubble formation, and multiple outlet ports.

In addition to, or instead of, the use of bubbles, the ore separation may make use of water currents of variable velocities to wash forward lower density materials, allowing higher density material (ore) to drop into a collecting vessel.

The foregoing description refers to conduits placed on a surface such as the seabed. Conduits could equally be buried in the seabed or the like, so long as means of communication are provided to conduct gas from the conduit into the body of liquid to form bubbles.

Other modifications and improvements may be made to the foregoing embodiments within the scope of the present invention.