Apparatus and method for liquid pumping

It is to be understood that embodiments of the present invention provide apparatus and a method for pumping a liquid, for example to recirculate liquid in a liquid storage tank by means of a gas lift pump. A perforated extension at the top of a gas lift allows the apparatus to be used in circumstances where the depth of liquid in the tank may vary over a wide range. Gases other than air may be used in the gas lift, so as to change the acidity and the concentrations of dissolved gases, particularly oxygen, in the liquid. The gas may be introduced into the gas lift through a whistle that generates intense sound waves and couples them into the liquid. These features when used in combination have particular application against invasive species in the ballast water of ocean-going tankers.

RELATED APPLICATIONS

This application is a 35 U.S.C. § 371 national stage application of PCT Application No. PCT/GB2012/053270, filed on Dec. 24, 2012, which claims priority from Great Britain Patent Application No. 1122211.4, filed Dec. 22, 2011, the contents of which are incorporated herein by reference in their entireties. The above-referenced PCT International Application was published in the English language as International Publication No. WO 2013/093527 A1 on Jun. 27, 2013.

FIELD OF THE INVENTION

The present invention relates to gas lift pump apparatus and to a method of pumping liquid by gas lift. In particular but not exclusively some embodiments of the present invention relate to circulation of liquid in a liquid storage tank.

BACKGROUND

The problem exists that aquatic nuisance species (ANS) such as Zebra mussels are being transported between locations such as between ports of different countries in the ballast tanks of maritime vessels. Aquatic nuisance species may be defined as waterborne, non-native organisms that threaten the diversity or abundance of native species, the ecological stability of impacted waters or commercial, agricultural, aquacultural or recreational activities. A variety of measures for preventing invasion of an environment by ANS have been proposed, including purging of ballast tanks at sea before a vessel enters an area sensitive to ANS.

However, purging of a ballast tank requires emptying and refilling of the ballast tank. It will be understood that such a procedure can have an adverse effect on the stability of a vessel particularly in rough seas and is not appropriate in certain cases.

STATEMENT OF THE INVENTION

Aspects of the invention provide an apparatus and a method as claimed in the appended claims.

According to another aspect of the invention for which protection is sought, there is provided gas lift pump apparatus comprising:a column having in use a substantially upright portion through which a liquid medium may be pumped by gas lift; anda fluid delivery device for delivering a flow of a gaseous fluid into the column at a first location of the column,wherein the column comprises a lift portion having a substantially continuous, unperforated wall and a perforated portion being a portion having a perforated wall, the fluid delivery device being operable to deliver the flow of gaseous fluid into the lift portion wherein the gaseous fluid rises through the lift portion a first distance before entering the perforated portion.

By perforated wall is meant that the wall has at least one aperture formed therein. Advantageously the perforated portion has a plurality of apertures formed in the wall thereof.

Embodiments of the invention have the advantage that liquid medium may be recirculated in a liquid storage tank by means of the apparatus even if a level of liquid in the storage tank fluctuates in depth over a wide range of depths. This is because liquid being pumped through the column may pass out from the column through perforations in the perforated portion of the column if the column is not itself fully immersed in the liquid. Thus liquid is not required to travel to a free (upper) end of the column before exiting the column, but can exit the column laterally through a wall of the column by means of the perforations.

In some arrangements the apparatus is operable to deliver a flow of gaseous fluid into the column only at the first location. In other words, there are no other locations at which gaseous fluid is injected into the column. In some embodiments a plurality of fluid delivering devices may each deliver a flow of gaseous fluid into the column substantially at the first location. In some alternative arrangements gaseous fluid may be injected at one or more locations along a length of the column in addition to the first location.

The feature that the gaseous fluid is injected into the lift portion allows the apparatus to establish pumping of liquid through the column before gas enters the perforated portion of the column where the differential pressure between liquid in the column and liquid external to the column is reduced.

It is to be understood that embodiments of the invention have the unexpected advantage that, once pumping of liquid through the column is established, gas injected into the column becomes entrained in the upward flow of liquid and the liquid in the column tends to remain in the column as it rises upwardly. This is because a head of pressure to which liquid in the column is subject is less than that of liquid outside the column, due to the presence of gas bubbles in the liquid reducing a mass of the column of liquid. Accordingly, entrained gas tends to remain within the column where it is also subject to a lower pressure.

Any gas that does escape from the column through the perforations therein may be drawn back into the column due to the adverse pressure gradient established between liquid on an inside of the column and liquid external to the column. Some of the gas that escapes from the column may become trapped in a boundary region or boundary layer surrounding the column and rises within this boundary region to a surface of the liquid.

The liquid (and entrained gas) tend to rise within the column and exit the column at or close to a surface of the liquid through the perforations in the sidewall. If the column is fully submerged the liquid with entrained gas may exit the column at a free end of the column without having to pass through the sidewall.

Advantageously an axial distance of the first location of the column from the perforated portion of the column may be a distance greater than or substantially equal to substantially ten times an average diameter of the column at the first location.

Optionally an axial distance of the first location of the column from the perforated portion of the column corresponds to a multiple of the average diameter of the column at the first location, the multiple being one selected from amongst from 10 to 15, from 15 to 20 and more than 20 diameters.

Advantageously the apparatus may further comprise a sonic energy generator, the generator being operable to launch sonic energy into a liquid medium flowing through the column.

It is to be understood that by the term ‘launch’ is meant that the generator is operable to transmit the sonic energy into the liquid medium. Thus the sonic energy generator may launch sonic energy (sound waves) into the liquid medium. The device itself may generate sonic shockwaves. In addition or instead the device may generate sonic waves that are not shockwaves. Sound waves launched into the liquid medium may be ordinary sound waves and not shockwaves.

The sonic energy generator may be provided by or be additional to the fluid delivery device.

The sonic generator may be arranged to generator sonic waves with a fundamental frequency in the range 20-50 kHz, optionally in the range 20-25 kHz. In some embodiments the sonic generator may be arranged to generator sonic waves with a fundamental frequency of around 22 kHz. The waves may be generated with overtones at 44 and 88 kHz. Other arrangements are also useful.

The advantage of this feature is that the sonic generator may cause collapse of gas bubbles present in the liquid medium. This may result in the destruction of aquatic nuisance species which may for example be attached to a wall of the bubbles, for example bacterial ANS. The apparatus may be operable to adjust a sonic frequency of sonic energy generated by the generator.

In embodiments in which sonic energy is obtained at a resonant frequency associated with the generator, the apparatus may be operable to adjust the resonant frequency.

Advantageously the sonic energy generator may comprise a nozzle member operable to direct a flow of gaseous fluid into or across an entrance to a receptor member provided in a spaced apart relationship with the nozzle member, the receptor member defining an open cavity, thereby to excite resonance of gaseous fluid in the receptor member to generate the sonic energy.

It is to be understood that dimensions of the nozzle and receptor member (which may also be described as a resonant cavity member) may be selected to provide a specific frequency of oscillation of an air column in the cavity. In some embodiments the apparatus is arranged wherein gas emerges from the nozzle at supersonic speed and forms a standing pressure wave. Alternatively the gas may emerge from the nozzle at subsonic speed and form a standing pressure wave.

A gap between the nozzle and the receptor member may be adjusted such that an open end of the receptor member is positioned at an optimum location with respect to the pressure wave.

It is to be understood that acoustic energy associated with the oscillating air column radiates outwardly into the surrounding gas.

The apparatus may be operable to cause a sonic standing wave such as an ultrasonic standing wave to be established between the nozzle member and the receptor member.

Optionally the apparatus may be operable to direct a supersonic flow of gaseous fluid through the nozzle.

Advantageously the apparatus may be operable to establish a stable shockwave pattern between the nozzle and the receptor member.

The apparatus may be operable to adjust a distance between the receptor member and the nozzle.

Advantageously the apparatus may be operable to adjust a depth of the cavity defined by the receptor member.

This feature has the advantage that the apparatus may be adjusted to enhance an amount of sonic energy of a required frequency that is generated by the apparatus. In some arrangements this feature may allow tuning of a frequency of sonic energy generated by the apparatus.

Optionally the receptor member is coupled substantially directly to the column wherein sonic energy may be launched into liquid medium flowing through the column.

By ‘coupled directly’ is meant that the receptor member is in substantially direct contact with the column whereby sonic energy is communicated to the liquid via the column itself.

The receptor member may be coupled directly to the column whereby the column vibrates at a frequency corresponding to that of sonic waves generated by the device thereby to introduce the sonic waves into liquid in the column.

It is to be understood that the sonic energy launched into the column may be in the form of ordinary sonic waves and not sonic shock waves. The waves may be of a frequency determined by the device such as an ultrasonic frequency.

Advantageously the receptor member is provided within a chamber, the nozzle being arranged to direct a flow of gaseous fluid into or across the entrance to the receptor member wherein sonic pressure waves are generated within the chamber.

It is to be understood that in some embodiments the chamber itself may be arranged to resonate due to resonance of air in and immediately outside the receptor member. Thus in some embodiments air in and immediately outside the receptor member may be arranged to resonate at an overtone of the chamber or optionally at two or more overtones.

The chamber may alternatively be referred to as a housing.

Further advantageously the nozzle member and receptor member may be provided within the chamber.

Thus the process of injecting gas from the nozzle member into the receptor member resulting in resonance of gas may take place substantially entirely within the environment defined by the chamber. This environment may be a substantially gas-filled environment under normal operating conditions in use. Thus any liquid medium that might enter the chamber when gas is not flowing through the nozzle member may be expelled when gas is introduced into the chamber through the nozzle member.

Advantageously the chamber may be provided in acoustic communication with liquid medium flowing through the column.

Advantageously the chamber may be provided within the column.

In some arrangements a flowstream of liquid medium through the column may be arranged to flow in direct contact with the chamber.

Advantageously the sonic energy generator may be operable to communicate sonic energy into the liquid medium by means of a flexible diaphragm.

The flexible diaphragm (which may also be referred to as a membrane) may provide amplification means for increasing an amplitude of sonic energy launched into the liquid medium.

The flexible diaphragm may be arranged to reduce a mismatch between an impedance of the sonic generator and an impedance of the liquid medium.

Optionally the diaphragm is arranged to resonate at a frequency corresponding to that of the sonic energy generated by the sonic generator.

Advantageously the diaphragm is formed from at least one selected from amongst a metallic material and a polymeric material.

The diaphragm may be arranged to provide amplification means in combination with a substantially horn-shaped chamber or housing. Other arrangements are also useful.

By horn shape is meant that a diameter of the chamber increases in a direction towards the diaphragm which may be arranged to seal a free end of the chamber in a substantially airtight manner. The diameter of the chamber may increase such that in side-view a wall of the chamber flares outwardly in a substantially curved manner.

Advantageously the receptor member may be mounted to the diaphragm thereby to couple sonic energy generated by the generator into liquid medium on an opposite side of the diaphragm.

Advantageously the diaphragm may be arranged to resonate in a mode in which the receptor member remains substantially stationary.

This feature has the advantage that the distance between the receptor member and nozzle member may be kept substantially constant whilst at the same time allowing improved coupling between the receptor member and diaphragm (and thereby the liquid medium) by virtue of the fact that the receptor member is coupled to the diaphragm.

Optionally the receptor member is provided with an aperture in a basal wall thereof whereby sonic energy may be coupled to the diaphragm.

Advantageously the diaphragm may be arranged to define a wall of the chamber.

Advantageously may have at least a portion of the chamber has a cross-sectional area that increases as a function of distance from the nozzle member.

This portion of the chamber may form an ‘amplification chamber’, a ‘horn’ or an ‘acoustic horn’. The diaphragm may provide a wall of the amplification chamber across a region of increased cross-sectional area relative to another portion of the chamber thereby to enhance an efficiency with which sonic energy may be coupled into the liquid medium.

The amplification chamber may increase in cross-sectional area in a linear manner or according to an alternative, prescribed mathematical relationship. In some embodiments an inner wall of the chamber may be shaped to correspond to a curve, optionally a logarithmic curve.

Advantageously at least a portion of the chamber may have a substantially tapered cross-section.

Optionally at least a portion of the chamber has a substantially conical shape.

Further optionally the at least a portion of the chamber may have a substantially frusto-conical shape.

Advantageously the fluid delivery device may comprise the sonic generator, wherein gaseous fluid employed to generate sonic energy is arranged to be injected into the column thereby to pump fluid through the column.

Thus a process of delivering gaseous fluid (or ‘gas’) into the column may be arranged to generate sonic energy.

Alternatively gaseous fluid employed to generate sonic energy may be arranged not to be injected into the column.

Thus in some arrangements, the gaseous fluid may to be vented to atmosphere, stored in a storage tank, or re-pressurised for use in continued operation of the sonic energy generator.

In some embodiments where a gas is used that may not be injected into the liquid medium the gas may therefore be directed other than into liquid in the column.

Advantageously sonic energy generated by the sonic energy generator may comprise ultrasonic energy.

Optionally sonic energy generated by the generator consists substantially of ultrasonic energy.

Advantageously the fluid delivery device may be arranged to be provided in a flowstream of the liquid medium through the column.

The device may have an upstream portion and a downstream portion.

Advantageously the downstream portion may be tapered thereby to reduce an amount of drag experienced by the device in the flowstream.

The receptor member may be provided in the upstream portion of the device.

Advantageously the diaphragm may be arranged to direct the sonic energy into the liquid medium in an upstream direction with respect to a flow of liquid medium through the column.

In some alternative embodiments the diaphragm may be arranged to direct sonic energy across the flow of liquid medium through the column.

In some embodiments the diaphragm may be arranged to direct sonic energy in a direction downstream of the flow of liquid medium through the column.

Optionally the apparatus may comprise a plurality of sonic energy generators.

This feature has the advantage that an amount of sonic energy introduced into liquid in the column may be increased.

The plurality of sonic generators may be provided substantially at the first location of the column.

Alternatively the plurality of generators may be provided at a different location, and/or at a plurality of locations of the column.

Advantageously the apparatus may comprise a bubble generator operable to provide gas bubbles in liquid in the column, the apparatus being operable to subject the bubbles to sonic energy generated by the sonic energy generator.

This feature has the advantage that an effect of sonic pressure waves generated by the sonic generator on aquatic organisms and bacteria may be enhanced.

The bubbles may be generated in liquid prior to injection of liquid into the column or in liquid as it flows through the column.

The bubble generator may be a microbubble generator operable to provide microbubbles in the column upstream of the sonic generator. By microbubble is meant a bubble having a size less than around 1 mm. It is to be understood that in some embodiments the bubble size may have a lower bound of around 1 micrometer. In some embodiments the generator may produce bubbles of sub-micrometer dimensions.

The generator may advantageously comprise a constriction portion through which the liquid medium is forced to flow, the constriction portion having a converging section of reducing cross-sectional area, a throat section and a diverging section of increasing cross-sectional area.

The constriction portion may be in the form of a venturi (or choke) portion.

The apparatus may advantageously be operable to inject gaseous fluid into liquid medium in the column at a location upstream of the constriction portion.

The gaseous fluid may be introduced into the column in such a manner that a shearing effect of a liquid flowing through the column reduces a size of the bubbles below a natural size of the bubbles in a case where gas was injected into liquid that was substantially stationary.

Advantageously the apparatus may be operable to inject gaseous fluid into liquid medium in the throat section.

This feature has the advantage that a shearing effect of liquid flowing through the throat section is greater (due to the greater speed of the liquid) thereby reducing a size of the bubbles below that which would form if bubbles were introduced upstream of the constriction portion.

Advantageously the apparatus may be arranged to provide a flow of the liquid medium into the constriction portion in the form of a vortex.

This feature has the advantage of enhancing generation of microbubbles in the liquid medium by enhancing a shearing effect of the liquid on any bubbles in the liquid and on any bubbles introduced into the liquid.

Further advantageously the apparatus may be arranged to generate a flow of liquid medium into the constriction portion in the form of a vortex by injecting a flow of liquid medium into the column of the apparatus in a direction substantially tangential to an inner surface of the column. The liquid may be injected into the column at a location that is substantially at or radially inward of an inner cylindrical surface of the column thereby to generate the flow vortex.

Advantageously the apparatus may be arranged to generate microbubbles having a diameter in the range of at least one selected from amongst from around 1 micrometer to around 1000 micrometers, around 1 micrometer to around 500 micrometers, around 500 micrometers to around 1000 micrometers, and from around 100 micrometers to around 1000 micrometers.

Advantageously the apparatus may be provided with a draw tube coupled to a base of the column, the draw tube extending in a direction away from a longitudinal axis of the column thereby to draw liquid into the column from a region away from the column.

This feature allows the apparatus to draw liquid into the column from a location distal the upright portion of the column, enhancing circulation of liquid in a tank.

Advantageously the draw tube may be oriented substantially normal to the column.

Advantageously the draw tube is arranged to allow the column to draw liquid therein in a direction substantially tangential to the inner surface of the column thereby to generate vortex flow in the column.

Optionally the column and draw tube define a substantially ‘J’ or ‘L’-shaped arrangement.

Advantageously the fluid delivery device is operable to introduce a gas into the column thereby to reduce a concentration of one or more gases in the liquid.

Further advantageously the fluid delivery device is operable to introduce a gas into the column thereby to reduce a concentration of oxygen in the liquid.

The apparatus may be operable to reduce a concentration of oxygen in the liquid thereby to induce hypoxia in aquatic nuisance species.

The apparatus may be operable to introduce a gas into the column thereby to increase a concentration of one or more gases in the liquid.

The apparatus may be operable to introduce a gas into the column thereby to change an acidity of liquid, for example by increasing a concentration of one or more gases in the liquid.

It is to be understood that apparatus that is operable to increase a concentration of one or more gases in a liquid may cause a decrease in a concentration of at least one other gas in the liquid in order that equilibrium conditions are maintained. For example, if a gas rich in carbon dioxide and low in oxygen (for example having less than one selected from amongst 5%, 4%, 3%, 2%, 1%, 0.5% 0.3% oxygen) is bubbled through seawater that has equilibrated with an ambient environmental atmosphere (such as a seawater or lake environment external to a vessel) an amount of dissolved carbon dioxide in the seawater increases whilst the amount of dissolved oxygen decreases.

Advantageously the fluid delivery device may be operable to introduce carbon dioxide into the column thereby to increase a concentration of carbon dioxide in the liquid.

The apparatus may be operable to increase a concentration of carbon dioxide in the liquid thereby to induce hypercapnia in aquatic nuisance species.

Advantageously the gas comprises carbon dioxide.

The gas may consist essentially of carbon dioxide.

It is to be understood that if the apparatus is arranged to recirculate water in a ballast tank of a vessel, water initially drawn into the ballast tank from the marine environment will likely have a gas concentration corresponding to an equilibrium concentration expected for that water when in equilibrium with atmospheric air. If gas is then introduced into the column of the apparatus to recirculate the water, and the gas has a higher concentration of carbon dioxide than is normally found in air and a lower concentration of oxygen (such as gas generated by an inert gas generator as discussed below), it is to be expected that a concentration of dissolved carbon dioxide will increase and a concentration of dissolved oxygen will decrease.

Advantageously the gas may comprise a gaseous mixture comprising carbon dioxide and nitrogen.

Such a gas mixture is readily available at relatively low cost from an inert gas generator (IGG), including shipboard IGGs as noted above.

The gaseous mixture may consist substantially of carbon dioxide and nitrogen. That is, any quantity of one or more other gases may be substantially negligible.

Optionally the gas comprises a gaseous mixture of carbon dioxide, nitrogen and oxygen.

The gaseous mixture may consist substantially of carbon dioxide, nitrogen and oxygen. That is, any quantity of one or more other gases may be substantially negligible.

The gaseous mixtures may be provided by an inert gas generator, a diesel engine exhaust and/or in the form of a ship's flue gas.

It is to be understood that a standard shipboard inert gas generator such as a generator of the ‘Holec’ type typically produces a gas having a composition of approximately 2-3% Oxygen, around 12-14% carbon dioxide and a balance of nitrogen. Such oxygen levels may in some cases be too high to kill aquatic nuisance species or to prevent regrowth thereof.

Shipboard flue gas systems, which are used only for blanketing of cargoes that can tolerate contamination by soot such as crude oil, typically contain around 4.5% oxygen. Legislation requires that the oxygen content be less than 5%. It is to be understood that such oxygen levels may be too high to kill aquatic nuisance species and/or prevent regrowth thereof.

In some embodiments the gas may contain only trace oxygen, in the range from around 0.1% to around 0.3%, optionally around 0.2% oxygen, around 12-14% carbon dioxide, the balance (remainder) being nitrogen. In some embodiments a concentration of oxygen may be less than 0.1%. In some embodiments the gas may comprise around 0.2% oxygen, around 12-14% carbon dioxide, the balance (remainder) being nitrogen. In some arrangements carbon monoxide may additionally be present, optionally only a trace amount and further optionally up to around 800 ppm carbon monoxide. The gas may comprise substantially no soot. In some arrangements a small amount of soot may be present.

In a further aspect of the invention for which protection is sought there is provided a liquid storage tank comprising apparatus according to the preceding aspect.

The tank may be in the form of a substantially L-shaped tank.

Advantageously the column may be provided in a leg portion of the tank and the apparatus may have a draw tube that extends into a (lower) foot portion of the tank laterally away from the leg portion.

In a still further aspect of the invention for which protection is sought there is provided a marine vessel comprising a ballast tank provided by a tank according to the preceding aspect.

In an aspect of the invention for which protection is sought there is provided a method of circulating a liquid medium comprising:pumping the liquid medium through a column of a gas lift pump by means of gas lift whereby a flow of gaseous fluid is introduced into a lift portion of the column being a portion having a substantially continuous, unperforated wall,the method comprising the step of allowing the gas to rise in the column through the lift portion a first distance before entering a perforated portion of the column.

The method may advantageously comprise subjecting liquid rising in the column to sonic energy.

Advantageously the method may comprise generating the sonic energy by means of a whistle device, the method comprising providing gaseous fluid to the whistle device thereby to generate the sonic energy.

Further advantageously the method may comprise exhausting into the column gas that has been introduced to the whistle device thereby to cause pumping of liquid medium through the column.

DETAILED DESCRIPTION

FIG. 1(a)shows gas lift pump apparatus150according to an embodiment of the invention installed in a substantially L-shaped ballast tank195of a vessel. The apparatus150may also be referred to as ballast water treatment apparatus. The shape of the ballast tank195shown is one commonly used in vessels, in particular ocean going cargo vessels. The tank195may be considered to have a substantially upright leg portion195L and a foot portion195F projecting laterally away from the upright leg portion195L.

The pump apparatus150may also be described as liquid circulation apparatus since in the arrangement shown it is employed to recirculate liquid in the ballast tank195.

The apparatus150has an immersion member160in the form of a substantially hollow tube member or column160provided in a substantially upright orientation within the ballast tank195.

In the embodiment shown, at a lower end of the column160a bend portion161is provided that couples the lower end of the column160to a draw tube or intake tube160H that projects laterally away from a longitudinal axis of the column160along the foot portion195F of the ballast tank195. The draw tube160H has a liquid inlet162at a free end thereof in a toe region195T of the tank195distal the leg portion195L. The column160has a liquid outlet aperture165E at an upper free end thereof.

As shown inFIG. 1(a)the foot portion195F of the ballast tank195has a similar height H to a width W of the leg portion195L although other arrangements are also useful.

In the arrangement shown the column160, bend portion161and draw tube160H are mounted in a spaced apart relationship with an outer wall195W of the ballast tank195. In some embodiments the column160may be provided in another location. In some embodiments the column160may be provided at a different location within the tank195. In some embodiments at least a portion of the column160(and in some embodiments substantially the whole of the column160) may be provided external to the tank195.

The feature that the column160extends from the toe region195T of the foot portion195F to the leg portion195L, enhances recirculation of liquid in the tank195and reduces a risk of ‘dead spots’ or substantially stagnant regions becoming established in the tank195. Thus substantially all liquid within the tank195is encouraged to flow through the column160.

In the embodiment ofFIG. 1(a)it can be seen that the column160extends to an upper region of the leg portion195L may further enhance circulation of ballast water.

This has the advantage that if the column160is employed to treat liquid in the tank195, for example by exposure to a particular gas or gas mixture, a risk that liquid in one of more zones of the tank185fails to be exposed to the gas is reduced. In the absence of the draw tube160H water in the toe region195T might otherwise fail to mix with water that has been drawn through the column160and therefore have a different composition of dissolved gas to that in the leg portion195L.

In the case that the apparatus150is used for the control of aquatic nuisance species populations, by control of an amount of one or more gases dissolved in the liquid, a risk that aquatic nuisance species fail to be exposed to liquid of a prescribed dissolved gas composition may be reduced by eliminating dead spots.

In some embodiments it is desirable to expose aquatic nuisance species to liquid having reduced levels of oxygen and/or increased levels of carbon dioxide and/or one or more other gases, depending on the gas treatment procedure employed. Reduced levels of oxygen can result in death of aquatic nuisance species by hypoxia. Increased levels of carbon dioxide can result in death of aquatic nuisance species by hypercapnia. If levels of oxygen are reduced and simultaneously levels of dissolved carbon dioxide are increased, death can be induced by a combination of reduced levels of oxygen and increased levels of carbon dioxide, optionally by a combination of hypoxia and hypercapnia.

A gas injector10is arranged to inject gas into the column160at position P1. In the embodiment shown the position P1is arranged to be a position below a lowest expected level of liquid in the ballast tank195(labelled197L) at which operation of the gas lift pump apparatus150is required in use. Level197L may be referred to as a lower or lowest working level.

A supply of gaseous fluid (or gas) is provided to the injector10when required by means of a gas supply conduit160G.

In the embodiment shown, an outlet aperture165E at an upper free end160E of the column160is provided, i.e. the tubular member defining the column160is open-ended. The upper free end160E is provided below an expected upper limit of a fill level197H of the tank195although other arrangements are also useful. Such a fill level197H may be referred to as an upper working level.

A portion160P of a wall of the column160from the upper free end160E over a length L2of the column from the free end160E is perforated. In the embodiment shown the wall is provided with a plurality of apertures165W allowing water within the column160to pass out from the column160. The perforated portion160P inFIG. 1(a)may also be referred to as a perforated guide tube or guide tube portion of the column160.

The apertures165W in the perforated guide tube160P are sufficiently large to allow passage therethrough of particles or other objects such as aquatic nuisance species that might become entrained in flow of liquid through the column160. This is in order to prevent blockage of the apertures165W. In some embodiments the apertures have a diameter of around 10 cm although other sizes are also useful. In some embodiments the apertures are around 15 cm in diameter. In some embodiments the apertures are formed to occupy an area of from around 25% to around 50% of a surface area of the guide tube160P. Other arrangements are also useful.

An unperforated portion160UP of the column160of length L1is provided between the guide tube portion160P and the gas injector10. The unperforated portion160UP may be referred to as a ‘lift portion’ or ‘lift tube’160UP. The lift tube160UP enables gas injected by the injector10to establish pumping of liquid through the column160before the liquid enters the perforated guide tube160P as will be described in more detail below. In some embodiments, including that ofFIG. 1(a), substantially the whole of the column below the guide tube160P and the bend portion161and draw tube160H are formed to have a substantially continuous, unperforated wall.

It can be seen that in the embodiment shown, the perforated guide tube160P is provided at a level that is a distance L3above the lowest expected level of liquid in the tank,197L (or lower working liquid level).

The position P1of gas injector10and the length L1of the lift tube160UP are selected such that distance L3(i.e. the length by which the lift tube160UP protrudes above the lower working liquid level) does not exceed 30% of the length L1of the lift tube160UP from the gas injector10to the guide tube160P although other values are also useful. This is so as to ensure sufficient pumping action may be achieved by injection of gas through gas injector10to lift liquid in the ballast tank from the lower working liquid level197L to the bottom of the perforated guide tube160P. This allows liquid rising through the lift tube160UP to be discharged through the apertures165W in the guide tube160P facilitating liquid circulation.

FIG. 1(b)shows gas lift pump apparatus250according to a further embodiment of the invention installed in a ballast tank295of a vessel. Like features of the embodiment of FIG.1(b) to that ofFIG. 1(a)are shown with like reference signs prefixed numeral2instead of numeral1.

The ballast tank295of the embodiment ofFIG. 1(b)is substantially identical to the tank195of the embodiment ofFIG. 1(a). The apparatus250is similar to the apparatus150ofFIG. 1(a)except that gas injector10is installed at a lower end of column260and not a location at or near a midpoint of the column with respect to a vertical height of the column. A lift tube portion260UP of the column260is of a similar length (L1) to the lift tube portion160UP of the embodiment ofFIG. 1(a). Because the injector10is located at the base of the column260(immediately above a bend portion261) a perforated guide tube portion260P of the column260is longer than that of the embodiment ofFIG. 1(a). However it can be seen that an overall length of the column260, bend portion261and draw tube260H is substantially the same as the embodiment ofFIG. 1(a).

It can be seen fromFIG. 1(b)that because the injector10is located at a lower position of the column260and the (perforated) guide tube portion260UP extends further down the column260, the gas lift pump apparatus250is able to maintain circulation of liquid in the tank295over a wider range of depths of liquid in the tank295. This range may be referred to as a ‘working range’ of the apparatus.

FIG. 1(c)shows the gas lift pump apparatus250of the embodiment ofFIG. 1(b)installed in a rectangular ballast tank295R of a vessel. It is to be understood that operation of the apparatus250is similar to that of the embodiment ofFIG. 1(b).

FIG. 2shows a fluid delivery device100according to an embodiment of the invention operable to generate sonic energy in the form of sonic waves by means of a flow of gas through the device100in the manner of a whistle. The device100is also operable to inject gas that has passed through the device100into liquid in the column of gas lift pump apparatus.

In some embodiments the device100may replace the injector10of the embodiments ofFIG. 1(a) to (c). In some embodiments the device100is arranged to generate sonic energy that is transmitted or launched into liquid flowing through the column of gas lift apparatus but to vent gas flowing therethrough to an alternative location (such as to a gas storage tank, a gas recirculation line or to atmosphere). The device100may be arranged to direct the sonic energy into liquid flowing through the column of the gas lift pump apparatus.

The device100has a chamber110forming a body portion of the device100and a fluid nozzle120arranged to supply a flow of gaseous fluid into the chamber110through an outlet aperture121of the nozzle120. In some embodiments the device100is operated to provide a flow of gas (such as air, nitrogen or other gas such as any suitable inert gas or gas mixture) out from the nozzle120at a supersonic velocity such as a speed of around 340 ms−1or greater. Other velocities are also useful including subsonic velocities.

In the embodiment shown the nozzle120is arranged to provide the flow of gaseous fluid into the chamber110in a direction towards a first end111of the chamber110being a closed end. The nozzle120has a substantially frusto-conical external and internal profile. An angle of taper of an inner frusto-conical surface of the nozzle120with respect to a cylinder axis thereof is less than that of the external frusto-conical surface although other arrangements are also useful.

At a second end112opposite the first end111the chamber110has openings141,142arranged to allow gaseous fluid to flow out from the chamber110.

In the embodiment ofFIG. 2a receptor member130is provided in the chamber110. The receptor member130is in the form of a cupped member having walls131defining an open cavity137, an opening135of the receptor member130facing in a direction towards the nozzle120.

The device100is arranged wherein gaseous fluid entering the chamber110is directed to flow towards the opening135of the receptor member130.

The flow of gaseous fluid through the nozzle120is arranged to occur at a substantially constant rate and pressure. As the gaseous fluid exits the nozzle120the fluid expands generating a forward pressure wave (being a shockwave) travelling in a forward direction towards the receptor member130.

A portion of the forward pressure wave impinges on the receptor member130. A pressure of fluid in the receptor member130thereby increases and a reverse pressure wave (being a shockwave) is generated, travelling in a reverse direction to the forward pressure wave. The reverse pressure wave may also be referred to as a ‘reflected’ pressure wave or shockwave.

The reverse pressure wave meets the forward pressure wave thus providing a ‘feedback’ mechanism to the propagation of the forward wave. Interaction of the forward and reverse waves as gaseous fluid exits the receptor member130may be arranged to result in the generation of sonic energy. In some arrangements ultrasonic energy may be produced. The sonic energy (which may be or include ultrasonic energy) propagates out from the chamber110into liquid102that is in contact with the chamber110. The sonic energy propagates into the liquid102in the form of longitudinal pressure waves that propagate through the liquid102away from the chamber110.

In the embodiment ofFIG. 2gas trapped in the receptor member130resonates at a resonant frequency as gas is directed towards the receptor member130by the nozzle120. It is to be understood that in some arrangements the chamber110may therefore be referred to as a resonance chamber110since resonance of gaseous fluid may take place therein. It is to be understood that the chamber110may not itself resonate, i.e. the chamber110may not vibrate at a resonant frequency of the chamber110. However gas trapped within the receptor member130may resonate at a frequency determined inter alia by a depth D of the cavity137defined by the receptor member130.

Gaseous fluid entering the chamber110is arranged to exit the chamber110through a plurality of outlet conduits141,142. In the embodiment ofFIG. 2, fluid exiting the chamber110flows over an outer surface of the nozzle120in a direction that is substantially the reverse of the direction in which fluid enters the chamber110through the nozzle120.

In the embodiment shown the device100is arranged to be immersed in a liquid medium thereby to launch the sonic energy into the liquid medium.

As noted above, the frequency of sonic energy generated by the device100may depend on a depth D of the cavity137defined by the receptor member130. In some embodiments the depth D may be increased or decreased thereby to tune operation of the apparatus. Adjustment of the depth D or distance of the receptor member130from the nozzle120may be required depending on an expected operating condition of the apparatus, such as temperature, pressure and/or one or more other operating conditions or parameters. Adjustment may also be required to accommodate tolerances in manufacture and/or assembly.

In the embodiment shown the position of the receptor member130is fixed. In some embodiments the distance between the receptor member130and the outlet aperture121of the nozzle120may be changed, for example by means of a screw mechanism. Adjustment of the position of the receptor member130is useful for example in compensating for machining tolerances associated with manufacture and tolerances associated with assembly of the device100. Other arrangements are also useful such as other means for adjusting a depth D of the receptor member130.

It is to be understood that the selection of a resonant frequency of the device100, i.e. a frequency of sonic energy generated by the device100, may be important in applications where killing of aquatic nuisance species is desirable, such as bacterial species. This is because some bacteria may be more susceptible to death when exposed to sonic waves such as ultrasonic waves of a prescribed frequency or range of frequencies compared with sonic waves of one or more other frequencies.

In some embodiments a plurality of devices100may be provided each arranged to generate sonic energy of substantially different frequencies or ranges of frequencies in order to enhance an efficiency of a liquid treatment apparatus in killing ANS.

FIG. 3shows a fluid delivery device200according to a further embodiment of the invention. Like features of the device200ofFIG. 3to those of the device100ofFIG. 2are provided with similar reference numerals prefixed numeral2instead of numeral1.

The device200has a chamber210into which a nozzle220is arranged to provide a flow of gaseous fluid. A receptor member230is provided in a wall of the chamber210and positioned in a direct line of sight of gaseous fluid entering the chamber210through the nozzle220.

As in the embodiment ofFIG. 2the receptor member230is in the form of a cupped member. An external portion of the cupped member is arranged to be in direct contact with an environment external to the device200.

In use, impingement on the receptor member230of gaseous fluid flowing into the resonance chamber210causes the generation of sonic energy as described with respect to the embodiment ofFIG. 2and the launching of sonic energy in the form of longitudinal sonic pressure waves into a liquid medium202in acoustic communication with the chamber210. The device200is thereby operable to kill certain ANS such as certain bacterial ANS. The device200may be arranged to launch ultrasonic energy (ultrasonic pressure waves) into the liquid medium202.

Furthermore, impingement of gaseous fluid on the receptor member230is arranged to cause heating of the receptor member230. Under certain conditions the temperature of the receptor member230may rise from an ambient temperature to a temperature injurious to ANS. It is to be understood that, advantageously, liquid in which the device200is immersed may flow in contact with an external surface of the receptor member230resulting in heating of the liquid. This may further contribute to death of bacteria or other ANS present in the liquid.

In some applications a fluid delivery device100,200according to an embodiment of the invention is provided in gas lift pump apparatus arranged to cause recirculation of liquid in a ballast tank of a marine vessel. Thus one or more of the devices100,200may be provided in addition to or instead of the injector10of the embodiments ofFIG. 1. One or more of the devices100,200may be provided at the same location as the injector10(for example when provided in place of the injector10) or at one or more different locations of the column160,260.

FIG. 4shows ballast water treatment apparatus450according to a further embodiment of the invention in which more than one column460is provided, each column460being in the form of a tube member460. In the embodiment ofFIG. 4three tube members460A,460B,460C are provided. It is to be understood that any suitable number of tube members may be provided.

In the embodiment shown each tube member460A,460B,460C has a single gas injector10A,10B,10C respectively coupled thereto through which gas may be forced into an inner volume465A,465B,465C of the respective tube member460A,460B,460C. Gas is supplied to each injector10A,10B,10C by a respective gas supply conduit480A,480B,480C.

A valve462A,462B,462C such as a check valve is provided in each respective conduit480A,480B,480C upstream of each injector10A,10B,10C in order to allow a flow of gas through each injector10A,10B,10C to be controlled by means of a controller450C. The valves462A,462B,462C may be positioned in the respective conduits at a location outside of the ballast tank495or inside the tank495and may optionally be pneumatically actuated, for example by means of an air supply. In some embodiments the valves are not provided in the conduits, but rather at a gas source or in a gas supply line feeding gas to respective conduits480A,480B,480C from a gas source.

Each tube member460A,460B,460C has a liquid level sensor471A,471B,471C, respectively, provided above the corresponding injector10A,10B,10C arranged to provide a signal to the controller450C when a level of liquid in the tank495reaches that of the respective sensor471A,471B,471C. Once a level of liquid in the ballast tank495reaches or exceeds a level of a given liquid level sensor471A,471B,471C, the controller450C allows gaseous fluid to pass into the corresponding tube member460A,460B,460C associated with that level sensor471A,471B,471C through the corresponding injector10A,10B,10C.

If gaseous fluid is being supplied to any other tube member460A,460B,460C when a further liquid level sensor471A,471B,471C is actuated, supply of gaseous fluid to the other tube member460A,460B,460C may be terminated although other arrangements are also useful. For example, a liquid level range over which one injector is arranged to perform gas delivery into its corresponding tube member may be arranged to overlap a liquid level range over which another injector is arranged to perform gas delivery into its corresponding tube member.

It is to be understood that the sonic energy generating fluid delivery devices ofFIG. 2orFIG. 3may be used in the apparatus450ofFIG. 4. Other fluid delivery devices according to embodiments of the invention are also useful such as that ofFIG. 6as described below.

In a similar manner to the column160of the embodiment ofFIG. 1(a)each of the tube members460A,460B,460C has a respective unperforated lift portion (or lift tube portion)460AUP,460BUP,460CUP into which a respective injector10A,10B,10C injects gas. Directly above each unperforated lift portion is a perforated guide tube portion460AP,460BP,460CP.

In some embodiments, instead of each tube member being provided with a level sensor, a separate level sensor may be provided, for example a sensor mounted to a sidewall of the tank. Controller450C may be arranged to receive a liquid level signal from an external source such as a separate ballast water system controller for controlling loading and unloading of ballast water.

FIG. 5shows apparatus550according to an embodiment of the invention in which an upright column560in the form of a tube member560is provided within a ballast tank595of a vessel. A fluid delivery device in the form of a gas injector510is provided for injecting gas into liquid in the column560. In the embodiment shown the gas injector510is provided at a free end of a hose580arranged to be wound on a drum585. The gas injector510may be raised or lowered within the column560by rotation of the drum585under the control of a controller550C.

The column560has an unperforated portion560UP of length LUP from a lower end thereof and a perforated portion560P of length LP along a remainder of the length to an upper end thereof. The unperforated portion may be referred to as a column lift tube portion560UP whilst the perforated portion may be referred to as a guide tube portion560P as described above with respect to the embodiments ofFIG. 1andFIG. 4.

A lift tube member580LT in the form of an unperforated tube is coupled to the hose580and positioned substantially coaxial therewith. The lift tube member580LT is arranged to be raised and lowered with the gas injector510. The gas injector510is operable to inject gas carried by the hose580into liquid in the column560at a lower end of the lift tube member580LT. The lift tube member580LT has a sufficiently large diameter to allow gas injected into the column560by the gas injector510to rise within the lift tube member580LT and induce pumping of gas in the column560by gas lift.

FIG. 5shows the lift tube member580LT substantially at a highest allowable position within the column560when the level of liquid in the tank595corresponds to that of the highest (upper) working level597H.

It is to be understood that the apparatus550is operable to position the gas injector510a suitable distance below a level of liquid in the tank595to allow effective circulation of liquid in the tank595.

In some embodiments a fluid level monitoring device S is provided that is arranged to determine the level of liquid in the tank595. The apparatus550is operable to determine a required vertical position of the gas injector510responsive to the level of liquid in the tank595as determined by reference to the monitoring device S.

The apparatus550has a ‘working range’ of liquid in the tank595being a range of liquid levels over which pumping of liquid by the apparatus550may be conducted. The range is defined by a lower working level597L and the upper working level597H. With the level of liquid in the tank595substantially at the upper working level597H and the lift tube member580LT at the position shown inFIG. 5, injection of gas through injector510causes liquid to rise within the lift tube member580LT and to emerge from the lift tube member580LT at the upper end thereof, substantially at the free surface of liquid in the ballast tank595. It is to be understood that in the absence of the lift tube member580LT, gas injected into the (perforated portion of the) column would fail to cause effective pumping of liquid through the column160. The presence of the lift tube member580LT promotes pumping of liquid through the column160and therefore effective circulation of liquid in the tank595.

It is to be further understood that if the lift tube member580LT is lowered within the column560, liquid and gas emerging from an upper end thereof as gas flows through the hose580rises within the guide tube portion560P of the column560towards the surface in a similar manner to the embodiments ofFIG. 1. As the lift tube member580LT is lowered, with the liquid level at the highest working level597H, the effective length of the guide tube portion560P increases. Thus for a given level of liquid in the tank595the embodiment ofFIG. 5allows the effective length of the guide tube portion560P to vary depending on the vertical location of the lift tube member580LT.

It is to be understood that if the level of liquid in the tank595falls below the upper working level595H the lift tube member580LT may be lowered. In some arrangements the lift tube member580LT may be lowered such that an upper end thereof is at or below the liquid level thereby to allow expulsion of pumped liquid from the upper end of the lift tube member580LT.

In some embodiments, instead of having a fluid level monitoring device S, the apparatus550may be arranged to determine a level at which gaseous fluid is to be supplied to the gas injector510by positioning the injector510at a vertical location within the column560at which a flow rate of gas through the hose580is within a prescribed range. In some embodiments the apparatus550may be arranged to position the injector510at a vertical location at which a head of pressure at the injector510is within a prescribed range.

Other arrangements are also useful.

In some embodiments the injector510has a plurality of gas outlet apertures or outlet nozzles through which gas may flow out from the injector510. In some embodiments the nozzles may be arranged to direct gas out from the injector510in a radial direction at circumferentially spaced positions.

FIG. 6shows a fluid delivery device600according to a further embodiment of the invention. Like features of the device600ofFIG. 6to that of the embodiment ofFIG. 3are shown with like reference signs prefixed numeral6instead of numeral2. The device600is operable in a similar manner to the embodiments ofFIG. 2andFIG. 3to generate sonic energy when gas is forced through the device600as described below. The device600is provided in a housing601arranged to be provided in a flowpath of fluid in a column of a gas lift pump apparatus.

Accordingly the device600has an upstream portion601A and a downstream portion601B as defined with respect to a direction in which fluid flow through the column is expected to occur during a pumping operation (normally an upward direction).

The downstream portion601B of the housing601is tapered to reduce an amount of drag on a liquid flowing past the device600as it is pumped by the ejection of gas through the outlets641,642.

The upstream portion601A of the device600has a nozzle620, a chamber610and gaseous fluid outlets641,642. The device600is operable to inject gas under pressure through the nozzle620and into a receptor member630. The receptor member630is coupled to an upstream portion of a wall of the chamber610and protrudes therethrough. In the embodiment ofFIG. 6the receptor member630projects upstream of the chamber610. This promotes exposure of liquid flowing past the device600to the outer surface of the receptor member630. Flow of gas from the nozzle620into the receptor member630results in the generation of sonic energy that may be transmitted (or launched) into a liquid medium in which the device600may be immersed.

In some embodiments such as that ofFIG. 6the receptor member630is arranged to be heated by the flow of gaseous fluid through the device600whereby certain ANS may be killed. Thus some of the kinetic energy associated with the flow of gas into the chamber610from the nozzle620may be dissipated by the receptor member630in the form of heat.

FIG. 7shows a fluid delivery device700according to a further embodiment of the invention. The device700has a fluid nozzle720and a receptor member730. The receptor member730has a cupped shape as in the case of the embodiments described above and defines a cavity735. The nozzle member720is arranged to direct a flow of gaseous fluid into the cavity735.

The receptor member730is coupled to a fluid conduit or pipe760through which liquid may be arranged to flow. In use, gaseous fluid is forced through the nozzle720and towards the cavity735of the receptor member730. A forward travelling sonic shockwave is generated when the rate of flow of gaseous fluid through the nozzle720is sufficiently high as described above and a backward travelling shockwave is generated as gas from the nozzle720is deflected out from the receptor member730. The device700is arranged such that the sound energy generated by the flow of gaseous fluid from the nozzle720is launched into the liquid flowing through the pipe760. In the embodiment shown the pipe may760provide at least a portion of a column of a gas lift pump apparatus.

Furthermore, in the embodiment shown the flow of gaseous fluid through the device700is arranged such that gaseous fluid emanating from the nozzle720ultimately flows into the pipe760thereby causing pumping of fluid in the pipe760by gas lift. To this end, apertures741,742are provided in a wall of the pipe760to allow gaseous fluid to flow into the pipe760. In some alternative embodiments the gas is not arranged to pass into the conduit760, but may be recycled through the nozzle720or vented to atmosphere. Other arrangements are also useful.

It is to be understood that, alternatively or in addition, gaseous fluid may be introduced into the pipe760by alternative means, such as a conventional gaseous fluid injector not being arranged to generate sonic energy.

It is to be understood that a position of the receptor member730and nozzle720with respect to a length of the pipe760may be important in some embodiments in order to enable or enhance the launching of the sonic energy into the pipe760.

It is to be understood that in some embodiments the Poisson effect may be exploited in order more efficiently to couple sonic energy into liquid in the conduit760. This may be accomplished by clamping the conduit760rigidly at positions of the conduit760that are at distances from the device700corresponding to odd multiples of one quarter of the wavelength of the sonic energy generated by the device700. Other arrangements are also useful.

It is to be understood that the length and diameter of the conduit760, the dimensions of the nozzle and receptor member configuration and the flow rate of fluid through the nozzle may be arranged to generate a desired frequency of sonic energy to optimise killing of ANS.

It is to be understood that multiple devices700may be provided at locations along a given conduit760or around a conduit760. Multiple gas vents allowing gas to flow into the conduit760may be provided around the conduit760in some arrangements.

Furthermore, in some embodiments of the invention the gaseous fluid delivered by the fluid delivery device is arranged to reduce survival of ANS and/or kill ANS. By the term ‘reduce survival’ is meant that ANS may be rendered more likely to die, either by hypercapnia, hypoxia, a combination of both, or by a further survival reducing process.

It is to be understood that in order to reduce the concentration of a given gas component in a liquid, a partial pressure of that gas component in gas that is in contact with the liquid (for example by being bubbled through the liquid) must be such that the partial pressure of the gas component in the liquid is higher than the partial pressure of the gas component in the gas. This pressure difference forces gas molecules through the liquid/gas interface into the gas bubble.

Thus if a gas having a lower oxygen content than the liquid is bubbled through the liquid (for example substantially zero oxygen), a concentration of oxygen in the liquid will be reduced. If a gas having a higher carbon dioxide content than the liquid is bubbled through the liquid, a concentration of carbon dioxide in the liquid may increase. Suitable gases for increasing carbon dioxide concentration and reducing oxygen concentration (relative to an equilibrium concentration of carbon dioxide and oxygen in the liquid when in contact with air) include combustion gases, for example ships flue gases or gas generated by an inert gas generator, for example of the Holec type.

FIG. 8is a schematic cross-sectional illustration of the fluid delivery device ofFIG. 2fitted with an amplification chamber290. The chamber290has a substantially frusto-conical body portion291having a flexible membrane293arranged to define a wall of the amplification chamber290at a basal (wider) end of the body portion291.

At an opposite end of the amplification chamber290the chamber290is coupled to the device200such that an external surface of the receptor member230forms a portion of an apical wall of the chamber290. Thus, the device200is arranged to direct sonic energy directly into the amplification chamber290. It is advantageous to minimise any restriction to flow of gas into the chamber290. In the embodiment shown the receptor member230is supported by an open frame structure210that allows gas emerging from the nozzle220or receptor member230to flow into the amplification chamber290.

In the embodiment ofFIG. 8the amplification chamber290is shown having a substantially frusto-conical shape. It is to be understood that other shapes are also useful, for example a logarithmic increase in cross-sectional area as a function of distance from the nozzle220/receptor230. A wall profile of the chamber290may follow a logarithmic curve. In use the chamber290enables an increase in the amplitude of sonic energy launched into liquid202in which the device200and chamber290are immersed. In some embodiments this is at least in part because the amplification chamber290is arranged to reduce a mismatch in impedance between the device200and the liquid202thereby more efficiently to communicate energy from the device200to the liquid202.

The amplification chamber290of the embodiment shown is formed from a metallic material. It is to be understood that other materials are also useful including plastics materials.

FIG. 9is a schematic illustration of a fluid delivery device600according to the embodiment ofFIG. 6fitted with an amplification chamber690similar to that of the embodiment ofFIG. 8.

The chamber690is fitted to the device600so as to enclose the receptor member630such that the receptor member630provides a portion of a wall of the chamber690. Thus the device600is arranged to direct sonic waves directly into the chamber690which in turn directs the waves into the surrounding liquid medium602.

In use the amplification chamber690is oriented substantially normal to a flow direction of liquid pumped. Gas emerging from outlets641,642therefore rises out of the plane of the figure, in use.

FIG. 10is a schematic illustration of gas lift pump apparatus750according to a further embodiment of the invention. Like features of the embodiment ofFIG. 10to those of the embodiment ofFIG. 1are shown with like reference signs prefixed numeral7instead of numeral1.

The apparatus750has a column760in the form of a substantially hollow tube member provided in a substantially upright orientation within a ballast tank (not shown).

In the embodiment shown, at a lower end of the column760a bend portion761is provided that couples the lower end of the column760to a draw tube or intake tube760H that projects laterally away from a longitudinal axis of the column760. The draw tube760H has a liquid inlet762at a free end thereof. The column760has a liquid outlet aperture765E at an upper free end thereof. It is to be understood that the draw tube760H may be considered to be part of the column760, and therefore the column may be described as a substantially L-shaped liquid column760similar to that of the apparatus550ofFIG. 5.

A fluid delivery device600of the type shown inFIG. 6is provided in the column720and oriented as shown, with receptor member630provided at an upstream end of the device600.

The apparatus750has a microbubble generator770upstream of the fluid delivery device600. In the embodiment ofFIG. 10the microbubble generator770is positioned below the fluid delivery device600.

The generator770has a venturi portion771having the shape of a conventional venturi device. In the embodiment ofFIG. 11the venturi portion771is arranged such that liquid flowing through the column760is forced to flow through the venturi portion771. The venturi portion has a converging portion C arranged to direct the liquid through a throat portion T and subsequently through a diverging portion D in the conventional manner.

A liquid injector775is arranged to inject a flow of liquid L2into the column760upstream of the venturi portion771. A cross-sectional view of the column760at position X-X is shown inFIG. 11.

It can be seen that the liquid injector775is configured to inject liquid L2into the column760in a direction substantially tangential to an inner surface760S of the column760such that the liquid L2has a component of velocity in a tangential direction within the column760. This causes liquid flowing up through the column760to swirl in substantially one direction.

It is to be understood that the fluid will also have a component of velocity in an axial direction along the column760as it moves up through the column760. Thus, the injector775is arranged to promote the establishment of a flow vortex within the column760.

A gas injector778is arranged to inject a flow of gas778F into the column760upstream of the venturi portion771. In the embodiment shown the gas injector778is arranged to inject the gas at a position downstream of the liquid injector775. As the gas rises it causes liquid to be drawn into the draw tube760H at a free end thereof distal the substantially vertical column760. The liquid is drawn through the draw tube760H and up through the column760.

The apparatus750is arranged such that as liquid from the liquid injector775and gas from the gas injector778enter the venturi portion771microbubbles are generated. The microbubbles act as sites to which bacterial ANS within the liquid may become attached.

A probability of death of bacterial ANS by sonic energy produced by the fluid delivery device600is increased by the formation of the microbubbles. This is at least in part because the sonic energy can cause violent rupture of the microbubbles causing generation of shockwaves such as ultrasonic shockwaves thereby causing damage and death to bacterial ANS trapped by a microbubble.

In some embodiments the column760has a diameter of around 8 inches (around 20 cm) and the liquid injector775has a diameter of around 2 inches (around 5 cm).

In some embodiments the fluid delivery device600may be supplied with a gas flow rate of around 50 normal m3/h at a pressure of around 3.5-4.0 bar gauge (350-400 kPa).

Other values of one or more dimensions and/or one or more operating parameters are also useful in some embodiments.

It is to be understood that some embodiments of the invention employing a microbubble generator770are operable more efficiently to destroy bacterial ANS. Furthermore, some embodiments of the invention employing an amplification chamber690are also operable more efficiently to destroy bacterial ANS.

FIG. 12is a schematic illustration of gas lift pump apparatus850according to a further embodiment of the invention. Like features of the apparatus ofFIG. 12to those of the apparatus ofFIG. 10are labelled with identical reference signs or like reference signs prefixed numeral8instead of numeral7.

The apparatus850is similar to that ofFIG. 10except that liquid can only enter the column860by means of the draw tube860H, i.e. no liquid injector775fed by a pressurised liquid source is provided in addition to the draw tube860H.

In the embodiment ofFIG. 12, liquid passing through the draw tube860H is arranged to enter the column860in a direction tangential to a wall of the column860thereby to induce swirl in liquid rising through the column860.

In the embodiments ofFIG. 10andFIG. 12all liquid flowing up the columns780,860from below the venturi portions771,871flows through the venturi portions771,871. In some embodiments some liquid is able to bypass the venturi portion (see for example the embodiment ofFIG. 15described below).

FIG. 13(a)is a perspective view of a microbubble generator970suitable for use with embodiments of the present invention.

The generator970has a body portion970B having a liquid inlet975and a gas injector978at one end, arranged to allow liquid and gas, respectively, to enter an internal fluid conduit973of the generator970. The conduit973is substantially circular in cross-section, the liquid inlet975being arranged to allow liquid into the conduit973along a direction substantially tangential to an inner wall of the conduit973as viewed along a longitudinal axis of the conduit973similar to the arrangement ofFIG. 11. This is so as to promote establishment of a liquid flow vortex as the liquid passes along the conduit973towards a venturi portion971. Establishment of the flow vortex may promote shearing of the gas and liquid and therefore shearing of bubbles entrained in the liquid, promoting formation of microbubbles.

The generator970is operable to generate microbubbles in the liquid as the liquid and gas pass through the venturi portion971. Thus a flow of liquid having microbubbles entrained therein may be provided from a fluid outlet972of the generator970.

It is to be understood that the generator970and a fluid delivery device according to an embodiment of the invention (see for example the devices ofFIGS. 2, 3 and 6 to 9) may be employed either in gas lift pump apparatus or separately in a ballast tank, a fluid conduit or any other suitable location.

In some embodiments the fluid outlet972faces in a vertically upwards direction and is arranged to direct microbubbles towards a fluid delivery device configured to launch sonic waves into liquid flowing through the column of a gas lift pump apparatus such as a gas lift pump apparatus similar to that ofFIG. 12. It is to be understood that the generator970may be arranged to form part of the column of gas lift apparatus in a similar manner to which the generator870of the embodiment ofFIG. 12forms part of the column. The liquid inlet975may be coupled to a draw tube in a similar manner to the apparatus ofFIG. 12. In some embodiments the liquid inlet975may be substantially the only liquid through which liquid enters a lower end of the column.

FIG. 14shows an embodiment of the invention in which a fluid delivery device600is provided in a column960of a gas lift pump apparatus950. Like features of the apparatus ofFIG. 14to those of the apparatus ofFIG. 10are labelled with identical reference signs or like reference signs prefixed numeral9instead of numeral7.

A microbubble generator970similar to that described above and illustrated inFIG. 13is mounted within the column960of the apparatus950.

The generator970is operable to inject a flow of liquid L2in which microbubbles are entrained into the column960via outlet972and towards the fluid delivery device600. It is to be understood that the apparatus950is also operable to pump liquid L1through the column from a draw tube960H by gas lift, by means of gas injected into the column via the fluid delivery device600, as well as by a pressure of liquid injected into the column960via liquid injector975.

It is to be understood that injection of gas into the column960in the form of microbubbles by means of gas injector978may also assist in pumping liquid L1through the column960by gas lift. Gas bubbles are formed within the generator970in liquid injected by injector975as gas is injected by injector978. A size of the bubbles is reduced by shear forces experienced as the liquid flows through the venturi (or choke) portion971, whereby microbubbles are formed.

It is to be understood that other arrangements are also useful in which a microbubble generator970provides a flow of entrained microbubbles to a fluid delivery device600. Embodiments of the invention are operable to kill bacterial ANS as well as non-bacterial ANS.

In the embodiment ofFIG. 14the generator970is shown positioned in the flowstream of liquid L1from the draw tube960H. The generator970may alternatively be provided at a base of a column960having a closed lower end, such as the end860L of the column860of the embodiment ofFIG. 12.

FIG. 15is a schematic illustration of gas lift pump apparatus1050according to a further embodiment of the invention. Like features of the apparatus ofFIG. 15to those of the apparatus ofFIG. 14are labelled with like reference signs prefixed numerals10instead of numeral9.

The apparatus1050ofFIG. 15is similar to that ofFIG. 14in that it has a substantially L-shaped gas lift column1060having a fluid delivery device600provided therein. It is to be understood that apparatus according to embodiments of the invention may have any number of fluid delivery devices600provided therein.

The apparatus1050has a microbubble generator1070provided upstream of the fluid delivery device600and within the column1060. The generator1070is similar to that of the embodiment ofFIG. 14except that the generator1070does not have a liquid injector975. Instead, an upstream end of the generator1070is arranged to receive a flow of liquid L1entering the column1060through draw tube1060H. In the embodiment shown the upstream end of the generator1070is also the lowermost end thereof. It can be seen that a portion of the liquid L1entering the column1060from the draw tube1060H flows around an outside of the generator1070. However a portion of the liquid flows through the generator1070. In some embodiments substantially all of the liquid L1flows through the generator1070.

A flow of gas1078F is provided through the generator1070by means of a gas injector1078. The generator1070is arranged such that as liquid L1flows therethrough microbubbles are formed in the liquid L1.

In the embodiment shown the column1060is arranged to introduce swirl into the liquid L1once it has entered the column1060from the draw tube1060H. Swirl may be useful in encouraging the formation of microbubbles in the flow of liquid L1through the generator1070as discussed above. Swirl is developed by introducing the liquid into the column1060in a direction tangential to an interior of a sidewall of the column1060in a similar manner to that described above.

In some alternative embodiments the generator1070is arranged to introduce swirl in liquid entering the generator1070. For example, flow deflectors may be provided around the injector1078or other portion of the generator1070such as an inner wall of the generator1070to induce swirl in liquid L1entering the generator1070.

FIG. 16shows a fluid delivery device1200according to a further embodiment of the invention. The device has a chamber1210in the shape of a horn, the chamber1210being coupled to a gas supply head1215. The supply head1215has a gas inlet12151N arranged to be coupled to a gas supply line G shown in dashed outline.

The head1215is arranged to deliver a flow of gas to a whistle portion1200W within the chamber1210. The whistle portion1200W has a nozzle member1220and a whistle body1225coupled to the nozzle member1220. The whistle body1225is arranged to support a receptor member1230in a substantially fixed spaced apart and substantially coaxial relationship with the nozzle member1220. The whistle body1225is in the form of a substantially open frame structure thereby to reduce an amount of sound energy absorbed thereby when the whistle member is in use.

The nozzle member1220is arranged to direct a flow of gaseous fluid through an opening1235of the receptor member1230into an open cavity1237defined by the receptor member1230. The receptor member1230is arranged to be screwed into a tapped aperture in the whistle body1225thereby to couple the receptor member1230to the whistle body1225.

A distance between the opening1235of the receptor member1230and nozzle1220may therefore be adjusted by means of the screw thread by rotation of the receptor member1230.

In some arrangements a depth D of the cavity defined by the receptor member1230may be adjusted. In some arrangements the adjustment is by means of a further screw adjustment, for example by adjusting a position of a screw defining at one end an interior basal surface of the cavity. This feature has the advantage that an amount of sound energy produced by the device1200may be optimised. A frequency of sound energy (i.e. a frequency of sound waves generated by the device1200) may also be adjusted.

As noted above the chamber1210is in the shape of a horn. A cross-sectional area of the chamber1210increases as a function of distance from the nozzle member1220in a direction away from the gas supply head1215. The cross-sectional area increases to a maximum size (corresponding to a position of maximum diameter of the chamber1210) and merges with a portion of the chamber1210having substantially constant cross-sectional area as a function of distance from the nozzle member1220. A diaphragm or membrane1293is provided at the end of the horn-shaped chamber1210and provides a wall of the chamber1210to communicate sound energy into liquid surrounding the chamber1210.

The device1200is provided with a gas outlet conduit1241through which gas that has been injected into the chamber1210may be vented, as shown by arrows F.

In some embodiments including the embodiment shown inFIG. 16the gas is vented into the column of gas lift pump apparatus in which the device1200is installed. In some embodiments the gas is vented to an alternative location such as to atmosphere. A volume1295of gas within the chamber1210is arranged to couple sonic energy in the form of sonic waves generated by the whistle portion1200W into liquid1202external to the device1200by means of the diaphragm1293as well as by transmission of sonic energy through the wall of the remainder of the chamber1210.

FIG. 17shows a fluid delivery device1300according to a further embodiment of the present invention. The device1300is relatively simple in construction, not having an amplification chamber having a membrane for communicating sonic energy into liquid external to the device1300. Rather, the device1300has a chamber1310formed substantially entirely from stainless steel although other materials are also useful.

FIG. 17 (a)is a side view of the device1300whilstFIG. 17(b)is a cross-sectional view along the same viewing direction asFIG. 17(a).

The device has a chamber1310that also provides a whistle body1325. A nozzle member1320and a receptor member1330are coupled to the whistle body1325in a similar manner to the embodiment ofFIG. 16described above.

The whistle body1325provides a substantially tubular sleeve coaxial with the nozzle member1320and receptor member1330. In contrast, in the embodiment ofFIG. 16the whistle body1225is in the form of a substantially open frame within a larger chamber1210rather than in the form of a sleeve. The open frame arrangement may reduce absorption of sound energy by the whistle body1225as described above.

The receptor member1330is arranged to close one end of the chamber1310. Apertures1341are formed in a wall of the chamber1310to allow gas that flows into the device1300from the nozzle1320to flow out from the device1300.

FIG. 18shows a portion of a column1360of gas lift pump apparatus according to an embodiment of the invention in (a) side view and (b) plan view. The column1360has two gas inlets GA, GB each arranged to deliver a flow of gas into a corresponding gas conduit1305A,1305B projecting into the column1360normal to a cylinder axis thereof.

Each conduit1305A,1305B has four gas delivery devices1300T-connected thereto and projecting upwardly, and four gas delivery devices T-connected thereto and projecting downwardly.

In the embodiment ofFIG. 18, for each conduit1305A,1305B the devices1300projecting upwardly are each paired with a corresponding device1300projecting downwardly such that paired devices are substantially coaxial with one another. Their common axes are substantially parallel to a cylinder axis of the column1360. This feature has the advantage that drag induced on a flow of fluid through the column1360may be reduced since a projected area of the sixteen devices1300in a plane normal to the cylinder axis of the column1360is reduced relative to non-coaxial positioning of the devices1300.

As described above, in the arrangement shown inFIG. 18the column1360is provided with sixteen fluid delivery devices1300. It is to be understood that a larger or smaller number of devices1300may be employed in some embodiments.

FIG. 19shows a fluid delivery device1400according to an embodiment of the invention similar to that shown inFIG. 16. Like features of the embodiment ofFIG. 19to that of the embodiment ofFIG. 16are shown with like reference signs prefixed numerals14instead of numerals12.

In the embodiment ofFIG. 19a receptor member1430is coupled directly to a diaphragm1493and is arranged to be movable therewith. It is to be understood that a distance between a nozzle member1420and receptor member1430may vary as the diaphragm1493vibrates. However if the diaphragm1493is arranged to vibrate at certain prescribed frequencies, at which the location of the receptor member1430defines a node, movement of the receptor member1430will be substantially reduced. In the configuration shown inFIG. 21the diaphragm1493is shown vibrating at such a frequency, the receptor member1430remaining substantially stationary as the diaphragm1493vibrates. Instantaneous positions of the diaphragm1493at opposite extrema of deflection thereof during operation of the device at a particular frequency are shown in dashed outline inFIG. 19.

FIG. 20shows a microbubble generator1370according to a further embodiment of the present invention. The generator1370is shown installed in a section of the column1360of the gas lift pump apparatus ofFIG. 18upstream of the fluid delivery devices1300. The generator1370is arranged to deliver a flow of microbubbles to the devices1300. It is to be understood that in some arrangements the generator1370may be arranged to inject microbubbles from an outlet1370OUT thereof into the column1360such that microbubbles are directed into a flowstream of liquid through the pump apparatus.

The generator1370has a liquid inlet1370IN and liquid outlet1370OUT at opposed ends thereof. Liquid passing through the inlet1370IN passes through a choke portion1371having a converging portion C, a throat portion T and a diverging portion D. It is to be understood that an angle of convergence and an angle of divergence of the converging and diverging portions C, D respectively may be selected so as to optimise performance of the generator1370. Steeper angles of divergence of the diverging portion D may result in the inducement of greater turbulence in liquid passing through the diverging portion D. In the embodiment shown an included angle of divergence6of the diverging portion with respect to a cylinder axis A of the column1360is in the range from around 150° to around 160°. Other angles are also useful.

In the embodiment ofFIG. 20the generator1370has four gas injectors1375arranged in quadrature about the throat portion T and arranged to inject gas into liquid flowing through the throat portion T. Liquid flowing through the throat portion T flows at a velocity greater than that at which it flows into the column1360upstream of the generator1370as it passes through inlet1370IN. Thus a shear force of liquid flowing through the throat portion T on gas bubbles entering the throat portion T is enhanced relative to injection of gas into the column1360in the absence of a throat portion. This results in the formation of smaller bubbles than would be formed if the bubbles were injected into liquid upstream of the generator1370. Furthermore, gas bubbles formed in the throat portion T pass into the diverging portion D where turbulence is induced in the liquid. This results in the application of severe shear forces to the bubbles. This further reduces a size of the bubbles before they are exposed to the sonic waves generated by the fluid delivery devices1300.

FIG. 21shows a cyclone (or ‘cyclonic’) microbubble generator1570arranged to induce swirl in liquid passing into a column of a gas lift pump apparatus according to an embodiment of the invention in order to promote formation of microbubbles in the liquid.

Like features of the generator ofFIG. 21to those of the generator ofFIG. 20are shown with like reference signs prefixed numerals15instead of numerals13. As in the case of the embodiment ofFIG. 20(and in contrast to the embodiment ofFIG. 13), in the embodiment ofFIG. 21gas is arranged to be injected into the generator in a throat portion T of a Venturi portion V of the generator1570.

FIG. 21(a)is a cross-sectional view of the generator1570as viewed normal to a cylinder axis A of the generator1570.FIG. 21(b)is a view along the cylinder axis A as viewed along the direction of arrow B.

The generator1570is arranged to form a connection between a column of a gas lift pump apparatus and a draw tube oriented substantially orthogonal to the column although other arrangements are also useful. Liquid outlet1570OUT is arranged to face in an upward direction and to be coupled to the column. A liquid inlet1575is arranged to face in a lateral (substantially horizontal) direction and to be connected to the draw tube. As can be seen fromFIG. 21(a), liquid entering the generator1570through inlet1575does so in a direction substantially tangential to an inner wall of the generator1570and this feature promotes swirl flow of liquid through the generator1570.

Liquid flowing through the generator1570is forced to flow through a choke or Venturi portion1571. The Venturi portion has a converging portion C being a portion over which a cross-sectional area of the generator1570decreases with distance from the liquid inlet1575, a throat portion T of substantially constant cross-sectional area and a diverging portion D of increasing cross-sectional area.

Gas inlets1575are provided in the throat portion T arranged to inject gas into liquid passing through the throat portion T. The inlets1575are provided at spaced apart locations around a circumference of the throat portion T, neighbouring inlets1575being substantially equidistant from one another. In the embodiment shown12inlets are provided. Other numbers of inlets1575and other arrangements of inlets1575are also useful.

In use, liquid passing through the Venturi portion1571is arranged to cause shear of gas bubbles forming in the liquid as gas is injected through the inlets1575. This causes a reduction in size of the bubbles compared with an equilibrium size of gas bubbles formed in stagnant liquid. Microbubble generators1570of the type shown inFIG. 21have been found to be highly effective in producing a stable flow of microbubbles.

Reference herein to a vessel includes reference to any boat, ship or other floating structure having at least one ballast tank in the form of a liquid storage tank.

It is to be understood that embodiments of the present invention provide apparatus and a method for pumping a liquid, for example to recirculate liquid in a liquid storage tank by means of a gas lift pump. A perforated extension at the top of a lift portion of the gas lift pump described herein allows the apparatus to be used in circumstances where the depth of liquid in the tank may vary over a wide range. Gases other than air may be used in the gas lift, so as to change the acidity and the concentrations of dissolved gases, particularly oxygen, in the liquid. The gas may be introduced into the gas lift through a whistle that generates intense sound waves and couples them into the liquid. These features when used in combination have particular application against invasive species in the ballast water of ocean-going tankers.

Thus, some embodiments of the invention provide apparatus for simultaneously circulating liquid in a tank and changing a concentration of one or more dissolved gases in the liquid. Some embodiments provide apparatus for simultaneously circulating liquid in a tank, changing a concentration of one or more dissolved gases in the liquid and in addition exposing the liquid to intense sound waves.