GB2598625A

GB2598625A - Submersible plough

Info

Publication number: GB2598625A
Application number: GB2014034.9A
Authority: GB
Inventors: Barry Ward David
Original assignee: Clean Power Ltd
Current assignee: Clean Power Ltd
Priority date: 2020-09-07
Filing date: 2020-09-07
Publication date: 2022-03-09
Also published as: GB202014034D0; WO2022049396A1

Abstract

A submersible plough 100 for controlling back pressure in a sand bed filter for filtering a flowing liquid or a multiphase flow, having a density. The plough comprises a first set of blades 110, including a first blade, for disturbing particulates accumulated on the sand bed filter. The first set of blades110 is arranged circumferentially about a first axis and the first blade of the first set of blades projects, at least in part, radially. The plough is arranged to be moved by the flowing liquid and has a negative buoyancy with respect to the liquid, to maintain the plough at least and/or at most in intermittent contact with the sand bed filter. Also disclosed is a method of controlling back pressure in a rapid (pressure or gravity) sand bed filter for filtering a flowing liquid and the use of a submersible plough to control back pressure in a rapid (pressure or gravity) sand bed filter. The submersible plough may reduce the need for backwashing, increase filtering time and reduce waste water.

Description

SUBMERSIBLE PLOUGH

Field

The present invention relates to a submersible plough for controlling back pressure in a rapid sand bed filter for filtering a flowing liquid.

Background to the invention

Sand bed filters are used to separate particulates (e.g. soil, dust, algae, organic material, detritus and/or debris) from fluids. Sand bed filters are used in the treatment and purification of water. For instance, sand bed filters are used to purify water by removing soil particulates. Failing to remove particulates from water intended for human use can have negative health and sanitary consequences.

A sand bed filter is a type of depth filter in which particulates are captured by a granular material. A granular material is a collection of distinct macroscopic particles, such as grains of sand. The evolution of these macroscopic particles follows Newton's laws of motion, with repulsive forces between the macroscopic particles being non-zero only when there is physical contact between them.

In rapid sand bed filters, (unfiltered) water, for example, is distributed on top of the sand bed filter, the sand bed filter comprising the granular material. As the water flows through the sand bed, either under gravity or under pumped pressure, particulates suspended in the unfiltered water are left behind in the pores of the sand bed filter. Particulates of larger size than the pores are unable to pass through the sand bed filter and so are retained therein. Different rapid sand bed filters may use sand grains of different diameters, depending on the particulate they are designed to remove from water. Removal efficiency depends, inter alia, on the depth of the sand bed filter; the deeper the sand bed filter the greater the efficiency.

As particulates collect in the sand bed filter, the pressure difference between the water entering at the top of the sand bed filter and the water leaving at the bottom of the sand bed filter increases. In other words, an increased pressure difference across the sand bed filter indicates that the sand bed filter is loaded with particulates. Over time, the accumulation of particulates in the pores of the sand bed filter hinders the flow of water. Eventually, water cannot pass through the sand bed filter due to the retained particulates.

Back washing of the sand bed filter is performed to remove the particulates that have polluted it. During back washing, water is pumped upwards from the bottom of the sand bed filter until the sand bed filter is fluidised, causing the particulates to be washed from the sand. These particulates, along with the water used for backwashing, are discharged from the rapid sand bed filter. Subsequently, the rapid sand bed filter can return to operation with the flow of water through the sand bed filter restored as a result of the back washing.

To perform back washing, the operation of the rapid sand bed filter for filtering has to be paused or stopped. This is time inefficient, while the process of back washing requires additional energy usage. Moreover, the back washing, as described, results in waste water that need to be disposed. Further complications may arise in disposing the waste water, because the particulates which it contains may require treatment for safe disposal.

Hence, there is a need to reduce the need for back washing of rapid sand filters in order to increase the length of time that they may be used for filtering without interruption and to reduce waste water.

Summary of the Invention

It is one aim of the present invention, amongst others, to provide a submersible plough which at least partially obviates or mitigates at least some of the disadvantages of the prior art, whether identified herein or elsewhere. For instance, it is an aim of embodiments of the invention to provide a submersible plough that reduces the need for back washing of a rapid sand bed filter by disturbing particulates accumulated in the rapid sand bed. For instance, it is an aim of embodiments of the invention to provide a submersible plough that enables rapid sand bed filters to operate more efficiently with less wastage.

Detailed Descrintion of the Invention According to the present invention there is provided a submersible plough for controlling back pressure in a rapid (pressure and/or gravity) sand bed, as set forth in the appended claims. Also provided is a method of controlling back pressure in a rapid (pressure or gravity) sand bed filter for filtering a flowing liquid and use of a submersible plough to control back pressure in a rapid (pressure or gravity) sand bed filter. Other features of the invention will be apparent from the dependent claims, and the description that follows.

According to a first aspect of the present invention, there is provided a submersible plough for controlling back pressure in a rapid (pressure and/or gravity) sand bed filter for filtering a flowing liquid (or a multiphase flow), having a density puq"id. The plough comprises a first set of blades, including a first blade, for disturbing particulates accumulated on the sand bed filter. The first set of blades is arranged circumferentially about a first axis and the first blade of the first set of blades projects, at least in part, radially. The plough is arranged to be propulsed (or urged) by the flowing liquid. The plough has a density ppionsie, and has a negative buoyancy with respect to the liquid, to maintain the plough at least and/or at most in intermittent contact with the sand bed filter.

A submersible plough means a device that operates at least partially under a surface of a fluid, in particular a liquid, to disturb particulates. The density of the liquid includes any particulates suspended in the liquid. A blade is any protrusion of the plough for disturbing particulates accumulated on the sand bed filter. The first blade of the first set of blades radially projecting means that the first blade extrudes from a surface of the plough. Intermittent contact means non-continuous contact, such as periodic contact to cause disturbance of particulates accumulated on the sand bed filter. The frequency of contact influences the effectiveness of disturbance of particulates. For example, although continuous contact with the sand bed filter results in its continuous disturbance, such disturbance is likely low intensity to due drag from the sand bed filter. In the moments the plough breaks contact with the sand bed filter, it becomes free of this drag, so can accelerate and build momentum. On re-establishing contact with the sand bed filter, this momentum is transferred in a high energy, high disturbance event.

By controlling the back pressure in a rapid sand bed filter, flow of the flowing liquid can be maintained. If back pressure is not controlled, specifically, if the back pressure increases, the flow of the flowing liquid is reduced. In this case, the filtering of the flowing liquid, such as water, by the rapid sand bed filter is less efficient compared with the case before the back pressure was reduced. In other words, the submersible plough improves the efficiency of operation of the rapid sand bed filter by reducing the need for back washing by disturbing particulates accumulated on the sand bed filter, preventing the back pressure from increasing.

The first set of blades being circumferentially arranged about a first axis enables the plough to disturb particulates accumulated on the sand bed filter regardless of orientation of the plough about the first axis. The plough being arranged to be propulsed (or urged) by the flowing liquid means that a single plough is capable of disturbing particulates across the sand bed filter (i.e. not just in a region of the sand bed filter to which the plough is added), because the flow of the liquid will cause the plough to move. Therefore, the plough does not require additional energy input to operate In one example, the plough is arranged to be propulsed by the flowing liquid by being arranged to be urged by the flowing liquid to roll on the accumulated particulates and/or rotate about an axis, for example the first axis. In this way, the effectiveness of the plough in disturbing particulates is increased compared with a plough that does not roll or rotate, because the contact between the plough and the sand bed filter varies such that an area of the sand bed filter in contact with the plough is increased.

In one example, the weight distribution of the plough is biased. In one example the plough comprises a swim bladder and/or ballast chamber such that the plough has an asymmetrical centre of gravity. The plough having an asymmetrical centre of gravity is advantageous in encouraging the plough to travel with an erratic/irregular motion such that greater coverage of the sand bed filter is realised (i.e. increased randomness of travel). In addition, if combined with appropriately angled blade design, such a feature would also encourage the plough to drift away from the centre of the sand bed filter during back washing. By ensuring the plough is deposited away from the centre of a surface of the sand bed filter following back washing (i.e. close to walls enclosing the sand bed filter), the chances of the plough initially being exposed to the fastest currents when operation of the sand bed for filtering is resumed is increased (the flowing liquid entering at or near edges of the sand bed filter). This exposure of the plough to the fastest currents, in turn, encourages the plough to be dragged from a state in which it is potentially buried in the granular material and returned to being entrained within a vortex created by the flowing liquid.

In one example, the plough comprises a plurality of swim bladders and/or ballast chambers. In one example, the plough comprises an array, for example a honey comb-like structure, of internal air pockets to engender ppiony".

In one example, the plough is arranged to be propulsed, at least in part, by the flowing liquid by a shape, size and/or orientation of the first set of blades. In one example, the shape, size and/or orientation of the first set of blades is adjustable, for instance, to increase or decrease the propulsion experienced by the plough. Changing the propulsion experienced by the plough changes the effectiveness of the plough in disturbing particulates.

In one example, the plough comprises a plastics material. In one example, the plough comprises rubber. Plastics materials and rubber are usually cheap, light and durable. In one example, the plough is produced by additive manufacturing. In one example, the plough is produced using a mould. These methods of manufacturing enable the plough to be reliably produced in large quantities.

In one example the plough is a sphere. In one example, the plough is a regular polyhedron. In one example, the plough is an irregular polyhedron. In one example, the plough comprises a plurality of spheres. In one example, the plough comprises two spheres at either end of a rod. In one example, the plough comprises a plurality of polyhedra. The plough comprising a plurality of spheres or polyhedra can increase a surface area of the plough over which blades can be arranged, for example the first set of blades, so as to increase the effectiveness of the plough in disturbing particulates.

In one example, the density p pip?, sm is in a range from 1.005Thiquid to 1.25piivid, preferably in a range from 1.01paquid to 1.15puquid; more preferably in a range from 1.025Thiquid to 1.05puquid.

These density ranges are advantageous in effecting intermittent contact of the plough with the sand bed filter.

In one example, the density ppip",p is adjustable, for example, wherein the plough comprises releasably-coupled ballast and/or buoys. By adjusting the density of the plough, maintenance of the plough at least and/or at most in intermittent contact with the sand bed filter is possible regardless of pli,"id.

In one example, the density p p limn is calculated by dividing a total mass of the plough by a total volume of the plough. The total mass of the plough is a sum of a mass of housing material and a mass of ballast material, for example obtained by weighing the plough. The total volume of the plough is the sum of a volume of the housing material and a volume of the ballast material, the total volume of the plough being a volume confined within an outer surface of the plough, such as a body of the plough, for example obtained by displacement or calculated. The housing material is the material from which the body of the plough is made. The ballast material is the material in the ballast chamber. In one example, there is more than one material in the ballast chamber (e.g. air, water and gravel), in which case the mass of the ballast material is the sum of masses of the more than one material, and the volume of the ballast material is the sum of volumes of the more than one material. In one example, the volume of the ballast material is equal to a volume of the ballast chamber.

In one example, the plough has a neutral buoyancy with respect to the fluidised sand bed filter during back washing thereof. Therefore, in case backwashing is necessary, the plough does not impinge backwashing. The plough does not have to be removed from the sand bed filterfor back washing to be effectively undertaken. For example, the plough does not sink into the fluidised sand bed filter during back washing thereof, thereby not becoming lost even when operation of the sand bed filter resumes.

In one example, the plough comprises a first set of fins, including a first fin, arranged to thrust, at least in part, the plough upwards during back washing of the sand bed filter. In this way, a plough that does not have a neutral buoyancy with respect to the fluidised sand bed filter during back washing thereof can nevertheless be used for backwashing. In one example, the first set of fins is adjustable in size to adjust the thrust experienced by the plough during back washing.

In one example, the plough comprises a second set of blades, including a first blade, for disturbing the particulates, wherein the second set of blades is arranged circumferentially about a second axis, transverse to the first axis, and wherein the first blade of the second set of blades projects, at least in part, radially. The second set of blades further enhances the ability of the plough to disturb particulates on the sand bed filter. In one example, a shape, size and/or orientation of the second set of blades is adjustable.

In one example, the plough comprises a third set of blades, including a first blade, for disturbing the particulates, wherein the first set of blades is arranged circumferentially about the first axis, wherein the first set of blades and the third set of plates are mutually spaced apart along the first axis and wherein the first blade of the third set of blades projects, at least in part, radially. In one example, a shape, size and/or orientation of the third set of blades is adjustable.

In one example the plough comprises a fourth set of blades, including a first blade, for disturbing the particulates, wherein the fourth set of blades is arranged circumferentially about a third axis, transverse to the first axis and the second axis, and wherein the first blade of the fourth set of blades projects, at least in part, radially. The fourth set of blades further enhances the ability of the plough to disturb particulates on the sand bed filter. In one example, a shape, size and/or orientation of the fourth set of blades is adjustable.

In one example, the first set of blades includes N blades, wherein N is a natural number greater than or equal to 1, for example 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or more, optionally wherein the N blades are mutually equispaced. In one example, individual blades of the first set of blades or the transverse set of blades are removable.

In one example, the plough comprises a first set of paddles, including a first paddle, arranged to urge, at least in part, the plough to roll on the accumulated particulates and/or rotate about an axis by the flowing liquid. Therefore, the first set of paddles increases an area of the sand bed filter over which the plough rolls.

In one example, the first set of blades is arranged circumferentially about the first axis having a diameter in a range from 1 cm to 20 cm, preferably in a range from 2 cm to 15 cm, more preferably in a range from 3 cm to 10 cm.

In one example, the sand bed filter includes a set of M ploughs according to any previous claim, wherein M is a natural number greater than or equal to 1, for example 1,2, 3, 4, 5,6, 7, 8, 9, 10 or more. In one example, the set of ploughs are connected by a rod. In one example, the set of ploughs are connected by a rope, cord or wire. In one example, each of the M ploughs is magnetised such that each of the M ploughs is configured to attach to another one or more of the ploughs in the set of M ploughs. In one example, the number of ploughs in the set of M ploughs is adjustable. By being able to change the number of ploughs in the set of ploughs, the set of ploughs can be customised to the size of the sand bed filter for which they are used. For example, it may be appropriate to use a large number of ploughs to control the back pressure of a large rapid sand bed filter. In one example, each of the M ploughs are connected linearly.

In one example, each of the M ploughs are connected circularly. In one example, each of the M ploughs have the same geometry.

In one example, each of the M ploughs is magnetised such that each of the ploughs is configured to repel other ploughs in the set of ploughs. In this way, clustering of the ploughs in the rapid sand bed filter can be prevented.

In one example, the plough further comprises a sensor to monitor the back pressure and a transmitter to transmit the back wash pressure to a receiver. In this way, performance of the plough can be monitored in real time.

According to a second aspect of the present invention, there is provided a method of controlling back pressure in a rapid (pressure or gravity) sand bed filter for filtering a flowing liquid. The method comprises submersing a first plough of a set of M ploughs in the flowing liquid above the sand bed filter; propulsing, by the flowing liquid, the first plough therethrough; contacting, by the first plough, the sand bed filter; and disturbing, by the first plough, particulates accumulated on the sand bed filter, thereby resuspending the particulates.

Each feature of the second aspect is as described with reference to the first aspect. The method of the second aspect comprises any of the steps described with reference to the first aspect.

According to third aspect, there is provided use of a submersible plough to control back pressure in a rapid (pressure or gravity) sand bed filter. Each feature of the third aspect is as described with reference to the first aspect.

Definitions Throughout this specification, the term "comprising" or "comprises" means including the component(s) specified but not to the exclusion of the presence of other components. The term "consisting essentially of" or "consists essentially of' means including the components specified but excluding other components except for materials present as impurities, unavoidable materials present as a result of processes used to provide the components, and components added for a purpose other than achieving the technical effect of the invention, such as colourants, and the like.

B

The term "consisting of' or "consists of" means including the components specified but excluding other components.

Whenever appropriate, depending upon the context, the use of the term "comprises" or "comprising" may also be taken to include the meaning "consists essentially of" or "consisting essentially of', and also may also be taken to include the meaning "consists or or "consisting of'.

The optional features set out herein may be used either individually or in combination with each other where appropriate and particularly in the combinations as set out in the accompanying claims. The optional features for each aspect or exemplary embodiment of the invention, as set out herein are also applicable to all other aspects or exemplary embodiments of the invention, where appropriate. In other words, the skilled person reading this specification should consider the optional features for each aspect or exemplary embodiment of the invention as interchangeable and combinable between different aspects and exemplary embodiments.

Brief description of the drawinqs

For a better understanding of the invention, and to show how exemplary embodiments of the same may be brought into effect, reference will be made, by way of example only, to the accompanying diagrammatic Figures, in which: Figure 1A schematically depicts a first plan view of a submersible plough according to an exemplary embodiment; Figure 1B schematically depicts a perspective view of the submersible plough of Figure 1A according to an exemplary embodiment; Figure 1C schematically depicts a second plan view of the submersible plough of Figure 1A according to an exemplary embodiment; Figure 1D schematically depicts a cross sectional view along the line A-A shown in Figure 1C according to an exemplary embodiment; Figure 2A schematically depicts a first plan view of a submersible plough according to an exemplary embodiment; Figure 2B schematically depicts a perspective view of the submersible plough of Figure 2A according to an exemplary embodiment; Figure 20 schematically depicts a second plan view of the submersible plough of Figure 2A according to an exemplary embodiment; Figure 2D schematically depicts a cross sectional view along the line B-B shown in Figure 20 according to an exemplary embodiment; Figure 3A schematically depicts a first plan view of a submersible plough according to an exemplary embodiment; Figure 3B schematically depicts a perspective view of the submersible plough of Figure 3A according to an exemplary embodiment; Figure 30 schematically depicts a second plan view of the submersible plough of Figure 3A according to an exemplary embodiment; Figure 3D schematically depicts a cross sectional view along the line B-B shown in Figure 3C according to an exemplary embodiment; Figure 4A schematically depicts a first plan view of a submersible plough according to an exemplary embodiment; Figure 48 schematically depicts a perspective view of the submersible plough of Figure 4A according to an exemplary embodiment; Figure 40 schematically depicts a second plan view of the submersible plough of Figure 4A according to an exemplary embodiment; Figure 4D schematically depicts a cross sectional view along the line B-B shown in Figure 40 according to an exemplary embodiment; Figure 5A schematically depicts a first plan view of a submersible plough according to an exemplary embodiment; Figure 5B schematically depicts a perspective view of the submersible plough of Figure 5A according to an exemplary embodiment; Figure 50 schematically depicts a second plan view of the submersible plough of Figure 5A according to an exemplary embodiment; Figure 5D schematically depicts a cross sectional view along the line B-B shown in Figure 50 according to an exemplary embodiment; Figure 6 schematically depicts the submersible plough of Figures 2A, 2B, 20 and 2D in use during backwashing according to an exemplary embodiment; and to Figure 7 schematically depicts a method of controlling back pressure in a rapid (pressure or gravity) sand bed filter for filtering a flowing liquid according to an exemplary embodiment.

Detailed Description of the Drawings

Figure 1A schematically depicts a first plan view of a submersible plough 100 according to an exemplary embodiment in which there is provided a submersible plough for controlling back pressure in a rapid (pressure and/or gravity) sand bed filter for filtering a flowing liquid (or a multiphase flow), having a density paquid The plough comprises a first set of blades, including a first blade, for disturbing particulates accumulated on the sand bed filter. The first set of blades is arranged circumferentially about a first axis and the first blade of the first set of blades projects, at least in part, radially. The plough is arranged to be propulsed (or urged) by the flowing liquid. The plough has a density n plough and has a negative buoyancy with respect to the liquid, to maintain the plough at least and/or at most in intermittent contact with the sand bed filter.

The body of the plough 100, which is formed of triangular faces 120, is a regular iscosahedron.

Each vertex and the centre of each face 120 of the body of the plough 100 has a blade 110 attached thereto. The blades 110 shown in Figure 1A have the form of cones. The blades 110 project from the body of the plough 100. In use, the blades 110 of the plough 100 disturb particulates accumulated on a sand bed filter.

Figure 1B schematically depicts a perspective view of the submersible plough of Figure 1A according to an exemplary embodiment. Figure 1B underlines the distribution of the blades 110 is across the entire surface of the body of the plough 100, such that the plough 100 in use disturbs particulates accumulated on the sand bed filter regardless of its orientation. The blades 110, along with the density of the plough 100, facilitate the plough 100 being propulsed by a flowing liquid.

Figure 10 schematically depicts a second plan view of the submersible plough of Figure 1A according to an exemplary embodiment Figure 1D schematically depicts a cross sectional view along the line A-A shown in Figure 1C according to an exemplary embodiment. Figure 1D shows a half 130 of the plough 100 shown in Figures 1A, 1B and 1C. Figure 1D shows that the body of the plough 100 is hollow, allowing the addition of ballast to the plough 100 to adjust its density in order to maintain the plough 100 at least and/or at most in intermittent contact with the sand bed filter regardless of puquid. The ballast is added and removed via a hole 140, which is plugged (e.g. using a blade 110) when the plough 100 is added to the sand bed filter.

Figure 2A schematically depicts a first plan view of a submersible plough 200 according to an exemplary embodiment. The body 220 of the plough 200 is spherical. The plough comprises three circumferential blades 201, 211, 212 that are mutually perpendicular and radially project. The projection of the first blade 210 from the body 220 is greater than the projection of the second blade 211 and the third blade 212, meaning that there is a gap between the edge of the first blade 210 and the edge of the second blade 211 and the third blade 212. The projection of the second blade 212 and the third blade 212 from the body 220 is the same. The edge 250 of each of the blades 210, 211,212 is undulating.

The blades 210, 211, 212 of the plough 200 disturb particulates accumulated on a sand bed filter. Having blades 210, 211, 212 projecting in different radial directions and the undulating edges 250 or crenellations of the blades 210, 211, 212 helps disturb particulates accumulated on a sand bed filter. The blades 210, 211, 212, along with the density of the plough 200, facilitate the plough 200 being propulsed by a flowing liquid.

Each of the blades 210, 211, 212 can also function as a fin arranged to thrust the plough 200 upwards during back washing of the sand bed filter. In this way, a plough 200 that does not have a neutral buoyancy with respect to the fluidised sand bed filter during back washing thereof can nevertheless be used for backwashing.

Figure 2B schematically depicts a perspective view of the submersible plough 200 of Figure 2A according to an exemplary embodiment, and Figure 2C schematically depicts a second plan view of the submersible plough 200 of Figure 2A according to an exemplary embodiment.

Figure 2D schematically depicts a cross sectional view along the line B-B shown in Figure 2C according to an exemplary embodiment. Figure 2D shows a half 230 of the plough 200 shown in Figures 2A, 2B and 2C. Figure 2D shows that the body of the plough 200 is hollow, allowing the addition of ballast to the plough 200 as described for Figure 1D. The ballast is added and removed via a hole (or passageway) 240 through a wall of the body of the plough 200, which is plugged when the plough 200 is added to the sand bed filter.

Figures 3A, 3B, 3C and 3D showing a plough 300 respectively correspond to Figures 2A, 2B, 20 and 2D for the plough 200. The plough 300 shown in Figures 3A, 3B, 30 and 3D differs from the plough 200 shown in Figures 2A, 2B, 20 and 2D in the arrangement of the blades 310, 311, 312. Unlike for the plough 200, for the plough 300 the radial projection of each of the mutually perpendicular, circumferential blades 310, 311, 312 is equal.

This difference in the arrangement of the blades 310, 311, 312 compared with the blades of the plough 200 shown in Figures 2A, 2B, 20 and 2D changes the propulsion of the plough 300 in the same way the circumferential blades of the plough 200 facilitate a change in the propulsion of the plough 200 compared with the conical blades 110 of the plough 100. Such a change in the propulsion can be useful depending on the properties of the particulates, for example. Similarly, the thrust provided by blades 310, 311, 312 when functioning as fins during backwashing is changed by the change in the projection of the blades 310, 311, 312 of the plough 300 compared with the blades 201, 211, 212 of the plough 200.

Figure 4A schematically depicts a first plan view of a submersible plough 400 according to an exemplary embodiment. The body 420 of the plough 400 is spherical. Similar to the ploughs 200, 300 shown in Figures 2A and 3A, the plough 400 shown in Figure 4A comprises three circumferential blades 401, 411, 412 that are mutually perpendicular and radially project. The projection of the first blade 410 from the body 420 is less than the projection of the second blade 411 and the third blade 412, meaning that there is a gap between the edge of the first blade 410 and the edge of the second blade 411 and the third blade 412. The projection of the second blade 412 and the third blade 412 from the body 420 is the same.

Figure 4B schematically depicts a perspective view of the submersible plough of Figure 4A according to an exemplary embodiment. As shown in Figure 4A, and more clearly in Figure 4B, each of the blades 410, 411, 412 comprise projections 450. These projections 450 are evenly spaced along each of the blades 410, 411, 412 and extend across the width of each blade 410, 411, 412. These projections 450 function as paddles to urge the plough 400 to roll on the accumulated particulates and/or rotate about an axis by the flowing liquid. Similar to the crenellations shown in Figure 2A, the paddles also help to disturb particulates accumulated on a sand bed filter.

Figure 40 schematically depicts a second plan view of the submersible plough 400 of Figure 4A according to an exemplary embodiment.

Figure 4D schematically depicts a cross sectional view along the line B-B shown in Figure 40 according to an exemplary embodiment. Figure 4D shows a half 430 of the plough 400 shown in Figures 4A, 4B and 40. Figure 4D shows that the body of the plough 400 is hollow, allowing the addition of ballast to the plough 400 as described for Figure 1D. The ballast is added and removed via a hole (or passageway) 440 through a wall of the body of the plough 200, which is plugged when the plough 400 is added to the sand bed filter.

Figures 5A, 5B, SC and 5D showing a plough 500 respectively correspond to Figures 4A, 4B, 40 and 4D for the plough 400. The plough 500 shown in Figures 5A, 5B, 5C and SD differs from the plough 400 shown in Figures 4A, 4B, 40 and 4D in that the paddles only partially extend across the width of each blade, reducing the amount of material required for the manufacture of the plough Figure 6 schematically depicts the submersible plough 200 of Figures 2A, 2B, 2C and 2D in use during backwashing according to an exemplary embodiment. Any of the ploughs 100, 300, 400, 500 may replace the plough 200 shown in Figure 6. Figure 6 shows a surface 1000 of the sand bed filter, which is enclosed by a wall 2000 so as to contain liquid distributed on top of the sand bed filter. Arrows 902 indicate a direction of flow of a liquid used for backwashing.

In Figure 6, the plough is shown as comprising a swim bladder 800 at an off centred position. As a result of the swim bladder, the blades 211, 212 of the plough 200 present at an angle to the direction of flow of the liquid during backwashing. Consequently, the liquid used for backwashing is deflected by the angled blade, causing the application of a driving force indicated by arrow 901. By ensuring the plough 200 is deposited away from the centre of the surface 1000 of the sand bed filter following back washing (i.e. close to the wall 2000), the chances of the plough 200 initially being exposed to the fastest currents when operation of the sand bed for filtering is resumed is increased (the flowing liquid entering at or near edges of the sand bed filter). This exposure of the plough 200 to the fastest currents, in turn, encourages the plough to be dragged from a state in which it is potentially buried in the granular material and returned to being entrained within a vortex created by the flowing liquid.

Figure 7 schematically depicts a method of controlling back pressure in a rapid (pressure or gravity) sand bed filter for filtering a flowing liquid according to an exemplary embodiment. The method comprises submersing a first plough of a set of M ploughs in the flowing liquid above the sand bed filter (3701). This set of M ploughs can comprise any number and any combination of the ploughs 100, 200, 300, 400, 500 shown in Figures 1A to 5D described above. The method also comprises propulsing, by a flowing liquid, a first plough therethrough (S702); contacting, by the first plough, a sand bed filter (S703); and disturbing, by the first plough, particulates accumulated on the sand bed filter, thereby resuspending the particulates (S704).

At 3701, the method comprises submersing a first plough of a set of M ploughs in the flowing liquid above the sand bed filter.

At 3702, the method comprises propulsing, by the flowing liquid, the first plough therethrough.

At 3703, the method comprises contacting, by the first plough, the sand bed filter.

At 3704, the method comprises disturbing, by the first plough, particulates accumulated on the sand bed filter, thereby resuspending the particulates.

The method may include any step described herein. The set of M ploughs may comprise any number and any combination of the ploughs 100, 200, 300, 400, 500 shown in Figures 1A to 5D described above, for example.

Although a preferred embodiment has been shown and described, it will be appreciated by those skilled in the art that various changes and modifications might be made without departing from the scope of the invention, as defined in the appended claims and as described above.

In summary, the invention provides a submersible plough that reduces the need for back washing of a rapid sand bed filter by disturbing particulates accumulated in the rapid sand bed.

Consequently, the invention provides a submersible plough that enables rapid sand bed filters to operate more efficiently with less wastage.

Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at most some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

CLAIMS1. A submersible plough for controlling back pressure in a rapid, for example a pressure and/or a gravity, sand bed filter for filtering a flowing liquid or a multiphase flow, having a density ptiquid, the plough comprising: a first set of blades, including a first blade, for disturbing particulates accumulated on the sand bed filter, wherein the first set of blades is arranged circumferentially about a first axis and wherein the first blade of the first set of blades projects, at least in part, radially; wherein the plough is arranged to be propulsed or urged by the flowing liquid; and wherein the plough, having a density pwough, has a negative buoyancy with respect to the liquid, to maintain the plough at least and/or at most in intermittent contact with the sand bed filter.
2. The plough according to claim 1, wherein the plough is arranged to be propulsed by the flowing liquid by being arranged to be urged by the flowing liquid to roll on the accumulated particulates and/or rotate about an axis, for example the first axis.
3. The plough according to any previous claim, wherein the plough is arranged to be propulsed, at least in part, by the flowing liquid by a shape, size and/or orientation of the first set of blades.
4. The plough according to any previous claim, wherein the density ppumd,, is in a range from 1.005/3id to 1.25p""id, preferably in a range from 1.01 pudidd to 1.15pui"d; more preferably in a range from 1.025p""id to 1.05puquid.
5. The plough according to any previous claim, wherein the density ppidud" is adjustable, for example, wherein the plough comprises releasably-coupled ballast and/or buoys.
6. The plough according to any previous claim, wherein the plough has a neutral buoyancy with respect to the fluidised sand bed filter during back washing thereof
7. The plough according to any previous claim, comprising a first set of fins, including a first fin, arranged to thrust, at least in part, the plough upwards during back washing of the sand bed filter.
8. The plough according to any previous claim, comprising a second set of blades, including a first blade, for disturbing the particulates, wherein the second set of blades is arranged circumferentially about a second axis, transverse to the first axis, and wherein the first blade of the second set of blades projects, at least in part, radially.
9. The plough according to any previous claim, comprising a third set of blades, including a first blade, for disturbing the particulates, wherein the first set of blades is arranged circumferentially about the first axis, wherein the first set of blades and the third set of plates are mutually spaced apart along the first axis and wherein the first blade of the third set of blades projects, at least in part, radially.
10. The plough according to any previous claim, wherein the first set of blades includes N blades, wherein N is a natural number greater than or equal to 1, for example 1, 2, 3,4, 5, 6, 7, 8, 9, 10 or more, optionally wherein the N blades are mutually equispaced.
11. The plough according to any previous claim, comprising a first set of paddles, including a first paddle, arranged to urge, at least in part, the plough to roll on the accumulated particulates and/or rotate about an axis by the flowing liquid.
12. The plough according to any previous claim, wherein the first set of blades is arranged circumferentially about the first axis having a diameter in a range from 1 cm to 20 cm, preferably in a range from 2 cm to 15 cm, more preferably in a range from 3 cm to 10 cm.
13. A sand bed filter including a set of M ploughs according to any previous claim, wherein M is a natural number greater than or equal to 1, for example 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or more.
14. A method of controlling back pressure in a rapid (pressure or gravity) sand bed filter for filtering a flowing liquid, the method comprising: submersing a first plough of a set of M ploughs in the flowing liquid above the sand bed filter; propulsing, by the flowing liquid, the first plough therethrough; contacting, by the first plough, the sand bed filter; and disturbing, by the first plough, particulates accumulated on the sand bed filter, thereby resuspending the particulates.
15. Use of a submersible plough to control back pressure in a rapid (pressure or gravity) sand bed filter.