WO2024184622A1

WO2024184622A1 - Method and apparatus for separating sand from slurry

Info

Publication number: WO2024184622A1
Application number: PCT/GB2024/050551
Authority: WO
Inventors: Richard Henry Coulton
Original assignee: Individual
Current assignee: Individual
Priority date: 2023-03-03
Filing date: 2024-02-29
Publication date: 2024-09-12
Anticipated expiration: 2025-09-03
Also published as: GB202303130D0; GB2627810A

Abstract

A method of separating sand from slurry is disclosed. The slurry comprises water and fibre. The method comprises passing sand-laden slurry (102), said sand laden slurry (102) comprising sand and slurry, through a spiral separator (114). The sand-laden slurry (102) is thereby separated into at least a sand/water stream (118) and a fibre/water stream (116). A separation unit (301) for carrying out the method is also disclosed.

Description

Method and apparatus for separating sand from slurry

Field of the Invention

The present invention concerns the separation of sand and animal excreta (slurry). More particularly, but not exclusively, this invention concerns a method for separating sand and slurry and an apparatus for use in such a method.

Background of the Invention

Sand is used as a bedding material for various animals including cows on dairy farms as it provides a comfortable medium for the cow to lie on and good traction/grip when the cows lie down or stand up. The animals produce slurry (faeces and urine) which comprises water and fibre. Slurry is typically 93 to 95 % water by weight. The fibre comprises partly digested and/or undigested fibre from the feed, the size of the fibre particles varying depending on the state of digestion. Thus, the fibre may comprise coarser fibre and finer fibre. Coarser fibre may be defined as fibre particles having a maximum dimension greater than or equal to 1 mm. Finer fibre may be defined as fibre particles having a maximum dimension of less than 1 mm, for example from 5 microns up to and including 950 microns.

Typically, slurry is collected in a collection area, for example a trough or alley way located at one end of the bedding area. Sand may become mixed with the slurry in the collection area as the animal moves around. This mixture of sand and slurry is commonly referred to as sand-laden slurry. The bedding area is periodically topped up with fresh sand to replace the sand lost in this way. The sand-laden slurry may also contain other debris (e.g. stones, hoof material, etc.) in addition to the sand, fibre and water. It is desirable to separate the sand from the sand-laden slurry so that the sand can be reused and to reduce the cost of handling and storing sand-laden slurry. Some known sand-laden slurry separation systems (such as a sand lanes and sand traps) rely on the difference between the settling velocity of the sand particles and fibre/debris particles contained in the slurry, with the larger sand particles settling faster than most of the other particles. However, fine sand particles settle at the same rate as coarse fibre particles and therefore, systems that rely on settling velocity are not suitable for separating fine sand from slurry. In the UK, the sand typically used for cow bedding has a particle size distribution where around 90% of the sand has a diameter of less than 0.2mm and around 90% of the sand has a diameter of more than 0.07mm. Many of the sandmanure separation systems currently used in the UK were designed in the US. US 5, 957,301 (Wedel et al.) and US 8,470,183 (Daritech, Inc) are examples of such US- originating systems. However, in the US the typical sand used for cow bedding has a particle size distribution where around 90% of the sand has a diameter of less than 3.0mm and around 90% of the sand has a diameter of more than 0.3mm. This means that many of the US separation systems currently employed to separate sand from manure in sand-laden slurry in the UK are inefficient and are not properly adapted to separating the fine sand used in the UK. For example, tests have shown that when used with the fine sand preferred by UK farms the primary separation stage of the US systems only recovers around 10% of the sand.

It is known to use sand lanes and settlement pond as the primary stage of separation for sand and slurry. These rely on settling velocity and so do not efficiently separate the fine sand commonly used in the UK. It is also known to use a hydrocyclone as a primary or secondary stage of separation. Hydrocyclones separate based on a combination of density and particle size. However, when used with sandladen slurry containing fine sand it has been found that the hydrocyclone separates predominantly on particle size. A significant fraction of the partly/undigested fibre is entrained with the sand and leaves the hydrocyclone with the sand, meaning that the sand is not effectively separated by the hydrocyclone. There is therefore a need to provide a sand-slurry separation system that is well adapted to the fine sand used as animal bedding on UK farms.

As a result of the presence of the fibre, the slurry is relatively nutrient rich. This makes the spreading of slurry difficult (irrespective of the presence of sand) because of the environmental impact of those nutrients. Accordingly, it would be advantageous to provide an improved method for treating the slurry to reduce its environmental impact.

The present invention seeks to mitigate the above-mentioned problems. Alternatively or additionally, the present invention seeks to provide an improved method and apparatus for separating sand from sand-laden slurry. Summary of the Invention

The present invention provides, according to a first aspect, a method of separating sand from slurry (animal excreta) comprising water and fibre. The method may comprise passing sand-laden slurry through a separator, for example a spiral separator. It may be that the sand-laden slurry comprises sand and slurry, the slurry comprising water and fibre. It may be that the sand-laden slurry is divided into at least a sand/water stream and a fibre/water stream as a consequence of passage through the separator.

Thus, a spiral separator may be used to separate the sand from the fibre in the slurry. Without wishing to be bound by theory, it is believed that the spiral separator separates the sand from the fibre based on its density rather than particle size or settling velocity (as in other sand-laden slurry separation systems). This may allow for improved sand separation, and particularly for fine sand as typically used in the UK to be separated from slurry more effectively than other sand-slurry separation systems currently on the market. This method may facilitate re-use of fine bedding sand even after it has been mixed with slurry.

It will be appreciated that water is used herein to refer to the liquid part of animal excreta. This will be primarily H2O but may include small amounts of other substances.

The sand-laden slurry may further comprise debris such as animal feed, leaves, sticks, stones, plastic bags and after birth.

It may be that the sand-laden slurry is first loaded into a feed hopper forming part of a separation apparatus, for example an apparatus in accordance with the second aspect below. Use of a feed hopper may allow for a controlled input rate of sand-laden slurry to the rest of the process, thereby ensuring the correct composition of liquids and solids downstream.

The method may comprise mixing a dilution liquid with the sand-laden slurry to increase the water content of the sand-laden slurry. Thus, the dilution liquid may be mixed with the sand, fibre and water of the sand-laden slurry. Increasing the water-content of the sand-laden slurry may aid the separation process. This step may comprise mixing the sand-laden slurry with the dilution liquid in a dilution compartment. It may be that the method comprises removing coarser fibre from the sandladen slurry before the sand-laden slurry is passed to the spiral separator. Removing the coarser fibre upstream of the spiral separator may increase the efficacy of separation in the spiral separator. Additionally or alternatively, coarser fibre removed at this stage of the process (which may be referred to as manure) may be used in other agricultural practices. The method may comprise removing debris before, after or while, mixing the sand-laden slurry with the dilution liquid. It may be that the step of removing coarser fibre comprises passing the sand-laden slurry through a screen that retains coarser fibre while allowing sand, water and finer fibre to pass through. The step of increasing the water content of the sand-laden slurry may comprise adding the dilution liquid to the sand-laden slurry as it is passed through the screen.

It may be that the method comprises removing debris from the sand-laden slurry before the sand-laden slurry is passed to the spiral separator. The method may comprise removing debris before, after or while, mixing the sand-laden slurry with the dilution liquid. It may be that the step of removing debris comprises passing the sandladen slurry through a screen that retains debris while allowing sand, water and fibre to pass through. Removing debris may reduce the risk of blockages in the spiral separator and/or prevent excessive wear on the spiral separator by preventing rocks and stones from entering the spiral separator with the sand-laden slurry.

It may be that the steps of removing debris and coarser fibre are carried out together. It may be that the method comprises passing the sand-laden slurry through the same screen (which may be referred to as a debris screen) that retains debris and coarser fibre while allowing sand, water and finer fibre to pass through.

It may be that some finer fibre is removed from the sand-laden slurry along with the coarser fibre and/or debris. It may be that some sand is removed from the sand-laden slurry along with the coarser fibre and/or debris. For example, the coarser fibre and/or debris may build up on a screen (e.g. the debris screen) thereby forming a mat which in turn retains some finer fibre and/or sand.

The step of increasing the water content of the sand-laden slurry may comprise adding the dilution liquid to the sand-laden slurry as it is passed through a screen, for example a screen configured to retain debris, coarser fibre or both. The sand, water and fibre, e.g. finer fibre, may be collected in a compartment after passage through the or each screen, e.g. the debris screen.

It may be that the sand-laden slurry is passed, for example pumped, from the feed hopper and/or the compartment where it is mixed with the dilution fluid to the debris screen or any other screen as described above. It may be that the sand-laden slurry is fed from the feed hopper to the debris screen or any other screen as described above either directly or, for example, using a pump or auger.

The debris screen, the screen for retaining coarser fibre and/or the screen for retaining debris, may be configured to retain particles that have a maximum dimension greater than 1 mm, for example greater than 5 mm, while allowing smaller particles to pass through. As used herein, maximum dimension refers to the size of whichever dimension of the particle in question is largest. For a regularly shaped particle, the maximum dimension may be e.g. a length, diameter, width, or thickness of the particle, but for irregular particles it may be some other dimension. For example, the or each screen may comprise a mesh, for example a mesh having a maximum grating size of 1 mm or greater, for example 5 mm or greater. The debris and/or coarse fibre separated by the debris screen may be collected in a debris hopper or stacked beneath the separator as manure comprised predominantly of coarse fibre and debris (if present).

The debris screen (or any other screen described above) may be a rotary drum screen. A rotary drum screen may comprise a substantially cylindrical screen mounted for rotation about a longitudinal axis relative to an inlet. The inlet is arranged such that sand-laden slurry from the inlet is deposited onto the screen as the screen rotates such that the screen retains debris and/or coarser fibre while sand, water and finer fibre pass through. The rotary drum screen may comprise an outlet arranged to collect the sand, water and fibre, e.g. finer fibre, after passage through the screen. The rotary drum screen may be an externally fed drum screen in which the inlet is located on the outside of the screen. The rotary drum screen may be an internally fed drum screen in which the inlet is located inside the screen. The screen may comprise a scraper or other mechanism arranged to remove debris and/or coarser fibre from the screen for discharge.

Alternatively the debris screen (or any other screen described above) may be a rundown screen. A rundown screen may comprise a screen inclined at an angle to the horizontal and configured such that in use, sand-laden slurry is deposited onto the screen and debris and/or coarser fibre slide to the bottom of the screen where they are collected for discharge, while sand, water and fibre (e.g. finer fibre) pass through the screen. The rundown screen may comprise an outlet arranged to collect the sand, water and fibre after passage through the screen. The rundown screen may comprise an inlet arranged to deposit sand-laden slurry onto the screen.

Alternatively, a centrifuge, or any other device capable of separating coarser fibre and/or debris from sand, water and finer fibre may be used instead of a screen.

The method may comprise passing the sand-laden slurry through the debris screen (and optionally adding dilution liquid at the screen) and then passing the resulting sand-laden slurry directly into the spiral separator. Alternatively, the method may comprise passing the sand-laden slurry through the debris screen into a dilution compartment and then adding the dilution liquid.

The dilution liquid may comprise water, for example the dilution liquid may be at least 98% by weight water. The method may comprise recycling water from the slurry for use as the dilution liquid. The dilution liquid may be recycled water from the slurry that has been treated with an antibacterial agent. The ratio of dilution of the sand-laden slurry to the dilution liquid may be between 1 :3 and 1 :2 (sand-laden slurry: dilution liquid), for example between 1 :2 and 1 :0.5 by volume.

It may be that water from the sand/water stream, the fibre/water stream and/or the mixed stream (if present) is recovered for subsequent use as the dilution liquid. It may be that said stream is used directly, or after further removal of the fibre and/or sand by settlement or other known physical separation technique (such as screening or dissolved air flotation) The dilution liquid may have a solids content of less than 2% by weight. The dilution liquid may include water separated from the fibre/water stream and/or the sand/water stream. Water may be separated from the fibre/liquid stream and/or the sand/liquid stream downstream of the spiral separator, as described below. By recycling water within the separation process the amount of fresh water required may be reduced, thereby reducing the amount of fluid that must be stored and/or reducing the cost associated with separation of the sand.

The dilution liquid may include fluid (water) taken from a region of, for example an upper region of, a slurry store in which at least a portion of the fibre/water stream is collected after passage through the spiral separator. It may be that fluid from said region of the slurry store is passed to the dilution compartment. The dilution liquid may include fluid (water) obtained from the upper region of the slurry store after the fibre has been allowed to settle.

The dilution liquid may include water separated from the fibre/water stream by passage through a slurry screen, solid separator and/or after dosing one or more flocculants, coagulants and pH adjustment chemicals as described below.

It may be that, during the step of passing the slurry through the spiral separator, the slurry flows down one or more spiral (helical) watercourses (also known as troughs) such that, as the sand-laden slurry travels down the spiral, sand concentrates in the region of the inner end of the width of the watercourse and fibre, for example finer fibre, concentrates in the region of the outer end of the width of the watercourse. The method may comprise using a first stream from the inner side of the watercourse as the sand/water stream and a second stream from the outer side of the watercourse as the fibre/water stream. The method may comprise using a third stream from in-between the first and second streams. The third stream may be a mixed stream comprising sand, water and fibre, for example finer fibre. Dividing the flow through the spiral separator into three streams may increase the purity of the first and second streams.

There may be one or more dividers located in the region of the outlet of the spiral separator. The or each divider may be spaced apart radially from any other divider(s) and the inner and outer edges of the watercourse and positioned so as to separate the flow into first, second and third (if present) streams. Each divider may be an elongate member, for example mounted in and/or on the watercourse. The dividers may be arranged to divide the watercourse into at least two, for example three channels. The method may comprise manually adjusting the dividers, for example the radial position of the dividers in the watercourse in response to flow conditions and the composition of the slurry in order to achieve a required level of sand recovery.

The method may comprise passing the mixed stream back into the spiral separator, for example by passing the mixed stream back to the slurry hopper and/or the feed hopper. Recycling the mixed stream may result in improved separation of the sand and slurry.

The fibre/water stream may be collected in the slurry store. The method may comprise removing fibre, for example finer fibre, from the fibre/water stream. Said fibre may be removed before the fibre/water stream is passed to the slurry store and/or in the slurry store. The remainder of the fibre/water stream after the fibre has been removed may be referred to as a residual slurry stream. The residual slurry stream may comprise at least 98% by weight water. Removing fibre may reduce the solids content of the fibre/water stream and thereby facilitate use of the residual slurry stream as the dilution liquid and recycling of water within the process. Use of the residual slurry stream as the dilution liquid reduces the amount of fresh water required for the process and/or the amount of liquid that must be stored. Additionally or alternatively, removal of the finer fibre may reduce the nutrient content of the residual slurry stream, and methods in accordance with the present process may provide a reduced nutrient level in the residual stream than prior art processes. This may reduce the environmental impact of the residual stream and thereby facilitate disposal and/or storage of animal slurry.

The fibre/water stream may pass through a slurry screen that retains fibre, for example finer fibre but allows water and/or the residual slurry stream to pass through.

The slurry screen may be configured to retain fine fibre particles that have a maximum dimension less than 1 mm, for example from 5 microns up to and including 950 microns, while allowing smaller particles to pass through. The screen may comprise a mesh, for example a mesh having a grating size of less than 1 mm, for example from 10 microns up to and including 950 microns. The fibre separated by the slurry screen may be collected in a fibre hopper or stacked beneath the separator (optionally after mechanical dewatering). The slurry screen may be a rotary drum screen or rundown stream as described above in connection with the debris screen.

Alternatively, a centrifuge, or any other device capable of separating fibre from water may be used instead of a screen.

The method may comprise dosing the fibre/water stream with one or more of a flocculant, coagulant or pH adjustment chemical to form agglomerations of fibre, for example finer fibre. The flocculant may be acrylamide, chitosen or any other suitable flocculant. The coagulant may be poly aluminium chloride (PAC), iron chloride or iron sulphate or any other suitable coagulant. The pH adjustment chemical may be sodium hydroxide, magnesium hydroxide, sodium bicarbonate, mineral acid (sulphuric or hydrochloric) or any other suitable substance. The agglomerations may be flocs, flakes or any other type of agglomeration. The method may comprise removing said agglomerations from the fibre/water stream to produce the residual slurry stream. At least part of the residual slurry stream may be used as the dilution liquid. Without wishing to be bound by theory, the finer fibre is nutrient rich but may include a significant component of the very small particles. Accordingly, dosing to form agglomerations of fibre, for example finer fibre, may reduce the nutrient content of the (residual) slurry in comparison to prior art methods, thereby reducing its environmental impact and facilitating disposal and/or storage.

The dosing and/or removal of the agglomerations may take place in a dosing tank (or compartment) followed by a settlement tank or in a single tank, for example before the fibre/water stream is passed to the slurry store. Thus, the method may comprise collecting the fibre/water stream in a dosing tank and separating the finer fibre in a dosing and/or settlement tank. Alternatively, the dosing and/or separation of agglomerations may take place in the slurry store itself (i.e. the dosing tank may be the slurry store).

The method may comprise allowing the agglomerations to settle and then removing the agglomerations from the fibre/water stream. For example, the agglomerations may rise to an upper region of the tank and be removed therefrom, for example using a scraper. The agglomerations may sink to a lower region of the tank, for example the bottom of the tank, and be removed therefrom, for example by an auger, pump, or via one or more outlets located in the bottom of the tank.

Additionally or alternatively, the agglomerations may be separated from the fibre/water stream by passing said stream through a screen that retains the agglomerations while allowing the residual slurry stream to pass through. Said screen may be located at an outlet from the dosing tank.

The method may comprise bubbling air or other gasses through the tank (or slurry store) to encourage the agglomerations to rise or fall within the tank. The method may comprise using DAF (dissolved air flotation) to separate the agglomerations from the residual stream.

Additionally or alternatively, the agglomerations may be separated from the fibre/water stream using a clarifier tank, e.g. a tank which may optionally include one or more inclined plates. Additionally or alternatively, the agglomerations may be separated from the fibre/water stream using a centrifuge or screw press (in which sludge is dewatered by conveying the sludge along the inside of permeable cylinder).

Following passage through the debris screen (if present) and the spiral separator, the particle size distribution of fibre in the fibre/water stream may be as follows; 95% to 100% having a maximum dimension less than 3mm, 90% to 100% having a maximum dimension less than 1mm, 60% and 80% having a maximum dimension less than 0.01mm (lOmicrons). It may be that 64% of said the fibre at this stage has a maximum dimension less than 10 microns.

The slurry store may be external to the apparatus comprising the spiral separator. For example the slurry store may be an above ground tank or below ground lagoon. The slurry store may be immobile, for example may be permanently located on the farm on which the sand-laden slurry is produced. Alternatively, the slurry store may be a container, for example a compartment, comprised within, e.g. formed as a unit with, the apparatus comprising the spiral separator. The method may comprise collecting the settled fibre from the bottom of the slurry store using an auger. The separated fibre may be suitable for reuse as fertiliser.

It may be that, after exiting the spiral separator, the water content of the sand/water stream is reduced by passage through a dewatering unit. The water so separated may be recombined with the fibre/water stream, for example upstream of the slurry store, or in the slurry store. The dewatering unit may comprise a vibrating screen, of a type known in the art. Sand separated from the sand/water stream may be passed through a dryer, in which the water content of the sand is further reduced by exposure to heat and/or airflow. Sand separated from the sand/water stream may be collected in a sand hopper (after passage through the dryer, if present) or other receptacle, for example a removable receptacle e.g. a bag. Reducing the water content of the sand may render the sand the easier to store and/or reuse, for example by reducing the possibility of bacterial grow within the sand during storage. Additionally or alternatively, increasing the amount of water extracted from the sand may allow that water to be recycled in the process, thereby decreasing the amount of fresh water required to separate the sand and slurry.

The method may comprise rinsing the recovered sand with water dosed with an antibacterial agent. The method may comprise dosing sand separated from the sand/water stream with an antibacterial agent. The antibacterial agent may be hypo- chloride

The steps described above may be carried out sequentially or simultaneously.

It may be that the method described above is carried out by apparatus permanently installed at the location where the sand-laden slurry is generated. It may be that a separation apparatus (for example the apparatus of the second aspect) is mobile and is periodically transported to the site.

The method may comprise a step of reconfiguring the apparatus between a transport configuration and an operative configuration. For example, by moving (for example rotating and/or displacing) the spiral separator between an operative configuration and a transport configuration. The method may comprise reducing the height of the separation unit by moving the spiral separator from an operative configuration to a transport configuration, for example from a substantially vertical orientation to a more horizontal, for example substantially horizontal orientation.

According to a second aspect of the invention there is provided an apparatus for separating sand from sand-laden slurry. The apparatus may comprise a spiral separator configured to separate sand-laden slurry comprising sand, and slurry, the slurry comprising fibre and water into at least a sand/water stream and a fibre/water stream.

The apparatus may comprise any of the features described above with reference to the first aspect and/or be suitable for performing the method according to the first aspect.

The spiral separator may comprise a spiral (helical) watercourse centred on a central axis. The central axis may run longitudinally through the centre of the spiral separator. The watercourse may define a flow path along, for example down which, in use, the sand-laden slurry flows. The geometry of the helical watercourse is such that an initially homogenous distribution of sand-laden slurry across the width of the watercourse changes with distance along the watercourse to have the sand concentrated on one side and the fibre concentrated on the other side. The watercourse may be a channel with raised sides. The spiral separator may comprise an inlet where, in use, the sand-laden slurry enters the spiral separator. The inlet may be located at a first end of the spiral separator. The spiral separator may comprise at least two outlets, for example three outlets, one for each stream. The outlet(s) may be located at a second end of the spiral separator, opposite to the first end. The spiral separator and/or apparatus may be configured such that, in use, the first end is located above the second end. The spiral separator and/or apparatus may be configured such that, in use in the operative configuration, the central axis is substantially vertical.

The apparatus may comprise a debris screen. The debris screen may be a rotary drum screen or inclined screen or other separation device as described above.

The apparatus may comprise a dilution compartment (or hopper) in which sand-laden slurry can be mixed with a dilution liquid. A liquid line may be connected to the dilution compartment to provide a liquid for dilution of the mixture. The dilution compartment may comprise an inlet via which dilution liquid can enter the compartment. The dilution compartment may be connected to the spiral separator by tubing. A pump may be arranged to pump the sand-laden slurry from the dilution compartment to the spiral separator. The dilution compartment may be located in the separation unit. The dilution compartment may be configured to collect sand, water and finer fibre after it has passed through the debris screen. The sand-laden slurry may be collected in the dilution compartment as it exits the debris screen.

The apparatus may comprise a feed hopper, for example in the form of a compartment, configured to receive sand-laden slurry. The apparatus may comprise an auger or other transport apparatus for transporting sand-laden slurry from the feed hopper to the debris screen (if present) and/or the slurry hopper. In the case that the apparatus if formed as a unit (see below) the auger may be mounted on the common platform, for example located wholly inside the unit. Alternatively, the auger may be located partially within the separation unit, and may be configured to connect the separation unit to an external feed hopper.

The apparatus may comprise a dewatering unit configured to separate water from the sand/water stream (i.e. to reduce the water content in the sand). The dewatering unit may be arranged to receive the sand/water stream from the spiral separator. The dewatering unit may comprise a screen and (optionally) one or more motors configured to vibrate the screen. The dewatering unit may be configured to reduce the water content of the separated sand. The dewatering unit may be configured to discharge the separated sand to a sand hopper or other sand receptacle, or to a conveyor or auger. The dewatering unit may be configured to discharge the separated water from the sand/water stream into the collection hopper. The apparatus may comprise further apparatus for drying the sand on exit from the dewatering screen.

The apparatus may comprise a slurry screen configured to separate fibre, for example finer fibre from the fibre/water stream (i.e. to reduce the solids content of the stream). The slurry screen may be an inclined screen, dewatering screen or a rotating drum screen. The apparatus may comprise a dosing tank. The apparatus may comprise a store of flocculant, coagulant and/or pH adjustment chemicals, for example received in one or more storage compartment(s). The apparatus may comprise a dosing system configured to provide a controlled supply of flocculant, coagulant and/or pH adjustment chemicals to the fibre/water stream (e.g. the dosing compartment) from said store/storage compartment.

The apparatus may comprise a slurry store in which the fibre/water stream or residual slurry stream is received, optionally after passage through the slurry screen, dosing tank and/or any other separator for removing agglomerations.

The apparatus may comprise one or more pumps for passing dilution liquid (if present), sand-laden slurry, the sand/water stream, the fibre/water stream and/or the mixed stream (if present) between the different elements, as described above. The apparatus may additionally comprise an outlet suitable for connection to an external slurry store. For example, where the apparatus comprises a slurry store in which the fibre/water stream is received, an outlet may be provided in a lower region of the slurry store for connection to an external slurry store.

The apparatus may be used to separate sand from slurry. For example, wherein 90% of the sand particles that make up the sand have a diameter of less than 0.2 mm and 90% of the sand particles that make up the sand have a diameter of more than 0.07 mm. The apparatus may be used to separate sand from slurry, wherein the sand has a median particle size of 0.1mm to 0.2mm.

The apparatus may be configured for movement between a transport configuration and an operative configuration. It may be that the central axis of the spiral separator is substantially vertical in the operative configuration and substantially horizontal in the transport configuration. The spiral separator may be mounted for movement, for example pivotal movement, between the transport and operative configuration. Alternatively, the spiral separator may be demounted and remounted to reconfigure the apparatus between the transport and operative configuration.

The apparatus as described above may be provided in a single unit. For example, wherein the elements of the apparatus described above are mounted on a common platform and/or framework. Providing the apparatus in a single unit may facilitate transport to the site. It may be that the spiral separator is located at least partial outside the framework of the unit in the operative configuration. It may be that the spiral separator is located within the framework of the unit in the transport configuration.

Alternatively, the apparatus may comprise separate components linked together via pipe or augers or other conveying devises.

Following separation, the sand may be almost pure, or have some small percentage of contaminants present. For example, the sand which is separated and collected may have a purity above 70%, for example above 80%. Where a purity is mentioned as a percentage, it is measured as a weight by weight basis.

The process may recover more than 75% percent (by weight), for example more than 80% (by weight) of the sand present in the sand-laden slurry. The recovered sand being the sand collected from the sand/water stream, for example collected in the sand hopper.

The apparatus may be configured to process between 1 and 30 metric tonnes, for example between 5 and 15 metric tonnes, of sand-laden slurry per hour.

The fibre may have a particle density from around 0.9 g/cm³ to around 1.5 g/cm³. The sand may have a particle density from around 2.6 g/cm³ to around 2.7 g/cm³. Coarser fibre may be defined as fibre particles having a maximum dimension of 1 mm or greater. Finer fibre may be defined as fibre having a maximum dimension of less than 1 mm, for example from 5 microns up to and including 950 microns.

The apparatus of the second aspect may be configured to carry out the method of the first aspect.

In a further aspect of the invention there is provided a kit of parts for use in assembling the apparatus of the second aspect. The kit of parts may comprise any of the elements discussed above in connection with the second aspect.

It will of course be appreciated that features described in relation to one aspect of the present invention may be incorporated into other aspects of the present invention. For example, the method of the invention may incorporate any of the features described with reference to the apparatus of the invention and vice versa.

Description of the Drawings

Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which:

Figure 1 shows a process flow diagram of an example method in accordance with the invention;

Figure 2 shows a process flow diagram of another example method in accordance with the invention;

Figure 3 shows a process flow diagram of another example method in accordance with the invention;

Figure 4a shows a schematic side view of a spiral separator according to an example embodiment;

Figure 4b shows schematic cross sectional view of region 108 of the spiral separator of Figure 4a; and

Figure 5 shows a schematic side view of a separation unit according to an example embodiment.

Detailed Description

Figure 1 shows a process 100 for separating sand from sand-laden slurry 102. The sand-laden slurry 102, which comprises sand, slurry (comprising water and partly or wholly undigested fibre from animal feed) and optionally debris, is fed into a slurry hopper 106 and is diluted with a dilution liquid 104 to form a dilute sand-laden slurry 108. The diluted sand-laden slurry 108 is then passed through a debris screen 110 that separates debris 130 (if present) and coarser fibre 131 from the sand, water and finer fibre. Debris can for example include stones or small plastic objects. In some embodiments, the debris screen is a rotary drum screen. The debris 130 is discharged from the screen 110 to a holding vessel (not shown) or forms a stack beneath the screen. The coarser fibre so extracted may be referred to as manure. In other embodiments, different methods of separating debris and coarser fibre from the slurry may be used (such as a rundown screen). In other embodiments, the sand-laden slurry 102 is passed through a debris screen prior to entering the slurry hopper 106. In yet further embodiments, the debris screen is absent. In yet further embodiments, separate screens (or other devices) may be used to remove the coarser fibre and debris from the dilute sand-laden slurry 108.

The screened sand-laden slurry 112 (comprising sand, water and finer fibre) is fed by gravity or pumped into a spiral separator 114. The spiral separator 114 separates the particles in the sand-laden slurry 112 by density. The spiral separator 114 acts to separate the sand-laden slurry into three streams (in the following order with radial distance from the centre of the spiral): a sand/water stream 118, a mixed stream 132 and a fibre/water stream 116. Dividers (not shown) at the output of the spiral separator 114 direct the three streams into different pathways. In some embodiments only a sand/water stream 118 and fibre/water stream 116 are output from the spiral separator 114.

The sand/water stream 118 passes into a dewatering unit 120 comprising a vibrating screen 120 which removes excess water from the sand. In some embodiments the sand/water stream 118 is rinsed with an antibacterial agent prior to passing into the dewatering unit 120. The excess water 126 that is separated from the sand by the dewatering unit 120 is passed into the slurry store 128. The separated sand 124 is discharged into a holding vessel (not shown) or is stacked next to the screen (not shown). Optionally, the sand passes through a dryer. The separated sand 124 can then be re-used as a bedding material.

The fibre/water stream 116 is passed into the slurry store 128 which may take the form of a large compartment or tank. Fibre particles settle to the bottom of the slurry store 128 over time leaving a layer of excess water 104b in the upper region of the slurry store 128. Some of this excess water 104b is then pumped off the top of the liquor store 128 into the slurry hopper 106 for use as the dilution liquid which is mixed with the sand-laden slurry 102 to form a dilute sand-laden slurry 108. Thus, processes in accordance with the present example may recycle the water used in the separation process and thereby the amount of water required by the separation process may be reduced. Once the process has been started up, fresh water 104a can be added to the system if necessary to replenish that lost to the separated sand 124 or which otherwise exits the system.

The mixed stream 132 contains both sand and finer fibre and is passed back into the slurry hopper 106, in order to be fed back through the spiral separator 114. In other embodiments, the mixed stream may be fed back into the spiral separator 114, for example downstream of the debris screen 110.

Figure 2 shows a variation of the process described in Figure 1. Like reference numerals denote like elements as between Figure 1 and Figure 2, for example the spiral separator is labelled 114 in both Figure 1 and Figure 2. Only those elements of the Figure 2 process which differ from Figure 1 will be described here.

In Figure 2, after exit from the spiral separator 114, the fibre/water stream 116 passes through a slurry screen 113, which retains finer fibre 117 while allowing water to pass through. The resulting residual slurry 123 (comprising primarily water) is directly returned as dilution water 104b to hopper 106 and/or passed to the slurry store 128. The finer fibre 117 is discharged from the slurry screen 113 to a holding vessel (not shown) or further dewatered (not shown) to form a stack beneath the screen. The slurry screen 113 may be a rotary drum screen, an inclined rundown screen, or any other screen suitable for separating finer fibre 117 from the fibre/water stream 116. In yet further embodiments, other device may be used to remove the finer fibre from the dilute fibre/water stream 116. Removing the finer fibre in this way may decrease the nutrient content of the residual slurry thereby reducing the environment impact of the residual slurry and facilitating disposal and/or storage of the residual slurry.

Figure 3 shows a variation of the process described in Figure 2. Like reference numerals denote like elements as between Figure 2 and Figure 3, for example the spiral separator is labelled 114 in both Figure 2 and Figure 3. Only those elements of the Figure 3 process which differ from Figure 2 will be described here.

In Figure 3, after exit from the spiral separator 114, the fibre/water stream 116 is dosed with coagulants and/or flocculants 119 causing coagulation and/or flocculation of the finer fibre particles in the fibre/water stream 116. Example coagulants include poly aluminium chloride (PAC), iron chloride or iron sulphate. Example flocculants include acrylamide, chitosen. pH adjustment may also take place at this stage, for example by dosing the fibre/water stream with sodium hydroxide, magnesium hydroxide, sodium bicarbonate, mineral acid (sulphuric or hydrochloric) . These coagulants, flocculants and pH adjustment chemicals will be well known to the skilled person in the field of water treatment. The resulting solids (e.g. flocs, flakes or other agglomerations of particles, which are composed predominantly of finer fibres) are then separated in a solids separator 121. In some embodiments the solids separator 121 may be a dissolved air flotation (DAF) apparatus. In DAF, air is dissolved in the liquid under pressure and then released at atmospheric pressure in a flotation tank containing the liquid to be treated. The released air forms bubbles which adhere to the suspended matter in the liquid to be treated, causing the matter to float to the surface where it may be removed, for example by a skimming device. In other embodiments, the solids separator 121 may be a screen (e.g. a slurry screen as described above), a centrifuge, or a screw press. In yet further embodiments, the solids separator 121 may take the form of a settlement tank in which the fibre/water stream 116 is received, and mixed with the coagulants and/or flocculants 119. The resulting solids (e.g. flocs, flakes, or other agglomerations) are then allowed to settle to the bottom of the tank (where they can be removed), float to the top of the tank (where they can be removed) and/or be filtered on outlet from the tank.

Excess water 126 from the dewatering unit 120 (if present) can be combined with the residual slurry 123 upstream of the slurry store 128.

In the description of Figures 4 and 5, reference numerals correspond to those of similar elements in Figure 1 to Figure 3, but incremented by one hundred. For example, spiral separator 114 of Figure 1 corresponds to spiral separator 214 of Figure 4a.

Figure 4a shows a spiral separator 214 for separating sand and fibre according to an example embodiment. The spiral separator 214 includes a watercourse 234 that is spiral shaped and is centred around a central axis 236 that runs longitudinally through the spiral separator 214. The watercourse 234 provides a spiral shaped flow path around the central axis 236. The spiral separator 214 includes an input 206 which is configured to feed sand-laden slurry to the watercourse 234 and an output region 238 which includes dividers (not shown) that divide the flow into separate streams as it exits the watercourse 234. In Figure 4a the spiral separator 214 is arranged such that the central axis 236 is vertical. As the sand-laden slurry passes around the watercourse 234 in a spiral flow path, the lower density fibre particles move in a radial direction away from central axis 236 and the higher density sand particles move in a radial direction towards the central axis 236. Region 240 is shown in Figure 4b as a schematic representation of the separation process that occurs within a cross-section of the watercourse 234 as the slurry moves along the flow path.

Figure 4b shows the sand particles (such as 247) as ovals with a solid outline, and the fibre particles (such as 249) as ovals with a dashed outline. The sand particles and the fibre particles are suspended in water (not shown). As the mixture flows down the watercourse 234, the denser sand particles are concentrated in a region located closer to the central axis 236 and the less dense fibre particles are concentrated in a region located further away from the central axis 236. Figure 4b shows a cross section of the watercourse 234 in a plane that is parallel to and passes through the central axis 236. As the mixture passes along the flow path, fibre particles are moved by the outward radial flow 248 away from the centre 236 of the spiral and concentrate in a first region 293, located towards the outer edge of the watercourse 234. Sand particles are moved by the inward radial flow 246 toward the centre of the spiral 236 and concentrate in a second region 297 located towards the inner edge of the watercourse 234. A third region 295, located between the first 293 and second 297 regions contains a mixture of sand and fibre particles. In an exit region 238 of the spiral separator 214, dividers form channels to separate the flow into a sand/water stream (corresponding to the second region 297) from the fibre/water stream (corresponding to the first region 293 and a mixed stream (corresponding to the third region 295).

Figure 5 shows a schematic of a separation unit 301 in accordance with an embodiment of the invention. The separation unit 301 includes a feed hopper 350 positioned at one end of the unit, that is configured to receive the sand-laden slurry. An auger 356 is located on an inner surface of the feed hopper 350 and is configured to draw the sand-laden slurry out of the feed hopper 350. The auger 356 is configured to deposit the sand-laden slurry onto a debris screen 362. The debris screen 362 has a mesh (not shown) which is configured to retain large pieces of debris and coarser fibre while sand, finer fibre and water passes through the mesh into the dilution hopper 352. A slurry hopper 354 is located adjacent to the dilution hopper 352. A first water feed line (not shown) provides water to the screen 362. Water mixes with the sand, finer fibre and water and passes through the screen 362 to form a diluted sand- laden slurry in the dilution hopper 352. Pumps (not shown) are used to push fluid through the various feed lines. The separation unit 301 includes a spiral separator 314 which is located above the slurry hopper 354. Figure 5 shows the spiral separator 314 in an operational position.

The dilution hopper 352 is connected to an input 306 of the spiral separator 314 via a feed line (not shown). A pump (not shown) acts to pump the sand-laden slurry from the dilution hopper 352 through the feed line. The sand-laden slurry is fed from the input 306 into the upper end of the spiral shaped watercourse 334 of the spiral separator 314, which is as described above for Figures 4(a) and 4(b). After being output from the spiral separator the sand/water stream is passed through a dewatering unit 360 which comprises a vibrating screen. The dewatering unit is positioned directly below the spiral separator 314 and above the slurry hopper 354. Water that is separated by the dewatering unit 360 is passed into the slurry hopper 354. Sand is passed from the dewatering unit 360 into a separate sand container or conveyor (not shown). The mixed stream contains a large number of sand particles and fibre. The mixed stream flows to the dilution hopper 352 via a pipe (not shown). The fibre/water stream is directed onto a separate slurry screen 360, where separation of the finer fibre takes place. In other embodiments the apparatus may include a rotary screen, centrifuge or other type of solids separator as discussed above. The apparatus may also include (space for) a store of flocculant, coagulant and/or pH adjustment chemicals for use in dosing the fibre/water stream as discussed above.

Figure 5 shows the unit 301 with the spiral separator 314 in an operational position. For transport, the spiral separator 314 may be moved to a stowed position in which the spiral separator 314 is substantially horizontal and positioned so that it is completely inside the separation unit 301. This is the transport configuration in which the separation unit can be transported.

Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein.

Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments.

Claims

1. A method of separating sand from slurry comprising water and fibre, the method comprising: passing sand-laden slurry, said sand-laden slurry comprising sand and slurry, through a spiral separator and thereby separating the sand-laden slurry into at least a sand/water stream and a fibre/water stream.

2. The method of claim 1, comprising increasing the water content of the sand-laden slurry by mixing the sand-laden slurry with a dilution liquid, before the sand-laden slurry is passed to the spiral separator.

3. The method according to claim 2, wherein water from the sand/water stream and/or the fibre/water stream is recovered for use as the dilution liquid.

4. The method according to claim 2 or claim 3, wherein the dilution liquid comprises water taken from an upper region of a slurry store in which at least a portion of the fibre/water stream is collected after passage through the spiral separator.

5. The method according to any of claims 2 to 4, wherein the dilution liquid has a solids content of less than 2% by weight.

6. The method according to any previous claim, wherein the fibre comprises coarser fibre and finer fibre, and the method comprises removing coarser fibre from the sandladen slurry before the sand-laden slurry is passed to the spiral separator.

7. The method according to any previous claim, wherein the sand-laden slurry further comprises debris and the method comprises removing debris from the sand-laden slurry before the sand-laden slurry is passed to the spiral separator.

8. The method according to claim 6 or claim 7, wherein removing debris and/or coarser fibre comprises passing the sand-laden slurry through a debris screen that retains debris and/or coarser fibre while allowing sand, water and finer fibre to pass through, and optionally, wherein the dilution liquid is added to the sand-laden slurry as the sand-laden slurry is passed through the debris screen.

9. The method according to claim 8, wherein the debris screen is configured to retain particles that have a maximum dimension greater than 1 mm, for example wherein the debris screen is a rotary drum screen and/or a rundown screen.

10. The method according to any previous claim, wherein the fibre comprises coarser fibre and finer fibre, and the method comprises removing finer fibre from the fibre/water stream after passage through the spiral separator.

11. The method according to claim 10, wherein removing finer fibre comprises dosing the fibre/water stream with one or more of a coagulant, a flocculant and a pH adjustment chemical to form agglomerations of finer fibre, and then removing said agglomerations from the fibre/water stream to produce a residual slurry stream.

12. The method according to claim 11, comprising removing agglomerations by allowing them to settle, using dissolved air flotation (DAF), using a screen, a clarifier tank, a centrifuge or a screw press.

13. The method according to any of claims 10 to 12, comprising passing the fibre/water stream through a slurry screen that retains finer fibre and/or agglomerations while allowing the residual slurry stream to pass through.

14. The method according to any previous claim, wherein during the step of passing the sand-laden slurry through the spiral separator, the sand-laden slurry flows down one or more spiral watercourses such that sand concentrates in the region of the inner end of the width of the watercourse and fibre concentrates in the region of the outer end of the width of the watercourse, and the method comprises using a first stream from the inner side of the watercourse as the sand/water stream and a second stream from the outer side of the watercourse as the fibre/water stream.

15. The method according to claim 14, comprising using a third stream from inbetween the first and second streams as a mixed stream comprising sand, fibre and water, and passing the mixed stream back to the spiral separator to be separated again.

16. The method according to any previous claim, wherein after exiting the spiral separator, the water content of the sand/water stream is reduced by passage through a dewatering unit and/or a dryer.

17. The method according to any previous claim, further comprising dosing sand separated from the sand/water stream with an antibacterial agent.

18. An apparatus for separating sand from slurry, the apparatus comprising a spiral separator configured to separate sand-laden slurry comprising sand and slurry, the slurry comprising fibre and water, into at least a sand/water stream and a fibre/water stream.

19. The apparatus of claim 18, wherein the spiral separator comprises one or more dividers arranged to split the flow through the separator into a sand/water stream, a fibre/water stream and a mixed stream comprising sand, water and fibre.

20. The apparatus of claim 18 or claim 19, wherein the apparatus comprises: a dilution hopper in the form of a compartment in which sand-laden slurry can be mixed with a dilution liquid; and a rotary drum screen comprising a substantially cylindrical screen mounted for rotation about a longitudinal axis relative to an inlet and being configured to retain debris and/or coarser fibre while sand, finer fibre and water passes through, and wherein the apparatus is configured such that sand-laden slurry from the dilution hopper is passed to the inlet of the rotary drum screen such that the rotary drum screen can remove debris and/or coarser fibre therefrom before the slurry is passed to the spiral separator.

21. The apparatus of any of claims 18 to 20, wherein the apparatus comprises a slurry store configured to receive the fibre/water stream from the spiral separator, and optionally wherein the apparatus is configured such that water from an upper region of said store is passed to the dilution hopper as the dilution liquid.

22. The apparatus of any of claims 18 to 21, wherein the apparatus comprises a slurry screen configured to retain finer fibre from the fibre/water stream, and the apparatus is configured such that the fibre/water stream from the spiral separator passes through the slurry screen and the resulting residual slurry stream is passed to the slurry store.

23. The apparatus of any of claims 18 to 22, further comprising a dosing tank in which the fibre/water stream is received, one or more storage compartment(s) for receiving a store of flocculant, coagulant and/or pH adjustment chemicals, and a dosing system configured to provide a controlled supply of flocculant, coagulant and/or pH adjustment chemicals to the dosing tank from said store(s) when received in said storage compartment(s).

24. The apparatus of any of claims 18 to 23, wherein the apparatus is provided as a single unit.

25. The apparatus of any of claims 18 to 24, configured to carry out the method of any of claims 1 to 17.

26. A kit of parts for assembling the apparatus of any of claims 18 to 25, the kit comprising one or more of the spiral separator, dividers, dilution hopper, rotary drum screen and slurry store.