WO2005044436A1

WO2005044436A1 - Improved mixing methods and associated mixing units

Info

Publication number: WO2005044436A1
Application number: PCT/NZ2004/000282
Authority: WO
Inventors: Kevin Cosgrove
Original assignee: Dan Cosgrove Ltd.
Priority date: 2003-11-07
Filing date: 2004-11-05
Publication date: 2005-05-19
Also published as: AU2004287348A1

Abstract

An apparatus and method for homogeneously mixing dry particulate fertilisers with a liquid using mixing units (50), in a batch or continuous controlled mixing processes, wherein the amount of dry particulate material is added in either; (a) small doses, maintaining ratios of between 1: 40 to 1: 500, weight dry particulate material to volume liquid (w/v), or (b) the particulate material is added to the liquid at a mass flow rate of 9 Kg/min or less.

Description

IMPROVED MIXING METHODS AND ASSOCIATED MIXING UNITS

TECHNICAL FIELD

The present invention relates to methods and mixing units for mixing dry particulate materials with liquid. More specifically the invention relates to methods and associated mixing units for bulk, in-situ, on-demand mixing of materials such as fertilisers, including urea, for use in liquid applications such as field irrigation.

BACKGROUND ART

Bulk mixing of dry particulate materials in liquids is completed in order to facilitate liquid application of the materials for a variety of applications such as via irrigation.

One type of particulate material, fertiliser, is an important tool for maximising the value of land. For example, by supplementation of soils to encourage strong growth of grass that would not normally support growth levels achieved without using fertilisers.

Many different fertilisers have been developed including: urea, various nitrate compounds, and more complex compounds such as complex fertiliser (NPK), mono-ammonium phosphate (MAP), and di-ammonium phosphate (DAP).

For ease of reference only, throughout this specification reference will be made to urea as the fertiliser. However, this should not be seen as limiting, as it should be appreciated by those skilled in the art, that the same issues regarding the application and mixing that occur for urea, also occur for other fertilisers and particulate materials generally. Urea fertiliser is typically marketed as a solid in powder or granule form which is then applied either directly to the soil in solid form, or it is dissolved and/or diluted into water or other solutions and irrigated onto soil.

When solid urea is added directly to the ground important considerations exist for the user. According to one source (www.montana.edu/wwwpb/ag/baudr131.html), this method of application is a gamble as urea can often be lost before absorption into the soil as it easily converts to a gas and dissipates into the atmosphere before being absorbed into the soil.

Recommendations to avoid this problem include applying solid forms of urea only when moisture is present on the area to be applied, or when there is a high likelihood of moisture occurring shortly after application, for example, from rain, dew or irrigation.

A further consideration when applying solid urea is that the uniformity of particle size is important. Where particles such as granules are not of a uniform size, variations in density of fertiliser applied to soil may result, as well as material handling issues from equipment not built to handle the unusual and/or variation in granule sizes.

Yet another difficulty with solid urea application is that wheel marks are left on pasture as the urea is applied using tractors, trucks or other vehicles.

Due to the above problems with solid urea, alternative means of application using liquid solutions of urea have been developed and are used commercially. In its simplest form, liquid urea is manufactured by mixing solid urea with a sufficient quantity of water to make up the desired concentration of dissolved urea. The liquid is then applied using an irhgator or similar device, to the ground to be fertilised (termed 'fertigation' for the purposes of this specification). However a variety of problems with this method have been found.

Firstly, the method is labour intensive. The expectation is that the end user, for example a farmer, will order the correct amount of urea (and typically store a considerable quantity of solid urea) and then, when it is required, measure out the desired quantity of solid urea and mix with water for application via an irrigation system.

A further problem is that fertilisers are difficult to mix evenly. Problems exist with a lack of uniformity during mixing and/or precipitate formation. Also urea also reacts endothermically during mixing with water which decreases the temperature to a point where precipitate formation is more likely. Also the dissolution rate slows or even stops in cooler temperatures caused by the endothermic reaction. Besides the problem of varying concentrations from non-uniform mixing and/or precipitate formation and/or un-dissolved solids, solids or precipitates can block irrigation equipment thus causing further undue labour and time being expended, and may also cause difficulties with achieving an even application of fertiliser.

Options considered to address the above issues include the use of impellers for thorough mixing, heating to counter the effects of endothermic reactions or cool temperatures, and use of additives such as the suspended water in oil solution of US 5,445,663. All of these options incur additional costs such as the capital cost of an impeller, the utility cost of heating and the material cost of oils.

Bulk production of liquid fertilisers including urea particularly by fertiliser manufacturer's, has been considered as one way of addressing the above problems. By producing the liquid fertiliser in bulk, by way of economies of scale, the capital cost is offset. However, with bulk production, the buyer in effect pays extra in transport costs in that they are paying to transport not only the fertiliser but also water to the distribution point. In addition, the fertiliser concentration (and as a result, nutrient content) of the liquid fertiliser is generally maintained at a lower level in bulk liquid preparations as the water content must be increased to avoid precipitation of nutrient salts during storage and transportation. Further, the user is forced to pre-order their fertiliser well in advance as they are competing with other users for the end product.

Yet a further problem of handling fertilisers generally is that of safety. Many solid or dried fertilisers are dangerous to health, for example, if fertiliser dust is inhaled and/or the fertiliser is handled using bare skin, the user may suffer an adverse toxic or allergic reaction. In addition, bulk amounts of fertiliser are difficult to handle due to physical size as lifting machinery and other equipment such as pumps and storage hoppers are required.

One ideal method of delivering a fertiliser would be an automated or semi- automated mixing unit and associated method that is available on demand, is cost effective, safe, applies an accurate amount of fertiliser to the area to be fertilised, and is able to be installed in-situ at or close to the distribution site.

It is an object of the present invention to address the foregoing problems or at least to provide the public with a useful choice.

All references, including any patents or patent applications cited in this specification are hereby incorporated by reference. No admission is made that any reference constitutes prior art. The discussion of the references states what their authors assert, and the applicants reserve the right to challenge the accuracy and pertinency of the cited documents. It will be clearly understood that, although a number of prior art publications are referred to herein, this reference does not constitute an admission that any of these documents form part of the common general knowledge in the art, in New Zealand or in any other country. It is acknowledged that the term 'comprise' may, under varying jurisdictions, be attributed with either an exclusive or an inclusive meaning. For the purpose of this specification, and unless otherwise noted, the term 'comprise' shall have an inclusive meaning - i.e. that it will be taken to mean an inclusion of not only the listed components it directly references, but also other non-specified components or elements. This rationale will also be used when the term 'comprised' or 'comprising' is used in relation to one or more steps in a method or process.

Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only.

DISCLOSURE OF INVENTION

For the purposes of this specification and for ease of reading, the term 'dry particulate material' will be used interchangeably with the term 'fertiliser'. This should not be seen as limiting as it should be appreciated by those skilled in the art that the method can also be applied for mixing dry particulate materials other than just fertilisers.

Further, for the purposes of this invention, the term 'bulk mixing' refers to amounts of greater than approximately 50 litres of aqueous solution but this should not be seen as limiting i.e. it is possible to use lesser amounts without departing from the scope of the invention as described.

According to one aspect of the present invention there is provided a method of bulk mixing a dry particulate material and a liquid to form an aqueous solution including the steps of:

(a) adding a dose of dry particulate material to a liquid in a mixing tank whereby the dose is at a ratio of approximately 1 :40 to 1 :500 weight dry particulate material to volume liquid (w/v);

(b) adding at least one further dose at a ratio of approximately 1 :40 to 1 :500 w/v until a required concentration of aqueous solution is reached; and characterised in that the resulting aqueous solution has substantially all dry particulate material mixed into the liquid to a uniform concentration in the aqueous solution.

Preferably, the method is achieved by adding a total of approximately 15 to 50 separate doses of dry particulate material to the liquid to form the resulting aqueous solution. In one embodiment, each dose may be approximately 10 kg of dry particulate material per 750 litres of liquid. It should be appreciated by those skilled in the art, however, that a dose above or below this range may also be used where greater or lesser concentrations of aqueous solution are desired.

According to a further aspect of the present invention there is provided a method of bulk mixing a dry particulate material and a liquid to form an aqueous solution including the step of:

(a) adding dry particulate material to a liquid in a mixing tank whereby the dry particulate material is added to the mixing tank at a flow rate of approximately 9 kg/min or less to form an aqueous solution in the mixing tank; and characterised in that the resulting aqueous solution has substantially all dry particulate material mixed into the liquid to a uniform concentration in the aqueous solution. Preferably, in the above embodiment, the flow of dry particulate material is on a continuous basis.

It is the applicant's experience that for the above embodiment, for flow rates greater than approximately 9 kg/min, incomplete mixing occurs, for example, due to the temperature becoming too cold when urea is used. An advantage of continuous processing is that the feed apparatus such as a auger runs for longer periods of time than for discrete batch mixing embodiments resulting in less equipment wear and tear.

In a preferred embodiment approximately 250 kg of dry particulate material is added to 750 litres of liquid. It should be appreciated that amounts outside of 250kg dry particulate material to 750 litres of liquid may also be used in accordance with the present invention and that this amount is given by way of illustration only.

Preferably, during step (b), the metered dose of dry particulate material and liquid is passed through an inlet filter before entry into the mixing tank. In preferred embodiments the inlet filter may be a metal mesh of substantially 20mm x 3mm holes. It is the applicant's experience that granules of dry particulate material strike the surface of the mesh and, if small enough, pass through the mesh or, if larger, are caught by the mesh and breakdown (to eventually pass through the mesh) due to the action of the liquid passing over the mesh and granules.

Preferably the filter is of a cylindrical shape with the liquid entering one end of the cylinder as a spray. Solid dry particulate material also enters the same end of the cylinder as the liquid. Preferably, the mesh is located at a point substantially central to the cylinder cross-section.

Preferably, the method includes a further step, step (d), after step (b) or step (c) of: (d) recycling the aqueous solution in the mixing tank through the inlet filter.

In preferred embodiments, the aqueous solution is recycled in step (d) by drawing aqueous solution from the mixing tank via a recycle pump preferably located at the bottom of the mixing tank.

Preferably, the mixing tank may be capable of retaining substantially from 500 to 3000 litres of liquid or an aqueous solution. It should be appreciated by those skilled in the art, however, that the size of the mixing tank may be dependent on the amount of dry particulate material to be mixed, hence, if a greater amount of aqueous solution is required, larger mixing tanks may be used and similarly, for smaller amounts, smaller mixing tanks may be used.

Preferably, the mixing tank may be at least partially filled with liquid before dry particulate material is added. Most preferably, the liquid added to the tank initially may be the total amount of liquid to be mixed.

Preferably, the liquid or aqueous solution in the mixing tank may be recycled back through the inlet filter. Most preferably, liquid may be recycled by drawing liquid from the base of the mixing tank via a pump. In further preferred embodiments it may be advantageous to include an outlet filter located between the tank outlet and the inlet filter, more preferably between the tank outlet and recycle pump. Most preferably this outlet filter may be made up of a smaller sized mesh than the inlet filter to remove any un-dissolved particulate material.

According to a further aspect of the present invention there is provided a method of bulk mixing a dry particulate material and a liquid to form an aqueous solution including the steps of: (a) adding a dose of dry particulate material to a liquid in a mixing unit that includes:

(i) an exterior tank;

(ii) an interior tank that: a. is situated at least partially within the exterior tank; b. drains liquid into an exterior tank via one or more narrow apertures; and, c. a recycle loop including a pump for conveying liquid from the base of the exterior tank into the top of the interior tank configured such that the flow rate of liquid through the recycle loop is sufficient to create a turbulent environment in the interior tank;

(b) running the recycle loop for a time period of approximately 10 minutes to 120 minutes; and characterised in that the resulting aqueous solution has substantially all dry particulate material mixed into the liquid to a uniform concentration in the aqueous solution.

Preferably, in the method described above, the mixing unit is also configured to, in- operation when the recycle pump is running, result in a liquid level differential between the liquid level in the interior tank and the liquid level in the exterior tank. Most preferably, this differential is approximately 50 to 300 mm, more preferably, approximately 200 mm. However, it should be appreciated by those skilled in the art that this amount may vary depending on the flow rate through the recycle loop and the scale and dimensions of the unit items such the as size of the interior tank outlets and the interior and exterior tank circumference. Preferably, the flow rate of liquid through the recycle loop is operated at approximately 200 to 300 litres per minute, more preferably, approximately 260 litres per minute. This flow rate amount should not be seen as limiting as it should be appreciated by those skilled in the art that this amount may vary depending on variables such as the stage of operation, the particulate material being mixed and aspects of the mixing unit design.

In preferred embodiments, the exterior tank holds approximately 500 to 6000 litres of liquid, preferably approximately 4000 litres and the interior tank holds approximately 100 to 1500 litres of liquid, preferably approximately 1150 litres.

In preferred embodiments of the above method, the interior tank is configured to include a total of six outlet apertures which are preferably hoses. Preferably, five of the outlet apertures are positioned equidistantly around the circumference of the bottom of the interior tank. More preferably, the outlet hoses are positioned such that their outlet is pointed in an upwards direction. Preferably, there is one centrally located outlet hose which is attached to the bottom of the interior tank. Preferably, the outlet of this hose is located towards or on the floor of the exterior tank.

In preferred embodiments, the interior tank of the above mixing unit further includes a number of wall sections within the interior tank. Preferably, the interior tank includes a plurality of wall sections (preferably a total of 10 sections) of equal width and height with every second section including slots in a mesh configuration through which liquid can pass. It should be appreciated by those skilled in the art that a variety of differing interior wall section configurations may be used without departing from the scope of the invention as described.

Preferably, the outlet apertures located around the circumference of the base of the interior tank are located to substantially correspond to each mesh wall section described above.

Preferably, the interior tank also has a mesh base section located above the actual floor of the interior tank.

Most preferably, the mesh in both the wall sections and base section are of a size sufficient to filter any large particles of solid fertiliser and, through the eroding action of liquid within the interior tank, be retained until reduced in size to a point when the particle can pass through the mesh. In the inventor's experience, the preferred mesh has a plurality of apertures of approximately 20mm x 3mm in size.

Most preferably, the time for the mixing operation is approximately 60 minutes. It should be appreciated that the time period may vary depending on the characteristics of the material being mixed and other variables such as the ambient temperature. However, it is the inventor's experience that a time period of 60 minutes is sufficient for most fertiliser applications such as for urea mixing.

In preferred embodiments, when mixing is complete, the recycle line may be detached from the interior tank inlet and the recycle pump used to pump the liquid fertiliser solution to a holding tank or directly into an irrigation system.

Preferably the exterior tank includes a level control mechanism to shut off the liquid supply when a predetermined level of liquid in the mixing unit is reached. Most preferably, the level control mechanism is a ballcock valve located at the liquid inlet.

Preferably, the dry particulate material is added to the mixing unit via apparatus including an auger, a hopper, a funnel and combinations of these apparatus.

The applicant has found that by carefully controlling the amount of dry particulate material added in small doses, or adding the material at or below the specified flow rate or by specific mixing unit design, the above methods and mixing units result in an unexpected improvement. Improvements such as disadvantages of the prior art including incomplete bulk mixing and high costs from equipment requirements, transport and other costs have been overcome. The machinery is simple in design and simple to operate, thus lowering capital costs and importantly, there is substantially no particulate formation that would lead to incomplete mixing. The methods and associated mixing units also enable the process of 'fertigation' or applying fertiliser directly to pasture via an irrigation system as the aqueous solution formed can be pumped directly into an irrigation system.

Preferably, the dry particulate material may be a fertiliser. In preferred embodiments, the fertiliser may be selected from the group consisting of: urea, ammonium nitrate, calcium nitrate, sodium nitrate, complex fertiliser (NPK), mono ammonium phosphate (MAP), di-ammonium phosphate (DAP), potassium phosphate, and combinations thereof. Most preferably, the dry particulate material may be urea.

In preferred embodiments, the dry particulate material is in the form of a plurality of granules. It is envisaged that granules need not be of uniform size or shape. An advantage of the present invention is that a range of dry particulate sizes may be used and where granules are large, they are reduced into smaller sizes via the mixing method and steps of the present invention.

Preferably, the liquid may be water. It should be appreciated by those skilled in the art that other liquids and/or solids suspended in the liquid may also be included, for example weed killers, pesticides and other compounds.

In preferred embodiments, no further liquid may be added to the mixing tank once addition of dry particulate material begins. In a further preferred embodiment, the aqueous solution obtained from the method substantially as described above may be transferred to either a storage tank or directly to an irrigation system. It is the applicant's experience that by use of a storage tank, a semi-continuous process is obtained whereby, as irrigation proceeds, the soil may be irrigated with the aqueous solution pumped from the storage tank, and the storage tank topped up as required from the mixing tank.

This can either be a manual system, for example via visual tank level checks by the operator or via an automated process such as by use of level controllers on the storage tank switching on or off the mixing process/addition of liquid.

In a further preferred embodiment, the dosing process, including the metering of dry particulate material, may be completed using an automated process and control system. Preferably the operator may insert into the control system either: the amount of dry particulate material to be mixed; the end concentration of aqueous solution required; or the end volume of aqueous solution required; and combinations thereof.

In a yet further preferred embodiment, the dry particulate material is stored before use in a storage hopper. Preferably, the hopper is substantially water and air tight. In preferred embodiments, the hopper includes weight measurement apparatus such as one or more load cells which measure the weight of dry particulate material held within the hopper.

In preferred embodiments, the weight measurement apparatus are preferably linked to an overall control system which monitors the weight of material added from the hopper into the mixing unit and starts and stops addition of material based on the weight parameters entered by the operator or according to a predetermined weight parameter or parameters. Preferably, the hopper is elevated above the ground. It is the inventor's experience that, by raising the hopper, the overall unit can be used for other applications such as for general storage of dry particulate material and material stored within the hopper can be easily emptied by gravity, for example into a truck. This is advantageous as it is preferable to have only one storage hopper per site to avoid unnecessary capital expense. A further advantage of easy emptying is that the dry particulate material used can be altered relatively easy without need for pumps or other solids transport devices.

An advantage of the above mixing methods are that the dose of aqueous solution added to a particular area for example a field, may be controlled and manipulated thus allowing the operator greater control of the dry particulate material/aqueous solution.

According to a further aspect of the present invention there is provided an aqueous solution produced in accordance with the method substantially as described above.

According to a further aspect of the present invention there is provided a mixing unit including: a feed mechanism for adding dry particulate material to a mixing tank; a mixing tank; a recycle loop for conveying liquid from the base of the mixing tank to the top of the mixing tank; characterised in that the feed mechanism is capable of adding a plurality of doses of dry particulate material to liquid in the mixing tank, whereby each dose is added at a ratio of approximately 1 :40 to 1 :500 weight dry particulate material to volume liquid (w/v). According to a yet further aspect of the present invention there is provided a mixing unit including: a feed mechanism for adding dry particulate material to a mixing tank; a mixing tank; a recycle loop for conveying liquid from the base of the mixing tank to the top of the mixing tank; characterised in that the feed mechanism is capable of adding a measured flow rate of dry particulate material to liquid in the mixing tank, whereby the flow rate does not exceed approximately 9 kg/min.

In a further preferred embodiment, the mixing unit may include an inlet filter through which the dry particulate material passes before entry into the mixing tank. Preferably, the liquid used may also pass through the same inlet filter as the dry particulate material. Most preferably, the dry particulate material and liquid may be in intimate contact within the inlet filter.

In a further preferred embodiment, the mixing unit may include an outlet filter located within the recycle loop through which the liquid and/or aqueous solution passes.

According to a yet further aspect of the present invention there is provided a mixing unit including: an exterior tank; an interior tank that:

(i) is situated at least partially within the exterior tank; (ii) drains liquid into an exterior tank via one or more narrow apertures; and, a recycle loop for conveying liquid from the base of the exterior tank into the top of the interior tank; a feed mechanism for adding dry particulate material to a mixing tank; characterised in that the flow rate of solution through the recycle loop is sufficient to create a turbulent environment in the interior tank.

Preferably, the mixing unit is also configured to, in-operation when the recycle pump is running, result in a liquid level differential between the liquid level in the interior tank and the liquid level in the exterior tank. Most preferably, this differential is approximately 50 to 300 mm, most preferably 200 mm. However, it should be appreciated by those skilled in the art that this amount may vary depending on the flow rate through the recycle loop and the scale and dimensions of the unit items such the as size of the interior tank outlets and the interior and exterior tank circumference.

Preferably, the flow rate of liquid through the recycle loop is approximately 200 to 300 litres per minute, more preferably approximately 260 litres per minute. Like the liquid differential, this flow rate should not be seen as limiting as it should be appreciated by those skilled in the art that this amount may vary depending on the scale and dimensions of the unit items such the as size of the interior tank outlets, the interior and exterior tank circumference and the recycle pump rating.

In preferred embodiments, the exterior tank holds approximately 500 to 6000 litres of liquid, preferably approximately 4000 litres and the interior tank holds approximately 100 to 1500 litres of liquid, preferably approximately 1150 litres. In the above embodiment, the interior tank is preferably elevated from the floor of the exterior tank by legs. In preferred embodiments, a total of five legs are used, with the legs being positioned equidistant from each other. Preferably, the legs elevate the interior tank approximately 500 to 900 mm above the floor of the exterior tank. More preferably, the interior tank is elevated approximately 700 mm above the floor of the exterior tank.

Preferably the interior tank has an inlet at the top of the tank for introducing a particulate material such as fertiliser into the interior tank.

In preferred embodiments, the interior tank is configured to include a total of six outlet apertures which are preferably hoses. Preferably, five of the outlet apertures are positioned equidistantly around the circumference of the bottom of the interior tank. More preferably, the outlet hoses are positioned such that their outlet is pointed in an upwards direction. Preferably there is one centrally located outlet hose which exits the bottom of the interior tank. Preferably the outlet of this hose is positioned on the floor of the exterior tank.

In preferred embodiments, the interior tank of the above mixing unit further includes a number of wall sections within the interior tank. Preferably, the interior tank includes a total of 10 sections of equal width and height with every second section including slots in a mesh configuration through which liquid can pass. It should be appreciated by those skilled in the art that a variety of differing interior wall section configurations may be used without departing from the scope of the invention as described.

Preferably, the outlet apertures located around the circumference of the base of the interior tank are located to substantially correspond to each mesh wall section described above. Preferably the interior tank also has a mesh base section located above the actual floor of the interior tank.

Preferably, the mesh in both the wall sections and base section are of a size sufficient to filter any large particles of solid fertiliser and, through the eroding action of liquid within the interior tank, be retained until reduced in size to a point when the particle can pass through the mesh. In the inventor's experience, the preferred mesh has a plurality of apertures of approximately 20mm x 3mm in size.

Preferably, the mixing unit feed mechanism may be an auger.

Preferably, the mixing unit may further include a storage hopper for storage of dry particulate material prior to entry into the feed mechanism.

In preferred embodiments, the storage hopper may include at least one weight measurement device such, as a load cell. Preferably, the weight measurement device or devices may be used to monitor the dose of dry particulate material added to the mixing unit and/or may be used to monitor the flow rate of dry particulate material added to the mixing unit.

Preferably, the amount of dose added and/or flow rate of dry particulate material added to the mixing unit may be controlled via an automated control system. In a further preferred embodiment, the mixing unit may include a storage tank for housing of aqueous solution after mixing in the mixing tank. In an alternative embodiment, the unit may be adapted to be able to deliver aqueous mixed solution directly into an irrigation system (termed 'fertigation' for the purposes of this specification).

It should be appreciated from the above description that there is provided a methods and mixing units for mixing together a dry particulate material and a liquid that overcome problems of prior art methods including undissolved particles, non- uniform mixing and/or precipitate formation resulting in, for example, uniform pasture growth where the material is fertiliser. A further advantage is that the methods and mixing units allow the ability of in-situ or on-demand mixing and application. Also the equipment required is simple in nature and cost effective to use. Further, as the mixing processes are self contained, the labour requirement is minimised, accuracy of application is increased and safety and handling issues are minimised. A further benefit in relation to fertiliser use, is that no wheel marks are left on pasture as tractors, trucks etc do not need to drive over pasture using the method of the present invention i.e. the liquid fertiliser produced is pumped directly into an irrigation system.

BRIEF DESCRIPTION OF THE DRAWINGS

Further aspects of the present invention will become apparent from the following description which is given by way of example only and with reference to the accompanying drawing in which:

Figure 1 is a flow diagram of a preferred embodiment of the present invention;

Figure 2 is a cross-section elevation view of one preferred mixing unit embodiment; and,

Figure 3 is a partial cross-section plan view of the embodiment shown in Figure 2.

BEST MODES FOR CARRYING OUT THE INVENTION

The methods of mixing and associated mixing units will now be described with reference to preferred embodiments.

General

Referring to Figures 1 to 3, dry particulate material such as urea (1 ) arrives at the processing site via standard transport methods, in this example depicted as a truck (2). In this case, the site is a mixing unit located on a farm (generally indicated by arrow 18).

For the purposes of this section, reference will be made to the dry particulate material being either a fertiliser, urea fertiliser or material. This should not be seen as limiting as it should be appreciated by those skilled in the art that other materials besides fertiliser may be used in accordance with the present invention.

The fertiliser (1 ) is transported using known means such as a pump (3) into a storage hopper (4) on the mixing unit (18). The hopper (4) is substantially watertight and air-tight and preferably capable of retaining a store of fertiliser (1) for use at a later time.

In preferred embodiments the hopper (4) is elevated above ground level sufficient to allow access underneath by a truck (2). This has the advantage of allowing easy access to transport vehicles (2) in the case where the hopper (4) is to be emptied and, as the hopper (4) is elevated, the material (1 ) within the hopper (4) can empty via gravity without need for various solids transport devices such as pumps.

Automated mini-batch mixing and semi-continuous mixing embodiments

The description is now made with reference to the embodiment shown in Figure 1.

The hopper (4) also preferably includes at least one weight sensing device, such as a load cell (not shown). This device aids in determining the dose of fertiliser (1 ) to be mixed into liquid (7) for example, an operator can visually monitor the weight of fertiliser (1 ) added from the hopper (4) by viewing the weight change as measured via the load cell or cells. Alternatively, the weight measurement devices are monitored by a control system which measures the weight of material (1 ) in the hopper (4) and, based on predetermined parameters starts, stops and/or controls the flow rate of fertiliser (1 ) added to the liquid (7) in the mixing tank (11).

When the fertiliser material (1 ) is required, the operator e.g. a farmer, enters a parameter into a control system (not shown) including: the desired quantity of dried particulate fertiliser (1) to be used; the volume of aqueous solution required; or the concentration of aqueous solution required. The control system then begins the mixing process by adding liquid (7) to a mixing tank (11 ) up to the desired quantity. The desired quantity of liquid (7) is based on at least one of the parameters chosen above. The liquid (7) is added using control and actuator devices, for example, a valve (8). It is desirable for the valve (8) opening (not shown) to be substantially water-tight and air-tight. This ensures that the hopper (4), auger (5) and measuring container (6) remain free of water residues and further, that particles from the fertiliser (1 ) do not spread into the environment. A further advantage of the water-tight and air-tight valve (8) is that it is simple to clean the auger (5) and measuring container (6) as the valve (8) prevents blockages due to lump formation with moisture in the auger (5).

Once the liquid (7) in the tank (11) reaches the desired level, measured for example using a level controller (not shown), the liquid flow (7) to the tank (11 ) is stopped and a recycle pump (14) is started. Liquid (7) then flows in a closed loop through an inlet filter (10), into the mixing tank (11 ), out of a tank outlet (12), through an outlet filter (13), through the recycle pump (14), and back through the inlet filter (10).

In one preferred method ('mini-batch mixing') a first metered dose of fertiliser (1) is transported to a measuring container (6) via a screw auger (5) or other solids transport device. The fertiliser (1) is preferably retained within the measuring container (6) until the first desired discrete dosage is reached (measured for example using a level controller on the container via load cells under the hopper (4) or a flow rate monitor on the auger (5)). Once the dosage amount is reached, for example between 5 and 20 kg of fertiliser (1 ), a valve (9) opens at the bottom of the container (6) and the fertiliser (1), via gravity, passes through to the inlet filter (10) where it mixes with the liquid (7) in the mixing tank (11 ). It should be appreciated that other transport mechanisms besides gravity may be used in accordance with the present invention.

In an alternative method ('semi continuous mixing') a metered volume of approximately 250 kg of fertiliser (1 ) is transported via a screw auger (5) or other solids transport device on a continuous basis to the mixing tank (11 ) containing approximately 750 litres of liquid (7) via the inlet filter (10). The flow rate of fertiliser (1) is carefully monitored so that it does not exceed approximately 9 kg/min.

The fertiliser (1 ) either passes directly through the inlet filter (10) or, if the particles are too large, the fertiliser (1 ) is retained by an inlet filter mesh (not shown) within the inlet filter (10). Through the dissolving action of liquid (7) passing over the retained fertiliser (1 ), the larger particles are broken down until they are small enough to pass through the inlet filter mesh.

Once in the mixing tank (11 ), the liquid (7) and fertiliser (1) mix to form an aqueous solution via the turbulent action of the solution in the tank (11 ). The turbulent action results from the liquid (7) entering the tank (11 ) and/or exiting the tank (11 ). It is the applicant's experience that it is preferable to avoid the use of impellers or other mixing elements in the mixing tank (11 ) to avoid extra capital cost, although it should be appreciated by those skilled in the art that such mixing elements could be included, if so desired.

After a predetermined period of time, further fertiliser (1 ) may be added to the mixing tank (11 ) in further amounts or does using either the 'mini-batch' or 'semi- continuous' methods until the desired volume or concentration of fertiliser (1) enters the mixing tank (11) and/or holding tank (16) and/or irrigation system (17).

Once mixing finishes, the aqueous solution formed in the mixing tank (11 ) may then either be pumped (15) to a larger holding tank (16) for later application via an irrigation system (17), or pumped (15) directly into an irrigation system (17) for application to soil, termed 'fertigation' for the purposes of this specification. By careful monitoring of the holding tank (16) and/or mixing tank (11 ) levels, semi- continuous irrigation (17) is possible i.e. holding tank (16) levels may be monitored and as they reduce, more aqueous solution may be produced, topping up the holding tank (16) level.

Manual Batch Mixing Unit Embodiment

The description is now made with reference to the embodiment shown in Figures 2 and 3.

The apparatus of an alternative embodiment of the present invention termed manual batch mixing unit for the purposes of this example is generally indicated in Figure 2 by arrow 50 and in Figure 3 by arrow 100. Figure 2 shows a front elevation of the manual batch mixing unit along section B shown in Figure 3. Figure 3 shows a partial plan elevation along section A shown in Figure 2.

The manual batch mixing unit 50,100 includes two tanks 51 ,52, one positioned within the other tank (the interior tank 51 ) and an outer larger tank (the exterior tank 52). In a preferred embodiment, the exterior tank 52 is approximately 6000 litres in size and in operation, holds approximately 4000 litres of liquid. In this embodiment, the interior tank 51 has a capacity of approximately 1150 litres.

The interior tank 51 is elevated from the floor of the exterior tank 52 by legs 53. In preferred embodiments, a total of five legs 53 are used. The legs 53 are positioned equidistant from each other and are located to correspond to each mesh wall section 57A.

The interior tank 51 has an inlet 54 at the top of the tank which is accessible from the exterior of the unit. Fertiliser 1 is inserted via a hopper 4 and transport device 5, in this case an auger 5, into the interior tank inlet 54.

The interior tank 51 is configured to include a total of six outlet hoses 55,56. There are five outlet hoses 55 positioned equidistantly around the circumference of the bottom of the interior tank 51. These outlet hoses 55 are positioned such that their outlet is pointed in an upwards direction. One centrally located outlet hose 56 exits the approximate centre of the bottom of the interior tank 51 and the outlet of this hose 56 is positioned on the floor of the exterior tank 56.

The interior tank 51 also includes a number of wall sections 57A, 57B within the interior tank 51. In the embodiment shown in Figures 2 and 3 a total of 10 sections of equal width and height 57A.57B are used. Every second section labelled 57A includes slots in a mesh configuration (not shown) through which liquid can pass. The remaining wall sections 57B are solid and do not include any mesh portions. It should be appreciated that a variety of differing wall section 57A.57B configurations may be used without departing from the scope of the invention as described.

The interior tank 51 also has a mesh base section 58 located above the actual floor of the interior tank 51.

The mesh in both the wall sections 57A and base section 58 is of a size sufficient to filter any large particles of solid fertiliser 1 and, through the eroding action of liquid within the interior tank 51 , be retained until reduced in size to a point when the particle can pass through the mesh.

As shown in Figures 2 and 3, the liquid that passes through the mesh wall sections 57A empties from the interior tank 51 via the outlet hoses 55 located around the circumference of the bottom of the interior tank 51. The liquid that passes through the mesh base section 58 flows from the interior tank 51 via the centrally located outlet hose 56.

To maintain a turbulent environment within the interior tank 51 during mixing, a recycle loop 59,60,61 ,62 is included as part of the unit. The loop includes a recycle line 59. Liquid from outlet 60 located at the bottom of the exterior tank 52 passes into a recycle pump 61 and, via the recycle line 59, into the interior tank 51 via the interior tank inlet 62. When mixing is complete, the recycle line 59 may be detached from the interior tank inlet 62 and the recycle pump 61 used to pump the liquid fertiliser solution to a holding tank (not shown) or directly into an irrigation system (not shown).

The exterior tank 52 also includes a liquid inlet 63, a ballcock valve 64 to turn the liquid flow off and an access way 67 for maintenance.

To operate the unit 50,100 the user fills the exterior and interior tanks 51 ,52 by adding liquid via the liquid inlet 63. The liquid for most applications is envisaged as being water however this should not be seen as limiting as other liquids may also be used without departing from the scope of the invention.

The tanks 51 ,52 are full at the appropriate level 65 once the ballcock valve 64 shuts off the liquid flow through the liquid inlet 63. The mixing unit 50, 100 is designed such that, through backflow through the outlet hoses 55,56, the interior tank 51 also fills to the same level as the exterior tank 52.

The user then starts the recycle pump 61 which is configured to transport liquid from the exterior tank 52 into the interior tank 51 via recycle line 59. It is the inventor's experience that the speed with which liquid is recycled is one critical factor in ensuring that uniform mixing results form the process. In the embodiment shown in Figures 2 and 3 a desirable flow rate is approximately 260 litres per minute of liquid. This flow rate enables a sufficient level of turbulence in the unit 50,100 to ensure complete uniform mixing of fertiliser 1 into solution. It should be appreciated that this rate is provided as an indication only and that other flow rates may also be appropriate such as: for different particulate materials 1 ; different scales of operation; and variations in tank 51 ,52 dimensions and configuration.

A further critical parameter found by the inventor is that the interior tank 51 outlet hoses 55,56 must sufficiently inhibit flow from the interior tank 51 such that an in- operation level differential results between the liquid level in the interior tank 66 and the exterior tank 65. It is the inventor's experience that this differential is approximately 100 mm to 200 mm however this should not be seen as limiting as it should be appreciated that this differential level may vary depending on variables such as: the particulate materials 1 used; different scales of operation; and variations in tank 51 ,52 dimensions and configuration.

Once the recycle pump 61 has started, fertiliser 1 is added via a hopper 4 and transport device 5, in this case an auger 5, into the interior tank inlet 54. A single dose of fertiliser 1 is preferably added and the inlet 54 closed. The amount of fertiliser 1 added is determined by the user based on the end concentration of fertiliser 1 in the liquid solution required.

The mixing unit 50,100 is then left to operate. In the inventor's experience, for most fertilisers 1 including urea, a total of 1 hour of mixing is required to ensure that a uniform concentration of liquid solution is reached.

After mixing has completed, the recycle pump 61 is stopped and the recycle line 59 is detached from the recycle inlet 62 on the interior tank 51. The recycle line 59 may then be attached to a storage tank (not shown) or directly to an irrigation system (not shown) and the mixing unit 50,100 emptied of liquid solution by operating the recycle pump 61. Summary

It should be appreciated from the above description that there are provided methods and mixing units that may be used to produce a liquid fertiliser solution with substantially all fertiliser mixed into solution overcoming problems found from prior art methods and mixing processes.

It should further be appreciated from the above description that other dry particulate materials may also be added besides fertiliser and further, that more than one type of material may be mixed. In addition, it should be appreciated that more than one liquid may be used, for example the addition of oil and water.

Aspects of the present invention have been described by way of example only and it should be appreciated that modifications and additions may be made thereto without departing from the scope thereof as defined in the appended claims.

Claims

WHAT WE CLAIM IS:

1. A method of bulk mixing a dry particulate material and a liquid to form an aqueous solution including the steps of:

(b) adding at least one further does at a ration of approximately 1 :40 to 1 :500 w/v until a required concentration of aqueous solution is reached; and characterised in that the resulting aqueous solution has substantially all dry particulate material mixed into the liquid to a uniform concentration in the aqueous solution.

2. A method as claimed in claim 1 wherein a total of approximately 15 to 50 separate doses of dry particulate material are added to the liquid to form the resulting aqueous solution.

3. A method of bulk mixing a dry particulate material and a liquid to form an aqueous solution including the steps of:

(a) adding dry particulate material to a liquid in a mixing tank whereby the dry particulate material is added to the mixing tank at a flow rate of approximately 9 kg/min or less to form an aqueous solution in the mixing tank; and characterised in that the resulting aqueous solution has substantially all dry particulate material mixed into the liquid to a uniform concentration in the aqueous solution.

4. A method as claimed in claim 3 wherein the dry particulate material is added to the mixing tank on a continuous basis.

5. A method as claimed in any of the above claims wherein during step (b), the metered dose of dry particulate material and liquid is passed through an inlet filter before entry into the mixing tank.

6. A method as claimed claim 5 wherein the inlet filter is a mesh of approximately 20mm x 3mm openings.

7. A method as claimed in claim 5 or claim 6 wherein the liquid enters the inlet filter as a spray.

8. A method as claimed in any of claims 5 to 7 wherein the dry particulate material enters the inlet filter with the liquid.

9. A method as claimed in any of the above claims wherein the method includes a further step, step (d), after step (b) or step (c) if present of:

(d) recycling the aqueous solution in the mixing tank through the inlet filter.

10. A method as claimed in claim 9 wherein the aqueous solution is recycled by drawing aqueous solution from the mixing tank via a recycle pump.

11. A method as claimed in any of claims 5 to 10 wherein an outlet filter is used, located between a mixing tank outlet and the inlet filter.

12. A method as claimed in claim 10 or claim 11 wherein an outlet filter is used, located between the mixing tank outlet and the recycle pump.

13. A method as claimed in claim 11 or claim 12 wherein the outlet filter includes a mesh.

14. A method as claimed in any of claims 11 to 13 wherein the outlet filter mesh has openings approximately 20mm x 3mm in size.

15. A method of bulk mixing a dry particulate material and a liquid to form an aqueous solution including the steps of: (a) adding a dose of dry particulate material to a liquid in a mixing unit that includes:

(i) an exterior tank;

16. A mixing unit as claimed in claim 15 wherein the mixing unit is also configured to have a liquid level differential between the liquid level in the interior tank and the liquid level in the exterior tank when the recycle pump operates during the mixing process.

17. A mixing unit as claimed in claim 16 wherein the differential is approximately 50 to 300 mm.

18. A mixing unit as claimed in any of claims 15 to 17 wherein the flow rate of liquid through the recycle loop is operated at approximately 200 to 300 litres per minute.

19. A mixing unit as claimed in any of claims 15 to 18 wherein the interior tank is configured to include a total of six outlet apertures.

20. A mixing unit as claimed in claim 19 wherein five of the outlet apertures are positioned equidistantly around the circumference of the bottom of the interior tank.

21. A mixing unit as claimed in claim 20 wherein the outlet apertures are hoses that are positioned such that their outlet is pointed in an upwards direction.

22. A mixing unit as claimed in claim 19 wherein one centrally located outlet aperture which is a hose which is attached to the bottom of the interior tank and the outlet of this hose is located towards or on the base of the exterior tank.

23. A mixing unit as claimed in any of claims 15 to 22 wherein the interior tank of the above mixing unit further includes a plurality of wall sections within the interior tank, with at least one of the sections including slots in a mesh configuration through which liquid can pass.

24. A mixing unit as claimed in any of claims 15 to 23 wherein the interior tank also has a mesh base section located above the floor of the interior tank.

25. A mixing unit as claimed in claim 23 or claim 24 wherein the mesh has a plurality of apertures of approximately 20mm x 3mm in size.

26. A mixing unit as claimed in any of claims 15 to 25 wherein the time for the mixing operation is approximately 60 minutes.

27. A method as claimed in any of the above claims wherein the dry particulate material is a fertiliser.

28. A method as claimed in claim 27 wherein the fertiliser is selected from the group consisting of: urea; ammonium nitrate; calcium nitrate; sodium nitrate; complex fertiliser (NPK); mono ammonium phosphate (MAP); di-ammonium phosphate (DAP); potassium phosphate; and combinations thereof.

29. A method as claimed in any of the above claims wherein the dry particulate material is urea.

30. A method as claimed in any of the above claims wherein the dry particulate material is in the form of a plurality of granules.

31. A method as claimed in any of the above claims wherein the liquid is water.

32. A method as claimed in any of the above claims wherein the mixing tank or tanks retain approximately 500 to 3000 litres of liquid or an aqueous solution.

33. A method as claimed in any of the above claims wherein the mixing tank or tanks are at least partially filled with liquid before dry particulate material is added.

34. A method as claimed in claim 33 wherein the liquid added to the mixing tank or tanks initially is the total amount of liquid to be used to form the aqueous solution.

35. A method as claimed in any of the above claims wherein the aqueous solution produced in the mixing tank is transferred to a storage tank

36. A method as claimed in any of claims 1 to 34 wherein the aqueous solution produced in the mixing tank or tanks is transferred to an irrigation system.

37. A method as claimed in any of the above claims wherein the dose of dry particulate material is monitored using a control system.

38. A method as claimed in claim 37 wherein the control system includes predetermined parameters selected from: the amount of dry particulate material to be mixed; the end concentration of aqueous solution required; the end volume of aqueous solution required; and combinations thereof.

39. A method as claimed in any of the above claims wherein the dry particulate material is stored before use in a storage hopper.

40. A method as claimed in claim 39 wherein the storage hopper is substantially water tight and air tight.

41. A method as claimed in claim 39 or claim 40 wherein the storage hopper includes weight measurement apparatus to measure the weight of dry particulate material held within the storage hopper.

42. A method as claimed in claim 41 wherein the weight measurement apparatus is a load cell or load cells.

43. A method as claimed in claim 41 or claim 42 wherein the weight measurement apparatus is or are linked to a control system which monitors the weight of material added from the hopper into the mixing tank and starts and stops addition of dry particulate material based on at least one pre-determined weight parameter.

44. A method as claimed in any of claims 39 to 43 wherein the storage hopper is elevated above ground level.

45. An aqueous solution produced in accordance with the method substantially as claimed in any one of claims 1 to 44.

46. A mixing unit including: a feed mechanism for adding dry particulate material to a mixing tank; a mixing tank; a recycle loop for conveying liquid from the base of the mixing tank to the top of the mixing tank; characterised in that the feed mechanism is capable of adding a plurality of doses of dry particulate material to liquid in the mixing tank, whereby each dose is added at a ratio of approximately 1 :40 to 1 :500 weight dry particulate material to volume liquid (w/v).

47. A mixing unit including: a feed mechanism for adding dry particulate material to a mixing tank; a mixing tank; a recycle loop for conveying liquid from the base of the mixing tank to the top of the mixing tank; characterised in that the feed mechanism is capable of adding a measured flow rate of dry particulate material to liquid in the mixing tank, whereby the flow rate does not exceed approximately 9 kg/min.

48. The mixing unit as claimed in claim 46 or claim 47 wherein the mixing unit includes an inlet filter through which the dry particulate material passes before entry into the mixing tank.

49. The mixing unit as claimed in claim 48 wherein the liquid used also passes through the same inlet filter as the dry particulate material.

50. The mixing unit as claimed in any of claims 46 to 49 wherein the mixing unit includes an outlet filter located within the recycle loop.

51. A mixing unit including: an exterior tank; an interior tank that:

52. A mixing unit as claimed in claim 51 wherein the mixing unit is also configured to have a liquid level differential between the liquid level in the interior tank and the liquid level in the exterior tank when the recycle pump operates during the mixing process.

53. A mixing unit as claimed in claim 52 wherein the differential is approximately 50 to 300 mm

54. A mixing unit as claimed in any of claims 51 to 53 wherein the flow rate of liquid through the recycle loop is approximately 200 to 300 litres per minute.

55. A mixing unit as claimed in any of claims 51 to 54 wherein the interior tank is elevated from the floor of the exterior tank by a leg or legs.

56. A mixing unit as claimed in claim 55 wherein a total of five legs are used, with the legs being positioned equidistant from each other around the circumference of the interior tank.

57. A mixing unit as claimed in any of claims 51 to 56 wherein the interior tank has an inlet at the top of the tank for introducing a particulate material such as fertiliser into the interior tank.

58. A mixing unit as claimed in any of claims 51 to 57 wherein the interior tank is configured to include a total of six outlet apertures.

59. A mixing unit as claimed in claim 58 wherein five of the outlet apertures are positioned equidistantly around the circumference of the bottom of the interior tank.

60. A mixing unit as claimed in claim 59 wherein the outlet apertures are hoses that are positioned such that their outlet is pointed in an upwards direction.

61. A mixing unit as claimed in claim 58 wherein one centrally located outlet aperture which is a hose which is attached to the bottom of the interior tank and the outlet of this hose is located towards or on the base of the exterior tank.

62. A mixing unit as claimed in any of claims 51 to 61 wherein the interior tank of the above mixing unit further includes a plurality of wall sections within the interior tank with at least one of the sections including slots in a mesh configuration through which liquid can pass.

63. A mixing unit as claimed in any of claims 51 to 62 wherein the interior tank also has a mesh base section located above the floor of the interior tank.

64. A mixing unit as claimed in claim 62 or claim 63 wherein the mesh has a plurality of apertures of approximately 20mm x 3mm in size.

65. A mixing unit as claimed in any of claims 51 to 64 wherein, when mixing is complete, the recycle line is detached from the interior tank inlet and the recycle pump used to pump the liquid fertiliser solution to a holding tank or directly into an irrigation system.

66. A mixing unit as claimed in any of claims 51 to 65 wherein the exterior tank includes a level control mechanism to shut off the liquid supply when a predetermined level of liquid in the mixing unit is reached.

67. A mixing unit as claimed in claim 66 wherein the level control mechanism is a ballcock valve.

68. The mixing unit as claimed in any of claims 46 to 67 wherein the feed mechanism is an auger.

69. The mixing unit as claimed in any of claims 46 to 68 wherein the unit further includes a storage hopper for storage of dry particulate material prior to entry into the feed mechanism.

70. The mixing unit as claimed in claim 69 wherein the storage hopper includes at least one weight measurement device which is used to monitor variables including: the amount of dose of dry particulate material added to the mixing tank; the flow rate of dry particulate material added to the mixing tank.

71. The mixing unit as claimed in claim 70 wherein the weight measurement device is a load cell.

72. The mixing unit as claimed in any of claims 46 to 71 wherein the unit includes a storage tank for holding aqueous solution after mixing in the mixing tank or tanks.

73. A method substantially as hereinbefore described with reference to the accompanying examples and figure 1.

74. A method substantially as hereinbefore described with reference to the accompanying examples and figures 2 and 3.

75. A mixing unit substantially as hereinbefore described with reference to the accompanying examples and figure 1.

76. A mixing unit substantially as hereinbefore described with reference to the accompanying examples and figures 2 and 3.