A granulated fertiliser

Abstract

A method of forming a granulated fertiliser including: (a) mixing together lignite having a moisture content ranging from 50-70% and urea until at least part of the urea is solubilised by moisture liberated from the lignite and forming a wet mixture; (b) mixing the wet mixture with more lignite or other absorbent materials to reabsorb at least part of the solubilised urea and form a drier mixture; (c) optionally extruding the drier mixture into an extrudate; and (d) feeding the drier mixture or the extrudate into a granulator and forming a granulated fertiliser having a maximum moisture content of up to 30wt%.

Description

[0001] A GRANULATED FERTILISER

[0002] TECHNICAL FIELD

[0003] The present invention relates to a method of forming a nitrogen-containing fertiliser.

[0004] The present invention also relates particularly, although by no means exclusively, to a nitrogen-containing fertiliser product.

[0005] BACKGROUND ART

[0006] The use of urea as a fertiliser in commercial crop growing has delivered high crop yields and protein content, but at the expense of soil condition, microbial health, farm profitability and the environment. In Australia, where a very high percentage of urea is imported, it also carries significant cost and supply chain risk.

[0007] Research has shown that in Australian conditions, up to 50% of the nitrogen applied to crops in the form of urea can be lost to the environment as either a potent greenhouse gas, many times more damaging than carbon dioxide, or through run off and leaching into waterways causing environmental damage through eutrophication.

[0008] Most urea is manufactured from coal or gas, causing significant emission of the greenhouse gas carbon dioxide. When urea is imported into Australia, further damaging greenhouse gas emissions come from the fuel oil used in international shipping.

[0009] Imported urea is expensive and accounts for a high proportion of farm input cost. Accordingly, it would be desirable if its use can be reduced whilst maintaining crop yields and quality. This would improve farm profitability with a potential flow on effect to consumers in terms of a reduction in product price whilst reducing the adverse environmental impact of urea such as the previously mentioned greenhouse gas emissions.

[0010] Discussions with farmers and farmer-funded research groups have identified desirable fertiliser properties, including:

[0011] The fertiliser should be suitable for use in existing farm machinery. The fertiliser should be capable of withstanding the rigors of normal bulk storage, handling and transport, i.e. be safe to use, be sufficiently abrasion and drop shatter resistant and be sufficiently dry to resist deterioration due to inherent moisture.

[0012] The fertiliser should contain sufficient nitrogen to act as a fertiliser and deliver the normal expected crop yield and protein content, given the predicted seasonal rainfall, climatic conditions and soil type / condition.

[0013] The fertiliser should be capable of being produced at a commercial scale in order to maintain consistent market supply.

[0014] The fertiliser should be cheaper than pure urea fertiliser.

[0015] Lignite is an abundant commodity with billions of tonnes of reserves available in Victoria, Australia. It is cheap to mine and has been traditionally used as a fuel for mine-mouth “brown coal” power stations - an era that is coming to an end due to climate impact concerns.

[0016] However, Victorian lignite has a very high moisture content, is extremely friable and prone to spontaneous combustion under certain conditions. It is these factors that have so far limited its use and commercial viability in alternative settings.

[0017] Lignite has a vast pore structure and therefore surface area. Laboratory research has shown that the surface-based, oxygen-containing functional groups in lignite mainly exist in the form of carboxyl group (COOH), phenolic hydroxyl group (Ar-OH), carbonyl group (CO), methoxyl group (OCH3) and ether bond (-O-). The strong ionic and covalent actions of these functional groups are closely related to the water-holding capacity of lignite. In Victoria, lignite mined in the Latrobe Valley and at Bacchus Marsh, can have a total moisture content of between 50% and 67wt%. When dried, lignite can rapidly reabsorb moisture.

[0018] The Applicant has realised that lignite can have significant benefits in a variety of agricultural applications due to its unique pore structure, surface area and chemistry, carbon and humic content and water holding capacity.

[0019] Lignite is rich in carbon, humic acid and fulvic acid. Together, over a series of crop-growing cycles, these functional groups in lignite help improve soil fertility, health and resilience. The resultant improved soil structure from the application of lignite attracts a healthier, beneficial soil microbial community. The humic and fulvic acids provide a natural detoxification function and the improved soil may have a higher drought tolerance than untreated soil.

[0020] However, whilst the application of lignite, in its as-mined (i.e. raw) form, to farm soil can provide some of the above benefits, its high moisture content, handling and storage difficulties (including generation of dust and a propensity to spontaneous combustion) and low natural nutrient levels make it impractical and commercially unattractive to use in this form.

[0021] Accordingly, it is desirable to develop a fertiliser product based on urea and lignite that provides properties desired by the farmers and farmer-funded research groups.

[0022] The above description is not to be taken as an admission of the common general knowledge in Australia or elsewhere.

[0023] SUMMARY OF INVENTION

[0024] The present invention was made in part due to a recognition by the Applicant that the above- mentioned functional groups of carbon, humic acid and fulvic acid in lignite can also interact with major nutrients such as nitrogen, potassium, phosphorous and sulphur in a way that binds the nutrients on lignite surfaces and pore structure. This holds the nutrients in a crop root-zone, making them more readily available to plants and minimising environmental and efficiency losses through volatilisation and run-off. In this way, lignite can be a useful carrier for nutrients, vastly improving fertiliser efficiency and yielding a slow release of nutrients over a crop growing cycle.

[0025] This Applicant has conducted research, development and field trials on wheat and sugar cane crops. The work resulted in the Applicant developing a granulated urea and lignite fertiliser (known as “granulated fertiliser” for the rest of the specification) which utilises the carrier ability of lignite to ameliorate at least some of inefficiencies of pure urea as a fertiliser, particularly to retain more nitrogen in a plant root zone to support crop yields and protein development (which provides the most immediate benefits to crop yields and crop quality). The Applicant found initially in the research, development and field trials that combining as- mined, high moisture lignite with urea resulted in the formation of a tarry, plasticised mixture that could not be granulated successfully, e.g. by fouling granulation and conveying equipment. It was postulated that this phenomenon was due to the deliquescent nature of crushed urea and its reaction with the moisture in lignite.

[0026] To overcome this problem, the Applicant dried the lignite feedstock, typically to a moisture content below 40wt%, by heating the feedstock before mixing and processing the dried feedstock with urea into a final fertiliser product. This heating step was identified by the Applicant as a shortcoming because drying mined lignite by heating is energy intensive and carries a high risk of uncontrolled combustion. This would limit the Applicant’s ability to scale production in a safe, efficient and cost-effective way. High drying temperatures can also significantly reduce the quality and effectiveness of the final fertiliser product.

[0027] Accordingly, the Applicant re-directed its research and development into developing a method of producing a granulated fertiliser that can reduce or avoid artificially heating the as- mined lignite feedstock and / or the lignite and urea mixture. In the specification, the term “artificial heating” refers to the heating of the feedstock by non-natural means such as an electric dryer or heater, and excludes air-drying using natural means such as by the natural evaporation of moisture from crushed lignite.

[0028] During the course of this research, the Applicant surprisingly realized that the deliquescent nature of urea can be harnessed to provide the binder required for granulation, whilst the addition of relatively small amounts of air-dried lignite or other absorbent material to the mixture can at least in part reduce the moisture content of the mined lignite and avoid the formation of a tarry, plasticised mixture and problematic artificial heating step.

[0029] This provides a benefit over existing processes for producing granulated urea-fertilizers such as those disclosed in W02005121049 (MANUF DES ENGRAIS VITAL) and Rose, et. al, "A slow release nitrogen fertiliser produced by simultaneous granulation and superheated steam drying of urea with brown coal", (2016), Chemical and Biological Technologies in Agriculture, 3:10, 1-14 which do not incorporate absorbent material during the granulation step to reduce the moisture content of the urea-lignite mixture containing lignite having at least 50% moisture content. In this respect, the present invention provides a method of forming a granulated fertiliser including:

[0030] (a) mixing together lignite having a moisture content ranging from 50-70% and urea until at least part of the urea is solubilised by moisture liberated from the lignite and forming a wet mixture;

[0031] (b) mixing the wet mixture with more lignite or other absorbent materials to reabsorb at least part of the solubilised urea and form a drier mixture;

[0032] (c) optionally extruding the drier mixture in an extrudate;

[0033] (d) feeding the extrudate or drier mixture into a granulator and forming a granulated fertiliser having a maximum moisture content of up to 30wt%.

[0034] In this specification, the term “fertiliser” encompasses any product that can improve the quality of soil for agricultural applications. It may also be known as a “soil amendment product”.

[0035] The lignite may be as-mined lignite, suitably crushed as-mined lignite.

[0036] The lignite may have a moisture content ranging from 55-67wt%, suitably having a moisture content ranging from 60-65 wt%, more suitably having a moisture content of around 61- 62wt%. Despite the high moisture content, the lignite having this moisture content was observed by the Applicant to be dry and friable. It is believed that most of the moisture is held ionically on the vast surface area of the lignite’s internal pore structure.

[0037] The lignite may be air-dried lignite that, for example has been crushed and naturally dried, for example by being stored or located at a site that allows natural evaporation. The air-dried lignite may have a moisture content below 20wt%.

[0038] The method may include comminuting the lignite to a maximum particle size of 7mm, suitably 5mm before step (a).

[0039] Suitably, the method includes crushing the lignite using a mill with an appropriately sized screen. More suitably, the method includes crushing the lignite using a hammer mill with a 5mm screen.

[0040] The urea may have at least 42wt%, suitably at least 45wt% nitrogen content. Suitably, the urea has at least 46wt% nitrogen content. The urea may include prilled urea.

[0041] The method may include comminuting the urea, suitably to a maximum particle size of 3mm before step (a).

[0042] Suitably, the method includes crushing the urea using a mill with an appropriately sized screen.

[0043] More suitably, the method includes crushing the urea using a hammer mill with a 3mm screen.

[0044] The method may include applying a vacuum across a screen to pull the comminuted urea through the screen and into a collector vessel. This step can minimise blockage of the screen and improve mass flowrate.

[0045] Step (a) may include mixing the urea and the lignite in a rotary drum mixer.

[0046] Alternatively, step (a) may include mixing the urea and the lignite using a ribbon mixer.

[0047] Step (a) may include mixing the urea and the lignite at a dry wt% ratio ranging from 40:60 to 60:40 urea to lignite. Suitably, step (a) includes mixing the urea and the lignite at a dry wt% ratio ranging from 45:55 to 55:45 urea to lignite. More suitably, step (a) includes mixing the urea and the lignite at a dry wt% ratio of 50:50 urea to lignite.

[0048] Laboratory tests, plot trials and larger, paddock-scale trials conducted with broad acre wheat and sugar cane conducted by the Applicant determined that these ratios, particularly a dry wt% ratio of 50:50 urea to lignite, allowed the granulated fertiliser to be handled and applied to crops in the same way as pure urea without adversely impacting on the quality and yield of the crop. For example, a 50:50 dry wt% ratio urea to lignite fertiliser would deliver 50% of the nitrogen supplied to the crop by full strength prilled urea but have an ability to release nitrogen in a controlled manner to be as effective as the full strength prilled urea.

[0049] This allows the granulated fertiliser to be applied at the same time and in the same quantity (per measure of land area) that full strength prilled urea would normally be applied to a crop but with significantly lower overall emissions, lower harmful impacts on waterways and lower cost. It is also envisioned that because lignite is readily available in vast quantities in Victoria, supply chain security and cost risks can be substantially reduced.

[0050] Step (a) may include mixing the urea and the lignite for up to 5 minutes. Suitably, step (a) includes mixing the urea and the lignite for up to 3 minutes. More suitably, step (a) includes mixing the urea and the lignite for 2 minutes. Even more suitably, step (a) includes uninterrupted mixing of the urea and the lignite during a stipulated mixing time. Typically, the time period is selected to ensure that the wet mixture has a required moisture content for step (c).

[0051] The lignite added in step (b) may be air-dried lignite.

[0052] The amount of the lignite added in step (b) may be up to 10wt% of the total dry weight of the urea and the lignite in the wet mixture. Suitably, the amount of the lignite added in step (b) may be up to 8wt% of the total dry weight of the urea and the lignite in the wet mixture. More suitably, the amount of the lignite added in step (b) may be up to 5wt% of the total dry weight of the urea and the lignite in the wet mixture.

[0053] The added lignite absorbs at least some of the liquid formed during step (a) to form a mixture that is easier to form the granulated fertiliser, particularly to form a mixture that is easier to extrude or agglomerate.

[0054] The method may include adding air-dried lignite in either or both steps (a) and (b). Suitably, air-dried lignite having a moisture content of less than 55wt%, suitably less than 30wt%, is added in either or both steps (a) and (b). More suitably, air-dried lignite having a moisture content of less than 20wt% is added in either or both steps (a) and (b). The lignite added in step (b) may have a maximum moisture content of 30wt%, suitably 20wt%, more suitably ranging from 17-20wt%.

[0055] Step (b) may include naturally drying the lignite to be added to the wet mixture to the required moisture content before being added to the wet mixture.

[0056] The lignite added in step (b) may have a maximum particle size of 5mm. Suitably, the lignite added in step (b) has a maximum particle size of 2mm.

[0057] Step (b) may include comminuting the lignite to a required particle size before being added to the wet mixture. The lignite may be comminuted by any suitable means.

[0058] Step (b) may include mixing for up to 5 minutes. Suitably, step (b) includes mixing for up to 3 minutes. More suitably, step (b) includes mixing for 2 minutes. Even more suitably, step (b) includes uninterrupted mixing during the stipulated mixing time.

[0059] The method may include resting the drier mixture after mixing.

[0060] Suitably, step (b) includes resting the mixture for up to 40 minutes after mixing. More suitably, step (b) includes resting the mixture for up to 30 minutes after mixing.

[0061] The resting period provides the added lignite time to reabsorb moisture from the wet mixture.

[0062] Either or both steps (a) and (b) may include adding an absorbent material. This step enables the added absorbent material to be used to absorb some free moisture generated at various stages of the production process. During mechanical excitation of lignite in processes such as comminuting, shearing, mixing or granulating, moisture is freed from lignite by transforming the pore structure and therefore the moisture to lignite bond (Johns, R.B., et al., Fuel Processing Technology, 21 (1989) 209-221 and US patent 4627575 (Johns)). Suitable absorbent materials include: o Potassium polyacrylate polymer. o Corn starch. o Agricultural lime, o Agricultural gypsum. o Sodium or calcium bentonite, o Diatomaceous earth.

[0063] Suitably, the absorbent material is added in its raw form. The absorbent material may not need to be comminuted to have a substantially uniform particle size distribution.

[0064] Step (c) may include extruding the drier mixture into an extrudate having an average diameter of less than 10mm, suitably 8mm, more suitably ranging from 4-6mm.

[0065] Step (d) may include operating the granulator to form generally spherical granules. Suitably, the generally spherical granules have a diameter ranging from 2-5mm. The granulator in step (d) may be a spheroniser.

[0066] Step (d) may include drying the drier mixture or the extrudate to form a granulated fertiliser having a total moisture content up to 30wt%, suitably a total moisture content having a moisture content up to 15wt%.

[0067] Suitably, step (d) includes drying the drier mixture or the extrudate in a rotating drum dryer.

[0068] More suitably, step (d) includes maintaining a maximum drying temperature of 120°C, suitably 100°C during the drying step.

[0069] The drying step may be used to meet a desired final moisture content of the granulated fertiliser.

[0070] Experiments performed by the Applicant have determined that higher moisture contents in the granulated fertiliser reduce the hardness of the granules and therefore their robustness during handling, storage and transport. The final desired moisture content can be determined by selecting the desired level of robustness. This can be measured by using compression, drop shatter and abrasion tests. Additionally, higher moisture content in the granulated fertiliser may encourage the formation of urea crystals on the surface of the granules, potentially reducing the granules effectiveness as a fertiliser. It was also observed by the Applicant that adding lignite in step (d) may form a dry shell around each granule. The dry shell may enhance the robustness of the granules and form a finished granulated fertiliser that can be stored in bulk containers without being crushed or abraded (forming dust).

[0071] Step (d) may include operating the granulator to form granules having an average particle size ranging from 1 to 6mm, suitably having an average particle size ranging from 2 to 5 mm.

[0072] Step (d) may include varying the rotating speed of the granulator when forming the granulated fertiliser.

[0073] Step (d) may include operating the granulator for up to 40 minutes, suitably up to 20 minutes, even more suitably up to 5 minutes.

[0074] Step (d) may include mixing the extrudate or drier mixture with more lignite, suitably airdried lignite.

[0075] Suitably, the amount of the lignite added in step (d) may be up to 5wt% of the total dry weight of the urea and the lignite in the drier mixture or extrudate. More suitably, the amount of the lignite added in step (d) may be up to 3wt% of the total dry weight of the urea and the lignite in the drier mixture or extrudate. Even more suitably, the amount of the lignite added in step (d) may be up to 2.5wt% of the total dry weight of urea and lignite in the drier mixture or the extrudate.

[0076] The lignite added in step (d) may have a maximum moisture content of 30wt%, suitably less than 20wt%.

[0077] Suitably, step (d) includes drying the lignite to a required moisture content before being added to the drier mixture or the extrudate. The lignite may be dried naturally or using any suitable means that leaves it in a hydrophilic state.

[0078] The lignite added in step (d) may have a maximum particle size of 5mm. Suitably, the lignite added in step (d) has a maximum particle size of 2mm. Step (d) may include comminuting the lignite to the required particle size before being added to the drier mixture or extrudate.

[0079] The method may include recycling any off specification material such as oversized or undersized granules and dust, for example recovered from a dust extraction system of an apparatus according to the present invention. Suitably, the method includes returning the off- specification material, suitably crushed off-specification material, to either mixing steps (a) or (b) or (d).

[0080] Beneficially, the present invention includes adding other beneficial additives (such as lime or gypsum) to ameliorate specific soil characteristics or improve the strength and handleability (such as bentonite) of the granulated fertiliser.

[0081] In this respect, the method may include adding an additive, suitably in either mixing steps (a) or (b).

[0082] The method of forming a granulated fertiliser may be a continuous process.

[0083] Alternatively, the method may be a batch process. However, there is a recognition that a batch process may adversely affect volume and production cost of the granulated fertiliser.

[0084] The present invention also provides a granulated fertiliser formed according to the previously described method.

[0085] The present invention also provides a granulated fertiliser comprising lignite and urea and having a maximum moisture content of up to 30wt%, wherein the relative amounts of the lignite and the urea deliver crop yields and quality comparable with crops grown using application of 100% urea.

[0086] The granulated fertiliser may have a maximum moisture content up to 20wt%, suitably a total moisture content up to 15wt%.

[0087] The granulated fertiliser may have a urea to lignite dry wt% ratio ranging from 40:60 to 60:40. Suitably, the granulated fertiliser has a urea to lignite dry wt% ratio ranging from 45:55 to 55:45. More suitably, the granulated fertiliser has a urea to lignite dry wt% ratio of 50:50.

[0088] The granulated fertiliser may comprise generally spherical granules.

[0089] Suitably, the granulated fertiliser comprises granules having a core shell structure comprising a dry shell. The dry shell may enhance the robustness of the granules and allows the granulated fertiliser to be stored, suitably in bulk containers, without being crushed or abraded (forming dust).

[0090] The granulated fertiliser may have an average particle size ranging from 1 to 6mm, suitably ranging from 2 to 5mm.

[0091] In one embodiment, the present invention provides a granulated fertiliser comprising a mixture of the lignite and the urea with a dry wt% ratio of 50:50 urea to lignite, and having generally spherical granules, that deliver crop yields and quality comparable with crops grown using application of 100% urea.

[0092] The present invention also provides an apparatus for forming the granulated fertiliser according to the previously described method.

[0093] The present invention also provides an apparatus for forming a granulated fertiliser comprising: a mixer (a) configured to mix lignite having a moisture content ranging from 50-70% and urea until at least part of the urea is solubilised by moisture liberated from the lignite, and (b) configured to receive more lignite or other absorbent materials to reabsorb at least part of the solubilised urea, and form a drier mixture; an optional extruder for extruding the drier mixture into an extrudate; and a granulator for granulating the drier mixture or the extrudate and forming the granulated fertiliser having a maximum moisture content of up to 30wt%.

[0094] The apparatus may include a comminutor to comminute the lignite. Suitably, the comminutor is a mill with an appropriately sized screen. More suitably, the comminutor is a hammer mill with a 5mm screen.

[0095] The apparatus may include a comminutor to comminute the urea.

[0096] Suitably, the comminutor is a mill with an appropriately sized screen. More suitably, the comminutor is a hammer mill with a 3mm screen.

[0097] The apparatus may include one comminutor to comminute both the lignite and the urea. In this embodiment, an appropriately-sized screen may be used on the comminutor depending on the feed material.

[0098] Suitably, at least one comminutor includes a vacuum system to facilitate flow of comminuted material through the screen.

[0099] The mixer may be a rotary drum mixer or a ribbon mixer.

[0100] One difference between the rotary drum mixer and the ribbon mixer is that a rotary drum mixer provides enhanced visibility of the mixing process.

[0101] The mixer may be configured to control the ratio of urea and lignite added to the mixer.

[0102] The mixer may be configured to stop operation for a rest period after the mixing step.

[0103] The extruder may have a die having a size ranging 4-6mm.

[0104] The granulator may be a spheroniser.

[0105] The apparatus may include a dyer for drying the drier mixture or the extrudate to form the granulated fertiliser.

[0106] The apparatus may include a recycle system to return any off-specification material such as over or under-sized granules and dust to the process. Suitably, the apparatus includes recycle loops to return the off-specification material to either the mixer or granulator.

[0107] The apparatus may be configured to operate a continuous process.

[0108] Accordingly, the present invention provides a method of producing a granulated fertiliser that may mediate lignite’s drawbacks with respect to dust generation and spontaneous combustion and a granulated fertiliser that may deliver crop yields and quality comparable with crops grown using 100% urea application but with a reduced nitrogen content leading to reduced environmental damage, reduced cost and reduced supply chain risk.

[0109] DESCRIPTION OF DRAWINGS

[0110] An embodiment of the invention is hereinafter described by way of example only with reference to the accompanying drawings, wherein:

[0111] Figure 1 is a block flow diagram of an apparatus for forming a granulated fertiliser according to one form of the present invention,

[0112] Figure 2 is a block flow diagram of an apparatus for forming a granulated fertiliser according to another form of the present invention, and

[0113] Figure 3 is a block flow diagram of an apparatus for forming a granulated fertiliser according to another form of the present invention.

[0114] DETAIEED DESCRIPTION

[0115] Guided by the comments from farmers and farmer-funded research groups as previously discussed, the Applicant focused its research and development work on a cost-effective granulated lignite / urea fertiliser that preferably enhances soil health and fertility while reducing environmental impact.

[0116] The two major hurdles identified by the Applicant to achieving the desired granulated fertilizer were the deliquescent nature of urea and the high moisture content of as-mined lignite.

[0117] With these two hurdles in mind, the Applicant focused on reducing:

[0118] (i) the amount of the urea in the fertilizer without significantly compromising the crop yields and quality; and (ii) the energy required to produce the granulated fertiliser.

[0119] One embodiment of an apparatus 100 and method of operating the apparatus developed by the Applicant is illustrated in Figure 1 and includes the following steps.

[0120] 1. Comminuting a measured quantity of as-mined, high moisture content (55 - 67wt%) lignite feedstock 10 in a crusher 12. The crusher is in the form of a hammer mill with a 5mm or finer screen. The crusher 12 may be any suitable crusher.

[0121] 2. Drying the crushed lignite from step (1) in a dryer 14 to reduce the total moisture content to a maximum of 38wt%, suitably to a maximum of 35wt%, at a temperature not exceeding 140°C, typically not exceeding 100°C, to produce dried lignite. The dryer 14 may use a variety of mild thermal evaporative processes such as air-drying to minimise the risk of spontaneous combustion. The dryer 14 may be in the form of a rotating drum. The dryer 14 may be any other suitable dryer. It is noted that other embodiments described below do not include this drying step.

[0122] During trials, the Applicant observed that lignite having a moisture level around 42wt% adversely affected the quality of the granulated fertiliser. This was because lignite having a moisture content above 42wt% was difficult to handle and led to a reduction in the ratio of the urea to the lignite and therefore the nitrogen content of the finished fertiliser and lower crop yields and quality. It was also observed that granulated fertiliser formed using such lignite spoilt more easily.

[0123] It was also observed that drying crushed lignite above 140°C was detrimental to the beneficial characteristics of lignite such as those due to the surface functional groups and humic / fulvic acids. Higher drying temperatures may also lead to the lignite becoming hydrophobic and therefore unsuitable for this invention.

[0124] 3. Comminuting a measured quantity of prilled urea 15, equal to 50% by dry weight of the lignite in step (2) in a crusher 16. The crusher 16 is in the form of a hammer mill with a 3mm or finer screen.

[0125] 4. Mixing (i) the lignite from step (2) and (ii) the urea from step (3) and (iii) a binder 19 in a mixer 18. The mixer 18 is in the form of a pin mixer. The mixer 18 may be any other suitable mixer. In this step, a measured volume of a liquid binder 19 (e.g. one part to 20 parts dilution of molasses and water) is sprayed into the pin mixer. Other additives 17 such as lime or gypsum can also be introduced to the pin mixer to meet specific customer requirements. The rotating pins inside the pin mixer barrel cause the lignite and the urea particles to spin. This action, in combination with the binder 19, initiates an agglomeration process which continues in subsequent step (5). Agglomerating the mixture formed in step (4) in a granulator 20. The granulator 20 is in the form of a pan granulator which forms spherical agglomerates in the 2 to 5mm diameter size range. The shape and size of the agglomerates ensures that the final product has flowability that enables application to farmland using existing farm equipment without modification. The vertical angle of the rotating pan granulator can be adjusted to ensure that agglomerates of the correct size and shape is transported to a spheroniser. Processing the spherical agglomerates in a spheroniser (also known as a marumeriser) 22 to form green granules having the desired consistency of shape, size and compaction. Depending on customer specification, the rotating speed and duration of spin of the spheroniser can be controlled to obtain the desired granule properties. Drying the green granules in a dryer 24 to have up to 20wt% moisture content at a temperature not more than 140°C and produce the finished granulated fertiliser. The dryer 24 is in the form of a rotating drum dryer. The horizontal angle of the rotating drum can be adjusted to ensure the dwell time is sufficient to produce finished granules at around 15% total moisture content. At the same time, the operating temperature was controlled to not exceed 140°C. During the trials, it was observed that a final moisture content of 15wt% moisture content was optimal because a higher moisture content reduced the hardness of the finished fertiliser product and therefore its robustness during handling, storage and transport. Cooling the finished granulated fertiliser in a cooler 26 in the form of a rotating cooler / sieve. Bagging and sealing the cooled finished product in a packaging unit 28. 10. Recycling any off-specification material including undersized or oversized granules and dust to any one of steps (4) to (6). In certain situations, it may be appropriate to comminute the off-specification material before returning the material to any one of steps (4) to (6).

[0126] The apparatus 100 is configured to operate continuously with a conveyor system to deliver material from one step to another.

[0127] Further research by the Applicant focusing on reducing the energy requirements of the granulated fertiliser production process led to the development of another embodiment of apparatus of the invention, which is identified by as apparatus 200 illustrated in Figure 2, and corresponding method of operating this apparatus as described below.

[0128] This method minimises the need to dry the raw as -mined lignite feedstock as required in the embodiment of the apparatus 100 and method of operating the apparatus illustrated in Figure 1.

[0129] The improved method includes:

[0130] A. Providing raw as-mined high moisture content (55% - 67wt%) lignite feedstock 210. One source of lignite was from the Latrobe Valley lignite which was measured using a Kern moisture analyser and found to have a total moisture content of 61.4wt%. Despite this very high moisture content, the lignite felt and appeared dry and friable. It is believed that most of the moisture was held ionically on the vast surface area of the internal pore structure of the lignite.

[0131] B. Comminuting a measured amount of the raw as-mined lignite feedstock 210 in crusher 212 in the form of a hammer mill with a 5mm screen.

[0132] C. Comminuting a measured amount of commercially procured prilled urea 215 containing 46% nitrogen in a crusher 216 in the form of a hammer mill with a 3mm screen. During the crushing step, it was observed that the very fine particle size of the crushed urea made it difficult for the crushed urea to flow through the screen. To address this problem, the hammer mill was fitted with a vacuum system to pull the crushed urea through the screen and into a collector vessel.

[0133] D. Mixing the lignite from step (B) and the urea from step (C) at a dry wt% ratio of 50:50 in a mixer 218 in the form of a ribbon mixer, rotary drum mixer or other mixer that does not impart too much energy into the mixture during the mixing process. Too much energy or lengthy duration in the mixer will cause the lignite and urea mixture to become very wet, sticky and plasticised which makes it difficult to handle. It is understood that the more mechanical work, such as mixing, grinding or spheronising for example, that lignite is subjected to, the more “free” moisture is released to the surface of the lignite particles and the more moisture that is available to liquify the urea. The resultant wet slurry is not suitable for granulation without further high- temperature drying. High-temperature drying of this slurry can result in uncontrolled combustion of the mixture and uncontrolled emission of ammonia.

[0134] In one example, a 4kg batch of lignite (calculated to have a dry weight of 1.544kg) and a same amount of urea (having an effective moisture content of crushed urea being 0%) were transferred to mixer 218.

[0135] The mixer was activated for 2 minutes. The mixer angle was adjusted so the full length of the mixer internal blades was in constant contact with the urea and lignite mixture. This ensured thorough mixing and initiated an osmosis type reaction between the urea and lignite that drew moisture from the lignite’s surfaces and pores to solubilise the urea.

[0136] Combining lignite with the urea in this manner slows the release of nutrients including nitrogen by the fertiliser over the crop growing cycle, making them more readily available to plants and avoiding environmental and efficiency losses through volatilisation and run-off. At the same time, the inherent properties of the lignite improved the soil structure which attracted a healthier, beneficial soil microbial community and potentially higher drought tolerance than untreated soil. The humic acid and fulvic acid content of lignite also provided a natural detoxification function.

[0137] After 2 minutes, the lignite and urea mixture had the appearance of tar and was wet and slimy to the touch. If required, additives 217 (such as lime or gypsum) to ameliorate specific soil characteristics or improve the final granulated product strength and handleability (such as bentonite) may also be added.

[0138] E. Extruding the mixture from step (D) in an extruder 220 in the form of a 3-phase mechanical extruder fitted with a 3 / 16-inch, size-32 die.

[0139] In preparation for the extrusion step, the extruder 220 was “primed” by feeding it with a pre-prepared mixture consisting of raw as-mined lignite and cold tap water. 0.5kg of raw lignite was mixed with 50ml of water, by shaking in a plastic container and fed into the operating extruder. This primed the internal screw of the extruder and brought the machine up to a constant internal operating temperature, ready for processing the lignite and urea mixture. Once fully charged, the 3 / 16-inch die was then replaced by a size 32 die with 6mm diameter holes and the extrudate from the priming process was removed for recycling in a separate process. The larger size 32 6mm die allows better throughput and reduced friction. It should be noted that the step of replacing the die is optional, and is typically performed when the feed mixture is slightly too dry and needs an extra initial compression to help bind the particles in the extrudate.

[0140] Immediately following the 2-minute mixing stage, the lignite and urea mixture was transferred to an input tray of the pre-primed extruder and manual fed into the extruder 220 using a plastic spatula.

[0141] To form a mixture having a consistency suitable for extrusion, 150 g of crushed lignite 221 (up to 5% of the total mixture by weight of crushed and dried lignite feedstock 210 and having a 20wt% moisture content) was added into the mixer 218 and mixed with the lignite and urea mixture for a further 2 minutes. This enabled reabsorption, by the lignite, of the solubilised urea. The mixture was observed to become visibly drier. The mixture was then left to stand for 30 minutes. This time period allowed the added lignite time to re-absorb some of the moisture from the mixture. The 150 grams of dried lignite was obtained by crushing, in a hammer mill with an appropriately sized screen, and may be dried using any known means to the specified moisture content. Following the 30-minute time period, the mixture was fed over a 3-minute period into the operating, pre-primed extruder 220 having a die size selected to ensure consistently sized granules with the desired diameter - usually a die size between 4mm and 6mm is chosen - providing an effective manual feed rate of approximately 1 kg per minute. In this example, a 6mm die was selected to produce 6mm diameter extrudate which reached lengths of approximately 40mm to 50mm before breaking off under their own weight and collecting in an output tray. The ambient temperature was around 14°C and the extrudate was seen to be “steaming” due to friction as it exited the extruder die. The extrudate had a shiny appearance (rather than furry), indicating good compaction.

[0142] F. Processing the extrudate in a spheroniser 222 to form green granules. The spheroniser was in the form of a 1 metre diameter, 3-phase mechanical spheroniser that had been fitted with a variable speed drive. The exit gate of the spheroniser 222 consisted of five removable stacked segments. Removal of the upper segments allowed granules that had reached a desired size of 4 or 5mm diameter to exit the machine while smaller, under-sized granules remained spinning and agglomerating.

[0143] In this step, the initial rotating speed of the spheroniser 222 was set to 60% of maximum and while the machine was turned off, all the extrudate from step (E) was placed on the stationary circular spheroniser bottom (spin) plate. The machine was then turned on, and the spinning bottom plate reached its set speed in less than 5 seconds. This caused the extrudate to be immediately thrown against the fixed wall of the spheroniser barrel. After 2 minutes of spinning, the spheroniser 222 was paused and the extrudate was examined. It was observed that the extrudate had broken into smaller pieces and had started to spheronise, but there were still several lozengeshaped granules and undersize granules. The spheroniser speed was increased to 75% and run for a further 3 minutes. After the first minute of this cycle, the extrudate was seen to be forming a traveling “rope” of uniformly and correctly sized spheres, but from time to time the granules could be seen to be getting wet and sticky, causing oversize spherical granules to start forming. It is believed that this was due to the mechanical forces, which can include centrifugal, tumbling, shearing or a combination of these forces, forcing moisture from the lignite pores to the surface of the forming spherical granules.

[0144] In this step, whilst maintaining the 75% speed, for the final 2 minutes of spinning, 75 grams of crushed lignite 221 (dried to 20% moisture content and passed through a 2mm sieve) was slowly and constantly added to the spinning extrudate to absorb excess moisture. This formed separate granules that felt firm to the touch and without stickiness. Little to no clumping was observed. The granules were also observed to have a reasonably uniform size distribution. The exit gate segments were then removed and the spheroniser was briefly restarted to discharge the green granules into a storage container.

[0145] G. Drying the green granules in dryer 224 to form the finished granulated fertiliser. The dryer 224 was in the form of a 1.8m long LPG fired rotating drum dryer. The LPG burner was set 120mm back from the dryer's open feed-end to ensure the internal temperature remains below 140°C, suitably below 120°C, as measured on a thermometer permanently mounted at the dryer's exit end. The dryer’s rotating speed was controlled using a variable speed drive and its horizontal angle can be set from horizontal to a 10° downward slope. Internally, there were 4 “L-shaped” longitudinal lifters or vanes that carried the green granules around the circumference walls of the drum.

[0146] In this step, the dryer 224 was pre- warmed for 5 minutes until the exit air temperature reached 120°C. A shallow angle of decline (approximately 2°) was selected and a slow rotating speed (20% of maximum) set to ensure the green granules move slowly through the dryer 224 without imparting stresses that may break them.

[0147] The green granules were subsequently fed manually, using a scoop, into the dryer feed chute, located at the burner end. A drying time of 20 minutes was selected. Within two or three minutes of commencing the drying cycle, the granules could be heard rotating inside the drum - sounding like tumbling grit. From the Applicant’s experience, this was a positive sign that the granules are hardening and are not sticking to each other or to the drum wall. No ammonia smell (indicating nitrogen loss) was detected during the drying process. After completion of the drying time, the slope and speed were increased and the exit end plate slid away from the drum dryer 224, allowing the finished granulated fertiliser to exit the dryer 224. At this stage, a robust and dry shell has formed on the finished fertiliser granules.

[0148] H. Cooling and sieving the finished granulated fertiliser using cooler 226 in the form of a rotating screen. Over a period of 7 to 10 days, the granules continued to air dry in ambient conditions and achieved an overall moisture content of around 20%, suitably 15wet%, without further forced drying. The granules at this stage are hard enough to completely resist forced crushing between thumb and finger and do not shatter when dropped from a height of > 2m.

[0149] I. Packaging the finished granulated fertiliser in packaging unit 228 by bagging and sealing the finished granulated fertiliser into a form that can be delivered to customers.

[0150] J. Optionally, off-specification material such as oversized or undersized granules and dust from the dust extraction system is collected and recycled in the process. The off- specification material may be collected from any one of steps D-I and returned to the process, suitably to step D.

[0151] A key feature of the improved method is the development of a non-heating methodology for drying the lignite and urea mixture in Step (E) by adding an additional dose of crushed and dried lignite before extrusion and during granulation.

[0152] The Applicant has also developed another embodiment of the apparatus of the invention, which is identified by as apparatus 300 (as illustrated in Figure 3) and a corresponding method of operating this apparatus. The reference numerals used in Figure 3 are based on the reference numerals used in Figure 2 but with the “2” suffix replaced with “3”.

[0153] Apparatus 300 is a variation of the apparatus 200 that excludes the extruder and feeds the lignite and urea mixture from mixer directly to the spheroniser. The corresponding method of operating the apparatus 300 involves steps (A)-(J) with a modified version of step (F) which directly receives and processes the mixture from step (D) in the spheroniser.

[0154] Avoiding the extrusion step provides cost and energy savings at the expense of granules having a broader size distribution. This may be acceptable depending on the customer preference or tolerance.

[0155] The dwell-time in the spheroniser 322 will be different and longer than the corresponding time for spheroniser 222.

[0156] The method of operating apparatus 300 may also require a small amount of a liquid binder (water) 319 to be added to the rotating spheroniser 322 to initiate agglomeration.

[0157] Once agglomeration commences, the speed of rotation and dwell-time in the spheroniser 322 is sufficient to cause more moisture to move to the surface (through centrifugal force) to continue forming agglomerates.

[0158] The exemplary finished granulated fertiliser products produced by the embodiments of the apparatus of the invention illustrated in Figures 1-3 being operated in accordance with the embodiments of the method of the invention described above in relation to the Figures have the following properties that are likely to appeal to customers including:

[0159] Spherical granules having a particle size ranging from 2mm to 5mm that are suitable for use in existing farm machinery.

[0160] Spherical granules having a core-shell structure with a robust and dry shell for withstanding normal bulk storage, handling and transport.

[0161] A composition providing a suitable balance between supplying enough nitrogen to maintain similar crop yields (e.g. by delivering the expected protein content) and quality compared to pure urea while reducing the harmful impact of urea on the environment including reducing greenhouse gas emissions and eutrophication of waterways.

[0162] A continuous manufacturing process enabling the granulated fertiliser to be produced at commercial scale. A manufacturing process involving a reduced amount of urea and energy that translates to lower production costs, and potentially cheaper product cost for customers.

[0163] Further research by the Applicant to improve the granulated fertiliser production process led to the following discoveries:

[0164] • Mechanical “working” of the raw lignite by grinding, milling, extrusion and spheronisation causes moisture to be “freed” from some areas of the lignite’s pore structure (consistent with the observation made in Johns, R.B., et al., Fuel Processing Technology, 21 (1989) 209-221). This occurs through a combination of shearing and compression mechanisms. Some moisture in the lignite remains “tightly held” in micropores. It is believed that the amount of “freed” moisture can be controlled to minimise unwanted re-crystallisation of urea.

[0165] • Using some inherent moisture from the raw lignite, as either a binder or lubricant at various stages in the process, is beneficial, however too much free moisture will cause the mixture to slurry and become unusable. It was found that careful control of the mixing and spheronisation stages of the production process can control the amount of work lignite is subjected to and therefore the amount of free moisture that is generated. For example, grinding and intensive mixing of raw lignite in the presence of a highly absorbent material can reduce the amount of free moisture that is available to interact with urea in a subsequent production stage.

[0166] • Whilst it was shown previously that air-dried lignite can be used to absorb some free moisture at various stages in the production process, there are other absorbent materials that can also be used to in the same way. Obtaining large quantities of airdried lignite at commercial scale may be time-consuming and require a large dedicated indoor space. Having other materials available that can be substituted for some of the air-dried lignite may be useful in this respect and may also provide other benefits such as pH control, super-absorbency and / or improved the agricultural efficacy of the finished fertiliser product.

[0167] • Ideally, all added absorbent materials should contribute to the agricultural efficacy of the finished fertiliser product. It is desirable that the improved agricultural efficacy is achieved without adding undue cost or introducing undesirable effects in the soil. Consideration of which additive to use may be driven by absorbency, availability, cost or pH. It is known that in some circumstances, a high pH mixture and high temperatures may cause the non-enzymatic hydrolysis of urea and the undesirable formation of ammonia and carbon dioxide. The pH of mixtures can differ depending on the lignite source. One or more of the following additives may be used to absorb free moisture created by the mechanical work inflicted on raw lignite: o Potassium polyacrylate polymer. o Corn starch. o Agricultural lime. o Agricultural gypsum. o Sodium or calcium bentonite. o Diatomaceous earth.

[0168] • Addition of phosphorus and / or sulfur-containing additives to increase the phosphorus and sulfur content in the finished fertiliser product. The Applicant has demonstrated that Diammonium Phosphate (DAP) and Sulphate of Ammonium (SOA) may be added during the production process to introduce a percentage of phosphorus and sulfur into the finished fertiliser product. Suitably, this step reduces the urea content in the product (e.g. by substituting some of the nitrogen in the DAP and SOA fertilizer product) with only a marginal increase in the overall cost of production.

[0169] Non-limiting examples of the invention involving the addition of absorbent materials are described below.

[0170] Example 1

[0171] Starting with raw lignite at approx. 61% total moisture content, the following absorbent materials were added (all % amounts are on a dry lignite basis): o Agricultural lime - 5%. o Air-dried lignite - 5% (at 17% total moisture content). o S odium Bentonite - 5%. o Potassium Polyacrylate - 0.3%. o Corn starch - 5%.

[0172] • The following N-based fertilisers were also added: o Hammer milled DAP - 25%. DAP contains 18%N (ammonium form), 20%P. o Hammer milled SOA - 25%. SOA contains 21%N (ammonium form), 24%S. • All the above ingredients were mixed together at 30 rpm in an open rotary mixer for 40 minutes and then ground in the hammer mill (with a 5mm mesh). The mixture was then left to rest for 24 hours to allow free moisture, released from the lignite by the mixing and milling processes, to be partially absorbed by the other ingredients.

[0173] • A quantity of urea calculated to result in finished granules containing 23% N (taking into account the N already provided by the DAP and SO A) was ground in the hammer mill and incorporated with the above mixture in the mixer and rotated at 30 rpm for 1 minute - this was to ensure the urea was fully incorporated in the mixture without mechanically releasing any more free moisture. It was observed that as the urea reacted with available free moisture in the lignite, the mixture started to become moist.

[0174] • The mixture was immediately transferred to an extruder with a 6 mm die plate and extruded. The mixture extruded easily with no evidence of excess friction heat or “steaming” - demonstrating that there was enough moisture available to bind the ingredients and lubricate the process.

[0175] • The extrudate was then transferred to a spheroniser, initially at half speed. After 1 minute, the mixture was observed to be forming into large “balls” (about 30 mm in diameter). The spheroniser speed was then increased to maximum and 100 ml of airdried lignite was added along with a one-minute blast of compressed air - it was observed that the large balls were disintegrating and forming into smaller spheres. Spinning was continued on maximum speed for 10 minutes during which time more air-dried lignite and compressed air was added, until a “rope” of consistent and appropriately sized granules was observed.

[0176] • Optionally, these “green” granules can be transferred to a gas-fired rotary drier where they were dried in a 90 - 95 °C air stream for 30 minutes until they were around 18% total moisture. No ammonia smell was detected during drying.

[0177] Example 2

[0178] Starting with raw lignite at approx. 62% total moisture content, the following absorbent materials were added (all % amounts are on a dry lignite basis): o Agricultural gypsum - 10%. o Air-dried lignite - 5% (at 17% total moisture content). o S odium Bentonite - 5%. o Potassium Polyacrylate - 0.3%. o Corn starch - 10%.

[0179] • The added absorbent materials were incorporated with the raw lignite in a mixer and rotated at 30 rpm for 30 minutes, before then grinding the mixture in a hammer mill with a 5 mm screen.

[0180] • The ground mixture was returned to the mixer and rotated at 30 rpm for a further 30 minutes and then allowed to rest for 24 hours to allow free moisture from the lignite to be partially absorbed by the ingredients.

[0181] • An amount of urea equal to the dry weight of raw lignite was ground in the hammer mill before being incorporated into the mixture in the mixer and rotated for just 30 seconds. It was observed that as the urea reacted with available free moisture in the lignite, the mixture started to become moist.

[0182] • The mixture was allowed to rest for 1 hour before being transferred to an extruder with a 6 mm die plate. The mixture extruded easily with no evidence of excess friction heat or “steaming”. The extrudate was firm and had a plasticised appearance.

[0183] • The extrudate was then transferred to a spheroniser, initially on half speed. After 1 minute, the mixture was observed to be forming into large “balls” (about 30 mm in diameter). The spheroniser speed was increased to maximum and 100 ml of air-dried lignite was added along with a one-minute blast of compressed air - it was observed that the large balls were disintegrating and forming into smaller spheres. Spinning was continued on maximum speed for 40 minutes during which time more air-dried lignite and compressed air was added, until a “rope” of consistent and appropriately sized granules was observed.

[0184] • Optionally, these “green” granules were transferred to a gas-fired rotary drier where they were dried in a 90 - 95 °C air stream for 30 minutes until they were around 18% total moisture. No ammonia smell was detected during drying. Ideally,

[0185] In both examples, the finished fertiliser granules were observed to possess the following properties:

[0186] Approximately 95% in the desired size range.

[0187] Could withstand crushing by finger pressure.

[0188] No surface re-crystallisation of urea was observed in the weeks following production. It will be understood to persons skilled in the art of the invention that many modifications may be made without departing from the spirit and scope of the invention.

[0189] In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word “comprise” or variations such as “comprises” or “comprising” is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.

[0190] Reference numerals

[0191] 100 - First embodiment of apparatus

[0192] 10 - As-mined lignite feedstock

[0193] 12 - Lignite crusher

[0194] 14 - Lignite dryer

[0195] 15 - Prilled urea

[0196] 16 - Urea crusher

[0197] 17 - Additive

[0198] 18 - Mixer

[0199] 19 - Binder

[0200] 20 - Granulator

[0201] 22 - Spheroniser

[0202] 24 - Green granule dryer

[0203] 26 - Cooler

[0204] 28 - Packaging unit

[0205] 200 - Second embodiment of apparatus

[0206] 210 - As-mined lignite feedstock

[0207] 212 - Lignite crusher

[0208] 215 - Prilled urea

[0209] 216 - Urea crusher

[0210] 217 - Additive

[0211] 218 - Mixer

[0212] 220 - Extruder

[0213] 221 - Added dried lignite

[0214] 222 - Spheroniser

[0215] 224 - Green granule dryer

[0216] 226 - Cooler

[0217] 228 - Packaging unit

[0218] 300 - Third embodiment of apparatus

[0219] 310 - As-mined lignite feedstock

[0220] 312 - Lignite crusher

[0221] 315 - Prilled urea

[0222] 316 - Urea crusher

[0223] 317 - Additive 318 — Mixer

[0224] 319 - Binder

[0225] 321 - Added dried lignite

[0226] 322 - Spheroniser 324 - Green granule dryer

[0227] 326 - Cooler

[0228] 328 - Packaging unit

Claims

CLAIMS:

1. A method of forming a granulated fertiliser including:(a) mixing together lignite having a moisture content ranging from 50-70% and urea until at least part of the urea is solubilised by moisture liberated from the lignite and forming a wet mixture;(b) mixing the wet mixture with more lignite or other absorbent materials to reabsorb at least part of the solubilised urea and form a drier mixture;(c) optionally extruding the drier mixture into an extrudate; and(d) feeding the drier mixture or the extrudate into a granulator and forming a granulated fertiliser having a maximum moisture content of up to 30wt%.

2. The method according to claim 1, wherein step (a) including mixing the urea and the lignite at a dry wt% ratio ranging from 40:60 to 60:40 urea to lignite.

3. The method according to claim 1 or claim 2, wherein the amount of the lignite added in step (b) is up to 10wt% of the total dry weight of the urea and the lignite in the wet mixture.

4. The method according to any one of the preceding claims, wherein the lignite added in step (b) has a maximum moisture content of 20wt%.

5. The method according to any one of the preceding claims, including comminuting the lignite to a maximum particle size of 7mm before step (a).

6. The method according to any one of the preceding claims, including comminuting the urea to a maximum particle size of 3mm before step (a).

7. The method according to any one of the preceding claims, wherein step (a) includes mixing the urea and the lignite for up to 5 minutes.

8. The method according to any one of the preceding claims, wherein the lignite added in step (b) has a maximum particle size of 5mm.

9. The method according to any one of the preceding claims, wherein step (b) includes mixing the wet mixture with more lignite for up to 5 minutes.

10. The method according to any one of the preceding claims, including resting the drier mixture after mixing.

11. The method according to any one of the preceding claims, wherein step (d) includes operating the granulator to form generally spherical granules.

12. The method according to any one of the preceding claims, wherein step (d) includes drying the drier mixture or the extrudate to form a granulated fertiliser having a total moisture content up to 20wt%.

13. The method according to any one of the preceding claims, wherein step (d) includes maintaining a maximum drying temperature of 140°C.

14. The method according to any one of the preceding claims, wherein step (d) includes mixing the drier mixture or the extrudate with more dried lignite.

15. The method according to any one of the preceding claims, including adding an absorbent material to either or both steps (a) and (b).

16. A granulated fertiliser comprising lignite and urea and having a maximum moisture content of up to 30wt%, wherein the relative amounts of lignite and urea delivers crop yields and quality comparable with crops grown using 100% urea application.

17. The granulated fertiliser according to claim 16, having a urea to lignite dry wt% ratio ranging from 40:60 to 60:40.

18. The granulated fertiliser according to claim 16 or claim 17, comprises generally spherical granules.

19. The granulated fertiliser according to any one of claims 16 to 18, including an absorbent material.

20. An apparatus for forming a granulated fertiliser comprising: a mixer (a) configured to mix lignite having a moisture content ranging from 50-70% and urea until at least part of the urea is solubilised by moisture liberated from the lignite and (b) configured to receive more lignite or other absorbent material to reabsorb at least part of the solubilised urea, and form a drier mixture; an optional extruder for extruding the drier mixture into an extrudate; and a granulator for granulating the drier mixture or the extrudate and forming the granulated fertiliser having a maximum moisture content of up to 30wt%.

21. The apparatus according to claim 20, wherein the granulator is a spheroniser.

22. The apparatus according to claim 20 or claim 21, including a dyer for drying the drier mixture or the extrudate to form the granulated fertiliser.

Images