A method for the production of a fertilizer granule

Abstract

The present invention relates to a method for producing a fertilizer granule comprising a mixture of polyhalite and melt urea, wherein said method comprises adding polyhalite to a granulator, providing a source of melt urea, transferring the melt urea to the granulator to form a mixture, and granulating the mixture to yield granules.

Description

[0001] A METHOD FOR THE PRODUCTION OF A FERTILIZER GRANULE

[0002] Field of the Invention

[0003] The present invention relates to the field of fertilizers, specifically to a method for producing a fertilizer granule comprising a mixture of polyhalite and melt urea.

[0004] Background of the Invention

[0005] To grow properly, plants need nutrients (nitrogen, phosphate, potassium, calcium, zinc, magnesium, iron, manganese, etc.).

[0006] Fertilizers are needed to achieve a desired plant growth and they typically provide, in varying proportions, three main macronutrients: N, P and K. Polyhalite is an evaporite mineral, a hydrated sulfate of potassium, calcium and magnesium with formula: K2Ca2Mg(S04)42H2O.

[0007] Polyhalite is used as a fertilizer since it contains four important nutrients which may be present in approximate amounts as follows (at an assumed purity of 90%).

[0008] • 48% SO3 (as sulfate);

[0009] • 14% K2O;

[0010] • 6% MgO; and

[0011] • 17% CaO. Polyhalite is also advantageously free of chlorine.

[0012] Urea is an organic compound with chemical formula CO(NH2)2. It is a colourless, odourless solid, highly soluble in water, and practically non-toxic. Dissolved in water, it is neither acidic nor alkaline. Urea is widely used in fertilizers as a source of nitrogen (N).

[0013] Nitrogen is essential component for the plant. Nitrogen containing fertilizers like urea, ammonium nitrate, ammonium sulphate calcium nitrate and magnesium nitrate are useful for the plant's growth. However, despite the potential of using urea as a fertilizer, or at least as a portion thereof, urea has various disadvantages, including for example, rapid breakdown and volatilization which causes substantial loss of urea, and potentially harm the environment through addition of biuret and leaching into watercourses.

[0014] The losses can be more than 10% depending on the temperature soil character.

[0015] More than 90% of world industrial production of urea is destined for use as a nitrogenrelease fertilizer. Urea has the highest nitrogen content of all solid nitrogenous fertilizers in common use. Therefore, it has a low transportation cost per unit of nitrogen nutrient. The most common impurity of synthetic urea is biuret, which impairs plant growth. Urea breaks down in the soil by enzymatic hydrolysis to give ammonium ions. The ammonium can be taken up by the plant through its roots. In some soils, the ammonium is oxidized by bacteria to give nitrate (NO-3), which is also a nitrogenrich plant nutrient. The loss of nitrogenous compounds to the atmosphere and runoff is wasteful and environmentally damaging so urea is sometimes modified to enhance the efficiency of its agricultural use. Techniques to make controlled-release fertilizers that slow the release of nitrogen include the encapsulation of urea in an inert sealant, and conversion of urea into derivatives such as urea-formaldehyde compounds, which degrade into ammonia at a pace matching plants' nutritional requirements. It is known in the art to use a fluid granulation process to produce granular urea by low-pressure ‘film’ spraying of liquid urea onto seed material in a fluidized state. In this process the liquid urea used is a concentrated solution and the granules are built up layer by layer through the film spraying nozzles. The resulting granules are said to exhibit good quality due to this controlled layering process. The particle is completely solidified before applying a new layer of liquid urea.

[0016] At the core of this process is a proprietary granulator. The art recognises that the granulator’s film spraying nozzles play a crucial role in building up the granules layer by layer. This results in a better-quality end-product compared to other fluidized granulation processes.

[0017] Other advantages of this process include:

[0018] □ Reduced formaldehyde content in the final product;

[0019] □ Low dust formation; and

[0020] □ Longer operation time (up to three months) without interruptions for cleaning.

[0021] It is noted that this is a fluidised bed process requiring a proprietary granulator.

[0022] A need exists for a cost-effective method of producing a fertilizer granule comprising urea and polyhalite which ameliorates the abovementioned disadvantages.

[0023] Summary of the Invention

[0024] According to a first aspect of the present invention there is provided a method for producing a fertilizer granule comprising a mixture of polyhalite and melt urea, wherein said method comprises:

[0025] • adding polyhalite to a granulator,

[0026] • providing a source of melt urea,

[0027] • transferring the melt urea to the granulator to form a mixture, and

[0028] • granulating the mixture to yield granules.

[0029] The method may consist essentially of the steps of:

[0030] • adding polyhalite to a granulator, providing a source of melt urea, transferring the melt urea to the granulator to form a mixture, and granulating the mixture to yield granules.

[0031] The method may consist of the steps of:

[0032] • adding polyhalite to a granulator,

[0033] • providing a source of melt urea,

[0034] • transferring the melt urea to the granulator to form a mixture, and

[0035] • granulating the mixture to yield granules.

[0036] The melt urea may be present in a ratio of 20:80 to 80:20 with the polyhalite.

[0037] The method may include the step wherein the melt urea is sprayed into the granulator. The method may include the step wherein the melt urea is dripped into the granulator. The method may include the step wherein the melt urea is dispensed as an aerosol or mist into the granulator.

[0038] It is to be noted that no additional mixer is required in accordance with the present invention as both addition and mixing occurs in a granulator. An example of a suitable granulator is an intensive mixer / granulator, e.g. as available from Maschinenfabrik Gustav Eirich GmbH & Co KG (RTM). The granulator may be configured to expel processed material as it operates, allowing it to run continuously. Alternatively, the granulator may operate on a batch basis, with material being processed according to a defined programme and then expelled en masse.

[0039] The polyhalite may be in the form of a powder. The average particle size (largest or average diameter) of the polyhalite may be from 20 to 2000 pm, including between 50 and 1500 pm. Conveniently at least 50% or more preferably at least 70% of the mass of the polyhalite powder is composed of particles having a size in the range from 50 to 400pm. The grain size may be as measured by means of a Malvern Mastersizer 2000 (RTM) or as measured by means of a sieve shaker. The D50 is preferably measured as a median value.

[0040] In one embodiment, no further or additional binder is added to the mixture. The melt urea binds the polyhalite to form granules. The melt urea may be considered to be a form of binder in so far as the melt urea acts in binding the components of the fertilizer granule together.

[0041] In one embodiment, the granules may be coated with one or more organic or inorganic coatings.

[0042] The method may include the step wherein said granules further undergo a sieving process to yield a desirable size granule at a size range of 2-6mm.

[0043] The method may include the step wherein any undersized granules are returned to the granulator, and any oversized granules are ground and transferred to the granulator for further processing.

[0044] The method may include the further step of adding a micronutrient to the mixture. The micronutrient may be selected from any one or more of iodine, sodium, copper, cobalt, iron, manganese, boron, nickel, zinc, selenium, molybdenum or silicon.

[0045] In one embodiment the source of melt urea may be provided by heating urea to provide a melt urea.

[0046] In one embodiment the source of melt urea may be provided by the synthetic production of urea. The synthetic production of urea may be the Haber-Bosch process.

[0047] The polyhalite may be or comprise at least one polyhalite analogue and / or other sulphate salts. As such, the invention extends to a method as hereinbefore described wherein the polyhalite is or includes at least one polyhalite analogue.

[0048] The polyhalite may comprise at least one polyhalite analogue and a naturally occurring polyhalite. In one embodiment, the polyhalite consists essentially of at least one polyhalite analogue and a naturally occurring polyhalite. In another embodiment, the polyhalite consists of at least one polyhalite analogue and a naturally occurring polyhalite.

[0049] The polyhalite analogue is preferably ASO4 ■ MSO4 ■ 2CaSO4 2H2O where A is selected from K+and NH4+, and M selected from Mn2+, Fe2+, Co2+, Ni2+, Cu2+and Zn2+.

[0050] The polyhalite may be naturally occurring. The polyhalite analogue may be synthesised.

[0051] The polyhalite may comprise a. 50 to 99 %wt polyhalite and / or other sulphate salts; and b. 1to 50] %wt polyhalite analogue or combinations thereof.

[0052] Other sulphate salts may be selected from Potassium Sulphate, Magnesium Sulphate and Calcium Sulphate.

[0053] The polyhalite may contain more than 55%wt polyhalite and / or other sulphate salts, more than 60%wt, more than 65%wt, more than 70%wt, more than 75%wt, more than 80%wt, more than 85%wt, more than 90%wt and more than 95%wt polyhalite and / or other sulphate salts.

[0054] The polyhalite may contain more than 5%wt polyhalite analogue or combinations thereof, more than 10%wt, more than 15%wt, more than 20%wt, more than 25%wt, more than 30%wt, more than 35%wt, more than 40%wt and more than 45%wt polyhalite analogue or combinations thereof.

[0055] The polyhalite may contain less than 95%wt polyhalite and / or other sulphate salts, less than 90%wt, less than 85%wt, less than 80%wt, less than 75%wt, less than 70%wt, less than 65%wt, less than 60%wt and less than 55%wt polyhalite and / or other sulphate salts.

[0056] The polyhalite may contain less than 45%wt polyhalite and / or other sulphate salts, less than 40%wt, less than 35%wt, less than 30%wt, less than 25%wt, less than 20%wt, less than 15%wt, less than 10%wt and less than 5%wt polyhalite and / or other sulphate salts.

[0057] The amount of polyhalite analogue present in the polyhalite may be predetermined to address a deficiency (preferably known or anticipated) in an area of application, for example the addition of a manganese or iron containing analogues into a polyhalite containing fertiliser composition for the prevention of deficiency symptoms of either that may be observed in crops grown in high organic matter or high pH soils. Alternatively, the addition of a cobalt containing analogue in small amounts to a polyhalite composition intended for use in crops such as Soya, where Cobalt is required during the fixation of nitrogen by rhizobia bacteria in nodules of leguminous plants, In other words, alterations to the chemical composition of the polyhalite in the fertiliser composition according to this aspect of the invention can be tailored to suit particular conditions.

[0058] The deficiency in an area of application of the fertiliser composition may be a mineral and / or nutrient imbalance in the area of application.

[0059] The area of application may be soil and / or water.

[0060] It will be appreciated that the characteristics of the polyhalite powder can be selected to determine the characteristics of the final product, both in terms of chemical composition (grade) and physical characteristics.

[0061] According to a second aspect of the present invention there is provided a fertilizer granule comprising a mixture of polyhalite and melt urea wherein the granule is substantially chlorine free. The fertilizer granule may be produced by a method according to the first aspect of the invention. The mixture of polyhalite and melt urea may be in a ratio of between 20:80 to 80:20.

[0062] Detailed Description of the Invention

[0063] According to the present invention there is provided a method for producing a fertilizer granule comprising a mixture of polyhalite and melt urea. As such, the present invention utilises melted urea that is received into the polyhalite, which is preferably in the form of a powder. The present invention substantially reduces urea loss, caused by the transformation of nitrogen in the soil, and allows for a more homogeneous supply of the nutrients to the plants, with no segregation and more control on the dissolution of the urea.

[0064] In addition, having the urea melt received directly into the polyhalite results in fewer lumps forming during granulation, resulting in a smoother product having more consistent release properties. Furthermore, polyhalite is a hard mineral that can be abrasive to equipment, in particular it can be abrasive when propelled at high speed / pressure over metal. By adopting this method of combining urea to polyhalite, equipment wear is avoided than is a slurry was pumped and discharged to the drum. In addition in this form, the melt urea binds the polyhalite to form granules. The melt urea may be considered to be a form of binder in so far as the melt urea acts to bind the components of the fertilizer granule together.

[0065] Spraying the urea into the granulator improves nozzle wear of the sprayer units in that the nozzles do not wear as much compared to their spraying polyhalite. The method according to the present invention also avoids blockages in the nozzles and pipes as well as sedimenting of pipework.

[0066] Finally, by avoiding the use of an additional mixer and / or specialised or proprietary equipment (such as a sprayer), significant savings are realised both in terms of capital expenditure and maintenance of equipment.

[0067] According to some embodiments, the granule of the present invention may further include one or more additional fertilizers, for example, selected from the group including any material of natural or synthetic origin that is applied to soils or to plant tissues to supply one or more plant nutrients essential to the growth of plants, including, for example, single nutrient ("straight") fertilizers such as ammonium nitrate, calcium ammonium nitrate, superphosphate, e.g., "single superphosphate" (SSP), phosphogypsum, triple superphosphate (TSP) or a mixture thereof; multinutrient fertilizers such as binary (NP, NK, PK) fertilizers, e.g. monoammonium phosphate (MAP) and / or diammonium phosphate (DAP), NPK fertilizers which are three component fertilizers providing nitrogen, phosphorus, and potassium; fertilizers which include one or more of the main micronutrients including sources of iron, manganese, boron, molybdenum, zinc, and copper and the like; compound fertilizers e.g., which contain N, P, and K; organic fertilizers such as peat, animal wastes, plant wastes from agriculture, and sewage sludge; and / or other elements such as calcium, magnesium, and sulfur.

[0068] In a preferred embodiment, the granule does not further comprise or include a binder.

[0069] According to embodiment of the present invention there is provided herein a method for granulating a fertilizer granule comprising a mixture of polyhalite and melt urea in a ratio of between 20:80 to 80:20 wherein said granule is mixed and granulated in a granulator to produce N, K, Ca, Mg, S complex fertilizer which may be chloride free.

[0070] Urea melt can also be granulated with other minerals such as kieserite, langbeinite, kainite in the same procedure as described herein with regard to polyhalite.

[0071] In one embodiment of the present invention, the method may comprise heating / warming urea to over its meting point but under the temperature at which it decomposes, for example over 130°C to melt the urea. Urea has a melting point of from 133 to 135 ° (deg) C.

[0072] In one embodiment the source of melt urea may be provided by the synthetic production of urea. The synthetic production of urea may be the Haber-Bosch process. The Haber-Bosch process is a main industrial procedure for the production of ammonia. The process converts atmospheric nitrogen (N2) to ammonia (NH3) by a reaction with hydrogen (H2) using an iron metal catalyst under high temperatures and pressures.

[0073] The melted urea is transferred to a mixer granulator already containing the polyhalite such that the melt urea is received into the polyhalite. According to some embodiments, the resulting mixture may be mixed for a few minutes, e.g., 3-4 minutes. According to some embodiments, the ratio between the melted urea and polyhalite may be 20:80 to 80:20, preferably 50:50, e.g. 50% melt urea and 50% polyhalite. It will be appreciated, that at least initially, the melt urea as added is present in a much smaller amount than the polyhalite, such that it results in the urea being fully integrated into the polyhalite to produce a fully homogenous mixture

[0074] According to some embodiments the temperature of the mixture may then be reduced to about 30-70°C.

[0075] According to some embodiments, the mixing / granulation process may be conducted using various machines like a pan granulator, a drum granulator, a plough shear mixer and / or the like.

[0076] According to some embodiments, the granulator / mixer is preferably a drum granulator.

[0077] According to some embodiments, the granules may undergo a sieving process to yield a desirable size granule at a size range of 2-6 mm, preferably 2- 4.75 mm.

[0078] According to some embodiments, any undersized granules may be returned to the granulator / mixer, and any oversized granules may be ground and transferred to the granulator / mixer for further processing.

[0079] According to some embodiments, the desired size granules may be further dried and cooled to yield the final product.

[0080] According to some embodiments, the resulting granule may be coated with one or more coatings, organic or inorganic coating e.g., to enable the delayed release of the materials of the granule or to add additional components to the fertilizer granule. This can help to resist the granules sticking or breaking up during screening or further processing and final application. Further polyhalite powder may be added to the granulator / mixer towards the end of the granulating process. The polyhalite powder may coat the granules with a dry coating which can assist with subsequent processing. The amount of polyhalite powder added at this stage may be between 5 and 15% by mass of the content of the granulator, more preferably between 8 and 12% by mass. The additional polyhalite powder may be added between 10 and 15 seconds prior to completion of the granulation process.

[0081] The present invention also avoids having to melt any urea for addition in a return cycle.

[0082] According to a further aspect of the present invention there is provided a method of making an evaporite mineral containing fertilizer composition, which may be in the form of a granule, the method comprising the step of adding melt urea by spraying, dripping or dispensed as a mist or aerosol to the evaporite mineral to result in a homogenous mixture.

[0083] Aspects of the invention as described previously apply mutatais mutandis to this aspect of the present invention.

[0084] Specific Description

[0085] The present invention will now be described by way of example with reference to the accompanying drawings in which Figure 1 is a diagram of the method according to the invention.

[0086] In Figure 1 a conventional granulation process 10 is shown where a drum granulator 13 is used to produce fertilizer granules 21 comprising N, K, S, Mg and Ca. The polyhalite powder 11 feeds a drum granulator 13 in a predetermined content (kg / h). The melt urea 12 from a melting unit (not shown) is added into the granulator 13 using a sparger.

[0087] The granulation discharge goes to a dryer 14 and where the granules will be dried reaching moistures up to 0.5%. After that the polyhalite and urea granules are classified (through the use of a screening section 15) into the desired particle size and the fines are directed back to the granulator. The coarse material are milled through a mill 16 and the fines to make up the recycle that will feed the granulator 13. The particles that fit the desired size go through the cooler 17 and afterwards to a polish / coating drum 20, where coating agents, for example, a talc (to prevent caking) 19 and an oil (to prevent dust generation) 18 are added to coat the grain. Additional coatings to improve the material performance in agricultural environments (e.g. micronutrients, urease inhibitors) can also be applied. The product 21 leaving the cooler 17 should be less the 85 deg C before being sent to storage.

[0088] Examples

[0089] Table 1: Product Nutrient Content - High Grade

[0090] When the melt urea is received into the High Grade Polyhalite Powder, a High Grade granule has the Final Nutrient Content as set out in Table 1.

[0091] Table 2: Product Nutrient Content - Low Grade

[0092] When the melt urea is received into the Low Grade Polyhalite Powder, a Low Grade granule has the Final Nutrient Content as set out in Table 2.

Claims

Claims1. A method for producing a fertilizer granule comprising a mixture of polyhalite and melt urea, wherein said method comprises:• adding polyhalite to a granulator,• providing a source of melt urea,• transferring the melt urea to the granulator such that the melt urea is received into the polyhalite and wherein the melt urea is sprayed, dripped or dispensed as a mist or aerosol into the granulator to form a mixture, and• granulating the mixture to yield granules.

2. The method according to claim 1, wherein the melt urea is transferred to the granulator in a ratio of 20:80 to 80:20 with the polyhalite.

3. The method according to any one of claims claim 1 or 2 wherein no further or additional binder is added to the mixture.

4. The method according to any preceding claim wherein the granules are coated with one or more organic or inorganic coatings.

5. The method according to any preceding claim wherein said granules further undergo a sieving process to yield a desirable size granule at a size range of 2-6mm.

6. The method according to claim 5 wherein any undersized granules are returned to the granulator, and any oversized granules are ground and transferred to the granulator for further processing.

7. The method according to any previous claim including the further step of adding a micronutrient to the mixture.

8. The method according to claim 7 wherein the micronutrient is selected from any one or more of iodine, sodium, copper, cobalt, iron, manganese, boron, nickel, zinc, selenium, molybdenum and silicon.

9. The method according to claim 1 wherein the source of melt urea is provided by heating urea to provide a melt urea.

10. The method according to claim 1 wherein the source of melt urea is provided by the synthetic production of urea.11 . The method according to claim 10 wherein the synthetic production of urea is the Haber-Bosch process.

12. The method according to any previous claim wherein the polyhalite is in the form of a powder.

13. The method according to claim 12 wherein the average particle size (largest or average diameter) of the polyhalite powder is from 20 to 2000 pm, including between 50 and 1500 pm.

14. The method of claim 12 or 13 wherein at least 50%, including at least 70% of the mass of the polyhalite powder is composed of particles having a size in the range from 50 to 400pm.

15. The method according to any previous claim wherein the polyhalite is or includes at least one polyhalite analogue.

16. A fertilizer granule produced by a method according to any one of claims 1 to 15.

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