Method for manufacturing solid granulated fertilizer composition comprising additive

Abstract

The present disclosure relates to a method for manufacturing a solid granulated fertilizer composition in a production facility comprising a nitrogen source selected from urea and ammonium salts and an additive selected from biostimulants and micronutrients, the production facility comprises at least a synthesis unit, an evaporator unit, a granulation unit, an effluent gas treatment unit comprising a scrubber, and optionally a scrubber evaporator.

Description

Technical Field

[0001] The present invention relates to a process for the manufacture of a solid particulate fertilizer composition comprising main nutrients, additives, in particular biostimulants and / or micronutrients. Background Art

[0002] Row crops require 12 nutrients to ensure optimal growth and yield. These nutrients are divided into three categories: major nutrients, which are nitrogen, phosphorus and potassium; minor nutrients, which are magnesium, calcium and sulfur; and micronutrients, which are boron, copper, iron, molybdenum, manganese and zinc.

[0003] These nutrients occur naturally in most soils, but not always in the concentrations that crops need, so it is common practice to apply fertilizer products to fields to ensure that crops receive adequate nutrients.

[0004] There are two main categories of fertilizer products: solid and liquid. Solid fertilizer products are generally favored by farmers because they are easier to distribute and are less expensive than liquids.

[0005] Solid fertilizer compositions may contain one or more nutrients. For example, urea pellets or granules contain only nitrogen, but so-called NPK products contain all three major nutrients. Solid fertilizer compositions containing at least one major nutrient and one or more minor nutrients and / or one or more micronutrients are becoming more common. These products reduce the number of operations required by the farmer.

[0006] In addition to nutrients, the use of a new class of products is also increasing: biostimulants. Biostimulants are chemical compounds that can be small organic molecules, inorganic salts, polymers, but can also be microorganisms, fungi, or plant extracts. Biostimulants are not used by crops for the chemical elements they contain, but they trigger a physiological response in the crop. The response can reduce damage to the crop due to abiotic stresses such as disease or drought, it can improve the way the crop absorbs or uses nutrients from the soil, or it can increase the amount or quality of the harvest. Therefore, the production of solid fertilizer compositions containing one or more biostimulants has become more interesting.

[0007] Solid fertilizer compositions can be prepared in a variety of ways. The method currently used in industry widely includes preparing a melt, i.e. a liquid composition comprising salts or small molecules and water, and solidifying the melt into a solid particle composition. This method allows continuous and efficient production of solid fertilizer compositions that can be stored and easily transported to the field.

[0008] A conventional way of adding additives such as biostimulants and micronutrients is to add these to the melt during concentration of the melt (ie when the melt typically contains more than 5 wt. % water), or just before the solidification step.

[0009] US2019256432 (Koch, 2019) discloses a method for recovering and reusing compounds from a high-efficiency urea processing facility, the method comprising: collecting a liquid waste stream from a scrubber designed to purify an exhaust waste stream; concentrating the liquid waste stream to produce a recovered material containing 4% or less water by weight; combining the recovered material with raw urea to produce a mixture; and introducing the mixture into a high-efficiency urea processing device to be combined with one or more efficiency additives.

[0010] US2021024460 (ThyssenKrupp Fertilizer Technology, 2021) discloses a urea production facility including a synthesis and recovery section, wherein the urea production facility has a first evaporation section and a first condensation section connected to the synthesis and recovery section. The granulation section is connected to the first evaporation section. The washing section is connected to the granulation section. The second evaporation section is connected to the washing section. The second evaporation section is connected to the granulation section. The second condensation section is connected to the second evaporation section. The quenching section includes a liquid inlet for distributing a quenching liquid, which is located and connected between the granulation section and the washing section, and the quenching section is connected to the quenching liquid supply section and the second condensation section.

[0011] AU2020358923 (Sabic Global Technologies, 2022) discloses urea calcium sulfate (UCS) fertilizer granules and methods of making and using the same. The granules may include urea-calcium sulfate (UCS) adducts. The manufacturing method may include producing a partially dried material comprising the UCS adduct, and forming the UCS fertilizer granules by feeding the partially dried material to a separate container for granulation or granulating the partially dried material after storage, or both. Summary of the invention

[0012] The above conventional methods are not always suitable because they may require additional equipment, and thus there is a need to provide new methods for producing solid granular fertilizer compositions containing additives such as biostimulants and micronutrients.

[0013] The inventors have now solved the above mentioned problem and have found that additives, for example additives selected from biostimulants and micronutrients, can be added in precise doses to a fertilizer melt using different addition points during the production of a solid granular fertilizer composition, wherein the additive is introduced into the fertilizer composition as an aqueous suspension of granular solid material, as a solution of the additive, for example an aqueous solution or an organic solvent solution, as an aqueous dispersion or as a solid.

[0014] The use of water as a suspension, solvent or dispersion medium, as well as the addition of water to a melt already containing water, does not affect the quality of the final solid particulate composition. Furthermore, the process for producing the solid particulate fertilizer composition already contains process steps and measures for removing water from the melt, thereby effectively removing the solvent, suspension or dispersion medium (i.e. water). As a result, no foreign matter remains in the final ammonium-based product except for the intended additives.

[0015] Adding the additive as a solid reduces the need for removing additional water from the melt and thus reduces the cost of the manufacturing process.

[0016] In one aspect, the present disclosure relates to a method for manufacturing a solid particulate fertilizer composition comprising a nitrogen source selected from urea and ammonium salts and an additive selected from biostimulants and micronutrients in a production facility comprising at least a synthesis unit, an evaporator unit, a granulation unit, an effluent gas treatment unit including a scrubber, and optionally a scrubber evaporator, wherein the method comprises at least the following steps:

[0017] (i) in a synthesis unit, producing an aqueous solution comprising a nitrogen source selected from urea and ammonium salts and water;

[0018] (ii) concentrating the aqueous solution produced in step (i) in an evaporator unit to obtain a fertilizer melt comprising 1.0% to 5.0% by weight of water;

[0019] (iii) granulating the melt obtained in step (ii) in a granulation unit, thereby obtaining a solid particulate fertilizer composition and generating an effluent gas comprising ammonia;

[0020] (iv) treating the effluent gas comprising ammonia from the granulation unit with an aqueous solution in an effluent gas treatment unit, thereby producing a scrubber solution; and

[0021] (v) optionally, concentrating scrubber solution from a scrubber solution storage vessel in a scrubber evaporator,

[0022] (vi) optionally, storing in a scrubber solution storage vessel the scrubber solution from the effluent gas treatment unit or the concentrated scrubber solution from the scrubbing evaporator produced in step (iii);

[0023] (vii) mixing the scrubber solution obtained in step (iv) or (v) with the aqueous solution in the synthesis unit in step (i), with the aqueous solution in the evaporator unit in step (ii), or with the fertilizer melt obtained in step (ii); wherein the additive is introduced as an aqueous suspension, aqueous dispersion, solution or solid into any one or more of:

[0024] (a) outflow gas treatment unit;

[0025] (b) A scrubber solution storage vessel containing scrubber solution.

[0026] In another aspect, the present disclosure relates to a system for manufacturing a solid particulate fertilizer composition, wherein the system is configured to manufacture the solid particulate fertilizer composition according to the method as described herein, characterized in that the system comprises an additive introduction device in the outflow gas treatment unit and / or the scrubber solution storage container. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A workflow of a method according to the present disclosure is represented.

[0028] Figure 2 A workflow of a method according to the present disclosure is represented. DETAILED DESCRIPTION

[0029] In the context of the present disclosure, unless defined otherwise, the expressions "weight percent", "% wt" or "weight %" here and throughout the specification refer to the relative weight of the respective component based on the total weight of the formulation.

[0030] Unless the context clearly dictates otherwise, as used herein, "a", "an", and "the" refer to both singular and plural references. For example, "an additive" refers to one or more than one additive.

[0031] In the context of the present disclosure, particulate form means a physical form which may also be designated as granules, pellets, crystals, compacts, powders, etc., in which the corresponding compound is in the form of small units.

[0032] In the context of the present disclosure, stabilizers mean compounds that are able to improve the chemical stability of the nitrification inhibitor.

[0033] In the context of the present disclosure, an aqueous suspension means any composition in which the additive is at least suspended as a particulate solid in water. Examples are calcium oxide in water or magnesium sulfate in water. The suspension may contain suspension stabilizers, wetting agents, surface-active compounds, etc.

[0034] In the context of this disclosure, aqueous dispersion means any composition wherein the additive is an at least partially water-immiscible liquid intimately mixed with water, wherein water or the at least partially water-immiscible liquid is the continuous phase.

[0035] In the context of this disclosure, an aqueous solution means any composition in which the additive is substantially dissolved in water. The aqueous solution may contain other ingredients such as co-solvents to improve the solubility of the additive.

[0036] In the context of the present disclosure, a solid homogeneous particle refers to a solid particle that is uniform in its composition throughout the particle. A homogeneous particle may still contain solid particles of different components, as long as the solid particles are much smaller than the homogeneous solid particles. In contrast, a heterogeneous particle has a different composition throughout the particle. It is worth noting that homogeneous particles are easier to produce because they require a single solidification step.

[0037] In one aspect, the present disclosure relates to a method for manufacturing a solid particulate fertilizer composition comprising a nitrogen source selected from urea and ammonium salts and an additive selected from biostimulants and micronutrients in a production facility comprising at least a synthesis unit, an evaporator unit, a granulation unit, an effluent gas treatment unit including a scrubber, and optionally a scrubber evaporator, wherein the method comprises at least the following steps:

[0038] (i) in a synthesis unit, producing an aqueous solution comprising a nitrogen source selected from urea and ammonium salts and water;

[0039] (ii) concentrating the aqueous solution produced in step (i) in an evaporator unit to obtain a fertilizer melt comprising 1.0% to 5.0% by weight of water;

[0040] (iii) granulating the melt obtained in step (ii) in a granulation unit, thereby obtaining a solid particulate fertilizer composition and generating an effluent gas comprising ammonia;

[0041] (iv) treating the effluent gas comprising ammonia from the granulation unit with an aqueous solution in an effluent gas treatment unit to produce a scrubber solution; and

[0042] (v) optionally, concentrating scrubber solution from a scrubber solution storage vessel in a scrubber evaporator,

[0043] (vi) optionally, storing in a scrubber solution storage vessel the scrubber solution from the effluent gas treatment unit or the concentrated scrubber solution from the scrubbing evaporator produced in step (iii);

[0044] (vii) mixing the scrubber solution obtained in step (iv) or (v) with the aqueous solution in the synthesis unit in step (i), with the aqueous solution in the evaporator unit in step (ii), or with the fertilizer melt obtained in step (ii); wherein the additive is introduced as an aqueous suspension, aqueous dispersion, solution or solid into any one or more of:

[0045] (a) outflow gas treatment unit;

[0046] (b) A scrubber solution storage vessel containing scrubber solution.

[0047] First, an aqueous solution comprising a nitrogen source selected from urea and ammonium salts is produced in a synthesis unit. The synthesis unit of the facility comprises various equipment required to convert the raw materials into an aqueous solution.

[0048] Different methods for preparing such aqueous solutions are known in the art. Conventional methods include reacting a gaseous or liquid ammonia stream with an acid (e.g., nitric acid, phosphoric acid, or sulfuric acid). The reaction produces a composition comprising an ammonium melt and water. The composition may comprise at least 20% by weight of water.

[0049] Fertilizers containing urea can be obtained by reacting an ammonia stream with carbon dioxide in a urea reactor. Such a reaction generates an aqueous solution containing urea, ammonium carbamate, free ammonia and water. The ammonium carbamate and ammonia can then be removed to provide an aqueous solution containing urea.

[0050] It is also possible to obtain an aqueous solution comprising urea or an ammonium salt by dissolving a solid product comprising urea and / or an ammonium salt in water.

[0051] In one embodiment, the aqueous solution produced in step i) comprises at least 5 wt % water. In one embodiment, the aqueous solution produced in step i) comprises 5 to 50 wt %, such as 10 to 50 wt %, 15 to 50 wt %, 20 to 50 wt %, 10 to 40 wt %, or 15 to 40 wt % water.

[0052] The aqueous solution can then be concentrated in an evaporator unit to remove some of the water contained therein. The evaporator unit may include one or more devices, such as an evaporator or a heat exchanger, which is designed to heat the composition and remove water therefrom. In the evaporator unit, the water content of the aqueous solution is reduced to 1.0 wt % to 5.0 wt %. The exact water content of the melt after the evaporator unit is determined by the granulation method selected for the process. Different granulation methods require melts with different water contents.

[0053] Optionally, additional components can be added to the melt before the melt is granulated. The addition can be carried out in a mixing unit, where the additional components are added to the melt and mixed to obtain a homogeneous melt. The additional components may be soluble or insoluble in the melt. A homogeneous melt is not limited to a melt comprising only soluble components, and in the present disclosure, a melt comprising insoluble components well distributed in the melt is considered to be homogeneous. For example, in order to produce a solid particulate composition based on ammonium nitrate for fertilizer purposes, it is well known that an inorganic filler is added to reduce the explosion risk of the solid particulate composition. The inorganic filler can be selected from limestone, dolomite, gypsum, kaolin clay or a mixture thereof.

[0054] In case the fertilizer melt comprises all necessary components, it is sent to a granulation unit to convert the melt into a solid particulate fertilizer composition. A variety of granulation methods are known in the art, and produce particles with different characteristics. The selection of granulation methods can be determined by the type of product requirements or melt. The granulation unit can include a fluidized bed, a pan granulator, a drum granulator, a granulating tower, a spherodizer, a kneader, a spray dryer, a high intensity mixer or a pastillizer. These granulation devices can be granulated into a homogeneous solid particulate composition by the effect of hyperplasia (fluidized bed) or agglomeration.

[0055] The granulation unit may also include a cooling unit. The granules formed from the melt have a high temperature, typically above 60° C. In order to facilitate their handling and storage, it may be advantageous to cool the granules slightly, for example below 40° C. This is typically achieved by introducing a gas stream (e.g. air) into the compartment containing the hot granules, wherein the gas has a lower temperature than the granules.

[0056] In many fertilizer production facilities, the granulation unit needs to use a gas flow (usually an air flow) to cool the melt and help form solid particles. In the granulation unit, the gas flow is polluted by solid or fluid pollutants (especially ammonia). In most countries, before the pollutants are removed from the gas flow, this gas flow cannot be discharged into the atmosphere, or at least the level of the pollutants must be below a certain threshold. Therefore, the production facility may include an outflow gas treatment unit to remove at least some pollutants from the gas flow before the gas flow is discharged into the atmosphere. The most common device in such a unit is a scrubber.

[0057] Scrubber is a device comprising a gas inlet and a gas outlet for injecting and collecting the gas flow from the granulation unit. It also comprises a device for capturing pollutants from the gas flow. Common devices in scrubbers are wash pads sprayed with a liquid composition (e.g., aqueous solution) thereon. Pollutants (solid or liquid) are absorbed by water and collected on the pads. Liquid compositions from all pads are gathered into a single stream to form a scrubber solution. The scrubber solution can be stored in a scrubber solution storage unit.

[0058] Since the scrubber solution contains elements from the product to be manufactured (e.g. ammonia), it may be of interest to reinject this solution back into the production process in order to save raw materials. The scrubber solution can be reinjected as it is collected from the pad, but it can also be concentrated, for example in a scrubbing evaporator, in order to increase the concentration of useful components and avoid reinjecting too much water (which must eventually be evaporated) into the production process. However, since the production process already includes a stage in which the composition is heated to remove water, such as the evaporator of step (ii), it may not be necessary to install a second evaporator in the process.

[0059] After the desired scrubber solution is obtained, whether concentrated or not, it can be added upstream (i.e. before) the granulation stage in the production process. For example, the scrubber solution can be added to the synthesis unit, to the aqueous solution of step (i) before it enters the evaporator unit, or to the melt before the granulation step.

[0060] In one embodiment, the method is carried out in a production facility comprising an evaporator unit, a granulation unit and an effluent gas treatment unit comprising a scrubber and a scrubber solution storage vessel.

[0061] In one embodiment, the process is carried out in a production facility comprising an evaporator unit, a mixing unit, a granulation unit and an effluent gas treatment unit comprising a scrubber and a scrubber solution storage vessel.

[0062] In one embodiment, the process is carried out in a production facility comprising an evaporator unit, a mixing unit, a granulation unit and an effluent gas treatment unit, a scrubber solution storage container and a scrubbing evaporator, the effluent gas treatment unit comprising a scrubber.

[0063] According to the present disclosure, the additive is introduced as an aqueous suspension, aqueous dispersion, solution, or solid into any one or more of:

[0064] (a) outflow gas treatment unit;

[0065] (b) A scrubber solution storage vessel containing scrubber solution.

[0066] It was found that it may be advantageous to introduce biostimulants and / or micronutrients in the outflowing gas treatment unit or in the scrubber solution storage container containing the scrubber solution.

[0067] The outflow gas treatment unit comprises a scrubber using an aqueous solution to capture pollutants contained in the gas stream from the granulation unit.Additives may be added to the aqueous solution used by the scrubber before or after the aqueous solution enters the scrubber.

[0068] The melt granulated in the granulation section contains a nitrogen source and an additive selected from biostimulants and micronutrients. The effluent gas produced by the granulation unit may contain traces of this additive and any other additives present in the melt. These traces of additives are captured by the scrubber into the scrubber solution and are finally mixed in the melt. However, the additive content in the scrubber solution caused only by the capture by the scrubber is not enough to reach the appropriate content in the melt. This is just a recycling cycle that reduces waste and pollution, but it does not introduce any new materials into the production process.

[0069] In order to produce a solid particulate fertilizer composition with a constant composition, it is necessary to continuously or regularly add an additive selected from the group consisting of biostimulants and micronutrients to the production process. The step of introducing the additive as contemplated herein as an aqueous suspension, aqueous dispersion, solution, or solid into the effluent gas treatment unit and / or the scrubber solution storage container containing the scrubber solution means adding the required or desired amount of the additive to the production process.

[0070] Surprisingly, it has been found to be very easy and effective to add the additive as an aqueous suspension to the water supply for use out of the gas treatment unit. The additive may be added to the tank storing the water for the scrubber. Alternatively, it may be added directly to the water stream before it enters the scrubber by means known in the art.

[0071] The additive may also be added to a scrubber solution storage container holding the scrubber solution. If the additive has a low solubility in water, it may be advantageous to add it to the scrubber solution storage container, as this container can hold a large volume of aqueous solution.

[0072] The scrubber solution can be conveyed to a scrubber evaporator where most of the water is removed, or it can be introduced directly into the production process. The scrubber solution, whether concentrated or not, can be added to an evaporation unit where it is mixed with the melt and the water is evaporated. This allows the process to effectively control the water content of the melt to be granulated. Alternatively, the scrubber solution can be added to a mixing unit (if present) where it is mixed with a high concentration fertilizer melt.

[0073] The choice of the method of addition of the additive (i.e. as an aqueous suspension, solution or dispersion) can depend on the characteristics of the additive. Some may dissolve easily in water and thus may be added to the method as an aqueous solution. Other additives with poor water solubility may have to be added as a suspension or dispersion.

[0074] Similarly, the step in which an additive is added may be guided or imposed by different factors, such as the exact nature of the additive, its stability to temperature and / or certain chemical environments.

[0075] In one embodiment, the additive comprises a biostimulant selected from seaweed extracts, plant extracts, enzymatic extracts, humic acid, fulvic acid, phosphites, chitosan, plant growth hormones, microorganisms and protein hydrolysates. So far, a variety of natural substances or microorganisms have been shown to have certain biostimulatory activity on one or more crops. The choice of biostimulant used in the present method can be based on the type of crop configured to receive the fertilizer composition and the problem to be solved in the crop.

[0076] In one embodiment, the solid particulate fertilizer composition obtained in step (iii) comprises 0.0001 wt.-% to 2.0 wt.-%, particularly 0.01 wt.-% to 1.0 wt.-%, more particularly 0.05 wt.-% to 0.5 wt.-% of additives relative to the total weight of the solid particulate fertilizer composition. Crops require small amounts of both biostimulants and micronutrients to achieve the desired effect.

[0077] In one embodiment, the additive comprises an extract of seaweed, the seaweed being a species selected from the group consisting of Kappaphycus alvarezii, Ascophyllum Nodosum, Ecklonia maxima, Durvillea potatorum, Macrocystis pyrifera, Sargassum, Laminaria digitata, and mixtures thereof. Extracts of various seaweed species have been shown to be suitable for use as biostimulants.

[0078] In one embodiment, the solid particulate fertilizer composition obtained in step (iii) comprises 40% to 80% by weight, 45% to 80% by weight, 50% to 80% by weight, 55% to 80% by weight, 40% to 75% by weight, or 40% to 70% by weight of an ammonium salt selected from ammonium nitrate, ammonium sulfate, ammonium phosphate, and mixtures thereof. Ammonium ions are a nitrogen source for crops. Ammonium ions cannot be well absorbed by the roots of crops, but ammonium ions can be slowly converted into nitrate ions by bacteria present in the soil or on or in the roots of crops. Nitrate is easily absorbed by crops and is a preferred nitrogen source for crops. Ammonium nitrate is a very concentrated nitrogen source. Ammonium sulfate is a source of nitrogen and sulfur. Ammonium phosphate is a source of nitrogen and phosphorus. Ammonium phosphate can include monoammonium phosphate (MAP) and / or diammonium phosphate (DAP).

[0079] In one embodiment, the solid particulate fertilizer composition obtained in step (iii) comprises 40% to 99%, 45% to 99%, 50% to 99%, 60% to 99%, 40% to 95%, or 40% to 90% urea by weight. Urea is a very concentrated nitrogen source (46% nitrogen by weight).

[0080] In one embodiment, the solid particulate fertilizer composition obtained in step (iii) comprises one or more compounds selected from the group consisting of calcium nitrate, sodium nitrate, calcium dihydrogen orthophosphate, superphosphate, triple superphosphate, rock phosphate, potassium sulfate, magnesium sulfate, urea, potassium chloride (MOP), potassium phosphate (SOP), urea potassium salt (UK), elemental sulfur and mixtures thereof.

[0081] In one embodiment, the additive comprises a micronutrient selected from the group consisting of boron, copper, iron, molybdenum, manganese, zinc, and mixtures thereof.Micronutrients are utilized by crops at different stages of the growth process, and different crops require different amounts of micronutrients.

[0082] In principle, the additive is suitably introduced into the fertilizer composition as an aqueous suspension, aqueous dispersion, solution (eg aqueous or organic solvent solution) or solid. However, depending on the specific equipment, one or more of the above may be preferred.

[0083] Adding the additive as a solid may be the preferred option, especially if the additive is free-flowing and non-dusty.

[0084] If the additive is very viscous at atmospheric pressure and ambient temperature, it may be advantageous to add it to the process as a solution or suspension.

[0085] In one embodiment, the additive is added as a solid to the scrubber solution obtained in step (iv) and added to the synthesis unit in step (i).

[0086] In one embodiment, the additive is added as a solid to the scrubber solution obtained in step (iv) and mixed with the aqueous solution in the evaporator unit in step (ii).

[0087] In one embodiment, the additive is added as a solid to the scrubber solution obtained in step (iv) and mixed with the fertilizer melt obtained in step (ii).

[0088] In one embodiment, the additive is added as an aqueous solution to the scrubber solution obtained in step (iv) and added to the synthesis unit in step (i).

[0089] In one embodiment, the additive is added as an aqueous solution to the scrubber solution obtained in step (iv) and mixed with the aqueous solution in the evaporator unit in step (ii).

[0090] In one embodiment, the additive is added as an aqueous solution to the scrubber solution obtained in step (iv) and mixed with the fertilizer melt obtained in step (ii).

[0091] In one embodiment, the additive is added as a solid to the scrubber solution obtained in step iv) and added to the synthesis unit in step (i).

[0092] In one embodiment, the additive is added as a solid to the scrubber solution obtained in step (v) and mixed with the aqueous solution in the evaporator unit in step (ii).

[0093] In one embodiment, the additive is added as a solid to the scrubber solution obtained in step (v) and mixed with the fertilizer melt obtained in step (ii).

[0094] In one embodiment, the additive is added as an aqueous solution to the scrubber solution obtained in step (v) and added to the synthesis unit in step (i).

[0095] In one embodiment, the additive is added as an aqueous solution to the scrubber solution obtained in step (v) and mixed with the aqueous solution in the evaporator unit in step (ii).

[0096] In one embodiment, the additive is added as an aqueous solution to the scrubber solution obtained in step (v) and mixed with the fertilizer melt obtained in step (ii).

[0097] In one embodiment, the production facility comprises a mixing unit, in particular a mixing unit configured to receive the fertilizer melt from the evaporator unit and to provide the fertilizer to the granulation unit. In one embodiment, the additive is added to the fertilizer melt in the mixing unit as an aqueous solution, an aqueous suspension or a solid. The mixing device, if present in the production facility, is an interesting location for adding the scrubber solution to the fertilizer composition, since the mixing device comprises adding and mixing equipment designed to mix additives or other compounds into the fertilizer melt.

[0098] In one embodiment, the method comprises the additional step of applying a conditioning agent to the solid particulate fertilizer composition. The conditioning agent can be applied as a coating, particularly a coating comprising wax (particularly petroleum wax or paraffin) and alkyl phosphate. As is well known, conditioning agents (e.g., in the form of a coating) are applied to the solid particulate composition to further improve its characteristics. Water absorption, dusting are characteristics that can be improved by adding such agents. For example, the composition based on ammonium nitrate is very water-absorbent, so it is advantageous to apply a coating that can slow down the water absorption rate of the composition. In particular, it is found that the coating comprising wax (particularly petroleum wax or paraffin) and alkyl phosphate is beneficial to the composition based on ammonium nitrate.

[0099] In some embodiments, the regulator comprises a micronutrient and / or a biostimulant selected from boron, manganese, molybdenum, iron, copper, and zinc.

[0100] In one embodiment, the solid particulate fertilizer composition obtained by the present method has an average particle size (dp50) as determined by sieve screening of 1.0 mm to 5.0 cm, preferably 1.0 mm to 1.0 cm, preferably 1.0 mm to 6.0 mm, preferably 2.0 mm to 4.0 mm, preferably 3.0 mm to 5.0 mm, preferably 2.5 mm to 3.6 mm.

[0101] In another aspect, the present disclosure relates to a system for manufacturing a solid particulate fertilizer composition as disclosed herein, wherein the system is configured to manufacture a solid particulate fertilizer composition according to a method as described herein, characterized in that the system comprises an additive introduction device in the outflow gas treatment unit and / or the scrubber solution storage container. More particularly, the additive introduction device is configured to introduce an additive into the scrubber solution, more particularly the first scrubber solution.

[0102] exist Figure 1 An embodiment of the method according to the present disclosure is disclosed in . Box 1 represents a synthesis unit in which an aqueous composition 10 comprising urea or an ammonium salt and water is prepared. The aqueous composition 10 comprising urea or an ammonium salt (e.g., ammonium nitrate) is directed to an evaporator unit 2. The water content in the fertilizer composition 10 is reduced to a range of 0.5 wt. % to about 5.0 wt. % to provide a fertilizer 11. The melt 11 is directed to a mixing unit 3 in which a solution 13 from a scrubber solution storage container 6 is added to the melt and mixed until homogeneous. The melt is then directed to a granulation unit 4, such as a fluidized bed granulator, where the melt 11 is converted into a solid fertilizer composition. The granulation unit 4 produces a polluted air stream 20 comprising ammonia, which is directed to an outflow gas treatment unit 5 comprising a scrubber. The outflow gas treatment unit 5 produces a first scrubber solution 12 comprising an ammonium salt (e.g., ammonium nitrate), which is directed to a scrubber solution storage 6. Additives 21 (micronutrients and / or biostimulants) are added to the first scrubber solution 12 in the scrubber solution reservoir 6 to provide a second scrubber solution 13 comprising ammonium salts, micronutrients and / or biostimulants.

[0103] exist Figure 2 An embodiment of the method according to the present disclosure is disclosed in . Box 1 represents a synthesis unit in which an aqueous composition 10 comprising urea or an ammonium salt and water is prepared. The aqueous composition 10 comprising urea or an ammonium salt (e.g. ammonium nitrate) is directed to an evaporator unit 2. The water content in the fertilizer composition 10 is reduced to a range of 0.5 wt. % to about 5.0 wt. % to provide a fertilizer 11. The melt 11 is directed to a granulation unit 4, such as a kneader, in which the melt 11 is converted into a solid fertilizer composition. The granulation unit 4 produces a polluted air stream 20 comprising ammonia, which is directed to an outflow gas treatment unit 5 including a scrubber. The outflow gas treatment unit 5 is provided with an acidic aqueous solution 22 comprising micronutrients and / or biostimulants and produces a scrubber solution 13 comprising ammonium salts (e.g. ammonium nitrate) and micronutrients and / or biostimulants, which is directed to the synthesis section 1, wherein the solution 13 is injected in the process and is contained in the aqueous solution 10 produced by the synthesis unit 1.

Claims

1. A method for producing a solid particulate fertilizer composition comprising a nitrogen source selected from urea and ammonium salts and additives selected from biostimulants and micronutrients in a production facility comprising at least a synthesis unit, an evaporator unit, a granulation unit, an effluent gas treatment unit including a scrubber, and optionally a scrubber evaporator, wherein the method comprises at least the following steps: (i) in the synthesis unit, producing an aqueous solution comprising a nitrogen source selected from urea and ammonium salts and water; (ii) concentrating the aqueous solution produced in step (i) in the evaporator unit to obtain a fertilizer melt comprising 1.0 to 5.0 wt. % of water; (iii) granulating the melt obtained in step (ii) in the granulation unit, thereby obtaining a solid particulate fertilizer composition and generating an effluent gas comprising ammonia; (iv) treating the effluent gas from the granulation unit comprising ammonia with an aqueous solution in the effluent gas treatment unit, thereby producing a scrubber solution; as well as (v) optionally, concentrating the scrubber solution from a scrubber solution storage container in the scrubbing evaporator, (vi) optionally, storing the scrubber solution from the effluent gas treatment unit or the concentrated scrubber solution from the scrubbing evaporator produced in step (iii) in the scrubber solution storage container; (vii) mixing the scrubber solution obtained in step (iv) or (v) with the aqueous solution in the synthesis unit in step (i), with the aqueous solution in the evaporator unit in step (ii), or with the fertilizer melt obtained in step (ii); Characterized in that the additive is introduced as an aqueous suspension, aqueous dispersion, solution or solid into any one or more of the following: (a) the outflow gas treatment unit; (b) the scrubber solution storage container containing the scrubber solution.

2. The method according to claim 1, wherein the additive comprises a biostimulant selected from seaweed extracts, plant extracts, enzymatic extracts, humic acid, fulvic acid, phosphites, chitosan, plant growth hormones, microorganisms and protein hydrolysates.

3. The method according to claim 1 or 2, wherein the granulation unit comprises a granulation device selected from a fluidized bed granulator, a pan granulator, a drum granulator, a granulation tower, a spheroidizer, a kneader, a spray dryer, a high intensity mixer and a tabletting machine.

4. The method according to any one of claims 1 to 3, wherein the solid particulate fertilizer composition obtained in step (iii) comprises 0.0001 to 2.0 wt.-%, particularly 0.01 to 1.0 wt.-%, more particularly 0.05 to 0.5 wt.-% of the additive, relative to the total weight of the solid particulate fertilizer composition.

5. The method according to any one of claims 1 to 4, wherein the additive comprises a seaweed extract, the seaweed being a species selected from the group consisting of Kappaphycus alvarezii, Ascophyllum Nodosum, Ecklonia maxima, Durvillea potatorum, Macrocystis pyrifera, Sargassum, Laminaria digitata, and mixtures thereof.

6. The method according to any one of claims 1 to 5, wherein the solid particulate fertilizer composition obtained in step (iii) comprises 40 to 80 wt.% of an ammonium salt selected from the group consisting of ammonium nitrate, ammonium sulfate, ammonium phosphate and mixtures thereof.

7. A process according to any one of claims 1 to 6, wherein the solid particulate fertilizer composition obtained in step (iii) comprises 40 to 99 wt% urea.

8. The method according to any one of claims 1 to 7, wherein the solid particulate fertilizer composition obtained in step (iii) comprises one or more compounds selected from the group consisting of calcium nitrate, sodium nitrate, calcium dihydrogen orthophosphate, superphosphate, triple superphosphate, rock phosphate, potassium sulfate, magnesium sulfate, urea, potassium chloride (MOP), potassium phosphate (SOP), urea potassium salt (UK), elemental sulfur and mixtures thereof.

9. The method according to any one of claims 1 to 8, wherein the additive comprises a micronutrient selected from the group consisting of boron, copper, iron, molybdenum, manganese, zinc and mixtures thereof.

10. A system configured for use in manufacturing a solid particulate fertilizer composition according to the method of any one of claims 1 to 9, characterized in that: The system comprises an additive introduction device in the effluent gas treatment unit and / or the scrubber solution storage container.

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