Urea compound fertilizer granules

Abstract

Disclosed is a process for the production of urea compound fertilizer granules. Herein an aqueous urea solution comprising urea and more than 5 wt.% of water is provided. To this solution at least one solid fertilizer macronutrient source is added in an amount suitable to form a slurry comprising solid particles of the macronutrient source. The slurry is subjected to mechanical treatment so as to produce a treated slurry having particles of reduced size. From the treated slurry water is removed so as to form a concentrated fertilizer liquid having a residual water content of at most 5 wt.%, which liquid is then subjected to granulation by crystallization.

Description

[0001] P138428PC00

[0002] Title: UREA COMPOUND FERTILIZER GRANULES

[0003] Field of the invention

[0004] The invention is in the field of compound fertilizers comprising urea and at least one further fertilizer macronutrient source. Particularly, the invention pertains to a granulation process for the production of urea compound fertilizer granules.

[0005] Background of the invention

[0006] In urea compound fertilizers, urea - which is a source of the fertilizer primary macronutrient nitrogen (N) - is combined with one or more further macronutrient sources, comprising one or more primary macronutrients phosphor (P) and potassium (K), and / or sources of secondary macronutrients such as sulfur (S), calcium (Ca), and magnesium (Mg).

[0007] These sources can be provided in the form of separate salts, but desirably also mixtures of fertilizer nutrient sources are provided in the form of minerals naturally providing combinations of nutrients.

[0008] It is desired to provide fertilizer nutrient sources as well as a fertilizer product in a solid form. This facilitates the transportation of this nutrient source and the fertilizer product over long distances, as well as its distribution over the land. This is reflected in background references, which disclose various solid compound fertilizers.

[0009] WO 2016 / 184615 pertains to a fluidized bed granulation process for making a combined fertilizer comprising urea or ammonium nitrate as a first fertilizer and a different second fertilizer. Urea as a first fertilizer is provided in the form of a urea melt.WO 2017 / 007315 concerns the manufacturing of granules of urea ammonium sulfate (UAS). In a fluid bed granulation process initially a granulate intermediate is provided comprising urea ammonium sulfate with a relatively high ammonium sulfate content, and ultimately a final granulation liquid is provided comprising urea with no ammonium sulfate, or a low amount of ammonium sulfate, in order to provide UAS granules having a smooth surface.

[0010] US2023 / 0227376 discloses the manufacture of a urea-calcium sulphate (UCS) adduct, where it is mentioned that the mentioned adduct is less susceptible to hydrolysis and nitrification of urea-through which loss of nitrogen from the soil is prevented. In the disclosed process, urea is contacted with water and phosphor gypsum to form a slurry. Mentioned is a slurry with 10-50wt% of water, urea and phosphor gypsum, made in a continuous stirred-tank reactor with an agitator operating at 5-60 rpm with up to 30 minutes mixing and reaction time to promote adduct formation. The slurry is subsequently fed to a dryer to obtain a dried fertilizer composition comprising a UCS adduct. UCS adduct levels of 30-40wt% are mentioned. The dried composition is subsequently fed to a granulator such as granulation drum, pugmill pan granulator etc. to produce UCS fertilizers granules through agglomeration which granules are subsequently dried to a moisture level of 0,5wt%.

[0011] EP 4 183764 Al further builds on US2023 / 0227376 and aims to increase the amount of UCS adduct formed. It is mentioned that mixing in continuous stirred-tank reactors as disclosed in said US publication is insufficient and that high conversion to UCS cannot be achieved. A high shear mixing design is proposed at shear rates of at least 50.000 / s to up to 10.000.000.000 / s to increase conversion levels to the UCS adduct to at least 80 - 90 wt%. These very high shear rates are especially achievable with an ultrasonicator, creating ultrasound, with shear forces through acoustic cavitation and bubble collapse. The ultrasonicator triggers deagglomerationof CaSCh and an increased reaction speed. Not unlikely these very high shear rates result in hot spots of high temperature. In the example, adduct conversions of 85-87% were reported whereby the obtained slurry was granulated in a pan- granulator and the obtained granules were dried overnight at 105 °C.

[0012] In providing the desired solid forms of macronutrient sources, a challenge in the art is to combine urea with a sufficiently high amount of further macronutrient sources. The achievable levels are dependent on the specific macronutrient source, but to combine urea with an amount of more than 30% by weight of macronutrient source is generally difficult. During production of a urea compound fertilizer, a macronutrient source and urea typically in some kind of liquid form, are combined.

[0013] Depending on the amount of the macronutrient source, some macronutrient sources will dissolve, while others (especially at high loadings) are still present as particles, as a result of which the combined composition is in the form of a urea-slurry. High loadings of one or more macronutrient sources in a urea compound fertilizer are particularly required in view of a desire to present a combination of fertilizer macronutrients in a single granule. This may be a combination of individual macronutrient sources, or this may comprise a single fertilizer macronutrient source comprising more than one primary and / or secondary macronutrient. In some instances, in a process for the production of a urea compound fertilizer, a wet-milling step can be conducted before subjecting such slurry to granulation. A drawback hereof is that during such wetmilling step a temperature increase of the slurry (e.g. of 5-10 °C) occurs. Particularly for urea this is undesirable, due to the formation of additional biuret, which is an unwanted side-product. As a result, an additional cooling step downstream of the milling equipment is required. This is not desired since it requires the installation of corresponding additional equipment, and the cooling contributes to additional operational expenses.It is therefore desired to provide a process for the production of granules comprising urea and at least one further (fertilizer) macronutrient source, allowing the incorporation of increased amounts of such further macronutrient, without the need for a cooling step after size reduction of the macronutrient source by means of e.g. wet milling.

[0014] Summary of the Invention

[0015] In order to better address one or more of the foregoing desires, the invention provides, in one aspect, a process for the production of urea compound fertilizer granules, the process comprising:

[0016] a. providing an aqueous urea solution comprising urea and more than 5 wt.% of water;

[0017] b. adding to said aqueous urea solution at least one solid fertilizer macronutrient source in an amount suitable to form a slurry comprising solid particles of the macronutrient source;

[0018] c. subjecting the slurry to mechanical treatment, applying a shear force between 10.000 / s and 250.000 / s, to reduce the particle size of the macronutrient source, to produce a treated slurry;

[0019] d. subjecting the treated slurry to a water-removal step, resulting in a concentrated fertilizer liquid having a residual water content of at most 5 wt.%;

[0020] e. subjecting the concentrated fertilizer liquid to granulation by crystallization and obtain urea compound fertilizer granules. In another aspect, the invention presents a urea production plant comprising a urea synthesis and recovery section configured to produce an aqueous urea solution; said urea synthesis and recovery section being in fluid communication with an evaporation section configured to produce aurea melt comprising at most 5 wt.% of water, said evaporation section comprising one or more evaporation units placed in series, said urea plant further comprising, downstream of the urea synthesis and recovery section, a urea outlet in fluid communication with a granulation liquid inlet of a granulation section, said urea outlet being configured to send a urea melt stream to said granulation section, wherein said urea outlet is positioned upstream of at least one of said one or more evaporation units, and wherein a mixing unit is positioned downstream of said urea outlet and a mechanical treatment unit is positioned between said mixing unit and said granulation inlet. An example of an embodiment hereof can e.g. be seen in figure 2, which will be further detailed later in this description.

[0021] In yet another aspect, the invention resides in a method of modifying a pre-existing urea plant, said urea plant comprising a urea synthesis and recovery section configured to produce an aqueous urea solution; said urea synthesis and recovery section being in fluid communication with an evaporation section configured to produce a urea melt comprising at most 5 wt.% of water, said evaporation section comprising one or more evaporation units placed in series, said urea plant further comprising, downstream of the evaporation section, a urea outlet in fluid communication with a granulation section, said urea outlet being configured to send a urea melt comprising at most 5 wt.% of water to said granulation section, the method comprising adding an aqueous urea solution outlet upstream of at least one of said one or more evaporation units, and connecting said aqueous urea solution outlet to a granulation liquid inlet of the granulation section, providing a mixing unit downstream of said urea outlet, and providing a mechanical treatment unit, for example a milling unit, between said mixing unit and said granulation liquid inlet. Preferably the milling unit is a wet-milling unit.

[0022] In a further aspect, the invention resides in a method of modifying a pre-existing urea plant, said urea plant comprising a urea synthesis andrecovery section configured to produce an aqueous urea solution; said urea synthesis and recovery section being in fluid communication with an evaporation section configured to produce a urea melt comprising at most 5 wt.% of water, said evaporation section comprising one more evaporation units placed in series, said urea plant further comprising, downstream of the evaporation section, a urea outlet in fluid communication with a granulation section, said urea outlet being configured to send a urea melt comprising at most 5 wt.% of water to said granulation section, the method comprising adding an aqueous urea solution outlet upstream of at least one of said one or more evaporation units, and connecting said aqueous urea solution outlet to a granulation liquid inlet of the granulation section, providing a mixing unit downstream of said urea outlet, and providing a mechanical treatment unit, such as a milling unit, preferably a wet-milling unit, between said mixing unit and said granulation liquid inlet.

[0023] In another aspect, based on a pre-existing urea plant from which an aqueous urea solution is obtained as a product, the invention provides a method of modifying a pre-existing urea plant, said urea plant comprising a urea synthesis and recovery section configured to produce an aqueous urea solution; said urea synthesis and recovery section being in fluid communication with an evaporation section configured to produce a urea melt comprising at most 5 wt.% of water, said evaporation section comprising one more evaporation units placed in series, said urea plant further comprising a aqueous urea solution outlet positioned downstream of the urea synthesis and recovery section and upstream of at least one of said one or more evaporation units, the method comprising adding a connection from said aqueous urea solution outlet to a mixing unit, providing a mechanical treatment unit, such as a milling unit, preferably a wet-milling unit, downstream of said mixing unit, and providing a connection from an outlet of said mixing unit to a granulation liquid inlet of a granulation unit.Modifications as mentioned for a pre-existing urea plant however can also be directly incorporated into a grass-root plant. The invention accordingly, in yet another aspect, presents a urea production plant comprising a urea synthesis and recovery section configured to produce an aqueous urea solution; said urea synthesis and recovery section being in fluid communication with an evaporation section configured to produce a urea melt comprising at most 5 wt.% of water, said evaporation section comprising one more evaporation units placed in series, said urea plant further comprising, downstream of the urea synthesis and recovery section, a urea outlet in fluid communication with a granulation liquid inlet of a granulation section, said urea outlet being configured to send a urea stream to said granulation section, wherein said urea outlet is positioned upstream of at least one of said one or more evaporation units, and wherein a mixing unit is positioned downstream of said urea outlet and a mechanical treatment unit, such as a milling unit, preferably a wet-milling unit, is positioned between said mixing unit and said granulation liquid inlet.

[0024] In still a further aspect, the invention provides urea compound fertilizer granules comprising urea and at least one other fertilizer macronutrient source in a concentration of 20 wt.% to 50 wt.%, preferably 35 wt.% to 50 wt.% relative to the final urea compound fertilizer, wherein the amount of the other fertilizer macronutrient source is the same throughout the cross section of the granules.

[0025] In yet another aspect, the invention presents a concentrated fertilizer liquid comprising urea, at most 5 wt.% of water, and 20 wt.% to 50 wt.%, preferably 35 wt.% to 50 wt.% of at least one solid fertilizer macronutrient source in the form of particles having a particle size reflected by a d90 of less than 100 pm, preferably between 3 pm and 50 pm.Brief description of the drawings

[0026] Figures FIG. 1 to FIG.4 present process schemes for various embodiments of the invention. FIG.5 and FIG.6 illustrate aspects of an example of a nozzle used with granulation.

[0027] Detailed description of the invention

[0028] The invention, in a general sense, is based on the judicious insight to prepare a fertilizer granulation liquid which contains solid particles starting from an aqueous urea solution, rather than from a urea melt, and to further enable granulation by subsequent mechanical treatment and water-removal steps.

[0029] Urea to be granulated, also when provided together with other fertilizer macronutrient sources, is customarily provided as a urea melt. A urea melt can be formed by literally melting solid urea, but more typically a urea melt to be used for granulation is a highly concentrated aqueous urea solution having a urea concentration of above 95 wt.%. Such urea melt is generally produced in a urea production plant in which an aqueous urea solution is produced that, in a final step preceding the granulation, is subjected to evaporation in an evaporation section.

[0030] The aqueous urea solution applied in the process of the present invention is more dilute than a urea melt. Accordingly, the aqueous urea solution comprises more than 5 wt.% of water. Generally an aqueous urea solution comprises at most 50 wt.% of water, preferably the aqueous urea solution comprises at most 30 wt.% of water. Alternatively, the aqueous urea solution comprises 5 wt.% to 28 wt.% of water, preferably 8 wt.% to 25 wt.% of water, more preferably 10 wt.% to 20 wt.% of water.To said aqueous urea solution, at least one solid fertilizer macronutrient source is added. In the art of crop and plant fertilizers, e.g. as defined in Ullmann’s Agrochemical Vol. 1, Fertilizers, macronutrients are nutrients that comprise primary macronutrients N, P, and K, and secondary macronutrients Ca, Mg, and S.

[0031] Said at least one fertilizer macronutrient source should be in an amount suitable to form a slurry comprising macronutrient particles. In the event that a single solid fertilizer macronutrient source is added, which will particularly be the case in the event that a complex fertilizer source is applied, the required amount will be higher than the maximum solubility of the solid fertilizer macronutrient source in the aqueous urea solution. The skilled person will be able to determine the amount needed in a simple solubility test to determine when the saturation concentration is exceeded. In the event that more than one solid fertilizer macronutrient source is added, the minimum amount of the solids added will be determined, in addition to the minimum amounts specified by regulation (EU Regulation 2019 / 100), by the first of the solid fertilizer macronutrient sources to exceed its saturation concentration and become excluded from dissolving. The maximum amount of total macronutrient sources is determined by the processing behavior, typically the flow behavior of the slurry after mechanical treatment or the melt after the evaporator, which the skilled person will be able to determine for the specific equipment, such as for e.g. granulation, used. Generally the maximum amount of total macronutrient sources, calculated in weight percentage of the total urea compound fertilizer is at most 66.6%, preferably at most 50 wt.%, more preferably at most 45 wt.%, such as at most 41 wt.%. If needed, the solid fertilizer macronutrient sources can be prepared for being dispersed in the aqueous urea solution and forming a slurry, by being crushed prior to use, generally to a d99 below 1 mm. For the macronutrient source as such, i.e. before being used in the process of the invention, the d99 value is determined by sieving.Preferably, the granules of the present invention may also comprise one or more micronutrient sources, in an amount of typically less than in total 10 wt.%, preferably less than 5 wt.%. Micronutrients especially are selected from the group consisting of Fe, Mn, Zn, Cu, B, Mo, and combinations thereof. To this end, in a preferred embodiment also one or more micronutrient sources are added to the aqueous urea solution.

[0032] The process of the present invention presents the skilled person with a large degree of freedom to choose the kind and amount of one or more solid fertilizer macronutrient and optional micronutrient sources. This is beneficial, since the need for the type of macronutrients and the amount thereof, can be subject to variation between crops to be grown, to seasonal variations, to variations in soil, in climate, and to variations depending on any further, separate, fertilizers that are possibly applied.

[0033] Beneficially, the process of the invention allows the incorporation of the desired amounts of primary and secondary fertilizer macronutrients into a single granule with urea. Hereby the fact that the process enables the provision of a single concentrated fertilizer liquid as a feed liquid to granulation, leads to advantages upon application of the granules as a fertilizer.

[0034] Particularly, the process allows obtaining a homogenous composition of each fertilizer granule. This has the advantage that, with the granule gradually decaying in soil, the fertilizer composition available after the generally fast delivery of N (by urea dissolving early in time) will not change. Also, each batch of granules produced, and in each run of a continuous process simply all granule produced, will show no substantial differences between individual granules. This secures that, upon regular homogenous distribution of the granules over a field, the amount of fertilizer macronutrients will be the same across the field. A further advantage of having all required macronutrients in a single granule gives less handling for the farmer, as compared to blending different fertilizers (and runningthe risk of granule segregation) or applying the different fertilizers in different runs.

[0035] In addition to the delivery of nitrogen (N) in the form or urea, the sohd fertilizer macronutrient source may or may not also contain N. Next to an amount of at least 5 wt.% of total nitrogen, in the process of the invention at least one of macronutrient source is provided with an amount of

[0036] a. P, expressed as P2O5, of between 0 wt.% and 30 wt.%, preferably between 0 wt.% and 20 wt.%, preferably at least 2 wt.%, more preferably at least 3 wt.%; and / or

[0037] b. K, expressed as K2O, of between 0 wt.% and 35 wt.%, preferably between 2 wt.% and 20 wt.%, more preferably at least 3 wt.%; and / or

[0038] c. S, expressed as SO3, of between 0 wt.% and 35 wt.%, preferably between 1 wt.% and 25 wt.%, more preferably at least 1.5 wt.%; and / or

[0039] d. Ca, expressed as CaO, of between 0 wt.% and 20 wt.%, preferably between 1 wt.% and 20 wt.%, more preferably at least 1.5 wt.%; and / or

[0040] e. Mg, expressed as MgO, of between 0 wt.% and 20 wt.%, preferably between 1 wt.% and 10 wt.%, more preferably at least 1.5 wt.%.

[0041] Suitable solid fertilizer macronutrient sources include KC1; K2SO4; KNO3; K2SO4.2MgSO4; Ca(NO3)2; CaSO4; CaCO3; CaMg(CO3)2; Ca3(PO4)2; Ca(H2PO4)2; Ca(H2PO4)2 + CaSO4; NH4H2PO4; (NH4)2HPO4; Ca3(PO4)2;

[0042] (NH4)2SO4; K2SO4; MgSO4; MgO; MgSO4(Kieserite); K2SO4MgSO4-2CaSO4(Polyhalite); MgNH4PO4. In this overview, references to the salts as such is given; crystal water - if present - is not referred to.

[0043] In a preferred embodiment, the at least one solid fertilizer macronutrient source is a mineral providing a combination of nutrients in a single compound, such as e.g. CaSO4, Cas(PO4)2, K2SO4, and minerals suchas Polyhalite, Kieserite, Dittmarite, or Struvite, preferably an evaporite mineral such as Polyhalite. More preferably, such mineral is the sole solid macronutrient source added.

[0044] The solid fertilizer macronutrient source that is to be supplied to the process of the invention preferably has a particle size of between 0.1 mm and 2.5 mm, more preferably between 0.25 mm and 1.5 mm, most preferable between 0.5 and 1.0 mm.

[0045] In order to convert the slurry as obtained into a suitable granulation liquid, the process of the invention comprises, as a subsequent step, a mechanical treatment of the slurry. Mechanically treating a slurry comprising especially solid particles, will result in reducing the size of said particles. Such size reduction will generally comprise at least a reduction of the size of solid particles and of aggregate particles, preferably such as to decompose or reduce the size of such particles and / or aggregates into their constituent particles. Preferably, the mechanical treatment will be a milling process, resulting in reduction in size also of primary (solid) particles through mechanical shear forces. To this end the mechanical treatment preferably comprise wet-milling. This wet-milling can be conducted in one or more milling steps, preferably involving at least one step of high-shear wet milling. The number of milling or mechanical treatment steps required to achieve the targeted value of less than 200 pm and preferably less than 100 pm depends on e.g. the start dimensions or the hardness of a solid fertilizer macronutrient source. As a preferred two-step process, wet-milling can be conducted by applying a first wet milling step followed by a subsequent second wet-milling step. Preferably, in a first step the slurry is pre-milled to an initially reduced size, e.g., d90 less than 500 pm, preferably less than 250 pm, and in a second step (or alternatively in a last step of a multi-step process) to the desired finally reduced size, generally less than a d90 of less than 200 pm, preferably less than 100 pm, more preferably less than 50 pm.Preferably, said first step is conducted in a high-shear wet mill, and the second step in a colloid cone wet mill.

[0046] The preferred maximum particle size in the treated slurry is characterized by a d90 below 100 pm, as determined by laser diffraction, such as by means of a Malvern Mastersizer 3000. Preferred particle sizes are reflected by a d90 of between 1 pm and 100 pm, more preferably between 3 pm and 50 pm.

[0047] In a preferred embodiment, the process comprises adding the at least one solid fertilizer macronutrient source by dispersing particles of said macronutrient source homogeneously into the aqueous urea solution, while at the same time reducing the size of the particles. This is preferably done by means of a high shear in-line disperser. Such a disperser is of special advantage if the particles are not easy mixed with the aqueous urea solution. An additional advantage of a high shear in-line disperser is that agglomerates, if present, may be broken up and then individual particles can be homogeneously distributed in the aqueous urea solution.

[0048] Subsequently, the process comprises subjecting the resulting slurry to mechanical treatment, preferably wet milling.

[0049] The mechanical treatment in the process of the invention can be performed by, for example a milling unit, which is positioned between said mixing unit and said granulation liquid inlet. The mechanical treatment unit exerts mechanical forces on the solid fertilizer macronutrient source aiming to physically break down solid particles, hence, to reduce particle size. Such mechanical forces may be generated by high shear mixers and / or rotor-stator mixers including colloid mills. Preferably the mechanical treatment is performed by a rotor-stator mechanical unit. This unit consists of 2 elements being a rotor, i.e. a rotating element that spins at high speed, and a stator, i.e. a stationary element adjacent to the rotor. Upon spinning, the rotor forces material through a narrow gap between rotor and stator, whereby the mechanical action in the form of shear forces physically breakdown particles to reduce particle size and consequently acts as a milling unit. Preferably the milling unit is a wet-milling unit.

[0050] The shear forces in a rotor stator unit are determined by the velocity gradient between rotor and stator, the gap between rotor and stator as well as the viscosity of the liquid / slurry. For a chosen liquid or slurry composition, the viscosity is a given and shear rates can be estimated by dividing the velocity of the rotor (rpm) by the gap distance between rotor and stator. For the present invention, the shear rate is between 10.000 / s and 250.000 / s, preferably between 20.000 / s and 200.000 / s, more preferably between 30.000 / s and 150.000 / s. Higher shear rates create too much friction resulting in undesirable heating of the liquid / slurry causing increased biuret levels or plugging of milling equipment. Lower shear rates create insufficient size reduction of the solid fertilizer macronutrient source particles which result in increased level of parasitic seeding and / or fines (in the off-gas) at the exit of the granulator during fluid bed granulation. Such would create many undersize granules with as consequence a need for higher recycle of undersize granules back to the inlet of the granulator. Final granules leaving a plant may typically be sieved or screened to obtain an end product with dimensions of between 2 and 4 mm.

[0051] Preferred equipment hereby used comprises, in series from upstream to downstream: a high shear in-line disperser, a high shear wet mill and a cone mill. Typically, the particles being dispersed, and before being subjected to particle size reduction, have a particle size below 2,5 mm, preferably below 1 mm and a d90 higher than 500 pm, and preferably a dlO higher than 50 pm.

[0052] In the event of a single wet milling step, the preferred equipment is a high shear rotor stator system, able to achieve a particle size below 200 pm, preferably below 100 pm.

[0053] Alternatives include replacing the in-line disperser by a dissolver disc and either or both wet mills can be replaced by, for example, a ball mill.The choice to start with an aqueous solution which is not as concentrated as a urea melt, provides for synergism with the mechanical treatment step. For melt processing special milling equipment would be needed, including special seals; and measures to prevent crystallization of the melt. For the present process, standard equipment can be used and no special measures required to prevent crystallization. Further, mechanical treatment, particularly wet-milling generally causes a temperature increase between 5-10 °C in the liquid subjected to milling. The application of an aqueous urea solution enables operating at a lower temperature, such as below 100°C, preferably below 85 °C and preferably at least 55 C, preferably at least 60 °C, more preferably 70-80 °C which as such reduces the possible otherwise undesirable effects of a temperature increase of a urea melt, notably the formation of the unwanted by-product biuret. This, at the same time, results in the possibility of dispensing with an additional cooling stage downstream of the milling equipment, which would otherwise, i.e., in the event of a urea melt be necessary to avoid additional biuret formation, and reduce the temperature to the desired temperature at the granulator inlet.

[0054] In order to complete the conversion of the slurry into a suitable granulation liquid, the treated slurry is subjected to concentrating by removing water. This water-removal step typically comprises evaporation, with or without pressure reduction. Concentrating the treated slurry is preferably conducted by evaporating water at a temperature between 80°C and 140 °C, at an absolute pressure between 0.05 bar and 0.95 bar, preferably 0.1 bar to 0.5 bar. The treated slurry is concentrated to a residual water content of between 1 wt.% and 5 wt.%. This results in a concentrated fertilizer liquid which is suitable to be supplied as a feed liquid to a fluid bed granulator.

[0055] The choice according to the invention for first preparing an aqueous urea solution also has an advantage related to the utilization of heat in the process. By virtue of the presence of an amount of more than 5%of water, the temperature increase that occurs upon mechanical treatment, notably upon wet milling, does not result in a temperature requiring cooling. Accordingly, the heat added as a result of said mechanical treatment remains available in the process. This results in a synergistic advantage with the water-removal step, as this results in a lower amount of heat that needs to be added to accomplish evaporation.

[0056] In a final step the process comprises subjecting the concentrated fertilizer liquid to granulation to obtain urea compound fertilizer granules. Optionally, at the entry of the granulator or at a preceding step, a granulation agent may be added. In preparing urea granules, notably in fluidized bed granulation, which normally involves fluidization air, the formation of urea dust can be a hampering factor. In order to keep the formation of urea dust manageable, one or more granulation aids can be added, for which typically formaldehyde is used.

[0057] A further advantage of the processing conditions in a process applying an aqueous solution rather than a urea melt, is that high shear equipment can be run under milder / lower temperature conditions therewith dispensing with the requirements for special high temperature resistant mechanical seals including diamond-coated seals and specialized crystallization prevention measures, such as high temperature and pressure flushing. The granulation step generally refers to a step of granulation by crystallization. The term “granulation” as used herein refers to granulation in a broad sense, and includes not only fluid bed granulation, but also prilling, pastillation and extrusion. The requirement that the granulation comprises solidification by crystallization refers to particle growth by allowing a granulation liquid (including a prilling liquid, a pastillation liquid, or an extrusion liquid) to crystallize from said liquid. In the event of prilling this is by first forming an finely distributed droplets of said liquid, and especially cooling droplets by natural draft or forced draft air, typically in a prilling tower. In the event of pastillation, typically conducted in arotoformer device, product droplets of a granulation liquid are deposited onto a moving belt, the drops are cooled on the belt and allowed to solidify by crystallization into pastilles. In the event of extrusion, the granulation liquid is forced under pressure through a die, after which the exiting liquid is solidified, typically by cooling, and shaped, typically by cutting the solidified extrudate. The granulation liquid needs to have a high enough viscosity for it to be extruded. The level of viscosity can be determined by the person skilled in extrusion, where variables are for example temperature and amount of solids. In the event of fluidized or spouted bed granulation, the granulation liquid is applied to preexisting granules in a layering process. Solidification takes place by crystallization of layers in the layering process. Such granulation is different from granulation processes involving agglomeration of small particles into a granule with the aid of a binder. In the granules of the process of the invention, a binder is not included. The aforementioned solidification techniques are well known and do not require elucidation to the skilled person. Preferably, the granulation is fluidized bed granulation.

[0058] In fluidized bed granulation, the concentrated fertilizer liquid is sprayed on seed granules that grow in size as the process continues. A fluidized bed granulator typically comprises an inlet for seed particles, an outlet for granule products, a perforated bottom plate for distributing fluidizing air, and a gas outlet. A preferred granulator further comprises a plurality of compartments configured in series between said inlet for seed particles and outlet for granule products. Each compartment contains at least one or a plurality of nozzles for feeding a concentrated aqueous urea solution, in the form of a urea melt, i.e. having at most 5 wt.% of water, preferably at most 1.5 wt.% of water, as a granulation liquid. Different types of nozzles can be employed, such as atomization nozzles (generating droplets) and film spray nozzles (also known as film-forming nozzles), the latter serving to feed the granulation liquid to the fluidized bed in the formof a film. Preferred are film spraying nozzles of conical shape. The granulator is configured to move the particles from the inlet to the outlet whereby the particle size increases from the inlet to the outlet.

[0059] In the fluid bed granulation process, the process benefits from film spray nozzles that are modified for handling slurries as it proved that regular nozzles, such as disclosed in WO2024049293A1 which is hereby incorporated in its entirety, give rise to processing and stability issues. The nozzle (3), FIG. IB of WO2024049293A1 (corresponding to FIG.5 of this application), is modified to handle slurries comprises a first channel (4) for granulation liquid (a) and a secondary gas channel (5) for the secondary gas (b) that is provided as an annulus (ring) around the first channel. The channels have an exit at the top side directly exposed to the fluidized bed of particles. The exit of the first channel is e.g. vertically above the exit of the secondary gas channel.

[0060] The nozzle (3) preferably comprises a unitary piece (3a). The piece (3a) has a channel for granulation liquid, i.e. the first channel (4), and has a tapered shoulder (7) and provides the convex inner wall (5a) of the annular channel (5) for secondary gas. A further piece (12) provides the concave inner wall (5b) of the annular channel (5) and is e.g. cylindrical. The exit of the first channel (4) is also referred to as bore hole, is defined by its diameter and its length (bore hole length). The ratio of the 2 is also referred to as L / D of the bore hole.

[0061] The nozzle (3) (in particular the piece (3a)) has a sloped shoulder (7) that guides the secondary gas (b) from the secondary gas channel (5) to a hollow conical film (f) exiting from the nozzle as mentioned below. The lower end (8) of the shoulder (7), is, for example and as illustrated in FIG.2A of WO2024049293A1 (corresponding to FIG.6A of this application), directly adjacent to the secondary gas channel (5). The secondary gas contacts the conical film at a height h (impact height) that is, for instance, in the range of5 mm to 15 mm above the exit of the nozzle for the conical film, preferably at a height in the range of 7.0 mm to 12 mm.

[0062] The nozzle enables the formation of a film of a granulation liquid in a form of a hollow conical frustum (i.e. conical film) projecting into a granulation compartment by supplying the granulation liquid through a first channel of a granulation nozzle. In a granulation process, the granulation liquid is ejected from the first channel as a film of the granulation liquid, which film has the shape of a hollow conical frustum. The secondary gas typically has a relatively high velocity of e.g. at least 200 or at least 250 m / s, for instance 200 to 350 m / s at the exit of the secondary gas channel. This velocity refers to the velocity of the secondary gas in the secondary gas channel at the exit of that channel. In embodiments, the mass ratio of the secondary gas flow to the granulation liquid flow is at least 0.40 and preferably in the range 0.40 - 1.0.

[0063] FIG.2B of WO2024049293A1 (corresponding to FIG.6B of this application) indicates a horizontal cross-section of the film of granulation liquid (a) through BB, showing that the film is in the shape of a conical frustum (f) that is hollow. A typical film thickness at the impact height for the present invention is calculated to be about 200 pm.

[0064] The nozzle is accordingly suitably a hollow cone nozzle. The granulation nozzle is provided at the bottom of a granulation compartment, and the nozzle is arranged with the exit in upward direction. The granulation liquid exits the nozzle in the upward direction. Preferably, the conical film is formed by giving the liquid material a rotational movement, in particular in the first channel; with rotation in the horizontal cross section or in the horizontal plane, i.e. about a vertical axis. For example a nozzle provided with a rotation chamber is used (also referred to as swirl chamber). A rotation chamber (swirl chamber) is for example a cylindrical chamber upstream of the granulation liquid exit having tangential inlet openings, e.g. provided as slits, in the cylindrical wall of the chamber forgranulation liquid; the chamber is at the top connected, in particular directly connected, to the outlet for granulation liquid. The outlet channel typically has a smaller diameter than the rotation chamber. In this arrangement, the liquid is under hydrostatic pressure pressed through one or more channels leading into the rotation chamber tangentially. The material, i.e. granulation liquid, moves in the form of a liquid film along the wall of the outlet channel (first channel) and has a horizontal velocity component there, i.e. in the outlet channel, resulting from the rotation, and a vertical velocity component depending on throughput. Hence, the process involves preferably supplying the granulation liquid as a rotating film through the first channel, with rotation in the horizontal cross-section. The nozzle has at least 2 swirl channels, preferably at least 4 swirl channels to provide a more symmetrical frustrum. Swirl channel diameter is at least 1.5 mm, preferably at least 1.6 and preferably at least 1.8 mm.

[0065] The film preferably has a thickness of at least, 300 pm, or at least 400 pm, more preferably at least 450 pm at the exit of the first channel, and the thickness is e.g. less than 600 pm. Suitably, the granulation nozzle is of the type giving a film with a thickness of at least 400 pm, e.g. in the range of 400 pm to 600 pm. The film thickness at the impact height, h, is between 150 and 450 pm; preferably 175-375 pm, and more preferably 200-300 pm.

[0066] In the granulation step, generally a desired granule size range will be set. Produced solids that are below this size range, i.e., fines, will preferably be recycled to the granulator, preferably a fluid bed granulator, and will then be used as seeds for further granulation. Produced granules that exceed said size range, i.e., coarse, will be subjected to crushing, preferably to a size corresponding to that of the fines. The crushed coarse will then also be recycled to the fluid bed granulator, and will also be used as seeds.

[0067] In the process of the invention, the applied urea can be synthesized by any suitable method. A frequently used process for the preparation ofurea according to a stripping process is the carbon dioxide stripping process as for example described in Ullmann's Encyclopedia of Industrial Chemistry, Vol. A27, 1996, pp 333-350. In this process, the synthesis section is followed by one or more recovery sections. The synthesis section comprises a reactor, a stripper, a condenser and a scrubber in which the operating pressure is in between 12 and 18 MPa and preferably in between 13 and 16 MPa. In the synthesis section the urea solution leaving the urea reactor is fed to a stripper in which a large amount of non-converted ammonia and carbon dioxide is separated from the aqueous urea solution. Such a stripper can be a shell and tube heat exchanger in which the urea solution is fed to the top part at the tube side and a carbon dioxide feed to the synthesis is added to the bottom part of the stripper. At the shell side, steam is added to heat the solution. The urea solution leaves the heat exchanger at the bottom part, while the vapor phase leaves the stripper at the top part. The vapor leaving said stripper contains ammonia, carbon dioxide and a small amount of water. Said vapor is condensed in a falling film type heat exchanger or a submerged type of condenser that can be a horizontal type or a vertical type. A horizontal type submerged heat exchanger is describedin Ullmann's Encyclopedia of Industrial Chemistry, Vol. A27, 1996, pp 333-350. The heat released by the exothermic carbamate condensation reaction in said condenser is usually used to produce steam that is used in a downstream urea processing section, generally indicated as being an evaporation section, for heating and concentrating the urea solution. Since a certain liquid residence time is created in a submerged type condenser, a part of the urea reaction takes already place in said condenser. The formed solution, containing condensed ammonia, carbon dioxide, water and urea together with the non-condensed ammonia, carbon dioxide and inert vapor is sent to the reactor. In the reactor the above mentioned reaction from carbamate to urea approaches the equilibrium. The ammonia to carbon dioxide molar ratio in the urea solution leaving thereactor is generally in between 2.5 and 4 mol / mol. It is also possible that the condenser and the reactor are combined in one piece of equipment. An example of this piece of equipment as described in Ullmann's Encyclopedia of Industrial Chemistry, Vol. A27, 1996, pp 333-350. The formed urea solution leaving the urea reactor is supplied to the stripper and the inert vapor containing non-condensed ammonia and carbon dioxide is sent to a scrubbing section operating at a similar pressure as the reactor. In that scrubbing section the ammonia and carbon dioxide is scrubbed from the inert vapor. The formed carbamate solution from the downstream recovery system is used as absorbent in that scrubbing section. The urea solution leaving the stripper in this synthesis section requires a urea concentration of at least 45 % by weight and preferably at least 50 % by weight to be treated in one single recovery system downstream the stripper. The recovery section comprises a heater, a liquid / gas separator and a condenser. The pressure in this recovery section is between 200 to 600 kPa. In the heater of the recovery section the bulk of ammonia and carbon dioxide is separated from the urea and water phase by heating the urea solution. Usually steam is used as heating agent. The urea and water phase, contains a small amount of dissolved ammonia and carbon dioxide that leaves the recovery section and is sent to a downstream urea processing section where the urea solution is concentrated by evaporating the water from said solution.

[0068] The present process is not limited to any particular urea production process. Other processes and plants include those that are based on technology such as total recycle plants, the HEC process developed by Urea Casale, the ACES process developed by Toyo Engineering Corporation and the process developed by Snamprogetti. All of these processes, and others, may be used in the method of the invention.

[0069] Preferably, the urea solution is produced in such a way as to have a low biuret content. Reference is made to processes as disclosed in WO2023 / 158314 or WO 2019 / 093891. This is preferably accomplished by injection of NH3 in the produced urea melt, as disclosed in WO 2017 / 192031.

[0070] The process of the invention can be conducted in equipment separate from the urea production plant. Frequently, urea production plants are provided with a granulation section. In the context of the present disclosure, such granulation section can be in the form of a separate granulation unit having a connection from the urea plant, or it can be considered a single urea granulation plant comprising a granulation section within battery limits of the urea plant.

[0071] Relating to either case, the invention also pertains to a plant as such, which can be a grassroots plant or a modified pre-existing plant. This refers to a urea production plant comprising a urea synthesis and recovery section configured to produce an aqueous urea solution; said urea synthesis and recovery section being in fluid communication with an evaporation section configured to produce a urea melt comprising at most 5 wt.% of water, said evaporation section comprising one more evaporation units placed in series, said urea plant further comprising, downstream of the urea synthesis and recovery section, a urea outlet in fluid communication with a granulation liquid inlet of a granulation section, said urea outlet being configured to send a urea stream to said granulation section, wherein said urea outlet is positioned upstream of at least one of said one or more evaporation units, and wherein a mixing unit is positioned downstream of said urea outlet and a milling unit is positioned between said mixing unit and said granulation liquid inlet. The milling, or mechanical treatment unit is preferably positioned upstream of the evaporator.

[0072] The mixing unit will generally have at least one inlet configured for feeding at least one solid fertilizer macronutrient source. The mixing unit will generally comprise equipment suitable to mix a aqueous urea solution with at least one solid fertilizer macronutrient source.The milling unit generally is a wet-milling unit and possibly comprises more than one wet mill in series. Preferably, the milling unit comprises a high-shear wet mill at an upstream side, i.e. configured to received mixed slurry from the mixing section. It then preferably comprises a colloid-cone wet mill at a downstream side, i.e., configured to received milled slurry from the high-shear wet mill, and having an outlet for colloidcone milled slurry in fluid connection with the granulation liquid inlet.

[0073] In some embodiments, pre-existing urea plants are designed to produce aqueous urea solutions as a product. This particularly pertains to Diesel Exhaust Fluid (DEF, e.g. known as AdBlue). Such plants already have a product outlet for aqueous urea solution. These plants may be modified to also have a granulation section. Possible products of such a plant are then either aqueous urea solution, obtained from a position upstream of an evaporation section or from within an evaporation section comprising more than one evaporator in series. These plants also can be dedicated DEF plants, in which case no granulation section it present.

[0074] According to the present invention, modification methods are provided for either case.

[0075] Thus, in one aspect, the invention resides in a method of modifying a pre-existing urea plant, said urea plant comprising a urea synthesis and recovery section configured to produce an aqueous urea solution; said urea synthesis and recovery section being in fluid communication with an evaporation section configured to produce a urea melt comprising at most 5 wt.% of water, said evaporation section comprising one more evaporation units placed in series, said urea plant further comprising, downstream of the evaporation section, a urea outlet in fluid communication with a granulation section, said urea outlet being configured to send a urea melt comprising at most 5 wt.% of water to said granulation section, the method comprising adding an aqueous urea solution outlet upstream of at least one of said one or more evaporation units, and connecting said aqueous ureasolution outlet to a granulation liquid inlet of the granulation section, providing a mixing unit downstream of said urea outlet, and providing a milling unit between said mixing unit and said granulation liquid inlet.

[0076] In another aspect of modifying pre-existing plants, the invention presents a method of modifying a pre-existing urea plant, said urea plant comprising a urea synthesis and recovery section configured to produce an aqueous urea solution; said urea synthesis and recovery section being in fluid communication with an evaporation section configured to produce a urea melt comprising at most 5 wt.% of water, said evaporation section comprising one more evaporation units placed in series, said urea plant further comprising an aqueous urea solution outlet positioned downstream of the urea synthesis and recovery section and upstream of at least one of said one or more evaporation units, the method comprising adding a connection from said aqueous urea solution outlet to a mixing unit, providing a milling unit downstream of said mixing unit, and providing a connection from an outlet of said mixing unit to a granulation liquid inlet of a granulation unit. The milling, or mechanical treatment unit is preferably positioned upstream of the evaporator.

[0077] In still a further aspect, the invention provides urea compound fertilizer granules comprising urea, and at least one other fertilizer macronutrient source in an amount of 20 wt.% to 50 wt.%, preferably 35 wt.% to 50 wt.% of the total and at least one macronutrient source comprising P, K, S, Ca and / or Mg, specified in an amount of at least 0.1 wt.% and at most 35 wt.%, of P2O5, K2O, SO3, CaO andMgO respectively, wherein the amount or concentration of the other fertilizer macronutrient source is substantially the same throughout the cross section of the granules. The latter is beneficial, and enabled by virtue of the process of the invention. A pre-existing process of adding certain amounts of a macronutrient source to urea, is that of WO 2017 / 007315. The granulestherein have differing compositions in their core as opposed to one or more outer layers.

[0078] The invention also extends to a concentrated fertilizer liquid as resulting from the process substantially described hereinbefore. This liquid comprises urea, at most 5 wt.% of water, and 20 wt.% to 50 wt.%, preferably 35 wt.% to 50 wt.% of at least one solid fertilizer macronutrient source in the form of particles having a particle size reflected by a d90 of less than 100 pm, preferably between 3 pm and 50 pm. It will be understood that the liquid, prior to solidification, is kept at conditions of pressure and temperature at which a urea melt is liquid.

[0079] In sum, the invention as disclosed is a process for the production of urea compound fertilizer granules. Herein an aqueous urea solution comprising urea and more than 5 wt.% of water is provided. To this solution at least one solid fertilizer macronutrient source is added in an amount suitable to form a slurry comprising solid particles of the macronutrient source. The slurry is subjected to mechanical treatment so as to produce a treated slurry having particles of reduced size. From the treated slurry water is removed so as to form a concentrated fertilizer liquid having a residual water content of at most 5 wt.%, which liquid is then subjected to granulation by crystallization.

[0080] In an alternative fashion, the process of the invention may also be applied for the manufacture and granulation of ammonium nitrate based compound fertilizers, whereby an aqueous ammonium nitrate solution is applied instead of an aqueous urea solution. In this alternative fashion, ammonium nitrate slurries are processed in a comparable manner as the mentioned aqueous urea solution. Processing temperature, due to a different melting temperature of ammonium nitrate, will preferably be between 80 and 180 °C, whereby slurry granulation of an ammonium nitrate melt will take place at a temperature of 170-175 °C. Concentration of ammoniumnitrate in the aqueous solution will be comparable to the concentration of urea and comparable nozzles may be used in the slurry granulation.

[0081] The invention will hereinafter be illustrated with reference to the following non-limiting drawings. Figures 1 to 7 illustrate, with reference to the process schemes as depicted, various embodiments of the process and equipment of the invention.

[0082] FIG.l presents the process steps of the invention in general. The scheme reflects a system comprising, in downstream order and in fluid connection in series, a mixing section (101), a mechanical treatment section (102), an evaporation section (103), and a granulation section (104). The process as presented comprises feeding a aqueous urea solution (a) and at least one solid macronutrient source (b) to the mixing section in order to form a slurry (c). Next it comprises feeding said slurry (c) to the mechanical treatment section (102) in order to form a treated slurry (d), and sending the treated slurry (d) to the evaporation section (103). In the evaporation section (103) water-removal takes place, resulting in a side stream of water (e), and a product stream (f) in the form of a concentrated fertilizer liquid. Finally, the process comprises sending the concentrated fertilizer liquid (f) to the granulation section (104), under formation of solid fertilizer granules (g) and, in the event of a fluidized bed granulation section, off-gas (h).

[0083] FIG.2 presents the general process and equipment as shown in Figure 1, with the addition of a urea synthesis and recovery section (5) from which the aqueous urea solution (a) is obtained that is fed to the mixing section (1).

[0084] FIG.3 presents an integrated system for producing urea granules and urea compound fertilizer granules. The system comprises a combination of the general process and equipment of the invention, as shown in FIG.2, with the urea granulation plant comprising a urea synthesis and recovery section (5) having, downstream thereof and in fluid communication therewith, a urea granules evaporation section (6), which urea granulesevaporation section (6) has an outlet for urea melt (i) connected with an inlet of the granulation section (4), and an outlet for water (e) from evaporation. The process and equipment serving to conduct the process for producing urea compound fertilizer granules of the invention, as integrated with the urea granulation plant. Accordingly, the urea synthesis and recovery section (5) has an outlet for an aqueous urea solution (a) which is in fluid communication with an inlet of the mixing section (1). In the set-up as schematically shown, both the urea production evaporation section (6), from which liquid urea (i) is obtained, and the evaporation section (3) from which a concentrated fertilizer liquid (f) is obtained, are connected with the granulation section (4). The integrated system as shown, advantageously allows a switchable controlling of the amounts of the aqueous urea solution (a) that are sent to either or both of the mixing section (1) and the urea granules evaporation section (6). Also, the system advantageously allows a switchable controlling of the feed liquid (f, i) to the granulation section, viz. from either or both of the evaporation sections (3, 6).

[0085] FIG.4 presents the general process and equipment of the invention, as shown in FIG.2, in an embodiment comprising a granulation off-gas scrubbing section (7) with scrubbing liquid recycle. The off-gas (h) from fluidized bed granulation comprises used fluidization air, which is generally laden with fertilizer dust originating from the concentrated fertilizer liquid, i.e. comprising urea and one or more of the fertilizer macronutrient source(s) added in the process. By subjecting the off-gas (h) to dust scrubbing, the fertilizer dust is recovered, and can be recirculated (j) to the process, upstream of the evaporation section (3). In the set-up as shown, an off-gas dust scrubbing section (7), downstream of the granulation section (4) and having a gas inlet for off-gas (h) in fluid communication with an outlet for off-gas from the granulation section (4), is integrated with the process for producing urea compound fertilizer granules of the invention. Dust scrubbing in urea granulation plants is usually done using acirculating urea solution as a washing agent. On top of this also fresh water scrubbing usually is applied. In the dust scrubbing section a effluent flow (j) of urea solution is obtained. This effluent flow usually has a concentration of 10 wt.% to 60 wt.% of urea. In order to reprocess the urea present in this effluent flow, the effluent flow is sent to an evaporation section, where it is further concentrated into a urea melt and then recycled to a granulation section. Cleaned air (k) is vented from the dust scrubbing into the atmosphere. In the integrated system shown in Figure 4, water (e) from the evaporation section (3) is sent to the scrubbing section (7) as a scrubbing liquid, and an effluent flow (j) comprising urea and macronutrient source(s) removed by scrubbing the off-gas from the granulation section, is sent upstream of the evaporation section, thus allowing recovered urea and macronutrient source(s) to become included in the concentrated fertilizer liquid. In the figure an option is included to send the scrubber effluent flow (j) to a (not shown) external section for further processing. Preferably the system allows switching the direction of the urea and macronutrient source(s) effluent from the scrubber (7) to either or both of the evaporation section (3) and said external section. FIG.4 illustrates an advantage of the involvement of an aqueous urea solution in the process of the invention. Since this further involves a water-removal step, the latter step can be combined with recycling scrubber liquid. The combined stream benefits from the economies of scale for heat transfer and water removal.

[0086] FIG.5, as descried above with reference to WO2024049293A1, illustrates a cross section of an example of the nozzle according to the invention, indicating the first channel and secondary gas channel.

[0087] FIG.6A schematically illustrates that the hollow conical frustum (f) of the film of granulation liquid (a) has a smaller radius rl at the nozzle and a larger radius r2 at a height h in an upward direction above the nozzle (3) and the process involves contacting the film with a secondary gas stream (b) at height h (the impact height). The conical frustum has a vertexangle (0). The nozzle (3) (in particular the piece (3a)) has a sloped shoulder (7) that guides the secondary gas (b) from the secondary gas channel (5) to the hollow conical film (f). The lower end (8) of the shoulder (7) is, for example and as illustrated, directly adjacent to the secondary gas channel (5). FIG.6B indicates a horizontal cross-section of the film of granulation liquid (a) through B-B, showing that the film is in the shape of a conical frustum (f) that is hollow.

[0088] Handling slurries in fluid bed granulation require additional considerations for optimal granulation efficiency, especially since physical parameters such as viscosity, density and surface tension of a slurry differs from straight urea, or ammonium nitrate. Such differences will influence the hydrodynamic / flow behavior. Fluid bed granulation initially was conducted according to the process as disclosed in WO2024049293A1 which, as also indicated above, is hereby incorporated by reference in its entirety. In trials processing a slurry comprising urea according to WO2024049293A1, undersized product, and high entrainment resultingin high recycle ratios were noted, which are obviously undesired. Modifications on nozzle and process design were experimented as can be seen from the Comparative Experiments and the Examples discussed below.

[0089] As a result, the invention also pertains to a fluidized bed granulation process comprising growth of particles in a fluidized bed granulator by causing a granulation hquid, to solidify on the particles. Said granulation hquid comprises a slurry of urea at a temperature of 140-145 °C and a solid fertilizer macronutrient source whereby the slurry has a density between 1250 and 2000kg / m3, preferably 1275-1750 kg / m3more preferably 1300-1600 kg / m3. The process comprises:

[0090] (a) providing a fluidized bed of the particles in a granulation compartment of the fluidized bed granulator;

[0091] (b) forming a film of the granulation hquid in the form of a hollow conical frustum projecting into the granulation compartment by supplyingthe granulation liquid through a first channel of a granulation nozzle wherein the bore hole of the first channel has a diameter of at least 4.5 mm at the exit, preferably at least 5mm, where the exit of the bore hole is effectively cylindrical; this particularly without the presence of a diffusor; preferably a rotational movement is created through a rotation chamber comprising at least 2 swirl channels, preferably 4 swirl channels, having a radius of at least 1.8 mm, and normalized to a throughput of 500kg / hr of 30 wt.%;

[0092] (c) supplying secondary gas stream through a secondary gas channel of the granulation nozzle into the granulation compartment, wherein the secondary gas channel is provided as an annulus around the first channel, wherein the exit of the secondary gas channel is directly exposed to the fluidized bed in the granulation compartment, wherein particles from the fluidized bed are entrained in said secondary gas stream;

[0093] (d) supplying entrained particles to said film by directing the secondary gas stream towards the film, causing the deposition of the granulation liquid on the surface of the particles and solidification of said deposited liquid resulting in growth of the particles.

[0094] The foregoing settings represent a judicious choice with a view to the fact that the process is essentially capable of handling solids. Particularly, this is believed to be provided by the combination of geometrical factors that lead to the formation of a hollow conical frustum of granulation liquid having a desired thin film thickness.

[0095] In the foregoing granulation process, preferably, the viscosity of the slurry of urea and a solid fertilizer macronutrients source is between 2.5 and lOOmPa.s; more preferably this is between 5 and 50 mPa.s, typically at a processing temperature of 140-145 °C. Preferably, the L / D ratio (length to diameter ratio) at the exit of the first channel of the granulation nozzle is between about 0.8- 1.2, more preferably between 0.9 and about 1.1.Without wishing bound by theory, the inventors believe that L / D settings are herewith optimized on the basis of the following considerations. D is increased to increase mass flow. At a relative fixed D, L is normally used to modify the spraying angle. Under increased viscosity conditions, however, a clear absence of the air column, air core, inside the nozzle was observed, which is normally featured in a hollowed cone nozzles profile. The lack of air column development has a direct impact on high velocities reachedinside the nozzle, in a “pool” of liquid, that, otherwise, under the standard properties of a pure urea melt this region is instead filled with air. This is believed to cause the presence of a zone of under-pressure at point of maximum velocity. Regions of liquid negative pressure are prone to cavitation. A poorly streamlined geometry can easily lead to cavitation, when a re-circulation area exists with low pressure and high velocity, even in a system with globally high pressure and relatively low velocities Larger outlet bore hole lengths have been found beneficial in the event of viscosities higher than pure urea, >2.9 mm. It is believed that an increase in the hydraulic entry length caused by the larger bore hole promotes the streamlining of the fluid and reducing the cavitation. Setting a maximum to the length L, such as 8.5mm, is beneficial in view of the developed friction. It has been observed that film is being compressed in the flow direction as a cause of the increased friction.

[0096] Preferably, in the aforementioned fluidized bed granulation process, the film thickness at the impact height h of 7 mm is between 150 and 450 pm; preferably 175-375 pm, more preferably 200-300 pm. As a further process preference, the secondary gas stream has a velocity at the exit of the secondary gas channel of at least 200 m / s, preferably at least 250 m / s. In a preferred embodiment of said fluidized bed granulation process, wherein the secondary gas is air and the mass ratio of the secondary gas flow to the granulation liquid flow is in a range of from 0.40 to 1.0. As yet another preference, the conical film is formed by imparting a rotationalmovement on the granulation liquid in the horizontal plane in the first channel.

[0097] The invention will hereinafter be illustrated with reference to the following non-limiting examples and comparative tests. Ultrasound is known, e.g. from the above-mentioned EP 4 183 764 Al, for creating high (acoustic) shear rates and its suitability for particle size reduction of solid fertilizer macronutrient source was evaluated in comparison to mechanical treatment for particle size reduction. Before running trials in a fluid bed granulator, the effectiveness of particle size reduction through a model system was evaluated in what is referred to as feasibility tests. The chosen model system was designed to be as simple as possible for the purpose of evaluation and consisted of a slurry consisting of 50 wt% of a solid fertilizer macronutrient source in water.

[0098] Comparative Experiment 1

[0099] As a feasibility test, an amount of 50 wt.% of a solid fertilizer macronutrient source, in this case Polyhalite, in water was treated by a sonication device with a specific energy input of 100 Ws / g while cooling. The shear rate was assumed to be about 1.000.000 / s. The initial particle size d90 of the Polyhalite was 600 pm and the after sonication the achieved d90 value was reduced to 400 pm while still particles with a particle size around 1 mm were present. These large particles would create clogging in nozzles of a fluid bed granulator, consequently, follow-up granulation trials were abandoned.

[0100] Example 1

[0101] As a feasibility test, an amount of 50 wt.% Polyhalite in water was mechanically treated through high shear in a wet milling set-up at a shear rate of about 150.000 / s. The initial particle size d90 of the Polyhalite was 600 pm and after milling in the high shear wet mill, followed by colloid wetmill, the d90 value was 177 pm after these 2 milling steps, while no particles larger than 500 pm were found. The wet milled material therefore is suitable for effective reduction in particle size which made this mechanical treatment suitable for use in follow-up trials.

[0102] Follow up trials include simulation of nozzle design through Computational Fluid Dynamics (CFD) and plant trials including fluid bed granulation. In CFD experiments, a prior art film spray bed nozzle (according to WO 2024 / 049293) has been evaluated in Comparative experiment 2 ( / a, b, c) and compared with a slurry nozzle according to the invention (Example 2) as shown in table 1.

[0103] Comparative experiment 2

[0104] This experiment covers three types of trials, herein referred to as 2a, 2b, 2c. As slurries have a high density (compared to plain urea) a high throughput was aimed for in these trials. In starting the series 2a, 2b, 2c, a high throughput was aimed for processing of ( / plain) urea, and a throughput of 380 kg / hr could be reached in comparative experiment 2a. It proved, however, that in 2a a film thickness at 7 mm was not high enough. This low film thickness of 94 pm has as disadvantage that increased level of dry fines recycle may be needed in a plant.

[0105] Throughput could be further increased in comparative experiment 2b, while film thickness did not improve. When moving from plain urea to processing a slurry with higher density and viscosity, as shown for comparative experiment 2c, a high throughput could be obtained, however frustrum development proved poor, indicating unstable processing in a plant.

[0106] By modifying the nozzle, regarding both the (L / D) ratio of the bore hole and the exit geometry of the bore hole (deleting the diffusor) a good frustrum was obtained as well as a film thickness of the targeted thickness, as shown in Example 2.Table 1

[0107]

[0108] * @ 140 °C in a shear rates range of 10-200 / s; Anton Paar Rheolab QC;

[0109] ** Poor formation of frustrum; causing process instabilities

[0110] *** Good frustrum development; stable process

[0111] Example 3 and comparative experiment 3

[0112] The nozzle used in the invention should be able to handle a slurry, as compared to a regular melt, which slurry furthermore has a high (er) density and a high(er) viscosity. As the required high film thickness at 7mm, i.e. the impact height h, of the nozzle of the invention was confirmed in CFD, plant trials were initiated.

[0113] In the plant trials, Polyhalite with a d90 of was 600 pm was taken as solid fertilizer macronutrient source. This macronutrient source was added in an amount of 30 wt.% to an aqueous urea solution comprising10wt% of water, at a temperature of 120 °C and mixed to form a slurry. The slurry was mechanically treated in a two-stage wet milling operation, with a high shear wet mill and a colloid wet mill at a shear rate of about 150.000 / s and 230.000 / s, after which the d90 value was about 150 pm. The slurry was sent to an evaporator for water removal, to obtain a moisture content of 2 wt.% whereby the temperature of the concentrated fertilizer liquid increased to 140 °C. The fertilizer liquid was granulated by crystallization in a fluid bed granulator to obtain urea compound fertilizer granules of dimensions between 2-4 mm. The results are included in Table 2.

[0114] In Table 2, Comparative experiment 3 relates to fluid bed granulation with said prior art nozzle processing a slurry comprising 30 wt.% solid fertilizer macronutrient source.

[0115] In Example 3, a slurry of 30 wt.% solid fertilizer macronutrient source is processed with the nozzle according to the invention. While conducting the granulation experiments, in the comparative experiment a high amount of dust entrainment can be observed. Also, the percentage of fines dry-recycle is high.Table 2

[0116] > <

[0117] > <

[0118]

[0119] Example 4 and comparative experiment 4

[0120] One of the advantages of the process of the invention is that high amounts of fertilizer macronutrient source can be added to the urea fertilizer. This is further exemplified in Table 3, where 40 wt.% of a macronutrient source is fed to a urea melt in Comparative experiment 4 and to an aqueous urea solution in Example 4.

[0121] In Table 3, the weight ratio between water and urea are kept constant by setting the mass flows independently to meet the 70 wt.% urea in water.

[0122] The slurry was mechanically treated in a two-stage wet milling operation, utilizing high shear mills, particle size (d90) of the Polyhalite was around 150 pm in Example 4.

[0123] The process according to Example 4 ran smooth, while for Comparative experiment 4, there were stability issues, such as pipe, valve and nozzle plugging, disturbing a smooth operation of the process. Compared to experiments using concentrated urea melt with less than 95% water, this water-based slurry offers several advantages, including:(1) overcoming pipe plugging by operating well above the crystallization point, and any solids that settle during flow interruptions in the slurry wet milling circuit are quickly redispersed;

[0124] (2) allowing higher solids processing — while 40%wt. solids was the operational limit for the melt under pilot plant conditions due to constant plugging and crystallization risk, the solution-based method easily manages 40%wt. solids, or more.

[0125] Additionally, final products could achieve 50%wt. solid content after water evaporation.

[0126] Table 3

[0127]

Claims

39Claims1. A process for the production of urea compound fertilizer granules, the process comprising:a. providing an aqueous urea solution comprising urea and more than 5 wt.% of water;b. adding to said aqueous urea solution at least one solid fertilizer macronutrient source in an amount suitable to form a slurry comprising solid particles of the macronutrient source;c. subjecting the slurry to mechanical treatment, applying a shear force between 10.000 / s and 250.000 / s, so as to produce a treated slurry;d. subjecting the treated slurry to a water-removal step, resulting in a concentrated fertilizer liquid having a residual water content of at most 5 wt.%;e. subjecting the concentrated fertilizer liquid, optionally with the addition of a granulation agent such as formaldehyde, to granulation by crystallization to obtain urea compound fertilizer granules.

2. A process according to claim 1, wherein the granulation by crystallization is fluidized bed granulation.

3. A process according to claim 1 or 2, wherein the aqueous urea solution comprises at most 30 wt.% of water.

4. A process according to any one of the preceding claims, wherein the maximum amount of total solid fertilizer sources, calculated in weight percentage of the total urea compound fertilizer, is 41 wt.% to 50wt%.

5. A process according to any one of the preceding claims, wherein, next to an amount of at least 5 wt.% of total nitrogen, the at least one further fertilizer macronutrient source is selected so as to provide an amount of fertilizer macronutrients selected from the group consisting of:40a. P, expressed as P2O5, of between 0 wt.% and 30 wt.%, preferably between 0 wt.% and 20 wt.%, preferably at least 2 wt.%, more preferably at least 3 wt.%; and / orb. K, expressed as K2O, of between 0 wt.% and 35 wt.%, preferably between 2 wt.% and 20 wt.%, more preferably at least 3 wt.%; and / orc. S, expressed as SO3, of between 0 wt.% and 35 wt.%, preferably between 1 wt.% and 25 wt.%, more preferably at least 1.5 wt.%; and / ord. Ca, expressed as CaO, of between 0 wt.% and 20 wt.%, preferably between 1 wt.% and 20 wt.%, more preferably at least 1.5 wt.%; and / ore. Mg, expressed as MgO, of between 0 wt.% and 20 wt.%, preferably between 1 wt.% and 10 wt.%, more preferably at least 1.5 wt.%.and combinations thereof.

6. A process according to any one of the preceding claims, wherein the at least one solid fertilizer macronutrient source is a salt or a mineral providing a combination of nutrients in a complex macronutrient source, preferably selected from the group consisting of KC1; K2SO4; KNO3;K2SO4.2MgSO4; Ca(NO3)2; CaSO4; CaCO3; CaMg(CO3)2; Ca3(PO4)2;Ca(H2PO4)2; Ca(H2PO4)2 + CaSO4; NH4H2PO4; (NH^HPCh; Ca3(PO4)2;(NH4)2SO4; K2SO4; MgSO4; MgO; MgSO4(Kieserite); K2SO4MgSO4-2CaSO4(Polyhalite); andMgNH4PO4.

7. A process according to claim 6, wherein the complex macronutrient source is an evaporite mineral, such as Polyhalite.

8. A process according to any one of the preceding claims, wherein the mechanical treatment comprises wet-milling in the form of a rotor-stator system, to a solid particle size reflected by a d90 of less than 200 pm, preferably less than 100 pm, more preferably between 3 pm and 50 pm.

419. A process according to claim 8, comprising applying a first wet milling step followed by a subsequent second wet-milling step, wherein the first milling step comprises pre-milling the slurry to an initially reduced size of d90 less than 500 pm and the second milling step comprises further milling to the finally reduced size of d90 less than 200 pm, preferably less than 100 pm and wherein, preferably, the first milling step is conducted in a high-shear wet mill, and the second step in a colloid wet mill.

10. A process according to anyone of the preceding claims, comprising adding to the aqueous urea solution one or more micronutrient sources, preferably sources for micronutrients selected from the group consisting of Fe, Mn, Zn, Cu, B, Mo, and combinations thereof.

11. Urea compound fertilizer granules comprising urea, at least one other fertilizer macronutrient source in an amount of 20 wt.% to 50 wt.%, preferably 35 wt.% to 50 wt.%, wherein the amount of the other fertilizer macronutrient source is the same throughout the cross section of the granules.

12. A concentrated fertilizer liquid comprising urea, at most 5 wt.% of water, and 20 wt.% to 50 wt.%, preferably 35 wt.% to 50 wt.% of at least one solid fertilizer macronutrient source in the form of particles having a particle size reflected by a d90 of less than 100 pm, preferably between 3 pm and 50 pm.

13. A fluidized bed granulation process comprising growth of particles in a fluidized bed granulator by causing a granulation liquid, to solidify on the particles, said granulation liquid comprising a slurry of urea at a temperature of 140-145 °C and a solid fertilizer macronutrient source whereby the slurry has a density between 1250 and 2000kg / m3, preferably 1275-1750 kg / m3 more preferably 1300-1600 kg / m3 the process comprising:(a) providing a fluidized bed of the particles in a granulation compartment of the fluidized bed granulator;(b) forming a film of the granulation liquid in the form of a hollow conical frustum projecting into the granulation compartment by supplyingthe granulation liquid through a first channel of a granulation nozzle wherein the bore hole of the first channel has a diameter of at least 4.5 mm at the exit, preferably at least 5mm, where the exit of the bore hole is effectively cylindrical;(c) supplying secondary gas stream through a secondary gas channel of the granulation nozzle into the granulation compartment, wherein the secondary gas channel is provided as an annulus around the first channel, wherein the exit of the secondary gas channel is directly exposed to the fluidized bed in the granulation compartment, wherein particles from the fluidized bed are entrained in said secondary gas stream;(d) supplying entrained particles to said film by directing the secondary gas stream towards the film, causing the deposition of the granulation liquid on the surface of the particles and solidification of said deposited liquid resulting in growth of the particles.

14. A fluidized bed granulation process according to claim 13, wherein the viscosity of the slurry of urea and a solid fertilizer macronutrients source is between 2.5 and lOOmPa.s; preferably between 5 and 50 mPa.s at said processing temperature of. 140-145 °C.

15. The fluidized bed granulation process according to claim 13 or claim 14, wherein the length to diameter (L / D) ratio at the exit of the first channel of the granulation nozzle is between about 0.8 andl.2 preferably between 0.9 and about 1.1.

16. The fluidized bed granulation process according to any one of the claims 13 to 15, wherein the secondary gas contacts the conical film at an impact height, and whereby the film thickness at an impact height of 7 mm is between 150 and 450 pm; preferably 175-375 pm, more preferably 200-300 pm.

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