Improved preparation process and particles

Abstract

A process for granulation of urea and related granules wherein urea granules are produced from a urea melt wherein at least one additive comprising gallic acid and / or methylene blue is used in the granulation process.

Description

Technical Field

[0001] The present invention relates to a method for granulating urea and urea granules obtained by the method. Background Art

[0002] Current agricultural systems face the challenge of feeding a growing world population while mitigating environmental impact. The world's population currently exceeds 8 billion and is projected to reach approximately 10 billion by 2050. Land available for food production is limited, and plants have critical limits on nutrient absorption. For these reasons, there is a strong incentive to increase yields and optimize resources.

[0003] Fertilization plays a fundamental role in crop production and significantly affects the environment, especially soil nitrogen (N) dynamics. In addition, agriculture is a significant source of anthropogenic N2O emissions due to fertilization.

[0004] Urea is the most common nitrogen source for fertilization. Solid urea granules used as fertilizer (so-called agricultural urea) are usually produced by a granulation process. Granulation processes are described in the literature on urea production (e.g., Ullmann's Encyclopedia of Industrial Chemistry).

[0005] In summary, known urea processes, such as CO2 stripping or self-stripping, produce an aqueous urea solution with a concentration of about 65% to 70%. This solution is treated in a suitable evaporation section to remove water, thereby obtaining a urea melt with a concentration suitable for urea granulation, which is generally 96% or more (by weight). The granulation process is carried out in a granulation plant, where the urea melt is sprayed and solidified on the granules until the target size of the granules is reached. The process is also fed with solid urea granules called seeds, which serve as the starting nucleus for the granulation process. The seeds can be prepared separately or obtained by crushing a portion of the granules (for example, the portion that does not meet the size specifications). The granulation process is preferably carried out under fluidized bed conditions. The granulation process may include the use of additives, the most common of which is formaldehyde, which is an anti-caking agent and can improve the mechanical properties of the granules (such as compressive strength).

[0006] Another well-known method for producing solid urea is the prilling method, which is also described in the literature.

[0007] Urea granulation and related equipment are disclosed in EP 2 077 147 and WO 2012 / 113473. EP 2 077 147 discloses a method in which a portion of the growth liquid is used directly to produce seed material, while WO 2012 / 113473 discloses a granulation method using additives. EP 1 935 482 describes a fluidized bed granulation method in which the fluidized bed is maintained under turbulent conditions. Granulation and pelletization methods are also described in urea literature (e.g., Ullmann's Encyclopedia).

[0008] During its use as a fertilizer, urea readily undergoes transformation processes such as hydrolysis (i.e., urease) and nitrification. While these processes are necessary for maintaining plant nutrition, they can also harm the environment by releasing ammonia (NH3) into the atmosphere and contaminating groundwater through NO3 leaching following nitrification. Therefore, nitrogen use efficiency (NUE) is one of the most critical research issues. Beyond nitrogen input, the overall nutritional status of crops should also be improved.

[0009] Against this backdrop, a variety of new fertilizers are being developed to tailor nutrient release to plant needs and improve nutrient efficiency. Crop nutrient uptake typically follows an S-shaped pattern, synchronized with crop phenology (such as germination, bud formation, flowering, grain filling, and fruit formation). Ideally, nutrient release should perfectly adhere to this S-shaped pattern to minimize losses.

[0010] Fertilizers that adjust nutrient release timing to plant nutrient needs are often referred to as "smart fertilizers" and are categorized based on their operating mechanism. Among the different mechanisms used to improve nitrogen use efficiency, inhibition of the urease reaction and inhibition of the nitrification process are the most effective. Slowing the nitrification process reduces nitrogen losses due to leaching and denitrification, while slowing the urease process reduces nitrogen losses due to ammonia volatilization.

[0011] In the prior art, N-(n-butyl)thiophosphoric acid triamide (NBPT) is used as a urease inhibitor. Meanwhile, dicyandiamide (DCD) is a consolidated nitrification inhibitor. These chemicals are typically dissolved in a solvent, and the resulting solution is sprayed onto the finished urea granules or pellets downstream of the granulation or pelletizing stage.

[0012] However, the use of these additives raises a number of health and safety concerns. The solvents used are volatile and therefore difficult to recover once evaporated. NBPT and DCD are also toxic to aquatic environments.

[0013] US 8 343 891 discloses a method for improving the properties of urea granules by adding additives to urea. Summary of the Invention

[0014] The present invention aims to provide a novel urea-based fertilizer and related production method to overcome the above-mentioned problems associated with the use of NBPT and / or DCD as additives. Another object of the present invention is to provide an environmentally friendly additive for use in the production of urea granules to replace the above-mentioned additives.

[0015] The above-mentioned object is achieved by a urea granulation method according to the claims. According to the invention, gallic acid is used as a urease inhibitor and / or methylene blue (methylthioninium chloride), also known as methylene blue, is used as a nitrification inhibitor. The invention provides that one or both of the additives are added directly to the granulation method. Thus, the urea granules obtained in this manner are not simply coated with the additives, but rather contain the additives in the urea granules according to the desired distribution.

[0016] According to some embodiments, at least one of the additives is added to a selected step of the granulation process. Thus, the additive can be concentrated in selected areas of the granule, for example, in a layer of the granule. In some embodiments, the method results in the additive being contained primarily or exclusively in a layer of the granule. In certain embodiments, the method produces granules having a layered structure comprising a layer containing most or all of the methylene blue and a layer containing most or all of the gallic acid. In embodiments using both additives, the gallic acid is preferably added after the methylene blue in the granulation process, such that the gallic acid is contained in the outer layer of the granule while the methylene blue is contained in the inner layer of the granule.

[0017] Another aspect of the present invention is a urea granule comprising at least one of the methylene blue and gallic acid according to claim 1. DETAILED DESCRIPTION

[0018] The amount of gallic acid added to the granulation process is preferably such that the total gallic acid content in the urea granules obtained after the granulation process is 0.2 to 10 g / kg, preferably 0.5 to 5.0 g / kg, more preferably 1.0 to 3.0 g / kg.

[0019] The amount of methylene blue (methylene blue) added to the granulation process is preferably such that the total content of methylene blue (methylene blue) in the urea granules obtained after the granulation process is 0.12 g / kg to 10 g / kg, preferably 0.5 g / kg to 5.0 g / kg, more preferably 0.8 g / kg to 1.5 g / kg.

[0020] The above ranges are to be understood as grams of additive per kilogram of granular urea.

[0021] The granulation process can be carried out in a granulation device in which a feed of urea melt is sprayed into the granulation device and the device is fed with solid particles of urea called seeds which are suitable as starting nuclei for the granulation process.

[0022] According to various embodiments, some or all of the granulation seeds are obtained by crushing a portion of the granules obtained after the granulation process; additionally or alternatively, some or all of the granulation seeds can be prepared separately from a portion of the urea melt.

[0023] The broken fraction of granules, which may include undersized and oversized granules, is separated by passing the product of the granulation plant (urea granules) through a suitable sieving machine.

[0024] The separate production of granulation seeds is preferably carried out by rotational molding, in which droplets of urea melt are deposited on a cooling belt. Alternatively, granulation seeds can be produced by a separate pelletizing or granulation process. For example, a small portion of the available urea melt can be fed to a pelletizing device or a separate granulator for the production of seeds.

[0025] In a preferred embodiment, all the granulation seeds are produced separately from a portion of the urea melt and no product recycling is performed by crushing the granules and reintroducing them into the granulator. This one-pass embodiment may be preferred to provide precise control over the amount of additives in the different layers of the granules.

[0026] The granulation process is preferably a fluidized bed process, wherein the urea granules are maintained in fluidized conditions by a suitable fluidizing medium, typically air. In a preferred embodiment, the granules are maintained in vortex or twin vortex conditions.

[0027] The granulation method may comprise a series of granulation stages from a first granulation stage to a final granulation stage, wherein in each granulation stage, a feed of urea melt is introduced into the granulation device via one or more sprayers. For example, in each granulation stage, a certain amount of urea feed is introduced via a set of sprayers arranged around the granulation device. The sprayers of different granulation stages may be fed via a urea melt header.

[0028] In a highly preferred embodiment, one or more initial granulation stages are performed without the addition of gallic acid and methylene blue, and at least one of the gallic acid and methylene blue is added to one or more subsequent granulation stages. Thus, granules can be obtained in which the core of the granules is free or substantially free of the aforementioned additives, with these additives being concentrated primarily or only in selected layers. For example, in an embodiment using two additives, methylene blue is preferably added to the first set of granulation stages, and gallic acid is added to the subsequent second set of granulation stages, thereby obtaining granules having a core substantially free of the additives; an inner layer comprising methylene blue; and an outer layer comprising gallic acid.

[0029] The lamellar structure of the urea granules is advantageous because the desired nutrient release is achieved while preventing urease and nitrification reactions.

[0030] In one interesting embodiment, methylene blue is added to a first series of one or more granulation stages and gallic acid is added to a second series of one or more granulation stages after an initial granulation stage performed without said additive, wherein the second series of stages is performed after and downstream of the first series of stages, wherein methylene blue is not added to the steps of the second series and gallic acid is not added to the steps of the first series.

[0031] Methylene blue and / or gallic acid can be introduced directly into the granulation device, or methylene blue and / or gallic acid can be added to the urea melt stream before the urea melt stream is introduced into the granulation device. Adding the additive to one or more urea melt streams is a preferred embodiment.

[0032] According to a preferred embodiment, each of the above-mentioned additives can be added to the urea melt header feeding the different granulation stages, or to a separate set of sprayers introducing the urea melt into a single granulation stage.

[0033] In order to prevent thermal degradation of gallic acid, it is advantageous to minimize the residence time from the injection point of the molten urea stream to the introduction into the granulation equipment. The residence time is preferably not more than 30 seconds, preferably not more than 15 seconds, most preferably not more than 10 seconds.

[0034] According to a preferred embodiment, methylene blue and / or gallic acid are introduced during the granulation process, whereby methylene blue or gallic acid is added to the urea granules in a layer having a volume of 0.2 to 0.4, preferably 0.3 or about 0.3, of the total volume of the urea granules. The total volume of the urea granules is understood to be the volume of the granules including the above-mentioned layer comprising methylene blue or gallic acid and any coating layers.

[0035] Preferably, the process is controlled such that the urea granules exiting the granulation plant have a spherical shape.

[0036] Preferably, the average diameter of the urea granules is from 2.8 mm to 3.5 mm, preferably from 2.9 mm to 3.1 mm, or more preferably at or about 3.0 mm. The average diameter refers to the granules including any additive-containing layers and coating layers.

[0037] Preferably, the urea content of the urea melt is at least 96% by weight and the nitrogen content of the urea granules is at least 46% by weight.

[0038] In some embodiments, the method may further comprise the step of adding additional additives (such as formaldehyde or formaldehyde-containing additives) in the granulation equipment to increase the mechanical strength of the granules.

[0039] Prior to injection into the granulator equipment or urea melt stream, the additives gallic acid and methylene blue are each preferably mixed with an aqueous urea solution to form an aqueous dispersion. Preferably, the concentration of the additives in the aqueous urea dispersion is selected to minimize the water input into the urea melt and to avoid precipitation of urea from the dispersion, especially when the dispersion is stored at relatively low temperatures.

[0040] In a particularly interesting embodiment, the above-mentioned aqueous urea solution is mixed with gallic acid or methylene blue to form a dispersion, and the urea concentration of the aqueous urea solution is 40% to 80% by weight.

[0041] According to a preferred embodiment of the invention, gallic acid and methylene blue are introduced into the granulation process in the form of a dispersion in an aqueous urea solution.

[0042] Preferably, the methylene blue is dispersed in the aqueous solution at a concentration of 15% to 30%.

[0043] Preferably, the gallic acid is dispersed in the urea aqueous solution at a concentration of 20% to 35%.

[0044] Another aspect of the present invention is a urea granule comprising methylene blue and / or gallic acid added to the granule as an additive.

[0045] Preferably, the amount of methylene blue is 0.12 to 10 g of methylene blue per kg of urea granules, more preferably 0.5 to 5.0 g / kg, particularly preferably 0.8 to 1.5 g / kg.

[0046] Preferably, the amount of gallic acid is 0.2 to 10 g of gallic acid per kg of urea granules, more preferably 0.5 to 5.0 g / kg, particularly preferably 1.0 to 3.0 g / kg.

[0047] In a preferred embodiment, the urea granules consist of a multilayer structure comprising a urea core, a first layer of methylene blue mixed with urea, and a second layer of gallic acid mixed with urea. The first layer of the granules surrounds the core, and the second layer surrounds the first layer.

[0048] In one interesting embodiment, the core of the particle contains no additives; thus, methylene blue and gallic acid are only added in a layer around the core.

[0049] According to a preferred embodiment, the urea granules are spherical and have an average diameter of 2.8 mm to 3.5 mm, preferably 2.9 mm to 3.1 mm, more preferably 3.0 mm or about 3.0 mm. Preferably, at least 90% by mass of the granular urea has a diameter of 2.0 mm to 4.0 mm. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 Schematic diagram of a urea granulation process according to one embodiment of the present invention, wherein the granulation process is a one-pass process.

[0051] Figure 2 FIG2 is a schematic diagram of a urea granulation process according to an embodiment of the present invention, wherein part of the urea granules are recycled to the granulation equipment.

[0052] Figure 1 and Figure 2 The following main contents were disclosed:

[0053] Evaporators 2, 5, and 14

[0054] Vacuum and wastewater treatment section (WWT) 3

[0055] Granulator 9

[0056] Rotational molding machine 7

[0057] Scrubber 12

[0058] Mixing tanks 21, 28

[0059] Vacuum device 15

[0060] Crusher 40( Figure 2 )

[0061] Screening machine 41( Figure 2 ).

[0062] Figure 1 A method for producing urea granules 100 containing methylene blue and gallic acid as additives is shown. The specific steps of the method are as follows.

[0063] A urea aqueous solution 50 is fed to a first evaporator 2 via line 1 to produce a more concentrated urea solution or urea melt. A first portion of the concentrated urea solution is sent to a granulator 9 via line 63. A second and smaller portion of the concentrated urea solution is sent to a second evaporator 5 via line 4 for further concentration to produce a high-concentration urea melt 6, which is fed to a seed crystal production device (e.g., a rotary molding machine 7). Water 53 and 54 removed from evaporators 2 and 5 is treated in a wastewater treatment section 3.

[0064] Formaldehyde or a formaldehyde-containing additive 17 is added to the first portion of the urea solution 63 to produce a formaldehyde-containing urea melt 44 which is supplied to the urea granulator 9 .

[0065] High concentration urea melt 6 is used to produce granulation seeds 8 for solid urea in a rotary molding machine 7. The seeds 8 are then fed to a granulator 9 to serve as growth precursors for granules 100. In this example, the urea melt 6 is supplemented with a recycle stream 16 obtained from the treatment of granulation off-gas 11.

[0066] In addition to the seed crystals 8 and the urea melt 44, the granulator 9 also receives a urea solution 23 containing methylene blue and a urea solution 31 containing gallic acid. The solutions 23, 31 are preferably dispersions of additives in urea solutions of appropriate concentrations, as described below.

[0067] The granulator 9 in the embodiment shown is a fluidized bed apparatus, wherein fluidized bed conditions of the urea granules are maintained by fluidizing air 25. The granulator 9 has a longitudinal direction 160 and is provided with a plurality of injection nozzles (or sprayers) 150 arranged longitudinally and located at the various granulation stages of the apparatus.

[0068] Specifically, Figure 1 A first granulation stage 150a, a second granulation stage 150b and a third granulation stage 150c are shown in sequence. Each granulation stage may include one or more nozzles 150. Figure 1 For illustrative purposes only, the actual number of granulation stages may vary and in particular may be greater.

[0069] The first granulation stage 150a is fed with urea melt 44, which is introduced into the granulator 9 through a nozzle 150 located at the first stage 150a. The second granulation stage 150b, located downstream of the injection point of the dispersion 23, is fed with urea melt 44 to which methylene blue dispersion 23 is added. The third granulation stage 150c is fed with urea melt 44 to which gallic acid dispersion 31 is added. Due to the presence of a separate urea melt header 102, the third granulation stage does not receive methylene blue dispersion 23.

[0070] In more detail, Figure 1The main manifold for conveying urea melt 44 is shown to be divided into a first manifold 101 for conveying a first portion of the urea melt and a second manifold 102 for conveying a second portion of the urea melt. The first manifold 101 feeds the nozzles of the first stage 150a and the second stage 150b, and the second manifold 102 feeds the nozzles of the third stage 150c alone.

[0071] The first granulation stage 150a receives the urea melt 44 to which the formaldehyde additive 17 is added, as in the main manifold. The second granulation stage 105b receives the urea melt 44 to which the methylene blue dispersion 23 is also added. The third granulation stage 150c, fed by the second manifold 102, receives the urea melt 44 to which the gallic acid dispersion 31 is also added. At each stage, the urea melt is introduced into the granulator 9 through the sprayer 150.

[0072] The configuration of the granulator 9 described is particularly advantageous since it allows the formation of granules 100 having a core of urea containing formaldehyde (obtained by spraying urea melt 44), which is surrounded by a first layer of urea containing methylene blue formed in a second stage 150b as a result of the injection of urea melt mixed with dispersion 23, and further surrounded by a second layer of urea containing gallic acid formed after the injection of urea melt mixed with dispersion 31 in a third stage 150c.

[0073] In this example, the formaldehyde initially added to the urea melt 63 is present in all layers of the granules.

[0074] Methylene blue dispersions and gallic acid dispersions 23, 31 were obtained as follows.

[0075] Methylene blue, designated MB, is added to a stirred mixing tank 21 via line 19 along with an aqueous urea solution 20 to produce dispersion 23. Similarly, gallic acid GA is added to a stirred mixing tank 28 via line 52 along with an aqueous urea solution 29 to produce dispersion 31. Urea solutions 20 and 29 preferably contain 50% urea by weight. Dispersions 23, 31 are fed to respective granulation stages 150b, 150c via pumps 22, 30.

[0076] Figure 1 The granulator 9 operates according to a once-through process, wherein all of the urea seeds 8 are obtained by converting the high concentration urea solution 6 into small granules or pastilles of solid urea, and no seed material is obtained by recycling the output granules into the process.

[0077] A by-product tail gas 11 is removed from the granulator 9. The tail gas 11 may contain fluidizing air, urea dust, and small amounts of additives used in the granulation process. The tail gas 11 is cleaned in a scrubber 12 using a scrubbing medium (e.g., water 13). The output of the scrubber 12 is an aqueous urea solution 45 and cleaned gas 32 that is discharged to the atmosphere.

[0078] The aqueous solution 45 is concentrated in an evaporator 14 connected to a vacuum device 15 to produce a recovered urea stream 16 which is mixed with the high concentration urea melt 6 to produce the input for the rotational molding machine 7 .

[0079] Figure 2 A granulation method is shown, which Figure 1 The method of is different in that the granulation seeds are obtained by crushing a portion of the product rather than being prepared separately from a portion of the urea melt, and methylene blue and gallic acid are added simultaneously to the mixed dispersion 105 .

[0080] exist Figure 2 In the embodiment, the granules 68 obtained in the granulator 9 are subjected to a screening step in the screener 41 to separate undersized or oversized granules 70, which are crushed in the crusher 40 to form seed crystals 71. Granules that meet the size specifications and are not rejected by the screener 41 form the granular product 100.

[0081] Since the additives are added with the same dispersion 105, the particle 100 has a uniform or nearly uniform distribution of the additives within the particle.

[0082] The urea melt 50 is fed via line 1 to an evaporator 2 to remove water 53 and produce a concentrated urea melt 4. To the concentrated urea melt 4 are added a recycle stream 16 and a formaldehyde-containing additive 17 to produce a urea melt 44.

[0083] Methylene blue dispersion 23 and gallic acid dispersion 31 are prepared in accordance with the above Figure 1 The methylene blue dispersion 23 and the gallic acid dispersion 31 are then mixed to form a mixed dispersion 105, which is then added to the urea melt 44. The urea melt feed thus obtained is supplied to all stages of the granulator 9 via a common header 70 and feeds all urea sprayers 150.

[0084] The treatment of tail gas 11 is equivalent to the above Figure 1 The processing described in the embodiment of the present invention.

[0085] Example 1

[0086] exist Figure 1In the process, 60,200 kg / h of urea solution 50 is fed to the first evaporator 2 to produce 41,570 kg / h (97 wt%) of urea melt 63. The urea melt 63 is mixed with 209 kg / h of formaldehyde-containing additive 17 to produce urea melt 44 which is supplied to the urea granulator 9.

[0087] The high-concentration melt 6 from the second evaporator 5 is mixed with 1,306 kg / h of recycled urea melt 16 to produce 2,446 kg / h of high-concentration urea melt (99.7 wt%), which is fed to the rotary molding machine 7. The rotary molding machine 7 produces granulated seeds 8 with a diameter of 1.20 mm.

[0088] 52 kg / h of methylene blue were added to the mixing tank 21 together with 252 kg / h of urea solution (50 wt. %) to produce 304 kg / h (16.7 wt. %) of methylene blue dispersion 23 .

[0089] Similarly, 89 kg / h of gallic acid were added to the mixing tank 28 together with 214 kg / h of urea solution (50 wt%) to produce 306 kg / h (29.0 wt%) of gallic acid dispersion 31 .

[0090] The granules 100 are spherical granules with a diameter of d=3.05 mm and contain 46.2% by weight of nitrogen. The off-gas 11 removed from the granulator 9 contains urea dust corresponding to approximately 3% of the sprayed urea melt.

[0091] The tail gas 11 is treated in a scrubber 12 to produce 3,255 kg / h of an aqueous urea solution 45 (40 wt %), which is then evaporated in an evaporator 14 to produce a recirculating urea melt 16 .

[0092] Example 2

[0093] exist Figure 2 In the process, 60,200 kg / h of urea melt 50 is fed to the first evaporator 2 via line 1; the urea melt produced in evaporator 2 receives 1,328 kg / h of urea melt 16 from evaporator 14 to produce 44,080 kg / h of 97% by weight urea melt 4. 209 kg / h of formaldehyde-containing additive 17 are added to the urea melt 4.

[0094] 52 kg / h of methylene blue were added to the mixing tank 21 together with 252 kg / h of urea solution (50 wt. %) to produce 304 kg / h (16.7 wt. %) of methylene blue dispersion 23 .

[0095] 89 kg / h of gallic acid were added to the mixing tank 28 together with 214 kg / h of urea solution (50 wt. %) to produce 306 kg / h (29.0 wt. %) of gallic acid dispersion 31 .

[0096] The methylene blue dispersion 23 is then mixed with the gallic acid dispersion 31 to produce a urea melt feed 105 of 610 kg / h.

[0097] Approximately 50% of the granules 68 entering the screen 41 are recycled back to the granulator after crushing.

[0098] The scrubber 12 produces 3,255 kg / h of an aqueous urea solution 45 (40 wt %), which is evaporated in the evaporator 14 to produce a recirculating urea melt 16 .

[0099] Experimental results

[0100] Several field trials (1 to 3) were conducted to determine the performance of the granules of the present invention as fertilizers. The field trials were conducted on three crops: corn, wheat, and hemp. All field trials were conducted at the "L. Toniolo" experimental farm of the University of Padova, Italy. The experimental tests are discussed in detail below, and the following terminology will be used to discuss the results.

[0101] U: stands for conventional urea fertilizer without added inhibitors or additives;

[0102] C: represents the control plot, without added particles;

[0103] NBPT: indicates urea granules with added NBPT;

[0104] O-GA: denotes urea particles having a urea core and a monolayer of gallic acid GA surrounding the core (concentration in the layer is 6.3 g / kg);

[0105] O-BM: represents a urea granule having a urea core and a methylene blue BM layer surrounding the core (concentration in the layer is 3.6 g / kg);

[0106] O-BMGA: refers to urea particles having a urea core, an inner layer of methylene blue (BM) surrounding the core (3.6 g / kg), and an outer layer of gallic acid (GA) surrounding the inner layer (6.3 g / kg).

[0107] In the field trials, when conventional urea granules (U) were used as fertilizer, two fertilization treatments were applied during the crop's growth cycle, both after stem elongation. In contrast, when urea granules containing additives were used, only one fertilization treatment was applied. These fertilization treatments were applied before sowing. At harvest, the grain and its nitrogen content were quantified. All doses (kg N / ha, kg nitrogen / hectare) reported in the following field trial reports are understood to refer to the total amount of fertilizer applied during the crop's entire agricultural cycle.

[0108] Field Trial 1 – Corn

[0109] The first field trial was conducted on maize. Each fertilizer treatment was applied at a dose of 150 kg N / ha (kilogram nitrogen per hectare), with four replicates per treatment.

[0110] The results are presented in the form of plant dry biomass growth [t / ha, tons / hectare] and nitrogen uptake [kg / ha]. In some cases, NUE% = N 吸收 / N 供应 NUE represents the ratio between nitrogen uptake and nitrogen supply. The results of the best fertilization treatments compared with conventional urea and the control plots are given in Table 1 below.

[0111] Table 1

[0112] C U NBPT O-GA O-BMGA Plant dry biomass [t / ha] 15.7 15.6 18 18.4 18.1 Nitrogen absorption [kg / ha] 179 197 243 230 224

[0113] Table 1 shows that O-GA granules achieved the highest growth (t / ha). Compared to conventional urea, O-GA granules increased dry biomass by approximately +15%. Table 1 shows that nitrogen uptake by plants was roughly equivalent across the different treatments.

[0114] Field Trial 2 – Wheat

[0115] The second field trial was conducted on wheat. In the current field trial, different dosage regimens (100 kg N / ha, 150 kg N / ha, and 200 kg N / ha) were explored for each fertilization treatment. The experimental results for the best fertilization treatment for each dosage, compared to conventional urea and the control plots, are reported in Table 2.

[0116] Table 2

[0117] C U O-GA U O-GA U O-BMGA Cereals [t / ha] 4.3 4.8 5.7 5.1 5.8 5.4 6.2 Nitrogen dosage [kg / ha] 0 100 100 150 150 200 200 Nitrogen absorption [kg / ha] 75.3 81.1 95.1 96.3 108.3 106.3 107.3 <![CDATA[NUE%=N 吸收 / N 供应 ]]> - 81％ 95.1％ 64％ 72％ 53％ 53.6％

[0118] Table 2 shows that GA granules performed best at dosages ≤ 150 kg N / ha.

[0119] Compared to conventional urea granules, a +15% increase in agricultural yield was measured. At higher doses, ≥200 kg N / ha, O-BMGA granules outperformed the other granules. Agricultural yield was still calculated to be +15% higher than conventional urea.

[0120] Field Trial 3 – Hemp Plant

[0121] The third field trial was conducted on hemp. Futura 75, a monoecious hemp variety, was used for the trial. Different fertilizer dosage regimens (50 kg N / ha, 100 kg N / ha, and 150 kg N / ha) were investigated. Table 3 reports the optimal fertilizer dosages.

[0122] Table 3

[0123] C U1 U NBPT O-GA O-BM O-BMGA Plant hemp seeds[t / ha] 0.78 0.85 0.87 1.0 0.92 0.97 1.07 Biomass [t / ha] 11.0 11.5 12.6 13.5 11.7 13.4 13.6 Nitrogen dosage [kg / ha] 0 50 50 100 150 100 150

[0124] The highest yield was achieved at a dosage of 150 kg N / ha. Compared to conventional urea granules (U), the measured agricultural yield was approximately +20%, and compared to NBPT granules, the measured agricultural yield was approximately +7%. BM granules performed best at a dosage of 100 kg / ha. Compared to conventional urea granules (U), the measured agricultural yield was approximately +11%, and compared to NBPT granules, the agricultural yield was estimated to be -3%. Fertilization treatment U1 refers to conventional urea applied only once during the crop's agricultural cycle.

[0125] In summary, the following improvements were observed: a +15% increase in dry biomass was observed for corn compared to conventional urea U; a +15% increase in wheat yield was observed compared to conventional urea U.

Claims

1. A method for granulating urea, wherein urea granules are produced from a urea melt, wherein at least one of gallic acid and methylene blue is used as an additive in the granulation process.

2. The method according to claim 1, wherein: Gallic acid is added during the granulation process in an amount such that the total content of gallic acid in the urea granules obtained after the granulation process is 0.2 to 10 g of gallic acid per kg of urea granules, preferably 0.5 to 5.0 g / kg, more preferably 1.0 to 3.0 g / kg, and / or The methylene blue is added during the granulation process, and the amount of methylene blue added is such that the total content of the methylene blue in the urea granules obtained after the granulation process is 0.12 g to 10 g of methylene blue per kg of urea granules, preferably 0.5 g / kg to 5.0 g / kg, and more preferably 0.8 g / kg to 1.5 g / kg.

3. The method according to claim 1 or 2, wherein: The granulation process is carried out in a granulation device, wherein the granulation process comprises spraying the urea melt into the granulation device and feeding solid seed crystals into the device as starting nuclei for the granulation process, wherein the seed crystals are obtained by crushing a portion of the granules obtained after the granulation process, or the seed crystals are prepared separately from a portion of the urea melt.

4. The process according to any one of the preceding claims, wherein the granulation process is carried out under fluidized bed conditions.

5. The method according to any one of the preceding claims, wherein the method comprises a series of granulation stages from a first granulation stage to a last granulation stage, wherein in each granulation stage, a feed of the urea melt is introduced into a granulation device by means of one or more sprayers, wherein one or more initial granulation stages are performed without the addition of the gallic acid and the methylene blue, and at least one of the gallic acid and the methylene blue is added to one or more subsequent granulation stages.

6. The method according to claim 5, wherein: After an initial stage carried out without the additive, the methylene blue is added to a first series of one or more granulation stages and the gallic acid is added to a second series of one or more granulation stages, wherein the second series of stages is carried out after and downstream of the first series of stages, wherein the methylene blue is not added to the steps of the second series and the gallic acid is not added to the steps of the first series.

7. The process according to any one of the preceding claims, wherein the methylene blue or the gallic acid is introduced directly into a granulation device or is added to the urea melt stream before the urea melt stream is introduced into a granulation device.

8. A process according to any one of the preceding claims, wherein each of the methylene blue and / or the gallic acid is introduced in the granulation process such that the methylene blue or the gallic acid is added to a layer of the urea granules having a volume of 0.2 to 0.4, preferably 0.3 or about 0.3, of the total volume of the urea granules including any coating layers.

9. The process according to any one of the preceding claims, wherein the process is controlled so that the urea particles have a spherical shape and the average diameter of the urea particles including any coating layer is from 2.8 mm to 3.5 mm, preferably from 2.9 mm to 3.1 mm.

10. The process according to any one of the preceding claims, wherein the urea content of the urea melt is at least 96% by weight.

11. The method according to any one of the preceding claims, wherein the method is controlled such that the nitrogen content in the urea granules is at least 46 wt%.

12. The process according to any one of the preceding claims, wherein the gallic acid and / or the methylene blue are introduced into the granulation process in the form of a dispersion in an aqueous urea solution.

13. The method according to claim 12, wherein the concentration of the methylene blue dispersion is 15% to 30%, and / or the concentration of the gallic acid dispersion is 20% to 35%.

14. Granular urea comprising at least one of methylene blue and gallic acid as an additive.

15. The granular urea according to claim 14, wherein the granular urea comprises: The methylene blue, wherein the amount of the methylene blue is 0.12 g to 10 g per kg of granular urea, preferably 0.5 g / kg to 5.0 g / kg, more preferably 0.8 g / kg to 1.5 g / kg; and / or The gallic acid is contained in an amount of 0.2 to 10 g of gallic acid per kg of granular urea, preferably 0.5 to 5.0 g / kg, more preferably 1.0 to 3.0 g / kg.

16. The granular urea according to claim 14 or 15, wherein the granular urea has a multi-layer structure including a core, a first layer surrounding the core, and a second layer surrounding the first layer, the first layer containing methylene blue as the additive, and the second layer containing gallic acid as the additive.

17. Granular urea according to claim 16, wherein the methylene blue is mainly or only contained in the first layer of the granule, and / or wherein the gallic acid is mainly or only contained in the second layer of the granule.

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