Urea particles containing bio-based polymer and methods for their production

Description

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[0006] Due to new regulations requiring higher nitrogen utilization efficiency (NUE) and a reduction in ammonia and greenhouse gas emissions, the demand for urea particles stabilized with urease inhibitors against enzymatic degradation is increasing and will be much higher in the future. 5 Regarding storage stability, a minimum concentration of the urease inhibitor in the urea particles must be ensured at the time of application in the field to guarantee sufficient nitrogen utilization efficiency. In most regions, the potential to reduce nitrogen losses must be demonstrated / verified. 10

[0007] Urease inhibitors such as thiophosphoric triamides, e.g. NBPT and NPPT, exhibit comparatively low storage stability after application to conventional urea particles. It has been found that the thiophosphoric triamides react with formaldehyde and urea-formaldehyde during storage.These reactions reduce the residual thiophosphoric acid triamide content below the prescribed minimum concentration. Urea particles produced with formaldehyde-containing additives are therefore unsuitable for the production of storage-stable fertilizers or at least of considerable disadvantage.

[0008] For the reasons mentioned above, there is a need to replace formaldehyde-containing additives with other additives. These other additives should improve the particulate formation (particle formation, i.e., for example, granulation or prillaging) of urea as well as the quality of the urea particles, and furthermore be safe, environmentally friendly, and inert to agronomic substances such as urease inhibitors.

[0009] Certain bio-based polymers can meet these criteria. However, due to their often low solubility in water and their tendency to gel, their large-scale application remains a challenge.

[0010] US20080041131A1 relates to a method for improving the fracture strength and reducing dust formation and clumping tendency of urea particles by adding an organic compound to the molten urea, wherein at least one carbohydrate and optionally a polyvinyl compound is added to the urea. The carbohydrate may be an oligosaccharide or polysaccharide, for example, starch, guarana, or xanthan gum. The carbohydrates may be added as solids to a urea melt, or they may be dissolved in a solvent, in an aqueous solution of polyvinyl alcohol, or in a urea solution before being added to the urea melt.

[0011] US20220089529A1 relates to a urea manufacturing process using a first and a downstream second evaporator in an evaporation section, a finishing section and a scrubber for treating the exhaust gas of the finishing section. Condensate from the condenser of the second evaporator is fed to the scrubber.

[0012] US2024 / 0051888A1 andUS20240300864A1 relate to methods for producing a homogeneous, solid, particulate, urea-based composition comprising urea and an additive in a urea production plant. The additive is preferably a urease inhibitor based on a thiophosphoric acid triamide or a nitrification inhibitor.

[0013] It is also known to use certain bio-based polymers in coatings of urea particles to delay the release of urea from these particles. For example, M.M. Fernández-Péreze et al., Journal of Applied Polymer Science, Vol. 108, 3796–3803 (2008), discusses the use of lignin and ethylcellulose as polymers in controlled-release urea formulations. B. Beige et al., Journal of Plant Nutrition, https: / / doi.org / 10.1080 / 01904167.2020.1744647, is a review of coating materials for slow release of nitrogen from urea-containing fertilizers. D. Lawrencia et al., Plants2021,10,238.https: / / doi.org / 10.3390 / plants10020238, is a review of coating materials and release mechanisms of controlled-release fertilizers.

[0014] It is an objective of the invention to overcome the disadvantages of the prior art and to provide improved methods for producing improved urea particles.

[0015] This objective is achieved by the subject matter of the patent claims.

[0016] It has been surprisingly found that water-soluble or dispersible bio-based polymers, when added to a urea-containing melt and / or solution instead of formaldehyde-based additives, have positive effects on the formation of the urea particles (e.g., dust formation, particle growth) and the quality of the particles (e.g., hardness, tendency to clump).BE2025 / 5093 4

[0017] Thus, even with the use of small amounts of bio-based polymers, urea particles with a narrow size distribution can be produced, which exhibit sufficient mechanical strength comparable to conventional urea particles, without the need to add formaldehyde-based additives. In contrast to urea particles with formaldehyde-based additives, the bio-based polymers improve the environmental compatibility of the urea particles and also reduce their hazard potential during production, storage and use.

[0018] It has proven particularly advantageous if the bio-based polymers are first dispersed or dissolved in an aqueous composition before being added to a solution and / or melt of urea and subsequently particulated.Furthermore, it was surprisingly found that the problems associated with the handling, storage, and transport of aqueous solutions of the bio-based polymers can be circumvented by initially using the bio-based polymers in solid form, whereby the dissolving / dispersing of these bio-based polymers in solid form is then integrated into the urea particulateation process. An aqueous urea-containing solution, which is generated during the conventional operation of a urea particulateation plant, e.g., as a washing solution during dust washing, is preferably used as the dissolving / dispersing medium. The aqueous urea-containing solution can also be taken from a urea synthesis plant upstream of the particulateation process.

[0019] A first aspect of the invention relates to urea particles comprising at least 20 wt.-% urea, based on the total mass of the particles; and - a bio-based polymer, which is distributed in the urea particles, preferably homogeneously; wherein the urea particles have a mean particle size in the range of 0.1 to 10 mm, preferably determined by sieve analysis according to DIN EN 1235:2003-08.

[0020] For the purposes of description, "particle" means a physical form which may be granulated, prilled, crystalline, compacted, pulverized or the like. 30The particles can exist as particles in a multitude of forms, for example in small units of shape of small size (e.g. as granules (granules / granules), prill, crystallite, pellet, powder or powder). Preferably the particles exist as granules, i.e. as a granular substance (granular matter, grains). BE2025 / 5093 5

[0021] For the purposes of description, “bio-based polymer” means a polymer within the meaning of the IUPAC recommendation: “composed or derived wholly or partly from biological products from biomass (including plant, animal, marine or forestry materials)” (M.Vertetal., Terminology for bio-related polymers and applications (IUPAC Recommendations 2012), Pure and Applied Chemistry, https: / / doi.org / 10.1351 / PAC-REC-10-12-04, page 381). A bio-based polymer preferably occurs as such in nature, preferably in polymeric form, and is usually obtained from a natural source, or it is derived as a derivative of such a polymer and is usually obtained starting from such a polymer, typically by polymer-analogous reaction. According to the invention, bio-based polymers preferably include native polymers, biogenic polymers, biopolymers, and their respective derivatives.

[0022] The urea particles according to the invention comprise a bio-based polymer which is distributed within the urea particles. The distribution is preferably homogeneous.However, according to the invention, it is also possible that the distribution is inhomogeneous; for example, an inner core of the urea particles may have a comparatively low or no content of bio-based polymer, and an outer shell of the urea particles surrounding the inner core (core shell) may have a comparatively high content of bio-based polymer. 20

[0023] Preferably, the content of bio-based polymer is at most 5.0 wt.%, preferably at most 4.0 wt.%, preferably at most 3.0 wt.%, even more preferably at most 2.0 wt.%, most preferably at most 1.0 wt.%, and in particular at most 0.5 wt.%, in each case based on the total mass of the urea particles. 25

[0024] Preferably, the content of bio-based polymer shall be at most 0.25 wt. %, preferably at most 0.10 wt. %, preferably at most 0.075 wt. %, even more preferably at most 0.050 wt. %, most preferably at most 0.040 wt. %, and in particular at most 0.030 wt. %, in each case based on the total mass of the urea particles.30

[0025] Preferably the content of bio-based polymer is at least 10 ppmw, preferably at least 20 ppmw, preferably at least 50 ppmw, more preferably at least 100 ppmw, most preferably at least 175 ppmw, and in particular at least 250 ppmw, in each case based on the total mass of the urea particles. BE2025 / 5093 6

[0026] The bio-based polymer preferably has a mean molecular weight of not more than 250,000 g / mol, preferably not more than 200,000 g / mol, preferably not more than 150,000 g / mol, even more preferably not more than 100,000 g / mol, most preferably not more than 75,000 g / mol, and especially not more than 50,000 g / mol, each determined by gel permeation chromatography.

[0027] Preferably, the bio-based polymer is water-soluble. Preferably, the solubility of the pure bio-based polymer in pure water at 23°C is at least 10 g / l, preferably at least 20 g / l, preferably at least 40 g / l, even more preferably at least 60 g / l, most preferably at least 80 g / l, and especially at least 100 g / l. Preferably, it is a true solution (this can be, if necessary,(later gels, but is initially a - possibly viscous - solution).

[0028] The bio-based polymer is preferably a polysaccharide or a derivative of a polysaccharide. If the bio-based polymer is a derivative of a polysaccharide, it is preferably selected from ethers and esters, preferably ethers. In principle, (further) linkages are also possible for derivatization, for example via glycosidic bonds.

[0029] The polysaccharide is preferably selected from the group consisting of cellulose, starch, pectin, alginate, chitin and chitosan; cellulose is particularly preferred. This also applies if the bio-based polymer is a derivative of such a polysaccharide. Other possible polysaccharides are heparin, chondroitin, keratin or hyaluronic acid.

[0030] In preferred embodiments, the bio-based polymer is a cellulose ester; preferably selected from the group consisting of methylcellulose (MC), ethylcellulose (EC), methylethylcellulose (MEC), hydroxyethylcellulose (HEC), hydroxopropylcellulose (HPC), hydroxyethylmethylcellulose (HEMC), hydroxypropylmethylcellulose (HPMC), and carboxymethylcellulose (CMC).

[0031] In other preferred embodiments, the bio-based polymer is a cellulose ester; preferably cellulose acetate.

[0032] In further preferred embodiments, the bio-based polymer is modified starch.

[0033] The urea particles according to the invention can contain a single bio-based polymer or a mixture of several different bio-based polymers (including bio-based copolymers, e.g., bio-based block copolymers).If the urea particles according to the invention contain several different bio-based polymers, then, unless expressly stated otherwise, all references refer to the totality of all bio-based polymers contained in the urea particles.

[0034] Preferably, the urea particles according to the invention contain a urease inhibitor and / or a nitrification inhibitor. It is also possible that the urea particles according to the invention contain several urease inhibitors and / or several nitrification inhibitors independently of one another. For example, combinations of NBPT and NPT are preferred as urease inhibitors.

[0035] A urease inhibitor is a substance that reduces or completely prevents the chemical activity of the enzyme urease. A nitrification inhibitor is a substance that delays or completely suppresses the bacterial oxidation of ammonium ions (nitrification).15

[0036] Preferred urease inhibitors are selected from the group consisting of N-(n-butyl)thiophosphoric triamide (NBPT), N-(n-propyl)thiophosphoric triamide (NPPT), hydroquinone, phosphoric triamide, p-benzoquinone, cyclohexyl phosphate triamide, and hexaamidocyclotrihosphazene; preferably N-(n-butyl)thiophosphoric triamide and N-(n-propyl)thiophosphoric triamide. 20

[0037] Preferred urea particles according to the invention comprise a urease inhibitor; preferably a thiophosphoric triamide; preferably N-(n-butyl)thiophosphoric triamide (NBPT) and / or N-(n-propyl)thiophosphoric triamide (NPPT).

[0038] Preferred nitrification inhibitors are selected from the group consisting of dicyandiamide, 1-methylpyrazole-1-hydroxyamide, 3-methylpyrazole, ethylene-25urea, chlorazole, 4-aminotriazole, thiourea, acetylene, 2-ethinylpyridine, sulfate thiazole, amidinothiourea, 1-amino-2,4-dimethylpyrazole phosphate, thiosulfates, for example sodium thiosulfate, calcium carbide, 2,5-dichloroaniline, 3-acetanilide, toluene, carbon disulfide, phenylacetylene, 2-propyn-1-ol and phenethylphosphonium diamide. 30

[0039] In preferred embodiments, the total content of urease inhibitor and / or a nitrification inhibitor is at most 1.0 wt.%; preferably at most 0.5 wt.%, preferably at most 0.1 wt.%, and still preferably at most 0.05 wt.%; in each case based on the sum of all the urea particles containing inhibitors and relative to the total mass of the urea particles.

[0040] In preferred embodiments, the total content of urease inhibitor and / or a nitrification inhibitor is in the range of 0.005 to 0.5 wt.%.-%; preferably 50.01 to 0.1 wt%, more preferably 0.02 to 0.08 wt%, and even more preferably 0.04 to 0.06 wt%; in each case based on the sum of all inhibitors contained in the urea particles and relative to the total mass of the urea particles.

[0041] In preferred embodiments, urease inhibitor and / or nitrification inhibitor are distributed in the urea particles, preferably homogeneously.

[0042] In preferred embodiments, the urea particles comprise a core and optionally a coating, wherein the bio-based polymer is distributed in the core, preferably homogeneously.

[0043] With homogeneous distribution, the urea particles form a phase in which the bio-based polymer is uniformly distributed. The amount and concentration of the bio-based polymer are essentially the same in each part of the phase, so that there are no significant differences or deviations.

[0044] Preferably, (i) the core of the urea particles comprises a urease inhibitor and the coating of the urea particles comprises a nitrification inhibitor; or (ii) the core of the urea particles comprises a nitrification inhibitor and the coating of the urea particles comprises a urease inhibitor.

[0045] In preferred embodiments, an additional coating of the urea particles retards the release of urea from the particles. Suitable materials for such a coating are known to those skilled in the art and include, for example, wax and polymers such as polylactic acid.

[0046] Preferably, the urea particles according to the invention have a tensile strength of at least 30 N, preferably at least 35 N, each determined according to the method “TVA procedures for determining physical properties of fertilizers”, Special Report No. 12, page 444, September 1970; or “Manual for determining physical properties of fertilizers”; International Fertilizer Development Centre, 1984. BE2025 / 5093 9

[0047] The urea particles according to the invention comprise at least 20 wt.-% urea, based on the total mass of the particles.

[0048] Preferably, the urea content is at least 40 wt.%, preferably at least 50 wt.%, preferably at least 60 wt.%, preferably at least 70 wt.%, preferably at least 80 wt.%, and in particular at least 90 wt.%, in each case based on the total mass of the urea particles.

[0049] The urea particles according to the invention have a mean weight particle size in the range of 0.1 to 10 mm, preferably determined by sieve analysis according to DIN EN 1235:2003-08. 10

[0050] The urea particles according to the invention preferably have a mean particle size in the range of 0.5 to 8.0 mm, preferably 0.5 to 6.0 mm, and more preferably 0.5 to 4.0 mm. The mean particle size (D50 (mass-averaged)) of the urea particles according to the invention is preferably in the range of 0.5 mm to 5.0 cm; preferably 1.0 mm to 1.0 cm, more preferably 1.0 mm to 6.0 mm, even more preferred 2.0 mm to 5.0 mm, and most preferred 2.0 mm to 4.0 mm; preferably determined by sieve analysis according to DIN EN 1235:2003-08.

[0051] In preferred embodiments, the urea particles according to the invention comprise one or more additives; preferably, the additives contain one or more of the following components: 20-sulfur; -ammonium sulfate; -at least one trace element.

[0052] The additive can comprise either (elemental) sulfur or ammonium sulfate or at least one trace element. Likewise, the additive can comprise any combination of the aforementioned components or may also contain further components. The sulfur can be used in its elemental form or as a component of a compound. For example, the additive can comprise sulfur in the form of sulfates. Trace elements are preferably those elements which are necessary for a living organism and usually occur in mass fractions of less than 50 mg / kg in an organism. Trace elements can, for example, comprise aluminum, boron, chlorine, iron, copper, manganese, molybdenum, and / or zinc.An expert recognizes that the term trace element encompasses both a single element and any possible mixture of two or more elements.

[0053] In preferred embodiments, the urea particles according to the invention comprise ammonium sulfate.

[0054] Preferably, the ammonium sulfate content is at most 1.0 wt.%; preferably at most 0.75 wt.%, preferably at most 0.5 wt.%, and still preferably at most 0.3 wt.%; in each case relative to the total mass of the urea particles.

[0055] Another aspect of the invention relates to a method for producing the urea particles described above according to the invention, wherein the method comprises the following steps: (a) providing an aqueous polymer preparation comprising a bio-based polymer; (b) optionally evaporating at least some of the water from the polymer preparation; (c) providing a melt and / or solution comprising freshly synthesized urea; (d) mixing the polymer preparation with the melt and / or solution to produce a mixture; (e) producing urea particles from the mixture.

[0056] Preferably, the method according to the invention comprises one or more of the following additional steps: (f) optionally pre-cooling the urea particles; (g) Classifying urea particles; and (h) optionally post-cooling urea particles. 25

[0057] In step (a) of the process according to the invention, an aqueous polymer preparation is provided which comprises a bio-based polymer.

[0058] Preferably, the aqueous polymer preparation is in the form of a solution or dispersion, preferably as a solution or suspension. The bio-based polymer may be swollen and contain water inclusions and / or water deposits. In addition to water, the aqueous polymer preparation may also contain other solvents, e.g., water-miscible organic solvents or monomers. Preferably, however, water is the only solvent contained in the aqueous polymer preparation.

[0059] Preferably, step (a) comprises the sub-steps 5(a1) Providing an aqueous composition; (a2) optionally Evaporating at least some of the water from the aqueous composition; and (a3) ​​Dissolving or dispersing bio-based polymer in the aqueous composition to produce the aqueous polymer preparation. 10

[0060] The aqueous polymer preparation produced in sub-step (a3) ​​differs from the aqueous composition provided in sub-step (a1) at least in terms of the bio-based polymer, if applicable.Additionally, the water content is also affected if, in optional step (a2), at least some of the water is evaporated from the aqueous composition. 15

[0061] Preferably, the aqueous composition provided in step (a1) is obtained as a by-product during the production of the urea particles.

[0062] In preferred embodiments, the aqueous composition provided in step (a1) is a urea-containing aqueous solution. Preferably, the urea-containing aqueous solution contains unreacted, excess, and / or sorted-out material.

[0063] In other preferred embodiments, the aqueous composition provided in partial step (a1) is an aqueous urea-containing solution and / or melt, e.g., a hydrated urea melt. Preferably, the urea-containing aqueous solution and / or melt contains unreacted, excess, and / or sorted-out material.

[0064] For the purposes of description, “unreacted, excess and / or sorted material” includes urea which is recovered during the manufacture of the urea particles and is recycled (recycled urea). For the purposes of description, such recovered urea differs from "freshly synthesized urea". Preferably, "unreacted, excess and / or rejected material" includes any urea-containing material that arises in or after a passing particulate unit and is not immediately incorporated into urea particles of the desired type and quality within the particulate unit. For example, "unreacted, excess and / or rejected material" includes urea-containing wash solutions from gas scrubbing or granulator scrubbing, oversized urea particles that are rejected and subsequently dissolved, steam / process condensate, etc. Oversized urea particles (>10 mm) fall directly after the particulate unit (e.g.,the particles are collected on a safety sieve (also referred to as "recycling system 1" according to the invention) and are usually sorted out directly after exiting the particle unit (e.g., the granulator). Besides urea, the material may contain solvents, especially water, as well as impurities, especially NH3.

[0065] A difference between step (b) and the optional sub-step (a2) of the process according to the invention consists in the presence or absence of the bio-based polymer. The evaporation of water from the aqueous composition in sub-step (a2) before the evaporation of at least part of the water from the polymer preparation in step (b) is preferred if the aqueous composition is itself already a urea-containing aqueous process fluid, but is too diluted, i.e., contains an excessively high water load.

[0066] Step (b) and sub-step (a2) are optional. In preferred embodiments, the process according to the invention includes sub-step (a2), but not step (b).In 20 other preferred embodiments, the inventive method comprises step (b) but not sub-step (a2). In further preferred embodiments, the inventive method comprises both sub-step (a2) and step (b). However, it is also possible that the inventive method comprises neither sub-step (a2) nor step (b). 25

[0067] Preferably, in sub-step (a3), the bio-based polymer is initially in solid form, e.g., as a powder or in the form of pellets, and is subsequently dissolved or dispersed in the aqueous composition. The dissolving or dispersing may include mixing or source preparation, provided that the aqueous composition is ultimately obtained as a solution or dispersion. The aqueous composition may be comparatively viscous, but is preferably pumpable with conventional equipment.

[0068] Preferably, the unreacted, excess, and / or rejected material is collected in one or more of the steps (e), (f), (g), and (h).Preferably, the unreacted, excess and / or sorted material falls as dust, as solution from the gas scrubbing and / or as oversized urea particles, which, after sorting, are preferably dissolved in an aqueous composition (see Recycling System 1). 5

[0069] Preferably, the material falls as dust and is separated from a gas phase by wet separation, generating the urea-containing aqueous solution.

[0070] Preferably, step (g) comprises separating oversized and / or undersized urea particles as reject material and returning the separated reject material as solid to step (e). 10

[0071] In optional step (b) of the process according to the invention, at least part of the water from the polymer preparation provided in step (a) is evaporated.

[0072] In step (c) of the process according to the invention, a melt and / or solution comprising freshly synthesized urea is provided.

[0073] For the purpose of description, "stones" comprise a urea-containing "melt" and / or "solution" a urea-containing fluid which contains urea and preferably water. It may be a melt, an aqueous solution, a water-containing melt, a hydrated melt, or the like.

[0074] For the purpose of description, "freshly synthesized urea" differs from recycled, i.e., recovered, urea. Preferably, "freshly synthesized urea" was synthesized immediately beforehand in a synthesis and recovery unit (urea synthesis plant), typically from CO2 and NH3, and is preferably still in liquid form due to the manufacturing process. The liquid urea has preferably not remained in the liquid state for too long in order to avoid the formation of biuret. However, according to the invention, it is also possible to first allow the freshly synthesized urea to cool down and only then use it. Prefabricated and, if necessary,The temporarily stored urea is also "freshly synthesized urea" within the meaning of the invention, provided that it is not recovered urea.

[0075] In step (d) of the process according to the invention, the polymer preparation 30 is mixed with the melt and / or solution to produce a mixture.

[0076] In step (e) of the process according to the invention, urea particles are produced from the mixture. BE2025 / 5093 14

[0077] In the optional step (f) of the process according to the invention, the urea particles are pre-cooled.

[0078] In the preferred step (g) of the process according to the invention, the urea particles are classified, preferably by sieving. 5

[0079] In the optional step (h) of the process according to the invention, the urea particles are cooled afterwards, i.e., in addition to pre-cooling in step (f), there is also a post-cooling step in step (h). Preferably, this is cooling before storage, typically as a separate cooling step after sieving / classifying in step (g).10

[0080] The urease inhibitor and / or the nitrification inhibitor is preferably added before or during particle formation, so that it is preferably distributed in the particles.

[0081] In preferred embodiments, a urease inhibitor and / or a nitrification inhibitor is added to the melt and / or solution provided in step (c). In other preferred embodiments, a urease inhibitor and / or a nitrification inhibitor is added to the mixture produced in step (d). In further preferred embodiments, a urease inhibitor and / or a nitrification inhibitor is added to the urea particles during their production in step (e). Combinations of these embodiments are also possible. 20

[0082] The urease inhibitor and / or the nitrification inhibitor is preferably added after particulateation, so that it is preferably present in a coating of the particles.

[0083] In preferred embodiments, the urea particles produced in step(e) are treated with a composition containing a urease inhibitor 25 and / or a nitrification inhibitor. In other preferred embodiments, the urea particles pre-cooled in step(f) are treated with a composition containing a urease inhibitor and / or a nitrification inhibitor. In further preferred embodiments, the urea particles classified in step(g) are treated with a composition containing a urease inhibitor 30 and / or a nitrification inhibitor. In additional preferred embodiments, the urea particles post-cooled in step(h) are treated with a composition containing a urease inhibitor and / or a nitrification inhibitor. Contains inhibitor. Combinations of these embodiments are also possible. BE2025 / 5093 15

[0084] Preferred embodiments of the invention are explained below with reference to the illustrations, which, however, are not to be interpreted as limiting.

[0085] Figure 1 schematically illustrates a preferred embodiment according to the invention, in which the addition of the biobasic polymer, preferably in solid form, is carried out in a tanker in which a urea-containing aqueous solution is stored, which is obtained during the recovery of urea.

[0086] According to the flow diagram shown in Figure 1, the synthesis of urea is carried out according to a conventional process from NH3 and CO2 in a synthesis and recovery unit (1) configured for this purpose. An evaporation stage of the synthesis and recovery unit (1) serves to concentrate the freshly synthesized urea and the urea recovered from particulateation. The recovery can be carried out as a process step, for which the synthesis unit is equipped with a recovery unit. The concentrated urea solution is then transferred to a particulateation unit (2), in which 15 urea-containing particles (P) are produced, preferably by prilling or granulation.The urea-containing particles (P) leaving the particulate unit (2) are then cooled in a pre-cooling unit (3) before being classified by sieving in a classification unit (4). Subsequently, the classified urea-containing particles (P) are preferably cooled further in a post-cooling unit (5) and then fed to a product storage unit (10).

[0087] A mass stream, which, in addition to the actual product stream, contains urea-containing particles (P) in the classification unit (4), preferably comprises urea-containing particles (P) that are too small (or possibly also too large) and are preferably returned to the particulate unit (2) (possibly after comminution). Further streams, which are generated in the particulate unit (2), the pre-cooling unit (3), the classification unit (4) and / or the post-cooling unit (5), preferably comprise urea-containing dust (S), which is fed to a gas cleaning unit (6). In this unit, urea-containing dust (S) is separated from the gas phase by wet scrubbing.The urea-containing dust (S) is preferably brought into contact with a liquid stream, preferably water or an aqueous solution, in a gas stream or as an aerosol stream in the gas purification unit (6) in order to absorb urea and possibly other components of the urea-containing dust (S) such as gases (NH3), biuret, impurities, traces of additives, inhibitors, sulfur, ammonium sulfate, etc. in the liquid (washing solution). The urea-containing aqueous solution (L) thus produced is fed to a tank (7). Also fed to the tank (7) is preferably additional, recovered urea (R) from other parts of the plant or mass flows. The urea-containing aqueous solution (L) thus preferably comprises the washing solution (i.e., the solution produced during wet separation in the gas purification unit (6))a urea-containing aqueous solution, which is generated during the washing of the exhaust air of the particle separator unit (2), preferably the granulator, and at least one of the following streams: - material from a safety screen at the outlet of the particle separator unit (2), preferably a granulator (recycling system 1); - material from a roller crusher (recycling system 2); - a urea-containing aqueous solution, which is generated during the washing of the particle separator unit, preferably the granulator, as part of maintenance (e.g., maintenance carried out continuously every 1 to 3 months) (recycling system 3); 15-steam (recycling system 4); and / or material from other sources. In the tank (7) a urea-containing aqueous solution (L) is therefore preferably stored, which contains urea that has been recovered from various plant components or mass streams.

[0088] The urea recovered from the urea-containing dust (S), which is present in the urea-containing aqueous solution (L), is preferably also returned to the particulate unit (2).However, for this purpose the urea-containing aqueous solution (L) is preferably first concentrated in an evaporation unit (8) or the liquid phase is evaporated or directed to the synthesis and recovery unit 1 for evaporation. 25

[0089] According to the invention, the addition of bio-based polymer takes place in the tank (7) in the preferred embodiment shown schematically in Figure 1. The bio-based polymer is preferably in solid form, for example, as a powder or pellets. The bio-based polymer can be in pure form or mixed with any additives. According to this embodiment, the tank (7) is equipped with a metering and mixing unit for the solid bio-based polymer. The addition of the solid bio-based polymer to the tank (7) is advantageous because the concentration of urea in the urea-containing aqueous solution (L) is comparatively high, and urea promotes the dissolution of bio-based polymers such as cellulose and related compounds in aqueous solutions.BE2025 / 5093 17

[0090] The dosing and mixing unit for solid bio-based polymer according to the invention can be any device which adds a specific amount of solid bio-based polymer to a liquid and produces a homogeneous dispersion and / or dissolves the solid bio-based polymer into the mass stream. Suitable devices are, for example, widely used in the food industry, e.g., the YTRON®-ZC powder dissolving system or the YTRON®-Y guide jet mixer (YTRON Process Technology, Bad Endorf, Germany).

[0091] Optionally, a urease inhibitor and / or a nitrification inhibitor can be added according to the embodiment shown in Figure 1 (not shown), preferably upstream of the particle unit (2), in the particle unit (2), immediately upstream of the pre-cooling unit (3), in the pre-cooling unit (3), immediately downstream of the pre-cooling unit (3), immediately upstream of the post-cooling unit (5), in the post-cooling unit (5), and / or immediately upstream of the product storage unit (10).

[0092] In further embodiments according to the invention, the solid bio-based polymer is added via a dosing and mixing unit for the solid bio-based polymer (9) into other plant components or flows (Figures 2-16). Unless otherwise specified, the units and material flows correspond to the reference symbols and functions previously mentioned in connection with Figure 1. Figure 2 schematically illustrates a preferred embodiment according to the invention, in which the addition of the solid bio-based polymer is carried out in a mass stream from the tank (7). The residence time of the urea-containing aqueous solution (L) in the tank (7) is not specified according to the invention. Since solutions of bio-based polymers such as cellulose may have a limited storage capacity due to, for example, gel formation, it may be advantageous to prepare the solution of the bio-based polymer immediately before its further use.For this purpose, according to the embodiment of the invention as schematically illustrated in Figure 2, a form-stable bio-based polymer is mixed in a separate dosing and mixing unit (9) with a partial stream of the urea-containing aqueous solution (L) from the tank (7). Another partial stream of the urea-containing aqueous solution (L) from the tank (7) is concentrated in the evaporation unit (8) and then combined with the solution containing the bio-based polymer. The combined mixture is then directed to the main urea feed immediately upstream of the particulate unit (2).

[0094] Optionally, a urease inhibitor and / or a nitrification inhibitor can also be added according to the embodiment shown in Figure 2 (not shown), preferably upstream of the particle unit (2), in the particle unit (2), immediately upstream of the pre-cooling unit (3), in the pre-cooling unit (3), immediately downstream of the pre-cooling unit (3), immediately upstream of the post-cooling unit (5), in the post-cooling unit (5), and / or immediately upstream of the product storage unit (10).

[0095] The urea-containing aqueous solution (L) from the tank (7) can have different compositions. Therefore, it can be advantageous to supply the dosing and mixing unit (9) with a concentrated urea-containing aqueous solution (L) from the evaporation unit (8) or from the main urea supply in order to ensure a desired composition of the mixture containing the bio-based polymer (Figure 3 and Figure 4).Figure 3 schematically illustrates a preferred embodiment according to the invention, in which the solid bio-based polymer is mixed in the dosing and mixing unit (9) with a mass flow of the urea-containing aqueous solution (L) from the tank (7) and a mass flow from the evaporation unit (8) to establish or maintain a desired urea concentration. The mixture is then directed into the main urea feed immediately upstream of the particle unit (2).

[0097] Optionally, a urease inhibitor and / or a nitrification inhibitor can also be added according to the embodiment shown in Figure 3 (not shown), preferably upstream of the particle unit (2), in the particle unit (2), immediately upstream of the pre-cooling unit (3), in the pre-cooling unit (3), immediately downstream of the pre-cooling unit (3), immediately upstream of the post-cooling unit (5), in the post-cooling unit (5), and / or immediately upstream of the product storage unit (10).

[0098] Figure 4 schematically illustrates a preferred embodiment according to the invention, in which the solid bio-based polymer in the dosing and mixing unit 30(9) is mixed with a mass stream of the urea-containing aqueous solution (L) from the tank (7) and a mass stream from the main urea feed immediately downstream of the synthesis and recovery unit (1) in order to establish or maintain a desired urea concentration. In principle, any partial stream originating from the synthesis and recovery unit (1) (in addition to the main stream) can also originate from a part of the synthesis and recovery unit (1), e.g., from a first evaporation stage (1a), an intermediate- The mixture is then fed into the urea main feed immediately upstream of the particle separator (2). (1b) and / or a second evaporation stage (1c) (not shown in Figure 4).

[0099] Optionally, a urease inhibitor and / or a nitrification inhibitor can also be added according to the embodiment shown in Figure 4 (not shown), preferably upstream of the particle unit (2), in the particle unit (2), immediately upstream of the pre-cooling unit (3), in the pre-cooling unit (3), immediately downstream of the pre-cooling unit (3), immediately upstream of the post-cooling unit (5), in the post-cooling unit (5), and / or immediately upstream of the product storage unit (10).

[0100] Not all urea particleization plants have a separate evaporation unit. Therefore, another evaporation unit is often used to concentrate urea-containing solutions, which is integrated into the synthesis and recovery unit (1) (Figure 5).

[0101] Figure 5 schematically illustrates a preferred embodiment according to the invention, in which the addition of the solid bio-based polymer to the urea-containing aqueous solution (L) is carried out without separate evaporation.To avoid contamination during urea synthesis, it is advantageous in such systems without a separate evaporation unit to feed a partial stream of the urea-containing aqueous solution (L) from the tank (7) to the dosing and mixing unit (9) and mix it with the solid bio-based polymer. The mixture is then directed into the main urea feed immediately upstream of the particulate unit (2). Another partial stream of the urea-containing aqueous solution (L) from the tank (7) is concentrated in the evaporation unit, which is integrated into the synthesis and recovery unit (1).

[0102] Optionally, a urease inhibitor and / or a nitrification inhibitor can also be added according to the embodiment shown in Figure 5 (not shown), preferably upstream of the particle unit (2), in the particle unit (2), immediately upstream of the pre-cooling unit (3), in the pre-cooling unit (3), immediately downstream of the pre-cooling unit (3), immediately upstream of the post-cooling unit (5), in the post-cooling unit (5), and / or immediately upstream of the product reservoir (10). BE2025 / 5093 20

[0103] To ensure better control over the urea concentration in the urea-containing aqueous solution, it may be advantageous to supply an additional partial stream from the main urea feed to the dosing and mixing unit (9) (Figure 6).Figure 6 schematically illustrates a preferred embodiment according to the invention, in which the addition of the solid bio-based polymer to the urea-containing aqueous solution (L) also takes place without separate evaporation, wherein a partial stream of the urea-containing aqueous solution (L) from the tank (7) and a partial stream from the main urea supply are fed to the metering and mixing unit (9) and 10 are mixed therein with the solid bio-based polymer. The mixture is then directed into the main urea supply immediately upstream of the particle unit (2). Another partial stream of the urea-containing aqueous solution (L) from the tank (7) is concentrated in the evaporation unit, which is located in the synthesis- and recovery unit(1) is integrated.15

[0105] Optionally, a urease inhibitor and / or a nitrification inhibitor may also be added in accordance with the embodiment shown in Figure 6 (not shown), preferably upstream of the particle unit (2), in the particle unit (2), immediately upstream of the pre-cooling (3), in the pre-cooling (3), immediately downstream of the pre-cooling (3), immediately upstream of the post-cooling (5), in the post-cooling (5), and / or immediately upstream of the product storage (10).

[0106] To reduce the amount of water in the urea-containing aqueous solution of the bio-based polymer, it may be advantageous to concentrate the mixture or solution in the evaporation unit (8). The metering and mixing unit for the solid bio-based polymer (9) is preferably arranged downstream of the tank (7) and upstream of the evaporation unit (8). In this way, the residence time of the bio-based polymer in the urea-containing aqueous solution before its further use in the particulateation can also be shortened (Figure 7).

[0107] Figure 7 schematically illustrates a preferred embodiment according to the invention, in which the addition of the solid bio-based polymer to the urea-30-containing aqueous solution (L) from the tank (7) takes place and is then concentrated in a separate evaporation unit (8). The mixture thus concentrated is then directed into the main urea feed immediately upstream of the particle unit (2). BE2025 / 5093 21

[0108] Optionally, a urease inhibitor and / or a nitrification inhibitor may also be added according to the embodiment shown in Figure 7 (not shown), preferably upstream of the particle unit (2), in the particle unit (2), immediately upstream of the pre-cooling (3), in the pre-cooling (3), immediately downstream of the pre-cooling (3), immediately upstream of the post-cooling (5), in the post-cooling (5), and / or immediately upstream of the product storage (10).

[0109] To reduce the amount of water in the urea-containing aqueous solution of the bio-based polymer, it may also be advantageous to supply a partial stream of the urea-containing aqueous solution (L) previously concentrated in the evaporation unit (8) to the dosing and mixing unit (9) and mix it with the solid bio-based polymer (Figure 8).

[0110] Figure 8 schematically illustrates a preferred embodiment according to the invention, in which the addition of the solid bio-based polymer is carried out in a partial stream from a separate evaporation unit (8). For this purpose, a partial stream 15 of the concentrated urea-containing aqueous solution (L) in the evaporation unit (8) is fed to the metering and mixing unit (9) and mixed therein with the solid bio-based polymer. The mixture is then combined with another partial stream of the concentrated urea-containing aqueous solution (L) in the evaporation unit (8) and finally directed into the main urea feed immediately upstream of the particle unit (2).

[0111] Optionally, a urease inhibitor and / or the nitrification inhibitor can also be added according to the embodiment shown in Figure 8 (not shown), preferably upstream of the particle unit (2), in the particle unit (2), immediately upstream of the pre-cooling unit (3), in the pre-cooling unit (3), immediately downstream of the pre-cooling unit (3), immediately upstream of the post-cooling unit (5), in the post-cooling unit (5), and / or immediately upstream of the product storage unit (10).

[0112] Alternatively, the entire mass flow of the urea-containing aqueous solution (L) previously concentrated in the evaporation unit (8) can be fed to the dosing and mixing unit (9) and mixed therein with the solid bio-based polymer. In this case, no division into partial flows takes place (Figure 9).

[0113] Figure 9 schematically illustrates a preferred embodiment according to the invention, in which the addition of the solid bio-based polymer is carried out in the entire mass flow from a separate evaporation unit (8).For this purpose, the entire mass flow of the previously concentrated urea-containing aqueous solution (L) from the tank (7) is fed to the dosing and mixing unit (9) in the evaporation unit (8) and mixed therein with the solid bio-based polymer. The mixture is then directed to the main urea feed immediately upstream of the particulate unit 5 (2).

[0114] Optionally, a urease inhibitor and / or the nitrification inhibitor can also be added according to the embodiment shown in Figure 9 (not shown), preferably upstream of the particle unit (2), in the particle unit (2), immediately upstream of the pre-cooling unit (3), in the pre-cooling unit (3), immediately downstream of the pre-cooling unit (3), immediately upstream of the post-cooling unit (5), in the post-cooling unit (5), and / or immediately upstream of the product storage unit (10).

[0115] To reduce the amount of water in the urea-containing aqueous solution of the bio-based polymer, it can also be advantageous to supply a partial stream of the main urea feed to the metering and mixing unit (9) (Figure 1510).

[0116] Figure 10 schematically illustrates a preferred embodiment according to the invention, in which the addition of the solid bio-based polymer is carried out in a partial stream from the main urea feed. For this purpose, a partial stream from the main urea feed is supplied to the metering and mixing unit (9) and mixed therein with the solid bio-based polymer. The mixture is then returned to the main urea feed immediately upstream of the particle unit (2).

[0117] Optionally, a urease inhibitor and / or the nitrification inhibitor can also be added (not shown) according to the embodiment shown in Figure 10, preferably upstream of the particle unit (2), in the particle unit (2), immediately upstream of the pre-cooling unit (3), in the pre-cooling unit (3), immediately downstream of the pre-cooling unit (3), immediately upstream of the post-cooling unit (5), in the post-cooling unit (5), and / or immediately upstream of the product storage unit (10).

[0118] Alternatively, the entire mass flow of the urea main feed can be fed to the dosing and mixing unit (9) and mixed therein with the solid bio-based polymer. There is then no division into partial flows (Figure 11).

[0119] Figure 11 schematically illustrates a preferred embodiment according to the invention, in which the addition of the solid bio-based polymer is made in the main urea feed, e.g. by an in-line dispersion system.For this purpose, the entire mass flow of the urea main feed is fed into the dosing and mixing unit (9) and mixed therein with the solid bio-based polymer. The mixture is then preferably combined with the concentrated urea-containing aqueous solution (L) in the evaporation unit (8) and directed to the particulate unit (2). 5

[0120] Optionally, a urease inhibitor and / or the nitrification inhibitor can also be added according to the embodiment shown in Figure 11 (not shown), preferably upstream of the particle unit (2), in the particle unit (2), immediately upstream of the pre-cooling (3), in the pre-cooling (3), immediately downstream of the pre-cooling (3), immediately upstream of the post-cooling (5), in the post-cooling (5), and / or immediately upstream of the product storage (10).

[0121] In the embodiments according to the invention as shown in Figures 1-4 and 7-9, the evaporation unit (8) can each consist of one or more evaporation stages independently of one another.In the case of multiple evaporation stages, further variations are preferred according to the invention (Figure 12-14). Figure 12 schematically illustrates a preferred embodiment according to the invention, in which the addition of the solid bio-based polymer takes place between different evaporation stages (8a) and (8b). A partial stream of the concentrated urea-containing aqueous solution (L) from the first evaporation stage (8a) is fed to the metering and mixing unit (9) and mixed therein with the solid bio-based polymer. The mixture is then combined with another partial stream of the concentrated urea-containing aqueous solution (L) from the first evaporation stage (8a) and fed to the second evaporation stage (8b). After further concentration in the second evaporation stage (8b), the mixture is fed into the The main urea supply is directed immediately upstream of the particle unit (2).25

[0123] Optionally, a urease inhibitor and / or the nitrification inhibitor can also be added (not shown) according to the embodiment shown in Figure 12, preferably upstream of the particle unit (2), in the particle unit (2), immediately upstream of the pre-cooling unit (3), in the pre-cooling unit (3), immediately downstream of the pre-cooling unit (3), immediately upstream of the post-cooling unit (5), in the post-cooling unit (5), and / or immediately upstream of the product storage unit (10).

[0124] Alternatively, the entire mass flow from the first evaporation stage (8a) can be fed to the metering and mixing unit (9) and mixed therein with the solid bio-based BE2025 / 5093 polymer. In this case, no division into partial flows takes place (Figure 13).

[0125] Figure 13 schematically illustrates a preferred embodiment according to the invention, in which the metering and mixing unit (9) is integrated into the evaporation section, downstream of the first evaporation stage (8a) and upstream of the second evaporation stage (8b).The entire mass flow from the first evaporation stage (8a) is fed to the dosing and mixing unit (9) and mixed therein with the solid bio-based polymer. The mixture is then further concentrated in the second evaporation stage (8b) and finally directed to the urea main feed immediately upstream of the particulate unit (2).

[0126] Optionally, a urease inhibitor and / or the nitrification inhibitor can also be added according to the embodiment shown in Figure 13 (not shown), preferably upstream of the particle unit (2), in the particle unit (2), immediately upstream of the pre-cooling unit (3), in the pre-cooling unit (3), immediately downstream of the pre-cooling unit (3), immediately upstream of the post-cooling unit (5), in the post-cooling unit (5), and / or immediately upstream of the product storage unit (10).

[0127] Figure 14 schematically illustrates a preferred embodiment according to the invention, in which the metering and mixing unit (9) is arranged downstream of the first evaporation stage (8a), wherein the concentrated urea-containing aqueous solution 20 in the first evaporation stage (8a) is subsequently divided into two partial streams. One partial stream from the first evaporation stage (8a) is fed to the metering and mixing unit (9) and mixed therein with the solid bio-based polymer. The mixture is then combined with another partial stream from the first evaporation stage (8a), which was previously further concentrated in the second evaporation stage 25 (8b). The metering and mixing unit (9) is thus in a A bypass is arranged around the second evaporation stage (8b). The mixture is finally directed into the main urea feed immediately upstream of the particle aggregation unit (2).

[0128] Optionally, a urease inhibitor and / or the nitrification inhibitor can also be added according to the embodiment shown in Figure 14 (not shown), preferably upstream of the particle unit (2), in the particle unit (2), immediately upstream of the pre-cooling unit (3), in the pre-cooling unit (3), immediately downstream of the pre-cooling unit (3), immediately upstream of the post-cooling unit (5), in the post-cooling unit (5), and / or immediately upstream of the product storage unit (10).

[0129] If the evaporation unit (8) has more than two evaporation stages, the embodiments illustrated in Figures 12-14 can preferably be extended analogously to each of the evaporation stages between the first evaporation stage and the last evaporation stage.

[0130] Figure 15 schematically illustrates a preferred embodiment according to the invention, in which the addition of the solid bio-based polymer is carried out in a mass stream from the tank (7) as well as a mass stream from the first evaporation stage (8a).For this purpose, the urea-containing aqueous solution (L) from the tank (7) is divided into partial streams, one of which is fed to the metering and mixing unit (9) and the other partial stream is fed to the first evaporation stage (8a) and concentrated therein. In the first evaporation stage (8a), a concentrated urea-containing aqueous solution is obtained, which is itself divided into partial streams, one of which is also fed to the metering and mixing unit (9) and the other partial stream is fed to the second evaporation stage (8b) and further concentrated therein, resulting in a further concentrated urea-containing aqueous solution. The metering and mixing unit (9) is thus supplied with the Partial flow of the urea-containing aqueous solution (L) from tank (7) and partial flow from the first evaporation stage (8a) are fed in and mixed with the solid bio-based polymer. The mixture is then directed into the main urea feed immediately upstream of the particle unit (2).The further concentrated urea-containing aqueous solution from the second evaporation stage (8b) is also directed into the main urea feed immediately upstream of the particle unit 25 (2). In this way, a constant concentration of urea can be maintained in the urea-containing aqueous solution of the bio-based polymer, because the partial stream from the first evaporation stage (8a), which is fed to the metering and mixing unit (9), has a higher concentration of urea than the partial stream of the urea-containing aqueous solution (L) from the tank (7), which is fed to the metering and mixing unit (9).

[0131] Optionally, a urease inhibitor and / or the nitrification inhibitor can also be added according to the embodiment shown in Figure 15 (not shown), preferably upstream of the particle unit (2), in the particle unit (2), BE2025 / 5093 26 immediately upstream of the pre-cooling unit (3), in the pre-cooling unit (3), immediately downstream of the pre-cooling unit (3), immediately upstream of the post-cooling unit (5), in the post-cooling unit (5), and / or immediately upstream of the product storage unit (10).

[0132] Figure 16 schematically illustrates a preferred embodiment according to the invention, in which the addition of the solid bio-based polymer to the main urea feed takes place without a separate evaporation unit (8).

[0133] Optionally, a urease inhibitor and / or the nitrification inhibitor can also be added (not shown) according to the embodiment shown in Figure 16, preferably upstream of the particle unit (2), in the particle unit (2), immediately upstream of the pre-cooling unit (3), in the pre-cooling unit (3), immediately downstream of the pre-cooling unit (3), immediately upstream of the post-cooling unit (5), in the post-cooling unit (5), and / or immediately upstream of the product storage unit (10).

[0134] Figure 17 schematically illustrates a preferred embodiment according to the invention, in which the synthesis and recovery units include, in addition to the urea synthesis stage (H2N-C(=O)-NH2), a recovery stage with a multi-unit

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