PROCESS FOR THE PRODUCTION OF FERTILIZER GRANULES

Description

[0001] The invention relates to a method for producing fertilizer granules by injecting starting materials into a moving particle tray using at least one multi-component nozzle, wherein the starting material is an acid and a suspension containing a phosphate-containing raw material, which are atomized as a spray jet in the moving particle tray by the multi-component nozzle, so that the starting materials react with each other in the spray jet and the fertilizer granules are formed in the spray jet.

[0002] Processes and equipment for the production of fertilizer granules have been state of the art for many years. Due to legal requirements and the decline of global phosphorus reserves, phosphorus recovery from phosphate-containing raw materials, such as ash from the mono- or co-incineration of sewage sludge, animal excrement, animal meal, animal remains and carcasses, and ash from the combustion of liquid manure and digestate as individual substances or mixtures thereof, is becoming increasingly important for industry.

[0003] German patent application DE 10 2009 020 745 A1 discloses a process for recovering valuable materials from sewage sludge products by extraction. This process involves preparing a suspension of the sewage sludge product in water, alcohol, a water / alcohol mixture, or an aqueous solution. Gaseous or supercritical carbon dioxide is introduced into this suspension as an extraction agent. Undissolved solids are separated from the liquid suspending agent, carbon dioxide is removed from the suspending agent, and valuable materials dissolved in the suspending agent are precipitated and separated from it. A disadvantage of this process is the very high cost and effort required to carry it out.

[0004] DE 10 2016 116 633 A1 discloses a process for producing fertilizer granules, wherein the phosphate-containing secondary raw material is mixed with a mineral acid to form a suspension, and the suspension is then subjected to granulation, as well as the fertilizer granules produced by the process. A disadvantage of this process is that the suspension processed into fertilizer granules contains raw material particles that are inert and tend to clog constrictions in devices such as nozzles.

[0005] EP 0 787 682 describes the use of multi-component nozzles for the production of sodium percarbonate in granular form in a spray jet of a fluidized bed.

[0006] US Patent 5,211,735 A discloses a process for fertilizer production in a tubular reactor, wherein phosphate-containing material is mixed with a mineral acid in the reactor and the reaction takes place under defined temperatures of 70 °C to 150 °C and pressures of approximately 2 bar to 5 bar. The resulting suspension is then granulated.

[0007] US patent 3,419,378 A also discloses a process for the production of monoammonium phosphate (MAP) by reaction of phosphoric acid and ammonia at about 3 bar.

[0008] In DE 43 29 205 A1 a process for the production of granular sodium percarbonate by fluidized bed spray granulation is shown.

[0009] The object of the invention is therefore to overcome the disadvantages known from the prior art and to provide a method with which fertilizer granules can be produced, whereby the fertilizer granules do not require large plant volumes for their production while achieving a high product quality.

[0010] The problem is solved by a process of the type mentioned above, whereby a grinding process of the suspension takes place in the moving particle reservoir before atomization as a spray jet. The particles generated and / or located in the fluidization apparatus are wetted or moistened by the atomized feedstock in the spray jet. The fertilizer granules are formed and further conditioned in the fluidized bed. For atomization, for example, one, two, three, four, five, six, etc. multi-component nozzles can be used. The moving particle reservoir is preferably a fluidized bed or a jet bed. The granules produced in a granulator (e.g., granulating disc, high-shear mixer, wet mixer, or the like) are also moving particle reservoirs in this sense. The reaction of the feedstock thus takes place directly in the spray jet in the moving particle reservoir, e.g.A fluidized bed is used instead, eliminating the need for a pre-processing external reaction in a reactor. This results in fewer plant components and consequently a smaller plant volume, for example, in the form of reactors. Investment costs are also reduced accordingly. Furthermore, the process is optimized for energy efficiency, as the heat of reaction is directly integrated into the process. Conditioning the individual feeds or lines, especially the suspension feed, is now very straightforward. This allows for processes such as the precipitation and separation of toxic substances like heavy metals, or the mixing and / or grinding of phosphate-containing raw materials.

[0011] Before being atomized as a spray jet into the moving particle reservoir, e.g., a jet or fluidized bed, the suspension undergoes a grinding process. This grinding process prior to granulation increases process stability by reducing the size of the phosphate-containing raw materials. This increases the reaction participation of the raw material particles by enlarging their surface area, thus accelerating the reaction kinetics. This, in turn, leads to a more uniform conversion of the phosphate-containing raw material and saves time. Simultaneously, the risk of clogging at constrictions in the equipment, particularly in nozzles, valves, and slides, is reduced. Furthermore, the grinding process minimizes sedimentation and the coarse sand content of the raw material particles.

[0012] Fertilizers are substances and mixtures of substances used in agriculture, forestry and horticulture to supplement the nutrient supply for cultivated plants, especially crops, with various properties, possibly combined and / or functionalized with other materials.

[0013] Fertilizer granules are fertilizers in granular form, in particular with an approximately spherical shape, preferably sufficient inherent strength and primarily an average granule size of 100 µ m to 25 mm, preferably from 100 µ m to 10 mm, particularly preferably from 250 µ m to 5 mm, especially preferred from 500 µ m to 3 mm.

[0014] In an advantageous embodiment of the process, the starting materials are atomized under the influence of an atomizing gas. In addition to supplying an atomizing gas for atomization, atomization using a pressure nozzle is also possible.

[0015] Preferably, the multi-component nozzle is designed as a three-component nozzle, in which two coaxially arranged outer tubes are arranged around a centrally located central tube. The acid is supplied to the central tube, the suspension to a first annular gap formed between the central tube and the first outer tube, and the atomizing gas to a second annular gap formed between the first and second outer tubes. Due to the aforementioned arrangement of the starting materials for the atomization process, the starting materials are ideally dispersed in the spray jet, the reactive surfaces are maximized, and they are mixed together, enabling them to react very effectively and rapidly.

[0016] According to a further advantageous development of the process, an additive is supplied to the multi-component nozzle via an additive inlet. Preferably, the multi-component nozzle is designed to atomize at least one additive in addition to the starting materials. The additive to the multi-component nozzle is preferably supplied in a further annular gap formed by arranging another coaxial sheathing tube around the central tube.

[0017] According to a further advantageous embodiment of the process, the suspension is formed from a phosphate-containing raw material and an aqueous solution, water, and / or an acid. When the suspension is formed from a phosphate-containing raw material and an acid, the acid already begins to break down the phosphates during the suspension's feed to the multi-component nozzle, thus improving the reaction in the spray jet and enabling the dissolution of further phosphates.

[0018] According to an advantageous further development of the process, the acid is a mineral acid, preferably hydrochloric acid, sulfuric acid, nitric acid or phosphoric acid, or any mixture of the mineral acids.

[0019] The grinding process is preferably carried out as dry and / or wet grinding. Dry grinding offers the advantages of high grinding efficiency with a small footprint and low specific energy consumption. With dry grinding, the desired final particle size of the phosphate-containing raw material can be freely and precisely adjusted. With wet grinding, even coarse phosphate-containing raw materials can be processed with low specific energy consumption. Furthermore, the agitator bearing does not come into contact with the product. A combination of dry and wet grinding allows for the re-grinding of suspensions and dry raw materials. This offers the advantages of significantly reduced overall energy consumption, increased throughput with consistent product fineness, or alternatively, an increase in product fineness with consistent throughput.Furthermore, the combination of dry and wet grinding makes the use of continuous and discontinuous mills possible.

[0020] The grinding process is particularly preferably carried out before, during, and / or after the production of the suspension. If the grinding process is carried out before the suspension is produced, it is performed as dry grinding of the phosphate-containing raw materials. In contrast, wet grinding of the phosphate-containing raw materials is used during and / or after the suspension is produced in the suspension feed, preferably designed as a reactor unit, e.g., a tubular reactor. In a combination of dry and wet grinding in the process, the grinding process takes place both before and during and / or after the suspension is produced in the suspension feed. The use of different grinding methods allows the plant engineer to adapt the process to the different phosphate-containing raw materials and to always optimally adjust the process to the specific phosphate-containing raw materials.

[0021] In a further advantageous embodiment of the process, the suspension is mixed by a mixing unit before being atomized as a spray jet in the moving particle reservoir. Particularly in reactions such as the breakdown of phosphates from phosphate-containing raw materials by acid, ensuring contact between the reactants is of utmost importance. The mixing unit therefore preferably comprises a mixing element, which is most preferably designed as a static mixer. Static mixers are devices with stationary internal components that use the flow energy to mix fluid product streams, such as the suspension in this case.

[0022] Advantageously, the suspension is produced by adding or removing heat. Adding or removing heat allows for particularly effective control of temperature changes resulting from exothermic or endothermic reactions, ensuring that the desired reaction conditions are always met and thus enabling optimal control over the process.

[0023] According to a further advantageous embodiment of the process, the sparingly soluble phosphates of the phosphate-containing raw material are at least partially dissolved in the spray jet and converted into a neutral ammonium citrate-soluble phosphate phase, resulting in a fertilizer granule whose P₂O₅ content is greater than 75% neutral ammonium citrate-soluble. The solubilities provide indications of the respective fertilizer's dynamic effect. The acid-soluble phosphorus fraction of fertilizers is considered usable over the long term. Long term here means over several crop rotations. This phosphorus fraction soluble in aqua regia is referred to as the total content. The neutral ammonium citrate-soluble phosphorus fraction can be used as an indicator of the medium-term availability of phosphate, i.e., over the period of approximately one crop rotation. The immediately available phosphorus fraction of a fertilizer is described by its solubility in water.The higher the water-soluble content, the faster and more readily the fertilizer phosphorus is available to the plant. The primary purpose of solubility values ​​is to characterize specific phosphate fertilizers, i.e., to describe their defining components.

[0024] According to a preferred method, the phosphate-containing raw material is classified before the suspension is produced. Classification is preferably carried out by sieving or screening. This achieves not only the removal of coarse waste but also a pre-selection of the phosphate-containing raw material particles to be processed further, resulting in a particularly high-quality fertilizer granulate, as only raw material particles with a specific maximum diameter are processed. The phosphate-containing raw material is separated into fractions, preferably according to particle size or particle density, with the aim of producing at least two subsets of the original phosphate-containing raw material, each subset meeting the specified particle size criteria for further processing as completely as possible.

[0025] Preferably, the pH of the suspension is adjusted before or during atomization as a spray jet in the moving particle feed to control the stickiness of the suspension or the resulting fertilizer granules. For this purpose, the actual pH of the suspension is preferably measured in the reactor unit after the grinding process. This measurement is then compared to a target pH value specified for the process, particularly spray granulation, and adjusted accordingly in a pH control unit. This is achieved by adding an acid or an alkali to the suspension to adjust the pH in the spray jet. Thus, pH control, for example using a pH control unit, makes it possible to adjust the pH in the spray jet of the moving particle feed, especially a fluidized bed.Adjusting the pH value in the spray jet of the moving particle feed directly affects the stickiness of the reacting components and is crucial for atomization. The pH control can also be implemented as an additional external control loop. The more acidic the pH value, the stickier the reacting components.

[0026] According to a further advantageous development of the process, the process is carried out in a fluidized bed or jet layer.

[0027] Following a further advantageous embodiment of the process, the process is carried out in a mixer or a mechanical granulator. In particular, the process is carried out, for example, in a granulating disc, a high-shear mixer, a wet mixer, or the like.

[0028] Further advantages and advantageous embodiments of the invention can be found in the following description and the claims.

[0029] The invention will now be explained in more detail with reference to the accompanying drawing, which shows Figure 1 is a basic flow diagram of a first embodiment of the preferred method, Figure 2 is a schematic bottom view of a multi-component nozzle designed as a three-component nozzle, Figure 3 is a basic flow diagram of a second embodiment of the preferred method and Figure 4 is a basic flow diagram of a third embodiment of the preferred method.

[0030] In the following exemplary embodiments, the process is illustrated using a moving particle feed configured as a fluidized bed. Other embodiments, not illustrated, feature, as previously described, jet sheets or moving granules in granulators as moving particle feeds.

[0031] This, in advance, shows Fig. 1 a basic flow diagram of a first embodiment of the preferred process for the production of fertilizer granules.

[0032] To produce fertilizer granules, one batch of raw materials is fed into a multi-component nozzle for atomization into a fluidized bed formed in a fluidization chamber of a fluidization apparatus. The fluidization apparatus is preferably designed as a fluidized bed or jet bed apparatus.

[0033] The starting materials used in the multi-component nozzle 1 are an acid supplied via an acid inlet 2 and a suspension containing a phosphate-containing raw material supplied via a suspension inlet 3.

[0034] The acid used as a starting material is preferably a mineral acid, namely hydrochloric, sulfuric, nitric, or phosphoric acid, or any mixture of these mineral acids. Mineral acids react very well with the phosphates contained in the phosphate-containing raw material in the fluidized bed spray and convert them.

[0035] Phosphate-containing raw materials include, for example, ash from the mono- or co-incineration of sewage sludge, animal excrement, animal meal, animal remains and carcasses, ash from the combustion of liquid manure and digestate as individual substances or mixtures thereof, which are becoming increasingly important for industry, or any mixtures thereof. In the first embodiment, the suspension is formed from the phosphate-containing raw material and water as a slurry.

[0036] Additionally, an atomizing gas is supplied to the multi-fuel nozzle 1 via an atomizing gas supply line 4.

[0037] The multi-component nozzle 1 atomizes the starting materials as a spray jet 5 in the fluidized bed under the influence of the atomizing gas, so that the starting materials supplied to the multi-component nozzle 1, which is designed as a three-component nozzle 6, react with each other in the spray jet 5 and the fertilizer granules are formed in the spray jet 5 of the fluidized bed.

[0038] The resulting fertilizer granules are then discharged from the fluidizing unit. Specifically, the discharge occurs via a classifying finished product discharge, ensuring that only fertilizer granules meeting the required minimum size are discharged.

[0039] A schematic bottom view of the multi-component nozzle 1 used in the first embodiment is shown in Fig. 2 depicted.

[0040] In the first embodiment, the multi-component nozzle 1 is designed as a three-component nozzle 6, in which two coaxially arranged outer tubes 8, 9 are arranged around a centrally located central tube 7. The acid is supplied to the central tube 7, the suspension to a first annular gap 10 formed between the central tube 7 and the first outer tube 8, and the atomizing gas to a second annular gap 11 formed between the first outer tube 8 and the second outer tube 9. This arrangement of the inlets or supply lines in the multi-component nozzle 1 ensures an optimal reaction of the reactants in the spray jet of the fluidized bed. The atomizing air atomizes the reactants and simultaneously brings them into contact in such a way that a reaction can take place between them.

[0041] Fig. 3 Figure 1 shows a basic flow diagram of a second embodiment of the preferred method for producing fertilizer granules with a multi-component nozzle 1 also designed as a three-component nozzle 6.

[0042] In contrast to the method described in the first embodiment, the suspension feed 3 has a grinding unit 12. The grinding process in the grinding unit 12 comminsulates or grinds the phosphate-containing raw materials in the suspension in the suspension feed 3. This results in a more homogeneous solid particle size of the phosphate-containing raw materials in the suspension.

[0043] In the Fig. 4 A basic flow diagram of a third embodiment of the preferred method for producing fertilizer granules is shown.

[0044] Unlike in Fig. 3In the second embodiment of the preferred method shown and described, the suspension inlet 3 has, in addition to the grinding unit 12, a mixing unit 13. This is arranged upstream of the grinding unit 12 in the suspension inlet 3. To ensure thorough mixing of the suspension in the suspension inlet 3, the mixing unit 13 includes a mixing element 15 designed as a static mixer 14. The static mixer 14 uses stationary internal components to effect mixing of the suspension through the flow energy.

[0045] In the third embodiment, the suspension is produced from the phosphate-containing raw material and an acid, in particular a mineral acid.

[0046] In addition to mixing and grinding the suspension containing phosphate-containing raw materials, it is possible to carry out further conditioning processes, e.g. precipitation and / or separation of the heavy metals from the suspension.

[0047] Furthermore, in the third embodiment, the multi-component nozzle 1 is configured as a four-component nozzle 16. Here, one or more additives are supplied to the multi-component nozzle 1 via an additive inlet 17. The additive is fed to the multi-component nozzle 1, configured as a four-component nozzle 16, into a further annular gap created by arranging another coaxial sheathing tube around the central tube 7. Multiple additive inlets are also conceivable.

[0048] Additives include, for example, binders for adjusting the hardness of fertilizer granules or fertilizer additives such as urea, ammonium sulfate salts, or nutrient components. Nutrient components are all substances that provide or supplement the nutrient supply for the cultivated plants in order to control and / or support plant growth and development. These include, for example, components containing nitrogen (N), phosphorus (P), potassium (K), magnesium (Mg), sulfur (S), and / or essential trace elements.

[0049] An acid or an alkali is supplied to the multi-component nozzle 1 via the acid inlet 2 to adjust the pH value in the spray jet. For this purpose, the actual pH value after the grinding process in the suspension flowing in the suspension inlet 2 is preferably measured and then compared with a target pH value specified for the process, in particular spray granulation, in a pH control unit 18 and adjusted accordingly. The more acidic the pH value, the stickier the reacting starting materials are. By means of pH control, e.g., using the pH control unit 18, it is thus possible to adjust the pH value in the spray jet of the fluidized bed. This adjustment of the pH value in the spray jet of the fluidized bed affects the stickiness of the reacting starting materials and is of great importance for atomization.

Claims

1. Method for the production of fertilizer granules by injecting raw materials by means of at least one multi-substance nozzle (1) into a moving particle bed, wherein an acid and a suspension comprising a phosphate-containing raw material are used as raw materials, which are atomized by the multi-substance nozzle (1) as a spray (5) in the moving particle bed, characterized in that the raw materials react with one another in the spray (5) and the fertilizer granules are formed in the spray (5), with a grinding process of the suspension taking place before the atomization as a spray (5) in the moving particle bed.

2. Method according to claim 1, characterized in that the raw materials are atomized in presence of an atomizing gas, the multi-substance nozzle (1) being expediently designed as a tri-substance nozzle (6) in which two coaxially arranged cladding tubes (8, 9) are arranged around a centrally arranged central tube (7), wherein the acid is fed to the central tube (7), the suspension is fed to a first annular gap (10) that is formed between the central tube (7) and the first cladding tube (8), and the atomizing gas is fed to a second annular gap (11) that is formed between the first cladding tube (8) and the second cladding tube (9).

3. Method according to one of claims 1 or 2, characterized in that at least one additive is fed to the multi-substance nozzle (1) via an additive feed (17), the multi-substance nozzle (1) being expediently designed to atomize at least one additive in addition to the raw materials.

4. Method according to claim 3, characterized in that the additive is fed to a further annular gap of the multi-substance nozzle (1), which annular gap is formed by arranging a further coaxial cladding tube around the central tube (7).

5. Method according to one of the preceding claims, characterized in that the suspension is formed from phosphate-containing raw material and an aqueous solution, water and / or an acid.

6. Method according to one of the preceding claims, characterized in that the acid is a mineral acid, preferably hydrochloric acid, sulfuric acid, nitric acid or phosphoric acid, or any mixture of the mineral acids.

7. Method according to one of the preceding claims, characterized in that the grinding process is conducted as dry grinding and / or wet grinding.

8. Method according to one of the preceding claims, characterized in that the grinding process takes place before, during and / or after the production of the suspension.

9. Method according to one of the preceding claims, characterized in that the suspension, prior to atomization as a spray (5), is thoroughly mixed in the moving particle bed by means of a mixing unit (13).

10. Method according to one of the preceding claims, characterized in that the suspension is produced with heat being added or removed.

11. Method according to one of the preceding claims, characterized in that the poorly soluble phosphates of the phosphate-containing raw material are at least partially dissolved in the spray (5) and converted into a phosphate phase soluble in neutral ammonium citrate, so that fertilizer granules are formed whose P2O5 content is greater than 75% soluble in neutral ammonium citrate.

12. Method according to one of the preceding claims, characterized in that the phosphate-containing raw material is classified before the suspension is produced, the classification being expediently carried out by means of screens or sifting.

13. Method according to one of the preceding claims, characterized in that a pH-value of the suspension is adjusted before or during the atomization as a spray (5) in the moving particle bed in order to adjust a stickiness of the suspension, wherein an acid or a base is expediently fed to the suspension for adjusting the pH-value in the spray (5).

14. Method according to one of the preceding claims, characterized in that the method is conducted in a fluidized bed or spouted bed.

15. Method according to one of the preceding claims, characterized in that the method is conducted in a mixer or a mechanical granulator.