Water-soluble solid continuous granulation process

Abstract

The invention relates to the field of chemical engineering and to a method for the continuous granulation of water-soluble solids. The method implements the following steps: a) feeding raw material and seed particles to a granulation pan; b) granulating the water-soluble solids during wetting with an aqueous phase; c) removing the granulation product from the granulation pan; d) drying the granulation product obtained in step c); e) dividing the dried granulation product obtained in step d) into several portions; removing the marketable portions obtained in this process. In step e), the dried granulation product obtained in step d) is divided into four portions: a marketable portion, a coarse fraction, a recycling portion and a fine fraction, in order to stabilize the granulation process without having to constantly adjust the process parameters.

Description

[0001] This invention relates to the field of chemical engineering, and particularly to a method for continuous granulation of water-soluble solids, comprising the following steps: a) feeding raw materials and seed particles into a granulation pan; b) granulating the water-soluble solids during wetting with an aqueous phase; c) removing the granulated product from the granulation pan; d) drying the granulated product obtained in step c); e) dividing the dried granulated product obtained in step d) into several portions; f) removing the commercially available portion obtained in this process, characterized in that in step e), the dried granulated product obtained in step d) is divided into four portions: a commercially available portion with a particle diameter ranging from D1 to D2; a coarse portion with a particle diameter > D2; and a portion with a particle diameter ranging from D1 to D2. The recycling section to D1; and the range of particle diameter is < The fine-grained portion; wherein, the recycled portion is supplied as seed particles to the raw material in step a), and the coarse-grained portion is ground to a particle size of... Within the range of D1, the process is then recycled to the raw material supply step a), where the fine particles are ground until no particles larger than the raw material particle size are found, and the process is also recycled to the raw material supply step a), wherein the raw material particle size is <

[0002] Beyond addressing the issues of standard chemicals, the production of bulk chemicals is also related to the need to impart the properties most desired by consumers to the finished product. A recent trend is that consumers prefer granulated bulk products with clearly controlled particle size distributions, as they perceive this as significantly simplifying further processing steps and providing economic advantages related to logistics and storage. Therefore, the development of granulation technologies for bulk chemicals is receiving increasing attention from manufacturers.

[0003] One of the most focused areas in the development of granulation technology is agriculture, as the granulation step is often critical in the production of mineral fertilizers. This is because powdered fertilizers, especially hygroscopic powdered fertilizers, have poor flowability and are dispersed very unevenly due to the adhesion of small crystals. Furthermore, powdered fertilizers tend to clump and harden severely, requiring significant labor for re-grinding. Fertilizer granulation is the most effective method to reduce clumping and improve fertilizer dispersibility. Regardless of the improvement in physical properties, granulation significantly enhances the agrochemical value of fertilizers, particularly water-soluble phosphates.

[0004] In addition, granulated fertilizers allow for the creation of nutrient-balanced compound fertilizer mixtures before application to crops, resulting in products with planned quantity and quality.

[0005] Currently, the development of granulation technology for bulk chemical products aims to reduce production costs, increase productivity, and improve the quality of the resulting products, particularly to obtain a finished product with a given particle size distribution and the highest possible yield, the so-called "commercially available portion".

[0006] The standard granulation process for bulk products includes the following steps: layering a liquid phase and / or a wetted solid phase on the surface of a so-called recycled product comprising small particles of a certain size; drying and / or cooling steps to stabilize the granule structure; classifying the granulated material and separating granules of the desired size (commercially available portion); crushing the coarse portion and recycling the resulting fine portion back to the granulator as a recycled product.

[0007] In the granulation process, the pellets typically have a fairly wide size distribution at the pellet mill outlet. Pellets with the required size range form the "commercially available portion", pellets larger than the required size form the "coarse portion", and small pellets form the "fine portion".

[0008] Granulation processes are highly unstable and are affected by many factors, from equipment performance to the composition and moisture content of raw materials. This can lead to two scenarios: fluctuations in the ratio of commercially available fraction to coarse and fine fractions, and the complete termination of the process due to a lack of commercially available fractions.

[0009] In this regard, an important issue is the need to provide the ability to control particle size distribution in order to obtain granulated products that are stable in both size and physicochemical properties.

[0010] Several methods for controlling the granulation process are known in the existing technology.

[0011] For example, when producing granulated ammonium phosphate, in order to control the granulation mode, the inventors of Russian Patent No. 2455228 proposed selecting certain process parameters, in particular, performing two-step granulation while controlling the moisture content of the slurry.

[0012] Russian Patent No. 2450854 discloses a method for producing granulated ammonium phosphate, wherein the granulation process is controlled by changing the density of the recycled product curtain during the slurry spraying and feeding pelletizing steps, as well as the feed residence time in these steps.

[0013] Russian Patent No. 2631073 discloses a method for producing granulated wood ash, comprising the following steps: forming granules with simultaneously supplied powder and liquid components, further drying the granules, and simultaneously sieving out wood ash with a particle size up to 1.5 mm for use as granules. The pelletizing is carried out in a disc pelletizer, the liquid component is water, and the bulk density is 560 kg / m³. 3 Up to 600kg / m3 Dried wood ash was used as the powder component. Particle size distribution was controlled by changing the tilt angle of the granulation disc, its rotation speed, and the water-ash ratio ranging from 0.27 to 0.29.

[0014] The above methods are effective, and the desired granulated product can only be obtained by strictly adhering to the process parameters. However, in large-scale production, process interruptions are inevitable due to the input raw materials and equipment operation. To adjust the particle size distribution of the finished product, it is necessary to change the process parameters.

[0015] Another method for controlling a granulation process is known in the prior art, as described in an embodiment of a continuous granulation method in U.S. Patent No. 4,501,773. This method includes: (a) injecting droplets of a liquid, viscous, hardened substance into a gas stream; (b) passing the gas stream containing the droplets through solid seed particles in a granulator (c) and obtaining enlarged seed particles at the granulator outlet (d) to control the particle size distribution of the finished product. The method proposes dividing the granulated particles into three portions: (i) a final granulated product with a particle size range within a desired particle size range; (ii) a finer granulated product with a particle size range below the desired particle size range; and (iii) a coarser granulated product with a particle size range exceeding the desired particle size range. The final granulated product is then discharged. The finer powder or granulated product (part A) is transferred to a first tank for storage. The coarser granulated product is transferred to a second tank for storage. A portion of the coarser granulated product stored in the second tank is removed and crushed, reducing the average particle size to be smaller than that of portion A. These particles are then recycled back into the granulator, and the final feed particle size distribution is controlled by varying the flow rate ratio between the first and second tanks.

[0016] The drawback of this method is that the control is only applied if the process deviates from specified parameters during continuous, automated analysis of the emitted products. Furthermore, a specific algorithm is required to change the particle ratio supplied as recycled products in the first and second tanks. The inventors themselves noted that if the change in the recycled particle ratio is not timely, the composition may fluctuate. Therefore, this method involves a highly complex control system that requires continuous monitoring by automation and maintenance personnel.

[0017] The closest prior art to this invention is Russian Patent No. 2545328C1, which discloses a method for controlling the granulation process of phosphorus fertilizers, comprising the following steps: dividing the granulated material into a fine-grained portion, a commercially available portion, and a coarse-grained portion, grinding the coarse-grained portion, and recycling the fine-grained portion, the crushed coarse-grained portion, and a portion of the commercially available portion into two streams, one of which is ground, and the stream is selected to the amount required to obtain a feed with a given equivalent particle size. However, the disadvantage of this method is that using a portion of the commercially available portion as a recycling product significantly reduces the yield of the finished product. In addition, due to changes in particle size distribution, continuous monitoring of the process is required, and if not done in a timely manner, it can lead to changes in the ratio of recycled particles, resulting in wavy component fluctuations.

[0018] Therefore, the object of the present invention is to provide a method for continuous granulation of water-soluble solids that is stable and does not require adjustment of production parameters during the granulation process, does not require recycling of a portion of the commercially available portion, but produces a product with a constant particle size distribution and a near-quantitative yield for the input starting material.

[0019] This problem is solved by a method for the continuous granulation of water-soluble solids, the method comprising the following steps:

[0020] a) Supply raw materials and seed pellets to the granulation tray;

[0021] b) Granulate water-soluble solids during wetting with the aqueous phase;

[0022] c) Remove the granulated product from the granulation tray;

[0023] d) The granulated product obtained from drying step c);

[0024] e) Divide the dried granulated product obtained in step d) into several parts;

[0025] f) Remove the commercially available portion obtained from this process;

[0026] The characteristic feature is that, in step e), the dried granulated product obtained in step d) is divided into four parts:

[0027] The commercially available portion of the granule diameter ranges from D1 to D2.

[0028] The coarse-grained portion with a particle diameter greater than D2;

[0029] The range of particle diameter is The recirculation portion to D1;

[0030] The fine-grained portion;

[0031] The characteristic is that the recycled portion is supplied as seed particles in step a), and the coarse portion is ground to a particle size of [missing information]. Within the range of D1, the process is then recycled to the raw material supply step a), where the fine particles are ground until no particles larger than the raw material particle size are found, and the process is also recycled to the raw material supply step a), wherein the raw material particle size is <

[0032] The proposed method for continuous granulation of water-soluble solids stabilizes the granulation process without requiring constant adjustments to production parameters or recycling of a portion of the commercially available product. Instead, it supplements the recycled product with coarse particles and provides a finished product with a particle size distribution that remains constant over time while ensuring a substantially quantitative yield for the input starting material. This increases economic profitability and the usability of the granulation process, particularly for industrial-scale production of water-soluble solids.

[0033] The method according to the invention is based on the following concept: in a solid granulation process, only particles with a size significantly smaller than that of the recycled particles can adhere to the recycled particles, while such adhesion will not occur when the size of the particles is close to that of the recycled particles.

[0034] Based on this, we believe that in continuous granulation processes, the continuous recycling of a portion of the granulated material back into the process leads to a continuous increase in particles slightly smaller than the recycled particles in the granulation product circulation loop. This results in insufficient adhesion, affecting the particle distribution within the granulator and consequently causing variations in particle size distribution and a reduction in the required commercially available quantity. To stabilize the process, facility operators attempt to change process parameters (such as the aqueous feed rate, granulation disc tilt angle, and rotational speed). In the first stage, this stabilizes the situation; however, the number of particles slightly smaller than the recycled particles continues to increase, and the process deviates from the desired particle size distribution again, necessitating further changes to process parameters. Therefore, the continuously generated undulating fluctuations should be leveled by the operator or the automatic control system.

[0035] Based on this concept, when recycling the fine fraction to the granulator, we propose removing particles slightly smaller than the recycled particles from the granulation product recycling loop. Specifically, when operating on a commercially available fraction within a desired range, expressed as D1 to D2 in terms of particle diameter, the particle size (diameter) range of the recycled fraction is... To D1, therefore it is necessary to start from Remove the fine particles with a size of to The particles. This removal is achieved through... This process is carried out in parts until no particles larger than the starting material are found. In addition, in order to further reduce the amount of granulator to This portion of the content can be determined by grading the raw materials before they enter the granulator, and the selected size can be > The particles are ground together with the recycled fine particles.

[0036] Therefore, the technical effect of the present invention is that there is no accumulation of the following particles in the granulation product recycling loop: particles that do not participate in the process of forming granules from the recycled particles, but interfere with the establishment of stable conditions required to form the desired particle size distribution. Thus, the present invention enables the reduction of equipment burden in the method and maximizes the use of production resources for the product, while improving the yield of the finished product.

[0037] According to the present invention, any solid material suitable for agglomeration and pelletizing when wetted with an aqueous phase in a granulator can be used as a water-soluble solid in the method.

[0038] In a preferred embodiment of the method according to the invention, the water-soluble solid is a mineral salt.

[0039] In a particularly preferred embodiment of the method according to the invention, the water-soluble solid is a sodium, potassium, or ammonium nitrate, sulfate, or chloride.

[0040] In the most preferred embodiment of the method according to the invention, the water-soluble solid is ammonium sulfate.

[0041] In another preferred embodiment of the method according to the invention, the water-soluble solid is a mineral fertilizer, particularly a mixture of mineral fertilizers.

[0042] Specifically, according to the method of the present invention, urea, magnesium sulfate, potassium sulfate, sodium sulfate and the following mixtures can be granulated: (NH4)2SO4-NH4NO3, KCl-(NH4)2SO4-NH4NO3-ammophos, KCl-(NH4)2SO4-ammophos, KCl-ammophos, KCl-H3BO3.

[0043] In the preferred embodiment, the range of commercially available portions D1-D2 corresponds to the following conditions: Where D1 ≥ 0.2 mm. In a particularly preferred embodiment, the diameter D1 ranges from 0.2 mm to 10.0 mm, and the diameter D2 ranges from 0.8 mm to 11.8 mm.

[0044] In the method according to the invention, water, an aqueous solution of the granulating material, an aqueous solution of a mixture of granulating materials, or an aqueous solution of one or more substances other than the granulating material may be used as the aqueous phase.

[0045] The method according to the invention can be carried out on standard industrial equipment known to those skilled in the art of chemical engineering.

[0046] In a preferred embodiment, the fine particles are ground in a vortex mill, and the raw material is also ground in the vortex mill if necessary. Alternatively, any other standard grinding equipment known to those skilled in the art, such as a tube mill, can be used instead of a vortex mill.

[0047] According to the present invention, the granulation step is carried out on a conventional disc granulator, which is equipped with an aqueous phase supply line for spray feeding.

[0048] In the method according to the invention, preferably, the step of drying the granulated mixture obtained after granulation in a fluidized bed dryer is included. A fluidized bed dryer may be omitted, and any other standard drying equipment, such as a drying drum, may be used; however, the choice of a fluidized bed dryer is based on economic factors, as fluidized bed dryers offer significantly higher drying rates.

[0049] According to the present invention, the step of dividing dried granulated product into several parts is carried out by two-step classification on a vibrating screen with a different number of screening levels. In the first step of the two-step classification, the dried granulated feed is divided into a commercially available part, a coarse part, a recyclable part, and a fine part using a vibrating screen with a three-stage sieve; in the second step of the two-step classification, the crushed coarse part is screened on a vibrating screen with a single-stage sieve.

[0050] In addition, the fine particles from the pulverization are classified in a pneumatic classifier before being fed to the granulator, and this can also be done to the raw materials if necessary.

[0051] If the raw materials supplied contain a very small amount of particles with a particle size of to The portion that can be processed can be fed to the granulator without grinding and grading. In this case, the graded and ground fine particles are fed into the granulator simultaneously with the raw material.

[0052] However, in a preferred embodiment, the method according to the invention includes an additional step of pulverizing and classifying the raw material before feeding it to the granulation disc. In a particularly preferred embodiment of the method, the raw material is pulverized and classified together with a recycled fine fraction, and the resulting combined raw material is fed to the next process step.

[0053] Figure 1The flowchart illustrates the process according to the present invention, including additional steps of grinding the raw materials and classifying them.

[0054] Based on this diagram, the method is implemented as follows.

[0055] The initial water-soluble solids are fed into the vortex mill. After the granulation feed is sieved and classified, the fine particles are also fed into the vortex mill. Grinding takes place in the vortex mill. The ground powder enters the air duct from the mill, where a circulating airflow generated by a fan transports it to the pneumatic classifier. The pneumatic classifier provides the final separation of particles larger than the size unsuitable for granulation. The portion and the particle size of the raw material used in the disc granulator are smaller than The portion with a particle size exceeding [a certain value]. Part of it is poured into the loading tube of the vortex mill through the gate valve and sent for regrinding.

[0056] The portion suitable for granulation is conveyed via an airflow to a stacked cyclone separator, where it is separated from the air and collected in the cyclone separator hopper. The powder is then conveyed from the hopper to a disc granulator via a screw conveyor. Furthermore, the powder is sieved and classified to a particle size of [missing information]. The recycled product from D1 is also supplied to the disc granulator. The granulation feed in the disc granulator is sprayed with the water phase.

[0057] In the granulator, fine particles are fed to the spray zone via scrapers. Coarse particles roll on the disc surface and are unloaded from the disc side after reaching a certain size; while fine particles are fed to the solid component supply zone and spray zone under the influence of centrifugal force for further agglomeration and pelletizing.

[0058] The wet granular flow passes through the disc side into an inclined chute, and then into a fluidized bed (FB) dryer, where the chute has a fluoroplastic liner to prevent the wet feed from adhering.

[0059] The drying process occurs by transferring heat from steam to the product through a tubular submerged heat exchanger. The equipment uses wet steam at a pressure of 10 atm (T = 183°C). The upward flow velocity within the dryer is maintained by supplying the required volume of air. Air at a temperature of 90°C to 140°C enters the drying zone of the FB dryer.

[0060] The granules are dried such that the product obtained at the dryer outlet has a temperature of 90°C to 140°C and a moisture content of no more than 0.5% by weight. The hot product enters the lower fluidized bed of the FB dryer through a vertical valve, where it is cooled by workshop air.

[0061] A fan is used to supply workshop air to the FB dryer through a perforated furnace to cool the product to 65°C to 70°C. The workshop air passes through a heat generator, where it is heated to a temperature of 90°C to 140°C, and then enters the drying zone of the FB dryer.

[0062] The pellets leaving the dryer are classified on two vibrating screens. The first screen has three stages of mesh. On the first screen, the pellets are divided into four fractions:

[0063] - A coarse fraction with a pellet diameter > D2;

[0064] - A commercially available fraction with a pellet diameter ranging from D1 to D2;

[0065] - The pellet diameter ranges from to D1, which is a recycle fraction;

[0066] - of fine fraction.

[0067] The screened fine fraction is fed via a pipeline to the start of the process for grinding in a vortex mill.

[0068] The screened coarse fraction is fed to a pulverizer, where it is pulverized into smaller sizes. The product pulverized in the pulverizer is fed to a second screen with one stage of mesh for screening. On the second screen, the pulverized pellets are divided into two fractions:

[0069] - A fraction with a pellet diameter > D1;

[0070] - A fraction with a pellet diameter < D1.

[0071] The fraction with a pellet diameter < D1 is fed to the first screen to re-screen out the size of to D1 as recycle pellets. The screened fraction with a pellet diameter > D1 is recycled to the pulverizer for re-pulverization. Thereby, a closed pulverizer-screen loop is formed, which processes the coarse pellets into recycle pellets, thus ensuring a sufficient amount of recycled product in the process.

[0072] The resulting recycle fraction is supplied to a disc granulator as seed particles.

[0073] When required, the commercially available fraction is supplied to a step of post-treating the pellets with an anti-caking agent, and then supplied to the finished product hopper.

[0074] The present invention is further illustrated in more detail by the examples.

[0075] Example

[0076] Example 1. Granulation of ammonium sulfate by means of the method according to the present invention.

[0077] The following main devices are used as equipment:

[0078] • Perlman PSKM 15-720 vortex mill (500×2400×2400mm, D=1500mm, motor N=315-500kW);

[0079] • Disc granulator D=8000mm, N=600mm, Q=50t / h, tilt angle=40-60°, n=2.2-6.6rpm, AIR 315 54 motor, N=160kW, n=1500rpm;

[0080] · 12X18N10T fluidized bed dryer, furnace bed area = 9m² 2 ;

[0081] Vibrating screen 1, Q = 75 t / h, single-stage screen area S = 9 m² 2 Three-stage screen, two vibrating motors N=15kW, n=960rpm. Mesh size for each stage: top - 5.0×5.0mm, middle - 2.0×2.0mm, bottom - 0.8×0.8mm;

[0082] • SMD-504 hammer mill;

[0083] • Vibrating screen 2, Q = 75 t / h, single-stage screen area S = 9 m² 2 The system consists of a primary screen and two vibrating motors, each with a capacity of 15kW and a rotation speed of 960rpm. The screen mesh size is 2.0 x 2.0 mm.

[0084] Standard auxiliary equipment for conveying, heating and storing, which is known to those skilled in the art.

[0085] Ammonium sulfate with a particle size of 0.5 mm to 6 mm (TS (Technical Specification) 113-03-625-90, produced by Kemerovo City SDSAzot JSC) was used as the starting material for granulation.

[0086] Process flow:

[0087] 32.7 t / h of crystalline ammonium sulfate is supplied to the vortex mill (conveying volume is approximately 11 m³). 3 The vortex mill also receives 5.2 t / h of fine particles, which are particles smaller than 0.8 mm separated after sieving and grading.

[0088] Ammonium sulfate is ground in a vortex mill. The initial classification of the powder is carried out within the vortex mill itself.

[0089] The ground powder enters the air duct from the mill, where a circulating airflow generated by a fan transports it to the pneumatic classifier. The pneumatic classifier provides a final separation into a fraction larger than 0.16 mm that is unsuitable for granulation, and a fraction smaller than 0.16 mm that can be used as feedstock for the disc granulator. The fraction larger than 0.16 mm (approximately 3 t / h) is poured through a gate valve into the loading tube of the vortex mill for regrinding.

[0090] Suitable powder for granulation is fed via an airflow into a stacked cyclone separator, where the powder is separated from the air and collected in the cyclone separator hopper. The powder is then conveyed from the hopper to a disc granulator by a screw conveyor at a rate of 37.9 t / h. A recycled product of 12.1 t / h, with a particle size of 0.8 mm to 2.0 mm after sieving and classification, is also fed to the disc granulator at a flow rate of 4.4 m³ / h. 3 / h water spray granulation feed.

[0091] To obtain spherical and durable ammonium sulfate granules with a diameter of 2 mm to 5 mm, a disc granulator with a diameter of 8.0 m, a side height of 0.6 m, and a dry matter capacity of 50 t / h was used. The rotational shaft was tilted at an angle of 48° relative to the horizontal direction. The disc rotation speed was 5.9 rpm.

[0092] In the spray zone, water is sprayed onto the fine particle layer via hydraulic nozzles. To maintain a high-quality ammonium sulfate granulation process, the water supply flow ensures that the moisture content of the feed is within the range of 7% to 9% by weight. The moisture content of the feed is continuously measured using a microwave sensor immersed in a region of the granule layer with minimal circulation.

[0093] After the granulator, a wet granule flow of 54.4 t / h enters the fluidized bed (FB) dryer.

[0094] The drying process involves steam passing through a tubular submerged heat exchanger (with a capacity of 260m³). 2 The heat transfer occurs by transferring heat from the heat exchanger surface area to the product. The facility uses wet steam at a pressure of 10 atm (183°C). The steam flow rate entering the tubular heat exchanger is automatically regulated according to the layer temperature of 120°C to 140°C. The required air volume to maintain an upward flow velocity of 2.5 m / s in the dryer is a physical 81,000 m³. 3 / h. Air at a temperature of 120°C to 140°C after passing through the heat generator enters the drying zone of the FB dryer through a perforated furnace.

[0095] The granules are dried such that the product obtained at the dryer outlet has a temperature of 120°C to 140°C and a moisture content of no more than 0.5% by weight. The hot product enters the lower fluidized bed of the FB dryer through a vertical valve, where it is cooled by workshop air.

[0096] Using fans to distribute a capacity of 60,000 m³ 3 The workshop air is supplied to the FB dryer through a perforated furnace at a rate of / h, cooling the product to 65°C to 70°C. The workshop air then passes through a heat generator, where it is heated to 120°C to 140°C before entering the drying zone of the FB dryer.

[0097] The granules leaving the dryer are graded on two vibrating screens. The first screen has three stages of mesh. Each stage has a screening surface area of ​​9 m². 2 On the first screen, the granules are separated into four parts:

[0098] - Coarse particles with a diameter greater than 5.0 mm;

[0099] - Commercially available portions of granules with a diameter of 2.0mm to 5.0mm;

[0100] - The recycling section has a particle diameter of 0.8 mm to 2.0 mm;

[0101] - Fine particles with a diameter of less than 0.8 mm.

[0102] The fine particles separated by screening at a rate of 5.2 t / h are fed through pipelines to the vortex mill for grinding.

[0103] The coarse particles screened out at a capacity of 5 t / h are fed to a crusher, where they are crushed into smaller sizes.

[0104] After the pulverizer, the ground product is conveyed to a second screen for sieving. The second screen has a sieving surface area of ​​9m². 2 The primary screen.

[0105] On the second sieve, the crushed granules are dispersed into two parts:

[0106] - Particles larger than 2.0 mm;

[0107] - Particles with a diameter less than 2.0 mm.

[0108] The portion with a particle size smaller than 2.0 mm is fed to a first screen to further screen out recyclable particles ranging in size from 0.8 mm to 2 mm. The portion with a particle size larger than 2 mm after screening is recycled to a crusher for further crushing. This forms a closed crusher-screen cycle, which processes coarse particles into recyclable particles, thereby ensuring a sufficient amount of recycled product in the process.

[0109] The 12.1 t / h recycled portion is supplied as seed pellets to the disc granulator.

[0110] The commercially available portion of 32.7 t / h is supplied to the step of post-treatment of granules with an anti-caking agent, and then to the finished product hopper.

[0111] Table 1 shows the main parameters of granulated ammonium sulfate obtained within 36 hours when the graded powder used for granulation contains 100% of the particles smaller than 0.16 mm.

[0112] As can be seen from Table 1, this method enables almost 100% of the agglomerates of the initial ammonium sulfate powder to become commercially available granules with diameters of 2 mm (D1) to 5 mm (D2) throughout the entire raw material supply period.

[0113] Table 1

[0114]

[0115] 1) The mill feed load includes 32.7±0.5 t / h of initial ammonium sulfate and 5.2±0.1 t / h of screened material (<0.8 mm).

[0116] 2) The yield of the finished product is calculated relative to the mill load.

[0117] 3) The yield of the finished product is calculated based on the initial ammonium sulfate consumed, without considering process losses.

[0118] Example 2 (Comparison). Granulation of ammonium sulfate without partially removing the fine particles.

[0119] Granulation was performed on the same equipment as in Example 1.

[0120] Ammonium sulfate with a particle size of 0.5 mm to 6 mm (grade B according to TS (Technical Specification) 113-03-625-90, produced by SDS Azot JSC in Kemerovo) was used as the starting material for granulation.

[0121] Process flow:

[0122] 10.0 t / h of crystalline ammonium sulfate is fed to a 40 m³ volume via an elevator. 3 The receiving hopper supplies ammonium sulfate from the receiving hopper to the belt conveyor scale, and then to the vortex mill via a screw conveyor.

[0123] Ammonium sulfate is ground in a vortex mill. The output ammonium sulfate contains 6% to 10% particles larger than 0.16 mm.

[0124] The ground powder is fed from the mill to the feed hopper of the disc granulator via an elevator and conveyor belt. Fine particles after screening and classification are also fed to the feed hopper. A mixed product flow rate of 11 t / h to 20 t / h is fed from the feed hopper to the disc granulator via a gate distributor. Furthermore, in proportion to the flow rate of the mixed product from the feed hopper, recycled granules are fed as seed particles from the recycled product hopper to the disc granulator at a rate of 2 t / h to 8 t / h via a gate distributor. In the granulator, a flow rate of 1.0 m³ / h is used. 3 / h to 2.2m 3 A mixture of water sprayed with powder and recycled products per hour.

[0125] To obtain spherical and durable ammonium sulfate granules with a diameter of 2 mm to 5 mm, a disc granulator with a diameter of 8.0 m, a side height of 0.6 m, and a dry matter capacity of 50 t / h was used. The rotational shaft was tilted at an angle of 48° relative to the horizontal direction. The disc rotation speed was 5.9 rpm.

[0126] In the spray zone, water is sprayed onto the fine particle layer via hydraulic nozzles. To maintain a high-quality ammonium sulfate granulation process, the water consumption is set so that the moisture content of the feed is within the range of 7% to 9% by weight. The moisture content of the feed is continuously measured using a microwave sensor immersed in the area of ​​the granule layer with minimal circulation.

[0127] After the granulator, the wet granules flow into the fluidized bed (FB) dryer.

[0128] The granules are dried such that the product obtained at the dryer outlet has a temperature of 120°C to 140°C and a moisture content of no more than 0.5% by weight. The hot product enters the lower fluidized bed of the FB dryer through a vertical valve, where it is cooled by workshop air.

[0129] The granules leaving the dryer are graded on two vibrating screens. The first screen has three stages of mesh. Each stage has a screening surface area of ​​9 m². 2 On the first screen, the granules are separated into four parts:

[0130] - Coarse particles with a particle size greater than 5.0 mm;

[0131] - Commercially available portions with particle sizes of 2.0mm to 5.0mm;

[0132] - The recycling portion has a particle size of 0.8mm to 2.0mm;

[0133] - Fine particles with a particle size of less than 0.8 mm.

[0134] Fine particles with a flow rate not exceeding 10 t / h are fed through a pipe from the screen to the feed hopper of the disc granulator under gravity, and the excess fine particles of 5 t / h are transferred from the circulation loop to the storage hopper.

[0135] A coarse fraction, at a rate of 1 to 4 t / h, is fed through a pipe from a screen to a pulverizer under gravity, where it is pulverized into a finer size. After the pulverizer, the ground product is fed to a second screen with a screening surface area of ​​9 m² for further sieving. 2 The first screen. On the second screen, the crushed particles are separated into two parts:

[0136] - Particles larger than 2.0 mm;

[0137] - Particles with a diameter less than 2.0 mm.

[0138] The portion with a particle size less than 2.0 mm is fed to the first screen to further screen out recyclable particles with a size ranging from 0.8 mm to 2 mm. The portion with a particle size greater than 2 mm after screening is recycled to the pulverizer for further crushing.

[0139] The recycled portion of 2t / h to 8t / h is fed into the recycled product hopper of the disc granulator and used as seed particles during fine particle granulation.

[0140] The commercially available portion is supplied to the step of post-treatment of granules with an anti-caking agent, and then supplied to the finished product hopper.

[0141] Table 2 shows the main parameters of granulated ammonium sulfate obtained by this method within 12 hours.

[0142] Table 2

[0143]

[0144] Table 3

[0145]

[0146] 1) The mill feed load includes 31.8 t / h of initial potassium sulfate consumption and 0.8 t / h of screened material (<0.8 mm).

[0147] 2) The yield of the finished product is calculated relative to the mill load.

[0148] 3) Without considering process losses, the yield of the finished product obtained from the consumed initial potassium sulfate is 100%.

[0149] Under the process conditions of Example 2, it is impossible to increase the feed mixture load of the pan to more than 27 t / h, because at values ​​greater than 27 t / h, there is almost no commercially available portion.

[0150] During the granulation process, a certain amount of fine particles (particle size less than 0.8 mm) accumulates, and the raw material mixture load in the pan cannot be increased to above 27 t / h. Therefore, from a certain point in time, it is necessary to transfer a portion of the fine particles (particle size less than 0.8 mm) to the storage hopper. Due to the limited volume of this hopper, the process must be stopped after 12 hours.

[0151] As shown in Table 2, when ammonium sulfate powder containing 6% to 10% particles larger than 0.16 mm was used for granulation, and the 0.16 mm to 0.8 mm fraction was not removed, the particle size distribution of the product leaving the pan was extremely uneven. The content of coarse particles larger than 5 mm was on average 4.5 times higher than in Example 1. The content of commercially available fractions with a size of 2 mm to 5 mm was on average 1.8 times lower.

[0152] With the feed moisture content automatically maintained at 7% to 9%, the granulation process is random: either coarse particles granulate, or non-granulated products are poured off the pan. The yield of the finished product is also inconsistent and does not exceed 50% relative to the ammonium sulfate consumption in the mill.

[0153] Example 3. Potassium sulfate was granulated using the method according to the present invention.

[0154] Granulation was performed using the equipment and methods specified in Example 1.

[0155] Crystalline potassium sulfate (TS(Technical Specification) 2184-093-43399406-2001) consisting of particles with a size of 0.5 mm to 6 mm was used as the starting material for granulation.

[0156] To obtain spherical and robust potassium sulfate granules with a diameter of 2 mm to 5 mm, a disc granulator with a diameter of 8.0 m, a side height of 0.6 m, and a dry matter capacity of 50 t / h was used. The rotational shaft was tilted at an angle of 48° relative to the horizontal. The disc rotation speed was 5.9 rpm. Water was added at a rate of 3.5 m... 3 Spray granulation mixture with a flow rate of / h.

[0157] The resulting granulated product was divided into four parts:

[0158] - Coarse particles with a particle size greater than 5.0 mm;

[0159] - Commercially available portions with a particle size of 2.0mm to 5.0mm;

[0160] - The recycling portion has a particle size of 0.8 mm to 2.0 mm;

[0161] - Fine particles with a particle size of less than 0.8 mm.

[0162] Table 3 shows the main parameters and results of the obtained granulated potassium sulfate.

[0163] Example 4. Urea granulation according to the method of the present invention.

[0164] Granulation was performed using the equipment and methods specified in Example 1.

[0165] Crystalline urea (Class A according to GOST (Russian National Standard) 2081-2010) consisting of particles with a size of 0.5 mm to 2 mm, and urea-formaldehyde concentrate (UFC-85 according to TS (Technical Specification) 2223-009-00206492-07) were used as starting materials for granulation.

[0166] To obtain spherical and robust urea granules with a diameter of 6 mm to 8 mm, a disc granulator with a diameter of 8.0 m, a side height of 0.6 m, and a dry matter capacity of 50 t / h was used. The rotational shaft was tilted at an angle of 40° relative to the horizontal direction. The disc rotation speed was 3.5 rpm. The granulation feed was sprayed with a granulation solution containing 45% to 50% urea and 4.0% to 4.4% UFC-85 at a rate of 3.4 t / h to 4.0 t / h.

[0167] Air at a temperature of 90°C to 100°C was used for drying in the fluidized bed dryer.

[0168] The resulting granulated product was divided into four parts:

[0169] - Coarse particles with a size greater than 8.0 mm;

[0170] - Commercially available portions with a particle size of 6.0mm to 8.0mm;

[0171] - Recycled portions with particle sizes from 1.6 mm to 6.0 mm;

[0172] - Fine particles with a particle size of less than 1.6 mm.

[0173] Table 4 shows the main parameters and results of the obtained granulated urea.

[0174] Table 4

[0175]

[0176] 1) The yield of the finished product is calculated relative to the mill load.

[0177] 2)Without considering process losses, the yield of the finished product obtained from the total consumption of urea (excluding UFC-85) is 100%.

[0178] The results in Examples 3 and 4 demonstrate that the method according to the invention can be applied to a wide range of different water-soluble solids and obtain different particle size distributions while maintaining process stability.

Claims

1. A method for continuously granulating water-soluble solids, comprising the following steps: a) Supply raw materials and seed pellets to the granulation tray; b) Granulate water-soluble solids during wetting with the aqueous phase; c) Remove the granulated product from the granulation tray; d) The granulated product obtained from drying step c); e) Divide the dried granulated product obtained in step d) into several parts; f) Remove the marketable portion obtained from this process; The characteristic feature is that, in step e), the dried granulated product obtained in step d) is divided into four parts: The commercially available portion of the granule diameter ranges from D1 to D2. The coarse-grained portion with a particle diameter greater than D2; The range of particle diameter is The recirculation portion to D1; The range of particle diameter is < The fine-grained portion; In step a), the recycled portion is used as the raw material for supplying the seed particles, and the coarse portion is used for grinding to a particle size of [missing information]. Within the range of D1, and then recycled to the raw material supply step a) of this process, the fine particles are ground until no particles larger than the particle size of the raw material are present, and also recycled to the raw material supply step a), wherein the particle size of the raw material is < .

2. The method according to claim 1, characterized in that, The method includes the additional step of crushing and classifying the raw material before feeding it to the granulation disc.

3. The method according to claim 2, characterized in that, The raw material is pulverized and graded together with the recycled fine portion, and the resulting combined raw material is fed to the next step of the method.

4. The method according to claim 1, characterized in that, The water-soluble solid is a mineral salt.

5. The method according to claim 4, characterized in that, The water-soluble solid is a sodium, potassium, or ammonium nitrate, sulfate, or chloride.

6. The method according to claim 5, characterized in that, The water-soluble solid is ammonium sulfate.

7. The method according to claim 1, characterized in that, The water-soluble solid is a mineral fertilizer.

8. The method according to any one of claims 1 to 7, characterized in that, The range of D1-D2 for the commercially available portion corresponds to the following condition: 0.5 mm ≤ ≤ 11 mm, where D1 ≥ 0.2 mm.

Images