Potassium magnesium sulphate fertilizer spherical particles and preparation method thereof

Abstract

The invention belongs to the technical field of fertilizer manufacturing, and particularly relates to potash magnesium sulphate fertilizer spherical particles and a preparation method thereof. The preparation method comprises the following steps: extruding and granulating a potash magnesium sulphate fertilizer wet material to obtain potash magnesium sulphate fertilizer crystal nucleus particles, and mixing the potash magnesium sulphate fertilizer crystal nucleus particles, potash magnesium sulphate fertilizer powder and water to obtain a mixed material; adding water into the mixed material, and carrying out wet granulation to obtain a wet potash magnesium sulphate fertilizer particle product; sequentially pre-drying and pre-screening the wet potash magnesium sulphate fertilizer particle product to obtain a potash magnesium sulphate fertilizer particle semi-finished product; and sequentially drying and screening the potash magnesium sulphate fertilizer particle semi-finished product to obtain the potash magnesium sulphate fertilizer spherical particles. The potash magnesium sulphate fertilizer spherical particles prepared by the preparation method provided by the invention are more regular in appearance and high in flowability, and the mixing uniformity of a compound fertilizer factory during subsequent processing is conveniently improved; and meanwhile, the forming rate is high, the particle product strength is high, and it is guaranteed that the particle abrasion loss is small in the secondary and multi-time transfer process.

Description

Technical Field

[0001] This invention belongs to the field of fertilizer manufacturing technology, specifically relating to a potassium magnesium sulfate fertilizer spherical granules and its preparation method. Background Technology

[0002] There are roughly three common granulation methods: extrusion, agglomeration, and spraying. 1. Spraying is mainly used for granulating low-melting-point fertilizers, characterized by a high forming rate. Its disadvantage is that it requires the product to have a low melting point, making it unsuitable for granulating high-melting-point potassium fertilizers such as potassium magnesium sulfate. 2. Agglomeration is currently the most widely used method for compound fertilizer granulation. Its characteristics include simple equipment structure, high single-machine output, and rounded granules. Its disadvantages are low granule strength and low forming rate. 3. Extrusion has a simple process flow, large processing capacity, high granule strength, and low energy consumption. Its disadvantages are irregular granules, rough granule surfaces, poor flowability, and low forming rate.

[0003] Currently, the granulation technology for potassium magnesium sulfate fertilizer granules on the market is extrusion granulation, but the system has a low forming rate, and the granule surface is irregular, mostly elliptical. Furthermore, this granulation process is dry granulation, which results in significant dust generation during production.

[0004] The related technology discloses a method for preparing spherical potassium magnesium sulfate fertilizer. The method involves mixing refined soft potassium magnesium fertilizer with a free water content of approximately 17% with recycled material crushed to a particle size <2mm, which has a free water content of 1.1%, at a mass ratio of 9:1 to obtain a mixture with a free water content of approximately 15.1%. This mixture is then sequentially fed into a spiral tube shaping machine, a disc granulator, and screened to obtain spherical potassium magnesium fertilizer particles. The disc granulator has a number of 4cm diameter particles arranged symmetrically and evenly on its disc surface. The process involves creating two 0.5cm deep circular granulation pits, each tangent to the others. Within each pit, near the outer edge of the granulation disc, a vertically positioned silica gel column, 4cm high and 1cm in diameter, is placed at the apex of an equilateral triangle. A hot air duct is positioned above the second layer of the discs, maintaining the material temperature at 70-80℃. The granules obtained from the second layer pass through a third receiving disc for further drying, resulting in potassium-magnesium fertilizer spherical granules with a free water content ≤1.5%. After sieving, the granules have a particle size of 2-4.5mm. This preparation method primarily uses disc granulation, resulting in a low throughput and relatively low strength of the finished granules. Summary of the Invention

[0005] The purpose of this invention is to provide a potassium magnesium sulfate fertilizer spherical granule and its preparation method. The potassium magnesium sulfate fertilizer spherical granules prepared by the method of this invention have a more regular appearance and high fluidity, which facilitates the improvement of the mixing uniformity in subsequent processing of compound fertilizer plants; at the same time, the forming rate is high and the granule product has high strength, ensuring that the granule wear is small during secondary and multiple transfer processes.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] This invention provides a method for preparing spherical potassium magnesium sulfate fertilizer granules, comprising the following steps:

[0008] (1) Extruding and granulating the wet potassium magnesium sulfate fertilizer to obtain potassium magnesium sulfate fertilizer nucleus particles, wherein the mass percentage of the potassium magnesium sulfate fertilizer nucleus particles with a particle size of 2-3 mm is ≥85%.

[0009] (2) Mix the potassium magnesium sulfate fertilizer nuclei particles, potassium magnesium sulfate fertilizer powder and water to obtain a mixture;

[0010] (3) Add water to the mixture and perform wet granulation to obtain wet potassium magnesium sulfate fertilizer granules;

[0011] (4) The wet potassium magnesium sulfate fertilizer granules are pre-dried and pre-screened in sequence. The pre-screening is a two-stage screening. The screen mesh sizes used in the two-stage screening are 4.75 mm and 2 mm, respectively. The material under the screen with a screen mesh size of 4.75 mm and the material over the screen with a screen mesh size of 2 mm are taken to obtain the potassium magnesium sulfate fertilizer granules semi-finished product.

[0012] (5) The potassium magnesium sulfate fertilizer granules semi-finished product is dried and sieved in sequence. The drying temperature is ≥100℃. The sieving is a two-stage sieve with screen apertures of 4.75mm and 2mm respectively. The material under sieve with a screen aperture of 4.75mm and the material over sieve with a screen aperture of 2mm are taken to obtain the potassium magnesium sulfate fertilizer spherical granules.

[0013] Preferably, the free water content of the potassium magnesium sulfate fertilizer wet material is 6-8%.

[0014] Preferably, in step (2): the mass ratio of the potassium magnesium sulfate fertilizer nucleus particles to the potassium magnesium sulfate fertilizer powder is 2-3:3; the mass of water accounts for 15-20% of the mass of the potassium magnesium sulfate fertilizer nucleus particles.

[0015] Preferably, in step (3), the mass of the water accounts for 25-30% of the mass of the potassium magnesium sulfate fertilizer nucleus particles.

[0016] Preferably, the pre-drying temperature is 65–75°C.

[0017] Preferably, the pre-screening also yields a first unqualified particle size product. After crushing the first unqualified particle size product, it is returned to step (1) for extrusion granulation. The mass ratio of the potassium magnesium sulfate fertilizer wet material to the first unqualified particle size product is 7:1 to 2.

[0018] Preferably, the drying temperature is 100℃~110℃.

[0019] Preferably, the screening also yields a second unqualified particle size product. After crushing the second unqualified particle size product, it is returned to step (1) for extrusion granulation. The mass ratio of the potassium magnesium sulfate fertilizer wet material to the second unqualified particle size product is 7:1 to 2.

[0020] This invention provides potassium magnesium sulfate fertilizer spherical granules prepared by the preparation method described in the above technical solution.

[0021] Preferably, the mass percentage of the potassium magnesium sulfate fertilizer spherical particles with a particle size of 2-4.75 mm is ≥90%, and the strength of the potassium magnesium sulfate fertilizer spherical particles is ≥35 N.

[0022] This invention provides a method for preparing spherical potassium magnesium sulfate fertilizer, comprising the following steps: (1) extruding and granulating wet potassium magnesium sulfate fertilizer to obtain potassium magnesium sulfate fertilizer crystal nuclei particles, wherein the mass percentage of particles with a diameter of 2-3 mm in the potassium magnesium sulfate fertilizer crystal nuclei particles is ≥85%; (2) mixing the potassium magnesium sulfate fertilizer crystal nuclei particles, potassium magnesium sulfate fertilizer powder and water to obtain a mixture; (3) adding water to the mixture and performing wet granulation to obtain wet potassium magnesium sulfate fertilizer granule products; (4) subjecting the wet potassium magnesium sulfate fertilizer granule products to pre-drying and pre-sieving sequentially, wherein the pre-sieving... For secondary screening, the screen mesh sizes used in the secondary screening are 4.75 mm and 2 mm respectively. The undersize material with a screen mesh size of 4.75 mm and the oversize material with a screen mesh size of 2 mm are taken to obtain potassium magnesium sulfate fertilizer granules semi-finished product; (5) The potassium magnesium sulfate fertilizer granules semi-finished product is dried and screened in sequence. The drying temperature is ≥100℃. The screening is secondary screening. The screen mesh sizes used in the secondary screening are 4.75 mm and 2 mm respectively. The undersize material with a screen mesh size of 4.75 mm and the oversize material with a screen mesh size of 2 mm are taken to obtain potassium magnesium sulfate fertilizer spherical granules. In this invention, the wet potassium magnesium sulfate fertilizer material is extruded and granulated. Small potassium magnesium sulfate fertilizer crystal nuclei particles are obtained by extrusion granulation. Then, it is fully mixed with potassium magnesium sulfate fertilizer powder and wet granulated. After wet granulation, it is pre-dried and pre-screened to obtain potassium magnesium sulfate fertilizer granules semi-finished product with a certain molding strength. Finally, it is dried and screened to obtain potassium magnesium sulfate fertilizer spherical granule product. This invention utilizes extrusion granulation to obtain small crystal nuclei, followed by wet agglomeration to form granules. Finally, it undergoes two stages of drying and sieving to optimize the sphericity of potassium magnesium sulfate fertilizer granules, fill surface defects, and result in more regular granule appearance, better flowability, and higher forming rate. The regular spherical granule products prepared by this invention are also easier for compound fertilizer plants to mix evenly during subsequent processing. Furthermore, this invention further enhances the strength of potassium magnesium sulfate fertilizer spherical granules while ensuring reduced particle wear during secondary and multiple transfers, expanding the target audience and enhancing brand benefits and value.

[0023] Meanwhile, the preparation method provided by this invention can effectively reduce dust during the production process and ensure high production safety. Attached Figure Description

[0024] Figure 1 The flowchart illustrates the preparation process of the potassium magnesium sulfate fertilizer spherical granules provided by this invention. Detailed Implementation

[0025] This invention provides a method for preparing spherical potassium magnesium sulfate fertilizer granules, comprising the following steps:

[0026] (1) Extruding and granulating the wet potassium magnesium sulfate fertilizer to obtain potassium magnesium sulfate fertilizer nucleus particles, wherein the mass percentage of the potassium magnesium sulfate fertilizer nucleus particles with a particle size of 2-3 mm is ≥85%.

[0027] (2) Mix the potassium magnesium sulfate fertilizer nuclei particles, potassium magnesium sulfate fertilizer powder and water to obtain a mixture;

[0028] (3) Add water to the mixture and perform wet granulation to obtain wet potassium magnesium sulfate fertilizer granules;

[0029] (4) The wet potassium magnesium sulfate fertilizer granules are pre-dried and pre-screened in sequence. The pre-screening is a two-stage screening. The screen mesh sizes used in the two-stage screening are 4.75 mm and 2 mm, respectively. The material under the screen with a screen mesh size of 4.75 mm and the material over the screen with a screen mesh size of 2 mm are taken to obtain the potassium magnesium sulfate fertilizer granules semi-finished product.

[0030] (5) The potassium magnesium sulfate fertilizer granules semi-finished product is dried and sieved in sequence. The drying temperature is ≥100℃. The sieving is a two-stage sieve with screen apertures of 4.75mm and 2mm respectively. The material under sieve with a screen aperture of 4.75mm and the material over sieve with a screen aperture of 2mm are taken to obtain the potassium magnesium sulfate fertilizer spherical granules.

[0031] In this invention, unless otherwise specified, all raw materials / components used in the preparation are commercially available products well known to those skilled in the art.

[0032] This invention involves extruding and granulating wet potassium magnesium sulfate fertilizer to obtain potassium magnesium sulfate fertilizer crystal nuclei particles. The mass percentage of particles with a diameter of 2-3 mm in these potassium magnesium sulfate fertilizer crystal nuclei particles is ≥85%. In this invention, the free water content of the wet potassium magnesium sulfate fertilizer is preferably 6-8%, and in the examples, it can be 6.21%, 7.32%, or 6.45%. The preferred grade of the wet potassium magnesium sulfate fertilizer includes: Na... + 0.49–0.74 wt%, K + 18.73–19.72 wt%, Mg 2+ 5.95–6.17 wt%, SO42- 49.20–49.82 wt%, Cl - 0.53–0.72 wt%. In the examples, the grade of the potassium magnesium sulfate fertilizer wet material can be: Na + 0.74wt%, K + 19.72 wt%, Mg 2+ 6.17wt%, SO4 2- 49.31 wt%, Cl - 0.64wt%, or Na + 0.65wt%, K + 18.73wt%, Mg 2+ 5.95wt%, SO4 2- 49.20 wt%, Cl - 0.72 wt%, or Na + 0.49wt%, K + 19.24 wt%, Mg 2+ 6.08wt%, SO4 2- 49.82wt%, Cl - 0.53 wt%. In a specific embodiment of the present invention, the extrusion granulation is preferably carried out using a small double-roller extruder.

[0033] In this invention, the mass percentage of particles with a diameter of 2-3 mm in the potassium magnesium sulfate fertilizer crystal nuclei is preferably 86-95%, and in the examples it can be 93.25%, 89.64% or 86.84%.

[0034] After obtaining potassium magnesium sulfate fertilizer crystal nuclei, the present invention mixes the potassium magnesium sulfate fertilizer crystal nuclei, potassium magnesium sulfate fertilizer powder, and water to obtain a mixture. In this invention, the preferred mass ratio of the potassium magnesium sulfate fertilizer crystal nuclei to the potassium magnesium sulfate fertilizer powder is 2-3:3, and in the embodiments, it can be 1:1.429, 1:1.5, or 1:1.2. The water is preferably production water or fresh water. The mass percentage of the water to the potassium magnesium sulfate fertilizer crystal nuclei is 15-20%, and in the embodiments, it can be 16%, 15%, or 18%.

[0035] After obtaining the mixture, the present invention adds water to the mixture for wet granulation to obtain wet potassium magnesium sulfate fertilizer granules. In this invention, the wet granulation is preferably carried out in a granulation drum, and the mixture is preferably conveyed to the granulation drum for wet granulation. The water is preferably production water or fresh water. The percentage of water by mass of the potassium magnesium sulfate fertilizer nucleus granules is preferably 25-30%, and in the examples, it can be 27%, 25%, or 26%. The water is preferably sprayed onto the surface of the mixture in the form of a water mist. In this invention, the free water content in the wet potassium magnesium sulfate fertilizer granules is preferably 16-19%, and in the examples, it can be 16.62%, 18.20%, or 17.79%.

[0036] After obtaining the wet potassium magnesium sulfate fertilizer granules, this invention sequentially pre-dries and pre-screens (also known as primary screening). The pre-screening is a two-stage screening process using sieves with apertures of 4.75 mm and 2 mm. The material passing through the 4.75 mm sieve and the material passing through the 2 mm sieve are collected to obtain the potassium magnesium sulfate fertilizer granule semi-finished product. In this invention, the pre-drying is preferably pre-drying, preferably carried out in a pre-drying device. The pre-drying temperature is 65–75°C, and in the embodiments, it can be 68°C, 73°C, or 70°C. In this invention, the pre-screening preferably also yields granules with a first unqualified particle size. After obtaining the granules with the first unqualified particle size, this invention preferably crushes the granules and returns them to the above steps for extrusion granulation. This invention does not have specific requirements for the specific implementation of the crushing process. The preferred mass ratio of the wet potassium magnesium sulfate fertilizer to the granules with the first unqualified particle size is 7:2.

[0037] After obtaining the semi-finished potassium magnesium sulfate fertilizer granules, the present invention sequentially dries and sieves the semi-finished product. The drying temperature is ≥100℃, and the sieving is a two-stage sieve with screen apertures of 4.75mm and 2mm. The material passing through the 4.75mm screen and the material passing through the 2mm screen are collected to obtain the spherical potassium magnesium sulfate fertilizer granules. In the present invention, the drying temperature is preferably 100℃~110℃, and in the embodiments, it can be 105℃, 108℃, or 104℃. The sieving preferably also yields a second unqualified particle size product. After obtaining the second unqualified particle size product, the present invention preferably crushes the second unqualified particle size product and returns it to the above steps for extrusion granulation. The mass ratio of the wet potassium magnesium sulfate fertilizer material to the second unqualified particle size product is preferably 7:1.

[0038] This invention provides potassium magnesium sulfate fertilizer spherical granules prepared by the preparation method described in the above technical solution.

[0039] In this invention, the preferred grade of the potassium magnesium sulfate fertilizer spherical particles is: Na + 0.50–0.67 wt%, K + 20-96-21.40 wt%, Mg 2+ 6.71–6.89 wt%, SO4 2- 53.27–53.72 wt%, Cl - 0.64–0.76 wt%. In the examples, the grade of the potassium magnesium sulfate fertilizer spherical particles can be: Na + 0.65wt%, K + 21.40 wt%, Mg 2+ 6.84 wt%, SO4 2- 53.70 wt%, Cl - 0.65wt%, or Na + 0.67wt%, K + 20.96 wt%, Mg 2+ 6.71 wt%, SO4 2- 52.72 wt%, Cl - 0.64 wt%; or: Na + 0.50wt%, K + 21.18 wt%, Mg 2+ 6.89 wt%, SO4 2- 53.27wt%, Cl - 0.76 wt%.

[0040] In this invention, the mass percentage of the potassium magnesium sulfate fertilizer spherical particles with a particle size of 2-4.75 mm is ≥90%, preferably 90-93%, and in the examples it can be 91.25%, 90.75% or 92.58%.

[0041] In this invention, the strength of the potassium magnesium sulfate fertilizer spherical particles is ≥35N, preferably 35-36N, and in the examples it can be 35.2N, 36.1N or 35.8N.

[0042] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0043] In the following embodiments, according to Figure 1 The preparation process of potassium magnesium sulfate fertilizer spherical granules is described in the provided flowchart.

[0044] Example 1:

[0045] Take a wet potassium magnesium sulfate fertilizer containing 6.45% free water (potassium magnesium sulfate fertilizer wet grade: Na).+ 0.74wt%, K + 19.72 wt%, Mg 2+ 6.17wt%, SO4 2- 49.31 wt%, Cl - 0.64wt%), pre-screened unqualified particle products, and screened unqualified particle products are extruded and granulated in an extrusion device at a mass ratio of 7:2:1. The mass percentage of particles with a diameter of 2mm to 3mm in the extruded potassium magnesium sulfate fertilizer nuclei particles is 93.25%. 10 tons of potassium magnesium sulfate fertilizer nuclei particles and 15 tons of potassium magnesium sulfate fertilizer powder are added to 1.6 tons of production water (slightly brackish water) or fresh water for thorough mixing. The mixture is conveyed to the granulation drum for wet granulation. 2.6 tons of production water (slightly brackish water) or fresh water are added again to the drum and sprayed evenly on the surface of the mixture in a mist. The wet potassium magnesium sulfate fertilizer granules obtained from the drum outlet contain 16.62wt% free water. The product enters a pre-drying device for pre-drying at 70℃, followed by pre-screening. This pre-screening is a two-stage process with screen apertures of 4.75mm and 2mm. The material passing through the 4.75mm screen and the material passing through the 2mm screen are collected, yielding 23.51 tons of potassium magnesium sulfate fertilizer granules as semi-finished product. 5.69 tons of substandard granules are crushed and returned to the extrusion unit. The potassium magnesium sulfate fertilizer granules then enter a drying device at 105℃, followed by sieving. This sieving is a two-stage process with screen apertures of 4.75mm and 2mm. The material passing through the 4.75mm screen and the material passing through the 2mm screen are collected, yielding the finished potassium magnesium sulfate fertilizer spherical granules (potassium magnesium sulfate fertilizer spherical granules grade: Na). + 0.65wt%, K + 21.40 wt%, Mg 2+ 6.84 wt%, SO4 2- 53.70 wt%, Cl - 20.60 tons of potassium magnesium sulfate fertilizer spherical granules (0.65wt%) were produced. The mass percentage of particles with a diameter of 2mm to 4.75mm in the finished product was 91.25%. The strength of the finished product was 35.2N. 2.06 tons of unqualified particle size products were crushed and returned to the extrusion unit.

[0046] Example 2:

[0047] Take a wet potassium magnesium sulfate fertilizer containing 7.32% free water (potassium magnesium sulfate fertilizer wet grade: Na). + 0.65wt%, K + 18.73wt%, Mg 2+ 5.95wt%, SO4 2-49.20 wt%, Cl - The unqualified particle size products obtained from pre-screening and screening are extruded and granulated in an extrusion device at a mass ratio of 7:2:1. The mass percentage of particles with a diameter of 2mm to 3mm in the extruded potassium magnesium sulfate fertilizer nuclei particles is 89.64%. 10 tons of potassium magnesium sulfate fertilizer nuclei particles and 12 tons of potassium magnesium sulfate fertilizer powder are added to 1.5 tons of production water (slightly brackish water) or fresh water for thorough mixing. The mixture is then conveyed to a granulation drum for wet granulation. Another 2.5 tons of production water (slightly brackish water) or fresh water is added to the drum and sprayed evenly on the surface of the mixture in a mist. The wet potassium magnesium sulfate fertilizer granules obtained at the drum outlet contain 18.20 wt% free water. The granules are pre-dried in a pre-drying device at 73℃, followed by pre-screening (two-stage screening with screen apertures of 4.75mm and 2mm). The material passing through the 4.75mm screen and the material passing through the 2mm screen yields 21.40 tons of potassium magnesium sulfate fertilizer granules. 4.60 tons of substandard granules are crushed and returned to the extrusion unit. The potassium magnesium sulfate fertilizer granules then enter a drying unit at 108℃, followed by screening (two-stage screening with screen apertures of 4.75mm and 2mm). The material passing through the 4.75mm screen and the material passing through the 2mm screen yields the finished potassium magnesium sulfate fertilizer spherical granules (potassium magnesium sulfate fertilizer spherical granules grade: Na). + 0.67wt%, K + 20.96 wt%, Mg 2+ 6.71 wt%, SO4 2- 52.72 wt%, Cl - 0.64wt%) 18.35 tons, the mass proportion of particles with a diameter of 2mm to 4.75mm in the finished spherical potassium magnesium sulfate fertilizer product is 90.75%, the strength of the finished spherical potassium magnesium sulfate fertilizer product is 36.1N, and 1.98 tons of unqualified particle size product are crushed and returned to the extrusion unit.

[0048] Example 3:

[0049] Take a wet potassium magnesium sulfate fertilizer containing 6.21% free water (potassium magnesium sulfate fertilizer wet grade: Na). + 0.49wt%, K + 19.24 wt%, Mg 2+ 6.08wt%, SO4 2- 49.82wt%, Cl -0.53wt%), pre-screened unqualified particle size products, and screened unqualified particle size products are extruded and granulated in an extrusion device at a mass ratio of 7:2:1. The mass percentage of particles with a diameter of 2mm to 3mm in the extruded potassium magnesium sulfate fertilizer nuclei particles is 86.84%. 10 tons of potassium magnesium sulfate fertilizer nuclei particles and 14.29 tons of potassium magnesium sulfate fertilizer powder are added to 1.8 tons of production water (slightly brackish water) or fresh water for thorough mixing. The mixture is conveyed to the granulation drum for wet granulation. 2.7 tons of production water (slightly brackish water) or fresh water are added again to the drum and sprayed evenly on the surface of the mixture in a mist. The wet potassium magnesium sulfate fertilizer granules obtained from the drum outlet contain 17.79wt% free water. The product enters a pre-drying device at 68℃ for pre-drying, followed by pre-screening. This pre-screening is a two-stage process with screen apertures of 4.75mm and 2mm. The material passing through the 4.75mm screen and the material passing through the 2mm screen yields 21.76 tons of potassium magnesium sulfate fertilizer granules (semi-finished product). 7.02 tons of substandard granules are crushed and returned to the extrusion unit. The potassium magnesium sulfate fertilizer granules then enter a drying device at 104℃, followed by sieving. This sieving is a two-stage process with screen apertures of 4.75mm and 2mm. The material passing through the 4.75mm screen and the material passing through the 2mm screen yields the finished potassium magnesium sulfate fertilizer spherical granules (potassium magnesium sulfate fertilizer spherical granules grade: Na). + 0.50wt%, K + 21.18 wt%, Mg 2+ 6.89 wt%, SO4 2- 53.27wt%, Cl - 0.76wt%) 19.06 tons, the mass percentage of spherical granules with a diameter of 2mm to 4.75mm in the finished product of potassium magnesium sulfate fertilizer is 92.58%, the strength of the finished product of spherical granules of potassium magnesium sulfate fertilizer is 35.8N, and 1.61 tons of unqualified particle size product are crushed and returned to the extrusion unit.

[0050] Comparative Example 1:

[0051] Take 10 tons of wet potassium magnesium sulfate fertilizer containing 6.76% free water (potassium magnesium sulfate fertilizer wet grade: Na). + 0.43wt%, K + 19.97wt%, Mg 2+ 6.24wt%, SO4 2- 49.72wt%, Cl -(0.51wt%) The potassium magnesium sulfate fertilizer nuclei are extruded and granulated in an extrusion unit. The mass percentage of particles with a diameter of 2mm to 3mm in the extruded potassium magnesium sulfate fertilizer nuclei is 86.65%. 10 tons of potassium magnesium sulfate fertilizer nuclei and 14.35 tons of potassium magnesium sulfate fertilizer powder are added to 1.7 tons of production water (slightly brackish water) or fresh water for thorough mixing. The mixture is then conveyed to a granulation drum for wet granulation. 2.6 tons of production water (slightly brackish water) or fresh water are added again to the drum and sprayed evenly on the surface of the mixture in a mist. The wet potassium magnesium sulfate fertilizer granules obtained at the drum outlet contain 17.57wt% free water. The wet potassium magnesium sulfate fertilizer granules are then pre-dried in a pre-drying unit at a temperature of 67℃. Then, pre-screening is performed, which is a two-stage screening with screen apertures of 4.75mm and 2mm. The material passing through the 4.75mm screen and the material passing through the 2mm screen are collected, yielding 21.56 tons of potassium magnesium sulfate fertilizer granules as semi-finished product. 7.09 tons of substandard granules are crushed, and some are returned to the extrusion unit. The potassium magnesium sulfate fertilizer granules semi-finished product enters the drying unit at 97℃, and is then screened again, this time in a two-stage screening process with screen apertures of 4.75mm and 2mm. The material passing through the 4.75mm screen and the material passing through the 2mm screen are collected, yielding the finished potassium magnesium sulfate fertilizer spherical granules (potassium magnesium sulfate fertilizer spherical granules grade: Na). + 0.48wt%, K + 20.47wt%, Mg 2+ 6.57wt%, SO4 2- 52.47wt%, Cl - 20.15 tons of potassium magnesium sulfate fertilizer spherical granules (0.74wt%) were produced. The mass percentage of particles with a diameter of 2mm to 4.75mm in the finished product was 92.58%. The strength of the finished product was 34.8N. 1.31 tons of substandard particle size were obtained, and some were crushed and returned to the extrusion unit. In this comparative example, the finished product's drying temperature was too low, resulting in substandard quality and strength in the finished potassium magnesium sulfate fertilizer spherical granules.

[0052] In this comparative example, the finished product drying temperature was too low, resulting in the potassium magnesium sulfate fertilizer spherical granules failing to meet the standards in terms of grade and strength, and thus the finished product quality was substandard.

[0053] Test example:

[0054] Comparison table of potassium magnesium sulfate fertilizer granules product standards and the finished spherical potassium magnesium sulfate fertilizer granules obtained in Examples 1-3 of this invention.

[0055] Table 1 Comparison of spherical potassium magnesium sulfate fertilizer products obtained in the examples.

[0056] project National Standard First-Class Product Enterprise Standards Example 1 Example 2 Example 3 <![CDATA[Mass fraction of potassium oxide (K2O) % ≥]]> 24 25 25.78 25.25 25.52 Magnesium (Mg) mass fraction % ≥ 6 6 6.84 6.71 6.89 Sulfur (S) mass fraction % ≥ 16 17 17.90 17.57 17.76 <![CDATA[Mass fraction % of chloride ion (Cl - )) ≤]]> 2.5 1.5 0.65 0.64 0.76 <![CDATA[Mass fraction of free water (H2O),% ≤]]> 1.5 1.5 0.63 0.42 0.71 Particle size (particle diameter 2.00mm~4.75mm) ≥ 90 90 91.25 90.75 92.58

[0057] As can be seen from Table 1, the product indicators obtained by this invention are superior to the enterprise standard and national standard first-class product standards recorded in Table 1, and the particles are round and uniform, which is more in line with market demand.

[0058] As can be seen from the above embodiments, the present invention uses a combination of extrusion and wet granulation to produce spherical potassium magnesium sulfate fertilizer granules, optimizing the sphericity of the granules (sphericity = surface area of ​​a sphere with the same volume as the granule / actual surface area of ​​the granule), filling surface defects of the granules, making the spherical potassium magnesium sulfate fertilizer granules more regular in appearance, and effectively reducing dust in the production process. While further improving the strength of the spherical granules, it also ensures that the granules are less worn during secondary and multiple transfers. In addition, the regular spherical granules are easier for compound fertilizer plants to mix evenly in subsequent processing, further expanding the target audience and enhancing brand benefits and value.

[0059] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing spherical potassium magnesium sulfate fertilizer granules, characterized in that, Includes the following steps: (1) Extruding and granulating the wet potassium magnesium sulfate fertilizer to obtain potassium magnesium sulfate fertilizer nucleus particles, wherein the mass percentage of the potassium magnesium sulfate fertilizer nucleus particles with a particle size of 2-3 mm is ≥85%. (2) Mix the potassium magnesium sulfate fertilizer nuclei particles, potassium magnesium sulfate fertilizer powder and water to obtain a mixture; (3) Add water to the mixture and perform wet granulation to obtain wet potassium magnesium sulfate fertilizer granules; (4) The wet potassium magnesium sulfate fertilizer granules are pre-dried and pre-screened in sequence. The pre-screening is a two-stage screening. The screen mesh sizes used in the two-stage screening are 4.75 mm and 2 mm, respectively. The material under the screen with a screen mesh size of 4.75 mm and the material over the screen with a screen mesh size of 2 mm are taken to obtain the potassium magnesium sulfate fertilizer granules semi-finished product. (5) The potassium magnesium sulfate fertilizer granules semi-finished product is dried and sieved in sequence. The drying temperature is ≥100℃. The sieving is a two-stage sieve with screen apertures of 4.75mm and 2mm respectively. The material under sieve with a screen aperture of 4.75mm and the material over sieve with a screen aperture of 2mm are taken to obtain the potassium magnesium sulfate fertilizer spherical granules.

2. The preparation method according to claim 1, characterized in that, The free water content of the potassium magnesium sulfate fertilizer wet material is 6-8%.

3. The preparation method according to claim 1, characterized in that, In step (2): the mass ratio of the potassium magnesium sulfate fertilizer nucleus particles to the potassium magnesium sulfate fertilizer powder is 2-3:3; the mass of water accounts for 15-20% of the mass of the potassium magnesium sulfate fertilizer nucleus particles.

4. The preparation method according to claim 1, characterized in that, In step (3): the mass of the water accounts for 25-30% of the mass of the potassium magnesium sulfate fertilizer crystal nuclei.

5. The preparation method according to claim 1, characterized in that, The pre-drying temperature is 65–75°C.

6. The preparation method according to claim 1 or 5, characterized in that, The pre-screening also yields a first unqualified particle size product. After crushing the first unqualified particle size product, it is returned to step (1) for extrusion granulation. The mass ratio of the potassium magnesium sulfate fertilizer wet material to the first unqualified particle size product is 7:1 to 2.

7. The preparation method according to claim 1, characterized in that, The drying temperature is 100℃~110℃.

8. The preparation method according to claim 1 or 7, characterized in that, The screening also yields a second unqualified particle size product. After crushing the second unqualified particle size product, it is returned to step (1) for extrusion granulation. The mass ratio of the potassium magnesium sulfate fertilizer wet material to the second unqualified particle size product is 7:1 to 2.

9. Spherical potassium magnesium sulfate fertilizer particles prepared by the preparation method according to any one of claims 1 to 8.

10. The potassium magnesium sulfate fertilizer spherical granules according to claim 9, characterized in that, The mass percentage of the potassium magnesium sulfate fertilizer spherical particles with a particle size of 2-4.75 mm is ≥90%, and the strength of the potassium magnesium sulfate fertilizer spherical particles is ≥35 N.

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