Balanced nitro compound fertilizer and its preparation method

Abstract

The application discloses a balanced nitro compound fertilizer and a preparation method thereof, and belongs to the technical field of compound fertilizer production. The compound fertilizer takes ammonium nitrate, monoammonium phosphate and potassium sulfate as basic raw materials, and is compounded with polymeric phosphorus additives, modified diatomite loaded chelated micro-fertilizers and surface modifiers. The preparation adopts a hierarchical melting-low temperature granulation process, and is prepared through raw material pretreatment, melting concentration, low-temperature mixing, emulsification homogenization, high-tower granulation and surface wrapping. The application can improve the particle compressive strength and storage stability, optimize the nutrient release characteristics, and reduce the production energy consumption and safety risks.

Description

Technical Field

[0001] This invention relates to the field of compound fertilizer production technology, and in particular to a balanced nitro compound fertilizer and its preparation method. Background Technology

[0002] Nitro compound fertilizers are high-concentration compound fertilizers with nitrate nitrogen as the core nitrogen source. They are characterized by rapid nutrient dissolution and early crop absorption, and are widely used as base fertilizers and top dressings for field crops such as wheat and corn, as well as cash crops such as fruits, vegetables, and tobacco. Among them, balanced nitro compound fertilizers with a nitrogen, phosphorus pentoxide, and potassium oxide ratio close to 1:1:1 can cover the basic nutrient needs of crops throughout their entire growth period and are the mainstream application category in the market.

[0003] Currently, the mainstream production process for nitro compound fertilizers in China is the high-tower melt granulation method. This involves mixing molten ammonium nitrate with powdered ammonium phosphate and potassium salts, then spraying the mixture onto the top of a tower and cooling and solidifying it into granules inside the tower. While this process boasts high production efficiency, it still suffers from the following technical shortcomings in practical applications:

[0004] Insufficient stability during granule storage and transportation: During rapid cooling within the high-tower process, numerous microcracks and pores easily form inside the granules. The compressive strength of conventional products in the industry is mostly 30-40N, and the agglomeration rate after 6 months of sealed storage at room temperature generally reaches 10%-15%. Powdering and caking easily occur during long-distance storage, transportation, and stacking, affecting application effectiveness. Uneven nutrient release and low utilization rate: The nitrogen in the product is mainly nitrate nitrogen, with rapid fertilizer release but short-lasting effect; phosphorus is mainly in orthophosphate form, easily fixed by calcium and iron ions after application to the soil. The apparent utilization rate of nitrogen in conventional products in the industry is about 35%-38%, and the apparent utilization rate of phosphorus is about 20%, resulting in significant nutrient waste. High production energy consumption and prominent safety risks: To ensure slurry fluidity, the melting and mixing temperature in traditional processes is mostly controlled at 165-180℃, with a saturated steam consumption of about 170-190kg per ton of product, resulting in high energy costs. At the same time, long-term high-temperature environments increase the safety hazard of ammonium nitrate thermal decomposition, requiring stringent production control. Poor compatibility of micronutrients: In conventional production, the direct addition of inorganic salt micronutrients can easily form insoluble precipitates with phosphate and nitrate ions in the slurry, making it impossible to disperse evenly within the particles; the effective proportion of micronutrients added directly in the industry is generally less than 55%, resulting in low actual absorption efficiency by crops. Summary of the Invention

[0005] In view of the above-mentioned shortcomings of the existing technology, the first objective of the present invention is to provide a balanced nitro compound fertilizer with good particle stability and balanced nutrient release; the second objective is to provide a method for preparing the compound fertilizer, thereby reducing production energy consumption and safety risks.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution: This invention provides a balanced nitro compound fertilizer, wherein the mass ratio of nitrogen, phosphorus pentoxide, and potassium oxide in the compound fertilizer is (14~16):(14~16):(14~16), and the total nutrient mass fraction based on nitrogen, phosphorus pentoxide, and potassium oxide is ≥45%. The raw materials for preparation, by dry basis weight, include 320~360 parts of ammonium nitrate, 220~250 parts of monoammonium phosphate, 240~270 parts of potassium sulfate, 15~30 parts of polymeric phosphorus additive, 8~15 parts of modified diatomaceous earth-supported chelated micronutrient fertilizer, and 2~5 parts of surface modifier.

[0007] The total nitrogen in compound fertilizer consists of nitrate nitrogen and ammonium nitrogen; the total phosphorus consists of orthophosphate phosphorus and polymeric phosphorus. Nitrate nitrogen accounts for 32% to 38% of the total nitrogen by mass, and ammonium nitrogen accounts for 62% to 68% of the total nitrogen by mass. The polymeric phosphorus additive is ammonium polyphosphate with a degree of polymerization of 2 to 5. Calculated as phosphorus pentoxide, polymeric phosphorus accounts for more than 15% of the total phosphorus by mass.

[0008] As a preferred embodiment of the present invention, the raw materials may further include 5-12 parts of mineral-derived potassium humate. The modified diatomaceous earth-loaded chelated micro-fertilizer is prepared by using purified calcined diatomaceous earth as a carrier, which is then grafted with organosilicon hydrophobically and loaded with EDTA-chelated iron, zinc, boron, and manganese; wherein the mass ratio of elemental iron, zinc, boron, and manganese is 2:2:1:1, and the total trace element mass fraction of the finished micro-fertilizer is 10% based on elemental composition; the total trace element mass fraction in the compound fertilizer is 0.2%-0.5% based on elemental composition. This micro-fertilizer is prepared using a pore adsorption loading process, and the carrier surface has hydrophobic barrier properties, which can prevent antagonistic reactions between trace elements and phosphate ions in the molten system. The surface modifier is a powder coating agent composed of octadecylamine and talc powder in a mass ratio of 1:2, which is uniformly coated on the outer surface of the compound fertilizer particles.

[0009] This invention also provides a method for preparing compound fertilizer using a staged melting-low temperature granulation process, the specific steps of which are as follows: 1. Raw material pretreatment: Monoammonium phosphate and potassium sulfate are crushed and dried separately. Polymerized phosphorus additives are premixed with modified diatomaceous earth-loaded chelated micro-fertilizer to obtain premixed powder.

[0010] 2. First-stage melt concentration: The ammonium nitrate solution is sent to an evaporator for vacuum concentration to a mass fraction of 98.5%~99.2%, and the temperature of the liquid is controlled at 145~155℃ to obtain ammonium nitrate melt.

[0011] 3. Secondary low-temperature mixing: Add preheated monoammonium phosphate and potassium sulfate to the mixing tank, stir and mix with molten ammonium nitrate, then add premixed powder, control the temperature of the mixing system at 135~145℃, stir until uniform, and obtain molten slurry.

[0012] 4. Emulsification and homogenization: The molten slurry is fed into a high-shear emulsifier for homogenization to eliminate air bubbles in the slurry and refine the particle size of the dispersed phase, thereby improving the uniformity of the slurry.

[0013] 5. High-tower spray granulation: The homogenized molten slurry is fed into the granulation device at the top of the tower and sprayed into droplets by centrifugal force; the droplets come into countercurrent contact with the rising cold air in the tower during the falling process, and gradually cool and solidify into granules.

[0014] 6. Post-processing coating: The solidified particles collected from the bottom of the tower are screened, cooled, and then fed into a roller coating device. Surface modifiers are added for coating treatment, and finally, the finished compound fertilizer is obtained.

[0015] Further, in step 1, monoammonium phosphate and potassium sulfate are pulverized to 100-120 mesh and dried to a moisture content of ≤0.5%; in step 3, monoammonium phosphate and potassium sulfate are preheated to 80-90℃, stirred at a speed of 60-80 r / min, and mixed for 8-12 min, with the moisture content of the resulting molten slurry controlled at 0.8%-1.2%.

[0016] Furthermore, in step 4, the high-shear emulsifier operates at a speed of 1200~1500 r / min, and the homogenization time is 2~3 min.

[0017] Furthermore, in step 5, the temperature of the molten slurry entering the granulation device is 130~140℃, the orifice diameter of the granulation nozzle is 3.0~4.0mm, the temperature of the rising cold air in the granulation tower is 20~30℃, the rising wind speed is 0.8~1.0m / s, and the falling time of the particles in the tower is ≥6s.

[0018] Furthermore, in step 6, qualified particles with a particle size of 1.5~4.0mm are screened and selected. The particles are then cooled to a temperature of ≤40℃ using a fluidized bed before being coated with a roller. The coating process takes 8~15 minutes.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. Significantly improved stability during storage and transportation of granules: Through the synergistic effects of low-temperature mixing to reduce crystal transformation, emulsification and homogenization to eliminate internal bubbles, and surface coating to block moisture adsorption, the compressive strength of the finished granules can reach over 55N, which is more than 40% higher than that of the traditional high-tower process; after 6 months of sealed storage at room temperature, the agglomeration rate is reduced to below 3%, which is more than 70% lower than that of the traditional process, effectively reducing the problems of pulverization and caking during storage and transportation; 2. By scientifically combining nitrate nitrogen and ammonium nitrogen, a combination of rapid and sustained effects is achieved. Polymerized phosphorus is introduced to reduce soil fixation. The apparent utilization rate of nitrogen in the finished product can reach more than 41%, and the apparent utilization rate of phosphorus can reach more than 25%, which is 12% and 20% higher than traditional processes, respectively. Nutrient release is more balanced, which can reduce the frequency of topdressing during the crop growth period. 3. Production energy consumption and safety risks are reduced simultaneously: The staged melting-low temperature mixing process reduces the secondary mixing temperature by about 30°C compared to the traditional process, and the saturated steam consumption per ton of product is reduced to less than 160 kg, which is more than 15% lower than the traditional process; at the same time, the lower system temperature reduces the safety hazards of high-temperature thermal decomposition of ammonium nitrate, and the production operation is more stable. 4. Significantly improved availability of micronutrients: Modified diatomaceous earth is used to load chelated micronutrients, avoiding the formation of insoluble precipitates due to inter-element antagonism. The effective micronutrient content in the finished product can reach more than 85%, which is more than 60% higher than the method of directly adding inorganic salts, thus significantly improving the crop absorption efficiency of micronutrients. Attached Figure Description

[0020] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Figure 1 This is a process flow diagram for preparing the balanced nitro compound fertilizer of the present invention; Figure 2 This is a schematic diagram of the granular cross-sectional structure of the balanced nitro compound fertilizer of the present invention; Figure 3 These are the particle compressive strength test results of various embodiments of the present invention; Figure 4 These are the nutrient utilization rate test results of various embodiments of the present invention; Figure 5 This is a comparison of the steam consumption per ton of product in various embodiments of the present invention; Figure 6 This is a comparison of the storage and transportation stability of various embodiments of the present invention; In the diagram: 101, raw material pretreatment unit; 102, primary melting and concentration unit; 103, secondary low-temperature mixing unit; 104, emulsification and homogenization unit; 105, high-tower granulation unit; 106, post-treatment and coating unit; 201, particle core; 202, chelated micro-fertilizer dispersed phase; 203, surface coating layer.

[0021] Note: Figure 3 is a bar chart comparing the compressive strength of the particles in each embodiment and the comparative example; Figure 4 is a comparison chart of nutrient utilization rate and the proportion of available trace elements in each embodiment; Figure 5 is a bar chart comparing the steam consumption per ton of product in each embodiment. Figure 6The graph shows a comparison of particle moisture content and 6-month agglomeration rate for each embodiment. Detailed Implementation

[0022] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0023] In the attached diagram, all identical reference numerals refer to the same components.

[0024] like Figure 1 As shown, this invention uses a staged melting-low temperature granulation process to prepare a balanced nitro compound fertilizer. The material flows sequentially through 6 functional units along the direction of the arrow. The equipment configuration and technical functions of each unit are as follows: Raw material pretreatment unit (101): Composed of hammer mill, rotary drum dryer and ribbon mixer, used to crush, dry and premix solid raw materials and functional additives, to ensure uniform feed particle size and moisture content, and to avoid local agglomeration in subsequent melting and mixing.

[0025] Primary melt concentration unit (102): The core is a rising film vacuum evaporator, equipped with a vacuum system and a heat transfer oil heating system, used to concentrate ammonium nitrate solution separately, reduce boiling temperature in a vacuum environment, and reduce the risk of thermal decomposition of ammonium nitrate while obtaining high-concentration melt.

[0026] Secondary low-temperature mixing unit (103): The core is an anchor-type mixing tank with jacket insulation, and a powder preheating and conveying device. It is the core unit that distinguishes this invention from the traditional high-temperature process. By preheating the powder and controlling the temperature of the low-temperature system, the mixing temperature is greatly reduced while ensuring the fluidity of the slurry.

[0027] Emulsification and homogenization unit (104): The core is a high-shear stator and rotor emulsifier, which breaks up the air bubbles and large-diameter dispersed phase in the slurry through high-speed shear force, refines the particle size of solid particles, reduces the internal stress and microcracks in the particle cooling process from the source, and improves the particle density.

[0028] High-tower granulation unit (105): It consists of a granulation tower with an effective height of 70~80m, a twin-shaft differential granulator at the top of the tower, and an air inlet system at the bottom of the tower. It adopts the counter-current cooling principle, where molten droplets are thrown down from the top of the tower and come into contact with the rising cold air in the opposite direction, gradually cooling and solidifying into granules.

[0029] Post-processing coating unit (106): Composed of a vibrating screener, a fluidized bed cooler, and an inclined roller coating machine, it is used to screen qualified particles, reduce particle temperature, and form a hydrophobic coating layer on the particle surface to block the crystal bridge connection between particles.

[0030] As shown in Figure 2, the balanced nitro compound fertilizer granules prepared by this invention have a spherical and dense structure, consisting of three layers from the inside out. The composition and technical function of each layer are as follows: Particle core (201): accounting for more than 95% of the total particle mass, it is formed by melting and solidifying ammonium nitrate, monoammonium phosphate, potassium sulfate and polymeric phosphorus; after emulsification and homogenization treatment, the core is dense and uniform inside, with a microcrack density of ≤5 lines / mm², and is the main carrier of nitrogen, phosphorus and potassium nutrients.

[0031] The chelated micronutrient dispersion phase (202) consists of independent micron-sized particles, primarily composed of chelated trace elements supported by modified diatomaceous earth, uniformly embedded within the particle core (201) matrix. The particle size range of this dispersion phase is 10–40 μm, with a volume average particle size D0. 50 With a particle size of 22-28 μm, it maintains the complete porous diatomaceous earth framework morphology. Chelated trace elements are stably adsorbed in the pores and surface of the carrier without melting agglomeration, dissolution loss, or crystal destruction. After two-stage low-temperature mixing and pre-dispersion and high-shear emulsification homogenization and refinement, the dispersed phase is homogeneously and randomly distributed in the three-dimensional space of the particle core. The trace element mass deviation rate of different cross sections from the surface to the inside of the particles is ≤8%, with no local enrichment, sedimentation stratification, or edge segregation. The number of dispersed phase particles in each cubic millimeter particle core can reach 1200-1800. The hydrophobic surface of modified diatomaceous earth forms a weak wetting interface with the molten ammonium nitrate and phosphate matrix, ensuring that the carrier particles are fully encapsulated by the molten slurry without dissolving themselves. The siliceous framework of diatomaceous earth forms a continuous physical barrier, completely isolating the internal chelated trace elements from the phosphate and ammonium ions in the slurry, preventing antagonistic reactions that could lead to the formation of insoluble phosphate precipitates under the 135-145℃ melting environment, and ensuring that the trace elements remain in their EDTA-chelated bioavailable form throughout the process. When the particles are applied to the soil and absorb water to dissolve, the outer layer of nitrogen, phosphorus, and potassium nutrients gradually dissolves and is released first, while the dispersed phase of modified diatomaceous earth is gradually exposed as the core matrix dissolves. After the carrier pores slowly absorb water, the internal chelated trace elements gradually diffuse and dissolve along the pore channels, exhibiting a slow-release characteristic that matches the release of macronutrients. The release cycle matches the release cycle of the main nitrogen, phosphorus, and potassium nutrients by ≥80%, which can prevent the concentrated leaching of trace elements in the early stages.

[0032] Surface coating layer (203): It is a continuous hydrophobic film layer with a thickness of 8~15μm, which is formed by compounding octadecylamine and talc powder and uniformly coating the outer surface of the particle core (201). It can block external moisture from penetrating into the particle interior, reduce direct contact between particles and crystal bridge formation, and is the core structure for reducing the agglomeration rate.

[0033] Specific preparation examples: All raw materials are industrial-grade qualified products, including: Monoammonium phosphate is of specification 11-44-0 (total nitrogen 11%, available phosphorus pentoxide 44%). Potassium sulfate contains ≥50% potassium oxide by mass. The modified diatomaceous earth-supported chelated micro-fertilizer was prepared using a four-step process: "carrier purification and calcination—organosilicon hydrophobic grafting—chelated salt pore loading—low-temperature solidification and sieving." The specific steps are as follows: Diatomaceous earth carrier purification pretreatment selects raw diatomaceous earth powder with a primary particle size D 50 The particle size is 15~25μm, and the specific surface area is 30~40m² / g. The raw powder is placed in a muffle furnace and calcined at 450~500℃ for 2~3h to remove organic matter and adsorbed impurities. After natural cooling, it is pulverized to 120~150 mesh by an air jet mill to obtain purified diatomaceous earth carrier.

[0034] A 2% (w / w) alkyltrimethoxysilane ethanol solution was prepared using 95% (v / v) industrial ethanol as the solvent. Purified diatomaceous earth was added to this solution at a liquid-to-solid mass ratio of 4:1. The mixture was stirred and impregnated at 120-150 rpm for 2 hours at room temperature to allow the siloxane monomers to graft onto the hydroxyl groups on the diatomaceous earth surface. After impregnation, the mixture was filtered, and the filter cake was washed twice with anhydrous ethanol to remove unreacted free siloxanes. The washed filter cake was then placed in a forced-air drying oven and dried at 105-110°C to constant weight, yielding a silicone-modified hydrophobic diatomaceous earth carrier with a surface water contact angle of 110°-125°, exhibiting stable hydrophobic barrier properties.

[0035] The chelated trace element pore loading was carried out according to the elemental mass ratio of iron:zinc:boron:manganese = 2:2:1:1. EDTA chelated iron (≥13% Fe), EDTA chelated zinc (≥15% Zn), borax (≥11% B), and EDTA chelated manganese (≥12% Mn) were weighed separately. These raw materials were dissolved in deionized water at 30-40℃ and stirred until completely dissolved to prepare a chelated salt mixed solution with a total trace element mass concentration of 80-100 g / L. Modified diatomaceous earth carrier was added to the mixed solution at a liquid-to-solid mass ratio of 3:1 and impregnated at a constant temperature of 35℃ with low stirring at 80-100 r / min for 3-4 hours, allowing the chelated salts to be uniformly loaded onto the internal pores and outer surface of the diatomaceous earth through capillary adsorption. After impregnation, the mixture was filtered and the solid-phase loaded material was collected.

[0036] Low-temperature curing and finished product sieving: The loaded material is spread into a layer with a thickness of ≤2cm and placed in a vacuum drying oven. It is dried for 6-8 hours under a vacuum of -0.06MPa and a temperature of 90-95℃ until the moisture content of the material is ≤1.0%. After drying, the material is sieved through a 100-mesh standard sieve. The undersize material is the modified diatomaceous earth-loaded chelated micro-fertilizer. The finished micro-fertilizer has a total trace element mass fraction of 10%±0.5% (based on elemental composition), a particle diameter of 18-30μm, and good dispersion compatibility with the high-tower molten slurry system.

[0037] The dry basis weight ratios of raw materials for each embodiment and comparative example are shown in Table 1.

[0038]

[0039] Example 1: (15-15-15 specification, optimal implementation) This embodiment corresponds completely to the process flow shown in Figure 1. The detailed operating parameters of each unit are as follows: Raw material pretreatment (corresponding to raw material pretreatment unit 101 in Figure 1): Monoammonium phosphate and potassium sulfate are crushed to 100 mesh using a hammer mill and then dried to a moisture content of 0.4% using a rotary dryer; ammonium polyphosphate, modified diatomaceous earth-loaded chelated micro-fertilizer, and mineral-derived potassium humate are weighed according to the formula and premixed in a ribbon mixer for 8 minutes to obtain a premixed powder with uniform composition.

[0040] Primary melt concentration (corresponding to primary melt concentration unit 102 in Figure 1): A 93% mass fraction industrial ammonium nitrate solution is continuously fed into a rising film evaporator and heated and concentrated under a vacuum of -0.085 MPa until the mass fraction of the solution reaches 99.0%. The discharge temperature is controlled at 150℃ to obtain a free-flowing ammonium nitrate melt, which is then kept warm and transported to the next unit.

[0041] Secondary low-temperature mixing (corresponding to secondary low-temperature mixing unit 103 in Figure 1): Monoammonium phosphate and potassium sulfate powder are preheated to 85°C and continuously added to a jacketed and insulated mixing tank. They are initially mixed with molten ammonium nitrate under stirring, and then premixed powder is added. The temperature is precisely controlled by the jacket heat transfer oil to maintain the system temperature at 140°C. The anchor-type stirring paddle speed is 70 r / min, and the mixing time is 10 min to obtain a uniform and non-agglomerated molten slurry. The measured slurry moisture content is 1.0%.

[0042] Emulsification and homogenization (corresponding to Emulsification and homogenization unit 104 in Figure 1): The molten slurry is continuously fed into a high-shear stator-rotor emulsifier, with a rotation speed of 1300 r / min and a material residence time of 2.5 min. After processing, the average particle size of the dispersed phase in the slurry is refined to 72 μm, and the volume ratio of bubbles is reduced to below 0.4%, providing a basis for the formation of dense particle cores (201).

[0043] High-tower spray granulation (corresponding to Figure 1, high-tower granulation unit 105): The homogenized molten slurry is kept warm and transported to the top of the tower to a twin-shaft differential granulator. The temperature of the slurry entering the machine is controlled at 135℃, and the granulation nozzle orifice diameter is 3.5mm. Under the action of centrifugal force, the slurry is sprayed into uniform droplets. During the process of falling along the 75m high tower, it comes into countercurrent contact with the rising cold air. The air temperature inside the tower is 25℃, the rising wind speed is 0.9m / s, and the particle falling time is about 6.5s. After being completely cooled and solidified, it falls into the collection hopper at the bottom of the tower.

[0044] Post-processing packaging (corresponding to post-processing packaging unit 106 in Figure 1): The particles discharged from the bottom of the tower are first screened by a vibrating screen to select qualified particles with a particle size of 1.5~4.0mm. Large particles on the screen and fine powder under the screen are returned to the melting system for reuse. Qualified particles are sent to a fluidized bed cooler and cooled to 38℃. Then they are sent to a roller packaging machine with an inclination angle of 3°. Surface modifiers are added according to the formula. The roller speed is 18r / min and the packaging process is 10min to make the modifier evenly coat the particle surface and form a continuous surface coating layer (203). Finally, the finished product is metered and packaged.

[0045] The measured indicators of the finished product in this embodiment are as follows: total nutrient mass fraction 45.2%, nitrate nitrogen mass fraction 35% of total nitrogen, polymeric phosphorus mass fraction 18% of total phosphorus (calculated as phosphorus pentoxide), and total trace element mass fraction 0.3% (calculated as elemental).

[0046] Example 2: (16-16-16 specification) The process flow in this embodiment is completely the same as that in Embodiment 1. The differences in process parameters for each unit in Figure 1 are as follows: Raw material pretreatment unit (101): Monoammonium phosphate and potassium sulfate are pulverized to 120 mesh and dried to a moisture content of 0.3%; Primary melt concentration unit (102): Ammonium nitrate solution with an initial mass fraction of 94% is concentrated to 99.2%, and the melt discharge temperature is 152℃; Secondary low-temperature mixing unit (103): Powder preheated to 88℃, mixing system temperature 142℃, stirring speed 75r / min, mixing time 9min, slurry moisture content 0.9%; Emulsification and homogenization unit (104): Emulsifier speed 1400 r / min, material residence time 2 min; High-tower granulation unit (105): granulation slurry temperature 138℃, nozzle orifice diameter 3.2mm, air inlet temperature 22℃, rising wind speed 1.0m / s, effective height of granulation tower 80m; Post-processing packaging unit (106): The particles are packaged after being cooled to 36°C, and the packaging time is 12 min.

[0047] The measured indicators of the finished product in this embodiment are as follows: total nutrient mass fraction 48.1%, nitrate nitrogen accounts for 33% of total nitrogen, polymeric phosphorus accounts for 20% of total phosphorus, and total trace element mass fraction 0.35%.

[0048] Example 3 (14-14-14 specification) The process flow in this embodiment is completely the same as that in Embodiment 1. The differences in process parameters for each unit in Figure 1 are as follows: Secondary low-temperature mixing unit (103): mixing system temperature 138℃, stirring rate 65r / min, mixing time 11min, slurry moisture content 1.1%; Emulsification and homogenization unit (104): Emulsifier speed 1200 r / min, material residence time 3 min; High-tower granulation unit (105): granulation slurry temperature 132℃, nozzle orifice diameter 3.8mm, air inlet temperature 28℃, rising wind speed 0.8m / s.

[0049] The measured indicators of the finished product in this embodiment are as follows: total nutrient mass fraction 42.3%, nitrate nitrogen accounts for 37% of total nitrogen, polymeric phosphorus accounts for 16% of total phosphorus, and total trace element mass fraction 0.25%.

[0050] Comparative Example 1 (Traditional high-tower granulation process) 15-15-15 nitro compound fertilizer was prepared using the industry-standard high-tower melt granulation process. The raw materials consisted only of ammonium nitrate, monoammonium phosphate, and potassium sulfate. No polyphosphate, modified diatomaceous earth-loaded chelated micro-fertilizer, or mineral-derived potassium humate were added, and no surface coating treatment was performed. The melt mixing temperature was 170°C, and there was no emulsification homogenization process. The granulation tower height and sieving specifications were the same as in Example 1.

[0051] Performance verification tests and results analysis: Test Methodology: All tests were performed in triplicate, and the results were averaged. The test methods strictly followed industry standards. 1. Particle compressive strength: According to GB / T 44750-2024, using a particle strength tester, 20 whole particles with a particle size of 2.0~2.8mm were randomly selected, and the maximum pressure during crushing was measured. Figure 3 As shown.

[0052] 2.6-month clumping rate: 5 kg of each sample was sealed in a woven bag and subjected to a pressure of 0.05 MPa under an environment of 25±2℃ and 65%±5% relative humidity to simulate stacking. After 6 months of storage, the samples were dropped freely from a height of 1 m three times and passed through a 2.0 mm standard sieve. The proportion of clumped mass to total mass was calculated.

[0053] 3. Apparent nutrient utilization rate: A pot experiment was conducted on maize with the crop variety Zhengdan 958 and the soil being alluvial soil. The basic fertility was: available nitrogen 82 mg / kg, available phosphorus 18 mg / kg, and available potassium 120 mg / kg. Each pot contained 5 kg of soil, and the fertilizer application was calculated based on 0.15 g / kg of pure nitrogen in the soil. The planting cycle was 30 days. After harvest, the nitrogen and phosphorus content of the plants was determined by the Kjeldahl method and the vanadium molybdenum yellow colorimetric method. The apparent utilization rate was calculated by the difference method. The relevant nutrient utilization rate test results are shown in Figure 4, and the summary of various performance test data is shown in Table 2.

[0054] 4. Steam consumption per ton of product: After 8 hours of continuous and stable production on the pilot production line, the total saturated steam consumption and total finished product output are statistically analyzed to calculate the average steam consumption per ton of product. Figure 5 As shown.

[0055] 5. Proportion of available trace elements: The mass of available trace elements in the particles was determined by the DTPA extraction method - standard method for available trace elements in soil, and the proportion of available trace elements in the particles was calculated.

[0056] The test results are as follows: The core performance test results of all samples are shown in Table 2, and the relative core performance values ​​of Example 1 and Comparative Example 1 are shown in Figure 3.

[0057] Table 2 Comparison of Core Performance Test Results

[0058] Experimental results demonstrate that, based on the experimental data in Table 2 and Figure 3, the beneficial effects of this invention can be verified. 1. Improved storage and transportation stability: The compressive strength of particles in all three examples was ≥55N, an increase of 47%~58% compared to Comparative Example 1; the 6-month agglomeration rate was ≤3%, a decrease of 76%~83% compared to Comparative Example 1. This demonstrates that the synergistic effect of emulsification homogenization refining the internal structure and surface hydrophobic coating can significantly improve particle strength and anti-agglomeration performance, reducing pulverization and caking problems during storage and transportation. Figure 6 As shown.

[0059] 2. Improved nutrient utilization: The apparent nitrogen utilization rate in the example was increased by 12%~18% compared to the control group, and the apparent phosphorus utilization rate was increased by 23%~30%. This demonstrates that the combination design of nitrate nitrogen and ammonium nitrogen, and polymerized phosphorus to reduce soil fixation, can optimize nutrient release characteristics, achieve a combination of rapid and sustained effects, and improve nutrient utilization efficiency.

[0060] 3. Energy saving and safety optimization: The steam consumption per ton of product in the example was reduced by 13% to 17% compared with the comparative example, with an average reduction of about 15%. The temperature of the mixing system was also reduced by about 30°C compared with the traditional process, which verified the energy saving effect of the staged melting-low temperature process and reduced the safety risk of high temperature thermal decomposition of ammonium nitrate.

[0061] 4. Improved micronutrient availability: In the examples, the proportion of available micronutrients was ≥85%, an increase of 65%~69% compared to the control group. This demonstrates that the modified diatomaceous earth-supported chelation technology can effectively avoid antagonistic reactions between elements and significantly improve the bioavailability of micronutrients.

[0062] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A balanced nitro compound fertilizer, characterized in that, The mass ratio of nitrogen, phosphorus pentoxide, and potassium oxide is (14~16):(14~16):(14~16), and the total nutrient mass fraction, calculated as nitrogen, phosphorus pentoxide, and potassium oxide, is ≥45%. The raw materials for preparing the compound fertilizer, based on dry weight, include 320~360 parts ammonium nitrate, 220~250 parts monoammonium phosphate, 240~270 parts potassium sulfate, 15~30 parts polymeric phosphorus additive, 8~15 parts modified diatomaceous earth-loaded chelated micronutrient fertilizer, and 2~5 parts surface modifier. The total nitrogen of the compound fertilizer consists of nitrate nitrogen and ammonium nitrogen, and the total phosphorus, calculated as phosphorus pentoxide, consists of orthophosphate and polymeric phosphorus.

2. The balanced nitro compound fertilizer according to claim 1, characterized in that, Of the total nitrogen, nitrate nitrogen accounts for 32% to 38% of the total nitrogen mass, and ammonium nitrogen accounts for 62% to 68% of the total nitrogen mass; based on phosphorus pentoxide, the polymeric phosphorus accounts for more than 15% of the total phosphorus mass; the polymeric phosphorus additive is ammonium polyphosphate with a degree of polymerization of 2 to 5.

3. The balanced nitro compound fertilizer according to claim 1, characterized in that, The raw materials for preparing the compound fertilizer also include 5-12 parts by dry weight of mineral-derived potassium humate; the modified diatomaceous earth-supported chelated micronutrient fertilizer includes a diatomaceous earth carrier modified by organosilicon hydrophobicity, and EDTA-chelated iron, zinc, boron, and manganese loaded on the carrier. The total mass fraction of trace elements in the compound fertilizer is 0.2%-0.5% by element.

4. The balanced nitro compound fertilizer according to claim 1, characterized in that, The surface modifier is a powder coating agent composed of octadecylamine and talc in a mass ratio of 1:2, which is uniformly coated on the outer surface of the compound fertilizer particles.

5. A method for preparing a balanced nitro compound fertilizer according to any one of claims 1 to 4, comprising raw material pretreatment, melt mixing, high-tower granulation, and post-treatment steps, characterized in that, The method adopts a graded melting-low temperature granulation process, specifically including the following steps: (1) Raw material pretreatment: Monoammonium phosphate and potassium sulfate are crushed and dried respectively, and polymerized phosphorus additives are premixed with modified diatomaceous earth-loaded chelated micro-fertilizer to obtain premixed powder; (2) First-stage melting concentration: Ammonium nitrate solution is vacuum concentrated to a mass fraction of 98.5%~99.2%, and the liquid temperature is controlled at 145~155℃ to obtain ammonium nitrate melt; (3) Second-stage low temperature mixing: The preheated monoammonium phosphate, potassium sulfate and ammonium nitrate melt are stirred and mixed, and then the premixed powder is added. Powder, control the temperature of the mixing system to 135~145℃, mix evenly to obtain molten slurry; (4) Emulsification and homogenization: send the molten slurry into a high shear emulsifier for homogenization treatment, eliminate air bubbles in the slurry and refine the particle size of the dispersed phase; (5) High tower spraying granulation: the homogenized molten slurry is centrifugally sprayed into droplets by the granulation device at the top of the tower, and the droplets come into countercurrent contact with the rising cold air in the tower, and are cooled and solidified into particles; (6) Post-treatment and coating: after the solidified particles are screened and cooled, surface modifiers are added for roller coating treatment to obtain the finished product.

6. The preparation method according to claim 5, characterized in that: In step (1), monoammonium phosphate and potassium sulfate are pulverized to 100~120 mesh and dried to a moisture content of ≤0.5%; in step (3), monoammonium phosphate and potassium sulfate are preheated to 80~90℃, stirred at a speed of 60~80r / min, and mixed for 8~12min, and the resulting molten slurry has a moisture content of 0.8%~1.2%.

7. The preparation method according to claim 5, characterized in that: In step (4), the high-shear emulsifier has a rotation speed of 1200~1500 r / min and a homogenization time of 2~3 min.

8. The preparation method according to claim 5, characterized in that: In step (5), the temperature of the molten slurry entering the granulation device is 130~140℃, the diameter of the granulation nozzle is 3.0~4.0mm, the temperature of the rising cold air in the granulation tower is 20~30℃, the rising wind speed is 0.8~1.0m / s, and the falling time of the particles in the tower is ≥6s.

9. The preparation method according to claim 5, characterized in that: In step (6), particles with a diameter of 1.5~4.0 mm are selected by sieving. The particles are cooled to a temperature of ≤40℃ by a fluidized bed and then coated with a roller for 8~15 minutes.

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