Anti-caking and anti-dusting method of full water-soluble nitro compound fertilizer by high tower melt granulation

Abstract

This invention discloses a method for preventing agglomeration and pulverization of a fully water-soluble nitro compound fertilizer produced by high-tower melt granulation. The method includes the following steps: a melt preparation step, including adding a water-soluble crystal growth regulator to the fertilizer melt; a high-tower granulation step; a gradient cooling step, sequentially including a first slow cooling stage with a cooling rate of 2–6 °C / min and a second rapid cooling stage with a cooling rate of 6–15 °C / min; a water-soluble anti-agglomeration coating step using polyethylene glycol as the main component; and a finished product finishing step. This invention introduces potassium polyaspartate or low molecular weight sodium polyacrylate into the fully water-soluble nitro compound fertilizer melt granulation system. The filling effect of polymer segments at grain boundaries can buffer the internal stress caused by the volumetric abrupt change during the crystal transformation of ammonium nitrate, significantly reducing the pulverization rate of the particles. By implementing slow cooling near the critical temperature range of the ammonium nitrate type III → type II crystal transformation, the temperature difference between the inside and outside of the particles is small when crossing this phase transition point. This process provides an engineering control method for preventing pulverization from the perspective of cooling parameters.

Description

Technical Field

[0001] This invention belongs to the field of fertilizer production technology, specifically relating to a production method for preventing caking and pulverization of fully water-soluble nitro compound fertilizer using a high-tower melt granulation process. Background Technology

[0002] Fully water-soluble nitro compound fertilizer (hereinafter referred to as "nitro water-soluble fertilizer") is a high-end water-soluble fertilizer produced using nitrate nitrogen salts such as ammonium nitrate and potassium nitrate, and water-soluble phosphorus and potassium salts such as ammonium dihydrogen phosphate and potassium dihydrogen phosphate as core raw materials through a specific process. High-tower melt granulation is one of the mainstream processes for producing compound fertilizer granules in China. High-tower melt granulation has advantages such as a short process flow, uniform particle shape, no need for drying, and high production efficiency, and has been widely used in the industrial production of nitro water-soluble fertilizers.

[0003] To address the caking problem of compound fertilizers, existing technologies typically employ coating the granule surface with inorganic inert powders such as diatomaceous earth, kaolin, or talc, or spraying with organic isolating substances like paraffin oil or mineral oil as anti-caking agents. These substances are all water-insoluble. While they have some anti-caking effect on ordinary compound fertilizers, when used in nitro water-soluble fertilizers, these water-insoluble substances remain as solid suspensions in the application solution. This directly leads to excessive water-insoluble content in the product, failing to meet the mandatory limit of no more than 0.2% in current national standards (such as GB / T 14816), fundamentally undermining the product's core quality attribute of "fully water-soluble."

[0004] To address the pulverization problem, existing technologies mainly control the particle cooling rate by adjusting the cooling air volume and temperature of the granulation tower, or by mixing a small amount of urea into the melt to improve the particle mechanical strength. However, these measures fail to fundamentally suppress the internal stress of particles induced by the crystal transformation of ammonium nitrate, resulting in limited improvement in the pulverization rate; moreover, the pulverization problem becomes more severe with the increase of the proportion of nitrate nitrogen salts in the formulation.

[0005] In summary, in the current high-tower melt granulation production of fully water-soluble nitro compound fertilizers, anti-caking and anti-pulverization are usually treated as independent technical problems, lacking a systematic method to simultaneously solve both problems while maintaining the product's full water solubility. How to achieve the dual goals of preventing agglomeration and pulverization of nitro water-soluble fertilizer granules without introducing water-insoluble substances is a pressing technical challenge in this field. Summary of the Invention

[0006] The technical problem to be solved by this invention is to address the two major quality defects of granular products in the production of fully water-soluble nitro compound fertilizer by high-tower melt granulation process: agglomeration and pulverization. In addition, the existing anti-agglomeration technology (inorganic powder or mineral oil coating) is not suitable for fully water-soluble products due to its insolubility. This invention provides a systematic production method that can simultaneously achieve the dual functions of anti-agglomeration and anti-pulverization while maintaining the fully water-soluble characteristics of the product.

[0007] To solve the above-mentioned technical problems, the present invention provides a method for preventing agglomeration and pulverization in the production of fully water-soluble nitro compound fertilizer by high-tower melt granulation, comprising the following steps:

[0008] Step (1) Melt preparation step: The compound fertilizer raw materials, including the nitrate nitrogen source, are melted and mixed at a temperature of 130-160℃ to form a fertilizer melt; and a water-soluble crystal growth regulator is added to the fertilizer melt, the amount of which is 0.05%-0.40% of the total mass of the fertilizer melt. The water-soluble crystal growth regulator is a water-soluble polymer with polycarboxylic acid groups or amino acid repeating units, preferably polyaspartic acid salt or low molecular weight sodium polyacrylate.

[0009] Step (2) High tower granulation step: The fertilizer melt obtained in step (1) is granulated in the granulation tower by spraying through the granulation nozzle. The droplets are cooled and solidified by the cooling airflow during the falling process to form spherical fertilizer particles.

[0010] Step (3) Gradient cooling step: The fertilizer granules obtained in step (2) are subjected to segmented gradient cooling, including a first slow cooling stage and a second rapid cooling stage. The first slow cooling stage reduces the temperature of the granules to 80-95℃ at a cooling rate of 2-6℃ / min; the second rapid cooling stage reduces the temperature of the granules to 40-55℃ at a cooling rate of 6-15℃ / min.

[0011] Step (4) Anti-caking coating step: Spray water-soluble anti-caking coating liquid onto the surface of fertilizer granules cooled in step (3); the water-soluble anti-caking coating liquid is mainly composed of polyethylene glycol, and the amount of coating liquid added is 0.15% to 0.60% of the granule mass based on the effective component of polyethylene glycol.

[0012] Step (5) Finished product finishing step: Cool the coated granules to below 35°C and control the moisture content of the final product to not exceed 0.3% to obtain the fully water-soluble nitro compound fertilizer finished product.

[0013] Compared with the prior art, the present invention has the following beneficial effects: (1) Introduce potassium polyaspartate or low molecular weight sodium polyacrylate into the melt granulation system of fully water-soluble nitro compound fertilizer. The polycarboxylic acid functional groups of the above polymers can bind to the active sites of crystal nuclei of salts such as ammonium nitrate, and inhibit the rapid growth of grains through the "molecular adsorption-crystal plane closure" mechanism, thereby refining the internal grain size of the particles and reducing the contact stress between grains; at the same time, the filling effect of polymer chain segments at the grain boundaries can buffer the internal stress of volume change generated during the crystal transformation of ammonium nitrate, reduce the formation of microcracks from the root, and significantly reduce the particle pulverization rate.

[0014] (2) By slowly cooling the particles near the critical temperature range of the phase transition from type III to type II of ammonium nitrate, the temperature difference between the inside and outside of the particles is small when they cross the phase transition point, which effectively suppresses the accumulation of internal stress during the phase transition. After the particles have completed the key phase transition, the cooling rate is increased to ensure production efficiency. This process provides an engineering control method for preventing pulverization from the perspective of cooling parameters.

[0015] (3) Polyethylene glycol is used as the main body of the anti-caking coating. This substance is completely water-soluble and forms a continuous hydrophilic isolation layer on the particle surface. By reducing the water activity conduction on the particle surface and direct contact between particles, it effectively blocks the agglomeration path. Water-soluble potassium humate is added to further improve the density and weather resistance of the isolation film. The above coating materials are completely water-soluble and dissolve completely with the fertilizer when used for fertilization, without producing water-insoluble residues. This ensures that the water-insoluble content of the product is stably controlled below 0.2%. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the steps in the anti-caking and anti-powdering method of the present invention. Detailed Implementation

[0017] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto. Modifications, substitutions or variations made by those skilled in the art based on the technical solutions of the present invention all fall within the protection scope of the present invention.

[0018] The specifications of the raw materials used in the following examples are as follows: Ammonium nitrate: content ≥99.0%, water-insoluble matter ≤0.05%; Ammonium dihydrogen phosphate: content ≥99.0%, water-insoluble matter ≤0.05%; Potassium dihydrogen phosphate: content ≥98.0%, water-insoluble matter ≤0.05%; Potassium nitrate: content ≥99.0%, water-insoluble matter ≤0.02%; Potassium polyaspartate (PASP-K), weight average molecular weight 1500–2500 Da, effective content 50% aqueous solution, water-insoluble matter ≤0.01%; Polyethylene glycol PEG-400: Number average molecular weight 380~420 Da, APHA color number ≤10, aqueous solution does not separate into layers; Potassium humate: Water-soluble, with a transmittance of ≥80% at 550 nm wavelength in a 5 g / L aqueous solution, and a moisture content of ≤15%. All the above raw materials meet the quality requirements for raw materials used in water-soluble fertilizers and do not introduce water-insoluble components after dissolving in water.

[0019] The performance testing methods for the following embodiments are uniformly as follows: (1) Agglomeration rate test: The product particles to be tested (about 200 g) were placed in a sealed PE bag and placed in a constant temperature and humidity chamber. They were left to stand for 30 days at a temperature of 25±2℃ and a relative humidity of 75±3%. After taking them out, the mass of the agglomerates that could not pass through the 6.7 mm sieve was weighed and the percentage of the agglomerates in the total mass of the sample was calculated. This is the standing agglomeration rate.

[0020] (2) Powdering rate test: Refer to the vibration test method in GB / T 17767.3, put about 1 kg of particle sample into a vibrating sieve (sieve hole 1.0 mm), vibrate for 20 min under the specified vibration parameters, weigh the mass of powder passing through the 1.0 mm sieve, and calculate its percentage of the total mass of the sample, which is the powdering rate.

[0021] (3) Water-insoluble matter content test: The water-insoluble matter content is determined according to the method specified in GB / T 8572. A 5% (mass fraction) fertilizer aqueous solution is prepared, filtered through a 0.2 μm filter membrane, the retained solid is weighed, and the percentage of water-insoluble matter is calculated.

[0022] Example 1: Step (1) Melt preparation: Based on the target nutrient ratio of N:P2O5:K2O=20:20:20, calculate and weigh the following raw materials: 395.6 kg of ammonium nitrate, 299.7 kg of ammonium dihydrogen phosphate, 115.5 kg of potassium dihydrogen phosphate, and 189.2 kg of potassium nitrate, totaling 1000.0 kg. The above raw materials are sequentially added to a stainless steel batching vessel equipped with a jacketed heater and an anchor-type stirrer. Steam is introduced to raise the temperature of the materials to 140°C, and stirring is continued until all raw materials are completely melted and homogeneous, forming a clear fertilizer melt. During the heating process, a PASP-K aqueous solution (equivalent to 1.5 kg of pure PASP-K, i.e., 0.15% of the melt mass) is slowly and metered into the melt. The mixture is then kept at 140°C and stirred for 20 min to ensure the regulator is evenly dispersed in the melt. The holding time should not exceed 25 min from the time the regulator is added to prevent material decomposition.

[0023] Step (2) High-tower granulation: The melt obtained in step (1) (temperature approximately 138℃) is delivered to the rotating nozzle at the top of the granulation tower via a constant-pressure pump at a constant flow rate. The effective height of the tower is 100 m, the inner diameter is 5.5 m, and the nozzle rotation speed is approximately 1200 r / min. Under centrifugal force, the melt is atomized into droplets with an average droplet diameter of approximately 2.2 mm. Simultaneously, a blower at the bottom of the tower draws clean air at 22℃ and 50% relative humidity through the tower at an apparent wind speed of approximately 3.5 m / s, allowing it to come into countercurrent contact with the falling droplets for heat exchange. The droplets completely solidify after falling approximately 100 m and are collected by a scraper conveyor at the bottom of the tower. The temperature of the granules exiting the tower is 92–98℃.

[0024] Step (3) Gradient Cooling: The particles collected at the bottom of the tower are conveyed by a scraper conveyor to the primary slow-cooling fluidized bed cooler. With an inlet air temperature of 18℃ and an air volume of approximately 12,000 m³ / h, the particles are slowly cooled at a cooling rate of approximately 3.5℃ / min. When the particle outlet temperature drops to 87℃, they are continuously conveyed to the secondary rapid-cooling fluidized bed cooler, where an inlet air temperature of 15℃ and an air volume of approximately 28,000 m³ / h rapidly cool the particles to 48℃ at a cooling rate of approximately 9℃ / min. The entire gradient cooling process is carried out in a closed environment to prevent the particles from absorbing moisture during the cooling process.

[0025] Step (4) Anti-caking coating: The cooled granules are continuously fed into a rotary drum coating machine (drum inner diameter 2.0 m, length 3.0 m, rotation speed 22 r / min). Anti-caking coating solution preparation: 30.0 kg of PEG-400 and 5.0 kg of dry-based potassium humate are heated and dissolved in 35.0 kg of 60℃ warm water, and thoroughly stirred to prepare a coating solution with a mass fraction of approximately 50%. The coating solution is evenly sprayed onto the surface of the granules tumbling inside the drum through a dual-fluid nozzle for approximately 10 min. The amount of coating solution added is approximately 0.30% of the granule mass based on PEG-400, and the amount of potassium humate added is approximately 0.05% of the granule mass. The granule temperature is maintained at 45–52℃ during coating.

[0026] Step (5) Finished Product Finishing: After coating, the granules enter an air-cooled vibrating screen and are cooled to below 28°C. Particle size is then graded, and particles with a diameter of 2.0–4.5 mm are considered qualified. After testing and confirming a moisture content of ≤0.3%, the granules are packaged and stored to obtain the finished NPK 20-20-20 type fully water-soluble nitro compound fertilizer. Testing showed that the product in Example 1 had a total nutrient content of 57.6%, a static agglomeration rate of 1.8%, a pulverization rate of 1.2%, a water-insoluble content of 0.07%, and a particle size qualification rate of 97.3%.

[0027] Example 2: Step (1) Melt preparation: Weigh 617.0 kg of ammonium nitrate, 145.7 kg of ammonium dihydrogen phosphate, and 237.3 kg of potassium nitrate (total 1000.0 kg) according to the target nutrient ratio of N:P2O5:K2O=30:10:10, put them into the mixing tank, heat to 138℃, and after they are completely melted and uniform, add 2.0 kg of pure PASP-K (accounting for 0.20% of the melt mass), and stir at 138℃ for 20 min.

[0028] Step (2) High-tower granulation: The process parameters are the same as in Example 1, with an average droplet diameter of about 2.5 mm, a cooling air temperature of 20°C, a relative humidity of ≤55%, and a particle outlet temperature of about 94-99°C. Due to the high proportion of ammonium nitrate in the high-nitrogen formulation and the slightly lower melting point of the melt, heat preservation control is particularly important, and the heat preservation time should not exceed 20 min.

[0029] Step (3) Gradient cooling: The cooling rate in the first slow cooling stage is controlled at about 3.0℃ / min, and the particle outlet temperature drops to 88℃; the cooling rate in the second rapid cooling stage is about 8℃ / min, and the particles are cooled to 45℃. Since the proportion of ammonium nitrate in this formula is high, the crystal transformation effect is more significant. The residence time in the first slow cooling stage is appropriately extended, and the air volume residence time is increased by 20% compared with Example 1.

[0030] Step (4) Anti-caking coating: The amount of PEG-400 added is 0.40% of the particle mass, and the amount of potassium humate added is 0.10% of the particle mass. Prepare a 50% aqueous solution for spraying. The coating temperature is 46-52℃, the drum speed is 20 r / min, and the spraying time is 12 min.

[0031] Step (5) Finished product finishing: Same as Example 1. Testing showed that the total nutrient content of the product in Example 2 was 47.4%, the static clumping rate was 2.3%, the pulverization rate was 1.5%, the water-insoluble matter content was 0.09%, and the particle size qualification rate was 96.5%.

[0032] Example 3: Step (1) Melt preparation: Weigh out 204.8 kg of ammonium nitrate, 72.7 kg of ammonium dihydrogen phosphate, 95.8 kg of potassium dihydrogen phosphate, and 572.9 kg of potassium nitrate (totaling 946.2 kg of effective raw materials, with the remainder being the trace moisture in the above raw materials to balance to 1000 kg of melt) according to the target nutrient ratio of N:P2O5:K2O=15:5:30. Heat to 135℃, and after complete and uniform melting, add 1.0 kg of pure PASP-K (accounting for 0.10% of the melt mass) and stir for 20 min. This formula has a relatively high proportion of potassium nitrate, resulting in moderate melt viscosity and good fluidity.

[0033] Step (2) High-tower granulation: The average diameter of the droplets is about 2.0 mm, the cooling air temperature is 20℃, the relative humidity is ≤55%, and the temperature of the particles exiting the tower is about 90~96℃.

[0034] Step (3) Gradient cooling: Since the potassium nitrate content in this formula is high, the crystal transformation temperature effect is relatively weak. The first slow cooling rate can be slightly higher, controlled at about 5℃ / min, to cool the particles from about 93℃ to 86℃; the second rapid cooling stage has a cooling rate of about 11℃ / min, cooling to 46℃.

[0035] Step (4) Anti-caking coating: The amount of coating liquid added is 0.25% of the particle mass based on PEG-400, the amount of potassium humate added is 0.08% of the particle mass, and the coating temperature is 44-50℃.

[0036] Step (5) Finished product finishing: Same as Example 1. Testing showed that the total nutrient content of the product in Example 3 was 57.4%, the static clumping rate was 1.5%, the pulverization rate was 1.0%, the water-insoluble matter content was 0.06%, and the particle size qualification rate was 97.8%.

[0037] Comparative Example 1: Based on the raw material ratio of Example 1 (NPK 20-20-20), no crystal growth regulator was added when preparing the melt; the high-tower granulation process parameters were the same as in Example 1; after granulation, uniform cooling was performed using a single cooling airflow, with an average cooling rate of approximately 12°C / min, directly cooling the particles from approximately 95°C to 48°C; no anti-caking coating was applied, and the particles were directly collected and bagged. Testing showed that the static agglomeration rate of Comparative Example 1 was 18.6%, the pulverization rate was 9.3%, and the water-insoluble matter content was 0.05%.

[0038] Comparative Example 2: Based on the raw material ratio of Example 1 (NPK 20-20-20), no crystal growth regulator was added when preparing the melt; the uniform cooling process of Comparative Example 1 was adopted; after granulation and cooling, diatomaceous earth powder with a particle size of 200 mesh (added at 0.5% of the particle mass) was evenly sprinkled on the surface of the particles as an anti-caking treatment. Testing showed that the static agglomeration rate of the product of Comparative Example 2 was 5.2%, the pulverization rate was 8.7%, and the water-insoluble matter content was 0.61% (exceeding the national standard limit). The particles appeared grayish-white, and the solution was turbid.

[0039] Comparative Example 3: Based on the raw material ratio of Example 1 (NPK 20-20-20), no crystal growth regulator was added when preparing the melt; the same gradient cooling process as step (3) of Example 1 was used; and no anti-caking coating was applied after cooling. Testing showed that the static agglomeration rate of Comparative Example 3 was 12.1%, the pulverization rate was 4.8%, and the water-insoluble content was 0.05%, indicating that gradient cooling alone could improve pulverization but could not effectively prevent agglomeration.

[0040] The main performance indicators of Examples 1-3 and Comparative Examples 1-3 are compared in the table below:

[0041] The table " This indicates that the content exceeds the national standard limit (≤0.2%), and the product does not meet the requirements for fully water-soluble fertilizer.

[0042] As can be seen from the data in the table above, the fully water-soluble nitro compound fertilizer produced using the method of this invention (Examples 1-3) has a static clumping rate of ≤3%, a pulverization rate of ≤2%, and a water-insoluble content of ≤0.2%. All key quality indicators are significantly better than those of the comparative examples, and fully meet the national standards for fully water-soluble fertilizers. Comparative Example 1 (no growth regulator + uniform cooling) had a clumping rate and pulverization rate in the double digits, indicating that technical intervention is urgently needed to prevent clumping and pulverization. Comparative Example 2 (diatomaceous earth anti-caking) reduced the clumping rate, but the introduction of water-insoluble substances resulted in a severely excessive water-insoluble content, making it unsuitable for fully water-soluble products. Comparative Example 3 (gradient cooling only) improved pulverization but could not effectively prevent clumping, with a clumping rate still as high as 12.1%. The above comparisons fully demonstrate that this invention, through the synergistic effect of a triple mechanism of "crystal growth regulator + gradient cooling + water-soluble anti-caking coating," can simultaneously achieve the technical goals of preventing clumping and pulverization while maintaining the fully water-soluble characteristics of the product.

Claims

1. A method for preventing agglomeration and pulverization of a high-tower melt granulation fully water-soluble nitro compound fertilizer, characterized in that, Includes the following steps: Step (1) Melt preparation step: The compound fertilizer raw materials, including the nitrate nitrogen source, are melted and mixed at a temperature of 130-160℃ to form a fertilizer melt; and a water-soluble crystal growth regulator is added to the fertilizer melt, the amount of which is 0.05%-0.40% of the total mass of the fertilizer melt; Step (2) High tower granulation step: The fertilizer melt obtained in step (1) is granulated in the granulation tower by spraying through a granulation nozzle to form spherical fertilizer particles; Step (3) Gradient cooling step: The fertilizer granules obtained in step (2) are subjected to segmented gradient cooling. The segmented gradient cooling includes a first slow cooling stage and a second rapid cooling stage. In the first slow cooling stage, the temperature of the granules is reduced to 80-95℃, and the cooling rate is controlled at 2-6℃ / min. In the second rapid cooling stage, the temperature of the granules is reduced to 40-55℃, and the cooling rate is controlled at 6-15℃ / min. Step (4) Anti-caking coating step: Spray a water-soluble anti-caking coating liquid onto the surface of the fertilizer granules after cooling in step (3); the water-soluble anti-caking coating liquid is mainly composed of polyethylene glycol, and the amount of coating liquid added is 0.15% to 0.60% of the granule mass based on the effective component of polyethylene glycol; Step (5) Finished product finishing step: Cool the coated granules to below 35°C so that the moisture content of the final product does not exceed 0.3% to obtain the fully water-soluble nitro compound fertilizer finished product.

2. The method according to claim 1, characterized in that, The water-soluble crystal growth regulator mentioned in step (1) is polyaspartic acid salt, and the weight-average molecular weight of the polyaspartic acid salt is 1000-5000 Da.

3. The method according to claim 2, characterized in that, The polyaspartic acid salt is potassium polyaspartic acid salt, and its addition amount is 0.08% to 0.25% of the total mass of the fertilizer melt.

4. The method according to claim 1, characterized in that, The water-soluble crystal growth regulator mentioned in step (1) is a low molecular weight sodium polyacrylate with a weight average molecular weight of 1000-4000 Da.

5. The method according to claim 1, characterized in that, The nitrate nitrogen source mentioned in step (1) is ammonium nitrate and / or potassium nitrate; the water-soluble phosphate is ammonium dihydrogen phosphate and / or potassium dihydrogen phosphate; and the water-soluble potassium salt is potassium nitrate and / or potassium dihydrogen phosphate.

6. The method according to claim 1, characterized in that, In step (1), the melting and mixing temperature is 135-150℃, and the heat preservation time from the completion of fertilizer melt preparation to entering step (2) does not exceed 30 min.

7. The method according to claim 1, characterized in that, In step (2), the effective drop height of the granulation tower is 80-130 m; the average diameter of the droplets sprayed from the granulation nozzle is 1.5-4.0 mm; the temperature of the cooling air introduced into the granulation tower is 10-30℃ and the relative humidity does not exceed 60%.

8. The method according to claim 1, characterized in that, In step (3), the first slow cooling stage reduces the particle temperature from 90-100℃ to 85-92℃ at a cooling rate of 2.5-5.0℃ / min; the second rapid cooling stage reduces the particle temperature from 85-92℃ to 42-52℃ at a cooling rate of 7-12℃ / min.

9. The method according to claim 1, characterized in that, The water-soluble anti-caking coating liquid in step (4) also contains potassium humate, with the amount of potassium humate added being 0.05% to 0.20% of the particle mass; the transmittance of the potassium humate at a wavelength of 550 nm after being prepared as a 5 g / L aqueous solution is not less than 80%; the number average molecular weight of the polyethylene glycol is 200 to 800 Da; the coating equipment is a rotary drum coating machine, with an operating speed of 15 to 35 r / min and a coating liquid spraying time of 5 to 15 min; the coating operation temperature is 42 to 52℃; the water-soluble anti-caking coating liquid also contains 5% to 15% C by mass. 12 ~C 18 Alkyl sulfonate potassium salt.

10. The method according to any one of claims 1 to 9, characterized in that, The N-P2O5-K2O nutrient ratio of the fully water-soluble nitro compound fertilizer is (15-35):(5-25):(5-35), and the total nutrient content (N+P2O5+K2O) is not less than 30%; the nitrogen content includes nitrate nitrogen (NO3) - The proportion of nitrogen (-N) in the total nitrogen content is 25% to 55%.

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