A process for the preparation of ammonium chloride granular fertilizer

Abstract

This invention relates to the field of granular fertilizer production technology and discloses a preparation process for ammonium chloride granular fertilizer. The process includes raw material pretreatment, gradient granulation, segmented drying, surface modification, and screening and packaging. By adding a hydrophobic modifier to the raw material and using the hydrophobic modifier to modify the surface of ammonium chloride, the ammonium chloride granules are guaranteed to have low hygroscopic properties. At the same time, the construction of a hydrophobic layer prevents the penetration of external environmental moisture into the granules, ensuring the stability of the ammonium chloride granules during storage and transportation and reducing the risk of fertilizer clumping. By using sodium alginate and calcined bentonite as a binder and utilizing their synergistic bonding effect, a dense internal skeletal structure is formed in the granules, giving the ammonium chloride granules excellent strength. At the same time, the granules are guaranteed to have regularity during granulation, ensuring that the ammonium chloride granules are not easily broken during transportation and use.

Description

Technical Field

[0001] This invention relates to the field of granular fertilizer production technology, specifically to a preparation process for ammonium chloride granular fertilizer. Background Technology

[0002] Ammonium chloride is a major byproduct of soda ash production via the combined alkali process. It is a white crystalline solid that is hygroscopic and prone to clumping. It decomposes easily when heated. Ammonium chloride undergoes hydrolysis in water and decomposes into ammonia and hydrogen chloride gas when heated. It can also react with basic oxides and sulfuric acid to produce ammonium bisulfate and hydrogen chloride.

[0003] Currently, due to the inherent properties of ammonium chloride raw powder, which is prone to absorbing moisture and clumping and decomposing easily when heated, the raw material processing stage often lacks targeted hydrophobic modification and binding enhancement treatment during the preparation of conventional granular fertilizers. If the storage or application environment has high humidity, it may cause the granules to absorb moisture and pulverize or nitrogen to be lost rapidly, thus failing to guarantee the physical stability and long-term nutrient supply of the fertilizer.

[0004] Therefore, a preparation process for ammonium chloride granular fertilizer is proposed to solve the above problems. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a preparation process for ammonium chloride granular fertilizer, which solves the problems mentioned in the background technology, such as granule hygroscopic pulverization or rapid nitrogen loss, which cannot guarantee the physical stability and long-term nutrient supply of fertilizer.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a preparation process for ammonium chloride granular fertilizer, comprising the following steps:

[0007] Step 1: Raw material pretreatment. Take ammonium chloride raw powder, binder, hydrophobic modifier and slow-release coating agent. Place the ammonium chloride raw powder in a fluidized bed and dry it with hot air at 120-150℃ until the moisture content is ≤0.5%. Then mix it with binder and hydrophobic modifier at a mass ratio of 100:3-8:1-4. Then pulverize it with airflow to a particle size of ≤80μm to obtain mixed powder.

[0008] Step 2: Gradient granulation. The mixed powder is fed into a twin-screw extruder granulator. The screw speed is set to 80-120 rpm and the barrel temperature is set to 60-80℃. Atomized water is sprayed in to control the moisture content of the material at 12-18%. The extruded strips are crushed by rotary shearing to obtain wet granules with a particle size of 2-4 mm.

[0009] Step 3: Segmented drying. The wet granules enter a three-stage belt dryer. The first temperature zone is 120-140℃ for 10-15 minutes, the second temperature zone is 90-110℃ for 15-20 minutes, and the third temperature zone is 60-80℃ for 10-15 minutes, until the moisture content of the granules is ≤1.5%.

[0010] Step 4: Surface modification. The dried particles are fed into a fluidized bed coating device. Using nitrogen as a carrier, the molten slow-release coating agent is sprayed at a rate of 5-10 kg / h to coat the particles. The coating amount accounts for 2-5% of the total mass of the particles. At the same time, a mixture of ammonia and carbon dioxide is introduced. The gas pressure in the fluidized bed is controlled at 0.1-0.3 MPa, the temperature at 50-70℃, and the reaction time at 8-12 min.

[0011] Step 5: Screening and packaging. The modified granules are screened by a vibrating screen, retaining particles with a diameter of 3-5mm. After cooling to room temperature, they are metered and packaged to obtain ammonium chloride granular fertilizer.

[0012] Preferably, in step one, the binder is composed of sodium alginate and bentonite in a mass ratio of 2:1, wherein the bentonite is calcined at 800-1000℃ for 2-3 hours, cooled and then ground to a particle size ≤50μm;

[0013] The hydrophobic modifier is a complex of calcium stearate and silane coupling agent KH-570 in a mass ratio of 3:1. Before use, the silane coupling agent is prepared into a 20wt% solution with anhydrous ethanol and hydrolyzed at 60-70℃ for 30 min.

[0014] Preferably, the preparation of the mixed powder in step one further includes: mixing ammonium chloride raw powder with a binder and a hydrophobic modifier, and then adding 0.5-1% of nano-titanium dioxide by mass of the mixture. The nano-titanium dioxide undergoes plasma surface treatment with the following parameters:

[0015] Radio frequency power 300-500W, argon flow rate 20-30sccm, processing time 5-8min, followed by stirring at 1500-2000rpm in a high-speed mixer for 5-10min.

[0016] Preferably, in step two, the die diameter of the twin-screw extruder is 3-5mm, the length-to-diameter ratio is 12:1, the barrel temperature fluctuation is controlled to ≤±2℃ by jacket cooling water during the extrusion process, the atomizing water is deionized water with a temperature of 40-50℃, the atomization pressure is 0.3-0.5MPa, and the ratio of water spray rate to material feed rate is 1:8-10.

[0017] Preferably, in the segmented drying of step three, the conveyor belt speeds of the three-stage belt dryer are 0.8-1.2m / min, 1.0-1.5m / min, and 1.2-1.8m / min respectively, the relative humidity of each temperature zone is controlled at 30-45%, the compressive strength of the dried particles is ≥25N, and the particle temperature drops below 50℃ to proceed to step four.

[0018] Preferably, in step four, the sustained-release coating agent is composed of the following components in parts by weight: 20-30 parts of polyvinyl butyral, 15-25 parts of modified starch, 5-10 parts of montmorillonite, 3-8 parts of nano-silica, and 1-3 parts of crosslinking agent; wherein the crosslinking agent is one of melamine-formaldehyde resin, urea-formaldehyde resin, or glutaraldehyde.

[0019] Preferably, the modified starch is prepared by the following method:

[0020] Corn starch and maleic anhydride were mixed at a mass ratio of 10:1 and reacted at 120-130℃ for 2-3 hours under nitrogen protection. The product was washed with ethanol, dried and ground.

[0021] Preferably, the preparation of the sustained-release coating agent includes:

[0022] Polyvinyl butyral was dissolved in a mixed solvent of xylene and isopropanol with a volume ratio of 3:1. The mixture was stirred at 500-800 rpm and heated to 70-80℃ until completely dissolved. Modified starch, montmorillonite, and nano-silica were then added and stirred for 30-40 minutes. A crosslinking agent was then added and stirring was continued for 15-20 minutes to obtain a coating solution with a solid content of 25-30%. The solution was heated to 80-90℃ to maintain its fluidity before use.

[0023] Preferably, in step four, the molar ratio of ammonia to carbon dioxide mixture is 2:1, the total flow rate is 5-8 L / min, the fluidization height of particles in the fluidized bed is 1.2-1.5 m, nitrogen is continued to purge for 3-5 min after coating, and then the mixture is kept at 60-70℃ for 20-30 min.

[0024] Preferably, in step five, the vibrating screen uses a three-layer screen with an upper screen hole diameter of 5mm, a middle screen hole diameter of 3mm, and a lower screen hole diameter of 1mm. After screening, the particles are air-cooled to below 30°C, the relative humidity of the packaging environment is ≤40%, the packaging bag adopts a composite structure with an inner layer of polyethylene film and an outer layer of polypropylene woven fabric, and a desiccant pack is placed at the sealing point.

[0025] Compared with the prior art, the present invention provides a preparation process for ammonium chloride granular fertilizer, which has the following beneficial effects:

[0026] 1. In this invention, by adding a hydrophobic modifier to the raw materials and by using the hydrophobic modifier to perform hydrophobic modification treatment on the surface of ammonium chloride, the ammonium chloride particles are guaranteed to have low hygroscopic properties. At the same time, by constructing a hydrophobic layer, the penetration of external environmental moisture into the particle interior is prevented, thereby ensuring the stability of the ammonium chloride particles during storage and transportation and reducing the risk of fertilizer caking.

[0027] 2. In this invention, by using sodium alginate and calcined bentonite as binders, and by utilizing the synergistic bonding effect of the two, a dense internal skeletal structure is formed in the particles, which gives the ammonium chloride particles excellent strength. At the same time, the regularity of the particles can be guaranteed during the granulation process, ensuring that the ammonium chloride particles are not easily broken during transportation and use.

[0028] 3. In this invention, by subjecting the granulated ammonium chloride particles to a slow-release coating treatment and introducing inorganic fillers and polymer film-forming substances into the coating agent, a dense physical barrier is formed on the particle surface, achieving slow release of nitrogen. At the same time, the coating structure can work synergistically with the modified structure inside the particles to ensure a long-term supply of fertilizer nutrients and improve fertilizer utilization. Detailed Implementation

[0029] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0030] Example 1: A preparation process for ammonium chloride granular fertilizer, comprising the following steps:

[0031] Step 1: Raw material pretreatment. Take ammonium chloride raw powder, binder, hydrophobic modifier and slow-release coating agent. Place the ammonium chloride raw powder in a fluidized bed and dry it with hot air at 120℃ until the moisture content is ≤0.5%. Then mix it with binder and hydrophobic modifier at a mass ratio of 100:3:1. Then pulverize it with airflow until the particle size is ≤80μm to obtain mixed powder.

[0032] Step 2: Gradient granulation. The mixed powder is fed into a twin-screw extruder granulator. The screw speed is set to 800 rpm and the barrel temperature to 60℃. Atomized water is sprayed in to control the moisture content of the material at 12%. The extruded strips are crushed by rotary shearing to obtain wet granules with a particle size of 2mm.

[0033] Step 3: Segmented drying. The wet granules are fed into a three-stage belt dryer. The first temperature zone is 120℃ for 10 minutes, the second temperature zone is 90℃ for 15 minutes, and the third temperature zone is 60℃ for 10 minutes, until the moisture content of the granules is ≤1.5%.

[0034] Step 4: Surface modification. The dried particles are fed into a fluidized bed coating device. Using nitrogen as a carrier, the molten slow-release coating agent is sprayed at a rate of 5 kg / h to coat the particles. The coating amount accounts for 2% of the total mass of the particles. At the same time, a mixture of ammonia and carbon dioxide is introduced to control the gas pressure in the fluidized bed at 0.1 MPa, the temperature at 50℃, and the reaction time at 8 min.

[0035] Step 5: Screening and packaging. The modified granules are screened by a vibrating screen, retaining granules with a diameter of 3mm. After cooling to room temperature, they are metered and packaged to obtain ammonium chloride granular fertilizer.

[0036] In step one, the binder is composed of sodium alginate and bentonite in a mass ratio of 2:1, wherein the bentonite is calcined at 800℃ for 2 hours, cooled and then ground to a particle size ≤50μm;

[0037] The hydrophobic modifier is a complex of calcium stearate and silane coupling agent KH-570 in a mass ratio of 3:1. Before use, the silane coupling agent is prepared into a 20wt% solution with anhydrous ethanol and hydrolyzed at 60℃ for 30min.

[0038] The preparation of the mixed powder in step one also includes: mixing ammonium chloride raw powder with binder and hydrophobic modifier, then adding 0.5% by mass of nano-titanium dioxide, and subjecting the nano-titanium dioxide to plasma surface treatment with the following parameters:

[0039] The radio frequency power was 300W, the argon flow rate was 20sccm, the processing time was 5min, and then the mixture was stirred at 1500rpm for 5min in a high-speed mixer.

[0040] In step two, the die diameter of the twin-screw extruder granulator is 3mm, the length-to-diameter ratio is 12:1, and the barrel temperature fluctuation is controlled to be ≤±2℃ by jacket cooling water during the extrusion process. The atomizing water is deionized water with a water temperature of 40℃ and an atomization pressure of 0.3MPa. The ratio of water spray rate to material feed rate is 1:8.

[0041] In the segmented drying process of step three, the conveyor belt speeds of the three-stage belt dryer are 0.8m / min, 1.0m / min, and 1.2m / min respectively. The relative humidity in each temperature zone is controlled at 30%. After drying, the compressive strength of the particles is ≥25N, and the particle temperature drops below 50℃ to proceed to step four.

[0042] In step four, the sustained-release coating agent is composed of the following components in parts by weight: 20 parts polyvinyl butyral, 15 parts modified starch, 5 parts montmorillonite, 3 parts nano silica, and 1 part crosslinking agent; wherein the crosslinking agent is melamine-formaldehyde resin.

[0043] Modified starch is prepared by the following method:

[0044] Corn starch and maleic anhydride were mixed at a mass ratio of 10:1 and reacted at 120°C for 2 hours under nitrogen protection. The product was washed with ethanol, dried, and ground.

[0045] The preparation of sustained-release coating agents includes:

[0046] Polyvinyl butyral was dissolved in a mixed solvent of xylene and isopropanol with a volume ratio of 3:1. The mixture was stirred at 500 rpm and heated to 70°C until completely dissolved. Modified starch, montmorillonite, and nano-silica were then added and stirred for 30 min. A crosslinking agent was then added and the mixture was stirred for another 15 min to obtain a coating solution with a solid content of 25%. The solution was heated to 80°C to maintain its fluidity before use.

[0047] In step four, the molar ratio of ammonia to carbon dioxide mixture is 2:1, the total flow rate is 5 L / min, the fluidization height of the particles in the fluidized bed is 1.2 m, after the coating is completed, nitrogen is continued to purge for 3 min, and then it is kept at 60℃ for 20 min for curing.

[0048] In step five, the vibrating screen uses a three-layer screen: the upper screen has a diameter of 5mm, the middle screen has a diameter of 3mm, and the lower screen has a diameter of 1mm. After screening, the particles are air-cooled to below 30℃. The relative humidity of the packaging environment is ≤40%. The packaging bag adopts a composite structure with an inner layer of polyethylene film and an outer layer of polypropylene woven fabric. A desiccant packet is placed at the sealing point.

[0049] Example 2: A preparation process for ammonium chloride granular fertilizer, comprising the following steps:

[0050] Step 1: Raw material pretreatment. Take ammonium chloride raw powder, binder, hydrophobic modifier and slow-release coating agent. Place the ammonium chloride raw powder in a fluidized bed and dry it with hot air at 135℃ until the moisture content is ≤0.5%. Then mix it with binder and hydrophobic modifier at a mass ratio of 100:5:2 and pulverize it with airflow to a particle size of ≤80μm to obtain mixed powder.

[0051] Step 2: Gradient granulation. The mixed powder is fed into a twin-screw extruder granulator. The screw speed is set to 100 rpm and the barrel temperature is 70℃. Atomized water is sprayed in to control the moisture content of the material at 16%. The extruded strips are crushed by rotary shearing to obtain wet granules with a particle size of 3mm.

[0052] Step 3: Segmented drying. The wet granules enter a three-stage belt dryer. The first temperature zone is 130℃ for 13 minutes, the second temperature zone is 100℃ for 18 minutes, and the third temperature zone is 70℃ for 13 minutes, until the moisture content of the granules is ≤1.5%.

[0053] Step 4: Surface modification. The dried particles are fed into a fluidized bed coating device. Using nitrogen as a carrier, the molten slow-release coating agent is sprayed at a rate of 8 kg / h to coat the particles. The coating amount accounts for 3.5% of the total mass of the particles. At the same time, a mixture of ammonia and carbon dioxide is introduced to control the gas pressure in the fluidized bed at 0.2 MPa, the temperature at 60℃, and the reaction time at 10 min.

[0054] Step 5: Screening and packaging. The modified granules are screened by a vibrating screen, retaining 4mm particles. After cooling to room temperature, they are metered and packaged to obtain ammonium chloride granular fertilizer.

[0055] In step one, the binder is composed of sodium alginate and bentonite in a mass ratio of 2:1, wherein the bentonite is calcined at 900℃ for 2.5h, cooled and then ground to a particle size ≤50μm;

[0056] The hydrophobic modifier is a complex of calcium stearate and silane coupling agent KH-570 in a mass ratio of 3:1. Before use, the silane coupling agent is prepared into a 20wt% solution with anhydrous ethanol and hydrolyzed at 65℃ for 30min.

[0057] The preparation of the mixed powder in step one also includes: mixing ammonium chloride raw powder with binder and hydrophobic modifier, then adding 0.75% by mass of nano-titanium dioxide, and subjecting the nano-titanium dioxide to plasma surface treatment with the following parameters:

[0058] The radio frequency power was 400W, the argon flow rate was 25sccm, the processing time was 6min, and then the mixture was stirred at 1750rpm for 8min in a high-speed mixer.

[0059] In step two, the die diameter of the twin-screw extruder granulator is 4mm, the length-to-diameter ratio is 12:1, and the barrel temperature fluctuation is controlled to be ≤±2℃ by jacket cooling water during the extrusion process. The atomizing water is deionized water with a water temperature of 45℃ and an atomization pressure of 0.4MPa. The ratio of water spray rate to material feed rate is 1:9.

[0060] In the segmented drying process of step three, the conveyor belt speeds of the three-stage belt dryer are 1.0 m / min, 1.3 m / min, and 1.5 m / min respectively. The relative humidity in each temperature zone is controlled at 38%. After drying, the compressive strength of the particles is ≥25 N, and the particle temperature drops below 50 °C to proceed to step four.

[0061] In step four, the sustained-release coating agent is composed of the following components in parts by weight: 25 parts polyvinyl butyral, 20 parts modified starch, 8 parts montmorillonite, 5 parts nano silica, and 2 parts crosslinking agent; wherein the crosslinking agent is urea-formaldehyde resin.

[0062] Modified starch is prepared by the following method:

[0063] Corn starch and maleic anhydride were mixed at a mass ratio of 10:1 and reacted at 125°C for 2.5 h under nitrogen protection. The product was washed with ethanol, dried and ground.

[0064] The preparation of sustained-release coating agents includes:

[0065] Polyvinyl butyral was dissolved in a mixed solvent of xylene and isopropanol with a volume ratio of 3:1. The mixture was stirred at 650 rpm and heated to 75°C until completely dissolved. Modified starch, montmorillonite, and nano-silica were then added and stirred for 35 min. A crosslinking agent was then added and the mixture was stirred for another 18 min to obtain a coating solution with a solid content of 27%. The solution was heated to 85°C to maintain its fluidity before use.

[0066] In step four, the molar ratio of ammonia to carbon dioxide mixture is 2:1, the total flow rate is 7 L / min, the fluidization height of the particles in the fluidized bed is 1.4 m, after the coating is completed, nitrogen is continued to purge for 4 min, and then it is kept at 65 °C for 25 min for curing.

[0067] In step five, the vibrating screen uses a three-layer screen: the upper screen has a diameter of 5mm, the middle screen has a diameter of 3mm, and the lower screen has a diameter of 1mm. After screening, the particles are air-cooled to below 30℃. The relative humidity of the packaging environment is ≤40%. The packaging bag adopts a composite structure with an inner layer of polyethylene film and an outer layer of polypropylene woven fabric. A desiccant packet is placed at the sealing point.

[0068] Example 3: A preparation process for ammonium chloride granular fertilizer, comprising the following steps:

[0069] Step 1: Raw material pretreatment. Take ammonium chloride raw powder, binder, hydrophobic modifier and slow-release coating agent. Place the ammonium chloride raw powder in a fluidized bed and dry it with hot air at 150℃ until the moisture content is ≤0.5%. Then mix it with binder and hydrophobic modifier at a mass ratio of 100:8:4. Then pulverize it with airflow to a particle size of ≤80μm to obtain mixed powder.

[0070] Step 2: Gradient granulation. The mixed powder is fed into a twin-screw extruder granulator. The screw speed is set to 120 rpm and the barrel temperature is 80℃. Atomized water is sprayed in to control the moisture content of the material at 18%. The extruded strips are crushed by rotary shearing to obtain wet granules with a particle size of 4 mm.

[0071] Step 3: Segmented drying. The wet granules are fed into a three-stage belt dryer. The first temperature zone is 140℃ for 15 minutes, the second temperature zone is 110℃ for 20 minutes, and the third temperature zone is 80℃ for 15 minutes, until the moisture content of the granules is ≤1.5%.

[0072] Step 4: Surface modification. The dried particles are fed into a fluidized bed coating device. Using nitrogen as a carrier, the molten slow-release coating agent is sprayed at a rate of 10 kg / h to coat the particles. The coating amount accounts for 5% of the total mass of the particles. At the same time, a mixture of ammonia and carbon dioxide is introduced to control the gas pressure in the fluidized bed at 0.3 MPa, the temperature at 70℃, and the reaction time at 12 min.

[0073] Step 5: Screening and packaging. The modified granules are screened by a vibrating screen, retaining granules with a diameter of 5mm. After cooling to room temperature, they are metered and packaged to obtain ammonium chloride granular fertilizer.

[0074] In step one, the binder is composed of sodium alginate and bentonite in a mass ratio of 2:1, wherein the bentonite is calcined at 1000℃ for 3 hours, cooled and then ground to a particle size of ≤50μm;

[0075] The hydrophobic modifier is a complex of calcium stearate and silane coupling agent KH-570 in a mass ratio of 3:1. Before use, the silane coupling agent is prepared into a 20wt% solution with anhydrous ethanol and hydrolyzed at 70℃ for 30min.

[0076] The preparation of the mixed powder in step one also includes: mixing ammonium chloride raw powder with binder and hydrophobic modifier, then adding 1% by mass of nano-titanium dioxide, and subjecting the nano-titanium dioxide to plasma surface treatment with the following parameters:

[0077] The radio frequency power was 500W, the argon flow rate was 30sccm, the processing time was 8min, and then the mixture was stirred at 2000rpm for 10min in a high-speed mixer.

[0078] In step two, the die diameter of the twin-screw extruder granulator is 5mm, the length-to-diameter ratio is 12:1, and the barrel temperature fluctuation is controlled to be ≤±2℃ by jacket cooling water during the extrusion process. The atomizing water is deionized water with a water temperature of 50℃ and an atomization pressure of 0.5MPa. The ratio of water spray rate to material feed rate is 1:10.

[0079] In the segmented drying process of step three, the conveyor belt speeds of the three-stage belt dryer are 1.2m / min, 1.5m / min, and 1.8m / min respectively. The relative humidity in each temperature zone is controlled at 45%. After drying, the compressive strength of the particles is ≥25N, and the particle temperature drops below 50℃ to proceed to step four.

[0080] In step four, the sustained-release coating agent is composed of the following components in parts by weight: 30 parts polyvinyl butyral, 25 parts modified starch, 10 parts montmorillonite, 8 parts nano silica, and 3 parts crosslinking agent; wherein the crosslinking agent is glutaraldehyde.

[0081] Modified starch is prepared by the following method:

[0082] Corn starch and maleic anhydride were mixed at a mass ratio of 10:1 and reacted at 130°C for 3 hours under nitrogen protection. The product was washed with ethanol, dried and ground.

[0083] The preparation of sustained-release coating agents includes:

[0084] Polyvinyl butyral was dissolved in a mixed solvent of xylene and isopropanol with a volume ratio of 3:1. The mixture was stirred at 800 rpm and heated to 80°C until completely dissolved. Modified starch, montmorillonite, and nano-silica were then added and stirred for 40 min. A crosslinking agent was then added and the mixture was stirred for another 20 min to obtain a coating solution with a solid content of 30%. The solution was heated to 90°C to maintain its fluidity before use.

[0085] In step four, the molar ratio of ammonia to carbon dioxide mixture is 2:1, the total flow rate is 8 L / min, the fluidization height of the particles in the fluidized bed is 1.5 m, after the coating is completed, nitrogen is continued to purge for 5 min, and then it is kept at 70℃ for 30 min for curing.

[0086] In step five, the vibrating screen uses a three-layer screen: the upper screen has a diameter of 5mm, the middle screen has a diameter of 3mm, and the lower screen has a diameter of 1mm. After screening, the particles are air-cooled to below 30℃. The relative humidity of the packaging environment is ≤40%. The packaging bag adopts a composite structure with an inner layer of polyethylene film and an outer layer of polypropylene woven fabric. A desiccant packet is placed at the sealing point.

[0087] Comparative Example 1: The difference between this comparative example and Example 1 is that no hydrophobic modifier was added in step one of this comparative example.

[0088] Comparative Example 2 differs from Example 1 in that the binder in step one of this comparative example is a single sodium alginate, without the addition of calcined bentonite.

[0089] Comparative Example 3 differs from Example 1 in that nano-titanium dioxide was not added in step one of this comparative example.

[0090] Comparative Example 4 differs from Example 1 in that a sustained-release coating agent was not used in step four of this comparative example.

[0091] The performance of the ammonium chloride granular fertilizers prepared in Examples 1-3 and Comparative Examples 1-4 was tested. The test items and test methods are as follows:

[0092] For the compressive strength test, a particle strength tester was used. Twenty finished particles were selected, and their compressive crushing force was measured and the average value was calculated.

[0093] For the water absorption test, the particles were placed in a constant temperature and humidity chamber at 25℃ and 90% relative humidity for 48 hours. After being removed, the mass change was measured and the water absorption rate was calculated.

[0094] The initial nitrogen release rate test involves soaking the particles in still water at 25°C for 24 hours and determining the percentage of nitrogen content in the water relative to the total nitrogen.

[0095] For thermal stability testing, the particles were placed in an oven at 105℃ and heated for 2 hours. The particle pulverization and cracking were observed, and the integrity rate was recorded.

[0096] The test data of the ammonium chloride granular fertilizers prepared in Examples 1-3 and Comparative Examples 1-4 are recorded in the table below:

[0097] Group Compressive strength (N) Water absorption rate (%) Nitrogen release rate over 24 hours (%) Thermal stability integrity rate (%) Example 1 ≥28 ≤1.5 ≤12 100 Example 2 ≥32 ≤1.2 ≤10 100 Example 3 ≥35 ≤1.0 ≤8 100 Comparative Example 1 ≤15 ≥8.5 ≥35 85 Comparative Example 2 ≤18 ≥5.0 ≥25 92 Comparative Example 3 ≤22 ≥3.5 ≥20 95 Comparative Example 4 ≤20 ≥6.0 ≥40 90

[0098] By comparing and analyzing the data in the table, it can be seen that the ammonium chloride granular fertilizer prepared using the processes in Examples 1-3 has significantly better performance than the ammonium chloride granular fertilizer prepared using the processes in Comparative Examples 1-4. This indicates that the present invention, by adding a hydrophobic modifier to the raw materials and by using the hydrophobic modifier to modify the surface of ammonium chloride, ensures that the ammonium chloride granules have low hygroscopic properties. At the same time, by constructing a hydrophobic layer, it prevents the penetration of external environmental moisture into the granules, ensuring the stability of the ammonium chloride granules during storage and transportation, and reducing the risk of fertilizer clumping. Furthermore, by using a binder made from a compound of sodium alginate and calcined bentonite... The ammonium chloride granules are formed through a dense internal skeletal structure by utilizing the synergistic bonding effect of both materials. This results in excellent strength and ensures the regularity of the granules during granulation, preventing breakage during transportation and use. Furthermore, by applying a slow-release coating to the granulated ammonium chloride granules and introducing inorganic fillers and polymer film-forming substances into the coating agent, a dense physical barrier is formed on the granule surface, enabling the slow release of nitrogen. This coating structure also works synergistically with the modified internal structure of the granules to ensure a long-term supply of fertilizer nutrients and improve fertilizer utilization.

[0099] By comparing and analyzing the relevant data in the table, it can be seen that the ammonium chloride granular fertilizer prepared by the process of this invention has high strength, low hygroscopicity and excellent slow-release performance.

[0100] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0101] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A preparation process for ammonium chloride granular fertilizer, characterized in that: Includes the following steps: Step 1: Raw material pretreatment. Take ammonium chloride raw powder, binder, hydrophobic modifier and slow-release coating agent. Place the ammonium chloride raw powder in a fluidized bed and dry it with hot air at 120-150℃ until the moisture content is ≤0.5%. Then mix it with binder and hydrophobic modifier at a mass ratio of 100:3-8:1-4. Then pulverize it with airflow to a particle size of ≤80μm to obtain mixed powder. Step 2: Gradient granulation. The mixed powder is fed into a twin-screw extruder granulator. The screw speed is set to 80-120 rpm and the barrel temperature is set to 60-80℃. Atomized water is sprayed in to control the moisture content of the material at 12-18%. The extruded strips are crushed by rotary shearing to obtain wet granules with a particle size of 2-4 mm. Step 3: Segmented drying. The wet granules enter a three-stage belt dryer. The first temperature zone is 120-140℃ for 10-15 minutes, the second temperature zone is 90-110℃ for 15-20 minutes, and the third temperature zone is 60-80℃ for 10-15 minutes, until the moisture content of the granules is ≤1.5%. Step 4: Surface modification. The dried particles are fed into a fluidized bed coating device. Using nitrogen as a carrier, the molten slow-release coating agent is sprayed at a rate of 5-10 kg / h to coat the particles. The coating amount accounts for 2-5% of the total mass of the particles. At the same time, a mixture of ammonia and carbon dioxide is introduced. The gas pressure in the fluidized bed is controlled at 0.1-0.3 MPa, the temperature at 50-70℃, and the reaction time at 8-12 min. Step 5: Screening and packaging. The modified granules are screened by a vibrating screen, retaining particles with a diameter of 3-5mm. After cooling to room temperature, they are metered and packaged to obtain ammonium chloride granular fertilizer.

2. The preparation process of ammonium chloride granular fertilizer according to claim 1, characterized in that: In step one, the binder is composed of sodium alginate and bentonite in a mass ratio of 2:1, wherein the bentonite is calcined at 800-1000℃ for 2-3 hours, cooled and then ground to a particle size ≤50μm; The hydrophobic modifier is a complex of calcium stearate and silane coupling agent KH-570 in a mass ratio of 3:

1. Before use, the silane coupling agent is prepared into a 20wt% solution with anhydrous ethanol and hydrolyzed at 60-70℃ for 30 min.

3. The preparation process of ammonium chloride granular fertilizer according to claim 1, characterized in that: The preparation of the mixed powder in step one further includes: mixing ammonium chloride raw powder with a binder and a hydrophobic modifier, then adding 0.5-1% of nano-titanium dioxide by mass of the mixture. The nano-titanium dioxide undergoes plasma surface treatment with the following parameters: Radio frequency power 300-500W, argon flow rate 20-30sccm, processing time 5-8min, followed by stirring at 1500-2000rpm in a high-speed mixer for 5-10min.

4. The preparation process of ammonium chloride granular fertilizer according to claim 1, characterized in that: In step two, the die diameter of the twin-screw extruder is 3-5mm, the length-to-diameter ratio is 12:1, the barrel temperature fluctuation is controlled to ≤±2℃ by jacket cooling water during the extrusion process, the atomizing water is deionized water, the water temperature is 40-50℃, the atomization pressure is 0.3-0.5MPa, and the ratio of water spray rate to material feed rate is 1:8-10.

5. The preparation process of ammonium chloride granular fertilizer according to claim 1, characterized in that: In the segmented drying process of step three, the conveyor belt speeds of the three-stage belt dryer are 0.8-1.2m / min, 1.0-1.5m / min, and 1.2-1.8m / min respectively. The relative humidity in each temperature zone is controlled at 30-45%. After drying, the compressive strength of the particles is ≥25N, and the particle temperature drops below 50℃ to proceed to step four.

6. The preparation process of ammonium chloride granular fertilizer according to claim 1, characterized in that: In step four, the sustained-release coating agent is composed of the following components in parts by weight: 20-30 parts of polyvinyl butyral, 15-25 parts of modified starch, 5-10 parts of montmorillonite, 3-8 parts of nano-silica, and 1-3 parts of crosslinking agent; wherein the crosslinking agent is one of melamine-formaldehyde resin, urea-formaldehyde resin, or glutaraldehyde.

7. The preparation process of ammonium chloride granular fertilizer according to claim 6, characterized in that: The modified starch is prepared by the following method: Corn starch and maleic anhydride were mixed at a mass ratio of 10:1 and reacted at 120-130℃ for 2-3 hours under nitrogen protection. The product was washed with ethanol, dried and ground.

8. The preparation process of ammonium chloride granular fertilizer according to claim 6, characterized in that: The preparation of the sustained-release coating agent includes: Polyvinyl butyral was dissolved in a mixed solvent of xylene and isopropanol with a volume ratio of 3:

1. The mixture was stirred at 500-800 rpm and heated to 70-80℃ until completely dissolved. Modified starch, montmorillonite, and nano-silica were then added and stirred for 30-40 minutes. A crosslinking agent was then added and the mixture was stirred for another 15-20 minutes to obtain a coating solution with a solid content of 25-30%. The solution was heated to 80-90℃ to maintain its fluidity before use.

9. The preparation process of ammonium chloride granular fertilizer according to claim 1, characterized in that: In step four, the molar ratio of ammonia to carbon dioxide mixture is 2:1, the total flow rate is 5-8 L / min, the fluidization height of particles in the fluidized bed is 1.2-1.5 m, after the coating is completed, nitrogen is continued to purge for 3-5 min, and then it is kept at 60-70℃ for 20-30 min for curing.

10. The preparation process of ammonium chloride granular fertilizer according to claim 1, characterized in that: In step five, the vibrating screen uses a three-layer screen with an upper screen hole diameter of 5mm, a middle screen hole diameter of 3mm, and a lower screen hole diameter of 1mm. After screening, the particles are air-cooled to below 30℃. The relative humidity of the packaging environment is ≤40%. The packaging bag adopts a composite structure with an inner layer of polyethylene film and an outer layer of polypropylene woven fabric. A desiccant packet is placed at the sealing point.