A high-tower nitro-polyphosphate-containing ammonium phosphate fertilizer and a production method thereof

Abstract

The application discloses a production method of high-tower nitro-containing polyphosphate ammonium fertilizer, and adds a polymerizer between a first mixing tank and a second mixing tank, so that ammonium nitrate / ammonium nitrate phosphate, monoammonium phosphate and potassium fertilizer are used as raw materials, and polyphosphate ammonium does not need to be purchased from outside. NP molten liquid with a temperature of 170-180 DEG C prepared in the first mixing tank is sent into the polymerizer to be dehydrated, 5%-40% orthophosphate is converted into polyphosphate ammonium in situ, low-concentration ammonia water is obtained through polymerization steam condensation, and the ammonia and process water are recycled. The NP molten liquid after polymerization is sent into the second mixing tank to be mixed with potassium fertilizer to obtain NPK molten liquid, and the NPK molten liquid is subjected to shearing and high-tower granulation to obtain finished products. Under the premise of not increasing production cost, the fertilizer efficiency is increased by more than 20%, the generation of double salt is effectively inhibited after the polymerization reaction of the high-tower compound fertilizer, the problems of pulverization, caking and bag swelling of the nitro-containing compound fertilizer are greatly relieved, the method is suitable for three process routes of old-tower transformation, new high-tower and nitric acid decomposition of phosphate rock to prepare NP solution, and the method has a wide application range.

Description

Technical Field

[0001] This invention belongs to the field of high-tower nitro compound fertilizer production technology, specifically relating to an in-situ synthesis method for ammonium polyphosphate and a low-cost high-tower nitro-containing ammonium polyphosphate fertilizer production method. Background Technology

[0002] Ammonium polyphosphate (MPP) is a high-quality slow-release phosphorus source that can improve the nutrient utilization rate of compound fertilizers. Currently, all high-tower nitro-containing MPP compound fertilizers are produced using an external addition process with purchased solid MPP raw materials. The existing standard process flow is as follows: 0.5% moisture content molten ammonium nitrate is fed into a primary mixing tank and mixed with monoammonium phosphate and purchased MPP at 170–180℃ to obtain an NP melt; the NP melt then enters a secondary mixing tank and is mixed with potassium sulfate / potassium chloride to obtain an NPK melt at 150–160℃, which is then sheared and granulated in a high-tower process to obtain the finished product.

[0003] Existing technology has two major flaws:

[0004] 1) Extremely high production costs: The unit price of purchased industrial ammonium polyphosphate is high, which increases the production cost of each ton of compound fertilizer by 50 to 500 yuan, resulting in weak market competitiveness of the product;

[0005] 2) Poor product stability: The orthophosphate, nitrate and potassium salt in the system are prone to combine with each other to form complex salt crystals. During the storage of finished products, common problems in the industry such as powdering, clumping and swelling of packaging bags are very likely to occur, which shortens the shelf life and reduces product quality.

[0006] Currently, the industry lacks a high-tower nitro compound fertilizer production process that eliminates the need for purchasing ammonium polyphosphate, allows for in-situ synthesis of ammonium polyphosphate, reduces costs, and improves the physical properties of the finished product. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a method for the in-situ synthesis of ammonium polyphosphate and the production of low-cost, high-tower nitro-containing ammonium polyphosphate fertilizer. This solves the problems of high raw material costs and poor market competitiveness associated with existing processes involving the addition of ammonium polyphosphate. The technical solution provided by this invention offers a universal process adaptable to three mainstream production lines: old tower renovation, new high-tower construction, and wet NP solution decomposition of phosphate rock using nitric acid.

[0008] Specifically, the technical solution of the present invention is implemented as follows:

[0009] The production method described in this invention is as follows: using ammonium nitrate, monoammonium phosphate, or ammonium nitrate phosphate and potassium fertilizer as raw materials, ammonium nitrate and monoammonium phosphate are first fed into a primary mixing tank for preliminary mixing, and the mixture is then pumped to the polymerizer via a circulating pump; gaseous ammonia is introduced into a sealed tank to adjust the pH value and then enters a secondary mixing tank along with the polymerizer output, while potassium fertilizer is added to the secondary mixing tank to complete secondary mixing; the output from the secondary mixing tank is sequentially fed into a shearing machine and a granulator to complete the finished product processing; the gaseous material generated during the polymerization reaction is sent to a condenser for condensation treatment, and the liquid phase generated by condensation enters a liquid seal tank for temporary storage; the material in the liquid seal tank is sent to a stripping device, where steam is introduced to strip and separate the material; the separated gaseous ammonia is sent to a neutralization process, the produced process water is sent out, and the uncondensed residual gas in the condenser is extracted by a vacuum pump and then directly discharged into the air.

[0010] The first technical solution of the present invention provides a method for producing a conventional modified high-tower nitro-containing ammonium polyphosphate fertilizer, wherein the high-tower nitro-containing ammonium polyphosphate fertilizer includes the following preparation steps:

[0011] S1. Melting and mixing: Concentrated ammonium nitrate or molten ammonium nitrate is fed into a primary mixing tank and mixed with monoammonium phosphate to obtain NP melt.

[0012] S2, Vacuum in-situ polymerization: The NP melt is sent to the polymerizer by a circulating pump or inflow from the bottom of the primary mixing tank. It is kept at a temperature under vacuum, and some of the orthophosphate is dehydrated to form polymeric phosphate.

[0013] S3, Compound Potassium Salt: The NP melt containing ammonium polyphosphate after polymerization is sent to a secondary mixing tank and mixed with potassium fertilizer to obtain NPK melt;

[0014] S4. High-tower granulation: The NPK molten liquid is sheared by a shearing machine and then fed into a granulator. The high-tower spray cooling granulation yields nitro-containing ammonium polyphosphate fertilizer.

[0015] The polymerizer is located between the primary mixing tank and the secondary mixing tank. The primary mixing tank discharges material to the polymerizer, and the polymerizer discharges material to the secondary mixing tank.

[0016] Furthermore, the melting and mixing step of the present invention is as follows: concentrated ammonium nitrate or molten ammonium nitrate with a water content of 0.5% is fed into a primary mixing tank and mixed with monoammonium phosphate at 170-180°C to obtain NP melt liquid;

[0017] Furthermore, the vacuum in-situ polymerization steps of the present invention are as follows: NP melt is fed into a polymerizer and kept at a constant temperature in a vacuum environment to dehydrate 5% to 40% of orthophosphate in the system and convert it into ammonium polyphosphate; the water vapor generated by polymerization is condensed by a condenser to form ammonia water with a concentration of 2% to 6%, and the ammonia water is sent to a stripping unit to separate gaseous ammonia and process water for recycling.

[0018] Furthermore, the step of compounding potassium salt according to the present invention is as follows: after polymerization, the NP melt containing ammonium polyphosphate is sent into a secondary mixing tank and mixed with potassium fertilizer to obtain NPK melt at 150-160℃.

[0019] Furthermore, the agglomerator of the present invention is located between the primary mixing tank and the secondary mixing tank, with a small height difference between the primary and secondary mixing tanks, and the height difference between the newly added agglomerator and the primary and secondary mixing tanks is 5-15 meters; furthermore, the agglomerator is located between the primary mixing tank and the secondary mixing tank, with a small height difference between the primary and secondary mixing tanks, and the height difference between the newly added agglomerator and the primary and secondary mixing tanks is 10 meters.

[0020] Furthermore, in this invention, the primary mixing tank and the agglomerator are arranged on the same plane, with a height difference of 5-15 meters from the secondary mixing tank; the primary mixing tank and the agglomerator are connected by a U-shaped pipe with a drop of 5-15 meters; furthermore, the primary mixing tank and the agglomerator are arranged on the same plane, with a height difference of 10 meters from the secondary mixing tank; the primary mixing tank and the agglomerator are connected by a U-shaped pipe with a drop of 10 meters.

[0021] The second technical solution of the present invention provides a newly constructed high-tower nitro-containing ammonium polyphosphate fertilizer comprising the following preparation steps:

[0022] S1. Melting and mixing: Concentrated ammonium nitrate or molten ammonium nitrate with a water content of 0.5% is fed into a primary mixing tank and mixed with monoammonium phosphate at 170-180℃ to obtain NP melt.

[0023] S2, Vacuum in-situ polymerization: The NP melt is fed into the polymerizer and kept at a constant temperature in a vacuum environment, so that 5% to 40% of the orthophosphate in the system is dehydrated and converted into ammonium polyphosphate; the water vapor generated by polymerization is condensed by the condenser to form ammonia water with a concentration of 2% to 6%, and the ammonia water is sent to the stripping unit to separate gaseous ammonia and process water for recycling.

[0024] S3, Compound Potassium Salt: The NP melt containing ammonium polyphosphate after polymerization is sent to a secondary mixing tank and mixed with potassium fertilizer to obtain NPK melt at 150-160℃;

[0025] S4. High-tower granulation: The NPK molten liquid is sheared by a shearing machine and then fed into a granulator. The high-tower spray cooling granulation yields nitro-containing ammonium polyphosphate fertilizer.

[0026] The agglomerator is located between the primary mixing tank and the secondary mixing tank. The primary mixing tank and the agglomerator are arranged on the same plane, with a height difference of 5-15 meters between them. The primary mixing tank and the agglomerator are connected by a U-shaped pipe with a drop of 5-15 meters.

[0027] Furthermore, the high-tower nitro-containing ammonium polyphosphate fertilizer includes the following preparation steps:

[0028] S1. Melting and mixing: Concentrated ammonium nitrate or molten ammonium nitrate with a water content of 0.5% is fed into a primary mixing tank and mixed with monoammonium phosphate at 170-180℃ to obtain NP melt.

[0029] S2, Vacuum in-situ polymerization: NP melt is fed into the polymerizer and kept at a constant temperature in a vacuum environment, so that 20% of orthophosphate in the system is dehydrated and converted into ammonium polyphosphate; the water vapor generated by polymerization is condensed by the condenser to form ammonia water with a concentration of 4%, and the ammonia water is sent to the stripping unit to separate gaseous ammonia and process water for recycling.

[0030] S3, Compound Potassium Salt: The polymerized NP melt containing ammonium polyphosphate is sent to a secondary mixing tank and mixed with potassium fertilizer to obtain NPK melt at 150-160℃;

[0031] S4. High-tower granulation: The NPK molten liquid is sheared by a shearing machine and then fed into a granulator. The high-tower spray cooling granulation yields nitro-containing ammonium polyphosphate fertilizer.

[0032] The agglomerator is located between the primary mixing tank and the secondary mixing tank. The primary mixing tank and the agglomerator are arranged on the same plane, with a height difference of 10 meters between them. The primary mixing tank and the agglomerator are connected by a U-shaped pipeline with a 10-meter drop.

[0033] The third technical solution of the present invention provides a method for producing high-tower nitro-containing ammonium polyphosphate fertilizer. The NP melt is produced by the wet process of nitric acid decomposition of phosphate rock. The NP solution is concentrated to 98% by an evaporator and then directly fed into the polymerizer for reaction. The vacuum degree of the polymerizer is provided by a vacuum pump, and the polymerization reaction is carried out in a closed negative pressure dehydration process.

[0034] A method for producing a high-tower nitro-containing ammonium polyphosphate fertilizer, characterized in that the production process is as follows:

[0035] 1) The NP solution obtained by wet nitric acid decomposition of phosphate rock is concentrated to about 98% by an evaporator and then enters the polymerizer. The NP melt is passed through the polymerizer under vacuum, where some of the orthophosphate is dehydrated to form polymeric phosphate. Furthermore, the proportion of the polyphosphate is 5-40% of the orthophosphate.

[0036] 2) The NP melt containing polyphosphate is mixed with potassium fertilizer in a two-stage mixing tank to form an NPK melt at a temperature of 150-160℃. The NPK solution at a temperature of 150-160℃ is sheared by a shearing machine to remove large particles and then granulated by a granulator.

[0037] In this process, water vapor in the polymerizer is condensed by a condenser under the action of a vacuum pump to form ammonia water with a concentration of 2-6%.

[0038] Furthermore, in the production method of the high-tower nitro-containing ammonium polyphosphate fertilizer of the present invention, the ratio of ammonium nitrate, monoammonium phosphate, and potassium fertilizer by weight is 35-65:10-30:15-40; further, the ratio of ammonium nitrate, monoammonium phosphate, and potassium fertilizer is 50:20:30.

[0039] This invention utilizes four steps: melt mixing, vacuum in-situ polymerization, compound potassium salt, and high-tower granulation. It is complemented by vacuum condensation and stripping to recover byproduct ammonia water, achieving material recycling. The core improvement involves adding a polymerizer between the primary and secondary mixing tanks. Instead of adding extra ammonium polyphosphate raw materials, it utilizes the existing orthophosphate in monoammonium phosphate for in-situ dehydration and polymerization under vacuum negative pressure and high-temperature melting conditions to generate ammonium polyphosphate. Combined with a height difference layout and an ammonia water recycling system, it achieves low-cost, high-efficiency, and highly stable fertilizer production.

[0040] Compared with the prior art, the present invention has produced unexpected technical effects:

[0041] 1) Significantly reduced production costs: By eliminating the purchase of ammonium polyphosphate raw materials, only three basic raw materials are used: ammonium nitrate / ammonium nitrate phosphate, monoammonium phosphate, and potash fertilizer. The polymerization reaction only consumes the water contained in the system, which hardly increases production energy consumption and raw material costs. This saves 50 to 500 yuan per ton of fertilizer, significantly improving market competitiveness.

[0042] 2) Significantly improved fertilizer efficiency: In-situ generated ammonium polyphosphate is a slow-release phosphorus, which releases nutrients slowly and increases crop absorption and utilization rate by more than 20%; The physical properties of the finished product are greatly optimized: After vacuum polymerization, the proportion of polymerized phosphate in the system is 5% to 40%, which can inhibit the combination of nitrate, potassium ions and orthophosphate to form complex salt crystals, thereby alleviating the problems of fertilizer powdering, clumping and bag swelling during storage from the root and extending the product storage period.

[0043] 3) Clean and circular production: The water vapor released from polymerization is condensed into dilute ammonia water, and the stripping recovery gaseous ammonia and process water are returned to the production system. There is no waste liquid or waste gas discharge, and the resource utilization rate is high. The three routes are universal and highly adaptable: It supports three production scenarios: renovation of old high towers, construction of new high towers, and feeding of wet NP solution from nitric acid decomposition of phosphate rock. Enterprises can flexibly choose according to their existing production lines. Attached Figure Description

[0044] Figure 1 Flowchart of the process for converting traditional high-tower fertilizer production lines to produce high-tower nitro-containing ammonium polyphosphate compound fertilizer;

[0045] Figure 2 Flowchart of the new high-tower nitro-containing ammonium polyphosphate compound fertilizer production process;

[0046] Figure 3Flowchart of the process for preparing high-tower nitro-containing ammonium polyphosphate compound fertilizer from nitric acid decomposition of phosphate rock NP solution;

[0047] Figure 4 Flowchart of traditional high-tower nitro-containing ammonium polyphosphate compound fertilizer production process;

[0048] Figure 5 Schematic diagram of high-level arrangement of the agglomerator;

[0049] Figure 6 A schematic diagram of the planar arrangement of the agglomerator and the primary mixing tank;

[0050] Figure 7 Schematic diagram of the NP melt polymerization reaction setup;

[0051] Figure 8 Schematic diagram of aggregator structure.

[0052] Example 1: A process for producing high-tower nitro-containing ammonium polyphosphate compound fertilizer

[0053] S1. Melting and mixing: Concentrated ammonium nitrate or molten ammonium nitrate with a water content of 0.5% is fed into a primary mixing tank and mixed with monoammonium phosphate at 170-180℃ to obtain NP melt.

[0054] S2, Vacuum in-situ polymerization: The NP melt is fed into the polymerizer and kept at a constant temperature in a vacuum environment, so that the 22% orthophosphate in the system is dehydrated and converted into ammonium polyphosphate; the water vapor generated by polymerization is condensed by the condenser to form 10% ammonia water, and the ammonia water is sent to the stripping unit to separate gaseous ammonia and process water for recycling.

[0055] S3, Compound Potassium Salt: The NP melt containing ammonium polyphosphate after polymerization is sent to a secondary mixing tank and mixed with potassium fertilizer to obtain NPK melt at 150-160℃;

[0056] S4. High-tower granulation: The NPK molten liquid is sheared by a shearing machine and then fed into a granulator. The high-tower spray cooling granulation yields nitro-containing ammonium polyphosphate fertilizer.

[0057] The material discharged from the bottom of the primary mixing tank is lifted by a circulating pump to a height difference of 10m and sent to the polymerizer; the vacuum pump provides negative pressure to the polymerizer; the polymerization steam enters the condenser and is condensed into dilute ammonia water, which is sent to the stripping unit to recover gaseous ammonia and process water; the molten liquid after polymerization overflows from the liquid seal tank to the secondary mixing tank, is mixed with potassium fertilizer, and then sent to the high tower granulator by the shearing machine.

[0058] The agglomerator is located between the primary mixing tank and the secondary mixing tank. The height difference between the primary and secondary mixing tanks is small, and the height difference between the newly added agglomerator and the primary and secondary mixing tanks is 10 meters.

[0059] In this invention, the weight ratio of the compound fertilizer raw materials—ammonium nitrate, monoammonium phosphate, and potassium fertilizer—is 40:30:30. Based on 1 ton of compound fertilizer, at a polymerization rate of 22%, the net production cost saving per ton of compound fertilizer is approximately 358 yuan; approximately 17.2 kg of 10% dilute ammonia water is produced as a byproduct, and after stripping, 1.7 kg of ammonia gas and 15.5 kg of process water can be recovered, all of which are reused with no waste liquid discharge.

[0060] See the detailed drawings for the embodiments. Figure 1 As shown.

[0061] Example 2: A process for producing a high-tower nitro-containing ammonium polyphosphate compound fertilizer

[0062] In the initial exploratory experiments, the vacuum in-situ polymerization steps were as follows: NP melt was fed into the polymerizer and kept at a constant temperature in a vacuum environment to dehydrate 20% of orthophosphate in the system and convert it into ammonium polyphosphate; the water vapor generated by polymerization was condensed by a condenser to form 10% ammonia water, which was then sent to a stripping unit to separate gaseous ammonia and process water for recycling.

[0063] The polymerizer is located between the primary and secondary mixing tanks. The height difference between the primary and secondary mixing tanks is small, and the height difference between the newly added polymerizer and the primary and secondary mixing tanks is 8. Furthermore, in this invention, the weight ratio of the compound fertilizer raw materials—ammonium nitrate, monoammonium phosphate, and potassium fertilizer—is 40:30:30. Based on 1 ton of compound fertilizer, the monoammonium phosphate consumption is 300 kg. Approximately 64.7 kg of monoammonium phosphate participates in the reaction, and 60 kg of polyphosphate with more than two dimers is generated in situ. After deducting energy consumption, approximately 325 yuan is saved net. Approximately 16.7 kg of 10% dilute ammonia water is produced as a byproduct, 1.7 kg of ammonia gas is recovered through stripping, and 15 kg of process water is generated.

[0064] See the detailed drawings for the embodiments. Figure 1 As shown. Everything else is the same as described in Example 1.

[0065] Example 3: A process for producing a high-tower nitro-containing ammonium polyphosphate compound fertilizer

[0066] In practical applications, the vacuum in-situ polymerization step with significant results is as follows: NP melt is fed into the polymerizer and kept at a constant temperature in a vacuum environment, allowing 15% of orthophosphate in the system to be dehydrated and converted into ammonium polyphosphate; the water vapor generated during polymerization is condensed by a condenser to form 10% ammonia water, which is then sent to a stripping unit to separate gaseous ammonia and process water for recycling.

[0067] The polymerizer is located between the primary and secondary mixing tanks, with a small height difference between them. The height difference between the newly added polymerizer and the primary and secondary mixing tanks is 15 meters. Furthermore, in this invention, the weight ratio of the compound fertilizer raw materials—ammonium nitrate, monoammonium phosphate, and potassium fertilizer—is 40:30:30. Based on 1 ton of compound fertilizer, the monoammonium phosphate consumption is 300 kg. 48.5 kg of monoammonium phosphate participates in the reaction, generating 45 kg of polyphosphate in situ. After deducting energy consumption, a net saving of 242.5 yuan per ton of fertilizer is achieved. 15.5 kg of 10% dilute ammonia water is obtained; 1.5 kg of ammonia gas is recovered through stripping; and 14 kg of process water is produced. Under these high polymerization conditions, the in-situ synthesis of polyphosphate is large, resulting in significant raw material cost savings. Simultaneously, the fertilizer's slow-release effect and anti-caking ability are optimal, leading to the best economic benefits.

[0068] See the detailed drawings for the embodiments. Figure 1 As shown. Everything else is the same as described in Example 1.

[0069] Example 4: A process for producing a high-tower nitro-containing ammonium polyphosphate compound fertilizer

[0070] The primary mixing tank (1) and the polymerizer (3) are arranged on the same plane and connected by a U-shaped gravity flow pipeline (11); the polymerizer and the secondary mixing tank (8) are 10m apart in height, and the molten liquid enters the secondary mixing tank by gravity without the need for a circulation pump.

[0071] S1. Melting and mixing: Concentrated ammonium nitrate or molten ammonium nitrate with a water content of 0.5% is fed into a primary mixing tank and mixed with monoammonium phosphate at 170-180℃ to obtain NP melt.

[0072] S2, Vacuum in-situ polymerization: NP melt is fed into the polymerizer and kept at a constant temperature in a vacuum environment, so that 20% of orthophosphate in the system is dehydrated and converted into ammonium polyphosphate; the water vapor generated by polymerization is condensed by the condenser to form ammonia water with a concentration of 4%, and the ammonia water is sent to the stripping unit to separate gaseous ammonia and process water for recycling.

[0073] S3, Compound Potassium Salt: The NP melt containing ammonium polyphosphate after polymerization is sent to a secondary mixing tank and mixed with potassium fertilizer to obtain NPK melt at 150-160℃;

[0074] S4. High-tower granulation: The NPK molten liquid is sheared by a shearing machine and then fed into a granulator. The high-tower spray cooling granulation yields nitro-containing ammonium polyphosphate fertilizer.

[0075] The primary mixing tank and the agglomerator are arranged on the same plane, with a height difference of 10 meters from the secondary mixing tank; the primary mixing tank and the agglomerator are connected by a U-shaped pipeline with a 10-meter drop.

[0076] In this invention, the weight ratio of the compound fertilizer raw materials—ammonium nitrate, monoammonium phosphate, and potassium fertilizer—is 60:20:20. Under a polymerization degree of 10%, the net production cost is reduced by approximately 105 yuan; 13.6 kg of 10% dilute ammonia water is produced as a byproduct; 1.3 kg of ammonia gas and 12.2 kg of process water are recovered through stripping; the materials are recycled in a closed loop, with no wastewater discharge.

[0077] Example 5: A process for producing a high-tower nitro-containing ammonium polyphosphate compound fertilizer

[0078] In the initial exploratory experiments, the vacuum in-situ polymerization steps were as follows: NP melt was fed into the polymerizer and kept at a constant temperature in a vacuum environment to dehydrate 6% orthophosphate in the system and convert it into ammonium polyphosphate; the water vapor generated by polymerization was condensed by a condenser to form 10% ammonia water, which was then sent to a stripping unit to separate gaseous ammonia and process water for recycling.

[0079] The primary mixing tank and the polymerizer are arranged on the same plane, with a height difference of 5-15 meters from the secondary mixing tank. The primary mixing tank and the polymerizer are connected by a U-shaped pipe with a 5-meter drop. Furthermore, in this invention, the weight ratio of the compound fertilizer raw materials—ammonium nitrate, monoammonium phosphate, and potassium fertilizer—is 41:27:32. Based on 1 ton of compound fertilizer, under a 6% polymerization conversion rate, the net cost saving per ton of compound fertilizer, after deducting energy consumption, is 34.6 yuan, far lower than the 358 yuan saving under a polymerization degree of 22% in Example 2; 12.6 kg of 10% dilute ammonia water is produced. This operating condition can only generate a small amount of ammonium polyphosphate, which has limited improvement on the fertilizer's anti-caking performance and can only serve as a control experiment in the exploratory stage.

[0080] Example 6: A process for producing a high-tower nitro-containing ammonium polyphosphate compound fertilizer

[0081] In practical applications, the vacuum in-situ polymerization step with significant results is as follows: NP melt is fed into the polymerizer and kept at a constant temperature in a vacuum environment, allowing 30% of the orthophosphate in the system to be dehydrated and converted into ammonium polyphosphate; the water vapor generated during polymerization is condensed by a condenser to form 10% ammonia water, which is then sent to a stripping unit to separate gaseous ammonia and recover and reuse it with process water.

[0082] The primary mixing tank and the polymerizer are arranged on the same plane, with a height difference of 5-15 meters from the secondary mixing tank. The primary mixing tank and the polymerizer are connected by a U-shaped pipeline with a 15-meter drop. Furthermore, in this invention, the weight ratio of the compound fertilizer raw materials ammonium nitrate, monoammonium phosphate, and potassium chloride is 38:34:28. Based on 1 ton of compound fertilizer, the monoammonium phosphate consumption is 340 kg. Under a 30% polymerization conversion rate, each ton of compound fertilizer can achieve a net cost saving of 736 yuan, far exceeding the 325 yuan saving under a 20% polymerization degree. It produces 25 kg of 10% concentration dilute ammonia water. This operating condition can generate a large amount of ammonium polyphosphate, which can maximize the reduction of raw material costs and significantly improve the fertilizer's anti-caking and slow-release performance, resulting in significant industrial application benefits.

[0083] Example 7: A process for producing a high-tower nitro-containing ammonium polyphosphate compound fertilizer

[0084] An evaporator is added upstream, and its discharge is directly connected to the polymerizer. The primary mixing tank melting unit is eliminated; the remaining downstream polymerization, mixing, granulation, and ammonia recovery systems are the same as shown in Figure 1. See attached diagram for details. Figure 3 .

[0085] The NP solution obtained by wet-line nitric acid decomposition of phosphate rock is concentrated to about 98% by an evaporator and then enters the polymerizer. The NP melt is held in the polymerizer under vacuum for a period of time, and part of the orthophosphate is dehydrated to form polymerized phosphate (the proportion of polyphosphate is 5-40% of the orthophosphate). The vacuum state of the polymerizer is provided by a vacuum pump.

[0086] The NP melt containing polyphosphate is mixed with potassium fertilizer (potassium sulfate or potassium chloride) in a two-stage mixing tank to form an NPK melt at a temperature of 150-160℃. The NPK solution at a temperature of 150-160℃ is then sheared by a shearing machine to remove large particles before being granulated by a granulator.

[0087] Under the action of a vacuum pump, water vapor in the polymer is condensed by a condenser to form ammonia water (ammonia water concentration of 10%). The ammonia water is then stripped to separate gaseous ammonia and process water, which are then sent to other processes.

[0088] Technical effect: equivalent to that of Example 1 or Example 2.

[0089] In summary, Examples 1-3 are applicable to the retrofitting of old towers. Figure 1 shows the production process flow diagram of the traditional high tower retrofitting. The box layout from top to bottom is: primary mixing tank → circulating pump → polymerizer; the polymerizer has two branches: one is a condenser → stripping unit; the other is a liquid seal tank → secondary mixing tank → shearing machine → high tower granulator; the vacuum pump is connected to the polymerizer pipeline; solid arrows indicate the material flow direction between all equipment.

[0090] Key features: The circulating pump enables 10m height difference conveying, making it suitable for older production lines with insufficient height difference.

[0091] Examples 4-6 are applicable to the construction of new high towers. Figure 2 shows the gravity flow process diagram of a new high tower. Specifically, the primary mixing tank and the polymerizer are horizontally arranged side by side and connected by a U-shaped pipeline; the polymerizer is vertically downwards to the secondary mixing tank with a height difference of 10m; the layout of the remaining condensation, stripping, and granulation equipment is the same as in Figure 1; there is no circulating pump equipment.

[0092] Example 7 is applicable to the production of NP solution from phosphate rock by nitric acid decomposition. Figure 3 shows the process flow diagram of NP solution production from phosphate rock by nitric acid decomposition. Specifically, an evaporator is added at the front end, and the evaporator discharge is directly connected to the polymerizer. The first-stage mixing tank melting unit is eliminated, and the remaining downstream polymerization, mixing, granulation, and ammonia recovery systems are the same as those in Figure 1.

[0093] Comparative Example 1: A process for producing a high-tower nitro-containing ammonium polyphosphate compound fertilizer

[0094] Appendix Figure 4 Flowchart of traditional high-tower nitro-containing ammonium polyphosphate compound fertilizer production process.

[0095] The cost of raw materials per ton of compound fertilizer increased by 358 yuan due to the purchase of ammonium polyphosphate; finished product testing: phosphorus nutrient utilization rate was 20% lower than in Example 1, caking rate was 12% after 30 days of storage, and 60% of the products were bulging after 60 days; there were no polymerization dehydration or ammonia recovery processes, and no gaseous ammonia or process water recovery products.

[0096] Specific process: Concentrated ammonium nitrate or molten ammonium nitrate (moisture content around 0.5%) is mixed with monoammonium phosphate and ammonium polyphosphate in a primary mixing tank at 170-180℃ to form NP melt. The NP melt is then mixed with potassium fertilizer (potassium sulfate or potassium chloride) in a secondary mixing tank to form NPK melt at 150-160℃. The NPK solution at 150-160℃ is sheared by a shearing machine and sent to a granulator for granulation.

[0097] Verification Example:

[0098] The technical effects of the above embodiments were tested, as follows:

[0099] Table 1. Index Detection of Relevant Examples

[0100] The increase in cost per ton of raw material 358 yuan / / Phosphorus nutrient utilization rate 30% 37.5% 42% 30-day storage clumping rate 12% 0.00% 0% Percentage of products with increased packaging size in 60 days 28% 0.00% 0%

[0101] Table 1 shows that the phosphorus nutrient utilization rate of the traditional process is only 30%, while Examples 1 and 6 increase it to 37.5% and 40% respectively, significantly improving fertilizer efficiency. Simultaneously, this invention inhibits the formation of compound salts at the source, greatly improving product storage stability: the 30-day clumping rate drops from 12% to 0, and the 60-day bag swelling rate drops from 28% to 0, completely solving the industry problem of easy clumping and bag swelling in nitro compound fertilizers. Example 1 is adapted for the renovation of old high-tower fertilizer production lines, and Example 4 uses a pump-free self-flowing structure adapted for newly built production lines. These two differentiated and innovative processes achieve both low-cost production and excellent fertilizer efficiency and storage performance, breaking through the technical bottlenecks of high cost and poor product stability in traditional processes, and possessing outstanding creative and industrial practical value.

[0102] Table 2

[0103] Monoammonium phosphate involved in the reaction / kg 71.2 64.7 48.5 21.6 7.8 129.4 In-situ generation of ammonium polyphosphate / kg 66 60 45 20 7.2 110 Total cost of purchased ammonium polyphosphate raw material / Yuan 660 600 450 200 72 1200 Net cost savings after deducting energy consumption / yuan 358 325 242.5 105 34.6 736 Dehydration amount of condensation reaction / kg 5.2 4.7 3.5 1.6 0.6 8 Total system water volume (including free water from raw materials) / kg 12 12 12 12 12 12 Total mass of condensed ammonia water (concentration 10%) kg 17.2 16.17 15.5 13.6 12.6 25 Ammonia recovered by stripping / kg 1.7 1.7 1.5 1.3 1.2 2.5 Stripping process water recovery / kg 15.5 15 14 12.2 11.3 22.5 30-day clumping rate 0 0 0 1% 5% 0% 60-day increase in baggage percentage 0 0 0 1% 3% 0%

[0104] In summary, Examples 1-6 in Table 2, employing different polymerization conversion rates and production line layouts, all stably achieve the core objective of this invention. Ammonium polyphosphate is generated through in-situ vacuum polymerization of NP melt, eliminating the need for external purchases and enabling the production of low-cost, high-performance nitro compound fertilizer. As the polymerization conversion rate increases from 5% to 30%, the amount of in-situ generated ammonium polyphosphate in each example gradually increases, resulting in continuously improved raw material cost savings. Simultaneously, the ammonia concentration increases, leading to a higher ammonia resource recovery rate. Furthermore, the increased ammonium polyphosphate content effectively inhibits the formation of compound salts in the fertilizer, resulting in a continuous decrease in the 30-day clumping rate and the 60-day bag swelling rate, and progressively optimizing product storage stability. Examples 1, 2, and 3 are suitable for older high-tower pumping processes, while Examples 4, 5, and 6 are suitable for newly built high-tower self-flowing pumpless processes. Both process routes achieve closed-loop material circulation and no waste liquid discharge, adapting to different production scenarios and fully covering the technical solution of this invention. This demonstrates the wide adaptability and strong repeatability of the process, enabling industrial-scale production applications.

[0105] Terminology Explanation

[0106] 1. NP molten liquid: A nitrogen-phosphorus molten slurry obtained by high-temperature melting and mixing of ammonium nitrate (nitrogen source) and monoammonium phosphate (phosphorus source);

[0107] 2. NPK melt: A ternary molten slurry of nitrogen, phosphorus, and potassium fertilizer, formed by mixing NP melt with potassium fertilizer;

[0108] 3. Polymerizer: A polymerizer is a device used in chemical engineering to carry out polymerization reactions. It is a closed negative pressure reaction device used to dehydrate orthophosphate in molten NP to produce ammonium polyphosphate.

[0109] 4. Ammonium polyphosphate: a slow-release phosphate fertilizer made by the dehydration condensation between orthophosphate molecules;

[0110] 5. Steam stripping unit: Equipment for separating gaseous ammonia from dilute ammonia water and recovering process water using steam;

[0111] 6. Potassium fertilizer: refers to potassium sulfate or potassium chloride.

[0112] The above description is merely an example and illustration of the process of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described or use similar methods to replace them, as long as they do not deviate from the process of the invention or exceed the scope defined in the claims, they should all fall within the protection scope of the present invention.

Claims

1. A method for producing a high-tower nitro-containing ammonium polyphosphate fertilizer, characterized in that, The method for preparing the high-tower nitro-containing ammonium polyphosphate fertilizer includes the following preparation steps: S1. Melting and mixing: Concentrated ammonium nitrate or molten ammonium nitrate is fed into a primary mixing tank and mixed with monoammonium phosphate to obtain NP melt. S2, Vacuum in-situ polymerization: The NP melt is sent to the polymerizer by a circulating pump or inflow from the bottom of the primary mixing tank. It is kept at a temperature under vacuum, and some of the orthophosphate is dehydrated to form polymeric phosphate. S3, Compound Potassium Salt: The NP melt containing ammonium polyphosphate after polymerization is sent to a secondary mixing tank and mixed with potassium fertilizer to obtain NPK melt; S4. High-tower granulation: The NPK molten liquid is sheared by a shearing machine and then fed into a granulator. The high-tower spray cooling granulation yields nitro-containing ammonium polyphosphate fertilizer. The polymerizer is located between the primary mixing tank and the secondary mixing tank. The primary mixing tank discharges material to the polymerizer, and the polymerizer discharges material to the secondary mixing tank.

2. The method for producing a high-tower nitro-containing ammonium polyphosphate fertilizer according to claim 1, characterized in that, The steps for melting and mixing are as follows: Concentrated ammonium nitrate or molten ammonium nitrate with a water content of 0.5% is fed into a primary mixing tank and mixed with monoammonium phosphate at 170-180°C to obtain NP molten liquid.

3. The method for producing a high-tower nitro-containing ammonium polyphosphate fertilizer according to claim 1, characterized in that, The steps of the vacuum in-situ polymerization are as follows: The NP melt is fed into the polymerizer and kept at a constant temperature under vacuum, allowing 5% to 40% of the orthophosphate in the system to be dehydrated and converted into ammonium polyphosphate. The water vapor generated during polymerization is condensed by a condenser to form ammonia water with a concentration of 2% to 10%. The ammonia water is sent to a stripping unit to separate gaseous ammonia and recover it with the process water for reuse.

4. The method for producing a high-tower nitro-containing ammonium polyphosphate fertilizer according to claim 1, characterized in that, The steps for compounding potassium salts are as follows: after polymerization, the NP melt containing ammonium polyphosphate is sent to a secondary mixing tank and mixed with potassium fertilizer to obtain NPK melt at 150-160℃.

5. The method for producing a high-tower nitro-containing ammonium polyphosphate fertilizer according to claim 1, characterized in that, The agglomerator is located between the primary mixing tank and the secondary mixing tank, with a small height difference between the primary and secondary mixing tanks. The height difference between the newly added agglomerator and the primary and secondary mixing tanks is 5-15 meters. Furthermore, the agglomerator is located between the primary mixing tank and the secondary mixing tank, with a small height difference between the primary and secondary mixing tanks. The height difference between the newly added agglomerator and the primary and secondary mixing tanks is 10 meters.

6. The method for producing a high-tower nitro-containing ammonium polyphosphate fertilizer according to claim 1, characterized in that, The primary mixing tank and the agglomerator are arranged on the same plane, with a height difference of 5-15 meters from the secondary mixing tank; the primary mixing tank and the agglomerator are connected by a U-shaped pipe with a drop of 5-15 meters; further, the primary mixing tank and the agglomerator are arranged on the same plane, with a height difference of 10 meters from the secondary mixing tank; the primary mixing tank and the agglomerator are connected by a U-shaped pipe with a drop of 10 meters.

7. The method for producing a high-tower nitro-containing ammonium polyphosphate fertilizer according to claim 1, characterized in that, The high-tower nitro-containing ammonium polyphosphate fertilizer comprises the following preparation steps: S1. Melting and mixing: Concentrated ammonium nitrate or molten ammonium nitrate with a water content of 0.5% is fed into a primary mixing tank and mixed with monoammonium phosphate at 170-180℃ to obtain NP melt. S2. Vacuum in-situ polymerization: The NP melt is fed into the polymerizer and kept at a vacuum of less than 50 kPa (absolute pressure) to dehydrate 5% to 40% of the orthophosphate in the system and convert it into ammonium polyphosphate; the water vapor generated by polymerization is condensed by the condenser to form ammonia water with a concentration of 2% to 6%, and the ammonia water is sent to the stripping unit to separate gaseous ammonia and process water for recycling. S3, Compound Potassium Salt: The NP melt containing ammonium polyphosphate after polymerization is sent to a secondary mixing tank and mixed with potassium fertilizer to obtain NPK melt at 150-160℃; S4. High-tower granulation: The NPK molten liquid is sheared by a shearing machine and then fed into a granulator. The high-tower spray cooling granulation yields nitro-containing ammonium polyphosphate fertilizer. The agglomerator is located between the primary mixing tank and the secondary mixing tank. The primary mixing tank and the agglomerator are arranged on the same plane, with a height difference of 5-15 meters between them. The primary mixing tank and the agglomerator are connected by a U-shaped pipe with a drop of 5-15 meters. Furthermore, the high-tower nitro-containing ammonium polyphosphate fertilizer includes the following preparation steps: S1. Melting and mixing: Concentrated ammonium nitrate or molten ammonium nitrate with a water content of 0.5% is fed into a primary mixing tank and mixed with monoammonium phosphate at 170-180℃ to obtain NP melt. S2, Vacuum in-situ polymerization: The NP melt is fed into the polymerizer and kept at a constant temperature in a vacuum environment, so that 20% of the orthophosphate in the system is dehydrated and converted into ammonium polyphosphate; the water vapor generated by polymerization is condensed by the condenser to form ammonia water with a concentration of 4%, and the ammonia water is sent to the stripping unit to separate gaseous ammonia and process water for recycling. S3, Compound Potassium Salt: The NP melt containing ammonium polyphosphate after polymerization is sent to a secondary mixing tank and mixed with potassium fertilizer to obtain NPK melt at 150-160℃; S4. High-tower granulation: The NPK molten liquid is sheared by a shearing machine and then fed into a granulator. The high-tower spray cooling granulation yields nitro-containing ammonium polyphosphate fertilizer. The agglomerator is located between the primary mixing tank and the secondary mixing tank. The primary mixing tank and the agglomerator are arranged on the same plane, with a height difference of 10 meters between them. The primary mixing tank and the agglomerator are connected by a U-shaped pipeline with a 10-meter drop.

8. A method for producing a high-tower nitro-containing ammonium polyphosphate fertilizer, characterized in that, The NP melt is produced by the wet process of nitric acid decomposition of phosphate rock, and is concentrated to 98% by an evaporator before being directly fed into the polymerizer for reaction; the vacuum degree of the polymerizer is provided by a vacuum pump, and the polymerization reaction is carried out in a closed negative pressure dehydration process; the other steps are the same as S3 and S4 in claim 7.

9. The method for producing a high-tower nitro-containing ammonium polyphosphate fertilizer according to claim 8, characterized in that, The production method described herein is as follows: 1) The NP solution obtained by wet nitric acid decomposition of phosphate rock is concentrated to about 98% by an evaporator and then enters the polymerizer. The NP melt is passed through the polymerizer under vacuum, where some of the orthophosphate is dehydrated to form polymeric phosphate. Furthermore, the proportion of the polyphosphate is 5-40% of the orthophosphate. 2) The NP melt containing polyphosphate is mixed with potassium fertilizer in a two-stage mixing tank to form an NPK melt at a temperature of 150-160℃. The NPK solution at a temperature of 150-160℃ is sheared by a shearing machine to remove large particles and then granulated by a granulator. In this process, water vapor in the polymerizer is condensed by a condenser under the action of a vacuum pump to form ammonia water with a concentration of 2-10%.

10. The method for producing a high-tower nitro-containing ammonium polyphosphate fertilizer according to claim 8, characterized in that, Calculated by weight ratio, the ratio of ammonium nitrate, monoammonium phosphate, and potassium fertilizer is 35-65:10-30:15-40; further, the ratio of ammonium nitrate, monoammonium phosphate, and potassium fertilizer is 50:20:30.

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