A method for preparing sulfur-containing ammonium polyphosphate for agricultural use and its production apparatus

Abstract

This invention relates to the field of fertilizer production technology. It discloses a method and apparatus for preparing agricultural sulfur-containing ammonium polyphosphate, comprising the following steps: 1) preparing the desired mixed acid a; 2) preparing mixed material b; 3) the mass ratio of ammonia to mixed material b is 0.14–0.17:1; 4) a polymerization reaction to generate acidic ammonium polyphosphate material c, which is discharged to a solidification reaction device via a double-screw discharge device; 5) adding an ammonia supplement to the solidification reaction device in proportion, mixing it evenly with the acidic ammonium polyphosphate material c, followed by a foaming reaction, gradually cooling to solidification, and then pre-crushing it by the stirring shaft of the solidification reaction device before cooling it to below 50°C in a cooler; 6) finally obtaining agricultural ammonium polyphosphate product d through sieving, crushing, and packaging. This invention has advantages such as simple raw material pretreatment and low energy consumption; it improves the initial fertilizer efficiency of sulfur-containing ammonium polyphosphate; and it accelerates the crystallization and solidification of ammonium polyphosphate.

Description

Technical Field

[0001] This invention relates to the field of fertilizer production technology, and in particular to a method for preparing agricultural sulfur-containing polyphosphate and its production apparatus. Background Technology

[0002] Ammonium polyphosphate (APP) is a nitrogen- and phosphorus-containing polyphosphate with the general chemical formula (NH4). n +2P n O 3n+1 Based on their degree of polymerization, ammonium polyphosphate can be classified into three types: oligomeric, mesomeric, and polymeric. When n is less than 20, it is water-soluble ammonium polyphosphate. Oligomeric ammonium polyphosphate has the characteristics of high solubility, near-neutral pH, low crystallization temperature, chelation effect on metal ions, and slow-release and long-lasting effect. Polymeric phosphorus can chelate ions such as calcium, magnesium, zinc, and iron in the soil, making it easier for crops to absorb micronutrients in the soil. The chelates formed have good water solubility and are not easily fixed, which can increase the migration distance of phosphorus in the soil, thereby improving the absorption and utilization rate of phosphorus. In addition, polymeric phosphorus cannot be directly absorbed and utilized by crops. It gradually hydrolyzes into orthophosphates that crops can absorb in the soil microenvironment, slowly releasing phosphorus and prolonging the fertilizer effect, thus meeting the phosphorus needs of crops in the middle and late stages. Therefore, when agricultural ammonium polyphosphate is used alone as a phosphate fertilizer, its polymerization rate should not be too high, otherwise it will affect its early fertilizer effect and lead to phosphorus deficiency in the early growth stage of crops.

[0003] CN105858633A describes a method for producing water-soluble ammonium polyphosphate from wet-process purified phosphoric acid. The method involves premixing 70-85% wet-process purified phosphoric acid with urea at 40-100°C, controlling the reaction temperature of the mixture at 130-200°C, and performing a polymerization reaction for 20-120 minutes. The reaction product is then cooled to obtain a solid water-soluble ammonium polyphosphate product. This method requires the phosphoric acid to undergo impurity removal and purification treatment, resulting in high production costs and intermittent operation, making large-scale production difficult.

[0004] CN108675275B describes a method for producing agricultural-grade ammonium polyphosphate using wet-process phosphoric acid. The method involves stepwise ammoniation and filtration to remove impurities from the wet-process phosphoric acid, followed by neutralization, concentration, freeze crystallization, and centrifugation to obtain ammonium phosphate salt. The ammonium phosphate salt is then heated to dehydrate and melt, condensing into molten acidic ammonium polyphosphate. Ammonia gas is then pressurized and introduced into the molten acidic ammonium polyphosphate. The product is then cooled and crushed to obtain agricultural-grade ammonium polyphosphate powder. This method suffers from several drawbacks, including numerous steps, complex operation, significant phosphorus loss during purification, high energy consumption due to the need to heat and melt the ammonium phosphate salt, and the difficulty of pressurizing and introducing ammonia gas into the molten acidic ammonium polyphosphate.

[0005] CN106865517A discloses a method and apparatus for preparing water-soluble ammonium polyphosphate from wet-process phosphoric acid. Using wet-process phosphoric acid and gaseous ammonia as raw materials, partial ammoniation is first carried out in a batch reactor, followed by polymerization in a graphite tube reactor. The polymer slurry is further aged in an aging evaporator to obtain molten water-soluble ammonium polyphosphate. The molten slurry is then dried in a spray drying tower to obtain powdered water-soluble ammonium polyphosphate. This method suffers from several drawbacks: the raw material used is refined phosphoric acid with a phosphoric acid content ≥75%, resulting in high raw material costs; the molten ammonium polyphosphate is acidic, making material molding difficult; and the aged ammonium polyphosphate has poor flowability, making material transportation difficult.

[0006] CN1116262606A discloses a method for preparing amorphous, highly water-soluble ammonium polyphosphate. Urea and phosphoric acid are mixed at an N / P molar ratio of 0.6-2.0, and a polymerization reaction is carried out at 120-200℃ for 0.3-3 hours. The product is cooled and crushed to obtain amorphous ammonium polyphosphate with a degree of polymerization <5. The phosphoric acid content is calculated to be 60%, and the Mg content in the phosphoric acid is... 2+ Content ranges from 1.0% to 8.0%, SO4 2- The content is ≥4%. The raw materials used in this method are wet-process phosphoric acid and / or thermal-process phosphoric acid, in which the phosphorus pentoxide content is 60%, which is a high-concentration phosphoric acid. The raw materials are not easy to obtain and the cost is high. The direct heating and polymerization reaction with urea results in high energy consumption. The production operation is an intermittent operation with a small production scale. In addition, urea is prone to producing water-insoluble substances such as biuret during the heating and melting process. When the biuret content in the fertilizer is high, there is a risk of burning crop seedlings.

[0007] In summary, existing technologies suffer from several problems: when using ordinary wet-process phosphoric acid as raw material, the phosphoric acid purification and impurity removal process is complex and the production cost is high; when using high-quality phosphoric acid as raw material, the raw material cost is high, and there are also production problems such as discontinuous production and difficulty in operation control. Summary of the Invention

[0008] This invention provides a method and apparatus for preparing sulfur-containing ammonium polyphosphate for agricultural use to solve the problems mentioned in the background. It addresses the issues of high raw material and manufacturing costs, and difficulty in controlling production operations inherent in existing ammonium polyphosphate production technologies.

[0009] The solution of the present invention is:

[0010] A method for preparing agricultural sulfur-containing ammonium polyphosphate includes the following steps:

[0011] 1) Wet-process concentrated phosphoric acid and concentrated sulfuric acid are mixed in a certain proportion in an acid mixer to prepare the required mixed acid a. After being evenly distributed on the surface of the conical falling film cylinder by an overflow distributor, the mixed acid flows into the mixed acid storage tank. The conical falling film cylinder and the mixed acid storage tank are a whole device operating under negative pressure. The negative pressure operation and heat preservation are conducive to evaporating the water in the concentrated phosphoric acid by using the dilution heat of concentrated sulfuric acid.

[0012] 2) Add urea to the mixed acid storage tank in a certain proportion, control the stirring speed of the impeller at 70-90 r / min, control the temperature of the dissolving material at 80-90℃, and completely dissolve the added urea in the mixed acid to obtain a mixture containing phosphoric acid, sulfuric acid, urea phosphate, urea sulfate, urea, sulfate, phosphate, etc.; avoid local overheating due to uneven stirring, which may lead to partial hydrolysis of urea;

[0013] 3) Preheat mixture b to 100-120℃ and pump it into a tubular neutralization reaction device. At the same time, a certain amount of ammonia gas is introduced into the tubular neutralization reaction device. After the neutralization reaction takes 2-10 seconds, a high-temperature slurry with a temperature of 200-230℃ is obtained. The mass ratio of ammonia gas to mixture b is 0.14-0.17:1. The amount of ammonia gas introduced is strictly controlled because high temperature will cause ammonium phosphate to decompose, especially diammonium phosphate, which is more likely to decompose, thereby increasing the escape and loss of ammonia.

[0014] 4) The high-temperature slurry obtained by the neutralization reaction is flash-evaporated and drained, and then sent to the polymerization reaction equipment. Under the conditions of heating and heat preservation, the reaction temperature is maintained at 150-170°C to carry out the polymerization reaction to generate acidic ammonium polyphosphate material c. The acidic ammonium polyphosphate material c is discharged to the curing reaction equipment through the double screw discharge equipment.

[0015] 5) Add a certain amount of ammonia supplement to the curing reaction equipment according to the proportion, and mix it evenly with the acidic ammonium polyphosphate material c. After foaming reaction at a temperature of 120-145℃, gradually cool down to cure. After being initially broken by the stirring shaft of the curing reaction equipment, it enters the cooler to be cooled to below 50℃.

[0016] 6) After screening, crushing and packaging, agricultural ammonium polyphosphate product d is obtained.

[0017] As a preferred technical solution, the P2O5 content in the wet-process concentrated phosphoric acid in 1) is 44-48%, and the solid content in the wet-process concentrated phosphoric acid is 2-20%.

[0018] As a preferred technical solution, the concentration of the concentrated sulfuric acid in step 1) is ≥98%.

[0019] As a preferred technical solution, the mass ratio of wet-process concentrated phosphoric acid to concentrated sulfuric acid in step 1) is 1:0.2 to 0.3.

[0020] As a preferred technical solution, the mass ratio of the mixed acid a to urea in step 2) is 1:0.15 to 0.25.

[0021] As a preferred technical solution, the ammonia supplement agent in step 5) is one or more of ammonium bicarbonate, ammonium carbonate and urea.

[0022] As a preferred technical solution, the mass ratio of the acidic ammonium polyphosphate material c to the ammonia supplement in step 5) is 1:0.10 to 0.20.

[0023] Polymerization mechanism:

[0024] 2NH3+CO(NH2)2·H2SO4→CO(NH2)2+(NH4)2SO4 (1)

[0025] 2(NH4)H2PO4+CO(NH2)2→(NH4)2H2P2O7+CO2↑+2NH3↑ (2)

[0026] (NH4)H2PO4+CO(NH2)2·H3PO4+CO(NH2)2→(NH4)3HP2O7+2CO2↑+2NH3↑ (3)

[0027] CO(NH2)2·H3PO4+CO(NH2)2·H3PO4→(NH4)3HP2O7+2CO2↑+NH3↑ (4)

[0028] CO(NH2)2·H3PO4+CO(NH2)2·H3PO4+CO(NH2)2→(NH4)3HP2O7+3CO2↑+3NH3↑ (5)

[0029] 3(NH4)H2PO4+CO(NH2)2→(NH4)3H2P3O 10 +CO2↑+2NH3↑ (6)

[0030] (NH4)HCO3+(NH4)3HP2O7→(NH4)4P2O7+CO2↑+H2O↑ (7)

[0031] (NH4)2CO3+(NH4)2H2P2O7→(NH4)4P2O7+CO2↑+H2O↑ (8)

[0032] (NH4)H2PO4+(NH4)2H2P2O7+CO(NH2)2→(NH4)5P3O 10 +CO2↑+H2O↑ (9)

[0033] Under high temperature conditions, firstly, urea sulfate reacts with ammonia to produce ammonium sulfate and urea (reaction 1); urea reacts with monoammonium phosphate or urea phosphate to produce polyphosphate or acidic ammonium pyrophosphate (reactions 2, 3, 4, 5, 6); secondly, acidic ammonium pyrophosphate further reacts with ammonium bicarbonate, ammonium carbonate and urea to produce polyphosphate (reactions 7, 8, 9).

[0034] This invention also discloses a production apparatus for producing sulfur-containing ammonium polyphosphate, comprising an acid mixer, an overflow distributor, a conical falling film cylinder, a stirring paddle, a storage tank, a circulating pump, a urea metering feeder, and a tail gas negative pressure pipe; the outlet of the acid mixer is connected to the inlet on one side of the storage tank; a stirring motor is provided at the center of the top of the storage tank, and the shaft of the stirring motor passes through the top of the storage tank and is fixedly connected to the stirring paddle inside the storage tank; the conical falling film cylinder and the overflow distributor are fixed on the shaft of the stirring paddle; a heat tracing pipe surrounds the side of the storage tank; a circulating pipe on one side of the bottom of the storage tank is connected to the inlet of the circulating pump; the return pipe of the circulating pump is connected to the inlet on the other side of the storage tank; a tail gas negative pressure pipe and a urea feed port are also provided at the top of the storage tank; a urea metering feeder is provided on the urea feed port.

[0035] As a preferred technical solution, the acid mixer is a heat-insulating device. The direction of the concentrated phosphoric acid inlet of the acid mixer is the axial feeding direction, and the direction of the concentrated sulfuric acid inlet is the radial feeding direction. The discharge port of the acid mixer is suspended above the overflow distributor with a certain spatial distance, which does not affect the rotation of the overflow distributor.

[0036] As a preferred technical solution, the outlet of the return pipe of the circulating pump is suspended above the overflow distributor with a certain spatial distance, so as not to affect the rotation of the overflow distributor.

[0037] As a preferred technical solution, the bottom of the overflow distributor is connected to the top of the conical falling film cylinder, and both the bottom of the overflow distributor and the conical falling film cylinder are fixed on the shaft of the agitator, and the shaft of the agitator rotates together.

[0038] As a preferred technical solution, the stirring paddle speed is 70-90 r / min to avoid affecting the downward flow of the mixed acid along the surface of the conical falling film cylinder due to excessive speed.

[0039] As a preferred technical solution, the two exhaust gas negative pressure pipe outlets at the top of the storage tank are arranged symmetrically, while the urea feed port is arranged at a 90° angle to the negative pressure pipe outlets.

[0040] A method for preparing agricultural sulfur-containing ammonium polyphosphate using the above-mentioned technical solution includes the following steps: 1) Wet-process concentrated phosphoric acid and concentrated sulfuric acid are mixed in a certain proportion by passing them into a mixing tank, and then evenly distributed on the surface of a conical falling film cylinder by an overflow distributor before flowing into a mixed acid storage tank to prepare the desired mixed acid a; the conical falling film cylinder and the mixed acid storage tank are a single unit operating under negative pressure, and the negative pressure operation and heat preservation are beneficial to evaporating the water in the concentrated phosphoric acid by utilizing the dilution heat of concentrated sulfuric acid; 2) Urea is added to the mixed acid storage tank in a certain proportion. In the process, the stirring paddle speed is controlled at 70-90 r / min, and the temperature of the solution is controlled at 80-90℃. The added urea is completely dissolved in the mixed acid to obtain a mixture b containing phosphoric acid, sulfuric acid, urea phosphate, urea sulfate, urea, sulfate, phosphate, etc.; avoid local overheating due to uneven stirring, which could lead to partial hydrolysis of urea; 3) preheat the mixture b to 100-120℃ and pump it into the tubular neutralization reaction equipment, while simultaneously introducing a certain amount of ammonia gas into the tubular neutralization reaction equipment. After a neutralization reaction of 2-10 seconds, a high-temperature slurry with a temperature of 200-230℃ is obtained; the mass ratio of ammonia to mixture b is 0.14-0.17:1; the ammonia flow rate is strictly controlled because high temperature will cause the decomposition of ammonium phosphate, especially diammonium phosphate, which is more easily decomposed, thereby increasing the escape and loss of ammonia; 4) After flash evaporation and drainage, the high-temperature slurry obtained from the neutralization reaction is sent to the polymerization reaction equipment, and under heating and heat preservation conditions, the reaction temperature is maintained at 150-170℃ for polymerization. Acidic ammonium polyphosphate material c should be generated. Acidic ammonium polyphosphate material c is discharged to the curing reaction equipment through a double spiral discharge device; 5) Add a certain amount of ammonia supplement to the curing reaction equipment in proportion. After mixing evenly with acidic ammonium polyphosphate material c, it undergoes a foaming reaction at a temperature of 120-145℃. Then, it is gradually cooled to solidify. After being initially crushed by the stirring shaft of the curing reaction equipment, it enters the cooler for cooling to below 50℃; 6) After screening, crushing, and packaging, agricultural ammonium polyphosphate product d is obtained.

[0041] Compared with the prior art, the advantages of the present invention are:

[0042] 1. The wet-process concentrated phosphoric acid raw material used in this invention is difficult to further concentrate under existing quality and normal production conditions, and it is also difficult to directly polymerize into ammonium polyphosphate under these acid concentration conditions. This invention, through innovative raw material formulation and pretreatment technology, obtains raw materials suitable for large-scale preparation of ammonium polyphosphate under lower energy consumption conditions, saving energy consumption and equipment investment in the further concentration of wet-process concentrated phosphoric acid. Compared with the process of concentrating wet-process phosphoric acid to an acid concentration of ≥54% before polymerization, this invention has advantages such as simple raw material pretreatment and low energy consumption.

[0043] 2. This invention employs a raw material pretreatment process that involves adding concentrated sulfuric acid to wet-process concentrated phosphoric acid for mixing, followed by adding urea for dissolution and mixing. This process has the following characteristics: First, it utilizes the heat of dilution from concentrated sulfuric acid and the heat of reaction from the formation of urea sulfate to evaporate some of the water, thereby reducing the moisture content of the mixed acid raw material and saving energy consumption for evaporation. Second, by adding concentrated sulfuric acid, the precipitated salts in the wet-process phosphoric acid can be dissolved, thus improving the fluidity and latent heat of reaction of the mixed acid. It can also promote the in-situ chelation efficiency of metal ions such as magnesium and iron in the polymerization reaction. Third, the sulfur-containing ammonium polyphosphate prepared by this invention contains a certain amount of ammonium sulfate. When it is dissolved in the soil, the ammonium sulfate, due to its excellent solubility, can quickly form an acidic solution environment, which can promote the hydrolysis of ammonium polyphosphate, causing the polymerized phosphorus to hydrolyze into orthophosphate that crops can absorb and utilize, thereby improving the initial fertilizer efficiency of the sulfur-containing ammonium polyphosphate.

[0044] 3. A special raw material pretreatment process is adopted to ensure thorough mixing of the condensing agent and the reaction substrate, thereby improving polymerization efficiency. Using wet-process concentrated phosphoric acid, concentrated sulfuric acid, and urea as raw materials, a mixture containing phosphoric acid, sulfuric acid, urea phosphate, urea sulfate, urea, sulfates, and phosphates is first prepared. Urea acts as a condensing agent, ensuring uniform mixing in the polymerization substrate, resulting in higher polymerization efficiency. The prepared urea phosphate is easier to polymerize than monoammonium phosphate. Urea sulfate decomposes into urea during the ammonia reaction, further providing a condensing agent for the polymerization reaction. Salts such as ammonium sulfate, magnesium sulfate, and ferric sulfate improve the physical properties of acidic ammonium polyphosphate.

[0045] 4. A staged, continuously controlled reaction process is adopted, consisting of neutralization (heating and dehydration), polymerization (decarbonization, dehydration, and polymerization), and solidification (nitrogen supplementation and crystallization). This effectively resolves the contradictions between the various reaction stages and fully utilizes the latent heat of the mixed acid neutralization reaction to achieve efficient polymerization of the target product. The contradictions among the three reaction stages are: removing moisture from the raw material phosphoric acid requires increased investment and energy costs, while the presence of moisture affects the heating effect and polymerization efficiency of the polymerization substrate; higher temperatures are more conducive to the polymerization reaction, but excessively high temperatures can cause ammonium polyphosphate to decompose, releasing ammonia and thus becoming acidic ammonium polyphosphate; in the solidification stage, lower temperatures are beneficial for the ammoniation of acidic ammonium polyphosphate, but excessively low temperatures reduce the material's fluidity, hindering the uniform mixing and reaction of acidic ammonium polyphosphate with the ammonia supplement. The neutralization reaction stage aims to rapidly heat the polymerization substrate and effectively evaporate the moisture introduced from the raw materials using flash evaporation, featuring short material residence time and high equipment space utilization. The polymerization reaction stage aims to achieve efficient polymerization of the target product, ammonium polyphosphate, by promoting decarbonization and drainage through stirring and reasonably extending the material residence time to ensure the polymerization reaction proceeds fully. The aging reaction stage aims to increase the nitrogen content and improve the physical properties of the product by adding an ammonia supplement to increase the nitrogen content and improve the physical properties, and by using the shearing action of stirring to accelerate the crystallization and solidification of ammonium polyphosphate. Attached Figure Description

[0046] Figure 1 This is a process flow diagram of the preparation method of agricultural sulfur-containing polyphosphate ammonium of the present invention;

[0047] Figure 2 This is a schematic diagram of the production apparatus used in the preparation method of agricultural sulfur-containing ammonium polyphosphate according to the present invention;

[0048] In the diagram: 1-Acid mixer; 2-Storage tank; 3-Overflow distributor; 4-Conical falling film cylinder; 5-Agitator; 6-Heating pipe; 7-Agitator motor; 8-Urea metering feeder; 9-Circulating pump; 10-Tail gas negative pressure pipe; 11-Concentrated phosphoric acid; 12-Concentrated sulfuric acid; 13-Negative pressure system; 14-Downstream process; 15-Urea. Detailed Implementation

[0049] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below with reference to specific embodiments.

[0050] Example 1

[0051] A method for producing sulfur-containing ammonium polyphosphate involves feeding concentrated phosphoric acid (46% acid concentration as P2O5) and 15% solids content, and concentrated sulfuric acid (98% concentration) at a feeding ratio (mass ratio) of 1:0.25 into an acid mixer. After mixing, the mixture is evenly distributed on the surface of a conical falling film cylinder by an overflow distributor and then flows into a mixed acid storage tank to obtain mixed acid a.

[0052] After measuring the prepared mixed acid a, add it to the dissolving equipment, add urea, control the stirring speed at 70-80 r / min, control the dissolving temperature at 80℃, and completely dissolve the added urea in the mixed acid to obtain mixed material b. Mixed acid a and urea are added at a feeding ratio (mass ratio) of 1:0.25. After dissolving, the temperature is raised and preheated to 105℃.

[0053] Mixture b is pumped into a tubular neutralization reaction device while ammonia gas is introduced into the device. The neutralization reaction lasts for 2 to 10 seconds at a temperature of 210 to 220°C and a pressure of 0.50 to 0.60 MPa to obtain a high-temperature slurry. The mass ratio of ammonia gas to mixture b is 0.14:1.

[0054] The high-temperature slurry obtained by the neutralization reaction is flash-evaporated and drained, and then sent to the polymerization reaction equipment. Under the conditions of heating and heat preservation by heat transfer oil, the polymerization reaction is carried out at a reaction temperature of 160-165℃ to generate acidic ammonium polyphosphate material c. The acidic ammonium polyphosphate material c is discharged to the curing reaction equipment through the double screw discharge equipment.

[0055] Ammonium supplement is added to the curing reaction equipment at a feeding ratio (mass ratio) of 1:0.15. After being stirred and mixed evenly with acidic ammonium polyphosphate material c, the mixture undergoes a foaming reaction at 125℃, and is then gradually cooled to solidify. After initial crushing by the stirring shaft of the curing reaction equipment, the mixture enters a cooler to be cooled to below 50℃, thus solidifying to obtain ammonium polyphosphate material. The ammonium supplement is ammonium bicarbonate, and the mass ratio of acidic ammonium polyphosphate material c to the ammonium supplement is 1:0.10.

[0056] After further screening, crushing, and packaging, sulfur-containing ammonium polyphosphate product d was obtained; its product analysis results were: N% = 16.58%.

[0057] P2O5% = 41.81%, S% = 6.57%, polymerization rate 66.8%.

[0058] Example 2

[0059] A method for producing sulfur-containing ammonium polyphosphate involves feeding concentrated phosphoric acid (44% acid concentration as P2O5 and 8% solid content) and concentrated sulfuric acid (98% concentration) into a mixing tank at a feeding ratio (mass ratio) of 1:0.30. After mixing, the mixture is evenly distributed on the surface of a conical falling film cylinder by an overflow distributor and then flows into a mixed acid storage tank to obtain mixed acid a.

[0060] After the mixed acid a is metered, it is added to the dissolving equipment. Urea is added, the stirring speed is controlled at 75-85 r / min, and the dissolving temperature is controlled at 85℃. The added urea is completely dissolved in the mixed acid to obtain mixed material b. Mixed acid a and urea are added at a feeding ratio (mass ratio) of 1:0.20. After dissolution, the temperature is raised to 110℃.

[0061] Mixture b is pumped into a tubular neutralization reaction device while ammonia gas is introduced into the device. The neutralization reaction lasts for 2 to 10 seconds at a temperature of 200 to 210°C and a pressure of 0.50 to 0.60 MPa to obtain a high-temperature slurry. The mass ratio of ammonia gas to mixture b is 0.15:1.

[0062] The high-temperature slurry obtained by the neutralization reaction is flash-evaporated and drained, and then sent to the polymerization reaction equipment. Under the conditions of heating and heat preservation by heat transfer oil, the polymerization reaction is carried out at a reaction temperature of 150-160℃ to generate acidic ammonium polyphosphate material c. The acidic ammonium polyphosphate material c is discharged to the curing reaction equipment through the double spiral discharge equipment.

[0063] Ammonia supplementer is added to the curing reaction equipment at a feeding ratio (mass ratio) of 1:0.10. After being stirred and mixed evenly with acidic ammonium polyphosphate material c, the mixture undergoes a foaming reaction at 130℃, and is then gradually cooled to solidify. After initial crushing by the stirring shaft of the curing reaction equipment, the mixture enters a cooler for cooling to below 50℃, thus solidifying to obtain ammonium polyphosphate material. The ammonia supplementer is ammonium carbonate, and the mass ratio of acidic ammonium polyphosphate material c to ammonia supplementer is 1:0.20.

[0064] After screening, crushing, and packaging, sulfur-containing ammonium polyphosphate product d was obtained; its product analysis results were: N% = 17.36%, P2O5% = 37.67%, S% = 8.13%, and polymerization rate 62.9%.

[0065] Example 3

[0066] A method for producing sulfur-containing ammonium polyphosphate involves feeding concentrated phosphoric acid (48% acid concentration as P2O5) and 18% solids content, and concentrated sulfuric acid (98% concentration) into a mixing tank at a feeding ratio (mass ratio) of 1:0.20. After mixing, the mixture is evenly distributed on the surface of a conical falling film cylinder by an overflow distributor and then flows into a mixed acid storage tank to obtain mixed acid a.

[0067] After the mixed acid a is metered, it is added to the dissolving equipment. Urea is added, the stirring speed is controlled at 80-90 r / min, and the dissolving temperature is controlled at 85℃. The added urea is completely dissolved in the mixed acid to obtain mixed material b. Mixed acid a and urea are added at a feeding ratio (mass ratio) of 1:0.15. After dissolution, the temperature is raised to 110℃.

[0068] Mixture b is pumped into a tubular neutralization reaction device, and ammonia gas is simultaneously introduced into the device. The neutralization reaction lasts for 2 to 10 seconds at a temperature of 220 to 230°C and a pressure of 0.50 to 0.60 MPa to obtain a high-temperature slurry. The mass ratio of ammonia gas to mixture b is 0.16:1.

[0069] The high-temperature slurry obtained by the neutralization reaction is flash-evaporated and drained, and then sent to the polymerization reaction equipment. Under the conditions of heating and heat preservation by heat transfer oil, the polymerization reaction is carried out at a reaction temperature of 165-170℃ to generate acidic ammonium polyphosphate material c. The acidic ammonium polyphosphate material c is discharged to the curing reaction equipment through the double spiral discharge equipment.

[0070] Ammonium supplement is added to the curing reaction equipment at a feeding ratio (mass ratio) of 1:0.20. After being stirred and mixed evenly with acidic ammonium polyphosphate material c, the mixture undergoes a foaming reaction at 135℃, and is then gradually cooled to solidify. After initial crushing by the stirring shaft of the curing reaction equipment, the mixture enters a cooler to be cooled to below 50℃, thus solidifying to obtain ammonium polyphosphate material. The ammonium supplement is ammonium bicarbonate, and the mass ratio of acidic ammonium polyphosphate material c to the ammonium supplement is 1:0.12.

[0071] After screening, crushing, and packaging, sulfur-containing ammonium polyphosphate product d was obtained; its product analysis results were: N% = 17.94%.

[0072] P2O5% = 43.63%, S% = 5.82%, polymerization rate 71.5%.

[0073] Example 4

[0074] The production apparatus used in the above embodiments for producing sulfur-containing ammonium polyphosphate, such as... Figure 2 As shown, the system includes an acid mixer 1, an overflow distributor 3, a conical falling film cylinder 4, a stirring paddle 5, a storage tank 2, a circulating pump 9, a urea metering feeder 8, and a tail gas negative pressure pipe 10. The outlet of the acid mixer 1 is connected to the inlet on one side of the storage tank 2. A stirring motor 7 is located at the center of the top of the storage tank 2. The shaft of the stirring motor 7 passes through the top of the storage tank 2 and is fixedly connected to the stirring paddle 5 inside the storage tank 2. The conical falling film cylinder 4 and the overflow distributor 3 are fixed on the shaft of the stirring paddle 5. The heat tracing pipe 6 surrounds the side of the storage tank 2. The circulating pipe on one side of the bottom of the storage tank 2 is connected to the inlet of the circulating pump 9. The return pipe of the circulating pump 9 is connected to the inlet on the other side of the storage tank 2. The top of the storage tank 2 is also provided with a tail gas negative pressure pipe 10 and a urea feeding port. A urea metering feeder 8 is provided on the urea feeding port.

[0075] The concentrated phosphoric acid inlet of the acid mixer 1 is axially fed into the acid mixer 1, and the concentrated sulfuric acid inlet is radially fed into the acid mixer 1. The outlet of the acid mixer 1 is suspended above the overflow distributor 3 with a certain spatial distance, so as not to affect the rotation of the overflow distributor 3.

[0076] The outlet of the return pipe of the circulating pump 9 is suspended above the overflow distributor 3 with a certain spatial distance, so as not to affect the rotation of the overflow distributor 3.

[0077] The bottom of the overflow distributor 3 is connected to the top of the conical falling film cylinder 4. The bottom of the overflow distributor 3 and the conical falling film cylinder 4 are both fixed on the shaft of the stirring paddle 5, and the shaft of the stirring paddle 5 rotates together.

[0078] The stirring paddle rotates at 70-90 r / min to avoid affecting the downward flow of the mixed acid along the surface of the conical falling film cylinder due to excessive speed.

[0079] The two exhaust gas negative pressure pipes 10 outlets at the top of the storage tank 2 are arranged symmetrically, while the urea feed port is arranged at a 90° angle to the exhaust gas negative pressure pipe 10 outlet.

[0080] The production apparatus of the sulfur-containing ammonium polyphosphate production method has the following beneficial technical effects: (1) The concentrated sulfuric acid and concentrated phosphoric acid are mixed evenly by the acid mixer, avoiding the excessive reaction of urea sulfate formation when urea is added due to the excessive concentration of concentrated sulfuric acid in some areas, which leads to the decomposition of urea; at the same time, when the mixed acid passes through the specially designed overflow distributor and conical falling film cylinder, the surface area of ​​the film layer formed on the surface of the conical falling film cylinder gradually increases from top to bottom, and the film thickness gradually decreases, which is conducive to the evaporation of water; (2) The mixture b obtained is circulated and evaporated by the circulating pump, making full use of the reaction heat of urea sulfate synthesis; combined with the negative pressure function of the apparatus, the efficiency of water evaporation is improved; (3) The overflow distributor and conical falling film cylinder are fixed on the shaft of the stirring paddle, so that they rotate together with the stirring paddle, and the centrifugal force generated by the rotation of the equipment makes the film layer formed on the surface of the conical falling film cylinder by the mixed acid a / mixture b more uniform.

[0081] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing agricultural sulfur-containing ammonium polyphosphate, characterized in that, Includes the following steps: 1) Wet-process concentrated phosphoric acid and concentrated sulfuric acid are mixed in a mixer, and then evenly distributed on the surface of a conical falling film cylinder by an overflow distributor before flowing into a mixed acid storage tank to prepare the desired mixed acid a. 2) After measuring the prepared mixed acid a, add it to the dissolving equipment, add urea, control the stirring speed at 70-90 r / min, control the dissolving temperature at 80-90℃, and completely dissolve the added urea in the mixed acid to obtain mixed material b. 3) Preheat mixture b to 100-120°C, pump it into a tubular neutralization reaction device, and simultaneously introduce ammonia into the tubular neutralization reaction device. After the neutralization reaction takes 2-10 seconds, a high-temperature slurry with a temperature of 200-230°C is obtained; the mass ratio of ammonia to mixture b is 0.14-0.17:

1. 4) The high-temperature slurry obtained by the neutralization reaction is flash-evaporated and drained, and then sent to the polymerization reaction equipment. Under the conditions of heating and heat preservation, the reaction temperature is maintained at 150-170°C to carry out the polymerization reaction to generate acidic ammonium polyphosphate material c. The acidic ammonium polyphosphate material c is discharged to the curing reaction equipment through the double screw discharge equipment. 5) Add ammonia supplement to the curing reaction equipment, stir and mix it evenly with acidic ammonium polyphosphate material c, and after foaming reaction at a temperature of 120-145℃, gradually cool down to cure. After initial crushing by the stirring shaft of the curing reaction equipment, it enters the cooler to be cooled to below 50℃. 6) After screening, crushing, and packaging, agricultural ammonium polyphosphate product d is obtained; The production apparatus used in the above-mentioned preparation method of agricultural sulfur-containing ammonium polyphosphate includes an acid mixer, an overflow distributor, a conical falling film cylinder, a stirring paddle, a storage tank, a circulating pump, a urea metering feeder, and a tail gas negative pressure pipe. The outlet of the acid mixer is connected to the inlet on one side of the storage tank. A stirring motor is provided at the center of the top of the storage tank. The shaft of the stirring motor passes through the top of the storage tank and is fixedly connected to the stirring paddle inside the storage tank. The conical falling film cylinder and the overflow distributor are fixed on the shaft of the stirring paddle. A heat tracing pipe surrounds the side of the storage tank. A circulation pipe on one side of the bottom of the storage tank is connected to the inlet of the circulating pump. The return pipe of the circulating pump is connected to the inlet on the other side of the storage tank. A tail gas negative pressure pipe and a urea feeding port are also provided at the top of the storage tank. A urea metering feeder is provided on the urea feeding port.

2. The method for preparing agricultural sulfur-containing ammonium polyphosphate as described in claim 1, characterized in that: The P2O5 content in the wet-process concentrated phosphoric acid in 1) is 44-48%, and the solid content is 2-20%.

3. The method for preparing an agricultural sulfur-containing ammonium polyphosphate as described in claim 1, characterized in that: The concentration of the concentrated sulfuric acid mentioned in 1) is ≥98%.

4. The method for preparing an agricultural sulfur-containing ammonium polyphosphate as described in claim 1, characterized in that: The mass ratio of wet-process concentrated phosphoric acid to concentrated sulfuric acid in 1) is 1:0.2 to 0.

3.

5. The method for preparing an agricultural sulfur-containing ammonium polyphosphate as described in claim 1, characterized in that: The mass ratio of the mixed acid a to urea in 2) is 1:0.15 to 0.

25.

6. The method for preparing an agricultural sulfur-containing ammonium polyphosphate as described in claim 1, characterized in that: The ammonia supplement agent mentioned in 5) is one or more of ammonium bicarbonate, ammonium carbonate and urea.

7. The method for preparing an agricultural sulfur-containing ammonium polyphosphate as described in claim 1, characterized in that: The mass ratio of the acidic ammonium polyphosphate material c to the ammonia supplement agent in 5) is 1:0.10 to 0.

20.

8. The method for preparing an agricultural sulfur-containing ammonium polyphosphate as described in claim 1, characterized in that: The concentrated phosphoric acid inlet of the acid mixer is axially fed into the acid mixer, and the concentrated sulfuric acid inlet is radially fed into the acid mixer; the outlet of the acid mixer is suspended above the overflow distributor; the return pipe outlet of the circulating pump is suspended above the overflow distributor.

9. The method for preparing an agricultural sulfur-containing ammonium polyphosphate as described in claim 1, characterized in that: The bottom of the overflow distributor is connected to the top of the conical falling film cylinder, and both the bottom of the overflow distributor and the conical falling film cylinder are fixed on the shaft of the stirring paddle. The top of the storage tank is equipped with two exhaust gas negative pressure pipes, and the outlets of the two exhaust gas negative pressure pipes are arranged symmetrically. The urea feeding port is arranged at a 90° angle to the outlet of the exhaust gas negative pressure pipe.

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