System and method for producing ammonium polyphosphate granular fertilizer

Abstract

The invention relates to a system and a method for producing ammonium polyphosphate granular fertilizer, and belongs to the field of chemical industry. The system comprises an absorption tower, a phosphoric acid pump, a tubular reactor, a gas-liquid separator, a granulator, a cooler, a classifying screen, a crusher and a finished product conveyor. By adopting the system and the method, the wet-process phosphoric acid containing P2O5 with the mass concentration of about 50% firstly enters the absorption tower to recover gaseous ammonia, and then the phosphoric acid is fed into the tubular reactor by using the phosphoric acid pump to react with the preheated gaseous ammonia to generate an ammonium polyphosphate molten mass; enabling the foamed ammonium polyphosphate molten mass to flow into a gas-liquid separator by virtue of self pressure, and enabling the separated ammonium polyphosphate to enter a granulator to be mixed with a returned material for granulation; the granular material discharged from the granulator is firstly cooled and then screened, and the qualified material is used as a target product, namely the ammonium polyphosphate granular fertilizer, and is debounded. The invention aims to produce the high-quality ammonium polyphosphate granular fertilizer by using wet-process phosphoric acid instead of hot-process polyphosphoric acid, so that the energy is saved, the consumption is reduced, the carbon emission of a production device is reduced, the production cost is reduced, and the environment is protected.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical production, and particularly to a system and method for producing granular ammonium polyphosphate fertilizer. Background Art

[0002] At present, the compound fertilizers containing ammonium phosphate produced are basically monoammonium phosphate and / or diammonium phosphate (hereinafter referred to as ammonium phosphate). The production process of ammonium phosphate is mature and the nutrient content is relatively high. It can be used directly as a fertilizer and is also an important phosphorus source for compound fertilizers. However, compared with granular ammonium polyphosphate fertilizer, the available phosphorus content of ammonium phosphate is still relatively low (the mass concentration of P2O5 is 38% - 48%), consuming excessive transportation and packaging costs; due to a large amount of metal ion impurities in wet-process phosphoric acid, a lot of water-insoluble phosphates will be produced, and the P2O5 occupied by this part of phosphates will account for 35% of the total P2O5; the wet materials coming out of the granulator in the production of ammonium phosphate usually contain more than 3% water, and they must be further dried to less than 1% water content to have good storage performance. Therefore, the wet materials coming out of the granulator need to be dried by a dryer, which not only requires more energy but also generates a large amount of dust and tail gas.

[0003] Thermal-process polyphosphoric acid can be used to produce ammonium polyphosphate with better quality than ammonium phosphate, but the price of thermal-process polyphosphoric acid is high, and the cost of ammonium polyphosphate produced by thermal-process polyphosphoric acid is too high to be used as a chemical fertilizer.

[0004] Therefore, it is necessary to improve the existing ammonium phosphate production system, and it is urgent to provide a system and method for producing new phosphorus- and ammonia-containing chemical fertilizer products with high available phosphorus content, chelating effect on metal ions, high content of water-soluble phosphates, without using thermal-process polyphosphoric acid, and without drying by a dryer. Summary of the Invention

[0005] The purpose of the present invention is to provide a system and method for producing granular ammonium polyphosphate fertilizer. First, wet-process phosphoric acid with a mass concentration of about 50% P2O5 is used to recover gaseous ammonia in the absorption tower, and then the phosphoric acid is sent into a tubular reactor by a phosphoric acid pump to react with preheated gaseous ammonia to generate a molten ammonium polyphosphate. The foamy molten ammonium polyphosphate flows into a gas-liquid separator by its own pressure, and the separated ammonium polyphosphate enters the granulator to be mixed with the returned material for granulation. The granular materials coming out of the granulator are first cooled and then screened, and the qualified materials are used as the target product - granular ammonium polyphosphate fertilizer to go to the battery limit. The present invention aims to use wet-process phosphoric acid to replace thermal-process polyphosphoric acid to produce high-quality granular ammonium polyphosphate fertilizer, saving energy and reducing consumption, reducing carbon emissions of the production device, reducing production costs, and protecting the environment.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] A system for producing granular ammonium polyphosphate fertilizer, the system includes an absorption tower, an output pipeline of gaseous ammonia is connected to a tubular reactor, an output end of the tubular reactor is connected to the lower part of the absorption tower through a gas-liquid separator, and an output end at the bottom of the absorption tower is respectively connected to the tubular reactor and several inlets at the upper part of the absorption tower.

[0008] In the above system: the liquid output end of the gas-liquid separator is successively connected through a granulator, a cooler and a classifier; the classifier also has an output end connected to the top of the classifier through a crusher.

[0009] In the above system: the output pipeline of the phosphoric acid solution is connected to the middle or lower part of the absorption tower, and the connection position of the phosphoric acid and the absorption tower is higher than the connection position of the gas-liquid separator and the absorption tower.

[0010] In the above system: the output end at the bottom of the absorption tower is connected to 1 to 5 inlets at the upper part of the absorption tower.

[0011] In the above system: there are two spiral bands on the stirring shaft of the gas-liquid separator; the granulator adopts a double-shaft granulator, and the two shafts rotate at the same speed in opposite directions; the classifier adopts a double-layer sieve.

[0012] A method for producing granular ammonium polyphosphate fertilizer by using the above system, the method includes the following steps:

[0013] Gaseous ammonia first enters the tubular reactor and the gas-liquid separator in sequence, and then enters the lower part of the absorption tower from the gas output end of the gas-liquid separator; the phosphoric acid solution also enters from the lower part of the absorption tower, and the downward flowing phosphoric acid solution reacts with the upward flowing gaseous ammonia to generate ammonium phosphate, and the mixed solution of ammonium phosphate and phosphoric acid solution enters the tubular reactor and the absorption tower respectively from the bottom of the absorption tower for reaction; in the absorption tower, the mixed solution of ammonium phosphate and phosphoric acid solution at the upper part of the absorption tower continues to react with gaseous ammonia to generate ammonium phosphate; in the tubular reactor, the mixed solution of ammonium phosphate and phosphoric acid solution reacts with gaseous ammonia to generate molten ammonium polyphosphate, the generated materials enter the gas-liquid separator for separation, the separated gas enters the absorption tower to continue the reaction, and the obtained ammonium polyphosphate is granulated, cooled and screened in sequence to obtain the final product.

[0014] In the above preparation method, the temperature of gaseous ammonia ≤ 180 °C, the mass concentration of P2O5 in the phosphoric acid solution ≥ 50%, and the temperature ≥ 60 °C.

[0015] In the above preparation method, the operating temperature in the absorption tower ≤ 150 °C; the mass ratio of P2O5 in the fed phosphoric acid solution to N in the fed gaseous ammonia is ≥ 4:1.

[0016] In the above preparation method, the reaction temperature in the tubular reactor ≤ 240 °C, and the granulation temperature in the granulator ≤ 110 °C.

[0017] In some specific technical solutions, a system for producing granular ammonium polyphosphate fertilizer, the system includes an absorption tower, a phosphoric acid pump, a tubular reactor, a gas-liquid separator, a granulator, a cooler, a grading screen, a crusher, and a finished product conveyor; the raw material - phosphoric acid pipeline from the battery limit is connected to the side inlet E1 of the absorption tower, the bottom outlet G1 of the absorption tower is connected to the side inlet B2 of the tubular reactor through the phosphoric acid pump, the raw material - gaseous ammonia pipeline from the battery limit is connected to the inlet C2 of the tubular reactor, the outlet A2 of the tubular reactor is connected to the side inlet B3 of the gas-liquid separator, the bottom outlet C3 of the gas-liquid separator is connected to the top inlet B4 of the granulator, the side outlet C4 of the granulator is connected to the top inlet A5 of the cooler, the bottom outlet B5 of the cooler is connected to the top inlet A6 of the grading screen, the side outlet C6 of the grading screen is connected to the feeding end of the finished product conveyor, and the discharging end of the finished product conveyor is connected to the battery limit;

[0018] In the above system: the top outlet A1 of the absorption tower is connected to the water vapor pipeline going to the battery limit, the side inlets B1, C1, D1 of the absorption tower are connected to the pipeline connecting the outlet of the phosphoric acid pump and the side inlet B2 of the tubular reactor, and the side inlet F1 of the absorption tower is connected to the top outlet A3 of the gas-liquid separator;

[0019] In the above system: the top inlet A4 of the granulator is connected to the bottom outlet D6 of the grading screen, and the side outlet B6 of the grading screen is connected to the top inlet A6 of the grading screen through the crusher;

[0020] In the above system: the side inlet B1 of the absorption tower is above the side inlet C1, the side inlet C1 is above the side inlet D1, the side inlet D1 is above the side inlet E1, the side inlet E1 is above the side inlet F1, the top inlet A4 of the granulator is closer to the motor than the top inlet B4, the top inlet B4 is closer to the side outlet C4 than the top inlet A4, the side outlet B6 of the grading screen is the upper screen surface outlet, the side outlet C6 is the lower screen surface outlet, and the side outlet B6 is above the side outlet C6;

[0021] In the above system: two spiral bands are provided on the stirring shaft of the gas-liquid separator; the granulator is a double-shaft granulator, and the two shafts rotate at the same speed in opposite directions; the grading screen is a double-layer screen, the polyphosphate ammonium coarse particles are screened out from the side outlet B6, the qualified granular ammonium polyphosphate fertilizer is screened out from the side outlet C6, and the polyphosphate ammonium fine powder is screened out from the bottom outlet D6;

[0022] A method for producing granular ammonium polyphosphate fertilizer by using the above system, the method includes the following steps:

[0023] (1) Raw material feeding and gaseous ammonia recovery section: Gaseous ammonia (temperature ≤ 180°C) from the battery limit enters the tubular reactor through inlet C2, and wet-process phosphoric acid (containing P2O5 mass concentration ≥ 50%, temperature ≥ 60°C) from the battery limit enters the absorption tower through side inlet E1; the wet-process phosphoric acid flows downward in the absorption tower and reacts with the gaseous ammonia flowing upward that enters the absorption tower through side inlet F1 to generate ammonium phosphate. The ammonium phosphate and the wet-process phosphoric acid flow downward together and exit the absorption tower through bottom outlet G1. After passing through the phosphoric acid pump, a part of the wet-process phosphoric acid enters the tubular reactor through side inlet B2, and another part of the wet-process phosphoric acid enters the absorption tower through side inlets B1, C1, and D1 and flows downward to react with the gaseous ammonia flowing upward that enters the absorption tower through side inlet F1 to generate ammonium phosphate. The ammonium phosphate and the wet-process phosphoric acid flow downward together and exit the absorption tower through bottom outlet G1 to complete a gaseous ammonia recovery cycle operation; the water vapor in the absorption tower exits the absorption tower through top outlet A1 and goes to the battery limit; the operating temperature in the absorption tower ≤ 150°C; the mass ratio of P2O5 in the wet-process phosphoric acid feed to N in the gaseous ammonia feed is ≥ 4:1;

[0024] (2) Ammonium polyphosphate preparation and granulation section: The wet-process phosphoric acid (temperature ≤ 150°C) entering through side inlet B2 reacts with the gaseous ammonia (temperature ≤ 180°C) entering through inlet C2 in the tubular reactor to generate a molten ammonium polyphosphate. The molten ammonium polyphosphate after the reaction (temperature ≤ 240°C) exits the tubular reactor through outlet A2 by its own pressure (pressure ≤ 0.37 MPa) and enters the gas-liquid separator through side inlet B3; in the gas-liquid separator, two spiral bands on the stirring shaft are used to stir to promote the gas-liquid separation of the foamy molten ammonium polyphosphate and push the solid material to the bottom outlet C3 of the gas-liquid separator and discharge it into the granulator through top inlet B4. The ammonia-containing gas separated by the gas-liquid separator exits the gas-liquid separator through top outlet A3 and enters the absorption tower through side inlet F1; the two shafts of the granulator rotate at the same speed in opposite directions, and the blades on the shafts push the ammonium polyphosphate fine powder returned from the bottom outlet D6 of the classifier screen and entering the granulator through top inlet A4 upward between the two shafts to mix and granulate with the molten ammonium polyphosphate entering through top inlet B4. The granulated ammonium polyphosphate particles (temperature ≤ 110°C) exit the granulator through side outlet C4 and enter the cooler through top inlet A5; the reaction temperature in the tubular reactor ≤ 240°C, and the granulation temperature in the granulator ≤ 110°C;

[0025] (3) Ammonium polyphosphate cooling and screening section: The ammonium polyphosphate particles (temperature ≤ 110 °C) from the granulator are cooled countercurrently by air in the cooler. After being cooled to the set temperature (temperature ≤ 45 °C), they exit the cooler from the bottom outlet B5 and enter the grading screen through the top inlet A6. In the grading screen, the ammonium polyphosphate particles are graded. The coarse ammonium polyphosphate particles (particle size > 4 mm) exit the grading screen from the side outlet B6 and enter the crusher through the top inlet A7. The fine ammonium polyphosphate powder (particle size < 2 mm) exits the grading screen from the bottom outlet D6 and enters the granulator as recycled material through the top inlet A4. The qualified ammonium polyphosphate product (4 mm ≥ particle size ≥ 2 mm) exits the grading screen from the side outlet C6 and is sent to the boundary area as the target product - ammonium polyphosphate granular fertilizer (water mass concentration ≤ 2%) through the finished product conveyor. The coarse ammonium polyphosphate particles from the grading screen are crushed in the crusher, and the crushed ammonium polyphosphate exits the crusher from the bottom outlet B7 and re-enters the grading screen through the top inlet A6 for screening. The ratio of recycled material to target product is ≤ 4:1.

[0026] In some more specific technical solutions, a method for producing ammonium polyphosphate granular fertilizer includes gaseous ammonia feeding, phosphoric acid feeding, circulating and washing ammonia-containing gas. Gaseous ammonia and phosphoric acid react at a certain temperature and pressure to form a foamy ammonium polyphosphate melt. The foamy ammonium polyphosphate melt is separated into gas and liquid. The ammonium polyphosphate melt is granulated. The ammonium polyphosphate particles are cooled and screened. The target product - ammonium polyphosphate granular fertilizer is discharged. It is characterized in that the production process includes a raw material feeding and gaseous ammonia recovery section, an ammonium polyphosphate preparation and granulation section, and an ammonium polyphosphate cooling and screening section. The steps are as follows:

[0027] (1) Raw material feeding and gaseous ammonia recovery section: The gaseous ammonia (temperature 100 °C - 180 °C) from the boundary area enters the tubular reactor through the inlet C2. The wet-process phosphoric acid (P2O5 mass concentration 50% - 60%, temperature 60 °C - 140 °C) from the boundary area enters the absorption tower through the side inlet E1. The wet-process phosphoric acid flows downward in the absorption tower and reacts with the gaseous ammonia flowing upward from the side inlet F1 in the absorption tower to form ammonium phosphate. The ammonium phosphate and the wet-process phosphoric acid flow downward together and exit the absorption tower from the bottom outlet G1. After passing through the phosphoric acid pump, a part of the wet-process phosphoric acid enters the tubular reactor through the side inlet B2, and another part of the wet-process phosphoric acid enters the absorption tower through the side inlets B1, C1, D1 and flows downward, reacting with the gaseous ammonia flowing upward from the side inlet F1 in the absorption tower to form ammonium phosphate. The ammonium phosphate and the wet-process phosphoric acid flow downward together and exit the absorption tower from the bottom outlet G1 to complete a gaseous ammonia recovery cycle operation. The water vapor in the absorption tower exits the absorption tower from the top outlet A1 and goes to the boundary area. The operating temperature in the absorption tower is 120 °C - 150 °C. The mass ratio of P2O5 in the wet-process phosphoric acid feed to N in the gaseous ammonia feed is 4 - 5:1.

[0028] (2) Ammonium polyphosphate preparation and granulation section: Wet-process phosphoric acid (temperature 130°C - 150°C) entering from side inlet B2 reacts with gaseous ammonia (temperature 100°C - 180°C) entering from inlet C2 in a tubular reactor to form a molten ammonium polyphosphate. The completed molten ammonium polyphosphate (temperature 210°C - 240°C) exits the tubular reactor through outlet A2 and enters the gas-liquid separator through side inlet B3 by its own pressure (pressure 0.34 MPa - 0.37 MPa); in the gas-liquid separator, the foamy molten ammonium polyphosphate is separated into gas and liquid by stirring with two spiral bands on the stirring shaft, and the solid material is pushed to the bottom outlet C3 of the gas-liquid separator and discharged, then enters the granulator through top inlet B4. The ammonia-containing gas separated by the gas-liquid separator exits the gas-liquid separator through top outlet A3 and enters the absorption tower through side inlet F1; the two shafts of the granulator rotate at the same speed in opposite directions, and the blades on the shafts push the ammonium polyphosphate fine powder returned from the bottom outlet D6 of the grading screen and entering the granulator through top inlet A4 upward between the two shafts for mixing and granulation with the molten ammonium polyphosphate entering through top inlet B4. The completed ammonium polyphosphate granules (temperature 70°C - 110°C) exit the granulator through side outlet C4 and enter the cooler through top inlet A5; the reaction temperature in the tubular reactor is 210°C - 240°C, and the granulation temperature in the granulator is 70°C - 110°C;

[0029] (3) Ammonium polyphosphate cooling and screening section: The ammonium polyphosphate granules (temperature 70°C - 110°C) from the granulator are cooled countercurrently by air in the cooler, and after being cooled to the set temperature (temperature 30°C - 45°C), they exit the cooler through bottom outlet B5 and enter the grading screen through top inlet A6; in the grading screen, the ammonium polyphosphate granules are graded. The coarse ammonium polyphosphate granules (particle size > 4 mm) exit the grading screen through side outlet B6 and enter the crusher through top inlet A7. The fine ammonium polyphosphate powder (particle size < 2 mm) exits the grading screen through bottom outlet D6 as returned material and enters the granulator through top inlet A4. The qualified ammonium polyphosphate products (4 mm ≥ particle size ≥ 2 mm) exit the grading screen through side outlet C6 as the target product - granular ammonium polyphosphate fertilizer (water mass concentration 0.5% - 2%) and are sent to the battery limit through the finished product conveyor; the coarse ammonium polyphosphate granules from the grading screen are crushed in the crusher, and the crushed ammonium polyphosphate exits the crusher through bottom outlet B7 and re-enters the grading screen through top inlet A6 for screening; the ratio of returned material to target product is 2 - 4:1.

[0030] Advantages of the present invention:

[0031] An absorption tower is adopted to perform multi-stage washing of gaseous ammonia with phosphoric acid to reduce ammonia loss;

[0032] A tubular reactor is adopted. The reaction time between phosphoric acid and ammonia in the tubular reactor is short, the reaction is intense, the temperature rises, the pressure is high, and more water is evaporated. It is easy to generate polyphosphate and evaporate more water;

[0033] The stirring shaft of the gas-liquid separator is equipped with two spiral bands. With the help of its stirring, gas-liquid separation is promoted, and the ammonium polyphosphate melt is pushed towards the bottom outlet of the gas-liquid separator for discharge. The shearing action of the spiral bands also reduces the viscosity of the ammonium polyphosphate melt, enabling it to flow freely.

[0034] The granulator uses a twin-shaft granulator. The two shafts rotate at the same speed in opposite directions. The blades on the shafts push the recycled ammonium polyphosphate fine powder towards the middle of the two shafts and turn it upwards, where it is mixed with the ammonium polyphosphate melt entering from the top for granulation. Adding urea to the recycled material can produce urea-based ammonium polyphosphate granular fertilizer, and adding potassium salt can produce nitrogen-phosphorus-potassium ammonium polyphosphate granular fertilizer.

[0035] The nutrient content of ammonium polyphosphate is higher than that of ammonium phosphate, saving transportation and packaging costs. The mass concentration of P2O5 in ammonium polyphosphate is 56.8%, which is higher than the mass concentration of P2O5 in ammonium phosphate, which is 38% - 48%. The content of water-soluble P2O5 in ammonium polyphosphate accounts for more than 99% of the total P2O5, which is also higher than the content of water-soluble P2O5 in ammonium phosphate, which accounts for 65% - 90% of the total P2O5.

[0036] Ammonium polyphosphate has a chelating effect on metal ions. Therefore, it is not easily fixed by metal ions such as iron and calcium in the soil. Instead, it can form soluble complexes with ineffective trace elements in the soil and be absorbed by plants. Polyphosphate is not directly absorbed by plants but is gradually hydrolyzed into orthophosphate in the soil and utilized by plants. Therefore, it is a slow-release long-acting fertilizer.

[0037] The ammonium polyphosphate particles coming out of the granulator have a very low water content (water mass concentration ≤ 2%), and there is no need for a dryer for drying, saving energy, reducing dust and tail gas.

[0038] The present invention uses wet-process phosphoric acid to replace thermal-process polyphosphoric acid to produce high-quality ammonium polyphosphate granular fertilizer, saving energy, reducing carbon emissions of the production device, reducing production costs, and protecting the environment. Description of the Drawings

[0039] Figure 1 It is the process flow schematic diagram in the present invention

[0040] Among them, absorption tower 1, phosphoric acid pump 2, tubular reactor 3, gas-liquid separator 4, granulator 5, cooler 6, sizing screen 7, crusher 8, finished product conveyor 9. Detailed Embodiments

[0041] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. The components of the embodiments of the present invention described and illustrated herein can be arranged and designed in various different configurations. Therefore, the detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the protection scope of the present invention. The embodiments of the present invention will be described in detail below. The examples of the embodiments are shown in the accompanying drawings, where the same or similar reference numerals denote the same or similar elements or elements with the same or similar functions throughout. The embodiments described below by referring to the accompanying drawings are exemplary and are intended to explain the present invention, but should not be construed as limiting the present invention.

[0042] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0043] As Figure 1 shown, a system for producing granular ammonium polyphosphate fertilizer is characterized in that: the system includes an absorption tower 1, a phosphoric acid pump 2, a tubular reactor 3, a gas-liquid separator 4, a granulator 5, a cooler 6, a sizing screen 7, a crusher 8, and a finished product conveyor 9; the raw material - phosphoric acid pipeline from the battery limit is connected to the side inlet E1 of the absorption tower 1, the bottom outlet G1 of the absorption tower 1 is connected to the side inlet B2 of the tubular reactor 3 through the phosphoric acid pump 2, the raw material - gaseous ammonia pipeline from the battery limit is connected to the inlet C2 of the tubular reactor 3, the outlet A2 of the tubular reactor 3 is connected to the side inlet B3 of the gas-liquid separator 4, the bottom outlet C3 of the gas-liquid separator 4 is connected to the top inlet B4 of the granulator 5, the side outlet C4 of the granulator 5 is connected to the top inlet A5 of the cooler 6, the bottom outlet B5 of the cooler 6 is connected to the top inlet A6 of the sizing screen 7, the side outlet C6 of the sizing screen 7 is connected to the feeding end of the finished product conveyor 9, and the discharging end of the finished product conveyor 9 is connected to the battery limit;

[0044] The top outlet A1 of the absorption tower 1 is connected to the water vapor pipeline to the battery limit. The side inlets B1, C1, and D1 of the absorption tower 1 are connected to the pipeline connecting the outlet of the phosphoric acid pump 2 to the side inlet B2 of the tubular reactor 3. The side inlet F1 of the absorption tower 1 is connected to the top outlet A3 of the gas-liquid separator 4;

[0045] The top inlet A4 of the granulator 5 is connected to the bottom outlet D6 of the sizing screen 7. The side outlet B6 of the sizing screen 7 is connected to the top inlet A6 of the sizing screen 7 through the crusher 8;

[0046] The side inlet B1 of the absorption tower 1 is above the side inlet C1, the side inlet C1 is above the side inlet D1, the side inlet D1 is above the side inlet E1, and the side inlet E1 is above the side inlet F1. The top inlet A4 of the granulator 5 is closer to the motor than the top inlet B4, and the top inlet B4 is closer to the side outlet C4 than the top inlet A4. The side outlet B6 of the sizing screen 7 is the upper sieve surface outlet, the side outlet C6 is the lower sieve surface outlet, and the side outlet B6 is above the side outlet C6;

[0047] The stirring shaft of the gas-liquid separator 4 is equipped with two spiral bands; the granulator 5 adopts a twin-shaft granulator, and the two shafts rotate at the same speed in opposite directions; the sizing screen 7 adopts a double-layer sieve. The side outlet B6 screens out coarse ammonium polyphosphate particles, the side outlet C6 screens out qualified granular ammonium polyphosphate fertilizers, and the bottom outlet D6 screens out fine ammonium polyphosphate powder;

[0048] The method for producing granular ammonium polyphosphate fertilizer using the above system includes the following steps:

[0049] (1) Raw material feeding and ammonia recovery section: The ammonia gas (temperature 150 °C) from the battery limit enters the tubular reactor 3 from the inlet C2, and the wet-process phosphoric acid (containing 50.1% mass concentration of P2O5, temperature 132 °C) from the battery limit enters the absorption tower 1 from the side inlet E1; the wet-process phosphoric acid flows downward in the absorption tower 1 and reacts with the ammonia gas flowing upward from the side inlet F1 of the absorption tower 1 to generate ammonium phosphate. The ammonium phosphate and the wet-process phosphoric acid flow downward together and exit the absorption tower 1 from the bottom outlet G1. After passing through the phosphoric acid pump 2, a part of the wet-process phosphoric acid enters the tubular reactor 3 from the side inlet B2, and another part of the wet-process phosphoric acid enters the absorption tower 1 from the side inlets B1, C1, and D1 and flows downward to react with the ammonia gas flowing upward from the side inlet F1 of the absorption tower 1 to generate ammonium phosphate. The ammonium phosphate and the wet-process phosphoric acid flow downward together and exit the absorption tower 1 from the bottom outlet G1 to complete a gas ammonia recovery cycle operation; the water vapor in the absorption tower 1 exits the absorption tower 1 from the top outlet A1 and goes to the battery limit; the operating temperature in the absorption tower 1 is 138 °C; the mass ratio of P2O5 in the wet-process phosphoric acid feed to N in the ammonia gas feed is 462:100;

[0050] (2) Ammonium polyphosphate preparation and granulation section: Wet-process phosphoric acid (temperature 138°C) entering from side inlet B2 reacts with gaseous ammonia (temperature 150°C) entering from inlet C2 in tubular reactor 3 to form a molten ammonium polyphosphate. The molten ammonium polyphosphate after the reaction (temperature 227°C) exits tubular reactor 3 from outlet A2 by its own pressure (pressure 0.35 MPa) and enters gas-liquid separator 4 through side inlet B3; in gas-liquid separator 4, the foamy molten ammonium polyphosphate is separated into gas and liquid by stirring with two spiral bands on the stirring shaft, and the solid material is pushed to the bottom outlet C3 of gas-liquid separator 4 and discharged, then enters granulator 5 from top inlet B4. The ammonia-containing gas separated by gas-liquid separator 4 exits gas-liquid separator 4 from top outlet A3 and enters absorption tower 1 through side inlet F1; two shafts of granulator 5 rotate at the same speed in opposite directions, and the blades on the shafts push the ammonium polyphosphate fine powder returned from the bottom outlet D6 of classifier 7 and entering granulator 5 from top inlet A4 upward between the two shafts for mixing and granulation with the molten ammonium polyphosphate entering from top inlet B4. The granulated ammonium polyphosphate particles (temperature 99°C) exit granulator 5 from side outlet C4 and enter cooler 6 through top inlet A5; the reaction temperature in tubular reactor 3 is 227°C, and the granulation temperature in granulator (5) is 99°C;

[0051] (3) Ammonium polyphosphate cooling and screening section: The ammonium polyphosphate particles (temperature 99°C) from granulator 5 are cooled in cooler 6 by countercurrent air cooling. After being cooled to the set temperature (temperature 38°C), they exit cooler 6 from bottom outlet B5 and enter classifier 7 through top inlet A6; in classifier 7, the ammonium polyphosphate particles are classified. The coarse ammonium polyphosphate particles (particle size > 4 mm) exit classifier 7 from side outlet B6 and enter crusher 8 through top inlet A7. The fine ammonium polyphosphate powder (particle size < 2 mm) exits classifier 7 from bottom outlet D6 as returned material and enters granulator 5 through top inlet A4. The qualified ammonium polyphosphate products (4 mm ≥ particle size ≥ 2 mm) exit classifier 7 from side outlet C6 as the target product - granular ammonium polyphosphate fertilizer (water mass concentration 0.8%) and are sent to the battery limit through finished product conveyor 9; the coarse ammonium polyphosphate particles from classifier 7 are crushed in crusher 8, and the crushed ammonium polyphosphate exits crusher 8 from bottom outlet B7 and re-enters classifier 7 through top inlet A6 for screening; the ratio of returned material to target product is 38:10.

[0052] The operation results of using the present invention are shown in Table 1 as follows

[0053] Table 1 Performance assessment results of 200 kg / h granular ammonium polyphosphate fertilizer plant

[0054]

Claims

1. A system for producing ammonium polyphosphate granular fertilizer, characterized in that: The system comprises an absorption tower (1), wherein an output pipeline of gaseous ammonia is connected to a tubular reactor (3), the output end of the tubular reactor (3) is connected to the lower part of the absorption tower (1) via a gas-liquid separator (4), and the output end at the bottom of the absorption tower (1) is respectively connected to the tubular reactor (3) and a plurality of inlets at the upper part of the absorption tower (1).

2. The system for producing ammonium polyphosphate granular fertilizer according to claim 1, characterized in that: The liquid output end of the gas-liquid separator (4) is connected in sequence through a granulator (5), a cooler (6) and a grading screen (7); The grading screen (7) also has an output end connected to the top of the grading screen (7) through a crusher (8).

3. The system for producing ammonium polyphosphate granular fertilizer according to claim 1, characterized in that: The output pipeline of the phosphoric acid solution is connected to the middle or lower part of the absorption tower (1), and the position where the phosphoric acid is connected to the absorption tower (1) is higher than the position where the gas-liquid separator (4) is connected to the absorption tower (1).

4. The system for producing ammonium polyphosphate granular fertilizer according to claim 1, characterized in that: The output end at the bottom of the absorption tower (1) is connected to 1 to 5 inlets at the top of the absorption tower (1).

5. The system for producing ammonium polyphosphate granular fertilizer according to claim 1, characterized in that: The gas-liquid separator (4) has two spiral belts on its stirring shaft; the granulator (5) is a double-shaft granulator, with two shafts rotating at the same speed and in opposite directions; and the grading screen (7) is a double-layer screen.

6. A method for producing ammonium polyphosphate granular fertilizer using the system of claim 1, characterized in that: The method comprises the following steps: The gaseous ammonia first enters the tubular reactor (3) and the gas-liquid separator (4) in sequence, and then enters the lower part of the absorption tower (1) from the gas output end of the gas-liquid separator (4); the phosphoric acid solution also enters from the lower part of the absorption tower (1), the phosphoric acid solution flowing downward reacts with the gaseous ammonia flowing upward to generate ammonium phosphate, and the mixed liquid of the ammonium phosphate and the phosphoric acid solution enters the tubular reactor (3) and the absorption tower (1) from the bottom of the absorption tower (1) to react; in the absorption tower, the mixed liquid of the ammonium phosphate and the phosphoric acid solution at the upper part of the absorption tower continues to react with the gaseous ammonia to generate ammonium phosphate; in the tubular reactor (3), the mixed liquid of the ammonium phosphate and the phosphoric acid solution reacts with the gaseous ammonia to generate a polyammonium phosphate melt, the reaction products enter the gas-liquid separator (4) for separation, the gas obtained after separation enters the absorption tower for further reaction, and the obtained polyammonium phosphate is granulated, cooled and sieved in sequence to obtain the final product.

7. The method according to claim 6, characterized in that The temperature of the gaseous ammonia is ≤180°C, the mass concentration of P2O5 in the phosphoric acid solution is ≥50%, and the temperature is ≥60°C.

8. The method according to claim 6, characterized in that The operating temperature in the absorption tower (1) is ≤150°C; The mass ratio of P2O5 in the feed phosphoric acid solution to N in the feed gas ammonia is ≥4:

1.

9. The method according to claim 5, characterized in that The reaction temperature in the tubular reactor (3) is ≤240°C, and the granulation temperature in the granulator (5) is ≤110°C.

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