System and method for producing ammonium polyphosphate liquid fertilizer

Abstract

The invention discloses a system and a method for producing an ammonium polyphosphate liquid fertilizer, and belongs to the field of chemical engineering. The system comprises a section I heat exchanger, a cold ammonium polyphosphate pump, a section II heat exchanger, a hot ammonium polyphosphate pump, a tubular reactor, a cooler and a mixed reaction scrubber. By adopting the system and the method, wet-process phosphoric acid containing P2O5 with the mass concentration of about 60% reacts with preheated gas ammonia in the tubular reactor to generate an ammonium polyphosphate melt, and then liquid ammonia reacts with polyphosphoric acid and phosphoric acid in the ammonium polyphosphate solution in the mixed reaction scrubber; the generated ammonium polyphosphate solution is subjected to secondary heat exchange and primary cooling and then is used as a target product, namely the ammonium polyphosphate liquid fertilizer, to be debounded. The wet-process phosphoric acid is used for replacing hot-process phosphoric acid to produce the high-quality ammonium polyphosphate liquid fertilizer, and the produced target product does not need the procedures of granulation, drying, screening, crushing and the like, so that the device is low in investment and low in production cost.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical production, and particularly relates to a system and method for producing ammonium polyphosphate liquid 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 fertilizer and is also an important phosphorus source for compound fertilizers.

[0003] Since wet-process phosphoric acid contains a large amount of metal ion impurities, a lot of water-insoluble phosphates will be generated. The P2O5 occupied by this part of phosphates will account for 35% of the total P2O5. Therefore, ammonium phosphate produced from wet-process phosphoric acid cannot be used to prepare liquid fertilizer; the wet materials coming out of the reactor in the production of ammonium phosphate need to be granulated, dried, cooled, screened, crushed and other processes for reprocessing. These processes not only consume a large amount of energy, but also generate a large amount of dust and tail gas.

[0004] Thermal-process polyphosphoric acid can be used to produce water-soluble ammonium polyphosphate with better quality than ammonium phosphate. However, the price of thermal-process polyphosphoric acid is high, and the cost of ammonium polyphosphate produced from thermal-process polyphosphoric acid is too high to be used as chemical fertilizer.

[0005] 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 water-soluble phosphate content, without using thermal-process polyphosphoric acid, and without the need for granulation, drying, screening, crushing and other processes for reprocessing. Summary of the Invention

[0006] The purpose of the present invention is to provide a system and method for producing ammonium polyphosphate liquid fertilizer. Wet-process phosphoric acid with a mass concentration of about 60% of P2O5 reacts with preheated gaseous ammonia in a tubular reactor to generate ammonium polyphosphate melt, and then liquid ammonia reacts with polyphosphoric acid and phosphoric acid in the polyphosphoric acid solution in a mixing reaction scrubber. The generated ammonium polyphosphate solution is used as the target product - ammonium polyphosphate liquid fertilizer to go to the battery limit after secondary heat exchange and primary cooling. The present invention uses wet-process phosphoric acid to replace thermal-process polyphosphoric acid to produce high-quality ammonium polyphosphate liquid fertilizer. The produced target product does not require processes such as granulation, drying, screening, and crushing, so the device investment is saved and the production cost is low. The present invention aims to save energy and reduce consumption, reduce the investment and carbon emissions of the production device, reduce the production cost, and protect the environment.

[0007] The purpose of the present invention can be achieved by the following technical solutions:

[0008] A system for producing ammonium polyphosphate liquid fertilizer, the system includes a tubular reactor and a mixing reaction scrubber; the output pipeline of liquid ammonia is connected to the tubular reactor after heat exchange through a multi-stage heat exchanger, the output end of the tubular reactor is connected to the mixing reaction scrubber, the material at the bottom of the mixing reaction scrubber is connected to the cooler after heat exchange through a heat exchange device, and the material at the bottom of the cooler can obtain the target product after heat exchange through a heat exchange device.

[0009] In the above system: the output end of liquid ammonia is sequentially connected to the tubular reactor through a stage I heat exchanger and a stage II heat exchanger.

[0010] In the above system: the material at the bottom of the mixing reaction scrubber is connected to the cooler after heat exchange through the stage II heat exchanger; the material at the bottom of the cooler can obtain the target product after heat exchange through the stage I heat exchanger.

[0011] In the above system: a scrubber is provided at the upper part of the mixing reaction scrubber, and a packing layer is provided at the lower part of the scrubber.

[0012] In the above system: the output end at the bottom of the cooler is also connected to the upper part of the scrubber, and a water washing spray layer is provided at the upper part of the scrubber.

[0013] In the above system: an input end of liquid ammonia is also provided at the upper part of the mixing reaction scrubber; an input end of phosphoric acid is provided in the middle of the tubular reactor; an exhaust fan is provided at the top of the cooler.

[0014] A method for producing ammonium polyphosphate liquid fertilizer by using the above-mentioned system, the method includes the following steps:

[0015] (1) Raw material feeding and liquid ammonia gasification section: Phosphoric acid from the battery limit enters the tubular reactor; liquid ammonia from the battery limit is gasified and enters the tubular reactor after multi-stage heat exchange; the mass ratio of P2O5 in the wet-process phosphoric acid feed to N in the liquid ammonia ① feed is ≥5:1;

[0016] (2) Ammonium polyphosphate preparation and ammonia gas recovery section: The reaction is carried out in the tubular reactor to generate molten ammonium polyphosphate, and after the reaction is completed, it enters the mixing reaction scrubber to continue the reaction with liquid ammonia from the battery limit; the hot ammonium polyphosphate solution after the reaction is heat-exchanged and enters the cooler;

[0017] (3) Ammonium polyphosphate cooling and discharging section: A part of the cooled ammonium polyphosphate goes to the mixing reaction scrubber, and the other part is used as the target product ammonium polyphosphate liquid fertilizer to go to the battery limit after heat exchange.

[0018] In the above method, in step (1), the phosphoric acid is wet-process phosphoric acid, the mass concentration of P2O5 is ≥60%, and the temperature is ≥80°C; the mass ratio of P2O5 in the wet-process phosphoric acid feed to N in the liquid ammonia ① feed is ≥5:1.

[0019] In the above method, in the wet-process phosphoric acid feed in the mixing reaction scrubber in step (2), the mass ratio of P2O5 to N in the liquid ammonia ② feed is ≥ 8:1.

[0020] In some specific technical solutions, the method includes the following steps:

[0021] (1) Raw material feeding and liquid ammonia gasification section: The wet-process phosphoric acid from the battery limit enters the tubular reactor; the liquid ammonia from the battery limit enters the first-stage heat exchanger. In the first-stage heat exchanger, the liquid ammonia in the shell side indirectly exchanges heat with the ammonium polyphosphate in the tube side and then enters the second-stage heat exchanger. In the second-stage heat exchanger, the liquid ammonia in the tube side indirectly exchanges heat with the ammonium polyphosphate in the shell side and is completely gasified and enters the tubular reactor.

[0022] (2) Ammonium polyphosphate preparation and gaseous ammonia recovery section: The reaction takes place in the tubular reactor to generate a molten ammonium polyphosphate. The completed molten ammonium polyphosphate enters the mixing reaction scrubber; the liquid ammonia from the battery limit also enters the mixing reaction scrubber; in the bottom of the mixing reactor, the polyphosphoric acid, phosphoric acid and ammonia in the ammonium polyphosphate continue to react; the completed hot ammonium polyphosphate solution enters the second-stage heat exchanger through the shell side inlet C2 of the second-stage heat exchanger for heat exchange.

[0023] (3) Ammonium polyphosphate cooling and discharging section: The hot ammonium polyphosphate solution in the shell side of the second-stage heat exchanger indirectly exchanges heat with the ammonia in the tube side and then enters the cooler; in the cooler, the ammonium polyphosphate solution is cooled. Part of it enters the scrubber, and the other part exchanges heat with the liquid ammonia in the shell side of the first-stage heat exchanger. The cooled ammonium polyphosphate solution after heat exchange is taken as the target product and sent to the battery limit.

[0024] In some more specific technical solutions, the method includes the following steps:

[0025] (1) Raw material feeding and liquid ammonia gasification section: The wet-process phosphoric acid (with a P2O5 mass concentration ≥ 60% and a temperature ≥ 80°C) from the battery limit enters the tubular reactor from the side inlet B3; a part of the liquid ammonia from the battery limit (hereinafter referred to as liquid ammonia ①) enters the first-stage heat exchanger from the shell side inlet B1. In the first-stage heat exchanger, the liquid ammonia ① in the shell side indirectly exchanges heat with the ammonium polyphosphate in the tube side and then exits the first-stage heat exchanger from the shell side outlet C1 and enters the second-stage heat exchanger through the tube side inlet A2. In the second-stage heat exchanger, the liquid ammonia ① in the tube side indirectly exchanges heat with the ammonium polyphosphate in the shell side and is completely gasified (the temperature of the gaseous ammonia ≥ 50°C) and then exits the second-stage heat exchanger from the tube side outlet D2 and enters the tubular reactor through the inlet C3; the mass ratio of P2O5 to N in the wet-process phosphoric acid feed is ≥ 5:1.

[0026] (2) Ammonium polyphosphate preparation and ammonia recovery section: Wet-process phosphoric acid (with a P₂O₅ mass concentration ≥ 60% and a temperature ≥ 80°C) entering from side inlet B3 reacts with gaseous ammonia (temperature ≥ 50°C) entering from inlet C3 in a tubular reactor to form a molten ammonium polyphosphate. The molten ammonium polyphosphate after the reaction (temperature ≤ 380°C) exits the tubular reactor through outlet A3 and enters the ammonium polyphosphate insertion tube in the mixing reaction scrubber through shoulder inlet D5 by its own pressure. Another part of the liquid ammonia from the battery limit (hereinafter referred to as liquid ammonia ②) enters the liquid ammonia insertion tube in the mixing reaction scrubber through shoulder inlet E5. The molten ammonium polyphosphate in the ammonium polyphosphate insertion tube enters the bottom of the mixing reactor through bottom opening F5, and liquid ammonia ② in the liquid ammonia insertion tube enters the bottom of the mixing reactor through several bottom openings G5. In the bottom of the mixing reactor, polyphosphoric acid, phosphoric acid and ammonia in the ammonium polyphosphate continue to react. The hot ammonium polyphosphate solution after the reaction (with an N mass concentration ≥ 8%, a P₂O₅ mass concentration ≥ 24%, and a temperature ≤ 100°C) exits the mixing reaction scrubber through bottom outlet H5, passes through the hot ammonium polyphosphate pump, and enters the shell-side inlet C2 of the second-stage heat exchanger. The water vapor evaporated in the mixing reactor enters the scrubber from the top of the mixing reactor. In the scrubber, the water vapor first passes through the packing layer to wash and recover gaseous ammonia, then passes through the ammonium polyphosphate solution entering from side inlet C5 to wash and recover gaseous ammonia, and then passes through the process water entering from side inlet B5 to wash and recover gaseous ammonia. The clean water vapor is discharged from the scrubber through top outlet A5. The mass ratio of P₂O₅ in the wet-process phosphoric acid feed to N in the liquid ammonia ② feed is ≥ 8:1;

[0027] (3) Ammonium polyphosphate cooling and discharging section: In the second-stage heat exchanger, the hot ammonium polyphosphate solution (temperature ≤ 100°C) in the shell side exchanges heat indirectly with ammonia in the tube side and exits the second-stage heat exchanger through shell-side outlet B2 and enters the cooler through side inlet B4. In the cooler, the ammonium polyphosphate solution is cooled and exits the cooler through bottom outlet D4 to the cold ammonium polyphosphate pump. The water vapor and non-condensable gas are discharged from the cooler through top outlet A4. A part of the ammonium polyphosphate passing through the cold ammonium polyphosphate pump goes to the mixing reaction scrubber and enters the scrubber through side inlet C5, and the other part enters the first-stage heat exchanger through tube-side inlet D1 to exchange heat with liquid ammonia ① in the shell side. The cooled ammonium polyphosphate solution after heat exchange (with an N mass concentration ≥ 8%, a P₂O₅ mass concentration ≥ 24%, and a temperature ≤ 40°C) is used as the target product - ammonium polyphosphate liquid fertilizer and exits the first-stage heat exchanger through tube-side outlet A1 to the battery limit.

[0028] In a more specific embodiment, the steps of the method are as follows:

[0029] (1) Raw material feeding and liquid ammonia gasification section: Wet-process phosphoric acid (containing 60% - 70% by mass of P2O5, temperature 80°C - 130°C) from the battery limit enters the tubular reactor through the side inlet B3; a part of the liquid ammonia from the battery limit (hereinafter referred to as liquid ammonia ①) enters the first-stage heat exchanger through the shell-side inlet B1. In the first-stage heat exchanger, liquid ammonia ① in the shell side exchanges heat indirectly with ammonium polyphosphate in the tube side and then exits the first-stage heat exchanger through the shell-side outlet C1, enters the second-stage heat exchanger through the tube-side inlet A2. In the second-stage heat exchanger, liquid ammonia ① in the tube side exchanges heat indirectly with ammonium polyphosphate in the shell side and is completely gasified (gas ammonia temperature 50°C - 60°C), then exits the second-stage heat exchanger through the tube-side outlet D2 and enters the tubular reactor through the inlet C3. The mass ratio of P2O5 in the wet-process phosphoric acid feed to N in the liquid ammonia ① feed is 5 - 6:1;

[0030] (2) Ammonium polyphosphate preparation and ammonia gas recovery section: Wet-process phosphoric acid (containing 60% - 70% by mass of P2O5, temperature 80°C - 130°C) entering through the side inlet B3 reacts with ammonia gas (temperature 50°C - 60°C) entering through the inlet C3 in the tubular reactor to form a molten ammonium polyphosphate. The molten ammonium polyphosphate after the reaction (temperature 240°C - 380°C) exits the tubular reactor through the outlet A3 and enters the ammonium polyphosphate insertion tube in the mixing reaction scrubber through the shoulder inlet D5; another part of the liquid ammonia from the battery limit (hereinafter referred to as liquid ammonia ②) enters the liquid ammonia insertion tube in the mixing reaction scrubber through the shoulder inlet E5; the molten ammonium polyphosphate in the ammonium polyphosphate insertion tube enters the bottom of the mixing reactor through the bottom opening F5, and liquid ammonia ② in the liquid ammonia insertion tube enters the bottom of the mixing reactor through several bottom openings G5. In the bottom of the mixing reactor, polyphosphoric acid, phosphoric acid and ammonia in the ammonium polyphosphate continue to react; the hot ammonium polyphosphate solution after the reaction (containing 8% - 15% by mass of N, containing 24% - 60% by mass of P2O5, temperature 70°C - 100°C) exits the bottom outlet H5 of the mixing reaction scrubber, passes through the hot ammonium polyphosphate pump and enters the second-stage heat exchanger through the shell-side inlet C2 of the second-stage heat exchanger. The water vapor evaporated in the mixing reactor enters the scrubber from the top of the mixing reactor. In the scrubber, the water vapor first passes through the packing layer to wash and recover ammonia gas, then passes through the ammonium polyphosphate solution entering through the side inlet C5 to wash and recover ammonia gas, and then passes through the process water entering through the side inlet B5 to wash and recover ammonia gas. The clean water vapor is discharged from the scrubber through the top outlet A5; the mass ratio of P2O5 in the wet-process phosphoric acid feed to N in the liquid ammonia ② feed is 8 - 9:1;

[0031] (3) Ammonium polyphosphate cooling and discharging section: In the shell side of the second-stage heat exchanger, the hot ammonium polyphosphate solution (temperature 70°C - 100°C) exchanges heat indirectly with ammonia in the tube side, and then exits the second-stage heat exchanger from the shell side outlet B2 and enters the cooler through the side inlet B4; in the cooler, the ammonium polyphosphate solution is cooled and exits the cooler from the bottom outlet D4 to the cold ammonium polyphosphate pump, and the water vapor and non-condensable gas are discharged from the cooler through the top outlet A4; a part of the ammonium polyphosphate after passing through the cold ammonium polyphosphate pump goes to the mixing reaction scrubber and enters the scrubber through the side inlet C5, and the other part enters the first-stage heat exchanger from the tube side inlet D1 and exchanges heat with liquid ammonia in the shell side. The cooled ammonium polyphosphate solution (N mass concentration 8% - 20%, P2O5 mass concentration 24% - 60%, temperature 20°C - 40°C) is used as the target product - ammonium polyphosphate liquid fertilizer and exits the first-stage heat exchanger from the tube side outlet A1 to the battery limit.

[0032] In some more specific technical solutions, the system includes a first-stage heat exchanger, a cold ammonium polyphosphate pump, a second-stage heat exchanger, a hot ammonium polyphosphate pump, a tubular reactor, a cooler, and a mixing reaction scrubber; the raw material - phosphoric acid pipeline from the battery limit is connected to the side inlet B3 of the tubular reactor, the raw material - liquid ammonia ① pipeline from the battery limit is connected to the shell side inlet B1 of the first-stage heat exchanger, the shell side outlet C1 of the first-stage heat exchanger is connected to the tube side inlet A2 of the second-stage heat exchanger, the tube side outlet D2 of the second-stage heat exchanger is connected to the inlet C3 of the tubular reactor, the outlet A3 of the tubular reactor is connected to the shoulder inlet D5 of the mixing reaction scrubber, the raw material - liquid ammonia ② pipeline from the battery limit is connected to the shoulder inlet E5 of the mixing reaction scrubber, the bottom outlet H5 of the mixing reaction scrubber is connected to the shell side inlet C2 of the second-stage heat exchanger through the hot ammonium polyphosphate pump, the shell side outlet B2 of the second-stage heat exchanger is connected to the side inlet B4 of the cooler, the bottom outlet D4 of the cooler is connected to the tube side inlet D1 of the first-stage heat exchanger through the cold ammonium polyphosphate pump, and the tube side outlet A1 of the first-stage heat exchanger is connected to the pipeline of the target product - ammonium polyphosphate liquid fertilizer going to the battery limit;

[0033] In the above system: the side inlet B5 of the mixing reaction scrubber is connected to the process water pipeline from the battery limit, and the side inlet C5 of the mixing reaction scrubber is connected to the pipeline connecting the outlet of the cold ammonium polyphosphate pump and the tube side inlet D1 of the first-stage heat exchanger;

[0034] In the above system: an exhaust fan is installed at the top outlet A4 of the cooler; the mixing reaction scrubber is an integrated device composed of an upper and a lower structure. The upper part is a scrubber and the lower part is a mixing reactor. The side inlet B5 of the scrubber is above the side inlet C5, a packing layer is installed below the side inlet C5, a polyphosphate insertion tube is installed at the shoulder inlet D5 of the mixing reactor, the polyphosphate insertion tube has an opening F5 at the bottom of the mixing reactor, a liquid ammonia insertion tube is installed at the shoulder inlet E5 of the mixing reactor, and the liquid ammonia insertion tube has several openings G5 at the bottom of the mixing reactor.

[0035] Advantages of the present invention:

[0036] An exhaust fan is installed at the top outlet of the cooler, and the cooling effect is good;

[0037] The gasification of liquid ammonia adopts a two-stage heat exchanger to ensure that all liquid ammonia is gasified;

[0038] The mixing reaction scrubber adopts an integrated device. The upper part is a scrubber for multi-stage scrubbing and recovery of gaseous ammonia, and the absorption effect is good; the lower part is a mixing reactor, where phosphoric acid and liquid ammonia are mixed and reacted at the bottom of the mixing reactor, with uniform mixing and complete reaction; the integrated device is compact and occupies little space;

[0039] A tubular reactor is adopted. The reaction time between phosphoric acid and ammonia in the tubular reactor is short, the reaction is violent, the temperature rises, and the pressure is high. It is easy to generate polyphosphate, and the polyphosphate contains 65% - 70% of P2O5 in the total P2O5;

[0040] Ammonium polyphosphate has high solubility and can chelate metal ions at the same time. It can prevent metal impurities in wet-process phosphoric acid from precipitating and increase the stability of liquid fertilizers. Ammonium polyphosphate is completely soluble in water without precipitation, which is better than the water-soluble P2O5 in ammonium phosphate accounting for 65% - 90% of the total P2O5. Therefore, ammonium polyphosphate is an excellent raw material for liquid fertilizers. The chelating effect of ammonium polyphosphate can be used to add trace element fertilizers to liquid fertilizers, and ammonium polyphosphate can be used as a carrier for trace element fertilizers; if pesticides and herbicides are added to ammonium polyphosphate liquid fertilizers, it can also save manpower and costs;

[0041] Ammonium polyphosphate is not easily degraded in the soil, so 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;

[0042] Polyphosphate is not directly absorbed by plants, but is gradually hydrolyzed into orthophosphoric acid in the soil and utilized by plants. Therefore, it is a slow-soluble long-acting fertilizer;

[0043] Ammonium polyphosphate liquid fertilizer does not require processes such as granulation, drying, screening, and crushing. Therefore, the device investment is saved, the production cost is low, energy is saved, and dust and tail gas are reduced;

[0044] The production of thermal-process polyphosphoric acid is to melt phosphate rock in an electric furnace, undergo a reduction reaction with carbon to release a mixed gas of phosphorus (P4) and carbon monoxide (CO), condense the phosphorus vapor into yellow phosphorus, and absorb the phosphorus pentoxide (P2O5) generated by the combustion of yellow phosphorus with water to obtain polyphosphoric acid. This method has high energy consumption and large pollution; the cost of producing ammonium polyphosphate with wet-process phosphoric acid is only 70% - 80% of that of thermal-process polyphosphoric acid. Therefore, the present invention uses wet-process phosphoric acid to replace thermal-process polyphosphoric acid to produce high-quality ammonium polyphosphate liquid fertilizer, saving energy, reducing carbon emissions of production devices, reducing production costs, and protecting the environment. Description of the Drawings

[0045] Figure 1 is the process flow schematic diagram in the present invention

[0046] Among them, the heat exchanger of section I is 1, the cold ammonium polyphosphate pump is 2, the heat exchanger of section II is 3, the hot ammonium polyphosphate pump is 4, the tubular reactor is 5, the cooler is 6, the exhaust fan is 6-1, the mixing reaction scrubber is 7, the scrubber is 7-1, the packing layer is 7-2, the mixing reactor is 7-3, the ammonium polyphosphate insertion pipe is 7-4, and the liquid ammonia insertion pipe is 7-5. Specific embodiments

[0047] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited thereto

[0048] As Figure 1 shown, a system for producing ammonium polyphosphate liquid fertilizer, characterized in that: the system includes a heat exchanger of section I 1, a cold ammonium polyphosphate pump 2, a heat exchanger of section II 3, a hot ammonium polyphosphate pump 4, a tubular reactor 5, a cooler 6, and a mixing reaction scrubber 7; the raw material - phosphoric acid pipeline from the battery limit is connected to the side inlet B3 of the tubular reactor 5, the raw material - liquid ammonia ① pipeline from the battery limit is connected to the shell side inlet B1 of the heat exchanger of section I 1, the shell side outlet C1 of the heat exchanger of section I 1 is connected to the tube side inlet A2 of the heat exchanger of section II 3, the tube side outlet D2 of the heat exchanger of section II 3 is connected to the inlet C3 of the tubular reactor 5, the outlet A3 of the tubular reactor 5 is connected to the shoulder inlet D5 of the mixing reaction scrubber 7, the raw material - liquid ammonia ② pipeline from the battery limit is connected to the shoulder inlet E5 of the mixing reaction scrubber 7, the bottom outlet H5 of the mixing reaction scrubber 7 is connected to the shell side inlet C2 of the heat exchanger of section II 3 through the hot ammonium polyphosphate pump 4, the shell side outlet B2 of the heat exchanger of section II 3 is connected to the side inlet B4 of the cooler 6, the bottom outlet D4 of the cooler 6 is connected to the tube side inlet D1 of the heat exchanger of section I 1 through the cold ammonium polyphosphate pump 2, and the tube side outlet A1 of the heat exchanger of section I 1 is connected to the pipeline of the target product - ammonium polyphosphate liquid fertilizer going to the battery limit;

[0049] The side inlet B5 of the mixing reaction scrubber 7 is connected to the process water pipeline from the battery limit, and the side inlet C5 of the mixing reaction scrubber 7 is connected to the pipeline connecting the outlet of the cold ammonium polyphosphate pump 2 and the tube side inlet D1 of the heat exchanger of section I 1;

[0050] An exhaust fan 6-1 is installed at the top outlet A4 of the cooler 6; the mixing reaction scrubber 7 is an integrated device composed of an upper and a lower structure. The upper part is the scrubber 7-1, and the lower part is the mixing reactor 7-3. The side inlet B5 of the scrubber 7-1 is above the side inlet C5, and a packing layer 7-2 is installed below the side inlet C5. The ammonium polyphosphate insertion tube 7-4 is installed at the shoulder inlet D5 of the mixing reactor 7-3, and the ammonium polyphosphate insertion tube 7-4 has an opening F5 at the bottom of the mixing reactor 7-3. The liquid ammonia insertion tube 7-5 is installed at the shoulder inlet E5 of the mixing reactor 7-3, and the liquid ammonia insertion tube 7-5 has a number of openings G5 at the bottom of the mixing reactor 7-3.

[0051] The method for producing ammonium polyphosphate liquid fertilizer by using the above system comprises the following steps:

[0052] (1) Raw material feeding and liquid ammonia gasification section: The wet-process phosphoric acid (with a P2O5 mass concentration of 68% and a temperature of 118 °C) from the battery limit enters the tubular reactor 5 from the side inlet B3; a part of the liquid ammonia from the battery limit (hereinafter referred to as liquid ammonia ①) enters the first-stage heat exchanger 1 from the shell-side inlet B1. In the first-stage heat exchanger 1, the liquid ammonia ① in the shell side exchanges heat indirectly with the ammonium polyphosphate in the tube side and then exits the first-stage heat exchanger 1 from the shell-side outlet C1, enters the second-stage heat exchanger 3 through the tube-side inlet A2. In the second-stage heat exchanger 3, the liquid ammonia ① in the tube side exchanges heat indirectly with the ammonium polyphosphate in the shell side and is completely gasified (the gas ammonia temperature is 54 °C), then exits the second-stage heat exchanger 3 from the tube-side outlet D2 and enters the tubular reactor 5 through the inlet C3; the mass ratio of P2O5 in the wet-process phosphoric acid feed to N in the liquid ammonia ① feed is 34:6.

[0053] (2) Ammonium polyphosphate preparation and ammonia recovery section: Wet-process phosphoric acid (with a mass concentration of P2O5 of 68% and a temperature of 118°C) entering from side inlet B3 reacts with gaseous ammonia (temperature 54°C) entering from inlet C3 in tubular reactor 5 to form a molten ammonium polyphosphate. The molten ammonium polyphosphate after the reaction (temperature 343°C) exits tubular reactor 5 through outlet A3 and enters the ammonium polyphosphate insertion tube 7-4 in mixing reaction scrubber 7 through shoulder inlet D5; Another part of the liquid ammonia from the battery limit (hereinafter referred to as liquid ammonia ②) enters the liquid ammonia insertion tube 7-5 in mixing reaction scrubber 7 through shoulder inlet E5; The molten ammonium polyphosphate in the ammonium polyphosphate insertion tube 7-4 enters the bottom of mixing reactor 7-3 through bottom opening F5, and liquid ammonia ② in the liquid ammonia insertion tube 7-5 enters the bottom of mixing reactor 7-3 through several bottom openings G5. In the bottom of mixing reactor 7-3, polyphosphoric acid, phosphoric acid in ammonium polyphosphate and ammonia continue to react; The hot ammonium polyphosphate solution after the reaction (with a mass concentration of N of 10%, a mass concentration of P2O5 of 34%, and a temperature of 82°C) exits mixing reaction scrubber 7 through bottom outlet H5, passes through hot ammonium polyphosphate pump 4, and enters shell-side inlet C2 of section II heat exchanger 3. The water vapor evaporated in mixing reactor 7-3 enters scrubber 7-1 from the top of mixing reactor 7-3. In scrubber 7-1, the water vapor first passes through packing layer 7-2 to wash and recover gaseous ammonia, then passes through the ammonium polyphosphate solution entering from side inlet C5 to wash and recover gaseous ammonia, and then passes through the process water entering from side inlet B5 to wash and recover gaseous ammonia. The clean water vapor is discharged from scrubber 7-1 through top outlet A5; The mass ratio of P2O5 in the wet-process phosphoric acid feed to N in the liquid ammonia ② feed is 34:4;

[0054] (3) Ammonium polyphosphate cooling and discharging section: The hot ammonium polyphosphate solution (temperature 82°C) in the shell side of section II heat exchanger 3 exchanges heat indirectly with ammonia in the tube side, and then exits section II heat exchanger 3 through shell-side outlet B2 and enters cooler 6 through side inlet B4; In cooler 6, the ammonium polyphosphate solution is cooled and exits cooler 6 through bottom outlet D4 to cold ammonium polyphosphate pump 2. The water vapor and non-condensable gas are discharged from cooler 6 through top outlet A4; Part of the ammonium polyphosphate pumped by cold ammonium polyphosphate pump 2 enters scrubber 7-1 in mixing reaction scrubber 7 through side inlet C5, and the other part enters section I heat exchanger 1 through tube-side inlet D1 to exchange heat with liquid ammonia in the shell side. The cooled ammonium polyphosphate solution after heat exchange (with a mass concentration of N of 10%, a mass concentration of P2O5 of 34%, and a temperature of 27°C) is used as the target product - ammonium polyphosphate liquid fertilizer and exits section I heat exchanger 1 through tube-side outlet A1 to the battery limit. The operation results of the present invention are shown in Table 1 as follows

[0055] Table 1 Performance assessment results of 1000 kg / h ammonium polyphosphate liquid fertilizer plant

[0056]

Claims

1. A system for producing ammonium polyphosphate liquid fertilizer, characterized in that: The system includes a tubular reactor (5) and a mixing reaction scrubber (7); the output pipeline of liquid ammonia is connected to the tubular reactor (5) after heat exchange through a multi-stage heat exchanger, the output end of the tubular reactor (5) is connected to the mixing reaction scrubber (7), the material at the bottom of the mixing reaction scrubber (7) is connected to the cooler (6) after heat exchange through a heat exchange device, and the material at the bottom of the cooler (6) can obtain the target product after heat exchange through a heat exchange device.

2. The system for producing ammonium polyphosphate liquid fertilizer according to claim 1, wherein: The output end of the liquid ammonia is sequentially connected to the tubular reactor (5) through a first-stage heat exchanger (1) and a second-stage heat exchanger (3).

3. The system for producing ammonium polyphosphate liquid fertilizer according to claim 2, characterized in that: The material at the bottom of the mixing reaction scrubber (7) is connected to the cooler (6) after heat exchange through the second-stage heat exchanger (3); the material at the bottom of the cooler (6) can obtain the target product after heat exchange through the first-stage heat exchanger (1).

4. The system for producing ammonium polyphosphate liquid fertilizer according to claim 1, characterized in that: The upper part of the mixing reaction scrubber (7) is provided with a scrubber (7-1), and the lower part of the scrubber is provided with a packing layer (7-2).

5. The system for producing ammonium polyphosphate liquid fertilizer according to claim 4, characterized in that: The output end at the bottom of the cooler (6) is also connected to the upper part of the scrubber (7-1), and the upper part of the scrubber (7-1) is provided with a water washing spray layer.

6. The system for producing ammonium polyphosphate liquid fertilizer according to claim 1, characterized in that: The upper part of the mixing reaction scrubber (7) is also provided with an input end of liquid ammonia; the middle part of the tubular reactor (5) is provided with an input end of phosphoric acid; the top of the cooler (6) is provided with an exhaust fan (6-1).

7. A method for producing ammonium polyphosphate liquid fertilizer using the system according to claim 1, characterized in that, The method includes the following steps: (1) Raw material feeding and liquid ammonia gasification section: The phosphoric acid from the battery limit enters the tubular reactor (5); the liquid ammonia from the battery limit is gasified after multi-stage heat exchange and enters the tubular reactor (5); the mass ratio of P2O5 in the wet-process phosphoric acid feed to N in the liquid ammonia ① feed is ≥5:

1. (2) Ammonium polyphosphate preparation and gaseous ammonia recovery section: A reaction occurs in the tubular reactor (5) to generate a molten ammonium polyphosphate, and after the reaction is completed, it enters the mixing reaction scrubber (7) to continue reacting with the liquid ammonia from the battery limit; the hot ammonium polyphosphate solution after the reaction is completed enters the cooler (6) after heat exchange. (3) Ammonium polyphosphate cooling and discharging section: A part of the cooled ammonium polyphosphate goes to the mixing reaction scrubber (7), and the other part goes to the battery limit as the target product, ammonium polyphosphate liquid fertilizer, after heat exchange.

8. The method according to claim 7, wherein In step (1), the phosphoric acid is wet-process phosphoric acid, the mass concentration of P2O5 is ≥60%, and the temperature is ≥80°C; the mass ratio of P2O5 in the wet-process phosphoric acid feed to N in the liquid ammonia ① feed is ≥5:

1.

9. The method according to claim 7, wherein In the mixing reaction scrubber (7) of step (2), the mass ratio of P2O5 in the wet-process phosphoric acid feed to N in the liquid ammonia ② feed is ≥8:

1.

10. The method according to claim 7, wherein The method includes the following steps: (1) Raw material feeding and liquid ammonia gasification section: The wet-process phosphoric acid from the battery limit enters the tubular reactor (5); the liquid ammonia from the battery limit enters the first-stage heat exchanger (1), and the liquid ammonia in the shell side of the first-stage heat exchanger (1) exchanges heat indirectly with the ammonium polyphosphate in the tube side and then enters the second-stage heat exchanger (3), and the liquid ammonia in the tube side of the second-stage heat exchanger (3) exchanges heat indirectly with the ammonium polyphosphate in the shell side and is completely gasified and enters the tubular reactor (5). (2) Ammonium polyphosphate preparation and ammonia gas recovery section: The reaction occurs in the tubular reactor (5) to generate the molten ammonium polyphosphate. The completed molten ammonium polyphosphate enters the mixing reaction scrubber (7); the liquid ammonia from the battery limit also enters the mixing reaction scrubber (7); in the bottom of the mixing reactor (7), the polyphosphoric acid, phosphoric acid and ammonia in the ammonium polyphosphate continue to react; the completed hot ammonium polyphosphate solution enters the shell-side inlet C2 of the second-stage heat exchanger (3) and exchanges heat in the second-stage heat exchanger (3). (3) Ammonium polyphosphate cooling and discharging section: The hot ammonium polyphosphate solution in the shell side of the second-stage heat exchanger (3) exchanges heat indirectly with the ammonia in the tube side and then enters the cooler (6); in the cooler (6), the ammonium polyphosphate solution is cooled. One part enters the scrubber (7-1), and the other part exchanges heat with the liquid ammonia in the shell side of the first-stage heat exchanger (1). The cooled ammonium polyphosphate solution after heat exchange is taken as the target product to the battery limit.

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