Device and method for continuously producing powdery ammonium polyphosphate

Abstract

The invention relates to the technical field of ammonium polyphosphate production, in particular to a device and a method for continuously producing powdery ammonium polyphosphate. The device comprises a molten material supply system used for outputting molten urea; the continuous synthesis system is used for producing powdery ammonium polyphosphate and comprises a multi-stage reactor, the multi-stage reactor is formed by connecting at least two double-cavity horizontal reactors in series, and outer cavities of the reactors are filled with heating media; continuously reacting the molten urea with the neutralized slurry or the reaction raw materials in each double-cavity horizontal reactor in sequence to obtain powdery ammonium polyphosphate; the product treatment system is used for circularly screening and crushing the generated powdery ammonium polyphosphate; a tail gas washing system; a circulating cooling system; and a dedusting system. According to the design, feeding and discharging can be achieved at the same time, complete continuous production is achieved, and the method is short in reaction time, easy to industrialize, low in investment cost, easy to operate and suitable for various technologies; the discharged materials are small granular materials, and the requirement for crushing is low.

Description

Technical Field

[0001] The invention relates to the technical field of ammonium polyphosphate production, in particular to a device and a method for continuously producing powdered ammonium polyphosphate. Background Art

[0002] Ammonium polyphosphate is also called ammonium polyphosphate or condensed ammonium phosphate (APP for short). Its general formula is: HYPERLINK "https: / / www.chembk.com / cn / search / (NH%E2%82%84,H)%E2%82%99+2P%E2%82%99O%E2%82%83%E2%82%99%E2%82%8A%E2%82%81" (NH4) n+2 P n O 3n+1 It is an inorganic polymer compound, in the form of white particles or crystals. It can be divided into three types according to the degree of polymerization: oligomeric, mesomeric and high-polymer. Oligomeric ammonium phosphate refers to short-chain APP with a degree of polymerization of n≤20, which is commonly used in the fertilizer industry. In addition to good water solubility, it also has the characteristics of strong compatibility, low crystallization temperature and good chelating properties. The degree of polymerization n>20 belongs to long-chain APP, which is almost insoluble in water and is often used in halogen-free phosphorus flame retardants.

[0003] At present, oligoammonium phosphate is widely used in the fertilizer industry. It can chelate trace metal elements in the soil, and will first be hydrolyzed into orthophosphate and then absorbed by crops, achieving a long-term slow-release effect. In addition, ammonium polyphosphate has a high phosphorus content and can be applied in a variety of ways. It can be used as a foliar fertilizer, will not burn crop leaves, and can remain on the leaves for several days without evaporation and crystallization.

[0004] Ammonium polyphosphate products have good activity and high fertilizer efficiency. Polyphosphate chelates trace elements, improves the effectiveness of phosphorus and trace elements, promotes dissolution and absorption, and has higher fertilizer efficiency; Polyphosphate can retain water, of which pyrophosphate and tripolyphosphate improve water retention, solve the water shortage problem of dryland crops, and reduce maintenance costs; High chelation fertilizer effect is long, polymerized phosphorus chelates metal ions and is not easily fixed, polymerized phosphorus has a high utilization rate and a long fertilizer effect, which can meet the phosphorus needs of mid- and late-stage crops; improve soil resistance to continuous cropping, polymerized phosphorus has a strong mobility, and has a greater mobility distance in saline-alkali soils. By chelating metal ions and phosphorus and nitrogen fixed by the soil, it activates compacted soil and corrects various malnutrition caused by plant deficiency. It has been vigorously promoted and used in developed agricultural countries abroad.

[0005] In the phosphate fertilizer system of my country's fertilizer industry, orthophosphate is the main component, while polyphosphate is used less frequently, and there are even fewer companies producing ammonium polyphosphate. Polyphosphate has high water solubility and the function of chelating metal ions. Foreign countries mainly use polyammonium phosphate and potassium to prepare chemical synthetic water-soluble fertilizers with high phosphorus and potassium formulas and polyphosphate trace element chelating agents. The development of domestic agricultural ammonium polyphosphate started late, and at this stage it is mainly based on the intermittent method, but the intermittent method has the characteristics of large investment, small production capacity, and high labor intensity. Common ammonium polyphosphate production processes include urea phosphate condensation method, ammonium phosphate condensation method, phosphoric acid method, superphosphoric acid method, and ammonium phosphate-phosphorus pentoxide synthesis method. However, because the ammonium polyphosphate material in the processing process has a strong viscosity, it is not easy to discharge the material continuously from the polymerization reactor. Now the production process selected by enterprises is basically intermittent.

[0006] Compared with the continuous process, the intermittent process requires more personnel and has a longer reaction time. Each time, the material from the previous reaction needs to be released before the new material can be added. However, the continuous process requires fewer personnel, is simpler to operate, and has a relatively good and safe working environment.

[0007] At present, there are many reports on the synthesis of ammonium polyphosphate. For example, patent 202020654562.9 discloses a continuous production equipment for ammonium polyphosphate. A phosphoric acid feed pipe and a liquid ammonia feed pipe are respectively installed at the inlet of the tubular reactor, and a polymerization reactor is connected to the lower part of the outlet. One side of the polymerization reactor is connected to the tail gas treatment device, and the lower outlet is connected to the cooler processing box. A screen bucket and a vibrating screen are set below the cooler processing box. The ammonium polyphosphate product can be obtained by production under certain conditions, but it has not achieved continuous production in the true sense. For example, patent 201710526911.1 discloses a continuous production method for powdery ammonium polyphosphate. The invention puts a phosphorus source and urea into a prepolymerizer, and reacts at 60 to 140 ° C for 2 to 10 minutes to obtain a liquid material. Then the liquid material is uniformly added to a belt polymerizer with a heating zone and a cooling zone. After heating polymerization and cooling and curing in turn, a solid material is obtained. After the solid material is crushed, a powdery ammonium polyphosphate is obtained. This method requires prepolymerization in advance and is not completely continuous. In addition, the liquid material has a high viscosity and is difficult to peel off cleanly once solidified on the equipment. In addition, the solids generated by the reaction are mostly in block form, making it difficult to handle the solids.

[0008] In view of this, we propose a device and method for continuously producing powdered ammonium polyphosphate. Summary of the invention

[0009] The object of the present invention is to provide a device and method for continuously producing powdered ammonium polyphosphate, so as to solve the problem that the prior art is difficult to achieve truly continuous production as mentioned in the above background technology.

[0010] In order to solve the above technical problems, one of the purposes of the present invention is to provide a device for continuously producing powdered ammonium polyphosphate, characterized in that it comprises: A molten material feeding system, used for outputting molten urea; A continuous synthesis system for producing powdered ammonium polyphosphate comprises a multi-stage reactor, wherein the multi-stage reactor is composed of at least two double-cavity horizontal reactors connected in series, and the outer cavities of the reactors are filled with heating medium; molten urea and reaction raw materials are continuously reacted in each double-cavity horizontal reactor in turn to obtain powdered ammonium polyphosphate; A circulating cooling system, which is cyclically connected to the outer cavity of the fourth-stage reactor; The product processing system is used to circulate, screen and crush the generated powdered ammonium polyphosphate; An exhaust gas washing system, used for receiving exhaust gas discharged from the molten material feeding system and the continuous synthesis system; The dust removal system is used to collect dust generated in the product processing system.

[0011] As a further improvement of the technical solution, the multi-stage reactor includes a primary reactor, a secondary reactor, and a tertiary reactor connected in series in sequence, and the discharge end of the tertiary reactor is connected to the feed end of the quaternary reactor; the primary reactor and the tertiary reactor are twin-screw reactors, and the screw length-to-diameter ratio of the primary reactor is 40:1 to 60:1; the screw length-to-diameter ratio of the tertiary reactor is 30:1 to 50:1; the secondary reactor is one of a twin-screw reactor, a double-blade reactor, and a twin-shaft reactor, and when the secondary reactor is a twin-screw reactor, the screw length-to-diameter ratio is 50:1 to 80:1.

[0012] As a further improvement of the present technical solution, the molten material feeding system includes a feeder, a storage bin and two parallel melting tanks connected in sequence; a weight sensor is provided at the bottom of the storage bin, and the discharge end of the storage bin is connected to the feed ends of the two melting tanks respectively through a pneumatic three-way steering valve; the discharge ends of the two melting tanks are connected to the feed end of the primary reactor through another pneumatic three-way steering valve, and a metering pump is also provided between the discharge end of the pneumatic three-way steering valve and the feed end of the primary reactor.

[0013] As a further improvement of the present technical solution, the feed end of the primary reactor is also connected to an ammonia neutralization reactor, the ammonia neutralization reactor is a double-layer kettle-type stirred reactor, and the product processing system includes a vibrating screen and a crusher which are sequentially connected to the discharge end of the tertiary reactor.

[0014] As a further improvement of the present technical solution, the inner cavities of the ammonia neutralization reactor, the primary reactor, the secondary reactor, the tertiary reactor and the tops of the two melting tanks are respectively connected with tail gas pipes, and several of the tail gas pipes are connected with the tail gas washing system; the connecting pipeline between the ammonia neutralization reactor and the primary reactor, the connecting pipeline between the primary reactor and the secondary reactor and all the tail gas pipes are provided with solenoid valves.

[0015] The second object of the present invention is to provide a method for continuously producing powdered ammonium polyphosphate, using the above-mentioned device for continuously producing powdered ammonium polyphosphate, comprising the following steps: S1. Ammonia neutralization: injecting a phosphorus source into an ammonia neutralization reactor, and injecting a certain proportion of a nitrogen source into the ammonia neutralization reactor, and obtaining a neutralized slurry in the ammonia neutralization reactor by stirring; S2, primary reaction: the neutralized slurry or reaction raw material output from the ammonia neutralization reactor and the molten urea prepared and output by the molten material feeding system are simultaneously injected into the primary reactor, and the primary reactor is heated and stirred and transported forward, and the polymerization rate is controlled to be 10% to 40%; S3, secondary reaction: the molten liquid material transported from the primary reactor enters the secondary reactor, the internal space of the secondary reactor is larger than that of the primary reactor; the secondary reactor also adopts the method of heating and stirring while transporting forward, and the degree of polymerization control is 50% to 80%; S4, tertiary reaction: After the material output from the secondary reactor enters the tertiary reactor, the material is transported forward under continuous heating, continues to polymerize and gradually solidifies; S5. Product processing: The high-temperature product output from the tertiary reactor enters the fourth-stage reactor. The circulating cooling system uses circulating water cooling to cool it down. The temperature after discharge is controlled at 40-50°C. The product then enters the vibrating screen to screen the materials that meet the specifications, while the materials with too large particle size enter the crusher for crushing. After crushing, it returns to the vibrating screen, and the powdered materials that meet the specifications are transported to the packaging machine for packaging.

[0016] As a further improvement of the present technical solution, in step S1, the phosphorus source includes one or more of wet-process phosphoric acid, wet-process phosphoric acid purification acid, raffinate acid, sludge acid, ammonium phosphate and urea phosphate; the nitrogen source includes one or both of liquid ammonia and urea; the degree of neutralization of the slurry in the ammonia neutralization reactor is controlled between 0.4 and 1.0, and the reaction raw material is diammonium phosphate or urea phosphate.

[0017] As a further improvement of the technical solution, in step S2, the molar ratio of urea to phosphorus in the primary reactor is controlled by the feeding speed of the two raw materials, the control range is 0.7 to 2.0:1, the heating temperature of the heating zone is 130 to 160°C, and the residence time of the material in the reactor is 1 to 12 minutes; The rotation speed of the primary reactor is set to 200-450 rpm; As a further improvement of the technical solution, in step S3, the heating temperature of the secondary reactor is 160-210° C., and the residence time of the material in the reactor is 10-35 min; The rotation speed of the secondary reactor is set to 12-80 rpm.

[0018] As a further improvement of the technical solution, in step S4, the heating temperature of the three-stage reactor is 160-200° C., and the residence time of the material in the reactor is 5-15 min; The rotation speed of the three-stage reactor is adjusted to 9-35 rpm; The curing catalyst is one or more of melamine, sodium tripolyphosphate, ammonium sulfate, ammonium chloride and the like.

[0019] As a further improvement of the technical solution, in step S5, the circulating water temperature of the circulating cooling system is 7 to 30° C., and the residence time of the material in the circulating cooling system is 15 to 25 minutes.

[0020] Compared with the prior art, the present invention has the following beneficial effects: 1. In the device for continuously producing powdered ammonium polyphosphate, an ammonia neutralization reactor is used for pre-reaction, and the materials are successively synthesized in the multi-stage reactor and then cooled and formed in the four-stage reactor. Urea is continuously input from the molten material feeding system, and the finished product is continuously output from the four-stage reactor, so as to realize complete continuous production. Compared with intermittent production or incomplete continuous production, the device has high thermal efficiency, is easier to scale up and expand, realizes short reaction time, is easy to industrialize, has low investment cost, is simple to operate, is applicable to a variety of processes, and can realize continuous production of ammonium polyphosphate; 2. The method for continuous production of powdered ammonium polyphosphate is different from the semi-continuous method and can achieve complete continuity; the main reaction of this scheme is completed by a horizontal reactor, which has the ability of stirring and conveying inside and has a certain foaming space, so it can achieve simultaneous feeding and discharging, and the whole process is completely continuous without a separate prepolymerization process; 3. The method for continuously producing powdered ammonium polyphosphate can give full play to the characteristics of the equipment, make the mass transfer and heat transfer functions of the equipment more fully manifested, and greatly improve the volume utilization rate of the reactor. Compared with the batch polymerization equipment, which requires a larger foaming space and a stronger stirring capacity, and the materials discharged after the reaction are mostly larger pieces, which has higher requirements for the crusher, the equipment of this scheme compresses the reaction into a horizontal reactor, completes the heat and mass transfer functions in a very short time, does not require a large space for foaming, and the discharged materials are smaller granular materials, which has lower requirements for the crusher; 4. The continuous production method of powdered ammonium polyphosphate greatly reduces the reaction time. The general batch method reaction time is 2 to 4 hours, and other continuous methods also vary in length, but basically all take about 2 hours; the continuous method of this scheme, due to the characteristics of the equipment and the fit of the process conditions, the time from adding the raw materials to the completion of the reaction and discharging the materials is ≤ 60min; 5. The method for continuously producing powdered ammonium polyphosphate adopts mutually independent equipment to complete the continuous production of ammonium polyphosphate. It can not only adjust and control each equipment separately according to different processes and different requirements, but also adjust and control parameters of different equipment for primary reaction, secondary reaction and tertiary reaction, so that continuous production can proceed normally and avoid premature solidification of materials at a certain stage. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of the structure of the device in the present invention.

[0022] Figure 2 It is a schematic diagram of the process flow in the present invention.

[0023] In the figure: 1-feeder; 2-storage bin; 3-pneumatic three-way steering valve; 4-melting tank; 5-metering pump; 6-ammonia neutralization reactor; 7-primary reactor; 8-secondary reactor; 9-fourth reactor; 10-vibrating screen; 11-crusher; 12-exhaust gas washing system; 13-circulating cooling system; 14-dust removal system; 15-weight sensor; 16-solenoid valve; 17-third reactor. DETAILED DESCRIPTION

[0024] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] Example like Figure 1As shown, this embodiment provides a device for continuously producing powdered ammonium polyphosphate, comprising: The molten material feeding system is used to output molten urea, and comprises a feeder 1, a storage bin 2 and two parallel molten tanks 4 connected in sequence; A continuous synthesis system for producing powdered ammonium polyphosphate includes an ammonia neutralization reactor 6 and a multistage reactor connected in sequence, wherein the multistage reactor includes a primary reactor 7, a secondary reactor 8 and a tertiary reactor 17 connected in series in sequence, the ammonia neutralization reactor 6 is a double-layer kettle-type stirred reactor, the primary reactor 7, the secondary reactor 8 and the tertiary reactor 17 are all double-cavity horizontal double-shaft reactors, the primary reactor; the outer cavities of the primary reactor 7, the secondary reactor 8 and the tertiary reactor 17 are all filled with a heating medium, and the heating medium is heat transfer oil or steam. The ammonia neutralization reactor 6 is used to prepare a neutralization slurry. When the reaction raw materials are diammonium hydrogen phosphate and urea phosphate, they directly enter the multistage reactor without the need for the ammonia neutralization reactor 6; the number of double-layer kettle-type stirred reactors can also be designed according to needs during the production process, with a minimum of 2 in series and an optimal of 3 in series.

[0026] The product processing system is used for cyclic screening and crushing of the generated powdered ammonium polyphosphate, and includes a vibrating screen 10 and a crusher 11 connected to the discharge port end of the tertiary reactor 17 in sequence.

[0027] The tail gas washing system 12 is used to receive the tail gas discharged from the molten material feeding system and the continuous synthesis system.

[0028] The circulating cooling system 13 is cyclically connected to the outer cavity of the quaternary reactor 9, and the quaternary reactor 9 is connected to the discharge end of the last reactor in the multi-stage reactor. The outer cavity of the quaternary reactor 9 is filled with a cooling medium, which is cooling water. The cooling water is circulated and replenished through a closed cooling tower or a cooler as the circulating cooling system 13.

[0029] The dust removal system 14 is used to collect dust generated in the product processing system. The working chambers of the vibrating screen 10 and the crusher 11 are connected to the dust removal system 14 to prevent floating dust generated by screening and crushing from being dispersed.

[0030] Specifically, the phosphorus source and the nitrogen source are pre-reacted in the ammonia neutralization reactor 6 in the form of a double-layer kettle stirred reactor to complete uniform mixing and neutralization. The urea becomes a molten state in the molten material feeding system. The two groups of slurries are added to the primary reactor 7 at the same time, and pass through the primary reactor 7, the secondary reactor 8, and the tertiary reactor 17 in turn. After completing the reaction in the primary reactor 7, the secondary reactor 8, and the tertiary reactor 17 of the double-cavity horizontal twin-axis reactor, they enter the fourth reactor 9 for cooling and solidification, and then discharge the material to form a finished product.

[0031] At the same time, after the ammonia neutralization reactor 6, the primary reactor 7, the secondary reactor 8, and the tertiary reactor 17 are set as relatively independent systems, not only can the solenoid valve on the connecting pipeline between the adjacent two-stage reactors be used to control the flow rate during the material transmission process; but also different types of stirring blades can be set in the primary reactor 7 and the secondary reactor 8, and the tertiary reactor 17, so that the materials at different reaction stages can react under different reaction conditions such as different shear forces and different conveying speeds, so that the adaptability of the entire system is better. In addition, in order to save more floor space in the production workshop, the ammonia neutralization reactor 6, the primary reactor 7, the secondary reactor 8, and the tertiary reactor 17 in this embodiment are arranged from top to bottom. This not only saves floor space, but also allows the material to be transported between different reaction vessels, so that the material can flow more easily under the action of its own gravity, and can better enter the next reaction vessel, reducing the risk of blockage.

[0032] In this embodiment, a weight sensor 15 is provided at the bottom of the storage bin 2, and the discharge end of the storage bin 2 is connected to the feed ends of the two melting tanks 4 respectively through a pneumatic three-way steering valve 3; the discharge ends of the two melting tanks 4 are connected to the feed end of the primary reactor 7 through another pneumatic three-way steering valve 3, and a metering pump 5 is also provided between the discharge end of the pneumatic three-way steering valve 3 and the feed end of the primary reactor 7 to achieve the purpose of constant speed and quantitative addition of molten urea.

[0033] Specifically, the two melting tanks 4 are used to melt urea, allowing the urea to enter the primary reactor 7 in a molten state; since it takes time for the material to melt, the two melting tanks 4 are arranged in parallel, so that when the urea is melted in one of the melting tanks 4, the urea that has been melted in the other melting tank 4 can enter the primary reactor 7 under the action of the metering pump 5, and when the urea in the other melting tank 4 begins to melt, the pneumatic three-way steering valve 3 is switched to allow the urea that has been melted in the previous melting tank 4 to enter the primary reactor 7 under the action of the metering pump 5, thereby avoiding production stoppage caused by the melting process of urea.

[0034] At the same time, the two melting tanks 4 are also connected to the process water of the plant area, and the heating device in the melting tank 4 is used to heat and melt the urea in the melting tank 4 within the temperature range required by the process to form molten urea. At the same time, by switching the pneumatic three-way steering valve 3, the urea raw materials stored in the storage bin 2 can enter the two melting tanks 4 as needed.

[0035] In this embodiment, the screw length-to-diameter ratio of the primary reactor 7 can be set as needed, specifically can be set to 40:1-60:1, the optimal choice is 60:1; the screw length-to-diameter ratio of the secondary reactor 8 can be set to 50:1-80:1, the optimal choice is 70:1; the screw length-to-diameter ratio of the tertiary reactor 17 can be set to 30:1-50:1, the optimal choice is 50:1.

[0036] In this embodiment, the inner cavities of the ammonia neutralization reactor 6, the primary reactor 7, the secondary reactor 8, the tertiary reactor 17 and the tops of the two melting tanks 4 are respectively connected to tail gas pipes, and the several tail gas pipes are connected to the tail gas washing system 12; all the tail gas generated in the entire production process can be transported to the tail gas washing system 12 for centralized treatment, which not only avoids the exhaust gas generated in the polymerization process from being discharged into the environment and affecting the environment, but also can timely relieve the pressure of the reaction container to avoid excessive internal pressure in the inner cavity, which causes the material in the reaction container to be squeezed out from the gap.

[0037] Furthermore, solenoid valves 16 are provided on the connecting pipeline between the ammonia neutralization reactor 6 and the primary reactor 7, the connecting pipeline between the primary reactor 7 and the secondary reactor 8, the connecting pipeline between the secondary reactor 8 and the tertiary reactor 17, and all tail gas pipes.

[0038] like Figure 2 As shown, this embodiment also provides a method for continuously producing powdered ammonium polyphosphate. The above-mentioned device for continuously producing powdered ammonium polyphosphate comprises the following steps: S1, ammonia neutralization: injecting a phosphorus source into the ammonia neutralization reactor 6, and injecting a certain proportion of a nitrogen source into the ammonia neutralization reactor 6, and obtaining a neutralized slurry in the ammonia neutralization reactor 6 by stirring; In this step, the phosphorus source includes one or more of wet-process phosphoric acid, wet-process phosphoric acid purification acid, raffinate acid, sludge acid, ammonium phosphate and urea phosphate; the nitrogen source includes one or more of liquid ammonia and urea; The degree of neutralization of the slurry in the ammonia neutralization reactor 6 is controlled between 0.4 and 1.0.

[0039] S2, primary reaction: the neutralized slurry output from the ammonia neutralization reactor 6, one of diammonium hydrogen phosphate and urea phosphate and the molten urea prepared and output by the molten material feeding system are simultaneously injected into the primary reactor 7, and the primary reactor 7 adopts a method of heating and stirring and conveying forward, and the degree of polymerization control is 10% to 40%; In this step, the molar ratio of urea to phosphorus in the primary reactor 7 is controlled by the feeding rate of the two raw materials, the control range is 0.7-2.0:1, the heating temperature of the heating zone is 130-160°C, and the residence time of the material in the reactor is 1-12 min; The rotation speed of the primary reactor 7 is set to 200-450rpm; in the primary reaction, under the condition of constant temperature and feeder speed, increasing the rotation speed of the primary reactor 7 can make the materials mixed more evenly, reduce the urea decomposition rate, and thus avoid N loss. In addition, the material needs to avoid staying in the primary reactor 7 for too long to prevent the material from solidifying and causing the material channel between the primary reactor 7 and the secondary reactor 8 to be blocked, thereby affecting the continuous production.

[0040] S3, secondary reaction: the molten liquid material transported from the primary reactor 7 enters the secondary reactor 8. The internal space of the secondary reactor 8 is larger than that of the primary reactor 7, leaving space for the molten material to foam and expand. The secondary reactor 8 also adopts the method of heating and stirring while transporting forward, and the polymerization rate is controlled to be 50% to 80%; Among them, the temperature used in the secondary reaction is the highest temperature in the entire production process. The secondary reaction is the most important part of the reaction between the phosphorus source and urea. The decomposition of a large amount of urea requires heat absorption, so a certain amount of heat is required to start. The temperature of the secondary reactor ensures that the internal materials have sufficient heat to react.

[0041] In this step, the heating temperature of the secondary reactor 8 is 160-210°C, the residence time of the material in the reactor is 10-35 minutes; the rotation speed of the secondary reactor 8 is set to 12-80rpm; to ensure that the material can flow normally during the secondary reaction, and there is no blockage of the pile and the material does not overflow. At the same time, combined with the progress of the primary reaction, the residence time of the material in the secondary reaction is controlled to avoid excessive decomposition of urea and blockage of the material flow of the secondary reactor 8.

[0042] Moreover, if the temperature of the secondary reaction is too low, such as below 160°C, the material will solidify in a short time, causing the secondary reactor 8 to be blocked, and the material cannot go down to the tertiary reaction. When the rotation speed of the secondary reactor 8 is too fast, it will also accelerate the curing speed inside the secondary reaction. At the same time, for the continuous production process of this scheme, when the temperature of the secondary reaction is set to 160-210°C, the material is not easy to solidify and has a certain fluidity. When the temperature of the secondary reaction exceeds 210°C, the material inside the secondary reaction will begin to solidify again, affecting the normal material flow of the secondary reactor 8.

[0043] S4, tertiary reaction: After the material output from the secondary reactor 8 (already almost in a viscous state and not foaming) enters the tertiary reactor 17, there is an opening at the material inlet of the tertiary reactor 17. If the sample is difficult to solidify, a curing catalyst is injected, and the material is transported forward under continuous heating, continues to polymerize and gradually solidifies; For a tertiary reaction, the first half of the tertiary reaction is usually the polymerization stage, and the second half is the curing stage. The reaction is an exothermic reaction, with urea as a nitrogen source and also as a condensation agent. As the reaction proceeds, the molecular chain grows, and after growing to a certain extent, it will begin to solidify.

[0044] In this step, the heating temperature of the tertiary reactor 17 is 160-200°C, and the residence time of the material in the reactor is 5-15 minutes; wherein, when the tertiary reaction is carried out, if the temperature is too high or the residence time is too long, the N element will be lost, and the overall reaction will be acidic. Under acidic conditions, the material is difficult to solidify. Moreover, the loss of the N element will lead to a decrease in the total nutrient content of the product, which cannot meet the standard.

[0045] The rotation speed of the tertiary reactor 17 is adjusted to 9-35 rpm. Since the tertiary reactor 17 and the secondary reactor 8 are two independent devices, the foaming of the material in the tertiary reactor 17 is more serious, and it is easy to overflow. The discharge state is also more viscous, and the reaction is incomplete. By lowering the rotation speed of the third reactor, it is ensured that a solid product with stable discharge is obtained.

[0046] The curing catalyst is one or more of melamine, sodium tripolyphosphate, ammonium sulfate, ammonium chloride and the like.

[0047] In summary, in the process of continuous reaction, the entire ammonium polyphosphate preparation process can basically be divided into several stages, namely: mixing and melting, foaming, polymerization, and solidification. The mixed melting part can basically be described as the powder material being transformed into a liquid molten material. The stirring current required for this reaction is relatively small. Foaming is essentially a semi-liquid foam with fluffy internal foam, and no large current is required to drive the motor for stirring. In the polymerization and solidification part, the material will gradually shrink from the foamed fluffy foam material to a viscous state. The viscosity of the material in this state is very large, and sufficient shear force is required for stirring. If the shear force is not enough, the material is easy to jam the stirring paddle. Therefore, the current required in the later stage of the reaction is extremely high. Therefore, if a single device is used, since the screw speed of a single device is fixed, it is impossible to achieve the three-stage reaction in this scheme, which will cause the device to jam and the motor to stop. Therefore, the primary reaction, the secondary reaction, and the tertiary reaction are respectively set to the state where the three devices of the primary reactor 7, the secondary reactor 8, and the tertiary reactor 17 are respectively carried out, which can not only ensure the normal progress of continuous production, but also greatly improve the energy utilization rate, so that each device is in the best output state.

[0048] S5, product processing: the high-temperature product (product temperature is about 160-180°C) output from the tertiary reactor 17 enters the quaternary reactor 9, and the circulating cooling system 13 uses circulating water cooling to cool it down. The temperature of the material after discharge is 40-50°C, and then enters the vibrating screen 10 to screen the materials that meet the specifications, and the materials with too large particle size enter the crusher 11 for crushing, and then return to the vibrating screen 10 after crushing, and the powdered materials that meet the specifications are transported to the packaging machine for packaging; In this step, the temperature of the circulating water in the circulating cooling system 13 is 7-30° C., and the residence time of the material in the circulating cooling system 13 is 15-25 minutes.

[0049] In this embodiment, the reactors for the three-stage reaction are all horizontal reactors, and the double shafts installed inside can be twin screws, and the components with stirring and pushing functions can achieve the purpose of mass transfer and heat transfer, and there is a certain space inside for material foaming. Among them, the horizontal reactor is used, and the driving force and shear force are applied inside, which increases the molecular diffusion rate of the reactants, accelerates the diffusion rate, and the reactants can reach the reaction interface more quickly, accelerating the reaction rate, so the reaction time is shortened. Thereby improving production efficiency.

[0050] The conveying material used in the reactor is stainless steel, which is not easy to stick and easy to clean. Two adjacent horizontal reactors are connected by a short pipe with an observation hole (preferably a slide pipe short connection) to facilitate observation of the state of the material when it enters the next reactor.

[0051] At the same time, the reactor heating method can be electric heating, thermal oil heating, or steam heating. At least two exhaust holes are provided on each reactor to connect the tail gas pipe so as to transport the reaction tail gas to the tail gas washing system 12. The ammonia tail gas is drawn into the acid washing tower in the tail gas washing system 12 for absorption and then discharged. The washing liquid can be used as raw materials after detection and treatment.

[0052] In this embodiment, a pressure gauge and a liquid level meter are provided on the ammonia neutralization reactor 6, and flow meters are also provided on the liquid ammonia pipe and the phosphoric acid pipe, so as to facilitate the control of the amount of liquid ammonia and phosphorus source added; a flow meter is provided at the outlet of the ammonia neutralization reactor 6 to control the amount of neutralization slurry added; a reflux pipe is provided at the outlet to prevent the slurry in the ammonia neutralization reactor 6 from solidifying or precipitating after a long reaction.

[0053] Furthermore, the molar ratio of urea to phosphorus is controlled by the constant speed and quantitative function of raw material feeding, and the multiple pump bodies installed in the system are all metering pumps 5, which is convenient for calculating the amount of raw material added. The slurry and liquid materials are transported by the metering pump 5.

[0054] The molten material feeding system comprises a feeder 1, a storage bin 2, two parallel molten tanks 4 and a metering pump 5 connected to the molten tanks 4, which are connected in sequence. The molten tanks 4 are heated by heat transfer oil and have a stirring function.

[0055] The tail gas washing system 12 includes a tail gas fan, a two-stage pickling tower, a delivery pump connected to a phosphoric acid storage tank, an exhaust chimney, a tail gas washing liquid circulation pump, etc. The tail gas enters the pickling tower through a tail gas pipe, is absorbed by the countercurrent spraying phosphoric acid in the pickling tower, and the clean tail gas is discharged from the exhaust chimney. After phosphoric acid absorbs a certain amount of ammonia, the washing liquid can be treated and tested and used as a raw material.

[0056] The product processing system includes a circulating cooling system 13, a crusher 11, a vibrating screen 10 and a packaging machine, and the equipment is connected by pipelines.

[0057] This scheme can obtain different grades of ammonium polyphosphate products by controlling parameters such as the selection of raw materials, the molar ratio of urea to phosphorus in the raw materials, the heating temperature, and the residence time.

[0058] Application Implementation Plan: Embodiment 1: A certain amount of wet-process phosphoric acid (P2O5≥46%) is injected into the ammonia neutralization reactor 6, and liquid ammonia is added thereto for ammonia neutralization until the degree of neutralization is 0.4.

[0059] The temperature of the primary reactor 7 is set to 150°C, the slurry is added to the primary reactor 7, and at the same time, the molten urea is quantitatively and constantly injected into the primary reactor 7 through the metering pump 5, so that the molar ratio of urea to phosphorus in the material is 1.2:1, the residence time is 9 minutes, and the rotation speed of the primary reactor 7 is set to 300rpm.

[0060] The liquid material discharged from the primary reactor 7 has a polymerization rate of 32.1% and flows into the secondary reactor 8 through a slide pipe. The temperature of the secondary reactor 8 is set to 210° C., the residence time is 35 min, and the rotation speed of the secondary reactor 8 is set to 12 rpm.

[0061] The material discharged from the secondary reactor 8 is a viscous semi-liquid material with a polymerization rate of 69.3%, which flows into the tertiary reactor 17 through a slide pipe. The temperature of the tertiary reactor 17 is set to 165°C, the residence time is 12 minutes, and the rotation speed of the tertiary reactor 17 is set to 13rpm. At the same time, at the inlet of the tertiary reactor 17, the amount of catalyst melamine added is 3‰ of the unit reaction raw material mass, and the discharge is a dry granular material.

[0062] After entering the fourth-stage reactor 9 for cooling, it is crushed, sieved and packaged to obtain a powdered ammonium polyphosphate product.

[0063] Embodiment 2: A certain amount of wet phosphoric acid (P2O5 ≥ 46%) is injected into the ammonia neutralization reactor 6, and then liquid ammonia is added thereto for ammonia neutralization until the degree of neutralization is 0.7. The temperature of the primary reactor 7 is set to 145°C, and the slurry is added to the primary reactor 7. At the same time, the molten urea is quantitatively and constantly injected into the primary reactor 7 through the metering pump 5, so that the molar ratio of urea to phosphorus in the whole material is 1.5:1, the residence time is 5min, and the rotation speed of the primary reactor 7 is set to 350rpm. The liquid material discharged from the primary reactor 7 has a polymerization rate of 14.6% and enters the secondary reactor 8. The temperature of the secondary reactor 8 is set to 190°C, the residence time is 30min, and the rotation speed is set to 20rpm. The material discharged from the secondary reactor 8 is a viscous semi-liquid material with a polymerization rate of 65.2%, which enters the tertiary reactor 17. The temperature of the tertiary reactor 17 is set to 175°C, the residence time is 10min, the rotation speed is set to 25rpm, and the discharge is a dry granular material. After entering the fourth-stage reactor 9 for cooling, it is crushed, screened and packaged to obtain a powdered ammonium polyphosphate product.

[0064] Embodiment 3: Take a certain amount of wet phosphoric acid (P2O5 ≥ 46%) and inject it into the ammonia neutralization reactor 6, and then add liquid ammonia to neutralize it until the degree of neutralization is 0.8. The temperature of the primary reactor 7 is set to 140°C, and the slurry is added to the primary reactor 7. At the same time, the molten urea is quantitatively and constantly injected into the primary reactor 7 through the metering pump 5, so that the molar ratio of urea and phosphorus in the whole material is 1.0:1, the residence time is 3min, and the rotation speed is set to 420rpm. The liquid material discharged from the primary reactor 7 has a polymerization rate of 11.2% and enters the secondary reactor 8. The temperature of the secondary reactor 8 is set to 185°C, the residence time is 35min, and the rotation speed is set to 12rpm. The material discharged from the secondary reactor 8 is a viscous semi-liquid material with a polymerization rate of 72.4%, which enters the tertiary reactor 17. The temperature of the tertiary reactor 17 is set to 170°C, the residence time is 15min, the rotation speed is set to 9rpm, and the discharge is a dry granular material. After entering the fourth-stage reactor 9 for cooling, it is crushed, screened and packaged to obtain a powdered ammonium polyphosphate product.

[0065] Embodiment 4: Take a certain amount of wet phosphoric acid (P2O5 ≥ 46%) and inject it into the ammonia neutralization reactor 6, and then add liquid ammonia to neutralize it until the degree of neutralization is 0.9. The temperature of the primary reactor 7 is set to 135°C, and the slurry is added to the primary reactor 7. At the same time, the molten urea is quantitatively and constantly injected into the primary reactor 7 through the metering pump 5, so that the molar ratio of urea to phosphorus in the whole material is 2.0:1, the residence time is 8min, and the rotation speed is set to 280rpm. The liquid material discharged from the primary reactor 7 has a polymerization rate of 24.7% and enters the secondary reactor 8. The temperature of the secondary reactor 8 is set to 180°C, the residence time is 28min, and the rotation speed is set to 25rpm. The material discharged from the secondary reactor 8 is a viscous semi-liquid material with a polymerization rate of 61.8%, which enters the tertiary reactor 17. The temperature of the tertiary reactor 17 is set to 170°C, the residence time is 9min, the rotation speed is set to 23rpm, and the discharge is a dry granular material. After entering the fourth-stage reactor 9 for cooling, it is crushed, screened and packaged to obtain a powdered ammonium polyphosphate product.

[0066] Embodiment 5: A certain amount of wet phosphoric acid (P2O5 ≥ 46%) is injected into the ammonia neutralization reactor 6, and then liquid ammonia is added thereto for ammonia neutralization until the neutralization degree is 1.0. The temperature of the primary reactor 7 is set to 135°C, and the slurry is added to the primary reactor 7. At the same time, the molten urea is quantitatively and constantly injected into the primary reactor 7 through the metering pump 5, so that the molar ratio of urea to phosphorus in the whole material is 1.3:1, the residence time is 12min, and the rotation speed is set to 200rpm. The polymerization rate of the liquid material from the primary reactor 7 is 39.3%. Entering the secondary reactor 8, the temperature of the secondary reactor 8 is set to 210°C, the residence time is 35min, and the rotation speed is set to 12rpm. The material discharged from the secondary reactor 8 is a viscous semi-liquid material with a polymerization rate of 76.4%, which enters the tertiary reactor 17. The catalyst melamine is uniformly added at the inlet of the tertiary reactor 17 at an amount of 3‰ of the raw material feeding rate. The temperature of the tertiary reactor 17 is set to 160°C, the residence time is 14min, the rotation speed is set to 33rpm, and the material is a dry granular material. After entering the quaternary reactor 9 for cooling, crushing, screening and packaging, a powdered ammonium polyphosphate product is obtained.

[0067] Embodiment 6: Take a certain amount of raffinate (P2O5≈45%) and inject it into the ammonia neutralization reactor 6, and then add liquid ammonia to neutralize it until the neutralization degree is 0.7. The temperature of the primary reactor 7 is set to 155°C, and the slurry is injected into the primary reactor 7. At the same time, the molten urea is quantitatively and constantly injected into the primary reactor 7 through the metering pump 5, so that the molar ratio of urea and phosphorus in the whole material is 1.2:1, the residence time is 12min, and the rotation speed is set to 210rpm. The liquid material discharged from the primary reactor 7 has a polymerization rate of 14.1% and enters the secondary reactor 8. The temperature of the secondary reactor 8 is set to 200°C, the residence time is 35min, and the rotation speed is set to 12rpm. The material discharged from the secondary reactor 8 is a viscous semi-liquid material with a polymerization rate of 53.1%, which enters the tertiary reactor 17. The temperature of the tertiary reactor 17 is set to 185°C, the residence time is 9min, the rotation speed is set to 25rpm, and the discharge is a dry granular material. After entering the fourth-stage reactor 9 for cooling, it is crushed, screened and packaged to obtain a powdered ammonium polyphosphate product.

[0068] Embodiment 7: Take a certain amount of raffinate (P2O5≈45%) and inject it into the ammonia neutralization reactor 6, and then add liquid ammonia to neutralize it until the degree of neutralization is 0.8. The temperature of the primary reactor 7 is set to 145°C, and the slurry is injected into the primary reactor 7. At the same time, the molten urea is quantitatively and constantly injected into the primary reactor 7 through the metering pump 5, so that the molar ratio of urea and phosphorus in the whole material is 1.0:1, the residence time is 6min, and the rotation speed is set to 330rpm. The liquid material discharged from the primary reactor 7 has a polymerization rate of 12.5% ​​and enters the secondary reactor 8. The temperature of the secondary reactor 8 is set to 190°C, the residence time is 28min, and the rotation speed is set to 25rpm. The material discharged from the secondary reactor 8 is a viscous semi-liquid material with a polymerization rate of 59.3%, which enters the tertiary reactor 17. The temperature of the tertiary reactor 17 is set to 175°C, the residence time is 13min, the rotation speed is set to 11rpm, and the discharge is a dry granular material. After entering the fourth-stage reactor 9 for cooling, it is crushed, screened and packaged to obtain a powdered ammonium polyphosphate product.

[0069] Embodiment 8: Take a certain amount of raffinate (P2O5≈45%) and inject it into the ammonia neutralization reactor 6, and then add liquid ammonia to neutralize it with a neutralization degree of 0.6. The temperature of the primary reactor 7 is set to 140°C, and the slurry is injected into the primary reactor 7. At the same time, the molten urea is quantitatively and constantly injected into the primary reactor 7 through the metering pump 5, so that the molar ratio of urea and phosphorus in the whole material is 0.9:1, the residence time is 10min, and the rotation speed is set to 245rpm. The liquid material discharged from the primary reactor 7 has a polymerization rate of 13.4% and enters the secondary reactor 8. The temperature of the secondary reactor 8 is set to 195°C, the residence time is 31min, and the rotation speed is set to 20rpm. The material discharged from the secondary reactor 8 is a viscous semi-liquid material with a polymerization rate of 52.2%, which enters the tertiary reactor 17. The temperature of the tertiary reactor 17 is set to 165°C, the residence time is 7min, the rotation speed is set to 28rpm, and the discharge is a dry granular material. After entering the fourth-stage reactor 9 for cooling, it is crushed, screened and packaged to obtain a powdered ammonium polyphosphate product.

[0070] Embodiment 9: Take a certain amount of sludge acid (P2O5≈40%~43%) and inject it into the ammonia neutralization reactor 6, and then add liquid ammonia to neutralize it until the neutralization degree is 0.7. The temperature of the primary reactor 7 is set to 150℃, and the slurry is injected into the primary reactor 7. At the same time, the molten urea is quantitatively and constantly injected into the primary reactor 7 through the metering pump 5, so that the molar ratio of urea and phosphorus in the whole material is 1.5:1, the residence time is 8min, and the rotation speed is set to 275rpm. The liquid material from the primary reactor 7 has a polymerization rate of 19.3% and enters the secondary reactor 8. The temperature of the secondary reactor 8 is set to 180℃, the residence time is 13min, and the rotation speed is set to 75rpm. The material discharged from the secondary reactor 8 is a viscous semi-liquid material with a polymerization rate of 51.7%, and enters the tertiary reactor 17. The catalyst melamine is added at the inlet of the tertiary reactor 17 at 3‰ of the raw material feeding rate. The temperature of the tertiary reactor 17 is set to 165°C, the residence time is 15min, the rotation speed is set to 9rpm, and the material is a dry granular material. After entering the quaternary reactor 9 for cooling, crushing, screening and packaging, a powdered ammonium polyphosphate product is obtained.

[0071] Embodiment 10: Take a certain amount of sludge acid (P2O5≈40%~43%) and inject it into the ammonia neutralization reactor 6, and then add liquid ammonia to neutralize it until the neutralization degree is 0.9. The temperature of the primary reactor 7 is set to 130℃, and the slurry is injected into the primary reactor 7. At the same time, the molten urea is quantitatively and constantly injected into the primary reactor 7 through the metering pump 5, so that the molar ratio of urea and phosphorus in the whole material is 1.9:1, the residence time is 12min, and the rotation speed is set to 200rpm. The liquid material from the primary reactor 7 has a polymerization rate of 21.7% and enters the secondary reactor 8. The temperature of the secondary reactor 8 is set to 210℃, the residence time is 31min, and the rotation speed is set to 20rpm. The material discharged from the secondary reactor 8 is a viscous semi-liquid material with a polymerization rate of 56.8%, and enters the tertiary reactor 17. The catalyst melamine is added at the inlet of the tertiary reactor 17 at 3‰ of the raw material feeding rate. The temperature of the tertiary reactor 17 is set to 200°C, the residence time is 10min, the rotation speed is set to 25rpm, and the material is a dry granular material. After entering the quaternary reactor 9 for cooling, crushing, screening and packaging, a powdered ammonium polyphosphate product is obtained.

[0072] Embodiment 11: Take a certain amount of sludge acid (P2O5≈40%~43%) and inject it into the ammonia neutralization reactor 6, and then add liquid ammonia to neutralize it until the neutralization degree is 0.8. The temperature of the primary reactor 7 is set to 160℃, and the slurry is injected into the primary reactor 7. At the same time, the molten urea is quantitatively and constantly injected into the primary reactor 7 through the metering pump 5, so that the molar ratio of urea and phosphorus in the whole material is 2.0:1, the residence time is 9min, and the rotation speed is set to 300rpm. The liquid material discharged from the primary reactor 7 has a polymerization rate of 17.4% and enters the secondary reactor 8. The temperature of the secondary reactor 8 is set to 195℃, the residence time is 33min, and the rotation speed is set to 15rpm. The material discharged from the secondary reactor 8 is a viscous semi-liquid material with a polymerization rate of 60.4%, which enters the tertiary reactor 17. The temperature of the tertiary reactor 17 is set to 160℃, the residence time is 12min, the rotation speed is set to 15rpm, and the discharge is a dry granular material. After entering the fourth-stage reactor 9 for cooling, it is crushed, screened and packaged to obtain a powdered ammonium polyphosphate product.

[0073] Embodiment 12: Urea is melted in the molten material feeding system, and then added to the primary reactor 7 at the same time as solid ammonium dihydrogen phosphate (73% MAP), and the amount of the two is set so that the molar ratio of urea to phosphorus in the overall material is 1.8:1. The temperature of the primary reactor 7 is set to 135°C, the residence time is 8min, and the speed is set to 280rpm. The liquid material discharged from the primary reactor 7 has a polymerization rate of 11.6% and enters the secondary reactor 8. The temperature of the secondary reactor 8 is set to 200°C, the residence time is 27min, and the speed is set to 25rpm. The material discharged from the secondary reactor 8 is a viscous semi-liquid material with a polymerization rate of 69.8%, which enters the tertiary reactor 17. The temperature of the tertiary reactor 17 is set to 180°C, the residence time is 11min, and the speed is set to 18rpm. The material is a dry granular material. After entering the quaternary reactor 9 for cooling, it is crushed, sieved and packaged to obtain a powdered ammonium polyphosphate product.

[0074] Embodiment 13: Urea is melted in the molten material feeding system, and then added to the primary reactor 7 simultaneously with solid ammonium dihydrogen phosphate (55% MAP), and the addition amount of the two is set so that the molar ratio of urea to phosphorus of the whole material is 2.0:1. The temperature of the primary reactor 7 is set to 145°C, the residence time is 10min, and the rotation speed is set to 250rpm. The liquid material discharged from the primary reactor 7 has a polymerization rate of 12.8%, and enters the secondary reactor 8. The temperature of the secondary reactor 8 is set to 190°C, the residence time is 31min, and the rotation speed is set to 22rpm. The material discharged from the secondary reactor 8 is a viscous semi-liquid material with a polymerization rate of 63.9%, which enters the tertiary reactor 17. The temperature of the tertiary reactor 17 is set to 175°C, the residence time is 13min, and the rotation speed is set to 10rpm. The material is a dry granular material. After entering the quaternary reactor 9 for cooling, it is crushed, sieved and packaged to obtain a powdered ammonium polyphosphate product.

[0075] Embodiment 14: Urea is melted in the molten material feeding system. Diammonium hydrogen phosphate needs to be crushed in advance because of its large particles. Then the two raw materials are added to the primary reactor 7 at the same time. The amount of the two is set so that the molar ratio of urea and phosphorus of the whole material is 1.9:1. The temperature of the primary reactor 7 is set to 150°C, the residence time is 10min, and the speed is set to 250rpm. The liquid material discharged from the primary reactor 7 has a polymerization rate of 13.3% and enters the secondary reactor 8. The temperature of the secondary reactor 8 is set to 195°C, the residence time is 23min, and the speed is set to 35rpm. The material discharged from the secondary reactor 8 is a viscous semi-liquid material with a polymerization rate of 62.7%, which enters the tertiary reactor 17. The temperature of the tertiary reactor 17 is set to 185°C, the residence time is 14min, the speed is set to 9rpm, and the material is a dry granular material. After entering the quaternary reactor 9 for cooling, it is crushed, screened and packaged to obtain a powdered ammonium polyphosphate product.

[0076] Embodiment 15: Urea is melted in the molten material feeding system, and then added to the primary reactor 7 at the same time as urea phosphate, and the amount of the two is set so that the molar ratio of urea to phosphorus in the overall material is 1.5:1. The temperature of the primary reactor 7 is set to 155°C, the residence time is 6min, and the rotation speed is set to 340rpm. The liquid material discharged from the primary reactor 7 has a polymerization rate of 14.5% and enters the secondary reactor 8. The temperature of the secondary reactor 8 is set to 185°C, the residence time is 32min, and the rotation speed is set to 15rpm. The material discharged from the secondary reactor 8 is a viscous semi-liquid material with a polymerization rate of 66.3%, which enters the tertiary reactor 17. The temperature of the tertiary reactor 17 is set to 160°C, the residence time is 12min, the rotation speed is set to 11rpm, and the discharge is a dry granular material. After entering the quaternary reactor 9 for cooling, it is crushed, sieved and packaged to obtain a powdered ammonium polyphosphate product.

[0077] Product indicators: The product indicators refer to the industry standards, and the indicators of the industry standard (HG / T 5939-2021) are shown in Table 1.

[0078] Table 1 Technical requirements for fertilizer grade ammonium polyphosphate The analysis and test results of the above embodiment are shown in Table 2. From the analysis results in Table 2, it can be seen that the ammonium polyphosphate prepared using different raw materials all meet the product requirements and above, and it can be seen that the above method is applicable to a variety of processes and realizes the continuous production of ammonium polyphosphate.

[0079] Table 2 Analysis results of ammonium polyphosphate in Example The above shows and describes 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 by the above embodiments. The above embodiments and descriptions are only preferred examples of the present invention and are not intended to limit the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A device for continuously producing powdered ammonium polyphosphate, characterized in that: include: A molten material feeding system, used for outputting molten urea; A continuous synthesis system for producing powdered ammonium polyphosphate comprises a multi-stage reactor, wherein the multi-stage reactor is composed of at least two double-cavity horizontal reactors connected in series, and the outer cavities of the reactors are filled with heating medium; molten urea and reaction raw materials are continuously reacted in each double-cavity horizontal reactor in turn to obtain powdered ammonium polyphosphate; A circulating cooling system (13) is cyclically connected to the outer cavity of the fourth-stage reactor (9); The product processing system is used to circulate, screen and crush the generated powdered ammonium polyphosphate; An exhaust gas washing system (12) is used to receive exhaust gas discharged from the molten material feeding system and the continuous synthesis system; The dust removal system (14) is used to collect dust generated in the product processing system.

2. The device for continuously producing powdered ammonium polyphosphate according to claim 1, characterized in that: The multistage reactor comprises a primary reactor (7), a secondary reactor (8), and a tertiary reactor (17) which are connected in series in sequence, and the discharge end of the tertiary reactor (17) is connected to the feed end of the quaternary reactor (9); the primary reactor (7) and the tertiary reactor (17) are twin-screw reactors, and the length-to-diameter ratio of the screw of the primary reactor (7) is 40:1-60:1; the length-to-diameter ratio of the screw of the tertiary reactor (17) is 30:1-50:1; the secondary reactor (8) is one of a twin-screw reactor, a double-blade reactor, and a double-shaft reactor, and when the secondary reactor (8) is a twin-screw reactor, the length-to-diameter ratio of the screw is 50:1-80:

1.

3. The device for continuously producing powdered ammonium polyphosphate according to claim 2, characterized in that: The molten material feeding system comprises a feeder (1), a storage bin (2) and two parallel molten tanks (4) connected in sequence; a weight sensor (15) is provided at the bottom of the storage bin (2); the discharge end of the storage bin (2) is connected to the feed ends of the two molten tanks (4) respectively through a pneumatic three-way steering valve (3); the discharge ends of the two molten tanks (4) are connected to the feed end of the primary reactor (7) through another pneumatic three-way steering valve (3); a metering pump (5) is also provided between the discharge end of the pneumatic three-way steering valve (3) and the feed end of the primary reactor (7).

4. The device for continuously producing powdered ammonium polyphosphate according to claim 2, characterized in that: The feed end of the primary reactor (7) is also connected to an ammonia neutralization reactor (6), and the ammonia neutralization reactor (6) is a double-layer kettle-type stirred reactor. The product processing system comprises a vibrating screen (10) and a crusher (11) which are sequentially connected to the discharge end of the tertiary reactor (17).

5. The device for continuously producing powdered ammonium polyphosphate according to claim 4, characterized in that: The inner cavities of the ammonia neutralization reactor (6), the primary reactor (7), the secondary reactor (8), the tertiary reactor (17) and the tops of the two melting tanks (4) are respectively connected to tail gas pipes, and several of the tail gas pipes are connected to the tail gas scrubbing system (12); the connecting pipeline between the ammonia neutralization reactor (6) and the primary reactor (7), the connecting pipeline between the primary reactor (7) and the secondary reactor (8) and all the tail gas pipes are provided with solenoid valves (16).

6. A method for continuously producing powdered ammonium polyphosphate, using the device for continuously producing powdered ammonium polyphosphate according to any one of claims 1 to 5, characterized in that: The steps include: S1, ammonia neutralization: injecting a phosphorus source into an ammonia neutralization reactor (6), and injecting a certain proportion of a nitrogen source into the ammonia neutralization reactor (6), and obtaining a neutralized slurry in the ammonia neutralization reactor (6) by stirring; S2, primary reaction: the neutralized slurry or reaction raw material output from the ammonia neutralization reactor (6) and the molten urea prepared and output by the molten material feeding system are simultaneously injected into the primary reactor (7), and the primary reactor (7) is heated and stirred and transported forward, and the polymerization rate is controlled to be 10% to 40%; S3, secondary reaction: the molten liquid material transported out of the primary reactor (7) enters the secondary reactor (8), the internal space of the secondary reactor (8) is larger than the internal space of the primary reactor (7); the secondary reactor (8) adopts a method of heating and stirring while transporting forward, and the degree of polymerization control is 50% to 80%; S4, tertiary reaction: After the material output from the secondary reactor (8) enters the tertiary reactor (17), the material is transported forward while being continuously heated, continues to polymerize and gradually solidifies; S5. Product processing: The high-temperature product outputted from the tertiary reactor (17) enters the fourth reactor (9), where it is cooled by a circulating cooling system (13) using circulating water cooling to control the temperature of the discharged material to be 40-50°C. The material then enters the vibrating screen (10) to screen the material that meets the specifications, while the material with a particle size that is too large enters the crusher (11) for crushing. After crushing, the material returns to the vibrating screen (10), and the powdered material that meets the specifications is transported to the packaging machine for packaging.

7. The method for continuously producing powdered ammonium polyphosphate according to claim 6, characterized in that: In step S1, the phosphorus source includes one or more of wet-process phosphoric acid, wet-process phosphoric acid purification acid, raffinate acid, sludge acid, ammonium phosphate and urea phosphate; the nitrogen source includes one or both of liquid ammonia and urea; the slurry neutralization degree in the ammonia neutralization reactor (6) is controlled between 0.4 and 1.0, and the reaction raw material is diammonium phosphate or urea phosphate.

8. The method for continuously producing powdered ammonium polyphosphate according to claim 6, characterized in that: In step S2, the molar ratio of urea to phosphorus in the primary reactor (7) is controlled by the feeding speed of the two raw materials, the control range is 0.7 to 2.0:1, the heating temperature of the heating zone is 130 to 160° C., and the residence time of the materials in the reactor is 1 to 12 min; The rotation speed of the primary reactor (7) is set to 200-450 rpm.

9. The method for continuously producing powdered ammonium polyphosphate according to claim 6, characterized in that: In step S3, the heating temperature of the secondary reactor (8) is 160-210° C., and the residence time of the material in the reactor is 10-35 min; The rotation speed of the secondary reactor (8) is set to 12 to 80 rpm; In step S4, the heating temperature of the tertiary reactor (17) is 160-200° C., and the residence time of the material in the reactor is 5-15 min; The rotation speed of the tertiary reactor (17) is adjusted to 9-35 rpm.

10. The method for continuously producing powdered ammonium polyphosphate according to claim 6, characterized in that: In step S4, the material inlet of the tertiary reactor (17) is provided with an opening. If the sample is difficult to solidify, a curing catalyst is injected from the opening. The curing catalyst is one or more of melamine, sodium tripolyphosphate, ammonium sulfate and ammonium chloride.

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