An apparatus and method for continuously producing powdered ammonium polyphosphate

Abstract

The present invention relates to the technical field of ammonium polyphosphate production, and specifically, to an apparatus and a method for continuously producing powdery ammonium polyphosphate. The apparatus includes a molten material feeding system for outputting molten urea; a continuous synthesis system for producing powdery ammonium polyphosphate, which includes a multi-stage reactor formed by at least two double-chamber horizontal reactors connected in series, and heating media are filled in the outer chambers of the reactors; the molten urea and the neutralization slurry or reaction raw materials continuously react in each double-chamber horizontal reactor in sequence to obtain powdery ammonium polyphosphate; a product treatment system for performing cyclic screening and crushing treatment on the generated powdery ammonium polyphosphate; a tail gas washing system; a circulating cooling system; and a dust removal system. The design of the present invention can achieve feeding and discharging simultaneously, realizing complete continuous production, with short reaction time, easy industrialization, low investment cost, simple operation, applicability to multiple processes; the discharged material is in the form of relatively small granular materials, and has low requirements for crushing.

Description

Technical Field

[0001] The present invention relates to the technical field of ammonium polyphosphate production, and in particular, to an apparatus and method for continuously producing powdery ammonium polyphosphate. Background Art

[0002] Ammonium polyphosphate, also known as polyphosphoric acid ammonium or condensed phosphoric acid ammonium (abbreviation: APP), has the general formula: . It belongs to an inorganic polymer compound, presenting as white particles or crystals. Classified by the degree of polymerization, it can be divided into three types: oligomeric, medium polymeric, and high polymeric. Oligomeric ammonium polyphosphate refers to short-chain APP with a degree of polymerization n ≤ 20, which is commonly used in the fertilizer industry. Besides good water solubility, it also has characteristics such as strong compatibility, low crystallization temperature, and good chelating property. While the degree of polymerization n > 20 belongs to long-chain APP, which is commonly used as a halogen-free phosphorus-based flame retardant due to its almost water-insoluble property.

[0003] Currently, oligomeric ammonium polyphosphate is widely used in the fertilizer industry. In the soil, it can chelate trace and medium metal elements, first hydrolyze into orthophosphate and then be absorbed by crops, achieving the effect of long-term slow release. Moreover, ammonium polyphosphate has a high phosphorus content and can be fertilized in various ways. It can be used as a foliar fertilizer without burning the crop leaves and can remain on the leaves for several days without evaporating and crystallizing.

[0004] Ammonium polyphosphate products have good activity and high fertilizer efficiency. The polymeric phosphorus chelates trace and medium elements, improving the effectiveness of phosphorus and trace and medium elements, promoting dissolution and absorption, and having a higher fertilizer efficiency; the polymeric phosphorus can retain water, and pyrophosphate and tripolyphosphate in it improve water retention, solve the water shortage problem of dryland crops, and reduce maintenance costs; the high chelating property has a long fertilizer effect. The polymeric phosphorus chelates metal ions and is not easily fixed. The polymeric phosphorus has a high utilization rate and a long fertilizer effect, which can meet the phosphorus demand of crops in the middle and late stages; it improves the soil and resists continuous cropping. The polymeric phosphorus has a strong mobility and a greater moving distance in saline-alkali soil. By chelating metal ions and the phosphorus and nitrogen fixed by the soil, it activates the compacted soil and corrects various malnutrition caused by plant nutrient deficiencies. It has been vigorously promoted and used in foreign agriculturally developed countries.

[0005] In the phosphate fertilizer system of China's fertilizer industry, orthophosphates are mainly used, and the use of polyphosphates is less. There are even fewer enterprises producing ammonium polyphosphate. Polyphosphates have high water solubility and the function of chelating metal ions. Abroad, ammonium polyphosphate and potassium are mainly used to prepare chemically synthesized water-soluble fertilizers with high phosphorus and potassium formulations and polyphosphate trace element chelating agents. The development of agricultural ammonium polyphosphate in China started relatively late. At present, the batch process is mainly used. However, the batch process has the characteristics of large investment, small production capacity, and high labor intensity. Common production processes of ammonium polyphosphate include the phosphoric acid-urea condensation method, the ammonium phosphate condensation method, the phosphoric acid method, the superphosphoric acid method, and the ammonium phosphate-phosphorus pentoxide synthesis method, etc. However, due to the strong viscosity of the ammonium polyphosphate material during the processing, it is not easy for the material to continuously discharge from the polymerization reactor. Currently, the production processes selected by enterprises are basically batch processes.

[0006] Compared with the continuous process, the batch process requires more personnel, and the reaction time is longer. Each time, the material from the previous reaction needs to be discharged first before the new material can be put in. However, the continuous process requires fewer personnel, is easier to operate, and the working environment of the personnel is relatively better and safer.

[0007] At present, there have been many research reports on the synthesis of ammonium polyphosphate. For example, Patent 202020654562.9 discloses a continuous production device for ammonium polyphosphate. A phosphoric acid feed pipe and a liquid ammonia feed pipe are respectively installed at the inlet of the tubular reactor. The outlet is connected to a polymerization reaction kettle below. One side of the polymerization reaction kettle is connected to a tail gas treatment device, and the lower end outlet is connected to a cooler processing box. A sieve bucket and a vibrating sieve are arranged below the cooler processing box. The ammonium polyphosphate product can be obtained by production under certain conditions, but true continuous production has not been achieved. Another example is Patent 201710526911.1, which discloses a continuous production method of powdery and granular ammonium polyphosphate. In this invention, a phosphorus source and urea are put into a pre-polymerizer and reacted at 60-140°C for 2-10 minutes to obtain a liquid material. Then the liquid material is uniformly added to a belt-type polymerizer equipped with a heating zone and a cooling zone. After passing through heating polymerization and cooling solidification in sequence, a solid material is obtained. After the solid material is crushed, powdery and granular ammonium polyphosphate is obtained. This method requires pre-polymerization in advance, is not completely continuous, and the viscosity of the liquid material is relatively large, making it difficult to completely peel off from the equipment. Moreover, the solids generated by the reaction are mostly in block form, and the treatment of the solids is difficult.

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

[0009] The purpose of the present invention is to provide a device and method for continuously producing powdery ammonium polyphosphate to solve the problem in the above-mentioned background technology that it is difficult to achieve true continuous production in the prior art.

[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:

[0011] A molten material feeding system, used for outputting molten urea;

[0012] 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;

[0013] A circulating cooling system, which is cyclically connected to the outer cavity of the fourth-stage reactor;

[0014] The product processing system is used to circulate, screen and crush the generated powdered ammonium polyphosphate;

[0015] An exhaust gas washing system, used for receiving exhaust gas discharged from the molten material feeding system and the continuous synthesis system;

[0016] The dust removal system is used to collect dust generated in the product processing system.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] As a further improvement of the technical solution, tail gas pipes are respectively connected to the inner cavities of the ammonia neutralization reactor, the first-stage reactor, the second-stage reactor, the third-stage reactor, and the tops of the two melting tanks, and several tail gas pipes are all connected to the tail gas scrubbing system; electromagnetic valves are arranged on the connecting pipelines between the ammonia neutralization reactor and the first-stage reactor, the connecting pipelines between the first-stage reactor and the second-stage reactor, and all the tail gas pipes.

[0021] The second object of the present invention is to provide a method for continuously producing powdered ammonium polyphosphate by using the above-mentioned device for continuously producing powdered ammonium polyphosphate, including the following steps:

[0022] S1. Ammonia neutralization: Inject the phosphorus source into the ammonia neutralization reactor, and at the same time inject a certain proportion of the nitrogen source into the ammonia neutralization reactor. Through stirring, a neutralized slurry is obtained in the ammonia neutralization reactor.

[0023] S2. First-stage reaction: Simultaneously inject the neutralized slurry or reaction raw materials output from the ammonia neutralization reactor and the molten urea prepared and output by the molten material feeding system into the first-stage reactor. The first-stage reactor adopts a method of heating while stirring and transporting forward, and the polymerization rate control degree is 10% - 40%.

[0024] S3. Second-stage reaction: The molten liquid material transported out of the first-stage reactor enters the second-stage reactor, and the internal space of the second-stage reactor is larger than that of the first-stage reactor; the second-stage reactor also adopts a method of heating while stirring and transporting forward, and the polymerization rate control degree is 50% - 80%.

[0025] S4. Third-stage reaction: After the material output from the second-stage reactor enters the third-stage reactor, the material is transported forward under continuous heating, continues to polymerize and gradually solidifies.

[0026] S5. Product treatment: The high-temperature product output from the third-stage reactor enters the fourth-stage reactor, and the circulating cooling system uses the circulating water cooling method to cool it down, controlling the temperature after discharging to be 40 - 50 °C. Then it enters the vibrating screen to screen the materials that meet the specifications, and the materials with too large particle size enter the crusher for crushing. After crushing, they are returned to the vibrating screen, and the powdered materials that meet the specifications are transported to the packaging machine for packing.

[0027] As a further improvement of the technical solution, in step S1, the phosphorus source includes one or more of wet-process phosphoric acid, purified wet-process phosphoric acid, raffinate acid, sludge acid, ammonium phosphate salt, and urea phosphate; the nitrogen source includes one or two of liquid ammonia and urea; the slurry neutralization degree in the ammonia neutralization reactor is controlled between 0.4 and 1.0, and the reaction raw material is ammonium dihydrogen phosphate or urea phosphate.

[0028] As a further improvement of this technical solution, in step S2, the molar ratio of urea to phosphorus in the primary reactor is controlled by the feeding rates of the two raw materials, and the control range is 0.7 to 2.0:1. The heating temperature in the heating zone is 130 to 160 °C, and the residence time of the material in the reactor is 1 to 12 min;

[0029] The rotation speed of the primary reactor is set to 200 to 450 rpm;

[0030] As a further improvement of this technical solution, in step S3, the heating temperature of the secondary reactor is 160 to 210 °C, and the residence time of the material in the reactor is 10 to 35 min;

[0031] The rotation speed of the secondary reactor is set to 12 to 80 rpm.

[0032] As a further improvement of this technical solution, in step S4, the heating temperature of the tertiary reactor is 160 to 200 °C, and the residence time of the material in the reactor is 5 to 15 min;

[0033] The rotation speed of the tertiary reactor is adjusted to 9 to 35 rpm;

[0034] The solidification catalyst is one or several of melamine, sodium tripolyphosphate, ammonium sulfate, ammonium chloride, etc.

[0035] As a further improvement of this 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 min.

[0036] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0037] 1. In the device for continuously producing powdered ammonium polyphosphate, the ammonia neutralization reactor is used for pre-reaction. After the materials are synthesized in multiple reactors in sequence, they are cooled and formed in the fourth reactor. By continuously inputting urea from the molten material feeding system and continuously outputting the finished product from the fourth reactor, complete continuous production is achieved. Compared with intermittent production or incomplete continuous production, this device has high thermal efficiency, is easier to scale up and expand, has a short reaction time, is easy to industrialize, has a low investment cost, is simple to operate, is applicable to various processes, and can realize the continuous production of ammonium polyphosphate;

[0038] 2. The method for continuously producing powdered ammonium polyphosphate is different from the semi-continuous method and can achieve complete continuity; the main reaction of this solution is completed by a horizontal reactor. The horizontal reactor has the ability of stirring and conveying inside and has a certain foaming space. It can feed and discharge materials simultaneously, and the whole process is completely continuous without a separate pre-polymerization process;

[0039] 3. The method for continuously producing powdered ammonium polyphosphate can greatly utilize the characteristics of the equipment, enabling the mass transfer and heat transfer functions of the equipment to be more fully realized, significantly improving the volume utilization rate of the reactor. Compared with the polymerization equipment in the batch process, which requires a large foaming space and strong stirring ability, and the discharged materials after the reaction are mostly large blocks, posing high requirements for the crusher, the equipment in this solution compresses the reaction into a horizontal reactor, completing the mass transfer and heat transfer functions in a very short time, without the need for a large space for foaming, and the discharged materials are small granular materials, with lower requirements for the crusher;

[0040] 4. The method for continuously producing powdered ammonium polyphosphate greatly reduces the reaction time. The reaction time in the general batch process varies from 2 to 4 hours, and the reaction times of other continuous processes also vary, but basically all require about 2 hours; in the continuous process of this solution, due to the characteristics of the equipment and the fit of the process conditions, the time from adding raw materials to discharging after the reaction is completed is ≤60 min;

[0041] 5. The method for continuously producing powdered ammonium polyphosphate uses independent equipment to complete the continuous production of ammonium polyphosphate. It can not only regulate each equipment separately according to different processes and different requirements, but also, by regulating the parameters of different equipment for the primary reaction, secondary reaction, and tertiary reaction, enable the continuous production to proceed normally, avoiding the situation of premature solidification of the materials at a certain stage. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is a schematic diagram of the device structure in the present invention.

[0043] Figure 2 It is a schematic diagram of the process flow in the present invention.

[0044] In the figure:

[0045] 1 - Feeding machine; 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 - Tail gas washing system; 13 - Circulating cooling system; 14 - Dust removal system; 15 - Weight sensor; 16 - Solenoid valve; 17 - Tertiary reactor. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0046] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention. Example

[0047] like Figure 1 As shown, this embodiment provides a device for continuously producing powdered ammonium polyphosphate, comprising:

[0048] 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;

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] Specifically, the phosphorus source and nitrogen source are pre-reacted in the ammonia neutralization reactor 6 in the form of a double-layer kettle-type stirring reactor to complete uniform mixing and neutralization. The urea becomes molten in the molten material feeding system. The two groups of slurries are simultaneously added to the primary reactor 7 and sequentially pass through the primary reactor 7, secondary reactor 8, and tertiary reactor 17. After the reaction is completed in the primary reactor 7, secondary reactor 8, and tertiary reactor 17 of the double-chamber horizontal double-shaft reactor, it enters the quaternary reactor 9 for cooling and solidification, and then the finished product is discharged.

[0055] Meanwhile, after setting the ammonia neutralization reactor 6, primary reactor 7, secondary reactor 8, and tertiary reactor 17 as relatively independent systems, not only can the electromagnetic valves on the connecting pipelines between adjacent two-stage reactors be used to control the flow rate during the material transfer process, but also different types of stirring blades can be set in the primary reactor 7, secondary reactor 8, and tertiary reactor 17, so that the materials in different reaction stages can react under different reaction conditions such as different shear forces and different conveying speeds, making the adaptability of the entire system better. In addition, in order to save more floor space in the production workshop, the ammonia neutralization reactor 6, primary reactor 7, secondary reactor 8, and tertiary reactor 17 in this embodiment are arranged in a top-down manner. This can not only save floor space but also make it easier for the materials to flow under the action of their own gravity during the transfer between different reaction vessels and better enter the next reaction vessel, reducing the risk of blockage.

[0056] In this embodiment, a weight sensor 15 is equipped at the bottom of the storage bin 2. The discharge end of the storage bin 2 is respectively communicated with the feed ends of two melting tanks 4 through a pneumatic three-way turning valve 3. The discharge ends of the two melting tanks 4 are communicated with the feed end of the primary reactor 7 through another pneumatic three-way turning valve 3. A metering pump 5 is also provided between the discharge end of this pneumatic three-way turning valve 3 and the feed end of the primary reactor 7 to achieve the purpose of constant-speed and quantitative injection of molten urea.

[0057] Specifically, both of the two melting tanks 4 are used to melt urea so that the urea enters 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. When the urea is melting in one melting tank 4, the molten urea in the other melting tank 4 can enter the primary reactor 7 under the action of the metering pump 5. When the urea in the other melting tank 4 starts to melt, by switching the pneumatic three-way turning valve 3, the molten urea in the previous melting tank 4 can enter the primary reactor 7 under the action of the metering pump 5, thus avoiding production stoppage caused during the melting process of urea.

[0058] Meanwhile, the two melting tanks 4 are also connected to the plant process water. Using the heating device in the melting tank 4, the urea in the melting tank 4 is heated and melted within the temperature range required by the process to form molten urea. At the same time, by switching the pneumatic three-way diversion valve 3, the urea raw materials stored in the storage bin 2 can enter the two melting tanks 4 respectively as needed.

[0059] In this embodiment, the screw length-diameter ratio in the primary reactor 7 can be set as needed, specifically it can be set to 40:1 to 60:1, and the optimal choice is 60:1; the screw length-diameter ratio of the secondary reactor 8 can be set to 50:1 to 80:1, and the optimal choice is 70:1; the screw length-diameter ratio of the tertiary reactor 17 can be set to 30:1 to 50:1, and the optimal choice is 50:1.

[0060] 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 with tail gas pipes, and several tail gas pipes are all connected with the tail gas scrubbing system 12; all the tail gases generated during the entire production process can be transported to the tail gas scrubbing system 12 for centralized treatment, which not only avoids the emission of tail gases generated during the polymerization process into the environment and affecting the environment, but also can timely relieve the pressure of the reaction vessel to avoid excessive internal pressure in the inner cavity and causing the materials in the reaction vessel to be extruded from the gaps.

[0061] Furthermore, electromagnetic valves 16 are provided on the connecting pipelines between the ammonia neutralization reactor 6 and the primary reactor 7, between the primary reactor 7 and the secondary reactor 8, between the secondary reactor 8 and the tertiary reactor 17, and on all the tail gas pipes.

[0062] As Figure 2 shown, this embodiment also provides a method for continuously producing powdered ammonium polyphosphate. The above-mentioned device for continuously producing powdered ammonium polyphosphate includes the following steps:

[0063] S1. Ammonia neutralization: Inject the phosphorus source into the ammonia neutralization reactor 6, and at the same time inject a certain proportion of nitrogen source into the ammonia neutralization reactor 6. Through stirring, a neutralized slurry is obtained in the ammonia neutralization reactor 6.

[0064] In this step, the phosphorus source includes one or more of wet-process phosphoric acid, purified wet-process phosphoric acid, raffinate acid, sludge acid, ammonium phosphate salt and urea phosphate; the nitrogen source includes one or more of liquid ammonia and urea.

[0065] The neutralization degree of the slurry in the ammonia neutralization reactor 6 is controlled between 0.4 and 1.0.

[0066] S2. Primary reaction: One of the neutralized slurry output from the ammonia neutralization reactor 6, diammonium hydrogen phosphate, and urea phosphate is injected into the primary reactor 7 simultaneously with the molten urea prepared and output via the molten material feeding system. The primary reactor 7 uses a method of heating while stirring and conveying forward, and the polymerization rate control level is 10% - 40%.

[0067] In this step, the molar ratio of urea to phosphorus in the primary reactor 7 is controlled by the feeding speeds of the two raw materials, and the control range is 0.7 - 2.0:1. The heating temperature in the heating zone is 130 - 160 °C, and the residence time of the material in the reactor is 1 - 12 min.

[0068] The rotation speed of the primary reactor 7 is set to 200 - 450 rpm. In the primary reaction, when the temperature and the rotation speed of the feeder are constant, increasing the rotation speed of the primary reactor 7 can make the material mix more evenly, reduce the urea decomposition rate, and thus avoid N loss. Moreover, the material needs to avoid staying in the primary reactor 7 for too long a time to prevent the material from solidifying and blocking the material channel between the primary reactor 7 and the secondary reactor 8, thereby affecting the continuous production.

[0069] S3. Secondary reaction: The molten liquid material conveyed out by 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 volume foaming and expansion of the molten material. The secondary reactor 8 also uses a method of heating while stirring and conveying forward, and the polymerization rate control level is 50% - 80%.

[0070] Among them, the temperature used in the secondary reaction is the highest temperature in the whole production process. The secondary reaction is the main part of the reaction between the phosphorus source and urea. A large amount of urea decomposition requires heat absorption, so a certain amount of heat is needed to start. The temperature of the secondary reactor ensures that the internal material has sufficient heat for the reaction.

[0071] In this step, 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 - 80 rpm to ensure that the material can flow normally during the secondary reaction without material accumulation blockage and overflow. At the same time, combined with the progress of the primary reaction, control the residence time of the material in the secondary reaction to avoid excessive urea decomposition and avoid blockage of the material flow in the secondary reactor 8.

[0072] Moreover, if the temperature of the secondary reaction is too low, such as below 160 °C, the material will solidify within a short time, resulting in the blockage of the secondary reactor 8, and the material cannot flow down to the tertiary reaction. When the rotation speed of the secondary reactor 8 is too fast, it will also accelerate the internal solidification speed of the secondary reaction. At the same time, for the continuous production process of this solution, when the temperature of the secondary reaction is set at 160 - 210 °C, the material is not easily solidified and has a certain fluidity. When the temperature of the secondary reaction exceeds 210 °C, the material inside the secondary reaction will start to solidify again, affecting the normal material flow of the secondary reactor 8.

[0073] S4. Tertiary reaction: After the material output from the secondary reactor 8 (which has basically approached the viscous state and does not foam) 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 continuously heated and transported forward, continuing to polymerize and gradually solidify.

[0074] For the 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, using urea as the nitrogen source and also as a condensing agent. As the reaction progresses, the molecular chain grows, and after growing to a certain extent, it will start to solidify.

[0075] 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 min. Among them, during the tertiary reaction, 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. And the loss of the N element will cause the total nutrient content of the product to decrease and fail to meet the standard.

[0076] 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 relatively serious, and it is easy to occur the situation of material overflow, and the discharging state is also relatively viscous, and the reaction is incomplete. By reducing the rotation speed of the third reactor, a stable discharging solid product can be ensured.

[0077] The curing catalyst is one or several of melamine, sodium tripolyphosphate, ammonium sulfate, ammonium chloride, etc.

[0078] In summary, during the continuous reaction process, the entire ammonium polyphosphate preparation process can basically be divided into several stages, namely: mixing and melting, foaming, polymerization, and curing. The mixing and melting part can basically be described as the transformation of powdery materials into liquid molten materials, and the stirring current required for this stage of the reaction is relatively small. The essence of foaming is also a semi-liquid foam with a fluffy interior, and a large current is not required to drive the motor for stirring. In the polymerization and curing parts, the materials will gradually shrink from the foamed fluffy foam materials into a viscous state. In this state, the material viscosity is very high, and sufficient shear force is required for stirring. If the shear force is insufficient, the material is likely 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 the single device is fixed, it is impossible to achieve for the three-stage reaction in this solution, which will cause the device to jam and the motor to trip. Therefore, setting the first-stage reaction, the second-stage reaction, and the third-stage reaction as three devices of the first-stage reactor 7, the second-stage reactor 8, and the third-stage reactor 17 respectively can not only ensure the normal progress of continuous production, but also greatly improve the energy utilization rate and make each device in the best output state.

[0079] S5. Product treatment: The high-temperature product (the product temperature is about between 160 and 180 °C) output from the third-stage reactor 17 enters the fourth-stage reactor 9, and the circulating cooling system 13 uses the circulating water cooling method to cool it. After discharging, the temperature is 40 to 50 °C, and then it enters the vibrating screen 10 to screen the materials that meet the specifications. The materials with too large particle size enter the crusher 11 for crushing, and after crushing, they are returned to the vibrating screen 10, and the powdery materials that meet the specifications are transported to the packaging machine for packing;

[0080] In this step, the circulating water temperature of the circulating cooling system 13 is 7 to 30 °C, and the residence time of the material in the circulating cooling system 13 is 15 to 25 min.

[0081] In this embodiment, the reactors for the third-stage reaction are all horizontal reactors. The double shafts installed inside can be double screws, and the components with stirring and pushing functions are used to achieve the purpose of mass transfer and heat transfer. There is a certain space inside for material foaming. Among them, a horizontal reactor is used, and a driving force and a shear force are applied inside, which increases the molecular diffusion rate of the reactants. The diffusion rate is accelerated, and the reactants can reach the reaction interface more quickly, accelerating the reaction rate. Therefore, the reaction time is shortened, thereby improving the production efficiency.

[0082] Among them, the conveying material used for the reactor is made of stainless steel, which is not easy to stick to materials and is easy to clean. Adjacent two horizontal reactors are connected by a short pipe with an observation hole (preferably a chute short connection), which is convenient for observing the state of the material when it enters the next-stage reactor.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] 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. Example

[0090] 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.

[0091] 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.

[0092] The liquid material discharged from the first-stage reactor 7 has a polymerization rate of 32.1% and flows into the second-stage reactor 8 through a chute. The temperature of the second-stage reactor 8 is set at 210 °C, the residence time is 35 min, and the rotation speed of the second-stage reactor 8 is set at 12 rpm.

[0093] The material discharged from the second-stage reactor 8 is a viscous semi-liquid material with a polymerization rate of 69.3% and flows into the third-stage reactor 17 through a chute. The temperature of the third-stage reactor 17 is set at 165 °C, the residence time is 12 min, and the rotation speed of the third-stage reactor 17 is set at 13 rpm. At the same time, at the inlet of the third-stage reactor 17, the addition amount of the catalyst melamine is 3‰ of the mass of the unit reaction raw material, and the discharged material is dry granular material.

[0094] After cooling in the fourth-stage reactor 9, it is crushed, screened and packaged. The powdery ammonium polyphosphate product is obtained. Example

[0095] Take a certain amount of wet-process phosphoric acid (P2O5≥46%) and inject it into the ammonia neutralization reactor 6, and then add liquid ammonia to it for ammonia neutralization until the neutralization degree is 0.7. The temperature of the first-stage reactor 7 is set at 145 °C, the slurry is added to the first-stage reactor 7, and at the same time, molten urea is quantitatively and constantly injected into the first-stage reactor 7 through the metering pump 5 so that the molar ratio of urea to phosphorus in the overall material is 1.5:1, the residence time is 5 min, and the rotation speed of the first-stage reactor 7 is set at 350 rpm. The liquid material discharged from the first-stage reactor 7 has a polymerization rate of 14.6% and enters the second-stage reactor 8. The temperature of the second-stage reactor 8 is set at 190 °C, the residence time is 30 min, and the rotation speed is set at 20 rpm. The material discharged from the second-stage reactor 8 is a viscous semi-liquid material with a polymerization rate of 65.2% and enters the third-stage reactor 17. The temperature of the third-stage reactor 17 is set at 175 °C, the residence time is 10 min, and the rotation speed is set at 25 rpm, and the discharged material is dry granular material. After cooling in the fourth-stage reactor 9, it is crushed, screened and packaged to obtain the powdery ammonium polyphosphate product. Example

[0096] A certain amount of wet-process 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 reaches 0.8. The temperature of the first-stage reactor 7 is set at 140 °C. The slurry is added to the first-stage reactor 7, and at the same time, molten urea is quantitatively and constantly injected into the first-stage reactor 7 through the metering pump 5 so that the molar ratio of urea to phosphorus in the overall material is 1.0:1, the residence time is 3 min, and the rotation speed is set at 420 rpm. The liquid material discharged from the first-stage reactor 7, with a polymerization rate of 11.2%, enters the second-stage reactor 8. The temperature of the second-stage reactor 8 is set at 185 °C, the residence time is 35 min, and the rotation speed is set at 12 rpm. The material discharged from the second-stage reactor 8 is a viscous semi-liquid material, with a polymerization rate of 72.4%, and enters the third-stage reactor 17. The temperature of the third-stage reactor 17 is set at 170 °C, the residence time is 15 min, and the rotation speed is set at 9 rpm. The discharged material is dry granular material. After cooling in the fourth-stage reactor 9, it is crushed, screened and packaged to obtain a powdery ammonium polyphosphate product. Example

[0097] A certain amount of wet-process 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 reaches 0.9. The temperature of the first-stage reactor 7 is set at 135 °C. The slurry is added to the first-stage reactor 7, and at the same time, molten urea is quantitatively and constantly injected into the first-stage reactor 7 through the metering pump 5 so that the molar ratio of urea to phosphorus in the overall material is 2.0:1, the residence time is 8 min, and the rotation speed is set at 280 rpm. The liquid material discharged from the first-stage reactor 7, with a polymerization rate of 24.7%, enters the second-stage reactor 8. The temperature of the second-stage reactor 8 is set at 180 °C, the residence time is 28 min, and the rotation speed is set at 25 rpm. The material discharged from the second-stage reactor 8 is a viscous semi-liquid material, with a polymerization rate of 61.8%, and enters the third-stage reactor 17. The temperature of the third-stage reactor 17 is set at 170 °C, the residence time is 9 min, and the rotation speed is set at 23 rpm. The discharged material is dry granular material. After cooling in the fourth-stage reactor 9, it is crushed, screened and packaged to obtain a powdery ammonium polyphosphate product. Example

[0098] Take a certain amount of wet-process phosphoric acid (P2O5 ≥ 46%) and inject it into the ammonia neutralization reactor 6. Then add liquid ammonia to it for ammonia neutralization until the neutralization degree reaches 1.0. Set the temperature of the first-stage reactor 7 to 135°C, add the slurry to the first-stage reactor 7, and at the same time inject molten urea into the first-stage reactor 7 quantitatively and at a constant speed through the metering pump 5, so that the molar ratio of urea to phosphorus in the overall material is 1.3:1, the residence time is 12 min, and the rotation speed is set to 200 rpm. The polymerization rate of the liquid material discharged from the first-stage reactor 7 is 39.3%. It enters the second-stage reactor 8, where the temperature of the second-stage reactor 8 is set to 210°C, the residence time is 35 min, and the rotation speed is set to 12 rpm. The material discharged from the second-stage reactor 8 is a viscous semi-liquid material, and the polymerization rate is 76.4%. It enters the third-stage reactor 17. In the third-stage reactor 17, melamine, a catalyst, is added uniformly at a rate of 3‰ of the raw material feeding speed at the inlet. The temperature of the third-stage reactor 17 is set to 160°C, the residence time is 14 min, and the rotation speed is set to 33 rpm. The discharged material is dry granular material. After cooling in the fourth-stage reactor 9, it is crushed, screened and packaged to obtain a powdery ammonium polyphosphate product. Example

[0099] Take a certain amount of raffinate acid (P2O5 ≈ 45%) and inject it into the ammonia neutralization reactor 6. Then add liquid ammonia to it for ammonia neutralization until the neutralization degree reaches 0.7. Set the temperature of the first-stage reactor 7 to 155°C, inject the slurry into the first-stage reactor 7, and at the same time inject molten urea into the first-stage reactor 7 quantitatively and at a constant speed through the metering pump 5, so that the molar ratio of urea to phosphorus in the overall material is 1.2:1, the residence time is 12 min, and the rotation speed is set to 210 rpm. The polymerization rate of the liquid material discharged from the first-stage reactor 7 is 14.1%. It enters the second-stage reactor 8, where the temperature of the second-stage reactor 8 is set to 200°C, the residence time is 35 min, and the rotation speed is set to 12 rpm. The material discharged from the second-stage reactor 8 is a viscous semi-liquid material, and the polymerization rate is 53.1%. It enters the third-stage reactor 17, where the temperature of the third-stage reactor 17 is set to 185°C, the residence time is 9 min, and the rotation speed is set to 25 rpm. The discharged material is dry granular material. After cooling in the fourth-stage reactor 9, it is crushed, screened and packaged to obtain a powdery ammonium polyphosphate product. Example

[0100] A certain amount of raffinate acid (P2O5 ≈ 45%) is injected into the ammonia neutralization reactor 6, and then liquid ammonia is added to it for ammonia neutralization until the neutralization degree reaches 0.8. The temperature of the first-stage reactor 7 is set at 145 °C. The slurry is injected into the first-stage reactor 7, and at the same time, molten urea is quantitatively and steadily injected into the first-stage reactor 7 through the metering pump 5, so that the molar ratio of urea to phosphorus in the overall material is 1.0:1, the residence time is 6 min, and the rotation speed is set at 330 rpm. The liquid material discharged from the first-stage reactor 7 has a polymerization rate of 12.5% and enters the second-stage reactor 8. The temperature of the second-stage reactor 8 is set at 190 °C, the residence time is 28 min, and the rotation speed is set at 25 rpm. The material discharged from the second-stage reactor 8 is a viscous semi-liquid material with a polymerization rate of 59.3% and enters the third-stage reactor 17. The temperature of the third-stage reactor 17 is set at 175 °C, the residence time is 13 min, and the rotation speed is set at 11 rpm. The discharged material is dry granular material. After cooling in the fourth-stage reactor 9, it is crushed, screened and packaged to obtain a powdery ammonium polyphosphate product. Example

[0101] A certain amount of raffinate acid (P2O5 ≈ 45%) is injected into the ammonia neutralization reactor 6, and then liquid ammonia is added to it for ammonia neutralization until the neutralization degree reaches 0.6. The temperature of the first-stage reactor 7 is set at 140 °C. The slurry is injected into the first-stage reactor 7, and at the same time, molten urea is quantitatively and steadily injected into the first-stage reactor 7 through the metering pump 5, so that the molar ratio of urea to phosphorus in the overall material is 0.9:1, the residence time is 10 min, and the rotation speed is set at 245 rpm. The liquid material discharged from the first-stage reactor 7 has a polymerization rate of 13.4% and enters the second-stage reactor 8. The temperature of the second-stage reactor 8 is set at 195 °C, the residence time is 31 min, and the rotation speed is set at 20 rpm. The material discharged from the second-stage reactor 8 is a viscous semi-liquid material with a polymerization rate of 52.2% and enters the third-stage reactor 17. The temperature of the third-stage reactor 17 is set at 165 °C, the residence time is 7 min, and the rotation speed is set at 28 rpm. The discharged material is dry granular material. After cooling in the fourth-stage reactor 9, it is crushed, screened and packaged to obtain a powdery ammonium polyphosphate product. Example

[0102] A certain amount of sludge acid (P2O5≈40% - 43%) is injected into the ammonia neutralization reactor 6, and then liquid ammonia is added to it for ammonia neutralization until the neutralization degree reaches 0.7. The temperature of the first-stage reactor 7 is set at 150°C. The slurry is injected into the first-stage reactor 7, and at the same time, molten urea is quantitatively and constantly injected into the first-stage reactor 7 through the metering pump 5, so that the molar ratio of urea to phosphorus in the overall material is 1.5:1, the residence time is 8 minutes, and the rotation speed is set at 275 rpm. The liquid material discharged from the first-stage reactor 7 has a polymerization rate of 19.3% and enters the second-stage reactor 8. The temperature of the second-stage reactor 8 is set at 180°C, the residence time is 13 minutes, and the rotation speed is set at 75 rpm. The material discharged from the second-stage reactor 8 is a viscous semi-liquid material with a polymerization rate of 51.7% and enters the third-stage reactor 17. Melamine, a catalyst, is added at 3‰ of the raw material feeding speed at the inlet of the third-stage reactor 17. The temperature of the third-stage reactor 17 is set at 165°C, the residence time is 15 minutes, and the rotation speed is set at 9 rpm. The discharged material is dry granular material. After cooling in the fourth-stage reactor 9, it is crushed, screened and packaged to obtain a powdery ammonium polyphosphate product.

[0103] Example 10:

[0104] A certain amount of sludge acid (P2O5≈40% - 43%) is injected into the ammonia neutralization reactor 6, and then liquid ammonia is added to it for ammonia neutralization until the neutralization degree reaches 0.9. The temperature of the first-stage reactor 7 is set at 130°C. The slurry is injected into the first-stage reactor 7, and at the same time, molten urea is quantitatively and constantly injected into the first-stage reactor 7 through the metering pump 5, so that the molar ratio of urea to phosphorus in the overall material is 1.9:1, the residence time is 12 minutes, and the rotation speed is set at 200 rpm. The liquid material discharged from the first-stage reactor 7 has a polymerization rate of 21.7% and enters the second-stage reactor 8. The temperature of the second-stage reactor 8 is set at 210°C, the residence time is 31 minutes, and the rotation speed is set at 20 rpm. The material discharged from the second-stage reactor 8 is a viscous semi-liquid material with a polymerization rate of 56.8% and enters the third-stage reactor 17. Melamine, a catalyst, is added at 3‰ of the raw material feeding speed at the inlet of the third-stage reactor 17. The temperature of the third-stage reactor 17 is set at 200°C, the residence time is 10 minutes, and the rotation speed is set at 25 rpm. The discharged material is dry granular material. After cooling in the fourth-stage reactor 9, it is crushed, screened and packaged to obtain a powdery ammonium polyphosphate product.

[0105] Example 11:

[0106] A certain amount of sludge acid (P2O5 ≈ 40% - 43%) is injected into the ammonia neutralization reactor 6, and then liquid ammonia is added to it for ammonia neutralization until the neutralization degree reaches 0.8. The temperature of the first-stage reactor 7 is set at 160°C, and the slurry is injected into the first-stage reactor 7. At the same time, molten urea is quantitatively and steadily injected into the first-stage reactor 7 through the metering pump 5, so that the molar ratio of urea to phosphorus in the overall material is 2.0:1, the residence time is 9 min, and the rotation speed is set at 300 rpm. The liquid material discharged from the first-stage reactor 7 has a polymerization rate of 17.4% and enters the second-stage reactor 8. The temperature of the second-stage reactor 8 is set at 195°C, the residence time is 33 min, and the rotation speed is set at 15 rpm. The material discharged from the second-stage reactor 8 is a viscous semi-liquid material with a polymerization rate of 60.4% and enters the third-stage reactor 17. The temperature of the third-stage reactor 17 is set at 160°C, the residence time is 12 min, and the rotation speed is set at 15 rpm. The discharged material is dry granular material. After cooling in the fourth-stage reactor 9, it is crushed, screened, and packaged to obtain a powdery ammonium polyphosphate product.

[0107] Example 12:

[0108] Urea is melted in the molten material feeding system and then added to the first-stage reactor 7 together with solid ammonium dihydrogen phosphate (73% MAP). The addition amounts of the two are set so that the molar ratio of urea to phosphorus in the overall material is 1.8:1. The temperature of the first-stage reactor 7 is set at 135°C, the residence time is 8 min, and the rotation speed is set at 280 rpm. The liquid material discharged from the first-stage reactor 7 has a polymerization rate of 11.6% and enters the second-stage reactor 8. The temperature of the second-stage reactor 8 is set at 200°C, the residence time is 27 min, and the rotation speed is set at 25 rpm. The material discharged from the second-stage reactor 8 is a viscous semi-liquid material with a polymerization rate of 69.8% and enters the third-stage reactor 17. The temperature of the third-stage reactor 17 is set at 180°C, the residence time is 11 min, and the rotation speed is set at 18 rpm. The discharged material is dry granular material. After cooling in the fourth-stage reactor 9, it is crushed, screened, and packaged to obtain a powdery ammonium polyphosphate product.

[0109] Example 13:

[0110] Melt urea in the molten material feeding system, and then add it to the first-stage reactor 7 simultaneously with solid ammonium dihydrogen phosphate (55% MAP). Set the addition amounts of the two to make the molar ratio of urea to phosphorus in the overall material 2.0:1. Set the temperature of the first-stage reactor 7 to 145 °C, the residence time to 10 min, and the rotation speed to 250 rpm. The liquid material discharged from the first-stage reactor 7 has a polymerization rate of 12.8% and enters the second-stage reactor 8. Set the temperature of the second-stage reactor 8 to 190 °C, the residence time to 31 min, and the rotation speed to 22 rpm. The material discharged from the second-stage reactor 8 is a viscous semi-liquid material with a polymerization rate of 63.9% and enters the third-stage reactor 17. Set the temperature of the third-stage reactor 17 to 175 °C, the residence time to 13 min, and the rotation speed to 10 rpm. The discharged material is dry granular material. After cooling in the fourth-stage reactor 9, it is crushed, screened and packaged to obtain a powdery ammonium polyphosphate product.

[0111] Example 14:

[0112] Melt urea in the molten material feeding system. Since diammonium hydrogen phosphate has relatively large particles, it needs to be crushed in advance, and then the two raw materials are added to the first-stage reactor 7 simultaneously. Set the addition amounts of the two to make the molar ratio of urea to phosphorus in the overall material 1.9:1. Set the temperature of the first-stage reactor 7 to 150 °C, the residence time to 10 min, and the rotation speed to 250 rpm. The liquid material discharged from the first-stage reactor 7 has a polymerization rate of 13.3% and enters the second-stage reactor 8. Set the temperature of the second-stage reactor 8 to 195 °C, the residence time to 23 min, and the rotation speed to 35 rpm. The material discharged from the second-stage reactor 8 is a viscous semi-liquid material with a polymerization rate of 62.7% and enters the third-stage reactor 17. Set the temperature of the third-stage reactor 17 to 185 °C, the residence time to 14 min, and the rotation speed to 9 rpm. The discharged material is dry granular material. After cooling in the fourth-stage reactor 9, it is crushed, screened and packaged to obtain a powdery ammonium polyphosphate product.

[0113] Example 15:

[0114] Urea is melted in the molten material feeding system and then added to the first-stage reactor 7 together with urea phosphate. The feeding amounts of the two are set so that the molar ratio of urea to phosphorus in the overall material is 1.5:1. The temperature of the first-stage reactor 7 is set at 155 °C, the residence time is 6 min, and the rotation speed is set at 340 rpm. The liquid material discharged from the first-stage reactor 7 has a polymerization rate of 14.5% and enters the second-stage reactor 8. The temperature of the second-stage reactor 8 is set at 185 °C, the residence time is 32 min, and the rotation speed is set at 15 rpm. The material discharged from the second-stage reactor 8 is a viscous semi-liquid material with a polymerization rate of 66.3% and enters the third-stage reactor 17. The temperature of the third-stage reactor 17 is set at 160 °C, the residence time is 12 min, and the rotation speed is set at 11 rpm. The discharged material is dry granular material. After cooling in the fourth-stage reactor 9, it is crushed, screened, and packaged to obtain a powdery ammonium polyphosphate product.

[0115] The product indicators refer to the industry standards. The indicators of the industry standard (HG / T 5939-2021) are shown in Table 1.

[0116] Table 1 Technical requirements for fertilizer-grade ammonium polyphosphate

[0117]

[0118] The analysis and test results of the above embodiments are shown in Table 2. It can be seen from the analysis results in Table 2 that the ammonium polyphosphate prepared from different raw materials all meet the product requirement standards and above, indicating that the above method is applicable to various processes and realizes the continuous production of ammonium polyphosphate.

[0119] Table 2 Analysis results of ammonium polyphosphate in the embodiments

[0120]

[0121] 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 the descriptions in the specification are only preferred examples of the present invention and are not used to limit the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of the present invention claimed is defined by the appended claims and their equivalents.

Claims

1. An apparatus 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; A dust removal system (14) for collecting dust generated in the product processing system; 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; 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); The heating temperature of the primary reactor (7) is 130-160°C; the heating temperature of the secondary reactor (8) is 160-210°C; and the heating temperature of the tertiary reactor (17) is 160-200°C.

2. The apparatus for continuously producing powdery ammonium polyphosphate according to claim 1, 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).

3. The apparatus for continuously producing powdered ammonium polyphosphate according to claim 2, wherein: The inner cavities of the ammonia neutralization reactor (6), the first-stage reactor (7), the second-stage reactor (8), the third-stage reactor (17), and the tops of the two melting tanks (4) are respectively connected with tail gas pipes, and a plurality of the tail gas pipes are all connected with the tail gas scrubbing system (12); solenoid valves (16) are arranged on the connecting pipeline between the ammonia neutralization reactor (6) and the first-stage reactor (7), the connecting pipeline between the first-stage reactor (7) and the second-stage reactor (8), and all the tail gas pipes.

4. A method for continuously producing powdered ammonium polyphosphate by using the apparatus for continuously producing powdered ammonium polyphosphate according to any one of claims 1 to 3, characterized in that It includes the following steps: S1. Ammonia neutralization: Inject the phosphorus source into the ammonia neutralization reactor (6), and at the same time inject a certain proportion of the nitrogen source into the ammonia neutralization reactor (6). Through stirring, a neutralized slurry is obtained in the ammonia neutralization reactor (6). S2. First-stage reaction: Simultaneously inject the neutralized slurry or reaction raw materials output from the ammonia neutralization reactor (6) and the molten urea prepared and output via the molten material feeding system into the first-stage reactor (7). The first-stage reactor (7) adopts the method of heating while stirring and transporting forward, and the polymerization rate control degree is 10% - 40%. S3. Second-stage reaction: The molten liquid material transported out of the first-stage reactor (7) enters the second-stage reactor (8). The internal space of the second-stage reactor (8) is larger than that of the first-stage reactor (7); the second-stage reactor (8) adopts the method of heating while stirring and transporting forward, and the polymerization rate control degree is 50% - 80%. S4. Third-stage reaction: After the material output from the second-stage reactor (8) enters the third-stage reactor (17), the material is transported forward under continuous heating, continues to polymerize and gradually solidifies. S5. Product treatment: The high-temperature product output from the third-stage reactor (17) enters the fourth-stage reactor (9), and the circulating cooling system (13) cools it by means of circulating water cooling, controls the temperature after discharging to be 40 - 50 °C, and then enters the vibrating screen (10) to screen the materials that meet the specifications. The materials with too large particle size enter the crusher (11) for crushing, and after crushing, they are returned to the vibrating screen (10), and the powdery materials that meet the specifications are transported to the packaging machine for packing.

5. The method for continuously producing powdered ammonium polyphosphate according to claim 4, characterized in that: In the step S1, the phosphorus source includes one or more of wet-process phosphoric acid, purified wet-process phosphoric acid, raffinate acid, sludge acid, ammonium phosphate salt, and urea phosphate; the nitrogen source includes one or two 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 ammonium dihydrogen phosphate or urea phosphate.

6. The method for continuously producing powdered ammonium polyphosphate according to claim 4, characterized in that: In the step S2, the molar ratio of urea to phosphorus in the first-stage reactor (7) is controlled by the feeding speeds of the two raw materials, and the control range is 0.7 - 2.0:

1. The residence time of the material in the reactor is 1 - 12 min. The rotation speed of the first-stage reactor (7) is set to 200 - 450 rpm.

7. The method for continuously producing powdered ammonium polyphosphate according to claim 4, characterized in that: In the step S3, the residence time of the material in the second-stage reactor (8) is 10 - 35 min; the rotation speed of the second-stage reactor (8) is set to 12 - 80 rpm. In the step S4, the residence time of the material in the tertiary reactor (17) is 5 to 15 minutes; the rotation speed of the tertiary reactor (17) is adjusted to 9 to 35 rpm.

8. The method for continuously producing powdered ammonium polyphosphate according to claim 4, characterized in that: In the step S4, 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 from the opening. The curing catalyst is one or more of melamine, sodium tripolyphosphate, ammonium sulfate, and ammonium chloride.

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