A high-pressure steam conversion device for preparing alpha-hemihydrate gypsum from phosphogypsum

Abstract

The utility model relates to a kind of high-pressure steam conversion device of phosphogypsum preparation alpha-hemihydrate gypsum, belong to phosphogypsum processing equipment technical field.Mainly including raw material pretreatment system, core high-pressure reaction system, fast depressurization system and product separation processing system;Instantaneous pressure relief valve set by the utility model can quickly reduce pressure, effectively prevent alpha-hemihydrate gypsum in the depressurization process is converted into β type again, keep the high-strength crystal structure of product, by the cooperation of grading pressure relief chamber and elastic diaphragm, high-pressure gas is released gradually, the impact damage of instantaneous pressure difference too big to crystal structure is avoided;Through the synergistic effect of pressure control valve group, temperature sensor array, realize sectional pressure and temperature synergic control, for accurately controlling the phosphogypsum reaction condition of pressure stage, conversion stage and stable stage, ensure that phosphogypsum is completely converted into alpha-hemihydrate gypsum under optimum process condition, to improve crystal type conversion efficiency and product quality stability.

Description

Technical Field

[0001] This utility model belongs to the technical field of phosphogypsum processing equipment, specifically relating to a high-pressure steam conversion device for preparing α-hemihydrate gypsum from phosphogypsum. Background Technology

[0002] Phosphogypsum is an industrial byproduct generated during phosphoric acid production. Large-scale stockpiling of phosphogypsum not only occupies land resources but also poses environmental pollution risks. Therefore, the resource utilization of phosphogypsum has become a key technological issue for the sustainable development of the phosphorus chemical industry.

[0003] The high-pressure steam method is a process for preparing α-hemihydrate gypsum through dissolution and recrystallization in a high-pressure saturated steam environment. It offers advantages such as high product quality and environmental friendliness. However, traditional high-pressure steam equipment typically employs a simple heating and pressurization process, lacking precise staged control. This leads to incomplete phosphogypsum conversion and low α-type content. Furthermore, the existing high-pressure steam method has a slow depressurization and cooling phase, which can easily cause the already formed α-hemihydrate gypsum to revert to the β-type. Simultaneously, the excessively abrupt depressurization process and large instantaneous pressure differences can damage the crystal structure of α-hemihydrate gypsum, affecting product quality stability. Therefore, there is an urgent need for a device capable of precise temperature and pressure control and efficient staged depressurization to meet the technical requirements of modern industry for high-quality α-hemihydrate gypsum production. Utility Model Content

[0004] To overcome the shortcomings of traditional high-pressure steam equipment in the prior art, which lacks precise segmented control leading to incomplete conversion of phosphogypsum, and because existing high-pressure steam methods suffer from slow depressurization and cooling stages that can easily cause the already formed α-hemihydrate gypsum to revert to the β-type, and because the depressurization process is too abrupt and the large instantaneous pressure difference can damage the crystal structure of α-hemihydrate gypsum, thus affecting product quality stability, this invention provides a high-pressure steam conversion device for preparing α-hemihydrate gypsum from phosphogypsum. By incorporating an instantaneous pressure relief valve, the reaction pressure can be reduced from 1.3 MPa to 0.1 MPa within 0.5 seconds. This effectively prevents α-hemihydrate gypsum from reverting to the β-type during the depressurization process, maintaining the product's high-strength crystalline structure. Simultaneously, the use of a staged pressure relief chamber in conjunction with an elastic diaphragm allows for the gradual release of high-pressure gas, avoiding the impact and damage to the crystalline structure caused by excessive instantaneous pressure differences. Through the synergistic action of the pressure control valve group and temperature sensor array, segmented pressure and temperature control is achieved, precisely controlling the phosphogypsum reaction conditions during the pressurization, conversion, and stabilization stages. This ensures that phosphogypsum is completely converted to α-hemihydrate gypsum under optimal process conditions, thereby improving crystalline transformation efficiency and product quality stability.

[0005] To achieve the above objectives, this utility model is implemented through the following technical solution: A high-pressure steam reforming device for preparing α-hemihydrate gypsum from phosphogypsum mainly includes a raw material pretreatment system, a core high-pressure reaction system, a rapid depressurization system, and a product separation and processing system; The raw material pretreatment system includes a silo, a metering feeder, a pre-screening device, and a premixer. The bottom of the silo is fixedly connected to the metering feeder by bolts. The outlet of the metering feeder is connected to the inlet of the pre-screening device through a flange. The outlet of the pre-screening device is connected to the top inlet of the premixer through a pipe. The core high-pressure reaction system includes a high-pressure steam reactor and a steam generator. The bottom outlet of the premixer is welded to the top inlet of the high-pressure steam reactor via a pipeline. The steam generator is connected to the steam inlet flange on the upper side wall of the high-pressure steam reactor via a steam pipeline. The rapid pressure reduction system includes an instantaneous pressure relief valve and a pressure reduction buffer tank. The bottom of the high-pressure steam reactor is connected to the inlet flange of the instantaneous pressure relief valve, and the outlet of the instantaneous pressure relief valve is connected to the top inlet flange of the pressure reduction buffer tank through a pipeline. The instantaneous pressure relief valve is provided with a staged pressure relief chamber, which is composed of a first pressure relief chamber, a second pressure relief chamber, and a third pressure relief chamber connected in sequence. Each pressure relief chamber is separated by an elastic diaphragm, which is embedded in an annular groove in the chamber wall and fixed by a pressure ring. The product separation and processing system includes a solid-liquid separator, a washing device, a dehydration dryer, and a product collection bin. The bottom of the pressure-reducing buffer tank is connected to the inlet flange of the solid-liquid separator via a pipe. The outlet of the solid-liquid separator is connected to the inlet flange of the washing device via a pipe. The outlet of the washing device is connected to the inlet flange of the dehydration dryer via a pipe. The outlet of the dehydration dryer is connected to the inlet flange of the product collection bin via a pipe. The core high-pressure reaction system also includes a pressure control valve group, a temperature sensor array, and a stirring device. The pressure control valve group is installed on the steam pipeline, the temperature sensor array is embedded in the side wall of the high-pressure steam reactor, and the stirring device is located inside the high-pressure steam reactor.

[0006] The rapid depressurization system also includes a cooling water circulation system and a pressure relief controller. The cooling water circulation system is connected to the cooling water inlet flange at the lower side wall of the depressurization buffer tank via a pipeline, and is used to regulate temperature changes during the depressurization process. The pressure relief controller is electrically connected to the stepper motor on the instantaneous pressure relief valve via a cable. The stepper motor is connected to the valve core inside the instantaneous pressure relief valve via a coupling.

[0007] The elastic diaphragm includes a first diaphragm, a second diaphragm, and a third diaphragm. The first diaphragm is located between the first pressure relief chamber and the second pressure relief chamber, the second diaphragm is located between the second pressure relief chamber and the third pressure relief chamber, and the third diaphragm is located on the outlet side of the third pressure relief chamber. The elastic diaphragm is made of polytetrafluoroethylene material.

[0008] The volume of the first pressure relief chamber is larger than that of the second pressure relief chamber, and the volume of the second pressure relief chamber is larger than that of the third pressure relief chamber. Each pressure relief chamber is connected by a conical transition section. The cone angle of the conical transition section is set between degrees and degrees to ensure that the airflow forms a gradual pressure release during each stage of pressure relief. The inner surface of the conical transition section is provided with a buffer groove. The buffer groove is distributed in a ring and has a depth of millimeters to millimeters to further reduce the impact of the airflow.

[0009] The device also includes a steam recovery system, which includes a condenser, a steam separator, a heat exchanger, and a circulating water pump. The condenser is connected to the top outlet flange of the steam generator via a pipe, the steam separator is connected to the bottom outlet flange of the condenser via a pipe, the heat exchanger is connected to the bottom outlet flange of the steam separator via a pipe, and the circulating water pump is connected to the bottom outlet flange of the heat exchanger via a pipe.

[0010] The crystal form conversion control system includes a programmable temperature controller, a heat preservation section controller, a crystal form detector, and a reaction time controller. The programmable temperature controller and the heat preservation section controller are electrically connected to the temperature sensor array on the high-pressure steam reactor via signal lines. The crystal form detector is installed on the outside of the side wall of the high-pressure steam reactor. The reaction time controller is linked to the programmable temperature controller via a timing module.

[0011] The stirring device includes a stirring shaft, a drive motor, and stirring blades. The drive motor is fixed to the top of the high-pressure steam reactor by bolts. The top of the stirring shaft is connected to the drive motor via a coupling. Multiple sets of stirring blades with an inclination angle of 45° are installed equidistantly along the axial direction of the stirring shaft.

[0012] The beneficial effects of this utility model are: The instantaneous pressure relief valve of this invention can reduce the reaction pressure from 1.3 MPa to 0.1 MPa within 0.5 seconds, effectively preventing α-hemihydrate gypsum from reverting to the β-type during the pressure reduction process and maintaining the high-strength crystalline structure of the product. Simultaneously, the use of a staged pressure relief chamber in conjunction with an elastic diaphragm enables the gradual release of high-pressure gas, avoiding the impact and damage to the crystalline structure caused by excessive instantaneous pressure differences. Through the synergistic action of the pressure control valve assembly and temperature sensor array, segmented pressure and temperature control is achieved, precisely controlling the reaction conditions of phosphogypsum during the pressurization, conversion, and stabilization stages. This ensures that phosphogypsum is completely converted to α-hemihydrate gypsum under optimal process conditions, thereby improving crystalline transformation efficiency and product quality stability. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the production line of this utility model.

[0014] Figure 2 This is a schematic diagram of the three-dimensional structure of an instantaneous pressure relief valve.

[0015] Figure 3 This is a 3D schematic diagram of the internal structure of an instantaneous pressure relief valve.

[0016] Figure 4 yes Figure 3 A magnified view of a portion of point A in the middle.

[0017] The attached figures are labeled as follows: 1. Silo; 2. Metering feeder; 3. Pre-screening device; 4. Premixer; 5. High-pressure steam reactor; 6. Steam generator; 7. Pressure control valve assembly; 8. Temperature sensor array; 9. Stirring device; 10. Programmable temperature controller; 11. Insulation section controller; 12. Crystal form detector; 13. Reaction time controller; 14. Instantaneous pressure relief valve; 15. Pressure reduction buffer tank; 16. Cooling water circulation system; 17. Pressure release controller; 18. Solid-liquid separator; 19. Washing device; 20. Dehydration dryer; 21. Product collection bin; 22. Condenser; 23. Steam separator; 24. Heat exchanger; 25. Circulating water pump; 26. Staged pressure relief chamber; 261. First pressure relief chamber; 262. Second pressure relief chamber; 263. Third pressure relief chamber; 264. Elastic diaphragm; 265. Conical transition section. Detailed Implementation

[0018] To make the objectives, technical solutions, and beneficial effects of this utility model clearer, the preferred embodiments of this utility model will be described in detail below with reference to the accompanying drawings, so as to facilitate the understanding of those skilled in the art.

[0019] This utility model discloses a high-pressure steam reforming device for preparing α-hemihydrate gypsum from phosphogypsum. The device mainly includes a raw material pretreatment system, a core high-pressure reaction system, a rapid depressurization system, a product separation and processing system, and a steam recovery and utilization system. The raw material pretreatment system consists of a silo 1, a metering feeder 2, a pre-screening device 3, and a premixer 4. The silo 1 is a cylindrical metal container, with its bottom fixedly connected to the metering feeder 2 by bolts. The metering feeder 2 employs a screw conveyor mechanism, and its outlet end is connected to the inlet of the pre-screening device 3 via a flange. The pre-screening device 3 is a vibrating screen structure with a screen mesh size of 2 mm, used to remove large particle impurities. Its outlet is connected to the top inlet of the premixer 4 via a pipe. The premixer 4 is a horizontal stirring drum with internal spiral blades. Its bottom outlet is welded to the top inlet of a high-pressure steam reactor 5 via a pipeline.

[0020] The core high-pressure reaction system includes a high-pressure steam reactor 5, a steam generator 6, a pressure control valve assembly 7, a temperature sensor array 8, and a stirring device 9. The high-pressure steam reactor 5 is a pressure-resistant vessel with a pressure rating of 1.5 MPa, and its inner wall is polished to reduce material adhesion. The steam generator 6 is connected to the steam inlet flange on the upper side wall of the high-pressure steam reactor 5 via a steam pipeline. The pressure control valve assembly 7 is installed on the steam pipeline to regulate the reaction pressure between 0.3 and 1.3 MPa. The temperature sensor array 8 is embedded in the side wall of the high-pressure steam reactor 5 for real-time monitoring of the temperature distribution inside the reactor. The stirring device 9 includes a drive motor, a stirring shaft, and stirring blades. The drive motor is bolted to the top of the high-pressure steam reactor 5, and the top of the stirring shaft is connected to the drive motor via a coupling. Multiple sets of stirring blades with an inclination angle of 45° are equidistantly installed along the stirring shaft to uniformly mix the materials and steam.

[0021] The rapid depressurization system includes an instantaneous pressure relief valve 14, a pressure relief buffer tank 15, a cooling water circulation system 16, and a pressure release controller 17. The cooling water circulation system 16 is connected via a pipe to the cooling water inlet flange at the lower side wall of the pressure relief buffer tank 15, used to regulate temperature changes during depressurization. The pressure relief buffer tank 15 is a cylindrical pressure-resistant vessel, with its bottom connected via a pipe to the inlet flange of the solid-liquid separator 18. The bottom of the high-pressure steam reactor 5 is connected to the inlet flange of the instantaneous pressure relief valve 14, and the outlet of the instantaneous pressure relief valve 14 is connected via a pipe to the top inlet flange of the pressure relief buffer tank 15. The pressure release controller 17 is electrically connected via a cable to a stepper motor on the instantaneous pressure relief valve. The stepper motor is connected via a coupling to the valve core inside the instantaneous pressure relief valve 14, used to convert the rotational motion of the stepper motor into the linear motion of the valve core. The valve core slides axially along the instantaneous pressure relief valve 14, with one end connected to the output shaft of the coupling via a keyway, and the other end extending to the inlet of the staged pressure relief chamber 26.

[0022] The instantaneous pressure relief valve 14 has a series of graded pressure relief chambers 26, which are sequentially connected and comprise a first pressure relief chamber 261, a second pressure relief chamber 262, and a third pressure relief chamber 263. The first pressure relief chamber 261, located at the high-pressure side inlet, has the largest volume and is used for initial high-pressure buffering; the second pressure relief chamber 262, located in the middle, has the next largest volume and is used for intermediate pressure release; and the third pressure relief chamber 263, located at the low-pressure side outlet, has the smallest volume and is used to balance the final pressure. The chambers are arranged in series along the axial direction and separated by an elastic diaphragm 264. This multi-stage chamber structure allows the pressure to decrease progressively, avoiding shock waves caused by excessive instantaneous pressure differences in a single chamber, thereby protecting the crystal morphology of the α-hemihydrate gypsum crystal structure. The pressure relief chambers are connected by conical transition sections 265, with a cone angle between 15 and 25 degrees (e.g., 20 degrees). The conical transition sections 265 are funnel-shaped, gradually narrowing from larger to smaller chambers to ensure a gradual pressure release during each stage of pressure relief. By guiding the airflow to diffuse slowly, excessive instantaneous pressure differences are avoided to prevent impact damage to the α-hemihydrate gypsum crystal structure. The inner surface of the conical transition sections 265 is provided with buffer grooves, which are distributed in a ring and have a depth of 2 to 4 millimeters. These grooves are evenly arranged along the conical wall, with a spacing of 5 millimeters between each ring, further mitigating the impact of the airflow. When gas passes through, the grooves generate a vortex effect, dispersing kinetic energy and enhancing the buffering effect, thus protecting the stability of the crystal structure.

[0023] Each pressure relief chamber is equipped with an elastic diaphragm 264 with different pressure thresholds. The elastic diaphragm 264 is disc-shaped and embedded in an annular groove in the chamber wall, and fixed by a pressure ring to ensure sealing. The arrangement of the elastic diaphragm 264 requires high-pressure gas to pass through the diaphragm in stages to flow, achieving staged pressure relief and effectively reducing the risk of airflow impact damaging the crystal structure. The elastic diaphragm 264 includes a first diaphragm 2641, a second diaphragm 2642, and a third diaphragm 2643. The first diaphragm 2641 is located between the first pressure relief chamber 261 and the second pressure relief chamber 262, and its rupture pressure is set to 2.5 MPa; the second diaphragm 2642 is located between the second pressure relief chamber 262 and the third pressure relief chamber 263, and its rupture pressure is set to 1.8 MPa; the third diaphragm 2643 is located on the outlet side of the third pressure relief chamber 263, and its rupture pressure is set to 1.2 MPa. Each diaphragm is made of polytetrafluoroethylene (PTFE) material of varying thicknesses; for example, the first diaphragm 2641 is 0.5 mm thick, the second diaphragm 2642 is 0.4 mm thick, and the third diaphragm 2643 is 0.3 mm thick. This material selection and thickness variation ensures that the diaphragms rupture in an orderly manner under specific pressure, forming a gradual release path and preventing sudden pressure changes from causing microscopic damage to the α-hemihydrate gypsum crystal structure.

[0024] The product separation and processing system includes a solid-liquid separator 18, a washing device 19, a dehydrator 20, and a product collection bin 21. The solid-liquid separator 18 adopts a centrifugal separation structure, and its outlet is connected to the inlet flange of the washing device 19 via a pipeline. The washing device 19 is a spray-type cleaning device, and its outlet is connected to the inlet flange of the dehydrator 20 via a pipeline. The dehydrator 20 is a rotary dryer, and its outlet is connected to the inlet flange of the product collection bin 21 via a pipeline.

[0025] The steam recovery system includes a condenser 22, a steam separator 23, a heat exchanger 24, and a circulating water pump 25. The condenser 22 is connected to the top outlet flange of the steam generator 6 via a pipe, and the steam separator 23 is connected to the bottom outlet flange of the condenser 22 via a pipe. The heat exchanger 24 is connected to the bottom outlet flange of the steam separator 23 via a pipe, and the circulating water pump 25 is connected to the bottom outlet flange of the heat exchanger 24 via a pipe, forming a steam recovery cycle.

[0026] The crystal form conversion control system includes a programmable temperature controller 10, a heat preservation section controller 11, a crystal form detector 12, and a reaction time controller 13. The programmable temperature controller 10 and the heat preservation section controller 11 are electrically connected to the temperature sensor array 8 on the high-pressure steam reactor 5 via signal lines to control the reaction temperature range between 124 and 180°C. The crystal form detector 12, using X-ray diffraction technology, is installed on the external side wall of the high-pressure steam reactor 5 to monitor the α-hemihydrate gypsum content online. The reaction time controller 13 is linked to the programmable temperature controller 10 via a timing module to set the reaction time parameters, ensuring precise control of the reaction conditions.

[0027] Work process: First, the phosphogypsum raw material enters the metering feeder 2 from the silo 1. The metering feeder 2 then uses a screw conveyor to evenly feed the raw material into the pre-screening device 3. The pre-screening device 3 uses a vibrating screen structure with a screen mesh size of 2 mm, which can effectively remove large particulate impurities and ensure the uniformity of the subsequent reaction materials. After pre-screening, the raw material is sent to the premixer 4 through a pipeline. The premixer 4 is equipped with spiral blades, which mix the raw material with an appropriate amount of liquid during the stirring process to form a uniform slurry. This slurry is then transported to the high-pressure steam reactor 5 through a pipeline.

[0028] High-temperature, high-pressure steam generated by steam generator 6 enters high-pressure steam reactor 5 through steam pipeline. Pressure control valve group 7 regulates steam flow to maintain reaction pressure between 0.3 and 1.3 MPa. Temperature sensor array 8 is arranged along the circumference of the reactor body, with a temperature measurement accuracy of ±2°C, to monitor the temperature distribution inside the reactor in real time and ensure stable reaction conditions. Programmable temperature controller 10 and heat preservation section controller 11 adjust heating power based on data feedback from temperature sensor array 8 to ensure the reaction temperature is stable between 124 and 180°C. Crystal form detector 12 uses X-ray diffraction technology to monitor the α-hemihydrate gypsum content online, and reaction time controller 13 dynamically adjusts the reaction time based on the monitoring results, thereby optimizing crystal form conversion efficiency. Stirring device 9 is driven by a motor to rotate the stirring shaft, with a speed adjustable within the range of 10-50 rpm. The stirring blade tilt angle is 45°, which can effectively promote uniform contact between materials and steam, thereby improving crystal form conversion efficiency. During this process, phosphogypsum gradually transforms into α-hemihydrate gypsum crystals.

[0029] After the reaction is complete, the crystal form detector 12 automatically detects the α-hemihydrate gypsum content in the product every 30 minutes and transmits the signal to the pressure release controller 17. When the α-type content reaches 95% or more, the pressure reduction program is automatically triggered. The pressure release controller 17 controls the stepper motor on the instantaneous pressure relief valve 14 to start according to the set program. The stepper motor drives the valve core inside the instantaneous pressure relief valve 14 to slide through the coupling, opening the inlet of the staged pressure relief chamber 26. The first diaphragm 2641, the second diaphragm 2642, and the third diaphragm 2643 rupture under pressures of 2.5MPa, 1.8MPa, and 1.2MPa, respectively, completing the staged pressure reduction process. The conical transition section 265 between each pressure relief chamber has a 20-degree conical angle structure. Combined with the structural characteristics of the buffer groove, it can effectively disperse the kinetic energy of the airflow and avoid impact damage to the α-hemihydrate gypsum crystals due to excessive flow velocity.

[0030] After depressurization, the material enters the depressurization buffer tank 15 through pipelines. The cooling water circulation system 16 injects cooling water into the depressurization buffer tank 15 through pipelines to regulate the material temperature and prevent crystal structure changes due to excessively rapid cooling. Subsequently, the material is transported to the solid-liquid separator 18 through pipelines. The solid-liquid separator 18 adopts a centrifugal separation structure to separate the solid product from the liquid. The separated solid enters the washing device 19, where surface residual impurities are removed by spray cleaning, and then it is dried in the dehydration dryer 20 before finally being transported to the product collection bin 21.

[0031] Meanwhile, the steam recovery system begins operation. Condenser 22 receives waste heat steam discharged from steam generator 6 via pipeline, condenses it into liquid water, and then sends it to steam separator 23. Steam separator 23 further separates incompletely condensed steam and introduces it into heat exchanger 24 for heat recovery. Circulating water pump 25 returns the condensate to steam generator 6, forming a steam recycling system and reducing energy consumption.

[0032] To enable those skilled in the art to fully understand and implement this utility model, the specific implementation principles of this utility model are further supplemented below in conjunction with specific application scenarios.

[0033] In the preparation of phosphogypsum, the raw material for phosphogypsum must have a moisture content of <15%, a particle size of 2-5 mm, and an SO3 content of >40%. The specific operation is as follows: Pretreatment stage: Add phosphogypsum raw material to silo 1 and feed it continuously at a speed of 50-200 kg / h through metering feeder 2. Remove impurity particles larger than 5 mm through pre-screening device 3. Then add 0.5% α-hemihydrate gypsum seed crystals to premixer 4, mix evenly, and send it to high-pressure steam reactor 5.

[0034] Pressure and temperature increase stage: Steam generator 6 is started to generate saturated steam. The pressure inside the reactor is slowly increased to 0.5 MPa through pressure control valve group 7. The programmable temperature controller 10 controls the temperature to rise from room temperature to 124°C, with the heating rate controlled at 2-3°C / min. At the same time, the stirring device 9 stirs at 20 rpm. This stage lasts for 30 minutes. Temperature sensor array 8 monitors the temperature distribution at various points inside the reactor in real time to ensure that the temperature uniformity error is <±5°C.

[0035] Conversion reaction stage: The pressure is further increased to 1.0-1.3 MPa, and the temperature is precisely controlled within the range of 160-175°C by the heat preservation section controller 11. The reaction time controller 13 is set to a reaction time of 4 hours. Under these conditions, gypsum dihydrate undergoes a dehydration reaction: CaSO4·2H2O → CaSO4·½H2O + 1.5H2O, forming α-hemihydrate gypsum crystals through a dissolution-recrystallization mechanism. The stirring device 9 is adjusted to a low stirring speed of 10 rpm to avoid damaging the crystal structure.

[0036] Online monitoring phase: The crystal form detector 12 uses X-ray diffraction technology to automatically detect the α-hemihydrate gypsum content in the product every 30 minutes. When the α-type content reaches 95% or more, the pressure reduction program is automatically triggered.

[0037] Rapid pressure reduction phase: Under the control of the pressure relief controller 17, the instantaneous pressure relief valve 14 rapidly reduces the reaction pressure from 1.3MPa to 0.1MPa within 0.5 seconds. At the same time, the cooling water circulation system 16 is activated to quickly reduce the temperature to below 80°C to prevent α-hemihydrate gypsum from reverting to β-type. The pressure reduction buffer tank 15 mitigates the impact of the instantaneous pressure reduction.

[0038] Product separation and processing stage: The reaction slurry enters the solid-liquid separator 18 for centrifugal separation. The separated α-hemihydrate gypsum solid is washed 2-3 times with deionized water through the washing device 19 to remove residual impurities. Then it is sent to the dehydration dryer 20 to dry at 110°C until the moisture content is <1%. The final product is stored in the product collection bin 21.

[0039] Steam recovery stage: The water vapor generated during the reaction is condensed and recovered by condenser 22, non-condensable gases are separated by steam separator 23, the feed is preheated by heat exchanger 24 using waste heat, and the cooling water is circulated by circulating water pump 25. The entire steam recovery and utilization system can recover more than 70% of the waste heat.

[0040] When the same equipment is used to process phosphogypsum containing a lot of impurities, with the reaction pressure set at 0.8 MPa, the reaction temperature at 150°C, and the reaction time at 6 hours, the α-type content of the product can reach 92%, and the compressive strength is 28 MPa.

[0041] When high-purity phosphogypsum is processed using the same equipment, with the reaction pressure set at 1.3 MPa, the reaction temperature at 180°C, and the reaction time at 3 hours, the α-type content of the product can reach 98%, and the compressive strength is 35 MPa.

[0042] All content not described in detail in this specification is prior art known to those skilled in the art, and the model parameters of each electrical appliance are not specifically limited; conventional equipment can be used. Electrical control components not mentioned in this technical solution are not shown in the figures because they are prior art, and will not be described further here.

[0043] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solution of this utility model and are not intended to limit it. Although the utility model has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made to it in form and detail without departing from the scope defined by the claims of this utility model.

Claims

1. A high-pressure steam reforming apparatus for preparing α-hemihydrate gypsum from phosphogypsum, characterized in that: It includes a raw material pretreatment system, a core high-pressure reaction system, a rapid depressurization system, and a product separation and processing system; The raw material pretreatment system includes a silo (1), a metering feeder (2), a pre-screening device (3), and a premixer (4). The bottom of the silo (1) is fixedly connected to the metering feeder (2) by bolts. The outlet of the metering feeder (2) is connected to the inlet of the pre-screening device (3) through a flange. The outlet of the pre-screening device (3) is connected to the top inlet of the premixer (4) through a pipe. The core high-pressure reaction system includes a high-pressure steam reactor (5) and a steam generator (6). The bottom outlet of the premixer (4) is welded to the top inlet of the high-pressure steam reactor (5) through a pipeline. The steam generator (6) is connected to the steam inlet flange on the upper side wall of the high-pressure steam reactor (5) through a steam pipeline. The rapid depressurization system includes an instantaneous pressure relief valve (14) and a pressure reduction buffer tank (15). The bottom of the high-pressure steam reactor (5) is connected to the inlet flange of the instantaneous pressure relief valve (14), and the outlet of the instantaneous pressure relief valve (14) is connected to the top inlet flange of the pressure reduction buffer tank (15) through a pipeline. The instantaneous pressure relief valve (14) is provided with a graded pressure relief chamber (26). The graded pressure relief chamber (26) is composed of a first pressure relief chamber (261), a second pressure relief chamber (262), and a third pressure relief chamber (263) connected in sequence. Each pressure relief chamber is separated by an elastic diaphragm (264). The elastic diaphragm (264) is embedded in the annular groove of the chamber wall and fixed by a pressure ring. The product separation and processing system includes a solid-liquid separator (18), a washing device (19), a dehydration dryer (20), and a product collection bin (21). The bottom of the pressure-reducing buffer tank (15) is connected to the inlet flange of the solid-liquid separator (18) through a pipe. The outlet of the solid-liquid separator (18) is connected to the inlet flange of the washing device (19) through a pipe. The outlet of the washing device (19) is connected to the inlet flange of the dehydration dryer (20) through a pipe. The outlet of the dehydration dryer (20) is connected to the inlet flange of the product collection bin (21) through a pipe. The core high-pressure reaction system also includes a pressure control valve group (7), a temperature sensor array (8), and a stirring device (9). The pressure control valve group (7) is installed on the steam pipeline, the temperature sensor array (8) is embedded in the side wall of the high-pressure steam reactor (5), and the stirring device (9) is located inside the high-pressure steam reactor (5).

2. The high-pressure steam reforming apparatus for preparing α-hemihydrate gypsum from phosphogypsum according to claim 1, characterized in that: The rapid depressurization system also includes a cooling water circulation system (16) and a pressure relief controller (17). The cooling water circulation system (16) is connected to the cooling water inlet flange at the lower side wall of the depressurization buffer tank (15) via a pipe, and is used to regulate the temperature change during the depressurization process. The pressure relief controller (17) is electrically connected to the stepper motor on the instantaneous pressure relief valve (14) via a cable. The stepper motor is connected to the valve core inside the instantaneous pressure relief valve (14) via a coupling.

3. The high-pressure steam reforming apparatus for preparing α-hemihydrate gypsum from phosphogypsum according to claim 1, characterized in that: The elastic diaphragm (264) includes a first diaphragm (2641), a second diaphragm (2642), and a third diaphragm (2643). The first diaphragm (2641) is located between the first pressure relief chamber (261) and the second pressure relief chamber (262). The second diaphragm (2642) is located between the second pressure relief chamber (262) and the third pressure relief chamber (263). The third diaphragm (2643) is located on the outlet side of the third pressure relief chamber (263). The elastic diaphragm (264) is made of polytetrafluoroethylene material.

4. A high-pressure steam reforming apparatus for preparing α-hemihydrate gypsum from phosphogypsum according to claim 1 or 3, characterized in that: The volume of the first pressure relief chamber (261) is larger than that of the second pressure relief chamber (262), and the volume of the second pressure relief chamber (262) is larger than that of the third pressure relief chamber (263). Each pressure relief chamber is connected by a conical transition section (265). The cone angle of the conical transition section (265) is set between 15 degrees and 25 degrees to ensure that the airflow forms a gradual pressure release during each stage of pressure relief. The inner surface of the conical transition section (265) is provided with a buffer groove. The buffer groove is distributed in a ring and has a depth of 2 mm to 4 mm to further reduce the impact of the airflow.

5. The high-pressure steam reforming apparatus for preparing α-hemihydrate gypsum from phosphogypsum according to claim 1, characterized in that: The device also includes a steam recovery system, which includes a condenser (22), a steam separator (23), a heat exchanger (24), and a circulating water pump (25). The condenser (22) is connected to the top outlet flange of the steam generator (6) through a pipe, the steam separator (23) is connected to the bottom outlet flange of the condenser (22) through a pipe, the heat exchanger (24) is connected to the bottom outlet flange of the steam separator (23) through a pipe, and the circulating water pump (25) is connected to the bottom outlet flange of the heat exchanger (24) through a pipe.

6. The high-pressure steam reforming apparatus for preparing α-hemihydrate gypsum from phosphogypsum according to claim 1, characterized in that: The device also includes a crystal form conversion control system, which includes a programmable temperature controller (10), a heat preservation section controller (11), a crystal form detector (12), and a reaction time controller (13). The programmable temperature controller (10) and the heat preservation section controller (11) are electrically connected to the temperature sensor array (8) on the high-pressure steam reactor (5) via signal lines. The crystal form detector (12) is installed on the outside of the side wall of the high-pressure steam reactor (5). The reaction time controller (13) is linked with the programmable temperature controller (10) via a timing module.

7. The high-pressure steam reforming apparatus for preparing α-hemihydrate gypsum from phosphogypsum according to claim 1, characterized in that: The stirring device (9) includes a stirring shaft, a drive motor and stirring blades. The drive motor is fixed to the top of the high-pressure steam reactor (5) by bolts. The top of the stirring shaft is connected to the drive motor via a coupling. Multiple sets of stirring blades with an inclination angle of 45° are installed equidistantly along the axial direction on the stirring shaft.

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