Device and method for preparing type II anhydrite from phosphogypsum and preventing skinning

Abstract

The invention provides a device and a method for preparing type II anhydrous gypsum from phosphogypsum and preventing crust, the device comprises a preheating drying unit, a calcining unit and a cooling separation unit, the preheating drying unit comprises a drying crushing device and at least one stage of preheating separation device; the calcining unit comprises a vertical calcining furnace, the lower part of the vertical calcining furnace is conical, the diameter is gradually reduced from top to bottom, and the side wall is provided with a feed port and multiple layers of combustion nozzles; and a solid phase outlet pipeline of the cooling separation unit is divided into two branches, one branch is connected with the vertical calcining furnace, and the other branch is a finished product collecting pipeline. According to the invention, through the arrangement of the preheating drying unit, the calcining unit, the cooling separation unit and other structural units, moisture is removed through preheating drying, easily-skinning components in the raw materials are taken away in advance, and through the design of the vertical calcining furnace, the temperature is accurately controlled, burning melting and skinning are avoided, and impurities are effectively removed, so that the high-quality II-type anhydrous gypsum is obtained; the device is reasonable in structural design, stable in operation and high in phosphogypsum utilization rate, and the application market of the device can be expanded.

Description

Technical Field

[0001] The invention belongs to the technical field of solid waste utilization, and relates to a device and a method for preparing type II anhydrous gypsum from phosphogypsum and preventing skinning. Background Art

[0002] Phosphoric acid is an important industrial product. Its production is mainly based on the sulfuric acid wet process. During the phosphoric acid production process, sulfuric acid is used to treat phosphate ore. The solid waste residue produced is phosphogypsum, which is the main by-product of phosphoric acid production. The output of phosphogypsum is extremely large, and the annual stockpile is increasing on a large scale. The comprehensive utilization rate is low, which not only occupies a large amount of land resources, but also causes greater environmental risks. In particular, when phosphogypsum is accumulated, soluble phosphorus and fluorine may leak with the water, causing serious pollution to the environment. Therefore, the recovery and resource utilization of phosphogypsum are essential.

[0003] The main component of phosphogypsum is calcium sulfate dihydrate. In addition, it also contains impurities such as undecomposed phosphate rock, fluoride, sulfuric acid, organic matter, acid insoluble matter, iron and aluminum compounds. Due to the presence of harmful impurities, if it is not fully removed, it is difficult to use it alone as a gypsum raw material, and the utilization rate is also low. Therefore, it is usually necessary to further transform the phosphogypsum on the basis of impurities removal to prepare products such as semi-hydrated gypsum or anhydrous gypsum. The preparation of type II anhydrous gypsum by calcining and dehydrating phosphogypsum is an important way to utilize phosphogypsum resources. At present, the preparation of anhydrous gypsum mostly adopts centralized calcination to treat phosphogypsum. The moisture in the phosphogypsum cannot be fully removed, resulting in poor product quality.

[0004] Based on the types of impurities in phosphogypsum, because it contains cement-like components such as silicon, calcium, and aluminum-iron compounds, when the calcination temperature is too high, it will produce clinker-like components such as aluminum prism. At the same time, because it contains potassium, chlorine, sulfur and other ions, if the calcination temperature is not well controlled, it is easy to generate compounds that are prone to skinning, such as alkali sulfate and alkali chloride. Moreover, the current calcination of phosphogypsum lacks precise temperature control function, which can easily cause safety hazards when the operating conditions are abnormal. In addition, the formation of skin during high-temperature calcination is usually unavoidable, and the calcination equipment and process need to be improved.

[0005] CN 110803878A discloses a device and method for producing type II anhydrous gypsum from phosphogypsum, the device comprising a pretreatment unit, a drying unit, a calcination unit and a product collection unit connected in sequence, the pretreatment unit comprising a spiral stirring device, the drying unit comprising a dispersing device and at least one primary drying device, the calcination unit comprising a calcination device, and a heat source pipeline is arranged in the calcination device. Although the device is also provided with a drying and calcination unit, the structure of the calcination equipment only discloses the use of a rotary kiln and a heat source pipeline for heat supply, and the calcination temperature cannot be precisely controlled, and the issue of whether crusting will occur when phosphogypsum is calcined is not involved.

[0006] CN 116003006A discloses a device and method for preparing type II anhydrous gypsum from suspended phosphogypsum, the device comprises a drying system, a preheating and calcining system, and a cooling and collecting system, which are connected in sequence through a pipeline system; wherein the drying system comprises a screw feeder, a flash dryer, a cyclone separator, a bag dust collector, a centrifugal fan, and a buffer bin, and the preheating and calcining system comprises a multi-stage suspension preheater, a reaction furnace, a hot air furnace, and a circulating fan, wherein the multi-stage suspension preheater comprises a multi-stage cyclone cylinder, and the reaction furnace is a U-shaped structure, on which a plurality of constrictions for adjusting the wind speed are arranged, and each constriction is arranged at intervals. Although the device also combines drying, preheating, calcining, cooling and other processes to remove impurities from phosphogypsum and convert it into type II anhydrous gypsum, the specific surface and internal structural components of the calcining equipment are not clearly defined, and the focus is on the cascade utilization of system heat, rather than being designed to accurately control the calcining temperature, and it does not involve how to solve the crusting problem during the calcination of phosphogypsum.

[0007] In summary, for the device and method for preparing type II anhydrous gypsum from phosphogypsum, it is necessary to accurately control the calcination temperature according to the impurity composition of the phosphogypsum to achieve accurate conversion of the phosphogypsum and avoid the stability of the calcination process affected by crusting during calcination. Summary of the invention

[0008] In view of the problems existing in the prior art, the object of the present invention is to provide a device and method for preparing type II anhydrous gypsum from phosphogypsum and preventing skinning. The device ensures precise control of the temperature during the calcination process and avoids the problem of skinning by setting structural units such as preheating and drying and calcination, especially the design of the internal structure of the calcining furnace, effectively removes impurities such as fluorine, phosphorus and organic matter in the phosphogypsum, obtains type II anhydrous gypsum with stable crystal form, ensures the quality of the product, and realizes efficient recycling of phosphogypsum.

[0009] To achieve this object, the present invention adopts the following technical solutions:

[0010] On the one hand, the present invention provides a device for preparing type II anhydrous gypsum from phosphogypsum and preventing skinning, the device comprising a preheating and drying unit, a calcining unit and a cooling and separating unit, the preheating and drying unit comprising a drying and crushing device and at least one preheating and separating device, the outlet of the drying and crushing device is connected to the inlet of the preheating and separating device, and the solid phase outlet of the preheating and separating device is connected to the inlet of the calcining unit;

[0011] The calcining unit comprises a vertical calcining furnace, the lower part of which is conical, the diameter of the conical section gradually decreases from top to bottom, a plurality of feed ports and multi-layer combustion nozzles are arranged on the side wall of the conical section, and a fluidizing gas inlet is arranged at the bottom of the vertical combustion furnace;

[0012] The solid phase outlet pipeline of the cooling and separation unit is divided into two branches, one is connected to the feed port of the vertical calcining furnace, and the other is the finished product collection pipeline. The gas phase outlet of the cooling and separation unit is connected to the gas phase inlet of the preheating separation device.

[0013] In the present invention, according to the source and composition of phosphogypsum, in order to realize its resource utilization, it needs to be calcined. The present invention sets structural units such as preheating and drying, calcining, cooling and separation. The present invention first performs preheating and drying to remove moisture, and uses hot air to remove some components in the raw materials that are easy to cause crusting, such as excessive sulfuric acid, in advance. Then, a vertical calcining furnace is used for calcining. By designing the overall and internal structure of the vertical calcining furnace, the distribution of the feed port and the combustion nozzle is controlled, and the temperature is controlled to ensure balanced combustion, so as to prevent the crusting from melting due to the high calcining temperature, effectively remove harmful impurities such as fluorine, phosphorus, and organic matter in the phosphogypsum, and convert it from acidic to neutral materials. Finally, the calcined material is collected or re-calcined through a cooling and separation unit, and the gas phase with the crusting component is separated as hot air after passing through the preheating and separation unit to avoid bringing too much of it into the calcining furnace, which is helpful to obtain high-quality II type anhydrous gypsum products. The device has reasonable structural design, stable and efficient operation, effectively improves the utilization rate of phosphogypsum, and expands its application market.

[0014] The following are preferred technical solutions of the present invention, but are not intended to be limitations of the technical solutions provided by the present invention. Through the following technical solutions, the technical objectives and beneficial effects of the present invention can be better achieved and realized.

[0015] As a preferred technical solution of the present invention, the device further comprises a feeding unit, the feeding unit comprises a raw material feeding bin, and the outlet of the raw material feeding bin is connected to the inlet of the drying and crushing device.

[0016] Preferably, the gas phase inlet of the drying and crushing device is connected to the gas phase outlet of the preheating separation device and / or the temperature reduction separation unit.

[0017] As a preferred technical solution of the present invention, the preheating and separation device is provided with two stages, namely a first preheating and separation device and a second preheating and separation device, and the preheating and separation device comprises a cyclone preheater.

[0018] Preferably, the solid phase outlet of the first preheating and separation device is connected to the inlet of the second preheating and separation device, and the gas phase outlet of the first preheating and separation device is connected to a dust collector and a powder temporary storage bin in sequence, and the outlet of the powder temporary storage bin is divided into two branches, one for external discharge and the other connected to the inlet of the raw material feeding bin.

[0019] In the present invention, the first preheating and separation device preheats and separates the raw materials. The gas phase hot air contains water vapor and fine particles. After separation by the dust collector, the powder is temporarily stored and inspected and analyzed. If the alkali content is high, it is discharged (for example, when the content of alkali sulfate and alkali chloride is high, it is easy to form a cohesive substance with dust after melting at above 650-700°C. The sticky film of liquid phase material formed on the surface of the raw material will hinder the flow of raw material particles, thereby causing cohesive skin and blockage), reducing the risk of skinning during calcination. If the alkali content is low, it is reused as a raw material to avoid waste.

[0020] Preferably, the solid phase outlet material of the first preheating and separation device is mixed with the outlet gas of the cyclone separation device in the cooling and separation unit and then connected to the inlet of the second preheating and separation device, the gas phase outlet of the second preheating and separation device is connected to the gas phase inlet of the drying and crushing device, and the solid phase outlet of the second preheating and separation device is connected to the feed inlet of the vertical calcining furnace.

[0021] Preferably, the lower portion of the preheating and separation device is conical, and compressed air blowing ports are provided along the annular circumference of the conical portion.

[0022] In the present invention, the cone part of the preheating and separation device is designed with a structure to prevent crusting, and adopts a programmed compressed air anti-blocking technology; when the negative pressure of the cone part is too high, the anti-blocking spray is turned on to prevent clogging and crusting.

[0023] As a preferred technical solution of the present invention, the aspect ratio of the vertical calcining furnace is 16:1 to 8:1, for example, 16:1, 15:1, 14:1, 12:1, 12:1, 9:1 or 8:1, but is not limited to the listed values, and other unlisted values ​​within the numerical range are equally applicable; the height of the conical section accounts for 25 to 40% of the total height of the vertical calcining furnace, for example, 25%, 27%, 30%, 32%, 34%, 36%, 38% or 40%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are equally applicable.

[0024] Preferably, the taper of the conical section is 5 to 12 degrees, such as 5 degrees, 6 degrees, 7 degrees, 8 degrees, 9 degrees, 10 degrees, 11 degrees or 12 degrees, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0025] In the present invention, the vertical calcining furnace adopts a vertical and slender calcining furnace, which can control the residence time of the material and the flame in the furnace, prolong the heat exchange time of the phosphogypsum in the furnace, and control the material temperature leaving the calcining furnace and entering the separation equipment not to reach the crusting temperature.

[0026] In the present invention, the bottom of the vertical calcining furnace is designed to be a conical structure. The wind speed in the lower section is high, which can easily blow up the materials. The speed slows down at the upper part of the cone, which can extend the residence time of the materials in the furnace.

[0027] Preferably, the cone section is provided with 4 to 8 layers of burners, such as 4 layers, 5 layers, 6 layers, 7 layers or 8 layers, and the burners in two adjacent layers are staggered.

[0028] Preferably, the number of the burners in each layer is 2 to 4, such as 2, 3 or 4, and they are evenly distributed along the circumference.

[0029] Preferably, the combustion nozzle introduces fuel and air together.

[0030] In the present invention, types of fuel that are easy to ignite, such as coal gas, water gas, natural gas, etc., are used to facilitate the control of the combustion temperature; the position setting of the combustion nozzle and the special flame design, the matching combustion-supporting air pressure and air volume are adjustable, and the furnace temperature range is controlled. The flame will not directly burn the refractory aggregate of the calcining furnace wall and will not melt the powder.

[0031] Preferably, the feed port on the conical section is located between the uppermost and lowermost layers of burners, preferably at the position of the middle layer of burners.

[0032] Preferably, the feed openings are evenly distributed on the annular circumference and are provided with a spreading box and / or a spreading plate.

[0033] In the present invention, the conical section is designed with multiple layers of burners, and the materials enter the furnace at different points. The feeding position is located between the combustion nozzles. Since the conical section of the vertical calcining furnace is connected to two feeding pipelines, there are at least two feeding ports. The feeding ports can be staggered up and down, and the materials are scattered into different layers of flames through the spreading plate. The flames are covered by powder, and the temperature is reduced by direct contact with the flames, so the combustion process is controlled and high-temperature sintering and crusting are prevented.

[0034] Preferably, the interior of the conical section is a fluidized bed structure, and the fluidizing gas inlet is connected to a fan.

[0035] In the present invention, a fluidized bed is used at the bottom of the calcining furnace, and a Roots blower is used for the fluidized bed blowing, so as to reduce the occurrence of bed pressing accidents, thereby preventing the material from blocking the lower part of the calcining furnace due to improper operation, causing local high temperature to cause overburning and crusting.

[0036] Preferably, a cold air inlet is further provided on the side wall between the upper fluidizing gas inlet of the conical section and the bottom layer of the combustion nozzle, and the cold air inlet is also connected to a fan.

[0037] In the present invention, the bottom of the calcining furnace adopts forced cold air supplement measures, and is equipped with a frequency conversion and adjustable air door calcining furnace air inlet fan. The top of the calcining furnace is negatively pressurized, and double insurance cold air is introduced to fluidize the powder, control the cross-sectional wind speed of the calcining furnace and the total air volume entering, and prevent high-temperature melting;

[0038] Preferably, the number of the cold air inlets is at least two, such as two, three or four, etc., which are evenly distributed along the circumference, and preferably the two cold air inlets are symmetrically arranged.

[0039] In the present invention, the cold air inlet is designed to enter the furnace symmetrically on the bottom conical section, and the wind has a slight rotation direction and mixes with the bottom fluidized air upward, thereby reducing wind resistance and optimizing the flow field in the calcining furnace, extending the residence time of the material in the calcining furnace, and enhancing the heat exchange effect.

[0040] Preferably, a temperature sensor is provided on the cylindrical section at the upper part of the conical section of the vertical calcining furnace, and preferably, temperature sensors are provided on the middle, upper part and top part of the vertical calcining furnace.

[0041] As a preferred technical solution of the present invention, the cooling and separation unit includes a cyclone separation device and a cooling and heat exchange device. The top outlet of the vertical calcining furnace is connected to the inlet of the cyclone separation device. The solid phase outlet of the cyclone separation device is divided into two paths through a three-way valve, one of which is connected to the feed port of the vertical calcining furnace, and the other is cooled by heat exchange in the cooling and heat exchange device to obtain the finished material.

[0042] Preferably, the lower portion of the cyclone separation device is conical, and compressed air blowing ports are provided along the annular circumference of the conical portion.

[0043] Preferably, the gas phase outlet of the cooling and heat exchanging device is connected to the gas phase inlet of the drying and crushing device. Preferably, the connecting pipelines between the second preheating and separating device and the cyclone separation device and the feed port of the vertical calcining furnace are both provided with an air locking device, preferably a weight valve.

[0044] In the present invention, by setting the circulating calcination return port, the circulation ratio can be adjusted through the three-way valve, and part of the material can be circulated back to the calcining furnace to gradually heat the material, which is convenient for adjusting the material temperature at the beginning, middle and end of the start-up and prolonging the residence time of the material in the calcining furnace, thereby reducing the total height of the calcining furnace; the setting of the air locking device ensures that the hot air flows along the route required by the process; by observing the action cycle of the heavy hammer valve under the preheating separation device and the cyclone separation device, it can be judged whether blockage is possible or blockage is caused by crusting.

[0045] In the present invention, a manhole door is provided opposite to the combustion nozzle of the conical section of the calcining furnace and several meters above it, so as to facilitate parking for inspection; the manhole door is provided with an inspection hole, which can be opened during operation to safely and roughly observe the operation of the furnace through the heat-resistant glass barrier; the observation glass of the combustion nozzle can also be used to observe the flame shape and the operation of the furnace. In addition, there is an inspection door at the back of the material spreading box, which can be used to check multiple channels after the hammer valve does not work normally, so as to prevent blockage and high-temperature crusting.

[0046] On the other hand, the present invention provides a method for preparing type II anhydrous gypsum and preventing skinning by using the above-mentioned device, the method comprising the following steps:

[0047] (1) crushing the phosphogypsum raw material and preliminarily drying it with airflow, and then preheating and separating them together to obtain dry material and dust-containing gas;

[0048] (2) calcining the dried material obtained in step (1), using multi-point feeding and ignition and heat supply by multi-layer combustion nozzles to obtain calcined material;

[0049] (3) The solid phase material after gas-solid separation of the calcined material obtained in step (2) is divided into two parts, one part is returned to step (2) for calcination again, and the other part is cooled and heat-exchanged to obtain the finished material.

[0050] As a preferred technical solution of the present invention, the particle size of the crushed phosphogypsum raw material in step (1) is 0 to 200 μm, for example, 2 μm, 10 μm, 30 μm, 50 μm, 80 μm, 100 μm, 120 μm, 150 μm, 180 μm or 200 μm, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0051] Preferably, the temperature of the air flow introduced during the preliminary drying of the phosphogypsum raw material in step (1) is 250-400°C, for example, 250°C, 270°C, 280°C, 300°C, 320°C, 340°C, 360°C, 380°C or 400°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0052] Preferably, the raw material and the airflow preliminarily dried in step (1) enter the preheating separation device together for preheating separation, and the number of preheating separation is at least once, for example, once, twice or three times, etc., preferably twice.

[0053] Preferably, the solid phase material after the primary preheating separation is mixed with the airflow again for secondary preheating separation. At this time, the temperature of the solid phase material is 100-200°C, for example, 100°C, 120°C, 140°C, 150°C, 160°C, 180°C or 200°C, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable. The temperature of the airflow used is 500-900°C, for example, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, 800°C or 900°C, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0054] Preferably, the dust-containing gas obtained after a preheating separation is subjected to dust removal treatment, and the obtained powder is temporarily stored. After inspection and analysis, if the alkali metal content is higher than 0.8-1.0%, for example, 0.8%, 0.85%, 0.9%, 0.95% or 1.0%, the powder is discharged; if the alkali metal content is lower than 0.5-0.8%, for example, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, 0.75% or 0.8%, the powder is re-processed as raw material.

[0055] Preferably, the temperature of the dried material obtained after the secondary preheating separation is 200-300°C, for example, 200°C, 220°C, 240°C, 250°C, 270°C, 280°C or 300°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0056] As a preferred technical solution of the present invention, the calcination in step (2) is carried out in a vertical calcination furnace, and the feed inlet of the vertical calcination furnace is located on the lower conical section.

[0057] Preferably, in step (2), the dry material is added from multiple feed ports through a spreading box and / or a spreading plate to evenly disperse the dry material to prevent short circuit of the material.

[0058] Preferably, air is locked on the feed pipeline of the vertical calcining furnace, preferably by using a weight valve.

[0059] Preferably, fuel and air are introduced into the burner that is ignited in step (2), and only air is introduced into the burner that is not ignited as burner protection gas.

[0060] In the present invention, during the calcination process, the air intake of the unignited part of the multi-layer combustion burner can be adjusted according to the temperature inside and on the surface of the furnace to protect the burner and adjust and reduce the overall temperature inside the furnace.

[0061] As a preferred technical solution of the present invention, the calcination temperature in step (2) is 450-1000°C, for example, 450°C, 500°C, 600°C, 700°C, 800°C, 900°C or 1000°C, but is not limited to the listed values. Other unlisted values ​​within the numerical range are also applicable, preferably 500-800°C.

[0062] Preferably, the residence time of the calcination in step (2) is 3 to 6 s, for example 3 s, 3.5 s, 4 s, 4.5 s, 5 s, 5.5 s or 6 s, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0063] Preferably, during the calcination in step (2), fluidizing air is introduced from the bottom of the vertical calcining furnace.

[0064] Preferably, during the calcination in step (2), cold air is also introduced from the bottom of the vertical calcining furnace for spraying, and the cross-sectional airflow velocity at the bottom of the vertical calcining furnace is 5 to 15 m / s, for example, 5 m / s, 6 m / s, 8 m / s, 10 m / s, 12 m / s, 14 m / s or 15 m / s, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0065] As a preferred technical solution of the present invention, the calcined material and the gas phase in step (2) enter the cyclone separation device together for gas-solid separation, and the obtained gas phase is mixed with the solid phase material after the primary preheating separation.

[0066] Preferably, during the preheating separation in step (1) and the gas-solid separation in step (3), the pressure of the lower cone of the preheating separation device and the cyclone separation device is independently -5000 to -400Pa, for example, -5000Pa, -4000Pa, -3000Pa, -2500Pa, -2000Pa, -1500Pa, -1000Pa, -800Pa, -600Pa or -400Pa, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are equally applicable.

[0067] Preferably, when the pressure of the lower cone of the preheating separation device and the cyclone separation device reaches -200 to 0Pa, for example, -200Pa, -180Pa, -150Pa, -120Pa, -100Pa, -80Pa, -50Pa, -20Pa or 0Pa, compressed air is used for spraying.

[0068] In the present invention, when the preheating separation device and the cyclone separation device are separated, the cone portion thereof maintains negative pressure to ensure smooth separation of the gas and solid phases, wherein the pressures of different devices are different. The pressure of the preheating separation device is -5000 to -4500 Pa, such as -4800 Pa, -4700 Pa, -4600 Pa or -4500 Pa, and the pressure of the cyclone separation device is -1800 to -1400 Pa, such as -1800 Pa, -1700 Pa, -16 00Pa, -1500Pa or -1400Pa, etc.; in addition, the pressure of the cooling and heat exchange device can also be selected as negative pressure, and multiple levels can be set, and the pressure selection ranges from -3300Pa to -400Pa, such as -3300Pa, -3000Pa, -2500Pa, -2000Pa, -1500Pa, -1000Pa or -400Pa, etc.; when the negative pressure is abnormal, that is, the pressure is too high and close to normal pressure, blowing is required to prevent the cone part from being blocked by material.

[0069] Preferably, the solid phase material obtained after the gas-solid separation in step (3) is divided into two parts, of which the proportion of the solid phase material returned to the vertical calcining furnace is 0 to 60%, for example, 0, 10%, 20%, 30%, 40%, 50% or 60%, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0070] In the present invention, the comparative temperature difference of the top temperature values ​​of the adjacent upper and lower preheating separation devices and the cooling heat exchange device and the temperature value of the top of the calcining furnace are observed. According to the feed amount and the temperature difference at the top of each level of the preheating separation device and the cooling heat exchange device, it can be judged whether the material in the preheater pipeline does not follow the designed process and short-circuits, thereby checking whether the system air volume is too small, whether there is a problem with the spreading plate, whether the heavy hammer valve is not sealed tightly, and timely adjusting the combustion firepower of the calcining furnace to control the total amount of cold air intake.

[0071] Preferably, the solid phase material obtained after the gas-solid separation is cooled to 50-80°C to obtain a Type II anhydrous gypsum product, for example, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C or 80°C, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0072] Preferably, the solid-phase material is cooled by fan fluidization and negative pressure cold air suction.

[0073] Compared with the prior art, the present invention has the following beneficial effects:

[0074] (1) The device of the present invention is provided with structural units such as preheating and drying, calcining, and cooling and separation. The moisture is first removed by preheating and drying, and the components in the raw materials that are easy to cause crusting are partially removed in advance by using hot air. Then, by designing the overall and internal structure of the vertical calcining furnace, the temperature is accurately controlled to ensure balanced combustion, prevent the crusting caused by the calcining temperature being too high, and effectively remove harmful impurities such as fluorine, phosphorus, and organic matter in the phosphogypsum to obtain type II anhydrous gypsum with stable crystal form, thereby ensuring the quality of the product;

[0075] (2) The device described in the present invention has a reasonable structural design, stable operation, energy saving and high efficiency, and can effectively improve the utilization rate of phosphogypsum and expand its application market. BRIEF DESCRIPTION OF THE DRAWINGS

[0076] Figure 1 Schematic diagram of the structure of the device for preparing type II anhydrous gypsum from phosphogypsum and preventing skinning provided in Example 1 of the present invention;

[0077] Among them, 1-raw material feeding bin, 2-drying and crushing device, 3-first preheating and separation device, 4-dust collector, 5-powder temporary storage bin, 6-second preheating and separation device, 7-cyclone separation device, 8-vertical calcining furnace, 9-fluidizing fan, 10-air inlet fan, 11-temperature sensor, 12-spreading box, 13-combustion nozzle, 14-three-way valve, 15-cooling and heat exchange device, 16-weight valve. DETAILED DESCRIPTION

[0078] In order to better illustrate the present invention and facilitate understanding of the technical solution of the present invention, the present invention is further described in detail below. However, the following embodiments are only simple examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0079] The following are typical but non-limiting embodiments of the present invention:

[0080] Embodiment 1:

[0081] This embodiment provides a device for preparing type II anhydrous gypsum from phosphogypsum and preventing skinning, and the structural schematic diagram of the device is shown in FIG. Figure 1 As shown, it includes a preheating and drying unit, a calcining unit and a cooling and separating unit, wherein the preheating and drying unit includes a drying and crushing device 2 and a two-stage preheating and separating device, wherein the outlet of the drying and crushing device 2 is connected to the inlet of the preheating and separating device, and the solid phase outlet of the preheating and separating device is connected to the inlet of the calcining unit;

[0082] The calcining unit comprises a vertical calcining furnace 8, the lower part of which is conical, and the diameter of the conical section gradually decreases from top to bottom. A plurality of feed ports and multi-layer combustion nozzles 13 are arranged on the side wall of the conical section, and a fluidizing gas inlet is arranged at the bottom of the vertical combustion furnace 8;

[0083] The solid phase outlet pipeline of the cooling separation unit is divided into two branches, one of which is connected to the feed port of the vertical calcining furnace 8, and the other is a finished product collection pipeline. The gas phase outlet of the cooling separation unit is connected to the gas phase inlet of the preheating separation device.

[0084] The device further comprises a feeding unit, which comprises a raw material feeding bin 1 , and an outlet of the raw material feeding bin 1 is connected to an inlet of the drying and crushing device 2 .

[0085] The gas phase inlet of the drying and crushing device 2 is connected to the gas phase outlets of the preheating separation device and the cooling separation unit.

[0086] The preheating and separation device is provided with two stages, namely a first preheating and separation device 3 and a second preheating and separation device 6, and the preheating and separation device is a cyclone preheater.

[0087] The solid phase outlet of the first preheating and separation device 3 is connected to the inlet of the second preheating and separation device 6, and the gas phase outlet of the first preheating and separation device 3 is connected to the dust collector 4 and the powder temporary storage bin 5 in sequence. The outlet of the powder temporary storage bin 5 is divided into two branches, one for external discharge and the other connected to the inlet of the raw material feeding bin 1.

[0088] The solid phase outlet material of the first preheating and separation device 3 is mixed with the outlet gas of the cyclone separation device 7 in the cooling and separation unit and then connected to the inlet of the second preheating and separation device 6. The gas phase outlet of the second preheating and separation device 6 is connected to the gas phase inlet of the drying and crushing device 2. The solid phase outlet of the second preheating and separation device 6 is connected to the feed port of the vertical calcining furnace 8.

[0089] The lower part of the preheating and separating device is conical, and compressed air blowing ports are arranged along the annular circumference of the conical part.

[0090] The aspect ratio of the vertical calcining furnace 8 is 12:1, the height of the tapered section accounts for 33% of the total height of the vertical calcining furnace 8, and the taper of the tapered section is 8 degrees.

[0091] The cone section has six layers of burner nozzles 13, and two adjacent layers of burner nozzles 13 are staggered.

[0092] The number of the burners 13 on each layer is 3, evenly distributed along the circumference;

[0093] The combustion nozzle 13 introduces fuel and air together, and the fuel is natural gas.

[0094] The feed inlet on the conical section is located at the position of the middle layer combustion nozzle 13, and the feed inlet is evenly distributed on the annular circumference and is provided with a spreading box 12 and a spreading plate.

[0095] The interior of the conical section is a fluidized bed structure, and the fluidizing gas inlet is connected to a fluidizing fan 9.

[0096] A cold air inlet is also provided on the side wall between the upper fluidizing gas inlet of the conical section and the bottom layer of the combustion burner 13 , and the cold air inlet is connected to an air inlet fan 10 .

[0097] The number of the cold air inlets is two, which are symmetrically distributed along the circumference.

[0098] Temperature sensors 11 are provided at the middle, upper and top of the upper cylindrical section of the conical section of the vertical calcining furnace 8 .

[0099] The cooling and separation unit includes a cyclone separation device 7 and a cooling and heat exchange device 15. The top outlet of the vertical calcining furnace 8 is connected to the inlet of the cyclone separation device 7. The solid phase outlet of the cyclone separation device 7 is divided into two paths through a three-way valve 14, one of which is connected to the feed port of the vertical calcining furnace 8, and the other is cooled by heat exchange through the cooling and heat exchange device 15 to obtain the finished material.

[0100] The lower part of the cyclone separation device 7 is conical, and a compressed air blowing port is provided along the annular circumference of the conical part.

[0101] The gas phase outlet of the cooling and heat exchanging device 15 is connected to the gas phase inlet of the drying and crushing device 2 .

[0102] A weight valve 16 is provided on the connecting pipelines of the second preheating separation device 6 and the cyclone separation device 7 and the feed port of the vertical calcining furnace 8 .

[0103] Embodiment 2:

[0104] The present embodiment provides a device for preparing type II anhydrous gypsum from phosphogypsum and preventing skinning. The structure of the device refers to the device structure in Example 1, with the following differences: the aspect ratio of the vertical calcining furnace 8 is 16:1, the height of the conical section accounts for 40% of the total height of the vertical calcining furnace 8, and the taper of the conical section is 5 degrees; 8 layers of combustion nozzles 13 are arranged on the conical section, and the number of combustion nozzles 13 on each layer is 2; the number of the cold air inlets is 3.

[0105] Embodiment 3:

[0106] The present embodiment provides a device for preparing type II anhydrous gypsum from phosphogypsum and preventing skinning. The structure of the device refers to the device structure in Example 1, with the difference that: the aspect ratio of the vertical calcining furnace 8 is 8:1, the height of the conical section accounts for 25% of the total height of the vertical calcining furnace 8, and the taper of the conical section is 12 degrees; the conical section is provided with 4 layers of combustion nozzles 13, the number of combustion nozzles 13 on each layer is 4, and the fuel is water gas.

[0107] Embodiment 4:

[0108] This embodiment provides a method for preparing type II anhydrous gypsum from phosphogypsum and preventing skinning, the method is carried out using the device in Example 1, and comprises the following steps:

[0109] (1) crushing the phosphogypsum raw material and preliminarily drying it with airflow, the average particle size after crushing is 60 μm, the temperature of the airflow introduced during the preliminarily drying is 300° C., and then the preliminarily dried raw material and airflow are jointly introduced into a preheating and separation device for two preheating and separations, the solid phase material after the first preheating and separation is mixed with the airflow again and then preheated for the second time, at which time the temperature of the solid phase material is 140° C., the temperature of the airflow used is 650° C., and the temperature of the dry material obtained after the second preheating and separation is 250° C. The dust-containing gas obtained after the first preheating and separation is subjected to dust removal treatment, and the obtained powder is temporarily stored. After inspection and analysis, if the alkali metal content is higher than 1.0%, the powder is discharged, and if the alkali metal content is lower than 0.5%, the powder is re-processed as raw material;

[0110] (2) calcining the dried material obtained in step (1) in a vertical calcining furnace, adding the dried material from the feed port through a spreading box and a spreading plate to evenly disperse the dried material, and igniting and heating the dried material by a multi-layer burner, wherein fuel and air are introduced into the ignited burner, and only air is introduced into the unignited burner as a protective gas, wherein the calcination temperature is 650° C. and the residence time is 6 s. During the calcination, air is introduced from the bottom of the vertical calcining furnace as a fluidizing gas, and cold air is also introduced at the same time, and the cross-sectional airflow velocity at the bottom of the vertical calcining furnace is 7 m / s, thereby obtaining a calcined material;

[0111] (3) The calcined material obtained in step (2) and the gas phase are fed into a cyclone separation device for gas-solid separation, the gas phase is mixed with the solid phase material after the preheating separation, and the solid phase material is divided into two parts, 30% of the solid phase material is returned to step (2) for calcination again, and the other part of the solid phase material is cooled to 50° C. The cooling method is Roots blower fluidization and negative pressure cold air suction, so as to obtain a type II anhydrous gypsum product.

[0112] In this embodiment, the above method is used to treat phosphogypsum, the temperature of the calcination process is controllable, no skinning phenomenon occurs, and the purity of the obtained type II anhydrous gypsum product is 97.01%.

[0113] Embodiment 5:

[0114] This embodiment provides a method for preparing type II anhydrous gypsum from phosphogypsum and preventing skinning, the method is carried out using the device in Example 1, and comprises the following steps:

[0115] (1) crushing the phosphogypsum raw material and preliminarily drying it with airflow, the average particle size after crushing is 74 μm, the temperature of the airflow introduced during the preliminarily drying is 350° C., and then the preliminarily dried raw material and airflow are jointly introduced into a preheating and separation device for two preheating and separations, the solid phase material after the first preheating and separation is mixed with the airflow again and then preheated for the second time, at which time the temperature of the solid phase material is 155° C., the temperature of the airflow used is 750° C., and the temperature of the dry material obtained after the second preheating and separation is 270° C. The dust-containing gas obtained after the first preheating and separation is subjected to dust removal treatment, and the obtained powder is temporarily stored. After inspection and analysis, if the alkali metal content is higher than 0.9%, the powder is discharged, and if the alkali metal content is lower than 0.6%, the powder is re-processed as raw material;

[0116] (2) calcining the dried material obtained in step (1) in a vertical calcining furnace, adding the dried material from the feed inlet through a spreading box and a spreading plate to evenly disperse the dried material, and igniting and heating the dried material by a multi-layer burner, wherein fuel and air are introduced into the ignited burner, and only air is introduced into the unignited burner as a protective gas, wherein the calcination temperature is 850° C. and the residence time is 4 s. During the calcination, air is introduced from the bottom of the vertical calcining furnace as a fluidizing gas, and cold air is also introduced at the same time, and the cross-sectional airflow velocity at the bottom of the vertical calcining furnace is 10 m / s to obtain a calcined material;

[0117] (3) The calcined material obtained in step (2) and the gas phase are sent into a cyclone separation device for gas-solid separation, the gas phase is mixed with the solid phase material after the preheating separation, and the solid phase material is divided into two parts, 10% of the solid phase material is returned to step (2) for calcination again, and the other part of the solid phase material is cooled to 70° C. The cooling method is Roots blower fluidization and negative pressure cold air suction, so as to obtain a type II anhydrous gypsum product.

[0118] In this embodiment, the above method is used to treat phosphogypsum, the temperature of the calcination process is controllable, no skinning phenomenon occurs, and the purity of the obtained type II anhydrous gypsum product reaches 98.34%, and the crystal form is stable.

[0119] Embodiment 6:

[0120] This embodiment provides a method for preparing type II anhydrous gypsum from phosphogypsum and preventing skinning, the method is carried out using the device in Example 1, and comprises the following steps:

[0121] (1) crushing the phosphogypsum raw material and preliminarily drying it with airflow, the average particle size after crushing is 20 μm, the temperature of the airflow introduced during the preliminarily drying is 270° C., and then the preliminarily dried raw material and airflow are jointly introduced into a preheating and separation device for two preheating and separations, the solid phase material after the first preheating and separation is mixed with the airflow again and then preheated for the second time, at which time the temperature of the solid phase material is 120° C., the temperature of the airflow used is 550° C., and the temperature of the dry material obtained after the second preheating and separation is 210° C. The dust-containing gas obtained after the first preheating and separation is subjected to dust removal treatment, and the obtained powder is temporarily stored. After inspection and analysis, if the alkali metal content is higher than 0.95%, the powder is discharged, and if the alkali metal content is lower than 0.55%, the powder is re-processed as raw material;

[0122] (2) calcining the dried material obtained in step (1) in a vertical calcining furnace, adding the dried material from the feed inlet through a spreading box and a spreading plate to evenly disperse the dried material, and igniting and heating the dried material by a multi-layer burner, wherein fuel and air are introduced into the ignited burner, and only air is introduced into the unignited burner as a protective gas, wherein the calcination temperature is 750° C. and the residence time is 5 s. During the calcination, air is introduced from the bottom of the vertical calcining furnace as a fluidizing gas, and cold air is also introduced at the same time, and the cross-sectional airflow velocity at the bottom of the vertical calcining furnace is 9 m / s, thereby obtaining a calcined material;

[0123] (3) The calcined material obtained in step (2) and the gas phase are sent into a cyclone separation device for gas-solid separation, the gas phase is mixed with the solid phase material after the preheating separation, and the solid phase material is divided into two parts, 20% of the solid phase material is returned to step (2) for calcination again, and the other part of the solid phase material is cooled to 60° C. The cooling method is Roots blower fluidization and negative pressure cold air suction, so as to obtain a type II anhydrous gypsum product.

[0124] In this embodiment, the above method is used to treat phosphogypsum, the temperature of the calcination process is controllable, no skinning phenomenon occurs, and the purity of the obtained type II anhydrous gypsum product can reach 98.05%.

[0125] Embodiment 7:

[0126] This embodiment provides a method for preparing type II anhydrous gypsum from phosphogypsum and preventing skinning, the method is carried out using the device in Example 2, and comprises the following steps:

[0127] (1) crushing the phosphogypsum raw material and preliminarily drying it with airflow, the average particle size after crushing is 120 μm, the temperature of the airflow introduced during the preliminarily drying is 400° C., and then the preliminarily dried raw material and airflow are jointly introduced into a preheating and separation device for two preheating and separations, the solid phase material after the first preheating and separation is mixed with the airflow again and then preheated for the second time, at which time the temperature of the solid phase material is 180° C., the temperature of the airflow used is 900° C., and the temperature of the dry material obtained after the second preheating and separation is 300° C. The dust-containing gas obtained after the first preheating and separation is subjected to dust removal treatment, and the obtained powder is temporarily stored. After inspection and analysis, if the alkali metal content is higher than 0.8%, the powder is discharged, and if the alkali metal content is lower than 0.7%, the powder is re-processed as raw material;

[0128] (2) calcining the dried material obtained in step (1) in a vertical calcining furnace, adding the dried material from the feed inlet through a spreading box and a spreading plate to evenly disperse the dried material, and igniting and heating the dried material by a multi-layer burner, wherein fuel and air are introduced into the ignited burner, and only air is introduced into the unignited burner as a protective gas, wherein the calcining temperature is 1000° C. and the residence time is 3 s. During the calcination, air is introduced from the bottom of the vertical calcining furnace as a fluidizing gas, and cold air is also introduced at the same time, and the cross-sectional airflow velocity at the bottom of the vertical calcining furnace is 12 m / s to obtain a calcined material;

[0129] (3) The calcined material obtained in step (2) and the gas phase are sent into a cyclone separation device for gas-solid separation, the gas phase is mixed with the solid phase material after the preheating separation, and the solid phase material is divided into two parts, 40% of the solid phase material is returned to step (2) for calcination again, and the other part of the solid phase material is cooled to 80° C. The cooling method is Roots blower fluidization and negative pressure cold air suction, so as to obtain a type II anhydrous gypsum product.

[0130] In this embodiment, the above method is used to treat phosphogypsum, the temperature of the calcination process is controllable, no skinning phenomenon occurs, and the purity of the obtained type II anhydrous gypsum product can reach 98.19%.

[0131] From the above embodiments, it can be seen that the device of the present invention, through the arrangement of structural units such as preheating and drying, calcination, cooling and separation, first removes moisture through preheating and drying, and uses hot air to take away the components in the raw materials that are prone to crusting in advance, and then through the design of the overall and internal structure of the vertical calcining furnace, accurately controls the temperature to ensure balanced combustion, prevents melting and crusting due to excessive calcination temperature, effectively removes harmful impurities such as fluorine, phosphorus, and organic matter in phosphogypsum, obtains type II anhydrous gypsum with stable crystal form, and ensures product quality; the device has a reasonable structural design, stable operation, energy saving and high efficiency, effectively improves the utilization rate of phosphogypsum, and expands its application market.

[0132] The applicant declares that the present invention uses the above embodiments to illustrate the detailed devices and methods of the present invention, but the present invention is not limited to the above detailed devices and methods, that is, it does not mean that the present invention must rely on the above detailed devices and methods to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of the device of the present invention, addition of auxiliary devices, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A device for preparing type II anhydrous gypsum from phosphogypsum and preventing skinning, characterized in that: The device comprises a preheating and drying unit, a calcining unit and a cooling and separating unit, wherein the preheating and drying unit comprises a drying and crushing device and at least one preheating and separating device, wherein the outlet of the drying and crushing device is connected to the inlet of the preheating and separating device, and the solid phase outlet of the preheating and separating device is connected to the inlet of the calcining unit; The calcining unit comprises a vertical calcining furnace, the lower part of which is conical, the diameter of the conical section gradually decreases from top to bottom, a plurality of feed ports and multi-layer combustion nozzles are arranged on the side wall of the conical section, and a fluidizing gas inlet is arranged at the bottom of the vertical combustion furnace; The solid phase outlet pipeline of the cooling and separation unit is divided into two branches, one is connected to the feed port of the vertical calcining furnace, and the other is the finished product collection pipeline. The gas phase outlet of the cooling and separation unit is connected to the gas phase inlet of the preheating separation device.

2. The device according to claim 1, characterized in that The device further comprises a feeding unit, the feeding unit comprises a raw material feeding bin, and the outlet of the raw material feeding bin is connected to the inlet of the drying and crushing device; Preferably, the gas phase inlet of the drying and crushing device is connected to the gas phase outlet of the preheating separation device and / or the temperature reduction separation unit.

3. The device according to claim 1 or 2, characterized in that: The preheating and separation device is provided with two stages, namely a first preheating and separation device and a second preheating and separation device, and the preheating and separation device comprises a cyclone preheater; Preferably, the solid phase outlet of the first preheating and separation device is connected to the inlet of the second preheating and separation device, the gas phase outlet of the first preheating and separation device is connected to a dust collector and a powder temporary storage bin in sequence, and the outlet of the powder temporary storage bin is divided into two branches, one for external discharge and the other connected to the inlet of the raw material feeding bin; Preferably, the solid phase outlet material of the first preheating and separation device is mixed with the outlet gas phase of the cooling and separation unit and then connected to the inlet of the second preheating and separation device, the gas phase outlet of the second preheating and separation device is connected to the gas phase inlet of the drying and crushing device, and the solid phase outlet of the second preheating and separation device is connected to the feed port of the vertical calcining furnace; Preferably, the lower portion of the preheating and separation device is conical, and compressed air blowing ports are provided along the annular circumference of the conical portion.

4. The device according to any one of claims 1 to 3, characterized in that: The aspect ratio of the vertical calcining furnace is 16:1 to 8:1, and the height of the tapered section accounts for 25 to 40% of the total height of the vertical calcining furnace; Preferably, the taper of the tapered section is 5 to 12 degrees; Preferably, the cone section is provided with 4 to 8 layers of burners, and the burners of two adjacent layers are staggered; Preferably, the number of burners per layer is 2 to 4, evenly distributed along the circumference; Preferably, the combustion nozzle introduces fuel and air together; Preferably, the feed port on the conical section is located between the uppermost and lowermost layers of burners, preferably at the position of the middle layer of burners; Preferably, the feed inlets are evenly distributed on the annular circumference and are provided with a spreading box and / or a spreading plate; Preferably, the interior of the conical section is a fluidized bed structure, and the fluidizing gas inlet is connected to a fan; Preferably, a cold air inlet is provided on the side wall between the upper fluidizing gas inlet of the conical section and the bottom layer of the combustion nozzle, and the cold air inlet is also connected to a fan; Preferably, the number of the cold air inlets is at least two, which are evenly distributed along the circumference, and preferably the two cold air inlets are symmetrically arranged; Preferably, a temperature sensor is provided on the cylindrical section at the upper part of the conical section of the vertical calcining furnace, and preferably, temperature sensors are provided on the middle, upper part and top part of the vertical calcining furnace.

5. The device according to any one of claims 1 to 4, characterized in that: The cooling and separation unit includes a cyclone separation device and a cooling and heat exchange device. The top outlet of the vertical calcining furnace is connected to the inlet of the cyclone separation device. The solid phase outlet of the cyclone separation device is divided into two paths through a three-way valve, one of which is connected to the feed port of the vertical calcining furnace, and the other is connected to the cooling and heat exchange device to obtain the finished material. Preferably, the lower portion of the cyclone separation device is conical, and a compressed air blowing port is provided along the annular circumference of the conical portion; Preferably, the gas phase outlet of the cooling and heat exchanging device is connected to the gas phase inlet of the drying and crushing device; Preferably, the connecting pipelines of the second preheating separation device and the cyclone separation device and the feed inlet of the vertical calcining furnace are all provided with an air locking device, preferably a weight valve.

6. A method for preparing type II anhydrous gypsum and preventing skinning by using the device according to any one of claims 1 to 5, characterized in that: The method comprises the following steps: (1) crushing the phosphogypsum raw material and preliminarily drying it with airflow, and then preheating and separating them together to obtain dry material and dust-containing gas; (2) calcining the dried material obtained in step (1), using multi-point feeding and ignition and heat supply by multi-layer combustion nozzles to obtain calcined material; (3) The solid phase material after gas-solid separation of the calcined material obtained in step (2) is divided into two parts, one part is returned to step (2) for calcination again, and the other part is cooled and heat-exchanged to obtain the finished material.

7. The method according to claim 6, characterized in that The particle size of the phosphogypsum raw material after crushing in step (1) is 0 to 200 μm; Preferably, the temperature of the air flow introduced during the preliminary drying of the phosphogypsum raw material in step (1) is 250-400° C. Preferably, the raw material preliminarily dried in step (1) and the airflow enter the preheating separation device together for preheating separation, and the number of preheating separation is at least once, preferably twice; Preferably, the solid phase material after the primary preheating separation is mixed with the airflow again and then subjected to secondary preheating separation, at which time the temperature of the solid phase material is 100-200° C., and the temperature of the airflow used is 500-900° C.; Preferably, the dust-containing gas obtained after the primary preheating separation is subjected to dust removal treatment, and the obtained powder is temporarily stored. After inspection and analysis, if the alkali metal content is higher than 0.8-1.0%, the powder is discharged, and if the alkali metal content is lower than 0.5-0.8%, the powder is reprocessed as raw material; Preferably, the temperature of the dried material obtained after the secondary preheating and separation is 200-300°C.

8. The method according to claim 6 or 7, characterized in that: The calcination in step (2) is carried out in a vertical calcination furnace, and the feed inlet of the vertical calcination furnace is located on the lower conical section; Preferably, in step (2), the dry material is added from multiple feed ports through a spreading box and / or a spreading plate to evenly disperse the dry material; Preferably, air is locked on the feed pipeline of the vertical calcining furnace, preferably by using a weight valve; Preferably, fuel and air are introduced into the burner that is ignited in step (2), and only air is introduced into the burner that is not ignited as burner protection gas.

9. The method according to any one of claims 6 to 8, characterized in that: The calcination temperature in step (2) is 450-1000° C., preferably 500-800° C.; Preferably, the residence time of the calcination in step (2) is 3 to 6 seconds; Preferably, during the calcination in step (2), fluidizing air is introduced from the bottom of the vertical calcining furnace; Preferably, during the calcination in step (2), cold air is also introduced from the bottom of the vertical calcining furnace for spraying, and the cross-sectional airflow velocity at the bottom of the vertical calcining furnace is 5 to 15 m / s.

10. The method according to any one of claims 6 to 9, characterized in that: Step (2) the calcined material and the gas phase enter a cyclone separation device for gas-solid separation, and the obtained gas phase is mixed with the solid phase material after the primary preheating separation; Preferably, during the preheating separation in step (1) and the gas-solid separation in step (3), the pressure of the lower cone of the preheating separation device and the cyclone separation device is independently -5000 to -400 Pa; Preferably, when the pressure of the lower cone of the preheating separation device and the cyclone separation device reaches -200 to 0Pa, compressed air is used for spraying; Preferably, the solid phase material obtained after the gas-solid separation in step (3) is divided into two parts, of which the proportion of the solid phase material returned to the vertical calcining furnace is 0-60%; Preferably, the solid phase material obtained after the gas-solid separation is cooled to 50-80° C. to obtain a finished type II anhydrous gypsum; Preferably, the solid-phase material is cooled by fan fluidization and negative pressure cold air suction.

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