阅读说明：本技术 一种由磷石膏生产ii型无水石膏的装置及方法 (Device and method for producing II type anhydrous gypsum by using phosphogypsum ) 是由 宋小霞 万建东 彭卓飞 唐永波 唐绍林 陈家伟 刘丽娟 于 2019-11-25 设计创作，主要内容包括：本发明提供了一种由磷石膏生产II型无水石膏的装置及方法,所述装置包括依次连接的预处理单元、干燥单元、煅烧单元和产品收集单元,所述预处理单元包括螺旋搅拌装置,所述干燥单元包括打散装置和至少一级干燥装置,所述煅烧单元包括煅烧装置,煅烧装置内设有热源管道。本发明所述装置通过预处理、干燥及煅烧工艺的结合,将磷石膏精准转化为II型无水石膏,有效去除磷石膏中可溶性磷、氟,实现难溶性磷的转化及有机物的分解,解决了酸的腐蚀问题,降低了有害杂质对石膏制品的影响；所述方法提高了磷石膏的综合利用效率,产品不易水化,可复配超硫酸盐水泥、石膏矿渣水泥或石膏复合胶凝材料,产品性能稳定,强度高,扩大了磷石膏的应用途径。(The invention provides a device and a method for producing II-type anhydrous gypsum by using phosphogypsum, wherein the device comprises a pretreatment unit, a drying unit, a calcining unit and a product collecting unit which are sequentially connected, the pretreatment unit comprises a spiral stirring device, the drying unit comprises a scattering device and at least one stage of drying device, the calcining unit comprises a calcining device, and a heat source pipeline is arranged in the calcining device. According to the device, the phosphogypsum is accurately converted into the type II anhydrous gypsum through the combination of pretreatment, drying and calcining processes, so that soluble phosphorus and fluorine in the phosphogypsum are effectively removed, the conversion of insoluble phosphorus and the decomposition of organic matters are realized, the corrosion problem of acid is solved, and the influence of harmful impurities on gypsum products is reduced; the method improves the comprehensive utilization efficiency of the phosphogypsum, the product is not easy to hydrate, the product can be compounded with super-sulfate cement, gypsum slag cement or gypsum composite cementing material, the product performance is stable, the strength is high, and the application approach of the phosphogypsum is expanded.)

1. The device for producing the II-type anhydrous gypsum from the phosphogypsum is characterized by comprising a pretreatment unit, a drying unit, a calcining unit and a product collecting unit which are sequentially connected, wherein the pretreatment unit comprises a spiral stirring device, the drying unit comprises a scattering device and at least one stage of drying device, the calcining unit comprises a calcining device, and a heat source pipeline is arranged in the calcining device.

2. The apparatus of claim 1, wherein the helical agitator comprises a twin helical agitator having a paddle disposed therein;

preferably, the stirring paddle is of an internal hollow structure;

preferably, heat source gas is introduced into the stirring paddle;

preferably, the upper part of the spiral stirring device is provided with a moisture discharging port;

preferably, the lower part of the spiral stirring device is also provided with an air supplementing opening;

preferably, the pretreatment unit further comprises a first induced draft fan, and an inlet of the first induced draft fan is connected with a moisture discharging port of the spiral stirring device.

3. The apparatus of claim 1 or 2, wherein the breaking apparatus comprises a drying breaker;

preferably, the drying means comprises a cyclonic dryer;

preferably, the number of stages of the drying device is 2-5;

preferably, the last stage drying device is a pre-calcining device;

preferably, the gas outlet of the drying unit is connected with a stirring paddle of a spiral stirring device;

preferably, the calcining apparatus comprises a rotary calciner;

preferably, the calcining device inclines downwards from the inlet to the outlet, and the inclination is 1-4%;

preferably, the heat source pipeline is a fuel pipeline or a hot air pipeline;

preferably, the calcining unit further comprises a feeder, a discharger and a temperature control device, wherein the feeder is arranged at the inlet of the calcining device, the discharger is arranged at the outlet of the calcining device, and the temperature control device is arranged at the inlet of the discharger;

preferably, the product collection unit comprises a bucket elevator and a finished product bin which are connected in sequence.

4. The apparatus according to any one of claims 1 to 3, further comprising a feeding unit, an outlet of the feeding unit being connected to an inlet of the helical stirring device;

preferably, the feeding unit comprises a phosphogypsum storage device, a phosphogypsum conveying device, an additive storage device and an additive feeding device, inlets of the phosphogypsum storage device, the phosphogypsum conveying device and the spiral stirring device are sequentially connected, and inlets of the additive storage device, the additive feeding device and the spiral stirring device are also sequentially connected.

5. The apparatus according to any one of claims 1 to 4, further comprising a cooling unit disposed between the calcining unit and the product collecting unit;

preferably, the cooling unit comprises a cooler, a first air blower, a dust collector and a product conveying device, an outlet of the calcining device is connected with an inlet of the cooler, an outlet of the first air blower is connected with an inlet of the cooler, a gas outlet of the cooler is connected with an inlet of the dust collector, a solid outlet of the cooler and a solid outlet of the dust collector are both connected with the product conveying device, and the product conveying device is connected with the product collecting unit;

preferably, the product conveying means comprises a screw conveyor;

preferably, the device further comprises a dust removal unit, the dust removal unit comprises a dust remover and a second induced draft fan, an inlet of the dust remover is connected with a gas outlet of a dust collector of the cooling unit and a gas outlet of the product collection unit, a solid outlet of the dust remover is connected with an inlet of the product collection unit, and a gas outlet of the dust remover is connected with the second induced draft fan;

preferably, the device further comprises a heat supply unit, the heat supply unit comprises a hot blast stove, and a gas outlet of the hot blast stove is connected with gas inlets of the drying unit and the calcining unit;

preferably, the heat supply unit further comprises a gas preheater and a second air blower, wherein the inlet of the gas preheater is connected with the outlet of the second draught fan, and the outlet of the gas preheater is connected with the inlet of the hot blast stove through the second air blower.

6. A method for producing type II anhydrite using the apparatus as set forth in any one of claims 1 to 5, characterized in that the method comprises the steps of:

(1) mixing the phosphogypsum and an additive, reacting, scattering and drying to obtain III type anhydrous gypsum;

(2) and (2) indirectly calcining the III type anhydrous gypsum obtained in the step (1) in a heat exchange mode to obtain II type anhydrous gypsum.

7. The method according to claim 6, wherein the phosphogypsum of step (1) is a by-product of a sulphuric acid process phosphoric acid production process;

preferably, the phosphogypsum of step (1) contains phosphoric acid, phosphate, fluoride and free water;

preferably, the content of the phosphoric acid meets the condition that the pH value is 1-5, and the content of free water accounts for 10-30 wt% of the total amount of the phosphogypsum;

preferably, the additive in step (1) comprises any one or a combination of at least two of calcium oxide, calcium hydroxide or calcium carbonate;

preferably, the mass ratio of the phosphogypsum to the additive in the step (1) is (150-34100): 1;

preferably, the mixing and reacting of step (1) are carried out in a helical stirring device;

preferably, the temperature of the reaction in the step (1) is 20-60 ℃;

preferably, after the scattering in the step (1), the average particle size of the raw material is 20-50 μm;

preferably, the drying grade in the step (1) is 2-5 grades;

preferably, the temperature of the next stage drying is higher than that of the previous stage drying;

preferably, the temperature of the final stage of drying is 250-400 ℃;

preferably, heat source gas is introduced in the scattering and drying process in the step (1).

8. The method according to claim 6 or 7, wherein the type III anhydrite of step (2) is indirectly calcined by a hot source gas;

preferably, the calcination treatment in the step (2) is carried out in a calcination device, and a heat source pipeline is arranged in the calcination device;

preferably, the temperature of the calcination treatment in the step (2) is 300-750 ℃, preferably 400-650 ℃;

preferably, the time of the calcination treatment in the step (2) is 20-50 min;

preferably, the heat source gas for the scattering, drying and calcining in the step (1) comes from a heat supply unit.

9. The method according to any one of claims 6 to 8, wherein the calcination treatment of step (2) is followed by a cooling treatment;

preferably, the cooling treatment is: introducing gas to cool the calcined product, then carrying out gas-solid separation, collecting the obtained solid product, and carrying out dust removal treatment on the obtained gas;

preferably, the temperature of the solid obtained after the gas-solid separation is reduced to below 100 ℃;

preferably, the gas after dust removal treatment enters a heat supply unit for generating hot source gas;

preferably, the heat supply unit generates a heat source gas by combustion of coal or natural gas;

preferably, the type II anhydrous gypsum of step (2) is used as a raw material for super sulfate cement, gypsum slag cement or gypsum composite cementitious material.

10. Method according to any of claims 6-9, characterized in that the method comprises the steps of:

(1) mixing phosphogypsum and an additive and reacting, wherein the additive comprises any one or a combination of at least two of calcium oxide, calcium hydroxide and calcium carbonate, the mass ratio of the phosphogypsum to the additive is (150-34100): 1, and the reaction temperature is 20-60 ℃;

(2) scattering and drying the product obtained in the step (1), wherein the average particle size of the scattered raw material is 20-50 microns, the number of drying stages is 2-5, the temperature of the next drying stage is higher than that of the previous drying stage, the temperature of the last drying stage is 250-400 ℃, and III type anhydrous gypsum is obtained, and heat source gas is introduced in the scattering and drying processes;

(3) indirectly calcining the III-type anhydrous gypsum obtained in the step (2) in a heat exchange mode through hot source gas, wherein the calcining temperature is 300-750 ℃, and the calcining time is 20-50 min;

(4) cooling the calcined product in the step (3) by using gas, then carrying out gas-solid separation, cooling the obtained solid to be below 100 ℃, and recovering the product to obtain II type anhydrous gypsum, wherein the II type anhydrous gypsum is used as a raw material of super-sulfate cement, gypsum slag cement or a gypsum composite cementing material; and (4) carrying out dust removal treatment on the gas obtained by gas-solid separation, and enabling the gas after dust removal treatment to enter a heat supply unit for generating heat source gas.

Technical Field

The invention belongs to the technical field of solid waste utilization, and relates to a device and a method for producing II-type anhydrous gypsum by using phosphogypsum.

Background

Phosphoric acid is an important industrial product, the production of the phosphoric acid is mainly carried out by a sulfuric acid method wet process, the by-product of the method is mainly phosphogypsum, about 7 tons of phosphogypsum containing 20 percent of free water is generated per 1 ton of phosphoric acid, the yield of the by-product is extremely high, a large storage space is occupied, and the peripheral environment is seriously polluted, so that the phosphogypsum is indispensable for recycling and resource utilization. However, due to the main and side reactions of phosphate ore and sulfuric acid, and the addition of additives during the beneficiation process, the impurities in the byproduct phosphogypsum are complex in type and wide in concentration range, which can seriously affect the performance of the prepared gypsum cementing material, limit the wide utilization of the phosphogypsum and cause the low comprehensive utilization rate of the phosphogypsum, so that the phosphogypsum needs to be subjected to impurity removal to reduce the harm of harmful impurities to the product strength and the application environment.

At present, the impurity removal mode of the phosphogypsum mainly comprises a water washing method, a neutralization method, a flotation method, an acid leaching method or the combination of the methods, but only soluble impurities can be removed, the impurity removal is insufficient, the water consumption is large, and the generated wastewater is easy to cause secondary pollution. Because of the existence of harmful impurities, the phosphogypsum which is not fully purified cannot be independently used as a gypsum raw material for a cement retarder, a road building filler and building gypsum powder, and a certain amount of natural gypsum or desulfurized gypsum is required to be added for compounding to realize product indexes, so that the comprehensive utilization rate of the phosphogypsum is low, the building material prepared from the phosphogypsum can only be used for a surface layer or decoration, cannot be applied to a main structure material, is limited by the application range, has the annual comprehensive utilization amplitude which is far lower than the annual production, and has the dosage which is far lower than the cement used for the main material. Therefore, the phosphogypsum needs to be converted to replace the traditional cement, so that the industrial byproduct gypsum can be digested in a large amount, and the environmental protection problem is solved.

CN 109553372A discloses a preparation and use method of a recyclable phosphogypsum roadbed material, which comprises the steps of adding phosphogypsum with a free water content of 7-20% into a saturated calcium hydroxide solution for neutralization reaction to obtain phosphogypsum with soluble phosphate radicals and fluoride ions removed, then carrying out high-temperature calcination at the temperature of 170-350 ℃ to convert dihydrate gypsum into III-type anhydrous gypsum, and mixing the prepared III-type anhydrous gypsum with water, a water reducing agent and a waterproof agent to prepare the phosphogypsum roadbed material.

CN 105985036A discloses a method for processing phosphogypsum, which comprises the steps of mixing phosphogypsum and lime, adding the mixture into a drying and calcining machine, arranging a flame-throwing furnace at the end part, enabling the temperature of a flame-throwing port to be higher than 800 ℃, enabling a grading outlet to be adopted at an outlet of the drying and calcining machine to respectively obtain semi-hydrated gypsum and anhydrous gypsum II, sending the outlet gypsum into a stirring, homogenizing, reducing and conveying device to enable the mixed gypsum to be fully contacted with air, distributing the gypsum in different forms, sending qualified gypsum into a gypsum crystal structure conversion device to perform crystal conversion to obtain finished gypsum, wherein the drying and calcining machine cannot accurately control a calcining process, needs to be provided with the grading outlet, and then performs mixing and aging to produce β type gypsum powder, and arranging the drying and calcining machine with the flame-throwing furnace to difficultly control calcining time and cause great product fluctuation.

At present, because the super-sulfate cement has the characteristics of low hydration heat, sulfate corrosion resistance and good frost resistance, the super-sulfate cement can effectively replace the traditional cement, the application range is continuously expanded, the main component of the super-sulfate cement comprises gypsum, wherein the effect of II type anhydrous gypsum is optimal, so that a method for accurately preparing the II type anhydrous gypsum by the phosphogypsum is necessarily sought, the influence of impurities in the phosphogypsum needs to be solved, and the resource utilization rate of the phosphogypsum is improved.

Disclosure of Invention

Aiming at the problems in the prior art, the invention aims to provide a device and a method for producing II type anhydrous gypsum by using phosphogypsum, wherein the device takes an industrial by-product phosphogypsum as a raw material, can effectively solve the problem of excessive acid in the phosphogypsum through pretreatment, drying and calcining processes, simultaneously removes soluble phosphorus and fluorine, converts eutectic phosphorus and insoluble phosphorus, eliminates the influence of impurities on gypsum products, and has stable quality of the obtained products; meanwhile, the invention is also assisted with cooling, waste heat recovery, dust removal and other processes, so that the phosphogypsum has high treatment capacity and comprehensive utilization degree, is energy-saving and environment-friendly, and does not generate secondary pollution.

In order to achieve the purpose, the invention adopts the following technical scheme:

on one hand, the invention provides a device for producing II-type anhydrous gypsum by using phosphogypsum, which comprises a pretreatment unit, a drying unit, a calcining unit and a product collecting unit which are sequentially connected, wherein the pretreatment unit comprises a spiral stirring device, the drying unit comprises a scattering device and at least one stage of drying device, the calcining unit comprises a calcining device, and a heat source pipeline is arranged in the calcining device.

According to the invention, the device uses industrial byproduct phosphogypsum as a raw material to produce II type anhydrous gypsum, acid, soluble phosphorus and soluble fluorine in the phosphogypsum are removed through reaction in a pretreatment unit, free water and most of bound water in the phosphogypsum are fully removed in a drying unit, and insoluble phosphorus such as calcium phosphate and eutectic phosphorus thereof in the phosphogypsum is converted into pyrophosphate through a calcining unit, so that the strength of a gypsum product is not influenced, organic matters possibly existing are decomposed, and the influence of impurities on subsequent gypsum products is reduced; the II type anhydrous gypsum is generated through the processes of pretreatment, drying and calcination, particularly the calcination process of the gypsum is accurately controlled, the quality is stable, the hydration and the condensation are difficult, the super-sulfate cement prepared from the raw material has stable product performance and high strength, and the resource utilization rate of the phosphogypsum is improved.

The following technical solutions are preferred technical solutions of the present invention, but not limited to the technical solutions provided by the present invention, and technical objects and advantageous effects of the present invention can be better achieved and achieved by the following technical solutions.

As a preferable technical scheme, the spiral stirring device comprises a double-spiral stirrer, and a stirring paddle is arranged in the double-spiral stirrer.

Preferably, the stirring paddle is of an internal hollow structure.

Preferably, the stirring paddle is internally filled with heat source gas.

In the invention, the stirring paddle of the double-helix stirrer is arranged into a hollow structure, and heat source gas is introduced to maintain the reaction temperature and assist in drying, wherein the heat source gas is gas discharged by the drying unit.

Preferably, the upper part of the spiral stirring device is provided with a moisture discharging port, and free water can leave from the moisture discharging port after being changed into water vapor in the pretreatment process.

Preferably, the lower part of the spiral stirring device is also provided with an air supplementing opening, and a small amount of hot air can be introduced to assist in moisture removal.

Preferably, the pretreatment unit further comprises a first induced draft fan, and an inlet of the first induced draft fan is connected with a moisture discharging port of the spiral stirring device.

As the preferable technical scheme of the invention, the scattering device comprises a drying scattering machine, namely, the pretreated raw materials are scattered and crushed before formal drying, so that drying and dehydration are facilitated.

Preferably, the drying means comprises a cyclonic dryer.

Preferably, the number of the drying devices is 2-5, such as 2, 3, 4 or 5, the number of the drying devices is selected to be changed along with the content of free water in the phosphogypsum, and the higher the content of the free water is, the more the number of the drying devices is required; and a step drying mode is adopted, and the temperature gradient of the heat source gas is reasonably utilized.

Preferably, the final stage drying device is a precalcination device.

In the invention, the outlet heat source gas of a lower-level drying device in a multi-level drying device is used as the inlet heat source gas of a higher-level drying device to carry out multi-level countercurrent drying; the drying scattering machine also needs to be introduced with hot source gas to take out scattered raw materials, and can also be used as a drying device to function, after gas-solid separation, the solid raw materials enter a subsequent drying device, and the gas enters a pretreatment unit.

Preferably, the gas outlet of the drying unit is connected with a stirring paddle of the spiral stirring device.

Preferably, the calcining apparatus comprises a rotary calciner.

Preferably, the calcining device is inclined downwardly from the inlet to the outlet at a slope of 1-4%, such as 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, or 4%, but not limited to the recited values, and other values not recited within the range are equally applicable.

In the invention, the calculation of the inclination refers to the ratio of the height difference between the inlet and the outlet of the calcining device to the length of the calcining device, and the certain inclination can ensure that the raw materials slowly move in the calcining reaction process and is convenient for controlling the retention time.

Preferably, the heat source pipeline is a fuel pipeline or a hot air pipeline.

In the invention, the heat source pipeline is arranged to isolate the phosphogypsum from a heat source, and the powdery material is not easy to be lifted by calcining the gypsum in a heat exchange mode, so that the calcining process and the retention time are easy to accurately control, and the type of a calcined product is ensured.

Preferably, the calcining unit further comprises a feeder, a discharger and a temperature control device, wherein the feeder is arranged at the inlet of the calcining device, the discharger is arranged at the outlet of the calcining device, and the temperature control device is arranged at the inlet of the discharger.

Preferably, the product collection unit comprises a bucket elevator and a finished product bin which are connected in sequence.

As a preferable technical scheme, the device also comprises a feeding unit, and an outlet of the feeding unit is connected with an inlet of the spiral stirring device.

Preferably, the feeding unit comprises a phosphogypsum storage device, a phosphogypsum conveying device, an additive storage device and an additive feeding device, inlets of the phosphogypsum storage device, the phosphogypsum conveying device and the spiral stirring device are sequentially connected, and inlets of the additive storage device, the additive feeding device and the spiral stirring device are also sequentially connected.

In the invention, the phosphogypsum and the additive are fed respectively, and the feeding amount of the phosphogypsum and the additive is controlled, the phosphogypsum conveying device can adopt a belt weighing machine, the additive feeding device can adopt a quantitative feeder, and a dust collecting device is arranged, so that dust diffusion is avoided.

As a preferable technical solution of the present invention, the apparatus further comprises a cooling unit disposed between the calcining unit and the product collecting unit.

Preferably, the cooling unit comprises a cooler, a first air blower, a dust collector and a product conveying device, an outlet of the calcining device is connected with an inlet of the cooler, an outlet of the first air blower is connected with an inlet of the cooler, a gas outlet of the cooler is connected with an inlet of the dust collector, a solid outlet of the cooler and a solid outlet of the dust collector are both connected with the product conveying device, and the product conveying device is connected with the product collecting unit.

Preferably, the product conveying means comprises a screw conveyor.

Preferably, the device still includes the dust removal unit, the dust removal unit includes dust remover and second draught fan, the entry of dust remover links to each other with the gas outlet of cooling unit's dust collector and the gas outlet of product collection unit, the solid export of dust remover links to each other with the entry of product collection unit, the gas outlet of dust remover links to each other with the second draught fan.

Preferably, the device further comprises a heat supply unit, the heat supply unit comprises a hot blast stove, and a gas outlet of the hot blast stove is connected with gas inlets of the drying unit and the calcining unit.

In the invention, the hot blast stove uses coal or natural gas as raw materials to burn, obtains hot air with required temperature as heat source gas of the drying unit and the calcining unit after dedusting, and obtains the temperature and air volume required by each unit by controlling the amount of the heat source gas and mixing with other supplementary air due to different temperatures of the heat source gas required by the drying unit and the calcining unit.

Preferably, the heat supply unit further comprises a gas preheater and a second air blower, wherein the inlet of the gas preheater is connected with the outlet of the second draught fan, and the outlet of the gas preheater is connected with the inlet of the hot blast stove through the second air blower.

In another aspect, the present invention provides a method for producing type II anhydrite using the above apparatus, the method comprising the steps of:

(1) mixing the phosphogypsum and an additive, reacting, scattering and drying to obtain III type anhydrous gypsum;

(2) and (2) indirectly calcining the III type anhydrous gypsum obtained in the step (1) in a heat exchange mode to obtain II type anhydrous gypsum.

As a preferable technical scheme of the invention, the phosphogypsum in the step (1) is a byproduct of a sulfuric acid method phosphoric acid production process.

Preferably, the phosphogypsum of step (1) contains phosphoric acid, phosphate, fluoride and free water.

Preferably, the phosphoric acid is present in an amount such that the pH is 1 to 5, e.g., 1, 1.5, 2, 2.5, 3, 3.5, or 4, but not limited to the recited values, and other values not recited within the range of values are equally applicable; the amount of free water is 10-30 wt% of the total amount of phosphogypsum, such as 10 wt%, 15 wt%, 20 wt%, 25 wt% or 30 wt%, but is not limited to the recited values, and other values not recited within this range are equally applicable.

Preferably, the additive of step (1) comprises any one or a combination of at least two of calcium oxide, calcium hydroxide or calcium carbonate, typical but non-limiting examples of which are: combinations of calcium oxide and calcium hydroxide, calcium hydroxide and calcium carbonate, calcium oxide, calcium hydroxide and calcium carbonate, and the like.

Preferably, the mass ratio of the phosphogypsum and the additive in the step (1) is (150-34100): 1, such as 150:1, 200:1, 400:1, 600:1, 1000:1, 2500:1, 5000:1, 10000:1, 17800 or 34100, but the invention is not limited to the enumerated values, and other non-enumerated values in the numerical range are also applicable.

In the invention, the selection of the addition amount of the additive is related to the contents of acid, soluble phosphorus and fluorine in the phosphogypsum, and the dosage of the additive is determined according to the molar ratio of hydrogen ions, the soluble phosphorus and the fluorine to the additive during reaction; the greater the pH, the less soluble phosphorus, fluorine and the less additives are required.

Preferably, the mixing and reacting of step (1) are carried out in a helical stirring device.

Preferably, the reaction temperature in step (1) is 20 to 60 ℃, for example 20 ℃, 25 ℃, 30 ℃, 35 ℃, 40 ℃, 45 ℃, 50 ℃, 55 ℃ or 60 ℃, but not limited to the recited values, and other values not recited in the range of the values are also applicable.

Preferably, after the breaking in step (1), the average particle size of the raw material is 20 to 50 μm, for example 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm or 50 μm, but is not limited to the recited values, and other values not recited in the range of the values are also applicable.

In the invention, the scattered raw material meets the requirement that the screen allowance after passing through a square-hole screen of 0.2mm is less than 6 percent besides the limit condition of the average particle size.

Preferably, the number of drying stages in step (1) is 2-5, such as 2, 3, 4 or 5, and the number of drying devices is selected according to the content of free water in the phosphogypsum, the drying temperature, the capacity of each stage of drying device and the like.

Preferably, the temperature of the next stage drying is higher than that of the previous stage drying.

Preferably, the temperature of the final stage drying is 250 to 400 ℃, for example 250 ℃, 270 ℃, 300 ℃, 320 ℃, 350 ℃, 380 ℃ or 400 ℃, but not limited to the recited values, and other values not recited in the range of the values are also applicable.

Preferably, heat source gas is introduced in the scattering and drying process in the step (1).

As a preferable technical scheme of the invention, the type III anhydrous gypsum in the step (2) is indirectly calcined by hot source gas.

Preferably, the calcination treatment in step (2) is performed in a calcination device, and a heat source pipeline is arranged in the calcination device.

Preferably, the temperature of the calcination treatment in step (2) is 300 to 750 ℃, for example 300 ℃, 350 ℃, 400 ℃, 450 ℃, 500 ℃, 560 ℃, 600 ℃, 650 ℃, 700 ℃ or 750 ℃, but is not limited to the recited values, and other values not recited in the range of the values are also applicable, preferably 400 to 650 ℃.

Preferably, the time of the calcination treatment in step (2) is 20-50 min, such as 20min, 25min, 30min, 35min, 40min, 45min or 50min, but not limited to the recited values, and other values not recited in the range of the recited values are also applicable.

In the invention, the calcining temperature and time are accurately controlled, so that the gypsum can be converted into II-type anhydrous gypsum which is difficult to hydrate and coagulate, and industrial by-product gypsum is subjected to reduction and harmless treatment and is used as a raw material for further utilization.

Preferably, the heat source gas for the scattering, drying and calcining in the step (1) comes from a heat supply unit.

As a preferable embodiment of the present invention, the calcination treatment in the step (2) is followed by cooling treatment.

Preferably, the cooling treatment is: and introducing gas to cool the calcined product, then carrying out gas-solid separation, collecting the obtained solid product, and carrying out dust removal treatment on the obtained gas.

Preferably, the temperature of the solid obtained after the gas-solid separation has been reduced to below 100 ℃, for example 100 ℃, 90 ℃, 80 ℃, 70 ℃, 60 ℃, 50 ℃ or 40 ℃ and the like, but is not limited to the recited values, and other values not recited in this range of values are equally applicable.

Preferably, the gas after dust removal treatment enters a heat supply unit for generating hot source gas.

Preferably, the heat supply unit generates the heat source gas by combustion of coal or natural gas.

Preferably, the type II anhydrous gypsum of step (2) is used as a raw material for super sulfate cement, gypsum slag cement or gypsum composite cementitious material.

As a preferred technical scheme of the invention, the method comprises the following steps:

(1) mixing phosphogypsum and an additive and reacting, wherein the additive comprises any one or a combination of at least two of calcium oxide, calcium hydroxide or calcium carbonate, the mass ratio of the phosphogypsum to the additive is (150-34100): 1, and the reaction temperature is 20-60 ℃;

(2) scattering and drying the product obtained in the step (1), wherein the average particle size of the scattered raw material is 20-50 microns, the number of drying stages is 2-5, the temperature of the next drying stage is higher than that of the previous drying stage, the temperature of the last drying stage is 250-400 ℃, and III type anhydrous gypsum is obtained, and heat source gas is introduced in the scattering and drying processes;

(3) indirectly calcining the III-type anhydrous gypsum obtained in the step (2) in a heat exchange mode through hot source gas, wherein the calcining temperature is 300-750 ℃, and the calcining time is 20-50 min;

(4) cooling the calcined product in the step (3) by using gas, then carrying out gas-solid separation, cooling the obtained solid to be below 100 ℃, and recovering the product to obtain II type anhydrous gypsum, wherein the II type anhydrous gypsum is used as a raw material of super-sulfate cement, gypsum slag cement or a gypsum composite cementing material; and (4) carrying out dust removal treatment on the gas obtained by gas-solid separation, and enabling the gas after dust removal treatment to enter a heat supply unit for generating heat source gas.

Compared with the prior art, the invention has the following beneficial effects:

(1) according to the device, the phosphogypsum is accurately converted into the II-type anhydrous gypsum through the combination of pretreatment, drying and calcining processes, so that soluble phosphorus and fluorine in the phosphogypsum can be effectively removed, the removal rate reaches more than 91%, the conversion of eutectic phosphorus and insoluble phosphorus and the decomposition of organic matters are realized, the problem of corrosion of excessive acid to equipment is effectively solved, and the influence of harmful impurities on gypsum products is greatly reduced;

(2) the invention combines the cooling, waste heat recovery, dust removal and other processes with the main process, improves the comprehensive utilization efficiency of the phosphogypsum, has the waste heat recovery rate of 65-88 percent, and does not bring the problems of dust pollution, tail gas pollution and the like;

(3) the device improves the productivity of producing II type anhydrous gypsum by using the phosphogypsum and further compounding the anhydrous gypsum with super-sulfate cement, has stable product performance and high strength, can replace the traditional cement, and enlarges the application approach of the phosphogypsum.

Drawings

FIG. 1 is a schematic structural connection diagram of a device for producing type II anhydrous gypsum from phosphogypsum, which is provided by specific example 1 of the invention;

wherein, 1-a feeding unit, 11-a phosphogypsum storage device, 12-a phosphogypsum conveying device, 13-an additive storage device, 14-an additive feeding device, 2-a pretreatment unit, 21-a spiral stirring device, 22-a first induced draft fan, 3-a drying unit, 31-a scattering device, 32-a first-level drying device, 33-a second-level drying device, 34-a third-level drying device, 35-a fourth-level drying device, 36-a dust collecting device, 37-an intermediate product conveying device, 4-a calcining unit, 41-a feeder, 42-a calcining device, 43-a discharging device, 44-a temperature control device, 5-a cooling unit, 51-a cooler, 52-a first air blower, 53-a dust collector and 54-a product conveying device, 6-dust removal unit, 61-dust remover, 62-second induced draft fan, 7-heat supply unit, 71-hot blast furnace, 72-gas preheater, 73-second blower, 8-product collection unit, 81-bucket elevator, 82-finished product bin.

Detailed Description

In order to better illustrate the present invention and facilitate the understanding of the technical solutions of the present invention, the following embodiments are only simple examples of the present invention and do not represent or limit the scope of the present invention, which is defined by the claims.

The device comprises a pretreatment unit 2, a drying unit 3, a calcining unit 4 and a product collecting unit 8 which are sequentially connected, wherein the pretreatment unit 2 comprises a spiral stirring device 21, the drying unit 3 comprises a scattering device 31 and at least one stage of drying device, the calcining unit 4 comprises a calcining device 42, and a heat source pipeline is arranged in the calcining device 42.

The method comprises the following steps:

(1) mixing the phosphogypsum and an additive, reacting, scattering and drying to obtain III type anhydrous gypsum;

(2) and (2) indirectly calcining the III type anhydrous gypsum obtained in the step (1) in a heat exchange mode to obtain II type anhydrous gypsum.

The following are typical but non-limiting examples of the invention: