Method for preparing alpha-semi-hydrated gypsum from desulfurized gypsum

Abstract

The invention provides a method for preparing alpha-semi-hydrated gypsum by using desulfurized gypsum, which comprises the following steps: mixing desulfurized gypsum with salt-making discharged mother liquor, and introducing air, so that calcium carbonate and calcium chloride in the desulfurized gypsum react with the discharged mother liquor to generate calcium sulfate, and meanwhile, oxidizing calcium sulfite into calcium sulfate. After a period of time, putting into a still kettle, adding a certain amount of crystal modifier, and uniformly stirring; and after the reaction is finished, immediately filtering and drying, and grinding to obtain the alpha-semi-hydrated gypsum. According to the method for preparing the alpha-semi-hydrated gypsum from the desulfurized gypsum, provided by the invention, the conversion rate of the desulfurized gypsum to the alpha-semi-hydrated gypsum can be increased, the requirements of green economy are met, and great economic and environment-friendly benefits are achieved.

Description

Technical Field

[0001] The present invention relates to the field of hemihydrate gypsum production, in particular to a method for preparing alpha-hemihydrate gypsum by utilizing desulfurized gypsum. Background Art

[0002] In industrial production, desulfurization gypsum, a byproduct of flue gas desulfurization in coal-fired power plants and steelmaking, is produced in significant quantities and is growing annually. Desulfurization gypsum, primarily composed of calcium sulfate dihydrate, also contains impurities such as calcium carbonate and calcium chloride. These impurities limit its high-value utilization. The effective treatment and utilization of this desulfurization gypsum has become a key issue in environmental protection and resource recycling.

[0003] Traditionally, desulfurized gypsum has been disposed of by stacking or simply processing it for use as a building material, such as a cement retarder or gypsum board raw material. However, these applications offer low added value and fail to fully realize the potential of desulfurized gypsum. With the increasing demand for high-quality gypsum in the building materials industry, particularly α-hemihydrate gypsum, which has attracted widespread attention due to its excellent physical properties, processing characteristics, and environmental friendliness, the conversion of desulfurized gypsum to α-hemihydrate gypsum has become a research hotspot.

[0004] On the other hand, the mother liquor produced by the salt production industry contains high concentrations of sulfate ions and sodium chloride. Direct discharge not only pollutes the environment but also wastes its useful components. How to effectively utilize this mother liquor is also a pressing issue in the fields of environmental protection and resource recycling. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for preparing α-hemihydrate gypsum using desulfurized gypsum, so as to solve the treatment problem of desulfurized gypsum and salt production effluent mother liquor, and realize the recycling of resources and the high value of products.

[0006] To achieve the above object, the technical solution adopted by the present invention is: to provide a method for preparing α-hemihydrate gypsum using desulfurized gypsum, the method for preparing α-hemihydrate gypsum using desulfurized gypsum comprising the following steps:

[0007] S1. After mixing desulfurized gypsum and salt production exhaust mother liquor in a reactor, air is introduced to react calcium carbonate and calcium chloride in the desulfurized gypsum with the exhaust mother liquor to form calcium sulfate, while simultaneously oxidizing calcium sulfite to form calcium sulfate;

[0008] S2. Add the liquid obtained in the above step into an autoclave, add a certain amount of a crystal-transforming agent into the autoclave, and stir evenly;

[0009] S3, after the reaction is completed, the material obtained in the autoclave is filtered;

[0010] S4. Drying the filtered solid material, and then grinding it to obtain α-hemihydrate gypsum.

[0011] In one embodiment, in step S1, when desulfurized gypsum is mixed with the mother liquor discharged from salt production, the calcium ion content of calcium carbonate and calcium chloride in the desulfurized gypsum and the sulfate content in the mother liquor are calculated as follows: 1t desulfurized gypsum and 2.5m 3 -5.0m 3 Mix the mother liquor discharged from salt production; while mixing, introduce 0.1-0.5m 3 / h of air to oxidize the calcium sulfite in the desulfurization gypsum and remove the impurity components of the desulfurization gypsum; the reaction time is 1-2h.

[0012] In one embodiment, the crystal-changing agent is a mixed solution of hydrochloric acid and citric acid, and the mass ratio of hydrochloric acid to citric acid is 7:3; wherein, the added amount of hydrochloric acid and citric acid is 0.01-0.05wt% of the dry weight of desulfurized gypsum.

[0013] In one embodiment, the autoclave has the following autoclave conditions: temperature 130-150° C., pressure 1.3-1.5 MPa, and autoclave time 5-8 h.

[0014] In one embodiment, in step S4, a steam tube bundle dryer is used for drying, and the drying temperature is greater than 110°C.

[0015] In one embodiment, part of the filtrate obtained by filtration in step S3 is refluxed into the reactor through a pipeline.

[0016] In one embodiment, steps S3 and S4 are completed using a continuous filtering, drying and grinding device, which includes: a housing, a belt filter unit, a drying unit, and a grinding unit;

[0017] A chamber is provided in the shell, a feed pipe is provided on the top of the shell, a liquid storage tank is provided on one side of the bottom of the shell, the feed pipe is connected to the output end of the autoclave, and the material to be filtered is input into the chamber of the shell through the feed pipe;

[0018] The belt filter is arranged in the chamber of the shell, and is used to filter the material entering the chamber of the shell, and transport the filtered solid material to the drying part, and the filtrate falls into the liquid storage tank below;

[0019] A drying section, which is provided on one side of the belt filter section and dries the solid material;

[0020] The grinding part is arranged below the drying part and is used to grind the solid material after the drying process.

[0021] In one embodiment, the belt filter unit comprises:

[0022] A driving roller and a tensioning roller, wherein the driving roller and the tensioning roller are rotatably disposed in the housing;

[0023] a first rotating power unit, the first rotating power unit being mounted on the housing, and a power output end of the first rotating power unit being connected to the driving roller;

[0024] A filter conveyor belt, the filter conveyor belt is installed on the driving roller and the tensioning roller, and the filter conveyor belt is provided with filter holes;

[0025] Baffles are provided on both sides of the filter conveyor belt.

[0026] In one embodiment, the drying section comprises:

[0027] a first wind blade, the first wind blade being disposed above the downstream end of the belt filter section, the wind direction of the first wind blade being opposite to the conveying direction of the belt filter section;

[0028] a second wind blade, the second wind blade being disposed below the downstream end of the belt filter portion;

[0029] a drying plate, the drying plate being arranged obliquely below the second wind blade, the drying plate being hollow, and being provided with a heat source input port and a heat source output port, through which an external heat source is input into the drying plate, and the heat source output port being connected to the first wind blade and the second wind blade via a pipe;

[0030] The solid material is transported by the belt filter and then falls onto the drying plate.

[0031] In one embodiment, the grinding section includes a second rotating power section, a grinding blade shaft, a filter screen and an aggregate shell; the aggregate shell is arranged at the bottom of the drying section; the filter screen is arranged in the aggregate shell, the grinding blade shaft is located in the filter screen and is rotatably arranged on the outer shell; the power output end of the second rotating power section is connected to the grinding blade shaft.

[0032] One or more of the above technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:

[0033] The method for preparing α-hemihydrate gypsum using desulfurized gypsum provided in an embodiment of the present invention realizes the effective conversion and recycling of two industrial wastes by utilizing desulfurized gypsum and salt production exhaust mother liquor as raw materials, thereby avoiding waste of resources and improving resource utilization efficiency. This method avoids the direct discharge of desulfurized gypsum and salt production exhaust mother liquor, reduces pollution to the environment, conforms to the green and environmentally friendly production concept, and helps to alleviate environmental pressure. In addition, the conversion of desulfurized gypsum into high-quality α-hemihydrate gypsum significantly increases the added value of the product, broadens the application field of desulfurized gypsum, and increases the economic benefits of the enterprise.

[0034] In addition, the present invention proposes a new process for preparing α-hemihydrate gypsum from desulfurized gypsum. This process accelerates the reaction process, improves the conversion rate and conversion rate by introducing salt production exhaust mother liquor and phase conversion promoter, and provides a new technical approach for the high-value utilization of desulfurized gypsum. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0036] Figure 1 A process flow chart of a method for preparing α-hemihydrate gypsum using desulfurized gypsum provided in an embodiment of the present invention;

[0037] Figure 2 A schematic structural diagram of a continuous filtering, drying and grinding device provided in an embodiment of the present invention;

[0038] Figure 3 This is a schematic diagram of the back side of the continuous filtering, drying and grinding device provided in an embodiment of the present invention.

[0039] The reference numerals are as follows:

[0040] 1. Outer casing; 11. Feed pipe; 12. Liquid storage tank; 21. Driving roller; 22. Tensioning roller; 23. First rotating power unit; 24. Filter conveyor belt; 31. First wind blade; 32. Second wind blade; 33. Drying plate; 41. Second rotating power unit; 42. Grinding knife shaft; 43. Filter screen; 44. Aggregate shell; 241. Baffle. DETAILED DESCRIPTION

[0041] The following describes embodiments of the present invention in detail, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and are not to be construed as limiting the present invention.

[0042] In the description of the present invention, it should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention.

[0043] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature identified as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, "plurality" means two or more, unless otherwise specifically defined.

[0044] In the present invention, unless otherwise expressly specified or limited, the terms "mounted," "connected," "connect," "fixed," etc. should be understood broadly. For example, they may refer to fixed connection, detachable connection, or integration; mechanical connection or electrical connection; direct connection or indirect connection through an intermediate medium; internal communication between two components or interaction between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0045] See also Figure 1 The present invention provides a method for preparing α-hemihydrate gypsum by using desulfurized gypsum, which specifically includes the following steps:

[0046] S1. After mixing desulfurized gypsum and salt production exhaust mother liquor in a reactor, air is introduced to react calcium carbonate and calcium chloride in the desulfurized gypsum with the exhaust mother liquor to form calcium sulfate, while simultaneously oxidizing calcium sulfite to form calcium sulfate;

[0047] S2. Add the liquid obtained in the above step into an autoclave, add a certain amount of a crystal-transforming agent into the autoclave, and stir evenly;

[0048] S3, after the reaction is completed, the material obtained in the autoclave is filtered;

[0049] S4. Drying the filtered solid material, and then grinding it to obtain α-hemihydrate gypsum.

[0050] The method for preparing α-hemihydrate gypsum using desulfurized gypsum provided in the embodiments of the present application has the following advantages:

[0051] (1) The process of the present invention is simple and can be industrialized.

[0052] (2) The salt content in the salt production mother liquor is utilized to increase the solubility of desulfurization gypsum and improve the conversion rate of desulfurization gypsum to α-hemihydrate gypsum.

[0053] (3) The sulfate in the mother liquor discharged from salt production is further reacted with the calcium carbonate and calcium chloride in the desulfurization gypsum, thereby removing impurities in the desulfurization gypsum and increasing the yield of α-hemihydrate gypsum.

[0054] (4) It can not only make high-value use of industrial by-product desulfurization gypsum, but also reduce the discharge of mother liquor discharged from salt production, solving two kinds of industrial waste at one stroke without generating new pollution, which is very consistent with the green economy.

[0055] In one embodiment, in step S1, when desulfurized gypsum is mixed with the mother liquor discharged from salt production, the calcium ion content of calcium carbonate and calcium chloride in the desulfurized gypsum and the sulfate content in the mother liquor are calculated as follows: 1t desulfurized gypsum and 2.5m 3 -5.0m 3 Mix the mother liquor discharged from salt production; while mixing, introduce 0.1-0.5m 3 / h of air to oxidize the calcium sulfite in the desulfurization gypsum and remove the impurity components of the desulfurization gypsum; the reaction time is 1-2h.

[0056] In one embodiment, the crystal-changing agent is a mixed solution of hydrochloric acid and citric acid, and the mass ratio of hydrochloric acid to citric acid is 7:3; wherein, the added amount of hydrochloric acid and citric acid is 0.01-0.05wt% of the dry weight of desulfurized gypsum.

[0057] In one embodiment, the autoclave has the following autoclave conditions: temperature 130-150° C., pressure 1.3-1.5 MPa, and autoclave time 5-8 h.

[0058] In one embodiment, in step S4, a steam tube bundle dryer is used for drying, and the drying temperature is greater than 110°C.

[0059] In one embodiment, a portion of the filtrate obtained in step S3 is recirculated into the reactor via a pipeline. The filtrate from step S3 is piped into the reactor to replenish the water in the reactor, thereby dissolving more calcium sulfate generated by the reaction. Furthermore, by utilizing the water in the filtered water reactor, the filtered water is reused, thereby conserving water resources.

[0060] The following are examples of the method for preparing α-hemihydrate gypsum using desulfurized gypsum provided in this application under different production conditions:

[0061] Example 1: 1 kg of desulfurized gypsum was mixed with 4 liters of salt production exhaust liquor and allowed to react in an autoclave at a flow rate of 0.5 liters / hour of air. The mixture was stirred and reacted for 1 hour. After the reaction, the mixture was transferred to an autoclave, 0.02 wt% of a crystallization agent was added, and the mixture was heated to 135°C and reacted at 1.4 MPa for 6 hours. The mixture was filtered and the solids were quickly dried in a dryer to yield 946 grams of α-hemihydrate gypsum. Testing revealed a whiteness of 96%, a compressive strength of 53 MPa, and a purity of 96%.

[0062] Example 2: 1 kg of desulfurized gypsum was mixed with 3.8 liters of salt production exhaust liquor and allowed to react in an autoclave at a flow rate of 0.5 liters / hour of air. The mixture was stirred and reacted for 1 hour. After the reaction, the mixture was transferred to an autoclave, 0.02 wt% of a crystallization agent was added, and the mixture was heated to 145°C and reacted at 1.4 MPa for 6 hours. The mixture was filtered and the solids were quickly dried in a dryer to yield 937 grams of α-hemihydrate gypsum. Testing revealed a whiteness of 90%, a compressive strength of 52 MPa, and a purity of 97%.

[0063] Example 3: 1 kg of desulfurized gypsum was mixed with 4 liters of salt production exhaust liquor and allowed to react in an autoclave at a flow rate of 0.5 liters / hour of air. The mixture was stirred and reacted for 1 hour. After the reaction, the mixture was transferred to an autoclave, 0.03 wt% of a crystallization agent was added, and the mixture was heated to 135°C and reacted at 1.4 MPa for 6 hours. The mixture was filtered and the solids were quickly dried in a dryer to yield 951 grams of α-hemihydrate gypsum. Testing revealed a whiteness of 93%, a compressive strength of 55 MPa, and a purity of 96%.

[0064] Example 4: 1 kg of desulfurized gypsum was mixed with 4 liters of salt production exhaust liquor and allowed to react in an autoclave at a flow rate of 0.5 liters / hour of air. The mixture was stirred and reacted in an autoclave for 1 hour. After the reaction, the mixture was transferred to an autoclave, 0.02 wt% of a crystallization agent was added, and the mixture was heated to 135°C and reacted at 1.4 MPa for 7 hours. The mixture was filtered and the solids were quickly dried in a dryer to yield 957 grams of α-hemihydrate gypsum. Testing revealed a whiteness of 95%, a compressive strength of 56 MPa, and a purity of 97%.

[0065] In summary, the method for preparing α-hemihydrate gypsum using desulfurized gypsum provided in this application can produce type α calcium sulfate with high purity, complete crystal development and excellent performance, that is, the whiteness reaches 85%, the purity ≧95%, and the compressive strength reaches more than 50MPa.

[0066] See also Figure 2-3In one embodiment, steps S3 and S4 are completed using a continuous filtering, drying and grinding integrated device, which includes: a shell 1, a belt filter section, a drying section, and a grinding section. A chamber is provided in the shell 1, a feed pipe 11 is provided at the top of the shell 1, and a liquid storage tank 12 is provided on one side of the bottom of the shell 1. The feed pipe 11 is connected to the output end of the autoclave, and the material to be filtered is input into the chamber of the shell 1 through the feed pipe 11. The belt filter section is provided in the chamber of the shell 1, and the belt filter section is used to filter the material entering the chamber of the shell 1, and transport the solid material obtained by filtration to the drying section, and the filtrate falls into the liquid storage tank 12 below. The drying section is provided on one side of the belt filter section, and the drying section dries the solid material. The grinding section is provided below the drying section, and the grinding section is used to grind the solid material after the drying process.

[0067] The material in the autoclave is filtered, dried, and ground by using a continuous filtering, drying, and grinding device. The material in the autoclave (including solid calcium sulfate hemihydrate and a liquid mixture) is continuously fed into the housing 1 through the feed pipe 11 through a pipeline. The material is first filtered by the belt filter section, and the filtered solid material (calcium sulfate hemihydrate) is automatically transported to the drying section on one side through the belt filter section, while the filtrate is downwardly collected into the liquid storage tank 12. After being dried in the drying section, the solid material enters the grinding section for grinding to obtain powdered α-hemihydrate gypsum. The continuous filtering, drying, and grinding device can realize continuous and automatic processing of the material in the autoclave, eliminating the process of manual material transportation, greatly improving the efficiency of material processing, and is suitable for large-scale continuous production.

[0068] Optionally, an outlet may be provided at the bottom of the drying section liquid storage tank 12, a reflux pipe may be provided at the outlet position, the other end of the reflux pipe may be connected to the reactor, and a reflux pump may be installed on the reflux pipe to reflux the filtrate into the reactor.

[0069] In one embodiment, the belt filter unit includes a drive roller 21, a tension roller 22, and a filter conveyor belt 24. A first rotating power unit 23, the drive roller 21, and the tension roller 22 are rotatably disposed within the housing 1; the first rotating power unit 23 is mounted on the housing 1, and the power output end of the first rotating power unit 23 is connected to the drive roller 21; the filter conveyor belt 24 is mounted on the drive roller 21 and the tension roller 22, and is provided with filter holes.

[0070] During filtration, the first rotary power unit 23 (specifically, a combination of a motor and a reducer) is activated, thereby rotating the drive drum 21 and operating the filter conveyor belt 24. After the material enters the housing 1 through the feed pipe 11, it falls onto the filter conveyor belt 24 (specifically, the upstream end of the filter conveyor belt 24). Due to the filter holes provided on the filter conveyor belt 24, the filter conveyor belt 24 can filter out the hemihydrate gypsum solids. The filtrate flows downward through the filter conveyor belt 24 into the liquid storage tank 12 below, thereby separating the hemihydrate gypsum solids from the filtrate. Simultaneously, the filter conveyor belt 24 transports the hemihydrate gypsum solids to the downstream end, allowing them to enter the drying section, achieving the purpose of filtration. Since the filter conveyor belt 24 is always in operation, the hemihydrate gypsum solids on the filter conveyor belt 24 can be delivered to the drying section in a timely manner, preventing the hemihydrate gypsum solids from accumulating on the filter conveyor belt 24 and causing blockage, which would affect the filter conveyor belt 24's continued filtration efficiency.

[0071] In addition, the filter conveyor belt 24 running at a uniform speed can deliver the hemihydrate gypsum solids to the drying section relatively evenly and continuously, which not only ensures the material supply for the subsequent drying and grinding processes, but also reduces the burden on the drying section, improves the uniformity and effect of drying, and avoids the phenomenon that the drying section cannot evenly and effectively dry the hemihydrate gypsum solids due to the concentrated delivery of the hemihydrate gypsum solids into the drying section.

[0072] Optionally, baffles 241 are provided on both sides of the filter conveyor belt 24. The baffles 241 prevent the semi-hydrated gypsum solid from leaking from both sides of the filter conveyor belt 24, ensuring that the semi-hydrated gypsum solid can smoothly enter the drying section under the transportation of the filter conveyor belt 24.

[0073] Optionally, the belt filter section is inclined, and the inclination direction is from downstream (close to one end of the drying section) toward upstream (close to the end of the feed pipe 11), so that the filtrate remaining on the filter conveyor belt 24 will move downward along the inclined surface of the filter conveyor belt 24 under the action of its own gravity. At the same time, the linear speed of the filter conveyor belt 24 is controlled at 4-5m / min, thereby avoiding the filtrate from entering the drying section along the filter conveyor belt 24 and increasing the drying burden of the drying section.

[0074] In one embodiment, the drying section includes a first wind blade 31, a second wind blade 32, and a drying plate 33. The first wind blade 31 is positioned above the downstream end of the belt filter section, with the air outlet direction of the first wind blade 31 being opposite to the conveying direction of the belt filter section. The second wind blade 32 is positioned below the downstream end of the belt filter section. The drying plate 33 is tilted and positioned below the second wind blade 32. The drying plate 33 is hollow and has a heat source input port and a heat source output port. External heat is input into the drying plate 33 through the heat source input port. The heat source output port is connected to the first wind blade 31 and the second wind blade 32 via a pipe. After being transported through the belt filter section, the solid material falls onto the drying plate 33.

[0075] Before drying, heat (specifically, hot steam, hot air, etc.) generated by an external heating device (such as a boiler) is introduced into the drying plates 33 through the heat source input port, raising the temperature of the drying plates 33. The drying plates 33 are made of a metal material with good thermal conductivity, such as iron or aluminum. After the heat fills the drying plates 33, it is discharged from the heat source output port and piped into the first and second wind blades 31, 32 for use, thereby improving heat source utilization. When the belt filter transports the calcium sulfate hemihydrate solids below the first wind blade 31, the hot air flow ejected from the first wind blade 31 removes moisture (filtrate) from the surface of the calcium sulfate hemihydrate solids and the surface of the belt filter, preventing moisture from falling onto the drying plates 33 below and providing preliminary drying of the calcium sulfate hemihydrate solids. After the belt filter transports the calcium sulfate hemihydrate solids above the drying plates 33, the calcium sulfate hemihydrate solids fall downward from the belt filter. When the second wind blade 32 is passed, the hot air flow ejected by the second wind blade 32 can dry the calcium sulfate hemihydrate solid again. And the horizontal air flow can make the calcium sulfate hemihydrate solid move downward while moving horizontally away from the second wind blade 32 (such as Figure 2 The large volume calcium sulfate hemihydrate solid is separated from the small volume calcium sulfate hemihydrate solid by the smaller volume calcium sulfate hemihydrate solid, so that the position where the small volume calcium sulfate hemihydrate solid falls on the drying plate 33 is lower than the position where the large volume calcium sulfate hemihydrate solid falls on the drying plate 33, thereby making the large volume calcium sulfate hemihydrate solid move a longer distance on the drying plate 33, that is, the drying time received by the drying plate 33 is longer, thereby ensuring the drying effect of the large volume calcium sulfate hemihydrate, while the small volume calcium sulfate hemihydrate solid moves a shorter distance on the drying plate 33, that is, the drying time received by the drying plate 33 is shorter, thereby preventing the small volume calcium sulfate hemihydrate solid from being over-dried and decomposed.

[0076] Therefore, the drying section provided in this embodiment dries the calcium sulfate hemihydrate solid three times in succession to ensure the drying effect, and can match the drying time appropriately according to the calcium sulfate hemihydrate solids of different sizes, thereby avoiding the phenomenon of excessive decomposition of the calcium sulfate hemihydrate solid.

[0077] Optionally, a temperature sensor may be provided on the drying surface of the drying plate 33 to monitor the temperature of the drying plate 33 in real time, and the temperature and flow of the input heat source may be controlled according to the temperature of the drying plate 33 .

[0078] In one embodiment, the grinding section includes a second rotating power section 41, a grinding blade shaft 42, a filter screen 43 and an aggregate shell 44; the aggregate shell 44 is arranged at the bottom of the drying section; the filter screen 43 is arranged in the aggregate shell 44, and the grinding blade shaft 42 is located in the filter screen 43 and is rotatably arranged on the outer shell 1; the power output end of the second rotating power section 41 is connected to the grinding blade shaft 42.

[0079] The calcium sulfate hemihydrate solid dried in the drying section enters the filter screen 43 (the filter screen 43 is cylindrical and has an inlet on one side). The second rotating power unit 41 (specifically, a motor) drives the grinding shaft 42 to rotate. The rotating grinding shaft 42 breaks the calcium sulfate hemihydrate solid into powder. The calcium sulfate hemihydrate that meets the particle size requirements can pass through the filter screen 43 and enter the space between the aggregate shell 44 and the filter screen 43. The calcium sulfate hemihydrate powder is collected by the aggregate shell 44 and discharged from the discharge port, thereby obtaining powdered calcium sulfate hemihydrate.

[0080] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing α-hemihydrate gypsum using desulfurized gypsum, characterized in that: The method for preparing α-hemihydrate gypsum by using desulfurized gypsum comprises the following steps: S1. After mixing desulfurized gypsum and salt production exhaust mother liquor in a reactor, air is introduced to react calcium carbonate and calcium chloride in the desulfurized gypsum with the exhaust mother liquor to form calcium sulfate, while simultaneously oxidizing calcium sulfite to form calcium sulfate; S2. Add the liquid obtained in the above step into an autoclave, add a certain amount of a crystal-transforming agent into the autoclave, and stir evenly; S3, after the reaction is completed, the material obtained in the autoclave is filtered; S4. Drying the filtered solid material, and then grinding it to obtain α-hemihydrate gypsum.

2. The method for preparing α-hemihydrate gypsum by utilizing desulfurized gypsum according to claim 1, characterized in that: In step S1, when desulfurized gypsum is mixed with the mother liquor discharged from salt production, the calcium ion content of calcium carbonate and calcium chloride in the desulfurized gypsum and the sulfate content in the mother liquor of salt production are calculated based on the ratio of 1t desulfurized gypsum to 2.5m 3 -5.0m 3 Mix the mother liquor discharged from salt production; while mixing, introduce 0.1-0.5m 3 / h of air to oxidize the calcium sulfite in the desulfurization gypsum and remove the impurity components of the desulfurization gypsum; the reaction time is 1-2h.

3. The method for preparing α-hemihydrate gypsum by utilizing desulfurized gypsum according to claim 1, characterized in that: The crystal-changing agent is a mixed solution of hydrochloric acid and citric acid, and the mass ratio of hydrochloric acid to citric acid is 7:3; wherein, the addition amount of hydrochloric acid and citric acid is 0.01-0.05wt% of the dry weight of desulfurized gypsum.

4. The method for preparing α-hemihydrate gypsum by utilizing desulfurized gypsum according to claim 1, characterized in that: The autoclave has the following autoclave conditions: temperature 130-150° C., pressure 1.3-1.5 MPa, and autoclave time 5-8 h.

5. The method for preparing α-hemihydrate gypsum by utilizing desulfurized gypsum according to claim 1, characterized in that: In step S4, a steam tube bundle dryer is used for drying, and the drying temperature is greater than 110°C.

6. The method for preparing α-hemihydrate gypsum from desulfurized gypsum according to claim 1, characterized in that: Part of the filtrate obtained by filtration in step S3 is refluxed into the reactor through a pipeline.

7. The method for preparing α-hemihydrate gypsum by utilizing desulfurized gypsum according to claim 1, characterized in that: Steps S3 and S4 are completed using a continuous filtering, drying and grinding device, which includes: a housing, a belt filter part, a drying part, and a grinding part; A chamber is provided in the shell, a feed pipe is provided on the top of the shell, a liquid storage tank is provided on one side of the bottom of the shell, the feed pipe is connected to the output end of the autoclave, and the material to be filtered is input into the chamber of the shell through the feed pipe; The belt filter is arranged in the chamber of the shell, and is used to filter the material entering the chamber of the shell, and transport the filtered solid material to the drying part, and the filtrate falls into the liquid storage tank below; A drying section, which is provided on one side of the belt filter section and dries the solid material; The grinding part is arranged below the drying part and is used to grind the solid material after the drying process.

8. The method for preparing α-hemihydrate gypsum by utilizing desulfurized gypsum according to claim 7, characterized in that: The belt filter unit includes: A driving roller and a tensioning roller, wherein the driving roller and the tensioning roller are rotatably disposed in the housing; a first rotating power unit, the first rotating power unit being mounted on the housing, and a power output end of the first rotating power unit being connected to the driving roller; A filter conveyor belt, the filter conveyor belt is installed on the driving roller and the tensioning roller, and the filter conveyor belt is provided with filter holes; Baffles are provided on both sides of the filter conveyor belt.

9. The method for preparing α-hemihydrate gypsum by using desulfurized gypsum according to claim 7, characterized in that: The drying section comprises: a first wind blade, the first wind blade being disposed above the downstream end of the belt filter section, the wind direction of the first wind blade being opposite to the conveying direction of the belt filter section; a second wind blade, the second wind blade being disposed below the downstream end of the belt filter portion; a drying plate, the drying plate being arranged obliquely below the second wind blade, the drying plate being hollow, and being provided with a heat source input port and a heat source output port, through which an external heat source is input into the drying plate, and the heat source output port being connected to the first wind blade and the second wind blade via a pipe; The solid material is transported by the belt filter and then falls onto the drying plate.

10. The method for preparing α-hemihydrate gypsum by utilizing desulfurized gypsum according to claim 7, characterized in that: The grinding section includes a second rotating power section, a grinding blade shaft, a filter screen, and an aggregate shell; the aggregate shell is arranged at the bottom of the drying section; the filter screen is arranged in the aggregate shell, and the grinding blade shaft is located in the filter screen and is rotatably arranged on the outer shell; The power output end of the second rotating power unit is connected to the grinding knife shaft.

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