A method and system for preparing anhydrous flake sodium sulfide from industrial waste salt containing sodium sulfate

Abstract

The application discloses a method and system for preparing anhydrous flaky sodium sulfide by using industrial waste salt containing sodium sulfate, and can realize direct continuous sheeting of high-purity high-temperature sodium sulfide melt (about 1000 DEG C) to obtain anhydrous flaky sodium sulfide product by means of high-efficiency continuous reduction reaction technology and high-temperature melt synchronous cooling and sheeting solidification technology, so as to achieve the purpose of continuous treatment and high-value utilization of industrial waste salt containing sodium sulfate. The application can greatly reduce the process flow and improve the production efficiency under the premise of ensuring the purity of the product, and has the advantages of small equipment area, simple operation, high production efficiency, short process operation flow, low energy consumption, high product quality, wide market prospect and remarkable economic benefits, and provides a new technical idea for preparing anhydrous flaky sodium sulfide by using industrial waste salt containing sodium sulfate.

Description

Technical Field

[0001] This invention relates to a process and equipment for treating industrial waste salt containing sodium sulfate, specifically to a method and system for preparing anhydrous flake sodium sulfide using industrial waste salt containing sodium sulfate, belonging to the field of industrial solid waste treatment technology. Background Technology

[0002] Sodium sulfide is an inorganic compound widely used in industries such as dyes, printing and dyeing, papermaking, textiles, leather making, electroplating, pharmaceuticals, mineral flotation, and wastewater treatment. Converting industrial waste salt into sodium sulfide can turn waste into treasure, representing an important pathway for the resource utilization and even high-value utilization of industrial waste salt.

[0003] Currently, commercially available industrial sodium sulfide mainly comes in red and yellow flake forms. There are two main methods for preparing sodium sulfide from sodium sulfate: the coal reduction method and the gas reduction method. Since the gas reduction method is still in the laboratory research stage and has not yet been industrialized, the production of industrial sodium sulfide mainly uses the coal reduction method, which accounts for approximately 95% of the total output.

[0004] The traditional coal reduction method involves mixing sodium sulfate and pulverized coal, reacting them at 950℃~1350℃ to produce sodium sulfide melt. The melt is then cooled to obtain lumpy crude alkali, which is further processed through hot alkali leaching, evaporation and concentration, and flake formation to obtain flake sodium sulfide product. This method primarily uses converters or rotary kilns as high-temperature reaction equipment, resulting in intermittent production with poor sealing. The process easily leads to dust and carbon monoxide emissions, causing severe environmental pollution. Furthermore, the resulting sodium sulfide melt has low purity, high impurity content, and low reaction efficiency, making it impossible to produce a qualified product. Therefore, it is necessary to cool the high-temperature melt, remove impurities through water dissolution, and then evaporate and concentrate it to obtain sodium sulfide product with a purity of 60%. This process is lengthy and costly. Summary of the Invention

[0005] The main objective of this invention is to provide a method and system for preparing anhydrous flake sodium sulfide using industrial waste salt containing sodium sulfate. This aims to solve the technical problems of low reduction reaction efficiency, high energy consumption, long production process, and low product purity in existing sodium sulfide preparation processes. This invention utilizes a highly efficient continuous reduction reaction technology combined with high-temperature melt synchronous cooling and flake solidification technology to directly and continuously flake anhydrous flake sodium sulfide from high-purity, high-temperature sodium sulfide melt (around 1000℃). This achieves the goal of continuous treatment and high-value utilization of industrial waste salt. The entire production process is short and energy-efficient, and the resulting product has high purity, providing a new technical approach for preparing high-value anhydrous flake sodium sulfide from industrial waste salt containing sodium sulfate.

[0006] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is specifically as follows:

[0007] According to a first embodiment of the present invention, a method for preparing anhydrous flake sodium sulfide using industrial waste salt containing sodium sulfate is provided:

[0008] A method for preparing anhydrous flake sodium sulfide using industrial waste salt containing sodium sulfate, the method comprising the following steps:

[0009] 1) Mix industrial waste salt containing sodium sulfate, carbon powder, and with or without a catalyst to obtain a mixture.

[0010] 2) The mixture is subjected to molten reduction treatment in an oxygen-free environment to obtain sodium sulfide melt.

[0011] 3) The sodium sulfide melt is cooled while being sheeted to obtain anhydrous flake sodium sulfide product.

[0012] Preferably, step 1) is: mixing industrial waste salt containing sodium sulfate, carbon powder, and with or without a catalyst, and then performing pelletizing treatment to obtain pellet material, and then performing melt reduction treatment on the pellet material in step 2) to obtain sodium sulfide melt.

[0013] Preferably, the industrial waste salt containing sodium sulfate has a sodium sulfate content of not less than 80% by mass, more preferably not less than 90%, and even more preferably not less than 95%.

[0014] Preferably, the mixing ratio of industrial waste salt containing sodium sulfate to carbon powder is Na2SO4:2C = 1:0.5~2, more preferably 1:0.8~1.5, and more preferably 1:0.9~1.2.

[0015] Preferably, the catalyst is one or more of iron, cobalt, nickel, copper and their oxides, and its addition amount is 0 to 5% of the total mass of industrial waste salt containing sodium sulfate and carbon powder, preferably 0.1 to 4%, more preferably 0.3 to 3%.

[0016] Preferably, the temperature of the melt reduction treatment is 1000℃~1400℃, more preferably 1050~1350℃, and even more preferably 1100~1250℃.

[0017] Preferably, the temperature of the sodium sulfide melt is 980~1200℃, more preferably 1000~1150℃, and even more preferably 1000~1100℃. The purity of the sodium sulfide melt is not less than 60%, preferably not less than 70%, and even more preferably not less than 80%.

[0018] Preferably, the particle size of the pellets is 2-10 cm, more preferably 2.5-8 cm, and even more preferably 3-6 cm.

[0019] Preferably, step 3) involves first cooling the sodium sulfide melt before sheet formation with nitrogen gas to 950-1140°C, preferably 955-1000°C, and more preferably 960-980°C (for example, one of 950°C, 955°C, 960°C, 965°C, 970°C, 975°C, 980°C, 985°C, 990°C, 995°C, or 1000°C, i.e., the temperature of the sodium sulfide melt before sheet formation). Then, during the sheet formation process, indirect water cooling is used to ensure that the temperature of the resulting flake sodium sulfide does not exceed 640°C, preferably not exceeding 635°C, and more preferably not exceeding 630°C (i.e., the temperature of the sodium sulfide melt immediately after sheet formation), thus obtaining anhydrous flake sodium sulfide product.

[0020] Preferably, the anhydrous flake sodium sulfide is further cooled to a temperature not exceeding 50°C, preferably 20~40°C, and more preferably 25~35°C (e.g., one of 20°C, 22°C, 24°C, 28°C, 30°C, 35°C, 40°C, 45°C, 48°C, or 50°C) by direct nitrogen cooling and / or indirect water cooling before packaging.

[0021] According to a second embodiment of the present invention, a system for preparing anhydrous flake sodium sulfide using industrial waste salt containing sodium sulfate is provided:

[0022] A system for preparing anhydrous flake sodium sulfide using industrial waste salt containing sodium sulfate, or a system for use in the method described in any one of claims, comprising a mixing and pelletizing device, a melt reduction device, and a two-roller cooling and flake-forming device arranged in series. The two-roller cooling and flake-forming device includes a housing and two cylindrical rollers. A flake-forming chamber is formed inside the housing, and the two cylindrical rollers are arranged in parallel within the flake-forming chamber. A melt inlet and a protective gas inlet communicating with the flake-forming chamber are provided on the housing located above the cylindrical rollers, and a finished product outlet and a protective gas outlet communicating with the flake-forming chamber are provided on the housing located below the cylindrical rollers (it should be noted that in this invention, the protective gas outlet can also be the same as the finished product outlet, i.e., the protective gas is discharged along with the finished product). The cylindrical rollers have a cavity inside, and a cooling medium inlet and a cooling medium outlet communicating with the cavity are provided on their axial surfaces.

[0023] Preferably, a core tube is also provided within the cavity of the cylindrical roller. One end of the core tube penetrates the axial surface of the cylindrical roller and extends axially into the cavity of the cylindrical roller. The axis of the core tube coincides with the axis of the cylindrical roller, and a sandwich chamber is formed between the outer wall of the core tube and the inner wall of the cylindrical roller. The cooling medium inlet is connected to the cavity of the core tube, and multiple through holes communicating with the sandwich chamber are formed on the wall of the core tube. The cooling medium outlet is connected to the sandwich chamber. Preferably, the length of the core tube extending into the cavity of the cylindrical roller is not less than two-thirds of the total axial length of the cylindrical roller. The cooling medium inlet and the cooling medium outlet are both located on the same side of the axial direction of the cylindrical roller.

[0024] Preferably, flow regulation control valves are independently installed on the cooling medium inlet and the protective gas inlet.

[0025] Preferably, the two cylindrical rollers are arranged in a staggered, parallel configuration within the film-making chamber, meaning that the vertical and horizontal projections of the two rollers do not completely overlap. A pneumatic push-pull mechanism is also provided outside the housing, connected to both ends of the lower-positioned cylindrical roller. This mechanism drives the lower-positioned roller to move relative to the higher-positioned roller, thereby adjusting the radial distance between the surfaces of the two rollers.

[0026] Preferably, the radial distance between the surfaces of the two cylindrical rollers is no more than 10 mm, preferably 1 to 8 mm, and more preferably 2 to 5 mm (for example, one of 0.5 mm, 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm, 4.5 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, and 10 mm).

[0027] Preferably, telescopic scrapers are independently installed on the inner wall of the housing on the side of each cylindrical roller away from the other.

[0028] Preferably, a drive motor is also provided on the outside of the housing, and a transmission wheel is provided at one end of the cylindrical roller. The drive wheel of the drive motor is connected to the transmission wheel through a transmission chain, and the drive motor drives the two cylindrical rollers to rotate relative to each other through the transmission chain and the transmission wheel.

[0029] Preferably, multiple drive motors are provided on the outside of the housing, and the multiple drive motors alternately drive the two cylindrical rollers to rotate relative to each other.

[0030] Preferably, a support frame is also provided at the bottom of the housing. An observation port is also provided at the top of the housing.

[0031] Preferably, the melt inlet is designed as an elongated opening extending along the axial direction of the cylindrical roller. Multiple guide plates are also provided inside the melt inlet (the number of guide plates is 1 to 20, preferably 3 to 15, more preferably 5 to 10; for example, one of 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 15, 18, or 20). The multiple guide plates are evenly distributed along the length of the melt inlet, dividing the space between the melt inlet and the cylindrical roller into multiple inclined feeding channels. A temperature sensor is provided at the bottom end of the guide plates.

[0032] Preferably, the length of the melt inlet along the axial direction of the cylindrical roller is not greater than the axial length of the cylindrical roller, preferably not greater than three-quarters of the axial length of the cylindrical roller, and more preferably one-half to three-quarters of the axial length of the cylindrical roller.

[0033] Preferably, the width of the melt inlet along the horizontal radial direction of the cylindrical roller is not greater than the radial distance between the central axes of the two cylindrical rollers, preferably not greater than three-quarters of the radial distance between the central axes of the two cylindrical rollers, and more preferably one-quarter to three-quarters of the radial distance between the central axes of the two cylindrical rollers.

[0034] Preferably, the projected width of the guide plate in the axial direction is greater than or equal to the length of the melt inlet in the axial direction.

[0035] As a preferred option, a melt conveying pipe cleaning device is also provided at the melt inlet.

[0036] Preferably, the melting reduction apparatus includes a furnace body and a furnace cavity. According to the material flow direction, a vertical partition wall is provided on the bottom plate in the middle of the furnace cavity, dividing the furnace cavity into a melting reduction zone and an overflow zone. A top notch is provided at the top of the vertical partition wall to connect the melting reduction zone and the overflow zone. A feed pipe is provided on the side wall of the melting reduction zone. A melt conveying pipe is provided on the side wall of the overflow zone, with the outlet end of the melt conveying pipe connected to the melt inlet.

[0037] Preferably, slag discharge ports and heating electrodes are independently provided in the molten reduction zone and overflow zone, respectively.

[0038] Preferably, an automatic electrode lifting mechanism is also provided on the upper surface of the furnace body. The upper end of each heating electrode passes through the furnace body and is connected to the automatic electrode lifting mechanism. The automatic electrode lifting mechanism independently controls the downward depth of each heating electrode in the melting reduction zone and overflow zone.

[0039] Preferably, the heating electrode is a heated graphite electrode.

[0040] Preferably, the furnace body consists of a stainless steel outer wall layer, a water-cooling layer, and a refractory casting layer, from the outside to the inside.

[0041] Preferably, the system also includes a discharge cooling device and a packaging device. The discharge cooling device is a closed spiral feeding mechanism, and its feeding channel is equipped with a nitrogen input pipe and a nitrogen output pipe. The finished product outlet of the twin-roll cooling sheet forming device is connected to the inlet of the packaging device through the discharge cooling device.

[0042] In existing technologies, the high-temperature sodium sulfide melt obtained by the coal reduction of Glauber's salt at 850℃~1200℃ has two main problems. First, the purity and color of the high-temperature sodium sulfide melt are affected. The sodium sulfide melt has low purity, many impurities, and unqualified color, making it impossible to directly produce qualified sodium sulfide products. It is necessary to cool the high-temperature melt to form a block of crude alkali, and then purify and remove impurities from the solution after redissolving the crude alkali at 100℃~200℃, and then evaporate, concentrate, and crystallize it to produce a sheet product. The production process is complicated and costly, and the sodium sulfide is severely oxidized, with a purity of about 60%. Second, there is the issue of the post-solidification and sheet-making technology for the high-temperature sodium sulfide melt. Even if the high-temperature molten sodium sulfide has qualified purity and few impurities, the high-temperature molten sodium sulfide is highly corrosive and causes significant corrosion to equipment. Furthermore, when its temperature decreases, its viscosity increases sharply, making it easy to solidify, which also makes it impossible to directly form sheets.

[0043] In this invention, the direct cooling and cold-forming of sodium sulfide molten sheets requires strict control, including control of sodium sulfide temperature, adhesion, corrosivity, and product morphology. Based on the characteristics of sodium sulfide melt, it solidifies below its melting point. When the sodium sulfide molten material flows into the sodium sulfide cooling and sheet-forming device and contacts the rotating double rollers, the melt rapidly cools and tends to solidify. This cooling and solidification continues during the double-roller extrusion molding process, ultimately producing sheet-like sodium sulfide products. Sodium sulfide temperature significantly affects its corrosivity and adhesion. High-temperature sodium sulfide is highly corrosive to equipment and has high viscosity; the resulting solid requires a scraper to remove it. This is why high-temperature sodium sulfide cannot be directly used to produce sheet-like products. Therefore, temperature control during the sheet-forming process is extremely important. This invention utilizes high-temperature molten sodium sulfide to form a solid on two rotating rollers, and produces a sheet-like product through the extrusion pressure between the rollers. By circulating low-temperature cooling water inside the rollers for heat exchange, the temperature of the sodium sulfide solid is instantly reduced, thereby minimizing the corrosiveness and adhesion of the sodium sulfide to the roller walls. The sheet-like product then falls directly into a conveying device. Furthermore, this invention allows control over the thickness and uniformity of the sheet-like product by adjusting the distance between the rollers, while also preventing deformation and damage to the rollers if they become jammed by sodium sulfide. With a roller distance set to 1-10 mm, the resulting product thickness is also 1-10 mm, avoiding the unevenness of sheet-like products produced by traditional sheet-making machines. A frequency converter controls the motor speed to prevent problems such as the rollers becoming jammed due to excessively slow motor speed and insufficient cooling efficiency of the sodium sulfide if the motor speed is too high. The roller speed is typically 30-100 r / min. In addition, to increase the contact area and accurate landing point between the twin rollers and the molten sodium sulfide, a diversion port and a guide plate are specially installed at the connection point before the molten sodium sulfide enters the twin rollers. The size of the inlet is also designed to ensure that the melt is evenly distributed on the surface of the twin roller wall. On the one hand, this can enhance the cooling effect, prevent pitting corrosion of the roller wall, and improve production efficiency. On the other hand, it can prevent the molten sodium sulfide from falling directly into the conveying device without being cooled by the twin rollers.

[0044] In this invention, after the raw materials are mixed evenly, pelletizing is performed to obtain pellet material. During the melt reduction process, the unreacted raw materials can sink to the bottom of the melt reduction zone, which facilitates the clear liquid of sodium sulfide melt after melt reduction to flow into the overflow zone without bringing in too much unreacted raw material and affecting the purity of the product. Moreover, the raw material pellets located at the bottom, compared with powdered materials that float on the top of the melt, increase the contact area and enhance the melt reduction reaction efficiency.

[0045] In this invention, by adding a catalyst (transition elements such as iron, cobalt, nickel, and copper and their oxides), the efficiency and extent of the reduction reaction can be enhanced when industrial waste salt containing sodium sulfate is melted and reduced. That is, the reduction temperature can be lowered and the reduction efficiency can be improved when obtaining sodium sulfide melt of the same purity.

[0046] In this invention, the furnace body of the melting reduction device is sealed during operation except for the feed inlet, discharge outlet, electrode insertion port, and flue gas outlet. Furthermore, the furnace pressure is controlled by adjusting the frequency of the induced draft fan in conjunction with the furnace pressure to ensure a slightly positive pressure inside the furnace and prevent air from entering.

[0047] In this invention, the furnace chamber of the melting and reduction device is designed with partitions, which solves the problems of the integrated raw material melting and reduction reaction in a monolithic furnace, where insufficiently reacted carbon powder or sodium sulfate directly enters the sodium sulfide melt, greatly affecting product purity and color. A transverse overflow channel is added between the melting and reduction zone and the overflow zone, allowing impurities in the sodium sulfide melt to settle in the overflow zone and then be statically overflowed and discharged again, which is beneficial for obtaining sodium sulfide products with fewer impurities. Furthermore, the partitioned structure in this invention not only facilitates continuous reaction but also effectively avoids problems such as excessive electrode wear due to frequent arc initiation and low production efficiency caused by stopping the reaction during the discharge phase.

[0048] In this invention, the heating electrode used in the melting reduction device is a graphite electrode. Since the graphite electrode is composed of carbon, it reacts with the molten sodium sulfate as the reaction proceeds, leading to electrode wear. Therefore, after the graphite electrode wears out, the electrode insertion depth needs to be adjusted to prevent the electrode from being suspended and unable to conduct electricity for heating. This invention controls the automatic raising and lowering of the graphite electrode by setting an automatic electrode lifting mechanism. This ensures personnel safety and prevents electric shock while simultaneously adjusting the raising and lowering of the heating electrode.

[0049] In this invention, the furnace body of the melting reduction device is integrally cast from refractory material and a water-cooling design is added, which causes the generated sodium sulfide to cool and form a protective layer on the inner wall of the furnace body, greatly enhancing the furnace body's high temperature resistance and corrosion resistance.

[0050] In this invention, a double-roller cooling tableting device with heat exchange cooling effect is used to rapidly cool the high-temperature sodium sulfide melt while simultaneously performing tableting. This couples the cooling and tableting processes of the high-temperature sodium sulfide melt into a single step. On one hand, it enables direct tableting of the sodium sulfide melt without the need for re-dissolving after cooling, effectively ensuring the purity of the sodium sulfide product (the purity of the melt directly correlates with the purity of the product, eliminating the need for intermediate processes and preventing the introduction of impurities). On the other hand, it significantly reduces the number of processes, improves production efficiency, and saves on equipment, space, and personnel costs.

[0051] In this invention, during the cooling and tableting process, in order to avoid oxidation of the high-temperature sodium sulfide melt, the entire process is carried out in a protective atmosphere (such as a nitrogen atmosphere). In addition, the introduction of nitrogen can also directly cool the sodium sulfide melt through heat exchange, which can assist and coordinate the two rollers to achieve the cooling effect and tableting control of sodium sulfide, and prevent the sodium sulfide after tableting from failing to cool to the set temperature and affecting the tableting effect.

[0052] In this invention, the use of a sleeve-type cooling structure inside the double rollers allows for the direct flow of cold water into the double rollers without filling the jacket. This reduces the amount of cold water used, extends the residence time of the cooling water in the sleeve, and improves the heat exchange effect. In addition, it can reduce the amount of water in the double rollers, thereby reducing the motor load and saving energy.

[0053] In this invention, the distance between the two rollers is adjusted by a roller spacing adjuster (pneumatic push-pull mechanism). Controlling the roller spacing controls the thickness and uniformity of the sheet product. For example, setting the roller spacing to 1-5mm results in a product thickness of 1-5mm, avoiding the unevenness of sheet products produced by traditional sheet-making machines. Furthermore, it prevents deformation and damage to the rollers after they become stuck due to sodium sulfide. A frequency converter controls the motor speed to prevent problems such as the rollers becoming stuck due to rapidly solidifying sodium sulfide if the motor speed is too slow, or the sodium sulfide failing to solidify due to low cooling efficiency if the motor speed is too high. The roller speed is typically 30-100 r / min. In addition, a pneumatic push device has been added. In case of unexpected situations such as the roller not moving or getting stuck, a cylindrical roller located at the bottom can be pulled out. A scraper is set at the pulled-out position to automatically clean the residual or solidified sodium sulfide on the roller. After cleaning, it is restored by the pneumatic push device. During this period, the upper single roller can be cooled, and the scraper next to the upper cylindrical roller can be used to slice the solidified sodium sulfide on the roller, ensuring the continuous operation of the cooling and film-making equipment.

[0054] In this invention, two drive motors with the same frequency can be used to drive the two cylindrical rollers simultaneously, so that the relative rotation speeds of the two cylindrical rollers are consistent. Alternatively, only one drive motor can be used to drive one cylindrical roller to rotate, while the other cylindrical roller achieves relative rotation through friction. Furthermore, in a preferred embodiment of the invention, irregular textures can be provided on the surfaces of the two rollers to increase the friction between the rollers and the squeezing effect on the material.

[0055] In this invention, to increase the contact area and accurate landing point between the twin rollers and the molten sodium sulfide, a diversion port and a guide plate are specially set at the connection port before the molten sodium sulfide enters the twin rollers. The dimensions of the inlet are also designed (for example, the width should not be greater than the roller diameter and the length should not be greater than 3 / 4 of the roller diameter) so that the melt is evenly distributed on the roller surface. On the one hand, this can enhance the cooling effect, prevent pitting corrosion of the roller wall, and improve production efficiency. On the other hand, it can prevent the molten sodium sulfide from falling directly into the conveying device without being cooled by the twin rollers.

[0056] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0057] 1. This invention, through raw material pelletizing and ingenious furnace design, features high heat utilization, good sealing, high efficiency in reducing industrial waste salt containing sodium sulfate to sodium sulfide, and high product purity. It achieves continuous, rapid, and stable conversion of industrial waste salt containing sodium sulfate into sodium sulfide, with low dust content and minimal environmental pollution during the reaction process.

[0058] 2: The sodium sulfide production system of the present invention can realize the direct flake processing of high-temperature sodium sulfide melt. While ensuring product purity, it reduces the process flow of water dissolution and impurity removal, evaporation and crystallization, improves production efficiency and saves costs such as equipment, site and personnel.

[0059] 3. The method of the present invention has a short process, low energy consumption, high product quality, and low production cost. The system of the present invention has a short process, simple structure, small footprint, simple operation, high production efficiency, and high degree of automation, and has broad market prospects and significant economic benefits. Attached Figure Description

[0060] Figure 1 This is a schematic diagram of the overall structure of the system described in this invention.

[0061] Figure 2 This is a schematic diagram of the overall structure of the melting reduction apparatus of the present invention.

[0062] Figure 3 This is a front view of the dual-roller cooling sheet-making apparatus of the present invention.

[0063] Figure 4 This is a schematic diagram of the left side of the twin-roller cooling sheet-making apparatus of the present invention.

[0064] Figure 5 This is a right-side structural schematic diagram of the dual-roller cooling sheet-making apparatus of the present invention.

[0065] Figure 6 This is a top view of the twin-roller cooling sheet-making apparatus of the present invention.

[0066] Figure 7 This is a cross-sectional schematic diagram of the two cylindrical rollers of the present invention when they are brought together.

[0067] Figure 8 This is a cross-sectional schematic diagram of the separation of the two cylindrical rollers of the present invention.

[0068] Figure 9 This is a schematic diagram of the internal structure of the two cylindrical rollers of the present invention.

[0069] Figure 10 This is a frontal view of the internal structure of the melt inlet of the present invention when a guide plate is provided inside.

[0070] Figure 11 This is a top view of the structure when a guide plate is provided inside the melt inlet of the present invention.

[0071] Figure reference numerals: 1: Mixing and pelletizing device; 2: Melting and reducing device; 201: Vertical partition wall; 202: Melting and reducing zone; 203: Overflow zone; 204: Feed pipe; 205: Melt conveying pipe; 206: Slag discharge port; 207: Heating electrode; 208: Automatic electrode lifting mechanism; 3: Double roller cooling and pelletizing device; 301: Shell; 302: Cylindrical roller; 303: Melt inlet; 304: Protective gas inlet; 305: Finished product 306: Protective gas outlet; 307: Cooling medium inlet; 308: Cooling medium outlet; 309: Shaft core tube; 310: Through hole; 311: Pneumatic push-pull mechanism; 312: Telescopic scraper; 313: Drive motor; 314: Transmission wheel; 315: Transmission chain; 316: Support frame; 317: Guide plate; 318: Melt conveying pipe cleaning device; 319: Observation port; 4: Discharge cooling device; 5: Packaging device. Detailed Implementation

[0072] The technical solution of the present invention will be illustrated below with examples. The scope of protection sought by the present invention includes, but is not limited to, the following embodiments.

[0073] A system for preparing anhydrous sodium sulfide flakes using industrial waste salt containing sodium sulfate is disclosed. The system includes a mixing and pelletizing device 1, a melt reduction device 2, and a double-roller cooling and flake-forming device 3, arranged in series. The double-roller cooling and flake-forming device 3 includes a housing 301 and two cylindrical rollers 302. A flake-forming chamber is formed inside the housing 301, and the two cylindrical rollers 302 are arranged in parallel within the chamber. A melt inlet 303 and a protective gas inlet 304, communicating with the flake-forming chamber, are provided on the housing 301 above the cylindrical rollers 302. A finished product outlet 305 and a protective gas outlet 306, also communicating with the flake-forming chamber, are provided on the housing 301 below the cylindrical rollers 302. Each cylindrical roller 302 has an internal cavity, and a cooling medium inlet 307 and a cooling medium outlet 308, communicating with the cavity, are provided on its axial surface.

[0074] Preferably, a core tube 309 is also provided inside the cavity of the cylindrical roller 302. One end of the core tube 309 penetrates the axial surface of the cylindrical roller 302 and extends axially into the cavity of the cylindrical roller 302. The axis of the core tube 309 coincides with the axis of the cylindrical roller 302, and a sandwich chamber is formed between the outer wall of the core tube 309 and the inner wall of the cylindrical roller 302. The cooling medium inlet 307 is connected to the cavity of the core tube 309, and multiple through holes 310 communicating with the sandwich chamber are opened on the wall of the core tube 309. The cooling medium outlet 308 is connected to the sandwich chamber. Preferably, the length of the core tube 309 extending into the cavity of the cylindrical roller 302 is not less than two-thirds of the total axial length of the cylindrical roller 302. The cooling medium inlet 307 and the cooling medium outlet 308 are both located on the same side of the axial direction of the cylindrical roller 302.

[0075] Preferably, flow regulation control valves are independently installed on the cooling medium inlet 307 and the protective gas inlet 304.

[0076] Preferably, the two cylindrical rollers 302 are arranged in the film-making chamber in a staggered and parallel manner, meaning that the projections of the two cylindrical rollers 302 in the vertical direction and in the horizontal direction do not completely overlap. A pneumatic push-pull mechanism 311 is also provided outside the housing 301. The pneumatic push-pull mechanism 311 is connected to both ends of the lower cylindrical roller 302 of the two cylindrical rollers 302. The pneumatic push-pull mechanism 311 drives the lower cylindrical roller 302 to move relative to the higher cylindrical roller 302, thereby adjusting the radial distance between the surfaces of the two cylindrical rollers 302.

[0077] Preferably, the radial distance between the surfaces of the two cylindrical rollers 302 is no more than 10 mm, preferably 1~8 mm, and more preferably 2~5 mm.

[0078] Preferably, telescopic scrapers 312 are independently provided on the inner wall of the housing 301 on the side of each of the two cylindrical rollers 302 away from each other.

[0079] Preferably, a drive motor 313 is also provided outside the housing 301, and a transmission wheel 314 is provided at one end of the cylindrical roller 302. The drive wheel of the drive motor 313 is connected to the transmission wheel 314 through a transmission chain 315. The drive motor 313 drives the two cylindrical rollers 302 to rotate relative to each other through the transmission chain 315 and the transmission wheel 314.

[0080] Preferably, multiple drive motors 313 are provided on the outside of the housing 301, and the multiple drive motors 313 alternately drive the two cylindrical rollers 302 to rotate relative to each other.

[0081] Preferably, a support frame 316 is also provided at the bottom of the housing 301. An observation port 319 is also provided at the top of the housing 301.

[0082] Preferably, the melt inlet 303 is designed as an elongated opening extending along the axial direction of the cylindrical roller 302. Multiple guide plates 317 are also provided inside the melt inlet 303. These guide plates 317 are evenly distributed along the length of the melt inlet 303, dividing the space between the melt inlet 303 and the cylindrical roller 302 into multiple inclined feeding channels. A temperature sensor is provided at the bottom end of each guide plate 317.

[0083] Preferably, the length of the melt inlet 303 along the axial direction of the cylindrical roller 302 is not greater than the axial length of the cylindrical roller 302, preferably not greater than three-quarters of the axial length of the cylindrical roller 302, and more preferably one-half to three-quarters of the axial length of the cylindrical roller 302.

[0084] Preferably, the width of the melt inlet 303 along the horizontal radial direction of the cylindrical roller 302 is not greater than the radial distance between the central axes of the two cylindrical rollers 302, preferably not greater than three-quarters of the radial distance between the central axes of the two cylindrical rollers 302, and more preferably one-quarter to three-quarters of the radial distance between the central axes of the two cylindrical rollers 302.

[0085] Preferably, a melt conveying pipe cleaning device 318 is also provided on the melt inlet 303.

[0086] Preferably, the melting reduction apparatus 2 includes a furnace body and a furnace cavity. According to the material flow direction, a vertical partition wall 201 is provided on the bottom plate in the middle of the furnace cavity, dividing the furnace cavity into a melting reduction zone 202 and an overflow zone 203. A top notch is provided at the top of the vertical partition wall 201 to connect the melting reduction zone 202 and the overflow zone 203. A feed pipe 204 is provided on the side wall of the melting reduction zone 202. A melt conveying pipe 205 is provided on the side wall of the overflow zone 203, with the outlet end of the melt conveying pipe 205 connected to the melt inlet 303.

[0087] Preferably, slag discharge ports 206 and heating electrodes 207 are independently provided in the molten reduction zone 202 and the overflow zone 203, respectively.

[0088] Preferably, an automatic electrode lifting mechanism 208 is also provided on the upper surface of the furnace body. The upper end of each heating electrode 207 passes through the furnace body and is connected to the automatic electrode lifting mechanism 208. The automatic electrode lifting mechanism 208 independently controls the downward depth of each heating electrode 207 in the melting reduction zone 202 and the overflow zone 203.

[0089] Preferably, the heating electrode 207 is a heating graphite electrode.

[0090] Preferably, the furnace body consists of a stainless steel outer wall layer, a water-cooling layer, and a refractory casting layer, from the outside to the inside.

[0091] Preferably, the system also includes a discharge cooling device 4 and a packaging device 5. The discharge cooling device 4 is a closed spiral feeding mechanism, and its feeding channel is equipped with a nitrogen input pipe and a nitrogen output pipe. The finished product outlet 305 of the double-roller cooling sheet forming device 3 is connected to the inlet of the packaging device 5 through the discharge cooling device 4. Example 1

[0092] like Figure 1-11 As shown, a system for preparing anhydrous flake sodium sulfide using industrial waste salt containing sodium sulfate is disclosed. The system includes a mixing and pelletizing device 1, a melt reduction device 2, and a double-roller cooling and flake-forming device 3, arranged in series. The double-roller cooling and flake-forming device 3 includes a housing 301 and two cylindrical rollers 302. A flake-forming chamber is formed inside the housing 301, and the two cylindrical rollers 302 are arranged in parallel within the chamber. A melt inlet 303 and a protective gas inlet 304, communicating with the flake-forming chamber, are provided on the housing 301 located above the cylindrical rollers 302. A finished product outlet 305 and a protective gas outlet 306, also communicating with the flake-forming chamber, are provided on the housing 301 located below the cylindrical rollers 302. Each cylindrical roller 302 has an internal cavity, and a cooling medium inlet 307 and a cooling medium outlet 308, communicating with the cavity, are provided on its axial surface. Example 2

[0093] The embodiment 1 is repeated, except that a core tube 309 is also provided inside the cavity of the cylindrical roller 302. One end of the core tube 309 penetrates the axial surface of the cylindrical roller 302 and extends axially into the cavity of the cylindrical roller 302. The axis of the core tube 309 coincides with the axis of the cylindrical roller 302, and a sandwich chamber is formed between the outer wall of the core tube 309 and the inner wall of the cylindrical roller 302. The cooling medium inlet 307 is connected to the cavity of the core tube 309, and multiple through holes 310 communicating with the sandwich chamber are opened on the tube wall of the core tube 309. The cooling medium outlet 308 is connected to the sandwich chamber. Example 3

[0094] Example 2 is repeated, except that the length of the shaft core tube 309 extending into the cavity of the cylindrical roller 302 is not less than two-thirds of the total axial length of the cylindrical roller 302. The cooling medium inlet 307 and the cooling medium outlet 308 are both located on the same side of the axial direction of the cylindrical roller 302. Example 4

[0095] The same method as Example 3 is used, except that flow regulation control valves are independently provided on the cooling medium inlet 307 and the protective gas inlet 304. Example 5

[0096] Example 4 is repeated, except that the two cylindrical rollers 302 are arranged in the film-making chamber in a staggered and parallel manner, that is, the projections of the two cylindrical rollers 302 in the vertical direction and in the horizontal direction do not completely overlap. A pneumatic push-pull mechanism 311 is also provided outside the housing 301. The pneumatic push-pull mechanism 311 is connected to both ends of the lower cylindrical roller 302 of the two cylindrical rollers 302. The pneumatic push-pull mechanism 311 drives the lower cylindrical roller 302 to move relative to the higher cylindrical roller 302, thereby adjusting the radial distance between the surfaces of the two cylindrical rollers 302. Example 6

[0097] Example 5 is repeated, except that the radial distance between the surfaces of the two cylindrical rollers 302 is 6 mm. Example 7

[0098] Example 6 is repeated, except that the radial distance between the surfaces of the two cylindrical rollers 302 is 4 mm. Example 8

[0099] Repeat Example 7, except that telescopic scrapers 312 are independently provided on the inner wall of the housing 301 on the side of each of the two cylindrical rollers 302 away from each other. Example 9

[0100] The embodiment 8 is repeated, except that a drive motor 313 is also provided outside the housing 301, and a transmission wheel 314 is provided at one end of the cylindrical roller 302. The drive wheel of the drive motor 313 is connected to the transmission wheel 314 through a transmission chain 315. The drive motor 313 drives the two cylindrical rollers 302 to rotate relative to each other through the transmission chain 315 and the transmission wheel 314. Example 10

[0101] Example 9 is repeated, except that multiple drive motors 313 are provided on the outside of the housing 301, and the multiple drive motors 313 alternately drive the two cylindrical rollers 302 to rotate relative to each other. Example 11

[0102] The embodiment 10 is repeated, except that a support frame 316 is also provided at the bottom of the housing 301. An observation port 319 is also provided at the top of the housing 301. Example 12

[0103] The embodiment 11 is repeated, except that the melt inlet 303 is designed as an elongated opening extending along the axial direction of the cylindrical roller 302. Multiple guide plates 317 are also provided inside the melt inlet 303. These guide plates 317 are evenly distributed along the length of the melt inlet 303, dividing the space between the melt inlet 303 and the cylindrical roller 302 into multiple inclined feeding channels. A temperature sensor is provided at the bottom end of each guide plate 317. Example 13

[0104] Example 12 is repeated, except that the length of the melt inlet 303 along the axial direction of the cylindrical roller 302 is one-half to three-quarters of the axial length of the cylindrical roller 302. Example 14

[0105] Repeat Example 13, except that the width of the melt inlet 303 along the horizontal radial direction of the cylindrical roller 302 is one-quarter to three-quarters of the radial distance between the central axes of the two cylindrical rollers 302. Example 15

[0106] The same as Example 14 is repeated, except that a melt conveying pipe cleaning device 318 is also provided on the melt inlet 303. Example 16

[0107] The embodiment 15 is repeated, except that the melting reduction apparatus 2 includes a furnace body and a furnace cavity. According to the material flow, a vertical partition wall 201 is provided on the bottom plate in the middle of the furnace cavity, dividing the furnace cavity into a melting reduction zone 202 and an overflow zone 203. A top notch is provided at the top of the vertical partition wall 201 to connect the melting reduction zone 202 and the overflow zone 203. A feed pipe 204 is provided on the side wall of the melting reduction zone 202. A melt conveying pipe 205 is provided on the side wall of the overflow zone 203, with the outlet end of the melt conveying pipe 205 connected to the melt inlet 303. Example 17

[0108] Example 16 is repeated, except that a slag discharge port 206 and a heating electrode 207 are independently provided in the molten reduction zone 202 and the overflow zone 203, respectively. Example 18

[0109] The same method as Embodiment 17 is used, except that an automatic electrode lifting mechanism 208 is also provided on the upper surface of the furnace body. The upper end of each heating electrode 207 passes through the furnace body and is connected to the automatic electrode lifting mechanism 208. The automatic electrode lifting mechanism 208 independently controls the downward depth of each heating electrode 207 in the melting reduction zone 202 and the overflow zone 203. Example 19

[0110] Example 18 is repeated, except that the heating electrode 207 is a heating graphite electrode. Example 20

[0111] The same as Example 19 is repeated, except that the furnace body is composed of a stainless steel outer wall layer, a water cooling layer and a refractory material casting layer from the outside to the inside. Example 21

[0112] The system repeats Example 20, except that it also includes a discharge cooling device 4 and a packaging device 5. The discharge cooling device 4 is a closed spiral feeding mechanism, and its feeding channel is equipped with a nitrogen input pipe and a nitrogen output pipe. The finished product outlet 305 of the double-roller cooling sheet forming device 3 is connected to the inlet of the packaging device 5 through the discharge cooling device 4.

[0113] Application Example 1

[0114] The method for preparing anhydrous flake sodium sulfide using the system described in Example 21 includes the following steps:

[0115] 1) The carbon powder and industrial sodium sulfate are mixed in a molar ratio of Na2SO4:2C=1:1.15 to obtain a mixture.

[0116] 2) The mixture is fed into the melting reduction device 2 for an oxygen-free melting reduction reaction. The reaction temperature is 1280℃, and the temperature of the obtained sodium sulfide melt is controlled at about 1050℃ (its purity was detected to be 63.7%).

[0117] 3) The sodium sulfide melt was directly fed into a two-roll cooling and sheeting device for cooling and sheeting. During the cooling and sheeting process, the flow rates of nitrogen and cooling medium were controlled. The temperature of the sodium sulfide melt before sheeting was 952℃, and the temperature after sheeting was 460℃, resulting in solid sheet sodium sulfide product (purity 62.1%).

[0118] 4) The flake sodium sulfide obtained in step 2) is further cooled with nitrogen in the discharge cooling device 4 until the temperature is below 50°C, and then sent to the packaging device 5 for packaging.

[0119] Application Example 2

[0120] The method for preparing anhydrous flake sodium sulfide using the system described in Example 21 includes the following steps:

[0121] 1) After mixing carbon powder and industrial sodium sulfate in a molar ratio of Na2SO4:2C=1:1.15, a mixture is obtained. After being stirred and mixed evenly, the mixture is sent to the mixing and pelletizing device 1 for pelletizing treatment to obtain pellets with an average particle size of about 8.1cm.

[0122] 2) The pellets are fed into the melting reduction device 2 for an oxygen-free melting reduction reaction. The reaction temperature is 1280℃, and the temperature of the obtained sodium sulfide melt is controlled at about 1050℃ (its purity was detected to be 67.9%).

[0123] 3) The sodium sulfide melt was directly fed into a two-roll cooling and sheeting device for cooling and sheeting. During the cooling and sheeting process, the flow rates of nitrogen and cooling medium were controlled. The temperature of the sodium sulfide melt before sheeting was 953℃, and the temperature after sheeting was 462℃, resulting in solid sheet sodium sulfide product (purity 66.5%).

[0124] 4) The flake sodium sulfide obtained in step 2) is further cooled with nitrogen in the discharge cooling device 4 until the temperature is below 50°C, and then sent to the packaging device 5 for packaging.

[0125] Application Example 3

[0126] The method for preparing anhydrous flake sodium sulfide using the system described in Example 21 includes the following steps:

[0127] 1) After mixing carbon powder and industrial sodium sulfate in a molar ratio of Na2SO4:2C=1:1.15, mixture I is obtained. Then, 0.1% nickel based on the total mass of the mixture is added to mixture I to obtain mixture II.

[0128] 2) The mixture II is fed into the melting reduction device 2 for an oxygen-free melting reduction reaction. The reaction temperature is 1280℃, and the temperature of the obtained sodium sulfide melt is controlled at about 1050℃ (its purity was detected to be 65.3%). Compared with application example 1, due to the addition of nickel as a catalyst, the reduction efficiency is improved and the temperature required for reduction is reduced, so a sodium sulfide melt with higher purity can be obtained.

[0129] 3) The sodium sulfide melt was directly fed into a two-roll cooling and sheeting device for cooling and sheeting. During the cooling and sheeting process, the flow rates of nitrogen and cooling medium were controlled. The temperature of the sodium sulfide melt before sheeting was 954℃, and the temperature after sheeting was 466℃, resulting in solid sheet sodium sulfide product (purity 64.4%).

[0130] 4) The flake sodium sulfide obtained in step 2) is further cooled with nitrogen in the discharge cooling device 4 until the temperature is below 50°C, and then sent to the packaging device 5 for packaging.

[0131] Application Example 4

[0132] The method for preparing anhydrous flake sodium sulfide using the system described in Example 21 includes the following steps:

[0133] 1) After mixing carbon powder and industrial sodium sulfate in a molar ratio of Na2SO4:2C=1:1.15, a mixture is obtained. Then, 0.1% nickel based on the total mass of the mixture is added to the mixture. After stirring and mixing evenly, the mixture is sent to the mixing and pelletizing device 1 for pelletizing treatment to obtain pellets with an average particle size of about 8.1 cm.

[0134] 2) The pellets are fed into the melting reduction device 2 for an oxygen-free melting reduction reaction. The reaction temperature is 1280℃, and the temperature of the obtained sodium sulfide melt is controlled at about 1050℃ (its purity was detected to be 80.6%).

[0135] 3) The sodium sulfide melt was directly fed into a two-roll cooling and sheeting device for cooling and sheeting. During the cooling and sheeting process, the flow rates of nitrogen and cooling medium were controlled. The temperature of the sodium sulfide melt before sheeting was 953℃, and the temperature after sheeting was 463℃, resulting in solid sheet sodium sulfide product (purity 79.6%).

[0136] 4) The flake sodium sulfide obtained in step 2) is further cooled with nitrogen in the discharge cooling device 4 until the temperature is below 50°C, and then sent to the packaging device 5 for packaging.

[0137] Application Example 5

[0138] Example 2 was repeated, except that the melt reduction reaction temperature was 1380°C, and the temperature of the obtained sodium sulfide melt was controlled to be around 1050°C (its purity was detected to be 79.2%). The temperature of the sodium sulfide melt before sheeting was 960°C, and the temperature after sheeting was 469°C, resulting in a solid sheet sodium sulfide product with a purity of 77.3%.

[0139] Application Example 6

[0140] Example 4 was repeated, except that 0.1% nickel was replaced with 0.1% cobalt. The purity of the obtained sodium sulfide melt was detected to be 80.9%.

[0141] Application Example 7

[0142] Example 4 was repeated, except that 0.1% nickel was replaced with 0.1% iron. The purity of the obtained sodium sulfide melt was detected to be 80.1%.

[0143] Comparative Example 1

[0144] Repeating Example 4, the temperature of the obtained sodium sulfide melt was controlled at around 1150°C (its purity was detected to be 80.4%). The melt was directly fed into the sheet-making machine. During the sheet-making process, nitrogen and cooling media were not introduced for cooling. Because the temperature of the sodium sulfide melt was too high and its corrosiveness was too great before sheet-making, it could not be cooled and solidified after passing through the double rollers, so no sheet-shaped sodium sulfide product could be obtained, and the double rollers were significantly corroded.

[0145] Comparative Example 2

[0146] The application of Example 1 was repeated, except that the temperature of the obtained sodium sulfide melt was controlled at approximately 1000°C (its purity was detected to be 80.1%). The nitrogen flow rate was increased during the cooling and sheet-making process, resulting in a sodium sulfide melt temperature of approximately 945°C before sheet-making. Because the sodium sulfide melt temperature was too low before sheet-making, it was rapidly cooled and solidified upon contact with the twin rollers. After further extrusion by the twin rollers, a fine powdery product was obtained, rather than flake-shaped sodium sulfide. Furthermore, because the sodium sulfide had already solidified before being extruded by the twin rollers, the gap between the rollers became smaller, leading to blockage of the gap after a period of time.

Claims

1. A method for preparing anhydrous flake sodium sulfide using industrial waste salt containing sodium sulfate, characterized in that: The method includes the following steps: 1) Mix industrial waste salt containing sodium sulfate, carbon powder, and with or without a catalyst to obtain a uniform mixture; 2) The mixture is subjected to melt reduction treatment in an oxygen-free environment to obtain sodium sulfide melt; 3) The sodium sulfide melt is cooled and then processed into flakes to obtain anhydrous flake sodium sulfide product; Step 3) specifically involves: first, using nitrogen to cool the sodium sulfide melt before tableting to 950-1140℃; then, during the tableting process, using indirect water cooling to ensure that the temperature of the resulting sodium sulfide flakes does not exceed 640℃; using a double-roller cooling tableting device (3) with heat exchange cooling effect to rapidly cool the high-temperature sodium sulfide melt while simultaneously performing tableting; the double-roller cooling tableting device (3) includes a shell (301) and two cylindrical rollers (302); the interior of the shell (301) forms a tableting chamber, and the two cylindrical rollers (302) form a tableting chamber. 02) The cylindrical roller (302) is arranged in parallel within the film-making chamber; a melt inlet (303) and a protective gas inlet (304) communicating with the film-making chamber are provided on the housing (301) located on the upper side of the cylindrical roller (302); a finished product outlet (305) and a protective gas outlet (306) communicating with the film-making chamber are provided on the housing (301) located on the lower side of the cylindrical roller (302); the cylindrical roller (302) has a cavity inside and a cooling medium inlet (307) and a cooling medium outlet (308) communicating with the cavity are provided on its axial surface. Two cylindrical rollers (302) are arranged in parallel and staggered manner in the film preparation chamber, that is, the projections of the two cylindrical rollers (302) in the vertical direction and in the horizontal direction are not completely overlapping; a pneumatic push-pull mechanism (311) is also provided outside the housing (301). The pneumatic push-pull mechanism (311) is connected to both ends of the lower cylindrical roller (302) of the two cylindrical rollers (302). The pneumatic push-pull mechanism (311) drives the lower cylindrical roller (302) to move relative to the higher cylindrical roller (302), thereby adjusting the radial distance between the surfaces of the two cylindrical rollers (302).

2. The method according to claim 1, characterized in that: Step 1) involves mixing industrial waste salt containing sodium sulfate, carbon powder, and catalyst evenly, then performing pelletizing treatment to obtain pellet material, and then performing melt reduction treatment on the pellet material in step 2) to obtain sodium sulfide melt.

3. The method according to claim 1 or 2, characterized in that: In industrial waste salt containing sodium sulfate, the mass content of sodium sulfate is not less than 80%; and / or The mixing ratio of industrial waste salt containing sodium sulfate to charcoal powder is Na₂SO₄:2C = 1:0.5~2 (molar ratio); and / or The catalyst is one or more of iron, cobalt, nickel, copper and their oxides, and its addition amount is 0 to 5% of the total mass of industrial waste salt containing sodium sulfate and carbon powder.

4. The method according to claim 3, characterized in that: In industrial waste salt containing sodium sulfate, the mass content of sodium sulfate is not less than 90%; the mixing ratio of industrial waste salt containing sodium sulfate and carbon powder is Na2SO4:2C=1:0.8~1.5 by molar ratio; the amount of catalyst added is 0.1~4% of the total mass of industrial waste salt containing sodium sulfate and carbon powder.

5. The method according to claim 4, characterized in that: The industrial waste salt containing sodium sulfate has a sodium sulfate content of not less than 95% by mass; the mixing ratio of industrial waste salt containing sodium sulfate and carbon powder is Na2SO4:2C = 1:0.9~1.2 by molar ratio; the amount of catalyst added is 0.3~3% of the total mass of industrial waste salt containing sodium sulfate and carbon powder.

6. The method according to any one of claims 1-2 and 4-5, characterized in that: The temperature for melt reduction treatment is 1000℃~1400℃; and / or The temperature of the sodium sulfide melt is 980~1200℃; the purity of the sodium sulfide melt is not less than 60%.

7. The method according to claim 6, characterized in that: The temperature for melt reduction treatment is 1050~1350℃; the temperature for sodium sulfide melt is 1000~1150℃; and the purity of sodium sulfide melt is not less than 70%.

8. The method according to claim 7, characterized in that: The temperature for melt reduction treatment is 1100~1250℃; the temperature for sodium sulfide melt is 1000~1100℃; and the purity of sodium sulfide melt is not less than 80%.

9. The method according to claim 6, characterized in that: The particle size of the pellets is 2~10cm.

10. The method according to claim 9, characterized in that: The particle size of the pellets is 2.5~8cm.

11. The method according to claim 10, characterized in that: The particle size of the pellets is 3~6cm.

12. The method according to claim 1, characterized in that: Step 3) Specifically, first use nitrogen to cool the sodium sulfide melt to 955-1000℃ before flake formation; then, while the flake formation process is underway, use indirect water cooling to ensure that the temperature of the resulting flake sodium sulfide does not exceed 635℃.

13. The method according to claim 12, characterized in that: Step 3) Specifically, nitrogen gas is used to cool the sodium sulfide melt before flake formation to 960-980℃; then, during the flake formation process, indirect water cooling is used to ensure that the temperature of the obtained flake sodium sulfide does not exceed 630℃, thus obtaining anhydrous flake sodium sulfide product.

14. The method according to claim 12 or 13, characterized in that: The anhydrous sodium sulfide flakes are further cooled to a temperature not exceeding 50°C using direct nitrogen cooling and / or indirect water cooling before packaging.

15. The method according to claim 14, characterized in that: The anhydrous sodium sulfide flakes are further cooled to 20-40°C using direct nitrogen cooling and / or indirect water cooling before packaging.

16. The method according to claim 15, characterized in that: The anhydrous sodium sulfide flakes are further cooled to 25-35°C using direct nitrogen cooling and / or indirect water cooling before packaging.

17. A system for use in the method according to any one of claims 1-16, characterized in that: The system includes a mixing and pelletizing device (1), a melting and reduction device (2), and a double-roller cooling and pelletizing device (3) arranged in series.

18. The system according to claim 17, characterized in that: A core tube (309) is also provided in the cavity of the cylindrical roller (302); one end of the core tube (309) passes through the axial surface of the cylindrical roller (302) and extends axially into the cavity of the cylindrical roller (302). The axis of the core tube (309) coincides with the axis of the cylindrical roller (302), and a sandwich chamber is formed between the outer wall of the core tube (309) and the inner wall of the cylindrical roller (302); the cooling medium inlet (307) is connected to the cavity of the core tube (309), and multiple through holes (310) connected to the sandwich chamber are opened on the tube wall of the core tube (309); the cooling medium outlet (308) is connected to the sandwich chamber.

19. The system according to claim 18, characterized in that: The length of the shaft core tube (309) extending into the cavity of the cylindrical roller (302) is not less than two-thirds of the total axial length of the cylindrical roller (302); the cooling medium inlet (307) and the cooling medium outlet (308) are both located on the same side of the axial direction of the cylindrical roller (302).

20. The system according to claim 18 or 19, characterized in that: Flow regulation control valves are independently installed on the cooling medium inlet (307) and the protective gas inlet (304).

21. The system according to claim 17, characterized in that: The radial distance between the surfaces of the two cylindrical rollers (302) is no more than 10 mm.

22. The system according to claim 21, characterized in that: The radial distance between the surfaces of the two cylindrical rollers (302) is 1~8mm.

23. The system according to claim 22, characterized in that: The radial distance between the surfaces of the two cylindrical rollers (302) is 2~5mm.

24. The system according to any one of claims 21-23, characterized in that: Telescopic scrapers (312) are independently provided on the inner wall of the housing (301) on the side of each of the two cylindrical rollers (302) away from each other.

25. The system according to any one of claims 17-19 and 21-23, characterized in that: A drive motor (313) is also provided outside the housing (301), and a transmission wheel (314) is provided at one end of the cylindrical roller (302). The drive wheel of the drive motor (313) is connected to the transmission wheel (314) through the transmission chain (315). The drive motor (313) drives the two cylindrical rollers (302) to rotate relative to each other through the transmission chain (315) and the transmission wheel (314).

26. The system according to claim 25, characterized in that: Multiple drive motors (313) are disposed outside the housing (301), and the multiple drive motors (313) alternately drive the two cylindrical rollers (302) to rotate relative to each other; and / or A support frame (316) is provided at the bottom of the housing (301); an observation port (319) is provided at the top of the housing (301).

27. The system according to any one of claims 17-19, 21-23, and 26, characterized in that: The melt inlet (303) is a long strip-shaped opening extending along the axial direction of the cylindrical roller (302); multiple guide plates (317) are also provided inside the melt inlet (303); the multiple guide plates (317) are evenly distributed along the length direction of the melt inlet (303) and divide the space between the melt inlet (303) and the cylindrical roller (302) into multiple inclined feeding channels; a temperature sensor is provided at the bottom of the guide plate (317).

28. The system according to claim 27, characterized in that: The length of the melt inlet (303) along the axial direction of the cylindrical roller (302) is not greater than the axial length of the cylindrical roller (302); and / or The width of the melt inlet (303) along the horizontal radial direction of the cylindrical roller (302) is not greater than the radial distance between the central axes of the two cylindrical rollers (302).

29. The system according to claim 28, characterized in that: The length of the melt inlet (303) along the axial direction of the cylindrical roller (302) is not greater than three-quarters of the axial length of the cylindrical roller (302); the width of the melt inlet (303) along the horizontal radial direction of the cylindrical roller (302) is not greater than three-quarters of the radial distance between the central axes of the two cylindrical rollers (302).

30. The system according to claim 29, characterized in that: The length of the melt inlet (303) along the axial direction of the cylindrical roller (302) is one-half to three-quarters of the axial length of the cylindrical roller (302); the width of the melt inlet (303) along the horizontal radial direction of the cylindrical roller (302) is one-quarter to three-quarters of the radial distance between the central axes of the two cylindrical rollers (302).

31. The system according to any one of claims 28-30, characterized in that: A melt conveying pipe cleaning device (318) is also provided at the melt inlet (303).

32. The system according to any one of claims 17-19, 21-23, 26, 28-30, characterized in that: The melting reduction device (2) includes a furnace body and a furnace cavity; according to the material flow, a vertical partition wall (201) is provided on the bottom plate in the middle of the furnace cavity, and the furnace cavity is divided into a melting reduction zone (202) and an overflow zone (203) in sequence by the vertical partition wall (201); the top of the vertical partition wall (201) has a top notch for connecting the melting reduction zone (202) and the overflow zone (203); a feed pipe (204) is provided on the side wall of the melting reduction zone (202); a melt conveying pipe (205) is provided on the side wall of the overflow zone (203), and the outlet end of the melt conveying pipe (205) is connected to the melt inlet (303); and / or The system also includes a discharge cooling device (4) and a packaging device (5); the discharge cooling device (4) is a closed spiral feeding mechanism, and its feeding channel is equipped with a nitrogen input pipe and a nitrogen output pipe; the finished product outlet (305) of the double roller cooling sheet making device (3) is connected to the feed inlet of the packaging device (5) through the discharge cooling device (4).

33. The system according to claim 32, characterized in that: A slag discharge port (206) and a heating electrode (207) are independently provided in the molten reduction zone (202) and the overflow zone (203), respectively.

34. The system according to claim 33, characterized in that: An automatic electrode lifting mechanism (208) is also provided on the upper surface of the furnace body; the upper end of each heating electrode (207) passes through the furnace body and is connected to the automatic electrode lifting mechanism (208). The automatic electrode lifting mechanism (208) independently controls the downward depth of each heating electrode (207) in the melting reduction zone (202) and the overflow zone (203).

35. The system according to claim 34, characterized in that: The heating electrode (207) is a heating graphite electrode.

36. The system according to claim 35, characterized in that: The furnace body consists of a stainless steel outer wall layer, a water cooling layer, and a refractory casting layer, from the outside to the inside.

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