Production line for synthesizing silicon nitride micropowder by using crystal silicon slice waste mortar

Abstract

The invention discloses a production line for synthesizing silicon nitride micropowder by using crystal silicon slice waste mortar. The production line comprises a filter press, a filtrate clarification tank, a vacuum dryer, a rotary vibration sieve, a silicon powder tank, a vector fluidization seat, an atomization ejector, an atomization synthesizer, a plasma spray gun, a plasma control cabinet, a circulating water high-level tank, a circulating water tank, a circulating water pump, a spray head, a nitrogen source device, a liquid nitrogen gasifier and a pressure regulating valve group, the system is composed of a flow control valve bank, a nitrogen recovery tank, a vacuum packaging machine, corresponding process pipelines and an automatic control system. The method comprises the following steps: preparing high-purity silicon powder by using crystalline silicon slice waste mortar, carrying out heat exchange and heating on fresh nitrogen and a reaction product, preheating fluidized silicon powder, atomizing, spraying into a synthesizer, reacting under specific process conditions to generate silicon nitride, introducing excess reaction nitrogen and the generated product into a quench cooler, carrying out heat exchange with the fresh nitrogen, and quenching to below 150 DEG C; fixing the crystal form and granularity of the silicon nitride structure, entering a gas-solid separator to complete the separation of Si3N4 and N2, entering the Si3N4 into a packaging inlet of a packaging machine to be sold, and emptying and discharging N2; the cooling water circulation system exchanges heat and cools the equipment, and the control cabinet detects and controls the operation condition of the process unit.

Description

Technical Field

[0001] The invention relates to a production line for synthesizing silicon nitride micropowder by using waste mortar of crystalline silicon slices, and belongs to the field of comprehensive utilization of photovoltaic crystalline silicon slice waste and silicon nitride powder production equipment. Background Art

[0002] Silicon nitride is an advanced engineering ceramic material with high room temperature and high temperature strength, high hardness, abrasion resistance, oxidation resistance, and good resistance to thermal shock and mechanical shock. It is considered by the materials science community to be a new material with excellent comprehensive performance in the field of structural ceramics and the most promising alternative to nickel-based alloys for wide application in high-tech and high-temperature fields.

[0003] The synthesis process of silicon nitride powder is generally:

[0004] Silicon powder direct nitridation 3Si(s)+2N2(g)=Si3N4(s)

[0005] Silicylimine gas phase reaction 3SiCl4(g)+4NH3(g)=Si3N4(s)+12HCl(g)

[0006] Carbon thermal reduction nitridation 3SiO2(s)+6C(s)+2N2(g)=Si3N4(s)+6CO(g)

[0007] Among them, direct nitridation of silicon powder is the earliest developed process for preparing silicon nitride powder and is also the most widely used method at present. This method is to load the raw silicon powder into a sagger and place it in a reaction furnace. First, the gas in the furnace is replaced, nitrogen is introduced to heat it, and argon is added to control the reaction rate to prevent the silicon powder from reacting rapidly and overheating to melt and form balls, causing the reaction to terminate. Until the silicon powder no longer absorbs nitrogen, the furnace is stopped to cool down and the furnace is taken out. The production cycle of a single furnace is about one week, and the output is 80-200kg / furnace. The product is in granular form and must undergo subsequent processing to obtain silicon nitride powder material. It is an intermittent production process with a long reaction cycle, high energy consumption, and poor quality reliability.

[0008] Since 2006, the applicant has been concerned about the treatment of waste mortar in the processing of crystalline silicon for photovoltaic cells and explored and studied the optimal recycling technology. On April 22, 2011, an invention patent application for "New Method for Comprehensive Treatment of Waste Mortar in Crystalline Silicon Processing of Photovoltaic Cells" with the application number 201110101064.7 was filed. On August 12, 2011, an invention patent application for "Comprehensive Treatment Technology of Waste Mortar in Photovoltaic Crystalline Silicon Processing" with the application number 201110238197.9 was filed, which supplemented and improved the previous patent application. On June 26, 2012, an application for "Comprehensive Treatment Technology of Waste Mortar in Crystalline Silicon Processing without Sewage and Solid Waste Discharge" with the application number 201210207989.4 was filed with the priority of the application number 201110238197.9, and the patent right was obtained on May 20, 2015. On January 23, 2013, a patent application for "Unit for Recycling Silicon Powder from Waste Mortar in Crystalline Silicon Processing to Prepare Silicon Nitride Products" with the application number 201310024134.2 was filed, and the patent right was obtained on November 19, 2014.

[0009] When the above patent applications were initially filed, the multi-wire cutting process was commonly used in the field of photovoltaic crystalline silicon slicing. The waste mortar generated during the crystalline silicon slicing process was a mixed slurry of four systems: silicon material chips - Si, cutting wire abrasion chips - Fe, ineffective abrasives - SiC, and cutting fluid - polyethylene glycol. Now, solar photovoltaic crystalline silicon slicing has been completely replaced by the new diamond wire cutting process. The waste mortar generated during the crystalline silicon slicing process has become a mixed slurry of three systems: silicon material chips - Si, coolant high-purity water, and trace diamond chips. After dehydration and drying, high-purity ultrafine silicon powder with a particle size of 0 - 8um and a silicon content of over 99.5% can be obtained, which is used as the raw material for producing silicon nitride powder. However, this silicon powder is too fine to produce silicon nitride by traditional nitriding processes, and a new method must be adopted. Summary of the Invention

[0010] The object of the present invention is to adapt to the new processes and new problems in the current photovoltaic crystalline silicon slicing, and solve the technical matching problems of the treatment and comprehensive utilization of diamond wire waste mortar in crystalline silicon slicing and the silicon nitride powder material production line.

[0011] The object of the present invention is achieved as follows: The production line for synthesizing silicon nitride micropowder from waste mortar of crystalline silicon slices consists of a filter press (1), a filtrate clarification tank (2), a vacuum dryer (3), a rotary vibrating screen (4), a silicon powder tank (5), a vector fluidization base (6), an atomizing injector (7), an atomizing synthesizer (8), a plasma spray gun (9), a plasma control cabinet (10), a circulating water elevated tank (11), a circulating water pool (12), a circulating water pump (13), a spray head (14), a nitrogen source device (15), a liquid nitrogen vaporizer (16), a nitrogen pressure regulating valve group (17), a nitrogen flow control valve group (18), a nitrogen recovery tank (19), a vacuum packaging machine (20) and corresponding process pipelines and an automatic control system; among which the atomizing synthesizer (8) is the core equipment of the production line and consists of an atomizing reaction furnace (8-1), a quencher (8-2), and a gas-solid separator (8-3), and is used to complete process procedures such as reaction synthesis, cooling heat exchange, and gas-solid separation of the product (applied separately); the nitrogen source device is divided into two types: purchased liquid nitrogen and self-made nitrogen. The purity of self-made nitrogen must be ≥99.99%, and the pressure must be ≥0.5 MPa. The purity of purchased liquid nitrogen can reach 99.999%, and the temperature is lower than -196°C. Nitrogen is the key resource of this technology. In addition to being used as the raw material for product production, it is also used for quenching heat exchange of reaction products, atomizing transportation of silicon powder, reaction temperature control, and production protection of silicon powder; the filter press (1), the filtrate clarification tank (2), the vacuum dryer (3), the rotary vibrating screen (4), and the silicon powder tank (5) constitute a waste mortar treatment system, which is used to treat waste mortar to obtain a particle size of 0-8 um and a purity of 99.5% or more of ultrafine silicon powder as a raw material for silicon nitride synthesis; a vector fluidization seat (6), a silicon powder tank (5), and an atomizing injector (7) constitute a silicon powder atomizing feeder (another application), which completes the preheating, fluidization, vector metering, airflow delivery, atomization and injection into the reaction furnace of the reaction raw materials silicon powder and nitrogen at one time. One atomizing synthesizer is equipped with 2-8 groups of silicon powder atomizing feeders, and the atomizing feeders are grouped in two, with one in each group and one in reserve, and the switching is linked to ensure uniform and continuous feeding; a plasma spray gun (9) is installed on the atomizing synthesizer. The top of the device is provided with nitrogen plasma for the atomizing synthesizer reactor under the control of the plasma control cabinet (10) for ignition of silicon-nitrogen reaction and heating of the furnace; the circulating water high-level tank (11), the circulating water pool (12), the circulating water pump (13), the nozzle (14) and the jacket of the gas-solid separator (8-3) silo constitute a cooling water circulation system. When self-made nitrogen is used as the nitrogen source, the cooling water circulation system needs to meet the cooling and cooling of the plasma device and the gas-solid separator silo. When liquid nitrogen is used as the nitrogen source, the cooling water circulation system is only responsible for the plasma The cooling of the sub-device; except for the atomizing synthesizer (8), the silicon powder tank (5), the vector fluidizing seat (6), and the atomizing injector (7), the rest are mature domestic equipment; the process method of the production line for synthesizing silicon nitride micropowder using waste slurry of crystalline silicon slices is as follows: the waste slurry containing silicon powder, high-purity water and other trace impurities generated in the photovoltaic crystalline silicon slice process is added to the filter press (1) for filtration to obtain filter cake and filtrate, the filtrate enters the clarification tank (2), the high-purity water after flocculation and clarification is input into the cooling water circulation tank (12) along the S001 water pipe, and the supplement The filter cake is added to the vacuum dryer (3) for vacuum low-temperature drying to prevent oxidation of silicon powder; the dried silicon powder is screened and removed under the protection of nitrogen N204 discharged from the nitrogen recovery tank (19) to obtain silicon powder with a particle size of 0-8um and a purity of more than 99.5%; the silicon powder is metered and loaded into the material tank (5) for standby use under the protection of nitrogen N203; the N2 raw material is obtained by purchasing liquid nitrogen or self-made nitrogen according to the conditions. The purity of the purchased liquid nitrogen is 99.99.9%, the temperature is below -196°C. The liquid nitrogen in the liquid nitrogen tank (15) enters the liquid nitrogen vaporizer (16) installed in the cooling water circulation pool (12) through the N001 pipeline and exchanges heat with the cooling return water S203 to complete the vaporization of liquid nitrogen and cool the circulating return water at the same time. The low-temperature nitrogen gas after the vaporization of liquid nitrogen enters the pressure regulating valve group (17). After regulating the nitrogen gas pressure, it enters the lower part of the jacket of the atomization synthesizer quencher (8-1) along the N101 low-temperature nitrogen gas pipeline under the control of the mass flow control valve group (18), and exchanges heat with the high-temperature Si3N4+N2 mixture in the quencher through the partition wall, reducing the temperature of the Si3N4+N2 product to below 150°C. The nitrogen gas N102 leaving the quencher has its temperature raised to about 600°C and is used for the atomized transportation of silicon powder. When the furnace temperature of the atomization reaction furnace (8-1) of the atomization synthesizer (8) reaches 1000 - 1450°C and the furnace atmosphere meets the conditions for the silicon powder nitridation reaction, install the prepared silicon powder tank (5) on the vector control fluidization base (6), and install the atomization emitter (7) in the reserved installation hole on the upper cover of the tank (5). Open the N105 valve to make nitrogen gas enter the nitrogen gas pipeline of the atomization feeder, open the N106 valve, the nitrogen gas enters the fluidization base (6), and the fluidization of the silicon powder in the tank is realized through the ceramic sintered microporous plate at the bottom of the silicon powder tank (5). Open the N107 valve and start the atomization reflector (7). Spray the silicon powder in an atomized state into the furnace chamber of the atomization reaction furnace (8-1) of the atomization synthesizer (8) along the (Si+N)101 pipeline according to the mass ratio of Si:N2 of 1:1 - 2. Start the plasma torch (9) to prepare nitrogen plasma for triggering the nitridation reaction and regulating the furnace temperature of the reactor well. The nitrogen gas enters the plasma control cabinet (10) through the N103 nitrogen gas pipeline, adjusts the flow rate and enters the plasma torch (11) through the N104 pipeline. The silicon powder and nitrogen gas atomized and sprayed into the reaction furnace chamber of the silicon nitride atomization synthesizer react at 1000 - 1450°C and a working pressure of 0.01 - 0.Under the conditions of 6MPa and excess nitrogen, silicon nitride is generated according to the reaction equation 3Si+2N2=Si3N4, with 20-60% of nitrogen remaining, forming a Si3N4+N2 mist mixture, which enters the atomizing synthesizer quencher (8-2), exchanges heat with the low-temperature nitrogen in the jacket, and is rapidly cooled to below 150°C to fix the structure, crystal form and particle size of silicon nitride, and enters the gas-solid separator (8-3) to complete the separation of Si3N4 and N2. The Si3N4 in the silo enters the packaging machine (20) for packaging and storage for sale, and the discharged nitrogen N201 enters the nitrogen recovery tank (19), and is sent to the rotary vibrating screen (4) of the waste slurry treatment system and the silicon powder canning process (5) through the guide pipe N202 for nitrogen protection for drying silicon powder; the plasma spray gun is installed in the atomizing reaction furnace of the silicon nitride synthesizer (8) and is always in a high temperature environment of 1000-1450℃ to ensure the safety of the plasma system. In order to ensure the safety of the plasma spray gun during operation, especially during unexpected power outages, a cooling water circulation system is provided. During normal operation, the cooling water S102 pumped out by the circulation pump group (12) fills the high-level tank (11) through the pipe S105, and at the same time enters the plasma control cabinet (10) and the plasma spray gun (9) through the branch pipe S104 of S102, and the cooling return water is respectively collected from S201 and S202 into the S203 spray head (14) and heat exchanged with the liquid nitrogen gasifier (16) to reduce the temperature, thereby maintaining the safe operation of the plasma system. When an unexpected power outage occurs, S107 of the high-level tank (11) is opened to provide emergency cooling water to the plasma spray gun, and the cooling water is returned to the circulation pool through S202, S203 and the spray head (14); thereby ensuring the safety of the plasma spray gun under the high temperature environment of the furnace; when the nitrogen source is homemade nitrogen, the heat exchange effect thereof is poor, and the cooling water circulation system also needs to cool the gas-solid separator at the bottom of the atomizing synthesizer. .

[0012] The waste mortar treatment system consists of a filter press (1), a filtrate clarifier (2), a vacuum dryer (3), a rotary vibrating screen (4), and a silicon powder tank (5), and is used to treat crystalline silicon slice waste mortar to obtain ultrafine silicon powder with a particle size of 0-8um and a purity of more than 99.5%, which is used as a raw material for silicon nitride synthesis; the bottom plate of the silicon powder tank (5) is a ceramic sintered microporous plate, and the upper cover is equipped with an atomizing injector installation socket, which also serves as a silicon powder container and a fluidized tank.

[0013] The silicon powder atomizing feeder is composed of a vector fluidizing seat (6), a silicon powder tank (5), and an atomizing injector (7); and is used to complete the preheating, fluidization, vector metering, airflow sending, atomization injection into the reaction furnace and other processes of the reaction raw materials silicon powder and nitrogen. One atomizing synthesizer is equipped with 2-8 groups of silicon powder atomizing feeders, and the atomizing feeders are grouped in two, with one in operation and one in standby, and the switching is linked to ensure uniform and continuous feeding.

[0014] The atomization synthesizer (8) (separate application) is the core equipment of the production line, which consists of an atomization reaction furnace (8-1), a quencher (8-2), and a gas-solid separator (8-3), and is used to complete the process of reaction synthesis, cooling heat exchange, gas-solid separation, etc. of the product; its comprehensive effect is excellent, but it is restricted by the surrounding resource conditions.

[0015] The nitrogen source device is purchased liquid nitrogen with a purity of ≥99.999% and a temperature below -196°C. In addition to being used as a raw material for product production, it is also used for rapid cooling heat exchange of reaction products, atomized transportation of silicon powder, regulation of reaction temperature, and protection of silicon powder production. Nitrogen resources can be obtained locally, but the comprehensive benefit is not as good as that of liquid nitrogen.

[0016] The atomization synthesizer (8), silicon powder tank (5), vector fluidization seat (6), and atomization injector (7) in the production line supporting equipment for synthesizing silicon nitride micropowder from waste mortar of crystalline silicon wafers are special equipment and require professional design and manufacturing; the rest are mature equipment and can be solved by supporting in the domestic market.

[0017] The present invention will be further described in conjunction with the accompanying drawings and embodiments. Description of the Drawings

[0018] Figure 1 Process flow chart of the liquid nitrogen process for the production line of synthesizing silicon nitride micropowder from waste mortar of crystalline silicon wafers.

[0019] Figure 2 It is the self-made process flow chart of the production line for synthesizing silicon nitride micropowder from waste mortar of crystalline silicon wafers.

[0020] The numbers in the figure represent the equipment and machines of the production line for synthesizing silicon nitride micropowder from waste mortar of crystalline silicon wafers: 1 - filter press, 2 - filtrate clarification tank, 3 - vacuum dryer, 4 - rotary vibrating screen, 5 - silicon powder tank, 6 - vector fluidizer, 7 - atomization injector, 8 - atomization synthesizer (divided into 8-1 - reaction furnace, 8-2 - quencher, 8-3 - gas-solid separator), 9 - plasma spray gun, 10 - plasma control cabinet, 11 - circulating water elevated tank, 12 - circulating water pool, 13 - circulating water pump, 14 - spray head, 15 - nitrogen source device ( Figure 1 in which is the liquid nitrogen storage tank, Figure 2 in which is the pressure swing adsorption nitrogen generation device), 16 - liquid nitrogen vaporizer, 17 - nitrogen pressure regulating valve group, 18 - nitrogen flow control valve group, 19 - nitrogen recovery tank, 20 - vacuum packaging machine.

[0021] The arrow in the figure indicates the operation direction of the process.

[0022] In the figure, the letters in the numbers such as N001 indicate the pipeline medium, the first digit indicates the medium state, and the last two digits indicate the medium pipeline number: N - nitrogen, the first digit 0 - liquid nitrogen, 1 - new nitrogen gas, 2 - recycled nitrogen gas; S - water, the first digit 0 - make-up fresh water, 1 - circulating water supply, 2 - circulating water return; Si - silicon powder, (Si + N) - atomized silicon-nitrogen mixed fluid, Si + N2 + Si3N4 - mixture of silicon powder, nitrogen gas and silicon nitride during the reaction, (Si3N4 + N2) - mixture of silicon nitride and remaining nitrogen gas after the reaction is completed, Si3N4 - silicon nitride powder. Detailed implementation manners

[0023] The following are specific embodiments of the present invention, but the method of the present invention is not completely limited thereto. Those skilled in the art can make changes or adjustments according to the actual situation of the unit. For example, the self-made nitrogen in Example 2 can use pressure swing adsorption nitrogen production, membrane separation nitrogen production or other nitrogen production methods, as long as it can provide suitable nitrogen resources for production.

[0024] Example 1:

[0025] Figure 1 Process flow diagram of liquid nitrogen for the production line of synthesizing silicon nitride micropowder from waste mortar of crystalline silicon slices.

[0026] The numbers in the figure represent the equipment and machines of the production line for synthesizing silicon nitride micropowder from waste mortar of crystalline silicon slices: 1 - filter press, 2 - filtrate clarification tank, 3 - vacuum dryer, 4 - rotary vibrating screen, 5 - silicon powder tank, 6 - vector fluidizer, 7 - atomizing injector, 8 - atomizing synthesizer (divided into 8-1 - reaction furnace, 8-2 - quench cooler, 8-3 - gas-solid separator), 9 - plasma spray gun, 10 - plasma control cabinet, 11 - circulating water elevated tank, 12 - circulating water pool, 13 - circulating water pump, 14 - spray head, 15 - liquid nitrogen storage tank, 16 - liquid nitrogen vaporizer, 17 - nitrogen pressure regulating valve group, 18 - nitrogen flow control valve group, 19 - nitrogen recovery tank, 20 - vacuum packaging machine, together with corresponding process pipelines and an automated control system, constitute the production line for synthesizing silicon nitride micropowder from waste mortar of crystalline silicon slices.

[0027] The atomizing synthesizer (8) is the core equipment of the production line, which consists of an atomizing reactor (8-1), a quencher (8-2), and a gas-solid separator (8-3). It is used to complete the product reaction synthesis, cooling and heat exchange, gas-solid separation and other process processes; the nitrogen source is purchased liquid nitrogen with a purity of 99.999% and a temperature below -196°C. In addition to being used as a raw material for product production, it is also used for rapid cooling and heat exchange of reaction products, atomization and transportation of silicon powder, reaction temperature control, silicon powder production protection, etc.; the filter press The waste slurry treatment system is composed of a machine (1), a filtrate clarifier (2), a vacuum dryer (3), a rotary vibrating screen (4), and a silicon powder tank (5). Ultrafine silicon powder with a particle size of 0-8um and a purity of more than 99.5% is obtained by treating the waste slurry, and is used as a raw material for silicon nitride synthesis. The bottom plate of the silicon powder tank (5) is a ceramic sintered microporous plate, and the upper cover is equipped with an atomizing injector installation socket, which also serves as a silicon powder container and a fluidizing tank; the vector fluidizing seat (6), the silicon powder tank (5), and the atomizing injector (7) constitute The silicon powder atomizing feeder is used to complete the preheating, fluidization, vector metering, airflow sending, atomization spraying into the reaction furnace of the raw silicon powder and nitrogen. One atomizing synthesizer is equipped with 2-8 groups of silicon powder atomizing feeders. The atomizing feeders are in groups of two, one in operation and one in standby, and the switching is linked to ensure uniform and continuous feeding. The plasma spray gun (9) is installed on the top of the atomizing synthesizer and provides nitrogen plasma for the atomizing synthesizer reaction furnace under the control of the plasma control cabinet (10) for ignition of silicon nitrogen reaction and heating of the furnace. The circulating water high-level tank (11), the circulating water pool (12), the circulating water pump (13), the nozzle (14) and the gas-solid separator (8-3) silo jacket constitute a cooling water circulation system, which is responsible for cooling the plasma device. Among them, the atomizing synthesizer (8), the silicon powder tank (5), the vector fluidization seat (6) and the atomizing injector (7) are special equipment and need to be professionally designed and manufactured. The rest are general equipment and can be purchased and matched in China.

[0028] The production method of the production line for synthesizing silicon nitride micropowder from waste mortar of crystalline silicon slices is as follows: The waste mortar containing silicon powder, high-purity water and other trace impurities from the photovoltaic crystalline silicon slicing process on the same day is added to a filter press (1) for pressure filtration to obtain a filter cake and filtrate. The filtrate enters a clarifying tank (2), and the flocculated and clarified high-purity water is input into a cooling water circulation tank (12) along a water pipe S001 to compensate for the water loss of the cooling water circulation system; The filter cake is added to a vacuum dryer (3) for vacuum low-temperature drying to prevent oxidation of the silicon powder; The dried silicon powder enters a vibrating screen (4) under the protection of nitrogen N204 discharged from a nitrogen recovery tank (19) for sieving and impurity removal to obtain silicon powder with a particle size of 0-8 μm and a purity of over 99.5%; It is filled into a feed tank (5) according to the measurement under the protection of recovered nitrogen N203 for standby; Liquid nitrogen in a liquid nitrogen tank (15) enters a liquid nitrogen vaporizer (16) installed in the cooling water circulation tank (12) along a pipeline N001 to exchange heat with the cooling return water S203 to complete the vaporization of the liquid nitrogen and cool down the circulating return water at the same time; The low-temperature nitrogen gas after the vaporization of the liquid nitrogen enters a pressure regulating valve group (17), and after regulating the nitrogen gas pressure, it enters the lower part of the jacket of a spray synthesis and quenching device (8-1) along a low-temperature nitrogen gas pipeline N101 under the control of a mass flow control valve group (18) to exchange heat with the high-temperature Si3N4+N2 mixture in the quenching device through the partition wall, so that the temperature of the Si3N4+N2 product is reduced to below 150 °C, and the temperature of the nitrogen gas N102 leaving the quenching device rises to about 600 °C for the atomized transportation of the silicon powder; When the furnace temperature of the atomization reaction furnace (8-1) of the spray synthesizer (8) reaches 1000-1450 °C and the furnace atmosphere meets the conditions for the silicon powder nitridation reaction, the prepared silicon powder feed tank (5) is installed on a vector control fluidization base (6), and an atomization emitter (7) is installed in the reserved installation hole on the upper cover of the feed tank (5). The N105 valve is opened, nitrogen gas enters the fluidization base (6), and the fluidization of the silicon powder in the tank is realized through the ceramic sintered microporous plate at the bottom of the silicon powder feed tank (5). The N106 valve is opened, and the atomization reflector (7) is started, and the silicon powder is sprayed into the furnace chamber of the atomization reaction furnace (8-1) of the spray synthesizer (8) in an atomized state according to the mass ratio of Si:N2 of 1:1-2 along a pipeline (Si+N)101; At the same time, the nitrogen gas N102 enters a plasma control cabinet (10) along a pipeline N103, adjusts the flow rate and enters a plasma spray gun (11) along a pipeline N104, and the plasma spray gun (9) is started to prepare nitrogen plasma for triggering the nitridation reaction and regulating the furnace temperature of the reactor well; The silicon powder and nitrogen gas atomized and sprayed into the reaction furnace chamber of the silicon nitride spray synthesis furnace react at 1000-1450 °C and a working pressure of 0.01-0.Under the conditions of 6 MPa and excess nitrogen, silicon nitride is formed by the reaction according to the equation 3Si + 2N2 = Si3N4. 20 - 60% of nitrogen remains, forming a Si3N4 + N2 mist-like mixture, which enters the quench cooler (8 - 2) of the atomization synthesizer, exchanges heat through the partition wall with the low-temperature nitrogen in the jacket, is quenched to below 150 °C to fix the crystal form and particle size of the silicon nitride structure, enters the gas-solid separator (8 - 3) to complete the separation of Si3N4 and N2. The Si3N4 in the lower silo of the gas-solid separator enters the packaging machine (20) for packaging and storage and sales. The discharged nitrogen N201 enters the nitrogen recovery tank (19) and is sent by the diversion pipe N202 to the vibrating screen (4) of the waste mortar treatment system and the nitrogen protection for drying silicon powder in the silicon powder canning process (5); the plasma spray gun is installed in the atomization reaction furnace of the silicon nitride synthesizer (8) and has been in a high-temperature environment of 1000 - 1450 °C. To ensure the safe operation of the plasma system, especially the safety of the plasma spray gun in case of unexpected power failure, a cooling water circulation system is equipped. When working normally, the S102 cooling water pumped out by the circulating pump group (12) fills the high-level tank (11) through the pipe S105. At the same time, it enters the plasma control cabinet (10) through the branch pipe S104 of S102, enters the plasma spray gun (9) through S106, and the cooling return water is respectively collected into the S203 spray head (14) through S201 and S202 and exchanges heat with the liquid nitrogen vaporizer (16) to cool down, maintaining the safe operation of the plasma system; when there is an unexpected power failure, the S107 of the high-level tank (11) automatically opens to provide emergency cooling water to the plasma spray gun, and flows back to the circulation pool through S202, S203 and the spray head (14); to ensure the safety of the plasma spray gun in the high-temperature environment of the furnace.

[0029] Example 2:

[0030] Figure 2 It is a self-made process flow chart of the production line for synthesizing silicon nitride micropowder from waste mortar of crystalline silicon slicing.

[0031] The numbers in the figure represent the equipment and machines of the production line for synthesizing silicon nitride micropowder from waste mortar of crystalline silicon slicing: 1 - filter press, 2 - filtrate clarification tank, 3 - vacuum dryer, 4 - vibrating screen, 5 - silicon powder tank, 6 - vector fluidizer, 7 - atomizing injector, 8 - atomization synthesizer (divided into 8 - 1 - reaction furnace, 8 - 2 - quench cooler, 8 - 3 - gas-solid separator), 9 - plasma spray gun, 10 - plasma control cabinet, 11 - circulating water high-level tank, 12 - circulating water pool, 13 - circulating water pump, 14 - spray head, 15 - pressure swing adsorption nitrogen production, 18 - nitrogen flow control valve group, 19 - nitrogen recovery tank, 20 - vacuum packaging machine, with corresponding process pipelines and an automated control system to form the production line for synthesizing silicon nitride micropowder from waste mortar of crystalline silicon slicing.

[0032] The atomizing synthesizer (8) is the core equipment of the production line, which consists of an atomizing reactor (8-1), a quencher (8-2), and a gas-solid separator (8-3). It is used to complete the product reaction synthesis, cooling and heat exchange, gas-solid separation and other process (separate application); a pressure swing adsorption nitrogen generator (15) is used to prepare nitrogen. The prepared nitrogen has a purity of ≥99.99% and a pressure of ≥0.5MPa. In addition to being used as a raw material for product production, it is also used for quenching and heat exchange of reaction products, atomization and transportation of silicon powder, etc. The waste mortar treatment system comprises a filter press (1), a filtrate clarifier (2), a vacuum dryer (3), a rotary vibrating screen (4), and a silicon powder tank (5). The waste mortar is treated to obtain ultrafine silicon powder with a particle size of 0-8um and a purity of more than 99.5%, which is used as a raw material for silicon nitride synthesis. The bottom plate of the silicon powder tank (5) is a ceramic sintered microporous plate, and the upper cover is equipped with an atomizing injector installation socket, which also serves as a silicon powder container and a fluidized tank; a vector fluidized seat (6), a silicon powder tank (5) and the atomizing injector (7) constitute a silicon powder atomizing feeder, which completes the preheating, fluidization, vector metering, airflow sending, atomization and injection into the reaction furnace of the reaction raw materials silicon powder and nitrogen at one time. One atomizing synthesizer is equipped with 2-8 groups of silicon powder atomizing feeders, and the atomizing feeders are grouped in two, with one in each group and one in reserve, and the switching is linked to ensure uniform and continuous feeding; the plasma spray gun (9) is installed on the top of the atomizing synthesizer, and is controlled by the plasma control cabinet (10) to feed the atomizing synthesizer reaction. The furnace provides nitrogen plasma for ignition of silicon-nitrogen reaction and heating of the furnace; the circulating water high-level tank (11), circulating water pool (12), circulating water pump (13), nozzle (14) and gas-solid separator (8-3) silo jacket constitute a cooling water circulation system, which needs to meet the cooling of the plasma device and the gas-solid separator silo at the same time; except for the atomizing synthesizer (8), silicon powder tank (5), vector fluidizing seat (6) and atomizing injector (7), the rest are mature domestic equipment.

[0033] The process method of the production line for synthesizing silicon nitride micropowder from waste mortar of crystalline silicon slices is as follows: The waste mortar containing silicon powder, high-purity water and other trace impurities produced on the same day in the photovoltaic crystalline silicon slicing process is added to a filter press (1) for filter pressing to obtain a filter cake and filtrate. The filtrate enters a clarification tank (2), and the flocculated and clarified high-purity water is input into a cooling water circulation tank (12) along the S001 water pipe to compensate for the water loss of the cooling water circulation system; The filter cake is added to a vacuum dryer (3) for vacuum low-temperature drying to prevent oxidation of the silicon powder; The dried silicon powder enters a vibratory screen (4) for sieving and impurity removal under the protection of nitrogen N204 discharged from a nitrogen recovery tank (19) to obtain silicon powder with a particle size of 0-8um and a purity of over 99.5%; It is filled into a feed tank (5) according to the measurement under the protection of recycled nitrogen N203 for standby; Nitrogen with a purity of ≥99.99% and a pressure of ≥0.5MPa prepared by a pressure swing adsorption nitrogen generation device (15) enters the lower part of the jacket of an atomizing synthesizer quencher (8-1) along the N101 nitrogen pipeline under the control of a mass flow control valve group (18), and exchanges heat with the high-temperature Si3N4+N2 mixture in the quencher through the partition wall to reduce the temperature of the Si3N4+N2 product to below 300°C. The temperature of the nitrogen N102 leaving the quencher rises to about 700°C and is used for the atomizing transportation of the silicon powder; When the furnace temperature of the atomizing reaction furnace (8-1) of the atomizing synthesizer (8) reaches 1000-1450°C and the furnace atmosphere meets the conditions for the silicon powder nitriding reaction, the prepared silicon powder feed tank (5) is installed on a vector control fluidizing base (6), and an atomizing emitter (7) is installed in the reserved installation hole on the upper cover of the feed tank (5). The N105 valve is opened, and nitrogen enters the fluidizing base (6), and the fluidization of the silicon powder in the tank is realized through the ceramic sintered microporous plate at the bottom of the silicon powder feed tank (5). The N106 valve is opened, and the atomizing reflector (7) is started, and it is sprayed into the furnace chamber of the atomizing reaction furnace (8-1) of the atomizing synthesizer (8) in an atomized state according to the Si:N2 mass ratio of 1:1-2 along the (Si+N)101 pipeline. The plasma torch (9) is started to prepare nitrogen plasma for triggering the nitriding reaction and regulating the furnace temperature of the reactor well; Nitrogen enters the plasma control cabinet (10) through the N103 nitrogen pipeline, and after adjusting the flow rate, it enters the plasma torch (11) through the N104 pipeline; The silicon powder and nitrogen atomized and sprayed into the reaction furnace chamber of the silicon nitride atomizing synthesizer react at 1000-1450°C and a working pressure of 0.01-0.Under the conditions of 6 MPa and excess nitrogen, silicon nitride is formed by the reaction according to the equation 3Si + 2N2 = Si3N4. There is a 20 - 60% surplus of nitrogen, forming a Si3N4 + N2 mist-like mixture, which enters the quencher (8 - 2) of the atomization synthesizer and exchanges heat with the low-temperature nitrogen in the jacket through a partition wall, and is quickly cooled to below 300 °C to fix the crystal form and particle size of the silicon nitride structure. Then it enters the gas-solid separator (8 - 3) to complete the separation of Si3N4 and N2. A cooling jacket is provided in the lower hopper of the gas-solid separator, and cooling circulating water is introduced to further reduce the temperature of the Si3N4 in the hopper of the gas-solid separator to about 150 °C. Then it enters the packaging machine (20) for packaging and storage for sale; the discharged nitrogen N201 enters the nitrogen recovery tank (19) and is sent by the diversion pipe N202 to the vibratory sieve loosening (4) of the waste mortar treatment system and the nitrogen protection for drying silicon powder in the silicon powder filling tank process (5); the plasma spray gun is installed in the atomization reaction furnace of the silicon nitride synthesizer (8) and has been in a high-temperature environment of 1000 - 1450 °C. To ensure the safe operation of the plasma system, especially the safety of the plasma spray gun in case of unexpected power failure, and to solve the problem of temperature reduction of the gas-solid separator, a cooling water circulation system is provided. When working normally, the S102 cooling water pumped out by the circulating pump group (12) fills the high-level tank (11) through the pipe S105. At the same time, it enters the plasma control cabinet (10) through the branch pipe S104 of S102, enters the plasma spray gun (9) through S106, and enters the jacket of the hopper of the gas-solid separator through S103. The cooling return water is respectively collected by S201, S202, and S204 and flows into the S203 spray head (14) for spray cooling to maintain the safe operation of the plasma system and the gas-solid separator. When there is an unexpected power failure, the S107 of the high-level tank (11) is opened to provide emergency cooling water for the plasma spray gun, and it flows back to the circulation pool through S202, S203, and the spray head (14); to ensure the safety of the plasma spray gun in the high-temperature environment of the furnace.

Claims

1. A production line for synthesizing silicon nitride micropowder from waste mortar of crystalline silicon slices, characterized in that: The production line for synthesizing silicon nitride micropowder from waste mortar of crystalline silicon slices consists of a filter press (1), a filtrate clarification tank (2), a vacuum dryer (3), a rotary vibrating screen (4), a silicon powder tank (5), a vector fluidization base (6), an atomizing injector (7), an atomizing synthesizer (8), a plasma spray gun (9), a plasma control cabinet (10), a circulating water elevated tank (11), a circulating water pool (12), a circulating water pump (13), a spray head (14), a nitrogen source device (15), a liquid nitrogen vaporizer (16), a nitrogen pressure regulating valve group (17), a nitrogen flow control valve group (18), a nitrogen recovery tank (19), a vacuum packaging machine (20) and corresponding process pipelines and an automatic control system; among them, the atomizing synthesizer (8) (applied for in another case) is the core equipment of the production line, which consists of an atomizing reaction furnace (8-1), a quencher (8-2), and a gas-solid separator (8-3), and is used to complete the process processes such as reaction synthesis, cooling heat exchange, and gas-solid separation of the product; the nitrogen source device is divided into two types: purchased liquid nitrogen and self-made nitrogen. The purity of self-made nitrogen must be ≥99.99%, and the pressure must be ≥0.5 MPa. The purity of purchased liquid nitrogen can reach 99.999%, and the temperature is lower than -196°C. Nitrogen is the key resource of this technology. In addition to being used as a raw material for silicon nitride production, it is also used for quenching heat exchange of reaction products, atomizing and conveying silicon powder, regulating reaction temperature, and protecting silicon powder production; the filter press (1), the filtrate clarification tank (2), the vacuum dryer (3), the rotary vibrating screen (4), and the silicon powder tank (5) constitute a waste mortar treatment system, which is used to treat waste mortar to obtain a particle size of 0-8um and a purity of 99.Ultrafine silicon powder with a content of more than 5% is used as a raw material for silicon nitride synthesis. The vector fluidization seat (6), silicon powder tank (5), and atomizing injector (7) constitute a silicon powder atomizing feeder (another application), which completes the preheating, fluidization mixing, vector metering, air flow sending, and atomization injection into the reaction furnace of the reaction raw material silicon powder and nitrogen. One atomizing synthesizer is equipped with 2-8 groups of silicon powder atomizing feeders, and the atomizing feeders are grouped in two. Each group has one in operation and one in standby, and the switching is linked to ensure uniform and continuous feeding. The plasma spray gun (9) is installed on the atomizing synthesizer. The top of the synthesizer is provided with nitrogen plasma for the atomizing synthesizer reactor under the control of the plasma control cabinet (10) for ignition of silicon-nitrogen reaction and heating of the furnace; the circulating water high-level tank (11), the circulating water pool (12), the circulating water pump (13), the nozzle (14) and the gas-solid separator (8-3) silo jacket constitute a cooling water circulation system. When homemade nitrogen is used as the nitrogen source, the cooling water circulation system needs to meet the cooling and cooling of the plasma device and the gas-solid separator silo. When liquid nitrogen is used as the nitrogen source, the cooling water circulation system is only responsible for the cooling of the plasma device and the gas-solid separator silo. The ion device is cooled; except for the atomizing synthesizer (8), the silicon powder tank (5), the vector fluidizing seat (6), and the atomizing injector (7), the rest are mature domestic equipment; the process method of the production line for synthesizing silicon nitride micropowder using waste slurry of crystalline silicon slices is as follows: the waste slurry containing silicon powder, high-purity water and other trace impurities generated in the photovoltaic crystalline silicon slice process is added to the filter press (1) for filtration to obtain filter cake and filtrate, the filtrate enters the clarification tank (2), and the high-purity water after flocculation and clarification is input into the cooling water circulation tank (12) along the S001 water pipe, Compensate for water loss in the cooling water circulation system; add the filter cake to a vacuum dryer (3) for vacuum low-temperature drying to prevent oxidation of the silicon powder; the dried silicon powder enters a rotary vibrating screen (4) under the protection of nitrogen N204 discharged from a nitrogen recovery tank (19) to loosen and remove impurities, thereby obtaining silicon powder with a particle size of 0-8um and a purity of more than 99.5%; under the protection of nitrogen N203, the silicon powder is metered and loaded into a material tank (5) for standby use; the N2 raw material is obtained by either purchasing liquid nitrogen or making nitrogen according to the conditions, and the purity of the purchased liquid nitrogen is 99.99.9%, the temperature is lower than -196 °C. The liquid nitrogen in the liquid nitrogen tank (15) enters the liquid nitrogen vaporizer (16) installed in the cooling water circulation pool (12) through the N001 pipeline and exchanges heat with the cooling return water S203 to complete the vaporization of the liquid nitrogen, and at the same time cools down the circulating return water; the low-temperature nitrogen gas after the vaporization of the liquid nitrogen enters the pressure regulating valve group (17), and after regulating the nitrogen gas pressure, it enters the lower part of the jacket of the atomization synthesizer quencher (8-1) along the N101 low-temperature nitrogen gas pipeline under the control of the mass flow control valve group (18), and exchanges heat through the partition wall with the high-temperature Si3N4+N2 mixture in the quencher, so that the temperature of the Si3N4+N2 product is reduced to below 150 °C, and the temperature of the nitrogen gas N102 leaving the quencher rises to about 600 °C, which is used for the atomization transportation of silicon powder; when the furnace temperature of the atomization reaction furnace (8-1) of the atomization synthesizer (8) reaches 1000-1450 °C and the furnace atmosphere meets the conditions for the silicon powder nitriding reaction, install the prepared silicon powder tank (5) on the vector control fluidization seat (6), and install the atomization emitter (7) on the reserved installation hole on the upper cover of the powder tank (5). Open the N105 valve to make nitrogen gas enter the nitrogen gas pipeline of the atomization emitter, open the N106 valve, nitrogen gas enters the fluidization seat (6), and the fluidization of the silicon powder in the tank is realized through the ceramic sintered microporous plate at the bottom of the silicon powder tank (5). Open the N107 valve to start the atomization reflector (7), and spray it into the furnace chamber of the atomization reaction furnace (8-1) of the atomization synthesizer (8) in an atomized state according to the Si:N2 mass ratio of 1:1-2 along the (Si+N)101 pipeline. Start the plasma torch (9) to prepare nitrogen plasma for triggering the nitriding reaction and regulating the furnace temperature of the reactor; nitrogen gas enters the plasma control cabinet (10) through the N103 nitrogen gas pipeline, adjusts the flow rate and enters the plasma torch (11) through the N104 pipeline; the silicon powder and nitrogen gas atomized and sprayed into the reaction furnace chamber of the silicon nitride atomization synthesizer react at 1000-1450 °C and the working pressure is 0.01-0.Under the conditions of 6 MPa and nitrogen excess, silicon nitride is produced by the reaction according to the equation 3Si + 2N2 = Si3N4. 20-60% of nitrogen remains, forming a Si3N4 + N2 mist-like mixture, which enters the quench cooler (8-2) of the atomization synthesizer, exchanges heat with the low-temperature nitrogen in the jacket through a partition wall, is quenched to below 150 °C to fix the crystal form and particle size of the silicon nitride structure, enters the gas-solid separator (8-3) to complete the separation of Si3N4 and N2. The Si3N4 in the lower bin of the gas-solid separator enters the packaging machine (20) for packaging and storage for sale. The discharged nitrogen N201 enters the nitrogen recovery tank (19) and is sent to the vibrating screen (4) of the waste mortar treatment system and the nitrogen protection for drying silicon powder in the silicon powder filling process (5) through the diversion pipe N202; the plasma spray gun is installed in the atomization reaction furnace of the silicon nitride synthesizer (8) and is always in a high-temperature environment of 1000-1450 °C. To ensure the safe operation of the plasma system, especially the safety of the plasma spray gun in case of an unexpected power outage, a cooling water circulation system is equipped. When working normally, the S102 cooling water pumped out by the circulating pump group (12) fills the high-level tank (11) through the pipe S105. At the same time, it enters the plasma control cabinet (10) through the branch pipe S104 of S102, enters the plasma spray gun (9) through S106, and the cooling return water is respectively merged into the S203 spray head (14) through S201 and S202 and exchanges heat with the liquid nitrogen vaporizer (16) to cool down, maintaining the safe operation of the plasma system. When an unexpected power outage occurs, the S107 of the high-level tank (11) opens to provide emergency cooling water to the plasma spray gun, and flows back to the circulation pool through S202, S203 and the spray head (14). To ensure the safety of the plasma spray gun in the high temperature environment of the furnace; when the nitrogen source is homemade nitrogen, its heat exchange effect is poor, and the cooling water circulation system also needs to cool the gas-solid separator at the bottom of the atomizing synthesizer.

2. The production line for synthesizing silicon nitride micropowder from waste mortar of crystalline silicon slices according to claim 1, characterized in that: The waste mortar treatment system consists of a filter press (1), a filtrate clarifier (2), a vacuum dryer (3), a rotary vibrating screen (4), and a silicon powder tank (5), and is used to treat crystalline silicon slice waste mortar to obtain ultrafine silicon powder with a particle size of 0-8um and a purity of more than 99.5%, which is used as a raw material for silicon nitride synthesis; the bottom plate of the silicon powder tank (5) is a ceramic sintered microporous plate, and the upper cover is equipped with an atomizing injector installation socket, which also serves as a silicon powder container and a fluidized tank.

3. The production line for synthesizing silicon nitride micropowder from waste mortar of crystalline silicon slices according to claim 1, characterized in that: The silicon powder atomizing feeder is composed of a vector fluidizing seat (6), a silicon powder tank (5), and an atomizing injector (7); and is used to complete the preheating, fluidization, vector metering, airflow sending, atomization injection into the reaction furnace and other processes of the reaction raw materials silicon powder and nitrogen. One atomizing synthesizer is equipped with 2-8 groups of silicon powder atomizing feeders, and the atomizing feeders are grouped in two, with one in operation and one in standby, and the switching is linked to ensure uniform and continuous feeding.

4. The production line for synthesizing silicon nitride micropowder from waste mortar of crystalline silicon slices according to claim 1, characterized in that: The atomizing synthesizer (8) (applied in another case) is the core equipment of the production line, which consists of three parts: an atomizing reactor (8-1), a quencher (8-2), and a gas-solid separator (8-3). It is used to complete the product reaction synthesis, cooling and heat exchange, gas-solid separation and other process processes.

5. The production line for synthesizing silicon nitride micropowder from waste mortar of crystalline silicon slices according to claim 1, characterized in that: The nitrogen source device is externally purchased liquid nitrogen with a purity of ≥99.999% and a temperature below -196°C. In addition to being used as a raw material for product production, it is also used for rapid cooling and heat exchange of reaction products, silicon powder atomization and transportation, reaction temperature control, and silicon powder production protection. Its overall effect is excellent, but it is subject to surrounding resource conditions.

6. The production line for synthesizing silicon nitride micropowder from waste mortar of crystalline silicon slices according to claim 1, characterized in that: The nitrogen source is homemade nitrogen. The purity of homemade nitrogen must be ≥99.99% and the pressure must be ≥0.5MPa. In addition to being a raw material for product production, it is also used as a heat exchange medium for reaction products, a silicon powder atomization conveying medium, a reaction temperature control medium, and a silicon powder production protection medium. Nitrogen resources can be obtained locally, but the comprehensive benefits are not as good as liquid nitrogen.

7. The production line for synthesizing silicon nitride micropowder from waste mortar of crystalline silicon slices according to claim 1, characterized in that: The atomizing synthesizer (8), silicon powder tank (5), vector fluidizing seat (6) and atomizing injector (7) in the supporting equipment of the production line for synthesizing silicon nitride micropowder using waste slurry of crystalline silicon slices are special equipment and need to be professionally designed and manufactured; the rest are mature equipment and can be matched with the domestic market.

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