Method for producing steelmaking alloyed pellets by using polycrystalline silicon cutting slag

Abstract

The invention discloses a method for producing steel-making alloyed pellets by using polycrystalline silicon cutting slag, which comprises the following steps of: firstly, crushing waste aluminum killed steel refining slag of a steel plant to 0.5-1mm, purchasing limestone powder with CaO content of more than 50% and the granularity of 0.5-1mm, and uniformly mixing the polycrystalline silicon cutting slag, the aluminum killed steel refining slag, the limestone powder and industrial kerosene to obtain the steel-making alloyed pellets. Uniformly mixing according to a mass ratio of 80: 10: 5: 5, and dehydrating in a centrifugal dehydrator until the water content of the dehydrated mixture is lower than 3%; the mixture is pressed into pellets with the diameter of 30-50 mm through a high-pressure dry powder ball press, when silicon killed steel or silicon-aluminum killed steel is smelted in a converter or an electric furnace and tapping is conducted, the pellets are added along with steel flow to adjust the silicon content and the carbon content of molten steel, and the other smelting processes are not changed.

Description

Technical Field

[0001] The invention relates to a method for producing steelmaking alloying pellets by utilizing polysilicon cutting slag. Background Art

[0002] To manufacture solar cells, polycrystalline silicon ingots or rods must be cut into wafers. Currently, this process is primarily accomplished using multi-wire sawing technology. The waste slurry generated during this cutting process is also known as sawing residue. This sawing residue primarily consists of approximately 30% high-purity silicon, approximately 35% SiC, approximately 28% polyethylene glycol and water, and approximately 5% iron oxide. Because it contains elemental silicon and silicon carbide, the sawing residue has high economic value. Literature review: (1) Xing Pengfei, Zhao Peiyu, Guo Jing, et al. published a paper titled “Comprehensive Recovery of Solar-Grade Polysilicon Cutting Waste Slurry” in the 1st issue of Materials Guide in 2011. The paper states that “Since the particle size of Si and SiC in cutting waste is very small (less than 15 μm) and their physical and chemical properties are very similar, it is very difficult to separate Si and SiC in the waste. Both domestic and foreign researchers are still in the research stage in this regard.” (2) Jin Xing, Xing Pengfei, Zhao Jing, et al. published a paper titled “Preparation of Si3N4-SiC Composite Materials from Solar-Grade Polysilicon Cutting Waste” in the 5th issue of Refractories in 2017. The paper states that “In order to comprehensively utilize single-crystal silicon cutting waste slurry and increase the added value of products, this work proposes to use purified solar-grade polysilicon cutting waste to prepare silicon nitride-bonded silicon carbide (Si3N4-SiC) materials.” According to the above-mentioned public documents, there is currently no process for producing steelmaking alloy pellets using polysilicon cutting residues.

[0003] During the steelmaking process, crude molten steel produced using the converter or electric furnace process requires the addition of different alloying materials to adjust the composition of the molten steel to meet the different performance requirements of different steel grades. This is the alloying process of the steelmaking process. During the alloying process of steelmaking production, the use of ferrosilicon alloys and silicon-manganese alloys is the main method for adjusting the silicon content of the molten steel. The searched literature revealed: (1) Wang Jing, Liu Kunlun, Kang Yanfei, and other authors published a paper titled "New High-Efficiency Reducing Agent and Key Points for Ferrosilicon Smelting" in the first issue of Ferroalloys in 2025. The paper states: "In ferrosilicon production, the use of a reducing agent with high porosity can adsorb the escaped SiO gas and promote its condensation reaction in the carbonaceous reducing agent, thereby reducing the SiO escape rate and the output of microsilicon powder. The results show that the optimal temperature of the coking process is higher than 800℃. Operating in the range of 900-1100℃ can eliminate the pyrolytic carbon inside the coke and ensure that the reducing agent has a high reaction capacity for gaseous SiO." (2) Li Songfeng published a paper titled "High-Purity Ferrosilicon Production Test" in the fifth issue of Ferroalloys in 2022. The paper states: "The selection, dosage and addition procedure of the refining agent used in the production of high-purity ferrosilicon are introduced, as well as the compressed air and oxygen dosage test. Through production practice results and data analysis, a reference is provided for the production of high-purity ferrosilicon."

[0004] According to the above literature discussion, there is currently no precedent for using polysilicon cutting residues to produce alloyed pellets for steelmaking. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for producing steelmaking alloyed pellets using polysilicon cutting slag. The alloyed pellets produced by using polysilicon cutting residues to replace ferrosilicon to adjust the silicon content in molten steel can reduce the amount of ferrosilicon used, which is beneficial to reducing costs and increasing efficiency in the steelmaking industry.

[0006] The technical solution adopted by the method of the present invention is: A method for producing steelmaking alloy pellets using polysilicon cutting slag is implemented according to the following steps: S1. First, the aluminum-killed steel refining slag discarded from the steel plant is crushed into 0.5-1mm and transported to the dry powder pelletizing production line for use; S2. Purchase limestone powder with CaO content greater than 50% and particle size of 0.5-1mm, and transport it to the dry powder pelletizing production line for use; S3. Purchase industrial kerosene and transport it to the dry powder pelletizing production line for use; S4, mixing polysilicon cutting residue, aluminum killed steel refining slag, limestone powder, and industrial kerosene in a ratio of 80:10:5:5 by mass, and dehydrating the mixture in a centrifugal dehydrator, wherein the moisture content of the mixture after dehydration is less than 3%; S5. The dehydrated mixture is pressed into pellets with a diameter of 30-50 mm using a high-pressure dry powder pelletizing machine, and transported to the converter production line for standby use; S6. When tapping silicon-killed steel or silicon-aluminum-killed steel in a converter or electric furnace, the above pellets are added along with the steel flow to adjust the silicon and carbon contents of the molten steel. The rest of the smelting process remains unchanged.

[0007] The inventors discovered the following scientific phenomena by studying the properties of polysilicon cutting residues: 1. The pure Si and SiC contained in the polysilicon cutting residue have the effect of increasing silicon and carbon in the molten steel during the steelmaking alloying process, and also have a deoxidation function; 2. The pure Si particles in the polysilicon cutting residue are small and easily oxidize and burn with oxides in the ambient air at room temperature. Direct resource utilization requires solving safety issues; Based on the above findings, the present invention uses polysilicon cutting residue as the main raw material, and high-aluminum refined slag, limestone powder and kerosene generated in the steelmaking process of producing aluminum-killed steel as additives, to produce polysilicon cutting residue into 30-50mm pellets, which are used to replace ferrosilicon alloy in the process of steelmaking to produce silicon-killed steel or silicon-aluminum-killed steel, and are added during the steelmaking process of the converter or electric furnace to adjust the silicon content and carbon content of the molten steel, thereby realizing the integrated development of the polysilicon industry and the steelmaking industry.

[0008] The innovative features of the present invention are as follows: 1. The inventors used kerosene as a binder and antioxidant, and took advantage of the fact that grease reacts with alkaline steel slag and alkaline limestone to form an alkaline grease film structure. This film structure is then used to bind polysilicon cutting residues, enabling them to be produced into alloyed pellets on a dry powder pelletizing line. The kerosene film prevents the metallic silicon from reacting with oxidants in the environment, ensuring that the pellets have a storage period that meets the requirements of the steelmaking process. 2. The inventors took advantage of the low thermal conductivity of steel slag and used it as a heat-insulating material within the pellets to prevent the heat release caused by local oxidation of the alloyed pellets, which would further increase the chain reaction caused by the oxidation reaction, thus solving the safety issues during the production and storage of alloyed pellets. 3. To improve the efficiency of converting metallic silicon and silicon carbide into alloying elements during the use of alloyed pellets, the inventors used limestone particles as an active material and added them to the above pellets. When the pellets were added to the molten steel, the calcium carbonate expanded due to heat, and the CO2 gas produced promoted the fragmentation of the pellets, which could improve the efficiency of the alloyed pellets in participating in the deoxidation and alloying reaction. 4. The inventors utilized the porous structure of aluminum-killed steel refined slag, which has a large number of penetrating pores, to create conditions for centrifugal dehydration of polysilicon cutting residues.

[0009] The beneficial contributions of the present invention are as follows: 1. Utilizing polysilicon cutting residues to produce alloyed pellets to replace ferrosilicon to adjust the silicon content in molten steel can reduce the amount of ferrosilicon used, which is beneficial to cost reduction and efficiency improvement in the steelmaking industry; 2. Large-scale application of the above pellets in the steelmaking industry can reduce the amount of ferroalloys used, which is beneficial to the integrated development of the polysilicon industry, ferroalloy industry and steelmaking industry, and achieve the process goal of joint carbon reduction in multiple industries. DETAILED DESCRIPTION

[0010] The embodiment of the present invention is described by taking a production line of a polysilicon enterprise as an example.

[0011] A method for producing steelmaking alloy pellets using polysilicon cutting slag is implemented according to the following steps: S1. First, the aluminum-killed steel refining slag discarded from the steel plant is crushed into 0.5-1mm and transported to the dry powder pelletizing production line for use; S2. Purchase limestone powder with CaO content greater than 50% and particle size of 0.5-1mm, and transport it to the dry powder pelletizing production line for use; S3. Purchase industrial kerosene and transport it to the dry powder pelletizing production line for use; S4, mixing polysilicon cutting residue, aluminum killed steel refining slag, limestone powder, and industrial kerosene in a ratio of 80:10:5:5 by mass, and dehydrating the mixture in a centrifugal dehydrator, wherein the moisture content of the mixture after dehydration is less than 3%; S5. The dehydrated mixture is pressed into pellets with a diameter of 30-50 mm using a high-pressure dry powder pelletizing machine, and transported to the converter production line for standby use; S6. When tapping silicon-killed steel or silicon-aluminum-killed steel in a converter or electric furnace, the above pellets are added along with the steel flow to adjust the silicon and carbon contents of the molten steel. The rest of the smelting process remains unchanged.

Claims

1. A method for producing steelmaking alloy pellets using polysilicon cutting slag, characterized in that Follow these steps to implement: S1. First, the aluminum-killed steel refining slag discarded from the steel plant is crushed into 0.5-1mm and transported to the dry powder pelletizing production line for use; S2. Purchase limestone powder with CaO content greater than 50% and particle size of 0.5-1mm, and transport it to the dry powder pelletizing production line for use; S3. Purchase industrial kerosene and transport it to the dry powder pelletizing production line for use; S4, mixing polysilicon cutting residue, aluminum killed steel refining slag, limestone powder, and industrial kerosene in a ratio of 80:10:5:5 by mass, and dehydrating the mixture in a centrifugal dehydrator, wherein the moisture content of the mixture after dehydration is less than 3%; S5. The dehydrated mixture is pressed into pellets with a diameter of 30-50 mm using a high-pressure dry powder pelletizing machine, and transported to the converter production line for standby use; S6. When tapping silicon-killed steel or silicon-aluminum-killed steel in a converter or electric furnace, the above pellets are added along with the steel flow to adjust the silicon and carbon contents of the molten steel. The rest of the smelting process remains unchanged.