Method for smelting molten iron by using organic solid waste and low-grade direct reduction iron electric furnace

Abstract

The invention provides a method for smelting molten iron in an electric furnace by utilizing organic solid waste and low-grade direct reduction iron, which belongs to the technical field of electric furnace steelmaking and comprises the following steps: adding auxiliary materials to form a slag system under the condition that molten iron is reserved in a molten pool of the electric furnace; adding the low-grade direct reduced iron into the electric furnace for multiple times under bottom blowing stirring until the low-grade direct reduced iron is molten; bottom blowing stirring continues, a large-current short-arc power supply system is adopted, and organic solid waste powder is blown into the electric furnace through the hollow graphite electrode; and when the temperature of the molten pool is higher than 1580 DEG C, bottom blowing of inert gas and blowing of organic solid waste powder are stopped for tapping. The method for smelting the molten iron through the electric furnace by means of the organic solid waste and the low-grade direct reduction iron is simple, efficient, low in cost, low in carbon and environmentally friendly.

Description

Technical Field

[0001] This invention relates to the field of electric arc furnace steelmaking technology, and in particular to a method for smelting molten iron in an electric arc furnace using organic solid waste and low-grade direct reducing iron. Background Technology

[0002] At a critical juncture when the global steel industry is accelerating its green and low-carbon transformation and actively implementing low-carbon goals, short-process electric arc furnace steelmaking is ushering in significant development opportunities due to its remarkable advantages in energy conservation and emission reduction.

[0003] Direct reduced iron (DRI) is a core raw material for electric arc furnace steelmaking. Due to its low content of harmful elements, stable composition, and ease of large-scale production, it has become an ideal choice for replacing scrap steel, optimizing furnace charge structure, and preparing high-quality steel grades.

[0004] However, the increasing depletion and rising costs of high-quality iron ore resources have severely constrained the large-scale application of direct reduced iron (DRI). Against this backdrop, low-grade DRI prepared from low-grade iron ore or steel dust has attracted widespread attention due to its cost advantage. However, this type of low-grade DRI typically contains a large amount of gangue minerals (such as SiO2) and insufficiently reduced ferrous oxide (FeO), requiring a large amount of carbon powder for deep reduction during electric arc furnace smelting. This not only leads to increased energy consumption and carbon emissions but also severely restricts the economic and environmental benefits of the smelting process.

[0005] For example, invention patent application CN119332041A discloses a method for smelting direct reduced iron (DRI) in an electric arc furnace. The method involves first preparing high-carbon DRI in a vertical shaft furnace, then adding the raw materials to the molten pool of an electric arc furnace. During charging, DRI is added first, followed by scrap steel, which is used to press the DRI into the molten pool. Finally, oxygen is blown to stir the molten pool until the carbon content of the molten steel reaches the required level. However, this method generates significant carbon emissions during the reduction of high-carbon DRI and the oxidation process of oxygen decarburization.

[0006] Patent application CN119193957A discloses a method for efficient smelting of molten iron in an electric furnace using direct reduction of low- and medium-grade iron ore. The method involves first preparing oxide pellets from the low- and medium-grade iron ore, then reducing the oxide pellets with hydrogen before feeding them into the electric furnace for further reduction. This method requires the addition of 4%-8% carbon during the furnace reduction stage, resulting in relatively high carbon emissions.

[0007] Chinese patent application CN118240988A discloses a low-carbon ironmaking process that couples direct reduction ironmaking and molten reduction ironmaking. This process involves injecting powdered direct reduced iron and pulverized coal into an SRV furnace, while simultaneously injecting reducing gases such as hydrogen to provide heat through combustion, thus achieving the melting and separation of the direct reduced iron. However, this method, due to the involvement of pulverized coal in the oxidation-reduction process, also suffers from high carbon emissions.

[0008] The above methods require the addition of carbonaceous reducing agents or the use of high-carbon raw materials to achieve deep reduction of direct reduced iron in electric arc furnace smelting. This results in a large amount of carbon emissions during the smelting process and does not have environmental benefits.

[0009] Currently, hydrogen is recognized as the cleanest energy source, and using hydrogen, especially hydrogen plasma, to reduce iron oxides is one of the effective ways to reduce carbon emissions.

[0010] For example, the invention patent with application number CN118726684B discloses a method for extracting iron from red mud based on electric arc furnace hydrogen plasma melting and reduction technology. In this method, after pressing the red mud into billets and roasting them, hydrogen plasma is used to deeply reduce the billets and remove impurities.

[0011] The invention patent with application number CN106011357B discloses a method and system for iron smelting by hydrogen plasma melting and reduction. It uses high-temperature hydrogen plasma to melt and reduce iron ore powder, avoiding excessive dependence on fossil fuels and the generation of polluting gases during the smelting process.

[0012] The invention patent with application number CN115522009B discloses a pure hydrogen plasma melting reduction ironmaking method. After nitrogen is used to start the arc, it is gradually switched to hydrogen. High-temperature hydrogen plasma is used to heat and reduce iron ore to form molten iron. This method effectively reduces CO2 emissions.

[0013] The invention patent with application number CN120888717A discloses a DC hollow electrode hydrogen plasma furnace ore powder smelting system, method and application. The method uses a hollow electrode and a furnace bottom electrode to form a DC electric arc, and injects hydrogen gas and ore powder through the hollow electrode. The high-temperature hydrogen plasma formed in the electric arc zone is used to reduce the ore powder and separate the metal from the slag.

[0014] The invention patent with application number CN109628676A discloses a short-process technology for directly producing pure molten iron. Iron ore powder, reducing gas, oxygen-enriched gas, flux and carburizing agent are injected into a smelting furnace together. After the gas-liquid melting reaction, pure molten iron is generated.

[0015] The above methods all utilize the high reactivity of hydrogen plasma, which can not only achieve deep reduction of iron ore powder, but also effectively solve the problem of high carbon emissions. However, hydrogen is relatively expensive, which will greatly increase the cost of steelmaking and reduce economic benefits, thus lacking economic advantages.

[0016] In summary, current low-grade direct reduced iron (DRI) generally suffers from low metallization rates and high iron oxide content. During electric arc furnace smelting, to achieve deep reduction of iron ore powder, large amounts of carbonaceous reducing agents such as carbon powder or coal powder need to be injected. This not only significantly increases energy and material consumption but also leads to a sharp increase in carbon dioxide emissions, contradicting the current goal of low-carbon transformation in the steel industry. Although hydrogen is the cleanest energy source, and deep reduction of slag can be achieved using hydrogen and hydrogen plasma, effectively reducing carbon emissions, hydrogen is expensive and lacks economic advantages.

[0017] Therefore, there is an urgent need for a simple, efficient, low-cost, and environmentally friendly method to smelt molten iron using organic solid waste and low-grade direct reduction ferroelectric furnace. Summary of the Invention

[0018] The technical problem to be solved by the present invention is to provide a simple, efficient, low-cost, low-carbon and environmentally friendly method for smelting molten iron using organic solid waste and low-grade direct reduction ferroelectric furnace.

[0019] To solve the above-mentioned technical problems, the present invention provides a method for smelting molten iron in a direct reduction ferroelectric furnace using organic solid waste and low-grade iron, comprising the following steps: With molten iron reserved in the electric furnace molten pool, electricity is supplied and the arc is ignited. Then, auxiliary materials are added to form a slag system with the composition of CaO 30%-35%, SiO2 30%-35%, Al2O3 15%-20%, MgO 10%-15%, and MnO 5%-10%. The submerged arc smelting and high-voltage long-arc power supply system are adopted. The preheated low-grade direct reduced iron is added into the electric furnace in multiple batches under bottom blowing and stirring. The smelting time is controlled until the low-grade direct reduced iron added each time melts. After the low-grade direct reduced iron is melted, bottom blowing and stirring are continued and a high-current short-arc power supply system is adopted to spray organic solid waste powder into the electric furnace through hollow graphite electrodes. When the molten pool temperature is >1580℃, stop the bottom blowing of inert gas and stop the injection of organic solid waste powder before tapping the iron. Reserve 30%-50% of the molten iron in the electric furnace for the next heat.

[0020] Furthermore, the preheating of the low-grade direct reduced iron involves loading the low-grade direct reduced iron into a preheating shaft, distributing it with a porosity of 0.75-0.85, and utilizing the high-temperature flue gas inside the shaft to preheat the low-grade direct reduced iron.

[0021] Furthermore, the low-grade direct reduced iron comprises, by mass percentage: TFe 60%-65%, MFe 30%-40%, FeO 30%-40%, C 1%-2%, S 0.3%-0.5%, SiO2 8%-10%, Al2O3 3%-4%, CaO 8%-10%, and MgO 2%-3%.

[0022] Furthermore, the organic solid waste powder is obtained by crushing organic solid waste, including waste rubber and / or waste tires, to a particle size of ≤200 mesh.

[0023] Furthermore, the molten iron reserved in the electric furnace molten pool is 30%-50% of the molten iron reserved when tapping iron after the previous furnace smelting is completed; if it is the first furnace smelting in the electric furnace, the molten iron reserved in the electric furnace molten pool is the molten iron formed after the scrap steel and / or low-grade direct reduced iron arranged in the electric furnace is melted.

[0024] Furthermore, the excipients are calcium oxide, magnesium oxide, and manganese oxide, and the amount of excipients added is calculated using FactSage thermodynamic software based on the composition and amount of low-grade direct reduced iron.

[0025] Furthermore, the bottom-blowing agitation is achieved by injecting 0.25 Nm of gas into the electric furnace through the vent plug at the bottom of the furnace. 3 / h•t iron-1.25 Nm 3 Argon or nitrogen gas per h•t of iron, with a bottom blowing pressure of 0.5 MPa - 1.0 MPa.

[0026] Furthermore, the low-grade direct reduced iron is added to the electric furnace in 2-4 batches per furnace. After each addition of low-grade direct reduced iron, the arc heating time is calculated and determined according to formula (1). (1) In the formula, t arc N is the arc heating time in seconds; U is the mass of low-grade direct reduced iron added each time in kilograms; U is the operating voltage in volts (V); and I is the operating current in amperes (A).

[0027] Furthermore, the injection intensity of the organic solid waste powder is 0.8 kg / min•t iron - 1.2 kg / min•t iron, and the carrier gas for the injection of the organic solid waste powder is argon or nitrogen, with a flow rate of 0.5 Nm³. 3 / h•t iron-2.0 Nm 3 / h•t iron, wherein the pressure of the carrier gas is 0.5 MPa - 0.9 MPa, and the spraying time of the organic solid waste powder is 1 min - 20 min.

[0028] Furthermore, the molten iron is tapped using a ladle that has been preheated to a temperature >800°C.

[0029] This invention provides a method for smelting molten iron in an electric arc furnace using organic solid waste and low-grade direct reduced iron. By adding slag-forming auxiliary materials to regulate the slag composition, a highly fluid, low-melting-point CaO-SiO2-Al2O3-MgO-MnO slag system can be formed. This improves the reaction conditions at the slag-steel-slag-iron interface, ensures that low-grade direct reduced iron melts through the slag layer quickly, and inhibits the accumulation of furnace charge.

[0030] Furthermore, the present invention provides a method for smelting molten iron using organic solid waste and low-grade direct reduced iron in an electric furnace. During the smelting stage of adding low-grade direct reduced iron, a submerged arc smelting system and a high-voltage long-arc power supply are adopted to increase the heating area. Bottom blowing stirring, multiple feeding strategies, and precise control of heating time are used to thoroughly melt the added low-grade direct reduced iron, ensuring the smooth progress of electric furnace smelting.

[0031] Meanwhile, this invention provides a method for smelting molten iron using organic solid waste and low-grade direct reduced iron in an electric arc furnace. When injecting organic solid waste powder into the furnace to reduce low-grade direct reduced iron, a high-current, short-arc power supply system is employed. Under the action of the high-temperature arc, the injected organic solid waste powder can pyrolyze into hydrogen-rich reducing gas and pyrolytic carbon. The pyrolytic carbon can act as a reducing agent to directly reduce the molten slag. Furthermore, the hydrogen-rich reducing gas further dissociates into high-temperature, highly reducing hydrogen-containing plasma, which, together with the pyrolytic carbon, reduces the molten slag, resulting in a better reduction effect. Moreover, bottom blowing to enhance molten pool stirring further strengthens the kinetic conditions for the reduction of pyrolytic carbon and hydrogen-containing plasma, further improving the reduction effect. Simultaneously, the hydrogen-rich reducing gas creates a reducing atmosphere above the molten pool, effectively isolating air and preventing nitrogen accumulation in the molten iron and oxidation of the slag, which would affect the reduction effect. Attached Figure Description

[0032] Figure 1 This is a flowchart illustrating a method for smelting molten iron using organic solid waste and a low-grade direct reduction ferroelectric furnace, as provided in an embodiment of the present invention. Detailed Implementation

[0033] See Figure 1 The present invention provides a method for smelting molten iron using organic solid waste and a low-grade direct reduction ferroelectric furnace, comprising the following steps: Step 1) With molten iron reserved in the electric furnace molten pool, power is supplied and the arc is ignited. Then, auxiliary materials are added to form a slag system with the composition of CaO 30%-35%, SiO2 30%-35%, Al2O3 15%-20%, MgO 10%-15%, and MnO 5%-10%.

[0034] Among them, the reserved molten iron in the electric furnace molten pool is 30%-50% of the molten iron reserved in the electric furnace when the previous furnace is tapped after ironmaking.

[0035] If the electric furnace is the first furnace for smelting, then scrap steel and / or low-grade direct reduced iron and other iron-containing furnace materials are placed into the electric furnace. After the furnace materials melt, a molten iron pool is formed, thus creating conditions for the electric furnace to reserve molten iron in the molten pool.

[0036] Power is supplied to the electric furnace with molten iron reserved in the molten pool. The electrode height is then lowered to form a circuit between the hollow graphite electrode inside the furnace and the anode at the bottom of the furnace. Then, the arc-starting operation is performed. After arc-starting, auxiliary materials such as calcium oxide, magnesium oxide, and manganese oxide are added to the molten iron reserved in the furnace to form slag.

[0037] The amount of auxiliary materials added was calculated using FactSage thermodynamic software based on the composition and amount of low-grade direct reduced iron.

[0038] Specifically, firstly, the Equilib module in the FactSage thermodynamic software was selected, along with the FactPS pure material database, the FSstel steel alloy database, and the FToxide oxide database. The mass and composition of the low-grade direct reduced iron added for the corresponding furnace batch were input into the calculation interface. Then, the melting temperature was set to 1600℃, and the melting environment pressure was set to standard atmospheric pressure. Through thermodynamic equilibrium calculations, the mass and composition of the slag phase formed during the melting process of the low-grade direct reduced iron were obtained. Finally, considering that the main components of the slag are CaO, SiO2, Al2O3, MgO, and MnO, the slag composition was adjusted by adding auxiliary materials, resulting in a final slag composition of: CaO 30%-35%, SiO2 30%-35%, Al2O3 15%-20%, MgO 10%-15%, and MnO 5%-10%. This slag system has the characteristics of high fluidity and low melting point, which can improve the reaction conditions at the slag-iron interface, ensure that low-grade direct reduced iron melts through the slag layer quickly, and inhibit the accumulation of furnace charge.

[0039] Step 2) Using a submerged arc smelting and high-voltage long-arc power supply system, the preheated low-grade direct reduced iron is added to the electric furnace in multiple batches under bottom blowing and stirring, and the smelting time is controlled until the low-grade direct reduced iron added each time melts.

[0040] The preheating of low-grade direct reduced iron involves loading low-grade direct reduced iron into a preheating shaft and distributing the low-grade direct reduced iron with a porosity of 0.75-0.85. The high-temperature flue gas in the shaft is used to preheat the low-grade direct reduced iron, so that the temperature of the low-grade direct reduced iron reaches the predetermined preheating temperature.

[0041] The components of low-grade direct reduced iron, by mass percentage, include TFe 60%-65%, MFe 30%-40%, FeO 30%-40%, C 1%-2%, S 0.3%-0.5%, SiO2 8%-10%, Al2O3 3%-4%, CaO 8%-10%, and MgO 2%-3%.

[0042] Bottom-blowing agitation involves injecting 0.25 Nm of air into the electric furnace through the vent plug at the bottom. 3 / h•t iron-1.25 Nm 3 Argon or nitrogen gas per h•t of iron, with a bottom blowing pressure of 0.5 MPa-1.0 MPa.

[0043] Bottom blowing and stirring can prevent uneven temperature in the molten pool and avoid the formation of a large amount of slag during the melting process when low-grade direct reduced iron is added to the molten pool, thereby avoiding the problem of crust formation caused by low surface slag temperature.

[0044] Furthermore, the use of submerged arc smelting and high-voltage long-arc power supply can increase the heating area and effectively prevent slag from forming a crust.

[0045] The low-grade direct reduced iron is added to the electric furnace in 2-4 batches per furnace. The arc heating time is calculated using formula (1) after each addition of low-grade direct reduced iron. (1) In the formula, tarc is the arc heating time in seconds; N is the mass of low-grade direct reduced iron added each time in kilograms; U is the working voltage in volts (V); and I is the working current in amperes (A).

[0046] By employing a strategy of adding materials in multiple stages during each smelting process and precisely controlling the heating time of each batch of low-grade direct reduced iron (DRI), the DRI added to the electric furnace can be fully melted, thus ensuring the smooth progress of electric furnace smelting.

[0047] Step 3) After the low-grade direct reduced iron is melted, continue bottom blowing and stirring and use a high current short arc power supply system to spray organic solid waste powder into the electric furnace through hollow graphite electrodes.

[0048] Among them, organic solid waste powder is obtained by crushing organic solid waste, including waste rubber and / or waste tires, to a particle size of ≤200 mesh.

[0049] In this process, organic solid waste powder is injected into the electric furnace from hollow graphite electrodes using high-pressure argon or nitrogen as the carrier gas.

[0050] The injection intensity of the organic solid waste powder injected into the electric furnace through the hollow graphite electrode is 0.8 kg / min•t iron - 1.2 kg / min•t iron, and the flow rate of argon or nitrogen as the carrier gas for injecting the organic solid waste powder is 0.5 Nm. 3 / h•t iron-2.0 Nm 3 / h•t iron, argon or nitrogen injection pressure is 0.5MPa-0.9MPa.

[0051] The spraying time for organic solid waste powder is 1 min to 20 min.

[0052] When organic solid waste powder is injected into the electric furnace, it pyrolyzes in the high-temperature electric arc zone into hydrogen-rich reducing gas and pyrolytic carbon. The hydrogen-rich reducing gas further dissociates into high-temperature, highly reducing hydrogen-containing plasma. This plasma can efficiently reduce iron oxides in the molten slag and forms a reducing gas curtain above the molten pool to isolate the air and prevent slag oxidation. Simultaneously, the generated pyrolytic carbon enters the molten slag and can also synergistically reduce iron oxides, significantly improving iron yield.

[0053] Furthermore, while continuing bottom blowing and stirring, the bottom blowing intensity remains constant, i.e., 0.25 Nm is injected through the vent plug at the bottom of the furnace. 3 / h•t iron-1.25 Nm 3 / h•t of iron inert gas such as N2 or Ar, with a bottom blowing pressure of 0.5MPa-1.0 MPa.

[0054] By continuing bottom blowing and stirring, compositional inhomogeneity within the molten pool can be avoided, thereby improving the kinetic conditions of hydrogen plasma and pyrolytic carbon reduction.

[0055] Step 4) When the molten pool temperature is >1580℃, stop the bottom blowing of inert gas and stop the injection of organic solid waste powder to tap the iron, and reserve 30%-50% of the molten iron in the electric furnace for the next heat.

[0056] In the ironmaking process of reducing low-grade direct reduced iron with organic solid waste powder, the temperature of the molten pool in the electric furnace is measured every 3-5 minutes. When the molten pool temperature exceeds 1580℃, the bottom blowing gas and the injection of organic solid waste powder are stopped. Then, the furnace cover is opened, the furnace body is tilted, and a ladle with a preheated temperature of >800℃ is used to collect the molten iron for tapping. At the same time, 30%-50% of the molten iron is reserved in the furnace for the next heat.

[0057] This invention provides a method for smelting molten iron using organic solid waste and low-grade direct reduced iron in an electric furnace. Organic solid waste powder is injected into the electric furnace through hollow graphite electrodes, and is pyrolyzed into hydrogen-rich reducing gas and pyrolytic carbon in the high-temperature zone of the electric arc. These components work synergistically in the smelting process of low-grade direct reduced iron, achieving efficient reduction of low-grade direct reduced iron and recycling of organic solid waste.

[0058] The following examples illustrate a method for smelting molten iron using organic solid waste and a low-grade direct reduction ferroelectric furnace, as provided by the present invention.

[0059] Example 1 This invention uses a 200 kg electric furnace for smelting, with a furnace volume of 160-220 kg. The composition (mass percentage) of the low-grade direct reduced iron used is: TFe 64.57%, MFe 34.45%, FeO 31.88%, C 1.93%, S 0.495%, SiO 29.31%, Al2O 33.39%, CaO 9.13%, MgO 2.26%. The method for smelting molten iron in the electric furnace includes the following steps: S1 Raw Material High-Efficiency Preheating Low-grade direct reduced iron (DRI) is loaded into a preheating shaft, where high-temperature flue gas is used to preheat it, thereby increasing its temperature. The porosity of the low-grade DRI fabric is 0.77-0.83. Organic solid waste powder, after being crushed, is placed in an organic solid waste powder container; the particle size of the organic solid waste powder is ≤200 mesh.

[0060] S2 Slag Composition Adjustment Power is supplied to the electric furnace with 72-80 kg of molten iron pre-filled. The height of the hollow graphite electrode is lowered to form a circuit between the hollow graphite electrode and the bottom anode, and then arc initiation is performed. The composition and weight of the slag after adding 108 kg of low-grade direct reduced iron are calculated using FactSage thermodynamic software. The slag composition is adjusted by adding alumina, magnesium oxide, and manganese oxide to be CaO 30%-35%, SiO2 30%-35%, Al2O3 15%-20%, MgO 10%-15%, and MnO 5%-10%. Calculations show that 2.16 kg of Al2O3, 1.08 kg of MgO, and 2.16 kg of MnO need to be added. At this point, the slag composition is CaO 31.33%, SiO2 31.95%, Al2O3 18.57%, MgO 11.22%, and MnO 6.93%.

[0061] S3 Continuous Feeding Smelting Submerged arc smelting and a high-voltage "long arc" power supply system (100 V, 1320 A) are adopted to increase the heating area, while 0.15 Nm of heat is injected through the vent plug at the bottom of the furnace. 3 Ar at a rate of / h, with a bottom blowing pressure of 0.6MPa, eliminates uneven molten pool temperature and increases the heating area of ​​the electric arc.

[0062] A "small amount, multiple times" feeding strategy was adopted, with 36 kg of material added in three separate applications. The arc heating time was calculated and determined according to formula (1). (1) In the formula, t arc denoted as arc heating time (s); N is the mass of low-grade direct reduced iron added each time (kg); U is the working voltage (V); and I is the working current (A). Calculations show that the arc heating time after each addition is 60 s, ensuring complete melting of the furnace charge.

[0063] S4 Collaborative High-Efficiency Restoration A high-current, short-arc power supply system (70 V, 1320 A) is employed. Organic solid waste powder is sprayed through hollow graphite electrodes at a spraying intensity of 0.18 kg / min. Argon is used as the carrier gas at a flow rate of 0.3 Nm³. 3 The blowing pressure is 0.7 MPa, and the blowing time is 3-5 min. The organic solid waste powder is pyrolyzed into hydrogen-rich reducing gas and pyrolytic carbon under the action of a high-temperature electric arc, synergistically reducing the molten slag and forming a reducing gas curtain to prevent slag oxidation. In this embodiment of the invention, the organic solid waste is crushed waste tire material.

[0064] Maintain a furnace bottom vent plug injection rate of 0.15 Nm. 3 The Ar content is 0.6 MPa per hour, the bottom blowing pressure remains constant, the inhomogeneity of the molten pool composition is eliminated, and the kinetic conditions of hydrogen plasma and pyrolytic carbon reduction are improved.

[0065] S5 Iron loss interruption during tapping process Temperature measurements are taken at 3-5 minute intervals. When the molten iron temperature is >1580℃, the bottom blowing gas circuit switch, powder tank switch, and carrier gas circuit switch are closed. The furnace cover is opened, the furnace body is tilted, and a ladle with a preheated temperature >800℃ is used to receive the molten iron for tapping.

[0066] This invention utilizes organic solid waste and low-grade direct reduced iron to smelt molten iron, achieving an iron recovery rate of up to 97% and reducing energy consumption by 20%.

[0067] Example 2 This invention uses a 200 kg electric furnace for smelting, with a furnace volume of 180-220 kg. The composition (mass percentage) of the low-grade direct reduced iron used is: TFe 63.80%, MFe 31.54%, FeO 34.11%, C 1.45%, S 0.41%, SiO2 9.52%, Al2O3 3.45%, CaO 9.01%, MgO 2.32%. The method for smelting molten iron in the electric furnace includes the following steps: S1 Raw Material High-Efficiency Preheating Low-grade direct reduced iron is loaded into the preheating shaft, where high-temperature flue gas is used to preheat the furnace charge, increasing the preheating temperature of the charge. The porosity of the low-grade direct reduced iron charge should be 0.77-0.80. Organic solid waste powder is crushed and placed in an organic solid waste powder container; the particle size of the organic solid waste is ≤200 mesh.

[0068] S2 Slag Composition Adjustment Power is supplied to the electric furnace with a reserve of 75-85 kg of molten iron. The height of the hollow graphite electrode is lowered to form a circuit between the hollow graphite electrode and the bottom anode, and then arc initiation is performed. The composition and weight of the slag after adding 120 kg of low-grade direct reduced iron are calculated using FactSage thermodynamic software. The slag composition is adjusted by adding alumina, magnesium oxide, and manganese oxide to achieve the following: CaO 30%-35%, SiO2 30%-35%, Al2O3 15%-20%, MgO 10%-15%, and MnO 5%-10%. Calculations show that 1.8 kg of Al2O3, 1.44 kg of MgO, and 2.88 kg of MnO are required, resulting in an oxide ratio of CaO 30.60%, SiO2 32.33%, Al2O3 16.86%, MgO 11.99%, and MnO 8.22%.

[0069] S3 Continuous Feeding Smelting Submerged arc smelting and a high-voltage "long arc" power supply system (100 V, 1400 A) are adopted to increase the heating area, while 0.18 Nm of heat is injected through the vent plug at the bottom of the furnace. 3 Ar at a rate of / h, with a bottom blowing pressure of 0.6 MPa, eliminates uneven molten pool temperature and increases the heating area of ​​the electric arc.

[0070] A "small amount, multiple times" feeding strategy was adopted, with 40 kg of material added in three separate applications. The arc heating time was calculated and determined according to formula (1). (1) In the formula, t arc N is the arc heating time in seconds; U is the mass of low-grade direct reduced iron added each time in kilograms; U is the operating voltage in volts (V); and I is the operating current in amperes (A).

[0071] Calculations show that the arc heating time after each feeding is 63 seconds, which is sufficient to melt the furnace charge.

[0072] S4 Collaborative High-Efficiency Restoration A high-current, short-arc power supply system (80 V, 1320 A) is employed. Organic solid waste powder is sprayed through hollow graphite electrodes at a spraying intensity of 0.2 kg / min. Argon is used as the carrier gas at a flow rate of 0.32 Nm³. 3 The blowing rate is 0.72 MPa per hour, and the blowing time is 3-5 minutes. The organic solid waste powder is pyrolyzed into hydrogen-rich reducing gas and pyrolytic carbon under the action of a high-temperature electric arc, synergistically reducing the molten slag and forming a reducing gas curtain to prevent slag oxidation. In this embodiment of the invention, the organic solid waste is crushed waste tires.

[0073] Maintain a furnace bottom vent plug injection rate of 0.18 Nm. 3 / h Ar, bottom blowing pressure is 0.6 MPa, intensity remains unchanged, eliminates non-uniform composition of molten pool, and improves the kinetic conditions of hydrogen plasma and pyrolytic carbon reduction.

[0074] S5 Iron loss interruption during tapping process Temperature measurements are taken at 3-5 minute intervals. When the molten iron temperature is >1580℃, the bottom blowing gas circuit switch, powder tank switch, and carrier gas circuit switch are closed. The furnace cover is opened, the furnace body is tilted, and a ladle with a preheated temperature >800℃ is used to receive the molten iron for tapping.

[0075] This invention utilizes organic solid waste and low-grade direct reduced iron to smelt molten iron, achieving an iron recovery rate of up to 97.5% and reducing energy consumption by 19.5%.

[0076] Example 3 This invention uses a 5-ton electric furnace for smelting, with a furnace capacity of 4-6 tons. The composition (mass percentage) of the low-grade direct reduced iron used is: TFe 64.75%, MFe 38.60%, FeO 30.30%, C 1.60%, S 0.45%, SiO2 9.50%, Al2O3 3.84%, CaO 9.17%, MgO 2.88%. The method for smelting molten iron in the electric furnace includes the following steps: S1 Raw Material High-Efficiency Preheating Low-grade direct reduced iron is loaded into the preheating shaft, where high-temperature flue gas is used to preheat the furnace charge, increasing the preheating temperature. The porosity of the low-grade direct reduced iron charge should be 0.80-0.83. Organic solid waste powder is crushed and placed in an organic solid waste powder container; the particle size of the organic solid waste is ≤200 mesh.

[0077] S2 Slag Composition Adjustment 1.8t-2.2t of low-grade direct reduced iron is placed into the electric furnace. After the charge melts, a molten pool is formed, creating conditions for steel retention. After power is supplied, the height of the hollow graphite electrode is lowered, forming a circuit with the bottom anode, and then arc ignition is initiated. The composition and weight of the slag after adding 5t of low-grade direct reduced iron are calculated using FactSage thermodynamic software. After the charge melts, the slag composition is adjusted by adding alumina, magnesium oxide, and manganese oxide to be CaO 30%-35%, SiO2 30%-35%, Al2O3 15%-20%, MgO 10%-15%, and MnO 5%-10%. Calculations show that 80 kg of Al2O3, 40 kg of MgO and 130 kg of MnO need to be added. The oxide proportions of the slag are CaO 30.38%, SiO2 31.47%, Al2O3 17.24%, MgO 12.21% and MnO 8.69%.

[0078] S3 Continuous Feeding Smelting Submerged arc smelting and a high-voltage "long arc" power supply system (160 V, 18000 A) are adopted to increase the heating area, while 2.4 Nm of heat is injected through the vent plug at the bottom of the furnace. 3 Ar at a rate of / h, with a bottom blowing pressure of 0.7 MPa, eliminates uneven molten pool temperature and increases the heating area of ​​the electric arc.

[0079] A "small amount, multiple times" feeding strategy was adopted, with 1000 kg of material added in three separate applications. The arc heating time was calculated and determined according to formula (1). (1) In the formula, t arc N is the arc heating time in seconds; U is the mass of low-grade direct reduced iron added each time in kilograms; U is the operating voltage in volts (V); and I is the operating current in amperes (A).

[0080] Calculations show that the arc heating time after each feeding is 64 seconds, which is sufficient to melt the furnace charge.

[0081] S4 Collaborative High-Efficiency Restoration A high-current, short-arc power supply system (120 V, 16500 A) is used to spray organic solid waste powder through hollow graphite electrodes. The spraying intensity of the organic solid waste powder is 5 kg / min, and the carrier gas is argon with a flow rate of 4 Nm³. 3 The blowing rate is 0.8 MPa per hour, and the blowing time is 5-10 minutes. The organic solid waste powder is pyrolyzed into hydrogen-rich reducing gas and pyrolytic carbon under the action of a high-temperature electric arc, synergistically reducing the molten slag and forming a reducing gas curtain to prevent slag oxidation. In this invention example, the organic solid waste is crushed waste tires.

[0082] Maintain 2.4 Nm of air injection through the furnace bottom vent plug. 3 The Ar content is 0.7 MPa per hour, the bottom blowing pressure remains constant, the inhomogeneity of the molten pool composition is eliminated, and the kinetic conditions of hydrogen plasma and pyrolytic carbon reduction are improved.

[0083] S5 Iron loss interruption during tapping process Close the bottom blowing gas circuit switch, powder tank switch, and carrier gas circuit switch. Open the furnace cover, tilt the furnace body, and use a ladle with a preheated temperature >800℃ to receive the molten iron for tapping.

[0084] The present invention utilizes organic solid waste and low-grade direct reduced iron to smelt molten iron, achieving an iron recovery rate of up to 96.5% and reducing energy consumption by 20.5%.

[0085] As can be seen from the above embodiments, the method for smelting molten iron using organic solid waste and low-grade direct reduced iron in an electric arc furnace provided by the present invention can improve the efficiency of smelting low-grade direct reduced iron by more than 20% and increase the iron yield to more than 96% compared with the conventional electric arc furnace smelting process for low-grade direct reduced iron. This method breaks through the bottleneck of the difficulty in efficiently utilizing low-grade direct reduced iron and also realizes the harmless utilization of organic solid waste, thus achieving both economic and environmental benefits.

[0086] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for smelting molten iron using organic solid waste and a low-grade direct reduction ferroelectric furnace, characterized in that, Includes the following steps: With molten iron reserved in the electric furnace molten pool, electricity is supplied and the arc is ignited. Then, auxiliary materials are added to form a slag system with the composition of CaO 30%-35%, SiO2 30%-35%, Al2O3 15%-20%, MgO 10%-15%, and MnO 5%-10%. The submerged arc smelting and high-voltage long-arc power supply system are adopted. The preheated low-grade direct reduced iron is added into the electric furnace in multiple batches under bottom blowing and stirring. The smelting time is controlled until the low-grade direct reduced iron added each time melts. After the low-grade direct reduced iron is melted, bottom blowing and stirring are continued and a high-current short-arc power supply system is adopted to spray organic solid waste powder into the electric furnace through hollow graphite electrodes. When the molten pool temperature is >1580℃, stop the bottom blowing of inert gas and stop the injection of organic solid waste powder before tapping the iron. Reserve 30%-50% of the molten iron in the electric furnace for the next heat.

2. The method for smelting molten iron using organic solid waste and a low-grade direct reduction ferroelectric furnace according to claim 1, characterized in that, The preheating of the low-grade direct reduced iron involves loading the low-grade direct reduced iron into a preheating shaft, distributing the material with a porosity of 0.75-0.85, and using the high-temperature flue gas in the shaft to preheat the low-grade direct reduced iron.

3. The method for smelting molten iron using organic solid waste and a low-grade direct reduction ferroelectric furnace according to claim 2, characterized in that, The low-grade direct reduced iron comprises, by mass percentage, 60%-65% TFe, 30%-40% MFe, 30%-40% FeO, 1%-2% C, 0.3%-0.5% S, 8%-10% SiO2, 3%-4% Al2O3, 8%-10% CaO, and 2%-3% MgO.

4. The method for smelting molten iron using organic solid waste and a low-grade direct reduction ferroelectric furnace according to claim 1, characterized in that, The organic solid waste powder is obtained by crushing organic solid waste, including waste rubber and / or waste tires, to a particle size of ≤200 mesh.

5. The method for smelting molten iron using organic solid waste and a low-grade direct reduction ferroelectric furnace according to claim 1, characterized in that, The reserved molten iron in the electric furnace molten pool is 30%-50% of the molten iron reserved when tapping iron after the previous furnace is completed; if it is the first furnace smelting in the electric furnace, the reserved molten iron in the electric furnace molten pool is the molten iron formed after the scrap steel and / or low-grade direct reduced iron arranged in the electric furnace is melted.

6. The method for smelting molten iron using organic solid waste and a low-grade direct reduction ferroelectric furnace according to claim 1, characterized in that, The auxiliary materials are calcium oxide, magnesium oxide and manganese oxide. The amount of the auxiliary materials added is calculated using FactSage thermodynamic software based on the composition and amount of low-grade direct reduced iron.

7. The method for smelting molten iron using organic solid waste and a low-grade direct reduction ferroelectric furnace according to claim 1, characterized in that, The bottom-blowing agitation is achieved by injecting 0.25 Nm of air into the electric furnace through the vent plug at the bottom of the furnace. 3 / h•t iron-1.25 Nm 3 Argon or nitrogen gas per h·t of iron, with a bottom blowing pressure of 0.5 MPa - 1.0 MPa.

8. The method for smelting molten iron using organic solid waste and a low-grade direct reduction ferroelectric furnace according to claim 1, characterized in that, The low-grade direct reduced iron is added to the electric furnace in 2-4 batches per furnace. After each addition of low-grade direct reduced iron, the arc heating time is calculated and determined according to formula (1). （1） In the formula, t arc N is the arc heating time in seconds; U is the mass of low-grade direct reduced iron added each time in kilograms; U is the operating voltage in volts (V); and I is the operating current in amperes (A).

9. The method for smelting molten iron using organic solid waste and a low-grade direct reduction ferroelectric furnace according to claim 1, characterized in that, The injection intensity of the organic solid waste powder is 0.8 kg / min·t iron - 1.2 kg / min·t iron, and the carrier gas for injection is argon or nitrogen, with a flow rate of 0.5 Nm³. 3 / h•t iron-2.0 Nm 3 / h·t iron, the pressure of the carrier gas is 0.5 MPa - 0.9 MPa, and the injection time of the organic solid waste powder is 1 min - 20 min.

10. The method for smelting molten iron using organic solid waste and a low-grade direct reduction ferroelectric furnace according to claim 1, characterized in that, The molten iron is collected in a ladle that has been preheated to a temperature >800℃.

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