Method for producing molten iron or alloys thereof from low-carbon direct reduced iron in electric arc furnace

Abstract

The present disclosure relates to a method for producing molten iron or an alloy thereof from low carbon direct reduced iron (DRI) in an electric arc furnace (EAF). The DRI comprises less than 0.1% by weight of carbon. The method includes a combined charging and melting stage including continuously charging DRI into a melt metal bath in an EAF and simultaneously operating the EAF to continuously melt the DRI. During this phase, the method is maintained within the following window of operation:-a bath temperature from about 1580 DEG C to about 1750 DEG C; -FeO in the slag is from about 25% by weight to about 40% by weight; -the B2 basicity of the slag is from about 1.5 to about 3.5, wherein the B2 basicity is calculated as (wt.% CaO) / (wt.% SiO2); mgO in the slag is from about 8 wt% to about 13 wt%; and carbon monoxide (CO) gt in the exhaust gas; and 26 Nm < 3 > / h / m < 2 >.

Description

Technical Field

[0001] This disclosure relates to a method for producing molten iron or its alloys from low-carbon direct reduced iron in an electric arc furnace. More specifically, this disclosure relates to a method for producing molten iron or its alloys from low-carbon direct reduced iron in an electric arc furnace as defined in the preamble of the independent claims. Background Technology

[0002] Steel is the world's most important engineering and construction material. In the modern world, it is difficult to find anything that does not contain steel or whose manufacture and / or transportation do not depend on it. In this way, steel is intricately involved in almost every aspect of our modern lives. Total global production of crude steel is approximately 1.9 billion tons per year, far exceeding any other metal, and is projected to reach 2.8 billion tons by 2050, with 50% expected to originate from primary iron ore sources.

[0003] Despite decades of improvements to steelmaking processes and their approach to theoretically minimum energy consumption, a fundamental problem remains unresolved: the reduction of iron ore using carbonaceous reducing agents results in the production of CO2 as a byproduct. In 2018, an average of 1.83 tons of CO2 were generated for every ton of steel produced. The steel industry is one of the highest CO2 emitters, accounting for approximately 7% of global CO2 emissions. As long as carbonaceous reducing agents are used, it is impossible to avoid excessive CO2 production during steelmaking.

[0004] The HYBRIT initiative was established to address this issue. HYBRIT (an abbreviation for HydrogenBreakthrough Ironmaking Technology) is a joint venture project, partly funded by the Swedish Energy Agency, involving SSAB, LKAB, and Vattenfall, and aims to reduce CO2 emissions and decarbonize the steel industry. At the heart of the HYBRIT concept is direct reduction based on a shaft furnace to produce sponge iron from primary ore. In direct reduction, the ore is reduced in a solid-state reduction process at temperatures below the melting point of iron. The shaft furnace-based direct reduction process utilizes pelletized iron ore as feedstock and produces a porous crude iron product called sponge iron or direct reduced iron (DRI). Instead of using carbon-containing reducing gases (such as natural gas) as in current commercial direct reduction processes, HYBRIT proposes using hydrogen as a reducing agent, known as hydrogen direct reduction (H-DR). Hydrogen can be produced primarily through the electrolysis of water using fossil-free and / or renewable primary energy sources. Therefore, the key steps of reducing iron ore can be achieved without the need for fossil fuels as input, with water as a byproduct instead of CO2.

[0005] Sponge iron produced by direct reduction is typically then processed in an electric arc furnace to melt and refine the crude iron before any further secondary metallurgical processing. However, DRI produced by direct hydrogen reduction (H2-DRI) exhibits different characteristics compared to conventional DRI, primarily due to the absence of carbon incorporation. This means that methods developed for processing conventional DRI are not necessarily applicable to processing H2-DRI. Therefore, there is still a need to develop steelmaking processes downstream of the direct reduction stage to accommodate the processing of substantially carbon-free DRI, such as that obtained through direct hydrogen reduction. Summary of the Invention

[0006] Since 2020, the HYBRIT initiative has been operating pilot direct reduction shaft furnaces, in which hydrogen-based methods can be used to produce DRI at a semi-industrial and commercially relevant scale. Based on subsequent experience processing such H2-DRI in electric arc furnaces, the inventors of this invention have identified the following considerations regarding conventional means of processing DRI.

[0007] Sponge iron produced using conventional fossil-based carbon-containing reducing agents typically contains a significant amount of dispersed carbon (usually up to 5% by weight) due to the incorporation of carbon by carbon-containing reducing gases during the reduction of iron ore. This dispersed carbon is primarily in the form of cementite (Fe3C), with a smaller portion consisting of graphite dispersed throughout the sponge iron. The eutectic (melting) temperature of the iron-cementite system is 1147°C (below the melting point of pure iron, 1536°C), and the cementite undergoes exothermic dissociation in the melt bath. This facilitates the melting of the sponge iron and generates a beneficial foamy slag due to “carbon boiling,” where carbon from the DRI (and often additional carbon) reacts with oxygen to produce carbon monoxide (CO). The foamy slag serves to isolate the molten metal bath, resulting in improved energy efficiency, reduced EAF electrode consumption, and a lower risk of unwanted nitrogen incorporation into the melt. However, due to the excessive carbon content, such conventional methods typically require a refining stage in the EAF after melting and before tapping, thereby supplying oxygen to the bath until the carbon levels reach acceptable levels.

[0008] Sponge iron produced by direct hydrogen reduction (H2-DRI) lacks carbon and is therefore more difficult to melt in an EAF. When the local rate of DRI charging exceeds the furnace's melting capacity, it can lead to the accumulation of unmelted DRI heaps ("ferroberg"), which may require extended time and power consumption to melt and disperse. This reduces process efficiency. Furthermore, the lack of carbon also means that carbon boiling will not be achieved without the supply of exogenous carbon, and therefore no foamy slag will be obtained.

[0009] Besides being used for DRI melting, electric arc furnaces (EAFs) are also used for processing scrap metal when available. Scrap metal may also have a low carbon content, potentially leading to problems with melting and carbon boiling. However, when melting scrap metal, EAFs are typically operated with an excessive amount of carbon in the bath. This improves the problem of insufficient carbon boiling, but at the cost of extensive refining after melting and before tapping to remove the excess carbon. Furthermore, scrap metal is usually loaded into the furnace as a single batch before the EAF top is shut off and the melting of the entire batch begins.

[0010] It would be advantageous to implement methods that overcome or at least mitigate some of the aforementioned disadvantages. In particular, it would be desirable to make EAF-based methods for processing low-carbon DRI efficient and to mitigate the disadvantages of iron buildup and poor slag foaming typically associated with processing low-carbon DRI. To better address one or more of these problems, methods having the features defined in the independent claims are provided.

[0011] This method is used to produce molten iron or its alloys from low-carbon direct reduced iron (DRI) in an electric arc furnace (EAF). DRI contains less than 0.1% by weight of carbon.

[0012] The method includes a combined charging and melting phase, comprising continuously charging the DRI into a molten metal bath in an EAF while simultaneously operating the EAF to continuously melt the DRI. During the charging and melting phase, DRI, electricity, carbon, oxygen, and optionally one or more slagging agents are supplied to the EAF as inputs; and the bath temperature, slag composition, and exhaust gas composition are determined. During the charging and melting phase, the DRI feed rate, applied power, carbon feed rate, oxygen feed rate, and slagging agent feed rate are adjusted to maintain the method within the following operating window:

[0013] - The bath temperature is approximately 1580°C to approximately 1750°C;

[0014] - The FeO content in the slag is approximately 25% to approximately 40% by weight;

[0015] - The B2 basicity of the slag is from about 1.5 to about 3.5, where the B2 basicity is calculated as (wt% CaO) / (wt% SiO2).

[0016] - The MgO content in the slag is approximately 8% to approximately 13% by weight; and

[0017] - Carbon monoxide (CO) in exhaust gas > 26 Nm 3 / hour / m 2 .

[0018] By keeping the method within a specific operating window, efficient melting of low-carbon / carbon-free DRI was achieved. In other words, keeping the method within a specific operating window provides a melting process that avoids the formation of iron mountains, provides sufficient foamed slag, and avoids unnecessary large additions of other inputs (such as carbon, slag-forming agents, and oxygen). This ultimately provides a highly time-efficient, material-efficient, and energy-efficient method.

[0019] Other objects, advantages and novel features of the present invention will become apparent to those skilled in the art from the following detailed description. Attached Figure Description

[0020] To gain a more complete understanding of the invention and its additional objects and advantages, the following detailed description should be read in conjunction with the accompanying drawings, in which like reference numerals denote similar items in the various figures, and wherein:

[0021] Figure 1 This is a graph plotted based on the raw materials (carbon-free or 1.5% C DRI), FeO (%) in the slag, and DRI feed rate (tons / hour), illustrating various EAF smelting processes. For each smelting process, it shows whether an iron mountain was formed.

[0022] Figure 2 It is based on the raw materials (carbon-free or 1.5% C DRI), the FeO (%) in the slag, and the CO (Nm³) in the exhaust gas. 3 A graph showing the various EAF smelting processes (per hour). For each smelting, it indicates whether sufficient foam slag was obtained.

[0023] The invention will now be described in more detail with reference to certain exemplary embodiments and the accompanying drawings. However, the invention is not limited to the exemplary embodiments discussed herein and / or shown in the drawings, but may vary within the scope of the appended claims. Furthermore, the drawings should not be considered to be drawn to scale, as some features may have been enlarged to illustrate certain features more clearly. Detailed Implementation

[0024] This disclosure relates to a method for producing molten iron or its alloys from low-carbon direct reduced iron (DRI) in an electric arc furnace (EAF). The alloy of the molten iron, for example, refers to molten steel. The method is applicable to any electric arc furnace, including AC and DC electric arc furnaces, but may be particularly suitable for three-electrode AC electric arc furnaces.

[0025] DRI

[0026] The main raw material used in this method is low-carbon DRI, meaning that the DRI contains less than 0.1% by weight of carbon. The DRI can preferably contain less than 0.05% by weight of carbon, and even more preferably, it can be essentially carbon-free. Such carbon-free DRI can be obtained, for example, as a product of hydrogen-based direct reduction from iron ore. DRI can be in the form of pellets, cold-briquetted iron (CBI), or hot-briquetted iron (HBI). According to the International Maritime Solid Bulk Cargo Codes (IMSBC), DRI pellets and cold-briquetted DRI are referred to as Type B DRI, while hot-briquetted DRI is referred to as Type A DRI.

[0027] The average metallization rate of DRI is preferably greater than or equal to 95%. Metallization rate is defined in a manner conventionally practiced in the art as (iron...) 金属化的 / iron 总的 (×100). This paper uses X-ray diffraction (XRD) measurements to determine the metallization, but other methods can also be used. These other methods include:

[0028] ISO 2597-1:2006 (Iron ores — Determination of total iron content — Part 1: Titrimetric method after tin (II) chloride reduction) combined with ISO 5416:2006 (Direct reduced iron — Determination of metallic iron — Bromine-methanol titrimetric method); and

[0029] ISO 10276-1:2000 (Chemical analysis of ferrous materials — Determination of oxygen in steel and iron Part 1: Sampling and preparation of steel samples for oxygen determination) and ISO 10276-2:2003 (Chemical analysis of ferrous materials — Determination of oxygen content in steel and iron — Part 2: Infrared method after fusion under inert gas) are combined.

[0030] This method allows the use of additional metallic feedstocks in limited quantities. For example, conventional carbon-containing DRI or scrap metal can be used up to 20% by weight of the total metallic feedstock, with the remainder consisting of low-carbon (or substantially carbon-free) DRI. If such additional feedstocks are used, they can be continuously fed into the EAF in the same manner as low-carbon DRI.

[0031] Run window

[0032] The method disclosed herein utilizes a combined charging and melting stage. This contrasts with the conventional EAF method, which more typically has separate charging and melting stages, in which crude metal is first charged into the EAF in batches, then the EAF top is closed and melting begins by applying electricity. The combined charging and melting stage requires continuous charging of the DRI into the EAF, with simultaneous charging and melting of the DRI. Initially, after the furnace is turned, the EAF can typically contain a “hot-heel” from the previous melt, and this hot-heel can help melt the initially charged DRI.

[0033] At the start of the charging and smelting stages, DRI, electricity, carbon, oxygen, and optionally one or more slagging agents are supplied to the EAF as inputs. The aim is to keep the method within the following operating window:

[0034] - The bath temperature is approximately 1580°C to approximately 1750°C;

[0035] - The FeO content in the slag is approximately 25% to approximately 40% by weight;

[0036] - The B2 basicity of the slag is from about 1.5 to about 3.5, where the B2 basicity is calculated as (wt% CaO) / (wt% SiO2).

[0037] - The MgO content in the slag is approximately 8% to approximately 13% by weight; and

[0038] - Carbon monoxide (CO) in exhaust gas > 26 Nm 3 / hour / m 2 .

[0039] This is achieved by determining the bath temperature, slag composition, and exhaust gas composition at regular intervals, and adjusting various inputs to keep the method within an operating window, including the DRI feed rate, applied power, carbon feed rate, oxygen feed rate, and slag-forming agent feed rate.

[0040] It has been found that efficient melting of low-carbon / carbon-free DRIs is achieved by keeping the method within a specific operating window. The formation of iron slag, which could otherwise be a significant challenge in the melting of carbon-free DRIs, is avoided. The method avoids the unnecessary addition of large amounts of material inputs (e.g., carbon, oxygen, and slagging agents) while keeping impurities (e.g., nitrogen, phosphorus, and sulfur) at acceptable levels. Sufficient foamy slag is obtained, providing improved energy efficiency and avoiding wear on refractory materials and electrodes. Ultimately, the method presented is highly time-efficient, material-efficient, and energy-efficient.

[0041] The bath temperature, slag composition, and exhaust gas composition can be readily measured or otherwise determined using conventional means and methods in the art.

[0042] It was found that the EAF exhaust gas contained approximately >26 Nm 3 / hour / m 2 The carbon monoxide limit provides sufficient slag foaming, provided that other parameters are kept within a specific window. The reference unit is nominal cubic meters of carbon monoxide per hour relative to the surface area of ​​the EAF bath in square meters. Electric arc furnaces typically have vertical or near-vertical walls, and therefore the surface area of ​​the bath remains substantially constant during smelting. The surface area of ​​the bath can be readily calculated from the diameter or other relevant dimensions of the EAF.

[0043] >26 Nm in exhaust gas 3 / hour / m 2The carbon monoxide (CO) limit is based on a theoretical 100% carbon yield, meaning all carbon charged into the process dissolves in the bath and contributes to increasing the bath's carbon content or forming CO through FeO reduction. In reality, some of the carbon charged into the EAF burns without dissolving in the bath and does not contribute to, for example, slag foaming. For efficient industrial EAF methods, a typical carbon yield is around 75%, and thus CO in the exhaust gas can be kept >35 Nm³. 3 / hour / m 2 (26 / 0.75) to account for “unutilized” carbon. With a slightly worse carbon yield (e.g., around 60%), CO in the exhaust gas can be maintained at >43 Nm³. 3 / hour / m 2 (26 / 0.6) to explain the “unused” carbon.

[0044] The CO in the exhaust gas can be kept below 150 Nm. 3 / hour / m 2 For example, less than 120 Nm 3 / hour / m 2 For example, less than 90 Nm 3 / hour / m 2 For example, less than 60 Nm 3 / hour / m 2 This can help avoid waste of material inputs and prevent excessive foaming of the slag.

[0045] The carbon content of the molten metal bath can be maintained at less than 0.7% by weight, for example, less than 0.5% by weight, for example, less than 0.3% by weight, for example, less than or equal to 0.2% by weight. Besides providing material savings, maintaining a low carbon content in the bath means there is a reduction in or elimination of separate refining stages for removing excess carbon. Therefore, shorter tap-to-tap times and further increased productivity can be achieved. The carbon content of the molten metal can be determined by direct measurement or by determining the bath composition, or by differential determination using reference to the carbon content of the charge and the CO content in the exhaust gas.

[0046] The bath temperature can be maintained below 1700°C, for example, below 1650°C. Lower bath temperatures can provide increased energy efficiency and produce lower levels of phosphorus impurities in the molten iron.

[0047] The FeO content in the slag can be maintained at approximately 30% to approximately 40% by weight. Within this window, the tendency to form iron peaks can be lower, and the resulting steel can have fewer phosphorus impurities.

[0048] The B2 basicity of the slag can be maintained at approximately 1.5 to approximately 2.5. Within this window, the resulting steel can have fewer phosphorus impurities and produce a good foamy slag.

[0049] The MgO content in the slag can be maintained at approximately 8% to approximately 13% by weight. Operating within this range helps limit refractory wear while still providing sufficient slag viscosity to ensure adequate slag foaming.

[0050] After the melt bath reaches the desired level in the EAF, the charging and melting stages can be completed.

[0051] Entering EAF input

[0052] Various inputs (energy inputs in the form of electricity, and material inputs in the form of DRI, carbon, oxygen, and optionally slagging agents) can interact with each other and can affect more than one of the parameters in the operating window. For example, starting from the nominal levels of all inputs, the following effects may occur: Increasing the DRI feed rate may tend to decrease the bath temperature, and decreasing the DRI feed rate may tend to increase the bath temperature. Increasing the applied power may tend to increase the bath temperature, and decreasing the applied power may tend to decrease the bath temperature. Increasing the carbon feed rate may tend to increase CO in the exhaust gas and decrease FeO in the slag. Decreasing the carbon feed rate may tend to decrease CO in the exhaust gas and increase FeO in the slag. Increasing the oxygen feed rate may tend to increase FeO in the slag and increase CO in the exhaust gas. Decreasing the oxygen feed rate may tend to decrease FeO in the slag and decrease CO in the exhaust gas. Changing the slagging agent feed rate can increase or decrease the B2 basicity of the slag and can increase or decrease the MgO in the slag, depending on whether the slagging agent contains CaO, SiO2, and / or MgO (or its analogues).

[0053] Initially, each input can be set at a nominal level, and then adjusted based on the determination of various operating parameters. The theoretical nominal feed rate for each input can be calculated as follows.

[0054] Preferably, in order to provide a fast method, the nominal applied power is... It should be at or near the system’s maximum applicable power, for example, greater than 90% of the maximum rated power or greater than 95% of the maximum rated power.

[0055] The DRI feed rate should then be adjusted. A suitable nominal DRI feed rate is required. It can be determined empirically, or it can be calculated using the following equation:

[0056]

[0057] in The nominal DRI feed rate is expressed in mass per unit time (e.g., tons per hour).

[0058] The nominal applied power is expressed in terms of energy per unit time (e.g., kW / hour).

[0059] To estimate system power loss, the unit is energy per unit time (e.g., kW / h, which can be determined empirically for any given system and nominal power).

[0060] The specific energy required to melt one unit mass of DRI (e.g., the specific heat required to bring DRI from ambient temperature to melting temperature, plus the specific heat of melting) is expressed in units of energy per unit mass (e.g., kWh / ton).

[0061] For industrial EAF methods with good carbon yield, a suitable nominal carbon feed rate can be sufficient to provide >35 Nm³. 3 / hour / m 2 The carbon feed rate of CO in the exhaust gas. This is equivalent to approximately 44 kg / h / m 2 CO, which is equivalent to approximately 19 kg / hour / m³ 2 Carbon. For industrial methods with low carbon yields (e.g., around 60%), this means a requirement of >43 Nm³. 3 / hour / m 2 The CO emitted in the exhaust gas is equivalent to approximately 54 kg / hour / m³. 2 CO, which is equivalent to approximately 23 kg / hour / m³ 2 carbon.

[0062] For a typical industrial EAF, a suitable nominal oxygen feed rate can be sufficient to provide >35 Nm³. 3 / hour / m 2 The oxygen feed rate of CO in the exhaust gas. This is equivalent to approximately 18 Nm. 3 / hour / m 2 .

[0063] The appropriate nominal slagging agent feed rate will depend on the inherent composition of the slagging agent in the DRI, as well as the nominal feed rate of the DRI.

[0064] The actual nominal feed rate used can be within a suitable range of these calculated theoretical nominal rates, for example, within + / -20% of the theoretical nominal rate, for example, within + / -10% of the theoretical nominal rate, for example, within + / -5% of the theoretical nominal rate.

[0065] DRI can be continuously charged into the furnace using methods known in the art. For example, DRI can be continuously charged into the furnace via the EAF top (e.g., the fifth hole) or via side charging.

[0066] As is known in the art, carbon can be charged into the furnace via top feed (e.g., through the top of the EAF) or by injection into the melt. The carbon can be conventional metallurgical-grade carbon (e.g., anthracite) or biochar. Using biochar can provide steel with lower sulfur levels.

[0067] Oxygen can be supplied to the furnace using methods known in the art, such as using an oxygen lance.

[0068] As is known in the art, slagging agents can be charged into the furnace via top feed or injection. Suitable slagging agents may include, but are not limited to, CaO, SiO2, calcined dolomite, and combinations thereof. Alternatively, the self-generated slag formed by DRI melting may possess sufficient properties to eliminate the need for additional slagging agents.

[0069] Iron tapping stage

[0070] After the charging and smelting stages are completed, the tapping stage can begin directly. This contrasts with the typical EAF method, which may often require one or more refining stages to burn off oxidizable impurities and remove excess carbon. During the tapping stage, all material input is stopped. Tapping can be conditional upon the bath reaching a suitable tapping temperature, such as above or equal to 1600°C, above or equal to 1630°C, or above or equal to 1650°C. If the bath has not reached the tapping temperature, power can be applied until the suitable temperature is reached. Afterward, power is stopped and the EAF discharges molten iron or its alloy.

[0071] experiment

[0072] An overview of the optimal process window has been established from previous pilot activities using various H2-DRI and NG-DRI materials. These pilot activities comprised approximately 200 smeltings in total to investigate the following melting processes: both hydrogen-reduced DRI pellets with carbon (Type B) and hydrogen-reduced DRI pellets without carbon (Type B); both hydrogen-reduced HBI with carbon (Type A) and hydrogen-reduced HBI without carbon (Type A); DRI pellets produced using conventional natural gas-based reducing gases; and HBI produced using conventional natural gas-based reducing gases. This optimal window was established to provide good foaming, good productivity (i.e., no iron hills), and a stable process (i.e., stable temperature and slag characteristics).

[0073] In recent activities, a total of 44 further smeltings were conducted. Each smelting used carbon-free H2-DRI as feedstock, or, for comparative purposes, H2-DRI subsequently carburized with natural gas-based carburizing gas to approximately 1.5% carbon content. All DRI feedstock used was supplied by the Hybrit pilot DRI plant. The metallization degree of each batch of DRI entering each smelting was typically 90% to 100%. The pilot-scale 3-electrode AC arc furnace used had a circular diameter of approximately 2.1 m, which provided approximately 3.46 m³ during operation. 2 The surface area of ​​the bath.

[0074] Begin smelting from the outlined method window and collect / measure and evaluate the following data:

[0075] Entering the analysis and quantification of materials

[0076] Steel samples and slag samples

[0077] temperature

[0078] The amount of steel and slag released

[0079] Exhaust gas analysis and temperature

[0080] Dust in the exhaust gas; quantity and analysis

[0081] Slag foaming (rated as 1 - Poor, 2 - Average, or 3 - Good)

[0082] Iron Mountain symbol (Yes / No)

[0083] CO generation from exhaust gas analysis

[0084] Carbon yield from exhaust gases, steel, and slag; material addition records

[0085] Oxygen yield from exhaust gases, steel, and slag; material addition records

[0086] Energy balance from steel and slag, temperature measurement, and material quantity

[0087] Electrical data

[0088] The following is a summary of some of the results obtained.

[0089] It was found that although the degree of metallization of the incoming DRI varied significantly, a reasonable level of FeO in the slag could be maintained through carbon balance during smelting. Most smelting maintained a slag FeO level of approximately 25 wt% to approximately 40 wt%.

[0090] Some smelting processes use biochar, while others use anthracite. The carbon is either top-feed or injected, and the type of carbon used is adjusted for specific charging methods, such as particle size. Generally, biochar and anthracite exhibit similar carbon yields, and the yields obtained through top feeding and injection are also similar. It has been found that although sulfur levels are generally acceptable for all smelting processes, those using biochar typically have lower final sulfur content in the steel.

[0091] The effects of various process parameters on key results (such as iron mountain formation, slag foaming, and steel impurity content (nitrogen, phosphorus, sulfur)) were investigated.

[0092] Some examples of the results obtained are shown in Figures 1 to 2 middle.

[0093] Figure 1 This graph plots various smelting processes based on the feedstock (carbon-free or 1.5% C DRI), the FeO percentage in the slag, and the DRI feed rate (tons / hour). For each smelting process, it shows whether iron hills formed. It can be seen that iron hills formed only when using carbon-free DRI feedstock; no iron hills formed when using carbon-containing DRI. Observing the smelting using carbon-free DRI, it can be seen that FeO in the slag is an important parameter. Iron hill formation was not observed in smelting with approximately 30% to 40% FeO in the slag, while iron hill formation was observed in some smelting processes with lower and higher FeO proportions in the slag. The graph also shows that within a defined window of %FeO in the slag, iron hill formation is relatively insensitive to the DRI feed rate, and no iron hill formation was observed in smelting processes with relatively high feed rates.

[0094] Figure 2 It is based on the raw materials (carbon-free or 1.5% C DRI), the FeO (%) in the slag, and the CO (Nm³) in the exhaust gas. 3 A graph was plotted for various smelting processes (per hour). For each smelting, it was shown whether good foaming was achieved. It can be seen that poor foaming is often associated with low CO in the exhaust gas (<approximately 100 Nm³ / h) and high FeO in the slag (>approximately 37%). Note Figure 2 The CO levels indicated in the report are not corrected for carbon production rates.

[0095] The phosphorus content of the steel was found to decrease with increasing FeO content in the slag and with bath temperatures below 1650°C. The nitrogen content was generally acceptable. The sulfur content was generally acceptable, with variations primarily depending on whether biochar or anthracite was used.

[0096] Based on the data from these and previous smelting accumulations, the optimal method window, as defined in this paper, can be obtained.

Claims

1. A method for producing molten iron or its alloys from low-carbon direct reduced iron (DRI) in an electric arc furnace (EAF), wherein... The DRI contains less than 0.1% by weight of carbon; and The method includes a combined charging and melting stage, which includes continuously charging the DRI into the molten metal bath in the EAF while simultaneously running the EAF to continuously melt the DRI. During the charging and smelting stages DRI, electricity, carbon, oxygen, and optionally one or more slagging agents are provided as inputs to the EAF; Determine the bath temperature, slag composition, and exhaust gas composition; as well as Adjust the DRI feed rate, applied power, carbon feed rate, oxygen feed rate, and slagging agent feed rate to keep the method within the following operating window: - The bath temperature is approximately 1580°C to approximately 1750°C; - The FeO content in the slag is approximately 25% to approximately 40% by weight; - The B2 basicity of the slag is from about 1.5 to about 3.5, wherein the B2 basicity is calculated as (wt% CaO) / (wt% SiO2). - The MgO content in the slag is approximately 8% to approximately 13% by weight; and - Carbon monoxide (CO) in exhaust gas > 26 Nm 3 / hour / m 2 .

2. The method according to any one of the preceding claims, wherein during the charging and smelting stages, the carbon content of the molten metal bath is maintained at less than 0.7% by weight.

3. The method according to any one of the preceding claims, wherein the power applied during the charging and melting stages is greater than 90% of the maximum rated power, and wherein the DRI feed rate is reduced if the determined bath temperature drops below 1580°C.

4. The method according to any one of the preceding claims, wherein the average metallization rate of the DRI is greater than or equal to 95%.

5. The method according to any one of the preceding claims, wherein the DRI is a DRI pellet or HBI.

6. The method according to any one of the preceding claims, wherein the carbon provided to the method is biochar.

7. The method according to any one of the preceding claims, wherein the carbon is provided by loading the carbon into the EAF at a height above the molten metal bath.

8. The method according to any one of the preceding claims, wherein the carbon is provided by injecting powdered carbon into the molten metal bath.

9. The method according to any one of the preceding claims, wherein during the charging and smelting stages, the carbon monoxide in the exhaust gas is maintained at greater than 35 Nm. 3 / hour / m 2 For example, greater than 43 Nm 3 / hour / m 2 .

10. The method according to any one of the preceding claims, wherein during the charging and smelting stages, the carbon monoxide in the exhaust gas is maintained at less than 120 Nm. 3 / hour / m 2 For example, less than 90 Nm 3 / hour / m 2 .

11. The method according to any one of the preceding claims, wherein during the charging and smelting stages, one or more slagging agents are provided to the EAF.

12. The method according to claim 11, wherein the one or more slag-forming agents are selected from CaO, SiO2, calcined dolomite, and combinations thereof.

13. The method according to any one of the preceding claims, wherein the molten metal bath is maintained at a temperature below 1650°C during the charging and melting stages.

14. The method according to any one of the preceding claims, wherein the method does not include a refining stage.

15. The method according to any one of the preceding claims, wherein the tapping stage begins precisely after the charging and smelting stages are completed, wherein the tapping stage comprises: Stop feeding all materials into the EAF; If the bath temperature is below 1600°C, the bath temperature is raised to above or equal to 1600°C by applying electricity; When the bath temperature is higher than or equal to 1600°C, the power supply is stopped; and The molten iron or its alloy is released.

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