A process for producing molten iron or an alloy thereof from low-carbon direct reduced iron in an electric arc furnace

Abstract

The disclosure relates to a process 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 wt% carbon. The process comprises a combined charging and melting stage comprising continuously charging DRI to a molten metal bath in the EAF and concurrently operating the EAF to continuously melt the DRI. During this stage, the process is maintained within the following operational window - bath temperature of from about 1580 °C to about 1750 °C; - FeO in slag of from about 25 wt% to about 40 wt%; - slag B2 basicity of from about 1.5 to about 3.5, wherein the B2 basicity is calculated as (wt% CaO) / (wt% SiO2); - MgO in slag of from about 8 wt% to about 13 wt%; and - carbon monoxide (CO) in offgas > 26 Nm3 / h / m2.

Description

[0001] A process for producing molten iron or an alloy thereof from low-carbon direct reduced iron in an electric arc furnace

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to a process for producing molten iron or an alloy thereof from low-carbon direct reduced iron in an electric arc furnace. More specifically, the disclosure relates to a process for producing molten iron or an alloy thereof from low-carbon direct reduced iron in an electric arc furnace as defined in the introductory parts of the independent claims.

[0004] BACKGROUND ART

[0005] Steel is the world's most important engineering and construction material. It is difficult to find any object in the modern world that does not contain steel, or depend on steel for its manufacture and / or transport. In this manner, steel is intricately involved in almost every aspect of our modern lives. The total global production of crude steel is approximately 1 900 million tonnes annually, by far exceeding any other metal, and is expected to reach 2 800 million tonnes in 2050 of which 50% is expected to originate from virgin iron sources.

[0006] Although steelmaking processes have been refined over decades and are approaching the theoretical minimum energy consumption, there is one fundamental issue not yet resolved. Reduction of iron ore using carbonaceous reductants results in the production of CO2 as a byproduct. For every ton steel produced in 2018, an average of 1.83 tonnes of CO2 were produced. The steel industry is one of the highest CO2-emitting industries, accounting for approximately 7% of CO2 emissions globally. Excessive CO2-generation cannot be avoided within the steel production process as long as carbonaceous reductants are used.

[0007] The HYBRIT initiative has been founded to address this issue. HYBRIT, short for HYdrogen BReakthrough Ironmaking Technology - is a joint venture between SSAB, LKAB and Vattenfall, funded in part by the Swedish Energy Agency, and aims to reduce CO2 emissions and decarbonize the steel industry. Central to the HYBRIT concept is a shaft-based direct reduction to produce sponge iron from virgin ore. In direct reduction, the ore is reduced in a solid-state reduction process at temperatures below the melting point of iron. Shaft-based direct reduction processes utilize pelletized iron ore as the feedstock and produce a porous crude iron product known as sponge iron or direct reduced iron (DRI). Instead of using carbonaceous reductant gases, such as natural gas, as in present commercial direct reduction processes, HYBRIT proposes using hydrogen gas as the reductant, termed hydrogen direct reduction (H- DR). The hydrogen gas may be produced by electrolysis of water using mainly fossil-free and / or renewable primary energy sources. Thus, the critical step of reducing the iron ore may be achieved without requiring fossil fuel as an input, and with water as a by-product instead of CO2.

[0008] Sponge iron produced by direct reduction is typically subsequently processed in an electric arc furnace in order to melt and refine the crude iron prior to any further secondary metallurgical processing. However, DRI produced by hydrogen direct reduction (H2-DRI) has different properties as compared to traditional DRI, primarily due to its lack of incorporated carbon. This means that the established means of processing traditional DRI are not necessarily applicable to the processing of H2-DRL Thus, there remains a need to develop steelmaking processes downstream of the direct reduction stage that are suitable for processing essentially carbon-free DRI, such as that obtained by hydrogen direct reduction.

[0009] SUMMARY OF THE INVENTION

[0010] The HYBRIT initiative has been operating a pilot direct reduction shaft since 2020 where it is possible to produce DRI using hydrogen-based methods in a semi-industrial and commercially relevant scale. Based upon experience of subsequently processing such H2-DRI in an electric arc furnace, the inventors of the present invention have identified the following considerations in relation to conventional means of processing DRI.

[0011] Sponge iron produced using traditional fossil-based carbonaceous reductants typically comprises significant amounts of dispersed carbon (typically up to 5 wt%), due to carbon incorporation from the carbonaceous reducing gas during reduction of the iron ore. The dispersed carbon is predominantly in the form of cementite (FesC), with a lesser proportion consisting of graphite dispersed throughout the sponge iron. The eutectic (melting) temperature of the iron-cementite system is 1147 °C (lower than the melting point of pure iron, 1536 °C), and cementite exothermally dissociates in the molten bath. This assists in melting of the sponge iron and leads to the production of a beneficial foaming slag due to "carbon boil" where the carbon from the DRI (and often additional carbon) reacts with oxygen to produce carbon monoxide (CO). The foaming slag serves to insulate the molten metal bath, leading to improved energy efficiency, decreased consumption of the EAF electrodes, and lesser risk of incorporating undesired nitrogen in the melt. However, due to the excessive carbon present, such conventional processes typically require a refining stage in the EAF subsequent to melting and prior to tapping, whereby oxygen is provided to the bath until the carbon is brought to acceptable levels.

[0012] Sponge iron produced by hydrogen direct reduction (H2-DRI) lacks carbon and therefore is more difficult to melt in the EAF. In cases where the localised rate of charging DRI exceeds the melting capacity of the furnace, the accumulation of unmelted mounds ("ferro bergs") of DRI may result, and such ferrobergs may require extended time and electricity consumption in order to be melted and disperse. This decreases the efficiency of the process. Moreover, the lack of carbon also means that no carbon boil, and therefore no foaming slag, will be obtained without the provision of exogenous carbon.

[0013] Besides being used for melting DRI, where available, electric arc furnaces are also used in the processing of scrap metal. Scrap metal may also have a low carbon content, potentially leading to issues regarding melting and carbon boil. However, when melting scrap, the EAF is typically operated with a large excess of carbon in the bath. This ameliorates the problem of lack of carbon boil, but at the cost of needing extensive refining post-melting and pre-tapping in order to drive off the excess carbon. Moreover, scrap metal is typically loaded as a single batch to the furnace prior to closing the EAF roof and initiating melting of the entire batch.

[0014] It would be advantageous to achieve a method overcoming, or at least alleviating, at least some of the above mentioned drawbacks. In particular, it would be desirable to enable an EAF-based method for processing low-carbon DRI that is efficient and alleviates the disadvantages of ferroberg formation and poor slag foaming that are typically associated with processing low carbon DRI. In order to better address one or more of these concerns, a process having the features defined in the independent claim is provided.

[0015] The process is 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 wt% carbon.

[0016] The process comprises a combined charging and melting stage comprising continuously charging DRI to a molten metal bath in the EAF and concurrently operating the EAF to continuously melt the DRI. During the charging and melting stage, DRI, electric power, carbon, oxygen and optionally one or more slag formers are provided as inputs to the EAF; and bath temperature, slag composition and offgas composition are determined. During the charging and melting stage a DRI feed rate, an applied power, a carbon feed rate, an oxygen feed rate and a slag former feed rate are adapted in order to maintain the process within the following operational window: bath temperature of from about 1580 °C to about 1750 °C;

[0017] FeO in slag of from about 25 wt% to about 40 wt%; slag B2 basicity of from about 1.5 to about 3.5, wherein the B2 basicity is calculated as (wt% CaO) / (wt% SiOz);

[0018] MgO in slag of from about 8 wt% to about 13 wt%; and carbon monoxide (CO) in offgas > 26 Nm3 / h / m2.

[0019] By maintaining the process within the specified operational window, efficient melting of low- carbon / carbon-free DRI is obtained. That is to say that maintaining the process within the specified operational window provides a melting process that avoids formation of ferrobergs, provides an adequately foaming slag and avoids unnecessarily large addition of other inputs such as carbon, slag formers and oxygen. This ultimately provides a process that is highly time- , material- and energy-efficient.

[0020] Further objects, advantages and novel features of the present invention will become apparent to one skilled in the art from the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] For a fuller understanding of the present invention and further objects and advantages of it, the detailed description set out below should be read together with the accompanying drawings, in which the same reference notations denote similar items in the various diagrams, and in which:

[0022] Fig. 1 a graph plotting a variety of EAF heats in terms of feedstock (C-free or 1.5% C DRI), FeO in slag (%) and DRI feed rate (ton / h). For each heat it is indicated whether a ferroberg was formed or not.

[0023] Fig. 2 is a graph plotting a variety of EAF heats in terms of feedstock (C-free or 1.5% C DRI), FeO in slag (%) and CO in offgas (Nm3 / h). For each heat it is indicated whether a adequately foaming slag was obtained or not.

[0024] The invention will now be described in more detail with reference to certain exemplifying embodiments and the figures. However, the invention is not limited to the exemplifying embodiments discussed herein and / or shown in the figures, but may be varied within the scope of the appended claims. Furthermore, the figures shall not be considered drawn to scale as some features may be exaggerated in order to more clearly illustrate certain features.

[0025] DETAILED DESCRIPTION

[0026] The present disclosure relates to a process for producing molten iron or an alloy thereof from low-carbon direct reduced iron (DRI) in an electric arc furnace (EAF). By alloy of molten iron it is for example meant molten steel. The process is applicable to any electric arc furnace including AC and DC electric arc furnaces, but may be particularly suited to a three-electrode AC electric arc furnace.

[0027] DRI

[0028] The main feedstock for the process is low-carbon DRI, that is to say DRI that comprises less than 0.1 wt% carbon. The DRI may preferably comprise less than 0.05 wt% carbon, and may even more preferably be essentially carbon-free. Such carbon-free DRI may for example be obtained as a product from hydrogen-based direct reduction of iron ore. The DRI may be in the form of pellets, cold-briquetted iron (CBI) or hot-briquetted iron (HBI). By the International Maritime Solid Bulk Cargo Codes (IMSBC Code), DRI pellets and cold-briquetted DRI are termed Type B DRI, whereas hot briquetted is termed Type A DRI.

[0029] The DRI may preferably have an average metallization of greater than or equal to 95 %. Metallization is defined in a manner conventional within the art as ( Femetaiiic / Fetotai) x 100. Metallization was determined herein using X-ray diffractometry (XRD), but may also be determined using other methods. Such other methods include:

[0030] ISO 2597-1:2006 (Iron ores — Determination of total iron content — Part 1: Titrimetric method after tin (II) chloride reduction) in combination with ISO 5416:2006 (Direct reduced iron — Determination of metallic iron — Bromine-methanol titrimetric method); and

[0031] 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) in combination with 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).

[0032] The process may use further metallic feedstocks in limited amounts. For example, conventional carbon-containing DRI or scrap metal may be used as up to 20 wt% of the total amount of metallic feedstock, with the balance consisting of low-carbon (or essentially carbon-free) DRI. If such further feedstocks are used, these may be continuously fed to the EAF in the same manner as the low-carbon DRI.

[0033] Operational window

[0034] The herein disclosed process utilizes a combined charging and melting stage. This is in contrast to conventional EAF processes that more typically have separate charging and melting stages, wherein crude metal is first charged in a batch to the EAF, prior to closing the roof of the EAF and initiating melting by application of power. A combined charging and melting stage entails that DRI is continuously charged to the EAF, and the charging and melting of the DRI are performed concurrently. Initially, after turnaround of the furnace, the EAF may typically contain a "hot-heel" from the previous melt, and this hot heel may assist in melting the initially charged DRI. Upon initiation of the charging and melting stage, DRI, electric power, carbon, oxygen and optionally one or more slag formers are provided as inputs to the EAF. The aim is to maintain the process within the following operational window: bath temperature of from about 1580 °C to about 1750 °C;

[0035] FeO in slag of from about 25 wt% to about 40 wt%; slag B2 basicity of from about 1.5 to about 3.5, wherein the B2 basicity is calculated as (wt% CaO) / (wt% SiO2);

[0036] MgO in slag of from about 8 wt% to about 13 wt%; and carbon monoxide (CO) in offgas > 26 Nm3 / h / m2.

[0037] This is done by determining bath temperature, slag composition and offgas composition at regular intervals; and adapting the various inputs, including DRI feed rate, applied power, carbon feed rate, oxygen feed rate and slag former feed rate in order to maintain the process within the operational window.

[0038] It has been found that by maintaining the process within the specified operational window, efficient melting of low-carbon / carbon-free DRI is obtained. Formation of ferrobergs are avoided, which otherwise may present a significant challenge when melting carbon-free DRI. The process avoids unnecessarily large addition of material inputs such as carbon, oxygen and slag formers, whilst controlling impurities such as nitrogen, phosphorus and sulfur to acceptable levels. An adequately foaming slag is obtained, which provides improved energy efficiency and avoids wear of refractory and electrodes. Ultimately, the provided process is highly time-, material- and energy-efficient.

[0039] Bath temperature, slag composition and offgas composition may be readily measured or otherwise determined using means and methods conventional in the art.

[0040] A limit of about > 26 Nm3 / h / m2carbon monoxide in the EAF offgas is found to provide adequate foaming of the slag provided that other parameters are maintained within the specified window. The unit of reference is normal cubic meters 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 the surface area of the bath is therefore more-or-less constant during the heat. The bath surface area can easily be calculated from the diameter or other relevant dimensions of the EAF.

[0041] The carbon monoxide (CO) limit of > 26 Nm3 / h / m2in the offgas is based on a theoretical 100% carbon yield, i.e. that all carbon charged to the process is dissolved in the bath and contributes to either increasing the carbon content of the bath or forming CO by reduction of FeO. In practice, a proportion of carbon charged to the EAF will combust without dissolving in the bath and will not contribute to e.g. slag foaming. A typical carbon yield for an effective industrial EAF process is about 75%, and therefore the CO in offgas may be maintained at > 35 Nm3 / h / m2(26 / 0.75) in order to account for the "non-utilized" carbon. In case of a process having a somewhat poorer carbon yield, such as about 60%, the CO in offgas may be maintained at > 43 Nm3 / h / m2(26 / 0.6) in order to account for the "non-utilised" carbon.

[0042] The CO in the offgas may be maintained at less than 150 Nm3 / h / m2, such as less than 120 Nm3 / h / m2, such as less than 90 Nm3 / h / m2, such as less than 60 Nm3 / h / m2. This may assist in avoiding waste of material inputs, and may prevent excessive foaming of the slag.

[0043] The carbon content of the molten metal bath may be maintained at less than less than 0.7 wt%, such as less than 0.5 wt%, such as less than 0.3 wt%, such as less than or equal to 0.2 wt%. As well as providing material savings, maintaining low carbon in the bath means that there is a diminished or no need for a separate refining stage in order to remove excess carbon. Consequently, shorter tap-to-tap times and further increased productivity may be obtained. The carbon content of the molten metal be determined by direct measurement or determination of bath composition, or may be determined by a differential determination with reference to carbon charged and CO in the offgas.

[0044] The bath temperature may be maintained at a temperature less than 1700 °C, such as at a temperature less than 1650 °C. Lower bath temperatures may provide increased energy efficiency and result in lower levels of phosphorus impurities in the molten iron.

[0045] The FeO in the slag may be maintained at from about 30 wt% to about 40 wt%. Within this window there may be a lower tendency to form ferrobergs and the resulting steel may have lower phosphorus impurities. The slag B2 basicity may be maintained at from about 1.5 to about 2.5. Within this window, the resulting steel may have lower phosphorus impurities and a good foaming slag is obtained.

[0046] The MgO in the slag may be maintained at from about 8 wt% to about 13 wt%. Operating within such a range helps limit refractory wear whilst still providing an adequate slag viscosity, and thereby adequate slag foaming.

[0047] The charging and melting stage may be complete once the desired level of the molten bath has been reached in the EAF.

[0048] Inputs to EAF

[0049] The various inputs (energy input in the form of electric power, and material inputs in the form of DRI, carbon, oxygen and optionally slag formers) may interact with each other and may affect more than one of the parameters in the operational window. For example, starting from 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 offgas and decrease FeO in the slag. Decreasing the carbon feed rate may tend to decrease CO in the offgas and increase FeO in the slag. Increasing the oxygen feed rate may tend to increase FeO in the slag and increase CO in the offgas. Decreasing the oxygen feed rate may tend to decrease FeO in the slag and decrease CO in the offgas. Varying the feed rate of slag formers may increase or decrease the slag B2 basicity, and may increase or decrease the MgO in slag, depending on whether the slag formers comprise CaO, SiO? and / or MgO (or analogues thereof).

[0050] Each of the inputs may initially be provided at nominal levels and thereafter adjusted based on determination of the various operational parameters. Theoretical nominal feed rates for the various inputs may be calculated as follows.

[0051] Preferably, in order to provide for a rapid process, the nominal applied power Pnomshould be at or close to the maximum appropriate for the system, such as greater than 90% of the maximum rated power, or greater than 95% of the maximum rated power. The DRI feed rate should be adjusted thereafter. A suitable nominal DRI feed rate mDRI-n°m may be determined empirically, or may be calculated using the following equation: wherein ^DR nom js t^e nomjna| DRI feec|rate in units of mass per unit time (e.g. ton / h),

[0052] Pnomis the nominal applied power in units of energy per unit time (e.g. kW / h),

[0053] Plossis the estimated system power losses in units of energy per unit time (e.g. kW / h, may e.g. be empirically determined for any given system and nominal power),

[0054] EDRi-spec jsthe specific energy required to melt one unit mass of DRI (e.g. the specific heat required to bring the DRI from ambient to melting temperature, plus the specific heat of melting), expressed in units of energy per unit mass (e.g. kWh / ton).

[0055] A suitable nominal carbon feed rate may be a carbon feed rate sufficient to provide CO in offgas of > 35 Nm3 / h / m2for an industrial EAF process with good carbon yield. This correlates to approximately 44 kg / h / m2CO, which correlates to approximately 19 kg / h / m2carbon. For an industrial process having a lower carbon yield, such as about 60%, meaning a required CO in offgas of > 43 Nm3 / h / m2, this correlates to approximately 54 kg / h / m2CO, which correlates to approximately 23 kg / h / m2carbon.

[0056] A suitable nominal oxygen feed rate may be an oxygen feed rate sufficient to provide CO in offgas of > 35 Nm3 / h / m2for a typical industrial EAF. This correlates to approximately 18 Nm3 / h / m2.

[0057] Suitable nominal slag former feed rates will depend on the intrinsic composition of slag formers in the DRI, as well as the nominal feed rate of the DRI.

[0058] The actual nominal feed rates used may be within a suitable range of these calculated theoretical nominal rates, for example within + / - 20 % of the theoretical nominal rate, such as within + / - 10% of the theoretical nominal rate, such as within + / - 5 % of the theoretical nominal rate. The DRI may be continuously charged to the furnace using means known in the art. For example, the DRI may be continuously charged to the furnace through the EAF roof (e.g. fifth hole) or by side charging.

[0059] Carbon may be charged to the furnace by top feeding (e.g. through roof of EAF) or by injection into the melt, as known in the art. The carbon may be conventional metallurgical quality carbon (e.g. anthracite) or may be biocarbon. Using biocarbon may provide a steel having lower sulfur levels.

[0060] Oxygen may be supplied to the furnace using means known in the art, such as using oxygen lances.

[0061] Slag formers may be charged to the furnace by top feeding or injection, as known in the art. Suitable slag formers may include, but are not limited to, CaO, SiOz, calcined dolomite, and combinations thereof. Alternatively, the autogenous slag formed by melting the DRI may have sufficient properties such that no additional slag formers are required.

[0062] Tapping stage

[0063] Once the charging and melting stage is complete, a tapping stage may be initiated directly. This is in contrast to typical EAF processes that may typically require one or more refining stages in order to burn out oxidisable impurities and remove excess carbon. In the tapping stage, all material inputs are stopped. Tapping may be conditional on the bath having obtained a suitable tapping temperature, such as greater than or equal to 1600 °C, such as greater than or equal to 1630 °C, such as greater than or equal to 1650 °C. If the bath has not reached the tapping temperature, application of electric power may continue until the appropriate temperature has been reached. Thereafter, the power is stopped and the EAF is tapped of the molten iron or alloy thereof.

[0064] Experimental

[0065] The outlines of an optimal process window had already been established from previous pilot campaigns using a variety of H2-DRI and NG-DRI materials. The previous pilot campaigns consist of a total of approximately 200 heats to investigate the melting of: hydrogen-reduced DRI pellets (type B) both with and without carbon, hydrogen-reduced HBI (type A) both with and without carbon, DRI pellets produced using conventional natural gas-based reducing gas, and HBI produced using conventional natural gas-based reducing gas. This optimal window had been established to provide good foaming, good productivity (i.e. no ferrobergs), and a stable process (i.e. steady temperature and slag characteristics).

[0066] In the most recent campaign, a total of 44 further heats were performed. The feedstock for each heat was either carbon-free H2-DRI, or, for comparative purposes, H2-DRI that was subsequently carburized using a natural gas-based carburizing gas to a carbon content of approximately 1.5%. All DRI feedstock used was provided by the Hybrit pilot DRI plant. The metallization degree per batch of ingoing DRI for each heat was typically between 90% - 100%. The pilot scale 3-electrode AC electric arc furnace used has a circular diameter of approximately 2.1 m, providing a bath surface area during operation of approximately 3,46 m2.

[0067] Starting from this outlined process window, the heats were performed, and the following data was collected / measured and evaluated:

[0068] Analysis & amounts of ingoing materials

[0069] Steel and slag samples

[0070] Temperature

[0071] Tons tapped steel & slag

[0072] Offgas analysis & temperature

[0073] Dust in offgas; amount and analysis

[0074] Slag foaming (Graded as 1-poor, 2-OK, or 3-good)

[0075] Ferroberg notations (Yes / No)

[0076] CO-generation from offgas analysis

[0077] Carbon yield from offgas, steel & slag, material additions logging

[0078] Oxygen yield from offgas, steel & slag, material additions logging

[0079] Energy balance from steel & slag, temperature measurements, material amounts Electrical data

[0080] Some of the results obtained are summarized below.

[0081] It was found that despite significant variation in the metallization degree of the ingoing DRI, it was possible to maintain reasonable FeO levels in the slag by carbon balancing during the heats. The majority of heats were maintained at slag FeO levels of from about 25 wt% to about 40 wt%.

[0082] Some heats were performed using biocarbon and some performed using anthracite. The carbon was either top-fed or injected, and the carbon used was suitably adapted with regard to e.g. particle size for the specific charge method. In general, biocarbon and anthracite demonstrated similar carbon yields, and the yields obtained by top-feeding and injection were also similar. It was found that heats where biocarbon was used typically had lower final sulfur content in the steel, although sulfur levels were generally acceptable for all heats.

[0083] The effect of the various process parameters on key outcomes such as ferroberg formation, slag foaming and steel impurity content (nitrogen, phosphorus, sulfur) was investigated.

[0084] Some examples of the results obtained are shown in Figures 1-2.

[0085] Figure 1 is a graph plotting the various heats in terms of feedstock (C-free or 1.5% C DRI), FeO in slag (%) and DRI feed rate (ton / h). For each heat it is indicated whether a ferroberg was formed or not. It can be seen that ferrobergs were formed only when using the C-free DRI feedstock, there were no instances of ferroberg formation when melting carbon-containing DRI. Looking to the heats using carbon-free DRI, it can be seen that FeO in slag is a critical parameter. No ferroberg formation was observed in heats having from about 30% to about 40% FeO in slag, whereas for lower and higher slag FeO proportions ferroberg formation was observed in some heats. For this Figure it can also be seen that within the identified %FeO in slag window, ferroberg formation is relatively insensitive to DRI feed rate, and heats have been performed having relatively high feedrates without ferroberg formation being observed.

[0086] Figure 2 is a graph plotting the various heats in terms of feedstock (C-free or 1.5% C DRI), FeO in slag (%) and CO in offgas (Nm3 / h). For each heat it is indicated whether a good foaming was obtained or not. It can be seen that poor foaming tends to be correlated with low CO in offgas (< approx. 100 Nm3 / h) and high FeO in slag (> approx. 37 %). Note that the CO levels indicated in Figure 2 are not corrected for carbon yield.

[0087] The phosphorous content of the steel was found to decrease with an increasing FeO-content of the slag and with temperature below 1650 °C in the bath. Nitrogen content was in general found to be acceptable. Sulfur content was in general acceptable and varied depending primarily on whether biocarbon or anthracite was used.

[0088] Based on the accumulated data from these and previous heats, the optimal process window as defined herein can be derived.

Claims

CLAIMS1. A process for producing molten iron or an alloy thereof from low-carbon direct reduced iron (DRI) in an electric arc furnace (EAF), wherein the DRI comprises less than 0.1 wt% carbon; and wherein the process comprises a combined charging and melting stage comprising continuously charging DRI to a molten metal bath in the EAF and concurrently operating the EAF to continuously melt the DRI; wherein during the charging and melting stageDRI, electric power, carbon, oxygen and optionally one or more slag formers are provided as inputs to the EAF; bath temperature, slag composition and offgas composition are determined; and a DRI feed rate, an applied power, a carbon feed rate, an oxygen feed rate and a slag former feed rate are adapted in order to maintain the process within the following operational window bath temperature of from about 1580 °C to about 1750 °C;FeO in slag of from about 25 wt% to about 40 wt%; slag B2 basicity of from about 1.5 to about 3.5, wherein the B2 basicity is calculated as (wt% CaO) / (wt% SiO2);MgO in slag of from about 8 wt% to about 13 wt%; and carbon monoxide (CO) in offgas > 26 Nm3 / h / m2.

2. The process according to any one of the preceding claims, wherein the carbon content of the molten metal bath is maintained at less than 0.7 wt% during the charging and melting stage.

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

4. The process according to any one of the preceding claims, wherein the DRI has an average metallization of greater than or equal to 95%.

5. The process according to any one of the preceding claims, wherein the DRI is DRI pellets or HBI.

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

7. The process according to any one of the preceding claims, wherein the carbon is provided by charging the carbon to the EAF above a level of the molten metal bath.

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

9. The process according to any one of the preceding claims, wherein during the charging and melting stage carbon monoxide in the offgas is maintained at greater than 35 Nm3 / h / m2, such as greater than 43 Nm3 / h / m2.

10. The process according to any one of the preceding claims, wherein during the charging and melting stage carbon monoxide in the offgas is maintained at less than 120 Nm3 / h / m2, such as less than 90 Nm3 / h / m2.

11. The process according to any one of the preceding claims, wherein one or more slag formers are provided to the EAF during the charging and melting stage.

12. The process according to claim 11, wherein the one or more slag formers are selected from CaO, SiOz, calcined dolomite, and combinations thereof.

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

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

15. The process according to any one of the preceding claims, wherein directly after completion of the charging and melting stage, a tapping stage is initiated, wherein the tapping stage comprisesstopping all material inputs to the EAF; if the bath temperature is less than 1600 °C then increasing the bath temperature to greater than or equal to 1600 °C by applying power; when the bath temperature is greater than or equal to 1600 °C, then stopping the application of power; and tapping the molten iron or alloy thereof.

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