Method for producing molten iron in an electric smelting furnace

Abstract

This invention relates to a method for producing molten iron in an electric smelting furnace of the submerged arc furnace (SAF) type, the submerged arc refining furnace (SARF) type or of the Open Slag Bath Furnace (OSBF) type, the method comprising providing a metalliferous charge comprising a final granulate of iron-containing reverts and / or iron-containing by-products from the iron- and steelmaking process and one or more of a pre-reduced charge (DRI HBI CBI) and scrap.

Description

[0001] METHOD FOR PRODUCING MOLTEN IRON IN AN ELECTRIC SMELTING FURNACE

[0002] Field of the invention

[0003] This invention relates to a method for producing molten iron in an electric smelting furnace of the submerged arc furnace (SAF) type, the submerged arc refining furnace (SARF) type or of the Open Slag Bath Furnace (OSBF) type.

[0004] Background of the invention

[0005] In the energy transition large efforts are being made to move away from traditional carbon-based steelmaking practices such as the conventional blast furnace route as these are significant contributors to carbon dioxide emissions in the atmosphere.

[0006] Several alternative carbon-based iron-making processes have been proposed that generate less carbon dioxide per ton of iron. Particular attention is directed towards production of iron by using (green) H2 as a reductor rather than carbon to produce direct reduced iron (DRI).

[0007] DRI is produced from the direct reduction of iron ore conglomerates (mainly hematite, Fe2O3) in the form of lumps, pellets, or briquettes into solid iron by a reducing gas. Due to its structure with a relatively high specific surface area, direct- reduced iron is also referred to as sponge iron. Direct reduction refers to a solid-state process which reduce iron oxides to metallic iron at temperatures below the melting point of iron. There are several processes for producing DRI known to the person skilled in the art. Known examples of direct-reduction processes (DRP) include the Midrex process, Tenova's HYL process, Tenova's HYL I and the HYL II and the HYL III process, Energiron, Posco's HyREX process, and SSAB's Hybrit process.

[0008] A known process relates to a direct reduction plant (DRP) or DRI reactor comprising a direct reduction shaft furnace having a reduction zone and a lower cooling zone and discharge zone from which direct reduced iron in solid form is discharged at a regulated rate by means of a suitable discharge mechanism. Iron oxide agglomerates in the form of pellets, lumps, briquettes or mixtures of these are fed to the reduction furnace and descend by gravity through the reduction zone were DRI is formed by reaction of said iron oxides with a counter current reducing gas stream at high temperature that is mainly composed of H2 and contains also CO, carbon dioxide, methane, and nitrogen in those embodiments wherein a hydrocarbon such as natural gas or a syngas derived from coal is used as the source of the reducing gas.

[0009] The reduction of iron oxides is carried out through the following net reactions: The DRI in solid form is further processed directly on exit from the discharge zone, and optionally also after being compacted into briquettes, in a melt shop typically comprising one or more arc furnaces (AF). The AF may be an electric arc furnace (EAF) operating under oxidising conditions. An EAF is charged with DRI and / or scrap and is used to melt the DRI and or scrap in the charge.

[0010] The AF may also be an electric smelting furnace (ESF) which operates under reducing conditions. In the ESF the iron in the charge is melted and iron oxides which are still present in the charge can be further reduced thereby increasing the metallic content of the melt. Submerged arc furnace (SAF) or open slag bath furnace (OSBF) are specific modes of operation an electric smelting furnace (ESF) in relation to slags, position of electrodes and heating. Submerged-arc furnaces (SAF) are sometimes also referred to as reducing electrical furnaces (REF).

[0011] In the majority of these known direct-reduction processes, natural gas is reformed on a catalyst bed with heat by burning gaseous reduction products evacuated from the iron-reduction reactor to produce a reducing gas which is supplied to the iron production reactor where it reacts with the iron oxides in the iron ore to generate reduced metallic iron. Partial oxidation processes which gasify liquid hydrocarbons, heavy residuals or coal have also been proposed to produce the reducing gas. Another option is to reform natural gas on the iron bed itself, by adding under-stoichiometric oxygen. In both cases, a reducing gas containing CO and H2 is obtained. Direct-reduction processes have thus far been of particular interest in regions which have access to inexpensive natural gas, non-coking coals and / or renewable energy sources, such as hydroelectric power. It is expected that non-coal based direct-reduction processes will gain in importance as the drive to reduce CO2 emissions in the global iron- and steel-industry gains further momentum.

[0012] Conventional integrated steel plants based on the blast-furnace - BOS-route (BF- BOS route) utilize materials such as iron ore, coal, air, water, fuel, and power to produce steel. During the production of steel typically about 60 to 70 kg of waste is generated per tonne of steel produced.

[0013] Basic Oxygen Steelmaking sludge (or BOS-sludge) is a by-product of the steelmaking process and contains iron in the form of hematite (Fe2Os), magnetite (FesO4), wiistite (FeO) or metallic iron (Fe). Typically, this sludge contains moisture, varying from about 20% (w / w) to about 40% (w / w).

[0014] In current practice this BOS-sludge is either recycled via the sinter plant or exported and discarded as waste material. Zinc also tends to accumulate in the sludge, and this is potentially harmful for the lining of the blast furnace if the sludge is recycled via the sinter into the blast furnace. Beside BOS-sludge there are other solid wastes and potentially valuable byproducts in the form of slags, dusts, and sludges such as blast furnace slag, blast furnace flue dust and sludge, BOS-converter slag, BOS dust, mill scale, mill sludge, etc. Of these, blast furnace slag is a well known and valuable byproduct for the cement industry. According to "B. Das et al. in "An overview of utilization of slag and sludge from steel industries" as published in Resources, Conservation and Recycling 50 (2007), pp. 40-57" per tonne of liquid metal produced via the BF-BOS route about 28 kg of BF- dust and sludge is produced, 15 kg of BOS sludge, 22 kg of mill scale and 12 kg of mill sludge. These byproducts comprise significant amounts of ferrous oxide.

[0015] With the increasing interest in and use of direct reduction processes the amount of iron containing dusts and sludges from the direct reduction process is expected to increase.

[0016] In the current route for steelmaking fine iron ore is processed in a sinter plant. The sinter plant turns fine iron ore into sinter, which are coagulated lumps of iron ore suitable for use in the blast furnace. Sinter is made by burning a mix of iron ore, carbon powder, fluxes, and recycled substances from the steel plant to create an open-grained, consistent substance. A sinter plant can absorb most of the iron-containing reverts and / or iron-containing by-products from the iron- and steelmaking process. Internal recycling of reverts is on a high level and only limited amounts of waste are landfilled. A problem with a direct-reduction process is that it mainly uses iron ore conglomerates in the form of small lumps, pellets, or fines. The use of sintered iron ore is problematic in a direct reduction shaft furnace based DRP because the sinter is not ideally suited for direct reduction shaft furnaces due to the generation of fines and its limited porosity. Contrary to pellets, which are generally smooth and round and approximately equally sized, the final sinter after the sinter-breaking is lumpy, ragged and varies in size. This may also lead o bridge forming or sticking of the burden in the shaft furnace of the most common direct reduction processes.

[0017] In an iron- and steelmaking process solely based on the direct reduction process without any blast furnaces there is no need for a sinter plant. In such a case an alternative solution must be sought because otherwise this leaves export of the waste or storing as waste material as sub-standard options in the context of circular and green economic thinking.

[0018] Objects of the invention

[0019] The object of the invention is to provide an alternative method that can recycle waste material and byproducts from the steelmaking process and use it in the direct reduction-based steelmaking route.

[0020] Further it is an object of this invention to make the waste material and byproducts easily transportable, to store it for later use. It is also an object to provide a method of drying the waste material and byproducts without excessive reoxidation of FeO.

[0021] It is another object to be able to store the waste material and byproducts in silos for later use.

[0022] Yet another object is to reduce the amount of dust in the process (dust carry-over) to prevent the emission of dust from the steel production site.

[0023] Description of the invention

[0024] One or more of the objects of the invention are met with a method for producing molten iron in an ironmaking process using an electric smelting furnace (ESF) of the submerged arc furnace (SAF) type, a smelting furnace of the submerged arc refining furnace (SARF) type or a smelting furnace of the Open Slag Bath Furnace (OSBF) type, wherein the method comprises providing a metalliferous charge to the ESF, said metalliferous charge comprises: i. a final granulate comprising iron-containing reverts and / or iron-containing byproducts from the iron- and steelmaking process, wherein the final granulate is provided into the electric smelting furnace by means of dump-charging into the electric smelting furnace, ii. a pre-reduced metalliferous charge, and / or iii. metalliferous scrap, and smelting said metalliferous charge to produce molten iron, wherein the final granulate is produced by a granulation method comprising the consecutive steps of

[0025] • a mixing step for producing a mixture of iron-containing reverts and / or iron- containing by-products from the iron- and steelmaking process;

[0026] • drying the mixture using drying means or adding water to the mixture to adjust the moisture level of the mixture to 15 to 30% (w / w) moisture to produce a mixture of moist reverts and by-products;

[0027] • mixing the moist reverts and by-products with a binder to obtain a green granulate wherein the granules have a size of 5.0 mm or less;

[0028] • optionally storing the green granulate for later use;

[0029] • further drying the green granulate to a maximum of 3.0% (w / w) moisture, thereby forming the final granulate to be added to the metalliferous charge.

[0030] Preferable embodiments are disclosed in the dependent claims and the description.

[0031] In the invention the final granulate comprising iron-containing reverts and / or iron- containing by-products from the iron- and steelmaking process is provided to the electric smelting furnace by means of dump charging.

[0032] The specific advantage of the method is that dump-charging the granulate with a granule size of at most 5.0 mm is an effective way of recycling reverts and by-products in an ESF. The gas streams in an ESF are considerably less strong compared to the gas stream in a Hisarna® or HIsmelt. This means that there is no need for pneumatic injection of the granulate, but that the granulate can be dump-charged in the ESF. When dump-charging the granulate in the Hisarna or HIsmelt or any similar methods operating at similar gas flows and speeds the granulate will be blown out and not become part of the metalliferous charge. In the ESF the granulate will not be blown out but be incorporated in the metalliferous charge and be reduced to iron.

[0033] In the context of this invention the mixture comprises iron-containing reverts and / or iron-containing by-products from the iron- and steelmaking process comprises metalliferous reverts and / or by-products of the steelmaking process such as BF-dust, DRP dust, BF Sludge, BOS sludge, mill scale and mill sludge which contain significant amounts of iron. The iron in this mixture may be present in the form of hematite (Fe2Os), magnetite (FesO4), wiistite (FeO) or metallic iron (Fe). Both BOS sludge and DRP dust are particularly rich in FeO. Mill scale may need to be ground to smaller particles or dust if the morphology of the mill scale is unsuitable for it to be incorporated in the mixture.

[0034] Pre-reduced charge may be Direct Reduced Iron (DRI) which is the product of the direct reduction of iron ore in the solid state by carbon monoxide and / or hydrogen, Cold- Briquetted Iron (CBI) which is as DRI which has been compacted at a temperature less than 650°C or with a density of less than 5000 kg / m3or Hot Briquetted Iron (HBI) which is a form of DRI that has been compacted at a temperature greater than 650°C and has a density greater than 5000 kg / m3.

[0035] Iron-containing granulated reverts and / or iron-containing granulated by-products from the iron- and steelmaking process are jointly referred to as the granulate in the context of this invention. A granulate consists of a collection of granules of a certain size. In the context of this invention the green granulate consists of granules of cold- bonded agglomerated fine particles of reverts or by-products having a maximum size of at most 5.0 mm. It should be noted that the particle size referred to in this description and claims means the maximum particle size diameter of the granulate. Optionally fine ores may be mixed into the granulate. Green granulate refers to the granulate after mixing, adjusting the moisture level to 15 to 30% (w / w) moisture, and binding the granulate with a binder. Final granulate refers to the granulate after the drying step to a moisture level of at most 3.0% (w / w) moisture.

[0036] In the first step a mixture of iron-containing reverts and / or iron-containing byproducts from the iron- and steelmaking process is produced and the moisture level if the mixture is adjusted to an amount of 15 to 30% (w / w) moisture. It is important that the moisture content of the mixture is between 15 to 30% (w / w). If this process is not controlled well and the mixture has too low a moisture content, it may cause the iron particles in the mixture re-oxidise which is unwanted because it would involve having to re-reduce the oxide in the ironmaking process. If it is too wet, then the granulation process is ineffective. The moisture content shall therefore be between 15-30% (w / w). As a next step the mixture is mixed with a binder to obtain a green granulate having the desired particle size.

[0037] The obtained green granulate has beneficial properties since they can be stored in silo's and because they are only further dried in a final drying step, re-oxidation is prevented.

[0038] In the drying step the green granulate is then dried to a maximum of 3% (w / w) moisture. Drying improves the handling of the granulate considerably, especially in a pneumatic transport system. The inventors have found that drying also increases the strength of the granulate. Before the final drying step the green granulate has a strength of approximately 7 Nm per granule. After the final drying step the final granulate has a strength of more than 20 Nm per granule. A suitable apparatus to measure the strength of the granules is an Eirich TAXT Texture Analyser. A suitable method to measure the strength of the granules is ISO 4700:2015.

[0039] It is important to note that the method is intended for use with electric smelting furnaces that work under reducing conditions. This is different from conventional electric arc melting furnaces which main aim is to melt a metallic charge i.e. by recycling scrap metal. Such a furnace is not ideally equipped to reduce the ferrous oxides, and certainly not to reduce the ferrous oxides to metallic iron because these conventional electric arc melting furnaces work under a non-reducing or even oxidising atmosphere. These furnaces are referred to as melting furnaces because they "only" melt a metal charge. The fundamental difference between "melting" and "smelting" is that melting is a process in which the state of a substance is changed from solid to liquid by heating it, while smelting is a process of obtaining pure metal from its oxides. The Electric Smelting Furnace therefore not only melts the metal already present, but it also refines any oxides to pure (molten) metal.

[0040] Direct Reduced Iron (DRI) is the product of the direct reduction of iron ore in the solid state by carbon monoxide and / or hydrogen.

[0041] Cold-Briquetted Iron (CBI) is defined as DRI which has been compacted at a temperature less than 650°C or with a density of less than 5000 kg / m3.

[0042] Hot Briquetted Iron (HBI) is DRI that has been compacted at a temperature greater than 650°C and has a density greater than 5000 kg / m3.

[0043] In a submerged arc furnace (SAF) the electrode tips are buried in the slag / charge, and arcing occurs through the slag, between the charge and the electrode. If the atmosphere is a reducing one, then the SAF functions as a smelting furnace and is sometimes referred to as a SARF. In an open slag bath furnace (OSBF) the raw materials (typically consisting of metal oxides, carbon, and fluxes) are heated using brush arcs. The heat generated by the arcs causes the raw materials to react with each other, resulting in the formation of a molten metal alloy and a molten slag. To react with each other the atmosphere in the furnace is a reducing atmosphere. This furnace type is sometimes also referred to as a reducing electric furnace (REF).

[0044] When a REF, SA(R)F or OSBF is operated with the aim to melt DRI according to the invention then the furnace can be loaded with a feed pile comprising DRI pellets and final granulate thus creating a significant burden of "to-be-melted" feedstock above the slag surface. Optionally scrap can be mixed into the feed pile. Suitably sized scrap and / or DRI may be injected into the ESF by injection means.

[0045] A significant advantage of the method according to the invention is that it the DRI- ESF route is well suited to replace emissions-intensive front-end of ironmaking namely the sinter plant (which currently absorbs most of iron-containing reverts and / or iron- containing by-products from the iron- and steelmaking process), the coke batteries and the blast furnace. The method according to the invention can beneficially take over this role of the sinter plant.

[0046] Tests have proven that the metalliferous feed thus formed has very beneficial properties as will be explained underneath and can be added the metalliferous charge for the SAF, SARF or OSBF without any further adjustments.

[0047] As a first step the mixture is de-watered, e.g. by a filter press, to an amount of 15 to 30% (w / w) moisture. It is important that the moisture level mixture is controlled between 15-30% to prevent that the mixture has too low a moisture content, because it may cause the metallic iron particles in the sludge to re-oxidise. This is unwanted because then the oxidized iron needs to be reduced again in the ESF. The moisture level of the moist reverts and by-products is preferably adjusted to 20 to 25% (w / w) moisture. The inventors have noted that 20% moisture (w / w) or less is possible if the sludge is mixed within 0 to 72 hours of pre-drying and preferably within 0 to 24 hours to avoid the re-oxidation process. A mixture that contains 20 to 25% moisture (w / w) is preferable since the inventors found that it optimises the particle size for use in the ironmaking process and that it requires a lower amount of binder. If the mixture has too low a moisture level then water needs to be added to increase the moisture level to within the desired range.

[0048] The dried metalliferous sludge is mixed with a binder to obtain a green granulate having a particle size of less than 5.0 mm, preferably less than 4.0 mm more preferably less than 3.0 mm and even more preferably less than 2.5 mm.

[0049] The binder is preferably an organic binder as this will prevent additional slag formation in the iron making process. The binder is preferably a cold binder, meaning that substantially no heat is needed to effectuate the binding. A suitable binder is a cellulose derivative, such as a carboxymethyl cellulose such as FINNFIX 30000®, a long chain polyelectrolyte based on cellulose, available through Nouryon. Binding is already achieved with the addition of an amount of 0.10% (w / w) of binder. Good results were achieved with the addition of an amount of 0.20 - 0.40% (w / w) binder. Below 0.20% (w / w) the integrity of the material is less, but the granules are suitable for dump charging. Above 0.40% (w / w), the green granulates tend to become too large. They also become too heavy for pneumatic transport. A suitable mixer is an Eirich intensive mixer, with a rotation speed of 1000 to 1500 rotations per minute. A particle size (diameter) of less than 10 mm was found to be a desirable particle size for pneumatic transportation purposes and a particle size of less than 8 mm is preferred by the inventors. Preferably the amount of binder added is in the range of 0.15 to 0.30 % (w / w).

[0050] The inventors found that a duration of the mixing step of less than 60 seconds, preferably less than 45 seconds, is usually sufficient to obtain the desired particle size of the green granulate. Optionally, the final granulate can be screened to ensure a desired particle size diameter range.

[0051] The obtained green granulate has very beneficial properties since they can be stored in silo's and because between forming the green granulate and the final drying step, re-oxidation of any metallic iron particles is at least partly prevented, which means that the caloric value of the partly pre-reduced iron oxide (FeO) is maintained. FeO is quite susceptible to reoxidation. If this happens, for instance in storage, then this can lead to an uncontrolled and undesirable temperature increase. A particular advantage of the granulation is therefore that the reactive surface of the FeO is significantly smaller so that the granules are more stable in storage and less susceptible to reoxidation.

[0052] Before adding the granulate to the metalliferous charge the green granulate is further dried in a final drying step to a maximum of 3% (w / w) moisture, thereby forming the final granulate, which will thereafter be added to the metalliferous charge. Drying improves the handling of the granulate considerably. This final drying step is preferably performed by a belt drier. This has the main advantage that heat from the environment in the plant itself can be used efficiently. Under normal processing conditions this heat is lost. Dust emissions are also drastically reduced, leading to better environmental circumstances for workers and people near the steel site. Another advantage of the use of a belt drier is that the final granulate will be stronger. Therefore, they are easy to transport. When leaving the drier this has increased to more than 20 N per granule. Instead of a belt drier a drum drier could also be used as an alternative. The type of dryer is not particularly relevant. Preferably the moisture content of the final granulate that will be added to the metalliferous charge is at most 2.5 %, preferably at most 2.2 % and more preferably at most 2.0% (w / w).

[0053] Using this granulation method has the benefit that there are no emissions of gas compounds like SOx or NOx since it is not a process that is performed at high temperatures, so these compounds are not formed during the process. Further it is beneficial that the granulate is relatively large and therefore they prevent the formation of dust during handling, and therefore also in the immediate environment of the plant via the outlets.

[0054] Because of the physical properties and the chemical composition that is obtained after the steps described above, the final granulate is ready to be introduced into the furnace. The final granulate was found to quickly melt in the slag. By adapting the composition of the granulate, for instance by allowing a certain amount of calcium, the melting behaviour of the granulate can be optimised. But, if the chemical composition of the iron containing sludge is less than optimal, carbon (coal or charcoal) could be added to improve the melting behaviour. Also fluxing materials (e.g. limestone) could be added for the same purpose. Since the furnaces in the method according to the invention all have reducing atmosphere to enable the reduction of the remaining ferrous oxides to metallic iron and subsequently melt the iron, the addition of carbon to the granulate may also help the reduction process of the iron oxides and increase the carbon content of the molten iron that is tapped from the furnace. The inventors found that the method according to the invention is applicable with any combination of the iron- containing reverts and / or iron-containing by-products as identified herein before.

[0055] Zinc containing dusts or sludges may be added to the iron-containing reverts and / or iron-containing by-products and incorporated into the green granulate. Zinc will evaporate in the electric smelting furnace and end up in the off-gas as zinc or zinc oxide from which it can be separated by the dust filters in the off-gas treatment. The zinc or zinc oxide containing dust can be filtered from the off gas by cyclone filters and / or baghouse filters and subsequently be available for later recycling to zinc metal. The method according to the invention also allows the recycling of zinc-containing ferrous waste or steel scrap as well as the use of zinc-rich ores by adding the zinc-containing ferrous waste or steel scrap to either the granulate (in case of zinc containing dusts or sludges), by adding the zinc-rich ores to the pellets for the direct reduction reactor, or for galvanised steel parts to be added to the scrap part of the metalliferous charge.

[0056] In an embodiment wherein the metalliferous scrap comprises galvanised scrap. The zinc will oxidise and evaporate during the processing in the furnace and become gaseous and escape with the off-gas. The zinc concentrates in the off-gas dust. The zinc oxide containing dust can then be separated from the off gas by off-gas cleaning and subsequently be recycled to produce zinc metal. Alternatively, the zinc containing dust collected from the off-gas is reintroduced into the granulation process if recirculation of the dust is expected to bring about a further enrichment of the off-gas dust with Zn.

[0057] After binding the green granulate can be stored in silos or hoppers for a long period. If the final granulate is stored then precautions need to be made to prevent reoxidation of the fine iron particles in the final granulate. Storing the final granulate under protective atmosphere could be envisaged.

[0058] The granulate can be further improved by adding a carbon source to the mixture from which the granules are prepared. This carbon source can be either a fossil carbon source such as anthracite or coke breeze or the carbon source can originate from a renewable source like charcoal. The incorporated carbon in the granules will react with the metal oxide in the granules in the electric smelting furnace.

[0059] In an embodiment the pre-reduced metalliferous charge is produced by reducing iron ore provided in the form of iron-ore (mainly hematite, Fe2O3) pellets in a direct reduction reactor by a reducing gas thereby producing directly reduced iron (DRI) which directly reduced iron is optionally compacted into cold briquetted iron (CBI) or hot briquetted iron (HBI).

[0060] Direct reduction refers to a solid-state process which reduce iron oxides to metallic iron at temperatures below the melting point of iron. There are several processes for producing DRI known to the person skilled in the art. Known examples of direct- reduction processes include the MIDREX process, Tenova's HYL process, Tenova's HYL- I, the HYL-II, and the HYL-III process, Posco's HyREX process, and the HYBRIT process.

[0061] A known process relates to a direct reduction plant (DRP) or DRI reactor comprising a direct reduction shaft furnace having a reduction zone and a lower discharge zone from which direct reduced iron (DRI) in solid form is discharged at a regulated rate by means of a suitable discharge mechanism.

[0062] Iron oxide conglomerates in the form of agglomerates, pellets, lumps or mixtures thereof are fed to the reduction furnace and descend by gravity through the reduction zone were DRI is formed by reaction of said iron oxides with a reducing gas stream at high temperature that is mainly composed of hydrogen and contains also carbon monoxide, carbon dioxide, methane, and nitrogen in those embodiments wherein a hydrocarbon such as natural gas or a syngas derived from coal is used as the source of the reducing gas.

[0063] The reduction of iron oxides is carried out through the following net reactions:

[0064] The DRI in solid form is further processed directly on exit from the discharge zone, and optionally also after being compacted into HBI or CBI, In a preferable embodiment the directly reduced iron discharged from the direct reduction reactor is provided into the ESF through a hot link. This way the most efficient use is made of the thermal energy stored in the hot DRI discharged from the reduction reactor.

[0065] In an embodiment the electric smelting furnace is fed continuously with one or more of DRI, HBI, CBI, scrap and final granulate to provide constant feed pile conditions. This allows the most constant process conditions and allows a continuous feeding of the furnace, tapping of molten iron from the furnace.

[0066] In an embodiment the liquid iron and / or slag is tapped from the furnace continuously to maintain constant feed pile, slag, and molten iron levels in the furnace. This allows the most constant process conditions and allows a continuous tapping of molten iron from the furnace.

[0067] In an embodiment wherein the final granulate is provided into the electric smelting furnace by a combination of i). dump charging the final granulate into the electric smelting furnace and ii). injection of the final granulate through injection means. This allows the bulk of the granulate to be provided to the furnace by dump-charging and to fine tune the charge in the furnace by continuous or batchwise addition of final granulate through injection means, such as lances, in the side or the top of the furnace.

[0068] According to a second aspect the invention is also embodied in the use of the final granulate comprising iron-containing reverts and / or iron-containing by-products from the iron- and steelmaking process produced according to the invention for producing molten iron by direct reduction in a direct-reduction plant, comprising the following steps: a) reducing iron ore, provided preferably in the form of iron-ore pellets, in a direct reduction reactor thereby producing directly reduced iron (DRI); b) optionally producing cold briquetted iron (CBI) or hot briquetted iron (HBI) from the directly reduced iron; c) temporarily storing the DRI, HBI or CBI, preferably in a silo or in a hopper, or loading the DRI in the ESF directly via a hot-link; d) providing the final granulate; e) loading the electric smelting furnace with a feed pile comprising final granulate, and one or more of a pre-reduced metalliferous charge comprising one or more of DRI, HBI or CBI, and metalliferous scrap, preferably wherein the said furnace is fed continuously with one or more of final granulate, pre-reduced metalliferous charge and metalliferous scrap to provide constant feed pile conditions; f) smelting the feed pile to produce molten iron; g) tapping the molten iron and / or slag from the furnace h) collecting the optional zinc oxide dust from the off-gases. This use of the final granulate allows recuperating the zinc as described above and, because of the reducing capability of the electric smelting furnace such as a SAF, SARF or OSBF also recuperation of iron by reducing the iron oxides in the final granulate. The use according to the invention also allows the recycling of zinc-containing ferrous waste or steel scrap as well as the use of zinc-rich ores by adding the zinc-containing ferrous waste or steel scrap to either the granulate (in case of zinc containing dusts or sludges), by adding the zinc-rich ores to the pellets for the direct reduction reactor, or for galvanised steel parts to be added to the scrap part of the metalliferous charge. The option to include zinc containing scrap is a very valuable option because it is an efficient way to recover the zinc from the scrap without having to remove the zinc from the scrap before loading the scrap into the furnace.

[0069] According to a third aspect the invention is also embodied in a final granulate comprising iron-containing reverts and / or iron-containing by-products from the iron- and steelmaking process produced according to the invention for use in producing molten iron in an electric smelting furnace of the submerged arc furnace (SAF) type, the submerged arc refining furnace (SARF) type or of the Open Slag Bath Furnace (OSBF) type, the final granulate having a size of 5.0 mm or less and a maximum of 3.0% (w / w) moisture. Optionally the final granulate also comprises zinc or zinc containing compounds to enable recovery of the zinc by concentrating the zinc oxide in the off-gas dust that is collected after the use of the final granulate in the electric smelting furnace.

[0070] Brief description of the experiments and drawing

[0071] The invention will now be explained by means of the following, schematic nonlimiting figures of an exemplary embodiment of an apparatus operating according to the method of the invention.

[0072] Iron-containing reverts and / or iron-containing by-products from the iron- and steelmaking process are combined with binder and, if necessary, water in a mixer. After forming and curing the granules the granules are stored. This green granulate still contain 15-30 wt.%. When needed the green granulate is taken from the storage unit, e.g. a hopper, dried to a maximum of 3% (w / w) moisture and are charged into the electric smelting furnace of the submerged arc furnace (SAF) type, a submerged arc refining furnace (SARF) or an Open Slag Bath Furnace (OSBF) and processed.

[0073] Table 1 - Typical analyses of BOS-sludge (wt.%) Experiments were conducted to study the size distribution and compressive strength of the granules. Granules were produced with a 5L Eirich mixer with a two-step mixing procedure. First, BOS-sludge and binder (Peridur® 300D) were loaded together and mixed at 2000 rpm for 45 sec to ensure good homogenisation. Secondly, the materials were mixed at 500 rpm for 45 sec to reach a stable granulation. The amount of moisture in the BOS sludge and binder content was varied. Table 2 shows the particle

[0074] Tab e 2 - Particle size distribution

[0075] Flowability studies with a Hosokawa powder tester on granulate filtered at different particle sizes (3 mm, 1 mm, 0.4 mm) indicated that the maximum particle size should preferably be less than 4 mm, more preferably less than 3 mm to enable efficient pneumatic injection into the arc furnace. Therefore, the granules should preferably have a D90 below 4 mm, more preferably below 3 mm. Granules with a larger particle size can optionally be removed by a screen. The DIO should preferably be above 0.5 mm to avoid dust-carry over. The mechanical resistance of the granules was tested by a drop test to establish the optimal binder content. 500 g of each sample was selected from the matured granules (dried from original moisture in the air) and dropped 2 times from a height of 2 m, the particle size distribution of the granules before and after were similarfor all granules, indicating a good mechanical resistance, even at a binder content of 0.2 %. In general, a lower binder content is desired, as this will reduce the overall costs of the granules.

[0076] In the method according to the invention dump charging is the method of providing the final granulate to the ESF.

[0077] Sample 4 was further subjected to a plate compression test, both for granules having 15 to 30% moisture and for dried granules having at most 3% moisture. The average breaking forces of these granules are 4.65 and 18.05 N, respectively. Hence, the dried granules are much stronger and better suitable for pneumatic transport and storage.

[0078] Although the invention has been discussed in the foregoing with reference to exemplary embodiments of the invention, the invention is not restricted to these embodiments which can be varied without departing from the invention. Comparable results were obtained with different mixtures of iron-containing reverts and / or iron- containing by-products from the iron- and steelmaking process.

[0079] In figure 1 a schematic representation is given of the relevant part of the process. A Direct Reduction Plant (1) for producing directly reduced iron (6) in the form of DRI pellets, HBI or CBI (6) is shown with an arc furnace (ESF) (2) which can reduce any remaining iron oxides in the charge. The DRP is fed with a reducing gas (7), which may be natural gas or hydrogen, and with iron oxide (4) which may be lump ore or pre- processed ore such as pellets or sinter. The directly reduced iron (6) can be stored temporarily or immediately subjected to further processing in the furnace (2) where it is (s)melted optionally along with scrap (5) and the final granulate according to the invention which may be dump charged (9) on the feed pile or injected into the furnace (8). The resulting molten metal is discharged into a ladle (3) and can be sent to the steel plant for further refining and casting.

[0080] In figure 2 a schematic flow chart of the production of the granules is depicted. A mixture of iron-containing reverts and / or iron-containing by-products from the iron- and steelmaking process is combined with a binder (organic or inorganic), water (if needed), and optionally carbon from a fossil or renewable source, lime, fluxes, and optional other additions in a mixer, dried (if needed to achieve the moisture level in the desired range) and processed into "green" granules. After the optional intermediate storage, the green granules are further dried to a moisture level of at most 3.0% (w / w) to produce the final granulate that can be introduced into the Electric Smelting Furnace by dumpcharging the final granulate.

[0081] Reference numbering as used in figure 1.

[0082] 1. Direct reduction plant

[0083] 2. Electric smelting furnace

[0084] 3. Ladle

[0085] 4. Pellets

[0086] 5. Scrap

[0087] 6. DRI, CBI or HBI or combination thereof

[0088] 7. Reducing gas

[0089] 8. Means for pneumatic injection of scrap

[0090] 9. Dump charging of one or more of final granulate, DRI, CBI, HBI and scrap

Claims

CLAIMS1. Method for producing molten iron in an ironmaking process using an electric smelting furnace (ESF) of the submerged arc furnace (SAF) type, a smelting furnace of the submerged arc refining furnace (SARF) type or a smelting furnace of the Open Slag Bath Furnace (OSBF) type, wherein the method comprises providing a metalliferous charge to the ESF, said metalliferous charge comprises: i. a final granulate comprising iron-containing reverts and / or iron-containing by-products from the iron- and steelmaking process, wherein the final granulate is provided into the electric smelting furnace by means of dump charging into the electric smelting furnace, ii. a pre-reduced metalliferous charge, and / or iii. metalliferous scrap, and smelting said metalliferous charge to produce molten iron, wherein the final granulate is produced by a granulation method comprising the consecutive steps of• a mixing step for producing a mixture of iron-containing reverts and / or iron- containing by-products from the iron- and steelmaking process;• drying the mixture using drying means or adding water to the mixture to adjust the moisture level of the mixture to 15 to 30% (w / w) moisture to produce a mixture of moist reverts and by-products;• mixing the moist reverts and by-products with a binder to obtain a green granulate wherein the granules have a size of 5.0 mm or less;• optionally storing the green granulate for later use;• drying the green granulate to a maximum of 3.0% (w / w) moisture, thereby forming the final granulate to be added to the metalliferous charge.

2. Method according to claim 1 wherein the pre-reduced metalliferous charge comprises one or more of directly reduced iron (DRI), cold briquetted iron (CBI) and hot briquetted iron (HBI).

3. Method according to claim 1 or 2, wherein the moisture level of the moist reverts and by-products is adjusted to 20 to 25% (w / w) moisture.

4. Method according to anyone of the claims 1 to 3, wherein the binder is an organic binder, and preferably a cellulose derivative.

5. Method according to anyone of the claims 1 to 4, wherein the binder is added to the moist reverts and by-products in an amount of 0.10% to 0.40% (w / w), preferably of 0.15 to 0.30 % (w / w).

6. Method according to any one of claims 1 to 5, wherein the final granulate is provided into the electric smelting furnace by means of dump into the electric smelting furnace.

7. Method according to anyone of the claims 1 to 6, wherein the size of the final granulate is less than 4.0 mm.

8. Method according to anyone of the claims 1 to 7, wherein the moisture content of the final granulate is at most 2.5 %, preferably at most 2.2 % and more preferably at most 2.0% (w / w).

9. Method according to anyone of the claims 1 to 8, wherein the granulate is dried by means of a belt drier, preferably wherein the granulate is dried by using residual heat of the iron- and steelmaking process, preferably by using the residual heat of the electric smelting furnace.

10. Method according to anyone of the claims 1 to 9, wherein the final granulate also comprises zinc or zinc containing compounds and / or wherein the metalliferous scrap comprises galvanised scrap, and wherein zinc oxide dust is collected from the off-gases of the electric smelting furnace.

11. Method according to anyone of the claims 1 to 10, wherein the final granulate further comprises zinc or zinc containing compounds, wherein the process allows the evaporation and oxidation of zinc during the smelting of the feed pile after which the off-gas is de-dusted by means of a filter system, optionally comprising one or more cyclone filters, one or more high temperature filters and one or more baghouse filters, or a combination thereof, and recovering the zinc or zinc oxide from the dust collected by said filter system.

12. Method according to anyone of the claims 1 to 11 wherein the pre-reduced metalliferous charge is produced by reducing iron ore provided in the form of iron- ore pellets in a direct reduction reactor thereby producing directly reduced iron (DRI) which directly reduced iron is optionally compacted into cold briquetted iron (CBI) or hot briquetted iron (HBI), preferably wherein at least part of the directly reduced iron discharged from the direct reduction reactor is provided into the electric smelting furnace through a hot link.

13. Method according to any one of the claims 1 to 12, wherein the electric smelting furnace is fed continuously with the final granulate and one or more of DRI, HBI, CBI and scrap to provide constant feed pile conditions, and / or wherein the liquid iron and / or slag is tapped from the furnace continuously to maintain constant feed pile, slag, and molten iron levels in the furnace.

14. Method according to any one of the claims 1 to 13 wherein the final granulate is provided into the electric smelting furnace by a combination of i). dump charging the granulate into the electric smelting furnace (9) and ii). injection of the final granulate through injection means (8).

15. Method according to claim 14 wherein the bulk of the granulate is provided to the furnace by dump-charging and wherein the charge in the furnace is fine-tuned by continuous or batchwise addition of final granulate through injection means (8) such as lances in the side or the top of the furnace.

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