EP4665878A1

EP4665878A1 - Method of producing direct reduced iron

Info

Publication number: EP4665878A1
Application number: EP24705606.2A
Authority: EP
Inventors: Sander Johannes Everstein
Original assignee: Tata Steel Ijmuiden BV
Current assignee: Tata Steel Ijmuiden BV
Priority date: 2023-02-14
Filing date: 2024-02-12
Publication date: 2025-12-24
Also published as: AU2024223739A1; WO2024170464A1

Abstract

The invention relates to a method of producing directly reduced iron having a carbon content of at least 1 wt.%, the method comprising reducing in a direct reduction plant (DRP) iron oxide and/or iron ore into DRI by means of a reducing gas entering the DRP through one or more gas inlets, wherein the reducing gas is composed of at least 90 vol.% of hydrogen, and wherein the iron oxide and/or iron ore is charged into the DRP through one or more inlets in the form of a solid agglomerated product comprising, 70-95 wt.% of iron-oxide and/or iron ore material, 1-10 wt.% of carbonaceous material, 0.05-15 wt.% of a binder, 0-5 wt.% of additives.

Description

METHOD OF PRODUCING DIRECT REDUCED IRON

FIELD OF THE INVENTION

The invention relates to a method of producing directly reduced iron (DRI) having a carbon content of at least 1 wt.% (percent by weight) by reducing iron oxide or iron ore in a direct reduction plant. The invention also relates to a solid agglomerated product for use in the method of producing DRI having a carbon content of at least 1 wt.%.

BACKGROUND TO THE INVENTION

Direct reduced iron (DRI) is produced from the direct reduction of iron ore conglomerates (mainly hematite, Fe₂O₃) in the form of lumps, pellets, or fines into iron by a reducing gas. Direct reduction refers to a solid-state process which reduces 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. 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. An example of a direct reduction shaft furnace is disclosed in patent document US-2021/0333048-A1. 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.

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

The carbon content in the DRI is mostly obtained from the cracking reactions of hydrocarbons, as illustrated by the reactions of methane as the main constituent of natural gas: Fe₃C + 2H₂, and to a lesser extent from the CO content of the reducing gas fed to the reduction reactor. The potential of CO to carburize the DRI in the reduction zone according to the reaction 2CO C+CO₂ is very low because at the inlet of the reduction zone the temperature is too high for the reaction to proceed and at the top of the reduction zone, where the temperature is favourable for the reaction to occur, there is no metallic iron to serve as a catalyst for the reaction. Carburization by cracking of hydrocarbons is favoured at high temperatures and is also catalysed by metallic iron. These two factors are present at the bottom part of the reduction zone, where the hot reducing gas is introduced into said reduction zone, but a high concentration of hydrocarbons is necessary. The hydrocarbon concentration in the reducing gases however is not high enough for producing DRI with a desired level of carbon because the gas effluent from the reformer has a low CH₄ concentration after having reacted with oxidants (H₂O and CO₂) to produce H₂ and CO. The amount of carbon in the DRI produced in the plants where off-gas from the reactor is recycled through an in-line reformer is typically between about 1.5-4 wt.%, while in those plants having a reformer outside of the recycled gas circuit and an independent recycle circuit through a gas heater, the carbon content in the DRI may be from about 1.5-2.5 wt.%.

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 electric-arc furnaces (EAF) or submerged-arc furnaces (SAF; in the art also known as a reducing electrical furnace or REF). The furnaces have electrodes and a gas extraction duct to collect the hot gases that are produced during the charging, melting and refining of the DRI. Optionally also steel scrap is charged into the furnaces together with the DRI. The melt shop typically further comprises ladle furnaces for metallurgical processing like alloying and refining to produce molten steel or other molten iron containing products, and subsequently cast into slabs or ingots ready for rolling and further heat treatment.

If no further measures are taken the carbon content of the resulting molten iron from the EAF/SAF in the melt shop is low and considerably lower than that of pig iron that is produced in a conventional coal-based blast furnace practice. This causes problems amongst others when the molten iron is subsequently processed in a conventional basic oxygen (i.e., BOF or BOS) steelmaking process.

The carbon content in the DRI can be adjusted for its further processing in the melting furnace in a wide range from about 1.5-4% by injecting a carburizing gas from a suitable source, which may be a hydrocarbon gas, coke oven gas, natural gas, syngas from biomass, or mixtures thereof, or other methane-containing and/or CO-containing syngas or any other carbon-containing gas that may deposit carbon in the DRI. This approach is for example disclosed in patent document EP-1160337-A1 . A disadvantage of this approach is the complex handling of hot DRI in combination with a mixture of carburizing gases. The contact time or reaction time is rather short and the subsequent carbonization or increase in carbon content is very limited. The use of hydrocarbon gases also leads to the production of CO₂ and adversely affects the CO₂ footprint. The DRI can be discharged cold from the reduction furnace by circulating a cooling gas in the lower portion of the reduction furnace in a manner known in the art. In this case, the carbon content of the DRI can be increased by using as cooling gas a DRI carburizing gas, which may be a hydrocarbon gas, coke oven gas, natural gas, syngas from biomass, or mixtures thereof, or other methane-containing and/or CO-containing syngas or any other carbon-containing gas that may deposit carbon in the DRI. More typically, DRI is discharged from said reduction furnace at high temperature in the range between about 300-750°C, preferably between about 500-700°C, and charged hot via a so-called “hot-connect” to a melting furnace, e.g. an EAF or SAF.

Patent document WO99/42624 discloses a method for producing direct reduced iron or prereduced iron ore with improved reducing gas utilization, the method comprising: feeding a stream of reducing gas mainly composed of hydrogen and carbon monoxide and also comprising methane, carbon dioxide and water, heated at a temperature between 750°C to 1050°C, to a reduction zone within a reduction reactor wherein solid particles containing iron oxides present therein are reduced by reaction of said iron oxides with said reducing gas; withdrawing from said reactor said reducing gas after reacting with said iron oxides as top gas; cooling and cleaning said top gas and removing water therefrom to produce a cooled top gas; heating and recycling a first portion of said cooled top gas to said reduction reactor as part of said stream of reducing gas; purging a second portion of said cooled top gas; adding make-up gas to gases eventually recycled to the reducing zone; separating from said second portion of said cooled top gas at least the majority of the hydrogen contained therein to form a hydrogen rich gas stream which is lean in carbon dioxide, and recycling said hydrogen rich gas stream to said reduction reactor. There is no disclosure regarding the composition of the iron-containing material feedstock to produce the DRI nor about the issues associated therewith.

Patent document US2019/0055616-A1 discloses an alternative method for producing metal from metal oxide by carbothermic reduction, the method comprising: providing a holed cake having a composition comprising 70-90 wt.% of metal oxide, 10 to 30 wt.% of a carbonaceous reducing agent, and 0.1 to 6 wt.% of a binder, and the holed cake having a plurality of holes; and placing the holed cake in a high-temperature furnace using radiation heat for carbothermic reduction, to reduce the metal oxide in the holed cake into a metal. The metal oxide is selected from the group of iron oxide, nickel oxide, copper oxide, lead oxide, manganese oxide, tin oxide, potassium oxide, sodium oxide, zinc oxide, or a combination of at least two of the foregoing, and wherein the metal oxide is powdered to improve the metal conversion rate. The disclosed method concerns a batch process using the holed cake. The holed cake comprises 10-30 wt.% of a carbonaceous material acting as reducing agent for the metal oxide.

Patent document W02005/028684-A1 discloses a self-reducing, cold-bonded pellets, comprising, by weight, 60-79 wt.% iron oxide-containing material, a main portion of said material being between about 200 mesh or smaller, 10-26 wt.% carbonaceous reducing agent with a particle size of about 48 mesh or smaller, and 10-20 wt.% finely divided Portland cement clinker as a binder wherein 90% or more of the total volume of the cement clinker particles measure less than 0.08 mm and the portion of dicalcium silicate contained in the cement clinker is less than 20% by weight, with the total weight of the iron oxide-containing material, carbonaceous reducing agent and cement clinker being 100 %. The pellets can be used in most smelting furnaces such as electric arc furnaces, converting furnaces, open-hearth furnaces for steelmaking, blast furnaces, non-blast furnaces for iron-making, and direct reduction iron furnaces for producing DRI products. The pellets comprise 10-26 wt.% of a carbonaceous material acting as reducing agent for the iron oxide-containing material.

There is a demand for a method for producing DRI having a controlled amount of carbon at a sufficiently high level.

DESCRIPTION OF THE INVENTION

It is an object of the invention to provide a method for producing directly reduced iron with a carbon content of at least 1 wt.%.

It is also an object of the invention to provide a solid agglomerated product or pellet based on iron ores which can be used efficiently and with high yields as a charge material in a direct reduction process for producing directly reduced iron with a carbon content of at least 1 wt.%.

These and other objects and further advantages are met or exceeded by the present invention defined in claim 1 and with further preferred embodiments in the dependent claims and the description.

In a first aspect the invention relates to a method of producing directly reduced iron (DRI) having a carbon content of at least 1 wt.%, the method comprising reducing in a direct reduction plant (DRP, 10), preferably at a temperature of 750°C or above, e.g. in a range of 750°C to 1050°C, iron oxide and/or iron ore into DRI by means of a reducing gas entering the DRP through one or more gas inlets, wherein the reducing gas is composed of at least 90 vol.% of hydrogen, and wherein the iron oxide and/or iron ore is charged into the DRP through one or more inlets and being in the form of a solid agglomerated product comprising, in weight percent, about 70 to 95 wt.% of iron-oxide and/or iron ore material; about 1 to 10 wt.% of carbonaceous material; about 0.05 to 15 wt.% of a binder; about 0 to 5 wt.% of additives; and the total is 100 wt.%.

And subsequently discharging of the DRI having a carbon content of at least 1 wt.% is from the DRP.

Due to the particular composition, and in particular due to the quantity of carbonaceous material present in the solid agglomerated product, it is possible to obtain a solid DRI pellet once processed in a DRP, said solid DRI pellet comprising reduced iron and at least 1 wt.% of carbon and it can be used in a DRI melting furnace facility, e.g. in an EAF or an REF or a SAF, that uses the DRI as the charge material, optionally the charge material further comprises steel scrap material. The carbonaceous material present in the solid agglomerated product will not be reduced or substantially not reduced in the DRP due to the use of very high levels of hydrogen as reducing gas for the reduction of the iron ore and/or iron oxides. The increased carbon content in the solid DRI leads to a lower melting temperature of the DRI and thus to lower operating temperatures of the EAF or REF or SAF offering substantial lower operational costs. It leads to lower nitrogen level in the molten iron produced in the melting furnace facility. The high carbon content already present in the DRI reduces the need for further carburization of the DRI or the amount of further carbonaceous material to be added to the molten iron in the EAF or REF or SAF. The addition of carbon, e.g., via injection lances, into the molten iron for subsequent steelmaking is otherwise very challenging and inefficient due to the significant different densities of carbonaceous materials and the molten iron and slag.

The method according to the invention is operated in a continuous fashion for months or even years without interruption by continuously feeding the solid agglomerated products into the DRP, injection of the reducing gas and discharging the solid DRI.

The term “agglomerate” as used in the description and claims shall mean the same as “pellet”. The term “pellet” includes objects commonly referred to as pellets, rods, pencils slugs. Pellets typically have a maximum average diameter of about 20 mm, more typically of about 16 mm, and a minimum average diameter of 2 mm, more typically of about 5 mm. A preferred average diameter of a pellet for the purpose of this invention is in a range of about 7 to 14 mm.

In an embodiment the DRI has a carbon content in a range of 1.0 wt.% to 6.0 wt.%, and preferably in the range of about 2.0 wt.% to 6.0 wt.%. In an embodiment the carbon content in the DRI is at least 3.0 wt.%, and more preferably at least 4.0 wt.%. In an embodiment the carbon content in the DRI is maximum 5.5 wt.%, and more preferably it does not exceed 5.0 wt.%.

The reducing gas used in the method according to the invention is composed of at least 90 vol.% (volume percent) of hydrogen. In an embodiment the reducing gas is composed of at least 93 vol.% of hydrogen, preferably of at least 95 vol.% of hydrogen, more preferably of at least 97 vol.% of hydrogen, and most preferably of at least 99 vol.% of hydrogen. The higher the hydrogen content, the less carbon present in the solid agglomerated product is oxidized in the DRP and thus the lower the CO₂ footprint, and the more carbon is available in the further processing of the DRI into steel or hot metal.

An important feature of the invention is that the content of carbonaceous material in the solid agglomerated product is ranging from about 1 to 10 wt.% to increase the carbon content in the pellet after reduction in the DRP to a level of 1 wt.% or higher. Preferable, the amount of carbonaceous material is at least 2.0 wt.%. Preferably the amount of carbonaceous material does not exceed 8 wt.%, and more preferably it does not exceed 6 wt.%. Too high a carbon content may decrease the hot strength of the pellet. The carbonaceous material present in the solid agglomerated product will not be reduced or substantially not reduced in the DRP due to the use of very high levels of hydrogen as reducing gas for the reduction of the iron ore and/or iron oxides.

The carbonaceous material is selected from the group: coke, graphite, carbon black, peat, coal, biomass or biochar. Coal may be any grade of coal, including lignite, sub-bituminous coal, bituminous coal, steam coal, or anthracite. The carbonaceous material is typically coal powder, and more preferably anthracite powder or coke breeze. The amount of fixed carbon contained in the carbonaceous materials is preferably 50 wt.% or more, more preferably of at least 60 wt.%; the higher the better.

In an embodiment the carbonaceous material, in particular the coal material or coal powder particles, used should have for more than 95% thereof a size less than 0.35 mm, and preferably of less than 0.25 mm, and more preferably of less than 0.05 mm. In a preferred embodiment all of the carbonaceous material, in particular the coal material or coal powder particles, has a size less than 0.35 mm, and preferably of less than 0.25 mm, and more preferably of less than 0.05 mm.

The main constituent of the solid agglomerated product is iron-oxide and/or iron ore material ranging from about 70 to 95 wt.%, and preferably from about 75 to 95 wt.%, and more preferably from about 80 to 95 wt.%. In an embodiment the solid agglomerate contains particulate of iron ore (e.g., hematite or magnetite) only, and preferably consisting of hematite. The iron content in the iron ore should be about 55 wt.% or more, and preferably of about 65 wt.% or more, the remainder is oxygen and gangue. The gangue is formed mainly by silicon oxide (silica), aluminium oxide (alumina), calcium oxide (lime), magnesium oxide, and other impurities in traces (e.g., sulphur, phosphorus, manganese oxide, sodium oxide), and is an inert solid material which does not participate in the reduction reactions in the DRP.

In an embodiment the solid agglomerate contains particulate of iron-oxide containing material formed only by iron- and/or steelmaking reverts, such as for example, steelmaking sludge, rolling scales or blast furnace dust.

In an embodiment the solid agglomerate contains a mixture of particulate of iron ore and particulate of iron-oxide containing material formed by iron- and/or steelmaking reverts.

In an embodiment the major portion, i.e. , at least 90%, and preferably at least 95%, of the particulates of iron ore and particulates of iron-oxide, should have a size of 6 mm or smaller, and preferably 2 mm or smaller, and more preferably between 0.8 mm and 0.05 mm, otherwise it may decrease pellet strength.

A binder or binder material for the solid agglomerated product comprises an inorganic binder, an organic binder, or a combination thereof. The binder is present in the solid agglomerated product ranging from about 0.05 wt.% to 15 wt.%. In an embodiment the solid agglomerated product comprises in total of 0.05 to 10 wt.% of a binder, and preferably in total of 0.05 to 8.0 wt.% of a binder, and more preferably in total of 0.05 to 5.0 wt.%.

In an embodiment the inorganic binder, either alone or in combination with one or more organic binders, is present in the range of 1 wt.% to 10 wt.%, preferably in the range of 2 wt.% to 8.0 wt.%.

In an embodiment the inorganic binder comprises one or more of clay or a salt thereof, lime, calcium aluminates cement, blast furnace cement, Portland cement, or pozzolanic binder. Preferably the clay is bentonite or a salt thereof.

The organic binder may be a polymeric binder, and may be selected from an organic resin, such as polyacrylamide resin, resole resin or Novolac resin, and/ or a polysaccharide such as starch, hydroxyethyl methyl cellulose, gum Arabic, guar gum, xanthan gum, or molasses. The polysaccharide may be used as a thickening agent. Hydroxyethyl methyl cellulose (MHEC) has been found to have particularly good shelf life. This may be mixed with the organic resin.

When an organic binder is used, the total amount of the organic binder is preferably up to about 1 wt.%. In an embodiment the total amount of organic binder is up to about 0.8 wt.%, and more preferably up to about 0.7 wt.%. The total amount of organic binder is at least 0.05 wt.%, preferably at least about 0.1 wt.%, and more preferably at least about 0.2 wt.%.

Polyvinyl alcohol (PVA) may be used as an organic binder in an amount of 0.05-0.8 wt.%, preferably 0.1-0.8 wt.%. Typically PVA is added in addition to the other binders as it provides rapid curing, and high green and cured strength of the pellet.

Polyvinyl alcohol is typically commercially formed from polyvinyl acetate by replacing the acetic acid radical of an acetate with a hydroxyl radical by reacting the polyvinyl acetate with sodium hydroxide in a process called saponification. Partially saponified means that some of the acetate groups having been replaced by hydroxyl groups and thereby forming at least a partially saponified polyvinyl alcohol residue.

The PVA used for this method is commercially available in powder form and covers all suitable grades that would be considered as being in the medium viscosity range and which are soluble in water as it is typically utilised as a solution in water as in known in the art. The PVA chain may be in various degrees of saponification and is typically of at least 80%, and more preferably of at least 90% saponification. The PVA may be modified to include, for example, a sodium hydroxide content. Typically the PVA binder has an active polymer content of about 12- 13% and a pH in the range of 4-7 when in solution. As an additive a cross-linking agent may be added during the formulation of the aqueous polymer solution to promote cross-linking of the PVA to further improve the bonding forces between the polymer chains increasing the strength of the pellet. A suitable cross-linking agent is for instance Gluteraldehyde.

Resoles are base catalysed phenol-formaldehyde resins with a formaldehyde to phenol ratio of greater than one, and usually around 1.5. Novolacs are phenol-formaldehyde resins with a formaldehyde to phenol molar ratio of less than one.

Optionally, the solid agglomerated product or pellet may comprise additives ranging from 0 to about 5 wt.%, preferably ranging from 0 to about 4%, and more preferably ranging from 0 to about 3.0 wt.%. The additives may include for example a cross-linking agent to increase the strength of PVA, if used, or a wetting agent or surfactant such as SLS (sodium lauryl sulphate) to improve the wetting of the particulates during mixing, or a waterproofing agent.

In an embodiment the solid agglomerated product or pellet consists of, in weight percent, 70-95 wt.% of iron-oxide and/or iron ore material, 1-10 wt.% of carbonaceous material, 0.05-15 wt.% of a binder, 0-5 wt.% of additives, and the total is 100 wt.%, and with preferred embodiments and narrower compositional ranges as herein described and claimed.

A process for producing pellets comprising iron oxide and/or iron ore as utilised in a DRP in accordance with this invention, said process comprising of steps of: (a) mixing the binder and optional additives with particulates of iron ore and/or iron oxide material and the carbonaceous material to an isotropic mixture; (b) agglomerating the mixture forming “green” pellets; and (c) drying and/or curing of the “green” pellets. The pellets are formed using a method selected from the group comprising: extrusion, drum pelletisation, pan pelletisation, and briquetting, all of which are known in the art.

In an embodiment the pellets are formed by means of extrusion.

In an embodiment the pellets are formed by means of pelletisation or briquetting.

Preferably after pelletising and prior to drying and/or curing, the “green” pellets will be graded such as being filtered by roller screens or the like, and the reasons for this is to separate the unwanted smaller or larger pellets and to either eliminate the loose powder from adhering to the pellets or cement it firmer to the pellets. The purpose of eliminating or fusing the loose powder onto the pellets is to prevent the pellets from adhering to each other. The extra loose powder and the smaller or larger pellets can then be recycled to be formed again into new pellets.

In a next process step, the pellets are dried and cured depending on the binder system used. The pellets may be dried and cured naturally in the air at a temperature of more than about 20°C for up to about 28 days. In another embodiment, the pellets may be dried and cured using low level heating, such as heating in a range up to 200°C, for example at a temperature in a range of 100°C to 180°C, preferably of 100°C to 150°C.

It is preferred that the pellets are dried and/or cured at a temperature not exceeding about 300°C, and preferably not exceeding about 250°C. In the art such pellets are referred to as cold- bonded pellets. By subjecting the pellets to too high a temperature will lead to the oxidation of parts of the carbonaceous material thereby adversely reducing the total amount of carbon in the DRI.

In an embodiment the solid agglomerated product is a cold-bonded solid agglomerated product or cold-bonded pellet.

In an embodiment the solid agglomerated product or cold-bonded pellet has a particle porosity P of at least 20%, and preferably of at least 24%, wherein the porosity percentage P is calculated via P(%) = 100 x (1 - Vs/Vt) , and wherein Vt is the total particle volume, and Vs is the particle solid volume. A higher particle porosity facilitates the direct reduction reactions.

In an embodiment the cold-bonded solid agglomerated product or cold-bonded pellet has a cold compressive strength of at least 235 kg/pellet, and preferably of at least 245 kg/pellet, and more preferably of at least 260 kg/pellet, when measured in accordance with ISO- 4700:2015. The cold compressive strength is the compressive load attained to cause breakage of a pellet.

In an embodiment the cold-bonded solid agglomerated product or cold-bonded pellet has a tumbler index of at least 93%, and preferably of at least 95%, when measured in accordance with ISO-3271 :1995. It forms an indication of the degradation that the product or pellet can suffer because of the contact among them during handling.

The solid agglomerated products or pellets typically have a maximum average diameter of about 20 mm, more typically of about 16 mm, and a minimum average diameter of 2 mm, more typically of about 5 mm, to avoid bridge formation in the DRP. A preferred average diameter of a pellet for the purpose of this invention is in a range of about 6 mm to 14 mm.

The pellet may be produced at a separate site to where it is used. That is the pellet may be produced where there are deposits of, for example, iron ore fines, made into pellets by combining with particulate carbonaceous material and with the binder, and then transported to the DRP at a geographically separate site. Transportation may be, for example, by boat, road or rail.

Alternatively, a binder may be mixed with particulate iron ore and/or iron oxide material and the particulate carbonaceous material on substantially the same site as the DRP, then charged into the DRP.

In an embodiment the direct reduction plant (DRP) or reduction reactor is a rotary hearth furnace (RHF).

In a preferred embodiment the direct reduction plant (DRP) or reduction reactor is of the gravitational type, more in particular it is a shaft furnace. Such a DRP is operated in a continuous fashion for months or even years without interruption by continuously feeding iron ore agglomerate into the DRP and discharging solid DRL

In a preferred embodiment, the DRP is of the gravitational type and comprises a reduction zone, inside which the iron ore reduction processes occur, feeding means to feed iron ore agglomerate to the reduction zone of said reactor, a reducing gas circuit being provided with injection means configured to feed the reducing gas into the reduction reactor, a reducing gas heater, an aperture to extract spent reducing gas, and a discharge zone to discharge reduced iron in solid form.

In an embodiment, the reducing gas circuit is configured to regenerate the spent reducing gas exiting the reactor and re-inject it into the reactor once it has been regenerated. In an embodiment of the method according to the invention, the DRI discharged from the DRP is charged subsequently into an electric arc furnace (SAF, REF, or EAF), preferably through a hot-connect between the DRP reactor and the electric arc furnace.

In a preferred embodiment the DRI is processed together with steel scrap material in the electric arc furnace.

In the embodiment where the DRI discharged from the DRP is charged into an EAF, optionally together with steel scrap material, to produce molten iron which when tapped from the EAF has a carbon content in the range of less than 2.5 wt.% and preferably less than 2.0 wt.%. In this embodiment the EAF is operated preferably with an oxidising atmosphere, and is often open to the outside atmosphere and having a favourable foamy slag. The preferred oxidising nature of the atmosphere enables the removal of carbon from the molten DRI such that steel is formed having less than about 2.0 wt.% carbon, and preferably less than 1.5 wt.%, and more preferably less than 0.5 wt.%.

In another embodiment the DRI discharged from the DRP is charged into an EAF or SAF, optionally together with steel scrap, to produce hot metal or crude iron which when tapped from the EAF or SAF has a carbon content in the range of about 2.5 to 6 wt.%, preferably in the range of about 3.0 to 6.0 wt.%, and more preferably of about 3.5 to 6.0 wt.%, and subsequently processed in a basic oxygen furnace. In this embodiment the EAF or SAF is operated preferably with a reducing atmosphere, and in the art often referred to as a SAF or REF. The use of oxygen/oxy-fuel injection is limited and preferably even absent such that the atmosphere is reducing, thereby enabling the further reduction of any remaining iron oxides in the DRI and allowing the molten iron to contain dissolved carbon.

In this embodiment the generated molten iron having 2.5 to 6 wt.% , preferably 3.0 to 6.0 wt.%, more preferably 3.5 to 6.0 wt.%, of carbon and tapped from the EAF or SAF is further processed in a basic oxygen furnace process converting the molten iron into molten steel by blowing oxygen into a BOF convertor containing the molten iron and by allowing the oxygen to combine with the carbon in the melt to form gaseous CO thereby converting the molten iron into molten steel with a low carbon content. The high carbon content at the beginning of the BOF processing is required to enable a sufficient control of the exothermic process in the BOF plant. The vigorous flushing of the bath also efficiently removes nitrogen gas in the molten metal and nitrogen inclusions, commonly present in EAF based steels are hereby prevented. The carbon content in the molten steel after BOF processing is preferably less than about 1 wt.%, and more preferably to less than about 0.5 wt.%. The molten steel is a carbon steel with a composition further comprising less than 1.0 wt.% Ni, less than 1.0 wt.% Cr, less than 0.5 wt.% Cu, and less than 200 ppm N. In an embodiment of the carbon steel the nitrogen content is less than 100 ppm N, and preferably less than 50 ppm.

The invention is also embodied in a solid agglomerated product or pellet, preferably a cold-bonded solid agglomerated product or pellet, to be used as charge material into a DRP in accordance with this invention, said solid agglomerated product comprising, in weight percent, about 70 to 95 wt.% of iron-oxide and/or iron ore material, about 1 to 10 wt.% of carbonaceous material, about 0.05 to 15 wt.% of a binder, 0 to 5 wt.% of additives, and the total is 100 wt.%, and with preferred embodiments as herein described and claimed.

The invention also relates to the use or method of use of the solid agglomerated product as herein described and claimed in a method of producing directly reduced iron with a carbon content of at least 1 wt.% in a direct reduction plant, preferably of the gravitational type in a shaft furnace, from reducing at a temperature of 750°C or above, of the iron oxide and/or iron ore by means of a reducing gas entering the DRP through one or more gas inlets as herein described and claimed. In an embodiment the carbon content in the DRI is at least 3.0 wt.%, and more preferably at least 4.0 wt.%. In an embodiment the carbon content in the DRI is maximum 5.5 wt.%, and more preferably it does not exceed 5.0 wt.%.

DETAILED DESCRIPTION OF THE FIGURE

The invention will now be explained by means of the following, non-limiting figure.

Fig. 1 shows schematically a direct reduction plant (DRP) of the gravitational type.

The DRP 10 is formed by a direct reduction shaft furnace or shaft furnace having a reduction zone 11 having a substantially cylindrical tubular shape, inside which the iron ore reduction processes occur, feeding means 13 to feed solid agglomerated product 2, either cold or hot, to the reduction zone 11 of said reactor 10, a reducing gas circuit 14 being provided with injection means 16 configured to feed the reducing gas 15 into the reduction reactor, a reducing gas heater 17, and an aperture 18 to extract spent reducing gas. The DRP 10 is operated in a continuous mode. Under the reduction zone 11 , the DRP is normally provided with a truncated cone part converging towards the inside along the axis X and inclined with respect thereto, also called discharge zone 12, the function of which is to convey the reduced material towards a lower exit and to discharge reduced iron (DRI) 1 in solid form. The DRI 1 is commonly discharged either continuously or continually at a regulated rate by means of a suitable discharge mechanism or discharge means 19, for example a rotary star discharger, a vibrating discharger, or a screw discharger, all of which are known in the art. Subsequently the DRI 1 is charged into an electric arc furnace (not shown), preferably through a hot-connect between the DRP reactor 10 and the electric arc furnace (e.g., an EAF or SAF), to generate molten iron 4.

Having now fully described the invention, it will be apparent to one of ordinary skill in the art that many changes and modifications can be made without departing from the spirit or scope of the invention as herein described.

Any reference signs in the claims should not be construed as limiting the scope of the appended claims.

List of reference numbers:

1 DRI, directly reduced iron.

2 solid agglomerated product, pellet.

3 iron oxide and/or iron ore.

4 molten iron.

10 DRP, direct reduction plant, reduction reactor.

11 reduction zone.

12 discharge zone.

13 feedings means, inlets for charging the DRP.

14 reducing gas circuit.

15 reducing gas.

16 gas inlets, injection means.

17 reducing gas heater.

18 aperture to extract spent reducing gas.

19 discharge means.

Claims

1. Method of producing directly reduced iron (DRI,1) having a carbon content of at least 1 wt.%, the method comprising reducing in a direct reduction plant (DRP, 10), and preferably at a temperature of 750°C or above, iron oxide and/or iron ore (3) into DRI (1) by means of a reducing gas (15) entering the DRP (10) through one or more gas inlets (16), wherein the reducing gas (15) is composed of at least 90 vol.% of hydrogen, and wherein the iron oxide and/or iron ore (3) is charged into the DRP (10) through one or more inlets (13) in the form of a solid agglomerated product (2) comprising, 70-95 wt.% of iron-oxide and/or iron ore material (3), 1-10 wt.% of carbonaceous material, 0.05-15 wt.% of a binder, 0-5 wt.% of additives, and the total is 100 wt.%.

2. Method according to claim 1 , wherein the DRI (1) has a carbon content in a range of 1.0 to 6.0 wt.%, and preferably in the range of 2.0 to 6.0 wt.%, and more preferably in the range of 3.0 to 6.0 wt.%.

3. Method according to claim 1 or 2, wherein the solid agglomerated product (2) comprises carbonaceous material in a range of 2.0 to 8.0 wt.%, preferably in a range of 2.0 to 6 wt.%.

4. Method according to any one of claims 1 to 3, wherein the solid agglomerated product (2) comprises in a range of 75 to 95 wt.% of iron-oxide and/or iron ore, preferably in a range of 80 to 95 wt.%.

5. Method according to any one of claims 1 to 4, wherein the solid agglomerated product (2) comprises 0.05-10 wt.% of a binder, and preferably 0.05 to 8.0 wt.%, and more preferably 0.05 to 5.0 wt.%.

6. Method according to any one of claims 1 to 5, wherein the solid agglomerated product (2) comprises 0.05-1.0 wt.% of an organic binder, preferably the organic binder is a polymeric organic binder.

7. Method according to any one of claims 1 to 6, wherein the solid agglomerated product (2) comprises 0.05-0.8 wt.% of at least partially saponified polyvinyl alcohol (PVA) as a binder.

8. Method according to any one of claims 1 to 7, wherein more than 95% of the carbonaceous material in the solid agglomerated product (2) has a maximum dimension of 0.35 mm, and preferably of less than 0.25 mm.

9. Method according to any one of claims 1 to 8, wherein the solid agglomerated product (2) comprises 70-95 wt.% of iron ore material, preferably being formed by hematite.

10. Method according to any one of claims 1 to 9, wherein the solid agglomerated product (2) comprises 70-95 wt.% of a mixture of iron ore material, preferably hematite, together with iron- and/or steelmaking reverts.

11. Method according to any one of claims 1 to 10, wherein the solid agglomerated product (2) has a maximum average diameter of 20 mm, and preferably a minimum average diameter of 2 mm, and more preferably an average diameter in a range of 7 to 14 mm.

12. Method according to any one of claims 1 to 11 , wherein the solid agglomerated product (2) is a cold-bonded solid agglomerated product.

13. Method according to any one of claims 1 to 12, wherein the reducing gas (15) is composed of at least 93 vol.% of hydrogen, preferably of at least 95 vol.% of hydrogen, more preferably of at least 97 vol.% of hydrogen, and most preferably of at least 99 vol.% of hydrogen.

14. Method according to any one of claims 1 to 13, wherein the direct reduction plant (10) is of the gravitational type, and preferably is a shaft furnace.

15. Method according to any one of claims 1 to 14, wherein the DRI (1) is charged subsequently into an electric-arc furnace (EAF/SAF), preferably through a hot-connect between the DRP (10) and the electric-arc furnace (EAF/SAF), to generate molten iron (4).

16. Method according to claim 15, wherein the DRI (1) is charged subsequently into an oxidising EAF, and generating molten iron (4) for tapping from the EAF and having a carbon content up to 2.5 wt.%, and preferably up to 2.0 wt.%.

17. Method according to claims 15, wherein DRI (1) is charged subsequently into a EAF or SAF, preferably a reducing EAF or SAF, and generating molten iron (4) for tapping from the EAF or SAF and having a carbon content in a range of 2.5 to 6 wt.%, preferably 3.0 to 6.0 wt.%, and is further processed in a basic oxygen furnace process converting the molten iron (4) into molten steel with a carbon content of less than 1 wt.% carbon, and preferably of less than 0.5 wt.% carbon.

18. Solid agglomerated product (2) for use as charge material in a DRP (10), the solid agglomerated product (2) comprising: 70-95 wt.% of iron-oxide and/or iron ore material, 1-10 wt.% of carbonaceous material, and preferably 2.0 to 8 wt.% of carbonaceous material, 0.05-15 wt.% of a binder, 0-5 wt.% of additives, and the total is 100 wt.%.

19. Use of a solid agglomerated product (2) as defined in any one of claims 1 or 3 to 12 as a charge material in a method of producing directly reduced iron (1) according to any one of claims 1 or 2 or 13 to 17.