EP4689195A1

EP4689195A1 - Direct reduction plant and method of manufacturing direct reduced iron

Info

Publication number: EP4689195A1
Application number: EP23720994.5A
Authority: EP
Inventors: Marcelo W. Muniz DE ANDRADE; Dmitri Boulanov; Dianbing Huang; Gabriel LUCENA MOGOLLON; Maude LEVESQUE; Jean-Philippe GUERIN; Sirisha PARVATHANENI
Original assignee: ArcelorMittal SA
Current assignee: ArcelorMittal SA
Priority date: 2023-04-05
Filing date: 2023-04-05
Publication date: 2026-02-11
Also published as: WO2024209233A1; JP2026511987A; AU2023439540B2; CN120731280A; KR20250149732A; AR132322A1; MX2025011717A; AU2023439540A1

Abstract

A direct reduction plant comprising a direct reduction furnace (1) and a reformer (33), said reformer (33) comprising several tubes (51) provided with gas supply means (64,65), at least one of said tubes (51A) being provided with at least one gas supply means (65) able to supply said tube (51A) with a gaseous hydrogen stream (25) and at least one other tube (51B) being provided with at least one gas supply means (64) able to supply said other tube (51B) with a methane-containing gas (24

Description

Direct reduction plant and method of manufacturing direct reduced iron

[001] The invention is related to a plant to manufacture Direct Reduced Iron (DRI) and to the associated method.

[002] Steel can be currently produced through two main manufacturing routes. Nowadays, most commonly used production route consists in producing hot metal in a blast furnace, by use of a reducing agent, mainly coke, to reduce iron oxides. In this method, approx. 450 to 600 kg of total fuel, is consumed per metric ton of hot metal; this method, both in the production of coke from coal in a coking plant and in the production of hot metal, releases significant quantities of CO2.

[003] The second main route involves so-called “direct reduction methods”. Among them are methods according notably to the brands MIDREX or ENERGIRON/HYL, in which sponge iron is produced in the form of HDRI (Hot Direct Reduced Iron), CDRI (cold direct reduced iron), or HBI (hot briquetted iron) from the direct reduction of iron oxide carriers. Sponge iron in the form of HDRI, CDRI, or HBI usually undergo further processing in electric arc furnaces.

[004] There are three zones in each direct reduction shaft with cold DRI discharge: Reduction zone at top, transition zone at the middle, cooling zone at the cone shape bottom. In hot discharge DRI, this bottom part is used mainly for product homogenization before discharge.

[005] Reduction of the iron oxides occurs in the upper section of the furnace, at temperatures up to 950°C. Iron ores, in form of lump ores and/or pellets, containing around 30% by weight of Oxygen are charged to the top of a direct reduction shaft furnace and are allowed to descend, by gravity, through a reducing gas. This reducing gas is entering the furnace from the bottom of reduction zone and flows counter-current from the charged iron ores. Oxygen contained in iron ore is removed via the stepwise reduction of iron oxides by the gaseous reductants. Oxidant content of the gas phase is increasing while the gas is moving to the top of the furnace.

[006] The reducing gas generally comprises hydrogen and carbon monoxide and is obtained by reforming natural gas. For example, in the so-called MIDREX method, first methane is transformed into a reformer according to the following reactions to produce the syngas or reduction gas:

CH4 + C02 -> 2C0 + 2H2 CH4 + H2O -> CO + 3H2 and the iron oxide reacts with the reduction gas, for example according to the following reactions:

3Fe203 + CO/H2 -> 2Fe3O4+CO2/H2O

Fe3O4 + CO/H2 -> 3 FeO + CO2/H2O

FeO + CO/H2 -> Fe + CO2/H20 at the end of the reduction zone the ore is metallized.

[007] A transition section is found below the reduction section; this section is of sufficient length to separate the reduction section from the cooling section, allowing an independent control of both sections. In this section carburization of the metallized product happens. Carburization is the process of increasing the carbon content of the direct reduced product inside the reduction furnace through notably following reactions:

3Fe + CH4 Fe3C + 2H2 (Endothermic)

3Fe + 2CO — > Fe3C + CO2 (Exothermic)

3Fe + CO + H2 — > Fe3C + H2O (Exothermic)

[008] Injection of natural gas in the transition zone is using sensible heat of the direct reduced product in the transition zone to promote hydrocarbon cracking and carbon deposition. Due to relatively low concentration of oxidants, transition zone natural gas is more likely to crack to H2 and Carbon than reforming to H2 and CO. Natural gas cracking provides carbon for DRI carburization and, at the same time adds reductant (H2) to the gas that increases the gas reducing potential.

[009] In view of the considerable increase in the concentration of CO2 in the atmosphere since the beginning of the last century and the subsequent greenhouse effect, it is essential to reduce emissions of CO2 where it is produced in a large quantity, and therefore in particular during DRI manufacturing. [0010] One solution which is currently developed is the progressive increase of the hydrogen content into the reducing gas, in view of reaching a pure hydrogen reducing gas. Following reduction reaction will then occur:

Fe2O3 + 3 H2 = 2 Fe + 3 H2O thus, releasing harmless H2O instead of the greenhouse gas CO2.

[0011] As mentioned below this switch from methane based DRI to H2 based DRI will be progressive for several reasons. Existing plants need to adapt their equipment and to assess impact on the subsequent steelmaking steps. Most preferable source of hydrogen is green hydrogen to reduce the overall carbon footprint, but it is nowadays not available in sufficient quantity to fulfil all needs. Although the future availability of green hydrogen will depend heavily on the capacity of renewable energy sources.

[0012] Consequently, the plants will have to operate in a hybrid mode between the NG based DRI and the H2-DRI technologies.

[0013] There is so a need for an equipment allowing to operate with a variable content of hydrogen in the reducing gas. There is also a need for a direct reduction method allowing to operate with an increased content of hydrogen in the reducing gas without detrimental impact on the productivity compared to natural gas based existing methods.

[0014] This problem is solved by a plant according to the invention comprising a direct reduction furnace and a reformer, this reformer comprising several tubes provided with gas supply means, at least one of said tubes being provided with at least one gas supply means able to supply said tube with a gaseous hydrogen stream and at least one other tube being provided with at least one gas supply means able to supply said other tube with a methane- containing gas.

[0015] The plant of the invention may also comprise the following optional characteristics considered separately or according to all possible technical combinations:

- at least one of the tubes is provided with gas supply means able to supply said tube with the gaseous hydrogen stream or with the methane-containing gas, said gas supply means further comprising selection means allowing to supply either only the gaseous hydrogen stream or only the methane containing gas to said tube,

- at least one of the tubes is provided with gas supply means able to supply said tube exclusively with the gaseous hydrogen stream, - the gas supply means designed to supply the tubes with a gaseous hydrogen stream is equipped with means to control the H2 flow rate,

- the at least one of said tube wherein the hydrogen stream is exclusively supplied is filled with solid particles,

- the solid particles are made of ceramic or of a high temperature alloy.

[0016] The invention is also related to a method to manufacture direct reduced iron in a direct reduction plant according to anyone of the previous combinations wherein oxidized iron is reduced in the direct reduction furnace using a reducing gas to produce direct reduced iron, the method comprising the supply of the a methane-containing gas with the gas supply means to at least one of the tubes of the reformer to subject said methane- containing gas to a reforming step to produce a reformed gas, the supply of a gaseous hydrogen stream with the gas supply means to at least one of the tubes of the reformer to heat said gaseous hydrogen stream to a temperature from 800°C to 1100°C, the mixing of at least the reformed gas and the heated gaseous hydrogen stream to form the reducing gas and the injection of the reducing gas into the direct reduction furnace.

[0017] The method of the invention may also comprise the following optional characteristics considered separately or according to all possible technical combinations:

- oxygen is injected in the reducing gas before its injection into the direct reduction furnace,

- the gaseous hydrogen stream comprises more than 70% in volume of hydrogen,

- the reducing gas comprises at least 50% in volume of H2,

- a direct reduction top gas exits the direct reduction furnace, and the methane-containing gas comprises at least a part of said direct reduction top gas,

- the gaseous hydrogen stream is green hydrogen.

[0018] Other characteristics and advantages of the invention will emerge clearly from the description of it that is given below by way of an indication, and which is in no way restrictive, with reference to the appended figures in which:

Figure 1 illustrates a direct reduction plant allowing to implement a method according to the invention

Figure 2 illustrates an embodiment of a reformer allowing to perform a method according to the invention

Figure 3A illustrates another of a reformer allowing to perform a method according to the invention

Figure 3B is an enlarged view of the injection means of the reformer of figure 3A [0019] Elements in the figures are illustration and may not have been drawn to scale.

[0020] Figure 1 illustrates a direct reduction (DR) plant according to the invention. This DR plant includes a DR shaft or furnace 1 comprising from top to bottom a charging device 10 for oxidized ore, such as iron ore, said iron ore travelling through the shaft 1 by gravity, a reduction section located in the upper part of the shaft, a transition section located in the midpart of the shaft, and optionally a cooling section located at the bottom and an outlet from which the direct reduced iron 12 is finally extracted.

[0021] The direct reduction furnace (or shaft furnace) 1 is charged at its top with iron ore which contains oxidized iron, such as hematite or magnetite. This oxidized iron is reduced in the furnace 1 by a reducing gas 11 injected into the furnace and flowing in counter-current to the oxidized iron. If cold DRI is expected as a final product, the direct-reduced iron needs to be cooled in the cooling zone. When such a cooling region is present, the reduced iron 12 exits the bottom of the furnace 1 at a temperature below 65°C, preferably from 30°C to 65°C, for further processing, such as briquetting, before being used in subsequent steelmaking steps. Reducing gas, after having reduced iron, exits at the top of the furnace as a top gas 20 (TG).

[0022] The direct reduction plant 1 further comprises a reformer 33 comprising several tubes 51 provided with gas supply means 64,65. At least one of the tubes 51 A is provided with at least one gas supply means 64 allowing to supply the associated tube 51 A with a gaseous hydrogen stream 25 and at least one other tube 51 B being provided with at least one gas supply means 65 allowing to supply this other tube 51 B with a methane-containing gas 24.

[0023] The reducing gas 11 comprises then a reformed gas 41 resulting from the reforming of the methane containing gas 24 in the reformer 33 and a heated hydrogen gas stream. This heated hydrogen gas stream has a temperature from 800°C to 1100°C and results from the heating of the hydrogen gas stream 25 into the same reformer 33 as used for the reforming of the methane containing gas 24.

[0024] Methane reforming is a well-known technology wherein methane reacts with steam and/or carbon dioxide in the presence of a catalyst to form carbon oxides and hydrogen.

[0025] In a preferred embodiment the hydrogen gas stream 25 is green hydrogen. Green hydrogen (GH or GH2) is hydrogen generated by renewable energy or from low-carbon power. This H2 stream may be provided by a dedicated H2 production plant, such as an electrolysis plant. It may be a water or steam electrolysis plant. It is preferably operated using CO2 neutral electricity which includes notably electricity from renewable sources which is defined as energy that is produced from renewable resources, which are naturally replenished on a human timescale, including sources like sunlight, wind, rain, tides, waves, and geothermal heat. In some embodiments, the use of electricity coming from nuclear sources can be used as it is not emitting CO2 to be produced.

[0026] In a preferred embodiment, the H2 stream 25 enters the reformer at a temperature from ambient to 400°C. It may have been preheated before its injection into the reformer 33. This preheating is preferably an electrically based heating powered by CO2 neutral electricity.

[0027] Before its injection into the furnace, oxygen 27 may be added to the reducing gas 11. This addition allows to increase the temperature of the reducing gas thanks to exothermic reactions induced by oxygen.

[0028] The reducing gas 1 is preferentially injected in the shaft furnace at a temperature from 900 to 1200°C. It preferentially comprises more than 50% in volume of hydrogen.

[0029] The top gas 20 exiting the DRI shaft 1 is collected in a pipe, and after having been optionally to a water removal step in a scrubber 30, might be split into a process gas stream 21 A and a top gas fuel stream 21 B. This top gas fuel stream 21 B might be supplied as fuel for the burners 53 in the reformer 33. The process gas stream 21A, after having been optionally subjected to a CO2 removal step in a CO2 removal equipment 31 and to a second water removal step in a scrubber 32, may be mixed with natural gas 23 to form the methane containing gas 24 supplied to the reformer 33. The process gas stream 21A may also be directly sent to the reformer 33 without addition of natural gas 23.

[0030] The top gas exiting from the DRI shaft furnace usually comprises H2, CO, CH4, H2O, CO2 and N2 in various proportions. The top gas scrubbing operation allows removing water vapor from the rest of the stream to improve its reduction potential.

[0031] The top gas 21 after scrubber 30 usually comprises, in volume, from 43 to 57 % of H2, from 13 to 28 % of CO, from 12 to 18 % of CO2, from 2 to 12 % of CH4, from 1 to 4 % of H2O and from 0-3% of N2. If subjected to a partial CO2 removal step in the CO2 removal equipment 22 it usually comprises from 50 to 69 % of H2, from 15 to 20 % of CO, from 2 to 13 % of CO2, from 9 to 14 % of CH4, from 1 to 4 % of H2O and from 0-3% of N2.

[0032] Figure 2 illustrates an embodiment of a reformer 33 according to the invention. The reformer 33 comprises gas supply means 64,65 allowing to supply gas to a series of reforming tubes 51 B, 51 A, at least one main collector pipe 52 allowing to collect gas existing the tubes 51 A, 51 B. The reformer also comprises burners 53 supplied with a fuel (not illustrated) and a combustion exhausts collector 54 to recover exhaust combustion gases. In this first embodiment, at least one reforming tube 51 A is supplied only with the hydrogen stream 25 via hydrogen gas injection means 65 and at the exit is collected a heated hydrogen 42 gas stream having a temperature from 800°C to 1100°C, this tube being operated in hydrogen heating mode. The other reforming tubes 51 B are supplied by appropriate gas injection means 64 with the methane containing gas 24 as done in prior art and at the exit is collected a reformed gas 41 , those tubes are operated in reforming mode. Typical composition of a reformed gas 41 , before mixing with the heated H2 stream 42 is, percentages being expressed in volume, from 54 to 75% of H2, from 14 to 35% of CO; from 2 to 7% of CO2; up to 5 % of CH4, up to 6% of H2O and up to 3% of N2. Both reformed gas 41 and heated hydrogen stream 42 are mixed to form a reducing gas 26 exiting the reformer 33.

[0033] In a preferred embodiment the reformer 33 is a catalytic reformer and the at least one reforming tube 51A supplied with the hydrogen stream is used to heat the H2 stream. The H2 heating tube 51A is preferably provided with means to adjust the gas flow rate and is preferably filled with inert particles such as ceramic or metallic particles such as alumina particles or high temperature alloys. High temperature alloys are alloys able to withstand temperatures above 500°C. With the use of those particles, the heat exchange between the hydrogen gas and the tubes wall is improved. Furthermore, the particles will also help reduce the velocity of the gas, hence preventing possible issues in the main collector 52.

[0034] In figure 2 only five tubes are represented, one of them being supplied in hydrogen but the invention obviously encompasses embodiments in which the reformer comprises several series of tubes and wherein either one of the tubes of the series or one series is dedicated to hydrogen heating.

[0035] Figure 3A and 3B illustrate another embodiment of a reformer allowing to perform a method according to the invention. Same references will be used when referring to same element as in the previous embodiment.

[0036] In this embodiment, the reformer 33, as for the previous embodiment, comprises main collector pipes 52 allowing to collect gas exiting the tubes 51, burners (not illustrated) supplied with a fuel (not illustrated) and a combustion exhausts collector 54 to recover exhaust combustion gases. In this embodiment at least one reforming tube 51 is provided with two gas supply means 64, 65 respectively able to supply the gaseous hydrogen stream 25 and the methane-containing gas 24. Those two gas supply means are equipped with selection means, such as opening I closing devices allowing to supply either the hydrogen stream 25 or the methane-containing gas 24 to the tube 51. This results in either only the gaseous hydrogen stream or only the methane-containing 24 gas are supplied into the tube. In this embodiment the methane-containing gas 24 is process gas 21.

[0037] Both the hydrogen supply means 65 and the process gas supply means 64 are connected to a gas injection device 66 designed to inject the required gas into the tube 51 . The hydrogen supply means 65 is connected to a source of hydrogen which may be a storage vessel or an H2 distribution grid. Each gas supply means 64, 65 is respectively equipped with an hydrogen opening device and a methane opening device and when sufficient hydrogen is available, the hydrogen opening device is opened while the methane opening device is closed so that only the hydrogen stream 25 flows through the tube which is operated in hydrogen heating mode, while, when hydrogen is lacking, the hydrogen opening device is closed and the methane opening device is opened so that only the methane containing gas 24 flows through the tube which operates thus in reforming mode. When several tubes are equipped with such double supply means it is possible that some of them are operating in hydrogen heating mode while the others operate in reforming mode.

[0038] This allows to have flexibility of the installation according to the hydrogen availability and to be able to operate in full methane, full hydrogen or hybrid methane/hydrogen modes.

[0039] In both embodiments it is clear for the person skilled in the art that gas supply means are related to the main gas supplied to the tubes, namely hydrogen and methane-containing gases so that tubes are operated in so-called hydrogen heating mode or reforming mode. In the case of a tube operated in reforming mode, steam or process top gas may for example be supplied along with the methane-containing gas to perform the reforming reaction.

[0040] With the plant according to the invention it is possible to adapt existing direct reduction plant towards hydrogen reduction with a minimal investment and equipment investments, it is moreover possible to operate with variable reducing gas compositions and to adapt to hydrogen availability without detrimental impact on the productivity.

Claims

1 ) A direct reduction plant comprising a direct reduction furnace (1 ) and a reformer (33), said reformer (33) comprising several tubes (51 ) provided with gas supply means (64,65), at least one of said tubes (51 A) being provided with at least one gas supply means (65) able to supply said tube (51 A) with a gaseous hydrogen stream (25) and at least one other tube (51 B) being provided with at least one gas supply means (64) able to supply said other tube (51 B) with a methane-containing gas (24).

2) A direct reduction plant according to claim 1 wherein at least one of the tubes (51 ) is provided with gas supply means (65,64) able to supply said tube (51 ) with the gaseous hydrogen stream (25) or with the methane-containing gas (24), said gas supply means further comprising selection means allowing to supply either only the gaseous hydrogen stream (25) or only the methane containing (24) gas to said tube.

3) A direct reduction plant according to claim 1 wherein at least one of the tubes (51 ) is provided with gas supply means (65) able to supply said tube (51 ) exclusively with the gaseous hydrogen stream (25).

4) A direct reduction plant according to anyone of claims 1 to 3 wherein the gas supply means (64) designed so as to supply the tubes (51A) with a gaseous hydrogen stream (25) is equipped with means to control the H2 flow rate.

5) A direct reduction plant according to claim 3 wherein the at least one of said tube (51 A) wherein the hydrogen stream (25) is exclusively supplied is filled with solid particles.

6) A direct reduction plant according to claim 5 wherein said particles are made of ceramic or of a high temperature alloy.

7) A method for producing direct reduced iron (12) in a direct reduction plant according to anyone of claims 1 to 6 wherein oxidized iron (10) is reduced in the direct reduction furnace (1 ) using a reducing gas (11 ) to produce direct reduced iron (12), the method comprising:

- supplying a methane containing gas (24) with the gas supply means (64) to at least one of the tubes (51 B) of the reformer (33) to subject said methane- containing gas (24) to a reforming step to produce a reformed gas (41 ),

- supplying a gaseous hydrogen stream (25) with the gas supply means (65) to at least one of the tubes (51 A) of the reformer (33) to heat said gaseous hydrogen stream (25) to a temperature from 800°C to 1100°C,

- mixing at least the reformed gas (41 ) and the heated gaseous hydrogen stream (42) to form the reducing gas (11 ),

- injecting the reducing gas (11 ) into the direct reduction furnace (1 ).

8) A method according to claim 7 wherein oxygen (27) is injected in the reducing gas (11 ) before its injection into the direct reduction furnace (1 ).

9) A method according to anyone of claims 7 or 8 wherein the gaseous hydrogen stream (25) comprises more than 70% in volume of hydrogen.

10) A method according to anyone of claims 7 to 9 wherein the reducing gas (11 ) comprises at least 50% in volume of H2.

11 ) A method according to anyone of claims 7 to 10 wherein a direct reduction top gas (20) exits the direct reduction furnace, and the methane-containing gas (24) comprises at least a part (21 A) of said direct reduction top gas (20).

12) A method according to anyone of claims 7 to 10 wherein the gaseous hydrogen stream (25) is green hydrogen.