Direct reduction plant and method for directly reducing iron

Abstract

A direct reduction plant comprising a direct reduction furnace (1) and a reformer (33), wherein the reformer (33) comprises several pipes (51) provided with gas supply means (64, 65), at least one of the pipes (51A) is provided with at least one gas supply means (65) capable of supplying a gaseous hydrogen stream (25) to the pipe (51A), and at least one other pipe (51B) is provided with at least one gas supply means (64) capable of supplying a methane-containing gas (24) to the other pipe (51B).

Description

Technical Field

[0001] The present invention relates to a plant for producing direct reduced iron (DRI) and related methods.

Background Art

[0002] Currently, steel can be produced through two main manufacturing routes. Today, the most commonly used production route is to produce hot metal in a blast furnace by using a reducing agent, mainly coke, to reduce iron oxide. In this method, a total of about 450 - 600 kg of fuel per metric ton of hot metal is consumed. This method emits a significant amount of CO2 both in the production of coke from coal in a coking plant and in the production of hot metal.

[0003] The second main route includes the so-called "direct reduction method". Among them, there are methods especially by the brands MIDREX or ENERGIRON / HYL, where sponge iron is produced in the form of HDRI (hot direct reduced iron), CDRI (cold direct reduced iron) or HBI (hot briquette iron) from the direct reduction of an iron oxide carrier. Sponge iron in the form of HDRI, CDRI, or HBI is usually further processed in an electric arc furnace.

[0004] Each direct reduction shaft with low-temperature DRI discharge has three zones: a top reduction zone, a central transition zone, and a conical bottom cooling zone. In high-temperature discharge DRI, this bottom is mainly used for homogenization of the product before discharge.

[0005] The reduction of iron oxide occurs in the upper part of the furnace at temperatures up to 950°C. Iron ore in the form of lumpy ore and / or pellets containing about 30% oxygen by weight can be charged to the top of the direct reduction shaft furnace and descend by gravity through a reducing gas. This reducing gas enters the furnace from the bottom of the reduction zone and flows countercurrently to the charged iron ore. The oxygen contained in the iron ore is removed through the stepwise reduction of iron oxide by the gaseous reducing agent. While the gas is moving to the upper part of the furnace, the oxidant content in the gas phase is increasing.

[0006] Reducing gases generally contain hydrogen and carbon monoxide and are obtained by reforming natural gas. For example, in the so-called MIDREX process, the first methane is converted into a reformer according to the following reaction to produce synthesis gas or reducing gas. CH4 + CO2 → 2CO + 2H2 CH4 + H2O → CO + 3H2

[0007] Iron oxide reacts with reducing gases, for example, according to the following reaction. 3Fe2O3 + CO / H2 → 2Fe3O4 + CO2 / H2O Fe3O4 + CO / H2 → 3FeO + CO2 / H2O FeO + CO / H2 → Fe + CO2 / H2O

[0008] At the edge of the reduction zone, the ore is metallized.

[0009] The transition zone is located below the reduction zone. This zone is long enough to separate the reduction zone from the cooling zone, allowing for independent control of both parts. In this zone, carbonization of the metallization products occurs. Carbonization is a method of increasing the carbon content of the direct reduction products inside the reduction furnace, particularly through the following reactions. 3Fe+CH4→Fe3C+2H2 (endothermic) 3Fe + 2CO → Fe3C + CO2 (exothermic reaction) 3Fe + CO + H2 → Fe3C + H2O (exothermic reaction)

[0010] Injecting natural gas into the transition zone promotes hydrocarbon cracking and carbon deposition by utilizing the sensible heat of the direct reduction products in the transition zone. Due to the relatively low concentration of oxidizer, natural gas in the transition zone is more prone to cracking to H2 and carbon than to reforming to H2 and CO. Cracking of natural gas provides carbon for DRI carbonization and simultaneously adds a reducing agent (H2) to the gas, increasing the gas reduction potential.

[0011] Given the significant increase in atmospheric CO2 concentration since the beginning of the last century and the subsequent greenhouse effect, it is essential to reduce emissions of CO2, particularly those generated during DRI production.

[0012] One solution currently under development involves gradually increasing the hydrogen content in the reducing gas, with the goal of reaching a pure hydrogen-reduced gas. The following reduction reaction then occurs. Fe2O3 + 3H2 = 2Fe + 3H2O

[0013] Thus, instead of releasing the greenhouse gas CO2, it releases harmless H2O.

[0014] As will be discussed later, this transition from methane-based DRI to H2-based DRI is gradual for several reasons. Existing plants need to adapt their equipment and assess the impact on subsequent steelmaking processes. The most preferred hydrogen source is green hydrogen, which reduces the overall carbon footprint, but currently, it is not available in sufficient quantities to meet all needs. However, the future availability of green hydrogen will depend heavily on the capacity of renewable energy sources.

[0015] As a result, the plant must operate in a hybrid mode between NG-based DRI technology and H2-DRI technology. [Overview of the Initiative] [Problems that the invention aims to solve]

[0016] Therefore, there is a need for equipment that can operate by changing the hydrogen content in the reducing gas. There is also a need for a direct reduction method that can operate by increasing the hydrogen content in the reducing gas without negatively impacting productivity, compared to existing natural gas-based methods. [Means for solving the problem]

[0017] This problem is solved by a plant according to the present invention comprising a direct reduction furnace and a reformer, the reformer comprising several pipes provided with gas supply means, at least one of the pipes provided with at least one gas supply means capable of supplying a gaseous hydrogen flow to the pipe, and at least one other pipe provided with at least one gas supply means capable of supplying a methane-containing gas to the other pipe.

[0018] The plant of the present invention may also include the following optional features, which may be considered separately or in all possible technical combinations. -At least one of the pipes is provided with a gas supply means capable of supplying a gaseous hydrogen stream or a methane-containing gas to the pipe, and the gas supply means further comprises a selection means that enables supplying either only a gaseous hydrogen stream or only a methane-containing gas to the pipe. -At least one of the pipes is provided with a gas supply means capable of supplying only a gaseous hydrogen flow to the pipe, - A gas supply means designed to supply a gaseous hydrogen flow to a pipe includes means for controlling the H2 flow rate, - At least one of the tubes to which only a hydrogen stream is supplied is filled with solid particles, -Solid particles are made from ceramics or high-temperature alloys.

[0019] The present invention also relates to a method for producing iron directly reduced in a direct reduction plant, which is any one of the prior combinations, in which iron oxide is reduced in a direct reduction furnace using a reducing gas to produce iron directly reduced, the method comprising: supplying a methane-containing gas to at least one of the pipes of a reformer by gas supply means and subjecting the methane-containing gas to a reforming step to generate a reformed gas; supplying a gaseous hydrogen stream to at least one of the pipes of a reformer by gas supply means and heating the gaseous hydrogen stream to a temperature of 800°C to 1100°C; mixing at least the reformed gas and the heated gaseous hydrogen stream to form a reducing gas; and injecting the reducing gas directly into a reduction furnace.

[0020] The method of the present invention can also include the following optional features, considered separately or in all possible technical combinations. - Oxygen is injected into the reducing gas before being injected into the direct reduction furnace, - The gaseous hydrogen stream contains more than 70% hydrogen by volume, - The reducing gas contains at least 50% H2 by volume, - The direct reduction top gas exits the direct reduction furnace and the methane-containing gas contains at least a portion of the direct reduction top gas, - The gaseous hydrogen stream is green hydrogen.

[0021] Other features and advantages of the present invention will become apparent from the description thereof, which is given below by reference to the accompanying drawings, which are by no means limiting.

Brief Description of the Drawings

[0022] [Figure 1] Shows a direct reduction plant that enables the method according to the present invention to be implemented. [Figure 2] Shows an embodiment of a reformer that enables the method according to the present invention to be implemented. [Figure 3A] Shows another reformer that enables the method according to the present invention to be implemented. [Figure 3B] It is an enlarged view of the injection means of the reformer of FIG. 3A.

Modes for Carrying Out the Invention

[0023] The elements of the figures are illustrative and may not be drawn to scale.

[0024] Figure 1 shows a direct reduction (DR) plant according to the present invention. The DR plant includes a DR shaft or furnace 1 from top to bottom, equipped with a charging device 10 for oxide ore, such as iron ore, the iron ore moving through the shaft 1 by gravity, and includes a reduction section located at the top of the shaft, a transition section located in the middle of the shaft, and optionally a cooling section located at the bottom, from which reduced iron 12 is finally extracted directly.

[0025] Iron ore containing iron oxide, such as hematite or magnetite, is charged into the upper part of the direct reduction furnace (or shaft furnace) 1. This iron oxide is injected into the furnace and reduced in the furnace 1 by a reducing gas 11 flowing countercurrently over the iron oxide. If cold DRI is expected as the final product, the directly reduced iron needs to be cooled in a cooling zone. If such a cooling zone exists, the reduced iron 12 exits the bottom of the furnace 1 at a temperature below 65°C, preferably 30°C to 65°C, for further processing such as briquetting before being used in subsequent steelmaking steps. The reducing gas exits the upper part of the furnace as top gas 20 (TG) after reducing the iron.

[0026] The direct reduction plant 1 further comprises a reformer 33 having several pipes 51 provided with gas supply means 64, 65. At least one of the pipes 51A is provided with at least one gas supply means 64 that enables the supply of a gaseous hydrogen flow 25 to the associated pipe 51A, and at least one other pipe 51B is provided with at least one gas supply means 65 that enables the supply of methane-containing gas 24 to this other pipe 51B.

[0027] Next, the reducing gas 11 includes the reformed gas 41 produced 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 of 800°C to 1100°C and is produced by heating the hydrogen gas stream 25 to the same reformer 33 used for reforming the methane-containing gas 24.

[0028] Methane reforming is a well-known technique in which methane reacts with vapor and / or carbon dioxide in the presence of a catalyst to form carbon oxides and hydrogen.

[0029] In a preferred embodiment, the hydrogen gas stream 25 is green hydrogen. Green hydrogen (GH or GH2) is hydrogen produced by renewable energy or low-carbon electricity. This H2 stream may be supplied by a dedicated H2 production plant, such as an electrolysis plant. It may be a water or steam electrolysis plant. It is preferably powered by CO2-neutral electricity, particularly electricity from renewable resources, which are defined as energy produced from renewable resources that are naturally replenished on a human timescale, including sources such as sunlight, wind, rain, tides, waves, and geothermal energy. In some embodiments, the use of electricity from nuclear sources can be used because it does not release CO2 during production.

[0030] In a preferred embodiment, the H2 flow 25 enters the reformer at a temperature of ~400°C relative to the ambient temperature. This may have been preheated before being injected into the reformer 33. This preheating is preferably electrically based, powered by CO2 neutral electricity.

[0031] Before its injection into the furnace, oxygen 27 can be added to the reducing gas 11. This addition allows the temperature of the reducing gas to rise as a result of the exothermic reaction induced by the oxygen.

[0032] Reducing gas 1 is preferentially injected into the shaft furnace at a temperature of 900-1200°C. It preferentially contains more than 50% hydrogen by volume.

[0033] The top gas 20 exiting the DRI shaft 1 is collected in a pipe and optionally sent to a water removal step in the scrubber 30, after which it can be split into a process gas flow 21A and a top gas fuel flow 21B. This top gas fuel flow 21B can be supplied as fuel for the burner 53 of the reformer 33. The process gas flow 21A can optionally be subjected to a CO2 removal step in the CO2 removal unit 31 and a second water removal step in the scrubber 32, and then mixed with natural gas 23 to form a methane-containing gas 24 supplied to the reformer 33. The process gas flow 21A may also be sent directly to the reformer 33 without the addition of natural gas 23.

[0034] The top gas emanating from a DRI shaft furnace typically contains H2, CO, CH4, H2O, CO2, and N2 in varying proportions. Top gas scrubbing allows for the removal of water vapor from the rest of the flow, thereby improving its reduction potential.

[0035] The top gas 21 after the scrubber 30 typically contains, by volume, 43-57% H2, 13-28% CO, 12-18% CO2, 2-12% CH4, 1-4% H2O, and 0-3% N2. When subjected to a partial CO2 removal process in the CO2 removal device 22, it typically contains 50-69% H2, 15-20% CO, 2-13% CO2, 9-14% CH4, 1-4% H2O, and 0-3% N2.

[0036] Figure 2 shows an embodiment of a reformer 33 according to the present invention. The reformer 33 comprises gas supply means 64, 65 that enable the supply of gas to a series of reforming tubes 51B, 51A, and at least one main collection tube 52 that enables the collection of gas present in the tubes 51A, 51B. The reformer also comprises a burner 53 to which fuel (not shown) is supplied, and a combustion exhaust collector 54 for recovering exhaust combustion gases. In this first embodiment, at least one reforming tube 51A is supplied with only a hydrogen flow 25 via a hydrogen gas injection means 65, and at the outlet, a heated hydrogen gas flow 42 having a temperature of 800°C to 1100°C is collected, and this tube operates in hydrogen heating mode. The other reforming tubes 51B are supplied with methane-containing gas 24 by appropriate gas injection means 64 as done in the prior art, and reforming gas 41 is collected at the outlet, and these tubes operate in reforming mode. The typical composition of the reformed gas 41 before mixing with the heated H2 stream 42 is, in terms of volume percentage, 54-75% H2, 14-35% CO, 2-7% CO2, up to 5% CH4, up to 6% H2O, and up to 3% N2. Both the reformed gas 41 and the heated hydrogen stream 42 are mixed to form the reduced gas 26 that exits the reformer 33.

[0037] In a preferred embodiment, the reformer 33 is a catalytic reformer, and at least one reforming tube 51A supplied with a hydrogen stream is used to heat the H2 stream. The H2 heating tube 51A is preferably provided with means for adjusting the gas flow rate and is preferably filled with inert particles such as ceramics, or metal particles such as alumina particles or high-temperature alloys. High-temperature alloys are alloys that can withstand temperatures exceeding 500°C. The use of these particles improves heat exchange between the hydrogen gas and the tube wall. Furthermore, the particles also help to reduce the gas velocity, thus preventing potential problems in the main collector 52.

[0038] In Figure 2, only five tubes are shown, one of which is supplied with hydrogen. However, the present invention clearly encompasses embodiments in which the reformer includes several sets of tubes, with either a set of tubes or one set of tubes dedicated to hydrogen heating.

[0039] Figures 3A and 3B show another embodiment of a modifier that enables the implementation of the method according to the present invention. The same reference numerals are used when referring to the same elements as in the previous embodiment.

[0040] In this embodiment, the reformer 33, as in the previously described embodiment, includes a main collector pipe 52 that allows for the collection of gases exiting the pipe 51, a burner (not shown) to which fuel (not shown) is supplied, and a combustion exhaust collector 54 for recovering exhaust combustion gases. In this embodiment, at least one reformer pipe 51 is provided with two gas supply means 64, 65 that can supply a gaseous hydrogen stream 25 and a methane-containing gas 24, respectively. These two gas supply means include selection means, such as an on / off device, that allows either the hydrogen stream 25 or the methane-containing gas 24 to be supplied to the pipe 51. This ensures that only the gaseous hydrogen stream or only the methane-containing gas 24 is supplied to the pipe. In this embodiment, the methane-containing gas 24 is a process gas 21.

[0041] 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 pipe 51. The hydrogen supply means 65 is connected to a hydrogen supply source, which may be a storage container or an H2 distribution grid. Each gas supply means 64, 65 is equipped with a hydrogen release device and a methane release device, respectively. When sufficient hydrogen is available, the hydrogen release device opens and the methane release device closes, thereby allowing only the hydrogen flow 25 to flow through the pipe operating in hydrogen heating mode. On the other hand, when hydrogen is insufficient, the hydrogen release device closes and the methane release device opens, thereby allowing only the methane-containing gas 24 to flow through the pipe operating in reforming mode. If several pipes are equipped with such dual supply means, it is possible that some of them operate in hydrogen heating mode and others operate in reforming mode.

[0042] This allows for equipment flexibility depending on hydrogen availability, enabling operation in pure methane, pure hydrogen, or hybrid methane / hydrogen modes.

[0043] In both embodiments, it will be apparent to those skilled in the art that the gas supply means relates to the main gas supplied to the tube, namely hydrogen and methane-containing gases, so that the tube operates in a so-called hydrogen heating mode or reforming mode. In the case of a tube operating in reforming mode, for example, steam or a process top gas may be supplied together with the methane-containing gas to carry out the reforming reaction.

[0044] The plant according to the present invention makes it possible to adapt existing direct reduction plants to hydrogen reduction with minimal investment and capital expenditure, and furthermore, it can operate with a variable reduction gas composition and adapt to the availability of hydrogen without adversely affecting productivity.

Claims

1. A direct reduction plant comprising a direct reduction furnace (1) and a reformer (33), wherein the reformer (33) comprises several pipes (51) provided with gas supply means (64, 65), at least one of the pipes (51A) is provided with at least one gas supply means (65) capable of supplying a gaseous hydrogen stream (25) to the pipe (51A), and at least one other pipe (51B) is provided with at least one gas supply means (64) capable of supplying a methane-containing gas (24) to the other pipe (51B).

2. The direct reduction plant according to claim 1, wherein at least one of the pipes (51) is provided with a gas supply means (65, 64) capable of supplying a gaseous hydrogen stream (25) or a methane-containing gas (24) to the pipe (51), and the gas supply means further includes a selection means that enables supplying either the gaseous hydrogen stream (25) or the methane-containing gas (24) to the pipe.

3. The direct reduction plant according to claim 1, wherein at least one of the pipes (51) is provided with a gas supply means (65) capable of supplying only a gaseous hydrogen flow (25) to the pipe (51).

4. A direct reduction plant according to any one of claims 1 to 3, wherein a gas supply means (64) designed to supply a gaseous hydrogen stream (25) to a pipe (51A) is provided with means for controlling the H2 flow rate.

5. The direct reduction plant according to claim 3, wherein at least one of the pipes (51A) to which only a hydrogen stream (25) is supplied is filled with solid particles.

6. The direct reduction plant according to claim 5, wherein the particles are made of ceramic or high-temperature alloy.

7. A method for producing directly reduced iron (12) in a direct reduction plant according to any one of claims 1 to 6, wherein iron oxide (10) is reduced in a direct reduction furnace (1) using a reducing gas (11) to produce directly reduced iron (12), - The methane-containing gas (24) is supplied by the gas supply means (64) to at least one of the pipes (51B) of the reformer (33), and the methane-containing gas (24) is subjected to a reforming step to generate reformed gas (41). - A gaseous hydrogen stream (25) is supplied by a gas supply means (65) to at least one of the pipes (51A) of the reformer (33) to heat the gaseous hydrogen stream (25) to a temperature of 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), Methods that include...

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

9. The method according to any one of claims 7 or 8, wherein the gaseous hydrogen stream (25) contains more than 70% hydrogen by volume.

10. The method according to any one of claims 7 to 9, wherein the reducing gas (11) contains at least 50% H2 by volume.

11. The method according to any one of claims 7 to 10, wherein the direct reduction top gas (20) exits the direct reduction furnace and the methane-containing gas (24) contains at least a portion (21A) of the direct reduction top gas (20).

12. The method according to any one of claims 7 to 10, wherein the gaseous hydrogen stream (25) is green hydrogen.

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