Method for producing direct reduced iron and DRI production facility

Abstract

A method for producing direct reduced iron, in which iron ore is reduced in a DRI shaft by reducing gas comprising hydrogen obtained by thermal cracking of methane inside a plasma torch, the reducing gas further comprising top gas coming from the DRI shaft, as well as a DRI production installation comprising a DRI shaft (1) and a plasma torch (40), the plasma torch being connected on one side to a methane source (41) and on the other side to the DRI shaft (1), the DRI shaft being provided with a recycle loop allowing the top gas to be injected back into the DRI shaft.

Description

[Technical Field]

[0001] The present invention relates to a method for producing direct reduced iron (DRI) and a DRI production facility. [Background technology]

[0002] Currently, steel can be produced through two main manufacturing routes. The most commonly used production route today is by producing pig iron in a blast furnace using a reducing agent, primarily coke, to reduce iron oxide. This process consumes approximately 450-600 kg of coke per metric ton of pig iron, and the process releases large amounts of CO2, both in the production of coke from coal in the coking plant and in the production of pig iron.

[0003] The second main route involves the so-called "direct reduction process", among which are processes under the brands MIDREX, FINMET, ENERGIRON / HYL, COREX, FINEX, etc., in which sponge iron is produced from the direct reduction of an iron oxide support in the form of HDRI (high-temperature direct reduced iron), CDRI (low-temperature direct reduced iron) or HBI (high-temperature briquetted iron). Sponge iron in the form of HDRI, CDRI and HBI is usually further processed in an electric arc furnace.

[0004] Each direct reduction shaft with low-temperature DRI discharge has three zones: a reduction zone at the top, a transition zone in the middle, and a conical bottom cooling zone. In high-temperature DRI, this bottom section is primarily used for homogenizing the product before discharge.

[0005] Iron oxide reduction occurs in the upper section of the furnace at temperatures up to 950°C. Iron oxide ore and pellets, containing approximately 30% oxygen by weight, are charged directly to the top of the reduction shaft and allowed to descend by gravity through the reducing gas. This reducing gas enters the furnace at the bottom of the reduction zone and flows countercurrently to the charged iron oxide. Oxygen contained in the ore and pellets is removed by the gradual reduction of the iron oxide in a countercurrent reaction between the gas and the oxide. As the gas moves to the top of the furnace, the oxidant content of the gas increases.

[0006] Reducing gases generally include hydrogen and carbon monoxide (synthesis gas) and are obtained by catalytic reforming of natural gas. For example, in the so-called MIDREX process, first methane is converted to a reformer to produce synthesis gas or reducing gas by the following reaction: CH4+CO2→2CO+2H2 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 / H20 At the end of the reduction zone, the ore is metallized.

[0007] A transition section is found below the reduction section, which is long enough to separate the reduction section from the cooling section, allowing independent control of both sections. In this section, carbonization of the metallization product occurs. Carbonization is a process that increases the carbon content of the metallization product inside the reduction furnace by the following reaction: 3Fe+CH4→Fe3C+2H2 (endothermic) 3Fe+2CO→Fe3C+CO2 (heat) 3Fe+CO+H2→Fe3C+H2O (heat)

[0008] Injection of natural gas into the transition zone uses the sensible heat of the metallization products in the transition zone to promote hydrocarbon cracking and carbon deposition. Due to the relatively low concentration of oxidants, natural gas in the transition zone is more likely to be cracked to H2 and carbon than reformed to H2 and CO. Natural gas cracking provides carbon for DRI carbonization while simultaneously adding a reducing agent (H2) to the gas to increase the gas reduction potential.

[0009] Considering the significant increase in atmospheric CO2 concentrations since the beginning of the last century and the subsequent greenhouse effect, it is essential to reduce CO2 emissions where CO2 is produced in large quantities, and therefore especially during DRI production.

[0010] As explained above, it is known to use reducing gas generated by chemically reforming a mixture of methane and overhead gas from a reduction furnace to produce a gas rich in hydrogen and carbon monoxide. The mixture flows through catalyst tubes where it is converted to a gas containing hydrogen and carbon monoxide. However, such a process requires the use of a catalyst, typically Ni / Al2O3, which is highly endothermic and must be used at high temperatures above 1100 K. Furthermore, the catalyst is very sensitive to impurities, which can poison the catalyst and significantly reduce the yield of such chemical reforming processes. Summary of the Invention [Problem to be solved by the invention]

[0011] Based on the above, there is a need for a process for producing direct reduced iron that is CO2 neutral, environmentally friendly, and easy to implement while exhibiting good yields. [Means for solving the problem]

[0012] This problem is solved by a method for producing direct reduced iron, in which iron ore is reduced in a DRI shaft by a reducing gas comprising hydrogen obtained by thermal cracking of methane inside a plasma torch, said reducing gas further comprising top gas coming from said DRI shaft.

[0013] The method of the invention may also comprise the following optional features, considered separately or according to all possible technical combinations: - hydrogen is mixed with the top gas before being injected into the DRI shaft; the reducing gas is heated after mixing with the top gas and said hydrogen, - Heating of reducing gas is carried out using CO2-neutral electricity, - the reducing gas is injected into the reducing section of the DRI shaft; - the top gas coming from the DRI shaft is scrubbed to remove water before being added to the reducing gas; The ratio of top gas to hydrogen is set between 5:1 and 1:5, The carbon content of the direct reduced iron is set to 0.5 to 5 wt%.

[0014] Within the scope of the present invention, direct reduced iron covers so-called DRI, but also high temperature briquette iron (HBI), low temperature direct reduced iron (CDRI) and high temperature direct reduced iron (HDRI). Such material can subsequently be used in different processes, for example to produce pig iron in a blast furnace or to produce steel in a BOF or electric arc furnace. It can also be used as a combustible or as an electrode in a battery.

[0015] The present invention also relates to a DRI production facility comprising a DRI shaft and a plasma torch, the plasma torch being connected on one side to a methane supply source and on the other side to the DRI shaft, the DRI shaft being provided with a recycle loop that allows its top gas to be injected back into the DRI shaft.

[0016] The installation may also include the following optional features, considered separately or according to all possible technical combinations: a mixer that can be connected to the outlet of the plasma torch and the top of the DRI shaft on one side and to the DRI shaft on the other side; heating means may be provided in the mixer, said heating means being powered by CO2-neutral electricity; The mixer may be connected to a reduction section of the DRI shaft; A scrubber may be connected to the top gas outlet of the DRI shaft.

[0017] Other characteristics and advantages of the present invention will become apparent from the description of the invention given below by way of indication and which is in no way limiting, with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 shows a DRI manufacturing facility according to the present invention. [Figure 2] 1 is a diagram showing a preferred embodiment of a DRI production facility according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0019] Elements in the figures are illustrative and may not be drawn to scale.

[0020] 1 is a schematic diagram of a DRI production facility according to the present invention. The DRI production facility includes a DRI shaft 1 that, from top to bottom, comprises an inlet 10 for iron ore moving through the shaft by gravity, a reduction section located in the middle of the shaft, a cooling section located at the bottom, and an outlet 12 from which direct reduced iron is finally extracted.

[0021] At the top of the shaft, the top gases exiting the DRI shaft are collected in pipe 20 connected to the DRI shaft 1, thereby creating a recycle loop for such top gases to be reinjected back into the DRI shaft. The gases travel countercurrent to the iron ore flow to the bottom.

[0022] In a preferred embodiment, the top gases can be reinjected into the reduction section of the DRI shaft through pipe 11.

[0023] The DRI production facility further comprises a plasma torch 40 connected on one side to a methane supply source 41 and on the other side to the DRI shaft 1 by a connecting pipe 42 .

[0024] A plasma torch is a device for generating a directional flow of plasma. Thermal plasma can be generated in a plasma torch by applying electrical energy to a gas. The electrical energy can be direct current, alternating current, radio frequency, or other types of electrical discharge. In a direct current torch, an electric arc is formed between electrodes, which can be made of, for example, copper, tungsten, graphite, or silver. The thermal plasma is formed from the input of gas and projects outward as a plasma jet.

[0025] The most commonly used plasma types are dielectric barrier discharge, microwave, and gliding arc plasma. Dielectric barrier discharges are created by applying a potential difference between two electrodes, at least one of which is covered by a dielectric barrier. They typically operate at room temperature and are called cold plasmas.

[0026] Microwave and gliding arc plasmas are called warm plasmas because they operate at higher temperatures (typically 1000-3000 K).

[0027] In the framework of the present invention, plasma can be created by using methane as a plasma generating gas, allowing the non-oxidative conversion of CH4 to hydrogen and solid carbon. Methane is converted into an ionized gas consisting of various chemically active species such as radicals, ions, excited atoms and molecules, and electrons. The electrons in the plasma absorb the applied electrical energy and activate molecules by excitation, ionization, and dissociation, creating the aforementioned reactive species that can further react to form new molecules. This allows chemical conversion to occur.

[0028] It is also possible to use another gas to initiate the plasma and introduce methane in a second step in such a plasma and convert it as described above.

[0029] Those skilled in the art know how to control the quality of the plasma as a function of gas pressure and torch input power. In a preferred embodiment, the specific energy input (SEI, i.e., the ratio of plasma power to gas flow rate) is between 0.1 and 500 kJ·l. -1 , preferably 100 to 400 kJ·l -1 This makes it possible to reach a conversion rate of methane to hydrogen of 50 to 99% by volume, preferably 70 to 99% by volume.

[0030] Plasma is highly flexible and can be easily switched on and off, allowing it to use intermittently produced, CO2-neutral electricity from renewable sources that cannot be stored on the grid.

[0031] CO2-neutral electricity from renewable sources is defined as energy collected from renewable sources that are naturally replenished on human timescales, including sources such as sunlight, wind, rain, tides, waves and geothermal heat.

[0032] In one embodiment, whenever hydrogen from the cracking of methane is not produced in sufficient quantities, for example due to partial unavailability of electricity from renewable sources, an additional supply of hydrogen can be injected into the reduction section of the DRI shaft.

[0033] The DRI production facility may further comprise a scrubber 2 located at the top gas outlet of the DRI shaft before reinjection into shaft 1. The top gas leaving the DRI shaft typically contains H, CO, CH, H0, CO, and N in varying proportions. The top gas scrubbing operation makes it possible to remove water vapor from the remainder of the stream, improving its reduction potential.

[0034] In a preferred embodiment, after scrubbing, the overhead gas contains 40-75% by volume H, 0-30% by volume carbon monoxide CO, 0-10% by volume methane CH, 0-25% by volume carbon dioxide CO, up to 5% by volume H0, and the remainder nitrogen N. After scrubbing, the H / N ratio in such overhead gas is preferably 1.5-3.

[0035] As the top gas leaves the scrubber 2, it can optionally be compressed and / or reheated before its re-injection in the DRI shaft through the connecting pipe 11. In a preferred embodiment, its temperature is set in the range of 700°C to 1000°C, preferably 800 to 1000°C.

[0036] To increase the carbon content of the direct reduced iron, an additional carbon source can be injected into the transition section 50 and / or the cooling section of the shaft 1. Such additional carbon source can be in gaseous and / or solid form, and can consist of, for example, biogas and / or biocoal. It is also possible to use solid carbon formed as a by-product of the plasma conversion of methane as such an additional carbon source, or even as the sole carbon source for setting the carbon content of the direct reduced iron.

[0037] Biogas is a renewable energy source that can be obtained by decomposing organic matter in the absence of oxygen inside a closed system called a bioreactor. Biogas can be produced from raw materials such as agricultural waste, manure, municipal waste, plant material, sewage, biological waste, food waste, or any biodegradable material.

[0038] Biocoal is a carbon-neutral fuel that can replace fossil coal in industrial processes. It is produced by pyrolysis and carbonization of biomass under controlled temperature and residence time conditions. Thermal conversion of biomass, carried out under oxygen-free conditions, removes volatile organic compounds and cellulose components from the feedstock, allowing for the creation of a solid biofuel with characteristics similar to fossil coal.

[0039] In a preferred embodiment, the carbon content of the direct reduced iron is set to 0.5 to 5% by weight, preferably 1 to 3% by weight, or 2 to 3% by weight, which makes it possible to obtain direct reduced iron that can be easily handled and maintains a good burning potential and a good level of passivation for its future use.

[0040] The DRI production facility may further comprise a recycle loop in the cooling section that allows a portion of the gas present at that level to be extracted and sent to a scrubber 30 and then sent to a compression unit 31 before being reinjected into shaft 1.

[0041] 2 shows a schematic DRI production facility according to another embodiment of the present invention. At the top of the shaft, the top gases exiting the DRI shaft are collected in a pipe 20 connected to a scrubber 2 for removing water vapor from the remainder of the stream, similar to the facility of FIG. 1.

[0042] In a preferred embodiment, after scrubbing, the overhead gas contains 40-75% by volume H, 0-30% by volume carbon monoxide CO, 0-10% by volume methane CH, 0-25% by volume carbon dioxide CO, up to 5% by volume H0, and the remainder nitrogen N. After scrubbing, the H / N ratio in such overhead gas is preferably 1.5-3.

[0043] The scrubbed gas can then be sent to one of the inlets of the mixer 4 through a connecting pipe 21 .

[0044] The other inlet of the mixer 4 is connected to the outlet of a plasma torch 40 to take in hydrogen produced by cracking methane coming from a methane source 41 .

[0045] After mixing, the reducing gas can optionally be heated through heating means provided in the mixer, such heating means being powered by CO2-neutral electricity. In a preferred embodiment, the temperature of the reducing gas is set in the range of 700°C to 1000°C, preferably 800 to 1000°C.

[0046] The reducing gas made from the overhead gas and hydrogen is then sent back through line 11 to the DRI shaft, preferably to the reducing section thereof.

[0047] In a preferred embodiment, the ratio of top gas to hydrogen is set to 5:1 to 1:5, preferably 2:1 to 1:2. Such a ratio is specifically defined to control the respective amounts of H2 and CO in the reducing stream. If the proportion of CO has to be increased, the proportion of top gas in the reducing gas is increased. If the proportion of H2 has to be increased, the proportion of top gas in the reducing gas is decreased.

[0048] To increase the carbon content of the direct reduced iron, an additional carbon source can be injected into the transition section 50 and / or the cooling section. Such additional carbon source can be in gaseous and / or solid form, and can consist of, for example, biogas and / or biocoal. It is also possible to use solid carbon formed as a by-product of the plasma conversion of methane as such an additional carbon source, or even as the sole carbon source for setting the carbon content of the direct reduced iron.

[0049] In a preferred embodiment, the carbon content of the direct reduced iron is set to 0.5 to 5 wt %, preferably 1 to 3 wt %, or 2 to 3 wt %, which makes it possible to obtain direct reduced iron that can be easily handled and maintains a good combustion potential for its future use.

[0050] By using the method according to the invention, direct reduced iron can be produced with suitable quality and yield while remaining CO2-neutral and making optimal use of green resources such as intermittent CO2-neutral electricity from renewable sources.

Claims

1. 1. A method for producing direct reduced iron, wherein iron ore is reduced in a DRI shaft by a reducing gas comprising hydrogen obtained by thermal cracking of methane inside a plasma torch, the reducing gas further comprising top gas coming from the DRI shaft, the thermal cracking of methane also producing solid carbon, the solid carbon being injected into a transition section and / or a cooling section of the DRI shaft as a carbon source for setting the carbon content of the direct reduced iron produced.

2. The method of claim 1 , wherein the hydrogen is mixed with the top gas before being injected into the DRI shaft.

3. 3. The method of claim 2, wherein such reducing gas is heated after mixing with said top gas and said hydrogen.

4. The heating of the reducing gas is ２ 4. The method of claim 3, performed using neutral electricity.

5. The method of any one of claims 1 to 4, wherein the reducing gas is injected into a reducing section of the DRI shaft.

6. The method of any one of claims 1 to 5, wherein the top gas coming from the DRI shaft is scrubbed to remove water before being added to the reducing gas.

7. The method according to any one of claims 1 to 6, wherein the ratio of top gas to hydrogen is set between 5:1 and 1:

5.

8. The method according to claim 7, wherein the carbon content of the direct reduced iron is set to 0.5 to 5 wt. %.

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