Process for producing direct reduced iron

Abstract

A method for producing direct reduced iron, in which iron ore is reduced in a direct reduction furnace by a reducing gas, which leaves the furnace through the top as top reducing gas, which is captured and at least partially subjected to a CO2 recovery step during which it is split into two streams, a CO2-rich stream and a CO2-poor stream, which is subjected to an alkanol production step to produce an alkanol product.

Description

[Technical Field]

[0001] The present invention relates to a method for producing direct reduced iron. [Background technology]

[0002] Currently, steel can be produced through two main manufacturing routes. The most commonly used production route today is to produce 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 very large amounts of CO2 in both the production of coke from coal in the coking plant and the production of pig iron. The produced pig iron is then decarburized, for example in a converter or basic oxygen furnace (BOF), to produce steel, which is then refined to obtain the appropriate composition. This is referred to as the BF-BOF route.

[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 / intermediate zone in the middle, and a conical bottom cooling zone. In high-temperature discharge DRI, this bottom section is primarily used for product homogenization before discharge, followed by overall solids control.

[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 3Fe+2CO→Fe3C+CO2 3Fe+CO+H2→Fe3C+H2O

[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, the natural gas in the transition zone is more likely to be cracked to H2 and carbon than reformed to H2 and CO. Hydrocarbon cracking provides carbon for DRI carbonization while simultaneously adding a reducing agent (H2) to the gas to increase the gas reduction potential.

[0009] Gas injection is also performed in the cooling zone, typically consisting of recirculating the cooling gas and adding natural gas. The addition of natural gas (NG) to the cooling gas allows operators to maintain a recirculating cooling gas circuit with a high methane content; otherwise, the main component in the cooling gas is nitrogen. Natural gas has a much higher heat capacity than N2: the cooling gas recirculation flow is 500-600 Nm3 / t with NG and 800 Nm3 / t without NG. While there is not much carbon deposition in the cooling zone, the upward flow of cooling gas to the higher furnace levels provides more hydrocarbons for cracking.

[0010] As can be seen from the above reactions, even though the direct reduction route has a lower CO footprint than the BF-BOF route, the direct reduction step is still a source of CO. Summary of the Invention [Problem to be solved by the invention]

[0011] There is a need for methods that allow for further reductions in carbon emissions.

[0012] There is also a need for a method that allows for increasing the carbon content of DRI products without the need for an external carbon source. The carbon content of DRI products is an important parameter in the process, playing a key role in subsequent steps, but also helping to improve the transportability of DRI products. [Means for solving the problem]

[0013] This problem is solved by a method according to the invention, in which iron ore is reduced in a direct reduction furnace by a reducing gas, which leaves the furnace through the top as top reducing gas, which is captured and at least partially subjected to a CO2 recovery step during which it is split into two streams, a CO2-rich stream and a CO2-poor stream, and the CO2-rich stream is subjected to an alkanol production step to produce the alkanol product.

[0014] The method of the invention may also comprise the following optional features, considered separately or according to all possible technical combinations: the alkanol product is then at least partially injected into a direct reduction furnace; The CO2-poor stream is reinjected into the furnace as a reducing gas, the CO2-rich stream contains 80-100% carbon dioxide by volume; 1 to 20% by volume of overhead reducing gas is subjected to the alkanol production step; - feeding the hydrogen stream to an alkanol production step to react with the CO2-rich stream; the alkanol product produced is a gas that is mixed with a reducing gas before its injection into the furnace; The alkanol produced is liquid, The produced alkanol is injected separately from the reducing gas in the transition zone of the furnace; The resulting alkanol is injected into the cooling zone of the furnace, - the alkanol chain contains 1 to 5 carbons, -alkanol product is methanol, -alkanol product is ethanol, Prior to its injection into the direct reduction furnace, the reducing gas is heated in a reducing gas preparation step, said reducing gas preparation step delivering a prepared exhaust gas which is at least partly fed to the alkanol production step.

[0015] The present invention also relates to a direct reduction plant for carrying out the process according to the invention, which comprises an alkanol production unit.

[0016] 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]

[0017] [Figure 1] FIG. 1 shows the layout of a direct reduction plant making it possible to carry out the method according to the invention. [Figure 2A] FIG. 1 shows curves simulating the increase in carbon content in DRI products when liquid ethanol or methanol is injected. [Figure 2B] FIG. 1 shows curves simulating the increase in carbon content in DRI products when liquid ethanol or methanol is injected. DETAILED DESCRIPTION OF THE INVENTION

[0018] Elements in the figures are illustrative and may not be drawn to scale.

[0019] Figure 1 shows the layout of a direct reduction plant making it possible to carry out the method according to the invention. A direct reduction furnace (or shaft) 1 is charged at its top with iron oxide 10 in the form of ore or pellets. The iron 10 is reduced in the furnace 1 by reducing gas 11, which is injected into the furnace and flows countercurrently to the iron oxide. Reduced iron 12 leaves the bottom of the furnace 1 for further processing, such as briquetting, before being used in a subsequent steelmaking step. After reducing the iron, the reducing gas leaves the top of the furnace as top reducing gas 20 (TRG).

[0020] The top reducing gas 20 typically contains 15-25% v CO, 12-20% v CO2, 35-55% H2, 15-25% v H2O, 1-4% N2. It has a temperature of 250-500°C.

[0021] Cooling gas 13 is captured from the cooling zone of the furnace, subjected to a cleaning step in a cleaning device 30 such as a scrubber, compressed in a compressor 31 and then sent back to the cooling zone of the shaft 1 .

[0022] According to the invention, the top reducing gas 20, preferentially after a dust and mist removal step in a washing device 5 such as a scrubber and demister, is sent to a CO2 recovery device 8, where CO2 from the top reducing gas is concentrated and split into a CO2-poor stream 21 and a CO2-rich stream 22. The CO2-poor first stream 21 is sent to a preparation device 7, where it is mixed with other gases, optionally reformed and heated to produce the reducing gas 11. In a preferred embodiment, the preparation device 7 is a reformer. The preparation device 7 outputs a prepared exhaust gas 27, also called stack gas.

[0023] The CO2 capture unit may be an absorber, an adsorber, a cryogenic distillation unit or a membrane. It may also be a combination of these different units.

[0024] The second stream 22, which is rich in CO2 and preferably represents 1-20% v of the overhead reduction gas 20, is sent to the alkanol generator 6 for an alkanol production step. This second stream may contain 80-100% v of CO2. In the alkanol generator 6, the CO2 may first be converted to carbon monoxide CO. This may be done, for example, if hydrogen is available in sufficient quantities, by a hydrogenation step to produce CO according to the following reaction: CO2+H2→CO+H2O This reaction is called the reverse water gas shift reaction (RGWS). This reaction is carried out in the presence of a catalyst such as ZnAl2O4 or Fe2O3 / Cr2O3.

[0025] It may also be done by thermochemical conversion such as the Boudoir reaction or methane reforming, by electrochemical conversion or using plasma technology.

[0026] The CO thus produced is then converted into alkanols according to the Fischer-Tropsch reaction: 2nH2+nCO→C n H 2n+1 OH+(n-1)H2O In the formula, n is an integer of 1 or more, and preferably 1 to 5.

[0027] Those skilled in the art know how to select the appropriate catalyst and / or process conditions to carry out the desired Fischer-Tropsch reaction and produce the target hydrocarbons.

[0028] The conversion of CO to alkanols can be carried out in a two-step process as described, but can also be carried out by direct synthesis, i.e., in a single step. In a preferred embodiment, it is a fermentation process.

[0029] In a preferred embodiment, the CO and H contained in the CO rich stream 22 react to form methanol CHOH according to the following reaction: CO2+4H2→CH3OH+2H2O

[0030] In this embodiment, the alkanol producer is a methanol producer 6, such as a catalytic reactor or a bioreactor.

[0031] If the H content in the overhead reduction gas, and thus in the second stream 22, is insufficient for the alkanol production reaction, an additional H stream 40 may be fed to the alkanol production unit 6. This H stream may be provided by a dedicated H production plant 9, such as an electrolysis plant. It may also be a water or steam electrolysis plant. It preferably operates using CO2-neutral electricity, which specifically includes electricity from renewable sources, 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. In some embodiments, the use of electricity from nuclear sources can be used, since the CO2 produced is not emitted.

[0032] This H2 stream 40 may also be added to the reducing gas 11.

[0033] The stack gas 27 may also be fed to the alkanol production unit 6 .

[0034] In a preferred embodiment, the alkanol product 23 exiting the hydrocarbon production unit 6 is reinjected into the furnace 1 .

[0035] In a first embodiment, represented by stream 24, this alkanol product 23 is a gas that is mixed with a reducing gas in the preparation apparatus.

[0036] In a second embodiment, represented by stream 25, it is either injected into the furnace together with the reducing gas or separately into the transition zone of the furnace. In a third embodiment, represented by stream 26, it is either injected into the furnace together with the cooling gas 13 or separately into the cooling zone of the furnace. The alkanol product 23 may be in gaseous and / or liquid form. All of these embodiments may be combined with each other.

[0037] In all embodiments, the alkanol product serves as a carbon source for the DRI product. In a preferred embodiment, the carbon content of the direct reduced iron is set to 0.5-3 wt.%, preferably 1-2 wt.%, which makes it possible to obtain direct reduced iron that is easy to handle and maintains good combustion potential for its future use. The amount of gas sent to the alkanol generator can be controlled depending on the amount of carbon required for the DRI product.

[0038] Figures 2A and 2B are curves simulating the evolution of the weight percentage of carbon in the direct reduced iron product versus temperature when injecting 100 kg / ton of liquid ethanol DRI (Figure 2A) or 430 kg / ton of liquid methanol DRI (Figure 2B), respectively. In both cases, we find that it is possible to reach a carbon content in the solid product of approximately 2% by weight when the liquid is injected into the transition and / or cooling zones of the furnace. The advantage of ethanol is that it is less needed and more available compared to methanol. The simulations were performed using a thermodynamic model.

[0039] The method according to the invention allows for reducing the carbon footprint of the direct reduction process by capturing and using the emitted CO2, and may avoid the need for an external source to increase the carbon content in the DRI product.

Claims

1. 1. A method for producing direct reduced iron, comprising: reducing iron ore in a direct reduction furnace with a reducing gas, the reducing gas exiting the furnace through the top as top reduction gas, the top reduction gas being captured and at least partially subjected to a CO2 capture step; during the CO2 capture step, the top reduction gas being split into two streams, a CO2-rich stream and a CO2-poor stream, the CO2-rich stream being subjected to an alkanol production step to produce an alkanol product; at least a portion of the alkanol product is then injected into the direct reduction reactor at a transition zone thereof, separately from the reducing gas; method.

2. 10. The method of claim 1, wherein the CO2-poor stream is reinjected into the furnace as a reducing gas.

3. 10. The method of claim 1, wherein the CO2-rich stream contains 80-100% carbon dioxide by volume.

4. 3. The method of claim 2, wherein the CO2-rich stream contains 80-100% carbon dioxide by volume.

5. 5. The method of any one of claims 1 to 4, wherein 1 to 20% by volume of the overhead reducing gas is subjected to the alkanol production step.

6. 5. The process according to any one of claims 1 to 4, wherein a hydrogen stream is fed to the alkanol production step to react with the CO2-rich stream.

7. 5. The method of claim 1, wherein the alkanol product produced is a gas, and at least a portion of the gas is injected into the direct reduction reactor separately from the reducing gas in a transition zone of the direct reduction reactor, and another portion of the gas is mixed with the reducing gas before injection into the reactor.

8. 5. The process of any one of claims 1 to 4, wherein the alkanol produced is a liquid.

9. A process according to any one of claims 1 to 4, wherein the alkanol produced is also injected into the cooling zone of the furnace.

10. 5. The method of claim 1, wherein the alkanol chain contains 1 to 5 carbons.

11. 5. The process of any one of claims 1 to 4, wherein the alkanol product is methanol.

12. 5. The process of any one of claims 1 to 4, wherein the alkanol product is ethanol.

13. 5. The method according to claim 1, wherein prior to injection into the direct reduction furnace, the reducing gas is heated in a reducing gas preparation step, said reducing gas preparation step delivering a prepared exhaust gas which is at least partially fed to the alkanol production step.

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