Ironmaking process

Abstract

An iron-making process comprising the production of molten iron (2) and top gas (10) from a blast furnace, the process comprising the steps of: capturing at least a portion of the top gas (10); separating CO2 from the captured top gas (10) to produce a CO2-rich stream (12) and a CO2-lean stream (11); mixing the CO2-rich stream (12) with a H2 make-up stream (30) and subjecting the obtained CO2 / H2 gas mixture to a reverse water gas shift reaction in a reactor (3) to produce a reducing stream (13) comprising CO and H2; separating H2 from the reducing stream to produce a CO-rich stream (14) and a H2-rich stream (15); mixing the H2-rich stream (15) with the CO2-rich stream (12) or with the CO2 / H2 gas mixture in the reactor (3) and subjecting the obtained gas mixture to a reverse water gas shift reaction; and feeding at least a portion of the CO-rich stream 14 (13) to at least one chemical or biochemical plant (4) to produce one or more chemical products (16).

Description

Technical Field

[0001] This invention relates to an ironmaking method and related ironmaking equipment. Background Technology

[0002] In a blast furnace, the conversion of iron-bearing furnace charge (sinter, pellets, and iron ore) into cast iron or molten iron is typically carried out by reducing iron oxides with reducing gas (particularly containing CO, H2, and N2), which is formed by the partial combustion of coke and a final auxiliary reducing agent at the tuyeres located at the bottom of the blast furnace. Air preheated to a temperature typically between 1000°C and 1300°C (called hot blast) is injected at these tuyeres.

[0003] To improve productivity and reduce costs, auxiliary reducing agents that can be injected at the vent can be powdered coal, fuel oil, natural gas, or other reducing agents, and combined with the oxygen-enriched hot air.

[0004] The gas recovered from the top of the blast furnace (called top gas) mainly consists of CO, CO2, H2, and N2, with proportions of 20-28% v, 17-25% v, 1-5% v, and 48-55% v, respectively. Although some of this gas is used as fuel for other facilities in the steel plant (coking plant, hot blast stove, etc.) or ultimately for power generation in a power plant, the blast furnace remains a significant source of CO2 production.

[0005] Given the significant increase in atmospheric CO2 concentration since the beginning of the last century and the resulting greenhouse effect, CO2 emissions must be reduced in places where large amounts of CO2 are produced (and therefore especially in blast furnaces).

[0006] As a result, the consumption of reducing agents in blast furnaces has been reduced by half over the past 50 years. Therefore, carbon consumption in conventionally configured blast furnaces has now reached the lower limit related to the laws of thermodynamics.

[0007] One solution considered for further reducing the consumption of this carbon-based reducing agent and thus the CO2 footprint of blast furnace power lines is to capture the top gas and use it for other production processes, such as chemical production—a technology known as carbon capture and utilization (CCU). However, these CCU applications typically require multiple processing steps to provide the appropriate syngas for a given chemical and produce tail gas that limits the amount of CO2 reduction.

[0008] Therefore, a method is needed that allows for further reduction of the CO2 footprint of ironmaking processes. Summary of the Invention

[0009] This problem is solved by an ironmaking method according to the present invention, the method comprising producing molten iron and blast furnace top gas in a blast furnace, the method comprising the steps of: capturing at least a portion of the blast furnace top gas; separating carbon dioxide from the captured blast furnace top gas to produce a CO2-rich stream and a CO2-lean stream; mixing the CO2-rich stream with a hydrogen makeup stream and subjecting the resulting CO2 / H2 gas mixture to a reverse water-gas shift reaction in a reactor to produce a reducing stream containing carbon monoxide (CO) and hydrogen (H2); separating H2 from the reducing stream to produce a CO-rich stream and a H2-rich stream; mixing the H2-rich stream with the CO2-rich stream or with the CO2 / H2 gas mixture in a reactor and subjecting the resulting gas mixture to a reverse water-gas shift reaction; and feeding at least a portion of the CO-rich stream to at least one chemical or biochemical unit to produce one or more chemical products.

[0010] The method of the present invention may also include the following optional features, either individually or according to all possible combinations of techniques:

[0011] - At least one chemical or biochemical device is selected from urea or ammonia production facilities, fermenters or Fischer-Tropsch reactors.

[0012] - At least one chemical or biochemical device is a fermenter capable of using microorganisms to biologically convert one or more of CO, H2, or CO2 into syngas fermentation products.

[0013] - The microorganisms in the fermenter are Clostridium bacteria.

[0014] - The chemical product is an alcohol.

[0015] - Alcohols are selected from the group consisting of methanol, ethanol, butanol and mixtures thereof.

[0016] - Before entering at least one chemical or biochemical unit, the secondary H2 makeup stream is mixed with the CO-rich stream.

[0017] - The H2 supplementary gas stream consists of hydrogen produced by water electrolysis.

[0018] - The gas stream undergoing the reverse water-gas shift reaction is first heated to a temperature of at least 400°C.

[0019] - The gas stream undergoing the reverse water-gas shift reaction is first heated to a temperature of at least 600°C.

[0020] - The airflow is heated by electric heating.

[0021] The electric heating is operated by renewable energy.

[0022] - The gas stream undergoing the reverse water-gas shift reaction has an H2 to CO2 molar ratio of at least 2.

[0023] - The gas stream undergoing the reverse water-gas shift reaction has a molar ratio of H2 to CO2 of 4. Attached Figure Description

[0024] Other features and advantages of the invention will become apparent from the following description, which is given by way of indication and not limitation, and with reference to the accompanying drawings, in which:

[0025] - Figure 1 An embodiment of the method according to the present invention is shown.

[0026] - Figure 2 Another embodiment of the method according to the present invention is shown. Detailed Implementation

[0027] First, it should be noted that in the accompanying drawings, the same reference numerals denote the same elements, regardless of which drawing they appear in or their shape. Similarly, if an element is not specifically labeled in one drawing, its reference numerals can be easily found by referring to another drawing.

[0028] It should also be noted that the accompanying drawings primarily represent one embodiment of the subject matter of the invention, but other embodiments may exist that conform to the definition of the invention. The elements in the drawings are schematic and may not be drawn to scale.

[0029] Figure 1 Ironmaking equipment is shown that allows for the execution of a method according to one embodiment of the invention. The equipment includes at least one blast furnace 1, wherein an iron-bearing charge 4, such as sinter, pellets, or iron ore, is charged into the throat of the blast furnace 1 together with a first carbon-based reducing agent 5. The first carbon-based reducing agent may be coke, but is preferably a non-fossil-based carbon reducing agent, such as biochar, bio-coal, or waste plastics.

[0030] Biochar, or bio-coal, refers to charcoal produced through the pyrolysis of biomass under anaerobic conditions. Biomass is a renewable organic material derived from plants and animals. Biomass sources used for energy primarily include wood and wood processing waste—firewood, wood pellets, and wood chips; sawdust and waste from wood and furniture factories; and black liquor from pulp and paper mills; agricultural crops and waste—corn, soybeans, sugarcane, switchgrass, woody plants, and algae; and agricultural and food processing residues; bio-based materials in municipal solid waste; paper, cotton, and wool products; as well as food, yard, and wood waste, animal manure, and human sewage.

[0031] Iron-containing furnace charge 4 is converted into molten iron 2 through the reduction of iron oxides. This reduction can be performed by means of three inputs: the first is the introduction of a first carbon-based reducing agent 5, the second is the injection of blast 22 at a first injection level 3A (also known as the tuyeres level), and optionally, the injection of reducing gas at a second gas injection level 3B located above the first level.

[0032] Such production processes emit blast furnace gas, at least a portion of which is recovered at the top of furnace 1. For illustration, the top gas may contain 15 to 25% v of CO, 20 to 30% v of CO2, 2 to 32% v of H2, and more than 30% v of N2. In a preferred embodiment where the blast is primarily composed of oxygen, the top gas may contain 40 to 50% v of CO, 30 to 40% v of CO2, 2 to 15% v of H2, and less than 20% v of N2. The unrecovered blast furnace gas is referred to as output gas 9.

[0033] Throughout all texts, dry basis % must be understood as a calculation of the gaseous composition ignoring the presence of water (H2O). Unless otherwise stated, all %v refers to dry basis volume %.

[0034] In a preferred embodiment, at least 80% by volume, preferably about 95% by volume, of BFG is captured. Capturing less than 95% by volume of BFG allows the remaining 5% of output gas 9 to be used for purging, particularly to prevent N2 accumulation in the circulation loop, since N2 is not extracted or consumed at any step of the process.

[0035] Blast furnace gas 10 undergoes a separation step in a CO2 separation unit 2 to produce a CO2-rich stream 12 and a CO2-lean stream 11. The CO2 separation unit 2 can be a chemical absorption unit (e.g., using amines), a pressure swing adsorption unit or PSA, a vacuum pressure swing adsorption unit (VPSA), a cryogenic unit, or a combination of these technologies. At the outlet of the CO2 separation unit 2, the CO2-rich stream 12 preferably contains more than 85% by volume of CO2, while the CO2-lean stream 11 preferably contains less than 5% by volume of CO2, more preferably less than 3% by volume of CO2.

[0036] Prior to this separation step, the recovered exhaust gas 10 may first undergo one or more pretreatment steps, such as dust removal and / or dehydration and / or desulfurization steps.

[0037] The lean CO2 stream 11 can be injected at least partially into blast furnace 1. This injection can take place at the first injection level 3A and / or the second injection level 3B. The injection at the tuyeres level 3A is carried out together with the blast 22.

[0038] The CO2 separation step allows a portion of the recovered waste gas to be directly reinjected into the BF as reducing gas, thereby reducing the need for carbon-based reducing agents and also reducing the amount of gas to be processed in subsequent steps.

[0039] The blower 22 may have a temperature of 950°C or higher, preferably 1000°C to 1300°C, and preferably contains a second carbon-based reducing agent. The second carbon-based reducing agent is preferably in powder form and may be coal, but is preferably a non-fossil-based carbon reducing agent (e.g., biochar or bio-coal) or waste plastic as described previously.

[0040] In a preferred embodiment, the blast 22 contains 35 to 70 Nm3 of oxygen per ton of molten iron to be produced. The remaining component of the hot blast is air. This oxygen is preferably mixed with air before heating. This hot blast allows coke and other carbonaceous reducing agents to burn at the tuyeres, thereby converting them into a reducing gas that allows the iron ore to be reduced.

[0041] Nm3 is a unit of measurement for gas quantity, which corresponds to the content of gas in one cubic meter under normal temperature and pressure conditions (0℃ and 1 atm).

[0042] In another embodiment, blast 22 consists of at least 75% by volume oxygen and is injected at ambient temperature (typically around 25°C). Compared to classic hot blast injection, this particularly allows for a reduction in the amount of nitrogen injected into the furnace, thereby reducing the amount of nitrogen in the blast furnace top gas. This nitrogen does not react in any step and therefore tends to accumulate in the gas loop, requiring additional purging equipment. Furthermore, due to the reduction in nitrogen in the top gas, only hydrogen and carbon monoxide, along with a very limited amount of nitrogen, are obtained after the oxidation and CO2 removal steps, making the circulation of this gas direct and highly profitable for blast furnace operation.

[0043] The reducing gas 20 injected at the second injection level 3B preferably has a temperature of at least 800°C, preferably at least 900°C.

[0044] According to the present invention, the CO2-rich stream 12 is mixed with the H2 supplemental stream 30. The resulting CO2 / H2 mixture then undergoes a reverse water-gas shift reaction (rWGS) in reactor 3 according to Equation 1 to produce a reducing stream 13 mainly containing carbon monoxide (CO) and hydrogen (H2).

[0045] Equation 1

[0046] The H2 supplementary airflow 30 is preferably added in an amount that allows for an H2 / CO2 molar ratio of at least 2, more preferably at least 3, or even better, at least 4.

[0047] The CO2 conversion rate of the rWGS reaction varies depending on temperature and the molar ratio of H2 to CO2. Calculations are performed using thermodynamic models such as commercial software ThermoCalc®, FastSage®, or ChemSims®. According to these calculations, under stoichiometric conditions (H2 / CO2 = 1), operation at a temperature of at least 800 °C is required to achieve a CO2 conversion rate equal to or greater than 50%. If the H2 / CO2 molar ratio is 2, the temperature required for the same conversion rate will be lower than 600 °C. To achieve a CO2 conversion rate of over 70%, the H2 / CO2 molar ratio must be at least 2, preferably at least 3, to keep the required temperature below 1000 °C.

[0048] The gas mixture undergoing the rWGS reaction can first be heated to a temperature above 400°C, preferably above 600°C. This heating is preferably accomplished by electric heating powered by CO2-neutral electricity. CO2-neutral electricity specifically includes electricity from renewable sources, defined as energy generated 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, electricity from nuclear sources can be used because it does not emit CO2 during production. Increasing the reaction temperature can shift the reaction toward CO formation.

[0049] In a preferred embodiment, the hydrogen is green hydrogen. Green hydrogen (GH or GH2) is hydrogen produced from renewable energy sources or low-carbon electricity. Renewable energy sources must be understood as energy generated from renewable sources as defined above. The H2 stream can be provided by a dedicated H2 production unit, such as an electrolysis unit. It can be a water or steam electrolysis unit.

[0050] The reduction stream 13 preferably contains at least 70% by volume of CO + H2 on a dry basis. The reduction stream 13 then undergoes an H2 separation step in the H2 gas separation unit 32 to produce a CO-rich stream 14 and an H2-rich stream 15. The CO-rich stream 14 preferably contains more than 45% by volume of CO, while the H2-rich stream 15 preferably contains more than 95% by volume of H2.

[0051] H2 gas separation unit 32 can be H2-PSA or membrane.

[0052] The H2-rich stream 15 is then returned to reactor 3 to be mixed with the CO2-rich stream 12 or with a CO2 / H2 gas mixture, and the resulting mixture undergoes a reverse water-gas shift reaction. The mixing of the H2-rich stream 15 and the CO2-rich stream 12 can take place within or upstream of reactor 3, as long as they are mixed before the reverse water-gas shift reaction occurs.

[0053] This hydrogen recycling allows the reaction equilibrium to shift towards CO production, thereby improving process efficiency while reducing the need for fresh H2 from external sources. External sources must be understood as H2 sources that are not derived from the steelmaking process itself, such as dedicated H2 production units or H2 purchased outside the steel plant.

[0054] According to the present invention, the CO-rich stream 14 is fed to at least one chemical or biochemical device 4 to produce one or more chemical products 16.

[0055] The chemical or biochemical apparatus can be a urea or ammonia production unit, a fermenter, or a Fischer-Tropsch synthesis reactor. The chemical products can be alcohols (e.g., ethanol, methanol, or butanol), hydrocarbons, urea, or ammonia, or mixtures of different products.

[0056] In a preferred embodiment, at least one chemical or biochemical device 4 is a fermenter capable of using microorganisms to bioconvert one or more of CO, H2, or CO2 into syngas fermentation product 16. The microorganisms in the fermenter 4 are preferably Clostridium bacteria.

[0057] Before being sent to the chemical or biochemical unit 4, the CO-rich stream 14 can be enriched with H2 via a secondary H2 supplement stream 31. The amount of H2 supplement stream will be adjusted according to the type of chemical product and the reactions occurring in the chemical or biochemical unit.

[0058] Since CO-rich stream 14 contains CO, H2 and the remaining CO2, it constitutes a suitable synthesis gas for many chemical or biochemical plants.

[0059] Prior to the H2 separation step, the reduction stream 13 may pass through a heat exchanger (not shown) to cool it and capture the released heat. This released heat can be transferred to a gas or gas mixture fed to reactor 3 for the rWGS reaction to raise its temperature. At the outlet of the heat exchanger, the reduction stream 13 preferably has a temperature below 100°C, more preferably below 50°C.

[0060] This method allows for the recycling of a portion of the blast furnace gas (lean CO2 stream) while simultaneously recycling or adding value to a second portion by producing CO-rich gas. This reduces CO2 emissions from the blast furnace without being limited by the availability of external hydrogen.

[0061] Another embodiment of the method according to the invention is shown in Figure 2 middle. Figure 1 All elements of the illustrated embodiment are in Figure 2 The figures have the same reference numerals, and where technically possible, Figure 1 All options described in the implementation plan can be combined with this implementation plan.

[0062] In this embodiment, the CO-rich stream 14 can be split into two CO-rich streams 14A and 14B. The first CO-rich stream 14A can be mixed with BFG 10 before the CO2 separation step in the CO2 separation unit 2. The second CO-rich stream 14B can be sent to the secondary CO2 separation unit 33 to produce a secondary CO2-rich stream 42 and a secondary CO2-lean stream 41. The secondary CO2-rich stream 42 preferably contains more than 90% by volume of CO2, and the secondary CO2-lean stream preferably contains less than 3% by volume of CO2.

[0063] The secondary CO2-enriched stream 42 can be returned to reactor 3 to enrich the CO2 in the inlet gas and improve the efficiency of the rWGS reaction. Due to its high CO2 content, it can also be used in carbon storage technologies that require high-purity gases.

[0064] Then, the secondary lean CO2 stream 41 is sent to at least one chemical or biochemical device 4 to produce one or more chemical products 16.

[0065] This secondary lean CO2 stream 41 has the advantage of very low CO2 content, but this may be detrimental to some applications.

Claims

1. A method for ironmaking, comprising producing molten iron (2) and blast furnace top gas (10) in a blast furnace (1), the method comprising the following steps: a. Capture at least a portion of the blast furnace top gas (10); b. Separate carbon dioxide from the captured blast furnace top gas (10) to produce a CO2-rich stream (12) and a CO2-lean stream (11). c. The CO2-rich stream (12) is mixed with the hydrogen supplement stream (30), and the resulting CO2 / H2 gas mixture undergoes a reverse water-gas shift reaction in the reactor (3) to produce a reducing stream (13) containing carbon monoxide (CO) and hydrogen (H2). d. Separate H2 from the reduction stream to produce a CO-rich stream (14) and an H2-rich stream (15); e. The H2-rich stream (15) is mixed with the CO2-rich stream (12) or the CO2 / H2 gas mixture in the reactor (3), and the resulting gas mixture undergoes a reverse water-gas shift reaction; f. Feed at least a portion of the CO-rich stream (14) to at least one chemical or biochemical device (4) to produce one or more chemical products (16).

2. The method according to claim 1, wherein, The at least one chemical or biochemical device (4) is selected from urea or ammonia production equipment, fermenters or Fischer-Tropsch synthesis reactors.

3. The method according to claim 1, wherein, The at least one chemical or biochemical device (4) is a fermenter capable of using microorganisms to bioconvert one or more of CO, H2 or CO2 into syngas fermentation products (16).

4. The method according to claim 3, wherein, The microorganisms in the fermenter (4) are Clostridium bacteria.

5. The method according to any one of claims 1 to 4, wherein, The chemical product (16) is an alcohol.

6. The method according to claim 5, wherein, Alcohols (16) are selected from the group consisting of methanol, ethanol, butanol and mixtures thereof.

7. The method according to any one of claims 1 to 6, wherein, Before entering the at least one chemical or biochemical device (4), the secondary H2 supplement stream (31) is mixed with the CO-rich stream (14).

8. The method according to any one of claims 1 to 7, wherein, The H2 supplementary gas streams (30, 31) consist of hydrogen produced by water electrolysis.

9. The method according to any one of the preceding claims, wherein, The gas stream undergoing the reverse water-gas shift reaction is first heated to a temperature of at least 400°C.

10. The method according to any one of the preceding claims, wherein, The gas stream undergoing the reverse water-gas conversion reaction is first heated to a temperature of at least 600°C.

11. The method according to any one of claims 9 or 10, wherein, The gas flow that has undergone the reverse water-gas conversion reaction is heated by electric heating.

12. The method according to claim 11, wherein, The electric heating is powered by CO2-neutral electricity.

13. The method according to any one of claims 1 to 12, wherein, The gas stream undergoing the reverse water-gas shift reaction has an H2 to CO2 molar ratio of at least 2.

14. The method according to any one of claims 1 to 13, wherein, The gas stream undergoing the reverse water-gas shift reaction has a molar ratio of H2 to CO2 of 4.

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