Steelmaking methods and related plants

Abstract

1. A method for producing hot metal in a blast furnace comprising at least two levels of gas injection, wherein blast furnace top gas (10) is recovered and subjected to an oxidation step using the water-gas shift reaction to convert at least a portion of the carbon monoxide from said recovered blast furnace top gas (10) into carbon dioxide and hydrogen, and then the carbon dioxide is separated to obtain a CO2-rich stream (12) and an H2-rich stream (13), at least a portion of which are injected into the blast furnace at a second level of gas injection (3B).

Description

[Technical Field]

[0001] The present invention relates to a method of making steel and an associated steel plant. [Background technology]

[0002] In blast furnaces, the conversion of iron-containing charges (sinter, pellets, and iron ore) into cast iron or hot metal is traditionally carried out by the reduction of iron oxide with reducing gases (containing, among others, CO, H2, and N2), which are formed by the partial combustion of coke and ultimately auxiliary reducing agents in tuyeres located at the bottom of the blast furnace, where air, called hot blast, usually preheated to temperatures between 1000°C and 1300°C, is injected.

[0003] The auxiliary reducing agent that can be injected into the tuyere to increase productivity and reduce costs can be coal in pulverized form, fuel oil, natural gas or reducing agent in combination with oxygen enrichment of the hot blast.

[0004] The gas recovered at the top of the blast furnace, called top gas, consists mainly of CO, CO2, H2 and N2, with proportions of 20-28%v, 17-25%v, 1-5%v and 48-55%v, respectively. Although this gas is partly used as fuel in other facilities of the steel plant (coking plant, blast heaters...) or ultimately in power plants to generate electricity, the blast furnace remains a significant source of CO2.

[0005] 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, which are produced in large quantities and therefore especially in blast furnaces.

[0006] To this end, over the past 50 years, the consumption of reducing agents in blast furnaces has been halved, and currently, in conventionally configured blast furnaces, the carbon consumption has reached the lower limit associated with the laws of thermodynamics.

[0007] One possible solution to further reduce this carbon-based reducing agent consumption, and therefore CO2 emissions in the blast furnace steelmaking route, is to capture the top gas, remove the CO2, and reinject the reduced portion into the blast furnace shaft above the normal tuyere level where hot air is injected. However, with this solution, the reduction in reducing agent consumption remains less than 30% compared to production with a conventional blast furnace (without top gas recirculation) according to numerous calculations and trials carried out. In terms of global CO2 emissions, this corresponds to a reduction of less than 20% by volume of emitted CO2.

[0008] One solution is to use hydrogen as a reducing gas. A hydrogen-rich stream is injected into the blast furnace as a reducing agent in place of some of the coke. In order to have an impact on the CO2 emissions of the entire process, this hydrogen must be green hydrogen or hydrogen recovered from the process itself.

[0009] Green hydrogen is not yet available in sufficient quantities to meet demand, supply fluctuates depending on renewable energy, hydrogen separation technology is not yet available on an industrial scale, and its energy demands and operating costs are high. Summary of the Invention [Problem to be solved by the invention]

[0010] Therefore, there is a need for a method of making iron that allows for a significant reduction in carbon-based reducing agent consumption in the blast furnace while limiting the overall carbon footprint of the process. [Means for solving the problem]

[0011] This problem is solved by a method according to the invention in at least one blast furnace in which hot metal is produced, said blast furnace comprising at least two levels of gas injection and releasing blast furnace top gas during operation, said method comprising at least the following steps: charging the blast furnace with iron-containing material and a first carbon-based reductant; injecting hot air at a first level having a temperature of 1000°C or higher, said hot air comprising oxygen; recovering the blast furnace top gas; subjecting the recovered blast furnace top gas to an oxidation step using the water-gas shift reaction to convert at least a portion of the carbon monoxide from the recovered blast furnace top gas into carbon dioxide and hydrogen; separating carbon dioxide from the oxidized blast furnace top gas to obtain a CO2-enriched stream and an H2-enriched stream; and injecting at least a portion of the H2-enriched stream into the blast furnace at a second level of gas injection.

[0012] The method of the invention may also comprise the following optional features, considered separately or according to all possible technical combinations:

[0013] The first carbon-based reductant comprises coke.

[0014] The first carbon-based reductant comprises a non-fossil carbon reductant.

[0015] The H2-rich stream contains more than 80% hydrogen by volume.

[0016] The oxidation step and the carbon dioxide separation step are carried out simultaneously by sorption-enhanced water-gas shift.

[0017] In step B, the hot air further comprises at least one second carbon-based reductant comprising a non-fossil carbon reductant.

[0018] The hydrogen produced in the hydrogen production step is added to the H2-rich stream before it is injected into the blast furnace.

[0019] The hydrogen production step is a water decomposition step that produces hydrogen and oxygen.

[0020] The hot air contains oxygen produced in the water decomposition step.

[0021] The water splitting step is an electrolytic reaction.

[0022] The electrolysis reaction is driven by CO2 neutral energy.

[0023] The H2-enriched stream is injected into the blast furnace at a temperature of 750℃~1100℃.

[0024] Between 200 and 700 Nm3 of hydrogen is injected into the blast furnace per tonne of hot metal to be produced.

[0025] More than 50% of the volume of hydrogen injected into the blast furnace comes from the blast furnace top gas.

[0026] Hydrogen extracted from the reduction top gas of the direct reduced iron production step is added to the H2-rich stream before it is injected into the blast furnace.

[0027] Hot air contains more than 80% oxygen by volume.

[0028] The present invention also relates to a network of plants comprising at least one blast furnace producing hot metal and emitting blast furnace top gas, said blast furnace comprising first and second gas injection means respectively arranged at two different levels over the height of the blast furnace, the first injection means designed to inject hot air having a temperature of 1000°C or more into the blast furnace, said hot air comprising oxygen, a gas recovery and treatment unit capable of capturing the blast furnace top gas and comprising means for oxidizing at least a portion of the carbon monoxide from the recovered blast furnace top gas to carbon dioxide and hydrogen and means for separating carbon dioxide from the oxidized blast furnace top gas to obtain a CO2-enriched stream and an H2-enriched stream, and the second injection means designed to inject the H2-enriched stream into the blast furnace.

[0029] The network of plants according to the invention may also include the following optional features, considered separately or according to all possible technical combinations:

[0030] The hydrogen production plant and hydrogen gas line allow the hydrogen produced in the hydrogen production plant to be mixed with the H2-rich stream before being injected into the blast furnace via the second injection means.

[0031] A hydrogen production plant is a water splitting plant that produces hydrogen and oxygen.

[0032] The oxygen gas line allows the produced oxygen to be injected together with the hot air before being injected into the blast furnace via the first injection means.

[0033] The direct reduction furnace produces direct reduced iron and reduced top gas, the second gas recovery and treatment device is capable of capturing the reduced top gas and extracting hydrogen from the reduced top gas to produce a directly reduced H stream, and the mixing means enables the directly reduced H stream to be mixed with an H-enriched stream before being injected into the blast furnace.

[0034] Other characteristics and advantages of the present invention will become apparent from the description of the invention given below by way of indication and in no way limiting, with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0035] [Figure 1] 1 shows a steel plant allowing the implementation of a method according to an embodiment of the present invention; [Figure 2] 2 shows a steel plant allowing the implementation of the method according to a second embodiment of the invention; [Figure 3] 3 shows a steel plant allowing the implementation of a method according to a third embodiment of the invention. DETAILED DESCRIPTION OF THE INVENTION

[0036] It should be noted first that in the figures, like reference numerals refer to like elements regardless of the figure they appear in and regardless of the shape of those elements. Similarly, if elements are not specifically referenced in one of the figures, their reference can be easily found by reference to another figure.

[0037] Also, the figures primarily represent one embodiment of the subject matter of the invention, but other embodiments may exist that correspond to the definition of the invention. Elements in the figures are illustrative and may not be drawn to scale.

[0038] 1 shows a steel plant that allows the implementation of a method according to one embodiment of the present invention, comprising at least one blast furnace 1, into whose throat an iron-containing charge 4, such as sinter, pellets, iron ore, etc., is charged together with a first carbon-based reducing agent 5. This first carbon-based reducing agent can be coke, but is preferentially a non-fossil carbon-based reducing agent, such as biochar or biocoal or waste plastic.

[0039] Biochar or biocoal refers to charcoal produced by pyrolysis of biomass in the absence of oxygen. Biomass is renewable organic material derived from plants and animals. Biomass sources for energy include, among others, wood and wood processing wastes—firewood, wood pellets and wood chips, sawdust and waste from lumber and furniture mills, and black liquor from pulp and paper mills; agricultural crops and waste materials—corn, soybeans, sugarcane, switchgrass, woody plants, and algae; crop and food processing residues; municipal solid waste; biogenic materials in paper, cotton, and wool products; food, yard, and wood waste; animal manure; and human sewage.

[0040] The iron-bearing charge 4 is converted to hot metal by reduction of the iron oxide. According to the invention, this reduction is carried out by three inputs: the first is the injection of a first carbonaceous reducing agent 5, the second is the injection of hot air 14 at the first level injection 3A, and the last is the injection of a reducing gas at the second level gas injection 3B. For clarity, the reference numerals 3A and 3B indicate both the injection levels and the associated injection means at the levels considered.

[0041] Furthermore, even though both gas injection levels 3A and 3B are shown as a pair of arrows in the figure, it should be noted that this is for illustrative purposes only and that these two gas injections are preferentially carried out at each level around the entire circumference of the blast furnace 1.

[0042] The hot blast 14 has a temperature above 1000°C, preferably between 1000°C and 1300°C, and contains oxygen 6 and preferably a second carbonaceous reductant 7. It is preferentially injected at the commonly known tuyere level, located at the bottom of the blast furnace 1. This second carbonaceous reductant 7 is preferentially in pulverized form and may be coal, but is preferentially a non-fossil carbonaceous reductant, such as biochar or biocoal according to the explanation given above, or waste plastic.

[0043] In a preferred embodiment, the hot blast contains 35-70 Nm3 of oxygen per ton of hot metal to be produced. The remaining component of the hot blast is air. This oxygen is preferentially mixed with the air before heating. This hot blast allows for the combustion of coke and other carbon-containing reducing agents in the tuyeres, thus converting them into reducing gases for iron ore reduction.

[0044] In all texts, Nm3 stands for standard cubic meter, a unit of measurement of the amount of gas corresponding to the content of a volume of 1 cubic meter for gases at normal temperature and pressure (0°C and 1 atm).

[0045] In another embodiment, the hot blast is composed of at least 75% by volume of oxygen. This allows, in particular, to reduce the amount of nitrogen injected into the furnace and therefore into the blast furnace top gas compared to classical hot blast injection. This nitrogen does not react in any of the steps and therefore tends to accumulate in the gas circuit, requiring additional purging equipment. Furthermore, due to the reduced nitrogen in the top gas, only hydrogen with a very limited amount of nitrogen is obtained after the oxidation and CO2 removal steps, and recycling this gas is simple and highly beneficial for blast furnace operation.

[0046] Thus, in the method according to the present invention, there is a third input for iron reduction. The third input consists of a hydrogen-rich stream 13 injected at the second level 3B of the blast furnace, preferably at the lower shaft level just above the belly level of the furnace. This hydrogen-rich stream 13 is preferentially injected at a temperature between 750°C and 1100°C, more preferentially between 900°C and 1000°C. The hydrogen-rich stream 13 may be subjected to a heating step prior to injection into the blast furnace to reach these temperatures. This heating step is preferably carried out using electrical energy, preferably CO2-neutral electricity. CO2-neutral electricity specifically includes electricity from renewable sources, which 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. In some embodiments, electricity from nuclear sources can be used because it does not emit the CO2 produced.

[0047] Hydrogen can be injected at 200 to 700 Nm3 per ton of hot metal produced. This hydrogen injection allows for the partial reduction of wüstite in the iron load at an earlier stage in the furnace and for in-situ metallization of the iron charge in the furnace. Below 200 Nm3 / thm, there are some problems with uniform distribution of reducing gas around the blast furnace, which can lead to disturbances induced by uneven metallization of the iron load. On the other hand, injecting 700 Nm3 / thm of hydrogen is sufficient to convert all the iron oxide in the iron load to metallic iron at the injection level. Injecting hydrogen at more than 700 Nm3 / thm does not provide any additional benefits, as this hydrogen does not react with the iron oxide; it will only contribute to heating of the blast furnace top gas.

[0048] By way of example, the top gas 10 may contain 15-25% v CO, 20-30% v CO2, 2-32% H2, and greater than 30% v N2. This composition will vary widely depending on the amount of hydrogen injected. In embodiments where the hot air is primarily composed of oxygen, the top gas may instead contain 40-50% v CO, 30-40% v CO2, 2-15% H2, and less than 20% v N2.

[0049] According to the invention, this hydrogen originates at least in part from the blast furnace top gas 10. Said top gas 10 is captured at the outlet of the blast furnace 1 and sent to a gas recovery treatment unit 30, 31. It is first subjected to an oxidation step in an oxidation unit 30, in which carbon monoxide contained in the recovered blast furnace gas 10 is oxidized to carbon dioxide and hydrogen according to the water-gas shift reaction. This oxidation gas 11 is then subjected to a CO2 separation step in a CO2 separator, producing a CO2-rich stream 12 and an H2-rich stream 13. The CO2 separator may be an absorption unit, a membrane separator, or an adsorption unit such as a pressure swing adsorption (PSA) unit or a vacuum pressure swing adsorption (VPSA) unit.

[0050] This H2-enriched stream 13 preferably contains more than 80% H by volume and is then injected into the blast furnace 1 at the second injection level 3B. The CO2-enriched stream preferably contains more than 90% CO2 by volume, more preferably more than 95% CO2 by volume.

[0051] The oxidation step is a water gas shift reaction step. The water gas shift reaction (WGSR) describes the reaction of carbon monoxide with water vapor to form carbon dioxide and hydrogen according to the following equation 1: formula 1

[0052]

number

[0053] In a preferred embodiment, both the oxidation and CO2 separation steps are carried out in the same device 30 using a sorption-enhanced water-gas shift reaction. Sorption-enhanced water-gas shift (SEWGS) is a technology that combines a pre-combustion carbon capture step with the water-gas shift reaction (WGS). While the WGS reaction occurs, carbon dioxide is captured and removed through an adsorption step. In situ CO2 adsorption and removal shifts the water-gas shift reaction to the right, thereby completely converting CO and maximizing the rate of hydrogen production.

[0054] The use of an oxidation and separation step allows more hydrogen to be recovered and injected into the blast furnace, thus reducing the amount of coke used, and it also allows for the production of a CO2-rich stream that can be more easily used for other purposes than the tail gas produced when using H2 separation techniques.

[0055] In a preferred embodiment shown in Figure 2, hydrogen 21 produced in a hydrogen production plant 20 is added to the H2-enriched stream 13, preferably prior to its heating and subsequent injection into the blast furnace 1. This can further reduce the need for the addition of carbon-based reductants. Preferably, less than 50% by volume of the total amount of hydrogen injected by the second injection means 3B comes from the hydrogen production plant 20.

[0056] In the most preferred embodiment, the hydrogen production plant 20 is a water splitting plant that produces hydrogen 21 and oxygen 22 from water, for example by electrolysis. As shown in Figure 2, the produced oxygen 22 can be used as the oxygen source 6 for the hot air 14. This can reduce the overall operating costs of the plant, as the need for external purchase of oxygen is eliminated or reduced.

[0057] In a most preferred embodiment, the hydrogen production plant 20 is powered by CO2-neutral energy.

[0058] In another embodiment, shown in FIG. 3, the plant further includes a direct reduction furnace 40. In operation, iron oxide ore and pellets 41 containing approximately 30% oxygen (by weight) are charged to the top of the furnace 40 and allowed to descend by gravity via reducing gas 42. This reducing gas 42 is injected into the furnace 40 countercurrently from the charged iron oxide. The 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, its oxidant content increases. Reduced iron, also referred to as DRI product 43, exits the bottom of the furnace 40, and reduced top gas 44 exits the top of the furnace 40. This reduced top gas 44 is captured and processed in a second gas processing unit 50 to extract hydrogen, at least a portion of which is mixed with the H-enriched stream 13. The composition of the reduced top gas 44 varies depending on the composition of the reducing gas 42 injected into the furnace 40. In a preferred embodiment, the reducing gas 42 comprises more than 90%v hydrogen, which hydrogen is preferentially green hydrogen.

[0059] All features described in relation to FIG. 1 are applicable to the embodiments described in relation to FIGS.

[0060] The method according to the invention allows, thanks to the various embodiments described, to reduce CO2 emissions by at least 35% by volume, and even more than 50%, compared to production in a conventional blast furnace (without top gas recirculation).

Claims

1. A method for producing hot metal (2) in at least one blast furnace (1), said blast furnace (1) comprising at least two levels of gas injection (3A, 3B) and releasing blast furnace top gas (10) during operation, said method comprising at least the following steps: A. Charging an iron-containing charge (4) and a first carbon-based reducing agent (5) into a blast furnace (1); B. Injecting hot air (14) at a first level (3A) having a temperature of 1000°C or higher, said hot air (14) containing oxygen (6); C. Recovering blast furnace top gas (10); D. subjecting the recovered blast furnace top gas (10) to an oxidation step using a water-gas shift reaction to convert at least a portion of the carbon monoxide from said recovered blast furnace top gas (10) to carbon dioxide and hydrogen; E. Separating carbon dioxide from the oxidized blast furnace top gas (11) to obtain a CO2-rich stream (12) and a H2-rich stream (13); F. Injecting at least a portion of the H2-enriched stream (13) into the blast furnace at a second level of gas injection (3B); A method comprising:

2. 2. The method of claim 1, wherein the first carbon-based reductant (5) comprises coke.

3. 3. The method of claim 1 or 2, wherein the first carbon-based reductant (5) comprises a non-fossil carbon reductant.

4. The method according to any one of claims 1 to 3, wherein the H2-enriched stream (13) comprises more than 80% by volume of hydrogen.

5. The method according to any one of claims 1 to 4, wherein the oxidation step and the carbon dioxide separation step are carried out simultaneously by sorption-enhanced water-gas shift.

6. The method according to any one of claims 1 to 5, wherein in step B the hot air (14) further comprises at least one second carbon-based reductant (7) comprising a non-fossil carbon reductant.

7. The method according to any one of the preceding claims, wherein the hydrogen (21) produced in the hydrogen production step is added to the H2-enriched stream (13) before being injected into the blast furnace (1).

8. 8. The method of claim 7, wherein the hydrogen production step is a water splitting step to produce hydrogen (21) and oxygen (22).

9. 9. The method of claim 8, wherein the hot air (14) comprises oxygen (22) produced in the water splitting step.

10. 10. The method according to claim 8 or 9, wherein the water splitting step is an electrolytic reaction.

11. 11. The method of claim 10, wherein the electrolysis reaction is driven by CO2 neutral energy.

12. The method according to any one of the preceding claims, wherein the H2-enriched stream (13) is injected into the blast furnace (1) at a temperature between 750°C and 1100°C.

13. 13. The method according to any one of claims 1 to 12, wherein 200 to 700 Nm3 of hydrogen per tonne of hot metal produced is injected into the blast furnace.

14. 14. The method according to claim 13, wherein more than 50% by volume of the hydrogen injected into the blast furnace (1) is hydrogen originating from the blast furnace top gas (10).

15. 15. The method according to any one of claims 1 to 14, wherein hydrogen (45) extracted from the reduced top gas (44) of the direct reduced iron production step is added to the H2-enriched stream (13) before it is injected into the blast furnace (1).

16. The method according to any one of the preceding claims, wherein the hot air (14) contains more than 80% by volume of oxygen.

17. A steel manufacturing plant, comprising: a. at least one blast furnace (1) producing hot metal (2) and discharging blast furnace top gas (10), said blast furnace (1) comprising first and second gas injection means (3A, 3B) respectively arranged at two different levels in the height direction of said blast furnace (1); b. a first injection means (3A) designed to inject hot air (14) having a temperature of 1000°C or more into the blast furnace (1), said hot air (14) containing oxygen (6); a gas recovery treatment device (30, 31) capable of collecting blast furnace top gas (10), the gas recovery treatment device (30, 31) comprising: means for oxidizing at least a portion of carbon monoxide from the recovered blast furnace top gas (10) to carbon dioxide and hydrogen; and means for separating carbon dioxide from the oxidized blast furnace top gas (11) to obtain a CO2-enriched stream (12) and an H2-enriched stream (13); d. A second injection means (3B) designed to inject the H2-enriched stream (13) into the blast furnace (1); A steel manufacturing plant comprising:

18. 18. The steel manufacturing plant of claim 17, further comprising a hydrogen generation plant (20) and a hydrogen gas line enabling the produced hydrogen (21) in the hydrogen generation plant (30) to be mixed with the H2-enriched stream (13) before being injected into the blast furnace (1) via the second injection means (3B).

19. 19. The steel manufacturing plant of claim 18, wherein the hydrogen production plant (20) is a water splitting plant that produces hydrogen and oxygen.

20. 20. The steel manufacturing plant of claim 19, further comprising an oxygen gas line (22) allowing the generated oxygen to be injected together with the hot blast (14) before being injected into the blast furnace (1) via the first injection means (3A).

21. a. a direct reduction furnace (40) producing direct reduced iron (43) and reduced top gas (44); b. a second gas recovery and processing unit (50) capable of collecting the reduced top gas (44) and extracting hydrogen from said reduced top gas (44) to produce a directly reduced H2 stream (45); c. Mixing means enabling said directly reduced H2 stream (45) to be mixed with a H2-enriched stream (13) before injection into the blast furnace (1); The iron and steel manufacturing plant according to any one of claims 1 to 20, further comprising:

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