Steelmaking method and related network of plants

Abstract

A method for producing steel, comprising the steps of producing direct reduced iron in a direct reduction plant (1) using synthesis gas (70) resulting from the gasification of solid waste fuel, producing hot metal (22) and blast furnace gas (21) in a blast furnace (2) using hot blast (20), the blast furnace gas (21) being at least partially (21A) used in the direct reduction plant (1), and using the produced direct reduced iron (12) to produce molten metal and electric furnace gas in an electric furnace (3). A network of associated plants.

Description

[Technical field]

[0001] The present invention relates to a steelmaking process and associated plant network having a reduced carbon footprint. [Background technology]

[0002] Steel can currently be produced through two main production routes. The production route currently most commonly used, called the "BF-BOF route", consists of reducing iron oxide by using a reducing agent, mainly coke, to produce hot metal in a blast furnace, and then converting the hot metal into steel in a converter process or basic oxygen furnace (BOF). This route releases significant amounts of CO2, both in the production of coke from coal in the coking plant and in the production of hot metal.

[0003] The second main route involves the so-called "direct reduction processes", among others according to the brands MIDREX, FINMET, ENERGIRON / HYL, COREX, FINEX etc., in which sponge iron is produced in the form of HDRI (hot direct reduced iron), CDRI (cold direct reduced iron) or HBI (hot briquetted iron) from the direct reduction of an iron oxide support. Sponge iron in the form of HDRI, CDRI and HBI is usually subjected to further processing in an electric furnace.

[0004] Reducing CO2 emissions to meet climate targets will be difficult as the currently dominant form of steelmaking, the blast furnace-basic oxygen furnace (BF-BOF) pathway, relies on coal as a reducing agent and fuel. There are two options to reduce CO2 emissions from steelmaking: maintain the BF-BOF pathway and implement carbon capture and / or storage (CCUS) technologies, or explore new low-emission processes.

[0005] Therefore, a first step towards reducing CO2 emissions could be to switch from the BF-BOF route to the DRI route, which represents a major change not only in terms of equipment but also in terms of processes, without replacing all blast furnaces with direct reduction facilities at once.

[0006] Also, although an ever-increasing part of steel demand will be covered by scrap / DRI-based production, the need for steel production remains high and it is still predicted that classical BF technology will be the main production route for decades to come. Therefore, there will be several plants with different equipment coexisting.

[0007] This switch from one pathway to the other represents both a technical and economic challenge that must first be solved before a carbon-neutral production pathway can be made available. For example, more DRI equipment means fewer blast furnaces and therefore less blast furnace gas. However, these blast furnace gases are used especially within steel plants as an energy source, and replacing them with fossil energy sources would not be a step in the right direction. Summary of the Invention [Problem to be solved by the invention]

[0008] There is therefore a need for a method that allows producing steel according to a hybrid BF / DRI route with a reduced CO2 footprint. [Means for solving the problem]

[0009] This object is achieved by a method according to the invention, which comprises the steps of producing direct reduced iron and reduced furnace gas in a direct reduction plant using a reducing gas, the direct reducing gas comprising synthesis gas resulting from gasification of solid waste fuel, producing molten iron and blast furnace gas in a blast furnace using hot blast, the blast furnace gas being at least partially used in the direct reduction plant, and producing molten metal and electric furnace gas in an electric furnace using the produced direct reduced iron.

[0010] The method of the invention may also have the following optional features, taken separately or according to all possible technical combinations: - the method further comprises the step of producing coke and coke oven gas in a coke plant, said coke being charged to a blast furnace for said hot metal production process and said coke oven gas being at least partially used as reducing gas to a direct reduction plant, - the reducing gas further comprises green hydrogen; - the coke oven gas is at least partially used as a reducing agent in the hot metal production, - the reducing furnace gas is at least partially used as a reducing agent in hot metal production, - the reducing furnace top gas is injected into the shaft of the blast furnace as a reducing agent; - the reduction furnace top gas is at least partially recycled as part of the reduction gas in the direct reduction plant; - the synthesis gas has a composition that satisfies a ratio of reductant to oxidant, calculated as (%H2+%CO) / (%H2O+%CO2), greater than 10, and a ratio of %H2 / %CO greater than 1; - the blast furnace top gas is at least partially recycled to the blast furnace as a reducing agent; - the blast furnace top gas is at least partially sent to a chemical production unit; - the blast furnace gas is used to heat the reducing gas; - the blast furnace gas is used for gasification of the solid waste fuel; - the hot metal is used in the electric furnace to produce molten metal, - the scrap is used in the electric arc furnace to produce molten metal; - The entire process is powered by renewable energy.

[0011] The invention also relates to a network of plants comprising a direct reduction plant for producing direct reduced iron and reduced furnace gas using a reducing gas, a blast furnace for producing hot metal and blast furnace gas using a reducing agent, an electric furnace for producing molten metal and electric furnace gas using the produced direct reduced iron, a waste gasification plant for producing synthesis gas from gasification of solid waste fuel, and a gas network connecting at least the direct reduction plant to the waste gasification plant and the blast furnace so that the reducing gas comprises at least a portion of the synthesis gas and the blast furnace gas is at least partially used for the direct reduction plant.

[0012] Other characteristics and advantages of the invention will become apparent from the description thereof given below by way of indication and which is in no way limiting, with reference to the attached drawings, in which: [Brief description of the drawings]

[0013] [Figure 1] 1 shows a plant making it possible to carry out the method according to the invention, the elements in the figure are exemplary and may not be drawn to scale. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] FIG. 1 shows a plant comprising a direct reduction plant 1 , a blast furnace 2 , an electric furnace 3 and a waste gasifier 7 .

[0015] The direct reduction plant 1 comprises a shaft furnace 4 and a gas preparation device 5. In working mode, iron oxide ore and pellets 10, containing around 30% by weight of oxygen, are charged at the top of the shaft furnace 4 and are allowed to fall by gravity via a reducing gas 11. This reducing gas 11, prepared by the gas preparation device 5, is injected into the furnace 4 in a countercurrent flow from the charged iron oxide. The oxygen contained in the ore and pellets is removed by gradually reducing the iron oxide in a countercurrent reaction between the gas and the oxide. The oxide content of the gas increases while the gas is moving to the top of the furnace. The reduced iron, also called DRI product 12, leaves the bottom of the furnace 4, while the reduced top gas 13 leaves the top of the furnace 4. This reduced top gas 13 is captured and treated in a first gas treatment unit 7. The composition of this reduced top gas 13 varies depending on the composition of the reducing gas 11 injected into the shaft furnace 4.

[0016] The blast furnace 2 is a gas-liquid-solid countercurrent chemical reactor whose main purpose is to produce hot metal 22, which can then be converted to steel by reducing its carbon content or used for other purposes. The blast furnace 2 is conventionally fed with solid materials, mainly sinter, pellets, iron ore and carbonaceous materials, generally coke, charged at the top, called the throat of the blast furnace. Liquid consisting of hot metal and slag is tapped from a crucible at the bottom of the blast furnace 2. The iron-bearing blast furnace charge (sinter, pellets and iron ore) is conventionally converted to hot metal 22 by reducing the iron oxide with reducing gas (including, inter alia, CO, H2 and N2), which is formed by partial combustion of the carbonaceous materials by hot air 20, injected by a tuyere located at the bottom of the blast furnace, at a temperature usually between 1000 and 1300 °C. Injection of the reductant may also occur at the top of the blast furnace, above the tuyere, which is commonly referred to as shaft injection.

[0017] The resulting gas is discharged at the top of the blast furnace and is called blast furnace top gas 21. This blast furnace top gas 21 is captured and treated in the second gas treatment unit 8. The composition of this blast furnace top gas 21 varies depending on the composition of the reducing agent injected into the blast furnace 2.

[0018] The type of electric furnace 3 may be different. In particular it may be an electric arc furnace (EAF), a submerged arc furnace (SAF) or an open slag bath furnace (OSBF). The purpose of this furnace is to melt the charged material, which is at least a part of the direct reduced iron 12 produced by the direct reduction plant 1. This direct reduced iron 12 can be charged hot or cold directly at the outlet of the direct reduction plant 1. The electric furnace may also be charged with hot metal 22 produced in the blast furnace and / or scrap. According to the technology and charge material used, the molten metal produced can either be sent to a converter, for example to reduce the carbon content, and / or sent to secondary metallurgy to refine the steel and bring it to the appropriate composition for further processing steps.

[0019] The waste gasifier 7 pyrolyzes and gasifies the waste liquid. Gasification is the thermochemical conversion of carbonaceous fuels at high temperatures (400-1000°C) with the presence of an oxidant to obtain gaseous products characterized by CO, CO2, H2, CH4, H2O, and N2, with compound ratios that vary depending on the gasification conditions and feedstock selection. In the method according to the invention, solid waste fuel is subjected to said gasification.

[0020] Solid waste fuels specifically include both types of waste, namely Refuse Derived Fuel (RDF) and Solid Recovered Fuel (SRF). In a preferred embodiment, gasification of SRF is performed. Refuse Derived Fuel (RDF) is produced from household and commercial waste, including biodegradable materials and plastics. Non-combustible materials such as glass and metal are removed, and the remaining material is then shredded. Solid Recovered Fuel (SRF) is produced primarily from commercial waste, including paper, cardboard, wood, textiles, and plastics.

[0021] In the embodiment of Figure 1, the plant further comprises a coke plant 6, which is optional for carrying out the method according to the invention. Coke 61 is produced by heating coal to very high temperatures, typically around 1000°C, in so-called "coke ovens", which are insulated chambers. During the coking of coal, organic material in the coal blend evaporates or decomposes, producing coke oven gas (COG) 62 and coal tar, a thick, dark liquid used in industry and medicine.

[0022] In preferred embodiments, these plants are all powered by renewable energy, defined as energy collected from renewable resources 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 derived from nuclear sources can be used, as it does not release the CO2 that is produced.

[0023] In the method according to the invention, the reducing gas 11 used in the direct reduction plant 1 comprises synthesis gas 70 resulting from gasification of solid waste fuel in a waste gasification plant 7, and at least a portion 21A of the blast furnace gas or BFG is used in the direct reduction plant 1.

[0024] The solid waste fuel is gasified in a waste gasification plant 7 and the gaseous product 70 thus obtained is used as the reducing gas 11 in the direct reduction plant. The compound ratio in the gaseous product 70 and the related process parameters of the gasification are determined according to the other components of the reducing gas 11 so as to meet the reduction conditions required for the direct reduction process. The gaseous product 70 may be subjected to a conditioning step, such as reforming or partial oxidation, to obtain a suitable composition for use as part of the reducing gas 11.

[0025] The use of said synthesis gas makes it possible to replace part of the natural gas used with reducing gas while using non-fossil fuels, thus contributing to reducing the overall carbon footprint of the process. Moreover, it creates synergies with the existing environment of the steel plant, making it possible to further reduce the carbon footprint on a global scale.

[0026] In a preferred embodiment, this synthesis gas composition meets a reductant to oxidant ratio, calculated as (%H2+%CO) / (%H2O+%CO2), higher than 10, and a %H2 / %CO ratio greater than 1. Said synthesis gas further preferentially contains less than 3%v CO2 and less than 0.5%v N2, all percentages expressed by volume. It further preferentially contains less than 5 mg / Nm 3 Tar and dust less than 0.1g / Nm 3 Less than 0.1g / Nm 3 Less than C 10 Includes H8.

[0027] In the most preferred embodiment, the waste gasification plant 7 discharges two gas streams 70 and 71, the first of which is used as synthesis gas for the reducing gas 11 and the second gas stream 71 can be used as heating gas in other facilities of the plant.

[0028] In another embodiment, the plant includes a coke plant 6 and the reducing gas also includes coke oven gas 62. Said coke oven gas 62 may also be injected into the shaft furnace 4 independently of the reducing gas. In this configuration, the coke oven gas 62 is used as a carbon source to increase the carbon content of the DRI product without the additional use of external carbon.

[0029] In a preferred embodiment, the reducing gas 11 also contains green hydrogen, preferably more than 50% by volume. Green hydrogen is a hydrogen-generating fuel obtained from the electrolysis of water by electricity produced by low-carbon electricity sources, which in particular includes electricity from renewable sources as defined above.

[0030] In another embodiment, the reducing gas 11 may also include a portion of the directly reduced top gas 13A after its processing in the first gas processing unit 7. This first gas processing unit 7 may comprise, among other equipment, a water removal unit and a CO2 separation unit. In another embodiment (not shown), this directly reduced top gas 13 may also be used as a heat source, for example for heating the reducing gas 11, or for other heating applications within the steel plant.

[0031] In another embodiment, reduced top gas 13B can also be sent to the blast furnace 2. It may be injected through the tuyeres as part of the hot blast 20 or preferentially as a reducing agent for injection at shaft level.

[0032] In the method according to the invention, the blast furnace gas 21 or BFG is at least partially used in the direct reduction plant 1. There, it can be used to heat the reducing gas 11 in the gas preparation unit 5, either by direct heat exchange or by use as fuel in a burner. The blast furnace gas 21 is recovered and treated in a second gas treatment unit 8. This second gas treatment unit 8 can comprise, among other units, a dust filter unit, a water remover and a CO2 separation unit such as a pressure swing adsorption unit. It can be split into two streams 21A, 21B, the first stream 21A being sent to the direct reduction plant 1. In a preferred embodiment, the second stream 21B of BFG is sent to a carbon conversion unit, where it is converted into other products such as chemicals. It can be sent, for example, to a fermentation unit, where it is converted into hydrocarbons. In another embodiment, this second stream 21C is reinjected into the blast furnace as part of the hot air 20 or as a reducing agent at the shaft level. In another embodiment, the BFG can be used in the waste gasification plant 7. The BFG can be split into as many streams as needed for different uses as described in the previous embodiment.

[0033] Using the method according to the invention it is possible to produce steel using a hybrid BF / DRI route with a reduced carbon footprint, which also allows the transition from the most commonly used BF / BOF route to a DRI-based carbon-neutral route in a sustainable way.

[0034] In the embodiment of FIG. 1, all the plants are shown together, but they may be located at different production sites and the different gases and materials may be transported from one plant to another by suitable means.

[0035] All different embodiments described can be used in combination with one another, where technically possible.

Claims

1. A method for producing steel, comprising the steps of: a. Producing direct reduced iron (12) and reduced furnace top gas (13) in a direct reduction plant (1), said direct reduction gas (11) comprising synthesis gas (70) resulting from gasification of solid waste fuel; b. Producing hot metal (22) and blast furnace gas (21) in a blast furnace (2) using hot blast (20), said blast furnace gas (21) being at least partially (21A) used in said direct reduction plant (1); c) Producing molten metal and electric furnace gas in an electric furnace (3) using the direct reduced iron (12) produced. The method includes:

2. 2. The method according to claim 1, further comprising a step of producing coke (61) and coke oven gas (62) in a coke plant (6), said coke (61) being charged to said blast furnace (2) for said hot metal production process and said coke oven gas (62) being at least partially used as reducing gas to said direct reduction plant.

3. The method according to claim 1 or 2, wherein the reducing gas (11) further comprises green hydrogen.

4. 4. The method according to claim 2 or 3, wherein the coke oven gas (62) is at least partly used as hot blast (20) in the hot metal production process.

5. The method according to any one of claims 1 to 4, wherein the reduced furnace top gas (13B) is at least partly used as a reducing agent in the hot metal production process.

6. 6. The method according to claim 5, wherein the reducing top gas (13B) is injected into the shaft of the blast furnace (2) as a reducing agent.

7. The method according to any one of the preceding claims, wherein the reduced top gas (13A) is at least partially recycled to the direct reduction plant (1) as part of the reducing gas (11).

8. The synthesis gas (70) has a content of 10% or more (% H ２ + % CO) / (% H ２ O + % CO ２ ) and a % H greater than 1. ２ The method according to any one of claims 1 to 7, wherein the composition satisfies the ratio of 0.1% CO / % CO.

9. The method according to any one of the preceding claims, wherein the blast furnace top gas (21) is at least partially recycled to the blast furnace (2) as part of the hot blast (20).

10. The method according to any one of the preceding claims, wherein the blast furnace gas (21) is at least partially sent to a chemical production unit.

11. The method according to any one of the preceding claims, wherein the blast furnace top gas (21) is used to heat the reducing gas (11).

12. The method according to any one of claims 1 to 11, wherein the blast furnace gas (21) is used for gasification of the solid waste-to-fuel.

13. The method according to any one of the preceding claims, wherein the hot metal (22) is used in the electric furnace to produce molten metal.

14. A method according to any one of the preceding claims, wherein scrap is used in the electric furnace to produce molten metal.

15. The method according to any one of claims 1 to 14, wherein all steps are supplied with renewable energy.

16. A network of a plant, comprising: a. a direct reduction plant (1) that uses reducing gas (11) to produce direct reduced iron (12) and reduced furnace top gas (13); b. a blast furnace (2) using a reducing agent (20) to produce molten iron (22) and blast furnace top gas (21); c. an electric furnace (3) that uses the produced direct reduced iron (12) to produce molten metal and electric furnace gas; d. A waste gasification plant (7) for producing synthesis gas (70) from the gasification of solid waste fuels; e. a gas network connecting at least the direct reduction plant (1) to the waste gasification plant (7) and the blast furnace (2), such that the reducing gas (11) comprises at least a portion of the synthesis gas (70) and the blast furnace top gas (21) is at least partially (21A) used for the direct reduction plant; The plant network, including:

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