Process for producing direct reduced iron with low carbon content

Abstract

A direct reduction process for producing a direct reduced iron product 12 having a carbon content of less than 1.8 wt. % and a shaft furnace outlet temperature of less than 65°C. The carbon-containing cooling gas 30 has a flow rate of 800 Nm3 per tonne of direct reduced iron produced. 3 is introduced into the cooling section 3 of the shaft furnace 1 at a flow rate higher than that of the

Description

[Technical Field]

[0001] This application claims priority to International Patent Application No. PCT / IB2022 / 062380, filed December 16, 2022, which is incorporated herein by reference.

[0002] The present invention relates to a method for producing direct reduced iron having a low carbon content. [Background technology]

[0003] Direct reduced iron is produced by the direct reduction of iron ore (lump, pelleted, or finely divided) to iron with a reducing gas. Hematite and magnetite ores are examples of iron ores suitable for direct reduction. The name "reduced iron" comes from the chemical changes that iron ore undergoes when heated in a furnace at high temperatures in the presence of a reducing gas. Direct reduction refers to the process of reducing iron oxide to metallic iron at temperatures below the melting point of iron. The product of such solid-state processing is called direct reduced iron (DRI).

[0004] Direct reduction processes, such as those marketed under the trademarks MIDREX®, FINMET, ENERGIRON® (HYL process), COREX®, and FINEX®, produce sponge iron in the form of HDRI (high-temperature direct reduced iron), CDRI (low-temperature direct reduced iron), or HBI (high-temperature briquette iron) by direct reduction of an iron oxide support. The HDRI, CDRI, and HBI forms of sponge iron are typically further processed in an electric arc furnace.

[0005] In many DRI processes, reducing gases of CO and H2 are produced either by continuous catalytic reforming of hydrocarbons such as natural gas, petroleum distillates, methane, ethane, propane, butane, or other readily vaporizable hydrocarbons, or by synthesis gas from any source such as a coal gasifier. The reducing gas flows over the iron ore to reduce a significant portion of the metal oxides; the gas remaining after interaction with the iron ore is called top gas; the top gas is typically discharged from the top as the reducing gas typically flows upward.

[0006] The reduction process removes oxygen from various forms of iron ore (size ore, concentrate, pellets, mill scale, furnace dust, etc.) to convert the ore to metallic iron without melting it. The reduction process temperature can typically be 800-1100°C. During reduction, the iron oxide reacts with the reducing gas, for example according to the following reaction:

[0007] 3Fe2O3+CO / H2→2Fe3O4+CO2 / H2O Fe3O4+CO / H2→3FeO+CO2 / H2O FeO+CO / H2→Fe+CO2 / H2O As a result, the ore becomes metallized.

[0008] After reduction, the metallized ore typically passes through the cooling section of the furnace where it interacts with a cooling gas, usually natural gas (NG). NG is particularly effective for cooling because the thermal decomposition of CH4 is an endothermic reaction and CH4 has a high heat capacity.

[0009] As the metallized ore cools or passes through a cooling zone, it is typically carburized (i.e., its carbon content is increased) with NG or other cooling gases.

[0010] At the furnace exit, the cooled DRI product may have a carbon content of 1.8-2.8 wt. %, which is the amount required for the subsequent steelmaking process in which it is used.

[0011] However, in some applications, because carbon can have a negative effect on efficiency, a lower DRI of less than 1.8% by weight, or more preferably less than 1.5% or 1.2%, may be desirable. A non-limiting example may be a battery application as described in International Publication No. WO 2022 / 103893, although other applications are possible. The method for determining the carbon content by weight percent may be that described in International Publication No. WO 2022 / 103893, although other methods known in the art may be used. International Publication No. WO 2022 / 103893 is incorporated herein by reference. However, for purposes of claim interpretation, the language found in International Publication No. WO 2022 / 103893, incorporated by reference, shall not take precedence over other language found herein. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] International Publication No. 2022 / 103893 Summary of the Invention [Problem to be solved by the invention]

[0013] One solution to obtain a lower carbon DRI is to suppress the injection of cooling gases that cause carburization, but this results in products being discharged at high temperatures that are reduced, typically above 800°C, necessitating investment in new equipment to handle such high-temperature products.

[0014] Thus, the present inventors have identified a need for a method for producing low temperature DRI (CDRI) products with low carbon content. [Means for solving the problem]

[0015] The present invention solves this problem by providing, in one embodiment of the present invention, a method for producing a direct reduced iron product in a shaft furnace having a reducing zone and a cooling zone, the method comprising: injecting a reducing gas into the shaft furnace to reduce the iron ore, and a top gas is discharged from the shaft furnace; 800 Nm per tonne of direct reduced iron produced 3 introducing a carbon-containing cooling gas into a cooling zone of the shaft furnace at a flow rate greater than 1.8 wt. %, wherein the direct reduced iron product has a carbon content of less than 1.8 wt. % and a temperature at an outlet of the shaft furnace of less than 65°C; Includes.

[0016] The method of the embodiments of the present invention may also include the following optional features, which are considered separately from or according to all possible technical combinations:

[0017] The direct reduced iron product has a carbon content of less than 1.5 wt. %, more preferably less than 1.2 wt. %.

[0018] The carbon-containing cooling gas contains up to 20% CH4 by volume.

[0019] The carbon-containing cooling gas includes top gas, reformate gas, reducing gas, natural gas, or carbon dioxide.

[0020] The top gas is subjected to a water removal step before being used as a cooling gas.

[0021] The top gas undergoes a CO2 removal step before being used as cooling gas.

[0022] Before being injected into the shaft furnace, the cooling gas has a temperature of 40 to 80°C.

[0023] A target value for the carbon content of the direct reduced iron product is set, the composition of the gas to be supplied to the cooling zone of the shaft furnace is determined, and the flow rate of the cooling gas is controlled based on the determined gas composition so that the carbon content in the direct reduced iron product reaches the set target value.

[0024] Vary the gas temperature at the outlet of the top gas scrubber in the range of 30-80°C.

[0025] Varying the amount of CO2 present after the CO2 removal unit.

[0026] A minimum temperature in the reducing zone of the shaft furnace is set, the temperature and volume of the gas in the transition zone between the reducing zone and the cooling zone of the shaft furnace are determined, and the temperature of the reducing gas before being injected into the shaft furnace is controlled based on the determined temperature and volume of the gas in the transition zone so that the temperature in the reducing zone exceeds the set minimum temperature.

[0027] After introduction into the cooling zone of the shaft furnace, the cooling gas flows upward through a portion of the transition zone of the shaft furnace where the cooling gas is recovered, cooled, purified, and mixed with a make-up gas stream to form new cooling gas that is injected into the cooling zone of the shaft furnace.

[0028] The make-up gas stream is selected from top gas, reducing gas, reformate gas, hydrogen, nitrogen, carbon dioxide, ammonia, or any combination of these gases.

[0029] The make-up gas flow is 60-130 Nm per tonne of direct reduced iron produced. 3 is added to the recovered cooling gas at a flow rate of

[0030] In an alternative embodiment, the present invention provides a method for producing a direct reduced iron product in a shaft furnace having at least both a reducing zone and a cooling zone, the method comprising: operating the shaft furnace to form a direct reduced iron product, the shaft furnace having a reducing zone, preferably having an operating temperature of 800°C or greater while the shaft furnace is operating; injecting a carbon-containing cooling gas into the cooling zone of the operating shaft furnace at a cooling gas flow rate; and receiving, during operation of the shaft furnace, the direct reduced iron product discharged from the cooling zone of the shaft furnace after injection of the cooling gas, wherein, upon discharge from the cooling zone, the received direct reduced iron product has a carbon content below a predetermined level and a temperature below a predetermined temperature, and the cooling gas flow rate is 800 Nm3 per tonne of DRI produced. 3 The flow rate is selected to exceed

[0031] Other embodiments of the invention may be disclosed herein in which carbon-containing cooling gas is supplied at higher than normal flow rates, e.g., increasing the current flow rates of current DRI shaft furnaces, in order to reduce the typical carbon content of the produced DRI to, e.g., 1.8 weight percent or less, while still providing a low temperature DRI product, e.g., to a temperature at the shaft furnace outlet of less than about 65°C, and maintaining a high metallization, e.g., 90% or greater. These higher flow rates of carbon-containing cooling gas may be greater than 800 Nm3 per ton of DRI produced. 3 and may include flow rates greater than or equal to any of the above features, alone or in combination.

[0032] The present invention also provides a method for producing a direct reduced iron product in a shaft furnace having a reducing section and a cooling section, the method comprising: injecting a reducing gas into the shaft furnace to reduce the iron ore, wherein the top gas is discharged from the shaft furnace towards a top gas scrubber; Varying the gas temperature at the outlet of the top gas scrubber in the range of 30 to 80°C; introducing a carbon-containing cooling gas into a cooling zone of the shaft furnace, wherein the direct reduced iron product has a carbon content of less than 1.8 wt.%, and the carbon content is adjusted by varying the gas temperature; Includes.

[0033] The present invention also provides a method for producing a direct reduced iron product in a shaft furnace having a reducing section and a cooling section, the method comprising: injecting a reducing gas into the shaft furnace to reduce the iron ore, and a top gas is discharged from the shaft furnace towards a CO2 removal unit; Varying the amount of CO2 present after the CO2 removal unit; introducing a carbon-containing cooling gas into a cooling zone of the shaft furnace, wherein the direct reduced iron product has a carbon content of less than 1.8 wt.%, and the carbon content is adjusted by varying the amount of CO; Includes.

[0034] The present invention also provides a low temperature DRI product produced by the method of the present invention.

[0035] Other characteristics and advantages of the present invention will become apparent from the following description of the invention, given by way of example and in no way limiting, with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0036] [Figure 1] FIG. 1 shows the layout of a direct reduction plant allowing the implementation of a method according to one embodiment of the present invention. [Figure 2] FIG. 1 shows the layout of a direct reduction plant allowing the implementation of a method according to another embodiment of the invention. DETAILED DESCRIPTION OF THE INVENTION

[0037] Elements in the figures are illustrative and may not be drawn to scale.

[0038] FIG. 1 shows the layout of a direct reduction plant which allows the implementation of one embodiment of the method according to the invention.

[0039] An exemplary DRI production apparatus includes a DRI furnace 1 with iron ore charging fixtures 10 from top to bottom, with the iron ore moving through the furnace 1 by gravity. The furnace has a reducing section 2 located at the top of the furnace 1, a transition section 3 located in the middle of the shaft, and a cooling section 4 located at the bottom and ultimately at the discharge or outlet where the direct reduced iron 12 is extracted. The transition section 3 in the exemplary embodiment typically has a length separating the reducing section from the cooling section, which length allows for independent control of the reducing and cooling sections and allows for cooling gas to be extracted.

[0040] The direct reduction furnace 1 is charged with iron oxide ore from the top. The iron oxide is injected into the furnace 1 and reduced therein by reducing gas 11 flowing countercurrently to the iron oxide. Reduced iron 12 is discharged from the cooling section 4 at the bottom opening or outlet of the furnace 1 at a temperature below 65°C, preferably in the range of 50°C to 65°C, for further processing, such as briquetting, before being used in the subsequent steelmaking process. After reducing the iron, the reducing gas is discharged at the top of the furnace as top reducing gas 20 (TRG).

[0041] In one embodiment of the method according to the invention, the carbon-containing cooling gas 30 has a carbon content of 800 Nm3 per tonne of DRI produced. 3 The gas is injected into the cooling zone of the shaft furnace at a flow rate exceeding 1000 psi. The inventors have discovered that introducing gas in such amounts allows for a steeper temperature gradient in the cooling / transition zone that allows for lower carburization of the product while avoiding reoxidation of the product. This allows the DRI to be cooled to the required temperature while limiting carburization and maintaining a high degree of metallization, preferably greater than 90%.

[0042] The degree of reduction of DRI is usually expressed as the product metallization ratio, which is the ratio of metallic iron present in the DRI divided by the total amount of iron present in the DRI. The degree of metallization is highly dependent on the type of reduction process used. A low degree of metallization leads to economic losses such as higher energy consumption, increased slag, longer heating times, and lower yields during steelmaking.

[0043] Nm 3 is a unit of measure of the amount of gas equivalent to the content of one cubic meter of gas under normal conditions of temperature and pressure (0°C and 1 atm).

[0044] The carbon-containing cooling gas 30 is preferably selected to have a high heat capacity for removing heat from the solids while limiting the required gas volume, and to have an endothermic reaction with the DRI product. The carbon-containing cooling gas 30 preferably comprises methane CH4, and most preferably comprises up to 20% CH4 by volume.

[0045] In a preferred embodiment shown in Figure 1, cooling gas flowing upward through the cooling and transition zones is captured in the transition zone. The temperature of this extracted cooling gas is typically about 300-400°C. In a preferred embodiment, the cooling gas is subjected to cooling and dehydration steps in a cooling unit 31, preferably a scrubber, and purification steps in a purifier 32. The optionally purified and dehydrated gas is then mixed with a make-up gas stream 33 before being reinjected into the cooling zone of the furnace.

[0046] In another embodiment shown in FIG. 2, reduced top gas 20 discharged from DRI shaft 1 is collected in a pipe and cooled to 30-80°C. Top gas 20 can then be optionally connected to a scrubber 21 to remove water, and also to a CO2 remover 23. A compression step in compressor 22 can be performed between both or after CO2 remover 23. Top gas discharged from the DRI shaft typically contains H2, CO, CH4, H2O, CO2, and N2 in varying proportions. The top gas scrubbing operation allows for the removal of water vapor from the remaining stream, improving its reduction potential.

[0047] The top gas after scrubber 21 typically contains, by volume, 43-57% H2, 13-28% CO, 12-18% CO2, 2-12% CH4, 1-4% H2O, and 0-3% N2. If a partial CO2 removal step in CO2 removal device 23 has been performed, the top gas typically contains 50-69% H2, 15-20% CO, 2-13% CO2, 9-14% CH4, 1-4% H2O, and 0-3% N2.

[0048] Upon discharge from the scrubber 21 or CO2 remover 23, the top gas 24 can be optionally compressed and used as the cooling gas 30 and / or the make-up gas stream 33. It can also be split into two or more streams, with one stream 24A being used as the cooling gas 30 and / or the make-up gas stream 33 and the other stream 24B being used as part of the reducing gas 11. When used as a make-up gas stream, it can be mixed with the reducing gas 11, natural gas, hydrogen, nitrogen, carbon dioxide, ammonia, or any combination of these gases. The make-up gas stream can have a flow rate of 60-80 Nm3 per tonne of DRI produced. 3 is added to the recovered cooling gas at a flow rate of

[0049] 2, the top gas 24 may be mixed with a reformate 42 discharged from a reformer 41. In the reformer, the fuel 40, typically natural gas, is converted into reformate gases 42A, 42B, which are primarily composed of CO, H2, CO2, and unreformed portions of CH4. A typical composition of the reformate gas, expressed by volume, is 54-75% H2, 14-35% CO, 2-7% CO2, up to 5% CH4, up to 6% H2O, and up to 3% N2.

[0050] This reformed gas 42A is primarily used to generate the reducing gas 11, either alone or in combination with recycled top gas 24B, optionally after a heating step in heater 25. However, reformed gas 42B can also be used as cooling gas 30 and / or make-up gas stream 33.

[0051] In a preferred embodiment, the flow rate of the cooling gas 30, and therefore optionally the flow rate of the make-up gas stream 33, is controlled according to a set target value for carbon reaching the DRI product 12 and a determination of the gas composition in the cooling section of the shaft furnace, which may be made by measurement or thermodynamic modeling.

[0052] As an example, if the carbon content of the DRI product must be reduced to reach a target value, a non-carbon-containing gas such as hydrogen or nitrogen may be added as a make-up gas stream and its flow rate increased. Conversely, if the carbon content needs to be increased while remaining below 1.8% by weight, the flow rate of the make-up gas stream can be decreased and / or reformate or natural gas can be added as a make-up gas stream.

[0053] The carbon content of the DRI product can also be adjusted by varying the gas temperature at the outlet of the top gas scrubber 21 within a range of 30-80°C, which in turn varies the water vapor content of the reducing gas 11. The lower limit is a function of the available cooling water temperature, and the upper limit is regulated by the requirement to maintain reducing gas quality. The exact upper limit depends on the CO2 content in the recycled reducing gas.

[0054] The CO content in the recycled reducing gas can be varied to adjust the carbon content of the product DRI. This CO content can be varied by varying the recycling rate of the reducing gas that bypasses the CO removal unit 23. The lower limit of the CO content depends on the capacity of the CO removal unit (if all gas passes through the removal unit) and can typically be as low as about 2%, but the upper limit must be low enough to maintain the quality of the reduced gas. Typically, the CO content in the recycled gas after the scrubber should be less than about 18%.

[0055] In another embodiment, a minimum temperature in the reduction zone of the shaft furnace is set, and the temperature and volume of the gas in the transition zone of the shaft furnace are determined so that the temperature of the reducing gas 11 before being injected into the shaft furnace is controlled to a temperature in the reduction zone that exceeds the set minimum temperature. This process ensures that iron is reduced despite the injection of a large amount of cooling gas.

[0056] The features of the foregoing embodiments are compatible with each other. The carbon-containing cooling gas 30 may be selected from the top reducing gas 24, reformed gas 42B, reducing gas 11, natural gas, carbon dioxide, or any combination of these gases. The carbon-containing cooling gas 30 is preferentially introduced into the furnace at a temperature between 40°C and 80°C. The make-up gas stream 33 may be selected from the reduced top gas 24, reformed gas 42B, reducing gas, hydrogen, nitrogen, carbon dioxide, ammonia, or any combination of these gases. The make-up gas stream is preferably 60-80 Nm3 per tonne of DRI produced. 3 is added to the recovered cooling gas at a flow rate of

[0057] In all embodiments, the cooling gas 30 and / or makeup gas stream 33 are selected from the various gases listed above or mixtures thereof, depending on the plant configuration and environment. For example, if a large amount of hydrogen is available, hydrogen is preferentially used as the makeup gas stream. In other cases, if the required equipment is already available due to top gas recovery already occurring, the top gas may be preferably used thereafter.

[0058] Non-limiting examples Experiments were carried out in a HYL reduction plant equipped with a reformer as shown in Figure 2, with a production rate of 47 T / h of DRI. Initially, the plant was operated with recycled cooling gas and with NG injected as a make-up gas stream. During the experiment, the NG was gradually replaced by an increasing flow rate of reformed gas. The composition of the reformed gas was 72.6 vol.% H, 15.1 vol.% CO, 7.2 vol.% CO, 3.8 vol.% CH, 0.4 vol.% N, and 1 vol.% H0. This transition phase was carried out until a steady state was reached, allowing the implementation of an embodiment of the method according to the invention. The flow rate of the cooling gas introduced into the furnace was 833 Nm per ton of DRI produced. 3 This flow rate included 83.3 Nm3 per tonne of DRI produced. 3 of reformed gas and 39.6 Nm per tonne of DRI produced 3 The make-up gas stream consisted of 1000 sachets of natural gas. These conditions resulted in a DRI product with a metallization of 93% and a carbon content of 0.6% by weight.

Claims

1. 1. A method for producing a direct reduced iron product in a shaft furnace having a reduction zone and a cooling zone, comprising: injecting a reducing gas into the shaft furnace to reduce the iron ore, and a top gas is discharged from the shaft furnace; 800 Nm per ton of direct reduced iron produced ３ introducing a carbon-containing cooling gas into a cooling zone of the shaft furnace at a flow rate greater than 1.8 wt. %, wherein the direct reduced iron product has a carbon content of less than 1.8 wt. % and a temperature at an outlet of the shaft furnace of less than 65°C; A method comprising:

2. 10. The method of claim 1, wherein the direct reduced iron product has a carbon content of less than 1.5% by weight.

3. 10. The method of claim 1, wherein the direct reduced iron product has a carbon content of less than 1.2% by weight.

4. The carbon-containing cooling gas may contain up to 20% CH by volume. ４ 4. The method of claim 1, comprising:

5. The method of claim 1 , wherein the carbon-containing cooling gas comprises top gas, reformate gas, reducing gas, natural gas, or carbon dioxide.

6. 6. The method of claim 5, wherein the top gas is subjected to a water removal step before being used as a cooling gas.

7. The top gas is cooled to CO before being used as a cooling gas. ２ 7. The method of claim 5, wherein a removal step is performed.

8. The method according to any one of claims 1 to 7, wherein the cooling gas has a temperature of 40 to 80°C before being injected into the shaft furnace.

9. a. A target carbon content for the direct reduced iron product is established; b. The gas composition to be supplied to the cooling section of the shaft furnace is determined; c. Based on the determined gas composition, the flow rate of the cooling gas is controlled to achieve a set target value for the carbon content of the direct reduced iron product; The method according to any one of claims 1 to 8.

10. Setting a minimum temperature in the reduction zone of the shaft furnace; Determining the temperature and volume of gas in the transition zone between the reduction zone and the cooling zone of the shaft furnace; Controlling the temperature of the reducing gas before it is injected into the shaft furnace based on the determined temperature and volume of the gas in the transition zone so that the temperature in the reducing zone exceeds a set minimum temperature; The method of any one of claims 1 to 9, further comprising:

11. 11. The method according to claim 1, wherein after introduction into the cooling zone of the shaft furnace the cooling gas flows upwardly in a part of the transition zone of the shaft furnace where the cooling gas is recovered, and the recovered cooling gas is cooled, cleaned and mixed with a make-up gas stream to form new cooling gas which is injected into the cooling zone of the shaft furnace.

12. 12. The method of claim 11, wherein the make-up gas stream is selected from a top gas, a reducing gas, a reformate gas, hydrogen, nitrogen, carbon dioxide, ammonia, or any combination of these gases.

13. The make-up gas flow is 60-130 Nm per tonne of direct reduced iron produced. ３ 13. The method of claim 11 or 12, wherein the cooled gas is added to the recovered cooled gas at a flow rate of

14. The method of any one of claims 1 to 13, further comprising varying the gas temperature at the outlet of the top gas scrubber in the range of 30°C to 80°C.

15. CO ２ CO present after the removal unit ２ The method of any one of claims 1 to 13, further comprising varying the amount.

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