Title - PROCESS FOR PRODUCING DIRECT REDUCTION IRON WITH A HYDROGEN-RICH REDUCING GAS, USING A COMBUSTION-FREE REDUCING GAS HEATER TO HEATER THE HYDROGEN-RICH REDUCING GAS TO A TEMPERATURE SUFFICIENT FOR IRON REDUCTION

Abstract

A process for producing direct reducing iron with a hydrogen-rich gas, using a combustion-free reducing gas heater such as an electric heater to heat the reducing gas to temperatures sufficient for iron reduction, includes: providing a shaft furnace to reduce iron oxide with the hydrogen-rich reducing gas; removing steam and particulates from the top gas of the shaft furnace with a scrubber; processing all or a portion of the scrubbed top gas in a gas separation unit, such as a membrane and PSA gas separation unit, to create a hydrogen-rich stream to be recycled back to the shaft furnace as a reducing agent, so that hydrogen consumption can be reduced when a combustion-free reducing gas heater is applied.

Description

METHOD FOR RECYCLING SPENT REDUCING GAS IN A DIRECT IRON ORE REDUCTION SYSTEM USING AN ELECTRIC GAS HEATER Haruyasu Michishita, Todd Astoria, Enrique José Cintrón CROSS REFERENCE TO RELATED APPLICATION

[0001] This non-provisional patent application claims the benefit of priority of U.S. Provisional Patent Application No. 63 / 232,748, filed on August 13, 2021, and entitled “METHOD FOR RECYCLING SPENT REDUCING GAS IN A DIRECT IRON ORE REDUCTION SYSTEM USING AN ELECTRIC GAS HEATER,” the contents of which are incorporated herein by reference in their entirety. TECHNICAL FIELD

[0002] This disclosure relates generally to the fields of steelmaking and direct reduced iron (DRI). More specifically, this description relates to a method and system for producing direct reduced iron (DRI) in which the reducing gas is heated using means other than combustion. BACKGROUND

[0003] Direct reduced iron (DRI), often called sponge iron, is normally produced by reacting iron ore with synthesis gas, a gas containing hydrogen and carbon monoxide. In conventional processes, the synthesis gas is generated from natural gas either by reforming it in situ within the reduction furnace or in a separate catalytic reformer. In this context, DRI refers to any of the common product forms, such as direct reduced iron. 1919456 of 22 cold reduced iron (CDRI), hot reduced iron (HDRI), hot briquetted iron (HBI) or any other DRI produced by gas-based reduction of iron ore in a shaft furnace.

[0004] As part of global efforts to combat climate change, the steel industry is seeking to reduce or eliminate its CO2 emissions. In conventional iron production, most CO2 emissions originate during the reduction of iron ore, where iron oxide is reduced to metallic iron using coal in the case of a blast furnace and natural gas in the case of a direct reduction furnace. Fossil fuel input is used not only to provide the necessary chemistry for reduction but also to supply the energy needed to drive the reaction. In the case of direct reduction, hydrogen produced from green sources—what we call green hydrogen—can potentially serve as a replacement for natural gas, which greatly reduces emissions during the reduction phase of iron production.

[0005] While considerable efforts have been made to develop and refine conventional processes for use with green hydrogen, significant challenges remain. A major problem is the large hydrogen consumption required by conventional processes. Because conventional reduction technologies rely on fire heaters to supply the energy for reduction, sufficient hydrogen must be added not only for the requirements of the reduction reaction but also to meet the process heat requirements through combustion. This can negatively impact costs, as additional electrolysis capacity must be installed and additional electricity must be used.

[0006] Consequently, there is a need for improved methods and systems for producing direct reduced iron (DRI) in which the reducing gas is heated using means other than combustion. 1919456 of 22 BRIEF SUMMARY OF THE INVENTION

[0007] Embodiments of the present invention improve upon prior methods and systems for direct reduced iron (DRI) production. For example, an electric gas heater using electricity derived from renewable energy sources, which is also used to produce green hydrogen by electrolysis, has been determined to be a typical example for reducing CO2 emissions.

[0008] Therefore, it has been advantageously determined in this document that replacing the flame-assisted reducing gas heater used in conventional technologies with an electric version can decrease not only the required green hydrogen but also the total electricity needed. The electricity consumption for the electric reducing gas heater is significantly less than the amount of electricity required to generate the hydrogen used by a flame-assisted reducing gas heater, due to the lower thermal efficiency of the flame-assisted heater. The adiabatic hydrogen combustion gas, when heating the reducing gas to the 800–1000°C typically required for iron oxide reduction, provides only 40–50% of the net energy available, as 50–60% of the energy is absorbed by the combustion gases. On the other hand, the efficiency of electric heating is usually greater than 90%, as it only has mechanical and electrical energy losses.

[0009] It has also been determined that state-of-the-art processes are not compatible with electric heating. For example, in the direct reduction furnace, excess inert and non-condensable oxidizing gas must be removed from the process to prevent accumulation in the main process gas circuit. Currently, this is done by purging a portion of the spent gas, called Top Gas Fuel in the MIDREX® Process (see FIG. 1), for use as fuel for the reformer / heater. In the state-of-the-art direct reduction process using a natural gas reformer, to compensate for the gas volume expansion resulting from the reforming reaction, the Top Gas Fuel flow rate can be as high as 1 / 3 of the overflow, meaning that 2 / 3 of the gas is recycled per pass. 1919456 of 22 However, in the modern Midrex Plant with natural gas, the amount of Top Gas Fuel generated is well balanced with the fuel gas requirement with the reformer and little fuel gas replacement is required.

[0011] In the state-of-the-art, near-100% direct hydrogen reduction process, we encounter a similar situation when producing DRI containing carbon, a desirable property for downstream smelting, when introducing carbonaceous gas such as natural gas. In this scenario, typically 10-20% of the top gas from the blast furnace must be purged as Top Gas Fuel, depending on the target carbon content in the DRI, to remove non-condensable oxidants like CO2. This results in a lack of reformed CO2, where the CO2 can be converted to CO for reuse within the reduction furnace. The hydrogen reduction process without the reformer will generate purged Top Gas Fuel containing a significant amount of valuable green hydrogen residue, as well as CO and CO2, which must be used by the reducing gas heater to fire with a fuel gas composition such as hydrogen or natural gas.Therefore, the hydrogen reduction processes to produce state-of-the-art carbon-containing DRI need to keep the reducing gas heater on fire to use Top Gas Fuel and tolerate the higher fuel gas consumption in the production of carbon-containing DRI.

[0012] Methods and systems exist for removing CO2 from top gas, but these also demonstrate limited effectiveness when hydrogen is used as the primary gas for reduction. The small amount of CO2 in the top gas of the shaft furnace limits the performance of conventional gas separation technologies, such as amine scrubbing and pressure swing adsorption. The low CO2 concentration in the gas stream can result in relatively large CO2 capture unit operations with lower efficiency or more hydrogen slippage into the gas removed for this application. Field examples also show high integration with fire heaters, as these are again used to handle the waste gases and utilize the excess heat for the process. 1919456 of 22

[0013] In the case of 100% hydrogen reduction to produce carbon-free DRI without the introduction of carbonaceous gas, the purge portion of the top gas from the shaft furnace is not as large as in the first case. However, non-condensable inert gas, such as nitrogen, must be removed to prevent accumulation in the process gas circuit as Top Gas Fuel, the main fraction of which is hydrogen. The purged Top Gas Fuel must be used by the flame-reducing gas heater unless other suitable consumers exist, or it is simply vented through a flare system, which increases the amount of H2 consumption as in the previous case.

[0014] Therefore, in embodiments of the invention, the present disclosure provides a method and system for the production of DRI from hydrogen using a combustion-free mechanism, such as an electric heating mechanism, while significantly improving energy efficiency compared to state-of-the-art technologies with fire heating.

[0015] In several embodiments, this disclosure provides new methods and systems for recycling spent top gas from the reduction shaft furnace and managing the accumulation of inert and non-condensable oxidizing gas within the main recycling circuit. Advantageously, hydrogen consumption for iron oxide reduction is reduced compared to existing technologies, thereby improving process efficiency.

[0016] In an exemplary embodiment, a method for recycling spent reducing gas in a direct iron ore reduction system using a combustion-free reducing gas heater, such as an electric gas heater, to heat the reducing gas to temperatures sufficient for iron reduction, comprises: a. provide a shaft furnace of a direct reduction plant to reduce iron oxide to metallic iron with a hydrogen-rich reducing gas; b. Remove vapor and particles from the spent reducing gas with a 1919456 of 22 scrubber to process the upper gas from the shaft furnace; c. process all or a portion of the scrubbed overhead gas in a gas separation unit to create a hydrogen-rich stream with its fraction of reduced non-hydrogen compounds and an oxidant / inert-rich stream containing CO2, CO, CH4, H2, N2 and other compounds; and d. Recycle the hydrogen-rich stream from the gas separation and the remaining portion of the cleaned overhead gas with fresh hydrogen to create the hydrogen-rich reducing gas for the process.

[0017] In some embodiments, when producing the carbon-containing DRI with the carbon deposit gas fed into the transition zone of the shaft furnace, the gas added to the transition zone is created by mixing a portion of the oxidizer / inert rich stream generated in the gas separation with an external carbon deposit gas.

[0018] In some embodiments, the method further comprises selectively removing all or a portion of the CO2 from the oxidant-rich / inert stream prior to mixing to create the transition zone gas.

[0019] In some embodiments, the method comprises processing all or a portion of the scrubbed overhead gas in a pressure swing adsorption (PSA) gas separation unit to generate two (2) gas streams; a hydrogen / nitrogen rich stream and a methane / oxidant rich stream, selectively recovering a hydrogen rich stream from the hydrogen / nitrogen rich stream with a membrane gas separation unit before recycling the hydrogen rich stream back to the main process gas circuit, and / or selectively recovering a methane from the methane / oxidant rich stream with a membrane gas separation unit before directing it to the transition zone after mixing it with an external carbon deposition gas.

[0020] In another exemplary embodiment, the present invention provides a process for 1919456 of 22 producing direct reduction iron with a hydrogen-rich reducing gas, using a combustion-free reducing gas heater to heat the hydrogen-rich reducing gas to a temperature sufficient for iron reduction. The process comprises providing a reduction shaft furnace of a direct reduction plant to reduce iron oxide to metallic iron with the hydrogen-rich reducing gas; providing an overhead gas stream from the reduction shaft furnace comprising spent reducing gas to a scrubber to remove vapor and particulates from the spent reducing gas; processing all or a portion of the scrubbed overhead gas in a gas separation unit to create a hydrogen-rich stream with its fraction of non-hydrogen compounds reduced, and an oxidant / inert-rich stream comprising CO2, CO, CH4, H2, and N2;and recycling the hydrogen-rich stream from the gas separation unit and at least a portion of the scrubbed overhead gas with hydrogen replenishment or feedstock from another hydrogen-rich stream to create the hydrogen-rich reducing gas introduced into the shaft furnace, wherein prior to introduction into the shaft furnace, the hydrogen-rich reducing gas is heated in the non-combustion reducing gas heater to heat the hydrogen-rich reducing gas to 800–1100°C. The process may comprise injecting a portion of the oxidizer / inert-rich stream taken from the gas separation unit into a transition zone of the shaft furnace to carburize the direct reduced iron, after mixing it with a hydrocarbon-containing gas. The process may comprise providing a CO2 separator;To process all or a portion of the oxidizer-rich / inert stream extracted from the gas separation unit with the CO2 separator to recover purified CO2; and to inject a portion of a lean CO2 gas discharged from the CO2 separator into a transition zone of the shaft furnace to carburize the direct reduction iron, after mixing it with a hydrocarbon-containing gas. The gas separation unit may be a membrane gas separator, a pressure swing adsorption gas separation unit, or a cryogenic gas separation unit. The CO2 separator may be an amine adsorption unit or a pressure swing adsorption gas separation unit. The reducing gas heater; 1919456 of 22 without combustion can be an electric heater that uses electrical energy.

[0021] In another exemplary embodiment, a process for producing direct reduction iron with a hydrogen-rich reducing gas, using a combustion-free reducing gas heater to heat the hydrogen-rich reducing gas to a temperature sufficient for iron reduction, comprises providing a reduction shaft furnace of a direct reduction plant to reduce iron oxide to metallic iron with the hydrogen-rich reducing gas; providing an overhead gas stream from the reduction shaft furnace comprising spent reducing gas to a scrubber for removing vapor and particulates from the spent reducing gas, with the scrubber to process the overhead gas from the shaft furnace and produce a scrubbed overhead gas;processing all or a portion of the cleaned overhead gas in a pressure swing adsorption gas separation unit to create a hydrogen / nitrogen-rich dry stream with its reduced fraction of non-hydrogen or non-nitrogen compounds, and a methane / oxidant-rich stream comprising CH4, CO2, CO, H2O, CH4, H2 and N2; further processing the hydrogen / nitrogen-rich dry stream in a membrane gas separation unit to recover a hydrogen-rich stream;and recycling the hydrogen-rich stream from the membrane gas separation unit and at least a portion of the hydrogen-purged overhead gas from another hydrogen-rich stream to create the hydrogen-rich reducing gas introduced into the shaft furnace, wherein prior to introduction into the shaft furnace, the created hydrogen-rich reducing gas is heated in the combustion-free reducing gas heater to heat the hydrogen-rich reducing gas to 800~1100°C. The combustion-free reducing gas heater can be an electric heater using electrical energy.

[0022] In a further exemplary embodiment, a process for producing direct reduction iron with a hydrogen-rich reducing gas, using a combustion-free reducing gas heater to heat the hydrogen-rich reducing gas to a temperature sufficient for iron reduction, comprises providing a reduction shaft furnace of a direct reduction plant to reduce iron oxide to 1919456 of 22 metallic iron with hydrogen-rich reducing gas; providing an overhead gas stream from the reduction shaft furnace comprising spent reducing gas to a scrubber for removing vapor and particulates from the spent reducing gas with the scrubber to process the overhead gas from the shaft furnace and produce a scrubbed overhead gas; processing all or a portion of the scrubbed overhead gas in a pressure swing adsorption gas separation unit to create a dry hydrogen / nitrogen-rich stream with its reduced fraction of compounds other than hydrogen or nitrogen, and a methane / oxidant-rich stream comprising CH4, CO2, CO, H2O, CH4, H2 and N2; further processing the methane / oxidant-rich stream in a membrane gas separation unit to create a methane-rich stream;and injecting the methane-rich stream from the membrane gas separation unit into a transition zone of the shaft furnace to carburize the direct reduced iron, after mixing it with a hydrocarbon-containing gas. The process may comprise recycling the hydrogen-rich stream from the gas separation unit and at least a portion of the hydrogen-purged overhead gas from another hydrogen-rich stream to create the hydrogen-rich reducing gas introduced into the shaft furnace, wherein prior to introduction into the shaft furnace, the hydrogen-rich reducing gas is heated in the fireless reducing gas heater to 800–1100°C. The fireless reducing gas heater may be an electric heater using electrical energy.

[0023] In another exemplary embodiment, a system for producing direct reduction iron with a hydrogen-rich reducing gas, utilizing a combustion-free reducing gas heater to heat the hydrogen-rich reducing gas to a temperature sufficient for iron reduction, comprises a reduction shaft furnace of a direct reduction plant configured to reduce iron oxide to metallic iron with the hydrogen-rich reducing gas; a scrubber configured to receive an overhead gas stream from the reduction shaft furnace comprising spent reducing gas and removing vapor and particulates from the spent reducing gas with the scrubber to process the overhead gas from the shaft furnace and produce a scrubbed overhead gas; a gas separation unit configured to process all or a portion of the overhead gas 1919456 of 22 purified to create a hydrogen-rich stream with its fraction of non-hydrogen compounds reduced, and an oxidant / inert-rich stream comprising CO2, CO, CH4, H2 and N2; and a recycling line configured to recycle the hydrogen-rich stream from the gas separation unit and at least a portion of the hydrogen-purged overhead gas from another hydrogen-rich stream to create the hydrogen-rich reducing gas introduced into the shaft furnace, wherein prior to introduction into the shaft furnace, the hydrogen-rich reducing gas is configured to be heated in the non-combustion reducing gas heater to heat the hydrogen-rich reducing gas to 800~1100 C. The system may comprise a compressor configured to pressurize the purified overhead gas.The system may include another recycling line configured to inject a portion of the inert / oxidant-rich stream extracted from the gas separation unit into a transition zone of the shaft furnace to carburize the direct reduced iron, after mixing it with a hydrocarbon-containing gas. The system may include a CO2 separator configured to recover purified CO2 from the oxidizer / inert-rich stream discharged from the gas separation unit for the purified overhead gas. The gas separation unit may be a membrane gas separator, a pressure swing adsorption gas separation unit, or a cryogenic gas separation unit. The CO2 separator may be an amine adsorption unit or a pressure swing adsorption gas separation unit. The non-combustion reducing gas heater may be an electric heater powered by electricity.

[0024] In another exemplary embodiment, a system for producing direct reduction iron with a hydrogen-rich reducing gas, utilizing a combustion-free reducing gas heater to heat the hydrogen-rich reducing gas to a temperature sufficient for iron reduction, comprises a reduction shaft furnace of a direct reduction plant configured to reduce iron oxide to metallic iron with the hydrogen-rich reducing gas; a scrubber configured to receive an overhead gas stream from the reduction shaft furnace comprising spent reducing gas and to remove vapor and particulates from the spent reducing gas with the scrubber to process the 1919456 of 22 top gas from the shaft furnace and produce a purified top gas; a pressure swing adsorption gas separation unit configured to process all or a portion of the purified top gas to create a hydrogen / nitrogen rich dry stream with its non-hydrogen or nitrogen compound fraction reduced, and a methane / oxidant rich stream comprising CH4, CO2, CO, H2O, CH4, H2 and N2; a secondary membrane gas separation unit configured to process the hydrogen / nitrogen rich dry stream and create a hydrogen rich stream;and a recycling line configured to recycle the hydrogen-rich stream from the secondary membrane gas separation unit and at least a portion of the hydrogen-purged overhead gas from another hydrogen-rich stream to create the hydrogen-rich reducing gas introduced into the shaft furnace, wherein prior to introduction into the shaft furnace, the hydrogen-rich reducing gas is configured to be heated in the non-combustion reducing gas heater to heat the hydrogen-rich reducing gas to 800–1100°C. The system may further comprise a compressor configured to pressurize the purified overhead gas. The non-combustion gas heater may be an electric heater using electrical energy.

[0025] In another exemplary embodiment, a system for producing direct reduction iron with a hydrogen-rich reducing gas, utilizing a combustion-free reducing gas heater to heat the hydrogen-rich reducing gas to a temperature sufficient for iron reduction, comprises a reduction shaft furnace of a direct reduction plant configured to reduce iron oxide to metallic iron with the hydrogen-rich reducing gas; a scrubber configured to receive an overhead gas stream from the reduction shaft furnace comprising spent reducing gas and removing vapor and particulates from the spent reducing gas with the scrubber to process the overhead gas from the shaft furnace and produce a scrubbed overhead gas;a pressure swing adsorption gas separation unit configured to process all or a portion of the cleaned overhead gas to create a hydrogen / nitrogen-rich dry stream with its non-hydrogen or non-nitrogen compound fraction reduced, and a methane / oxidant-rich stream comprising CH4, CO2; 1919456 of 22 CO, H2O, CH4, H2, and N2; a secondary membrane gas separation unit configured to process the methane / oxidant-rich stream to create a methane-rich stream; and an injection line configured to inject the methane-rich stream from the membrane gas separation unit into a transition zone of the shaft furnace to carburize the direct reduced iron, after mixing it with a hydrocarbon-containing gas. The combustion-free reducing gas heater can be an electric heater powered by electricity. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The present description is illustrated and described with reference to the various drawings, in which:

[0027] FIG. 1 is a schematic diagram illustrating the aforementioned MIDREX® process;

[0028] FIG. 2 is a schematic diagram illustrating an exemplary embodiment of the method and system of the present disclosure for recycling spent reducing gas in which a portion of the Top Gas is pressurized and sent to a membrane separation unit in which hydrogen is recovered back into the main process circuit and the removed inert and non-condensable oxidizing gas stream is directed, e.g., to a flare system for venting;

[0029] FIG. 3 is a schematic diagram illustrating another exemplary embodiment of the method and system herein described for recycling spent reducing gas in which a portion of the Top Gas is pressurized and sent to a membrane separation unit in which hydrogen is recovered back into the main process circuit and the removed non-condensable inert and a portion of the oxidizing gas stream are mixed with hydrocarbon-containing gas for injection into the transition zone of the reducing shaft furnace; 1919456 of 22

[0030] FIG. 4 is a schematic diagram illustrating another exemplary embodiment of the method and system of the present disclosure for recycling spent reducing gas in which a portion of the Top Gas is pressurized and sent to a multi-stage separation unit including a PSA and an amine scrubber in which hydrogen is recovered back into the main process circuit, high-purity carbon dioxide (e.g., at least 95%) is recovered in the amine scrubber, and a remaining portion of the CO2-lean stream is blended with hydrocarbon-containing gas for injection into the transition zone of the reducing shaft furnace; and

[0031] Figure 5 is a schematic diagram illustrating another exemplary embodiment of the method and system of the present disclosure for recycling spent reducing gas, in which a portion of the top gas is pressurized and sent to a multi-stage separation unit that includes membrane and PSA separation units. The hydrogen / nitrogen-rich gas recovered with the PSA unit is further processed with the membrane unit to remove nitrogen, in which the hydrogen is recycled to the main process circuit and the nitrogen is directed, for example, to a flare system for venting. The methane / oxidant-rich stream removed with the PSA is further processed with the membrane unit to recover methane, in which the methane-rich stream is injected into the transition zone with the hydrocarbon-containing gas composition and the remaining gas stream from the membrane unit is directed to a flare system for venting. DETAILED DESCRIPTION OF ACHIEVEMENTS

[0032] Again, in several exemplary embodiments, the present disclosure advantageously provides a method and system for the production of DRI from hydrogen using electric heating while significantly improving energy efficiency compared to current state-of-the-art technologies. Furthermore, in several embodiments of the disclosure, novel methods and systems are provided for recycling spent top gas from the reduction furnace and managing the accumulation of inert and non-condensable oxidizing gas within the recycling circuit. 1919456 of 22 main, where the accumulation of inert gas mainly occurs. This is due to nitrogen in the sealing gas used in the material loading / unloading system in the shaft furnace, and the accumulation of non-condensable oxidizing gas is mainly caused by CO2, especially when carbonaceous gas is introduced to produce the carbon-containing DRI. Advantageously, hydrogen consumption for reducing iron oxide is reduced compared to existing technologies, thus managing the accumulation of inert and non-condensable oxidizing gas and improving process efficiency.

[0033] Referring specifically to FIG. 1, system / method 90 represents the latest generation direct reduction process using natural gas. Iron oxide 2 is charged from the top of the shaft furnace 1 and reduced to DRI 3 discharged from the bottom of the shaft furnace 1, where hot reducing gas 11 produced by the MIDREX reformer is introduced into the stirring chamber of the shaft furnace 1. The top gas 4 from the shaft furnace, containing many reduction products such as H2O and CO2, is processed with the top gas scrubber 5, where the top gas is cooled to reduce the H2O content and particulates are removed. A portion of the scrubbed top gas must be purged and used as fuel for the reformer / heater, referred to as Top Gas Fuel in the MIDREX Process, to remove excess inert and non-condensable oxidizers, such as nitrogen and CO2, remaining in the recycled gas.In the conventional MIDREX process with the efficient reformer that converts CO2 into CO for reuse within the reduction furnace, to compensate for the expansion of the gas volume resulting from the reforming reaction, the proportion of purge gas after the scrubber can reach 1 / 3 of the overhead gas, meaning that only 2 / 3 of the gas can be recycled per pass.

[0034] With reference now specifically to FIG. 2, for the production of DRI from hydrogen, the system / method 100 depicted therein is configured to recycle the spent reduction gas in which a portion of the purified overhead gas is purged, pressurized and sent to a membrane separation unit in the 1919456 of 22 that the hydrogen is recovered back into the main process gas circuit and the removed inert and non-condensable oxidizing gas stream is directed, for example, to a flare system.

[0035] In an exemplary embodiment, the top gas 4 from the shaft furnace, which contains many reduction products as in the MIDREX process of FIG. 2, such as H2O and CO2, is processed with the scrubber 5, in which the gas is cooled to reduce the H2O content and particulates are removed from the top gas. To remove excess non-condensable inert and oxidizing agents, such as CO2, and to manage accumulation in the main process gas circuit, a portion of the scrubbed top gas 12 is purged, in which typically between 10 and 20% of the top gas from the shaft furnace should be purged, depending on the target carbon content in DRI. The purged overhead gas is pressurized by compressor 13 and sent to a membrane gas separation unit 15 through stream 14. Two gas streams are generated from the gas separation unit 15, a hydrogen-rich stream 20 and an oxidant / inert-rich stream 21.The hydrogen-rich stream 20, which normally comprises more than 90% hydrogen, is recovered back into the main process circuit and mixed with the remaining exhaust gas from the scrubber 6. These gas mixtures are pressurized by process gas compressors 7, followed by preparation with the hydrogen stream of the fresh gas 9 to remake the reducing gas 11. The reducing gas 11 is heated in an electric heater 10 or other suitable fireless heating device to the typical temperature of 800–1000°C required for the reduction of iron oxide in the shaft furnace 1. This mixing point for the hydrogen-rich stream 20 with the exhaust gas from the scrubber 6 can occur before or after the process gas compressors 7 depending on the pressure balance.The oxidizer / inert rich stream 21, which is the dry gas that normally comprises more than 70% of compounds other than hydrogen, is used by other site users or burned through conventional means such as a flare or thermal oxidizer.

[0036] In the case of a 100% hydrogen reduction to produce the DRI without 1919456 of 22 carbon without the introduction of carbonaceous gas, the amount of the oxidizer / inert rich stream 21 is less than that produced by the carbon-containing DRI, although the amount depends on the nitrogen content remaining in the reducing gas 11. The hydrogen rich stream 20 typically comprises more than 90% hydrogen, and the oxidizer / inert rich stream 21 typically comprises nitrogen and some slipped H2. Therefore, the system / method 100 of FIG. 2 can probably be applied to decrease hydrogen consumption.

[0037] With reference now specifically to FIG. 3, the system / method 110 depicted therein is configured to recycle spent reduction gas in which a portion of the purged overhead gas is purged, pressurized, and sent to a membrane separation unit where hydrogen is recovered and returned to the main process gas circuit. A portion of the removed non-condensable inert and waste gas stream is mixed with hydrocarbon-containing gas before being injected into a transition zone of the shaft furnace. This configuration is advantageous for the hydrogen reduction process when producing carbon-containing DRI by introducing carbonaceous gas such as natural gas into the transition zone of the reduction shaft furnace.

[0038] In an exemplary embodiment shown in FIG. 3 and similar to FIG. 2, the purged, cleaned overhead gas 12 is pressurized by the compressor 13 and sent to a membrane gas separation unit 15 via stream 14. Two gas streams are generated from the gas separation unit 15: a hydrogen-rich stream 20 and an oxidant / inert-rich stream 16 (see FIG. 21). The hydrogen-rich stream 20 typically comprises more than 90% hydrogen. The oxidant / inert-rich stream 16 is the dry gas, which normally comprises more than 70% non-hydrogen compounds, including methane and CO, that have DRI carburizing potential. The difference from FIG. 2 is that here the inert / oxidant-rich stream is directed to the transition zone of the shaft furnace, as shown in FIG. 3 for reuse as fuel gas, instead of sending it to other users or burning it in a flare or thermal oxidizer as in FIG. 2.To avoid it. 1919456 of 22. To prevent the accumulation of inert and oxidizing gases, such as N2 and CO2, in the process gas circuit, a portion of the oxidizer / inert rich stream 16, as shown in stream 22, can be purged for external use or burned by conventional means, such as a flare or thermal oxidizer. A remaining portion of the oxidizer / inert rich stream 16 is directed to the transition zone in the fuel gas stream 19 after a carbon-favoring gas 17, such as natural gas, is added in a gas mixer 18.

[0039] Different gases can be supplied as desired for mixing the transition zone in gas mixer 18. A primary factor in selecting the gas composition is its ability to deposit carbon onto iron at temperatures above 650 °C. Suitable gases include those with medium to high levels of methane and heavier hydrocarbons. Gases with low levels of methane can also be used, but this may result in a potential reduction of carbon in the DRI product.

[0040] The required amount of inert / oxidant-rich gas purge in stream 21 of FIG. 2 or stream 22 in FIG. 3 is determined by the accumulation of inert and oxidizing gas in the process gas circuit. In the case of 100% hydrogen reduction to produce carbon-free DRI without the introduction of carbon dioxide, the amount in stream 21 in FIG. 2 will likely be adjusted by the nitrogen content in the reducing gas stream 11. In the case of producing carbon-containing DRI, the amount in stream 21 in FIG. 2 will likely be adjusted by the CO2 content in the reducing gas stream 11, and the amount in stream 22 in FIG. 3 will likely be adjusted by the CO2 content in the fuel gas stream 19, as well as the CO2 content in the reducing gas stream 11.The amount of gas purge can be reduced and hydrogen consumption can be further improved by removing more inert and oxidant from the inert / oxidant rich stream 16 before it goes to the transition zone of the shaft furnace, as also mentioned below. 1919456 of 22

[0041] With reference now specifically to FIG. 4, the system / method 120 depicted therein is configured to recycle spent reduction gas in which a portion of the scrubbed overhead gas is pressurized and sent to a pressure swing adsorption (PSA) and amine scrubber in which hydrogen is recovered back into the main process circuit, high-purity carbon dioxide is recovered in the amine scrubber, and a portion of the remaining CO2-lean gas stream is mixed with hydrocarbon-containing gas before being injected into the transition zone of the reduction shaft furnace.

[0042] In an exemplary embodiment, the purged overhead gas 12 is pressurized by the compressor 13 and sent to the pressure swing adsorption (PSA) unit 23 via stream 14. Two gas streams are generated (similar to Figures 2 and 3): a hydrogen-rich stream 20 and an inert / oxidant-rich stream 24 (21 in Figure 2). The hydrogen-rich stream 20 is the dry gas, typically comprising more than 90% hydrogen, to be recovered back into the main process circuit and blended with the remaining outlet gas from the scrubber 6. These gas mixtures are pressurized by the process gas compressor 7, followed by preparation with the fresh hydrogen stream 9 to remake the reducing gas 11.The reducing gas 11 is heated in an electric heater 10 or other suitable electric heating device to the desired temperature, typically 800~1000 C, for the reduction of iron oxide in the shaft furnace 1. This mixing point for the hydrogen-rich stream 20 with the remaining exhaust gas from the scrubber 6 can occur before or after the process gas compressor 7 depending on the pressure equilibrium.

[0043] A portion or all of the oxidant / inert-rich stream 24, which typically comprises more than 70% non-hydrogen compounds such as N2, CO, CO2, H2O, and methane, is pressurized by compressor 24 and directed to an amine absorption / separation unit 25 for further processing. A high-purity CO2 stream 26, which typically comprises more than 99% CO2 on a dry basis, is recovered for external uses. Examples of potential uses include 1919456 of 22 the utilization of CO2 in another process or sequestration in long-term storage. To manage the accumulation of N2 and CO2 in the main process gas circuit, a portion of the remaining CO2-poor gas 16' from the amine absorption / separation unit 25 is purged in stream 22. The remaining portion of the CO2-poor gas 16' is then directed to the transition zone of the reduction shaft furnace 1 in stream 19 after a carbon-favoring gas 17, such as natural gas, is added in a gas mixer 18. The purge stream 22 is located upstream or downstream of the amine absorption / separation unit 25 to maintain N2 and CO2 levels in the main gas circuit and is directed to external uses or can be burned through conventional means, such as in a flare or thermal oxidizer.

[0044] Referring now specifically to FIG. 5, the system / method 130 depicted therein is configured to recycle spent reducing gas in which a portion of the scrubbed overhead gas is pressurized and sent to a pressure swing adsorption (PSA) unit via stream 14, followed by several membrane gas separation units to recover hydrogen and methane-rich gas after removing N2 and CO2. The hydrogen is recovered back into the main process gas circuit. The methane-rich gas is directed to gas mixer 18 and blended with the additional hydrocarbon-containing gas 17 before being injected into the transition zone of the reducing shaft furnace 1 via stream 19.

[0045] In an exemplary embodiment as also shown in FIG. 5, the purged overhead gas 12 is pressurized by the compressor 13 and sent to the pressure swing adsorption (PSA) unit 23, where two gas streams are generated: a hydrogen / nitrogen-rich stream 20' and a methane / oxidant-rich stream 24. The hydrogen / nitrogen-rich stream 20' is the dry gas, normally comprising more than 90% hydrogen / nitrogen, which is sent to a membrane gas separation unit 27 to separate the hydrogen-rich gas 29 and the nitrogen-rich gas 28. The hydrogen-rich gas 29 is recovered back into the main process circuit and mixed with the remaining outlet gas from the scrubber 6. 1919456 of 22 The nitrogen-rich gas 28 is sent, for example, to a flare for venting. The methane / oxidant-rich stream 24, which typically comprises more than 70% non-hydrogen compounds such as CO, CO2, H2O, and methane, is pressurized by compressor 24' and sent to another membrane gas separation unit 30 to separate the methane-rich stream 16'' from the remaining oxidizing gas stream 31. The methane-rich stream 16'' is directed to the gas mixer 18 and supplemented with additional hydrocarbon carrier gas 17 before being injected into the transition zone via stream 19 into the carbon-containing DRI product. The remaining oxidizing gas stream 31 is sent, for example, to a flare for venting.

[0046] The system / method 130 shown in FIG. 5 comprises multiple gas separation units to advantageously minimize the amount of vent gas used to manage CO2 and N2 buildup and maximize the hydrogen and methane recovery rate. The methane-rich stream 16'' in FIG. 5 from membrane gas separation unit 30 is dry gas consisting primarily of methane with minimal CO2 and is suitable for carburizing the DRI in the shaft furnace. Furthermore, reusing the recovered methane for injection into the transition zone will effectively reduce CO2 emissions compared to state-of-the-art technology.

[0047] Therefore, in accordance with advantageous embodiments, a process / system for producing direct reducing iron with a hydrogen-rich gas is described, using a combustion-free reducing gas heater such as an electric heater to heat the reducing gas to temperatures sufficient for iron reduction. The process may include providing a shaft furnace to reduce iron oxide with the hydrogen-rich reducing gas; removing steam and particulates from the top gas of the shaft furnace with a scrubber; processing all or a portion of the scrubbed top gas in a gas separation unit, such as a membrane and PSA gas separation unit, to create a hydrogen-rich stream that will be recycled back to the shaft furnace as a reducing agent, so that hydrogen consumption can be reduced when the combustion-free reducing gas heater is applied. 1919456 of 22 combustion and none consume the purged upper gas from the shaft furnace to manage the accumulation of inert and non-condensable oxidizing gas in the process gas circuit. The process can be further optimized to increase the amount of recycled hydrogen and methane with secondary gas separation units when a carbonaceous gas such as natural gas is introduced into the plant that operates with almost 100% hydrogen and operates to produce DRI containing carbon.

[0048] Although the present invention is illustrated and described herein with reference to particular and preferred embodiments and specific examples thereof, it shall be evident to persons skilled in the art that other embodiments and examples may perform similar functions and / or achieve similar results. All equivalent embodiments and examples are within the spirit and scope of the present invention, contemplated herein, and intended to be covered by the following non-limiting claims. Furthermore, all features, elements, and embodiments described herein may be used in any combination. 1919456 of 22 CAROLINA FERNÁNDEZ - 27221005797 Digitally signed by PORTALTRAM ITES - INPI Date: 2022.08.12 15:17:58 -03:00 Reason: Digitally Signed by the INPI Location: Buenos Aires, Argentina 1919456

Claims

1. A process for producing direct reduction iron with a hydrogen-rich reducing gas, using a combustion-free reducing gas heater to heat the hydrogen-rich reducing gas to a temperature sufficient for iron reduction, characterized in that it comprises: providing a reduction shaft furnace of a direct reduction plant for reducing iron oxide to metallic iron with the hydrogen-rich reducing gas; providing an overhead gas stream from the reduction shaft furnace comprising spent reducing gas to a scrubber for removing vapor and particulates from the spent reducing gas, with the scrubber for processing the overhead gas from the reduction shaft furnace and producing a scrubbed overhead gas;processing all or a portion of the scrubbed overhead gas in a gas separation unit to create a hydrogen-rich stream with its fraction of non-hydrogen compounds reduced, and an oxidant / inert-rich stream comprising CO2, CO, CH4, H2, and N2; and recycling the hydrogen-rich stream from the gas separation unit and at least a portion of the scrubbed overhead gas with hydrogen replenishment from another hydrogen-rich stream to create the hydrogen-rich reducing gas introduced into the reduction furnace, wherein prior to introduction into the reduction furnace, the hydrogen-rich reducing gas is heated in the combustion-free reducing gas heater to heat the hydrogen-rich reducing gas to 800–1100°C. Eight claims follow;