Method and system for producing steel or molten-iron-containing material with reduced emission

Abstract

To provide a method for producing steel or molten-iron-containing materials with reduced emissions of carbon dioxide.SOLUTION: A method for producing steel or molten-iron-containing materials 22 with reduced emissions of carbon dioxide includes producing DRI 18 in a direct reduction furnace 12 with a reducing gas comprising hydrogen 16. The method further includes: melting at least a portion of DRI in a melting furnace 20 and generating hot gases 24; producing steam and / or hot water 28, 40 using heat contained in the generated hot gases; using them to generate electrical energy 42, and then using the electrical energy 42 to produce the hydrogen 16 by electrolysis; obtaining at least a portion of water to be used for producing hydrogen by electrolysis from condensed steam contained in an exhaust reducing gas stream drawn from the direct reduction furnace as an upper gas; producing the hydrogen 16 from the steam and / or hot water 28, 40 by electrolysis; and providing at least a portion of the hydrogen 16 as a component of the reducing gas to the direct reduction furnace 12.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention generally relates to a method and system for producing steel or similar molten iron-containing materials in a melting or smelting furnace that utilizes pre-reduced iron ore, also known as direct reduced iron (DRI) or sponge iron, with significantly low emissions of CO2 and other greenhouse gases.

Background Art

[0002] Steel production mainly contributes to a significant proportion of industrial CO2 emissions through the use of coal and raw materials as energy sources in integrated steel plants equipped with blast furnaces and blast furnace oxygen converters. Steel is also produced by another route that includes the direct reduction of iron ore.

[0003] Although several proposals for methods and systems for heat recovery from hot gases to produce steam and electricity have been found in the prior art, the present invention provides an integrated system for "green" steelmaking, where the reducing agent is hydrogen converted from water in the iron reduction facility, and the water is used to produce hydrogen by electrolysis, which has a significant economic advantage as it greatly reduces the consumption of CO2. Such an integrated system is the essence of the present invention.

[0004] The applicant has found, as an example of several proposals, U.S. Patent No. 8,587,138 to Statler et al., which utilizes the heat generated in the metal melting process and ore smelting to generate electricity. However, Statler does not disclose or suggest the integration of a metal melting plant and a direct reduction plant to minimize the CO2 emissions of the steelmaking process.

[0005] Some proposed methods for reducing CO2 emissions in steelmaking mention the use of renewable energy sources such as solar, wind, and biomass energy to produce the electricity used to produce hydrogen by electrolysis. However, these systems are still under development, and the cost of such electricity is still high compared to grid power available from other sources.

[0006] Approximately 70% of the energy loss in EAF (Electric Arc Furnace) steelmaking is associated with the exhaust gas where approximately 15% of the energy input is lost as sensible heat. During the melting and refining process executed in the EAF, the unburned CO released is burned with air in a post-combustion chamber for the exhaust gas. It is estimated that more than 25% of the shaft energy input of the EAF (Electric Arc Furnace) is recovered and utilized. However, this heat recovery from the EAF exhaust gas is not widely implemented due to the harsh environment of the EAF steam system and the discontinuity of gas generation as the EAF process is a batch process.

[0007] The heat of the EAF (Electric Arc Furnace) exhaust gas is recovered using a high-pressure pipe designed to withstand steam system conditions at pressures from 15 to 40 bar and produce high-pressure steam at 216 °C. The temperature of the exhaust gas after the heat recovery step drops to about 600 °C. Using a steam accumulator, the production of high-pressure steam is utilized in a continuous manner regardless of the cyclicity of the EAF (Electric Arc Furnace) process. An average steam production of 20 t / h from a 140 t / h EAF (Electric Arc Furnace) has been demonstrated by Tenova S.p.A. After steam production, a second heat recovery stage is added to utilize the heat content of the steam gas, and the temperature of the exhaust gas is lowered from about 600 °C to about 200 °C using a standard waste heat boiler. By utilizing two heat recovery stages, about 75% to 80% of the total energy content of the EAF exhaust gas is recovered. This recovered energy reaches about 24,000 megawatt-hours (MWh / year).

[0008] The present invention utilizes the thermal energy produced in a steelmaking process that would otherwise be wasted by the integration of a DRI melting furnace, a DRI production plant, and an electrolysis unit to generate hydrogen, thereby reducing the use of hydrocarbons and thus CO2 emissions to the atmosphere for the production of said DRI.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Summary of the Invention

[0010] The present invention provides a method for producing a steel or molten iron-containing material with reduced carbon dioxide emissions, comprising the step of producing DRI in a direct reduction furnace with a reducing gas containing hydrogen, melting at least a part of the DRI in a melting furnace, generating hot gas, and using the heat contained in the hot gas to produce steam and / or hot water. Hydrogen and / or hot water are produced from the steam by electrolysis, and at least a part of the hydrogen is supplied as a component of the reducing gas to the direct reduction furnace to produce the DRI (direct reduced iron).

[0011] The present invention also provides a system for producing a steel or molten iron-containing material, minimizing CO2 emissions by using the hydrogen of the DRI production facility produced by electrolysis using the energy from the DRI melting facility.

[0012] In one embodiment, the system of the present invention comprises a direct reduction furnace for producing DRI, a DRI melting furnace (EAF) for melting the DRI to generate hot gas, a heat recovery unit for producing steam and / or hot water using the heat contained in the hot gas, and an electrolysis unit for producing hydrogen from the steam and / or hot water, and the hydrogen is supplied to the direct reduction furnace to produce DRI.

[0013] In one embodiment, the system of the present invention further comprises a generator for producing electrical energy using the steam from the heat recovery unit, and the electricity is used in the electrolysis unit to produce hydrogen.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

[0015] Referring to FIG. 1, reference numeral 10 generally designates a steelmaking system that reduces CO2 emissions with a direct reduction facility 12, and iron oxide 14 is chemically reduced in solid form by a reducing agent such as hydrogen 16, for example, into solid direct reduced iron (DRI) 18 containing metallic iron. The DRI 18 is further processed alone or mixed with steel scrap in a melting plant 20 equipped with an electric arc furnace (EAF) and a ladle furnace for normal metallurgical processing to produce steel 22 or other molten iron-containing products such as pig iron or alloy iron. The EAF of the melting plant 20 produces a significant amount of hot gas 24 at a high temperature on the order of 1000° C. to 1400° C. The heat of these hot gases 24 is recovered by a suitable heat exchanger into a heat recovery unit 26 to produce steam 28 and / or hot liquid water from a water supply device 30 and a cold blast gas 32 at a temperature of about 100° C. or less is processed in a manner known in the art before being properly released to the atmosphere.

[0016] The steam 28 and the hot liquid water produced by utilizing the heat of the hot gas 24 are supplied to an electrolysis unit 34 where water is split into hydrogen steam 16 and oxygen steam 36. The hydrogen steam 16 is supplied to the direct reduction facility 12 to produce DRI 18 from the material 14 having iron oxide. The iron oxide 14 is chemically reduced by hydrogen 16 into metallic iron (DRI) 18, whereby water 38 is produced by the reaction: Fe x O y +yH2→xFe+yH2O. The oxygen 36 is used in the direct reduction plant 12 and / or in the DRI melting furnace 20 and for many other purposes of the steelmaking system 10.

[0017] In the steelmaking system according to the present invention, the water 38 produced by the reduction reaction of iron oxide and hydrogen is purified, properly handled, heated, and converted into steam 28 that is again divided into hydrogen 16 that is reused for the reduction of iron oxide, thus forming a hydrogen recycling loop. This synergistic effect of the direct reduction plant 12 equipped with the heat recovery unit 26 and the electrolysis unit 34 significantly reduces the carbon consumption of the steelmaking process.

[0018] In another embodiment of the present invention, all or part of the steam 40 produced in the heat recovery unit 26 is used to generate electricity 42 in the generator 44, and the electricity is then used in the electrolysis unit 34 together with or instead of another power source 43. After the generation of electricity, the condensed water 45 is also utilized in the electrolysis unit 34 for hydrogen generation.

[0019] Referring to FIG. 2, the direct reduction plant 12 includes a direct reduction shaft furnace 50 having a reduction region 52 and a low discharge region 54 where the DRI 18 is discharged at a rate adjusted by a suitable discharge mechanism 56, such as a rotary star feeder, a vibration feeder, a screw feeder, etc. Iron oxide in the form of pellets, lumps, or a mixture thereof 14 is supplied to the reduction furnace 50, descends by gravity through the reduction region 52, and in the reduction region, the DRI-containing metallic iron is at a high temperature in the range of about 800 °C to about 1050 °C, mainly consisting of hydrogen 16, and in those embodiments where hydrocarbons such as syngas obtained from natural gas or coal, for example, are used as a source of the reducing gas 6, it is formed by the reaction of the reducing gas stream 6 containing carbon monoxide, carbon dioxide, methane, nitrogen with the iron oxide.

[0020] The flow of the exhaust reducing gas is, due to the chemical equilibrium of the reduction reaction and the limitations of reaction kinetics, the upper gas 58 containing unreacted hydrogen, water produced as a by-product of the reduction reaction, and in some embodiments, hydrocarbons such as, for example, synthesis gas obtained from natural gas or coal, when used as a source of the reducing gas 6 in the direct reduction furnace 50, withdrawn from the reduction furnace 50 as carbon monoxide, carbon dioxide, methane, and nitrogen. The upper gas 58 exits the direct reduction furnace 50 at a temperature in the range of about 300 °C to 450 °C and passes through a heat exchanger 60 where a suitable fluid 62, such as water, is heated to produce steam 64. The steam 64 is utilized in any CO2 removal unit or utilized to produce hydrogen in the electrolysis unit 34, or alternatively, the heat of the upper gas 58 is utilized to preheat the reducing gas stream 6 supplied to the reduction furnace.

[0021] After exiting the heat exchanger 60 through the conduit 158, the upper gas 58 is purified and cooled in the gas cooler 66 by water. The water vapor contained in the upper gas 58 is condensed in the cooler 66 as a water stream 68 and, after appropriate treatment by methods known in the art, is supplied through the conduit 168 to the electrolysis unit 34.

[0022] A portion of the clean cooled upper gas 70 added in FIG. 2 is withdrawn from the reduction system as a gas stream 72 to prevent, where applicable, the accumulation of inert gas in the reducing gas recycle. The valve 74 is used to adjust the amount of the upper gas removed from the reduction plant 12 and also to adjust the operating pressure of the reduction plant 12. Most of the clean upper gas 70, 76, is recycled through a compressor 78 that raises its pressure to reuse the upper gas 70 in the reduction furnace 50.

[0023] The recycle gas stream 80 consisting mainly of hydrogen then passes through a gas heater 85 to raise its temperature to a range of about 800 °C to about 1000 °C so that the reduction reaction with iron oxide occurs inside the reduction furnace 50.

[0024] Optionally, the fabricated hydrocarbon gas stream 82 is added to the recycle gas stream 80 from a suitable source 84 and generates hydrogen and carbon monoxide that form part of the reducing gas 6 supplied to the reduction furnace 50.

[0025] In one embodiment, the hydrocarbon gas 82, such as natural gas for example, is converted to hydrogen and carbon monoxide by reaction of the water and carbon dioxide contained in the recycle gas stream 80 in a catalytic reformer 85, thereby forming the reducing gas stream 6.

[0026] In a further embodiment, the reforming of the hydrocarbon gas 82 to hydrogen and carbon monoxide is carried out in the reduction furnace 50 together with the reduction reaction. In such a case, the combined stream 86 of the recycle gas 80 and the fabricated hydrogen gas 82 is heated in a heating unit 85 without a catalyst as compared to the case where the unit 85 is a reformer.

[0027] In embodiments of the invention where the hydrocarbon gas 82 is also utilized as a source of the reducing gas 6, the recycle gas stream 80 is processed in a CO2 removal unit 88 to separate the CO2 89 produced as a byproduct of the reduction reaction of iron oxide and carbon monoxide. The CO2 removal unit is of a type in which CO2 is selectively removed by the action of a solvent such as a solution of amine or potassium carbonate, or of a type in which CO2 is separated by physical adsorption in a PSA (pressure swing adsorption), VPSA (vacuum pressure swing adsorption) or gas membrane unit.

[0028] Optionally, the fabricated hydrocarbon gas 82 is coke oven gas, natural gas, synthesis gas from biomass, or other methane-containing and / or H2- or CO-containing gas.

[0029] Optionally, the carbon content of the DRI is adjusted for further processing in the melting furnace 90 in a wide range from about 0.5% to about 6%, preferably from about 2.5% to 3.5%, by blowing carburizing gas 46 from a suitable source 48, which is a hydrocarbon gas, coke oven gas, natural gas, synthesis gas from biomass, or a mixture thereof, or other methane-containing and / or CO-containing synthesis gas, or other carbon-containing gas that deposits carbon on the DRI.

[0030] In one embodiment, the DRI is cooled and discharged from the reduction furnace 50 by circulating the cooling gas in the lower part 54 of the reduction furnace 50 in a manner known in the art. In this case, the carbon content of the DRI is brought about by using the cooling gas to introduce DRI carburizing gas, which is a hydrocarbon gas, coke oven gas, natural gas, synthesis gas from biomass, or a mixture thereof, or other methane-containing and / or CO-containing synthesis gas, or other carbon-containing gas that deposits carbon on the DRI.

[0031] Typically, the DRI is discharged from the reduction furnace 50 at a high temperature in the range from about 300°C to about 750°C, preferably from about 600°C to about 700°C, and heated and charged into a melting furnace 90, typically an electric arc furnace, having a gas extraction duct 94 for collecting the hot gas produced during the charging, melting, and refining of the electrodes 92 and the DRI and optionally steel scrap. These hot gases exit the electric arc furnace 90 at a high temperature in the range from 1000°C to 1400°C.

[0032] The heat contained in the hot gas 24 drawn from the melting furnace 90 through the duct 94 is utilized to produce steam 108 in a heat exchanger 96 where water 98 is supplied from a suitable source 100. The steam drum 102 collects the steam and forms part of a heat recovery loop in which water is circulated by one or several pumping units 104 and pipes 106, 108, and 110.

[0033] Optionally, hot water is also drawn from the steam drum 102 through pipes 112 and a pumping unit 114 and supplied to the electrolysis unit 34.

[0034] The water collected in the electrolysis unit 34 is mixed with the recirculation gas stream 80 and the hydrocarbon gas 82 of the combined stream 86 that enters a gas heater or catalytic reformer indicated by reference numeral 85 according to the alternative embodiment described above, and then is used to produce hydrogen 16 that is supplied directly to the reduction furnace 50 through the pipe 116.

[0035] In another embodiment, the energy of the steam 40 withdrawn from the steam drum 102 is supplied to a turbine 118 to drive a generator 120 and produce electricity 122 that is used in the electrolysis unit 34 for the generation of hydrogen 16.

[0036] Optionally, the hot water exiting the turbine 118 is supplied to the electrolysis unit 34 through a conduit 168 after appropriate treatment by methods known in the art.

[0037] In the electrolysis unit 34, the stream of oxygen 124 is produced and used to increase the temperature of the reducing gas 6 by partial combustion that supplies the reducing gas to the pipe 116 through the pipe 126 optionally, or in the DRI melting or refining process carried out in the electric arc furnace 90, or else in the direct reduction plant 12 or the melting furnace facility 20.

[0038] The electrolysis unit 34 is of any type available for industrial use and is also a co-electrolysis unit in which water is decomposed into hydrogen and oxygen and CO2 is also separated into carbon monoxide and oxygen. The electricity 122 produced by the generator 120 is used in the electrolysis unit 34 together with or in place of other available electrical sources 43.

[0039] In another embodiment, the system of the present invention comprises a polymer electrolyte membrane electrolyzer (PEM) or an alkaline electrolyzer in which a liquid alkaline solution of sodium hydroxide or potassium hydroxide is used as an electrolyte, or a solid oxide electrolyzer (SOE) that uses a solid ceramic material as an electrolyte that selectively conducts negatively charged oxygen ions at high temperatures.

[0040] The present invention thus provides a synergistic system for producing steel or iron-containing materials by integrating a direct reduction plant 12 with lower CO2 emissions than currently used steelmaking systems, a DRI melting furnace 20, a heat recovery unit 26, a steam turbine generator 44, and an electrolysis unit 34.

[0041] Of course, the above description of the present invention is provided for purposes of explanation, and the scope of the present invention is not limited to the embodiments described herein but is defined by the appended claims, and it should be understood that many changes and improvements may be made to the embodiments of the present invention that are included within the scope of these claims.

Claims

**Claim 1** A method for producing a steel or molten iron-containing material (22) with reduced carbon dioxide emissions, comprising the step of producing DRI (18) in a direct reduction furnace (12, 50) with a reducing gas (6) containing hydrogen (16), melting at least a part of the DRI in a melting furnace (20) to generate hot gas (24), using the heat contained in the hot gas (24) to produce steam and / or hot water (28, 40), utilizing the steam (40) to generate electrical energy (42) and producing the hydrogen (16) by electrolysis using the electrical energy (42), obtaining at least a part of the water used for producing hydrogen by electrolysis from the condensed steam contained in the exhaust reducing gas stream drawn from the direct reduction furnace as the top gas (58), producing hydrogen (16) from the steam and / or hot water (28, 40) by electrolysis, and supplying at least a part of the hydrogen (16) to the direct reduction furnace (12, 50) as a component of the reducing gas (6) to produce the DRI (18), a method for producing a steel or molten iron-containing material (22). **Claim 2** The method for producing a steel or molten iron-containing material (22) according to claim 1, wherein the melting furnace (20) is an electric arc furnace (EAF). **Claim 3** Furthermore, producing oxygen (36, 124) by electrolysis and raising the temperature of the reducing gas (6) before supplying at least a part of the oxygen (36, 124) to the reduction reactor (12, 50) to supply the reducing gas (6), the method for producing a steel or molten iron-containing material (22) according to claim 1. **Claim 4** Furthermore, producing oxygen (36, 124) by electrolysis and using a part of the oxygen in the electric arc furnace (20) to produce the steel or molten iron-containing material (22), the method for producing a steel or molten iron-containing material (22) according to claim 1. **Claim 5** A system (10) for producing a steel or molten iron-containing material (22) with reduced carbon dioxide emissions, a direct reduction furnace (12, 50) for producing DRI (18) with a reducing gas (6) containing hydrogen (16), a DRI melting furnace (20) for melting the DRI (18) to generate hot gas (24), a heat recovery unit (26) for producing steam and / or hot water (28, 40) using the heat contained in the hot gas (24), An electrolysis unit (34) for producing hydrogen (16) from the steam and / or hot water (28), A system (10) for producing a steel or molten iron-containing material (22) in which hydrogen (16) is supplied as a component of the reducing gas (6) to the direct reduction furnace (12, 50) to produce DRI (18).

6. Further comprising a generator (44) for producing electrical energy (42) using the steam (40) from the heat recovery unit (26), The electricity is used in the electrolysis unit (34) to produce hydrogen (16). The system (10) for producing a steel or molten iron-containing material (22) according to claim 5.

7. The DRI (18) is melted in an electric arc furnace (20) to generate a high-temperature gas (24), Furthermore, a first heat exchange unit (26) for producing steam or hot water (28, 40) using the heat from the high-temperature gas (24) flowing out of the electric arc furnace, Furthermore, an electrolysis unit (34) for producing hydrogen (16) from the steam or hot water (28), A first conduit (116) connecting the electrolysis unit (34) and the direct reduction furnace (12, 50) to supply at least a part of the hydrogen (16) to produce the DRI, An electric arc furnace (20, 90) for melting the DRI (18) to produce the steel or molten iron-containing material (22). The system (10) for producing a steel or molten iron-containing material (22) according to claim 5.

8. Furthermore, a generator (44) for producing electrical energy (42) using the steam (40), Conductive means connecting the generator (44) and the electrolysis unit (34) to produce the hydrogen (16) by electrolysis. The system (10) for producing a steel or molten iron-containing material (22) according to claim 5.

9. Furthermore, at least a part of the oxygen (36, 124) produced by electrolysis in the electrolysis unit (34) is supplied, and a second conduit (126) connecting the electrolysis unit (34) and the first conduit means (116) is provided to increase the temperature of the reducing gas (6) before it is supplied to the direct reduction furnace (12, 50). The system (10) for producing a steel or molten iron-containing material (22) according to claim 7.

10. Furthermore, at least a part of the discharged reducing gas drawn from the direct reduction furnace (12, 50) is cooled as an upper gas (58) containing water formed by the reduction of iron oxide to metallic iron, and a gas cooler (66) connected to the direct reduction furnace (12, 50); a fourth conduit (158) connecting the direct reduction furnace and the gas cooler; a fifth conduit (168) connecting the gas cooler and the electrolysis unit (34). The system (10) for producing a steel or molten iron-containing material (22) according to claim 7. **Claim 11** Furthermore, a water treatment unit for purifying and conditioning condensed water (68) before being used in the electrolysis unit (34) is provided. The system (10) for producing a steel or molten iron-containing material (22) according to claim 10.

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