Use of tail gas made of the discharged gas of a reduction process of iron oxide-containing material

Abstract

The invention relates to a method for producing molten iron (20). The reduction of iron oxide-containing material (50) in order to form a metallized product (30) is carried out using a reduction gas consisting at least largely of hydrogen H2, and a top gas (60) is accumulated during the reduction process, wherein - optionally after a treatment of the top gas (60) - a first sub-quantity (100) of the top gas (60) is combined with reducing reduction gas components (110) in order to provide reduction gas, and a second sub-quantity (120) of the top gas (60), as a discharged gas, is subjected to a gas separation process into a hydrogen-enriched gas flow (140) and a hydrogen-depleted tail gas flow (150). The metallized product (30) of the reduction process is combined with carbon carriers so as to be melted in a melting device (10) in order to form a molten iron (20), and a smelting exhaust gas (180) is accumulated. In the process, at least a sub-quantity of the tail gas flow (150) is combined with at least a sub-quantity of the smelting exhaust gas (180), and a tail gas mixture (190) is produced. At least a sub-quantity of the tail gas mixture (190) is supplied to a thermal use (200).

Description

[0001] Description

[0002] Title of the invention

[0003] Use of tail gas from the reduction of iron oxide-containing material

[0004] field of technology

[0005] The application relates to processes for producing an iron melt, wherein reduction of iron oxide-containing material to a metallized product is carried out by means of a reducing gas consisting at least predominantly of hydrogen H2, wherein top gas is produced during the reduction.

[0006] State of the art

[0007] It is known to reduce materials containing metal oxides, such as iron oxide, such as ores, oxide briquettes, or pellets, using reducing gas. This is done, for example, by direct reduction in a fixed bed or fluidized bed with reducing gas. In conventional pre-reduction or direct reduction processes currently used on a large industrial scale, the reducing gas is based primarily on hydrogen and carbon—for example, carbon monoxide CO and / or methane CH4—from natural gas. Therefore, large amounts of carbon dioxide CO2 are produced, which is undesirable for environmental reasons, among other things.

[0008] To reduce CO2 emissions during the direct reduction of metal oxide-containing materials, it is known to use hydrogen (H2) as a reducing gas. Hydrogen can be used as the sole reducing gas or in combination with other gases, such as carbon from natural gas or coal or coke. The greater the proportion of hydrogen (H2), which is CO2-neutral with respect to reduction reactions, in the reducing gas, the less CO2 is emitted. Depending on the availability of natural gas or other gases and hydrogen, the ratio of their contribution to the reducing gas can be varied by mixing different amounts.

[0009] The more hydrogen is available, the more climate-problematic contributions based on carbon from natural gas or other gases can be avoided. It is advantageous to operate existing plants and processes, in which the reducing gas is based predominantly on carbon and partly on hydrogen from natural gas or other gases, even with increased proportions of hydrogen in the reducing gas. This enables flexible response to the availability of natural gas or other gases and hydrogen, and allows the utilization of existing plant investments. At least until sufficient quantities of hydrogen are available for the use of reducing gases based entirely on hydrogen, reducing gas will have to rely not only on hydrogen but also on reducing components from natural gas or other gases.

[0010] To conserve resources, it is common practice in direct reduction processes to use spent reducing gas – known as top gas – to prepare reducing gas. For this purpose, the top gas, possibly after treatment steps such as dedusting or compression, is mixed with fresh reducing gas components – for example, gas from a reformer for reforming natural gas, hydrogen H2 from a hydrogen production plant, or ammonia NH3. This allows any reducing components remaining in the top gas to be recycled to the direct reduction process and used as a reducing agent. A disadvantage of this type of top gas recycling is that non-reducing components – such as nitrogen N2 or carbon dioxide CO2 – are also present in the top gas. Recycling can cause these components to become increasingly concentrated in the reducing gas.In order to limit enrichment, a portion of the top gas is removed from the circulation system as so-called bleed gas.

[0011] To conserve resources, it is desirable to utilize the discharge gas. This is especially true when using hydrogen-rich reducing gas, since the hydrogen content of the top gas also increases with the increasing hydrogen content in the reducing gas.

[0012] It is known to utilize exhaust gas thermally, for example, by combusting it with an oxidizing agent, such as air, and using the heat to heat a medium; the medium can, for example, be a reducing gas precursor.

[0013] It is also known to separate hydrogen H2 from other components of the discharge gas and use it to prepare reducing gas. The portion of the discharge gas remaining after the separation of hydrogen H2—also called tail gas—is unsuitable for thermal use due to its low calorific value and is flared unused after the addition of fuel.

[0014] Summary of the invention

[0015] Technical task

[0016] It is the object of the present invention to present methods and devices which enable the use of tail gas when using reducing gas consisting predominantly of hydrogen H2.

[0017] Technical solution

[0018] The task is solved by a

[0019] Process for producing an iron melt, wherein

[0020] Reduction of iron oxide-containing material to a metallized product by means of a reducing gas consisting at least predominantly of hydrogen H2, wherein top gas is produced during the reduction, and wherein - optionally after treatment of the top gas - a first portion of the top gas is used to prepare reducing gas with reducing

[0021] Reduction gas components are combined, and a second portion of the top gas is subjected as discharge gas to gas separation into a hydrogen-enriched gas stream and a hydrogen-depleted tail gas stream, and wherein the metallized product of the reduction, combined with carbon carriers, is melted in a melting device to form an iron melt, whereby a melt exhaust gas is produced, characterized in that at least a portion of the tail gas stream is combined with at least a portion of the melt exhaust gas, whereby a tail gas mixture is formed, and at least a portion of the tail gas mixture is fed to thermal utilization. The reduction gas consists at least predominantly of hydrogen H2.This means that the reducing gas contains hydrogen as a reducing gas component, wherein the hydrogen content in volume % is greater than that of any other reducing gas components that may be present; preferably, the hydrogen content is at least 50 volume %, more preferably more than 50 volume %, most preferably at least 60 volume %.

[0022] Other reducing gas components that may be present and can also have a reducing effect are, for example, carbon monoxide CO or hydrocarbons or ammonia NH3.

[0023] The metallized product is preferably direct reduced iron (DRI), also called sponge iron.

[0024] Any treatment of the top gas may include dedusting (which can be wet or dry), compression, heat exchange, and cooling. Treatment can be single-stage or multi-stage, and one or more treatment types may be used.

[0025] The first and second subsets of the top gas may have the same composition, or they may differ in composition.

[0026] It is preferred if the first and second partial quantities of the top gas have the same composition, i.e. only the volume flow is divided into two partial flows.

[0027] The metallized product of the reduction is combined with carbon carriers and melted in a melting apparatus to form an iron melt. Combination with carbon carriers can occur before introduction into the melting apparatus or in the melting apparatus.

[0028] The melting device is, for example, a member of the group consisting of electric arc furnace EAF;

[0029] Submerged arc furnace SAF,

[0030] Open slag bath furnace OSBF melting unit, converter vessel.

[0031] A melting unit melts at least partially using electrical energy. EAF, SAF, and OSBF are not considered melting units for the purposes of this application.

[0032] A converter vessel is, for example, a steelworks converter for steel production.

[0033] Thermal utilization is understood to mean an exothermic reaction with a reaction partner, for example combustion with oxygen or other oxidizing reaction partners.

[0034] Thermal utilization preferably occurs in the context of the process for producing molten iron, for example thermal utilization for heating process gas streams or for producing steam for the purpose of generating electricity required in the process.

[0035] Advantageous effects of the invention

[0036] Due to the presence of carbon carriers during melting, the melt gas contains, for example, carbon monoxide (CO), and consequently has a higher calorific value than tail gas. Therefore, the tail gas mixture obtained according to the invention has a higher calorific value than tail gas and is suitable for thermal utilization. Combining the two gases produced in the inventive process for producing molten iron thus enables the utilization of tail gas.

[0037] Preferably, the thermal use includes a heat supply in a member of the group

[0038] reformer

[0039] Reducing gas heater

[0040] Drying device for iron oxide-containing material

[0041] - Heating device for iron oxide-containing material

[0042] - Treatment device for iron oxide-containing material Steam or hot water generation device.

[0043] In a reformer, for example, it can contribute to the provision of the heat required for reforming.

[0044] In a reducing gas heater, for example, it can contribute to achieving the desired temperature for the reducing gas. In a drying device for iron oxide-containing material, it can contribute to providing heat to assist drying.

[0045] In a heating device for iron oxide-containing material, a contribution can be made to providing the heat required for heating; for example, heating can be used to support the pre-oxidation of the material. In a processing device for iron oxide-containing material, for example, a sintering plant or a pelletizing plant, a contribution can be made to providing the heat required for processing.

[0046] In a steam or hot water generation device, a contribution can be made to providing the heat necessary for steam or hot water production; the steam or hot water can then be used directly or to generate electricity, for example.

[0047] During the thermal utilization of the tail gas mixture, an initial exhaust gas is produced.

[0048] Preferably, at least a portion of the tail gas mixture is used in an inert gas generator.

[0049] In an inert gas generator, inert gas is produced by burning the tail gas mixture with air - for example, the combustion produces the inert gas carbon dioxide CO2, which hardly reacts under the operating conditions.

[0050] The inert gas can be used, for example, in the reduction unit, in which the iron oxide-containing material is reduced to a metallized product, or in the melting device - for example for rinsing purposes.

[0051] In principle, following the formation of a tail gas mixture as described above, the entire tail gas mixture could also be used in an inert gas generator, so that no part of the inert gas mixture is used for thermal purposes.

[0052] Preferably, at least a portion of the melt exhaust gas is used in a reformer.

[0053] The reformer can supply reducing components for the reducing gas.

[0054] Use can be made, for example, in accordance with

[0055] CO2+CH4->2CO+2H2 or H2O+CH4->CO+3H2.

[0056] Carbon dioxide CO2 or water vapor H2O in the melt exhaust gas are reacted with natural gas in the reformer, for example, so that the reducing components carbon monoxide CO and hydrogen H2 are produced and serve as reducing components of the reduction gas.

[0057] In principle, melt exhaust gas from a melting device in which metallized product of a reduction is combined with carbon carriers to form an iron melt can also be fully utilized in a reformer to supply reducing components for the reducing gas carrying out the reduction.

[0058] However, when combining a melting device in which the metallized product of a reduction is combined with carbon carriers to form an iron melt, with the formation of a tail gas mixture as described above, no part of the melt exhaust gas would be available for combination with tail gas.

[0059] The iron oxide-containing material is reduced to the metallized product in a reduction unit. The reduction unit in which the iron oxide-containing material is reduced to a metallized product can be, for example, a fixed-bed shaft or a fluidized-bed reactor. Vent gas is generated during the process when the metallized product—for example, directly reduced iron (DRI)—is pneumatically conveyed from the reduction unit into a DRI bunker. There, the solids and gas are separated, producing vent gas. The vent gas can be used as fuel, if necessary after dedusting (wet or dry).

[0060] According to one embodiment, at least a portion of the process-specific vent gas is added to the discharge gas before the gas separation into a hydrogen-enriched gas stream and a hydrogen-depleted tail gas stream takes place. In this case, a mixture of discharge gas and process-specific vent gas is subjected to gas separation into a hydrogen-enriched gas stream and a hydrogen-depleted tail gas stream.

[0061] Preferably, the thermal utilization takes place by adding at least one fuel to the tail gas mixture, for example natural gas or process-specific vent gas.

[0062] The calorific value of the tail gas mixture can thus be increased.

[0063] Preferably, the tail gas mixture is fed to a gas storage facility prior to thermal utilization and removed from the gas storage facility for thermal utilization. This allows temporal fluctuations in the composition and / or accumulating quantities of the tail gas stream and / or the melt gas stream and / or the fuel—such as process-specific vent gas or natural gas—to be compensated. Both the tail gas stream and the melt waste gas stream, as well as fuel streams—such as process-specific vent gas or natural gas—can fluctuate in composition and size over time.

[0064] It is preferred if at least one fuel is also introduced into the gas storage unit. A mixture of fuel and tail gas mixture can then be fed for thermal utilization. Fluctuations in the calorific value of the tail gas stream and / or the melt gas stream and / or the fuel—for example, process-specific vent gas or natural gas—and thus of the tail gas mixture can thus be compensated for in the gas storage unit. The introduction into the gas storage unit is preferably controlled so that the calorific value of the mixture of tail gas mixture and fuel withdrawn from the gas storage unit corresponds to the desired value for thermal utilization.

[0065] Short description of the drawings

[0066] The present invention is described below by way of example using a schematic figure.

[0067] The above-described properties, features, and advantages of this invention, as well as the manner in which they are achieved, will become clearer and more readily understood in connection with the following description of embodiments, which are explained in more detail in conjunction with the schematic and exemplary drawings.

[0068] Fig. 1 schematically shows the implementation of an embodiment of the method according to the invention.

[0069] Description of the embodiments

[0070] Examples

[0071] Figure 1 schematically shows how an iron melt 20 is produced in a melting device 10. For this purpose, the metallized product 30—for example, DRI—is obtained from iron oxide-containing material 50 by reduction using a reducing gas consisting predominantly of hydrogen in a reduction unit 40. Top gas 60 produced during the reduction is discharged from the reduction unit 40 and, after a multi-stage treatment with heat exchange 70, dry dust removal 80, and cooling 90 with water, is divided into two portions. A first portion 100 is combined with reducing reduction gas components 110, and a second portion 120 is fed to a gas separation device 130, in which a hydrogen-enriched gas stream 140 and a hydrogen-depleted tail gas stream 150 are produced.It is shown that the hydrogen-enriched gas stream 140 is directed to supply the reducing gas components 110; it may be one of several reducing gas components or the only one.

[0072] After combining with reducing reducing gas components, the resulting reducing gas precursor is heated by means of heat exchange 70 and electrical heating 160, and the reducing gas 170 thus produced is fed to the reduction unit 40.

[0073] The metallized product 30 is fed to the melting device 10 and combined with carbon carriers in the melting device 10 to form an iron melt 20. The addition of carbon carriers is represented by wavy arrows; the two variants are shown: combination with carbon carriers before introduction into the melting device 10 and combination with carbon carriers in the melting device 10. Each of the variants can be present alone, or both variants can be present together.

[0074] Melt offgas 180 generated in the melting device 10 is combined with the tail gas stream 150, forming a tail gas mixture 190. The tail gas mixture 190 is fed to a thermal utilization unit 200. Optionally, it is fed to a gas storage unit 210 prior to the thermal utilization unit 200.

[0075] Optionally, fuel is supplied to the tail gas mixture 190 and / or the gas storage 210, indicated by dashed arrows. List of reference symbols

[0076] 10 Melting device

[0077] 20 iron smelter

[0078] 30 metallized product

[0079] 40 Reduction unit

[0080] 50 Iron oxide-containing material

[0081] 60 Top Gas

[0082] 70 Heat exchange

[0083] 80 T dry dust extraction

[0084] 90 Cooling

[0085] 100 first subset

[0086] 110 reducing gas components

[0087] 120 second subset

[0088] 130 Gas separation device

[0089] 140 hydrogen-enriched gas stream

[0090] 150 tail gas stream

[0091] 160 electric heating

[0092] 170 Reducing gas

[0093] 180 melt gas

[0094] 190 tail gas mixture

[0095] 200 Thermal use

[0096] 210 gas storage facilities

Claims

Claims 1. A method for producing an iron melt (20), wherein Reduction of iron oxide-containing material (50) to a metallized product (30) takes place by means of a reducing gas consisting at least predominantly of hydrogen H2, wherein top gas (60) is produced during the reduction, and wherein - optionally after a treatment of the top gas (60) - a first partial amount (100) of the top gas (60) is combined with reducing reducing gas components (110) to prepare reducing gas, and a second partial amount (120) of the top gas (60) is subjected as discharge gas to a gas separation into a hydrogen-enriched gas stream (140) and a hydrogen-depleted tail gas stream (150), and wherein the metallized product (30) of the reduction, combined with carbon carriers, is melted in a melting device (10) to form an iron melt (20), wherein a melt exhaust gas (180) is produced, characterized in thatthat at least a portion of the tail gas stream (150) is combined with at least a portion of the melt exhaust gas (180), whereby a tail gas mixture (190) is formed, and at least a portion of the tail gas mixture (190) is fed to a thermal utilization (200).

2. Method according to claim 1, characterized in that the thermal utilization (200) comprises a heat supply in a member of the group reformer Reducing gas heater Drying device for iron oxide-containing material - Heating device for iron oxide-containing material - Processing device for iron oxide-containing material steam or hot water generating device.

3. Method according to claim 1 or 2, characterized in that at least a portion of the tail gas mixture (190) is used in an inert gas generator.

4. Method according to one of claims 1 to 3, characterized in that at least a portion of the melt exhaust gas (180) is used in a reformer.

5. Method according to one of claims 1 to 4, characterized in that at least a portion of the process-specific vent gas is added to the discharge gas before the gas separation into a hydrogen-enriched gas stream (140) and a hydrogen-depleted tail gas stream (150) takes place.

6. Method according to one of claims 1 to 5, characterized in that the thermal utilization (200) takes place by supplying at least one fuel to the tail gas mixture (190).

7. Method according to one of claims 1 to 6, characterized in that the tail gas mixture (190) is fed to a gas storage (210) before the thermal utilization (200) and is removed from the gas storage (210) for the thermal utilization (200).

8. Method according to claim 7, characterized in that at least one fuel is also introduced into the gas storage (210).

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