Utilization of tail gas consisting of reduced exhaust gas of iron oxide-containing material

Abstract

The invention relates to a method for producing an iron melt (20), in which a reduction of an iron oxide-containing material (50) is carried out using a reducing gas consisting at least predominantly of hydrogen H2 to provide a metallization product (30), in which the reduction produces a top gas (60), and wherein-optionally after treating the top gas (60)-a first partial quantity (100) of the top gas (60) is combined with a reducing component (110) of a reducing gas in order to produce the reducing gas and a second partial quantity (120) of the top gas (60) as exhaust gas is subjected to gas separation into a hydrogen-rich gas stream (140) and a hydrogen-depleted tail gas stream (150), and wherein the reduced metallization product (30) is melted together with a carbon support in a melting device (10) to provide an iron melt (20), wherein a molten off-gas (180) is generated. At least a partial amount of the tail gas stream (150) is combined with at least a partial amount of the molten exhaust gas (180) to form a tail gas mixture (190), and at least a partial amount of the tail gas mixture (190) is sent to a heat utilization (200).

Description

Field of the Invention

[0001] The present application relates to a method for producing a molten iron, in which a reducing gas consisting at least mainly of hydrogen H2 is used to reduce a material containing iron oxide to provide a metallized product, wherein the reduction generates a top gas. Prior Art

[0002] It is known to reduce metal oxides, such as materials containing iron oxide, such as ores, oxide compacts or pellets, using a reducing gas. The reduction is carried out, for example, by direct reduction with a reducing gas in a fixed bed or fluidized bed. In conventional pre-reduction or direct reduction processes currently in large-scale industrial use, the reducing gas is not only based on hydrogen but also mainly on carbon from natural gas, such as carbon in carbon monoxide CO and / or methane CH4. As a result, a large amount of carbon dioxide CO2 is generated, which is undesirable especially for environmental policy reasons.

[0003] In order to reduce CO2 emissions in the direct reduction of materials containing metal oxides, it is known to use hydrogen H2 as the reducing gas. It is possible here to use hydrogen as the sole reducing gas or in combination with other gases, for example based on carbon from natural gas or based on coal or coke. The greater the proportion of hydrogen H2 in the reducing gas that is CO2-neutral for the reduction reaction, the lower the CO2 emissions. Depending on the availability of natural gas or other gases and hydrogen, their contribution ratios to the reducing gas can be changed by mixing different amounts.

[0004] The more hydrogen is available, the more the climate-problematic contribution based on carbon from natural gas or other gases can be avoided.

[0005] It is advantageous to operate existing plants and processes - in which the reducing gas is mainly based on carbon from natural gas or other gases and partly on hydrogen, including an increased proportion of hydrogen in the reducing gas. This enables a flexible response to the availability of natural gas or other gases and hydrogen and allows the utilization of existing equipment investments. At least until sufficient amounts of hydrogen are available to use a reducing gas based entirely on hydrogen, the reducing gas must still utilize the reducing components from natural gas or other gases in addition to hydrogen.

[0006] For the purpose of protecting the execution of resources, in the direct reduction process, the used reducing gas (referred to as top gas) is usually utilized to prepare the reducing gas. For this purpose, optionally after treatment steps such as dust removal or compression, the top gas is mixed with fresh reducing gas components such as the gas from a reformer for reforming natural gas, hydrogen H2 from a hydrogen production facility, ammonia NH3. The reducing components retained in the top gas can thus be sent back to the direct reduction and used as a reducing agent again. The disadvantage of such recycling of the top gas is that non-reducing components such as nitrogen N2 or carbon dioxide CO2 also exist in the top gas. Due to recycling, these components may accumulate more and more in the reducing gas. To limit the enrichment, a partial amount of the top gas is discharged from this recycling as a so-called off-gas (also referred to as bleed gas).

[0007] To contribute to resource conservation, it is desirable to utilize the off-gas. This is especially the case when using a hydrogen-rich reducing gas, because as the hydrogen content in the reducing gas increases, the hydrogen content in the top gas also increases.

[0008] The thermal utilization of the off-gas (by burning it, for example, with an oxidant such as air) and using this heat to heat a medium is known; the medium can be, for example, a reducing gas precursor.

[0009] It is also known to separate hydrogen H2 from the other components of the off-gas and use it to prepare the reducing gas. The partial amount of the off-gas remaining after separating hydrogen H2 (also referred to as tail gas) is not suitable for thermal utilization alone due to its low calorific value and is burned without utilization after adding fuel. Summary of the Invention

[0011] Technical Problem

[0012] The problem solved by the present invention is to provide a method and device capable of utilizing the tail gas when using a reducing gas mainly composed of hydrogen H2.

[0013] Technical Solution

[0014] This problem is solved by a method for producing an iron melt, wherein

[0015] a reducing gas at least mainly composed of hydrogen H2 is used to reduce a material containing iron oxide to provide a metallized product,

[0016] wherein the reduction generates top gas,

[0017] and wherein - optionally after treating the top gas – a first partial amount of the top gas is combined with the reducing components of the reducing gas to prepare the reducing gas, and a second partial amount of the top gas as the off-gas is subjected to gas separation into a hydrogen-rich gas stream and a hydrogen-poor tail gas stream.

[0018] And the reduced metallized product is melted together with a carbon carrier in a melting device to provide an iron melt, wherein a melting exhaust gas is generated.

[0019] It is characterized in that

[0020] At least a partial amount of the off-gas stream is combined with at least a partial amount of the melting exhaust gas to form an off-gas mixture.

[0021] And at least a partial amount of the off-gas mixture is sent for heat utilization.

[0022] The reducing gas consists at least mainly of hydrogen H2. This is understood to mean that the reducing gas contains hydrogen as the reducing component of the reducing gas, wherein the hydrogen content in volume % is greater than the content of any other optionally present reducing gas component; the hydrogen content is preferably at least 50 volume %, particularly preferably greater than 50 volume %, and very particularly preferably at least 60 volume %.

[0023] Other optionally present reducing gas components that may also have a reducing effect are, for example, carbon monoxide CO or hydrocarbons or ammonia NH3.

[0024] The metallized product is preferably direct reduced iron DRI (direct reduced iron), which is also known as sponge iron.

[0025] The optionally carried out treatment of the top gas can include, for example, treatment types such as dust removal (which can be carried out wet or dry), compression, heat exchange, cooling, etc. This treatment can be single-stage or multi-stage, and one or more treatment types can be used.

[0026] The first partial amount and the second partial amount of the top gas can have the same composition, or their compositions can be different.

[0027] Preferably, the first partial amount and the second partial amount of the top gas have the same composition, that is, only this volume stream is divided into two sub-streams.

[0028] The reduced metallized product is melted together with a carbon carrier in a melting device to provide an iron melt. The combination with the carbon carrier can be carried out before introducing the melting device or in the melting device.

[0029] The melting device is, for example, a member of the following:

[0030] - Electric arc furnace (EAF),

[0031] - Submerged arc furnace (SAF),

[0032] - Open slag bath furnace (OSBF),

[0033] - Melting unit,

[0034] - Converter vessel.

[0035] The melting unit melts at least partially based on electric energy.

[0036] EAF, SAF, and OSBF should not be understood as melting units in this application.

[0037] The converter body is understood to refer to, for example, a steelmaking converter used for producing steel.

[0038] Heat utilization is an exothermic reaction with reaction participants, such as combustion with oxygen or other oxidizing reaction participants.

[0039] Heat utilization is preferably carried out in the context of a method for producing an iron melt. For example, heat utilization is used to heat a process gas stream or to produce steam for generating electricity required in the method.

[0040] Advantages of the present invention

[0041] Due to the presence of a carbon carrier during the melting process, the melting exhaust gas contains, for example, carbon monoxide (CO), and thus has a higher calorific value than the tail gas. The tail gas mixture obtained according to the present invention therefore has an increased calorific value compared to the tail gas and is suitable for heat utilization. Therefore, the combination of the two gases generated in the method for producing an iron melt according to the present invention enables the utilization of the tail gas.

[0042] Preferably, heat utilization includes supplying heat to the following members:

[0043] - A reformer

[0044] - A reducing gas heater

[0045] - A drying device for materials containing iron oxide

[0046] - A heating device for materials containing iron oxide

[0047] - A processing device for materials containing iron oxide

[0048] - A steam or hot water generating device.

[0049] For example, it can contribute to providing the heat required for reforming in a reformer.

[0050] For example, it can help reach the temperature required for the reducing gas in a reducing gas heater.

[0051] In the drying device for materials containing iron oxide, it can help provide the heat for promoting drying.

[0052] In the heating device for materials containing iron oxide, it can help provide the heat required for heating; heating can be carried out, for example, to promote the pre-oxidation of the materials.

[0053] In a treatment apparatus for materials containing iron oxide, such as a sintering apparatus or a granulation apparatus, it can help provide the heat required for treatment.

[0054] In a steam or hot water generation apparatus, it can help provide the heat required for generating steam or hot water; the steam or hot water can then be directly utilized, for example, or used for generating electricity, for example.

[0055] The heat utilization of the tail gas mixture generates a first exhaust gas.

[0056] Preferably, at least a partial amount of the tail gas mixture is used for an inert gas generator.

[0057] In the inert gas generator, the tail gas mixture is burned with air to generate an inert gas. For example, the combustion generates an inert gas carbon dioxide CO2 that hardly reacts under the use conditions.

[0058] The inert gas can be used, for example, in a reduction unit where the iron oxide-containing material is reduced to provide a metallized product or in a melting apparatus, for example, for purging purposes.

[0059] After forming the tail gas mixture as described above, in principle, the entire tail gas mixture can also be used for the inert gas generator so that no partial amount of the inert gas mixture is sent to the heat utilization.

[0060] Preferably, at least a partial amount of the molten exhaust gas is used for a reformer.

[0061] The reformer can supply a reducing component for the reducing gas.

[0062] The utilization can be carried out, for example, as follows

[0063] CO2 + CH4 -> 2CO + 2H2

[0064] Or

[0065] H2O + CH4 -> CO + 3H2.

[0066] Carbon dioxide CO2 or water vapor H2O in the molten exhaust gas reacts with natural gas in the reformer, for example, to produce a reducing component carbon monoxide CO and hydrogen H2, and serves as the reducing component of the reducing gas.

[0067] The molten exhaust gas from the melting apparatus (where the reduced metallized product is melted together with a carbon carrier to provide an iron melt) can also be completely utilized in the reformer in principle, thereby providing a reducing component for the reducing gas for reduction.

[0068] However, in this case, when connecting the melting device (where the reduced metallized product is melted together with the carbon carrier to provide an iron melt) to the formation of the above-mentioned tail gas mixture, no partial amount of the melting exhaust gas is provided for merging with the tail gas.

[0069] The iron oxide-containing material is reduced to a 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 or a fluidized-bed reactor. Process-inherent exhaust gas is generated when the metallized product - for example, direct reduced iron DRI - is pneumatically conveyed from the reduction unit to a DRI silo (where solids and gases are separated from each other to generate exhaust gas). This exhaust gas can optionally be used as fuel after (wet or dry) dust removal.

[0070] According to one embodiment, at least a partial amount of the process-inherent exhaust gas is added to the discharged gas before separating the gas into a hydrogen-rich gas stream and a hydrogen-poor tail gas stream. In this case, the mixture of the discharged gas and the process-inherent exhaust gas is subjected to gas separation into a hydrogen-rich gas stream and a hydrogen-poor tail gas stream.

[0071] Preferably, thermal utilization is carried out in the case of supplying at least one fuel, such as natural gas or process-inherent exhaust gas, to the tail gas mixture.

[0072] This makes it possible to increase the calorific value of the tail gas mixture.

[0073] The tail gas mixture is preferably sent to a gas storage device before thermal utilization and taken out from the gas storage device for thermal utilization. This makes it possible to compensate for fluctuations in the composition and / or production amount of the tail gas stream and / or the melting gas stream and / or the fuel (such as process-inherent exhaust gas and / or natural gas) over time.

[0074] The tail gas stream, the melting exhaust gas stream, and the fuel (such as process-inherent exhaust gas and / or natural gas) stream may all fluctuate in composition and amount over time.

[0075] Preferably, at least one fuel is also introduced into the gas storage device. Then, the mixture of the fuel and the tail gas mixture can be sent to thermal utilization. Thereby, fluctuations in the calorific value of the tail gas stream and / or the melting gas stream and / or the fuel (such as process-inherent exhaust gas or natural gas) and thus the calorific value of the tail gas mixture can be compensated in the gas storage device. Preferably, the introduction into the gas storage device is controlled so that the calorific value of the mixture of the tail gas mixture and the fuel taken out from the gas storage device corresponds to the value required for thermal utilization. Brief Description of the Drawings

[0077] Next, the present invention will be described by way of example with reference to the schematic drawings.

[0078] In connection with the following description of the embodiments, the above-mentioned properties, features and advantages of the present invention, as well as the ways and means of their implementation, will become clearer and more readily understandable. These embodiments are described in more detail in conjunction with the schematic and exemplary drawings. In the drawings:

[0079] Figure 1 Schematically shows the execution of an embodiment of the method according to the present invention.

[0080] Description of the embodiment Example

[0081] Figure 1 Schematically shows how to produce an iron melt 20 in a melting device 10. For this purpose, a metallized product 30 - for example DRI - is obtained by reducing a material 50 containing iron oxide using a reducing gas mainly composed of hydrogen in a reduction unit 40. The top gas 60 generated during the reduction is discharged from the reduction unit 40 and divided into two partial amounts after a multi-stage treatment including a heat exchanger 70, a dry dust collector 80 and water cooling 90. The first partial amount 100 is combined with the reducing component 110 of the reducing gas, and the second partial amount 120 is sent to a gas separation device 130, where a hydrogen-rich gas stream 140 and a hydrogen-poor tail gas stream 150 are generated. As shown, the hydrogen-rich gas stream 140 is sent to the feed of the reducing component 110 of the reducing gas; it can be one of the multiple reducing components of the reducing gas or the only one.

[0082] After being combined with the reducing component of the reducing gas, the resulting reducing gas precursor is heated by the heat exchanger 70 and an electric heater 160, and the resulting reducing gas 170 is supplied to the reduction unit 40.

[0083] The metallized product 30 is sent to the melting device 10 and melted in the melting device 10 together with a carbon carrier to provide the iron melt 20. The addition of the carbon carrier is indicated by a wavy arrow; the figure shows two variants: being combined with the carbon carrier before being introduced into the melting device 10, and being combined with the carbon carrier in the melting device 10; each variant can exist alone, or the two variants can exist in combination.

[0084] The melting exhaust gas 180 generated in the melting device 10 is combined with the tail gas stream 150 to form a tail gas mixture 190. The tail gas mixture 190 is sent to heat utilization 200. Optionally, it is sent to a gas storage device 210 before heat utilization 200.

[0085] Optionally - indicated by a dashed arrow - fuel is sent to the tail gas mixture 190 and / or the gas storage device 210.

[0086] List of reference numerals

[0087] 10 Melting device

[0088] 20 Iron melt

[0089] 30 Metallized product

[0090] 40 Reduction unit

[0091] 50 Material containing iron oxide

[0092] 60 Top gas

[0093] 70 Heat exchange

[0094] 80 Dry dust removal

[0095] 90 Cooling

[0096] 100 First partial quantity

[0097] 110 Reducing component of reducing gas

[0098] 120 Second partial quantity

[0099] 130 Gas separation device

[0100] 140 Hydrogen-rich gas stream

[0101] 150 Tail gas stream

[0102] 160 Electric heating

[0103] 170 Reducing gas

[0104] 180 Molten exhaust

[0105] 190 Tail gas mixture

[0106] 200 Heat utilization

[0107] 210 Gas storage device

Claims

1. A method for producing an iron melt (20), wherein a reducing gas consisting at least mainly of hydrogen H2 is used for reducing an iron oxide-containing material (50) to provide a metallized product (30), wherein said reduction generates a top gas (60), and wherein - optionally after treating the top gas (60) – a first partial amount (100) of the top gas (60) is combined with the reducing components (110) of the reducing gas to prepare a reducing gas, and a second partial amount (120) of the top gas (60) as an exhaust gas is subjected to gas separation into a hydrogen-rich gas stream (140) and a hydrogen-poor tail gas stream (150), and wherein the reduced metallized product (30) is melted together with a carbon carrier in a melting device (10) to provide an iron melt (20), wherein a melting exhaust gas (180) is generated, characterized in that at least a partial amount of the tail gas stream (150) is combined with at least a partial amount of the melting exhaust gas (180) to form a tail gas mixture (190), and at least a partial amount of the tail gas mixture (190) is sent to heat utilization (200).

2. The method according to claim 1, wherein The heat utilization (200) includes supplying heat to the following members: - a reformer - a reducing gas heater - a drying device for the iron oxide-containing material - a heating device for the iron oxide-containing material - a processing device for the iron oxide-containing material - a steam or hot water generating device.

3. The method according to claim 1 or 2, characterized in that At least a partial amount of the tail gas mixture (190) is used for an inert gas generator.

4. The method according to any one of claims 1 to 3, characterized in that At least a partial amount of the melting exhaust gas (180) is used for a reformer.

5. The method according to any one of claims 1 to 4, characterized in that Before performing gas separation into a hydrogen-rich gas stream (140) and a hydrogen-poor tail gas stream (150), at least a partial amount of the process-inherent exhaust gas is added to the exhaust gas.

6. The method according to any one of claims 1 to 5, characterized in that The heat utilization (200) is performed in the case of supplying at least one fuel to the tail gas mixture (190).

7. The method according to any one of claims 1 to 6, characterized in that The tail gas mixture (190) is sent to a gas storage device (210) before heat utilization (200), and is taken out from the gas storage device (210) for heat utilization (200).

8. The method according to claim 7, characterized in that At least one fuel is also introduced into the gas storage device (210).

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