EP4389920A1 - Use of tail gas from lock-out gas of a reduction of material containing iron oxide - Google Patents

Abstract

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 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.

In this case, at least a partial amount of the tail gas stream (150) is combined with at least a partial amount of the melt exhaust gas (180), whereby a tail gas mixture (190) is formed, and at least a partial amount of the tail gas mixture (190) is fed to a thermal utilization (200).

Description

Field of technology

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.

State of the art

It is known to reduce material containing metal oxides, such as iron oxides - such as ores, oxide briquettes or pellets - using reducing gas. For example, reduction by direct reduction in a fixed bed or a 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 on hydrogen and mainly on carbon - for example in carbon monoxide CO and/or methane CH ₄ - from natural gas. This therefore produces large amounts of carbon dioxide CO ₂ , which is undesirable for environmental reasons, among other things.

To reduce CO ₂ emissions during the direct reduction of metal oxide-containing material, it is known to use hydrogen H ₂ as a reducing gas. Hydrogen can be used as the sole reducing gas, or in combination with other gases based, for example, on carbon from natural gas or on coal or coke. The greater the proportion of hydrogen H ₂ , which is CO ₂ neutral with regard to reduction reactions, in the reducing gas, the less CO ₂ is emitted. Depending on the availability of natural gas or other gases and of hydrogen, the ratio of their contribution to the reducing gas can be changed by mixing different amounts.

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 plant investments already made. 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 on reducing components from natural gas or other gases in addition to hydrogen.

In order to conserve resources, it is common practice in direct reduction processes to use used reducing gas - known as top gas - to prepare reducing gas. To do this, the top gas is mixed with fresh reducing gas components - for example gas from a reformer for reforming natural gas, hydrogen H2 from a hydrogen production plant, ammonia NH3 - if necessary after treatment steps such as dedusting or compression. This means that reducing components remaining in the top gas can be fed back into the direct reduction and used as a reducing agent. The disadvantage of this type of top gas recycling is that the top gas also contains non-reducing components - for example nitrogen N2 or carbon dioxide CO2. Through recycling, these components can become increasingly enriched in the reducing gas. In order to limit enrichment, a portion of the top gas is discharged from the circulation system as so-called discharge gas - also known as bleed gas.

In order to conserve resources, it is desirable to use the discharge gas. This is especially true when using hydrogen-rich reducing gas, since the hydrogen content of the top gas also increases as the hydrogen content in the reducing gas increases.

It is known to use exhaust gas thermally, for example by burning it with an oxidizing agent - for example air - and using the heat to heat a medium; the medium can be, for example, a reducing gas precursor.

It is also known to separate hydrogen H2 from other components of the discharge gas and use it for the preparation of reducing gas. The portion of the discharge gas remaining after the separation of hydrogen H2 - also called tail gas - is not suitable for solely for thermal use and is flared unused after the addition of fuel.

Summary of the invention Technical task

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.

Technical solution

• Verfahren zur Herstellung einer Eisenschmelze, wobei
• Reduktion von eisenoxidhaltigem Material zu einem metallisierten Produkt mittels eines zumindest überwiegend aus Wasserstoff H2 bestehenden Reduktionsgases erfolgt, wobei bei der Reduktion Topgas anfällt,
• und wobei - gegebenenfalls nach einer Behandlung des Topgases - eine erste Teilmenge des Topgases zur Zubereitung von Reduktionsgas mit reduzierenden Reduktionsgaskomponenten vereinigt wird, und eine zweite Teilmenge des Topgases als Ausschleusegas einer Gasauftrennung in einen wasserstoffangereicherten Gasstrom und in einen wasserstoffabgereicherten Tailgasstrom unterworfen wird,
• und wobei das metallisierte Produkt der Reduktion mit Kohlenstoffträgern vereinigt in einer Schmelzvorrichtung zu einer Eisenschmelze geschmolzen wird, wobei ein Schmelzabgas anfällt,
• dadurch gekennzeichnet, dass
• zumindest eine Teilmenge des Tailgasstromes mit zumindest einer Teilmenge des Schmelzabgases vereinigt wird, wobei ein Tailgasgemisch entsteht,
• und zumindest eine Teilmenge des Tailgasgemisches einer thermischen Nutzung zugeführt wird.

The task is solved by a

• Process for producing an iron melt, wherein
• Reduction of iron oxide-containing material to a metallized product by means of a reducing gas consisting at least predominantly of hydrogen H2, whereby top gas is produced during the reduction,
• and wherein - optionally after a treatment of the top gas - a first portion of the top gas is combined with reducing gas components to prepare reducing gas, and a second portion of the top gas is subjected as discharge gas to a gas separation into a hydrogen-enriched gas stream and a hydrogen-depleted tail gas stream,
• and wherein the metallized product of the reduction is combined with carbon carriers in a melting device to form an iron melt, whereby a melt 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, thereby forming a tail gas mixture,
• and at least a portion of the tail gas mixture is subjected to thermal utilization.

The reducing gas consists at least predominantly of hydrogen H2. This means that the reducing gas contains hydrogen as a reducing reducing gas component, wherein the hydrogen content in volume % is greater than any of the other reducing gas components that may be present; preferably the hydrogen content is at least 50 volume %, particularly preferably more than 50 volume %, most preferably at least 60 volume %.

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.

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

The treatment of the top gas may include treatment types such as dust removal - which can be wet or dry -, compression, heat exchange, cooling. The treatment can be single-stage or multi-stage; one or more treatment types can be used.

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

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

The metallized product of the reduction is combined with carbon carriers and melted in a melting device to form an iron melt. Combination with carbon carriers can take place before introduction into the melting device or in the melting device.

• Elektrolichtbogenofen electric arc furnace EAF;
• Submerged arc furnace SAF,
• Open slag bath furnace OSBF
• Schmelzaggregat,
• Konvertergefäß.

The melting device is, for example, a member of the group consisting of

• electric arc furnace EAF;
• Submerged arc furnace SAF,
• Open slag bath furnace OSBF
• Melting unit,
• Converter vessel.

A melting unit melts at least partially based on electrical energy.

EAF, SAF and OSBF are not to be understood as a melting aggregate in the context of this application.

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

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

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.

Advantageous effects of the invention

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 use. The combination of the two gases produced in the process according to the invention for producing molten iron therefore enables the use of tail gas.

• Reformer
• Reduktionsgasheizer
• Trocknungsvorrichtung für eisenoxidhaltiges Material
• Aufheizvorrichtung für eisenoxidoxidhaltiges Material
• Aufbereitungsvorrichtung für eisenoxidhaltiges Material
• Dampf- oder Heißwassererzeugungsvorrichtung.

Preferably, the thermal use includes 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.

In a reformer, for example, it can help to provide the heat necessary for reforming.

In a reducing gas heater, for example, a contribution can be made to achieving the desired temperature for the reducing gas.

In a drying device for iron oxide-containing material, a contribution can be made to the provision of heat to assist drying.

In a heating device for iron oxide-containing material, a contribution can be made to the provision of heat necessary for heating; for example, it can be heated to support pre-oxidation of material.

In a processing facility for iron oxide-containing material, for example a sintering plant or a pelletizing plant, a contribution can be made to the provision of heat necessary for processing.

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

During the thermal utilization of the tail gas mixture, a first exhaust gas is produced.

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

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.

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.

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.

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

The reformer can supply reducing components for the reducing gas.

Use can be made, for example, in accordance with

CO2+CH4->2CO+2H2

or

H2O+CH4->CO+3H2.

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

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.

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 portion of the melt exhaust gas would be available for combination with tail gas.

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. Process-specific vent gas is produced when the metallized product - for example, directly reduced iron DRI - is pneumatically conveyed from the reduction unit into a DRI bunker; there, solids and gas are separated from one another, producing the vent gas. The vent gas can be used as fuel, if necessary after dedusting - wet or dry.

According to one embodiment, at least a portion of the process's own 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's own vent gas is subjected to gas separation into a hydrogen-enriched gas stream and a hydrogen-depleted tail gas stream.

Preferably, the thermal utilization is carried out by supplying at least one fuel to the tail gas mixture, for example natural gas or process-specific vent gas.

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

Preferably, the tail gas mixture is fed to a gas storage facility before thermal use and is removed from the gas storage facility for thermal use. This makes it possible to compensate for temporal fluctuations in the compositions and/or the quantities of the tail gas flow and/or the melt gas flow and/or the fuel - such as the process's own vent gas or natural gas.

Both the tail gas flow and the melt exhaust gas flow, but also fuel flows - such as process-specific vent gas or natural gas - can fluctuate in composition and size over time.

It is preferred if at least one fuel is also introduced into the gas storage facility. A mixture of fuel and tail gas mixture can then be fed for thermal use. Fluctuations in the calorific value of the tail gas flow and/or the melt gas flow and/or the fuel - for example, process-specific vent gas or natural gas - and thus the tail gas mixture can thus be balanced out in the gas storage facility. The introduction into the gas storage facility is preferably regulated in such a way that the calorific value of the mixture of tail gas mixture and fuel taken from the gas storage facility corresponds to the value aimed for thermal use.

Short description of the drawings

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

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 connection with the schematic and exemplary drawings, in which:
Fig. 1 schematically the implementation of an embodiment of the method according to the invention.

Description of the embodiments Examples

Figure 1 shows schematically how an iron melt 20 is produced in a melting device 10. For this purpose, the metallized product 30 - for example DRI - is obtained by reduction in a reduction unit 40 from iron oxide-containing material 50 using a reducing gas which consists predominantly of hydrogen.

Top gas 60 arising during the reduction is discharged from the reduction unit 40 and, after a multi-stage treatment with heat exchange 70, dry dust removal 80, cooling 90 with water, is divided into two parts. A first part 100 is combined with reducing gas components 110, and a second part 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 fed to the supply of the reducing gas components 110; it can be one of several reducing gas components or the only one.

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.

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 shown with wavy arrows; the two variants can be seen: 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.

Melt exhaust gas 180 arising in the melting device 10 is combined with the tail gas stream 150, whereby a tail gas mixture 190 is formed. Tail gas mixture 190 is fed to a thermal utilization 200. Optionally, it is fed to a gas storage 210 before the thermal utilization 200.

Optionally - shown by dashed arrows - fuel is supplied to the tail gas mixture 190 and/or the gas storage 210.

List of reference symbols

10

Melting device

20

Iron smelting

30

metallized product

40

Reduction unit

50

Iron oxide-containing material

60

Top gas

70

Heat exchange

80

Dry dust extraction

90

cooling

100

first subset

110

reducing reducing gas components

120

second subset

130

Gas separation device

140

hydrogen-enriched gas stream

150

Tail gas flow

160

electric heating

170

Reducing gas

180

Melt exhaust gas

190

Tail gas mixture

200

Thermal use

210

Gas storage

Claims (8)

Method for producing an iron melt (20), wherein Reduction of iron oxide-containing material (50) to a metallized product (30) by means of a reducing gas consisting at least predominantly of hydrogen H2, where 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 is combined with carbon carriers in a melting device (10) to form an iron melt (20), whereby a melt exhaust gas (180) is produced, characterized in that 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). Method according to claim 1, characterized in that the thermal utilization (200) provides a heat supply in a member of the group - Reformers - 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 generation device includes. 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. Method according to one of claims 1 to 3, characterized in that at least a partial amount of the melt exhaust gas (180) is used in a reformer. Method according to one of claims 1 to 4, characterized in that at least a partial amount 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. 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). 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). Method according to claim 7, characterized in that at least one fuel is also introduced into the gas storage (210).

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