US20140083252A1

US20140083252A1 - Reduction of metal oxides using gas stream containing both hydrocarbon and hydrogen

Info

Publication number: US20140083252A1
Application number: US14/123,020
Authority: US
Inventors: Christian Boehm; Robert Millner
Original assignee: Siemens VAI Metals Technologies GmbH Austria
Current assignee: Primetals Technologies Austria GmbH
Priority date: 2011-05-30
Filing date: 2012-05-07
Publication date: 2014-03-27
Also published as: EP2714942B1; EP2714942A1; AU2012265081B2; RU2013157801A; UA111488C2; ZA201308896B; KR101890788B1; TW201307578A; WO2012163628A1; AT510955B1; AT510955A4; CA2837611A1; TWI565806B; CN103562412A; BR112013030747A2; KR20140048898A; CN103562412B

Abstract

A gas stream containing both hydrocarbon and hydrogen is separated into a hydrogen-rich fraction and a hydrocarbon-rich fraction. Then at least one sub-quantity of the hydrocarbon-rich fraction is subjected to at least one operation from the group oxidation using technically pure oxygen and reforming using CO₂and H₂O. The result is introduced at least as a component of a reduction gas into a reduction unit containing the metal oxides. As a result of the at least one operation, the hydrocarbon content in the reduction gas on entry into the reduction unit is below 12% by volume.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the U.S. national stage of International Application No. PCT/EP2012/054863, filed Mar. 7, 2012 and claims the benefit thereof. The International Application claims the benefit of Austrian Application No. A785/2011 filed on May 30, 2011, both applications are incorporated by reference herein in their entirety.

BACKGROUND

Described below are a process for reducing metal oxides, such as iron oxides, using a gas stream containing both hydrocarbon and hydrogen and a device for carrying out such a process.
Coke oven gas is formed when coke is generated in integrated smelting works or stand-alone production plants and is used to date, for example, for reinforcing the heating value of the blast furnace top gases before use thereof in recuperators, as fuel gas in slab reheating furnaces or roller hearth furnaces, and for electricity generation in power plants. As main components it contains not only hydrocarbon—for example one or more hydrocarbons C_nH_2n+2, wherein n can be 1 or 2 or 3 or 4; but chiefly methane, that is to say n=1—but also hydrogen. In some integrated smelting works, coke oven gas is also used for generating technically pure hydrogen, for example for use in annealing furnaces. Typical coke oven gas compositions formed in integrated smelting works are as follows


COG analysis (dry):

H₂[% by volume]	65	62.1
N₂[% by volume]	2.5	Included in remainder
CO [% by volume]	6	6.2
CH₄[% by volume]	22	21.4
C_nH_m[% by volume]	3	Included in remainder
CO₂[% by volume]	1.5	Included in remainder
H₂O [% by volume]	Saturated	Included in remainder
H₂S [g/Nm³(S.T.P)]	0.35	n.a.
Tar [g/Nm³(S.T.P)]	5	n.a.
Dust [g/Nm³(S.T.P)]	5	n.a.
Remainder [% by volume]	—	10.3

Although the coke oven gas contains components such as hydrogen and carbon monoxide which are readily usable for reducing metal oxides in general, and iron oxides in particular, on account of the hydrocarbon content, it can only be used with restrictions for reducing metal oxides, especially iron oxides, in a reducing unit, since, as a consequence of highly endothermic reactions of the hydrocarbons proceeding on the introduction of coke oven gas into the reducing unit, for example hydrocarbon CH₄
CH₄→2H₂+C Cracking ΔH₂₉₈=+74.86[kJ/mol]
3Fe+CH₄→Fe₃C+2H₂Carbonizing ΔH₂₉₈=+99.7[kJ/mol]
the reduction temperature would decrease too greatly, which in turn would greatly restrict the productivity of the reducing unit.

SUMMARY

Described below are a process which permits the use of a gas stream containing hydrocarbon and hydrogen for reducing metal oxides and a device for carrying out such a process.
This process for reducing metal oxides uses a gas stream containing not only hydrocarbon but also hydrogen, which is characterized in that the gas stream containing not only hydrocarbon but also hydrogen is separated into a hydrogen-rich fraction and a hydrocarbon-rich fraction, and subsequently at least a subquantity of the hydrocarbon-rich fraction is subjected to at least one operation of the group

oxidation using technically pure oxygen,
reformation using CO₂and H₂O,
and then it is introduced at least as a component of a reducing gas into a reducing unit containing the metal oxides, wherein the hydrocarbon content is adjusted by the at least one operation of the aforementioned group, in such a manner that the hydrocarbon content in the reducing gas is, on entry into the reducing unit, less than 12% by volume, such as less than 10% by volume, particularly less than 8% by volume.

Metal oxides can be, for example, iron oxides, or oxides of nickel, copper, lead, cobalt.
The reduction of the metal oxides proceeds to form extensively metalized metal—that is to say the degree of metalization is greater than or equal to 90%, which may be greater than or equal to 92%, for example sponge iron.
The gas stream containing not only hydrocarbon but also hydrogen can contain one or two or more types of hydrocarbon.
For example, it contains relatively low-saturated hydrocarbons C_nH_2n+2, wherein n=1, that is to say methane, or n=2, that is to say ethane, or n=3, that is to say propane, or n=4, that is to say butane or isobutane. It can also contain relatively low-monounsaturated or polyunsaturated hydrocarbons, wherein, for example, C_nH_2napplies, for example ethene. It can also contain aromatic hydrocarbons, such as benzene or toluene. In the gas stream containing not only hydrocarbon but also hydrogen, one or more types of hydrocarbon having the general formula C_nH_mcan also be present, wherein m can be
m=n,
m=2n,
m=2n+2.
The gas stream containing not only hydrocarbon but also hydrogen is separated into a hydrogen-rich fraction and a hydrocarbon-rich fraction. In this case the hydrocarbon-rich fraction contains not only hydrocarbons, but also further components such as argon, nitrogen, carbon monoxide, carbon dioxide and steam. The term hydrocarbon-rich relates to the fact that this fraction, compared with the gas stream containing not only hydrocarbon but also hydrogen, has a higher content of hydrocarbon. \
The hydrogen-rich fraction contains not only hydrogen.
The term hydrogen-rich relates to the fact that this fraction, compared with the gas stream containing not only hydrocarbon but also hydrogen, has a higher content of hydrogen.
Subsequently for the separation, at least a subquantity of the hydrocarbon-rich fraction obtained in the separation is subjected to at least one operation of the group

oxidation using technically pure oxygen,
reforming using CO₂and H₂O.

It can also be subjected to a combination of these two operations.
In the case of a combination, partial oxidation may be performed first using technically pure oxygen for the purpose of temperature elevation, and subsequently reforming is performed using CO₂and H₂O, for example in an autothermal reformer. In an autothermal reformer, the reformer does not need to be fired, because no feed line of fuel gas to the autothermal reformer is necessary. This saves expenditure on construction and reduces the exhaust gases of the reformer.
In this case, in the oxidation, the total amount of hydrocarbons is not oxidized, but only a part of the amount of hydrocarbons—in the context of this application, this is also termed partial oxidation.
In this case, in the reforming, the total amount of hydrocarbons is not reformed, but a predominant part of the amount of hydrocarbons.
Via the operations described, alone or in combination, the content of hydrocarbons decreases.
After at least a subquantity of the hydrocarbon-rich fraction obtained in the separation has been subjected to at least one operation of the group, it is introduced at least as a component of a reducing gas into a reducing unit containing the metal oxides—this means of course that the product obtained in the operation or operations is introduced.
At least as a component of a reducing gas means that the reducing gas can also contain other components which may optionally be added before a mixture obtained in the addition is introduced as reducing gas into the reducing unit.
As described below, the hydrocarbon content of the subquantity is set by the at least one operation of the group in such a manner that the hydrocarbon content in the reducing gas, on entry into the reducing unit, is less than 12% by volume, such as less than 10% by volume, particularly less than 8% by volume, but greater than 1% by volume, desirably greater than 2% by volume, particularly desirably greater than 3% by volume. These limits are included herein. The higher the hydrocarbon content is in the reducing gas on entry into the reducing unit, the higher the reduction temperature must be set—in reducing shafts as reducing unit, also termed—gas temperature bustle or the lower is the productivity of the plant. At a set hydrocarbon content, the reduction temperature owing to a lower endothermic reactions of the hydrocarbons does not fall so greatly that the productivity of the reducing unit decreases below an economically acceptable level.
The lower limit of the hydrocarbon content is determined, for example, in the reduction of iron oxides, by the required carbon content—carbon bound as Fe₃C or elemental carbon—in the reduced product for the steelworks—there, for example, an electric arc furnace. With increasing carbon content in the reduced product, the energy requirement in the subsequent treatment in the electric arc furnace decreases. A hydrocarbon content in the reducing gas on entry into the reducing unit in the range of the lower limit is used, for example, for generating a minimum content of carbon in a sponge iron, in particular in the form of Fe₃C, or such a hydrocarbon content is necessary optionally for controlling the temperature in the reducing unit.
In addition, for example in the production of sponge iron, hot briquetted iron (HBI) plants—as are customary in direct reduction (DR) plants—also require certain minimum briquetting temperatures—desirably >650° C. for avoidance of increased maintenance costs and to achieve product densities >5 g/cm³—which, in the event of excessive cooling of the DRI in the reducing unit, cannot be achieved owing to endothermal reactions.
According to an embodiment, the gas stream containing not only hydrocarbon but also hydrogen is coke oven gas.
The latter embodiment is desirable because coke oven gas, in an integrated smelting works, is usually formed in any case, or, in a stand-alone coking plant, is only used for electricity generation, or is flared off without being used. Using the process, it can be utilized for efficient iron production; the material utilization thereof achieved in this case has a higher efficiency than, for example, utilization for electricity generation. An integrated smelting works is taken to mean a steel generation route which consists, inter alia, of coking plant, sintering plant and blast furnace. The gas stream containing not only hydrocarbon but also hydrogen can also be gas generated in a coal gasifier.
According to an embodiment, the gas stream containing not only hydrocarbon but also hydrogen is separated into a hydrogen-rich fraction and a hydrocarbon-rich fraction by at least one operation of the group

pressure-swing adsorption,
membrane separation.

The pressure-swing adsorption proceeds, for example, in a PSA or VPSA plant, wherein PSA means Pressure Swing Adsorption and VPSA means Vacuum Pressure Swing Adsorption. More desirably, a prepurification of the gas stream proceeds before the pressure-swing adsorption, for example in a prepurification appliance for separating off tar and dust using tar filters made of fibers or adsorption materials. Owing to the differing adsorption forces, a gas stream containing not only hydrocarbon but also hydrogen, for example coke oven gas, in the case of an appropriate design of the plant size of pressure-swing adsorption plants and by operation using correspondingly designed cycle times using a PSA plant or a VPSA plant can be separated into a hydrogen-rich fraction and a hydrocarbon-rich fraction. The hydrogen is formed on the product side virtually without a significant pressure drop. The hydrocarbon-rich fraction is formed at very low pressure or a vacuum and is then compressed to the required pressure subsequently in the process.
In the case of membrane separation, the separation proceeds on the basis of the differing permeability of a membrane. Hydrogen is produced in this case in the concentrated state on the low-pressure side of the membrane.
According to an embodiment, at least a proportion of the at least one subquantity of the hydrocarbon-rich fraction which was subjected to at least one operation of the group

oxidation using technically pure oxygen,
reforming using CO₂and H₂O, is mixed with an auxiliary reducing gas, before the resultant mixture of these two components is introduced as reducing gas into the reducing unit containing the metal oxides.

In this case the reducing gas introduced into the reducing unit containing the metal oxides is generated by mixing two components, wherein the one component is obtained by oxidizing and/or reforming at least one subquantity of the hydrocarbon-rich fraction.
In such a procedure, other gases having a reduction potential can also be materially utilized for the reduction of metal oxides by adding them as auxiliary reducing gas.
In a device for carrying out the process, corresponding feed lines are present for introducing auxiliary reducing gases to the proportion of the hydrocarbon-rich fraction, or optionally to the total amount of the hydrocarbon-rich fraction, which has been subjected to at least one operation of the group

oxidation using technically pure oxygen,
reforming using CO₂and H₂O.

According to an embodiment, the mixing ratio of the two components is set in dependence on a preset temperature for the mixture. In this manner, it is ensured that the reducing gas is in the temperature region which is favorable in terms of the process and economics for reducing metal oxides. By setting the temperature, the reaction rate in the reducing reactor—kinetics, can be set optimally. In addition, the efficiency of the reducing gas preheating can be optimized.
Corresponding devices for controlling the mixing ratio and also temperature measuring devices for measuring the temperature of the mixture and/or for measuring the temperatures of the components are present in a device for carrying out the process.
According to an embodiment, the two components are mixed after the auxiliary reducing gas has been heated in a gas furnace. This makes possible an improved temperature setting of the reducing gas. The temperature of the reducing gas may be in the range 780-1050° C., according to the H₂/CO ratio in the reducing gas.
According to an embodiment, top gas is taken off from the reducing unit, and the auxiliary reducing gas is obtained at least in part by mixing top gas that is dedusted and substantially freed from CO₂, and at least one further gas. In this manner, the reductants (CO and H₂) still present in the top gas are utilized again for reducing the metal oxides.
Advantageously, the at least one further gas includes the hydrogen-rich fraction obtained in the separation of the gas stream, such as coke oven gas, containing not only hydrocarbon but also hydrogen.
In this manner, the reduction potential present in this fraction is also utilized for reducing metal oxide; utilized, especially in that the reduction rate—kinetics—is generally more rapid via hydrogen:
3Fe₂O₃+H₂→2Fe₃O₄+H₂O ΔH₂₉₈=−2.72 [kJ/mol]
Fe₃O₄+H₂→3FeO+H₂O ΔH₂₉₈=+59.83 [kJ/mol]
FeO+3H₂→Fe+2H₂+H₂O ΔH₂₉₈=+29.60 [kJ/mol]
Advantageously, the gas furnace is operated with a fuel gas which at least in part includes at least one gas of the group

tail gas formed in the removal of CO₂from the top gas,
top gas,
gas stream, such as coke oven gas, containing not only hydrocarbon but also hydrogen,
hydrogen-rich fraction obtained by separation of the gas stream, such as coke oven gas, containing not only hydrocarbon but also hydrogen,
hydrocarbon-rich fraction obtained by separation of the gas stream, such as coke oven gas, containing not only hydrocarbon but also hydrogen.

In this manner, these gases are utilized in the process for reducing metal oxides, which increases the efficiency thereof. When hydrogen-rich gases are used for firing the gas furnace from below, the CO₂emission can be kept correspondingly low.
Single, a plurality of, or all of the corresponding fuel gas feed line(s) to the gas furnace is/are present in a device for carrying out the process:

a tail gas feed line for feeding tail gas produced in the removal of CO₂from the top gas, which tail gas feed line exits from the CO₂removal plant.
A top gas feed line for feeding top gas, which top gas feed line exits from a top gas outlet line withdrawing top gas from the reducing unit.
A fuel gas feed line for feeding gas stream containing not only hydrocarbon but also hydrogen, which fuel gas feed line exits from a feed line for a gas stream containing not only hydrocarbon but also hydrogen and which itself opens out into a device for separating a gas stream containing not only hydrocarbon but also hydrogen into a hydrogen-rich fraction and a hydrocarbon-rich fraction.
A fuel gas feed line for feeding a hydrogen-rich fraction obtained by separation of the gas stream, such as coke oven gas, containing not only hydrocarbon but also hydrogen, which fuel gas feed line exits from a device for separating a gas stream containing not only hydrocarbon but also hydrogen into a hydrogen-rich fraction and a hydrocarbon-rich fraction, or from an outlet line for the hydrogen-rich fraction which itself arises from a device for separating a gas stream containing not only hydrocarbon but also hydrogen into a hydrogen-rich fraction and a hydrocarbon-rich fraction,
a fuel gas feed line for feeding a hydrocarbon-rich, hydrogen-rich fraction obtained by separation of the gas stream, such as coke oven gas, containing not only hydrocarbon but also hydrogen, which fuel gas feed line exits from a feed line for the hydrocarbon-rich, hydrogen-rich fraction which itself arises from a device for separating a gas stream containing not only hydrocarbon but also hydrogen into a hydrogen-rich fraction and a hydrocarbon-rich fraction, or a device for separating a gas stream containing not only hydrocarbon but also hydrogen into a hydrogen-rich fraction and a hydrocarbon-rich fraction.

Advantageously, the reducing unit is a reducing shaft and a first subquantity of the hydrocarbon-rich fraction is introduced directly into the reducing shaft, and a second subquantity of the hydrocarbon-rich fraction before introduction thereof into the reducing shaft is subjected to at least one operation of the group

oxidation using technically pure oxygen
reforming using CO₂and H₂O, and then is introduced at least as component of a reducing gas into a reducing unit containing the metal oxides, and the hydrocarbon content is set by the at least one operation of the group, in such a manner that the hydrocarbon content in the reducing gas, on entry into the reducing unit, is less than 12% by volume, such as less than 10% by volume, particularly less than 8% by volume.

The first subquantity can thus be utilized for carbonization of the metal generated in the reducing unit; for example, it can be utilized for carbonization of metallic iron.
Advantageously, the at least one gas stream containing CO₂and/or H₂O is added to the hydrocarbon-rich fraction before reforming using CO₂and H₂O. In this process, this can be, for example, steam, tail gas from a CO₂removal process—for example from the removal of CO₂from the top gas—top gas from the reducing shaft, or converter gas. Water can also be added.
In this manner, these gases are utilized in the process for reducing metal oxides, which increases the efficiency thereof, and reduces the environmental emissions, since CO₂is converted back to CO.
Corresponding feed lines for feeding one or more of these gases which exit from devices producing such gases or lines bearing such gases are present in a device for carrying out the process.
In the hydrocarbon-rich fraction, H₂S is also enriched. According to an embodiment, therefore, desulfurization of the hydrocarbon-rich fraction is carried out before it is subjected to at least one operation of the group

oxidation with technically pure oxygen,
reforming using CO₂and H₂O or.

The sulfur content can thereby be reduced in the largely metalized metal.
In a device for carrying out the process, then, in a feed line for the hydrocarbon-rich fraction 3, a desulfurization device is present, before—seen in the direction of flow—the feed line opens out into a unit for carrying out an operation of the group

oxidation with technically pure oxygen,
reforming using CO₂and H₂O.

The process has the following advantages:

efficient material utilization of coke oven gas for reducing metal oxides, especially for reducing iron oxides for sponge iron production—advantage in comparison with the thermal utilization of coke oven gas proceeding to date according to the related art,
in comparison with utilization of natural gas for reducing metal oxides, especially for the reduction of iron oxides for sponge iron production, high economic advantages in comparison with natural gas, since the coke oven gas is produced at lower costs
very environmentally friendly process, in particular owing to low CO₂and NO_xemissions, since firstly in some embodiments a very hydrogen-rich gas can be used for the reduction and secondly by utilization of low-carbon gases in the reformer and/or gas furnace, emissions thereof can further be reduced.
Furthermore, in the reformer, some of the CO₂emissions can be converted back to CO and subsequently utilized for the reduction.

The specific carbon emission factor in the case of coke oven gas is 43.7 kg of CO₂/GJ of fuel, while in the case of natural gas it is 55.7 kg of CO₂/GJ of fuel. The use of coke oven gas is therefore considerably more environmentally friendly than the use of natural gas.
A further subject matter of the present application is a device for carrying out the process having a reducing unit for reducing metal oxides, having a device for separating a gas stream containing not only hydrocarbon but also hydrogen into a hydrogen-rich fraction and a hydrocarbon-rich fraction, having, arising therefrom, a feed line for the hydrocarbon-rich fraction which opens out into a unit for carrying out an operation of the group

oxidation using technically pure oxygen
reforming using CO₂and H₂O, and having one or more introduction lines for introducing at least one gas stream from the group
hydrocarbon-rich fraction,
gas stream obtained in the unit for carrying out oxidation using technically pure oxygen,
gas stream obtained in the unit for carrying out reforming using CO₂and H₂O, into the reducing unit.

The device for separating a gas stream containing not only hydrocarbon but also hydrogen into a hydrogen-rich fraction and a hydrocarbon-rich hydrogen-rich fraction may be a device for separating coke oven gas into a hydrogen-rich fraction and a hydrocarbon-rich fraction.
The device for separating a gas stream containing not only hydrocarbon but also hydrogen into a hydrogen-rich fraction and a hydrocarbon-rich fraction may be a device of the group

device for pressure-swing adsorption,
device for membrane separation.

The one or more introduction lines may open out into the reducing unit, wherein upstream of the opening of at least one of the introduction lines into the reducing unit, an auxiliary reducing gas line for feeding auxiliary reducing gas to the reducing unit opens out into this introduction line.
Upstream of the opening of the auxiliary reducing gas line into the introduction line, a gas furnace may be present in the auxiliary reducing gas line.
Desirably, x introduction lines are present, wherein x is greater than 2 or is equal to 2, of the at most x−1 introduction lines it is true that, upstream of the opening of at least one of the introduction lines into the reducing unit, an auxiliary reducing gas line, for feeding auxiliary reducing gas to the reducing unit, opens out into this introduction line.
In this manner, at least one introduction line is present into which no auxiliary reducing gas line opens out. Therefore, a subquantity of the hydrocarbon-rich fraction can be introduced directly into the reducing shaft without being mixed with auxiliary reducing gas; this subquantity can be used, for example, for carbonizing the metal generated in the reducing unit; for example it can be used for carbonizing metallic iron.
According to one embodiment, the reducing unit is a reducing shaft, for example a fixed-bed reducing shaft for carrying out a MIDREX® or HYL® reduction process.
According to one embodiment, the reducing unit is a fluidized-bed cascade.
An exemplary embodiment will be described in detail with reference to a drawing. In the drawings:

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects and advantages will become more apparent and more readily appreciated from the following description of the exemplary embodiments, taken in conjunction with the schematic and exemplary drawings of which:

FIG. 1 is block diagram of a device for carrying out a process in which coke oven gas is separated into a hydrogen-rich fraction and a hydrocarbon-rich fraction and the latter is subjected to an oxidation before it is introduced into a reducing shaft as part of a reducing gas.

FIG. 2 is block diagram of a device and procedure similar to FIG. 1, with the difference that the hydrocarbon-rich fraction is subjected to reforming using CO₂and H₂O before it is introduced as part of a reducing gas into a reducing shaft.

FIG. 3 is block diagram of a device and procedure which chiefly differs from FIG. 1 in that a fluidized-bed cascade is present as reducing unit, and the device present for separating coke oven gas, instead of a device for pressure-swing adsorption, is a device for membrane separation.

FIG. 4 is block diagram of a device and procedure which chiefly differs from FIG. 1 in that a fluidized-bed cascade is present as reducing unit, and the device for separating coke oven gas, instead of a device for pressure-swing adsorption, is a device for membrane separation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Reference will now be made in detail to the preferred embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout.
FIG. 1 shows a device for carrying out a process. This includes, as a reducing unit for reducing metal oxides, a reducing shaft 1 which contains iron ore, that is to say iron oxides. It likewise includes a device for separating a gas stream containing not only hydrocarbon but also hydrogen, in this case a PSA or a VPSA plant 2 using pressure-swing adsorption, into a hydrogen-rich fraction and a hydrocarbon-rich fraction. In the present example, the gas stream containing not only hydrocarbon but also hydrogen is coke oven gas. From the PSA or VPSA plant 2 there arises a feed line for the hydrocarbon-rich fraction 3 which opens out into a unit for carrying out an oxidation using technically pure oxygen 4. In this unit for carrying out an oxidation using technically pure oxygen 4, the hydrocarbon-rich fraction is partially oxidized; that is, the entire amount of substance is not oxidized, but only a part of the amount of substance of the hydrocarbon-rich fraction. Via an introduction line 5 for introducing the gas stream obtained in the unit for carrying out oxidation using technically pure oxygen 4, this gas stream is introduced as a component of a reducing gas into the reducing shaft 1. In the partial oxidation the hydrocarbon content is set in such a manner that the hydrocarbon content in the reducing gas is less than 12% by volume on entry into the reducing shaft.
The gas stream obtained in the unit for carrying out oxidation using technically pure oxygen 4 is mixed with an auxiliary reducing gas, the resultant mixture is introduced as reducing gas into the reducing shaft 1. The two components of the reducing gas are mixed after the auxiliary reducing gas has been heated in a gas furnace 6. The auxiliary reducing gas is added via an auxiliary reducing gas line 7 for feeding auxiliary reducing gas to the reducing unit 1, which reducing gas line 7 opens out into the introduction line 5. Via the introduction line 5, therefore, not only the gas stream obtained in the unit for carrying out oxidation using technically pure oxygen 4, but also the auxiliary reducing gas is introduced into the reducing shaft 1, specifically as a mixture termed reducing gas. The temperature preset of the auxiliary reducing gas which is heated in the gas furnace 6 is set in dependence on a temperature preset for the mixture. The gas furnace 6 is arranged in the auxiliary reducing gas line 7.
From the reducing shaft 1, top gas is conducted away via a top gas outlet line 8. The auxiliary reducing gas, in the example shown, is formed by mixing dedusted—a gas scrubber 9 is present in the top gas outlet line 8—top gas that is largely freed from CO₂—a CO₂removal plant 10 is present in the top gas outlet line 8—and a further gas. The further gas is the hydrogen-rich fraction obtained in the separation of the coke oven gas.
The gas furnace 6 is operated using a fuel gas. The fuel gas is burnt with feed of air through an air feed line 11 opening out into the gas burner. The fuel gas contains gases of the group

tail gas formed in the removal of CO₂from the top gas,
top gas,
coke oven gas,
hydrogen-rich fraction obtained by separation of coke oven gas.

For feeding these gases into the gas burner 6, there are present

a tail gas feed line 12 for feeding tail gas formed in the removal of CO₂from the top gas which exits from the CO₂removal plant 10 and opens out into the gas burner,
a top gas feed line 13 for feeding top gas which exits from the top gas outlet line 8 conducting away top gas from the reducing unit and opens out into the gas burner,
a coke oven gas feed line 14 for feeding coke oven gas, which exits from a feed line for coke oven gas 15 and opens out into the top gas feed line 13,
a hydrogen fraction feed line 16 which branches off from a hydrogen fraction outlet line 17 exiting from the PSA or VPSA plant 2 and opens out into the coke oven gas feed line 14.

In order that auxiliary reducing gas can be obtained by mixing top gas that is dedusted and largely freed from CO₂and the hydrogen-rich fraction obtained in the separation of the coke oven gas, not only the hydrogen fraction outlet line 17 but also the top gas outlet line 8 open out into the auxiliary reducing gas line 7.
The feed line for coke oven gas 15 exits from a coke oven gas source that is not shown and opens out into the PSA or VPSA plant 2.
In the device shown in FIG. 1, two introduction lines opening out into the reducing shaft 1 are present. The introduction line 5, called first introduction line, has already been described. A further introduction line, called second introduction line 18, branches off from the feed line for the hydrocarbon-rich fraction 3 and opens out into the reducing shaft. Via this second introduction line 18, a subquantity of the hydrocarbon-rich fraction can be introduced directly into the reducing shaft. This subquantity can thus be used for carbonizing the metallic iron, in this case sponge iron, generated in the reducing shaft 1. A cooling gas line for feeding cooling gas into the reducing shaft 1 is not shown for reasons of clarity; in principle, for the purpose of carbonization, a subquantity of the hydrocarbon-rich fraction could also be added to the cooling gas via a corresponding branch from the feed line for the hydrocarbon-rich fraction 3 which opens out into the cooling gas line.
In the tar filter appliance 19 arranged in the feed line for coke oven gas 15, tar is removed from the coke oven gas.
In the burner 20, the auxiliary reducing gas can be partially oxidized with feed of technically pure oxygen, if this is wanted for temperature elevation.
For reasons of clarity, depiction of device parts which are not essential has been dispensed with, for example the depiction of diverse compressors, bypass lines, gas holders, gas coolers, flare stacks.
In FIG. 2, in an otherwise similar device and procedure, the hydrocarbon-rich fraction, instead of a partial oxidation, is subjected to reforming using CO₂and H₂O before it is introduced as part of a reducing gas into a reducing shaft. Plant parts and processes which are identical to FIG. 1 are not described again here for the most part, and the reference signs for the same plant parts, for better clarity, are not entered into the drawing. The reforming takes place in a unit for carrying out reforming using CO₂and H₂O, here a reformer 21, into which the feed line for the hydrocarbon-rich fraction 3 opens out. Off-gas from the reformer 21 is used via a heat exchanger 22 for heating the hydrocarbon-rich fraction before entering into the reformer 21.
Via a plurality of feed lines 23 a, 23 b, which open out into the feed line for the hydrocarbon-rich fraction 3, before entry into the reformer 21, a plurality of CO₂-containing gas streams are added to the hydrocarbon-rich fraction. Via feed line 23 a, tail gas from the CO₂removal plant 10 is added; the feed line 23 a arises from the tail gas feed line 12. Via feed line 23 b, top gas is added. Via a water feed line 24 which opens out into the feed line for the hydrocarbon-rich fraction 3, before entry into the reformer 21, steam and/or water is added to the hydrocarbon-rich fraction.
The reformer 21 can be fired using top gas, coke oven gas or with the hydrocarbon-rich fraction; corresponding lines opening out into the reformer 21, for the sake of clarity, are not shown.
Via a branch line 29 which branches off from the second introduction line 18 and opens out into the first introduction line 5, the hydrocarbon content in the reducing gas on entry into the reducing shaft 1 can be influenced via the feed of hydrocarbon-rich fraction.
In FIG. 3, the reducing unit is a fluidized-bed cascade 25, from the last fluidized-bed reactor 26 of which, seen in the direction of flow of the reducing gas, top gas is taken off; the top gas line is given the reference sign 8, as is the top gas line in FIG. 1. The introduction line 5, which in FIG. 1 is shown opening out into the reducing shaft 1, is, in FIG. 3, shown opening out into the first fluidized-bed reactor 27, similarly seen in the direction of flow of the reducing gas. As a device for separating coke oven gas—instead of, as in FIG. 1, a device for pressure-swing adsorption—there is a device for membrane separation 28. Via a branch from the feed line for the hydrocarbon-rich fraction 3, hydrocarbon-rich fraction can be fed into the first introduction line 5, which offers a possibility for influencing the hydrocarbon content in the reducing gas.
FIG. 4 differs from FIG. 2 by the same modifications by which FIG. 3 differs from FIG. 1. In addition, in FIG. 1, in contrast to FIG. 2, no heat exchanger 22 is present.
A description has been provided with particular reference to preferred embodiments thereof and examples, but it will be understood that variations and modifications can be effected within the spirit and scope of the claims which may include the phrase “at least one of A, B and C” as an alternative expression that means one or more of A, B and C may be used, contrary to the holding in Superguide v. DIRECTV, 358 F3d 870, 69 USPQ2d 1865 (Fed. Cir. 2004).

Claims

1-12. (canceled)

13. A method for reducing metal oxides using a coke oven gas, comprising:

separating the coke oven gas into a hydrogen-rich fraction and a hydrocarbon-rich fraction;

subjecting at least a subquantity of the hydrocarbon-rich fraction to at least one operation of the group consisting of oxidation using technically pure oxygen and reforming using CO₂and H₂O to obtain at least a component of a reducing gas;

obtaining an auxiliary reducing gas at least in part by mixing top gas that is dedusted and substantially freed from CO₂, and at least one further gas, including the hydrogen-rich fraction produced by said separating of the coke oven gas;

mixing at least a portion of the component obtained by said subjecting with the auxiliary reducing gas to obtain the reducing gas; and

introducing the reducing gas after said mixing, into a reducing unit containing the metal oxides, where a hydrocarbon content of the reducing gas, as a result of said subjecting and said mixing, is on entry into the reducing unit, less than 12% by volume.

14. The method as claimed in claim 13, wherein the hydrocarbon content of the reducing gas, on entry into the reducing unit, is less than 10% by volume.

15. The method as claimed in claim 14, wherein the hydrocarbon content of the reducing gas, on entry into the reducing unit, is less than 8% by volume, but greater than 1% by volume.

16. The method as claimed in claim 15, wherein the hydrocarbon content of the reducing gas, on entry into the reducing unit, is greater than 2% by volume.

17. The method as claimed in claim 16, wherein the hydrocarbon content of the reducing gas, on entry into the reducing unit, is greater than 3% by volume.

18. The method as claimed in claim 17, wherein said separating includes at least one operation of the group consisting of pressure-swing adsorption and membrane separation.

19. The method as claimed in claim 18, further comprising heating the auxiliary reducing gas in a gas furnace prior to said mixing.

20. The method as claimed in claim 19, wherein the gas furnace is operated with a fuel gas which at least in part includes at least one gas of the group consisting of tail gas formed in removal of CO₂from the top gas, the top gas, the coke oven gas, the hydrogen-rich fraction obtained by said separating of the coke oven gas, and the hydrocarbon-rich fraction obtained by said separating of the coke oven gas.

21. The method as claimed in claim 13,

wherein the reducing unit is a reducing shaft,

wherein said method further comprises introducing a first subquantity of the hydrocarbon-rich fraction directly into the reducing shaft, and

wherein said subjecting subjects a second subquantity of the hydrocarbon-rich fraction to the at least one operation of the group consisting of oxidation using technically pure oxygen and reforming using CO₂and H₂O, prior to said mixing.

22. The method as claimed in claim 21, wherein the hydrocarbon content of the reducing gas, on entry into the reducing unit, is less than 10% by volume

23. The method as claimed in claim 22, wherein the hydrocarbon content of the reducing gas, on entry into the reducing unit, is less than 8% by volume, but greater than 1% by volume.

24. The method as claimed in claim 21, further comprising adding at least one gas stream containing at least one of CO₂and H₂O to the hydrocarbon-rich fraction before reforming using CO₂and H₂O.

25. A device for reducing metal oxides using a coke oven gas, comprising:

a reducing unit reducing metal oxides;

a separating device separating coke oven gas into a hydrogen-rich fraction and a hydrocarbon-rich fraction;

a feed line, connected to the separating device, supplying the hydrocarbon-rich fraction;

an operation unit, connected to the feed line, carrying out on at least a subquantity of the hydrocarbon-rich fraction an operation of the group consisting of oxidation using technically pure oxygen and reforming using CO₂and H₂O, to produce an operation gas stream;

at least one introduction line introducing into said reducing unit a reducing gas including at least one from the group consisting of the hydrocarbon-rich fraction and the operation gas stream produced by the operation unit; and

an auxiliary reducing gas line feeding an auxiliary reducing gas into at least one of the at least one introduction line upstream of the reducing unit, the auxiliary reducing gas including top gas that is dedusted and substantially freed from CO₂and the hydrogen-rich fraction produced by said separating device, whereby the reducing gas and the auxiliary reducing gas introduced into said reducing unit by the at least one introduction line having a hydrocarbon content that is less than 12% by volume on entry into said reducing unit.

26. The device as claimed in claim 25, wherein the hydrocarbon content of the reducing gas and the auxiliary reducing gas, on entry into said reducing unit, is less than 10% by volume.

27. The device as claimed in claim 26, wherein the hydrocarbon content of the reducing gas and the auxiliary reducing gas, on entry into said reducing unit, is less than 8% by volume.

28. The device as claimed in claim 27, wherein the hydrocarbon content of the reducing gas and the auxiliary reducing gas, on entry into said reducing unit, is greater than 2% by volume.

29. The device as claimed in claim 28, wherein the hydrocarbon content of the reducing gas and the auxiliary reducing gas, on entry into said reducing unit, is greater than 3% by volume.

30. The device as claimed in claim 29, wherein said separating device includes at least one of a pressure-swing adsorption device and a membrane separation device.

31. The device as claimed in claim 30, further comprising gas furnace in said auxiliary reducing gas line upstream of said introduction line.

32. The device as claimed in claim 31, wherein said at least one introduction line includes at least two introduction lines of which at least one is not connected to the auxiliary reducing gas line.

33. The device as claimed in claim 32, wherein said reducing unit is a reduction shaft.

34. The device as claimed in claim 32, wherein said reducing unit is a fluidized-bed cascade.