Patent Application
20140083252
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 CnH2n+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
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+2H2 Carbonizing ΔH298=+99.7[kJ/mol]
the reduction temperature would decrease too greatly, which in turn would greatly restrict the productivity of the reducing unit.
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
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 CnH2n+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, CnH2n applies, 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 CnHm can 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
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 CO2 and 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
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
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
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
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 CO2 emission 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:
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
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 CO2 and/or H2O is added to the hydrocarbon-rich fraction before reforming using CO2 and H2O. In this process, this can be, for example, steam, tail gas from a CO2 removal process—for example from the removal of CO2 from 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 CO2 is 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
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
The process has the following advantages:
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
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
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:
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:
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.
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 CO2 removal 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
For feeding these gases into the gas burner 6, there are present
In order that auxiliary reducing gas can be obtained by mixing top gas that is dedusted and largely freed from CO2 and 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
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
Via a plurality of feed lines 23a, 23b, 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 23a, tail gas from the CO2 removal plant 10 is added; the feed line 23a arises from the tail gas feed line 12. Via feed line 23b, 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
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).
| Number | Date | Country | Kind |
|---|---|---|---|
| A785/2011 | May 2011 | AT | national |
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.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2012/058360 | 5/7/2012 | WO | 00 | 11/27/2013 |
