Patent Application
20210246521
The present technology relates to a process for producing directly reduced iron sponge from iron oxide material, wherein direct reduction is carried out by means of a reduction gas consisting at least predominantly of H2.
Producing iron sponge by direct reduction of iron oxide material by means of hydrogen is known. Such processes are described in, for example, WO 9924625 and WO 2014040989. Consumed reduction gas exiting from the reduction apparatus after the direct reduction, referred to as topgas, can be recirculated very simply for reduction purposes since virtually only dust and water have to be separated off to any appreciable extent from the reducing component hydrogen H2. The topgas may also contain some CO2 due to calcination of iron oxide material used. When nitrogen is used for sealing purposes during charging of the iron oxide material into the reduction apparatus and/or during discharge of iron sponge, for example conceived as a cyclic material lock system or dynamic lock system, the topgas can also contain some nitrogen. However, the use of a reduction gas having a high hydrogen content leads to the carbon content in the iron sponge being very low compared to conventional direct reduction using mainly carbon monoxide CO or other carbon-containing gases such as methane CH4. This can be disadvantageous in the further processing of the iron sponge, for example in EAF, since the consumption of electric energy and electrode consumption and also tap-to-tap time are increased for iron sponge having a low carbon content. This results in a significantly lower productivity of the electric arc furnace. Although an increase in the proportion of carbon-containing gases in the reduction gas can increase the carbon content in the iron sponge, this leads to an increase in the concentration of carbon-containing gas components, for instance CO, CO2, CH4, and increased CO2 emissions in the topgas. This makes a considerable outlay in terms of apparatus and energy necessary for the removal of CO2, and other undesirable nonaqueous constituents which may be present in the hydrogen H2 when topgas is recirculated.
The present invention addresses the problem of providing a process and an apparatus which make it possible, in a simple way with little outlay, to obtain an iron sponge which has a carbon content capable for further processing in the direct reduction of iron oxide material using predominantly hydrogen-containing reduction gas.
This problem is solved by a process for producing carburized directly reduced iron sponge from iron oxide material, where direct reduction is firstly carried out by means of a reduction gas consisting at least predominantly of hydrogen H2, characterized in that the carbon content in the iron sponge is then increased by means of a carburizing gas fed in, after which used carburizing gas is at least partly taken off while largely avoiding mixing with the reduction gas.
For the purposes of the present invention, iron oxide material is any iron oxide-containing material suitable as starting material for direct reduction for producing iron sponge. Depending on the process used for direct reduction, it can be lumpy material such as ore pellets, lump ore, oxide briquettes, or be finely particulate material. Lumpy material is suitable, for example, for direct reduction in fixed-bed reactors. Finely particulate material is suitable, for example, for direct reduction in fluidized-bed reactors.
In carburized iron sponge, the carbon content is from at least 0.5% by weight up to 5.0% by weight, and is preferably in the range from 1.0 to 3.5% by weight, with the two limits being included. The carbon can be present in bound form as iron carbide Fe3C and/or in free form as graphitic carbon C. Chemically bound carbon as iron carbide Fe3C is better and more effective for operation of an electric arc furnace (EAF).
The iron oxide material is firstly directly reduced by means of a reduction gas consisting at least predominantly of hydrogen H2, for example in a reduction zone. The hydrogen content of the reduction gas can be up to 100% by volume. Preference is given to a hydrogen content of at least 80% by volume, particularly preferably at least 90% by volume, with the balance to 100% by volume being, for example, nitrogen N2, carbon monoxide CO, carbon dioxide CO2, water vapor H2O, methane CH4. The carbon content of the iron sponge obtained in this direct reduction is then increased, for example in a carburization zone. To bring about the increase, a carbon-containing gas, known as carburizing gas, is supplied to the sponge. The carburizing gas contains carbon in carbon-containing molecules. The carburizing gas can, for example, be natural gas, methane CH4, ethane C2H6, propane C3H8, butane C4H10, carbon monoxide CO or a mixture of a plurality of these gases. The carbon-containing molecules react with the iron sponge to form iron carbide Fe3C, or they react with liberation of carbon C.
For example, the carburization using methane proceeds as follows
3Fe+CH4→Fe3C+2H2
Or elemental carbon is formed, for example, by cracking of methane
CH4→C+2H2
Owing to the subsequent reduction reaction of the resulting hydrogen H2 with iron ore, water vapor (H2O) is formed according to the following reaction and this also reacts with the methane (CH4) which may be present by way of example via a reforming reaction:
FeO+H2→Fe+H2O
CH4+H2O→CO+3H2
Subsequently, CO2 and water vapor are also formed from the CO
FeO+CO→Fe+CO2
3Fe+2CO→Fe3C+CO2
3Fe+CO+H2→Fe3C+H2O
CO+H2→C+H2O
CO+H2O↔CO2+H2
2CO→C+CO2
The product of this carburizing step having a carbon content which is increased compared to the product of the first step, namely the direct reduction, iron sponge, is for the purposes of the present patent application referred to as carburized iron sponge. In effecting the increase in the carbon content, here referred to as carburizing or carburization, carburizing gas is partially reacted. Mixing of non-hydrogen H2 gaseous products, for example CO2, CO, of the reactions leading to carburization or of unreacted partial amounts of the carburizing gas, for example N2, with the reduction gas consisting predominantly of hydrogen H2 introduced into the reduction apparatus may make an outlay for removal necessary when topgas is recirculated.
In order to keep this outlay small, or avoid it entirely, used carburizing gas is at least partly taken off while largely avoiding mixing with the reduction gas. The used carburizing gas, which is at least partly, preferably completely, taken off, contains both gaseous products of the reactions leading to carburization and also unreacted partial amounts of the carburizing gas. The taking-off is carried out in such a way that mixing of the used carburizing gas with the reduction gas is largely, preferably completely, avoided.
Substantial avoidance of mixing with the reduction gas is considered to have taken place when the total proportion of carbon-containing gases, for example CO, CO2, CH4 or higher hydrocarbons, in the topgas is below 20% by volume, preferably below 10% by volume, particularly preferably below 5% by volume. These values are based on measurements after cooling of the topgas and condensation of water vapor from the topgas. “Total” means that the proportions of the individual carbon-containing gases are added up; for example at 8% by volume of CO, 7% by volume of CO2 and 4% by volume of CH4 the total would be 19% by volume and thus below the required limit of 20% by volume.
The used carburizing gas is thus at least partly, preferably completely, taken off before mixing with the reduction gas occurs. The objective here is to have only very small or no gas flows from the carburization zone into the reduction zone. This can, for example, be achieved by such an amount of used carburizing gas being taken off from the carburization zone and such an amount of used carburizing gas being separated off from a circuit of the carburizing gas that backflow from the carburization zone into the reduction zone does not take place. The used carburizing gas is effectively discharged, for example, laterally from an upper region of the carburization zone before it reaches the reduction zone above.
Accordingly, a reduction, for example, of the amount of CO2 in the topgas intended for recirculation, for example by means of a CO2 scrub or CO2/H2O reformer, is dispensed with in the process of the invention. The process is also then carried out without reduction of the amount of CO2 in the topgas intended for recirculation, if the topgas also contains some CO2 due to calcination of the iron oxide material used. To avoid accumulation of this CO2 or other undesirable gas components which may be present in the topgas when recirculation is carried out, a first partial amount of the topgas is excluded from the recirculation and discharged from the circuit. This first partial amount may optionally be fed to a use, for example use as fuel gas.
The less mixing of the carburization offgas with the reduction gas takes place, the smaller the amount of topgas which has to be excluded from the recirculation, and the more energy-efficiently can the production of the carburized directly reduced iron sponge be carried out.
An outlay for separating undesirable components from a topgas to be recirculated can be avoided by carrying out the carburization as per the invention after the direct reduction and subsequently taking off used carburizing gas.
In a preferred embodiment, a first partial amount of the used carburizing gas is, after treatment such as dust removal, combined again with fresh carburizing gas components as carburizing gas for increasing the carbon content of the iron sponge.
In this way, the carburization can be carried out more economically with greater conservation of resources since unreacted components present in the used carburizing gas can again have the opportunity of contributing to the carburization.
In a preferred embodiment, the carburizing gas or the treated used carburizing gas is heated before or after being combined with fresh carburizing gas components before coming into contact with the iron sponge. Thus, heating of at least one member of the group consisting of the two members, carburizing gas and treated used carburizing gas before or after being combined with fresh carburizing gas components, occurs before it comes into contact with the iron sponge.
The carburization reactions proceed better at relatively high temperatures. Accordingly, the efficiency of the carburization is increased by increasing the temperature.
In a preferred embodiment, the reduction gas is heated before it comes into contact with the iron oxide material. A second partial amount of the used carburizing gas is, optionally after dust removal, advantageously fed to utilization as fuel gas for heating the reduction gas. Components having a calorific value which are present in the used carburizing gas are utilized within the process, which reduces the use of resources required and improves the economics of the process. The utilization within the process can, for example, also encompass a steam generator or a power station. The reduction gas is preferably heated to above 700° C. by indirect heat exchange. Single-stage heating by indirect heat exchange, i.e. heating with retention of the reduction potential of the reduction gas, or without oxidative destruction of reduction potential of the reduction gas, is preferably carried out.
However, multistage heating of the reduction gas, in which one stage is indirect heat exchange, can also be carried out. For example, heating by indirect heat exchange to a temperature above 700° C. can be carried out in a first stage and then, in a second stage, direct heating by means of another type of heating, for example by means of partial oxidation, can be carried out to set an even higher temperature.
In a preferred embodiment, a further partial amount of the used carburizing gas is, optionally after dust removal, fed to utilization as fuel gas for heating the carburizing gas. Components having a calorific value which are present in the used carburizing gas are utilized within the process; this reduces the use of resources necessary and improves the economics of the process.
In a preferred embodiment, the heating of the reduction gas and the heating of the carburizing gas are carried out in the same heating apparatus. This requires less outlay in terms of apparatus and makes the process simpler to carry out.
In a preferred embodiment, used reduction gas is taken off as topgas and a first partial amount of the topgas is fed to a use as fuel gas for heating the reduction gas and/or the carburizing gas. Components having a calorific value which are present in the topgas are utilized within the process; this reduces the use of resources necessary and improves the economics of the process.
In a preferred embodiment, the carburizing gas contains components which react exothermically with the directly reduced iron sponge. The carburization reactions proceed better at relatively high temperatures. Accordingly, increasing the temperature improves the efficiency of the carburization.
In a preferred embodiment, the iron sponge is heated before and/or during the introduction of the carburizing gas. The carburization reactions proceed better at relatively high temperatures. Accordingly, the efficiency of the carburization is increased by the temperature increase.
In a preferred embodiment, solid carbon C is mixed with the iron sponge before and/or during and/or after introduction of the carburizing gas. This supplements the increase in the carbon content by means of the carburizing gas. This also assists in the desired maintenance of the carbon content in the iron sponge at a constant value, for example a constant carbon content is desirable in the case of later use in an EAF.
For example, the following reaction occurs:
3Fe+C→Fe3C
The solid carbon can, for example, be anthracite.
To set a very constant carbon content in the iron sponge, elemental carbon can be added in metered form, for example by means of a metering screw or star feeder. In addition to the addition of carbon, carbon can optionally also be mixed with the iron sponge, for example in a mixing chamber or a mixer in order to achieve thorough mixing and an increased proportion of iron carbide. Here the term mixer refers to an apparatus having moving internals, while a mixing chamber does not have any moving internals.
In a preferred embodiment, the size of the second partial amount of the used carburizing gas is regulated as a function of carbon dioxide CO2 and/or carbon monoxide CO and/or methane CH4 content in the topgas.
The regulation is preferably carried out as a function of the content at the outlet from the reduction zone.
Mixing of the used carburizing gas with the circuit of the reduction gas should be largely, preferably completely, avoided. Monitoring of the topgas for components which indicate that mixing has occurred, carbon dioxide CO2 and/or carbon monoxide CO and/or methane CH4, warns of mixing. Increasing the second partial amount of the used carburizing gas contributes to suppressing any mixing which may take place.
In a preferred embodiment, the size of the first partial amount of the topgas is regulated as a function of nitrogen N2 and/or carbon dioxide CO2 and/or carbon monoxide CO and/or methane CH4 content in the topgas.
An accumulation of these components in the recirculated topgas would have an adverse effect on the efficiency of the direct reduction. For this reason, such components should be at least partly discharged from the recirculation circuit. Monitoring of the topgas for components which indicate that mixing of used carburizing gas and reduction gas has occurred, carbon dioxide CO2 and/or carbon monoxide CO and/or methane CH4, warns of mixing. The adverse effects of any mixing of carburizing gas or used carburizing gas with the reduction gas which occurs can be decreased by increasing the first partial amount of the topgas.
Utilization of the discharged gas as first partial amount allows its energy to be utilized for heating. Components having a calorific value which are present in the topgas are utilized within the process; this reduces the use of resources necessary and improves the economics of the process.
The present patent application further provides a plant for producing carburized directly reduced iron sponge from iron oxide material, comprising a reduction zone for the direct reduction of introduced iron oxide material to directly reduced product by means of reduction gas consisting predominantly of hydrogen H2, and comprising a reduction gas feed conduit opening into the reduction zone, characterized in that the plant also comprises a carburization zone for carburizing the directly reduced product, having a carburizing gas feed conduit opening into the carburization zone and a carburization offgas conduit going out from the carburization zone for taking off used carburizing gas from the carburization zone, and also at least one device for avoiding mixing of reduction gas with carburizing gas and/or used carburizing gas.
It is also possible for a plurality of devices for avoiding mixing of reduction gas with carburizing gas and/or used carburizing gas to be present.
A device for avoiding mixing of reduction gas with carburizing gas and/or used carburizing gas can, for example, be made up as follows: regulating device, for example a regulating valve, in the carburization offgas conduit, a compressor or a blower for discharging from the carburization zone and thus for avoiding introduction of carburizing gas into the reduction gas circuit, reduction zone and carburization zone separated by a conduit filled with iron sponge, for example with or without gas lock, with or without material flow apparatus such as a lock hopper system z, a hot rotary feeder or gravity transport.
In a preferred embodiment, the carburization offgas conduit opens into a recirculation device for treatment, for example purification, compression, heating, and recirculation of used carburizing gas into the carburizing gas feed conduit.
Such a recirculation device can, for the purposes of treatment, contain, for example, at least one dust removal device.
Such a recirculation device comprises a recirculate conduit which opens into the carburizing gas feed conduit in order to make treated used carburizing gas available as partial amount of the carburizing gas.
In this way, the carburization can be carried out more economically and with greater conservation of resources since unreacted components present in the used carburizing gas can again have the opportunity of contributing to the carburization.
In a preferred embodiment, a gas heating device is present in the carburizing gas feed conduit and/or in the recirculate conduit. The carburization reactions proceed better at relatively high temperatures. Accordingly, the efficiency of the carburization is increased by increasing the temperature.
In a preferred embodiment, a reduction gas heating device is present in the reduction gas feed conduit. This heating device is preferably a single-stage reduction gas heating device. It is preferably an indirect heat exchanger. However, it can also be a multistage heating device in which one stage is an indirect heat exchanger.
A fuel gas conduit opening into the reduction gas heating device advantageously goes out from the carburization offgas conduit and/or the recirculation device. A fuel gas feed conduit opening into the gas heating device advantageously goes out from the carburization offgas conduit and/or the recirculation device. The gas heating device is preferably a single-stage gas heating device. It is preferably an indirect heat exchanger. Components having a calorific value which are present in the used carburizing gas can then be utilized within the process; this reduces the use of resources necessary and improves the economics of the process. In a preferred embodiment, the reduction gas heating device and the gas heating device are both integrated into one heating device and the fuel gas conduit and/or the fuel gas feed conduit open into the heating device. This requires less outlay in terms of apparatus.
The plant for producing carburized directly reduced iron sponge from iron oxide material comprises a topgas conduit for taking off used reduction gas from the reduction zone. In a preferred embodiment, the topgas conduit opens into a recycling device for treatment and recycling of topgas into the reduction gas feed conduit.
Such a recycling device can, for the purposes of treatment, contain, for example, at least one dust removal device, preferably a dry dust removal device since in this case it is possible to dispense with complicated purification of process wastewater from wet dust removal in the case of a wet dust removal apparatus which is likewise possible.
Such a recycling device comprises a recirculate conduit which opens into the reduction gas feed conduit in order to provide treated topgas as partial amount of the reduction gas.
The direct reduction can in this way be carried out more economically with greater conservation of resources since unreacted components present in the topgas again have the opportunity of contributing to the direct reduction.
In a preferred embodiment, the plant for producing carburized directly reduced iron sponge from iron oxide material also comprises a fuel conduit which goes out from the topgas conduit and/or the recycling device and opens into the reduction gas heating device and/or into the gas heating device and/or the heating device. Components having a calorific value which are present in the topgas can then be utilized within the process; this reduces the use of resources necessary and improves the economics of the process.
When a dust removal device is present in the recycling device, preference is given to the fuel conduit going out downstream of the dust removal device, viewed in the flow direction of the topgas from the reduction zone. This decreases the load on plant parts gone through later, for example compressors.
In a preferred embodiment, a heating unit for heating the directly reduced product before entry into the carburization zone is present between the reduction zone and the carburization zone. In a preferred embodiment, a heating unit for heating the directly reduced product is present in the carburization zone.
In a preferred embodiment, a carbon addition device is present between the reduction zone and the carburization zone. In a preferred embodiment, a carbon addition device is present in the carburization zone.
In a preferred embodiment, a carbon addition device is present downstream, viewed in the flow direction of the directly reduced product from the reduction zone, of the carburization zone.
The carbon addition device is suitable for adding solid carbon. It can comprise metering devices such as a metering screw or star feeder. In a preferred embodiment, it also comprises mixing devices such as a mixing chamber or mixer in order to make mixing and an increased proportion of iron carbide possible.
In a preferred embodiment, the plant of the invention also comprises a regulating device for regulating the gas flow in the fuel gas conduit and/or the fuel gas feed conduit as a function of measured values obtained from the topgas. Thus, a regulating device can be one of the devices for avoiding mixing of reduction gas with carburizing gas and/or used carburizing gas.
In a preferred embodiment, the plant of the invention also comprises a regulating device for regulating the gas flow in the fuel conduit as a function of measured values obtained from the topgas.
In a preferred embodiment, the plant of the invention does not comprise any device for decreasing the amount of CO2 in the topgas provided for recycling.
In a preferred embodiment, the plant of the invention comprises a discharge conduit for discharging topgas from the recycling.
In a preferred embodiment, the reduction zone and the carburization zone are accommodated within one apparatus. For example, the apparatus can be a shaft in the upper part of which the reduction zone is located and in the lower part of which the carburization zone is located. Iron oxide material is introduced from the top into the shaft and migrates downward therein under the force of gravity. During this, it is directly reduced. After passing through the reduction zone, directly reduced product goes into the carburization zone. After passing through the carburization zone, it exits from the shaft.
In a preferred embodiment, the reduction zone and the carburization zone are accommodated in different apparatuses. For example, the directly reduced product can be taken off from a direct reduction apparatus containing the reduction zone and then be introduced into a separate carburization apparatus containing the carburization zone. The directly reduced product is iron sponge. Direct reduction apparatus and carburization apparatus are connected via a supply conduit for introducing iron sponge into the carburization apparatus.
The at least one device for avoiding mixing of reduction gas with carburizing gas and/or used carburizing gas can, for example, be present in the supply conduit. It can also be present in the end of the direct reduction apparatus nearest the supply conduit. It can also be present in the end of the carburization apparatus nearest the supply conduit. It can also be present at the end of the supply conduit closest to the direct reduction apparatus, or at the end of the supply conduit closest to the carburization apparatus.
The present invention will be illustrated by way of example below with the aid of a number of schematic figures.
It is also indicated in
Although the invention has been illustrated and described in detail by means of the preferred working examples, the invention is not restricted by the examples disclosed and other variants can be derived therefrom by a person skilled in the art without going outside the scope of protection of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 18177161.9 | Jun 2018 | EP | regional |
The present application is a national phase application of PCT Application No. PCT/EP2019/065283, filed Jun. 12, 2019, entitled “PRODUCING CARBURIZED SPONGE IRON BY MEANS OF HYDROGEN-BASED DIRECT REDUCTION”, which claims the benefit of European Patent Application No. 18177161.9, filed Jun. 12, 2018, each of which is incorporated by reference in its entirety.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2019/065283 | 6/12/2019 | WO | 00 |
