METHOD FOR PRODUCING STEEL

Abstract

A method for producing steel in which iron ore is reduced with hydrogen and the resulting intermediate product of reduced iron ore is subjected to further metallurgical processing; the hydrogen is produced through electrolysis of water; the electrical energy required for the electrolysis is regenerative energy from hydroelectric, wind, and/or photovoltaic sources and the hydrogen and/or the intermediate product is produced regardless of demand, whenever enough regeneratively produced electrical energy is available; and unneeded intermediate product is stored until there is demand or it is used so that the regenerative energy that is stored therein is also stored; and using a calculation model to calculate a required discharge rate in a reduction shaft to achieve a desired metallization grade of the steel by tracing batches of the iron ore in the reduction shaft, and using the calculation model to calculate the amount of carbon-containing gas or hydrogen-containing gas to add to the hydrogen for the reduction.

Claims

1. A method for producing steel, comprising: reducing iron ore with hydrogen and subjecting a resulting intermediate product of reduced iron ore to further metallurgical processing, wherein the hydrogen is produced through electrolysis of water, and electrical energy required for the electrolysis is regenerative energy selected from the group consisting of hydroelectric sources, wind sources, and photovoltaic sources; and the hydrogen and/or the intermediate product is produced regardless of demand for energy, whenever enough regeneratively produced electrical energy is available, where unneeded intermediate product is stored until there is demand or it is used so that the regenerative energy that is stored therein is also stored, and in reducing the iron ore to produce the intermediate product, a carbon-containing or hydrogen-containing gas is added to the hydrogen in order to incorporate carbon into the intermediate product; and the hydrogen for the reduction has at least enough carbon-containing gas or hydrogen-containing gas added to it to make a carbon content in the intermediate product 0.0005 mass % to 6.3 mass %; using a calculation model to calculate a required discharge rate in a reduction shaft to achieve a desired metallization grade of the steel by tracing batches of the iron ore in the reduction shaft; and using the calculation model to calculate the amount of carbon-containing gas or hydrogen-containing gas to add to the hydrogen for the reduction; wherein the calculation model is Fe.sub.2O.sub.3+6CO.fwdarw.2Fe+3CO+3CO.sub.2 for carbon-containing gas flows and Fe.sub.2O.sub.3+6H.sub.2.fwdarw.2Fe+3H.sub.2+3H.sub.2O for hydrogen-containing gas flows.

2. The method according to claim 1, wherein the carbon-containing or hydrogen-containing gas is obtained from a source selected from the group consisting of industrial processes, biogas production, pyrolysis, and synthesis gas from biomass.

3. The method according to claim 1, wherein the hydrogen for the reduction has at least enough carbon-containing-or hydrogen-containing gas added to it to make the carbon content in the intermediate product 1 mass % to 3 mass %.

4. The method according to claim 1, wherein the reduction gas composed of hydrogen and possibly a carbon-containing gas is introduced into the reduction process at a temperature of 450° C. to 1200° C.

5. The method according to claim 1, wherein excess pressure in the reduction is between 0 bar and 15 bar.

6. The method according to claim 1, wherein a ratio between hydrogen from regenerative production and carbon-containing or hydrogen-containing gas flows is varied continuously as a function of availability; when there is sufficient regenerative energy, hydrogen from the production with regenerative energy is used and in the absence of regenerative energy, then the system switches to purely carbon-containing or hydrogen-containing gas flows.

7. The method according to claim 1, wherein an adjustment of the content of hydrogen and, or carbon-containing or hydrogen-containing vas flows in the overall gas flow is carried out using a predictive control; the predictive control is used to measure at least one of the group consisting of a predicted yield/production quantity of hydrogen, regenerative energy, carbon-containing or hydrogen-containing gas flows from biogas production or from pyrolysis of renewable resources, and forecasts flow into an estimation of regenerative energy; and demand predictions of other external consumers also flow into the process, thus permitting the electrical energy from regenerative sources to be distributed optimally and in a most economical fashion.

8. The method according to claim 1, wherein gas flow that is emitted as exhaust by a direct reduction system is conveyed into the process as a carbon-containing or hydrogen-containing gas flow.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The invention will be explained by way of example in conjunction with the drawings. In the drawings:

[0024] FIG. 1 shows an overview of the method according to the invention in an exemplary embodiment (electric arc furnace);

[0025] FIG. 2 shows an overview of the method according to the invention in a second exemplary embodiment (LD process);

[0026] FIG. 3 schematically depicts the flows of materials and energy.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] According to the invention, a method for producing steel includes reducing iron ore with hydrogen and subjecting a resulting intermediate product of reduced iron ore to further metallurgical processing. The hydrogen may be produced through electrolysis of water. Electrical energy required for the electrolysis may be regenerative energy, such as from hydroelectric sources, wind sources, and/or photovoltaic sources.

[0028] According to certain embodiments, the reduction of the primarily iron oxide carriers is carried out by means of hydrogen and if necessary carbon carriers, either CO.sub.2 from industrial processes with inevitable CO.sub.2 emissions or methane particularly from regenerative processes such as biogas production.

[0029] As is known, the iron reduction can occur in three possible ways: [0030] “classic” blast furnace process—production of pig iron from iron carriers and reducing agents, primarily coke [0031] direct reduction—for example MIDREX—sponge iron (HDRI, CDRI, and HBI), [0032] smelting reduction—combination of the smelting process, reduction gas production, and direct reduction, for example COREX OR FINEX,

[0033] Iron reduction (hematite, iron(III)) oxide is carried out by means of:

carbon monoxide: Fe.sub.2O.sub.3+6CO.fwdarw.2Fe+3CO+3CO.sub.2

hydrogen: Fe.sub.2O.sub.3+6H2.fwdarw.2Fe+3H.sub.2+3H.sub.2O

[0034] In this case, the intermediate product obtained in the direct reduction method can be so-called DRI (direct reduced iron) or HBI (hot briquetted iron), which can be smelted into steel in accordance with FIG. 1 in an electric arc furnace, possibly with the addition of scrap.

[0035] FIG. 1 also shows that HDRI car CDRI can also be conveyed, without the “detour” of HBI production, directly into the electric furnace.

[0036] According to the invention, HBI can also be used in other metallurgical processes in addition to the electric arc furnace process, e.g. in the blast furnace process or as a scrap replacement in the LD process.

[0037] Such an embodiment is shown in FIG. 2. In this case, it should also be noted that CDRI and HDRI can also be conveyed, directly into the blast furnace process or LD process.

[0038] The amount of available renewable energy varies during the production of steel. In a preferred embodiment, in order to compensate for temporary fluctuations in the production of renewable energy, this energy can be stored in the form of hydrogen if a surplus of it is available. This storage can occur, for example, in a gas holder. Such a store can then be used in the event of fluctuations. Temporary fluctuations can be predictable, e.g. at night in solar installations, or unpredictable, e.g. fluctuations in wind intensity in wind energy plants.

[0039] Longer-term fluctuations that can occur among other things due to the different seasons can preferably be factored into the energy storage in the form of HBI.

[0040] If necessary, it is also possible to draw on the use of carbon-containing or hydrogen-containing gases such as natural gas and a use of hydrogen can be optimally carried out only with sufficiently renewable electrical power.

[0041] This advantageously yields the optimal potential uses of regenerative energy since this energy can be used continuously as a function of the availability of the corresponding form of energy and the remaining energy that is lacking can be supplemented as needed by means of other energy carriers. It is thus possible at any time to reduce the emission of CO.sub.2 to the minimum possible at this moment through the use of regenerative energy sources.

[0042] Another advantage of the invention lies in the spatial decoupling of the locations of the production of regenerative energy and the use of this energy. For example, solar power stations can be constructed in warmer regions with favorable amounts of solar radiation in which space is plentiful, whereas steel mills are often found in the vicinity of rivers or seas.

[0043] Since the energy produced is stored in HBI, for example, it can be transported easily and efficiently.

[0044] To compensate for fluctuations as explained above, the hydrogen and/or the intermediate product may be produced regardless of demand for energy, whenever enough regeneratively produced electrical energy is available. Unneeded intermediate product is stored until there is demand or it is used so that the regenerative energy that is stored therein is also stored. In reducing the iron ore to produce the intermediate product, a carbon-containing or hydrogen-containing gas is added to the hydrogen in order to incorporate carbon into the intermediate product. The hydrogen for the reduction has at least enough carbon-containing gas or hydrogen-containing gas added to it to make a carbon content in the intermediate product 0.0005 mass % to 6.3 mass %.

[0045] Due to the fluctuations, it is beneficial to track the material in a reduction shaft in batches. As used herein, the term “batch” refers to an amount of material charged to the reduction shaft in a given time period. For each of these batches, the reduction level and the carbonization level have to be calculated over time, taking into account that the reduction gas will change due to non-availability of hydrogen from renewable sources. So each batch will be confronted with a more hydrogen-containing gas flow, if hydrogen is available from either renewable energy sources or from an external buffer. Alternatively, the reduction gas will contain more carbon if no hydrogen is available, and other sources, like natural gas, have to be used. Since this influences metallization and carbon-content of the product, as well as cementation of the product, a solution is needed to achieve consistent product quality over time.

[0046] A calculation model may be run during operation to calculate the actual values for metallization and carbon-content for each batch. More particularly, the calculation model may be used to calculate a required discharge rate in a reduction shaft to achieve a desired metallization grade of the steel by tracing batches of the iron ore in the reduction shaft. The same calculation model may be used to calculate the amount of carbon-containing gas or hydrogen-containing gas to add to the hydrogen for the reduction. The calculation model is:

Fe.sub.2O.sub.3+6CO.fwdarw.2Fe+3CO+3CO.sub.2 for carbon-containing gas flows; and

Fe.sub.2O.sub.3+6H.sub.2.fwdarw.2Fe+3H.sub.2+3H.sub.2O for hydrogen-containing gas flows.

[0047] To correct for the right carbon-content, carbon-containing gas has to be added to the hydrogen gas flow or, vice versa, hydrogen to the carbon-containing gas flow of, for example, natural gas. It is important that these calculations are not performed for the complete reduction shaft, but for each individual batch.