Process for converting electric energy to chemical energy of iron

Abstract

The present invention relates to a process for converting electric energy to chemical energy of iron for the purpose of producing sponge iron, hydrogen, power, optionally carbon monoxide from carbon dioxide, as required, and exhaust steam for the reoxidation of iron for the purpose of the temporally off-set on-site generation of hydrogen and power.

Description

[0001] Process for converting electrical energy into chemical energy of iron

[0002] The present invention relates to a process for converting electrical energy into chemical energy of iron for the purpose of the demand-based production of sponge iron, hydrogen, electricity, optionally carbon monoxide from carbon dioxide and exhaust steam for the reoxidation of iron for the purpose of the time-shifted decentralized production of hydrogen and electricity.

[0003] According to the Energetic Imperative formulated by Nobel Laureate Wilhelm Ostwald regarding the sustainable use of solar power, it is necessary to convert not only electricity and heat generation, as well as mobility, to electricity from volatile solar-renewable energy, but also chemical conversion. Electricity from solar-renewable energy thus replaces coal, oil, gas, and nuclear fuels as primary energy sources and becomes "primary energy" itself.

[0004] The necessity of the availability of new primary energy derives from the fact that the physical performance and working capacity of people is still and increasingly insufficient for the maintenance and expansion of their civilization.

[0005] From the Earth's radiation balance, it can be calculated that there is significantly more solar-renewable energy available on Earth than is required for conversion into the new primary energy "electricity".

[0006] However, the local power and energy supply of the sun and its derivatives in biomass, wind, and hydropower is not in line with people's local and temporal energy needs. This requires new methods for the material-based storage and transport of solar-renewable energy, for example, as first proposed in patent no. EP 3310709 B1.Compared to this patent, the present invention has the particular task of designing ways for the production of iron in the form of sponge iron for the iron and steel industry independent of the availability of hydrogen, the feasibility of a controlled reduction of iron oxides, in particular of magnetite to iron, and the reoxidation of iron to iron oxides, in particular to magnetite, as well as the combination of thermodynamically opposing cycles to form reversible cycles for the purpose of a significantly better energy efficiency of the material transformations relevant to the invention compared to the prior art.

[0007] Although the Earth's supply of solar-renewable energy is very large, it is imperative, also for reasons of human performance and work capacity, to realize the task of converting volatile solar-renewable energy into usable energy with high energy efficiency. Iron oxides are well suited for this purpose; their chemical enthalpy difference to iron is so large that, based on volume, iron achieves a heat of combustion equivalent to that of petroleum. However, iron is 10 times heavier than petroleum.

[0008] According to the invention, this problem is solved by using exergy, in the form of electricity, as driving energy for closed-loop energy and material conversion technologies, within the framework of the thermodynamic system iron-carbon-hydrogen-oxygen (Fe-CHO).

[0009] According to the invention, the problem is solved by using the calculation of the thermodynamic system Fe-CHO defended by B. Wolf as a dissertation at the TU Bergakademie in 1976.

[0010] The invention thus relates to a process for producing sponge iron from iron oxides by means of electrical energy, in which the iron oxides are fed to the process, preferably as magnetite and / or hematite, and are reduced to sponge iron by means of hydrogen, characterized in that the hydrogen is obtained by electrolysis from the water vapor produced during the reduction with the removal and storage of the oxygen and the sponge iron is optionally diverted for iron and steel production or is fed to a further oxidation by means of water vapor.

[0011] Preferably, in the case of the production of hydrogen for external applications, the steam required for the reoxidation of the sponge iron is supplied from an external source and the resulting hydrogen is diverted or fed to a process-integrated combustion of in-process hydrogen and oxygen for the purpose of power generation and the resulting waste steam from the power generation is used for the reoxidation of the sponge iron.

[0012] Particularly preferably, the oxygen required for the process-integrated combustion is supplied by the electrolysis provided according to claim 1.

[0013] It is particularly preferred that the reoxidation of the sponge iron is carried out alternatively with external carbon dioxide or CO2-water vapor mixtures produced therefrom and that the resulting carbon monoxide or hydrogen-carbon monoxide mixture is subjected to chemical recycling.

[0014] According to a further preferred embodiment, the reduction of magnetite (Fe3O4) to iron and the reoxidation of iron by steam are carried out with a time delay.

[0015] According to a further preferred embodiment, the heat input during the reduction of the iron oxides and the heat output during the reoxidation of iron take place via gas circuits consisting of hydrogen-steam mixtures or steam-hydrogen-inert gas mixtures.

[0016] On this basis, Figure 1 shows application and embodiment examples in which, according to the invention, electricity, in particular from renewable sources, particularly preferably from solar-renewable energy, is converted directly into chemical energy of iron in the form of sponge iron, regardless of the availability of external hydrogen and water vapor, which enables the storage and transport of volatile, in particular solar-renewable energy and its conversion into hydrogen, synthesis gas and, on-demand electricity, according to the invention via the following steps: a) The production of sponge iron from iron oxides using hydrogen, which is produced by electrolysis from the water vapor generated during the reduction process. b) The production of hydrogen and / or carbon monoxide, in particular for the production of synthesis gas, by reoxidation of iron with external water vapor and / or carbon dioxide.c) The generation of electricity via the working capacity of steam from the combustion of process-internal hydrogen and oxygen, e.g. by means of a steam turbine. d) The process-internal use of the exhaust steam from the electricity extraction for the reoxidation of process-internal sponge iron to magnetite for the purpose of the delayed production of hydrogen and its extraction for direct external use and / or the generation of synthesis gas and / or combustion for the purpose of electricity extraction combined with the generation of exhaust steam for the process-internal reoxidation of sponge iron to magnetite. e) The reoxidation of iron to magnetite by means of steam-carbon dioxide mixtures for the purpose of the inventive production of synthesis gas for the carbon and hydrocarbon industry. f) The inventive control of optimal process temperatures via cycles of equilibrium gases for reduction and reoxidation, to which inert gases, e.g.Nitrogen or argon can be added, into which, on the one hand, only as much hydrogen and heat is added in a controlled manner by electrical heating for the reduction of the magnetite to iron that the hydrogen is completely converted into water vapor to the desired extent, and on the other hand, during the reoxidation of iron to magnetite, only as much water vapor is injected that the oxidation achieves the desired performance in the range of the specified temperatures.

[0017] Preferably, the reduction of iron oxides to iron and the reoxidation of iron by steam are carried out at different times and / or spatially separated, i.e. advantageously at different locations.

[0018] The particular technical and economic advantage of the invention is

[0019] • ensuring optimal energy efficiency by minimizing the electricity requirements for sponge iron production,

[0020] • the use of steam from the reduction of iron oxides for the electrolytic production of hydrogen and oxygen, and

[0021] • the use of the exhaust steam from the power reproduction for the reoxidation of the sponge iron into magnetite.

[0022] This enables the location-independent direct conversion of electricity, preferably from renewable sources, especially solar energy, into sponge iron and the use of the chemical energy of the iron for the storage and transport of renewable, especially solar-renewable energy, as well as for the local, demand-based supply of electricity, hydrogen, fuel and methane.

[0023] In principle, this process can be carried out using electricity from any source. However, electricity generated from renewable sources, such as wind and solar energy, biogas, and especially solar energy, is preferred.

[0024] Execution and

[0025] The description of the application and implementation examples is as follows according to Figure 1:

[0026] 1 . According to the invention, process stage 1 serves to produce iron from iron oxides in the form of sponge iron as an energy source and, for example, as a feedstock for iron and steel production, which can be carried out in two variants according to the invention.

[0027] Either for the production of sponge iron for smelting using externally supplied iron oxides, which was generated by hydrogen, which according to the invention is produced electrolytically using electricity, preferably from renewable sources, from the exhaust steam of the reduction of the oxides by hydrogen, or by using in-process magnetite for the production of sponge iron as an energy carrier, which is produced by reoxidation of sponge iron from a 2nd process stage for the purpose of the time-delayed production of iron for the production of hydrogen and / or electricity and exhaust steam, which is used for the reoxidation of the in-process iron sponge to magnetite.

[0028] The variant according to the invention with the use of external magnetite is particularly suitable for locations with a lot of solar-renewable energy, but little water, since the water vapor for the hydrogen-producing electrolysis is provided according to the invention by the materially closed reduction of the magnetite to iron.

[0029] It is advantageous that process stage 1, also known as reduction of magnetite or hematite to iron, which serves to store energy and remove iron and oxygen, is carried out in two stages.

[0030] Step 1.1 involves the electrolytic splitting of water vapor, typically from the subsequent step 1.2, into hydrogen and oxygen, which is removed and stored, using electricity from a power source (in particular from renewable energy):

[0031] Current + 4 H2O (g) ■=> 4 H2 + 2 O2

[0032] Step 1.2 concerns a stepwise reduction of magnetite (process-internal or external FeaC, e.g. an initial filling) by hydrogen, preferably from step 1.1, to iron and water vapor and preferably recycling of the water vapor in step 1.1:

[0033] 4 H2 + FeaO4 ■=> 4 H2O + 3 Fe

[0034] 2. Process stage 2 serves to reoxidize sponge iron using waste steam from power generation, releasing the chemical energy stored in the sponge iron for the delayed production of hydrogen, electricity, and waste steam for the reoxidation of sponge iron to magnetite compared to process stage 1. Process stage 2, also referred to as iron reoxidation, is advantageously a two-stage process, which serves to discharge electricity and / or hydrogen and, preferably, to recover waste steam for the reoxidation.

[0035] Step 2.1 involves a step-by-step reoxidation of the iron from step 1.2 to magnetite with steam, preferably from step 2.2, to form hydrogen and in-process magnetite, which is advantageously used in step 1.2:

[0036] 4 H2O + 3 Fe <=> Fe3O4 + 4 H2

[0037] Step 2.2 concerns the export of hydrogen obtained in step 2.1 for external use and / or the generation of electricity from steam, e.g. by means of a steam turbine, which is obtained from the combustion of the hydrogen from step 2.1 with oxygen, advantageously from step 1.1, and preferably recirculation of the resulting waste steam to step 2.1:

[0038] 4 H2or

[0039] 4 H2 + 2 O2 ■=> 4 H2O ■=> electricity + exhaust steam

[0040] The invention also relates to all combinations of preferred embodiments, provided they are not mutually exclusive, in particular also to combinations of upper and lower limits of various specified ranges. A specified range includes and discloses all individual values ​​and subranges between the upper and lower limits. For example, in a range of 5 to 45, the value can range from a lower limit of 5, 10, 15, or 20 to an upper limit of 30, 35, 40, or 45. The terms "about" or "approx." in conjunction with a number or range mean that values ​​that are at least 10% higher or lower, or 5% higher or lower, and in any case 1% higher or lower are included.

[0041] Application in sponge iron production for steel and iron production:

[0042] Currently, sponge iron is produced in direct reduction plants (DRI plants) using hydrogen heated to approximately 1000 °C and natural gas in a continuous process. The exhaust gases from the direct reduction process must be chemically scrubbed, thereby removing water vapor and carbon dioxide, in order to recycle the reducing residual gas consisting of hydrogen and carbon monoxide.

[0043] The present invention makes it possible to dispense with the aforementioned gas scrubbing and avoids the associated material and energy losses. According to the invention, a sponge iron storage device according to Figure 2 is used, preferably reduced by electrolysis, in which a water vapor-carbon dioxide mixture is converted back into gas with predominantly hydrogen and carbon monoxide proportions. Thus, according to the invention, a gas cycle is provided in which the exhaust gas from the direct reduction, in particular without pretreatment such as separation of water vapor or carbon dioxide, is transferred directly to the sponge iron storage device at the operating temperature of the DRI plant between approximately 700 and 900 °C, since the sponge iron storage device operates in the same temperature range. According to the invention, the sponge iron storage device operates exothermically during reoxidation and releases hydrogen and carbon monoxide at approximately the desired inlet temperature of the DRI plant of approximately1050°C. According to the invention, it is possible to operate the gas cycle at temperatures well below the optimal temperature of the DRI plant, e.g., at approximately 200°C, 250°C, 400°C, or 450°C. The operating range of the process can thus be between approximately 200°C and approximately 1050°C. According to the invention, complete reoxidation of the sponge iron storage is not necessary. Partial reoxidation is sufficient, which, in the equilibrium reaction, almost completely converts the exhaust gases from the DRI plant into reducing gas. This results in improved energy efficiency of the DRI plant compared to the externalization of water vapor and carbon dioxide known from the prior art.

[0044] The cyclically required reduction of the sponge iron storage is carried out with hydrogen, preferably by electrolysis, which is operated in particular with renewable energy, using the steam generated during the reduction of the sponge iron storage for hydrogen and oxygen production. By constructing several sponge iron storage units operating in parallel according to a preferred embodiment, the reduction can take place in batch operation when electricity from renewable energies is available. The reoxidation for gas processing or hydrogen production can thus be carried out exothermically, even if no such electricity is available and the electrolysis therefore does not produce hydrogen. In this way, an energy storage effect of the process according to the invention is realized.The present invention enables the integration of renewable energy via electrolysis into the production of DRI (direct reduced iron) by combining state-of-the-art DRI plant operation with the gas cycle according to the invention by incorporating a sponge iron storage system. A gradual combination is also possible, in which only a portion of the hydrogen required for the DRI process is obtained via the gas cycle according to the invention.

[0045] A further aspect of the present invention relates to the temporally and / or spatially separated reduction of iron oxides and reoxidation of iron. If the resulting DRI pellets are transported, e.g., by ship, to another location for further processing in electric melting furnaces, the pellets can alternatively be used there to generate hydrogen or electricity, for example, if sufficient electricity or hydrogen is temporarily insufficient due to a lack of renewable energy. For this purpose, the invention provides for the provision of a sponge iron storage facility, optionally with a steam turbine for electricity generation, which can be used as a redundant system for hydrogen generation if necessary.This sponge iron storage facility is started up using external steam, which reoxidizes the DRI pellets and releases hydrogen for external use or for reconversion to electricity with oxygen. The latter, according to the invention, preferably recirculates the turbine exhaust steam for the reoxidation of the DRI pellets in the gas cycle. The advantage of this design is the efficient emergency supply of hydrogen and electricity at a production site that, for example, has no electrolysis and can otherwise only cover its energy needs via its electricity and hydrogen grid connection. The desired energy efficiency at such sites results in particular from the coupling of external steam from various hot waste heat sources at the steel and iron processing production site into the exothermic reoxidation of the DRI pellets; this steam can then be superheated using the heat from the reoxidation.Even at such production sites, the described process can therefore optimally compensate for the volatility of renewable electricity and hydrogen production through its flexibility and enable the gradual, and thus economically advantageous, integration of renewable electricity into the fossil production of iron and steel in the transition to a production method based purely on renewable energies.

[0046] The functional principle of the sponge iron storage system according to the invention is not limited to use in the production of iron and steel. According to the invention, it is also suitable for use in chemical production sites and refineries with similar mixed exhaust gases, for example, and can be used for the synthesis of hydrocarbons from the reducing gas as synthesis gas by supplying external steam for electrolysis in process step 1.1. Those skilled in the art will readily recognize further areas of application in which the storage and transport of volatile, particularly solar-renewable energy, as well as its conversion into hydrogen, synthesis gas, and on-demand electricity, are required.

Claims

Patent claims 1. A process for producing sponge iron from iron oxides by electrical energy, in which the iron oxides are fed to the process, preferably as magnetite and / or hematite, and are reduced to sponge iron by hydrogen, characterized in that the hydrogen is obtained by electrolysis from the steam produced during the reduction with removal and storage of the oxygen and the sponge iron is optionally diverted for iron and steel production or is fed to a further oxidation by steam.

2. A process according to claim 1, characterized in that the steam required for the reoxidation of the sponge iron is supplied from an external source in the case of the production of hydrogen for external applications and the hydrogen produced thereby is diverted or fed to a process-integrated combustion of process-internal hydrogen and oxygen for the purpose of power generation and the resulting waste steam from the power generation is used for the reoxidation of the sponge iron.

3. Process according to claim 2, characterized in that the oxygen required for the process-integrated combustion is supplied by the electrolysis provided according to claim 1.

4. A process according to claim 2, characterized in that the reoxidation of the sponge iron is carried out alternatively with supplied external carbon dioxide or carbon dioxide resulting from the direct reduction or CO2-water vapor mixtures produced therefrom and the resulting carbon monoxide or hydrogen-carbon monoxide mixture is supplied internally or externally for chemical utilization.

5. Process according to claim 1 and 2, characterized in that the reduction of magnetite (FeaC ) to iron and the reoxidation of iron by steam take place with a time delay and / or spatial separation.

6. A process according to claim 1, characterized in that the heat input during the reduction of the iron oxides and the heat output during the reoxidation of iron take place via gas circuits consisting of hydrogen-steam mixtures or steam-hydrogen-inert gas mixtures.

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