Abstract:
A method for temporarily storing energy in which iron ore is reduced with hydrogen and the resulting intermediate product of reduced iron ore and possibly accompanying substances 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 and/or wind and/or photovoltaic sources or other regenerative forms of energy and the hydrogen and/or the intermediate product is produced regardless of the current 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 a method for storing discontinuously produced energy in which the discontinuously produced energy, when it is present or after its production, is conveyed into a process in which a storable intermediate product is produced from a source material and the storable intermediate product is stored until it is required and retrieved for the production of an end product.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to a method for storing discontinuously produced energy. 
       BACKGROUND OF THE INVENTION 
       [0002]    The percentage of regenerative energy should be increased globally; regenerative energy includes not only energy from renewable resources, but also energy generated from hydroelectric power, sunlight, and wind. Frequently, renewable resources can be used to produce energy continuously, for example in biomass power plants or biogas production plants. 
         [0003]    When solar energy or wind energy is used, however, energy is produced discontinuously due to its dependence on the weather. This discontinuously produced energy is not always available when it is actually needed, presenting the problem of storing this energy and making it available when needed. 
         [0004]    In particular, it is difficult to store this discontinuously produced energy in a form that can be easily made immediately available for the retail customer or for feeding into networks for retail customers. 
         [0005]    The object of the present invention is to create a method for storing discontinuously produced energy. 
       SUMMARY OF THE INVENTION 
       [0006]    According to the invention, the goal is not to use discontinuously produced energy in its originally produced form, but rather to use the energy for producing an easily storable intermediate product and thus to incorporate the energy into this intermediate product, with the intermediate product being a product that is required all over the world. When discontinuous energy is present, this intermediate product is produced and stored regardless of the demand for the intermediate product and then is supplied for further processing as needed. Since the production of the intermediate product requires large quantities of energy anyway, the energy consumption that would already occur in the production would be shifted in terms of time and location. 
         [0007]    According to the invention, metal, for example, in particular steel, is produced as the end product. Basically, the method according to the invention is suitable for all forms of industrial production in which a storable intermediate product is generated. 
         [0008]    In this connection, it is advantageous that the storage of the discontinuously produced energy in this case does not require a feeding back from a storage reservoir—of whatever type—into the original energy, but instead the original energy is used in a practical way and stored in the intermediate product and additional energy does not have to be expended in order to produce the intermediate product at the production site of the end product. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The invention will be explained by way of example in conjunction with the drawings. In the drawings: 
           [0010]      FIG. 1  shows an overview of the method according to the invention in an exemplary embodiment (electric arc furnace); 
           [0011]      FIG. 2  shows an overview of the method according to the invention in a second exemplary embodiment (LD process); 
           [0012]      FIG. 3  schematically depicts the flows of materials and energy. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0013]    According to the invention, the intermediate product is an intermediate product whose production requires an expenditure of energy that is quite high, in particular intermediate products for which a smelting process and/or a reduction process is required, which is in particular carried out using electricity, e.g. by means of an electric arc. In particular, however, this intermediate product can also be composed of iron directly reduced primarily from iron oxide carriers, e.g. in the form of a sponge iron or so-called hot briquetted iron (HBI). The use of the discontinuously produced regenerative energy and the storage thereof in the intermediate product also has the advantage that it is possible to operate in a climate neutral fashion. 
         [0014]    Steel production is currently carried out in a variety of ways. Classic steel production is carried out by producing pig iron in the hot furnace process, primarily out of iron oxide carriers. In this method, approx. 450 to 600 kg of reducing agent, usually coke, is consumed per metric ton of pig iron; this method, both in the production of coke from coal and in the production of the pig iron, releases very significant quantities of CO 2 . In addition, so-called “direct reduction methods” are known (methods according to the brands MIDREX, FINMET, ENERGIRON/HYL, etc.), in which the sponge iron is produced primarily from iron oxide carriers in the form of HDRI (hot direct reduced iron), CDRI (cold direct reduced iron), or so-called HBI (hot briquetted iron). 
         [0015]    There are also so-called smelting reduction methods in which the melting process, the production of reduction gas, and the direct reduction are combined with one another, for example the methods of the brands COREX, FINEX, HiSmelt, or HiSarna. 
         [0016]    Sponge irons in the form of HDRI, CDRI, and HBI usually undergo further processing in electric furnaces, which is extraordinarily energy-intensive. The direct reduction is carried out using hydrogen and carbon monoxide from methane and synthesis gas if necessary. For example, in the so-called MIDREX method, first methane is transformed according to the following reaction: 
         [0000]      CH 4 +CO 2 =2CO+2H 2    
         [0017]    and the iron oxide reacts with the reduction gas, for example according to the following formula: 
         [0000]      Fe 2 O 3 +6CO(H 2 )=2Fe+3CO 2 (H 2 O)+CO(H 2 ). 
         [0018]    This method also emits CO 2 . 
         [0019]    DE 198 53 747 C1 has disclosed a combined process for the direct reduction of fine ores in which the reduction is to be carried out with hydrogen or another reduction gas in a horizontal turbulence layer. 
         [0020]    DE 197 14 512 A1 has disclosed a power station with solar power generation, an electrolysis unit, and an industrial metallurgical process; this industrial process relates either to the power-intensive metal production of aluminum from bauxite or is intended to be a metallurgical process with hydrogen as a reducing agent in the production of nonferrous metals such as tungsten, molybdenum, nickel, or the like or is intended to be a metallurgical process with hydrogen as a reducing agent using the direct reduction method in the production of ferrous metals. The cited document, however, does not explain this in detail. 
         [0021]    WO 2011/018124 has disclosed methods and systems for producing storable and transportable carbon-based energy sources using carbon dioxide and using regenerative electrical energy and fossil fuels. In this case, a percentage of regeneratively produced methanol is prepared together with a percentage of methanol that is produced by means of non-regenerative electrical energy and/or by means of direct reduction and/or by means of partial oxidation and/or reforming. 
         [0022]    According to the invention, the intermediate product for the steel production is produced using a hot furnace and a subsequent LD process or using an electric arc furnace with regenerative energy and is stored in this way. A particular advantage is that the intermediate product produced by means of regenerative energy can be stored until it is processed further, which means that the method according to the invention permits a storage of regenerative energy. Up to now, this very storage of regenerative energy has presented a very large problem since in particular, electrical energy that is generated from wind or sun depends on climatic conditions that are not always the same. Even hydroelectrically generated electrical energy is not always available. Often, the consumers are not in the same locations as the production of regenerative energy. This problem of storage and subsequent mobility of the stored energy is solved by means of the invention since the intermediate product produced according to the invention can be efficiently transported in small units and in any quantity to any location, for example by marine transport. 
         [0023]    The energy in the method according to the invention is not in fact stored in a form that is accessible to virtually anyone and for general use from the storage reservoir; but the global demand for certain intermediate products is so high that according to the invention, the intermediate product constitutes the energy storage for other forms of energy demand, e.g. providing retail electricity customers with electrical energy from other sources or other storage reservoirs, thus permitting better management and planning of the total energy balance. 
         [0024]    In particular, the method according to the invention can be used in regions of the world in which the raw material for the intermediate product and the corresponding discontinuously produced regenerative energy are present in the same location. An example of this can be the magnesia storage facilities for the production of fused magnesia (e.g. for use in the flame retardant industry) that exist, for example, in Canada or China and correspondingly, the use of hydroelectric power or wind energy or (China) solar energy. In iron ores that are to be transformed into the corresponding intermediate product with direct reduction methods, such locations e.g. Sweden and Norway (hydroelectric power) or Australia (solar energy) in which the regenerative energy is used on the one hand to mechanically prepare the corresponding raw material, namely the iron ore (among other things breaking, grinding, agglomerating), and also for producing hydrogen for the direct reduction or for example for pyrolysis of wood to produce corresponding carbon-containing or hydrogen-containing gas flows. 
         [0025]    In the method according to the invention, this electrical energy generated from wind, hydro, or solar energy is used to produce hydrogen from water by electrolysis. Preferably at the site of the production of the hydrogen, a direct reduction system is operated, which is used for reducing iron ores - which are likewise particularly preferably completely prepared with electrical energy produced in this way. The intermediate product obtained in this way, in particular hot briquetted iron HBI, HDRI, or CDRI is an ideal way to store this regenerative energy, can be stored without restriction in large quantities, and is accessible via any form of transportation to a system for processing it further, particularly when it is needed there. In particular, this intermediate product can be produced at its production site—in large quantities that exceed the present requirement—when the corresponding electrical energy is available in sufficient quantity. If this energy is not available, then there are sufficient quantities of the intermediate product and thus of the energy in a stored form in order to be able to meet the need. 
         [0026]    Operating a corresponding electrical arc, likewise using only energy produced from wind-, hydroelectric-, or solar energy, succeeds in achieving a CO 2 -free steel production or smelting production (e.g. fused magnesia) and also in storing regenerative energy. 
         [0027]    According to the invention, the hydrogen from the regenerative processes can be used with carbon-containing or hydrogen-containing gas flows such as CH4, COG, synthesis gas etc., in a direct reduction system. The ratio of hydrogen from the regenerative processes to carbon-containing or hydrogen-containing gas flows can be continuously varied as a function of availability. For example, if a very large amount of hydrogen is available, this can be used up to almost 100% for the direct reduction; if necessary, however, it is also possible to switch to purely carbon-containing or hydrogen-containing gas flows (for example natural gas, biogas, gas from pyrolysis, renewable resources). 
         [0028]    Preferably, however, the method is carried out so that regenerative energy, when present, is used to produce as much hydrogen as the existing energy permits and this hydrogen is used for the direct reduction. It goes without saying that carbon-containing or hydrogen-containing gas flows also include gas flows from biogas production and pyrolysis or synthesis gas from biomass, i.e. renewable resources. 
         [0029]    Excess hydrogen that cannot be used immediately can be temporarily stored. 
         [0030]    This temporary storage of hydrogen can, for example, be provided by a gas holder and the adjustment of the contents of carbon-containing or hydrogen-containing gas flows can be carried out by means of a predictive control. This predictive control can measure the predicted yield/production quantity of hydrogen or regenerative energy, but can also be used, for example, to estimate the production quantity of regenerative energy based on weather forecasts. Demand forecasts of other external consumers can also flow into this predictive control so that the electrical energy produced from regenerative sources is optimally used in the most economical fashion. 
         [0031]    The temperatures of the gas flow that prevail in this case are adjusted by heating—for example with reformers, heaters, or partial oxidation—to 450° C. to 1200° C., preferably 600° C. to 1200° C., in particular 700° C. to 900° C. and then introduced into the direct reduction method in order to perform a chemical reaction there. In addition, the gas flow that [sic] exits the direct reduction method can be fed back into the process as a carbon-containing or hydrogen-containing gas flow. 
         [0032]    The resulting possible intermediate products according to the invention are HBI, HDRI, or CDRI. 
         [0033]    In this case, excess pressures of 0 bar to 15 bar are adjusted. For example, excess pressures of approx. 1.5 bar are preferred in the MIDREX process and excess pressures of approximately 9 bar are preferred in the Energiron process. 
         [0034]    When regeneratively produced hydrogen is mixed with carbon-containing or hydrogen-containing gas flows, the carbon content can be adjusted in an ideal fashion and in fact can be adjusted to 0.0005% to 6.3%, preferably 1% to 3%, and directly incorporated into the intermediate product as C or Fe 3 C. An intermediate product of this kind is ideally adjusted in terms of the carbon content and is particularly well suited to further processing since it contributes the carbon content that is required for the metallurgical process. 
         [0035]    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. 
         [0036]    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. 
         [0037]    Another possibility for compensating for fluctuations can lie in the variable use of natural gas. The thermal state of the plant can thus be kept advantageously stable. 
         [0038]    Another advantage of the invention lies in the spatial decoupling of the locations of the production of regenerative energy and the use of this stored 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. 
         [0039]    Since the energy produced is stored in HBI, for example, it can be transported easily and efficiently.