Process for converting process heat and energy in form of hydrogen

Abstract

The invention relates to a method (1) for converting energy in the form of process heat (7) and hydrogen (3). In an aluminum oxidation step (11), aluminum (10) is reacted with water (6) in an aluminum reaction chamber (9) at an elevated temperature and is thereby oxidized into aluminum oxide (12). Process heat (7) and hydrogen gas (3) are released. The hydrogen (3) released during the reaction of the aluminum (12) and the water (6) is at least partially supplied to the hydrogen reaction chamber (5), wherein the hydrogen (3) reacts with the oxygen (4) in the water preparation step (11) to produce the water (6). Water (6) previously made from hydrogen (3) is supplied to the aluminum reaction chamber (11) to oxidize the aluminum (12).

Description

[0001] The present invention relates to a method for converting energy in the form of process heat and hydrogen, wherein in an aluminum oxidation step, aluminum reacts with water in an aluminum reaction chamber at an elevated temperature and is thereby oxidized to aluminum oxide, with process heat and hydrogen being released during the reaction.

[0002] Carbon dioxide is a greenhouse gas that is part of the cause of the greenhouse effect and thus global warming. Here, a large part of the carbon dioxide emitted globally is generated by the combustion, i.e., oxidation and processing, of carbonaceous fossil energy carriers such as oil or coal. In addition to gaseous by-products of oxidation (which also include carbon monoxide), a large amount of fine dust in the form of nanoparticles is also emitted, which leads to the deterioration of air quality, especially in winter, and this has an adverse impact especially on large urban areas.

[0003] To solve this problem, metals are therefore being discussed as carbon-free energy carriers. Substances that are pure chemical elements with a metallic bond between atoms in the zero oxidation state are collectively referred to below as metals. The metal species obtained during the oxidation of metals, such as metal oxides, are referred to below as oxidized metals.

[0004] Metals exhibit a high potential for storing energy and releasing it at the desired time through controlled oxidation. The chemical energy stored in metals can be converted, for example, into electrical energy through the oxidation process of the consumer itself. Generally, no greenhouse gases and carbon monoxide are produced during this conversion. Then, the oxidized metal can be reduced back to the metal in a separate process and reused repeatedly for energy storage. If renewable energy sources such as wind power plants or photovoltaic devices are used to reduce the oxidized metal, an environmentally friendly energy supply is achieved. This has a significant advantage over traditional carbonaceous energy carriers, which cannot be recycled after oxidation and thus cannot enter the loop.

[0005] The transportability of metal energy carriers opens up the possibility of storing renewable energy in energy carriers through chemical reduction in regions rich in wind and solar energy (possibly far from consumers) and then using them anywhere in the world.

[0006] Metals that have proven to be advantageous include, in particular, iron, copper, nickel, manganese, silicon, and aluminum. It is known that aluminum can react with air or oxygen in an aluminum reaction chamber, thereby oxidizing aluminum to aluminum oxide in an aluminum oxidation step. This reaction is exothermic here, and the oxidation temperature of aluminum during the reaction can exceed the boiling points of aluminum on the one hand and aluminum oxide on the other hand. The aluminum or aluminum particles used here can enter the gas phase, so that after the gaseous aluminum particles condense in a region of lower temperature, nanoparticles with a size range of a few nanometers can be formed, the diameter of which is smaller than the original aluminum particles used. The disadvantage of these nanoparticles is that they can only be separated from other reaction products with great effort and can therefore be supplied back to the circulation loop again.

[0007] In contrast, the reaction of aluminum with water has the following advantages on the one hand: it will not exceed the boiling points of both the metal and the metal oxide under a slightly increased pressure. On the other hand, the reaction of aluminum with water not only produces aluminum oxide and energy in the form of process heat, but also produces hydrogen. In addition to the process heat generated during the oxidation process, the hydrogen produced can also be used advantageously.

[0008] When converting the chemical energy of aluminum into heat energy, it is particularly necessary to select and adjust the oxidation temperature specifically, and two opposite processes must be considered. On the one hand, the advantage of as low an oxidation temperature of aluminum as possible is that only a small amount of nanoparticles are formed during the oxidation process. On the other hand, it is advantageous that process heat can be obtained at as high an oxidation temperature as possible. Therefore, it is particularly advantageous that during the controlled oxidation process, the oxidation temperature of aluminum remains slightly lower than the boiling point of aluminum.

[0009] In addition, it is desirable that the process of energy conversion by the metal at the location where oxidation occurs can be carried out as efficiently as possible and no nanoparticles are formed.

[0010] Therefore, the object of the present invention is to further improve the method known in the prior art, in which the efficiency should be kept as high as possible and the proportion of nanoparticles obtained during the oxidation process should be kept as small as possible.

[0011] This object is achieved in that at least part of the hydrogen released during the reaction of aluminum with water is supplied to a hydrogen reaction chamber, in which hydrogen reacts with oxygen to form water, and the water previously made from hydrogen is supplied to the aluminum reaction chamber to oxidize aluminum.

[0012] Hereinafter, aluminum is understood to mean metallic aluminum, and the term aluminum oxide is understood to mean ternary and fully oxidized aluminum oxide Al2O3.

[0013] Through the two-stage reaction chamber concept with an aluminum reaction chamber and a hydrogen reaction chamber, it is possible to easily keep the oxidation temperature of the reaction of aluminum with water in the aluminum reaction chamber below a threshold temperature, that is, below the boiling point of aluminum and also below the boiling point of aluminum oxide. The oxidation temperature of aluminum can be adjusted together here by specifically introducing the water formed in the hydrogen reaction chamber. This can be achieved on the one hand by the amount of water supplied to the aluminum reaction chamber and by the temperature of the supplied water. In addition, the oxidation temperature can also be adjusted by the amount of aluminum introduced into the aluminum reaction chamber.

[0014] Advantageously, the water introduced into the aluminum reaction chamber is conditioned and preferably has a high temperature above the ignition point of the reaction of aluminum with water. By the exothermic reaction of hydrogen with oxygen to form water, it is possible to easily provide water with the required high temperature without separately heating it by inputting energy from an external energy source.

[0015] Furthermore, the method according to the present invention can flexibly separate the process heat and the energy in the form of hydrogen. The process heat can be extracted on the one hand from the hydrogen reaction chamber heated by the highly exothermic and very rapid reaction of hydrogen with oxygen or air, and on the other hand also from the aluminum reaction chamber. For example, the process heat extracted from the circuit can be used to heat water by means of a heat exchanger and form steam, which can then be converted into electricity. Similarly, the generated hydrogen can be converted into electricity using a fuel cell, or supplied back to the circuit to be further converted and reacted in the hydrogen reaction chamber to produce water. This enables the hydrogen to circulate in the circuit without being extracted, while it is oxidized to water by the supplied oxygen in the water preparation step. Subsequently, the produced water is oxidized to alumina in the aluminum oxidation step, thereby forming hydrogen again, which can be supplied back to the hydrogen reaction chamber to produce water.

[0016] The alumina produced by the reaction can be reduced back to aluminum by the Hall-Héroult process. In addition, hydrogen can also be used alone in a separate circuit to reduce the produced alumina.

[0017] The use of aluminum as a chemical energy storage material is particularly advantageous due to its high energy density of about 23 kWh / dm 3 compared with other chemical energy storage materials. In addition, due to the non-toxic nature of aluminum, it is easy to handle and no special protection measures are required. It can be shown that by reacting aluminum with water at high temperature, the passivation layer on the aluminum surface can be ignored, but the quantitative conversion of aluminum and water can still be achieved.

[0018] In particular, the method according to the present invention can be used for the decentralized energy supply of industrial and chemical industrial parks and the centralized energy supply of power plants. As mentioned above, the method can either be used for the polygeneration of energy in the form of process heat and hydrogen, especially in industrial or chemical industrial parks where both process heat and hydrogen can be used, or only the process heat can be used according to the application field, and the hydrogen can be supplied back to the circuit.

[0019] Furthermore, it is also stipulated that an excess of hydrogen is used in the water preparation step to prepare water. To prepare water from hydrogen and oxygen, two hydrogen molecules react spontaneously with one oxygen molecule according to the simplified reaction equation H2 + 1 / 2O2 → H2O. Since the reaction is super-stoichiometric, i.e., the reaction is carried out with an excess of hydrogen, where the amount of hydrogen supplied to the reaction is more than the amount of hydrogen actually required for the reaction according to the above reaction equation, the reaction product formed is a mixture of water and a small amount of hydrogen. However, the small amount of residual hydrogen does not further adversely affect the further reaction of water with aluminum. By reacting hydrogen and oxygen in a stoichiometric to super-stoichiometric manner, complete reaction of oxygen and hydrogen can be achieved, and no oxygen will enter the aluminum reaction chamber. Thus, hydrogen generated from the reaction of aluminum with water can be obtained, and aluminum will not directly react with oxygen to form aluminum oxide bypassing the formation of hydrogen. A too high hydrogen concentration is also not desirable because otherwise the formed aluminum oxide will be reduced back to aluminum in an uncontrolled manner in the aluminum reaction chamber.

[0020] However, by performing a stoichiometric conversion according to the above reaction equation, complete conversion to water can be achieved, and there are no other by-products that may interfere with the required oxidation pathway except water.

[0021] The required oxygen can be directly introduced into the hydrogen reaction chamber here in the form of oxygen or a gas mixture such as air. The advantage of the direct conversion of hydrogen and oxygen is that unwanted side reactions between the highly reactive hydrogen and the components of air can be avoided. In addition, during the subsequent aluminum reaction process, especially at higher temperatures, an unwanted conversion of aluminum with, for example, nitrogen compounds can also be envisaged.

[0022] The ignition point of the reaction between aluminum and water is on the order of about 2200 °C, depending on the conditions at that time. Therefore, it is advantageously stipulated that in the water preparation step, water with a temperature higher than 2200 °C, preferably higher than 2500 °C, especially higher than 2800 °C is prepared and introduced into the aluminum reaction chamber. Through the very rapid reaction of hydrogen and oxygen, a high temperature is generated in the hydrogen reaction chamber, especially when oxygen is directly provided rather than in the form of a gas mixture. Therefore, it is particularly advantageous to adjust the reaction of hydrogen and oxygen in the water preparation step so that the temperature of the prepared water (more precisely, the temperature of the water vapor) is higher than 2200 °C, preferably higher than 2500 °C, especially higher than 2800 °C, so as to reach the ignition point of aluminum and initiate the oxidation of aluminum in the aluminum reaction chamber. The oxidation temperature of aluminum can be affected together by the temperature of the water entering the aluminum reaction chamber.

[0023] Furthermore, it may be advantageous that the higher the temperature of the water prepared in the water preparation step, the longer the transmission path of the prepared water to the aluminum reaction chamber, so that the water flowing into the aluminum reaction chamber can have the required ignition point.

[0024] The oxygen or air required for the reaction can be provided at room temperature and advantageously does not need to be heated before reacting with hydrogen.

[0025] In order to avoid as much as possible a controlled reaction between hydrogen and oxygen and to regulate the reaction temperature, it can also be provided that, in order to regulate the temperature of the water produced in the hydrogen reaction chamber, water is introduced from a water reservoir into the hydrogen reaction chamber to provide water at the required temperature. Supplying additional water can on the one hand reduce the temperature of the hydrogen reaction chamber to minimize the heat load on the reaction chamber, and on the other hand can thereby inhibit the formation of nitrogen oxides when using air instead of pure oxygen in this process. In addition to hydrogen, the water to be introduced can also be extracted from the process itself. For this purpose, more water can be supplied in the aluminum oxidation step of the aluminum reaction chamber than is required for conversion to aluminum oxide. The excess water can optionally be supplied to the hydrogen reaction chamber for cooling after being cooled by means of a heat exchanger.

[0026] According to the invention, it is also provided that aluminum with a particle size of 1 to 1000 μm, preferably 2 to 80 μm, in particular 5 to 40 μm is used in the aluminum oxidation step. Here, the particle size is understood as the average equivalent diameter of the particles. In order to make the conversion of aluminum with water as complete and rapid as possible, the aluminum used advantageously exists in the form of aluminum particles with dimensions in the micron range. The oxidation of aluminum in the micron range can here be described as depending on the adiabatic flame temperature T f and the vapor pressure T b . In order to prevent the aluminum from evaporating uncontrollably and undesirably during the reaction and thus forming fine dust in the form of nanoparticles that are difficult to separate, which makes the recovery of the metal oxide difficult, it is advantageous that the ratio of T f to T b is < 1.

[0027] The aluminum particles introduced into the aluminum reaction chamber are at least partially melted due to the exothermic reaction of aluminum with water, so that the aluminum is mainly or completely in a liquid state. Since water acts as an oxidizing agent, during the aluminum oxidation process, an oxide layer that grows from the particle surface towards the particle core is formed on the aluminum particles, which surrounds the optionally still partially solid particle core. Oxidation occurs due to the "attached" oxygen, and the mass of the aluminum-aluminum oxide particles increases. If the metal oxide layer is porous, the density of the metal oxide is lower than the density of the metal. Then, the size of the oxidized metal particles increases compared to the original metal particles. This helps to effectively deposit the produced aluminum oxide particles, thereby enabling as complete an oxidation and subsequent reduction cycle as possible in a separate process.

[0028] Advantageously, therefore, the oxidation reaction of aluminum occurs heterogeneously on the aluminum surface as a type C reaction, in which neither the aluminum nor the oxide produced therefrom enters the gas phase and forms nanoparticles (J.M. Bergthorson, S. Goroshin, M.J. Soo, P. Julien, J. Palecka, D.L. Frost and D.J. Jarvis, Applied Energy, 2015, 160, 368–382).

[0029] It is also provided that in the aluminum oxidation step in the aluminum reaction chamber, in addition to aluminum, at least partially oxidized aluminum is also or can be oxidized by water. At least partially oxidized aluminum (e.g., aluminum hydroxide Al(OH)3) can also be mixed into the aluminum. These energy carriers, which are of lower energy due to at least partial oxidation compared to aluminum, can be mixed into the aluminum here, in particular to adjust the oxidation temperature, or supplied separately to the aluminum reaction chamber. In addition to aluminum species, other metal or metal oxide species can also be used and mixed into the aluminum and / or at least partially oxidized aluminum.

[0030] To prevent or at least minimize the formation of fine dust in the form of nanoparticulate alumina, it is advantageous that the aluminum used and introduced into the aluminum reaction chamber is completely oxidized to alumina according to type C. In addition to providing aluminum in the micron range, the complete conversion also depends on the oxidant provided. Advantageously, therefore, an excess of water is used for the oxidation of aluminum. For this purpose, the molar ratio λ of the water introduced into the aluminum reaction chamber to the stoichiometrically required water must be specifically selected H2O , such that λ H2O ≥ 1. The ratio λ used H2O < 1 leads in particular at temperatures above 2000 °C to the formation of aluminum nanoparticles and other undesired substances, since aluminum in the non-fully oxidized alumina phase is in the oxidation state +1, e.g., Al2O.

[0031] According to an advantageous embodiment of the inventive concept, it is optionally provided that the oxidation temperature of aluminum in the aluminum oxidation step is below the boiling temperature of aluminum and aluminum oxide under a predetermined pressure. In this way, the formation of alumina nanoparticles can be effectively prevented or at least substantially minimized. In particular, when the temperature during the aluminum oxidation process is above the boiling temperature of aluminum under an appropriate pressure, alumina nanoparticles can be formed. On the one hand, during the process of aluminum turning into the gas phase and undergoing gas-phase oxidation there, especially during the subsequent condensation process, alumina nanoparticles can be formed. However, the gas-phase transformation can also occur at a temperature below the boiling temperature of aluminum as long as the vapor pressure of the aluminum particles is sufficient to enable such a transformation. In addition, if the oxidation temperature exceeds the boiling point of alumina, nanoparticles will also be formed. In the first step, aluminum can be oxidized to alumina, whereupon the temperature of the particles continues to rise due to the exothermic oxidation reaction and a gas-phase transformation will occur. If the alumina then condenses in the low-temperature region, it may lead to the formation of unwanted nanoparticles.

[0032] By appropriately adjusting and predetermining the oxidation temperature, the formation of such nanoparticles can be substantially avoided. Because the formation of alumina nanoparticles during the evaporation of aluminum makes it difficult to separate and recover the alumina from the simultaneously produced hydrogen.

[0033] In order to produce as few nanoparticles as possible during the aluminum oxidation process, it is advantageous that the oxidation temperature of aluminum in the aluminum oxidation step is below the boiling temperature of aluminum under a predetermined pressure, and an excess amount of water is used for the aluminum oxidation so that the aluminum is completely oxidized by water at a temperature below the boiling temperature of aluminum. It has been found that the formation of alumina nanoparticles can be controlled particularly by controlling the aggregation state of aluminum and by the amount of the supplied oxidant.

[0034] Preferably, the oxidation temperature of the used aluminum is below the boiling temperature of aluminum. Because if the temperature is above the boiling temperature, most of the used aluminum will evaporate, and alumina nanoparticles with a diameter smaller than the original used aluminum particles will be formed during subsequent condensation. The disadvantage of these nanoparticles is that it takes great effort to separate them from other reaction products, such as hydrogen, and thus supply them back into the circulation loop again.

[0035] The formation of nanoparticles can also be regulated by the amount of water used. Since the aluminum is completely oxidized according to type C, fewer aluminum species in the gas phase are produced, thus also producing fewer nanoparticles. In addition, if the amount of water used is more than the amount stoichiometrically consumed for the aluminum oxidation, the side reaction between aluminum and water can be suppressed, and thus the formation of, for example, incompletely oxidized aluminum species (such as Al2O) can be suppressed. Since the reaction is incomplete, the energy that can be generated by the oxidation will be lower than that during a complete reaction.

[0036] Advantageously, the oxidation of aluminum is carried out under elevated pressure. Thus, it is stipulated that the oxidation of aluminum in the aluminum oxidation step is carried out at a pressure of 1.7 bar to 50 bar, preferably at a pressure of 2 bar to 20 bar, and particularly at a pressure of 5 bar to 10 bar. This can promote hydrogen storage and process intensification. In addition, at high pressure, i.e., at a pressure of 1.7 bar, the temperature of the aluminum particles can be easily kept below the boiling point, since the boiling temperature is also a function of the pressure. The higher the pressure, the higher the oxidation temperature, and the aluminum used will not evaporate. The higher oxidation temperature is accompanied by an increase in process heat. Thus, gas phase transformation and the formation of nanoparticles in the gas phase associated therewith can be substantially avoided or at least reduced.

[0037] Advantageously, the aluminum oxide produced during the oxidation of aluminum with water is separated from the simultaneously produced hydrogen. In this way, the aluminum oxide can be collected and reduced to metal again to store energy. Thus, optionally, it is stipulated that the aluminum oxide formed in the aluminum oxidation step has a larger particle size than the aluminum used for oxidation to enable the easiest possible separation of the aluminum oxide from the hydrogen that is also formed during the oxidation. Since the particle size of the obtained aluminum oxide is larger than that of the aluminum used, the aluminum oxide can be easily separated.

[0038] The particle size of the aluminum oxide obtained in the aluminum oxidation step can be adjusted by appropriately presetting the reaction parameters, for example, in particular, by appropriately presetting the particle size of the aluminum used, the temperature of the water used, the pressure in the aluminum reaction chamber, the oxidation temperature of the aluminum, and the ratio of the aluminum used to the water.

[0039] By appropriately presetting the reaction parameters, aluminum oxide nanoparticles can also be produced purposefully, which can then be used for subsequent industrial applications. For this purpose, it can be stipulated that the particle size of the produced aluminum oxide nanoparticles is 1 to 1000 nm, preferably 2 to 500 nm, and particularly 5 to 40 nm.

[0040] According to an advantageous embodiment of the inventive concept, it is optionally provided that, in the aluminum oxidation step, aluminum oxide nanoparticles are produced in an amount of less than 1 ppm, preferably less than 0.15 ppm, particularly preferably less than 0.01 ppm. The ppm data is based on the total amount of aluminum oxide produced during the oxidation process, and it is preferred that as little aluminum oxide nanoparticles as possible are formed during the oxidation process. By appropriately selecting reaction parameters, such as in particular pressure, temperature, and oxidizing agent, the formation of nanoparticles can be substantially prevented. Advantageously, conditions are selected during the oxidation of aluminum such that a heterogeneous surface reaction of type C aluminum particles occurs. It can thus be expected that the resulting aluminum oxide particles are mostly larger and heavier than the aluminum particles used for the reaction. The formation of only a negligible amount of aluminum oxide nanoparticles has the following advantages: on the one hand, these particles are not released into the environment as fine dust, and the small amount of aluminum oxide particles formed do not have to be laboriously separated from the hydrogen gas also produced. This advantageously enables the easy separation and collection of the aluminum oxide formed during the reaction of aluminum with water, and thus enables the complete recycling of the aluminum oxide into aluminum in a separate step.

[0041] It is also optionally provided that the aluminum oxide produced in the aluminum oxidation step is separated from the hydrogen gas produced by means of a separation device. The separation device can here be a centrifuge separator, by means of which the solid aluminum oxide can be separated from the gaseous hydrogen, and optionally also from water when λ H2O ≥ 1. In addition to or as a supplement to the separation by means of a centrifuge separator, separation can also be carried out by filtration, wherein the reaction product of the reaction of aluminum with water is passed through a suitable filter to separate the solid particles from the gaseous products.

[0042] In an advantageous embodiment of the inventive concept, it is optionally provided that, by appropriately predetermining the amount of aluminum used, the temperature of the water used, the pressure in the aluminum reaction chamber, and the ratio of aluminum to water used, the oxidation of aluminum is carried out in such a way that the hydrogen gas produced in the aluminum oxidation step leaves the aluminum reaction chamber at a temperature higher than 2200 °C, preferably higher than 2500 °C, particularly preferably higher than 2800 °C. The temperature of the released hydrogen gas can be adjusted, for example, by the amount of aluminum used for the oxidation, by the pressure in the reaction chamber, and by the temperature of the water used as well as the ratio of water to aluminum. The higher the temperature in the aluminum reaction chamber, the higher the temperature of the hydrogen gas. The higher the temperature, the more energy can be obtained in the form of process heat when using a heat exchanger.

[0043] It is also provided that the process heat produced in the aluminum oxidation step and / or the water preparation step is extracted in the energy conversion step. The process heat produced in the heat exchanger can be used to generate steam. The steam can be mostly used for heating industrial processes, district / local heating, or driving a steam turbine to generate electricity without CO2. In addition to utilizing the process heat, the hydrogen gas produced can also be used to generate steam by means of a heat exchanger.

[0044] As described above, water vapor can also be used in small amounts, optionally after cooling, to reduce the temperature of the hydrogen reaction chamber.

[0045] Furthermore, it can be stipulated that at least part of the hydrogen produced in the aluminum oxidation step is converted into electric current. For this purpose, the hydrogen produced can be used electrochemically in a fuel cell or thermochemically to generate heat and electric current.

[0046] It is also advantageously optionally stipulated that at least part of the hydrogen produced in the aluminum oxidation step is used to produce water in the water preparation step. In addition to extracting the hydrogen produced from the process and using it for heat exchangers, storage, or conversion in a fuel cell, the hydrogen can also be supplied back into the circuit for further conversion and reaction in the hydrogen reaction chamber.

[0047] It is also optionally stipulated that the hydrogen produced in the aluminum oxidation step and optionally present water are introduced into the aluminum reaction chamber. Thereby, the proportion of heat obtained from the aluminum reaction chamber and the hydrogen reaction chamber can be increased by circulation.

[0048] The following figures show further advantageous embodiments of the inventive method for converting process heat and energy in the form of hydrogen. Wherein:

[0049] Figure 1 Shows a schematic diagram of the inventive method,

[0050] Figure 2 Shows an improved Figure 1 Schematic diagram of the method, in which the hydrogen produced circulates in a circuit,

[0051] Figure 3 Shows a schematic diagram of the inventive method, in which the hydrogen reaction chamber is arranged inside the aluminum reaction chamber, and

[0052] Figure 4 Shows a schematic diagram of the inventive method, which has the shown reaction parameters based on thermodynamic equilibrium calculations.

[0053] Figure 1 The inventive method 1 for producing process heat and energy in the form of hydrogen is shown schematically. The solid lines here schematically show the paths along which the respective products or reactants are guided. The dashed lines here represent optional paths along which the reactants or products can optionally be further guided. The branches within the lines represent path intersections, where the reactants or products can be further guided along one and / or the other of the said paths as required.

[0054] In this method, aluminum reacts with water, thereby forming aluminum oxide and converting the chemically stored energy in the aluminum into process heat and hydrogen. The method 1 of the present invention enables, on the one hand, energy conversion without carbon dioxide emissions and, on the other hand, prevents the formation of fine dust in the form of nanoparticles by controlling the oxidation temperature of aluminum. In addition, the process heat, hydrogen, and water vapor can be flexibly separated. This is also advantageously possible in high-temperature processes.

[0055] In the water preparation step 2, hydrogen 3 reacts with oxygen 4, thereby generating water 6 in a spontaneous and very rapid reaction in the hydrogen reaction chamber 5 according to the simplified reaction formula H2 + 1 / 2O2 → H2O. The hydrogen 3 reacts stoichiometrically with the oxygen 4 here, thereby generating water 6. If a super-stoichiometric reaction occurs, in which the amount of hydrogen 3 is more than the amount required to prepare water 6, the excess hydrogen 3 can also be further directed. To cool the hydrogen reaction chamber 5, the process heat 7 generated during the reaction of hydrogen 3 and oxygen 4 is extracted in the energy conversion step 8, whereby the process heat can be first converted into steam, for example, through a heat exchanger, which can be used directly or also for power generation. The generated water 6 or any remaining hydrogen 3 present is directed from the hydrogen reaction chamber 5 to the aluminum reaction chamber 9 at a temperature above 2200 °C. In the aluminum reaction chamber 9, the water 6 and any remaining hydrogen 3 after the incomplete reaction of hydrogen 3 and oxygen 4 react with the finely dispersed aluminum 10 in the aluminum oxidation step 11. The temperature required for the reaction is achieved by introducing water 6 with a temperature above 2200 °C into the aluminum reaction chamber 9, where the aluminum 10 reacts with the water 6 to form ternary aluminum oxide 12. In addition, hydrogen 3 is also formed in addition to the aluminum oxide 12. The process heat 7 generated during the conversion of aluminum 10 is also extracted in the energy conversion step 8 through a heat exchanger not shown in the figure and further utilized.

[0056] To prevent or at least reduce the formation of aluminum oxide nanoparticles 12, the water 6 used in the aluminum oxidation step 11 is used in excess. For this purpose, the molar ratio λ of the water 6 introduced into the aluminum reaction chamber 9 to the stoichiometrically required water 6 H2O should be specifically selected as λ H2O ≥ 1. The ratio λ used H2O < 1 especially at temperatures above 2200 °C leads to the formation of aluminum oxide nanoparticles 12 and other unwanted substances because aluminum in the incompletely oxidized aluminum oxide phase is in the oxidation state +1, such as Al2O. If excess water 6 is used, the excess water 6 that does not react with the aluminum 10 to form aluminum oxide 12 will also be further directed like the formed hydrogen 3.

[0057] Another aspect of preventing the formation of aluminum oxide nanoparticles 12 is to regulate the temperature inside the aluminum reaction chamber 9. The oxidation of aluminum 10 in the micron range can be described as depending on the adiabatic flame temperature T of the resulting aluminum oxide 12 f and the vapor pressure Tb In order to prevent uncontrolled and undesired evaporation of the aluminum 10 during the reaction and thus prevent the formation of condensed alumina fine dust in the form of aluminum oxide nanoparticles 12 that are difficult to separate (which would complicate the recovery of the metal oxide 12), it is advantageous for T f to be in a ratio with T b less than 1.

[0058] The aluminum particles 10 introduced into the aluminum reaction chamber 9 are at least partially melted due to the exothermic reaction of the aluminum 10 with the water 6, so that the aluminum 10 is mainly in a liquid state. Since water 6 acts as an oxidizing agent, an oxide layer that grows from the particle surface towards the particle core is formed on the aluminum particles 10 during the oxidation of the aluminum 10, which surrounds the optionally still partially solid particle core. Oxidation occurs due to the "attached" oxygen, and the mass of the aluminum-aluminum oxide particles increases. If the metal oxide layer is porous, the density of the metal oxide is lower than that of the metal. Then, the size of the oxidized metal particles increases compared to the original metal particles, which is advantageous for separation from the hydrogen 3.

[0059] Subsequently, in the separation device 13 designed as a centrifugal separator, the aluminum oxide 12 generated in the aluminum oxidation step 11 is separated from the generated hydrogen 3 and optionally from the water 6.

[0060] Then, the generated hydrogen 3 and optionally the water 6 can be removed from the circuit, or at least partially returned to the circuit again. In addition, the generated hydrogen 3 can be used electrochemically in a fuel cell or thermochemically to generate heat and electricity simultaneously.

[0061] Figure 2 shows an improved Figure 1 schematic diagram of method 1, in which the hydrogen 3 generated in the aluminum oxidation step 11 is not extracted but returned to the hydrogen reaction chamber 5 and used to prepare water 6 in the water preparation step 2. In addition, the hydrogen 3 generated during the oxidation process can be guided along the hydrogen return path 14, and optionally the water 6 can be guided along the water return path 15 to the aluminum reaction chamber 9.

[0062] Figure 3 Schematically shows the integrated two-stage concept of the method of the present invention. Here, the hydrogen reaction chamber 5 is located inside the aluminum reaction chamber 9.

[0063] Figure 4 Schematically shows based on Figure 1Method 1 of the embodiment, in which reaction parameters based on thermodynamic equilibrium calculations are shown. Here, hydrogen 3 reacts with oxygen 4 in the hydrogen reaction chamber 5 in the water preparation step 2, where water 6 with a production temperature T of 2350 °C is generated. Here, more hydrogen 3 is introduced into the hydrogen reaction chamber 5 than is required for the production of water 6 to achieve complete conversion of oxygen 3. For this purpose, the molar ratio λ of the oxygen 3 introduced into the hydrogen reaction chamber 5 to the stoichiometrically required oxygen 3 O2 has a value of 0.6. The conditioned and excessive λ H2O = 1.6 of water 6 reacts with aluminum 10 in the aluminum reaction chamber 9 at a pressure P R of 7 bar and a temperature of the aluminum reaction chamber 9 of 2300 °C, where aluminum 10 is oxidized to aluminum oxide 12. By appropriately predetermining the reaction parameters, only a negligible small amount of aluminum oxide nanoparticles 12N NP (Al2O3) below 400 ppm is formed in this reaction. This quantity data here corresponds to the ratio of the nanoparticles Al2O3 in the gas phase to the total amount of aluminum 10 and aluminum oxide 12 particles at chemical equilibrium. In the energy conversion step, process heat of 34 MJ per kilogram of aluminum used is extracted from the aluminum reaction chamber 9. The excessively used water 6 leaves the aluminum reaction chamber 9 at a temperature T of 900 °C. During the oxidation of aluminum 10, 0.05 kg of hydrogen 3 is also produced per kilogram of aluminum used.

[0064] List of reference numerals

[0065] 1 Method

[0066] 2 Water preparation step

[0067] 3 Hydrogen

[0068] 4 Oxygen

[0069] 5 Hydrogen reaction chamber

[0070] 6. Water

[0071] 7 Process heat

[0072] 8 Energy conversion step

[0073] 9 Aluminum reaction chamber

[0074] 10 Aluminum

[0075] 11 Aluminum oxidation step

[0076] 12 Aluminum oxide

[0077] 13 Separation device

[0078] 14 Hydrogen return path

[0079] 15 Water return path

Claims

1. A method (1) for converting energy in the form of process heat (7) and hydrogen (3), wherein in an aluminum oxidation step (11), aluminum (10) reacts with water (6) in an aluminum reaction chamber (9) at an elevated temperature and is thereby oxidized to aluminum oxide (12), with process heat (7) and hydrogen (3) being released, characterized in that, Hydrogen (3) released during the reaction of aluminum (12) and water (6) is at least partially supplied to a hydrogen reaction chamber (5), where hydrogen (3) reacts with oxygen (4) to form water (6), and water (6) previously made from hydrogen (3) is supplied to an aluminum reaction chamber (11) to oxidize aluminum (10).

2. The method (1) according to claim 1, characterized in that, Hydrogen (3) is used in excess in the water preparation step (2) to prepare water (6).

3. The method (1) according to claim 1 or 2, characterized in that, In the water preparation step (2), water (6) having a temperature higher than 2200 °C, preferably higher than 2500 °C, particularly preferably higher than 2800 °C is prepared for introduction into the aluminum reaction chamber (9).

4. The method (1) according to any one of claims 1 to 3, characterized in that To adjust the temperature of the water (6) produced in the hydrogen reaction chamber (5), water (6) is introduced from a water reservoir into the hydrogen reaction chamber (5) to provide water (6) having a desired temperature.

5. The method (1) according to any one of the preceding claims, characterized in that, In the aluminum oxidation step (11), aluminum (10) having a particle size of 1 to 1000 μm, preferably 2 to 80 μm, particularly preferably 5 to 40 μm is used.

6. The method (1) according to any one of the preceding claims, characterized in that In the aluminum oxidation step (11), in the aluminum reaction chamber (9), at least partially oxidized aluminum is oxidized with water (6) in addition to aluminum (10).

7. The method (1) according to any one of the preceding claims, characterized in that, Water (6) for oxidizing aluminum (10) is used in excess.

8. The method according to any one of the preceding claims, characterized in that, In the aluminum oxidation step (11), the oxidation temperature of aluminum (10) is lower than the boiling temperature of aluminum (10) and alumina (12) under a predetermined pressure.

9. The method (1) according to claims 7 and 8, characterized in that, In the aluminum oxidation step (11), the oxidation temperature of aluminum (10) is lower than the boiling temperature of aluminum (10) under a predetermined pressure, and water (6) for oxidizing aluminum (10) is used in excess so that aluminum (10) is completely oxidized by water (6) at a temperature lower than the boiling temperature of aluminum (10).

10. The method (1) according to any one of the preceding claims, characterized in that, In the aluminum oxidation step (11), the oxidation of aluminum (10) is carried out at a pressure of 1.7 bar to 50 bar, preferably at a pressure of 2 bar to 20 bar, particularly preferably at a pressure of 5 bar to 10 bar.

11. The method (1) according to any one of the preceding claims, characterized in that, The alumina (12) formed in the aluminum oxidation step (11) has a larger particle size than the aluminum (10) used for oxidation to separate the alumina from the hydrogen (3) also formed during oxidation as easily as possible.

12. The method (1) according to any one of the preceding claims, characterized in that, In the aluminum oxidation step (11), alumina nanoparticles (12) of less than 1 ppm, preferably less than 0.1 ppm, particularly preferably less than 0.01 ppm are produced.

13. The method (1) according to any one of the preceding claims, characterized in that, Using a separation device (13), the alumina (12) formed in the aluminum oxidation step (11) is separated from the hydrogen (3) formed.

14. The method (1) according to any one of the preceding claims, characterized in that, By appropriately predetermining the amount of aluminum (10) used, the temperature of the water (6) used, the pressure in the aluminum reaction chamber (11), and the ratio of the aluminum (10) to the water (6) used, the oxidation of aluminum (10) is carried out in such a way that the hydrogen (3) produced in the aluminum oxidation step (11) leaves the aluminum reaction chamber (9) at a temperature higher than 2200 °C, preferably higher than 2500 °C, particularly preferably higher than 2800 °C.

15. The method (1) according to any one of the preceding claims, characterized in that, The process heat (7) generated in the aluminum oxidation step (11) and / or the water preparation step (2) is extracted in the energy conversion step (8).

16. The method (1) according to any one of the preceding claims, characterized in that At least part of the hydrogen (3) produced in the aluminum oxidation step (11) is converted into electric current.

17. The method (1) according to any one of the preceding claims, characterized in that, The hydrogen gas (3) generated in the aluminum oxidation step (11) is at least partially used to produce water (6) in the water production step (2).

18. The method (1) according to any one of the preceding claims, characterized in that The hydrogen gas (3) generated in the aluminum oxidation step (11) and optionally present water (6) are introduced into the aluminum reaction chamber (9).

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