Process for conversion of energy in the form of process heat and hydrogen

Abstract

The present invention relates to processes (1) for conversion of energy in the form of process heat (7) and hydrogen (3). Aluminium (10) is reacted with water (6) at elevated temperature in an aluminium reaction chamber (9) in an aluminium oxidation step (11) and thus oxidized to form aluminium oxide (12). This liberates process heat (7) and hydrogen (3). The hydrogen (3) liberated in the reaction of aluminium (12) and water (6) is at least partially supplied to a hydrogen reaction chamber (5), wherein the hydrogen (3) reacts with oxygen (4) to form water (6) in a water production step (2). The water (6) previously produced from the hydrogen (3) is supplied to the aluminium reaction chamber (11) for oxidation of the aluminium (12).

Description

[0001] Technical University of Darmstadt

[0002] Process for converting energy into process heat and hydrogen

[0003] The invention relates to a process for converting energy in the form of process heat and hydrogen, wherein aluminum is reacted with water at an elevated temperature in an aluminum reaction chamber in an aluminum oxidation step and is thereby oxidized to aluminum oxide, wherein process heat and hydrogen are released during the reaction.

[0004] Carbon dioxide, as a greenhouse gas, is partly responsible for the greenhouse effect and thus for global warming. A large portion of the carbon dioxide emitted worldwide is produced by the combustion, i.e., the oxidation and processing of fossil carbon-based fuels such as oil or coal. In addition to the gaseous byproducts of oxidation, which also include carbon monoxide, large quantities of particulate matter in the form of nanoparticles are emitted. These can lead to impaired air quality, particularly in the winter months, with detrimental effects, especially in urban areas.

[0005] To counteract this problem, metals are being considered as carbon-free energy sources. Pure chemical elements with metallic bonds between their atoms in the zero oxidation state are referred to collectively as metals. The metal species obtained during the oxidation of metals, such as metal oxides, are referred to as oxidized metals.

[0006] Metals have a high potential for storing energy and releasing it at a desired time through controlled oxidation. The chemical energy stored in a metal can be converted into electrical energy, for example, by the consumer themselves through oxidation processes. This conversion usually produces neither greenhouse gases nor carbon monoxide. The oxidized metal can then be reduced to metal again in a separate process and repeatedly used to store energy. If the reduction of the oxidized metal is fed by renewable sources such as wind turbines or photovoltaic systems, this enables an environmentally friendly supply of energy. This offers a significant advantage over conventional carbon-based energy sources, which cannot be recycled after oxidation and therefore cannot be kept in a closed loop.

[0007] The transportability of the metallic energy carrier opens up the possibility of storing renewable energies in the energy carrier by means of chemical reduction in wind and sun-rich regions, possibly far away from the consumer, and then using them anywhere in the world.

[0008] Metals that have proven advantageous for this purpose include iron, copper, nickel, manganese, silicon and also aluminum. It is already known that aluminum can be reacted with air or oxygen in an aluminum reaction chamber, whereby the aluminum is oxidized to aluminum oxide in an aluminum oxidation step. This reaction is exothermic, and the oxidation temperature of the aluminum during the reaction can exceed the boiling point of both aluminum and aluminum oxide. The aluminum or aluminum particles used can pass into the gas phase, and after condensation of the gaseous aluminum particles in regions of reduced temperature, nanoparticles in a size range of a few nanometers can form. These nanoparticles have a diameter smaller than the original aluminum particles used.These nanoparticles have the disadvantage that they can only be separated from the other reaction products with great effort and thus returned to the recycling cycle.

[0009] The reaction of aluminium with water, on the other hand, offers the advantage that the boiling points of neither the metal nor the metal oxide are exceeded at a slightly increased pressure and that the reaction of aluminium with water produces not only aluminium oxide and energy in the form of process heat but also hydrogen.

[0010] The resulting hydrogen can also be used advantageously in addition to the process heat generated during oxidation.

[0011] When converting the chemical energy of aluminum into thermal energy, it is particularly desirable to select and regulate the oxidation temperature precisely, whereby two opposing processes must be taken into account. Firstly, an oxidation temperature of the aluminum that is as low as possible offers the advantage that only a few nanoparticles are formed during oxidation, and secondly, it is advantageous if the process heat can be obtained at the oxidation temperature that is as high as possible. It is therefore particularly advantageous that the oxidation temperature of the aluminum during controlled oxidation remains slightly below the boiling point of aluminum.

[0012] Furthermore, it is desirable that the process of energy conversion from the metal at the site of oxidation can be carried out as efficiently as possible and without the formation of nanoparticles.

[0013] The object of the present invention is therefore to further improve the process already known from the prior art, whereby the efficiency should be as high as possible and the proportion of nanoparticles obtained during the oxidation should be kept as small as possible.

[0014] The problem is solved in that the hydrogen released during the reaction of aluminum and water is fed at least in part to a hydrogen reaction chamber, wherein the hydrogen reacts with oxygen to form water, and in that the water previously produced from the hydrogen is fed to the aluminum reaction chamber for the oxidation of the aluminum.

[0015] In the following, aluminum is understood to mean the metal aluminum, while the term aluminum oxide is understood to mean the ternary and fully oxidized aluminum oxide AI2O3. The two-stage reaction chamber concept with an aluminum reaction chamber and a hydrogen reaction chamber makes it possible to easily keep the oxidation temperature of the reaction of aluminum with water to form aluminum oxide in the aluminum reaction chamber below a threshold temperature, i.e. below the boiling point of aluminum and also below the boiling point of aluminum oxide. The oxidation temperature of the aluminum can be regulated by the targeted introduction of water formed in the hydrogen reaction chamber. This can be achieved both by the amount of water fed into the aluminum reaction chamber and by the temperature of the water fed in.Furthermore, the oxidation temperature can also be regulated by the amount of aluminum introduced into the aluminum reaction chamber.

[0016] The water introduced into the aluminum reaction chamber is advantageously conditioned and preferably has an elevated temperature above the ignition temperature of the reaction between aluminum and water. The exothermic reaction of hydrogen with oxygen to form water makes it easy to provide water at the desired elevated temperature without the need for separate heating by the input of energy from an external energy source.

[0017] Furthermore, the method according to the invention enables the flexible extraction of energy in the form of process heat and hydrogen. Process heat can be taken from the hydrogen reaction chamber, which is heated by the highly exothermic, very rapid reaction of the hydrogen with oxygen or air, and also from the aluminum reaction chamber. For example, the process heat taken from the circuit can be used to heat water with the help of a heat exchanger and to form steam, which can then be converted into electricity. In a similar way, the hydrogen produced can be converted into electricity using a fuel cell or fed back into the circuit for further conversion and reaction in the hydrogen reaction chamber to produce water.This allows the hydrogen to circulate in a circuit without removing the hydrogen, while it is oxidized to water with added oxygen in the water production step. The water produced is then oxidized to aluminum oxide in the aluminum oxidation step, producing more hydrogen, which can be fed back into the hydrogen reaction chamber to produce water.

[0018] The resulting aluminum oxide from the reaction can be reduced to aluminum again using the Hall-Heroult process. Furthermore, it is also possible to use the hydrogen separately in a separate cycle to reduce the resulting aluminum oxide.

[0019] The use of aluminium as a chemical energy storage device is particularly due to its high energy density in the range of 23 kWh / dm 3It can be used advantageously compared to other chemical energy storage media. Furthermore, due to its non-toxic nature, aluminum can be handled easily, requiring no special protective measures. It has been shown that by reacting aluminum with water at elevated temperatures, the passivation layer on the aluminum surface can be neglected, while still allowing a quantitative conversion of the aluminum with water.

[0020] In particular, the process according to the invention can be used for decentralized energy supply in industry and chemical parks, as well as for centralized energy supply in power plants. As already mentioned, the process can be used either for the polygeneration of energy in the form of process heat and hydrogen, particularly in industry or chemical parks, in which case both the process heat and the hydrogen can be used, or, depending on the application, only the process heat can be used, in which case the hydrogen can be recycled.

[0021] In addition, it is also envisaged that the hydrogen is used in excess in the water preparation step to prepare the water. To prepare water from hydrogen and oxygen, two hydrogen molecules react spontaneously with one oxygen molecule according to the reduced reaction equation H2 + k O2 H2O. By means of a superstoichiometric reaction, i.e. a reaction with an excess of hydrogen, in which more hydrogen is added to the reaction than is actually required for the reaction according to the above reaction equation, the product formed is a mixture of water and small amounts of hydrogen. The small residual amount of hydrogen is not, however, detrimental to the further reaction of the water with the aluminum.The stoichiometric to superstoichiometric conversion of hydrogen with oxygen ensures that the oxygen reacts completely with the hydrogen and no oxygen can enter the aluminum reaction chamber. This means that the hydrogen produced during the reaction of aluminum and water can be recovered and the aluminum does not react directly with oxygen to form aluminum oxide, bypassing the formation of hydrogen. An excessively high concentration of hydrogen is also undesirable, as the aluminum oxide formed can otherwise be reduced back to aluminum in an uncontrolled manner in the aluminum reaction chamber.

[0022] However, with a stoichiometric conversion according to the above reaction equation, a complete conversion to water can be achieved, which, apart from water, does not contain any other by-products that could interfere with the desired oxidation pathway.

[0023] The required oxygen can be introduced into the hydrogen reaction chamber either directly as oxygen or in a gas mixture such as air. The direct conversion of hydrogen with oxygen offers the advantage of avoiding undesirable side reactions resulting from the reaction of highly reactive hydrogen with air components. Furthermore, during the subsequent reaction of the aluminum, particularly at higher temperatures, undesirable conversions of the aluminum with, for example, nitrogen compounds are also conceivable.

[0024] The ignition temperature of the reaction of aluminum with water is, depending on the prevailing conditions, in the order of magnitude of approximately 2200 °C. It is therefore advantageous that in the water preparation step, water with a temperature of greater than 2200 °C, preferably greater than 2500 °C, and in particular greater than 2800 °C is prepared for introduction into the aluminum reaction chamber. The very rapid reaction of hydrogen with oxygen creates high temperatures in the hydrogen reaction chamber, particularly when oxygen is provided directly and not in a gas mixture. It is therefore particularly advantageous if the reaction of the hydrogen with oxygen in the water preparation step is regulated such that the temperature of the water prepared, orMore precisely, the temperature of the water vapor is above 2200 °C, preferably above 2500 °C, and especially above 2800 °C, so that the ignition temperature of the aluminum is reached to initiate the oxidation of the aluminum in the aluminum reaction chamber. The temperature of the water introduced into the aluminum reaction chamber can also influence the oxidation temperature of the aluminum.

[0025] Furthermore, it may be advantageous that the temperature of the water presented in the water presentation step is higher the longer the transport path of the presented water to the aluminum reaction chamber, in order to enable the water flowing into the aluminum reaction chamber to have the required ignition temperature.

[0026] The oxygen or air required for the reaction can be provided at room temperature and advantageously does not require heating before the reaction with the hydrogen.

[0027] In order to avoid a controlled reaction of hydrogen with oxygen as far as possible and to regulate the reaction temperature, it can also be provided that water from a water reservoir is introduced into the hydrogen reaction chamber to regulate the temperature of the water produced in the hydrogen reaction chamber in order to provide water at a desired temperature. The introduction of additional water makes it possible, on the one hand, to lower the temperature of the hydrogen reaction chamber in order to minimize the heat load on the reaction chamber and, on the other hand, to suppress the formation of nitrogen oxide when the process is operated with air instead of pure oxygen. In addition to the hydrogen, the water required for the introduction can also be taken from the process itself.For this purpose, more water can be added to the aluminum oxidation step in the aluminum reaction chamber than is required for the conversion to aluminum oxide. This excess water can be fed to the hydrogen reaction chamber for cooling, optionally after cooling with the aid of a heat exchanger.

[0028] According to the invention, it is also provided that aluminum with a particle size of between 1 and 1000 pm, preferably between 2 and 80 pm and in particular between 5 and 40 pm is used in the aluminum oxidation step. The particle size is understood to mean the average equivalent diameter of the particles. In order to enable the most complete and rapid conversion of the aluminum with water possible, the aluminum used is advantageously present in the form of aluminum particles having a size in the micrometer range. The oxidation of the aluminum in the micrometer range can be described as a function of the adiabatic flame temperature Tf and the vapor pressure Tb of the aluminum oxide formed.In order to prevent the uncontrolled and undesired evaporation of the aluminum during the reaction and thus the formation of fine dust in the form of nanoparticles that are difficult to separate and that make recycling of the metal oxide difficult, it is advantageous if the ratio of Tf to T. b < 1 is .

[0029] The aluminum particles introduced into the aluminum reaction chamber melt at least partially due to the exothermic reaction of aluminum with water, whereby the aluminum is predominantly or completely in liquid form. With water as the oxidizing agent, an oxide layer grows on the aluminum particles from the particle surface towards the particle core during the oxidation of the aluminum, surrounding the particle cores, which may still be partially solid. The mass of the aluminum-aluminum oxide particle increases due to the oxidation and the "deposition" of oxygen. If the metal oxide layer is porous, the density of the metal oxide is lower than that of the metal. The size of the oxidized metal particle then increases compared to the original metal particle.This facilitates effective deposition of the resulting aluminum oxide particles, thereby enabling a complete cycle of oxidation and subsequent reduction in a separate process. Advantageously, the aluminum oxidation reaction therefore occurs as a heterogeneous type C reaction on the surface of the aluminum, whereby neither the aluminum nor its resulting oxides pass into the gas phase and form 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).

[0030] It is also envisaged that in the aluminum oxidation step in the aluminum reaction chamber, in addition to aluminum, at least partially oxidized aluminum is or can be oxidized with water. At least partially oxidized aluminum, such as aluminum hydroxide Al(OH)3, can also be added to the aluminum. These energy carriers, which are lower in energy than aluminum due to the at least partial oxidation, can be added to the aluminum, in particular to regulate the oxidation temperature, or can be fed separately to the aluminum reaction chamber. In addition to aluminum species, other metals or oxidized metal species can also be used and added to the aluminum and / or the at least partially oxidized aluminum.

[0031] In order to prevent the formation of fine dust in the form of nanoparticulate aluminum oxide, or at least to minimize it as much as possible, it is advantageous that the aluminum used and introduced into the aluminum reaction chamber is completely oxidized to aluminum oxide according to type C. In addition to the provision of aluminum in the micrometer range, the complete conversion also depends on the oxidizing agent provided. Therefore, it is advantageous that the water used for the oxidation of the aluminum is used in excess. For this purpose, the molar ratio X H 2o of the water introduced into the aluminum reaction chamber to the stoichiometrically required water, in particular, such that X H 2o - 1 is . A used ratio of X H2O < 1 leads, especially at temperatures above 2000 ° C, to the formation of aluminum nanoparticles as well as other undesirable, because not completely oxidized, aluminum oxide phases with aluminum in the oxidation state + 1 such as Al2O .

[0032] According to an advantageous implementation of the inventive concept, it is optionally provided that an oxidation temperature of the aluminum in the aluminum oxidation step is below the boiling point of aluminum and aluminum oxide at a predetermined pressure. In this way, the formation of aluminum oxide nanoparticles can be effectively prevented or at least largely minimized. Nanoparticles of aluminum oxide can be formed in particular when the temperature during the oxidation of the aluminum is above the boiling point of the aluminum at a suitable pressure. Firstly, nanoparticles of aluminum oxide can be formed during the transition of the aluminum into the gas phase and a gas phase oxidation taking place there, in particular during a subsequent condensation.However, a gas phase transition is also possible below the boiling point of aluminum, provided the vapor pressure of the aluminum particles is sufficient for such a transition. Furthermore, nanoparticles can also be formed if the oxidation temperature exceeds the boiling point of aluminum oxide. In a first step, the aluminum can be oxidized to aluminum oxide, with the temperature of the particle subsequently rising further due to the exothermic oxidation reaction, and a gas phase transition can occur. If the aluminum oxide subsequently condenses in low-temperature regions, this can lead to undesirable nanoparticle formation.

[0033] This nanoparticle formation can be largely avoided by appropriate regulation and specification of the oxidation temperature. The formation of aluminum oxide nanoparticles, such as those produced during the evaporation of aluminum, makes it difficult to separate and recycle the aluminum oxide from the hydrogen that is also produced.

[0034] In order to generate as small a quantity of nanoparticles as possible during the oxidation of the aluminum, it is advantageous for the oxidation temperature of the aluminum in the aluminum oxidation step to be below the boiling point of aluminum at a given pressure, and for the water used to oxidize the aluminum to be used in excess, so that the aluminum is completely oxidized by the water at a temperature below the boiling point of aluminum. It has been found that the formation of aluminum oxide nanoparticles can be controlled, in particular, by controlling the state of aggregation of the aluminum and by the amount of oxidizing agent added.

[0035] The oxidation temperature of the aluminum used is preferably below the boiling point of the aluminum. If this temperature is above the boiling point, most of the aluminum used evaporates. Subsequent condensation can lead to the formation of aluminum oxide nanoparticles that are smaller in diameter than the original aluminum particles used. These nanoparticles have the disadvantage that they can only be separated from the other reaction products, such as hydrogen, with great effort and thus returned to the recycling cycle.

[0036] The formation of nanoparticles can also be regulated by the amount of water used. Complete oxidation of aluminum according to type C results in fewer aluminum species in the gas phase and thus fewer nanoparticles. Furthermore, if more water is used than is stoichiometrically consumed for the oxidation of the aluminum, side reactions between aluminum and water, and thus, for example, the formation of incompletely oxidized aluminum species such as Al2O, can be suppressed. An incomplete reaction would result in a lower amount of energy achievable from the oxidation than with a complete reaction.

[0037] It is advantageous to carry out the oxidation of the aluminum at an elevated pressure. It is therefore envisaged that the oxidation of the aluminum in the aluminum oxidation step is carried out at a pressure between 1.7 bar and 50 bar, preferably at a pressure between 2 and 20 bar, and in particular at a pressure between 5 and 10 bar. This promotes both hydrogen storage and process intensification. Furthermore, at an elevated pressure, i.e. at pressures 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 can be without the aluminum used evaporating. A higher oxidation temperature is accompanied by increased process heat.Thus, the gas phase transition and the associated nanoparticle formation in the gas phase can be largely avoided or at least reduced.

[0038] Advantageously, the aluminum oxide formed during the oxidation of the aluminum with water is separated from the hydrogen that is also formed. In this way, the aluminum oxide can be collected and reduced to the metal again in order to store energy. Therefore, it is optionally provided that the aluminum oxide formed in the aluminum oxidation step has a larger particle size than the aluminum used for the oxidation in order to achieve the simplest possible separation of the aluminum oxide from the hydrogen that is also formed during the oxidation. Because the aluminum oxide formed has a particle size that is larger than the particle size of the aluminum used, the aluminum oxide can be separated in a simple manner.

[0039] The particle size of the aluminum oxide obtained in the aluminum oxidation step can be regulated by a suitable specification of reaction parameters such as, among others, by a suitable specification of 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.

[0040] It is also possible to specifically produce aluminum oxide nanoparticles by appropriately specifying the reaction parameters mentioned, which in turn can be used for subsequent industrial applications. For this purpose, the produced aluminum oxide nanoparticles can have a particle size between 1 and 1000 nm, preferably between 2 and 500 nm, and in particular between 5 and 40 nm.

[0041] According to an advantageous implementation of the inventive concept, it is optionally provided that in the aluminum oxidation step aluminum oxide nanoparticles are produced in a range below 1 ppm, preferably below 0.15 ppm, and particularly preferably below 0.01 ppm. The specification ppm refers to the total aluminum oxide produced during the oxidation, with preferably no aluminum oxide nanoparticles being formed during the oxidation. The formation of nanoparticles can be largely prevented by a suitable choice of reaction parameters, such as pressure, temperature and the oxidizing agent, the formation of nanoparticles can be prevented. It is advantageous to choose the conditions during the oxidation of the aluminum such that a heterogeneous surface reaction of the type C aluminum particles occurs.It can therefore be expected that the resulting aluminum oxide particles will for the most part be larger and heavier than the aluminum particles used for the reaction. The formation of only negligible amounts of aluminum oxide nanoparticles offers the advantage that these cannot be released into the environment as fine dust, and the few aluminum oxide particles that are formed do not have to be separated from the hydrogen that is also formed, which is a major effort. This makes it easy to separate and collect the aluminum oxide formed during the reaction of aluminum with water, so that the aluminum oxide can be completely recycled back into aluminum in a separate step.

[0042] It is also optionally provided that the aluminum oxide produced in the aluminum oxidation step is separated from the hydrogen produced by means of a separation device. The separation device can be a centrifugal separator, with which the solid aluminum oxide is separated from the gaseous hydrogen and, if appropriate, at X H 2o - 1 can also be separated from the water. In addition to or in addition to separation by means of a centrifugal separator, separation can also be carried out by filtration, whereby the reaction products of the reaction of the aluminum with the water are passed through a suitable filter in order to separate solid particles from the gaseous products.

[0043] In an advantageous implementation of the inventive concept, it is optionally provided that by suitable specification of the amount of aluminum used, the temperature of the water used, the pressure in the aluminum reaction chamber and the ratio of the aluminum used to the water, the oxidation of the aluminum takes place in such a way that the hydrogen produced in the aluminum oxidation step leaves the aluminum reaction chamber at a temperature greater than 2200 ° C, preferably greater than 2500 ° C, and in particular greater than 2800 ° C. The temperature of the hydrogen released can be regulated, for example, via the amount of aluminum used for the oxidation, the pressure in the reaction chamber, as well as the temperature of the water used and the ratio of water to aluminum. The higher the temperature in the aluminum reaction chamber, the higher the temperature of the hydrogen.The higher the temperatures, the more energy can be obtained in the form of process heat when extracted using heat exchangers.

[0044] It is also planned that the process heat generated in the aluminum oxidation step and / or in the water preparation step will be extracted in an energy conversion step. The resulting process heat can be used in heat exchangers to generate steam. The steam can largely be used to heat industrial processes, as district / local heating, or to operate a steam turbine for CO2-free electricity generation. In addition to the use of process heat, the resulting hydrogen can also be used to generate steam using heat exchangers.

[0045] As already mentioned, the steam can also be used to a small extent, possibly after cooling, to lower the temperature of the hydrogen reaction chamber. Furthermore, it can be provided that the hydrogen produced in the aluminum oxidation step is at least partially converted into electrical current. For this purpose, the resulting hydrogen can be used electrochemically in fuel cells or thermochemically to generate heat and electrical current.

[0046] It is also advantageously optionally provided that the hydrogen produced in the aluminum oxidation step is used at least partially to produce the water in the water production step. In addition to removing the hydrogen produced from the process and using it in heat exchangers, for storage, or for conversion in fuel cells, the hydrogen can be returned to the cycle for further conversion and reaction in the hydrogen reaction chamber.

[0047] It is also optionally provided that the hydrogen produced in the aluminum oxidation step and any water present are introduced into the aluminum reaction chamber. This circulation can increase the proportion of heat extracted from the aluminum reaction chamber and also from the hydrogen reaction chamber.

[0048] Further advantageous embodiments of the process according to the invention for converting energy into process heat and hydrogen are shown in the following drawing. It shows:

[0049] Figure 1 is a schematic view of an inventive

[0050] Process, Figure 2 shows a schematic representation of a modified process from Figure 1, wherein the hydrogen produced is circulated in a circuit,

[0051] Figure 3 is a schematic view of a process according to the invention, wherein a hydrogen reaction chamber is arranged within an aluminum reaction chamber, and

[0052] Figure 4 is a schematic representation of a process according to the invention with specified reaction parameters based on a thermodynamic equilibrium calculation.

[0053] Figure 1 shows a schematic drawing of the method 1 according to the invention for producing energy in the form of process heat and hydrogen. Solid lines schematically represent paths along which individual products or reactants are conveyed. Dashed lines represent optional paths along which reactants or products can optionally be forwarded. Branches within the lines represent path intersections at which reactants or products can be forwarded along one path and / or the other path as desired.

[0054] In the process, aluminum is reacted with water, forming aluminum oxide and converting the energy stored chemically in the aluminum into process heat and hydrogen. The process 1 according to the invention makes it possible, on the one hand, to carry out the energy conversion without emitting carbon dioxide and, on the other hand, to prevent the formation of fine dust in the form of nanoparticles by controlling the temperature of the oxidation of the aluminum. Furthermore, flexible extraction of the process heat, hydrogen and also water vapor can be achieved. This is also advantageously possible in a high-temperature process.

[0055] In a water production step 2, hydrogen 3 is reacted with oxygen 4, whereby water 6 is formed in a hydrogen reaction chamber 5 in a spontaneous and very rapid reaction according to the reduced reaction equation H2 + UO2 H2O. The hydrogen 3 is reacted stoichiometrically with the oxygen 4, whereby water 6 is formed. In the case of a superstoichiometric reaction with more hydrogen 3 than is required to produce the water 6, the excess hydrogen 3 can also be passed on. In order to cool the hydrogen reaction chamber 5, the process heat 7 produced during the reaction of the hydrogen 3 with the oxygen 4 is removed in an energy conversion step 8, whereby the process heat can first be converted into steam, for example via a heat exchanger, which can be used directly or to generate electricity.The resulting water 6 and any residues of hydrogen 3 that may be present are passed at a temperature of more than 2200 ° C from the hydrogen reaction chamber 5 to an aluminum reaction chamber 9. In the aluminum reaction chamber 9, the water 6 and any residues of hydrogen 3 from an incomplete reaction of the hydrogen 3 with oxygen 4 are reacted with finely dispersed aluminum 10 in an aluminum oxidation step 11. The temperature required for the reaction is introduced by the water 6 that is passed into the aluminum reaction chamber 9 at a temperature of more than 2200 ° C, the aluminum 10 being reacted with the water 6 to form ternary aluminum oxide 12. Furthermore, hydrogen 3 is also formed alongside aluminum oxide 12.The process heat 7 generated during the conversion of the aluminum 10 is also extracted and reused in the energy conversion step 8 by means of a heat exchanger not shown in the drawing.

[0056] In order 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 X H 2o of the water 6 introduced into the aluminum reaction chamber 9 to the stoichiometrically required water 6 X H 2o in particular, to be chosen so that X H 2o - 1 is . A used ratio of X H2o < 1 leads, particularly at temperatures above 2200 ° C, to the formation of aluminum oxide nanoparticles 12 as well as other undesirable, incompletely oxidized aluminum oxide phases with aluminum 10 in the oxidation state + 1, such as Al2O . If an excess of water 6 is used, the excess water 6, which does not react with aluminum 10 to form aluminum oxide 12, is also passed on, as is the resulting hydrogen 3 .

[0057] Another aspect to the formation of

[0058] To prevent the formation of aluminum oxide nanoparticles 12, the temperature must be regulated within the

[0059] Aluminum reaction chamber 9. The oxidation of aluminum 10 in the micrometer range can be described as a function of the adiabatic flame temperature Tf and the vapor pressure Tb of the resulting aluminum oxide 12. To prevent the uncontrolled and undesired evaporation of aluminum 10 during the reaction and thus the formation of difficult-to-separate fine dust from condensed aluminum oxide in the form of aluminum oxide nanoparticles 12, which complicate the recycling of the metal oxide 12, it is advantageous if the ratio of Tf to Tb is < 1.

[0060] The aluminum particles 10 introduced into the aluminum reaction chamber 9 melt at least partially due to the exothermic reaction of aluminum 10 with water 6, whereby the aluminum 10 is predominantly in liquid form. Due to the water 6 as the oxidizing agent, a growing oxide layer forms on the aluminum particles 10 during the oxidation of the aluminum 10, from the particle surface toward the particle core, surrounding the possibly still partially solid particle cores. The mass of the aluminum-aluminum oxide particle increases due to the oxidation through the "deposition" of oxygen. If the metal oxide layer is porous, the density of the metal oxide is lower than that of the metal. The size of the oxidized metal particle then increases compared to the original metal particle, which facilitates separation from the hydrogen 3.

[0061] The resulting aluminum oxide 12 of the aluminum oxidation step 11 is then separated from the resulting hydrogen 3 and optionally from the water 6 in a separation device 13 designed as a centrifugal separator.

[0062] The resulting hydrogen 3 , as well as water 6 if necessary, can then be removed from the cycle or at least partially returned to the cycle. Furthermore, the resulting hydrogen 3 can also be used electrochemically in fuel cells or thermochemically to simultaneously generate heat and electricity.

[0063] Figure 2 shows a schematic representation of such a modified process 1 from Figure 1, wherein the hydrogen 3 produced in the aluminum oxidation step 11 is not removed, but is returned to the hydrogen reaction chamber 5 and used to produce water 6 in the water production step 2. Furthermore, the hydrogen 3 produced during the oxidation can be fed along the hydrogen return path 14 and, if appropriate, water 6 along the water return path 15 to the aluminum reaction chamber 9.

[0064] Figure 3 schematically illustrates an integrated two-stage concept of the process according to the invention. The hydrogen reaction chamber 5 is located within the aluminum reaction chamber 9.

[0065] Figure 4 schematically shows a process 1 based on the embodiment of Figure 1, wherein reaction parameters are given based on a thermodynamic equilibrium calculation. In the water preparation step 2, hydrogen 3 is reacted with oxygen 4 in the hydrogen reaction chamber 5, wherein water 6 is formed at a temperature T of 2350 °C. In this case, more hydrogen 3 is introduced into the hydrogen reaction chamber 5 than would be required for the preparation of water 6 in order to achieve complete conversion of the oxygen 3. For this purpose, the ratio X02 of the oxygen 3 introduced into the hydrogen reaction chamber 5 to the stoichiometrically required oxygen 3 is at a value of 0.6. The conditioned oxygen 3 in an excess of X H 2O = 1 , 6 used water 6 is in the aluminum reaction chamber 9 with aluminum 10 at a pressure PR of 7 bar and a temperature TR the aluminum reaction chamber 9 at 2300 ° C , whereby the aluminum 10 is oxidized to aluminum oxide 12 . By setting the appropriate reaction parameters , only a negligible number of aluminum oxide nanoparticles 12 N is formed during this reaction. NP (AI2O3) of less than 400 ppm. This quantity corresponds to the proportion of AI2O3 nanoparticles in relation to the total amount of aluminum 10 and aluminum oxide 12 particles in the gas phase in chemical equilibrium. In the energy conversion step, process heat of 34 MJ per kilogram of aluminum used is withdrawn from the aluminum reaction chamber 9. The excess water 6 leaves the aluminum reaction chamber 9 at a temperature T of 900 °C. During the oxidation of the aluminum 10, 0.05 kg of hydrogen 3 is also produced per kilogram of aluminum 10 used. LIST OF REFERENCE SYMBOLS

[0066] 1 Procedure 2 Water representation step

[0067] 3 Hydrogen

[0068] 4 Oxygen

[0069] 5 Hydrogen reaction chamber

[0070] 6 Water 7 Process heat

[0071] 8 Energy conversion step

[0072] 9 Aluminum reaction chamber

[0073] 10 aluminum

[0074] 11 Aluminium oxidation step 12 Aluminium oxide

[0075] 13 Separation device

[0076] 14 Hydrogen recycling path

[0077] 15 Water return path

Claims

PATENT CLAIMS 1. Method (1) for converting energy in the form of process heat (7) and hydrogen (3), wherein aluminum (10) is reacted with water (6) at an elevated temperature in an aluminum reaction chamber (9) in an aluminum oxidation step (11) and is oxidized to aluminum oxide (12), wherein process heat (7) and hydrogen (3) are released, characterized in that the hydrogen (3) released during the reaction of aluminum (12) and water (6) is at least partially fed to a hydrogen reaction chamber (5), wherein the hydrogen (3) reacts with oxygen (4) to form water (6), and that the water (6) previously produced from the hydrogen (3) is fed to the aluminum reaction chamber (11) for the oxidation of the aluminum (10).

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

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

4. Method (1) according to one of claims 1 to 3, characterized in that for regulating the temperature of the represented water (6) in the hydrogen reaction chamber (5) , water (6) from a water reservoir into the Hydrogen reaction chamber (5) is introduced to produce water (6) with a desired temperature.

5. Method (1) according to one of the preceding claims, characterized in that in the aluminum oxidation step (11) aluminum (10) with a particle size between 1 and 1000 pm, preferably between 2 and 80 pm and in particular between 5 and 40 pm is used.

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

7. Process (1) according to one of the preceding claims, characterized in that the water (6) used for the oxidation of the aluminum (10) is used in an excess.

8. Method according to one of the preceding claims, characterized in that an oxidation temperature of the aluminum (10) in the aluminum oxidation step (11) at a predetermined pressure is below the boiling temperature of aluminum (10) and aluminum oxide (12).

9. Method (1) according to claim 7 and 8, characterized in that the oxidation temperature of the aluminum (10) in the aluminum oxidation step (11) at a predetermined pressure below the boiling temperature of Aluminium (10) and that the water (6) used to oxidise the aluminium (10) is used in excess so that the aluminium (10) is completely oxidised by the water (6) at a temperature below the boiling point of aluminium (10).

10. Method (1) according to one of the preceding claims, characterized in that the oxidation of the aluminum (10) in the aluminum oxidation step (11) is carried out at a pressure between 1.7 bar and 50 bar, preferably at a pressure between 2 and 20 bar, and in particular at a pressure between 5 and 10 bar.

11. Method (1) according to one of the preceding claims, characterized in that the aluminum oxide (12) formed in the aluminum oxidation step (11) has a larger particle size than the aluminum (10) used for the oxidation in order to achieve the simplest possible separation of the aluminum oxide from the hydrogen (3) also formed during the oxidation.

12. Method (1) according to one of the preceding claims, characterized in that in the aluminum oxidation step (11) aluminum oxide nanoparticles (12) in a range below 1 ppm, preferably below 0.1 ppm, and particularly preferably below 0.01 ppm.

13. Method (1) according to one of the preceding claims, characterized in that the Aluminium oxide formed in the aluminium oxidation step (11) (12) is separated from the resulting hydrogen (3) by means of a separation device (13).

14. Method (1) according to one of the preceding claims, characterized in that by a suitable specification of 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) used to the water (6), the oxidation of the aluminum (10) takes place in such a way that the hydrogen (3) produced in the aluminum oxidation step (11) leaves the aluminum reaction chamber (9) at a temperature greater than 2200 °C, preferably greater than 2500 °C, and in particular greater than 2800 °C.

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

16. Process (1) according to one of the preceding claims, characterized in that the hydrogen (3) produced in the aluminum oxidation step (11) is at least partially converted into electrical current.

17. Method (1) according to one of the preceding claims, characterized in that the Hydrogen (3) produced in the aluminum oxidation step (11) is used at least partially to represent the water (6) in the water representation step (2).

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

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