CN106537035A - Combustion of lithium at different temperatures and pressures and with gas surpluses using porous tubes as burners - Google Patents

Abstract

This invention relates to a method for burning a metal M with fuel gas, the metal M being selected from alkali metals, alkaline earth metals, aluminum and zinc, and their alloys and/or mixtures, wherein the combustion is carried out by means of a porous burner (3) comprising a porous tube as a burner. The invention also relates to apparatus for carrying out the method and to the use of a porous burner comprising a porous tube as a burner in burning a metal M with fuel gas.

Description

Combustion of Lithium at Different Temperatures, Pressures, and Gas Excesses Using Porous Tubes as Burners

The invention relates to a method for burning a metal M selected from the group consisting of alkali metals, alkaline earth metals, aluminum and zinc and their alloys and/or mixtures with gas, wherein the combustion takes place by means of a porous burner comprising a porous tube as burner. The invention also relates to a device for carrying out said method and to the use of a porous burner comprising a porous tube as burner for the combustion of a metal M selected from the group consisting of alkali metals, alkaline earth metals, aluminum and zinc and its alloys and/or mixtures.

Over the years, a number of energy generating units have been proposed which work with the heat generated during the oxidation of metallic lithium (eg US patent 33 28 957). In such a system, water and lithium react with each other to form lithium hydroxide, hydrogen and steam. Elsewhere in the system, hydrogen gas generated from the reaction between lithium and water combines with oxygen to form additional steam. This steam is then used to drive a turbine or the like, thereby obtaining a source of energy generation. Lithium can additionally be used to obtain base materials. For example, reaction with nitrogen to lithium nitride followed by hydrolysis to ammonia, or carbon dioxide to lithium oxide and carbon monoxide. The solid end product of said reaction of lithium (optionally after hydrolysis, as in the case of nitrides) is an oxide or carbonate, respectively, which can then be reduced again by electrolysis to lithium metal. This establishes a cycle in which excess electricity can be generated with wind power, photovoltaics or other renewable energy sources, stored and converted back into electricity when needed, or chemical building blocks can be obtained.

Lithium is typically produced using a melt flow electrolysis process. For this process, efficiencies of about 42%-55% were produced, calculated from temperature-corrected process data without standard potential. In addition to lithium, similar metals such as sodium, potassium, magnesium, calcium, aluminum and zinc can also be used.

Particular care must be taken when burning lithium, since solid or liquid residues can be produced depending on temperature and gas. Furthermore, depending on the configuration and operation of furnaces used to burn lithium metal (eg, in liquid form) in different atmospheres and under pressure, exhaust gases and solids/liquids may be produced as combustion products. These solids and liquids must be separated from the exhaust gas as completely as possible.

Here, it is important to substantially completely separate liquid and solid combustion residues from the exhaust gas flow in order not to produce any surface deposits or blockages in downstream devices. In particular it is highly desirable to lead the exhaust gas flow directly to the gas turbine, where it must then be ensured that all particles have been completely removed from the exhaust gas flow. These particles cause long-term damage to the blades of gas turbines and lead to equipment failure.

The object of the present invention is to provide a method and a device with which a metal M selected from the group consisting of alkali metals, alkaline earth metals, Al and Zn and their alloys and mixtures can be efficiently removed from the exhaust gas when combustion gas is used. Removal of solid and/or liquid reaction products. Another object of the present invention is to provide a device with which an efficient and locally limited combustion of metal M with gas can be achieved without excessive distribution of the combustion products in the combustion chamber and thus can be more efficiently Easily separates. In addition, the object of the present invention is to be able to effectively control the combustion of the metal M and gas.

This object is achieved by using a perforated burner comprising a perforated tube as a burner during the combustion of the metal M with gas. It has been found that the combustion at the porous burner can be localized by using a porous burner where combustion products also occur. For example, in the case of atomization, the reaction products appear throughout the reactor and solid and liquid reaction products must be separated again in a complex (time-consuming and labor-intensive) manner from the gaseous reaction products; while in the case of combustion with porous burners the solid and liquid reaction products are specifically positioned near the porous burner, thereby facilitating their separation from gaseous combustion products. In this way, the entire combustion device can also be designed to be more compact and the combustion can be designed to be more gentle to the device by positioning the combustion process.

According to a first aspect, the present invention relates to a method for burning a metal M selected from the group consisting of alkali metals, alkaline earth metals, aluminum and zinc and their alloys and/or mixtures with gas, wherein by means of a porous A burner performs the combustion.

According to another aspect, the present invention relates to a plant for the combustion of a metal M selected from the group consisting of alkali metals, alkaline earth metals, aluminum and zinc and alloys and/or mixtures thereof, comprising:

- a porous burner comprising a porous tube as a burner,

- feeding means for metal M, preferably in liquid form, opening into the interior of the porous burner, which is designed to feed said porous burner with metal M, preferably in liquid form Metal M,

- a feeding device for gas, which is designed for feeding gas, and

- optionally, heating means for supplying the metal M in liquid form, designed to liquefy the metal M

Furthermore, the present invention according to another aspect relates to the use of a porous burner comprising a porous tube as a burner for the combustion of a metal M selected from the group consisting of alkali metals, alkaline earth metals, aluminum and zinc and their alloys and/or mixtures.

Further aspects of the invention can be derived from the dependent claims and the detailed description of the invention as well as the drawings.

The accompanying drawings are intended to illustrate embodiments of the present invention and provide further understanding of the present invention. In conjunction with the detailed description of the invention, they serve to illustrate the concepts and principles of the invention. Further embodiments and the many advantages mentioned are obtained with reference to the drawings.

The elements of the drawings are not necessarily shown to scale relative to each other. Unless otherwise stated, elements, features and parts that are the same, have the same function and the same effect are respectively marked with the same reference numerals in the drawings.

Fig. 1 schematically shows an exemplary arrangement of a device according to the invention.

Fig. 2 schematically shows a detail view of another exemplary arrangement of the device according to the invention.

Fig. 3 schematically shows a further detail view of a further exemplary arrangement of the device according to the invention.

FIG. 4 schematically shows an exemplary cross-section through an exemplary apparatus according to the invention in the region of the feed of the carrier gas to the reactor.

Figure 5 shows a schematic diagram of an exemplary reaction of lithium and carbon dioxide to lithium carbonate that can be carried out in accordance with the methods of the present invention.

Figure 6 shows a schematic diagram of an exemplary reaction of lithium and nitrogen to lithium nitride and other secondary products that may be carried out in accordance with the methods of the present invention.

The present invention relates in a first aspect to a method for burning a metal M selected from the group consisting of alkali metals, alkaline earth metals, aluminum and zinc and alloys and/or mixtures thereof, with gas, wherein the device for the combustion.

According to a specific embodiment, the metal M is selected from: alkali metals, preferably Li, Na, K, Rb and Cs; alkaline earth metals, preferably Mg, Ca, Sr and Ba, Al and Zn; and mixtures and/or alloys thereof . In a preferred embodiment, the metal M is selected from Li, Na, K, Mg, Ca, Al and Zn, further preferably lithium or magnesium, and the metal M is particularly preferably lithium.

Depending on the specific embodiment, gases that can react exothermicly with the metal M or mixtures and/or alloys of the metals M come into consideration as fuel gas, wherein these gases are not particularly restricted. For example, the gas may comprise air, oxygen, carbon dioxide, hydrogen, water vapour, nitrogen oxides NOx such as nitrous oxide, nitrogen, sulfur dioxide or mixtures thereof. Therefore, this method can also be used for desulfurization or NOx removal. Depending on the gas, various products can be obtained here from different metals M, which can be present as solids, liquids and even in gaseous form.

Thus, for example, the reaction of a metal M (e.g. lithium) with nitrogen can form a further metal nitride, such as lithium nitride, which can then be further reacted later to ammonia, while the reaction of a metal M (e.g. lithium) with carbon dioxide can form e.g. Metal carbonates (e.g. lithium carbonate), carbon monoxide, metal oxides (e.g. lithium oxide), or metal carbides (e.g. lithium carbide), and also mixtures thereof, of which higher values are obtainable from carbon monoxide (e.g. also Long-chain) hydrocarbon-containing products, such as methane, ethane, etc. up to gasoline, diesel oil, and methanol, etc., for example by Fischer-Tropsch (Fischer-Tropsch); Acetylene. Furthermore, it is also possible, for example, to use nitrous oxide as the fuel gas to form, for example, metal nitrides.

Other said metals may also have a similar response.

The porous burner is not particularly limited according to the present invention, as long as it comprises a porous tube as the burner, to which the metal M can be fed at at least one opening. Preferably, the metal M is fed through only one opening of the tube and the other end of the tube is closed or likewise consists of the material of the porous tube. The porous tube can be, for example, a ceramic tube made of aluminum oxide or magnesia or a porous metal tube, for example made of iron, chromium, nickel, niobium, tantalum, molybdenum, tungsten, zirconium alloys and alloys of these metals as well as steel such as stainless steel and Made of chrome-nickel steel. The porous burner is preferably constructed of a material selected from iron, chromium, nickel, niobium, tantalum, molybdenum, tungsten, zirconium alloys and alloys of these metals and steels such as stainless steel and chrome-nickel steel. Suitable materials are for example austenitic chromium-nickel steels which are very resistant to sodium attack at high temperatures, but materials with 32% nickel and 20% chromium such as AC66, Incoloy 800 or Pyrotherm G 20132 Nb also show relatively favorable corrosion characteristic. Other components of the porous burner are not further limited and may include feed means for the metal M and optionally an ignition source and the like.

According to a particular embodiment, the metal M is introduced in liquid form into the porous burner and burned by means of the porous burner, wherein gas is optionally guided to the outer surface of the porous burner and burns together with the metal M. However, according to a particular embodiment no internal mixing is performed as in conventional multi-hole burners in order to avoid clogging of the pores with solid reaction products. Thus, according to a particular embodiment, the porous burner is a porous burner without internal mixing. In the case of using a porous burner, these holes serve only to increase the surface area of the alloy L according to the specific embodiment. However, in the case of a continuous feed of alloy L of electropositive metals, the reaction with the combustion gas can take place near the surface of the porous burner at the outlet of these holes, provided it can be ensured that the resulting reaction product is subsequently transported by the alloy L can be delivered from the porous burner. However, depending on the particular embodiment, the combustion reaction takes place outside the pores of the porous burner, eg on the surface of the porous burner or even after the alloy L has been discharged from the porous burner, ie only on the surface of the discharged alloy L.

According to a particular embodiment, the metal M in liquid form is supplied to the porous burner inside the porous burner. This results in a better distribution of the metal M in the perforated burner and a more uniform discharge of the alloy from the pores of the perforated tube so that a more uniform reaction between the metal M and the combustion gas can take place. For example the diameter of the holes that can pass through the tube, the metal M used, the density of the metal M (the density can be related to the temperature of the metal M), the pressure at which the metal M is introduced into the perforated burner, the gas pressure or the gas application/feed Rate, etc. to properly control the combustion of metal M and gas. Thus, the metal M, for example lithium, is used according to a particular embodiment in liquid form, ie for example 180° C. above the melting point of lithium. The liquid metal M can here be pressed into the perforated tube, for example also by means of another gas under pressure, which is not confined. Then, the liquid metal M reaches the surface through the pores of the porous tube, and is burned with gas to obtain the corresponding reaction product.

According to a particular embodiment, the gas is directed onto the outer surface of the porous burner and burns with the metal M. Clogging of the pores of the perforated tube can thus be avoided or reduced, thereby preventing cleaning of the perforated burner or reducing wear.

The tendency of small particles to transfer into the gas/reaction chamber is reduced by the combustion of the metal M on the surface of the porous tube, so that at most larger droplets of reaction products are produced, but these droplets can be easily separated from the gaseous reaction products, Deposition on the reactor wall can be achieved, for example, by cyclones (cyclones). Here, the reactor walls can be cooled, for example, with heat exchangers, wherein these heat exchangers can also be connected to turbines and generators.

According to a particular embodiment, the combustion takes place at a temperature above the melting point of the salt formed in the reaction of the metal M and the fuel gas. In this case, the salt formed in the combustion of the metal M and the gas may have a melting point higher than that of the metal M, so that it may be necessary to feed the liquid metal M at an elevated temperature. In addition, the burning at a temperature above the melting point of the salt formed prevents the porous burner from being contaminated or covered by the salt formed, so that fouling of the porous burner, eg also the pores, can be prevented better. This enables better handling of the device and less cleaning of the device, eg even longer periods of use without cleaning. Liquid reaction products on the burner can also simply drip off. Especially in the case of these processes where the temperature is higher than the melting point of the salt formed, the materials of the burner are preferably those capable of withstanding said temperature, such as iron, chromium, nickel, niobium, tantalum, molybdenum, tungsten, zirconium Alloys and alloys of these metals, as well as stainless steel.

The combustion temperature is preferably above the melting point of the corresponding reaction product, so that the pores of the perforated burner are not blocked and the reaction product can be discharged. Furthermore, depending on the reaction product, a certain degree of mixing between the liquid metal M and the reaction product is also possible, so that the combustion takes place not only locally at the outlet of the hole opening but also in a distributed manner over the entire surface of the tube. . This can be controlled, for example, via the feed rate of the metal M.

According to a particular embodiment, the metal M is fed to the porous burner as an alloy of at least two metals M. A lowering of the melting point of the metal M and of the metal salt formed can thus be achieved, so that the process can be carried out at lower temperatures and thus in a gentler manner to the plant, and the use of highly refractory materials in the plant can be reduced or avoided. s material.

In addition, according to specific embodiments, combustion can be carried out with a certain excess gas, for example, the molar ratio of gas to metal M is 1.01:1 or greater, preferably 1.05:1 or greater, further preferably 5:1 or greater, Still further preferred is 10:1 or greater, such as even 100:1 or greater, to stabilize the exhaust gas temperature within a certain temperature range. The gas can also be used here to dissipate heat to the expander section of the turbine or the like.

In the process, it is additionally possible to separate off-gases from the solid and/or liquid reaction products during combustion of the metal M with gas, wherein, according to a specific embodiment, the gas is combusted with the metal M in a reaction step and produces off-gases as well as other solid and and/or liquid reaction products, and the waste gas is separated from the solid and/or liquid reaction products in a separation step. In this case, a carrier gas can additionally be added during the separation step and can be discharged as a mixture with the exhaust gas. Here, the carrier gas can also correspond to the exhaust gas, so that, for example, during combustion an exhaust gas corresponding to the supplied carrier gas is produced; or the carrier gas can also correspond to the combustion gas. Thus, according to a particular embodiment, these reaction products may be separated after combustion in the process of the invention.

According to the present invention, the carrier gas is not particularly limited, and may correspond to gas, but may also be different therefrom. As the carrier gas, for example, air, carbon monoxide, carbon dioxide, oxygen, methane, hydrogen, water vapor, nitrogen, nitrous oxide, a mixture of two or more of these gases, or the like can be used. Various gases, such as methane, can be used here for heat transfer and to remove the reaction heat of the reaction of the metal M with the fuel gas from the reactor. The various carrier gases can, for example, be suitably adapted to the reaction of the fuel gas and the metal M, so that a synergistic effect can be achieved here. The gas optionally used when feeding the metal M can likewise correspond to a carrier gas.

For the combustion of carbon dioxide with a metal M such as lithium, during which carbon monoxide can be formed, carbon monoxide can be used, for example, as carrier gas and optionally recirculated, ie recirculated at least partially as carrier gas after being discharged. In this case, the carrier gas is matched to the waste gas so that optionally a part of the carrier gas can be withdrawn as a useful product, for example for a subsequent Fischer-Tropsch synthesis, while the carrier gas is regenerated by combustion of carbon dioxide with metal M , so that carbon dioxide is at least partially converted to carbon monoxide overall, preferably up to 90% by volume or more, further preferably 95% by volume or more, still further preferably 99% by volume or more and particularly preferably up to 100% by volume, Based on the carbon dioxide used and taken off as a useful product. The more carbon monoxide produced, the cleaner the exported carbon monoxide.

In the case of the combustion of nitrogen with a metal M (e.g. lithium), for example nitrogen can be used as carrier gas, so that in addition to this carrier gas nitrogen unreacted nitrogen from the combustion can also be present as "exhaust gas" in the exhaust gas , whereby the desired gas separation can be carried out more simply and, depending on the specific embodiment, it may not even be necessary to burn metal M and nitrogen correspondingly, preferably quantitatively, using suitable, easily determinable parameters for gas separation. For example, ammonia can be easily removed from the nitrides formed by washing or cooling.

According to a particular embodiment, at least a portion of the exhaust gas may correspond to a carrier gas. For example, the exhaust gas may be at least 10% by volume, preferably 50% by volume or more, further preferably 60% by volume or more, still further preferably 70% by volume or more, and even more preferably 80% by volume or more The degree is equivalent to the carrier gas, based on the total volume of exhaust gas. Depending on the particular embodiment, the fuel gas may correspond to the carrier gas to an extent of 90% by volume or more, and in some cases even to an extent of 100% by volume, based on the total volume of the exhaust gas.

According to a particular embodiment, in the process according to the invention the mixture of exhaust gas and carrier gas can be fed at least partly again to the separation step as carrier gas and/or to the combustion step as fuel gas. The recirculation of the mixture of exhaust gas and carrier gas can be, for example, at 10% by volume or more, preferably 50% by volume or more, further preferably 60% by volume or more, still further preferably 70% by volume or more, even More preferably this is done to an extent of 80% by volume or more, based on the total volume of carrier gas and exhaust gas. According to a particular embodiment, the recirculation of the mixture of exhaust gas and carrier gas can be carried out to an extent of 90% by volume or more, based on the total volume of carrier gas and exhaust gas. According to a preferred embodiment of the present invention, the reaction between the gas and the metal M can be carried out in such a way that the carrier gas is formed as an exhaust gas, for example using carbon dioxide as the fuel gas and carbon monoxide as the carrier gas, so that the mixture of the carrier gas and the exhaust gas is substantially, preferably at 90% by volume or more, more preferably 95% by volume or more, still more preferably 99% by volume or more, particularly preferably 100% by volume Carrier gas composition, based on a mixture of exhaust and carrier gas. Here, the carrier gas can then be circulated continuously and withdrawn in an amount regenerated by the combustion of the metal M and the gas. In contrast to a pure cycle of carrier gas, in which a separation of carrier gas and exhaust gas is optionally carried out, useful products such as carbon monoxide can be obtained here, which can be withdrawn continuously.

According to a particular embodiment, the separation step in the process of the invention is carried out in a cyclone separator or a cyclone reactor. The cyclone reactor here is not particularly limited in its configuration, and may have, for example, a form that conventional cyclone reactors have.

For example, a cyclone reactor can include:

A reaction zone to which feed devices for fuel gas, metal M and carrier gas (which optionally can also be combined beforehand and then fed together into the reaction zone) can be connected, for example in a rotationally symmetrical the form of the upper part,

The separating area is, for example, configured as a cone,

and a pressure relief chamber, to which a discharge device for solid and/or liquid reaction products obtained by combustion of metal M with gas can be connected, for example in the form of a rotary vane feeder; and for waste gas and carrier gas The unloading device of the mixture obtained after the combustion of the metal M in the combustion gas after mixing the two gases.

These plant elements are usually present, for example, in cyclones. However, the cyclone reactor used according to the invention can also have a different configuration and optionally can also comprise further zones. For example, various zones (eg, reaction zone, separation zone, plenum chamber) may also be combined in one section of an exemplary cyclone reactor and/or extend across multiple sections of the cyclone reactor. Here, for example, the addition of carrier gas can also take place in regions in which the reaction of metal M and fuel gas is ongoing or has even ended.

The reaction product is kept substantially in the center of the reactor, such as a furnace chamber, by the cyclone. And since the exhaust gas does not contain solid or liquid particles due to the combustion at the surface of the perforated tube, which does not generate small particles as in the case of atomization, it is also possible to connect a gas turbine or expansion turbine downstream in the exhaust gas flow. Utilizing this combustion concept in these cases makes it possible to introduce the exhaust gas stream directly into the gas turbine after combustion of the metal M and separation of the reaction products.

According to a particular embodiment, the exhaust gas temperature can be controlled by means of a gas excess during the various combustion processes so that it is above the melting temperature of the reaction product or its mixture.

According to a specific embodiment, the cyclone reactor also comprises a grid through which solid and/or liquid reaction products can be conducted off during the combustion of the metal M with the gas. Such a grid additionally prevents subsequent swirling of solid and/or liquid reaction products in the cyclone reactor.

The reaction products of the combustion can be used to generate energy, preferably by using at least one expansion turbine and/or at least one gas turbine, such as a steam turbine, and/or at least one heat exchanger and/or at least one boiler, wherein according to a particular embodiment, here It is possible to utilize both solid and/or liquid reaction products formed, for example using heat exchangers at the reactor, and also gaseous reaction products.

Depending on the specific embodiment, when using a cyclone reactor with a carrier gas supply, the mixture of exhaust gas and carrier gas can be used for heating, for example, in the reactor and/or during and/or after discharge from the reactor Boilers or for heat transfer in heat exchangers or turbines such as gas turbines or expansion turbines.

Furthermore, the mixture of carrier gas and exhaust gas may be at elevated pressure after combustion, eg greater than 1 bar, at least 2 bar, at least 5 bar or at least 20 bar, depending on the particular embodiment.

Furthermore, according to another aspect of the present invention, there is disclosed an apparatus for burning a metal M selected from the group consisting of alkali metals, alkaline earth metals, aluminum and zinc and alloys and/or mixtures thereof, comprising:

- a porous burner comprising a porous tube as a burner,

- feeding means for metal M, preferably in liquid form, opening into the interior of the porous burner, which is designed for feeding metal M, preferably in liquid form, to said porous burner Metal M,

- a feeding device for gas, which is designed for feeding gas, and

- Optionally, heating means for supplying the metal M in liquid form, designed to liquefy the metal M.

Here, the porous burner can be configured as described above. The feed device for the metal M can be, for example, a heatable pipe or hose or a conveyor belt, which can be suitably determined, for example depending on the state of aggregation of the metal M. Optionally, a further feed device for the gas can also be connected to the feed device for the metal M, which feed device optionally has a control unit, such as a valve, with which the The feed of metal M is adjusted. Likewise, the feed means for the gas can be configured as pipes or hoses etc., which can optionally be heated, wherein the feed means can suitably be determined according to the state of the gas, which optionally can also be under pressure Down. It is also possible to provide several feeding devices for metal M or gas.

According to a specific embodiment, the feed device for the gas is arranged in such a way that it guides the gas at least partially and preferably completely to the surface of the perforated burner. An improved reaction between the metal M and the gas is thereby achieved.

Furthermore, according to a preferred embodiment, the porous burner is arranged such that the reaction products of the combustion and optionally unreacted metal M can be separated from the surface of the porous burner by gravity, for example by having the porous burner pointing vertically, towards the ground installed in the reactor. With the perforated combustion tubes arranged vertically in the furnace chamber, the resulting liquid reaction products can flow out of the tubes and drip down into the furnace floor. In this way, possibly dissolved metal M, such as lithium, which was previously unreacted on the porous burner, is also burned and the heat of reaction is transferred to the flowing combustion gas and carrier gas.

According to a particular embodiment, the porous burner consists of a material selected from iron, chromium, nickel, niobium, tantalum, molybdenum, tungsten, zirconium and alloys of these metals and steels such as stainless steel and chrome-nickel steel. These materials are preferably used for applications at relatively high temperatures, in which the reaction with the liquid metal M and optionally with the resulting liquid metal salt can be carried out in a simpler manner.

In a particular embodiment, the plant according to the invention can also have a separation device for the combustion products of metal M, which is designed to separate the metal M from the combustion products of the gas, wherein the separation device is preferably a cyclone reactor .

Separation means may be used here to separate exhaust gases when metal M is combusted with gas and may include:

- a reactor in which a porous burner is provided and a feeding device for the metal M is installed or arranged and gas is fed into the reactor, i.e. the feeding device for the gas is connected to or arranged in the reactor;

- feeding device for carrier gas, which is designed for feeding carrier gas to the reactor;

- a discharge device for the mixture of waste gas and carrier gas, which is designed to lead off the mixture of metal M and the waste gas and carrier gas obtained by combustion of the combustion gas; and

- a discharge device for the solid and/or liquid reaction products obtained from the combustion of the metal M with the gas, designed to discharge the solid and/or liquid reaction products obtained from the combustion of the metal M with the gas.

The feeding means for the carrier gas is also not particularly limited and includes, for example, pipes, hoses, etc., wherein the feeding means for the carrier gas can be appropriately determined according to the state of the carrier gas, which optionally can be under pressure .

The reactor is also not particularly limited as long as combustion of gas and metal M can be performed therein. According to a particular embodiment, the reactor may be a cyclone reactor as shown exemplarily in FIG. 1 and in another embodiment in detail in FIG. 2 .

According to a specific embodiment, the cyclone reactor may comprise:

a reaction zone, to which feed devices and porous burners for gas, metal M and carrier gas can be connected, for example in the form of a rotationally symmetrical upper part,

The separating area is, for example, configured as a cone,

and a pressure relief chamber, which can be connected to a discharge device for the solid and/or liquid reaction product obtained by the combustion of metal M and gas, such as a discharge device in the form of a rotary vane feeder, and for Discharging device for the mixture of exhaust gas and carrier gas obtained after the combustion of metal M in fuel gas after mixing the two gases.

These plant elements are usually present, for example, in cyclones. However, the cyclone reactor used according to the invention can also have a different configuration and optionally can also comprise further zones. For example, various zones (eg, reaction zone, separation zone, plenum chamber) may also be combined in one section of an exemplary cyclone reactor and/or extend across multiple sections of the cyclone reactor.

An exemplary cyclone reactor is shown in FIG. 1 . The cyclone reactor 6 shown in FIG. 1 comprises a reaction zone 20a, a separation zone 20b and a pressure relief chamber 20c, the separation zone 20b being both in the upper part 6a with the reaction zone 20a and in the lower part 6b with the pressure relief chamber 20c. Connected to the cyclone reactor in the upper part is a feed 1 for the gas (e.g. in the form of an optionally heated pipe or hose) and a feed 2 for the metal M (e.g. in the form of an optionally heated in the form of a heated tube or hose), in which the feeding of the metal M to the perforated burner 3 takes place. According to FIG. 1, the feeding of metal M is effected by means of a feeding device 2' for gas, such as a gas in a pipe or hose, the feeding of which can be controlled with a valve 2". The metal M and the gas are fed to the reaction zone 20a. Through the feed device 4, the carrier gas is fed to the zone 4' for gas distribution, and from said zone 4' the carrier gas is fed to the separation zone 20b through the nozzle 5, through which the Cyclone. A detail view of such a feed device 4 with a region 4' for gas distribution and nozzles 5 is shown exemplarily in cross-section in FIG. 4 (illustration without porous burner 3), but also There may be a plurality of nozzles, for example at suitable intervals around the inner wall of the region 4', in order to generate suitable cyclones. The solid and/or liquid reaction products obtained by the combustion of the metal M with the combustion gas 7 are removed from the The solid and/or liquid reaction products are discharged from the lower part 6 b including the relief chamber 20 c , while the mixture of exhaust gas and carrier gas is discharged via a discharge device 8 for the mixture of exhaust gas and carrier gas.

Optionally, ignition means, such as electrical ignition means or a plasma arc, may be required in the apparatus of the invention, where this depends on: the type and state of the metal M, such as its temperature and/or state of aggregation; gas properties, such as its pressure and/or temperature; and the arrangement of components in the equipment, such as the type and performance of the feeding device.

To be configured to achieve high exhaust gas temperatures (eg, greater than 200°C, eg, even 600°C or higher, and in certain embodiments 700°C or higher), and high (eg, 5 bar or higher) or high (20 bar or higher) operating pressure, the internal material of the reactor can consist of high heat-resistant alloys, for example of the alloys mentioned above and in extreme cases even of the material Haynes 214. Thermal insulation can then be arranged around this material (which is only supposed to withstand high temperatures), which allows sufficiently little heat to pass through that the outer steel wall (which can additionally be cooled with air or water) absorbs the pressure load. The off-gas can then be fed to further process steps with elevated or high operating pressure.

Furthermore, reactors, such as cyclone reactors, may also comprise heating and/or cooling devices, which are present in the reaction zone, separation zone and/or decompression chamber, and also in various feeding and/or discharging devices , optionally in a burner, and/or optionally in an ignition device. Furthermore, other components may be present in the device of the invention, such as pumps for generating pressure or vacuum, etc.

In those embodiments in which the reactor takes the form of a cyclone reactor, the cyclone reactor may comprise a grid designed such that solid and/or liquid reaction products may be conducted through the grid when the metal M is combusted with the gas. Furthermore, such grids can also be present in other reactors which can be arranged in the apparatus of the invention. The use of grids in the reactor or cyclone reactor allows for a better separation of the solid and/or liquid reaction products obtained when the metal M is combusted with the fuel gas from the mixture of waste gas and carrier gas. Such a grid is shown schematically in FIG. 2 , where the grid 6 ′ is shown as an example in the lower part 6 b of the cyclone reactor 6 shown in FIG. 1 above the discharge device 7 and below the discharge device 8 . Reliable deposition of solid and liquid reaction products or mixtures thereof is ensured by means of the grid, which is preferably spaced at a sufficiently large distance from the reactor wall. As a result, already deposited solid or liquid combustion products are no longer swirled up by the cyclone.

The geometry of the feeding device for the carrier gas is not particularly limited as long as the carrier gas can be mixed with the exhaust gas obtained from the combustion of the metal M and the gas. A cyclone is preferably formed here, for example using the device shown in FIG. 1 . However, cyclones can also be generated by other arrangements of the feed devices relative to one another. It is thus also possible, for example, that the feed for the carrier gas can also be located above the reactor in the vicinity of the feed for the metal M and the fuel. A correspondingly suitable injector geometry can easily be determined in a suitable manner, for example by means of a flow simulation.

The unloading device is also not particularly limited, wherein, for example, the unloading device for the mixture of exhaust gas and carrier gas can be configured as a pipe, while the unloading device for the solid and/or liquid reaction product obtained by combustion of the metal M with the gas is for example Can be configured as a rotary vane feeder and/or as a tube with siphon. Various valves can also be provided here, such as pressure valves and/or other regulators. The exemplary discharge device 7 shown in FIG. 3 , such as the discharge device 7 of the cyclone reactor 6 shown in FIG. 1 , may here comprise a siphon 9 , a valve 10 for degassing and a pressure regulator 11 , however It is not limited to this. In order to achieve elevated or high operating pressures, such a siphon on the unloader for the solid and/or liquid reaction products obtained by the combustion of metal M with gas can be used, optionally with a suitable combined with a pressure regulator for operating pressure.

According to a specific embodiment, the discharge device for the mixture of exhaust gas and carrier gas may also comprise a separation device for exhaust gas and carrier gas and/or the individual components of the exhaust gas.

According to a specific embodiment, the discharge device for the mixture of exhaust gas and carrier gas can be connected to the feed device for carrier gas and/or the feed device for fuel gas in such a way that the mixture of exhaust gas and carrier gas is at least partially It is fed to the reactor as carrier gas and/or to the burner as fuel gas. The proportion of recovered gas may here be 10% by volume or more, preferably 50% by volume or more, further preferably 60% by volume or more, still further preferably 70% by volume or more, and even more preferably 80% by volume or more, based on the total volume of carrier gas and exhaust gas. According to a particular embodiment, the recovery of the mixture of exhaust gas and carrier gas can be performed to an extent of 90% by volume or more, based on the total volume of carrier gas and exhaust gas.

According to a particular embodiment, the plant of the invention additionally comprises at least one boiler and/or at least one heat exchanger and/or at least one gas turbine and/or at least one expansion turbine in the reactor and/or for the waste gas and the carrier In the discharge device of the gas mixture. Thus, for example, in the plant of FIG. 1 comprising the cyclone reactor 6, one or more heat exchangers and /or a boiler and/or a gas turbine and/or an expansion turbine (not shown). The heat exchange can also take place automatically on the cyclone reactor 6, for example on the outer walls in the reaction zone 20a and/or the separation zone 20b, but optionally also in the area of the pressure relief chamber 20c, where the corresponding heat exchange The generator can also be connected to the turbine used to generate electricity in the generator.

The exhaust gas can thus be supplied as a mixture with a carrier gas to another application, such as heating a boiler to generate steam, releasing heat in a heat exchanger, running a turbine, etc.

If no suitable heat exchanger can be found, by means of which, for example, air with a corresponding pressure is heated and introduced into the gas turbine as an exhaust gas replacement, a boiler can be used, for example. Depending on the particular embodiment, the approach of using a boiler may be promising and also technically simpler, since this approach can be realized at lower temperatures and only elevated pressures.

Electricity can then be generated by means of one or more heat exchangers and/or one or more boilers, for example by using steam turbines and generators. It is also possible, however, to conduct the mixture of exhaust gas and carrier gas directly to a turbine, such as a gas turbine or an expansion turbine, for direct power generation. However, this presupposes a good separation of the metal M and the solid and/or liquid reaction products resulting from the combustion of the gas, as can be provided according to the invention, especially when gratings are used in the reactor. The choice of whether to use a boiler or a heat exchanger may depend, for example, on the formation of solid or liquid reaction products, but may also be determined by plant technology. _In the case of liquid reaction products, such as liquid _Li2CO3 , the reactor walls can be used, for example, as heat exchangers, whereas in the case of solid reaction products, special heat exchangers may be required. In the case of a corresponding separation of the mixture of exhaust gas and carrier gas from the solid and/or liquid reaction products, the mixture of exhaust gas and carrier gas can optionally also be conducted directly to the turbine, so that heat in the exhaust gas flow can also be unnecessary here. exchangers and/or boilers.

According to a specific embodiment, the device of the invention may comprise an extraction device in the discharge device for the mixture of exhaust gas and carrier gas, which extraction device is designed for the discharge of the mixture of exhaust gas and carrier gas through the connection Device with feeding device for carrier gas and/or feeding device for fuel gas, when recycling the mixture of waste gas and carrier gas to the feeding device for carrier gas and/or feeding device for fuel gas Extract part of the mixture of exhaust gas and carrier gas. This fraction can for example be more than 1% by volume, preferably 5% by volume and higher, further preferably 10% by volume or more, based on the total volume of the mixture of exhaust gas and carrier gas. In addition, depending on the particular embodiment, up to 50% by volume, preferably 40% by volume or less, further preferably 30% by volume or less, particularly preferably 20% by volume or more, may be extracted from the mixture of recovered waste gas and carrier gas Less, based on the total volume of the mixture of exhaust and carrier gases. The extracted gas can then be used, for example, as a useful product for other reactions, thus for example when carbon monoxide is vented and subsequently converted into high-value hydrocarbons in a Fischer-Tropsch process.

The exported solid can be further converted into useful products. Thus, for example, metal nitrides, which can be produced from combustion with nitrogen, are converted by hydrolysis with water into ammonia and bases, the bases formed which can then be used as carbon dioxide and/or sulfur dioxide traps.

According to another aspect, the invention also relates to the use of a porous burner comprising a porous tube as burner for the combustion of a metal M selected from the group consisting of alkali metals, alkaline earth metals, aluminum and zinc and their alloys and/or mixtures.

The above-described embodiments, configurations and developments can be combined with one another in any desired manner, if appropriate. Further possible configurations, developments and embodiments of the invention also include combinations of features of the invention described above or below with reference to the exemplary embodiments which are not explicitly mentioned. In particular, those skilled in the art will also add various aspects as improvements or supplements to the corresponding basic form of the invention.

The invention is now illustrated with reference to exemplary embodiments, which do not limit the invention in any way.

According to an exemplary embodiment, the metal M, such as lithium, is used in liquid form, ie above the melting point of lithium of 180°C. Liquid metal M, such as lithium, can be introduced into the porous burner and then reacted directly, optionally after ignition for starting the reaction, with the corresponding gas, such as air, oxygen, carbon dioxide, sulfur dioxide, Hydrogen, water vapour, nitrogen oxides NOx such as nitrous oxide or nitrogen. Combustion of a metal M (for example lithium) can be carried out in the plant shown in FIG. 1 , for example with a gas quantity greater than stoichiometric, in order to prevent excessively high exhaust gas temperatures. However, the gas can also be added in a stoichiometric or non-stoichiometric amount relative to the metal M. After combustion, a carrier gas (eg nitrogen, air, carbon monoxide, carbon dioxide and ammonia) which can also be equivalent to fuel gas is added for dilution in order to lower the temperature and create a cyclone for depositing solid or liquid reaction products. The hot exhaust gas stream can then be used to heat boilers, for heat transfer in heat exchangers, and the like.

According to a second exemplary embodiment, carbon dioxide may be used as a fuel gas and carbon monoxide as a carrier gas in the apparatus shown in FIG. 1 . The metal M used is, for example, lithium, for example in liquid form, ie above a melting point of 180°C. Liquid lithium is introduced into the porous burner 3 and reacts directly with the gas. It may be the case that electric ignition or an additional pilot burner is required.

The reaction proceeds according to the following formula:

2Li+2CO ₂ →Li ₂ CO ₃ +CO

Combustion of the metal M is carried out at the porous burner 3, preferably with the stoichiometrically required amount of carbon dioxide, wherein a slightly higher or lower stoichiometric ratio (CO ₂ :alloy L ratio of e.g. 0.95:1 to 1:0.95). Using very high carbon dioxide deficiencies, for example, lithium carbonate can be produced, from which acetylene can be obtained.

In a second step, in the middle part of the reactor/furnace 6 in zone 4 ′, the combustion products are mixed with the carrier gas carbon monoxide blown into the reactor 6 through the nozzle 5 . This produces a cyclone, the effect of which is that solid and/or liquid reaction products swirl around and are mainly deposited at the reactor wall. Preferably, an excess of carrier gas is used in order to ensure that the heat generated by the combustion is adequately dissipated. The temperature in the reactor 6 can thereby be appropriately adjusted.

For combustion in pure carbon dioxide, the lithium carbonate formed in the case of the eutectic mixture has a melting point of 723°C. Liquid reaction products are contemplated for combustion if the combustion temperature of the reaction products is maintained above at least 723°C by mixing carrier gas and/or fuel gas from the feed means 1,5. The feed device can be used here for cooling in strongly exothermic reactions, whereby the plant is not overheated, the lower limit of the temperature being the melting point of the salt formed (here lithium carbonate). If the cyclone is additionally operated with a gas other than carbon dioxide, such as air or nitrogen or other gases, lithium oxide (melting point Mp 1570° C.) or lithium nitride (Mp 813° C.), for example, can also form in the reaction product. After deposition of liquid and solid reaction products, which deposition can be improved by means of a grid 6', the mixture of exhaust gas and carrier gas is led, for example, into a boiler and used to evaporate water in order to then drive a motor with a downstream connected generator. Steam turbines or for operating other technical devices (eg heat exchangers). The mixture of exhaust gas and carrier gas cooled after the process can then be used again as carrier gas for forming cyclones in the furnace, for example. Therefore, the waste heat of the exhaust gas is used in the boiler after the evaporation process, and only the stoichiometric amount of CO2 required for combustion with Li is obtained by, for example, exhaust gas cleaning of coal-fired power plants.

Table 1 shows the relationship between the exhaust gas temperature and the stoichiometric excess for the combustion of lithium in pure carbon dioxide, the calculation being performed using a temperature-independent specific heat.

Table 1: Furnace operation with carbon dioxide as fuel gas and as carrier gas

According to a specific embodiment, the combustion can be carried out with a certain excess gas, for example, the molar ratio of gas to metal M is greater than 1.01:1, preferably greater than 1.05:1, more preferably 5:1 or higher, even more preferably 10:1 or higher, such as even 100:1 or higher, to stabilize the exhaust gas temperature within a specific temperature range, and in addition to adding gas and metal M such as lithium to flow into the nozzle array, additional gas or Carrier gas to absorb heat, as shown in Figure 1 and Figure 4. Depending on the specific embodiment, the exhaust gas temperature can be controlled by excess gas in different combustion processes so that it can be higher than the melting temperature of the reaction products or their mixtures (Table 1).

Carbon monoxide can be enriched in the exhaust gas by recirculation of the exhaust gas cooled by the downstream process steps. Here, depending on the specific embodiment, a certain proportion of the exhaust gas can be extracted and a gas mixture of carbon monoxide and carbon dioxide is thus obtained which has a significantly higher proportion of carbon monoxide, as indicated in Table 1. Carbon monoxide can be purified from carbon dioxide by downstream gas separation and the carbon dioxide can be used further in the cycle or in the burner.

In the furnace, the combustion temperature can again be lowered by the recovery of the product gas CO. Gas temperatures of more than 3000 K can be reached with stoichiometric combustion, which poses material problems. The reduction in combustion temperature can also be achieved by an excess of _CO2 . However, this excess must be about 16 times higher than the stoichiometric amount, so that the product gas CO is greatly diluted in the excess _CO2 (concentration is only about 6 vol%). Depending on the specific embodiment, it therefore makes sense to recycle a portion of the product gas CO into the burner and use it as a thermal ballast for temperature reduction. It is preferred here to regulate a specific reaction temperature by recovering a constant amount of a mixture of exhaust gas and carrier gas as carrier gas. In this case no CO/CO ₂ mixtures are formed which have to be separated with great effort. The product gas consists mostly of CO and has only minor impurities due to _CO2 . Most of the CO is fed into the cycle under static conditions and exactly as much CO is exported from the cycle as is subsequently produced by the reaction of _CO2 with Li (and generally also with electropositive metal alloys). Such a cycle can be obtained, for example, when CO is used as carrier gas in a proportion of 90% by volume or more, based on a mixture of exhaust gas and carrier gas. A suitable amount of carbon dioxide can thus be continuously fed into the combustion process, whereas a corresponding amount of carbon monoxide can be continuously withdrawn from the cycle as a useful product.

The corresponding reaction scheme is also shown exemplarily in FIG. 5 . In _CO2 removal 101, carbon dioxide is removed from exhaust gas 100, for example from a combustion power plant such as a coal-fired power plant, and then in step 102 the carbon dioxide is combusted with the alloy, using CO as a carrier gas. This forms Li ₂ CO ₃ 103 and, optionally after separation 104 , the mixture of exhaust gas and carrier gas comprising CO ₂ and CO can be led through boiler 105 , by means of which steam turbine 106 and thus generator 107 are operated. The waste gas is recovered 108 as a carrier gas, wherein CO can be vented in step 109 .

According to a third exemplary embodiment, nitrogen gas may be used as a fuel gas and a carrier gas in the apparatus shown in FIG. 1 . The metal used is, for example, lithium, for example in liquid form, ie above a melting point of 180°C. Liquid lithium can be fed to the porous burner 3 and then directly reacted with the gas. Electric ignition or additional pilot burners may be required.

Combustion of lithium takes place in the porous burner 3 with the stoichiometrically required amount of nitrogen, where a slightly over or under stoichiometric ratio can also be selected (e.g. _N2 :Li ratio of 0.95:1 to 1:0.95 ).

Here, the reaction is as follows:

6Li+N ₂ →2Li ₃ N

In a second step, in the middle part of the reactor 6 , the combustion products are mixed with a carrier gas, such as nitrogen, which is blown into the reactor 6 through the nozzle 5 . This creates a cyclone, which causes the solid and liquid reaction products to swirl around the reactor wall and mainly deposit there. For combustion in pure nitrogen, the resulting lithium nitride has a melting point of 813°C. If the combustion temperature of the reaction products is maintained above at least 813° C. by mixing carrier gas and/or fuel gas from the feed means 1 , 5 , liquid reaction products are expected to be combusted. Here, the feed device can be used for cooling during strongly exothermic reactions, whereby the apparatus is not overheated, where the lower limit of temperature can be the melting point of the salt formed (here lithium nitride). Lithium oxide (Mp 1570° C.) or lithium carbonate (Mp 723° C.) may also be formed in the reaction product if the cyclone is operated with a gas other than nitrogen, such as air or carbon dioxide or other gases. After deposition of liquid and/or solid reaction products (which deposition can be improved by means of a grid 6'), the exhaust gas is for example directed into a boiler and used to evaporate water in order to subsequently drive a turbine with a downstream connected generator or to operate other Technical installations (eg heat exchangers). The exhaust gas cooled after this process can then be used again, for example, to generate cyclones in the reactor 6 . The residual heat of the exhaust gas after the evaporation process in the boiler is thus utilized and only the stoichiometric amount of nitrogen required for combustion is obtained, for example by air splitting.

Table 2 shows the relationship between the exhaust gas temperature and the stoichiometric excess for the combustion of lithium in pure nitrogen, the calculation being performed using a temperature-independent specific heat.

Table 2: Furnace operation with nitrogen as fuel gas and as carrier gas

temperature in exhaust gas Gas excess as factor, based on gas quality 1600℃ 5.6 1400°C 8.5 1200℃ 10.2 1000℃ 13.3 800℃ 16.1 600°C 18.5

According to a specific embodiment, the combustion can be carried out with a certain excess gas, for example, the molar ratio of gas to metal M is greater than 1.01:1, preferably greater than 1.05:1, more preferably 5:1 or greater, even more preferably 10:1 or higher, such as even 100:1 or greater, in order to stabilize the exhaust gas temperature within a specific temperature range, and in addition to adding gas and metal M such as lithium to flow into the nozzle array, additional gas or Carrier gas to absorb heat, as shown in Figure 1 and Figure 4. Depending on the specific embodiment, the exhaust gas temperature can be controlled by gas excess in different combustion processes so that it can be higher than the melting temperature of the reaction products or their mixtures (Table 2).

The corresponding reaction scheme is schematically shown in FIG. 6 . Nitrogen is separated from air 200 in air splitting 201 and then combusted together with lithium in step 202 , using, for example, nitrogen also from air splitting 201 as carrier gas. This forms Li ₂ N ₃ 203 , and the mixture of exhaust gas and carrier gas including N ₂ 204 can be led through a boiler 205 by means of which a steam turbine 206 and thus a generator 207 is operated. The waste gas is recovered 208 as a carrier gas. Ammonia 210 can be obtained from nitride salt mixture 203 by hydrolysis 209 , wherein hydroxide 211 is formed, which can react with carbon dioxide to give lithium carbonate 212 .

According to a fourth exemplary embodiment, it is possible, for example in the case of using air as fuel gas, to use two reactors connected in series, for example two cyclone reactors, wherein in the first cyclone reactor a metal M such as Lithium and oxygen from the air produce metal oxides such as _Li2O , the waste gas mainly consists of nitrogen, which can then be used as fuel gas in the second cyclone reactor to react with metal M such as Li to obtain metal nitrides such as _Li3N . Nitrogen, for example, can be used here as a carrier gas, which can also be obtained from the first off-gas or can be the first off-gas itself (for example when it is in circulation).

Through the configuration of the device according to the invention, in particular through the use of porous combustion tubes, solid or liquid reaction products or mixtures thereof can be separated in a simple manner from the exhaust gases formed and the exhaust gases can then be fed to e.g. gas turbines or expander turbines, heat exchanger, or boiler. In addition, in this way the entire combustion system can be constructed more compactly, and the combustion process can be configured more gently for the installation due to the positioning of the combustion process.

Furthermore, the device, eg a reactor like a furnace, can be operated at elevated operating pressure and thus the combustion and deposition processes can be matched to the corresponding conditions of the subsequent steps. In a particular embodiment, the possibility of distinguishing (dividing) the combustion gas and the carrier gas used to form the cyclone makes it possible to recover the exhaust gas after releasing the heat. Cycling can be easily achieved with this configuration. Gas mixtures are also available as fuel and carrier gases. Energy and material can be saved by recycling exhaust gases after process steps.

Claims (15)

1. A method of burning a metal M selected from the group consisting of alkali metals, alkaline earth metals, aluminum and zinc and their alloys and/or mixtures with gas, wherein the combustion takes place by means of a porous burner comprising a porous tube as burner. 2. The method according to claim 1, wherein the porous burner is fed with the metal M in liquid form inside the porous burner. 3. A method according to claim 1 or 2, wherein the gas is directed on the outer surface of a porous burner and burns with the metal M. 4. The method according to one of the preceding claims, wherein the combustion takes place at a temperature above the melting point of the salt formed when the metal M and the gas react. 5. The method as claimed in one of the preceding claims, wherein the metal M is fed as an alloy of at least two metals M. 6. The method as claimed in one of the preceding claims, wherein the reaction products are separated after combustion. 7. The method according to claim 6, wherein said separation is effected by means of a cyclone. 8. The method according to one of the preceding claims, wherein the reaction products of the combustion are used to generate energy, preferably using at least one expansion turbine and/or at least one steam turbine and/or at least one heat exchanger and/or In the case of at least one boiler. 9. A plant for burning metal M, wherein said metal M is selected from the group consisting of alkali metals, alkaline earth metals, aluminum and zinc and alloys and/or mixtures thereof, comprising: - a porous burner comprising a porous tube as a burner, - feeding means for metal M, preferably in liquid form, opening into the interior of the porous burner, which is designed for feeding metal M, preferably in liquid form, to said porous burner Metal M, - a feeding device for gas, which is designed for feeding gas, and - Optionally, heating means for supplying the metal M in liquid form, designed to liquefy the metal M. 10. Apparatus according to claim 9, wherein the feed means for the gas is arranged such that it directs the gas at least partially to the surface of the perforated burner. 11. Apparatus according to claim 9 or 10, wherein the porous burner is arranged such that reaction products of combustion and optionally metal M can be separated from the surface of the porous burner by gravity. 12. Apparatus according to any one of claims 9 to 11, wherein said porous burner is constructed of a material selected from the group consisting of iron, chromium, nickel, niobium, tantalum, molybdenum, tungsten, zirconium and the metals A group consisting of alloys and steels such as stainless steel and chrome-nickel steel. 13. Apparatus according to any one of claims 9 to 12, further comprising a separation device for combustion products of metal M, which is designed to separate metal M from combustion products of gas, wherein said separation device is preferably cyclone reactor. 14. The plant according to one of claims 9 to 13, further comprising at least one expansion turbine and/or at least one steam turbine and/or at least one heat exchanger and/or at least one boiler. 15. Use of a porous burner comprising a porous tube as burner for burning a metal M selected from alkali metals, alkaline earth metals, aluminum and zinc and alloys and/or mixtures thereof with gas.