US20170089569A1

US20170089569A1 - Method For The Combustion Of An Alloy Of An Electropositive Metal

Info

Publication number: US20170089569A1
Application number: US15/311,229
Authority: US
Inventors: Helmut Eckert; Renate Elena Kellermann; Guenter Schmid; Dan Taroata
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2014-05-20
Filing date: 2015-05-04
Publication date: 2017-03-30
Also published as: CN107046808A; KR20180095137A; EP3146265A1; WO2015176944A1; DE102014209527A1; KR20170007453A; RU2656217C1

Abstract

A method is provided for the combustion of an alloy of an electropositive metal using a fuel gas, wherein the electropositive metal may be selected from alkaline-, alkaline earth metals, aluminium and zinc, as well as mixtures thereof, and the alloy of the electropositive metal may inlcude at least two electropositive metals. According to the method, the alloy of the electropositive metal is combusted using the fuel gas.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National Stage Application of International Application No. PCT/EP2015/059728 filed May 4, 2015, which designates the United States of America, and claims priority to DE Application No. 10 2014 209 527.1 filed May 20, 2014, the contents of which are hereby incorporated by reference in their entirety.

TECHNICAL FIELD

The present invention relates to a process for combusting an alloy of an electropositive metal, wherein the electropositive metal is selected from alkali metals, alkaline earth metals, aluminum and zinc, and mixtures thereof, with a fuel gas, wherein the alloy of the electropositive metal comprises at least two electropositive metals, in which the alloy of the electropositive metal is combusted with the fuel gas, and to an apparatus for conducting the process.

BACKGROUND

Fossil fuels deliver tens of thousands of terawatt hours of electrical, thermal and mechanical energy per year. However, the end product of the combustion, carbon dioxide (CO₂), is increasingly becoming an environmental and climatic problem.
Over the years, a multitude of energy generation units which work with heat generated in the oxidation of metallic lithium have been proposed (e.g. U.S. Pat. No. 3,328,957). In such a system, water and lithium are reacted with one another to produce lithium hydroxide, hydrogen and steam. Elsewhere in the system, the hydrogen produced by the reaction between lithium and water is combined with oxygen to form additional steam. The steam is then used to drive a turbine or the like, and so an energy generation source is obtained. Lithium can also be used additionally to obtain commodity materials. Examples are the reaction with nitrogen to give lithium nitride and subsequent hydrolysis to give ammonia or with carbon dioxide to give lithium oxide and carbon monoxide. The solid final end product of the reaction of lithium in each case, optionally after hydrolysis, as in the case of nitride, is the oxide or carbonate, which can then be reduced again by means of electrolysis to lithium metal. This establishes a circuit in which, by means of wind power, photovoltaics or other renewable energy sources, surplus power can be produced, stored and converted back to power at the desired time, or else chemical commodity materials can be obtained.
How a complete energy circuit can be formed with electropositive metals is indicated in DE 10 2008 031 437 A1 and DE 10 2010 041033 A1. Specifically lithium serves as a case study here, both as an energy carrier and as an energy storage means, and it is also possible to use other electropositive metals such as sodium, potassium or magnesium, calcium, barium or aluminum and zinc.
Since solid or liquid residues can arise in the combustion of lithium, according to the temperature and fuel gas, particular attention should be paid to these. Moreover, according to the construction and operation of an oven for the combustion of lithium metal (for example in liquid form) in different atmospheres and under pressure, offgases and solids/liquids can arise as combustion products. These solid and liquid substances have to be very substantially separated from the offgases.
Substantially complete separation of liquid and solid combustion residues from the offgas stream is important in order not to generate any surface deposits or blockages in the downstream apparatuses. More particularly, it is very demanding to guide the offgas stream directly to a gas turbine, since it has to be ensured in that case that all particles have been completely removed from the offgas stream. Such particles cause long-term damage to the gas turbine blades and lead to failure of the plant.
Moreover, DE 10 2014 203039.0 describes the use of alkali metals as energy storage means and utilization thereof in power plant operation, and DE 10 2014 203039.0 a construction—cyclone burner—for combustion of lithium in CO₂- or N₂-containing atmospheres and simultaneous separation of the solid and gaseous reaction products by means of the cyclone.
A problem here is the high temperatures in the combustion of the electropositive metal and the exothermicity of the reaction, which lead to high demands on the combustion apparatus and the control of the reaction.

SUMMARY

One embodiment provides a process for combusting an alloy of an electropositive metal, wherein the electropositive metal is selected from alkali metals, alkaline earth metals, aluminum and zinc, and mixtures thereof, with a fuel gas, wherein the alloy of the electropositive metal comprises at least two electropositive metals, in which the alloy of the electropositive metal is combusted with the fuel gas.
In one embodiment, the alloy of the electropositive metal is combusted in liquid form.
In one embodiment, the combustion takes place at a temperature above the melting point of the salts formed in the reaction of the alloy of the electropositive metal and the fuel gas.
In one embodiment, the alloy of the electropositive metal is guided in liquid form into a pore burner and combusted with the aid of the pore burner, wherein the fuel gas is optionally guided to the outer surfaces of the pore burner and combusted with the alloy of the electropositive metal.
In one embodiment, the alloy of the electropositive metal, preferably in liquid form, is atomized and combusted with the fuel gas.
In one embodiment, the reaction products are separated after the combustion, preferably with the aid of a cyclone.
In one embodiment, the reaction products of the combustion are used to generate energy, preferably using at least one expander turbine and/or at least one steam turbine and/or at least one heat exchanger and/or at least one boiler.
Another embodiment provides an apparatus for combustion of an alloy of an electropositive metal, wherein the electropositive metal is selected from alkali metals, alkaline earth metals, aluminum and zinc, and mixtures thereof, and the alloy of the electropositive metal includes at least two electropositive metals, comprising a pore burner or a unit for atomizing the alloy of the electropositive metal, a feed unit for the alloy of the electropositive metal, preferably in liquid form, to the interior of the pore burner or the unit for atomizing the alloy, which is designed to supply the pore burner or the unit for atomizing the alloy with the alloy of the electropositive metal, preferably in liquid form, a feed unit for a fuel gas, which is designed to supply fuel gas, and optionally a heating apparatus for providing the alloy of the electropositive metal in liquid form, which is designed to liquefy the alloy of the electropositive metal.
In one embodiment, the apparatus comprises a pore burner, comprising a pore burner, wherein the feed unit for the fuel gas is arranged such that it guides the fuel gas at least partly to the surface of the pore burner.
In one embodiment, the pore burner is arranged such that reaction products that form from the combustion and optionally the electropositive metal can be separated by gravity from the surface of the pore burner.
In one embodiment, the pore burner or the unit for atomizing the alloy of the electropositive metal consists of a material selected from the group consisting of iron, chromium, nickel, niobium, tantalum, molybdenum, tungsten, zircalloy and alloys of these metals, and also steels such as stainless steel and chromium-nickel steel.
In one embodiment, the apparatus comprises a separating unit for the products of the combustion of the electropositive metal, preferably a cyclone, wherein the cyclone may further preferably have a perforated plate.
In one embodiment, the apparatus further comprises at least one expander turbine and/or at least one steam turbine and/or at least one heat exchanger and/or at least one boiler.

BRIEF DESCRIPTION OF THE DRAWINGS

Example aspects and embodiments of the invention are described below iwth reference to the drawings, in which:

FIG. 1 shows, in schematic form, an illustrative arrangement for an apparatus of the invention.

FIG. 2 shows, in schematic form, a detail view in a further illustrative arrangement for an apparatus of the invention.

FIG. 3 shows, in schematic form, a further detail view in an additional illustrative arrangement for an apparatus of the invention.

FIG. 4 illustrates, in schematic form, an illustrative cross section through an illustrative apparatus of the invention in the region of the feed unit of the carrier gas to the reactor.

FIG. 5 shows, in schematic form, a further possible arrangement for an apparatus of the invention.

FIG. 6 illustrates, in schematic form, another possible arrangement for an apparatus of the invention.

FIG. 7 shows a scheme for an illustrative reaction of an alloy of an electropositive metal according to the invention and carbon dioxide to give carbonate, which can be conducted by the process according to the invention.

FIG. 8 shows a scheme for a further illustrative reaction of an alloy of an electropositive metal according to the invention and nitrogen to give nitride and further conversion products, which can be conducted by the process according to the invention.

DETAILED DESCRIPTION

Some embodiments of the present invention provide a process and an apparatus in which combustion of electropositive metals can be conducted at lower temperatures. Some embodiments provide a process in which effective combustion of electropositive metals can be conducted with avoidance of excessive cooling for protection of the plant and hence with reduction of heat losses. Some embodiments provide a process in which the starting materials from the combustion of the electropositive metals can be obtained in a simple and energetically improved manner. Some embodiments provide a process in which the energy required for activation of the combustion reaction can be lowered. Some embodiments provide a process in which liquid transport of combustion products away from the combustion can take place at minimum temperature, since the longer these remain liquid, the lower the temperature can be in the combustion, which also protects the plant.
It has now been found that the use of alloys of electropositive metals, wherein the electropositive metal is selected from alkali metals, alkaline earth metals, aluminum and zinc, and mixtures thereof, and wherein the alloy of the electropositive metal comprises at least two electropositive metals, enables lowering of the reaction temperature in the combustion, and better controllability of the exothermic combustion reaction and more effective control of the plant. In addition, the separation of the gases formed in the reaction (for example CO in the case of combustion in CO₂) from the salt mixture (for example carbonates in the case of combustion in CO₂) can be effected in a simple and effective manner via the use of a cyclone and the removal of the salt melt in liquid form. Moreover, the alloys can usually be provided more easily than the pure electropositive metals, since the electrolysis of salt mixtures of various electropositive metals can also be conducted more easily and less energy-intensively than the electrolysis of salts of just one electropositive metal.
Embodiments of the present invention thus relate to a process and a construction for combustion, optionally under pressure, of alloys comprising alkali metals and/or alkaline earth metals, aluminum and/or zinc, in different reaction gas atmospheres such as carbon dioxide, nitrogen, steam, oxygen, air, etc.
Some embodiments provide a process for combusting an alloy of an electropositive metal, wherein the electropositive metal is selected from alkali metals, alkaline earth metals, aluminum and zinc, and mixtures thereof, with a fuel gas, wherein the alloy of the electropositive metal comprises at least two electropositive metals, in which the alloy of the electropositive metal is combusted with the fuel gas.
Other embodiments provide an apparatus for combustion of an alloy of an electropositive metal, wherein the electropositive metal is selected from alkali metals, alkaline earth metals, aluminum and zinc, and mixtures thereof, and the alloy of the electropositive metal includes at least two electropositive metals, comprising a pore burner or a unit for atomizing the alloy of the electropositive metal, a feed unit for the alloy of the electropositive metal, preferably in liquid form, to the interior of the pore burner or the unit for atomizing the alloy, which is designed to supply the pore burner or the unit for atomizing the alloy with the alloy of the electropositive metal, preferably in liquid form, a feed unit for a fuel gas which is designed to supply fuel gas, and optionally a heating apparatus for providing the alloy of the electropositive metal in liquid form, which is designed to liquefy the alloy of the electropositive metal.
One embodiment provides a process for combusting an alloy of an electropositive metal, wherein the electropositive metal is selected from alkali metals, alkaline earth metals, aluminum and zinc, and mixtures of such alloys, with a fuel gas, wherein the alloy of the electropositive metal comprises at least two electropositive metals, in which the alloy of the electropositive metal is combusted with the fuel gas.
The electropositive metal in the alloy L, in particular embodiments, 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 preferred embodiments, the electropositive metal in the alloy is selected from Li, Na, K, Mg, Ca, Al and Zn, and the alloy further preferably comprises at least two electropositive metals selected from Li, Na, K, Ca and Mg, where the alloy in particular embodiments more preferably comprises at least lithium or magnesium. However, it is possible to combine any of the metals mentioned. The alloy is additionally not particularly restricted and may, for example, be in solid or liquid form. Preferably, the alloy in the combustion, however, is liquid, since simple transport of the alloy can take place in this way.
Useful fuel gases, in particular embodiments, are those which can react with the alloy L mentioned in an exothermic reaction, although these are not particularly restricted. By way of example, the fuel gas may comprise air, oxygen, carbon dioxide, hydrogen, water vapor, nitrogen oxides NO_xsuch as dinitrogen monoxide, nitrogen, sulfur dioxide, or mixtures thereof. The process can thus also be used for desulfurization or NOx removal. According to the fuel gas, it is possible here to obtain various products with the various alloys L, which may be in solid, liquid or else gaseous form.
For example, a reaction of an alloy L, for example an alloy of lithium and magnesium, with nitrogen can give rise, inter alia, to metal nitride, such as a mixture of lithium nitride and magnesium nitride, which can then be allowed to react further at a later stage to give ammonia, whereas a reaction of alloy L, for example lithium and sodium, with carbon dioxide can give rise, for example, to metal carbonate, for example a mixture of lithium carbonate and sodium carbonate, carbon monoxide, metal oxide, for example lithium oxide and sodium oxide, or else metal carbide, for example lithium carbide and sodium carbide, or else mixtures thereof, it being possible to use the carbon monoxide to obtain higher-value products, for example including longer-chain hydrocarbonaceous products such as methane, ethane, etc., up to and including benzine, diesel, but also methanol etc., for example in a Fischer-Tropsch process, whereas it is possible to use metal carbide, for example lithium carbide and sodium carbide, to obtain acetylene, for example. In addition, for example, it is also possible with dinitrogen monoxide as fuel gas to form metal nitride, for example. Analogously, an alloy of lithium and potassium, on combustion, gives rise, for example, to a salt mixture of the corresponding lithium and potassium salts, and an alloy of sodium and potassium, on combustion, gives rise, for example, to a salt mixture of the corresponding sodium and potassium salts. Corresponding reactions can also be conducted with alloys comprising 3 or more metals, for example lithium, sodium and potassium. Also equally conceivable are alloys, for example, composed of magnesium and calcium or magnesium and zinc, or composed of magnesium and aluminum, etc. For a conversion to nitride, preference is given, for example, to Li/Mg or any mixture of the alkaline earth metals, especially Mg/Ca, although Be, for example, does not work as well. Suitable alloys for combustion with CO₂are, for example, Na/K, Na/Li/K, Li/K, Li/Na, Li/Mg, the above alloys. Alloys with barium, for example, can also be obtained and used in a simple manner, since barytes are very common in nature.
Analogous reactions can also arise for the other metals mentioned in the alloys.
One example reaction for Na/K alloys is:
2 Na/K+4 CO₂→Na₂CO₃/K₂CO₃+2 CO ΔH_reaction=−454 kJ/mol
The use of alloys, by virtue of the lower melting temperature of the salt mixture compared to the melting temperature of the individual alkali metal and alkaline earth metal carbonates, can enable flexible adjustment of flame temperature, with simultaneous assurance of removal of the salt mixture in liquid form.
For example, the adiabatic flame temperature of the stoichiometric combustion reaction in the case of combustion of lithium in carbon dioxide or nitrogen atmosphere is in the region of >2000 K.
Further enthalpies of reaction of individual electropositive metals with various fuel gases reported, from which the exothermicity of the reactions is apparent.

TABLE 1

Enthalpies of formation in the reactions
of individual electropositive metals

Enthalpy
of	En-	En-
reaction	thalpy	thalpy	Com-
kJ/mol	kJ/mol	kJ/g	pound

Combustion equations

6 Li + N₂→ 2 Li₃N	−414	−69	−10	Li
2 Li + 2 CO₂→ Li₂CO₃+ CO	−539	−270	−39	Li
2 Li + 2 H₂O → 2 LiOH + H₂	−404	−202	−29	Li
4 Li + O₂→ 2 Li₂O	−1196	−299	−43	Li
2 Na + 4 CO₂→ Na₂CO₃+ CO	−454	−227	−10	Na
Mg +2 CO₂→ MgCO₃+ 2 CO	−435.2	−435.2	−18	Mg
Ca + 2 CO₂→ CaCO₃+ CO	−529.93	−529.93	−13	Ca
2 K + 2 CO₂→ K₂CO₃+ CO	−474	−237	−6	K

Promoting interactions

Li₃N + 3 H₂O → 3 LiOH + NH₃	−444	−444	−26	NH₃
Li₂O + CO₂→ Li₂CO₃	−224	−224	−5	CO₂

The exothermic reaction releases heat, at a comparable thermal level to that in the combustion of carbon-based energy carriers under air. For these reasons, simpler control of the combustion reaction is advantageous.
Nor is it ruled out that, aside from the two electropositive metals selected from alkali metals, alkaline earth metals, aluminum and zinc, and mixtures thereof, further components are present in the alloy L, for example further metals. Such further components, in particular embodiments, are present in a total amount of less than 50% by weight, preferably less than 25% by weight, further preferably less than 10% by weight and even further preferably less than 5% by weight, based on the alloy.
In particular embodiments, the alloy, however, contains only metals selected from alkali metals, alkaline earth metals, aluminum and zinc, and mixtures thereof, but unavoidable impurities may likewise be present, for example in an amount of less than 1% by weight, based on the alloy.
The quantitative ratios of the electropositive metals and of any further components in the alloy L are not particularly restricted in accordance with the invention. In particular embodiments, the alloy constituents, however, are adjusted so as to give rise to approximately a minimum of the melting point for the alloy—i.e. a eutectic mixture of the metals—and/or a minimum of the melting point of the corresponding salts, with possible temperature deviations in the melting point of the alloy or the salt mixture of not more than +200° C. in relation to the temperature minimum. Preferably, for the alloy, there is a minimum of the melting point (eutectic mixture) and/or a minimum of the melting point of the corresponding salts (eutectic mixture/eutectic). The corresponding melting points of the alloys or the salts formed in the combustion can be found in a suitable manner from known phase diagrams or calculated in a simple manner. For example, for an alloy of sodium and potassium, on combustion with carbon dioxide, the salts obtained are sodium carbonate and potassium carbonate, for which a melting point minimum of 709° C. is found at a molar ratio of sodium salt to mixture of 0.59. For lithium and sodium, for the carbonates, a value of 498° C. is found at a molar ratio of sodium salt to mixture of 0.49. For lithium and potassium, for the carbonates, there are actually two melting point minima of 503° C. at a molar ratio of lithium salt to mixture of 0.416 and 0.61, the melting temperature being only minimally increased between these values and corresponding alloys also being included. In particular embodiments, the proportion of the electropositive metals and further components in the alloy is chosen so as to give a melting point of the salts formed which is lower than the lowest melting point of each of the individual salts; in other words, for example, that for the lithium carbonate/sodium carbonate system is lower than the melting point of lithium carbonate, since potassium carbonate has a higher melting point.
In particular embodiments, the alloy of the electropositive metal is combusted in liquid form. In this way, the alloy can be easily transported and the reaction of the alloy with the fuel gas can be more easily localized. In particular embodiments, the combustion additionally takes place at a temperature above the melting point of the salts formed in the reaction of the alloy of the electropositive metal and the fuel gas. This configuration gives rise, on combustion of the alloy, to liquid reaction products which, in contrast to reaction products in the form of dusts or powder, can be separated relatively easily from the gaseous reaction products which form. Moreover, it is possible here to more easily control the combustion reaction, since the reaction products having the highest melting point, i.e. the salts, are in liquid form and, just like the further gaseous and any liquid reaction products or unconsumed reactants, for example liquid alloy L or liquid metal, can be removed easily from the reaction site. This is advantageous especially where the combustion takes place at the exit site of the alloy from a feed unit, for example in the case of atomization or combustion using a pore burner.
Atomization of the alloy can be effected here in a suitable manner and is not particularly restricted. The type of nozzle is likewise not particularly restricted and may include one-phase and two-phase nozzles. In particular embodiments, the alloy L of the electropositive metal is atomized, preferably in liquid form, and combusted with the fuel gas. An alternative possibility is atomization of alloy particles. However, more efficient atomization can be achieved by using the alloy L in liquid form, in which case self-ignition of the combustion reaction may also be possible as a result of the temperature, such that no ignition source is required.
In particular embodiments, the alloy of the electropositive metal is guided in liquid form into a pore burner and combusted with the aid of the pore burner, wherein the fuel gas is optionally guided to the outer surfaces of the pore burner and combusted with the alloy of the electropositive metal. However, no internal mixing takes place as in a conventional pore burner in particular embodiments, in order to avoid blockage of the pores by solid reaction products. In particular embodiments, the pore burner is thus a pore burner without internal mixing. In the case of use of the pore burner in particular embodiments, the pores serve solely to increase the surface area of the alloy L. In the case of continuous supply of the alloy L of the electropositive metal, however, a reaction with the fuel gas can take place at the exit of the pores close to the surface of the pore burner, provided that it can be ensured that reaction products that form are conveyed out of the pore burner by further delivery of alloy L. In particular embodiments, however, the combustion reaction takes place outside the pores of the pore burner, for example at the surface of the pore burner or even after exit of the alloy L from the pore burner, i.e. only at the surface of the exiting alloy L.
In particular embodiments, there is an additional requirement for a reactor/combustion space in which the combustion of the alloy L with the fuel gas can take place, for example in the case of atomization or combustion with the aid of a pore burner. Here too, the reactor/combustion space is not particularly restricted, provided that the combustion can take place therein.
In the case of use of the pore burner, there is the further advantage that the combustion can be localized in the pore burner, in which case the combustion products are also obtained in or close to the pore burner. Whereas, for example, in the case of atomization the reaction products are obtained throughout the reactor and solid and liquid reaction products have to be separated again in a complex manner from gaseous reaction products, in the case of combustion with a pore burner there is localization of solid and liquid reaction products in particular close to the pore burner, which facilitates separation thereof from gaseous combustion products. In this way, the entire combustion apparatus can also be made more compact and the combustion can be configured so as to be gentler in respect of the apparatus through localization of the combustion process.
The pore burner is not particularly restricted in terms of its form and, in particular embodiments, comprises a porous tube as burner. In particular embodiments, the pore burner comprises a porous tube which can be supplied with the alloy L at at least one orifice. Preferably, the alloy L is supplied only through one orifice 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 here may, for example, be a porous metal tube, for example made of iron, chromium, nickel, niobium, tantalum, molybdenum, tungsten, zircalloy and alloys of these metals, and also steels such as stainless steel and chromium-nickel steel. The pore burner preferably consists of a material selected from the group consisting of iron,
chromium, nickel, niobium, tantalum, molybdenum, tungsten, zircalloy and alloys of these metals, and also steels such as stainless steel and chromium-nickel steel. Suitable examples are austenitic chromium-nickel steels which are very resistant, for example, to erosion by sodium at high temperature, but materials having 32% nickel and 20% chromium, such as AC 66, Incoloy 800 or Pyrotherm G 20132 Nb also exhibit relatively favorable corrosion characteristics. The further constituents of the pore burner are not subject to any further restriction and may comprise the feed unit for the metal M and optionally an ignition source, etc.
In particular embodiments, the pore burner is supplied with the alloy L in liquid form in the interior of the pore burner. This leads to better distribution of the alloy L in the pore burner and more homogeneous exit of the alloy from the pores of the porous tube, such that a more homogeneous reaction can take place between alloy L and fuel gas. The combustion of alloy L and fuel gas can be suitably controlled for example, via the pore size of the pores of the tube, the alloy L used, the density thereof—which can be correlated to the temperature of the alloy L, the pressure with which the alloy L is introduced into the pore burner, the pressure or the application/feed rate of the fuel gas, etc.; the alloy L, for example comprising lithium and sodium, in particular embodiments, is accordingly used in liquid form, i.e., for example, above the melting point of the alloy. The liquid alloy L can be injected here into the porous tube, for example also with the aid of a further gas under pressure, which is not restricted, provided that it does not react with the alloy L, for example an inert gas. The liquid alloy L then passes through the pores of the tube to the surface and burns with the gas to give the respective reaction product(s).
In particular embodiments, the fuel gas is guided to the outer surfaces of the pore burner and combusted with the alloy L. This can reduce or prevent blockage of the pores of the porous tube, such that cleaning of the pore burner is prevented or else wear can be reduced.
The combustion of the alloy L at the surface of the porous tube reduces the tendency for passage of small particles into the gas space/reaction space, such that, at best, relatively large droplets of reaction products arise, but these can be easily separated from gaseous reaction products, for example be deposited onto the reactor wall by means of a cyclone. The main portion of the combustion products can be separated out, for example, in liquid form. In this case, the reactor wall can be cooled, for example with heat exchangers, in which case these may also be connected to turbines and generators.
In particular embodiments, the combustion is effected at a temperature above the melting point of the salts formed in the reaction of alloy L and fuel gas. The salts formed in the combustion of alloy L and fuel gas may have a melting point here above the melting point of the alloy L, such that supply of liquid alloy L at elevated temperature may be required. The combustion at a temperature above the melting point of the salts formed can additionally avoid contamination or coverage of the pore burner or a nozzle by the salts formed, such that the pore burner or the nozzle can be better protected against contamination, for example of the pores as well. This enables better operation and reduced cleaning of the apparatus, and also longer use times without cleaning. It is also possible for liquid reaction products to simply drip off the burner. Especially in the case of those processes at temperatures above the melting point of the salts formed, preferred materials for the burner and the nozzle are those that can withstand the temperatures, for example iron, chromium, nickel, niobium, tantalum, molybdenum, tungsten, zircalloy and alloys of these metals, and also steels such as stainless steel and chromium-nickel steel.
The combustion temperature is thus preferably higher than the melting point of the respective reaction product(s), in order that the pores of the pore burner or the nozzle are not blocked and the reaction products can be transported away. In addition, according to the reaction product, a certain degree of mixing between the liquid alloy L and the reaction product can also take place, such that the combustion can take place not only locally at the pore opening or the nozzle exit, but distributed over the entire surface of the tube or the nozzle. This can be controlled, for example, via the feed rate of the alloy L.
Through supply of the alloy L as an alloy of at least two electropositive metals, it is possible to achieve melting point depression of the alloy compared to the respective metals and of the metal salts formed, such that the process can be conducted at lower temperatures and hence in a gentler manner in respect of the apparatus, and the use of highly refractory materials in the apparatus can be reduced or avoided.
The gaseous products formed in the reaction (for example CO in the case of combustion in CO₂) can be separated from the solid and liquid combustion products and utilized further. In the combustion process, it is preferable that the salts formed in the exothermic reaction can be drawn off in liquid form and the offgas (composed of gaseous reaction products and any reaction gas introduced in excess) can be conducted under pressure through an expander turbine free of solid particles. Through the suitable use of alkali metal and/or alkaline earth metal alloys or alloys of Al and/or zinc, with adjustment via the air ratio (stoichiometry of the reaction), it is possible to ensure a lower combustion temperature. Because of the low melting temperature of a salt mixture, removal of the products in liquid form can be more easily assured. Thus, it is possible to avoid the use of costly burner materials. Moreover, potentially higher dynamics in the combustion process are possible, at different temperatures as a function of the stoichiometry (air ratio) of the combustion reaction, with simultaneous assurance of removal of the salt mixture formed in liquid form.
In addition, in particular embodiments, the combustion can be effected with a certain excess of fuel gas, for example in a molar ratio of fuel gas to metal M of 1.01:1 or more, preferably 1.05:1 or more, further preferably 5:1 or more, even further preferably 10:1 or more, for example even 100:1 or more, in order to stabilize the offgas temperature within a particular temperature range. The fuel gas can also serve here for removal of heat in the expander portion of a turbine etc.
In the process, a separation of offgas from solid and/or liquid reaction products can additionally be effected in the case of combustion of the alloy L with a fuel gas, in which case, in particular embodiments, in a reaction step, the fuel gas is combusted with the alloy L and offgas and further solid and/or liquid reaction products are formed, and, in a separation step, the offgas is separated from the solid and/or liquid reaction products. In this case, in the separation step, a carrier gas can additionally be added and the carrier gas can be removed as a mixture with the offgas. The carrier gas here may also correspond to the offgas, such that, for example, the combustion gives rise to an offgas corresponding to the carrier gas supplied, or else may correspond to the fuel gas. In the process of the invention, it is thus possible, in particular embodiments, to separate the reaction products after the combustion.
According to some embodiments, the carrier gas is not particularly restricted, and may correspond to the fuel gas, but may also be different therefrom. Carrier gases employed may, for example, be air, carbon monoxide, carbon dioxide, oxygen, methane, hydrogen, water vapor, nitrogen, dinitrogen monoxide, mixtures of two or more of these gases, etc. It is possible here for various gases, for example methane, to serve for heat transport and remove the heat of reaction of the reaction of metal M with the fuel gas from the reactor. The various carrier gases can, for example, be suitably matched to the reaction of the fuel gas with the alloy L, in order possibly to achieve synergistic effects here. The gas which is optionally used in the supply of the alloy L may likewise correspond to the carrier gas.
For combustion of carbon dioxide with the alloy L, for example composed of lithium and sodium, where carbon monoxide can form, the carrier gas used may, for example, be carbon monoxide and may optionally be circulated, i.e. at least partly recycled again as carrier gas after removal. In this case, the carrier gas is matched to the offgas, such that a portion of the carrier gas can optionally be withdrawn as product of value, for example for a subsequent Fischer-Tropsch synthesis, while it is regenerated by the combustion of carbon dioxide with alloy L, such that there is at least partial conversion of carbon dioxide to carbon monoxide overall, preferably to an extent of 90% by volume or more, further preferably 95% by volume or more, even further preferably 99% by volume or more and especially preferably to an extent of 100% by volume, based on the carbon dioxide used, and is withdrawn as product of value. The more carbon monoxide is generated, the cleaner the carbon monoxide removed.
In the case of combustion of nitrogen with alloy L, for example composed of lithium and magnesium, the carrier gas used may, for example, be nitrogen, such that unreacted nitrogen in the offgas from the combustion may be present as “offgas” alongside the nitrogen carrier gas, as a result of which a separation of gas, if desired, can be conducted in a simpler manner and, in particular embodiments, in the case of appropriate, preferably quantitative, combustion of alloy L and nitrogen using suitable, easily determinable parameters, may even not be required. It is possible, for example, to easily remove ammonia from the nitride formed by scrubbing or cooling.
In particular embodiments, at least a portion of the offgas may correspond to the carrier gas. For example, the offgas may correspond to the carrier gas to an extent of at least 10% by volume, preferably 50% by volume or more, further preferably 60% by volume or more, even further preferably 70% by volume or more, and even more preferably 80% by volume or more, based on the total volume of the offgas. In particular embodiments, the fuel gas may correspond to the carrier gas to an extent of 90% by volume or more, based on the total volume of the offgas, and may in some cases even correspond to the carrier gas to an extent of 100% by volume.
In particular embodiments, in the process of the invention, the mixture of offgas and carrier gas can be supplied at least partly back to the separation step as carrier gas and/or to the combustion step as fuel gas. Recycling of the mixture of offgas and carrier gas can be effected, for example, to an extent of 10% by volume or more, preferably 50% by volume or more, further preferably 60% by volume or more, even 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 offgas. In particular embodiments, recycling of the mixture of offgas and carrier gas can be effected to an extent of 90% by volume or more, based on the total volume of carrier gas and offgas. In embodiments that are preferred in accordance with the invention, a reaction between fuel gas and alloy can be effected in such a way that the offgas formed is the carrier gas, for example with carbon dioxide as fuel gas and carbon monoxide as carrier gas, such that the mixture of
carrier gas and offgas then consists essentially of the carrier gas, preferably to an extent of 90% by volume or more, further preferably to an extent of 95% by volume or more, even further preferably to an extent of 99% by volume or more and more preferably to an extent of 100% by volume, based on the mixture of offgas and carrier gas. In this case, the carrier gas can then be continuously circulated and withdrawn in such an amount as it is reformed by the combustion of alloy L and fuel gas. Compared to pure cycling of the carrier gas, where a separation of carrier gas and offgas is optionally effected, it is possible here, for example, to obtain a product of value, for example carbon monoxide, which can be withdrawn continuously.
In particular embodiments, the separation step in a process of the invention is effected in a cyclone or a cyclone reactor. The cyclone reactor here is not particularly restricted in terms of its setup and may, for example, have a form as possessed by standard cyclone reactors.
For example, a cyclone reactor may comprise a reaction region to which there may be connected feed units for the fuel gas, alloy L and the carrier gas (which may optionally also be combined and then supplied together to the reaction region), for example in the form of a rotationally symmetric upper section, a separation region which has a conical configuration, for example, and an expansion chamber to which there may be connected a removal apparatus for solid and/or liquid reaction products from the combustion of metal M with the fuel gas, for example in the form of a star feeder, and a removal unit for the mixture of offgas and carrier gas, which arises after the mixing of the two gases after the combustion of the metal M in the fuel gas.
Such apparatus components are, for example, typically present in cyclone separators. A cyclone reactor used in accordance with the invention may alternatively have a different construction and may optionally also comprise further regions. For example, individual regions (e.g. reaction region, separation region, expansion chamber) may also be combined in one component of an illustrative cyclone reactor and/or extend over two or more components of a cyclone reactor. It is possible here, for example, for carrier gas also to be added in a region in which the reaction of the alloy L and the fuel gas is advanced or even already complete.
The cyclone keeps the reaction products largely in the center of the reactor, for example of a furnace space. One advantage of the use of a pore burner is that the combustion at the surface of the porous tube does not give rise to any small particles as in the case of atomization, such that the offgas is free of solid or liquid particles, such that it is also possible to connect a gas turbine or expanded turbine downstream in a simple manner within the offgas stream. By suitable supply of carrier gas, however, it is also possible to achieve an efficient separation of offgas from solid and liquid reaction products in the case of atomization of the alloy L. Under these circumstances, it is possible with this combustion concept to introduce the offgas stream directly into a gas turbine after the combustion of the alloy L and the separation of the reaction products.
The offgas temperature, in particular embodiments, in the different combustion processes, can be controlled via the excess of gas, such that it is higher than the melting temperature of the reaction products or mixture thereof.
In particular embodiments, the cyclone reactor additionally comprises a grid, by means of which the solid and/or liquid reaction products can be removed in the combustion of the alloy L with the fuel gas. Such a grid can additionally
prevent subsequent vortexing of solid and/or liquid reaction products in the cyclone reactor.
The reaction products of the combustion can be used to generate energy, preferably using at least one expander turbine and/or at least one gas turbine, for example a steam turbine, and/or at least one heat exchanger and/or at least one boiler, for which it is possible here, in particular embodiments, to use either the solid and/or liquid reaction products formed, for example with use of a heat exchanger in the reactor, or else the gaseous reaction products. The thermal energy released in the combustion can thus be converted (for example via an expander turbine and/or steam turbine) to electrical energy. The thermal energy released can, for example, be converted back to power by means of a heat exchanger and downstream steam turbine. Higher efficiencies are achievable, for example, via the use of gas turbines in combination with steam turbines. For this purpose, in particular embodiments, it has to be ensured that the offgas is free of particles after the metal combustion, since these particles can otherwise cause long-term damage to the turbine.
In the case of use of a cyclone reactor with carrier gas supply, the mixture of offgas and carrier gas, in particular embodiments, for example in the reactor and/or in the case of and/or after removal from the reactor, can be used for heating of a boiler or for heat transfer in a heat exchanger or a turbine, for example a gas turbine or an expander turbine.
In addition, the mixture of the carrier gas and the offgas, in particular embodiments, may be under elevated pressure after the combustion, for example more than 1 bar, at least 2 bar, at least 5 bar or at least 20 bar.
Furthermore, in a further aspect of the invention, an apparatus for combustion of an alloy L of an electropositive metal is disclosed, wherein the electropositive metal is selected from alkali metals, alkaline earth metals, aluminum and zinc, and mixtures thereof, and the alloy L of the electropositive metal includes at least two electropositive metals, comprising a pore burner or a unit for atomizing the alloy L of the electropositive metal, a feed unit for the alloy L of the electropositive metal, preferably in liquid form, to the interior of the pore burner or the unit for atomizing the alloy L, which is designed to supply the pore burner or the unit for atomizing the alloy L with the alloy L of the electropositive metal, preferably in liquid form, a feed unit for a fuel gas, which is designed to supply fuel gas, and optionally a heating apparatus for providing the alloy L of the electropositive metal in liquid form, which is designed to liquefy the alloy L of the electropositive metal.
The unit for atomization of the alloy L is not particularly restricted here and may comprise, for example, a one-phase nozzle or a two-phase nozzle. The pore burner may be configured as described above. The feed unit used for alloy L may, for example, be tubes or hoses, or else conveyor belts, which may be heated, which can be suitably determined, for example, on the basis of the state of matter of the alloy L. Optionally, the feed unit for the alloy L may also be connected to a further feed unit for a gas, optionally with a control unit such as a valve, with which the supply of the alloy L can be regulated. It is likewise possible for the feed unit for the fuel gas to be configured as a tube or hose, etc., which may optionally be heated, in which case the feed unit can be
suitably determined on the basis of the state of the gas, which may optionally also be under pressure. It is also possible for several feed units to be provided for alloy L or fuel gas.
In particular embodiments, the feed unit for the fuel gas is arranged such that it guides the fuel gas, at least partly and preferably completely, to the surface of the pore burner or to the exit of the nozzle. This achieves an improved reaction between alloy L and fuel gas.
Moreover, the pore burner, in preferred embodiments, is arranged such that reaction products formed in the combustion and optionally the unreacted alloy L can be removed from the surface of the pore burner by gravity, for example by virtue of the pore burner being mounted vertically in the reactor, pointing toward the surface of the earth. In the case of vertical arrangement of the porous combustion tubes in the furnace space, the liquid reaction product formed can run out of the tube and then drip downward into the furnace bottom. In this way, the possibly dissolved alloy L, for example composed of lithium and sodium, which has not reacted in the pore burner beforehand is also combusted, and the heat of reaction is released to the fuel gas and carrier gas flowing past.
In particular embodiments, the pore burner or the nozzle consists of a material selected from the group consisting of iron, chromium, nickel, niobium, tantalum, molybdenum, tungsten, zircalloy and alloys of these metals, and also steels such as stainless steel and chromium-nickel steel. Suitable examples are austenitic chromium-nickel steels which are very resistant, for example, to erosion by sodium at high temperature, but materials having 32% nickel and 20% chromium, such as AC 66, Incoloy 800 or Pyrotherm G 20132 Nb also exhibit relatively favorable corrosion characteristics. These materials are preferred for use at relatively high temperatures, where the reaction with liquid
alloy L and optionally with liquid metal salts formed can take place in a simpler manner.
In particular embodiments, the apparatus of the invention may further include a separation unit for the products of the combustion of the alloy L, which is designed to separate the combustion products of the alloy L and of the fuel gas, the separation unit preferably being a cyclone reactor.
The separation unit may serve here for separation of offgas in the combustion of the alloy L with a fuel gas, and may comprise:

- a reactor in which the pore burner or the unit for atomization is provided and the feed unit for alloy L is mounted or provided, and to which the fuel gas is supplied, i.e. to which the feed unit for the fuel gas is connected or provided;
- a feed unit for carrier gas, which is designed to supply carrier gas to the reactor;
- a removal unit for a mixture of offgas and carrier gas, which is designed to remove a mixture of the offgas from the combustion of alloy L with the fuel gas and the carrier gas; and
- a removal unit for solid and/or liquid reaction products from the combustion of alloy L with the fuel gas, which is designed to remove solid and/or liquid reaction products from the combustion of alloy L with the fuel gas.

The feed unit for carrier gas is likewise not particularly restricted and comprises, for example, tubes, hoses, etc., it being possible to suitably determine the feed unit for carrier gas on the basis of the state of the carrier gas, which may optionally also be under pressure.
The reactor is likewise not particularly restricted, provided that the combustion of the fuel gas with the alloy L can take place therein. In particular embodiments, the reactor may be a cyclone reactor as shown by way of example in FIG. 1 and in detail in a further embodiment in FIG. 2.
The cyclone reactor may, in particular embodiments, comprise a reaction region to which there may be connected the feed units for the fuel gas, alloy L and the carrier gas and the pore burner, for example in the form of a rotationally symmetric upper section, a separation region which has a conical configuration, for example, and an expansion chamber to which there may be connected a removal apparatus for solid and/or liquid reaction products from the combustion of alloy L with the fuel gas, for example in the form of a star feeder, and a removal unit for the mixture of offgas and carrier gas, which arises after the mixing of the two gases after the combustion of the alloy L in the fuel gas.
Such apparatus components are, for example, typically present in cyclone separators. A cyclone reactor used in accordance with the invention may alternatively have a different construction and may optionally also comprise further regions. For example, individual regions (e.g. reaction region, separation region, expansion chamber) may also be combined in one component of an illustrative cyclone reactor and/or extend over two or more components of a cyclone reactor.
An illustrative cyclone reactor is shown in FIG. 1. The cyclone reactor 6 shown in FIG. 1 comprises a reaction region 20 a, a separation region 20 b which is both together with the reaction region 20 a in the upper component 6 a and together with the expansion chamber 20 c in the lower component 6 b, and an expansion chamber 20 c. Connected to the cyclone reactor in the upper section are a feed unit 1
for fuel gas, for example in the form of an optionally heated tube or a hose, and a feed unit 2 for alloy L, for example in the form of an optionally heated tube or a hose, the alloy L being supplied to the pore burner 3. According to FIG. 1, the alloy L is fed in with the aid of a gas in a feed unit 2′ for gas, for example a tube or hose, the feed of which can be controlled with a valve 2″. The alloy L and the fuel gas are fed to the reaction region 20 a. Through the feed unit 4, the carrier gas is supplied to a region 4′ for gas distribution, from which the carrier gas is then supplied to the separation region 20 b via nozzles 5 with which a cyclone can be formed. A detail of such a feed unit 4 having a region 4′ for gas distribution and a nozzle 5 is specified in cross section, by way of example, in FIG. 4 (illustration without pore burner 3), but it is also possible for more nozzles 5 to be present, for example at a suitable distance in a ring around the inner wall of the region 4′, in order to generate a suitable cyclone. Solid and/or liquid reaction products are removed from the lower component 6 b comprising the expansion chamber 20 c via the removal unit 7 for solid and/or liquid reaction products of the combustion of alloy L with the fuel gas, while the mixture of offgas and carrier gas is removed via the removal unit 8 for the mixture of offgas and carrier gas.
Optionally, in an apparatus of the invention, an ignition apparatus, for example an electrical ignition apparatus or a plasma arc, may be required, which may depend on the nature and state of the alloy L, for example the temperature and/or state of matter thereof, the characteristics of the fuel gas, for example the pressure and/or temperature thereof, and the arrangement of components in the apparatus, for example the nature and characteristics of the feed units.
In order to achieve, by means of construction, both a high offgas temperature of, for example, more than 200° C., for example even 400° C. or more, and in particular embodiments 500° C. or more, and an elevated (e.g. 5 bar or more) or high (20 bar or more) operating pressure, the internal reactor material may consist of alloys of high heat resistance, for example the abovementioned alloys and, in the extreme case, even of the material Haynes 214. Around this material, which is merely supposed to withstand the high temperature, it is then possible to arrange a thermal insulation which allows a sufficiently small amount of heat through, such that a steel wall on the outside, which may additionally also be air- or water-cooled, absorbs the compressive stress. The offgas can then be supplied to the further process step with the elevated or high operating pressure.
Furthermore, the reactor, for example a cyclone reactor, may also comprise heating and/or cooling apparatuses which may be present in the reaction region, the separation region and/or the expansion chamber, and also in the various feed and/or removal apparatuses, optionally the burner, and/or optionally the ignition apparatus. Furthermore, further components such as pumps for generation of a pressure or a vacuum, etc. may be present in an apparatus of the invention.
In embodiments in which the reactor takes the form of a cyclone reactor, the cyclone reactor may comprise a grid which is designed such that the solid and/or liquid reaction products can be removed through the grid on combustion of the alloy L with the fuel gas. Furthermore, such a grid may alternatively also be present in other reactors which may be provided in the apparatus of the invention. The use of the grid in the reactor or cyclone reactor can achieve better separation of the solid and/or liquid reaction products in the combustion of the alloy L with the fuel gas from the mixture of offgas and carrier gas. Such a grid is shown by way of example in FIG. 2, in which the grid
6′ is present by way of example in the cyclone reactor 6 shown in FIG. 1 in the lower component 6 b above the removal unit 7 and below the removal unit 8. By means of the grid, preferably with a sufficiently large distance from the reactor wall, it is possible to ensure reliable separation of solid and liquid reaction products or a mixture thereof. In this way, the already deposited solid or liquid combustion products are not vortexed by the cyclone either.
The geometry of the feed units for the carrier gas is not particularly restricted, provided that the carrier gas can be mixed with the offgas from the combustion of alloy L and fuel gas. A cyclone preferably forms here, for example with the apparatus shown in FIG. 1. A cyclone can alternatively be generated by other arrangements of the feed units with respect to one another. For example, it is not impossible that the feed unit for the carrier gas is also present at the top of the reactor close to the feed units for alloy L and fuel. Correspondingly suitable geometries for the injection can easily be determined in a suitable manner, for example on the basis of flow simulations.
Nor are the removal units particularly restricted, it being possible, for example, for the removal unit for the mixture of offgas and carrier gas to be configured as a tube, while the removal unit for the solid and/or liquid reaction products of the combustion of metal M with the fuel gas may be configured, for example, as a star feeder and/or as a tube with a siphon. It is also possible here for various valves, such as pressure valves, and/or further regulators to be provided. An illustrative removal unit 7 shown in FIG. 3, for example of the cyclone reactor 6 shown in FIG. 1, may, in this context, comprise a siphon 9, a valve 10 for degassing and a pressure regulator 11, but is not restricted to such a removal unit. Such a siphon in the removal unit for the solid and/or liquid
reaction products of the combustion of alloy L with the fuel gas, optionally in conjunction with a supply pressure regulator suitable for the particular operating pressure, may be used, for example, in order to enable an elevated or high operating pressure.
The removal unit for the mixture of offgas and carrier gas may, in particular embodiments, also comprise a separation apparatus for the offgas and carrier gas and/or individual components of the offgas.
In particular embodiments, the removal unit for a mixture of offgas and carrier gas may be connected to the feed unit for carrier gas and/or the feed unit for fuel gas in such a way that the mixture of offgas and carrier gas is fed at least partly to the reactor as carrier gas and/or to the burner as fuel gas. The proportion of recycled gas here may be 10% by volume or more, preferably 50% by volume or more, further preferably 60% by volume or more, even 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 offgas. In particular embodiments, recycling of the mixture of offgas and carrier gas can be effected to an extent of 90% by volume or more, based on the total volume of carrier gas and offgas.
In particular embodiments, an apparatus of the invention may additionally further comprise at least one boiler and/or at least one heat exchanger and/or at least one gas turbine and/or at least one expander turbine present in the reactor and/or the removal unit for the mixture of offgas and carrier gas. It is thus possible, for example, in the apparatus of FIG. 1 comprising a cyclone reactor 6, for one or more heat exchangers and/or boilers and/or gas turbines and/or expander turbines, which are not shown, to be provided in the reactor 6, in the removal unit 8 and/or in a unit connected to the removal unit 8.
It is also possible for heat exchange to take place in the cyclone reactor 6 itself, for example at the outer walls in the reaction region 20 a and/or the separation region 20 b, or else optionally in the region of the expansion chamber 20 c, in which case the corresponding heat exchangers can also be connected to turbines for power generation in generators.
The offgases can thus, as a mixture with carrier gas, be sent to a further use, for example heating of a boiler for steam raising, release of heat in a heat exchanger, operation of a turbine, etc.
If it is not possible to find a suitable heat exchanger by means of which, for example, air with appropriate pressure is then heated and guided into the gas turbine as replacement for the offgas, it is possible to use a boiler, for example. The route using a boiler is more promising in particular embodiments and is also technically simpler, since it is implementable at lower temperatures and only elevated pressure.
With the aid of one or more heat exchangers and/or one or more boilers, it is then subsequently possible to generate electrical energy, for example through use of a steam turbine and a generator. Alternatively, it is possible that the mixture of offgas and carrier gas is guided directly to a turbine, for example a gas turbine or expander turbine, in order thus to directly generate power. However, this requires very good removal of solids and/or liquid reaction products from the combustion of alloy L and fuel gas, as can be provided in accordance with the invention, especially using a grid in the reactor. The selection of whether a boiler or a heat exchanger is used may also depend, for example, on whether solid or liquid reaction products are formed, but may also depend on the plant. In the case of liquid reaction products, for example liquid Li₂CO₃and Na₂CO₃, it is possible, for example, for the reactor wall to function as heat exchanger, whereas, in the case of solid reaction products that form, special heat exchangers may be required. In the case of a corresponding separation of the mixture of offgas and carrier gas from the solid and/or liquid reaction products, direct guiding of the mixture of offgas and carrier gas to a turbine may also be possible, such that it may then be the case here too that no heat exchangers and/or boilers are required in the offgas stream.
In particular embodiments, an apparatus of the invention may comprise a withdrawal apparatus in the removal unit for the mixture of offgas and carrier gas, which is designed to remove a portion of the mixture of offgas and carrier gas in the case of recycling of the mixture of offgas and carrier gas to the feed unit for carrier gas and/or the feed unit for fuel gas through connection of the removal unit for the mixture of offgas and carrier gas to the feed unit for carrier gas and/or the feed unit for fuel gas. Such a portion may, for example, be more than 1% by volume, preferably 5% by volume or more and further preferably 10% by volume or more, based on the total volume of the mixture of offgas and carrier gas. In addition, in particular embodiments, not more than 50% by volume, preferably 40% by volume or less, further preferably 30% by volume or less, more preferably 20% by volume or less, based on the total volume of the mixture of offgas and carrier gas, may be removed from the recycled mixture of offgas and carrier gas. The gas withdrawn may then be available, for example, as product of value for further reactions, for example when carbon monoxide is discharged and then converted in a Fischer-Tropsch process to higher-value hydrocarbons.
It is also possible for the solids removed to be converted further to substances of value. For example, metal nitride prepared from combustion with nitrogen can be converted by hydrolysis with water to ammonia and alkali, in which case the alkali formed can also serve as scavenger for carbon dioxide and/or sulfur dioxide.
The above embodiments, configurations and developments can, if viable, be combined with one another as desired. Further possible configurations, developments and implementations of the invention also include combinations of features of the invention that have been described above or are described hereinafter with reference to the working examples but have not been mentioned explicitly.
More particularly, the person skilled in the art will also add individual aspects as improvements or additions to the respective base form of the present invention.
The invention is now illustrated hereinafter with reference to illustrative embodiments which do not restrict the invention in any way.
In an illustrative embodiment, the alloy L, for example composed of lithium and sodium, is used in liquid form, i.e. above the melting point of the alloy. The liquid alloy L, for example composed of lithium and sodium, can be introduced into a pore burner and then reacts directly, optionally after ignition to start the reaction, with the particular fuel gas, for example air, oxygen, carbon dioxide, sulfur dioxide, hydrogen, water vapor, nitrogen oxides NO_xsuch as dinitrogen monoxide, or nitrogen. The combustion of the alloy L can be effected in the apparatus shown in FIG. 1, for example with more than the stoichiometric amount of the fuel gas, in order not to generate excessively high offgas temperatures. Alternatively, the fuel gas can be added in a stoichiometric or substoichiometric amount compared to the metal M. After the combustion, a carrier gas (for example nitrogen, air, carbon monoxide, carbon dioxide and ammonia), which may also correspond to the fuel gas, is added for dilution, in order to reduce the temperature and in order to generate a cyclone for deposition of the solid or liquid reaction products. The hot offgas stream can then be used to heat a boiler or for heat transfer in a heat exchanger or the like.
In a second illustrative embodiment, the fuel gas used may be carbon dioxide and the carrier gas used may be carbon monoxide in the apparatus shown in FIG. 1. The alloy L used is, for example, one of lithium and sodium, for example in liquid form. The liquid alloy is introduced into the pore burner 3 and then reacts directly with the fuel gas. It may be the case that electrical ignition or an additional ignition burner are required. In a modification thereof, for example, a reaction can also be effected with an alloy of sodium and potassium according to this example, in which case the alloy of sodium and potassium may be in liquid form at room temperature.
The combustion of the alloy L is effected in the pore burner 3, preferably with the amount of carbon dioxide required in stoichiometric terms, although it is also possible to choose a slightly super- or substoichiometric ratio (e.g. 0.95:1 to 1:0.95 for the ratio of CO₂:alloy L). In the case of use of a very high deficiency of carbon dioxide, it is possible, for example, for carbide to form as the salt, from which acetylene can then be obtained.
In the second step, in the middle portion of the reactor/furnace 6, in the region 4′, the combustion products are mixed with the carbon monoxide carrier gas which is blown into the reactor 6 by nozzles 5. This gives rise to a cyclone, the effect of which is that the solid and/or liquid reaction products are vortexed at the reactor wall and are deposited primarily there. Preferably, an excess of carrier gas is used in order to ensure that the heat that arises through the combustion is transported away sufficiently. As a result, it is possible to suitably adjust the temperature in the reactor 6.
For combustion in pure carbon dioxide, the lithium carbonate-sodium carbonate mixture formed, in the case of a eutectic mixture, has a melting point of 498° C. If the
combustion temperature of the reaction products is kept above at least 498° C. by mixing in carrier gas and/or fuel gas through the feed units 1, 5, liquid reaction products can be expected for the combustion. The feed units can be used here for cooling in the strongly exothermic reaction, in order that the plant does not heat up too much, and the lower temperature limit may be the melting point of the salt mixture formed. If the cyclone is additionally operated with gases other than carbon dioxide, for example air or further gases, it is also possible, for example, for the oxides of lithium and sodium to form as a mixture in the reaction products. After separation of the liquid and solid reaction products, which can be improved by means of a grid 6′, the mixture of offgas and carrier gas is guided, for example, into a boiler and utilized for evaporation of water, in order then to drive a steam turbine with downstream generator or to operate other technical apparatuses (for example heat exchangers). The mixture of offgas and carrier gas cooled down by this process can then, for example, be utilized again as carrier gas for heating of the cyclone in the furnace. Thus, the residual heat from the offgas after the evaporation process is utilized in the boiler, and only the amount of carbon dioxide needed in stoichiometric terms for the combustion with Li/Na has to be obtained by offgas cleaning, for example in coal-fired power plants.
In particular embodiments, the combustion can be effected with a certain excess of fuel gas, for example in a molar ratio of fuel gas to alloy L of more than 1.01:1, preferably more than 1.05:1, further preferably 5:1 or more, even further preferably 10:1 or more, for example even 100:1 or more, in order to stabilize the offgas temperature within a particular temperature range, and it is possible to add further fuel gas or carrier gas for absorption of heat by means of a cyclone as well as the addition of fuel gas and the inflow of the alloy L in an arrangement of nozzles, as shown in FIG. 1 and FIG. 4. The offgas temperature, in particular embodiments, in the different combustion processes, can be controlled via the excess of gas, such that it may be higher than the melting temperature of the reaction products or mixture thereof.
With a recirculation of the offgas cooled by the downstream process step, it is possible to enrich carbon monoxide in the offgas. It is possible in particular embodiments to withdraw a proportion from the offgas, and hence to obtain a gas mixture of carbon monoxide and carbon dioxide having a significantly higher proportion of carbon monoxide. A subsequent separation of gas can purify the carbon monoxide to remove carbon dioxide, and the carbon dioxide can be used further in the circulation or in the burner.
By recycling of the CO product gas, it is possible to further lower the combustion temperature in the oven. Lowering of the combustion temperature would also be possible by means of an excess of CO₂. However, this excess would have to be about 16 times higher than the stoichiometric amount, and so the CO product gas would be highly diluted in the excess of CO₂. Therefore, it is sensible in particular embodiments to recycle a portion of the CO product gas into the burner and use it as thermal ballast for lowering the temperature. Preference is given here to establishing a particular reaction temperature by recycling a constant amount of the mixture of offgas and carrier gas as carrier gas. In this case, there is no formation of a CO/CO₂mixture which has to be separated in a complex manner. The product gas consists mainly of CO and only of small impurities of CO₂. In the steady state, the majority of the CO is circulated and the amount of CO removed from the circuit is just as much as is reformed by the reaction of CO₂and Li/Na—and also generally with electropositive metal alloy. For example, such a circuit may arise when CO is used as carrier gas in a ratio of 90% by volume or more, based on the mixture of offgas and carrier gas. A suitable amount of carbon dioxide can thus be supplied constantly to the combustion process, whereas a corresponding amount of carbon monoxide can be withdrawn constantly from the circuit as product of value.
A corresponding reaction regime is also shown by way of example in FIG. 5. Carbon dioxide is separated from an offgas 100, for example from a combustion power plant such as a coal-fired power plant, in a CO₂removal 101, and then it is combusted with the alloy in step 102, using CO as carrier gas. This forms the carbonate salt mixture 103, and a mixture of offgas and carrier gas comprising CO₂and CO, optionally after a separation 104, can be passed through a boiler 105, with the aid of which a steam turbine 106 and hence a generator 107 are operated. There is recycling of offgas 108 as carrier gas, it being possible to discharge CO in the step 109.
In a third illustrative embodiment, the fuel gas and carrier gas used may be nitrogen in the apparatus shown in FIG. 1. The alloy L used is, for example, one of lithium and magnesium, for example in liquid form. The alloy L is fed to the pore burner 3 and then reacts directly with the fuel gas. It may be the case that electrical ignition or an additional ignition burner are required.
The combustion of the alloy L is effected in the pore burner 3 with the amount of nitrogen required in stoichiometric terms, although it is also possible to choose a slightly super- or substoichiometric ratio (e.g. 0.95:1 to 1:0.95 for the ratio of N₂:alloy L).
In the second step, in the middle portion of the reactor 6, the combustion products are mixed with the carrier gas, for example nitrogen, which is blown into the reactor 6 through the nozzles 5. This gives rise to a cyclone, the effect of which is that the solid and liquid reaction products are vortexed at the reactor wall and are deposited primarily there. The feed units can be used here for cooling
in the strongly exothermic reaction, in order that the plant does not heat up too much, and the lower temperature limit may be the melting point of the salt mixture formed. If the cyclone is operated with gases other than nitrogen, for example air or carbon dioxide or further gases, it is also possible for oxide or carbonate to form in the reaction products. After separation of the liquid and/or solid reaction products, which can be improved by means of a grid 6′, the offgas is guided, for example, into a boiler and utilized for evaporation of water, in order then to drive a turbine with downstream generator or to operate other technical apparatuses (for example heat exchangers). The offgas cooled after this process can then, for example, be utilized again to generate the cyclone in the reactor 6. Thus, the residual heat from the offgas after the evaporation process is utilized in the boiler, and only the amount of nitrogen needed in stoichiometric terms for the combustion has to be obtained, for example by fractionation of air.
In particular embodiments, the combustion can be effected with a certain excess of fuel gas, for example in a molar ratio of fuel gas to alloy L of more than 1.01:1, preferably more than 1.05:1, further preferably 5:1 or more, even further preferably 10:1 or more, for example even 100:1 or more, in order to stabilize the offgas temperature within a particular temperature range, and it is possible to add further fuel gas or carrier gas for absorption of heat by means of a cyclone as well as the addition of fuel gas and the inflow of the alloy L in an arrangement of nozzles, as shown in FIG. 1 and FIG. 4.
A corresponding reaction regime is also shown by way of example in FIG. 6. Nitrogen is separated from the air 200 in an air fractionation 201 and then combusted with the alloy L in step 202, using nitrogen, for example likewise from the air fractionation 201, as carrier gas. This forms a nitride salt mixture of lithium nitride and magnesium nitride 203, and the mixture of offgas and carrier gas
comprising N ₂ 204 can be guided through a boiler 205, with the aid of which a steam turbine 206 and hence a generator 207 are operated. There is recycling of offgas 208 as carrier gas. Ammonia 210 can be obtained from the nitride salt mixture 203 by hydrolysis 209, forming hydroxide 211 which can be reacted with carbon dioxide to give carbonate 212.
In a fourth illustrative embodiment, it may also be possible, for example in the case of use of air as fuel gas, to use two reactors, for example two cyclone reactors, connected in series, in which case, in the first cyclone reactor, the alloy and the oxygen from the air can be used to produce a metal oxide mixture and the offgas contains primarily nitrogen, and this offgas can then react in a second cyclone reactor as fuel gas with alloy L to give metal nitride. In this case, for example, nitrogen can function as carrier gas, which can also be obtained from the first offgas, or the first offgas itself if it is being circulated, for example.
A fifth illustrative embodiment is shown in FIG. 5, in which the reactor is similar to the reactor shown in FIG. 1. The alloy L, for example Na/K, is fed to the cyclone reactor 6 (6 a, 6 b) via the pore burner 3, optionally in liquid form at room temperature, and the fuel gas, for example carbon dioxide, via the feed unit 1. A particularly advantageous feature is the injection of the fuel in the cyclone reactor (6 a, 6 b) at points with high gas velocity, in order that the liquid metal droplets can be easily torn away from the pore burner 3. It is possible to adjust the offgas temperature via the stoichiometry of the reaction. This should advantageously be chosen such that the salt mixture formed remains in liquid form. In this case, the melting temperature of the salt mixture can be lowered to about 700° C., compared to 900° C. for potassium carbonate and 858° C. for sodium carbonate.
After the combustion, the reaction products are separated by the cyclone and the salt products of the alloy L, for
example in liquid form, withdrawn at the reactor exit and collected in a vessel 15 for solid and liquid reaction products. By means of a heat exchanger 12, thermal energy can be obtained from these reaction products at the lower end of the reactor, for example at the reactor wall, where a salt melt flows away, and this energy can then be converted to electrical energy by means of a steam turbine 13 and a generator 14. The hot and particle-free gas removed under pressure can thus be converted to power with high efficiency. The offgas is guided through the removal unit 8 to an expander turbine 16, from which power can be obtained in turn with the generator 14′. In the case of an excess of CO₂in the reaction gas, the offgas, after exit from the expander turbine 16, can be recycled to the cyclone reactor 6 as reaction gas and hence the CO concentration in the offgas can be increased. Recycling of offgas thus takes place via a recycling unit 18, and the offgas can in turn be used as carrier gas in the cyclone reactor 6 (6 a, 6 b). In addition, offgas can be withdrawn via a withdrawal port and fed to an offgas separation 17, for example in the case of use of CO₂as fuel gas and CO as carrier gas and product of the combustion.
A sixth illustrative embodiment is shown in FIG. 6, wherein, instead of a pore burner 3, atomization of the alloy L takes place at the end of the feed unit 2 and, in the reaction space 30, the reaction then takes place with the fuel gas from the feed units 1. Thereafter, the reaction products formed are transferred into the cyclone reactor 6 (6 a, 6 b). Even though the reaction space 30 is connected laterally in FIG. 6, it may also be connected to the cyclone reactor in other ways, for example at the top, provided that the reaction products are subjected to the cyclone separation.
The invention describes the suitable use of alloys of electropositive metals as physical energy storage means, which can be produced electrochemically with utilization of renewable electrical energy (overproduction,
charging process). The discharge of the energy storage means can be achieved in the form of a combustion process in carbon dioxide, nitrogen, oxygen, air, atmosphere, etc.
The present invention, in particular embodiments, can ensure the separation of the gaseous reaction products from the salts formed in the reaction by the use of a cyclone and the liquid removal of the salt mixture. In addition, it is possible through the use of alloys L of electropositive metals and the lower melting temperature of the salt mixtures formed, in the case of combustion compared to the individual metal compounds, to establish the combustion reaction at lower temperatures as well and hence avoid the use of costly materials for the combustion space, with simultaneous assurance of liquid removal of the salt mixture. Reconversion of the thermal energy released in the combustion to power can be effected, for example, either through the use of an expander turbine for the gases which may be removed under pressure and at high temperature or by heat exchangers at the reactor wall and subsequently a steam turbine.
Through the construction of the apparatus of the invention, especially through the use of porous combustion tubes, it is possible to separate the solid or liquid reaction products or mixtures thereof in a simple manner from the offgases formed, and hence to send the offgases to a use in, for example, a gas turbine or expander turbine, a heat exchanger, or a boiler. In this way, in addition, the entire combustion apparatus can also be made more compact and the combustion can be configured so as to be gentler in respect of the apparatus through localization of the combustion process.
In addition, the apparatus, for example a reactor such as a furnace, can be run at elevated operating pressure, and thus the combustion and deposition process can be matched to the respective conditions of the downstream step. The
possibility of distinction of fuel gas and carrier gas for establishment of a cyclone, in particular embodiments, enables the recycling of offgases after the release of heat. Recirculation is easily possible with this construction. Gas mixtures are also possible as fuel gas and carrier gas. By recycling of the offgas after the process step(s), it is possible to save energy and material.

Claims

What is claimed is:

1. A process, comprising:

providing an alloy of an electropositive metal selected from the group consisting of alkali metals, alkaline earth metals, aluminum, zinc, and mixtures thereof,

wherein the alloy of the electropositive metal comprises at least two electropositive metals, and

combusting the alloy of the electropositive metal with fuel gas.

2. The process of claim 1, wherein the alloy of the electropositive metal is combusted in liquid form.

3. The process of claim 1, wherein the combustion is performed at a temperature above the melting point of salts formed in the reaction of the alloy of the electropositive metal and the fuel gas.

4. The process of claim 1, comprising:

guiding the alloy of the electropositive metal, in liquid form, into a pore burner, and

guiding the fuel gas to an outer surfaces of the pore burner and combusting the fuel gas with the alloy of the electropositive metal.

5. The process of claim 1, wherein the alloy of the electropositive metal, in liquid form, is atomized and combusted with the fuel gas.

6. The process of claim 1, comprising using a cyclone to separate reaction products of the reaction of the alloy of the electropositive metal and the fuel gas.

7. The process of claim 1, comprising using reaction products of the combustion of the reaction of the alloy of the electropositive metal and the fuel gas to generate energy using at least one of an expander turbine, a steam turbine, a heat exchanger, or a boiler.

8. An apparatus for combustion of an alloy of an electropositive metal selected from the group consisting of alkali metals, alkaline earth metals, aluminum, zinc, and mixtures thereof with fuel gas, wherein the alloy of the electropositive metal includes at least two electropositive metals, the apparatus comprising:

a pore burner or a unit for atomizing the alloy of the electropositive metal,

a metal allow feed unit configured to supply the alloy of the electropositive metal, in liquid form, to an interior of the pore burner or the unit for atomizing the alloy,

a fuel gas feed unit configured to supply fuel gas to the pore burner.

9. The apparatus of claim 8, wherein the fuel gas feed unit is configured to guide at least a portion of the fuel gas to a surface of the pore burner.

10. The apparatus of claim 9, wherein the pore burner is configured such that reaction products that form from the combustion are separated from the surface of the pore burner by gravity.

11. The apparatus of claim 8, wherein the pore burner or the unit for atomizing the alloy of the electropositive metal is formed from a material selected from the group consisting of iron, chromium, nickel, niobium, tantalum, molybdenum, tungsten, zircalloy, alloys of these metals, stainless steel, and chromium-nickel steel.

12. The apparatus of claim 8, further comprising a separating unit for products of the combustion of the electropositive metal, wherein the separating unit comprises a cyclone having a perforated plate.

13. The apparatus of claim 8, further comprising at least one of an expander turbine, a steam turbine, a heat exchanger, or a boiler.

14. The apparatus of claim 8, further comprising a heating apparatus configured to liquefy the alloy of the electropositive metal prior to the alloy being supplied to the interior of the pore burner.