Furnace operation method

Abstract

To provide a method for operating a furnace that generates smoke at a temperature of at least 900°C.SOLUTION: A method includes: step (a) for burning fuel with an oxidizer, and generating thermal energy and smoke; step (b) for heating a furnace with a first part of the thermal energy generated in the step (a); step (c) for discharging the smoke generated from the furnace at a temperature of at least 900°C, the discharged smoke including a second part of the thermal energy generated in the step (a); and step (d) for using the second part of the thermal energy generated in the step (a) as a heat source for heating the oxidizer, and decomposing ammonia into a mixture containing hydrogen, nitrogen, and undecomposed ammonia in a decomposition device, at least part of the mixture generated in step (d-ii) being burned as fuel in the step (a) together with at least part of the oxidizer generated and heated in step (d-i).SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a method for operating a furnace that generates smoke at a temperature of at least 900°C. [Background technology]

[0002] Hydrogen (H2) is an extremely useful and interesting molecule for a variety of applications, including its use as a chemical reactant and as a fuel for energy production.

[0003] Hydrogen atoms (H) are abundant on Earth, but generally in the form of molecules in which they are chemically bound to other (i.e., non-hydrogen) atoms, such as in water, but also in hydrocarbons, ammonia, and biomass.

[0004] In reality, hydrogen (H2) is produced by a variety of processes in which hydrogen atoms are separated from the non-hydrogen atoms to which they are bonded.

[0005] With climate change caused by greenhouse gas emissions in the atmosphere, there is a trend towards reducing, and preferably ultimately towards zero, GHG (greenhouse gas) emissions.

[0006] Most industrial combustion facilities, such as glass melting furnaces, currently burn CH4 or other hydrocarbons to generate heat.

[0007] Combustion of methane produces one molecule of CO2 per molecule of methane.

[0008] For other hydrocarbons, including biomass hydrocarbons, the number of CO2 molecules produced per molecule of hydrocarbon combusted depends on the chemical formula of the hydrocarbon.

[0009] Conventionally, the CO2 is released into the atmosphere. To avoid releasing this CO2 into the atmosphere, processes have been developed to capture and store or use the generated CO2. However, these CO2 capture processes are complicated and expensive.

[0010] It is desirable to reduce or avoid CO2 emissions to the atmosphere even for industrial facilities / processes that generate relatively small amounts of CO2, but currently it is not cost-effective to do so for processes and facilities that generate relatively small amounts of CO2.

[0011] It is therefore desirable to avoid the generation of these CO2 emissions by using carbon-free molecules as fuels. An example of such a carbon-free combustible molecule is ammonia (NH3).

[0012] The flammability limits of NH3 are close to those of methane, but the laminar flame speeds achieved with ammonia are about five times slower compared to those achieved with methane. This increases the risk of flame lift-off (and incomplete combustion), especially when conventional burners designed for CH4 and similar gaseous hydrocarbon fuels are used to burn ammonia. Summary of the Invention [Problem to be solved by the invention]

[0013] The object of the present invention is to overcome this problem and to produce a stable flame starting from ammonia. The aim of this project is to make it possible for [Means for solving the problem]

[0014] The present invention relates to a method for operating a furnace that generates smoke at a temperature of at least 900°C.

[0015] According to the method, a fuel is combusted with an oxidant, said combustion generating thermal energy and smoke, and a furnace is heated with a first portion of the thermal energy thus generated.

[0016] The generated fumes are exhausted from the furnace at a temperature of at least 900° C. (as indicated above), preferably at a temperature between 1250° C. and 1650° C. The exhausted fumes contain a second portion of the generated thermal energy, said second portion often being referred to as "residual" or "residual" heat.

[0017] This second portion of the thermal energy generated by the combustion is used both (i) to heat the oxidant before it is used to combust the fuel in step a, and (ii) as a heat source to decompose the ammonia in the decomposer into a mixture comprising hydrogen, nitrogen, and undecomposed ammonia.

[0018] During the combustion of the fuel with the oxidizer described above, at least a portion of the mixture is combusted as fuel together with at least a portion of the heated oxidizer.

[0019] When the second portion of the generated thermal energy is used to heat the oxidant, the oxidant as the heated fluid is heated by heat exchange with the heat-retaining fluid, i.e. the exhausted smoke as the heat source, said heat exchange may be direct or indirect.

[0020] During direct heat exchange, the heat-retaining fluid and the heated fluid are physically separated from each other by a fluid-impermeable, heat-conducting wall, which allows heat to be transferred from the heat-retaining fluid to the heated fluid while preventing mixing between the heat-retaining fluid and the heated fluid.

[0021] During indirect heat exchange, an intermediate heat transfer fluid is used. The heat retaining fluid and the intermediate fluid are physically separated from each other by a first fluid-impermeable heat-conducting wall, which transfers heat from the heat retaining fluid to the intermediate fluid while preventing mixing between the heat retaining fluid and the intermediate fluid. This results in a heated intermediate fluid, which is used to heat the heated fluid. More specifically, the heated intermediate fluid and the heated fluid are separated from each other by a second fluid-impermeable heat-conducting wall, which transfers heat from the heated intermediate fluid to the heated fluid while preventing mixing between the intermediate fluid and the heated fluid. In other words, indirect heat exchange includes (a) direct heat exchange between the heat retaining fluid and the intermediate fluid, and (b) direct heat exchange between the heated intermediate fluid and the heated fluid. The two direct heat exchange substeps may be performed in a common heat exchange device or in separate heat exchange devices.

[0022] Compared to indirect heat exchange, direct heat exchange between the heat-retaining fluid and the fluid to be heated has the advantage of being simpler (no additional fluid is required) and allowing a more compact construction (no volumes or flow paths for intermediate fluids are required).

[0023] Compared to direct heat exchange, indirect heat exchange can provide an additional means of controlling the heat exchange process (especially when the intermediate fluid is not stationary but flowing) and, by selection of a suitable, typically inert, intermediate fluid, can provide additional peace of mind / safety (if a leak in the heat-conducting wall (first or second) occurs, the heat-retaining fluid or the non-heated fluid (depending on the leaking wall) may mix with the intermediate fluid, but mixing of the heat-retaining fluid with the heated fluid is avoided).

[0024] As used herein, the term "cracker" refers to any device suitable for cracking ammonia into the above-mentioned mixtures.

[0025] In principle, it is desirable for the ammonia decomposition reaction to be as complete as possible, i.e., to maximize hydrogen generation and limit the amount of ammonia remaining in the mixture. However, in practice, it is typically found to be too expensive to seek complete (100%) decomposition of ammonia, and some ammonia remains in the mixture.

[0026] The present invention is particularly useful when the oxidizer used in the combustion fuel for heating the furnace is an oxygen-enriched oxidizer, more specifically an oxidizer having an oxygen content of more than 21% to 100% by volume, preferably 70% to 100% by volume, more preferably 90% to 100% by volume. Indeed, oxygen-enriched oxidizers generally produce hotter flames and hotter smoke than non-oxygen-enriched oxidizers.

[0027] The fuel burned may be a combination of the mixture obtained by decomposing ammonia (or a part thereof) and one or more further fuels, however, it is preferred that the fuel burned to heat the furnace consists of the mixture produced by ammonia decomposition or a part of said mixture.

[0028] According to the invention, the residual heat from the furnace, i.e. the second portion of the thermal energy generated by the combustion, is used not only for heating the oxidizer but also as a heat source for decomposing the ammonia.

[0029] The mixture produced by ammonia decomposition contains nitrogen in the form of N2 and generally also as part of the undecomposed ammonia fraction, so the exhausted smoke generally contains NO X Other possible NO X The sources are any nitrogen present in the combustion oxidant, nitrogen present in the charge being heated in the furnace, and nitrogen present in the incoming air if the furnace is operated at subatmospheric pressure.

[0030] Nitrogen oxides are pollutants whose release into the atmosphere is highly undesirable. In many countries, industrial combustion processes produce NOX Follow standards that limit emissions.

[0031] According to the present invention, NO X The exhaust is NO to the smoke emitted. X This may be reduced or eliminated by adding a reducing agent. X The reducing agent is the NOx that is present in the exhausted smoke. X Then, NO X And NO X The products of the chemical reaction with the reductant are separated from the exhausted smoke.

[0032] NO X Reductants may be added to the exhausted fumes before they are used to heat the oxidizer and decompose the ammonia, after they are used to heat the oxidizer and decompose the ammonia, or between their use to heat the oxidizer and their use to decompose the ammonia, regardless of the order in which the exhausted fumes are used for these two purposes. X A reducing agent may also be added to the smoke emitted in two or more of the above steps. One particular NO X The reducing agent is ammonia.

[0033] There are several ways in which the residual heat from the furnace may be used as a heat source for ammonia decomposition.

[0034] One such method is to detect the presence of ammonia in the exhaust smoke by a cracker where the ammonia cracking takes place. This is by heating with a second portion of the generated thermal energy present.

[0035] Another possibility, which may or may not be combined with such heating of the cracker, is to use a second portion of the generated thermal energy present in the exhausted fumes to heat the ammonia by direct or indirect heat exchange.

[0036] According to one embodiment of the present invention, (a) the oxidant is heated by indirect heat exchange with the exhausted fumes and (b) the ammonia is heated by direct heat exchange with the exhausted fumes upstream of and / or within the cracker.

[0037] In that case, the exhausted fumes may be split into multiple portions, a first portion of the exhausted fumes being used to heat the oxidant by indirect heat exchange and a second portion of the exhausted fumes being used to heat the ammonia by direct heat exchange.

[0038] It is also possible to heat the oxidant by indirect heat exchange with the exhausted fumes and to heat the ammonia by direct heat exchange with the exhausted fumes previously used in the step for heating the oxidant by indirect heat exchange, i.e. to heat the intermediate fluid used to heat the oxidant by direct heat exchange. Alternatively, the oxidant may be heated by indirect heat exchange with the exhausted fumes previously used to heat the ammonia.

[0039] Finally, the intermediate fluid and the ammonia may be heated in parallel by direct heat exchange with the exhausted fumes, or the same part of the exhausted fumes if one heat exchanger is used for that purpose. For example, in a shell-and-tube heat exchanger, the exhausted fumes may flow through the shell side of the heat exchanger, while the intermediate fluid for heating the oxidant flows in one part of the tube as the heated fluid, and the ammonia flows in the other tube of the heat exchanger as the heated fluid.

[0040] According to an alternative embodiment, the oxidant and ammonia are both heated by direct heat exchange with the exhausted fumes, and the ammonia is heated by direct heat exchange with the exhausted fumes upstream and / or within the cracker.

[0041] It may be advantageous, and particularly more compact, to heat the oxidant and ammonia by direct heat exchange with the exhausted fumes in a combined heat exchanger / decomposer.

[0042] Further, the exhausted fumes may be split into multiple portions, a first portion of the exhausted fumes being used to heat the oxidant by direct heat exchange, and a second portion of the exhausted fumes being used to heat the ammonia by direct heat exchange.

[0043] Alternatively, exhausted fumes previously used to heat an oxidant by direct heat exchange can be used to heat ammonia by direct heat exchange, or exhausted fumes previously used to heat ammonia by direct heat exchange can be used to heat an oxidant by direct heat exchange.

[0044] It is further possible to heat the oxidant and ammonia in parallel by direct heat exchange with the exhausted fumes or the same portions of the exhausted fumes if one heat exchanger is used for that purpose, for example a shell-and-tube heat exchanger with the exhausted fumes flowing through the shell side of the heat exchanger and the oxidant and ammonia flowing as heating fluids in different tubes of the heat exchanger.

[0045] According to a further possible embodiment, both the oxidant and the ammonia are heated by indirect heat exchange with the exhausted fumes, the ammonia being heated upstream and / or inside the cracker.

[0046] In addition, the exhausted fumes may be split into multiple portions, a first portion of the exhausted fumes being used to heat the oxidant by indirect heat exchange, and a second portion of the exhausted fumes being used to heat the ammonia by indirect heat exchange.

[0047] It is also possible to heat the first and second intermediate fluids using the exhausted fumes, whereby the heated first intermediate fluid is used to heat the oxidant and the heated second intermediate fluid is used to heat the ammonia. The first and second intermediate fluids may be heated by different parts of the exhausted fumes, i.e. the first intermediate fluid is heated by a first part of the exhausted fumes and the second intermediate fluid is heated by a second part of the exhausted fumes. It is also possible to heat the second intermediate fluid used to heat the ammonia by direct heat exchange with the exhausted fumes previously used to heat the first intermediate fluid used to heat the oxidant. Alternatively, the first intermediate fluid used to heat the oxidant may be heated by direct heat exchange with the exhausted fumes previously used to heat the second intermediate fluid used to heat the ammonia. The first and second intermediate fluids may also be heated in parallel by direct heat exchange with the exhausted fumes or the same part of the exhausted fumes in one heat exchange device.

[0048] A further option is to use the same intermediate fluid to heat both the oxidant and the ammonia.

[0049] According to one such embodiment, the intermediate fluid is heated by direct heat exchange with the exhausted fumes and the heated intermediate fluid thus obtained is divided into a plurality of portions, a first portion of the thus heated intermediate fluid being used for heating the oxidant and a second portion of the heated intermediate fluid being used for heating the ammonia.

[0050] According to a further such embodiment, the heated intermediate fluid is first used to heat the oxidant, and the heated intermediate fluid previously used to heat the oxidant is used to heat the ammonia. Alternatively, the heated intermediate fluid may be first used to heat the ammonia, and the heated intermediate fluid previously used to heat the ammonia is used to heat the oxidant. The oxidant and ammonia may be heated in parallel by direct heat exchange with the heated intermediate fluid in one heat exchange device.

[0051] In all of these cases, heating of the oxidant and ammonia by heat exchange with an intermediate fluid may take place in a combined heat exchanger / decomposer.

[0052] The cracker used to crack the ammonia may be a non-catalytic cracker or a catalytic cracker.

[0053] The temperature to which the ammonia is heated depends on the nature of the cracker (in particular catalytic or non-catalytic) and, in the case of a catalytic cracker, on the nature of the catalyst. Known examples of suitable ammonia decomposition catalysts include catalysts based on rare metals such as ruthenium and cobalt. In most cases, the temperature to which ammonia must be heated for effective ammonia decomposition is lower in catalytic crackers than in non-catalytic crackers. For example, with a suitable catalyst, H2 with a purity of about 75% by volume can be produced at a temperature of about 500°C. Heating ammonia to 1000°C without a catalyst can produce 100% H2 with an equilibrium of NH3 decomposition without a catalyst, as shown in Figure 1, which is an equilibrium graph for NH3 decomposition without a catalyst. This allows production of H2 with nearly 70% purity.

[0054] Due to the high temperatures of the fumes emitted from glass furnaces, the method according to the invention is particularly suitable for use in glass furnaces, which include in particular glass melting furnaces, glass refining furnaces and glass melting and refining furnaces.

[0055] According to the invention, a stable flame can be obtained when ammonia is supplied as fuel by decomposing ammonia to produce hydrogen and burning the hydrogen in a furnace. This can be done efficiently in that waste heat from the furnace is used to decompose the ammonia. The furnace efficiency is further increased because the waste heat is also used to preheat an oxidant, preferably oxygen-enriched air or oxygen, before the oxidant is used to combust the hydrogen. [Brief description of the drawings]

[0056] [Figure 1] Equilibrium graph for NH3 decomposition without catalyst. [Diagram 2] FIG. 1 is a schematic diagram of a first embodiment of the method according to the invention, in which the furnace is a glass melting furnace. [Diagram 3] Schematic diagram of another embodiment of the method according to the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0057] FIG. 2 is a schematic diagram of a first embodiment of the method according to the invention, in which the furnace 10 is a glass melting furnace.

[0058] Combustion gases or fumes 20 exit the furnace 10 at a temperature T20 of about 1350°C.

[0059] Ammonia 30 is fed to cracker 40. Cracker 40 is non-catalytic.

[0060] The hot gases 20 exiting the furnace 10 are used to raise the temperature of the ammonia 30 in the cracker 40 to about 1000° C., the temperature at which non-catalytic ammonia decomposition occurs, by direct heat exchange between the hot gases 20 and the ammonia 30. Thus, the cracker 40 is a combined cracker / heat exchanger.

[0061] At this temperature, ammonia decomposes to produce a gas mixture 50 containing approximately 65% ​​H2 by volume.

[0062] The gas mixture 50 is supplied as fuel to one or more burners (not shown) of the furnace 10. By first decomposing the ammonia 30 and supplying the gas mixture 50 thus produced as fuel for combustion in the furnace 10, a more stable combustion is obtained compared to when the ammonia 30 is directly supplied as fuel to the furnace 10. In this manner, the present invention improves the efficiency and reliability of the furnace 10.

[0063] After being used to heat ammonia 30 in cracker 40, fumes 60 still contain a high level of residual heat energy. In the illustrated embodiment, fumes 60 are used to heat oxygen 70, having a purity of at least 95% by volume, to a temperature between 550-800° C., for example 650° C., in heat exchanger 80. Heat exchanger 80 may be a direct or indirect heat exchanger.

[0064] Oxygen 90 thus heated by heat exchanger 80 is also supplied to the burners of furnace 10 as a combustion oxidant, thereby further improving the efficiency of furnace 10.

[0065] The smoke 100 exiting the heat exchanger 80 is still NO X to the smoke 100 for reduction The temperature is high enough to allow NH3 injection. Therefore, a small amount of NH3 (NO formed) X (depending on the level of NO) into the smoke 100 downstream of the heat exchanger 80 to X can be reduced.

[0066] Although FIG. 2 shows the decomposer / heat exchanger 40 and the oxidant heat exchanger 80 as two separate units, it is possible to combine the decomposer / heat exchanger 40 and the oxidant heat exchanger 80 in one unit where both the ammonia 30 and oxygen 70 are heated and the ammonia is decomposed.

[0067] FIG. 3 is a schematic diagram of another embodiment of the method according to the invention.

[0068] According to said alternative embodiment, the residual thermal energy present in the discharged fumes 20 at about 1350 ° C is used to heat air 41, typically ambient air, used as intermediate fluid for indirect heat exchange in the air heat exchanger 40a, to about 550 ° C. The hot air 42 generated in the heat exchanger 40a is then fed to the decomposition device 40b to heat the ammonia 30 to about 500 ° C. The decomposition device 40b is a catalytic decomposition device. The catalyst present in the decomposition device 40b makes it possible to decompose the ammonia at 500 ° C to produce a gas mixture 50 containing about 75% by volume of H2. The gas mixture 50 is sent as fuel to the burners of the furnace 10. After being used to heat the intermediate fluid air 41 in the heat exchanger 40a, the fumes 60 are used to heat the oxygen 70 in the oxidant heat exchanger 80, in a similar manner to that shown in FIG. 2. The oxygen 90 heated in the heat exchanger 80 is also fed again as a combustion oxidant to the burners of the furnace 10.

[0069] Ammonia is NO X It may be injected (not shown) as a reductant into the fumes 100 exiting the oxidant heat exchanger 80. A major advantage of an embodiment such as that shown in Figure 3 in which a catalytic decomposition unit 40a is used is that the ammonia 30 does not need to be heated to the high temperatures required for non-catalytic ammonia decomposition as shown in Figure 2.

Claims

1. A method for operating a furnace (10), The aforementioned method, 1. A step of burning fuel with an oxidizer to generate thermal energy and smoke (20), 2. A step of heating the furnace (10) with the first portion of the thermal energy generated in step a, 3. A step of discharging the generated smoke (20) from the furnace (10) at a temperature of at least 900°C, preferably 1250°C to 1650°C, wherein the discharged smoke includes a second portion of the thermal energy generated in step a.

4. The second portion of the thermal energy generated in step a is 1. Before the heated oxidizer (90) is used to burn the fuel in step a, the oxidizer (70) as the fluid to be heated is heated by direct or indirect heat exchange with the emitted smoke (20) as the heat-retaining fluid.

2. As a heat source for decomposing ammonia (30) into a mixture (50) containing hydrogen, nitrogen, and undecomposed ammonia in the decomposition apparatus (40, 40a), Use During direct heat exchange, the heat-retaining fluid and the fluid to be heated are physically separated from each other by a fluid-impermeable heat conduction wall through which heat is transferred from the heat-retaining fluid to the fluid to be heated, while preventing mixing between the heat-retaining fluid and the fluid to be heated. And during indirect heat exchange, An intermediate heat transfer fluid (41) is used, and the heat-retaining fluid and the intermediate fluid (41) are physically separated from each other by a first fluid-impermeable heat conduction wall through which heat is transferred from the heat-retaining fluid to the intermediate fluid, while preventing mixing between the heat-retaining fluid and the intermediate fluid (41), in order to obtain a heated intermediate fluid (42). The heated intermediate fluid (42) and the fluid to be heated are separated from each other by a second fluid-impermeable heat conduction wall that prevents mixing between the heated intermediate fluid (42) and the fluid to be heated, while transferring heat from the heated intermediate fluid (42) to the fluid to be heated. A method wherein, in step a, at least a portion of the mixture (50) produced in step d-ii is burned as fuel in step a together with at least a portion of the heated oxidizer (90) produced in step d-i.

2. The method according to claim 1, wherein the NOx reducing agent is added to the exhausted smoke (20) before step d and / or after step d and / or between steps d-i and d-ii.

3. The method according to claim 2, wherein ammonia is used as an NOx reducing agent.

4. The method according to any one of claims 1 to 3, wherein in step d-i, the oxidizing agent (70) is heated by indirect heat exchange with the discharged smoke (20), and in step d-ii, the ammonia (30) is heated by direct heat exchange with the discharged smoke (20) upstream and / or inside the decomposition apparatus (40, 40b).

5. (a) The first portion of the emitted smoke (20) is used to heat the oxidizing agent (70) in step d-i, and the second portion of the emitted smoke (20) is used to heat the ammonia (30) in step d-ii, or (b) In step d-ii, the ammonia (30) is heated by direct heat exchange with the exhausted smoke (20) previously used in step d-i to heat the oxidizing agent (70). or (c) The method according to claim 4, wherein in step d-i, the oxidizing agent (70) is heated by indirect heat exchange with the exhausted smoke (20) previously used in step d-ii to heat the ammonia (30).

6. The method according to any one of claims 1 to 3, wherein the oxidizing agent (70) and the ammonia (30) are heated in steps d-i and d-ii, respectively, by direct heat exchange with the discharged smoke (20).

7. (a) The first portion of the emitted smoke (20) is used to heat the oxidizing agent (70) in step d-i, and the second portion of the emitted smoke (20) is used to heat the ammonia (30) in step d-ii, or (b) In step d-ii, the ammonia (30) is heated by direct heat exchange with the exhausted smoke (20) previously used in step d-i to heat the oxidizing agent (70), or (c) The method according to claim 6, wherein in step d-i, the oxidizing agent (70) is heated by direct heat exchange with the exhausted smoke (20) previously used in step d-ii to heat the ammonia (30).

8. The method according to any one of claims 1 to 3, wherein the oxidizing agent (70) and the ammonia (30) are heated in steps d-i and d-ii, respectively, by indirect heat exchange with the discharged smoke (20).

9. (a) The first portion of the emitted smoke (20) is used to heat the oxidizing agent (70) in step d-i, and the second portion of the emitted smoke (20) is used to heat the ammonia (30) in step d-ii, or (b) In step d, the second portion of the thermal energy generated in step a is used to heat the first and second intermediate fluids, the first intermediate fluid is used in step d-i to heat the oxidizer (70), and the second intermediate fluid is used in step d-ii to heat the ammonia (30) upstream and / or inside the decomposition apparatus (40, 40a). or (c) The method according to claim 8, wherein the discharged smoke (20) is used to heat the intermediate fluid (41), and the heated intermediate fluid (42) is used to heat the oxidizer (70) in step d-i, and to heat the ammonia upstream and / or inside the decomposition apparatus (40, 40a).

10. In step d, the second portion of the thermal energy generated in step a is used to heat the first and second intermediate fluids, the first intermediate fluid is used in step d-i to heat the oxidizer (70), and the second intermediate fluid is used in step d-ii to heat the ammonia (30) upstream and / or inside the decomposition apparatus (40, 40a). (a) The second intermediate fluid is heated by heat exchange with the exhausted smoke (20) previously used to heat the first intermediate fluid, or (b) The method according to claim 9, wherein the first intermediate fluid is heated by heat exchange with the exhausted smoke (20) previously used to heat the second intermediate fluid.

11. The discharged smoke (20) is used to heat the intermediate fluid (41), and the heated intermediate fluid (42) is used to heat the oxidizer (70) in step d-i, and to heat the ammonia upstream and / or inside the decomposition apparatus (40, 40a). (a) The first portion of the heated intermediate fluid (42) is used in step d-i to heat the oxidizing agent (70), and the second portion of the heated intermediate fluid (42) is used in step d-ii to heat the ammonia (30) upstream and / or inside the decomposition apparatus (40, 40a), or (b) In step d-ii, the ammonia (30) is heated by direct heat exchange with the heated intermediate fluid (42) previously used in step d-i to heat the oxidizing agent (70), or (c) The method according to claim 9, wherein in step d-i, the oxidizing agent (70) is heated by direct heat exchange with the heated intermediate fluid (42) previously used in step d-ii to heat the ammonia (30).

12. The method according to any one of claims 1 to 3, wherein the oxidizing agent (70) and the ammonia (30) are heated in a combined heat exchanger / decomposition apparatus (40a) in steps d-i and d-ii, respectively.

13. The method according to any one of claims 1 to 3, wherein the decomposition apparatus (40, 40a) is a non-catalytic decomposition apparatus.

14. The method according to any one of claims 1 to 3, wherein the decomposition apparatus (40, 40a) is a catalytic decomposition apparatus.

15. The method according to any one of claims 1 to 3, wherein the furnace is a glass furnace selected from the group consisting of a glass melting furnace, a glass refining furnace, and a glass melting and refining furnace.

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