A PROCESS OF NOx-FREE COMBUSTION OF NH3 FOR POWER PRODUCTION

Abstract

The present invention relates to a gaseous fuel composition comprising O2, N2, H2O, NH3, H2 and optionally further atmospheric components the molar content of H2 is denoted a, the molar content of NH3 is denoted b, the molar content of O2 is denoted c, the molar content of N2 is denoted d, and the molar content of H2O is denoted e, and (a + 1.5b – 2c) / (a + 2b + c + d + e) is in the range of 0 to 0.01, and a constitutes at least 3 mol% of the gaseous fuel composition. The gaseous fuel composition can be produced in a process of the invention and combusted in another process of the invention. The invention further includes a process set-up and a process of combustion of NH3. In the invention, NH3 is 15 combusted to form a flue gas stream virtually free of NOx.

Description

[0001]A PROCESS OF NOX-FREE COMBUSTION OF NH3 FOR POWER PRODUCTION Field of the invention The present invention relates to the combustion of NH3 and provides a gaseous fuel composition with a balance of O2, N2, H2O, NH3, H2allowing that NH3is combusted while minimising formation of NOx during the combustion. The invention also provides a process set-up with catalytic reactors for combusting NH3with minimal formation of NOx, and the invention provides methods of combusting NH3. Background Ammonia (NH3) is an interesting carbon-free fuel for power production, and NH3 may be combusted directly in an oxygen (O2) rich atmosphere, e.g. in engines, gas turbines, boilers for steam turbines or steam or other machines. However, compared with conventional fuels, e.g. carbon based fuels, the use of NH3 as a fuel is associated with serious technical problems caused by low flammability and high formation of so-called NOx gasses, which are unacceptable in an exhaust gas. In particular, the combustion will generally occur according to a combination of Reaction 1 and Reaction 2. Reaction 1 2 NH3+ 5 / 2 O2→ 2 NO + 3 H2O Reaction 2 2 NH3+ 3 / 2 O2→ N2+ 3 H2O In principle, a clean combustion of NH3 according to Reaction 2 is thinkable, but achieving this can involve deficit oxygen and tight control of the combustion process, especially in consideration of the low flammability of NH3 and the high selectivity for NO formation, whenever NH3 is exposed to excess O2. As an alternative to direct combustion of NH3, cracking NH3to H2and N2 according to Reaction 3 prior to the combustion has also been used, so that the fuel includes H2 that allows a simple and clean combustion according to Reaction 4. A23115-WO-PCT Reaction 3 2 NH3 ↔ N2 + 3 H2 Reaction 4 H2+ ½ O2↔ H2O The enthalpies of Reaction 1 to Reaction 4 at 25°C are summarised in Table 1. Table 1 – Enthalpies Reaction 1 + 400 kJ / mol NH3-gas Reaction 2 + 318 kJ / mol NH3-gas Reaction 3 - 46.2 kJ / mol NH3-gas Reaction 4 +241.9 kJ / mol H2The equilibrium mol fractions of NH3, H2and N2from Reaction 3 may be estimated from Equation 1, where P is the absolute pressure in bar, Teqis the temperature (in K), and (NH3), ((N2) and (H2) are the respective mol fractions. Equation 1 (NH3)2 / ((N2) x (H2)3x P2) = Kp= 10↑(5455 / Teq– 11.9) However, as NH3 may also be present after the cracking process there is still a risk that NO is formed according to Reaction 1, so that the cracking process does not remove the need for combustion at fuel rich conditions. US 2003 / 232224 discloses a method for hydrogen production from ammonia based on the catalytic dissociation of gaseous ammonia in a cracker, where the ammonia cracker supplies a fuel cell with a mixture of hydrogen and nitrogen, and where most of the supplied hydrogen is burned in the ammonia cracker for the supply of the energy needed for the ammonia dissociation process. US 2018 / 355794 discloses a gas turbine system having a source of ammonia and a source of an oxygen-containing gas, a first combustion chamber connected to receive ammonia, a hydrogen-rich gas stream and oxygen-containing gas, a turbine connected to receive an exhaust gas stream from the first combustion chamber; and a second combustion chamber A23115-WO-PCT connected to receive an exhaust gas from the turbine, ammonia and a hydrogen-rich gas stream. JP2020147478A discloses a gas turbine plant that uses gas obtained by decomposition of ammonia as fuel. JP2018095512 discloses a system for supplying a hydrogen-containing fuel to a plant including a steam turbine, the system including: a first ammonia- decomposing apparatus for decomposing ammonia to generate nitrogen and hydrogen; a fuel supply line for supplying a hydrogen-containing fuel containing the hydrogen generated with the first ammonia-decomposing apparatus to a combustion unit in the plant; and an extraction steam line for leading extraction steam of a steam turbine driven by steam heated by heat exchange with a combustion gas generated with the combustion unit to the first ammonia- decomposing apparatus. Summary The present invention relates to a gaseous fuel composition comprising O2, N2, H2O, NH3, H2 and optionally further atmospheric components the molar content of H2is denoted a, the molar content of NH3is denoted b, the molar content of O2 is denoted c, the molar content of N2 is denoted d, and the molar content of H2O is denoted e, and (a + 1.5b – 2c) / (a + 2b + c + d + e) is in the range of 0 to 0.01, and a constitutes at least 3 mol% of the gaseous fuel composition. In a specific example, the molar ratio of H2to NH3≥ 1.5x / (1-x) with x being in the range of 0.16 to 0.98. The ratio (a + 1.5b – 2c)) / (a + 2b + c + d + e) corresponds to the molar fraction of H2 in a flue gas obtained from combustion, e.g. equilibration, of the gaseous fuel composition, and the molar fraction may also be referred to as a4* in the context of the present disclosure. The ratio (a + 1.5b – 2c)) / (a + 2b + c + d + e) is preferably in the range of 0.001 to 0.005. The relation between a, b and c may also be referred to as a*. Thus, (a + 1.5b – 2c) / (a + 2b + c + d + e) = a*, where a* represents the molar content of H2 in the flue gas. In another aspect, the gaseous fuel composition can be produced in a process of producing a gaseous fuel composition comprising the steps of: providing a stream of gaseous NH3; providing a catalytic decomposition reactor A23115-WO-PCT having an NH3 inlet and a decomposition product outlet, which catalytic decomposition reactor comprises an NH3-decomposition catalyst between the NH3 inlet and the decomposition product outlet, and a heating arrangement configured to increase the temperature of a gas in the catalytic decomposition reactor; applying the stream of gaseous NH3at the NH3inlet at a temperature in the range of 50°C to 150°C and passing the stream of gaseous NH3 through the decomposition catalyst to obtain a stream of decomposed NH3 corresponding to a decomposition of NH3in the range of 0.16 to 0.98 and having a temperature in the range of 400°C to 650°C at the decomposition product outlet, the stream of decomposed NH3 comprising H2, N2, and NH3; providing an oxygen rich gas containing N2, H2O and optionally further atmospheric components, and an amount of O2in the range of 0.70 mol to 0.75 mol per mol of NH3 in the stream of gaseous NH3; and mixing the stream of decomposed NH3 with the oxygen rich gas, and optionally also a diluent gas, to obtain the gaseous fuel composition. The gaseous fuel composition can be combusted to form a flue gas stream virtually free of NOx, and in another aspect the invention relates to a process of producing a heated flue gas stream comprising the steps of: providing a catalytic combustion reactor having a catalyst chamber with a fuel gas inlet and a flue gas outlet, which catalyst chamber comprises a combustion catalyst between the fuel gas inlet and the flue gas outlet; providing a gaseous fuel composition of the disclosure; applying the gaseous fuel composition at the fuel gas inlet at an ignition temperature in the range of 50°C to 450°C, e.g. 200°C to 300°C, and a pressure in the range of 1 bar abs to 80 bar abs, e.g. in the range of 10 bar abs to 30 bar abs; passing the gaseous fuel composition through the combustion catalyst to convert the gaseous fuel composition to the heated flue gas stream having a temperature in the range of 700°C to 1500°C; and obtaining the heated flue gas stream at the flue gas outlet. The temperature at the fuel gas inlet may also be referred to as T3 and temperature at the flue gas outlet may also be referred to as T4. In general, the increase in temperature between the fuel gas inlet and the flue gas outlet, i.e. T4– T3, should be ≥400°C. A23115-WO-PCT The processes of the invention can be performed in an appropriately designed process set-up, and in another aspect, the invention relates to a process set-up comprising: a catalytic decomposition reactor having an NH3 inlet and a decomposition product outlet, which catalytic decomposition reactor comprises an NH3-decomposition catalyst between the NH3inlet and the decomposition product outlet, and a heating arrangement configured to increase the temperature of a gas in the catalytic decomposition reactor; a catalytic combustion reactor having a catalyst chamber with a fuel gas inlet and a flue gas outlet, which catalyst chamber comprises a combustion catalyst between the fuel gas inlet and the flue gas outlet; an air inlet, an exhaust gas outlet, an oxidant mixing site having a diluent inlet, a fuel composition mixing site; and a pipe network comprising pipes providing that the air inlet is in fluid communication with the oxidant mixing site, the decomposition product outlet is in fluid communication with the diluent inlet, and the oxidant mixing site is in fluid communication with the fuel composition mixing site, the fuel composition mixing site is in fluid communication with the fuel gas inlet, the flue gas outlet is in fluid communication with the exhaust gas outlet. In an example, the process set-up further comprises a flue gas branching site, and the flue gas outlet is in fluid communication with the flue gas branching site, which is in fluid communication with the exhaust gas outlet and the diluent inlet. The diluent inlet may also be at the fuel composition mixing site. The invention also relates to a process of combustion of NH3comprising providing a process set-up of the invention; providing a stream of gaseous NH3; applying the stream of gaseous NH3 at the NH3 inlet at a temperature in the range of 50°C to 150°C and passing the stream of gaseous NH3through the decomposition catalyst to obtain a stream of decomposed NH3 corresponding to a decomposition of NH3 in the range of 0.16 to 0.98 and having a temperature in the range of 400°C to 650°C at the decomposition product outlet, the stream of decomposed NH3 comprising H2, N2, and NH3; providing an oxygen rich gas containing an amount of O2 in the range of 0.70 mol to 0.75 mol per mol of NH3 in the stream of gaseous NH3and leading the oxygen rich gas to the oxidant mixing site, mixing the stream of oxygen rich gas with a diluent gas stream comprising at least one of N2, H2O, and H2 to provide an oxidising gas A23115-WO-PCT comprising O2, and at least one of N2, H2, and H2O; leading the oxidising gas and the stream of decomposed NH3to the fuel composition mixing site and mixing the oxidising gas and the stream of decomposed NH3 to provide a gaseous fuel composition; applying the gaseous fuel composition at the fuel gas inlet at an ignition temperature in the range of 50°C to 450°C, e.g.200°C to 300°C, and a pressure in the range of 1 bar abs to 80 bar abs, e.g.10 bar abs to 30 bar abs; passing the gaseous fuel composition through the combustion catalyst to convert the gaseous fuel composition to a heated flue gas stream having a temperature in the range of 700°C to 1500°C. The temperature at the fuel gas inlet may also be referred to as T3 and temperature at the flue gas outlet may also be referred to as T4. In general, the increase in temperature between the fuel gas inlet and the flue gas outlet, i.e. T4– T3, should be ≥400°C. It is preferred that H2, NH3 and O2 in the inlet gas stream and the gaseous fuel composition are equilibrated in the catalytic combustion reactor at deficit O2thereby forming a flue gas stream with only H2, N2and H2O and substantially no NO and no O2 when completely equilibrated. In particular, NO may be formed whenever NH3 is exposed to excess O2 which may be the case locally where the gas is not sufficiently mixed. The flue gas stream may be used as a diluent flue gas stream that is mixed with the decomposed NH3 and the oxygen rich gas to provide a gaseous fuel composition of the disclosure. In an example, the process set-up has a flue gas branching site as defined above, and the diluent gas stream is a diluent flue gas stream composed of N2, H2O, H2 and optionally further atmospheric components from the flue gas branching site, and the method comprises dividing the heated flue gas stream into an exhaust gas stream and the diluent flue gas stream at the flue gas branching site, wherein the ratio between the exhaust gas stream to the diluent flue gas stream is in the range of 2 / 3 to 3 / 2, and leading the exhaust gas stream to the exhaust gas outlet and leading the diluent flue gas stream to the oxidant mixing site. The contents of the components may also indicate the respective stream, so that (a3+1.5b3-2c3) / (a3+2b3+d3+e3) = a4*, with 3 representing the gaseous fuel composition entering the catalytic combustion reactor, and 4 represents flue gas the exiting the catalytic combustion reactor. The invention can also be A23115-WO-PCT said to relate to a process of combustion of NH3 and H2 in a gaseous fuel composition at an ignition temperature in the range of 50°C to 400°C, e.g. 200°C to 300°C, at a pressure in the range of 2 bar abs to 80 bar abs. to a flue gas stream with the gaseous fuel composition composed of: a3mol / s H2, b3mol / s NH3, c3mol / s O2, d3mol / s N2(optionally including further atmospheric components), and e3mol / s H2O mol / s, wherein a3+ 1.5b3– 2c3= a4≥ 0, and with the flue gas stream being in a total amount of a3+ 2b3+ d3+ e3mol / s and with the flue gas stream being composed of: a4mol / s H2, d3+ 0.5b3mol / s N2 (optionally including further atmospheric components), and e3+ 2c3mol / s H2O, with the flue gas stream being substantially free of NH3, O2, NO, N2O and NO2and with the flue gas stream containing a4* mol % H2calculated by Equation 2: Equation 2 a4* = 100 (a3+1.5b3-2c3) / (a3+2b3+d3+e3) mol% H2wherein a4* is in the range of 0 mol% to 1 mol%, e.g.0.1 mol% to 0.5 mol% H2. The components described above have a subscripted number, and this number refers to the number of the stream as shown in Figure 1 and Figure 3. Thus, a4* is H2 in the flue gas stream and c3is O2 in the gaseous fuel composition, and so forth. The streams as shown in Figure 1 may also be referred to with the letter “F” likewise having the subscripted number of the corresponding stream, so that F3 is the gaseous fuel composition, and F4 is the flue gas stream. A23115-WO-PCT The amounts of H2, O2 and N2 can be measured using a GC-TCD (gas chromatography with thermal conductivity detector). A GC-TCD can also be used to detect NOx and NH3. The amounts of H2O and NH3 can be determined, for instance, by Fourier transform infrared spectroscopy (FTIR). GC-TCD and FTIR measurement are well know to the skilled person, and they can be used to measure the amounts of H2, O2, N2, NOx, H2O and NH3 as described above without departing from the scope of the claims. The enthalpy Hn of stream Fn at temperature Tn may be calculated as the sum of enthalpies of each component calculated as ideal gases at Tnaccording to Equation 3: Equation 3 Hn = Ha + Hb + Hc + Hd + He kJ / s = kW As summarised above, (a3+1.5b3-2c3) / (a3+2b3+d3+e3) = a4≥ 0, although it is preferred that 0.2 mol% H2. It is preferred that the ignition temperature in the range of 200°C to 300°C. It is further preferred that the pressure in the range of 10 bar abs to 30 bar abs. The processes of the invention may use a diluent gas stream, e.g. a diluent flue gas stream. In general, the diluent gas stream is added to form the gaseous fuel composition, where it serves to control, especially lower, the amount of H2 in gaseous fuel composition. By adding a diluent gas stream, the temperature obtained during the combustion of the gaseous fuel composition can be controlled, especially lowered, to be in appropriate temperature regime in the catalytic combustion reactor. The appropriate temperature regime is determined by the general design of the combustion system with due consideration of how the provided streams are to be utilised, e.g. as dependent on their temperatures. For example, with a diluent stream, an increase of the temperature, e.g. T4 – T3, in the catalytic combustion reactor beyond 1500°C can avoided. In an example, the diluent gas stream is a flue gas stream obtained from the combustion of the gaseous fuel composition. In another example, the diluent gas stream is a stream of vapour. A23115-WO-PCT In a further example, a diluent gas stream is not added in the formation of the gaseous fuel composition, e.g. the content of H2in the gaseous fuel composition is at least 5 mol%, e.g. 8 mol% to 10 mol%, which can stabilise the thermal combustion. When the gaseous fuel composition is undiluted, thermal combustion, e.g. thermal combustion upstream of the combustion catalyst, of the un-diluted fuel gas can reach a temperature above 2000°C, e.g. about 2130°C, and the process set-up may contain one or more additional heat exchangers configured to extract heat from the thermal combustion, e.g. to be utilised in steam turbines. An additional heat exchanger can reduce the temperature at the at the flue gas outlet to be in the range of 700°C to 1500°C. Thus, in an example, the process of combustion of NH3does not comprise mixing the stream of oxygen rich gas with a diluent gas stream. For example, steam superheaters upstream of the catalytic combustion reactor, in which the equilibration is completed, may cool the stream to about 1250°C. The invention relates to a gaseous fuel composition, processes and to a process set-up for performing the processes of the invention. The process set- up comprises a catalytic decomposition reactor, a catalytic combustion reactor, an air inlet, an exhaust gas outlet, a diluent inlet, an oxidant mixing site, a fuel composition mixing site, a flue gas branching site, and a pipe network. In general, the catalytic decomposition reactor, the catalytic combustion reactor, the air inlet, the diluent inlet, the exhaust gas outlet, the oxidant mixing site, the fuel composition mixing site, and the flue gas branching site may be referred to collectively as “process set-up elements” so that when a process set-up element is mentioned, this may refer to any of the catalytic decomposition reactor, the catalytic combustion reactor, the air inlet, the diluent inlet, the exhaust gas outlet, the oxidant mixing site, the fuel composition mixing site, and the flue gas branching site. Moreover, the process set-up may comprise additional functions and these may also be referred to as process set-up elements. The process set-up comprises various mixing sites and the reactors generally have appropriate inlets and outlets, also when these are not specified. In general, sites in the process set-up may have several of the defined functions. For example, the oxidant mixing site and the fuel composition A23115-WO-PCT mixing site may be combined into one site, and the site may be at the fuel gas inlet or upstream from the fuel gas inlet. The pipe network provides useful connections between the process set- up elements. The pipes of the pipe network may be selected freely based on the specific gases, temperatures, and pressures, but in general pipes made from steel or stainless steel can be used for any pipe in the pipe network. The pipes in the pipe network may be connected to each other and to relevant process set-up elements using any type of connection available in the field. Reactions taking place in the process set-up elements, except in the catalytic decomposition reactor, although especially in the catalytic combustion reactor, are generally performed without adding heat to the reaction and further without adding mass except as otherwise defined for the corresponding reaction. When no heat is added, a reaction is considered to take place under adiabatic conditions. However, there may be an inevitable loss of heat from a process set-up element, but the reaction taking place is still considered to be under adiabatic conditions despite the inevitable loss of heat. Thus, in the present context the term “adiabatic” refers to conditions where heat is not added to or removed from the reaction. The process set-up elements, e.g. the catalytic decomposition reactor, the catalytic combustion reactor and / or pipes in the process set-up, may include thermal insulation to minimise loss of heat from a thermally insulated process set-up element. The process set-up elements, especially the catalytic decomposition reactor and the catalytic combustion reactor, are preferably designed to allow a reaction taking place in the process set-up element to reach equilibrium. For example, in a catalytic reactor, e.g. the catalytic decomposition reactor or the catalytic combustion reactor, the distance between the inlet for reactants, e.g. the NH3inlet for the catalytic decomposition reactor or the fuel gas inlet for the catalytic combustion reactor, and the product outlet, e.g. the decomposition product outlet for the catalytic decomposition reactor or the flue gas outlet for the catalytic combustion reactor, combined with the amount and packing of catalyst, e.g. the NH3-decomposition catalyst for the catalytic decomposition reactor or the combustion catalyst for the catalytic combustion reactor, may be A23115-WO-PCT configured so that the reaction reaches equilibrium between the inlet and the outlet. However, the process set-up elements are not required to be configured for a reaction taking place in a process set-up element to reach equilibrium. Designing a reactor to allow a reaction in the reactor to reach equilibrium is within the knowledge of the skilled person. The present processes may employ atmospheric air. Correspondingly, the gaseous fuel composition and other gaseous compositions and reaction streams employed in the process can contain components present in the atmosphere and thereby also in atmospheric air. In general terms, the atmosphere and atmospheric air contains a majority of N2, a significant fraction of O2, and other components generally present at levels of up to about 1%. Any other component present in the atmosphere other than N2and O2is referred to as a “further atmospheric component” in the present context. In the present context, the further atmospheric components may include noble gases, e.g. argon, neon, and helium, CO2, and H2O, although the further atmospheric components are not limited to these species. In addition, when N2 is mentioned in the present context, it is to be understood that N2 may mean N2 alone or N2 may also include further atmospheric component even when these are not mentioned or specified together with the N2. The processes of the invention are based on gaseous streams, and the pressures of the gasses in the different steps can be selected freely as appropriate for the specific reaction. The processes, and also the process set- up, may include compressors or decompressors to modify the pressure of a gaseous stream to have an appropriate value. However, the NH3 to be decomposed according to the processes can be supplied as liquid NH3, e.g. from a storage tank. The liquid NH3 is then converted to gaseous form before being decomposed. The basic idea behind the process is that in order to avoid any NOx- formation, NH3 should only be exposed to O2 in the presence of excess H2 that will remove O2 very fast and before O2 can react with NH3. The process of the production of a heated flue gas stream may employ any example of the gaseous fuel composition of the present disclosure, and in particular, the gaseous fuel composition may be provided in the process of producing a A23115-WO-PCT gaseous fuel composition of the present disclosure. Excess H2 may be provided from the catalytic decomposition reactor in which NH3is decomposed into N2 + 3 H2, i.e. according to Reaction 3, across the NH3-decomposition catalyst in the catalytic decomposition reactor. Combustion of decomposed NH3generates heat. The generated heat can be used in the generation of kinetic energy as is commonly done for a conventional combustion process. However, in the present invention, especially the heat generated in the combustion of the decomposed NH3is also used to heat process streams to appropriate temperatures depending on the relevant process step. Thereby, an improved energy balance is obtained, which in turn results in a higher energy efficiency for the process. In this regard, combustion of the decomposed NH3can be compared to directly combusting NH3 and the invention thereby provides a much improved combustion of NH3. This advantage is relevant not just for the aspect relating to the process of combustion of NH3, but also for all other aspects of the invention, i.e. the gaseous fuel composition, the process of producing a gaseous fuel composition, the process of producing a heated flue gas stream and the process set-up. The present inventor believes that the improved energy efficiency in the combustion of NH3 is provided by the combination of using catalytic decomposition of NH3 and catalytic combustion of the decomposed NH3provided from the decomposition. Furthermore, by controlling the amount of O2relative to the amount of NH3for the decomposition reaction, i.e. in the range of 0.70 mol O2 to 0.75 mol O2 per mol of NH3 before decomposition, e.g. 0.73 mol O2 to 0.75 mol O2 per mol of NH3 before decomposition, the present inventor has found that substantially no NOxgasses, especially no NO, but also no N2O and NO2, are formed in the combustion of the decomposed NH3. It is particularly advantageous for avoiding formation of NOx gasses when the gaseous fuel composition comprises a small excess of H2compared to the composition obtained from decomposition of NH3. As for the improved energy efficiency, the present inventor also believes that this effect is obtained by using a combination catalytic decomposition of NH3and catalytic combustion of the decomposed NH3provided from the decomposition. The control of the combustion process with respect to avoiding formation of NOx gasses is even A23115-WO-PCT more pronounced when an H2-containing diluent gas is included in the gaseous fuel composition of the invention. Thus, the invention provides substantially NOx-free combustion of NH3 at high energy efficiency. In the present disclosure, a stream of NH3 may be decomposed according to Reaction 3 in the provision of a gaseous fuel composition. The gaseous fuel composition may thus comprise NH3 and H2 from the decomposed NH3. In the present context, the according to Reaction 3 may be referred to as a decomposition or a cracking reaction, and the two terms may be used interchangeably. The decomposition process may be described in terms of a conversion factor x, where x is the fraction of NH3 decomposed. Correspondingly, x can have a value of up to 1. When the decomposition is performed at a value of x of 1, no NH3will be included in the decomposed stream, and therefore no NOx components can be formed in the subsequent combustion. The process of the invention advantageously provides combustion where no NOxcomponents are formed despite a content of NH3in the gaseous fuel composition being combusted, and in order to achieve this, x is below 1 so that the decomposed NH3 comprises residual NH3 and x should therefore not exceed 0.98. However, x should be at least 0.16. For example, x may be in the range of 0.20 to 0.96. The conversion factor x also describes the amount of H2 obtained in the decomposition process. In general terms, the molar ratio of H2to NH3obtained from the decomposition process is 1.5x / (1-x). In the present disclosure, the molar ratio of H2 to NH3 ≥ 1.5x / (1-x). Thus, when the molar ratio of H2 to NH3 = 1.5x / (1-x), H2 in the gaseous fuel composition may be provided only from the decomposition process. When the molar ratio of H2to NH3> 1.5x / (1-x), a further source of H2 is included in the gaseous fuel composition than H2 obtained from the decomposition process. However, it is also contemplated that the gaseous fuel composition is provided from mixing H2and NH3obtained from other sources that decomposition of NH3. The decomposition process may be performed in any appropriate reactor. In an example, the decomposition process is performed in a catalytic decomposition reactor comprising a catalyst, which catalyses the reaction according to Reaction 3. The catalyst may for example be a catalyst for the A23115-WO-PCT synthesis of NH3, e.g. according to the Haber–Bosch process. In general, any catalyst useful in the Haber–Bosch process may also be useful in the decomposition of NH3 according to Reaction 3. Multiple commercial NH3 synthesis catalysts are readily available commercially, and more catalysts are known to the skilled person. In general, x is in the range of 0.16 to 0.98, and the decomposition process may be set up to obtain any value of x within this range. For example, x may be in the range of 0.2 to 0.8, or 0.3 to 0.7. In an aspect, the invention relates to a gaseous fuel composition. The gaseous fuel composition may be provided from decomposed NH3 mixed with a source of O2at an appropriate ratio. Being a mixture of decomposed NH3, the gaseous fuel composition comprises O2, N2, NH3, and H2. The source of O2is preferably atmospheric air, and in this case, the gaseous fuel composition comprises a balance of O2, N2, H2O, NH3, H2 and optionally further atmospheric components. As the NH3has been decomposed, the molar ratio of H2to NH3from the decomposition is 1.5x / (1-x) with x being in the range of 0.16 to 0.98, e.g. 0.2 to 0.96. The gaseous fuel composition may comprise H2 from an additional source, in particular recycled exhaust gas from the decomposition of the gaseous fuel composition, and therefore the gaseous fuel composition may have a molar ratio of H2 to NH3 ≥ 1.5x / (1-x), with x being in the range of 0.16 to 0.98, e.g.0.2 to 0.96. In an example, the gaseous fuel composition has a molar ratio of H2to NH3> 1.5x / (1-x), with x being in the range of 0.16 to 0.98, e.g.0.2 to 0.96, 0.2 to 0.8, or 0.3 to 0.7. The present inventor has found that despite decomposing the NH3 prior to combusting the decomposed NH3, control of the amount of O2relative to the amount of NH3before decomposition can be used to ensure that the combustion of residual NH3 in the gaseous fuel composition takes place without formation of NOx gasses. The clean combustion is particularly relevant, when the combustion of the gaseous fuel composition of the invention is performed in a catalytic combustion reactor of the present disclosure. Without being bound by theory, the inventor believes that the combustion catalyst allows that when gaseous fuel composition of the invention is combusted via the combustion catalyst, the overall effect is that NH3is combusted without formation of NOx gasses. Thereby, the invention provides A23115-WO-PCT a gaseous fuel composition that can be combusted catalytically without formation of NOxgasses. Specifically, the amount of O2relative to the amount of NH3 before decomposition is in the range of 0.70 to 0.75, e.g. in the range of 0.7 to 0.75 or 0.74 to 0.745. The appropriate relation between the components of the gaseous fuel composition may also be expressed in terms of the amounts of the components. For example, the molar content of H2 may be denoted a, the molar content of NH3 may be denoted b, and the molar content of O2may be denoted c, and (a + 1.5b – 2c) / (a + 2b + c + d + e) is in the range of 0 to 0.01, e.g. in the range of 0.001 to 0.005. In addition, H2 constitutes at least 2 mol%, in particular at least 3%, at least 4%, or at least 5%, of the gaseous fuel composition. A particularly preferred range for a is 6 mol% to 9 mol%. In a specific example, a diluent flue gas has been added to form the gaseous fuel composition, and the gaseous fuel composition comprises O2 in the range of 7 mol% to 8 mol%; N2 in the range of 63 mol% to 65 mol%; H2O in the range of 15 mol% to 17 mol%; NH3in the range of 1 mol% to 10 mol%; H2 in the range of 2 mol% to 15 mol%; and optionally further atmospheric components to balance. The catalytic decomposition reactor has an NH3inlet and a decomposition product outlet, and the NH3-decomposition catalyst is contained between the NH3 inlet and the decomposition product outlet. Thereby, the NH3 entering the catalytic decomposition reactor at the NH3inlet is brought into contact with the NH3-decomposition catalyst. The NH3-decomposition catalyst catalyses the reaction according to Reaction 3 to convert the NH3 to a mixture of H2 and N2 with residual NH3 depending on the value of x, which leaves the catalytic decomposition reactor at the decomposition product outlet. In the present context, the stream of material between the NH3 inlet and the decomposition product outlet may be referred to as the “decomposing NH3”. Thus, the term “decomposing NH3” may refer to NH3, a mixture of H2and N2with residual NH3, or a mixture of H2 and N2 without residual NH3. The gas leaving the catalytic decomposition reactor at the decomposition product outlet, i.e. the mixture of H2and N2with or without residual NH3, is generally referred to as a stream of “decomposed NH3”. Thus, the term “decomposed NH3” refers to a mixture of A23115-WO-PCT H2 and N2 with or without residual NH3 as dependent on the value of x in the decomposition process. The NH3-decomposition catalyst may be any catalyst capable of catalysing the reaction according to Reaction 3. Relevant catalysts include commercial Haber-Bosch catalysts. A preferred NH3-decomposition catalyst is an iron-based NH3-synthesis catalyst. Iron-based NH3-synthesis catalyst are well-known to the skilled person and commercially readily available. The catalytic decomposition reactor further comprises a heating arrangement configured to increase the temperature of a gas in the catalytic decomposition reactor. For example, the catalytic decomposition reactor may be configured to increase the temperature of the decomposing NH3so that the decomposition product, i.e. the mixture of H2and N2with residual NH3, at the decomposition product outlet has a higher temperature than the NH3 at the NH3 inlet. In an example, the catalytic decomposition reactor comprises an external container housing an internal container for the NH3-decomposition catalyst, which internal container has the NH3 inlet and the decomposition product outlet, and which external container has a heating medium inlet and a heating medium outlet. Thereby a heating medium in the external container is brought into thermal contact with the internal container allowing transfer of heat from the heating medium to the decomposing NH3 in the internal container. The NH3 inlet may be at any location of the catalytic decomposition reactor, and the decomposition product outlet may likewise be at an any location of the catalytic decomposition reactor. The heating medium inlet and the heating medium outlet may be at any location in the external container. For example, the heating medium inlet may be adjacent to the NH3inlet, or the heating medium inlet may be adjacent to the decomposition product outlet. Correspondingly, the heating medium outlet may be adjacent to the NH3 inlet, or the heating medium outlet may be adjacent to the decomposition product outlet. When the heating medium inlet is adjacent to the NH3 inlet, and the heating medium outlet is adjacent to the decomposition product outlet, the heating medium and the decomposing NH3are considered to flow in a co-current fashion. When the heating medium inlet is adjacent to the decomposition product outlet, and the heating medium outlet is adjacent to the NH3 inlet, the heating medium and the A23115-WO-PCT decomposing NH3 are considered to flow in a counter current fashion. In the present context, the co-current set-up and the counter current set-up are considered equivalent to a co-current heat exchanger and a counter current heat exchanger, respectively, and heat transfer between the decomposing NH3 in the internal container and the heating medium in the external container can be calculated as for conventional co-current heat exchangers and counter current heat exchangers, respectively. In an example, the catalytic decomposition reactor comprises an external container housing an internal container for the NH3-decomposition catalyst, and the external container has a heating medium inlet opposite a heating medium outlet to define a heating medium flow direction from the heating medium inlet to the heating medium outlet, and the internal container comprises a plurality of tubes containing NH3-decomposition catalyst, which tubes are placed at an angle in the range of 45° to 135°, e.g.60° to 120°, such as about 90°, to the heating medium flow direction. Thereby, the heating medium is provided in a cross-flow relative to the flow direction of the decomposing NH3. This catalytic decomposition reactor may also be referred to as a tubular catalytic decomposition reactor in the present context. The tubes of the plurality of tubes may be parallel to each other, although they are not limited to be parallel to each other. The tubes of the plurality of tubes may comprise an inlet subset of tubes and an outlet subset of tubes, e.g. the inlet subset of tubes may be in an NH3inlet section of the external container, and the outlet subset of tubes may be in a decomposition product outlet section of the external container. Thus, the inlet subset of tubes is configured to receive NH3 from the NH3 inlet and supply decomposing NH3to the outlet subset of tubes, which outlet subset of tubes is configured to provide decomposed NH3 to the decomposition product outlet. The NH3 inlet section of the external container may be adjacent to the heating medium inlet or the NH3inlet section of the external container may be adjacent to the heating medium outlet. It is preferred that the NH3 inlet section of the external container may be adjacent to the heating medium inlet. The tubular catalytic decomposition reactor allows a more efficient control of the temperature of the decomposing NH3compared to a catalytic decomposition reactor working in a counter current fashion or in a co-current heat fashion. In A23115-WO-PCT an aspect, the invention relates to the tubular catalytic decomposition reactor, e.g. to any example of the tubular catalytic decomposition reactor defined above. The tubular catalytic decomposition reactor is especially advantageous in decomposing NH3 to be used for subsequent combustion of the decomposed NH3, as it allows more efficient recycling of heat generated in the combustion of the decomposed NH3. Regardless of the principle of heat transfer, i.e. if the catalytic decomposition reactor works in a counter current fashion or in a co-current heat fashion, or if the catalytic decomposition reactor is a tubular catalytic decomposition reactor having a cross-flow of heating medium relative to the flow of decomposing NH3, the NH3may enter the NH3inlet at a temperature in the range of 50°C to 150°C, e.g.100°C to 150°C, and the decomposed NH3may have a temperature in the range of 400°C to 650°C at the decomposition product outlet, with the exhaust gas entering the heating medium inlet at a temperature in the range of 500°C to 800°C. In an example, the fuel composition mixing site comprises an ejector, e.g. an ejector configured to provide an increase in the pressure of the fuel gas stream by 2 bar to 4 bar by injecting the NH3decomposed gas at 20 bar to 40 bar above the pressure of the main gas stream. The process set-up of the invention includes a catalytic combustion reactor, and correspondingly the processes of the invention may also employ a catalytic combustion reactor. The catalytic combustion reactor may be any reactor that can combust the decomposed NH3, i.e. a mixture of H2 and N2 with residual NH3 as dependent on the value of x in the decomposition process. The catalytic combustion reactor has a catalyst chamber with a fuel gas inlet and a flue gas outlet. The fuel gas inlet receives the gaseous fuel composition. However, it is also contemplated that the catalytic combustion reactor has an inlet to receive the decomposed NH3, and a separate inlet to receive the oxygen rich gas. The catalyst chamber comprises a combustion catalyst between the fuel gas inlet and the flue gas outlet. The combustion catalyst may be any catalyst capable of oxidising NH3, in particular according to Reaction 2, and H2according to Reaction 4. The combustion catalyst may for example comprise a carrier material and a catalytic metal or a catalytic metal compound, e.g. a A23115-WO-PCT metal oxide. It is also contemplated that the combustion catalyst does not comprise a carrier material but that a catalytic metal and / or a catalytic metal compound are provided in an appropriate from without need for a carrier material. A carrier material included in the catalytic combustion reactor should withstand the high temperature obtained during the combustion, but otherwise the carrier material may be selected freely. A carrier material may also be relevant for the catalyst in the catalytic decomposition reactor, and as for the carrier material of the catalytic decomposition reactor, the carrier material of the catalytic decomposition reactor, the carrier should be able to withstand the temperatures during the decomposition process, but the carrier material is not otherwise limited. Exemplary carrier materials, e.g. for the catalytic combustion reactor or for the catalytic decomposition reactor, comprise an atom of a metal or a metalloid, or atoms of a metal in combination with atoms of a metalloid, and a counter atom, e.g. oxygen, carbon and / or nitrogen. The carrier material may for example be a ceramic material. For example, the carrier material may be an oxide of aluminium, silicon or a transition metal, a nitride of aluminium, silicon or a transition metal, or a carbide of aluminium, silicon or a transition metal. Preferred carrier materials for the catalytic combustion reactor comprise α-Al2O3 and SiC. The carrier material may have any form as desired. For example, the carrier material may have a particulate form. When the carrier material has a particulate form the specific surface area of the carrier material should be as large as possible. For example, the specific surface area of the carrier material may be at least 10 m2 / g, e.g.at least 50 m2 / g, at least 100 m2 / g, or preferably at least 200 m2 / g. The dimensions of particles of a carrier material may be approximately the same in the three dimensions, or one dimension may vary from the other two dimensions. When the carrier material has a particulate form, the carrier material may be present in the corresponding reactor as a packed bed of carrier material particles. The carrier material may also include structures of a defined shape and size to improve the flow of fluid through the catalytic reactor. For example, the carrier material may have a ring shape, e.g. the carrier material may have a A23115-WO-PCT shape known as a Raschig ring, or another shape. A ring-shaped carrier material may for example be made from α-Al2O3, MgOAl2O3or SiC. The carrier material may be sintered. In another example, the carrier material is present in the catalytic reactor, e.g. the catalytic combustion reactor or the catalytic decomposition reactor, in a monolithic form, e.g. as a sintered carrier material. Monolithic carrier materials are well-known to the skilled person, and the specific monolithic form may be selected freely. Preferred monolithic include α-Al2O3, MgOAl2O3and SiC and combinations and mixtures of these materials. In general, a monolithic carrier material comprises pores or channels to provide an appropriate specific surface area. For example, a monolithic carrier material, e.g. a monolithic carrier material made from a ceramic material, such as alumina or silicon carbide, may comprise channels in the range of 0.5 mm to 5 mm, e.g.1 mm to 3 mm. The channels may have any cross-sectional shape. A monolithic carrier material having channels may also be said to have a honeycomb structure. In an example, the carrier material, e.g. of the catalytic combustion reactor, is a monolithic honeycomb with channels having a cross-sectional dimension, e.g. a diameter in the range of 1 mm to 2 mm. The catalytic combustion reactor comprises a combustion catalyst that may comprise the carrier material and a catalytic metal or a catalytic metal compound, or the combustion catalyst may comprise a catalytic metal or a catalytic metal compound without a carrier material, e.g. the catalytic metal or a catalytic metal compound is in the form of a gauze. Catalytic metals and catalytic metal compounds for catalysis the combustion of H2 and / or NH3 are well-known to the skilled person and the catalytic metal and the catalytic metal compound may be selected freely. Exemplary catalytic metals include nickel (Ni), platinum (Pt), palladium (Pd), rhodium (Rh), and ruthenium (Ru). The catalytic metal may also comprise tungsten (W). In a specific example, the combustion catalyst comprises at least one catalytic metal selected from Pt and Rh combined with another metal with a melting point above 2000°C, e.g. W. Other metals with melting points above 2000°C are Rhenium (Re). Relevant catalytic metal compounds include oxides of iron (Fe), Nickel (Ni) and cobalt (Co). A23115-WO-PCT In a specific example, the combustion catalyst comprises, or is, a fibrous material, e.g. of a catalytic metal, such platinum or Rh and another metal with a melting point above 2000°C, e.g. up to 8 wt % Rh and another metal, e.g. W, with a melting point above 2000°C, provided as 10 to 30 layers of 50 μm to 200 μm gauze filaments, or of a carrier material, such α-Al2O3, MgOAl2O3or SiC, provided as 10 to 30 layers of 50 μm to 200 μm gauze filaments alloyed with Rh and another metal with a melting point above 2000°C, e.g. up to 8 wt % Rh and another metal, e.g. W, with a melting point above 2000°C. In another example, the combustion catalyst comprises, or is, a monolithic high temperature carrier material, e.g. α-Al2O3 or SiC with monolith channels having a diameter in the range of 1 mm to 2 mm, impregnated with Pt. In a further example, the combustion catalyst comprises, or is, a monolithic high temperature carrier material, e.g. a layer of monolithic high temperature carrier material, impregnated with oxides of at least one of Fe, Ni and Co, the high temperature carrier material may for example be α-Al2O3or SiC, in particular with monolith channels having a diameter in the range of 1 mm to 2 mm. The features of these examples may also be combined differently. For example, the combustion catalyst may comprise, or be, a fibrous catalytic material, e.g. of a catalytic metal, provided as 10 to 30 layers of 50 μm to 200 μm gauze filaments, or the combustion catalyst may comprise, or be, a monolithic high temperature carrier material, e.g. α-Al2O3or SiC with monolith channels having a diameter in the range of 1 mm to 2 mm, impregnated with Rh and another metal with a melting point above 2000°C, e.g. up to 8 wt % Rh and another metal, e.g. W, with a melting point above 2000°C. Likewise, the combustion catalyst may comprise, or be, a carrier material, e.g. of α-Al2O3or SiC, with oxides of at least one of Fe, Ni and Co. It is also possible to combine the features of these examples. In order to achieve stable operation and approach equilibration in practice, the catalyst operates in an “ignited state”, similar to that of the platinum gauze catalyst employed in nitric acid plants. An ignited state of a platinum gauze catalyst in a nitric acid plant corresponds to a temperature in the in range of 850°C to 950°C with an inlet gas temperature in the in range of 200°C to 250°C with excess air to NO at 1-9 bar abs. and an amount of platinum A23115-WO-PCT gauze catalyst corresponding to a net hourly space velocity (NHSV) of about 106Nm3gas / h / m3of metal gauze woven of 0.08 mm filaments of platinum alloyed with 5-10 % Rhodium. In the present disclosure, operating the catalyst bed in the catalytic combustion reactor in “ignited state” generally means that the reaction is gas film controlled with catalyst temperature close to the adiabatic exit temperature through-out the catalyst bed in the catalytic combustion reactor, which may consist of a layer of platinum gauze similar to that used in nitric acid plants and operated at a load (NHSV) of about 800 kNm3 / h feed per m3of a metal gauze, e.g. woven of 0.08 mm filaments of Pt alloyed with 5-10 % Rh supported on a bed of ceramics impregnated or coated with Fe or Ni oxides and Pt. However, due to the low flammability and low reactivity of NH3compared to that of H2, the ignition can be initiated by combustion of H2 in a platinum, e.g. platinum gauze, catalyst at an inlet temperature down to about 200°C, or even lower. When the catalyst temperature caused by combustion of H2exceeds 500-600°C, the rate of decomposition of NH3 and subsequent combustion of H2 speeds up and can complete the equilibration at an exit temperature, i.e. relative to the catalytic combustion reactor, above 800°C, e.g. above 900°C. The present inventor has found that an exit temperature of about 1250°C is judged to be the highest sustainable operating temperature of the catalysts in the catalytic combustion reactor and 1250°C may be chosen because the thermal efficiency of the process increases with increasing exit temperature, when the exit temperature is also the inlet temperature of a gas turbine included in the process set-up of the disclosure. In general, the temperature increase, in particular the adiabatic temperature increase, caused by combustion of the H2 in the gaseous fuel composition is about 45°C per mol % H2 in the gaseous fuel composition, so that combustion of, e.g.6% H2in the gaseous fuel composition heats the gas up from, e.g.300°C to 300°C + 280°C = 580°C thereby securing ignition and equilibration of the gas with an appropriate catalysts in the catalytic combustion reactor. Experimental bench scale simulations indicate that stable ignition and complete equilibration may be achieved with down to 5 mol% H2, e.g.6 mol% A23115-WO-PCT H2, in the gaseous fuel composition corresponding to x = 35-40% decomposition in the catalytic decomposition reactor. In another example, the combustion catalyst comprises a catalytic metal or a catalytic metal compound in a fibrous form, but which combustion catalyst does not comprise a ceramic carrier material. For example, the catalytic metal may comprise wires or filaments of the catalytic metal. Individual wires or filaments of a catalytic metal may have any diameters and may be assembled together using any approach, in particular depending on the diameter of the wires or filaments. For example, the combustion catalyst may comprise a catalytic metal as filaments, e.g. “catalytic filaments”, with a diameter in the range of 0.01 mm to 0.1 mm, or the combustion catalyst may comprise a catalytic metal as wires, e.g. “catalytic wires” with a diameter in the range of 0.1 mm to 1 mm. Catalytic filaments and / or catalytic wires may be bundled together in an ordered or a random form. For example, catalytic filaments and / or catalytic wires may be knitted together or form a structured net, or the catalytic filaments and / or catalytic wires, in particular catalytic filaments, may be assembled in the form of a mesh of catalytic wires or catalytic filaments. The fibrous form comprising catalytic wires and / or catalytic filaments may be provided in sheets or layers, and a sheet of a carrier metal in a fibrous form may have any thickness, as appropriate, e.g. in the range of 10 μm to 1 mm, such as 50 μm to 200 μm. When the combustion catalyst comprises a catalytic metal in a fibrous form, the combustion catalyst may also comprise wires or filaments of a non-catalytic metal to provide support to the combustion catalyst. When the carrier material, the catalytic metal or the catalytic metal compound is in a fibrous form, e.g. as a sheet of a fibres, the combustion catalyst may be referred to as a “gauze filament”. A gauze filament may be included in the corresponding catalytic reactor as desired. For example, a gauze filament, e.g. sheets of fibrous carrier material, or sheets of a catalytic metal, may be included in the catalytic reactor as a stack of individual sheets of the combustion catalyst. In another example, the carrier material comprises at least one sheet of combustion catalyst present as concentric cylinders of the combustion catalyst or rolled into a spiralling form around a central axis of the catalytic reactor. In a specific example, the combustion catalyst comprises 10 A23115-WO-PCT to 30 layers of 50 μm to 200 μm gauze filaments. In general terms, a combustion catalyst in a fibrous form comprises the solid material, i.e. the carrier material, the catalytic metal without a carrier material or the catalytic metal compound without a carrier material, at a volumetric fraction in the range of 10% to 50% of the bulk volume of the sheet or sheets. In an aspect, the invention relates to a process of producing a gaseous fuel composition. The gaseous fuel composition is particularly the gaseous fuel composition of the invention. A step of the process is the provision of a catalytic decomposition reactor. The catalytic decomposition reactor may be any catalytic decomposition reactor as described above for the invention, and the catalytic decomposition reactor is preferably a tubular catalytic decomposition reactor. In the process, a stream of gaseous NH3 is applied at the NH3 inlet at a temperature in the range of 50°C to 150°C, and the stream of gaseous NH3 is passed through the decomposition catalyst in the tubes containing the NH3- decomposition catalyst. Upon entering the tubular catalytic decomposition reactor, the decomposing NH3 is heated by a heating arrangement to a temperature in the range of 400°C to 650°C at the decomposition product outlet. It is preferred that the heating medium inlet of the catalytic decomposition reactor, in particular a tubular catalytic decomposition reactor, is in fluid communication with the flue gas outlet of a catalytic combustion reactor of the process set-up of the invention so that the decomposing NH3is heated by the flue gas from the process of producing a heated flue gas stream of the invention. By using the heated flue gas stream, an optimal energy balance is provided to ensure efficient utilisation of the NH3so that the NH3can be decomposed to H2 and N2 without requiring an external source of heat. For example, the heating medium, e.g. the flue gas, may be provided at a temperature in the range of 500°C to 800°C. When exiting the decomposition product outlet, the decomposed NH3 has a temperature in the range of 400°C to 650°C, and the decomposition of NH3 is in the range of 0.16 to 0.98, e.g.0.2 to 0.96. Thus, per mol of NH3introduced into the catalytic decomposition reactor, the decomposed NH3contains 0.08 mol to 0.49 mol N2, 0.02 mol to 0.84 mol NH3, and 0.24 mol to 1.47 mol A23115-WO-PCT H2. The decomposed NH3 is then mixed with an oxygen rich gas, preferably atmospheric air, containing an amount of O2in the range of 0.70 mol to 0.75 mol per mol of NH3, e.g. in the range of 0.74 mol to 0.75 mol per mol of NH3. Thus, the gaseous fuel composition is provided. It is preferred that the gas is further mixed with a diluent gas stream, e.g. a diluent gas stream composed of H2 and optional further components, e.g. N2 and / or H2O, and optionally also NH3. It is particularly preferred that the diluent gas stream is a diluent flue gas stream composed of N2, H2O and H2and provided from the combustion of the gaseous fuel composition of the invention. In particular according to the process of producing a heated flue gas stream of the invention. By using a diluent flue gas stream provided from the combustion of the gaseous fuel composition of the invention, better control of the combustion process, in particular the temperature increase in the catalytic combustion reactor, is obtained. The diluent flue gas stream further allows to control conditions optimal for the catalyst, in particular, when a stream of gaseous fuel composition of the invention is combusted to provide a heated flue gas, 30% to 60% of the heated flue gas may be used as the diluent gas stream. The diluent gas stream can be used to control the temperature T4of the catalyst at the maximum acceptable catalyst temperature, e.g. to about 1250°C by controlling the temperature increase T4 – T3. About 1:1 recirculation of the flue gas stream for dilution is usually appropriate. In an aspect, the invention relates to a process of producing a heated flue gas stream. The process employs a catalytic combustion reactor as defined for the process set-up of the invention. The catalytic combustion reactor may be any example of a catalytic combustion reactor of this disclosure. In particular, the catalytic combustion reactor may be part of a process set-up of the disclosure. In the process, a gaseous fuel composition of the disclosure is combusted. Thus, the process includes the step of providing a gaseous fuel composition of the disclosure. The gaseous fuel composition may be provided by mixing the components of the gas, but it is preferred that the gaseous fuel composition is provided in the process of producing a gaseous fuel composition of the disclosure. The gaseous fuel composition may be provided according to A23115-WO-PCT any example of the process of producing a gaseous fuel composition of the disclosure. The disclosure includes a process for the production of a heated flue gas stream. At least one of the increased temperature and the increased pressure of the heated flue gas stream may be utilised in any subsequent process step. For example, the heated flue gas stream may power a gas turbine, or heat from the heated flue gas stream may be recovered in a heat exchanger, a steam generator, or a boiler. In particular, heat from the heated flue gas stream may be utilised in heating other process streams in other process aspects of the invention. In general terms, the gas leaving the catalytic combustion reactor is referred to as a flue gas, and the flue gas may be used in another step in a process of the invention. As long as the flue gas is present in the process set- up of the disclosure, the gas is referred to as the flue gas. The flue gas stream may be divided into a diluent flue gas stream and an exhaust gas stream, but in general, the exhaust gas is the gas exiting the process set-up at the exhaust gas outlet. In the process of producing a heated flue gas stream, the gaseous fuel composition is applied at the fuel gas inlet at an ignition temperature in the range of 50°C to 450°C and a pressure in the range of 1 bar abs to 80 bar abs. When a gas comprising at least 2 mol% H2, e.g. at least 3 mol% H2, and O2 is brought into contact with the combustion catalyst at the ignition temperature, the H2is ignited. A preferred temperature at the fuel gas inlet is in the range of 200°C to 300°C. Ignition of the H2 further results in ignition of residual NH3 from the decomposition of NH3 and present in the gaseous fuel composition. In an aspect, the invention relates to a process of combustion of NH3. The process employs a process set-up of the invention, and furthermore, the process of combustion of NH3 can be considered to combine the process of producing a gaseous fuel composition and the process of producing a heated flue gas stream. Thus, the process of combustion of NH3 may employ any example or embodiment of the process of producing a gaseous fuel composition of the invention and any example or embodiment of the process of producing a heated flue gas stream of the invention. Correspondingly, the A23115-WO-PCT process of combustion of NH3 may employ any example or embodiment of the process set-up of the invention. The process of combustion of NH3 includes the provision of a stream of gaseous NH3 and an oxygen rich gas. The oxygen rich gas, e.g. atmospheric air, contains an amount of O2in the range of 0.70 mol to 0.75 mol, e.g. in the range of 0.73 mol to 0.75 mol, or 0.74 mol to 0.747 mol, per mol of NH3 in the stream of gaseous NH3. The stream of gaseous NH3 is decomposed to a decomposition of NH3in the range of 16% to 98%, and thereby x is in the range of 0.16 to 0.98. In further examples, x is in the range of 0.20 to 0.96, or 0.3 to 0.7. A diluent flue gas stream comprising O2, N2, H2, and H2O may be provided, and the diluent flue gas is mixed with the stream of decomposed NH3and the oxygen rich gas, so that a gaseous fuel composition is provided, which has a molar ratio of H2 to NH3 > 1.5x / (1-x) with x being in the range of 0.16 to 0.98, e.g.0.20 to 0.96, or 0.3 to 0.7. The gaseous fuel composition is applied at the fuel gas inlet at an ignition temperature in the range of 50°C to 450°C, e.g.200°C to 300°C, and a pressure in the range of 1 bar abs to 80 bar abs, and the gaseous fuel composition through the combustion catalyst to convert the gaseous fuel composition to a heated flue gas stream, i.e. combust the gaseous fuel composition, having a temperature in the range of 900°C to 1500°C. The thus produced heated flue gas stream containing N2, H2O and H2, e.g.H2at a molar content of a*, may be divided into an exhaust gas stream and the diluent flue gas stream that is explained above to be mixed with the oxygen rich gas and the decomposed NH3 to provide the gaseous fuel composition. The ratio between the exhaust gas stream to the diluent flue gas stream may be selected freely, but a preferred range is 2 / 3 to 3 / 2. Thus, 40% to 60% of the flue gas from the flue gas outlet may be diverted to the exhaust gas outlet or to the oxidant mixing site. Between the flue gas outlet and exhaust gas outlet, the flue gas may pass through any number and type of unit operations, i.e. process set-up elements, to utilise the increased temperature and / or pressure of the heated flue gas stream. Correspondingly, between the flue gas outlet and oxidant mixing site, the flue gas may pass through any number and type of unit operations, i.e. process set- up elements, to utilise the increased temperature and / or pressure of the heated A23115-WO-PCT flue gas stream. For example, flue gas to be led to the exhaust gas outlet may be led to and drive a gas turbine, and the flue gas leaving the gas turbine may be led to one or more heat exchangers to heat various streams in the process set-up before finally being led to the flue gas outlet as an exhaust gas stream. Likewise, the flue gas stream to be led to the oxidant mixing site may be led through any number of heat exchangers, e.g. including the catalytic decomposition reactor, to heat various streams in the process set-up before finally being led to the oxidant mixing site as a diluent flue gas stream. The process set-up of the invention comprises any example of the catalytic decomposition reactor described above and any example of the catalytic combustion reactor described above. In addition, the process set-up comprises an air inlet, a diluent inlet, an exhaust gas outlet, an oxidant mixing site, a fuel composition mixing site, and a flue gas branching site. Via the pipe network, the fuel composition mixing site is in fluid communication with the fuel gas inlet. Thereby, a relevant gaseous fuel composition is provided to the catalytic combustion reactor. In the process of the invention, the gaseous fuel composition may be provided from decomposing NH3 and mixing the decomposed NH3with atmospheric air at an appropriate ratio, and in the process set-up, exhaust gas from the flue gas outlet of the catalytic combustion reactor may be included in the gaseous fuel composition. Thus, in an example the process set-up comprises a flue gas branching site at which flue gas from the flue gas outlet of the catalytic combustion reactor is split into an exhaust gas stream leaving the process set-up via the exhaust gas outlet and a pipe leading to the oxidant mixing site. In general, the amount of flue gas from the flue gas outlet of the catalytic combustion reactor led to the oxidant mixing site is in the range of 30% to 60%, e.g.45% to 55%, of the stream from the flue gas outlet. Thus, 40% to 70% of the stream from the flue gas outlet leaves the process set-up via the exhaust gas outlet. In another example, another diluent gas, e.g. steam, is added via the diluent inlet to eventually provide the gaseous fuel composition. Any embodiment of the invention may be used in any aspect of the invention, and any advantage for a specific embodiment applies equally when an embodiment is used in a specific aspect. A23115-WO-PCT Brief description of the drawings In the following the invention will be explained in greater detail with the aid of an example and with reference to the schematic drawings, in which Figure 1 shows an example of a process set-up of the invention; Figure 2 shows an example of tubular catalytic decomposition reactor of the invention; Figure 3 shows an example of a process set-up of the invention. The invention is not limited to the embodiment / s illustrated in the drawings. Accordingly, it should be understood that where features mentioned in the appended claims are followed by reference signs, such signs are included solely for the purpose of enhancing the intelligibility of the claims and are in no way limiting on the scope of the claims. The term “comprising” as used in this specification and claims means “consisting at least in part of”. When interpreting statements in this specification and claims which include the term “comprising”, other features besides the features prefaced by this term in each statement can also be present. Related terms such as “comprise” and “comprised” are to be interpreted in a similar manner. Detailed Description The present invention relates to a gaseous fuel composition, a process set-up (100), a process of producing a gaseous fuel composition 3, a process of producing a heated flue gas stream 4 and a process of combustion of NH3. An example of the process set-up 100 is illustrated Figure 1. The process set-up of Figure 1 employs a tubular catalytic decomposition reactor E2R2 that is illustrated in further detail in Figure 2. A preferred example of the process set-up 100 is illustrated in Figure 3. In the Figures, single- and double-digit numbers refer to the gaseous process streams whereas other numbers refer to features of the process set-up 100. However, certain unit operations are indicated with a letter. Thus, a heat exchanger unit operation is indicated with “E”, a compressor unit operation is indicated with “M”, a gas turbine unit A23115-WO-PCT operation is indicated with “G”, a steam turbine unit operation is indicated with “S”, a condenser unit operation is indicated with “D”, an ejector unit operation is indicated with “J”, and a catalytic reactor unit operation is indicated with “R”. Moreover, a heat exchanger unit operation may also be referred to as a cooling unit or a heating unit, or appropriately derived words, even though a heat exchanger includes both heating and cooling. The process set-up may generally include more than one unit of a specific unit operation, and therefore a number may be added to a letter representing a specific unit operation. Different unit operation types, e.g. two unit operation types, may also be combined into single units, so that a unit may have more than one letter indicated. For example, “ER” indicates a unit having a heat exchange function and a reactor, especially a catalytic reactor, function. Figure 1 shows a process set-up 100 of the invention. The process set- up 100 includes a pipe network 200 providing appropriate fluidic connections between the unit operations of the process set-up 100. The pipe network 200 provides an air inlet 201 and an exhaust gas outlet 202. Unless otherwise noted, the unit operations and the pipes of the pipe network 200 are made from stainless steel. The process set-up 100 has a catalytic decomposition reactor E2R2, which is illustrated in Figure 2. The catalytic decomposition reactor E2R2 has an NH3inlet 101 and a decomposition product outlet 102 with an NH3- decomposition catalyst 103 between the NH3inlet 101, and the decomposition product outlet 102, and the catalytic decomposition reactor E2R2 includes a heating arrangement 104 with a heating medium inlet 108 and a heating medium outlet 109. The heating arrangement 104 is configured to increase the temperature of a gas 105 in the catalytic decomposition reactor E2R2. Specifically, the catalytic decomposition reactor E2R2 is a tubular. The catalytic decomposition reactor E2R2 comprises an external container 106 housing an internal container 107 for the NH3-decomposition catalyst 103, and the external container 106 has a heating medium inlet 108 opposite a heating medium outlet 109 to define a heating medium flow direction f from the heating medium inlet 108 to the heating medium outlet 109, and the internal container 107 comprises a plurality of tubes 112 containing NH3-decomposition catalyst 103. The tubes A23115-WO-PCT 112 are placed at an angle of about 90° to the heating medium flow direction f. Thereby, the heating medium 6 is provided in a cross-flow relative to the flow direction of the decomposing NH321,22. The tubes of the plurality of tubes 112 are generally parallel to each other. The tubes 112 of the plurality of tubes 112 comprise an inlet subset 113 of tubes 112 and an outlet subset 114 of tubes 112, and the inlet subset 113 of tubes 112 is at an NH3 inlet section 110 of the external container 106, and the outlet subset 114 of tubes 112 are in a decomposition product outlet section 111 of the external container 106. The inlet subset 113 of tubes 112 is configured to receive NH321 from the NH3 inlet 101 and supply decomposing NH3to the outlet subset 114 of tubes 112, and the outlet subset of tubes 114 is configured to provide decomposed NH322 to the decomposition product outlet 102. The tubes 112 contain an NH3 decomposition catalyst 103 provided as elements of a commercial Haber-Bosch catalyst, specifically a commercial iron- based NH3-synthesis catalyst. Gaseous NH3 enters the catalytic decomposition reactor E2R2 at the NH3 inlet 101 at a temperature in the range of 50°C to 150°C, e.g. about 100°C. The NH3 is heated by the heating medium 6 and decomposed to N2 and H2. Specifically, the decomposition of NH3 is performed to a conversion factor x of about 0.3, although x may be in the range of 0.16 to 0.98. The decomposed NH322 exits catalytic decomposition reactor E2R2 via the decomposition product outlet 102 at a temperature of about 500°C to 600°C. The process set-up 100 of Figure 1 has a catalytic combustion reactor R1. The catalytic combustion reactor R1 has a catalyst chamber 120 with a fuel gas inlet 121 and a flue gas outlet 122, and the catalyst chamber 120 comprises a combustion catalyst 123 between the fuel gas inlet 121 and the flue gas outlet 122. The combustion catalyst 123 comprises 25 layers of a fibrous fibres of Pt alloyed with about 10 wt% Rh and W as a catalytically active substance. The catalytically active substance catalyses oxidation of NH3 and H2 present in the gaseous fuel composition 3. The catalytic combustion reactor R1 has flue gas outlet 122. The gaseous fuel composition 3 enters the catalytic combustion reactor R1 at the fuel gas A23115-WO-PCT inlet 121 at a temperature in the range of 200°C to 300°C and the gaseous fuel composition 3 is led through the combustion catalyst 123 where H2is oxidised before oxidation of NH3 takes place to provide an adiabatically equilibrated flue gas 4. The hot flue gas 4 exits the catalytic combustion reactor R1 from flue gas outlet 122 at a temperature in the range of 1100°C to 1300°C. Due to the composition of the gaseous fuel composition 3, in particular the balanced content of O2 relative to NH3 and H2, e.g. relative to the amount of NH3 at the NH3inlet 101, the heated flue gas 4 contains substantially no NOx, NH3and O2. N2O, NH3 and O2 are in particular avoided due to the excess of H2. The heated flue gas 4 may contain a residual amount of H2, e.g. denoted a*, in the range of 0.001 to 0.005 mol per mol hot flue gas 4 exiting the catalytic combustion reactor R1. The heated flue gas 4 is led to a flue gas branching site 205 from which about 50% of the heated flue gas 4 exits the pipe network 200 at the exhaust gas outlet 202, and the remaining about 50% is led as heated flue gas 5 from the exhaust gas outlet 202 to a heat exchanger E where the temperature of the heated flue gas 5 is reduced to a temperature in the range of 600°C to 700°C before the stream of flue gas is used as heating medium 6 in the heating arrangement 104 of the catalytic decomposition reactor E2R2. The flue gas stream 6 is cooled further in the heating arrangement 104 to exit the heating arrangement 104 via the heating medium outlet 109 as flue gas stream 7. The flue gas stream 7 is the led, via a further heat exchanger E that reduces the temperature of flue gas stream 7 to provide flue gas stream 8 that is led as a diluent gas 8 to the diluent inlet 206 at the oxidant mixing site 203 of the process set-up 100. At the oxidant mixing site 203, the diluent gas 8 is mixed with atmospheric air that enter the pipe network 200 at the air inlet 201 as an oxygen rich gas 1 to thereby provide an oxidising gas 2. The oxidising gas 2 from the oxidant mixing site 203 is mixed with the decomposed NH322 at the fuel composition mixing site 204 to provide the gaseous fuel composition 3, before ejecting the gaseous fuel composition 3 from ejector J to the fuel gas inlet 121. The ejector J is configured to increase the pressure with 2 to 4 bar with 20 to 40 bar surpressure of the stream of decomposed NH3 being injected in the ejector. A23115-WO-PCT Thereby, a part of the heated flue gas 4 is recycled into the decomposed NH322 and the oxidising gas 2. As the heated flue gas 4 contains an amount of residual H2, the gaseous fuel composition 3 contains an excess of H2. The following guidelines for the choice of operating conditions may be applied for achieving a flue gas with < 3 ppm total NOx: (1) A well-mixed gaseous fuel composition F3 with contents of H2, NH3 and O2 that meets the condition that a4* ≥ 0.2 mol%, e.g.0.1 to 0.6 mol % H2 in the flue gas F4, corresponding to over-all O2 / NH3feed gas ratio of 0.746, e.g.0.735 to 0.748. (2) A minimum of 5-6 mol % H2 in the gaseous fuel composition F3, corresponding to a minimum x = 35-40% decomposition of the NH3prior to adding it to the gaseous fuel composition F3in order to secure and stabilise ignition of the gas in the catalytic combustion reactor R1. (3) An inlet temperature T3 for the catalytic combustion reactor R1 of 200°C to 300°C, e.g. 100°C to 400°C, depending on the activity of the combustion catalyst 123 employed. (4) Adjusting the flue gas recycle ratio at about 1:1 so that the adiabatic temperature increase between the inlet temperature T3and the exit temperature T4 across the combustion catalyst 123 in the catalytic combustion reactor R1 is 950°C to 1000°C, or the exit temperature T4 = 1200°C to 1250°C at the inlet temperature T3= 250°C. The exit temperature T4is generally limited by the highest sustainable temperature of the combustion catalyst 123 which may be in the range 1000°C to 1300°C, tentatively about 1250°C. Figure 3 shows a simplified flow scheme of a preferred embodiment of the invention featuring all important innovations of the process. Key operating parameters and compositions of gas streams 1, 20, 13, are summarised in Table 2, Table 3, Table 4 and gas streams 22, 1, 3, 4 and 12 as well as key operating parameters are summarised in Table 5, respectively. This embodiment is in particular suited for providing the energy for propulsion of A23115-WO-PCT large ships down to 5 MW power capacity needed for propulsion and other power consumption on the vessel. This example is, with reference to Figure 3, a calculated example referring to a plant 100 combusting 1.004 kmol / s of liquid NH3 with lower heating value 297 MJ / kmol, generating a net effect of about 164 MW on shaft corresponding to a net 55% thermal efficiency on shaft of the plant emitting flue gas 11 with 0.12 % H2 and less than 3 ppm NOx (in general, this depends on how well the gas is mixed in the combustion reactor) and no other pollutants than 3 ppm NOx (NO + N2O) in the exhaust gas 13 at 0% O2. Table 2 – composition of atmospheric air as the oxygen rich gas 1 Atm. Air 15°C 1.000 bar abs Kmol / s mol % O2 0,75 20.7 N2 2,837 78.3 H2O 0,036 1.0 Σ3,623 100.0H0 = -9.75 MW Table 3 – the inlet stream of NH320 NH3 Liq 15°C 7.3 bar abs. 1.004 Kmol / s H19= -48 MW A23115-WO-PCT Table 4 – Composition of exhaust gas 13 Exhaust gas 90°C Td= 70.5° Kmol / s mol % O2 0 0 N2 3,338 86.4 H2O 1,536 31.5 H20,006 0.12 Σ4,880 100.0H13 = A23115-WO-PCT Table 5 – Compositions of streams 22,1, 3, 4 and 12 °0211 ..1 H W2 7 0 9M.8 - 63 .052 2%l0o4.5.2 .02m86113.001 1mas / ler o 836 6335008t mK.8S 3.1.0.4°0 415H42,.2.W82830M -7255- -.03- %l0o4.5.2 .0m08611. 043 0 0 1mas / ler o 772 2 16701 6tSmK0.6.03 0.70.9°0 30 H5.7.3W30..5362. 73.0M6 53-7- 93- %l9 5 0 0o827 ...2 8 73. 9 . 0m7 651. 1 031 1 1mas / ler o55 2 4 677 7 0 0 8t m .5 5 2 2 8S K 0.6.1.0.1.4°0 20 H3.2W M01%lo7.30.0.80.0m2 7 1 - -011ma / le7 6 3r o5 3 3 2t m7.8.0 6S K s 0 2.0 - -.3°0265264 H W0M -. 7.9.25-5-4,1 341%lo2.30.22.51. 0m2- 2 - 16601ma / ler o 004400040t2 2 8SmKs 0.0 0.0.1.1O32 2 2H2O N H N HΣA23115-WO-PCT Thus, 3.673 kmol / s of ambient air 1 at 15°C with 20.7 mol% O2is compressed in 2 stages, via compressors M1 and M2, with inter-cooling in the air cooler E6 transferring the cooling duty of 10.3 MW to heating of boiler feed water of the steam cycle of the plant 100. The air 1 leaves the compressor M2 at 18 bar and T1 = 209°C and is mixed with 4.88 kmol / s of recycled flue gas 8 at 220°C at the oxidant mixing site 203 upstream of the ejector J in which 1.804 kmol / s of 80% decomposed NH3fuel gas 22 at about 400°C is injected at ejector J at 40 bar thereby boosting the pressure to 22 bar of the R1 inlet gas stream 3, i.e. the gaseous fuel composition 3, of 10.3 kmol / s with 7.28% O2 + 1.98% NH3+ 11.7% H2at 280-290°C securing stable ignition of the below catalyst bed 123 and thereby achievement of flue gas 4 of 9.76 kmol / s of equilibrated gas at 1250°C ab R1 calculated according to Equation 4 with 0.12% H2 and expected less than 3 ppm NO + N2O (at 0% O2) caused by assumed imperfect gas mixing. Equation 4 F3 mol / s = a3mol H2 / s + b3mol NH3 / s + c3mol O2 / s + d3mol N2 / s + e3mol H2O / s In Equation 4, the letters a, b, c, d, and e refer to the amounts of H2, NH3, O2, N2, and H2O, respectively, where “N2” includes further atmospheric component, in particular noble gases, and the subscripted number 3 indicates the process stream 3, the gaseous fuel composition, and F indicates the total molar content of the process stream 3. The catalyst bed of combustion catalyst 123 in R1 consists of 10 to 20 layers platinum gauze of the high temperature type of Pt / Pd / Rh gauze otherwise used in NH3 oxidation reactors of nitric acid plants, operating at a surface velocity of about 5000 Nm3 / h per m2of bed cross section area. The gauze 123 is placed on top of a supporting bed of ceramic material 124 causing a pressure drop securing uniform surface velocity across the cross section of the catalyst bed 123,124. Said ceramic material 124 may be a 10 to 20 cm high layer of 5 to 10 mm rings or honeycomb elements with 1 to 1.5 mm channels made of high temperature ceramics such as α-alumina, Mg-spinel or silicon A23115-WO-PCT carbide impregnated or coated with 2 to 10 wt% of Fe-, Ni- and / or Co oxides and about 1000 ppm platinum in order to complete the equilibration in addition to securing even flow-distribution. The flue gas stream 4 of 9.76 kmol / s at 1250°C is split in a flue gas stream 10 of 4.88 kmol / s being passed to the gas turbine G generating 123 MW on shaft by expanding the gas stream 10 from 19 bar, 1250°C to 1.25 bar, 651°C at 86% turbine efficiency, and a flue gas stream 5 of 4.88 kmol / s being recycled and cooled first in heat exchanger E1 at tentatively 600°C, then tentatively at 340°C in the tubular catalytic reactor E2R2 and finally tentatively at 220°C in heat exchanger E3 before passed as flue gas 8 to be mixed with the combustion air 1 at oxidant mixing site 203. The content of H2, NH3and O2in the inlet gas stream 3 is equilibrated in R1 at deficit of O2 thereby forming a flue gas stream 4 with only H2, N2 and H2O and zero NO and O2 according to Equation 5: Equation 5 F4 mol / s = (a3+ 1.5·b3– 2·c3) mol H2 / s + (d3+ 0.5·b3) mol N2 / s + (e3+ a3+1.5·b3) mol H2O / s = a3+ 2·b3+ d3+ e3mol / s In Equation 5, the letters a, b, c, d, and e refer to the amounts of H2, NH3, O2, N2, and H2O, respectively, where “N2” includes further atmospheric component, in particular noble gases, and the subscripted number 3 indicates the process stream 3, the gaseous fuel composition, and F indicates the total molar content of the process stream 4, the flue gas from R1, thus corresponding to the presence of a4 / F4 x 100 mol% H2 in flue gas stream 4 when the gaseous fuel composition 3 is completely equilibrated. Equilibration of the flue gas stream 4 is achieved by passing the gaseous fuel composition stream 3 through a number of layers of H2-combustion- and NH3-decomposition catalysts installed in the reactor R1 whereby the gaseous fuel composition 3 is equilibrated according to Equation 5 at sufficient catalyst activity and temperature of the catalyst. In order to achieve full equilibration and stable operation in practice, the combustion catalyst 123 should operate in an “ignited state” (similar to that of platinum gauze catalyst working in “ignited state” at 800 to 1000°C with an inlet A23115-WO-PCT gas at 200 to 250°C in a nitric acid plants where NH3 is oxidised to NO with excess air). Operating a catalyst bed in “ignited state” indicates that the reaction is gas film controlled with a catalyst temperature close to the adiabatic exit temperature through-out a relatively shallow (e.g. 10 to 20 cm) catalyst bed operating at, at least, 100 kNm3of feed gas per hour per m3of catalyst volume. The catalyst bed may consist of 10 to 20 layers of platinum gauze supported on a bed of ceramics impregnated or coated with Fe, Ni or Co oxides. 1.004 kmol / s liquid NH3fuel is passed from a liquid NH3storage tank (not shown) at 15°C, 7 bar by the liquid NH3 pump 19 increasing its pressure to 45 bar in line 20 upstream of the NH3-evaporater E5 wherein the NH3 is vaporised and heated at 100°C in line 21 by cooling the exhaust gas from 110°C in line 12 to 90°C in line 13 before of emitted in line 13 to the atmosphere. The NH3-gas in line 21 heated and partly decomposed when passed through the catalyst loaded tubes of the tubular catalytic reactor E2R2 seen in Figure 2 wherein the NH3-gas is heated at 450°C and 80% decomposed according to Reaction 3 by passing the NH3-gas through a number of parallel tubes loaded with NH3-decomposition catalyst, said tubes being heated by exhaust gas in cross flow with two passes counter current as seen in Figure 2. The heat recovered in the gas coolers E1, E3, E4, E6 and E7 is used for generating 59 kg / s of live steam at tentatively 50 bar, 550°C for the steam turbine generating about 75 MW of power with condensation at 27°C. NOxwould be formed when NH3is oxidised in the presence of excess O2which may be the case locally where the gas may not be sufficiently mixed. A content of 0.1 to 0.2% H2 in the equilibrated flue gas 4 should be a sufficient content of H2in the gaseous fuel composition 3 to prevent a presence of NOxin a well mixed gas at catalyst temperatures > 800°C. Experimental bench scale simulations thus indicate that optimal performance with stable ignition, complete equilibration and high thermal efficiency of the over-all process can be achieved when the process is operated according to following guidelines: 1) a well mixed reactor feed gas, gaseous fuel composition 3, with 0.1 to 0.2 mol% H2in equilibrated reactor exit gas, flue gas 4, calculated according to Equation 5; A23115-WO-PCT 2) a content of 8-12 mol % H2 in the reactor inlet gas, the gaseous fuel composition 3, (in order to stabilise the “ignited state” and secure that all NH3is completely decomposed before all H2 is oxidised; 3) a reactor inlet temperature T3 at 100 to 300°C, depending on the activity of the combustion catalyst 123; 4) the catalyst bed, the combustion catalyst 123, should be operated at the highest possible adiabatic temperature increase ΔTa = T4 – T3 in the combustion reactor R1. The temperature T4is limited by the highest acceptable temperature of the combustion catalyst(s) 123 which may be in the range 1000 to 1400°C, most likely about 1200°C. Example 2 In a further example, also with reference to Figure 3, 1.004 kmol NH3 / s is applied with an over-all O2 / NH3 feed ratio of 0.747 corresponding to a4* = 0.123 mol% H2, and a flue gas recycle ratio R = 1:1 and x = 40% decomposition in the catalytic decomposition reactor E2R2 of the NH3-feed stream corresponding to 6.1% H2 in the gaseous fuel composition F3. The plant 100 generates net 171 MW on shaft corresponding to 57% net thermal efficiency and emits 4.88 kmol / s of flue gas 13 at about 90°C composed of 68.4 mol% N2 + 31.5 mol% H2O + 0.12 mol% H2 + 0.0 mol% O2 and with expected less than 3 ppm NOx(NO+N2O+NO2) and no other pollutants in the flue gas. This embodiment is in particular suited for providing the energy for propulsion of large ships down to 5 MW power capacity needed for propulsion and other power consumption on the vessel. Specifically, in this Example, 3.623 kmol / s of ambient air 1 at 15°C with 20.7 mol % O2 is compressed in two stages with inter-cooling in E6 transferring the cooling duty of 14.4 MW to heating of boiler feed water (BWF) in the steam cycle of the plant. The air 1 leaves the compressor M2 in line 1 at 18 bar and T1 = 209°C and is mixed with 4.88 kmol / s of recycled flue gas 8 at 220°C upstream of the ejector J in which 1.404 kmol / s of 40% decomposed NH322 at 450°C is injected the ejector J at 55 bar, thereby boosting the pressure to 22 bar of the R1 inlet gas stream F3= 9.907 kmol / s with 7.57% O2+ 6.10% NH3+ 6.12% H2 at 280°C thereby securing stable ignition of the catalyst bed 123 A23115-WO-PCT and generating F4 = 9.76 kmol / s = 788,000 Nm3 / h of equilibrated gas at T4 = 1250°C exit R1, with 0.123 mol% H2, and with expected <3 ppm NO+N2O and no other pollutants in the 4.88 kmol / s of exhaust gas 13. 1.004 kmol / s liquid NH3 fuel 20 is pumped from a liquid NH3storage tank at 15°C, 7 bar by a liquid NH3-pump increasing its pressure to 58-60 bar in line 20 upstream of the NH3-evaporater E5 where the NH3 is vaporised and heated at 100°C by heat exchange with the exhaust gas 12 being cooled from 112°C to 90°C and emitted from line 13 to the atmosphere. The flue gas stream in line 4 of F4 of 9.76 kmol / s at 1250°C is split 1:1 in a flue gas stream F10 of 4.88 kmol / s being passed to the gas turbine G generating 118 MW on shaft by expanding the gas stream F10 from 20 bar, 1250°C to 1.25 bar, 660°C at 86% turbine efficiency, and a gas stream F5=4.88 kmol / s being recycled and cooled first in E1 at tentatively 600°C, then at 340°C on shell side in the tubular catalytic reactor E2R2 and finally tentatively at 220°C in E3 before being passed in line 8 to be mixed with the combustion air in line 1. The heat recovered in the gas coolers E1, E3, E4, E6 and E7 is used for generating live steam at 50 bar, 550°C for the steam turbine S generating about 75 MW of power on shaft with steam condensation at 27°C. Design of air compressor M, gas turbine G and steam cycle with steam turbine S and optimal incorporation in the steam cycle of the heat recovered in the above heat exchangers E is based on known technology. The catalyst bed 123 in R1 for this Example is 0.8-1 m3of platinum gauze of the high temperature type of Pt / Pd / Rh gauze used in NH3 oxidation reactors of nitric acid plants. For this application the gauze may be further alloyed with other metals with high melting points in order to improve thermal resistance of the alloy. The diameter of the catalytic reactor R1 of this Example is 3 m corresponding to 7.06 m2cross section area of the catalyst bed 123 in R1 corresponding to 11-15 cm height of the bed of gauze catalyst 123 installed in R1, and vs= 9.76x22.4x(1523 / 273) / 20 / 7.06 = 8.53 m / s superficial gas velocity downwards in R1 at 1250°C, 20 bar. A23115-WO-PCT The gauze 123 is placed on top of a supporting bed 124 of ceramic material causing a pressure drop of 0.3-0.4 bar thereby securing uniform gas distribution of across the cross section of the catalyst bed 123. The ceramic material 124 of this Example is a 20-40 cm high layer of 5-10 mm rings or honeycomb elements with approx.1.5 mm channels made of high temperature ceramics such as α-alumina, Mg-spinel, cordierte or SiC silicium impregnated or coated with 2-10 wt% of Fe-, Ni- and / or Co oxides and about 100-1000 ppm platinum in order to support the catalyst, complete the equilibration and secure even flow-distribution by known methods of design and pressure drop calculation. A23115-WO-PCT Key operating parameters and heat balance calculations are seen in Table 6. %lo4.5 200 °8.11 .M6 3.0510521.. .W2 29 2 0M62 0 - 5 .0 - 334s / lo 77272 161 6m0 0 7K 0.6.3 0.0.9%lo°mW M082. 2 50~6.6.33 W2 6.68-8 6.12 03M.57435-2 . 3=- 4 -H4 3 / l=o 5 2 4 6 73577375060609HmKs.0.6.1.0.0.9W M21s / lo 83633 6 8m5 0 8K 0.3.1 0.0.4rab8 5 6.1W2. 5 7.1.1 ° M4 18- 1902s / W1lo5736937 82M m0 6K.0.2. .9. 0 3113 -05.4=°W6 77 2M.621-..7720 -25H4-H1r 5a %l42203 0.b- 0o .4.79.200 36m1 4 4 1H=8 H2 s / 2lo 004 0 4m2060604K -.0 -.0.0.1n%o0 it4i=s 3XoP2 2O2H2O N H N HΣA23115-WO-PCT Increasing the degree of decomposition x of the feed NH322 from 40% to 60% increases the concentration a3* of H2in the gaseous fuel composition F3from 6.1 to 9.6% H2. Higher NH3-decomposition ratio x gives higher tolerance for deactivation of the catalyst(s) in the catalytic combustion reactor R1 and higher investment costs but a change in x does not change the over-all energy efficiency of the plant. Example 3 In an alternative embodiment, the process of the invention is performed in a process 100 set-up not having a diluent inlet 206, and correspondingly, the process is performed without adding a diluent gas stream to the gaseous fuel composition 3. The specific process set-up is not explicitly illustrated in the Figure, but otherwise specific unit operations are generally as shown in Figure 1 and Figure 3. Thus, 1.004 kmol / s NH3at 50-60 bar is heated at 400°C and decomposed at x ≈ 30% before being combusted with 3.623 kmol / s air with 20.7 mol% O2 at 24 bar, 295°C abs without dilution in a thermal burner R1 of appropriate design thus forming a gas stream at 2130°C with 68.4% N2+ 31.5% H2O + 0.123% H2, when completely adiabatically equilibrated. The gas stream is cooled to 1250°C in the two steam superheaters (not shown) extracting heat from the gas stream in the thermal burner R1. The final, equilibrated flue gas F4at 1250°C is then expanded in a gas turbine G and cooled in a steam generator (not shown) and finally cooled to 70°C in an NH3 vaporiser. The high temperature at or above 2000°C of the gas stream makes it possible to achieve 60 % total thermal efficiency due to the higher energy efficiency of the steam cycle with heating and re-heating of the steam at 600°C or higher upstream of the high pressure (HP) and the low pressure (LP) steam turbine. Furthermore, the more efficient cooling of the flue gas makes it possible to condense H2O for boiler feed water make up by cooling the exhaust gas below its dew point. A23115-WO-PCT Reference signs list Process streams 1 Oxygen rich gas 2 Oxidising gas 20, 21, 22 NH321 Gaseous NH3 22 Decomposed NH3 3 Gaseous fuel composition 4, 5, 6, 7, 8, 9, 10, 11, 12 Flue gas Diluent flue gas 9, 13 Exhaust gas Process set-up elements 100 Process set-up E2R2 Catalytic decomposition reactor 101 NH3 inlet 102 Decomposition product outlet 103 NH3decomposition catalyst 104 Heating arrangement 105 Gas in the catalytic decomposition reactor 106 External container 107 Internal container 108 Heating medium inlet 109 Heating medium outlet 110 NH3inlet section 111 Decomposition product outlet section f Heating medium flow direction 112 Plurality of tubes 113 Inlet subset 114 Outlet subset R1 Catalytic combustion reactor 120 Catalyst chamber 121 Fuel gas inlet A23115-WO-PCT 122 Flue gas outlet 123 Combustion catalyst 124 Carrier material 200 Pipe network 201 Air inlet 202 Exhaust gas outlet 203 Oxidant mixing site 204 Fuel composition mixing site 205 Flue gas branching site 206 Diluent inlet E Heat exchanger M Compressor G Gas turbine S Steam turbine D Condenser J Ejector R Catalytic reactor A23115-WO-PCT

Claims

P A T E N T C L A I M S1. A gaseous fuel composition (3) comprising O2, N2, H2O, NH3, H2and optionally further atmospheric components wherein the molar content of H2 is denoted a, the molar content of NH3 is denoted b, the molar content of O2 is denoted c, the molar content of N2is denoted d, and the molar content of H2O is denoted e, and (a + 1.5b – 2c) / (a + 2b + c + d + e) is in the range of 0 to 0.01, and a constitutes at least 3 mol% of the gaseous fuel composition (3).

2. The gaseous fuel composition (3) according to claim 1, wherein the molar ratio of H2 to NH3 ≥ 1.5x / (1-x) with x being in the range of 0.16 to 0.

98.

3. A process set-up (100) comprising: a catalytic decomposition reactor (E2R2) having an NH3 inlet (101) and a decomposition product outlet (102), which catalytic decomposition reactor (E2R2) comprises an NH3-decomposition catalyst (103) between the NH3inlet (101) and the decomposition product outlet (102), and a heating arrangement (104) configured to increase the temperature of a gas (105) in the catalytic decomposition reactor (E2R2); a catalytic combustion reactor (R1) having a catalyst chamber (120) with a fuel gas inlet (121) and a flue gas outlet (122), which catalyst chamber (120) comprises a combustion catalyst (123) between the fuel gas inlet (121) and the flue gas outlet (122); an air inlet (201), an exhaust gas outlet (202), an oxidant mixing site (203) having a diluent inlet (206), a fuel composition mixing site (204); and a pipe network (200) comprising pipes providing that the air inlet (201) is in fluid communication with the oxidant mixing site (203), the decomposition product outlet (102) is in fluid communication with the diluent inlet (206), and the oxidant mixing site (203) is in fluid communication with the fuel composition mixing site (204), the fuel composition mixing site (204) is in fluid communication with the fuel gas inlet (121), the flue gas outlet (122) is in fluid communication with the exhaust gas outlet (202). A23115-WO-PCT4. The process set-up (100) according to claim 3, wherein the combustion catalyst (123) comprises at least one of (a) 10 to 30 layers of 50 μm to 200 μm gauze filaments (123) alloyed with up to 8 wt % Rh and another metal with a melting point above 2000°C, (b) Pt impregnated on a layer of a high temperature carrier material (124) and (c) a layer of high temperature carrier material (124) impregnated with oxides of at least one of Fe, Ni and Co.

5. The process set-up (100) according to claim 4, wherein the fuel composition mixing site (204) comprises an ejector (J) configured to provide an increase in the pressure in the range of 20 bar to 40 bar.

6. The process set-up (100) according to any one of claims 3 to 5, wherein the process set-up (100) further comprises a flue gas branching site (205), and the flue gas outlet (122) is in fluid communication with the flue gas branching site (205), which flue gas branching is in fluid communication with and the exhaust gas outlet (202) and the diluent inlet (206).

7. A process of producing a gaseous fuel composition (3) comprising the steps of: providing a stream of gaseous NH3 (21); providing a catalytic decomposition reactor (E2R2) having an NH3inlet (101) and a decomposition product outlet (102), which catalytic decomposition reactor (E2R2) comprises an NH3-decomposition catalyst (103) between the NH3 inlet (101) and the decomposition product outlet (102), and a heating arrangement (104) configured to increase the temperature of a gas in the catalytic decomposition reactor (E2R2); applying the stream of gaseous NH3 (21) at the NH3 inlet (101) at a temperature in the range of 50°C to 150°C and passing the stream of gaseous NH3 (21) through the decomposition catalyst (103) to obtain a stream of decomposed NH3 (22) corresponding to a decomposition (x) of NH3 in the range of 0.16 to 0.98 and having a temperature in the range of 400°C to 650°C at the decomposition product outlet (102), the stream of decomposed NH3(22) comprising H2, N2, and NH3; A23115-WO-PCTproviding an oxygen rich gas (1) containing N2, H2O and optionally further atmospheric components, and an amount of O2in the range of 0.70 mol to 0.75 mol per mol of NH3 in the stream of gaseous NH3 (21); and mixing the stream of decomposed NH3 (22) with the oxygen rich gas (1) to obtain the gaseous fuel composition (3).

8. The process of producing a gaseous fuel composition (3) according to claim 7 further comprising providing a diluent gas stream (8) comprising at least one of N2, H2O and H2 and mixing the diluent gas stream (8), the stream of decomposed NH3 (22) and the oxygen rich gas (1) to obtain the gaseous fuel composition (3).

9. The process of producing a gaseous fuel composition (3) according to claim 8, wherein the diluent gas stream is a diluent flue gas stream composed of N2, H2O and H2optionally further atmospheric components.

10. A process of producing a heated flue gas stream (4), the process comprising the steps of: providing a catalytic combustion reactor (R1) having a catalyst chamber (120) with a fuel gas inlet (121) and a flue gas outlet (122), which catalyst chamber (120) comprises a combustion catalyst (123) between the fuel gas inlet (121) and the flue gas outlet (122); providing a gaseous fuel composition (3) according to claim 1 or 2; applying the gaseous fuel composition (3) at the fuel gas inlet (121) at an ignition temperature in the range of 50°C to 450°C and a pressure in the range of 1 bar abs to 80 bar abs; passing the gaseous fuel composition (3) through the combustion catalyst (123) to convert the gaseous fuel composition (3) to the heated flue gas stream (4) having a temperature in the range of 700°C to 1500°C; and obtaining the heated flue gas stream (4) at the flue gas outlet (122). A23115-WO-PCT11. The process of producing a heated flue gas stream (4) according to claim 10, wherein the gaseous fuel composition (3) is provided in a process according to any one of clams 7 to 9.

12. A process of combustion of NH3comprising: providing a process set-up (100) according to any one of claims 3 to 6; providing a stream of gaseous NH3 (21); applying the stream of gaseous NH3(21) at the NH3inlet (101) at a temperature in the range of 50°C to 150°C and passing the stream of gaseous NH3 (21) through the decomposition catalyst (103) to obtain a stream of decomposed NH3(22) corresponding to a decomposition of NH3in the range of 0.16 to 0.98 and having a temperature in the range of 400°C to 650°C at the decomposition product outlet (102), the stream of decomposed NH3 (22) comprising H2, N2, and NH3; providing an oxygen rich gas (1) containing an amount of O2in the range of 0.70 mol to 0.75 mol per mol of NH3 in the stream of gaseous NH3 (21) and leading the oxygen rich gas (1) to the oxidant mixing site (203), mixing the stream of oxygen rich gas (1) with a diluent gas stream (8) comprising at least one of N2, H2O, and H2, to provide an oxidising gas (2) comprising O2, and at least one of N2, H2, and H2O; leading the oxidising gas (2) and the stream of decomposed NH3(22) to the fuel composition mixing site (204) and mixing the oxidising gas (2) and the stream of decomposed NH3 (22) to provide a gaseous fuel composition (3); applying the gaseous fuel composition (3) at the fuel gas inlet (121) at an ignition temperature in the range of 50°C to 450°C and a pressure in the range of 1 bar abs to 80 bar abs; passing the gaseous fuel composition (3) through the combustion catalyst (123) to convert the gaseous fuel composition (3) to a heated flue gas stream (4) having a temperature in the range of 700°C to 1500°C .

13. The process of combustion of NH3according to clam 12, wherein the oxygen rich gas (1) is atmospheric air (1). A23115-WO-PCT14. The process of combustion of NH3 according to clam 12 or 13, wherein the process set-up (100) is according to claim 6, and the diluent gas stream (8) is a diluent flue gas stream (8) composed of N2, H2O, H2 and optionally further atmospheric components from the flue gas branching site (205), and the method comprises dividing the heated flue gas stream (4) into an exhaust gas stream (9) and the diluent flue gas stream (8) at the flue gas branching site (205), wherein the ratio between the exhaust gas stream (9) to the diluent flue gas stream (8) is in the range of 2 / 3 to 3 / 2, and leading the exhaust gas stream (9) to the exhaust gas outlet (202) and leading the diluent flue gas stream (8) to the oxidant mixing site (203).

15. The process of producing a gaseous fuel composition (3) according to any one of clams 7 to 9, or the process of combustion of NH3 according to any one of clams 12 to 14, wherein the amount of O2 is in the range of 0.74 mol to 0.75 mol per mol of NH3in the stream of gaseous NH3(21). A23115-WO-PCT

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