Nitric acid production methods and facilities with oxygen supply units

Abstract

The present invention relates to a nitric acid production method and facility. The method involves supplying an oxygen stream and an ammonia feedstock to a burner section. In an embodiment, a portion of the tail gas stream (4) is heated in a tail gas heating section (7) and supplied to the burner section (1).

Description

Technical Field

[0001] The present invention relates to the production of nitric acid by oxidation of an NH3 feedstock. Background Art

[0002] Nitric acid (NA) is produced industrially by catalytic combustion of NH3 feedstock. Ullmann's Encyclopedia of Industrial Chemistry, Nitric Acid, Nitrous Acid and Nitrogen Oxides, 2012, provides a general discussion of such facilities and processes. The process described therein involves three chemical steps: catalytic combustion of ammonia with atmospheric oxygen to produce NO, oxidation of the NO product to NO2, and absorption of the nitrogen oxides in water to produce nitric acid as a liquid stream and tail gas. The ammonia-air mixture is used for catalytic combustion.

[0003] A nitric acid facility typically includes a burner section containing an ammonia oxidation catalyst, a cooling / condensing section, an absorption section with a liquid outlet for a nitric acid stream and a gas outlet for tail gas. The absorption section is typically an absorption column. Oxidation typically also occurs in the column. An example dual pressure facility is described in WO 2018 / 052304.

[0004] The challenge is that the tail gas from the absorber contains nitrogen oxides (NOx), and it is environmentally undesirable to discharge this gas stream, and it is usually necessary to clean the tail gas to remove NOx. Various methods are used in practice to reduce tail gas NOx levels, such as improved absorption, chemical scrubbing, adsorption and catalytic tail gas reduction (see Ullmann's Nitric Acid, paragraph 1.4.2.3). However, meeting modern stringent environmental limits on NOx emissions remains challenging. Tail gas treatment also increases capital expenditures (equipment costs) and operating expenses for facilities and processes.

[0005] US3927182A describes a method for producing nitric acid using an oxygen make-up gas having a molecular oxygen content of about 90 vol.% to 99 vol.% as the oxygen supply source for the process and recovering at least about 40 vol.% of the tail gas. In this method, the amount of nitrogen oxides emitted to the atmosphere is said to be significantly reduced. Figure 2 It is shown that if an oxygen supply gas is used with at least 90 mol % O2, more than 90 % of the tail gas is recycled. A portion of the tail gas is purged directly into the chimney and discharged.

[0006] The NH3 feedstock for the NA production facility is derived from an NH3 production facility, where H2 and N2 react to form NH3. In many existing facilities and processes, the H2 feedstock for NH3 production is derived from steam reforming based on hydrocarbon feedstocks, especially synthesis gas facilities based on, for example, steam methane reforming. Steam reforming of hydrocarbon feedstocks requires a lot of heating and generally involves significant CO2 emissions.

[0007] CN106185984A describes a system for the combined production of ammonia and nitric acid based on a steam electrolysis process.

[0008] CN109516445A describes a closed cycle technology for producing nitric acid by combining water electrolysis and air separation.

[0009] In the chemical industry, there is a general desire to reduce CO2 emissions, and also to reduce NH3 production, including H2 feedstock production ('green hydrogen'). There is also a trend to use electricity, such as from solar, hydroelectric or wind power, for feedstock production. One challenge is that solar and wind power are fluctuating energy sources.

[0010] Improved nitric acid production facilities and methods are still desired. For example, it is desirable to provide nitric acid production facilities and methods that can be coupled with upstream production methods and facilities in a flexible manner using electricity. Methods for modifying existing nitric acid facilities to benefit from green NH3 production are also desired. Summary of the invention

[0011] A first aspect of the present invention relates to a method for producing nitric acid carried out in a nitric acid production section, wherein the nitric acid production section includes a burner section, a cooling / condensation section and an absorption section, the absorption section having an outlet for a tail gas stream, the method comprising: a) providing an oxygen stream, the oxygen stream comprising at least 90 vol.% O2 from one or more oxygen supply units; b) supplying the oxygen stream and an ammonia feedstock to the burner section; and c) wherein at least a portion of the tail gas stream, preferably a first portion, is heated in a tail gas heating section to obtain a heated tail gas stream, and supplied to the burner section.

[0012] The present invention also relates to a nitric acid production facility, which includes a nitric acid production section, wherein the nitric acid production section includes a burner section, a cooling / condensation section and an absorption section, wherein the absorption section has an outlet for the exhaust gas flow, wherein the nitric acid production facility further includes a first flow line and an oxygen flow supply line and a second flow line, wherein the first flow line is used to allow the exhaust gas to pass from the absorption section through at least one heater in the exhaust gas heating section into the inlet of the burner section, the oxygen flow supply line passes from one or more oxygen supply units into the burner section, and the second flow line is used to allow the exhaust gas to pass from the absorption section into the exhaust gas treatment section.

[0013] The present invention also relates to a method for modifying an existing nitric acid production facility, wherein the existing nitric acid production facility includes a burner section, a cooling / condensing section, an absorption section having an outlet for a tail gas flow, a tail gas heating section, and a flow line for passing the tail gas from the absorption section to the tail gas treatment section, and optionally an air supply line, wherein the air supply line includes an air compressor entering the burner section; the method includes adding to the facility: a flow line for passing the tail gas from the absorption section through at least one heater in the tail gas heating section to the inlet of the burner section; and an oxygen flow supply line from one or more oxygen supply units to the burner section; preferably a nitric acid production section is obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 An exemplary method approach according to the invention is schematically illustrated.

[0015] Figure 2 An example of a nitric acid production facility according to the invention is shown.

[0016] Figure 3 An example of a single-pressure nitric acid (NA) production process according to the present invention is shown, involving the heating of tail gas (TG).

[0017] Any embodiments shown in the accompanying drawings are examples only and do not limit the present invention. DETAILED DESCRIPTION

[0018] The present disclosure provides a nitric acid production facility, which includes a nitric acid production section, the nitric acid production section including a burner section, a cooling / condensing section and an absorption section. A nitric acid production method carried out in such a nitric acid production facility is also provided. In the method, ammonia is reacted with oxygen in the burner section using an ammonia oxidation catalyst. The effluent from the burner section is cooled in the cooling / condensing section. The effluent from the cooling / condensing section is contacted with water in the absorption section to obtain a liquid stream including a nitric acid product and a tail gas stream.

[0019] The nitric acid process and the facility are, for example, of the dual pressure type or, for example, of the single pressure type.

[0020] In some embodiments, the nitric acid production process and facility are of dual pressure type, and the absorption section is operated at a pressure of, for example, 10-14 bara. The term "dual pressure" recognizes that in these embodiments, the production process uses different pressures (e.g., 4-6 bara) in the reactor and the absorption section. In other embodiments, the facility and process are of single pressure type, wherein the reactor and the absorption section are operated at the same pressure.

[0021] In the burner section, oxygen and ammonia react to form a burner gas stream. The burner gas stream includes nitrogen dioxide formed by oxidation of nitrogen oxides, and further includes a certain amount of unoxidized nitrogen oxides, nitrous oxide (N2O) as a byproduct and possibly N2 as a byproduct, and water obtained from the oxidation of ammonia.

[0022] The burner section specifically includes a reactor, which includes a combustion chamber. The reactor includes, for example, a burner hood, a gas distributor, at least one catalyst mesh or multiple catalyst meshes, and optionally a basket. Typically, the reactor will include a combustion chamber in which a suitable catalyst is placed. Catalysts for the oxidation of ammonia are known to those skilled in the art and typically include precious metals. A typical way to provide a catalyst is by placing one or more wire meshes, such as a pile of wire meshes, in the reactor, such as in the combustion chamber. A preferred metal catalyst is a combination of platinum and rhodium, such as a pack of platinum-rhodium meshes produced by weaving fine metal wires.

[0023] As used herein, 'cooling / condensing section' comprises a gas cooling section and a condensing section, optionally combined in a single unit.

[0024] In the gas cooling section, the burner gas stream is typically cooled by heat exchange with a cooling fluid and / or with a process stream to be heated, thereby forming a cooled burner gas stream and generating steam, for example, on the cooling fluid side. The gas cooling section comprises, for example, one or more heat exchange sections.

[0025] In the condensing section, the cooled combustor gas stream undergoes condensation, thereby forming a nitric acid solution and an uncondensed nitrogen oxide (NOx) gas stream.

[0026] In the absorption section, the nitrogen oxide gas stream undergoes absorption in water to form a raw nitric acid product stream and a tail gas comprising primarily N2, some nitrogen oxides such as NO x (nitrogen oxides and nitrogen dioxide), nitrous oxide (N2O and any excess oxygen). Preferably, in this section the gas has a residence time that allows further oxidation of NO to NO2. The absorption section is, for example, an absorption / oxidation column.

[0027] The absorption section comprises, for example, an inlet connected to the liquid outlet of the cooling / condensing section, and an inlet connected to the gas outlet of the cooling / condensing section, an inlet for water, a liquid outlet for the nitric acid stream and a gas outlet for tail gas. The liquid nitric acid stream is, for example, supplied to the bleaching section.

[0028] Downstream of the reactor, optionally by other equipment, such as for the unit for oxidizing nitrogen monoxide to nitrogen dioxide, a gas cooling section is provided. The unit for oxidation can, for example, work by providing a residence time that allows NO to be converted into NO2 to NOx gas. The gas cooling section has a gas inlet, and the gas inlet is in fluid communication (directly or indirectly) with the outlet of the burner gas of the reactor. The gas cooling section can have a conventional arrangement, such as including one or more shell and tube heat exchangers. For example, the gas cooling section includes one or more heat exchangers, and the heat exchanger is configured to have heat transfer contact between the gas flow (that is, method gas flow) produced by the chemical conversion in the facility and the service medium and / or method flow to be heated by the wall. The service medium is usually water or steam, which is usually provided as a separate flow system or loop in the facility. This heat exchanger using water or steam as a cooling fluid is referred to as a steam loop heat exchanger. The gas cooling section includes, for example, one or more of such steam loop heat exchangers and optionally one or more other heat exchangers. The heat exchange of the steam loop is usually used to produce superheated steam, and one or more heat exchangers are sometimes also referred to as superheaters. In a preferred embodiment, the gas flow from the burner is cooled by a steam superheater. The steam produced is used, for example, to drive rotating equipment, such as an air compressor (and / or a NOx compressor) and / or for steam export. In certain embodiments, the method and apparatus are of dual pressure type and use, for example, NO x compressor.

[0029] In an interesting embodiment, the gas cooling section further comprises a heat exchanger as a steam evaporator for generating steam and a heat exchanger as an economizer.The steam evaporator and the economizer are in particular part of a so-called steam circuit.

[0030] In some embodiments, the cooling section includes a tail gas heater, wherein the tail gas heater is a heat exchanger between the process gas stream (burner gas) to be cooled and the tail gas to be heated.

[0031] The output of the gas cooling section, for which the cooled process gas stream as a result of the heat exchanger is referred to as cooled burner gas, has a gas outlet in direct or indirect fluid communication with the next downstream section, ie the condensation section.

[0032] The condensation section therefore has a gas inlet, which is in fluid communication with the outlet fluid of the burner gas for cooling of the gas cooling section. In the method for producing nitric acid based on the oxidation of ammonia, the gas stream produced by oxidation, i.e., the burner gas, will necessarily include water, which is formed by the reaction of ammonia and oxygen. It should be understood that in water, nitrogen dioxide forms nitric acid. The condensation section is configured to allow this to happen by subjecting the cooled burner gas including water vapor to condensation. This condensation produces nitric acid condensed water, which is generally referred to as weak nitric acid. Regarding the conditions for condensing water vapor, it should be understood that the type and amount of gas that does not participate in the formation of nitric acid condensed water will remain in the gas phase. This refers in particular to uncondensed nitrogen oxides, nitrogen monoxide including any excess nitrogen dioxide, including nitrogen monoxide formed in the reaction between nitrogen dioxide and water, and any unoxidized nitrogen monoxide and nitrous oxide that initially exist. The condenser accordingly has a liquid outlet for nitric acid condensed water and a gas outlet for uncondensed nitrogen oxide gas streams. The condensation section can be a conventional condensing device, such as a shell and tube condenser.

[0033] In an interesting embodiment, the method and the plant are of the dual pressure type and the condensation section comprises a low-pressure condensation section and a high-pressure condensation section, wherein the nitrogen gas stream leaving the low-pressure condensation section is compressed before being fed to the high-pressure condensation section.

[0034] Preferably an expander is used. The expander is associated with a compressor, for example an air compressor and / or a compressor for increasing the pressure in the condensation section in a dual pressure process. Thus, the low pressure condensation section comprises a tail gas heater and a low pressure cooler / condenser. In an example embodiment, the process gas is supplied from a steam evaporator to a heat exchanger for heat exchange contact with the tail gas to be heated and subsequently supplied to a separate heat exchanger using cooling water.

[0035] In this dual pressure embodiment, the nitrogen oxide stream leaving the low pressure section is sent to the high pressure condensation section through a compressor. This compressor (nitrogen oxide compressor) is placed downstream of the gas cooling section (low pressure cooling / condensation section) and upstream of the high pressure condensation section, the terms downstream and upstream referring to the process gas stream. The high pressure condensation section of the dual pressure process and facility includes a high pressure nitrogen oxide gas cooler and a high pressure cooler / condenser. The acid product stream leaving the high pressure condensation section is sent to the absorption / oxidation section.

[0036] In order to complete the formation of nitric acid based on the excess nitrogen dioxide that is not condensed with water, the nitrogen oxide gas stream obtained from the condenser, especially from the high-pressure condenser in the dual-pressure process, is then subjected to absorption in a suitable aqueous liquid. Before absorption, it is preferably given a gas residence time to allow further oxidation of NO to NO2. The aqueous liquid can be water itself, but it can also be a dilute nitric acid solution. In the latter case, the dilute nitric acid solution will become a more concentrated nitric acid solution due to the absorption of nitrogen dioxide. Preferably, the absorption heat is usually removed by cooling water on the trays of the absorption column. The absorption is carried out in the absorption section. This section accordingly has a gas inlet, which is directly or indirectly connected to the gas outlet fluid of the condensation section. It should be understood that the nitrogen dioxide is allowed to form nitric acid by absorption in water.

[0037] The absorption section, which usually comprises an absorption column, preferably also functions as an oxidation section, in order to allow the formation of additional nitrogen dioxide from the nitrogen monoxide which is inevitably present, for example as a result of a reaction between nitrogen dioxide and water. To this end, for example, a secondary air stream is introduced into the bleacher and an oxygen-containing gas is supplied from the bleacher to the absorption column, for example, said gas being mixed with a nitrogen oxide stream obtained from a condenser, so that the NO formed by the reaction of NO2 with H2O is reoxidized. This secondary air also removes NO2 from the product acid in the bleacher. In a single pressure embodiment, the bleacher is optionally arranged as the bottom section of the absorption column.

[0038] The nitric acid condensate obtained in the condenser is fed directly or indirectly to the absorption section. To this end, the absorption section comprises a liquid inlet, which is in fluid communication with the liquid outlet of the condensation section. The absorption section, such as the absorption / oxidation section, produces a raw nitric acid product stream and a nitrogen oxide tail gas. The tail gas comprises NO x (unoxidized nitrogen oxides and unreacted nitrogen dioxide) and nitrous oxide (N2O). Thus, the absorption section comprises a gas outlet for the nitrogen oxide tail gas and a liquid outlet for the raw nitric acid product stream. The raw nitric acid product stream is supplied, for example, to the bleaching section.

[0039] The nitric acid facility provided in the present disclosure preferably comprises a tail gas treatment section receiving at least a portion of the tail gas.

[0040] The tail gas treatment section includes nitrogen oxides (NO x The invention relates to a nitrogen oxide gas removal zone, wherein the nitrogen gas received at the inlet of the nitrogen oxide gas removal zone is purified to form a purified tail gas. The purification uses, for example, a catalyst, in particular a catalytic reduction. The purified tail gas is, for example, expanded. The expanded purified tail gas is, for example, cooled and discharged to the atmosphere.

[0041] The tail gas treatment section, in particular the nitrogen oxide gas removal zone, includes, for example, a mitigation reactor comprising a catalytic bed for removing N2O and a catalytic bed for removing NO arranged in series. x Catalytic beds, one or more of which are used to remove NO x The catalytic bed for removing N2O is arranged downstream of the catalytic bed for removing N2O. Such a section can be used, for example, with a dual pressure method and / or a single pressure method.

[0042] For example, N2O is converted in two stages: In the first stage, N2O is decomposed into O2 and N2 with the help of a catalyst. For example, an iron zeolite catalyst is used. In the second stage, NOx is mixed with injected NH3 to produce N2 and H2O. For example, an iron zeolite catalyst is used.

[0043] The first upstream catalyst bed is used to remove N 2 O. The first catalyst bed preferably receives only tail gas.

[0044] The N2O removal catalyst bed is preferably operated in the temperature range of 400-490°C, for example using a dual pressure process.

[0045] The abatement reactor includes, for example, one or more x downstream catalyst bed.

[0046] NH3 is preferably added to the tail gas downstream of the catalyst bed for removing N2O. NH3 can be used for NO x In some embodiments, the abatement reactor includes a downstream catalytic bed for removing N2O and a downstream catalytic bed for removing NO x An ammonia distributor is provided upstream of the catalyst bed.

[0047] In a preferred embodiment, the exhaust gas reacts with ammonia under the influence of a catalyst (such as a non-precious metal catalyst) according to reaction equation (1) to form nitrogen and water vapor, which can be safely released into the atmosphere.

[0048] NO + NO2 + 2 NH3→ 2 N2 + 3 H2O (1)

[0049] In some other embodiments, the abatement reactor includes one bed for reducing both N2O and NO2, and natural gas is added to the gas stream upstream of the catalyst bed for removing N2O, and ammonia is added for reducing NO2. This embodiment is advantageously used with a lower temperature tail gas at the abatement reactor inlet.

[0050] The work generated by the expansion of the cleaned tail gas is usually used to drive a turbine (which is adjacent to a steam turbine and / or a gas turbine utilizing the steam generated in the process) to drive one or more compressors. This usually refers to a preferred air compressor preferably used to provide air to the oxidation process and / or to a NOx compressor for dual pressure embodiments; these compressors can be combined into a single device, or for example be two different sections connected to a single drive shaft.

[0051] Advantageously, in some embodiments, due to the recirculation of (part of) the tail gas to the combustor, the abatement reactor is relatively small, with a relatively small volume of catalyst relative to the nitric acid production capacity.

[0052] The method of the present invention involves providing an oxygen stream from one or more oxygen supply units and supplying the oxygen stream to a burner section, and then supplying an ammonia feedstock to the burner section. The oxygen supply unit preferably comprises an electrolyser, more preferably a water electrolysis unit, wherein the H2 gas stream and the oxygen stream are generated by electrolysis, preferably by water electrolysis, more preferably by liquid water electrolysis.

[0053] The oxygen supply unit may also include an air separation unit. In some embodiments, the oxygen supply unit includes both an electrolyzer and an air separation unit. In some embodiments, the oxygen flow comes only from the electrolyzer, and the reactor also receives air.

[0054] The oxygen flow includes at least 90 vol. % O 2 , such as at least 95 vol. % O 2 , or at least 99 vol. % O 2 , or at least 99.9 vol. % O 2 . High purity oxygen can contribute to stable operation of the combustor section.

[0055] As an example, a water electrolysis unit can be used to provide such a high purity oxygen stream. Other sources of oxygen stream are also possible. For example, a nitrogen generation unit can be used. For example, an air separation unit (ASU) with regulation of the oxygen stream from the ASU is used to provide the high purity oxygen stream.

[0056] Suitable types of electrolyzers include alkaline electrolyzers, solid oxide electrolyzers, and proton exchange membrane (PEM) electrolyzers. If necessary, a compressor and / or a blower can be used to compress the oxygen stream to the operating pressure of the reactor. In an embodiment with a PEM electrolyzer, the oxygen stream can be obtained at a pressure of, for example, 20-30 bar.

[0057] The facility preferably also includes an air supply line for supplying air to the burner. The air supply line includes, for example, an air compressor. Advantageously, the recirculation of at least a portion of the tail gas provides a lower air compressor load in the method of the present invention. Advantageously, a high-efficiency air compressor can be used. Even when the compressed air temperature is low, a good temperature of the air flow entering the burner can be achieved by including at least a portion of the heated tail gas flow in the air flow entering the burner.

[0058] Preferably, the arrangement comprises means in the air supply line for regulating the amount of air supplied to the burner, for example by operating an air compressor.

[0059] Preferably, in the method, air is supplied to the burner during at least a portion of the time, for example continuously or during a time period. This provides the advantage that in embodiments in which the preferred water electrolysis unit uses electricity from a fluctuating source (such as from solar and / or wind energy), more air can be supplied to the burner during operation of the water electrolysis unit at a lower or zero oxygen production rate. This advantageously allows stable operation of the facility, even in the case of using fluctuating energy sources, especially with a stable pressure in the burner, thereby achieving a constant nitric acid strength. The oxygen included in the air can react with ammonia feed, for example from an ammonia storage unit and / or from an ammonia facility.

[0060] In some embodiments, the nitric acid production section can be operated in both a first mode, in which oxygen from one or more oxygen supply units (such as from a water electrolysis unit) and ammonia feedstock from an ammonia facility are used, and a second mode, in which oxygen from air and ammonia feedstock from an ammonia storage unit are used. Preferably in the second mode, all oxygen supplied to the burner is provided as air. In this embodiment, the facility can provide greater flexibility. Equipment costs may be relatively high.

[0061] In a preferred embodiment where a water electrolysis unit is used to provide part or all of the oxygen stream, the hydrogen stream from the water electrolysis unit is preferably reacted with N2 in an ammonia plant to form at least a portion of the NH3 feedstock for the nitric acid production plant and process. Thus, advantageously, both the H2 stream and the O2 stream from the water electrolysis unit are effectively used for nitric acid production, unlike the concept where only ammonia is produced and oxygen is discharged.

[0062] Typically, the NH3 feedstock for nitric acid production is formed by reacting an N2 feedstock with an H2 feedstock in an ammonia plant. Preferably, the H2 feedstock is provided by water electrolysis. Preferably, the N2 feedstock is at least partially provided by an air separation unit (ASU), such as a cryogenic air separation unit, or for example by a vacuum pressure swing adsorption unit using, for example, zeolites, or for example a membrane-based ASU.

[0063] As used herein, the term ASU is not limited to cryogenic separation plants, but also encompasses pressure swing adsorption based plants and membrane separation based plants. In a broad sense, such plants may be referred to as nitrogen generating units.

[0064] The ASU also typically provides an oxygen stream or an oxygen-enriched air stream which is also supplied to the burner section of the nitric acid production section. The preferred presence of a tail gas treatment unit in the nitric acid production section may allow for the treatment of an oxygen-containing gas stream which does not have a very high oxygen purity, such as an oxygen-containing gas stream from an ASU for N2 feedstock production for an ammonia plant, in the burner section. The presence of a tail gas treatment unit also provides for the flexibility desired when modifying an existing nitric acid production facility comprising an ammonia plant and a nitric acid production section, wherein the existing ammonia plant comprises an ASU.

[0065] A preferred embodiment of the present invention is directed to combining green ammonia production with nitric acid production. Thus, the N2 used in NH3 production is preferably produced by an ASU, and the H2 feedstock for NH3 production is produced by water electrolysis. Green ammonia is used as feed to the nitric acid process, and the oxygen produced by the electrolyser and the ASU is combined with the tail gas in the NA production section to produce synthetic air, wherein the inlet composition to the burner (i.e., the total gas received by the burner) includes less than 11% vol. NH3.

[0066] In the process of the present invention, at least a portion of the tail gas stream from the absorption section is heated in the tail gas heating section. At least a portion of the heated tail gas is preferably supplied to the burner section via a tail gas compression unit, such as a tail gas compressor or ejector.

[0067] Typically, a portion (but not all) of the tail gas stream is heated in the tail gas heating section and supplied to the burner section. Therefore, in some embodiments, all tail gas streams are heated, and a portion of the heated tail gas stream is supplied to the burner section. In some other embodiments, part of the tail gas stream is heated, and all heated tail gas is supplied to the burner section. In other embodiments, a portion of the tail gas stream is heated, and a portion of the heated tail gas stream is supplied to the burner section. For example, a second portion of the tail gas stream is supplied to the burner section without heating, and / or another portion of the heated tail gas stream, for example, is supplied to the tail gas treatment section.

[0068] The tail gas stream comprises, for example, at least 90 vol.% N2 and, for example, less than 10 vol.% O2. Thus, the heated tail gas is advantageously used to dilute the oxygen stream from the oxygen supply unit. This advantageously contributes to a good operation of the burner.

[0069] Preferably, the inlet composition of the burner (ie the total gas received by the burner) comprises less than 11% vol. NH3. Thus, the recovered tail gas can be used as a diluent for the gas stream received by the burner.

[0070] For example, in an embodiment using a single pressure process and facility, optionally, a tail gas compressor compresses the tail gas stream received by the compressor from a pressure of, for example, 6.5 bar to an operating pressure of the process, for example, 8 bar. In some embodiments, an ejector is used to deliver the tail gas from a tail gas heater of a tail gas heating section to a burner section. An oxygen stream can advantageously be used as a motive fluid for the ejector, particularly when a PEM electrolyzer is used as a source of the oxygen stream.

[0071] The tail gas stream may include NO which is at least partially recycled to the combustor in the process. x This can help to increase the efficiency of the ammonia burner. Exhaust gas blowers are used, for example, to convey the exhaust gas in a dual-pressure process.

[0072] Ammonia feedstock is also supplied to the burner section. Preferably, the oxygen stream is mixed with at least a portion of the heated tail gas stream upstream / before mixing with the ammonia feedstock, and optionally also mixed with one or more other gas streams, such as additionally mixed with a portion of the cold tail gas stream. Preferably, the oxygen stream is mixed with at least a portion of the heated tail gas stream to form a (first) mixed gas stream in the tail gas / O2 mixing unit. The mixed gas stream has an oxygen concentration lower than the oxygen concentration of the oxygen stream, for example, including less than 50vol.% or less than 25vol.% oxygen, such as 20-25vol.% oxygen. Preferably, the mixed gas stream has an oxygen content (21vol.%) the same as that of the air. This very advantageously allows the ratio between the air and the mixed gas stream in the feed stream passing into the burner to be easily and flexibly adjusted. In addition, the temperature of the mixed gas stream is preferably in the range of 100-200°C, so as to have substantially the same pressure as the air supplied to the burner using an air compressor. This allows flexible switching between operations using air and using oxygen streams.

[0073] Preferably, the installation comprises an O2 sensor to achieve an optimal mixing ratio.

[0074] Preferably, the mixed gas stream is mixed with at least an ammonia feed and supplied to a burner section. Optionally, the method involves combining the ammonia feed with air to produce a second mixed gas stream, and combining the first mixed gas stream and the second mixed gas stream and supplying the combined gas stream to the burner. In other embodiments, the tail gas, the O2 gas stream, and the ammonia feed are mixed in a single mixer.

[0075] In the method according to the invention, at least a portion of the tail gas supplied to the burner is heated. This contributes to an optimum temperature of the gas flow at the burner inlet.

[0076] The temperature of the gas flow at the burner inlet is, for example, in the range of 160°C to 200°C.

[0077] Advantageously, the tail gas heating section or at least one tail gas heater is preferably used to heat (simultaneously and / or continuously) the tail gas supplied to the tail gas treatment section and the tail gas recycled to the burner. For example, in some embodiments, the tail gas heating section or at least one tail gas heater is used to heat the tail gas flow simultaneously, the tail gas flow comprising both the tail gas supplied to the tail gas treatment section and the tail gas recycled to the burner. In other embodiments, or in combination, the tail gas heating section is used to continuously (or subsequently) heat both the tail gas supplied to the tail gas treatment section and the tail gas recycled to the burner. For example, during some time periods, the heated tail gas is completely recycled to the burner, and during other time periods, a first portion of the heated tail gas is recycled to the burner and a second portion is supplied to the tail gas treatment section.

[0078] Preferably, the facility includes at least one heat exchanger for heating the tail gas, the heat exchanger having a gas flow line to the burner and a gas flow line to the tail gas treatment section. In operation, the gas from the heat exchanger can be directly or indirectly supplied to the burner, the tail gas treatment section, or both. In some embodiments, the gas from the heat exchanger can be directly or indirectly supplied to the burner, the tail gas treatment section, or both alternately.

[0079] The tail gas treatment section includes, for example, one or more sections for removing N2O and NO x The tail gas treatment section includes, for example, an upstream (to the gas stream) catalytic bed for removing N2O and an upstream (to the gas stream) catalytic bed for removing NO x a downstream catalytic bed, wherein preferably NH 3 is supplied only to the downstream catalytic bed as a reducing agent.

[0080] Preferably a tail gas treatment section having two such catalytic beds operates for example at a gas inlet temperature of at least 420° C., such as at least 450° C. and / or below 550° C. Operating at such temperatures may offer the advantage that no reducing agent is required in the upstream catalyst bed.

[0081] The tail gas temperature at the gas outlet of the absorber is, for example, in the range of up to 60°C.

[0082] Preferably, the temperature of the heated off-gas stream received by the off-gas / O2 mixing unit is in the range of 180° C. to 200° C. Very simply subjecting the off-gas supplied to the burner and the off-gas supplied to the off-gas treatment section to combined heating can be used in a nitric acid production process that meets these temperature requirements, thereby providing efficient heating.

[0083] In particular, in embodiments where the burner also receives air, or during an operating period of the method where the burner receives a flow of air and oxygen, a first portion of the tail gas is heated and supplied to the burner, and a second portion of the tail gas is cooled and sent to the tail gas treatment section. Preferably, both the first portion and the second portion are heated in the tail gas heating section.

[0084] Advantages of heating the tail gas upstream of dividing the tail gas into the first and second portions include great flexibility in distributing the heated tail gas to the tail gas treatment sections and burners in various ratios.

[0085] The cleaned tail gas including N2 is released from the tail gas treatment section and exhausted to the atmosphere.In some embodiments, the third portion of the tail gas flow is not heated in the tail gas heating section and is mixed with the first portion to achieve a desired temperature of the tail gas portion supplied to the combustor.

[0086] By supplying only a portion of the tail gas to the tail gas treatment section, the method advantageously allows for a smaller catalyst volume in the tail gas treatment section. Reduced air intake can also help reduce catalyst degradation by supplying fewer impurities in the tail gas flow to the tail gas treatment section. Advantageously, the total NOx emissions from the tail gas can be reduced.

[0087] If desired, greater flexibility with respect to feedstocks may be obtained by using relatively larger catalyst volumes for the tail gas treatment section.

[0088] Typically, in some embodiments, the method further involves supplying another portion of the tail gas stream to the burner, wherein this portion of the tail gas stream has a lower temperature than the temperature of the first portion / heated portion of the tail gas stream. The other portion of the tail gas stream may be the same temperature as the tail gas at the outlet of the absorption column (e.g., 20-40° C.), or may be heated to a temperature lower than the temperature of the heated tail gas stream / first portion.

[0089] In one embodiment, the first part of the tail gas stream is heated in the tail gas heating section to obtain a heated tail gas stream and supplied to the burner section, and the second part of the tail gas stream is heated in the tail gas heating section and supplied to the tail gas treatment section including a catalyst bed. In this embodiment, the facility includes an air supply line for supplying air to the burner section, which advantageously increases flexibility. In this embodiment, the temperature of the heated first part of the tail gas stream is reduced, for example, by mixing with another part of the tail gas stream, and then it is supplied to the burner section. Preferably, the first part and the second part are usually heated in one or more heat exchangers, for example, as described below. For example, the tail gas stream is separated in the first part and the second part downstream of the second heat exchanger for heat exchange with the burner gas, especially for a single pressure facility, for example, a second heat exchanger as described below. The temperature of the tail gas stream from the second heat exchanger is, for example, at least 350° C. or at least 400° C., which is advantageously high enough for effective catalytic tail gas treatment of the second portion of the tail gas, for example for catalytic reduction using natural gas or methane and ammonia, more particularly using a single catalyst bed. The temperature of the first portion of the tail gas is, for example, at least 50° C. or at least 100° C., for example by mixing with a third portion of the tail gas stream, for example a third portion of the tail gas stream bypassing the second heat exchanger.

[0090] Therefore, in a more specific preferred embodiment of the method having the first part and the second part, in particular for a single pressure method, heating the first part and the second part of the exhaust gas flow in the exhaust gas heating section includes heat exchange with the burner gas flow to reach a temperature of, for example, at least 350°C, and supplying the second part of the exhaust gas flow from the exhaust gas heating section to the catalytic exhaust gas treatment section at a temperature of at least 350°C.

[0091] The tail gas heating section preferably comprises a plurality of heat exchangers in series, each heat exchanger having the tail gas to be heated on one side and the fluid stream to be cooled on the other side. In an optional embodiment, a portion of the tail gas stream is separated from the tail gas stream between two of the heat exchangers and supplied to the burner. Thus, the separated tail gas stream portion can have a temperature that is favorable for the supply of the gas stream to the burner.

[0092] The tail gas heating section may include, for example, a first heat exchanger for heat exchange between the tail gas from the tail gas outlet of the absorption column and the expanded tail gas to be heated, and a second heat exchanger downstream thereof (for the tail gas to be heated) for heat exchange with the process gas (burner gas) from the burner. Optionally, the steam heater is arranged between the first heat exchanger and the second heat exchanger. In an optional embodiment, a portion of the tail gas flow is separated from the tail gas flow between the first heat exchanger and the second heat exchanger and supplied to the burner. Optionally, a portion of the tail gas flow is separated from the tail gas flow between the absorber and the first heat exchanger and also supplied to the burner.

[0093] The tail gas heating section may include, for example, a first heat exchanger for heat exchange between the tail gas from the tail gas outlet of the absorption column and the expanded tail gas to be heated, and a second heat exchanger for heat exchange with the condensed process gas from the cooling section downstream thereof (for the tail gas to be heated), and optionally a third heat exchanger for heat exchange with the process gas from the burner downstream thereof (for the tail gas to be heated). Optionally, the steam heater is arranged between the first heat exchanger and the second heat exchanger. The second heat exchanger for heat exchange with the condensed process gas from the cooling section is used, for example, in a dual pressure embodiment. In an optional embodiment, a portion of the tail gas stream is separated from the tail gas stream between the first heat exchanger and the second heat exchanger and supplied to the burner. In an optional embodiment, a portion of the tail gas stream is separated from the tail gas stream between the second heat exchanger and the third heat exchanger and supplied to the burner. Optionally, a portion of the tail gas stream is separated from the tail gas stream between the absorber and the first heat exchanger and also supplied to the burner. The exhaust gas stream from the third heat exchanger has, for example, a favourable temperature for catalytic reduction in the exhaust gas treatment section.

[0094] In some embodiments using a single pressure method and facility, at least a portion of the tail gas from the absorption column is heated in one or more heat exchangers (e.g., a boiler) and subsequently divided into a first portion that is supplied to a combustor and a second portion that is supplied to a tail gas treatment section, wherein the first portion, after being separated from the second portion, is cooled by heat exchange in a tail gas-to-tail gas heat exchanger with a tail gas flow upstream of at least one of the heat exchangers.

[0095] Controlling the temperature of the burner at the inlet to the catalytic screen into the burner provides the advantage of a more efficient process and preferably the use of a more efficient air compressor.

[0096] In embodiments using a dual pressure process, the burner operates at a pressure in the range of, for example, 4-6 bara, and for a single pressure process, the burner operates at a pressure in the range of 7-10 bara (eg, 8 bara).

[0097] For a single pressure process, the absorption section is operated at a pressure of, for example, 5-8 bara, and for a dual pressure process, the absorption section is operated at a pressure of, for example, 9-12 bara. In a dual pressure process, the tail gas is usually expanded between the absorption section and the burner, for example through a valve in the gas flow line leading from the absorption section to the burner. Advantageously, such tail gas expansion can be used, for example, in an ejector in the oxygen flow supply line in the case where the oxygen supply unit provides oxygen at a pressure of less than 1 bara, as is the case with some electrolysers.

[0098] Tail gas recirculation advantageously allows a higher energy recovery than in plants without such recirculation, since less compression power is required for air compression. In addition, tail gas recirculation reduces NO per unit of nitric acid produced. x As another advantage, the burner catalyst is exposed to less dust and other impurities in the air (even after filtering), thereby extending catalyst life through exhaust gas recirculation.

[0099] The present invention also relates to a nitric acid production facility, comprising a nitric acid production section, the nitric acid production section comprising a burner section, a cooling / condensing section and an absorption section having an outlet for a tail gas flow. The NA production section comprises a first flow line for passing tail gas from the absorption section through at least one heater in the tail gas heating section to the inlet of the burner section and a second flow line for passing tail gas from the absorption section to the tail gas treatment section. The first flow line and the second flow line provide improved flexibility of the facility, especially for different O2 feeds. For example, if more O2 feed is supplied as air, more tail gas can be supplied to the tail gas treatment section.

[0100] The NA production section further comprises an oxygen flow supply line from the oxygen supply unit into the burner section. The facility is preferably suitable for the nitric acid production method of the present invention. The NA production section preferably further comprises an air supply line, the air supply line comprising an air compressor into the burner section.

[0101] In a preferred embodiment, the nitric acid production facility further comprises an ammonia facility, an air separation unit and a water electrolysis unit. The water electrolysis unit has an outlet for oxygen preferably connected to the oxygen stream supply line and an outlet for H2 connected to the inlet of the ammonia facility. The air separation unit has an outlet for N2 connected to the inlet of the ammonia facility. The ammonia facility has an outlet for NH3 connected to the inlet of a burner section included in the nitric acid production section.

[0102] For example, the facility further comprises an ammonia storage unit, such as a storage tank, having an outlet connected to the ammonia feed supply line of the burner. Thus, if the ASU and / or the water electrolysis unit are operated at a lower or zero rate, the nitric acid production section can advantageously still operate in a stable manner.

[0103] The present disclosure also provides a method for modifying an existing nitric acid production facility, wherein the existing nitric acid production facility includes a burner section, a cooling / condensing section, and an absorption section having an outlet for a tail gas flow and a tail gas heating section. The existing facility includes a tail gas treatment section and a flow line for passing tail gas from the absorption section through the tail gas heating section to the tail gas treatment section. The existing facility includes an air supply line that passes into the burner section. The air supply line includes, for example, an air compressor.

[0104] The method comprises adding to the facility:

[0105] - a flow line for passing at least a portion of the tail gas flow from at least one heater in the tail gas heating section to the inlet of the burner section; and

[0106] - an oxygen flow supply line leading from an oxygen supply unit into the burner section.Preferably, the method provides a nitric acid production section and / or a nitric acid production facility as described herein as a modified facility.

[0107] In a preferred embodiment, the method further comprises adding a water electrolysis unit as the oxygen supply unit, and a flow line for feeding H2 to the NH3 facility included in the nitric acid production facility.

[0108] Preferably, the existing facility comprises a tail gas treatment section, preferably as described herein, and a gas flow line leading from a heater of the tail gas heating section to an inlet of the tail gas treatment section, in particular wherein the tail gas treatment section comprises a reduction reactor comprising a catalytic bed as described herein. Preferably, the method involves providing a flow control element, such as a splitter, in the gas flow line. The flow control element has a first outlet fluidly connected to the tail gas treatment section and a second outlet fluidly connected to the burner. Preferably, the flow control element is configured to divide the gas flow above the first outlet and the second outlet in an adjustable manner. The flow control element may, for example, comprise a three-way valve.

[0109] Advantageously, this method of modifying existing facilities provides minimal modifications to existing facilities while, for example, integrating with a water electrolysis unit, with low capital expenditure and few changes on the process side, for example for cooling the burner gases.

[0110] Figure 1 An exemplary nitric acid production method and a nitric acid production section according to the present invention are shown. The nitric acid production section (100) includes a burner section (1), a cooling / condensing section (2), and an absorption section (3). The absorption section has an outlet for a tail gas stream (4). An oxygen stream (5) comprising at least 90 vol.% O2 is supplied from one or more oxygen supply units (6), such as from a water electrolyzer. At least a portion of the tail gas stream (4) is heated in a tail gas heating section (7) to obtain a heated tail gas stream (8). At least a portion of the heated tail gas stream (8) is supplied to the burner section (1) together with the oxygen stream (5) and an ammonia feedstock (9). In a preferred embodiment, only a portion of the tail gas is heated and recycled to the burner section.

[0111] Preferably, air (11) is also supplied to the burner. Preferably, the air (11) is mixed with ammonia (9) to obtain a first mixed gas stream, and preferably, the oxygen stream (5) is mixed with the heated tail gas (8) to obtain a second mixed gas stream, and the first mixed gas stream is mixed with the second mixed gas stream and supplied to the burner. Preferably, the oxygen concentration of the second mixed gas stream is in the range of 10-30 vol.%, such as about 20 vol.%, and / or the N2 concentration is in the range of 70-90 vol.%. The N2 / O2 ratio of the second mixed gas stream can be adjusted by the mixing ratio of the component gas streams, i.e. the oxygen stream and the heated tail gas. Advantageously, the N2 / O2 ratio of the second mixed gas stream is similar to the N2 / O2 ratio of air and replaces the air (11).

[0112] Hot gases are supplied from the burner section (1) to the cooling / condensing section (2). In a dual pressure embodiment, the cooling / condensing section (2) optionally comprises a low pressure section, a compressor and a high pressure section. One or more streams (10) with cooling gases and condensate are supplied from the cooling / condensing section (2) to the absorption section (3), preferably as separate condensate and gas streams.

[0113] Preferably, an aqueous liquid (15) is supplied to the upper part of the absorption section (3), and a liquid stream (16) comprising nitric acid is discharged from the bottom of the absorption section (3) and supplied, for example, to a bleacher.

[0114] The nitric acid production section (100) includes a tail gas treatment section (13) and a flow line (12) for supplying tail gas to the tail gas treatment section (13).

[0115] Preferably, a first portion (4) of the tail gas stream is heated and supplied to the burner section (1). Preferably, a second portion (12) of the tail gas stream is supplied to a tail gas treatment section (13).

[0116] In some embodiments, the facility comprises a gas flow line (8) for passing a heated tail gas stream from a tail gas heating section (7) to a burner section (1), and one or more flow lines from the group consisting of: a gas flow line (12) for passing heated tail gas from a tail gas heating section (7) to a tail gas treatment section (13); and a gas flow line (14) for passing unheated or less tail gas to the burner section (1). The gas flow line (14) specifically bypasses at least one heat exchanger included in the gas flow line for passing the first portion (4) of the tail gas through the tail gas heating section (7).

[0117] Figure 2An exemplary nitric acid production facility is shown that includes a nitric acid production section (100) and an ammonia plant (101), an air separation unit (103) (ASU), and a water electrolysis unit (105). The water electrolysis unit (105) has an outlet (5) for oxygen connected to an oxygen flow supply line and an outlet (104) for H2 connected to an inlet of the ammonia plant (101). The ASU (103) has an outlet (102) for N2 connected to an inlet of the ammonia plant (101). The ammonia plant has an outlet (9) for NH3 connected to an inlet of a burner section (1), which is included in the nitric acid production section (100). The facility further optionally includes an O2 supply line (5A) that passes from the ASU (103) into the burner section (1). The facility includes a second air supply line (11A) that passes into the ASU. The facility optionally comprises an NH3 storage unit (106) and an ammonia supply line (9A) leading from the ammonia facility into the storage unit (106) and from the storage unit into the nitric acid production section (100).

[0118] The preferences given to the facility also apply to the method. The preferences given to the method also apply to the facility. The method is preferably carried out in a facility as described. The preferences given to the facility also apply to the method of modifying an existing nitric acid production facility. The method preferably results in the facility of the invention.

[0119] The abbreviation 'bara' indicates bar absolute. Unless otherwise indicated, pressures are absolute.

[0120] The expressions 'usually' and 'generally' indicate characteristics that are frequently used but are not mandatory.

[0121] In summary, the present disclosure relates to a nitric acid production method and facility. The method involves supplying an oxygen stream and an ammonia feedstock to a burner section. In an embodiment, a portion of the tail gas stream is heated in a tail gas heating section and supplied to the burner section.

[0122] Figure 3 An example of a single-pressure nitric acid (NA) production process according to the present invention is shown, involving the heating of tail gas (TG).

[0123] Ammonia (301) passes through an evaporator / superheater (302) and is supplied to a mixing unit (304) in a first part (303) and a reduction unit (316) in a second part (317). Air (305) is supplied to the mixing unit (304) through an air heater (306) and an air compressor (307). An oxygen stream (308) having a purity of at least 99 vol.% and supplied, for example, by an electrolyzer is also supplied to the mixing unit (304). The mixture (324) from the mixing unit (304) is supplied to an NH3 burner (309), and the resulting burner gas (310) is sent to an oxidation / absorption tower (313) after being cooled by generating superheated steam in a tail gas heater (311) and heating the tail gas and by boiler feed water (BFW) in a cooling condenser (312). The boiler feed water from the cooling condenser (312) is further supplied to the tail gas heater (311).

[0124] The tail gas heater (311) is positioned as a final tail gas heater. Initially, the tail gas from the oxidation / absorption tower (313) is heated in the first tail gas heater (314) and then heated from about 25-35°C to about 135°C by the steam heater (315). The tail gas from the other heater (315) is supplied to the above-mentioned final tail gas heater (311) as a first part under heat exchange with the burner gas (310); this achieves the heating of the tail gas from, for example, about 135°C to about 480°C. A part of the tail gas from the final tail gas heater (311) is supplied to the reduction unit (316), which also receives some NH3, i.e., the second part (317). Depending on the relative amount of oxygen flow (308) relative to air (305), the fraction of the tail gas from the final tail gas heater (311) supplied to the reduction unit (316) can be changed.

[0125] The reduction unit contains a x catalyst; and for example, no inlet for natural gas or fuel. The treated tail gas from the reduction unit (316) is expanded in the expander (318) and supplied to the chimney (319) for exhaust through the first tail gas heater (314). Another part of the tail gas from the final tail gas heater (311) is combined with a second part of the tail gas from the steam heater (315). This second part bypasses the final tail gas heater (311). The combined tail gas flow is compressed in the first tail gas compressor (320) and recycled to the mixing unit (304).

[0126] The nitric acid from the oxidation / absorption tower (313) is supplied to a bleaching section (321) arranged, for example, at the bottom of the tower. A portion of the tail gas from the first tail gas heater (314) and optionally also from the oxidation / absorption tower (313) is compressed in a second tail gas compressor (322) and mixed with a portion of the oxygen stream (308) in a second mixing unit (323). The resulting gas mixture having a temperature of, for example, about 55° C. to about 60° C. is used in the bleaching section (321).

Claims

1. A method for producing nitric acid, which is carried out in a nitric acid production section (100), The nitric acid production section comprises a burner section (1), a cooling / condensing section (2) and an absorption section (3), wherein the absorption section has an outlet for a tail gas stream (4), The method comprises: a) providing an oxygen flow (5) comprising at least 90 vol.% O2 from one or more oxygen supply units (6); b) supplying the oxygen stream (5) and ammonia feedstock (9) to the burner section; and c) wherein a first portion of the tail gas stream (4) is heated in a tail gas heating section (7) to obtain a heated tail gas stream (8), and is supplied to the burner section (1); wherein a second portion of the tail gas stream is heated in the tail gas heating section (7) and is supplied to a tail gas treatment section (13), the tail gas treatment section comprising a catalyst bed, wherein the nitric acid production section comprises an air supply line (11) for supplying air to the burner section, and wherein the temperature of the heated first portion of the tail gas stream (4) is reduced, and the first portion of the tail gas stream (4) is thereafter supplied to the burner section (1).

2. A method according to claim 1, wherein step b) involves reacting oxygen and ammonia in the burner section to form a burner gas flow, wherein the heating of the first and second parts of the exhaust gas flow in the exhaust gas heating section (7) involves heat exchange with the burner gas flow, and wherein the second part of the exhaust gas flow is supplied from the exhaust gas heating section (7) to the exhaust gas treatment section (13) at a temperature of at least 350°C.

3. The method according to claim 1, wherein the oxygen supply unit (6) comprises an electrolyzer.

4. The method according to any one of claims 1 to 3, wherein the oxygen supply unit (6) comprises an air separation unit.

5. The method according to claim 1, comprising supplying the ammonia raw material (9) from an ammonia plant (101), and supplying N2 feed (102) to the ammonia plant from an air separation unit (103).

6. The method according to claim 5, further comprising supplying a H2 feed (104) from a water electrolysis unit (105) to the ammonia facility (101), and using oxygen produced in the water electrolysis unit (105) as the oxygen flow (5).

7. The method according to claim 1, wherein in step c), the oxygen flow (5) is mixed with at least a portion of the heated tail gas flow (8) to form a mixed gas flow, and the mixed gas flow is mixed with at least the ammonia feedstock (9) and supplied to the combustor section (1).

8. The method according to claim 1, wherein a third portion of the off-gas stream having a temperature lower than the temperature of the heated off-gas stream (8) is additionally supplied to the combustor section (1).

9. The method according to claim 1, wherein the tail gas treatment section (13) comprises a catalytic bed for removing N2O and a catalytic bed for removing NO arranged in series. x Catalytic beds, one or more of which are used to remove NO x The catalyst bed is arranged downstream of the catalyst bed for removing NO, wherein the method comprises adding NH3 to the tail gas downstream of the catalyst bed for removing NO, wherein NH3 x in the catalyst bed for NO x reduction.

10. A nitric acid production facility, comprising a nitric acid production section (100), the nitric acid production section comprising a burner section (1), a cooling / condensing section (2) and an absorption section (3), the absorption section having an outlet for a tail gas stream (4), wherein the nitric acid production facility further comprises a first flow line and an oxygen flow supply line and a second flow line (12), the first flow line being used to allow a first portion of the tail gas stream (4) to pass from the absorption section (3) through at least one heater in the tail gas heating section (7) to the inlet of the burner section (1), the oxygen flow supply line being passed from one or more oxygen supply units (6) into the burner section (1), and the second flow line being used to allow a second portion of the tail gas stream (4) to pass from the absorption section (3) through at least one heater in the tail gas heating section (7) to the inlet of the burner section (1). A third portion of the exhaust gas stream is passed from the absorption section (3) to the exhaust gas treatment section (13), wherein the second flow line (12) for the second portion of the exhaust gas stream passes through the exhaust gas heating section (7), wherein the exhaust gas treatment section (13) includes a catalyst bed, and the facility includes a gas flow line (14) for a third portion of the exhaust gas stream passing from the absorption section to the burner section (1), the gas flow line bypassing at least one heat exchanger contained in the flow line of the first portion of the exhaust gas stream passing through the exhaust gas heating section (7), wherein the facility further includes an air supply line (11), the air supply line including an air compressor passing into the burner section.

11. The facility according to claim 10, further comprising an ammonia facility (101), an air separation unit (103) and a water electrolysis unit (105), wherein the water electrolysis unit (105) has an outlet for oxygen connected to the oxygen flow supply pipeline and an outlet for H2 feed (104) connected to the inlet of the ammonia facility (101), wherein the air separation unit (103) has an outlet for N2 connected to the inlet of the ammonia facility (101), and wherein the ammonia facility has an outlet for NH3 connected to the inlet of the burner section (1) included in the nitric acid production section (100).

12. A method of modifying an existing nitric acid production facility into a modified nitric acid production facility, the existing nitric acid production facility comprising a burner section (1), a cooling / condensing section (2), an absorption section (3) having an outlet for a tail gas stream (4), a tail gas heating section (7) and an existing flow line (12) for passing the tail gas stream from the absorption section through the tail gas heating section (7) to a tail gas treatment section (13), and an air supply line (11), the air supply line comprising an air compressor leading to the burner section; The method comprises adding to the facility: - an additional flow line for passing a portion of the tail gas flow (4) from the absorption section through at least one heater in the tail gas heating section (7) to the inlet of the burner section (1); and - an oxygen flow supply line from one or more oxygen supply units (6) to the burner section (1); wherein the tail gas treatment section (13) comprises a catalyst bed, and the method comprises adding a gas flow line (14) from the absorption section to the burner section, wherein the gas flow line (14) bypasses at least one heat exchanger contained in the additional flow line; wherein the modified nitric acid production facility is as defined in claim 10.

13. The method according to claim 12 further comprises adding a water electrolysis unit (105) to the facility as the oxygen supply unit, and a flow pipeline for H2 feed (104) from the water electrolysis unit (105) to the ammonia facility (101) included in the nitric acid production facility.

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