System for integrated nitric acid and ammonia production and production method thereof

Abstract

The present disclosure relates to the field of integrated nitric acid and ammonia production. After NOx consumption to 100 ppm or less, the nitric acid off-gas is combined with hydrogen produced at least in part by the water electrolyzer. The tail gas combined with hydrogen or the combined tail gas and hydrogen are further treated to remove NOx, CO, CO2 and O2 and compressed to synthesize ammonia. At least partial compression is performed prior to further treatment of the nitric acid tail gas combined with hydrogen, or prior to treatment of the combined tail gas and hydrogen.

Description

Technical Field

[0001] The present disclosure relates to the field of integrated nitric acid and ammonia production. Background Art

[0002] Integration of nitric acid production and ammonia production can present various benefits.

[0003] If the production of nitric acid could be made more energy efficient so that additional steam could be exported from a conventional steam turbine, or more power could be generated from the tail gas expansion via a conventional tail gas expander, then the integration of the nitric acid process into the ammonia production process could allow for the supply of, for example, electricity to an electrolyser that produces hydrogen for ammonia production, or for supplying heat to natural gas to convert it into carbon monoxide and hydrogen for ammonia production.

[0004] In particular, the integration of nitric acid production and ammonia production can be further beneficial if the tail gas generated by nitric acid production (because it contains about 85.0% to 99.5% nitrogen) is used in the production of ammonia rather than being discharged to the atmosphere. In fact, it is recognized that nitric acid tail gas can be used as a precursor for synthesis gas for ammonia synthesis.

[0005] WO2018054565 (Casale, 2017) discloses an integrated process for the synthesis of ammonia and nitric acid, which includes the synthesis of nitric acid and the synthesis of ammonia, wherein the synthesis of nitric acid includes the following steps: a) subjecting an ammonia stream to catalytic oxidation to obtain a gaseous stream containing nitrogen oxides; b) subjecting the gaseous stream to a process for absorbing nitrogen oxides to provide nitric acid and a tail gas containing nitrogen and residual nitrogen oxides; c) subjecting at least a portion of the first tail gas to a process for removing nitrogen oxides to provide a tail gas depleted of nitrogen oxides, and synthesizing ammonia by catalytic conversion of a supplementary gas containing hydrogen and nitrogen in an ammonia synthesis loop, wherein at least a portion of the second tail gas is used as a nitrogen source for obtaining the supplementary gas.

[0006] GB1597070A (Humphreys and Glasgow Ltd, 1978) discloses a process for producing ammonia synthesis gas, which process comprises providing a stream of hydrogen, obtaining a nitrogen-containing effluent stream from a process for producing nitric acid from ammonia by oxidizing ammonia with atmospheric air, and reacting a portion of the hydrogen in the hydrogen stream with the effluent gas to remove oxygen therefrom and leave a mixture of hydrogen and nitrogen suitable for the ammonia-forming reaction.

[0007] WO2005082779A2 (Uhde Gmbh) discloses a method for reducing nitrogen oxide emissions during the production of nitric acid, and a suitable apparatus for implementing the method. The method comprises the following steps: i) producing ammonia in an ammonia plant by catalytic reaction of nitrogen and hydrogen, ii) introducing the ammonia thus produced into a nitric acid plant, iii) combusting the ammonia into nitrogen oxides in the nitric acid plant, iv) scrubbing the nitrogen oxide-containing gas with water in at least one absorption column arranged downstream of the ammonia combustion, thereby producing nitric acid, and v) returning at least a portion of the residual gas leaving the nitric acid plant and containing nitrogen oxides to the ammonia plant.

[0008] GB2536996A (Johnson Matthey PLC, 2016) discloses the production of ammonium nitrate (NH4NO3) from ammonia and nitric acid (HNO3), comprising the following steps: a) providing a reaction gas mixture comprising hydrogen and nitrogen; b) passing the reaction gas mixture over a catalyst to form ammonia; c) catalytically oxidizing a first portion of the ammonia to form a gas mixture comprising nitrogen, oxygen and nitric oxide (NO); and d) converting NO into HNO3, thereby forming a gas mixture comprising nitrogen, oxygen and nitrogen oxide (NO x ), wherein the process comprises treating the exhaust gas mixture to produce a nitrogen stream and using at least a portion of the nitrogen stream (e.g. having less than 10 ppm oxygen) in the reaction gas mixture, and reacting a second portion of the ammonia recovered in step (b) with a portion of the nitric acid recovered in step (d) to form NH4NO3. Hydrogen may be produced by steam reforming of hydrocarbons to form synthesis gas, followed by a water gas shift (WGS) stage, carbon dioxide removal and a methanation stage. NO x The exhaust gas treatment may include reducing it with ammonia from an ammonia production unit to form nitrogen.

[0009] WO2019214921A1 (Casale, 2019) discloses an integrated process for the synthesis of ammonia and nitric acid, comprising: producing an ammonia make-up synthesis gas, comprising steam reforming a hydrocarbon feedstock in the presence of steam reforming heat; catalytically converting the make-up synthesis gas into ammonia; catalytically oxidizing a stream of ammonia to obtain a process gas; absorbing the process gas with water to obtain nitric acid, wherein at least a portion of the steam reforming heat is recovered from the hot process gas.

[0010] Therefore, it can be concluded that the prior art discloses an integrated system for recycling nitric acid tail gas to ammonia production. The prior art further discloses utilizing heat from nitric acid processes in gray ammonia production, i.e., involving reforming of hydrocarbon feedstocks. However, there remains a need to optimize the energy requirements associated with recycling nitric acid tail gas in ammonia production. Summary of the Invention

[0011] In one aspect of the present disclosure, a system for combined nitric acid and ammonia production is disclosed. The system comprises:

[0012] • Nitric acid plant for producing nitric acid, the nitric acid plant comprising:

[0013] oAbsorption tower, which is used to absorb NO x gas, thereby generating nitric acid and gases containing nitrogen, NO x and exhaust gas of O2 gas;

[0014] o a tail gas expander configured to expand a first portion of the tail gas to recover energy from the first portion of the tail gas;

[0015] o A first treatment unit located upstream of the tail gas expander, the first treatment unit being configured to remove NO from at least a first portion of the tail gas x , such that the first portion of the tail gas provided to the tail gas expander contains 100 ppm by volume or less of NO x ;

[0016] o means for heating upstream of the first treatment unit for heating at least a first portion of the tail gas; and

[0017] • an ammonia production plant for producing ammonia and comprising:

[0018] o Water electrolyzers for generating hydrogen and oxygen;

[0019] o means for mixing at least a first portion of the hydrogen gas and a second portion of the tail gas to produce synthesis gas;

[0020] o a first compression system configured for compressing gas, said compression system comprising one or several compression units and generating compressed gas,

[0021] o A second treatment unit, which is used to remove NO from the gas stream x , CO, CO2 and O2, a second treatment unit is located upstream or downstream of the means for mixing, for generating a mixture containing less than 10 ppm by volume of NO x , CO, CO2 and O2 atomic oxygen gas flow; and

[0022] o An ammonia synthesis unit for reacting compressed synthesis gas to produce ammonia.

[0023] The system is characterized in that at least one compression unit of the first compression system is located upstream of the second treatment unit.

[0024] More particularly, the second treatment unit may be located upstream or downstream of the means for mixing at least the first portion of the hydrogen gas and the second portion of the tail gas. The second treatment unit is configured to remove NO from the gas stream. x , CO, CO2 and O2, so that the gas stream leaving the second treatment unit contains less than 10 ppm by volume in total as NO x , CO, CO2 and atomic oxygen of O2. If the second treatment unit is located upstream of the means for mixing, it receives the compressed second portion of the tail gas, and if the second treatment unit is located downstream of the means for mixing, the second treatment unit receives the compressed synthesis gas.

[0025] The inventors have found that by placing at least one compression unit upstream of the second process unit, heat provided by the gas leaving the compression unit upstream of the second process unit can be used to operate the second process unit, which means that the energy requirement for operating the second process unit is reduced.

[0026] Thus, the system of the present disclosure allows for optimization of the energy requirements associated with the recycling of nitric acid tail gas in ammonia production.

[0027] In one embodiment of the system according to the present disclosure, the system further comprises an air separation unit configured to provide nitrogen to the syngas.

[0028] In one embodiment of the system according to the present disclosure, in the device for mixing, the first portion of the hydrogen is mixed with the second portion of the tail gas, and the system further includes a second compression system configured to compress the second portion of the hydrogen; or, in the device for mixing, all of the hydrogen generated by the water electrolyzer is mixed with the second portion of the tail gas.

[0029] In one embodiment of the system according to the present disclosure, the first compression system further comprises at least one compression unit located downstream of the second processing unit, and:

[0030] • the system further comprises a first cooling unit between the second processing unit and at least one compression unit downstream of the second processing unit, the first cooling unit being configured to exchange heat between the syngas and the coolant or between the second portion of the tail gas and the coolant to obtain a first heated coolant, and the first cooling unit being further configured to provide the first heated coolant to the second processing unit; and / or

[0031] •The system includes a second cooling unit, the second cooling unit being located downstream of at least one compression unit, the at least one compression unit being located downstream of the second processing unit, the second cooling unit being configured to exchange heat between the syngas and the coolant to obtain a second heated coolant, and the second cooling unit being further configured to provide the second heated coolant to the second processing unit.

[0032] In one embodiment of the system according to the present disclosure, the device for mixing is in direct fluid communication with the exhaust gas upstream of the device for heating, and / or is in direct fluid communication with the exhaust gas downstream of the device for heating and upstream of the first treatment unit, and / or is in direct fluid communication with the exhaust gas downstream of the first treatment unit.

[0033] In one embodiment of the system according to the present disclosure, the system further comprises a hydrogen production unit comprising:

[0034] • a steam reforming unit, which is used to convert hydrocarbons into carbon monoxide and hydrogen;

[0035] • a shift unit for converting the carbon monoxide and hydrogen provided by the steam reforming unit into carbon dioxide and hydrogen; and

[0036] • a carbon dioxide removal unit for removing carbon dioxide from the carbon dioxide and hydrogen provided by the shift unit;

[0037] And the hydrogen production unit is configured to provide hydrogen to the syngas.

[0038] In one embodiment of the system according to the present disclosure, the first treatment unit and / or the second treatment unit is a non-selective catalytic reduction unit or a selective catalytic reduction unit combined with a dedicated deoxygenation unit, and in particular the selective catalytic reduction unit is supplied with ammonia produced by an ammonia synthesis unit, or the non-selective catalytic reduction unit is supplied with hydrogen produced by a water electrolyzer or by a carbon dioxide removal unit, ammonia produced by an ammonia synthesis unit, or hydrocarbons.

[0039] In one aspect of the present disclosure, a method for the combined production of nitric acid and ammonia in a system according to the present disclosure is disclosed. The method comprises the following steps:

[0040] • Production of tail gas in nitric acid plants;

[0041] • mixing the hydrogen with a second portion of the tail gas to produce synthesis gas;

[0042] • treating a second portion of the tail gas or the synthesis gas in a second treatment unit, in particular wherein the second treatment unit is located upstream or downstream of the device for mixing;

[0043] • compressing the gas in a first compression system, thereby generating compressed gas, wherein at least one compression unit of the first compression system is located upstream of the second processing unit; and

[0044] • The compressed synthesis gas is reacted in an ammonia synthesis unit to produce ammonia.

[0045] The method is characterized in that part of the step of compressing the gas is performed in at least one compression unit upstream of the second treatment unit, in particular wherein the second portion of the tail gas or the synthesis gas is compressed in at least one compression unit upstream of the second treatment unit.

[0046] In one embodiment of the method according to the present disclosure, the method further comprises the step of providing nitrogen to the synthesis gas, and the nitrogen is produced by an air separation unit.

[0047] In one embodiment of the method according to the present disclosure, only a portion of the hydrogen is mixed with the second portion of the tail gas in the mixing step and the remaining portion of the hydrogen is compressed separately in the second compression system; or wherein in the mixing step, all of the hydrogen generated by the water electrolyzer is mixed with the second portion of the tail gas.

[0048] In one embodiment of the method according to the present disclosure, the method further comprises the following steps:

[0049] • exchanging heat between the syngas and the coolant in the first cooling unit to obtain a first heated coolant, and providing heat from the first heated coolant to the second processing unit; and / or

[0050] • exchanging heat between the syngas and the coolant in the second cooling unit, thereby obtaining a second heated coolant, and providing heat from the second heated coolant to the second process unit.

[0051] In one embodiment of the method according to the present disclosure, the second part of the tail gas that is mixed with hydrogen in the mixing step is a part of the tail gas upstream of the device for heating, and / or a part of the tail gas downstream of the device for heating and upstream of the first treatment unit, and / or a part of the tail gas downstream of the first treatment unit.

[0052] In one embodiment of the method according to the present disclosure, the method further comprises the following steps:

[0053] • Hydrogen is produced from hydrocarbons by steam reforming in the hydrogen production unit through the following steps:

[0054] o Reforming of hydrocarbons into carbon monoxide and hydrogen in a steam reforming unit;

[0055] o converting the carbon monoxide and hydrogen provided by the steam reforming unit into carbon dioxide and hydrogen in a shift unit; and

[0056] o removing carbon dioxide in a carbon dioxide removal unit from the carbon dioxide and hydrogen provided by the shift unit; and

[0057] •Provide hydrogen to the synthesis gas.

[0058] In one embodiment of the method according to the present disclosure, the treatment of the first part and / or the second part of the tail gas is performed by combined selective catalytic reduction and deoxygenation in a selective catalytic reduction unit combined with a deoxygenation unit, or is performed in a non-selective catalytic reduction unit by non-selective catalytic reduction, and in particular the selective catalytic reduction is performed using ammonia produced by an ammonia synthesis unit, or wherein the non-selective catalytic reduction is performed using hydrogen produced by a water electrolyzer or by a hydrogen production unit, or using ammonia produced by an ammonia synthesis unit, or using hydrocarbons.

[0059] In one aspect of the present disclosure, a method for modifying an ammonia production facility is disclosed, wherein the ammonia production facility comprises:

[0060] o Water electrolyzers for generating hydrogen and oxygen;

[0061] o a first compression system for compressing a synthesis gas comprising hydrogen and nitrogen, the compression system comprising a plurality of compression units for generating compressed synthesis gas; and

[0062] o an ammonia synthesis unit for reacting compressed synthesis gas to produce ammonia;

[0063] And wherein the method comprises the following steps:

[0064] o introducing a second portion of the tail gas generated in the nitric acid production plant into the ammonia production plant;

[0065] o introducing means for mixing hydrogen with the second portion of the tail gas to produce synthesis gas,

[0066] o Introducing a second treatment unit upstream or downstream of the means for mixing, and wherein at least one compression unit of the first compression system is located upstream of the second treatment unit, wherein the second treatment unit is configured to remove NO from the gas stream x , CO, CO2 and O2, and is used to generate a gas stream containing less than 10 ppm of atomic oxygen. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] Figure 1 One embodiment of a system according to the present disclosure is shown. DETAILED DESCRIPTION

[0068] Throughout the description and claims of this application document, the word "comprise" and its variations mean "including but not limited to", and are not intended to (and do not) exclude other parts, additives, components, integers, or steps. Throughout the description and claims of this disclosure, references to the singular include the plural unless the context requires otherwise. In particular, where the indefinite article is used, the disclosure is to be understood as contemplating plural as well as singularity unless the context requires otherwise.

[0069] Features, integers, characteristics, compounds, chemical moieties, or groups described in conjunction with a particular aspect, embodiment, or example of the present disclosure are to be understood to be applicable to any other aspect, embodiment, or example described herein unless incompatible therewith. All features disclosed in the features of this disclosure (including the description, claims, abstract, and drawings), and / or all steps of any method or process disclosed thereby, may be combined in any combination, except where at least some of the features and / or steps are mutually exclusive. The present disclosure is not to be limited in detail to any foregoing embodiments. The present disclosure extends to any novel feature or any novel combination of features disclosed in the features of this disclosure (including the description, claims, abstract, and drawings), or to any novel step or any novel combination of steps of any method or process disclosed thereby.

[0070] Numerical values ​​recited in the accompanying drawings include all values ​​and fractions within those ranges, as well as the recited endpoints. Terms such as "from ... to ..." or "in the range of ... to ..." or "up to ..." when referring to a range of measurable values ​​(such as a parameter, amount, time period, etc.) are intended to include the limits associated with the disclosed ranges.

[0071] In one aspect of the present disclosure, a system for the combined production of nitric acid and ammonia is disclosed. The system comprises a nitric acid plant for producing nitric acid, in particular starting from ammonia, the nitric acid plant comprising: an absorption tower for absorbing NO x gas, thereby generating nitric acid and gases containing nitrogen, NO x and O2 gas; a tail gas expander configured to expand a first portion of the tail gas, thereby recovering energy from the first portion of the tail gas; a first processing unit located upstream of the tail gas expander, the first processing unit being configured to process at least the first portion of the tail gas, in particular to remove NO from at least the first portion of the tail gas. x , such that the first portion of the tail gas provided to the tail gas expander contains 100 ppm by volume or less of NO x ; and means for heating upstream of the first treatment unit for heating at least a first portion of the tail gas. In other words, the nitric acid plant comprises: an absorption tower which generates nitric acid and a gas containing nitrogen, NO xand O2 gas; a device for heating at least a first portion of the tail gas; a first processing unit located downstream of the absorption tower, the first processing unit for removing NO from at least a first portion of the tail gas x and a tail gas expander located downstream of the first treatment unit, configured to expand the first portion of the tail gas, thereby recovering energy from the first portion of the tail gas. Typically, the absorption tower is in fluid communication with an ammonia oxidation unit, wherein ammonia catalytically reacts with oxygen, typically provided by compressed air, to produce a product containing NO. x of airflow.

[0072] The system further comprises an ammonia production plant for producing ammonia and comprising: a water electrolyzer for generating hydrogen and oxygen; a device for mixing at least a first portion of the hydrogen with a second portion of the tail gas to generate synthesis gas; a first compression system configured to compress gas, in particular for compressing the synthesis gas and / or for compressing the second portion of the tail gas, the compression system comprising one or several compression units and generating compressed gas, in particular compressed synthesis gas, in particular directly or after mixing the compressed second portion of the tail gas with hydrogen; a second treatment unit for removing NO from the gas stream, in particular from the second portion of the tail gas or from the synthesis gas x , CO, CO2 and O2, for the production of NO x , CO, CO2 and O2 of atomic oxygen gas, the second treatment unit is located upstream or downstream of the device for mixing; and an ammonia synthesis unit for reacting the compressed synthesis gas to produce ammonia.

[0073] The system is characterized in that at least one compression unit of the first compression system is located upstream of the second treatment unit.

[0074] In particular, if the second treatment unit is located upstream of the means for mixing, it receives the compressed second portion of the exhaust gas and will remove NO from the second portion of the exhaust gas. x , CO, CO2 and O2, thereby generating a second portion of the tail gas containing less than 10 ppm by volume of NO in total x , CO, CO2 and atomic oxygen of O2. In addition, if the second process is located downstream of the device for mixing, it receives the compressed synthesis gas and will remove NO from the synthesis gas. x , CO, CO2 and O2, thereby obtaining a compressed synthesis gas containing less than 10 ppm by volume of NO in total x , CO, CO2 and atomic oxygen of O2.

[0075] Thus, in certain embodiments, a system for integrated nitric acid and ammonia production is provided, wherein the system comprises (a) a nitric acid plant for producing nitric acid, the nitric acid plant comprising (i) an absorption tower for absorbing NO x gas, thereby generating nitric acid and gases containing nitrogen, NO x and O2 gas; (ii) a tail gas expander configured to expand a first portion of the tail gas, thereby recovering energy from the first portion of the tail gas; (iii) a first processing unit located upstream of the tail gas expander, the first processing unit being configured to remove NO from at least the first portion of the tail gas x , such that the first portion of the tail gas provided to the tail gas expander contains 100 ppm by volume or less of NO x ; and (iv) means for heating upstream of the first treatment unit for heating at least a first portion of the tail gas; and (b) an ammonia production plant for producing ammonia, comprising (v) a water electrolyzer for generating hydrogen and oxygen; (vi) means for mixing at least a first portion of the hydrogen and a second portion of the tail gas to generate synthesis gas; (vii) a first compression system configured for compressing the synthesis gas, the compression system comprising one or more compression units and generating compressed synthesis gas; and (viii) a second treatment unit for removing NO from the synthesis gas x , CO, CO2 and O2, thereby generating a compressed synthesis gas, the first treatment unit being located downstream of the device for mixing, the compressed synthesis gas containing less than 10 ppm by volume of NO x , atomic oxygen of CO, CO2 and O2; and (ix) an ammonia synthesis unit for reacting the compressed synthesis gas to produce ammonia; wherein at least one compression unit of the first compression system is located upstream of the second processing unit.

[0076] In addition, in certain embodiments, a system for combined nitric acid and ammonia production is provided, wherein the system comprises (a) a nitric acid plant for producing nitric acid, the nitric acid plant comprising (i) an absorption tower for absorbing NO x gas, thereby generating nitric acid and gases containing nitrogen, NO x and O2 gas; (ii) a tail gas expander configured to expand a first portion of the tail gas, thereby recovering energy from the first portion of the tail gas; (iii) a first processing unit located upstream of the tail gas expander, the first processing unit being configured to remove NO from at least the first portion of the tail gas x , such that the first portion of the tail gas provided to the tail gas expander contains 100 ppm by volume or less of NO xand (iv) means for heating upstream of the first treatment unit for heating at least a first portion of the tail gas; and (b) an ammonia production plant for producing ammonia, comprising (v) a water electrolyzer for generating hydrogen and oxygen; (vi) means for mixing at least a first portion of the hydrogen with a second portion of the tail gas to generate synthesis gas; (vii) a first compression system configured to compress the second portion of the tail gas, the compression system comprising one or several compression units and generating a compressed second portion of the tail gas; and (viii) a second treatment unit for removing NO from the second portion of the tail gas. x , CO, CO2 and O2, thereby generating a compressed second portion of the tail gas, the second treatment unit being located downstream of the means for mixing, the compressed second portion of the tail gas containing less than 10 ppm by volume of NO x , atomic oxygen of CO, CO2 and O2; and (ix) an ammonia synthesis unit for reacting the compressed synthesis gas to produce ammonia; wherein at least one compression unit of the first compression system is located upstream of the second processing unit.

[0077] It is further understood that the second processing unit is in fluid communication with the absorption column. In fact, in the case where the second processing unit is located upstream of the device for mixing, the second portion of the off-gas leaving the absorption column can be first provided to the compression unit of the first compression system, and then provided to the second processing unit and the mixing unit. In the case where the second processing unit is located downstream of the mixing unit, the second portion of the off-gas leaving the absorption column can first be provided to the device for mixing to generate synthesis gas, which is then compressed in the compression unit of the first compression system and processed in the second processing unit.

[0078] Those skilled in the art will recognize that the consumption of NO by the first processing unit x and consume NO through the second treatment unit x , N2O, CO, CO2 and O2 are necessary to prevent oxidation of the catalyst that catalyzes the formation of ammonia from the compressed synthesis gas.

[0079] As defined herein, means for heating is any means for heating the first portion of the exhaust gas to be expanded. In particular, the first portion of the exhaust gas is heated by a heat exchanger by transferring heat from a heating fluid that is cooled while heating the first portion of the exhaust gas.

[0080] As defined herein, means for mixing gases such as hydrogen and the second portion of the tail gas are known to those skilled in the art and include, for example, a mixing vessel, a mixing valve comprising two gas inlets and one outlet for the mixed gases, a piping system equipped with a static mixer, an injector, an injection nozzle, etc.

[0081] In particular, the compressor is powered by electricity. In particular, the compression unit is powered by a turbine running on high quality steam (ie, greater than 99% or higher pure steam), which prevents fouling, reduces the need for maintenance and increases the life of the turbine and the compression unit.

[0082] The inventors have discovered that by placing at least one compression unit upstream of the second process unit, the heat provided to the gas exiting the compression unit upstream of the second process unit can be used to operate the second process unit, meaning that the energy requirements for operating the second process unit are reduced. In effect, the compression unit upstream of the second process unit helps pressurize the syngas to achieve the necessary process conditions for converting the syngas into ammonia in the ammonia synthesis unit. Simultaneously, the compression of the gas increases the temperature of the gas, thereby contributing to the heat and temperature conditions required to operate the second process unit.

[0083] Thus, the system of the present disclosure allows for optimization of the energy requirements associated with the recycling of nitric acid tail gas in ammonia production.

[0084] Together with the second treatment unit, a methanogen may be provided upstream of the second treatment unit or downstream of the second treatment unit. The methanogen can convert the remaining CO and CO2 into methane to further reduce the amount of atomic oxygen entering the ammonia synthesis unit. When the methanogen is located upstream of the second treatment unit, the heat generated by the treatment in the methanogen and provided by the gaseous products at the outlet of the methanogen can be used for the treatment in the second treatment unit. When the methanogen is located downstream of the second treatment unit, the heat generated by the treatment in the methanogen and provided by the gaseous products at the outlet of the methanogen can be recovered, for example, via a heat exchange system, and supplied to the second treatment.

[0085] In particular, the system of the present disclosure allows for a portion of the nitric acid tail gas to be recycled within the nitric acid plant. This is achieved by fluidly connecting the nitric acid tail gas to an oxygen-containing gas to obtain a nitric acid tail gas-containing gas having an oxygen content that allows it to be fed to an ammonia oxidation burner and / or a nitric acid absorption tower to convert ammonia to nitric oxide and absorb NO. x The tail gas is then fluidly connected to an ammonia oxidation burner and / or a nitric acid absorption tower, downstream of the connection to the oxygen-containing gas fluid.

[0086] By means of the latter fluid connection to the ammonia oxidation burner and / or the nitric acid absorption tower, the power of the air compressor is reduced and the emissions to the air are reduced.

[0087] In one embodiment of the system according to the present disclosure, the system further comprises an air separation unit configured to provide nitrogen to the syngas.

[0088] The system disclosed herein allows for the integration of an air separation unit. In this manner, ammonia production does not need to be synchronized with nitric acid production. This means that ammonia production is not dependent on tail gas production from the nitric acid production facility. In the event of an interruption in nitric acid production, for example due to an emergency shutdown or maintenance required within the nitric acid production facility, the ammonia production facility can still operate and still produce ammonia, provided that nitrogen is supplied from the air separation unit. The nitrogen supply from the air separation unit can be supplied directly to ammonia production, or it can be liquefied for subsequent storage, as the liquid nitrogen constituting the nitrogen supply can be supplied as needed for ammonia production.

[0089] In one embodiment of the system according to the present disclosure, the first portion of the hydrogen gas is mixed with the second portion of the tail gas in the means for mixing, and the system further comprises a second compression system configured to compress the second portion of the hydrogen gas.

[0090] In another embodiment, all of the hydrogen generated by the water electrolyzer is mixed with the second portion of the tail gas in the means for mixing.

[0091] Therefore, the system of the present disclosure is flexible, allowing control over the amount of hydrogen that is processed in the second treatment unit along with the second portion of the tail gas. This means that the system can be controlled based on the amount of CO, CO2, and O2 gases remaining in the hydrogen. In fact, if such residual amounts require the hydrogen to be completely processed by the second treatment, it can be completely processed along with the second portion of the tail gas. In the absence of a second compression system, the modification of ammonia plants of the prior art is simplified because the existing compression units can be used to perform the functions of the compression units in the first compression system of the system of the present disclosure, and there is no need to add additional compression units to form the second compression system.

[0092] However, if it is not necessary to perform a complete treatment of the hydrogen in the second treatment unit in order to obtain a synthesis gas suitable for treatment in the ammonia synthesis unit, only part of the hydrogen may be treated in the second treatment unit.

[0093] Furthermore, the presence of the second compression system allows for better control of the pressure of the second portion of the combined hydrogen tail gas prior to final compression of the combined gas, making it suitable for conversion in the ammonia synthesis unit. This means that overall, the pressure of the synthesis gas entering the ammonia synthesis unit is better controlled, which in turn leads to better control of the actual ammonia synthesis in the ammonia synthesis unit.

[0094] In one embodiment of the system according to the present disclosure, the first compression system further includes at least one compression unit located downstream of the second processing unit. In addition, the system further includes a first cooling unit between the second processing unit and the at least one compression unit downstream of the second processing unit, the first cooling unit being configured to exchange heat between the second portion of the synthesis gas or tail gas and the coolant to obtain a first heated coolant, and the first cooling unit being further configured to provide the first heated coolant to the second processing unit; and / or the system includes a second cooling unit downstream of the at least one compression unit downstream of the second processing unit, the second cooling unit being configured to exchange heat between the synthesis gas and the coolant to obtain a second heated coolant, and the second cooling unit being further configured to provide the second heated coolant to the second processing unit.

[0095] In the presence of the first cooling unit, the gas that must be compressed in the remaining compression units is colder, which means that less power is required to operate the compression units. In addition, the first heated coolant can supply heat to the second processing unit, which means that the heat in the process is properly used for the operation of the second processing unit, and therefore, less heat must be supplied to the second processing unit. In the presence of the second cooling unit, the gas that must be compressed in any remaining compression units is colder, which means that less power is required to operate the remaining compression units. In addition, the second heated coolant can supply heat to the second processing unit, which means that the heat in the process is properly used for the operation of the second processing unit, and therefore, less heat must be supplied to the second processing unit.

[0096] The tail gas can be diverted into a first portion of the tail gas and a second portion of the tail gas at different locations between the absorption tower and the tail gas expander, such as between the absorption tower and the device for heating, between the device for heating and the first treatment unit, and / or between the first treatment unit and the tail gas expander. In other words, in one embodiment of the system according to the present disclosure, the device for mixing is in direct fluid communication with the tail gas upstream of the device for heating, and / or in direct fluid communication with the tail gas downstream of the device for heating and upstream of the first treatment unit, and / or in direct fluid communication with the tail gas downstream of the first treatment unit. Suitable devices for diverting the gas flow are known to those skilled in the art and include, for example, a T-shaped connector having one inlet and two outlets, so that the gas flowing through the inlet of the T-shaped connector is diverted into two gas flows having the same chemical composition.

[0097] Thus, the system is flexible so as to allow control of the temperature and the chemical content of atomic oxygen in the second portion of the tail gas. Thus, the system allows control of the chemical content of atomic oxygen in the second portion of the tail gas, and thus allows control of the treatment required in the second treatment unit. Furthermore, the system allows control of the temperature of the second portion of the tail gas, thereby allowing control of the treatment in the second treatment unit, and also controls the power required to operate the remaining compression units of the first compression system.

[0098] In one embodiment of the system according to the present disclosure, the system further includes a hydrogen production unit, which includes: a steam reforming unit for converting hydrocarbons into carbon monoxide and hydrogen; a shift unit for converting the carbon monoxide and hydrogen provided by the steam reforming unit into carbon dioxide and hydrogen; and a carbon dioxide removal unit for removing carbon dioxide from the carbon dioxide and hydrogen provided by the shift unit; and the hydrogen production unit is configured to provide hydrogen to the synthesis gas.

[0099] As defined herein, a steam reforming unit is a conventional steam reforming unit (SMR) comprising a primary reforming unit and a secondary reforming unit located downstream of the primary reforming unit, or a conventional autothermal reforming unit (ATR) fed by oxygen-enriched air (i.e., air with greater than 21% oxygen) or pure oxygen, the ATR unit being located downstream of a conventional fired heater.

[0100] The system of the present disclosure is flexible such that not all of the hydrogen mixed with the second portion of the tail gas must be produced by a water electrolyzer, and it can be produced by a conventional SMR or ATR ammonia production plant involving treating hydrocarbons with steam and oxygen.

[0101] Since the transition to producing hydrogen solely using water electrolyzers will take time, during this transition period, hydrogen will be produced by a mixture of water electrolysis and SMRs or ATRs. This means that the hydrogen production system will be a hybrid system including water electrolyzers and SMRs or ATRs, and importantly, the system of the present disclosure can operate with hydrogen produced by this hybrid system.

[0102] In one embodiment of the system according to the present disclosure, the first treatment unit and / or the second treatment unit is a non-selective catalytic reduction unit or a selective catalytic reduction unit combined with a dedicated deoxygenation unit, and in particular, the selective catalytic reduction unit is supplied with ammonia produced by an ammonia synthesis unit, or the non-selective catalytic reduction unit is supplied with hydrogen produced by a water electrolyzer or a carbon dioxide removal unit, ammonia produced by an ammonia synthesis unit, or hydrocarbons. The advantage of using hydrogen is that it is carbon-free.

[0103] The system of the present disclosure allows for both the first treatment unit and the second treatment unit to be non-selective catalytic reduction units (SNCR), selective catalytic reduction units (SCR) combined with deoxygenation units, or a combination thereof.

[0104] Thus, the system allows for the advantageous utilization of both the benefits of a non-selective catalytic reduction unit, including ease of installation, lower capital and operating costs compared to SCR, lower costs associated with catalyst replacement, and easy retrofitting of components in large-scale boiler units resulting in less downtime, and the benefits of SCR, including suitability for NO x Restore up to 90%.

[0105] In the case of an SCR unit, the deoxygenation unit is located downstream of the SCR unit and must reduce the oxygen content to 10 ppm or less of atomic oxygen. As long as the amount of water flowing out of the SCR is sufficient, it is not necessary to remove the oxygen in the form of water. This is because during the compression phase, in order to cool the gas stream to be compressed, water can be removed very easily by introducing liquid ammonia into the stream, which absorbs liquid nitrogen with a very strong affinity.

[0106] An advantage of the system of the present disclosure is that, given that the system provides hydrogen and ammonia, there is a source of clean fuel, that is, a fuel whose use results in reduced greenhouse gas emissions generated by the combustion of the fuel.

[0107] Where the hybrid device utilizes hydrocarbon gas in an SMR or ATR process, an advantage is that the fuel source (such as hydrocarbon) is already part of the system and therefore no additional fuel source is required to supply the second process unit. This advantage also exists when hydrogen or ammonia is supplied as fuel to the second process unit, as these are also part of the system, as described above.

[0108] In one aspect of the present disclosure, a method for integrated nitric acid and ammonia production performed in a system according to the present disclosure is disclosed. The method comprises the following steps:

[0109] - Production of tail gas in nitric acid plants;

[0110] - operating the water electrolyzer of an ammonia production facility to generate hydrogen;

[0111] - mixing the hydrogen with a second portion of the tail gas to produce synthesis gas;

[0112] - treating the gas in a second treatment unit, in particular treating the second portion of the tail gas or the synthesis gas, ie the mixed hydrogen and the second portion of the tail gas, in a second treatment unit to remove NO from the gas x, CO, CO2 and O2, thereby generating a gas stream, in particular a second portion of the tail gas or synthesis gas, which contains less than 10 ppm by volume of NO in total x , CO, CO2 and O2 atomic oxygen;

[0113] - compressing the gas in a first compression system, thereby generating compressed gas, in particular wherein at least one compression unit of the first compression system is located upstream of the second processing unit; and

[0114] - The compressed synthesis gas is reacted in an ammonia synthesis unit to produce ammonia.

[0115] The method is characterized in that a portion of the compressing step is performed before the treatment step, or in other words, the step of compressing the gas is performed in at least one compression unit upstream of the second treatment unit. In a particular embodiment, the second portion of the tail gas or the syngas is compressed in at least one compression unit upstream of the second treatment unit, and the compressed second portion of the tail gas or the compressed syngas is subsequently treated in the second treatment unit.

[0116] The inventors have found that by performing part of the compression step before the processing step, heat is provided by the gas leaving the compression unit upstream of the second processing unit and can be used to operate the second processing unit, which means that the energy requirement for operating the second processing unit is reduced.

[0117] Thus, the method of the present disclosure allows for optimization of the energy requirements associated with the recycling of nitric acid tail gas in ammonia production.

[0118] Together with the second treatment unit, a methanogen may be provided upstream of the second treatment unit or downstream of the second treatment unit. The methanogen can convert the remaining CO and CO2 into methane to further reduce the amount of atomic oxygen entering the ammonia synthesis unit. When the methanogen is located upstream of the second treatment unit, the heat generated by the treatment in the methanogen and provided by the gaseous products at the outlet of the methanogen can be used for the treatment in the second treatment unit. When the methanogen is located downstream of the second treatment unit, the heat generated by the treatment in the methanogen and provided by the gaseous products at the outlet of the methanogen can be recovered, for example, via a heat exchange system, and supplied to the second treatment.

[0119] In particular, the nitric acid tail gas is also recycled within the nitric acid plant. This is achieved by mixing part of the nitric acid tail gas with an oxygen-containing gas in order to obtain a nitric acid tail gas-containing gas having a sufficient oxygen content to be fed to the ammonia oxidation burner and / or the nitric acid absorption tower, so that ammonia is converted into nitric oxide and NO is absorbed. x The gas to provide nitric acid can be carried out with the desired efficiency.

[0120] By feeding the nitric acid tail gas and oxygen to the ammonia oxidation burner or the nitric acid absorption tower, the air compressor power is reduced and emissions to air are reduced.

[0121] In one embodiment of the method according to the present disclosure, the method further comprises the step of providing nitrogen to the synthesis gas, and the nitrogen is produced by an air separation unit.

[0122] The disclosed method allows the use of nitrogen provided by an air separation unit. In this way, ammonia production does not need to be synchronized with nitric acid production. This means that ammonia production is not dependent on the production of tail gas from the nitric acid production facility. In the event of an interruption in nitric acid production, for example due to an emergency shutdown or maintenance within the nitric acid production facility, nitrogen can still be supplied with the air separation unit in operation, and the ammonia production facility can still operate and produce ammonia.

[0123] In one embodiment of the method according to the present disclosure, only a portion of the hydrogen is mixed with the second portion of the tail gas in the mixing step, and the remaining portion of the hydrogen is compressed separately in the second compression system.

[0124] In another embodiment of the method according to the present disclosure, in the mixing step, all of the hydrogen produced by the water electrolyzer is mixed with the second portion of the tail gas.

[0125] Therefore, the method of the present disclosure is flexible, allowing control over the amount of hydrogen that is processed in the second processing unit along with the second portion of the tail gas. This means that the system can be controlled based on the amount of CO, CO₂, and O₂ gases remaining in the hydrogen. In fact, if such residual amounts require the hydrogen to be completely processed by the second processing unit, it can be completely processed along with the second portion of the tail gas. This simplifies the operation of the system by eliminating the need for additional compression of the hydrogen that is not directly mixed with the second portion of the tail gas.

[0126] However, if it is not necessary to perform a complete treatment of the hydrogen in the second treatment unit in order to obtain a synthesis gas suitable for treatment in the ammonia synthesis unit, only part of the hydrogen may be treated in the second treatment unit.

[0127] Furthermore, by compressing the hydrogen that is not directly mixed with the second portion of the tail gas, the pressure of the combined hydrogen-tail gas second portion can be better controlled before the final compression of the combined gas, so that it is suitable for conversion in the ammonia synthesis unit. This means that the pressure of the synthesis gas entering the ammonia synthesis unit is better controlled overall, which in turn leads to control of the actual ammonia synthesis in the ammonia synthesis unit.

[0128] In one embodiment of the method according to the present disclosure, the method further comprises the following steps: exchanging heat between the synthesis gas and the coolant or between the second part of the tail gas and the coolant in the first cooling unit to obtain a first heated coolant, and providing the heat from the first heated coolant to the second processing unit, and / or exchanging heat between the synthesis gas and the coolant in the second cooling unit to obtain a second heated coolant, and providing the heat from the second heated coolant to the second processing unit.

[0129] In the presence of the first cooling unit, the gas that must be compressed in the remaining compression units is colder, which means that less power is required to operate the compression units. In addition, the first heated coolant can supply heat to the second processing unit, which means that the heat in the process is properly used for the operation of the second processing unit, and therefore, less heat must be supplied to the second processing unit. In the presence of the second cooling unit, the gas that must be compressed in any remaining compression units is colder, which means that less power is required to operate the remaining compression units. In addition, the second heated coolant can supply heat to the second processing unit, which means that the heat in the process is properly used for the operation of the second processing unit, and therefore, less heat must be supplied to the second processing unit.

[0130] In particular, the synthesis gas is cooled to a temperature of 50°C or less. More particularly, the synthesis gas is cooled to a temperature of 10°C to 50°C.

[0131] In one embodiment of the method according to the present disclosure, the second part of the tail gas mixed with hydrogen in the mixing step is a part of the tail gas upstream of the device for heating (i.e., between the absorption tower and the device for heating), and / or a part of the tail gas downstream of the device for heating and upstream of the first treatment unit (i.e., between the device for heating and the first treatment unit), and / or a part of the tail gas downstream of the first treatment unit (i.e., between the first treatment unit and the tail gas expander).

[0132] The method is thus flexible, allowing control of the temperature of the second portion of the tail gas and the chemical content of the atomic oxygen. The method thus allows control of the chemical content of the atomic oxygen in the second portion of the tail gas, thereby allowing control of the treatment required in the second treatment unit. Furthermore, the method allows control of the temperature of the second portion of the tail gas, thereby allowing control of the treatment in the second treatment unit, and also controlling the power required to operate the remaining compression units of the first compression system.

[0133] In one embodiment of the method according to the present disclosure, the method further comprises the steps of producing hydrogen from hydrocarbons by steam reforming in a hydrogen production unit by the steps of: reforming the hydrocarbons into carbon monoxide and hydrogen in the steam reforming unit; converting the carbon monoxide and hydrogen provided by the steam reforming unit into carbon dioxide and hydrogen in a shift unit; and removing carbon dioxide from the carbon dioxide and hydrogen provided by the shift unit in a carbon dioxide removal unit; and providing hydrogen to the synthesis gas.

[0134] As defined herein, a steam reforming unit is a conventional steam reforming unit (SMR) comprising a primary reforming unit and a secondary reforming unit located downstream of the primary reforming unit, or a conventional autothermal reforming unit (ATR) fed by oxygen-enriched air (i.e., air with greater than 21% oxygen) or pure oxygen, the ATR unit being located downstream of a conventional fired heater.

[0135] The system of the present disclosure is flexible such that not all of the hydrogen mixed with the second portion of the tail gas must be produced by a water electrolyzer, and it can be produced by a conventional SMR or ATR ammonia production plant involving treating hydrocarbons with steam and oxygen.

[0136] Since the transition to producing hydrogen solely using water electrolyzers will take time, during this transition period, hydrogen will be produced by a mixture of water electrolysis and SMRs or ATRs. This means that the hydrogen production system will be a hybrid system including water electrolyzers and SMRs or ATRs, and importantly, the system of the present disclosure can operate with hydrogen produced by this hybrid system.

[0137] In one embodiment of the method according to the present disclosure, the treatment of the first part and / or the second part of the tail gas is performed by combined selective catalytic reduction and deoxygenation in a selective catalytic reduction unit combined with a deoxygenation unit, or is performed in a non-selective catalytic reduction unit by non-selective catalytic reduction, and in particular the selective catalytic reduction is performed using ammonia produced by an ammonia synthesis unit, or wherein the non-selective catalytic reduction is performed using hydrogen produced by a water electrolyzer or by a hydrogen production unit, or using ammonia produced by an ammonia synthesis unit, or using hydrocarbons.

[0138] In one embodiment of the method according to the present disclosure, the treatment of the first and / or second portion of the tail gas is performed in a selective catalytic reduction unit combined with a deoxygenation unit by combined selective catalytic reduction and deoxygenation, or in a non-selective catalytic reduction unit by non-selective catalytic reduction, and in particular the selective catalytic reduction is performed using ammonia produced by an ammonia synthesis unit, or wherein the non-selective catalytic reduction is performed using hydrogen produced by a water electrolyzer or by a hydrogen production unit, or using ammonia produced by an ammonia synthesis unit, or using hydrocarbons such as methane. The advantage of using hydrogen is that it is carbon-free.

[0139] The method of the present disclosure allows both the first and second portions of the tail gas to be treated by a non-selective catalytic reduction unit (SNCR), a selective catalytic reduction unit (SCR) combined with a deoxygenation unit, or a combination thereof.

[0140] Thus, the method allows to advantageously utilize both the benefits of non-selective catalytic reduction units, including lower operating costs compared to SCR, lower costs associated with catalyst replacement, and easy retrofitting of components in large-scale boiler units resulting in little downtime, and the benefits of SCR, including up to 90% NO x reduction.

[0141] In the case of SCR treatment, deoxygenation is performed downstream of the SCR treatment step and must reduce the oxygen content to an atomic oxygen content of 10 ppm or less. This is because during the compression phase, in order to cool the gas stream to be compressed, water can be removed very easily by introducing liquid ammonia into the stream, which absorbs liquid nitrogen with a very strong affinity.

[0142] An advantage of the process of the present disclosure is that, given that the process provides hydrogen and ammonia, a source of clean fuel is produced, which is a fuel whose use results in reduced greenhouse gas emissions generated by the combustion of the fuel.

[0143] In the case of a hybrid device utilizing hydrocarbon gas in an SMR or ATR process, an advantage is that the fuel source (such as hydrocarbon) has already been produced by the process, and therefore no additional fuel source needs to be produced to supply the second process unit. This advantage also exists when hydrogen or ammonia is supplied as fuel to the second process unit, as, as mentioned above, hydrogen and ammonia are also part of the process.

[0144] In one aspect of the present disclosure, a method for modifying an ammonia production plant is disclosed, which ammonia production plant includes: a water electrolyzer for generating hydrogen and oxygen; a first compression system for compressing a synthesis gas containing hydrogen and nitrogen, which includes several compression units, which are used to generate compressed synthesis gas; and an ammonia synthesis unit, which is used to react the compressed synthesis gas to generate ammonia, in particular to obtain a system for the combined production of nitric acid and ammonia according to the present disclosure.

[0145] The method comprises the steps of introducing a device for mixing hydrogen with a second portion of the tail gas generated in a nitric acid production plant to generate synthesis gas, the nitric acid production plant comprising an absorption tower for absorbing NO x The gas thus generates nitric acid and contains nitrogen, NO xand O2 gas; a tail gas expander for expanding at least a first portion of the tail gas, thereby recovering energy from the tail gas; a first processing unit located upstream of the tail gas expander, the first processing unit for processing at least the first portion of the tail gas, in particular for removing NO from the first portion of the tail gas x , such that at least a first portion of the tail gas provided to the tail gas expander contains 100 ppm by volume or less of NO x and means for heating upstream of the first treatment unit for heating at least a first portion of the tail gas; and introducing a second treatment unit upstream or downstream of the means for mixing for removing NO from the second portion of the tail gas or the synthesis gas x , CO, CO2 and O2, for generating a second portion of the tail gas containing less than 10 ppm atomic oxygen or a synthesis gas containing less than 10 ppm atomic oxygen, respectively.

[0146] The method is characterized in that the second treatment unit is introduced downstream of at least one compression unit of the several compression units.

[0147] In other words, a method for retrofitting an existing ammonia production facility is disclosed, wherein the existing ammonia production facility comprises:

[0148] o Water electrolyzers for generating hydrogen and oxygen;

[0149] o a first compression system for compressing a synthesis gas comprising hydrogen and nitrogen, said compression system comprising a plurality of compression units for generating compressed synthesis gas; and

[0150] o an ammonia synthesis unit for reacting compressed synthesis gas to produce ammonia;

[0151] The method comprises the following steps:

[0152] o introducing a second portion of the off-gas generated in the nitric acid production plant into the ammonia production plant;

[0153] o introducing means for mixing the hydrogen with the second portion of the tail gas to produce synthesis gas;

[0154] o Introducing a second treatment unit upstream or downstream of the means for mixing, and wherein at least one compression unit of the first compression system is located upstream of the second treatment unit, wherein the second treatment unit is configured to remove NO from the gas stream x , CO, CO2 and O2, and is used to generate a gas stream containing less than 10 ppm of atomic oxygen.

[0155] In a particular embodiment, the method comprises the steps of introducing a compression unit and a second treatment unit downstream of the compression unit and upstream of the mixing unit for removing NO from a second portion of the tail gas. x , CO, CO2 and O2 and used to generate a compressed second portion of the tail gas containing less than 10 ppm atomic oxygen.

[0156] In a particular embodiment, the method comprises the steps of introducing, downstream of the means for mixing and downstream of the compression unit of the first compression system, a gas for removing NO from the synthesis gas. x , CO, CO2 and O2 for generating a compressed synthesis gas containing less than 10 ppm of atomic oxygen.

[0157] In one aspect of the present disclosure, use of the system of the present disclosure for performing the method of the present disclosure is disclosed.

[0158] Examples

[0159] Reference Figure 1 Nitric acid is produced in a nitric acid production plant. The off-gas leaving the absorber 1 of the nitric acid production plant is split into a first off-gas stream 2 and a second off-gas stream 3 having the same chemical composition. The first off-gas stream 2 is heated in a heating unit 4. The gas stream leaving the unit 4 is then treated in a first treatment unit 5, in particular a non-selective catalytic reduction unit, in order to obtain a gas containing less than 100 ppm NO x This gas stream exiting the non-selective catalytic reduction unit is used to rotate an exhaust turbine 6 connected to a generator (not shown), which generates electricity. The gases exiting the exhaust turbine are discharged into the atmosphere. In a water electrolyzer 7, hydrogen 10 and oxygen 11 are generated from water 8 and electricity 9. The second exhaust gas stream 3 and hydrogen 10 are mixed and compressed in a compressor 12 to produce a compressed synthesis gas 13 having a temperature of up to 300°C. The compressed synthesis gas 13 is treated in a second treatment unit 14 (typically a non-selective catalytic reduction unit) at a temperature ranging from 450°C to 650°C to produce a compressed and treated product synthesis gas containing less than 10 ppm of atomic oxygen. Due to the temperature of the compressed synthesis gas 13, less heat must be supplied to the second non-selective catalytic reduction unit 14. No further treatment to remove traces of water is performed. The remaining CO and CO2 are converted to methane in a methanator (not shown). Next, after further compression to 130 bar in a compressor (not shown) including a liquid ammonia scrubbing cooling system, the compressed and treated synthesis gas is converted into ammonia 17 in an ammonia synthesis unit 16. Part of the hydrogen leaving the electrolyzer 7 and not mixed with the second part of the tail gas stream 3 can be used as a reducing agent 18 in a non-selective catalytic reduction or burned as fuel to provide heat.

Claims

1. A system for combined nitric acid and ammonia production, the system comprising: • A nitric acid plant for producing nitric acid, the nitric acid plant comprising: oAbsorption tower, which is used to absorb NO x gas, thereby generating nitric acid and gases containing nitrogen, NO x and exhaust gas of O2 gas; o a tail gas expander configured to expand a first portion of the tail gas, thereby recovering energy from the first portion of the tail gas; o a first treatment unit located upstream of the tail gas expander, the first treatment unit being configured to remove NO from at least the first portion of the tail gas x , such that the first portion of the tail gas provided to the tail gas expander contains 100 ppm by volume or less of NO x ;as well as o means for heating upstream of the first treatment unit for heating at least the first portion of the tail gas; and • an ammonia production plant for producing ammonia and comprising: o Water electrolyzers for generating hydrogen and oxygen; o means for mixing at least a first portion of the hydrogen and a second portion of the tail gas to produce synthesis gas; o a first compression system comprising one or several compression units and generating compressed gas; o A second treatment unit, which is used to remove NO from the gas stream x , CO, CO2 and O2, wherein the second treatment unit is located upstream or downstream of the device for mixing, for generating a gas containing less than 10 ppm by volume of NO x , CO, CO2 and O2 atomic oxygen gas flow; and o an ammonia synthesis unit for reacting compressed synthesis gas to produce ammonia; At least one compression unit of the first compression system is located upstream of the second processing unit. 2 . The system of claim 1 , further comprising an air separation unit configured to provide nitrogen to the syngas.

3. The system according to any one of claims 1 to 2, wherein in the means for mixing, the first portion of the hydrogen gas is mixed with the second portion of the tail gas, and wherein the system further comprises a second compression system configured to compress the second portion of the hydrogen gas; or Wherein in the device for mixing, all of the hydrogen generated by the water electrolyzer is mixed with the second portion of the tail gas.

4. The system according to any one of claims 1 to 3, wherein the first compression system further comprises at least one compression unit located downstream of the second processing unit, and: • wherein the system further comprises a first cooling unit between the second processing unit and the at least one compression unit downstream of the second processing unit, wherein the first cooling unit is configured to exchange heat between the syngas and a coolant or between the second portion of the tail gas and a coolant, thereby obtaining a first heated coolant, and wherein the first cooling unit is further configured to provide the first heated coolant to the second processing unit; and / or •Wherein the system comprises a second cooling unit, the second cooling unit being located downstream of the at least one compression unit, the at least one compression unit being located downstream of the second processing unit, wherein the second cooling unit is configured to exchange heat between the syngas and a coolant to obtain a second heated coolant, and wherein the second cooling unit is further configured to provide the second heated coolant to the second processing unit.

5. The system according to any one of claims 1 to 4, wherein the means for mixing is in direct fluid communication with the exhaust gas upstream of the means for heating, and / or in direct fluid communication with the exhaust gas downstream of the means for heating and upstream of the first treatment unit, and / or in direct fluid communication with the exhaust gas downstream of the first treatment unit.

6. The system according to any one of claims 1 to 5, further comprising a hydrogen production unit, the hydrogen production unit comprising: • a steam reforming unit, which is used to convert hydrocarbons into carbon monoxide and hydrogen; • a shift unit for converting the carbon monoxide and hydrogen provided by the steam reforming unit into carbon dioxide and hydrogen; and • a carbon dioxide removal unit for removing carbon dioxide from said carbon dioxide and hydrogen provided by said shift unit; The hydrogen production unit is configured to provide hydrogen to the synthesis gas.

7. The system according to claim 1 , wherein the first treatment unit and / or the second treatment unit is a non-selective catalytic reduction unit or a selective catalytic reduction unit combined with a dedicated deoxygenation unit, in particular wherein the selective catalytic reduction unit is supplied with the ammonia produced by the ammonia synthesis unit, or wherein the non-selective catalytic reduction unit is supplied with the hydrogen produced by the water electrolyzer or by the carbon dioxide removal unit, with the ammonia produced by the ammonia synthesis unit, or with hydrocarbons.

8. A method for the combined production of nitric acid and ammonia, the method being carried out in a system according to any one of claims 1 to 7, the method comprising the following steps: • production of tail gas in said nitric acid plant; • mixing hydrogen with a second portion of the tail gas to produce synthesis gas; • treating the second portion of the tail gas or the synthesis gas in the second treatment unit; • compressing gas in a first compression system, thereby generating compressed gas, wherein at least one compression unit of the first compression system is located upstream of the second processing unit; as well as • reacting the compressed synthesis gas in the ammonia synthesis unit to produce ammonia; Characterized in that part of the step of compressing the gas is carried out in the at least one compression unit located upstream of the second treatment unit, in particular wherein the second part of the tail gas or the synthesis gas is compressed in the at least one compression unit upstream of the second treatment unit.

9. The method of claim 8, further comprising the step of providing nitrogen to the syngas, wherein the nitrogen is produced by an air separation unit.

10. The method according to claim 8 or 9, wherein in the mixing step, only a portion of the hydrogen produced by the water electrolyzer is mixed with the second portion of the tail gas, and wherein the remaining portion of the hydrogen is compressed separately in a second compression system; or wherein in the mixing step, all of the hydrogen produced by the water electrolyzer is mixed with the second portion of the tail gas.

11. The method according to any one of claims 8 to 10, further comprising the steps of: • exchanging heat between the second portion of the syngas or the tail gas and a coolant in a first cooling unit, thereby obtaining a first heated coolant, and providing heat from the first heated coolant to the second processing unit; and / or • exchanging heat between the syngas and a coolant in a second cooling unit, thereby obtaining a second heated coolant, and providing heat from the second heated coolant to the second process unit.

12. The method according to any one of claims 8 to 11, wherein the second portion of the tail gas mixed with the hydrogen in the mixing step is a portion of the tail gas upstream of the device for heating, and / or a portion of the tail gas downstream of the device for heating and upstream of the first treatment unit, and / or a portion of the tail gas downstream of the first treatment unit.

13. The method according to any one of claims 8 to 12, further comprising the steps of: • Hydrogen is produced from hydrocarbons by steam reforming in the hydrogen production unit by the following steps: o reforming the hydrocarbons into carbon monoxide and hydrogen in the steam reforming unit; o converting the carbon monoxide and hydrogen provided by the steam reforming unit into carbon dioxide and hydrogen in the shift unit; as well as o removing carbon dioxide in the carbon dioxide removal unit from the carbon dioxide and hydrogen provided by the shift unit; as well as • Providing said hydrogen to said synthesis gas.

14. The method according to claim 8 , wherein the treatment of the first and / or second portion of the tail gas is carried out by combined selective catalytic reduction and deoxygenation in the selective catalytic reduction unit combined with a deoxygenation unit, or by non-selective catalytic reduction in the non-selective catalytic reduction unit, in particular wherein the selective catalytic reduction is carried out using the ammonia produced by the ammonia synthesis unit, or wherein the non-selective catalytic reduction is carried out using the hydrogen produced by the water electrolyzer or by the hydrogen production unit, or using the ammonia produced by the ammonia synthesis unit, or using hydrocarbons.

15. A method for modifying an ammonia production plant, The ammonia production equipment comprises: o Water electrolyzers for generating hydrogen and oxygen; o a first compression system for compressing a synthesis gas comprising hydrogen and nitrogen, the compression system comprising a plurality of compression units for generating compressed synthesis gas; as well as an ammonia synthesis unit for reacting the compressed synthesis gas to produce ammonia; The method The following steps are involved: o introducing a second portion of the tail gas generated in the nitric acid production plant into the ammonia production plant; introducing means for mixing said hydrogen with said second portion of said tail gas to produce synthesis gas, o introducing a second treatment unit upstream or downstream of the means for mixing, and wherein at least one compression unit of the first compression system is located upstream of the second treatment unit, wherein the second treatment unit is configured to remove NO from the gas stream x , CO, CO2 and O2, and is used to generate a gas stream containing less than 10 ppm atomic oxygen.

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