WO2023249492A1 - Ammonia production with co2 capture - Google Patents

Ammonia production with co2 capture Download PDF

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WO2023249492A1
WO2023249492A1 PCT/NO2023/050140 NO2023050140W WO2023249492A1 WO 2023249492 A1 WO2023249492 A1 WO 2023249492A1 NO 2023050140 W NO2023050140 W NO 2023050140W WO 2023249492 A1 WO2023249492 A1 WO 2023249492A1
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gas
reformer
steam
stream
hydrogen
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French (fr)
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Jostein Sogge
Gelein De Koeijer
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Equinor Energy As
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    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B3/00—Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
    • C01B3/02—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen
    • C01B3/025—Preparation or purification of gas mixtures for ammonia synthesis
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    • C01C1/02—Preparation, purification or separation of ammonia
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    • C01B3/00—Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
    • C01B3/02—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen
    • C01B3/32—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by reaction of gaseous or liquid organic compounds with gasifying agents, e.g. water, carbon dioxide, air
    • C01B3/34—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by reaction of gaseous or liquid organic compounds with gasifying agents, e.g. water, carbon dioxide, air by reaction of hydrocarbons with gasifying agents
    • C01B3/38—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by reaction of gaseous or liquid organic compounds with gasifying agents, e.g. water, carbon dioxide, air by reaction of hydrocarbons with gasifying agents using catalysts
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    • C01B3/02—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen
    • C01B3/32—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by reaction of gaseous or liquid organic compounds with gasifying agents, e.g. water, carbon dioxide, air
    • C01B3/34—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by reaction of gaseous or liquid organic compounds with gasifying agents, e.g. water, carbon dioxide, air by reaction of hydrocarbons with gasifying agents
    • C01B3/48—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by reaction of gaseous or liquid organic compounds with gasifying agents, e.g. water, carbon dioxide, air by reaction of hydrocarbons with gasifying agents followed by reaction of water vapour with carbon monoxide
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    • C01B3/00—Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
    • C01B3/50—Separation of hydrogen or hydrogen containing gases from gaseous mixtures, e.g. purification
    • C01B3/56—Separation of hydrogen or hydrogen containing gases from gaseous mixtures, e.g. purification by contacting with solids; Regeneration of used solids
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01C—AMMONIA; CYANOGEN; COMPOUNDS THEREOF
    • C01C1/00—Ammonia; Compounds thereof
    • C01C1/02—Preparation, purification or separation of ammonia
    • C01C1/04—Preparation of ammonia by synthesis in the gas phase
    • C01C1/0405—Preparation of ammonia by synthesis in the gas phase from N2 and H2 in presence of a catalyst
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    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B1/00—Electrolytic production of inorganic compounds or non-metals
    • C25B1/01—Products
    • C25B1/02—Hydrogen or oxygen
    • C25B1/04—Hydrogen or oxygen by electrolysis of water
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B15/00—Operating or servicing cells
    • C25B15/08—Supplying or removing reactants or electrolytes; Regeneration of electrolytes
    • C25B15/081—Supplying products to non-electrochemical reactors that are combined with the electrochemical cell, e.g. Sabatier reactor
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    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/02—Processes for making hydrogen or synthesis gas
    • C01B2203/0205—Processes for making hydrogen or synthesis gas containing a reforming step
    • C01B2203/0227—Processes for making hydrogen or synthesis gas containing a reforming step containing a catalytic reforming step
    • C01B2203/0233—Processes for making hydrogen or synthesis gas containing a reforming step containing a catalytic reforming step the reforming step being a steam reforming step
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    • C01B2203/0205—Processes for making hydrogen or synthesis gas containing a reforming step
    • C01B2203/0227—Processes for making hydrogen or synthesis gas containing a reforming step containing a catalytic reforming step
    • C01B2203/0244—Processes for making hydrogen or synthesis gas containing a reforming step containing a catalytic reforming step the reforming step being an autothermal reforming step, e.g. secondary reforming processes
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    • C01B2203/02—Processes for making hydrogen or synthesis gas
    • C01B2203/0283—Processes for making hydrogen or synthesis gas containing a CO-shift step, i.e. a water gas shift step
    • C01B2203/0288—Processes for making hydrogen or synthesis gas containing a CO-shift step, i.e. a water gas shift step containing two CO-shift steps
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    • C01B2203/04—Integrated processes for the production of hydrogen or synthesis gas containing a purification step for the hydrogen or the synthesis gas
    • C01B2203/042—Purification by adsorption on solids
    • C01B2203/043—Regenerative adsorption process in two or more beds, one for adsorption, the other for regeneration
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    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/06—Integration with other chemical processes
    • C01B2203/068—Ammonia synthesis
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    • C01B2203/08—Methods of heating or cooling
    • C01B2203/0805—Methods of heating the process for making hydrogen or synthesis gas
    • C01B2203/0811—Methods of heating the process for making hydrogen or synthesis gas by combustion of fuel
    • C01B2203/0816—Heating by flames
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    • C01B2203/0805—Methods of heating the process for making hydrogen or synthesis gas
    • C01B2203/0811—Methods of heating the process for making hydrogen or synthesis gas by combustion of fuel
    • C01B2203/0827—Methods of heating the process for making hydrogen or synthesis gas by combustion of fuel at least part of the fuel being a recycle stream
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    • C01—INORGANIC CHEMISTRY
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    • C01B2203/08—Methods of heating or cooling
    • C01B2203/0872—Methods of cooling
    • C01B2203/0888—Methods of cooling by evaporation of a fluid
    • C01B2203/0894—Generation of steam
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    • C01B2203/12—Feeding the process for making hydrogen or synthesis gas
    • C01B2203/1205—Composition of the feed
    • C01B2203/1211—Organic compounds or organic mixtures used in the process for making hydrogen or synthesis gas
    • C01B2203/1235—Hydrocarbons
    • C01B2203/1241—Natural gas or methane
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    • C01B2203/14—Details of the flowsheet
    • C01B2203/142—At least two reforming, decomposition or partial oxidation steps in series
    • C01B2203/143—Three or more reforming, decomposition or partial oxidation steps in series
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    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10J—PRODUCTION OF PRODUCER GAS, WATER-GAS, SYNTHESIS GAS FROM SOLID CARBONACEOUS MATERIAL, OR MIXTURES CONTAINING THESE GASES; CARBURETTING AIR OR OTHER GASES
    • C10J2300/00—Details of gasification processes
    • C10J2300/16—Integration of gasification processes with another plant or parts within the plant
    • C10J2300/164—Integration of gasification processes with another plant or parts within the plant with conversion of synthesis gas
    • C10J2300/1656—Conversion of synthesis gas to chemicals
    • C10J2300/1668—Conversion of synthesis gas to chemicals to urea; to ammonia
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    • C25B15/00—Operating or servicing cells

Definitions

  • ammonia is a very carbon intensive process, accounting for 1.8% of annual global energy output. 80% of this energy is used to obtain the hydrogen by steam reforming of natural gas.
  • One way to potentially reduce the carbon intensity of ammonia production is to find an alternative method of making the hydrogen used in its production.
  • An object of the invention is to provide a process which can be used to manufacture ammonia which is less carbon intensive than conventional steam methane reforming, while making use of the waste oxygen stream from electrolysis.
  • the present inventors have unexpectedly found that this may be achieved by combining hydrogen streams from water electrolysis and reforming of natural gas to prepare a make-up gas for ammonia production.
  • the carbon intensity of the process is reduced by using the waste oxygen stream from the electrolyser in the combustion chamber of the steam methane reformer to improve the efficiency of the steam methane reforming process.
  • this oxygen stream (termed the first oxygen stream) is advantageously fed to the combustion chamber of an oxyfuelled steam reformer. This potentially allows for a reduction in the size of the air separation unit required in the apparatus as it provides an alternative source of oxygen. This is advantageous because air separation units are typically bulky and expensive.
  • the need for a compressor to deliver the oxygen is eliminated when oxygen from water electrolysis is used in the combustion chamber of the oxyfuelled steam reformer.
  • the invention provides a process for manufacturing ammonia, comprising: a) electrolysing water in an electrolyser to form a first oxygen stream and a first hydrogen stream; b) separating air in an air separation unit to form a second oxygen stream and a nitrogen stream; c) generating a second hydrogen stream by a two-stage reforming process comprising: i) feeding a reformer feed gas to reformer tubes of an oxyfuel steam methane reformer, wherein the reformer feed gas comprises a hydrocarbon feedstock and steam; ii) mixing the first oxygen stream with an at least partially recycled flue gas stream from said reformer, to form a combustion mixture; iii) introducing the combustion mixture to a combustion chamber of the oxyfuel steam methane reformer to burn a fuel gas so as to provide heat for steam reforming of the feed gas to a product gas in the reformer tubes and a flue gas in the combustion chamber; iv) feeding the product gas from the oxyfuel steam reformer to an autotherm
  • the electrolyser in a) is powered using renewable electricity.
  • the hydrocarbon feedstock in the reformer feed gas is natural gas.
  • the molar ratio of hydrogen to nitrogen in the make-up gas of d) is 2.7-3.3.
  • the reactor in e) is a Haber-Bosch reactor.
  • the flue gas generated in iii) is introduced to a flue gas waste heat recovery section after having exited the combustion chamber to remove heat from the flue gas.
  • the portion of the flue gas which is not recycled in ii) is further cooled to remove water and obtain a purified flue gas comprising carbon dioxide and minor impurities.
  • the water from the flue gas is used to generate the steam in the reformer feed gas in i).
  • the purified flue gas comprising carbon dioxide and minor impurities is introduced to a compressor train for storage, for example, for treatment and permanent storage of the CO2.
  • natural gas is added to the offgas to form the fuel gas in iii).
  • the molar ratio of steam to carbon of the hydrocarbon feedstock in the reformer feed gas in i) is from 1 to 5.
  • the invention provides an apparatus arranged to perform the process as claimed in any of claims, said apparatus comprising an electrolyser (3) configured to receive water (2) via at least one inlet, wherein oxygen exits the electrolyser via a first gas phase conduit (5) and hydrogen exits via a second gas phase conduit (1); an oxyfuel steam reformer (6) comprising reformer tubes (8) and a combustion chamber (9), wherein the first gas phase conduit from the electrolyser is in fluid communication with the combustion chamber; an air separation unit (21), wherein oxygen exits the air separation unit via a third gas phase conduit (22) and nitrogen exits via a fourth gas phase conduit (26); an autothermal reformer (7), wherein the third gas phase conduit from the air separation unit is in fluid communication with the autothermal reformer; a water-gas shift reactor unit (24); a pressure swing adsorption unit (13), wherein hydrogen exits the pressure swing adsorption unit via a fifth gas phase conduit (27) and offgas exits via a sixth gas phase conduit (12) and
  • the present invention describes a process for manufacturing ammonia.
  • the make-up gas used to make ammonia comprises approximately 3 parts hydrogen to 1 part nitrogen.
  • the hydrogen is supplied from two sources.
  • the first hydrogen stream is generated from water via electrolysis.
  • the second hydrogen stream is generated from a hydrocarbon feedstock via a two-stage reforming process.
  • the first hydrogen stream is generated by electrolysis of water using an electrolyser.
  • Any electrolyser known in the art can be used in the process and apparatus of the present disclosure to convert water to hydrogen and oxygen, i.e. a first oxygen stream and a first hydrogen stream as defined herein.
  • the electrolyser may be a polymer electrolyte membrane electrolyser or an alkaline electrolyser.
  • the hydrogen produced by the electrolyser may have a purity of greater than 99.999%.
  • the electrolyser is powered by electricity.
  • the electricity can be produced using conventional methods known to the person skilled in the art.
  • the electricity is produced from renewable sources, i.e. the electricity is renewable electricity.
  • renewable sources include wind energy, tidal energy, geothermal energy, solar energy, hydro energy and biomass energy.
  • Hydro energy is particularly preferred.
  • Hydrogen produced from an electolyser using renewable electricity may be termed “green hydrogen”.
  • the second hydrogen stream is generated by a two-stage reforming process involving a primary reformer and a secondary reformer.
  • the primary reformer is an oxyfuel steam methane reformer.
  • the oxyfuel steam methane reformer may be top-fired, bottom-fired or side fired.
  • fired means heated by means of combusting a fuel gas in a combustion chamber.
  • the primary reformer is fed with a reformer feed gas which comprises a hydrocarbon feedstock.
  • the hydrocarbon feedstock may be natural gas, naphtha or a refinery offgas.
  • the preferred hydrocarbon feedstock is natural gas, thus comprising methane (CH4).
  • the hydrocarbon feedstock can be treated to remove impurities.
  • the hydrocarbon feedstock can be desulphurised using methods and apparatus known to the person skilled in the art.
  • the reformer feed gas further comprises steam.
  • Steam may be added to the reformer feed gas using methods known to the person skilled in the art. For example, by injecting steam into the hydrocarbon feedstock or by passing the hydrocarbon feedstock through a saturator.
  • the amount of steam in the reformer feed gas can be adjusted according to the amount of carbon in the hydrocarbon feedstock.
  • the steam to carbon ratio i.e. the molar ratio of steam to carbon in the hydrocarbon feedstock, may be from 1 to 5, or from 2 to 5, or from 2.5 to 4, or from 2.5 to 3.5, or from 2.5 to 3.
  • the reformer feed gas is fed to an oxyfuel steam methane reformer.
  • This reformer contains reformer tubes in contact with a combustion chamber, i.e. the reformer tubes are externally heated by the burners in the combustion chamber.
  • the reformer tubes contain a steam reforming catalyst, typically a nickel-based catalyst as is known in the art.
  • the catalyst may comprise nickel in an amount of 1-30 wt.% and be supported on shaped refractory oxides such as alpha alumina or magnesium or calcium aluminates.
  • the catalyst may be in the form of a mixed bed or a mesh.
  • oxyfuel we mean that the fuel gas in the combustion chamber is burned in the presence of oxygen (rather than air) to provide heat. This heat is absorbed by the reformer tubes by radiation and drives the chemical reaction which converts methane to product gas. This strongly endothermic chemical reaction occurs above 350°C and is represented by the below equation.
  • both carbon monoxide and carbon dioxide may be produced as by-products of steam methane reforming.
  • the “product gas” from the oxyfuel steam reformer thus typically comprises hydrogen, carbon dioxide and carbon monoxide.
  • the oxygen in the combustion chamber is the first oxygen stream described above which is produced by water electrolysis.
  • this also provides a use for what would otherwise be a waste product.
  • the oxygen produced from water electrolysis is advantageously at a pressure compatible with the oxyfuel steam reformer. Thus, no energy intensive compressors are usually required.
  • the fuel gas in the combustion chamber comprises at least partially recycled offgases from the upstream process, specifically the offgas from a pressure swing adsorption unit which will be described hereinbelow. If the offgas is not available in sufficient quantities to fuel the primary reformer, other fuel gas, such as natural gas, can be added to the offgas stream before introduction of the fuel gas to the combustion chamber.
  • Typical flue gases from combustion processes comprise mainly nitrogen as the combustion occurs in air. However, because oxygen, rather than air, is introduced to the combustion chamber in the oxyfuel reformer in the present process, the flue gas does not contain nitrogen. Rather, the flue gas produced in the present process comprises primarily CO2 and H2O, in addition to a small amount of unburned oxygen.
  • the flue gas typically leaves the combustion chamber at a temperature of approximately 1000°C via an outlet and can be channelled to a flue gas waste heat recovery section. Once waste heat has been recovered from the flue gas, at least some of the flue gas is recycled to the combustion chamber. Specifically, this recycled flue gas is mixed with the first oxygen stream to produce a combustion mixture.
  • the combustion temperature may be too high and there is a risk that the reformer tubes may rupture due to exposure to such intense heat.
  • the recycled flue gas stream can therefore advantageously be used for flame temperature control.
  • the temperature in the reactor tubes of the oxyfuel steam methane reformer may be 700-850°C, for example 700-800°C.
  • the remainder of the flue gas which is not recycled, can be cooled and condensed water separated therefrom, generating a purified flue gas comprising carbon dioxide.
  • the condensed water can advantageously be used to produce the steam added to the reformer feed gas, reducing the overall water consumption of the process.
  • the purified flue gas typically comprises carbon dioxide and minor impurities.
  • oxygen rather than air
  • the flue gas can be simply cooled to condense and remove water and obtain a gas comprising carbon dioxide and minor impurities.
  • This carbon dioxide can then be channelled to a compressor train for treatment and storage, and is thereby captured, e.g. in injection wells. At an intermediate pressure in the compressor train, treatment of the carbon dioxide may be required to remove the remaining oxygen and dehydrate the carbon dioxide product.
  • the recovered carbon dioxide from the flue gas is introduced to a compressor train where it may be compressed and treated to meet the required specifications of the carbon dioxide product.
  • Example CO2 specifications include: National Energy Technology Laboratory 2012 (a maximum of 730 ppmv H2O, 100 ppmv H2S, 35 ppmv CO, 40000 ppmv O2, 100 ppmv SO X and 100 ppmv NO X ), National Energy Technology Laboratory 2013 (a maximum of 500 ppmv H2O, 100 ppmv H2S, 35 ppmv CO, 10 ppmv O2, 100 ppmv SO X and 100 ppmv NO X ), and Northern Light 100 bar (a maximum of 122 ppmv H2O, 130 ppmv H2S, 0 ppmv CO, 275 ppmv O2, 96 ppmv SO X and 69 ppmv NO X ).
  • methane from the hydrocarbon feedstock and steam (water) are at least partially converted to a product gas, i.e. a gas comprising carbon dioxide and hydrogen.
  • a product gas i.e. a gas comprising carbon dioxide and hydrogen.
  • the output stream from the reformer tubes of the primary reformer is a gas mixture which typically comprises unreacted methane-rich gas, carbon dioxide, carbon monoxide and hydrogen.
  • This gas mixture i.e. the product gas, is channelled to a secondary reformer.
  • the secondary reformer is an autothermal reformer.
  • Autothermal refomers are known to the person skilled in the art.
  • the autothermal reformer at least a part of the residual hydrocarbon feedstock, typically natural gas, (e.g. unreacted CH4) is reacted with oxygen by means of an oxygen burner to form carbon monoxide, carbon dioxide and hydrogen.
  • the heat generated by this partial combustion is utilised to steam reform the remaining part of the unconverted hydrocarbon feedstock in the presence of a nickel catalyst to form a synthesis gas.
  • an air separation unit is used to supply a second oxygen stream to the autothermal reformer to react with the gas mixture.
  • Any air separation unit known in the art may be used, for example a cryogenic air separation unit.
  • the majority of the remaining hydrocarbon feedstock is converted in the autothermal reformer to form a synthesis gas.
  • the synthesis gas generally comprises hydrogen, carbon monoxide, carbon dioxide, steam, and can further comprise a small amount of unreacted methane.
  • This synthesis gas which may exit the autothermal reformer at a temperature of 1000-1050°C and a pressure of 30-45, for example 35-40, bar, is typically first cooled (usually to around 300 - 350 °C) by generation of high pressure steam, then channelled to a water-gas shift reactor unit.
  • the water-gas shift reactor unit may be a high temperature shift reactor or a low temperature shift reactor, or may include both, as known in the art.
  • the use of a water-gas shift reactor unit including both a high temperature shift reactor and a low temperatures shift reactor may be advantageous as it results in a more energy efficient plant and ensures maximum conversion of carbon monoxide.
  • the shifted synthesis gas may then be cooled by heat recovery and is then channelled to a pressure swing adsorption (PSA) unit.
  • PSA pressure swing adsorption
  • impurities principally carbon dioxide but also residual carbon monoxide, steam and hydrocarbon feedstock (e.g. CH4)
  • a purified stream of hydrogen gas i.e. a second stream of hydrogen gas
  • an offgas comprising said impurities.
  • this second stream of hydrogen gas can be considered “blue hydrogen”.
  • the first and second hydrogen streams are then mixed with a nitrogen stream from the air separation unit in the correct proportions to obtain a make-up gas for ammonia synthesis.
  • the molar ratio of hydrogen to nitrogen in the make-up gas for the ammonia synthesis is ideally in the range of 2.7 to 3.3.
  • the relative proportions of the first and second hydrogen streams in the make-up gas can be adjusted depending on, e.g. the intermittency of the supply of renewable electricity.
  • This make-up gas can then be fed to an ammonia synthesis reactor, such as a Haber- Bosch reactor, to generate ammonia.
  • an ammonia synthesis reactor such as a Haber- Bosch reactor, to generate ammonia.
  • Such reactors are known to the person skilled in the art.
  • the process and apparatus disclosed herein may be suitable for generation of 500-1000 tonnes or even more of ammonia per day.
  • Figure 1 shows a schematic representation of an embodiment of the process and apparatus of the present disclosure.
  • the first hydrogen stream 1 is generated by electrolysis of water 2 using an electrolyser 3.
  • the electrolyser 3 is powered using renewable electricity 4.
  • the second hydrogen stream 27 is generated by a two-stage reforming process involving an oxyfuel steam methane reformer 6 and an autothermal reformer 7.
  • the oxyfuel steam methane reformer 6 contains reformer tubes 8 assembled in a combustion chamber 9.
  • the combustion chamber 9 is fed with a fuel gas 11 which contains offgas 12 from the pressure swing adsorption unit 13. If the offgas 12 is not available in sufficient quantities to fuel the primary reformer, natural gas can be added to the offgas stream as a make-up fuel gas 14 before introduction of the fuel gas to the combustion chamber.
  • methane and steam are partially converted to a product gas, i.e. gas mixture 20.
  • gas mixture 20 which comprises unreacted natural gas, carbon dioxide, carbon monoxide and hydrogen. This gas mixture 20 is channelled to the autothermal reformer 7.
  • the first hydrogen stream 1 and the second hydrogen stream 27 are then mixed with a nitrogen stream 26 from the air separation unit in the correct proportions to obtain a make-up gas 28.
  • This make-up gas is then fed to an ammonia synthesis reactor 29, e.g. a Haber-Bosch reactor, to generate an ammonia stream 30.

Abstract

The invention provides a process for manufacturing ammonia, comprising: a) electrolysing water in an electrolyser to form a first oxygen stream and a first hydrogen stream; b) separating air in an air separation unit to form a second oxygen stream and a nitrogen stream; c) generating a second hydrogen stream by a two-stage reforming process comprising: i) feeding a reformer feed gas to reformer tubes of an oxyfuel steam methane reformer, wherein the reformer feed gas comprises a hydrocarbon feedstock and steam; ii) mixing the first oxygen stream with an at least partially recycled flue gas stream from said reformer, to form a combustion mixture; iii) introducing the combustion mixture to a combustion chamber of the oxyfuel steam methane reformer to burn a fuel gas so as to provide heat for steam reforming of the feed gas to a product gas in the reformer tubes and a flue gas in the combustion chamber; iv) feeding the product gas from the oxyfuel steam reformer to an autothermal reformer and reacting said product gas with the second oxygen stream in the autothermal reformer to form a synthesis gas; v) passing the synthesis gas from the autothermal reactor through a water-gas shift reactor unit to form a shifted synthesis gas; vi) introducing the shifted synthesis gas to a pressure swing adsorption unit to form a second hydrogen stream and a separate offgas, wherein the fuel gas in the oxyfuel steam reformer unit in iii) comprises at least a portion of the offgas from the pressure swing adsorption unit; d) mixing the first and second hydrogen streams and the nitrogen stream to produce a make-up gas; and e) feeding said make-up gas to a reactor to form ammonia.

Description

Ammonia production with CO2 capture
Technical field
The present invention relates to a process for manufacturing ammonia and an apparatus arranged to perform said process. In particular, the process comprises all of: electrolysing water in an electrolyser to form a first oxygen stream and a first hydrogen stream; separating air in an air separation unit to form a second oxygen stream and a nitrogen stream; generating a second hydrogen stream via a two-stage reforming process; and using said first and second hydrogen streams and said nitrogen stream to manufacture ammonia.
Background of the invention
Ammonia is an important industrial chemical, with a current global production of about 176 million tonnes per year. Ammonia is typically produced using the Haber-Bosch process by the reaction of hydrogen and nitrogen (this mixture is typically termed “make-up” gas) according to the following equation:
N2 + 3 H2 -> 2 NH3
However, production of ammonia is a very carbon intensive process, accounting for 1.8% of annual global energy output. 80% of this energy is used to obtain the hydrogen by steam reforming of natural gas. One way to potentially reduce the carbon intensity of ammonia production is to find an alternative method of making the hydrogen used in its production.
One such method that has been considered is the generation of hydrogen by electrolysis of water. However, electricity is typically far more expensive than natural gas, and electricity generation can itself be associated with a significant carbon footprint. Furthermore, production of hydrogen by electrolysis generates a waste oxygen stream, which is typically vented to the atmosphere.
The present invention is conceived to solve or at least alleviate the problems identified above. An object of the invention is to provide a process which can be used to manufacture ammonia which is less carbon intensive than conventional steam methane reforming, while making use of the waste oxygen stream from electrolysis.
The present inventors have unexpectedly found that this may be achieved by combining hydrogen streams from water electrolysis and reforming of natural gas to prepare a make-up gas for ammonia production. In particular, the carbon intensity of the process is reduced by using the waste oxygen stream from the electrolyser in the combustion chamber of the steam methane reformer to improve the efficiency of the steam methane reforming process.
The use of hydrogen produced by electrolysis in ammonia synthesis has previously been contemplated. However, production of hydrogen using an electrolyser results in a waste stream of pure oxygen. In prior art processes, this oxygen stream may have simply been vented to the atmosphere. However, in the present disclosure, this oxygen stream (termed the first oxygen stream) is advantageously fed to the combustion chamber of an oxyfuelled steam reformer. This potentially allows for a reduction in the size of the air separation unit required in the apparatus as it provides an alternative source of oxygen. This is advantageous because air separation units are typically bulky and expensive. In addition, the need for a compressor to deliver the oxygen is eliminated when oxygen from water electrolysis is used in the combustion chamber of the oxyfuelled steam reformer. This is because the burners in the combustion chamber operate at atmospheric pressure, and therefore only a fan or blower is required to direct the oxygen to the reformer. Furthermore, because the oxygen streams for the autothermal reformer and the combustion chamber of the oxyfuelled steam reformer are separate, the apparatus required to manufacture ammonia is simplified compared to prior art processes where a single oxygen stream has to be split or where two oxygen streams have to be combined. A further advantage of having two separate oxygen streams is that it potentially increases the flexibility of the ammonia plant. For example, additional oxygen could be supplied to the oxyfuelled reformer by the air separation unit.
Further advantages of the present process and apparatus include easy, efficient and cheap CO2 capture, low water consumption by utilizing condensed water from the flue gas for steam generation, and the utilization of both the nitrogen and oxygen products from the air separation unit.
Summary of the Invention
In a first aspect, the invention provides a process for manufacturing ammonia, comprising: a) electrolysing water in an electrolyser to form a first oxygen stream and a first hydrogen stream; b) separating air in an air separation unit to form a second oxygen stream and a nitrogen stream; c) generating a second hydrogen stream by a two-stage reforming process comprising: i) feeding a reformer feed gas to reformer tubes of an oxyfuel steam methane reformer, wherein the reformer feed gas comprises a hydrocarbon feedstock and steam; ii) mixing the first oxygen stream with an at least partially recycled flue gas stream from said reformer, to form a combustion mixture; iii) introducing the combustion mixture to a combustion chamber of the oxyfuel steam methane reformer to burn a fuel gas so as to provide heat for steam reforming of the feed gas to a product gas in the reformer tubes and a flue gas in the combustion chamber; iv) feeding the product gas from the oxyfuel steam reformer to an autothermal reformer and reacting said product gas with the second oxygen stream in the autothermal reformer to form a synthesis gas; v) passing the synthesis gas from the autothermal reactor through a water- gas shift reactor unit to form a shifted synthesis gas; vi) introducing the shifted synthesis gas to a pressure swing adsorption unit to form a second hydrogen stream and a separate offgas, wherein the fuel gas in the oxyfuel steam reformer unit in iii) comprises at least a portion of the offgas from the pressure swing adsorption unit; d) mixing the first and second hydrogen streams and the nitrogen stream to produce a make-up gas; and e) feeding said make-up gas to a reactor to form ammonia.
In an aspect, the electrolyser in a) is powered using renewable electricity.
In an aspect, the hydrocarbon feedstock in the reformer feed gas is natural gas.
In an aspect, the molar ratio of hydrogen to nitrogen in the make-up gas of d) is 2.7-3.3.
In an aspect, the reactor in e) is a Haber-Bosch reactor.
In an aspect, the flue gas generated in iii) is introduced to a flue gas waste heat recovery section after having exited the combustion chamber to remove heat from the flue gas. In an aspect, after heat is removed from the flue gas, the portion of the flue gas which is not recycled in ii) is further cooled to remove water and obtain a purified flue gas comprising carbon dioxide and minor impurities.
In an aspect, the water from the flue gas is used to generate the steam in the reformer feed gas in i).
In an aspect, the purified flue gas comprising carbon dioxide and minor impurities is introduced to a compressor train for storage, for example, for treatment and permanent storage of the CO2.
In an aspect, natural gas is added to the offgas to form the fuel gas in iii).
In an aspect, the molar ratio of steam to carbon of the hydrocarbon feedstock in the reformer feed gas in i) is from 1 to 5.
In a further aspect, the invention provides an apparatus arranged to perform the process as claimed in any of claims, said apparatus comprising an electrolyser (3) configured to receive water (2) via at least one inlet, wherein oxygen exits the electrolyser via a first gas phase conduit (5) and hydrogen exits via a second gas phase conduit (1); an oxyfuel steam reformer (6) comprising reformer tubes (8) and a combustion chamber (9), wherein the first gas phase conduit from the electrolyser is in fluid communication with the combustion chamber; an air separation unit (21), wherein oxygen exits the air separation unit via a third gas phase conduit (22) and nitrogen exits via a fourth gas phase conduit (26); an autothermal reformer (7), wherein the third gas phase conduit from the air separation unit is in fluid communication with the autothermal reformer; a water-gas shift reactor unit (24); a pressure swing adsorption unit (13), wherein hydrogen exits the pressure swing adsorption unit via a fifth gas phase conduit (27) and offgas exits via a sixth gas phase conduit (12) and further wherein said sixth gas phase conduit is in fluid communication with the combustion chamber of the oxyfuel steam reformer; and an ammonia synthesis reactor (29). Detailed Description of the Invention
The present invention describes a process for manufacturing ammonia. As shown in the equation above, the make-up gas used to make ammonia comprises approximately 3 parts hydrogen to 1 part nitrogen. In the process described herein, the hydrogen is supplied from two sources. As will be detailed below, the first hydrogen stream is generated from water via electrolysis. The second hydrogen stream is generated from a hydrocarbon feedstock via a two-stage reforming process.
The first hydrogen stream is generated by electrolysis of water using an electrolyser. Any electrolyser known in the art can be used in the process and apparatus of the present disclosure to convert water to hydrogen and oxygen, i.e. a first oxygen stream and a first hydrogen stream as defined herein. For example, the electrolyser may be a polymer electrolyte membrane electrolyser or an alkaline electrolyser. The hydrogen produced by the electrolyser may have a purity of greater than 99.999%.
The electrolyser is powered by electricity. The electricity can be produced using conventional methods known to the person skilled in the art. Preferably, the electricity is produced from renewable sources, i.e. the electricity is renewable electricity. Such renewable sources include wind energy, tidal energy, geothermal energy, solar energy, hydro energy and biomass energy. Hydro energy is particularly preferred. Hydrogen produced from an electolyser using renewable electricity may be termed “green hydrogen”.
The second hydrogen stream is generated by a two-stage reforming process involving a primary reformer and a secondary reformer.
The primary reformer is an oxyfuel steam methane reformer. The oxyfuel steam methane reformer may be top-fired, bottom-fired or side fired. In this context, “fired” means heated by means of combusting a fuel gas in a combustion chamber.
The primary reformer is fed with a reformer feed gas which comprises a hydrocarbon feedstock. The hydrocarbon feedstock may be natural gas, naphtha or a refinery offgas. The preferred hydrocarbon feedstock is natural gas, thus comprising methane (CH4). Before introduction to the primary reformer, the hydrocarbon feedstock can be treated to remove impurities. For example, the hydrocarbon feedstock can be desulphurised using methods and apparatus known to the person skilled in the art.
The reformer feed gas further comprises steam. Steam may be added to the reformer feed gas using methods known to the person skilled in the art. For example, by injecting steam into the hydrocarbon feedstock or by passing the hydrocarbon feedstock through a saturator.
The amount of steam in the reformer feed gas can be adjusted according to the amount of carbon in the hydrocarbon feedstock. The steam to carbon ratio, i.e. the molar ratio of steam to carbon in the hydrocarbon feedstock, may be from 1 to 5, or from 2 to 5, or from 2.5 to 4, or from 2.5 to 3.5, or from 2.5 to 3.
The reformer feed gas is fed to an oxyfuel steam methane reformer. This reformer contains reformer tubes in contact with a combustion chamber, i.e. the reformer tubes are externally heated by the burners in the combustion chamber. The reformer tubes contain a steam reforming catalyst, typically a nickel-based catalyst as is known in the art. For example, the catalyst may comprise nickel in an amount of 1-30 wt.% and be supported on shaped refractory oxides such as alpha alumina or magnesium or calcium aluminates. The catalyst may be in the form of a mixed bed or a mesh. By oxyfuel, we mean that the fuel gas in the combustion chamber is burned in the presence of oxygen (rather than air) to provide heat. This heat is absorbed by the reformer tubes by radiation and drives the chemical reaction which converts methane to product gas. This strongly endothermic chemical reaction occurs above 350°C and is represented by the below equation.
CH4 + H2O CO + 3H2
Other side reactions may occur in the reformer, such as the water-gas-shift reaction: CO + H2O CO2 + H2
Thus, in addition to hydrogen, both carbon monoxide and carbon dioxide may be produced as by-products of steam methane reforming. The “product gas” from the oxyfuel steam reformer thus typically comprises hydrogen, carbon dioxide and carbon monoxide.
The oxygen in the combustion chamber is the first oxygen stream described above which is produced by water electrolysis. Advantageously, this also provides a use for what would otherwise be a waste product. Furthermore, the oxygen produced from water electrolysis is advantageously at a pressure compatible with the oxyfuel steam reformer. Thus, no energy intensive compressors are usually required.
The fuel gas in the combustion chamber comprises at least partially recycled offgases from the upstream process, specifically the offgas from a pressure swing adsorption unit which will be described hereinbelow. If the offgas is not available in sufficient quantities to fuel the primary reformer, other fuel gas, such as natural gas, can be added to the offgas stream before introduction of the fuel gas to the combustion chamber. Typical flue gases from combustion processes comprise mainly nitrogen as the combustion occurs in air. However, because oxygen, rather than air, is introduced to the combustion chamber in the oxyfuel reformer in the present process, the flue gas does not contain nitrogen. Rather, the flue gas produced in the present process comprises primarily CO2 and H2O, in addition to a small amount of unburned oxygen. The flue gas typically leaves the combustion chamber at a temperature of approximately 1000°C via an outlet and can be channelled to a flue gas waste heat recovery section. Once waste heat has been recovered from the flue gas, at least some of the flue gas is recycled to the combustion chamber. Specifically, this recycled flue gas is mixed with the first oxygen stream to produce a combustion mixture.
If pure oxygen is used for combustion in the oxyfuel steam methane reformer, the combustion temperature may be too high and there is a risk that the reformer tubes may rupture due to exposure to such intense heat. By mixing the oxygen stream with a recycled flue gas stream as described above, the combustion temperature can advantageously be controlled to the desired level. The recycled flue gas stream can therefore advantageously be used for flame temperature control. The temperature in the reactor tubes of the oxyfuel steam methane reformer may be 700-850°C, for example 700-800°C. The remainder of the flue gas which is not recycled, can be cooled and condensed water separated therefrom, generating a purified flue gas comprising carbon dioxide. The condensed water can advantageously be used to produce the steam added to the reformer feed gas, reducing the overall water consumption of the process.
After this separation, the purified flue gas typically comprises carbon dioxide and minor impurities. The use of oxygen, rather than air, to provide the oxidant in the combustion chamber thus simplifies carbon dioxide recovery, avoiding the need for an amine plant for absorption, as the flue gas can be simply cooled to condense and remove water and obtain a gas comprising carbon dioxide and minor impurities. This carbon dioxide can then be channelled to a compressor train for treatment and storage, and is thereby captured, e.g. in injection wells. At an intermediate pressure in the compressor train, treatment of the carbon dioxide may be required to remove the remaining oxygen and dehydrate the carbon dioxide product.
Thus, in one aspect, the recovered carbon dioxide from the flue gas is introduced to a compressor train where it may be compressed and treated to meet the required specifications of the carbon dioxide product. Example CO2 specifications include: National Energy Technology Laboratory 2012 (a maximum of 730 ppmv H2O, 100 ppmv H2S, 35 ppmv CO, 40000 ppmv O2, 100 ppmv SOX and 100 ppmv NOX), National Energy Technology Laboratory 2013 (a maximum of 500 ppmv H2O, 100 ppmv H2S, 35 ppmv CO, 10 ppmv O2, 100 ppmv SOX and 100 ppmv NOX), and Northern Light 100 bar (a maximum of 122 ppmv H2O, 130 ppmv H2S, 0 ppmv CO, 275 ppmv O2, 96 ppmv SOX and 69 ppmv NOX).
In the reformer tubes, methane from the hydrocarbon feedstock and steam (water) are at least partially converted to a product gas, i.e. a gas comprising carbon dioxide and hydrogen. The output stream from the reformer tubes of the primary reformer is a gas mixture which typically comprises unreacted methane-rich gas, carbon dioxide, carbon monoxide and hydrogen. This gas mixture, i.e. the product gas, is channelled to a secondary reformer.
The secondary reformer is an autothermal reformer. Autothermal refomers are known to the person skilled in the art. In the autothermal reformer, at least a part of the residual hydrocarbon feedstock, typically natural gas, (e.g. unreacted CH4) is reacted with oxygen by means of an oxygen burner to form carbon monoxide, carbon dioxide and hydrogen. The heat generated by this partial combustion is utilised to steam reform the remaining part of the unconverted hydrocarbon feedstock in the presence of a nickel catalyst to form a synthesis gas.
In the present disclosure, an air separation unit is used to supply a second oxygen stream to the autothermal reformer to react with the gas mixture. Any air separation unit known in the art may be used, for example a cryogenic air separation unit. The majority of the remaining hydrocarbon feedstock is converted in the autothermal reformer to form a synthesis gas. The synthesis gas generally comprises hydrogen, carbon monoxide, carbon dioxide, steam, and can further comprise a small amount of unreacted methane. This synthesis gas, which may exit the autothermal reformer at a temperature of 1000-1050°C and a pressure of 30-45, for example 35-40, bar, is typically first cooled (usually to around 300 - 350 °C) by generation of high pressure steam, then channelled to a water-gas shift reactor unit.
In the water-gas shift reactor unit, steam and carbon monoxide are converted to hydrogen and carbon dioxide by passing the gas mixture over a water-gas shift catalyst at high temperature and pressure. The water-gas shift reaction proceeds according to the following equation:
H2O + CO H2 + CO2
The water-gas shift reactor unit may be a high temperature shift reactor or a low temperature shift reactor, or may include both, as known in the art. The use of a water-gas shift reactor unit including both a high temperature shift reactor and a low temperatures shift reactor may be advantageous as it results in a more energy efficient plant and ensures maximum conversion of carbon monoxide. The shifted synthesis gas may then be cooled by heat recovery and is then channelled to a pressure swing adsorption (PSA) unit. PSA’s are known to the person skilled in the art. In the PSA unit, impurities, principally carbon dioxide but also residual carbon monoxide, steam and hydrocarbon feedstock (e.g. CH4), are removed to produce a purified stream of hydrogen gas, i.e. a second stream of hydrogen gas, and an offgas comprising said impurities. When combined with carbon capture and storage technologies (for example the carbon dioxide compressor train described above), this second stream of hydrogen gas can be considered “blue hydrogen”.
As described above, at least a portion of the offgas is used as the fuel gas in the combustion chamber of the oxyfuel steam reformer. When the offgas is used as a fuel gas in this way, all of the carbon dioxide generated in the reformers and the shift reactors is directed to the combustion chamber of the oxyfuel steam reformer. This means that any carbon dioxide generated in the process can be recovered by cooling the flue gas from the oxyfuel steam reformer.
The first and second hydrogen streams are then mixed with a nitrogen stream from the air separation unit in the correct proportions to obtain a make-up gas for ammonia synthesis. The molar ratio of hydrogen to nitrogen in the make-up gas for the ammonia synthesis is ideally in the range of 2.7 to 3.3. The relative proportions of the first and second hydrogen streams in the make-up gas can be adjusted depending on, e.g. the intermittency of the supply of renewable electricity. This make-up gas can then be fed to an ammonia synthesis reactor, such as a Haber- Bosch reactor, to generate ammonia. Such reactors are known to the person skilled in the art.
The make-up gas may be converted to ammonia by catalytic conversion in a high-pressure (typically 80-300 bar) synthesis loop. In conventional high-pressure synthesis loops for ammonia production, it is necessary to have a purge stream to remove unwanted inert gases which would otherwise reduce the overall process efficiency. By inert gases we mean gases which do not take part in the catalytic conversion, such as argon, helium, excess nitrogen, or methane. However, as a result of the use of an electrolyser, an oxygen-fired autothermal reactor and a pressure swing adsorption unit, the make-up gas prepared by the process of the present disclosure contains almost no inert gas. This means that there is a high synthesis loop efficiency, and that the purge stream can be eliminated or reduced in frequency and/or volume, thereby simplifying the ammonia synthesis and eliminating the need for a purge gas hydrogen recovery unit. The process and apparatus disclosed herein may be suitable for generation of 500-1000 tonnes or even more of ammonia per day.
Also disclosed herein is an apparatus arranged to perform the process described herein. The apparatus comprises an electrolyser (3) configured to receive water (2) via at least one inlet, wherein oxygen exits the electrolyser via a first gas phase conduit (5) and hydrogen exits via a second gas phase conduit (1); an oxyfuel steam reformer (6) comprising reformer tubes (8) and a combustion chamber (9), wherein the first gas phase conduit from the electrolyser is in fluid communication with the combustion chamber; an air separation unit (21), wherein oxygen exits the air separation unit via a third gas phase conduit (22) and nitrogen exits via a fourth gas phase conduit (26); an autothermal reformer (7), wherein the third gas phase conduit from the air separation unit is in fluid communication with the autothermal reformer; a water-gas shift reactor unit (24); a pressure swing adsorption unit (13), wherein hydrogen exits the pressure swing adsorption unit via a fifth gas phase conduit (27) and offgas exits via a sixth gas phase conduit (12) and further wherein said sixth gas phase conduit is in fluid communication with the combustion chamber of the oxyfuel steam reformer; and an ammonia synthesis reactor (29).
Preferable aspects discussed in the context of the processes of the invention apply equally to the apparatus embodiments. For example, the apparatus may further comprise a flue gas waste heat recovery section and/or a carbon dioxide compressor train. The apparatus is arranged such that the oxygen stream (first oxygen stream) generated by the electrolyser is channelled to the combustion chamber of the oxyfuel steam reformer, while the oxygen stream (second oxygen stream) generated by the air separation unit is channelled to the autothermal reformer. The first and second oxygen streams are not typically mixed with one another.
Description of Figure
Figure 1 shows a schematic representation of an embodiment of the process and apparatus of the present disclosure.
The first hydrogen stream 1 is generated by electrolysis of water 2 using an electrolyser 3. The electrolyser 3 is powered using renewable electricity 4. The second hydrogen stream 27 is generated by a two-stage reforming process involving an oxyfuel steam methane reformer 6 and an autothermal reformer 7. The oxyfuel steam methane reformer 6 contains reformer tubes 8 assembled in a combustion chamber 9.
The reformer tubes 8 are fed with a reformer 10 feed gas which comprises natural gas and steam.
The combustion chamber 9 is fed with a fuel gas 11 which contains offgas 12 from the pressure swing adsorption unit 13. If the offgas 12 is not available in sufficient quantities to fuel the primary reformer, natural gas can be added to the offgas stream as a make-up fuel gas 14 before introduction of the fuel gas to the combustion chamber.
The combustion chamber 9 is also fed with a combustion mixture 15. The combustion mixture 15 comprises the first oxygen stream 5 and recycled flue gas 16 from the combustion chamber 9. The flue gas 16 leaves the combustion chamber via an outlet and is channelled to a flue gas waste heat recovery section 17. Once waste heat has been recovered from the flue gas 16, part of the flue gas 16 is recycled to the combustion chamber as part of the combustion mixture 15. The remainder of the flue gas 16 is cooled and condensed water 18 and carbon dioxide 19 separated therefrom. This carbon dioxide 19 is then channelled to a compressor train (not shown) for storage.
In the reformer tubes 8, methane and steam (water) are partially converted to a product gas, i.e. gas mixture 20. The output stream from the reformer tubes of the primary reformer is a gas mixture 20 which comprises unreacted natural gas, carbon dioxide, carbon monoxide and hydrogen. This gas mixture 20 is channelled to the autothermal reformer 7.
In the autothermal reformer 7, the unreacted natural gas is reacted with oxygen and steam to form carbon monoxide, carbon dioxide and hydrogen. An air separation unit 21 is used to supply a second oxygen stream 22 to the authothermal reformer to react with the gas mixture 20. The majority of the remaining natural gas is converted to hydrogen and carbon oxides to form a synthesis gas 23. The synthesis gas 23 comprises hydrogen, carbon monoxide, carbon dioxide, steam and residual methane. This synthesis gas 23 exits the autothermal reformer 7 and is then channelled to a water-gas shift reactor unit 24.
In the water-gas shift reactor unit 24, steam and carbon monoxide are converted to hydrogen and carbon dioxide. The shifted synthesis gas 25 is then channelled to the pressure swing adsorption (PSA) unit 13. In the PSA unit 13, carbon dioxide, residual carbon monoxide, steam and natural gas are removed to produce the second stream of hydrogen gas 27 and the offgas 12, which is recycled as described above.
The first hydrogen stream 1 and the second hydrogen stream 27 are then mixed with a nitrogen stream 26 from the air separation unit in the correct proportions to obtain a make-up gas 28. This make-up gas is then fed to an ammonia synthesis reactor 29, e.g. a Haber-Bosch reactor, to generate an ammonia stream 30.
References to “comprises” and/or “comprising,” should be understood to also encompass “consist(s) of”, “consisting of”, “consist(s) essentially of” and “consisting essentially of”.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, element components, and/or groups thereof.
It will be readily appreciated by the skilled person that the various optional and preferred features of the disclosure as described above may be applicable to all the various aspects of the disclosure discussed.
While the present disclosure has been described with reference to an exemplary embodiment or embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the present disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the present disclosure without departing from the essential scope thereof. Therefore, it is intended that the present disclosure not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this present disclosure, but that the present disclosure will include all embodiments falling within the scope of the claims.

Claims

CLAIMS:
1. A process for manufacturing ammonia, comprising: a) electrolysing water in an electrolyser to form a first oxygen stream and a first hydrogen stream; b) separating air in an air separation unit to form a second oxygen stream and a nitrogen stream; c) generating a second hydrogen stream by a two-stage reforming process comprising: i) feeding a reformer feed gas to reformer tubes of an oxyfuel steam methane reformer, wherein the reformer feed gas comprises a hydrocarbon feedstock and steam; ii) mixing the first oxygen stream with an at least partially recycled flue gas stream from said reformer, to form a combustion mixture; iii) introducing the combustion mixture to a combustion chamber of the oxyfuel steam methane reformer to burn a fuel gas so as to provide heat for steam reforming of the feed gas to a product gas in the reformer tubes and a flue gas in the combustion chamber; iv) feeding the product gas from the oxyfuel steam reformer to an autothermal reformer and reacting said product gas with the second oxygen stream in the autothermal reformer to form a synthesis gas; v) passing the synthesis gas from the autothermal reactor through a water-gas shift reactor unit to form a shifted synthesis gas; vi) introducing the shifted synthesis gas to a pressure swing adsorption unit to form a second hydrogen stream and a separate offgas, wherein the fuel gas in the oxyfuel steam reformer unit in iii) comprises at least a portion of the offgas from the pressure swing adsorption unit; d) mixing the first and second hydrogen streams and the nitrogen stream to produce a make-up gas; and e) feeding said make-up gas to a reactor to form ammonia.
2. The process of claim 1 , wherein the electrolyser in a) is powered using renewable electricity.
3. The process of claim 1 or claim 2, wherein the hydrocarbon feedstock in the reformer feed gas is natural gas.
4. The process of any one of claims 1-3, wherein the molar ratio of hydrogen to nitrogen in the make-up gas of d) is 2.7-3.3.
5. The process of any one of claims 1-4, wherein the reactor in e) is a Haber- Bosch reactor.
6. The process of any one of claims 1-5, wherein the flue gas generated in iii) is introduced to a flue gas waste heat recovery section after having exited the combustion chamber to remove heat from the flue gas.
7. The process of claim 6, wherein, after heat is removed from the flue gas, the portion of the flue gas which is not recycled in ii) is further cooled to remove water and obtain a purified flue gas comprising carbon dioxide and minor impurities.
8. The process of claim 7, wherein the water from the flue gas is used to generate the steam in the reformer feed gas in i).
9. The process of claim 7 or claim 8, wherein the purified flue gas comprising carbon dioxide and minor impurities is introduced to a compressor train for storage.
10. The process of any one of claims 1-9, wherein natural gas is added to the offgas to form the fuel gas in iii).
11. The process of any one of claims 1-10, wherein the molar ratio of steam to carbon of the hydrocarbon feedstock in the reformer feed gas in i) is from 1 to 5.
12. An apparatus arranged to perform the process as claimed in any of one of the preceding claims, said apparatus comprising an electrolyser (3) configured to receive water (2) via at least one inlet, wherein oxygen exits the electrolyser via a first gas phase conduit (5) and hydrogen exits via a second gas phase conduit (1); an oxyfuel steam reformer (6) comprising reformer tubes (8) and a combustion chamber (9), wherein the first gas phase conduit from the electrolyser is in fluid communication with the combustion chamber; an air separation unit (21), wherein oxygen exits the air separation unit via a third gas phase conduit (22) and nitrogen exits via a fourth gas phase conduit (26); an autothermal reformer (7), wherein the third gas phase conduit from the air separation unit is in fluid communication with the autothermal reformer; a water-gas shift reactor unit (24); a pressure swing adsorption unit (13), wherein hydrogen exits the pressure swing adsorption unit via a fifth gas phase conduit (27) and offgas exits via a sixth gas phase conduit (12) and further wherein said sixth gas phase conduit is in fluid communication with the combustion chamber of the oxyfuel steam reformer; and an ammonia synthesis reactor (29).
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Citations (3)

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EP2589574A1 (en) * 2011-11-02 2013-05-08 Ammonia Casale S.A. Method for load regulation of an ammonia plant
WO2019020378A1 (en) * 2017-07-25 2019-01-31 Haldor Topsøe A/S Method for the preparation of ammonia synthesis gas
WO2019020376A1 (en) * 2017-07-25 2019-01-31 Haldor Topsøe A/S Method for the preparation of ammonia synthesis gas

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2589574A1 (en) * 2011-11-02 2013-05-08 Ammonia Casale S.A. Method for load regulation of an ammonia plant
WO2019020378A1 (en) * 2017-07-25 2019-01-31 Haldor Topsøe A/S Method for the preparation of ammonia synthesis gas
WO2019020376A1 (en) * 2017-07-25 2019-01-31 Haldor Topsøe A/S Method for the preparation of ammonia synthesis gas

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