Adjustment of purge gas in NH3 plant

Abstract

Embodiments of the present disclosure relate to the regulation of a purge gas flow in an NH3 synthesis plant comprising a water electrolyzer for generating an H2 flow, an ammonia synthesis loop, and a processing section for treating the purge gas at 10–70 bar(a) using absorption washing and membrane separation.

Description

Technical Field

[0001] The present disclosure generally relates to the production of NH3. Embodiments of the present disclosure relate to the regulation of purge gas flow in an ammonia synthesis plant. In particular, the NH3 plant comprises a water electrolysis device for generating a H2 stream and an ammonia synthesis loop for reacting the H2 stream with a N2 source.

Background Art

[0002] Introduction Ammonia is a raw material for the production of major synthetic chemicals and fertilizers. Generally, a H2-N2 mixture reacts on a catalyst at a high temperature (e.g., above 300 °C) and a high pressure, e.g., above 100 bar(a), the unreacted portion of the synthesis gas is recycled, and the ammonia product is separated under high pressure. In addition to nitrogen and hydrogen, the fresh makeup gas fed to the synthesis loop usually contains a small amount of inert gas. Usually, these inert gases include methane (from hydrocarbon-derived gas production), argon (from process air), and helium (from natural gas, which has been conventionally used for H2 production in many prior art plants). Due to their inert nature under the reaction conditions, these components tend to accumulate in the synthesis loop and must be removed to maintain the loop's mass balance. A small portion of the inert gas dissolves in the liquid produced in the ammonia separator. In addition, the inert gas must also be removed from the gas phase by withdrawing a small purge gas stream from the loop. For this point, see Ullmann’s Encyclopedia of Industrial Chemistry, 2012, vol. 3, Chapter Ammonia 2.

[0003] Several methods are known to reduce losses associated with purge gas, including hydrogen recovery at cryogenic temperatures, hydrogen recovery by pressure swing adsorption (PSA), and hydrogen recovery by membrane separation. Ullmann's Encyclopedia of Industrial Chemistry, 2012, vol.3, Chapter Ammonia 2, pp.208-209 discusses membrane separation for hydrogen removal. The purge gas is depressurized, absorbed and washed with water at 135-145 bar, and sent to a membrane separator. Hydrogen from the permeate side is sent to a synthesis gas compressor and recycled into the ammonia synthesis loop. The same document states that the remaining non-permeate gas flow "usually flows into the primary reformer fuel."

[0004] However, so-called "green ammonia plants," that is, plants where hydrogen raw materials are prepared by water electrolysis, typically do not have primary reformers. Therefore, there is a need for processes and systems for disposing of the purge from green ammonia plants.

[0005] In green ammonia plants, the amount of inert gas is typically less than in "gray" ammonia plants, i.e., plants that produce hydrogen from conventional hydrocarbons, usually by steam reforming. At least in green ammonia plants where the N2 supply source is not purified upstream of ammonia synthesis, the amount is never zero, and the purge flow must be discarded. N2 is usually obtained from air, and it is possible to purify the N2 supply flow upstream of synthesis by argon removal (by cryogenics), but such purification is not always desirable, for example, from the standpoint of cost (capital investment and / or operating costs).

[0006] US20190092645A1 describes a method for producing ammonia, comprising: using water and nitrogen as raw materials, synthesizing ammonia by electrolysis; processing the resulting gas using an ammonia separation membrane or ammonia PSA to separate the gas into high-concentration ammonia and residual gas; recirculating the residual gas as nitrogen gas raw material for an ammonia synthesis reactor; and liquefying the high-concentration ammonia recovered through the ammonia separation membrane or ammonia PSA. [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] Improved purging systems and methods for ammonia plants, including water electrolysis, are desired for generating H2 sources. [Means for solving the problem]

[0008] Summary of the Invention In a first embodiment, the present invention relates to a process for regulating a purge gas flow in an ammonia synthesis plant, the plant comprising a water electrolyzer for generating an H2 flow and an ammonia synthesis loop for reacting the H2 with an N2 source, the process comprising obtaining, preferably separating, a purge flow from the ammonia synthesis loop, wherein the purge flow is a gas and contains N2, H2, NH3, and Ar; subjecting the purge gas flow to treatment, preferably at a pressure of 10 to 70 bar(a), including absorption washing in an absorption washing device and membrane separation in a membrane separation device, in order to remove at least a portion of NH3 and at least a portion of H2 from the purge gas flow and provide a treated purge flow, a gaseous flow containing H2, and a liquid flow, wherein the membrane separation includes using a hydrogen-selective membrane having a permeate side and a residual side, and supplying a sweep gas containing N2 on the permeate side of the membrane; and recirculating a portion or all of the gaseous flow to the ammonia synthesis loop.

[0009] The present invention also provides an ammonia synthesis plant comprising: a water electrolyzer for generating an H2 flow; an ammonia synthesis loop having an outlet for a gaseous purge flow for reacting H2 with an N2 supply source; a section (processing section) comprising an absorption scrubbing device and a membrane separator, wherein the section subjects the purge flow to processing, preferably at a pressure of 10 to 70 bar(a), including absorption scrubbing in an absorption scrubbing device and membrane separation in a membrane separator, in order to remove at least a portion of NH3 and at least a portion of H2 from the purge gas flow and to supply a treated purge flow, a gaseous flow containing H2, and a liquid flow, the membrane separator comprising a hydrogen-selective membrane, a permeate side compartment and a residual side compartment, and a sweep gas supply unit to the permeate side compartment; and a flow path for recirculating a portion or all of the gaseous flow to the ammonia synthesis loop.

[0010] We also provide methods for modifying existing ammonia synthesis plants.

[0011] Embodiments of the present disclosure relate to the regulation of a purge gas flow in an NH3 synthesis plant, comprising a water electrolyzer for generating an H2 flow, an ammonia synthesis loop, and a processing section for treating the purge gas using absorption washing and membrane separation, preferably at 10 to 70 bar(a). [Brief explanation of the drawing]

[0012] [Figure 1] An example of a process and plant according to the present invention is schematically illustrated. [Figure 2] An example of an ejector configuration used in a preferred embodiment is schematically illustrated. [Figure 3] A schematic example of an ammonia synthesis loop configuration used in a preferred embodiment is shown.

[0013] Any embodiments illustrated in the figures are merely examples and do not limit the present invention. [Modes for carrying out the invention]

[0014] In one embodiment, the present invention relates to a process for regulating a purge gas flow in an ammonia synthesis plant. The present invention also provides an ammonia production process that includes a regulation process. The process for regulating a purge gas flow may also be called a process for recovering NH3 and H2 from the purge gas flow, where NH3 is optionally recovered as an ammonium salt. Optionally, argon (Ar) is also recovered from the purge gas flow. In this specification, component recovery broadly includes reducing the content of a component in the gas flow and obtaining the removed component for, for example, further disposal, recycling, or as a product.

[0015] This process is carried out in an ammonia synthesis plant. The plant comprises a water electrolytic apparatus for producing H2 and an ammonia synthesis loop for reacting the H2 with an N2 supply source. As used herein, the term water electrolytic apparatus includes apparatus for electrolyzing H2O, which may be supplied as liquid water or as vapor. A water electrolytic apparatus is, for example, a solid oxide electrolytic cell.

[0016] In embodiments of the present invention relating to an ammonia production process including a conditioning process, the process also includes electrolyzing water in the water electrolyzer to produce H2 (and O2), and in the ammonia synthesis loop, reacting the H2 from the water electrolyzer with an N2 source to produce NH3. All preference trends and details for the conditioning process also apply to an ammonia production process including a conditioning process.

[0017] Optionally, this process includes a step of producing N2 raw materials for ammonia synthesis. Preferably, this step is carried out in a nitrogen generator (NGU), more preferably by air separation.

[0018] The H2 raw material for NH3 synthesis is preferably 90 mol% or more obtained from water electrolysis. This ensures that the purge gas flow is preferably less than, for example, 10 ppmv and essentially free of hydrocarbons. Water electrolysis, air separation, other nitrogen generation devices, and NH3 synthesis are all well known in the art.

[0019] NH3 synthesis is generally carried out in a synthesis loop equipped with a converter operated at pressures above 70 bar(a), e.g., above 100 bar(a), e.g., 150–400 bar(a), e.g., 150–300 bar(a) or 150–250 bar(a). The waste liquid from the converter is condensed to obtain a high-pressure liquid stream containing NH3 (or essentially consisting of NH3), as well as a high-pressure gas stream above 70 bar(a), e.g., above 100 bar(a), or above 150 bar(a), and up to e.g., 400 bar(a). Part of the high-pressure gas stream is purged as a purge stream, and part is recirculated within the synthesis loop. Optionally, the waste liquid from the converter is compressed before condensation. The raw materials are supplied to the synthesis loop as makeup gas and are typically compressed to the synthesis pressure by a compressor, which may be, for example, a dedicated compressor, the same compressor used for waste liquid or recirculated gas flow (optional), or a combination thereof.

[0020] Therefore, this process involves separating or obtaining a purge gas stream from the ammonia synthesis loop. The purge gas stream contains N2, H2, NH3, and Ar, and may optionally contain additional components. If additional components are present, they are typically present in amounts less than 5 volume percent of the total volume of the purge gas stream. The purge gas stream is obtained at a pressure, for example, above 100 bar(a) or above 150 bar(a), and preferably up to 350 bar(a) or 300 bar(a), and then the pressure is reduced to a pressure preferably in the range of 10 to 70 bar(a). This separation step may involve separating the gas stream in the purge gas stream from the gas stream that is recirculated in the synthesis loop.

[0021] This process includes subjecting the purge stream to a purification treatment, preferably at a pressure of 10 to 70 bar(a), which treatment includes absorption cleaning of the purge stream in an absorption cleaning device and membrane separation of the purge stream in a membrane separation device, in either order. This treatment is used to remove at least a part of NH3 and at least a part of H2 from the purge gas stream. By this treatment, a treated purge stream, a gas stream containing H2, and a liquid stream are obtained. The membrane separation uses a hydrogen-selective membrane having a permeate side and a residue side, and a sweep gas containing N2 is supplied to the permeate side of the membrane. This process preferably includes performing absorption cleaning upstream of the membrane separation for the stability of the membrane. Details of this embodiment will be described later. However, in principle, it is also possible to perform absorption cleaning downstream of the membrane separation. The described preference trends and details also apply to this embodiment.

[0022] This process preferably includes subjecting the purge stream to a treatment for removing NH3 from the purge stream (reducing the NH3 content of the purge stream), preferably absorption cleaning for removing NH3 from the purge gas stream, for example, aqueous absorption cleaning or absorption cleaning with an acid, thereby providing a purge stream that has been absorption cleaned. The absorption cleaning is preferably carried out at a pressure of at least 10 bar(a) and / or a maximum of 70 bar(a), particularly within the range of 10 to 70 bar(a), more preferably within the range of 10 to 50 bar(a), or even within the range of 10 to 40 bar(a), or 20 to 50 bar(a), or 20 to 40 bar(a).

[0023] This process usually includes reducing the pressure of the purge gas stream by at least 10 bar(a), or at least 50 bar(a), or at least 100 bar(a), for example, between a synthesis loop and an absorption cleaning device, that is, from the synthesis loop pressure to the absorption cleaning device pressure. Therefore, the plant includes a pressure reduction element, such as an ejector, a control valve, or a turboexpander, in the purge gas stream path from the synthesis loop to the absorption cleaning device.

[0024] This pressure reduction element preferably also receives the gas stream obtained from the step of flash treating the high-pressure NH3 liquid stream, i.e., the flash gas obtained from the flash treatment of the NH3 liquid stream formed (and withdrawn) within the ammonia synthesis loop. For example, it includes (or is) an ejector. In particular, ammonia synthesis is generally carried out within an ammonia synthesis loop including a converter operated within a range of above 70 bar(a), for example above 100 bar(a), for example 150 - 300 bar(a) or 150 - 250 bar(a). The waste liquid from the converter is used for the condensation of NH3, and a high-pressure liquid stream containing (or consisting essentially of) NH3 and a separate high-pressure gas stream within a range of above 70 bar(a), for example above 100 bar(a), or above 150 bar(a), and for example up to 400 bar(a), preferably 150 bar(a) - 300 bar(a) or 150 bar(a) - 250 bar(a) are obtained. The high-pressure gas stream is usually partly purged as a purge stream and partly recycled within the synthesis loop. The liquid stream is preferably flash treated to obtain a gas stream and a flash-treated liquid stream. The relatively low pressure of the purge gas after passing through the ejector is advantageous for transporting the flash gas to the treatment section.

[0025] For example, in the NH3 plant and process of the present invention, the liquid ammonia in the HP (high-pressure) gas-liquid separator (where HP indicates above 70 bar(a), for example above 100 bar(a)) is flash treated (in one or more steps) down to about 20 bar(a) and further down to atmospheric pressure, whereby most of the dissolved gas is released within the let-down vessel (i.e., flash vessel). The gas from the pressure reduction vessel is also optionally subjected to a treatment including absorption washing and membrane separation, for example, it is supplied to an absorption washing device using the ejector. The gas-liquid separator is provided, for example, by a condenser.

[0026] Absorption cleaning involves bringing a gaseous purge stream into contact with an absorption cleaning solution, preferably a liquid film, for example, in countercurrent contact. The absorption cleaning solution contains water and may optionally contain other components, such as acids, preferably inorganic acids, preferably nitric acid, phosphoric acid, or sulfuric acid. The use of acids for the removal of NH3, accompanied by the formation of ammonium salts, may be advantageous when the operating pressure of the absorption cleaning apparatus is relatively low. Most or essentially all of the NH3 in the gas phase, for example, at least 90 mol%, or at least 99 mol%, or at least 99.9 mol%, of the NH3 is absorbed into the liquid (migrates to the liquid phase) and removed from the gas stream. Suitable absorption cleaning systems, with or without the use of acids, are known in the art.

[0027] By operating the absorption and scrubbing system at this pressure range, i.e., at pressures lower than the combined pressure, particularly below 70 bar(a), or below 50 bar(a), or below 30 bar(a), high-pressure equipment (especially the construction of pressure walls) becomes unnecessary, thus allowing for a relatively simpler structure for the absorption and scrubbing system.

[0028] Furthermore, considering the Henry coefficients and physical absorption mechanisms of H2 and N2 in water, the amount of N2, H2, and Ar dissolved in the liquid phase is reduced, and the recirculation of supplied H2 into synthesis is advantageously improved. Operating the absorption and washing apparatus at pressures exceeding 10 bar(a) is advantageous for downstream membrane separation.

[0029] It was also found that the relatively low pressure in the absorption scrubbing step is advantageous in obtaining a suitable volumetric flow rate of purge gas by absorption scrubbing, even at a predetermined mass flow rate, in the specific situation where the H2 supply source is obtained from water electrolysis.

[0030] The absorption and cleaning apparatus is, for example, a columnar structure comprising an internal device (e.g., a ball ring) or a packed bed, and typically has a gas outlet for the absorbed and cleaned gas flow and a separate liquid outlet, usually with the gas outlet at the top and the liquid outlet at the bottom. The absorption and cleaning apparatus has, for example, an inlet for the absorption and cleaning liquid at the top and a gas inlet at the bottom. The absorption and cleaning liquid is, for example, repeatedly circulated and partially purged while being cooled. The NH3 content is, for example, not limited to, at least 10 and / or up to 40% by weight of NH3, for example, kept within the range of 20-30% by weight of NH3 as an aqueous solution, although lower and higher concentrations of NH3 are also possible. The liquid from the absorption and cleaning apparatus is regenerated, for example, in a desorption unit with heating to boil NH3 from water, or supplied to a device that uses the liquid, or, for example, NO from the exhaust gas of a combustion engine. x It is sold as a standalone product useful for the selective reduction of catalysts.

[0031] Optionally, the purge gas flow is passed through the catalytic reactor entirely or partially before the reduction in pressure (upstream), where unreacted H2 and N2 can react with NH3. Therefore, the catalytic reactor is operated at pressures exceeding 100 bar(a). Plants with such reactors typically also include a bypass channel for the purge gas flow to bypass the reactor.

[0032] In some embodiments, the absorption wash upstream of the membrane separation includes, as described above, absorption wash with acid, where the purge gas stream is contacted with an acid solution, particularly an aqueous acid solution, at the pressure (preferably 10-70 bar(a)) such that NH3 from the gas stream is converted into an ammonium salt solution. Inorganic acids are typically used. In this case, the membrane and membrane separation apparatus of the membrane separation step are acid-resistant. The membrane is, for example, a hollow fiber membrane, or a polymer membrane, for example, based on polyimide. Other types of membranes are known in the art and include, for example, poly(dimethylsiloxane), polysulfone, poly(phenylene oxide), cellulose acetate, polyimide, and polynorvonene / 6FDA-Duren blend.

[0033] In embodiments using a hollow fiber membrane, for example, the residual side compartment may be provided by the internal volume of the fiber and the permeable side compartment by the shell, or vice versa.

[0034] Other film options include, for example, Pd films and carbon-based films.

[0035] This process more preferably involves bringing the absorbed and washed purge stream into contact with a hydrogen-selective membrane having a permeate side and a residual side, thereby obtaining a gaseous permeate stream and a gaseous residue.

[0036] This step is carried out, for example, in a membrane separation apparatus, which is a separate, dedicated apparatus from the absorption and washing apparatus. The membrane can divide the apparatus into a permeate side compartment and a residual side compartment. The residual side compartment preferably has a gas inlet for the absorbed and washed purge gas flow and a gas outlet for gaseous residue, and optionally an inlet for flush washing with H2 feedstock. When used optionally, flush washing typically involves supplying N2 to the residual compartment to remove absorbed NH3.

[0037] The permeate side compartment has an inlet for the sweep gas flow and an outlet for the permeate flow.

[0038] This process involves sweeping the membrane on the permeate side with a sweeping gas flow containing N2. Therefore, a sweeping gas flow containing N2 is supplied to the permeate side of the membrane. The sweeping gas preferably has a pressure of 5 to 20 bar(a), more preferably 5 to 15 bar(a), and contains, for example, at least 98 volume% N2.

[0039] This process involves selectively moving hydrogen from the residue side to the permeate side through the membrane. The partial pressure of H2 in the residue is lower than the partial pressure of H2 in the permeate gas, preferably the absorbed and washed purge gas. The sweep gas contains, for example, a partial pressure of H2 of less than 0.01 bar at the inlet of the permeate compartment. The sweep gas provides a low partial pressure of H2 on the permeate side and contributes to the driving force for transporting H2 through the membrane, even when the total pressure is balanced on both sides of the membrane. This is advantageous as it allows for a large driving force without sacrificing (total) pressure.

[0040] The sweeping gas is preferably supplied in a countercurrent direction relative to the gas flow in the residual side compartment within the permeate side compartment, in an embodiment where the membrane module comprises a hollow fiber membrane, and most preferably, when the permeate side is the shell side.

[0041] In an interesting embodiment, the sweep gas stream is generated from the outlet of the N2 gas stream of a nitrogen generator (NGU), which also supplies the N2. The NGU is a device that generates nitrogen from air, which optionally also generates a high-purity O2 stream.

[0042] An NGU is, for example, an air separator (ASU). Therefore, the nitrogen-enriched gas flow from the ASU is divided into a first portion supplied to the NH3 synthesis loop and a second portion supplied to the permeate section of the membrane separator, with an optional third portion used elsewhere. Preferably, the NGU or ASU makes available an N2-enriched gas flow at a pressure of 10–30 bar(a), which is favorable for membrane separation, and typically containing at least 98 volume% N2, or at least 99.5 mol% N2.

[0043] Other suitable types of NGU that can be used in embodiments of the present invention include cryogenic distillation, pressure swing adsorption (PSA), and membrane purification.

[0044] In embodiments of membrane separation downstream of an absorption and washing apparatus, this process involves recirculating part or all of the permeate to the ammonia synthesis loop. The permeate typically contains at least 90% or at least 95% by volume of N2 and H2 in total at the outlet of the permeate compartment. The permeate typically contains, for example, 70–95% by volume of N2 and 5–30% by volume of H2. The permeate is usually of sufficient purity to be supplied to the ammonia synthesis loop. The permeate is usually supplied to the ammonia synthesis loop or to a compressor within the ammonia synthesis loop after a suitable treatment to remove water, which is optional. It should be noted that compressing the N2 / H2 mixture to the synthesis pressure is relatively advantageous from an energy standpoint.

[0045] The permeate flow has a pressure in the range of 10 to 70 bar(a), for example, 10 to 30 bar(a), at the outlet of the permeate section of the membrane separator, and is typically the same pressure as N2 from the nitrogen generator. A pressure of 20 to 30 bar(a) at the outlet of the permeate section of the membrane separator is also advantageous when the water electrolyzer produces H2 at a pressure greater than 10 bar(a) or within the range of 20 to 30 bar(a).

[0046] The combination of recirculating permeates into synthesis and using sweep gas and membrane separation provides a configuration that is very suitable for relatively small-scale plants, and this is particularly advantageous for ammonia plants using H2 as a raw material from water electrolysis.

[0047] In an exemplary embodiment, the treated purge flow, preferably the residue, is recycled in part or in whole, for example, 10 to 90% by weight, preferably the residue, into the ammonia synthesis loop. In this way, at least a portion of the N2 and H2 contained in the treated purge flow, preferably the residue, can be recovered. The treated purge flow, preferably the residue, contains, for example, at least 95% by volume of N2 and less than 1.0% by volume of H2.

[0048] Preferably, the treated purge flow, preferably the residue, is vented in part or in whole, or supplied to Ar recovery, i.e., an argon recovery unit or argon recovery step. For example, the remainder of the treated purge flow, preferably the residue, is vented or supplied to Ar recovery. Venting optionally means releasing into the environment (atmosphere) after further treatment such as absorption washing. For example, the treated purge flow, preferably the residue, is subjected to acid absorption washing with a mineral acid, such as phosphoric acid, nitric acid, or sulfuric acid, partially or whole, upstream of venting or Ar recovery, to remove (or remove more of) NH3 from the gas flow. The acid absorption washing unit is optionally a unit shared within the vent line of a fertilizer plant. For example, at least a portion of the treated purge flow, preferably the residue, is supplied to an acid washing unit in a urea plant, or to a finishing section of a urea plant (e.g., a granulation tower or sizing machine), or to a nitrate plant or ammonium nitrate plant, or generally to a fertilizer plant or fertilizer finishing section.

[0049] Another possibility is to supply the treated purge stream, preferably the residue, to a device for recovering Ar, at least in part, for example, by cooling. In this way, an advantageous Ar product can be obtained. The treated purge gas, preferably the residual gas stream supplied to Ar recovery, can also be subjected to upstream processing of Ar recovery, such as absorption washing with the acid.

[0050] The plant may be configured to operate in a mode in which the entire treated purge gas, preferably residue, is recirculated, in a mode in which the treated purge gas, preferably residue, is not recirculated into NH3 synthesis, and in further modes with optional partial recirculation, preferably these modes can be switched between. The proportion of treated purge gas, preferably residue, that is recirculated into the NH3 synthesis loop can vary, in principle, from 0 to 100 volume%, for example, from 10 to 90 volume%. The adjustment process of the present invention may also be carried out in such a plant and / or in modes in which the recirculation of treated purge gas, preferably residue, into NH3 synthesis is performed completely, partially, or not at all. Those skilled in the art will know that the proportion of treated purge flow, preferably residue, that is vented can be adjusted as needed to keep the concentration of inert gas species in the ammonia synthesis loop sufficiently low.

[0051] Typically, in embodiments where the treated purge gas, preferably a portion or all of the residue, is optionally vented to the environment after further treatment, incineration is not used. Preferably, the treated purge gas, preferably the residue, is not subjected to combustion. This favorably reduces CO2 emissions compared to prior art processes that incinerate the hydrocarbon-containing purge gas stream from NH3 synthesis. Further advantages include a simpler design, as well as the elimination of noise, light, and heat pollution from incineration, and a further reduction in the installation area.

[0052] The process and plant configuration of the present invention are particularly advantageous for relatively small-scale modular plants, for example, that can be operated independently without being connected to a larger chemical plant.

[0053] The present invention also provides an ammonia synthesis plant comprising a water electrolyzer that generates an H2 stream and an ammonia synthesis section (loop) for reacting the H2 with an N2 supply source. The plant typically also includes an NGU, such as an ASU, for providing an N2 supply source. The process preference trends apply to this plant as well, and vice versa.

[0054] The ammonia synthesis section is provided with an outlet for a gaseous purge flow. The plant includes a section (processing section) comprising an absorption scrubbing unit and a membrane separator. This processing section is configured to subject the purge flow to a purification treatment at a pressure of 10 to 70 bar(a), which includes absorption scrubbing of the purge gas flow in the absorption scrubbing unit and membrane separation in the membrane separator to remove at least a portion of NH3 and at least a portion of H2 from the purge gas flow. This treatment yields a treated purge flow, a gaseous flow containing H2, and a liquid flow. The absorption scrubbing unit is preferably located upstream of the membrane separator (for the gaseous flow) or downstream of the membrane separator. The membrane separator comprises a hydrogen-selective membrane, a permeate side compartment, and a residual side compartment, as well as a supply unit for sweep gas to the permeate side compartment. The plant includes a flow path for recirculating part or all of the gaseous flow to the ammonia synthesis loop. The plant preferably includes a flow path from the NGU to the permeate side compartment to provide N2 from the NGU as the sweep gas.

[0055] In a preferred embodiment where the absorption and washing device is located upstream of the membrane separator, the absorption and washing device has an outlet for a liquid stream containing a solution of ammonia or an ammonium salt, and an outlet for the absorbed and washed purge stream. In this embodiment, the membrane separator has an inlet for the absorbed and washed purge stream within the residual side compartment, an outlet for a gaseous stream from the permeate side compartment (connected to a recirculation channel to the ammonia synthesis section), and an outlet for the treated purge stream from the residual side compartment.

[0056] The plant configuration of the present invention is advantageous for grassroots plants and for modifying existing plants.

[0057] A method is provided for modifying an existing ammonia synthesis plant, the existing plant comprising an ammonia synthesis loop having a water electrolyzer for generating an H2 flow and an outlet for a gaseous purge flow for reacting the H2 with an N2 supply source, the method comprising providing the plant with a section comprising an absorption scrubbing device and a membrane separator, and a flow path for recirculating part or all of the gaseous flow into the ammonia synthesis loop, the section providing the purge flow to a process including absorption scrubbing in the absorption scrubbing device and membrane separation in the membrane separator, at a pressure of 10 to 70 bar(a) to remove at least part of NH3 and at least part of H2 from the purge gas flow and to supply a treated purge flow, a gaseous flow containing H2 and a liquid flow, the membrane separator comprising a hydrogen-selective membrane, a permeate side compartment and a residual side compartment, and a sweep gas supply unit to the permeate side compartment. The priority trends and details relating to the plant of the present invention also apply to the modified plant. In this method, existing sections for processing the purge gas flow can be replaced or adapted to have the cited features.

[0058] Figure 1 schematically illustrates an example of a process and plant according to the present invention. The ammonia synthesis plant (100) comprises a water electrolyzer (1) having an outlet for an H2 stream (5) supplied to an ammonia synthesis loop (2). The plant also comprises an N2 generator (14) that produces an N2 stream (15) used partially or entirely as an N2 source for the ammonia synthesis loop (2), and preferably partially as a sweep gas (10). As illustrated, a first portion (15a) of the N2 stream (15) is used as an N2 source for the ammonia synthesis loop (2), and a second portion (15b) of the N2 stream (15) is used as a sweep gas (10) within a membrane separator (4). The ammonia synthesis loop (2) has an outlet (16) for NH3 products and an outlet for a purge stream (6). The purge flow (6) is reduced to 10-70 bar(a) in a pressure-reducing element (13), for example, in a control valve or ejector, or a combination thereof. The plant (100) comprises a processing section (101) into which the purge flow (6) is processed, the processing section comprising an absorption washing unit (3) and a membrane separator (4). The processing section (101) has separate outlets for the processed purge flow (12), a gas flow (11) containing H2, and a liquid flow (8). In the illustrated example, the purge flow (6) is first absorbed and washed in the absorption washing unit (3) at 10-70 bar(a) using an absorption washing liquid (17), which is preferably an acidic absorption washing liquid. A used absorption washing liquid flow (8) is obtained. The absorbed and washed purge stream (7) is supplied to a membrane separator (4) which comprises a hydrogen-selective membrane (9), a permeate side compartment (19), a residual side compartment (18), and has an outlet for the treated purge stream (12) in the residual side compartment (18). On the permeate side, a sweep gas (10) containing N2 is supplied, usually from an N2 generator (14), and the resulting gas stream (11) containing H2 is supplied from the permeate side compartment (19) to the NH3 synthesis loop (2), for example, in combination with an H2 stream (5). The pressure in the residual side compartment (18) is, for example, up to 5 bar lower than in the absorbed and washed apparatus (3). The pressure in the permeate side compartment (19) is, for example, at least 10 bar lower than in the residual side compartment (18).

[0059] Figure 2 schematically illustrates an example of the configuration of the pressure reduction element (13), namely, an ejector configuration that receives a purge gas flow (6) at a combined pressure (e.g., above 70 bar(a), e.g., 150-400 bar(a)) as the driving fluid, and also separately receives a flash gas flow (20) at a lower pressure than the purge flow (6). The flash gas flow (20) is generated from a flash vessel (21) in the ammonia synthesis plant. In this flash vessel, a high-pressure liquid ammonia flow (16) is depressurized using flash treatment, i.e., gas-liquid separation, to obtain a flash-treated liquid flow and gas flow (20) that supply NH3 products (22). The high-pressure liquid ammonia flow (16) is generated from a gas-liquid separator (23), which is part of the synthesis loop, particularly downstream of the converter. The gas-liquid separator is in particular a condenser (23), and the waste liquid (24) from the converter is separated into a high-pressure ammonia liquid stream (16) and a gas stream (25) by condensation at a high pressure, for example, greater than 70 bar(a) or greater than 100 bar(a). For example, a portion (26) of the gas stream (25) is recycled to the converter, and a portion provides a purge gas stream (6). Alternatively, the entire gas stream (25) can be supplied to the converter, and the purge gas (6) can be drawn from a synthesis loop between the converter and the condenser. This loop may contain one or more NH3 condensers as the gas-liquid separator. The synthesis loop generally includes a compressor (particularly a supply compressor) located upstream or downstream of the NH3 condenser. Here, the NH3 products from the condenser (device B or C) are flashed to obtain a flash gas stream (20) and a liquid product stream.

[0060] To be attractive to plants having ammonia synthesis combined with water electrolysis, it has been observed that relatively low ammonia synthesis pressures (e.g., 100-300 bar(a), preferably 150-300 bar(a), more preferably 150-250 bar(a)) can result in a relatively large amount of purge gas drawn from the synthesis loop and a small amount of gas supplied to the flash vessel to dissolve in the high-pressure liquid ammonia flow (16). The purge gas flow has been found to be cleverly used as a driving fluid for an ejector for the flash gas in a more preferred embodiment of the present disclosure.

[0061] The ejector (13) has an outlet for a mixed gas stream (6b) connected to a processing section (101), for example, an absorption and washing device (3).

[0062] Figure 3 schematically illustrates an example configuration of an ammonia synthesis loop. The compressor (27) receives the supply flow (28) and the recirculated gas flow (26). The supply flow (28) is supplied by an H2 flow (5) from the water electrolyzer (1) and an N2 flow (15) or a portion thereof (15a) from the nitrogen generator (14).

[0063] The compressed gas stream (29) is supplied to the converter (30). The waste liquid (24) from the converter is supplied to the condenser (23). The gas (25) from the condenser is partially (26) recirculated to the converter (30) through the compressor (27), and partially purged as a purge stream (6). The liquid (16) from the condenser (23) contains NH3 products and is obtained from the loop, preferably supplied to a flush vessel (21). Those skilled in the art will understand that other configurations of the ammonia synthesis loop are also possible; see, for example, Ullmann's Encyclopedia of Industrial Chemistry, 2012, vol.3, Chapter Ammonia 2, Figure 30.

[0064] Unless otherwise specified, all pressures are expressed in absolute pressure in bars and are abbreviated as bar(a). The term “typical” as used herein indicates a frequently used but not essential characteristic.

[0065] Examples The present invention is further illustrated by the following non-limiting embodiments. These embodiments are not intended to limit the present invention or the scope of the claims.

[0066] Example 1 An example of a simulated inventive process for adjusting the purge gas flow, implemented in the system shown in Figure 1, is operated using the gas flow shown in Table 1.

[0067] The nitrogen stream (10) is detailed in Table 1, based on N2 production via a cold-box cryogenic method (i.e., relatively low argon content) for a 450 MTPD (metric tons / day) green ammonia plant.

[0068] The entire volume of the gaseous flow (11) containing H2 is supplied from the permeate side compartment (19) and recycled for NH3 synthesis.

[0069] Table 2 shows a reference process, which differs from Table 1 in that it does not use sweep gas (10), and this process is not part of the present invention. Unlike Table 1, the residue (12) in Table 2 has an undesirable high concentration of H2.

[0070] [Table 1]

[0071] [Table 2]

[0072] Example 2 Table 3 shows the flow of the purge gas recovery process according to the present invention, which is similar to the process in Table 1, but assumes N2 generation via pressure swing adsorption (i.e., a relatively high argon content) for a 450 MTPD green ammonia plant.

[0073] Table 4 shows a process similar to that in Table 3, but differs in that it does not use a sweeping gas (10), and this process is not according to the present invention. Unlike in Table 3, the residue (12) has an undesirable high concentration of H2.

[0074] The process configurations in Tables 2 and 4 are presented as reference processes without implying or acknowledging that these processes are prior art. The claimed processes of the present invention may differ from prior art processes in one or more other or additional features other than the use of sweep gas.

[0075] [Table 3]

[0076] [Table 4] [Explanation of Symbols]

[0077] 1 Water electrolysis device 2. Ammonia synthesis loop 3 Absorption and washing device 4 Membrane separation equipment 5 H2 style 6. Purge flow 7. Purge Flow 8 liquid flow 9. Hydrogen-selective membrane 10 Sweep gas 11 Gas flow 12 Processed purge flow 13 Pressure reduction factors 14. Nitrogen generator 15 N2 style 16 High-pressure ammonia liquid flow 17 Absorbent Washing Solution 18 Remaining side section 19 Permeable side compartment 20 Flash gas flow 21 Flush container 22 NH3 product 23 Capacitors 24. Waste liquid 25 Gas flow 26 Recirculating gas flow 27 Compressor 28 Feed stream 29 Gas flow 30 Converters 100 Ammonia Synthesis Plant 101 Processing Section

Claims

1. H ２ A water electrolysis device (1) for generating flow (5), and the H ２ to N ２ A process for adjusting the purge gas flow in an ammonia synthesis plant (100) comprising an ammonia synthesis loop (2) for reacting with a supply source, wherein the process is: a) Obtaining a purge flow (6) from the ammonia synthesis loop (2), wherein the purge flow is a gas and N ２ H ２ NH ３ And to obtain a purge flow (6) including Ar, b) removing at least a portion of the NH ３ and at least a portion of the H ２ from the purge gas stream (6), and subjecting the purge stream (6) to a treatment including absorption cleaning in an absorption cleaning device (3) and membrane separation in a membrane separation device (4) at a pressure of 10 to 70 bar(a) to supply a treated purge stream (12), a gas stream (11) containing H ２ and a liquid stream (8), wherein the membrane separation uses a hydrogen-selective membrane (9) having a permeate side and a retentate side, and includes supplying a sweep gas (10) containing N ２ to the permeate side of the membrane (9), subjecting to the treatment; c) A process comprising recirculating part or all of the gas flow (11) into the ammonia synthesis loop (2).

2. The process according to claim 1, wherein the sweep gas flow is the N of the nitrogen generator (14) ２ The outlet (15) for the gas flow originates from the aforementioned device, and the N ２ A process comprising supplying a supply source, wherein the nitrogen generator is preferably an air separator.

3. The process according to claim 1, wherein the sweeping gas has a pressure of 5 to 20 bar and contains at least 98 volume% N ２ A process that includes this.

4. The process according to claim 1, wherein the absorption washing and the membrane separation are carried out at 20 to 50 bar(a).

5. The process according to claim 1, wherein the treated purge flow (12) is partially recycled into the ammonia synthesis loop.

6. A process according to claim 1, wherein a portion or all of the treated purge flow (12) is vented or supplied to Ar recovery, the venting preferably without combustion.

7. A process according to claim 1, wherein the absorption washing is performed upstream of the membrane separation, the absorption washing provides the liquid stream (8) containing a solution of ammonia or an ammonium salt, and the absorbed-washed purge stream (7), and the membrane separation includes contacting the absorbed-washed purge stream (7) with the hydrogen-selective membrane (9) having a permeate side and a residual side within the membrane separation apparatus (4), thereby obtaining the gaseous stream (11) on the permeate side and the treated purge stream (12) on the residual side.

8. The process according to claim 1, wherein the membrane is a polymer membrane, preferably a hollow fiber membrane.

9. The process according to claim 1, wherein step a) in an ammonia synthesis plant (100) high pressure NH ３ A process comprising reducing the pressure of the purge flow (6) to a pressure in the range of 10 to 70 bar(a) from the pressure of the ammonia synthesis loop using a pressure reduction element including an ejector that also receives a gas flow obtained from a step of flashing a liquid flow, wherein the ammonia synthesis loop is operated at a pressure preferably greater than 100 bar(a), more preferably in the range of 150 to 300 bar(a).

10. The process according to claim 1, wherein the absorption wash includes absorption wash with an acid.

11. Ammonia production process, - The H ２ A flow (5) is generated, and within the ammonia synthesis loop (2), NH ３ To form the H ２ Flow N ２ Reacting with the supply source, A process comprising obtaining and adjusting a purge flow (6) from the ammonia synthesis loop (2) using the process described in claim 1, preferably using the process defined in any one of claims 2 to 10.

12. Ammonia synthesis plant (100), H ２ A water electrolysis device (1) for generating flow (5), and the H ２ to N ２ A processing section (101) includes an ammonia synthesis loop (2) that reacts with a supply source and has an outlet for a gaseous purge flow (6), and an absorption washing device (3) and a membrane separation device (4), wherein the NH is supplied from the purge gas flow (6). ３ At least a portion of and the H ２ Remove at least a portion of the treated purge flow (12), H ２ An ammonia synthesis plant comprising: a processing section (101) in which the purge flow (6) is subjected to a pressure of 10 to 70 bar(a) to supply a gaseous flow (11) and a liquid flow (8) including absorption washing in the absorption washing device (3) and membrane separation in the membrane separation device (4), wherein the membrane separation device (4) comprises a hydrogen-selective membrane (9), a permeate side compartment (19) and a residual side compartment (18), and a supply section for sweep gas (10) to the permeate side compartment (19); and a flow path for recirculating part or all of the gaseous flow (11) to the ammonia synthesis loop (2).

13. The plant according to claim 12, wherein the absorption and washing device is located upstream of the membrane separator (4), the absorption and washing device has an outlet for the liquid stream (8) containing a solution of ammonia or an ammonium salt, and an outlet for the absorbed and washed purge stream (7), and the membrane separator (4) has an inlet for the absorbed and washed purge stream (7) in the residual side compartment (18), an outlet for the gas stream (11) from the permeate side compartment (19), and an outlet for the treated purge stream (12) from the residual side compartment (18).

14. The plant according to claim 12, wherein the nitrogen generating device (14) is the N ２ N provides a supply source and is connected to the supply unit for sweep gas (10). ２ A plant further having an outlet (15) for gas flow, wherein the nitrogen generator is preferably an air separator.

15. The plant according to claim 12, wherein the outlet of the treated purge flow (12) is connected to a recirculation channel to the ammonia synthesis loop.

16. A plant according to claim 12, wherein the outlet of the treated purge flow (12) is connected to a device for venting and / or Ar recovery.

17. The plant according to claim 12, wherein the ammonia synthesis plant (100) is configured to supply high-pressure NH from the ammonia synthesis loop (2). ３ A plant comprising a flash vessel (21) for flashing a liquid flow (16), wherein the flash vessel has a gas outlet (20) and a liquid outlet (22), and the gas outlet (20) is connected to an ejector (13) provided in the flow path for the purge flow (6) from the synthesis loop to the processing section (101).

18. H ２ A water electrolysis device (1) for generating flow (5), and the H ２ to N ２ A method for modifying an ammonia synthesis plant (100) comprising an ammonia synthesis loop (2) that reacts with a source and has an outlet for a gaseous purge flow (6), and a flow path for recirculating part or all of a gaseous flow (11) to the ammonia synthesis loop (2), wherein the method comprises providing the plant with a section including an absorption and washing device (3) and a membrane separator (4), and a flow path for recirculating part or all of the gaseous flow (11) to the ammonia synthesis loop (2), the section comprising the NH ３ At least a portion of and the H ２ At least a portion of it is removed from the purge gas flow (6), and the treated purge flow (12), H ２ A method comprising supplying the purge flow (6) at a pressure of 10 to 70 bar(a) to a process including absorption washing in the absorption washing device (3) and membrane separation in the membrane separation device (4) in order to provide the gas flow (11) and liquid flow (8) including the gas flow (11) and liquid flow (8), wherein the membrane separation device (4) comprises a hydrogen-selective membrane (9), a permeate side compartment (19), a residual side compartment (18), and a supply unit for sweep gas (10) to the permeate side compartment (19), and the modified plant preferably having the features described in any of claims 12 to 17.

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