GREEN AMMONIA ABSORPTION COOLING

Abstract

An ammonia synthesis process and plant comprising an ammonia synthesis converter and a downstream ammonia cooling system, wherein the ammonia synthesis converter is arranged to receive an ammonia synthesis gas comprising hydrogen and nitrogen and to produce an ammonia product gas stream and an ammonia gaseous effluent stream; the ammonia cooling system comprises: an ammonia evaporator for evaporating a liquid ammonia stream and generating an ammonia vapor stream; an effluent gas cleaning unit for cleaning the ammonia gaseous effluent stream by adding water as a cleaning agent, generating a water stream and an ammonia-depleted effluent gas stream; an absorption cooling unit comprising water for cooling the ammonia vapor stream and for collecting a condensed ammonia-water stream;a regeneration unit to generate from the ammonia-condensed water stream: a purified water stream, the liquid ammonia stream and an overhead ammonia gas stream.;

Description

GREEN AMMONIA ABSORPTION COOLING Technical Field of the Invention The present invention relates to an ammonia cooling (refrigeration) system for cooling ammonia product gas from the ammonia synthesis converter of an ammonia synthesis plant or process. The present invention also relates to an ammonia synthesis plant and process comprising the ammonia cooling system, wherein ammonia is produced from hydrogen by electrolysis using energy from renewable energy sources. Background of the Invention A conventional, i.e. traditional, ammonia synthesis plant, as is well known in the field, typically comprises a reforming section including a steam methane reforming unit and / or an autothermal reforming unit for catalytic steam reforming of a hydrocarbon feedstock, typically natural gas, or a hydrocarbon feed originating from renewable sources, to consequently produce a raw synthesis gas, which is then 1 2137510 of 46 is enriched in hydrogen and combined with nitrogen to produce ammonia synthesis gas. The ammonia synthesis plant therefore comprises a downstream ammonia synthesis section, e.g., an ammonia synthesis loop, including an ammonia synthesis converter where the ammonia synthesis gas is converted into the ammonia product gas stream. In conventional ammonia synthesis plants, the commonly referred to turndown ratio is approximately 100%. The turndown ratio, also referred to hereafter as reduction, is the ratio of operating at normal load, for example, a normal load of the upstream hydrocarbon feed, typically natural gas, used to generate the ammonia synthesis gas and consequently the ammonia product gas, with respect to the amount that the ammonia synthesis plant is able to tolerate. Therefore, in conventional ammonia synthesis plants, a turndown of, for example, 10% is never considered because the natural gas supply is constant and thus at normal load, the turndown is 100%. However, for dynamic ammonia synthesis plants, such as ammonia synthesis plants 2 2137510 of 46 green whereby hydrogen from ammonia synthesis gas is produced by means of electrolysis of water or steam powered by electricity from renewable sources such as solar, wind or hydroelectric sources, the energy input from these sources can vary significantly during the day and during seasons, which is why a reduction of for example 10% of load frequently occurs and in this way it becomes an issue which is very pertinent to address. In conventional natural gas-based ammonia synthesis plants or processes, an ammonia cooling circuit is typically employed to condense the ammonia produced. The ammonia produced is therefore separated from the circulating ammonia synthesis gas by cooling / condensation. To prevent the buildup of inert elements in the plant, small amounts of ammonia-containing gases, i.e., a gaseous effluent ammonia stream, are released from the plant. For environmental reasons, this stream is treated in a scrubber, and the absorbed ammonia is recovered by distillation. The well-known operating principle in the ammonia cooling circuit is the use of the 2137510 of 46 commonly called mechanical refrigeration, whereby ammonia is evaporated at low pressure, thereby producing low temperatures which are in turn used for cooling the main process streams of the upstream ammonia synthesis plant. The liberated ammonia vapor is then compressed in a multi-stage ammonia compressor, e.g., a multi-stage centrifugal compressor driven by a steam turbine, and the compressed vapor is condensed by means of cooling water or air in an ammonia condensing unit. The resulting liquid ammonia is then collected and reused for cooling.For example, in a standard, i.e. conventional, natural gas-based ammonia synthesis plant, an ammonia refrigeration compressor and an ammonia recovery unit comprising two gas effluent scrubbers and a distillation column are typically provided. Since cooling is traditionally provided by a multi-stage cooling compressor operating at several pressure levels, this leads to an ammonia cooling circuit with high energy efficiency at high loads, but also to a complicated design and due to the limitations 2137510 of the 46 compressor also exhibits low efficiency at low loads (or low reduction ratios). This is a problem when the plant load varies significantly and the compressor is driven by steam. At full plant load, the steam produced as a byproduct in the ammonia plant will be produced in sufficient quantities to operate the cooling compressor, while at reduced load this is not possible. In this way, the heat generated from the ammonia synthesis converter of a conventional ammonia synthesis plant is typically removed in steam boilers, and the generated superheated steam can be used in steam turbines to either drive the multistage compressor of the ammonia refrigeration circuit or an alternator to generate power.However, the reduction in a steam turbine is lower than that of the ammonia synthesis plant, for example, the ammonia synthesis loop. Therefore, a low load on the ammonia synthesis plant, for example, below 50%, creates an imbalance between the steam produced in the ammonia synthesis plant and the steam used in the downstream ammonia refrigeration circuit, and consequently, an imbalance in how this steam is utilized in the turbine. 2137510 of 46 steam. This requires shutting down the steam turbine and using additional energy to condense the steam. A traditional steam turbine operates with superheated steam, and a steam superheater must be included as part of the steam generation section, resulting in increased capital expenditures (CAPEX) and more complicated operation. Document WO 2020057818 A1 discloses a water / ammonia absorption cooling system and a method for retrofitting it. A preferred application relates to an absorption cooling system for cooling process gas from an ammonia synthesis plant. US 4376758 discloses a process for synthesizing ammonia from hydrocarbons, which includes cooling and purification. The gaseous effluent, containing as little as 0.48% ammonia, is withdrawn at the top of an ammonia absorption column. Summary of the Invention Therefore, an objective of the present invention is to provide a consistent system of 2137510 of 46 ammonia cooling capable of withstanding load variation in an ammonia synthesis plant due to fluctuating power sources, particularly in a green ammonia synthesis plant, i.e. where the hydrogen required to produce ammonia synthesis gas is obtained from the electrolysis of water or steam powered by electricity from renewable energy sources. Another objective of the present invention is to provide improved recovery of ammonia from a gaseous effluent ammonia stream generated in an ammonia synthesis plant. These and other objectives are solved by the present invention. Detailed Description of the Invention Accordingly, in a first aspect, the invention relates to an ammonia synthesis plant comprising an ammonia synthesis converter and a downstream ammonia cooling system, wherein the ammonia synthesis converter is arranged to receive an ammonia synthesis gas comprising hydrogen and nitrogen and to produce an ammonia product gas stream, wherein the ammonia synthesis plant is arranged to receive an ammonia synthesis gas comprising hydrogen and nitrogen and to produce an ammonia product gas stream. 2137510 of 46 ammonia is arranged to generate a gaseous effluent ammonia stream and wherein the ammonia cooling system comprises: - an ammonia evaporator for evaporating a liquid ammonia stream and generating an ammonia vapor stream; - a gaseous effluent cleaning unit for cleaning the gaseous effluent ammonia stream under the addition of water as a scrubbing agent (absorption agent), generating a water stream and an ammonia-depleted gaseous effluent stream; - an absorption cooling unit comprising water for cooling the ammonia vapor stream and collecting a condensed ammonia-water stream; - a regeneration unit for the generation of the ammonia-water condensate stream: a purified water stream, the liquid ammonia stream, and a gaseous overhead ammonia stream; - the ammonia evaporator is arranged to receive the liquid ammonia stream and a heat exchange medium to evaporate the liquid ammonia stream, to consequently generate the ammonia stream. 2137510 of 46 ammonia vapor; - the off-gas cleaning unit, suitably a off-gas purification unit, i.e. a off-gas scrubber, is arranged to receive: the purified water stream from the regeneration unit as the scrubbing agent and the off-gas ammonia stream, suitably also comprising the overhead ammonia gas stream from the regeneration unit, to consequently generate the ammonia-depleted off-gas stream and the water stream; - the absorption cooling unit, suitably a mixing vessel containing water, is arranged to receive the water stream and the ammonia vapor stream, to generate and collect accordingly the condensed ammonia-water stream; the absorption cooling unit further comprises a cooling device such as a coil arranged to receive a cooling medium such as water and an outlet for withdrawing the condensed ammonia-water stream; - the regeneration unit is a distillation column, i.e. an ammonia recovery distillation column, arranged to receive the 2137510 of 46 ammonia-water condensed stream the regeneration unit comprising: an outlet for withdrawing as a bottom stream the purified water stream, an outlet for withdrawing an overhead ammonia stream and a separation unit, such as an ammonia recovery overhead drum, for separating the overhead ammonia stream from a gaseous overhead ammonia stream and the liquid ammonia stream. As used herein, the term comprising also includes comprising only, i.e., consisting of. As used herein, the term properly means optionally, i.e., an optional modality. As used herein, the term "first aspect" or "first aspect of the invention" means the plant (system). The term "second aspect" or "second aspect of the invention" means the process. As used herein, the term "present invention" or "invention" may be used interchangeably with the term "present application" or "application." Other definitions are provided in relation to one or more of the modalities below. 2137510 of 46 In one embodiment, the ammonia synthesis plant comprises a water or steam electrolysis unit to produce hydrogen. Suitably, the electrolysis unit is powered by electricity from renewable energy sources such as solar, wind, or hydroelectric sources. Optionally, the electrolysis unit is powered by electricity from thermonuclear energy. The water electrolysis unit is an alkaline / polymer electrolytic membrane electrolysis unit, i.e. an alkaline / PEM electrolysis unit (alkaline cell or polymer cell units). For the purposes of the present invention, the term alkaline / PEM electrolysis unit means an alkaline and / or PEM electrolysis unit. The steam electrolysis unit is a solid oxide electrolysis cell unit (SOEC unit). Operation with SOEC units is typically conducted at high temperatures (700-800°C), which frequently provides advantages over alkaline / PEM electrolysis, since the latter operates at a much lower temperature, i.e. in the range of 60-160°C. It would be understood that water is used for alkaline / PEM electrolysis, while steam is used for SOEC. 2137510 of 46 The term green ammonia absorption cooling would be understood to mean the cooling of ammonia product gas in the ammonia cooling system, where electrolysis of water or steam is provided to produce hydrogen. The term "green ammonia plant" or "green ammonia synthesis plant" would also be understood to mean an ammonia synthesis plant comprising a water or steam electrolysis unit to produce hydrogen from ammonia synthesis gas, and the electrolysis unit is powered by electricity from renewable energy sources such as solar, wind, or hydroelectric sources. Optionally, the electrolysis unit may also be powered by electricity from thermonuclear energy. It would be understood that the ammonia cooling system may comprise a closed circuit and thus can also be interpreted, for example, as an ammonia cooling circuit. The term "ammonia cooling circuit" can be used interchangeably with the term "ammonia refrigeration circuit." The term mechanical refrigeration can be used interchangeably with the term cooling circuit. 2137510 of 46 compressor-driven cooling or compressor-driven ammonia cooling. The term ammonia evaporator is used interchangeably with the term ammonia cooler or simply cooler. The term "ammonia evaporator" or "cooler" would also be understood to mean one or more ammonia evaporators, i.e., one or more coolers. A similar interpretation can be applied to other units. For example, the term "absorption cooling unit" means one or more absorption cooling units. Suitably, the ammonia cooling system comprises a plurality of ammonia evaporators, i.e., a plurality of chillers, such as two chillers, arranged in series. One chiller enables the condensation of ammonia into the ammonia product gas, and the provision of a plurality of chillers enables greater energy efficiency in the plant or process. The term flue gas cleaning unit means a unit for removing ammonia from flue gas. The flue gas cleaning unit is properly a scrubbing tower or a dewatering tower. 2137510 of 46 purification where a scrubbing agent is used to wash the ammonia present in the gaseous effluent. Scrubbing agent can be understood to have the same meaning as absorption agent. The term absorption cooling unit is used interchangeably with the term absorber. The term regeneration unit is used interchangeably with the term regenerator. The term "load" refers to the percentage of hydrogen feed used to drive ammonia synthesis in the ammonia synthesis plant relative to the load during normal operation (100% load). The ammonia production capacity of the plant is assumed to be directly proportional to the hydrogen feed used. Therefore, 10% load would be understood to mean 10% of the hydrogen used for ammonia synthesis relative to normal operation. The hydrogen used is from water (steam) electrolysis, as is well known in the field. 100% load corresponds to normal operation of the ammonia synthesis plant, where the natural gas supply is constant. As stated above, the term reduction ratio is also referred to simply as reduction and means the operating ratio in 14 2137510 of 46 normal load, for example, the normal upstream hydrocarbon feedstock, typically natural gas, used to generate ammonia synthesis gas and, consequently, ammonia product gas, relative to the amount the ammonia synthesis plant is capable of handling. The term normal load or normal operation would also be understood to mean conditions where the load is 100%. Therefore, a 100% load, i.e., a normal load, corresponds to a 100% reduction, while a 10% load corresponds to a 10% reduction. The term "turndown" also applies to parts of the ammonia synthesis plant, such as its units or equipment. Consequently, the term "turndown" also applies to, for example, the steam turbine used to drive the compressor of a conventional ammonia refrigeration circuit. A turndown of, for example, 50% in the steam turbine refers to the ratio of normal-load operation to the amount the steam turbine is capable of handling. It has now been discovered that for an ammonia plant operating at widely different loads and rapid load changes, these green ammonia plants which operate only with 15% energy sources 2137510 of 46 renewables, absorption cooling is advantageously suited to mechanical refrigeration, since the ammonia cooling system can be designed with a better turndown ratio than that available in compressor-operated cooling units and thus follows overall plant variations. By means of the present invention, absorption cooling is combined with off-gas cleaning, e.g., off-gas absorption, resulting in a cooling system design with a considerably lower number of equipment units than in a traditional compressor-driven cooling circuit plus a traditional off-gas cleaning unit. While the use of absorption cooling for cooling in conventional ammonia synthesis plants is known, for reasons of energy saving it has typically been operated only to generate an ammonia-water solution for the absorber at the required concentration. The present invention differs at least in that ammonia and water are separated into almost pure components. Therefore, the ammonia cooling system is adapted to both produce water. 2137510 of 46 purified, i.e. ammonia-free water, as well as an ammonia liquid, a portion of which can be removed as additional ammonia product. Therefore, the invention makes it possible to replace in a system a traditional compressor-driven cooling circuit (i.e. mechanical refrigeration) and traditional absorption of gaseous effluent. As used in this document, the term integration means providing synergy when combining traditional autonomous units or systems, such as by significantly reducing the resulting number of equipment units. It would be understood that, in one embodiment, the gaseous effluent cleaning unit (132) is a gaseous effluent scrubbing unit and the gaseous effluent cleaning unit (132) is also arranged to receive the gaseous overhead ammonia stream (139) from the regeneration unit (126), such as in a mixture with the gaseous effluent ammonia stream (143). As set forth above, suitably, the gaseous effluent ammonia stream also comprises the gaseous overhead ammonia stream from the regeneration unit. Therefore, in a particular embodiment, 17 2137510 of 46 means such as a joining or mixing unit for adding or mixing the overhead ammonia gas stream to the effluent gas ammonia stream. The stream combined in this manner is supplied to the effluent gas cleaning unit. This achieves greater integration. For environmental reasons, any gaseous effluent, such as off-gases from the upstream ammonia synthesis plant or from the ammonia cooling system itself, containing ammonia, must be cleaned. The gaseous effluent containing ammonia is scrubbed with purified water generated in the ammonia cooling system, more specifically the regenerator underflow stream, to recover ammonia and minimize ammonia escape into the atmosphere. The water stream generated in this way from the off-gas cleaning unit is added to the absorption cooling unit, such as the mixing vessel, to then recover ammonia as a product downstream, as well as purified water, which is sent back to the off-gas cleaning unit. Ammonia present in the gaseous effluent ammonia stream, as well as in stream 18 2137510 of 46 overhead ammonia gas is reduced to a level that is not otherwise obtainable by other traditional plants or processes and whereby the ammonia-containing streams are left for disposal by the end user, which is highly undesirable. By means of the present invention, the ammonia content in the ammonia-depleted off-gas stream from the off-gas cleaning unit is reduced to below 10 ppmv, such as 7 or 5 ppmv ammonia. The off-gas ammonia stream entering the off-gas cleaning unit may contain, for example, 10-15% (mol %) ammonia, while the overhead ammonia gas stream may contain, for example, 80-90% ammonia. In an embodiment according to the first aspect of the invention, in the ammonia cooling system the heat exchange medium of the ammonia evaporator is the ammonia product gas stream. Consequently, the ammonia cooling system can be fully integrated into the ammonia synthesis plant. In addition to green ammonia synthesis plants, where fluctuating energy supply is inherent due to the intermittent nature of renewable sources such as wind, 19 2137510 of 46 solar or hydroelectric plants, the present invention is also suitable for cooling the ammonia product gas from any ammonia synthesis plant with a fluctuating power supply or with a fluctuating hydrocarbon feed supply. In an embodiment according to the first aspect of the invention, in the ammonia cooling system, the regeneration unit comprises an upper section (I) and a lower section (II); the lower section (II) comprises: a power-driven heating device and / or a reboiler unit arranged to receive a heat exchange medium; and an outlet for withdrawing the purified water stream as an underflow; The upper section (I) comprises: - an inlet to receive the condensed ammonia-water stream, - a head section comprising: an outlet to withdraw the overhead ammonia stream; an ammonia condensing unit arranged to receive the overhead ammonia stream and a cooling medium, such as water, to generate a stream 2137510 of 46 condensed head ammonia; a separation unit, suitably an ammonia recovery drum, arranged to receive the condensed overhead ammonia stream, the separation unit comprising an outlet for removing a liquid fraction of ammonia and an outlet for removing the gaseous overhead ammonia stream; a reflux pump arranged to receive the liquid ammonia fraction and direct a portion thereof as an overhead reflux stream to the head section; means for removing the remaining portion of the liquid ammonia fraction as the liquid ammonia stream. The term reboiler unit can be used interchangeably with the term reboiler. The term ammonia condensing unit can be used interchangeably with the term ammonia condenser. The term "power-operated heating device" means a heating element powered by electricity, which thereby converts electricity or electrical energy into heat, for example, via the heating process. 2137510 of 46 Joule heating. Consequently, contrary to the traditional system for the absorption of ammonia, as illustrated for example in the attached Figure 1, whereby an ammonia-water mixture is sent to a distillation column, where the overhead ammonia is condensed and used for cooling in the ammonia evaporator (cooler), thus without overhead reflux, while the bottom product relatively rich in water is used in the absorber, the present invention as illustrated for example in Figure 2 provides an overhead reflux which thus makes possible a distillation column with a lower number of trays, and at the same time the purified water stream from the bottom of the distillation column is used as scrubbing agent (e.g. absorption agent) in the gaseous effluent cleaning unit. Traditional systems for ammonia absorption also require the addition of significant amounts of demineralized water, while the present invention significantly reduces this requirement. In an embodiment according to the first aspect of the invention, the ammonia synthesis plant 22 2137510 of 46 further comprises upstream of the ammonia cooling system one or more steam boilers arranged to receive the ammonia product gas stream, to recover heat therefrom and produce steam, and wherein the plant is further arranged to provide at least a portion of the steam as the heat exchange medium to the reboiler unit i.e. the reboiler. The reboiler, as is well known in the field, is a heat exchanger, for example, a tube and jacket heat exchanger, which provides the heat required to boil the liquid at the bottom of the regenerator, the regenerator is properly a distillation column, for the purpose of generating steam which is returned to the distillation column to drive the separation of ammonia. Consequently, by means of the present invention, the reboiler load follows the ammonia production load and therefore there is also a balanced use of steam at any turndown level, particularly well below 100%, for example 10%, i.e. where the load of the ammonia synthesis plant is 10%. In other words, it is now possible to additionally balance the steam produced in the synthesis plant. 2137510 of 46 ammonia with the steam used in the ammonia cooling system at any operating load between for example 10-100%. The steam generated in the ammonia synthesis plant can be adequately supplied at a pressure level corresponding to that required in the reboiler, thereby also enabling thermal efficiency at least as good as using mechanical refrigeration. Suitably, the steam is medium-pressure steam, for example, steam at 5000 kPa (50 bar) (at 264°C). Furthermore, when operating at low turndowns, such as turndowns below 50%, for example, 30% or 10%, the availability of steam generated in ammonia synthesis to external users is limited—if possible. The invention also solves this problem, again by coupling the ammonia cooling system that accommodates absorption cooling with a dynamic ammonia synthesis gas plant, such as a green ammonia synthesis plant, which has fluctuating ammonia and steam production. Additionally, the invention avoids the use of a steam turbine connected to the operation of a traditional ammonia refrigeration circuit. More specifically, 24 2137510 of 46 there is no steam turbine, since there is no centrifugal compressor in the ammonia cooling system and which is normally driven by this steam turbine. Instead of the reboiler, or in combination with the reboiler, a power-driven heating device is provided. This heating device is suitably fitted within the regenerator in its lower portion. Consequently, greater flexibility is achieved, since the electricity required for the heating device can be provided by renewable sources, as described above, and if for some reason the steam reboiler's requirements cannot be met, the power-driven heating device supplies the required heat to the regenerator. Furthermore, under transient conditions, such as startup conditions, the regenerator can operate solely with the power-driven heating device. In an embodiment according to a first aspect of the invention, in the ammonia cooling system, the ammonia evaporator further comprises an outlet for withdrawing a purge ammonia stream and the ammonia cooling system further comprises means upstream of the regeneration unit, such as a regeneration unit. 2137510 of 46 union or mixing, to combine the purge ammonia stream with the condensed ammonia-water stream. Providing an outlet to remove the purge ammonia stream, i.e. reducing liquid blow-through, eliminates water accumulation within the cooler. Suitably, an ammonia recovery circulation pump conducts the combined stream to the regeneration unit. As an example, the ammonia-water stream condensed for example after adding the cooler blowdown stream is a stream containing 30-50% by weight of ammonia, for example 35, 40, 45% by weight of ammonia, where the remainder is water. In a traditional system, as illustrated for example in Figure 1, the ammonia purge stream from the cooler is sent directly to the distillation column. By combining the purge ammonia stream with the condensed ammonia-water stream, as in the present invention, a single pump is used to feed ammonia-water to the regenerator, thereby increasing energy efficiency. The ammonia evaporator purge stream contains water as well as ammonia, which is subsequently recovered in 26 2137510 of 46 instead of being disposed of as acidic water or similar. In an embodiment according to the first aspect of the invention, the ammonia cooling system further comprises: a heat exchanger, also referred to hereinafter as an aftercooler, upstream of the ammonia evaporator and which is arranged to receive the liquid ammonia stream and to receive a cooling medium such as water as the heat exchange medium, to cool the liquid ammonia stream before entering the ammonia evaporator. In an embodiment according to the first aspect of the invention, the regeneration unit of the ammonia cooling system further comprises a feed / effluent heat exchanger (F / E HEX) which is arranged to receive the condensed ammonia-water stream or the stream resulting from the combination of the blowdown ammonia stream with the condensed ammonia-water stream, as well as to receive the purified water stream as the heat exchange medium, for preheating the condensed ammonia-water stream, or preheating the stream resulting from the combination of the blowdown ammonia stream with the condensed ammonia-water stream. 2137510 of 46 ammonia-water condensate stream, before entering the regeneration unit. Suitably, the purified water stream cooled in this manner is further cooled in an additional heat exchanger, also referred to hereinafter as an ammonia recovery cooler. This additional unit is therefore suitably arranged to receive the purified water stream and a cooling medium, such as water, as the heat exchange medium, to further cool the purified water stream before entering the gaseous effluent cleaning unit. The provision of the F / E HEX and also the appropriate ammonia recovery chiller makes it possible to maintain an energy efficiency which at least matches that obtained if mechanical cooling were used instead, where these heat exchangers are not normally necessary. In an embodiment according to the first aspect of the invention, the ammonia cooling system further comprises a conduit for withdrawing from the purge ammonia stream, or from the liquid ammonia stream, a portion thereof as a further ammonia product, suitable for export as a 28 product. 2137510 of 46 excess ammonia. Suitably, the remaining portion of the liquid ammonia fraction in the overhead section of the regeneration unit is withdrawn as the liquid ammonia stream. While known (conventional) ammonia refrigeration circuits using ammonia absorption generate regenerator overhead ammonia, which is then condensed, collected in an overhead drum and then used for cooling, and the regenerator bottom stream which is relatively rich in water is then used for absorption as a recycle stream (see for example Figure 1), the present invention makes it possible that the regenerator overhead ammonia stream which is then condensed and collected in the overhead drum, can not only be used for cooling i.e. in the ammonia evaporator, but also as part of the ammonia product stock - and all this while at the same time mitigating the problems related to load variations and consequently turndowns below 100% of particularly green ammonia synthesis plants (see Figure 2). Additionally, while a circuit of 2137510 of 46 Traditional ammonia refrigeration using ammonia absorption produces in the regenerator a water rich bottoms stream, typically about 25% by weight ammonia, 75% water and which is recycled to the absorber by combining it with the ammonia vapor stream from the ammonia cooler, by means of the present invention the purified water bottoms stream from the regenerator according to the present invention, having much more than 75% water, such as at least 99%, i.e. pure water, is advantageously used in the off-gas scrubber, thereby avoiding the need to resort to external sources of pure water, such as by means of the use of demineralized water. In a second aspect, the invention relates to a process for generating an ammonia product gas from an ammonia synthesis gas stream comprising hydrogen and nitrogen, the process also generating a gaseous effluent ammonia stream, the process comprising the steps of: a) optional electrolysis of water or steam to produce hydrogen; the electrolysis is suitably powered by electricity from renewable energy sources such as solar, wind, or hydroelectric sources; 2137510 of 46 b) converting the ammonia synthesis gas into the ammonia product gas in an ammonia synthesis converter; The process also includes cooling the ammonia product gas according to the steps of: c) evaporating a liquid ammonia stream in an ammonia evaporator to generate an ammonia vapor stream by virtue of the provision of ammonia product gas as a heat exchange medium; (d) supplying the effluent gas ammonia stream to an effluent gas cleaning unit by virtue of the provision of the purified water stream as a scrubbing agent (absorption agent) to generate a water stream and an ammonia-depleted effluent gas stream; e) withdrawing the water stream from the gaseous effluent cleaning unit and supplying it, together with the ammonia vapour stream, to an absorption cooling unit by virtue of the provision of a cooling medium, such as water, to generate and collect a condensed ammonia-water stream; f) withdraw the condensed ammonia-water stream from the absorption cooling unit and supply it to a regeneration unit, such as a 2137510 of 46 distillation column, to generate: the liquid ammonia stream, an overhead ammonia gas stream and a purified water stream. Accordingly, in relation to the first aspect of the invention, absorption cooling is combined with off-gas absorption, resulting in a much simpler process design with a considerably lower number of equipment units and, consequently, fewer process steps than in a traditional compressor-driven ammonia cooling circuit plus a traditional off-gas absorption unit. Consequently, a high level of process and plant integration is achieved. The provision of absorption cooling - instead of the traditional and usually more efficient compressor-driven ammonia cooling (mechanical refrigeration) in an ammonia production process that operates under widely varying loads and rapid load changes, such as green ammonia plants operating solely on renewable energy sources - offers a better turndown ratio than that available with mechanical refrigeration and so tracks overall plant variations. In a modality according to the second 2137510 of 46 aspect of the invention, the process further comprises: g) supply the gaseous ammonia overhead stream to the gaseous effluent cleaning unit. Bypass streams in the process and plant containing ammonia, such as the ammonia effluent gas stream generated upstream to prevent the buildup of inert materials during the conversion of ammonia synthesis gas to ammonia product gas, as well as the ammonia overhead gas stream formed in the regeneration unit, are advantageously treated in the effluent gas cleaning unit. This also relieves an end user of the burden of finding ways to treat the overhead ammonia stream. In one embodiment according to the second aspect of the invention, prior to step c) the ammonia product gas is first cooled by passing it through one or more steam boilers to generate steam, suitably intermediate pressure steam; and in step f) the regeneration unit comprises a power-driven heating device or a reboiler unit, and the process further comprises supplying the steam to the reboiler unit. 2137510 of 46 It has been discovered that when ammonia product gas cooling is traditionally provided by a multi-stage cooling compressor operating at various pressure levels, ammonia cooling can be provided with high energy efficiency at high loads. However, at low loads, this results in a complicated process and plant design due to compressor limitations, which also include low efficiency at low loads. This is a problem if the plant load varies significantly and the compressor is steam-driven. At full plant load, the steam produced as a byproduct in the ammonia plant will be produced in sufficient quantities to operate the compressor for the ammonia cooling compressor, while at reduced load, this is not possible. Now, by means of the present invention, the produced steam can be adjusted to the steam needed, for example, for use as a heat exchange medium in the regenerator's reboiler. The use of a steam turbine otherwise required in a compressor-driven cooling system is avoided. Additionally, by providing the power-driven heating device, which is suitably adapted within the 34 2137510 of 46 regenerator in its lower portion, greater flexibility in the process is achieved. The electricity required for the heating device can be provided by renewable sources, and if for some reason the steam requirements of the reboiler cannot be met, the power-driven heating device supplies the required heat to the regenerator. Furthermore, in relation to the first aspect of the invention, under transient conditions, such as under start-up conditions, the regenerator can operate only with the heating device powered by electricity. In an embodiment according to the second aspect of the invention, in step c) a purge ammonia stream is generated (liquid blowdown) and the process further comprises withdrawing the purge ammonia stream and combining it with the condensed ammonia-water stream. The ammonia evaporator blowdown stream contains water, as well as ammonia, which is subsequently recovered rather than being disposed of as acidic water or similar. Additionally, the removal of the blowdown ammonia stream eliminates water buildup inside the chiller. In a modality according to the second 2137510 of 46 aspect of the invention, the process further comprises diverting a portion of the liquid ammonia stream or the purge ammonia stream (i.e., the liquid blow-off from the cooler) as an additional ammonia product. Either stream is subsequently used as excess ammonia export. The process therefore makes it possible not only to cool the ammonia product gas, but also to generate an additional valuable ammonia product, instead of simply having a closed ammonia cooling circuit. For example, the liquid ammonia stream, a portion of which is diverted as additional ammonia product, has a purity of at least 99.5% NH3 by weight. It would be understood that any of the embodiments and associated benefits according to the first aspect of the invention may be used with the second aspect of the invention, and vice versa. Brief Description of the Figures Figure 1 shows an ammonia cooling system according to the prior art, more specifically an ammonia refrigeration circuit with absorption cooling according to the prior art. 2137510 of 46 previous. Figure 2 shows an ammonia cooling system with absorption cooling according to an embodiment of the present invention. With reference to both figures, absorption cooling is used in the ammonia refrigeration circuit. The basic principle is the absorption of ammonia vapor from an ammonia cooler into a liquid ammonia / water mixture, where the heat of absorption is removed through the use of water cooling. The resulting condensed ammonia / water mixture is pumped to a regenerator (distillation column), where the overhead ammonia is condensed and used for cooling (Figures 1, 2) and optionally also as additional ammonia product (Figure 2), while the regenerator bottom product is used directly in ammonia absorption (Figure 1) or as a pure water stream in a gaseous effluent cleaning unit (Figure 2). With specific reference to Figure 1 according to the prior art, an ammonia cooling circuit 10 is shown. A liquid ammonia stream 1 from the ammonia recovery drum 12 passes to a first exchanger 14 upstream of the evaporator 37. 2137510 of 46 ammonia (cooler) 16 and by means of using the ammonia vapor stream 7 as the heat exchange medium. The resulting liquid ammonia stream 1' is then evaporated in the cooler 16 by means of the use of ammonia product gas 5 from the ammonia synthesis converter of an ammonia synthesis plant (not shown), to consequently generate the ammonia vapor stream 7. After providing cooling in the heat exchanger 14, the ammonia vapor stream 7' is combined with the water-rich bottom stream 25', for example 25% by weight ammonia / 75% by weight water, from the regenerator (distillation column) 26 which has arranged in its upper section I a quantity of trays 26'. The combined ammonia-water stream is then conducted to an absorber 18 comprising a cooling unit 18' and a mixing vessel 18.The cooling water 39 in the cooling device 18' removes the heat of absorption, which consequently generates a stream of ammonia-water condensate 15 which is fed to a mixing vessel 18. A stream of ammonia-water condensate 19 is withdrawn from the mixing vessel 18, transported via pump 22 and is heated by heat exchanger 24 by 38. 2137510 of 46 by means of using the bottom stream 25 of regenerator 26 as a heat exchange medium, and is fed as stream 21 to regenerator 26. A purge (liquid blow-through) ammonia stream 29 is conveyed via a separate pump 20 to the top of regenerator 26. The regenerator 26 comprises an upper section I and a lower section II. In the lower section, a reboiler 28 is provided which boils the liquid from the lower part 33 and generates a steam 35 to drive the distillation separation. The reboiler 28 is normally driven by steam 37 generated in a steam turbine (not shown). An overhead ammonia stream 23 is withdrawn and conducted to the ammonia condenser 30 by means of the use of a cooling medium 41 such as water. The thus condensed ammonia stream 27 is conducted to an ammonia recovery drum 12 from which the liquid ammonia stream 1 is withdrawn, thereby closing the ammonia cooling circuit. If mechanical refrigeration is used for the same service, a centrifugal compressor driven by a condensing steam turbine would be required. The compressor would then replace the following units: heat exchanger 14, absorber 18 comprising the cooling unit 39. 2137510 of 46 18' and mixing vessel 18, heat exchanger 24, reboiler 28, regenerator 26, pump 22, pump 20. By means of the present invention, in a chiller treating nearly pure ammonia, ammonia vapors are evaporated at low pressure, which consequently cools and partially condenses the ammonia product gas, optionally ammonia synthesis gas, on the tube side. The ammonia vapors are routed to the absorber, suitably a mixing vessel containing primarily water, and are absorbed in the water. The condensed ammonia-water mixture is then sent to the regeneration unit, suitably a distillation column. Pure ammonia, i.e., greater than 99% by weight ammonia, such as 99.5% by weight or higher, is recycled as the liquid ammonia stream to the chiller. Excess ammonia export is also suitably taken from the chiller bleed stream, i.e., the chiller liquid blowdown.The purified water from the regenerator is routed to the off-gas cleaning unit, which subsequently removes ammonia from the off-gas to negligible levels, such as less than 10 ppmv of ammonia. From the bottom of the off-gas cleaning unit, the water is routed to the 40-liter vessel. 2137510 of 46 mix . Accordingly, now with specific reference to Figure 2 in accordance with one embodiment of the present invention, there is shown an ammonia cooling system 100. A liquid ammonia stream 101' diverted from the overhead reflux stream 101' in the downstream regenerator 126, passes to the heat exchanger 114 (after-cooler, by means of the use of for example cooling water 131 as the heat exchange medium) and is disposed upstream of the ammonia evaporator (cooler) 116. The thus cooled liquid ammonia stream 101iv is then evaporated in the cooler 116 by means of the use of ammonia product gas 105 from the ammonia synthesis converter of an ammonia synthesis plant (not shown). Consequently, the ammonia vapor stream 107 is generated which is then conducted to an absorber 118 comprising a cooling unit 118' and a mixing vessel 118.The cooling water 139 in the cooling device 118' removes the heat of absorption, thereby generating a stream of ammonia-water condensate 119, which is withdrawn from the mixing vessel 118 and transported via the pump 122, heated by the heat exchanger of the. 2137510 of 46 feed / effluent 124 by using the bottoms stream 125 of regenerator 126 as a heat exchange medium and fed as stream 121 to regenerator 126. The thus cooled purified water stream 125' is further cooled in stream 125 in ammonia recovery cooler 144 by using e.g. quench water 147. A blowdown (liquid blow-down) ammonia stream 129 is suitably combined with the condensed ammonia-water stream 119 from absorber 118 before being conveyed via pump 122 to regenerator 126. Excess ammonia export 129' is also suitably taken from the blowdown stream of cooler 129. The regenerator 126 comprises an upper section I which includes a number of trays 126', and the lower section II. In the lower section a reboiler 128 is provided which boils the liquid from the lower part 133 and generates a steam 135 to drive the distillation separation. The reboiler 128 is driven by steam 137, which is suitably generated in steam boilers to cool the ammonia product gas exiting an ammonia converter, thereby supplying the ammonia product gas 105. The lower section II of the regenerator 126 is also 42 2137510 of 46 may be provided with a power-driven heating device (not shown), which is adapted for example to the bottom of the column. The upper section I comprises a head section: an overhead ammonia stream 123 is withdrawn and conducted to the ammonia condenser 130 by means of the use of a cooling medium 141 such as water. The thus condensed overhead ammonia stream 127 is conducted to the separation unit 112, suitably an ammonia recovery drum, from which the liquid ammonia fraction 101 is removed, as well as the gaseous overhead ammonia stream 139. A reflux pump 134 is arranged to convey the liquid ammonia fraction 101, 101' and direct a portion thereof as the overhead reflux stream 101 to the regenerator head section 126. The remaining portion of the liquid ammonia fraction is diverted as the liquid ammonia stream 101'. In the lower section II of the regenerator 126, the reboiler 128 is driven by steam 137 generated in one or more steam boilers (not shown) that recover heat from the ammonia product gas stream. In this way, it is possible to balance the steam produced in the ammonia synthesis plant, for example, in the loop 43. 2137510 of 46 ammonia synthesis upstream thereof, with the steam used in the ammonia cooling system 100 at any operating load—or correspondingly at any turndown between 10-100%. A steam turbine is not required. Additionally, from the separation unit 112 in the head section of the regenerator 126, part of the liquid ammonia stream 101', 101iv used in the ammonia cooler 16, can be obtained as a stream 101v, which is used as additional product ammonia, for example, as excess ammonia export. Furthermore, instead of recycling the bottom stream 25 from regenerator 26 to absorber 18 of Figure 1, the bottom purified water stream 125, 125', 125 containing at least 99% by weight water, for example as pure water having 99.98% by mol H2O or more, such as 100% by mol H2O wherein NH3 is less than 50 ppmv, is conducted to the gaseous effluent cleaning unit 132 to remove ammonia from the gaseous effluent ammonia stream 143 produced in the ammonia synthesis plant, suitably together with the gaseous overhead ammonia stream 139. The purified water stream 125 is therefore used as the scrubbing agent. From the cleaning unit 44 2137510 of 46 off-gas 132, for example, an off-gas scrubber, a water stream 117 is withdrawn as the bottoms stream, which is then sent to absorber 118 along with ammonia vapor stream 107 from cooler 116. From off-gas cleaning unit 132, a clean off-gas stream, i.e., an ammonia-depleted off-gas stream 145 having less than 10 ppmv of NH3, for example, 7 ppmv or less, is withdrawn. 2137510 of 46 DANIEL NIETO - 20116441714 Digitally signed by PORTALTRAMITES - INPI Date: 2023.02.01 12:31:36 -03:00 Reason: Digitally signed by the INPI Location: Buenos Aires, Argentina 2137510

Claims

1. An ammonia synthesis plant comprising an ammonia synthesis converter and a downstream ammonia cooling system (100), characterized in that the ammonia synthesis converter is arranged to receive an ammonia synthesis gas comprising hydrogen and nitrogen and to produce an ammonia product gas stream (105), wherein the ammonia synthesis plant is arranged to generate a gaseous effluent ammonia stream (143), and wherein the ammonia cooling system (100) comprises: - an ammonia evaporator (116) for evaporating a liquid ammonia stream (101, 101', 101''', 101 iv) and generating an ammonia vapor stream (107), wherein the heat exchange medium of the ammonia evaporator (116) is the ammonia product gas stream. (105);- a gaseous effluent cleaning unit (132) for cleaning the gaseous effluent ammonia stream (143) by adding water as a cleaning agent, generating a water stream (117) and an ammonia-depleted gaseous effluent stream (145); - an absorption cooling unit (118) comprising water for cooling the ammonia vapor stream (107) and collecting a condensate ammonia-water stream (119); - a regeneration unit (126) for generating the condensate ammonia-water stream (119, 121): a purified water stream (125, 125', 125''), the liquid ammonia stream (101, 101', 101''', 101 iv), and an overhead gaseous ammonia stream (139);- the ammonia evaporator (116) is arranged to receive the liquid ammonia stream (101, 101', 101''', 101 iv ) and the heat exchange medium (105) for the evaporation of the liquid ammonia stream (101, 101', 101''', 101 iv ), to consequently generate the ammonia vapor stream (107); - the gaseous effluent cleaning unit (132), properly a gaseous effluent purification unit, is arranged to receive: the purified water stream (125, 125', 125'') from the regeneration unit as the purifying agent and the gaseous effluent ammonia stream (143), to generate accordingly the ammonia-depleted gaseous effluent stream (145) and the water stream (117);- the absorption cooling unit (118), suitably a mixing vessel (118'') containing water, is arranged to receive the water stream (117) and the ammonia vapor stream (107), to generate and collect accordingly the condensed ammonia-water stream (119); the absorption cooling unit further comprises a cooling device (118') such as a coil arranged to receive a cooling medium (139) such as water and an outlet for removing the condensed ammonia-water stream (119);- The regeneration unit (126) is a distillation column arranged to receive the ammonia-condensed water stream (119, 121) and the regeneration unit (126) comprises: an outlet for removing the purified water stream (125) as a bottom stream, an outlet for removing an overhead ammonia stream (123), and a separation unit (112) for separating the overhead ammonia stream (123), the overhead ammonia gas stream (139), and the liquid ammonia stream (101). Fourteen claims follow;