Method and apparatus for producing ammonia using renewable energy

Abstract

The present disclosure relates to an apparatus for producing ammonia. The ammonia is produced from hydrogen obtained by electrolyzing water. The electrolysis is powered by an energy source of renewable origin, supplemented by a power source obtained from the apparatus during periods of low or no availability of the renewable energy source. To this end, the device is configured such that it can operate in a charging configuration (taking and storing a power source) and a discharging configuration (employing the power source).

Description

Technical Field

[0001] The present invention belongs to the technical field of green ammonia production. In particular, the present invention relates to a method and an apparatus for producing ammonia, wherein renewable energy sources can be used. The present invention further relates to a method for retrofitting a pre-existing ammonia plant.

[0002] introduction

[0003] Challenges in today's chemical industry include transitioning away from fossil fuels and adopting renewable energy sources. Ammonia is considered one of the key chemicals in such a transition. One reason is that, for its part, it can be used as a source of hydrogen, for example in fuel cells. Another reason is that, as an inorganic chemical, it does not require carbon for its production.

[0004] The most widely used industrial process for producing ammonia, the Haber-Bosch process, involves the catalytic reaction of hydrogen and nitrogen. Hydrogen is usually obtained from natural gas, but in today's ideal carbon-free chemistry, it is obtained by electrolysis of water. The latter requires energy, which in a "green" ammonia process is desirably provided by renewable energy sources.

[0005] A general problem with renewable energy sources is presented by the inherent fluctuations in their supply. Renewable energy sources typically exhibit both primary and secondary fluctuations. For example, primary fluctuations in solar energy are due to the day / night cycle. On shorter time scales (such as hours to minutes), secondary fluctuations may be caused by changes in conditions such as wind speed and cloud cover.

[0006] Fluctuations in the supply of renewable energy present problems for the operation of equipment producing green ammonia. If the productivity of ammonia is reduced during a period of low energy supply, the temperature within the equipment may change, causing thermal stress or shock. The life of the ammonia converter (including the ammonia production catalyst) may also be shortened by temperature fluctuations. Therefore, it is desirable to minimize these effects by wisely managing the energy supply and turning down operating conditions. Continuous operation or substantially continuous operation is desirable. When a renewable energy source is unavailable or reduced, such operation generally requires a supplemental energy source.

[0007] WO 2020 / 05521 attempts to solve this problem of a nitric acid production method based on the combustion of ammonia. The reference also relates to the production of ammonia, which is integrated with the production of nitric acid. The method recovers heat energy as electrical energy by turbine expansion of a pressurized liquid gas, wherein the liquid gas is in turn used as a reactant supply for the method. Therefore, liquefied oxygen is used in the production of nitric acid and liquefied nitrogen is used in the production of ammonia. The heat required to evaporate the pressurized liquid gas before it is expanded by a turbine is waste heat generated in the corresponding nitric acid or ammonia production process. Therefore, typically, the electrolysis of water to produce hydrogen for the production of ammonia benefits from energy storage in the production of nitric acid as integrated therewith.

[0008] It is also known from CN112179046 to employ cryogenic energy storage via liquefied gaseous reactants. This reference relates to the production of ammonia and is intended to adapt ammonia production equipment to differences in energy supply. This reference is not concerned with fluctuations in renewable energy supply, but rather with electricity supply for expensive peak electricity prices and reduced off-peak electricity prices. Therefore, a method is disclosed that aims to reduce energy consumption during peak hours by employing energy stored during off-peak hours. This storage is provided by using nitrogen for cryogenic energy storage during off-peak hours, allowing such nitrogen to be released into ammonia synthesis during peak hours. This helps to avoid consuming expensive peak energy to produce nitrogen.

[0009] The aforementioned references do not serve to optimize the energy supply required for the electrolysis reaction to produce hydrogen in the ammonia plant itself, in the case where the electrolysis reaction is operated as a substantially continuous process based on energy from a renewable energy source. In this regard, as well as in terms of judicious energy management and reactant supply in general, it is desirable to provide a method and apparatus that is more optimally suited for the production of green ammonia. In particular, for such a process, if carried out as a substantially continuous process, despite fluctuations in the renewable energy supply. Summary of the invention

[0010] In a first aspect, the present invention relates to an apparatus for producing ammonia, the apparatus comprising:

[0011] (a) a catalytic reactor having a nitrogen inlet for nitrogen feed, a hydrogen inlet for hydrogen feed and an ammonia outlet for produced ammonia;

[0012] (b) an electrolysis cell having a water inlet for water feed, an oxygen outlet for oxygen and a hydrogen outlet for hydrogen, said hydrogen outlet being in fluid communication with the hydrogen inlet of the reactor;

[0013] (c) a nitrogen supply unit having at least one air inlet for an air flow, an oxygen outlet for an oxygen-rich flow and a nitrogen outlet for a nitrogen flow; said nitrogen outlet being in fluid communication with the nitrogen inlet of the reactor;

[0014] (d) a low pressure air compression and adsorber section having an air inlet for an external air feed and an air outlet for compressed air, the air outlet being switchably fluidly connected to an air inlet of an optional nitrogen supply unit and an air liquefaction section or a high pressure air compression unit having an outlet for compressed air in fluid communication with the air liquefaction section, the air liquefaction section including a turboexpander configured to drive a generator to provide a first energy source;

[0015] (e) a liquid air reservoir having a liquid air inlet for liquid air obtained from the air liquefaction section, a closable outlet for the liquid air fluidly connected to the nitrogen supply unit, and a closable outlet for the liquid air fluidly connected to the generator section, the generator section being configured to provide a second energy source and an expanded air stream;

[0016] (f) an electrical control unit configured to supply power to the device;

[0017] Wherein the device has a power supply connection to the renewable energy source and to the first energy source and the second energy source, and wherein the electrical control unit is configured to be switchable between the renewable energy source and the first energy source and the second energy source, including a combination of the first energy source and the second energy source.

[0018] In a second aspect, the present invention provides a method for producing ammonia, the method being carried out in an apparatus as described in the preceding paragraph, the method comprising the following steps:

[0019] (i) obtaining nitrogen from a nitrogen supply unit;

[0020] (ii) obtaining hydrogen from an electrolysis unit;

[0021] (iii) reacting nitrogen and hydrogen under ammonia forming conditions in a catalytic reactor;

[0022] The method comprises operating the device in a charging mode, the charging mode comprising compressing air in a low-pressure air compression and adsorber section to provide LP compressed air; compressing the LP compressed air in a high-pressure air compression unit to provide HP compressed air, subjecting the HP compressed air to expansion and liquefaction in a turboexpander so as to obtain liquefied air; storing the liquefied air in a liquid air storage; feeding air from the liquid air storage to a nitrogen supply unit and / or feeding air from the low-pressure air compression and adsorber section to a nitrogen supply unit;

[0023] Therein the method comprises operating an electrolysis unit with energy from a renewable energy source to provide hydrogen.

[0024] In a further aspect, the present invention provides a method for producing ammonia, the method being carried out in an apparatus as described in the preceding paragraph, the method comprising the steps of:

[0025] (i) obtaining at least a portion of the nitrogen from a nitrogen supply unit;

[0026] (ii) obtaining at least a portion of the hydrogen from an electrolysis unit;

[0027] (iii) reacting nitrogen and hydrogen under ammonia forming conditions in a catalytic reactor;

[0028] The method includes operating the device in a discharge mode, the discharge mode including compressing air in a low pressure air compression and adsorber section to provide LP compressed air; sending the LP compressed air to an air liquefaction section; subjecting the LP compressed air to expansion and liquefaction in a turboexpander to obtain liquefied air; the turboexpander providing a first energy source; storing the liquefied air in a liquid air storage; feeding air from the liquid air storage to a generator section, thereby expanding the air to provide a second energy source and expanded air, feeding air from either or both of the liquid air storage and the expanded air to a nitrogen supply unit, wherein the method includes adjusting the operating rates of the nitrogen supply unit, the electrolysis unit and the catalytic reactor according to the amount of air available to the nitrogen supply unit, and operating a control unit to power the method via the first energy source and the second energy source.

[0029] In yet another aspect, the present invention relates to a method of retrofitting a pre-existing plant for producing ammonia, the pre-existing plant comprising:

[0030] - a catalytic reactor having a nitrogen inlet for nitrogen feed, a hydrogen inlet for hydrogen feed and an ammonia outlet for produced ammonia;

[0031] a hydrogen supply section having a hydrogen outlet for hydrogen, said hydrogen outlet being in fluid communication with a hydrogen inlet of the reactor;

[0032] a nitrogen supply unit having at least one air inlet for an air flow, an oxygen outlet for an oxygen-rich flow and a nitrogen outlet for a nitrogen flow; said nitrogen outlet being in fluid communication with the nitrogen inlet of the reactor;

[0033] - an electrical control unit configured to supply power to the device;

[0034] The method involves adding to a pre-existing device:

[0035] - an electrolysis unit having a water inlet for water feed, an oxygen outlet for oxygen and a hydrogen outlet for hydrogen, said hydrogen outlet being in fluid communication with the hydrogen inlet of the reactor;

[0036] a low pressure air compression and adsorber section having an air inlet for external air feed and an air outlet for LP compressed air, the air outlet optionally being in fluid communication with an air inlet of a nitrogen supply unit and switchably in fluid communication with an air liquefaction section or a high pressure air compression unit having an outlet for compressed air in fluid communication with the air liquefaction section, the air liquefaction section comprising a turboexpander configured to drive a generator to provide a first energy source;

[0037] - a liquid air storage having a liquid air inlet for liquid air obtained from an air liquefaction section, a closable outlet for liquid air fluidly connected to a nitrogen providing unit and a closable outlet for liquid air fluidly connected to a generator section, the generator section being configured to provide a second energy source and an expanded air flow; the generator section having an air outlet fluidly connected to the air inlet of the nitrogen providing unit; and an arrangement such that the device has a power supply connection to a renewable energy source and to a first energy source and a second energy source, and the electrical control unit is configured to be switchable between the renewable energy source and the first energy source and the second energy source, including a combination of the first energy source and the second energy source. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 Parts of a device according to the invention are schematically shown in order to illustrate the charging configuration.

[0039] Figure 2 Portions of a device according to the invention are schematically shown in order to illustrate alternative charging configurations.

[0040] Figure 3 Parts of a device according to the invention are schematically shown in order to illustrate the discharge configuration.

[0041] Figure 4 Portions of a device according to the invention are schematically shown in order to illustrate alternative discharge configurations.

[0042] Figure 5 A schematic diagram depicting an embodiment of an apparatus according to the present invention is shown, indicating process, thermal and power connections. DETAILED DESCRIPTION

[0043] In a broad sense, the present invention relates to an ammonia production plant capable of operating on a renewable energy source by switching between a charging mode and a discharging mode. In particular, this is based on the sensible insight of using a reservoir for liquid air as a tool to achieve said switching capability. More particularly, the present invention also utilizes this insight to combine a liquid air refrigerant with the heat for expansion extracted from the ammonia synthesis.

[0044] The devices and methods disclosed herein are used to better account for long-term secondary fluctuations exhibited by renewable energy sources as well as primary fluctuations. For example, switching from charging mode to discharging mode can be done according to the day / night solar rhythm, but can also be triggered by extended periods of cloud cover or (in the case of wind power) by a lack of wind.

[0045] Thus, the apparatus and method disclosed herein also solve the problem that otherwise conventional energy sources (such as energy sources based on fossil fuels and / or nuclear energy) should be available as a supplement to compensate for fluctuations in the availability of renewable energy sources. Preferably, the apparatus and method disclosed herein operate without any supplementary energy source. Advantageously, the apparatus is provided as one or more modular, local, independent units provided only with renewable energy sources.

[0046] According to the present disclosure, ammonia can be produced by a Haber-Bosch type process, wherein nitrogen and hydrogen undergo a catalytic reaction to form ammonia according to the equation 2H2+N2→NH3. The reaction occurs in a reactor (referred to as a catalytic reactor in the present disclosure) provided with a suitable catalyst bed. The catalyst is generally a promoted iron-containing catalyst, typically a multi-promoted magnetite catalyst. An alternative to the iron catalyst is ruthenium. Therefore, the apparatus comprises (a) a catalytic reactor having a nitrogen inlet for nitrogen feed, a hydrogen inlet for hydrogen feed, and an ammonia outlet for the ammonia produced. Ammonia synthesis is generally carried out at a pressure in the range of 70 to 350 bar and at a temperature in the range of ambient temperature (such as 20°C) to 600°C. Preferably, the pressure is in the range of 130 to 330 bar, wherein a further preferred range is 140 to 250 bar or 280 to 320 bar. The ammonia product thus synthesized is generally decompressed and stored at about 15 to 17 bar. It will be appreciated that obtaining ammonia at atmospheric pressure will require a further reduction in temperature, which is typically achieved via a cooling radiator.

[0047] In most current conventional ammonia plants, hydrogen is provided by fossil fuels such as natural gas. In contrast, the green ammonia plant of the present disclosure operates based on the electrolysis of water to provide hydrogen. Therefore, the plant comprises (b) an electrolysis unit having a water inlet for water feed, an oxygen outlet for oxygen and a hydrogen outlet for hydrogen, the hydrogen outlet being in fluid communication with the hydrogen inlet of the reactor.

[0048] Suitable electrolyzers (electrolyzers) are well known to those skilled in the art. Suitable electrolyzers for large power sources (>0.1MW) are usually bipolar electrolyzers with forced convection of electrolytes. Typically, alkaline electrolyzers can be used. These are mostly operated using 25%-35% KOH (most manufacturers) or 14% NaOH (hydrogen system water electrolyzer). The cathode reaction is usually catalyzed by nickel, which is typically in the form of a porous nickel coating produced in situ by the cathode reduction of a nickel sulfide coating with a high surface area nickel layer, such as Raney nickel or a nickel sulfide coating. The diaphragm used to separate the hydrogen formed by electrolysis is usually made of asbestos, but more modern electrolyzers use composite materials, such as polysulfone or polytetrafluoroethylene based on hydrophilization of finely dispersed zirconium oxide. Suitable alternatives include ceramics supported by nickel mesh, such as NiO or CaTiO-Ni cermets. Water electrolysis can also be carried out using cation exchange membranes, known as solid polymer exchange (SPE) electrolysis. It operates on the basis of a water-swelled cation exchange polymer with protons as an electrolyte. In this article, platinum group metal catalysts are generally used. Preferred types of electrolytic cells include alkaline batteries, polymer electrolyte membrane batteries. Another preferred type of electrolytic unit is a solid oxide electrolyzer unit (SOEC). It is a solid oxide fuel cell that operates in a regenerative mode to achieve the electrolysis of water by using a solid oxide or ceramic, electrolyte to produce hydrogen and oxygen.

[0049] The skilled person is well aware of the different types of electrolysis units, and how to operate them.The apparatus of the present invention is not limited to any particular type of electrolysis cell.

[0050] The nitrogen is usually provided by separating nitrogen from air. In the present disclosure, any such unit is referred to simply as a nitrogen providing unit. Typically, such a nitrogen providing unit is an air separation unit or a nitrogen generating unit. Air separation may be performed by cryogenic distillation of a liquefied gas or by non-cryogenic techniques such as pressure swing adsorption, vacuum pressure swing adsorption or membrane separation. Thus, the apparatus comprises (c) a nitrogen providing unit having at least one air inlet for an air stream, an oxygen outlet for an oxygen-enriched stream and a nitrogen outlet for a nitrogen stream; said nitrogen outlet being in fluid communication with a nitrogen inlet of the reactor;

[0051] The low pressure compression and adsorber section is used to compress the air to a pressure of typically 8 to 20 bar gauge, such as 8 to 10 bar gauge. The air is cleaned in the compressor inlet filter and is typically compressed using a two-stage compressor. The outlet pressure value represents a desired optimum between typical design parameters for the nitrogen generation unit and the maximum pressure ratio that can still be managed by a standard non-adiabatic compressor. The air from the compressor is sent to, for example, a first thermal storage that utilizes an external heat source of about 235 to 250° C. with a sufficient temperature difference to drive sensible heat into the stored air.

[0052] Compressed air is usually passed through CO2 / H2O removal stage. After CO2 / H2O is removed, the purified air enters the aftercooler. Before being sent to the method air cooler, the compressed air is further precooled in the spray cooler. Typically, the wire mesh at the top of the spray cooler acts as a water separator, to separate the air stream from its crude moisture component before the air stream enters the subsequent molecular sieve adsorber. In some configurations, it is conceivable to use TSA (temperature swing absorber) to replace more standard adsorbers. Water, CO2 and hydrocarbons are usually absorbed by one of the two molecular sieve adsorbers. When one molecular sieve is in operation, the other molecular sieve can be regenerated.

[0053] According to the present invention, the apparatus comprises (d) a low pressure air compression and adsorber section having an air inlet for external air feed and an air outlet for compressed air. The air outlet is switchably fluidly connected to an air liquefaction section or a high pressure air compression unit having an outlet for compressed air in fluid communication with the air liquefaction section, the air liquefaction section comprising a turbo expander configured to drive a generator to provide a first energy source. The air outlet is optionally in fluid communication with an air inlet of a nitrogen supply unit.

[0054] The aforementioned switchable fluid connection enables the device to operate in a mode of further compressing the LP compressed air and a mode of bypassing the HP compression, wherein the LP compressed air is directly sent to the air liquefaction section. In charging mode, renewable energy from an external source is available. In this mode, the device is switched so that the LP compressed air is further compressed in the HP air compression unit. The operating pressure in the unit is typically in the range of 50 to 200 bar gauge, preferably 100 to 200 bar gauge. Therefore, the air liquefaction unit downstream of the HP compression unit can function optimally to establish cryogenic energy storage. In discharge mode, the HP compression unit is bypassed. It should be understood that, in itself, this reduces the energy consumption of the device. In particular, the configuration in discharge mode can effectively recover energy from the cryogenic energy storage by judiciously using the liquefied air stored in the air liquefaction section. As further discussed below, this involves using liquefied air to effectively recover energy in the generator section. The device is configured so that, in particular when operating in discharge mode, the amount of liquefied air sent to the nitrogen supply unit can be reduced compared to operation in charging mode. In a preferred embodiment, the apparatus comprises a connection for air from the adsorber (in the LP compression and adsorber unit) to the nitrogen supply unit. This allows to further reduce or even completely avoid the use of liquefied air in the nitrogen supply unit. This, in turn, allows to increase the amount of liquefied air sent to the generator section, so as to allow said section to provide a larger amount of energy that can be used as a second energy source.

[0055] Preferably, the apparatus of the present invention utilizes an industrial concept, such as that used for air separation units, known as "cold box" technology. A cold box is a self-supporting structure that protects cryogenic equipment, such as brazed plate-fin heat exchangers, core-in drums, distillation columns, piping, valves and instrumentation. In the apparatus of the present invention, the cold box is preferably used for nitrogen generation (i.e., nitrogen providing unit) in combination with cold storage of ammonia. A cooling radiator is provided upstream of the latter, which is preferably also integrated in the cold box, for decompressing ammonia from storage pressure (typically 15 to 17 bar gauge) to atmospheric pressure.

[0056] It should be understood that clean and compressed air (from LP compression or HP compression) enters the liquid air / nitrogen to provide a cold box. The molecular sieve adsorber is a cylindrical container filled with molecular sieve fillers, which are supported between the sieves at the air inlet and outlet. The molecular sieve filler absorbs moisture, carbon dioxide and hydrocarbons from the air flowing through it, and because the filler has a given maximum capacity for these components, it must be regenerated after a given time, and regeneration is achieved by passing a hot dry gas stream through the bed in the opposite direction to the air flow: after regeneration, the adsorber must be cooled with cold dry gas. The purge enriched air from the cold box is reheated in the hot storage section and used for the regeneration of the adsorber.

[0057] In a cold box turboexpander, liquefaction of the air is achieved, followed by distillation of the product (air / nitrogen) stream and the purge enriched air into a rectification column. The cold box is a fully insulated packaged unit containing a plate-fin heat exchanger in which the gas and liquid streams are divided into a number of channels separated from each other by flat plates. The air is cooled from approximately ambient temperature to the liquefaction temperature, while the outgoing gas stream is heated almost to the temperature of the incoming air. The turboexpander is designed to operate under nearly isentropic expansion conditions: radial inflow is generally capable of achieving such conditions, and is efficiently converted to electricity generation via a synchronous generator. It consists of a housing, a wheel and a generator assembled on a common shaft, and an oil supply system. The clean air stream to be cooled enters the turbine under pressure and drives the wheel coupled to the generator. The expansion of the gas through the turbine reduces the gas temperature at the outlet to close to the liquefaction temperature of the air.

[0058] Thus, the air liquefaction section comprises a turboexpander configured to drive a generator to provide a first energy source. The first energy source, as applicable in charging mode, is preferably used to supplement the renewable energy source.

[0059] On the liquid air side of the air liquefaction section, the outlet is connected to the air inlet of the liquid air storage. Such storage is provided with the necessary insulating material to maintain a cold environment sufficient to keep the air in liquid form. The liquid air storage is configured as a key unit for enabling the device to operate in charging and discharging modes. To this end, the liquid air storage has a closable outlet for liquid air that is fluidly connected to the nitrogen supply unit. By allowing closure or opening, the outlet enables an operational selection to provide liquid air to the nitrogen supply unit or not to provide liquid air to the nitrogen supply unit. Preferably, a fluid connector is provided between the liquid air storage and the nitrogen supply unit, and the fluid connector is configured to adjust the amount of liquid air sent to the nitrogen supply unit. The liquid air storage further has a closable outlet for liquid air that is fluidly connected to the generator section. In addition, the connector is preferably configured to adjust the amount of liquid air sent to the generator section. It should be understood that the above-mentioned closable connectors can be completely separated or can be combined. In the former case, the liquid air reservoir may be provided with two closable outlets for two corresponding fluid connections. In the latter case, the liquid air reservoir may be provided with a single outlet connected to a three-way valve or other system, allowing the connection to be switched from the outlet to either or both of the nitrogen supply unit and the generator section. Preferably, such a switch or switchable connection is configured to regulate the amount of liquid air flowing to either or both of the nitrogen supply unit and the generator section.

[0060] The generator section is configured to provide a second energy source and an expanded air flow. To this end, the generator section comprises, in sequence, an evaporator having a heat source, an expansion turbine mechanically connected to an electrical generator, and preferably also another heat exchanger. The latter is used to provide gas with a suitable temperature (typically about 100° C.) for the regeneration of the adsorber. The generator section optionally has an air outlet fluidly connected to the air inlet of the nitrogen supply unit. Alternatively, or in combination with the above-mentioned air outlet, the generator section has an air outlet allowing the expanded air from the generator section to be discharged into the atmosphere, preferably after being used to regenerate one or more adsorbers as described above. The generator section upstream of the expansion typically operates in a pressure range of 120 to 250 bar, such as 180 to 220 bar, for example at 200 bar.

[0061] The device has a power connection with the renewable energy source and with the first energy source and the second energy source. In order to enable the device to operate in a charging mode and in a discharging mode, the device is provided with an electrical control unit, which is configured to switch between the renewable energy source and the first energy source and the second energy source. Therefore, the control unit is configured to power the device and to achieve this using either or both of an external energy source based on renewable energy and using an internally provided energy source.

[0062] The renewable energy source is preferably selected from the group consisting of solar energy, wind energy, water energy, tidal energy, geothermal energy, biomass energy and combinations thereof. Among them, in particular, solar energy and wind energy are prone to strong fluctuations, such as fluctuations caused by day and night in the case of solar energy, and fluctuations caused by weather changes in the case of both solar energy and wind energy. In order to best benefit from the judicious configuration of the devices disclosed herein, the renewable energy source is preferably solar energy, wind energy or a combination thereof.

[0063] In addition to being configured to cope with fluctuations in the power supply from renewable source energy, the apparatus is preferably also configured to thereby allow for thermal management, preferably improved thermal management.

[0064] To this end, the apparatus preferably comprises a heat storage unit configured to receive heat from the various units as provided by the relevant method steps. These units include the catalytic reactor, the low-pressure air compression and adsorber section and the high-pressure air compression unit. The heat storage unit is configured to provide heat to the generator section (i.e. the section used as an additional internal energy source during operation of the apparatus in the discharge mode).

[0065] The operation of the device in charging and discharging operations will be explained hereinafter with reference to the methods in which the device is configured to operate.

[0066] In broad terms, the process of the invention is performed as a substantially continuous process for producing ammonia. The process is performed in a charging mode at times when the renewable energy source is abundant and in a discharging mode at other times.

[0067] During charging mode, the air is compressed in the LP stage (preferably to about 10 bar gauge) and the heat generated is preferably stored in a heat storage unit. The heat storage unit also stores heat from the reaction of nitrogen and hydrogen to form ammonia. The LP air passes through the adsorber to the HP compression stage, where the air is compressed, preferably to about 150 bar gauge, cooled, and converted to liquid air for storage in a tank. The liquid air is then fed to a nitrogen supply unit, typically an air separation unit (ASU) or a nitrogen generation unit (NGU), to provide a nitrogen flow sufficient for full operation of the ammonia synthesis reactor. In this mode, the electrolysis unit is operated by a renewable energy source to provide the required hydrogen flow. In an alternative embodiment, the air for the ASU or NGU is drawn from the adsorber output rather than from storage as liquid air.

[0068] During the discharge mode, the ammonia synthesis reactor is operated at a lower rate. This is typically reduced to about 30% to 90% of the charge mode, such as 40% to 80%, such as 50% to 70%. This enables the nitrogen supply unit (such as an ASU or NGU) and the electrolysis unit to also operate at a lower rate. The reduced rate of the nitrogen supply unit corresponds to a lower demand for liquid air by the unit. This allows the HP compression stage to be bypassed. A smaller amount of liquid air is extracted from the liquid air tank, which is sufficient to supply the lower nitrogen demand of the ASU / NGU. A large amount of liquid air is extracted from the tank, compressed and heated, and expanded on the generator. Thus, the pressure is typically in the range of about 100 bar gauge to about 250 bar gauge, such as 180 bar gauge to 220 bar gauge, for example 200 bar gauge. The temperature is typically in the range of about 250°C to about 650°C, such as 500°C to 600°C, for example 550°C. Higher pressures and temperatures bring the advantage of corresponding higher power output.

[0069] The generator provides power during the discharge mode to operate the method, including operating the electrolysis unit.In an alternative embodiment, the air supply to the ASU / NGU is provided by expanded air rather than liquid air, as discussed above with reference to the possible connection of air from the LP compression and adsorber section to the nitrogen supply section.

[0070] Optionally, the expanded air is used to regenerate the adsorber (eg, two towers are operated in parallel, one in operation and one undergoing regeneration, and are alternated).

[0071] Thus, in charging mode, the method comprises operating the electrolysis unit using energy from a renewable energy source to provide hydrogen. Preferably, the method thereby further comprises storing heat from compressing the air in the low pressure air compression and adsorber section and from reacting nitrogen and hydrogen in the catalytic reactor in a heat storage unit.

[0072] In the discharge mode, the LP compressed air is sent to the air liquefaction section. In this mode, air is fed from the liquid air storage to the generator section, thereby expanding the air so as to provide the second energy source and the expanded air. The expanded air, possibly in addition to the air from the liquefied air storage, is fed to the nitrogen supply unit. Thus, the method includes adjusting the operating rates of the nitrogen supply unit, the electrolysis unit and the catalytic reactor according to the amount of air available to the nitrogen supply unit. The discharge mode involves operating the control unit so as to power the method by the first energy source and the second energy source.

[0073] It will be appreciated that various combinations of power sources may be applied. For example, it is conceivable that in the discharge mode, in addition to the energy provided from the generator section, some energy from a renewable external energy source is available. The skilled person will be able to adjust the operation of the apparatus accordingly. For example, by having a smaller reduced operating rate in the nitrogen supply unit (and correspondingly the other chemical process units).

[0074] As previously mentioned, in a further aspect, the present invention may also be applied to a method for modifying a pre-existing device for producing ammonia (i.e., a modification method). The pre-existing ammonia device will typically be a "grey" ammonia device, operating on the basis of hydrogen produced from hydrocarbons. Thus, typically, the pre-existing ammonia device will include corresponding sections, including desulfurization, catalytic shifting, carbon dioxide removal, and catalytic methanation. Whether or not such sections will continue to operate as a source of alternative hydrogen in such devices, the modification method of the present invention will be used to add a water electrolysis unit as described above, as well as a low-pressure air compression and adsorber section, a liquid air storage, all of which are configured as previously described. It should be understood that the modification method needs to be arranged so that the device has a power connection with a renewable energy source and with the above-mentioned first energy source and second energy source, and the electrical control unit is configured to be switchable between a renewable energy source and a first energy source and a second energy source, including a combination of a first energy source and a second energy source. The method preferably includes adding any unit and / or connector to the pre-existing device, which allows modernization to produce a device as described above in any of its embodiments.

[0075] Preferably, the plant of the invention is built as a new base plant. In fact, an advantage of the plant of the invention is that it requires much less chemical conversion technology than a "grey" ammonia plant. Therefore, it can be built in a wide variety of locations and on a wide variety of scales.

[0076] In summary, the present disclosure relates to an apparatus for producing ammonia. Ammonia is produced from hydrogen obtained by electrolysis of water. The electrolysis is powered by energy from a renewable source, supplemented by power obtained from the apparatus during periods of low or no availability of renewable energy. To this end, the apparatus is configured so that it can operate in a charging configuration (obtaining and storing power) and a discharging configuration (employing said power).

[0077] The present invention will be further described below with reference to the non-limiting accompanying drawings discussed below. The units and streams shown in the accompanying drawings are general representations. In addition, as examples of how to implement the present invention, specific numbers are given below for possible amounts, pressures and temperatures at various stages. The disclosure of the embodiments of the apparatus and method of the present invention is clearly not limited by the specific numbers.

[0078] Figure 1is a schematic diagram showing the charging mode configuration of the device applied to the present invention. Air (flow (a), total air intake 215000Nm 3 / h) is compressed to 10 bar at 170°C in the LP compressor (1); after heating to 230°C in the first heat exchanger (2) and cooling to 60°C to 80°C in the second heat exchanger (3), the LP compressed air (b) is directed to the HP compressor (5) via the adsorber section (4), where the air is compressed to 150 bar at 550°C. In the heat exchanger (6), the HP compressed air (c) is cooled to 100°C and sent to the cold box section (7). In the downstream turboexpander (8) (which is optionally included in the cold box section), the air is liquefied and sent (stream (d); 215000 Nm 3 / h) to the liquid air storage tank (9); the turboexpander is configured to drive a generator (10), which provides a first energy source that generates 2 to 4 MW. The liquid air (d) from the storage tank (9) is connected to a nitrogen supply unit (12) via a pump (11) (typically a cryogenic pump) at a rate of 8.74 t / h, resulting in 2810 Nm 3 / h of nitrogen production. The charging mode as depicted is typically operated for a period of 12 hours.

[0079] Figure 2 is a schematic diagram showing an alternative charging mode configuration for the device of the present invention. Air (flow (a), total air intake 222000Nm 3 / h) is compressed to 10 bar in the LP compressor (1) at 170° C.; after heating to 230° C. in the first heat exchanger (2) and cooling to 60° C. to 80° C. in the second heat exchanger (3), the LP compressed air (b) is led through the adsorber section (4). Thus, a portion of the LP compressed air at 9.5 bar gauge and 40° C. (stream (b'), 7000 Nm 3 / h) is sent to the nitrogen supply unit (12), resulting in 2810Nm 3 / h of nitrogen production. The remaining part (b") of the LP compressed air is sent to the HP compressor (5), where the air is compressed to 150 bar at 550°C. In the heat exchanger (6), the HP compressed air (c) is cooled to 100°C and sent to the cold box section (7). In the downstream turboexpander (8), the air is liquefied and sent (stream (d); 215000Nm 3 / h) to a liquid air storage tank (9); the turboexpander is configured to drive a generator (10) which provides a first energy source producing 2 to 4 MW. The charging mode as depicted is typically operated for a period of 12 hours.

[0080] Figure 3Schematic diagram showing the discharge mode configuration of the device applied to the present invention. Air (flow (a), total air intake 5000Nm 3 / h) is compressed to 10 bar in the LP compressor (1) at 170°C; after heating to 230°C in the first heat exchanger (2) and cooling to 60 to 80°C in the second heat exchanger (3), the LP compressed air (b) is directed to the cold box section (7) via the adsorber section (4). In the downstream turboexpander (8), the air is liquefied and sent (stream (d); 215000Nm 3 / h) to the liquid air storage tank (9); the turbo expander is configured to drive a generator (10), which provides a first energy source. The first liquid air flow (d') from the storage tank (9) is connected to the nitrogen supply unit (12) via a pump (11) at a rate of 8.74 t / h, resulting in 2810 Nm 3 / h of nitrogen production. A second liquid air stream (d") is sent to another compressor (13) at a rate of 250 t / h and compressed, and heated via a heat exchanger (14). The resulting compressed air (stream (e) at 200 bar and 550°C) is sent to a generator section (15). This section produces an expanded air stream (f), which is brought to a temperature of 100°C by a heat exchanger (17) and is used for regeneration of one or more adsorbers in the adsorber section (4) and discharged to the atmosphere (not shown). The generator section is configured to drive a generator (16) which provides a second energy source that generates 44 MW. The discharge mode as depicted is typically operated for a period of 12 hours.

[0081] Figure 4 is a schematic diagram showing an alternative discharge mode configuration for the apparatus of the present invention. Air (flow (a), total air intake 5000Nm 3 / h) is compressed to 10 bar in the LP compressor (1) at 170°C; after heating to 230°C in the first heat exchanger (2) and cooling to 60 to 80°C in the second heat exchanger (3), the LP compressed air (b) is directed to the cold box section (7) via the adsorber section (4). In the downstream turboexpander (8), the air is liquefied and sent (stream (d); 215000Nm 3 / h) to a liquid air storage tank (9); air is extracted from the tank, whereby a liquid air stream (d") is sent to another pump (13) at a rate of 250 t / h and pressurized and heated via a heat exchanger (14). The resulting compressed air (stream (e) at 200 bar and 550°C) is sent to a generator section (15). This section produces an expanded air stream, a portion of which (5000 Nm at 9.5 bar and 40°C) 3 / h flow (f')) is sent to the nitrogen supply unit (12), resulting in 2000Nm 3 / h of nitrogen production. Another part (f") of the expanded air flow is passed through a heat exchanger (17) to a temperature of 100°C and is used for regeneration of the adsorber (18) and discharged to the atmosphere. The generator section is configured to drive a generator (16) which provides a second energy source that produces 44 MW. The discharge mode as depicted is typically operated for a period of 12 hours.

[0082] Figure 5 The ammonia plant of the present invention is schematically represented. The ammonia synthesis stream is depicted in solid lines. Thus, ammonia is produced and stored in an ammonia synthesis and product storage section (501), from which an ammonia product stream (5a) can be obtained. The ammonia production and storage section comprises a reactor (not shown), to which nitrogen and hydrogen can be fed. In the method, nitrogen (5b) can be obtained from either or both of a liquid nitrogen storage unit (502) or a nitrogen supply unit (503), both of which are connected to the ammonia synthesis and product storage section (501). Hydrogen (5c) is produced by water (input not shown) in an electrolysis unit (504), which is connected to the ammonia synthesis and product storage section (501). The device further has an inlet for air, which is subjected to low-pressure compression in a LP compression unit (505). The LP compression unit (505) has a switchable connection with the HP compression unit (506), allowing the LP compressed air (5d) to be further compressed to obtain HP compressed air (5e). The HP compression unit (506) is connected to an air liquefaction section, which includes a refrigeration unit (507) connected to a turbo expander (508) to allow the cooled HP air (5f) to expand, thereby generating a power source (not shown) and liquid air (5g). The turbo expander (508) has a connection for the liquid air (5g) to a liquid air storage unit (509). The liquid air storage unit (509) has a closable connection for the liquid air (5g) to a generator section (other optional connections not shown), which includes a liquid air compression unit (510) connected to an evaporation unit (511), which is further connected to a turbo expander (512), thereby allowing the liquid air (5g) obtained from the liquid air storage unit (509) to be compressed into compressed liquid air (5h) at a pressure of 200 bars and evaporated, thereby generating an air stream (5i), which is expanded in the turbo expander (512). Thus, the air stream (5h) can be sent to the nitrogen supply unit (503), which has a switchable connection to the generator section, i.e. to the turboexpander (512). The nitrogen supply unit (503) also has a switchable connection on the downstream side of the LP compression unit (505), allowing the LP compressed air (5d) to be sent to the nitrogen supply unit (503).

[0083] The figure further shows thermal connections (5j) and (5k) and power connections (51), (5m) and (5n).

[0084] Thus, the apparatus comprises a hot storage section (513) in thermal communication with the LP compression unit (505), the HP compression unit (506) and the turbo expander unit (512) of the generator section, allowing heat exchange (5j) with any one or more of these units. The apparatus further comprises a cold storage section (514) in thermal communication with any one or more of the refrigeration unit (507), the evaporation unit (511) and the ammonia synthesis and product storage section (501). Such thermal communication is cryogenic and is preferably entirely contained in the cold box section. Thus, a cryogenic temperature is maintained for the cold stream (5k) between the cooling radiator from the ammonia synthesis and product storage section (501), the liquid air evaporation unit (511) and the cold storage section (515).

[0085] The power connections as shown relate to power generated by the process carried out in the plant and power from renewable energy sources. Thus, the renewable energy unit (515) provides power (51) to the electrolysis unit (504). The latter unit may also receive power (5m) from the generator section. The power output from the plant may be managed by the power output unit (516) and may also be used to power the ammonia synthesis and product storage section (501).

Claims

1. A device for producing ammonia, comprising: (a) a catalytic reactor having a nitrogen inlet for nitrogen feed, a hydrogen inlet for hydrogen feed and an ammonia outlet for produced ammonia; (b) an electrolysis cell having a water inlet for water feed, an oxygen outlet for oxygen and a hydrogen outlet for hydrogen, said hydrogen outlet being in fluid communication with said hydrogen inlet of said reactor; (c) a nitrogen supply unit having at least one air inlet for an air flow, an oxygen outlet for an oxygen-enriched flow and a nitrogen outlet for a nitrogen flow; said nitrogen outlet being in fluid communication with said nitrogen inlet of said reactor; (d) a low pressure air compression and adsorber section having an air inlet for external air feed and an air outlet for LP compressed air, the air outlet optionally being in fluid communication with the air inlet of the nitrogen supply unit and switchably in fluid communication with an air liquefaction section or a high pressure air compression unit having an outlet for compressed air in fluid communication with the air liquefaction section, the air liquefaction section including a turboexpander configured to drive a generator to provide a first energy source; (e) a liquid air reservoir having a liquid air inlet for liquid air obtained from the air liquefaction section, a closable outlet for liquid air fluidly connected to the nitrogen supply unit, and a closable outlet for liquid air fluidly connected to a generator section, the generator section being configured to provide a second energy source and an expanded air flow; (f) an electrical control unit configured to supply power to the device; wherein the device has a power supply connection to a renewable energy source and to the first energy source and the second energy source, and wherein the electrical control unit is configured to be switchable between the renewable energy source and the first energy source and the second energy source, including a combination of the first energy source and the second energy source.

2. The apparatus according to claim 1, further comprising: (g) a heat storage unit configured to receive heat from a heat generating unit selected from the group consisting of the catalytic reactor, the low-pressure air compression and adsorber section, the high-pressure air compression unit, and combinations thereof, the heat storage unit configured to provide heat to the generator section.

3. The apparatus according to claim 1 or 2, wherein the renewable energy source is selected from the group consisting of solar energy, wind energy, water energy, tidal energy, geothermal energy, biomass energy and combinations thereof.

4. The apparatus according to claim 3, wherein the renewable energy source is solar energy, wind energy or a combination thereof.

5. The apparatus of claim 4, wherein the renewable energy source is solely solar energy.

6. The apparatus of claim 5, wherein the air outlet for LP compressed air is in fluid communication with an air inlet of the nitrogen providing unit.

7. Apparatus according to any preceding claim, wherein the generator section has an air outlet fluidly connected to an air inlet of the nitrogen providing unit.

8. A method for producing ammonia, the method being carried out in a plant according to any one of the preceding claims, the method comprising the steps of: (i) obtaining at least a portion of the nitrogen from the nitrogen supply unit; (ii) obtaining at least a portion of the hydrogen from the electrolysis unit; (iii) reacting said nitrogen and said hydrogen in said catalytic reactor under ammonia forming conditions; The method includes operating the apparatus in a charging mode, the charging mode including compressing air in the low pressure air compression and adsorber section to provide LP compressed air; compressing the LP compressed air in the high-pressure air compression unit to provide HP compressed air, subjecting the HP compressed air to expansion and liquefaction in the turboexpander to obtain liquefied air; storing the liquefied air in the liquid air storage; feeding air from the liquid air storage to the nitrogen supply unit and / or feeding air from the low pressure air compression and adsorber section to the nitrogen supply unit; Wherein the method comprises operating the electrolysis unit using energy from the renewable energy source to provide the hydrogen.

9. The method of claim 8, comprising storing heat from compressing air in the low pressure air compression and adsorber section and from reacting the nitrogen and the hydrogen in the catalytic reactor in a heat storage unit.

10. A method for producing ammonia, the method being carried out in the apparatus according to any one of claims 1 to 7, the method comprising the following steps: (iv) obtaining at least a portion of the nitrogen from the nitrogen supply unit; (v) obtaining at least a portion of the hydrogen from the electrolysis unit; (vi) reacting said nitrogen and said hydrogen in said catalytic reactor under ammonia forming conditions; The method includes operating the apparatus in a discharge mode, the discharge mode including compressing air in the low pressure air compression and adsorber section to provide LP compressed air; sending the LP compressed air to the air liquefaction section; subjecting the LP compressed air to expansion and liquefaction in the turboexpander to obtain liquefied air; The turboexpander provides a first energy source; the liquefied air is stored in the liquid air reservoir; air from the liquid air reservoir is fed to the generator section, thereby expanding the air to provide a second energy source and the expanded air, and air from either or both of the liquid air reservoir and the expanded air is fed to the nitrogen supply unit, wherein the method includes adjusting the operating rates of the nitrogen supply unit, the electrolysis unit and the catalytic reactor according to the amount of air available to the nitrogen supply unit, and operating the control unit to power the method with the first energy source and the second energy source.

11. The method of claim 10, comprising using heat from a heat storage unit configured to receive heat from a heat generating unit selected from the group consisting of the catalytic reactor, the low pressure air compression and adsorber section, the high pressure air compression unit, and combinations thereof, the method comprising using heat from the heat storage unit to heat air in the generator section.

12. A method of retrofitting a pre-existing plant for producing ammonia, the pre-existing plant comprising: - a catalytic reactor having a nitrogen inlet for nitrogen feed, a hydrogen inlet for hydrogen feed and an ammonia outlet for produced ammonia; - a hydrogen supply section having a hydrogen outlet for hydrogen, said hydrogen outlet being in fluid communication with said hydrogen inlet of said reactor; a nitrogen supply unit having at least one air inlet for an air flow, an oxygen outlet for an oxygen-enriched flow and a nitrogen outlet for a nitrogen flow; said nitrogen outlet being in fluid communication with said nitrogen inlet of said reactor; - an electrical control unit configured to supply power to the device; The method comprises adding to the pre-existing device: - an electrolysis unit having a water inlet for water feed, an oxygen outlet for oxygen and a hydrogen outlet for hydrogen, said hydrogen outlet being in fluid communication with said hydrogen inlet of said reactor; a low pressure air compression and adsorber section having an air inlet for external air feed and an air outlet for LP compressed air, the air outlet optionally being in fluid communication with the air inlet of the nitrogen supply unit and switchably in fluid communication with the air liquefaction section or a high pressure air compression unit having an outlet for compressed air in fluid communication with the air liquefaction section, the air liquefaction section comprising a turboexpander configured to drive a generator to provide a first energy source; a liquid air reservoir having a liquid air inlet for liquid air obtained from the air liquefaction section, a closable outlet for liquid air fluidly connected to the nitrogen providing unit and a closable outlet for liquid air fluidly connected to a generator section, the generator section being configured to provide a second energy source and an expanded air flow; the generator section having an air outlet fluidly connected to the air inlet of the nitrogen providing unit; and arranged so that the device has a power connection to a renewable energy source and to the first energy source and the second energy source, and the electrical control unit is configured to be switchable between the renewable energy source and the first energy source and the second energy source, including a combination of the first energy source and the second energy source.

13. The method of claim 12, further comprising adding a heat storage unit to the pre-existing equipment, the heat storage unit being configured to receive heat from a heat generating unit selected from the group consisting of the catalytic reactor, the low pressure air compression and adsorber section, the high pressure air compression unit, and combinations thereof, the heat storage unit being configured to provide heat to the generator section.

14. A method according to claim 12 or 13, comprising adding a connection for fluid communication between the air outlet for LP compressed air and an air inlet of the nitrogen supply unit.

15. A method according to any one of claims 12 to 14, comprising adding a connection for fluid communication between an air outlet of the generator section and an air inlet of the nitrogen providing unit.

Images