Device and method for using ammonia synthesis plants operated using renewable energies

Abstract

The invention relates to a simplified method and to a corresponding device that can be used to supply waste heat from ammonia synthesis plants, in which the hydrogen required to produce the ammonia is produced with the aid of water electrolysis, for further application with the aid of low-pressure steam. In the method and the corresponding device, low-pressure steam at a temperature of less than 200 °C and with a pressure of 5 to 15 bar is generated from the waste heat of the ammonia synthesis plant, said steam being usable for further applications. By using low-pressure steam, significant economical advantages can be achieved in comparison to the conventional use of medium-pressure steam when the method is carried out using discontinuous power sources. The invention further relates to devices which are designed to carry out such methods and to plants which have a part for generating ammonia and a part for utilizing waste heat from the aforementioned part, said second part being formed from the specified device.

Description

[0001] Device and method for the use of ammonia synthesis plants powered by renewable energies

[0002] Description

[0003] The present invention relates to a simplified process by which waste heat from ammonia synthesis plants, in which the hydrogen required for ammonia production is produced by water electrolysis, can be further utilized with the aid of low-pressure steam. The present invention further relates to devices designed to carry out such processes and to plants comprising a plant section for producing ammonia and a plant section for utilizing waste heat from this plant section, wherein this second plant section is formed from the specified device.

[0004] State of the art

[0005] Ammonia is a fundamentally important substance for the production of fertilizers and is now produced in large-scale plants on a multi-ton scale. This typically involves the Haber-Bosch process, in which nitrogen and hydrogen are directly reacted to produce ammonia.

[0006] In plants for the production of ammonia using the Haber Bosch process, a large amount of waste heat is generated because the reactant gases, nitrogen and hydrogen, must be heated to high temperatures of 400 to 500°C for the reaction to ensure optimal efficiency of the catalyst used. Since the reaction is exothermic (see the reaction equation below), the mixture heats up further during the reaction and must subsequently be cooled to significantly lower temperatures to condense the ammonia formed and separate residual reactant gases. kJ / mol (AH 298K = -46.14 kJ / mol)

[0007] Cooling is usually carried out using water as a cooling medium, which absorbs the heat from the gas mixture, which can then be used in further processes.

[0008] In today's typical plants, this utilization occurs by heating water as a cooling medium to temperatures above approximately 450°C in order to operate a steam turbine and a generator for electricity generation. To this end, the ammonia synthesis plant, for example, is thermally coupled to the waste heat system in such a way that the gas flowing out of the ammonia synthesis plant first passes through a heat exchanger where some of the heat is transferred to the water, and is then guided to a position upstream in the waste heat system where residual heat can be transferred to the water via a second heat exchanger. Using the heat transferred to the water at two points in this way, the water is heated in two stages to the temperature required to operate the steam turbine.

[0009] In order to make effective use of the temperature from the ammonia synthesis plant, the waste heat system is designed to operate at a higher temperature in the range of approximately 250°C to 300°C at a system pressure of approximately 40 bar (medium pressure steam or MD steam) or 300°C to 350°C at a system pressure of approximately 125 bar (high pressure steam or HP steam). If the steam is superheated with the hot gas from the ammonia converter, temperatures can even reach around 400°C. If other heat sources are used, e.g. hot exhaust gas from the primary reformer in a conventional ammonia plant, the temperatures of the superheated steam can reach over 500°C. Therefore, part of the waste heat system in the area between the heat exchanger and the steam turbine must be designed for higher temperatures and pressures.

[0010] For example, CN 117 599 703 A discloses a plant with a unit for producing ammonia. The hot ammonia product is cooled to a temperature of 210 to 220°C in a sequence of steam heaters, waste heat boilers, and water heaters. These units are connected in series so that the hot ammonia gas first passes through the steam heater, then the waste heat boiler, and finally the water heater. All of these units are operated with water as the cooling medium, with the water passing through the plant components in reverse order. The product produced is highly heated steam with, for example, a pressure of 4.0 MPaG (40 bar) and a temperature of 400°C.

[0011] CN 117 585 686 A describes a plant with a unit for producing ammonia, in which ammonia is sequentially passed through a steam heater, waste heat boiler, and water heater. Water, as a coolant, passes through this sequence in reverse, producing highly heated steam.

[0012] CN 117 566 760 A generally describes the use of solar energy to operate an ammonia synthesis plant.

[0013] A conventional (i.e., typically natural gas-fired) plant design as described above relies on a continuous energy source for economical operation. This poses a significant problem for the operation of corresponding plants using renewable energy sources such as solar or wind power (due to changing annual precipitation patterns, this can also affect hydropower), as these are not always consistently available, while power generation using steam generators requires a constant energy supply. If this is not available, the steam generator must be shut down, and the cooling medium of the waste heat system may need to be cooled by other means.On the other hand, depending on the location, operating an ammonia synthesis plant with renewable energy, particularly solar and / or wind energy, can be very economically advantageous. Firstly, rising prices for conventionally generated energy are expected as a result of the decarbonization of the global economy, and secondly, the costs of solar and wind energy have fallen sharply in recent years. The costs of plant components used to generate electricity in conventional ammonia synthesis plants are a significant disadvantage if the plant cannot operate at 100% capacity.Against this background, there is a need for a cost-effective process and a corresponding device for utilising the waste heat from ammonia synthesis plants, which can be operated economically even in the event of inconsistent plant capacity utilisation due to lulls or times of the year when renewable energy is less available.

[0014] Another goal in ammonia synthesis is to produce the hydrogen required for ammonia synthesis not from methane (because conventional technology also releases carbon dioxide), but through water electrolysis. Obviously, plants in which the hydrogen required for ammonia synthesis is produced through hydrogen electrolysis require a different setup upstream of the ammonia production unit than conventional plants because the entire process for generating make-up gas (a hydrogen-nitrogen mixture with, if necessary, inert argon and methane) from methane and water is not required, but rather replaced by water electrolysis units. In this way, an ammonia synthesis plant can be operated entirely "green" or without carbon dioxide production (while simultaneously utilizing renewable electrical energy).

[0015] The present invention deals with the problem of providing such largely or completely carbon dioxide-neutral ammonia synthesis plants, or with the economic use of waste heat from such plants.

[0016] Description of the invention

[0017] To solve the problems described above, the invention proposes using the waste heat from an ammonia synthesis plant, in which the hydrogen required for the production of ammonia is produced by means of water electrolysis, not via a medium-pressure or high-pressure steam system and a downstream steam turbine, but via a low-pressure steam system in which the "cooling water" is fed into the cooling system at a significantly lower temperature and pressure. Although this cooling water is then no longer available for the generation of electricity, it can be used as a heat source in other technical processes, thus saving costs for the plant components used for electricity generation.In addition, the use of low-pressure steam instead of medium-pressure steam allows the entire waste heat recovery system to be designed for the lower pressure, which also results in significant cost savings compared to a conventionally designed system.

[0018] Accordingly, a first aspect of the present invention relates to a process for utilizing waste heat from ammonia synthesis plants in which the hydrogen required for the production of ammonia is produced by means of water electrolysis, wherein waste heat from the ammonia synthesis plant is transferred to water as a cooling medium via a heat exchanger, and wherein the water is heated to a temperature of less than 200°C at a pressure in the range of 5 to 15 bar. Preferably, the water in this process is used as steam, i.e. at a temperature of more than 100°C. Water as a cooling medium has the advantage, on the one hand, of a particularly high heat capacity and a particularly high enthalpy of vaporization, so that a comparatively large amount of heat can be absorbed from the system, and on the other hand, water is readily available in most cases and, compared to other solvents, is also harmless from an ecological point of view.

[0019] The statement "at a pressure in the range of 5 to 15 bar" is to be understood here as meaning that this pressure refers to the maximum pressure under which the water is subjected for the heating process. This pressure is generally reached before and upon entry of the water into the heat exchanger (for example, in the pipe area between a boiler water pump and the heat exchanger, where, as a result of the heat absorption by the water, the water evaporates and a slight pressure drop (usually in the range of 0.5 to 2 bar) can occur). The pressure specification therefore refers to the pressure before or immediately upon entry of the water into the heat exchanger.

[0020] In contrast, the temperature "less than 200°C" refers to the maximum temperature to which the water is heated in the heat exchanger and which is reached at the outlet of the water from the heat exchanger.

[0021] The term "heat exchanger" in the context of the invention described herein refers to a device in which thermal energy (heat) is transferred from one medium to another without the media mixing. This is achieved, for example, by passing the media in opposite flow directions through thermally coupled pipes that are closed for the passage of material, whereby the warmer medium cools down and the colder medium heats up by absorbing energy released by the warmer medium.

[0022] For the method according to the invention, it is preferred if the cooling medium downstream of the heat exchanger is used to heat another medium, whereby cooled cooling medium is produced in this way.

[0023] The term "downstream" refers to a system in which a material is conveyed from one side to the other, or a recirculating system in which a material circulates. In this context, "downstream" refers to a point in the flow direction that is passed by the circulating material at a later time than the reference point. Similarly, "upstream" refers to a point that is passed by the material at an earlier time than the reference point.

[0024] The method is further preferably designed so that the cooling medium can also be cooled using a cooling water system instead of heating the additional medium. Such a design can be such that the cooling medium can be supplied via a line to the heat exchanger for heating an additional medium and via a separate line to a cooling water system, whereby the supply of the cooling medium can be switched via a corresponding distributor or a heat exchanger that can also be used as a cooling water system. The "switching" preferably occurs depending on the amount of heat transferred to the cooling medium in the heat exchanger during the method. If a threshold value is undershot, the method is conducted such that the cooling medium is supplied to the cooling water system, and if the threshold value is exceeded, the cooling medium is supplied to the heat exchanger for heating an additional medium.

[0025] The "cooling water system" refers to a system by which heat is transferred from the cooling medium to the cooling water without the heat being used for further purposes. Examples of suitable cooling media include river water, water from a larger reservoir that can release absorbed heat to the environment, or a cooling tower system or similar. Such systems are known to those skilled in the art and can be selected accordingly based on the respective local conditions.

[0026] In a preferred embodiment, the heating of the further medium or the removal of the waste heat from the ammonia synthesis plant into the cooling water system are designed separately in the process according to the invention, ie they take place in separate plant parts.

[0027] Further possible uses for the cooling medium as a heat supplier include uses that are effective within the specified process, as well as external uses in which the heat is used for purposes that are not related to an ammonia synthesis plant or a waste heat system of such a plant. One possible use within the specified process is, for example, the (pre)heating of demineralized water in a deaerator through which the cooling medium passes during the process according to the invention. Other internal uses include, for example, use in a stripper during residual gas scrubbing, in particular for preheating the column bottom in the reboiler (see description below), or in the context of an adsorption chiller for condensing product ammonia and regenerating the cooling brine, or in air conditioning systems.

[0028] External uses for which the cooling medium can be used include, for example, the preheating of electrolysis cells used for alkaline water electrolysis, the heating or preheating of water for solid oxide electrolysis (SOEC = solid oxide electrolyzer cell), for heating water in the context of a water desalination plant, in particular in the context of multi-stage flash evaporation (where the seawater can be heated to a temperature of e.g. 115°C), for the generation of external steam or district heating, or for salt production.

[0029] In a particularly preferred embodiment, the cooling medium is used to heat water in the context of water desalination, in particular seawater, which is very particularly preferably carried out as multistage flash evaporation or multi-effect distillation. Very particularly preferably, the water or seawater desalination is designed as a process referred to as "boosted multi-effect distillation" or "flash-boosted multi-effect distillation." In a particularly preferred embodiment, the cooling medium is used in a direct-air capture process (i.e., a process in which CO2 is removed directly from the air, and the cooling medium is required for the regeneration of the absorbent that absorbs the CO2).

[0030] In a further preferred embodiment, the cooling medium is used to heat electrolysis cells in an alkaline water electrolysis plant, or as external steam, district heating, or other heat source. In yet another preferred embodiment, the cooling medium is used to (pre)heat demineralized water in a deaerator used in the context of utilizing waste heat from ammonia production plants.

[0031] In the process according to the invention, it is further preferred if the water as cooling medium in the heat exchanger is heated to a temperature in the range of 150 to 190°C, preferably 158 to 189°C, more preferably 164 to 180°C, and most preferably 167 to 176°C. Furthermore, or alternatively, it is preferred that the water as cooling medium in the heat exchanger is set to a pressure of 6 to 12 bar, preferably 7 to 10 bar, and most preferably 7.5 to 9 bar.

[0032] Furthermore, in the context of the process according to the invention, the water as a cooling medium is circulated, i.e., the water is used in multiple cycles, with it being heated in the heat exchanger during each cycle, and the thermal energy absorbed therein being subsequently transferred to another medium or dissipated via a cooling water system. Since the water used to operate the cooling system should be as salt-free as possible to prevent salt deposits in the system that can form as a result of water evaporation, multiple use of the water as a cooling medium is expedient. This multiple use avoids the high technical and energy expenditure for water treatment and desalination.

[0033] Within the cooling circuit, the water is conveniently pumped. It may also be appropriate to conduct the water as a cooling medium after heating another medium through a condenser, then through a condensate polisher and a deaerator. However, a condenser can also be omitted, for example, if so much heat has been removed from the cooling medium by heating another medium that condensation is no longer necessary.

[0034] In the context of the invention described herein, a condensate polisher is understood to be a device in which condensed water from a steam cycle is filtered. A condensate polisher is typically filled with a polymeric ion exchange resin, which can be used to remove ions from the condensed water. After passing through these units, the cooling medium, water, is returned to the heat exchanger by means of the pump arranged in the circuit, which is usually positioned downstream of the deaerator.

[0035] As mentioned above, the key advantage of the process described here is that it allows the economical operation of an ammonia synthesis plant using renewable energies that are not continuously available in consistent quantities throughout the year, and in particular using wind and / or solar energy. Therefore, in a preferred embodiment, the process is operated using electricity from corresponding renewable energies, and in particular using electricity from wind and / or solar energy. A "renewable energy" that is continuously available in consistent quantities throughout the year is, for example, hydropower or biogas; accordingly, the process is preferably not operated using hydropower or biogas. Depending on the design in different countries, nuclear power can also be considered "renewable energy."

[0036] A further aspect of the present invention relates to a device for utilizing waste heat from ammonia synthesis plants in which the hydrogen required for ammonia production is produced by means of water electrolysis. The device comprises a heat exchanger 4 in which heat from an ammonia plant is transferred to water as a cooling medium, and the device is designed for operation at a temperature of less than 200°C and a pressure of 5 to 15 bar. The statement "designed for operation at a temperature of less than 200°C and a pressure of 5 to 15 bar" means that the plant is adapted to corresponding temperatures and pressures and can be operated safely under these conditions, but on the other hand, cannot be operated safely at significantly higher temperatures and pressures or is not designed for such conditions.Since higher temperatures and pressures place significantly greater demands on the material from which the device is constructed, the investment costs for such devices can be significantly reduced in comparison to conventional devices. A further advantage is that the lower pressure and lower temperatures require less complex boiler feedwater treatment. In a preferred embodiment, the device according to the invention further comprises a further heat exchanger 14, via which heat can be transferred from the cooling medium to another medium. For this purpose, the heat exchanger 14 is fluid with the heat exchanger 4, i.e. the cooling medium can reach the heat exchanger 4 from the heat exchanger 14 via appropriate lines (directly or indirectly via intermediate device elements). The statements made in the context of the method described above apply analogously to this cooling medium.The cooling medium can then be used to heat demineralized water in a deaerator, to heat electrolysis cells in an alkaline water electrolysis plant, for seawater desalination, or for the generation of external steam or district heating, or for one of the other uses mentioned above.

[0037] Alternatively or additionally, it is preferred if the device is designed as a circuit for the cooling medium, wherein the cooling medium, after passing through the heat exchanger 4, in which heat from an ammonia plant is transferred to water as the cooling medium, and the heat exchanger 14, is circulated via a pump 3 and wherein the device has a switchable T-junction 15 upstream of the heat exchanger 14, via which the cooling medium can be returned to the heat exchanger 14 and / or to the pump via a cooling unit 16.

[0038] The cooling unit, as stated above, is a unit in which the cooling medium is cooled without the thermal energy being used for other purposes. While energy is lost unused in this way, this may be economically acceptable if the alternative is that costly energy utilization devices cannot be operated economically.

[0039] In the cooling unit, the water used as the cooling medium can be brought into contact with "cooling" water that has a lower temperature via a thermally conductive barrier, whereby the water used as the cooling medium can transfer thermal energy to the "cooling" water and is thus cooled. A possible source for "cooling" water as a receiver of thermal energy is, for example, river water or water from a larger reservoir that can release absorbed heat to the environment. Alternative cooling units include, but are not limited to, cooling water pumps, cooling tower systems, or air coolers.

[0040] For the specified device designed as a circuit for the cooling medium, it is further preferred if it has a condenser 8, a condensate polisher 10 and a deaerator 12 downstream of the heat exchanger 14, via which the cooling medium is fed to the pump 3. In another preferred embodiment, the device does not have a condenser 8, i.e., on the heat exchanger 14, the water used as the cooling medium is fed directly to the condensate polisher 10. For this embodiment, it is further expedient if the deaerator is arranged downstream of the condensate polisher. A unit for preheating the water can additionally be arranged between them. If the device contains a condenser 8, it is further preferred if it is arranged upstream of the condensate polisher 10 and downstream of the heat exchanger 14 in the device.Here, too, the individual device elements are connected to one another by corresponding lines. In yet another aspect, the present invention relates to a plant comprising a plant section for generating ammonia, in particular from hydrogen and nitrogen, and a plant section for utilizing waste heat from the plant section for generating ammonia, wherein the plant section for utilizing waste heat is designed as a device as described above and is thermally connected to the plant section for generating ammonia. In this plant, the plant section for generating ammonia has a water electrolysis device for generating the hydrogen required for ammonia synthesis. Corresponding plants are described, for example, in WO 2023 / 114890 A1 or US 2021 / 0340017 A1.

[0041] In a particularly preferred embodiment, the plant component for producing ammonia is an ammonia synthesis plant according to the Haber-Bosch process, in particular with a connection to a power supply that is designed to supply wind and / or solar power and / or is connected to corresponding wind and / or solar systems.

[0042] To utilize the waste heat from the ammonia production section, the plant, in a preferred embodiment, has a further (additional) plant section, which is selected in particular from a plant section for alkaline water electrolysis, a plant section for seawater desalination, or a plant section for the generation of external steam or district heating. The term "external steam" here means that the steam generated in this plant section is used for external purposes and can be supplied to an external user (i.e., not integrated into the plant) via a corresponding supply system.

[0043] In conventional ammonia synthesis plants, ammonia is recovered from the plant's flash gas in a "residual gas scrubbing" process by washing it with water. The resulting ammonia-laden water is then heated in a stripper so that the ammonia gas (approximately 80 vol% NH3) leaves the stripper via the column head, and the ammonia-depleted scrubbing water exits the column bottom. The column bottom is heated to approximately 216°C using medium-pressure steam (MD steam, approximately 40 bar and 400°C) in a separate heat exchanger (reboiler), with a condensate separator connected in series after the reboiler. However, such utilization requires a comparatively high water temperature. Since suitable water is no longer available in the plant concept according to the invention, it is preferred if this part of the stripper is operated with an electrically heated system.As mentioned above, however, the cooling medium heated in the device according to the invention can also be used to preheat the process condensate, through which the process condensate passes before it reaches the part of the stripper in which the process condensate is heated as column bottom.

[0044] For the device specified above and the system comprising such a device, it is preferred if it is powered by a power grid that includes one or more renewable energy sources. "Powered" in this case refers to the fact that the power grid supplies the device and in particular the system with the power required for its operation. It is preferred if the power grid is supplied by renewable energy sources to at least 70%, more preferably at least 80%, and even more preferably at least 90%. In one embodiment, the renewable energy sources are supplied by intermittent renewable energy sources to at least 70%, in particular at least 80%, and most preferably at least 90%, (i.e., those that are not available around the clock and in the same quantity throughout an operating year). Intermittent renewable energy sources here include, in particular (but not exclusively), wind and solar.The advantages of the device according to the invention and the corresponding system are best realized through the use of such renewable energy.

[0045] In the following, the present invention is further illustrated and explained with reference to the accompanying drawings 1 and 2.

[0046] Figure 1 shows a waste heat system 1 for an ammonia synthesis plant 2 according to the prior art. The waste heat system comprises a waste heat pump (3, "WSW" = boiler feed water), and, in the flow direction of the cooling medium (indicated here by arrows), a waste heat boiler 4 and a heat exchanger 5, which, in the context of the device shown, is designed as a steam superheater. In the waste heat boiler, the water used as the cooling medium is heated to a temperature of approximately 260°C, and in the steam superheater, the temperature is further increased to approximately 470°C. The superheated steam thus generated is fed to a steam turbine 6 coupled to a generator 7, which is used to generate electricity. The steam derived from the steam turbine and partially cooled is subsequently fed to a condenser 8 and, via a subsequent condenser pump 9, to a polishing unit 10 and then to a preheater 11, from which it returns to the pump 3 via a vent 12.A portion of the superheated steam is used in the stripper unit of the ammonia synthesis plant 2, and in particular in the part of the stripper where process condensate is heated as column bottoms ("reboiler" 13). A portion of the water discharged from the steam turbine can also be fed directly to the deaerator 12. Such a plant is designed, for example, as a medium-pressure system with a working pressure of approximately 40 to 80 bar. The expansion in the turbine occurs, for example, from 45 bar or 80 bar to 8 bar.

[0047] Figure 2 shows a waste heat system 1 according to the inventive concept explained above. In this system, as in the prior art, water is circulated as the cooling medium in a circuit driven by a waste heat recovery pump 3. In contrast to the prior art, however, this water only passes through a heat exchanger 4 designed as a waste heat boiler, in which the water is heated to a temperature of approximately 152°C (at a pressure of, for example, 5 bar). Any greater energy densities that must be dissipated due to the lower temperature of the cooling medium are taken into account by appropriately dimensioning the ratio of heating medium (waste heat from ammonia production) to cooling medium.

[0048] After the heat exchanger, the water used as a cooling medium (in the form of steam) is fed to a T-junction 15, from which it can be led to a heat exchanger 14 or a cooling unit. In the heat exchanger 14, the heat from the cooling medium is transferred to another medium, which can subsequently be used, for example, to operate a seawater desalination plant (not shown in Figure 2). Depending on how much energy is extracted from the water in the heat exchanger, a condenser 8 can be connected downstream to further cool the water. As in a conventional waste heat system, the water thus obtained then passes through a polishing unit 10 and then a preheater 11, from which it returns to pump 3 via a vent 12.

[0049] The water cooled in the cooling unit is also fed to the vent 12.

[0050] The described waste heat system 1 corresponds to the device according to the invention as described above, while the specified plant comprises such a device and at least additionally an ammonia synthesis plant 2.

[0051] As can be seen from the specific description above, in the device concept according to the invention, several plant components that are present in a conventional waste heat system can be eliminated or designed more cost-effectively due to the other characteristics of the process. In particular, the units required for power generation, such as the steam superheater, the steam turbine itself, the generator, and the downstream condensate pump, can be eliminated. A reboiler for the stripper can be replaced by a corresponding electrically operated heating device. In some cases, the condenser downstream of the turbine can also be eliminated. In this case, the elimination of the turbine has the greatest cost impact, since it must be switched on and off when the partial load falls below a certain limit (approximately 22%), which requires corresponding preparation and costs.Regular costs for turbine maintenance can also be eliminated.

[0052] In addition, the heat exchanger (waste heat boiler), the waste heat pump, and the waste heat and steam lines can be designed more cost-effectively due to the lower temperatures and pressures. While this is offset by additional investments for a cooling system and an electric heating system for the stripper's reboiler, the overall cost of the waste heat system is still significantly lower.

[0053] As the following calculation shows, this also applies when the costs for ungenerated electricity are included in the calculation. The calculations are based on the following key data from a real project:

[0054] Plant data: 3400 tons of ammonia per day (tato), generator capacity 27 MW, electricity price from renewable energy (wind farm) 18.3$ / MWh

[0055] Total operating hours when supplied by wind power: 8,760 hours, of which 272 hours at partial load of 1%, 203 hours at partial load of 1% to 8%; 2,650 hours at full load, and 5,635 hours during periods of electricity surplus (assuming that during periods of electricity surplus, the ungenerated electricity costs nothing).

[0056] During total operation of the plants, 27 MW x 2650 h = 71550 MWh of electricity are generated. Eliminating this generation, at the current electricity price, would result in a loss of approximately $1.3 million. This is offset by savings of approximately $29 million in costs for components no longer required or requiring a different design, as well as investment and interest costs. This does not include savings from potential waste heat recovery (e.g., for seawater desalination), nor costs for the larger pumps required for the low-pressure system, any additional space for a cooling tower that may need to be provided, and any necessary low-pressure steam condenser. However, these costs are estimated to be small compared to the savings.

[0057] The calculation shows that, even without considering financial benefits from the use of low-pressure steam (which is usually the case for seawater desalination), there is a clear financial advantage for the system according to the invention if the electricity price is low and there is a surplus of electricity for many hours a year (e.g., through appropriate dimensioning of the wind turbines used to operate them). By utilizing the heat from low-pressure steam (34.5 MW for the proposed plant), the CAPEX of a wind-powered ammonia synthesis plant can be significantly reduced, possibly even without increasing OPEX. Using low-pressure steam beyond 34.5 MW would not only further decrease CAPEX but also reduce OPEX. A further significant advantage is the significant simplification of the plant, which reduces maintenance costs and the risk of plant failure.

[0058] List of reference symbols

[0059] 1 waste heat device

[0060] 2 ammonia synthesis plant

[0061] 3 (KSW) pump

[0062] 4 waste heat boilers

[0063] 5 heat exchangers

[0064] 6 steam turbines

[0065] 7 Generator

[0066] 8 Capacitor

[0067] 9 Condensate pump

[0068] 10 polishing unit

[0069] 11 Preheater for demineralized water

[0070] 12 vents

[0071] 13 Reboiler from the stripper (component of the ammonia synthesis plant)

[0072] 14 heat exchangers for heating additional medium

[0073] 15 T-junction

[0074] 16 Cooling unit

Claims

Claims 1. A process for the utilization of waste heat from ammonia synthesis plants in which the hydrogen required for the production of ammonia is produced by means of water electrolysis, wherein waste heat from the ammonia synthesis plant is transferred via a heat exchanger to water as a cooling medium, wherein the water is heated or adjusted to a temperature of less than 200°C and a pressure of 5 to 15 bar.

2. Method according to claim 1, characterized in that the cooling medium downstream of the heat exchanger is used to heat a further medium, whereby cooled cooling medium is produced, and the method is preferably designed such that the cooling medium can also be cooled with the aid of a cooling water system instead of heating the further medium.

3. A method according to claim 2, characterized in that the cooling medium is used for heating demineralized water in a deaerator, and / or for heating electrolysis cells in an alkaline water electrolysis, and / or for seawater desalination, and / or for direct air capture and / or as external steam, district heating or other heat source.

4. Process according to one of claims 1 to 3, characterized in that the water is heated or adjusted to a temperature in the range of 150 to 190°C, preferably 158 to 189°C, more preferably 164 to 180°C, more preferably 167 to 176°C and / or a pressure of 6 to 12 bar, preferably 7 to 10 bar, more preferably 7.5 to 9 bar.

5. Method according to one of the preceding claims, characterized in that the water is circulated as a cooling medium by means of a pump, and wherein the water is preferably heated after heating a further medium via a condenser, a condensate polisher and a vent before the water is returned to the heat exchanger.

6. A method according to any one of the preceding claims, characterized in that the ammonia synthesis plant is operated with electricity from renewable energies, in particular with electricity from wind and / or solar.

7. Device (1) for utilizing waste heat from an ammonia synthesis plant (2) in which the hydrogen required for the production of ammonia is produced by means of water electrolysis, the device comprising a heat exchanger (4) in which heat from an ammonia synthesis plant (2) is transferred to water as a cooling medium, the device (1) being designed to operate at a temperature of less than 200°C and a pressure of 1 to 20 bar.

8. Device (1) according to claim 7, characterized in that the device further comprises a heat exchanger (14) via which heat can be transferred from the cooling medium to another medium and which is fluidly connected to the heat exchanger (4).

9. Device (1) according to claim 7 or 8, characterized in that the device is designed as a circuit for the cooling medium, wherein the cooling medium can be circulated via a pump (3) after passing through the heat exchanger (4) and the heat exchanger (14), and wherein the device has a switchable T-junction (15) upstream of the heat exchanger (14), via which the cooling medium can be returned to the heat exchanger (14) and / or to the pump via a cooling unit (16).

10. Device according to claim 9, characterized in that the device has a condenser (8), a condensate polisher (10) and a vent (12) downstream of the heat exchanger (14), via which the cooling medium is led to the pump (3).

11. Plant comprising a plant part for producing ammonia (2) from hydrogen and nitrogen, wherein the plant part for producing ammonia has a water electrolysis device for generating the hydrogen required for ammonia synthesis, and a plant part for utilizing waste heat from the plant part for producing ammonia, wherein the plant part is designed as a device according to claim 7 and is thermally coupled to the plant part for producing ammonia.

12. Plant according to claim 11, further comprising a plant part for alkaline water electrolysis, for seawater desalination, or for the generation of external steam or district heating.

13. Plant according to claim 11 or 12, wherein the plant section for producing ammonia comprises a stripper in which the ammonia-laden water in the column bottom is electrically heated for the purpose of recovering the ammonia from the flash gas from the ammonia synthesis.

14. Device according to one of claims 7 to 10 or plant according to one of claims 11 to 13, wherein the device or plant is powered by a power grid comprising one or more renewable energy sources, preferably wherein the power grid is powered by at least 90% renewable energy sources.

Images