Process and plant for producing ammonia
Patent Information
- Application Number
- EP2023744050
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-09-02
- Filing Date
- 2023-07-14
- Publication Date
- 2025-07-09
AI Technical Summary
Industrial ammonia production is inefficient due to high energy consumption and investment costs, primarily driven by the performance of compressors and refrigerant compressors, with significant exergy losses from converting mechanical energy into heat.
A process that utilizes an expansion machine to generate mechanical power from ammonia synthesis gas, which is then used to drive refrigerant compressors and other apparatus, reducing the need for external drive power and minimizing heat dissipation, thereby reducing energy consumption and investment costs.
This approach reduces energy losses by utilizing mechanical power to drive compressors directly, lowering the energy required for ammonia synthesis and reducing investment costs, while maintaining efficient ammonia production.
Smart Images
Figure 1.1
Abstract
Description
[0001] Description
[0002] Process and plant for the production of ammonia
[0003] The invention relates to a process and a plant for producing ammonia.
[0004] background
[0005] In the large-scale production of ammonia, a so-called ammonia synthesis gas can be used. This gas mixture consists primarily of nitrogen and hydrogen, with traces of inert gases due to the process. This gas can be compressed in a synthesis gas compressor to a high pressure of typically 100 to 250 bar and then heated to typically 350 to 500°C.
[0006] Since the conversion of ammonia synthesis gas to ammonia in an ammonia synthesis reactor only occurs partially due to the unfavorable reaction equilibrium, ammonia is condensed out as a reaction product from the gas mixture leaving the ammonia synthesis reactor, and the remaining, unconverted ammonia synthesis gas is recycled to the ammonia synthesis reactor. Details are explained again below with reference to Figure 1.
[0007] To condense the ammonia from the partially converted ammonia synthesis gas, it is cooled to the extent that is economically feasible. The high-temperature heat of the hot ammonia synthesis gas at the outlet of the ammonia synthesis reactor is typically used for steam generation, and the subsequent temperature window is used to heat the ammonia synthesis gas and boiler feedwater. The waste heat for the final cooling to ambient temperature cannot usually be used economically due to the low temperature level and is therefore typically removed via air or water coolers.
[0008] In addition, to condense sufficient ammonia and operate the process economically, energy must be used to generate cold to achieve temperatures below ambient. This requires a refrigeration system that generates cold by compressing, removing heat, and then expanding a refrigerant. Ammonia is also often used as a refrigerant in current technology.
[0009] In conventional processes, the energy requirements and investment costs for ammonia synthesis are mainly determined by the performance of the compressors used (compressors for ammonia synthesis gas and refrigerant compressors) and their drives (electric motors or turbines).
[0010] The present invention aims to realize processes for ammonia synthesis of the type described more efficiently and with lower energy consumption and investment costs.
[0011] Disclosure of the invention
[0012] This object is achieved by a process and a plant for producing ammonia having the features of the respective independent patent claims. Further embodiments are the subject of the dependent patent claims and the following description.
[0013] One aspect of the method proposed within the scope of the present invention consists in directing a gas mixture emerging from an ammonia synthesis reactor to an expansion machine (also referred to synonymously as an expander) and expanding it to such an extent that the resulting shaft power of the expander approximately corresponds to the shaft power of a coupled device, for example, but not necessarily, the refrigerant compressor, and the expander thus partially or completely drives the coupled device. The coupled device can generally be any machine, for example a rotating machine such as a compressor, a pump, a booster, a blower, or the like, but also a generator for generating electrical power. In the following, reference is made in particular to the refrigerant compressor solely for reasons of clarity and to avoid repetition.This proposes a process for the production of ammonia in which an ammonia synthesis gas is subjected to compression and is fed to a partial conversion in an ammonia synthesis reactor.
[0014] Ammonia synthesis gas is, in particular, a gas mixture consisting essentially of hydrogen and nitrogen. The term "essentially" should be understood here in particular to mean that, in addition to the mandatory components, further components are permitted in a claimed composition, a material stream, etc., provided that these do not significantly change the essential characteristics of the claimed composition. For example, an ammonia synthesis gas "consisting essentially of hydrogen and nitrogen" is suitable for the production of ammonia without secondary components or trace gases having a significant impact on the quantity or reaction technology. A gas mixture "essentially" containing or consisting of one or more components can, in particular, contain more than 95, 99, 99.9, or 99.99% of these components, either in total or as individual values.Conversely, a gas mixture is "essentially free" of one or more components if it contains less than 5, 1, 0.1, or 0.01% of these components, either in total or as individual values. The percentages may refer to molar, quantitative, or volume fractions.
[0015] In the context of the present invention, a gas mixture is withdrawn from the ammonia synthesis reactor, which gas mixture contains (essentially) ammonia and unreacted components of the ammonia synthesis gas and which is expanded at least in part using an expansion machine, wherein at least one further apparatus coupled to the expansion machine is driven using the expansion machine.
[0016] In embodiments of the invention, the gas mixture withdrawn from the ammonia synthesis reactor is subjected at least in part to a plurality of cooling steps, wherein the plurality of cooling steps comprise a cooling step which is carried out using a refrigerant guided in a refrigerant circuit, wherein at least a portion of the refrigerant is compressed using a refrigerant compressor, and wherein at least a portion of a drive power of the refrigerant compressor is provided using the expansion machine in which at least a portion of the gas mixture withdrawn from the ammonia synthesis reactor is expanded.
[0017] The advantages of embodiments of the present invention include that a portion of the energy contained in the synthesis gas can be utilized as mechanical power, whereby less energy needs to be dissipated in the form of heat in the steam generator and boiler feedwater heater. In contrast to known processes, less drive power (e.g., compressor power for the refrigerant compressor) needs to be supplied externally (e.g., as electrical power or steam turbine power) within the scope of the present invention. In known processes, the supplied mechanical energy is largely dissipated as heat (via steam generation and heat dissipation to the environment). The conversion of mechanical energy into heat represents a significant exergy loss. Corresponding losses can be reduced through the use of the present invention.
[0018] In embodiments of the present invention, mechanical shaft power is provided using the expansion machine, with at least a portion of the mechanical shaft power of the expansion machine being mechanically introduced into the coupled device, such as the refrigerant compressor. Thus, in particular, a direct or indirect mechanical coupling can be achieved, so that conversion losses can be avoided in such an embodiment.
[0019] Embodiments of the present invention may include driving one or more compressor stages of the refrigerant compressor (if present), possibly even all compressor stages, using at least a portion of the mechanical shaft power. The same applies to driving all or a portion of subunits of another coupled device.
[0020] In general, multi-stage turbo compressors can be used within the scope of the present invention. The mechanical structure of turbo compressors is generally known to those skilled in the art. In a turbo compressor, the medium to be compressed is compressed by means of turbine blades arranged on a turbine wheel or directly on a shaft. A turbo compressor forms a structural unit which, however, in the case of a multi-stage turbo compressor, can have several compressor stages. A compressor stage generally comprises a turbine wheel or a corresponding arrangement of turbine blades. All of these compressor stages can be driven by a common shaft. However, it can also be provided to drive the compressor stages in groups with different shafts, wherein the shafts can be connected to one another via gears.
[0021] An expansion machine suitable for use in the present invention can be, in particular, a turboexpander. A turboexpander can be constructed similarly to a turbocompressor, but with shaft power generated by expanding a fluid.
[0022] For a particularly efficient mechanical coupling, one or more compressor stages of the refrigerant compressor, or one or more subunits of another coupled device, or the coupled device as a whole, and one or more expansion stages of the expansion machine can be arranged on a common mechanical shaft. This enables a particularly direct, low-loss power transmission.
[0023] In embodiments of the present invention, however, it can also be provided that at least part of the mechanical shaft power is converted in a gearbox. In this way, advantageous speed adjustment can be carried out, for example, to be able to process different volume flows or quantities of process gas, i.e., the gas mixture removed from the reactor, and the coolant or a medium processed, in particular compressed, in another coupled device.
[0024] In embodiments of the present invention, it can also be provided that at least a portion of the mechanical shaft power is converted into electrical power. This electrical power can, for example, also be used to operate an electric motor, which provides at least a portion of the drive power of the refrigerant compressor. Any other units such as compressors, heaters, fans, and the like can also be driven in this way.
[0025] In embodiments of the present invention, it can be provided that the mechanical shaft power of the expansion machine exceeds the drive power of the refrigerant compressor or another coupled device, and a portion of the mechanical shaft power of the expansion machine that exceeds the drive power of the refrigerant compressor or the other coupled device is used to drive one or more units selected from one or more compressor stages of a compressor used in the compression of the ammonia synthesis gas, one or more boiler feedwater pumps, and one or more gas compressors or gas compressor stages. Corresponding embodiments of the present invention can therefore utilize the mechanical power generated during expansion particularly advantageously.
[0026] In embodiments of the present invention, the expansion machine can be arranged at various suitable positions, such as downstream of the ammonia synthesis reactor and upstream or downstream of one of the multiple cooling steps. The positioning depends on the respective practicality and feasibility.
[0027] In embodiments of the present invention, the process can be carried out in a first process mode and a second process mode, wherein the expansion machine is bypassed in the first process mode and only activated in the second process mode. The first process mode can be carried out, in particular, during commissioning ("start-up") of a corresponding plant until a sufficient amount of the gas emerging from the ammonia synthesis reactor is present.
[0028] For the sake of completeness, it should be noted here that in embodiments of the present invention, a portion of the ammonia synthesis gas not converted in the ammonia synthesis reactor is returned to the compression.
[0029] Ammonia synthesis can be carried out in a pressure range of 100 to 250 bar absolute pressure and / or in a temperature range of 350 to 500°C. In particular, a modification of a known Haber-Bosch process can be used.
[0030] The cooling step, which is carried out using the refrigerant in the refrigerant circuit, is in particular a cooling step to a temperature in a temperature range of -40 to +40°C. Ammonia can be used as the refrigerant, and the refrigerant circuit can be a closed or open refrigerant circuit. An open refrigerant circuit is characterized in that a portion of the ammonia formed in the ammonia synthesis is separated, expanded, thereby evaporated, and used as a refrigerant, and the corresponding ammonia is then converted into a product. A refrigerant in a closed refrigerant circuit has no material contact with the process gas, i.e. the gas mixture from the ammonia synthesis to be cooled.
[0031] A plant for producing ammonia is also the subject of the present invention, wherein the plant is designed to subject an ammonia synthesis gas to compression and to supply it to a partial conversion in an ammonia synthesis reactor, to withdraw a gas mixture from the ammonia synthesis reactor which contains unreacted components of the ammonia synthesis gas, to expand the gas mixture at least in part using an expansion machine, and to drive one or more apparatuses coupled to the expansion machine using the expansion machine.In particular, the system can be configured to subject the gas mixture at least in part to a plurality of cooling steps, to carry out one cooling step of the plurality of cooling steps using a refrigerant conducted in a refrigerant circuit, to compress at least a portion of the refrigerant using a refrigerant compressor, and to provide at least a portion of a drive power of the refrigerant compressor using the aforementioned expansion machine.
[0032] For further features and advantages of a corresponding system and embodiments thereof, reference is expressly made to the above explanations concerning the method proposed according to the invention and its embodiments, since these apply equally to this.
[0033] The same applies to a system which, according to an embodiment of the invention, is designed to carry out a method according to any embodiment of the present invention.
[0034] Brief description of the drawings Embodiments of the invention are described below purely by way of example with reference to the accompanying drawings, in which
[0035] Figure 1 illustrates a process for ammonia synthesis according to an embodiment not according to the invention,
[0036] Figure 2 illustrates a process for ammonia synthesis according to an embodiment of the present invention,
[0037] Figure 3 illustrates partial aspects of a process for ammonia synthesis according to an embodiment of the present invention, and
[0038] Figure 4 illustrates partial aspects of a process for ammonia synthesis according to an embodiment of the present invention.
[0039] Embodiments of the invention
[0040] The embodiments described below are described solely for the purpose of assisting the reader in understanding the claimed and previously discussed features. They are merely representative examples and are not intended to be exhaustive and / or limiting with regard to the features of the invention. It is to be understood that the advantages, embodiments, examples, functions, features, structures, and / or other aspects described above and below are not to be considered as limitations on the scope of the invention as defined in the claims or as limitations on equivalents to the claims, and that other embodiments may be utilized and changes may be made without departing from the scope of the claimed invention.
[0041] Different embodiments of the invention may include, comprise, consist of, or consist essentially of other useful combinations of the described elements, components, features, parts, steps, means, etc., even if such combinations are not specifically described herein. Furthermore, the disclosure may encompass other inventions that are not currently claimed but that may be claimed in the future, particularly if they are encompassed within the scope of the independent claims.
[0042] Explanations relating to devices, apparatus, arrangements, systems, etc. according to embodiments of the present invention may also apply to methods, processes, methods, etc. according to the embodiments of the present invention, and vice versa. Elements, method steps, etc. that are identical, have the same effect, are functionally equivalent, are structurally identical, or are comparable may be identified by identical reference numerals.
[0043] Figure 1 illustrates a process for ammonia synthesis according to an embodiment not according to the invention in the form of a schematic diagram to which reference has already been made at the outset.
[0044] In this process, an ammonia synthesis gas 101 is subjected to compression 10, wherein the compression 10 is carried out to the pressure mentioned above, and several compression stages 11, 12, and 13 of a (turbo) compressor of the type described can be used. At an intermediate stage, a recycle stream 105 can be fed in, which contains the aforementioned components of ammonia synthesis gas as well as uncondensed ammonia.
[0045] The compressed ammonia synthesis gas 101, designated 110, is heated, fed into an ammonia synthesis reactor 20, and partially converted there. A gas mixture 102 containing unreacted components of the ammonia synthesis gas 110 is withdrawn from the ammonia synthesis reactor 20.
[0046] The gas mixture 102 is subjected to cooling 30, in particular in a feed-effluent heat exchanger against the fed-in ammonia synthesis gas 110. Several optional further cooling steps are represented in the form of a dotted heat exchanger. A cooling step 40 is carried out using a refrigerant 103 guided in a refrigerant circuit 50, wherein at least a portion of the refrigerant 103 is compressed using a refrigerant compressor 60. The compressed refrigerant can, in particular, be expanded and fed into a heat exchanger used in the cooling step 40. Downstream of the cooling step is a separation 65 of liquid ammonia, wherein unconverted ammonia synthesis gas and uncondensed gaseous ammonia remain and can be recirculated to the compression 10 as material stream 105, as mentioned. Liquid ammonia can be fed to the plant boundary in the form of a product stream 104.
[0047] Figure 2 illustrates a process for ammonia synthesis according to an embodiment of the present invention and is designated overall by 100.
[0048] Aspects of the embodiment of the invention illustrated in Figure 2 have already been explained, so that the following explanations focus essentially on the differences.
[0049] As illustrated in Figure 2, at least a portion of the drive power of the refrigerant compressor 60 is provided using an expansion machine 70, in which at least a portion of the gas mixture 102 taken from the ammonia synthesis reactor 20 is expanded. As illustrated here, one or more compressor stages of the refrigerant compressor 60 and one or more expansion stages of the expansion machine 70 can be arranged on a common mechanical shaft 80.
[0050] Instead of the refrigerant compressor 0, as mentioned several times, another device coupled to the expansion machine 70 can also be driven, which can be the previously explained (rotating) machines or a generator for generating electrical current.
[0051] Figure 3 illustrates partial aspects of a method for ammonia synthesis according to an embodiment of the present invention, wherein only a coupling of one or more compressor stages of the refrigerant compressor 60 and one or more expansion stages of the expansion machine 70 is illustrated. As shown here, a gear 90 is provided, in which at least part of the mechanical shaft power is converted. Furthermore, an auxiliary electric motor 95 is provided, which additionally drives the refrigerant compressor 60. Figure 4 illustrates further partial aspects of a method for ammonia synthesis according to a further embodiment of the present invention. Here, it is shown that a compressor stage 61 of the refrigerant compressor 60 is coupled to the expansion machine 70 via a shaft 80 and a compressor stage 62, for example for higher pressure, is coupled to an auxiliary electric motor 95 via a further
[0052] Shaft 81 is driven.
[0053] In general, whenever the above-mentioned drive of “a compressor” by means of “an expansion machine” is mentioned, it is always also intended to refer to a drive of only a part of the existing compressor stages and by means of only a part of the existing
[0054] Expander stages may be meant without this being specifically stated.
Claims
Patent claims 1. A process (100) for producing ammonia, in which an ammonia synthesis gas (101) is subjected to compression (10) and is fed to a partial conversion in an ammonia synthesis reactor (20), wherein a gas mixture (102) containing ammonia and unreacted components of the ammonia synthesis gas (20) is withdrawn from the ammonia synthesis reactor (20), wherein the gas mixture (102) is expanded at least in part using an expansion machine (70), and wherein one or more further apparatuses coupled to the expansion machine (70) are driven using the expansion machine (70).
2. The method (100) according to claim 1, wherein at least a portion of the gas mixture (102) withdrawn from the ammonia synthesis reactor (20) is subjected to a plurality of cooling steps (30, 40), wherein the plurality of cooling steps (30, 40) comprise a cooling step (40) which is carried out using a refrigerant (103) guided in a refrigerant circuit (50), wherein at least a portion of the refrigerant (103) is compressed using a refrigerant compressor (60), wherein at least a portion of a drive power of the refrigerant compressor is provided as the or one of the apparatuses (60) coupled to the expansion machine (70) using the expansion machine (70).
3. Method (100) according to claim 1 or 2, wherein mechanical shaft power is provided using the expansion machine (70), wherein at least a portion of the mechanical shaft power of the expansion machine (70) is introduced into the apparatus(es) coupled to the expansion machine (70).
4. The method (100) according to claim 3, wherein one or more compressor stages of the one or more further apparatuses (60) coupled to the expansion machine (70) are driven using at least a portion of the mechanical shaft power. Method (100) according to claim 3 or 4, wherein one or more compressor stages of the one or more further apparatuses (60) coupled to the expansion machine (70) and one or more expansion stages of the expansion machine (70) are arranged on a common mechanical shaft (80). Method (100) according to one of claims 3 to 5, wherein at least a portion of the mechanical shaft power is converted in a transmission (90). Method (100) according to one of claims 3 to 6, wherein at least a portion of the mechanical shaft power is converted into electrical power.Method (100) according to one of the preceding claims, in which the mechanical shaft power of the expansion machine (70) exceeds the drive power of the one or more further apparatuses (60) coupled to the expansion machine (70), and a portion of the mechanical shaft power of the expansion machine (70) that exceeds the drive power of the refrigerant compressor (60) is used to drive one or more units that are selected from one or more compressor stages (11, 12, 13) of a compressor used in the compression (10) of the ammonia synthesis gas (101), one or more boiler feedwater pumps, and one or more gas compressors or gas compressor stages. Method (100) according to one of the preceding claims, in which the expansion machine (70) is arranged downstream of the ammonia synthesis reactor (20) and upstream or downstream of a cooling step (30) of the plurality of cooling steps (40, 50).Method (100) according to one of the preceding claims, which is carried out in a first method mode and a second method mode, wherein the expansion machine (70) is bypassed in the first method mode and is only switched on in the second method mode.
11. Method (100) according to one of the preceding claims, in which a Ammonia synthesis reactor (20) unreacted part of the Ammonia synthesis gas is returned to the compression (10).
12. The process (100) according to any one of the preceding claims, wherein the ammonia synthesis is carried out at a pressure in a pressure range of 100 to 250 bar absolute pressure and / or at a temperature in a temperature range of 350 to 500°C.
13. The method (100) according to any one of the preceding claims, wherein the cooling step (40) carried out using the refrigerant (103) conducted in the refrigerant circuit (50) is a cooling step to a temperature in a temperature range of -40 to +40°C.
14. The method (100) according to any one of the preceding claims, wherein ammonia is used as the refrigerant, wherein the refrigerant circuit (50) is a closed or open refrigerant circuit.
15. Plant for the production of ammonia, which is designed to subject an ammonia synthesis gas (101) to a compression (10) and to supply it to a partial conversion in an ammonia synthesis reactor (20), to withdraw from the ammonia synthesis reactor (20) a gas mixture (102) which contains ammonia and unreacted components of the ammonia synthesis gas (20), to drive the gas mixture (102) at least in part to an expansion using an expansion machine (70), and to drive one or more apparatuses coupled to the expansion machine (70) using the expansion machine (70).