System and method for the combined compression of hydrogen and natural gas

Abstract

The present invention relates to a system and a method for the combined compression of "green" hydrogen and natural gas in a natural gas compressor when "green" hydrogen is added into a conventional NH3 system or to an NH3-urea complex.

Description

[0001] Plant and process for the joint compression of hydrogen and natural gas

[0002] The present invention relates to a plant and a method for the (partial) compression of "green" hydrogen together with natural gas in a natural gas compressor when adding "green" hydrogen to a conventional NH3 plant or an NH3-urea complex.

[0003] State of the art

[0004] Given global population growth, the development of flexible and efficient fertilizers is becoming increasingly important. Urea-based fertilizers account for a very large proportion of global fertilizer production. These water-soluble fertilizers decompose in the soil into ammonium salts or nitrates and represent an important base fertilizer. These urea-based fertilizers can be combined with other elements such as potassium, manganese, phosphates, sulfur, sulfur compounds, selenium, and calcium.

[0005] Urea can be produced according to the simplified equations [1] and [2]:

[0006] 2 NH3+ CO2H2N-COONH4[1]

[0007] H2N-COONH4(NH2)2CO + H2O [2]

[0008] The two starting materials, ammonia and carbon dioxide, can be provided in ammonia synthesis based on the Haber-Bosch process. Ammonia is the world's second most produced synthetic chemical (Ullmann's Encyclopedia of Industrial Chemistry, 2012, Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim, DOI: 10.1002 / 14356007.002_011, hereinafter "Ullmann's").

[0009] Ammonia is produced primarily from the elements hydrogen and nitrogen in the presence of an iron catalyst. Temperatures often range between 400 °C and 500 °C at a pressure of over 100 bar. The main factor influencing the process costs is the provision of hydrogen from synthesis gas production (Ullmann's, page 139). Ammonia is therefore preferably produced in accordance with the principle described, for example, in Holleman, Wiberg, Textbook of Inorganic Chemistry, 102nd edition, 2007, pages 662-665 (ISBN 978-3-11-017770-1), based on the "Haber-Bosch process" from the elements according to equation [3]:

[0010] 3 H2+ N22 NH3+ 92.28 kJ [3]

[0011] The reactant nitrogen (N2) can be obtained, for example, by low-temperature air separation or by reducing oxygen in the air through combustion. Hydrogen is preferably obtained via the steam reforming process according to equation [4]:

[0012] CnH2m + nH20 (n+m) H2+ nCO [4]

[0013] In the subsequent “carbon dioxide conversion” a further conversion takes place according to equation (5):

[0014] CO + H2O C02 + H2[5]

[0015] The carbon dioxide (C02) produced according to equation [5] serves preferentially as a carbon dioxide source for urea synthesis according to equations [1] and [2].

[0016] According to equation [4], fossil fuels, typically methane from natural gas, serve as the starting material for hydrogen production. Due to limited resources and the diverse consequences of climate change, a reduction in the consumption of fossil fuels, such as natural gas, is being sought worldwide.

[0017] One approach with regard to ammonia and urea synthesis is the construction of pure "green" ammonia plants ("gNH3 plants") powered by "green" hydrogen ("gH2") from renewable sources. While these pure gNH3 plants are desirable and relevant for the future, their high operating costs have so far prevented a complete transition to such gNH3 plants. An alternative approach is to convert existing, conventional, so-called "gray" NH3 plants to the use of gH2. However, the existing concepts for this conversion are also too expensive and often severely limited in their applicability.

[0018] However, an economical alternative to purely new or converted gNH3 plants is the (partial) injection of gH2 into an existing “grey” NH3 plant.

[0019] This feed-in is intended to reduce natural gas consumption and CO2 emissions. The hydrogen comes, for example, from electrolysis (powered by renewable energy) and, after compression and removal of residual oxygen in a de-oxo reactor, is usually mixed with the remaining make-up gas upstream of the syngas compressor.

[0020] The disadvantage is that the actual front-end relief through the injection of gH2 leads to significant deviations from the design case of the plant, which is geared to pure natural gas operation. Among other things, the following points must be taken into account:

[0021] Although the steam demand remains almost unchanged, the steam quantity decreases due to reduced flue gas and process gas quantities.

[0022] The gH2 feed-in results in lower primary reformer performance and consequently less usable waste heat, potentially reducing the k values / heat transfer coefficients of the heat exchangers. However, the outlet temperatures of the streams should remain as unchanged as possible from the normal case, i.e., the design case for pure natural gas operation.

[0023] Furthermore, the FL compressors installed are usually piston compressors, because only at a plant capacity of approximately 600 tpd NH3 does the feed-in H2 demand reach a level that allows for the economical operation of a centrifugal compressor. When feeding gH2 into an existing NH3 plant, gH2 quantities will be generated, at least in the near future, that are significantly lower than this value. Compared to a centrifugal compressor, a piston compressor often has significant technical disadvantages (e.g., high maintenance costs), and its operation is generally less economical.WO 2021 / 151453 A1 relates to a process for producing hydrogen, in which a carbon-containing feedstock is converted in a non-electrolytic process to form non-electrolytically produced hydrogen and one or more further non-electrolytically produced products, wherein using the non-electrolytic process, excess steam is further provided by at least temporarily using at least a portion of the excess steam to provide feed steam, wherein the feed steam is converted by steam electrolysis to electrolysis hydrogen and electrolysis oxygen.

[0024] WO 2019 / 020377 Ai relates to a process for ammonia synthesis in which hydrogen is provided by electrolysis and fed either into the methanation unit or into the synthesis gas compressor. This process suffers from the aforementioned disadvantages, particularly with regard to the reduction in steam volume and the lower amount of usable waste heat. Furthermore, the use of economically less favorable piston compressors is necessary if a gH2 mass flow rate is to be compressed that is too small for a centrifugal compressor (which can be operated significantly more economically than piston compressors). With these piston compressors, the gH2 must be compressed to a relatively high pressure level.

[0025] WO 2022 / 157223 A1 relates to a process for ammonia or methanol synthesis in which hydrogen is provided by electrolysis and fed into the process either after the primary reformer or later. This process also suffers from the aforementioned disadvantages, particularly with regard to the reduction in steam volume and the lower amount of usable waste heat. Furthermore, the use of economically less favorable piston compressors is necessary if a gH2 mass flow rate is to be compressed that is too small for a centrifugal compressor (which can be operated significantly more economically than piston compressors). With these piston compressors, the gH2 must be compressed to a relatively high pressure level.

[0026] Furthermore, the injection of gH2 into an existing natural gas grid is known from the state of the art.

[0027] For example, in the publication "Large scale of green hydrogen storage: Opportunities and challenges," International Journal of Hydrogen Energy, Elsevier, Amsterdam, NL, Volume 50, ISSN: 0360-3199, DOI: 10.1016 / J.IJHYDENE.2023.09.021, Chapter 3.3 (see Fig. 10) describes that hydrogen can be fed into an existing natural gas grid. Specifically, it describes:

[0028] "As shown in Fig. 10, hydrogen is produced from renewable energy sources (sun, wind, etc.). The produced hydrogen is injected into the natural gas pipeline network (...) and transported to end users. This process is known as 'gas power' and is practiced in many countries, including the United Kingdom, Germany, and France."

[0029] The aforementioned publication therefore explicitly concerns enriching the natural gas stream in an existing natural gas network with gH2 and then supplying the mixture to a large number of consumers. This application thus differs significantly from the present invention. The present invention relates to the injection of gH2 within a single ammonia synthesis plant that is downstream of the natural gas network. The invention proposes a plant configuration and a method for an ammonia synthesis plant (and thus completely independent of the natural gas network) in which the CAPEX requirement (i.e., the investment costs for the plant components) and the OPEX requirement (i.e., the operating costs of the ammonia synthesis plant) are lower than in the prior art solutions for the injection of gH2 within an ammonia synthesis plant.Feeding gH2 into the existing natural gas network cannot provide a solution to this problem.

[0030] The benefits that can be achieved by injecting gH2 into the existing natural gas grid are also described in the aforementioned Chapter 3.3. The described benefits do not provide any indication of how natural gas consumption, CAPEX, and OPEX requirements can be reduced in an ammonia synthesis plant downstream of the natural gas grid.

[0031] The present invention aims to provide improved plants and processes for ammonia synthesis that enable the partial use of gH2 and thus reduce the consumption of fossil natural gas resources. In particular, the improved plants should have lower CAPEX requirements. The improved process should lead to lower operating costs and thus have lower OPEX requirements. Solution according to the invention

[0032] The object of the invention is surprisingly achieved by a plant for ammonia synthesis according to claim 1. Further advantageous embodiments can be found in the dependent claims.

[0033] The invention further comprises a process for ammonia synthesis according to claim 7. Further advantageous embodiments can be found in the respective dependent claims.

[0034] The invention further comprises the use of the plant according to the invention for ammonia synthesis for the production of ammonia and / or urea as well as the reduction of natural gas consumption.

[0035] It was surprisingly found that the (partial) compression of the gH2 already in the natural gas compressor has several advantages:

[0036] The H2 piston compressor can be designed smaller because the hydrogen only needs to be compressed to the comparatively low pressure present in the natural gas supply line to the natural gas compressor. If hydrogen can be supplied from an H2 network at the same pressure as natural gas (or at a higher pressure), the H2 compressor can be eliminated entirely.

[0037] The de-oxo reactor is no longer required, since all O2 residues are removed by reaction in the secondary reformer at the latest.

[0038] The return of the make-up gas from an intermediate stage of the synthesis gas compressor for desulfurization is also eliminated.

[0039] Furthermore, the required power of the primary reformer is desirably reduced, since the reforming power is shifted to the secondary reformer.

[0040] The flue gas flow is increased, which is also desirable to supply the heat exchangers with sufficient heat. Overall, the mass flow after the secondary reformer increases, which is beneficial for steam production. Despite the addition of gH2, sufficient steam production can thus be ensured.

[0041] According to the invention, because the gH2 is introduced upstream of or into the natural gas compressor, only the compression of the gH2 to 10 to 20 bar is required, whereas with the later injection of the gH2 known from the prior art (for example, upstream of the synthesis gas compressor), this gH2 must be compressed to 20 - 25 bar. This allows the electric compressor, which can be designed as a piston compressor, for example, to be smaller (reducing CAPEX requirements) or operated at a lower power (reducing OPEX requirements) than in the plant configurations known from the prior art, in which a significantly later injection of the gH2 in the process is planned.

[0042] The ammonia synthesis plant according to the invention comprises at least the components described below.

[0043] Conventional natural gas compressors, as known from the state of the art, can be used as natural gas compressors. The natural gas compressor compresses the natural gas and the hydrogen, preferably from 10 to 20 bar to 35 to 45 bar.

[0044] The desulfurization unit can be a state-of-the-art desulfurization unit. The desulfurization unit can be designed according to conventional standards without restrictions.

[0045] To produce hydrogen from natural gas (in addition to the injected gH2), a reformer is used, preferably a primary and a secondary reformer and / or an autothermal reformer (ATR). The formation of hydrogen preferably occurs according to the above equation:

[0046] CnH2m + nH20 (n+m) H2+ nCO [4]

[0047] A description of the reformer's operation can be found in Ullmann's, Chapter 6.1.1, pages 174 to 179. Furthermore, the system according to the invention can preferably comprise a carbon monoxide (CO) converter (not shown). In this converter, the carbon monoxide (CO) formed in equation [4] and not required for the actual ammonia synthesis is converted into carbon dioxide, preferably according to equation [5], with further hydrogen formation.

[0048] CO + H2O C02 + H2[5]

[0049] A description of the operation and structure of possible carbon monoxide (CO) converters ("Carbon Monoxide Shift Conversion") can be found in Ullmann's, Chapter 6.1.2, pages 179 to 182. The carbon monoxide (CO) converter can preferably be followed by a carbon dioxide (CO2) scrubber unit with regeneration (not shown). Within the meaning of the invention, the term "unit" encompasses devices and apparatus known to the person skilled in the art for the stated purpose, in this case typically / for example an absorber, a desorber, one or more circulation pumps, and heat exchangers for heating / cooling the solvent.A carbon dioxide (CO2) scrubber unit with regeneration can, for example, be designed as a known device / arrangement in which carbon dioxide is dissolved in a suitable solvent—for example, potassium carbonate or amines—under pressure in an absorber and then flashed separately from the remaining synthesis gas (the synthesis gas depleted of carbon dioxide or freed of carbon dioxide in the carbon dioxide (CO2) scrubber unit with regeneration). The solvent can then be reheated and regenerated in a stripping column (desorber). A detailed description can be found, for example, in Ullmann's, Chapter 6.1.3, pages 182 to 184.A carbon dioxide (CO2) scrubber unit with regeneration differs from an adsorption process (e.g. pressure swing adsorption PSA) in that the former does not remove the nitrogen (N2) component, which is essential for the subsequent ammonia synthesis, from the synthesis gas stream and has an overall selectivity in the removal of gas components that corresponds to the intended use.

[0050] A methanation unit enables further reduction of carbon oxides (COX). This is achieved, for example, according to equations [6] and [7]:

[0051] CO + 3 H2CH4 + H2O [6]

[0052] C02+ 4 H2CH4+ 2 H2O [7]

[0053] Within the meaning of the invention, the methanation unit preferably comprises further plant elements for purification, for example, via the Selectoxo process, methanation, dryers, cryogenic processes, washing with liquid nitrogen, and / or pressure swing adsorption. The term "unit" within the meaning of the invention encompasses devices and apparatus known to the person skilled in the art for the stated purpose. A detailed description can be found in Ullmann's, Chapter 6.1.3, pages 184 to 186. Process conditions for equations [6] and [7] are, for example, 25 bar to 35 bar and 250 °C to 350 °C over a nickel catalyst.

[0054] The plant according to the invention further comprises an ammonia synthesis unit (not shown). The term "unit" within the meaning of the invention encompasses devices and apparatus known to those skilled in the art for the stated purpose. The ammonia synthesis unit comprises the actual ammonia synthesis reactor for converting hydrogen and nitrogen according to equation [3]. The nitrogen can preferably be provided in a connected air separation plant or from the process air processed (= "burned") in the secondary reformer. Examples of suitable reactors can also be found in EP 0 345504 Ai and DE 35 22 308 A1, Examples 1 to 7 and the description. The ammonia synthesis unit is preferably connected to devices for purification, compression and / or liquefaction.

[0055] In a preferred embodiment, the system further comprises an H2 compressor in connection with the H2 supply line.

[0056] In another preferred embodiment, the H2 pressure in the H2 supply line is equal to or greater than the natural gas pressure in the natural gas supply line.

[0057] Particularly preferably, the H2 pressure in the H2 supply line is 10 to 20 bar.

[0058] The natural gas pressure in the natural gas supply line is particularly preferably 10 to 20 bar.

[0059] In a further preferred embodiment, the hydrogen is provided by renewable sources, preferably by means of water electrolysis powered by renewable energy. Particularly preferably, the hydrogen is provided by an alkaline water electrolysis device (AWE) powered by electricity from wind energy and / or solar energy and / or other so-called renewable energies. In principle, other water electrolysis technologies can also be used. The combination of preferred embodiments is particularly preferred.

[0060] The invention further comprises a process for ammonia synthesis comprising at least the following steps: a) compressing natural gas and hydrogen in a natural gas compressor (10); b) desulfurization, reforming, and methanation to obtain a synthesis gas; c) compressing the synthesis gas to feed it to the ammonia synthesis, wherein the hydrogen is introduced into the natural gas supply line (11) or into the natural gas compressor (10) upstream of the natural gas compressor (10) and is compressed together with the natural gas.

[0061] Preferably, an alkane-containing gas (especially methane-containing gas) is compressed together with H2 in a natural gas compressor, then desulfurized and introduced into one or more reformers to obtain a first synthesis gas mixture comprising hydrogen, carbon monoxide, and carbon dioxide as described above according to equation [4]. The first synthesis gas mixture can then be transferred to a carbon monoxide (CO) converter. In the carbon monoxide (CO) converter, the carbon monoxide (CO) formed in equation [4], which is not required for the actual ammonia synthesis and problematic for many catalysts, can be converted into carbon dioxide according to equation (5) with further hydrogen formation to obtain a second synthesis gas mixture. The second synthesis gas mixture can then be introduced into a carbon dioxide (CO2) scrubber unit with regeneration and transferred.The scrubber unit can, for example, be designed as a device / arrangement in which carbon dioxide is dissolved in a suitable solvent—for example, potassium carbonate or amines—under pressure in an absorber and then expanded ("flashed") separately from the remaining (virtually carbon dioxide-free) synthesis gas. The solvent can, for example, be reheated and regenerated in a stripping column (desorber). Subsequently, a third (virtually carbon dioxide-free or carbon dioxide-depleted) synthesis gas mixture and a carbon dioxide (CO2)-containing exhaust gas are obtained. The third synthesis gas mixture can be transferred to a methanation unit. The methanation unit enables the further reduction of carbon oxides (COX), for example, according to equations [6] and [7]. A fourth synthesis gas mixture is then obtained, and the fourth synthesis gas mixture can be introduced into an ammonia synthesis unit.The ammonia synthesis unit comprises the actual ammonia synthesis reactor for the conversion of hydrogen and nitrogen, preferably according to equation [3]. Ammonia is obtained in the ammonia synthesis unit. This is then processed, compressed, and / or liquefied, preferably by one or more pressure and temperature reductions.

[0062] Preferably, the resulting ammonia and a large portion of the carbon dioxide (CO2)-containing exhaust gas are converted to urea in a urea plant, preferably a urea plant connected to an ammonia production plant. Further utilization enables effective use of the ammonia and, in particular, the natural gas, which is preferably used to produce the synthesis gas.

[0063] The invention further comprises the use of the ammonia synthesis plant according to the invention for producing ammonia and simultaneously reducing the consumption of fossil resources.

[0064] The invention is further explained in more detail with reference to the following figures. These figures do not limit the scope of the invention, but serve only as examples. The figures show schematic plant flow diagrams.

[0065] They show:

[0066] Figure 1 shows a schematic flow diagram of a conventional ammonia synthesis plant with feed of gH2.

[0067] Figure 2 is a schematic flow diagram of a plant according to the invention for ammonia synthesis with feed of gH2 according to one embodiment.

[0068] Figure 3 shows a schematic flow diagram of a plant according to the invention for ammonia synthesis with the feed of gH2 according to a further embodiment. Figure 1 shows a schematic representation of a conventional plant and the implementation of a conventional process for producing ammonia or for producing synthesis gas for further conversion to ammonia with the feed of gH2.

[0069] Natural gas from a natural gas supply line 11 is compressed in a natural gas compressor 10 and fed to the other units of synthesis gas production, such as the desulfurization unit 20, the primary reformer 30, and the methanation unit 40. Hydrogen is fed between the methanation unit 40 and the synthesis gas compressor 50 via a hydrogen supply line 61, before the hydrogen-enriched synthesis gas is further compressed in the synthesis gas compressor 50 and forwarded to the actual ammonia synthesis unit (not shown) via the ammonia synthesis supply line 53. The hydrogen fed in is obtained here in an alkaline hydrogen electrolysis unit 70, compressed in an H2 compressor 80, transferred via the H2 feed line 81 into a de-oxo reactor 60 and freed from oxygen in the de-oxo reactor 60 before being fed in via the H2 feed line 61.The H2 compressor 80 must compress the gH2 gas stream to a relatively high pressure level between 25 and 30 bar, because the gH2 gas loses pressure in the de-oxo reactor and must be fed at a pressure of 20 to 25 bar upstream of the synthesis gas compressor 50. The H2 compressor 80 must therefore be designed for this compression.

[0070] Starting from the synthesis gas compressor 50, a portion of the hydrogen-enriched synthesis gas is also returned to the desulfurization unit 20 via the H2 return line 51 in order to ensure the hydrogen content required for desulfurization.

[0071] Fig. 2 shows a schematic representation of a plant according to the invention and the implementation of a process according to the invention for producing ammonia or for producing synthesis gas for further conversion to ammonia with feed of gH2.

[0072] In the illustrated embodiment, the "green" hydrogen is produced in an alkaline hydrogen electrolysis unit 70 powered by electricity from renewable energies, compressed in an H2 compressor 80, and added to the natural gas in the natural gas supply line 11 via the H2 supply line 81. The mixture of H2 and natural gas is compressed in a natural gas compressor 10 and fed to the other units of the synthesis gas production, such as the desulfurization unit 20, the primary reformer 30, and the methanation unit 40. The resulting synthesis gas is further compressed in the synthesis gas compressor 50 and passed on to the actual ammonia synthesis unit (not shown) via the ammonia synthesis supply line 53. Compared to Fig. 1, the de-oxo reactor 60 can be omitted. Another advantage is that the H2 compressor 80 can be designed significantly smaller than in the system configuration shown in Fig. 1 (reduction of CAPEX requirements).The reason for this is that in the plant configuration according to Fig. 2, the H2 compressor 80 only has to compress the gH2 gas flow to a significantly lower pressure level of 10 - 20 bar 8, while in the plant configuration according to Fig. 1, the gH2 must be compressed to a pressure level of 25 - 30 bar due to the pressure loss occurring in the de-oxo reactor.

[0073] Fig. 3 shows a schematic representation of a further plant according to the invention and the implementation of a process according to the invention for producing ammonia or for producing synthesis gas for further conversion to ammonia with feed-in of gH2.

[0074] The "green" hydrogen is provided here either from an electrolysis unit (e.g., PEM electrolysis), which supplies gH2 at an elevated pressure, or directly from an H2 network at the same pressure as the natural gas. It is added to the natural gas in the natural gas supply line 11 via the H2 supply line 81. The mixture of gH2 and natural gas is compressed in a natural gas compressor 10 and fed to the other units of the synthesis gas production, such as the desulfurization unit 20, the primary reformer 30, and the methanation unit 40. The resulting synthesis gas is further compressed in the synthesis gas compressor 50 and passed on to the actual ammonia synthesis unit (not shown) via the ammonia synthesis supply line 53. Compared to Fig. 1, the de-oxo reactor 60 and the H2 compressor 80 can be omitted (reduction in CAPEX requirements).

[0075] List of reference symbols

[0076] 10 Natural gas compressor n Natural gas supply line

[0077] 20 desulfurization unit

[0078] 30 primary reformers

[0079] 40 methanation unit

[0080] 50 Synthesis gas compressor

[0081] 51 Ha return line

[0082] 53 Supply line for ammonia synthesis

[0083] 60 De-Oxo reactor

[0084] 61 H2 supply line from de-oxo reactor

[0085] 70 Alkaline water electrolysis (AWE)

[0086] 80 hydrogen compressor

[0087] 81 H2 supply line

Claims

Patent claims 1. Plant for ammonia synthesis at least comprising: a) a natural gas compressor (10) b) a natural gas supply line(s) for supplying natural gas to the natural gas compressor (10) c) a desulfurization unit (20) d) a primary reformer (30) e) a methanation unit (40) f) a synthesis gas compressor (50), characterized in that an H2 supply line (81) upstream of the natural gas compressor (10) is connected to the natural gas supply line (11) or to the natural gas compressor (10).

2. Plant according to claim 1, characterized in that the plant further comprises an H2 compressor (80) in connection with the H2 supply line (81).

3. Plant according to claim 1 or 2, characterized in that the H2 pressure in the H2 supply line (81) is equal to or greater than the natural gas pressure in the natural gas supply line (11).

4. Plant according to one of the preceding claims, characterized in that the H2 pressure in the H2 supply line (81) is 10 to 20 bar.

5. Plant according to one of the preceding claims, characterized in that the hydrogen is provided by renewable sources, preferably by water electrolysis powered by electricity from renewable energies.

6. Plant according to one of the preceding claims, characterized in that the hydrogen is provided by an alkaline water electrolysis device (AWE).

7. A process for ammonia synthesis, comprising at least: a) compressing natural gas and hydrogen in a natural gas compressor (10); b) desulfurization, reforming, and methanation to obtain a synthesis gas; c) compressing the synthesis gas to feed it to the ammonia synthesis, characterized in that the hydrogen is introduced into the natural gas feed line (11) or into the natural gas compressor (10) upstream of the natural gas compressor (10) and is compressed together with the natural gas.

8. Process according to claim 7, characterized in that the hydrogen and the natural gas are compressed in the natural gas compressor from 10 to 20 bar to 35 to 45 bar.

9. A process according to claim 7 or 8, characterized in that the hydrogen is provided by renewable sources, preferably by alkaline water electrolysis powered by electricity from renewable energies.

10. Use of the plant according to claims 1 to 6 for ammonia synthesis for the production of ammonia and / or urea.

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