CN117355482A - Ammonia cracking for hydrogen production - Google Patents

Ammonia cracking for hydrogen production Download PDF

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Publication number
CN117355482A
CN117355482A CN202280036646.8A CN202280036646A CN117355482A CN 117355482 A CN117355482 A CN 117355482A CN 202280036646 A CN202280036646 A CN 202280036646A CN 117355482 A CN117355482 A CN 117355482A
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stream
ammonia
hydrogen
gas
cracking
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S·潘扎
D·迪阿代齐奥
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Casale SA
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Casale SA
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B3/00—Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
    • C01B3/02—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen
    • C01B3/04—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by decomposition of inorganic compounds, e.g. ammonia
    • C01B3/047—Decomposition of ammonia
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01C—AMMONIA; CYANOGEN; COMPOUNDS THEREOF
    • C01C1/00—Ammonia; Compounds thereof
    • C01C1/24—Sulfates of ammonium
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/04—Integrated processes for the production of hydrogen or synthesis gas containing a purification step for the hydrogen or the synthesis gas
    • C01B2203/0405—Purification by membrane separation
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/04—Integrated processes for the production of hydrogen or synthesis gas containing a purification step for the hydrogen or the synthesis gas
    • C01B2203/042—Purification by adsorption on solids
    • C01B2203/043—Regenerative adsorption process in two or more beds, one for adsorption, the other for regeneration
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/04—Integrated processes for the production of hydrogen or synthesis gas containing a purification step for the hydrogen or the synthesis gas
    • C01B2203/046—Purification by cryogenic separation
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/08—Methods of heating or cooling
    • C01B2203/0805—Methods of heating the process for making hydrogen or synthesis gas
    • C01B2203/0811—Methods of heating the process for making hydrogen or synthesis gas by combustion of fuel
    • C01B2203/0827—Methods of heating the process for making hydrogen or synthesis gas by combustion of fuel at least part of the fuel being a recycle stream
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/08—Methods of heating or cooling
    • C01B2203/0805—Methods of heating the process for making hydrogen or synthesis gas
    • C01B2203/085—Methods of heating the process for making hydrogen or synthesis gas by electric heating
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/08—Methods of heating or cooling
    • C01B2203/0872—Methods of cooling
    • C01B2203/0883—Methods of cooling by indirect heat exchange
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P20/00—Technologies relating to chemical industry
    • Y02P20/10—Process efficiency
    • Y02P20/129—Energy recovery, e.g. by cogeneration, H2recovery or pressure recovery turbines
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P20/00—Technologies relating to chemical industry
    • Y02P20/10—Process efficiency
    • Y02P20/133—Renewable energy sources, e.g. sunlight

Abstract

A method for synthesizing hydrogen by catalytic cracking of ammonia; the process comprises the step of subjecting an ammonia-containing stream (10) to a catalytic cracking step (11) in the presence of heat to produce combustion gases and a thermally cracked stream (14) containing nitrogen, hydrogen and potentially residual ammonia and optionally water; the method further includes the step of subjecting the thermal cracking stream to a hydrogen recovery step to produce a high purity hydrogen stream (22).

Description

Ammonia cracking for hydrogen production
Technical Field
The present invention is in the field of hydrogen production and in particular relates to a method and apparatus for producing hydrogen from an ammonia cracking unit.
Background
Excessive use of fossil fuels in the power industry and transportation has a detrimental impact on human health and welfare and the environment. There is an urgent need to provide some environmentally friendly and sustainable alternative fossil fuels.
Hydrogen and ammonia are carbon-free carriers that are considered ideal substitutes for fossil fuels.
On a small scale, hydrogen can be produced by various domestic sources (e.g., solar, wind) and electrolysis. In contrast, on an industrial scale, hydrogen is obtained by reforming fossil fuels, mainly by reforming of natural gas (steam reforming) or water-gas shift of coal-derived synthesis gas.
The hydrogen produced by steam reforming requires a multi-step process, starting with natural gas purification, high temperature reforming, high temperature Water Gas Shift (WGS) and purification.
Unfortunately, due to the reforming process, a large amount of CO 2 Is discharged to the atmosphere.
In the art, it is desirable to find an industrial scale hydrogen synthesis process that can produce clean hydrogen without venting any carbon dioxide to the atmosphere. This process should also be economically competitive with conventional processes.
Green ammonia synthesized from renewable energy sources is a carbon-free storage carrier for hydrogen gas, with many potential energy applications including the production of green hydrogen gas. Hydrogen can be obtained from ammonia by a thermal decomposition process known as catalytic cracking.
In the catalytic cracking process, ammonia is decomposed or cracked back into H in the presence of heat and a catalyst (Ni or Ru or Pt) according to the following endothermic equilibrium 2 And N 2 ：
At temperatures as low as 425 ℃, ammonia can be thermodynamically converted to hydrogen. In practice, however, the conversion depends on the type of catalyst used. Typically, ni is active at higher temperatures (500-750 ℃) than Ru (400 ℃) but the latter catalysts are more expensive.
The heat required for the thermocatalytic conversion of ammonia is typically provided by electrical heating in an electrical heating furnace or in a reformer by combustion of fuel.
Unfortunately, the ammonia cracking techniques described above suffer from several drawbacks. First, ammonia cracking technology is mature and is commercially available primarily for small scale applications (i.e., with less than 100kg H 2 Hydrogen production rate per h).
The main difficulty in expanding this technology is to design a cracking unit that is sufficiently compact but capable of decomposing ammonia at a rate consistent with consumption.
Furthermore, a typical problem observed in projects using adiabatic cracking units is the relatively low conversion of ammonia (i.e., high ammonia slip). In contrast, cracking plants utilizing oxygen converting autothermal reformers require the installation of expensive air separation units ASUs.
In addition, for high hydrogen production rate>1000m 3 /h), natural gas reforming remains the most cost-effective option.
Accordingly, in view of the above-mentioned considerations, it is highly desirable to provide a cost-effective hydrogen synthesis process and apparatus suitable for large-scale hydrogen production. In addition, the improved hydrogen synthesis process should be environmentally friendly and therefore not result in carbon dioxide emissions to the atmosphere.
Disclosure of Invention
The present invention aims to overcome the above-mentioned drawbacks of the prior art. In particular, the problem addressed by the present invention is how to reduce carbon dioxide emissions and equipment costs, and how to provide methods and equipment suitable for large scale production.
The invention relates to a method in which a high-purity hydrogen stream is obtained by cracking ammonia.
A first aspect of the invention is a carbon-free hydrogen production process for the catalytic synthesis of hydrogen according to claim 1.
The method according to claim 1, comprising the steps of: the ammonia stream, optionally with the addition of water, is subjected to a preheating step to produce an ammonia-containing stream, which is subjected to a catalytic ammonia cracking step in the presence of heat to produce a thermal cracking stream containing nitrogen, hydrogen and potentially residual ammonia and water.
The method of claim 1 further comprising the step of: the thermal cracking stream is subjected to a hydrogen recovery step to produce a high purity hydrogen stream and a tail gas, or the thermal cracking stream is subjected to a scrubbing step in the presence of water to produce a purified gas stream, and the purified gas stream is further subjected to a hydrogen recovery step to produce a high purity hydrogen stream and a tail gas.
Furthermore, the method according to claim 1 comprises the steps of: at least a portion of the tail gas is recycled as fuel gas to provide heat for the step of catalytically cracking and to vent the high purity hydrogen stream.
Another aspect of the invention is a method for producing hydrogen according to claim 7.
The method of claim 7 comprising the steps of: the ammonia stream is subjected to a heating stage to produce an ammonia-containing stream that is subjected to a catalytic ammonia cracking step in the presence of heat to produce combustion gases and a thermal cracking stream containing nitrogen, hydrogen and residual ammonia.
The method of claim 7 further comprising the step of: optionally mixing the thermal cracking stream with water to produce a thermal cracking stream with water added, and feeding the thermal cracking stream or the thermal cracking stream with water added to a cooling stage to produce a cooled stream, subjecting the cooled stream to a flash separation step to produce an ammonia-lean stream and an ammonia stream or an aqueous ammonia solution, and further subjecting the ammonia-lean stream to a hydrogen recovery step to produce a high purity hydrogen stream and a tail gas.
Alternatively, the ammonia-lean gas stream is subjected to a scrubbing step in the presence of water to produce purified gas. The purified gas is further subjected to a hydrogen recovery step to produce a high purity hydrogen stream and a tail gas.
Furthermore, the method according to claim 7 comprises the steps of: at least a portion of the tail gas is recycled as fuel gas to provide heat for the step of catalytically cracking and to vent the high purity hydrogen stream.
Another aspect of the invention is an apparatus for producing hydrogen according to the claims.
A hydrogen production plant adapted to perform the method of claim 1 comprising at least one furnace adapted for ammonia cracking comprising a plurality of externally heated catalytic tubes, an input line arranged to feed an ammonia-containing stream into the tubes, and an output line arranged to collect a thermal cracking stream from the tubes.
An apparatus adapted to perform the method of claim 1 comprising a hydrogen recovery unit configured to recover a high purity hydrogen stream and a tail gas, a line configured to recycle at least a portion of the tail gas separated from the hydrogen recovery unit into a furnace for use as additional fuel, and a line configured to withdraw the high purity hydrogen stream from the hydrogen recovery unit.
An apparatus adapted to perform the method of claim 7 comprising a furnace adapted for ammonia cracking comprising a plurality of externally heated catalytic tubes, an input line arranged to feed an ammonia-containing stream into the tubes, an output line arranged to collect a thermal cracking stream from the tubes, and optionally a line configured to provide water to the thermal cracking stream.
The apparatus adapted to perform the method of claim 7 further comprising a flash separator unit in communication with the output line and configured to separate an ammonia lean gas stream from an ammonia stream or an aqueous ammonia solution, a hydrogen recovery unit in fluid communication with the flash separator and configured to recover a high purity hydrogen stream and a tail gas, a line configured to recycle at least a portion of the tail gas separated from the hydrogen recovery unit to a furnace for use as additional fuel, and a line configured to withdraw a high purity hydrogen stream from the hydrogen recovery unit.
Advantageously, by feeding air instead of oxygen into the furnace, an air separation unit is not required. Even more advantageously, by adjusting the fuel-air ratio (i.e., operating in excess air), the NOx content of the combustion gases exiting the furnace may be minimized. Furthermore, by installing an SCR selective catalytic reduction SCR or a non-selective catalytic reduction system NSCR, NOx present in the system can be completely removed or reduced to several ppm.
Even more advantageously, in contrast to reforming processes performed using natural gas as a fuel source in the process of the present invention, a carbon-free source (e.g., ammonia) is used as the combustible gas so as not to release carbon dioxide emissions into the atmosphere.
Advantageously, in a method and apparatus configuration wherein the electro-cracking unit is provided before or integrated with the furnace, a high flexibility in the synthesis of hydrogen is envisaged.
Preferred embodiments
According to a particularly preferred embodiment of the invention, the heat required to maintain the endothermic cracking of ammonia is provided by the combustion reaction of the fuel gas in the presence of preheated air to produce combustion gases.
Preferably, the fuel gas used as the combustible gas in the catalytic cracking step comprises ammonia, or a mixture of nitrogen and hydrogen, or a mixture of ammonia, nitrogen and hydrogen. Advantageously, no carbon dioxide emissions are released into the atmosphere.
According to alternative embodiments of the present invention, the remainder of the fossil fuel (e.g., natural gas) may be added to the fuel gas to maintain combustion. Because of the low amount of natural gas used, in this alternative embodiment, the carbon dioxide emissions of the process are still lower than those expected in conventional hydrogen synthesis processes.
According to an alternative embodiment of the invention, the method further comprises the steps of: the fuel gas retaining ammonia is subjected to cracking in the presence of electrical heating to produce a gas mixture retaining hydrogen and nitrogen and potentially unconverted ammonia, and further subjected to combustion in the presence of preheated air to provide reforming heat in the catalytic cracking step.
Alternatively, the fuel gas retaining ammonia may also be subjected to a catalytic cracking step, wherein the heat required to maintain the cracking reaction is recovered from the combustion gas. The thermal cracking step and the electrical cracking step may be performed in a single furnace. In this particular embodiment, the furnace may include a burner and an electrical cracking unit.
Preferably, the burner is designed to burn ammonia, or a mixture of ammonia and a hydrogen-rich stream and a tail gas, or a mixture of a hydrogen-rich stream and a tail gas. Furthermore, the burner may be operated in a mixture of the above streams with the addition of natural gas or fossil fuel.
According to a particularly preferred embodiment, the fuel gas is further subjected to a heat recovery step, wherein heat is indirectly transferred from the combustion gas to the fuel gas, before being subjected to said cracking step or before being subjected to combustion in the furnace.
The heat of reforming required for the ammonia catalytic cracking step may be provided by combustion of the fuel gas in the presence of preheated air.
According to an alternative embodiment, the aqueous ammonia solution may be subjected to a distillation step to separate an ammonia stream from the aqueous solution, and at least a portion of the ammonia stream may be recycled as fuel to provide heat to the catalytic cracking step.
In addition, a portion of the ammonia stream may be recycled to the heating stage to undergo an ammonia catalytic cracking step with the main ammonia stream.
The method may further comprise the steps of: heat is recovered from the combustion gas by indirectly contacting a portion of the aqueous solution with the combustion gas and feeding the portion of the aqueous solution to a distillation step after heat recovery to provide distillation heat. Advantageously, a heat integration between the distillation step and the ammonia catalytic cracking step can be achieved and the energy consumption of the process can be reduced.
The method may further comprise the steps of: a portion of the aqueous solution obtained from the distillation is fed to the thermal cracking stream optionally with the addition of a water make-up stream.
According to a particularly preferred embodiment of the invention, the hydrogen purification step is carried out by means of a pressure swing adsorption unit or a cryogenic separation unit or a membrane purification unit. It is well known to those skilled in the art when to select one unit over the other depending on the concentration of hydrogen retained by the thermal cracking stream.
Preferably, the high purity hydrogen obtained after the hydrogen purification step has a concentration of higher than 95% wt, preferably higher than 99% wt, more preferably higher than 99.9% wt.
Preferably, the temperature of the thermal cleavage stream leaving the catalytic cleavage step is between 400 and 950 ℃, more preferably between 550 and 650 ℃.
Preferably, the catalytic cracking step is carried out at a pressure of about 5 to 65barg, more preferably 15 to 30barg (bar gauge).
According to a particularly preferred embodiment of the invention, the combustion gases leaving the catalytic cracking step undergo a NOx reduction step before being discharged into the atmosphere. Alternatively, the NOx reduction step may be performed in a portion of the furnace.
According to an embodiment of the invention, the apparatus may further comprise a purification unit configured to recover ammonia from the thermal cracking stream to produce a purified gas stream and a recycle gas, and a line configured to feed at least a portion of the recycle gas into the furnace.
Furthermore, the apparatus may comprise an electrical cracking unit configured to crack fuel gas retaining ammonia. Alternatively, the apparatus may comprise a coil filled with catalyst and disposed in the convection section of the furnace. The catalyst-filled coil is configured to catalytically crack the fuel gas using heat retained by the combustion gas passing through the convection section.
According to an embodiment of the invention, the catalytic cracking of the fuel may be performed in a combined process, wherein the fuel is partly cracked in coils arranged in the convection section of the furnace, followed by further cracking of the partly cracked fuel leaving the coils in an electric cracking unit.
The electro-lysis unit may be arranged before the furnace and the electro-lysis unit may be in communication with the furnace by means of a gas production line (gas flow line). Alternatively, the electrical cracking unit may be integrated into the furnace and the electrical cracking unit may be used to crack the fuel gas prior to combustion.
According to a particularly preferred embodiment of the invention, the apparatus comprises a distillation unit configured to separate water and ammonia in the aqueous ammonia solution, a line connecting the flash separator unit to the distillation unit and configured to convey the aqueous ammonia solution to said distillation unit.
The apparatus may furthermore comprise a gas production line connecting the distillation unit to the furnace, a heat exchanger section configured to recover heat from combustion gases in the furnace by means of a water flow, a line connecting the distillation unit to said heat exchanger section and configured to convey a water flow to be used for heat integration purposes between the furnace and the distillation unit.
According to an embodiment of the invention, the furnace may comprise a unit adapted to remove NOx (also called denox unit), preferably an SCR unit, or an SNCR unit, or a combination of both. NOx removal by SCR may be performed in a temperature range of 150-600 ℃, or preferably in a temperature range comprised between 350 and 600 ℃. In contrast, NOx removal by SNCR may be performed in the temperature range of 850-1200 ℃, or preferably in the range including 900 to 1050 ℃. The term NOx denotes nitrogen oxides, mainly NO and NO 2 。
Preferably, the hydrogen recovery unit is a pressure swing adsorption unit or a cryogenic separation unit or a membrane separation unit.
According to an embodiment of the invention, the ammonia catalytic cracking step is carried out in a furnace provided with a radiant section and a convection section. The radiant section retains a tube bundle preferably comprising a nickel-based catalyst or a ruthenium-based catalyst or a molybdenum-based catalyst or a platinum-based catalyst, possibly with the addition of molybdenum, cobalt and lithium.
In one particularly interesting embodiment of the invention, the convection section of the furnace comprises a plurality of heat exchangers (coil sets) arranged in the convection section of the furnace. Preferably, at least one of the heat exchangers is a steam superheater, and additionally, the waste heat boiler coil and the boiling water coil may also be integrated in the furnace. The heat recovered in the convection section of the furnace can be used for heat integration purposes in the process or for energy production. Alternatively, heat recovery may be accomplished downstream of the furnace.
The furnace outlet may be quenched directly with a cooling medium, preferably water, ammonia or a cooler gaseous stream.
Downstream of the cooling process, the ammonia aqueous solution may be separated from the gas phase, preferably in a flash evaporator, and the heat available in the convection section of the furnace may be used to distill the liquid in a dedicated column, and ammonia may be recovered in the same distillation column.
Drawings
Fig. 1 is a schematic diagram of a hydrogen synthesis process according to one embodiment of the invention.
Fig. 2 is a schematic diagram of a hydrogen synthesis process according to another embodiment of the invention.
Fig. 3 is a schematic diagram of a hydrogen synthesis process according to an alternative embodiment of the invention.
Fig. 4 is a schematic diagram of a hydrogen synthesis process according to another embodiment.
Detailed Description
Fig. 1 shows a schematic diagram of a hydrogen synthesis method according to a first embodiment of the present invention.
Liquid ammonia stream 2 is withdrawn from storage feed tank 1 and fed via pump 3 to a first pre-heating unit 6, whereby an evaporated or partially evaporated ammonia stream 7 or hot liquid ammonia 7 is obtained.
The ammonia stream 7 is mixed with water 8 and preheated in a second preheating unit 9 to complete the evaporation of the ammonia stream, thereby producing an ammonia-containing stream 10. The ammonia-containing stream 10 is then fed to a catalytic cracking unit 11 for catalytic cracking in the presence of heat, thereby producing a cracked stream 14.
The catalytic cracking unit 11 generally comprises a furnace provided with a radiant section and a convection section. The radiant section includes a tube bundle that retains a cracking catalyst (typically a nickel-based catalyst).
The heat required to maintain the endothermic ammonia cracking reaction is provided by combustion of the fuel gas 12 in the presence of preheated air 28.
The preheated air 28 fed to the catalytic cracking furnace as combustion improver is obtained by preheating the air stream 27 leaving the blower 26 in the convection section of the furnace. In the convection section, pressurized steam 29 is also generated by recovering heat from the combustion gases 60. The combustion gases are then treated in a denox stage (not shown) to remove NOx before being discharged to the atmosphere.
Thermal cracking stream 14 (typically with residual ammonia retained) is subjected to a scrubbing step 20 in the presence of water 17 to produce a purified gas stream 51 and recycle gas 21. The water 17 is used as an absorbent in the washing step to take advantage of the high solubility of ammonia in water to remove ammonia from the stream.
The purified gas stream 51 is then fed to a hydrogen recovery step 19 to produce a high purity hydrogen stream 22 and a tail gas 23. The hydrogen stream 22 is withdrawn from the hydrogen recovery step and stored and/or exported according to hydrogen demand.
The tail gas 23 and recycle gas 21 are then mixed together to produce a mixed stream 25 and recycled back to the ammonia cracking step/unit 11.
In fig. 2, a hydrogen synthesis method according to another embodiment of the present invention is shown.
The process represented in fig. 2 can be used for synthesizing hydrogen when the ammonia content retained by the thermal cracking stream 14 is on the order of a few ppm, preferably on the order of ppb.
In this particular embodiment, the cleavage stream 14 is fed directly to the hydrogen recovery step 19 without going through a scrubbing stage. The hydrogen recovery step is performed in a pressure swing adsorption unit.
Alternatively, the hydrogen may be recovered in a cryogenic unit, wherein a series of compression and cooling stages are performed to remove nitrogen from the purified gas stream, or in a hydrogen membrane separation unit, wherein the selective permeability of hydrogen across a particular membrane is utilized.
In fig. 3, an alternative embodiment of the hydrogen synthesis process is shown.
The ammonia stream 7 is subjected to a heating stage 6, 51 in which heat is exchanged with the thermal cracking stream 14 leaving the furnace 11. In addition, the ammonia stream is further heated 9 in the convection section of the furnace to produce an ammonia-containing stream 10 prior to being fed to the ammonia catalytic cracking step in the furnace.
Thermal cracking stream 14 containing nitrogen, hydrogen and residual ammonia is mixed with water 74 after leaving the furnace to produce a thermal cracking stream 75 with water added, which thermal cracking stream 75 exchanges heat with ammonia stream 7 in heat exchangers 51 and 6 before further air cooling in column 70 to produce cooled stream 79.
The cooled stream 79 is then sent to a flash separator 80 where an ammonia lean (ammonia depleted) gas stream 81 is separated from an aqueous ammonia solution 82.
The lean ammonia stream 81 is then fed to a hydrogen recovery step 19 to produce a high purity hydrogen stream 22 and a tail gas 23.
Then, after exchanging heat 120 with the aqueous solution 74, the tail gas 23 is fed as fuel to provide heat to the catalytic cracking step 11.
The hydrogen 22 is taken out of the hydrogen recovery step 19 and stored or output as required. The aqueous ammonia solution 82 is then sent to distillation 83 to separate aqueous solution 84 from ammonia stream 86.
The first portion 91 of the ammonia stream 86 is recycled as fuel to the furnace to provide heat for the catalytic cracking step 11, while the second portion 92 of the ammonia stream is mixed with the ammonia stream 7 and then fed to the catalytic cracking step 11 of ammonia in the furnace after preheating.
A portion 87 of the aqueous solution 84 is used to recover heat from the combustion gases 60 by indirect heat exchange (indirect heat transfer) with the combustion gases 60 in the convection section of the furnace. The combustion gases undergo a NOx removal step 131 before being removed from the furnace.
A second portion 88 of the aqueous solution 84 obtained from distillation 83 is mixed with make-up water stream 17 and fed into thermal cracking stream 14.
In fig. 4, a hydrogen synthesis process according to an alternative embodiment of the invention is shown.
In the figures, it can be appreciated that the ammonia-retaining fuel gas 12 is subjected to a cracking step 100 in the presence of electrical heating to produce a gas mixture 101 retaining hydrogen and nitrogen, and optionally unconverted ammonia.
The gas mixture 101 is then mixed with the tail gas 23 and then subjected to combustion in the presence of preheated air 28 to provide heat of reforming in the catalytic cracking step 11.
As an alternative embodiment not shown in the figures, the cleavage step performed in the presence of electrical heating may also be performed in a furnace.

Claims (23)

1. A process for the catalytic synthesis of hydrogen comprising the steps of:
a) Subjecting the ammonia stream (7), optionally with the addition of water (8), to a preheating step (9) to produce an ammonia-containing stream (10);
b) Subjecting the ammonia-containing stream (10) to a catalytic ammonia cracking step (11) in the presence of heat to produce a thermal cracking stream (14) containing nitrogen, hydrogen and potentially residual ammonia, and optionally water;
c) Subjecting the thermal cracking stream (14) to the steps of:
c1 A hydrogen recovery step (19) to produce a high purity hydrogen stream (22) and a tail gas (23),
or (b)
c2 A washing step (20) in the presence of water (17) to produce a purified gas stream (51), and further subjecting the purified gas stream (51) to a hydrogen recovery step (19) to produce a high purity hydrogen stream (22) and a tail gas (23);
d) Recirculating at least a portion of the tail gas (23) as fuel to provide heat for the catalytic ammonia cracking step (11);
e) The high purity hydrogen stream (22) is withdrawn.
2. The method of claim 1, further comprising the step of: the fuel gas (12) is subjected to combustion in the presence of preheated air (28) to provide heat of reforming and to produce combustion gas (60) in said catalytic ammonia cracking step (11).
3. The method according to claim 1 or 2, wherein the fuel gas (12) comprises ammonia, or a mixture of nitrogen and hydrogen, or a mixture of ammonia, nitrogen and hydrogen.
4. The method of claim 1, further comprising the step of: subjecting the ammonia-retaining fuel gas (12) to a cracking step (100) in the presence of electrical heating to produce a gas mixture (101) retaining hydrogen and nitrogen and potentially unconverted ammonia, and further subjecting the gas mixture (101) to combustion in the presence of preheated air (28) to provide reforming heat in the catalytic cracking step (11).
5. The method of claim 4, wherein the cracking step (100) and the combustion are performed in a single unit.
6. The method according to any one of the preceding claims, wherein the fuel gas (12) is further subjected to a heat recovery step prior to being subjected to the cracking step (100) or prior to being subjected to combustion, wherein heat is indirectly transferred from combustion gas (60) to the fuel gas (12).
7. A process for the catalytic synthesis of hydrogen comprising the steps of:
a) Subjecting the ammonia stream (7) to a heating stage (6, 51, 9) to produce an ammonia-containing stream (10);
b) Subjecting the ammonia-containing stream (10) to a catalytic ammonia cracking step (11) in the presence of heat to produce combustion gases (60) and a thermal cracking stream (14) containing nitrogen, hydrogen and residual ammonia;
c) Optionally mixing the thermal cracking stream with water (74) to produce a thermal cracking stream (75) with water added;
d) Feeding the thermal cracking stream (14) or the thermal cracking stream (75) with added water to a cooling stage (51, 6, 70) to produce a cooled stream (79);
e) Subjecting the cooled stream (79) to a flash separation step (80) to produce an ammonia-lean stream (81) and an ammonia stream or aqueous ammonia solution (82), and further subjecting the ammonia-lean stream (81) to the steps of:
e1 A hydrogen recovery step (19) to produce a high purity hydrogen stream (22) and a tail gas (23),
or (b)
e2 A washing step (20) in the presence of water (17) to produce a purified gas stream (51), and further subjecting the purified gas stream (51) to a hydrogen recovery step (19) to produce a high purity hydrogen stream (22) and a tail gas (23);
f) Recirculating at least a portion of the tail gas (23) as fuel to provide heat for the catalytic cracking step (11);
g) The high purity hydrogen stream (22) is withdrawn.
8. The method of claim 7, wherein the heat of reforming for the ammonia catalytic cracking step is provided by combustion of the fuel gas (12) in the presence of preheated air (28).
9. The method of claim 7, further comprising the step of: subjecting the ammonia-retaining fuel gas (12) to a cracking step (100) in the presence of electrical heating to produce a gas mixture (101) retaining hydrogen and nitrogen and optionally unconverted ammonia, and further subjecting the gas mixture (101) to combustion in the presence of preheated air (28) to provide reforming heat in the catalytic cracking step (11).
10. The method according to any of the preceding claims, further comprising the step of:
h) Subjecting the aqueous ammonia solution (82) to a distillation step (83) to separate an ammonia stream (86) from the aqueous solution (84);
i) Recirculating at least a portion of the ammonia stream (86) as fuel to provide heat for the catalytic cracking step (11);
j) Optionally recycling a portion of the ammonia stream (86) to step (a) to undergo the heating stage (6, 51, 9) in the presence of the ammonia stream (7);
k) Heat is recovered from the combustion gas (60) by indirectly contacting a portion (87) of the aqueous solution (84) with the combustion gas (60) and feeding the portion of the aqueous solution to the distillation step (83) after heat recovery to provide distillation heat.
11. The method of claim 10, further comprising the step of: a second portion (88) of the aqueous solution (84) obtained from the distillation step (83) is mixed with a thermal cracking stream (14) optionally added with a water make-up stream (17).
12. The method according to any of the preceding claims, wherein the hydrogen purification step (19) is performed by a pressure swing adsorption unit, or a cryogenic separation unit, or a membrane purification unit.
13. The method according to any of the preceding claims, wherein the concentration of the high purity hydrogen stream (22) is higher than 95%wt, preferably higher than 99%wt, more preferably higher than 99.9%wt.
14. A process according to any one of the preceding claims, wherein the temperature of the thermal cleavage stream (14) leaving the catalytic cleavage step (11) is between 400 and 950 ℃, preferably between 550 and 650 ℃.
15. A process according to any one of the preceding claims, wherein the catalytic cracking step (11) is carried out at a pressure of about 5 to 65barg, preferably between 15 and 30barg inclusive.
16. The method according to any one of the preceding claims, wherein the combustion gas (60) is subjected to a nitrogen oxide (NOx) reduction step.
17. Apparatus for producing hydrogen according to the method of claim 1, comprising at least:
a furnace (11) suitable for ammonia cracking, comprising a plurality of externally heated catalytic tubes; an input line arranged to feed an ammonia-containing stream (10) into the tubes, and an output line arranged to collect a thermal cracking stream (14) from the tubes;
a hydrogen recovery unit (19) configured to recover a high purity hydrogen stream (22) and a tail gas (23);
-a line arranged to recycle at least a portion of the off-gas (23) separated from the hydrogen recovery unit (19) to the furnace (11) for use as additional fuel;
-a line arranged to withdraw a high purity hydrogen stream (22) from said hydrogen recovery unit (19).
18. The apparatus of claim 17, further comprising:
-a purification unit (20) configured to recover ammonia from the thermal cracking stream (14) to produce a purified gas stream (51) and a recycle gas (21);
-a line arranged to feed at least a portion of the recycle gas (21) to the furnace (11).
19. The apparatus of claim 17 or 18, further comprising an electrical cracking unit (100), the electrical cracking unit (100) being configured to crack fuel gas retaining ammonia, wherein:
the electrical cracking unit is disposed above the furnace and is in fluid communication with the furnace by means of a gas production line;
or (b)
The electrical cracking unit is disposed within the furnace and is configured to crack the fuel gas prior to combustion.
20. Apparatus for producing hydrogen according to the method of claim 7, comprising at least:
a furnace (11) suitable for ammonia cracking, comprising a plurality of externally heated catalytic tubes; an input line arranged to feed an ammonia-containing stream (10) into the tubes, and an output line arranged to collect a thermal cracking stream (14) from the tubes;
optionally a line configured to feed water to an output line arranged to collect the thermal cracking stream (14);
a flash separator unit (80) in communication with the output line, the flash separator unit (80) configured to separate an ammonia lean gas stream (81) and an ammonia stream or aqueous ammonia solution (82);
a hydrogen recovery unit (19), the hydrogen recovery unit (19) being in fluid communication with the flash separator and configured to recover a high purity hydrogen stream (22) and a tail gas (23);
-a line arranged to recycle at least a portion of the off-gas (23) separated from the hydrogen recovery unit (19) to the furnace (11) for use as additional fuel;
a line arranged to withdraw a high purity hydrogen stream (22) from said hydrogen recovery unit (19).
21. The apparatus of claim 20, further comprising:
a distillation unit (83) configured to separate water and ammonia in the aqueous ammonia solution;
-a line connecting the flash separator unit (80) to the distillation unit (83) and configured to convey the aqueous ammonia solution (82) to the distillation unit (83);
-a gas production line connecting the distillation unit (83) to the furnace (11);
a heat exchanger section configured to recover heat from combustion gases in the furnace by means of a water stream;
a line connecting the distillation unit to the heat exchanger section and configured to convey the water stream for heat integration purposes between the furnace and the distillation unit.
22. The apparatus according to any of the preceding claims, wherein the furnace further comprises a unit for removing nitrogen oxides, NOx, preferably an SCR unit.
23. The apparatus of any one of the preceding claims, wherein the hydrogen recovery unit is one of the following units: a pressure swing adsorption unit; a low temperature separation unit; a membrane separation unit.
CN202280036646.8A 2021-05-21 2022-05-19 Ammonia cracking for hydrogen production Pending CN117355482A (en)

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US7354560B2 (en) * 2006-01-31 2008-04-08 Haldor Topsoe A/S Process for the production of hydrogen
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WO2011107279A1 (en) * 2010-03-02 2011-09-09 Amminex A/S Apparatus for generating hydrogen from ammonia stored in solid materials and integration thereof into low temperature fuel cells
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