Ammonia cracking

Abstract

The ammonia cracking method for purifying cracked gases in a PSA system is improved by feeding PSA tail gas or gases derived from it into a secondary cracking reactor and further processing the second cracked gas to convert residual ammonia in the first cracked gas into hydrogen and nitrogen.

Description

Background Art

[0001] Global focus on renewable energy and the use of it to produce green hydrogen has fueled interest in converting green hydrogen into green ammonia, due to the greater ease of transporting ammonia over distances of hundreds or thousands of miles. Specifically, transporting liquid hydrogen is currently commercially impossible, but transporting liquid ammonia is feasible.

[0002] For use in commercial fuel cells, ammonia must be converted back to hydrogen according to the reaction.

[0003]

[0004] This is an endothermic process, meaning it requires heat and takes place over a catalyst. This process is called cracking. The resulting gas (or "cracked gas") is a combination of hydrogen (H2) and nitrogen (N2). Because cracking is an equilibrium reaction, some residual ammonia is also present. Currently, in most applications of crackers, the hydrogen + nitrogen mixture is used as is. However, since ammonia can be a poison for fuel cells, this stream can be used directly for fuel cells, for example, by properly removing ammonia through washing with water. However, if hydrogen is used for vehicle refueling, the presence of nitrogen will adversely affect the process. Fuel in vehicle refueling systems is compressed to fairly high pressures—up to 900 bar. This means that nitrogen, which is only used as a diluent in the process, is also compressed, resulting in energy consumption, increased storage volume, and increased anode gas purging requirements, reducing efficiency. Therefore, when hydrogen is used for vehicle refueling, purification of the hydrogen + nitrogen is beneficial.

[0005] Small-scale cracking reactors or “crackers” typically use pressure swing adsorption (“PSA”) units to separate cracked gases, recover hydrogen, and produce PSA tail gas (or exhaust gas). However, these crackers are usually electrically heated, and the PSA tail gas is typically released into the atmosphere.

[0006] Similar to the common practice in hydrogen production from steam methane reforming (SMR) reactors, nitrogen + hydrogen can be purified using PSA. The cracking reaction takes place in a catalyst-filled tube, which is externally heated by a furnace (see GB1142941).

[0007] GB1142941 discloses a method for producing city gas from ammonia. The ammonia is cracked, and the cracked gas is washed with water to remove residual ammonia. The purified hydrogen / nitrogen mixture is then enriched with propane and / or butane vapors to produce city gas for distribution.

[0008] US6835360A discloses an endothermic catalytic reaction apparatus for converting hydrocarbon feedstocks and methanol into useful gases, such as hydrogen and carbon monoxide. The apparatus includes a tubular endothermic catalytic reactor integrated with a radiant combustion chamber. The resulting cracked gas is then directly used in a fuel cell after passing through a gas conditioning system.

[0009] GB977830A discloses a method for cracking ammonia to produce hydrogen. In this method, hydrogen and nitrogen are separated by passing cracked gas through a molecular sieve bed that adsorbs nitrogen. The nitrogen is then removed from the bed and can be stored in a holder.

[0010] JP5330802A discloses an ammonia cracking process, wherein ammonia reacts with an ammonia decomposition catalyst at a concentration of 10 kg / cm³. 2 Contact at a pressure of (or approximately 9.8 bar) and a temperature of 300 to 700°C. Hydrogen is recovered from the cracked gas using a PSA unit. The reference mentions that the desorbed nitrogen can be used to promote upstream processes, but no details are provided.

[0011] US2007 / 178034A discloses a method in which a mixture of ammonia and hydrocarbon feedstocks is passed through a combustion steam reformer at 600°C and 3.2 MPa (or about 32 bar), where it is converted into syngas containing about 70 vol% hydrogen. The syngas is enriched with hydrogen in a shift reaction, cooled, and condensate is removed. The resulting gas is fed into a PSA system to produce a purified hydrogen product with 99 vol% or more hydrogen. Exhaust gas from the PSA system is fed as fuel into the combustion steam reformer.

[0012] CN111957270A discloses a method in which ammonia is cracked in a tubular reactor within a furnace. The cracked gas is separated by adsorption to produce hydrogen and nitrogen-rich waste gas. The use of a combination of cracked gas, hydrogen product gas, and / or waste gas appears to meet the furnace's fuel requirements.

[0013] There is a general need for improved methods of producing hydrogen from ammonia, and in particular, for methods that are more energy efficient and / or have higher levels of hydrogen recovery and / or reduce or eliminate the need to burn fossil fuels.

[0014] In the following discussion of embodiments of the present invention, unless otherwise stated, the pressure given is absolute pressure. Summary of the Invention

[0015] According to a first aspect of the present invention, a method for producing hydrogen from ammonia is provided, comprising:

[0016] Pressurize liquid ammonia;

[0017] The liquid ammonia is heated (and optionally evaporated) by heat exchange with one or more hot fluids to produce heated ammonia;

[0018] Fuel is burned in the furnace to heat the first set of catalyst-containing reactor tubes and form flue gas;

[0019] The heated ammonia is supplied to the first set of catalyst-containing reactor tubes to crack the ammonia into a first cracked gas containing hydrogen, nitrogen, and residual ammonia; and

[0020] Purifying the first cracked gas in the first PSA to produce a first hydrogen product gas and a first PSA tail gas; and

[0021] The first PSA tail gas or the gas derived therefrom is fed into a secondary cracking reactor containing a catalyst to crack ammonia into a second cracked gas containing hydrogen and nitrogen.

[0022] The one or more thermal fluids include the flue gas and / or the first cracked gas.

[0023] Liquid ammonia is typically pressurized to a pressure greater than 1.1 bar, such as at least 5 bar or at least 10 bar. In some embodiments, liquid ammonia is pressurized to a pressure in the range of about 5 bar to about 50 bar, or in the range of about 10 bar to about 45 bar, or in the range of about 30 bar to about 40 bar.

[0024] Liquid ammonia is typically heated to produce heated ammonia at temperatures above about 250°C, for example, in the range of about 350°C to about 800°C or about 400°C to about 600°C. Under said pressure, the liquid ammonia typically evaporates completely to form heated ammonia vapor.

[0025] The temperature is ultimately determined by the characteristics of the catalyst, the operating pressure, and the desired "leakage" (i.e., the amount of ammonia that passes through the cracking reactor without being cracked). In this respect, the method is typically operated with a leakage of no more than about 4%, which would be the leakage amount if the cracking process were operated near equilibrium at 5 bar and 350°C. Some building materials may have problems at temperatures above about 700°C under any apparent pressure.

[0026] The first cracking reaction occurs in a first set of catalyst-filled reactor tubes heated by a furnace. However, theoretically, any heterogeneous catalytic gas reactor could be used for the conversion.

[0027] A large number of catalysts for ammonia cracking reactions are known in the art, and any of these conventional catalysts can be used in this invention.

[0028] The primary fuel for the furnace typically comprises methane. The fuel can be pure methane, but more likely it is natural gas or biogas. In some embodiments, the primary fuel is natural gas or biogas supplemented with hydrogen as an auxiliary fuel, optionally in the form of ammonia cracked gas. In these embodiments, liquid ammonia can be pumped and cracked to form cracked gas added to the primary fuel.

[0029] The first PSA unit can operate on a PSA cycle or a vacuum pressure swing adsorption (VSA) cycle. The TSA unit can be used in conjunction with the first PSA unit, a TSA unit for ammonia removal (see US10787367), and a first PSA unit for nitrogen removal and the production of hydrogen products. Suitable PSA cycles include any cycle disclosed in US9381460, US6379431, and US8778051, the disclosures of which are incorporated herein by reference.

[0030] Typically, secondary cracking reactors operate in the range of about 250°C to about 700°C, for example, in the range of about 300°C to about 700°C or in the range of about 400°C to about 600°C. Therefore, the feed to the secondary cracking reactor must generally be heated before being fed into the reactor. In a preferred embodiment, the feed to the secondary cracking reactor is heated by heat exchange with the second cracking gas and / or flue gas. For example, the heating of the secondary cracking reaction and the reaction feed can be carried out in a single "heat exchanger reactor".

[0031] The secondary cracking reactor can operate at pressures from about 1.5 bar to about 50 bar, for example, from about 1.5 bar to about 40 bar. Typically, the secondary cracking reactor operates at pressures from about 2 bar to about 15 bar, preferably from about 10 bar to about 12 bar, more preferably from about 11 bar or about 12 bar. In other embodiments, the secondary cracking reactor operates at pressures from about 2 bar to about 5 bar, preferably from about 4 bar. Therefore, the feed to the secondary cracking reactor may need to be compressed to the operating pressure of the secondary cracking reactor before being fed into the reactor. The first PSA tail gas can be supplied to the secondary cracking reactor without compression.

[0032] In some implementations, the first PSA tail gas is compressed before being fed into the secondary cracking reactor. In this regard, the method may include compressing the first PSA tail gas in a multi-stage compressor comprising at least two stages, the method comprising removing the feed to the secondary cracker from the interstage of the compressor and supplying a second cracked gas back to the interstage of the compressor for further compression.

[0033] Hydrogen can be recovered from the second cracked gas. Recovery can be achieved by purifying the second cracked gas in the second PSA to produce a second hydrogen product gas and a second PSA tail gas. The second hydrogen product gas can be combined with the first hydrogen product gas to form a combined hydrogen product gas. Alternatively or additionally, the fuel burned in the furnace may include the second PSA tail gas.

[0034] In some embodiments, the first PSA tail gas is purified in the second PSA to produce a second hydrogen product gas and a second PSA tail gas. The second PSA tail gas can be supplied as feed to the secondary cracking reactor. Optionally, the fuel burned in the furnace contains the second cracked gas.

[0035] The second PSA unit can operate on a PSA cycle or a vacuum pressure swing adsorption (VSA) cycle. The TSA unit can be used in conjunction with the second PSA unit, a TSA unit for ammonia removal, or a second PSA unit for nitrogen removal and hydrogen production. Suitable PSA cycles include any cycle disclosed in US9381460, US6379431, and US8778051.

[0036] In other embodiments, the method includes using a membrane separator to separate the first PSA tail gas. Like hydrogen, ammonia is a "fast gas" that readily permeates through the membrane used for gas separation. In these embodiments, the method may include compressing the first PSA tail gas in a first compressor to produce compressed first PSA tail gas, and using a membrane separator to separate the compressed first PSA tail gas to produce a hydrogen-rich permeate gas containing ammonia and a nitrogen-rich permeate gas, wherein the permeate gas is supplied as feed to the secondary cracking reactor.

[0037] The permeate gas can also be compressed in a second compressor before being supplied as feed to the secondary cracking reactor.

[0038] Recirculating hydrogen-rich permeate gas for further processing in a PSA unit (or, for simplicity, "PSA") significantly improves hydrogen recovery, with recovery rates approaching 100%, for example, around 99%.

[0039] The method may include taking feed from the interstage of a multistage compressor comprising at least two stages from the secondary cracker and supplying a second cracked gas to the interstage of the compressor for further compression.

[0040] Typically, in methods utilizing membrane separators, hydrogen is recovered from the second cracked gas. Optionally, hydrogen is recovered from the second cracked gas by purifying the second cracked gas with the first cracked gas in a first PSA.

[0041] According to a second aspect of the present invention, an apparatus for producing hydrogen from ammonia is provided, comprising:

[0042] A pump, used to pressurize liquid ammonia;

[0043] At least one heat exchanger, which is in fluid communication with the pump, is used to heat (and optionally evaporate) the liquid ammonia from the pump by heat exchange with one or more hot fluids;

[0044] The first set of catalyst-containing reactor tubes, which are in fluid communication with the heat exchanger, are used to crack heated ammonia from the heat exchanger to produce a first cracked gas containing hydrogen, nitrogen and residual ammonia.

[0045] A furnace, which is thermally connected to the first group of catalyst-containing reactor tubes, is used to burn fuel to heat the first group of catalyst-containing reactor tubes and form flue gas;

[0046] The first PSA unit, which is in fluid communication with the first set of catalyst-containing reactor tubes, is used to purify the first cracked gas to produce the first hydrogen product gas and the first PSA tail gas.

[0047] A secondary cracking reactor comprising a catalyst for cracking the first PSA tail gas or gases derived therefrom to produce a second cracked gas comprising hydrogen and nitrogen; and

[0048] A second PSA unit is used to recover hydrogen from the second cracked gas or the first PSA tail gas to produce a second hydrogen product gas and a second PSA tail gas.

[0049] The device includes a flue gas conduit for feeding the flue gas as a hot fluid from the furnace to the heat exchanger and / or a cracked gas conduit for feeding the first cracked gas as a hot fluid from the first set of catalyst-containing reactor tubes to the heat exchanger.

[0050] Although the furnace and the catalyst-filled reactor tubes are preferably integrated within the same unit, the furnace can be separated from the catalyst-filled reactor tubes. In a preferred embodiment, a steam methane reforming (SMR) reactor is used, wherein the furnace includes a radiant section through which the catalyst-containing reactor tubes pass.

[0051] The device may include a compressor for compressing the first PSA tail gas upstream of the secondary cracking reactor.

[0052] Alternatively, the device may include a multi-stage compressor comprising a first stage for compressing a first PSA tail gas upstream of the secondary cracking reactor and a second stage for compressing a second cracked gas downstream of the secondary cracking reactor.

[0053] The second PSA unit can be located downstream of the compressor and upstream of the secondary cracking reactor.

[0054] The equipment may include a compressor for compressing a second cracked gas upstream of a second PSA unit.

[0055] Typically, the apparatus also includes a first economizer for heating the PSA tail gas feed to the secondary thermal cracking reactor by heat exchange with the second cracking gas. Alternatively or additionally, the apparatus typically includes a second economizer for heating the PSA tail gas feed to the secondary cracking reactor by heat exchange with the flue gas.

[0056] According to a third aspect of the present invention, an apparatus for producing hydrogen from ammonia is provided, comprising:

[0057] A pump, used to pressurize liquid ammonia;

[0058] At least one heat exchanger, which is in fluid communication with the pump, is used to heat (and optionally evaporate) the liquid ammonia from the pump by heat exchange with one or more hot fluids;

[0059] The first set of catalyst-containing reactor tubes, which are in fluid communication with the heat exchanger, are used to crack heated ammonia from the heat exchanger to produce a first cracked gas containing hydrogen, nitrogen and residual ammonia.

[0060] A furnace, which is thermally connected to the first group of catalyst-containing reactor tubes, is used to burn fuel to heat the first group of catalyst-containing reactor tubes and form flue gas;

[0061] The first PSA unit, which is in fluid communication with the first set of catalyst-containing reaction tubes, is used to purify the first cracked gas to produce hydrogen product gas and the first PSA tail gas.

[0062] A secondary cracking reactor comprising a catalyst for cracking the first PSA tail gas or gases derived therefrom to produce a second cracked gas comprising hydrogen and nitrogen; and

[0063] A membrane separator is used to separate the first PSA tail gas to produce a nitrogen-rich permeate gas and a hydrogen-rich permeate gas containing ammonia, for further processing in the secondary cracking reactor.

[0064] The device includes a flue gas conduit for feeding the flue gas as a hot fluid from the furnace to the heat exchanger and / or a cracked gas conduit for feeding the first cracked gas as a hot fluid from the first set of catalyst-containing reactor tubes to the heat exchanger.

[0065] The device may include a first compressor to compress the first PSA tail gas before separation in the membrane separator. Optionally, the Haloxylon ammodendron device may include a second compressor for compressing hydrogen-rich gas.

[0066] In some embodiments, the apparatus includes a multi-stage compressor comprising a first stage for compressing hydrogen-rich gas upstream of the secondary cracking reactor and a second stage for compressing second cracked gas downstream of the secondary cracking reactor.

[0067] In another embodiment, the device includes a second compressor for compressing the second cracked gas.

[0068] Typically, the apparatus also includes a first heat exchanger for heating the PSA tail gas feed to the secondary thermal cracking reactor by heat exchange with the second cracking gas. Alternatively or additionally, the apparatus typically includes a second heat exchanger for heating the PSA tail gas feed to the secondary cracking reactor by heat exchange with the flue gas. Attached Figure Description

[0069] Figure 1 This is a process flow diagram of the first reference embodiment of the ammonia cracking method for producing hydrogen;

[0070] Figure 2 Based on Figure 1 A process flow diagram of another reference embodiment of the ammonia cracking method, in which no hydrogen product is used as fuel;

[0071] Figure 3 Based on Figure 1 and Figure 2 A process flow diagram of another reference embodiment of the ammonia cracking method, wherein only PSA tail gas is used as fuel;

[0072] Figure 4 This is a process flow diagram of the fourth reference embodiment of the ammonia cracking method for producing hydrogen using a membrane separator;

[0073] Figure 5 This is a process flow diagram of the fifth reference embodiment of the ammonia cracking method for producing hydrogen using two PSA units;

[0074] Figure 6 This is a process flow diagram of the first embodiment of the ammonia cracking method for producing hydrogen according to the present invention;

[0075] Figure 7 It shows Figure 6 The process flow diagram of the first alternative arrangement for ammonia cracking described in the document;

[0076] Figure 8 It shows Figure 6 The process flow diagram of the second alternative arrangement of the ammonia cracking process described in the document;

[0077] Figure 9 It shows Figure 6 The process flow diagram of the third alternative arrangement of ammonia cracking described in the text;

[0078] Figure 10 This is a process flow diagram of a second embodiment of the ammonia cracking method for producing hydrogen according to the present invention;

[0079] Figure 11 It shows Figure 10 The process flow diagram of the first alternative arrangement for ammonia cracking described in the document; and

[0080] Figure 12 It shows Figure 10 The process flow diagram of the second alternative arrangement for ammonia cracking described in the text. Detailed Implementation

[0081] This article describes a method for producing hydrogen by cracking ammonia. The method is particularly suitable for producing so-called “green” hydrogen, i.e., hydrogen produced using renewable energy sources instead of fossil fuels. In this case, ammonia is typically produced by electrolyzing water using electricity generated from renewable energy sources such as wind and / or solar power to produce hydrogen, which is then catalytically reacted with nitrogen (the Haber method) to produce ammonia, which is easier to transport than hydrogen. Upon arrival at its destination, the ammonia is cracked to regenerate hydrogen.

[0082] In the method of this invention, the heat required for the reaction is typically provided by the combustion of PSA tail gas (which typically contains a certain amount of residual hydrogen and ammonia) in a furnace. If the calorific value of the PSA tail gas is lower than that of the evaporated ammonia, a portion of the product hydrogen or alternative fuel can be used as trim fuel along with the tail gas.

[0083] In practice, natural gas can be used as a corrective fuel along with PSA tail gas, as is done for hydrogen in SMR. However, there is an incentive to use “renewable fuels” because of the desire to maintain the “green” or renewable status of hydrogen produced in this way. This could be cracking “renewable” ammonia, ammonia itself, or another renewable energy source such as biogas, or actually electric heating, regardless of whether the electricity itself comes from renewable sources. In this case, the electricity itself is local in the cracking process, unlike the renewable electricity used to produce hydrogen transported in the form of ammonia.

[0084] A reference embodiment of the method is described in Figure 1The method is shown in the figure. Liquid ammonia is removed from a storage tank (not shown). The ammonia to be cracked (line 2) is pumped as a liquid (pump P201) to a pressure higher than the required cracking pressure (see GB1142941). According to the Le Chatelier principle, the reaction pressure is a trade-off between the operating pressure and the conversion rate. There is an incentive to operate the reactor (8) at a higher pressure because pumping liquid ammonia requires less power and capital than compressing the product hydrogen.

[0085] The pressurized liquid ammonia (line 4) is then heated, evaporated (if below its critical pressure), and further heated via heat exchanger (E101) using available heat from the cracked gas exiting the reaction tube and the flue gas from the furnace until it reaches a temperature above 250°C. In the diagram, heat exchanger (E101) is shown as a single heat exchanger, but in reality, it would be a series of heat exchangers in a network.

[0086] Initial heating and evaporation of pressurized liquid ammonia can alternatively be carried out using alternative heat sources, such as cooling water or ambient air. Typical reaction temperatures are above 500°C (see US2601221), palladium-based systems can operate at 600°C and 10 bar, while RenCat's metal oxide-based systems can operate below 300°C and 1 bar. (See https: / / www.ammoniaenergy.org / articles / ammonia-cracking-to-high-purity-hydrogen-for-pem-fuel-cells-in-denmark / ). The operating pressure of the cracker is typically optimized for several factors. Lower pressures favor the cracking of ammonia into hydrogen and nitrogen, but other factors favor higher pressures, such as power consumption (which is minimized by pumping the feed ammonia instead of compressing the product hydrogen) and PSA size (which is smaller at higher pressures).

[0087] Hot ammonia (line 6) enters the reaction tube of reactor (8) at the required pressure, where additional heat is provided by furnace (10) to crack the ammonia into nitrogen and hydrogen. The resulting mixture of residual ammonia, hydrogen, and nitrogen exits the reaction tube (8) (line 12) at the reaction temperature and pressure. The reaction products are cooled in a heat exchanger (E101) by a combination of feed ammonia (from line 4), furnace fuel (in this case, pumped ammonia from line 14, pump P202, and line 16; PSA tail gas from line 18; and product hydrogen to be used as fuel in line 20) and combustion air (from line 22, blower K201, and line 24) to reduce the temperature as close as possible to the required inlet temperature of the PSA unit (26). Any residual heat in the cracked gas mixture (line 28) is removed in a water cooler (not shown) to achieve an inlet temperature of the PSA unit (26) in the range of about 20°C to about 60°C, for example, about 50°C.

[0088] The PSA product (line 30) is pure hydrogen, conforming to ISO standard 14687 – quality of hydrogen fuel, wherein at approximately the reaction pressure, residual ammonia <0.1 ppmv and nitrogen <300 ppmv. The product hydrogen (line 30) is further compressed (not shown) for filling into a pipeline trailer (not shown) for transport, or it can be liquefied in a hydrogen liquefaction unit (not shown) after any required compression. The PSA tail gas (line 18) or “purge gas” from the PSA unit (26) is shown heated via heat exchanger E101 before being fed to the furnace (in line 34) as combustion fuel using cracked gas (line 12) or furnace flue gas (line 32) exiting the reaction tube. However, the PSA tail gas (line 18) can be fed directly into the furnace (10) without heating.

[0089] The resulting warm ammonia fuel (line 36) and warm hydrogen (line 40) are described as being combined in a mixer (42) with (optionally) warm PSA tail gas (line 38) to produce a combined fuel, which is fed (line 44) into the furnace (10) for combustion to produce flue gas (line 32, and line 48 after cooling in E101). However, it should be noted that one or more fuels may be fed directly into the furnace without premixing. Warm air (for fuel combustion) is fed into the furnace (10) in line 46.

[0090] One of the objectives of the preferred embodiments of this method is to maximize the amount of hydrogen produced by cracking renewable ammonia. This means minimizing the amount of hydrogen used as fuel, or minimizing the amount of ammonia if it is to be used directly as fuel. Therefore, thermal integration is important to properly utilize hot flue gas and cracked gas, such as preheating the air (line 24) and ammonia (line 4) entering the cracker, as this reduces the amount of “fuel” used in the burners of the furnace (10). This results in a higher hydrogen recovery rate because less hydrogen is lost as water in the furnace flue gas (lines 32 and 48). Therefore, steam generation should be minimized, for example, to facilitate thermal integration within the method.

[0091] Figure 1 It shows ammonia supplied as fuel (pipelines 34 and 44) ​​and feed (pipeline 6), and it also shows product hydrogen as fuel (pipelines 40 and 44)—in reality, it is highly likely that only one of these streams will be used as fuel. At this point, Figure 2 Depicting and Figure 1 A similar method is used, where ammonia is used as fuel (pipeline 34) instead of the product hydrogen. Figure 2 All other features of the method described in it are the same as Figure 1 The same and common features are given the same reference numerals.

[0092] The inventors realized that if hydrogen were also used as fuel, especially during startup and preheating, it would benefit the stable combustion of ammonia.

[0093] Figure 3 Depicting and Figure 2 The method described is similar to that in this method. In this method, hydrogen can be recovered from the PSA (line 30) to provide exhaust gas (line 18), which, when burned, will provide all the heat required by the method, thus eliminating the need for correction fuel. Figure 3 All other features of the method described in it are the same as Figure 1 The same and common features are given the same reference numerals.

[0094] As mentioned above, if viable alternative sources of renewable energy for the cracking reaction exist, recovering hydrogen from PSA tail gas can be considered to increase the net hydrogen production from the method in addition to the hydrogen generated from the PSA. Such methods can utilize membranes with selective layers that readily permeate hydrogen but are relatively impermeable to nitrogen to separate hydrogen from nitrogen-rich PSA tail gas streams. Figure 4 ).

[0095] If a membrane is used as part of the separation process, ammonia may need to be removed specifically, but not exclusively, because the membrane material may not tolerate high concentrations of ammonia, and ammonia is a fast-moving gas that will permeate along with hydrogen, thus accumulating during the process if not removed. Ammonia can be removed upstream of the membrane by, for example, water washing or other well-known ammonia removal techniques. Ammonia can be recovered from the ammonia solution produced in the water washing using a stripping column, and the recovered ammonia can be recycled back into the feed to the cracking reactor. Theoretically, this can increase the hydrogen recovery rate of the method up to 100%. Recovering ammonia from the cracking gas simplifies the hydrogen purification steps; if the separated ammonia is recovered as feed, hydrogen recovery from ammonia can be increased, and ammonia is also removed from the feed to the burner, thus eliminating the risk of NO2 produced by burning ammonia. x The concerns that arise.

[0096] It may also be necessary to remove water from the feed ammonia to prevent damage to the ammonia cracking catalyst. Typically, ammonia contains a small amount of water added to prevent stress corrosion cracking of the container during transport and storage. This may need to be removed. However, water removal can be incorporated into the stripping tower described above. The ammonia will evaporate at the required pressure, and care must be taken in the design of the evaporator to ensure that water is also carried to the stripping tower along with the evaporator ammonia. This predominantly gaseous ammonia enters the midpoint of the tower, and pure ammonia exits through the top of the tower. The tower has a partial condenser (condensing only enough liquid for reflux), and the overhead vapor contains the feed ammonia (water-free) plus ammonia recovered from the cracker gas stream.

[0097] Feeding the cracked gas into the membrane first to produce a hydrogen-rich permeate and a nitrogen-rich residual stream that can be discharged may be more energy-efficient. The hydrogen-rich permeate can be further purified in the PSA. A second membrane can be added to the PSA tail gas stream to further improve the overall hydrogen recovery rate. This configuration will significantly reduce the size of the tail gas compressor.

[0098] Using a membrane separator to improve hydrogen recovery allows nitrogen to be evacuated from the process without passing through the combustion section. During the process where the nitrogen gas stream is pressurized, it is beneficial to expand the nitrogen to atmospheric pressure before it is exhausted through the expansion turbine to recover power. If the pressurized nitrogen is heated using heat available in the flue gas or cracked gas stream before expansion, the amount of power recovered will increase.

[0099] Figure 4 A method involving a membrane for recovering hydrogen from PSA exhaust gas while simultaneously removing nitrogen is described. Figure 4 The methods and Figures 1 to 3 The common features of the methods described are given the same reference numerals. The following are... Figure 4 Discussion of the new characteristics of China.

[0100] The fuel (line 50), which may be “renewable” fuel, but is usually natural gas or biogas, is heated in a heat exchanger (E101) and fed (line 52) into a furnace (10) for combustion to heat the catalyst-filled tubes of the cracking reactor (8).

[0101] Cooled cracked gas (line 28) is combined with compressed hydrogen-rich permeate gas (line 62) to form a combined gas, which is fed (line 64) to the PSA unit (26). The combined gas is separated to form hydrogen products (line 30). The tail gas from the PSA (line 54) is compressed in a first compressor (K301), and the compressed gas is fed (line 56) to a membrane separation unit (M301) to produce a hydrogen-rich permeate stream (line 58) and a nitrogen-rich permeate stream (line 60). The membrane separation unit may consist of multiple membrane devices arranged in parallel or in series, as determined by the feed flow rate and the desired hydrogen recovery rate. The permeate stream is compressed in a second compressor (K302) to form compressed hydrogen-rich gas (line 62), which, together with the cooled cracked gas (line 28), is recycled (line 64) to the PSA (26) to improve the overall hydrogen recovery rate.

[0102] Assuming the hydrogen produced by the membrane is of sufficiently high purity, a portion (line 68) of the hydrogen permeate gas can be combined with the hydrogen product (line 30) after compression, with the remainder being recycled (line 64) to the PSA along with cooled cracked gas (line 28). Combining a portion of the hydrogen permeate gas with the hydrogen product in this manner will reduce the required size of the PSA and the power of K301 and K302.

[0103] Alternatively, all compressed hydrogen-rich permeate gas (line 62) can be combined with hydrogen products (line 30), none of which are recycled to the PSA (26).

[0104] Figure 4 A system (described as unit 90) for removing and recovering ammonia from cracked gas is provided. This system may involve a scrubber for removing ammonia from the gas with water and a stripping tower for recovering ammonia from the water, or it may involve a TSA unit for removing ammonia by adsorption (see US10787367).

[0105] Alternatively, the exhaust gas from the first PSA can be compressed and fed into the second PSA for further hydrogen recovery. Figure 5 The PSA exhaust gas from the second PSA is optionally used as part of the fuel for the cracking process. The second PSA maximizes the recovery rate of renewable hydrogen from renewable ammonia. The exhaust gas from the first PSA is compressed to a level that exposes the hydrogen from both PSAs to the same high pressure.

[0106] Both types of PSAs must be able to withstand ammonia in the feed stream. The adsorbent in the PSA needs to be suitable for the adsorption and desorption of ammonia.

[0107] The second PSA tail gas pressure can be higher than the first PSA tail gas pressure—lower in the first PSA to maximize recovery—and higher in the second PSA to allow for pressure drops in the heat exchangers used for preferential reheating of the PSA tail gas and feed to the burner. The energy efficiency (carbon intensity) requirements of renewable fuel processes necessitate more efficient thermal integration than is typically considered for similar hydrogen production methods. Optionally, the low pressure from the PSA tail gas can be tolerated by using low-pressure-drop heat exchangers or intermediate heat exchange fluids.

[0108] If low-carbon fuels cannot be found for use as burner fuel, then high-hydrogen recovery methods (e.g.) Figure 5 The two PSA methods shown will have high carbon intensity, which is partly related to the fuel if it is a non-renewable hydrocarbon (e.g., natural gas), and the emitted carbon dioxide (CO2) cannot be considered as carbon dioxide from renewable fuels. A lower amount of natural gas fuel is required if a lower hydrogen recovery rate is tolerable.

[0109] Figure 5 A method for recovering hydrogen from the tail gas of a first PSA is described. Figure 5 The methods and Figures 1 to 4 The common features of the methods described are given the same reference numerals. The following are... Figure 5 Discussion of the new characteristics of China.

[0110] Fuel (line 50), such as natural gas or renewable fuel, is heated in a heat exchanger (E101) to produce warm fuel (line 52). The warm fuel (line 52) is fed into a mixer (42) to produce a combined fuel (line 44), which is fed into a furnace (10) for combustion to heat the catalyst-filled tubes of the cracking reactor (8). Cooled cracked gas (line 28) is fed into a first PSA unit (26). The gas is separated to form a first hydrogen product (line 30). The tail gas (line 70) from the first PSA unit (26) is compressed in a compressor (K301), and the compressed gas is fed (line 72) to a second PSA unit (74). The gas is separated to form a second hydrogen product (line 78), which is combined with the first hydrogen product (line 30) in line 80. The second PSA exhaust gas (line 76) is heated via heat exchanger E101 to produce warm second PSA exhaust gas (line 82), which is fed into mixer (42).

[0111] Secondary cracking allows for the recovery of ammonia leaking through the main cracking reactor (8) by converting it into hydrogen, which is then recovered in the PSA unit. Alternatively, placing the secondary cracking reactor over the PSA tail gas before using it as fuel in the cracking reactor facilitates combustion and reduces NO production during combustion. x The possibility is that hydrogen is more easily combusted than ammonia.

[0112] Secondary cracking reactors can be adiabatic fixed-bed reactors, but they can also be other types of reactors, such as catalytic heat exchanger reactors. Typically, secondary cracking reactors are adiabatic fixed-bed reactors.

[0113] A secondary cracking reactor can be used, in which PSA tail gas from the first PSA unit (26) (before or after recompression – or interstage) is fed into a catalyst in a second cracking reactor (88) to further crack the ammonia in the first PSA tail gas. This means recovering more hydrogen in the second PSA unit (74) and reducing problems associated with ammonia in the combustor fuel. Figure 6 Such methods are described in [the document / article].

[0114] Figure 6 The methods and Figures 1 to 5 The common features of the methods described are given the same reference numerals. The following are... Figure 6 Discussion of the new characteristics of China.

[0115] Figure 6The method according to the invention is described, wherein PSA tail gas (line 70) from a first PSA unit (26) is compressed in a compressor (K301) to produce compressed PSA tail gas (line 72). The compressed PSA tail gas (line 72) is heated by heat exchange with second cracked gas (line 92) in a first heat exchanger (E102) to produce heated compressed PSA tail gas (line 84). The heated compressed PSA tail gas (line 84) is further heated to 550°C by heat exchange with flue gas (line 32) in a second heat exchanger (E103) to produce feed (line 86) for a secondary cracker (88). The feed passes through a catalyst within the secondary cracking reactor (88) to produce the second cracked gas (line 92). The catalyst used in the secondary cracking reactor can be any suitable catalyst for ammonia cracking, such as a nickel catalyst (GB768091A), an iron catalyst (GB1353751A), a ruthenium catalyst, a rhodium catalyst, and / or an iridium catalyst (US2601221). Suitable organometallic catalysts, such as metal amides and / or metal imides (GB2589621A), can also be used. The catalyst can be the same as that used in the first ammonia cracker, or it can be a different catalyst. The catalyst can contain one type of metal or more than one type of metal. The second cracked gas (line 92) is cooled by heat exchange with the compressed PSA tail gas (line 72) in the first heat exchanger (E102) to produce a cooled second cracked gas (line 94), which is fed into the second PSA unit (74). The second cracked gas is separated to form a second hydrogen product (line 98) and a second PSA tail gas (line 96). The first hydrogen product (pipeline 30) and the second hydrogen product (pipeline 98) are combined to produce a combined hydrogen product (pipeline 100). The second PSA tail gas (pipeline 96) is then mixed with the fuel source (pipeline 50) in a mixer (42).

[0116] The secondary cracking reactor (88) can be located in Figure 6 Several different positions in the method shown. At this point, Figure 6 Alternative arrangements of the methods described in Figures 7 to 9 As described in the text. It should also be noted that when pumped liquid ammonia is used as fuel for the furnace, the secondary cracking reactor can be used to crack the pumped liquid ammonia to produce cracked gas, which is optionally added to the primary fuel in mixer 42.

[0117] Figure 7A secondary cracking reactor (88) is shown, located upstream of the compressor (K301) and the second PSA unit (74) and downstream of the first PSA unit (26). PSA tail gas (line 70) from the first PSA unit (26) is heated by heat exchange with second cracked gas (line 108) in a first heat exchanger (E102) to produce heated PSA tail gas (line 104). The heated PSA tail gas (line 104) is further heated by heat exchange with flue gas (line 32) in a second heat exchanger (E103) and fed into the secondary cracker (88). The second cracked gas (line 108) is cooled by heat exchange with the first PSA tail gas (line 70) in the first heat exchanger (E102) to produce a cooled second cracked gas (line 110), which is fed into compressor K301 and compressed to produce a compressed and cooled second cracked gas (line 112). The compressed and cooled second cracked gas (line 112) is fed into the second PSA unit (74) and separated to form a second hydrogen product (line 116) and a second PSA tail gas (line 114). Placing the secondary cracking reactor (88) upstream of the compressor (K301) increases the conversion of ammonia to hydrogen, as the conversion of ammonia is preferred at lower pressures rather than higher pressures.

[0118] Figure 8 A secondary cracking reactor (88) located between stages in a multi-stage compression system (K301A, K301B) is shown. Cracking at the interstage pressure is more favorable for the reaction products than at the final pressure of the compression system. Therefore, ammonia is converted at lower pressures than at higher pressures.

[0119] PSA tail gas (line 70) from the first PSA unit (26) is compressed in the first stage (K301A) of a multistage compressor to produce compressed PSA tail gas (line 72). Compressed PSA tail gas (line 72) is removed from the interstage of the multistage compressor and heated by heat exchange with second cracked gas (line 92) in a first heat exchanger (E102) to produce heated compressed PSA tail gas (line 84). Heated compressed PSA tail gas (line 84) is further heated to 550°C by heat exchange with flue gas (line 32) in a second heat exchanger (E103) to produce feed (line 86) for the secondary cracker (88). The feed passes through a catalyst within the secondary cracking reactor (88) to produce second cracked gas (line 92). The second cracked gas (line 92) is cooled by heat exchange with the compressed PSA tail gas (line 72) in the first heat exchanger (E102) to produce cooled second cracked gas (line 94). The second cracked gas is fed back to the interstage of the multi-stage compressor and compressed in the second stage (K301B) of the compressor to produce compressed-cooled second cracked gas (line 122). The compressed-cooled second cracked gas (line 122) is fed into the second PSA unit (74) and separated to form a second hydrogen product (line 126) and a second PSA tail gas (line 124). The first hydrogen product (line 30) and the second hydrogen product (line 168) are combined to form a combined hydrogen product (line 128). The second PSA tail gas (line 124) is then mixed with a fuel source (line 50) in a mixer (42).

[0120] Figure 9A secondary cracking reactor (88) located downstream of the second PSA unit (74) is shown. PSA tail gas (line 70) is compressed in a compressor (K301) to produce compressed PSA tail gas (line 72). Compressed PSA tail gas (line 72) is fed into the second PSA unit (74) to produce a second hydrogen product (line 134) and a second PSA tail gas (line 132). The first and second hydrogen products (lines 30 and 134) are combined to form a combined hydrogen product (line 136). The second PSA tail gas (line 132) is heated by heat exchange with a second cracked gas (line 142) in a first heat exchanger (E102) to produce heated second PSA tail gas (line 138). The heated second PSA tail gas (line 138) is further heated by heat exchange with flue gas (line 32) in a second heat exchanger (E103) to produce feed (line 140) for the secondary cracker (88). The feed passes through a catalyst within the secondary cracking reactor (88) to produce a second cracked gas (line 142). The second cracked gas (line 142) is cooled by heat exchange with the second PSA tail gas (line 132) in a first heat exchanger (E102) to produce cooled second cracked gas (line 144), which passes through unit E101 to mixer 42 to produce fuel (line 44). In this arrangement, although hydrogen recovery is not increased, the high levels of ammonia in the fuel lead to increased NO recovery. x The generation-related problems are greatly reduced, so hydrogen is easier to burn than ammonia.

[0121] exist Figure 10 In this process, unconverted ammonia from the secondary cracking reactor (88) is recycled through the first PSA unit (26) and membrane unit (M301), resulting in nearly 100% ammonia conversion to hydrogen, with the only ammonia loss coming from the non-permeable nitrogen-rich stream. The first PSA tail gas is separated using a membrane to obtain a hydrogen-permeable gas containing ammonia. This gas passes through the cracking catalyst. The advantages of this option include (i) lower velocities in the catalyst bed (meaning longer residence times) and (ii) removal of nitrogen products that alter equilibrium positions.

[0122] Figure 10The method according to the invention is described, wherein PSA tail gas (line 54) from a first PSA unit (26) is compressed in a compressor (K301) to produce compressed PSA tail gas (line 56). The compressed PSA tail gas (line 56) passes through a membrane separator (M301) to produce a nitrogen-rich purge stream (line 60) and a hydrogen-rich gas containing ammonia (line 58). The membrane separator (M301) can be any suitable membrane separator known in the art. Conventional membranes include those made of polyamide or polysulfone polymers known to have better tolerance to ammonia, or those made of polyimide polymers known to be less tolerant to ammonia. The hydrogen-rich gas (line 58) is compressed in a second compressor (K302) to produce compressed hydrogen-rich gas (62). The compressed hydrogen-rich gas (line 62) is heated to 350°C by heat exchange in a first heat exchanger (E102) to produce heated hydrogen-rich gas (line 148). The heated hydrogen-rich gas (line 148) is further heated to 550°C via heat exchange in the second heat exchanger (E103) to produce feed (line 150) for the secondary cracker (88). The feed passes through the secondary cracker (88) to produce second cracked gas (line 152). The second cracked gas (line 152) is cooled by heat exchange (E102) with the hydrogen-rich gas (line 62) in the first heat exchanger (E102) to produce cooled second cracked gas (line 154). The cooled second cracked gas (line 154) is recycled to the first PSA unit (26) via line 156.

[0123] In the options of a first PSA unit and a second PSA unit with a two-stage compressor, the lower pressure feed using a secondary cracker offers a balancing advantage. In this PSA / membrane configuration, any unconverted ammonia is recycled back through the PSA and membrane, thus eliminating the need to achieve high conversion rates by operating the secondary cracker at lower pressures.

[0124] Figures 10 to 12 The hydrogen recovery rate in the PSA unit does not need to be as high as in the PSA-only scheme because the hydrogen in the first PSA tail gas is recirculated. Higher PSA tail gas pressure will reduce the compressor power on the first PSA tail gas compressor, which will reduce the PSA hydrogen recovery rate, but due to tail gas recirculation, minus any losses in the non-permeable nitrogen-rich stream, the total hydrogen recovery rate will still be 100%.

[0125] The secondary cracking reactor (88) can be located in Figure 10 Several different positions in the method shown. At this point, in Figure 11 and Figure 12 It is described Figure 10 Alternative arrangements to the methods described in the text.

[0126] Figure 11A secondary cracker (88) is shown located downstream of the membrane separator (M301) and upstream of the second compressor (K302). PSA tail gas (line 54) from the first PSA unit (26) is compressed in the compressor (K301) to produce compressed PSA tail gas (line 56). The compressed PSA tail gas (line 56) passes through the membrane separator (M301) to produce a nitrogen-rich purge stream (line 60) and a hydrogen-rich gas containing ammonia (line 58). The hydrogen-rich gas (line 58) is heated by a heat exchanger in a first heat exchanger (E102) to produce heated hydrogen-rich gas (line 158). The heated hydrogen-rich gas (line 158) is further heated by a heat exchanger in a second heat exchanger (E103) to produce feed gas (line 160) for the secondary cracker (88). The feed gas passes through the secondary cracker (88) to produce second cracked gas (line 162). The second cracked gas (line 162) is cooled by heat exchange (E102) with hydrogen-rich gas (line 58) in the first heat exchanger (E102) to produce cooled second cracked gas (line 164). The cooled second cracked gas (line 164) is compressed in a compressor (K302) to produce compressed-cooled second cracked gas (line 166), which is recycled to the first PSA unit (26) via line 168. The advantage of this arrangement is that a higher ammonia conversion rate is achieved because the conversion rate of ammonia is greater at lower pressures than at higher pressures.

[0127] Figure 12A secondary cracker (88) located between stages in a multi-stage compression system (K302A, K302B) is shown. PSA tail gas (line 54) from the first PSA unit (26) is compressed in a compressor (K301) to produce compressed PSA tail gas (line 56). The compressed PSA tail gas (line 56) is fed to a membrane separator (M301) to produce a nitrogen-rich purge stream (line 60) and a hydrogen-rich gas containing ammonia (line 58). The hydrogen-rich gas (line 58) is compressed in the first stage (K301A) of the multi-stage compressor to produce compressed hydrogen-rich gas, which is removed from the interstage of the compression system (line 62) and heated by heat exchange in a first heat exchanger (E102) to produce heated hydrogen-rich gas (line 148). The heated hydrogen-rich gas (line 148) is further heated by heat exchange in the second stage heat exchanger (E103) to produce feed (line 150) for the secondary cracker (88). The feed passes through the secondary cracker (88) to produce a second cracked gas (line 152). The second cracked gas (line 152) is cooled by heat exchange (E102) with the hydrogen-rich gas (line 62) in the first stage heat exchanger (E102) to produce a cooled second cracked gas (line 154). The cooled second cracked gas (line 154) is fed back to the interstage of the compression system and compressed in the second stage (K301B) to produce a compression-cooled second cracked gas (line 170). The compression-cooled second cracked gas (line 170) is recycled to the first PSA unit (26) via line 172.

[0128] The present invention will now be described with reference to the following reference embodiments and non-limiting inventive embodiments.

[0129] Example

[0130] For simulation purposes, both the embodiments of the present invention and the reference embodiments assume that the cracking reaction is in equilibrium at 11 bar and 500°C.

[0131] Refer to Example 1

[0132] It has been simulated using a computer (Aspen Plus, version 10, Aspen Technology, Inc.). Figure 2 The method described in the document is presented, and the results are shown in Table 1.

[0133]

[0134]

[0135] Table 1

[0136] In this reference embodiment, the hydrogen recovery rate in ammonia is 77.18%, of which the PSA recovery rate is 83.5%. The total power of the ammonia feed pump (P201), ammonia fuel pump (P202), and blower (K201) is approximately 1.36 kW.

[0137] Refer to Example 2

[0138] It has been simulated using a computer (Aspen Plus, version 10). Figure 3 The method described in the document is presented, and the results are shown in Table 2.

[0139]

[0140] Table 2

[0141] In this reference embodiment, the hydrogen recovery rate in ammonia is 77.05%, of which the PSA recovery rate is 79.4%. The total power of the ammonia feed pump (P201) and the blower (K201) is approximately 1.37 kW.

[0142] Refer to Example 3

[0143] It has been simulated using a computer (Aspen Plus, version 10). Figure 5 The method described in the document is presented, and the results are shown in Table 3.

[0144]

[0145] Table 3

[0146] In this reference embodiment, the hydrogen recovery rate from ammonia is 93.65%. The total power of the ammonia feed pump (P201), blower (K201), and PSA tail gas compressor is approximately 27.92 kW.

[0147] Invention Embodiment 1

[0148] It has been simulated using a computer (Aspen Plus, version 10). Figure 6 The method described in the document is presented, and the results are shown in Table 4.

[0149]

[0150]

[0151] Table 4

[0152] In this embodiment of the invention, the hydrogen recovery rate in ammonia is 95.60%. The total power of the ammonia feed pump (P201), blower (K201), and first PSA tail gas compressor is approximately 28.36 kW. Slightly less than 80% of the ammonia leaking through the first cracking reactor is cracked into additional hydrogen and nitrogen in a second cracking reactor operating at 11 bar.

[0153] Invention Embodiment 2

[0154] It has been simulated using a computer (Aspen Plus, version 10). Figure 8 The method described in the document is presented, and the results are shown in Table 5.

[0155]

[0156]

[0157] Table 5

[0158] In this embodiment of the invention, the hydrogen recovery rate from ammonia is 95.87%. The total power of the ammonia feed pump (P201), blower (K201), and first PSA tail gas compressor is approximately 28.32 kW. Slightly more than 92% of the ammonia leaking from the first cracking reactor is cracked into additional hydrogen and nitrogen via a second cracking reactor operating at a lower pressure (4 bar) than in Embodiment 1.

[0159] Invention Embodiment 3

[0160] It has been simulated using a computer (Aspen Plus, version 10). Figure 10 The method described in the document is presented, and the results are shown in Table 6.

[0161]

[0162]

[0163] Table 6

[0164] In this embodiment of the invention, the hydrogen recovery rate in ammonia is 99.00%. The total power of the ammonia feed pump (P201), blower (K201), PSA tail gas compressor, and membrane compressor is approximately 59.24 kW. Approximately 70% of the ammonia leaking through the first cracking reactor is converted into additional hydrogen and nitrogen in the second cracking reactor.

[0165] The scope of this invention is not limited to the specific aspects or embodiments disclosed in the examples, which are intended to illustrate several aspects of the invention, and any functionally equivalent embodiments are within the scope of this invention. Various modifications to the invention, in addition to those shown and described herein, will become apparent to those skilled in the art and are intended to fall within the scope of the appended claims.

Claims

1. A method for producing hydrogen from ammonia, comprising: Pressurize liquid ammonia; The liquid ammonia is heated by heat exchange with one or more hot fluids to produce heated ammonia; Fuel is burned in the furnace to heat the first set of catalyst-containing reactor tubes and form flue gas; The heated ammonia is supplied to the first set of catalyst-containing reactor tubes to crack the ammonia into a first cracked gas containing hydrogen, nitrogen and residual ammonia; as well as Purifying the first cracked gas in the first PSA to produce a first hydrogen product gas and a first PSA tail gas; and The first PSA tail gas or the gas derived therefrom is fed into a secondary cracking reactor containing a catalyst to crack ammonia into a second cracked gas containing hydrogen and nitrogen. The one or more thermal fluids include the flue gas and / or the first cracked gas.

2. The method according to claim 1, wherein the feed to the secondary cracking reactor is heated by heat exchange with the second cracking gas.

3. The method according to claim 1, wherein the feed to the secondary cracking reactor is heated by heat exchange with the flue gas.

4. The method according to any one of claims 1 to 3, wherein the secondary cracking reactor is operated at a temperature in the range of 250°C to 700°C.

5. The method according to any one of claims 1 to 3, wherein the feed to the secondary cracking reactor is compressed before being supplied to the reactor.

6. The method according to any one of claims 1 to 3, wherein the secondary cracking reactor is operated at a pressure of 1.5 bar to 50 bar.

7. The method of claim 6, wherein the secondary cracking reactor is operated at a pressure of 10 bar to 12 bar.

8. The method of claim 6, wherein the secondary cracking reactor is operated at a pressure of 3 to 5 bar.

9. The method of claim 8, wherein the secondary cracking reactor is operated at a pressure of 4 bar.

10. The method according to any one of claims 1 to 3, wherein the first PSA tail gas is compressed before being fed into the secondary cracking reactor.

11. The method of claim 10, wherein the first PSA exhaust gas is compressed in a multi-stage compressor comprising two stages, the method comprising: The feed to the secondary cracking reactor is taken out from between the stages of the multi-stage compressor; as well as The second cracked gas is supplied to the interstage of the multi-stage compressor for further compression.

12. The method according to any one of claims 1 to 3, wherein hydrogen is recovered from the second cracked gas.

13. The method of claim 12, wherein hydrogen is recovered from the second cracked gas by purifying the second cracked gas in the second PSA to produce a second hydrogen product gas and a second PSA tail gas.

14. The method of claim 13, wherein the fuel burned in the furnace comprises the second PSA exhaust gas.

15. The method according to any one of claims 1 to 3, comprising purifying the first PSA tail gas in a second PSA to produce a second hydrogen product gas and a second PSA tail gas, and supplying the second PSA tail gas as feed to the secondary cracking reactor.

16. The method of claim 15, wherein the fuel burned in the furnace comprises the second cracked gas.

17. The method according to any one of claims 1 to 3, wherein the first PSA tail gas is supplied to the secondary cracking reactor without compression.

18. The method according to any one of claims 1 to 3, comprising: The first PSA exhaust gas is compressed in the first compressor to produce compressed first PSA exhaust gas; as well as The compressed first PSA tail gas is separated using a membrane separator to produce a hydrogen-rich permeate gas containing ammonia and a nitrogen-rich permeate gas. The permeate gas is supplied as feed to the secondary cracking reactor.

19. The method of claim 18, wherein the permeate gas is compressed in a second compressor before being supplied as feed to the secondary cracking reactor.

20. The method of claim 19, wherein the second compressor comprises two stages, the method comprising: The feed to the secondary cracking reactor is taken out from the interstage of the second compressor; as well as The second cracked gas is supplied to the interstage of the second compressor for further compression.

21. The method of claim 18, wherein hydrogen is recovered from the second cracked gas.

22. The method of claim 18, wherein hydrogen is recovered from the second cracked gas by purifying the second cracked gas with the first cracked gas in the first PSA.

23. The method of claim 1, further comprising evaporating the liquid ammonia by heat exchange with one or more hot fluids to produce heated ammonia.

24. An apparatus for producing hydrogen from ammonia, comprising: A pump, used to pressurize liquid ammonia; At least one heat exchanger, which is in fluid communication with the pump, is used to heat liquid ammonia from the pump by heat exchange with one or more hot fluids; The first set of catalyst-containing reactor tubes, which are in fluid communication with the heat exchanger, are used to crack heated ammonia from the heat exchanger to produce a first cracked gas containing hydrogen, nitrogen and residual ammonia. A furnace, which is thermally connected to the first group of catalyst-containing reactor tubes, is used to burn fuel to heat the first group of catalyst-containing reactor tubes and form flue gas; The first PSA unit, which is in fluid communication with the first set of catalyst-containing reactor tubes, is used to purify the first cracked gas to produce the first hydrogen product gas and the first PSA tail gas. A secondary cracking reactor comprising a catalyst for cracking the first PSA tail gas or gases derived therefrom to produce a second cracked gas comprising hydrogen and nitrogen; and A second PSA unit is used to recover hydrogen from the second cracked gas or the first PSA tail gas to produce a second hydrogen product gas and a second PSA tail gas. The device includes a flue gas conduit for feeding the flue gas as a hot fluid from the furnace to the heat exchanger and / or a cracked gas conduit for feeding the first cracked gas as a hot fluid from the first set of catalyst-containing reactor tubes to the heat exchanger.

25. The apparatus of claim 24, wherein the apparatus includes a compressor for compressing the first PSA tail gas upstream of the secondary cracking reactor.

26. The apparatus of claim 25, wherein the apparatus comprises a multi-stage compressor, the multi-stage compressor comprising: The first stage is used to compress the first PSA tail gas upstream of the secondary cracking reactor; and The second stage is used to compress the second cracked gas downstream of the secondary cracking reactor.

27. The apparatus of claim 25, wherein the second PSA unit is located downstream of the compressor and upstream of the secondary cracking reactor.

28. The apparatus of claim 24, wherein the apparatus includes a compressor for compressing the second cracked gas upstream of the second PSA unit.

29. The apparatus of claim 28, wherein the at least one heat exchanger is in fluid communication with the pump for evaporating liquid ammonia from the pump by heat exchange with one or more hot fluids.

30. An apparatus for producing hydrogen from ammonia, comprising: A pump, used to pressurize liquid ammonia; At least one heat exchanger, which is in fluid communication with the pump, is used to heat liquid ammonia from the pump by heat exchange with one or more hot fluids; The first set of catalyst-containing reactor tubes, which are in fluid communication with the heat exchanger, are used to crack heated ammonia from the heat exchanger to produce a first cracked gas containing hydrogen, nitrogen and residual ammonia. A furnace, which is thermally connected to the first group of catalyst-containing reactor tubes, is used to burn fuel to heat the first group of catalyst-containing reactor tubes and form flue gas; The first PSA unit, which is in fluid communication with the first set of catalyst-containing reaction tubes, is used to purify the first cracked gas to produce hydrogen product gas and the first PSA tail gas. A secondary cracking reactor comprising a catalyst for cracking the first PSA tail gas or a gas derived therefrom to produce a second cracked gas comprising hydrogen and nitrogen. as well as A membrane separator is used to separate the first PSA tail gas to produce a nitrogen-rich permeate gas and a hydrogen-rich permeate gas containing ammonia, for further processing in the secondary cracking reactor. The device includes a flue gas conduit for feeding the flue gas as a hot fluid from the furnace to the heat exchanger and / or a cracked gas conduit for feeding the first cracked gas as a hot fluid from the first set of catalyst-containing reactor tubes to the heat exchanger.

31. The apparatus of claim 30, comprising a first compressor for compressing the first PSA exhaust gas prior to separation in the membrane separator.

32. The apparatus of claim 30, further comprising a second compressor for compressing the hydrogen-rich gas.

33. The apparatus of claim 30 or claim 31, wherein the apparatus comprises a multi-stage compressor, the multi-stage compressor comprising: The first stage is used to compress the hydrogen-rich gas upstream of the secondary cracking reactor; and The second stage is used to compress the second cracked gas downstream of the secondary cracking reactor.

34. The apparatus of claim 30 or claim 31, comprising a second compressor for compressing the second cracked gas.

35. The apparatus according to any one of claims 30 to 32, comprising a first heat exchanger for heating the PSA tail gas feed of the secondary cracking reactor by heat exchange with the second cracked gas.

36. The apparatus according to any one of claims 30 to 32, comprising a second heat exchanger for heating the PSA tail gas feed of the secondary cracking reactor by heat exchange with the flue gas.

37. The apparatus of claim 30, wherein the at least one heat exchanger is in fluid communication with the pump for evaporating liquid ammonia from the pump by heat exchange with one or more hot fluids.

Images