Recovery of renewable hydrogen product from ammonia decomposition process

Abstract

and recovery of a renewable hydrogen product from the ammonia decomposition process, wherein the cracked gas is purified in a first PSA device and at least a portion of the first PSA tail gas is recycled as fuel to reduce the carbon intensity of the renewable hydrogen product.

Description

[Background technology]

[0001] The global interest in renewable energy, and the use of this renewable energy to generate green hydrogen, has fueled interest in converting the green hydrogen to green ammonia, as ammonia is easier to transport over distances of hundreds or thousands of miles, In particular, the transportation of liquid hydrogen is not currently commercially possible, whereas the transportation of ammonia in liquid state is currently practiced.

[0002] For use in commercial fuel cells, ammonia must be reactively converted to hydrogen.

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[0003] Small scale cracking reactors, or "crackers," typically use pressure swing adsorption ("PSA") devices to separate the cracked gases, recover hydrogen, and produce a PSA tail gas (or off-gas). However, these crackers are generally electrically heated, and the PSA tail gas is typically vented to the atmosphere.

[0004] PSA can be used to produce nitrogen + hydrogen, as is common in hydrogen production from steam methane reforming (SMR) reactors. The cracking reaction is carried out in a catalyst-packed tube that is externally heated by a furnace (see GB1142941).

[0005] GB1142941 discloses a process for making city gas from ammonia. The ammonia is decomposed and the decomposed gas is scrubbed with water to remove residual ammonia. The purified hydrogen / nitrogen mixture is then condensed with propane and / or butane vapors to produce city gas for distribution.

[0006] US6835360A discloses an endothermic catalytic reactor for converting hydrocarbon feedstocks and methanol into useful gases such as hydrogen and carbon monoxide. The reactor comprises a tubular endothermic catalytic reactor in combination with a radiative combustion chamber. The resulting cracked gases are used directly in a fuel cell after passing through a gas regulation system.

[0007] GB977830A discloses a process for decomposing ammonia to produce hydrogen, in which the hydrogen is separated from the nitrogen by passing the decomposed gas through a bed of molecular sieves which adsorb the nitrogen. The nitrogen can then be driven from the bed and stored in a holder.

[0008] JP5330802A is ammonia at 10 kg / cm 2(or about 9.8 bar) pressure and temperatures of 300-700°C. Hydrogen is recovered from the cracked gas using a PSA device. The reference mentions that the desorbed nitrogen can be used to boost upstream processes, but no details are provided.

[0009] US2007 / 178034A discloses a process in which a mixture of ammonia and a hydrocarbon feedstock is passed through a fired steam reformer at 600°C and 3.2 MPa (or about 32 bar) and converted to synthesis gas containing about 70% by volume of hydrogen. The synthesis gas is enriched in hydrogen in a shift reaction, cooled, and condensates are removed. The resulting gas is fed to a PSA system to produce a purified hydrogen product having more than 99% by volume of hydrogen. Off-gas from the PSA system is fed to the fired steam reformer as fuel.

[0010] CN111957270A discloses a process in which ammonia is decomposed in a tubular reactor within a furnace. The decomposed gases are separated by adsorption to produce hydrogen gas and a nitrogen-rich off-gas. The fuel demand of the furnace appears to be met using a combination of the decomposed gases, hydrogen product gas, and / or the off-gas.

[0011] In general, there is a need for improved processes for the production of hydrogen from ammonia, specifically processes that are more efficient in terms of energy consumption and / or have higher levels of hydrogen recovery and / or reduce or eliminate the need to burn fossil fuels.

[0012] In the following discussion of embodiments of the present invention, pressures given are absolute pressures unless otherwise specified. Summary of the Invention

[0013] According to a first aspect of the present invention, there is provided a process for recovering renewable hydrogen from ammonia derived from a renewable hydrogen source, comprising: providing a liquid ammonia feed derived from a renewable hydrogen source; pressurizing a liquid ammonia feed; heating (and optionally vaporizing) a liquid ammonia feed by heat exchange with one or more hot fluids to produce heated ammonia; combusting a primary fuel in a furnace to heat reactor tubes containing a catalyst and form a flue gas; supplying heated ammonia to a reactor tube containing a catalyst to cause decomposition of the ammonia into a cracked gas comprising hydrogen gas, nitrogen gas, and residual ammonia; purifying the cracked gas, or an ammonia-depleted gas derived therefrom, in a first PSA device to produce a renewable hydrogen product gas comprising a first PSA tail gas and a first hydrogen gas; the one or more hot fluids include flue gas and / or cracked gas; the primary fuel is optionally supplemented with a secondary fuel comprising at least a portion of the first PSA exhaust gas and / or a PSA exhaust gas derived therefrom; hydrogen is recovered from any remaining portion of the first PSA tail gas into a renewable hydrogen product gas; The total carbon intensity value of the process is altered by adjusting the ratio of secondary fuel to primary fuel such that the total carbon intensity value of the renewable hydrogen product gas remains below a predetermined value.

[0014] Carbon intensity (CI) can be defined as the amount of carbon dioxide by weight emitted per unit of energy contained within the renewable hydrogen produced. 2 / M.J.H. 2The carbon intensity is reported as grams (g) of carbon dioxide per megajoule (MJ) of hydrogen produced, based on the lower heating value of the renewable hydrogen product. Carbon intensity can be used as a measure of how "green" a fuel is. The total carbon intensity of a hydrogen fuel is made up of several parts. These include the carbon intensity associated with the conversion of renewable hydrogen to ammonia for transportation, the amount of carbon dioxide associated with shipping and transporting the ammonia feed from the source of renewable hydrogen to the point where the renewable hydrogen is released from the ammonia carrier by cracking, the fuel needed to crack the ammonia, the amount of carbon dioxide associated with the electricity used to run the plant, and the amount of carbon dioxide associated with the distribution of the product hydrogen.

[0015] As the carbon intensity of electricity production decreases as more renewable electricity is added to the grid, and as ships, trucks, and other transportation reduce their carbon intensity (e.g., by using renewable ammonia as fuel, or hydrogen fuel cells, or batteries charged with renewable electricity), the carbon intensity of the hydrogen fuel produced by ammonia decomposition also decreases. As the carbon intensity of the entire chain decreases, the recovery of renewable hydrogen can be increased, thereby controlling the carbon intensity value of the renewable hydrogen product while reducing the cost of hydrogen.

[0016] The phrase "total carbon intensity value of the process" refers to the carbon intensity of a process for recovering renewable hydrogen from ammonia as defined by the essential features of the process, optionally including any or all of the optional features of the process described herein.

[0017] The phrase "total carbon intensity value of the renewable hydrogen product gas" is the carbon intensity of the hydrogen product gas, including the entire upstream and downstream supply chain of the process and the process itself.

[0018] The inventors have recognized that by adjusting the ratio of secondary fuel to primary fuel, it is possible to control the carbon intensity value of the cracking process such that the overall carbon intensity value of the renewable hydrogen product gas remains below a predetermined value. The predetermined value may be as prescribed by national regulations. For example, the European Red II Directive stipulates that hydrogen labeled as "renewable hydrogen" has a carbon intensity of 28.2 g of CO 2 / M.J.H. 2 The UK has 32.9g of CO 2 / M.J.H. 2 There are limitations.

[0019] The carbon intensity values ​​associated with the conversion of renewable hydrogen to ammonia and the distribution of ammonia back to renewable hydrogen to capture sites are between 10 and 20 g CO 2 / MJH2 can be consumed, leaving only a relatively small allowance for the carbon intensity of the capture process before regulatory limits are exceeded.

[0020] The total carbon intensity value of the process can also be reduced by operating the cracking reactor at a lower temperature to increase ammonia slip, reduce the conversion of ammonia to hydrogen, and increase the heating content (i.e., calorific value) of the PSA tail gas used as fuel, thereby reducing the amount of primary fuel required, thereby reducing the carbon intensity.

[0021] The liquid ammonia feed 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, the 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 to about 45 bar, or in the range of about 30 bar to about 40 bar.

[0022] The liquid ammonia feed is typically heated to produce heated ammonia at a temperature greater than about 250° C., such as within a range of about 350° C. to about 800° C., or about 400° C. to about 600° C. At the pressures of interest, the liquid ammonia typically vaporizes completely to form heated ammonia vapor.

[0023] The temperature is ultimately determined by the identity of the catalyst, the operating pressure, and the desired "slip", i.e., the amount of ammonia that passes through the cracking reactor without being cracked. In this regard, the process typically operates with a slip of about 4% or less, which is the amount of slip when operating at 5 bar and 350°C with the cracking process approaching equilibrium. Some materials of construction can experience problems at temperatures above about 700°C at any appreciable pressure.

[0024] The decomposition reaction takes place in a catalyst-filled reactor tube heated by a furnace, however, in theory any heterogeneously catalyzed gas reactor could potentially be used for the conversion.

[0025] There are many catalysts known in the art as being useful for the ammonia decomposition reaction, and any of these conventional catalysts may be used in the present invention.

[0026] The primary fuel for the furnace typically includes methane. The fuel can be pure methane, but is also more likely to be natural gas or biogas. In some embodiments, the primary fuel is natural gas or biogas, optionally supplemented with hydrogen as a secondary fuel, in the form of ammonia cracking gas. In these embodiments, liquid ammonia can be pumped and cracked to form cracking gas that is added to the primary fuel.

[0027] The first PSA device may operate a PSA cycle or a vacuum swing adsorption (VSA) cycle. The TSA device may be used in combination with the first PSA device, a TSA device for removing ammonia (see US10787367), and a first PSA device for removing nitrogen and producing a hydrogen product. Suitable PSA cycles include any of those disclosed in US9381460, US6379431, and US877051, the disclosures of which are incorporated herein by reference.

[0028] The method may optionally include recycling any remaining portion of the first PSA tail gas (i.e., any portion not used to supplement the primary fuel) for further processing in the first PSA device. In such an embodiment, the process may include compressing any remaining portion of the first PSA tail gas to produce a compressed PSA tail gas, and recycling the compressed PSA tail gas to the first PSA device for purification with cracked gas or ammonia-depleted gas derived therefrom. Recycling the first PSA tail gas in this manner can achieve an overall recovery of about 94% to about 96%.

[0029] The first PSA tail gas is typically compressed to the pressure of the feed to the first PSA device. The first PSA tail gas is typically compressed to a pressure greater than 1.1 bar, such as at least 5 bar or at least 10 bar. In some embodiments, the first PSA tail gas is compressed to a pressure in the range of about 5 bar to about 50 bar, or in the range of about 10 to about 45 bar, or in the range of about 30 bar to about 40 bar.

[0030] The method may optionally include purifying any portion of the first PSA tail gas that is not used to supplement the primary fuel in the second PSA device. In such an embodiment, the process may include compressing any remaining portion of the first PSA tail gas to produce a compressed PSA tail gas, and purifying the compressed PSA tail gas in the second PSA device to produce a second PSA tail gas (i.e., a tail gas derived from the first PSA tail gas) and a second hydrogen gas. The fuel combusted in the furnace may include the second PSA tail gas.

[0031] In such an embodiment, the renewable hydrogen product gas includes the first hydrogen gas and the second hydrogen gas. Further processing in this manner can achieve an overall hydrogen recovery of about 95% to about 97%.

[0032] Similar to the first PSA device, the second PSA device may operate a PSA cycle or a vacuum swing adsorption (VSA) cycle. The TSA device may be used in combination with a second PSA device, where the TSA device removes ammonia and the second PSA device removes nitrogen and produces hydrogen product. Suitable PSA cycles include any of those disclosed in US9381460, US6379431 and US8778051.

[0033] The secondary fuel may include the first PSA exhaust gas, the second PSA exhaust gas, or a mixture of both the first PSA exhaust gas and the second PSA exhaust gas. In embodiments where the compressed PSA exhaust gas is recirculated to the first PSA device, the remaining portion of the first PSA exhaust gas used to supplement the primary fuel is greater than 0 and up to 100%, i.e., the portion cannot be zero. In embodiments where the compressed PSA exhaust gas is purified in the second PSA device, the remaining portion of the first PSA exhaust gas used to supplement the primary fuel is between 0 and 100%, i.e., the portion can be zero.

[0034] The higher the portion of the first PSA tail gas that is recycled as a secondary fuel (e.g., the higher the ratio of secondary fuel to primary fuel), the lower the hydrogen recovery, but the lower the total carbon intensity value of the process, and therefore the lower the overall carbon intensity value of the renewable hydrogen product. When none of the first PSA tail gas is recycled as a secondary fuel (i.e., when only the primary fuel and the second PSA tail gas are combusted in the furnace), the hydrogen recovery, as well as the carbon intensity value, are typically at their highest. When all of the first PSA tail gas is recycled as a secondary fuel, the hydrogen recovery, as well as the total carbon intensity value of the process and the overall carbon intensity of the renewable hydrogen product, will be at their lowest.

[0035] A further portion of the first or second PSA tail gas, or a gas derived therefrom, can optionally be separated using a membrane separator to release a nitrogen-rich retentate gas and a hydrogen-rich permeate gas can be recycled for further processing in the PSA device and / or mixed with the hydrogen product gas.

[0036] Like hydrogen, ammonia is a "fast gas" that easily permeates the membranes used in gas separation. Some membranes, such as those made of polyamide or polysulfone polymers, are more resistant to ammonia. However, some membranes, such as those made of polyimide polymers, are less resistant to ammonia. Therefore, ammonia is typically removed or at least its concentration is reduced upstream of the membrane separator.

[0037] Ammonia removal can be accomplished at several different points in the process. Ammonia can be removed from the PSA tail gas prior to separating the PSA tail gas. Alternatively, ammonia can be removed from the cracked gas prior to purifying the cracked gas. In both cases, the removed ammonia can be recovered and recycled to the ammonia fed to the reactor tubes containing the catalyst.

[0038] Ammonia can be removed from the gas by adsorption (e.g. by TSA) or by absorption in water, e.g. by scrubbing the gas with water in a scrubber. The resulting ammonia-depleted gas and ammonia solution are separated so that the ammonia-depleted gas can be further processed without the ammonia causing difficulties. Ammonia can be recovered from the ammonia solution by stripping in a column. Such a process can be applied to the cracked gas before being fed to the PSA unit, or alternatively to the PSA tail gas before being fed to the membrane separator.

[0039] According to a second aspect of the present invention, there is provided an apparatus for recovering renewable hydrogen from ammonia derived from a source of renewable hydrogen, comprising: a pump for pressurizing a liquid ammonia feed derived from a renewable hydrogen source; at least one heat exchanger in fluid communication with the pump for heating (and optionally vaporizing) a liquid ammonia feed from the pump by heat exchange with one or more hot fluids to produce heated ammonia; a reactor tube containing a catalyst in fluid communication with the first heat exchanger for decomposing heated ammonia from the first heat exchanger to produce a cracked gas comprising hydrogen gas, nitrogen gas, and residual ammonia; a furnace in thermal communication with the catalyst-containing reactor tubes for combusting a primary fuel to heat the catalyst-containing reactor tubes and generate flue gas; a fuel conduit for supplying a primary fuel to the furnace, optionally including a passage through the heat exchanger; a fuel valve in the fuel conduit for regulating the flow of primary fuel to the furnace; a flue gas conduit for supplying flue gas to the heat exchanger; a first PSA device in fluid communication with the reactor tube containing the catalyst for purifying the cracked gas after passing through the heat exchanger to produce a renewable hydrogen product gas comprising a first PSA tail gas and a first hydrogen gas; a first hydrogen gas conduit for removing the first hydrogen gas from the first PSA device; a first PSA exhaust gas conduit for recirculating a portion of the first PSA exhaust gas from the first PSA device to the furnace, the first PSA exhaust gas conduit optionally including a passage through at least one heat exchanger; a PSA exhaust gas valve in the first PSA exhaust gas conduit for adjusting a flow rate of the first PSA exhaust gas to the furnace; The apparatus includes a control system for operating the fuel valve alone, the PSA exhaust valve alone, or the fuel valve and the PSA exhaust valve in parallel to adjust the ratio of secondary fuel to primary fuel for combustion in the furnace.

[0040] The furnace may be separate from the catalyst-filled reactor tubes, but the furnace and catalyst-filled reactor tubes are preferably integrated within the same unit. In a preferred embodiment, a steam methane reforming (SMR) type reactor is used, and the furnace includes a radiation section that passes through the reactor tubes containing the catalyst.

[0041] In some preferred embodiments, the control system automatically adjusts the ratio of secondary fuel to primary fuel, determined by the carbon intensity already allocated by the upstream processing and distribution of the renewable ammonia delivered to the cracking plant, and any carbon intensity that may need to be allocated to downstream processing or distribution of the renewable hydrogen product to achieve the goal of not exceeding a predetermined carbon intensity value of the renewable hydrogen product gas.

[0042] A compressor is typically provided downstream of the first PSA device to compress the first PSA tail gas to produce a compressed PSA tail gas. The compressor may consist of one or more stages, with cooling occurring between each stage and after the final stage. Water typically condenses from the compressed PSA tail gas in an interstage or aftercooler stage. Aqueous condensate is typically removed after each cooling stage of the compressor, and a small amount of ammonia leaves the first PSA tail gas with this condensate.

[0043] Any portion of the first PSA tail gas that is not recycled to the furnace from the first PSA device may be recycled to the first PSA device for further purification with cracked gas or ammonia-depleted gas derived therefrom. In such an embodiment, the apparatus comprises: a compressor in fluid communication with the first PSA device for compressing the first PSA exhaust gas to produce a compressed PSA exhaust gas; a recirculation conduit for recirculating the compressed PSA exhaust gas to the first PSA device. Any portion of the first PSA exhaust gas that is not recycled to the furnace from the first PSA device may optionally be purified in a second PSA device. In such an embodiment, the apparatus comprises: a compressor in fluid communication with the first PSA device for compressing the first PSA exhaust gas to produce a compressed PSA exhaust gas; a second PSA device in fluid communication with the compressor for purifying the compressed PSA tail gas to produce a second PSA tail gas and a second hydrogen gas; a second hydrogen gas conduit for removing the second hydrogen gas from the second PSA device; a second PSA exhaust gas conduit for removing the second PSA exhaust gas from the second PSA device.

[0044] In these embodiments, the first and second hydrogen gas conduits may combine to form a renewable hydrogen product gas conduit.

[0045] A secondary PSA exhaust gas conduit typically recirculates the second PSA exhaust gas from the second PSA device to the furnace, optionally after passing through a heat exchanger.

[0046] The invention will now be described in detail with reference to the following drawings. [Brief description of the drawings]

[0047] [Figure 1] FIG. 1 is a process flow diagram of a first embodiment of an ammonia decomposition process for producing hydrogen. [Diagram 2] FIG. 2 is a process flow diagram of another example based on the ammonia decomposition process of FIG. 1 , which does not use the hydrogen product as fuel. [Diagram 3] FIG. 3 is a process flow diagram of a further example based on the ammonia decomposition process of FIGS. 1 and 2, using only PSA tail gas as fuel. [Figure 4] FIG. 1 is a process flow diagram of a first embodiment of a process for recovering renewable hydrogen from ammonia derived from a renewable hydrogen source, in accordance with the present invention. [Diagram 5] FIG. 2 is a process flow diagram of a second embodiment of a process for recovering renewable hydrogen from ammonia derived from a renewable hydrogen source, in accordance with the present invention. [Figure 6] 1 is a graph showing the carbon intensity of renewable hydrogen product gas and hydrogen recovery as a function of the percentage of the first PSA tail gas recycled as fuel. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0048] A process for producing hydrogen by decomposing ammonia is described herein. The process has particular application for producing so-called "green" hydrogen, which is hydrogen produced using renewable energy instead of fossil fuels. In this case, ammonia is typically produced by electrolyzing water using electricity generated from renewable energy, such as wind and / or solar energy, to produce hydrogen, which is then catalytically reacted with nitrogen to produce ammonia, which is easier to transport than hydrogen (Haber process). After reaching its destination, the ammonia is then decomposed to regenerate hydrogen.

[0049] In the process of the present invention, the heat required for the reaction is typically provided by combustion of the PSA tail gas (which usually contains some residual hydrogen and ammonia) in a furnace. If the PSA tail gas has poorer heating value than either the vaporized ammonia, a portion of the product hydrogen, or an alternative fuel, it can be used along with the tail gas as a trim fuel.

[0050] In practice, natural gas may be used as a trim fuel along with the PSA tail gas, as is practiced in SMR for hydrogen. However, there is an incentive to use a "renewable fuel" in the hope of maintaining the "green" or renewable qualities of the hydrogen so produced. This may be cracked "renewable" ammonia, ammonia itself, or another renewable energy source such as biogas, or it may actually be electrical heating, whether the electricity is itself from a renewable source, in this case local to the cracking process, as opposed to the renewable electricity used to generate the hydrogen transported in the form of ammonia.

[0051] A reference example of the process is shown in Figure 1. The process takes liquid ammonia from storage (not shown). The ammonia to be decomposed (line 2) is pumped as a liquid (pump P201) to a pressure above the desired decomposition pressure (see GB1142941). The reaction pressure is a compromise between operating pressure and conversion, according to Le Chatelier's principle. Pumping liquid ammonia requires less power and capital than compressing the product hydrogen, so there is an incentive to operate the reactor (8) at a higher pressure.

[0052] Pressurized liquid ammonia (line 4) is then heated and vaporized (if it is below its critical pressure) and further heated via heat exchanger (E101) to temperatures up to above 250° C. using the heat available in the cracked gases leaving the reactor tubes and in the flue gases from the furnace. In the diagram, heat exchanger (E101) is shown as one heat exchanger, but in reality it will be a series of heat exchangers in a network.

[0053] Alternatively, initial heating and vaporization of the pressurized liquid ammonia may be performed against an alternative heat source such as cooling water or ambient air. Typical reaction temperatures are over 500°C (see US2601221), with palladium-based systems capable of operating at 600°C and 10 bar, while RenCat's metal oxide-based systems operate at less than 300°C and 1 bar. (See https: / / www.ammoniaenergy.org / articles / ammonia-cracking-to-high-purity-hydrogen-for-pem-fuel-cells-in-denmark / ). The cracker operating pressure is typically an optimization of several factors. The cracking of ammonia to hydrogen and nitrogen is favored by low pressure, while other factors favor higher pressures, such as power consumption (minimized by pumping feed ammonia rather than compressing product hydrogen) and PSA size (smaller at higher pressures).

[0054] Hot ammonia (line 6) enters the reactor tubes (8) at the desired pressure, where additional heat is provided by the furnace (10) to decompose the ammonia into nitrogen and hydrogen. The resulting mixture of residual ammonia, hydrogen, and nitrogen leaves the reactor tubes (8) at the reaction temperature and pressure (line 12). The reaction products are cooled in a heat exchanger (E101) against 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 used as fuel in line 20), and combustion air (from line 22, fan K201 and line 24) to reduce the temperature as close as possible to the temperature required for the inlet of the PSA device (26). Residual heat in the cracked gas mixture (line 28) is removed in a water cooling system (not shown) to achieve an inlet temperature to the PSA device (26) in the range of about 20°C to about 60°C, for example about 50°C.

[0055] The PSA product (line 30) is pure hydrogen conforming to ISO standard 14687 (hydrogen fuel quality) with residual ammonia <0.1 ppmv and nitrogen <300 ppmv at about the reaction pressure. The product hydrogen (line 30) can be further compressed (not shown) for packing into tube trailers (not shown) for transportation or liquefied in a hydrogen liquefier (not shown) after any necessary compression. The PSA tail gas (line 18) or "purge gas" from the PSA device (26) is shown to be heated via heat exchanger E101 using the cracked gas (line 12) or furnace flue gas (line 32) leaving the reaction tubes of the reactor (8) before being sent to the furnace (in line 36) as combustion fuel. However, the PSA tail gas (line 18) may also be fed directly to the furnace (10) without heating). Alternatively, the PSA tail gas may be preheated by an intermediate fluid to allow a lower pressure for the PSA tail gas, which increases hydrogen recovery.

[0056] The resulting warmed ammonia fuel (line 34) and warmed hydrogen (line 40) are depicted as being combined with (optionally) warmed PSA tail gas (line 36) in a mixer (42) to produce a combined fuel, which is fed (line 44) to the furnace (10) for combustion to produce flue gas (lines 32 and, after cooling with E101, line 48). However, it should be noted that one or more fuels may be fed directly to the furnace without premixing. Warmed air (for combustion of the fuel) is fed to the furnace (10) in line 46.

[0057] One of the objectives of the preferred embodiment of the process is to maximize the amount of hydrogen produced by cracking renewable ammonia. This means minimizing the amount of hydrogen used as fuel, or ammonia if ammonia is used directly as fuel. Therefore, heat integration is important to properly use the hot flue gas and cracked gas, for example to preheat the air (line 24) and ammonia (line 4) to the cracker, thereby reducing the amount of "fuel" used in the burners of the furnace (10). This leads to higher hydrogen recovery, since less hydrogen is lost as water in the furnace flue gas (lines 32 and 48). Thus, for example, steam generation should be minimized in favor of in-process heat integration.

[0058] Figure 1 shows ammonia provided as fuel (lines 34 & 44) and feed (line 6), and also shows product hydrogen (lines 40 & 44) as a fuel, although in practice only one of these streams will likely be used as a fuel. In this regard, Figure 2 depicts a similar process to Figure 1 in which ammonia is used as a fuel (line 34), but product hydrogen is not. All other features of the process depicted in Figure 2 are the same as Figure 1, and common features have been given the same reference numbers.

[0059] The inventors have recognized that when hydrogen is also used as a fuel, it promotes stable combustion of ammonia, especially during start-up and warm-up.

[0060] Figure 3 depicts a similar process to that depicted in Figure 2, in which recovery of hydrogen from the PSA (line 30) can be coordinated to provide tail gas (line 18) that, when combusted, provides all the heat required for the process, thus eliminating the need for trim fuel. All other features of the process depicted in Figure 3 are the same as Figure 1, and common features have been given the same reference numbers.

[0061] As discussed above, if there are viable alternative sources of renewable energy for the cracking reaction, one can consider recovering hydrogen from the PSA tail gas to increase the net hydrogen production from the process, in addition to the hydrogen produced from the PSA. Such a process can separate hydrogen from the nitrogen-rich PSA tail gas stream using a membrane with a selective layer that is readily permeable to hydrogen but relatively impermeable to nitrogen (Figure 4).

[0062] Ammonia needs to be specifically removed, but not if the membrane is used as part of a separation process, because the membrane material cannot tolerate high concentrations of ammonia and ammonia is a fast gas and permeates with hydrogen, resulting in accumulation in the process if not removed. Ammonia can be removed upstream of the membrane, for example, by water washing or other well-known techniques for ammonia removal. Ammonia can be recovered from the aqueous ammonia solution produced in the water wash using a stripping column, and the recovered ammonia can be recycled to the feed to the cracker reactor. This can theoretically increase the hydrogen recovery from the process up to 100%. Recovering ammonia from the cracked gas simplifies the hydrogen purification step, can increase the recovery of hydrogen from ammonia if the separated ammonia is recovered as a feed, and can also remove ammonia from the feed to the burner, eliminating the NOx reduction caused by burning ammonia. x Eliminate concerns about generation.

[0063] It may also be necessary to remove water from the feed ammonia to prevent damage to the ammonia cracking catalyst. Typically, a small amount of water is added to ammonia to prevent stress corrosion cracking in vessels during transport and storage. This may need to be removed. However, water removal can be incorporated into the stripping column described above. Care is taken in the design of the evaporator to ensure that the ammonia vaporizes at the required pressure and the water is carried through the stripping column with the evaporator ammonia. This primarily vapor phase ammonia enters the midpoint of the column and pure ammonia leaves through the top of the column. The column has a partial condenser (condenses only enough liquid for reflux) and the overhead vapor comprises the feed ammonia (no water) and ammonia recovered from the cracker gas stream.

[0064] It may be more energy efficient to feed the cracked gas to a membrane first to produce a hydrogen-enriched permeate stream and a nitrogen-rich retentate stream that can be vented. The hydrogen-enriched permeate can be further purified in a PSA. A second membrane can be added to the PSA tail gas stream to further enhance overall hydrogen recovery. This configuration would significantly reduce the size of the tail gas compressor.

[0065] The use of membrane separators to increase hydrogen recovery allows the nitrogen to be vented from the process without passing through the combustion section of the process. In processes where the nitrogen stream is under pressure, it may be beneficial to expand the nitrogen to atmospheric pressure before venting for power recovery through an expansion turbine. If heat available in the flue gas or cracked gas stream is used to heat the pressurized nitrogen before expansion, the amount of power recovered is increased.

[0066] Figure 4 depicts a process according to a first embodiment of the invention in which a primary fuel is supplemented with a secondary fuel comprising a portion of the first PSA exhaust gas. Features of the process of Figure 4 that are common to the processes of Figures 1-3 have been given the same reference numerals. Following is a discussion of the new features of Figure 4.

[0067] The primary fuel (line 50) is warmed in a heat exchanger (E101) and is optionally combined with the warmed PSA tail gas (line 36) to produce a combined fuel (line 44) that is fed to the furnace (10) for combustion, heating the catalyst-filled tubes of the cracking reactor (8) and producing flue gas (line 32, and line 48 after cooling in E101). Warmed air is fed to the furnace (10) in line 46. The primary fuel (line 50) and the PSA tail gas (line 36) can be fed to the furnace separately without mixing (not shown).

[0068] The cooled cracked gas (line 28) is fed to the first PSA device (26). The cracked gas is separated to form a hydrogen product (line 30) and an exhaust gas (line 18). A first portion of the exhaust gas (line 54) from the first PSA device (26) is compressed in a compressor (K301) to produce a compressed PSA exhaust gas (line 62). The compressed PSA exhaust gas (line 62) is recycled to the first PSA device (26) for purification with the cooled cracked gas (28) or an ammonia-depleted gas derived therefrom.

[0069] A second portion of the first PSA tail gas (line 56) is fed through a PSA tail gas valve (58) that controls the portion of the first PSA tail gas (60) that is fed back to the furnace (optionally via heat exchanger (E101) and mixer (42)). If all of the first PSA tail gas is fed back to the furnace, hydrogen recovery is at its minimum (typically about 50%). If about 50% of the first PSA tail gas is recirculated as fuel, hydrogen recovery of about 95% can be achieved.

[0070] Alternatively, as shown in Figure 5, the compressed PSA tail gas (line 62) can be fed to a second PSA device (64). Product hydrogen from the second PSA device (line 68) is combined with the hydrogen product (line 30) from the first PSA device (26) to form a combined hydrogen product gas (line 70). The portion of the first PSA tail gas used as fuel (line 60) is combined with the PSA tail gas (line 66) from the second PSA device (64) to produce a combined PSA tail gas (line 72). Similar to the processes of Figures 1 and 2, the combined PSA tail gas (line 66) can be heated via heat exchanger E101 using cracked gas (line 12) leaving the reactor tubes or furnace flue gas (line 32) before being sent to the furnace as combustion fuel (at line 36). However, the combined PSA exhaust gas (line 72) may be fed directly to the furnace (10) without heating (not shown). EXAMPLES

[0071] The invention will now be illustrated with reference to the following inventive examples and by comparison with the following reference examples. For simulation purposes, both the inventive examples and the reference examples assume equilibrium of the decomposition reaction at 11 bar and 500° C.

[0072] Reference example 1 The process depicted in FIG. 2 was simulated by computer (Aspen Plus, ver. 10, Aspen Technology, Inc.) and the results are depicted in Table 1. Table 1 [Table 1]

[0073] In this reference example, the hydrogen recovery rate from ammonia is 77.18%, and the PSA recovery rate is 83.5%. The total output of the ammonia supply pump (P201), the ammonia fuel pump (P202), and the air fan (K201) is about 1.36 kW.

[0074] Reference example 2 The process depicted in FIG. 3 was simulated by computer (Aspen Plus, ver. 10) and the results are depicted in Table 2. Table 2 [Table 2]

[0075] In this reference example, the hydrogen recovery rate from ammonia is 77.05%, and the PSA recovery rate is 79.4%. The total output of the ammonia supply pump (P201) and the air fan (K201) is about 1.37 kW.

[0076] Example 1 of the invention The process depicted in FIG. 5 was simulated by computer (Aspen Plus, ver. 10) and the results are depicted in Table 3. Table 3 [Table 3]

[0077] In the example of the invention, the hydrogen recovery from ammonia is 93.85%. In the example of the invention, the PSA tail gas valve is closed so that all of the first PSA tail gas is recycled for further purification in the second PSA device. The second PSA tail gas from the second PSA device is recycled to the furnace as a secondary fuel. This is provided as a starting point to show the effect of recirculating tail gas from the first PSA device to fuel on the carbon intensity value of the process.

[0078] Example 2 of the present invention The process depicted in FIG. 5 was simulated by computer (Aspen Plus, ver. 10) and the results are depicted in Table 4. Table 4 [Table 4]

[0079] In an embodiment of the invention, the portion of the first PSA tail gas that is diverted through the fuel valve and recirculated as a secondary fuel is varied from 0% to 100%. In this embodiment, hydrogen production was kept constant and the ammonia feed rate through line 2 was increased to compensate for the reduction in hydrogen recovery. The data in Figure 6 shows that increasing the amount of first PSA tail gas recirculated as a secondary fuel reduces hydrogen recovery, but also reduces the carbon intensity of the renewable hydrogen product because less primary fuel is required.

[0080] These data demonstrate the effect of the combustion process on the carbon intensity value of the renewable hydrogen product. The data also demonstrate that the carbon intensity value of the renewable hydrogen product can be controlled by varying the ratio of primary to secondary fuels.

[0081] The present invention should not be limited in scope by the specific aspects or embodiments disclosed in the examples, which are intended as illustrations of some aspects of the invention, and any embodiments that are functionally equivalent are within the scope of the invention. Various modifications of the invention in addition to those shown and described herein will become apparent to those skilled in the art and are intended to be within the scope of the appended claims. The present invention can be embodied in the following manner. (Appendix 1) 1. A process for recovering renewable hydrogen from ammonia derived from a renewable hydrogen source, comprising: providing a liquid ammonia feed derived from a renewable source of hydrogen; pressurizing the liquid ammonia feed; heating (and optionally vaporizing) the liquid ammonia feed by heat exchange with one or more hot fluids to produce heated ammonia; combusting a primary fuel in a furnace to heat reactor tubes containing a catalyst and form a flue gas; supplying the heated ammonia to a reactor tube containing the catalyst to cause decomposition of the ammonia into cracked gases comprising hydrogen gas, nitrogen gas, and residual ammonia; purifying the cracked gas, or an ammonia-depleted gas derived therefrom, in a first PSA device to produce a first PSA tail gas and a renewable hydrogen product gas comprising a first hydrogen gas; the one or more hot fluids include the flue gas and / or the cracked gas; the primary fuel is optionally supplemented with a secondary fuel comprising at least a portion of the first PSA exhaust gas and / or a PSA exhaust gas derived therefrom; hydrogen is recovered from any remaining portion of the first PSA tail gas into the renewable hydrogen product gas; a process wherein a total carbon intensity value of the process is altered by adjusting the ratio of the secondary fuel to the primary fuel such that the overall carbon intensity value of the renewable hydrogen product gas remains below a predetermined value. (Appendix 2) compressing the remaining portion of the first PSA tail gas to produce a compressed PSA tail gas; and recycling the compressed PSA tail gas to the first PSA device for purification with the cracked gas or the ammonia-depleted gas derived therefrom. (Appendix 3) compressing the remaining portion of the first PSA tail gas to produce a compressed PSA tail gas; and purifying the compressed PSA tail gas in a second PSA device to produce a second PSA tail gas and a second hydrogen gas. (Appendix 4) 4. The process of claim 3, wherein the secondary fuel comprises the second PSA exhaust gas. (Appendix 5) 5. The process of claim 3 or 4, wherein the renewable hydrogen product gas comprises the first hydrogen gas and the second hydrogen gas. (Appendix 6) 6. The process of any one of claims 1 to 5, wherein the primary fuel is supplemented by 0 to greater than 100% of the first PSA exhaust gas. (Appendix 7) 6. The process of any one of claims 3 to 5, wherein the primary fuel is supplemented with 0-100% of the first PSA exhaust gas. (Appendix 8) 8. The process of any one of claims 1 to 7, wherein the primary fuel comprises one or more of ammonia, hydrogen, and methane. (Appendix 9) 9. The process of any one of claims 1 to 8, wherein the primary fuel is natural gas or biogas. (Appendix 10) 1. An apparatus for recovering renewable hydrogen from ammonia derived from a renewable hydrogen source, comprising: a pump for pressurizing a liquid ammonia feed derived from a renewable hydrogen source; at least one heat exchanger in fluid communication with the pump for heating (and optionally vaporizing) the liquid ammonia feed from the pump by heat exchange with one or more hot fluids to produce heated ammonia; a catalyst-containing reactor tube in fluid communication with the first heat exchanger for decomposing heated ammonia from the first heat exchanger to produce a cracked gas comprising hydrogen gas, nitrogen gas, and residual ammonia; a furnace in thermal communication with the catalyst-containing reactor tubes for combusting a primary fuel to heat the catalyst-containing reactor tubes and generate flue gas; a fuel conduit for supplying a primary fuel to said furnace, said fuel conduit optionally including a passage through said heat exchanger; a fuel valve in the fuel conduit for regulating the flow of the primary fuel to the furnace; a flue gas conduit for supplying flue gas to the heat exchanger; a first PSA device in fluid communication with the catalyst-containing reactor tube for purifying the cracked gas after passing through the heat exchanger to produce a first PSA tail gas and a renewable hydrogen product gas comprising a first hydrogen gas; a first hydrogen gas conduit for removing the first hydrogen gas from the first PSA device; a first PSA exhaust gas conduit for recirculating a portion of a first PSA exhaust gas from the first PSA device to the furnace, optionally after passing through the heat exchanger; a PSA exhaust valve in the first PSA exhaust conduit for regulating a flow rate of the first PSA exhaust gas to the furnace; the apparatus comprising a control system for operating the fuel valve alone, the PSA exhaust valve alone, or the fuel valve and the PSA exhaust valve in parallel to adjust the ratio of the secondary fuel to the primary fuel for combustion in the furnace. (Appendix 11) 11. The apparatus of claim 10, wherein the control system automatically adjusts the ratio of the secondary fuel to the primary fuel. (Appendix 12) a compressor in fluid communication with the first PSA device for compressing the first PSA exhaust gas to produce a compressed PSA exhaust gas; and a recirculation conduit for recirculating the compressed PSA exhaust gas to the first PSA device. (Appendix 13) a compressor in fluid communication with the first PSA device for compressing the first PSA exhaust gas to produce a compressed PSA exhaust gas; a second PSA device in fluid communication with the compressor for purifying the compressed PSA tail gas to produce a second PSA tail gas and a second hydrogen gas; a second hydrogen gas conduit for removing the second hydrogen gas from the second PSA device; and a second PSA exhaust gas conduit for removing the second PSA exhaust gas from the second PSA device. (Appendix 14) 14. The apparatus of claim 13, wherein the first and second hydrogen gas conduits combine to form a renewable hydrogen product gas conduit. (Appendix 15) 15. The apparatus of claim 13 or 14, wherein the second PSA exhaust gas conduit recirculates the second PSA exhaust gas from the second PSA device to the furnace, optionally after passing through the heat exchanger.

Claims

1. 1. A process for recovering renewable hydrogen from ammonia derived from a renewable hydrogen source, comprising: providing a liquid ammonia feed derived from a renewable source of hydrogen; pressurizing the liquid ammonia feed; heating (and optionally vaporizing) the liquid ammonia feed by heat exchange with one or more hot fluids to produce heated ammonia; combusting a primary fuel in a furnace to heat reactor tubes containing a catalyst and form a flue gas; supplying the heated ammonia to a reactor tube containing the catalyst to cause decomposition of the ammonia into cracked gases comprising hydrogen gas, nitrogen gas, and residual ammonia; purifying the cracked gas, or an ammonia-depleted gas derived therefrom, in a first PSA device to produce a first PSA tail gas and a renewable hydrogen product gas comprising a first hydrogen gas; the one or more hot fluids include the flue gas and / or the cracked gas; the primary fuel is optionally supplemented with a secondary fuel comprising at least a portion of the first PSA exhaust gas and / or a PSA exhaust gas derived therefrom; hydrogen is recovered from any remaining portion of said first PSA tail gas into said renewable hydrogen product gas; a process wherein a total carbon intensity value of the process is altered by adjusting the ratio of the secondary fuel to the primary fuel such that the overall carbon intensity value of the renewable hydrogen product gas remains below a predetermined value.

2. compressing the remaining portion of the first PSA tail gas to produce a compressed PSA tail gas; and recycling the compressed PSA tail gas to the first PSA device for purification with the cracked gas or the ammonia-depleted gas derived therefrom.

3. compressing the remaining portion of the first PSA tail gas to produce a compressed PSA tail gas; and purifying the compressed PSA tail gas in a second PSA device to produce a second PSA tail gas and a second hydrogen gas.

4. The process of claim 3 , wherein the secondary fuel comprises the second PSA exhaust gas.

5. 5. The process of claim 3 or 4, wherein the renewable hydrogen product gas comprises the first hydrogen gas and the second hydrogen gas.

6. The process of any one of claims 1 to 5, wherein the primary fuel is supplemented by greater than 0% to 100% of the first PSA exhaust gas.

7. The process of any one of claims 3 to 5, wherein the primary fuel is supplemented with 0 to 100% of the first PSA exhaust gas.

8. The process of any one of claims 1 to 7, wherein the primary fuel comprises one or more of ammonia, hydrogen, and methane.

9. The process according to any one of claims 1 to 8, wherein the primary fuel is natural gas or biogas.

10. 1. An apparatus for recovering renewable hydrogen from ammonia derived from a renewable hydrogen source, comprising: a pump for pressurizing a liquid ammonia feed derived from a renewable hydrogen source; at least one heat exchanger in fluid communication with the pump for heating (and optionally vaporizing) the liquid ammonia feed from the pump by heat exchange with one or more hot fluids to produce heated ammonia; a reactor tube containing a catalyst in fluid communication with the heat exchanger for decomposing the heated ammonia from the heat exchanger to produce a cracked gas comprising hydrogen gas, nitrogen gas, and residual ammonia; a furnace in thermal communication with the catalyst-containing reactor tubes for combusting a primary fuel to heat the catalyst-containing reactor tubes and generate flue gas; a fuel conduit for supplying a primary fuel to said furnace, said fuel conduit optionally including a passage through said heat exchanger; a fuel valve in the fuel conduit for regulating the flow of the primary fuel to the furnace; a flue gas conduit for supplying flue gas to the heat exchanger; a first PSA device in fluid communication with the catalyst-containing reactor tube for purifying the cracked gas after passing through the heat exchanger to produce a first PSA tail gas and a renewable hydrogen product gas comprising a first hydrogen gas; a first hydrogen gas conduit for removing the first hydrogen gas from the first PSA device; a first PSA exhaust gas conduit for recirculating a portion of a first PSA exhaust gas from the first PSA device to the furnace, optionally after passing through the heat exchanger; a PSA exhaust valve in the first PSA exhaust conduit for regulating a flow rate of the first PSA exhaust gas to the furnace; a secondary fuel comprising at least a portion of the first PSA exhaust gas and / or a PSA exhaust gas derived therefrom; The apparatus includes a control system for operating the fuel valve alone, the PSA exhaust valve alone, or the fuel valve and the PSA exhaust valve in parallel to adjust the ratio of the secondary fuel to the primary fuel for combustion in the furnace.

11. The apparatus of claim 10 , wherein the control system automatically adjusts the ratio of the secondary fuel to the primary fuel.

12. a compressor in fluid communication with the first PSA device for compressing the first PSA exhaust gas to produce a compressed PSA exhaust gas; and a recirculation conduit for recirculating the compressed PSA exhaust gas to the first PSA device.

13. a compressor in fluid communication with the first PSA device for compressing the first PSA exhaust gas to produce a compressed PSA exhaust gas; a second PSA device in fluid communication with the compressor for purifying the compressed PSA tail gas to produce a second PSA tail gas and a second hydrogen gas; a second hydrogen gas conduit for removing the second hydrogen gas from the second PSA device; a second PSA exhaust gas conduit for removing the second PSA exhaust gas from the second PSA device.

14. 14. The apparatus of claim 13, wherein the first and second hydrogen gas conduits combine to form a renewable hydrogen product gas conduit.

15. 15. The apparatus of claim 13 or 14, wherein the second PSA exhaust gas conduit recirculates the second PSA exhaust gas from the second PSA device to the furnace, optionally after passing through the heat exchanger.

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