Method and apparatus for producing hydrogen from an ammonia feedstock

Abstract

Apparatus and method for producing hydrogen via multiple reactors connected in a looped flow pathway or circuit. Specifically, the present process provides a series of connected reactors within which a catalytic metal oxide may be circulated and reacted at different stages of the hydrogen manufacturing process.

Description

[0001] Method and Apparatus for Producing Hydrogen from an Ammonia Feedstock

[0002] Field of invention

[0003] The present invention relates to apparatus and method for producing hydrogen and in particular, although not exclusively, to a reaction pathway comprising a metal oxide reactant flow loop.

[0004] Background

[0005] Traditionally, hydrogen has been generated from low carbon fuels (LCFs) using catalytic thermal cracking. This is typically followed by pressure absorption to provide hydrogen separation. Conventional ammonia cracking to produce hydrogen involves high temperatures (700 to 1100°C) as an attempt to improve efficiency of the process. Such high temperatures are typically energy intensive. Additionally, hydrogen from catalytic cracking produces mixed streams of hydrogen and nitrogen that typically require downstream compression and cryogenic separation. Alternative approaches to hydrogen production are based on membrane systems that both require high capital investment and are also energy intensive.

[0006] Other more recent approaches focus on the development of specific catalysts to try and lower the required cracking temperatures. The use of transition metals, rare earth and alkaline earth metals as active sites for fuel decomposition to produce hydrogen have been proposed. Temperatures around 400 to 700°C have been attempted. Mixed oxide catalysts have been investigated including in particular aluminium and magnesium mixed oxides. However, such decomposition processes are limited by efficient heat transfer and scalepotential associated with heat release from the catalytic oxide pellets. Additionally, the materials and energy costs of manufacturing ammonia via such thermal cracking catalysts increases the energy demand of these processes. Accordingly, what is required is a process for the generation of hydrogen from an ammonia-based fuel source that addresses these problems.

[0007] Summary of the invention

[0008] It is an objective of the present concept to provide an energy efficient process for the production of hydrogen from a low carbon fuel (LCF) such as ammonia. It is a further specific objective to provide a hydrogen production process that utilises readily available reactants, source feedstocks and catalysts.

[0009] It is a further objective to provide a hydrogen production process adapted to achieve high purity hydrogen and to obviate costly mixed gas separation processes. It is a yet further objective to provide a hydrogen manufacturing process being an auto-thermal process i.e., that does not require or minimises additional heat sources / heat energy demand. It is a yet further objective to provide a process for the production of hydrogen that may be conveniently and efficiently scaled for production of low to high volumes on demand.

[0010] The objectives are achieved via a production process and apparatus that comprises multiple reactors connected together to provide a looped flow pathway circuit for at least one reactant / catalyst. Specifically, the present process provides a series of interconnected reactors within which a catalytic metal oxide may be circulated and reacted at different stages of the manufacturing process as described herein. In particular, and according to one implementation, the present process comprises three reactors including specifically an initial fuel reactor connected to a downstream steam-iron reactor that is in turn connected to a downstream air and / or oxygen reactor. The air and / or oxygen reactor is coupled via a return flow conduit to the initial fuel reactor. Respective inlets and outlets provide a means of coupling the reactors in communication suitable for the transfer of reactants and reaction products between the reactors. Inlet and outlet discharge ports may be provided at the respective reactors so as to allow both introduction of reactant fuel sources and the discharge of reaction products.

[0011] Reference within this specification to an air reactor encompasses a reactor to receive a supply of air and / or oxygen and allow reaction of the air and / or oxygen with other compounds, materials, reaction products and / or reactants mentioned herein. Alternative terms for ‘air reactor’ used herein include an ‘oxygen reactor’ and similar.

[0012] The present process is configured to achieve high purity hydrogen for fuel cell applications, typically requiring a purity of around 98%, 99% or above 99% such as 99.99%. The present process is advantageous by separating reduction and oxidation reactions via separate reactors (fuel reactor and air reactor). Accordingly, costly separation of mixed hydrogen / nitrogen gas is avoided. In particular, pure hydrogen is produced via a separate and intermediate steam-iron reactor into which is fed water and reaction products output from the fuel reactor.

[0013] Furthermore, the present system is energy efficient via a harvesting of heat energy from the air reactor which may then be utilised to heat the reaction at the first fuel reactor, the fuel source fed to the first fuel reactor, the reaction at the second steam-iron reactor and / or water fed to the steam-iron reactor.

[0014] Additionally, the present system is further advantageous for energy efficiency by cooling or transferring heat energy from the hydrogen produced at the steam-iron reactor to an initial feed of the fuel source fed to the first fuel reactor. This in turn provides heating of the initial fuel source to obviate or reduce specific fuel pre-heating. Cooling the hydrogen reaction product is advantageous to improve purity and to facilitate separation with other reaction product gases.

[0015] According to a first aspect of the present concept there is provided a method of producing hydrogen comprising: receiving a supply of an ammonia fuel source and a supply of an oxidised first form of a metal oxide at a first reactor; allowing the ammonia fuel source and the metal oxide to react within the first reactor to produce a second form of the metal oxide; transferring the second form of the metal oxide from the first reactor to a second reactor; receiving a supply of water at the second reactor; allowing the second form of the metal oxide and the water to react within the second reactor to produce a third form of the metal oxide and hydrogen; discharging the hydrogen from the second reactor; transferring the third form of the metal oxide from the second reactor to a third reactor; receiving a supply of air and / or oxygen at the third reactor; allowing the third form of the metal oxide and the air and / or oxygen to react within the third reactor to produce the oxidised first form of the metal oxide; transferring the oxidised first form of the metal oxide to the first reactor; wherein the metal oxide is circulated through the first, second and third reactors as a flow loop.

[0016] Optionally, the method comprises discharging nitrogen and / or water from the first reactor. Optionally, the method comprises discharging nitrogen and / or oxygen from the third reactor.

[0017] Optionally, the first reactor may be a counter-current reactor, the method further comprising: providing a flow of the ammonia fuel source in a first direction through the first reactor and providing a flow of the metal oxide in a second direction through the first reactor, the second direction orientated counter to the first. Such an arrangement may comprise an in-series arrangement of reactor units or modules with each of unit or module comprising at least two inlets and at least two outlets for the in-flow and output of reactants and reaction products, respectively.

[0018] Optionally, the step of allowing the ammonia fuel source and the metal oxide to react within the first reactor comprises providing a reaction temperature in a range 400 to 1000°C; 500 to 1000°C; 600 to 1000°C; 800 to 1000°C; 400 to 800°C; or 500 to 800°C. Optionally, the step of allowing the second form of the metal oxide and water to react in the second reactor comprises providing a reaction temperature in a range 80 to 150°C. Optionally, the step of allowing the third form of the metal oxide and air and / or oxygen to react in the third reactor comprises providing a reaction temperature in a range 800 to 1400°C; 800 to 1300°C; or 800 to 1100°C.

[0019] Optionally, a metal oxide-to-ammonia fuel source ratio value within the first reactor is in a range 1 to 1.5 or 1 to 1.2. Optionally, generating steam from the water within the second reactor wherein a steam-to-metal oxide ratio value is in a range 1.5 to 4.5; 2.5 to 4.5; or 3.5 to 4.5. Optionally, an air-to-metal oxide or oxygen-to-metal ratio value within the third reactor is in a range 1 to 2; 1 to 1.8; 1 to 1.6; or 1 to 1.4.

[0020] Optionally, an ammonia fuel source-to-metal oxide ratio value within the first reactor is in a range 8 to 20; 10 to 18; 12 to 16. Preferably, the ammonia fuel source-to-metal oxide ratio is in a range 13 to 16.

[0021] Optionally, the metal oxide may comprise iron oxide. Optionally, the metal oxide may comprise any one or a combination of iron oxide and / or an oxide of a metal selected from Fe, Ti, Al, Co, Ni, V, Cr, Cu, Mg, Mn, Zn, La, Pr, Nd, Sm, Eu, and Gd. Optionally, the metal oxide may comprise a transition metal oxide. Optionally, the metal oxide may comprise any one or a combination of Fe, Ni, Co, Mn, Zn, Cu, Ti, V.

[0022] Optionally, the metal oxide may comprise a perovskite metal oxide or a perovskite type metal oxide. Optionally, the metal oxide may comprise any one or a combination a lanthanum-based oxide (such as LaMnOs, LaFeOs, LaCoOs, LaNiOs and associated alternative oxide forms). Optionally, the metal oxide may comprise any one or a combination a copper oxide (La2CuO4 and associated alternative oxide forms). Optionally, the metal oxide may comprise any one or a combination a rare-earth metal oxide such as REMnOs and associated alternative oxide forms (where RE is a rare earth element such as Pr, Nd, Sm, Eu, and Gd). Optionally, the metal oxide may comprise any one or a combination oxides of iron Fe, Mn, Cr. Optionally, the metal oxide may comprise a transition metal oxide any one or a combination of Fe2O3, NiO, LaFeOs and associated alternative oxide forms. Optionally, the reaction between the third form of the metal oxide and the air and / or oxygen within the third reactor is exothermic and the method further comprises capturing heat energy produced at the third reactor.

[0023] Optionally, the method may comprise transferring the heat energy to the ammonia fuel source and / or the first reactor to provide heat energy to the reaction between the ammonia fuel source and the oxidised first form of the metal oxide. Optionally, the method may further comprise transferring the heat energy to the water and / or the second reactor to provide heat energy to generate steam within the second reactor. Optionally, the method may further comprise cooling hydrogen produced at the second reactor using a flow stream of the ammonia fuel source. Optionally, the second reactor may be operated at a pressure in the range 0.05 MPa to 4 MPa or 0.1 MPa to 3 MPa. Optionally, the method may further comprise transferring heat energy to the ammonia fuel source via the step of cooling the hydrogen produced at the second reactor. Optionally, the method comprises cooling the hydrogen produced at the second reactor by cooling and compression of the hydrogen. Optionally, the step of cooling the hydrogen comprises an in-series cooling-compression- cooling-compression cycle of the hydrogen using at least one compressor, at least one evaporator; and / or at least one absorption cooler arrangement.

[0024] According to a further aspect of the present concept there is provided apparatus to produce hydrogen comprising: a first reactor having a first inlet to receive a supply of an ammonia fuel source, a second inlet to receive a supply of an oxidised first form of a metal oxide to react with the fuel source, a first outlet to discharge a second form of the metal oxide being a reaction product of a first reaction between the first form of the metal oxide and the fuel source; a second reactor having a first inlet connected in communication to the first outlet of the first reactor to receive the second form of the metal oxide discharged from the first reactor, a second inlet to receive a supply of water, a first outlet to discharge a third form of metal oxide being a product of a second reaction between the second form of the metal oxide and the water and a second outlet to discharge hydrogen being a further reaction product of the second reaction; a third reactor having a first inlet to receive a supply of air and / or oxygen, a second inlet connected in communication with the first outlet of the second reactor to receive a supply of the second form of the metal oxide, and a first outlet connected in communication with the second inlet of the first reactor to discharge the oxidised first form of the metal oxide for supply to the first reactor, the first form of the metal oxide being a reaction product of a third reaction between the third form of the metal oxide and air and / or oxygen; wherein the first, second and third reactors are thereby connected in communication to provide a flow loop of the metal oxide.

[0025] Optionally, a vessel or reservoir of the ammonia fuel source connected to the first inlet of the first reactor. Optionally, the metal oxide, the apparatus configured to circulate the metal oxide between the first, second and third reactors via the inlets and outlets of the first, second and third reactors. Optionally, the metal oxide comprises iron oxide and / or any one or a combination of an oxide of a metal selected from Ti, Al, Co, Cu, Mg, Mn, Zn. Optionally, the metal oxide may comprise any one or a combination of iron oxide and / or an oxide of a metal selected from Fe, Ti, Al, Co, Ni, V, Cr, Cu, Mg, Mn, Zn, La, Pr, Nd, Sm, Eu, and Gd. Optionally, the first reactor comprises a second outlet to discharge nitrogen and / or water being a further reaction product of the first reaction. Optionally, the third reactor comprises a second outlet to discharge nitrogen and / or oxygen being a further reaction product of the third reaction. Optionally, the metal oxide comprises iron oxide and wherein the first form is Fe2O3 ; the second form is a mixed iron oxide and the third form is Fe3O4. Optionally, the first reactor is a counter-current reactor configured to allow a flow in a first direction of the metal oxide and a flow of the ammonia fuel source in a second direction orientated countered to the first direction.

[0026] Optionally, the apparatus may further comprise a heat energy capture arrangement provided at the third reactor to capture heat energy produced at the third reactor. Optionally, a heat energy transfer conduit and / or circuit connected to the third reactor and / or conduit or vessel to contain the ammonia fuel source for supply to the third reactor to provide heat energy to the reaction between the ammonia fuel source and the oxidised first form of the metal oxide. Optionally, a heat energy transfer conduit and / or circuit connected to the second reactor and / or a conduit or vessel to contain the water for supply to the second reactor to provide heat energy to generate steam within the second reactor. Optionally, a vapour absorption refrigeration arrangement provided at and / or connected to the first outlet of the second reactor to cool the hydrogen produced at the second reactor. Optionally, the vapour absorption refrigeration arrangement or network comprises any one or a combination of the following set of: at least one compressor; at least one evaporator; at least one absorption cooler, flow circuit and / or absorption cooler arrangement; at least one flow pump; at least one throttle valve.

[0027] Optionally, the system may comprise a first heater provided at or proximate to the first reactor to heat the ammonia fuel source and the metal oxide at the first reactor to a temperature in a range 400 to 1000°C. Optionally, the system may comprise a second heater provided at or proximate to the second reactor configured to heat the water and the metal oxide to a temperature in a range 80 to 150°C. Optionally, the system may comprise a third heater provided at or proximate to the third reactor configured to heat the metal oxide and air and / or oxygen at a temperature in a range 800 to 1400°C.

[0028] Brief description of the drawings

[0029] A specific implementation of the present invention will now be described, by way of example only, and with reference to the accompanying drawings in which:

[0030] Figure 1 is a schematic diagram of a hydrogen production system having a fuel reactor, steam-iron reactor and air reactor connected in a loop to provide a three-reactor ammonia cracking system according to a specific implementation of the present invention;

[0031] Figure 2 is a schematic illustration of a fuel reactor comprising a counter-current moving bed configuration according to a specific implementation;

[0032] Figure 3 is a further schematic illustration of the three-reactor ammonia chemical cracking system of figure 1 according to a specific implementation;

[0033] Figure 4 is a further schematic illustration of the three-reactor ammonia chemical cracking system of figure 1 according to a specific implementation; Figure 5 is a further schematic illustration of the three-reactor ammonia chemical cracking system of figure 1 according to a specific implementation;

[0034] Figure 6 is a schematic illustration of a part of a three-reactor ammonia chemical cracking process and system according to figures 1 to 5 including a vapour absorption refrigeration arrangement according to a specific implementation.

[0035] Detailed description of preferred embodiment of the invention

[0036] Referring to figure 1 a three-reactor ammonia chemical cracking system 10 comprises a first fuel reactor 11; a second steam -iron reactor 12; and a third air reactor 13. Each of the reactors 11, 12, 13 are interconnected in a looped configuration via respective conduits as described herein so as to provide a circulating and / or looped arrangement for the cycling of at least one of the reactants and / or reaction products as part of the cracking process.

[0037] Fuel reactor 11 comprises a first inlet 14 to receive an inflow of ammonia and a second inlet 25 configured to receive a return flow of a first form of a metal oxide and specifically Fe2O3. Fuel reactor 11 further comprises a first outlet 16 to provide an outflow of a second form of the metal oxide and in particular Fe / Fex.oOy-obeing a reaction product of the first reactor and in particular a reaction between the ammonia and the first form metal oxide. Fuel reactor 11 further comprises a second outlet 15 to exhaust selected reaction products of the reaction within fuel reactor 11 including in particular nitrogen and water.

[0038] Steam-iron reactor 12 comprises a first inlet 18 to receive an inflow of the second form metal oxide (Fe / Fex.oOy-o) output from the first fuel reactor 11. Reactor 12 further comprises a second inlet 17 to receive a supply of water, and a first outlet 20 to output a third form of the metal oxide i.e. FesCh generated from the reaction within the steam reactor 12 between the first form of the metal oxide (Fe / Fex.oOy-o) and the water. Reactor 12 further comprises an outlet 19 for the discharge of hydrogen being a further reaction product of the reaction between the second form metal oxide and water within the reactor 12. Air reactor 13 comprises a first inlet 21 to receive an inflow of air and / or oxygen, and a second inlet 22 to receive the third form of the metal oxide (Fe / Fex-aOy-o) output from the steam -iron reactor 12. Air reactor 13 further comprises a first outlet 24 to discharge the first form metal oxide i.e. Fe2Cf being the reaction product of the reaction within air reactor 13 between the air and / or oxygen and the third form metal oxide (Fe^Cf). Air reactor 13 further comprises a second outlet 23 to discharge further reaction products including specifically nitrogen and oxygen.

[0039] Figure 2 illustrates a specific implementation of fuel reactor 11 comprising an in-series arrangement of fuel reactor modules I la, 11b, 11c, l id and l ie. Each of the module I la to l ie is interconnected with one another by respective inlets 14a to 14e, 25a to 25e and outlets 15a to 15e and 16a to 16e. Accordingly, the ammonia fuel source is adapted to flow through the fuel reactor modules I la to l ie in a first directi on / orientati on via respective inlets 14a to 14e and outlets 15a to 15e whilst the feed and throughput of the metal oxide is achieved via inlets 25a to 25e and outlets 16a to 16e in a second direction / orientation being counter / opposite to the flow direction of the ammonia.

[0040] A more detailed representation of the thermal cracking system of figure 1 comprising the three-reactor arrangement (reactors 11, 12 and 13) is illustrated in figure 3. Notably, the reaction between the air and / or oxygen and the third form of the metal oxide (Fe^Cf) within air reactor 13 is exothermic. Accordingly, the system comprises heat energy capture components and / or assembly in addition to respective heat energy transfer conduits or components 33, 34. In particular, a first heat energy transfer conduit 33 extends between air reactor 13 and fuel reactor 11 whilst a second heat energy transfer conduit 34 extends between air reactor 13 and steam-iron reactor 12. According to further implementations, the system may comprise a single heat energy transfer conduit 33 or 34. The system further comprises a first heat exchanger 30 to transfer heat from the nitrogen and oxygen discharged from the air reactor 13; a further heat exchanger 31 to provide heat exchange with water associated with the supply to / from the steam -iron reactor 12 and a further heat exchanger 32 to transfer heat from the nitrogen and / or water (output from the fuel reactor 11) to the inflow of ammonia fuel source introduced into fuel reactor 11 via inlet 14. The system further comprises a condenser 35. Condenser 35 is connected to the outlet side of heat exchanger 32; the inflow conduit of the water to be introduced into steam -iron reactor 12; and the outflow conduit from the steam -iron reactor through which the hydrogen and / or water is discharged. Condenser 35 is further connected to heat exchanger 31 to provide heat exchange with the water.

[0041] Figure 4 illustrates a yet further representation of the ammonia fuel source cracking system having the three reactors 11, 12, 13 connected in a looped configuration for the cyclical transfer / flow of the different forms of the metal oxide that is capable of being transferred between each of the reactors 11, 12 and 13. Such an arrangement provides a cracking process and system for the continual automated / semi-automated generation of hydrogen from an inflow of an ammonia fuel source.

[0042] As illustrated in figure 4, the system further comprises a first cyclonic separator 36 to separate the reaction products (mixed gas stream) generated within the fuel reactor 11 including in particular the second form of metal oxide, nitrogen and / or water vapour. The nitrogen separated by separator 36 may be discharged to the atmosphere after being fed to the heat exchanger 32 for heat transfer processing. As illustrated in figure 3, water, processed by condenser 35 and heat exchanger 31 may be fed to the steam -iron reactor 12 via inlet 17 (17a, 17b) to provide a heated supply of water / water vapour into reactor 12. Additionally, a separate source supply of water may be fed to heat exchanger 31 prior to introduction into reactor 12. The second form of metal oxide separated by separator 36 is then fed to the steam -iron reactor 12 via a suitable transfer conduit / network.

[0043] The system further comprises a second cyclonic separator 37 to receive a supply of the reaction products of the steam -iron reactor 12 including in particular hydrogen, water vapour and the second form of metal oxide. The hydrogen is separated and fed to a further separator 26 to generate purified hydrogen and other waste gases / products. The third form of metal oxide created at reactor 12 is extracted at separator 37 and fed to the air reactor 13 via inlet 22. Air and / or oxygen is introduced into reactor 13 via inlet 21. The gas products of air reactor 13 are discharged from outlet 23. The system further comprises a third cyclonic separator 38 to receive the reaction products (nitrogen, oxygen and the first form metal oxide) discharged from reactor 13 via outlet 23. Separator 38 is configured to generate the feed flow of the first form metal oxide (Fe2C>3) to the fuel reactor 11 at inlet 25. The nitrogen and oxygen extracted by separator 38 may then be vented to the environment and / or transferred for downstream processing.

[0044] A more detailed illustration of the ammonia fuel source cracking system is illustrated in figure 5. Fuel reactor 11 comprises the in-series fuel reactor units illustrated and described referring to figure 2 having initial ammonia fuel source inlet 14 to receive a supply of preheated ammonia. The pre-heating of the ammonia is described and illustrated referring to figure 6. The second form metal oxide reaction product of fuel reactor 11 is discharged at outlet 16 and transferred to the steam reactor 12 via inlet 18. The third form metal oxide is discharged from steam reactor 12 via outlet 20 and transferred to the air reactor 13 via inlet 22. Hydrogen generated by the steam reactor is transferred via conduit 43 to a heat exchanger / ammonia vaporiser 41 at hydrogen conduit region 42. The ammonia vaporiser 41 forms part of the ammonia inlet conduit network extending from an ammonia reservoir or source 40 and is adapted to exchange heat with the heated hydrogen gas discharged from steam reactor 12. That is, via vaporiser 41, liquid ammonia from source 40 provides cooling of the hydrogen gas at conduit region 42. Accordingly, the ammonia stream is cooled via heat exchange with the hydrogen discharged from steam reactor 12 with the ammonia then being transferred as a heated fuel source to the fuel reactor 11 via inlet 14.

[0045] A vapour absorption refrigeration assembly is illustrated schematically in figure 6 to provide processing of the various reaction product streams including in particular vents from the fuel reactor 11, steam reactor 12 and air reactor 13. The assembly comprises steam reactor vent conduit 57 having an evaporator 46, a compressor 44, a vaporiser 41, an evaporator 45, a further compressor 54, a further evaporator 53 and a discharge outlet 56. The vapour absorption refrigeration assembly further comprises a cooling / refrigeration network 58 that includes evaporator 46, throttle valve 47, condenser 48, generator 49, pump 51, absorption cooler circuit 52, further evaporator 53 and evaporator 45. A fuel reactor vent conduit 60 comprises evaporator 50 that is coupled to generator 49 and the refrigeration conduit 58. Refrigeration circuit 58 is coupled for heat exchange with the steam reactor vent conduit 57 via evaporator 46, 45 and 53. As illustrated, the pre-heated feed conduit of the ammonia supplied to the fuel reactor 11 interfaces with the hydrogen within the steam reactor vent conduit 57 via vaporiser 41. Accordingly, an effective and efficient system is provided for the auto-thermal heat exchange between the exothermic reaction within the air reactor 13 and at least one or both of the fuel reactor 11 and steam - iron reactor 12. Accordingly, heat energy from the air reactor 13 is supplied to the fuel reactor 11 and / or the steam-iron reactor 12. Furthermore, the heated hydrogen reaction product of the steam-iron reactor 12 is cooled by the ammonia fuel source which in turn provides heat energy to the ammonia fuel source prior to supply to the fuel reactor 11.

[0046] The various reactions within the three different reactors 11, 12 and 13 are detailed below. In particular, the reaction within the fuel reactor 11 comprises: 2NH3+3Fe2O3=N2+3H2O+6FeO

[0047] 2NH3+Fe2O3=N2+3H2O+2Fe

[0048] H2+Fe2O3=H2O+2FeO

[0049] 3H2+Fe2O3=3H2O+2Fe

[0050] The reaction within the steam reactor 12 comprises:

[0051] 4H2O+3Fe=Fe3O4+2H2

[0052] H2O+3FeO=Fe3O4+H2

[0053] H2O+Fe=FeO+H2

[0054] The reaction within the air reactor 13 comprises: 4Fe3O4+O2=6Fe2O3

[0055] The reaction parameters of several example implementations of the present concept are detailed in Tables 1-3. Example 1

[0056] Items Description

[0057] Fuel Reactor TFR=900 °C; Atmospheric pressure; Fe2O3 / NH3 molar ratio:

[0058] 1.175

[0059] NH3 preheating Inlet temperature of Fuel Reactor: 850 °C;

[0060] Steam Reactor Adiabatic; Atmospheric pressure; Steam excess ratio: 4.11;

[0061] Steam generator Outlet temperature of flue gas and production gas: 75 °C;

[0062] Air Reactor TAR=950 °C; atmospheric pressure; Air and / or oxygen excess ratio: 1.12;

[0063] Air and / or Outlet temperature of depleted-oxygen air: 75 °C; oxygen preheating

[0064] Feedstock NH3:2 kmol / h, atmospheric pressure; 15 °C; H2O: atmospheric pressure; 25 °C; Air: atmospheric pressure; 25 °C; consist of N2 (79%, vol) and O2 (21%, vol).

[0065] Table 1. Reaction parameters for the generation of hydrogen from a reaction of an ammonia fuel source with an iron-based metal oxide catalyst.

[0066] Example 2

[0067] Items Description

[0068] Fuel Reactor TFR=900 °C; Atmospheric pressure; NiO / NFF molar ratio: 1.5

[0069] NH3 preheating Inlet temperature of Fuel Reactor: 850 °C;

[0070] Steam Reactor Adiabatic; Atmospheric pressure; Steam excess ratio: 4.11;

[0071] Steam generator Outlet temperature of flue gas and production gas: 75 °C;

[0072] Air Reactor TAR=950 °C; atmospheric pressure; Air and / or oxygen excess ratio: 1.12;

[0073] Air and / or Outlet temperature of depleted-oxygen air: 75 °C; oxygen preheating

[0074] Feedstock NHa:2 kmol / h, atmospheric pressure; 15 °C; H2O: atmospheric pressure; 25 °C; Air: atmospheric pressure; 25 °C; consist of N2 (79%, vol) and O2 (21%, vol).

[0075] Table 2. Reaction parameters for the generation of hydrogen from a reaction of an ammonia fuel source with a nickel-based metal oxide catalyst.

[0076] Example 3

[0077] Items Description

[0078] Fuel Reactor TFR=900 °C; Atmospheric pressure; LaFeCh / NHa molar ratio:

[0079] 1.03

[0080] NH3 preheating Inlet temperature of Fuel Reactor: 850 °C;

[0081] Steam Reactor Adiabatic; Atmospheric pressure; Steam excess ratio: 4.11;

[0082] Steam generator Outlet temperature of flue gas and production gas: 75 °C;

[0083] Air Reactor TAR=950 °C; atmospheric pressure; Air and / or oxygen excess ratio: 1.12;

[0084] Air and / or Outlet temperature of depleted-oxygen air: 75 °C; oxygen preheating

[0085] Feedstock NHa:2 kmol / h, atmospheric pressure; 15 °C; H2O: atmospheric pressure; 25 °C; Air: atmospheric pressure; 25 °C; consist of N2 (79%, vol) and O2 (21%, vol).

[0086] Table 3. Reaction parameters for the generation of hydrogen from a reaction of an ammonia fuel source with a perovskite catalyst.

[0087] The energy efficiency performance results for the generation of hydrogen via the parameters of example 1 and the system of figures 1 to 6 are detailed in table 4. Items Proposed process Conventional process'

[0088] Energy Input

[0089] NH3 feedstock (kmol / h) 2 900

[0090] Higher heating value (kJ / mol) 383 383

[0091] Energy of NH30.21 95.75

[0092] Electricity requirement (MW) 0 3.2

[0093] Subtotal 0.21 98.95

[0094] Energy output

[0095] H2 production (kmol / h) 2.19 1028.8

[0096] Higher heating value (kJ / mol) 286 286

[0097] Energy ofH20.17 81.73

[0098] Thermal efficiency 81.6% 82.6%

[0099] H2yield 72.9% 76.2%

[0100] Ammonia conversion ratio 99.5% 96.1%

[0101] Table 4. Energy efficiency performance results for the generation of hydrogen via example 1 and the system of figures 1 to 6.

[0102] Where, the values detail in table 2 are calculated based on the following definitions:

[0103] Enerv efficiency 100

[0104] The present invention provides an ammonia cracking chemical looping method and apparatus for high-purity hydrogen production. The present system was designed and evaluated through process modelling and thermodynamic analysis. Iron oxide was selected as a preferred oxygen carrier. A parametric study was undertaken to evaluate the effect of key operating conditions on the process performance. The results support the following operating conditions: an operating temperature of 800 to 1100°C within (at an outlet of) air reactor 13; an operating temperature of 400 to 800°C within (at an outlet of) the fuel reactor 11, an ammonia to metal oxide ratio value of 12 to 16 that provided optimal conditions for maximising hydrogen yield and energy efficiency, while minimising process energy losses. Process intensification strategies, such as increasing the steam reactor pressure to 0.1 to 1 MPa, was found to achieve an overall energy efficiency of 70 to 80%, exergy efficiency of 65 to 75% and a hydrogen yield of 60 to 80% with a purity above 99%. Under steady operation, the present H2 production process is autothermal, without the requirement of external heating.

[0105] The present system provides a (closed) loop chemical looping ammonia cracking assembly that is scalable as well as an energy-efficient method for producing high-purity hydrogen from ammonia. In particular, according to one embodiment, a closed-looped three-reactor system for ammonia cracking used iron oxide as an oxygen carrier to crack ammonia and produce ultra-high purity hydrogen. Iron oxide was selected as the oxygen carrier (OC) due to its abundance, thermal stability, and low cost. In the present chemical looping reforming process, iron oxides also showed good reactivity, high oxygen adsorption capacity, and high resistance against sintering. Studies on iron ore direct reduction using ammonia have suggested that it is feasible to use iron oxides as an oxygen carrier for ammonia reduction. Furthermore, experimental thermogravimetric analyses demonstrated that Fe2C>3 can be fully reduced under NH3 at 700 °C without the formation of NOX, confirming its reducibility under ammonia-rich environments. In addition, metallic Fe formed upon complete reduction of iron oxides has been demonstrated to be active for ammonia decomposition. Such experimental findings are consistent with the reaction pathways of the present system.

Claims

Claims1. A method of producing hydrogen comprising: receiving a supply of an ammonia fuel source and a supply of an oxidised first form of a metal oxide at a first reactor; allowing the ammonia fuel source and the metal oxide to react within the first reactor to produce a second form of the metal oxide; transferring the second form of the metal oxide from the first reactor to a second reactor; receiving a supply of water at the second reactor; allowing the second form of the metal oxide and the water to react within the second reactor to produce a third form of the metal oxide and hydrogen; discharging the hydrogen from the second reactor; transferring the third form of the metal oxide from the second reactor to a third reactor; receiving a supply of air and / or oxygen at the third reactor; allowing the third form of the metal oxide and the air and / or oxygen to react within the third reactor to produce the oxidised first form of the metal oxide; transferring the oxidised first form of the metal oxide to the first reactor; wherein the metal oxide is circulated through the first, second and third reactors as a flow loop.

2. The method as claimed in claim 1 further comprising discharging nitrogen and / or water from the first reactor.

3. The method as claimed in claims 1 or 2 further comprising discharging nitrogen and / or oxygen from the third reactor.

4. The method as claimed in any preceding claim wherein the first reactor is a counter-current reactor, the method further comprising:providing a flow of the ammonia fuel source in a first direction through the first reactor and providing a flow of the metal oxide in a second direction through the first reactor, the second direction orientated counter to the first.

5. The method as claimed in any preceding claim wherein the step of allowing the ammonia fuel source and the metal oxide to react within the first reactor comprises providing a reaction temperature in a range 400 to 1000°C; 500 to 1000°C; 600 to 1000°C; 400 to 800°C; or 500 to 800°C.

6. The method as claimed in any preceding claim wherein the step of allowing the second form of the metal oxide and water to react in the second reactor comprises providing a reaction temperature in a range 80 to 150°C.

7. The method as claimed in any preceding claim wherein the step of allowing the third form of the metal oxide and air and / or oxygen to react in the third reactor comprises providing a reaction temperature in a range 800 to 1400°C; 800 to 1300°C; or 800 to 1100°C.

8. The method as claimed in any preceding claim wherein an ammonia fuel source- to-metal oxide ratio value within the first reactor is in a range 8 to 20; 10 to 18; 12 to 16.

9. The method as claimed in any preceding claim further comprising generating steam from the water within the second reactor wherein a steam-to-metal oxide ratio value is in a range 1.5 to 4.5; 2.5 to 4.5; or 3.5 to 4.5.

10. The method as claimed in any preceding claim wherein an air-to-metal oxide or oxygen-to-metal oxide ratio value within the third reactor is in a rangel to 2; 1 to 1.8; 1 to 1.6; or 1 to 1.4.

11. The method as claimed in any preceding claim wherein the metal oxide comprises iron oxide and / or any one or a combination of an oxide of a metal selected from Fe, Ti, Al, Co, Ni, V, Cr, Cu, Mg, Mn, Zn, La, Pr, Nd, Sm, Eu, and Gd.

12. The method as claimed in any preceding claim wherein the reaction between the third form of the metal oxide and the air and / or oxygen within the third reactor is exothermic and the method further comprises capturing heat energy produced at the third reactor.

13. The method as claimed in claim 12 further comprising transferring the heat energy to the ammonia fuel source and / or the first reactor to provide heat energy to the reaction between the ammonia fuel source and the oxidised first form of the metal oxide.

14. The method as claimed in claims 12 or 13 further comprising transferring the heat energy to the water and / or the second reactor to provide heat energy to generate steam within the second reactor.

15. The method as claimed in any preceding claim further comprising cooling hydrogen produced at the second reactor using a flow stream of the ammonia fuel source.

16. The method as claimed in any preceding claim wherein the second reactor is operated at a pressure in the range 0.1 MPa to 3 MPa.

17. The method as claimed in claim 13 and 16 further comprising transferring heat energy to the ammonia fuel source via the step of cooling the hydrogen produced at the second reactor.

18. The method as claimed in any preceding claim comprising cooling the hydrogen produced at the second reactor by cooling and compression of the hydrogen.

19. The method as claimed in claim 18 wherein cooling the hydrogen comprises an in-series cooling-compression-cooling-compression cycle of the hydrogen using at least one compressor, at least one evaporator; and / or at least one absorption cooler arrangement.

20. Apparatus to produce hydrogen comprising:a first reactor having a first inlet to receive a supply of an ammonia fuel source, a second inlet to receive a supply of an oxidised first form of a metal oxide to react with the fuel source, a first outlet to discharge a second form of the metal oxide being a reaction product of a first reaction between the first form of the metal oxide and the fuel source; a second reactor having a first inlet connected in communication to the first outlet of the first reactor to receive the second form of the metal oxide discharged from the first reactor, a second inlet to receive a supply of water, a first outlet to discharge a third form of metal oxide being a product of a second reaction between the second form of the metal oxide and the water and a second outlet to discharge hydrogen being a further reaction product of the second reaction; a third reactor having a first inlet to receive a supply of air and / or oxygen, a second inlet connected in communication with the first outlet of the second reactor to receive a supply of the second form of the metal oxide, and a first outlet connected in communication with the second inlet of the first reactor to discharge the oxidised first form of the metal oxide for supply to the first reactor, the first form of the metal oxide being a reaction product of a third reaction between the third form of the metal oxide and air and / or oxygen; wherein the first, second and third reactors are thereby connected in communication to provide a flow loop of the metal oxide.

21. The apparatus as claimed in claim 20, further comprising a vessel or reservoir of the ammonia fuel source connected to the first inlet of the first reactor.

22. The apparatus as claimed in claims 20 or 21 comprising the metal oxide, the apparatus configured to circulate the metal oxide between the first, second and third reactors via the inlets and outlets of the first, second and third reactors.

23. The method as claimed in any preceding claim wherein the metal oxide comprises iron oxide and / or any one or a combination of an oxide of a metal selected from Fe, Ti, Al, Co, Ni, V, Cr, Cu, Mg, Mn, Zn, La, Pr, Nd, Sm, Eu, and Gd.

24. The apparatus as claimed in any one of claims 20 to 23 wherein the first reactor comprises a second outlet to discharge nitrogen and / or water being a further reaction product of the first reaction.

25. The apparatus as claimed in any one of claims 20 to 24 wherein the third reactor comprises a second outlet to discharge nitrogen and / or oxygen being a further reaction product of the third reaction.

26. The apparatus as claimed in any one of claims 20 to 25 wherein the metal oxide comprises iron oxide and wherein the first form is Fe2O3 ; the second form is a mixed iron oxide and the third form is FesC .

27. The apparatus as claimed in any one of claims 20 to 26 wherein the first reactor is a counter-current reactor configured to allow a flow in a first direction of the metal oxide and a flow of the ammonia fuel source in a second direction orientated countered to the first direction.

28. The apparatus as claimed in any one of claims 20 to 27 further comprising a heat energy capture arrangement provided at the third reactor to capture heat energy produced at the third reactor.

29. The apparatus as claimed in any one of claims 20 to 28 further comprising a heat energy transfer conduit and / or circuit connected to the third reactor and / or conduit or vessel to contain the ammonia fuel source for supply to the third reactor to provide heat energy to the reaction between the ammonia fuel source and the oxidised first form of the metal oxide.

30. The apparatus as claimed in any one of claims 20 to 29 further comprising a heat energy transfer conduit and / or circuit connected to the second reactor and / or a conduit or vessel to contain the water for supply to the second reactor to provide heat energy to generate steam within the second reactor.

31. The apparatus as claimed in any one of claims 20 to 30 further comprising a vapour absorption refrigeration arrangement provided at and / or connected to the first outlet of the second reactor to cool the hydrogen produced at the second reactor.

32. The apparatus as claimed in claim 31 wherein the vapour absorption refrigeration arrangement comprises any one or a combination of the following set of:• at least one compressor;• at least one evaporator;• at least one absorption cooler, flow circuit and / or absorption cooler arrangement;• at least one flow pump;• at least one throttle valve.

Images