Device for producing hydrogen

Abstract

The invention provides a device for producing hydrogen gas and a process therefor. It also provides a system for generating electrical energy from hydrogen gas. More particularly, the invention provides a device for producing hydrogen comprising an ammonia cracker having one or more raw cracked gas outlets in fluid communication with a common raw cracked gas flow conduit, one or more gas separators in fluid communication with the ammonia cracker via the common raw cracked gas flow conduit, and in fluid communication with a common partially purified cracked gas flow conduit; one or more filter assemblies, each having a first container having one or more walls, one or more partially purified cracked gas inlets and one or more purified cracked gas outlets, wherein the one or more partially purified cracked gas inlets are in fluid communication with the one or more gas separators via the common partially purified cracked gas flow conduit, the first container containing a single mass of adsorbent comprising silica gel, wherein the one or more partially purified cracked gas inlets and one or more purified cracked gas outlets are arranged such that a partially purified cracked gas flows through the single mass of adsorbent in use.

Description

[0001] DEVICE FOR PRODUCING HYDROGEN

[0002] Background

[0003] Hydrogen gas is a promising clean fuel with a significant role to play as part of the global effort to reduce climate change. It can be readily combusted, as well as being used to generate electrical energy using specialized devices such as fuel cells. There are a number of methods of generating hydrogen, for example steam reformation of natural gas or water electrolysis. However, one promising method of generating clean hydrogen is the catalytic breakdown (commonly referred to as ‘catalytic cracking’ or simply ‘cracking’) of ammonia gas into hydrogen and nitrogen according to the following reaction:

[0004] 2NH3N2+ 3H2

[0005] Devices for producing hydrogen by this means are commonly referred to as ‘ammonia crackers’ and involve providing a heated chamber containing catalyst through which ammonia gas flows. Upon contact with the catalyst, the ammonia is cracked and the hydrogen and nitrogen gas are produced. Such devices are known in the art (see, for example, W02009098452A2).

[0006] The output gas is generally a hydrogen rich gas mixture comprising hydrogen gas, nitrogen gas, and ammonia gas. One of the technical challenges of hydrogen production by ammonia cracking is to separate the hydrogen rich gas mixture into its constituents. Depending on the downstream use, different purities of hydrogen gas may be required. For example, the ISO14687:2019 standard provides guidance on the purity of hydrogen gas required for use in stationary fuel cell systems. Ammonia gas residing in the output gas mixture is particularly troublesome in certain applications, as it invalidates the standard and can create technical issues in downstream equipment should any pass through the various gas separation means employed in a typical system for purifying the hydrogen gas.

[0007] At present, several purification methods are employed to purify the hydrogen gas for further use. One method of purifying the hydrogen gas is to bubble the impure gas through water such that ammonia is removed. The downside of this method is that nitrogen will not be removed and so further treatment would be required. Another common method uses pressure swing adsorption (“PSA”) devices, such as those disclosed in WO2022265651A1 . In this system, impurities in the hydrogen rich gas mixture are bound to at least two adsorbent materials under pressure (non-zeolitic adsorbent e.g. activated carbon for ammonia gas; and zeolitic adsorbent e.g.5A zeolite or 13X zeolite for nitrogen gas). Such systems are invaluable for removing nitrogen and ammonia gas for downstream usage, but in practice such systems are expensive and cannot guarantee an ammonia free gas under all conditions. Additionally, ammonia adsorption and nitrogen adsorption require different adsorbent materials due to the different properties each impurity has.

[0008] Applicants have discovered a low-cost, reliable, and environmentally friendly solution for further purifying hydrogen gas from a gas mixture from an ammonia cracking system which has had some but not all of the ammonia removed therefrom by, for example, pressure swing adsorption, with numerous advantages over the prior art devices as discussed below.

[0009] Summary of the Invention

[0010] In a first aspect, the invention provides a device for producing hydrogen comprising an ammonia cracker having one or more raw cracked gas outlets in fluid communication with a common raw cracked gas flow conduit, one or more gas separators in fluid communication with the ammonia cracker via the common raw cracked gas flow conduit, and in fluid communication with a common partially purified cracked gas flow conduit; one or more filter assemblies, each having a first container having one or more walls, one or more partially purified cracked gas inlets and one or more purified cracked gas outlets, wherein the one or more partially purified cracked gas inlets are in fluid communication with the one or more gas separators via the common partially purified cracked gas flow conduit, the first container containing a single mass of adsorbent comprising silica gel, wherein the one or more partially purified cracked gas inlets and one or more purified cracked gas outlets are arranged such that a partially purified cracked gas flows through the single mass of adsorbent in use.

[0011] In one embodiment, the one or more walls are made of a metal. In a further embodiment, the metal is stainless steel, high carbon steel, aluminium, or titanium.

[0012] In a further embodiment, the metal comprises a polymer coating. In a further embodiment, the polymer coating is a fluorinated polymer, preferably PTFE or PFA.

[0013] In an embodiment, the one or more walls comprise a plastic, optionally a clear plastic and / or an opaque plastic. In an embodiment, the plastic is a fluorinated plastic or a polycarbonate.

[0014] In an embodiment, each filter assembly further comprises a sight glass for viewing the single mass of adsorbent.

[0015] In an embodiment, the device further comprises an ancillary container containing a second mass of adsorbent comprising silica gel, the ancillary container being disposed downstream of and in fluid communication with the first container via the one or more purified cracked gas outlets, wherein the ancillary container comprises a second sight glass for viewing the second mass of adsorbent. In a further embodiment, the one or more walls further comprise a sight glass. In a further embodiment, the sight glass is proximal to at least one of the one or more purified cracked gas outlets. In a further embodiment, the sight glass comprises a portion proximate to at least one of the one or more partially purified cracked gas inlets.

[0016] In some embodiments, the filter assembly further comprises a flow structure for lengthening the path of travel of the partially purified cracked gas through the single mass of adsorbent.

[0017] In some embodiments the flow structure is chosen from a group consisting of one or more permeable tubes disposed within the single mass of adsorbent and connected at one end to the one or more partially purified cracked gas inlets; one or more baffles extending from the one or more walls of the filter assembly; one or more inserts disposed in the container; wherein the container comprises a substructure formed of a substrate forming an internal volume filled at least partially with the single mass of adsorbent, the substructure in fluid communication with the one or more partially purified cracked gas inlets and the one or more purified cracked gas outlets; or any combination of the above.

[0018] In some embodiments the silica gel comprises silica gel beads, silica gel powder, and / or silica gel granules.

[0019] In some embodiments, each filter assembly comprises an indicator adsorbed into, disposed on and / or proximal to the silica gel.

[0020] In some embodiments, the device further comprises an ammonia gas sensor. In a further embodiment the ammonia gas sensor is disposed downstream from and in fluid communication with the one or more purified cracked gas outlets. In a further embodiment the ammonia gas sensor is connected to the one or more purified cracked gas outlets via a regulator.

[0021] In an embodiment, the one or more filter assemblies are each in fluid communication with the common partially purified cracked gas flow conduit via the one or more partially purified cracked gas inlets, each filter assembly having a first valve between the one or more partially purified cracked gas inlets and the common partially purified cracked gas flow conduit.

[0022] In an embodiment, the one or more filter assemblies are each in fluid communication with a common purified cracked gas flow conduit via the one or more purified cracked gas outlets, each filter assembly having a second valve between the one or more purified cracked gas outlets and the common purified cracked gas flow conduit.

[0023] In an embodiment, the one or more gas separators comprise a pressure swing adsorption device and / or a palladium filter and / or a catalytic conversion reactor and / or a temperature swing adsorption device and / or a hollow fibre membrane filter.

[0024] In an embodiment, the one or more gas separators are proximal or integral to the ammonia cracker.

[0025] In an embodiment, greater than 30% of the single mass of adsorbent is silica gel, optionally wherein the single mass of adsorbent consists essentially of silica gel.

[0026] In a second aspect, the invention provides a system for generating electrical power using ammonia comprising the device according to the first aspect or any embodiment thereof and a hydrogen fuel cell, wherein the hydrogen fuel cell is in fluid communication with the device for producing hydrogen via the common purified cracked gas flow conduit.

[0027] In a third aspect, the invention provides a process for producing a purified cracked gas of high purity hydrogen comprising: providing ammonia gas to an ammonia cracker having one or more raw cracked gas outlets in fluid communication with a common raw cracked gas flow conduit to produce a raw cracked gas comprising hydrogen gas, nitrogen gas, and ammonia gas; a first purification stage comprising conveying the raw cracked gas via the common raw cracked gas flow conduit to one or more gas separators, wherein the one or more gas separators at least partially remove the ammonia gas and nitrogen gas from the raw cracked gas to produce a partially purified cracked gas; and a second purification stage comprising conveying the partially purified cracked gas via a common partially purified cracked gas flow conduit to one or more filter assemblies, each having a first container having one or more walls, one or more partially purified cracked gas inlets and one or more purified cracked gas outlets, the one or more partially purified cracked gas inlets being in fluid communication with the common partially purified cracked gas flow conduit , the first container containing a single mass of adsorbent comprising silica gel, wherein the one or more partially purified cracked gas inlets and one or more purified cracked gas outlets are arranged such that the partially purified cracked gas flows through the single mass of adsorbent, wherein the single mass of adsorbent selectively adsorbs the ammonia in the partially purified cracked gas to produce a purified cracked gas; wherein the partially purified cracked gas is conveyed through the one or more filter assemblies at a process pressure, wherein the process pressure is substantially constant.

[0028] In an embodiment, the process pressure is 35 bar or less.

[0029] In an embodiment, at least one of the one or more gas separators is a pressure swing adsorption device, wherein the pressure swing adsorption device comprises a plurality of vessels, each vessel comprising a first pressure swing adsorbent for adsorbing nitrogen gas from the raw cracked gas and a second pressure swing adsorbent for adsorbing ammonia gas from the raw cracked gas, optionally comprising a third pressure swing adsorbent for adsorbing water, wherein the plurality of vessels comprises a first pair of vessels comprising a first vessel and a second vessel, wherein the process comprises the sequence of: (a) fluidly connecting the first vessel of the first pair vessels to the common raw cracked gas flow conduit and the common partially purified cracked gas flow conduit and conveying the raw cracked gas to the first vessel at the process pressure, wherein the ammonia gas and nitrogen gas (and optionally water) in the raw cracked gas are at least partially removed to produce the partially purified cracked gas; (b) conveying the partially purified cracked gas from the first vessel to the common partially purified cracked gas flow conduit at the process pressure; (c) fluidly isolating the first vessel from the common partially purified cracked gas flow conduit and the common raw cracked gas flow conduit; (d) fluidly connecting the first vessel to the second vessel of the first pair of vessels, the second vessel being at atmospheric pressure, such that the first vessel undergoes a decrease in pressure and the second vessel undergoes an increase in pressure such that the first vessel and the second vessel are at half of the process pressure; (e) fluidly isolating the first vessel from the second vessel and fluidly connecting the first vessel to a common waste gas flow conduit and conveying a waste gas containing nitrogen gas and ammonia gas from the first vessel to the common waste gas flow conduit, wherein the first vessel undergoes a further depressurisation such that the first vessel is at atmospheric pressure; (f) fluidly connecting the first vessel to a common purge gas flow conduit and conveying a purge gas at atmospheric pressure to the first vessel to remove any remaining waste gas from the first vessel via the common waste gas flow conduit; (g) fluidly isolating the first vessel from the common waste gas flow conduit and the common purge gas flow conduit; (h) fluidly connecting the first vessel to the second vessel, the second vessel being at the process pressure, such that the first vessel undergoes an increase in pressure and the second vessel undergoes a decrease in pressure such that the first vessel and the second vessel are at half of the process pressure; (i) fluidly isolating the first vessel from the second vessel and fluidly connecting the first vessel to a common backfill gas flow conduit and conveying a backfill gas such that the first vessel undergoes an increase in pressure such that the first vessel is at the process pressure; and (j) fluidly isolating the first vessel from the common backfill gas flow conduit and fluidly connecting the first vessel to the common raw cracked gas flow conduit and the common partially purified cracked gas flow conduit; wherein during steps (a) to (j), the partially purified cracked gas is conveyed through the one or more filter assemblies at the process pressure.

[0030] In an embodiment, the partially purified cracked gas is conveyed from multiple gas separators to the one or more filter assemblies.

[0031] In an embodiment, the single mass of adsorbent comprises at least 30% by mass of silica gel, optionally wherein the single mass of adsorbent consists essentially of silica gel.

[0032] In an embodiment, the partially purified cracked gas is conveyed through the one or more filter assemblies at a process temperature, wherein the process temperature is 100 °C or below, preferably wherein the process temperature is between -50 °C and 50 °C.

[0033] Brief Description of the Drawings

[0034] Figure 1 shows a device for generating purified hydrogen gas comprising an ammonia cracker, one or more gas separators, and one or more filter assemblies according to the invention.

[0035] Figure 2 shows an exemplary filter assembly according to the invention as a cutaway diagram having one partially purified cracked gas inlet and one purified cracked gas outlet.

[0036] Figure 3 shows an exemplary filter assembly according to the invention as a cutaway diagram having multiple partially purified cracked gas inlets and purified cracked gas outlets.

[0037] Figure 4 shows an exemplary filter assembly according to the invention having one or more walls which are opaque, with a sight glass disposed therein.

[0038] Figure 5 shows an alternative filter assembly according to the invention wherein the sight glass extends substantially the length of the filter assembly.

[0039] Figure 6 shows an exemplary filter assembly where the filter assembly has an auxiliary container having one or more walls with a sight glass disposed therein, in fluid communication with the first container of the invention.

[0040] Figure 7 shows an exemplary filter assembly according to the invention as a cutaway diagram having a perforated tube for extending the gas flow path from the one or more partially purified cracked gas inlets.

[0041] Figure 8 shows an exemplary filter assembly with baffles to extend the flow path of the gas.

[0042] Figure 9 shows a system for generating hydrogen gas comprising a gas separator and a plurality of filter assemblies according to the invention.

[0043] Figure 10 shows a system for generating hydrogen gas comprising an ammonia cracker, a gas separator, and a filter assembly, wherein the filter assembly is in fluid communication with a common purified cracked gas flow conduit and an ammonia gas sensor via a regulator.

[0044] Figure 11 shows a system for generating electricity from hydrogen comprising an ammonia cracker, a gas separator, a filter assembly, and a hydrogen fuel cell.

[0045] Detailed Description

[0046] CN1 14408860 A discloses a two stage pressure swing adsorption device. The first stage of this device includes three adsorbent masses comprising activated alumina, activated carbon, silica gel, and a molecular sieve. The second stage comprises activated alumina and / or a molecular sieve. WO 2022 / 265651 A1 discloses a pressure swing adsorption device having two adsorbent masses, the first being a non-zeolitic adsorbent to adsorb water and ammonia and the second being a zeolitic adsorbent to adsorb nitrogen.

[0047] US 3352716 A discloses a drying device for drying exhaust gases from a combustion chamber of an ammonia cracker.

[0048] US 2023 / 0174375 A1 discloses a system which uses either a single stage or a two- stage system involving conventional pressure swing adsorption devices to purify the hydrogen. Each unit contains two masses of adsorbent, a zeolitic adsorbent to adsorb nitrogen and a non-zeolitic adsorbent to adsorb water and ammonia.

[0049] The invention will now be described and exemplified with particular embodiments discussed below, with reference to the figures.

[0050] In a first aspect, the invention provides a device for producing hydrogen comprising an ammonia cracker having one or more raw cracked gas outlets in fluid communication with a common raw cracked gas flow conduit; one or more gas separators in fluid communication with the ammonia cracker via the common raw cracked gas flow conduit, and in fluid communication with a common partially purified cracked gas flow conduit; and one or more filter assemblies as described below. Figure 1 shows such a device with arrows indicating gas flow, wherein the ammonia cracker 111 is in fluid communication with a common raw cracked gas flow conduit 112a, which fluidly connects the ammonia cracker to one or more gas separators 116. The one or more gas separators 116 are in fluid communication with one or more filter assemblies 101 via a common partially purified cracked gas flow conduit 112b. The device of the invention may be thought of and described as a ‘system’. The figures are diagrams only and each component of the device may be orientated as required.

[0051] The common raw cracked gas flow conduit, one or more gas separators, and common partially purified cracked gas flow conduit may be thought of and described as a single conduit, which may be referred to as the ‘common raw cracked gas flow conduit’. As such, the one or more gas separators described herein may be described as forming part of the common raw cracked gas flow conduit which runs between the ammonia cracker and the one or more filter assemblies and the one or more gas separators may be described as disposed between and in fluid communication with the ammonia cracker and the one or more filter assemblies. As such, herein where we refer to a Taw cracked gas’, this may mean a partially purified cracked gas, provided the raw cracked gas has passed through one or more gas separators. The ‘common partially purified cracked gas flow conduit’ downstream of the one or more gas separators may be referred to as a ‘common raw cracked gas flow conduit’, and the one or more ‘partially purified cracked gas inlets’ of the one or more filter assemblies may be referred to as one or more Taw cracked gas flow inlets’.

[0052] In use, ammonia gas is supplied to the ammonia cracker 111 to produce a raw cracked gas containing (or comprising) hydrogen gas, nitrogen gas, and ammonia gas, which flows out of the ammonia cracker and to one or more gas separators 116 via the common raw cracked gas flow conduit 112a. The one or more gas separators 116 at least partially remove the nitrogen gas and the ammonia gas from the raw cracked gas to produce a partially purified cracked gas, which then flows to one or more filter assemblies 101 via the common partially purified cracked gas flow conduit 112b. The skilled person would understand that the ammonia cracker and the one or more gas separators may have any number of inlets and outlets suitable for supplying them with the gases required for the function of the device. The ammonia cracker has at least one inlet and at least one outlet. The one or more gas separators each have at least one inlet and at least one outlet. The ammonia cracker is in fluid communication with at least one source of ammonia gas. This could be a storage tank or a common ammonia gas flow conduit. For simplicity, the common raw cracked gas flow conduit 112a may be referred to as the first common gas flow conduit, and the common partially purified cracked gas flow conduit 112b may be referred to as the second common gas flow conduit.

[0053] The invention provides a device for producing hydrogen comprising an ammonia cracker having one or more raw cracked gas outlets in fluid communication with a common raw cracked gas flow conduit, one or more gas separators in fluid communication with the ammonia cracker via the common raw cracked gas flow conduit, wherein the one or more gas separators are also in fluid communication with a common partially purified cracked gas flow conduit, and one or more filter assemblies in fluid communication with the one or more gas separators via the common partially purified cracked gas flow conduit, each filter assembly having a first container having one or more walls, one or more partially purified cracked gas inlets and one or more purified cracked gas outlets, wherein the one or more partially purified cracked gas inlets are in fluid communication with the common partially purified cracked gas flow conduit, the first container containing a single mass of adsorbent comprising silica gel, wherein the one or more partially purified cracked gas inlets and one or more purified cracked gas outlets are arranged such that a partially purified cracked gas flows through the single mass of adsorbent in use. The one or more partially purified cracked gas inlets and one or more purified cracked gas outlets must therefore be arranged so that the single mass of adsorbent is in an internal volume of the first container and is disposed between the one or more partially purified cracked gas flow inlets and the one or more purified cracked gas flow outlets.

[0054] In some embodiments, the invention provides a device for producing hydrogen comprising an ammonia cracker having one or more raw cracked gas outlets in fluid communication with a common raw cracked gas flow conduit, the ammonia cracker configured to produce a raw cracked gas comprising hydrogen gas, nitrogen gas, and ammonia gas, and to provide the raw cracked gas to the common raw cracked gas flow conduit via the one or more raw cracked gas outlets; one or more gas separators in fluid communication with the ammonia cracker via the common raw cracked gas flow conduit, and in fluid communication with a common partially purified cracked gas flow conduit, the one or more gas separators configured to at least partially remove the ammonia gas and nitrogen gas from the raw cracked gas to produce a partially purified cracked gas and to provide the partially purified cracked gas to the common partially purified cracked gas flow conduit; and one or more filter assemblies each having a first container having one or more walls, one or more partially purified cracked gas inlets and one or more purified cracked gas outlets, wherein the one or more partially purified cracked gas inlets are in fluid communication with the one or more gas separators via the common partially purified cracked gas flow conduit, the first container containing a single mass of adsorbent comprising silica gel, wherein the one or more partially purified cracked gas inlets and one or more purified cracked gas outlets are arranged such that a partially purified cracked gas flows through the single mass of adsorbent in use, the single mass of adsorbent configured to selectively adsorb the ammonia in the partially purified cracked gas that is provided to the one or more purified cracked gas outlets.

[0055] The one or more filter assemblies of the invention may be better understood with reference to Figure 2. The invention provides a device comprising one or more filter assemblies 200, each filter assembly having a first container 201 having one or more walls 202, one or more partially purified cracked gas inlets 203 in fluid communication with the common partially purified cracked gas flow conduit, each filter assembly having one or more purified cracked gas outlets 204 which may be fluidly connected to a common purified cracked gas flow conduit, the first container containing a single mass of adsorbent 205 comprising silica gel, wherein the one or more partially purified cracked gas inlets and one or more purified cracked gas outlets are arranged such that a partially purified cracked gas flows through the single mass of adsorbent in use. An exemplary filter assembly is shown in Figure 2. For simplicity, the common purified cracked gas flow conduit may be referred to as the third common gas flow conduit.

[0056] As discussed, the device for producing hydrogen from ammonia is, for example an ammonia cracker. These devices work by catalytic decomposition of ammonia at high temperatures to produce nitrogen and hydrogen gas (see e.g. US 2003 / 0232224 A1 , which is incorporated by reference herein). Typically, an ammonia cracker comprises a reaction chamber containing an ammonia decomposition catalyst, the reaction chamber having an inlet and outlet configured to allow the flow of ammonia gas into the reaction chamber where it contacts the ammonia decomposition catalyst and is decomposed into a raw cracked gas comprising nitrogen gas and hydrogen gas (and residual ammonia gas) which flows out of the outlet and onwards to further downstream systems. The reaction chamber is heated by a heat source (internal and / or external) to allow the decomposition reaction to proceed. Ammonia decomposition catalysts are known in the art. Typical ammonia decomposition catalysts which can be used are, for example, supported monometallic catalysts (e.g. Fe, Ru, Cu, Ni, Ir, Co, Mo, Pt and Pd) multimetallic catalysts or alloy catalysts (e.g. Ni-Pt, Ni-Co, Ir-Ni, Co-Mo, Fe-Co, Fe-Mo, Cu-Zn), nitride and carbide catalysts (e.g. Carbides and nitrides of Mo, Fe, Co, Ni, Ti, V, Mn and Cr), and metal amide / imide catalysts (e.g. UNH2, NaNFh, KNH2). The reaction chamber can take any shape provided it is gas tight except for inlets and outlets. It can be made of any suitable ammonia resistant material or composite, for example austenitic stainless steel. Any heat source may be used provided it can heat the volume defined by the reaction chamber to an appropriate temperature for the decomposition of ammonia reaction to occur. For example, the volume defined by the reaction chamber could be heated to between 400 to 950 degrees Celsius. The reaction chamber is typically operating at pressure in use, for example 100 bar (or barg) or less, preferably 50 bar (or barg) or less (for example, 0.1 barg to 50 barg). As such, it is suitably constructed to withstand such pressure. The raw cracked gas produced by an ammonia cracker typically contains a mixture of hydrogen gas, nitrogen gas, and residual ammonia gas left over from the equilibrium reaction which occurs in the ammonia cracker. Once the raw cracked gas exits the ammonia cracker, it is first separated using one or more gas separators to remove the majority of the nitrogen and / or ammonia therefrom prior to entry into the one or more filter assemblies. This is preferable as the filter assembly described in this embodiment does not remove nitrogen gas, only ammonia. Each filter assembly of the invention is a container into which the partially purified cracked gas flows. The container 201 (i.e. the first container) has one or more walls 202 and is gas tight with the exception of the one or more partially purified cracked gas inlets 203 which allow the flow of partially purified cracked gas into an internal volume of the container, and the one or more purified cracked gas outlets 204 which allow the flow of purified cracked gas out of the internal volume of the container. The container contains a single mass of adsorbent comprising silica gel 205 which is disposed in the internal volume of the container such that the partially purified cracked gas flows through the single mass of adsorbent comprising silica gel in close proximity therewith. The silica gel in this single mass of adsorbent readily absorbs any ammonia in the partially purified cracked gas, thus removing the ammonia and purifying the gas to produce the purified cracked gas which is mostly hydrogen gas. This removal of ammonia gas produces a purified hydrogen gas mixture which exits the first container for downstream use or storage.

[0057] The shape of the (first) container does not matter provided it is gas tight except for the one or more partially purified cracked gas inlet(s) and one or more purified cracked gas outlet(s) and can hold the single mass of adsorbent comprising silica gel in an appropriate manner to cause the gas to flow through the single mass of adsorbent comprising silica gel. In the shown embodiments, the container is shown as a cylinder, but this is an arbitrary shape for the purposes of illustration. The filter assembly may have two or more (i.e. multiple) partially purified cracked gas inlets 303 and / or two or more (i.e. multiple) purified cracked gas outlets 304 as shown in Figure 3, which has the advantage of spreading the gas flow throughout the width of the single mass of adsorbent comprising silica gel and providing a fail-safe in case of blocking of one of the inlets and / or outlets.

[0058] The one or more filter assemblies each contain a single mass of adsorbent comprising silica gel. This means that there is only a single adsorbent mass within each of the one or more filter assemblies. In some embodiments, the single mass of adsorbent comprising silica gel may distributed throughout the container either as a single layer, or as multiple separate layers. In some embodiments, the single mass of adsorbent may reside in the container as a single portion, or there may be a plurality of separate portions of said adsorbent distributed through the container. In some embodiments, the phrase ‘single mass of adsorbent’ may be understood to mean a homogenous mass of adsorbent material which comprises silica gel. In some embodiments, there are not multiple differing adsorbent masses in the device i.e. the constituents making up the single mass of adsorbent are the same and are in the same proportion. In other words, this may be thought of as a single type of adsorbent or a single mixture of adsorbent. This single mass of adsorbent comprises silica gel. This single mass of adsorbent only adsorbs ammonia, which is adsorbed into the silica gel. In contrast, PSA devices used for the purpose of the present invention have at least two distinct masses of adsorbent therein, typically a first mass comprising a zeolitic adsorbent to adsorb nitrogen and a second mass comprising a non-zeolitic adsorbent to adsorb ammonia. Suitable adsorbents would be known to those skilled in the art. For example, the zeolitic adsorbant may be 5A zeolite or 13X zeolite, and the non-zeolitic adsorbant may be activated carbon.

[0059] In the one or more filter assemblies of the present invention, the filter assemblies act to adsorb any leftover ammonia only, which produces highly pure product gas suitable for use with, for example, fuel cells. Such filter assemblies are simpler than e.g. a PSA, because there are none of the valves and inlets or outlets required by a PSA for the pressure swing step of their operation. The filter assemblies as described herein are not PSAs and have advantages by virtue of their simplicity over such gas separators. Applicants envision that the one or more filter assemblies of the present invention can simply be used until the single mass of adsorbent is near saturated with ammonia before being replaced, with the spent (i.e. near-fully saturated) filter assemblies being sent for reprocessing. The advantage is that each filter assembly can be quickly swapped, minimizing downtime for the device for producing hydrogen. This contrasts with a PSA, where it must be shut down and go through a purge cycle to clear the impurities from the two adsorbent layers, with said impurities requiring further system architecture to remove and dispose of. In addition, PSAs are not typically releasably secured in the sense that they can be swapped quickly, in contrast to the one or more filter assemblies of the present device. The single mass of adsorbent comprises silica gel, which readily adsorbs ammonia gas. The single mass of adsorbent may comprise 30%, 40%, 50%, 60%, 70%, 80%, 90%, or more silica gel by mass. The single mass of adsorbent may consist essentially of silica gel or may consist of silica gel. As such, it may be described as an adsorbent mass consisting essentially of or consisting of silica gel. What the remaining percent by mass of the single mass of adsorbent comprises is immaterial provided it does not interfere with the function of the silica gel. Each filter assembly has a single mass of adsorbent only. In other words, there is only a mass of adsorbent comprising silica gel and no other adsorbent masses.

[0060] The one or more walls of the first container can be made from any suitable material. In some embodiments, the one or more walls are made of or comprise a metal. Example metals for this use are stainless steel, high carbon steel, aluminium, or titanium. In one embodiment, the one or more walls are made of or comprise stainless steel. A metal construction has the advantage that it can withstand high pressures. This is particularly useful for applications where the partially purified cracked gas enters the container and exerts a high pressure on the container. For example, metal is preferred when the pressure is greater than 1 barg. The one or more walls of the container are preferably made of materials which do not readily absorb ammonia. Ammonia may react with some metals and embrittle them or otherwise alter their physical properties. For example, high carbon steel is susceptible to ammonia, absorption of which degrades the metal. As such, in some embodiments, at least the inner face of the one or more walls of the container are coated with a resistive coating. The inner face is the face of the one or more walls of the vessel facing the silica gel disposed within the internal volume of the container. The resistive coating allows a range of materials to be used to construct the container, whilst conferring resistance to the effects of ammonia gas to the material of construction. In some embodiments, the coating may be a polymer coating. For example, the coating may be a fluorinated polymer, such as polytetrafluoroethylene (PTFE) or perfluoroalkoxy alkanes (PFA).

[0061] In some embodiments, the one or more walls are made of or comprise a plastic. In some embodiments, the plastic is a clear plastic and / or an opaque plastic. In some embodiments, the plastic is a fluorinated plastic or a polycarbonate. Such construction may be preferable for filter assemblies according to the invention which are not subjected to high internal pressures. Such pressures may be less than 10 barg. In some embodiments, the fluorinated plastic is polytetrafluoroethylene (PTFE) or perfluoroalkoxy alkanes (PFA). These plastics are particularly tolerant to ammonia adsorption.

[0062] In a further embodiment of the invention, the filter assembly may comprise a sight glass for viewing the silica gel. The sight glass may be disposed within the one or more walls of the container such that the single mass of adsorbent comprising silica gel can be observed from the outside as shown in Figure 4. Here, the sight glass 406 is disposed proximal to the one or more purified cracked gas outlets 404, such that the single mass of adsorbent 405 comprising silica gel can be seen from the outside. In some embodiments, the sight glass is proximal to at least one of the one or more purified cracked gas outlets. In addition or in the alternative, the sight glass is proximal to at least one of the one or more partially purified cracked gas inlets 403. For example, it may extend from one end of the container to the other such that it is proximal to the one or more partially purified cracked gas inlets and the one or more purified cracked gas outlets. In Figure 5, an embodiment is shown wherein the sight glass 506 extends such that it is proximal to both the one or more partially purified cracked gas inlets 503 and the one or more purified cracked gas outlets 504 and allows the user to see the single mass of adsorbent 505 silica gel . The sight glass can be made of any suitable material, for example a clear or translucent plastic or a glass. Soda lime glass is a suitable glass for this application, though other suitable glasses will be known to the skilled person such as quartz, sapphire, and borosilicate glass. The clear or translucent plastic could be, for example, PTFE or PFA. The sight glass must not affect the gas tightness of the container. In addition, it must withstand the pressures which the container is subjected to.

[0063] Additionally or alternatively, the invention may include an ancillary container having a sight glass for viewing the internal volume thereof, said ancillary container containing a second mass of silica gel, disposed downstream of and in fluid communication with the first container. Downstream is in reference to the flow of gas through the device in use. As such, the ancillary container is disposed near the end of the first container proximal to the one or more purified cracked gas outlets. The gas can flow from the first container into the ancillary container. The sight glass is disposed in one or more walls of the ancillary container. An exemplary embodiment is shown in Figure 6, with the ancillary container 607 in fluid communication with the first container 602 via the one or more purified cracked gas outlets 604. The ancillary container contains a second mass of adsorbent comprising silica gel 608, and the sight glass 606 is disposed in the one or more walls thereof and allows the second mass of adsorbent 608 comprising silica gel to be viewed from the outside.

[0064] In an embodiment, the filter assembly further comprises a flow structure for lengthening the path of travel of the partially purified cracked gas through the single mass of adsorbent comprising silica gel. Each partially purified cracked gas inlet may be connected to one or more flow structures as required. The flow structure comprises, for example, one or more permeable tubes connected to said inlet(s), which direct the gas along a predetermined path, but allow it to flow out of the tube and into contact with the single mass of adsorbent comprising silica gel. An example embodiment is shown in Figure 7, wherein a perforated tube 709 is shown connected to the one or more purified cracked gas inlet(s) 703 and disposed within the single mass of adsorbent 705 comprising silica gel . Such a tube could be shaped to extend the gas flow path throughout the internal volume of the first container of the filter assembly. For example, it could be coiled substantially perpendicularly to the length of the container. In addition or alternatively, the flow structure comprises one or more baffles which extend from the inner wall(s) of the container and physically direct the flow of gas along a longer path. An example embodiment of this is shown in Figure 8, where multiple baffles 810 extend from the inner wall of the first container 802 into the internal volume thereof and thus force the partially purified cracked gas to travel a longer path through the single mass of adsorbent 805 comprising silica gel . The baffles may be made of the same material as the first container or may be made of a different material to the first container. The material may be ammonia resistant. For example, they could be made of a metal (e.g. stainless steel, high carbon steel, aluminium, or titanium) or a plastic (e.g. PTFE or PFA). The baffles could each be made of a different material or the same material as each other. The one or more baffles could comprise at least one baffle made of each of the above materials, in any combination. The baffles are attached to the inner face of the one or more walls of the container by any means known to the skilled person. For example they could be attached by mechanical fasteners (e.g. bolts, rivets, and the like), welded thereto, brazed thereto, or indeed they could form part of the inner wall such that it is a one-piece construction (e.g. if the container is made by casting), or any combination of these techniques.

[0065] In an embodiment, the flow structure may comprise one or more inserts disposed in the container. These may rest on the single mass of adsorbent comprising silica gel and provide a physical barrier to prevent gas flow, thus forcing the gas to flow around a longer path. They are essentially the baffles above, but they do not extend from the inner side of the one or more walls. The inserts may be made of the same material as the first container or may be made of a different material to the first container. The material may be ammonia resistant. For example, they could be made of a metal (e.g. stainless steel, high carbon steel, aluminium, or titanium) or a plastic (e.g. PTFE or PFA). The inserts could each be made of a different material or the same material as each other. The one or more inserts could comprise at least one baffle made of each of the above materials, in any combination. The shape and dimensions of the inserts are immaterial provided they are gas impermeable.

[0066] In an embodiment, the flow structure may comprise a substructure formed of a substrate which is filled at least partially with the single mass of adsorbent comprising silica gel, the substructure being in fluid communication with the one or more partially purified cracked gas inlets and the one or more purified cracked gas outlets. For example, it may be a series of plastic or metal internal walls which essentially form a long tube which snakes (coils or winds) through the substantially all of the inner volume of the first container thus forcing the gas to flow through almost all of the inner volume of the first container. The substructure may be made of the same material as the first container or may be made of a different material to the first container. The material may be ammonia resistant. For example, it could be made of a metal (e.g. stainless steel, high carbon steel, aluminium, or titanium) or a plastic (e.g. PTFE or PFA). The substructure could be made of a composite of these materials.

[0067] The skilled person will appreciate that any of the abovementioned flow structures may be combined with any other, or indeed all of the listed embodiments without limitation. For example, the flow structure could comprise:

[0068] - one or more baffles and one or more inserts,

[0069] - one or more baffles and one or more permeable tubes,

[0070] - one or more baffles and a substructure,

[0071] - one or more baffles, one or more inserts, and one or more permeable tubes,

[0072] - one or more baffles, one or more inserts, and a substructure;

[0073] - one or more baffles, one or more permeable tubes, and a substructure,

[0074] - one or more baffles, one or more permeable tubes, one or more inserts, and a substructure.

[0075] The first container contains a single mass of adsorbent comprising silica gel. As discussed earlier, the single mass of adsorbent may be a homogenous mass of adsorbent comprising silica gel. Whilst the single mass of adsorbent may comprise other constituents, at least 30% of said mass is silica gel, in some embodiments. Silica gel is a well-known entity often used for water adsorption in various applications. Silica gel readily adsorbs ammonia, and applicants have found that surprisingly small amounts of silica gel can purify a partially purified cracked gas stream to remove ammonia therefrom. It is particularly useful where the raw cracked gas has already been (at least partially) purified (for example in a gas separator), but very high levels of purity are required for the downstream use of the hydrogen gas. Preferably, the internal volume of the first container is at least partially filled with the single mass of adsorbent comprising silica gel. In some embodiments, the silica gel may be in the form of silica gel beads, silica gel powder, and / or silica gel granules, or a combination thereof. Silica beads of a uniform size are particularly preferred as a uniform bead size reduces gas flow channeling and reduces pressure drop. Suitable beads can be any size, though they are typically in the range of 3 to 5 mm in diameter. The silica gel in the filter assembly adsorbs ammonia and once fully saturated can be at least partially regenerated, meaning it can be reused.

[0076] In some embodiments, an indicator is mixed / embedded with the (mass of) silica gel such that it is adsorbed into, disposed on or proximal to it. The indicator may be an ammoniation indicator, a hydration indicator, a pH indicator, or any combination thereof. Moisture indicators which are typical to silica gel products can serve this purpose due to similarity of function of indicator, Several suitable indicators are known in the art and are suitable for this purpose. For example, the silica gel may be mixed with cobalt(ll) chloride, and non-toxic organic (e.g. methyl violet) and iron salts. These indicators change colour when the chemical additive undergoes a chemical change or a change in pH. In practice, this means that you can observe when the silica gel beads are becoming saturated with ammonia, giving a visual indication that the silica gel is nearly spent and requires replacement and regeneration. Using the sight glass and / or when the one or more walls comprise a clear plastic, the change of colour of the indicator can be readily assessed by the skilled person to provide advanced warning that a filter assembly may need to be changed to prevent ammonia leakage into the purified cracked gas.

[0077] The one or more filter assemblies are readily swappable in the device of the present invention and may be thought of as cartridges. In some embodiments, each of the one or more filter assemblies are releasably secured to the device in fluid communication with the common partially purified cracked gas flow conduit and the common purified cracked gas flow conduit. Any suitable fixtures could be used to achieve this releasable securing of each filter assembly as would be known to the skilled person. In some embodiments, each filter assembly is fluidly connected to the device via valves. Said valves are one or more partially purified cracked gas inlet valves and one or more purified cracked gas outlet valves. These valves allow isolation of each filter assembly such that once the single mass of adsorbent therein is nearly saturated with ammonia, the gas flow may be ceased to allow depressurization and removal of each filter assembly. This is advantageous over systems such as a pressure swing adsorption (PSA) device as the overall downtime is reduced by the simplicity of replacement of each filter assembly. In embodiments where the one or more filter assemblies comprises a plurality of filter assemblies, one filter assembly can be isolated and removed whilst operation of the device continues using the other filter assemblies of the plurality of filter assemblies to purify the partially purified cracked gas arriving from the one or more gas separators. This is a technical advantage over the prior art systems using PSA devices which are generally not releasably secured to the device and instead require more complex system architecture to enable the ‘pressure swing’ in the PSA to release impurities from the adsorbents and then allowing a purge of said impurities to a waste gas stream. In addition, PSA devices are not generally releasably secured. Instead, the adsorbents therein are removed and replaced whilst the PSA device is isolated from the rest of the device for producing hydrogen. Replacing the actual PSA device is a much more complex procedure than the filter assemblies of the present invention. As such, further purifying a partially purified cracked gas by having a filter assembly as in the device of the present invention is advantageous compared to, for example, having two PSA devices connected in series.

[0078] In some embodiments, the filter assembly further comprises an ammonia gas sensor. This allows very small concentrations of ammonia to be detected in gas flowing to or from the filter assembly. Typically, the sensor is downstream from and in fluid communication with the one or more purified cracked gas outlets. This means that the sensor is positioned in order to detect ammonia in the purified cracked gas flowing from the filter assembly and can detect if ammonia begins to exit the internal volume of the first container. This allows the filter to be replaced before significant amounts of ammonia gas leak downstream, thus avoiding damage to any downstream devices. Different sensors are available, for example a tuned infrared sensor for ammonia or an Optical Feedback Cavity Enhanced Absorption Spectroscopy sensor (also referred to as an Optical Feedback Cavity Enhanced Absorption Spectroscopy instrument), which is a standard sensor known to the skilled person for the measurement of ammonia in parts per billion. In some embodiments, a pair of sensors can be used, one upstream of the first container and one downstream of the first container. Such sensors can measure ammonia concentrations at both sides and / or calculate a differential thereof. In some embodiments, a single sensor is disposed downstream from and in fluid communication with the one or more purified cracked gas outlets. For example, it could be connected to the one or more purified cracked gas outlets via a conduit including a regulator to reduce the pressure of the sampled gas to a suitable pressure for the sensor. In some embodiments, an alarm is configured to trigger when a set concentration of ammonia is detected. Figure 10 shows a gas separator 1016 in fluid communication with a filter assembly 1001 via a common partially purified cracked gas flow conduit 1012b, the filter assembly being in fluid communication with a common purified cracked gas flow conduit 1013, with an ammonia gas sensor 1018 being in fluid communication with said common purified cracked gas flow conduit 1013 via a regulator 1017. As indicated by the arrows, raw cracked gas enters the gas separator 1016 and nitrogen gas and hydrogen gas are at least partially removed to produce a partially purified cracked gas containing hydrogen gas, nitrogen gas, and ammonia gas. The partially purified cracked gas exits the gas separator 1016 and flows to the filter assembly 1001 via the common partially purified cracked gas flow conduit 1012b. The single mass of adsorbent comprising silica gel in the filter assembly 1001 essentially removes any residual ammonia gas to produce a purified cracked gas, and then a purified cracked gas exits the filter assembly 1001 and flows to a purified cracked gas flow conduit 1013 and a portion of the purified cracked gas flows into an ammonia gas sensor 1018 via a regulator 1017. The ammonia gas sensor 1018 will detect and signal if ammonia is present in the purified cracked gas above a threshold value determined and set by the skilled person. As shown, the majority of purified cracked gas will flow past the regulator 1017 and onward to downstream systems or storage. In some embodiments, the one or more filter assemblies may be a plurality of filter assemblies. An exemplary device is shown in Figure 9. Each of the plurality of filter assemblies downstream of the cracker and the one or more gas separators 916 may be connected to the common partially purified cracked gas flow conduit 912b via a first valve 914. This valve can shut off the flow of the partially purified cracked gas from the common partially purified cracked gas flow conduit 912b into the internal volume of the first container via the one or more partially purified cracked gas inlets. This means that in a device for producing hydrogen gas, the flow can be redirected from one filter assembly to a different downstream assembly, for example a second filter assembly. Each filter assembly may thus be isolated from the common partially purified cracked gas flow conduit 912b without affecting operation of the device.

[0079] In some embodiments, the one or more filter assemblies are each in fluid communication with a common purified cracked gas flow conduit 913 via the one or more purified cracked gas outlets, each filter assembly having a second valve 915 between the one or more purified cracked gas outlets and the common purified cracked gas flow conduit 913. This means that in a device for producing hydrogen gas, the flow can be prevented from leaving the filter assembly. For example, where a leak is detected in the common purified cracked gas flow conduit proximal to the one or more purified cracked gas outlets. This means that each filter assembly may thus be isolated from the common purified cracked gas flow conduit 913 without affecting operation of the device.

[0080] In some embodiments, the hydrogen production device comprises one or more filter assemblies having the first valve and the second valve as described above. By shutting off both valves for any given filter assembly, the filter assembly can be isolated entirely from the rest of the device, which allows such a filter assembly to be replaced safely in situ as described above.

[0081] In a further embodiment, the common raw cracked gas flow conduit comprises a gas separator for separating the raw cracked gas into its constituent gases of hydrogen, nitrogen, and ammonia. Such a gas separator is disposed in between and in fluid communication with the ammonia cracker and the one or more filter assemblies. In some embodiments, the gas separator is a pressure swing adsorption device as previously described and / or may comprise a palladium filter and / or a catalytic conversion reactor and / or a temperature swing adsorption device and / or a hollow fibre membrane filter. Such gas separators are known in the art. See, for example, US6340382B1 , GB969673A, US4293419A; and Kheimi & Salamah 2023 (incorporated by reference herein). The one or more gas separators are used to remove the nitrogen and the majority of the ammonia from the raw cracked gas before it passes into the one or more filter assemblies for the removal of the remaining ammonia. Having the gas separator between the cracker and the one or more filter assemblies allows for the removal of the majority of nitrogen and ammonia from the gas mixture which exits the ammonia cracker, and thus extends the life of the single mass of adsorbent comprising silica gel in each filter assembly as the majority of ammonia is removed before the partially purified cracked gas stream enters the one or more filter assemblies. Such a gas separator may be disposed in a conduit separate to the ammonia cracker, it may be integral to the ammonia cracker, or it may be integral to the one or more filter assemblies. In any case, the raw cracked gas must flow through the gas separator upon exiting the ammonia cracker and prior to entering the one or more filter assemblies. In some embodiments the gas separator may be chosen from the group consisting of: a metal hydride-based purification device, a low temperature distillation device with a fractionation column device, or any combination thereof.

[0082] The one or more gas separators may comprise a PSA having a first pressure swing adsorbent for the adsorption of nitrogen gas, a second pressure swing adsorbent for the adsorption of ammonia, and a third pressure swing adsorbent for the adsorption of water. In a typical PSA system, the raw cracked gas would flow first through the third pressure swing adsorbent to remove water, then the second pressure swing adsorbent to remove ammonia, and then the first pressure swing adsorbent to remove nitrogen. As such, the adsorbent masses in the pressure swing adsorption device may be layered from bottom to top as the third pressure swing adsorbent, the second pressure swing adsorbent, and the first pressure swing adsorbent, and the device is arranged such the raw cracked gas enters the bottom of the device and flows through the third pressure swing adsorbent, the second pressure swing adsorbent, and the first pressure swing adsorbent in that order, producing a partially purified cracked gas, which flows out of an outlet at the top of the device. The pressure swing adsorption device may comprise any number of vessels, provided the device is configured such that it comprises at least the first pressure swing adsorbent and the second pressure swing adsorbent, and the feed gas (the raw cracked gas) flows through both. Where there are multiple vessels, each vessel may comprise the first pressure swing adsorbent, the second pressure swing adsorbent, and optionally the third pressure swing adsorbent as described above.

[0083] In some embodiments, the one or more gas separators may comprise a palladium filter. In a further embodiment, the palladium filter in fluid communication with a heat exchanger disposed between the palladium filter and the one or more filter assemblies, the heat exchanger being in fluid communication with the one or more filter assemblies. Such a device acts to cool the partially purified cracked gas leaving the palladium filter prior to entering the one or more filter assemblies.

[0084] In some embodiments, there are a plurality of filter assemblies according to the first aspect in fluid communication with the one or more gas separators via the common partially purified cracked gas flow conduit. These can be connected in parallel, in series, or both. The advantage of having multiple filter assemblies is that there is redundancy in the system in case of a fault. In addition, when connected in parallel, once the mass of adsorbent comprising silica gel in any one filter assembly is spent or nearly spent, it can be isolated using valves as described above and replaced. Once isolated, the gas will flow through a different filter assembly in the plurality whilst the isolated assembly is replaced. This allows for continuous safe operation of the device without any shut down required and the associated loss of productivity by the device. The advantage of having multiple filter assemblies fluidly connected in series is that should the first filter assembly fail, any ammonia will be readily adsorbed by the second preventing any effect on downstream assemblies of the device. This has advantages over PSAs as described above. A further aspect of the invention provides a system for generating electrical power using ammonia comprising the device of the prior aspect and a hydrogen fuel cell, wherein the hydrogen fuel cell is in fluid communication with the hydrogen production system via the common purified cracked gas flow conduit. In this system, the ammonia cracker produces hydrogen gas which is purified by the gas separator and the one or more filter assemblies, and from the one or more filter assemblies, purified hydrogen gas flows to the hydrogen fuel cell where it is readily converted to electrical power. The advantage of such a system is that there is no need for hydrogen storage. Instead, the energy can be transported as ammonia, and converted on-site. Ammonia is easier and safer to transport than hydrogen gas, and so this modality allows power to be supplied remotely without the costly infrastructure required for hydrogen gas transport and storage. Figure 11 shows an exemplary system comprising an ammonia cracker 1111 in fluid communication with a gas separator 1116 via a common raw cracked gas flow conduit 1112a, the gas separator 1116 is in fluid communication with a filter assembly 1101 via a partially purified cracked gas flow conduit 1112b, a hydrogen fuel cell 1119 is in fluid communication with the filter assembly 1101 via a common purified cracked gas flow conduit 1113. As indicated by arrows, ammonia gas flows into a heated chamber of the ammonia cracker 1111 where it contacts an ammonia decomposition catalyst and is decomposed into a raw cracked gas comprising nitrogen gas and hydrogen gas, the raw cracked gas containing residual ammonia gas which did not react. The raw cracked gas flows out of the ammonia cracker 111 1 via the common raw cracked gas flow conduit 1112a to a gas separator 1116 which removes the majority of the nitrogen gas and ammonia gas to produce a partially purified cracked gas comprising nitrogen gas, hydrogen gas, and ammonia gas. The partially purified cracked gas exits the gas separator 1116 and is conveyed to a filter assembly 1101 via the common partially purified cracked gas flow conduit 1112b, where the single mass of adsorbent comprising silica gel essentially removes any remaining ammonia in the partially purified cracked gas to produce a purified cracked gas. The purified cracked gas then flows to the hydrogen fuel cell 1119 via the common purified cracked gas flow conduit 1113. The hydrogen gas in the purified cracked gas is used to generate electricity by the fuel cell. Suitable hydrogen fuel cells are well-known in the art. See, for example, GB2508649A (incorporated by reference herein). In some embodiments, nitrogen may remain in the purified cracked gas, but this is immaterial as it will not have negative effects on the fuel cell device.

[0085] A further aspect of the invention provides a process for producing a purified cracked gas of high purity hydrogen comprising: providing ammonia gas to an ammonia cracker in fluid communication with a common raw cracked gas flow conduit to produce a raw cracked gas comprising hydrogen gas, nitrogen gas, and ammonia gas; a first purification stage comprising conveying the raw cracked gas via the common raw cracked gas flow conduit to one or more gas separators, wherein the one or more gas separators at least partially remove the ammonia gas and nitrogen gas from the raw cracked gas to produce a partially purified cracked gas; and a second purification stage comprising conveying the partially purified cracked gas via a common partially purified cracked gas flow conduit to one or more filter assemblies, each having a first container having one or more walls, one or more partially purified cracked gas inlets and one or more purified cracked gas outlets, the one or more partially purified cracked gas inlets being in fluid communication with the common partially purified cracked gas flow conduit, the first container containing a single mass of adsorbent comprising silica gel, wherein the one or more partially purified cracked gas inlets and one or more purified cracked gas outlets are arranged such that the partially purified cracked gas flows through the single mass of adsorbent to produce a purified cracked gas, wherein the single mass of adsorbent selectively adsorbs the ammonia in the partially purified cracked gas; wherein the partially purified cracked gas is conveyed through the one or more filter assemblies at a process pressure, wherein the process pressure is substantially constant.

[0086] In this aspect the ammonia cracker uses an ammonia decomposition catalyst in order to decompose ammonia into a raw cracked gas comprising nitrogen and hydrogen gas. This is an equilibrium reaction, so some ammonia gas will remain in the raw cracked gas also. Such ammonia crackers are well known in the art (see, e.g. US20030232224A1 (incorporated by reference herein)). The raw cracked gas travels at pressure out of the reaction chamber of the ammonia cracker into a common raw cracked gas flow conduit and is directed to one or more gas separators in fluid communication with the ammonia cracker via the common raw cracked gas flow conduit. The one or more gas separators remove at least a portion of the nitrogen gas and / or at least a portion of the ammonia gas to produce a partially purified cracked gas. The partially purified cracked gas travels at pressure out of the one or more gas separators into a common partially purified cracked gas flow conduit and is directed to one or more filter assemblies having the features described in the first aspect. The single mass of adsorbent comprising silica gel selectively adsorbs the ammonia gas in the partially purified cracked gas to produce a purified cracked gas, which then flows out of the one or more assemblies and downstream for further use or storage. The term ‘selectively’ means that whilst a negligible proportion of nitrogen gas and hydrogen gas may be adsorbed by the single mass of adsorbent, the majority of gas adsorbed by the single mass of adsorbent will be ammonia gas.

[0087] The partially purified cracked gas flows through each of the one or more filter assemblies at a process pressure. This is the pressure of the partially purified cracked gas entering the one or more filter assemblies whilst the device is in operation, when raw cracked gas and partially purified cracked gas are actively being produced by the ammonia cracker and the one or more gas separators, respectively. During operation of the device, the process pressure is constant. This means that it does not vary substantially. This contrasts with systems using e.g. PSA devices, which require a pressure swing to release adsorbed impurities for removal and disposal. In some embodiments, the process pressure is 35 bar or less. In some embodiments, the process pressure may be 30 bar or less, 25 bar or less, 20 bar or less, 15 bar or less, 10 bar or less, 5 bar or less, 4 bar or less, 3 bar or less, 2 bar or less, or 1 bar or less. In some embodiments bar is barg. In some embodiments, the process pressure is greater than atmospheric pressure and less than 35 bar.

[0088] In some embodiments, at least one of the one or more gas separators is a pressure swing adsorption device comprising a first pressure swing adsorbent and a second pressure swing adsorbent, wherein the pressure swing adsorption device operates at a pressure equal to the process pressure and adsorbs nitrogen from the raw cracked gas into the first pressure swing adsorbent and adsorbs ammonia from the raw cracked gas into the second pressure swing adsorbent, wherein the pressure changes (e.g. decreases) to release said nitrogen and ammonia as a waste gas which is conveyed out of the pressure swing adsorption device via a waste gas outlet in fluid communication with a common waste gas flow conduit. The pressure swing adsorption device operates at the same pressure as the one or more filter assemblies, but when being purged it undergoes its characteristic pressure swing (i.e. a change in pressure) to release the impurities for removal. The first pressure swing adsorbent may be a non-zeolitic adsorbent for adsorbing ammonia and the second pressure swing adsorbent may be a zeolitic adsorbent for adsorbing nitrogen. The PSA device may include further pressure swing adsorbents. For example, in some embodiments the pressure swing adsorbent comprises a third pressure swing adsorbent which adsorbs water. Suitable adsorbents are known. For example, alumina may be used for water removal. In terms of arrangement of the two or three pressure swing adsorbents, the device is configured such that the raw cracked gas first flows through the third pressure swing adsorbent (if present), followed by the second pressure swing adsorbent and then the first pressure swing adsorbent. In typical devices, the raw cracked gas flows into the bottom of the device via an inlet, flows through each layer as described above to produce a partially purified cracked gas, which then flows out of an outlet to further downstream systems as described herein. The adsorbents may be layered, or may be separate masses in the same vessel, or in separate vessels. When the device is considered as a whole, there is always more than a single mass of adsorbent, typically two or three as described above.

[0089] In some embodiments, at least one of the one or more gas separators is a pressure swing adsorption device, wherein the pressure swing adsorption device comprises a plurality of vessels, each vessel comprising (or containing) a first pressure swing adsorbent for adsorbing nitrogen gas from the raw cracked gas and a second pressure swing adsorbent for adsorbing ammonia gas from the raw cracked gas, optionally comprising (or containing) a third pressure swing adsorbent for adsorbing water, wherein the plurality of vessels comprises a first pair of vessels comprising a first vessel and a second vessel, wherein the process comprises the sequence of an adsorption step, a first equalisation step, a blowdown step, a purge step, a second equalisation step, and a backfill step, as follows.

[0090] The adsorption step comprises fluidly connecting the first vessel of the first pair of vessels to the common raw cracked gas flow conduit and the partially purified cracked gas flow conduit and conveying the raw cracked gas to the first vessel at the process pressure, wherein the ammonia gas and nitrogen gas (and optionally water) in the raw cracked gas are at least partially removed to produce the partially purified cracked gas; and conveying the partially purified cracked gas from the first vessel to the common partially purified cracked gas flow conduit at the process pressure.

[0091] The first equalization step comprises fluidly isolating the first vessel from the common partially purified cracked gas flow conduit and the common raw cracked gas flow conduit; fluidly connecting the first vessel to the second vessel of the plurality of vessels, the second vessel being at atmospheric pressure, such that the first vessel undergoes a decrease in pressure and the second vessel undergoes an increase in pressure such that the first vessel and the second vessel are at half of the process pressure.

[0092] The blowdown step comprises fluidly isolating the first vessel from the second vessel and fluidly connecting the first vessel to a common waste gas flow conduit and conveying a waste gas containing (or comprising) nitrogen gas and ammonia gas from the first vessel to the common waste gas flow conduit, wherein the first vessel undergoes a further depressurisation such that the first vessel is at atmospheric pressure.

[0093] The purge step comprises fluidly connecting the first vessel to a common purge gas flow conduit and conveying a purge gas at atmospheric pressure to remove any remaining waste gas from the first vessel via the common waste gas flow conduit; and fluidly isolating the first vessel from the common waste gas flow conduit and the common purge gas flow conduit. The purge gas may be, for example, hydrogen gas. This may be sourced from the device of the present invention itself, or from another source.

[0094] The second equalization step comprises fluidly connecting the first vessel to the second vessel, the second vessel being at the process pressure, such that the first vessel undergoes an increase in pressure and the second vessel undergoes a decrease in pressure such that the first vessel and the second vessel are at half of the process pressure.

[0095] The backfill step comprises fluidly isolating the first vessel from the second vessel and fluidly connecting the first vessel to a common backfill gas flow conduit and conveying a backfill gas such that the first vessel undergoes an increase in pressure such that the first vessel is at the process pressure and fluidly isolating the first vessel from the common backfill gas flow conduit. The backfill gas may be, for example, hydrogen gas. It may be obtained from the device of the invention or from another source.

[0096] The first vessel is then fluidly connected to the common raw cracked gas flow conduit and the common partially purified cracked gas flow conduit for the adsorption step in a new PSA cycle as per the above sequence.

[0097] During these steps, the partially purified cracked gas is conveyed through the one or more filter assemblies at the process pressure. This demonstrates that whilst the pressure swing adsorption device undergoes its characteristic pressure swings, there is no such swing in the one or more filter assemblies of the present process. Instead, they operate at a pressure which is substantially constant.

[0098] In some embodiments, the plurality of vessels in the pressure swing adsorption device may comprise the first pair of vessels and a second pair of vessels, the first pair of vessels comprising the first vessel and second vessel as described above, and the second pair of vessels comprising a third vessel and a fourth vessel. The third vessel undergoes the same sequence as described for the first vessel above, and the fourth vessel acts as described above for the second vessel. Each pair of vessels operates according to the sequence described above but their operation is offset. Operating this way allows for a consistent conveyance of partially purified cracked gas to the one or more filter assemblies via the common partially purified cracked gas flow conduit. Each of the vessels undergoes the sequence in the same order but offset such that they carry out their function as described above.

[0099] When the first vessel is undergoing the adsorption step, the second vessel is undergoing a purge step. Next, the first and second vessel undergo the equalization step. Next, whilst the first vessel undergoes a blowdown step, the second vessel undergoes a backfill step. Next, the first vessel undergoes a purge step whilst the second vessel undergoes an adsorption step. Then each vessel undergoes the second equalisation step. Finally, the first vessel undergoes the backfill step whilst the second vessel undergoes the blowdown step. This cycle repeats during the process of the invention.

[0100] Where the process includes second pair of vessels comprising a third vessel and a fourth vessel, these act in counterpart in the same way as described for the first vessel and the second vessel above. However, as mentioned their cycle is offset. For example, when the first vessel is at the first adsorption stage, the third vessel is undergoing a first equalisation step as described above with the fourth vessel, followed by a backfill step whilst the fourth vessel undergoes its blowdown step. When the first vessel undergoes the first equalization step and blowdown step, the third vessel undergoes its adsorption step whilst the fourth vessel undergoes its purge step. When the first vessel undergoes its purge step, the third vessel undergoes a second equalisation step as described above with the fourth vessel, followed by a blowdown step with the fourth vessel undergoing its backfill step.

[0101] When the first vessel undergoes its second equalisation step and its backfill step, the third vessel undergoes its purge step and the fourth vessel undergoes its adsorption step. As is clear, the third and fourth vessels operate as the first and second vessels do relative to each other. Each pair can be thought of as two counterpart vessels, each having a first vessel and a second vessel undergoing the sequence as described above, the third vessel undergoing the sequence as described for the first vessel, and the fourth vessel undergoing the sequence as described for the second vessel.

[0102] In some embodiments, the common backfill gas flow conduit is used to fluidly connect the first vessel and the second vessel during the first equalisation step and the second equalisation step. Alternatively, there can be a separate conduit independent from the common backfill gas flow conduit connecting the first vessel and the second vessel. Where there is a first pair of vessels and a second pair of vessels, the common backfill gas flow conduit may be used to fluidly connect the first vessel and the second vessel, as well as being used to fluidly connect the third vessel and the fourth vessel. In some embodiments, the partially purified cracked gas is conveyed from multiple gas separators to the one or more filter assemblies. In other words, the one or more gas separators comprises a plurality of gas separators, each conveying partially purified cracked gas to the one or more filter assemblies. These can be any of the gas separators discussed in the first aspect of the invention, in any combination or number. For example in some embodiments, the process comprises at least two of the one or more gas separators being pressure swing adsorption devices, wherein a first pressure swing adsorption device is fluidly disconnected from the common raw cracked gas flow conduit and the partially purified cracked gas flow conduit, and a second pressure swing adsorption device is in fluid communication with the raw cracked gas flow conduit and the partially purified cracked gas flow conduit. This would be the case where one of the pressure swing adsorption devices was undergoing a maintenance cycle whilst the other continued normal operation to supply the one or more filter assemblies with partially purified cracked gas at the process pressure. This process allows for continuous operation of the device for producing high purity hydrogen gas. In some embodiments, the process comprises the step of conveying the raw cracked gas via the common raw cracked gas flow conduit to one or more gas separators, the gas separators comprising a first pressure swing adsorption device and a second pressure swing adsorption device, wherein during operation the first pressure swing adsorption device is fluidly disconnected from the common raw cracked gas flow conduit and the common partially purified cracked gas flow conduit, wherein during operation the second pressure swing adsorption device remains in fluid communication with the common raw cracked gas flow conduit and the common partially purified cracked gas flow conduit. In other words, when the first pressure swing adsorption device is disconnected from the device, the second pressure swing adsorption device remains connected and continues to operate at the process pressure. As discussed, each PSA device may include further pressure swing adsorbents, for example a third pressure swing adsorbent for the removal of water e.g. alumina.

[0103] In some embodiments, the single mass of adsorbent comprises at least 30% by mass of silica gel, optionally wherein the adsorbent consists substantially of silica gel. As such, the single mass of adsorbent could comprise at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, or at least 90% by mass of silica gel. It may consist essentially of silica gel or consist of silica gel. What the remaining percent by mass of the single mass of adsorbent comprises is immaterial provided it does not interfere with the function of the silica gel.

[0104] In some embodiments, the partially purified cracked gas is conveyed through the one or more filter assemblies at a process temperature, wherein the process temperature is 100 °C or below. In some embodiments the process temperature is between -50 and 90 °C, -50 and 80 °C, -50 and 70 °C, -50 and 60 °C or -50 and 50 °C. In some embodiments, the partially purified cracked gas may be conveyed to the one or more filter assemblies via one or more heat exchangers to cool the partially purified cracked gas to the appropriate process temperature prior to entry into the one or more filter assemblies.

[0105] References

[0106] Kheimi, Marwan, and Sultan K. Salamah. "Simulation of temperature swing adsorption process to purify hydrogen for fuel cell uses by SAPO34 as adsorbent." Chemosphere 338 (2023): 139454.

Claims

Claims1 . A device for producing hydrogen comprising: an ammonia cracker having one or more raw cracked gas outlets in fluid communication with a common raw cracked gas flow conduit; one or more gas separators in fluid communication with the ammonia cracker via the common raw cracked gas flow conduit, and in fluid communication with a common partially purified cracked gas flow conduit; and one or more filter assemblies each having a first container having one or more walls, one or more partially purified cracked gas inlets and one or more purified cracked gas outlets, wherein the one or more partially purified cracked gas inlets are in fluid communication with the one or more gas separators via the common partially purified cracked gas flow conduit, the first container containing a single mass of adsorbent comprising silica gel, wherein the one or more partially purified cracked gas inlets and one or more purified cracked gas outlets are arranged such that a partially purified cracked gas flows through the single mass of adsorbent in use.

2. The device of claim 1 , wherein the one or more walls comprise a metal.

3. The device of claim 2, wherein the metal is stainless steel, high carbon steel, aluminium, or titanium.

4. The device of claim 3, wherein the metal comprises a polymer coating.

5. The device of claim 4, wherein the polymer coating is a fluorinated polymer, preferably PTFE or PFA.

6. The device of any one of the preceding claims, wherein the one or more walls comprise a plastic, optionally a clear plastic and / or an opaque plastic.

7. The device of claim 6, wherein the plastic is a fluorinated plastic or a polycarbonate.

8. The device of any one of the preceding claims, wherein each filter assembly further comprises a sight glass for viewing the single mass of adsorbent.

9. The device of any one of the preceding claims, further comprising an ancillary container containing a second mass of adsorbent comprising silica gel, the ancillary container being disposed downstream of and in fluid communication with the first container via the one or more purified cracked gas outlets, wherein the ancillary container comprises a second sight glass for viewing the second mass of adsorbent.

10. The device of claim 8, wherein the one or more walls further comprise a sight glass.11 . The device of claim 10, wherein the sight glass is proximal to at least one of the one or more purified cracked gas outlets.

12. The device of claim 10 or 11 , wherein the sight glass comprises a portion proximate to at least one of the one or more partially purified cracked gas inlets.

13. The device of any one of the preceding claims, further comprising a flow structure for lengthening the path of travel of the partially purified cracked gas through the single mass of adsorbent.

14. The device of claim 13 wherein the flow structure is chosen from a group consisting of: one or more permeable tubes disposed within the single mass of adsorbent and connected at one end to the one or more partially purified cracked gas inlets; one or more baffles extending from the one or more walls of the filter assembly; one or more inserts disposed in the container; wherein the container comprises a substructure formed of a substrate forming an internal volume filled at least partially with the single mass of adsorbent, the substructure in fluid communication with the one or more partially purified cracked gas inlets and the one or more purified cracked gas outlets; or any combination of the above.

15. The device of any one of the preceding claims, wherein the silica gel comprises silica gel beads, silica gel powder, and / or silica gel granules.

16. The device of any one of the preceding claims, further comprising an indicator adsorbed into, disposed on and / or proximal to the silica gel.

17. The device of any one of the preceding claims, further comprising an ammonia gas sensor.

18. The device of claim 17, wherein the ammonia gas sensor is disposed downstream from and in fluid communication with the one or more purified cracked gas outlets.

19. The device of claim 18, wherein the ammonia gas sensor is connected to the one or more purified cracked gas outlets via a regulator.

20. The device of any one of the preceding claims wherein the one or more filter assemblies are each in fluid communication with the common partially purified cracked gas flow conduit via the one or more partially purified cracked gas inlets, each filter assembly having a first valve between the one or more partially purified cracked gas inlets and the common partially purified cracked gas flow conduit.21 . The device of any one of the preceding claims, wherein the one or more filter assemblies are each in fluid communication with a common purified cracked gas flow conduit via the one or more purified cracked gas outlets, each filterassembly having a second valve between the one or more purified cracked gas outlets and the common purified cracked gas flow conduit.

22. The device of any one of the preceding claims, wherein the one or more gas separators comprise a pressure swing adsorption device and / or a palladium filter and / or a catalytic conversion reactor and / or a temperature swing adsorption device and / or a hollow fibre membrane filter.

23. The device of any one of the preceding claims, wherein the one or more gas separators are proximal or integral to the ammonia cracker.

24. The device of any one of the preceding claims, wherein greater than 30% of the single mass of adsorbent is silica gel, optionally wherein the single mass of adsorbent consists essentially of silica gel.

25. A system for generating electrical power using ammonia comprising:- the device for producing hydrogen according to any one of the preceding claims; and- a hydrogen fuel cell; wherein the hydrogen fuel cell is in fluid communication with the device for producing hydrogen via the common purified cracked gas flow conduit.

26. A process for producing a purified cracked gas of high purity hydrogen comprising:- providing ammonia gas to an ammonia cracker having one or more raw cracked gas outlets in fluid communication with a common raw cracked gas flow conduit to produce a raw cracked gas comprising hydrogen gas, nitrogen gas, and ammonia gas;- a first purification stage comprising conveying the raw cracked gas via the common raw cracked gas flow conduit to one or more gas separators, wherein the one or more gas separators at least partially remove the ammonia gas and nitrogen gas from the raw cracked gas to produce a partially purified cracked gas; and- a second purification stage comprising conveying the partially purified cracked gas via a common partially purified cracked gas flow conduit to one or more filter assemblies, each having a first container having one or more walls, one or more partially purified cracked gas inlets and one or more purified cracked gas outlets, the one or more partially purified cracked gas inlets being in fluid communication with the common partially purified cracked gas flow conduit, the first container containing a single mass of adsorbent comprising silica gel, wherein the one or more partially purified cracked gas inlets and one or more purified cracked gas outlets are arranged such that the partially purified cracked gas flows through the single mass of adsorbent,wherein the single mass of adsorbent selectively adsorbs the ammonia in the partially purified cracked gas to produce a purified cracked gas; wherein the partially purified cracked gas is conveyed through the one or more filter assemblies at a process pressure, wherein the process pressure is substantially constant.

27. The process according to claim 26, wherein the process pressure is 35 bar or less.

28. The process according to claim 26 or claim 27, wherein at least one of the one or more gas separators is a pressure swing adsorption device, wherein the pressure swing adsorption device comprises a plurality of vessels, each vessel comprising a first pressure swing adsorbent for adsorbing nitrogen gas from the raw cracked gas and a second pressure swing adsorbent for adsorbing ammonia gas from the raw cracked gas, optionally comprising a third pressure swing adsorbent for adsorbing water, wherein the plurality of vessels comprises a first pair of vessels comprising a first vessel and a second vessel, wherein the process comprises the sequence of:(a) fluidly connecting the first vessel of the first pair of vessels to the common raw cracked gas flow conduit and the common partially purified cracked gas flow conduit and conveying the raw cracked gas to the first vessel at the process pressure, wherein the ammonia gas and nitrogen gas (and optionally water) in the raw cracked gas are at least partially removed to produce the partially purified cracked gas;(b) conveying the partially purified cracked gas from the first vessel to the common partially purified cracked gas flow conduit at the process pressure;(c) fluidly isolating the first vessel from the common partially purified cracked gas flow conduit and the common raw cracked gas flow conduit;(d) fluidly connecting the first vessel to the second vessel of the first pair of vessels, the second vessel being at atmospheric pressure, such that the first vessel undergoes a decrease in pressure and the second vessel undergoes an increase in pressure such that the first vessel and the second vessel are at half of the process pressure;(e) fluidly isolating the first vessel from the second vessel and fluidly connecting the first vessel to a common waste gas flow conduit and conveying a waste gas containing nitrogen gas and ammonia gas from the first vessel to the common waste gas flow conduit, wherein the first vessel undergoes a further depressurisation such that the first vessel is at atmospheric pressure;(f) fluidly connecting the first vessel to a common purge gas flow conduit and conveying a purge gas at atmospheric pressure to the first vessel to remove any remaining waste gas from the first vessel via the common waste gas flow conduit;(g) fluidly isolating the first vessel from the common waste gas flow conduit and the common purge gas flow conduit;(h) fluidly connecting the first vessel to the second vessel, the second vessel being at the process pressure, such that the first vessel undergoes an increase in pressure and the second vessel undergoes a decrease in pressure such that the first vessel and the second vessel are at half of the process pressure;(i) fluidly isolating the first vessel from the second vessel and fluidly connecting the first vessel to a common backfill gas flow conduit and conveying a backfill gas such that the first vessel undergoes an increase in pressure such that the first vessel is at the process pressure; and(j) fluidly isolating the first vessel from the common backfill gas flow conduit and fluidly connecting the first vessel to the common raw cracked gas flow conduit and the common partially purified cracked gas flow conduit; wherein during steps (a) to (j), the partially purified cracked gas is conveyed through the one or more filter assemblies at the process pressure.

29. The process according to any one of claims 26 to 28, wherein the partially purified cracked gas is conveyed from multiple gas separators to the one or more filter assemblies.

30. The process according to any one of claims 26 to 29, wherein the single mass of adsorbent comprises at least 30% by mass of silica gel, optionally wherein the single mass of adsorbent consists essentially of silica gel.

31. The process according to any one of claims 26 to 30, wherein the partially purified cracked gas is conveyed through the one or more filter assemblies at a process temperature, wherein the process temperature is 100 °C or below, preferably wherein the process temperature is between -50 °C and 50 °C.

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