WO2025202876A1 - Improved cryo-separation system and method - Google Patents

Abstract

A cryo-separation system receiving a mixed gas to be separated having an initial liquefaction chamber to separate the mixed gas into a first product and a second product by liquefying the second product, a final liquefaction chamber to receive the first product and separate out remaining second product impurities by liquefying the second product. At least one cryocooler configured to cool the mixed gas entering the initial liquefaction chamber, and to cool the first product entering the final liquefaction chamber.

Description

IMPROVED CRYO-SEPARATION SYSTEM AND METHOD

FIELD OF THE INVENTION

The present invention relates to a cryo-separation system and a related method of cryogenically separating mixed gas. More particularly, but not exclusively, it relates to the separation of mixed gas when the constituent gases have significantly different boiling points, for example hydrogen and oxygen, or hydrogen and nitrogen.

BACKGROUND OF THE INVENTION

The process of distillation has been known for many centuries, and involves heating a liquid mixture to separate its components via a difference in their boiling points (as one component will evaporate first). For substances which are gaseous under ambient conditions, the equivalent method of separation involves cooling the gas instead of heating (as one component will condense first). This process is commonly known as cryogenic separation, and is used in industry in the production of hydrogen, oxygen, nitrogen, and other substances in pure liquid form.

One context in which cryogenic separation is useful is in separating mixed hydrogen and oxygen gas produced by the splitting of water in a process such as electrolysis, photocata lytic separation, or thermolysis. Another context in which cryogenic separation is useful is in separating mixed hydrogen and nitrogen gas produced by decomposing ammonia. These processes will generally involve connecting an appropriate cryo-separation system to the output of the splitting/decomposing process, with the higher boiling point of oxygen or nitrogen (-183 °C and -196 °C respectively at atmospheric pressure) compared to hydrogen (- 252.9 °C at atmospheric pressure) causing the oxygen or nitrogen to condense out of the mixed gas as it cools. It may also be necessary to separate out water vapour or other contaminants. Once the hydrogen and oxygen or nitrogen are separated, they can exit from the system as gases or be liquefied for storage in appropriate vessels.

Many configurations for cryo-separation systems are possible, but generally they involve a cryocooler that has a heat transfer path established with a conduit or vessel containing the gas. The heat transfer path may be via a coolant jacket (containing e.g. liquid nitrogen, or helium gas) surrounding the conduit or vessel, rather than by direct contact. The actual cooling cycle occurs within one or more cold heads of the cryocooler, and could be of any suitable type known in the art such as the Stirling cycle, the Gifford-McMahon cycle, or the Joule-Thompson cycle.

The quality of a cryo-separation system is largely determined by the achievable purity of the separated components (or by the useful product), by the energy efficiency of the separation process, and by the production capacity i.e. the mass of product produced in a given timeframe. An especially relevant performance metric is the product flow rate at a target purity for a typical input power. In general, higher energy efficiency allows a higher product flow rate for a fixed input power/cooling load.

For the example given above, oxygen impurities may remain in the hydrogen gas stream after exiting the cooling stage in which oxygen is condensed out. The efficiency of cryocoolers also reduces when cooling to such low temperatures, making the process very energy-intensive when carried out on an industrial scale with high product flow rates. Thus, it is desirable to develop new configurations for cryo-cooling systems which can achieve high purity and improved energy efficiency (and therefore improved production capacity), especially for applications such as hydrogen and oxygen separation where very low temperatures are required.

It is an object of the present invention to provide a cryo-separation system which overcomes or at least partially ameliorates some of the abovementioned disadvantages or which at least provides the public with a useful choice.

BRIEF DESCRIPTION OF THE INVENTION

According to a first aspect the invention broadly comprises a cryo-separation system comprising: a mixed gas inlet for receiving a mixed gas to be separated; an initial liquefaction chamber connected to the mixed gas inlet and configured to separate the mixed gas into a first product and a second product by liquefying the second product; a final liquefaction chamber connected to the initial liquefaction chamber to receive the first product therefrom, and configured to separate out remaining second product impurities by liquefying the second product; at least one cryocooler configured to cool the mixed gas entering the initial liquefaction chamber to an initial temperature, and to cool the first product entering the final liquefaction chamber to a final temperature which is lower than the initial temperature; a first product outlet connected to the final liquefaction chamber to discharge the first product; and one or more second product outlets connected to the initial liquefaction chamber and the final liquefaction chamber to discharge the second product.

According to another aspect the cryo-separation system further comprises an initial heat exchanger connected to the mixed gas inlet, the first product outlet, and the one or more second product outlets, such that incoming mixed gas is cooled by outgoing first product and second product.

According to another aspect the cryo-separation system further comprises a water outlet connected to the first heat exchanger and upstream of the initial liquefaction chamber, such that water vapour liquefied from the mixed gas stream by the initial heat exchanger is removed via the water outlet.

According to another aspect the first heat exchanger is split into a first stage and a second stage and the water outlet is connected between the first stage and second stage, such that the first stage liquefies water vapour from the mixed gas stream and the second stage provides further cooling of the mixed gas.

According to another aspect the initial heat exchanger is a counterflow heat exchanger.

According to another aspect the cryo-separation system further comprises a final heat exchanger connected between the initial liquefaction chamber and the final liquefaction chamber such that first product flowing therebetween is cooled by first product and second product exiting the final liquefaction chamber.

According to another aspect the final heat exchanger is a counterflow heat exchanger.

According to another aspect the cryo-separation system further comprises an intermediate liquefaction chamber connected between the initial liquefaction chamber and the final liquefaction chamber to receive first product from the former before it is transported to the latter, and configured to separate out remaining second product impurities by liquefying the second product, wherein the at least one cryocooler is configured to cool the first product entering the intermediate liquefaction chamber to an intermediate liquefaction temperature between the initial and final liquefaction temperatures.

According to another aspect the one or more second product outlets are a single, shared second product outlet which connects to the initial liquefaction chamber and the final liquefaction chamber via a junction.

According to another aspect the at least one cryocooler is a single cryocooler configured to cool both the mixed gas entering the initial liquefaction chamber and the first product entering the final liquefaction chamber.

According to another aspect the cryocooler comprises a plurality of cold heads.

According to another aspect each of the liquefaction chambers is allocated at least one of the plurality of cold heads to provide cooling of the gas entering the respective liquefaction chamber.

According to another aspect more of the cold heads are allocated to cooling of the mixed gas entering the first liquefaction chamber than are allocated to cooling of the first product entering the final liquefaction chamber.

According to another aspect the plurality of cold heads is three cold heads.

According to another aspect the cryocooler is rated for input power of at least 20 kW.

According to another aspect the initial liquefaction chamber comprises a coolant jacket, and the at least one cryocooler is configured to indirectly cool the mixed gas entering the initial liquefaction chamber by cooling a heat transfer fluid circulated through the coolant jacket.

According to another aspect the cryo-sepa ration system further comprises a water splitting unit connected to the mixed gas inlet such that the mixed gas is hydrogen gas and oxygen gas.

According to another aspect the cryo-separation system further comprises an ammonia decomposition unit connected to the mixed gas inlet such that the mixed gas is hydrogen gas and nitrogen gas.

According to another aspect the invention broadly comprises a method of cryogenically separating a mixed gas, the method comprising: an initial liquefaction step of actively cooling the mixed gas to an initial liquefaction temperature sufficient to separate the mixed gas into a first product and a second product by liquefying the second product; a final liquefaction step of actively cooling the first product produced by the initial liquefaction step to a final liquefaction temperature lower than the initial liquefaction temperature, the final liquefaction temperature sufficient to separate out remaining second product impurities by liquefying the second product; outputting first product produced by the final liquefaction step at a target purity, and outputting second product produced by the initial liquefaction step and the final liquefaction step.

According to another aspect the final liquefaction temperature is between 15-30 K lower than the initial liquefaction temperature.

According to another aspect the final liquefaction temperature is just above the melting point of the second product.

According to another aspect the mixed gas comprises a mass fraction of the second product at least four times greater than that of the first product.

According to another aspect the mixed gas is hydrogen gas and oxygen gas obtained from a water splitting process.

According to another aspect the method further comprises the final liquefaction temperature is approximately 55 K.

According to another aspect the initial liquefaction temperature is approximately 77 K.

According to another aspect the mixed gas is hydrogen gas and nitrogen gas obtained from an ammonia decomposition process.

According to another aspect the method further comprises an intermediate liquefaction step of actively cooling the first product produced by the initial liquefaction step to an intermediate liquefaction temperature between the initial and final liquefaction temperatures, the intermediate liquefaction temperature sufficient to separate out remaining second product impurities by liquefying the second product, the intermediate liquefaction step being performed before the final liquefaction step, and wherein outputting second product also includes that produced by the intermediate liquefaction step. According to another aspect the liquefaction temperatures are selected such that no more than one third of total cooling load between the liquefaction steps is associated with the final liquefaction step.

According to another aspect the target purity is at least 99.95%.

According to another aspect the method further comprises transferring heat from the mixed gas to be used in the initial liquefaction step to the first product and the second product to be output.

According to another aspect the method further comprises transferring heat from the first product to be used in the final liquefaction step to the first product and the second product to be output.

According to another aspect the method further comprises removing water vapour from the mixed gas prior to the initial liquefaction step.

Other aspects of the invention may become apparent from the following description which is given by way of example only and with reference to the accompanying drawings.

As used herein the term "and/or" means "and" or "or", or both.

As used herein "(s)" following a noun means the plural and/or singular forms of the noun.

The term "comprising" as used in this specification and claims means "consisting at least in part of". When interpreting statements in this specification and claims which include that term, the features, prefaced by that term in each statement, all need to be present but other features can also be present. Related terms such as "comprise" and "comprised" are to be interpreted in the same manner.

In this specification, where reference has been made to external sources of information, including patent specifications and other documents, this is generally for the purpose of providing a context for discussing the features of the present invention. Unless stated otherwise, reference to such sources of information is not to be construed, in any jurisdiction, as an admission that such sources of information are prior art or form part of the common general knowledge in the art.

For the purpose of this specification, where method steps are described in sequence, the sequence does not necessarily mean that the steps are to be chronologically ordered in that sequence, unless there is no other logical manner of interpreting the sequence. BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described by way of example only and with reference to the drawings in which:

Figure 1 shows a schematic of a cryo-separation system with one heat exchanger, and direct cryocooling for gas entering each of two liquefaction chambers;

Figure 2 shows a schematic of a cryo-separation system with a liquid coolant jacket for cooling the initial liquefaction chamber;

Figure 3 shows a schematic of a cryo-separation system with two heat exchangers, and direct cryocooling for gas entering each of two liquefaction chambers;

Figure 4 shows a schematic of a cryo-separation system with three heat exchangers, and direct cryocooling for gas entering each of three liquefaction chambers;

Figure 5 shows a perspective view of the cryo-separation system of figure 3 arranged within a cryostat;

Figure 6 shows a top view of the cryo-separation system showing three cold heads;

Figure 7A shows a side view of the cryo-separation system without the shell of the cryostat; and

Figure 7B shows a side view of the cryo-separation system with the shell of the cryostat.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

According to various aspects of the various embodiments of the present invention as illustrated in figures 1-7B, there is provided a cryo-separation system 10 which will now be described. An associated method of cryogenically separating a mixed gas also follows naturally from the description of the cryo-separation system 10.

As shown in figure 1, the cryo-separation system 10 comprises a mixed gas inlet 12 for receiving a mixed gas to be separated. The mixed gas may for example be hydrogen gas and oxygen gas, although the cryo-separation system 10 can function with other gas mixtures provided there is a suitable difference in boiling point. The cryo-separation system 10 further comprises an initial liquefaction chamber 14 connected to the mixed gas inlet 12 and a final liquefaction chamber 16 connected to the initial liquefaction chamber 14 to receive gas therefrom. Each liquefaction chamber is configured to separate the gas within into a first product and a second product by liquefying the second product. However, the cryo-separation system 10 is configured such that the majority of liquefaction occurs in the initial liquefaction chamber 14, and thus gas passed to the final liquefaction chamber 16 is primarily first product with some second product impurities remaining. The purpose of the final liquefaction chamber 16 is therefore to increase the purity of the first product by an additional stage of liquefaction.

The second product is whichever of the mixed gases has the higher boiling point. For the example of hydrogen and oxygen, hydrogen is therefore the first product and oxygen is the second product. Thus, the gas passed from the initial liquefaction chamber 14 to the final liquefaction chamber 16 is primarily hydrogen.

The cryo-separation system 10 further comprises at least one cryocooler 18 configured to cool the mixed gas entering the initial liquefaction chamber 14 (the first flow of gas) and to cool the first product entering the final liquefaction chamber 16 (the second flow of gas). One cryocooler 18 may cool both flows of gas, either using separate cold heads for each flow or by using separate thermal connections to the same cold head. Alternatively, independent cryocoolers 18 may be provided for the two flows, although this may be less efficient and compact. The at least one cryocooler 18 is configured to cool the first flow of gas to an initial liquefaction temperature, and to cool the second flow of gas to a final liquefaction temperature which is lower than the initial liquefaction temperature.

The at least one cryocooler 18 may directly cool each flow of gas prior to entry into the respective liquefaction chamber, or indirectly cool one or both flows of gas via cooling of a heat transfer fluid circulated through a coolant jacket 19 of the respective liquefaction chamber as shown in figure 2. Where a coolant jacket 19 is used, preferably the heat transfer fluid is liquid nitrogen or helium gas. Cryocooling of the heat transfer fluid can allow it to be circulated in a closed loop (including re-liquefaction if applicable) instead of supplying heat transfer fluid as a consumable. However, direct cooling can be advantageous as it can eliminate the need to manage a separate coolant store and flow.

Cooling the two flows of gas to different temperatures allows for more efficient operation of the cryo-separation system 10. Cryocooler efficiency drops off at lower temperatures and the cooling power available becomes more limited. Thus, the initial liquefaction temperature can be selected to be low enough to cause the majority of the second product to be liquefied in the initial liquefaction chamber 14, but not low enough to achieve the final target purity. The final liquefaction temperature can then be set low enough to achieve the target purity. As a result, the larger cooling load will occur at the initial liquefaction temperature where the cryocooler 18 is more efficient, and the cooling load at the final liquefaction temperature where the cryocooler 18 is less efficient is reduced. For a set input power to the at least one cryocooler 18, the capacity of the cryo-separation system 10 (i.e. the product flow rate) is therefore increased.

A first product outlet 20 is connected to the final liquefaction chamber 16 to discharge the first product after its purity has been increased. Preferably a second product outlet 22 is connected to the initial liquefaction chamber 14 and to the final liquefaction chamber 16 to discharge the second product, but alternatively the second product could be discharged through a different second product outlet for each liquefaction chamber. If the second product outlet 22 is shared, the fluid connections from the liquefaction chambers and the second product outlet 22 may meet at a junction 23. Although the second product is in liquid form upon exiting each liquefaction chamber, it may be discharged from the second product outlet 22 as a gas.

Because it is generally acceptable to discharge both the first product and the second product as gases, it may not be necessary to maintain cryogenic temperatures at the first product outlet 22 and the second product outlet 24. Thus, the cryo-separation system 10 can be made more efficient by transferring heat from incoming mixed gas into the outgoing product gases. This exchange of heat may cause vaporisation of the second product. To facilitate this heat transfer, an initial heat exchanger 24 may be connected to the mixed gas inlet 22, the first product outlet 22, and the second product outlet 24. The initial heat exchanger 24 is connected upstream of where the cryocooler 18 actively cools the first flow of gas, such that the initial heat exchanger 24 provides pre-cooling of the flow. Preferably the initial heat exchanger 24 is a three-channel heat exchanger, and preferably counterflow to increase efficiency.

As shown in figure 3, efficiency may be further increased by provision of a final heat exchanger 28 that transfers heat from the second flow of gas entering the final liquefaction chamber 16 to the outgoing first product and second product. The final heat exchanger 24 is connected upstream of where the cryocooler 18 actively cools the second flow of gas, such that the final heat exchanger 24 provides pre-cooling of the flow. The final heat exchanger 28 is likewise preferably three-channel and counterflow.

It will be appreciated that transfer of heat between the incoming and outgoing fluid flows may be achieved by any suitable arrangement, and is not limited to the specific heat exchanger configurations described.

The initial heat exchanger 24 may also incorporate or be connected to a water outlet 26 for removing trace quantities of water vapour from the mixed gas stream. When it is water splitting that provides a mixed gas stream of hydrogen and oxygen, water vapour or droplets may inevitably be introduced into the mixed gas - a typical moisture content may be around 0.065%. It is undesirable to have water passing through the cryogenic components of the cryoseparation system 10, as the water may freeze and cause icing problems. Hence it is preferable to remove water content close to the mixed gas inlet 22, which requires relatively little cooling power due to the much higher boiling point of water compared to hydrogen and oxygen. Thus, cooling provided by the initial heat exchanger 24 may be sufficient to liquefy any water vapour and allow it to be discharged via the water outlet 26.

Discharging of water via the water outlet 26 may be periodic, given the much smaller flow rate compared to the production of the first product and the second product. Opening the water outlet 26 only periodically can reduce heat leakage into the system via the water outlet 26. To further reduce such heat leakage, the initial heat exchanger 24 may be split into two stages such that the first stage is sized to provide only the temperature drop necessary to liquefy water out of the mixed gas and the second stage provides further pre-cooling of the mixed gas. This allows the first stage, connected to the water outlet 26, to have a lower thermal mass and thus absorb less heat during the periodic discharge of water. The second stage may be situated further from the water outlet 26 to avoid thermal coupling therebetween.

As shown in figure 4, one or more intermediate liquefaction chambers 27 may be connected between the initial liquefaction chamber 14 and the final liquefaction chamber 16, and likewise configured to liquefy second product out of the flow of gas that cascades between each liquefaction chamber. The at least one cryocooler 18 may be configured to cool the first product entering each intermediate liquefaction chamber 27 to a respective intermediate liquefaction temperature in between the initial liquefaction temperature and the final liquefaction temperature, which may facilitate further improvement in cryocooler efficiency by further reducing the cooling load at the final liquefaction temperature.

Each intermediate liquefaction chamber 27 may have an associated intermediate heat exchanger, configured in the same way as those described previously to provide precooling of the incoming gas using outgoing gas. Connections are also largely similar to those of the initial liquefaction chamber 14.

As shown in figure 5, the low-temperature components of the cryo-separation system 10, including the final heat exchanger 28 described above, may be assembled within a cryostat 29 of a single cryocooler 18. This provides thermal insulation and makes the cryo- separation system 10 especially compact. The initial heat exchanger 24 may be mounted directly above the initial liquefaction chamber 14, and the final heat exchanger 28 may be mounted directly above the final liquefaction chamber 16. This assists in better utilising the space available within the cryostat 29, and may also facilitate shorter fluid connections between the components. However, it will be appreciated that many placements of the components within the cryostat 29 are possible, and some components may be mounted outside the cryostat 29 for example in a secondary cryostat.

As shown in figure 6, the cryocooler 18 preferably has a plurality of cold heads 30, for example three cold heads 30 as shown. This allows each cold head 30 to be allocated to the cooling of gas flowing into a particular liquefaction chamber. However, if the number of liquefaction chambers exceeds the number of cold heads 30 (e.g. for an alternative embodiment with only a single cold head 30), at least one of the cold heads 30 may service more than one liquefaction chamber. The cryo-separation system 10 can then be configured such that one cold head 30 can still provide cooling to different liquefaction temperatures.

For embodiments in which two liquefaction chambers are used and the number of cold heads 30 is greater than two, preferably the majority of the cold heads 30 are connected to cool the first flow of gas, in order to provide additional cooling power to the initial liquefaction chamber 14 where the majority of the second product is to be liquefied. For example, two cold heads 30 may cool the first flow of gas while one cold head 30 cools the second. Where multiple cold heads 30 are allocated to cooling the same flow of gas, they may be connected in parallel and operated at the same temperature such that the fluid connections split to pass through the cold heads 30 and then converge again to enter the respective liquefaction chamber.

If one or more intermediate liquefaction chambers 27 are used, their number may be selected such that the total number of liquefaction chambers matches the number of cold heads 30 available from the at least one cryocooler 18. For example, if the cryocooler 18 has three cold heads 30 then a single intermediate liquefaction chamber 27 allows each liquefaction chamber to be allocated a different cold head 30 operated at a different temperature. Thus, the initial liquefaction chamber 14 and the intermediate liquefaction chamber 27 are between them allocated a greater share of the available cold heads 30, and are associated with a greater share of the cooling load. However, the intermediate liquefaction chamber 27 could alternatively share one of the cold heads 30 with one of the other liquefaction chambers, as previously described.

As shown in figures 7A and 7B, the low-temperature components of the cryo- separation system 10 can be fully contained within the shell of the cryostat 29. The mixed gas inlet 22, the first product outlet 22, and the second product outlet 24 may be the only points of ingress or egress into the cryostat 29. Where the mixed gas inlet 22 is connected to a water splitting process to provide hydrogen gas and oxygen gas, this process will generally be located outside of the cryostat 29 as such processes do not require cryogenic temperatures. Components of the cryocooler 18 other than the cold heads 30 will also be located outside of the cryostat 29.

Ideal operating parameters for the cryo-separation system 10 will depend on various factors such as the gases to be separated and their respective boiling points, the target purity for the first product (which may be dependent on what the first product is to be used for), and the type of cryocooler 18 used. Preferably the mixed gas inlet temperature is above the freezing point of water to avoid icing issues prior to water removal via the water outlet 26, for example 274 K.

For an example cryo-separation system 10 operated to separate hydrogen and oxygen output from a water splitting process the target hydrogen purity may be approximately 99.98%. In general, the lower the final liquefaction temperature, the greater the purity of the first product will be. The limiting factor may be the melting point of the second product, past which freezing will occur and become problematic - thus it may be preferable to set the final liquefaction temperature just above this melting point. For oxygen, the melting point (at atmospheric pressure) is 54.3 K and thus the final liquefaction temperature which is sufficient to achieve the above target purity may be approximately 55 K.

For other gas mixtures or use cases, a lower purity may be sufficient - and thus the final liquefaction temperature may be raised further above the melting point of the second product, where the cryocooler 18 may operate more efficiently. Conversely, the target purity may be even higher in some cases. If the mixed gas is received at higher than atmospheric pressure, the melting point of the second product and thus the ideal final liquefaction temperature may also change accordingly.

The initial liquefaction temperature is preferably set such that the majority of total cooling load is at this temperature. If one or more intermediate liquefaction chambers 27 are used, then preferably the sum of cooling load at the initial and intermediate liquefaction temperature(s) is a majority of the total cooling load. More preferably, at least two thirds of the total cooling load on the cryocooler 18 occurs at the initial liquefaction temperature and optionally the intermediate liquefaction temperature(s). In other words, preferably no more than one third of the total cooling load occurs at the final liquefaction temperature.

Preferably the final liquefaction temperature is between 15-30 K lower than the initial liquefaction temperature, for example approximately 22 K lower. Thus, for a mixed gas of hydrogen and oxygen the initial liquefaction temperature may be approximately 77 K. An intermediate liquefaction temperature, if used, may therefore be between 55-75 K. Where the mixed gas stream is hydrogen and nitrogen or some other gas mixture, the liquefaction temperatures will differ accordingly.

The cryo-separation system 10 of the present invention provides a number of key benefits over alternative systems:

Firstly, liquefying the second product in successive stages at different temperatures greatly increases the efficiency of the system and thus the throughput capacity for typical use cases. When the cryo-separation system 10 is operated using mixed gas obtained from water splitting, with the above example parameters, and at an input power to the cryocooler 18 of approximately 30 kW, the cryo-separation system 10 may achieve an increase in hydrogen production of approximately 80% compared to an equivalent single-stage system which directly cools to 55 K.

The above performance improvement arises because when the mixed gas comes from a water splitting process, the mass fraction of oxygen in the mixed gas will typically be close to eight times higher than that of hydrogen, meaning a significant portion of the cooling load can be attributed to the liquefaction of oxygen rather than the cooling of hydrogen - making it much more efficient to conduct the majority of liquefaction via cryocooling at a higher temperature. A similar relationship will apply to the mass fractions in many other gas mixtures (e.g. hydrogen and nitrogen) obtained from common industrial processes, and the invention is especially well-suited to use with mixed gases in which the mass fraction of the second product is at least four times greater than that of the first product. Secondly, the use of a cryocooler 18 with multiple cold heads 30 allows for convenient provision of the different liquefaction temperatures, and facilitates an especially compact cryo-separation system 10 which may fit entirely within the cryostat 29 of the cryocooler 18. Such cryocoolers 18 are readily available, and the cryo-separation system 10 can be easily assembled by integration with an existing cryocooler 18.

Thirdly, the use of pre-cooling via heat exchangers at each stage in combination with active cryocooling by the at least one cryocooler 18 allows much of the cooling effort to be recovered, further improving overall thermal efficiency of the system and allowing higher flow rates.

Where components are referred to as 'connected to' or 'connectable to' other components throughout the specification and in the appended claims, it will be understood that such terminology references fluid connections, via appropriate fluid conduits, which are not necessarily direct. There may be intermediate components which form part of any such fluid connection, whether or not such intermediate components are explicitly referenced.

To those skilled in the art to which the invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the scope of the invention as defined in the appended claims.

This invention may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, and any or all combinations of any two or more of said parts, elements or features, and where specific integers are mentioned herein which have known equivalents in the art to which this invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth.

Claims

1. A cryo-separation system comprising: a mixed gas inlet for receiving a mixed gas to be separated; an initial liquefaction chamber connected to the mixed gas inlet and configured to separate the mixed gas into a first product and a second product by liquefying the second product; a final liquefaction chamber connected to the initial liquefaction chamber to receive the first product therefrom, and configured to separate out remaining second product impurities by liquefying the second product; at least one cryocooler configured to cool the mixed gas entering the initial liquefaction chamber to an initial temperature, and to cool the first product entering the final liquefaction chamber to a final temperature which is lower than the initial temperature; a first product outlet connected to the final liquefaction chamber to discharge the first product; and one or more second product outlets connected to the initial liquefaction chamber and the final liquefaction chamber to discharge the second product.

2. The cryo-separation system of claim 1, further comprising an initial heat exchanger connected to the mixed gas inlet, the first product outlet, and the one or more second product outlets, such that incoming mixed gas is cooled by outgoing first product and second product.

3. The cryo-separation system of claim 2, further comprising a water outlet connected to the first heat exchanger and upstream of the initial liquefaction chamber, such that water vapour liquefied from the mixed gas stream by the initial heat exchanger is removed via the water outlet.

4. The cryo-separation system of claim 3, wherein the first heat exchanger is split into a first stage and a second stage and the water outlet is connected between the first stage and second stage, such that the first stage liquefies water vapour from the mixed gas stream and the second stage provides further cooling of the mixed gas.

5. The cryo-separation system of any one of claims 2 to 4, wherein the initial heat exchanger is a counterflow heat exchanger.

6. The cryo-separation system of any one of claims 2 to 5, further comprising a final heat exchanger connected between the initial liquefaction chamber and the final liquefaction chamber such that first product flowing therebetween is cooled by first product and second product exiting the final liquefaction chamber.

7. The cryo-separation system of claim 6, wherein the final heat exchanger is a counterflow heat exchanger.

8. The cryo-separation system of any one of claims 2 to 7, further comprising an intermediate liquefaction chamber connected between the initial liquefaction chamber and the final liquefaction chamber to receive first product from the former before it is transported to the latter, and configured to separate out remaining second product impurities by liquefying the second product, wherein the at least one cryocooler is configured to cool the first product entering the intermediate liquefaction chamber to an intermediate liquefaction temperature between the initial and final liquefaction temperatures.

9. The cryo-separation system of any one of the preceding claims, wherein the one or more second product outlets are a single, shared second product outlet which connects to the initial liquefaction chamber and the final liquefaction chamber via a junction.

10. The cryo-separation system of any one of the preceding claims, wherein the at least one cryocooler is a single cryocooler configured to cool both the mixed gas entering the initial liquefaction chamber and the first product entering the final liquefaction chamber.

11. The cryo-separation system of claim 10, wherein the cryocooler comprises a plurality of cold heads.

12. The cryo-separation system of claim 11, wherein each of the liquefaction chambers is allocated at least one of the plurality of cold heads to provide cooling of the gas entering the respective liquefaction chamber.

13. The cryo-separation system of claim 12, wherein more of the cold heads are allocated to cooling of the mixed gas entering the first liquefaction chamber than are allocated to cooling of the first product entering the final liquefaction chamber.

14. The cryo-separation system of any one of claims 11 to 13, wherein the plurality of cold heads is three cold heads.

15. The cryo-separation system of any one of claims 10 to 14, wherein the cryocooler is rated for input power of at least 20 kW.

16. The cryo-separation system of any one of the preceding claims, wherein the initial liquefaction chamber comprises a coolant jacket, and the at least one cryocooler is configured to indirectly cool the mixed gas entering the initial liquefaction chamber by cooling a heat transfer fluid circulated through the coolant jacket.

17. The cryo-separation system of any one of the preceding claims, further comprising a water splitting unit connected to the mixed gas inlet such that the mixed gas is hydrogen gas and oxygen gas.

18. The cryo-separation system of any one of the preceding claims, further comprising an ammonia decomposition unit connected to the mixed gas inlet such that the mixed gas is hydrogen gas and nitrogen gas.

19. A method of cryogenically separating a mixed gas, the method comprising: an initial liquefaction step of actively cooling the mixed gas to an initial liquefaction temperature sufficient to separate the mixed gas into a first product and a second product by liquefying the second product; a final liquefaction step of actively cooling the first product produced by the initial liquefaction step to a final liquefaction temperature lower than the initial liquefaction temperature, the final liquefaction temperature sufficient to separate out remaining second product impurities by liquefying the second product; outputting first product produced by the final liquefaction step at a target purity, and outputting second product produced by the initial liquefaction step and the final liquefaction step.

20. The method of claim 19, wherein the final liquefaction temperature is between 15-30 K lower than the initial liquefaction temperature.

21. The method of claim 19 or 20, wherein the final liquefaction temperature is just above the melting point of the second product.

22. The method of any one of claims 19 to 21, wherein the mixed gas comprises a mass fraction of the second product at least four times greater than that of the first product.

23. The method of any one of claims 19 to 22, wherein the mixed gas is hydrogen gas and oxygen gas obtained from a water splitting process.

24. The method of claim 23, wherein the final liquefaction temperature is approximately 55 K.

25. The method of claim 23 or 24, wherein the initial liquefaction temperature is approximately 77 K.

26. The method of any one of claims 19 to 22, wherein the mixed gas is hydrogen gas and nitrogen gas obtained from an ammonia decomposition process.

27. The method of any one of claims 19 to 26, further comprising an intermediate liquefaction step of actively cooling the first product produced by the initial liquefaction step to an intermediate liquefaction temperature between the initial and final liquefaction temperatures, the intermediate liquefaction temperature sufficient to separate out remaining second product impurities by liquefying the second product, the intermediate liquefaction step being performed before the final liquefaction step, and wherein outputting second product also includes that produced by the intermediate liquefaction step.

28. The method of any one of claims 19 to 27, wherein the liquefaction temperatures are selected such that no more than one third of total cooling load between the liquefaction steps is associated with the final liquefaction step.

29. The method of any one of claims 19 to 28, wherein the target purity is at least 99.95%.

30. The method of any one of claims 19 to 29, further comprising transferring heat from the mixed gas to be used in the initial liquefaction step to the first product and the second product to be output.

31. The method of any one of claims 19 to 30, further comprising transferring heat from the first product to be used in the final liquefaction step to the first product and the second product to be output.

32. The method of any one of claims 19 to 31, further comprising removing water vapour from the mixed gas prior to the initial liquefaction step.