Transportable micro-scale liquid natural gas (LNG) liquefaction plant and method

Abstract

Provided are a micro-scale apparatus and method for liquefying natural gas The apparatus comprises a first heat exchanger that cools a natural gas feed stream by heat exchange with a first cooling fluid from a chiller, a compressor configured to compress the cooled natural gas, an air cooler configured to further cool the compressed natural gas, a second heat exchanger configured to further cool the natural gas by heat exchange with a second cooling fluid, a third heat exchanger configured to further cool the cooled natural gas, a joule-thompson (JT) valve configured to cool the flow of cooled natural gas to create LNG, a separator configured to separate a liquified LNG from a vapour phase, and a return flow path connected to the natural gas inlet, wherein the return flow path is optionally configured to pass as cooling medium via the third heat exchanger, wherein optionally the return flow path is configured to transport the vapour phase from the separator via the third heat exchanger for heating by heat exchange a gas flow entering the inlet of the third heat exchanger, and to combine the heated vapour phase with the natural gas feed stream.

Description

[0001] Transportable Micro-scale Liquid Natural Gas (LNG) Liquefaction Plant and Method

[0002] The present invention relates to a micro-scale liquid natural gas (LNG) liquefaction plant for the liquefaction of natural gas (NG) in gas form to liquid natural gas (LNG) in a liquid form. In example embodiments, the liquefaction plant may provide a highly compact and efficient plant that may be mobile and transportable (i.e., easily moveable between locations, which may include being vehicle mountable, or being mounted to a vehicle in normal use), and that is particularly well suited for the liquefaction of low-pressure flare gas, biomethane, natural gas.

[0003] A micro-scale LNG plant is an LNG plant that is substantially smaller than traditional, fixed industrial LNG plants. Such micro-scale LNG plants may be easily transportable, meaning that they may be attached to, or may be fully integrated onto, a vehicle chassis, allowing them to be easily moved to different locations. The attachment to a vehicle may be permanent or temporary.

[0004] In general, LNG plants, which may also be referred to as liquefaction plants, allow natural gas (NG) to be liquefied, i.e. converted it to a liquid, thereby reducing its volume to approximately l / 600th of its original gas volume. Accordingly, due to the decreased volume following liquefaction, the resulting LNG may be transported far more cost- effectively. Liquefaction is thus an essential element to the commercialisation of NG, by reducing the cost of transportation and / or distribution.

[0005] Large scale industrial LNG plants allow for the production of LNG from huge volumes of relatively high-pressure NG that is extracted from the ground. These plants typically comprise very substantial components and complex cooling systems to allow these very large volumes of NG to be processed into a more compact liquid form. The process of liquefaction, i.e. the process of converting the natural gas to liquid natural gas, generally comprises compressing and cooling the natural gas repeatedly until condenses to liquid form at approximately -165 degrees Celsius (at atmospheric pressure).

[0006] Industrial LNG plants typically result in a small volume of low-pressure boil-off gas (BOG) as an inevitable by-product of the liquefaction process. This relatively small and inconsequential volume of BOG, compared to the volume of natural gas that is processed by the plant, means it is generally not cost effective to re-process the BOG, since this would require additional complexity and cost for relatively little gain. Accordingly, this BOG is typically vented into the atmosphere or flared (burned).

[0007] US11340013 discloses an LNG plant suitable for the processing of relatively high- pressure natural gas. Disclosed is a system comprising compressors for compressing the NG coupled with heat exchangers for cooling the natural gas. Also disclosed is a bypass line which allows boil-off gas (BOG) to be mixed with source natural gas and directed through one of the heat exchangers to improve efficiency of the plant. Large compressors are required to achieve the necessary liquefaction.

[0008] US2023288137 discloses an LNG plant comprising a mixed refrigerant cycle. Therein, natural gas is cooled to a first temperature level in a first cooling step using a first mixed refrigerant, and is subsequently subjected to counter-current absorption using an absorption liquid, wherein a gas fraction depleted in the higher hydrocarbons is formed, at least a portion of the gas fraction is cooled to a second temperature level in a second cooling step using a second mixed refrigerant and is liquefied to form the LNG. Such a system as disclosed therein requires highly precise control of the composition of the refrigerants, and such composition control systems are very complex and expensive. The cost of such composition control systems does not scale linearly with the size of plant, and therefore such a system and process as disclosed is only commercially feasible in large industrial LNG plants.

[0009] CN1 11607423 describes a vehicle-mounted mobile oilfield vent gas recovery system that includes a liquefaction unit to convert such oilfield vent gas to more compact and useable form. The system is designed for processing the venting gas that occurs at oil fields, and an aim of the system disclosed is to ensure effective liquefaction. In the system disclosed therein, the source NG passes through several regulating valves that reduce the pressure from the natural gas stream until it liquifies. To operate in this way, there must be relevant inlet pressure for the cycle to be operated.

[0010] In known LNG distribution facilities, where LNG is loaded onto trucks for transportation, trucks arriving at the distribution facility need to first offload BOG to lower their internal pressure prior to starting filling. Such tankers don’t have high design pressure and therefore they need to send the BOG to somewhere with lower pressure. However, the BOG pressure in the tankers is insufficient to initiate a cycle such as that in CN111607423. Thus, prior to filling with LNG, it is typical for the tanker BOG to be simply vented into the atmosphere or flared (burned) prior to filling, causing emissions to the atmosphere.

[0011] According to the foregoing, there is a need to provide an LNG liquefaction system and apparatus that may mitigate some or all of the above-mentioned drawbacks.

[0012] According to a first aspect of the invention, there is provided a micro-scale liquid natural gas plant for liquefying a natural gas feed stream, comprising: a first heat exchanger with natural gas inlet and a first cooled gas outlet wherein the first heat exchanger is configured to cool the natural gas feed stream by heat exchange with a first cooling fluid from a vapour-compression chiller; a compressor with a compressor inlet connected to the first heat exchanger outlet and a compressed gas outlet, wherein the compressor is configured to compress the cooled natural gas; an air cooler with an air cooler inlet connected to the compressed gas outlet of the compressor and an air cooler outlet, wherein the air cooler is configured to further cool the compressed natural gas; a second heat exchanger with an inlet connected to the air cooler outlet and a second cooled gas outlet, wherein the second heat exchanger is configured to further cool the natural gas by heat exchange with a second cooling fluid; a third heat exchanger with an inlet connected to the second cooled gas outlet and a third cooled gas outlet, configured to further cool the cooled natural gas; a joule-thompson valve with an inlet connected to the outlet of the third heat exchanger and a JT cooled gas outlet, configured to cool the flow of cooled natural gas to create LNG by reducing its pressure; a separator with an inlet connected to the JT cooled gas outlet of the joule-thompson valve, an LNG outlet and a vapour phase outlet, wherein the separator is configured to separate a liquified LNG from a vapour phase; and a return flow path with an inlet connected to the vapour phase outlet and an return path outlet connected to the natural gas inlet, wherein the return flow path is configured to pass as cooling medium via the third heat exchanger, wherein the return flow path is configured to transport the vapour phase from the separator via the third heat exchanger for heating by heat exchange a gas flow entering the inlet of the third heat exchanger, and to combine the heated vapour phase with the natural gas feed stream.

[0013] The invention thus provides an ultra-compact micro-scale LNG plant that is highly efficient and that is suitable for the processing of low-pressure gas. The invention thus provides, in a compact, transportable and efficient manner, the means for the processing of BOG from existing LNG liquefaction and transportation processes and / or the processing of or low-pressure co-incident associated gas present at oilfields. Accordingly, the invention provides for a significant improvement in environmental sustainability, by reducing flaring and venting of low-pressure gases in existing processes, and also provides for a further improvement in productivity by utilizing an otherwise waste product from existing production methods.

[0014] In the context of the invention, micro-scale means of a scale that may be no bigger than approximately one or two orders of magnitude smaller than existing LNG plants. For example, a micro-scale LNG plant may process a tenth or less the volume of an existing LNG plant, perhaps only one hundredth of the volume.

[0015] The invention employs a chiller fluid from a vapour-compression chiller to cool down the natural gas before and optionally after a compressor stage, thereby decreasing the volume of the natural gas. Therefore, this approach using a chiller fluid from a vapourcompression chiller to cool down the gas before compression, increases the mass throughput of a same compressor, keeping the equipment size small enough to fit in mobile applications but with higher throughput, especially in places with high ambient temperature. The use of a vapour-compression chiller to cool the natural gas results in a significant reduction in size compared to conventional heat exchangers because of its density which is very high compared to refrigerants at low pressure.

[0016] Typically, portable LNG plants have a genset that powers one or more compressors. A genset is a portable device that converts fuel to electricity using an engine and a generator. The waste heat from the genset, or the heat of the compressed gas, is often directed to the chiller. An adsorption chiller works by using a solid adsorbent material to capture and release a refrigerant in cycles. The process starts when heat is applied to the adsorbent, causing it to release the refrigerant vapor. This vapor then condenses, releasing heat and creating a cooling effect. Afterward, the adsorbent cools down and re-adsorbs the refrigerant, restarting the cycle. This cycle allows the chiller to provide cooling without needing a mechanical compressor, which is why adsorption chillers are always chosen in known prior designs, and why there is a strong prejudice to using adsorption chillers in the prior art.

[0017] The present application provides the inventive insight to use a compression chiller (more formally a vapour-compression chiller) instead of the accepted and commonly utilised adsorption chiller. (References to a compression chiller herein should be understood to mean, formally, a vapour-compression chiller).

[0018] A compression chiller works by using a compressor to pressurize and circulate a refrigerant. The refrigerant is compressed, raising its temperature, and it then flows through a condenser where it releases heat and turns into a liquid. This liquid refrigerant is then expanded, lowering its temperature, and flows into the evaporator, where it absorbs heat and creates a cooling effect. The cycle then repeats, using the compressor to maintain continuous cooling.

[0019] Compression chillers have crucial advantages over the adsorption chiller for the objective of the present application. Firstly, compression chillers are lighter and smaller than adsorption chillers for the same size, allowing them to be compact enough for a mobile liquefaction plant. Secondly, compression chillers do not require an external source of heat to operate, allowing for a more compact design. Thirdly, adsorption chillers generally have a lower chiller efficiency than compression chillers (chiller efficiency is measured and expressed in several units, one of which is COP). This is very important on electrical compressors, because the heat generated on the compression of the natural gas is very low - and since this heat is used to power the compression chiller, the adsorption chiller refrigerating capacity is limited. As a result of this low adsorption chiller refrigerating capacity, the chiller effect with an adsorption chiller is typically not being enough to cooldown the natural gas to low temperatures, therefore the LNG production decreases drastically making the project unfeasible.

[0020] Furthermore, compression chillers can get to lower temperatures than adsorption chillers. This has an impact on the process conditions of the liquefaction cycle, enhancing the production of LNG. This is because, with compression chillers, it is possible to get the chiller fluid to a temperature as low as -40F. A second impact of compression chillers being able to get to lower temperatures is that the natural gas can become significantly more dense on the suction of the compressor, since it can go to temperatures of -20F instead of the temperature of around 35F that commonly enters in the compressor described in known designs. This increases the mass flow of the compression in about 12% on every stage of the compressor.

[0021] Accordingly, the present disclosure provides an entirely novel approach to micro - scale LNG production, by providing a solution that does not have compressors driven by a genset and that uses compression chillers.

[0022] In the present disclosure, the novel micro-scale LNG plant directly cools the NG entering the system with a cooling stage (comprising a heat exchanger configured to heat exchange using a cooling fluid from a compression chiller) that precedes the compressor. That is, in embodiments of the invention, natural gas entering the LNG plant passes immediately through a heat exchanger fed by a compression chiller, so that the heat exchanger chills the natural gas. The chilled natural gas then flows directly through a compressor. In contrast, in many prior designs, any heat exchanger prior to the compressor is configured to warm up the natural gas, thus teaching away from the concept disclosed herein. By using a compression chiller prior to the heat exchanger, in embodiments the mass flow of the compressor has been found to increase by around 18%, having an important impact on the efficiency and effectiveness of the micro -scale LNG plant compared to known designs.

[0023] The use of a vapour-compression chiller also allows use of cooling in several parts of the plant without increasing significantly the footprint. A chiller is a known technology with very compact equipment, when compared to other cooling methods. It is not required to have a large size chiller tank since the volume inside pipelines are small due to the compactness of the plant. Typical LNG plants do not use this kind of system because they have independent equipment that are not tightly integrated together, and furthermore space is not at a premium in a conventional LNG plant.

[0024] The vapour-compression chiller removes heat from a liquid coolant via a vapourcompression cycle. Such chillers have not been contemplated in the context of LNG plants previously.

[0025] The invention also provides a design that uses low inlet pressure to match with the boil-off gas from LNG trailers. Accordingly, the BOG from these trailers, which is of too low pressure to be processed by prior designs, can now be processed and does not need to vent.

[0026] The invention provides a novel approach using a vapour-compression chiller and associated chiller fluid to cool down natural gas before each compression stage, increasing mass throughput and preventing the need to vent BOG. A vapour-compression chiller and a chiller fluid is used to cool down the compressed gas.

[0027] Additionally, utilizing low inlet pressure matches seamlessly with BOG from LNG trailers, eliminating the necessity for venting from these trailers.

[0028] In some known designs of micro-scale LNG plant, multi-stream heat exchangers are used and combine the vapour return, vapour from storage tank and an expanded gas. In other designs, the volume of vapour stream from a separator vessel is high and is either consumed by a power generator or recycled into the system. The volume of vapour stream is too high to be consumed in a generator that will exclusively feed such a micro-scale LNG plant. Since it’s not realistic to consume all the stream in the generator, using this stream to recycle will require the heat exchanger to be multistream. Accordingly, in prior art designs, multistream heat exchangers are necessary. Such multi stream heat exchangers are custom made and are therefore expensive with a long lead time for production. In contrast, the design of micro-scale LNG plant proposed herein allows standard heat exchangers to be used, which are much cheaper than multistream heat exchangers, thereby making the design significantly more cost effective than known designs.

[0029] The use of the separator vessels in the manner disclosed herein changes the composition of the LNG, because when the separation happens on a separator vessel, the flash gas has a different composition than the liquid that remains on the vessel . The flash gas is mostly methane and nitrogen (typically 98%+) but the liquid is a mixture that can contain more heavier hydrocarbon components (such as ethane, propane etc.). The heavier stream can liquify at warmer temperatures, and therefore the mass production of the plant is increased, compared to prior art designs that do not use such separator vessels. In prior art designs, the flashgas from the storage tank or separator is warmed up, therefore the stream that is injected into those compressors is not cooled down. Accordingly, in such known designs the throughput of the compressor is limited. In contrast, in this disclosure, the return stream is not warmed up and therefore it enters the compressor at a lower temperature than in prior designs. Accordingly, due to the lower temperature, the density of the return stream is increased, and the mass throughput of the compressor is increased.

[0030] The invention provides an ultra-compact solution, that may be readily transportable and that may be vehicle mounted. This provides further flexibility over the known LNG plants, providing a moveable means of processing otherwise waste gases from existing oil and gas production.

[0031] As noted earlier, existing, industrial, LNG plants are very large, with substantial components and complex systems. Accordingly, traditional LNG plants are fixed in position proximal to a natural gas deposit and are entirely unsuitable for road transportation. Furthermore, existing industrial LNG plants are designed to operate with very high volumes of relatively high-pressure NG and are thus in general unsuited to the processing of BOG, which is thus flared or otherwise released causing damage to the environment. However, because the volume of BOG is relatively tiny, it is generally not commercially viable to adapt the plant to harvest and process this BOG; instead, BOG it is accepted as a by-product of the known process. According to the compact and self- contained nature of the invention, and its suitability for operating with low-pressure gas, the invention thus allows this waste gases to be effectively processed, without needing to make costly modifications to the LNG plant.

[0032] A further insight of the present invention is that by designing a road-transportable micro-scale liquefaction plant, for the processing of lower pressure BOG or associated gas, an LNG production process with compactness, simplicity and efficiency can be provided. Space and simplicity are not major design drivers in existing industrial LNG plants, where space is not at a premium. The invention thus provides a novel concept of a transportable micro-scale LNG liquefaction plant, that is suitable for the processing of low-pressure BOG or associated gas.

[0033] Commonly, flare gas comes from associated natural gas. This associated natural gas comes from oil wells along with the oil at enough pressure to pass through the pipeline to the oil storage tanks, that are at atmospheric pressure. Therefore, the pressure for associated natural gas streams are typically low. Such flaring is a relatively safe method of disposing of the gas that come from oil production, albeit wasteful and polluting. The invention provides a road-transportable method of converting this low pressure associated gas into LNG thus preventing waste and improving efficiency.

[0034] Furthermore, known mobile liquefaction plants have a requirement for high inlet pressure, so are not suitable for processing such associated natural gas from the flare pipeline without any extra equipment. Adding such additional equipment would cause such systems to no longer be sufficiently compact or lightweight to be road -transportable or mobile. According to the design herein, there is provided a means to process such low- pressure gas that is sufficiently compact to be road-transportable.

[0035] The present invention discloses a liquefaction cycle where the inlet natural gas pressure can be low, avoiding any extra equipment, and keeping the solution compact and mobile. Accordingly, the system is thus suitable both for the processing and liquefaction of relatively low-pressure BOG from existing plants, and for the processing and liquefaction of relatively low pressure associated gas from oil production. Accordingly, the invention improves the environmentally-friendliness and sustainability of oil and gas production, since it can assist to prevent the need to vent BOG in industrial LNG plants or the need to vent or flare gas in oil production.

[0036] Embodiments of the invention disclose a system comprising compressors with an optimized geometry keeping all distance pieces and strokes required for alternative compressors for LNG plants but with enough width to fit in typical transportation vehicles, enabling road-transportable micro-scale LNG plants with enhanced capacity. Thus, an inventive insight of the invention is that, by carefully considering the compressor geometry and by designing the system from the bottom up to conform to specific size and weight parameters, a road -transportable micro-scale LNG plant can be realised.

[0037] The design is tailored to efficiently handle low-pressure flare gas without the need for extra booster compressors, making it adaptable to various applications and avoiding venting / flaring during typical LNG liquefaction and oil extraction operations.

[0038] This moveable and transportable design can be used for biomethane applications for which the seasonal biomethane availability requires a solution that is mobile and can be moved a couple of times per year. Furthermore, the low-pressure solution proposed is suitable for the low pressure biomethane production.

[0039] The versatile design of the plant and its capacity to handle low pressure gas means the plant can liquify other gases such as ethane, biomethane and other gases.

[0040] As used herein, in relation to describing the plant the term “connected” such as when any outlet is connected to any inlet the term “connected” is to be understood as fluidly connected.

[0041] In some embodiments, no other components are present. That is, the method consists only of the components listed. In one aspect, the second heat exchanger is configured to further cool the natural gas by heat exchange with a second cooling fluid from a vapour-compression chiller.

[0042] Utilising a cooling fluid from a vapour-compression chiller for cooling in both the first and second heat exchanger allows for a more compact system.

[0043] In one aspect, the first cooling fluid and the second cooling fluid, for the first heat exchanger and the second heat exchanger respectively, are provided by the same chiller.

[0044] Conventional designs employ a plurality of different, separated cooling loops in their heat exchangers, which may for example feed to different cooling tanks positioned on a building. By connecting the heat exchangers to a vapour-compression chiller and connecting both to the same chiller, and ultra-compact and lower weight plant design can be realised, thus enabling a small and transportable solution. There is no motivation to provide a more compact design for existing industrial plants, since space is not at a premium.

[0045] Utilising a cooling fluid from the same vapour-compression chiller for cooling in both the first and second heat exchanger allows for a more compact system since only one component is required to provide two chilling fluids and vapour-compression chillers are highly compact. Accordingly, system size may be significantly reduced compared to prior designs.

[0046] In one aspect, the LNG plant comprises a flexible connection portion that is adapted to attach to an existing industrial plant or process, to enable the direct processing of otherwise waste gases.

[0047] The connection is a fluid connection and can be made with industrial plants connecting on the natural gas feed stream.

[0048] Providing a flexible connection portion enables the system to easily connect to an existing industrial plant or production process, directly at a position in which otherwise waste gases are located.

[0049] The self-contained nature of the invention permits it to be employed as an adjunct to an existing industrial plant, by simply connecting it to the plant or distribution facility at the position where the gases that are usually vented or flared are present.

[0050] In one aspect, the flexible connection portion is configured to releasably attach to an existing industrial plant or process.

[0051] Providing a releasable connection portion enable the micro-scale LNG plant to be readily employed and deployed in different locations where otherwise gas may be present.

[0052] In one aspect, the LNG plant comprises a multiple-stage compressor, configured to cool natural gas by heat exchange with a third cooling fluid from a vapour-compression chiller.

[0053] Providing the design in the form of a multi-stage compressor cooled by cooling fluid from a vapour-compression chiller results in a highly compact design, especially when compared to separate compressors, and one or more vapour-compression chillers, connected together.

[0054] In one aspect, the first cooling fluid, second cooling fluid and third cooling fluid are the same.

[0055] Providing the design in the form of a multi-stage compressor cooled by cooling fluid from a single vapour-compression chiller that provides both the cooling fluid to the first heat exchanger and the second cooling fluid to the second compressor, results in a highly compact design, especially when compared to a design where the cooling fluids come from different components.

[0056] In one aspect, the LNG plant is adapted to be mounted upon a vehicle.

[0057] This enables the plant to be transported, allowing flexibility in where it is deployed.

[0058] The vehicle may be road-legal, thereby permitting transportation of the LNG plant over roads shared with other road users. Road-legal means complaint with laws, rules and regulations governing the allowability of using a vehicle on public roads, in at least one country of the world.

[0059] In one aspect, the LNG plant is adapted to be releasably mounted upon a vehicle.

[0060] For example, the LNG plant may be mounted on a frame that can be lifted on an off a vehicle and releasably attached thereto. In embodiments, a power connection may be a provided allowing the LNG plant to receive power from the host vehicle, for example to power the vapour-compression chiller.

[0061] For example, the LNG plant may be housed within an ISO container, enabling it to be easily attached to and removed from vehicles, and also allowing it to be shipped, providing a high degree of flexibility in its deployment and transportation.

[0062] In one aspect, there is provided a vehicle comprising a micro-scale LNG plant according to any previous claim.

[0063] Providing a vehicle comprising the LNG plant enables the plant to be readily moved or repositioned, without the need to first attach or secure it to a vehicle. Accordingly, this provides a high degree of flexibility in its deployment and transportation.

[0064] According to a second aspect of the invention, there is provided a micro-scale LNG production method for liquefying a natural gas feed stream, the method comprising: a first cooling step for cooling the natural gas feed stream using a cooling fluid from a vapour-compression chiller; compressing the output from the first cooling step; air cooling the output from the compressing step; a second cooling the output from the air cooling step, using a cooling fluid from a vapour-compression chiller; third cooling the output of the second cooling step; pressure reducing the output of the third cooling step; separating the output from the pressure reducing step to provide a supply of liquid natural gas and a vapour phase; and returning and heating the vapour phase from the separating step and recombining the heated vapour phase with the natural gas feed stream.

[0065] In some methods, no other steps are present. That is, the method consists only of the steps listed.

[0066] In one aspect, the step of first cooling step of the natural gas feed stream and the second cooling step of the output from the compressing step, is performed by using cooling fluid from a same vapour-compression chiller.

[0067] Certain embodiments of the present invention will now be described by way of example only and with reference to the accompanying drawings in which:

[0068] Fig. 1 is a view illustrating a configuration of an apparatus for liquefying natural gas according to a first embodiment of the disclosure;

[0069] Fig. 2 is a view illustrating a series of steps for liquefying natural gas according to a first embodiment of the disclosure;

[0070] Fig- 3 is a view illustrating a configuration of an apparatus for liquefying natural gas according to a second embodiment of the disclosure; and

[0071] Fig. 4 is a view illustrating an optional configuration that may be present in either or both of dashed box A or dashed box B as shown in Fig. 1 and Fig.3.

[0072] The figures and embodiment of the invention will now be described in more detail. Fig- 1 shows a configuration of an apparatus for liquefying natural gas according to a first embodiment.

[0073] A first embodiment of a micro-scale liquid natural gas (LNG) plant 100 is suitable for liquefying a natural gas feed stream 102, meaning an input source of gas comprising natural gas. The input source may also comprise a vapour phase, which vapour phase is fed back from a separator 118 at later stage in the plant 100, as will be described later.

[0074] The components in the LNG plant 100 are fluidly connected together and may also be mechanically connected together.

[0075] The LNG plant 100 comprises a first heat exchanger 104 with natural gas inlet and a first cooled gas outlet wherein the first heat exchanger 104 is configured to cool the natural gas feed stream 102 by heat exchange with a first cooling fluid from a vapour-compression chiller 114. The vapour-compression chiller 114 provides chilled first cooling fluid to the first heat exchanger 104, and the first cooling fluid is returned to the vapour-compression chiller in a return loop so that it can be re-chilled after absorbing heat in the first heat exchanger 104.

[0076] The LNG plant 100 comprises a compressor 106 with a compressor inlet connected to the first heat exchanger outlet and a compressed gas outlet, wherein the compressor 106 is configured to compress the cooled natural gas that comes from the first heat exchanger 104. The compressor thus compresses the output of the first heat exchanger resulting in a compression and cooling of the natural gas feed stream.

[0077] The LNG plant 100 comprises an air cooler 108 with an air cooler inlet connected to the compressed gas outlet of the compressor 106 and an air cooler outlet, wherein the air cooler is configured to further cool the compressed natural gas.

[0078] The LNG plant 100 comprises a second heat exchanger 110 with an inlet connected to the air cooler outlet and a second cooled gas outlet, wherein the second heat exchanger is configured to further cool the natural gas by heat exchange with a second cooling fluid from a vapour-compression chiller 114. The vapour-compression chiller 114 provides chilled second cooling fluid to the second heat exchanger 110, and the second cooling fluid is returned to the vapour-compression chiller in a return loop so that it can be re-chilled after absorbing heat in the second heat exchanger 110.

[0079] The LNG plant 100 comprises a third heat exchanger 112 with an inlet connected to the second cooled gas outlet and a third cooled gas outlet, and is configured to further cool the cooled natural gas. Accordingly, the third heat exchanger 112 further cools the cooled natural gas coming from the second heat exchanger 110. The LNG plant 100 comprises a joule-thompson (JT) valve 116 with an inlet connected to the outlet of the third heat exchanger 112 and a JT cooled gas outlet, and is configured to cool the flow of cooled natural gas to create liquified LNG 122 by reducing its pressure. The function of such valves is well known in the art so it is not described herein in detail.

[0080] The LNG plant 100 comprises a separator 118 with an inlet connected to the JT cooled gas outlet of the joule-thompson (JT) valve 116 and has an LNG outlet and a vapour phase outlet, wherein the separator is configured to separate a liquified LNG 122 from a vapour phase.

[0081] The LNG plant 100 comprises a return flow path 120 with an inlet connected to the vapour phase outlet and an return path outlet connected to the natural gas inlet (of the first heat exchanger 104), wherein the return flow path is configured to pass as cooling medium via the third heat exchanger 112, wherein the return flow path is configured to transport the vapour phase from the separator 118 via the third heat exchanger 112 for heating by heat exchange a gas flow entering the inlet of the third heat exchanger, and to combine the heated vapour phase with the natural gas feed stream 102. Accordingly, any vapour phase from the separator 118 may fed back into earlier stages of the LNG plant 100 where it may be processed through the LNG plant 100.

[0082] As shown in Fig. 1, in this first embodiment, the first heat exchanger 104 and second heat exchanger 110 are connected to a same vapour-compression chiller 114 with a feed and return loop each. However, it will be appreciated that separate vapour-compression chillers may be provided and connected to each of heat exchangers 104 and 110. By using a same vapour-compression chiller, system complexity, size and weight may be reduced, resulting in a highly compact system.

[0083] Fig- 2 shows A series of steps for liquefying natural gas according to a first method, which may be employed through the LNG plant 100 of the first embodiment. As discussed above in relation to the LNG plant 100, the method is suitable for liquefying a natural gas feed stream 102, meaning an input source of gas comprising natural gas. This natural gas feed stream 102 is variously compressed and cooled through the system, amongst other steps.

[0084] In step 202, inlet gas is received by a heat exchanger. This inlet gas comprises the natural gas feed stream but may also incorporate other constituent parts.

[0085] In step 204, this inlet gas is cooled in a heat exchanger via a vapour-compression chiller. For example, the inlet gas may be cooled through a heat exchanger which is fluidly connected to a chiller with a feed and return loop, so that the inlet feed from the vapour-compression chiller cools the inlet gas in the heat exchanger.

[0086] In step 206, the output of step 204 is compressed in a compressor. In step 208, the output of step 206 is air cooled via an air cooler.

[0087] In step 210, the output of step 208 is further cooled in a heat exchanger via a vapourcompression chiller. For example, the outputs of step 208 may be cooled through a heat exchanger which is fluidly connected to a vapour-compression chiller with a feed and return loop, so that the inlet feed from the vapour-compression chiller cools the output of step 208 in the heat exchanger.

[0088] In step 212, the output of step 210 is further chilled through a heat exchanger.

[0089] In step 216, the output from step 212 is flow controlled. This may be, for example, through a joule-thompson (JT) valve. The flow control of step 216 cools the flow of the cooled natural gas to create liquified LNG 122 by reducing its pressure.

[0090] In step 218, a separator is used to separate the liquified LNG 122 from a vapour phase.

[0091] In step 220, the vapour phase is returned to the inlet of the heat exchanger of step 202, wherein it may be reprocessed by the method steps in the process set out above. The vapour phase before reaching the inlet optionally passes through a heat exchanger of step 212, wherein the vapour phase extracts heat from the inlet gas passing therethrough.

[0092] In some methods, in step 220, the vapour phase may not be heated by the heat exchanger of step 212 and may be returned to combine with the inlet gas without heating. Optionally, the vapour phase may be directly returned to combine with the inlet gas, directly meaning without any further deliberate processing such as heating or compressing.

[0093] In step 222, a supply of LNG is provided at the separator. This may comprise providing a supply of LNG at the separator, which LNG may be caused to flow by connecting a device to the separator and opening a valve. Providing LNG at the separator should not be interpreted to require that the LNG is actively flowing or supplied.

[0094] Fig- 3 is a view illustrating a configuration of an apparatus for liquefying natural gas according to a second embodiment of the disclosure.

[0095] The components and operation of the design shown in Fig. 3 is substantially the same as the design shown in Fig. 1, except for the return flow path 620. In some embodiments, the return flow path 120 returns to the combine with the natural gas feed stream 102 without passing through the third heat exchanger 112 as a cooling medium. In some embodiments, as is shown in Fig. 3, the return flow path 620 passes any vapour phase from the separator 118 directly back to the natural gas inlet to combine with the natural gas feed stream 102.

[0096] Fig- 4 is a view illustrating an optional configuration that may be present in either or both of dashed box A or dashed box B as shown in Fig. 1 and Fig. 3. As shown in Fig. 4, in one optional configuration of chiller and heat exchanger, there is, a natural gas path 300 comprising sections 300a and 300b, a chiller fluid loop path 400 comprising sections 400a-400g and a refrigerant loop 500 comprising sections 500a-500d. The natural gas flows along the natural gas path 300 through the heat exchanger 104, 110 for cooling.

[0097] The configuration will now be described as it functions in use.

[0098] A first path loop path in the chiller fluid loop path 400 comprises sections 400a, 400b, 400c and 400d. Cooling fluid in the form of chiller fluid circulated through the heat exchanger 104, 110 to cool the natural gas flowing along the natural gas path 300. The chiller fluid flows from the heat exchanger 104, 110 into a cold chiller fluid storage tank 401, through chiller fluid loop sections 400a and 400b. A chiller fluid secondary pump 402 is configured to pump the chiller fluid in a loop through both the chiller fluid storage tank 401 and the heat exchanger 104, 110, and may be (as shown) positioned in the chiller fluid flow path sections 400c-400d between the cold chiller fluid storage tank 401 and the heat exchanger 104, 110, or (not shown) in the chiller fluid flow path sections 400a-400b between the heat exchanger 104, 110 and the cold chiller fluid storage tank 401.

[0099] A second path in the chiller fluid loop path 400 comprising sections 400e, 400f, 400g, 400b, is configured to keep the chiller fluid in the cold chiller fluid storage tank 401 chilled. A chiller fluid main pump 403 is configured to pump fluid through a heat exchanger (evaporator) 404 and through the cold chiller fluid storage tank 401, and may be positioned along the chiller fluid path between sections 400g, 400b between the heat exchanger (evaporator) 404 and the cold chiller fluid storage tank 401, or (as shown) between sections 400e, 400f between the cold chiller fluid storage tank 401 and the heat exchanger (evaporator) 404.

[0100] A refrigerant loop 500 comprising sections 500a - 500d circulates a refrigerant fluid through the aforementioned heat exchanger (evaporator) 404, to cool the chiller fluid passing through it. In use, refrigerant fluid flows through the refrigerant loop 500 passing along section 500a and through a refrigerant compressor 501, then along section 500b and through a heat exchanger (condenser) 502, then along section 500c and through an expansion valve 503, and along section 500d and before flowing back through the heat exchanger (evaporator) 404 and again along section 500a through the refrigerant compressor 501. As shown in Figure 4, the components may be connected directly to each other as shown and described, although in embodiment other components may be present.

[0101] According to the design, the refrigerant of the refrigeration loop 500 exchanges heat with a chiller fluid (normally water plus glycol), and this intermediate chiller fluid exchanges heat with the natural gas flowing through the heat exchanger 104, 110. Positioned between the heat exchanger 104, 110 and the heat exchanger (evaporator) 404 there is a chiller fluid that is kept very cold. This provides a buffer of cold that is used to stabilize the refrigeration load that can change due to feed gas compositions changes, which are very relevant whenever it’s a single source of gas (like a well, or a flare stream). Accordingly, the system provides stabilised chilling to the natural gas flowing through the LNG plant.

[0102] In contrast, in known LNG plants it is usual to have a refrigeration cycle where the refrigerant exchanges heat with the natural gas. Such a system lacks the intermediate loop (in the form of chiller fluid path 400) and the cold chiller storage tank 401 of the disclosure and therefore lacks the stabilised chilling effect.

[0103] Embodiments of the disclosure introduce a significant technical advantage by utilizing an intermediate fluid loop and storage tank, acting as a thermal buffer between the vapourcompression refrigeration cycle and the natural gas feed stream. Conventional LNG liquefaction plants typically employ direct heat exchange between the refrigerant and natural gas without buffering. In these traditional designs, rapid fluctuations in natural gas composition - common when sourced from a single, directly connected pipeline, well or flare gas - can cause sudden and significant changes in refrigeration load, potentially leading to operational instability, compressor inefficiencies, or even temporary shutdowns.

[0104] By contrast, embodiments of the disclosure employ an intermediate fluid loop with a storage tank to absorb and stabilize transient variations in thermal load. This buffering ensures continuous stable operation, significantly reducing operational disruptions, compressor inefficiencies, or system shutdowns. Additionally, the selected vapour-compression chillers, when combined with intermediate fluid buffering, achieve approximately a 50% reduction in equipment footprint and a 40-60% reduction in weight compared to adsorption chillers of equivalent cooling capacity. Importantly, vapour-compression chillers can achieve significantly lower outlet temperatures, down to approximately -40°F (-40°C), compared to adsorption chillers that typically have a minimum achievable temperature of around 35°F (2°C). This lower achievable temperature enhances gas density at the compressor inlet, significantly improving compressor mass throughput and overall plant efficiency. These substantial advantages in compactness, weight, operational stability, and achievable temperatures strongly underline the inventive step of this solution, clearly distinguishing it from conventional technologies.

[0105] Moreover, the industry-standard practice explicitly teaches against cooling gas streams immediately before compression, due to concerns such as potential condensation causing compressor damage. Contrary to this accepted technical prejudice, the current invention demonstrates that pre-cooling significantly enhances compressor throughput — achieving approximately an 18% improvement — without the expected detrimental condensation effects. This surprising technical advantage substantially deviates from prior art expectations and thus clearly indicates inventive step.

[0106] Additionally, prior known micro-scale LNG plants typically rely on multistream heat exchangers due to the high volumes of recycled gas streams. The current invention, through careful arrangement of system components and separator integration, entirely eliminates the need for these complex and custom-made multistream heat exchangers, allowing standard heat exchangers to be used instead. The reduction in complexity, coupled with improved efficiency, compactness, and ease of transport, further underscores the non-obvious synergy of the combined features, thus clearly surpassing prior art capabilities.

[0107] Taken together, these technical decisions and their combined synergetic effects provide substantial improvements in operational efficiency, compactness, mobility, and LNG yield - none of which are individually or collectively suggested by existing prior art or obvious from standard engineering practices.

[0108] Variations to the embodiments and methods discussed herein may be envisaged.

[0109] Some variations will now be described, and it should be understood that these variations and enhancements may optionally be applied, in any combination, to any embodiment or method discussed above.

[0110] In embodiments of the invention, the LNG plant may comprise a flexible connection portion that is adapted to attach to an existing industrial plant or process, to enable the direct processing of otherwise waste gases from existing plants or processes. Since the plant as disclosed herein is highly mobile, a flexible connection portion allows it to be easily connected to existing infrastructure. Methods may comprise flexibly coupling an LNG plant to an existing plant of process, as a first step of the process.

[0111] The flexible connection portion may be designed to releasably attach to an existing industrial plant or process. For example, the flexible connection portion may comprise a quick release clamp or valve, allowing it to be quickly and securely fixed (and later released) from an existing plant or apparatus.

[0112] In embodiments, the LNG plant may comprise a multiple-stage compressor, configured to cool natural gas by heat exchange with a third cooling fluid from a vapour-compression chiller. The first cooling fluid, second cooling fluid and third cooling fluid may be the same. For example, the plant may comprise a single multi-stage compressor that comprises integrated heat exchangers, which comprises chilling loops from one or more vapour-compression chillers. The vapour-compression chiller(s) may be integrated into the multi-stage compressor. By tightly integrating the components in this manner, interconnections are simplified and shortened, and a highly compact LNG plant may be realised. In contrast, with conventional plants where conventional components are sourced and then interconnected, the size weight and complexity of the plant is significantly greater.

[0113] In embodiments, the LNG plant is adapted to be mounted upon a vehicle. In an embodiment, the LNG plant is mounted on a frame wherein it may be affixed to mounting points on a vehicle. In a further variation, the LNG plant is entirely contained within a standardised shipping container, which contains external mount points and dimensions allowing it to be shipped, craned and transported easily.

[0114] In embodiments, the LNG plant is adapted to be releasably mounted upon a vehicle. In an embodiment, the LNG plant is attached to a frame which can be lifted onto vehicle and clamped to corresponding mounting points that align with fixing points on the LNG plant frame. This allows the LNG plant to be easily moved between vehicles.

[0115] In embodiments, a vehicle is provided with the LNG plant incorporated. In a further variation, the LNG plant is fully integrated to the vehicle, such that, for example power may flow between the vehicle and the LNG plant. In an embodiment, the vehicle supplies power to an LNG plant integrated into the vehicle.

[0116] The examples provided herein are not limiting and merely provide illustrative examples of how the invention may be put into effect.

[0117] EXAMPLE CLAUSES:

[0118] Any of the example clauses in this section may be used with any other of the example clauses and / or any of the other examples or embodiments described herein.

[0119] 1. A micro-scale liquid natural gas (LNG) plant (100) for liquefying a natural gas feed stream (102), comprising: a first heat exchanger (104) with natural gas inlet and a first cooled gas outlet wherein the first heat exchanger is configured to cool the natural gas feed stream (102) by heat exchange with a first cooling fluid from a vapour-compression chiller (114); a compressor (106) with a compressor inlet connected to the first heat exchanger outlet and a compressed gas outlet, wherein the compressor is configured to compress the cooled natural gas; an air cooler (108) with an air cooler inlet connected to the compressed gas outlet of the compressor (106) and an air cooler outlet, wherein the air cooler is configured to further cool the compressed natural gas; a second heat exchanger (110) with an inlet connected to the air cooler outlet and a second cooled gas outlet, wherein the second heat exchanger is configured to further cool the natural gas by heat exchange with a second cooling fluid; a third heat exchanger (112) with an inlet connected to the second cooled gas outlet and a third cooled gas outlet, configured to further cool the cooled natural gas; a joule-thompson (JT) valve (116) with an inlet connected to the outlet of the third heat exchanger (112, 312) and a JT cooled gas outlet, configured to cool the flow of cooled natural gas to create liquified LNG (122) by reducing its pressure; a separator (118) with an inlet connected to the JT cooled gas outlet of the joule- thompson (JT) valve (116), an LNG outlet and a vapour phase outlet, wherein the separator is configured to separate a liquified LNG (122) from a vapour phase; and a return flow path (120) with an inlet connected to the vapour phase outlet and a return path outlet connected to the natural gas inlet, wherein the return flow path is configured to pass as cooling medium via the third heat exchanger (112), wherein the return flow path is configured to transport the vapour phase from the separator (118) via the third heat exchanger (112) for heating by heat exchange a gas flow entering the inlet of the third heat exchanger, and to combine a heated vapour phase with the natural gas feed stream (102).

[0120] 2. A micro-scale liquid natural gas (LNG) plant (100) for liquefying a natural gas feed stream (102), comprising: a first heat exchanger (104) with natural gas inlet and a first cooled gas outlet wherein the first heat exchanger is configured to cool the natural gas feed stream (102) by heat exchange with a first cooling fluid from a vapour-compression chiller (114); a compressor (106) with a compressor inlet connected to the first heat exchanger outlet and a compressed gas outlet, wherein the compressor is configured to compress the cooled natural gas; an air cooler (108) with an air cooler inlet connected to the compressed gas outlet of the compressor (106) and an air cooler outlet, wherein the air cooler is configured to further cool the compressed natural gas; a second heat exchanger (110) with an inlet connected to the air cooler outlet and a second cooled gas outlet, wherein the second heat exchanger is configured to further cool the natural gas by heat exchange with a second cooling fluid; a third heat exchanger (112) with an inlet connected to the second cooled gas outlet and a third cooled gas outlet, configured to further cool the cooled natural gas; a joule-thompson (JT) valve (116) with an inlet connected to the outlet of the third heat exchanger (112, 312) and a JT cooled gas outlet, configured to cool the flow of cooled natural gas to create liquified LNG (122) by reducing its pressure; a separator (118) with an inlet connected to the JT cooled gas outlet of the joule- thompson (JT) valve (116), an LNG outlet and a vapour phase outlet, wherein the separator is configured to separate a liquified LNG (122) from a vapour phase; and a return flow path (120) with an inlet connected to the vapour phase outlet and a return path outlet connected to the natural gas inlet, wherein the return flow path is configured to pass as cooling medium via the third heat exchanger (112), wherein the return flow path is configured to transport the vapour phase from the separator (118) via the third heat exchanger (112) for heating by heat exchange a gas flow entering the inlet of the third heat exchanger, and to combine a heated vapour phase with the natural gas feed stream (102), or the return flow path is connected directly to the natural gas inlet.

[0121] 3. A micro-scale LNG production method (200) for liquefying a natural gas feed stream (102), the method comprising: a first cooling step (204) for cooling the natural gas feed stream (102) using a cooling fluid from a vapour-compression chiller (114); compressing (206) the output from the first cooling step (204); air cooling (208) the output from the compressing step (206); a second cooling (210) the output from the air cooling step (208), using a cooling fluid from a vapour-compression chiller (114); third cooling (212) the output of the second cooling step (210); pressure reducing (216) the output of the third cooling step (212); separating (218) the output from the pressure reducing step (216) to provide a supply of liquid natural gas (122) and a vapour phase; and returning (220) and heating the vapour phase from the separating step (218) and recombining a heated vapour phase with the natural gas feed stream (102).

[0122] 4. A micro-scale LNG production method (200) for liquefying a natural gas feed stream (102), the method comprising: a first cooling step (204) for cooling the natural gas feed stream (102) using a cooling fluid from a vapour-compression chiller (114); compressing (206) the output from the first cooling step (204); air cooling (208) the output from the compressing step (206); a second cooling (210) the output from the air cooling step (208), using a cooling fluid from a vapour-compression chiller (114); third cooling (212) the output of the second cooling step (210); pressure reducing (216) the output of the third cooling step (212); separating (218) the output from the pressure reducing step (216) to provide a supply of liquid natural gas (122) and a vapour phase; and returning (220) the vapour phase from the separating step (218) and recombining the vapour phase with the natural gas feed stream (102).

[0123] 5. A micro-scale LNG production method (200) for liquefying a natural gas feed stream (102), the method comprising: a first cooling step (204) for cooling the natural gas feed stream (102) using a cooling fluid from a vapour-compression chiller (114); compressing (206) the output from the first cooling step (204); air cooling (208) the output from the compressing step (206); a second cooling (210) the output from the air cooling step (208), using a cooling fluid from a vapour-compression chiller (114); third cooling (212) the output of the second cooling step (210); pressure reducing (216) the output of the third cooling step (212); separating (218) the output from the pressure reducing step (216) to provide a supply of liquid natural gas (122) and a vapour phase; and returning (220) and optionally heating the vapour phase from the separating step (218) and recombining the vapour phase with the natural gas feed stream (102).

[0124] 6. A micro-scale LNG production method (200) for liquefying a natural gas feed stream (102), the method comprising: a first cooling step (204) for cooling the natural gas feed stream (102) using a cooling fluid from a vapour-compression chiller (114); compressing (206) the output from the first cooling step (204); air cooling (208) the output from the compressing step (206); a second cooling (210) the output from the air cooling step (208), using a cooling fluid from a vapour-compression chiller (114); third cooling (212) the output of the second cooling step (210); pressure reducing (216) the output of the third cooling step (212); separating (218) the output from the pressure reducing step (216) to provide a supply of liquid natural gas (122) and a vapour phase; and returning (220) the vapour phase from the separating step (218) and directly recombining the vapour phase with the natural gas feed stream (102).

[0125] 7. A micro-scale liquid natural gas (LNG) plant (100) for liquefying a natural gas feed stream (102) according to clause 1, wherein the vapour-compression chiller (114) comprises: a chiller fluid loop path (400) configured to configured to cool the natural gas feed stream (102) by heat exchange; and a refrigerant loop (500) configured to supply cooled refrigerant to cool a chiller fluid in the chiller fluid path (400), wherein the chiller fluid loop path (400) comprises a cold chiller fluid storage tank (401) configured to stablise the cooling of the natural gas feed stream.

[0126] 8. A micro-scale liquid natural gas (LNG) plant (100) for liquefying a natural gas feed stream (102) according to clause 7, wherein: the chiller fluid loop path (400) comprises a first path (400a, 400b, 400c, 400d) comprising a cold chiller fluid storage tank (401), a chiller fluid secondary pump (402), and the heat exchanger (104, 110), wherein the chiller fluid secondary pump (402) is configured to circulate a chiller fluid between the heat exchanger (104, 110) and the cold chiller fluid storage tank (401); the chiller fluid loop path 400 comprises a second path (400b, 400e, 400f, 400g) comprising a heat exchanger (evaporator) (404), the cold chiller fluid storage tank (401) and a chiller fluid main pump (403), wherein the chiller fluid main pump (403) is configured to circulate the chiller fluid through the heat exchanger (evaporator) (404) and the cold chiller fluid storage tank (401); the refrigerant loop (500) comprises a refrigerant compressor (501), an output of which is connected to a heat exchanger (condenser) 502, an output of which is connected to an expansion valve 503, an output of which is connected to the heat exchanger (evaporator) (404), an output of which is connected to the refrigerant compressor (501), wherein the compressor (501) is configured to circulate a refrigerant through the refrigerant loop (500) that passes through the heat exchanger (evaporator) (404) to cool the chiller fluid flowing through the heat exchanger (evaporator) (404).

Claims

CLAIMS1. A micro-scale liquid natural gas (LNG) plant (100) for liquefying a natural gas feed stream (102), comprising: a first heat exchanger (104) with natural gas inlet and a first cooled gas outlet wherein the first heat exchanger is configured to cool the natural gas feed stream (102) by heat exchange with a first cooling fluid from a vapour-compression chiller (114); a compressor (106) with a compressor inlet connected to the first heat exchanger outlet and a compressed gas outlet, wherein the compressor is configured to compress the cooled natural gas; an air cooler (108) with an air cooler inlet connected to the compressed gas outlet of the compressor (106) and an air cooler outlet, wherein the air cooler is configured to further cool the compressed natural gas; a second heat exchanger (110) with an inlet connected to the air cooler outlet and a second cooled gas outlet, wherein the second heat exchanger is configured to further cool the natural gas by heat exchange with a second cooling fluid; a third heat exchanger (112) with an inlet connected to the second cooled gas outlet and a third cooled gas outlet, configured to further cool the cooled natural gas; a joule-thompson (JT) valve (116) with an inlet connected to the outlet of the third heat exchanger (112, 312) and a JT cooled gas outlet, configured to cool the flow of cooled natural gas to create liquified LNG (122) by reducing its pressure; a separator (118) with an inlet connected to the JT cooled gas outlet of the joule- thompson (JT) valve (116), an LNG outlet and a vapour phase outlet, wherein the separator is configured to separate a liquified LNG (122) from a vapour phase; and a return flow path (120 / 620) with an inlet connected to the vapour phase outlet and a return path outlet connected to the natural gas inlet.

2. A micro-scale liquid natural gas (LNG) plant (100) according to claim 1, wherein the return flow path is configured to transport the vapour phase from the separator (118) via the third heat exchanger (112) for heating by heat exchange a gas flow entering the inlet of the third heat exchanger, and to combine a heated vapour phase with the natural gas feed stream (102).

3. A micro-scale LNG plant (100) according to claim 1 or claim 2, wherein the second heat exchanger (110) is configured to further cool the natural gas by heat exchange with a second cooling fluid from a vapour-compression chiller (114).

4. A micro-scale LNG plant (100) according to any of claims 1 to 3, wherein the first cooling fluid and the second cooling fluid, for the first heat exchanger (104) and the second heat exchanger (110) respectively, are provided by the same vapour-compression chiller (114).

5. A micro-scale liquid natural gas (LNG) plant (100) according to any of claims 1 to 4, wherein the vapour-compression chiller (114) comprises: a chiller fluid loop path (400) configured to configured to cool the natural gas feed stream (102) by heat exchange; and a refrigerant loop (500) configured to supply cooled refrigerant to cool a chiller fluid in the chiller fluid path (400), wherein the chiller fluid loop path (400) comprises a cold chiller fluid storage tank (401) configured to stablise the cooling of the natural gas feed stream.

6. A micro-scale liquid natural gas (LNG) plant (100) according to claim 5, wherein: the chiller fluid loop path (400) comprises a first path (400a, 400b, 400c, 400d) comprising a cold chiller fluid storage tank (401), a chiller fluid secondary pump (402), and the heat exchanger (104, 110), wherein the chiller fluid secondary pump (402) is configured to circulate a chiller fluid between the heat exchanger (104, 110) and the cold chiller fluid storage tank (401); the chiller fluid loop path 400 comprises a second path (400b, 400e, 400f, 400g) comprising a heat exchanger (evaporator) (404), the cold chiller fluid storage tank (401) and a chiller fluid main pump (403), wherein the chiller fluid main pump (403) is configured to circulate the chiller fluid through the heat exchanger (evaporator) (404) and the cold chiller fluid storage tank (401); the refrigerant loop (500) comprises a refrigerant compressor (501), an output of which is connected to a heat exchanger (condenser) 502, an output of which is connected to an expansion valve 503, an output of which is connected to the heat exchanger (evaporator) (404), an output of which is connected to the refrigerant compressor (501), wherein the compressor (501) is configured to circulate a refrigerant through the refrigerant loop (500) that passesthrough the heat exchanger (evaporator) (404) to cool the chiller fluid flowing through the heat exchanger (evaporator) (404).

7. A micro-scale LNG plant (100) according to any previous claim, wherein the microscale LNG plant comprises a flexible connection portion that is adapted to attach to an existing industrial plant or process, to enable the direct processing of otherwise waste gases.

8. A micro-scale LNG plant (100) according to claim 7, wherein the flexible connection portion is configured to releasably attach to an existing industrial plant or process.

9. A micro-scale LNG plant (100) according to any previous claim, comprising a multiplestage compressor, configured to cool natural gas by heat exchange with a third cooling fluid from a vapour-compression chiller (114).

10. A micro-scale LNG plant (100) according to claim 9, wherein the first cooling fluid, second cooling fluid and third cooling fluid are the same.

11. A micro-scale LNG plant (100) according to any preceding claim, wherein the microscale LNG plant is adapted to be mounted upon a vehicle.

12. A micro-scale LNG plant (100) according to any preceding claim, wherein the microscale LNG plant is adapted to be releasably mounted upon a vehicle.

13. A vehicle comprising a micro-scale LNG plant (100) according to any previous claim.

14. A micro-scale LNG production method (200) for liquefying a natural gas feed stream (102), the method comprising: a first cooling step (204) for cooling the natural gas feed stream (102) using a cooling fluid from a vapour-compression chiller (114); compressing (206) the output from the first cooling step (204); air cooling (208) the output from the compressing step (206); a second cooling (210) the output from the air cooling step (208), using a cooling fluid from a vapour-compression chiller (114); third cooling (212) the output of the second cooling step (210);pressure reducing (216) the output of the third cooling step (212); separating (218) the output from the pressure reducing step (216) to provide a supply of liquid natural gas (122) and a vapour phase; and returning (220) and vapour phase from the separating step (218) and recombining the vapour phase with the natural gas feed stream (102).

15. The micro-scale LNG production method according to claim 14, wherein the step of returning (220) and vapour phase from the separating step (218) and recombining the vapour phase with the natural gas feed stream (102) comprises returning (220) and heating the vapour phase from the separating step (218) and recombining a heated vapour phase with the natural gas feed stream (102).

16. A micro-scale LNG production method (200) according to claim 14 or claim 15, wherein the first cooling step (204) of cooling the natural gas feed stream (102) and the second cooling step (208) of cooling the output from the compressing step (206), is performed by using a cooling fluid from the same vapour-compression chiller (114).

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