Cryocooler Suitable for Gas Liquefaction Applications, Gas Liquefaction System and Method Comprising the Same

Abstract

The present invention relates to a cryocooler suitable for gas liquefaction applications, that comprises a coldhead (1) with one or more refrigeration stages (2, 3); further comprising: a refrigerator compressor (4) for distributing compressed gas-phase cryogen inside the coldhead (1); a heat exchanging coil (9) arranged at least partially around the external region of the coldhead (1); at least one extraction orifice (8) communicating a gas circulation circuit (5) inside the coldhead (1) with the heat exchanging coil (9); acting said extraction orifice/s (8) as pass-through port/s which allow the gas inside the coldhead (1) to flow through the inside of the heat exchanger coil (9) for exchanging heat with the exterior thereof, and wherein the heat exchanging coil (9) is adapted to connect and redirect the gas to one return port (8) connected to the gas circulation circuit (5). Another object of the invention relates to a cryogen-gas liquefaction system (11) and a method for liquefaction of gases that comprises said system (11).

Claims

1. A cryocooler suitable for gas liquefaction applications, the cryocooler comprising: a coldhead with one or more refrigeration stages; a refrigerator compressor for distributing compressed cryogen gas inside the coldhead, acting as refrigeration means for lowering the temperature of the refrigeration stages, wherein said cryogen gas is supplied to and returned from the coldhead through a gas circulation circuit comprising input and output gas lines, which connect the coldhead with the refrigerator compressor; and at least one extraction orifice communicating the gas circulation circuit inside the coldhead with the external region of the refrigeration stages, acting as a pass-through port which allows the gas inside the coldhead to flow to the exterior thereof; wherein the cryocooler further comprises a heat exchanging coil arranged at least partially around the external region of the coldhead, and wherein said heat exchanging coil is connected at one end to the gas circulation circuit through the extraction orifice, and at other end to one return port connected to said gas circulation circuit.

2. The cryocooler of claim 1, wherein the return port is arranged at the coldhead.

3. The cryocooler of claim 1, wherein the return port is arranged at the output gas line between the coldhead and the refrigerator compressor.

4. The cryocooler of claim 1, further comprising a thermally insulating layer arranged between the heat exchanging coil and the external region of the coldhead.

5. The cryocooler of claim 1, wherein the heat exchanging coil is connected to the extraction orifice and/or to the return port through one or more of the following elements: one or more cryogenic flow valves, a mass flow controller a control volume, a capillary tube, an insulating seal and/or or one or more joints.

6. The cryocooler of claim 1, further comprising a PLC connected to the refrigerator compressor for controlling the pressure within the coldhead.

7. The cryocooler of claim 1, wherein the cryogen gas within the refrigerator compressor is helium.

8. A cryogen-gas liquefaction system comprising: the cryocooler of claim 1; a storage container comprising a liquid storage portion and a neck portion extending therefrom, the liquid storage portion being adapted to contain a liquefied gas bath at the bottom of the storage container and comprising a liquefaction region above said bath; a gas pressure control mechanism for controlling the cryogen gas pressure within the liquefaction region of the storage container; and a PLC connected to the gas refrigerator compressor, for controlling the pressure within the coldhead; wherein the coldhead of the cryocooler is arranged at the neck portion of the storage container, so that the gas circulating through the inside of the heat exchanging coil can exchange heat with the gas stored at said neck portion, and wherein the heat exchanging coil is adapted to connect and redirect the gas from the gas circulation circuit through the extraction orifice to one return port connected to said gas circulation circuit.

9. The cryogen-gas liquefaction system of claim 8, further comprising a gas source module containing an amount of gas-phase cryogen for its introduction into the liquefaction region of the storage container.

10. The cryogen-gas liquefaction system of claim 9, wherein the gas source module contains high purity helium gas, recovered and/or purified from a helium-using equipment.

11. The cryogen-gas liquefaction system of claim 8, further comprising a level meter for measuring the volume of liquid within the storage container, and/or a transfer port extending from the liquid storage portion to an external surface of the storage container.

12. The cryogen-gas liquefaction system of claim 8, wherein the cryogen gas within the storage container and/or within the compressor is helium, nitrogen, oxygen, hydrogen or neon.

13. A cryogen-gas liquefaction method for use in the cryogen-gas liquefaction system of claim 8, wherein the cryogen-gas liquefaction method comprises: (i) providing at least: a storage container having a liquefaction region and defined by a storage portion and a neck portion extending therefrom; a pressure control mechanism for controlling the pressure within the liquefaction region of the storage container; and a cryocooler coldhead at least partially disposed within the neck portion, the coldhead being adapted to condense a cryogen contained within the liquefaction region from a gas-phase to a liquid phase; wherein the cryocooler coldhead comprises: a refrigerator compressor for distributing cold compressed gas-phase cryogen inside the coldhead, wherein said cryogen is supplied to and returned from the coldhead and acts as refrigeration means for lowering the temperature of one or more refrigeration stages of the coldhead; a heat exchanging coil arranged around the external region of the refrigeration stages of the coldhead; one or more extraction orifices communicating a gas circulation circuit inside the coldhead with the heat exchanger coil, acting as pass-through ports which allow the gas inside the coldhead to flow through the inside of the heat exchanging coil for exchanging heat with the gas in the liquefaction region of the storage container; and wherein the heat exchanging coil is adapted to connect and redirect the gas to one return port connected to said gas circulation circuit; and a PLC connected to the refrigerator compressor for controlling the pressure within the coldhead; (ii) measuring and controlling the vapor pressure within said liquefaction region of the storage container with the pressure control mechanism and the PLC; and (iii) maintaining the vapor pressure within said liquefaction region of the storage container by means of the pressure control mechanism.

14. The cryogen-gas liquefaction method of claim 13, wherein step (i) further comprises measuring the internal pressure within the coldhead and step (ii) further comprises maintaining said pressure the coldhead with the PLC.

15. The cryogen-gas liquefaction method of claim 13, further comprising the step of injecting gas into the liquefaction region of the storage container with a gas source module, in collaboration with the gas pressure controller for maintaining the vapor pressure during step (iii).

Description

DESCRIPTION OF THE DRAWINGS

[0078] The features and advantages of this invention will be apparent from the following detailed description, when read in conjunction with the accompanying drawings, in which:

[0079] FIG. 1 shows a schematic diagram of a preferred embodiment of the cryocooler and the gas liquefaction system according to the invention.

[0080] FIG. 2 shows a schematic diagram of a preferred embodiment of the cryocooler, wherein the heat exchanging coil is arranged around all the refrigeration stages of the coldhead, with the return port at the gas output line, according to the invention.

[0081] FIG. 3 shows a schematic diagram of a preferred embodiment of the cryocooler, wherein the heat exchanging coil is arranged around the second refrigeration stage of the coldhead, with the return port at the end of the first refrigeration stage, according to the invention.

[0082] FIGS. 4-6 show a schematic diagram of a preferred embodiment of the cryocooler, wherein the heat exchanging coil is arranged around all the refrigeration stages of the coldhead, with the return port at the gas output line and wherein the thermally insulating layer is arranged around the coldest refrigeration stage (FIG. 4), around the warmest refrigeration stage (FIG. 5) or around all the refrigeration stages (FIG. 6), according to the invention.

[0083] FIG. 7 shows a schematic diagram of a preferred embodiment of the cryocooler, wherein the heat exchanging coil is arranged around the second refrigeration stage of the coldhead, with the return port at the end of the first refrigeration stage and wherein the thermally insulating layer is arranged around the second refrigeration stage

NUMERICAL REFERENCES USED IN THE DRAWINGS

[0084] In order to provide a better understanding of the technical features of the invention, FIGS. 1-7 are accompanied of a series of numeral references which, with illustrative and non limiting character, are hereby represented:

TABLE-US-00001 (1) Coldhead (2, 3) Refrigeration stages (2, 3) Insulating layer (4) Refrigerator compressor (5) Gas circulation circuit (6) Gas input line (7) Gas output line (8) Extraction orifice (8) Return port (9) Heat exchanging coil (10) Cryogenic valves (10) Mass flow controller (10) Control volume (11) Liquefaction system (12) Storage container (12) Level meter (12) Transfer port (13) Liquid storage portion (14) Neck portion (15) Outer vessel (16) Shell (17) Liquefied gas bath (18) Liquefaction region (19) Pressure control mechanism (20) Pressure sensor (21) Programmable Logic Controller (PLC) (22) Gas source module

DETAILED DESCRIPTION OF THE INVENTION

[0085] In the following description, for purposes of explanation and not limitation, details are set forth in order to provide a thorough understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced in other embodiments that depart from these details and descriptions without departing from the spirit and scope of the invention. Certain embodiments will be described below with reference to the drawings wherein illustrative features are denoted by reference numerals.

[0086] In a general embodiment according to FIGS. 1-7, the cryocooler according to the invention comprises: [0087] a coldhead (1) equipped with one or more refrigeration stages (2, 3); preferably comprising a first stage (2) and a second stage (3); [0088] a refrigerator compressor (4) for distributing compressed gas-phase cryogen inside the coldhead (1), wherein said cryogen gas is supplied to and returned from the coldhead (1) and acts as refrigeration means for lowering the temperature of the one or more refrigeration stages (2, 3) of said coldhead (1); [0089] a refrigerator compressor (4) for distributing compressed cryogen gas inside the coldhead (1) and acting as refrigeration means for lowering the temperature of the refrigeration stages (2, 3) of the coldhead, wherein said cryogen gas is supplied to and returned from the coldhead (1) through a gas circulation circuit (5) comprising gas input (6) and output (7) lines connecting the coldhead (1) to the refrigerator compressor (4); [0090] at least one extraction orifice (8) communicating the gas circulation circuit (5) inside the coldhead (1) with the external region of the refrigeration stages (2, 3), acting as a pass-through port which allows the gas inside the coldhead (1) to flow to the exterior thereof. [0091] a heat exchanging coil (9) arranged at least partially around the external region of the coldhead (1), wherein said heat exchanging coil (9) is connected at one end with the gas circulation circuit (5) through the at least one extraction orifice (8), and at other end to a return port (8) connected to the gas circulation circuit (5).

[0092] In a particular embodiment, according to FIGS. 1 and 2, the return port (8) is at the output gas line (7) of the gas circulation circuit (5) and the heat exchanging coil (9) is arranged around the external region of the coldhead (1) along the whole extension of the coldhead (1).

[0093] In the embodiment of FIGS. 1 and 2, the cryocooler of the invention comprises means for deviating a small fraction of the internal cooling gas flow inside the coldhead (1) through the extraction orifice (8), perforated preferably on the expansion volume of the second stage (3). Preferably, the extraction orifice (8) has a typical diameter of 0.5-5.0 mm. The fraction of the gas flowing out of the gas circulation circuit (5) is conducted through a heat exchanging coil (9) which surrounds the coldhead (1) outer sleeve and connects the coldest second stage (3) at the bottom of the coldhead (1) (coldest point) with the top region of the coldhead (1) at the first stage (2) (warmest point).

[0094] In yet another embodiment, according to FIG. 3, the return port (8) is located at the coldhead (1) itself and the heat exchanging coil (9) is arranged around the second refrigeration stage (3) but not around the first refrigeration stage (2) of the coldhead (1). Particularly, said extraction orifice (8) is at the end of the second refrigeration stage (3) (coolest point) and said return port (8) is at the end of the first refrigeration stage (2) of the coldhead (1). As the gas inside the second refrigeration stage (3) is the coolest in this embodiment, the regenerator in the second refrigeration stage (3) is the farthest from being ideal because its volumetric heat capacity is not very high compared with that of helium. Hence a relative larger extra cooling power from such gas is extracted from the gas inside through the heat exchanging coil (9), allowing the thermal exchange of said cool gas with the exterior thereof. Also, it is much more efficient for the main purpose of the invention (i.e., improving the liquefaction rate obtained through the cryocooler coldhead (1)), to extract the cold from the inside of the second refrigeration stage (3) (through the heat exchanging coil (9)) than to simply allow a thermal exchange between the external region of the coldhead (1) and the gas in the exterior thereof (without the presence of the heat exchanging coil (9)).

[0095] Thus, as described in preceding sections, the main advantage of the proposed cryocooler is that it takes advantage of the already cooled gas circulating inside the coldhead (1), causing a part of said cold gas to travel through the interior of the heat exchanging coil (9), located in an external region of the coldhead (1) winding around the refrigeration stages (2, 3) (FIG. 2) or around the second refrigeration stage (3) (FIG. 3). Also, the aforementioned route ends in a return port (8) at the gas output line (7) returning to the compressor (4) (FIG. 2) or ends in a return port (8) at the coldhead (1) itself (FIG. 3), thus maintaining closed the gas circuit of the cryocooler. In this way, the helium (or other) cold gas that circulates inside the heat exchanging coil (9) contributes to refrigerate the outside region of the coldhead (1) but without exchanging matter (helium or other) with the exterior thereof. In this manner, it is possible to extract near 100% of the extra cooling power of the second stage regenerator.

[0096] In yet another embodiment, a thermally insulating layer (2, 3) (FIGS. 4-7) is disposed around the coldhead (1), between the heat exchanging coil (9) and the coldhead (1). In this manner, the thermal exchange between the heat exchanging coil (9) and the gas that is to be liquefied is optimized, whereas the coldhead (1) is working mainly in order to cool the gas inside said coldhead (1). In this manner, the rate of liquefaction of the gas can be improved.

[0097] In the embodiments where the heat exchanging coil (9) is arranged around the second refrigeration stage (3) of the coldhead (1), with the return port (8) at the end of the first refrigeration stage (2) (FIG. 3), the thermally insulating layer (3) is preferably disposed around the second refrigeration stage (3) (FIG. 7). As the excess cooling power of the regenerator inside the second refrigeration stage (3) is much larger than the excess cooling power of the regenerator inside the first refrigeration stage (2), isolating said second refrigeration stage (3) makes a large difference (in exploiting the cooling power for only cooling the gas inside).

[0098] Alternatively, the thermally insulating layer (2) is preferably disposed around the first refrigeration stage (2) (FIG. 5).

[0099] As shown in FIGS. 4-7, with the using of a thermally insulating layer (2, 3), it is possible to have a better control of the application of the cooling power of the coldhead (1) and, particularly, of the cooling power of each one of the refrigeration stages (2, 3) by selecting the portion of the external surface of the coldhead (1) that is thermally isolated. In this manner, it is possible to exploit the cooling power for cooling the gas inside the coldhead (1) or for extracting a part of the cooling power to the outside of the coldhead (1) through its walls. Note that the way the present invention takes advantage of the cooling power is a completely different approach in order to exploit the cooling power of a coldhead (1) if compared to typical cryocoolers that work in vacuum, because the last cannot exploit or configure coldheads for this purpose, as there is no such thermal exchange with the exterior thereof, except for the typical thermal exchange at the coldest end of the coldheads, wherein a thermally conducting block is in direct contact with the recipient or tube containing the gas to be liquefied.

[0100] In the embodiment corresponding to FIG. 2, the extraction of gas from the cold head (1) for its circulation through the heat exchanging coil (9) is preferably carried out by means of a cryogenic flow valve (10), connected to the extraction orifice (8), which communicates the gas circulation circuit (5) inside the coldhead (1) with the external region of the cooling stages (2, 3). The cryogenic flow valve (10) is preferably placed at one end of the heat exchanging coil (9), immediately after the perforated orifice/s (8). More preferably, the cryogenic flow valve (10) is a mechanical check valve.

[0101] In this manner, it is possible to regulate the amount of gas that is to be extracted from the coldhead (1) and flows through the heat exchanger coil (9), returning eventually to the compressor (4). Therefore, the extraction orifice (8) and the cryogenic flow valve (10) act as a passage port, which allows the gas inside the cold head (1) to flow out to the heat exchanging coil (9) and exchange heat with the region outside the coldhead (1).

[0102] The pass-through extraction orifice (8) can be performed over one or more of the refrigeration stages (2, 3) of the coldhead (1) by means of screws, rivets or analogous fixing means and they can also comprise insulating seals or joints to prevent undesired gas flow there through. The connection between the heat exchanging coil (9) and the output gas line (7) of the gas circulation circuit (5) can also comprise a mass flow controller (10) as well as other elements such as insulating seals or joints.

[0103] Another object of the invention, also according to FIG. 1, refers to a liquefaction system (11) that comprises a cryocooler according to any of the embodiments described in the preceding paragraphs. The liquefaction system (11) further comprises an isolated storage container (12) or Dewar comprising a liquid storage portion (13) and a neck portion (14) extending therefrom, and connected to an outer vessel (15) which is typically at ambient temperature. The storage container (12) is insulated by a shell (16) with the volume within the shell (16) being external to the storage portion (13) and substantially evacuated of air. Also, in order to measure the volume of liquid within the storage container (12), the system can optionally include a level meter (12).

[0104] Alternatively to the embodiment of FIG. 1, the mass flow controller (10) can be located in the neck portion (14) of the Dewar (12), in the gas circulation circuit (5) or even, in yet another embodiment of the invention, the cryogenic flow valve (10) can be an electronic valve comprising a mass flow controller (10) or an equivalent element as well.

[0105] In the embodiment according to FIG. 3, there are two cryogenic valves (10) connected to the heat exchange coil (9), one immediately after the extraction orifice (8) and another cryogenic valve (10) immediately before the return port (8) at the first refrigeration stage (2). Optionally, between both cryogenic valves (10) and connected to them, there is also disposed a control volume (10). Said valves (10) and control volume (10) are configured so that the flow inside the heat exchanging coil (9) goes only in one direction, from the extraction orifice (8) to the return port (8) and not backwards, and the flow rate is adjusted to an optimum value.

[0106] The storage portion (13) is adapted to contain a liquefied gas bath (17) at the bottom of the storage container (12) and a liquefaction region (18) above said bath (17), wherein the gas to be liquefied exchanges heat with the liquefaction system. In order to do so, the neck portion (14) is adapted to at least partially receive the cryocooler coldhead (1). As previously disclosed, the coldhead (1) may comprise one or more refrigeration stages (2, 3), each preferably having a distinct cross section. In different embodiments of the invention, the cryocooler can be either of the Gifford-McMahon (GM) or pulse-tube (PT) type.

[0107] The neck portion (14) of the storage container (12) may be optionally adapted to geometrically conform to the one or more refrigeration stages (2, 3) of the cryocooler coldhead (1), preferably in a stepwise manner. The storage container (12) further comprises a transfer port (12) extending from the liquid storage portion (13) to an external surface of the storage container (12).

[0108] A forward pressure control mechanism (19) that integrates a mass flow meter and a proportional valve (FPC) is further provided for controlling gas flow and thereby pressure within the liquefaction region (18) of the storage container (12). The forward pressure control mechanism (19) generally includes a pressure regulator or other means for regulating pressure of gas entering the liquefaction region (18) of the storage container (12). The pressure control mechanism (19) also makes use of an external pressure sensor (20), or integrates it, for detecting pressure within the liquefaction region (18) of the storage container (12). In this regard, the pressure control mechanism (19) is further connected to a computer Programmable Logic Controller (PLC) (21) (or equivalently, any suitable computing or processing means) for dynamically modulating input gas flow, and hence, pressure within the liquefaction region (18) of the storage container (12) for yielding optimum efficiency. Preferably, the PLC (21) is also connected to the refrigerator compressor (4) for controlling the pressure within the coldhead (1).

[0109] It should be recognized that although depicted as a distinct unit in several descriptive embodiments herein, the components of the pressure control mechanism (19) can be individually located near other system components and adapted to effectuate a similar liquefaction process. Accordingly, the pressure control mechanism (19) is intended to include a collection of components in direct attachment or otherwise collectively provided within the system for dynamically controlling input gas flow, and thus pressure within the liquefaction region (18) of the storage container (12).

[0110] As referred in preceding sections, in the present liquefaction system (11) the coldhead (1) comprising one or more stages (2, 3) operates in the neck portion (14) of the storage container (12) or Dewar. A first stage (2) is the warmest and operates in the neck portion (14) farther from the liquefaction region (18) than the other stages (3). Thus, the gas enters at the warm end of the neck portion (14) and is pre-cooled by the walls of the first stage (2) of the coldhead (1), by the coldest end of the first stage (2), further pre-cooled by the walls of the colder stages (3), and is then condensed at the coldest end of the coldest stage (3) of the coldhead (1). For a one-stage coldhead (1) embodiment, the condensation occurs at the coldest end of the first stage (2). Once condensed, the liquefied gas falls by gravity from the liquefaction region (18) down to the bath (17) at the bottom of the storage portion (13) in the interior of the storage container (12). The cooling power that each stage (2, 3) of a closed-cycle cryocooler generates, is determined mainly by its temperature, but also depends to second order on the temperature of the previous stages (2, 3). This information is generally supplied by the cryocooler manufacturer as a two-dimensional load map that plots the dependence of the power of the first (2) and second (3) stages versus the temperatures of the first and second stages (2, 3).

[0111] In addition to generating cooling power at the first (2) and second (3) stages, the coldhead (1) also generates cooling power along its entire length, in particular along the surface of the cylindrical so called cold finger between room temperature and the coldest end of the first stage (2), and along the length of the cylindrical cold finger between the stages (2, 3).

[0112] The liquefaction system (11) also comprises the refrigerator compressor (4) for distributing compressed gas inside the coldhead (1), wherein said gas is supplied to and returned from the coldhead (1) via the gas circulation circuit (5) and the heat exchanging coil (9) which are connected to the input (6) and output (7) gas lines of the compressor (4) for supplying and returning the pressurized gas which act as refrigeration means for lowering the temperature of the refrigeration stages (2, 3). In known small-scale helium liquefiers, the supply pressures are typically between 1.5-2.5 MPa and the return pressures are typically between 0.3-1 MPa. The distributed gas inside the compressor (4) can be different or of the same type of the gas to be liquefied (for example, helium).

[0113] The system of the invention is preferably supplied with gas from a gas source module (22), preferably being recovered gas from a cryogen-using equipment. The gas source module (22) is connected to the storage container (12) and preferably controlled by the pressure control mechanism (19). The condensation process of the cold vapor accumulating as liquid in the storage container (12) corresponds to an isobaric process during which any disturbance in pressure yields a diminished liquefaction rate. For the gas liquefaction system to perform at optimum efficiency, it is therefore necessary to perform precise control of the interior pressure conditions, maintaining it throughout the entire process.

[0114] With the aim of improving the known liquefaction systems in the state of the art, it is also an object of this invention to optimize the heat exchange between the gas and the various refrigeration elements of the liquefaction system (11), as well as obtaining further auxiliary means for improving the liquefaction rate obtained through the cryocooler coldhead (1).

[0115] In order to carry out the said object, the system (11), through the heat exchanger coil (9), takes advantage of the already refrigerated gas circulating inside de coldhead (1), by extracting a small amount thereof, and conducting it through the inside of the heat exchanging coil (9), located in a portion of the neck (14) of the Dewar (12), winding around the refrigeration stages (2, 3). In this way, the refrigerated gas, preferably helium, that circulates inside the heat exchanger coil (9) contributes to the liquefaction of the helium that gets inside the Dewar (12), thereby increasing the average liquefaction rate of the system (11) while maintaining the pressure inside the storage container (12) at a constant value by means of the gas source module (22), the pressure control mechanism (19), the pressure sensor (20) and/or the PLC (21).

[0116] The most remarkable advantage of this solution is that it avoids the transfer of matter (helium gas) in the liquefaction process. In this manner, other complexities required in the prior art (as supplementary high-purity and high pressure gas sources connected to the gas circulation circuit (5)) are avoided.

[0117] When referring to small volumes of gas extracted from the coldhead (1), without altering its functioning, these should be interpreted, within the scope of the invention, as volumes which do not alter the refrigeration operations or capacities of the compressor (4) over the coldhead (1) stages (2, 3), maintaining the temperature of the coldest stage (3) of the coldhead (1) stable, preferably at a constant value of substantially 4.2 K for the case of helium liquefaction applications.

[0118] In another general embodiment, a method for liquefaction of gas is provided in conjunction with the described liquefaction system (11) of the invention that comprises a cryocooler as previously described in the present application. The method preferably comprises the following steps:

[0119] (i) Providing at least: [0120] a storage container (12) having a liquefaction region (18) and defined by a storage portion (13) and a neck portion (14) extending therefrom; [0121] a pressure control mechanism (19) for controlling the pressure within the liquefaction region (18) of the storage container (12); [0122] a cryocooler coldhead (1) at least partially disposed within the neck portion (14), the coldhead (1) being adapted to condense a cryogen contained within the liquefaction region (18) from a gas-phase to a liquid phase; [0123] optionally, a gas source module (22) containing an amount of gas-phase cryogen; [0124] wherein the cryocooler coldhead (1) comprises: [0125] a refrigerator compressor (4) for distributing compressed gas-phase cryogen inside the coldhead (1), wherein said cryogen is supplied to and returned from the coldhead (1) and acts as refrigeration means for lowering the temperature of one or more refrigeration stages (2, 3) of the coldhead (1); [0126] a heat exchanging coil (9) arranged around the external region of the refrigeration stages (2, 3) of the coldhead (1); [0127] one or more extraction orifices (8) communicating a gas circulation circuit (5) inside the coldhead (1) with the heat exchanger coil (9), acting as pass-through ports which allow the gas inside the coldhead (1) to flow through the inside of the heat exchanging coil (9) for exchanging heat with the gas in the liquefaction region (18) of the storage container (12); and wherein the heat exchanging coil (9) is adapted to connect and redirect the gas to a return port (8) connected to the gas circulation circuit (5), such as a return port (8) in the output gas line (7) of the refrigerator compressor (4) or a return port (8) at the coldhead (1). [0128] connecting a PLC (21) to the refrigerator compressor (4) for controlling the pressure within the coldhead (1).

[0129] (ii) Measuring and controlling the vapor pressure within said liquefaction region (18) of the storage container (12) with the pressure control mechanism (19), and optionally the internal pressure within the coldhead (1) with the PLC (21).

[0130] (iii) Maintaining the vapor pressure within said liquefaction region (18) of the storage container (12) by means of the pressure control mechanism (19), and optionally maintaining the internal pressure within the coldhead (1) within an operating range by means of the PLC (21).

[0131] (iv) Optionally, injecting gas into the liquefaction region (18) of the storage container (12) with a gas source module (22) in collaboration with the pressure control mechanism (19) for maintaining the vapor pressure during step (iii).

[0132] Although in principle the present invention allows the use of any multi-stage cryocooler coldhead (1), the following description is directed to an embodiment comprising a coldhead (1) with two refrigeration stages (2, 3). Nonetheless, it should be apparent to the person skilled in the art that the application to other types of cryocoolers (comprising a coldhead (1) equipped with one, two, or more refrigeration stages (2, 3)) is analogously achievable with equivalent increase in the liquefaction rates.

[0133] To sum up, the present invention proposes a cryocooler, a liquefaction system (11) and a liquefaction method which allow extracting increased extra cooling power from the low temperature regenerator of the coldhead (1), thus, enhancing the refrigeration capacities thereof, for different gas cooling and liquefaction applications.