Methods for Managing Cryogen Within the Core of a Cryogenic Cell

This application is a continuation of U.S. patent application Ser. No. 18/733,742, filed Jun. 4, 2024, the contents of which are incorporated by reference herein in their entirety.

The invention relates, in general, to cryogenic technology, and more particularly, to a cryogenic cell with an integrated cold head.

U.S. Pat. No. 11,448,459 discloses a cryogenic cell, a device that can bring a space to essentially any conditions of temperature and pressure, down to cryogenic temperatures and up to relatively high pressures. In a cryogenic cell, a central core is filled with a cryogen, such as liquid nitrogen. The central core is in selective thermal communication with a pressurizable space. The pressurizable space can be pressurized with a fluid, such as a gas, up to pressures of, e.g., about 750 psi. By heat exchange with the core, the pressurizable space can be cooled to a temperature at or near the temperature of the cryogen within the core. The rate of heat exchange with the core is dependent, at least in part, on the pressure within the pressurizable space.

As heat exchange between the core and the pressurizable space occurs, the cryogen within the core vaporizes. To regenerate the cryogen into liquid phase and allow the core to continue cooling the pressurizable space, the core includes a commercial cold head filled with a colder cryogen, such as liquid helium.

Cryogenic cells have a number of applications. U.S. Pat. No. 11,448,459 describes a gas separation and purification system that uses cryogenic cells. In the disclosed system, mixed-gas streams are fed into the pressurizable space of a cryogenic cell or a number of such cells. The pressurizable space is set to conditions of temperature and pressure that cause at least one gas of the mixed-gas stream to undergo a phase change, after which it can be separated from the stream. As another example, international publication WO2023/004433 proposes the use of cryogenic cells in atmospheric water harvesting.

The present inventor has found that the use of a cold head to regenerate the cryogen within a cryogenic cell puts meaningful, and often unwanted, limitations on the size, features, and function of cryogenic cell. For example, the cold head has specific dimensions, thus imposing certain minimum dimensions on the cryogenic cell as a whole. Additionally, conventional cold heads usually have a limited volume of cryogen within them. This can limit the rate at which the cold head and the core can absorb heat and, consequently, the volume of fluid that can be processed by a cryogenic cell in a given period of time. Such limitations are particularly a problem with, e.g., gas separation applications in which it is desirable to process large volumes of gas in a short period of time.

One aspect of the invention relates to a cryogenic cell. The cryogenic cell includes a core adapted to contain a cryogen. The core has one or more ports to an outside of the cryogenic cell that allow the cryogen to circulate into and out of the core. A mid-wall is disposed around the core and is spaced from the core. The mid-wall defines, in part, a space in selective, partial thermal communication with the core. The space is at least substantially airtight and is adapted to be evacuated or filled with a compressible fluid that (1) increases or decreases thermal communication with the core in accordance with a pressure of the compressible fluid within the space, and (2) places contents of the space under the pressure of the compressible fluid. A conduit is positioned within the space such that the conduit does not make physical contact with the core. The conduit is connected with inlet and outlet ports in the cryogenic cell. The cryogenic cell does not include a cold head within the core.

To prevent heat loss, the cryogenic cell also typically includes an outer sidewall, a top, and a bottom, each made of a thermally insulative material. The thermally insulative material of the top and bottom may be different than the thermally insulative material of the outer sidewall. The conduit may comprise a set a set of coils arranged around the core. The space may include at least one pressurization port that communicates with the outside of the cryogenic cell. The one or more ports in the core may comprise a cryogen inlet port and a cryogen outlet port.

Another aspect of the invention relates to a system. The system comprises a cryogenic cell as described above and a cryogenic compressor. The cryogenic compressor is connected to the cryogen inlet port and the cryogen outlet port of the cryogenic cell, and is arranged and adapted to remove cryogen vapor resulting from heat exchange between the core and the space from the core through the cryogen outlet port, compress the cryogen vapor into liquid cryogen, and return the liquid cryogen to the core through the cryogen inlet port.

In this system, there may be multiple cryogenic compressors, arranged either in series or in parallel with one another. If arranged in series, bypasses may be installed so that one compressor can be used at a time. Series-connected cryogenic compressors may be the same or different. If different, the cryogenic vapor may be subjected to a multiple-stage compression.

Yet another aspect of the invention also relates to a system. The system comprises a manifold, a cryogenic cell as described above, and two or more cryogenic compressors. The cryogenic cell and the cryogenic compressors are placed in selective communication with one another through the manifold to remove cryogen vapor resulting from heat exchange between the core and the space from the core through the cryogen outlet port, compress the cryogen vapor into liquid cryogen, and return the liquid cryogen to the core through the cryogen inlet port.

In this system, there may be a plurality of cryogenic cells and a plurality of compressors. The system may also comprise a controller. The controller controls the manifold to independently control the rate at which the cryogen is removed from, compressed, and returned to the cores of the plurality of cryogenic cells in accordance with the thermal load on each of the plurality of cryogenic cells.

Other aspects, features, and advantages of the embodiments of the invention will be set forth in the following description.

is a perspective view of a cryogenic cell, generally indicated at, according to an embodiment of the invention. The cryogenic cellofis generally cylindrical in overall shape, with a cylindrical sidewall, a top, and a bottom. The topand the bottomare reinforced with reinforcing plates,, which will be discussed in greater detail below. As can be seen in, the cryogenic cellis reinforced and held together along its longitudinal axis by a number of tie rods, which extend from, and are received in, the topto the bottom, and are bolted in place.

As used here, the term “longitudinal axis” refers to an axis aligned with the centers of the topand the bottomand extending between the topand the bottom. The term “longitudinal direction” refers to a direction parallel to or along the longitudinal axis. The terms “radial direction” and “radially” refer to a direction that extends between the longitudinal axis and the sidewall.

In the cryogenic cell, the exterior sidewall, top, and bottomprimarily offer thermal insulation. To that end, it is helpful if the materials of which these components,,are made have thermal insulating properties, can withstand cryogenic temperatures without shattering, and are machinable, moldable, castable, or otherwise workable. Ultra-high molecular weight (UHMW) polyethylene is one such material and, e.g., the topand the bottommay be made of UHMW polyethylene. However, the cryogenic celland its components,,need not be made, or made entirely, of expensive or exotic materials. For example, the sidewallmay be made of high-density polyethylene (HDPE), e.g., HDPE pipe. A wall thickness of about 2-3 inches (5-7.6 cm) may be appropriate in at least some embodiments. In one embodiment, the sidewallmay be an HDPE pipe with an outer diameter of 34 inches (86.4 cm) and an inner diameter of 31 inches (78.7 cm).

is a cross-sectional view of the cryogenic cell, taken through Line-of. The cryogenic cellhas a core, which is centered about the longitudinal axis. The coreis a vessel with at least a sidewallthat is made of a thermally-conductive material. In the illustrated embodiment, the entire coreis made of 6061 T6 aluminum, although other materials, like copper, may be used depending on the pressures at which the cryogenic cellis to operate.

A pressurizable spaceis defined between the sidewallof the coreand a mid-wallthat is positioned radially outward of the sidewallof the core. The mid-wallextends between the topand the bottom, fully separating the pressurizable spacefrom other compartments and portions of the cryogenic cell. The sidewallis positioned radially outward of the mid-wall, with a gap between the mid-walland the sidewall.

A set of tubingruns within the pressurizable space, generally coiled around the core. However, the set of tubingis not in direct physical contact with the sidewallor any other portion of the core. If spacers or other such structures are needed to maintain the position of the tubing, those spacers would generally not be thermally conductive. The set of tubingis continuous between an inlet portand an outlet port, both of which connect to the set of tubingand penetrate the top. A length of the tubingpasses under the coreand is shown longitudinally sectioned in. The set of tubingis but one example of the kind of conduit that may be present in the pressurizable space. In some embodiments, conduit may be used that does not coil around the core, is not round, or is otherwise adapted for a particular application.

At least one additional portis used to charge the pressurizable spaceand, when necessary, to remove pressure. For example, air or nitrogen gas may be pumped into the pressurizable spaceto create a pressure. Additionally, the spacebetween the mid-walland the outer sidewallmay include a portthat, among other things, allows the spaceto be evacuated for better thermal insulation, if needed.

The corealso includes a number of ports. More specifically, the core includes cryogen inlet and outlet ports,. The purpose of these ports will be explained in more detail below. Although there are only two ports,that penetrate into the core, various connectors may be used to provide for additional connections, or to provide additional functionality.

is an enlarged view of a portion of, showing a boltand one of the portsin the core. The boltinserts through the plateand the top, terminating in the lidof the core. The portinserts through all three layers,,and opens into the coreitself. To prevent leaks around the penetrations, circular O-ring groovesare cut in the upper faceof the lidof the coreand in the upper faceof the toparound the positions of each penetration. O-ringsare installed in those grooves.

In some applications, the O-ringsmight be made of a conventional elastomer. However, it has been found that when conventional elastomeric O-rings are exposed to cryogenic temperatures, they lose all elasticity and shatter. Therefore, the O-ringsof the illustrated embodiment are made of a composite of materials. More specifically, an outer tube of polymeric materialis backed by an inner coilof metal wire, such as a helix or double helix of 316 stainless steel wire. The outer tube of polymeric materialmay be, e.g., perfluoroalkoxy (PFA) plastic.

As those of skill in the art will appreciate, heat transfer occurs by conduction, convection, and radiation. By adding gas to the pressurizable spacethrough the port, one increases the amount of mass in the space, and thus, the level of heat transfer that can occur by conduction and convection. By withdrawing gas from the pressurizable space(or drawing a vacuum on the pressurizable space), one reduces the amount of mass in the space, and thus, the ability of heat to flow between the coreand the pressurizable spaceby conduction and convection.

Thus, the pressurizable spacecan be placed under essentially any conditions of temperature and pressure: as pressure is increased within the pressurizable space, conduction and convection increase, and thus, the rate of heat exchange with the corealso increases, making the pressurizable spaceboth colder and higher-pressure. When pressure within the pressurizable spaceis lessened, the rate of heat transfer with the coredecreases. This has a number of potential uses, some of which will be described below.

As the coreexperiences heat transfer with the pressurizable space, the cryogen within the corewill heat up and begin to vaporize. As that occurs, the ability of the coreto absorb heat will gradually decline. In the cryogenic cell of U.S. Pat. No. 11,448,459, the cryogen within the core is regenerated into cold, liquid phase by a cold head filled with a colder cryogen (e.g., liquid helium if liquid nitrogen is the primary cryogen within the core).

By contrast, the cryogenic cellof the present embodiment, there is no cold head in the core, as can be seen in.is a cross-sectional view of the cryogenic cell, again taken through Line-of. In the view of, two of the ports,that connect to the coreare connected to a compressor. The compressormay be specially adapted to compress cryogenic fluids. The compressormay be, for example, a Sumitomo Cryogenics F-70 compressor.

In operation, the compressorforms a closed circuit with the coreof the cryogenic cell. In that circuit, one of the portsserves as an inlet port, through which the compressordeposits liquid cryogen. The other portserves as an outlet port, through which the compressorremoves vaporized cryogen.

During operation, because of heat transfer with the core, there will typically be both liquid-phase cryogen, labeled L in, and vapor-phase cryogen, labeled V in, in the coreat any one time. The rate of heat transfer with the corewill determine the rate at which the liquid cryogen L vaporizes. The capacity of the cryogenic cellto cool the pressurizable space(i.e., the heat transfer rate with the coreper unit time) will depend on the rate at which the compressorcan remove cryogenic vapor V, compress it back into liquid cryogen L, and return the liquid cryogen L to the core.

This arrangement—connecting the coreto a cryogenic compressor—removes the cold head found in prior cryogenic cell designs but retains its function; i.e., the cryogenic cellcan still regenerate the cryogen in its core. A cryogenic cellwithout a cold head also has certain other advantages. For example, removing the cold head from the cryogenic cellmay, in many cases, have the effect of removing all moving parts from the cryogenic cell. This, in turn, may improve reliability and reduce the risk that fluids flowing through the set of tubing, which may be flammable, will come into contact with a spark.

Although the compressoris illustrated as being relatively close to the cryogenic cellin the view of, the cryogenic compressormay be remote from the cryogenic cell, e.g., in the next room. So long as the supplyand returnlines can be kept properly insulated or otherwise arranged to minimize heat transfer with the surrounding environment, the cryogenic compressormay be placed at any distance relative to the cryogenic cell.

The cryogen inlet and outlet ports,are shown in the embodiment ofas being separate physical structures that enter the cryogenic celland the coreat separate points. This may be the case in many embodiments. In other embodiments, inlet and outlet ports may enter the cryogenic cellas part of a single, combined structure that penetrates the cryogenic cellat a single location. From that single structure, separate inlet and outlet conduits may branch away from one another within the core.

As those of skill in the art will appreciate, in some applications, the cryogenic compressoris an optional component. That is, there may be applications in which the amount of mass to be processed by the cryogenic cellis small enough and the volume of the coreis large enough that it is not necessary to regenerate the cryogen vapor V that forms within the coreinto liquid form. In that case, one would simply fill the coreand seal the port or ports,—and it may not be necessary to have or to use both ports,.

However, for perhaps the vast majority of applications, particularly those involving continuous flow through the pressurizable space, some form of regeneration using a cryogen compressorwill be used. Depending on the heat transfer requirements of the application, the cryogen compressormay be used either intermittently or continuously.

As shown in, a single cryogenic cellconnected to a single cryogenic compressorform a system. In that system, the cryogenic compressoris a single point of failure; that is, if the cryogenic compressorfails, the system as a whole fails. To prevent that from happening, it is possible to connect more than one compressorto a single cryogenic cell.

is a schematic illustration of a system, generally indicated at, in which two compressors,are connected to the same cryogenic cell. Each compressor,is connected to the input and output ports,of the cryogenic cell. In general, any number of compressors,,may be connected to a cryogenic cell, and those compressors,,may be arranged either in serial or in parallel. The arrangement ofis with the two compressors,in parallel. With two compressors,in parallel, should one compressor,fail, the other compressor,can be brought online to perform its function. However, the compressors,need not be operated one-at-a-time. In some situations, it may be advantageous to use two or more compressors,in parallel, as doing so may increase the volume of cryogen vapor V that can be compressed back into liquid form per unit of time. Variations on this are also possible: e.g., one cryogenic compressor,can be engaged when the other cryogenic compressor,reaches its functional limits, or the load can be balanced between the two cryogenic compressors,. If two cryogenic compressors,are arranged in parallel and used simultaneously, they may be the same, i.e., have the same functional characteristics and specifications, or they may be different.

is a schematic illustration of a systemin which two cryogenic compressors,are used in series. If the two cryogenic compressors,are the same, one compressor,may be activated to take over for a failed compressor,. In that case, bypasses may be installed so that an inoperative compressor,can be bypassed.

is an illustration of a variation on systemin which such bypasses are installed. More specifically, in, fluid flows through a first conduitand encounters a first three-way valve. The first three-way valveeither allows the fluid to continue to flow through a conduittoward the first compressoror diverts the fluid flow through a first bypass loopwhich avoids the first compressorand directs the fluid flow through a conduittoward the second compressor. Fluid in the conduitencounters a second three-way valvewhich either allows the fluid flow to continue through a conduittoward the second compressoror diverts the flow through a second bypass loopwhich avoids the second compressor.

If the two compressors,are not identical, various possibilities arise. For example, two compressors,used in series could allow for a multi-stage compression process, where a first cryogenic compressorcompresses the incoming cryogen vapor V to particular conditions, and the second cryogenic compressorcompletes the compression into liquid form.

As was described above, although the cryogenic cellsdescribed above have only two ports,that penetrate into the core, those ports,may be connected to various connectors to provide for additional connections and, in some cases, additional functionality. For example, in the schematic view of, one of the portsis coupled to a T-connector, which is, in turn, connected to a pressure relief valve. If the compressorfails, there is no backup compressor, and liquid cryogen L within the corecontinues to vaporize, as the pressure within the coremounts, there is the chance of failure of the vessel; that is, the cryogenic cellcould ultimately burst. The pressure relief valveprevents this: if the pressure within the coreexceeds the limit of the pressure relief valve, the pressure relief valveopens, releasing the excess pressure.

In a variation on this,shows an alternate configuration of this, in which the portis connected to a T-connector, one outlet of which is connected to a pneumatically-actuated valve. Such a valvewould allow the compressorto be bypassed and the contents of the coreto be either diverted or vented to atmosphere.

Although the above focuses on multiple compressors being connected to a single cryogenic cell, the converse is also possible, i.e., one compressor may be connected to more than one cryogenic cell.is an illustration of a system, generally indicated at, in which two cryogenic cellsare connected to a single compressor. In this system, depending on the particular arrangement, cryogen vapor V that is withdrawn from one cryogenic cellmay or may not be returned to the same cryogenic cellas liquid cryogen L. In order to monitor the flow into and out of the cryogenic cellsand ensure that the coreof each cryogenic cellis properly filled, systemhas flow metersin or coupled to the input and output lines. Temperature sensors, such as thermocouples, may also be included.

In system, the compressormay serve both cryogenic cellssimultaneously, or the compressormay serve the cryogenic cellsone at a time, switching back and forth between the cryogenic cellsto serve them. Various valves and fittings, which for the sake of simplicity are not shown in, may be used to isolate one cryogenic cellor the other.

Systems like systemmay not provide the redundancy of systems in which there are multiple cryogenic compressors,,,,, but where cost is a particular consideration, reliability is less of a concern, and the rate of heat exchange with the coreis not extreme, a system like systemmay be ideal.

In all of the description above, it is assumed that the connections between the cryogenic celland any cryogenic compressors,,,,that are connected to it are individual connections made with various connectors. That may not always be the case.is a schematic diagram of a system, generally indicated at, in which there are six cyrogenic compressorsserving four cryogenic cellsthrough a manifold.

As in system, with the manifoldof system, cryogenic vapor V removed from one cryogenic cellwill not always be redeposited as liquid cryogen L in the same cryogenic cell. Therefore, a sensor or sensor suitemonitors the inflow and outflow lines,into and out of the cryogenic cells. The contents and particular sensors in the sensor suitemay vary from embodiment to embodiment, depending on how systemis controlled. Typically, the sensor suitewould include a flow sensor, to monitor the flow into and out of the core, and optionally, a temperature sensor. Additionally, the sensor suitemay be equipped with a pressure sensor in each of the lines,, or at least in the outflow lineof each cryogenic cell. Althoughshows multiple sensor suites, one in each line,, in some cases, a single instrument that can receive and process multiple flows simultaneously may be used. The lines,may be diverted through such an instrument, instead of extending directly between the cryogenic cellsand the manifold.

In some embodiments, a system like systemmay optionally include, or be coupled to, a surge tank, which contains additional cryogen that can be introduced into systemin case of high demand, leaks, and other situations in which additional cryogen would be useful. In the illustrated embodiment, the surge tankis connected to the manifold, but not directly to any of the cryogenic cells. A valve or valves (for simplicity, not shown in) may be placed to control flow into and out of the surge tank.

A controller, which may be a microprocessor, a microcontroller, an application-specific integrated circuit (ASIC), an integrated, embedded system including one of those components, or a programmable logic controller (PLC), controls the manifoldto control the flows of cryogen into and out of the cryogenic cells. Several general principles may guide the manner in which the controllercontrols the manifold. For example, as may be apparent from the description above, ideally, the pressure of cryogen vapor V within the core is as low as possible. That is, ideally, as soon as cryogen vapor V is formed by heat exchange with the pressurizable space, that cryogen vapor V is removed and replaced by liquid cryogen L. If cryogen vapor V is forming rapidly within the core, it means that the cryogenic cellis experiencing a heavy thermal load. As the amount of cryogen vapor V increases, the pressure within the coreincreases, and the controllershould act to relieve that pressure. However, as cryogen flows into and out of the coreof each cryogenic cell, the controllershould maintain at least some threshold volume of liquid cryogen L in the core. That is, the compressorsand manifoldshould maintain a dynamic equilibrium that keeps at least a threshold amount of liquid cryogen L in the coreof each cryogenic cell, as a corethat is completely drained will be unable to absorb any heat from the pressurizable space.

is a schematic flow diagram of a method, generally indicated at, for controlling a manifold-based system like system. Methodoperates according to the general principles outlined above and begins at. For simplicity in explanation, methodwill be set forth with reference to a single cryogenic celland its core. In task, the controllermeasures the temperatures in the inflow and outflow lines,of the core, as well as the pressures in the lines,, and the flow rates in the lines,. Additionally, prior to task, the controllerwould typically be programmed with the initial volume or mass of cryogen in the cryogenic cell, as well as other operating parameters. Methodcontinues with task.

Taskis a decision task. In task, if the measured pressure in the outflow lineis higher than a predefined threshold TH (task: YES), that is an indication that heat transfer within the coreis high. Thus, methodcontinues with task. If the measured pressure in the outflow lineis not higher than the defined threshold (task: NO), methodcontinues with task.