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Title:
IMPROVED CRYOGENIC STORAGE TANK WITH AN INTEGRATED CLOSED COOLING SYSTEM
Document Type and Number:
WIPO Patent Application WO/2022/084432
Kind Code:
A1
Abstract:
The present invention disclose an improved cryogenic storage tank with an integrated heat exchanger comprising a closed cooling system constituted by a vertically oriented closed space having a vapor generating section in one bottom end and a cooling section in an upper end.

Inventors:
SKOVHOLT OTTO (NO)
Application Number:
PCT/EP2021/079171
Publication Date:
April 28, 2022
Filing Date:
October 21, 2021
Export Citation:
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Assignee:
IC TECH AS (NO)
International Classes:
F17C3/08
Foreign References:
US10781975B22020-09-22
US4899546A1990-02-13
EP2618038A22013-07-24
US20150013350A12015-01-15
US5226299A1993-07-13
KR20070074486A2007-07-12
US5226299A1993-07-13
US20200208777A12020-07-02
Other References:
ADAM SWANGER, INTEGRATED REFRIGERATION AND STORAGE FOR ADVANCED LIQUID HYDROGEN OPERATIONS, January 2017 (2017-01-01)
INTERNATIONAL CRYOCOOLER CONFERENCE, vol. 19, January 2017 (2017-01-01)
Attorney, Agent or Firm:
LINCOLN IP (GB)
Download PDF:
Claims:
CLAIMS

1. A cryogenic storage tank comprising a vertical oriented cooling heat exchanger,

- wherein the cooling heat exchanger (20, 20a) is integrated with an inner tank wall (10) of the storage space of the cryogenic storage tank,

- wherein the vertical oriented heat exchanger comprises an internal closed space (19, 19a, 19b) wherein an upper part (18) of the closed space is cooled by an external cooling machine, and

- wherein a bottom end (23) of the closed space comprises liquid hydrogen.

2. The storage tank of claim 1, wherein the heat exchanger is integrated with the inner tank wall (10) on a side surface of the inner tank wall facing towards the storage space.

3. The storage tank of claim 1, wherein the heat exchanger is integrated with the inner tank wall (10) on a side surface of the inner tank wall (10) facing away from the storage space.

4. The storage tank of claim 1, wherein the cooling heat exchanger is constituted by closed tubes (20) attached vertically to the tank wall of the cryogenic storage tank, wherein an inner space (19a) of the closed tubes (20) constitutes the internal closed space of the cooling heat exchanger.

5. The storage tank of claim 1, wherein the cooling heat exchanger is constituted by a first corrugated steel plate Ila arranged in a parallel distance from a second corrugated steel plate lib, wherein an inner space (19b) in between the first and second steel plates (Ila, 11b) constitutes the internal closed space of the cooling heat exchanger.

6. The storage tank of claim 5, wherein the first corrugated steel plate (Ila) or the second corrugated steel plate (11b) is spotwelded onto a surface of an inner tank wall (10).

7. The storage tank of claim 4 or 5, wherein the cooling heat exchanger is arranged centered inside a vacuum space (16) arranged in-between an inner tank wall (10) and an outer tank wall (13).

8. The storage tank of claim 1, wherein the cooling heat exchanger is constituted by a single corrugated steel plate (11) point welded to a surface of an inner tank wall (10) of the cryogenic storage tank, wherein an inner space (19) in between the single corrugated steel plate (11) and the inner tank wall surface the single corrugated steel plate is spot welded to constitutes the internal closed space of the cooling heat exchanger.

9. The storage tank of any previous claim, wherein the cooling heat exchanger covers up to a whole circumference of the storage space of the cryogenic storage tank.

10. The storage tank of claim 5 or 8, wherein distal elements (14,14a) are used to define a thickness of the internal closed space.

11. The storage tank of claim 1, wherein the cooling heat exchanger comprises a first external section (33) in thermal communication with a second external section (30), wherein the first external section (33) is arranged with a closed internal space constituting the internal closed space of the cooling heat exchanger arranged with a cooling section (18) at the upper part of the first external section (33) and a liquid hydrogen reservoir at a bottom end (23) of the first external section (33), wherein an insulated pipe (31) transfers liquid hydrogen from the liquid hydrogen reservoir of the second external section (33) to an upper end of the second external section (30), wherein an insulated pipe (32) transfers generated hydrogen vapor from the second external section (30) back to the cooling upper end (18) of the first external section (30). The storage tank of claim 11, wherein the second external section (30) is in thermal contact with a storage space of the cryogenic storage tank.

Description:
Improved cryogenic storage tank with an integrated closed cooling system

FIELD OF THE INVENTION

The present invention relates to an improved cryogenic handling system comprising a cryogenic storage tank integrated with an internal cooling facility.

BACKGROUND OF THE INVENTION

Hydrogen (H2) and Liquid Natural Gas (LNG) are normally stored in a liquified state since the volume is significantly less when in a liquid state compared to the gas state. However, there are some different physical properties between LH2 and LNG.

The density of LH2 decreases significantly when the pressure and temperature increases. For example, if the pressure is about 10 barg2 and the temperature increases 10 °C the density is about 50 kg per m 3 - If LH2 is stored at a temperature about -253 °C and at atmospheric pressure the density is about 71kg per m 3 - This implies that the effective storage capacity of LH2 increases with about 40% if LH2 is stored at atmospheric pressure at -253 °C compared with a situation where the pressure is 10 barg and the temperature increases, for example with 10 °C.

Therefore, utilizing full storage tank capacity, or transport tank capacity, for LH2 may be a challenge.

A common tank design used for storage and transport of LH2 comprises two layers of steel plates with vacuum insulation between the steel plate layers. There is also some insulation, for example heat radiation reflecting materials inside the two steel plate layers. Usually these tanks are shaped as a cylinder or are spherically shaped. The principal design of such tanks resembles the commonly known thermos. Despite the god insulation properties of such tanks there is a leakage of heat into such tanks, which results in an increase of pressure inside these tanks, which for example reduces available storage volume for LH2.

When LNG is stored in such tanks the same problem of heat leakage results in a pressure increase. Therefore, it is necessary to release some gas or use some of the cryogenic fluid to avoid buildup of pressures inside tanks above a level which may harm the tank. The challenge with LH2 is that the boiling point at atmospheric pressure is about -253 °C. Typically the holding time or storage time for LH2 in for example vacuum insulated tanks is about 15 days before the pressure reaches a dangerous level. For LNG, which has a boiling point around - 163 °C, the holding or storage time is typically 25 days. The typical pressure a Ll-h tank should be able to withstand is around 10 barg.

Release of excessive pressure in tanks is normally done by releasing some gas or fluid to the surroundings. If the storage time is over a longer time period, for example for LH2 in a vacuum insulated tank, the available content of LH2 decreases after each consecutive 15 days periods due to the necessity of releasing some of the stored content at least after 15 days. Some long-term storage facilities for LNG is known to capture released gases from tanks and converting the gases back to a liquid state and insert the liquified gasses back into the storage tanks.

Another phenomenon with cryogenic stored fluids is that a layering of stored liquified fluids may happen. Especially in large open LNG storage tanks. A vertical liquified LNG fluid column inside a tank will sometimes have different density at the bottom of the column than at the top layer of the liquified column due to temperature influx and the static liquid pressure, while LNG at the top evaporates at near ambient pressure and will be kept cold near boiling point. Then a phenomenon denoted rollover may occur when heavier LNG fluid layers at the top of the LNG fluid column changes place with lighter LNG fluid layers at the bottom of the LNG fluid column. This may happen abruptly inducing mechanical stress in the tank which may damage the construction.

A more detailed description of roll-over problems can be found in the link https://giignl.org/sites/default/files/PUBLIC AREA/Publications/rollover in Ing stora qe tanks public document low-res. pdf

From a chemical point of view LH2 is a uniform commodity in contrast to LNG. However, LH2 can have different electron spin dependent on pressure and temperature, which respectively is denoted orthohydrogen and parahydrogen. Parahydrogen has the lowest energy level. In liquid form this implies that when the LH2 is stored at lower temperatures the LH2 is mainly parahydrogen. If some heating occurs (leakage trough the insulation for example), a transfer to orthohydrogen occurs. This transfer to orthohydrogen develops some heat adding heat to the heat transferred through the insulation.

An aspect of the present invention is to preserve a specific quality of cryogenic commodities obtained at a production site until delivery at a consumer site. At the production site the cryogenic commodity may be produced according to a specific specification ordered by a consumer and should be deliverable with the same specified quality independent of how long a commodity is stored or how it is transported and delivered to a consumer.

In prior art it is known several examples of LNG storage tanks. However, utilizing known LNG tanks for storage of hydrogen may not be a straightforward possibility. As indicated above there are also some common problems shared between the two types of cryogenic fluids like limited holding times.

With respect to LH2 storage tanks a well-known example is a LH2 storage tank designed and used by NASA to store and supply hydrogen-based rocket fuel. The article "Integrated Refrigeration and Storage for Advanced Liquid Hydrogen Operations" by Adam Swanger et.al. disclosed January 2017 at the conference "International Cryocooler Conference" in January 2017, volume 19, discloses an example of a design denoted IRAS. In experiments conducted by NASA a spherical shaped cryogenic tank with a coiled tube with a circulating cooling liquid was inserted into the spherical shaped cryogenic tank. A holding time of about 11 months was obtained for LH2 in this tank.

KR 20070074486 Al disclose a cryogenic storage tank arranged with insulated pipes around an inner tank section circulating a cooling agent.

US 5226299 A disclose a cryogenic storage tank comprising a heatshield 2 with arranged channels 6 circulating a cooling agent, which can be an evaporated cryogenic fluid.

US 2020208777 Al discloses a liquid oxygen storage tank comprising an outer tank 10 and an inner tank 16. A cooling heat exchanger is arranged with a pipe loop 12 in contact with an outer surface of an inner tank wall, thereby cooling heat exchanger is in thermal contact with liquid oxygen stored in the storage tank. The growing interest in using hydrogen as a fuel, for example in fuel cells for cars, or as a fuel cell for ship propulsion etc. is due to the beneficial aspect of the rest product from hydrogen used in fuel cells etc., which is pure water. To be able to utilize hydrogen on a larger scale in society this will probably require much longer holding times than what is known today. Also, storage, transport and distribution systems that can keep a specified quality intact of hydrogen commodities is necessary.

OBJECT OF THE INVENTION

It is a further object of the present invention to provide an alternative to the prior art.

In particular, it may be seen as an object of the present invention to provide a cryogenic storage tank with a self-regulating cooling system being integral part of tank walls of the cryogenic storage tank.

SUMMARY OF THE INVENTION

Thus, the above described object and several other objects are intended to be obtained in a first aspect of the invention by providing a cryogenic storage tank, wherein a heat exchanger is attached to at least a part of an inner wall of the cryogenic storage tank.

The invention is particularly, but not exclusively, advantageous for obtaining a cryogenic storage tank comprising a vertical oriented cooling heat exchanger,

- wherein the cooling heat exchanger is integrated with an inner tank wall of the storage space of the cryogenic storage tank,

- wherein the vertical oriented heat exchanger comprises an internal closed space wherein an upper part of the closed space is cooled by an external cooling machine, and

- wherein a bottom end of the closed space comprises liquid hydrogen.

Respective aspects of the present invention may each be combined with any of the other aspects. These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described herein. DESCRIPTION OF THE FIGURES

The cryogenic storage tank according to the present invention will now be described in more detail with reference to the accompanying figures. The attached figures illustrates an example of embodiment of the present invention and is not to be construed as being limiting to other possible embodiments falling within the scope of the attached claim set.

Figure 1 illustrates an example of a prior art cryogenic storage tank

Figure 2A illustrates an aspect of the present invention.

Figure 2B illustrates an example of embodiment of the present invention.

Figure 3 illustrates an example of embodiment of the present invention.

Figure 4 illustrates another example of embodiment of the present invention.

Figure 5 illustrates further details of the example of embodiment illustrated in Figure 4.

Figure 6 illustrates further details of the example of embodiment illustrated in Figure 4.

Figure 7 illustrates another example of embodiment of the present invention.

DETAILED DESCRIPTION OF AN EXAMPLE OF EMBODIMENT

Although the present invention has been described in connection with the specified embodiments, it should not be construed as being in any way limited to the presented examples. The scope of the present invention is set out by the accompanying claim set. In the context of the claims, the terms "comprising" or "comprises" do not exclude other possible elements or steps. Further, the mentioning of references such as "a" or "an" etc. should not be construed as excluding a plurality. The use of reference signs in the claims with respect to elements indicated in the figures shall also not be construed as limiting the scope of the invention. Furthermore, individual features mentioned in different claims, may possibly be advantageously combined, and the mentioning of these features in different claims does not exclude that a combination of features is not possible and advantageous.

An aspect of the present invention is to arrange a cooling system as an integral part of the walls of a cryogenic storage tank thereby stopping external heat already at the wall level of the tank thereby increasing the ability to keep a stored cryogenic fluid at a stable defined low temperature level over longer time periods.

According to an aspect of the present invention, an effective cooling system needs to provide a high enough heat absorption rate and not only a sufficient heat capacitance to remove heat. If the heat absorption rate is too low, influx of heat from the surroundings may be larger than what the cooling system may remove per time unit and a resulting heat accumulation may occur. If the heat absorption rate of the cooling system is higher than the influx of heat the system will probably be able to keep cryogenic fluids at a stable lower temperature over time.

An aspect of the present invention is to provide a self-regulating closed cooling system enabling long term storage of cryogenic fluids, wherein the cooling system is capable of automatically reacting quickly to changing influx of heat into the storage space of a cryogenic storage tank.

Figure 1 illustrates an example of a prior art storage tank comprising an outer metal container with a metal wall 13 and an inner metal container with a metal wall 10. The space 16 between the outer wall 13 and the inner wall 10 is kept at vacuum. Spacer elements 15 are arranged to keep the inner and outer walls of the storage tank in a fixed position relative to each other.

According to an aspect of the present invention a control of internal temperature of a cryogenic fluid in a tank can be obtained with a heat exchanger design as illustrated in Figure 2A. A metal wall 10, which may be similar to the inner wall 10 of Figure 1 has a corrugated thin steel plate 11 arranged for example on a surface of the inner wall 10 facing towards the storage space of the tank. The corrugated thin steel plate is point-welded 12 to the inner wall 10 in a regular pattern as illustrated in Figure 2A.

Figure 2B illustrates further details of the section B of Figure 2A. Point welding spots 14 (which may comprise distal elements) is illustrated which leaves a space 19 between the corrugated steel plate 11 and the inner surface of the inner wall 10, which may be used to provide cooling of the cryogenic storage tank. According to an aspect of the present invention a closed cooling system may be arranged inside the space 19. Further details is given below.

Figure 3 illustrates another example of embodiment of a heat exchanger according to the present invention. The principle of a cooling heat exchanger according to the present invention is inspired by a design denoted a heat pipe commonly found in cooling systems for electronics. In prior art a heatpipe is constructed using a metal tube that is sealed under a partial vacuum. Inside the copper heatpipe is an inner wick lining that acts as a capillary material for a small amount of fluid. The copper heatpipe is usually oriented horizontally. When heat is applied to the heatpipe surface in the evaporator region the fluid is heated and since it is under a vacuum it is easier to change to vapor. This phase change from a fluid to vapor creates pressure. As pressure increases the vapor will naturally flow into the cooler section of the heatpipe. Heat is then released as the vapor condenses back into a fluid. The fluid will then flow back into the warm region, where the cycle will repeat while heat is applied to the warm region..

According to an example of embodiment of the present invention, a vertical oriented tube 20 comprises a closed space 19a wherein a sample of LHz is arranged in a reservoir at a bottom end 23 of the vertical tube 20. At a top end of the vertical tube 20 opposite the bottom end 23 of the tube 20 there is arranged a closed channel 18 wherein a cooling agent is circulated, for example by an external cooling machine. When arranging at least one such vertical tubing 20 onto an inner surface of a tank wall cooling will take place when heat enters the bottom of the tube 20. The added heat will create H2 vapor which will be moving upwards inside the tubing 20 as illustrated by the arrow 21. When the H2 vapor reaches the top section the cooling channel 18 will cool down the H2 vapor which then changes state back to LH2 and LH2 droplets will fall down (due to gravitation) as illustrated by the arrows 22 towards the LH2 reservoir at the bottom 23 of the tube 20 and be mixed with the LH2 resting in the reservoir. This process of generating vapor and cooling will cool down the surroundings as known in prior art. Since the vapor is cooled again the process will continue until a thermal stable situation is created. This kind of cooling system is known in prior art as a closed cooling system. Another beneficial aspect of the closed system is that it is self-regulating. More influx of heat generates more vapor, and hence a higher cooling effect. Since the boiling point of LHz at atmospheric pressure is -253 °C the generation of vapor can be viewed as happening instantly. There is no significant temperature increase of the LH2 before vapor is generated. If external heat influx towards the tank is increasing, more H2 vapor is generated increasing the cooling capacity automatically. If external heat influx decreases less vapor is generated and the cooling capacity slows down automatically.

A plurality of vertical tubes 20 arranged around an inner surface of a tank wall facing towards cryogenic fluids being stored in the tank constitutes an example of a heat exchanger according to the present invention. The example of a heat exchanger can maintain a low temperature of the cryogenic fluid over a longer time period. It is also within the scope of the present invention to arrange a plurality of vertical tubes 20 on side face(s) of the inner tank wall facing away from the storage space of the tank, for example inside a vacuum space 16 as illustrated in Figure 1.

Figure 4 illustrates another example of embodiment of a heat exchanger according to the present invention comprising two vertically oriented corrugated steel plates Ila, 11b assembled together in parallel wherein a closed space 19b is constituted between the parallel corrugated plates Ila, 11b. An upper end 18 of the heat exchanger 20a comprises a closed compartment which is arranged to cool the upper part of the closed space 19b. In the bottom end 23 of the two corrugated plates Ila, lib there is arranged a reservoir with LH2. The closed space 19b corresponds to the closed space 19a of the example of embodiment illustrated in Figure 3. The example of embodiment in Figure 4 is not restricted to a tube-like construction but can for example stretch around a whole circumference of an inner tank wall. It is also possible to arrange optional spacer elements 14a in the space 19b supporting the respective corrugated plates Ila, 11b. This may be necessary if thin steel plates are used thereby strengthening the mechanical integrity of the example of heat exchanger 20a. The thickness of the corrugated steel plates may be adapted to a specific heat transfer capacity of the steel plates. Thinner steel plates has less thermal resistance as known in prior art.

Figure 5 illustrates further details that may be embodied in the example of a heat exchanger 20a depicted in Figure 4. A capillary felt mat 24, or another similar absorbent material, is arranged on inner surfaces of respective corrugated plates Ila, 11b facing towards the closed space 19b such that the capillary effect of the felt mat 24 helps in transporting condensed H2 vapor, i.e. LH2 from the cooling end 18 of the heat exchanger down to the reservoir of LH2 at the bottom section 23 of the heat exchanger. In this manner there will always be sufficient LH2 in the reservoir. If optional distal elements 14a are used, holes 24a enables a distal element to pass through the capillary felt 24 as illustrated.

The necessary volume of LH2 in the reservoir at the bottom end 23 is a function of maximum vapor that is needed to be generated to keep the cryogenic fluid at a desired temperature level. However, this is also a function of the insulating technique and property of insulating materials used around the cryogenic storage tank. However, it is within the scope of the present invention that extra LH2 can be added to the LH2 reservoir, if necessary, for example via an adapted vent (not illustrated).

It is common to use vacuum insulation in cryogenic storage tanks as illustrated in Figure 1. According to an aspect of the present invention, the heat exchanger based on the heat pipe concept for example illustrated in Figure 3 and 4 can be positioned inside a vacuum space 16 as illustrated in Figure 1. It is also within the scope of the present invention to locate the heat exchanger illustrated for example in Figure 3 and 4 centered inside a vacuum space 16. This arrangement improves the control and cooling of heat radiation passing the vacuum space.

Figure 6 illustrates how the corrugated plate 11a of the heat exchanger illustrated in for example Figure 4 and 5 can be spotwelded onto for example an inner tank wall surface in a regular spot-welding pattern illustrated by the spot-welding points 12 distributed across the surface of the corrugated plate Ila.

With reference to Figure 2a and 2b, an example of embodiment of the present invention utilizes the space 19 constituted by a single corrugated plate 11 spot- welded onto an inner tank wall surface 10. A top end and a bottom end of the single corrugated plate 11 can be closed thereby the space 19 will be a closed space. In a top end of the corrugated plate 11 there will be arranged a colling element (not illustrated) like the cooling element 18 discussed in the other examples of embodiments. Likewise, at a bottom end of the single corrugated plate 11 there will be a reservoir of LH2. If a capillary felt is arranged in the closed space 19, holes in the capillary felt mat like the holes 24a illustrated in Figure 5 can be arranged at the location for respective spot-welding locations.

Figure 7 illustrates an alternative construction of a heat exchanger according to the present invention. A unit like a cryogenic storage tank in need of cooling is illustrated as a first separate section 30. Another second external section 33 comprises a reservoir of LH2 at bottom end 23 and a cooling section 18 being cooled for example by an external cooling machine (not illustrated). LH2 is pumped from the external section 33 to an upper end of the separate section 30. The arrow 31 indicates this transport which may be done with a heat insulated pipe and an adapted pump. The received LH2 in the separate section 30 fall downwards due to gravitation but can also be moved by an adapted capillary felt mat as discussed above. When heat heats up the separate section 30 LH2 is transformed into H2 vapor. The vapor is then transported back into the external section 33 wherein the H2 vapor will be condensed back to LH2 and fall downwards into the LH2 reservoir at the bottom of the external section 33, and the process can be repeated as discussed above. The arow 32 illustrates the transport of H2 vapor back to the external section 33, which may be done with an insulated pipe and an adapted pump.

According to an example of embodiment of the present invention a cryogenic storage tank comprises a vertical oriented cooling heat exchanger,

- wherein the cooling heat exchanger 20, 20a is integrated with an inner tank wall 10 of the storage space of the cryogenic storage tank,

- wherein the vertical oriented heat exchanger comprises an internal closed space 19, 19a, 19b wherein an upper part (18) of the closed space is cooled by an external cooling machine, and

- wherein a bottom end 23 of the closed space comprises liquid hydrogen.

According to the example of embodiment disclosed above, the heat exchanger may further be arranged integrated with the inner tank wall 10 on a side surface of the inner tank wall facing towards the storage space. According to the example of embodiment disclosed above, the heat exchanger may further be arranged integrated with the inner tank wall 10 on a side surface of the inner tank wall facing away from the storage space.

According to the example of embodiment disclosed above, the heat exchanger may further be constituted by closed tubes 20 attached vertically to the tank wall of the cryogenic storage tank, wherein an inner space 19a of the closed tubes 20 constitutes the internal closed space of the cooling heat exchanger.

According to the example of embodiment disclosed above, the heat exchanger may further be constituted by a first corrugated steel plate Ila arranged in a parallel distance from a second corrugated steel plate 11b, wherein an inner space 19b in between the first and second steel plates Ila, lib constitutes the internal closed space of the cooling heat exchanger.

According to the example of embodiment disclosed above, wherein the first corrugated steel plate Ila or the second corrugated steel plate lib of the heat exchanger is spotwelded onto a surface of an inner tank wall 10.

According to the example of embodiment disclosed above, the heat exchanger may further be constituted by a single corrugated steel plate 11 point welded to a surface of an inner tank wall 10 of the cryogenic storage tank, wherein an inner space 19 in between the single corrugated steel plate 11 and the inner tank wall surface the single corrugated steel plate is spot welded onto constitutes the internal closed space of the cooling heat exchanger.

According to the example of embodiment disclosed above, the heat exchanger may further comprise a heat exchanger covering up to a whole circumference of the storage space of the cryogenic storage tank.

According to the example of embodiment disclosed above, wherein distal elements 14,14a further are used to define a thickness of the internal closed space. According to the example of embodiment disclosed above, the heat exchanger may further comprise a first external section 33 in thermal communication with a second external section 30, wherein the first external section 33 is arranged with a closed internal space constituting the internal closed space of the cooling heat exchanger arranged with a cooling section 18 at the upper part of the first external section 33 and a liquid hydrogen reservoir at a bottom end 23 of the first external section (33), wherein an insulated pipe 31 transfers liquid hydrogen from the liquid hydrogen reservoir of the second external section 33 to an upper end of the second external section 30, wherein an insulated pipe 32 transfers generated hydrogen vapor from the second external section 30 back to the cooling upper end 18 of the first external section (30).

According to the example of embodiment disclosed above, wherein the second external section 30 may further be in thermal contact with a storage space of the cryogenic storage tank.




 
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