Cryogenic thermo-structural insulation system

Abstract

Disclosed is a cryogenic storage tank including an inner wall 50 and an outer wall 54 defining a space, wherein the space is filled at least in part with dried-in-place hollow glass microspheres 58 wh

Description

25 09 23

[0001] The present disclosure relates to cryogenic storage tanks. The disclosure has particular utility in connection with cryogenic storage tanks for containing highly volatile materials such as liquid hydrogen for powering stationary applications and vehicles such as airplanes, and will be described in connection with such utility, although other utilities are contemplated.

[0002] This section provides background information related to the present disclosure which is not necessarily prior art. This section provides a general summary of the disclosure and is not a comprehensive disclosure of its full scope or all its features.

[0003] There are many types of cryogenic tank designs and some are even semi-structural like Stanley’s ingenious design of a vacuum flask from the 1900’s, however this design could not be effective at soft or moderate vacuum pressures. Because of this the Stanley design required advanced manufacturing processes, such as furnace welding in a purged environment. Typical prior art cryogenic tank formats include: • Vacuum Jacketed Multi-layer insulation (VJ MLI) which has very high thermal performance, but is not thermo structural by design, and is difficult to produce. • Foamglas for liquid natural gas (LNG), which is thermo structurally not good, heavy, time consuming to produce and not suitable for flight, plus made for ambient pressures. • Spray on foam insulation (SOFI) is generally not thermo structural, is of much lower thermal performance and is better suited to ambient pressures. • Perlite or microspheres have been used in soft vacuum (SV) in heavy ground standing double walled tanks, but are poured into the annulus as a bulk fill material and do not provide potential structural strength. 25 09 23

[0004] The use of cryogenic fluids such as LNG for powering vehicles such as aircraft, or hydrogen for powering fuel cell powered aircraft offer attractive alternatives to conventional liquid fossil fuel burning engines. LNG and liquid hydrogen (LH2) are stored in a liquid state at very low temperature. For example, liquid hydrogen is stored at below -252°C; and LNG (predominantly methane) is stored at below -162°C. In order to maintain these fuel stores in the tank in liquid state, the tank must be strong to maintain pressure on the fluid, and must be insulated. Typically cryogenic tanks are multiwalled structures with some insulating material between the walls. The space between the tank walls also typically is evacuated, i.e., to form a vacuum.

[0005] In the case of an airplane, weight and space also are at a premium. Accordingly, the tank should be as light weight as possible, while still maintaining sufficient structural integrity to contain the liquified fuel stores, and have sufficiently thermal insulating value, and able to withstand temperature cycling, shock and high G (gravity) loading. That is to say, cryogenic tanks must be light weight, strong, and relatively low cost to produce and service.

[0006] A conventional cryogenic tank 10 is illustrated in Fig. 1, and includes an inner wall 12 and an outer wall 14. Inner wall 12 is separated from outer wall 14 by a plurality of supports or studs 16. The space between inner wall 12 and outer wall 14 is sealed fluid tight and is evacuated, i.e., to form a vacuum. The void 18 between the inner and outer walls 12, 14 also may be filled with a thermal insulating material, or the inner surface 20 of the inner wall 12, the outer surface 22 of outer wall 14, and the walls 24 of the studs 16 may be coated at least in part with insulation.

[0007] Referring to Fig. 2, another prior art tank 30 includes an inner wall 32, an outer wall 34 separated from the inner wall. A microsphere powder is loaded in the space 36 between inner and outer walls 32, 34, flowing around the supports 24 to fill the void between the walls 32, 34 spaced from the one another. 25 09 23

[0008] In accordance with the present disclosure, there is provided a cryogenic storage tank comprising an inner wall and an outer wall defining a space, wherein the space is filled at least in part with a high angle of repose particulate material consisting of dried-in-place hollow glass microspheres which provides both insulating and structural properties to maintain the space.

[0009] In one aspect the inner wall and the outer wall are formed of different materials.

[00010] \a built-up wall including one or more non-metallic layers.

[00011] In yet another aspect the inner wall comprises a metal wall and the outer wall comprises one or more layers formed of a metal foil, or one or more layers formed of a fiber reinforced material, or one or more layers of a metal foil and one or more layers formed of a fiber reinforced material.

[00012] The present disclosure also provides a method of forming a cryogenic tank as above described, comprising providing a first walled structure configured to form the tank inner wall; wrapping the first wall in a flexible bladder; injecting a putty comprising glass microspheres in a volatile organic solvent between the outer wall of the first walled structure and the bladder; driving off the solvent to form a high angle of repose material; removing the bladder, and forming a built-up layer over the glass microspheres to form the tank outer wall, or forming a built-up layer directly over the bladder to flow the tank outer wall.

[00013] In one aspect of the method the solvent is driven off by heat, by vacuum, or by a combination of heat and vacuum.

[00014] In another aspect of the method the built-up layer comprises one or more layers formed of a metal foil, or one or more layers formed of a fiber reinforced plastic materials, or one or more layers formed of a metal foil and one or more layers formed of a fiber reinforced material. 25 09 23

[00015] In another aspect of the method includes adding a thermal insulating layer over the built-up layer.

[00016] The present disclosure also provides an alternative method of forming a cryogenic tank, comprising providing a first walled structure configured to form the tank inner walk applying a putty comprising glass microspheres in a volatile organic solvent on an outer wall surface of the first walled structure; applying a release agent over the putty; applying a bladder over the release agent, and heating and / or pulling a vacuum to draw off the organic solvent to form a high angle of repose material, removing the bladder, and forming a built-up layer over the glass microsphere to form the tank outer wall, or forming a built-up layer directly over the bladder to flow the tank outer wall.

[00017] In one aspect of the alternative method, the built-up layer wall comprises one or more layers formed of a metal foil, one or more layers formed of a fiber reinforced plastic material, one or more layers formed of a metal foil and one or more layer of a fiber reinforced plastic material.

[00018] In another aspect of the alternative method involves adding a thermal insulating layer over the built-up layer.

[00019] In yet another aspect of the disclosure is provided a fuel cell powered aircraft comprising a cryogenic storage tank as above described.

[00020] More particularly, in accordance with the present disclosure, we provide a cryogenic storage tank comprising an inner wall, and an outer wall forming a space between them. The space is filled with a high angle of repose granular material such as hollow glass microspheres, as will be described below. The hollow glass microspheres are available commercially from a variety of sources and usually have diameters ranging from between about 1 and 1,000 25 09 23 micrometers. Hollow glass microspheres, sometimes termed “micro balloons” or “glass bubbles” have been used in the past in composite materials such as syntactic foam and lightweight concrete. They are characterized by having a relatively low thermal conductivity. Glass microspheres typically are made by heating tiny droplets of dissolved water glass in a process known as ultrasonic spray pyrolysis.

[00021] A feature and advantage of the present disclosure is by filling the space between the tank walls with glass microspheres, the glass microspheres provide both thermal insulating and structural properties. Thus, structural supports between the tank walls used in prior vacuum cryogenic tanks are not necessary. This eliminates weight in the construction of the tanks, and also eliminates potential thermal paths between the inner and outer walls of the tank. Tanks made in accordance with the present disclosure have other advantages. The glass microspheres filling the space between the inner and outer walls of the tank form a high angle of repose material, whereby to create a lightweight strong sandwich composite structure. Also, the outer tank wall does not need to be built to withstand high vacuum pressures or need supports to withstand soft / medium vacuum pressures. Thus further reducing weight and costs.

[00022] The overall process is as follows. First a wall structure destined to become the inner wall of a tank is wrapped in a bladder formed of a stretchable but strong material, e.g., latex. Then a microsphere “putty” is created using a volatile organic solvent, such as acetone, to fully saturate a solution of glass microspheres such as 3M™ KI glass microspheres which have a diameter of approximately 0.05-0.1mm in a ratio such that the putty is neither too clumpy or too sticky. In other embodiments, a silica anti-caking agent may be added to the putty. The putty is then inserted (e.g., injected, blown in) directly into the space between the tank inner wall and the elastic latex bladder using, e.g., a texture gun. In another embodiment, the microsphere “putty” can be applied 25 09 23 mechanically, e.g., by hand, or by robot over the wall structure destined to become the tank inner wall, and the bladder is then wrapped onto the structure. The microsphere fill is then “wetted out” with volatile organic solvent such as acetone. The tank then may be vibrated or rolled while slowly depressurizing the bladder to evenly distribute the microspheres.

[00023] The resulting putty holds its shape and conforms to orifices and complex geometry of the tank.

[00024] Also, in the case of larger size tanks, a vacuum may be applied and a heat / pressure cycle used to consolidate and drive off solvent, in a vacuum baking process, to form the glass microspheres into a high angle of repose material. Once the high angle of repose material sets, the bladder may be removed.

[00025] Once the tank inner wall is fully encapsulated by the set high angle repose material, with or without a bladder, it can be sprayed with a suitable setting or curing, low outgassing polymer, e.g., fast cure two part epoxy strengthener, with two or three coats each reaching tack before continuing. The fast cure spray is then allowed to reach full cure.

[00026] From here a composite shell is progressively built-up, starting optionally with layers of, e.g., aluminum foil and epoxy, moving on to fiber reinforced plastics (FRP) such as Carbon Fiber Reinforced Plastics (CFRP) layers in a staged process to create the outer tank wall.

[00027] Optionally conventional ambient pressure insulation then can be added such as a spray on foam insulation (SOFI), expanded cork, or a non-vacuum layered composite insulation (NVLCI).

[00028] In still yet another embodiment a microsphere “putty” or glass microspheres is created, that is neither too clumpy or too sticky, and the microsphere putty is directly applied to the outer wall of the structure destined to become the tank inner wall. A silica anti-caking agent 25 09 23 also may be added to the “putty”. The putty holds its shape and conforms to orifices and complex geometry of the tank wall. Additionally, the putty is such that it may be tailored to specific layer thickness depending on degree of thermal protection required for particular areas of the tank, allowing for a highly optimized product.

[00029] Once the tank is sculpted, a release film is applied over the microsphere putty, and using a breather blanket and a vacuum bag to apply vacuum, a heat and external pressure cycle is used to consolidate and drive off the organic solvent, whereby to form the glass microsphere into a high angle of repose material. Upon setting of the high angle of repose material, the breather blanket vacuum bag is removed.

[00030] Once the structure is fully encapsulated with the glass microbead high angle of repose material it is sprayed with a suitable setting or curing, low outgassing polymer, with two or three coats each reaching tack before continuing, it is then allowed to reach full cure, as before.

[00031] From here a composite shell is progressively built-up, starting optionally with layers of metal foil and polymer, moving on to spray on foam insulation, fiber reinforced plastics layers and non-vacuum layered composite insulation layers in a staged process to create the outer tank wall.

[00032] Optionally, conventional ambient pressure insulation then can be added such as a spray on foam insulation (SOFI), expanded cork, a non-volatile, multi-layered insulation, as before.

[00033] In other embodiments, an aerogel may be mixed into the microsphere putty. In yet other embodiments, an aerogel and other material with desirable structural properties such as a polymer or fibers (e.g., fiberglass) may be mixed into the microsphere putty. 25 09 23

[00034] According to aspect A of the present invention there is provided a cryogenic storage tank comprising an inner wall and an outer wall defining a space, wherein the space is filled at least in part with a high angle of repose particulate material consisting of dried-in-place hollow glass microspheres which provides both insulating and structural properties to maintain the space.

[00035] Preferably the inner wall and the outer wall are formed of different materials.

[00036] Preferably the outer wall comprises a built-up wall including one or more non-metallic layers.

[00037] Preferably the inner wall comprises a metal wall and the outer wall comprises one or more layers formed of a metal foil, or one or more layers formed of a fiber reinforced material, or one or more layers of a metal foil and one or more layers formed of a fiber reinforced material.

[00038] According to aspect B of the present invention there is provided a method of forming a cryogenic tank according to aspect A of the present invention, comprising providing a first walled structure configured to form the tank inner wall; wrapping the first walled structure in a flexible bladder; inserting a putty comprising glass microsphere particles in a volatile organic solvent between the outer wall of the first walled structure and the bladder; driving off the solvent to form said glass microsphere particles into a high angle of repose material; optionally removing the bladder; and forming a built-up layer over the glass microsphere particles to form the tank outer wall, or forming a built-up layer directly over the bladder to flow the tank outer wall.

[00039] Preferably the solvent is driven off by heat, by vacuum, or by a combination of heat and vacuum. 25 09 23

[00040] Preferably the built-up layer comprises one or more layers formed of a metal foil, or one or more layers formed of fiber reinforced plastic materials, or one or more layers formed of a metal foil and one or more layers formed of a fiber reinforced material.

[00041] Preferably the method further includes adding a thermal insulating layer over the built-up layer.

[00042] Preferably the putty is inserted by injection or blowing.

[00043] Preferably the method further includes the step of wetting out the glass microspheres with acetone.

[00044] Preferably the glass microspheres are vibrated or rolled while the bladder is depressurized to drive off the volatile organic solvent.

[00045] Preferably the glass microspheres are sculpted to a shape by said vibration or rolling.

[00046] Preferably a heat / pressure cycle is used to drive off the volatile organic solvent.

[00047] Preferably the glass microspheres have diameters of between 1 and 100 micrometers.

[00048] Preferably the method further comprises applying a spray-on foam insulation or expanded cork insulation over the built-up layer.

[00049] Preferably the method further includes the step of mixing an aerogel or carbon nano tubes into the putty.

[00050] According to aspect C of the present invention there is provided a method of forming a cryogenic tank according to aspect A of the present invention, comprising providing a first walled structure configured to form the tank inner wall; 25 09 23 applying a putty comprising glass microsphere particles in a volatile organic solvent on an outer wall surface of the first walled structure; applying a release agent over the putty; applying a bladder over the release agent and heating and / or pulling a vacuum to draw off the organic solvent to form said glass microsphere particles into a high angle of repose material, removing the bladder, and forming a built-up layer over the glass microsphere particles to form the tank outer wall, or forming a built-up layer directly over the bladder to grow the tank outer wall.

[00051] Preferably the built-up layer wall comprises one or more layers formed of a metal foil, one or more layers formed of a fiber reinforced plastic materials, one or more layers formed of a metal foil and one or more layer of a fiber reinforced plastic material.

[00052] Preferably the method further includes adding a thermal insulating layer over the built-up layer.

[00053] Preferably the putty is applied by hand.

[00054] Preferably the putty is applied by a robot.

[00055] Preferably the built-up layer comprises layers of metal foil and polymer and / or a reinforced plastic.

[00056] Preferably the method further comprises applying a spray-on foam insulation or expanded cork insulator over the built-up layer.

[00057] Preferably the method further includes the step of mixing an aerogel or carbon nanotubes into the putty.

[00058] According to aspect D of the present invention there is provided a fuel cell powered aircraft comprising a cryogenic storage tank according to aspect A of the present invention. 25 09 23

[00059] Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for the purposes of illustration only and are not intended to limit the scope of the present disclosure.

[00060] Further features and advantages of the disclosure will be seen in the following detailed description, taken in conjunction with the accompanying drawings. The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations and are not intended to limit the scope of the present disclosure. Fig. 1 is a cross-sectional view of a prior art cryogenic tank; Fig. 2 is a view, similar to Fig. 1 of another prior art cryogenic storage tank; Fig. 3 is a flow diagram of a process for manufacturing a cryogenic storage tank in accordance with a first embodiment of the disclosure; Fig. 3A is a cross-sectional view of a cryogenic storage tank made in accordance with the present disclosure, before optional conventional insulation is added to the exterior of the tank; Fig. 4 is a flow diagram of a process for manufacturing a cryogenic storage tank in accordance with a second embodiment of the disclosure; Fig. 5 is a flow diagram of a process for manufacturing a cryogenic storage tank in accordance with a third embodiment of the disclosure; and Fig. 6 is a schematic view of a hydrogen fuel cell powered airplane having a novel cryogenic hydrogen fuel storage tank in accordance with the present disclosure.

[00061] Example embodiments will now be described more fully with reference to the accompanying drawings. Example embodiments are provided so that this disclosure will be thorough and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a 25 09 23 thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail.

[00062] The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed.

[00063] When an element or layer is referred to as being “on,” “engaged to,” "connected to,” or “coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on," “directly engaged to,” “directly connected to,” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” 25 09 23 etc.). As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[00064] Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and / or sections, these elements, components, regions, layers and / or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments.

[00065] Spatially relative terms, such as “inner,” “outer,” “beneath,” “below,” “lower,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the example term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

[00066] Referring to Figs. 3 and 3A, in accordance with a first embodiment of the present disclosure, we provide a cryogenic storage tank comprising an inner wall structure 50, and an outer wall 54 forming a space 56 between them. The space 56 is filled with a high angle of repose 25 09 23 granular material such as hollow glass microspheres 58, which material is loaded into the space between the inner and outer walls 50, 54, as follows.

[00067] First a walled structure 50 is wrapped at a wrapping step 120 with an elastic bladder 52. Then a microsphere “putty” is created at a mixing step 122 using a volatile organic solvent, such as acetone, to fully saturate a solution of glass microspheres such as 3M™ KI glass microspheres which have a diameter of approximately 0.05-0.1mm in a ratio such that the putty is neither too clumpy or too sticky. In other embodiments, a silica anti-caking agent may be added to the putty. The putty is then inserted (e.g., injected, blown in) in an inserting step 124 directly into the space 56 between the elastic latex bladder 52 and the wall structure 50 destined to become the tank inner wall. The microsphere fill is then “wetted out” with volatile organic solvent such as acetone in a wetting step 126. The putty is then distributed (e.g., one or more of vibrated, rolled, sculpted) while slowly depressurizing the bladder in a distributing step 128 to evenly distribute the microspheres, so that they set in a high angle of repose material. The distributing step 128 may be used to achieve a custom geometry thickness.

[00068] The resulting putty holds its shape and conforms to orifices and complex geometry of the tank.

[00069] Also, in the case of larger size tanks, a vacuum may be applied and a heat / pressure cycle used to consolidate and drive off solvent, to form the glass microspheres into a high angle of repose material in a heating / pressure step 130. Once the high angle of repose material sets, the bladder can be removed.

[00070] Once the tank inner wall is fully encapsulated by the set high angle repose material, the bladder may be removed, or left in place, and with or without a bladder it can be sprayed in 25 09 23 spraying step 132 with a suitable setting or curing, low outgassing polymer, with two or three coats each reaching tack before continuing. The fast cure spray is then allowed to reach full cure.

[00071] From here a composite shell is progressively built-up, starting with layers 140 of, e.g., aluminum foil and epoxy, moving on to carbon fiber reinforced plastic layer in a staged process step 134 to create the outer tank wall 54.

[00072] Conventional ambient pressure insulation 150 then can be added such as a spray on foam insulation, expanded cork, or a non-volatile, multi-layer insulation, etc., in an optional step 136. Layers 140 and insulation 150 may optionally conform to the outer vessel. Since the outer vessel is a composite, it can be made to vary in thickness to allow for mounting points appropriate to the installation location. In other embodiments, the insulation may accommodate tank mounting points.

[00073] In an alternative embodiment, the microsphere “putty” can be applied mechanically, e.g., by hand, or by robot, over the wall structure destined to become the tank inner wall 50 in a step 138. See Fig. 4.

[00074] Referring to Fig. 5, in still yet another embodiment a microsphere “putty” or glass microspheres is created, as before, and the microsphere putty is applied directly to the outer surface 53 of the inner wall structure 50 destined to become the tank inner wall in a step 138. Conventional ambient pressure insulation 150 then can be added such as a spray on foam insulation, expanded cork, or a non-volatile, multi-layer insulation, etc., in an optional step 136.

[00075] Thereafter a release film, e.g., a P3 release film is applied over the microsphere putty (step 162), and using a breather blanket and a vacuum bag to apply vacuum, a heat / pressure cycle, step 164, is used to consolidate and drive off the organic solvent, whereby to form the glass 25 09 23 microsphere into a high angle of repose material. Upon setting of the high angle of repose material, the blanket and vacuum bag is removed in a step 144.

[00076] Once the structure is fully encapsulated with or without a bladder it is sprayed with a suitable setting or curing, low outgassing polymer, with two or three coats each reaching tack before continuing, it is then allowed to reach full cure, as before.

[00077] From here a composite shell is progressively built-up, optionally starting with layers of metal foil and polymer, e.g., aluminum foil and epoxy, moving on to carbon fiber reinforced plastic layer in a staged process to create the outer tank wall, as before.

[00078] Conventional ambient pressure insulation then can be added such as a spray on foam insulation, expanded cork, a non-vacuum, multi-layered insulation, as before.

[00079] In other embodiments, an aerogel may be mixed into the microsphere putty. In yet other embodiments, an aerogel and other material with desirable structural properties a polymer or carbon nanotubes may be mixed into the microsphere putty.

[00080] Fig. 6 schematically illustrates an airplane 180 which includes two electric motors 152 A, 152B which are supplied by two parallel hydrogen fuel cell systems 154A, 154B including two cryogenic hydrogen fuel tanks 156A, 156B.

[00081] Cryogenic tanks made in accordance with the present disclosure offer many advantages, including: • Tanks made according to the instant disclosure can be lightweight, as the outer vessel is fully supported by the high angle of repose material between the tank walls, this creates a lightweight strong sandwich composite structure. Such a design also negates additional weight by having no inner vessel supports. 25 09 23 • Adaptable design, so the heat flux of a system can be tailored in such a way to ensure specific areas of a tank possess a localized flux specific to a particular boil off regime. • The tanks that are low cost to produce but also to maintain since they uniquely operate in the soft vacuum (SV) range, yet provide performance normally only available to HV systems. This can be done thanks to utilizing the Fesmire Effect: as tank cools down, micro-cryopumping of SO2 within the microspheres results in millions of High Vacuum (HV) regions within a SV environment (pseudo MV). • Made using REACH-(Registration, Evaluation, Authorization, and Restriction of Chemicals) compliant, non-toxic chemicals. • Can mold to custom geometries (especially useful, e.g., for integration within an airplane’s existing spaces). • Robust to cryogenic cycling (existing tank designs are significantly cycle life limited). • Robust to vibration. • The tanks are intrinsically safe, and provide redundancy in the event of loss of vacuum as may result from a tank breach. That is to say, due to the presence of the glass microsphere which provide some thermal insulation, tanks made in accordance with the present disclosure possesses good thermal performance even in the event of a loss of vacuum, unlike more conventional tanks such as double walled stainless steel, vacuum jacketed multi-layer insulation tanks. And previous attempts to avoid the danger of vacuum though Multi-Layer Insulation without vacuum are not performant. • Tanks made in accordance with the present disclosure also provide significant weight savings over traditional designs with supports. 25 09 23 • Tanks made in accordance with the present disclosure have a potential for a high IQF (insulation quality factor) attainable relative to other designs since areas around feedthroughs, lines and sensors can be better insulated. • The high angle of repose materials between the tank inner and outer walls can tolerate high compression loading and are fully aggregated and encapsulated, which removes the need for vessel supports between the tank walls. • Tanks made in accordance with the present disclosure provide thermal performance at low pressure and low temperatures (soft vacuum - SV, e.g., 100mTorr@20K).

[00082] The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. By way of example, but not limitation, the cryogenic tanks advantageously may be employed as fuel tanks and / or oxidant tanks for rockets and space vehicles. The tanks also may be employed with conventional land and sea vehicles including, for example, LNG tankers, and as fixed storage tanks, and portable tanks for consumer, industrial, educational and military uses, including, for example, for forming Dewar vessels.

[00083] Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure. Various changes and advantages may be made in the above disclosure without departing from the spirit and scope thereof. 25 09 23

Claims

1. A cryogenic storage tank comprising an inner wall and an outer wall defining a space, wherein the space is filled at least in part with a high angle of repose particulate material consisting of dried-in-place hollow glass microspheres which provides both insulating and structural properties to maintain the space.

2. The cryogenic storage tank of claim 1, wherein the inner wall and the outer wall are formed of different materials.

3. The cryogenic storage tank of claim 1 or claim 2, wherein the outer wall comprises a built-up wall including one or more non-metallic layers.

4. The cryogenic storage tank of any preceding claim, wherein the inner wall comprises a metal wall and the outer wall comprises one or more layers formed of a metal foil, or one or more layers formed of a fiber reinforced material, or one or more layers of a metal foil and one or more layers formed of a fiber reinforced material.

5. A method of forming a cryogenic tank as claimed in any of claims 1 to 4, comprising providing a first walled structure configured to form the tank inner wall;wrapping the first walled structure in a flexible bladder;inserting a putty comprising glass microsphere particles in a volatile organic solvent between the outer wall of the first walled structure and the bladder;driving off the solvent to form said glass microsphere particles into a high angle of repose material;optionally removing the bladder, andforming a built-up layer over the glass microsphere particles to form the tank outer wall, or forming a built-up layer directly over the bladder to flow the tank outer wall.25 09 236. The method of claim 5, wherein the solvent is driven off by heat, by vacuum, or by a combination of heat and vacuum.

7. The method of claim 5 or claim 6, wherein the built-up layer comprises one or more layers formed of a metal foil, or one or more layers formed of a fiber reinforced plastic materials, or one or more layers formed of a metal foil and one or more layers formed of a fiber reinforced material.

8. The method of any of claims 5 to 7, including adding a thermal insulating layer over the built-up layer.

9. The method of any of claims 5 to 8, wherein the putty is inserted by injection or blowing.

10. The method of any of claims 5 to 9, including the step of wetting out the glassmicrospheres with acetone.

11. The method of any of claims 5 to 10, wherein the glass microspheres are vibrated or rolled while the bladder is depressurized to drive off the volatile organic solvent.

12. The method of claim 11, wherein the glass microspheres are sculpted to a shape by said vibration or rolling.

13. The method of any of claims 5 to 12, wherein a heat / pressure cycle is used to drive off the volatile organic solvent.

14. The method of any of claims 5 to 13, wherein the glass microspheres have diameters of between 1 and 100 micrometers.

15. The method of any of claims 5 to 14, further comprising applying a spray-on foam insulation or expanded cork insulation over the built-up layer.

16. The method of any of claims 5 to 15, including the step of mixing an aerogel or carbon nanotubes into the putty.25 09 2317. A method of forming a cryogenic tank as claimed in any of claims 1 to 4, comprising providing a first walled structure configured to form the tank inner wall;applying a putty comprising glass microsphere particles in a volatile organic solvent on an outer wall surface of the first walled structure;applying a release agent over the putty;applying a bladder over the release agent and heating and / or pulling a vacuum to draw off the organic solvent to form said glass microsphere particles into a high angle of repose material, removing the bladder, andforming a built-up layer over the glass microsphere particles to form the tank outer wall, or forming a built-up layer directly over the bladder to grow the tank outer wall.

18. The method of claim 17, wherein the built-up layer wall comprises one or more layers formed of a metal foil, one or more layers formed of a fiber reinforced plastic materials, one or more layers formed of a metal foil and one or more layer of a fiber reinforced plastic material.

19. The method of claim 17 or claim 18, including adding a thermal insulating layer over the built-up layer.

20. The method of any of claims 17 to 19, wherein the putty is applied by hand.

21. The method of any of claims 17 to 20, wherein the putty is applied by a robot.

22. The method of any of claims 17 to 21, wherein the built-up layer comprises layers of metalfoil and polymer and / or a reinforced plastic.

23. The method of claim 22, further comprising applying a spray-on foam insulation or expanded cork insulator over the built-up layer.

24. The method of any of claims 17 to 23, including the step of mixing an aerogel or carbon nano tubes into the putty.

25. A fuel cell powered aircraft comprising a cryogenic storage tank as claimed in any ofclaims 1 to 4.25 09 23

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