Cryogenic liquid container

A container for low temperature liquefied gas includes inner and outer shells forming a sealed evacuated space around the inner shell to insure low heat conduction from the ambient surroundings through the container to the liquefied gas in the inner shell. The container provides gas at relatively low pressure by drawing the liquefied gas from the inner shell to a heat exchanger where it evaporates and is fed to a user. A vacuum insulated access channel is provided through the shells for a fluid output tube through which the liquefied gas is drawn from the inner shell to the heat exchanger. The channel is formed by a thin wall sealing tube that conducts little heat, because the wall is so thin, sealed to the inner shell and enclosed by a support structure including a thick wall structural tube enclosing the thin wall tube and connected rigidly and sealed to the outer shell for structural support between the shells and also provides an annular space around the thin wall tube that is evacuated. The structural tube also connects securely, but moveably, to the inner shell, via a spacer made of low thermal conductivity material, so that the inner shell can move slightly within the outer shell, but not so much as to break the vacuum seal of the thin wall tube to the inner shell.

BACKGROUND OF THE INVENTION 
This invention relates to liquefied gas containers and more particularly to 
such containers having two walls that are sealed together and evacuated 
between the walls for low heat transfer and the liquid is drawn from the 
container through a heat exchanger where it is turned to a gas and fed on 
demand as a gas to a user. The advantage of such containers over high 
pressure gas containers for the same gas is that the gas is stored as a 
low (cryogenic) temperature liquid at relatively low pressure and the 
liquid volume stored is substantially less than the high gas pressure 
volume stored in conventional high pressure containers. 
Heretofore, containers for low temperature liquefied gas have included an 
inner stainless steel shell that contains the low temperature liquified 
gas and an outer stainless steel shell that encloses the inner shell and 
is sealed to it. The space in between the shells is evacuated and the 
connections and support structures between the inner and outer shell are 
held to a minimum, because each such connection and structure is a conduit 
for heat. It has been the practice to provide a passage or channel at the 
top of the container from the outside to inside the inner shell through a 
thin wall stainless steel tube, sometimes called a neck, that is sealed to 
an opening in the inner shell and projects through and is sealed to an 
opening in the outer shell. The thin wall tube provides access to the 
inner shell from outside of the container and is thin walled so that it 
will be a minimum conductor of heat from the outer shell to the inner 
shell. 
One of the problems with such prior containers is that the top end of the 
inner shell is supported within the outer shell only by the thin wall 
tube. This suspension with no support at the bottom of the container acts 
like a pendulum. When the container is tilted, the thin wall tube (called 
the neck) will often break. If the inner shell is also supported by the 
outer shell at the bottom of the container, the bottom support does not 
penetrate the shells and so does not have to make vacuum seals with them 
and so can be very sturdy and made of low thermal conductivity material. 
In that case, the lateral forces on the thin wall tube at the top when the 
container is tipped are worse, because the inner shell cannot swing as a 
pendulum against the outer shell and so the thin wall tube cannot bend to 
release the lateral forces and will rupture sooner than without the bottom 
support. 
Another feature of prior containers is that the low temperature liquid, 
such as liquid nitrogen, is loaded into the container inner shell through 
a thin wall stainless steel input tube that extends from outside the 
container through the neck to the inner shell to substantially the bottom 
thereof. Low temperature liquid is drawn from the container by another 
stainless steel tube, the output tube, that enters the inner shell at the 
bottom from the evacuated space between the shells and immediately 
attaches to a copper tube that extends upward in the evacuated space 
between the shells and is attached by soldering to the inside of the outer 
shell. This copper tube often circles around the inner shell several times 
like a coil to provide a large surface area for conducting heat from the 
outer shell into the liquid to vaporize it as it is drawn through the 
copper tube. At the top of the container the copper tube connects to a 
stainless steel tube that penetrates and is welded to the outer shell and 
then to a gas output valve outside the container. 
Another problem with such prior containers is that any leaks in the vacuum 
space between the shells will ruin the performance of the container. Any 
metal parts (for example support structures and the input and output 
tubes) and gas flow inside the output tubing running between the shells 
adds to the heat leak significantly. 
As a consequence of these problems with prior containers and the high heat 
leakage, the user had to use many container loads each week to justify the 
cost of using the container. As mentioned, the copper vaporizer coil is 
soldered to the inside of the stainless steel outer shell. In order to 
solder these metals, corrosive flux must be used which leaves a residue 
that later produces gases in vacuum and so reduces the effectiveness of 
the vacuum space. Furthermore, because of the high conductivity of copper 
tubing, it is impractical to run copper tubing from the outer shell back 
to the inner shell of the container through the vacuum space and so 
several transitions are required from stainless steel to copper tubing 
inside the vacuum space with a soldered joint for each transition. 
SUMMARY OF THE INVENTION 
It is the object of the present invention to provide a liquefied gas 
container with double walls, evacuated between the walls for low heat 
conduction, wherein the disadvantages and problems with prior containers, 
mentioned above, are avoided. It is another object to provide a container 
for liquefied gas that has inner and outer shells that are sealed together 
and evacuated between the shells, has an access channel from outside the 
container to the inside shell that is enclosed by vacuum and also has an 
adequate structural support of the inner shell from the outer shell at the 
access channel and yet does not provide a ready path for conducting heat 
between the shells. 
It is another object to provide such a container wherein the channel from 
outside the container to the inside shell is formed in part by relatively 
heavy structural members that ensure adequate structural support of the 
inner shell from the outer shell and such structural support does not 
provide a ready path for conducting heat between the shells. 
It is a further object that the channel extend from the outer shell of the 
container to an input/output flow control system and the inner wall of 
such extension is enclosed by an evacuated space that is evacuated at the 
same time the space between the inner and outer shells is evacuated. 
It is another object to provide a double walled liquefied gas container 
wherein the space between walls is evacuated for low heat transfer 
therethrough and liquefied gas is drawn from the container through a 
conduit in the access channel to a heat exchanger outside of the 
container, wherein the liquified gas is evaporated. 
In accordance with the present invention, the container for low temperature 
liquefied gas includes inner and outer shells with an evacuated space in 
between surrounding the inner shell to insure low heat conduction to the 
liquefied gas inside. The container has a channel through the shells to 
inside the inner shell for an input/output fluid conduit tube through 
which liquefied gas is loaded into the container or drawn from the 
container to a heat exchanger outside of the shells. The channel is formed 
by a thin wall inner tube that conducts very little heat because the wall 
is so thin, and a thick wall structural tube that encloses the thin wall 
tube and provides structural support between the two shells and also 
provides an evacuated annular space around the thin wall tube where it 
extends outside the container as the neck. The thick wall structural tube 
connects rigidly to the outer shell and connects securely, but moveably, 
to the inner shell, via a spacer made of low thermal conductivity 
material, so that the inner shell can move laterally slightly within the 
outer shell, but not so much as to break the vacuum seal of the thin wall 
tube with the shells. Thus the inner shell is adequately supported from 
the outer shell by the structural tube, and yet the support structure does 
not provide a ready path for heat flow between the shells, because the 
structural tube is insulated from the inner shell by the spacer and 
contacts the spacer only when the inner shell moves laterally within the 
outer shell. This is called "Lost Motion Support". Liquefied gas is drawn 
from the inner shell through the fluid input/output tube that is inserted 
from outside the container through to the inside of the inner shell and 
the liquefied gas so drawn is fed through a heat exchanger outside of the 
container in which it is heated to gaseous state and fed on demand to the 
user.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION 
Container And Controls 
Turning first to FIG. 1 there is shown a liquefied gas container 1 that is 
a double walled container evacuated between the walls to thermally 
insulate the inside from the ambient surroundings. Access to the inside of 
the container for filling it with liquefied gas and for drawing liquefied 
gas from it and for connection to a liquid level meter 43 is all through 
an access channel 30 in the neck 2 at the top of the container. The neck 
is specially constructed according to the present invention using a 
support technique referred to herein as "lost motion support" so that it 
provides substantial structural support of the inner shell 3 of the 
container from the outer shell 4 when needed and, at the same time, 
provides access channel 30 to the inside of the inner shell 3 which is 
insulated by vacuum as is the rest of the container. Details of 
constructions of the special insulated structural neck 2 are described 
herein more fully with respect to FIGS. 2 and 3. 
As shown in FIG. 1, an input/output liquid conduit tube 5 extends from the 
bottom of inner shell 3 at point 6, upwards through channel 30 of neck 2 
to line 7 that connects to liquefied gas fill valve 8 and to output 
vaporizer coils 9 and from coils 9 to gas use valve 10. Liquid level meter 
43 shows the position of float 12 extending rod 12a, indicating the level 
19 of liquefied gas in the container. 
Gas vent tube 11, extends from the top of inner shell 3 up through neck 2 
to tube 13 that connects to vent valve 14, pressure gauge 15, burst disk 
16, and relief valve 17. Between tubes 7 and 13 is economizer valve 18 
that feeds gas from the top of the container to the vaporizer 9, whenever 
gas use valve 10 opens. The purpose of economizer valve 18 is to feed gas 
from the top of the container at 13 before liquid is drawn through tube 5 
from the bottom of shell 3 and so the head of gas that builds up in the 
container is drawn off before liquid is drawn off for use. 
A pressure building system 20 consists of pressure fitting 21 at the bottom 
of the inner shell that connects to another fitting 22 through the outer 
shell to pressure building vaporizing coil 23 and from that coil to 
another fitting 24 back through the outer shell to a length of rigid 
tubing 25 extending from fitting 24 upwards in the container in the vacuum 
space 50 between the shells to fitting 26 at the top of the outer shell. 
From fitting 26 the pressure building system goes to pressure building 
valve 27 and pressure regulator 28 that connects to gas line 13 at the top 
of gas vent tube 11. The purpose of the pressure building system is to 
draw liquid from the bottom of the container as necessary to build the gas 
pressure in the container and valve 27 and pressure regulator 28 are 
adjusted to accomplish this. 
Typical operation of a container such as the one shown in FIG. 1 to store 
liquefied gas such as liquid nitrogen, oxygen, or argon, is as follows: 
the container may be about two feet in diameter and about six feet high 
and stores a maximum of 65 gallons at 235 pounds per square inch (psi) 
pressure. For storing liquid oxygen, such a container would hold about 525 
pounds of liquid oxygen which has a gaseous equivalent (NTP) of about 
6,360 cubic feet. From such a container, continuous gas flow from the gas 
use valve 10 in an ambient surrounding at standard temperature and 
pressure, is about 350 cubic feet per hour and can peak for short 
durations as high at 1000 cubic feet per hour. The normal daily 
evaporation rate of oxygen is less than 1 percent of the total capacity. 
The pressure relief valve 17 is set for 235 psi and the input/output 
tubings 5 and 7 and the gas vent line 11 and 13 are all one half inch OD 
tubing. A single container such as this has the equivalent capacity of 
approximately 24 high pressure gas cylinders with greatly reduced handling 
system contamination, purging and down time involved. In addition such a 
container is quite safe, because it operates at a maximum of 235 psig 
instead of about 2400 psig for compressed gas cylinders and it produces 
purer gas with less water contamination and it can be used for both liquid 
withdrawal at low pressure (about 22 psi) or gas withdrawal at pressure up 
to 255 psi. 
Structural Insulated Neck 
According to features of the present invention shown in FIGS. 2 and 3, the 
neck 2 that extends from the inner shell 3 of the container 1 provides 
access channel 30 into the inner shell that is vacuum insulated the full 
length of the channel. The channel and neck are formed by two concentric 
tubes, a thick wall outer structural tube 31 and a thin wall inner tube 
32, the structural tube providing support for the inner shell from the 
outer shell and the thin wall tube providing the vacuum enclosed, low 
thermal conductivity channel 30 to the inner shell. A fiber glass spacer 
33 is used between the extension of the structural tube from the outer 
shell into the vacuum space 50 and a heavy boss 34 welded to the top of 
the inner shell. Should the inner shell sway, the fiber glass spacer is 
moved by the boss against the structural tube at 35 which keeps the inner 
shell from moving so far that the seal of the thin wall inner tube 32 to 
the inner shell breaks. The fiber glass spacer 33 normally does not bear 
against the inner shell boss, and so there is essentially zero heat leak 
through the structure in normal use. The only time the spacer 33 bears 
against inner shell boss 34 is when the inner shell moves laterally. This 
is called "Lost Motion Support". 
FIG. 2 shows the container 1 of the schematic of FIG. 1 and represents a 
typical container of the size and use described. The cross section view 
reveals the access channel and tubing connections to the container, but 
none of the control valves and pressure regulating systems of FIG. 1. FIG. 
3 is an enlarged cross section view of neck 2 and access channel 30 
showing details of the channel and support structure for the inner shell 
where it extends from the container to the control valve system shown in 
FIG. 1. The neck 2 extends between a central opening 36 at the top of 
inner shell 3 and a central opening 37 at the top of outer structural 
shell 4. The support structure of the neck includes boss 34 welded to the 
inner shell at the opening 36 and extending into vacuum space 50 
concentric with the axis 40 of the container, and structural tube 31 which 
is welded to the outer shell at hole 37 and extends into the space 50 
overlapping part of boss 34 and spaced therefrom by fiberglass spacer 33. 
Structural tube 31, spacer 33 and boss 34 are loosely connected by radial 
bolts 38 that screw firmly into the boss and fit loosely through holes in 
tube 31 and spacer 33. This structure allows some lateral motion of the 
top of the inner shell with respect to the outer shell, but not so much as 
would damage the seal of thin wall tube to the inner shell. 
The other end of structural tube 31 extends upward beyond the outer shell 
to a sealing flange 39. Thin wall tube 32 is inside the structural tube 
and inside boss 34 and is welded to hole 36 in the inner shell or is 
welded to boss 34 and extends upward within tube 31 to flange 39 and is 
welded to the flange. Flange 39 is attached and sealed to a header 42, 
shown in FIG. 4, to which tubes 7 and 13 connect, and a liquid level fill 
gauge 43 is carried on the header as described more fully herein with 
respect to FIG. 4. 
Thus, at the top of the container the connection from inner shell 3 to boss 
34 and from the boss to structural tube 32, via spacer 33, and bolts 38 is 
a loose connection that allows limited lateral motion without damage to 
the thin wall tube seal to the inner shell. At the bottom of the 
container, the inner shell is held rigidly where it rests on a cylindrical 
fiberglass support member 45 that fits inside of metal sleeve 46 that is 
welded to the outside of inner shell 3 and fits outside of an inner sleeve 
47 that is welded to the inside of the outer shell 4. This bottom support 
provides rigid support for the inner shell from the inside of the bottom 
of the outer shell and that support includes the thermal barrier offered 
by fiberglass support 45. In this way, the inner shell is supported at the 
top and bottom by connections to the outer shell that include thermal 
barriers provided by fiberglass spacer 33 at the top and fiberglass 
support 45 at the bottom. 
Since the neck 2 at the top extends beyond the container to header 42 and 
thin wall tube 32 of the neck exposes the low temperature gas and liquid 
within the inner shell to structural outside tube 31, it must be 
insulated. Insulation is provided by the extension of the vacuum from 
space 50 up into the annular space 60 that encloses tube 31. Annular space 
60 is sealed at flange 39 at one end and at the other end it opens through 
fiber glass spacer 33 to vacuum space 50. Thus, when a vacuum pump is 
attached to fitting 29 drawing down a vacuum in space 50 between the 
shells, it also draws down the same vacuum in the annular space 60 and so 
protects the access channel 30 in neck 2 from heat flow. 
Vaporizer 
In order to avoid the heat leaks associated with an output vaporizer coil 
located in the vacuum space between the shells as in prior cryogenic 
containers, the output vaporizer coil 9 in the present invention is 
located on the top of the container in ambient air. By this improvement 
alone, the loss of gas due to heat leak per day is reduced by more than 
fifty percent. This improvement greatly expands the range of uses for such 
a container. For example, a user using only a few high pressure gas 
cylinders a week can economically use the improved container to replace 
high pressure cylinders. 
In addition, this improvement avoids the use of dissimilar metals, 
corrosive fluxes, and difficult soldering inside the space between shells 
and results in significant cost savings as well as improved reliability of 
the container. 
According to another feature of the present invention, input and output to 
the container (loading and unloading) is through a single line of 
stainless steel tubing 5 that is simply lowered into access channel 30 
opening at the top of the container from header 42 and output valve 10 
controls the output flow through vaporizer coil 9 wherein the liquid is 
heated by ambient air and delivered at room temperature through the valve. 
Vaporizer 9 may be several hundred feet of copper tubing which has been 
formed in alternate pancake rolls as described more fully therein with 
respect to FIG. 4. 
Turning next to FIG. 4 there is shown an enlarged view of the top of the 
container, partially in cross section, showing outer shell 4, neck 2 and 
header 42, already described with reference to FIGS. 2 and 3. In addition, 
FIG. 4 shows liquid fill valve 8 leading from tube 7 from the header, 
pressure building regulator 18 and the arrangement of the vaporizer coils 
9 at the top of the container within a partially enclosed area 70 that 
insures circulation of ambient air around and about the coils for 
efficient vaporization of the liquefied gas drawn from the container. A 
shroud 71 is spaced around the top of the container so that the cold air 
can circulate out from underneath the shroud. A cover 72 for coil 9 is 
provided on the top of the container with perforated holes in it to let 
ambient air in. Shroud 71 meets the outside of outer shell 4 at the top, 
providing a moat around the top for accumulating water condensate from 
ambient air from output vaporizer coils 9 and the rest of the valves etc. 
on top of the container. An overflow tube 73 pours this accumulation into 
a suitable collector so that it does not flow down around the container. 
This arrangement allows use of natural convection for warming the liquid 
flowing through the coils and avoids flow of condensation and melted ice 
down the container. 
As shown in FIG. 4, the first turn of the coil from the header (tube 7) is 
turn 91 of bottom row 101 carried at the bottom step 92 of wire rack 93. 
This bottom row is wound from the inside to the outside and so the first 
turn 91 is at the inside of bottom step 92. The last turn 94 of bottom row 
101 is followed by the first turn 95 of the second row 102 which is wound 
from the outside to the inside. Following that, the coil turn spacing 
repeats this sequence for each successive row from row 101 to row 107. 
Thus, the vaporizer turns alternately begin the rows of turns at the 
inside, and the outside. In this way the vaporizer conducts liquefied gas 
from the container over a path that spirals outward and downward, then 
inward and upward, then outward and downward, then inward and upward, and 
so forth. 
Output vaporizer 9 receives the cold liquefied gas at the bottom row 101 
and delivers gas from the outside turn 99 of top row 107. This arrangement 
provides a counter current flow of warm ambient air coming down from the 
top to the bottom and the cold liquefied gas coming in from the bottom and 
the warmer gas leaving from the top and insures the most efficient use of 
the ambient air that flows in by thermal convection at the top through 
openings in cover 72 and out at the bottom through openings such as 74. 
The benefit of this reversing pattern between the rows of coils is to 
insure gradual change from low temperature liquid to higher temperature 
gas as it flows through the coil and so the crossover tube from one row to 
the next row (ie from 94 to 95) does not pass much colder or much warmer 
tubes. 
The container inner and outer shells and all tubing are preferably made of 
stainless steel. Fittings, valves and other controls are preferably made 
of brass. Output vaporizing coil 9 at the top is preferably made of copper 
and pressure building vaporizing coil 23 at the bottom is preferably made 
of stainless steel. There are several reasons for this including the fact 
that the thermal conductivity of copper is high, while the thermal 
conductivity of stainless steel is relatively lower. Vaporizers are the 
only parts of the container and its controls where high thermal 
conductivity is desired. Elsewhere, vacuum insulation is provided and 
structural connections to the inner shell are interposed between stainless 
steel parts to provide barriers to thermal conduction. 
The container for liquefied gas described herein, its structures, 
insulation, vaporization, flow and controls incorporates in the several 
embodiments described all features of the present invention and represents 
the best known use of those features. It should be clearly understood that 
these features may be used in other equipments by those skilled in the art 
with some variations without departing from the spirit and scope of the 
invention set forth in the appended claims.