US3864928A

US3864928A - All-attitude cryogenic vapor vent system

Info

Publication number: US3864928A
Application number: US452119A
Authority: US
Inventors: Lester Kurt Eigenbrod
Original assignee: Union Carbide Corp
Current assignee: Puritan Bennett Corp
Priority date: 1972-12-01
Filing date: 1974-03-18
Publication date: 1975-02-11
Anticipated expiration: 1992-02-11
Also published as: DE2510739A1; GB1483182A; DE2510739B2; DE2510739C3

Abstract

Oxygen gas is vented so as to avoid overpressure in an inadvertently horizontally positioned liquid storage-gas dispensing container having top and bottom ends and being invertible between top-up normal dispensing and bottom-up normal filling positions.

Description

United States Patent Eigenbrod 51 Feb. 11, 1975 ALL-ATTITUDE CRYOGENIC VAPOR VENT SYSTEM lnventor: Lester Kurt Eigenbrod,

Indianapolis, Ind.

Union Carbide Corporation, New York, NY.

Filed: Mar. 18, 1974 Appl. No.: 452,119

Related U.S. Application Data Assignee:

Continuation-impart of Ser. No. 311,091, Dec. 1,

1972, Pat. No. 3,797,262.

U.S. Cl 62/50, 62/55, 128/203,

141/5, 222/3 Int. Cl. F17c 7/02 Field of Search 62/50, 52, 55; 128/203,

l28/DlG. 27', 141/5; 222/3 Primary E.\'aminerMeyer Perlin Ass'islanl ExaminerRonald C. Capossela Attorney, Agent, or Firm-.lohn C. LeFever [57] ABSTRACT Oxygen gas is vented so as to avoid overpressure in an inadvertently horizontally positioned liquid storagegas dispensing container having top and bottom ends and being invertible between top-up normal dispensing and bottom-up normal filling positions.

10 Claims, 7 Drawing Figures JVVS/ VVVVVVW PAIENIED Y 3.864.928

SHE'ETZUFE.

F 1 sfz PATENIEI] FEB I I I975 I SHEET 3 DFB TIME IN MINUTES 9ISd 38088388 IPAIENTEI] FEB! 1 I975 SHEET 5 OF 6 ALL-ATTITUDE CRYOGENIC VAPOR VENT SYSTEM This application is a continuation-in-part of Ser. No. 311,091, filed Dec. 1, 1972 now U.S. Pat. No. 3,797,262 in the name of Lester K. Eigenbrod.

BACKGROUND OF THE INVENTION This invention relates to a method of and apparatus for venting gas, e.g., breathing oxygen, from a cryogenic liquid storage gas supply system.

In the prior art systems for supplying breathing oxygen from a liquid oxygen source as for example described in U.S. Pat. No. 3,199,303, certain disadvantages have become apparent as the system is used in the home or hospital for medical therapy of pulmonary and cardiac disorders.

For example, it has been impossible to completely fill the inverted liquid oxygen storage-dispensing container from the larger liquid oxygen container positioned beneath and connected to the first-mentioned smaller vessel. This is because the same conduit in the smaller container is relied on for gas venting in both the inverted liquid filling step and the top-up liquid dispensing step. Stated otherwise, the gas vent conduit terminates at about the midpoint of the smaller container so that it may be used for venting oxygen vapor when the container is in the bottom-up position for filling. Accordingly, the container may only be half-filled or the gas vent conduit would be submerged. This of course means that the liquid storage volume is only half-used, an important disadvantage when one recognizes that the cryogenic liquid storage-dispensing container must be sufficiently small for manual handling by one person, in particular repositioning between top-up and bottom-up.

The aforementioned disadvantages have been overcome by the cryogenic fluid supply system described and claimed in my aforementioned application Ser. No. 311,091 now U.S. Pat. No. 3,797,262. An important characteristic of this improved system is the dual function of certain elements. For example, the conduit means used for gas venting of the storage-dispensing container highest zone (top-up end) to avoid overpressure during the gas supply step becomes the liquid fill conduit means when the container is inverted to the bottom-up position. Cryogenic liquid is upwardly charged from the supply container through this same conduit into the lowest zone (top-down end) of the inverted storage-dispensing container. Also, the conduit used for liquid withdrawal from the lowest zone (bottom-down end) of the storage-dispensing container during the gas supply step becomes the gas vent conduit during the liquid charging step when the container is inverted. The atmospheric vaporizer used for vaporizing liquid discharged from the storage-dispensing container during the gas supply step is used to warm the cold vent gas during the liquid charging step, thereby avoiding the discharge of cold gas in the close vicinity of the user. This interchangability of function facilitates an extremely light and compact system well-suited for supplying breathing oxygen to people who must move about while carrying the storage-dispensing container. lt also permits complete filling of the storage dispensing container with cryogenic liquid.

Notwithstanding the advantages of this cryogenic fluid supply system (hereinafter referred to as the invertible dual vent system), it has a specific unique disadvantage. If the container is inadvertently placed in a non-vertical position (i.e., either inclined or horizontal) when nearly or completely filled with cryogenic liquid, then the internal ends of both the gas vent-liquid fill conduit (terminating in the container normally top end) and the liquid withdrawal-gas vent conduit (terminating' in the container normally bottom end) may be immersed in liquid. Such immersion reduces drastically the pressure relieving capabiligy of the venting circuits and may produce hazardous overpressures. Moreover, discharging of cold cryogenic liquid could result with potential risk to the user and with attendant high loss of stored fluid.

In the prior art systems for supplying breathing oxygen from liquid oxygen, these dangers were not present because the gas vent conduit is always in the interior vapor space regardless of the overall position of the liquid storage dispensing container. Liquid was thereby prevented from being discharged through the gas vent conduit; The importance of these features will be appreciated by a brief consideration of the practical usage of such oxygen supply systems. The invertible liquid oxygen storage-dispensing container is designed to be carried by a moving patient and consequently is relatively small, as for example containing only about 1.6 pounds of liquid oxygen. Considering the small size of this container, any liquid venting would be highly undesirable and represent an important loss of breathing oxygen capacity. Even more importantly, such venting is hazardous to the user because of the possibility of severe burns from skin contact with the liquid oxygen. Also, venting ofliquid could result in highly localized oxygen concentrations as the liquid vaporizes with the danger of ignition of nearby combustible materials.

It might appear that the cold fluid venting problem of such horizontally positioned invertible dual vent systems could be solved by simply installing automatic closure means on both gas vent conduits and activating such closure means when the container is displaced from the vertical. This however is not a practical solution to the problem because of the dual functions of these conduits, i.e., both conduits are employed when the container is inverted in the bottom-up filling position. In addition with both conduits closed there would be no provision for relieving over-pressure due to evaporation of the contained liquid.

Another possible approach to the venting problem would appear to be merely increasing the venting capacity of the safety relief means provided on the gas vent-liquid fill conduit, and by passing the fluid thus vented through vaporizing and superheating apparatus external of the container. The capacity of the safety relief means and its associated vaporizer could be made sufficiently large to appropriately limit over-pressure even when the internal end of the gas vent-liquid fill conduit is inadvertently submerged. However, the physical size and weight of such a vaporizersuperheater would become prohibitively large. The magnitude of the increase in capacity of the safety relief means which is needed in order to properly function with the inlet end submerged can be better appreciated from the following comparison. Assume that one unit volume of cryogenic fluid is removed from a container at 50 psig and is warmed at this pressure to C for venting. If the unit volume is removed as liquid, then its volume at 50 psig after warming will be over 50 times greater than if the unit volume has been removed as vapor. Moreover, the unit volume of liquid requires about 100 times more heat for warming to 70F than does one unit volume of vapor. This approach to the venting problem would add excessive weight and bulk to a small portable oxygen breathing apparatus. It is estimated that the size of a practical breathing apparatus would be necessarily increased about 30-35 percent by such approach.

An object of this invention is to provide an improved invertible dual vent cryogenic fluid supply system which will vent only gas if inadvertently placed in a non-vertical position.

Another object is to provide such a cryogenic fluid supply system with a gas venting system which does not necessitate a larger apparatus.

Other objects and additions will be apparent from the ensuing disclosure and claims.

SUMMARY This invention relates to an all-attitude pressure relief system for invertible dual vent cryogenic fluid supply systems as for example used for portably dispensing oxygen breathing gas.

1n this cryogenic liquid storage gas supply system a thermally insulated cryogenic liquid storage-dispensing container is included; it has top and bottom ends and is invertible between top-up dispensing and bottom-up filling positions.

Gas vent liquid fill conduit means are also provided with a first end terminating in the container top end and a second end outside the container top end. This system further includes liquid withdrawal-gas vent conduit means with a first end terminating in the container bottom end and the second end outside the container top end. An invertible liquid vaporizing-gas vent control circuit is located outside the container and joined at a first inlet end to the liquid withdrawal-gas vent conduit means second end. This circuit includes a first atmospheric vaporizer, and gas flow regulating means between the first atmospheric vaporizer and the gas discharge other end of the circuit.

The apparatus of this invention includes an allattitude pressure relief system for the container comprising (a) first higher pressure relief means between said first atmospheric vaporizer and said gas flow regulating means, (b) branch conduit means having one end in flow communication with the gas-vent-liquid fill conduit second end, (c) second flow restriction-pressure relief means in the branch conduit (b) constructed to vent gas at lower abs. pressure than said first pressure relief means and at a maximum rate between 3 and 25 times the normal evaporation rate from the container, and (d) a second atmospheric vaporizer in flow communication at its inlet end with the branch conduit one end and in flow communication at its discharge end with the second flow restriction-pressure relief means. The second atmospheric vaporizer is constructed with a heat transfer capacity not greater than one-third the first atmospheric vaporizer heat transfer capacity and also sufficient to vaporizer cryogenic liquid entering its inlet end and to discharge warmed gas at its discharge end at a rate between 1.04 and 1.30 times said maximum rate.

In another aspect of this invention a method is provided for supplying gas from a thermally insulated cryogenic liquid-storage-dispensing container having top and bottom ends and being invertible between top-up dispensing and bottom-up filling positions and wherein during the gas supplying step, cryogenic liquid is flowed by overhead vapor pressure upwardly from the lowest zone of the container, discharged from the container top end and vaporizer by atmospheric heat to form gas supply. More particularly, in the improved method and in the top-up dispensing position: (a) when gas is not being supplied vapor is vented through a passage from the highest zone of the container at flow-restricted maximum rate between 3 and 25 times the normal evaporation rate from the container, warmed by atmospheric heat and discharged when the container pressure is above a first lowest superatmospheric relief pressure. Also (b) when gas is being supplied, cryogenic liquid is flowed by overhead vapor pressure upwardly from the lowest zone of the container and discharged from the latters top end. The so-discharged liquid is vaporized by atmospheric heat, warmed and withdrawn as the gas supply, and vapor is simultaneously vented in accordance with step (a).

When the container is in a non-vertical position such that liquid flow through the passage of step (a) and if the container gas pressure rises above the first lowest superatmospheric relief pressure, first liquid is discharged from the normally top end at a first lower flowrestricted rate, vaporized and warmed to ambient tem perature and then released at pressure above the first lowest superatmospheric relief pressure. The container pressure rises to a second higher superatmospheric relief pressure which is between 1.08 and 1.75 times the first superatmospheric relief pressure on an absolute basis, second liquid is simultaneously discharged from the normally bottom end of the container at a second higher rate, vaporized and warmed to ambient temperature and finally released at pressure above the second superatmospheric relief pressure.

As used herein, atmospheric vaporizer means a heat exchanger with a closed passage for receiving cryogenic liquid and discharging gas and for supplying latent heat of vaporization to the cryogenic liquid only from the ambient atmosphere rather than from a second fluid flowing in a second closed passage. Also, heat transfer capacity of the first and second atmospheric Vaporizers refers to their external surface areas since the latter comprises the controlling resistance of heat transfer. When one or both of the atmospheric vaporizers is provided with external secondary heat transfer surface such as fins, then heat transfer capacity refers to the equivalent primary surface area of the vaporizer. That is, such secondary surface area is converted to equivalent primary surface area by applying fin efficiency factors in the well-known manner.

As used herein, normal evaporation rate means the average rate at which stored oxygen liquid is vaporized internally of an insulated container and the gas discharged therefrom solely to compensate for heat inleakage from the surroundings. The determination of the normal evaporation rate is made by employing a container having thermal insulation of normal effectiveness, filling the container to normal full level, p0- sitioning the container in normal top-up orientation, allowing the container and contents to thermally equilibrate at an internal pressure substantially equal to the minimum intended operating pressure for liquid oxygen discharge, and measuring the rate at which gas is vented. The condition of thermal equilibration is assumed to be reached when the initially high vent rate after filling has subsided to a steady, uniform rate. After equilibration, the vent rate may be measured directly by instantaneous rate of gas flow and several such measurements are preferably taken at spaced intervals of time and averaged. Alternatively, the container with contents may be carefully weighed at the beginning and end of a time period of uniform venting and the weight change may be ratioed to the lapsed time to obtain an average vent rate. The average vent rate so determined is then converted to normal temperature and pressure, i.e., 1 atmosphere pressure and 70F, to obtain the normal evaporation rate of the container.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic drawing taken in cross-sectional elevation of a cryogenic liquid storage-dispensing container and liquid vaporizing-gas discharge control circuit in the top-up position with the all-attitude gas relief circuit of this invention.

FIG. 2 is a schematic drawing taken in cross-sectional elevation of the FIG. 1 container, liquid vaporizing-gas discharge gas relief circuit in the inverted bottom-up position and joined to a cryogenic liquid supply container, during the liquid charging the gas vent step.

FIG. 3 is a schematic drawing in cross-sectional elevation of a preferred liquid vaporizing-gas vent control circuit in the top-up position, and differing from the FIG. 1 embodiment by the employment of pneumatic control and a four-way atmospheric gas vent valve means.

FIG. 4 is a graph showing the oxygen gas pressure DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now more specifically to the drawings, FIG. 1 illustrates a vertical cryogenic liquid storagedispensing container 10 and all-attitude gas relief circuit during the gas supplying period. Container 10 comprises an outer casing 11 and an inner vessel 12 for holding the cryogenic liquid, with an evacuable space therebetween preferably filled with thermal insulation 13 as for example the alternate layers of aluminum foil and glass fiber sheets described in US. Pat. No. 3,007,596 to L. C. Matsch. Container 10 has top and bottom ends 14 and 15, respectively, and is invertible between top-up and bottom-up positions. It is preferably sufficiently small for manual movement and inverting. Gas vent-liquid fill conduit means 16 has a first end 17 extending through and terminating in the normally top-up end 14 of container 10 and a second end 18 outside and above such normally top-up end. Second coupling means 19 is joined to and above second end 18 when container 10 is in the top-up position.

Liquid withdrawal-gas vent conduit means 21 also extends through the container top end 14 with the first end 22 thereof terminating in the normally bottomdown end 15 above the inner vessel base. The second end 23 of liquid withdrawal-gas vent means 21 is outside and above the normally top-up end 14 of container 10. Invertible liquid vaporizing-gas vent control circuit 24 comprises liquid sensing means 25 joined to the liquid withdrawal-gas vent means second end 23, first atmospheric vaporizer 26 joined at one end to the liquid sensing means 25, and atmospheric gas vent valve means 27 joining the other end of the atmospheric vaporizer.

Signal transmitting means are also provided for automatically closing atmospheric gas vent valve means 27 in response to the sensing of liquid by the liquid sensing means. Such means may for example be based on a thermistor 25a and comprise electric signal receiving wire 28, controller 29, and electric signal transmitting wire 30 joined to a solenoid-operated vent gas valve 27. More particularly, controller 29 contains a relay and low amperage current flows from the relay coil through wire 28 and thermistor 25a. With only gas flow around thermistor 25a its resistance is 100-300 ohms but when wet with cryogenic liquid its resistance increases to 6,000-l0,000 ohms. This increased resistance trips the controller 29 relay so that its contacts open in the wire 30 circuit to vent valve 27, closing same.

During the gas supplying period, the user may select gas (e.g., oxygen) supplying rates by manually controlling the gas flow regulating means as for example supply valve 31 located between the first atmospheric vaporizer other end (opposite liquid sensing means 25) and gas vent valve 27. When valve 31 is open, overhead vapor pressure forces cryogenic liquid upwardly from the container lowest zone or end 15 and through liquid withdrawal-gas vent conduit 21, past liquid sensing means 25, and through first atmospheric vaporizer 26 where the liquid is vaporized.

The all-attitude gas relief circuit includes first pressure relief valve 32 in branch conduit 33 downstream of first atmospheric vaporizer 26. Stated otherwise, first pressure relief valve 32 is in communication with the conduit system between the other end of atmospheric vaporizer 26, atmospheric vent valve 27 and gas supply valve 31, and is constructed to release gas at superatmospheric pressure.

The gas relief circuit also includes branch conduit 34 in flow communication at its inlet end with gas ventliquid fill conduit 16, and having second flow restriction pressure relief means 36 therein constructed to release gas at lower superatmospheric pressure than first pressure relief valve 32 and at maximum predetermined rate between 3 and 25 times the normal evaporation rate from the container. Second atmospheric vaporizer 35 is in branch conduit 34 with its inlet end in flow communication with the branch conduit inlet end and with its discharge end in flow communication with the second flow restriction pressure relief means 36. Second atmospheric vaporizer 35 is constructed with a heat transfer capacity sufficient to vaporize liquid entering its inlet end and to deliver warmed gas at its discharge end at a rate between 1.04 and 1.30 times the maximum flow rate through second flow restriction pressure relief means 36.

Although flow restriction-pressure relief valve 36 illustrated in FIG. 1 may comprise the major flow restriction pressure relief means, other structural components may be used in addition thereto as performing part of the same function. For example, a separate flow restriction element 36a such as an orifice or porous member may be placed at the discharge end of the conduit 34, downstream valve 36. If the passage size of conduit 34 and vaporizer 35 are relatively large, e.g., the same size diameter as branch conduit 33, a separate flow restrictor element is needed in order to limit flow to within 3 and 25 times the normal evaporation rate and to keep the required length of vaporizer 35 small, consonant with a small overall apparatus size. Flow restrictor 3611 may alternatively be located upstream rather than downstream pressure relief means 36 and will provide the same overall system performance, but the downstream location is preferred since it prevents introduction of atmospheric contaminants such as dust through the conduit 34 discharge end.

In preferred practice of the invention, a fixed flow restriction element 36a is provided in series with relief valve 36 in order to provide more positive assurance that the heat transfer capacity of the second atmospheric vaporizer will not be exceeded. For many relief valves, the size of the flow passage through the valve increases with pressure above its set point such that its effectiveness as a flow-limiter is diminished. With a fixed restriction in the circuit, an increase in valve opening transfers a larger fraction of the total circuit flow resistance to the fixed restriction, thereby preventing an overloaded condition in the relief circuit.

in the practice of this invention second atmospheric vaporizer 35 will be limited by space and weight considerations to a heat transfer capacity not greater than one-third and preferably not greater than one-fifth the capacity of first vaporizer. With such limitation the overall size of the portable package is not greatly increased thereby, yet only gas venting can be assured if the package is inadvertently positioned horizontally. To insure that the second vaporizer capacity is not exceeded, the second flow restriction-relief means 36 is constructed to limit the maximum rate of flow to a value below that which would exceed the vaporizer capacity. Since the ambient air side of these vaporizers controls the fluid (heat transfer) capacity, the outer surface areas may be used for this comparison.

It will also be understood that for safety reasons a high pressure bursting disk 38 may be located in conduit 34 between second vaporizer 35 and second flow restriction-pressure relief means 36. Alternatively the bursting disk may be positioned in gas delivery conduit 33 immediately upstream gas delivery valve 31, but the former is the preferred location. The reasons for this preference are: l the bursting disk is directly in communication with the gas phase in the container top-up position, (2) the length of delivery gas conduit 33 is minimized and (3) the bursting disk is maintained at ambient temperature during operation so that its accuracy is not impaired.

it has previously been indicated that according to the apparatus of this invention, the second flow restrictionpressure relief means 36 is constructed to vent gas at lower pressure than first pressure relief means 32 and at maximum rate between 3 and 25 times the normal evaporation rate (NER) from the container, preferably between 5 and times the NER. Similarly, in the instant method in the top-up dispensing position vapor is vented through a passage from the highest zone of the 8 container at flow restricted maximum rate between 3 and 25 times the NER and preferably between 5 and 20 times the NER.

The lower pressure portion of the all-attitude gas relief circuit is primarily intended to avoid overpressure when container 10 is in its normal top-up fluid dispensing position and with a reasonably high quality thermal insulation 13 and low absolute pressure in the evacuable space on the order of 1 micron Hg. Under these circumstances the maximum vent gas rate need only be about three times the NER so as to insure protection against the possibility that the insulation vacuum might be partially lost due to leakage, such that the evaporation rate increases substantially above the NER. It will of course be noted that the higher pressure first relief means 32 serves as backup for lower pressure second flow restriction-pressure relief means 36, but operation of the latter should be avoided except in instances when unexpected cryogenic fluid vent loads occur, i.e., when container 10 is inadvertently placed in a nonvertical position. This is because such operation rather quickly releases virtually the entire contents of the container, tends to cause frosting (and loss of effectiveness) of first va'porizers 26 external surface and may even cause freeze up of relief means 32.

The maximum vent gas rate of second flow restriction-pressure relief means 36 does not exceed 25 times the container NER so as to avoid the necessity of a prohibitively large and heavy second atmospheric vaporizer 35 which would not be portable. The maximum vent gas rate range of between 5 and 20 represents a preferred balance of the foregoing considerations.

Another requirement of the instant apparatus is that the second atmospheric vaporizer be constructed with a heat transfer capacity not greater than one-third and preferably not greater than one-fifth the first atmospheric vaporizer heat transfer capacity. The latters capacity is determined by the need for warming cold vapor discharge from container 10 in the top-down liquid filling position, thereby avoiding pressure buildup and release of cold vapor during the fast liquid fill, i.e., less than about 4 minutes. The first atmospheric vaporizer 26 must be relatively large, e.g. 17 feet of unfinned A inch tubing, and occupies most of the available space within the case surrounding container 10. Under these circumstances second atmospheric vaporizer 35 can only be a small fraction of the first vaporizer size or the overall assembly becomes so large and heavy as to be non-portable.

in the method of this invention and with the container in a non-vertical position, it has been stated that when the container pressure rises to a second higher superatmospheric relief pressure between 1.08 and 1.75 times the first atmospheric relief pressure on an absolute basis and preferably between H5 and 1.4 times the first relief pressure, second liquid is discharged from the normally bottom end simultaneously with the first liquid discharge from the normally top end of the container. The aforementioned lower limit of 1.08 and preferably 1.15 is needed to insure that the higher pressure first relief valve 32 will operate only when the pressure relieving capability of the lower pressure second relief means 36 has been exceeded. This lower limit reflects manufacturing and adjustment tolerances of commercially available pressure relief devices.

The aforementioned upper limit of 1.75 and preferably 1.4 is due to the increased mass flow through branch conduit 34 and the low pressure relief circuit when the container pressure rises to the second higher superatmospheric relief pressure. if the pressure difference between the settings of the two

relief valves

32 and 36 is too great and first end 17 of gas vent-liquid fill conduit 16 is submerged in cryogenic liquid, the heat transfer capacity of second atmospheric vaporizer 35 would be exceeded. This would be due to the increased flow, resulting in cold gas reaching and possibly freezing second relief valve 36.

it will also be recalled that in the present apparatus, the second atmospheric vaporizer is constructed with a heat transfer capacity sufficient to vaporize cryogenic liquid entering its inlet end and discharge gas at rate between 1.04 and l.30 times the maximum vent rate of the second flow restriction-pressure relief means 36, and preferably between 1.08 and 1.2 times the maximum vent rate. The increase in pressure between the set points of the two relief devices also produces an increase in flow rate through the low pressure relief circuit, as discussed in the previous paragraph. This flow rate increase is most likely to occur when the container is in a non-vertical position and first end 17 is immersed in liquid. The flow rate ratio lower limit reflects the need for an adequate difference between the relief pressures of the two devices as previously discussed. The flow rate ratio upper limit is to avoid exceeding the heat transfer capacity of second atmospheric vaporizer 35 due to increased liquid flow.

FIG. 2 illustrates the step of charging storagedispensing container with cryogenic liquid from supply container 40. The latter is similar in basic construction to container 10 but usually larger, and comprises outer casing 41 and inner vessel 42 for holding the cryogenic liquid, with an evacuable space therebetween preferably filled with thermal insulation 43. Cryogenic liquid may be introduced to supply container 40 through feed valve 44 and inlet conduit 45, also provided with safety relief valve 46. This liquid is prefera bly prewarmed prior to or during introduction such that it is saturated at the operating pressure desired for discharging same into container 10 as for example described in US. Pat. No. 2,951,348 to Loveday et a]. For example, if the desired oxygen vapor pressure is 40 psig, saturated liquid oxygen at -l68C (105K) may be introduced to a supply container of 17.5 liters liquid capacity and provided with 0.4 inch of aluminum foilglass paper alternate layer insulation of 0.040 X 10' Btu/hr. X ft. X F/ft. thermal conductivity in the evacuated space at a density of about 60 foils/inch. Alternatively, subcooled liquid oxygen may be introduced to the same supply container and upon mild, occasional agitation of the supply container, sufficient saturated pressure can be eventually obtained to operate the system. If such pressure is substantially lower than 40 psig than an appropriate revision must be made in the set point of the liquid sensor when the pneumatic system of FIG. 3 is employed (discussed hereinafter in detail).

As an alternative for insuring that the vapor pressure in container 41 is sufficient to discharge the cryogenic fluid into container 10 at the desired temperature and pressure, means may be provided for controllably introducing external heat to container 41. More particularly when and if the vapor pressure drops below a predetermined level, liquid may be controllably withdrawn through conduit 50 by opening valve 51 therein, vaporized in atmospheric vaporizer 52 and returned as vapor to the top end of inner vessel 42. Mild agitation of the contents will avoid Stratification and obtain a uniformly saturated condition throughout the liquid body. It should be understood that the aforedescribed pressure building circuit 50-52 is not required if the cryogenic liquid is introduced to container 40 in the prewarmed saturated container.

For charging of container 10, the latter is inverted and positioned with its top end in flow communication with supply container 40. The latter is provided with liquid discharge conduit 53 having first end 54 terminating in the bottom end of inner vessel 2 and second end 55 outside the container top end. First coupling means 56 is provided at the conduit second end 55 and joined to second coupling means 19 preferably in a manner such that fluid communication is established on joining.

Cryogenic liquid flows upwardly through conduit 53, second coupling means 56, first coupling means 19, and vapor vent-liquid fill conduit means 16, and merges from the latters first end 17 into the lowest zone of inverted container 10 which is its normally top end 14. The conduit 16 previously used for vapor venting dur ing the liquid storage-dispensing and gas supply step is now used for liquid filling.

As liquid transfer progresses, cryogenic vapor in the highest zone of inverted container 10 which is its normally bottom end 15, must be vented in order that the pressure in 15 will be lower than that in container 41 by an amount greater than the hydrostatic head to be overcome. To insure that such pressure differential exists, vapor from container 10 is admitted to the first end 22 of liquid withdrawal-gas vent conduit 21 for flow through inverted circuit 24 past liquid sensing means 25, further warming in first atmospheric vaporizer 26 and released through opened atmospheric gas vent valve means 27. Accordingly, during the liquid charging step the invertible circuit 24 previously used for liquid discharge and vaporization during the gas supply step is now used for gas venting.

The cryogenic fluid discharged from inverted container 10 during the liquid charging step is sensed by element 25a. When container 10 is full of liquid, the latter will start to flow into the inverted liquid vaporizing-gas vent control circuit 24. Element 25a detects the presence of liquid prior to its reaching first atmospheric vaporizer 26, and the detection is used as a signal to automatically close gas vent valve means 27, i.e., through electric signal receiving wire 28, controller 29, and electric signal transmitting wire 30. Once vent valve means 27 is closed the pressure differential between containers l0 and 40 will drop to a value substantially equal to the hydrostatic head produced by the difference between the liquid-gas interfaces in the two containers. When this occurs liquid transfer ceases. First and second coupling means 56 and 19 respectively are now disconnected, container 10 is returned to its normally top-up position and the previously described gas supply step is reinstated. First and second coupling means 56 and 19 are preferably of the type that automatically close when disconnected so that shut-off valves are not needed in gas vent-liquid fill conduit means 16 and liquid discharge conduit 53.

FIG. 3 illustrates another and preferred liquid charging termination control system based on the generation of a pressure rise on liquid sensing in circuit 24, and pneumatic rather than electric signal transmission to gas vent valve 27. The cryogenic liquid storagedispensing container 10, gas vent-liquid fill conduit means 16, and liquid withdrawal-gas vent conduit means 21 are substantially identical to FIG. 1 and operate in the previously described manner.

The FIG. 3 liquid vaporizing-gas vent control circuit 24 includes smaller size control fluid conduit 60 joined at one end as liquid sensing means 25 to the second end 23 of liquid withdrawal-gas vent conduit 21 outside and above the normally top end 14 of container upstream of first atmospheric vaporizer 26. A smaller third atmospheric vaporizer 62 is provided in control fluid conduit 60 and a first flow restrictor as for example orifice 63 is positioned between the one end 25 of conduit 60 and secondary atmospheric vaporizer 62. Second flow restrictor 64 is located between third atmospheric vaporizer 62 and the other end 65 of fluid control conduit 60. Such other end 65 is joined to atmospheric gas vent valve 27, preferably the illustrated four-way type. With such a valve, during the cryogenic liquid charging of container 10 gas may be simultaneously vented through a major vent gas circuit and a minor vent gas circuit. When the liquid charging is completed, the four-way valve 27 closes the two separate vent gas circuits from communication with the atmosphere by interconnected same. More particularly, a first flow passage is established through the valve connecting first inlet port 27a and first outlet port 27b, and permits venting of a major portion of the vent gas through primary atmospheric vaporizer 26. A second flow passage is also established connecting second inlet port 27c and second outlet port 27d, and permits venting of a minor vent gas portion through control fluid conduit 60. To terminate the liquid charging, the flow passages are realigned so that first and

second inlet ports

27a and 27c are connected. A small diameter pressure transmitting conduit- 66 has one end joining control fluid conduit 60 between

flow restrictors

63 and 64 and preferably between third atmospheric vaporizer 62 and second flow restrictor 64, and the other end joined to pneumatic actuator 67 mechanically coupled to four-way atmospheric gas vent valve 27. First flow restrictor 63 and second flow restrictor 64 are sized so that a pneumatic signal is transmitted through conduit 66 to close valve 27 when the pressure in control fluid conduit 60 intermediate third atmospheric vaporizer 62 and second flow restrictor 64 rises to a predetermined level.

When the FIG. 3 container 10 and liquid vaporizing gas vent control circuit 24 are in the inverted bottomup position and connected to cryogenic liquid supply container 40 in a manner analogous to FIG. 2, four-way valve 27 is manually set to the open position. The vent fluids flow from inverted container 10 through both the major and minor vent gas circuits to the atmosphere. During this cryogenic liquid charging step, the resistance to fluid flow in the minor vent gas circuit is much greater than that in the major circuit due to first and

second flow restrictors

63 and 64. Accordingly, most of the venting gas flows through first vaporizer 26. During the succeeding gas supplying step, all of the cryogenic liquid discharged from top-up container 10 flows to first vaporizer 26.

When the inverted FIG. 3 container 10 is filled with cryogenic liquid, the latter begins to exit through both the major and minor vent circuits. Again, most of the liquid flows to the major circuit including first vaporizer 26, is vaporized and released to the atmosphere as a warm gas. Some of the overflowing liquid is carried into the control fluid conduit 60. Compared to the previously flowing cold gas, first flow restrictor 63 passes relatively more mass of fluid as liquid with a much reduced pressure drop, and supplies this liquid to the third atmospheric vaporizer 62. The liquid is vaporized and warmed rapidly therein and increases several hundred fold in volume. Suddenly, a much larger volume of gas flows to the second flow restrictor 64 which now becomes the major resistance in conduit 60. The pressure in this conduit between first and

second flow restrictors

63 and 64 will rise abruptly to balance the new flow of inlet liquid (instead of inlet gas). This pressure rise is transmitted by conduit 66 to pneumatic actuator 67 which operates to set four-way gas vent valve 27 to the closed position. When this occurs, the pressure levels throughout the supply and storage-dispensing containers l0 and 40 and the interconnected fluid conduits will equalize (except for the aforementioned hydrostatic head) and liquid charging is stopped.

The elements of the liquid vaporizing-gas vent control circuit 24 are sized and selected so that the necessary pressure level to actuate the pneumatic system for closing gas vent valve 27 is readily and dependably obtained well within the limitations of acceptable pressures for

containers

10 and 40. Further, the circuit elements are preferably sized so that the liquid sensing response is sufficiently fast to prevent cryogenic liquid spillage from vent valve 27. For example, the first flow restrictor 63 is preferably sized so that when cryogenic liquid reaches the liquid vaporizing gas vent control circuit 24 at the end of liquid charging, only a small quantity of liquid passes through the restrictor and it does not exceed the capacity of third vaporizer 62. The second flow restrictor 64 downstream vaporizer 62 is sized to provide sufficient flow resistance to the nowvaporized liquid so that the gas pressure level sharply rises to the desired level between the two flow restrictors thereby generating a reliable signal.

The advantages of the invention were demonstrated in a test wherein a liquid oxygen storage-dispensing container and the all-attitude gas relief circuit as schematically illustrated in FIG. 3 and shown in the assembly drawings of FIGS. 5-7 was placed in the horizontal position. The container was provided with alternate layers of glass fiber paper and aluminum foil insulation wrapped around the inner vessel as thermal insulation to be provide about 14 layers in a thickness of about three-eights inch. The insulation space was also provided with molecular sieve zeolite adsorbent and hydrogen-selective getter and evacuated to an absolute pressure ofless than 1 micron Hg. The thermal conductivity of the insulation at this pressure was about 2.5 X 10 Btu/hr. X ft. X F. The oxygen gas pressure within the container and the container weight were both monitored with respect to time, and the results are illustrated in the FIG. 4 graph. In brief, the container held about 3.35 lbs oxygen when full, and its total weight was about 15.7 lbs. Second atmospheric vaporizer 35 (substantially the entire length of low pressure relief conduit 34) comprised about 24 inches of 0.25-inch outer diameter, 0.032-inch thick aluminum tubing including second vaporizer '35. Low pressure second relief valve 36 was set at 62 psig, and flow restrictor ele- FLOW CHARACTERISTICS PRESSURE (PSlG) FLOW RATE Upstream Downstream Liters Per Minute Gas (NTP) The first atmospheric vaporizer 26 was formed of 0.25-inch outer diameter, 0.032 inch thick aluminum tubing, so that the second atmospheric vaporizer heat transfer capacity was about 0.12 times the first atmospheric vaporizer capacity (based on a of outside surface areas). The high pressure relief valve 32 was set at 67 psig. However, it is preferred to maintain a Wider spread in pressure settings between the first and

second relief valves

32 and 36, and typical settings are 68 psig and 52 psig. respectively.

Referring now more specifically to the FIG. 4 graph about 1 hour was required after filling for the horizontally aligned container pressure to reach the 62 psig. setting of low pressure second relief valve 36 as represented by vertical dotted-line line (a). During this initial period there was of course no loss of stored oxygen so that the total weight (lower) curve was horizontal. During the succeeding 1 /2 hour period average oxygen boil-off loss rate through this valve was 1.52 liters oxygen (NTP) per minute and the container pressure increased to 67 psig. the setting of high pressure first relief valve 32. The latter opened, as represented by vertical dotted line (b), and both relief valves were open for the ensuing one hour-and the average oxygen boil off loss rate through the valves was 6.84 liters oxygen (NTP) per minute. After a total elapsed time of 210 minutes as represented by vertical dotted line (0), the second end 22 of liquid withdrawal-gas vent conduit 21 was no longer immersed in liquid oxygen. After a total elapsed time of 254 minutes as represented by vertical dotted line (d) the oxygen boil-off rate was equal to the normal evaporation rate at 62 psig for the container in the vertical top-up position.

No liquid oxygen was vented at any time during the aforedescribed test. The total boil-off of gas amounted to 1.8 lbs. 0 a low of about 54 percent was thus sustained but 1.55 lbs. 0 remained in the container. This remaining amount of liquid is equivalent to over 1 hours breathing atmosphere at the relatively high demand rate of 7 liters oxygen (NTP)/minute for a pul monary or cardiac patient, and is approximately equal to the maximum rate at which oxygen could be supplied by the prior art system of US. Pat. No. 3,199,303.

The preceding results indicate that with the allattitude gas relief circuit of this invention, thegcryogenic liquid storage-dispensing container remains operable even after being placed in a horizontal position for an extended period of time. It has been demonstrated that the all-attitude gas relief circuit has the capability of preventing cryogenic liquid discharge, and the overall size of the liquid container-vaporizing and gas vent control circuit assembly is not significantly increased by the all-attitude gas relief circuit.

The key dimensions of the assembly comprising the liquid oxygen storage-dispensing container, vaporizing and gas vent control circuit, and all-attitude gas vent control circuit used in the aforedescribed test are set forth in Table 1.

TABLE 1 KEY DIMENSIONS OF THE ASSEMBLY Characteristic Specification Storage-Dispensing Container 10):

Capacity, Liquid Oxygen 3 lbs. Capacity, Equivalent Oxygen Gas (NT?) 1026 liters Inner Diameter (inches) 3.96 Wall Thickness (inches) 0018-.030 Height (inches) 8-7/32 Overall Assembly:

Height (inches) 13% Width (inches) 9-11/32 Depth (Thickness) 5% Oxygen Gas Withdrawal Rates 1,2,3,4,5,6,7 (through valve 31): liters/min.

Normal Evaporation Rate: 0.34lb O /day Gas Vent-Liquid Fill Conduit (16):

Inner Diameter (inches) 0.1 13 Outer Diameter (inches) 0 125 Liquid Withdrawal-Gas Vent Conduit (21 )1 Inner Diameter (inches) 0.1675 Outer Diameter (inches) 0.1875

First Atmospheric Vaporizer (26):

Inner Diameter (inches) 0186 Outer Diameter (inches) 0.250 Length (feet) 16-18 Second Atmospheric Vaporizer (35):

Inner Diameter (inches) 0.186 Outer Diameter (inches) 0.250 Length (feet) 2 First Orifice (63) Diameter (inches) 0.016

Second Orifice (64) Diameter (inches- 0.026

First Orifice (63) 0.016

Diameter (inches) Second Orifice (64) 0.026

Diameter (inches) Second Relief Valve (36) 52 psig Set Point Pressure (psig) First Relief Valve (32) 68 psig Set Point Pressure (psig) Bursting Disk (38) psig Set Point Pressure (psig) Maximum Vent Rate for Second 17.5

Relief Valve/Normal Evaporation Rate Heat Transfer Capacity 1/8.5

Second Atmospheric Vaporizer/ First Atmospheric Vaporizer Vent Rate for Second Relief Referring now to the assembly drawing of FIGS. 5-7, the same identification numerals have been used for elements corresponding to elements in the schematic drawing of FIG. 3, and the system operates in the previously described manner. The entire functional assembly is inside carrying case 70. Also, phase separator assembly 71 insures that any entrained liquid inadvertently discharged through valve 27 during a fill will not be sprayed outside carrying case 70. Such liquid will be separated from high velocity vapor and fall harmlessly to the bottom of the enclosure.

Although certain embodiments have been described in detail, it will be appreciated that other embodiments are contemplated and that modifications of the disclosed features are within the scope of the invention.

What is claimed is:

1. In a cryogenic liquid storage-gas supply system including a thermally insulated cryogenic liquid storagedispensing containing having top and bottom ends and being invertible between top-up dispensing and bottom-up filling positions, gas vent-liquid fill conduit means with a first end terminating in the container top end and a second end outside said container top end, liquid withdrawal-gas vent conduit means with a first end terminating in the container bottom end and a second end outside said container top end, an invertible liquid vaporizing-gas vent control circuit outside the container and joined at a first inlet end to the liquid withdrawal-gas vent conduit means second end and including a first atmospheric vaporizer, and gas flow regulating means between said first atmospheric vaporizer and the gas discharge other end of said circuit: the improvement of an all-attitude gas relief circuit for said container comprising (a) first pressure relief means between said first atmospheric vaporizer and said gas flow regulating means, (b) branch conduit means having one end in flow communication with the gas vent-liquid fill conduit second end, (c) second flow restrictionpressure relief means in branch conduit (b) constructed to vent gas at lower pressure than said first pressure relief means and at maximum rate between 3 and 25 times the normal evaporation rate from the container, and (d) a second atmospheric vaporizer in flow communication at its inlet end with the branch conduit (b) one end and in flow communication at its discharge end with the second flow restriction-pressure relief means, and constructed with a heat transfer capacity not greater than one-third the first atmospheric vaporizer capacity and also sufficient to vaporize cryogenic liquid entering its inlet end and discharge gas at rate between 1.04 and 1.30 times the maximum vent rate of 2. A cryogenic liquid storage-gas supply system according to claim 1 wherein the second flow restrictionpressure relief means is constructed to vent gas at maximum rate between and 20 times the normal evaporation rate from the container.

3. A cryogenic liquid storage-gas supply system according to claim 1 wherein the second atmospheric vaporizer heat transfer capacity is not greater than onefifth the first atmospheric vaporizer capacity.

4. A cryogenic liquid storage gas supply system according to claim 1 wherein the second atmospheric vaporizer heat transfer capacity is sufficient to vaporizer cryogenic liquid entering the inlet end and discharge gas at rate between 1.08 and 1.25 times the maximum vent rate of (c).

5. A cryogenic liquid storage-gas supply system according to claim 1 wherein a pressure relief valve and a separate flow restriction element in flow communication with each other comprise the second flow restriction-pressure relief means (c).

6. A cryogenic liquid storage-gas supply system according to claim 1 wherein a pressure relief valve and a porous member in downstream flow communication with said pressure relief valve comprise the second flow restriction-pressure relief means (c).

7. A cryogenic liquid storage-gas supply system according to claim 1 wherein the second flow restrictionpressure relief means is constructed to vent gas at maximum rate between 5 and 20 times the normal evaporation rate from the container, the second atmospheric vaporizer is constructed with a heat transfer capacity not greater than one-fifth the first atmospheric vaporizer capacity and also sufficient to vaporize cryogenic liquid entering its inlet end and discharge gas at rate between l.08 and 1.25 times the maximum vent rate of (c), and wherein a pressure relief valve and a porous member in downstream flow communication with said pressure relief valve comprise the second flow restriction-pressure relief means (0).

8. In a method for supplying gas from a thermally insulated cryogenic liquid-storage-dispensing container having top and bottom ends and being invertible between top-up dispensing and bottom-up filling positions and wherein during the gas supplying step cryogenic liquid flows by overhead vapor pressure upwardly from the lowest zone of the container, discharged from the container top end and vaporized by atmospheric heat to form thegas supply, the improvement comprising: in a top-up dispensing position,

a. when gas is not being supplied, venting vapor through a passage from the highest zone of the container, at flow-restricted maximum rate between 3 and 25 times the normal evaporation rate from the container, warming the vapor by atmospheric heat and discharging the warmed vapor when the container pressure is above a first lowest superatmospheric relief pressure; and

b. when gas is being supplied, flowing cryogenic liquid by overhead vapor pressure upwardly from the lowest zone of the container, discharging such liquid from the container top end, vaporizing the sodischarged liquid by atmospheric heat, warming the vapor and withdrawing the warmed vapor as the gas supply and simultaneously venting vapor in accordance with step (a); and

c. in a non-vertical position such that liquid flows through the passage of step (a) and the container gas pressure rises above the first lowest superatmospheric relief pressure: discharging first liquid from the normally top end of the container at a first lower flow restricted rate, vaporizing the discharged first liquid, warming the cold first vapor to ambient temperature and releasing the warmed first vapor at pressure above said first lowest superatmospheric relief pressure; and when the container pressure rises to a second higher superatmospheric relief pressure between 1.08 and 1.75 times the first superatmospheric relief pressure on an absolute basis, simultaneously discharging second liquid from the normally bottom end of the container at a second higher rate, vaporizing the discharged second liquid by atmospheric heat, warming the cold second vapor and releasing the 18 10. A method according to claim 8 wherein said second higher superatmospheric relief pressure is between 1.15 and 1.4 times the superatmospheric relief pressure on an absolute basis.

Claims

1. In a cryogenic liquid storage-gas supply system including a thermally insulated cryogenic liquid storage-dispensing containing having top and bottom ends and being invertible between top-up dispensing and bottom-up filling positions, gas vent-liquid fill conduit means with a first end terminating in the container top end and a second end outside said container top end, liquid withdrawal-gas vent conduit means with a first end terminating in the container bottom end and a second end outside said container top end, an invertible liquid vaporizing-gas vent control circuit outside the container and joined at a first inlet end to the liquid withdrawal-gas vent conduit means second end and including a first atmospheric vaporizer, and gas flow regulating means between said first atmospheric vaporizer and the gas discharge other end of said circuit: the improvement of an all-attitude gas relief circuit for said container comprising (a) first pressure relief means between said first atmospheric vaporizer and said gas flow regulating means, (b) branch conduit means having one end in flow communication with the gas ventliquid fill conduit second end, (c) second flow restrictionpressure relief means in branch conduit (b) constructed to vent gas at lower pressure than said first pressure relief means and at maximum rate between 3 and 25 times the normal evaporation rate from the container, and (d) a second atmospheric vaporizer in flow communication at its inlet end with the branch conduit (b) one end and in flow communication at its discharge end with the second flow restriction-pressure relief means, and constructed with a heat transfer capacity not greater than onethird the first atmospheric vaporizer capacity and also sufficient to vaporize cryogenic liquid entering its inlet end and discharge gas at rate between 1.04 and 1.30 times the maximum vent rate of (c).

2. A cryogenic liquid storage-gas supply system according to claim 1 wherein the second flow restriction-pressure relief means (c) is constructed to vent gas at maximum rate between 5 and 20 times the normal evaporation rate from the container.

3. A cryogenic liquid storage-gas supply system according to claim 1 wherein the second atmospheric vaporizer heat transfer capacity is not greater than one-fifth the first atmospheric vaporizer capacity.

7. A cryogenic liquid storage-gas supply system according to claim 1 wherein the second flow restriction-pressure relief means is constructed to vent gas at maximum rate between 5 and 20 times the normal evaporation rate from the container, the second atmospheric vaporizer is constructed with a heat transfer capacity not greater than one-fifth the first atmospheric vaporizer capacity and also sufficient to vaporize cryogenic liquid entering its inlet end and discharge gas at rate between 1.08 and 1.25 times the maximum vent rate of (c), and wherein a pressure relief valve and a porous member in downstream flow communication with said pressure relief valve comprise the second flow restriction-pressure relief means (c).

8. In a method for supplying gas from a thermally insulated cryogenic liquid-storage-dispensing container having top and bottom ends and being invertible between top-up dispensing and bottom-up filling positions and wherein during the gas supplying step cryogenic liquid flows by overhead vapor pressure upwardly from the lowest zone of the container, discharged from the container top end and vaporized by atmospheric heat to form the gas supply, the improvement comprising: in a top-up dispensing position, a. when gas is not being supplied, venting vapor through a passage from the highest zone of the container, at flow-restricted maximum rate between 3 and 25 times the normal evaporation rate from the container, warming the vapor by atmospheric heat and discharging the warmed vapor when the container pressure is above a first lowest superatmospheric relief pressure; and b. when gas is being supplied, flowing cryogenic liquid by overhead vapor pressure upwardly from the lowest zone of the container, discharging such liquid from the container top end, vaporizing the so-discharged liquid by atmospheric heat, warming the vapor and withdrawing the warmed vapor as the gas supply and simultaneously venting vapor in accordance with step (a); and c. in a non-vertical position such that liquid flows through the passage of step (a) and the container gas pressure rises above the first lowest superatmospheric relief pressure: discharging first liquid from the normally top end of the container at a first lower flow restricted rate, vaporizing the discharged first liquid, warming the cold first vapor to ambient temperature and releasing the warmed first vapor at pressure above said first lowest superatmospheric relief pressure; and when the container pressure rises to a second higher superatmospheric relief pressure between 1.08 and 1.75 times the first superatmospheric relief pressure on an absolute basis, simultaneously discharging second liquid from the normally bottom end of the container at a second higher rate, vaporizing the discharged second liquid by atmospheric heat, warming the cold second vapor and releasing the warmed vapor at pressure above said second superatmospheric relief pressure.

9. A method according to claim 8 wherein vapor is vented during step (a) at flow-restricted maximum rate between 5 and 20 times the normal evaporation rate from the container.

10. A method according to claim 8 wherein said second higher superatmospheric relief pressure is between 1.15 and 1.4 times the superatmospheric relief pressure on an absolute basis.