US2997855A - Apparatus for storing and dispensing liquefied gases - Google Patents

Description

1951 c E. TEMPLER ET'AL 2,997,855

APPARATU FOR STORING AND DISPENSING LIQUEFIED GASES Filed Aug. 19, 1960 2 Sheets-Sheet 1 I Q Q Inventor's CHARLES EJWAR) TEHPLER Mum/1 Mzclmsz Lawn/aw g 1961 c. E. TEMPLER ETAL 2,997,855

APPARATUS FOR STORING AND DISPENSING LIQUEFIED GASES 2 Sheets-Sheet 2 Filed Aug. 19, 1960 F/GZ.

q l l l I I l l I l I ll m mhHlj Inventors United States Patent r 2,997,855 APPARATUS FOR STORING AND DISPENSING LIQUEFIED GASES Charles Edward Templer, London, and David Michael Lainchhury, Worcester Park, England, assignors to The British Oxygen CompanyLimited, a British company Filed Aug. 19, 1960, Ser. No. 50,772 7, Claims priority, application Great. Britain Aug. 20, 1959 2 Claims. (Cl. 6252) This application relates to the dispensing of liquefied gases having a boiling point substantially below atmospheric temperature at norinal atmospheric pressure, such as, for example liquid oxygen or liquid nitrogen.

Such liquefied gases are conveniently stored under pressure in thermally insulated containers. In many cases, it is possible to withdraw the liquid through an outlet at the bottom of the container but there are circumstances where it is advantageous to dispense with a bottom outlet and to arrange for liquid to be withdrawn from the container through a dip pipe extending through the top of the container into the liquid in order to reduce heat inleakage or to simplify construction, particularly where the equipment has to be readily transportable. If the bottom outlet is eliminated, however, the normal methof for pressurising such a container by evaporating liquid withdrawn through the bottom outlet in a pressure buildup coil and allowing the vapour to return to the gas space of the container cannot be used.

If, in the absence of some means of maintaining the pressure, it is desired to discharge a container in a relatively short period of time, such that the pressure cannot be maintained by heat inleak from the surroundings, it has been found that with fully stabilised liquid (that is, with constant temperature conditions throughout both the liquid and vapour phases in the container), complete discharge can only be achieved at the expense of the pressure within the container. For example, in a vessel stabilized at 150 p.s.i.g. pressure, the pressure may fall to 95 p.s.i.g. before all the liquid is discharged.

It is an object of the present invention to provide apparatus for storing and dispensing a liquefied gas from a container therefore by the use of which the container pressure may be maintained constant throughout withdrawal of liquid.

It is a further object to provide such apparatus which may be adapted to raise the container pressure initially to the desired operating pressure.

According to the present invention, apparatus for storing and dispensing a liquefied gas as hereinbefore defined comprises a thermally insulated container for the liquefied gas, a liquid withdrawal pipe opening at a point near to the bottom of the container and extending through the top thereof, a liquid feed line connecting the liquid withdrawal pipe with one end of a pressure raising coil located below the level of the bottom of the container, a vapour feed line connecting the other end of the pressure raising coil with the vapour space of the container through an automatic valve arranged to open when the pressure in the container falls below a predetermined value and a jacket surrounding the part of the liquid feed line above the level of the bottom of the container, said jacket having a connection to the liquid withdrawal pipe through valve means arranged to maintain a pressure drop between the liquid feed line and the jacket, and a liquid service connection.

Since the pressure raising coil is located at a lower level than the liquid in the container, the liquid withdrawal pipe and the liquid feed pipe to the coil will act as a syphon when filled with liquid and liquid will therefore syphon from the container through the liquid withdrawal pipe and the liquid feed pipe to the pressure raising coil as soon as the automatic valve in the vapour feed line from the pressure raising coil is opened, this liquid being vaporised in the pressure raising coil and the vapour fed back to the container until the pressure therein rises to the predetermined value and the autoinatic valve closes. Vaporisation of liquid in the liquid feed line to the pressure raising coil, which might cause vapour locking in the line and hence prevent the syphoning action, is prevented by the cooling effect of the liquid in the jacket, which liquid being-at a lower pressure than that in the liquid feed line is cooled below the temperature of the liquid in the liquid feed line by partial vaporisation.

Vaporisation in the lower part of the jacketed portion of the liquid feed line by heat inleak along the line while the automatic valve is closed may be prevented by inserting a bleed line between the liquid feed line downstream of the end of the jacket and the service connection from the jacket, this bleed line being arranged to allow a continuous but slow flow of liquid through it. In addition, when the service connection is closed, any small accumulation of liquid in the jacket may pass back through the bleed line to the pressure raising coil and thence to the container. Alternatively this bleed line may be located between the vapour feed line upstream of the automatic valve and the service connection.

The apparatus of the present invention may easily be modified to enable it to function to re-build pressure in the container should pressure have been lost owing to some unusual circumstance such as leakage or emergency repair. This modification merely consists in the provision of a valve-controlled connection to atmosphere in the vapour feed line from the pressure raising coil. Should'pressure be lost, the automatic valve will of course be open. The valve controlling the connection to atmosphere is opened, until a mixture of gas and liquid at high velocity travels through the liquid feed pipe and cold gas is discharged through the connection to atmosphere. The valve controlling this connection is then closed, when the energy of the fluid stream passing through the liquid feed line and the pressure raising coil will be suflioient to carrythe vapour back into the container. If this is insufi'icient to raise the pressure in the container to a value sufiiciently high to permit normal operation to commence, the procedure may be repeated as often as necessary. It will, however, be appreciated that some vapour will inevitably be lost by discharge to atmosphere each time the valve controlling the connection to atmosphere is opened.

One form of apparatus according to the invention arranged for the'delivery of the stored liquid in the form of gas, will now be described by way of example with reference to the accompanyingdrawing in Which- FIGURE 1 is a diagrammatic side sectional view of the apparatus; and

FIGURE 2 is a side sectional view of a preferred form of valve for use in the apparatus of FIGURE 1.

Referring to FIGURE 1, the liquefied gas 10, for example, liquid oxygen, is stored within an inner (Xmtainer 11 surrounded by thermal insulant 12 in an outer container 13. A liquid withdrawal pipe 14 opening at a point within the liquid 10 adjacent the bottom of the container 11, extends through the top of the container 11 and is connected through a stop valve 15 to a delivery pipe.16 which is connected at a T-junction 17 to a liquid feed line 18 having a horizontal portion and a vertical portion extending downwardly to a point below the level of the bototm of the liquid 10 in the container 11. The line 18 is surrounded by an annular jacket 19, the outer surface of which may be thermally insulated. The end of the jacket 19 adjacent the T-junction 17 is connected to the remaining arm of this junction by a line 20, flow 3 of liquid through which is controlled by a valve 21 whose construction is described hereafter. The other end of the jacket 19 is connected to a vaporiser 22 and thence to a valve 23 which controls the flow of gas from the system. It is from this valve that the gas is drawn to supply the demand.

The line 18 is connected through a T-junction 24 with a pressure raising coil 25 in which liquid fed through the line 18 is vaporised, the vapour being fed through a vapour feed line 26 via an automatic control valve 27 and a non-return valve 28 to the vapour space 29 of the container 11. The control valve 27 is arranged to be opened automatically should the pressure in the container 11 fall below a predetermined value. The non-return valve 28 prevents reverse flow through the line 26 under start-up conditions. The line 26 is also provided with a connection to atmosphere controlled by a stop valve 30. The other arm of the T-junction 24 is connected through a vaporiser 31 and an orifice 32 to the inlet to the vaporiser 22.

The jacket 19 is provided with a safety valve 33 and the inner vessel 11 with a safety valve 34.

The construction of the valve 21 is shown in FIGURE 2. In it, a weight 35 is mounted for vertical movement and tends to hold a stainless steel ball 36 on a square shouldered seating 37. The valve is contained in a casing 38 which is connected on the downstream side of the seating 37 to the jacket 19 by the line 20. Upstream the seating 37, the casing 38 is connected to the T-junction 17. Owing to the downward force produced by gravity acting on the weight 35 and hence on the ball 36, a corresponding upward force must be exerted on the ball 36 by the fluid to open the valve and permit flow through it to take place. This results in a pressure difference on either side of the valve, that is the pressure of the fluid in the liquid feed line 18 is maintained higher than that in the jacket 19. This pressure difference is substantially independent of flow rate in the range required.

Normal operation of the apparatus is as follows. When the stop valve 15 and the demand valve 23 are opened, first vapour and then liquid will be forced by the pressure within the container up the liquid withdrawal tube 14, through line 16, T-junction 17, valve 21 and line 20 into the jacket 19. In passing through the valve 21, the pressure in the jacket 19 is reduced below that in the liquid feed line 18 and consequently some of the liquid in the jacket 19 will boil ofi, lowering the temperature of the remainder of the liquid in the jacket 19. The temperature in the jacket 19 will therefore be slightly lower than that in the liquid feed line 18 once the cooling down process is complete and a continuous column of liquid will be formed in the line 18. A small flow of liquid is bled from the line 18 through the vaporiser 31 and the orifice 32 and fed to the vaporiser 22. By this means any gas less condensible than the liquefied gas will be purged from the line 18 and any 'vaporisation of the liquid at the base of the vertical part of the line 18 due to heat leakage along the line is avoided. In addition, when the valve 23 is again closed, i.e. when the supply is discontinued, any small accumulation of liquid in the jacket 19 and the vaporiser 22 will pass via the orifice 32, the vaporiser 31, the T-junction 24, the liquid feed line 18, the T-junction 17 and the liquid withdrawal pipe 14 back into the container, providing that the stop valve 15 is left open. The safety valve 33 is, however, provided to vent the jacket 19 should both valves 15 and 23 be closed at the same time.

Thus, during normal operation, liquid flows through the liquid withdrawal pipe 14 and the valve 21, to the jacket 19 and passes thence to the vaporiser 22 where it is vaporised and is withdrawn from the system as gas through the valve 23 to supply the demand.

At the same time, liquid also flows very slowly from the liquid withdrawal pipe 14 through the liquid feed line 18, the vaporiser 31 and the orifice 32 and also leaves the system through the valve 23 as gas. For practical purposes, under these conditions, the liquid column in the vertical portion of the line 18 may be regarded as static since the fiow rate is small. Thus, when the pressure within the container 11 falls below the predetermined value and the automatic valve 27 opens, the liquid Withdrawal pipe 14 and the liquid feed line 18 act as a syphon and liquid is syphoned from the container to the pressure raising coil 25 where it is vaporised, the vapour so formed passing through the vapour feed line 26 back to the container to raise the pressure therein. This syphoning effect will continue until the pressure in the container 11 rises again to the predetermined value, when the valve 27 Will shut and syphoning will cease.

As a practical example of normal operation, it has been found that with a container of approximately 4 cu. ft. internal volume containing liquid oxygen, a differ ence in level of 18 inches between the liquid surface and the pressure raising coil is sufficient to produce rates of pressure rise in excess of 10 p.s.i.g./minute even though liquid was removed at such a rate that the container was emptied in three hours.

Where, owing to some unusual circumstance, such a leakage or emergency repairs, there is only a small initial pressure with in the container 11 (say, 10 p.s.i.g.) which is insufficient to obtain a useful discharge of gas through the valve 23, it is possible to obtain an initial pressure build up by opening the valve 30 connecting the vapour feed line 26 to atmosphere until a mixture of liquid and gas at high velocity is travelling through the liquid feed line 18 and cold gas is discharged to atmosphere through the valve 30. If the valve 30 is then closed, the energy of the fluid stream passing through line 18 and the pressure raising coil 25 will be sufficient to carry some vapour through the vapour feed line 26 back to the container 11. The procedure may then be repeated until a pressure is obtained which is sufliciently high for normal operation.

In order to avoid difliculty in removing liquid from the vessel 11 when the level of liquid therein is low, it is desirable that, as indicated in FIGURE 1, the length of pipe 16 between the valve 15 and the union 17 should be relatively long. The effect of this is that any gas bubbles in the liquid ascending the pipe 16 act as a vapour lift and help to force liquid past the valve 21 and into the jacket 19. At the same time, liquid only travels down tube 18. By this means an unbroken column of liquid is maintained throughout the length of the tube 18 and an adequate amount of liquid is maintained within the jacket 19.

We claim:

1. Apparatus for storing and dispensing a liquefied gas having a boiling point substantially below atmospheric temperature at normal atmospheric pressure comprising a thermally insulated container for the liquefied gas, a liquid withdrawal pipe opening at a point near to the bottom of said container and extending through the top thereof, a liquid feed line connecting said liquid withdrawal pipe with one end of a pressure raising coil located below the level of the bottom of said container, a vapour feed line connecting the other end of said pressure raising coil with the vapour space of said container through an automatic valve arranged to open when the pressure in said container falls below a predetermined value, a jacket surrounding the part of said liquid feed line above the level of the bottom of said container, said jacket having a connection to said liquid withdrawal pipe through valve means arranged to maintain a pressure drop between said liquid feed line and said jacket, a liquid service connection from said jacket, and a bleed line connected between said liquid feed line downstream of the end of said jacket and said liquid service connection, said bleed line being arranged to allow a continuous but slow flow of liquid therethrough.

2. Apparatus for storing and dispensing a liquefied gas having a boiling point substantially below atmospheric temperature at normal atmospheric pressure comprising a thermally insulated container for the liquefied gas, a liquid withdrawal pipe opening at a point near to the bottom of said container and extending through the top thereof, a liquid feed line connecting said liquid withdrawal pipe with one end of a pressure raising coil located below the level of the bottom of said container, 21 vapour feed line connecting the other end of said pressure raising coil with the vapour space of said container through an automatic valve arranged to open when the pressure in said container falls below a predetermined value, a jacket surrounding the part of said liquid feed line above the level of the bottom of said container, said jacket having a connection to said liquid withdrawal pipe through valve means arranged to maintain a pressure drop between said liquid feed line and said jacket, a liquid service connection from said jacket, and a bleed line connected between said vapour feed line upstream of said automatic valve and said liquid service connection, said bleed line being arranged to allow a continuous but slow flow of 10 vapour therethrough.

References Cited in the file of this patent UNITED STATES PATENTS Steele Mar. 24, 1953 Hansen et al. Dec. 20, 1960

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