US2796739A

US2796739A - Underground storage system

Info

Publication number: US2796739A
Application number: US356798A
Authority: US
Inventors: Leonard P Meade; Jr George F Downs
Original assignee: Phillips Petroleum Co
Current assignee: Phillips Petroleum Co
Priority date: 1953-05-22
Filing date: 1953-05-22
Publication date: 1957-06-25
Anticipated expiration: 1974-06-25

Description

June 25, 1957 1 P. MEADE ETAI- UNDERGROUND STORAGE SYSTEM Filed May 22, 1953 2 Sheets-Sheet l .n L. PMM@ @d BY 6J. Dommxpd? Hwaw *M ATTORNEYS June 25 11957 L p, MEADE ETAL. 2,796,739

UNDERGROUND STORAGE SYSTEM Filed May 22, 1953 2 Sheets-Sheet 2 A TTOR/VEY' nited States UNBERGRUND STORAGE SYSTEM Application May 22, 1953, Serial No. 356,798

20 Claims. (Cl. 62-1) This invention relates to underground storage systems. In a further aspect this invention relates to a novel method for sealing underground storage systems for fluids. In a still further aspect this invention relates to underground storage systems for the storage of liqueed petroleum gas.

Constantly expanding production of uids for the industries of this country and elsewhere has created a definite problem in providing suitable storage facilities for these fluids. In the petroleum industries in particular the problem of storage of liquefied petroleum gas is presently an urgent one due to the cost of storage in surface equipment, such as steel tanks, and due to the massive construction required to withstand the vapor pressure of such liquids. Also adding to this problem of adequate storage facilities is the fact that many industries experience seasonal peak loads in the requirements for their fluid products and corresponding seasonal slack periods. These fluctuations in requirements require large storage facilities and the advantages of underground storage -of fluids have lately come to the attention of the industry.

The known methods of underground storage of fluids comprise storage in impermeable caverns, either naturally formed or mined out of impermeable rock, such as shales and limestone. Naturally occurring formations such as these are difficult to find and present problems in perfecting a closed container to hold the fluids to be stored. Often expensive linings are required to make suchl natural or mined caverns impermeable.

Underground storage systems have been developed in salt formations but the disadvantage of these systems lies in part in the fact that there are practical limitations to the maximum size of such underground storage Caverns. As a result, the most difficult problems in the development of underground storage systems to date usually are the selection of a suitable site and the attainment of a sealed container.

In accordance with this invention, an underground storage system is provided which is adaptable to a wide range of sites and thereby diminishes the problem of finding an advantageous location for the underground storage system. Furthermore, a method for sealing the containers of an underground storage system is provided which is economical and yet is extremely effective to prevent fluid losses therefrom. We have discovered that an undergroundY storage cavern located in a permeable, water-bearing formation in which the water in the cavern walls is frozen to render said walls impermeable to the uids stored, furnishes a reliable, economical and trouble-free underground storage system. In accordance with a preferred embodiment of our invention the refrigeration required yto freeze the water in the cavern walls is provided in the uid stored by withdrawing the vapors of the stored fluid, compressing, condensing and returning these condensed vapors to the underground storage cavern. Additionally, the system is provided with automatic controls which continuously pump 17 from the ice in well 5 to therposition shown f 2,796,739 Patented June 25, 1957,

monitor the temperature of the frozen cavern walls and the vapor pressure of the fluids stored and start the withdrawal of the vapors of the stored liquid as required to maintain said walls in a frozen and therefore imf permeable condition.

It is an object of this invention to provide a novel and improved underground storage system.

It is a further object to provide an underground storage system for uids where the diculty of selection of a. site is minimized.

It is a Vfurther object to provide a novel method for sealing the containers of an underground storage sysf tem for uids.

Various other objects, advantages and features of this invention will become apparent from the following d e.- tailed description taken in conjunction with the accompanying drawings in which:

Figure lY is a vertical sectional view, partly in elevaf tion, of the underground storage system of this invention; and

Figure 2 is a diagrammatic representation in further detail of the component parts of the automatic control assembly.

Referring no w to Figure 1 of the drawings, reference numeral 1 identities the surface of the earth under which our storage Caverns are located. It is to be understood that our disclosure encompasses a plurality of Caverns as well as a single underground storage cavern such as 1s illustrated in Figure 1. The earth in which our under: ground storage cavern is located should b e a waterf bearing formation and permeable, and generally it is preferred that the cavern be located below the minimum water table in such a formation. A shaft 3 extends from the surface of the earth downward to a position adjacent to cavern 2, and below, to form a recess orwell 5.-' Tunnels 7 and 9 connect shaft 3 to the storage cavern 2. The lower tunnel 7 connects the lower region of cavern 2 to shaft 3 and tunnel 9 connects the upper region of cavern 2 to shaft 3. The shaft 3 is provided with a metal liner 13 which is embedded in cement 11 in the earth surrounding shaft 3 and a metal liner head 15 is attached to liner 13, as shown to seal the contents of the underground storage system.

A pipe 14 and valve 16 connected thereto are provided in the liner head 15 to permit purging of the storage system of air when the uids to be stored are rst introduced. A i

A motor and pump combination 17 as disclosed in lthe copending application of L. P. Meade, Serial No.

314,541, tiled on October 13, 1952, now abandoned, is provided and placed as shown in Figure l by the dotted lines in the well or recess 5 to remove water from' the system during excavation operations through the withdrawal pipe 19 connected thereto. Attached to liner head 15 is a stripper-type tubing head 20, such as those used in the petroleum industry,lwhich provides means for supporting withdrawal pipe 19 as well as preventing loss of stored fluids when withdrawal pipe V19 is raised. The motor and pump combination 17 Vis provided with a heating element 18 to allow the raising of motor and by solid lines when the storage system becomes frozen. When the cavern has been frozen the motor andpump V17 are raised above the level of ice 22 in the bottom of cavern 2 and are used for withdrawing product from the underground storage system. A Vtill pipe 21 is provided for introducing iluids to be stored into the underground storage systemv and it is to be noted Athat Yfansubstantial length of fill pipe 21 is positioned belowthe level of the ice 2.2 in the bottom ofthe cave-m12 wit-h the outlet of lill pipe 21 protruding above the level of said ice 22 and in heat exchange relationship thereto, which provides a source of stored refrigeration for the incorning uids to the storage system.

A vapor withdrawal pipe 23 is Yprovided to withdraw the vapors of the Vfluids stored in the system, thereby decreasing the pressure in the underground storage cavern and producing a cooling effect which causes the water in the cavern walls to become frozen. The vapors are withdrawn through pipe 23 by the Vmotor and compressor combination 25 and passed through pipe 27 to condenser 29. The condensed and compressed vapors are drawn through pipe 31 by pump 30 and passed via fill pipe 21 back to the undergroundy storage system. A check valve 32 is provided in fil-l pipe 21 to prevent the compressed and condensed vapors from being pumped out of the system through pipe 21.

Y A liquid level assembly 33 is provided so that the level of liquids in the cavern can be readily determined at all times. Also, when the storage system has been frozen,

the floatV indicates the level of ice 22 in the bottom of the system, `as well. The details of tliquid level indicator assembly 33 are disclosed in the copending application of L. P. Meade, Serial No. 314,541, le'd October 13, 1952, now abandoned. Liquid level indicator assembly 33 includes a perforated well or tube 35 which extends downwardly to the lowest regions of shaft 3. Movable vertically in tube 35 is a oat 37 secured to a tape 38 which extends upwardly through the tube 35 to the liquid level indicator assembly 33.

An automatic control assembly is connected to motor and compressor combination 25 by wires 26 and is provided to initiate the withdrawal of the vapors of the stored fluids as required to cool the contents of the cavern and thereby maintain the water in the earth surrounding said cavern in a frozen condition. Lead Vwires 41 extend from the automatic control assembly 39 into cavern 2 and are attached to temperature vresponsive switches 43, 45, 47, 49, 51, 53, and 57. 'Ihese temperature responsive 'switches are connected to lead wires 41 and are placed in the walls of the cavern and arerresponsive to temperature changes therein in a manner that the electrical circuit in lead wires 41 is closed when the temperature surrounding said temperature responsive switches rises to a rst preselected temperature. Such a'rst p-reselected temperature is approximately the freezing point of the water in the particular earth and water formation surrounding storage cavern 2 and may be easily ascertained 'during the construction of the cavern. In addition to thetemperature responsive switches the automatic control assembly 39 includes a pressure controller switch 59 which is connected through the liner head 15 to shaft 3 by pipev 61. The pressure controller switch 59 also is connected to lead .wires 41 and will close the circuit in said lead wires when the pressure within the shaft 3 exceeds a tirstrpreselected pressure in'controller switch S9. Such a preselected pressure is approximately the vapor pressure of the iluid stored at approximately the temperature at which the water in the earth surrounidinng the cavern freezes.

In the situation where the underground storage system comprises a plurality of Caverns, tunnels 7a and 9a, ller pipe 21aand lead wires 41a represent features corresponding thereto in the single cavern shown.

l YReferring now Vto Figure 2 of the drawings, the automatic control assembly is illustrated further.

AB-phase current source 42 is connected tothe motor and compressor combination 25 by wires 26 througha relay or contactor switch 40 having contacts` 44 to disengage current sourcev42 from motor and compressor combination 25.` The contacts 44 are closed upon energization of a solenoid coil 46 by a current source 48.

nected in a parallel circuit with solenoid coil 46. Pressure responsive switch 59 is connected through liner head 15 to shaft 3 by pipe 61 and thereby is responsive to the pressure of the vapors of the fluid stored in the cavern. Pressure responsive switch 59 remains open until the pressure of said vapors reaches a first preselected value which is preferably approximately the vapor pressure of the uid stored which is exhibited at approximately the temperature at which the water in the earth surrounding the cavern freezes. When the vapor pressure of the uid stored exceeds this last described pressure, pressure responsive switch 59 closes and the motor and compressor combination 25 is thereby started. Temperature responsive switches 43, 45, etc., operate in an analogous manner, closing the circuit in the relay and thereby starting motor and compressor combination 25 when the temperature of the water and earth surrounding the cavern exceeds a irst preselected value, which is preferably approximately the freezing point of water in the earth surrounding the cavern. When one any one of the pressure responsive switch and temperature responsive switches closes, the motor and compressor combination 25 is actuated to draw ot vapors of the stored fluid and thereby cool the cavern. Our invention is applicable to the storage of any uid whose freezing point is below the freezing point of the water in the earth wherein the storage cavern is located.

The system herein disclosed, whereby refrigeration is provided by the fluid stored, is applicable to any ilui'd which is stored in the liquid Istate. Liqueed petroleum gas and liqueiied ammonia are illustrative of lluids which are applicable to the underground storage system of our invention. However, the novel system herein disclosed for storing fluids in an underground storage system is broadly applicable to fluids whether or not in a liquid state. Where liquids are stored which boil above the freezing point of the water in the cavern walls at atmos-l pheric conditions it is advantageous to admix `with such liquids more volatile components in concentrations which will not disturb the specifications for such stored liquids Means to actuate sai'd'relay are provided which `comprise f and yet will allow the withdrawal of such volatile components by the motor 'and compressor combination 2S and thereby make such heavier liquids applicable to a self refrigeration process.

1 There are two conditions which arise in the construction and rst operation of our storage system. One concerns the condition when the volume of water in the earth and water formation isV not so great that earth formation is unconsolidated, and in this case the water encountered is pumped out continuously while the cavern is being excavated. However if the amount of water is excessive to the extent that the earth and water formation is unconsolidated, the water in the entire mass of earth where the cavern is to be located must be frozen before excavation is begun and maintained frozen throughout the construction of the underground storage system and first filling. A suitable refrigerating medium, e. g., brine, is circulated through ydrilled holes in the earth formation to freeze the water in the earth Aand thereby allow the excavation operation toY be accomplished.

In the case where the amount of water in the earth is not so large as to requireV freezingbefore excavation is begun, the pump and motor. combination 17 is operated continu-V ously in well 5 to prevent theY accumulation of water in the cavern. When the excavation work is complete and Vthe necessary shaft liner, lling and withdrawal lines and surface equipment are installed, theiilling operation is started. Since the pressureginside the cavern is lower than the pressure in the surrounding earth and water due to the continuous Withdrawal of water, the uids introduced to the cavern Vwill vaporize immediately and begin to cool the cavern walls.k Air in the system is bled of through Y Y pipe 14 and valve 16 to prevent a buildup inl pressure. l

When the cavern is thoroughly purged, valve 16 'is closed and the motor and Ycompressor assembly 25 is started. During the time that the uids are first being introduced to are thestorge cavern, before the water in the cavern Walls is frozen, the rstored fluids will not escape through the cavern walls because the pressure within the cavern is maintained lower than the pressure outside the cavern due to the continuous withdrawal of water by motor and pump 17. After the water in the cavern walls bceomes frozen as evidenced by the opening of the circuit in lead lines 41 by the temperature responsive switches and the pressure responsive switch, the motor and pump 17 is heated by heating elements 18 to free motor and pump 17 from the ice and raised to a position above the ice level 22 in the bottom of the cavern to be used to Withdraw the stored fluidsvas desired from the storage system.

In the case where the amount of water in the earth surrounding the cavern is so great that the entire formation must be frozen before excavation is begun, the entire operation in constructing the undergro-und storage system of our invention is completed While the water in the earth is maintained in a frozen condition by external refrigeration before the fluid to be stored is introduced. Upon the introduction of the uid to be stored, the starting operation then becomes identical with that described above and the external refrigeration is discontinued when the rate of vaporization of the stored fluid is sufficient to maintain the vtemperature of the underground cavern below the freezing point of the water in the earth surrounding the cavern.

In the case where the entire earthen formation is not frozen by external refrigeration during the excavation operation, the pressure within the cavern is controlled, as stated above, by the continuous withdrawal of water from the shaft 3 and well 5. Therefore it is not necessary that the minimum water table in the site selected for the underground storage system of our invention be far above the cavern roof. It is only preferred that the earthen formation be saturated with water to a distance far enough above the cavern roof that a substantial layer of ice can be formed in the cavern walls.

It is to be noted that the distance from the surface of the ground to the top of the cavern can be varied according to the vapor pressure of the fluid to be stored therein at or near the freezing point of the water in the earth surrounding said cavern. A workable rule to follow is that the cavern be located at a distance below the surface of the earth approximately equal to one foot for each pound of vapor pressure exhibited by the stored fluid at thefreezing temperature of the water in the earth surrounding the storage cavern.

While our invention has been described in connection with a present preferred embodiment thereof, it is to be understood that this description is illustrative only, and is not intended to limit the invention.

We claim:

1. A method for sealing an underground cavern for the storage of liquids, said cavern having been formed in a permeable water-bearing formation underground, which comprises introducing said liquids into said cavern, withdrawing the vapors of said liquids to produce a cooling effect to freeze the water in the earth surrounding said cavern, comprising and condensing said vapors and returning said compressed and condensed vapors to said cavern.

2. A method for sealing an underground cavern for the storage of liquefied petroleum gas, said cavern having been formed in a permeable, water-bearing formation underground, which comprises introducing said liquefied petroleum gas into said cavern, withdrawing the vapors of said liquefied petroleum gas to produce a cooling effect to freeze the water in the earth surrounding said cavern, compressing and condensing said vapors and returning said compressed and condensed vapors to said cavern.

3. A method for sealing a plurality of underground caverns for the storage of liquefied petroleum gas, said caverns having been formed in a permeable, water-bearing formationiunderground, which comprises introducingsaid liqueedpetroleum gas into `said Caverns, withdrawingthe vapors of said liquefied petroleum gas to produce a cooling 6 elect to freeze the Water in the? earth surroundingsaid Caverns, compressing and condensing said vaporsfand re-` turning said compressed and condensed' vapors to said caverns.

4. In an underground storage system for liquids, in combination, an underground storage cavern, the Walls of said cavern being defined by and consisting of the surrounding subsurface media, said media being in their ordinary condition permeable, water-bearing subsurface strata, a shaft extending from the surface of the earth to a region adjacent to said cavern, means for connecting said shaft with said cavern, means for introducing a liquidY to be stored into said cavern and meansfor cooling said cavern by withdrawing vapors of said liquid so as to freeze the water in the earth surrounding said cavern.

5. In an underground storage .system for liquids, in com-- bination, an underground storage cavern, a shaft extendf ing from the surface of the earth to a regionv adjacent to said cavern, means for connecting said shaftY with said cavern, and means for cooling said cavern to freeze `the water in the earth surrounding said cavern which comprises means for introducing said liquids into said cavern, and means for withdrawing, compressing, condensing and returning the vapors of said liquids to said cavern. Y

6. In an underground storage system for liquids, in combination, an underground storage cavern, a shaft extending from the surface of the earth to a region adjacent to said cavern, means for connecting said shaft with said cavern, means for cooling said cavern to freeze the water in the earth surrounding said cavern comprising means for introducing said liquids into said cavern, means for withdrawing, compressing, condensing and'returning the vapors of said liquids to said cavern, and an automatic control assembly means to actuate said withdrawal and compressor means, said automatic control assembly means being re.- sponsive to an increase in the temperature above a first preselected temperature of the water in the earth surrounding said cavern.

7. In an underground storage system for liquids, in combination, an underground storage cavern, a shaft extending from the surface of the earth to a region adjacent to said cavern, means for connecting said shaft with said cavern, means for cooling said cavern to freeze the water -in the earth surrounding said cavern comprising means for introducing said liquids into said cavern, means for withdrawing, compressing, condensing and returning the vapors of said liquids to said cavern, and an automatic control assembly means to actuate said withdrawal and compressor means, said automatic control assembly means being responsive to an increase in the pressure above a first preselected pressure of said vapors.

8. In an underground storage system Lfor liquefied petroleum gas, in combination, an underground storage cavern, a shaft extending from the surface of the earth to a region adjacent to said cavern, means for connecting said shaft with said cavern, means for ascertaining the evel of the fluids in said cavern comprising a liquid level gauge assembly including a float positioned within said shaft, and means for cooling said cavern to freeze the water in the earth surrounding said cavern comprising means for introducing said liquefied petroleum gas'into said cavern, means for withdrawing, compressing, condensing and returning the vapors of said liquefied petroleum gas to said cavern.

9. In a system for the underground storage of liquids, in combination, an underground storage cavern in -a permeable, water-bearing formation below the minimum water table, a shaft connecting the surface of the earth to a region below and adjacent to said cavern, means for connecting said shaft with said cavern, means for cooling said cavern to freeze the water in the earth surrounding said cavern, said means comprising a compressor, amotor operatively connected to said compressor, a conduit having an inlet positioned above the level of `saidliquidsin said cavern and its outlet connected toV theinlet of said compressor, a condenser receiving the discharge of said 7 compressor, a conduit having one end thereof attachedtothe outlet of said condenser and having its other end positioned within said cavern which returns said compressed and condensed vapors to the region of the iloor of said cavern, and means for the introduction and withdrawal of liquids to be stored in said cavern.

10. In a system for the underground storage of liquids according to' claim 9, a layer of ice covering the floor of said cavern, said conduit returning the'compressed and condensed vapors to the region of the floor of said cavern having a substantial length thereof adjacent said other end embedded in said layer of ice and in heat exchange relationship thereto, the outlet of said conduit protruding upwardly above said layer of ice'.V

1l. In a system for the underground storage of liquids, in combination, a plurality of underground storage caverns in a permeable, water-bearing formation below the minimum water table, a shaft connecting the surface of the earth to a region below and adjacent to said caverns, means for connecting said shaft with said caverns, means for cooling said caverns to freeze the water in the earth t surrounding said caverns, said means comprising a compressor, a motor operatively connected to said compressor, a conduit having an inlet positioned above the level of said liquids in said cavern and its outlet connected to the inlet ofrsaid compressor, a condenser receiving the discharge of said compressor, a conduit having one end thereof attached to the outlet of said condenser and having its other end positioned within said cavern which returns said compressed and condensed vapors to the region of the floors of said caverns, and means for the introduction and withdrawal of liquids to be stored in said caverns.

12. In a system for the underground storage of liquids, in combination, an underground storage cavern in a permeable, water-bearing formation of earth, a shaft exmotor to thereby withdraw the vapors of said liquids to cool said cavern to maintain the water in the earth surrounding said cavern in a frozen condition which comprises a current source connected to said motor, a switch to disengage said current source from said motor, a relay to actuate saidrswitch, and means to actuate said relay including a current source, a pressure responsive switch connected by a conduit means to the vapors in said cavern and temperature responsive switches positioned in the earth and water surrounding said cavern, said pressure responsive switch and temperature responsive switches being connected in a parallel circuit with the coil of said relay and said current source, said pressure responsive switch opening at a rst preselected pressure in said cavern and closing at a second higher preselected pressure in said cavern, said temperature responsive switches opening at a rst preselected temperature in the earth and water surrounding said cavern and closing at a second higher preselected temperature in said earth and water surrounding said cavern, means for condensing the withdrawn vapors, and means for returning the condensed vapors to the lower region of said cavern.

13. An underground storage system according to claim ll wherein said liquids stored therein are liquefied petroleum gases, wherein said cavern is located below the minimum water table and at a depth below the surface of the earth equal to approximately one foot of overburden for each pound of pressure exhibited by said liquefied 8 petroleum gases at a temperature approximately equal to the freezing point of the water in the earth surrounding said cavern.

14. In a system for the underground storage of liquefied petroleum gas, in combination, an underground storage cavern in a permeable, water-bearing formation, a shaft connecting the surface of the earth to a region adjacent to and below said cavern, a tunnel connecting said shaft with the upper region of said cavern, a tunnel connecting said shaft with the lower region of said cavern, afmetal liner in said shaft cemented in concrete in the earth surrounding said shaft extending from the shaft opening at the earths scrface t0 the top of the tunnel connecting said shaft to the upper region of said cavern, a liquid level gauge assembly including a iioat positioned within said liner in said shaft to indicate the liquid level therein and thereby the 'liquid level in said cavern, 'a metal Iliner head attached to said metal liner in said shaft to seal said shaft atthe earths surface, a liquid withdrawal pipe means within said shaft and metal liner connecting the bottom region of said shaft to the earths surface and a heated pump at the bottom end of said withdrawal pipe means, a liquid filler pipe means within said shaft and metal liner, extending through said 'liner head to the surface of the earth and connectingV the lower region of said cavern through said tunnel connecting said shaft with the lower region of said shaft, vapor withdrawal pipe means within said shaft and metal liner extending from a region above the liquid level in said cavern through said liner head to the surface of the earth, and compressor means and motor therefor to withdraw vapors from said liquefied petroleum gas, said compressor means and motor therefor automatically being actuated to withdraw said vapors by an automatic control assembly comprising temperature responsive switches installed in the earth and water surrounding said cavern and responsive to an increase in temperature above a first preselected temperature of the water in the earth surrounding said cavern, and a pressure responsive switch connected by a conduit means to the vapors in said cavern responsive to an increase in the pressure above a first preselected pressure of said vapors, condenser means to condense said withdrawn vapors and connected to said liquid filler pipe means to return said condensed vapors to said cavern, and a layer of ice covering the oor of said cavern, said :liquid filler pipe means returning the compressed and condensed vapors to the region of the floor of said cavern having a substantial length thereof adjacent its outlet embedded in said layer of ice and in heat exchange relationship thereto, said outlet protruding upwardly above said layer of ice.

15. An underground storage system for liquefied petroleum gas according to claim 14 wherein said cavern is located below the minimum water table and at a depth below the earths surface equal to about one foot of cverburden for each pound of vapor pressure exhibited by said liquefied petroleum gas where the maximum temperature of said liquefied petroleum gas is below the freezing point of the water in the earth surrounding saidV cavern.

16. A method for sealing an underground cavern for the storage of liquid whose freezing point is below the freezing point of water measured under standard conditions, said cavern having been formed in a permeable water-bearing formation underground, which comprises introducing said liquid into said cavern, vaporizing a portion of said liquid in direct contact with the `geologic formation and thus freezing water held therein, withdrawing the vapors of said liquid from said cavern, compressing and condensing said vapors, and returning said cornpressed and condensed vapors to sai-d cavern.

17 A method according to claim 16 wherein a plurality of underground caverns are sealed.

18. An underground storage system for liquefied petroleum gas according to claim 14 in which the heated pump and withdrawal pipe means can be raised and lowered as a unit, said pump being adapted for `use in its lower 9 position for the removal of water and in its raised position for withdrawing product from the underground storage system.

19. The apparatus of claim 18 in which the Withdrawal pipe means is provided with a seal to prevent loss of stored fluids during raising and lowering of said pipe means, said seal being positioned at the upper end of said shaft.

20. The apparatus of claim 18 in which the heated pump is disposed in a well below the water level in the storage system and is provided with suitable heating means whereby said pump can be released and raised from the Well when the storage system becomes frozen.

References Cited in the iile of this patent UNITED STATES PATENTS Sooysmith Oct. 14, 1902 Sooysmth Nov. 11, 1902 Vedder June 8, 1920 Bowie Mar. 12, 1940 Kerr Jan. 18, 1949 Thompson May 1, 1951 Daxelhofer July 14, 1953 Phelps Nov. 17, 1953 FOREIGN PATENTS Germany June 17, 1920