US3123981A - Volatile liquid storage container pressure regulating means - Google Patents

Description

March 10, 1964 R. R. CARNEY ETAL 3,123,981

VOLATILE LIQUID STORAGE CONTAINER PRESSURE REGULATING MEANS Filed Dec. 5, 1961 Y RE 20 23a 30a fi- V v w 22 26 INVENTORS RICHARD R. CARNEY STANLEY R. KOCH "WW/w? A T TORNEV United States Patent Oflice 3,123,981 VOLATILE LIQUID STORAGE CONTAINER PRESSURE REGULATING MEANS Richard R. Carney, Kenmore, and Stanley R. Koch, Tonawanda, N.Y., assignors to Union Carbide Corporation,

a corporation of New York Filed Dec. 5, 1961, Ser. No. 157,087 19 Claims. (Cl. 6251) This invention relates in general to volatile liquid storage containers and in particular to pressure regulating means for containers holding such liquids as liquid methane, carbon dioxide, oxygen, nitrogen, argon, hydrogen, helium and neon.

The specific volume of any volatile liquid is Well-known to increase substantially with an increase in the liquid saturation pressure accompanied by a corresponding decrease in liquid density. When storing or transporting such liquids for relatively long periods of. time, the expansion of the liquid volume due to absorption of sensible heat from the ambient surroundings tends to markedly raise the liquid level and unless sufficient vapor space is provided within the storage container to accommodate such expansion, the liquid will be expelled through the container vapor vent. Even if sufficient gas space is provided to prevent the container from overflowing due to such expansion when the stored liquid body expands, the vapor in the gas space is compressed and, because of poor heat exchange with the liquid surface, non-equilibrium pressures can develop i.e.. the vapor pressure is higher than that pressure at which the vapor is in equilibrium with its liquid at the temperature of the liquid.

Of necessity then, a volatile liquid storage container can be only partially filled to provide sufiicient vapor space to permit a reasonable amount of expansion in liquid volume without loss of the valuable product by venting. Consequently, when storing such liquids, it is highly desirable to maintain the liquid in a saturated state at or near ambient atmospheric pressure in order to efiiciently utilize the container storage space.

It is advantageous to employ a lowpressure vapor space relief valve when storing or transporting such liquids to not only permit more complete initial filling of the container and thus provide maximum as-filled densitiy, but also to conserve the refrigerating properties of the liquid and, further, to prevent subsequent flashing of the liquid after transfer to another container at a reduced pressure. However, when the liquid is to be transferred out of the storage container, it is usually desirable to do so at a higher pressure to achieve a rapid transfer of the liquid out of the container without pumping when such liquid is to be delivered for use at a pressure higher than the saturated storage pressure. The Well-established practice of non-equilibrium pressure building is usually employed for this purpose.

Several solutions to the problem of providing low pressure venting and high pressure liquid transfer, all of which have been tried and found inadequate although currently in use, are listed below:

I) Use of a low pressure safety hand-operated valve which may be manually closed during high pressure transfer. The difficulty with this arrangement is that an operator may forget to open the hand valve on cessation of the liquid transferring operation. Due to this lack of complete reliability, the low-pressure valve cannot be employed to comply with I.C.C. code regulations for filled density; instead a higher pressure valve employed to regulate the high pressure transfer must be used as the safety valve; thus limiting the container filling density. For some liquids and saturation pressures, the adverse effect achieved by employing a high pressure safety valve makes use of such a device impractical and uneconomical.

3,123,981 Patented Mar. 10, 1964 (2) A low pressure safety valve may be employed as in (1) above except that a plug is placed manually in the valve outlet. An operator may forget to remove the plug with the resultant deficiencies inherent in (1) above. Conversely, if the plug is not installed before the high pressure liquid transfer, no means will exist for building increased vapor pressure to effect rapid liquid transfer.

(3) A medium pressure safety valve may be employed to also provide regulation of the high pressure liquid transfer. This is a compromise between the higher pressure required for liquid transfer and the desired lower venting pressure. Of course, neither pressure is opti mum. Because of the inherent deficiencies of (l) and (2) above, however, this compromise arrangement is now most usually employed.

It is an object of this invention to provide improved means for venting a container at a low pressure and yet permit transferring liquid at a higher pressure. It is a further object to provide a container pressure regulating system which permits increased utilization of the storage space within the container. These and other objects of the invention will be apparent from the following description of the invention in conjunction with the accompanying drawing which depicts:

A schematic diagram illustrating the principal features of this invention.

The present invention comprises means providing auto matic pressure relief at two pressure levels for containers for volatile liquids. The higher pressure may be selected to protect the container from excessive stress due to overpressure and the lower pressure may be selected to maintain the containers contents at a low saturation pressure and temperature when the liquid is not being transferred from the container.

In the preferred embodiment, a low pressure relief means is connected in parallel with a gas phase shut-off means such that the relief means is ineffective when the shut-otf means is open, in order to build non-equilibrium pressure required to transfer the liquid from the container, and is automatically reactivated when the shut-off means is closed. In addition, blow-off means may be provided for safely and controllably reducing the container pressure from the high transfer pressure to the lower safety relief pressure.

Referring particularly to the figure, container 10 is shown partially filled with a volatile liquid 12 above which is a vapor space 14. When the volatile liquid is a cryogenic liquid, container 10 is preferably insulated with a high quality insulation system such as described in U.S.P. 3,009,601, U.S.P. 2,967,152 or U.S.P. 2,396,459. The container 10 may be filled and emptied through conduit 16 containing a shut-off valve 18 and a suitable connector 20 which is employed to connect the conduit 16 to another container or a liquid source (not shown). A vapor phase conduit 22 is provided and contains a vapor shut-off valve 24, vapor connector 26, a branch 28a to a high pressure vapor relief valve 28 and a branch 30a to a lower pressure vapor relief valve 30 both connected upstream of the valve 24. Outlet conduit 32 from lower pressure vapor relief valve 30 is connected to conduit 22 between vapor shut-off valve 24 and vapor connector 26. Thus, lower pressure vapor relief valve 30 is connected in parallel with vapor shut-off valve 24 and operates independently of high pressure vapor relief valve 28.

Vapor relief valve 30 has a pressure-tight enclosure so that all vapor passing therethrough is discharged into conduits 32 and 22 rather than being diffused directly to the atmosphere. Such a pressure-tight enclosure prevents moisture-laden atmospheric air from contaminating the inner valve parts.

To assist in rapidly transferring the liquid 12 from container 10 through conduit 16 upon demand therefor, a

vapor pressurizing source (not shown) may be connected to vapor connector 26. Such source should preferably be of the same composition as the liquid 12 to prevent contamination of the latter but alternatively may be a vapor of a lower boiling point liquid. Examples of substantially non-condensible lower boiling point gases used are helium to pressurize oxygen and nitrogen to pressurize methane. When the vapor pressurizing source is connected to vapor connector 26. the pressure across the lower pressure vapor relief valve 30 will be equalized thereby rendering such valve inoperative during the liquid transfer operation. After termination of the liquid transfer operation, when the valve 24 is closed and the pressurizing source is disconnected, lower pressure vapor relief valve 30 will again be permitted to automatically vent container 10 at the lower pressure.

Since it is frequently necessary to transfer the liquid contents to a higher pressure level, non-equilibrium pressurizing of the liquid from an external source, or the alternative of pumping the liquid. is usually essential. The elimination of liquid pumping is ordinarily sufficiently desirable that liquid containers are almost invariably built which are capable of storing liquid at high pressures. However. employment of the present invention will permit transport and delivery of a pressurized liquid at a lower pressure and therefore more efficiently inasmuch as the effective shipping capacity of the container will be substantially increased because the stored liquid will have a greater filled density.

Typical examples illustrating the value of this invention when employed with cryogenic liquid storage containers are given below:

(1) With a liquid hydrogen container normally holding 150 liters when typical prior art venting devices are employed. use of the present invention with relief valve pressure settings of 35 and l p.s.i.g. the container may be safely filled to 157 litersan increase in capacity of 4.66%.

(2) With a liquid hydrogen container normally holding 1000 liters at a compromise pressure of 45 p.s.i.g. when the working pressure is 150 p.s.i.g., employment of the present invention with pressure settings of 150 and 10 p.s.i.g. permits the container to be safely filled to 1040 liters. Only 730 liters could be safely stored in such a container at a pressure of 150 p.s.i.g. Thus, employment of the present invention permits an increase of safe container capacity of 4% and 42% respectively depending on whether a working pressure of 45 or 150 p.s.i.g. is required.

While the present invention is most useful with mobile or portable containers because of the necessity of meeting the ICC. requirements, it is also useful for large sta tionary containers.

It will be understood that modifications and variations may be effected without departing from the scope of the novel concepts of the present invention. If desired, rupture disk 33 designed to rupture at a pressure above high pressure vapor relief valve 28 may be additionally used to protect container 10 from overpressure.

In addition. following termination of liquid product transfer from container 10, the vapor pressure in space 14 will usually exceed the setting of low pressure vapor relief valve 30. Removal of the pressurizing connection from vapor connector 26 would cause rapid reduction of the vapor pressure to the low pressure setting accompanied by a rapid and uncontrolled discharge of vapor from container 10 through vapor connector 26. If such discharge will present a hazard to the operator. or if it is desired that the gas be passed to a receiving means or to a point of safe disposal, it is further contemplated that a gas phase manual blow-off valve 34 be installed in a branch of conduit 32 downstream from low pressure vapor relief valve 30. Such blow-off valve 34 may be used to controllably reduce the vapor pressure within container 10 thereby safely dcpressuring the container to the low pressure regulated by low pressure vapor relief valve 30.

What is claimed is:

1. In a volatiie liquid storage container having liquid and gas phase communication means, the improvement consisting of container pressure regulating means connected to the gas phase communication means comprising in combination means for venting the container at a predetermined low pressure; means for venting the container at a predetermined higher pressure; means for automatically inactivating the low pressure venting means upon transfer of stored liquid from the container including gas phase shut-off means connected in parallel with said low pressure venting means; such container pressure regulating means being so cooperatively associated with the gas phase communication means such that the aforementioned venting means are in gas communication with the container vapor space.

2. Container pressure regulating means according to claim 1 wherein the lower and higher pressure venting means comprise pressure relief valves; and wherein the gas phase shut-off means includes a vapor shut-off valve cooperatively associated with said gas phase communication means such that said vapor shut-off valve and the lower pressure relief valve are connected in parallel to an outlet.

3. Container pressure regulating means according to claim 2 wherein the lower pressure relief valve is constructed and arranged to have a pressure-tight discharge enclosure.

4. Container pressure regulating means according to claim 2 including means for controllably venting said container to a predetermined lower pressure upon cessation of a higher pressure liquid transfer operation.

5. In a volatile liquid storage container having liquid and gas phase communication means, the improvement consisting of container pressure regulating means connected to the gas phase communication means comprising in combination a pressure-tight pressure relief valve for venting the container at a predetermined lower pressure; a higher pressure relief valve for venting the container at a predetermined higher pressure; means for automatically inactivating the lower pressure relief valve upon transfer of stored liquid from the container including a vapor shut-off valve: means for controllably venting the container to a predetermined lower pressure on cessation of a higher pressure stored liquid transfer operation; such container regulating means being cooperatively associated with the gas phase communication means such that the lower and higher pressure relief valves and said vapor shut-off valve are in gas communication with the container vapor space, and further cooperatively associated such that said vapor shut-off valve and said lower pressure relief valve are connected in parallel to an outlet.

6. A method for storing a volatile liquid in a container and regulating the pressure therein which comprises the steps of providing a storage body of volatile liquid in a container; venting the container at a predetermined lower pressure through low pressure venting means; simultaneously equalizing the pressure across the low pressure venting means and pressurizing said storage body at a higher pressure thereby terminating the lower pressure venting of the container simultaneously in response to the pressurizing; transferring said storage body from the container at substantially said higher pressure; terminating the pressurizing of said storage body on cessation of the storage body transferring step and restoring the venting of the container at said predetermined lower pressure.

7. A method for storing a volatile liquid in a container and regulating the pressure therein which comprises the steps of providing a storage body of volatile liquid in a container; venting the container at a predetermined lower pressure through low pressure venting means; simultaneously equalizing the pressure across the low pressure venting means and pressurizing said storage body at a higher pressure thereby terminating the lower pressure venting of the container simultaneously in response to the pressurizing; transferring said storage body from the container at substantially said higher pressure; terminating the pressurizing of said storage body on cessation of the storage body transferring step; controllably venting the container from said higher pressure to said lower pressure and restoring the venting of the container at said predetermined lower pressure.

8. A volatile liquid storage container pressure regulating means comprising in combination a vent conduit connected to the upper portion of the container; an outlet connected to said vent conduit such that said vent conduit provides gas communication between the container vapor space and said outlet: a pressure relief valve communicating with the vapor space of the container for venting the container at a predetermined higher pressure; a pressuretight pressure relief valve for venting the container at a predetermined lower pressure; first and second conduits connecting respectively, inlet and discharge portions of 20 the lower pressure relief valve to said vent conduit between the container and said outlet such that said vent conduit provides gas communication between the container vapor space and the lower pressure relief valve; a vapor shut-off valve connected to said vent conduit between the connections thereof with said first and second conduits such that said vapor shut-off valve and the lower pressure relief valve are connected in parallel to said outlet.

9. Container pressure regulating means according to claim 8 wherein said outlet comprises a pressurizing-gas connector coupling.

10. Container pressure regulating means according to claim 8 wherein said outlet comprises a pressurizing-gas connector coupling and a valve-controlled conduit for controllably venting the container from a higher pressure to a predetermined lower pressure, such connector and conduit being connected in parallel to the vapor shut-off valve and the lower pressure relief valve.

References Cited in the file of this patent UNITED STATES PATENTS 1,942,944 Smith Jan. 9, 1934 2,884,943 Dobrick May 5, 1959 2,958,204 Spaulding Nov. 1, 1960

Claims (1)

1. 6. A METHOD FOR STORING A VOLATILE LIQUID IN A CONTAINER AND REGULATING THE PRESSURE THEREIN WHICH COMPRISES THE STEPS OF PROVIDING A STORAGE BODY OF VOLATILE LIQUID IN A CONTAINER; VENTING THE CONTAINER AT A PREDETERMINED LOWER PRESSURE THROUGH LOW PRESSURE VENTING MEANS; SIMULTANEOUSLY EQUALIZING THE PRESSURE ACROSS THE LOW PRESSURE VENTING MEANS AND PRESSURIZING SAID STORAGE BODY AT A HIGHER PRESSURE THEREBY TERMINATING THE LOWER PRESSURE VENTING OF THE CONTAINER SIMULTANEOUSLY IN RESPONSE TO THE PRESSURIZING; TRANSFERRING SAID STORAGE BODY FROM THE CONTAINER AT SUBSTANTIALLY SAID HIGHER PRESSURE; TERMINATING THE PRESSURIZING OF SAID STORAGE BODY ON CESSATION OF THE STORAGE BODY TRANSFERRING STEP AND RESTORING THE VENTING OF THE CONTAINER AT SAID PREDETERMINED LOWER PRESSURE.

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