Liquefied gas storage
US 2488813 A
Description (OCR text may contain errors)
Nov. 22, 1949 o. L. GARRETSON LIQUEFIED GAS STORAGE Filed Feb. 18, 1946 mVENR.
.1.. GARRETsoN ATTORNEYS low temperature.
Patented Nov. 22, 1949,
` 2,488,813 LIQUEFIED Ges s'ronaon Owen L. Garretson, Bartlesville, Okla., assigner to Phillips Petroleum Company, a corporation of Delaware Application February 18, 1946, Serial No. 648,497
'z claims. l
This invention relates to the storage of liqueed gases. In one of its more speciilc aspects it relates to a method for the storage of liquefied petroleum gas.
Because of their high vapor pressure at atmospheric temperature, liquefied gases such as hquid propane require high pressure storage vessels or lower pressure vessels thermally insulated and their contents kept cool by some type of ar- Aticial cooling. Large size or large capacity` refrigeration units are frequently used 1n an attempt to maintain low pressure storage through Even in large L. P. G. (liqueiied petroleum gas) installations such as required by utilities, the amount of refrigeration required for simple storage purposes is not large. This fact is yoccasioned by eilicient insulation of the storage tanks.
Maximum refrigeration loads occur at times when tank car or transport truck quantities of liquefied gas are transferred to the storage tanks. A large quantity of warm liqueed gas may warm the tank and its small volume of remaining liquid to such a temperature that the corresponding vapor pressure may be too high for safe storage. The liquid then should be cooled prior to transfer to storage. A refrigeration unit sulciently large to cool a tank car of liquid propane from say 100 F. to a desired storage temperature of say F. during a normal unloading period of time would be greatly oversize for temperature maintenance merely for storage. Since a refrigeration unit is a type of equipment which is quite expensive it is desirable to use as small a unit as possible. By the application of my invention I am able to use a relatively small refrigeration unit to serve the two-fold purpose of temperature maintenance in storage and cooling during unloading.
For practicingthe process of my invention I use a refrigeration unit of a size slightly larger than that required for merely temperature maintenance and store up the excess refrigeration for use during occasional L. P. G. unloading periods.
One object Y of my invention is to provide a method for the low pressure storage of liquefied ases. g Another object of my invention is to provide a method for the low pressure storage of liquefied petroleum gases such as propane.
- Another object of my invention is to provide an apparatus and a method of operation of this apparatus for the low pressure storage of liquefied petroleum gas. y
Yet another object of my invention is to Provide a refrigeration storage unit to operate in conjunction with a refrigeration apparatus for use in cooling liquefied petroleum gas during unloading times as well as for normal cooling of the liquid in storage.
Other objects and advantages of my invention will be apparent from a study of the following description and drawing which respectively describes and illustrates a preferred embodiment of my invention.
The ligure is in part a. diagrammatic sectional elevation of a preferred form of the apparatus of my invention.
Referring to the drawing, a liquefied petroleum gas storage tank I is covered with a thick layer of insulation 2. This storage vessel may be vertically disposed, as shown, or may be horizontally arranged if desired. The tank has an upper vapor outlet line 3 and a lower drainage line 4. A side outlet line 5 is located in the tank at such a point as to permit withdrawal of liquid from the tank at a point at least some distance from the bottom. A return line 6 is located at any desired point butA preferably at some distance from the vapor outlet pipe 3.
A brine or other solution tank I2 is also covered with a thick layer of insulation. Disposed in the lower portion of this tank is a coil Bone end of which is joined to a line 'I which in turn is joined with pipes Sand II, as shown. The other end of the coil 8 connects with a line 9 and this line serves as an inlet to a pump I0, while the tank inlet pipe 6 serves to convey fluid from the pump into the tank I.
In the upper portion of the brine tank I2 is disposed a coil I4 the ends of which are connected tosome lines I5 and I8 by connecting pipes or tubes I1 and I8, respectively. Line I8 carries a motor valve I9 which is adapted to operate according to the temperature within the tank I2. A thermostat 20 is located in the tank as shown and is adapted through a controller mechanism 2| to cause the valve I9 to open and to close. When the temperature within the tank I2 rises to above a predetermined value the thermostat 20 causes controller 2| to open the valve I9, and the valve closes when the temperature in the tank drops below a predetermined value.
The storage tank I is also equipped with a series of coils 22 the ends of which are connected to the pipes I5 and I6. In a manner similar to that given for tank I2, the tank I is equipped with a thermostat 23 which is adapted to operate through a controller mechanism 35 to open and to close a valve 24 in line Il.
The lines I and I6 are adapted to carry a refrigerant material, line I6 carrying the liquid refrigerant and line I5 being the return line. A compressor is adapted to compress the gaseous refrigerant while in condenser 26 the compressed refrigerant is cooled and condensed. Connections 21 and 28 carry coolant to and from the condenser 26.
Someanchors 29 are adapted and arranged to ilx the coils 8 and the coils I4 against movement and to steady them against vibration. In addition the anchors hold the coils against any buoyant effect occasioned bythe presence of ice in case the tank I2 contains a. water solution.
In the operation of my apparatus the compressor 25 and the cooler or condenser 26 are operated for a period of time to circulate a refrigerant through lines I6, I8, expansion valve I9. coil I4, and return lines I1 and I5. On passage through the expansion valve I9, cooling occurs and this cooling is transferred from coils I4 to water, or a brine solution or other liquid cold storing medium 30. Water may be used for this purpose When it is desired to store the liquefied gas at temperatures about 35 F. or higher. When the heat exchange medium 30 in tank I2 has been suillciently cooled then the system is in condition to receive a car of liquefied gas for storage.
For unloading a car of liquefleld gas, a valve 3| in line I6 just ahead of the expansion valve 24 is opened and refrigerant passed through the eX- pansion valve 24, cooling coil 22 in the storage tank I. The source of liquid is connected with the inlet line II, and the inlet valve 32 opened, a valve 33 in line 'I is opened and liquefied gas under tank car pressure ilows through the lines II, 1, coils 8, line 9, and through pump I0 and line 6 into the storage tank I. Pump I0 may be turned on at any desired time.
As liquefied gas from the tank car flows through the coil 8 in the chilling tank I2, the liquid becomes cooled and is passed in this condition into the storage tank I. With refrigerant in the storage tank coil 22 the liqueed gas entering the storage tank I is maintained in a cooled condition, Thus with the refrigeration reservoir in a fully chilled condition, I am able to unload a tank car of liquefied petroleum gas in a relatively short time.
After a. car of the liquefied gas has been unloaded into the storage tank I, not much refrigeration is required to keep it in a sufficiently cooled condition. Thus for maintaining the liquefied gas at a predetermined low temperature, it is merely necessary to open a valve 34 in line 5, and the valve 33 in line 1, with valve 32 in line II of course closed and by means of pump Ill circulate the liquid from the storage tank through the cooling coil 8 and back to the storage tank.
As mentioned hereinbefore, to maintain the liquefied gas, once cooled, in the cooled condition requires a relatively small amount of refrigeration, and this consideration is the main factor in determining the size of refrigeration unit (compressor 25condenser 26) to install. I use a compressor 25condenser 26 just slightly larger in capacity than that required for temperature maintenance and I operate this refrigeration at capacity and in do doing am able to impart sufficient chilling to the solution 30 to cool the liqueed gas circulating in coils 8 and to cool the solution 30 to a sufficiently low temperature for cooling liquefied gas during unloading times.,
'I'he capacity of the brine tank I3 is so designed that the liquid 30 therein can store up sufficient cooling for tank car unloading purposes. And similarly the size and capacity of the refrigeration unit is so selected that it can maintain the liquefied gas in storage at a desired temperature and simultaneously cool the liquid 30 in the brine tank I2 so as to have sufficient cooling in storage for tank car unloading purposes.
The brine or other solution in the tank I2 may become frozen in part or entirely during the refrigeration storing up period. If water solutions such as salt and water, or calcium chloride and water or another salt solution is used, the water may freeze and if continued for a sufdciently long period the entire brine or salt solution may freeze. Under these conditions rather large amounts of refrigeration can be stored and yet be readily available. If such a material as ethylene glycol or the like is used, and freezing occurs, the frozen mass will be slushy at first and will not harden until after its temperature has been decreased to quite an appreciable extent. Under this condition then a large amount of refrigeration is in storage.
Conventional procedure is to use a large size refrigeration' unit corresponding to 25--26, in fact one which is suiliciently large for temperature maintenance purposes (in tank I) and at the same time to cool propane being unloaded, It will be obvious to those skilled in the art that without my herein disclosed refrigeration storage an excessively large amount of refrigeration is required during unloading times in order to unload car of liquid propane in a reasonable length of ime.
Demurrage payments on tank cars is an additional consideration in favor of my refrigeration storage for rapid tank car unloading. Further, overtime labor required for night unloading, runs up costs when my storage system is not used.
From vapor pressure data of propane it is obvous to those skilled in such art that by storing at low temperatures, low pressure tanks may be used. At F. propane has a vapor pressure of about 184 pounds per square inch, at 32 F. its vapor pressure is about 68 pounds per square inch, and at 0 F. its vapor pressure is about 39 pounds. From these gures it will be obvious that much lighter steel can be used in making the storage tank I for storing propane under 39 pounds pressure than for storage under 184 pounds pressure. When installing storage tanks sufliciently large to hold from 11/2 to 21/2 tank cars capacity, the cost of such tanks for high pressure storage is excessive.
For the storage liquid 30 in tank I2, I may use water in case storage in tank I is desired to be about 35 F. For lower storage temperature a salt water brine, or a calcium chloride brine, or an ethylene glycol-water mixture may be used. The particular material to be used may be selected from among many available depending upon conditions of a given installation.
The refrigerant to use in the refrigeration circuit may be ammonia, or ethane or even propane, or any other material desired. If using propane from the storage system for use in the refrigeration circuit provision will probably need be made for making certain the propane is dry from moisture, or of refrigeration grade.
The type of compressor 25 and condenser 28 may be selected from among those commercially available. The thermostats 20 and 23, and their auxiliary apparatus, such as controllers 2l and l5, and motor operated expansion valves I8 and 2l may be selected from standard equipment from equipment supply houses.
The kind and method of application of the insulation 2 and I3 applied to tanks I and I2 may be any type desired, as long as it is suitable for the purpose at hand. The pump I 0 need not be special, but may be obtained commercially from supply houses selling such equipment.
Valves and other auxiliary equipment have not been shown for purposes of simplicity but the use of such equipment will be readily understood by those skilled in the art.
It will be obvious to those skilled in such art that many variations and alterations of my broad idea may be made without departing from the intended spirit and scope of my invention.
Having disclosed my invention. I claim:
1. A liquefied gas storage system comprising a storage tank having an outlet; a refrigeration reservoir; a first conduit commuicating at one end with said storage tank circuitously passing through said refrigeration reservoir and communicating at its downstream end with said storage tank; a pump in said first conduit downstream of said refrigeration reservoir; a second conduit circuitously passing through said storage tank and being joined at its .ends by a condenser, said condenser being adapted for the passage of coolant therethrough; a compressor in said second conduit upstream of said condenser; a third conduit communicating with said second conduit at a point downstream of said condenser, circuitously passing through said refrigeration reservoir and communicating at its downstream end with said second conduit at a point upstream f said compressor; a valve in said third conduit upstream of said reservoir; thermostat means within said reservoir; control means adapted so as to operate said valve in said third conduit in accordance with temperature change in said reservoir; a valve in said second conduit downstream of said condenser; thermostat means 'in said storage tank; control means adapted so as to operate said valve in said second conduit in accordance with temperature change in said storage tank; and an inlet conduit communicating with said first conduit upstream of said reservoir.
2. A liquefied gas storage system-adaptedfor the storage of. said liquefied gas at a temperature below atmospheric and at a correspondingly lower pressure, adapted for said lower temperature storage during periods of adding liquefied gas to increase the Volume of liquid in storage, comprising a liquefied gas storage tank; refrigeration reservoir means: first conduit means passing through said reservoir means to said storage tank; third conduit means for adding liquefied gas to said first conduit means; second conduit means extending between said storage tank and the inlet end of said first conduit means; and refrigeration means in direct heat exchange with said refrigeration reservoir means and said flrst conduit means.
3. A method for maintaining stored liquefied gas in a cooled condition in a storage system during periods oi' addition of liquefied gas, at substantially atmospheric temperature, to said cooled liquefied gas in storage which comprises passing a refrigerant in indirect heat exchange with said liquefied gas in storage; passing a portion of said refrigerant in indirect heat exchange through a refrigeration reservoir zone; and passing additional liquefied gas in indirect heat exchange through said refrigeration reservoir zone into said storage. r
4. The method of claim 3 wherein the liqueed gas is a liquefied petroleum gas.
5. A method for maintaining a liquefied gas in a cooled condition in a storage system during and after addition of liquefied gas to said system which comprises passing a refrigerant in a first indirect heat exchange with said liquefied gas in storage; controlling the flow of said refrigerant in said first heat exchange in accordance with temperature change within said storage; passing a portion of said refrigerant in a second indirect heat exchange through a refrigeration reservoir zone; controlling the flow of said refrigerant in said second heat exchange in accordance with temperature change in said refrigeration reservoir zone; passing additional liquefied gas in indirect heat exchange through said refrigeration reservoir zone into said storage; and after said addition of liquefied gas cycling a portion of said liquified gas from storage in indirect heat exchange through said refrigeration reservoir zone and back to said storage.
6. A method for maintaining a liquefied gas in storage in a cooled condition during periods of.
addition of liquefied gas from a transportation source, at substantially atmospheric' temperature, to said cooled liquefied gas in storage, comprising maintaining a first liquefied gas in storage in a cooled condition by passing a major portion of a stream of refrigerant in indirect heat exchange with said first liquefied gas in storage; passing a minor portion of said stream of refrigerant during an extended period of time in Indirect heat exchange relation with a refrigeration storage zone, whereby said refrigeration storage zone becomes cooled; passing a second liquefied' gas from said transporation source in indirect heat exchange relation with said cooled refrigeration storage zone, whereby said second liquefied gas becomes' cooled; and passing said cooled second liquefled gas into the main body of cooled rst liquefied gas in storage.
7. The method of claim 6 wherein the liquefied gas is a liquefied petroleum gas.
AOWEN L. GARRE'rsoN.
REFERENCES CITED The following references areof record in the /f//f//f/ Certificate of Correction Patent No. 2,488,813 November 22, 1949 OWEN L. GARRETSON It is hereby certied. that errors appear in the printed specification of the above numbered patent requiring correction as follows:
Column 3, line 69, for the words in do read fifn, so; column 5, line 61, for direct read lindirect;
and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case m the Patent Oflice.
Signed and sealed this 18th day of April, A. D. 1950.
THOMAS F. MURPHY,
Assistant Commissioner of Patents.