US1963922A - Storage of liquefied gas - Google Patents

Description

J 19, 1 3 Q J. ROBINSON v 3953592 STORAGE OF LIQUEFIED GA-S Filed Jan. 11, 1954 INVENTQR Jack R0bz w0n.

ATTORNEY Patented June 19, 1934 UNITED STATES 1,963,922 STORAGE F LIQUEEIED GAS Jack Robinson, East Alton, Ill., assignor to Standan] Oil Company, Chicago, a corporation of Indiana Application January 11, 1934, Serial No 706,223

16 Claims. (01. 62122) mer for use in winter gasoline or where large vol-' umes of propane are stored for use is deasphalt-.

mg, dewaxing, or solvent extraction processes, it is necessary to store large volumes of these liquefied gases under conditions of hot and' widely varying temperatures. Pressure storage tanks could be designed which would hold the liquefied gases even at high temperatures, but the cost of such vessels would be prohibitive in storage tanks of one hundred thousand gallons capacity. Ordi-' nary petroleum storage tanks may be employed if liquefied gases are maintained atsufficiently-low temperatures, but these large diameter tanks will not stand wide variations in pressure; they must be provided with pressure-vacuum release valves which will permit rapid admission of air when the temperature drops or liquid is withdrawn from the tank, and which will permit the rapid exhaust of gases and vapors with rises in temperature or with the admission of liquid into the storage tank.

This so-called breathing? results in the loss of large quantities of the stored material and some- 0 times incurs a serious health, fire, and explosion hazard.

An object of my invention is to minimize this breathing action and to avoid as far as possible the opening of the pressure or vacuum release valves or, in other words, my object is to maintain the pressure in the vapor space of the storage tank between certain upper and lower limits.

Brine chillers, ammonia refrigeration systems, etc. for cooling the liquefied gas in the storage '40 tank are not only expensive and cumbersome to install and to operate, but they lack the necessary ease of control,they cannot respond quickly enough to large temperature changes and they are not amenable to automatic control.

Another cooling method is to withdraw vapors from the top of the storage tank, so that the refrigeration is effected by vaporization of the liquefiedgas itself. This provides a means for rapidand inexpensive chilling, but the vapors which are withdrawn are necessarily mixed with air which has been suckedin through the vacuum release valve. It is therefore necessary to compress this air as well as vapors, which results in increased compressor costs, and it is necessary to provide a means for separating air and non-confineries it is possible to vent propane or butane gases together with air to a gas-main which in turn leads to an absorption system or stabilizer for'recovering the valuable hydrocarbons, but the wide fluctuations inthe amount of vapor and air which is thus injected into the system may impair the function of the stabilizers and absorption systems. When vapors are being withdrawn from the storage tank by a compressor, it is practically impossible to prevent the vacuum release valve from opening and this in turn increases the vexatious problem of separating air from condensable vapors.

An object of my invention is'to provide a systemwherein the temperature of the stored liquid is regulated by controlled vaporization-of apart of the liquid, but wherein it is impossible for air to be admixed with the vapors which are to be compressed and condensed. In other words, my object is to provide a system wherein the cooling can be effected by the simplest and most inexpen-' sive methods and wherein there will be no problem of separating air from condensed vapors.

Another object is to provide a system of this type which is extremely sensitive to automatic control. I v

A further object is to avoid any possible injury to the storage tank by abrupt pressure changes and at the same time to minimize breathing?- with its consequent loss of v pors.

Other objects will be apparent as the detailed description of my invention proceeds.

In practicing my. invention, I employ the. conventional petroleum storage tanks which may be forty or fifty feet in diameter and ten or twenty feet high. These storage tanks are provided with the usual pressure-vacuum release valves which will permit a variation in pressure of about two or three inches of water. Alongside of the storage tank I erect a tower which is slightly higher tower, but I allow liquids to flow freely from the tower to the tank and back again; in other words, if the liquid levelv in the storage tank falls below one of the upper connecting pipes,

that pipe is closed so that the vapors in the storage tank can never find their way to the compressed vapors being condensed and returned to the base of the chilling tower. This evaporative refrigeration in the chilling tower causes a.

very rapid cooling therein and this in turn sets up a thermosiphon flow of liquids from the lower part of the chilling tower to the storage tank and from the upper part of the storage tank to the chilling tower. relatively small, can easily be designed to withstand relatively high pressures or vacuums. A high vacuum in the chilling tower means that the liquid level in the chilling tower is higher than that in the storage chamber, but since their cross sectional areas are so vastlydifferent a considerable elevation of level in the chilling tower will produce a negligible decrease in level in the storage tank. Thus a high vacuum may be obtained in the chilling tower and extremely rapid chilling may be effected without causing any pressure strains on the storage tank. The

compressor does not have to handle any air at all and it. therefore operates at maximum efliciency. Furthermore, the compressor may be started and stopped by a sensitive mercoid switch so that the compressor may be started just before the pressure relief valve opens and the compressor may be cut off just before the vacuum relief by reference to the accompanying drawing, which forms a part of this specification and which represents partially in section an elevational plan of my improved apparatus.

Storage tank 1 may be forty or fifty feet in diameter and ten or twenty feet high, although it should be understood that the invention is Y equally applicable to smaller tanks, to horizontal,

cylindrical tanks, or tp any storage means designed to hold large volumes of liquefied gases or volatile liquids. The storage tank does not have to be designed to withstand high pressures,--it may be built as if it were intended to serve as a holder for water or oil. However, since the contents of the tank will have to be maintained at a temperature far below ordinary The chilling tower, being" ten feet higher than the storage tank, and which is designed to withstand a relatively high vacuum. The chilling tower is likewise insulated with rock wool or other suitable material 5 and it is connected to the storage tank by a vertical series of spaced horizontal connecting pipes 6 of relatively large cross sectional area. Each of these pipes is provided with a manually operated cutoff valve 7 and all of them except the bottom pipe is provided with an automatically c bntrolled valve operated by float 7a through bell crank 7b and operating rod 7c, the rod being pivoted to the bell crank and the bell crank being pivotally supported by bracket 7d. Floatsfla normally hold these automatically operated valves wide open to allow for the therm'osiphon flow of liquefied gas therethrough, but when the liquid level permits the float to fall, '10(1 7c closes a clap valve which prevents any gases from the storage tank from entering the chill chamber.

The intake of compressor 8 is connected by pipe 9 to the top of chilling tower 4, the compressorbeing driven by. an electric motor through a driving belt or chain 10. Compressed vapors are passed from the discharge side of compressor 8 through pipe 11 to condenser coils 12, which-are summer temperatures, I prefer to insulate the storage tank with two or three inches of air felt, rock wool, or equivalent insulating material 2. At the upper part of the storage-tank and connected to the vapor space therein I provide a suitable pressure-vacuum release valve 3 which may be of the type described in United States Atwell Patent No. 1,628,348. Any device may be employed, however, which will permit a ready inlet for air when the pressure falls below a critical value and which will permit the escape of air and gases whenthe pressure exceeds a critical value. I may, of course, employ a balloon such as described in Wilson United States Patent No. 1,596,385, or other suitable means for preventing loss of material through breathing" action.

Adjacent to the storage tank 1, I erect a chilling tower 4 which is preferably only three or 'four feet in diameter, which is about five or cold water or brine in condenser box 13. The. liquefied gas is then introduced by pipe 14 intocollector 15'from which itis returned through pipe 16 to the base of chilling tower 4. If any air or non-condensable gas should-happen toget into the system, it may be released through valve 17, I

but this valve is-normally closed.

I The compressor is driven by an electric motor 18 which, is started and stopped "by a mercoid switch or equivalent device in response to the pressure in storage tank 1. For example, I may employ an auxiliary pressure-vacuumdevice 19 of the tilting seal type described in theAtwell patent and I may mount mercoid switches on said devices (which aradesigned to operate just prior to the operation of the main pressure release valve) sothat the motor 18 is started just before the main pressure valve 3 is opened, and so that the motor is cut 03 just before the main vacuum release valve 3 is opened. I do not limit myself to any specific means for controlling the operation of the compressor pump in response to pressure conditions in the storage tank since these expedients are familiar to those skilled in the art. Furthermore, I may, if desired, control the pump by thermostatic means instead of pressure means. It will be noted that even though a substantial vacuum is created in the upper part of the chilling tower and even though there is an appreciable difference in the level of liquids in the chilling tower and the storage tank, there will not be a sumcient variation in the pressure of the storage tank to cause the immediate opening of the vacuum release valve. The raising of the level of the liquid in the chilling tower at the beginning of the cooling operation.

tends to remedy immediately the high pressure the compressor load is not unduly augmented, and i.-- J

- promote the tank. In such cases,

line 16 may terminate to any of said lowing claims,

4. A storage system for liquefied gases comit is unnecessary to provide an expensive system for separating air from liquefied vapors. It will thus be seen that I have largely eliminated the danger of damaging the main storage tank due to excessive pressure changes, I have provided a system wherein only condensable gases are handled by the compressor, and I have provided a system which is adapted to automatic control and which is extremely sensitive and quick to react in accordance with temperature and pressure changes.

While I have discovered a system for storing propane, butane, and the like, it will be under stood that the invention is equally applicable to the storage of any other liquefiable gases, particularly liquid sulfur dioxide, liquid prussic acid (HCN), liquid ammonia, dimethyl ether, etc. Also, the invention is applicable tothe storage of gasoline or other liquids containing volatile constituents.

The invention is not limited to the storage problem, but it may be useful also in processes which require the chilling of mixtures containing liquefiable gases; for example, in propane dewaxing systems, propane deasphalting systems, solvent extraction systems, etc. I

In many cases, the thermosiphon action may not be sufficient to maintain an even temperature throughout the chilling tower and the storage I may provide mechanical for forcing the liquid from to the storage tank propellers or injectors the base of the chilling tower and from the top of the storage tank to thechilling tower.

Also the return line age tank instead of to 16 may go back to the storthe chilling tower. In fact in an injector in lower pipe 6 so that the return of condensate will of itself of the chiller to the base of the storage tank. It may sometimes be advantageous to have liquid enter the bottom of the chiller and leave it at the top, in which case the injection action of the returned, liquid or equivalent mechanical means may be used to cause a flow in the opposite direction from that shown in the drawing.

While I have described my invention in detail, it should be understood that I do not limit myself details except as defined by the folwhich should be construed as broadly as the prior art will permit.

'1 claim:

1. A method of storing hydrocarbon liquids of high vapor pressure which consists, in placing the liquid in a closed storage tank, in withdrawing liquid from the tank, in reducing the temperature of the liquid thus withdrawn by evaporat ing a part thereof, and in returning the cooled liquid to the-storage tank. I

2. A method of storing hydrocarbon liquids of high vapor pressure which consists, in withdrawing some of the liquid from the tank, in subjecting the liquid withdrawn to reduced pressure to reduce the temperature thereof by evaporation, in returning the liquid thus cooled to the storage tank, in condensing the vapors thus formed, and in returning the condensate to the cooled liquid.

3. A method of storing liquefied gases which consists, in placing the liquid in a closed storage tank, in; withdrawing liquid from the tank, in

- reducingthe temperature of the liquid thus withdrawn by evaporation, in controlling the evaporation in accordance with the pressure in the storage tank, and in returning the cooled liquid to the storage tank.

flow of cold liquid from the base.

prising, a normally closed storage tank, a tower located adjacent to the tank, means providing for the circulation of liquid through the tank and the tower, and means for reducing the pressure within the tower to cause liquid therein to evaporate thereby to effect cooling.

'5. A storage system for hydrocarbon liquids capable of vaporizing at they are normally stored comprising, a normally closed storage tank, a tower located adjacent to the tank, means providing for the circulation of the liquid through the tank and the tower, means for reducing the pressure within the tower to cause liquid therein to evaporate thereby to efthe pressures at which feet cooling, and means for condensing the evapnected withthe upper end ofthe tower'for re-- ducing the pressure therein, and means for condensing the vaporsdrawn off by said pump.-

- l. A storage system for volatile hydrocarbon liquids comprising, a normally closed storage tank, a tower located adjacent to the tank, means providing for the circulation of the liquid through the tank and the tower, a suction pump connected with the upper end of the tower for reducing the pressure therein, means responsive to pressure in-said storage tank for controlling the operation of said pump, and means for recovering vapors drawn ofi by said pump.

I 8. The method of storing liquefied gases in a warm environment without the useof high pressures which comprises maintaining a chilling zone separate from thestorage' zone, causing a liquid'flow to and from the chilling zone and the storage zone respectively, maintaining separate vapor spaces above the storage zone and the chilling zone, respectively, and preventing any communication between the respective vapor spaces, withdrawing vapors from the space above step of regulating the withdrawal of vapors from the space above with pressure conditions storage zone.

'10. In apparatus of the class described, a storage tank of large cross sectional area, a chilling tower of small cross sectional area adjacent to said storage tank, means of liquidsbetween the storage tank andthe chilling tower at different elevations and for preventing communication between the vapor space of the storage tank with the vapor space of the chillabove the space in-the ing tower, means for w'thdrawing vapors from the top of the chilling tower, and means for compressing said vapors and for liquefying them and returning them to said storage tank.

11. The combination of pressure operated means in the vapor space of the storage tank for controlling the operation of the compressing means. 1

12. The combination of claim 10 which includes means for creating a flow of liquids between the storage tank and the chilling tower.

13. The combination of claim 10 which includes automatic means for closing the comfor permitting the new claim 10 which includes the chilling zone in accordance munication between the storage tank and the chilling tower when the liquid level -reaches said communication.

14. In apparatus of the classdescribed, a storage tank of relatively large cross sectional area,

a chilling tower adjacent thereto which is taller than said storage tank and which is smaller in cross sectional area, a plurality of cross pipes connecting the storage tank to the chilling tower at diflerent levels, and means for automatically closing each of said pipes except the lower-one when the liquid level in the storage tank falls to the level .of said pipe whereby communication of the vapor space in the storage-tank with vapor space in the chilling tower is prevented.

15. An apparatus for chilling a liquefied gas which comprises a storage tank of large cross sectional area, an adjacent chilling tower of small cross sectional area, said tower being high-, er than said tank, a plurality of pipes connecting said tank with said tower at spaced elevations, and means for evaporatively refrigerating the liquefied gas in the chilling tower whereby a,

thermosiphon flow of liquids between said chilling tower and said storage tank is effected.

16. In apparatus of the class described, a stor-' age tank, a chilling tower adjacent thereto, pipes.

- means and thereby cause a raising of the liquid level in the chilling tower and a decrease in pressure inthe storage tank-and whereby a decrease in pressure in the storage tank cuts oil? the driving means which in turn causes a lowering of the liquid head in the chilling tower and an equalization of pressure in the storage tank.

JACK ROBINSON.

Images