US3464219A - Storage of normally gaseous material in subterranean caverns - Google Patents

Description

Sept. 2, 1969 G. M. cLoss ET AL 3,464,219 STORAGE OF NORMALLY GASEOUS MATERIAL IN SUBTERRANEAN CAVERNS Filed April 17, 1968 INVENTORS'.

Lilli SY Y S W OR A LE CH O @D ,/U o A EK m United States Patent US. Cl. 62-45 7 Claims ABSTRACT OF THE DISCLOSURE A normally gaseous material having a low critical temperature is stored in liquid phase in a subterranean cavern,

by placing the material in a pressure-resistant receptacle.

located in the cavern, and surrounding this receptacle with a different material having a much higher critical temperature, this latter material being chilled to a temperature substantially below the critical temperature of the first material. The latter material may be a normally gaseous material which is stored in liquid phase in the cavern.

This invention relates to the storage of normally gaseous material in subterranean caverns, and more particularly concerns the use of subterranean caverns for storing in liquid phase normally gaseous material which has a critical temperature below the normal wall temperature of the subterranean cavern. The invention has particular utility for the storage of ethylene in liquid form.

Subterranean caverns which have been prepared by mining out rock from a solid rock formation, or by washing out salt from a salt deposit, have been used for the storage of hydrocarbons. Such caverns generally are situated at depths ranging from 300 to 3,000 feet below ground level, and the normal temperature of the cavern walls typically is in the range of 60-85 F., depending upon the depth of the cavern. When the hydrocarbon ma terial has a critical temperature above the normal cavern wall temperature, it is stored in the cavern as a liquid. Thus, normally gaseous hydrocarbons such as propane and butane conventionally are stored in subterranean caverns under sufficient pressure to maintain the hydrocarbon in liquid phase, since their critical temperatures (about 204 F. and about 307 B, respectively) are well above the normal cavern wall temperature. However, ethylene (which has a critical temperature of 49.5" F., below the normal cavern wall temperature) presents a problem. It is desirable to be able to store this material as a liquid rather than as a gas, since in the case of a gas the amount of material that can be stored in a cavern of given size is considerbly less than in the case of a liquid. The problem is then to continuously maintain the ethylene at a temperature below its critical temparature, in spite of the normally higher Wall temparature of the cavern.

The storage of ethylene in subterranean caverns presents another problem, which is due to its high vapor pressure. At 32 F., the vapor pressure of ethylene is 40.6 atmospheres, it being remembered that one atmosphere is equivalent to 760 mm. of mercury pressure; at 4 F., the vapor pressure is 24.8 atmospheres; even at the low temperature of 40 F., the vapor pressure of this material is quite high, being 14.2 atmospheres. This means that for conventional storage of the ethylene as a liquid under pressure in a subterranean cavern, an excessive pressure would have to be used in the cavern, or else the ethylene would have to be refrigerated to an inordinately low temperature. For various reasons, it is desirable to avoid exerting a dangerously high pressure 3,464,219 Patented Sept. 2, 1969 on the shaft leading to the cavern, and the refrigeration of the ethylene to such low temperatures as would be necessary to avoid the use of such high pressures would be impractical and uneconomic.

The present invention provides a novel method of and arrangement for storing a light hydrocarbon such as ethylene as a liquid in subterranean caverns havin a normal wall temperature which is above the critical temperature of the hydrocarbon. The arrangement is such that both excessive pressures and any necessity for refrigerating to an inordinately low temperature, are avoided. In the arrangement of the invention, ethylene and a higher critical temperature (and higher boiling) hydrocarbon are simultaneously stored in a subterranean cavern, both in the liquid phase. While the invention is particularly applicable to the storage of ethylene, it can also be used for storing other normally gaseous materials that have a critical temperature below the normal wall temperature of the cavern, for example, silicon tetrahydride of xenon. In this connection, it is noted that the vapor pressure of xenon is comparable to that of ethylene. The invention can also be used for the liquid phase storage of ethane, in a situation where the normal cavern wall temperature is above the critical temperature F.) of this hydrocarbon.

According to this invention, a pressure-resistant storage receptacle is positioned in the cavern, and the ethylene is placed as a liquid in this receptacle, for storage. A different material, whose critical temperature is above the normal temperature of the cavern walls, is stored as a liquid in the cavern, around the ethylene storage receptacle. The last-mentioned material, which is in thermal contact with the ethylene receptacle, is chilled to a temperature substantially below the critical temperature of the ethylene. The last-mentioned material is prefera-bly a normally gaseous hydrocarbon.

A detailed description of the invention follows, taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a schematic illustration of an arrangement according to the present invention; and

FIG. 2 is a simplified schematic illustration of a modified arrangement.

Referring first to FIG. 1, numeral 1 indicates a subterranean cavern which has been prepared either by mining out a rock formation, or by washing salt from a rock salt deposit; for convenience, the cavern is illustrated as being in a rock formation such as granite. Positioned in cavern 1 are one or more (three are illustrated in FIG. 1) storage receptacles 2 that are pressure-resistant, or in other words than can withstand a relatively high pressure. The receptacles can take the form of a plurality of relatively small storage tanks (as illustrated in FIG. 1), or a coil of large-diameter pipe, or a series of pipes, any of which would provide sufficient volume for the desired ethylene storage capacity. Preferably, the receptacles 2 are made of a high heat-conductivity material, such as a suitable metal.

The inlet connections of the receptacles 2 may be manifolded underground as illustrated, and an inlet line 3 having a pump 4 therein leads from the surface to the manifolded receptacle inlets. Through pump 4, line 3 i connected to an ethylene storage tank (not shown) through a chiller (not shown) adapted to reduce the temperature of the ethylene to the desired low level, such as 15 F. Line 3 and pump 4 enable liquefied ethylene to be fed into the receptacles 2, for storage as a liquid therein.

The outlet connections of the receptacles 2 (indicated as being at the lower ends of the tanks) are manifolded underground, and an outlet line 5 connected to a subterranean (and submersible) pump 6 is provided for withdrawal of the stored ethylene from the ethylene storage receptacles.

Since the storage receptacles 2 (which are designed to withstand a relatively high pressure) are sealed off from the walls of cavern 1 and are thus isolated therefrom, it may be seen that excessive pressures on the cavern walls, or on the shaft (not shown) leading there to, are avoided.

According to one aspect of this invention, a normally gaseous material, whose critical temperature is above the normal temperature of the cavern walls, is stored as a liquid body 7 in the cavern interior space, this liquid body surrounding the storage receptacles 2 and being in thermal contact therewith. An inlet line 8 having a valve 9 and connected to a pump 10 is provided for introducing the liquid 7 into the cavern, line 8 being connected by way of a valve 11 to a suitable storage tank when this liquid is being introduced into cavern 1. An outlet line 12 having a valve 13 and connected to a subterranean (and submersible) pump 14 is provided for withdrawing the liquid 7 from the cavern, line 12 being connected by way of a valve 15 to a surface outlet line 16 when this liquid is being withdrawn from cavern 1.

The material utilized for the liquid body 7 is preferably selected from the C -C hydrocarbon group, comprising propylene, propane, isobutane, n-butane, l-butene, 2-butene, and Z-methyl-propene, the last three of which are known collectively as butenes or the butylenes. All of these hydrocarbons have critical temperatures well above the normal wall temperature of the cavern 1, and so do not present any problem (in this regard) for their storage in liquid phase in a subterranean cavern. The critical temperatures of certain members of the above group are as follows, all given in degrees Fahrenheit: propylene, 198.1; propane, 204.1; isobutane, 273.2; nbutane, 307.4.

The boiling points of the C -C hydrocarbons mentioned are all considerably higher than that of ethylene (C H and as a result the vapor pressures of these C -C hydrocarbons are all small compared to that of ethylene, for equivalent temperatures. Therefore, the storage of these C -C hydrocarbons in liquid form in the cavern (even though they are normally gaseous) does not result in excessive pressures on the walls of the cavern, or on the shaft leading thereto. The boiling points of these C C hydrocarbons are as follows, again in degrees Fahrenheit, ethylene also being included for purposes of comparison: ethylene, l55; propylene, -52.6; propane, 48.1; isobutane, 14.4; n-butane, 31.5; l-butene, 23; 2-butene, 33.8; Z-methyl-propene, 21.2. For r comparison with the vapor pressures given hereinabove for ethylene, the following vapor pressures are given for some C -C hydrocarbons: propylene at approximately -30 F., 1307 mm. of mercury; isobutane at -4 F., 646 mm. of mercury.

Preferably, the C -C hydrocarbon liquid 7 is kept refrigerated to a temperature substantially below 495 R, which temperature, as previously stated, is the critical temperature of ethylene. This may be done by means of a chiller 17, whose inlet is coupled through valve 18 to line 12 and whose outlet is connected through valve 19 to line 8. Thus, the liquid 7 may be pumped from the cavern 1 to chiller 17 by means of pump 14, by way of valves 13 and 18; the chilled liquid may be returned to the cavern by pump 10, through valves 19 and 9.

Subterranean caverns usually contain free water. As a result, the C C hydrocarbon liquid 7, initially at least, contains water, which could interfere with the refrigeration of the liquid 7 (by the formation of ice, for example). This problem may be eliminated by passing the refrigerant liquid 7 through a liquid-phase-dryer 25 (which removes the water from the hydrocarbon liquid), before the refrigerant enters the chiller 17.

As a result of the chilling or cooling (of the hydrocarbon liquid 7) previously described, this chilled high boiling hydrocarbon 7, which is in thermal relationship with the stored ethylene via the walls of receptacle 2, serves to refrigerate the ethylene and hold the latter below its critical temperature, so that it can be maintained in liquid phase. The ethylene must be kept below 495 F. by means of this refrigeration, but this is obviously not an inordinately low temperature.

Instead of the chiller 17, a conventional auto-refrigeration arrangement may be used for refrigerating the hydrocarbon liquid 7, a dryer preferably being used in this case, also, prior to the refrigeration unit.

In some instances, it might not be necessary to refrigerate the liquid 7 in order to maintain the ethylene below its critical temperature. In such instances, the chiller 17 could be dispensed with, and the receptacles 2 would be provided with vacuum jackets to reduce heat transfer to the stored ethylene; the ethylene would be chilled to a fairly low temperature before being placed for storage in receptacles 2.

Refer now to FIG. 2, which illustrates a modified arrangement according to the invention. In the figure, elements the same as those of FIG. 1 are denoted by the same reference numerals, while elements similar to those of FIG. 1 are denoted by the same reference numerals butbearing a prime designation. Positioned in subterranean cavern 1' are two storage receptacles 2 and 20 that are pressure-resistant, and which may be small storage tanks as illustrated, or may be pipes, as previously mentioned in connection with FIG. 1. Line 3 and pump 4, coupled to receptacle 2, enable liquefied ethylene to be fed into this receptacle, for storage as a liquid therein. Line 5 and pump 6, coupled to receptacle 2, enable withdrawal of the stored ethylene from this receptacle.

An inlet line 21 having a pump 22 therein leads from the surface to the inlet connection of receptacle 20. Through pump 22, line 21 is connected to a storage tank (not shown containing a C -C hydrocarbon (for example, propylene, butylene). Line 21 and pump 22 enable the liquefied C -C hydrocarbon to be fed into receptacle 20, for storage as a liquid therein.

The outlet connection of the receptacle 20 (indicated as being at the lower end of this tank) is connected through a subterranean pump 23 to an outlet line 24; this arrangement provides for withdrawal of the stored C -C hydrocarbon from receptacle 20.

Another C -C hydrocarbon (for example, butane) is stored as a liquid body 7 in the cavern interior space, surrounding the storage receptacles 2 and 20. Inlet line 8, valve 9, and pump 10 (not shown) enable the liquid 7 to be fed into the cavern interior, while outlet line 12and pump 14 enable the stored liquid 7 to be withdrawn from the cavern.

In the FIG. 2 embodiment, the liquid 7 could be chilled as described in connection with FIG. I, and used to refrigerate the ethylene stored in receptacle 2, thereby holding the latter below its critical temperature so that it can be maintained in liquid phase.

Summarizing, the embodiment of FIG. 2 represents an arrangement for storing three different hydrocarbons (one of which is ethylene) in liquid phase in a subterranean cavern.

The invention claimed is:

1. In the storage of a first normally gaseous material in a subterranean cavern the walls of which normally have a temperature above the critical temperature of said material, the method of storing said material in liquid phase which comprises placing said material as a liquid in the cavern interior space while isolating such liquid from the cavern walls, storing as a liquid in the cavern interior space, and in thermal relationship with said material, a second material whose critical temperature is above the normal temperature of the cavern walls, and refrigerating said second material to a temperature substantially below the critical temperature of said first material.

2. Method according to claim 1, wherein said first material is ethylene.

3. Method according to claim 1, wherein said second material is C -C hydrocarbon.

4. Arrangement for storing a first normally gaseous material in a subterranean cavern the walls of which normally have a temperature above the critical temperature of said material, comprising a pressure-resistant receptacle positioned in said cavern, means for feeding said material as a liquid into said receptacle, means for removing the material from said receptacle, and means for feeding as a liquid into the cavern interior space surrounding said receptacle, and in thermal contact therewith, a second material whose critical temperature is above the normal temperature of the cavern walls, said second material being chilled to a temperature substantially below the critical temperature of said first material.

5. Arrangement according to claim 4, wherei said first material is ethylene.

References Cited UNITED STATES PATENTS 2,440,930 5/1948 Camilli et al. 6250'2 2,947,147 8/1960 Johnson 6l0.5 3,350,888 11/1967 Shrier 610.5 3,163,013 12/1964 Webster 6245 FOREIGN PATENTS 914,193 12/ 1962 Great Britain.

LLOYD L. KING, Primary Examiner

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