US3724898A

US3724898A - Solution mining of salt and storage of industrial fluids

Info

Publication number: US3724898A
Application number: US00128768A
Authority: US
Inventors: C Jacoby
Original assignee: International Salt Co
Current assignee: Akzo Nobel Salt Inc
Priority date: 1971-03-29
Filing date: 1971-03-29
Publication date: 1973-04-03
Anticipated expiration: 1990-04-03
Also published as: FR2132135B1; NL7200734A; GB1396381A; DE2215144A1; DE2215144B2; FR2132135A1; IT959490B

Abstract

A system for solution mining a salt deposit and simultaneously storing an industrial fluid, while conserving system heat input and minimizing earth surface polluting impurity extractions from an underground salt deposit. The invention provides an improved method for conserving system input heat, and utilizing it to improve a solution mining operation in an underground salt mineral deposit; whereby to produce a purified brine at reduced cost. The majority of the mineral deposit impurities are left underground, thereby reducing the recovery plant earth surface polluting effluent problem. Incidentally, the system provides an improved underground storage system for industrial fluid commodities such as liquid chlorine; carbon tetrachloride; carbon bisulfide, and the like.

Description

United States Patent [191 [111 3,724,898 Jacoby [451 Apr. 3, 1973 [54] SOLUTION MINING OF SALT AND STORAGE OF INDUSTRIAL FLUIDS H07 BR/Nf l, PRODUCT Primary Examiner-Ernest R. Purser Attorney-Bean & Bean [57] ABSTRACT A system for solution mining a salt deposit and simultaneously storing an industrial fluid, while conserving system heat input and minimizing earth surface polluting impurity extractions from an underground salt deposit. The invention provides an improved method for conserving system input heat, and utilizing it to improve a solution mining operation in an underground salt mineral deposit; whereby to produce a purified brine at reduced cost. The majority of the mineral deposit impurities are left underground, thereby reducing the recovery plant earth surface polluting effluent problem. lncidentally, the system provides an improved underground storage system for industrial fluid commodities such as liquid chlorine; carbon tetrachloride; carbon bisulfide, and the like.

12 Claims, 1 Drawing Figure PATENTED APR 3 I975 l2 LL/0 U/Q CHL OQ/NE HOT BR/A/f PRODUCT AIR may

SALT E :IZLji HOT WATER CENTRAL/ZEPS I I I I i glm fm lm fim ROCK LA YER CHARLES H. JACOBY I A TTOANE Y5 SOLUTION MINING OF SALT AND STORAGE OF INDUSTRIAL FLUIDS BACKGROUND AND OBJECTS OF THE INVENTION This invention relates to the mining of soluble minerals and concomitant storage of fluid commodities; and more particularly to the mining of sodium chloride or other such soluble mineral salt deposits including impurities; the absolute and relative solubilities of which vary with temperature and/or pressure changes. More specifically, the invention relates to an improved process for simultaneously beneficiating and mining salt from a rock salt deposit, as discussed for example in commonly assigned US. Pat. Nos. 2,555,340; 2,876,182 and 3,348,883.

As explained in the aforesaid patents, sources of salt such as mined rock salt, usually consists of sodium chloride to the extent of about 90 to 99 percent; the balance being impurities such as sulphates, silicates, carbonates, etc.; calcium sulphate being the principal impurity. According to typical prior refining procedures, such impure salts have been refined" in some instances by treatment of saline solutions obtained directly from wells, or from water-solutions produced by dissolving previously mined impure rock salt substances in water or other suitable solvents, by the use of vacuum-evaporator systems.

Uniquely encountered in the art of solution-mining underground rock salt deposits is the fact that rock salt in situ is an exceptionally high rate heat conductive medium compared to the other geological formations environmental thereto. In consequence, a typical rock salt solution mining operation in a horizontally disposed rock salt deposit employing heated water as the mining solvent is inherently beset with huge and expensive operational heat input losses, due to the rapid dissipation of heat from the solvent solution through the relatively broad surface areas of the floor and ceiling of the solution cavity. Such heat losses typically account for enormous operating heat supply requirements, such as may render an operation marginally profitable or unprofitable; and it is specifically an ob ject of the present invention to provide an improved operative system and technique for such purposes; whereby to realize substantial product improvement and plant completion investment and operating economies.

Another object is to provide an improved system as aforesaid whereby to better conserve the heat involved in a solution mining operation, while usefully and simultaneously storing a liquid or gas commodity.

Other objects and advantages of the present invention will be apparent from the following specification and the accompanying drawing wherein:

THE DRAWING The FIGURE illustrates diagrammatically by way of a vertical sectional view, a geological formation including a typical salt bed in process of being mined in accordance with the present invention.

As discussed in detail by way of example herein, the invention is embodied in a system for simultaneously mining a purified sodium chloride salt product from an underground deposit of relatively impure rock salt or the like, while simultaneously storing a reserve supply of liquid chlorine. Further, by way of example the invention is illustrated as being employed in conjunction with a solution mining system wherein a reserve supply of liquid chlorine is disposed to cover the bottom of the solution cavity while a heat insulating pneumatic pad of air (or nitrogen, Freon, krypton, xenon, neon, argon, benzine or other light hydrocarbons, or the like) is maintained on top of the solvent circulating within the cavity, so as to heat-insulate the solvent from the roof of the cavity. However, it is to be understood that the invention may be usefully applied to the mining of other forms of soluble mineral deposits, such as sodium borate, potash, and the like; and to the storage of liquid commodities other than chlorine, such as carbon tetrachloride, carbon bisulphide, or the like.

In any case, inasmuch as the mining solvent preferably comprises water or dilute brine which is heated at the earth surface plant, the'pads of air and chlorine or the like function as efficient heat insulating devices operating to conserve the heat of the solvent supply. The inverse solubility characteristic of sodium chloride vs. calcium sulphate (a common impurity) is thus utilized to improved advantage to minimize dissolution of impurities into the product brine at the situs of the solution mining action. The cavity is maintained under sufficient pressure so as to keep the chlorine or other commodity in liquid state; whereby the cavity also provides an ideal reserve chlorine supply storage facility.

The solution mining cavity is illustrated by way of example in the drawing herewith at 10, and is interconnected with the well head and surface plant facility as illustrated diagrammatically at 12 by means of a single well bore 14. The well bore is lined by means of an outer casing 16 inside of which progressively reduced diameter tubings 18-20-22 are hung. The outer casing 16 is preferably anchored to the bore hole wall as by means of concrete or the like as indicated at 24.

The central tube 22 extends at its nether end beyond the lower level of the casing 20 and is fitted at its upper end with a supply conduit and control valve arrangement as indicated at 26, whereby liquid chlorine or the like (as explained hereinabove) may be pumped into the cavity under pressure so as to provide the liquid chlorine pad across the bottom of the solution cavity. The casing 18 terminates at its lower end at a level somewhat higher than the lower end of the casing 20, and thus the annular space between the

casings

18 and 20 provides the passageway for inlet of solvent (such as hot water or heated dilute brine). The solvent is thereby circulated throughout the solution cavity to provide a concentrated brine solution which then exits from the solution cavity upwardly through the annular space provided between the tubing 22 and the casing 20.

Supply of solvent to the system is provided for at the surface plant facility and is controlled by an inlet control valve unit as illustrated at 28; while the brine product exits from the casing 20 through means of an outlet conduit and control valve arrangement as illustrated at 30. The outer casing 16 terminates at its lower end at an elevation somewhat higher than the bottom level of the casing 18, and thus the annular space between the casings l6 and 18 provides a passageway for supply of air (or other gaseous material) whereby to maintain the upper heat insulating pad within the cavity above the body of solvent as it circulates throughout the cavity in contact with the peripheral walls thereof. Control of the supply and level of air or other gas in the cavity is maintained by means of an inlet conduit and control valve as shown at 32.

Thus, it will be appreciated that whereas the chlorine or similar commodity is maintainable in the cavity under pressure pending its recovery and use, it functions in the meantime as a heat insulating blanket between the floor of the cavity and the body of solvent and brine as it circulates around the cavity walls; while the pneumatic pad heat-insulates the brine from the roof of the cavity. The height of rock salt wall or face exposed to the solvent is readily controlled by adjustments of the pneumatic and chlorine levels; and thus it will be understood that the mining operation may be readily controlled through simple adjustments of the valve devices at the surface plant facility. In this manner the rate of flow of materials through the system, as well as the temperatures and pressures thereon, may be effectively monitored to maintain the optimum processing conditions for full utilization of the inverse solubility phenomenon as explained hereinabove. Hence, a consistently improved quality purified salt product is produced, while underground heat losses are reduced with substantial consequent operating economies. Whereas the invention has been illustrated and described in detail hereinabove in conjunction with a single well bore system, it is to be understood that the invention is equally applicable to a multiple well bore system wherein one or more well bores operate as ,injection wells, and one or more well bores operate as production wells.

I claim:

1. A salt mine comprising,

a horizontally extended cavity in a salt deposit,

a blanket of a low heat conductivity liquid commodity-in-storage substantially covering the floor of the cavity,

a body of salt brine floating on top of the liquid commodity,

a blanket of fluid of low heat conductivity material floating on top of the brine and against the roof of the cavity, whereby the salt brine contacts the cavity walls substantially only at the peripheral side wall portions thereof,

means for continuously removing brine from the cavity,

and means-for continuously adding salt solvent to the cavity at a temperature substantially higher than that of the salt deposit surrounding said cavity.

2. A salt mine according to claim 1 wherein the fluid of low conductivity is air in gaseous form, and wherein means are provided for independently and selectively supplying the liquid commodity and air in the cavity and maintaining them under controlled pressures in the cavity.

3. A salt mine according to claim 2 wherein the liquid commodity ischlorine and the means for supplying chlorine to the cavity isa central pipe and concentric with it are annular passageways for flowing hot water to the cavity and brine away from the cavity.

4. A salt mine according to claim 3 wherein the cavity is maintained under sufficient pressure to keep the chlorine in liquid form and prevent appreciable boiling away thereof.

5. A method of mining salt from the sides of a cavity in a salt deposit without removing salt from the top and bottom thereof which comprises,

adding to a cavity in a salt deposit in any suitable order chlorine and water or brine, and a fluid of low conductivity which is lighter than the water or brine and chlorine whereby to fill the cavity with three layers of fluids, comprising liquid chlorine at the bottom; brine at an intermediate level, and the lightweight fluid in the upper portion of the cavity; adding water or unsaturated brine to the cavity at a temperature substantially higher than that of the salt deposit surrounding said cavity and removing a brine of higher concentration from the cavity, whereby the cavity is enlarged at the sides thereof from which the salt has been solution mined.

6. A method according to claim 5 wherein the cavity is substantially horizontal, the fluid of low conductivity is air in gaseous form, pressure is maintained on the cavity to keep the chlorine in liquid form, water is added to the brine in the cavity, brine is removed from the cavity and the air and chlorine are maintained in their respective positions in the cavity.

7. A method according to claim 6 wherein water is added to the cavity and brine is removed therefrom through concentrically disposed contiguous passageways, whereby heat losses to the walls surrounding such passageways are minimized.

8. A method according to claim 7 wherein the brine removal passageway is inside the hot water addition passageway thereby preventing cooling of the brine and avoiding crystallizing out of salt, and wherein the hot water addition passageway is insulated from the surrounding wall materials by a layer of confined air.

9. The method of solution mining salt while simultaneously effecting storage of at least one fluid, which comprises the steps of:

a. forming a solution mining cavity in an underground salt deposit;

b. forming a first heat insulating layer covering and in contact with the floor area of said cavity and a second heat insulating layer covering and in contact with the roof area of said cavity and continuously introducing a liquid solvent for said salt into said cavity while simultaneously continuously withdrawing said solvent with the salt dissolved therein from said cavity, said first heat insulating layer consisting of a storage liquid which is a nonsolvent for the salt and is more dense than said solvent, said second heat insulating layer consisting of a gas, and said solvent being introduced from a surface facility at a temperature substantially higher than that of said cavity;

. maintaining flow communication from a point within said first layer to a surface facility whereby to allow storage introduction and use withdrawal of said storage liquid at will and independently of the solution mining of said salt;

. maintaining flow communication from a point within said second layer and a surface facility whereby to allow introduction and withdrawal of troduced and maintained at a pressure sufficient to maintain said storage liquid in liquid form while said second layer is maintained in gaseous form.

11. The method of solution mining and storage as defined in claim 10 wherein said storage liquid is chlorine.

12. The method of solution mining and storage as defined in claim 11 wherein said gas constituting the second layer is air.

Claims

2. A salt mine according to claim 1 wherein the fluid of low conductivity is air in gaseous form, and wherein means are provided for independently and selectively supplying the liquid commodity and air in the cavity and maintaining them under controlled pressures in the cavity.
3. A salt mine according to claim 2 wherein the liquid commodity is chlorine and the means for supplying chlorine to the cavity is a central pipe and concentric with it are annular passageways for flowing hot water to the cavity and brine away from the cavity.
4. A salt mine according to claim 3 wherein the cavity is maintained under sufficient pressure to keep the chlorine in liquid form and prevent appreciable boiling away thereof.
5. A method of mining salt from the sides of a cavity in a salt deposit without removing salt from the top and bottom thereof which comprises, adding to a cavity in a salt deposit in any suitable order chlorine and water or brine, and a fluid of low conductivity which is lighter than the water or brine and chlorine whereby to fill the cavity with three layers of fluids, comprising liquid chlorine at the bottom; brine at an intermediate level, and the lightweight fluid in the upper portion of the cavity; adding water or unsaturated brine to the cavity at a temperature substantially higher than that of the salt deposit surrounding said cavity and removing a brine of higher concentration from the cavity, whereby the cavity is enlarged at the sides thereof from which the salt has been solution mined.
6. A method according to claim 5 wherein the cavity is subsTantially horizontal, the fluid of low conductivity is air in gaseous form, pressure is maintained on the cavity to keep the chlorine in liquid form, water is added to the brine in the cavity, brine is removed from the cavity and the air and chlorine are maintained in their respective positions in the cavity.
7. A method according to claim 6 wherein water is added to the cavity and brine is removed therefrom through concentrically disposed contiguous passageways, whereby heat losses to the walls surrounding such passageways are minimized.
8. A method according to claim 7 wherein the brine removal passageway is inside the hot water addition passageway thereby preventing cooling of the brine and avoiding crystallizing out of salt, and wherein the hot water addition passageway is insulated from the surrounding wall materials by a layer of confined air.
9. The method of solution mining salt while simultaneously effecting storage of at least one fluid, which comprises the steps of: a. forming a solution mining cavity in an underground salt deposit; b. forming a first heat insulating layer covering and in contact with the floor area of said cavity and a second heat insulating layer covering and in contact with the roof area of said cavity and continuously introducing a liquid solvent for said salt into said cavity while simultaneously continuously withdrawing said solvent with the salt dissolved therein from said cavity, said first heat insulating layer consisting of a storage liquid which is a nonsolvent for the salt and is more dense than said solvent, said second heat insulating layer consisting of a gas, and said solvent being introduced from a surface facility at a temperature substantially higher than that of said cavity; c. maintaining flow communication from a point within said first layer to a surface facility whereby to allow storage introduction and use withdrawal of said storage liquid at will and independently of the solution mining of said salt; d. maintaining flow communication from a point within said second layer and a surface facility whereby to allow introduction and withdrawal of said gas at will and independently of the solution mining of said salt; and e. maintaining the introduction of said solvent at a point above said first layer and the withdrawal of solvent with dissolved salt at a point between said first and second layers whereby to leave the first and second layers undisturbed by the solution mining operation.
10. The method of solution mining and storage as defined in claim 9 wherein said storage liquid is a gas at atmospheric pressure and wherein said solvent is introduced and maintained at a pressure sufficient to maintain said storage liquid in liquid form while said second layer is maintained in gaseous form.
11. The method of solution mining and storage as defined in claim 10 wherein said storage liquid is chlorine.
12. The method of solution mining and storage as defined in claim 11 wherein said gas constituting the second layer is air.