US1764538A - Mining of sulphur - Google Patents

Description

June 17, 1930. R. H. STEWART MINING OF SULPHUR Filed sept. 22, 192e ,l/m INVENToR ATTORNEYS Patented Julie 17, 1930 'i e UNITEDSTATES ROBERT HOLDEN STEWART, or

To TEXAS GULF TExAs l MINING o'E PATENT foFFlcs vANcoUvER, BRITISH COLUMBIA, CANADA, AssIsNoR SULFUR COMPANY, E NEW YoRx, N. Y., AcoRroRATIoN 0E,

SULEIIUR i Application led September 22,l 1926.' Serial No. 137,098.

This invention Ilates to improvements in the mining of sulphur, and includes an improved method for the mining of sulphur by underground fusion,as well as an improved system or apparatus therefor.

" In the mining of sulphur by underground fusion, in accordance with lthe so-called Frasch process, a hole or well is drilled through the overlying strata to the bottom of the sulphur formation, which hole is usually cased with an eight-inch or ten-inch pipe, andthen, through a system of concentric pipes appropriately,V arranged within this casing, superheated water is pumped down to the foot of the hole or well where it is discharged into the sulphur formation and melts the sulphur. The melted and liquid sulphur enters one of the concentric pipes, usually through a strainer, and is raised to the surface of the ground, generally by meansof an air lift. The well continuesvto operate andproduce sulphur until the sulphur-bearing formation is locally exhausted, or until the plping equipment is broken` by subsidence of the ground- .due tdthe extraction ofthe sulphur content. The sulphur formation is usually found in the form of so-.called domes, at depths varying from around 500 to 1500 feet below the surface of the ground. These sulphur domes are usually overlaid by a porous' cap rock formaby gumbo, quicksand and clay. Beneath the sulphur formation is usually found a layer of gypsum or anhydrite, and layers or domes of salt. i

The sulphur formation itself usuallyfcontains the sulphur distributed in a porous lrock formation which also contains a large amount of water forming what may be considered an underground lake of brine or salt watercontaining, for example, about 4800 grainsper gallon of solids in solution, mainly sodlum` chloride, and in addition hydrogen sulfide and other soluble sulides.

In the so-called Frasch system of mining sulphur by lunderground fusion, hot water is the Vehicle commonly used for conveying and transmitting heat to the sulphur. Inasmuch as sulphur melts at a temperature around 240 F. which is above the boiling point of tion of limestone which in turn is overlaid water at atmosphericpressure, the heating water is highly superheated and is pumped into the mine under a high pressure. The l temperature to which the water can' be superheated is however limited by the danger of overheating the sulphur in which case it becomesviscous. Accordingly, the water is heatedV to a temperature which avoids overheating of the sulphur but which is suilivciently above the melting point of the sulphur 6o to bring about effective melting thereof-as the highly heated water comes in contact with the underground sulphur. The water may' thus be heated under pressure to about 320 F. and pumped into the sulphur deposit, this `waterv replacing the sulphur removed by the well .together with water already contained in the` deposit, which may be withdrawn by means of bleed-wells, situated at suitable points in the deposit. f The bleed-wells are lo usually located so as to withdrawA the cold brinev orsallt water from the lower part of the sulphur'formation. s

The sulphur dome may underlie a considerable surface area of ground. The dome may,`for example, be as much as a mile in diameter; and the underground lake forming a part of the deposit or adjacent thereto may contain billions of gallons of undergroundl water or brine. I

In the mining-of such a sulphur deposit, one or several wells are usually drilled and operated at one part of the deposit until the sulphur bearing formation is exhausted locally and then other Wells are drilled 'at 85 another par-t ofthe deposit, and the deposit` is progressively `worked in this way until exhausted. The operation of a sulphur mine in this way is an operation of largemagnitude. The amount of highlyheatedv water 9o which it is necessary to pump into the deposit in a single day may amount to several million gallons in commercial operations.

The pumping of `a large amount of superheated water into the deposit results` in the 195 gradual accumulation of a progressively increased amount of hot Water in the deposit.'- The specific gravity of the original deposit ywater is for example about 1.08-, and the` temperature for example about 1O8YF. while 100 the specific gravity of the clean hot water pumped into the mine is in the neighborhood of 0.91. Owing to this difference in specific gravity, the hot water rises or tends to rise 5 tor the top of the dome, displacing the cold deposit water downward, and, whlle there is some diffusion and mixing, in a general way the-water at the to of the dome becomes cleaner and hotter w1th only a small amount of solids in solution, while the water in the lower part of the depdsit contains its original content of dissolved solidsjuntil displaced by the Cleaner water from above. A

The continued supply of a large amount of highly heated water to the mine forms one of the major expenses of the operation, this water being commonly obtained from a source several miles distant from the mine at a temperature around, for example, 68 F.,

and being heated to a temperature around 324 F. before it is pumped into the mine. Of the total heat supplied to the water, only a small part is available for melting the sulphur. Thus, in 'heating water from 68 F.

' 25 to 324 F., 256 B. t. us are supplied by the combustion of fuel to each pound of watery which is pumped into the deposit. sulphur melts at around 240 F. the only `effective heat supplied to the water is that between the maximum temperature of the Water and the melting point of sulphur, Vfor example, around 85 B. t. us of the total of 256 B. t. us supplied to the water.

The lpresent invention provides an improved method and system of mining sulphur whereby important economy of operation is obtained, and whereby a greatly increased fuel eiciency, and decreased fuel consumption can be edected.

The present invention is of particular advantage in the mining of sulphur from deposits which have' been operated for considerable time until there has accumulated a large amount of hot water in the upper portion of the dom@ or formation from which the sulphur has been exhausted. After long periods 0f operation, the temperature of this hot water, accumulating in the upper portion of the dome, will be considerably above the melting point of sulphur, which is about 240 F. and the temperature of this water may be as high as 300 F. or even higher. This hot water is contained under considerable pres-` Sure, which pressure is usually in excess of the hydrostatic pressure.

The present invention is a modification of the invention of my Patent No. 1,615,051 and includes the invention of said application, together with `modifications thereof which result in a modified and improved method of ,mining of the sulphur.

According to the present invention, I make further use of the accumulated hot water in the dome and take advantage -of the heat 65 whichA it contains by withdrawing hot water Since from the top or upper part of the dome or deposit where it accumulates in the exhausted area and in the orous cap rock, maintaining this water umlr pressure to prevent vaporization and cooling, and again forcing it down into the deposit through a well or wells where active mining operations are going on; and, in conjunction with vsuch withdrawal and reutilization of the accumulated hot. water, I operate other wellsv with fresh hot water so that the accumulated supply of hot water in the deposit is replenished from the hotwater so introduced at the same time that the accumulated supplyis being utilized for further mining operations.

The continued and prolonged withdrawal and reutilization of accumulated hot water in the manner described in my companion application, will, unless additional heat is supplied, gradually lower or tend to lower, the temperature of the hot underground lake in the deposit, and particularly ofthe hottest part of this accumulated supply which tends to accumulate in the upper levels of the deposit. By operating wells in whichl fresh hot water is supplied in conjunction with other wells in which hot recirculated mine water is used, the loss in heat due to the recirculation is more or less compensated for by the additional heat supplied by the fresh hot water, which as hereinbefore pointed out, is heated` to a temperature considerably in excess of the melting point of the sulphur. This fresh water, because of its high temperature, will rise or tend to rise tol the top of the deposit and to the upper levels of the accumulated underground supply of hot water, thereby replenishing the supply from which the recirculated hot` water is withdrawn for further use in minin operations.

The wells which are operated with fresh hot water can be operated in accordance with the present day mining operations, according to the so-called Frasch method, hereinbefore described and will result'in an increase in the amount of hot4 superheated water under pressure contained in the deposit. The wells operating upon recirculated hot water from the deposit can be operated in accordance with the process more fully described in my Patent No. 1,615,051. The combined operations of wells in accordance with both procedures, and with withdrawal of cool or cold water through so-called bleed, wells from a lower level of the deposit, tends to maintain constant or to slowly and gradually increase the supply of underground hot water and tends to maintain or to slightly increase or decrease the -temperature of t such body, while tending further to insure a supply of hot water at a suiciently high temperature in the upper part of the deposit from which the water is withdrawn and recirculated to a remote well zone for further euse in the mining operation.

soy

The vhot"-re'ecirculat-e'dpirater which is suffif ciently above'the melting point of sulphur to enable it to be used 'without-,further heating,

is maintained under presslraild with little 1f any loss in temperature -while it is being .withdrawn and reintroducdthroughthe active sulphur mining well or wells. The hot water so introduced in the localized well zone s will tend to rise agaimafter serving its purpose of melting sulphur, to unite withthe large body of hot water in the top of the deposit. The gradual withdrawal of hot'water' in this way, with return of the hot water withdrawn to the deposit,I will result in atendency to reduce the temperature of the hot water in the deposit, but after a large under-l ground lake of hot waterhas been `accumulated by prolonged miningoperation with fresh hot water, this tendency will not be felt until after operations have continued ,for a considerable time; and, bythe introduction j of additional fresh `hot water-at other operating wells, this tendency may be overcome either completely or suilicientlyto,insurecontinuation of the recirculation vwithout reduction of temperature below that which will be' sufficient in `the vwithdrawn and recirculated water. l p

Inasmuch as the continued introductionof fresh hot water increases the amount of water f in the deposit, a corresponding amount'of cool or cold water can advantageously be `withdrawn froma lower level-of the deposit .through one or more bleed-wells, thus maintaining substantially constant the amountof underground water and tending to increase the accumulated 'supply of 'hpt water. Thls increase in supply will be much less than would be the case if fresh hot water were used in all of the active wells, but it is nevertheless suilicient to avoid undue coollng of the accumulated water supply by admixture of and at a pressure greaterthan atmospheric,l is

withdrawn and kept under'pressure while it is being withdrawn, by means ofa pump, a

steam injectoror other suitable means, and

this water so withdrawn under pressure and with its temperature maintained by the pressure and by preventing vaporizatlon, 1s again introduced into the deposit for further use 1n the mining operation.

One advantageous method of maintalnmg this water under pressure, and of preventing it from being cooled below 240 F. throughi'eduction of its pressure, is to introduce. a cen# trifugal pumpinto the line through.whichI i the water is withdrawn, and at a sufficiently low level' to receive the water whilestill undersuilicient pressure to prevent its partial vaporization. i

sired, be puriied, but ordinarilyv it can be used again without purification. So also, lthe water withdrawn may be subjected to further heating, as byinjectio of `steam, but if the water isat a suliiciently high temperatureit can be used againwithout further heating. v

The invention will be further described in connectionwith the accompanying drawing, l

which illustrates in a conventional and graph- D .ic manner a section of a mine and of apparal us' embodying the inventionl and adapted or the tion. Y

' The showingl is largely conventional, and

various parts are magniied, and the horizontal dimensions of the pipe and .f various parts are magnified for convenience of illus- -trat-ion.

In .such a mine as yrepresented in the ac-i companying drawing, the sulphur'deposit is limestone, above which is gumbo`,quicksand and clay. Below thesulphur deposit there are usuallyl bodies of gypsum and salt.l

practice of thepro'cessof the invenv usually overlaid by a cap rock formation of i mil the drawing, .there is represented a region marked"Hot water zone from which it is assumed the sulphur has been melted, and which is assumed to be full of hot water accumulated from the mining operation. The

ioo

hot water will also extend upwardly into the;

porous caprock. It will be apparent that as -the sulphur ismelted and withdrawn,I the space origlnally occupied by the sulphur must-be filled either bythe subsidence ofthe earth above or by the hot water pumped into the mine. It will also be understood, as above explained, that thehotwater which is pumped into the mine where the active mining operation is going on, is lighter than the cold salt water originally contained in the mine, .so

that the fresh hot water tends to rise and to accumulate in the upper levels ofthe dome.

.In the drawing, one of aseries of activesulphurwells is lindicated at 1,"this well. being made up as usual of a series of' concentric,I

pipes within a casing tube.` For convenience of illustrat'on, the'entire series of pipes is omitted an .only two concentric pipes are shown, the inner pipe 3 being intended to illustrate graphically the pipe through which the molten sulphur is pumpedl from the mine and which extends to the bottom of thedeposit, and the outer casing 2 illustrating the' outer pipe within which the hotv water f pumped` down into the mine. Y

4Another. activev orfa series ofactive sul- 'phur wells is indicated at 20, this Well being similar in construction to the well 1 except for the supply of resh'hotv water instead of re- The hot water thus Ywithdrawn may, if de- 7-0* I' circulated `hot water. The fresh hot water is supplied through the pipe 21 from a power plant suitably located and the molten suli pliur is drawn off through the pipe. 22 in the as to accommodate a suitablevpuinp, shown as a centrifugal pump 8 driven by a motor 9 and having anV extension 10 extending down into the hot water zone and which may terminate ina perforated end 11 through which the hot water is admitted into the pipe 10 and thence into the centrifugal pump 8. The well pump 8 may be of any suitable construction for keeping the water under pressure so that no expansion or freeingof steamcan take place' near'or at the surfaceof-the 5 srround. A heavy duty centrifugal pump such as a Layne multi-stage centrifugal pum can be used. This pump s'hou-ld be located at a sufficient distance below the surface of the ground to receive the water before its pressure has been reduced sufficiently to permit vaporization and cooling thereby. The pump maybe located for example from 60 to 100 Afeet below the surface of the ground, or it C `i`nay be located at even a lower level if desired or necessary.

The water pumpedfrom the ground passes through the pipe 13 to the well 1 where it is again forced down into the ground. A pump 17 is provided which may supplement the centrifugal pump 8, but with a suitable centrifugal pump, the pump 17 may be omitted,

or may be used only for supplementing the centrifugal pump as occasion may arise for doing so. A

By withdrawing the hot water from the mine in this way and maintaining it under pressure `and at itsLoriginal temperature, or with only a minimum drop in temperature, the water can be used over again in a different location of the mine for melting vfurther amounts of sulphur. This reutilization of the hot mine .water results in large economies -as compared with ordinary mining operations where all of the hot water utilized in the vmining operation is fresh water which requires heating, e. g. from around 68 F. to around 324 F. By reutilizing the accumulated supply of hot water in accordance with the present invention, the amount of fresh hot water employed can be greatly reduced and the consumption of heat required for heating fresh `waterfor the entire mining operation can be greatly reduced.

v fAt the beginning of the mining operations of the dome, the sulphur wells are usually located` near the top of the dome near the vlocation of the well 6 and suchlwells are operated until the sulphur is exhausted at that 'location for until subsidence of the ground causes breaking of the piping equipment. As the ground surrounding the first wells becomes exhausted, additional wells are drilled at a distance from the first wells.

' These wells may be at a location such'as illustrated by the well 1 in the drawing and the well 6 may be an exhausted well which is used merely for the purpose of'withdrawing the hot water from the upper part of the deposit. rThe upper part' of the deposit forms a heat reservoir where the hottest water tends to accumulatein a portion of the deposit from which the sulphur has been exhausted and in the porous caprock where it serves no useful purpose in melting sulphur and where it causes great heat loss and low heat eiliciency.`

Such operations-represent the usualxoperations. Instead of continuing these operations in the usual way, they are continued,

according to the present invention, 0n a P reduced scale as compared to the entireniining operation, and such reduced operation isI combined with the recirculation of water from the deposit in such a way that it is employed instead of fresh hot water for part of the mining operation.

If the hot water Withdrawn from the de- Y posit had its pressure reduced to atmospheric, the reduction in pressure would cause reduction in temperature by vaporization and the water escaping atthe surface of the ground would have a temperature not exceeding 2122 F. which would be too glow for further use without reheating in the melting of sulphur.' i I I According tothe present invention, such reduction in temperature due to vaporization is avoided by maintaining the `hot water under a suicient pressure t'o prevent cooling by-vaporization so ,that it can be maintained at substantially its original temperature and` reintroduced into an operating well or wells while still under pressure and at approxi-A mately its origina1.temperature. If, for example, the temperature of the accumulated body of hot water in the deposit is in the neighborhood of 275 to 300.F., this water is Withdrawn under sufficient pressure to prevent vaporization and pooling and 1s I (ept under pressure and forced again down into the deposit at the operating lwell or wells at a temperature approximately the same as that of withdrawal from therunderground body of hot water or with onlya'small temperature drop due by vaporization during the recirculation.

Along with th operation of such wells with recirculated ot water from the deposit,

other Wells arey operated with fresh superto heat lossesother than heated Water introduced in accordance with present day practice, and these operations wlth fresh superheated hot water supplement those with recirculated hot water in themanner hereinbefore described to overcome undue coohng of the recirculated water and to replenish the supply of accumulated hot water at the top of the deposit from which the recirculated Water is withdrawn.

W'ith the combined operations of the present invention there will be underground circulation of both the fresh lot water and of the recirculated hot water. The hot Water,

whether fresh or recirculated, will be intro-V duced at Wells where sulphur is being melted and where part of the heat'of the -hot water is utilized for such melting. The water after such use tends to iow to the upper part of the deposit to admix with the accumulated supply there. The recirculated water will be somewhat lower in temperature than'when withdrawn, while the fresh hot waterfrom the' wells where it is used will ordinarily be at a somewhat higher temperature thanthe water withdrawn. The composite result willbe to maintain the temperature of the water withdrawn so that it does not vary greatly and does not fall below an active .melting temperature even after. long continued use of accumulated hot water by recirculating and f reutilizing it in the manner described.

The present invention includes as an appa'- ratus or system, an `arrangement of wells, one or more of which is connected to and operated with al lsupplyof fresh hot water, one or' more of which is connected with the hot accumulatedbody of water in the dome and one or more of which are .used as the active operating v wells, with outside connections such that the Water can be withdrawn-and directly reintroduced, without substantial loss of temperature, and maintained con? tinuously under pressure.

yWhere' the mining operation is carried out with a hotbrinevof high speciiic gravlty,

which tends to settle to the bottom of the sulphur deposit-,athis accumulated, heavy brine can, after it has reached asuicient volume and temperature, be withdrawn and reintroduced in a similar manner to that above described in connection with the use .of hot water. The operation will lbe somewhat reversed, however, in that the heavy brine will be introduced at a higher level than that from which it is withdrawn and the accumulated body of hot brine will be in the lower parts of the sulphur mine or deposit rather thanin theupper portion thereo I claim: i L t l. The improvement 1n the mining of sul.-

phur by underground fusion from partially exhausted sulphur deposits, which comprises withdrawing from the upper'part of a de- 'posithot water at a temperature higher than the melting point of sulphur, maintainingthe' temperature `ofthe water above the melting pomt of sulphur, .reintroducing the' withdrawn hot Water intov the deposit at a localized well zone remote from the point of'withdrawal and coincidentally therewith introducing freshhot water into and removing sulphur from the deposit at another localized Well zone. 'l

2. The improvement-in the mining of sulphur, by underground fusion from partially,

exhausted sulphur deposits,`which comprises withdrawing from the deposit hot brine at a temperature considerably above the melting point of sulphur, maintaining'the withdrawn brine under pressure to preventjvaporizationand cooling below the melting point of' sul- D- phur, reintroducing the withdrawn hot brine into the deposit at a well zone remote from the point of withdrawal and coincidentally therewith introducing. fresh Vhot brine` into and removing sulphurfrom the deposit at another localized well zone.

3. In the mining of sulphur by underground fusion from partially exhausted sul-` phur deposits, onel or more -Wells arrangedto permit the withdrawal of hot water 'at a temperature abovethe melting point of sulphur from near the top of the deposit, one o r more wells 1arranged- .for conducting superheated Water into "the sulphur containing formation,

means for pumping hot water from the said withdrawing'wells and maintaining it under pressure from the top of the deposit to the` d sur-face of the ground, means. for reintroduc-y ing, still under pressure, the withdrawnl hot water into the sulphur mining well or wells as 1 the heating medium therefor and one or 'more and designed to `Withdraw hot water`at a tem.

vperature above the melting point of sulphur from the upper part of the deposit through the last mentioned wells, means for maintaining thewithdrawn hot water under' pressure and returningit to said first mentioned wells, means for lwithdrawing cold water at a temperature below the melting point of sulphur from a lower level of the deposit and one or more wells provided'with a supply of fresh superheated water arranged to introduce the same into the deposit and to remove molten sulphur therefrom.

In testimony whereof I ax my signature.

' Y ROBERTl HOLDEN STEWART.

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