US1719981A - Mining of sulphur - Google Patents

Description

July 9, 1929. W, JUDSON 1,719,981

MINING OF SULPHUR Filed April 2l, 1926 BLEED WELL Dummies HoT WATEn ZONE INVENTOR @wir - ATTORNEYS Patented Jully9,y 19.29.

UNITED STATES PATENT OFFICE.

WILBER JUDSON, F GULF, TEXAS, ASSIGNOR T0 TEXAS GULF SULPHUR 00mm,

-OF NEW YORK, N. Y., A CORPORATION 0F TEXAS.

MINING oF sunrnun.

Application led April-21,

l'lhis invention relatesto the mining of sul phur,"t and has for its object the provision of certain improvements in the mining of sulphur by underground fusion.

In the mining of sulphur by underground fusion, in accordance with the so-called lfrasch process, a hole or Well is drilled through the overlying strata to the bottom of the sulphur formation, Which hole is usually lo cased with an eight inch or ten inch pipe,

and then, through a system of vconcentric pipes properly arranged Within-this casing, superheated water is pumped down near 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, usuallythrough a strainer, and is raised to the surface of the ground, The well continues to operate and'produce' sulphur until the sulphur-bearing formation is locally exhausted or until the piping equipmcntis broken by subsidence of the ground due to the extraction of the sulphur content. The underground sulphur formation is usually found in the form of so-called domes, at depths varying around`500 to 1500 feet below the surface of the ground. These sulphur domes are usually immediately overlaid by a cap rock formation of porous limestone, which in turn Vis overlaid by strata of gumbo, quicksand, sand, gravel, and clay. Beneath the sulphur formation is usually found a layer of gypsum or anhydrite and layers or domes of salt.

The'sulphur formation itself usually con sists of an extremely porous or reticulated rock with the interstitial spaces filled With sulphur. The'sulphur formation often contains an amount of Water, formingv what might be considered an underground lake of brine or salt Water containing. for example, 4800 grains per gallon of solids in solution, mainly, sodium chloride, and in addition hydrogen sulfide and other soluble suliides. In the so-called Frasch system of mining sulphur by underground fusion, hot Water is the vehicle commonly used for conveying and tra nmitting heat to the sulphur. Inasmuch as sulphur melts at a temperature around 240 F., which is above the boiling poi-nt of Water at atmospheric pressure, the heating water is highly superheated, and is pumped into the sulphur deposit under a high pressure. The temperature to which the Water can be supergenerally by means of an air lift..

192e. serial no. 103,420.

heated, is, however, limited by the danger of overheating the sulphur, in which case it .becomes viscous. Accordingly, the Water is heated to atemperature that avoids over heating of the sulphur, but which is suiiciently above the melting point of the sulphur to bring about effective melting thereof as the y highly heated Water comes in contact with the underground sulphur. The sulphur thus melted flows to the lowest part ofthe deposit and surrounds the sulphur-withdrawing pipe, whence it is elevated, usually by means'of an air lift, to the surface of the ground. The water introduced may consequently be heated under pressure to about 320 F. and pumped into the sulphur deposit, this Water replacing the sulphur removed Iby the Well, together With Water already contained in the deposit, which may be Withdrawn by meansV of bleed- Wells, situated at suitable points in the de posit. The bleed-wells are usually located so 'as to withdraw'the cold Water or salt-Water from the lower part of the sulphur formation.

The sulphur dome may underlie a considerableY 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 underground Water or brine. v p

ln the mining of sulphur in an underground sulphln 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 another part of the deposit, and the deposit is progressively Worked 4in this Way until exhausted. The operation of a sulphur mine in this Way is an operation of large magnitude. The amount of highly heated Water that it is necessary to pump into a deposit in a single day may amount to several million gallons in commercial op.- erations. v

rlhe pumping of a largeamount of super- 1 heated Water into rthe deposit results in the gradual accumulation of a progresssively increasing amount of hot- Water in the deposit. rlhe specificy gravity of the original deposit Water is,`for example, about 1.08 and the 105 `temperature, for example, about 108 F.; vwhile the specific gravi-ty 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 11o tends to rise 'to the top of the dome,displac ing the cold water downward and while there is some diffusion and mixing, in a general Way the water at the top of the dome becomes cleaner with only a small amount of solids in solution, while the Water in the lower part of the deposit contains about its original content of dissolved solids until displaced vby the cleaner water from above.

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 sourceV several miles distant from the mine at a temperature around, for example, 68 F., and being heated to a temperature around 324o 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 the water from 68 F. to 324 F., 256 B. t. u.s are supplied by the combustionof fuel to each pound of water which is pumped into the disposit. Since sulphur`melts at around 240 F., the only effective heat supplied to the water is that between the maximum temperature of the water andthe melting point of sulphur, for -example, around 85 B. t. u.s of the total of 256 B. t. u.s supplied to the water.'

My present invention' broadly -involves main aining a predetermined pressure of the body of hot water accumulating in the underground sulphur deposit. In another aspect,

the invention contemplates a balan'tjng of the underground pressures in the sulphur deposit whereby the pressure of the hot water accumulating in the deposit is maintained approximately equivalent to the normal hydrostatic head or pressure of water at.this level. .This I accomplish b y a regulated withdrawal of cold water from the lower part of the deposit together with the with drawal of regulated amounts of hot water from the upperpart of thedeposit. The Withdrawal of this hot and cold water is so correlated with the introduction of superheated liquid into the deposit as to maintain a predetermined pressure of the body oi hot waterin the upper part of the deposit. Preferably, this predetermined pressure is substantially the normal hydrostatic head or' pressure of water at the level of the deposit where the hot water accumulates The hot water withdrawn from the deposit is reintroduced into the deposit, with or without purification and/or further heating, preferably at a well zone remote from the zone of withdrawal.

Throughout the specification and the appended claims cold water withdrawn from the deposit is to be understood as water or brine at a temperature well below the melting temperature or" sulphur, and hot water, withdrawn from the deposit is to be understood as water or brine at a temperature arrasar tice 'from about .200Q C. to about 30000.

The present invention is of particular advantage in the mining oic sulphurfrom deposits Which have been operated for a considerable time until there has accumulated a large amount of hot water in the upper portion of the dome or formation from which the sulphur has been exhausted: After long periods of operation, the temperature of this hot Water, accumulating in the upper por; of the dome, will be' considerably above the melting point of sulphur, which is about 240o F., and the temperature of this water may be as high as 300 F., or even higher. This hot water is containedunder considerable pressure, usually in excess of the normal hydrostatic pressure or head of water at that level. The pressure of this hot water may develop to a considerable magnitude unless means are taken to control it, or unless it is relieved by a natural or artificial outlet for the hot water.

The pat-h of the hoty water introduced into the sulphur deposit is towards the highest point, due to the difference in specific gravity between the fresh hot water and the cold brine with which the deposit is filled. lf the overlying stratum above the porous cap rock are impervious to water, the accumulation of hot waterv at the high point beeoines greater and greater, and is only subject to heat loss through radiation. The situation is somewhat different, however, if the material above the cap rock is a sand or gravel,

'or if there is any channel between the hot water pool and porous strata higher up in series above the cap rock. lf a channel is opened into any such upper layer the escape of hot water is easy.

i During the mining of sulphur by underground fusion, it is necessary to pump supertemperature above 212 F.) is released, a

portion of it will vaporize and an explosion comparable to a bo1ler explosion can result.

It is the practice in mining sulphur from deposits where there is an impervious capping to drill bleed-wells into the lower and colder portion of the deposit and use these bleedwells to relieve the pressure. The pressure in the deposit necessary to force the water or brine out through these bleedfsvells depends, of course, upon their size and number, but

there may also be a considerable pressure above the hydrostatic head on the hot water accumulation at the top ofthe deposit. This will be due to the greater speciiic gravity of the cold brine the deposit ywhich is bledl oil', and also to the velocity and friction heads which must be overcome in the bleed-wells.-

F or instance, it is very difficult to keep the i surface pressure above the top portion of the deposit down to-as low as 10 pounds per square inch from .wells having the same discharge elevation as the bleed-wells.

The hot water is introduced and the sulphur taken out through a series of drill holes or wells.A After a certain time of operation these wells fail, generally from `breaking of the equipment dueto ground movement and also from corrosion and other causes. The well then has to be abandoned and 1t 1s generally impossible to recover any considerable portion of the casing or equipment which was in the hole, and in many cases impossible to plug the hole at any, considerable depth. Even it the-stratum directly above the cap rock are impervious, such as for instance, a heavy clay, there are always a number of sand strata in the sediments overlying these sulphur domes. Itis quite-probably that broken drill hole casings extending into the cap rock.

may give a communication between thehot water zone in the cap rock and porous stratal in the overlying sediments.` If A there Iis a pressure at Athe surface, of a few pounds per square inch, this pressure can, of course,4 force` the' hot water from the heated water zone through such, channels of communication as broken pipes or cracks through any overlying strata into porous strata where the hot water can run olf laterally even to considerable distances and the heat units contained in it will be lost.

There seems to be no doubt that this con dition h as existed at various times in the mining of sulphur by underground fusion. In one case it is stated that for several years there was not sufficient pressure in the deyposit to'returnv any bleed water, all Aof the fresh Water, which was introduced in large quantities'into the deposit, flowing off laterally through porous sand beds.

I have discovered that thesel operating difliculties can be ameliorated by a balancing of the underground pressures in accordance with the principles of my present invention. Thus, the pressure at the bleed-wells maybe reduced so as-to maintain a pressure overthe hot water pool, at the top of the deposit, approximately equivalent to the normal hydrostatic pressure or head on the deposit. There is then little tendency for either a flowing out of the hot water into porous strata or a.l

-flowing in of cold. water from .such porous strata into the deposit: this latter condition being etherwise possible where the pressure on the hot water in the deposit'islower than the normal hydrostatic head. Where this condition of balanced pressure is approximately maintained, there will be little lossof heat, excepting through radiatiomfrom the hot water pool or reservoir` and this reservoir Willincrease in size or the heat from it can be reused as desired, both of which materially assist in the mining of sulphur by underground fusion.

The pumping of bleed wells for thepurpose of balancing or equaliz'ing pressures may be done by air lifts or more economi-cally by the use of standard pumping equipment, such as sucker rod pumps or centrifugal pumps. Generally, there is suiicient hydrogen sulfide dissolved in the original deposit water so that the .use ol a centrifugal pump at the outlet ol a bleed-well is impractical on account of the release of hydrogen snllide gas and the stopping of liquid flow through the pump from accumulation of such gas in the suction line. This can he readily overcome by the use of a deep-well centrifugal pump, placing the pump in the. hole Vseveral feet be'- low the surface and suiliciently deep so that the gas dissolved in the water will notbe released under the. pressure existing on the suction'side of the pump.

The balancing of underground pressure may also be of great advantage in the mining of sulphur deposits where there is a pervious l layer just above the cap rock. This periious layer may be sealed by a heavy mud pumped into the porous cap rock. vThis mud will work its way into the interstices of the pervious layer ot' sand and eventually form a seal that will be thoroughly effective in holding back the hot water below it, providing the presing, which illustrates in a conventional and graphic manner a section of a sulphur mine and apparatus embodying the invention and adapted for the practice of the improvements of the invention. ,The showing is largely conventional and various parts are relatively `magnified and the horizontal dimensions of the pipe and of various parts are relatively magnified for convenience of-llustration.

In'such a mine as represented in the accompanying drawing` the sulphur deposit isusually overlaid by a cap rock oflimestone. above which are strata of gumbo, quicksand, sand, gravel and clay. Below the sulphur deposit there are usually bodies of gypsum and salt. In the drawing` there is represented a region marked Het water zone from which it is assumed the sulphur` has been melted and removed, and which is assumed to be full of hot water accumulated from the mining operation.V The hot water will also extend upwardly into the porous cap rock.

It will'be apparent that as the sulphur is melted and withdrawn, the space originally occupied by the sulphur must be filled either bythe subsidence of the earth above or by the hot water p'umpedinto the mine. It will also be understood,'as above explained, that the hot water 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 tresh hot water tends to rise and accumulate in the Yupper levels of the dome.

ln the drawing, one of a series of active' sulphur wells is indicated at l, this well being made up as usual ol" a. series of concentric pipes with a. casing'. For convenience of illustration. the entire series of pipes is omitted and only two concentric pipes are shown, the inner pipe 3 heilig intended to illustrate graphicallyv the pipe through which the molten sulphur is pumped from the mine and which extends to the bottom of the deposit, and the outer easing 2 illustrating the 'outer pipe within which the hot water is pumped. down into the mine.

A bleed-well 5 is shown as located at a distance from the active sulphur wells and as leading from a lower level ol. the deposit i" rom which the colder water may be withdrawn in regulated amounts. A well 6 is shown as located so to withdraw water from the top of the dome. This well extends down into the porous cap rock and at its upper end is enlarged so as to accommodate a suitable pump, shown as a centrifugal pump 8 driven hy a motor 9 and having an extension-10 extending down in the'hot water zone and which may terminate in a 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 con struction :l'or keeping the wat-er under pressure so that no expansion or freeing of steam an take place near or at the surface of the ground. A heavy duty centrifugal pump such as a multi-stage centrifugal pump can be used. This pump should be located at a sulicient distance below the surface `of the ground lo receive the hot Wa ter before its pressure has been reduced sufficiently to per mit vaporization and cooling thereby. The pump may be located, for e.\an'iple,l from 60 to 1U() feet below the surface' of the ground or it may be located at an even lower level il' desired.

The water pumped from the well 6 passes lthrough pipe 13 to the well 1 where it is again forced down into the deposit. A- pump 17 is provided which may supplement the centrifugal pump 8, luitwith a suitable centrifugal pump, the pump 17 may be omit-ted, or it may he used only tor supplementing the centrifugal pump as occasion may arise Vfor doingr so.

. rl`he well 5 is illustrated as extending into the sulphur-.bearing strata and to a. point 'below thepoint at which the sulphur is withdrawn by well 1. A pump 12 is shown as lo- 'cated within the casing of well 5 driven by a motor 14. The pump 12 may either be a 70 centrifugal ora commonsucker rod pump. It the pump 12 is a centrifugal pump, it is located a suiiicient distance below the surface of the ground so that the dissolved gases willnot be released by reduced pressure on 7'5 the suction side and thus stop its use. If the pump 12 is of the sucker rod type, the rod will be longer than illustrated in the drawing so as to carry 'the pumping mechanism lower in. the well and nearer to the .water level of 30 the deposit.' v

An old well casing which has been broken a nd abandoned by subsidence ofthe ground is represented at 15 on the drawing. The porous cap rock is shown as distorted as well aS the layer of porous sand and gravel and the rupture of the `pipe is exaggerated so as to graphically illustrate the communication which might be attained by means of the broken well casing between the hot water zone and the porous gravel.

At 16, on the drawing, is illustrated a rupture of the porous cap rock and the thin layer v of impervious clay immediately above it so as to form an avenue of communication bee5 tween the hot water zone and a porous sand or gravel stratum.

An-illustration is not given in the drawing of a case where the pervious stratum of gravel directly `overlies the porous cap rock, and it is 10o considered that it will not be necessary to illustrate this point, nor will it be necessary to illustrate an extra well which might be used to force mud into such a pervious stratum in order to seal it against admission of hot water from the hot water zone. v In the pending applications of Robert H. Stewart, Serial No. 699,448 and Serial No. 95,542, there are described certain methods of withdrawing hot water from the hot Water zone as it accumulates in the mining ofsulphur by underground fusion. My present invention aims to maintain this zone of hot water in the mine and to prevent it from flowing away through porous underground strata.. The invention more specifically aims to maintain a pressure or head of hot water in the hot waterzone, approximately equiva- -lent to the hydrostatic head of water at this level.' 120 At the beginning of the mining operations of the dome, lthe sulphur wells are'conven- 'iently located near the top of the dome, near the location of well 6 in the drawing, and such wells are operated until the sulphur is exhausted at that location. Usually at the beginning such Wells are operated independently of any other wells such as for instance, bleed-wells. These wells are operated until the sulphur is exhausted at that location or 13 i 1ov until Ithe subsidence of the ground causes breaking of the piping equipment. As the deposit surrounding theA first wells becomes exhausted, additional' wells are drilled at a 4distance from the first wells. -These wells hot water zone to melt more sulphur, or to build up an accumulation of hot water so that it will extend low enough in the deposit to melt'more sulphur.

It is at this stage of the mining operation that the operation of the bleed-wells, the hot water with-drawing wells, 'and the hot water introducing wells may be so carried on that, with the accumulation of a large reservoir of hot water, such high pressures may build up as to cause this hot water to either rise to'the surface of the' groundior flow away underground. y

The present inventionfaims to prevent this objectionable condition by maintaining a predetermined pressure in the accumulated reservoir or underground pool of hot water. To this endpu1ups are preferably located in the bleed-wells to supplement and increase the withdrawal of water from these wells so that the pressure as indicated in pipe 13 will only be slightly above the normal hydrostatic pressure o the mine.

In elfect, I am dealing with three factors that influence the pressure of the accumulated reservoir or underground pool of hot water, viz: (1) the introduction into the deposit of super-heated liquid, (I2) the withdrawal from the depositA of relatively cold water, and (3) the withdrawal from the deposit ot hot water. In accordance with my present invention, these three factors are regulated and correlated so as to maintain 4'the desired 'predetermined pressure of the accumulated pool of hot water in the upper portion of the deposit In ot ier words, the th mmmg of Sulphur by underground fw introduction into the deposit of superheated water and the withdrawal of both hot and cold water from the deposit are' controlled and regulated so as to maintain the desired 4predetermined pressure of the accumulated pool of hot water.

The practice of the invention brings about a pronounced conservation of heat or hot water in the mining of, sulphur by underground fusion. Decreased fuel consumption,

as well as increased fuel eciency, required.

for supplying heat to the water introduced into -the sulphur deposit, are attained, and in general there results an important all around economy.

The present invention, by maintaining a. predetermined pressure of the under ound pool of hot water, precludes'the possibility of any great amount of this 'hot water escaping from-the mine through underground strata, and at the same time insures a more uniform distribution of the heated water in the sulphur-bearing strata, thus accomplishing two important economies. It is Apossible by the careful regulation of the Withdrawals of water from an old working, to carry on sulphur mining operations by means of fusion for long periods of time 4withoutthe addition of any fresh heated water, thus allowing the power house to operate entirely on new deposits and at the same time keeping the Old deposits in operation and producing sulphur. I

It may be found advantageous'in working a sulphur deposit according to the method of the present invention to increase slightly the temperature of the hotwater withdrawn from the mine or to clarify this water by sedimentation or chemical treatment before reintroduction 'intothe mine. Means for carrying out these operations have not been described or illustrated, but it is to be understood that such' operations may be embodied in the system where desirable or necessary.

Iclaimz- 1. The'improvement in the mining of sulphur by underground fusion from partially exhausted sulphur deposits, which comprises maintaining a predetermined pressure in the l deposit by withdrawing water from the cold i lower portion of the deposit and withdrawing hot wat-er from the upper portion of the deposit and reintroducing the withdrawn hot water into the deposit. e

2. The improvement in the mining of sulphur by underground fusion 'from partially exhausted sulphur deposits, which comprises maintaining a predetermined pressure in the deposit by pumping cold water from the lower portion of the deposit and withdrawingl hot water from the u per portion of the de'-A posit and reintroduemg the withdrawn hot water into the deposit ata well zone remote from the zone of withdrawal of the hot water from the deposit.

3. The method of conserving hot water in derground pressures by regulated Withdrawal of cold Water from .the lower portion of the deposit, regulated withdrawal of spuperheated water from the upper-portion of the deposit, maintaining the withdrawn supcrheated water under fessure, raising the' temperature of the wit drawn superheated water, and reintroducingthe resulting superlower portion of the deposit, regulated with-l drawal of superheated Water from the upper `portion of the deposit, and maintaining the withdrawn superheated water 'under pressure and reintroducing it into the deposit at alocalized well zone.

' .6. The im Y rovement in the miningof sulphur by un erground fusion from partially exhausted sulphur deposits, which comprises balancing the rate4 of introduction of hot water into the deposit lwith the rate of withdrawal of water from the 'deposit in such manner as to build up and maintain a pressure within the deposit adapted to prevent the seepage of substantial amounts of hot 'water from the system.

7. The improvement in the mining of sulphur by underround fusion from partially exhausted sulpliurdepo'sits which comprises carefully regulating the rateof introduction ofhot water' into'the'deposit and the rate of Withdrawal of cold water from the deposit so as to maintain a -working pressure in theexhaustedportion of the deposit at or near the normal hydrostatic pressure of the deposit.

8. The im rovement in themining of sulphur by un ergroun'd'fusion from partially exhausted sulphur deposits which comprises carefully regulating the rate of introduction of superheated liquid into the-deposit and the rate of Withdrawal of relatively cold liquid from the deposit so as to maintain a predetermined pressure of the hot liquid accumulating near the upper portion of the deposit.

ln testimony whereof I affix m signature.

WILBER UDSON.

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