US2137619A - Process and apparatus for mining sulphur - Google Patents

Description

C. O. LEE' PROCESS AND APPARATUS FOR MINING SULPHUR Filed April 10, 1936 Nov. 22, 1938.

lNvl-:NTOR BY mi# Za/wm f ATT RNEYS Patented Nov. 22, 1938 PRocEss AND APPARATUS Foa MINING sULPHUa Clarence 0. Lee, Port Sulphur, La., assignor, by

mesne assignments, to Freeport Sulphur Company, a corporation of Delaware Application April 10, 1936, Serial No. 73,606

7 Claims.

This invention relates to a process of mining sulphur by the practice of so-called underground fusion, and has for its object generally an improved procedure which increases the amount of sulphur produced per heat unit expended and facilitates the mining operation.

In the mining of sulphur by underground fusion, which was originally proposed by H. Frasch, a hole or well is drilled through the overlying strata to the bottom of the sulphur deposit. 'I'his hole is preferably provided with a suitable casing, for example, a 10-inch pipe, in which a system of concentric pipes is disposed. The mlning operation is customarily carried out by passing a mining uid, such as superheated water under pressure, down one of the annular spaces, and thence out into the sulphur-bearing formation. Such fluid is at a temperature such that sulphur is melted and ows in.consequence by gravity downwardly to the bottom of the Well. From thence the molten sulphur is forced upward through another of the annular spaces a certain distance by the hydrostatic pressure on the formation; then it is picked up in the well piping by a stream of compressed air, and raised to a point where it is discharged above the surface of the ground.

When mining sulphur by underground fusion from deposits which occur in rock strata over salt domes of the Gulf Coast type, certain difliculties are encountered due to the inherent nature of the geological formation encountered, which result in gradually increasing costs of operation as the mining progresses. A specific object of the present invention is to provide an improved procedure which is convenient in the salt dome region and effects a decrease in the cost of the mining operation.

The sulphur of deposits over salt domes is found both disseminated and in narrow veins in dense limestone. The formation itself, however, is often highly porous so that the mining uid employed frequently passes away from the vicinity of the well through a system of connected cavities, without having given up its heat to the dense masses of limestone containing the sulphur. What is termed theA "thermal efficiency of the process", i. e., the ratio of sulphur produced to heat units expended, is, in such cases, relatively low. In addition to this, the nature of the cavities and channels may be such that even though sulphur is melted, instead of running to the bottom of the well it may run off through a channel, heated by the ow of hot mining fluid,

no heat could be given up to the sulphur.

and not be recoverable in the particular area affected by the well under operation.

Another apparent cause for low thermal .eiliciency associated with this method of mining is the fact that the hot mining fluid, because of its high temperature, has a lower density than the natural waters which saturate the formation. Convection currents produced in the formation rapidly carry the hot mining water to the top of the formation, Where little, if any, sulphur is located, and the heat is dissipated without useful results.

Various methods have been proposed from time to time for overcoming these dimculties. It has been proposed, for example, that the hot water which has found its way to the top of the formation be withdrawn and returned to the producing wells, after first being reheated to a point sufficiently high to melt sulphur. A principal difficulty in carrying out this proposal is that the mine waters are highly corrosive and also contain salts which sometimes form deposits in heating apparatus used to raise the temperature. A further dimculty is that these returned waters are still too low in density compared with the colder natural formation waters and tend to return directly to the point of withdrawal without having given up'their heat content. Another specific object accordingly is to provide a method and means for utilizing the waste heat contained in the hot water from the upper portions of the sulphur formation while eliminating the diiculties with corrosiion and scale formation heretofore encountered.

The use of heated fluids of higher density than water has been suggested for the purpose of preventing convection currents and consequent dissipation of heat. Hot concentrated common salt solutions have been suggested to this end but no cheap and practical means have been proposed for carrying out the suggestions. One such previous suggestion is impractical to practice in a region where salt domes prevail, because of the fact that a dense layer of anhydrite invariably separates the sulphur formation from the body of salt and effectively prevents contact between the hot salt solution and the sulphur. No provision is made which would penetrate the anhydrite layer and bring the hot salt solution into effective contact with the sulphur; consequently Another object of this invention accordingly is to provide means for effecting such contact, when an anhydrite layer is present, in a convenient and inexpensive manner.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others, and the apparatus embodying features of construction, combinations of elements and arrangement of parts which are adapted to effect such steps, all as exemplified in the following detailed disclosure, and the scope of the invention will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention reference should be had to the following detailed description taken in connection with the accompanying drawing, in which:

The figure is a fragmentary cross sectional view showing a usual sulphur-bearing formation of the Gulf Coast type having a well drilled ltherein and provided with apparatus for mining sulphur in accordance with the invention.

Referring to the drawing, geological fcrmation, common in the Gulf Coast region, is shown formed over a salt dome, indicated generally at S, which has overlying rock strata. These are here indicated as comprising a lowermost stratum known as anhydrite, shown at A. Over this is a sulphur-bearing formation which is here indicated as consisting of a stratum of limestone impregnated with sulphur and denoted B. Above this is a stratum of sulphur-barren limestone generally referred to as "cap rock" and shown at C. Above the rock strata are layers of sand, clay and soil, here generally denoted by D. To mine sulphur in accordance with the original Frasch process, a well is drilled into a sulphur-bearing stratum B, and a casing inserted in a fashion such as to admit of introducing a mining or fusion nuid whereby sulphur is melted and lifted to the surface as above described. 'I'he anhydrite stratum accordins to such practice is not drilled and, therefore, remains imperforate.

In the practice of the present invention, the drilling is continued through the entire rock strata, including the anhydrite layer into the salt, as shown in Figs. l and 2. A main well casing Il is then inserted to such a depth that its lower end depends somewhat below the anhydrite stratum, penetrating slightly into the top of the salt dome. The anhydrite is preferably counterbored inorder to provide an annular clearance space Il about the lower end of the casing Il, which permits the easy passage of molten sulphur therethrough from the rock strata down to the salt. The casing I 0 is preferably provided with perforations I2 in that zone which traverses the sulphur-bearing stratum. Concentrically disposed within the pipe or casing I3, but not so as to close its lower end, is a second pipe I3 arranged to have limited vertical movement in pipe III, the lower end preferably being made to depend below the lower end of the casing pipe and has oriiices I4 for admitting a heated medium to the mine, as pointed out below. Within pipe I3 is another pipe I 5, concentrically disposed and arranged in a manner also permitting limited vertical movement and having the lower end depending below the lower end of the pipe I3. Pipe I5, thus arranged, serves as the means for lifting molten sulphur, which may collect as a pool I6 in the mine, and lift the same to the surface. This lifting action is in part effected by the hydrostatic pressure that obtains in the formation and in part by air, which may be heated, admitted through a stili smaller pipe I'I that is concentrically disposed within the pipe I l, and controlled, for example, by a valve Il. Pipe I1 has its lower end terminating short of the lower end of the pipe IB.

At the upper end of the pipe I3 there is provided a connection 2| leading from a source that supplies a suitable heated medium, which, when admitted to the mine, provides a fluid at a temperature sumciently high to melt sulphur (the melting point of sulphur in mining practice being generally taken as in the neighborhood of 235 FJ. Such heated medium can be comparatively salt-free and may be either superheated water under pressure, or steam, or both. The medium supplied through pipe I3, of course, initially dissolves salt. The piping il has a connection 22 adapted to deliver molten sulphur to a' suitable point on the surface of the ground, such as a receiving vessel or storage vat.

When a well has been constructed as above described, the mining operation may be then carried out as follows: 'I'he heated medium admitted to the mine, by way of pipe I3, does not immediately melt sulphur but first passes out through the perforations Il into the region below the anhydrite layer and dissolves salt. A cavity in the salt immediately below the end of the casing is thus excavated. I'he further admission of fluid into the mine forces the brine thus provided to pass up into casing I l or through clearance space I I, or both, and out into the sulphur formation: thereby causing sulphur in the stratum B to melt. The molten sulphur, because of its higher density, flows downwardly under the influence of gravity against the stream of entering fluid and forms the pool Il indicated at the bottom of the cavity in the salt. By causing the lower end of the pipe Ii to depend into the pool, the sulphur may be pumped to the surface in the manner above indicated.

The position of pipe I l may be so adjusted as to determine the size of the pool I3 which may be' substantially any size desired. By keeping the pool relatively large, it may be made to form a protective covering for the bottom of the salt cavity so as to prevent further downward leaching of the salt by the fluid admitted, any further leaching which takes place being compelled to take place in a lateral direction. On the other hand, by lowering pipe Il from time to time, the cavity may be deepened. In this way, the shape of the cavity can be controlled to substantially any desirable or convenient extent.

While the mining fluid dispersed in the mine through pipe III, may at the first instant be merely heated water having relatively little salt content and having less density than the natural mine waters contained in the sulphur formation, it is seen that the leaching out of a cavity in the salt bodyprovides a fluid having a substantial salt content whereby the average density is increased and the tendency for the fusion iluid to get away through channels in the rock strata is decreased. Accordingly, the thermal efilciency of the mining operation, as herein practiced, increases with the progress of the mining operation.

The medium that is first supplied through pipe I3 is preferably heated water since a quantity of brine for mining purposes is thus quickly formed. When this is accomplished, the medium thereafter admitted may be merely steam, or steam and water, introduced in such quantity as to supply tlie heat to the brine, needed to maintain it at a desired temperature level for mining sulphur. In this manner, subterranean heating of the mining iiuid in the mine is practiced. The resulting fusion iluid avoids the temperature drop incident to pumping hot water into the mine. -Consequently only a relatively small quantity oi heat is expended; the heat supplied in this manner being small as compared with that expended in the usual practice of supplying the fusion fluid at a temperature suiiiciently high to be-at the desired temperature in the ground when the drop in temperature, incident to the conveying of the fusion uid from its place of heating into the ground, is allowed for.

Continued mining operations by the Frasch process are known to cause an increase in or building up of the underground formation pressure, which requires in consequence the use of continuously increased supply pressures in order to introduce the necessary water or mining iluid. To correct or oiset this condition, bleed wells are usually drilled into the sulphur formation to permit mold water to flow away. As the formation warms up, the bleed wells yield water of higher and higher temperature. It has been proposed to conserve this heat by providing equipment for reheating the withdrawn bleedwater on the surfare to a desired temperature and reintroducing it into the mine. These mine waters, however, being highly corrosive, react on the equipment, especially when heated, with the result that the cost of upkeep in furnishing the additional heat necessary to raise the water above the melting point of sulphur becomes excessive.

In the present invention, such eii'ects are avoided by providing one or more bleed wells of a new type, hereinafter referred to as recirculation bleed wells. Such wells are operatively associated with a sulphur producing well and are situated to take bleedwater from a point suitably adjacent to the salt cavity of the well and at a depth just above the sulphur-bearing stratum, thus assuring that the water which is no longer in contact with sulphur to be melted shall be withdrawn. In the figure, the bleed well is shown as comprising a pipe 23 which is preferably of smaller diameter than pipe l0 and is disposed sufficiently close to be over an outer edge of the cavity in the'salt. A pump 2l is connected to the upper end of pipe 23, and the water, which is discharged from the pump, is re-introduced into the cavity by way of a pipe 25, such pipe being made to depend into the salt cavity or sump. The water thus re-introduced is also heated in the mine by means of the steam introduced through pipe I 3. In this way, only a relatively small amount of water need be removed from the mine, an amount which approximately equals the condensate from the steam used when steam only is being supplied to heat the circulated water. It will also be seen that the use of a recirculation bleed well provides an additional means for controlling the size of the cavity in the 1. The process of4 mining sulphur occurring in rock strata over salt domes of the Gulf Coast type by underground fusion in which the rock strata includes a stratum of anhydrite overlying the salt dome, which process comprises the steps of drilling a well entirely through the rock strata into the salt, then counterboring the lowermost strata to provide a passage for molten sulphur through the anhydrite stratum.' casing the well through the rock strata into the salt in a manner which provides for ingress of mining fluid and egress of molten sulphur, initiating the mining operation by the admission of heated mining uid comparatively salt free, forming a brine therewith by leaching out a cavity in the salt, and thereafter continuing the mining operation with the brine formed by causing it to pass into the rock formation whereby sulphur is melted and then collected in the cavity provided.

2. The process of mining sulphur occurring in rock strata over salt domes of the Gulf Coast type by underground fusion in which the rock strata includes a stratum of anhydrite overlying the salt dome, which process comprises the steps of drilling a well entirely through the rock strata into the salt, then counterboring the lowermost strata to provide a passage for molten sulphur through the anhydrite stratum, casing the well through the rock strata into the salt in a manner which provides for ingress of mining iluid and egress of molten sulphur, initiating the mining operation by the admission of heated mining fluid comparatively salt free, forming a brine therewith by leaching out a cavity in the salt, thereafter subterraneously imparting heat to the brine to maintain a temperature above the melting point of sulphur by the direct admission of a heating medium to the mine, continuing the mining operation with the brine so prepared. and collecting molten sulphur from the rock formation in the cavity provided preparatory to being lifted to the surface oi' the ground.

3. 'Ihe process of mining sulphur occurring in rock strata over salt domes of the Gulf Coast type by underground fusion in which the rock strata includes a stratum of anhydride overlying the salt dome, which process comprises the steps of drilling a well entirely through the rock strata into the salt, then counterboring the lowermost strata to provide a passage for molten sulphur through the anhydrite statum, casing the well` through the rock strata into the salt in a manner which provides for ingress of mining fluid and egress of molten sulphur, initiating the mining operation by the admission of heated mining iluid comparatively salt free, forming a brine therewith by leaching out a cavity in the salt, continuing the mining operation with the brine formed by causing it to pass into the rock formation, and during such continued operation offsetting locally the increase in formation pressures.

4. The process of mining sulphur occurring in rock strata over salt domes oi' the Gulf Coast type by underground fusion in which the rock strata includes a stratum of anhydrite overlying the salt dome, which process comprises the steps of drilling a well entirely through the rock strata into the salt, then counterboring the lowermost strata to provide a passage for molten sulphur through the anhydrite stratum, casing the well through the rock strata into the salt in a manner which provides for ingress of mining fluid and egress of molten sulphur, initiating the mining operation by the admission of heated mining fluid comparatively salt free, forming a brine therewith by leaching out a cavity in the salt, continuing the mining operation with the brine formed by causing it to pass into the rock formation, and during such continued operation offsetting locally the increase in formation pressures by withdrawing bleedwater at one or more points relatively close to the leached-out cavity.

5. The process of`mining .sulphur occurring in rock strata over salt domes of the Gulf Coast type by underground fusion in which the rock strata includes a stratum of anhydrite overlying the salt dome, which process comprises the steps of drilling a well entirely through the rock strata into the salt, then counterboring the lowermost strata to provide a passage for molten sulphur through the anhydrite stratum, casing the well through the rock strata into the salt in a manner which provides for ingress of mining i'iuid and egressof molten sulphur, initiating the mining operation by the admission of heated mining fluid comparatively salt free, forming a brine therewith by leaching out a cavity in the salt, continuing the mining operation with the brine formedgby causing it to pass into the rock formation, and during such continued operation offsetting locally the increase in formation pressures by withdrawing and re-introducing bleedwater at points in the rock strata in the area normally over the region of the cavity leached out in the salt.

6. In apparatus fox mining sulphur occurring in rock strata over salt domes of the Gulf Coast type which includes a stratum of anhydrite overlying the salt dome, the combination comprising a pipe serving as a well casing having an open lower end and of a length adapted to pass entirely through the rock strata of the sulphur formation into the salt and provided with one or more openings through its lower wall portion at a level adapted to supply mining duid entering its lower end into the rock strata, said lower end. being formed to cooperate with a counterbored portion of the well in the lowermost rock' strata and provide a passage for molten sulphur from the rock strata into said region below the rock strata, an inner pipe concentric with said casing pipe of a length depending slightly below the lower end of said casing pipe and provided with anq opening adapted to communicate with said region below the rock strata, a sulphur withdrawal pipe within said inner pipe adapted to withdraw sulphur that accumulates in said region, means in said sulphur withdrawal pipe for introducing a sulphur uiting agent, and means for supplying a heated medium to said inner pipe.

'1. In apparatus for mining sulphur as set forth vin claim 6, the combination being characterized by the employment of an inner pipe having limited axial movement in the casing pipe and pro# vided with a perforated lower wall for directing the heated medium laterally, the lower end having the sulphur withdrawal pipe extending therebelow, whereby molten sulphur that has collected therebelow may be withdrawn without interference from the heating medium supplied.

CLARENCE O. LEE.

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