EXPERIENCE IN STUDYING THE TEMPERATURE AND GAS COMPOSITION ON BURNING WASTE ROCK DUMPS OF THE STALIN MINE IN KUZBASS

P. A. LEONOV and B. A. SURNACHEV

Presented at the scientific seminar of the Department of Mining of Bedded Deposits, Mining of Ore Deposits, Mine Construction, Safety Engineering, and Mine Ventilation

Purpose, objects, and methodology of the investigations

In carrying out the work “Development of safe methods for operating burning spoil banks of the mines of the Kuzbassugol Combine” in 1954–1955, staff members of the Department of “Safety Engineering and Mine Ventilation” of the Tomsk Polytechnic Institute, together with a number of organizations in Kuzbass, made temperature measurements and studied a considerable number of air samples on burning waste rock dumps.

Up to the present time, the investigation of these dumps has been carried out almost exclusively from the surface. The temperature inside the dumps has been measured only once, during experimental work on extinguishing them¹.

The investigation in 1954–1955 of the temperature and gas composition on burning waste rock dumps had as its objectives: 1) study of the character of combustion of waste rock dumps (distribution of combustion centers on the surface and within the dump); 2) determination of the gas composition on the surface and within the dump.

Two adjoining waste rock dumps of the Stalin mine of the Prokopyevsk mine administration were chosen as the objects of observation (Fig. 1). Both dumps are more than 70 m high, each has a volume of more than 1 million m³, and they have been burning since 1945.

Depending on the degree of heating of the rock and a number of other factors (depth of measurement, accuracy, speed), various methods of temperature observation were used. The most convenient proved to be measuring the temperature on the surface of the dump and in boreholes up to 5 m deep with pyrometers, by means of which more than 80% of all measurements were made. The principal advantages of this method are simplicity and speed (one measurement takes 5–10 min). The accuracy of the readings for the pyrometers was 5° and 10°.

Attempts to use thermocouples for boreholes 10–12 m deep, at temperatures along their entire length on the order of 800–900°, proved unsuccessful.

To check the correctness of pyrometer readings, and for independent measurements of temperatures below 100°, inert (“lazy”) thermometers at 70° and 500° were used, with a measurement accuracy of 0.5–1.0°.

Temperature determination with thermometers was carried out selectively, chiefly to check the results of measurements by pyrometers. The reasons for the limited use of thermometers, despite their greater accuracy, were as follows: 1) the rate of measurement with thermometers is 5–10 times lower than with pyrometers; 2) on burning waste dumps the air is poisoned by combustion products and does not allow observers to remain for a long time at the measuring points; 3) the thermometers had a maximum measuring temperature of only 500°, whereas at many points of the dump the temperature of the rock reached 600–800°.

Temperature measurements in deep boreholes (10–12 m), owing to the reasons and circumstances indicated above, were made with pyroscopes. At the suggestion of Associate Professor P. G. Usov, pyroscopes made of pure chemical salts with an admixture of a binder—a solution of rosin in xylene or toluene—were used.

The table indicates the salts and the melting temperature of pyroscopes made from these salts.

The temperature difference between two adjacent pyroscopes was 90°, 103°, 129°, 120°, 50°. The accuracy of the measurements is equal to half of each temperature difference in the corresponding interval and on average is 50°. To measure temperature with pyroscopes, a special assembly was made. It consisted of six metal cups fastened every 2 m to two parallel iron wires 2 mm in diameter. The cups were made from pieces of gas pipe 70 mm high and with an internal diameter of 32 mm. After being loaded with pyroscopes, the assembly was lowered into the borehole and remained there from 5 to 12 hours. In further investigations it may be recommended to reduce this time to two hours. This method has serious shortcomings, the chief of which are: low accuracy, long holding time, and considerable labor intensity in the work of mounting the pyroscopes.

Laboratory studies and procedure for carrying out measurements

Field temperature observations on the rock dumps were preceded by substantial laboratory studies of inert (“lazy”) thermometers. For them, the time during which they assume the temperature of the medium was determined.

At each point, temperature measurements were, as a rule, made twice. Large intervals of time between two temperature determinations had to be abandoned for the following reasons: on the operating dump, some boreholes were filled with fresh rock; some of the boreholes drilled in strongly heated rocks became deformed—

was considered. Temperature observations were carried out on the surface of the dump, in boreholes, and in probes. Temperature measurements on the surface were made with pyrometers and thermometers. During measurement, the thermometer and thermocouple were sunk into the surface layer of the dump by 5–10 cm.

To measure the temperature inside the rock dumps, 25 boreholes were driven. A diagram of their arrangement is shown in Fig. 1. On the southern dump of the Stalin Mine, boreholes Nos. 1, 2, 3, 4, 5, 6, 7, 8, 9, and 19 were driven along line I—I (along the crest); boreholes Nos. 10, 11, 15, 16, 17, and 20—along line II—II, passing through the summits of dumps No. 1 (Northern) and No. 2 (Southern); boreholes Nos. 12, 13, 14—along line III—III, parallel to line II—II and located 50 m from it. On the northern dump, boreholes Nos. 21, 22, 26 were driven along line IV—IV (along the crest), and boreholes Nos. 23, 24, and 25—along line II—II. The depth of the boreholes ranged from 1 to 5 m. This was due to the fact that the driving of the boreholes was carried out to the line of incandescent rock; if the latter was not reached, the depth was limited to 5 m. The distance between adjacent boreholes on the transverse lines was taken as 17 m, which gave a difference in vertical elevations of 10 m (the inclination of the side and frontal slopes is usually 35–40°). On the longitudinal lines the boreholes were driven at a distance of 20–25 m from one another. Boreholes Nos. 19, 20, 25, and borehole No. 18, driven off the lines to characterize the northeastern slope of the southern dump, are located 17 m from the base of the dumps. The boreholes were driven by manually hammering a string of seamless steel pipes with outside diameters of 56, 65, and 108 mm into the rock of the dump. For convenience in work, the pipes were 1 m long and had screw threads at the ends. The end of the lower pipe was forged in the form of a spear; a plug was screwed onto the upper pipe, projecting 0.5 m above the surface of the dump. To take air samples from the boreholes, 5 holes 5 mm in diameter were drilled in a spiral near the lower casing pipe. During one shift (6–7 hours) two workers drove 12–15 m (depending on the diameter) of boreholes 3–5 m deep. To accelerate the work, temperature measurements at a depth of 1 m were made in probes. The probe consists of a pipe \(d = 35\) mm, 1.2 m long. One end of it is forged in the form of a spear; handles up to 30 cm long made of round iron \(d = 19\) mm are welded to the other. After the temperature measurements were completed, the probe was removed with the aid of the handles.

Temperature measurement in shallow boreholes was carried out with a 1350° pyrometer at every meter as the borehole advanced. After the borehole had been deepened by the next meter, its driving was stopped for a period of 30 min (established experimentally) so that the pipe could assume the temperature of the surrounding rocks. The productivity of the measurements was determined by the following factors: 1) the rate of driving the boreholes (from 0.05 to 0.2 m/min, depending on the depth of driving and the diameter of the borehole); 2) the holding time of the borehole for assuming the temperature of the surrounding medium (30 min); 3) the number of probes (the time for driving them in is not taken into account, since it does not exceed 1–2 min); 4) the time of a single temperature measurement in the borehole (not more than 10 min), including the transition from borehole to borehole; 5) the contamination of the atmosphere by combustion products. After a careful analysis of all factors, the following procedure was adopted for driving boreholes and measuring temperature: 4 boreholes were driven and deepened simultaneously, and 2 probes were used. While one borehole was being driven and deepened, another was being held, in a third the temperature was being measured, and one borehole was kept in reserve in case of delay.

during the sinking of any borehole, the temperature in the probes was measured simultaneously.

To investigate the temperature at a considerable depth below the surface of the waste-rock dump, deep driven boreholes A, B, and V, from 10 to 11.5 m deep, were sunk (Fig. 1). It should be noted that a depth of 10–12 m for driven boreholes in waste-rock dumps sunk by hand is the limiting one.

• boreholes
• outline of the emission crater

Fig. 1. Layout of boreholes on the waste-rock dumps of the Stalin Mine

Work on sinking boreholes and measuring temperature on the waste-rock dumps was carried out under difficult conditions. In some places the atmosphere of the waste-rock dump contained a considerable amount of CO and SO₂, which led to poisoning of the workers. Therefore the working shift was reduced to 6–7 hours.

Results of temperature measurements

Studies of the temperature on the surface of burning dumps, carried out along the ridge (line 1—1), gave the following results. The top of the dump has a low temperature—only 20°; 25 m lower, heating of the rock at the surface increases to 70°; still lower, to 180°, and 110 m from borehole No. 1 it reaches 240°. High tem-

the temperature at the surface continues to hold at boreholes Nos. 6 and 7 (240 and 140°), and then at borehole No. 8 drops sharply to 20°. In places where there are combustion foci on the surface, a temperature of 810° was measured. Of some interest is the temperature under the sleepers of the rail track on the dump. On the Southern waste-rock dump the ballast section of the track is made of fine waste-rock crushed stone 0.5–0.8 m thick. The temperature under the sleepers of the track from borehole No. 3 to No. 6 (over a distance of 75 m) varies within 40–70°. In the settlement crack between boreholes Nos. 15 and 16, heating of the rock to 150–250° was noted.

Temperature observations in the boreholes (180 measurements) make it possible to determine the nature of burning on the waste-rock dumps. Borehole No. 1, drilled at the crest of the Southern dump, shows, down to a depth of 3.5 m, a temperature of not more than 160°; only at a depth of 5 m did it rise to 510°. Borehole No. 2, 20 m from the first, has at a depth of 2 m a temperature of 410°. Borehole No. 11 at a depth of 3 m gave a temperature of 540°. On the southern side of the dump, near the crest, in borehole No. 15 at a depth of 3 m heating of the rock to 270° was recorded, and at 4 m—to 540°; at the surface near the noted boreholes the temperature proved to be as follows: 30°, 50°, 120°, 45°. These measurements give grounds for considering that the upper part of the dump (the “cap”), 40–50 m in diameter and about 5 m thick, is not burning, but is only heated to 200–300°. Boreholes Nos. 3, 4, 5, 6, 7, 10, 12, 13, 14, 18, 19, 20, located in the middle part of the dump and on the fresh fill 10 m above the base, show that intense burning is taking place in this place and that the rocks are strongly heated. The lower ends of the pipes in the listed boreholes are red-hot at depths of 1–4 m; the temperature, determined approximately from the colors of incandescence, is 700–800°. Boreholes Nos. 8 and 9, located in the tail part of the dump, show at a depth of 3 m temperatures of 370° and 310°, respectively, which indicates its cooling. Boreholes Nos. 18, 19, 20, made in the fresh fill, make it possible to assert that the fresh rocks immediately begin to burn and, as visual observations on the surface in this part of the dump show, burn very intensely and often with open flame. Borehole A, made at the crest of the Southern dump, owing to its deformation at a depth of 2 m, adds nothing new to the conclusions made above. The casing pipe of borehole B, 11.5 m deep, has dull-red incandescence (700°) beginning at 3 m and down to the lower end. The same temperature was also measured by means of pyroscopes. Analysis of the temperature data in the boreholes of the Southern dump gives grounds for saying that the upper boundary of the red-hot rocks in the dump in its middle part is at a depth of 1 m, in places coming out to the surface. In the region of the crest the indicated boundary is 4–5 meters below the surface; the same is observed in the tail part of the dump (Figs. 2 and 3).

Scale along boreholes 1:1000

— — — boundary of the red-incandescence zone (700°)

Fig. 2. Section of the Southern dump along line I—I

On the Northern dump, borehole No. 21, drilled at the summit, showed a temperature at the surface of 25–40°, at a depth of 1 m—240–320°, and at 4 m—160–220°. Borehole B, also located at the summit, showed a temperature of 398° at a depth of 3.5 m, and more than 500° at 5.5 m. On this basis it may be said that on the Northern dump the upper part (the “cap”) is not burning, but only heated. The higher temperature of the rock in the “cap” of this dump may be explained by the fact that from May to September no rock was deposited in this place, since work was being carried out to level the ridge part of the dump.

Borehole No. 22, 25 m from borehole No. 21, showed at a depth of 1 m a temperature of 150–220°, at 2 m—320°, and at 3 m—240°. Boreholes Nos. 23 and 24 (in the hollow) give a high temperature at the surface (90–100°), at a depth of 1 m—700–760°, 2 m—760–840°, and 3 m—700°. Borehole No. 25 is located on the northern slope in the middle part. Fresh rock had not been deposited on this slope for several months.

Scale by boreholes 1:1000

Fig. 3. Section of waste-rock dumps along line II—II

Studies of the composition of gases on the surface and inside waste-rock dumps

The study of air contamination by combustion products in the area of waste-rock dumps was carried out at the Stalin Mine in September 1954. Air samples were taken on the surface of the dumps and at distances of up to 300 m from their base in the direction of the prevailing winds, in calm and windy weather. Analysis was carried out for CO, CO₂, O₂, combustibles, SO₂, and H₂S; samples for analysis only for the first four determinations were taken by the wet method, while for analysis for all six determinations or only for the last two they were taken into rubber bags with the aid of a pump.

From most of the boreholes drilled on the waste-rock dumps, air samples were taken and analyzed for the content of CO₂, O₂, CO, combustibles, and, in some samples, for the sum of H₂S and SO₂. It was not possible to carry out a detailed analysis of the combustible gases, since the chemical laboratories of VGSCh that performed the analyses lacked the necessary apparatus.

All boreholes drilled on burning dumps discharged air rather than took it in. This circumstance considerably facilitated the operations of taking air samples, since only slight pumping of air from the boreholes was required.

Studies of the composition of the gas on the surface of waste-rock dumps gave the following results. At the top and on the slope of a dump, the air contains carbon monoxide within the range of 0.003–0.008%. At the base of the dump and at a distance from it, carbon monoxide is absent. Carbon dioxide of noticeable concentration (0.1–0.2%) is observed in the middle of the frontal slope and 25 m from the base. A mixture of hydrogen sulfide and sulfurous gas at the top of the dump was determined in amounts of 0.00570 and 0.01220%. These gases were detected in the air at the slopes and base of the dump, and also at points on the ground surface at a distance of 300 m (0.00417%).

Analyses of air samples taken from boreholes on the mine’s burning waste-rock dumps showed that the gases located inside the burning dumps consist of carbon dioxide, carbon monoxide, hydrocarbons (methane), sulfurous gas, hydrogen sulfide, oxygen, and nitrogen. The amount of carbon dioxide varies over wide limits, from 0.1 to 17%. In places of intense burning (boreholes Nos. 2, 3, 4, 11, 14, 21, 22), the carbon dioxide content was determined as 4–12%. Analysis of gases from deep boreholes A, B, V shows the amount of carbon dioxide to be 10–15.5%; only two samples from these boreholes gave 3.5 and 5% of the indicated gas.

The carbon monoxide content inside the waste-rock dumps is very small. It varies within the limits of 0–1%. The low concentration of CO gives grounds to assert that fairly intense burning is taking place inside the dump.

The specific gravity of combustible gases (mainly methane) in the gases inside burning dumps amounts to 0–20%. In boreholes along line 1—1 (Nos. 1, 2, 3, 4, 5), combustibles from 2 to 20% were detected. Gas samples from boreholes Nos. 2, 3, 4 had 5–20% combustibles. At the boundary of the upper part of the dump (“cap”) and its middle part, in boreholes Nos. 2, 11, and 15, analysis for combustibles shows their high content in air samples: No. 2—12 and 20%; No. 11—8, 11, and 15%; No. 15—4, 11, and 18%. Evidently, the indicated boreholes emit gases from the dry distillation of rocks composing the summit. In deep boreholes (A, B, V), the amount of combustibles in the gases was determined within the limits of 6.3–19%.

The presence of sulfurous gas and hydrogen sulfide was found in all samples from boreholes that were analyzed for the content of these gases. Inside the dump their concentration ranges from 0.00048 to 0.00966%.

The oxygen content in gases inside the dump varies within the limits of 3 to 20.9%.

Conclusions

1. Boreholes driven by the percussion method are the most suitable for studying the temperature and composition of gases at burning waste-rock dumps at depths down to 10–12 m. According to experimental data, the optimal depth of such boreholes is determined as 5–6 m.

2. Temperature measurements in boreholes up to 5 m deep on burning dumps can conveniently be made with pyrometers with an accuracy of up to 10°. The method for measuring temperature in deep boreholes still needs to be developed.

3. Visual investigation of the surface of burning dumps and measurement of temperature on them established that intense burning at the surface is observed on the frontal slope, where fresh rock enters, and around the summits within a radius of 20–30 m, in a belt 5–10 m wide. The summit rocks do not burn on the surface, while the rocks of the tail part and side slopes have burned out.

1. Investigation of the temperature in the boreholes showed that the upper part of the dump (the crest), with a thickness of up to 6 m, is not burning, but is heated. In the middle part, inside the dump, intensive combustion is taking place. All boreholes drilled in this zone at various depths show a high rock temperature \((600—800^\circ)\). The lower part of the side slopes and the tail part of the dump have burned out and are cooling. The frontal slope should be especially noted: on it, except for the crest, intensive combustion of the rocks is taking place.

2. Temperature observations in boreholes, including deep ones, make it possible to assume that inside the burning dump there is a mass of incandescent rocks. Its upper boundary is defined by the shallow boreholes and is located, from the surface, in the middle part of the dump at a depth of 1 m. The lower boundary remains to be determined in further investigations.

3. Analyses of gas samples taken through boreholes on the dumps showed that the following gases are present inside them: oxygen, nitrogen, carbon dioxide, carbon monoxide, sulfurous gas, hydrogen sulfide, and combustible gases (hydrocarbons). The carbon monoxide content was established within the range of 0—1%, carbon dioxide from 0.1 to 17%, and in deep boreholes 10—15.5%. Hydrocarbons (combustibles) are present in the gases in amounts of 0—20%, more often 5—20%, and in deep boreholes 15—19%. The content of sulfurous gas and hydrogen sulfide (in total) was found within the range of 0.00048—0.00966%. The amount of oxygen in the gases inside the dumps was established as 3.0—20.9%, and in deep boreholes as 8.5—11.3%.

4. The products of rock combustion in the dump are located at its surface and in the nearest zone. At the crest and on the slopes, a constant presence of carbon monoxide in the air is observed. Analyses detected sulfurous gas and hydrogen sulfide not only on the burning dump, but also in places located 200—300 m from its base.

1. A. A. Skachinsky, S. Z. Makarov, Investigations on the Use of Antipyrogens in Combating Mine Fires, Publishing House of the Academy of Sciences of the USSR, 1947. ↩