STUDY OF BROWN COALS FROM THE ITATSKOYE DEPOSIT

K. K. STRAMKOVSKAYA, A. V. KRAVTSOV

The Itatskoye brown-coal deposit is located in the western part of the Kansk-Achinsk basin, on the territory of the Itatsky and Tisulsky districts of Kemerovo Oblast.

The fuel reserves in this deposit are enormous. The average seam thickness is 55 m, and within the Barandat trough it reaches 80 and even 100 m. Natural conditions are favorable for mining the seams by the most economical open-pit method.

However, the technological properties of these coals in the various sectors of the extensive deposit have not yet been sufficiently studied.

In the present work, coal samples delivered to the laboratory by the Itatskaya geological exploration party of the Kuzbassuglegeologiya trust were investigated. The sampling locations are given in Table 1. Only samples 4273, 4274, 2482a, 4282a, and 4284a were received in hermetic packaging; all the others arrived at the laboratory in wooden boxes.

Proximate and ultimate analyses of the coal were carried out according to the corresponding GOST standards [2], are presented in Table 2, and show that the coals of the Itatskoye deposit of the Barandat trough are low-ash coals \((A—3.6—7.2\%)\). The ash composition of almost all coal samples (Table 3) is distinguished by a high CaO content—from 39 to 49%. The amount of \(\mathrm{SiO}_2\) varies from 10 to 30%, while in the upper, more ashy parts of the coal seam the amount of silica in the ash reaches 46%. The content of iron oxides is low—7–13%, and only in two samples does it reach 26.5–28.678%. The ash melting temperature is 1180–1400°C (see Table 4).

The working moisture of the coal samples delivered in hermetic packaging reached 37%.

The amounts of carbon and hydrogen in samples taken from different sectors of the deposit varied within the following limits: carbon from 70.50 to 73.63; hydrogen from 4.73 to 5.12. The carbon and hydrogen content changed little with the depth of occurrence of the seam within a single borehole. Thus, in borehole 2206, sample 2281a, characterizing the sampling interval from 103.3 to 125.4 m, and sample 2284a—the sampling interval from 149.9 to 174 m—have small deviations in carbon and hydrogen content. However, the carbon content is somewhat

Table 1

Sampling locations

increases with the depth of occurrence of the seam at different points of the deposit. For example, samples 2837 and 2838, whose sampling intervals were respectively 228.7–235.7 m and 240–318 m, contain carbon on the combustible mass of 72.76 and 73.63%, while sample 4625—the sampling interval 24–59 m—has \(C^{\mathrm{g}} = 71.20\%\).

A characteristic feature of this coal is its low sulfur and nitrogen content. Only in two samples was sulfur 0.42–0.57%, and in all the others no more than 0.2%. The nitrogen content is 0.7–0.9%.

In connection with the constancy of the elemental composition, the calorific value of the coals changed little: \(Q^{\mathrm{b}} = 6400\text{–}6750\) kcal/kg.

Table 2

Analytical characterization of Itatsk borehole coal

These coals give a high yield of volatile matter—from 43.5 to 46.3%—and are completely non-caking.

The data of Table 5 show that all the coal samples investigated give a high yield of humic acids, amounting to 35–40%, and a low yield of bitumen, not exceeding 5% on the combustible mass.

Low-temperature carbonization of these coals in a standard aluminum retort at a temperature of \(550^\circ\) showed a low yield of primary tar (5.0–7.5%). In only two samples out of 15 was about 8% primary tar obtained.

The yield of primary gas on dry fuel is 17.5–20% or 187–200 nm\(^3\)/t. This gas contains from 43 to 52% carbon dioxide, which accounts for its low calorific value, amounting to 2500–3000 kcal/nm\(^3\).

The yield of semicoke on dry fuel is 66.0–67.5%.

For one of the samples, in accordance with the instructions appended to GOST 3848—47 [3], the shatter index was determined. Pieces of grain with a diameter of 70 mm were subjected to the test.

It was found that these coals in the freshly mined state are quite strong. Thus, the shatter index for coal with a moisture content of 30.48% is equal to 77.4. It is known that, according to GOST 3846—47, anthracites having a shatter index greater than 70 belong to the first grade. Thus, in the moist state the brown coals of the Itatsk deposit may be placed in the same category as very strong anthracites, but the strength of this coal fell sharply as it dried. After five days of storage in air in the laboratory, the coal shatter index decreased to 38.

In addition, for several samples of these coals the true and apparent specific gravities, as well as their dielectric and optical properties, were determined.

Table 3

Chemical composition of ash

Table 4

Ash melting temperature

For testing, the analytical samples were dried to constant weight at \(105^\circ\) and then pressed at a pressure of \(2000\ \text{kg}/\text{cm}^2\). For the pressed tablets, on an apparatus intended for determining the conductivity of semiconductors, the current-decay curve was determined, and the specific resistance was calculated from the established current. The calculation of the specific resistance of the coal was carried out according to the formula:

\[ \rho=\frac{S\cdot U}{J\cdot l}, \]

where \(S\) is the area of the electrode, in \(\text{cm}^2\); \(l\) is the thickness of the sample, in cm; \(J\) is the established current in A; \(U\) is the applied voltage.

The specific resistances are presented in Table 6.

For dry Moscow-region coal the specific resistance is equal to \(4\cdot 10^{10}\ \Omega\cdot\text{cm}\). The results of many studies show that at room temperature the electrical resistance of dry brown coals of various degrees of metamorphism ranges from \(10^9\) to \(10^{11}\ \Omega\cdot\text{cm}\) [4]. The specific resistances obtained by us for dry Itatsk coals are somewhat higher than those for the Moscow-region coals, because the ash content of the Itatsk coals is considerably lower than that of the Moscow-region coals.

The dielectric permittivity of Itatsk brown coal was determined as follows: an analytical coal sample, dried to constant weight at \(105^\circ\), was pressed under a pressure of \(1000\ \text{kg}/\text{cm}^2\), and immediately the tangent of the loss angle and the dielectric permittivity were determined by means of an MDP bridge. The dielectric permittivity \(\varepsilon\) was calculated according to the formula:

\[ \varepsilon=\frac{4\pi\cdot d\cdot C_x}{S}, \]

where \(d\) is the thickness of the sample, \(S\) is the area of the sample, and \(C_x\) is the capacitance, calculated from the experimental data,

\[ C_x=C_0\cdot\frac{R_4}{R_3}, \]

where \(R_3\) and \(R_4\) are the bridge readings.

The data obtained are given in Table 6.

The refractive index, which is the ratio of the speed of light in a standard medium to the speed of light in the given substance, was measured by us by the immersion method [5].

The experimental data (Table 6) show that the dielectric permittivity and the refractive index for Itatsk...

Table 5

Group composition, yield of semicoking products, and composition of the primary gas

brown coals, as in most cases, does not obey J. Maxwell’s equation, which shows the relationship between the electrical and optical properties of substances, expressed by the equation \(\varepsilon = n^2\), where \(\varepsilon\) is the dielectric constant of the substance; \(n\) is the coefficient of refraction of light.

Table 6

Physical properties of Itatsk brown coals

The dielectric constant of a substance in J. Maxwell’s equation is the ratio of the force of interaction of electric charges in a vacuum to the force of their interaction in the given dielectric, which is determined by a change in the arrangement of molecules in the latter and is connected with molecular structure. For most electrical insulating materials this quantity ranges from two to six. As for various fossil coals, only a few studies on this question have been published recently [4].

Of the optical properties of this coal, we also determined its reflectivity, which amounts to 1.5–3% at different wavelengths of the incident waves.

Conclusions

1. A study was carried out of 15 coal samples taken from various areas; it showed that the coals of the Itatsk deposit are low-bituminous, dense brown humic coals with low ash content and a high yield of volatiles, and are completely non-caking.

2. During low-temperature carbonization these coals give a small tar yield, not exceeding eight percent on dry fuel, and a high yield of primary gas, up to 200 m³/t, whose composition contains almost 50% CO₂.

3. The ash composition of these coals is distinguished by a high content of calcium oxide (39–49%). The ash-fusion temperature of the samples studied varied over wide limits, 1180–1400°C.

4. In the freshly mined state this fuel possesses high mechanical strength, which decreases sharply during short-term storage in air (the “breakage index” decreases over five days from 77.4 to 38).

5. Some dielectric and optical properties of the Itatsk brown coals have been determined.

Literature

1. S. G. Aronov, L. L. Nesterenko. Chemistry of Solid Combustible Minerals. KhGU Publishing, 1960.

2. USSR. State Standards for Solid Fuels. Coal. Method of Investigation. State Publishing House of Standards, 1962.

3. Z. E. Taits, N. G. Titov, N. V. Shishakov. Methods for Evaluating Coal as Raw Material for Industrial Use. Ugletekhizdat, 1949.

4. A. A. Agroskin. Physical Properties of Coals. Metallurgizdat, 1961.