BROWN COALS OF THE TUGAN DISTRICT OF TOMSK OBLAST

I. V. GEBLER, S. I. SMOLYANINOV

Coal samples were supplied by a geological exploration party working in the Tugan district, in the form of drill samples.

In appearance the samples are an earthy mass with separate lumps, among which inclusions of a woody structure occur. The color of the samples ranges from gray to brown.

Moisture Content of the Coals

The moisture content in air-dry samples varies from 4.12 to 10.14%, i.e., it indicates an unequal hygroscopicity of the coals, which depends on their organic mass, since the same content of hygroscopic moisture, for example 4.12%, occurs at ash contents of 28.75 and 81.96%.

Ash Content of the Coals

Most of the coal samples have a high ash content, which, on a dry basis, ranges from 12.04 to 83.42%.

During the study of the coal samples, the following circumstance was noted. The specific gravity of the coals is in complete correspondence with their ash content. This is revealed best and most simply by briquetting the coal. A charge of 1–2 g of coal is briquetted in the form of a cylinder on a hand press, the weight of the briquette is determined, and its volume is measured. The weight of the briquette is recalculated to an anhydrous substance, and in this way the specific gravity of the dry briquette is determined. Figure 1 gives the dependence of the specific gravity of the briquette on ash content for five coal samples with different ash contents.

Fig. 1. Relationship between ash content and specific gravity of briquetted coals.

The relationship found for the given coal samples, with the obvious constancy of the enclosing rocks with respect to their composition, as well as of the ash of the coals, makes it possible to express considerations on calculating the geological reserves of coal.

Taking the correlation between specific gravity and ash content as linear and extrapolating it to the intersection with the abscissa axis, we find the specific gravity also of the combustible mass of the coal: in the present case it will be equal to 1.12.

Combustible mass of the coals

For its characterization, in addition to ultimate analysis, the following determinations were made: the content of bitumens, humic acids, and yields of low-temperature carbonization products.

All the indicated determinations were made for samples with an ash content of up to 34%, since only up to this ash content can the coals be of practical interest.

The amount of volatile matter for these coals is insufficiently indicative. Under the conditions of the usual determination of volatile humic substances, the substance loses constitution water at high temperatures (300–400° and even higher), whereas for coals, in calculating anhydrous volatile matter, the hygroscopic moisture determined by drying the coals to constant weight at 105° is deducted. With a large content of mineral ballast, the amount of volatiles may be increased due to the decomposition of carbonates and due to the loss of chemically bound water by the clay. The latter occurs in the present case; carbon dioxide, however, was not detected in the samples upon treatment with hydrochloric acid. For an approximate characterization of the coals by volatiles, only samples with ash content up to 30–32% may be taken, for which the amount of volatiles varies within the range of 53–72% on the combustible mass.

In terms of carbon and hydrogen content, the extreme figures for the first are 61.80 and 70.49%, and for the second—4.71 and 6.69%. Without these extreme values, the more stable figures will be for carbon within the range of 64–68% and for hydrogen 5.50–6.50%, which may also be accepted, together with the amount of oxygen (22.39–31.40%), for characterizing the type of coals and the degree of metamorphism.

As for the sulfur content, it is generally insignificant. Only in two samples does it exceed 1% (1.20 and 1.39%); in the remaining samples it is represented by fractions of a percent.

Fig. 2. Low-temperature carbonization apparatus. 1—control panel, 2—furnace, 3—retort, 4—thermocouple, 5—gas-discharge tube, 6—tar receiver, 7—bath, 8, 11—manometers, 9, 10, 12, 14—clamps, 13—glass tube, 15—equalizing vessel, 16—gas meter, 17—tube for gas removal, 18—tube for gas removal, 19—vessel for collecting water.

Determination of the yield of low-temperature carbonization products was carried out on a modernized conventional installation (according to GOST 3168–46), including as its main part a Fischer aluminum retort. The general appearance of the installation is shown in Fig. 2. It has the following features. Heating of the retort is carried out by means of a special electric furnace. The furnace heaters consist of vertically arranged spirals of nichrome wire 0.8 mm in diameter, which surround the body of the retort on all sides. Automation of the heating is achieved by setting (by current) the initial heating period (510° in 30 min.) and subsequently maintaining the final temperature by means of an electronic regulator.

The constancy of the hydraulic regime is ensured by using a gas meter to take off the gas under constant pressure. The hydraulic regime of gas takeoff is set by a definite position of the submerged end of gas-discharge tube 17 of gas meter 16 relative to drain fitting 13 and, during the experiment, is maintained constant automatically. Thus, from the moment of start-up until the end of the experiment the apparatus operates automatically.

The yield of primary tar on the combustible mass varies within very wide limits: 8.6–28.2%, which is probably explained by the uneven distribution, in the coal mass, of woody resinous inclusions. In general, in terms of tar yield the coals should be classified as bituminous.

With respect to tar yield on dry substance, they may be divided into three grades.

1. With a high tar yield, above 15%.
2. With an average tar yield of 10–15%.
3. With a low tar yield, below 10%.

The relative quantity of such grades in the samples studied is: the first—25%, the second—31.2%, and the third—43.8%.

The bitumen content was determined by exhaustive extraction of an analytical sample with alcohol-benzene (1 : 1) in a Soxhlet extractor. The bitumen content—a mixture of tar and wax—on the dry and combustible substance of the coals varies, for the combustible mass, within wide limits (3.10–19.30%).

In practical terms, coal with a bitumen content in the analytical sample of about 12% apparently could serve as a material for obtaining so-called montan wax, a valuable product used in various branches of the chemical industry and in electrical engineering.

Conclusions

1. According to the samples examined, the brown coals of the Tugan district are young coals with a low degree of metamorphism, of the lipto-biolith type, formed from resinous trees of the Tertiary period (sequoias).

2. They occur in clayey rocks and, in many samples, have a high ash content.

3. Their direct combustion in furnaces is difficult because of their ability, in the dried state, to give off a large amount of slack and entrainment, and requires the use of special furnaces, such as shaft-mill furnaces and others.