Briquetting of Brown Coals from the Yarskoye Deposit in Tomsk Oblast

V. M. Vityugin, G. F. Atknin

(Presented by Prof. I. V. Gebler, Doctor of Technical Sciences.)

Geological investigations as early as the years of the first five-year plans discovered, in the area of the city of Tomsk, deposits of brown coal significant in reserves, including the Yarskoye deposit. At that time the question was raised of using these coals [1]. Attempts to use Yarskoye coal as a local fuel did not give good results because of the low calorific value of the raw coal, the impossibility of storing it for long periods in stockpiles, and the large amount of dust carryover when it was burned in bed furnaces.

The practice of using brown coals in other regions of the USSR and abroad shows that their rational use as a local fuel is possible only after preliminary briquetting.

Experimental Part¹

For the study, a 100 kg sample of coal was taken from an exposed upper seam. After manual removal of woody inclusions, the raw coal was a homogeneous earthy mass of brown color. Technical analysis of the coal gave the following results:

The results of the analysis show that Yarskoye coal belongs to the class of typical young brown coals. Consequently, the briquettability of the coal should be comparatively easy. The high bitumen content and the large yield of primary tar make it possible to expect good water resistance of the briquettes. Moreover, briquettes from Yarskoye coal under [[unclear: word cut off at page break]]

their treatment by the Lurgi method will simultaneously yield both high-quality semicoke and valuable tar products. In the latter case it is necessary only to obtain a briquette with increased mechanical strength.

For the investigation of briquettability, the raw brown coal was crushed in an impact mill to a size of 5–0 mm and dried to a specified moisture content. Pressing was carried out on a hydraulic press in cylindrical dies with slight taper and with external electric heating. After cooling to room temperature, the briquettes were tested for mechanical strength and water resistance. Mechanical strength was determined from the resistance to bending and crushing, and water resistance from the residual bending resistance after the briquettes had been kept under water for two hours. Briquettes obtained under optimum conditions were also tested for heat resistance during combustion.

The principal factors affecting the briquettability of brown coals are the specific pressing pressure, moisture content, size, and temperature of the partially dried coal. From the practice of briquetting young brown coals it is known that the required specific pressing pressure lies within the range from 1000 to 1500 kg/kg·cm, the moisture content of the dried coal from 15 to 20%, the upper size limit of the dried coal from 3 to 5 mm, and the temperature of the dried coal from 40 to 70°C [2]. In this case briquettes are usually obtained with a crushing resistance of not less than 100 kg/kg·cm, a bending resistance of not less than 8–10 kg/kg·cm, and a residual crushing strength after two hours in water of not less than 75 kg/kg·cm.

For the experimental study of the influence of the specific pressing pressure in the present investigation, the initial raw coal was crushed so that its sieve composition corresponded to the standard industrial one, namely, so that the content of the 3–5 mm fraction was 20%, and that of the 0.5–3 mm and 0.5–0 mm fractions was 40% each, respectively. The coal was then dried to a moisture content of 20% and heated in the press mold to 50°C. The briquettes had a diameter of 36 mm, a height of 20–22 mm, and a weight of 25 g.

The results of the first series of experiments are presented in Table 1.

Table 1

Influence of the specific pressing pressure on briquette quality

The results of the above experiments show the exceptionally high briquettability of Yarskoye coal. It is evident that industrial pressing of these coals will be readily feasible in the simplest connecting-rod crank-stamp presses with an increased number of revolutions of the crankshaft and, consequently, with high productivity without detriment to the quality of the briquettes.

The degree of drying of the raw coal is of substantial importance in the economics of brown-coal briquetting. To determine the influence of the moisture content of the dried coal on the quality of the briquettes, a second series of experiments was carried out. In this case the raw coal was crushed to a size of 3–0 mm and pressed at a specific pressure of 1200 kg/kg·cm and a temperature of 50°C.

The results of the second series of experiments are shown in Table 2.

Table 2

Effect of the moisture content of the dried coal on briquette quality

High-quality briquettes are obtained over a wide range of moisture contents in the dried coal. This greatly simplifies the drying of coal before briquetting. It should be borne in mind, however, that drying the coal to a moisture content below 15% will be associated with a decrease in dryer capacity and an increase in fuel consumption, while insufficient drying of the coal will lower the heating value of the briquettes. The optimum moisture content of the dried coal will evidently fluctuate between 16 and 18%.

In the third series of experiments, the effect of the temperature of the dried coal on briquette quality was investigated. The results of these experiments, given in Table 3, show that as the temperature of the dried coal is raised up to 90°C, the strength of the briquettes, and especially their water resistance, increases. This is probably explained by the elevated bitumen content in the coal and the high yield of primary tar. The rationality of briquetting dried coal at a temperature of 70–90°C is beyond doubt also because, in this case, the laborious operation of cooling the dried coal is eliminated.

Table 3

Effect of the temperature of the dried coal on briquette quality

To study the effect of the size of the dried coal on briquette quality, four types of charges with different screen compositions were prepared (see Table 4). The dried coal was pressed at a specific pressure of 1200 kg/cm², at a temperature of 50°C and a moisture content of 14.5%. The results of this series of experiments are shown in Table 5.

The somewhat elevated values of mechanical strength and water resistance of the briquettes of the fourth series are explained mainly by the smaller thickness of the briquettes and, consequently, by their better pressing.

Table 4

Size and sieve composition of dried coal in the fourth series of experiments

In general, decreasing the size of the dried coal, as can be seen from Table 5, leads to an improvement in briquette quality. However, excessive grinding of the coal is uneconomical, since pressing dried coal of size less than 0.5 mm requires an increase in specific pressure and, most importantly, preparation of dried coal of such size is associated with a complication of the technology. The high degree of plasticity of Yarskoye brown coal makes it possible to obtain high-quality fuel briquettes from dried coal of size 5–0 mm, and only when briquettes for semicoking are to be obtained does it make sense to crush the coal to a size of 3–0 mm.

Table 5

Effect of the size and sieve composition of the dried coal on briquette quality

Several briquettes obtained under the optimal conditions indicated above were tested for heat resistance during combustion. A batch of briquettes was burned in a muffle furnace preheated to 750°C. The briquettes ignited 30–50 seconds after being charged into the furnace and burned with an even, slightly smoking flame. When poked, the briquettes did not fall apart, although their surface became covered with a network of fine cracks. Overall, the heat resistance of the briquettes proved quite satisfactory.

Conclusions

1. Yarskoye brown coal has good briquetting ability.

2. Raw coal, after crushing to a size of 5–0 mm, is dried to a moisture content of 15–18% and, without cooling, is fed to pressing. Crushing of the coal is readily accomplished in hammer crushers; drying is possible in the simplest tube dryers, and pressing with high

productivity can be carried out in crank-and-toggle ram presses.

1. Briquettes made from Yarskoye coal can be successfully used for semicoking.

REFERENCES

1. Gebler I. V. and Stramkovskaya K. K. Study of bitumens of brown coals from the Yarskoye deposit in Tomsk Oblast. Proceedings of the Tomsk Polytechnic Institute, vol. 64, pp. 291–294, 1948.

2. Pakhalyuk I. F., Boldyrev V. A. Briquetting of coals. Ugletekhizdat, 1952.

1. Note. Students G. R. Bochkarev and A. I. Sadov took part in the experimental portion of the work. ↩