THERMOBRIQUETTING OF ITAT BROWN COALS

S. G. MASLOV, S. I. SMOLYANINOV

One way of increasing the raw-material base for coking is the use of brown coals, the reserves of which are unlimited. The reserves of brown coals of all categories in the USSR amount to 3.6 trillion tons, of which more than three quarters are located in the eastern regions. In the Itat, Bogotol, Nazarovo, and Irsha-Borodino deposits of the Kansk-Achinsk basin alone, more than 1.6 trillion tons are concentrated. Organizing the production of metallurgical coke from brown coals would not only expand the resources of metallurgical fuel, but would also facilitate the development of ferrous metallurgy in regions that do not have their own reserves of coking coals.

In the practical part of this work we determined the following optimal conditions for obtaining thermobriquettes from Itat brown coal: briquetting temperature, thermobriquetting pressure, holding time under pressure, and degree of grinding. Thermobriquettes obtained under optimal conditions were tested for crushing resistance, abrasion, moisture absorption, storage stability, and heat resistance.

The experiments were carried out in a closed die, 31 mm in diameter and 70 mm high, with electric heating. The heating rate was 5–6° per minute. An oil hydraulic press with a force of 5 t was used for briquetting.

Briquetting temperature

Initial data: degree of grinding 0.25 mm, briquetting pressure 280 kgf/cm², holding time under pressure 2 min.; the heating temperature was varied from 200 to 300°C. The curves of the dependence of crushing resistance and abrasion on the heating temperature are shown in Fig. 1. It can be seen from them that thermobriquettes have maximum strength at a temperature of 260°C.

Thermobriquetting pressure. Initial data: temperature 260°C, holding time under pressure 2 min., degree of grinding 0.25 mm. The pressure was varied from 200 to 700 kgf/cm². The test results are shown graphically in Fig. 2. Comparing these results with the requirements that briquettes made from brown coals of the 2nd group must satisfy (crushing resistance 170 kgf/cm², abrasion 10.6%), we find that they exceed them.

Holding under pressure. Initial data: temperature 200°C, pressure 300 kgf/cm², degree of grinding 0.25 mm. Holding under pressure was varied from 0 to 10 min. The test results are presented in Fig. 3. We see that, with an increase in holding under pressure, the strength of the briquettes first increases rapidly and then more slowly. The optimum holding under pressure is 2 min.

Fig. 1. Dependence of the crushing resistance and abrasion of thermobriquettes on the coal heating temperature before the application of pressure: 1 — dependence of crushing resistance on temperature, 2 — dependence of abrasion on temperature

Fig. 2. Dependence of the crushing resistance and abrasion of thermobriquettes on briquetting pressure: 1 — dependence of crushing resistance on pressure, 2 — dependence of abrasion on pressure

Fig. 3. Dependence of the crushing resistance and abrasion of thermobriquettes on the holding time under pressure: 1 — dependence of crushing resistance on holding time, 2 — dependence of abrasion on holding time

Degree of grinding. Initial data: temperature 200°C, pressure 300 kgf/cm², holding under pressure 2 min. The following fractions were taken for the study: 0–0.25; 0–0.5; 0–1.0; 0–5.0. As a result, briquettes obtained from coal with a degree of grinding greater than 0.25 have an abrasion of 100%.

Special tests. The special tests were performed on briquettes that were obtained at a temperature of 260°C, pressure of 700 kgf/cm², holding under pressure of 2 min; degree of grinding 0.25. Tests for moisture absorption and thermal stability were carried out according to standard methods for testing brown-coal briquettes.

1. Water absorption after 2 hours of immersion under water was 12.5%, and after 24 hours—25%, which is no greater than the corresponding value for briquettes made from brown coals of the 2nd group.

2. Thermal stability. The tests were carried out in a muffle furnace, without a free inflow of air; the load on the briquette was \(1\ \mathrm{kg/cm^2}\). The ignition temperature was \(440^\circ\mathrm{C}\). The briquette retained its shape until complete combustion.

3. Storability. Four batches of briquettes were taken. The first was tested immediately. The second was stored indoors from 15/XII-64 to 15/I-65. The third batch was stored from 15/XII-64 to 15/I-65 under snow; the temperature reached \(-40^\circ\mathrm{C}\). The briquettes were tested for crushing resistance and abrasion; the test data are given in Table 1.

Table 1

Change in briquette strength during storage

From the data presented in Table 1, it is evident that, during storage indoors, the strength of the briquettes decreases only slightly. Briquettes must not be stored at low temperatures in the open air.

Conclusions

1. The possibility of obtaining lump fuel from Itat brown coal by the method of thermobriquetting has been demonstrated. The optimum conditions for producing thermobriquettes have been found: temperature \(260^\circ\mathrm{C}\), pressure \(700\ \mathrm{kg/cm^2}\), holding under pressure 2 min, degree of grinding 0.25 mm.

2. The briquettes may be used as fuel (domestic fuel, in locomotive fireboxes, and at power stations), but not as metallurgical fuel.

3. The briquettes should be stored in closed warehouses.