Effect of the Coking Regime on the Strength of Coke from Peat Thermal Briquettes

S. G. Maslov, S. I. Smolyaninov, V. G. Teteryak, G. F. Kraskov

(Presented by the scientific-methodological seminar of the Chemical-Technological Faculty)

Summarizing the literature on the coking of briquetted fuel [1—10], the following conclusions may be drawn:

1. In coking peat and brown-coal briquettes, a mild coking regime of about 2° per minute should be maintained, especially up to the stage of semicoke formation.

Table 1

Dependence of the strength of coke briquettes on the coking regime

Note: compressive strength values are the average of three tests.

1. The best results, taking economy into account, are obtained by coking with a controlled variable heating rate.

2. No special work had been carried out to determine the influence of the heating rate on the strength of coke from peat thermal briquettes.

Thermal briquettes produced from peat from the Taganskoye deposit in Tomsk Oblast, using the method of high-rate heating of peat in a falling layer, were subjected to coking. Coking was carried out in electric crucible furnaces of the TEP-1 type. The test thermal briquette was loaded into a porcelain crucible, covered with charcoal, and the crucible was placed in the furnace. Heating was carried out at a rate of 2° per minute to the specified temperature; up to the final coking temperature it was conducted at an increased rate of 5° per minute. Holding at the final temperature was 20 minutes. The coke briquettes obtained were tested for crushing resistance and abrasion under laboratory conditions. The results are given in Table 1.

The data show that the strength of coke briquettes at first increases sharply with an increase in the temperature up to which coking was carried out at a rate of 2° per minute; then, in the interval 550–650°C, there is a smooth transition, and subsequently the strength of the coke briquettes depends only slightly on the indicated temperature. To determine more accurately the temperature from which the heating rate can be increased without impairing coke quality, a special series of experiments was carried out. The temperature was varied from 550 to 650°C in steps of 20°C. The experimental data are shown graphically in Fig. 1. The graph shows that the desired temperature is 610°C.

Fig. 1. Dependence of the strength of coke briquettes on the temperature up to which coking is carried out at a rate of 2° per minute. 1—abrasion, %; 2—crushing resistance, kg/cm².

In determining the reason for the existence of a temperature interval from which the temperature rise can be intensified without reducing the strength of the coke briquettes, we proceeded from the premise that the strength of coke from briquettes depends on the following factors:

a) the rate of release of volatile substances in certain temperature intervals during coking;

b) the rate of shrinkage;

c) the magnitude of the temperature gradient in the briquette, which depends on the thermal-conductivity coefficient of the briquette material during coking.

The rate of release of volatiles (the rate of weight loss) was determined on a derivatograph for two heating rates, 2° and 5° per minute (Fig. 2).

Fig. 2. Weight loss of thermal briquettes during coking.
1 — weight loss at a heating rate of 2° per minute, %; 2 — weight loss at a heating rate of 5° per minute, %; 3 — rate of weight loss at a heating rate of 2° per minute, % per minute; 4 — rate of weight loss at a heating rate of 5° per minute, % per minute.

Table 2

Dependence of shrinkage of thermal briquettes on the final coking temperature

The shrinkage rate was determined in a special series of experiments. For this purpose, the shrinkage of the briquettes was measured after coking them to a specified temperature, which was increased in steps of 100° (Table 2).

These data show that the highest rates of volatile release and shrinkage are observed in the temperature range 300–500°C; consequently, during this period the thermobriquettes being coked must be heated at the lowest rate.

REFERENCES

1. Kh. I. Rivkina, “Production of metallurgical coke from milled peat by briquetting during the coking period,” Torfyanoe delo, 9, 28–32, 1934.

2. B. N. Zlobinskii, Investigation of a Peat Briquette as Fuel for Blast-Furnace Smelting. Author’s abstract of dissertation, 1946.

3. E. M. Taits and A. O. Andreeva, “On the strength of coke briquettes from brown coal,” Trudy IGI, Vol. XX, 34–43, 1963.

4. E. M. Taits and F. I. Pokrovskaya, “Formation of coke from briquetted fuel,” Trudy IGI, Vol. XX, 28–34, 1963.

5. G. K. Gerlakh, “On the technology of producing high-temperature brown-coal coke and factors affecting the technology,” Bergbautechnik, 61, 15–19, 1959.

6. B. M. Zlobinskii, Brown Coal as a Metallurgical Fuel. Ugletekhizdat, 1956.

7. V. I. Chistyakov and N. A. Basov, “Thermobriquetting of peat and coking of briquettes,” Bulletin of Scientific and Technical Information of VNIITP, issue 12, 30–40, 1961.

8. B. M. Babakin and L. I. Erkin, “Study of the influence of the rate of temperature rise at various stages of the coking process on the mechanical properties of formed coke,” in: Preparation and Coking of Coals, 103–114, 1965.

9. B. I. Babakin, “Influence of the heating rate on the change in the mechanical strength of moldings during the coking process,” in: Preparation and Coking of Coals, 114–131, 1965.

10. P. Z. Shubenko, “Development of conditions for a continuous process of coking coals in several successive stages,” Trudy IGI, Vol. X, 1959.