EFFECT OF HEATING RATE ON THE STRENGTH OF COKE FROM LUMP PEAT AND PEAT FUEL–SMELTING MATERIALS

S. I. Smolyaninov, G. G. Krinitsyn

(Recommended by the scientific-methodological seminar of the Faculty of Chemical Technology)

The screw molding press used in the production of lump peat develops a pressure of \(2\text{–}5\ \mathrm{kgf/cm^2}\). After drying and molding, its strength does not reach high values because the structure of the peat lump is disrupted by a large number of gas inclusions, and it is not sufficient for use as blast-furnace fuel.

The coking regime of the fuel, and above all the heating rate, also has a noticeable effect on the strength of coke from lump peat.

While the influence of molding pressure and heating rate for lump peat has been studied more or less fully, for fuel–smelting materials based on machine-molded peat it is necessary to carry out special studies on the influence of the factors indicated above.

For the preparation of fuel–smelting materials, peat from the Tagan deposit of Tomsk Region was taken (quality indicators are given in Table 1), and Bakchar iron ore with an iron content of 41.0%. The composition of the fuel–smelting materials was calculated from the ratio between iron and the nonvolatile carbon of the fuel, equal to 1:1.

Table 1

Characteristics of peat from the Tagan deposit

Peat at working moisture content was processed three times in a meat grinder and thoroughly mixed with the calculated amount of iron ore. From the resulting mass, specimens were prepared at different molding pressures. For comparison, under the very same conditions, specimens were prepared from pure peat.

All specimens were dried under natural conditions. The weight of the specimens and their geometric dimensions were monitored daily. The ratio of the weight of the molding before drying to the weight of the molding after drying for peat moldings and FPM moldings at molding pressures of 20, 15, 10, 5, and \(2\ \mathrm{kgf/cm^2}\) was, respectively, 3.2; 2.9; 2.9; 3.3. And for FPM these ratios were 2.75; 2.5; 2.45; 2.4; 2.3.

It follows from this that the moldings of the fuel–smelting material

during molding, they lose moisture in direct proportion to the molding pressure, which was not observed for compacts made from pure peat.

After the specimens reached the air-dry state, they were tested for resistance to crushing and abrasion. The test results are given in Table 2.

Table 2

Strength of air-dry compacts

According to the data in Table 2, the maximum strength is attained at the maximum molding pressure. The FSM, when tested, did not show a clear dependence.

In studying specimens heated at a heating rate of 3–4°/min, the data summarized in Table 2 were obtained.

The data of Table 3 show that at a heating rate of 3–4°/min no clear dependence is observed between molding pressure and the strength of the coke obtained.

Table 3

Strength of compacts after heating to 850°C at a rate of 3–4°/min

At a heating rate of 6°/min, the resistance to crushing and abrasion, with the exception of the specimen with a molding pressure of 10 kgf/cm², are approximately the same; for the FSM, however, the resistance to crushing and abrasion attain their best values at the maximum molding pressure. Moreover, at a heating rate of 6°/min, the average strength value is lower than at a heating rate of 3–4°/min (Table 4).

If the heating rate is 10°/min, then, in the absence of a dependence between molding pressure and coke strength, a decrease in the latter is observed in comparison with the preceding experiments, i.e., at heating rates of 3–4°/min.

Thus, in developing the TFM technology, replacement of the auger former of the Stilochnaya machine with a more powerful pressing unit is not necessary. With an appropriate degree of peat processing, peat-ore briquettes will be sufficiently strong even at low forming pressures.

Table 4

Strength of briquettes after heating to 850°C at a rate of 6°/min

Table 5

Strength of briquettes after heating to 850°C