MACROSTRUCTURE OF CROSS SECTION OF BLAST-FURNCACE SLAG SAMPLES IN IRON MELTING WITH DUST-COAL FUEL INJECTION

Abstract

The macrostructure of blast furnace slag cross section samples during melting of pig iron with pulverized coal fuel injection on three blast furnaces with a volume of 1500 and 1386 m3 (2 units) was studied. The range of changes in the basicity of the studied slag samples (СаО/SiO2) was 0.98—1.30; corresponding to the temperature samples of cast iron and its silicon content ranged from 1324—1510 °С and 0.13— 1.17 %. To identify blast furnace slag samples in specific operating conditions, the samples were basically divided into five groups from acidic (В1<1,0) to highly basic (В1>1,25). By its physical heating characterictics the cast iron was divided into 3 groups: cold (<1400 °С ); heated (1400—1480 °С ); hot (>1480 °С ). According to chemical heating, the division was also carried out into three groups: cold (<0.5% Si); heated (0.5—0.8) hot (> 0.8). The look of cross section surface of acidic and low-basic slag is the same for former slag regime and the new, due to the use of coke and pulverized fuel with limited sulfur; in conditions of normal heating the cross section is vitreous, shiny dark color. When cooled, the vitreous and luster of cross section of such slags disappears — the chip becomes stone-like gray or black with some difference in the formation of macropores in the sample mass. Common for slag samples with В1>1,1 is a decrease in the vitreous amorphous part with increasing modulus of basicity. The difference for such slags in comparison with those known for melting in other raw material conditions is the lack of clear delimitation of layers in the cross section of the samples, especially noticeable for half-slags. It is established that the macrostructure of slag samples apart from the main В1 and furnace heating is influenced by the magnitude of the alumina-magnesium modulus; this fact should be taken into account in the operational control of the blast furnace for external conditions. It was also found that the deviation of the basicity towards acidic or highly basic slags was accompanied by the absorption of coal dust particles by slag melt. The properties of samples in terms of fluidity and desulfurizing ability of corresponding slags are considered.