Primary Slag Research Articles

Effect of alkalis on reduction behavior of acid iron ore pellets.

Under conditions relevant to the process of an iron blast furnace with alkali cycling, acid iron ore pellets were tested. The alkalis were introduced in three different ways: as part of the pellets gangue phase, as fine crystals of alkali carbonates near the pellets surface, and, as metal vapor mixed with the reducing gas.During reduction alkalis flux the silicate binding bridges and react with ferrous iron oxide forming low melting point slag which weakens the pellets and causes them to degrade. A mechanism of degradation will be given which relates the behavior of the pellets to the formation of this primary slag. Also, certain measures to control the reduction will be discussed.

Effect of viscosity and phase composition of converter slags on the destruction of refractories

Converter slags formed in the first 10–12 min of the blowing of the iron, after cooling consist mainly of manganese-iron monticellite, glassy, and cryptocrystalline substances, free calcium oxide, and metallic iron. The primary slags are characterized by a low basicity, refractoriness, and viscosity, and rapidly react with the refractory during the period of their formation in the converter at 1150–1360°C. The primary slags are changed into the truly liquid state at 1256–1312°C.

戸畑第1高炉におけるスラグの組成変化

Chemical and mineral composition of samples taken from the peripheral region of the blast furnace at the belly, bosh and tuyere level was examined. In the small lumps from the belly three kinds of primary slag were found, which were considered to correspond to FeO-Al2O3-SiO2, K2O-Al203-SiO2 and CaO-K2O-Al2O3-SiO2, coexisting with the spinel, FeO·(Fe, Al) 2O3, in molten state. Bosh slag which remained in or separated from metallic iron granules consisted only of the CaO-K2O-Al2O3-SiO2 system. Most of the belly and bosh slags bad greater amount of K2O, Al203 and SiO2 than the final slag. The role of minor constituents in ascending gas, i. e. vapors of potassium cyanide and silicon mono-oxide and dusts of some aluminum compounds, is discussed in relation to the process of primary slag formation.

Service of refractories in a blast furnace shaft

The destruction of the refractory structure of a blast furnace depends on the properties of the refractory, the system of cooling the lining, the furnace operating cycle, the action of alkalis, primary slags, zincite, and sooty carbon, the running of the furnace, the thermal stresses in the structure, abrasion of the batch, and other factors. To increase the life of the shaft lining in a blast furnace it is necessary to use dense, high-fired brick for the structure, prepared on the basis of high-grade kaolin raw materials with the minimum content of fluxing oxides; to use the best system of cooling the shaft; and to stabilize the blast furnace working cycle, especially during the first period of operation after the blow right up to complete drying-out of the refractory structure.