TAILIEUCHUNG - handbook of extractive metallurgy 1 Part 3

Tham khảo tài liệu 'handbook of extractive metallurgy 1 part 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 76 Handbook of Extractive Metallurgy Figure Phase diagrams of the system CaO-Al2O3-SiO 35 . These requừements are in part complementary and in part mutually exclusive. It is therefore necessary to state priorities. About 95 of the slag consists of SiO2 CaO MgO and A12O3. The reqmrement of low viscosity can be met by a variety of components in this quaternary system. Ignoring the presence of MgO the phase diagram of the ternary system CaO-Al2O3-SiO2 illustrated in Figure shows a low melting temperature region which is parallel to the CaO-SiO2 binary for low A12O3 content. This region extends from high S1O2 content to the saturation isotherm for 2CaO-SiO2 and then for essentially constant CaO content toward high A12O3 content. The MgO content of the slag does not substantially affect the relative position of the low melting temperature region and only affects the absolute values of the melting temperatures. The compositions of blast furnace slags as encountered under various operating conditions are shown in Figure . The desulfurization of the hot metal increases with slag basicity . with increasing CaO and or MgO content. Region 1 in Figure can therefore be used only for processing low sulfur burden . in Brazil where very low sulfur content charcoal is often used as reductant . Because the gangue constituents usually form a low basicity slag region 1 largely represents the slag composition without addition of fluxes. The furnace can be operated at a relatively low temperature because of the low melting points. Region 2 is reached for low iron content burden with acid gangue constituents. This mode of operation prevails for example in Salzgitter and requires extensive desulfurization of the hot metal outside of the blast furnace. The attainment of a basicity that would result in adequate desulfurization within the furnace would require a large lime addition which leads to a high slag volume and consequently to higher coke rate. Region 3 .

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