Study On Ring Formation Mechanism In Coal-fired Lime Rotary Kiln Of Bao-steel

In order to reveal the ring formation mechanism in the coal-fired active lime rotary kiln of Bao-steel, influence of calcining process on the activity of lime and the chemical composition, phase composition and microstructure of the ring were studied. The high temperature simulation experiment and Factsage thermodynamical calculation were used to reveal the effect of coal ash content and calcination temperature on ring formation. The results as follows:(1) the activity of lime increases firstly and then decreases with increasing calcination temperature. It reaches the maximum at one specific calcination temperature. There exists an optimum calcinations time for the activity of lime at one specific calcination temperature. The particle size and microstructure of limestone influence the activity of lime momentously.(2) The main chemical constituents of kiln lining are CaO, SiO2, MgO, Al2O3 and Fe2O3, the main phase constituents are lime, tricalcium silicate, calcium silicate and periclase. Kiln lining is porous.(3) The main chemical constituents of ash of five kinds of fuels are SiO2, Al2O3, CaO, MgO, Fe2O3 and SO3. The ash of Shenfu coal contained the maximum Fe2O3 and CaO, lower content SiO2 and Al2O3 among the five kinds of fuel. These led that it had the lowest melting temperature. However, Gaoping and Yongcheng coal contain high SiO2 and Al2O3 content and lower flux, so they had high melting temperature.(4)Equilibrium calculation reveals that liquid content becomes more and more with increasing calcination temperature and 1150-1200℃ is the temperature range in which a large number of high temperature liquid is produced.(5) The conditions for the ring formation are that low melting point matter functions as binding phase and the ash after coal burning reacts with calcium oxide to form low melting point oxides, these low melting point oxides stick to calcium oxides and the matters on the ring become thicker with the process progress. The liquid phase formation of the ash in coal under high temperature is the key problem for the ring formation in the active lime rotary kiln fired with coal.(6) The addition of sodium silicate, forsterite or their mixture to the kiln lining can decrease the viscosity and increase the fluidity of kiln lining at high temperature and results in its fall-off.