Study On High-Efficiency And Low-Cost Dephosphorization Process Of80t Converter In Xinxing Ductile Iron Pipes Ltd.

Under the depression environment of steel industry, after comprehensively considering the process of hot metal pretreatment and the methods of "double-slag" and "duplex process" for dephosphorization, many steel plants are expecting to control the phosphorus content at reasonable level only in the converter. Therefore, it is significantly neccessary to study the high-efficiency and low-cost dephosphorizaiton process.The influence rules of all the factors including slag basicity, temperature and the content of the main components of FeO, P2O5, MgO and MnO were analyzed thermodynamically. Based on the theoritical research results and thermal state experiments carried out in the lobaratory, the best slag system for dephophorization is presented as follows:(%CaO)=49%-54%,(%SiO2)=15%-20%,(%FetO)=15%-20%,(%MgO)=6%～8%,(%MnO)<6%,(%P2O5)<3%. The results of industrial tests showed that the phosphorus content could be reduced to a lower level of0.027%with the slag system recommended above, which is obviously superior to the original level of0.033%. Besides, the converter flow field and dephosphorization dynamic model have been constructed through which the effect of each process parameter on the flow field and dephophorization effectiveness was studied. On account of the results, the best process parameters are listed below:(1) the modified oxygen lance structure is recommnended of which the throat diameter expands to37.3mm and the inclination angle increases to12°;(2) a new operating method of high-low collocation for lance;(3) the lance should be operated with the pressure of0.8MPa or a little higher. The slag system with high dephosphorization ratio and the best process parameters will be applied to construct the practice to achieve a lower final phosphorus content.On the basis of cyclic utilization and accuracy control, reducing the raw materials cost counts most for the low-cost dephosphorization process. The new dephosphorization process with lower cost by substituting lime with limestone was studied in this paper. The calculated results of materials balance, thermal balance and multiple phase equilibrium show that the limestone substitution ratio can be up to100%theoretically, and the oxidation by CO2produced by the limestones decomposition is12.5%higher to that of all O2blown in converter as well as the production cost saving can be up to60RMB per ton steel.Furthermore, to guide the practical production better, high-temperature experiments of dephosphorization with limestone substituting some lime were performed, and the results showed that the practices with substitution ratio of40%and60%achieved more satisfactory final phosphorus level compared with the rest. However, which one of40%and60%will be chosen is upon the production cost and dephosphorization efficiency.60%of the substitution ratio makes the cost lower while40%does the dephosphorization efficiency higher.In addition, industrial experiments of dephosphorization with limestone were carried out. In consideration of the steadiness and safety during production, the quantity of limestone was increased from1.5t to3t gradually (1.5t,2t,3t) per heat. According to the results, the best scheme recommended for dephosphorization with limestone is that:3t limestone,2.5t lime,0.43t magnesium oxide pellets,0.4t agglomerate,0.6t light burned dolomite. In the performance the limestone substitution ratio is41%and it will help reduce the production cost by10.6RMB per ton steel.