KTH Industrial Engineering and Management Sulfur and Nitrogen in Ladle Slag
Sweden Akademisk avhandling som med tillstånd av Kungliga Tekniska Högskolan i Stockholm, framlägges för offentlig granskning för avläggande av Teknologie Doktorsexamen, fredagen den 1 april 2016, ABSTRACT The present work deals with some aspects of slags related to secondary metallurgy in the steelmaking process. More specifically the focus is given to sulfur and nitrogen in ladle slags. Even though slags have been fairly well–researched in the past, the available data for these elements in typical ladle slag compositions is rather scarce. In some cases the available data is in discordance. There are also inconsistencies between the literature data and what is commonly observed in the industrial processes. Sulfide capacities were measured at steelmaking temperatures, 1823–1873 K, in ladle slags. The data was found to be in reasonable agreement with the industrial process norms. The sulfide capacity was found to increase with the basic oxides CaO and MgO; and decrease with the acidic components Al 2 O 3 and SiO 2. The sulfide capacity was also found to increase with temperature. The dependence of sulfide capacity on the oxygen partial pressure, for slags containing multivalent elements, was investigated experimentally at 1873 K with a slag containing vanadium oxide. A strong dependence of oxygen partial pressure was observed. The sulfide capacity increase by more than two orders of magnitude when the oxygen partial pressure was increased from 4.6×10-16 atm to 9.7×10-10 atm. The nitrogen solubility and the effect of carbon was investigated in typical ladle slags and the CaO–MgO–SiO 2 system at 1873 K. Carbon increases the nitrogen solubility substantially. In the absence of carbon, the nitrogen solubility is extremely low. Low concentrations of cyanide was detected in the carbon saturated slag. This was much lower than the total nitrogen content and formation of cyanide cannot explain the large increase. The possibility of removing sulfur with oxidation from used ladle slag was investigated experimentally at 1373–1673 K. The sulfur removal of mostly solid slag was found to be a slow process, and would not suitable for industrial practice. At 1673 K the slag was mostly liquid and more than 85% of the sulfur was removed after 60 min of oxidation in pure oxygen atmosphere. ii ACKNOWLEDGEMENTS
Nitride Capacities in the CaO-base Ternary Slags at 1873K
Nitride capacities (CN=(mass%N)·PO23/4/PN21/2) in the CaO-Al2O3-MgO(ZrO2) and CaO-SiO2-MgO(TiOx) ternary slags were measured at 1873K by a gas-slag equilibration technique, using an Mo, Al2O3 or MgO crucible under controlled partial pressures of oxygen (log(PO2/atm)=-11--14) and nitrogen (PN2=0.9 atm). The CN values increased with increasing the contents of nitride former oxides. The CN values in the CaO-AlO1.5-MOx (MOx=MgO, SiO2, ZrO2, TiOx) slags at XCaO/XAlO1.5=0.4-0.7 increased in the order of MgO<SiO2<ZrO2<TiOx and those in the CaO-SiO2-MOx (MOx=MgO, AlO1.5, TiOx) slags at XCaO/XSiO2=1.0-1.5 increased in the order of MgO<AlO1.5<TiOx at a given MOx content.
Simulation of pneumatically agitated metallurgical vessels through water modelling
Fluid flow studies in gas-stirred metallurgical vessels have been carried out by employing a water model. It has been shown that the vessel dimensions, depth of immersion of the lancing head (plunger), are some of the factors critical in getting optimum mixing for achieving uniform composition and temperature. It has also been shown that off-centre plunger placement gives a more effective fluid-flow pattern and better mixing conditions