Basing on the data of Al2O3 and SiO2 thermodynamic acnvrties in SiO2-containing calcium aluminates of three formulae, CaO · Alz03, I 2CaO · 7Alz03 and 3Ca0 · Alz03 (shortly denoted as C1A" C12A7 and C3A1), at 1873K for the wide range of SiO2 mole fractions [!], we propose their activities expressed as functions of CaO contents provided there is no change in SiO2 mole fraction. The proposed relations allow to follow the change of the inclusions and steel composition during calcium treatment when calcium or calcium-silicon are added. An evolution of inclusion and steel compositions during calcium treatment was investigated starting from the partly modified inclusions C1A1-SiO2 with x;,02 = O.IO and 0.03. It was shown that the change of calcium aluminosilicates composition is slightly different for the pure calcium and calcium-silicon additions. With the calcium treatment the mole fraction of SiO2 in inclusions is decreasing less significant.

Natural gas combustion was carried out in air enriched with oxygen in the amount of 25 and 29% with addition of CO2 in place of part of nitrogen. The research was carried out at different flow rates of gas and oxygen excess ratios. The concentration of CO and NOx was analyzed. It has not been proved that the increased oxygen concentration influences significantly the CO concentration. However, the addition of CO2 caused a substantial variability of CO concentration in the exhaust gas, in contrast to the concentration of NOx which decreased monotonically. Model calculations, performed with use of FactSage, indicate an increase in the concentration of CO not only for the air enriched with oxygen, but after adding CO2 too, as well