Study On Limestone Decomposition In CaO-SiO₂-Fe_tO Slag And Hot Metal

Using limestone instead of lime as slagging flux is a new technology in converter steelmaking process.It is an important way for saving energy,reducing emissions and reducing the refining cost.The process can use the heat of hot metal efficiently,decrease the comsuption of scrap,improve the economic efficiency,and thus lead to the reduction of CO₂ emission at the same time.However,up to now,very little previous work about limestone decomposition in CaO-SiO₂-Fe_tO slag and hot metal has been done.Compared with the traditional limestone calcination,this paper fouses on the conditions and temperature in steelmaking converter where the limestone experiences its decomposition.Considering heat transfer,mass transfer driven by concentration gradient and mass transfer?CO₂ gas flow?driven by pressure gradient,macro kinetic models are established to describe limestone decomposition rate respectively.The method of rotating cylinder sample has been used in the experiment of limestone decomposition in the converter early slag and hot metal.The image processing software Image-Pro Plus has been used to analyze the cross section of limestone calcined to get the thickness of calcined lime layer.The controlling step of limestone decomposition has been discussed,and corresponding kinetic equation has been established.The main results are as follows.?1?The decomposition mechanism of limestone follows the unreacted shrinking core model.The thickness of lime layer increases with temperature in molten slag,but it is has nothing to do with rotating speed.The thickness of lime layer increases with temperature in hot metal,but it is has nothing to do with rotating speed.?2?The temperature of reaction interface is higher in hot metal and slag than the standard critical temperature?902??of limestone decomposition.The heat conduction and CO₂ migration through the product layer determine the rate of limestone decomposition.When calcined in slag,dicalcium silicate coating layer is found on the sample which inhibits the removal of CO₂.CO₂ accumulates at the reaction interface,retarts the progress of decomposition reaction and thus leading to higher interface temperature.When calcined in hot metal,little dicalcium silicate is formed,the decomposition reaction is faster and the interface temperature is lower.?3?The decomposition rate of limestone in both molten slag and hot metal can be characterized by the same macro kinetic equation as follows,but with different values of the kinetic parameter KL under different environments?hot metal/slag?and temperatures.?1-f?ln?1-f?+f=K_L/r₀²?For calcinations in molten slag,KL is 1.60×10^-7m²/s?83×10^-7m)2/s?2.17×10^-7m²/s at 1250??1300? and 1350? respectively.For calcinations in hot metal,KL is 1.78×10^-72/s?2.56×10^-7m²/s?3.16×10^-7m²/s at 1250??1300? and 1350? respectively.