Effects of CaO addition on the reactivity and reaction kinetics of coke

Abstract

ABSTRACTIn recent years, researches have shown that highly reactive coke for blast furnace ironmaking not only reduces fuel ratio but also reduces carbon emissions. Therefore, the research on developing high reactivity coke has received unprecedented attention. In this work, CaO was added into coals with different degrees of metamorphism to caking coke to study the effect of CaO amount on the non-isothermal gasification reaction behavior of coke. Results showed that the reactivity is significantly improved as the mass of added calcium oxide accounting for less than 0.4% of the dry coal mass. However, CaO exerted little effect on the micro-strength and structural strength of coke. The analysis of Mercury intrusion porosimetry of coke samples demonstrates that the addition of CaO increased the porosity of coke, resulting in the contact area with CO2, leading further to an increase in coke reactivity. At different heating rates, as the amount of CaO added increased, both the initial reaction temperature and the corresponding temperature of the maximum reaction rate of the gasification from CO2 decreased little by little. The addition of CaO was increased from 0% to 0.6%, the activation energy of the reaction was decreased by 16.41 kJ/mol. The kinetic model of the gasification of coke by CO2 conforms to the unreacted shrinking core model. The reaction mechanism function is converted from f(α) = 3(1-α)2/3 to f(α) = 2(1-α)1/2 (α means carbon conversion ratio), indicating that the addition of CaO accelerates the dissolution rate of coke by CO2.