A study of non-isothermal kinetics of limestone decomposition in air (O2/N2) and oxy-fuel (O2/CO2) atmospheres

Abstract

The non-isothermal experiments of limestone decomposition at multi-heating rates in O2/N2 and O2/CO2 atmospheres were studied using thermogravimetry. The limestone decomposition kinetic model function, kinetic parameters of apparent activation energy (E), and pre-exponential factor (A) were evaluated by Bagchi and Malek method. The results shown that in 20 % O2/80 % N2 atmosphere, the limestone decomposed slowly following the contracting sphere volume model controlled by boundary reaction (spherical symmetry) in two stages, and the E increased by about 50 kJ mol−1 in the second decomposition stage. But in 20 % O2/80 % CO2 atmosphere, the presence of high-concentration CO2 significantly inhibited the limestone decomposition, and made the decomposition process occur at high temperature with a rapid rate; the decomposition kinetics was divided into three stages, the first stage was an accelerated decomposition process following the Mampel Power law model with the exponential law equation, the second stage followed the nth order chemical reaction model as an α–t deceleration process, and the third stage belonged to the random nucleation and nuclei growth model with the Avrami–Erofeev equation. And with the heating rate increasing, the reaction order n showed a slight rise tendency. The E was about 1,245 kJ mol−1 in 20 % O2/80 % CO2 atmosphere, but was only about 175 kJ mol−1 in 20 % O2/80 % N2 atmosphere. The E and A increased markedly in the O2/CO2 atmosphere.