Effect of Three Different Catalysts (KCl, CaO, and Fe2O3) on the Reactivity and Mechanism of Low-Rank Coal Pyrolysis

The pyrolysis behavior of Huangling coal (HL) was investigated using KCl, CaO, and Fe2O3 as the catalysts. The catalytic pyrolysis characteristics of coal were studied by thermogravimetry, as well as from the yield of the pyrolysis products and gas and tar composition. The catalytic mechanism was discussed in terms of the changes in gas composition and kinetic analysis. The Doyle integral method was employed for investigating the reaction kinetics of the coal catalyst mixture. The general effect of the additive on the reactivity of coal pyrolysis was evaluated using the pyrolysis characteristic index P. The results show that KCl, CaO, and Fe2O3 exhibit a catalytic effect on the pyrolysis of HL. The char and gas yield increased with the addition of catalysts, and the tar yield first increased and then decreased. With the addition of 1.5% of KCl or Fe2O3 catalyst or 0.5% CaO, the best catalytic effect was observed for the pyrolysis of coal. Coal pyrolysis can be divided into two regions: 472–655 °C and 655–800 °C. With the addition of catalysts, the activation energy and pre-exponential factor decreased. Experiments were conducted using the three catalysts, and the pyrolysis characteristics of P were in the order of Fe2O3 > KCl > CaO.