Oxy - fuel combustion kinetics and morphology of coal chars obtained in N 2 and CO 2 atmospheres in an entrained flow reactor

The thermal reactivity and kinetics of four coal chars (HVN, UM, SAB and BA) in an oxy-fuel combustion atmosphere (30%O2-70%CO2) were studied using a thermobalance. The coal chars were obtained by devolatilization in an entrained flow reactor (EFR) at 1000 oC for 2.5 s under 100% N2 and CO2 atmospheres. The reactivity tests were carried out by isothermal thermogravimetric analysis at different temperatures in a kinetically controlled regime. Three nth-order representative gas-solid models -the volumetric model (VM), the grain model (GM) and the random pore model (RPM)were employed in order to describe the reactive behaviour of the chars during oxy-fuel combustion. From these models, the kinetic parameters were determined. The RPM model was found to be the best for describing the reactivity of the HVN, UM and BA chars, while VM was the model that best described the reactivity of the SAB char. The reactivities of the chars obtained in N2 and CO2 in an oxy-fuel combustion atmosphere with 30% of oxygen were compared using the kinetic parameters, but no differences were observed between the two devolatilization atmospheres. The apparent volatile yield after the coal devolatilization under CO2 in the EFR was greater than under N2 for all the coals studied. According to the scanning electron microscopy * Corresponding author. Tel.: +34 985 118 975; Fax: +34 985 297 662 E-mail address: [email protected] (F. Rubiera)