Pyrolysis and char oxidation characteristics of oil shales and coal in a thermogravimetric analyzer

Abstract

AbstractNon‐isothermal thermogravimetric analysis was carried out on two different oil shales and sub‐bituminous coal in order to evaluate effects of the fuel properties and compare the reaction characteristics. The samples and their chars after the devolatilization were heated up to 900 °C at a constant heating rate of 10 K/min under inert and oxidizing atmospheres, respectively. Experimental results exhibit distinct behaviour between the samples for both pyrolysis and char oxidation processes. Pyrolysis of oil shale occurs in two temperature regimes corresponding to its organic and mineral degradation, and mineral matter plays important roles in production of the residual char at the second pyrolysis stage and its reactivity to the subsequent char oxidation. Kinetic analysis was performed using the global one‐ and multi‐step models with nth order reaction mechanism. Organic devolatilization processes of coal and oil shale are analyzed by three‐ and two‐step models, respectively, however mineral degradation of oil shale and char oxidation are analyzed by a one‐step model. Finally, a reasonable fit to the experimental data can be achieved for all the samples and their chars at different atmospheres.