Co-combustion of pulverized coal and walnut shells in air and oxy-fuel atmospheres: Thermal behavior, synergistic effect and kinetics

Abstract

In this work, the combustion characteristics of pulverized coal, walnut shells, and their blends in the oxy-fuel atmosphere (21% O2/79% CO2) and air atmosphere (21% O2/79% N2) were investigated by the thermogravimetric analyzer (TGA). The interaction between the blends was quantified by the overlap ratio (OR) and the difference between theoretical and experimental weight loss (ΔW). The results showed that the combustion characteristics of walnut shells were better than coal attributed to its higher volatile components, whereas co-combustion of walnut shells with coal could improve the reactivity of coal. The replacement of the air atmosphere with the oxy-fuel atmosphere had a negligible effect on the ignition temperature of the selected materials but generated an increase in the burnout temperature to some extent. The activation energy was calculated by using Kissinger-Akahira-Sunose (KAS) and Flynn-Wall-Ozawa (FWO) methods, and the order of reaction and pre-exponential factor of the selected samples was determined by the master plots method. The results of this study confirmed the feasibility of the co-combustion of walnut shells with coal under the oxy-fuel atmosphere and provided certain theoretical guidance to realize the operation of existing boilers in the oxy-fuel atmosphere.