Effect of Metal Oxides on Combustion Characteristics of Excess Sludge

Abstract

In this paper, it was studied that the effects of heating rate and four metal oxide on the combustion characteristics of excess sludge, such as CaO, Fe2O3, MgO and Al2O3, and the combustion kinetic parameters of sludge were obtained based on Coats-Redfern model. This result indicated that the ignition of sludge can be restricted with the increase of heating rate, but it was conducive to burnout, and the increasing about the flammability, stability and comprehensive combustion characteristic index of sludge. The addition of Fe2O3 and Al2O3 could improve the ignition performance of sludge to a certain extent, which was most obvious at the heating rate of 10 and 20 °C/min, respectively. Furthermore, the existence of Fe2O3, MgO and Al2O3 can improve the burnout performance of sludge, represented by MgO. Under the condition of low heating rate, the presence of Fe2O3 and MgO was beneficial to improve the comprehensive combustion characteristics of sludge. According to the distribution of combustion kinetics parameters, it was showed an increasing trend about the activation energy of sludge with the increase of heating rate at the range of 374.88-575.61 °C, which was also unfavorable to the combustion of fixed carbon. At the same heating rate, the activation energy decreased by adding Fe2O3 and Al2O3 at the range of 148.40-374.88 °C, which was beneficial to the release of volatiles and the combustion reaction, while the activation energy at the range of 374.88-575.61 °C decreased after adding CaO, which promoted the combustion of fixed carbon.