Effect of Metal Oxides on Combustion Characteristics of Excess Sludge

¹ School of Energy and Power Engineering, Changsha University of Science & Technology, Changsha 410076, PR China
² State Key Laboratory of Utilization of Woody Oil Resource, Hunan Academy of Forestry, Changsha, Hunan 410004, PR China

^* Corresponding author e-mail address: gavinhj@163.com (J Huang)

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.