Insight into the Effects of Inorganic Element Catalysis and Basic Fuel Properties on the Self-Sustained Smoldering Process of Sewage Sludge

Abstract

The objective of this study is to investigate the effects of inorganic element catalysis and basic fuel properties of sewage sludge on pyrolysis kinetics and self-sustained smoldering characteristics. The sludge pyrolysis process was explored by thermogravimetric and iso-conversion methods, and it was found that the pyrolysis process can be divided into two stages, which are mainly determined by the organic and inorganic components of the fuel. The inorganic components (e.g., Na, Fe and Mn) have a significant catalytic effect on the release of volatiles and the decomposition of macromolecules. The smoldering experiment revealed that the smoldering front and the evaporation front propagated at stable but different speeds. Among the five fuels, SS4 has the highest smoldering temperature (1070 °C) and the lowest propagation velocity (0.7 cm/min of smoldering velocity and 0.3 cm/min of evaporation velocity), while the carbon density mainly determines the heat release in the oxidation process, and the inorganic elements play a significant catalytic role at different temperatures. The obtained thermodynamic and smoldering characteristics facilitate the development and optimization of the disposal of sewage sludge, emphasizing the importance of considering feedstock composition.