Study on pyrolysis behavior of municipal sludge based on TG-FTIR-MS

Sludge pyrolysis, as a new sludge disposal technology, can realize the reduction and resource utilization of municipal sludge. Based on TG-FTIR-MS technology, pyrolysis behaviors such as pyrolysis reaction kinetics, pyrolysis product composition and other pyrolysis behaviors of four common municipal sludges (SD, NJ, CS, TJ) at different pyrolysis rates were investigated in this paper, and the migration and transformation of nitrogen elements in municipal sludge were analyzed. The results showed that the pyrolysis of municipal sludge was mainly divided into three stages: dewatering (below 160 °C), volatile decomposition (160–550 °C), and carbonization stage (550–900 °C). The activation energies of the four sludge pyrolysis stages were 189.75 kJ/mol, 138.13 kJ/mol, 300.76 kJ/mol, and 237.83 kJ/mol, respectively. It was found that the sludge pyrolysis stage followed the stochastic nucleation and subsequent growth mechanism through the study of SD and CS sludge. The pyrolysis gaseous product content was affected by the rate of heating and pyrolysis temperature. Moderate temperatures (400–550 °C) favored complete sludge decomposition. Sludge is more likely to decompose in a narrow temperature range at higher heating rates, and increasing the heating rate accelerates sludge decomposition. The nitrogenous compounds in sludge are mainly pyrrole nitrogen, protein nitrogen, and pyridine nitrogen. During sludge pyrolysis, the nitrogenous compounds decompose and precipitate in the form of heterocyclic nitrogen (pyridine, pyrrole), and release small molecules of nitrogenous compounds (NH₃, HCN, HCNO). The experimental results can provide a reference for the disposal of municipal sludge by pyrolysis.