Pyrolysis of pre-dried dewatered sewage sludge under different heating rates: Characteristics and kinetics study

The pyrolysis characteristics and kinetics of pre-dried dewatered sewage sludge under different heating rates (10, 20, and 30 °C/min) were investigated by thermogravimetric analyzer-fourier transform infrared analysis (TG-FTIR) and differential scanning calorimetry (DSC), and a heated tubular reactor. The thermal analysis results showed that four weight loss zones (<165, 165–400, 400–600, and >600 °C) were observed in TG curve, and a higher heating rate led to the increase of the maximum devolatilization rate and the higher temperature corresponding to the peak. The activation energy of different heating rate (10, 20, and 30 °C/min) was 70.0, 60.6 and 65.0 kJ/mol, respectively. The FTIR analysis of gaseous products indicated the concentrations of CO₂ and CO increased steadily with the increased heating rate, while the concentration of CH₄ first increased then decreased. Moreover, the yield of gaseous products and bio-oil increased with the increasing of the heating rate. Finally, the surface structure of chars and the chemical properties of bio-oil obtained were characterized using nitrogen adsorption, scanning electron microscopy, elemental analysis and gas chromatography–mass spectrometry. Overall, the results highlighted that pre-dried dewatered sewage sludge can be effectively converted into biofuel and porous material.