Co-pyrolysis behavior of sewage sludge and coal slurry: Pyrolysis characteristics, interaction mechanisms, and gas emissions

The co-pyrolysis behaviors of sewage sludge (SS) and coal slurry (CS), including pyrolysis characteristics, kinetics, interactions, and gas emissions, were investigated using the thermogravimetric-mass spectrometry method. The interaction mechanism was revealed by investigating the effect of the pretreatment method on the interaction. The results showed that the addition of SS improved the comprehensive pyrolysis performance of CS. Artificial neural networks were applicable for predicting the co-pyrolysis process, with the optimal model being a 3 × 5 × 7 model. The synergistic effect occurs at 410-609 °C, and 50% CS addition resulted in a reduction of the maximum weight loss peak temperature by 12.3 °C, along with a reduction of the apparent activation energy by 19.2 kJ/mol. For the whole co-pyrolysis process, the most significant synergistic effect was exhibited at CS ratios of 50% and 60%. The synergistic effect was mainly caused by SS volatiles-CS char and SS minerals-CS char interactions. Co-pyrolysis promoted the release of CH₃⁺, CH₄, H₂O, and CO₂ but suppressed the release of H₂, NH₃, NO, and SO₂. The releases of NO and SO₂ were 7.3% and 5.8% lower than the theoretical values, respectively. Co-pyrolysis of SS and CS in a mixture of 5:5 or 6:4 is recommended for synergistic effects.