Comprehensive pyrolysis characteristic and kinetic analysis of industrial-sludge and rice straw: Blending and pellet

The amount of industrial sludge (IS) produced in the treatment of industrial wastewater is significant, with high water and ash content, and low calorific value. However, the recovery of energy from IS can be improved through the coordinative processing with biomass. In this study, we explored the comprehensive pyrolysis characteristics of IS, rice straw (RS), and the synergistic effects of blending and pelletization. Additionally, this study investigated the pyrolysis kinetic behavior of IS-RS pellets for the first time. Our findings suggest that both blending and pelletization treatments improved heat and mass transfer characteristics. Pelletization treatment also promotes low-temperature pyrolysis, torrefaction (<553 K), over direct blending. Blending and pelletization contribute to the release of gaseous products at a lower temperature, which improved the inner passage of pellets, leading to CO₂ reduction. Pelletization also hindered the emission of N and S-related gases, while blending facilitated the release of NO at a high heating rate. Moreover, our study found that direct blending treatment had no significant effect on pyrolysis activation energy (E_a) based on Friedman model-free estimation. The first stage of pellet feedstock had an E_a value of 115.05 kJ/mol, while the second stage had an E_a value of 226.50 kJ/mol. Lastly, we applied the compensation effect method to investigate pre-exponential factor ln A(α), and mechanism values (f(α)) were also estimated, along with the list of compensating parameter functions. Our finding could be helpful in the design of sludge thermal treatment.