Study on the co-pyrolysis characteristics of sewage sludge and wood powder and kinetic analysis

How to treat and recycle sewage sludge quickly and harmlessly has been widely concerned. In this study, the pyrolysis of sewage sludge, wood powder, and their mixtures in different proportions was carried out in the TGA and fixed-bed reactor. Co-pyrolysis products including char, pyrolytic liquid, and gas composition were evaluated based on different mixtures of sewage sludge and wood powder. The results show that there is a significantly synergistic effect between sewage sludge and wood powder during the co-pyrolysis process, and the strongest synergetic effect of sewage sludge and wood powder appears at the biomass proportion of 60 wt.%. The synergetic effect resulted in an increase in gas yield but a decrease in char yield, which improves the utilization of sludge and the characteristics of pyrolysis products. The gas composition and synergetic effect degree are strongly affected by the wood powder percentages. In addition, the Coats-Redfern integral method was used to calculate the pre-exponential factor and activation energy of sewage sludge, wood powder, and blends. The results show that when the reaction order is 1.5, equation describes the co-pyrolysis process well, so the kinetic mechanism function of co-pyrolysis is F(α) = (1-α)^1.5. In a nutshell, the amount of wood powder has a great influence on co-pyrolysis characteristics and the degree of synergistic effect.