Co-Pyrolysis of CaO with Lignite Powder and Sawdust: Synergistic Effects and Model Characterization of Low-Temperature Convective Drying Kinetics of Municipal Sludge

In order to explore the effects of CaO, lignite dust and sawdust on the drying characteristics of municipal sludge at different concentrations, a three-factor three-level regression experiment was carried out based on the results of thermogravimetric experiment and single factor experiment. By fitting three common mathematical models, the Page model with the highest fitting degree was selected to determine the most suitable mathematical model to describe the municipal sludge drying process. In addition, the Box-Behnken design principle in the response surface method was used to analyze the interaction of three factors on the drying characteristics of municipal sludge. The results of the study show that below 100°C is the optimal drying temperature range for municipal sludge. The results of single factor experiments showed that the order of influence of the three factors on sludge drying time was CaO concentration > sawdust concentration > lignite dust concentration. In the single factor experiment, the optimal process parameters were CaO concentration 3%, lignite powder concentration 7%, and sawdust concentration 7%. In the multi-factor interaction analysis, the interaction between CaO and sawdust had the most significant effect on the reduction of drying time, and the order of influence was as follows: CaO interaction with sawdust > lignite dust interaction with sawdust > CaO interaction with lignite powder. Further analysis showed that the optimal process ratio was 3% CaO concentration and 3% sawdust concentration.