Abstract
Walnut shell is characterized by high yield, high fixed carbon content, and low ash content. In this paper, the thermodynamic parameters for walnut shell during the carbonization process is investigated, and its carbonization and mechanism are discussed. Then, the optimal carbonization process of walnut shell is proposed. Results demonstrated that the comprehensive characteristic index of pyrolysis first increases and then decreases with the increase of heating rate and reaches the peak at about 10 °C min-1. Note that the carbonization reaction intensifies at this heating rate. The carbonization process of walnut shell is a complex reaction involving multiple steps. It decomposes hemicellulose, cellulose, and lignin in stages, and the activation energy of this process gradually increases. The simulation and experimental analyses showed that the optimal process presents a heating time of 14.8 min, final temperature of 324.7 °C, holding time of 55.5 min, particle size of material of about 2 mm, and optimum carbonization rate of 69.4%.