Effect of Microstructure and Macro Size of Walnut Shell Chars on Their Electromagnetic Induction Heating Behavior

With increasing global demand for renewable energy, biomass and renewable electricity will be more and more widely applied in chemical processes. A promising direction is heating biochar directly by electromagnetic induction to support their high-temperature reactions, such as calcium carbide synthesis. To clearly understand the fundamental principles in biochar’s induction heating, this study investigates the relations between the physicochemical properties of walnut shell chars prepared at pyrolysis temperatures of 600–1400 °C and their induction heating behavior. The properties of chars include their electrical conductivity and structure parameters characterized by X-ray diffraction (XRD), Raman spectroscopy, electron spin resonance (ESR), ultimate analysis, as well as chars’ geometrical sizes. It is found that the chars prepared at pyrolysis temperatures equal to and higher than 800 °C are semiconductors with electric conductivities of 44–510 S/m. The threshold parameters for XRD, Raman, ESR, and ultimate analysis as well as geometrical size for induction heating are determined.