In-situ measurements of high-temperature dielectric properties of municipal solid waste incinerator bottom ash

[EN] Microwave heating is a potential green technology demonstrating many advantages over conventional heating methods. Prior to designing an industrial microwave process, however, a fundamental knowledge of the dielectric properties of the material to be thermally treated is imperative, as these properties determine the response of the material to an applied electromagnetic field. In this study, the fundamental interactions between microwave energy and municipal solid waste incinerator (MSWI) bottom ash (BA) are investigated through in situ complex permittivity measurements. Using an enhanced version of the cavity perturbation method, the dielectric properties were determined from room temperature up to 1100 degrees C at a frequency close to the industrial 2.45 GHz. The results demonstrated that BA is a low-loss microwave absorber up to 320 degrees C, above which microwave flash pyrolysis of the organic matter abruptly enhances the dielectric loss of BA, resulting in a thermal runaway. The addition of water and graphite to BA induces a higher dielectric constant and loss factor. The evolution of the dielectric properties as a function of temperature is correlated to changes in the material as determined by Simultaneous Differential Scanning Calorimetry, Thermogravimetric Analysis and High Temperature X-ray Diffraction. The reported results form a baseline for the assessment of the MSWI BA response under microwave irradiation.