The generation of microwave-induced plasma in granular active carbons under fluidised bed conditions

Some of the phenomena associated with the interaction of microwave (MW) radiation with a granular activated carbon (GAC) fluidised bed were studied in a single mode microwave apparatus. The sample heating section incorporated ports for a light measurement device (light dependent resistor, LDR) and camera, and a fluoroptic probe was used for sample temperature measurement. During fluidisation under various MW power regimes, the discharge activity and plasma generation within the carbon bed were quantified using the LDR and images captured. The MW dielectric heating of the carbons was measured with the fluoroptic probe and its relation to the fundamental dielectric parameter, the loss factor, ε″, studied. Factors found to affect the MW heating and plasma generation within the fluidised carbon were the thermal history of the sample and presence of trace amounts of metals, especially potassium. These factors influenced the degree to which a tendency to thermal runaway was observed during MW plasma generation.