Electrical resistance of gas fluidized natural flake graphite

Resistance and bulk resistivity of three commercial grades of fluidized natural flake graphite were determined with a high-frequency data acquisition system at ambient conditions and low voltage. Resistance was measured for up to 5 h over a wide range of superficial gas velocities up to 7 times the minimum fluidization velocity. Resistivities between 1 and 5 Ω∙m were measured for the two largest flake graphite populations used while fully fluidized. The relationship of resistance as a function of flow rate is influenced by the fluidized bed geometry and the particle population used. Resistance was found to fluctuate at frequencies between 3 and 10 Hz and demonstrate a strong link between physical particle properties, fluid-dynamic properties of the bed and the resistive behaviour of the fluidized flakes. When poor quality or partial fluidization occurs, as evidenced by a low relative pressure drop across the bed at steady state, 100 min or more of data is insufficient to capture the probability distribution. When the bed is well fluidized, 3 min or less are required for a representative sample. To operate a direct ohmic heating electric fluidized bed (DOH-ERB) purification reactor for natural graphite, pseudo-steady resistances are achievable with larger natural flake graphite sizes and at flow rates above the full fluidization velocity. • Electrical resistance and resistivity of fluidized natural flake graphite are analysed. • Power spectral density and probability density of resistance are interpreted. • Bulk resistivity is found to be geometry, gas velocity and particle-type dependent. • Strong link between particle properties, hydrodynamic and electrical behaviour.