Abstract
Demand for battery-grade graphite, used as anode material in electric vehicle batteries, is expected to increase tenfold in the coming decades. Mined graphite must be purified and transformed before being used in batteries. An ambient-temperature investigation of Canadian natural flake graphite fluidization properties was undertaken to better understand the fluid dynamics of electric fluidized beds for thermochemical purification.
Three graphite particle populations (jumbo, large and medium), obtained from a floatation separation process, were characterized by various particle size analysis methods. Sauter mean diameters were measured for the flakes by microscopic image analysis as 114, 76 and 56 μm, and by sieve analysis as 93, 57 and 31 μm respectively. Sauter mean diameters of the flake graphite samples were obtained by fitting the Ergun equation for operation in a fixed bed. Characteristic diameters were adequately bounded by the image and sieve analysis. Gas channeling occurred near minimum fluidization but disappeared with increasing gas velocity. Jumbo flake graphite experienced smoother fluidization, likely due to less particle-particle cohesion, whereas large and medium flake graphite did not completely fluidize until 2-3 times the minimum fluidization velocity. A change in cross-sectional area of the fluidized bed due to the presence of an electrode was shown to affect the fluidization by affecting the local gas velocity, without affecting fluidization behavior.