The main advantage of carbon material treatment in electro-thermal furnaces with fluidized bed [EFFB] at 2000–3000C is that they allow producing graphite of high chemical purity, which is especially important in manufacture of ion-lithium batteries. The team conducted extensive research into hydraulic and heat modes of such units and developed a methodology for their design based on the concept of increase in electric resistance with fluidization. The choice of the working space configuration and the operation mode of EFFB are largely determined by the specific electrical resistance [SER] of the fluidized bed. This parameter is a complex function of a number of factors: fluidization character, uniformity of the bed and the temperature, nature and size of the material fractions, current density and furnace atmosphere composition. It is vital to take into account relationships between SER, working temperature T and current density i, which eventually define electrothermal mode of the unit operation. Thus, if graphite size is d = 130μm within temperature range T = 0–2500C and current density i = 0,004–1.0 A/cm2, SER varies in reverse proportion to these parameters Statistic processing of the experimental data allowed to obtain regressive function SER = f (i, t), which we used as the basis of mathematic modeling, heat balance calculation and predicting transitory and operation modes of EFFB with 10kg/hour productivity:

Resulting volt-ampere characteristics (VACs) of the furnace have maximum values at constant temperature (T = const) which is explained by the non-linear character of the SER function. There exists a technological temperature limit of EFFB responsible for its stable operation. The furnace operation beyond the stability margin depends on the power source characteristics which may cause a sharp power drop or a shorting. The VAC characteristics are determined by the type of material, geometry of the furnace working space, electrode diameter, active zone height, the gap between the electrode and the lining, design of heat insulation and the cooling system. Taking these parameters into consideration, it is possible to conduct a preliminary analysis of the unit stable operation modes as early as during the design stage.

Volume Subject Area:
14th International Symposium on Gas-Solid Flows: Dedicated to the Memory of Professor Clayton T. Crowe
Topics:
Modeling, Temperature, Furnaces, Current density, Design, Heat, Electrodes, Fluidization, Fluidized beds, Graphite, Amperes, Carbon, Cooling systems, Electrical resistance, Electrical resistivity, Geometry, Insulation, Linings (Textiles), Lithium, Stability, Teams
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