Mathematical modelling of a continuous, direct resistive heating furnace for the regeneration of activated carbon

Abstract

A mathematical model of the steady-state performance of a continuous, direct resistive heating furnace (DRHF), used for regenerating granular activated carbon in gold-recovery circuits, has been developed. This mathematical model can be used as a design tool to predict the axial and radial temperature profiles, as well as the electrical potential and power requirements for a given set of carbon and steam flowrates, electrical current, and furnace dimensions. The validity of the model has been verified on a small-scale (up to about 3 kg/h) DRHF. The temperatures could mostly be predicted to within 20 K, while the electrical potential and power requirements were predicted correctly to within 10%. When the carbon's effective mean specific heat capacity was used as a fitting factor, it was concluded that the thermal decomposition of the carbon contributes about 300 J/(kg K) to the effective specific heat capacity of the sample of carbon used. Furthermore, it was concluded that carbon approaching the inlet is pre-heated by water vapour rising from the furnace, which condenses on the carbon, hence increasing its moisture content above the original moisture content of the carbon fed into the furnace hopper.