Modeling of dilatation behavior of packed bed of coal during carbonization

The new mathematical model is proposed to estimate the dilatation/contraction behavior and coking pressure of packed bed of coal during carbonization. Volume fractions of gas, liquid and solid phase are determined from coal pyrolysis rate equations and the tar devolatilization is also estimated. We assume that the dilatation of packed bed of coal is caused by impermeability of plastic layer where the tar released from coal mainly exists in the void. The gas released from coal pushes the impermeable plastic layer and then the dilatation pressure is detected. The calculated result using this model is compared with one calculated using the ordinary method where the dilatation of the bed is estimated by true dilatation as a function of heating rate. The model proposed in this study can simulate the decrease of permeability caused by tar release and formation of coking pressure in the plastic layer. The coking pressure becomes large with an increase in the heating rate. On the other hand, the ordinary model predicts very large coking pressure in any heating rate. The proposed model may be a useful tool to estimate the dilatation/contraction behavior of packed bed of coal.