Modeling the evolution of particle morphology during coal devolatilization

The evolution of particle morphology during coal devolatilization has a significant influence on the pyrolysis and the combustion of the resulting char. In the present paper a model is proposed to describe the evolution of particle morphology during coal devolatilization. The chemical percolation devolatilization model is used to describe the devolatilization rate and volatile composition. In particular, the behavior of metaplast is considered to describe the viscosity model. The whole process of the particle morphology evolution was modeled by three stages: the softening stage, the plastic stage, and the resolidifying stage according to coal viscosity. The softening stage and the resolidifying stage are modeled with a volumetric reaction mechanism. The transient swelling of coal particles during the plastic stage is modeled on the basis of a single bubble and a porous shell assumption. The initial bubble formation depends on a characteristic fraction of particle pore volume. Volatile release within the shell diffuses to the bubble and out the particle, allowing modeling of the Formation, growth and rupture of the bubble, and thus the swelling and shrinking of the particle. Literature data covering a wide range of heating rates and coal types are employed in the model development and validation. The comparison of model predictions with experimental observations suggests that the model describes the transient evolution of particle size as well as the final swelling ratio and the final porosity of the resulting char. The model accounts for the effects of heating rate, temperature, and coal type on the evolution of particle morphology.