Finite Element Analysis of Bubble Growth and Particle Swelling during Coal Pyrolysis

This study develops a finite element-based numerical model to analyze the swelling behavior of coal particles during pyrolysis. The model incorporates volatile matter release, gas diffusion, viscoelastic deformation of the coal matrix, and internal bubble pressure to reproduce realistic deformation. Simulations on single coal particles revealed non-uniform swelling, with expansion concentrated in the central region where the matrix is thinner and softer, and suppressed near the particle edges due to higher stiffness. To evaluate the influence of coal properties, the model was applied to various coal types. The results showed clear differences in swelling behavior depending on volatile content and rheological properties. Coals with higher plasticity and volatile yield exhibited earlier and more pronounced expansion, while non-caking coals showed limited swelling and high internal pressure due to their high viscosity. This indicates that both volatile generation characteristics and the temperature-dependent mechanical properties of the coal matrix play key roles in determining swelling behavior. The proposed model provides a useful tool for quantitatively evaluating deformation mechanisms in coal particles and may contribute to the optimization of pore structure in coke manufacturing for ironmaking applications.