Simulation of the swelling of high-volatile bituminous coal during pyrolysis

In this paper, a model is established to predict the swelling ratio of high-volatile bituminous coal during pyrolysis, based on the assumption that the structure of bubble distribution in the particle at the beginning of the plastic stage is a central bubble surrounded by many surrounding bubbles. The initial number and size of the bubbles when the particles become plastic are calculated by the pressure in the particle. The chemical percolation devolatilization (CPD) model is used to describe pyrolysis. The pyrolysis of eight types of high-volatile bituminous coals is simulated, and the results are compared with experimental results to verify the model. The particle size during pyrolysis increases then decreases during pyrolysis. The model predicts experimentally observed trends in swelling ratio with heating rate; particle swelling during pyrolysis increases with heating rate, up to ∼10⁴ K/s, and then decreases with further increases in heating rate. Predictions of increasing then decreasing swelling with increases in ambient pressure also agree with trends that have been observed experimentally.