Modeling Coal Swelling during Pyrolysis at Elevated Pressure by Using a Single Bubble Model: Validation and Application

Pressurized oxy-coal combustion technologies are attracting more attention of researchers because of their advantages of carbon capture. While the ambient pressure could significantly influence the coal pyrolysis behavior. In this study, Yulin coal was used for the pyrolysis experiment in a pressurized drop tube furnace. Pyrolysis temperature of 1273 K, and pressures of 1, 4, 7, 10 atm were considered. The swelling behavior of produced char was analyzed by the scanning electron microscope (SEM). The char evolution process during pyrolysis at elevated pressure was simulated by a revised single bubble model, in which the volatile releasing rate and yield by residence time can be obtained from the CPD (chemical percolation devolatilization) model. Results show that the revised single bubble model is suitable for predicting the char evolution over a wide range of pressure and heating rate. Optimum pressure is present in the range of 7–15 atm, where the swelling ratio and porosity reach the maximum value. This model can predict the two regimes of coal swelling in varied heating rates, which is more obvious at high pressure. The porosity development by time can also be output, and the variation trends are similar to the swelling ratio.