Prediction of ethylene and propylene release during coal pyrolysis with modified CPD model

The well-known CPD model (chemical percolation model for devolatilization) is further developed to simulate typical volatile organic compounds (ethylene and propylene) release during coal pyrolysis. A look-up table of ethylene corresponding to the extent of light gas release is constructed and added to the light gas sub-model. With the updated CPD model, the mass fractions of the released ethylene from the flash pyrolysis experiments in a Currie Point pyrolyzer are successfully predicted for a set of coals under different pyrolysis temperatures. The results suggest that, the predicted ethylene yields are accurate when the coal is located in the vicinity of the reference coal in the interpolation mesh and the secondary reactions are insignificant. The predicted release of ethylene during the pyrolysis of an anthracite coal and a bituminous coal using a tube furnace also compares well with the available experimental data. It reveals that as long as the temperatures of coal/char particles are estimated accurately, the prediction of the ethylene mass fraction can be applied to a wider range of heating rates. In addition, the propylene is estimated based on the time-resolved profiles obtained from an online single-photon ionization time-of-flight mass spectrometry (SPI-TOFMS) and the main pyrolysis products acquired from an offline gas chromatograph/mass spectrometry (GC/MS). Accordingly, the prediction of propylene is carried out. The consistent yields of ethylene and/or propylene at identical pyrolysis temperatures, regardless of coal types, indicate that the evolution of these light gases is insensitive to coal type. When the ratio of the final mass fraction between ethylene and propylene is fixed to be 1.1, the predicted release profiles of these compounds correlate well with the published experimental data, indicating the effectiveness of the modified CPD model.