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Abstract
An improved fragmentation and diffusion (FD) coal pyrolysis model was developed based on the diffusivity correlation for the diffusion in fractal pores. Fitting functions to describe the continuous variation of pore structure during pyrolysis were obtained by fitting experimental data for coal pyrolysis in a drop-tube furnace. With the empirical functions as inputs, the improved FD model was used to simulate the pyrolysis in the drop-tube furnace and the model proved to be reliable. With this model, we found that the physical structure of char affects the diffusion, which then influences the pyrolysis. The effects of the four structural parameters (fractal dimension, porosity, average pore diameter, and specific surface area) are investigated quantitatively.
| = | ideal gas constant ( | |
| = | density (g/cm3) | |
| = | pore fractal dimension | |
| = | accumulated specific pore surface area measured by mercury porosimetry | |
| = | pore radius measured by the mercury porosimetry | |
| = | equivalent pore diameter | |
| = | coal pyrolysis conversion percentage | |
| = | molecular effective collision diameter | |
| = | molecular weight | |
| = | molecular number density (1/m3) | |
| = | specific pore surface area (1/m) | |
| = | mean molecular velocity (m/s) | |
| = | porosity (%) | |
| = | mean free path (m) | |
| = | reaction rate | |
| = | temperature (K) | |
| = | reaction pre-exponential factor (1/s) | |
| = | activation energy (J/mol) | |
| = | mean molecular weight | |
| = | ASTM volatile matter content (%) | |
| = | weight of tar undergoing crosslinking | |
| = | weight of tar undergoing secondary decomposition reaction | |
| = | diffusion coefficient (m2/s) |