Mechanism analysis and experimental verification of pore diffusion on coke and coal char gasification with CO2

• Intrinsic gasification rate formulas for coal and coke char from 850 °C to 1000 °C.
• The effectiveness factor with an nth-order model was developed to study the diffusion.
• The experimental effectiveness factor agrees with the calculated result.
• The char with higher reactivity possesses stronger pore diffusion resistance.

CO2 gasification with different coals and a petroleum coke from China were performed in a thermogravimetric analyzer (TGA). Initial gasification rates of these sample chars were measured at different gasification temperatures (850–1300 °C) and four particle sizes (<40, ∼100, ∼250, and ∼500 μm). An nth-order model was used to describe the gasification kinetics. It is found that the measured gasification rate decreases as the particle size increases for three coal chars. For PC char, the gasification rate of size about 250 μm at temperatures of 850–1000 °C is similar to that of <40 μm, whereas the gasification rate of size about 250 μm is obviously different from that of size about 500 μm. The sensitivity of gasification rates to particle sizes for these samples is quite different. The effectiveness factor and the Thiele modulus with an nth-order model were calculated in order to quantify the influence of the pore diffusion resistance on char gasification. The results show that for the char with higher gasification reactivity, the effect of particle size on the char gasification is more prominent and the pore diffusion resistance is stronger. Furthermore, comparisons between experimental effectiveness factors and calculated effectiveness factors were made to confirm the validity of the model used in this study.