Effect of reaction atmosphere on the products of slow pyrolysis of coals

- Physicochemical and combustibility of char and coals depend of reaction atmosphere.
- Study of the effects of reaction atmosphere on the products of pyrolysis.
- Changes coal structures during pyrolysis are critical in performance oxy-combustion.

Slow pyrolysis of semianthracite (SA) and high volatile bituminous C (HVBC) coals was performed under two reaction atmospheres (CO2 and N2) and three different particle size distributions. It was found that the physicochemical properties of a char and its respective combustibility depend significantly on the reaction atmosphere under which it was produced. For SA char particles larger than 0.7 mm, the BET surface area increases when the atmosphere is enriched in CO2 due to intraparticle side reactions, differences in the thermal-diffusive properties of N2 and CO2, and the reactive effects of the latter. When particle size ​​decreases below 45 μm, no mesoporous surface area developed with either atmosphere. The combustibility of char formed in CO2 was higher than in N2; furthermore, the pore size distribution (PSD) is different in both environments. ATR-FTIR spectrometry indicates that char formed under N2 is more aromatic. Additionally, FE-SEM visualization showed the occurrence of softening more evident in N2 than in CO2; however the char obtained in CO2 looked as if it had lost more material, which agrees with other experiments showing lower elemental and fixed carbon contents for this condition.