Investigation on the effect of particle size and heating rate on pyrolysis characteristics of a bituminous coal by TG-FTIR

- Mass loss increased with increase of coal particle size during pyrolysis in TGA.
- Effect of coal particle size and heating rate on the characteristic parameters of coal pyrolysis was distinguished.
- Tin, Tmax and Tf displayed the logistic distribution along with heating rate up to 1000 K/min.
- The yields of all the gas species at maximum releasing rate enhanced with increasing the heating rate.
- A mechanism corresponding to metaplast forming was proposed to explain the experimental results reasonably.

In this work, thermal behavior of five different coal particle fractions were investigated using thermogravimetric analyzer (TGA) under various heating rates with the maximum of 1000 K/min. An on-line Fourier Transform Infrared Spectrometry (FTIR) was employed to evaluate the evolution characteristics of the gaseous products. The results showed that the coal particle size remarkably affected the mass loss and the ash amount. The larger the particle size was, the higher mass loss and the more ash could be, which revealed its high pyrolysis reactivity. In addition, with increasing the particle size, the initial devolatilization temperature (Tin) and devolatilization index (Di) increased, whereas, the final devolatilization temperature (Tf) decreased. This phenomenon was explained by a proposed mechanism of the obstacle escaping of volatiles from the interparticles corresponding to forming large block unit of metaplast. The heating rate has significant effect on the performance of devolatilization profiles and gaseous products releasing. Tin, Tmax and Tf displayed the logistic distribution along with heating rate up to 1000 K/min, whereas, Rmax and the heating rate were highly linear correlated with different particle fractions. The enhanced yield at maximum releasing rate for all the gas species were observed with increasing the heating rate. Moreover, the peak of maximum releasing rate on the evolving profiles of gaseous products became narrower and sharper, and releasing time of the gaseous products reduced extremely with increasing the heating rate. These findings can provide fundamental data for practical applications, plant designing, handling, and modeling of integrated coal fluidized bed gasification system as well as other coal fluidized bed pyrolysis/gasification process.