Experimental study of pore diffusion effect on char gasification with CO_2 and steam

摘要

Reactivities of three chars with CO_2 and steam were examined using a Thermogravimetric Analyzer (TGA). Similarities and differences between kinetics of char-CO_2 gasification and char-steam gasification have been discussed. As a result, for both reactions, the measured gasification rate increases with temperature and decreases as the particle size increases. And the initial rate of char-steam gasification is always several times faster than that of char-CO_2 gasification. Moreover, for the char with lower reactivity, the activity of its steam gasification reaction possesses larger difference with that of CO_2 reaction. An nth-order model with the effectiveness factor was used and a characteristic parameter (Tc, which is the temperature in the case of Thiele modulus φ = 3.) was proposed to compare the difference between the pore diffusion effect on steam gasification and CO_2 gasification. The results show that the pore diffusion resistance increases with the gasification temperature and particle size. However, for each sample, Tc of char-steam gasification is always lower than that of char-CO_2 gasification. The pore diffusion effect on char-steam gasification is more significant than that on char-CO_2 gasification. Moreover, the difference between the pore diffusion effect on char-steam gasification and char-CO_2 gasification is larger for the char with lower reactivity.