The differential thermogravimetric (DTG) analysis of the conversion
curve gives the conversion rate variation of the biochar
during the combustion process. Fig. 3 presents the conversion
curves and DTG curves of CS and BS biochars at a heating rate of
10 C/min in a mixture gas of 10% O2 and 90% N2. From Fig. 3, it
was found that the two kinds of the biochars both have a main conversion
stage during their combustion processes. In addition, the
main conversion zone moves to the higher temperature ranges
and the peak temperature increases with the carbonization temperature
rising. The results indicate that the carbonization degree
of the biochar increases and its reactivity decreases as the final
carbonization temperature increases. Hence, a higher carbonization
temperature is disadvantageous to the combustion behaviors
of the biochars.
Fig 3 shows that CS biochar has two minor peaks after the maximum
peak while BS biochar does not have. From Table 1 and 2, it
can be seen that the ash yield of CS is 3.78%, higher than that of BS.
The mineral matters contained in CS are mainly alkali metal-based
compounds which may be decomposed under high temperature.
Therefore, the appearance of the two minor peaks on DTG curves
of CS biochars may be ascribed to the mineral decomposition.