Chars of the single fuels and of their blends, as obtained in the HTWM reactor, were subjected to tests of reactivity and combustion behaviour by TPO analysis in the thermogravimetric apparatus. The results are reported in Table 2 and Figs. 3 and 4.
In particular, the residual weight after combustion is shown in Table 2. Fig. 3 reports the comparison between the combustion profiles of wood char, coal К char and their blend char while Fig. 4 shows the corresponding profiles for cocoa shells and coal K.
Fig. 3. Comparison between TPO profiles of chars of coal K, wood chips and their blend.
TPO tests, not reported here, were also carried out with the uncharred samples. The main considerations that can be drawn from the comparison between TG and DTG profiles of fresh and charred samples are:
a) the combustion profile of coal К char differs from that of the parent because the peak temperature of the char (810 K, Figs. 3 and 4) is shifted 60 К towards higher temperatures and there is the lack of a shoulder (shown by the fresh sample) at about 600 K, attributable to the presence of volatiles.
b) The wood chips char shows one DTG peak at temperature (750 K; Fig. 3) correspondent to that of the higher temperature peak shown by the fresh sample, which also presents a lower temperature peak at 610 K. It is as though the loss of volatiles left the resulting char as reactive as the less reactive part of the fresh sample;
c) The cocoa shells char shows one DTG peak at temperature intermediate (700 K; Fig. 4) with respect to those of the two peak shown by the fresh sample. It is as though the loss of volatiles made the resulting char more reactive than the less reactive part of the fresh sample.
Fig. 4. Comparison between TPO profiles of chars of coal K, coca shells and their blend.
With reference to the charred samples, Fig. 3 shows that the coal К-wood blend char results less reactive than both chars of the blend components. Given the much higher volatile yield of the biomass (Table 2) and the weight ratio of the two components in the blend (10 wt%), most of the blend char derives from coal. Therefore, it seems that the presence of the biomass inhibits coal char combustion. In contrast, the char of the cocoa – coal К blend behaves as though the two components were burned independently (Fig. 4).