An evaluation on rice husks and pulverized coal blends using a drop tube furnace

An evaluation on rice husks and pulverized coal blends using a drop tube furnace

(Parte 2 de 2)

The DTA curves of the unburned char with the BBR of 0%, 50% and 100% are provided in Fig. 8. Basically, the distributions of thermal reactions of the unburned char are similar to that of their parent fuels (Fig. 5). These results elucidate that a relationship, like a fingerprint, between the raw materials and their unburned char exists. However, the endothermic reactions excited at higher heating temperature are relatively violent compared to those of the raw materials. It is not surprising that these characteristics are due to the partial liberation of the volatiles contained in the feeding fuels.

3.5. SEM observations of raw materials and unburned char

Scanningelectronmicroscope(SEM)imagesof theblendedfuels at the BBRs of 0%, 50% and 100% are provided in Figs. 9a, 9b and 9c, respectively, whereas the images of the unburned char corresponding to the preceding BBRs are presented in Figs. 9d, 9e and 9f, respectively. These images were amplified by a factor of 5 K. It is evident that the surface structure of the coal (Fig. 9a) is obviously different from that of the rice husk (Fig. 9c). Specifically, in view of higher volatiles in the biomass, the rice husk particles tend to agglomerate together and the surface is relatively bright. In contrast, the coal particles are markedly dispersed and the surface is darker. For this reason, from the microstructure of the blended fuel (Fig. 9b) one is able to clearly identify the coal and the biomass. Once the coal particles pass through the DTF, the rapid heating causes a lot of debris on the unburned char surface (Fig. 9d). An examination on the unburned char with the BBR of 50% (Fig. 9e) shows that the debris is smaller and brighter which is obviously different from the previous case (Fig. 9d). With the BBR of 100%, the unburned char particles also accumulate together (Fig. 9f). Nevertheless, the particles are smaller and the surface is more wrinkled. Because of this, some volatiles are kept in the unburned char, which results in a relatively significant decrease in weight loss from the TGA (Fig. 6c).

4. Conclusions

For the purpose of recognizing the possibility of biomass to partially replace the pulverized coal used in blast furnaces, a DTF has been employed to simulate the reaction dynamics of the blended fuels in the raceway. The TGA of the blends of the raw materials showed that a three-stage reactionwas exhibited and the correlation between the char yield and the BBR was strongly characterized by a linear relationship. This reveals that the synergistic effects between the coal and the biomass were absent or that the fuels had no interaction. Accordingly, it is anticipated that coal blended with certain amount of rice husks is conducive to gasphase combustion in the raceway, as a consequence of enriched volatiles in the fuel. When the unburned char was examined, the TGA curves indicated the char yield with respect to the BBR follows the relationship of second order polynomial rather than the linear distribution. It indicates that unburned char was significantly characterized by the synergistic effects. Moreover, a relationship of

Fig. 8. Differential thermal analyses of the unburned chars at the biomass blending ratios of (a) 0%, (b) 50% and (c) 100%.

thermal reaction resembling fingerprint between the raw materials and unburned chars was observed. As long as the BBR of the blended fuel was less than 50%, the char yields of the unburned char, with different BBRs, were similar. This implies that the reduction characteristic of the unburned char in the hearth of the blast furnace is hardly affected. The obtained results have provided a useful insight into the blended fuel used in the raceway and the unburned char staying in the bird’s nest.


The authors acknowledge the financial support of the National

Science Council, Taiwan, ROC, under contract NSC 97-2622-E-024- 002-CC3.


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