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.

Acknowledgements

The authors acknowledge the financial support of the National

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

References

[1] Ariyama T, Sato M, Yamakawa YI, Yamada Y, Suzuki M. Combustion behavior of pulverized coal in tuyere zone of blast furnace and influence of injection lance arrangement on combustibility. ISIJ International 1994;34:476–83.

[2] Wu L, Paterson N, Dugwell DR, Kandiyoti R. Simulation of blast-furnace raceway conditions in a wire-mesh reactor: interference by the reactions of molybdenum mesh and initial results. Energy & Fuels 2006;20:2572–9. [3] Du SW, Chen WH, Lucas J. Performances of pulverized coal injection in blowpipe and tuyere at various operational conditions. Energy Conversion and Management 2007;48:2069–76. [4] Chen WH, Du SW, Yang JH. Volatile release and particle formation characteristics of injected pulverized coal in blast furnace. Energy Conversion and Management 2007;48:2025–3. [5] Chen WH, Lu J. Microphysics of atmospheric carbon dioxide uptake by a cloud droplet containing a solid nucleus. Journal of Geophysical Research - Atmospheres 2003;108:4470–8. [6] Mofarahi M, Khojasteh Y, Khaledi, Farahnak A. Design of CO2 absorption plant for recovery of CO2 from flue gases of gas turbine. Energy 2008;3:1311–9. [7] Mohamadabadi HS, Tichkowsky G, Kumar A. Development of a multi-criteria assessment model for ranking of renewable and non-renewable transportation fuel vehicles. Energy 2009;34:112–25. [8] Hamelinck CN, Faaij APC, Den Uil H, Boerrigter H. Production of FT transportation fuels from biomass; technical options, process analysis and optimisation, and development potential. Energy 2004;29:1743–71. [9] Sami M, Annamalai K, Wooldridge M. Co-firing of coal and biomass fuel blends. Progress in Energy and Combustion Science 2001;27:171–214. [10] Williams RH, Larson ED. Biomass gasifier gas turbine power generating technology. Biomass & Bioenergy 1996;10:149–6. [1] Biagnini E, Lippi F, Petarca L, Tiognotti L. Devolatilization rate of biomasses and coal-biomass blends: an experimental investigation. Fuel 2002;81:1041–50.

Fig. 9. Scanning electron microscope images ( 5 K) of the raw materials (a-c) and unburned chars (d-f) at various biomass blending ratios.

[12] Liu DC, Zhang CL, Mi B, Shen BK, Feng B. Reduction of N O and NO emissions by co-combustion of coal and biomass. Journal of the Institute of Energy 2002;75:81–4. [13] Pan YG, Velo E, Roca X, Manya J, Puigjaner L. Fluidised-bed co-gasification of residualbiomass/poorcoalblendsforfuelgasproduction.Fuel2000;79:1317–26. [14] McLendon TR, Lui AP, Pineault RL, Beer SK, Richardson SW. High-pressure co-gasification of coal and biomass in a fluidized bed. Biomass & Bioenergy 2004;26:377–8. [15] McIlveen-Wright DR, Pinto F, Armesto L, Caballero MA, Aznar MP, Cabanillas A,

Huang Y, Franco C, Gulyurtlu I, McMullan JT. A comparison of circulating fluidised bed combustion and gasification power plant technologies for processing mixtures of coal, biomass and plastic waste. Fuel Processing Technology 2006;87:793–801. [16] Pan YG, Velo E, Puigjaner L. Pyrolysis of a blend of biomass with poor coals.

Fuel 1996;75:412–8. [17] Kastanaki E, Vamvuka D, Grammelis P, Kakaras E. Thermogravimetric studies of the behavior of lignite–biomass blends during devolatilization. Fuel Processing Technology 2002;7-78:159–6. [18] Vuthaluru HB. Thermal behaviour of coal/biomass blends during co-pyrolysis.

Fuel Processing Technology 2003;85:141–5. [19] Vuthaluru HB. Investigations into the pyrolytic behaviour of coal/biomass blends using thermogravimetric analysis. Bioresource Technology 2004;92:187–95. [20] Ishii K. Advanced pulverized coal injection technology and blast furnace operation. Pergamon; 2000.

[21] Smoot LD, Smith PJ. Coal combustion and gasification. New York: Plenum

Press; 1985. [2] Werther J, Saenger M, Hartge EU, Ogada T, Siagi Z. Combustion of agricultural residues. Progress in Energy and Combustion Science 2000;26:1–27. [23] Naredi P, Pisupati SV. Interpretation of char reactivity profiles obtained using a thermogravimetric analyzer. Energy & Fuels 2008;2:317–20. [24] Card JBA, Jones AR. A drop tube furnace study of coal combustion and unburned carbon content using optical techniques. Combustion and Flame 1995;101:539–47. [25] Chen WH, Du SW, Yang H, Wu JS. Formation characteristics of aerosol particles from pulverized coal pyrolysis in high-temperature environments. Journal of Air & Waste Management Association 2008;58:702–10. [26] Meesri C, Moghtaderi B. Lack of synergistic effects in the pyrolytic characteristics of woody biomass/coal blends under low and high heating rate regimes. Biomass & Bioenergy 2002;23:5–6. [27] Caballero JA, Marcilla A, Conesa JA. Thermogravimetric analysis of olive stones with sulphuric acid treatment. Journal of Analytical and Applied Pyrolysis 1997;4:75–8. [28] Helsen L, Van den Bulck E. Kinetics of the low-temperature pyrolysis of chromated copper arsenate-treated wood. Journal of Analytical and Applied Pyrolysis 2000;53:51–79. [29] Antal MJ. Biomass pyrolysis: a review of the literature. Part I – Carbonydrate pyrolysis. Advances in Solar Energy 1983;1:61–11. [30] Mansaray KG, Ghaly AE. Thermal degradation of rice husks in nitrogen atmosphere. Bioresource technology 1998;65:13–20.

(Parte 2 de 2)

Comentários