SİRKÜLASYONLU BİR AKIŞKAN YATAKLI YAKICIDA İŞLETME PARAMETRELERİNİN SO2 EMİSYONU ÜZERİNDEKİ ETKİLERİ

Abstract

Çevresel korunma göz önüne alındığında, güç santrallerinde SO2 emisyonunun indirgenmesi ana konulardan biridir. Kömürün sirkülasyonlu akışkan yatak (SAY) yakma teknoloji ile yakılmasının en önemli avantajlarından birisi de genellikle kalsine olmamış kireçtaşı (CaCO3) gibi sorbentlerin eklenmesiyle doğal SO2 tutma kabiliyetidir. Bu teorik çalışmada, sorbent tane çapı, Ca/S mol oranı ve yatak işletme hızı gibi işletme parametrelerinin SO2 emisyonu üzerindeki etkileri; daha önce SAY yakıcılar için geliştirilmiş olan dinamik model kullanılarak tahmin edilmiştir. Modelde reaksiyona girmemiş büzülen tanecik modeli kükürt indirgenmesine adapte edilmiştir. Bu çalışma sonucunda; yatak işletme hızının SO2 emisyonu üzerinde pozitif bir etkiye sahip olduğu, ikincil hava kullanmanın yatak içerisindeki sülfür dağılımı ve konsantresi üzerinde güçlü bir etkiye sahip olduğu ve beslenen kireçtaşının içeriğinin yüksek oranda toz içermesi durumunda yatak içerisinde kükürt indirgemesini arttırdığı görülmüştür.

Keywords

• Sirkülasyonlu akışkan yatak, kömür yanması, modelleme, SO2 emisyonu

EFFECTS OF OPERATIONAL PARAMETERS ON SO2 EMISSION IN A CIRCULATING FLUIDIZED BED COMBUSTOR

Abstract

Reducing SO2 emission from power plants is one of the main issues for the environmental protection. One of the advantages of the CFB combustion technology of coal is in situ SO2 capture by added sorbents, usually uncalcined limestone (CaCO3). In this theoretical study effects of operational parameters such as sorbent particle diameter, Ca/S molar ratio and superficial velocity on SO2 emission have been estimated using a previously developed dynamic 2D model for CFBCs. In the model, the unreacted shrinking core model has been adopted for desulphurization. As a results of this study; it is observed that operational bed velocity has positive effect on SO2 emission. Air-staging strongly influences the concentration and distribution of sulphur compounds in the combustion chamber of fluidized beds. Feeding limestone with high proportion of fines into the combustor causes high sulphur retentions.

Keywords

• Circulating fluidized bed, coal combustion, modeling, SO2 emission

References

1. [1] OZKAN, G., DOGU, G., “Combustion of a high ash and sulfur containing lignite in a pilot circulating fluidized bed combustor and its pollution characteristics”, Chemical Engineering and Processing, 41 (1), 11-15. 2002.
2. [2] REH, L., “Development potentials and research needs in circulating fluidized bed combustion”, China Particuology, 1 (5), 185-200. 2003.
3. [3] BOSOAGA, A., PANOIU, N., MIHAESCU, L., BACKREEDY, R.I., MA, L., POURKASHANIAN M., WILLIAMS, A., “The combustion of pulverised low grade lignite”, Fuel, 85 (10-11), 1591-1598. 2006.
4. [4] ADANEZ, J., GAYÁN, P., GRASA, G., DE DIEGO, L. F., ARMESTO, L., CABANILLAS, A., “Circulating fluidized bed combustion in the turbulent regime: modeling of carbon combustion efficiency and sulfur retention”, Fuel, 80, 1405-1414. 2001.
5. [5] ZHAO, Y., XU, P.Y., FU, D., “Experimental study on simultaneous desulfurization and denitrification based on highly active absorbent”, Journal of Environmental Sciences-China, 18 (2), 281-286. 2006.
6. [6] BARLETTA, D., MARZOCCHELLA, A., SALATINO, P., “Modelling the SO2–limestone reaction under periodically changing oxidizing/reducing conditions: the influence of cycle time on reaction rate”, Chemical Engineering Science, 57, 631–641. 2002.
7. [7] GUNGOR, A., ESKIN, N., “Analysis of environmental benefits of CFB combustors via one-dimensional model”, Chemical Engineering Journal, 131 (1-3), 301-317. 2007.
8. [8] GUNGOR, A., ESKIN, N., “Two dimensional coal combustion modeling of CFB”, International Journal of Thermal Sciences, 47, 157-174. 2008.

9. [9] TARELHO, L.A.C., MATOS, M.A.A., PEREIRA, F.J.M.A., “The influence of operational parameters on SO2 removal by limestone during fluidized bed coal combustion”, Fuel Processing Technology, 86, 1385-1401. 2005.
10. [10] MANOVICA, V., GRUBORB, B., LONCAREVICC, D., “Modeling of inherent SO2 capture in coal particles during combustion in fluidized bed”, Chemical Engineering Science, 61, 1676-1685. 2006.
11. [11] GUNGOR, A., ESKIN, N., “Hydrodynamic modeling of a circulating fluidized bed”, Powder Technology, 172, 1-13. 2007.
12. [12] HORIO, M., Hydrodynamics, in: Grace, J.R., Avidan, A.A., Knowlton, T.M., (Eds.), Circulating Fluidized Beds, Blackie Academic & Professional, London, 1992.
13. [13] MARTENS, F.J.A., Freeboard Phenomena in a Fluidized Bed Coal Combustor, Delft University of Technology, Delft University Press, Netherlands, 1996.
14. [14] WERTHER, J., WEIN, J., “Expansion behavior of gas fluidized beds in the turbulent regime”, AIChE Symposium Series, 301 (90), 31-44. 1994.
15. [15] GREGORY, D.R., LITTLEJOHN, R.F., “A survey of numerical data on the thermal decomposition of coal”, The BCURA Monthly Bulletin, 29 (6), 173-179. 1965.
16. [16] LOISON, R., CHAUVIN, R., “Pyrolyse rapide du charbon”, Chemie et. Industrie, 91, 269-274. 1964.
17. [17] FINE, D.H., SLATER, S.M., SAROFIM, A.F., WILLIAMS, G.C., “Nitrogen in coal as a source of nitrogen oxide emission from furnaces”, Fuel, 53, 120-128. 1974.
18. 18] ARTHUR, J.R., “Reactions between carbon and oxygen,” Trans. Faraday Soc., 47, 164. 1951.
19. [19] RAJAN, R.R., WEN, C.Y., “A comprehensive model for fluidized bed coal combustors”, AIChE Journal, 26, 642-655. 1980.
20. [20] HUA, Y., FLAMANT, G., LU, J., GAUTHIER, D., “Modelling of axial and radial solid segregation in a CFB boiler,” Chemical Engineering and Processing, 43 (8), 971-978. 2003
21. [21] KILPINEN, P., KALLIO, S., KONTTINEN, J., BARISIC, V., “Char-nitrogen oxidation under fluidised bed combustion conditions: single particle studies”, Fuel, 81, 2349-2362. 2002.
22. [22] WINTER, F., WARTHA, C., HOFBAUER, H., “NO and N2O formation during the combustion of wood, straw, malt waste and peat,” Bioresource Technology, 70 (1), 39-49. 1999.
23. [23] WERTHER, J., HARTGE, E.U., LUECKE, K., FEHR, M., AMAND, L.E., LECKNER, B., “New air-staging techniques for co-combustion in fluidized bed combustors,” VGB-Conference Research for Power Plant Technology, 1-27. 2000.
24. [24] TUNG, S.E., WILLIAMS, G.C., “Atmospheric Fluidized Bed Combustion”, Massachusetts Institute of Technology, Cambridge, MA, 1987 .
25. [25] MARSH, D.W., ULRIEHSON, D.L., “Rate and diffusional study of the reaction of calcium oxide with sulfur dioxide”, Chemical Engineering Science, 40, 423–433. 1985.
26. [26] LALVANI, S., PATA, M., COUGHLIN, R.W., “Sulphur removal from coal by electrolysis”, Fuel, 62 (4), 427- 437. 1983.
27. [27] DAM-JOHANSEN, K., HANSEN, P.F.B., OSTERGAARD, K., “High-temperature reaction between sulphur dioxide and limestone-III. A grain-micrograin model and its verification”, Chemical Engineering Science, 46, 847-853. 1991.
28. [28] Laursen, K., Grace, J.R., Lim, C.J., “Enhancement of the sulfur capture capacity of limestones by the addition of Na2CO3 and NaCl”, Environmental Science and Technology, 35(21), 4384-4389. 2001.
29. [29] DUCARNE, E.D., DOLIGNIER, J.C., MARTY, E., MARTIN, G., DELFOSSE, L., “Modelling of gaseous pollutants emissions in circulating fluidized bed combustion of municipal refuse”, Fuel, 77 (13), 1399-1410. 1998.
30. [30] TALUKDAR, J., BASU, P., GREENBLATT, J.H., “Reduction of calcium sulfate in a coal-fired circulating fluidized bed furnace”, Fuel, 75 (9), 1115-112. 1996.
31. [31] LYNGFELT, A., AMAND, L.E., LECKNER, B., “Reversed air staging - a method for reduction of N20 emissions from fluidized bed combustion of coal”, Fuel, 77, 953-959. 1998.
32. [32] FERNANDEZ, M.J., LYNGFELT, A., “Concentration of sulphur compounds in the combustion chamber of a circulating fluidised-bed boiler,” Fuel, 80, 321-326. 2001.