THERMAL SCIENCE

International Scientific Journal

MECHANISM OF PRIMARY FRAGMENTATION OF COAL IN FLUIDIZED BED

ABSTRACT
In order to lay a foundation of a credible primary fragmentation model, a theoretical analysis of the thermo-mechanical processes in a devolatilizing solid fuel particle was carried out. The devolatilization model comprises heat transfer, chemical processes of generation of gaseous products of combustion (volatiles), volatile transfer, and solid mechanic processes. A spatial and temporal analysis of the stresses within the particle showed that the radial stress is caused primarily by the pressure of generated volatiles. This stress monotonously decreases from the particle center towards the particle surface, without changing its sign. The tangential stress is caused primarily by the thermal shock. Close to the surface, it changes its sign. In the particle cross-section, the radial stress prevails close to the particle center, whilst the tangential stress is dominant in the surface region. At the points where these stresses exceed the particle tensile strength, cracks occur. Cracks extend tangentially close to the surface, and radially close to the center of the particle.
KEYWORDS
PAPER SUBMITTED: 2015-06-03
PAPER REVISED: 2015-12-17
PAPER ACCEPTED: 2015-12-21
PUBLISHED ONLINE: 2016-01-01
DOI REFERENCE: https://doi.org/10.2298/TSCI150603224P
CITATION EXPORT: view in browser or download as text file
THERMAL SCIENCE YEAR 2016, VOLUME 20, ISSUE Supplement 1, PAGES [S125 - S132]
REFERENCES
  1. Agarwal, P.K., et al., Model for devolatilization of coal particles in fluidized beds, Fuel, 63. (1984), 8, pp. 1157-1165, DOI No. dx.doi.org/10.1016/0016-2361(84)90205-9
  2. Pou, J.O., et al., Co-primary thermolysis molecular modeling simulation of lignin and subbituminous coal via a reactive coarse-grained simplification, Journal of Analytical and Applied Pyrolysis, 95. (2012), pp. 101-111, DOI No. dx.doi.org/10.1016/j.jaap.2012.01.013
  3. Solomon, P.R., et al., General model of coal devolatilization, Energy & Fuels, 2. (1988), 4, pp. 405-422, DOI No. 10.1021/ef00010a006
  4. Yu, D., et al., Swelling Behavior of a Chinese Bituminous Coal at Different Pyrolysis Temperatures, Energy & Fuels, 19. (2005), 6, pp. 2488-2494, DOI No. 10.1021/ef0501647
  5. Fletcher, T.H., Time-resolved particle temperature and mass loss measurements of a bituminous coal during devolatilization, Combustion and Flame, 78. (1989), 2, pp. 223-236, DOI No. dx.doi.org/10.1016/0010-2180(89)90127-2
  6. Paprika, M.J., et al., Prediction of Coal Primary Fragmentation and Char Particle Size Distribution in Fluidized Bed, Energy & Fuels, 27. (2013), 9, pp. 5488-5494, DOI No. 10.1021/ef400875q
  7. Komatina, M., et al., Temperatures of Coal Particle During Devolatilization in Fluidized Bed Combustion Reactor, Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 28. (2006), 15, pp. 1387-1396, DOI No. 10.1080/009083190910569
  8. Anthony, D.B., et al., Rapid devolatilization and hydrogasification of bituminous coal, Fuel, 55. (1976), 2, pp. 121-128, DOI No. dx.doi.org/10.1016/0016-2361(76)90008-9
  9. Sasongko, D.,J.F. Stubington, Significant factors affecting devolatilization of fragmenting, non-swelling coals in fluidized bed combustion, Chemical Engineering Science, 51. (1996), 16, pp. 3909-3918, DOI No. 10.1016/0009-2509(96)00242-4
  10. Senneca, O., et al., A semidetailed model of primary fragmentation of coal, Fuel, 104. (2013), 0, pp. 253-261, DOI No. dx.doi.org/10.1016/j.fuel.2012.09.026
  11. Pan, J., et al., Coal strength and Young's modulus related to coal rank, compressional velocity and maceral composition, Journal of Structural Geology, 54. (2013), 0, pp. 129-135, DOI No. dx.doi.org/10.1016/j.jsg.2013.07.008
  12. Viljoen, J., et al., The qualification of coal degradation with the aid of micro-focus computed tomography, South African Journal of Science, 111. (2015), pp. 01-10
  13. Speight, J.G., The Chemistry and Technology of Coal. The Chemistry and Technology of Coal. Boca Raton, USA, 2013.
  14. Sreekanth, M., et al., Stresses in a Cylindrical Wood Particle Undergoing Devolatilization in a Hot Bubbling Fluidized Bed, Energy & Fuels, 22. (2008), 3, pp. 1549-1559, DOI No. 10.1021/ef700658k
  15. Dacombe, P., et al., Combustion-induced fragmentation behavior of isolated coal particles, Fuel, 78. (1999), 15, pp. 1847-1857, DOI No. 10.1016/s0016-2361(99)00076-9
  16. Senneca, O., et al., An experimental study of fragmentation of coals during fast pyrolysis at high temperature and pressure, Fuel, 90. (2011), 9, pp. 2931-2938, DOI No. 10.1016/j.fuel.2011.04.012
  17. Nevalainen, H., et al., Firing of coal and biomass and their mixtures in 50 kW and 12 MW circulating fluidized beds - Phenomenon study and comparison of scales, Fuel, 86. (2007), 14, pp. 2043-2051, DOI No. 10.1016/j.fuel.2007.04.006
  18. Feng, B.,S.K. Bhatia, Percolative Fragmentation of Char Particles during Gasification, Energy & Fuels, 14. (2000), 2, pp. 297-307, DOI No. 10.1021/ef990090x
  19. Senneca, O., et al., A semidetailed model of primary fragmentation of coal, Fuel. (2013), 0, DOI No. 10.1016/j.fuel.2012.09.026

© 2018 Society of Thermal Engineers of Serbia. Published by the Vinča Institute of Nuclear Sciences, Belgrade, Serbia. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International licence