THERMAL SCIENCE

International Scientific Journal

NOVEL FRAGMENTATION MODEL FOR PULVERIZED COAL PARTICLES GASIFICATION IN LOW TEMPERATURE AIR THERMAL PLASMA

ABSTRACT
New system for start-up and flame support based on coal gasification by low temperature air thermal plasma is planned to supplement current heavy oil system in Serbian thermal power plants in order to decrease air pollutions emission and operational costs. Locally introduced plasma thermal energy heats up and ignites entrained coal particles, thus starting chain process which releases heat energy from gasified coal particles inside burner channel. Important stages during particle combustion, such as particle devolatilisation and char combustion, are described with satisfying accuracy in existing commercial CFD codes that are extensively used as powerful tool for pulverized coal combustion and gasification modeling. However, during plasma coal gasification, high plasma temperature induces strong thermal stresses inside interacting coal particles. These stresses lead to "thermal shock" and extensive particle fragmentation during which coal particles with initial size of 50-100 μm disintegrate into fragments of at most 5-10 μm. This intensifies volatile release by a factor 3-4 and substantially accelerates the oxidation of combustible matter. Particle fragmentation, due to its small size and thus limited influence on combustion process is commonly neglected in modelling. The main focus of this work is to suggest novel approach to pulverized coal gasification under high temperature conditions and to implement it into commercial comprehensive code ANSYS FLUENT 14.0. Proposed model was validated against experimental data obtained in newly built pilot scale D.C plasma burner test facility. Newly developed model showed very good agreement with experimental results with relative error less than 10%, while the standard built-in gasification model had error up to 25%.
KEYWORDS
PAPER SUBMITTED: 2015-12-22
PAPER REVISED: 2016-01-09
PAPER ACCEPTED: 2016-01-11
PUBLISHED ONLINE: 2016-01-30
DOI REFERENCE: https://doi.org/10.2298/TSCI151222015J
CITATION EXPORT: view in browser or download as text file
THERMAL SCIENCE YEAR 2016, VOLUME 20, ISSUE Supplement 1, PAGES [S207 - S221]
REFERENCES
  1. D. Ivezić et al, The draft of the Energy Development Strategy for the period until 2025 with forecasts until 2030, Public documents of Ministry of Energy and Mining of the Republic of Serbia, 2012
  2. D. Cvetinović, P. Stefanović, Z. Marković, V. Bakić, V. Turanjanin, M. Jovanović and B. Vučićević: GHG (Greenhouse Gases) emission inventory and mitigation measures for public district heating plants in the Republic of Serbia, Energy, Volume 57, (2013), pp. 788-795; DOI:10.1016/j.energy.2012.09.063
  3. R. Jovanović, B. Swiatkowski, D. Cvetinović, P. Stefanović, Z. Marković and Z. Pavlović: Turbulent Two‐Phase Flow Modeling of Air‐Coal Mixture Channels with Single Blade Turbulators, American Institute of Physics - AIP Conf. Proc. 936, (2007), pp. 300-303; DOI:10.1063/1.2790135
  4. A. Williams, R. Backreedy, R. Habib, J.M. Jones and M. Pourkashanian, Modelling coal combustion: the current position. Fuel, Volume 81, Issue 5 (2002), pp. 605-618; DOI:10.1016/S0016-2361(01)00158-2
  5. Z. Jankoski, Improvement of Coal Combustion Efficiency and Decrease of Harmful Emission Under the Influence of Plasma - Modelling. 31st EPS Conference on Plasma Phys. London, 28 June - 2 July 2004 ECA Vol.28G, P-4.063 (2004)
  6. M. A. Gorokhovski et al, Enhancement of pulverized coal combustion by plasma technology, Combustion Science and Technology, Volume 179, Issue 10 (2007), pp. 2065-2090; DOI:10.1080/00102200701386115
  7. A. S. Askarova et al, Plasma-Supported Coal Combustion in Boiler Furnace. IEEE Transactions on plasma science, Volume 35, Issue 6 (2007), pp. 1607-1616; DOI:10.1109/TPS.2007.910142
  8. ANSYS, Inc. ANSYS FLUENT 14.0 theory guide release 13.0; 2011.
  9. R. Jovanović, D. Cvetinović, M. Erić, B. Rašuo and M. Adžić, Sensitivity analysis of different kinetic factors for numerical modeling of Serbian lignite devolatilization process, International Journal of Heat and Mass Transfer, Volume 72, May 2014, Pages 489-500; DOI:10.1016/j.ijheatmasstransfer.2014.01.036
  10. W. P. Jones and R. P. Lindstedt, Global reaction schemes for hydrocarbon combustion. Combustion and Flames, 73, Issue 3 (1988), pp. 233-249; DOI:10.1016/0010-2180(88)90021-1
  11. C. K. Westbrook and F. L. Dryer, Simplified reaction-mechanisms for the oxidation of hydrocarbon fuels in flames. Combustion Science and Technology, Volume 27, Issue 1-2 (1981), pp. 31-43; DOI:10.1080/00102208108946970
  12. M. Field, Rate of combustion of size-graded fractions of char from a low-rank coal between 1200 K and 2000 K. Combustion and Flame, 13, Issue 3 (1969), pp. 237-252; DOI:10.1016/0010-2180(69)90002-9
  13. D. Smoot and D. Pratt, Pulverised-coal Combustion and Gasification Theory and Applications for Continuous Flow Processes. Plenum Press, New York, USA, 1979; DOI: 10.1007/978-1- 4757-1696-2
  14. N. Syred, K. Kurniawan, T. Griffiths, T. Gralton and R. Ray, Development of fragmentation models for solid fuel combustion and gasification as subroutines for inclusion in CFD codes. Fuel, 86, Issue 14 (2007), pp. 2221-2231; DOI:10.1016/j.fuel.2007.05.060
  15. R. Mitchell and A. Akanetuk, The impact of fragmentation on char combustion during pulverized coal combustion. Symposium (International) on Combustion, Volume 26, Issue 2, (1996), pp. 3137-3144; DOI:10.1016/S0082-0784(96)80158-5
  16. B. Kreutzkam, C. Wieland and H. Spliethoff, Improved numerical prediction of ash formation and deposition using a novel developed char fragmentation model. Fuel, 98 (2012), pp. 103-110; DOI:10.1016/j.fuel.2012.02.056
  17. V. E. Messerle and A. B. Ustimenko, Solid Fuel Plasma Gasification, In Book: Advanced Combustion and Aerothermal Technologies, Springer Netherlands, (2007), pp 141-156; DOI: 10.1007/978-1-4020-6515-6_12

© 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