Production of Cenospheres from Coal Fly Ash through Vertical Thermal Flame (VTF) Process


Article Preview

Coal fly ash is a complex mixture of anthropogenic materials produced during the combustion of pulverised coal in coal fired power plants. They pose environmental concerns that lead to air and water pollution. Effort has been done to reduce the production of coal fly ash or to extract potentially valuable products from coal fly ash, such as cenospheres. Cenospheres are light, low density, thin-walled hollow ceramic microsphere with unique properties. Conventional cenosphere production methods involve the separation of cenospheres from coal fly ash. Due to its small quantities in fly ash (1 % wt.), separation process results in low production of cenospheres. In this work, an attempt by applying a vertical thermal flame (VTF) process is done to produce cenospheres from coal fly ash. Particle size of coal fly ash 63 to 90 μm and 90 to 126 μm are selected to undergo the VTF process. Effect of size of precursor, number of passes through the thermal process, density, morphology and particles size of generated spheres are evaluated. The results show that different sizes of coal fly ash and number of passes through the VTF process affect the morphology of obtained spheres and the overall real density. Further optimization of the VTF process design in terms of heat source and the feeding mechanism are required to increase the transformation of coal fly ash to cenospheres.



Edited by:

Mohd Hamdi Abdul Shukor and Hao Gong




W. M. Soh et al., "Production of Cenospheres from Coal Fly Ash through Vertical Thermal Flame (VTF) Process", Materials Science Forum, Vol. 880, pp. 7-10, 2017

Online since:

November 2016




[1] A. Arizmendi-Morquecho, A. Chávez-Valdez and J. Alvarez-Quintana: High temperature thermal barrier coatings from recycled fly ash cenospheres, Applied Thermal Engineering, 48 (2012) 117-121.


[2] J. Ward Inc: The value of coal combustion products: an economic assessment of CCP utilization for the U. S. economy, Washington (DC) American Coal Council, 2nd ed. (2010).

[3] Kolay, K. Prabir, and S. Bhusal: Recovery of hollow spherical particles with two different densities from coal fly ash and their characterization, Fuel, 117 (2014) 118-124.


[4] L. N. Ngu, H. Wu, and D. K. Zhang: Characterization of ash cenospheres in fly ash from Australian power stations, Energy & Fuels Energy Fuels, 21(6) (2007) 3437-3445.


[5] K. Dutta, A. Garg, S. Sangal, B.K. Mishra, P. Vankar and P.K. Rohatgi: A characterization study to ascertain cenosphere content in fly ash, International Conference on Emerging Trends in Mineral Processing and Extractive Metallurgy, New Delhi, (2005).

[6] S. Vassilev, R. Menendez, D. Alvarez, M. Diaz-Somoano, M.R. Martinez-Tarazona: Phase-mineral and chemical composition of coal fly ashes as a basis for their multicomponent utilization. 1. characterization of feed coals and fly ashes, Fuel, 82(14) (2003).


[7] E. Raask: Mineral impurities in coal combustion, Behavior, problems, and remedial measures, Washington, D.C., Hemisphere Pub. Corp. (1985).

[8] A. Chávez-Valdez, A. Arizmendi-Morquecho, G. Vargas, J. M. Almanza, and J. Alvarez-Quintana: Ultra-low thermal conductivity thermal barrier coatings from recycled fly-ash cenospheres, Acta Materialia, 59(6) (2011) 2556-2562.


[9] E. M. Saucedo, Y. M. Perera, and D. Robles: Plasma assisted novel production process of glass-ceramic spheres in the quaternary system CaO–SiO2–Al2O3–MgO, Ceramics International, 38(4) (2012) 3161-3165.


[10] I. Kourti and C. Cheeseman: Properties and microstructure of lightweight aggregate produced from lignite coal fly ash and recycled glass, Resources, Conservation and Recycling, 54 (2010) 769–775.


[11] E. M. Saucedo-Salazar, Y.A. Perera-Mercado, F. R. Rodríguez-Ruiz, and A. Arauza-Villarreal: Production of glass spheres from blast furnace slags by a thermal flame projection process, Ceramics International, 40(1) (2014) 1177-1182.


[12] S. Torey: Coal Ash Utilization: Fly Ash, Bottom Ash, and Slag, Park Ridge, Noyes Data Corp. (1978).