Statistical Modeling of Constituents in Ash Evolved From Pulverized Coal Combustion

Authors: Esam Jassim

Abstract:

Industries using conventional fossil fuels have an  interest in better understanding the mechanism of particulate  formation during combustion since such is responsible for emission  of undesired inorganic elements that directly impact the atmospheric  pollution level. Fine and ultrafine particulates have tendency to  escape the flue gas cleaning devices to the atmosphere. They also  preferentially collect on surfaces in power systems resulting in  ascending in corrosion inclination, descending in the heat transfer  thermal unit, and severe impact on human health. This adverseness  manifests particularly in the regions of world where coal is the  dominated source of energy for consumption.  This study highlights the behavior of calcium transformation as  mineral grains verses organically associated inorganic components  during pulverized coal combustion. The influence of existing type of  calcium on the coarse, fine and ultrafine mode formation mechanisms  is also presented. The impact of two sub-bituminous coals on particle  size and calcium composition evolution during combustion is to be  assessed. Three mixed blends named Blends 1, 2, and 3 are selected  according to the ration of coal A to coal B by weight. Calcium  percentage in original coal increases as going from Blend 1 to 3.  A mathematical model and a new approach of describing  constituent distribution are proposed. Analysis of experiments of  calcium distribution in ash is also modeled using Poisson distribution.  A novel parameter, called elemental index λ, is introduced as a  measuring factor of element distribution.  Results show that calcium in ash that originally in coal as mineral  grains has index of 17, whereas organically associated calcium  transformed to fly ash shown to be best described when elemental  index λ is 7.  As an alkaline-earth element, calcium is considered the  fundamental element responsible for boiler deficiency since it is the  major player in the mechanism of ash slagging process. The  mechanism of particle size distribution and mineral species of ash  particles are presented using CCSEM and size-segregated ash  characteristics. Conclusions are drawn from the analysis of  pulverized coal ash generated from a utility-scale boiler.

 

Keywords: Calcium transformation, Coal Combustion, Inorganic Element, Poisson distribution.

Digital Object Identifier (DOI): doi.org/10.5281/zenodo.1090886

References:

[1] Qiu, F. Li, C.G. Zheng, "Mineral Transformation during Combustion of Coal Blends,” Int. J. Energy Res., vol.23, 1999, pp. 453-463.
[2] L.L Baxter, "The evolution of mineral particles size distributions during early stages of coal combustion,” Prog. Energy Combust Sci., vol. 16, 1990, pp. 261–266.
[3] WP Linak, CA Miller, WS Seames et al. Proc. Combust. Inst., 29 (2002), pp. 441–447.
[4] W. Seames, "An initial study of the fine fragmentation fly ash particle mode generated during pulverized coal combustion,” Fuel process Technology, vol. 81, pp.109-125, 2003.
[5] R.P. Gupta, L. Yan, S.K. Gupta, T.F. Wall, T. Kiga, and S. Watanabe, "CCSEM analysis of minerals in coal and thermal performance of PC-Fired boilers,” Clean Air, vol. 6, 2005, pp. 157-170.
[6] Z. Ma, F. Iman, P. Lu, R. Sears, L. Kong, A.S. Rokanuzzaman, D.P. McCollor, and S.A. Benson, "A comprehensive slagging and fouling prediction tool for coal-fired boilers and its validation/application,” Fuel Processing Technology, vol. 88, pp.1035–1043, 2007.
[7] E. Raask, "Mineral impurities in coal combustion”. Hemisphere Publishing, Washington, 1985, pp 484.
[8] C. Sheng, and Y. Li, "Experimental study of ash formation during pulverized coal combustion in O2/CO2 mixtures,” Fuel 87, 2008, pp.1297–1305.
[9] L. Yan, "CCSEM analysis of minerals in pulverized coal and ash formation modelling,” PhD thesis, The University of Newcastle, Australia, 2000.
[10] T. Zeng, A.F. Sarofim, and C.L. Senior, "Vaporization of Arsenic, Selenium and Antimony during Coal Combustion,” Combustion and Flame, vol. 126, 2001, pp.1714-1724.