Experimental studies of ash film fractions based on measurement of cenospheres geometry in pulverized coal combustion

doi:10.1007/s11708-020-0806-9

Front. Energy

2021, Vol. 15

Issue (1) : 91-98 https://doi.org/10.1007/s11708-020-0806-9

RESEARCH ARTICLE

Experimental studies of ash film fractions based on measurement of cenospheres geometry in pulverized coal combustion

Siqi LIU, Yanqing NIU(

), Liping WEN, Yang LIANG, Bokang YAN, Denghui WANG, Shi’en HUI

State Key Laboratory of Multiphase Flow in Power Engineering, Department of Thermal Engineering, School of Energy and Power Engineering, Xi’an Jiaotong University, Xi’an 710049, China

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Abstract

In pulverized coal particle combustion, part of the ash forms the ash film and exerts an inhibitory influence on combustion by impeding the diffusion of oxygen to the encapsulated char core, while part of the ash diffuses toward the char core. Despite the considerable ash effects on combustion, the fraction of ash film still remains unclear. However, the research of the properties of cenospheres can be an appropriate choice for the fraction determination, being aware that the formation of cenospheres is based on the model of coal particles with the visco-plastic ash film and a solid core. The fraction of ash film X is the ratio of the measuring mass of ash film and the total ash in coal particle. In this paper, the Huangling bituminous coal with different sizes was burnt in a drop-tube furnace at 1273, 1473, and 1673 K with air as oxidizer. A scanning electron microscope (SEM) and cross-section analysis have been used to study the geometry of the collected cenospheres and the effects of combustion parameters on the fraction of ash film. The results show that the ash film fraction increases with increasing temperature and carbon conversion ratio but decreases with larger sizes of coal particles. The high fraction of ash film provides a reasonable explanation for the extinction event at the late burnout stage. The varied values of ash film fractions under different conditions during the dynamic combustion process are necessary for further development of kinetic models.

Keywords ash film fraction cenospheres coal combustion fly ash

Corresponding Author(s): Yanqing NIU

Online First Date: 17 April 2020 Issue Date: 19 March 2021

Cite this article:

Siqi LIU,Yanqing NIU,Liping WEN, et al. Experimental studies of ash film fractions based on measurement of cenospheres geometry in pulverized coal combustion[J]. Front. Energy, 2021, 15(1): 91-98.

URL:

https://academic.hep.com.cn/fie/EN/10.1007/s11708-020-0806-9
https://academic.hep.com.cn/fie/EN/Y2021/V15/I1/91

Fig.1 Cumulative size distributions of sieved coal particles (61–75, 75–90, and 90–125 mm).

Tab.1 Ultimate and proximate analysis of Huangling bituminous^a

Fig.2 Schematic of laboratory-scale experiment system.

Fig.3 Schematic of the cross-section analysis of the cenosphere particle.

Fig.4 SEM image of cenosphere after polishing resin mixture (1673 K, 75–90 mm coal particles, N>95%).

Fig.5 Ash film thickness from coal particles of different sizes as a function of ash cenosphere diameter (N>95%).

Fig.6 Ash film fractions of three coals of different sizes (61–75, 75–90, and 90–125 mm) at 1273 K, 1473 K, and 1673 K.

Fig.7 Ash film fraction of 75–90 mm coal particles at different carbon conversion ratios (85%–90%, 90%–95% and>95%).

Fig.8 Change of ash film with carbon conversion under different combustion conditions.

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