Reaction kinetics and internal diffusion of Zhundong char gasification with CO<sub>2</sub>

doi:10.1007/s11705-020-1949-2

Front. Chem. Sci. Eng.

2021, Vol. 15

Issue (2) : 373-383 https://doi.org/10.1007/s11705-020-1949-2

RESEARCH ARTICLE

Reaction kinetics and internal diffusion of Zhundong char gasification with CO₂

Yun Liu^1,², Jiangyuan Qu¹, Xuehui Wu¹, Kai Zhang¹(

), Yuan Zhang²(

)

¹. Beijing Key Laboratory of Emission Surveillance and Control for Thermal Power Generation, North China Electric Power University, Beijing 102206, China
². College of Metallurgy & Energy, North China University of Science and Technology, Tangshan 063009, China

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Abstract

Mass transfer usually affects the rate of chemical reactions in coal. The effect of internal diffusion on char gasification with CO₂ in the temperature range from 1123 K to 1273 K was investigated via thermo-gravimetric analysis and assessment of char morphology features. The results revealed that the effect of internal diffusion on the initial reaction rate was more significant with an increase of particle size, due to the concentration gradient of the gasification agent within the solid particles. In the early stage of gasification, the generation of new micropores and the opening of closed pores led to an increase in specific surface area. As the reaction proceeded, the openings were gradually expanded and the specific surface area continued to increase. However, with further reaction, disappearance of edge pores, melting and collapse of the pore structure led to a decrease in specific surface area. The intrinsic activation energy and reaction order based on the nth-order model were 157.67 kJ∙mol⁻¹ and 0.36, respectively. Thus, temperature zones corresponding to chemical reaction and diffusion control were identified. Moreover, the calculated effectiveness factor provided a quantitative estimation of internal diffusion in the initial stage.

Keywords coal char CO₂ gasification internal diffusion pore evolution

Corresponding Author(s): Kai Zhang,Yuan Zhang

Just Accepted Date: 28 June 2020 Online First Date: 30 July 2020 Issue Date: 10 March 2021

Cite this article:

Yun Liu,Jiangyuan Qu,Xuehui Wu, et al. Reaction kinetics and internal diffusion of Zhundong char gasification with CO₂[J]. Front. Chem. Sci. Eng., 2021, 15(2): 373-383.

URL:

https://academic.hep.com.cn/fcse/EN/10.1007/s11705-020-1949-2
https://academic.hep.com.cn/fcse/EN/Y2021/V15/I2/373

Tab.1 Proximate and ultimate analysis of Zhundong coal

Tab.2 Ash analysis of Zhundong coal (ZD coal)????????????????????????????????? (Unit: wt-%)

Tab.3 The average particle size of the samples

Fig.1 The effect of temperature on carbon conversion for ZD-char (<40 mm).

Tab.4 The initial gasification rate of ZD-char

Fig.2 SEM images of non-gasified chars with particle size of (a, b) 425?550 mm, (c, d) 80?106 mm, and (e, f)<40 mm.

Fig.3 SEM images of char samples with particle size of (a?c) 425?550 mm, (d?f) 80?106 mm and (g?i)<40 mm.

Tab.5 The evolution of pore structures of char samples (<40 mm) with different carbon conversion

Tab.6 Thiele modulus and the effectiveness factor for the fine particles (<40 mm).

Fig.4 Thiele modulus of ZD-char with various particle sizes at different temperatures.

Fig.5 Experimental and calculated effectiveness factors of ZD-char with various particle sizes.

Fig.6 Effectiveness factors of different particle sizes at 1273 K (a) h_exp; (b) h_cal.

Fig.7 Illustration of the mechanism of ZD-char gasification with CO₂.

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[1]	Xuantao Wu, Jie Wang. Intrinsic kinetics and external diffusion of catalytic steam gasification of fine coal char particles under pressurized and fluidized conditions[J]. Front. Chem. Sci. Eng., 2019, 13(2): 415-426.

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