Effective diffusivity of oxygen in the ash layer of Huadian oil shale semicoke

doi:10.1007/s11708-020-0674-3

Front. Energy

2021, Vol. 15

Issue (2) : 320-327 https://doi.org/10.1007/s11708-020-0674-3

RESEARCH ARTICLE

Effective diffusivity of oxygen in the ash layer of Huadian oil shale semicoke

Yiqun HUANG¹, Yiran LI¹, Man ZHANG¹, Boyu DENG¹, Hao KONG¹, Junfeng WANG², Junfu LYU¹, Hairui YANG¹(

), Lingmei WANG³(

)

¹. Key Laboratory for Thermal Science and Power Engineering of the Ministry of Education, State Key Laboratory of Power Systems, Department of Energy and Power Engineering, Tsinghua University, Beijing 100084, China
². State Key Laboratory of Efficient and Clean Coal-fired Utility Boilers (Harbin Boiler Co., Ltd.), Harbin 150046, China
³. Department of Automation, Shanxi University, Taiyuan 030006, China

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Abstract

Diffusion of oxygen in the ash layer usually dominated the combustion of oil shale semicoke particles due to the high ash content. Thus, effective diffusivity of oxygen in the ash layer was a crucial parameter worthy of careful investigation. In this paper, the effective diffusivity of oxygen in the ash layer of Huadian oil shale semicoke was measured directly using an improved Wicke-Kallenbach diffusion apparatus. The experimental results showed that higher temperature would lead to a higher effective diffusivity and a thicker ash layer had the negative effect. Especially, the effective diffusivity along the direction perpendicular to bedding planes was much lower than that along the direction parallel to bedding planes. In addition, an effective diffusivity model was developed, which could be used to describe the mass transfer of oxygen in the ash layer of oil shale semicoke.

Keywords oil shale semicoke diffusivity pore structure ash layer

Corresponding Author(s): Hairui YANG,Lingmei WANG

Online First Date: 11 June 2020 Issue Date: 18 June 2021

Cite this article:

Yiqun HUANG,Yiran LI,Man ZHANG, et al. Effective diffusivity of oxygen in the ash layer of Huadian oil shale semicoke[J]. Front. Energy, 2021, 15(2): 320-327.

URL:

https://academic.hep.com.cn/fie/EN/10.1007/s11708-020-0674-3
https://academic.hep.com.cn/fie/EN/Y2021/V15/I2/320

Fig.1 Wicke-Kallenbach diffusion apparatus.

Fig.2 Experimental results of four different gas admission rates (at an ash thickness of 5 mm and a diffusion temperature of 293 K).

Tab.1 Proximate analysis, ultimate analysis, and heat value of Huadian oil shale

Fig.3 Schematic of samples in the direction parallel and perpendicular to bedding planes.

Fig.4 Effective diffusivities in the direction parallel to bedding planes at different gradients of oxygen concentration (at an ash thickness of 10 mm).

Fig.5 Effective diffusivities in the direction parallel to bedding planes at different diffusion temperatures.

Fig.6 Effective diffusivities in the direction parallel to bedding planes at different ash layer thicknesses.

Fig.7 Pore size distributions of ash layers at different thicknesses.

Fig.8 Schematic of oxygen diffusion in ash layer.

Fig.9 Comparison of effective diffusivity in the direction parallel and perpendicular to bedding planes (at a diffusion temperature of 293 K and an ash layer thickness of0.005 m).

Fig.10 SEM photography of ash layer plane.

Fig.11 A diffusion example with two diffusivities.

Fig.12 Experimental results versus model results.

Fig.13 Effective diffusivity of the whole ash layer versus diffusivity at the infinitesimal element (at a diffusion temperature of 1073 K)

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