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

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.

Graphical abstract

Keywords

oil shale semicoke / diffusivity / pore structure / ash layer

References

[1] Strizhakova Y A, Usova T V. Current trends in the pyrolysis of oil shale: a review. Solid Fuel Chemistry, 2008, 42(4): 197–201

[2] Kok M V. Oil shale: pyrolysis, combustion, and environment: a review. Energy Sources, 2002, 24(2): 135–143

[3] Kuang W, Lu M, Yeboah I, Qian G, Duan X, Yang J, Chen D, Zhou X. A comprehensive kinetics study on non-isothermal pyrolysis of kerogen from green river oil shale. Chemical Engineering Journal, 2019, 377: 120275

[4] Tian Y, Li M, Lai D, Chen Z, Gao S, Xu G. Characteristics of oil shale pyrolysis in a two-stage fluidized bed. Chinese Journal of Chemical Engineering, 2018, 26(2): 407–414

[5] Han X, Kulaots I, Jiang X, Suuberg E. Review of oil shale semicoke and its combustion utilization. Fuel, 2014, 126(12): 143–161

[6] Yang Y, Lu X, Wang Q, Mei L, Song D, Hong Y. Experimental study on combustion of low calorific oil shale semicoke in fluidized bed system. Energy & Fuels, 2016, 30(11): 9882–9890

[7] Qin H, Sun B, Wang Q, Zhou M, Liu H, Li S. Analysis on influence factors of the characteristic of pore structure during combustion of oil shale semi-coke. Proceedings of the CSEE, 2008, 28(35): 14–20 (in Chinese)

[8] Wang X, Wang J, Qian J, Zhu Y. Diffusion effects in the ash layer of the oil shale char combustion. Acta Petrolei Sinica (Petroleum Processing Section), 1987, 3(4): 4–11

[9] Yang Y, Wang Q, Lu X, Li J, Liu Z. Combustion behaviors and pollutant emission characteristics of low calorific oil shale and its semi-coke in a lab-scale fluidized bed combustor. Applied Energy, 2018, 211: 631–638

[10] Mu M, Han X, Chen B, Jiang X. Oxidation characteristics of the semicoke from the retorting of oil shale and wheat straw blends in different atmospheres. Oil Shale, 2019, 36(1): 43–61

[11] Yörük C R, Meriste T, Sener S, Kuusik R, Trikkel A. Thermogravimetric analysis and process simulation of oxy-fuel combustion of blended fuels including oil shale, semicoke, and biomass. International Journal of Energy Research, 2018, 42(6): 2213–2224

[12] Wang P, Wang C, Du Y, Feng Q, Wang Z, Yao W, Liu J, Zhang J, Che D. Experiments and simulation on co-combustion of semi-coke and coal in a full-scale tangentially fired utility boiler. Energy & Fuels, 2019, 33(4): 3012–3027

[13] Wang J, Wang X. A study of the combustion reaction model of oil shale particles. Acta Petrolei Sinica (Petroleum Processing Section), 1987, 3(3): 1–9

[14] Huang Y, Zhang M, Lyu J, Yang H. Modeling study of combustion process of oil shale semicoke in a circulating fluidized bed boiler. Carbon Resources Conversion, 2018, 1(3): 273–278

[15] Han X, Jiang X, Yan J, Liu J. Effects of retorting factors on combustion properties of shale char. 2. porestructure. Energy & Fuels, 2011, 25(1): 97–102

[16] Bai J, Wang Q, Jiao G. Study on the pore structure of oil shale during low-temperature pyrolysis. Energy Procedia, 2012, 17(1): 1689–1696

[17] Tiwari P, Deo M, Lin C L, Miller J D. Characterization of oil shale pore structure before and after pyrolysis by using X-ray micro CT. Fuel, 2013, 107(9): 547–554

[18] Sun W, Chen S, Xu M, Wei Y, Fan T, Guo J. The diffusion of molecules inside porous materials with bidisperse pore structures. Chemical Engineering Journal, 2019, 365: 201–219

[19] Le Blévec J M, Barthel E, Briens C. Measurement of volatile diffusivity in polymer particles. Chemical Engineering & Processing Process Intensification, 2000, 39(4): 315–322

[20] Zheng Y, Wang Q, Yang C, Qiu T. Experimental study on mass transport mechanism in poly (styrene-co-divinylbenzene) microspheres with hierarchical pore structure. Chemical Engineering and Processing, 2019, 139: 183–192

[21] Wheeler A. Reaction rates and selectivity in catalyst pores. Advances in Catalysis, 1951, 3(6): 249–327

[22] Mota O D S, Campos J B L. Combustion of coke with high ash content in fluidised beds. Chemical Engineering Science, 1995, 50(3): 433–439

[23] Laurendeau N M. Heterogeneous kinetics of coal char gasification and combustion. Progress in Energy and Combustion Science, 1978, 4(4): 221–270

[24] Sun J K, Hurt R H. Mechanisms of extinction and near-extinction in pulverized solid fuel combustion. Proceedings of the Combustion Institute, 2000, 28(2): 2205–2213

[25] Wakao N, Smith J M. Diffusion in catalyst pellets. Chemical Engineering Science, 1962, 17(11): 825–834

[26] Johnson M F L, Stewart W E. Pore structure and gaseous diffusion in solid catalysts. Journal of Catalysis, 1965, 4(2): 248–252

[27] Fu W B, Zhang B L. Experimental determination of the equivalent mass diffusivity for a porous coal-ash particle. Journal of Combustionence & Technology, 1995, 101(3): 371–377 (in Chinese)

[28] Yan J H, Ni M J, Zhang H T, Cen K F. Gas diffsuion through the ash layer of coal particle. Journal of Engineering Thermophysics, 1994, 15(3): 341–344 (in Chinese)

[29] Liu J, Yan J, Han X, Jiang X. Study on the anisotropy of mass transfer for oxygen in the ash layer of shale char particles. Energy & Fuels, 2010, 24(6): 3488–3497

[30] Yang Y, Lu X, Wang Q, Song D, Chen Y, Hong Y. Study on the anisotropy of mass transfer for oxygen in the ash layer of extremely low calorific oil shale semi-coke. Applied Thermal Engineering, 2018, 128: 1494–1501

[31] Wicke E, Kallenbach R. The surface diffusion of carbon dioxide in active carbons. Colloid Journal, 1941, 97(2): 135–151 (in German)

[32] Cao L, He R. Gas diffusion in fractal porous media. Combustion Science and Technology, 2010, 182(7): 822–841

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