(690b) Study on the Migration of Sodium during the Combustion and Gasification of Zhundong Coal

Haixia Zhang^1*, Xiaoyu Zhang^1,2, Yongjie Na¹, Zhiping Zhu¹

¹Institute of
Engineering Thermophysics, Chinese Academy of Sciences, Beijing, China

²University of Chinese
Academy of Sciences, Beijing, China

*Mailing Address: 11 Beisihuanxi Road, Beijing
100190, China

E-mail
of Corresponding Author: zhanghaixia@iet.cn Abstract:

Zhundong coalfield
in Xinjiang, with reserves of 390 billion tons, is the largest integrated coal basin in China. With low mining
costs, good reactivity and great reserves, Zhundong coal can be potentially used
to generate electricity and supply chemical products. However, practical utilization of
Zhundong coal in power plants shown that, the high sodium content in Zhundong
coal induced to agglomeration and erosion influencing safety and efficiency
of the equipment operation, and there is no fundamental solution till now.
Circulating fluidized bed (CFB) gasification is one of the key technologies for
the high efficiency and clean use of coal resources, but the high sodium content
in Zhundong coal would also induce to agglomeration or even to de-fluidization
phenomenon during
gasification process. It has significant research and practical value to study
the migration of sodium during combustion and gasification of Zhundong coal,
and then provide basic data for the design and operation of CFB gasifier with
the utilization of such a cheap but important coal resource.

In this work, the migration of
sodium during combustion and gasification of Zhundong coal was investigated and
the cause of agglomeration phenomenon was also studied. Thermogravimetric
analysis was adopted to analyze the combustion and gasification characteristics
of Zhundong coal. Coal sample was ashed at 575^oC, 815^oC and
900 ^oC, respectively, following the slow ashing process in a muffle
furnace to obtain combustion residual. Gasification residual was obtained with a
horizontal tube furnace at 900 ^oC in CO₂ atmosphere. The
element contents, phase components, morphology and sodium content of the residuals
were characterized with X-ray fluorescence (XRF), X-ray
diffraction (XRD), scanning electron
microscope & energy dispersive spectrometry (SEM-EDS).

The results show that Zhundong
coal has good combustion and gasification reaction activities. The sodium
content decreases with the increase of the ashing temperatures. At 900 ^oC,
the mass contents of combustion and the gasification residuals are almost the
same but the compositions are quite different. The Si
and Fe contents of the gasification residual are much higher than that of the combustion
residual, but the Na content is slightly lower. The S content of the combustion
residual is much higher than that of the gasification residual. On the phase
composition, both of the residuals contain SiO₂ and NaAlSiO₄;
Fe₂O₃ and CaSO₄ shows up in the combustion
residual while Fe₃O₄ and Ca₂SiO₄ in
the gasification residual. NaAlSi₃O₈ is also detected in
the gasification residual. The agglomeration phenomenon is more obvious for the
gasification residual. The sodium-containing compounds seem much easier to form
low temperature eutectic by reacting with oxide, such as SiO₂ and Al₂O₃,
increasing agglomeration phenomenon.

Keywords: Zhundong coal; sodium;
combustion; gasification; agglomeration

Acknowledgements:

This work was
financially supported by the Strategic Priority Research Program of the Chinese
Academy of Sciences (No. XDA07030100) and the National Natural Science
Foundation of China (No. 21306193).