Synergistic Effect of Alkali Metals in Coal and Introduced CaO during Steam Gasification
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https://doi.org/10.1007/s11630-020-1250-1
Article ID: 1003-2169(2019)00-0000-00
Synergistic Effect of Alkali Metals in Coal and Introduced CaO during Steam Gasification LIU Yang1,2,3, YANG Xinfang1,2, LEI Fulin1,2,3*, XIAO Yunhan1,2,3 1. Key Laboratory of Advanced Energy and Power, Institute of Engineering Thermophysics, Chinese Academy of Sciences, Beijing 100190, China 2. Research Center for Clean Energy and Power, Chinese Academy of Sciences, Lianyungang, Jiangsu 222069, China 3. University of Chinese Academy of Sciences, Beijing 100049, China © Science Press, Institute of Engineering Thermophysics, CAS and Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract: The steam gasification kinetics of Zhundong raw coal and the washed coal by deionized water or hydrochloric acid with/ without addition of CaO were tested by thermogravimetric analyzer (TGA) at medium temperatures (650–800oC). The cation contents of potassium and sodium in samples were determined by Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES). The Brunauer-Emmett-Teller (BET) surface area of the samples was tested by N2 adsorption, and the morphologies of the samples were characterized by scanning electron microscopy (SEM). Experimental results showed that the organic sodium was the main catalyst for the gasification of the pyrolysis char, and the gasification rate of the char could be enhanced further with the introduction of CaO. The inherent alkali metals in coal and the introduced CaO showed a synergistic effect that occurred obviously above 735oC. The char conversion curves with or without CaO were fitted by the modified volumetric model (MVM). The calculated results indicated that the addition of CaO increased the pre-exponential factor obviously, but made little changes on the activation energy. It was proposed that the synergistic effect was resulted from the co-melting of the sodium and CaO, which facilitated the migration of the catalyst ions and the generation of C(O) intermediates for the gasification.
Keywords: Zhundong coal, alkali metals, CaO, synergistic effect, steam gasification
1. Introduction Zhundong coalfield, newly under exploration, is the largest integrated coal basin in Xinjiang, China. It has a large forecasted coal reserve of 390 billion tons [1], which is promising to serve China’s coal demand for almost a century. As a low rank coal, Zhundong coal has ultra-low ash and sulfur contents and high volatiles, which results in the characteristics of high ignition quality and low environmental pollution. Zhundong coal Received: Jan 04, 2019
AE: TONG Huiling
is a potential supply for the production of hydrogen, electricity and gas fuels. However, the high contents of alkali metals, especially sodium, whose mass fraction in ash is usually more than 2%, have the possibility to form low-melting eutectics and can volatilize into gas phase, which consequently induces the serious slagging, contamination and corrosion on boiler water wall [2–4]. It is the high sodium content that restricts the direc
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