Spectroscopic Analysis of Products from Low-Rank Coal Microwave Pyrolysis: Effect of Reaction Atmosphere
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Journal of Applied Spectroscopy, Vol. 87, No. 4, September, 2020 (Russian Original Vol. 87, No. 4, July–August, 2020)
SPECTROSCOPIC ANALYSIS OF PRODUCTS FROM LOW-RANK COAL MICROWAVE PYROLYSIS: EFFECT OF REACTION ATMOSPHERE J. Zhou,a,c L. Wu,b* K. Liang,a J. Zhou,a Q. Zhang,a,c Y. Song,b,c Y. Tian,a,c and X. Lanc
UDC 543.42
The pyrolysis of low-rank coal is considered as the optimal method of realizing clean and efficient production of blue coke, tar, and gas. The experiments of low-rank coal microwave pyrolysis under CO2, CH4, H2, and circulating gas (CG) are studied in a custom-designed microwave oven to clearly clarify the effects of reaction atmospheres on pyrolysis temperature, products yields, and spectroscopic characteristics of pyrolysis products by the analysis techniques of FT-IR and GC-MS. The results show that among four pyrolysis atmospheres, the temperature-rise rate and final pyrolysis temperature under H2 atmosphere are both highest, taking only 5.6 min to arrive at 750oC, and the final temperature is greater than 950oC. The liquid yields under CO2, CH4, H2, and CG atmospheres are 21.8, 24.4, 28.2, and 26.8 wt.%, respectively. The contents of –OH, aromatic ring C=C double bond, and –C=O in the solid product under CH4 atmosphere are highest, possibly because of the thermal polycondensation and the secondary degassing of the solid product. The hydrogenation of H free radicals dissociated from "rich hydrogen" gas results in an improvement in the alkane content and a decrease in the aromatic hydrocarbon content in tar, which is confirmed by the change in oxygen content in the solid product. The hydrogenation technique of circulating coal gas on low-rank coal microwave pyrolysis is economical, energy-efficient, and feasible, which is helpful in the development of coal processing technologies. Keywords: microwave pyrolysis, reaction atmosphere, spectroscopic analysis, tar, low-rank coal. Introduction. With the development of electromagnetic theory and technology, microwave technology is not only applied in industrial production and daily life but also widely used in multidisciplinary fields of studies [1–4]. Among these researches, microwave technology-assisted thermal decomposition of solid fossil fuels is concerned especially with coal, which improves the temperature-rising rate of the pyrolysis reaction to enhance the pyrolysis efficiency, including improvement of yield and quality of tar and coal gas [5]. It is necessary for China to develop coal microwave pyrolysis technology, which is one of the advanced methods of coal treatment. Not all types of coal are suitable for pyrolysis; only low-rank coals that are rich in organic matter can benefit from pyrolysis. According to the BP statistical review of world energy [6], the total proven coal reserves of China comprise 138.819 billion tons at the end of 2017, and more than 55% of the coal reserves is low-rank coal. The other question refers to energy safety. The crude oil dependency of China has already broken through 70% in 2018 [7], which is a chall
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