| Hesigewula lignite and a mixture of Hesigewula lignite with CaO was studied by thermogravimetric analyzer (TGA) and fixed bed to explore its pyrolysis characteristics, trying to find a new technological process of comprehensive utilization of lignite.We study the effects of heating rates on pyrolysis characteristics of Hesigewula lignite mixed with CaO or not by TGA, and then analysis pyrolysis kinetics using distributed activation energy model (DAEM). The results show that Hesigewula lignite has similar pyrolysis process with typical coal. Pyrolysis process can be divided into degasification (50～250℃), pyrolysis (250～650℃) and degasification again (650～850℃) three stages with the increase of temperature. The characteristic temperature is higher and the solid residue is more slightly when the heating rate is increased. Hesigewula lignite and CaO mixed in difference ratios is analyzed by TGA, it is found that with the increase of the ratio of CaO, the final weight-loss ratio decreases, and the DTG curves show that weight loss peak is higher in the third stage. The pyrolysis kinetics analysis results show that the activation energy increases with convert ratio x, from 62.62kJ/mol to 376.34kJ/mol at convert ratio 0.1 and 0.85. Activation energy distribution is more concentrated after Hesigewula lignite mixed with CaO. Before the conversion ratio of 0.5, the activation energy ranges from 64.11kJ/mol to 156.88kJ/mol, and it is increased at the same conversion ratio. CaO can make the early pyrolysis reactivity of lignite fall. When the conversion ratio is greater than 0.5, the activation energy ranges from 130.01kJ/mol to 161.68kJ/mol, and it is decreased at the same conversion ratio, it means that CaO can increase the reaction rate of the second degassing stage.In the present work, we try to optimize the pyrolysis conditions. The influence of pyrolysis temperature, holding time and gas carrier flow rate on product yields of Hesigewula lignite was investigated by fixed bed pyrolysis experiment under N2 atmosphere, 0.5MPa. We achieved the maximum tar yield 6.60wt% under 50 mL/min of gas carrier,500 ℃,0.5MPa and holding for 15 min, char and water yields are 69.85% and 12.5%. At the same time we investigate co-pyrolysis behavior of Hesigewula lignite mixed with CaO, results show that the char yield is higher than before, water and tar is decreased. Yields of CO, H2, CH4 in pyrolysis gas are significantly increased, CO2 is decreased. We achieved the maximum tar yield 6.20wt% under 50 mL/min of gas carrier,520 ℃,0.5MPa and holding for 15 min for 1:1 mixed of CaO and Hesigewula lignite, char and water yields are 85.3% and 3.8%. Compared with the lignite pyrolysis under the same conditions, tar and water decreased 2.21% and 69.55%, respectively. And the yields of H2, CH4, CO increased from 0.57ml/g, 1.60ml/g and 1.70ml/g to 6.17ml/g,5.74ml/g and 5.10ml/g, respectively. The yield of CO2 decreased from 10.79ml/g to 0.84ml/g.Pyrolysis tar from the optimal condition is isolated by column chromatography, and then analyzed by gas chromatography-mass spectrometry (GC/MS). The results show that pyrolysis tar of 1:1 mixed of CaO and Hesigewula lignite contains less phenolic compounds. The contents of phenol, cresol, xylenol decrease from 5.29%,9.70%,3.14% to 2.53%,5.96%, 2.85%. The total content of aliphatic in tar increases from 15.47% to 20.16%. Polycyclic aromatic hydrocarbons, such as phenanthrene, fluorene, anthracene and their derivatives in tar decrease from 1.32%,1.08%,0.67% to 1.26%,0.88%,0.53%, on the other hand, more light fractions. CaO can significantly improve the quality of Hesigewula lignite pyrolysis tar. |
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