基于分布活化能模型法的农林生物质热解动力学对比研究

Comparative study on pyrolysis kinetics of agroforestry biomass based on distributed activation energy model method

  • 摘要: 采用热重质谱(TG-MS)联用技术,考察杏壳、小麦秸秆与杨树木屑等典型农林生物质的热解行为及动力学。结果表明,组分差异使得三种生物质在主要反应区间内(200–450 ℃)表现出不同的特征。采用等转化率法计算发现,杏壳平均活化能为188.22 kJ/mol,秸秆平均活化能为220.77 kJ/mol,木屑平均活化能为175.87 kJ/mol。利用分布活化能模型(DAEM)法计算生物质中各组分的平均活化能,发现三种生物质中存在平均活化能较高的第四组分(杏壳297.44 kJ/mol、秸秆284.35 kJ/mol和木屑309.96 kJ/mol),而半纤维素与纤维素呈现“秸秆<杏壳<木屑”规律。各类动力学计算方法能够互为补充,等转化率方法的整体计算结果与单组分分布活化能模型法结果接近,方法更简便,而分布活化能模型法可以求得原料不同组分的动力学参数,弥补等转化率法的不足,综合使用可以形成对热解反应更为全面的认识。

     

    Abstract: Pyrolysis behavior and kinetics of three typical agroforestry biomasses including apricot shell, wheat straw and poplar sawdust were investigated by thermogravimetric mass spectrometry (TG-MS). The results show that the differences of the main components make the three biomasses exhibit different characteristics in the main reaction range (200–450 ℃). It is found that the average activation energy of apricot shell, straw and sawdust is 188.22, 220.77, and 175.87 kJ/mol, respectively based on the typical isoconversional methods. The average activation energy of each component in biomass was calculated by the distributed activation energy model (DAEM) method, indicating that there is a fourth component with high average activation energy in biomass (297.44 kJ/mol for apricot shell, 284.35 kJ/mol for straw and 309.96 kJ/mol for sawdust). The activation energy of hemicellulose and cellulose shows an increasing order of straw < apricot shell < sawdust. The two kinds of kinetics methods are complementary to each other. The overall calculation results by the isoconversional method are close to those by the single-component distributed activation energy model method, but the isoconversional method is simpler; while the distributed activation energy model method can be used to obtain the kinetic parameters of different components of raw materials, which makes up for the deficiency of the isoconversional method. A combined use of the two methods can form a more comprehensive understanding of the pyrolysis reaction.

     

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