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芦苇秆热解特性及动力学分析

Pyrolysis Characteristics and Kinetic Analysis of Phragmites australis Stalk

  • 摘要: 为了充分利用芦苇秆生物质能源,以不同升温速率对芦苇秆进行热重实验,分别运用Coats-Redfern(CR)法、Flynn-Wall-Ozawa(FWO)法、Kissinger-Akahira-Sunose(KAS)法计算芦苇秆热解动力学参数,并利用主函数图法确定反应机理和动力学。结果表明:芦苇秆热解可分为4个阶段,其中190~400℃为主要热解阶段。在此阶段,将3种方法计算所得转化率(α)与实验数据进行对比,发现当温度大于250℃时,Coats-Redfern法计算值与实验数据偏差较大,而Flynn-Wall-Ozawa法与Kissinger-Akahira-Sunose法在整个阶段内吻合度较高。由主函数图法可知芦苇秆热解最佳反应机理为随机成核,反应级数为2。对比残差平方和发现,Kissinger-Akahira-Sunose法相比于Flynn-Wall-Ozawa法更适合计算芦苇秆热解动力学参数,计算的表观活化能随转化率的增大呈先增大后减小的趋势,并在转化率为50%时达到最大值286.9 kJ/mol。

     

    Abstract: In order to make full use of the Phragmites australis as biomass energy, pyrolysis test for Phragmites australis stalk was performed at different heating rates. The kinetic parameters of Phragmites australis pyrolysis were calculated by Coats-Redfern(CR) method, Flynn-Wall-Ozawa(FWO) method and Kissinger-Akahira-Sunose(KAS) method. The results showed that the pyrolysis of Phragmites australis stalk could be divided into four stages, of which the stage of 190-400℃ was the main pyrolysis stage. At this stage, comparing the conversion rate(α)calculated from the three methods with the experimental data, it was found that the deviation between the calculated values of the Coats-Redfern method and the experimental data was larger when the temperature was more than 250℃. The conversion rates obtained by using Flynn-Wall-Ozawa method and Kissinger-Akahira-Sunose method were in good agreement with the experimental values at the whole pyrolysis stage. According to the master-plots method, the optimal reaction mechanism of pyrolysis was random nucleation and the reaction series was 2.It was found that the Kissinger-Akahira-Sunose method was more suitable for calculating the kinetic parameters of Phragmites australis stalk pyrolysis compared with the Flynn-Wall-Ozawa method. The apparent activation energy calculated by the Kissinger-Akahira-Sunose method increased first and then decreased with the increase of conversion rate. And the activation energy reached the maximum(286.9 kJ/mol) when the conversion rate was 50%.

     

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