低阶煤干燥过程水分析出动力学行为分析

Analysis of the kinetic characteristic of water emission during low-rank coal drying process

  • 摘要: 使用热重分析仪对伊敏褐煤(YM煤)和天池能源次烟煤(TC煤)进行干燥过程实验研究,采用等转化率等方法对低阶煤热重数据进行分析,得到煤中水分析出活化能E。根据求得的活化能,由Achar方程和Coats-Redfern方程确定最概然机理函数,并确定干燥过程级数n和指前因子A。同时,采用差式扫描量热法(DSC)对煤中不同赋存形式的水分进行定量分析,以此验证热重分析结果。结果表明:低阶煤水分析出的活化能E为45~55 k J/mol,干燥过程遵循简单级数模型f(α)=(1-α)n,n≠1。YM煤水分析出活化能为53.28 k J/mol,干燥过程级数n=1.82~1.95,指前因子A=(3.52~3.96)×108s-1;TC煤水分析出活化能为47.44 k J/mol,干燥过程级数n=1.39~1.44,指前因子A=(6.62~8.17)×107s-1。DSC的定量分析结果表明,低阶煤中以自由水和弱束缚水为主的不稳定组分含量达到70%~80%。干燥过程中,自由水先析出,其析出活化能略高于纯水蒸发活化能;强束缚水在干燥末期析出,其析出活化能随干燥过程的进行急剧升高,且远大于纯水蒸发活化能。

     

    Abstract: The drying processes of Yimin lignite (YM) and Tianchi subbituminous ( TC) were studied using thermo- gravimetric analysis. Isoconversion method was used to analyze the TG data to obtain the drying activation energy E. Based on the activation energy obtained,the most probable mechanism function was determined by Achar equation and Coats-Redfern equation,and then the reaction order n and the pre-exponential factor A were obtained. At the same time,the differential scanning calorimetry (DSC) method was used to quantitatively analyze the moisture contained in the coals and verified the thermogravimetric results. The experimental results show that the activation energy E of the water emission process is 45-55 kJ / mol and the drying process follows the simple series model for the low-rank coals. For YM coal,E = 53. 28 kJ / mol,n = 1. 82-1. 95,A = (3. 52 -3. 96) ×108 s-1 and for TC coal,E = 47. 44 kJ / mol,n =1.39-1. 44,A = (6. 62-8. 17) ×107 s-1 . The quantitative analysis on the water existence form using DSC method indi- cates that the content of unstable water mainly in the form of free water and weak bound water is 70% -80% . During the drying process,the free water first releases from the coal particle and the strong bound water releases at the end of the period. The activation energy of the strong bound water emission increases abruptly with the drying process and is much larger than that of pure water.

     

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