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不同镜惰比低阶煤燃烧特性及动力学分析

The combustion characteristics and kinetic analysis of low-rank coals with different vitrinite/inertinite ratio

  • 摘要: 为解释显微组分对低阶煤燃烧特性的影响,以一系列不同镜惰比低阶煤为研究对象,利用热重−质谱−差热(TG-MS-DTA)联用技术,研究了样品在空气气氛下的燃烧特性、热量变化过程以及气体逸出行为。结果表明:煤的显微组分含量对煤燃烧达到最大反应速率时的温度影响不大,但对反应最大速率的大小有影响,富惰质组煤燃烧的反应最大速率更大。同时,煤中较多矿物使得反应达到最大速率时温度更高。燃烧过程呈现出明显的两个阶段,第一阶段(400 ℃之前)缓慢放热,对应脱挥发分过程,第二阶段(400 ℃之后)快速放热,对应固定碳燃烧过程,燃烧放热特征呈现出缓慢到快速放热的转变。不同镜惰比煤在燃烧过程中主要释放CO2、CO、H2O等气体,但释放的相对含量不同,脱挥发分阶段,有较少的CO2、CO气体释放,H2O的释放相对量较多。而在固定碳燃烧阶段,CO2大量释放,CO释放量略低,H2O最少。其中,富惰质组煤在燃烧过程中释放相对更多的CO2,在相同条件下,燃烧更加充分。此外,还借助Coats-Redfern积分法对煤燃烧过程进行动力学计算,得到随着镜惰比含量减小,反应活化能增加的趋势,但这并不影响富惰质组煤在固定碳燃烧阶段能快速燃烧的特性,这可能是由于惰质组中大量丝质体形成的细胞胞腔结构,增大了与O2的接触面积,燃烧反应充分。

     

    Abstract: To explain the effect of maceral composition on the combustion characteristics of coal, a series of low-rank coals with different vitrinite/inertinite ratio were collected as the research object, and the combustion characteristics, heat change process and gas escape behavior of the samples under air atmosphere were investigated using thermoanalytical methods (TG-MS-DTA). The results show that the maceral content has little effect on the temperature of the maximum reaction rate. However, it has an effect on the value of the maximum reaction rate, and the maximum reaction rate of the inertinite-rich coal is larger. Meanwhile, higher minerals in coal allow the reaction to reach its maximum rate at a higher temperature. The combustion process shows two obvious stages. The first stage (before 400 ℃) is exothermic slowly, corresponding to the devolatilization process, and the second stage (after 400 ℃) is exothermic rapidly, corresponding to the fixed-carbon combustion process. The exothermic characteristics of coal combustion show a slow to fast exothermic transition. Coal with different vitrinite/inertinite ratio mainly release CO2, CO, H2O during the combustion process, however, the relative content of the released gas is different. In the devolatilization stage, there is less CO2 and CO released, while more H2O release. In the fixed-carbon combustion stage, a large amount of CO2 is released, the amount of CO released is slightly lower, and H2O is the lowest. Among them, the inertinite-rich coal releases relatively more CO2 during the combustion process and burns more completely under the same conditions. In addition, the kinetic calculation of the coal combustion process is carried out with the Coats-Redfern method, and the trend of reaction activation energy increases as the vitrinite/inertinite ratio decreases. However, it does not affect the inertinite-rich coal in the fixed-carbon combustion stage. The ability to burn rapidly may be due to the cell lumen structure formed by a large number of fusinites, which enlarges the contact area between the surface of coal particles and O2, and the combustion reaction is sufficient.

     

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