升温速率及氧浓度对长焰煤煤氧复合过程特性的影响

Effect of the oxygen content and heating rate on the oxidation process of the long-flame burning coal

利用热重试验对粒径小于0.2 mm的长焰煤煤粉进行了不同氧体积分数(21%、40%、50%、60%和80%)和升温速率(20℃/min、30℃/min、40℃/min、50℃/min和60℃/min)的25种工况下煤氧复合过程中热解特性的测定,分析了两种因素对各特征值的影响。结果表明:以热失重速率为基准,长焰煤在含氧气氛下的热解过程可分为失水失重阶段、氧化增重阶段及着火、燃烧和炭化3个阶段;通用着火特性指标越大,煤样燃烧特性越好,自燃点越小,煤样工业分析结果应与其实际生产过程中的自燃危险性相结合;升温速率不变时自燃点随氧体积分数上升而下降,而煤氧复合时间随氧体积分数上升呈现先降低再微弱增加的趋势;氧体积分数一定时自燃点随升温速率上升而上升,煤氧复合时间则随之下降。对自燃点及煤氧复合时间进行均值无量纲化,并将其与无量纲化升温速率进行拟合,决定系数(R^2)约为1.0;提出了煤氧复合难易程度参数(D),计算结果表明,即使自燃点随升温速率上升发生滞后,煤氧复合难度仍然减弱。

This paper is inclined to make a study on the effect of the oxygen content and heating rate on the oxidation process of the long-flame burning coal via a series of thermogravimetric experiments,which tends to prove that there exists a strong spontaneous combustion tendency. The particle sizes of the experimental samples turn to be smaller than 0. 2 mm. Besides,the aforementioned experiments are all realized under the twenty-five kinds of experimental conditions in hoping to identify the pyrolysis properties and characteristic features such as the self-ignition point and the length of the oxidation process. The experimental conditions include two factors of the oxygen content and the heating rate. Among them,the above mentioned five kinds of oxygen contents account for 21%,40%,50%,60% and 80%,respectively.Moreover,according to the burning last length,the aforementioned five kinds of heating rates can range from 20 ℃/min to 60℃/min with an interval of 10 ℃/min. Results show：（ 1） According to the weight loss rate,the pyrolysis process experiences three stages in the oxidizing atmosphere,that is,the water evaporation phase,the structure oxidation phase and the weight-gaining phase,through self-ignition,full burning and the continual combustion phase;（ 2） Referring to the previous research results,the universal ignition index not only presents the combustion feature of the coal,but also has a certain influence on its own self-ignition point. In other words,the self-ignition point tends to decrease with the enhancement of the general ignition index to some extent;（ 3） The spontaneous combustion point tends to decrease with the increase of the oxygen content,with the variation trend of oxidation process includes a slight rise when it begins to fall under the fixed heating rate;（ 4） As the heating rate increases,the spontaneous burning points may tend to rise with the decrease of the thermal effect at the fixed oxygen content;（ 5） The non-dimensionalized spontaneous point and the non-dimensionalized oxidation process length should be fitted by the different functions of non-dimensionalized heating rates,respectively,with the R^2 is getting closer to 1. 00. In addition,a parameter determining the risk of the oxidation process of coal（ D） was presented for analyzing the influence effect of heating rate. It is proven that,although the self-ignition point is supposed to be with the enhancement of the heating rate,the burning risk likely to be faced with the oxidation process of coal still remains growing up.