基于交叉点温度法煤自燃倾向性评定指标的物理内涵

Physical nature of the indexes for ranking self-heating tendency of coal based on the conventional crossing-point temperature technique

为了探索基于传统交叉点温度法建立的煤自燃倾向性评定指标的物理本质和相互间联系,对线性升温环境中具反应活性固体样品热响应进行理论模拟,同时跟踪含水量对交叉点温度(CPT)以及衍生指标HR和FCC结果的影响。结果显示,线性升温环境中样品中心温度呈典型变化,即初期线性升温、缓慢升温和后续急剧升温3个阶段。计算结果与现有的实验数据高度吻合。随着样品含水量的增加,其CPT温度升高,表明样品自加热和自燃倾向性降低;而指标HR和FCC的评定结果却相反。进一步分析表明,CPT温度间接表征样品走向显著氧化和自加热的起始(临界)温度,反映样品发生氧化自加热的难易程度,可以作为评定材料自加热和自燃倾向性的主要指标。指标HR和FCC是对处于CPT温度情形下样品产热能力的表征,与材料原始状态下的属性没有直接关联,因而只适合在CPT测试结果接近时对样品间自加热和自燃倾向性差异进行补充评定。

The physical nature of the parameters defined by the conventional crossing-point temperature technique was investigated for the purposes of identifying their reliability in assessing the tendency of coal towards self-heating and spontaneous combustion. By theoretically simulating the thermal response of a coal sample in a linearly heating environment, the effects of sample moisture content on the crossing-point temperature （CPT）measured and the derived indexes such as HR and FCC were studied. Typical pattern was observed for the temperature variation at the sample center, which can be classified into three stages, initially linear temperature increase, progressive temperature increase, and the subsequent stage of drastic temperature increase. The simulated results were compared with those available in the literature. With the increase of sample moisture content, the CPT value increases, indicating the moderation of the sample＇ s self-heating tendency; however, the assessment results of the indexes HR and FCC show the reverse. It was confirmed that the CPT of a sample corresponds to the critical temperature for the sample to undertake significant oxidation, signifying the hardness of the sample to undergo self-heating. It can be used as a major index for ranking the selfheating tendency of coal. The indexes HR and FCC are the indicators of a sample to release heat at the CPT, which have no direct link to the oxidation capacity of a sample at the ambient temperature. Therefore, these two indexes are only suitable for the further assessment of the samples having an identical CPT.