He Xin, Zhu Hongqing, Huo Yujia, Wang Wei
School of Emergency Management and Safety Engineering, China University of Mining and Technology, Beijing 100083, China.
ACS Omega. 2021 Dec 15;6(51):35572-35583. doi: 10.1021/acsomega.1c05275. eCollection 2021 Dec 28.
The internal part of coal that is not in contact with oxygen will undergo pyrolysis reaction due to heat conduction, and the active groups generated can reverse-aggravate the degree of coal spontaneous combustion. At present, a few studies have been conducted on the pyrolysis mechanism of coal at different temperatures by using mutually validated experimental and simulation methods, resulting in the mismatch between the microscopic mechanism and macroscopic characteristics. In this paper, DH lignite is taken as the research object, and its macromolecular model is established. The pyrolysis reaction of lignite is studied by the experimental methods of coal pyrolysis index gas collection and detection experimental and thermogravimetric analyses and the simulation method of ReaxFF-MD. The influence of temperature on lignite pyrolysis is explored by analyzing the distribution of products at different temperatures and the formation mechanism of typical products, so as revealing the microscopic mechanism of lignite pyrolysis. The results show that 110-500 K of experimental temperature corresponds to 1400-2400 K of simulation temperature. CO and CH are the main gas products during pyrolysis simulation. Carboxyl and ester groups are the main source of CO, which gradually increases with the rise of temperature. Since CO can be reduced to produce CO, HO, and CHO at high temperatures, the yield decreases when the temperature is higher than 2000 K. CH is derived from the decomposition of long-chain aliphatic hydrocarbons, and its yield fluctuation rises with the rise of temperature. The formation of HO and H mainly occurs in the secondary pyrolysis stage. When 1400 K < < 2100 K, the primary pyrolysis is the main reaction, where the weak bridge bonds and macromolecular structure undergo cleavage to form gas products and tar free radical fragments. When > 2100 K, the secondary pyrolysis reactions were significant. Tar free radicals and char undergo decomposition, hydrogenation, and polymerization reaction, gas products and tar free radicals increase, and the char yield decreases compared with the primary pyrolysis stage, so 2100 K is the key temperature of the pyrolysis reaction. The research is of great importance in improving the accurate control of coal spontaneous combustion.
煤体内部未与氧气接触的部分会因热传导发生热解反应，生成的活性基团会反向加剧煤自燃程度。目前，利用相互验证的实验和模拟方法对不同温度下煤的热解机理开展了一些研究，但存在微观机理与宏观特征不匹配的问题。本文以DH褐煤为研究对象，建立其大分子模型，通过煤热解指标气体采集检测实验、热重分析等实验方法及ReaxFF-MD模拟方法研究褐煤热解反应，通过分析不同温度下产物分布及典型产物生成机理探究温度对褐煤热解的影响，从而揭示褐煤热解微观机理。结果表明，实验温度110 - 500 K对应模拟温度1400 - 2400 K。热解模拟过程中主要气体产物为CO和CH。羧基和酯基是CO的主要来源，其随温度升高逐渐增加，因CO在高温下可还原生成CO、HO和CHO，温度高于2000 K时产率降低。CH源于长链脂肪烃分解，其产率波动随温度升高而增大。HO和H的生成主要发生在二次热解阶段。当1400 K < < 2100 K时，一次热解为主反应，弱桥键和大分子结构发生断裂形成气体产物和焦油自由基碎片；当 > 2100 K时，二次热解反应显著，焦油自由基和半焦发生分解、氢化和聚合反应，气体产物和焦油自由基增多，与一次热解阶段相比半焦产率降低，故2100 K是热解反应关键温度。该研究对提高煤自燃精准防治具有重要意义。
