煤自燃氧化放热效应的影响因素分析

任何一种煤都具有氧化放热性是煤自燃的根本原因,煤自燃氧化放热效应的主要影响因素包括煤分子结构、温度、氧浓度和松散煤松粒度。通过总结前人提出的煤化学结构模型,参照现代研究的成果,提出了描述煤自燃的煤分子化学结构模型。从煤分子结构上看,主要是煤分子中的非芳香结构侧链、桥链与氧发生反应,煤的氧化放热效应主要取决于煤表面活性分子种类、数量和空间结构特性。氧化放热强度和耗氧速率分别是描述煤氧化放热效应和煤氧复合速度的主要指标,利用化学动力学理论和煤低温自然发火实验测算出不同煤温时的氧化放热强度,利用程度升温实验测算出不同氧浓度时的耗氧速率,从定性和定量两个方面分析了氧浓度、温度和松散煤体粒度对煤氧化放热效应的影响。     

煤低温氧化结构变化的红外光谱研究

煤与氧易在低温下发生复合反应,煤中的活性基团被氧化,导致煤结构发生了变化.制备不同氧化温度的煤样,采用红外光谱法进行了研究;对红外谱进行差示光谱分析,得到各基团在煤氧升温过程中的变化规律,并对各基团进行煤氧复合反应的活性排序为:胺基甲基、芳香亚甲基羧酸、脂类、乙烯基醚类.     

好氧微生物抑制煤自燃机理研究现状及展望

综述了微生物对煤脱硫、降解方面的研究现状，利用好氧微生物处理煤可降低煤中硫含量(黄铁矿)、破坏煤中羟基、羰基、羧基等活性基团以及消耗O₂、产生CO₂气体等特性，提出用生物技术来延缓煤氧化进程、阻断煤氧化路径从而抑制煤自燃的设想。基于利用微生物对煤表面环境状态以及微观结构改变的特性，从煤氧化反应本身为切入点防控煤自燃。针对好氧微生物改性驯化对煤中硫含量、活性基团的影响，对现阶段常用的煤炭脱硫、降解类微生物(如嗜酸氧化亚铁硫杆菌、黄孢原毛平革菌等)进行分析，总结了可用于抑制煤自燃的微生物生长特性及其差异性，最终提出可用多种功能微生物分步协同作用来抑制煤自燃的思路，对煤自燃新型绿色阻化剂的开发进行了展望。     

预氧化处理后基团对煤氧化反应活性的影响

使用氧化剂对无烟煤进行预氧化处理,利用TPD-MS和TG-DTA等表征方法,研究了煤表面官能基团种类、含量的变化及其对煤氧化活性的影响.结果表明,使用氧化剂处理煤样可以不同程度地改变煤表面官能基团及其分布.双氧水、次氯酸钠处理后的无烟煤,其氧化反应活性的变化不明显;硝酸处理的无烟煤,其低温氧化反应活性有所提高.根据处理前后煤表面基团及其分布的变化推测:无烟煤中的羧基等含氧基团明显提高煤的低温氧化活性,而烷基对煤的低温氧化活性影响不明显,但对煤氧化反应热有一定影响.     

O2在-CH2-CH2OH基团上的化学吸附

煤炭自燃是煤表面与氧气发生吸附进而发生化学反应的结果,在定义煤表面的基础上,应用量子化学理论和方法,研究煤表面中的-CH2-CH2OH基团对氧分子的化学吸附过程,无论吸附单氧分子或是多氧分子,氧分子的O-O键都被拉长并断裂,氧原子与-CH2-CH2OH基团的C原子或H原子形成了新的化学键.吸附能随着吸附氧分子数的增加而增大,呈二次函数关系.     

煤化学结构模型研究进展及应用

为了解煤结构与反应性之间的关系,论述了褐煤、次烟煤、烟煤、无烟煤的典型化学结构模型,分析了煤的化学结构模型在煤热解、煤气化、煤液化、煤自燃及煤的溶剂溶胀性中的应用。煤的化学结构模型有助于在分子水平上研究煤反应过程中的反应路径和反应机理。煤结构模拟的方法能够有效捕获煤热解过程中化学键的生成和断裂行为,解释煤气化反应机理,有效检测或捕获煤液化时生成的不稳定自由基,从微观方面分析影响煤自燃的因素,达到预防煤炭自燃的目的。     

对煤分子中活性基团氧化机理的分析

根据煤分子结构的研究成果,推断桥键中的次甲基醚键、α位碳原子带羟基和带支链亚甲基的次烷基键、与两个芳环相连的次甲基键,以及侧链中的甲氧基、醛基、α位碳原子带羟基的烷基为常温常压下发生煤氧复合的活性结构。其氧化活性以醛基侧链、次甲基西边键、α位带羟基的次烷基键、α位带亚甲基的次烷基键、甲氧基、α位带羟基的烷基侧链、与两个芳环相连的次甲基键的顺序排列。由于氧分子存在两个未饱和分子轨道,煤分子活性基团在共轭效应和诱导效应作用下,呈现部分未成对的电子云进入氧分子轨道产生化学吸附,进而有部分发生各步氧化反应,放出热量。根据每步反应的键能变化,采用加权平均法可推算出煤氧复合每产生1mol CO,CO2和H2O的热效应值。由于煤中七种活性结构的氧化性不同及不同种类煤中各种活性结构的数量不同,煤氧化反应放出的热量不同,煤自然性也就不同。     

硫化矿石堆氧化自燃全过程特征综述与分析

针对能产生自燃内因火灾的典型硫化矿石类型,介绍了其堆积、氧化自热、着火及燃烧各阶段的特征,分析了氧化自燃发生的原因和发展过程,并探讨了影响硫化矿石自燃的各种因素及其作用机理.在此基础上,澄清了对硫化矿山火灾防治有重要指导意义的自燃发火初期的概念及其征兆识别方法,可为现场硫化矿山自燃火灾的早期识别与防治提供指导.     

煤自燃生成水的反应机理研究

应用傅立叶变换红外光谱仪研究了煤在氧化自燃过程中不同温度下生成的气体产物.在30℃～100 ℃左右有水和二氧化碳气体析出,温度升至105℃～150℃左右时,有一氧化碳生成.采用密度泛函B3LYP方法,在6-311G基组水平上研究了煤与氧发生自燃反应生成水和一氧化碳的反应体系,对反应势能面上各驻点的几何构型进行了全优化,用频率分析方法和内禀反应坐标(IRC)方法对过渡态进行了验证.计算结果表明,煤氧化自燃生成水的反应是氧分子攻击苯环侧链上的伯胺基团-C(29)H2-N(22)H2中间的N(22)原子,使煤分子苯环侧链上的伯胺基团生成了-CH2-N=O基团和水.由反应活化能可知,生成水的反应是一个自发式反应.     

圆柱型煤自然发火实验台的误差分析

煤自然发火实验真实的模拟煤低温自燃全过程,跟踪测定煤体的温度、氧浓度和其他气体含量的变化,研究煤的氧化放热特性,实验模拟的关键在于蓄热环境的控制。根据圆柱型煤自然发火实验台的结构特点,在实验结果的基础上,从煤体自然放热量和炉体散热量的角度,理论分析不同温度阶段散热量所占放热量的比率（即散热率）的变化关系,从而得出该实验台中将煤体与保温水层的温差控制在1℃左右,散热率小于10％,平均散热率为6％,实验误差在充许范围内。     

低阶煤在干燥氧气下低温氧化过程的机理研究

采用pulse calorimeter仪器，对低阶煤在干燥氧气下低温氧化过程进行了研究．实验结果表明，低阶煤在干燥氧气下的氧化反应热随着温度的上升而增加，并得到了与Arrhenius公式相同的动力学方程以及反应过程的活化能．提出了干燥氧气下低阶煤低温氧化过程的反应历程为：氧在煤粒表面吸附并生成氧自由基、氧自由基与煤发生氧化反应生成CO2（或CO）、CO2（或CO）由煤粒表面向本体扩散等三步过程．并通过计算和模拟，证明了该反应机理的正确性．     

煤表面对氧分子物理吸附的微观机理

应用量子化学的理论和方法研究煤这种非晶体物质的物理吸附机理,从微观上揭示其吸附机理和吸附过程,定量研究煤对氧分子发生物理吸附过程中吸附量和放出热量的关系,从而揭示煤炭氧化自燃初始反应的本质.从煤表面对多个氧分子吸附优化后的平衡几何构型可以看出,煤表面吸附5个以下的氧分子时,1个氧分子在煤表面含氮的侧链吸附,其余的氧分子被苯环所吸附.煤表面吸附6个氧分子以上时,苯环对氧分子的吸附减弱,被吸附的氧分子偏向侧链端,在煤表面侧链部位吸附了大量的氧分子,这也证明了在煤的氧化自燃过程中侧链首先被氧化的结论的正确性.煤表面对氧分子的吸附量与吸附能呈线性关系.     

隔氧材料防煤自燃阻化效果的红外光谱研究

在煤体上覆盖隔氧材料能有效地防治自燃。将配置好的一种有机隔氧材料覆盖到煤堆表面,在大气中放置一段时间后,对其覆盖下的煤体作红外光谱分析,并与未覆盖隔氧材料的煤体和新鲜原煤分别进行比较。结果发现,随着氧化进程的递进煤中含氧官能团不断增加,而且覆盖隔氧材料煤体的含氧官能团峰面积远小于未覆盖的,却与新鲜原煤的十分相近。这说明未覆盖的煤体发生了明显的氧化反应,而覆盖后的煤体基本上未发生氧化。因此,该隔氧材料能达到隔断氧气、防治煤自燃的效果。     

Numerical study on effects of coal properties on spontaneous heating in longwall gob areas

A computational fluid dynamics (CFD) study was conducted to model effects of coal properties on the potential for spontaneous heating in longwall gob (mined-out) areas. A two longwall panel district using a bleeder ventilation system was simulated. The permeability and porosity profiles for the longwall gob were generated from a geotechnical model and were used as inputs for the three-dimensional CFD modeling. The spontaneous heating is modeled as the low-temperature oxidation of coal in the gob using kinetic data obtained from previous laboratory-scale spontaneous combustion studies. Heat generated from coal oxidation is dissipated by convection and conduction, while oxygen and oxidation products are transported by convection and diffusion. Unsteady state simulations were conducted for three different US coals and simulation results were compared with some available test results. The effects of coal surface area and heat of reaction on the spontaneous heating process were also examined.     

Moisture readsorption and low temperature oxidation characteristics of upgraded low rank coal

This study investigated the behavior of upgraded low rank coal produced by a coal-oil slurry dewatering process regarding moisture readsorption, low temperature oxidation, and spontaneous combustion. The upgraded low rank coal had higher heating values than raw coal. It also showed lower moisture readsorption than raw coal and had less susceptibility to low temperature oxidation and spontaneous combustion. This seemed to result from the coating of the asphalt on the surface of the coal, which covered fine pores and suppressed the active functional groups from reacting with moisture and oxygen in the air. The increasing upgrading pressure negatively affected the moisture readsorption, low temperature oxidation, and spontaneous combustion.     

Numerical simulation and application experiment of the spontaneous combustion tendency of a coal stockpile covered with pulverized coal

In this paper, we developed a new method for preventing the spontaneous combustion of a coal stockpile covered by pulverized coal. This technique is based on the numerical-simulation analysis of endothermic/exothermic balance in coal stockpile. Depth and height are confirmed to be the main factors influencing the endothermic/exothermic balance in coal stockpiles and the hot-spot region is easily formed at a coal stockpile height of 1-1.5 m and a depth of 2-3 m, where there is the highest tendency for spontaneous combustion. The numerical simulation and the 120-day application test both confirm that the diffusion process of oxidation can be prevented and the coal oxidation reaction can be hindered by covering the surface of the hot region with pulverized coal. As a result, the coal spontaneous combustion is prevented effectively.     

Prediction of BP neural network and preliminary application for suppression of low-temperature oxidation of coal stockpiles by pulverized coal covering

We have developed a new method to suppress spontaneous combustion of coal piles by covering the surface of coal piles with pulverized coal. Experimental studies of three type of coal samples from China (YJL, CYW, and SW) with particle size ratio of 10:1 were performed to investigate the low-temperature oxidation of coal pillars. In this work, we have also demonstrated that the distributions of oxygen concentration, the temperature field, as well as the spontaneous combustion of three typical Chinese coal samples can be predicted accurately using back-propagation neural network (BPNN) by MATLAB. Pearson correlation analysis showed that temperature and oxygen concentration highly depend on the ratio of pulverized coal thickness to coal piles thickness, activation energy, void ratio, wind speed, and low-temperature oxidation time. Three-layer BPNN models with five input factors were developed to predict the low-temperature oxidation process under pulverized coal. The prediction data of BPNN are fitting better with our experimental data, which confirms that BPNN modelling can accurately predict the low temperature oxidation process of coal.     

A model for the spontaneous heating of coal

As part of an investigation into the spontaneous heating of coal piles, a one-dimensional model has been developed to describe the spontaneous heating process at relatively low temperatures (< ≈ 100 °C). The ultimate unsteady-state model takes into account depletion of oxygen and production of heat by chemisorption of oxygen in the coal, transport of oxygen by diffusion and convection and transport of heat by conduction, convection and evaporation/condensation of coal moisture. It consists of four differential equations, for conservation of oxygen mass, of coal moisture and of heat and rate of reaction of oxygen with coal. Calculations using data from laboratory and field experiments give results that describe the process of spontaneous heating semiquantitatively. The most important parameters in the process of spontaneous heating, particularly for the time between stacking and spontaneous ignition, are the porosity of the pile (degree of compaction), the initial temperature of the coal and the evaporation and condensation of coal moisture. The influence of other parameters (e.g. reactivity of the coal, thermal conductivity) is much less pronounced.