煤中原生活性位点的水−气掩蔽效应及脱附后煤体的常温氧化

Water-gas masking effect of the primary active sites in coal and room temperature oxidation of coal after desorption

煤的常温氧化为煤炭自燃提供初始热量来源,探究煤中可与氧气常温条件下发生氧化反应的原生活性物质是煤自燃理论研究的难题。此前进行的受热分解实验发现,热解煤中含有能在惰性气体中稳定存在并与氧气发生常温氧化的活性位点,因此推测煤中同样可能存在惰性介质下被迫封存的原生活性位点。为进行煤中原生活性位点的探寻,运用真空干燥技术,使原煤中能够在高负压的低温环境下完成水分的蒸发和气体的脱除。同时借助循环氧化在线监测技术,设计实施不同因素(煤种、脱附温度、氧化温度、粒径)条件下脱附后煤样的常温氧化实验,并结合相应的低温氮吸附、XPS、ESR实验分析反应机理。循环条件下的常温氧化实验表明,真空脱附后的煤体在常温氧化过程中会形成大量的CO和CO_(2)等气体氧化产物,且气体在通入氧气后很快出现并不断积累,证明煤在常温下即可发生氧化反应。原生煤体脱附后的常温氧化实验说明原始煤体中存在大量受水−气掩蔽影响的活性位点,而负压脱附水分和气体后会导致活性位点的大量暴露并形成有利于氧气输运和反应的通道,从而迅速发生氧化反应。因此实验找到了导致原生煤体自发氧化的活性结构,实验将活性位点的常温氧化观点从受热分解的特殊状态扩展到一般状态。由气体产物生成规律对比可知,不易被孔隙吸附的CO会在原生活性位点与氧气接触瞬间迅速产生,据此得到CO相较于CO_(2)而言更适合作为活性位点浓度的直观气体评价指标。煤体原生活性位点的常温氧化有助于煤炭自燃机理的揭示,为高瓦斯矿井瓦斯抽采自燃及低阶煤井下CO超限问题提供解决思路。

The oxidation of coal at room temperature provides the initial heat source for spontaneous coal combustion(CSC).In the CSC theoretical study,exploring the active substances in coal that can be oxidized at room temperature is a complex problem.Previous thermal decomposition experiments have found that coal after pyrolysis contains active sites that can exist stably in inert gases and be oxidized at room temperature.Thus it is speculated that there may also be primary active sites that are forced to be stored under inert media in coal.In order to explore the primary active sites of coal,the vacuum drying technology is applied.Based on that,the water in the raw coal can reach the boiling point under the low-temperature environment of negative vacuum pressure to complete the removal of water and gas.Under different experimental conditions(coal,desorption temperature,oxidation temperature,particle size),the cyclic oxidation online monitoring technology is used to design and implement the room temperature oxidation experiment of the desorbed coal samples.At the same time,the reaction mechanism is analyzed by the corresponding low-temperature nitrogen adsorption,XPS,ESR experiments.After vacuum desorbed,the oxidation experiments under cyclic conditions show that the massive gaseous oxidation products such as CO and CO_(2) will be formed in the process of raw oxidation at room temperature,and the gases appear and accumulate soon after oxygen is introduced,which proves that coal oxidation can occur at room tem-perature.The room temperature oxidation experiment after the desorption of raw coal indicates that there are a large num-ber of active sites affected by water-gas masking in the raw coal.They are unable to undergo the oxidation exothermic processes,while the coal after the desorption of water and gas under negative pressure exposes massive active sites and forms a channel conducive to oxygen transport and reaction,which rapidly occur oxidation exothermic phenomenon and lead to the rise of coal temperature.Therefore,the active structure leading to the spontaneous warming of the raw coal is found,and the experiments extend the view of room temperature oxidation of the active sites from the particular case state of the pyrolysis to the general state.From the comparison of gas product generation,it can be seen that CO,which is not easy to be adsorbed by pores,is produced quickly at the moment of contact between the primary active site and oxygen.Therefore,it can be concluded that CO is more suitable as an intuitive gas evaluation index of the concentration of the act-ive sites compared with CO_(2).The room temperature oxidation of the primary active sites of coal helps reveal the mechan-ism of coal spontaneous combustion and provides a solution to the problem of spontaneous combustion during gas extrac-tion in high-gas mines and the problem of CO over-limit in low-rank coal mines.