Study of coal oxidation behaviour in re-opened sealed heating

Possible changes in the oxidation behaviour of coal in the spontaneous combustion site of re-opened sealed heating were studied. Two samples of bituminous coal and three types of coal pre-treatment procedures were applied to simulate in situ conditions at the “spon-com” site: i) pre-oxidation of coal, ii) pre-heating of coal under inert gas, and iii) immersion of pre-heated coal in liquid water. Pre-treated samples were then examined for the production rate of the indication gases evolved during oxidation and for oxidation heat effects. Two main conclusions were drawn with respect to oxidation of the coal in re-opened sealed heating: i) carbon monoxide and unsaturated hydrocarbons maintain their relevance as spontaneous combustion indication gases, however, increased production of both carbon oxides can be expected; ii) coal in the extinguished spontaneous combustion site gains increased susceptibility to the self-heating process.     

Imidazolium based ionic liquids affecting functional groups and oxidation properties of bituminous coal

Low temperature oxidation of coal will result in coal spontaneous combustion in mined-out areas. We proposed to use ionic liquids to inhibit the coal spontaneous combustion in this paper. In order to study the inhibiting effect of ionic liquid (IL) on coal oxidation, we successfully dissolved bituminous coal samples in six kinds of imidazolium based ionic liquids, [AOEmim][BF₄], [HOEmim][BF₄], [Amim][Cl], [Emim][AC], [Bmim][AC] and [Bmim][OTf]. The functional groups in the coal samples pre-treated by different ILs were detected by Fourier Transform Infrared Spectroscopy (FTIR) in detail. It is found that the ILs are capable of breaking the associated hydroxyls into dissociated hydroxyls. And during the interaction between coal and ILs, the carboxyl groups have been created. Thermo Gravimetric experiment results show that the weight loss ratios of the IL-treated coals were less during 20–400 °C stage, compared with the IL-untreated coal, which indicates that most of the easily reductive groups effectively dissolved in the ionic liquids. According to the exothermic rate curves and the computed activation energy values, it is demonstrated that the [Bmim][OTf] and [Bmim][AC] make better effect than the other ILs for depressing the oxidation rate of bituminous coal.     

水溶剂效应对煤氧化特性的影响

水既可以隔绝空气,又可以吸热降温,是防火、灭火的绝好材料。但经过大量的煤矿现场应用及实验研究发现:很多情况下,注水不仅不能预防煤炭自燃灾害,反而易于灾害发生。为了揭示煤矿井下注水易引起煤自燃的原因,应用Gaussian09程序,采用含时密度泛函理论（TD-DFT）,在B3LYP/6-31G (d,p)水平上,分析水溶剂效应对煤氧化特性的影响。由计算结果可知:煤各模型的HOMO与O2的LUMO对称性相同,且能级差均小于0.4 eV,符合前线轨道理论提出的反应条件,所以煤HOMO轨道的电子将流向O2未占据的LUMO轨道,从而发生氧化反应,氧化反应剧烈时将引起煤炭自燃;当煤浸泡在水中,煤分子与水分子间将产生静电相互作用,氢键及孔洞能等相互作用,这些相互作用影响了煤分子的核外电子排布,改变了煤的前线轨道能级,煤各模型的HOMO与O2的LUMO能级差比在气相中更小,因此,被水浸泡的煤更容易发生氧化自燃。     

The application of kinetics based simulation method in thermal risk prediction of coal

Coal spontaneous combustion is one of the major natural disasters faced in coal mines. The accurate prediction of the thermal risk of coal is of great importance. However, there isn't a widely accepted approach to get the oxidation process of coal that under adiabatic condition or in a specific environment under mine at present. To demonstrate whether the advanced kinetics simulation method could be employed to obtain the accurate oxidation process of coal for determining the coal's thermal risk in the mine design phase and mining phase, DSC experiments were conducted by C80 micro-calorimeter to get the heat behavior of coal, based on which the kinetic parameters can be solved and the oxidation process of coal can be predicted.The results showed that the kinetics based simulation method was successfully used to predict the adiabatic temperature rise process of coal for risk prediction. The deviation between the predicted curve and tested curve that obtained by adiabatic test is small enough to be accepted. Kinetics based simulation method is a promising candidate, instead of adiabatic test, to assess the propensity of coal to spontaneous combustion, which can play an important role in the design phase of the mine and mining area. Moreover, through establishing the heat balance equation of residual coal and with the aid of kinetics based simulation method, the oxidation process of coal that in the suffocation zone of the gob was also accurately predicted. According to the index t₇₀ (the time required for coal to reach 70 °C) and v_min (the lower limit of the advancing speed of the working face) obtained from the predicted curve, the thermal risk of coal was predicted to guide the further adjustment of the advancing speed of the working face, the amount of the injected mud and the determination that whether to add other fire prevention measures. Kinetics based simulation method, be of great practical importance in risk prediction of coal that in the gob, can be also used as a convenient tool to guide the safe production in the actual mining process.     

The relationship between oxygen consumption rate and temperature during coal spontaneous combustion

Spontaneous combustion is a major natural disaster in coal production. In the process of exploring coal self-ignition, a series of hypotheses have been put forward, most scholars agree that the current coal-oxygen compound theory. Oxygen consumption rate reflects the status of coal spontaneous combustion, and it is also one of the parameters necessary for numerical simulation of coal spontaneous combustion. In this paper, a coal heating and oxidation experiment was designed, Experimental device consists of heating and oxidation furnace, gas chromatograph, temperature control and data acquisition systems and other equipment components. Three coal samples whose weight each is 5 g were selected for the study. By experiment, oxygen concentration at the inlet and outlet of temperature oxidation furnace was measured. Oxygen consumption rate is calculated in the heating process of coal according to air flow. In the Cartesian coordinate system, the temperature as abscissa and the oxygen consumption rate for the longitudinal coordinates, drawing the relationship between oxygen consumption rate and temperature plot. And then regression analysis was used to analyze the relationship between oxygen consumption rate and coal temperature during the heating and oxidation process of coal. The results show that the oxygen consumption rate and temperature of coal were linear relationships both before and after the critical temperature when the coal temperature is less than 180 °C. Before the critical temperature oxygen consumption rate is low, however it increases rapidly when coal temperature reaches a critical temperature. The result is important for the prevention and treatment of spontaneous combustion of coal.     

Evaluation of the spontaneous combustion characteristics of coal of different metamorphic degrees based on a temperature-programmed oil bath experimental system

Research on the micro- and macrocharacteristics of different metamorphic degrees of coal helps improve the control and protection techniques used during spontaneous combustion. Nine coals with different properties were thoroughly investigated in this study. Fourier transform infrared spectroscopy and a self-designed temperature-programmed oil bath experimental system were adopted to analyze the molecular structure and macrocharacteristic parameters of the spontaneous combustion of coal. Additionally, the influence of particle size on spontaneous combustion was considered. Various functional groups were employed as microcharacteristic parameters to capture the principal active groups in oxidation. The gas production rate, oxygen consumption rate, gas concentration, heat energy release rate, and characteristic temperatures were evaluated as macrocharacteristic parameters to investigate the changes in coal during oxidation. The results establish that the microcharacteristics of coal molecules determine the degree of spontaneous combustion based on intrinsic properties and that changes in the macrocharacteristics of the spontaneous combustion of coal reflect the microstructural changes. The contents of the hydroxyl groups, carbonyl groups, alkyl ether and aryl ether in the coal molecules gradually decrease with the metamorphic increase. Oxygen-containing functional groups have higher reactivities and easily react with oxygen, causing the macroparameters, such as the oxygen consumption rate, the gas generation rate and the heat energy release rate, to consistently decrease with the increase of the metamorphic degree. Small-particle-size coal molecules have more active aliphatic hydrocarbons, oxygen-containing functional groups and a larger specific surface area, increasing the chances of adsorbing the oxygen of active groups and promoting the reaction between coal and oxygen. The experimental results indicate that coal samples with higher metamorphic degrees or larger sizes exhibit lower tendencies toward spontaneous combustion. Evaluation of the spontaneous combustion of coal based on a temperature-programmed oil bath experimental system is of great practical importance for preventing the spontaneous combustion of coal during storage, processing and utilization and can serve as a convenient reference for production safety in mining applications.     

Sources of underground CO: Crushing and ambient temperature oxidation of coal

As a harmful gas in underground coal mine, CO seriously threatened the safety of miners. Currently, the spontaneous combustion of residual coal in goaf is generally considered as the main source of underground CO. CO gas is also widely used as an indicator gas in fire prediction in mines. However, high concentrations of CO are also detected in some mines without spontaneous combustion of coal. Therefore, in the paper, with four ranks of coal, we studied other two potential CO sources: crushing and oxidation at ambient temperature. The more completely crushed coal produces more CO. The concentration of generated CO is inversely proportional to moisture content in coal. Therefore, the addition of water can inhibit the generation process of CO during the crushing process of coal. Lignite with low metamorphic grade can be oxidized to produce CO at ambient temperature (25 °C), and anthracite with high coal rank can be only oxidized to produce CO at 60 °C. Infrared spectra indicated that the coal with rich aliphatic hydrocarbons and oxygen-containing functional groups are more susceptible to oxidation at room temperature. Moreover, the smaller particle size of coal is more beneficial to the oxidation at ambient temperature to generate CO. CO generation during coal oxidation is also closely related to the ventilation rate.     

不同粒径易自燃煤常温氧化实验研究*

为探究易自燃煤在常温条件下的氧化特性,自行设计煤常温封闭氧化实验装置,采用实验研究与回归分析2种方法,分析易自燃煤发生氧化反应的气体变化过程,探究3种粒径煤样在20 ℃有限空间内的耗氧与产气特征。结果表明:易自燃煤样在16 d常温封闭氧化过程中,容器内O2体积浓度呈指数衰减、CO和CO2体积浓度呈指数增长的变化规律;在0.06~0.83 mm范围内,粒径越大,易自燃煤耗氧速率越大,CO和CO2产生速率则先增大后减小;介于中间的粒径为0.13~0.25 mm易自燃煤氧化反应最强烈,更容易发生氧化。研究结果对揭示生产环境温度下煤粒粒径对煤自燃的影响有一定的意义。     

吨量煤体的自燃过程实验模拟研究

为更好地弄清矿井实际的煤自然发火规律，利用装煤量达5吨的大型实验台对两种烟煤分别进行了自燃模拟实验。大煤量的实验能够很好地模拟煤矿中煤低温氧化和传热传质共同作用导致的发火过程，实验得到的自然发火期与煤矿实际发火期也是一致的。实验中煤样从缓慢氧化变为快速氧化的临界温度为100～110℃。当煤温低于，临界温度时，煤样的升温受到空气流带走热量和向外界散热的影响很大，因此夹层水的保温作用就很关键。当煤温超过临界温度后，反应加快，温度急剧上升，散热的影响明显降低，反应主要受限于氧气的供应情况。     

煤矸石山自然发火数学模型在红阳三矿新矸石山自燃防治中的应用

煤矿矸石山自燃现象普遍存在 ,对环境污染及危害极大 ,防治矸石山自燃是矿区环境修复的重点研究内容。笔者利用宏观的连续介质研究方法 ,以多孔介质流体动力学理论为指导 ,建立了煤矿矸石山自然发火数学模型 ,从数学上揭示了矸石山自燃的动态演变过程。通过分析矸石山内的渗流场明确了自然发火的影响因素及内在联系 ,针对红阳三矿新矸石山的自燃预防问题 ,提出了碾压、覆盖和边界注浆相结合的综合防治施工方案。该技术在红阳三矿新矸石山的现场应用表明 ,治理方案科学、经济、合理 ,实施效果良好。研究结果对预防矸石山自燃具有理论指导意义与实际应用价值。     

不同自燃倾向性煤的指标气体产生规律实验研究

为研究不同自燃倾向性煤的自燃指标气体变化规律，提高对煤早期自燃预测预报的准确度，采用程序升温实验系统，得到内蒙古褐煤、神东长焰煤、河南气煤及枣庄焦煤4种不同变质程度煤的氧化时间随温度的变化关系，以及指标气体浓度在煤氧化过程中的变化规律。结果表明:自燃倾向性最高的褐煤应以CO和乙烯作为煤自燃早期预报的首选指标气体；易自燃的长焰煤应采用乙烯和烯烷比为主、以CO为辅的煤自燃判定指标；自燃倾向性较低的气煤应以乙烯和烯烷比作为煤自燃预报指标；CO是自燃倾向性最低的焦煤的最佳自燃预报指标气体。     

煤热动力学参数、特征温度与挥发分关系的试验研究

通过煤的热动力学参数和特征温度可以表征煤自燃危险程度。而在实际情况中,这些数据缺少,往往只有煤的工业参数。因此,研究工业参数与表征煤自燃危险参数的关系十分必要。为了分析和建立该关系,基于非等温试验方法对不同煤样进行热重试验分析,得出8个煤样在10℃/min升温速率下的反应动力学参数与煤工业分析参数的关系,揭示挥发分与煤的氧化特性、特征温度的关系。试验结果表明:8个煤样的挥发分排序F3>F8>F4>F7>F2>F1>F5>F6,各特征温度排序基本满足T3相似文献   

基于Logistic回归分析的煤自燃多级预警方法研究

为实现煤自燃过程的精细分级与自燃隐患的精确预警,保障井下煤自燃防治工作有效开展和煤炭资源安全开采.以甘肃王家山矿202工作面煤样为测试对象,采用煤自然发火试验与程序升温试验手段模拟煤体自然发火过程.测定煤自燃指标气体等特性参数数据,分析相关指标气体特征,将煤自燃过程划分为稳定、波动和剧烈反应3大区间.通过处理指标数据以...     

吸水性还原性材料对煤自燃影响的实验研究

为了解决吸水性盐和还原性材料仅依靠其单一特性抑制煤自燃而抑制效果并不理想的问题,提出了利用羟甲基磺酸钠的吸水性和还原性来抑制煤自燃。将原煤-20%羟甲基磺酸钠通过对比原煤、原煤-20%MgCl2和原煤-20%VC,利用程序升温实验和FTIR测试来研究其抑制煤自燃的效果。研究结果表明:3种溶液处理煤均在一定程度上抑制了煤自燃,其中,20%羟甲基磺酸钠溶液对抑制煤低温氧化的效果最好,经过其处理的煤样表观活化能最大,同时,依靠其还原性很好地保护了煤中的亚甲基和羟基不被破坏,抑制煤自燃效果明显优于20%MgCl2溶液和20%VC溶液。     

煤低温恒温氧化过程反应特性的试验研究

为进一步揭示煤低温氧化机理、指导煤矿安全开采过程中的煤自燃火灾防治工作,根据CO,CO2是煤低温氧化的主要气体产物这一反应特性,同时CO是判断煤自燃程度的重要指标性气体这一工程实际,采用恒温试验方法研究某烟煤在30℃,50℃和70℃解吸附和解吸附后再氧化过程中的CO,CO2气体产物的产生特性。研究结果表明,新鲜煤中就存大量活泼的络合物,并且这种络合物在高于常温的情况下就可以自身发生分解,产生的主要气体产物为CO2,在较高的温度下,CO的生成量才逐渐增加;在煤的低温氧化阶段,煤与氧气发生的化学反应并不强烈,气体产物CO和CO2主要由络合物分解产生。因此,在煤自燃火灾防治时要及时控制煤在低温情况下,由于络合物分解放热而使煤温逐渐升高从而导致自燃发生。     

水对防治煤炭自燃的作用及注水周期的研究

通过对水在采空区遗煤氧化及自燃的作用机理两重性的分析以及实验室试验与现场应用实际效果研究 ,证实了笔者提出的清水灌注措施是一种新的、经济有效的、操作简便的防治采空区遗煤自燃的技术措施。同时 ,对传统的黄泥灌浆技术措施中的泥浆浓度要求提出了新的看法。此外 ,还对往采空区注水的周期进行了专门的研究     

以活化能的观点研究煤炭自燃机理

笔者对煤体的性质和结构进行了分析 ,简要地介绍了关于煤炭自燃机理的各种学说。目前有许多学者用不同的方法来研究煤炭的自燃机理 ,笔者从煤活化能的角度来研究煤炭的自燃。由氧化反应方程提出了活化能 ,根据活化分子运动理论解释了活化能的基本概念 ;并建立了相应的煤氧化反应的活化能方程 ,该方程直线部分的斜率 (E/R)可求出氧化反应的活化能。在煤炭自燃进程中 ,随着煤体温度的升高 ,活化能降低 ,氧化反应加速 ,大量的热量产生 ,如此循环 ,最终导致了煤的燃烧。     

The effect of N2/CO2 blend ratios on the pyrolysis and combustion behaviors of coal particles: Kinetic and thermodynamic analyses

The aim of this work is to investigate the impact of various CO₂/N₂ ratios on coal pyrolysis and combustion properties and to provide theoretical guidance for better preventing and controlling coal spontaneous combustion in the goaf. The dynamic pyrolysis and combustion characteristics of DX coal were analyzed by using a thermal gravimetric analyzer (TGA) in a constant oxygen atmosphere with different CO₂/N₂ blend ratios. The Málek method combining Coats-Redfern and Achar methods was used to determine the most probable mechanism functions. CO₂ containing atmospheres increased characteristic temperatures, burnout rate, maximum mass loss rate and comprehensive combustion performance index compared to O₂/N₂ atmospheres. In stages I-III, a lower apparent activation energy was observed in O₂/CO₂ atmospheres. Apparent activation energy and enthalpy changes showed upward trends in the reaction stage (I→III→IV), whereas Gibbs free energy change and entropy change decreased. The dynamic pyrolysis and combustion of DX coal necessitated increased energy in environment with a CO₂/N₂ ratio of 4:6, revealing the optimal inhibitory effect on DX coal with this particular ratio.     

碱性水对煤自燃特性影响实验研究

为了研究碱性水对煤自燃特性的影响，选取葫芦素煤矿102工作面煤样作为实验煤样，利用STA-449C型同步热分析仪进行热重实验，研究加入PH=8 NaOH的煤样与原煤以及加入蒸馏水煤样在空气氛围中燃烧失重、放热量、特征温度点等变化规律，并根据Coats-Redfern积分模型计算了3种煤样燃烧反应动力学参数（活化能、指前因子）。研究结果表明:加入碱性水的2号煤样失重量较1，3号少，燃烧失重速率更低；2号煤氧化燃烧温度区间缩短，着火温度点升高，放热量少，比1，3号煤分别少485.0，480.4 J/g；3种煤样反应机理基本遵循一级化学反应函数，2号煤各段活化能高于1，3号煤，但2号煤失水活化能小于3号，表明碱性水具有抑制煤自燃效应。     

立体抽采条件下高瓦斯采空区煤自燃危险性预测

为准确预测高瓦斯采空区煤自燃的状况,通过分析发现高抽巷是监测采空区遗煤自然发火的最有效地点。推算出采空区气体在高抽巷中所占的体积分数,进而确定采空区遗煤不同的燃烧阶段所对应的CO体积分数和CO指数。结果表明:当高抽巷中的CO体积分数Chdr CO<30×10-6或CO指数ICO<0.5%时,采空区的遗煤处于低温氧化阶段;当高抽巷中的CO体积分数Chdr CO≥30×10-6或CO指数ICO≥0.5%时,采空区遗煤进入自然发火危险阶段,此时必须采取措施控制采空区自燃氧化的进一步发展。对80501工作面的采空区煤自燃成功地进行预测预报,实现了安全生产。