Analysis of spontaneous combustion liability indices and coal recording standards/basis

The characterization of the physical and chemical properties of coal on a standard provides an understanding of its characteristics towards spontaneous combustion.The trend of linear relationships between coal recording standards(%air-dried(ad),%dry(db)and%dry ash free(daf)basis)of 30 selected coal samples from the Witbank coalfields and spontaneous combustion liability indices were evaluated.The spontaneous combustion liability indices of these samples were evaluated by crossing point temperature(XPT),Stage II Slope,FCC(Feng,Chakravorty,Cochrane)and the Wits-Ehac tests,while the coal properties were determined from the proximate and ultimate analyses.The results obtained from these coal properties were related to different liability indices to develop trends of linear relationships using regression analysis.The ad basis indicated higher correlation coefficients than the db and daf basis for the XPT and FCC index,while the daf showed higher correlation coefficients than the ad and db basis for the Wits-Ehac index.It was found that the trend of linear relationships of these coal properties differs from one liability index to the next.The XPTs showed a better trend followed by the Stage II Slope on the coal properties among the spontaneous combustion liability indices evaluated.

Statistical analysis to establish an ignition scenario based on extrinsic and intrinsic variables of coal seams that affect spontaneous combustion

Spontaneous combustion of coal seams in open pit mines is a problem that occurs in coal mines around the world.Theories have been developed that express several factors which generate self-heating in the coal and favor combustion.The synergy of these factors contributes to the increase in the temperature of oxidation reactions,facilitating the culmination of the activation energy of the system,in which the ignition develops and the reaction is spontaneous.Currently,the incidence of each variable’s susceptibility to coal combustion is unknown,so in this work a methodology was developed to determine statistically which of the variables has the greatest contribution in the phenomenon.Descriptive statistics,atypical values detection,principal component determination,cluster analysis,and logistic regression were used to determine how many indicator variables are necessary to describe susceptibility to coal combustion.For the analysis,21,000 data from different seams of two open-pit coal mines in endwalls and abandoned pits were processed with consideration given to extrinsic and intrinsic factors.Seam temperature,atmospheric pressure,wind speed,oxygen,methane,height,ash,volatile matter,heat power,vitrinite,liptinite and the Hardgrove Index are the most influential variables in the phenomenon.

Thermogravimetric study of the effect of a PVA oxygen-insulating barrier on the spontaneous combustion of coal

Coal samples in the air for three months were characterized by Thermogravimetric Analysis (TGA). The effect of a PVA oxygen-insulating barrier on the spontaneous combustion of coal was examined. The moisture loss activation energy, oxidation activation energy and combustion activation energy were calculated by an integral method using the Coats-Redfen formula. The results show that the tendency for spontaneous combustion of three coal samples (judged by the activation energy) falls in the order: CYW>YJL>SW. The oxidation activation energy and combustion activation energy of coal protected by the PVA oxygen-insulating barrier increased. A significant increase in the combustion activation energy was noted, especially for the CYW coal where the in-crease was 28.53 kJ/mol. Hence, oxidation of the protected coal samples was more difficult. The PVA oxygen-insulating barrier helps to prevent spontaneous combustion of the coal.

Spontaneous combustion of coals and coal-shales

Spontaneous combustion of coal is a well-known phenomena around the globe. Apart from the coal itself,burning coal-shales is becoming a problem in the South African coal mines. Serious incidents of spontaneous combustion have been reported as a result of self-heating of reactive coal-shales. The intrinsic properties and spontaneous combustion tests of 28 selected coal and coal-shale samples were conducted and a relationship between the two has been established. Intrinsic properties were obtained by using the proximate and ultimate analysis, and spontaneous combustion liability tests results were obtained by using the Wits-Ehac and Wits-CT indices. The experimental results show that intrinsic properties of these materials complement to the spontaneous combustion liability tests results. Comparative analyses of intrinsic properties and spontaneous combustion characteristics indicate similarities between the mechanism of coal oxidation and that of the oxidative processes undergone by coal-shales. For the tested samples, coal samples have a higher intrinsic spontaneous combustion reactivity rating than the coal-shales.Furthermore, an increase in carbon, moisture, hydrogen, volatile matter, nitrogen and a decrease in ash content indicate an increased proneness to self-heating. The concentration of pyrite found in the coal-shales accelerates self-heating. The event of spontaneous combustion can occur if coal-shales absorb sufficient oxygen when subjected to atmospheric conditions.

Experimental Study of Spontaneous Combustion Rule of Ground Coal Storage Pile

By field measurement and laboratory experiment, a yieldable thermometric instrument was studied and manufactured on the basis of the spontaneous combustion rule of ground coal storage pile The instrument has been applied to the ground coal storage pile in Meiyukou Coal Mine of Datong Bureau and the depths of its self-heating and combustion layers and the inherent property of its spontaneous combustion have been obtained.

Comparative Experimental Analysis on Coal Spontaneous Combustion

The goal of this study was to investigate coal quality features and their relationship to coal spontaneous combustion characteristics in multi-seam coal mines to better predict when coal spontaneous combustion is likely to occur.To that end,coal samples of various particle sizes were obtained from five coal seams(Nos.6,8,9,12 and 20)in the Shuangyashan City Xin’an Coal Mine.The samples were then respectively heated using a temperature programming system to observe and compare similarities and differences in the sponta-neous combustion process of different particle sizes in response to rising temperature.The experimental results show,that in all five coal seams,the concentration of CO,C_(2)H_(4),and C_(2)H_(6) increased with a certain degree of regularity as a function of rising temperature.However,of these three gasses,only CO and C_(2)H_(4) can be used as indicators to predict coal mine spontaneous combustion.The critical temperature for samples from all five coal seams ranged from 50–85℃,while the dry cracking temperature of coal seams 8 and 12(80–100℃)were lower than those of 6,9,and 20(100–120℃).Furthermore,the production rate of CO,C_(2)H_(4),and C_(2)H_(6) is related to both coal particle size and temperature.The smaller the particle size,the faster the production rate;and the higher the temperature,the more gas that gets produced.All five coal seems are mainly com-posed of long flame coal.However,they differ in that the No.12 coal seam contains weak cohesive coal;the No.8 coal seam contains lean and gas coal;and the Nos.6,9,and 20 coal seams contain a certain amount of anthracite.During the programmed coal heating,the CO,C_(2)H_(4),and C_(2)H_(6) release trend for the coal seams was No.12>No.8>Nos.6,9,and 20.These results demonstrate that the presence of weak cohesive coal and anthracite highly influence the concentration of CO,C_(2)H_(4),and C_(2)H_(6) released during coal spontaneous combustion.

Modelling spontaneous combustion liability of carbonaceous materials

This paper presents predictive models to determine spontaneous combustion liability of carbonaceous materials （coals and coal-shales） using statistical analysis. The intrinsic properties and spontaneous combustion liability index were determined by testing 14 coals and 14 coal-shales from Witbank coalfields, South Africa. The relationship between these intrinsic properties （obtained from proximate, ultimate and petrographic analysis） and spontaneous combustion liability indices （the Wits-Ehac Index and Wits-CT Index） were established. The influence of the intrinsic properties of coal-shales in relation to coal properties affecting spontaneous combustion has been established using a statistical method. The linear regression analysis indicates better linear relationships between some of the selected intrinsic properties and spontaneous combustion liability index and thus, identifies the major intrinsic factors affecting their liability toward spontaneous combustion. It was found that a definite positive or negative correlation coefficient exists between the intrinsic factors and spontaneous combustion liability. A set of models to predict the spontaneous combustion liability was derived. The best significant correlation along with the most appropriate model as indicated by R-squared values, the coefficient of corre- lations and standard error was used to predict the incident of spontaneous combustion.

Crossing point temperature of coal

A further understanding of the self-heating of coal was obtained by investigating the crossing point temperature（CPT） of different ranks of coal.The tests were carried out using a self-designed experimental system for coal self-heating.50 g（±0.01 g） of coal particles ranging from 0.18 mm to 0.38 mm in size were put into a pure copper reaction vessel attached to the center of a temperature programmed enclosure.The temperature program increased the temperature at a rate of 0.8℃/min.Dry air was permitted to flow into the coal reaction vessel at different rates.The surrounding temperature and the coal temperature were monitored by a temperature logger.The results indicate that CPT is affected by coal rank,moisture,sulfur, and the experimental conditions.Higher ranked coals show higher CPT values.A high moisture content causes a delay phenomenon during the self-heating of the coal.Drying at 40℃decreases the effects of moisture.The reactivity of sulfur components in the coal is low under dry and low-temperature conditions. These components form a film that covers the coal surface and slightly inhibits the self-heating of the coal. The flow rate of dry air,and the heating rate of the surroundings,also affect the self-heating of the coal.The most appropriate experimental conditions for coal samples of a given weight and particle size were determined through contrastive analysis.Based on this analysis we propose that CPTs be determined under the same,or nearly the same conditions,for evaluation of the spontaneous combustion of coal.

Spontaneous combustion influenced by surface methane drainage and its prediction by rescaled range analysis

This study established numerical modeling using COMSOLTMto examine the influence of horizontal location and drainage ability of surface borehole on spontaneous combustion in longwall working face gob. Rescaled Range Analysis(R/S analysis) was employed to investigate the chaos characteristic of N_2/O_2 ratio from a surface borehole in 10416 working face gob, Yangliu Colliery, China. The simulation results show that there is always a circular ‘‘dissipation zone" around the drainage borehole and an elliptic ‘‘spontaneous combustion zone" in deep gob. Little influence was found on spontaneous combustion zone on the intake side of the gob but the width of spontaneous combustion zone in middle gob is enlarged, while the depth of spontaneous combustion zone near the return side is reduced. The R/S analysis indicates that the influence of surface borehole on spontaneous combustion can be divided into two stages by the chaos feature of N_2/O_2: safety drainage stage and spontaneous combustion initiating stage. It can be concluded that the methane drainage from gob through surface borehole can intervene in the distribution of spontaneous combustion zone in gob and the chaos feature of N_2/O_2 from surface borehole can effectively reflect coal spontaneous combustion condition in gob.

Spontaneous Combustibility Characterisation of the Chirimiri Coals, Koriya District, Chhatisgarh, India

Representative coal samples were collected from different coal seams of the Chirimiri coalfield which covered the entire stratigraphic sequence. These samples were tested for Chemical analysis, Crossing Point Temperature (CPT), Petrography, Infrared studies (IR) and Differential Thermal Analysis (DTA). All the test results vindicated that the aforesaid parameters had a definite relationship with the stratigraphic disposition or the ranks of coal. The low rank coals found as younger seams in the stratigraphic sequence were more prone to spontaneous combustion whereas the higher rank coals found at the bottom of stratigraphic sequence were less prone to spontaneous combustion. Through combustibility characterisation by different tests, it was found that the upper Duman and Kaperti seams placed as younger seams in the stratigraphic sequence are highly prone to spontaneous combustion whereas the lower Karakoh and Sonawani seams seem to be least prone to spontaneous combustion.

Combustion characteristics of high ash Indian thermal,heat affected coal and their blends

Onsite mine fire generates large volumes of heat-affected coal in Jharia coalfields,India.Direct utilization of such heat-affected coal in thermal utilities is not feasible as such coal does not have the desirable volatile matter required for combustion.In the present work,experimental studies have been carried out to investigate the possible utilization of such heat-affected coal in thermal utilities by blending with other coal.Heat-affected coal(31%ash and 5300 kcal/kg GCV)collected from Jharia coalfield were blended with thermal coal(28%ash and 5650 kcal/kg GCV)in different ratios of 90:10,80:20,70:30 and 60:40 to identify the desirable blend ratio for burning of blended coal in thermal utilities.Burning characteristics of all the coals were carried out using TGA.Various combustion parameters such as ignition temperature,peak temperature,burnout temperature,ignition index,burnout index,combustion performance index,rate and heat intensity index of the combustion process and activation energy were evaluated to analyse the combustion process.Experimental and theoretical analysis shows the blend ratio of 90:10 can be used in place of only thermal coal in utilities to reduce the fuel cost.

煤自燃程序升温实验及其在实验教学中的应用

该文利用程序升温实验系统,对三种氧气浓度(20.9%、10%和7%)所代表的采空区散热带、氧化带、窒息带进行了煤样自燃发火实验,采集了不同温度阶段的气体产物,分析了温度及氧气浓度对气体产物浓度的影响,并对指标气体进行了详细分类和评估。实验结果表明:交叉点温度CPT随着氧气浓度的升高而降低,干空气的交叉点温度为144.6℃,由经验关系计算得到的CPT值与实验数据相差仅6.08%;氧气浓度越高,临界温度越低,所产生的气体浓度越高;CO气体在不同的含氧环境下都是主要的氧化产物,可作为判断煤自燃发火的主要指标,C_(2)H_(4)和C_(3)H_(6)的产生表示煤体进入加速氧化状态,可作为判断煤自燃发火的辅助指标。

基于SSA-RBF神经网络的煤自然发火预测模型

为解决传统煤自燃预测模型预测状态单一和预测精度不高的问题,提出基于麻雀搜索算法(SSA)优化的径向基(RBF)神经网络煤自然发火预测模型。首先,采用程序升温试验分析煤样指标气随温度的变化特征,将煤自然发火过程按煤温分为缓慢(80≤t_(i)<120℃)、加速(120≤t_(i)<160℃)和激烈(t_(i)≥160℃)3个氧化阶段,同时分析这3个阶段指标气与煤温的灰色关联度;其次通过不同维度测试函数检验粒子群算法(PSO)、灰狼算法(GWO)和SSA算法性能;最后利用6个矿区数据验证基于SSA-RBF神经网络的煤自燃预测模型的优越性。结果显示,缓慢氧化阶段CO/ΔO_(2)、CO、C_(2)H_(4)这3种指标气体与煤温的灰色关联系数最大;而加速氧化阶段C_(2)H_(4)/C_(2)H_(6)、CO/ΔO_(2)、CO_(2)/CO_(3)种指标与煤温的灰色关联系数最大。3种不同维度函数的测试结果表明:SSA与PSO、GWO相比具有更好的全局搜索能力和稳定性,其收敛速度更快;神经元数量为5个、迭代次数为300次时,SSA-RBF神经网络预测模型对缓慢氧化和加速氧化阶段的预测准确性分别达到了99%和93%。

淮南矿区典型煤样自燃特性热重-红外联用实验研究

为降低煤矿安全事故发生风险,针对煤自燃氧化出现紧急危险性等问题,研究淮南矿区典型煤样的自燃特性。以淮南张集煤矿6、8、11-2和13-1煤样为例,通过热重-红外(TG-FTIR)联用技术分析煤样在升温氧化过程中的质量变化和气相产物析出特性。实验结果表明:四种煤样的升温氧化过程均可分为5个阶段,包含6个特征温度点;燃烧阶段各煤样反应活化能按由大到小排序为6煤、8煤、11-2煤、13-1煤;主要气相产物吸收峰强度按由高到低排序为13-1煤、11-2煤、8煤、6煤;根据活化能大小和主要气相产物吸收峰强度判断各煤样自燃风险按由高到低排序为13-1煤、11-2煤、8煤、6煤。本文结果可为类似矿区矿井火灾防治提供基础理论支撑。

硫含量对煤自燃特性的影响实验与模拟研究

为了探究硫含量对煤炭自燃特性的影响,寻找防治高硫煤自燃灾害的高效途径;使用程序升温实验系统、综合热分析仪(TG/DSC)对典型高硫煤和典型低硫煤的氧化过程进行分析;使用量子化学模拟软件对高硫煤常用阻化剂Ca(OH)_(2)、Na_(2)CO_(3)、MgCl_(2)和2种煤中典型有机硫结构二苯硫醚(C_(12)H_(10)S)、苯硫醇(C6H5SH)的络合作用进行计算。结果表明:高硫煤氧化过程中质量下降更快,放热量更大;热解失重和燃烧阶段中高硫煤的活化能相比低硫煤分别小9.16%和15.07%,高硫煤发生煤自燃的倾向更高;煤矿常用阻化剂中的Ca^(2+)、Na^(+)、Mg^(2+)可以与二苯硫醚和苯硫醇络合形成络合物,形成络合物后2种有机硫结构的化学反应活性降低,能够对煤自燃起到抑制作用。

采空区煤自燃高温点识别与探测技术研究与展望

我国因采煤活动造成的采空区总量大、范围广,针对采空区煤自燃高温点的有效识别与探测是煤矿安全生产的重要保障。从采空区煤自燃发生过程、高温点的形成运移特点概述了采空区高温点的生成演化特性,为采空区煤自燃高温点的有效识别与探测提供基础理论支撑。围绕地下直探技术、地表及空天探测技术的基本原理、研究进展以及现场实际应用效果,从可靠性、稳定性等方面进行多元比较,剖析现有煤自燃高温点识别探测技术的适用性。针对探测中存在的实际难点,拓展分析了矿井声波温度信息探测、基于量子技术的热源探测、毫米雷达波探测技术等新兴技术的研究现状和应用潜力,进一步推动采空区隐蔽火源精细化探测技术发展创新。通过对现有技术的综合性研判及新兴技术的前瞻性思考,展望了煤自燃隐蔽火源探测技术的未来发展趋势,结合当前物探技术和多元信息融合理论的发展趋势,提出了采空区高温点动态运移智能可视化系统构想,从“空-天-地-孔”的综合化分时分区多维探测模式应用、“特征获取-场景仿真规划-动态决策”逐级时空演化数字孪生模型两方面阐述了矿井开采全生命周期平台建设的现实意义。通过该构想的逐步实施,为实现采空区隐蔽火源的高效识别预测和矿井智能化建设提供新的决策思路。

煤矸石低温氧化官能团演化与气体相关性分析

为研究煤矸石自燃的低温氧化过程中活性官能团的演化规律及与气体释放之间的联系,利用傅里叶变换红外光谱仪和程序升温控制装置组成的实验系统对煤矸石样品在空气氛围下30~350℃的光谱实验数据进行分析,并采用Spearman法对气体释放与官能团进行相关性研究。结果表明:自燃过程中羟基含量整体呈上升趋势,脂肪烃在氧化反应中含量较高且反应活跃,含氧官能团在氧化中受脂肪烃影响;CH_(4)析出量随着脂肪烃-CH_(2)-、取代芳烃C-H、羟基含量升高而升高,CO则随羰基、芳香烃C-H含量升高而升高、随含氧官能团含量升高而下降,CO_(2)在氧化过程中的释放主要随羟基和羰基含量升高而升高,呈现出极高的相关性。

酸洗脱灰处理对煤自燃倾向性的影响分析

煤自燃倾向性是矿井火灾预测的关键参数之一,受煤的化学成分、孔隙结构、官能团等多种自身理化性质的影响,酸洗脱灰处理可以有效去除煤中杂质,提高煤的纯度。为深入探究酸洗处理对煤自燃倾向的影响,采用2 mol/L的硫酸对煤样品进行酸洗处理。通过气相色谱、热分析及红外光谱等实验,将酸洗煤样品与原煤样品进行对比分析。结果表明,酸洗脱灰处理能够有效去除煤中赤铁矿等金属氧化物类矿物,以及高岭土等矿物。同时对煤中芳香类官能团的取代结构、含氧官能团中的羟基以及脂肪类官能团中的侧链结构等产生显著影响。与原煤相比,经处理的煤样品脱灰率为26.4%,交叉温度点由203.6℃变为205.5℃,热失重速率从11.27%/min降为10.21%/min,峰值温度由503.77℃升高为521.66℃,自燃倾向性降低,为酸洗后煤自燃的预测和防控提供了理论指导。

常温氧化中预氧化温度对煤体影响规律和机理研究

在预氧化过程中,会产生温度分布变化,从而影响煤的自燃特性规律。通过进行常温氧化试验对不同预氧化温度煤体的煤心温度变化、CO和CO_(2)等指标性气体变化进行分析,得出随着预氧化温度的提高,会促进煤体发生自燃的结论,并对其产生的可能环境原因进行了分析和探讨。

不同通风速率下水浸煤燃烧特性及氧化动力学研究

煤样在长期的浸水过程中突然风干会增加煤自燃风险,进而发生煤自燃现象。通风速率是影响煤自燃的一个关键因素,但它对水浸煤自燃的影响尚不清楚。为了研究通风速率对水浸煤燃烧特性的影响,先利用程序升温系统测试了煤样在低温氧化过程中的交叉点温度和CO与CO_(2)释放规律,然后利用同步热分析仪对水浸煤的燃烧特性进行了测试,最后利用红外光谱测试了水浸煤的官能团含量。结果表明:通风速率为60 mL/min时煤样的交叉点温度最低,但是CO与CO_(2)释放量随着通风速率的增加而增加;煤燃烧过程中存在最佳通风速率,此时煤的活化能最小,煤更容易燃烧,释放出的热量也更多;通风速率越高,煤中含有越多的羰基和羧基等含氧官能团,为煤氧化提供了足够的能量来源。