How moisture loss affects coal porosity and permeability during gas recovery in wet reservoirs?

Moisture in coal seams changes gas adsorption capacity, induces coal deformation, and affects coal porosity. However, fewer studies have investigated the dynamic process of moisture loss. In this study, a fully coupled multi-physical model for coal deformation, gas flow and moisture loss was implemented. It validated the coal-gas-moisture interactions of the decay of gas adsorption capacity and the coal shrinkage.Subsequently, the proposed model was applied to a simulation of coal seam gas recovery from wet reservoir and solved using the finite method in COMSOL Multiphysics 3.5. Analyses of the component factors and the sensitive parameters of moisture loss on coal porosity and permeability were comprehensively studied at last. The results reveal that moisture loss enhances coal porosity and permeability. The decay of gas adsorption capacity decreases coal permeability while the coal shrinkage promotes it. The decrease of the adsorption decay coefficient and the increase of the initial density of saturated water vapor and water evaporation constant can enhance the permeability of wet coal seams.

Effect of coal moisture content on coke’s quality and yields of products during coal carbonization

The coal with low moisture during carbonization could not only increase the yield of coke,but also promote the coke quality and reduce the energy consumption.In this paper,the influence of the moisture in the blend coal(1.8%10.13%)on the product yields and coke quality during coal carbonization were investigated.The results show that the coke yield is increased from 75.90%to 77.16%,and the coke qualities such as coke strength after reaction with CO2(CSR),coke reactivity index(CRI),fragmentation index(M25)and abrasion index(M10))are also improved when the moisture of the blend coal decreases from 10.13%to 1.80%in a bench scale reactor.Due to the secondary reaction,tar become lighter when the moisture is decreased.In order to further prove the above results,the blend coal with 1.8%and 9%10%(common moisture used in coke plant)moisture is carbonized in a coke oven with 6 m height,the results show that CRI are 23.4%and 27.3%,CRS are 67.1%and 62.2%under 1.8%and 9%10%moisture of blend coal.Moreover,the variation of the moisture in blend coal has a limited influence on dust emission at the ascension pipe and the charging car.

Study on Spatial Variation of Soil Moisture in Coal Mining Subsidence Area in Mu Us Sandy Land

In order to explore the spatial distribution and variation characteristics of soil moisture in coal mining subsidence area in Mu Us sandy Land,and provide theoretical basis for the restoration of the mining area,experiments based on a linear sampling and classic statistical and geostatistical methods were conducted. Spatial distribution characteristics and variation of soil moisture in the typical 0 to 100 cm dune area in the subsidence area and the non-subsidence area( control) were studied. The results showed that in the typical sand dune location of nonsubsidence area( control),the probability distribution curves of soil moisture changes in all layers along vertical and horizontal directions were all normal distribution,and it was consistent with the temporal and spatial variation characteristics of soil moisture in conventional dunes in Mu Us sandy land. By contrast,two years after the coal mine collapsed,the variations of soil moisture in different layers along vertical and horizontal directions were different,and soil moisture loss was more serious than that of control dune by nearly 10% to 30%,and the standard deviation varied from 0. 54 to 1. 05,increasing by 52. 08% compared with the non-subsidence area( control). The probability of positive and negative deviation greater than 1 was over 50%,and the coefficient of variation varied from 0. 14 to 0. 28,which was 80% higher than that of nonsubsidence area( control). After collapsing,the average level of soil moisture,standard deviation,variance and variation coefficient had greatly changed,and influence of coal mining subsidence on soil moisture was the most in the middle layer( 30-70 cm),and was not obvious in the surface( 0-20 cm) and lower layer( 80-100 cm). In coal mining subsidence area,the dispersion degree of soil moisture in different layers along the vertical and horizontal direction was greatly improved,which increased spatial variation of soil moisture.

A novel method for measuring the moisture content of coal powder by microwave resonator

A novel technique for the quick measurement moisture content of coal powder by microwave was studied. The effects of the various moisture contents on the measurement results were also discussed. The experimental results show that the standard deviation is less than 0.36% when the moisture content of coal powder is 0.74%-16.90% and the standard deviation is less than 0.16% when the moisture content is 0.31%-1.49%. The experimental results indicate that a process of quick measurement moisture content of coal powder by microwave is practical.

Interactions of dynamic supercritical CO_(2) fluid with different rank moisture-equilibrated coals: Implications for CO_(2) sequestration in coal seams

The interactions between CO_(2) and coals during CO_(2)-ECBM(CO_(2) sequestration in deep coal seams with enhanced coal-bed methane recovery)could change pore morphology and chemistry property of coals,thereby affecting adsorption,diffusion and flow capability of CO_(2) and CH_(4) within coal reservoirs.To simulate CO_(2)-ECBM process more practically,the dynamic interactions of supercritical CO_(2)(sc CO_(2))and moisture-equilibrated coals were performed at temperature of 318.15 K,pressure of 12.00 MPa,and duration of 12.00 h.The impacts of the interactions on physicochemical properties of coals were investigated.Results indicate that sc CO_(2)/H_(2)O exposure shows minor effect on micropores of coals.However,the exposure significantly decreases the mesopore surface area of bituminous coals,while increases that of anthracites.The mesopore volume and the average mesopore diameter of all the coals after sc CO_(2)/H_(2)O exposure decrease.The multi-fractal analysis verifies that the sc CO_(2) exposure can enhance the pore connectivity of various rank coals.Apart from the pore morphology,the exposure of sc CO_(2)/H_(2)O also affects the oxygenic functional groups on coal surface.Particularly,the exposure of sc CO_(2)/H_(2)O reduces the content of CAO and C@O of coals.The content of COOH of low rank coals including Hehua-M2#coal,Zhongqiang-4#coal,Buliangou-9#coal and Tashan-5#coal decreases,while the high rank Laochang^(-1)1#coal and Kaiyuan-9#coal witness a growth in COOH.The content of total oxygenic functional groups of all coals after interaction with sc CO_(2)/H_(2)O decreases;on the contrary,that of CAC/CAH of all coals after sc CO_(2)/H_(2)O exposure increases.In summary,the interaction with sc CO_(2)/H_(2)O significantly changes the pore system and oxygenic functional groups of various rank coals,which needs further attention regarding CO_(2)-ECBM.

Effect of Moisture on Combustion Characteristics of High⁃Moisture⁃Content Coal Slime

The effects of moisture content on the combustion characteristics and pore structure change of coal slime are studied in this paper.The effect of moisture content on the bed temperature change,combustion efficiency,and NO_(x)and SO_(2)emission were obtained in a bench⁃scale fluidized bed reactor,revealing that the lowest bed temperature decreases with the increase in moisture content,but the effect on the highest bed temperature is not the same.Moreover,with the increase in moisture content,the observed degree of blackening of the flue gas increased,and more CO was produced,which in turn leads to a lower combustion efficiency of the coal slime.However,the presence of moisture plays a positive role in the reduction of NO_(x)and SO_(2).With the increase in moisture content,the amount of NO_(x)and SO_(2)produced tends to decrease.The effect of water on the combustion process of slime is mostly the impact of the severe vaporization process in the early stage to form a large water vapor channel,which is beneficial to the evaporation and loss of water,conducive to the reaction of water and coal combustion products,such as the formation of CO,reduction of NO_(x),SO_(2),etc.The large holes formed by the impact of water vapor decreased with the decrease of moisture content,and the nanoscale pores are mostly caused by the combustion process of volatilization and coke formation after the end of vaporization,and increase with the decrease of moisture content.

Discussion on Selection of Pulverizer and Moisture of Pulverized Coal for Lignite Boilers

In China,the abrasion index and the free moisture are regarded as the criteria for determining whether the medium-speed pulverizer or the fan pulverizer could be selected.Based on comprehensive studies on foreign methods for choosing the pulverizing system for lignite boilers,it is suggested that the particle size of coal,the drying time,the drying temperature and the humidity should be taken into account when measuring the free moisture of lignite,and the total moisture could also be the principle for type selection of pulverizer for lignite boilers.Furthermore,the determination of pulverized-coal moisture has great influence on the running of pulverizing systems.The actual moisture of certain pulverized coals is compared with that calculated with different methods and a feasible method for determining the moisture of the pulverized coal is suggested.

Investigating spatial and temporal variations of soil moisture content in an arid mining area using an improved thermal inertia model

Mining operations can usually lead to environmental deteriorations. Underground mining activities could cause an extensive decrease in groundwater level and thus a dramatic variation in soil moisture content（SMC）. In this study, the spatial and temporal variations of SMC from 2001 to 2015 at two spatial scales（i.e., the Shendong coal mining area and the Daliuta Coal Mine） were analyzed using an improved thermal inertia model with a long-term series of Landsat TM/OLI（TM=Thematic Mapper and OLI=Operational Land Imager） data. Our results show that at large spatial scale（the Shendong coal mining area）, underground mining activities had insignificant negative impacts on SMC and that at small spatial scale（the Daliuta Coal Mine）, underground mining activities had significant negative impacts on SMC. Trend analysis of SMC demonstrated that areas with decreasing trend of SMC were mainly distributed in the mined area, indicating that underground mining is a primary cause for the drying trend in the mining region in this arid environment.

Mechanism and control of water seepage of vertical feeding borehole for solid materials in backflling coal mining

To solve the problem of water seepage of vertical feeding borehole for solid materials,we established the fluid-solid coupling dynamic model of groundwater flowing in rock mass adjacent to the vertical feeding borehole.Combining with the engineering geological conditions,we built a numeral model to study the influence rule of the aquifer hydraulic pressure and seepage location of feeding borehole on the amount of seepage with fnite element numerical method.The results show that the nonlinear relationship is presented among the amount of seepage,the seepage location and aquifer hydraulic pressure.The higher the aquifer hydraulic pressure is,the closer the distance between seepage location and aquifer is,and the faster the harmful levels of aquifer will grow.In practice,we calculated the allowable seepage of feeding borehole by the optimum moisture content and natural moisture content of backflling materials,and then determined the protection zone of feeding borehole,so the moisture content of backflling materials can be controlled within the scope of optimum moisture content.

An Experimental Study on the Conductivity Changes in Coal during Methane Adsorption-Desorption and their Influencing Factors

During the processes of methane adsorption and desorption,the internal structure of coal changes,accordingly leading to changes in electrical conductivity.In this paper,using low rank coal seams of the Yan'an Formation in the Dafbsi field as the research subject,the relationship between coal resistivity,methane adsorption quantity,and equilibrium pressure is analyzed through proximate analysis,mercury injection tests,low temperature liquid nitrogen adsorption tests,and coal resistivity measurements during methane adsorption and desorption.The results show that during the process of pressure rise and methane adsorption,the conductivity of coal increases,resulting from heat release from methane adsorption,coal matrix swelling and adsorbed water molecules replaced by methane,but the resistivity reduction gradually decreases.The relationship between coal resistivity and methane adsorption quantity and equilibrium pressure can be described by a quadratic function.During the processes of depressurization and desorption,the resistivity of coal rebounds slightly,due to decalescence of methane desorption,coal matrix shrinkage and water-gas displacement,and the relationship coincides with a linear function.Methane adsorption leads to irreversible changes in coal internal structure and enhances the coal conductivity,and resistivity can not be restored to the initial level even after methane desorption.The resistivity and reduction rate of durain are higher than those of vitrain,with relatively greater homogeneous pore throat structure and fewer charged particles in the double electric layer.In addition,moisture can enhance the conductivity of coal and makes it change more complexly during methane adsorption and desorption.

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.

含水率对松软煤体波速及破坏特征影响的试验研究

为研究含水率对松软煤体超声波波速与破坏特征的影响,针对不同含水状态型煤试样,采用岩石力学试验机(mechanical testing&simulation,简称MTS)、超声波监测仪,结合图像处理技术(digital image correlation,简称DIC)开展单轴压缩条件下煤体波速、表面形态监测试验,分析波速及变形演化特征;运用计算机断层(computed tomography,简称CT)扫描试验系统进行破坏煤体细观结构观测试验,获取三维裂隙分布形态和特征参数;探讨初始波速和破坏煤体波速随含水率变化规律。研究结果表明:(1)随轴向应变的增加,各含水率下煤体波速均呈现平稳-缓慢下降-急剧下降-再平稳4个变化阶段,且随含水率的增加,波速变化的缓慢下降、急剧和再平稳现象均推迟启动。(2)煤体初始波速及破坏后波速随含水率的增加均先增后减,荷载作用后煤体波速降低值与含水率呈线性关系。(3)随含水率的增加,破坏煤体内部裂隙表面积、裂隙体积及三维分形维数均具有线性增大的变化趋势,煤体由剪切破坏向拉伸破坏转变。(4)微观结构是导致各含水率下煤体初始波速差异的主要原因,而破坏煤体波速由微观结构和细观裂隙分布共同决定。研究结果可为揭示注水煤体声学力学响应特征,防控失稳灾害提供试验依据。

采煤沉陷区地裂缝对土壤含水率的影响

为了探究地裂缝对深层土壤含水率的影响,以陕北某煤炭基地煤矿区为研究对象,利用统计分析方法分析动态地裂缝和边缘地裂缝对浅层(0.1~0.3 m)和深层(0.5~6.0 m)土壤含水率的影响,并基于克里金插值法解析土壤含水率的时空变化规律.研究结果表明:①竖直方向上,深度为0~2.0 m时,动态地裂缝区和边缘地裂缝区的土壤含水率均低于未扰动区的值;深度为2.0~6.0m时,各区土壤含水率差异不明显,表明地裂缝对土壤含水率的影响深度约为0~2.0 m,即地裂缝对浅层土壤含水率的影响较大,对更深层土壤含水率的影响相对较小.②水平方向上,动态地裂缝区土壤含水率整体低于闭合区,而1年边缘裂缝区土壤含水率整体高于2年边缘裂缝区,表明地裂缝会对土壤含水率的空间分布产生较大影响.综合来看,地表塌陷与地裂缝的出现改变了土壤的结构状态,加速了土壤水分的蒸发,降低了土壤持水性.

低温和含水率对重塑性煤体抗剪强度影响研究

为了研究温度—含水率耦合作用下重塑性煤体抗剪强度的变化规律,保障松软煤层安全高效稳定开采,采用直剪试验分析了重塑性煤体在较低温度(20、0、-10、-20、-30、-40℃)、一定含水率(0、0.8%、4%、8%、12%、16%)耦合作用下的抗剪强度特性,并通过数学统计分析了温度与含水率对抗剪强度的影响。研究结果表明:含水率为0时重塑性煤体的黏聚力随着温度的降低呈幂指数增加;温度—含水率耦合作用下重塑性煤体的抗剪强度均与垂向应力成正比,均符合莫尔-库仑准则;在温度为10~20℃、含水率为12%~16%时,黏聚力达到最大值322.9 kPa,最小值138.0 kPa出现在温度-40℃、含水率4%附近;在-20~-40℃温度下,重塑性煤体内摩擦角随含水率的增加逐渐降低至最小值18.25°;当含水率为6%~13%、温度为-20~10℃时,内摩擦角达到最大值31.45°,对应抗剪强度达到最大值。温度—含水率耦合作用下,重塑性煤体抗剪强度、内摩擦角与黏聚力均受温度的影响较大。

基于EMD-GRU的港口堆场煤炭含水率智能预测与实验研究

针对煤炭港口堆场洒水抑尘需求,提出了基于EMD-GRU的煤炭含水率预测模型并进行了实验验证。通过建立煤炭堆场含水率预测模型,利用实时数据驱动预测煤炭堆垛含水率变化,根据气象数据与含水率变化情况判断煤炭堆垛未来起尘情况并制定相应的洒水策略。实验结果表明,EMD-GRU模型的均方根误差、平均绝对误差、平均绝对百分比误差和决定系数分别为0.768、0.566、9.52%、0.944,与SVR、DTR、RNN、LSTM、GRU等预测模型相比,EMD-GRU预测模型的各误差值均最低,决定系数为最高,且预测精度与拟合效果最好。

高水分褐煤流动性实验研究

【目的】研究原煤中水分、粒径以及煤仓材质对原煤流动性的影响,找出造成原煤仓堵煤的主要原因。【方法】设计并搭建了原煤流动性实验装置,对不同水分、粒径的原煤进行流动性实验,并绘制流动特性图,得到各要素对原煤流动性的影响。【结果】原煤水分越大,流动特性图折线越靠右,下落质量越少,流动性越差,完全下落所需的旋转角度越大;煤下落的初始位置不同是由于不同粒径之间的静摩擦力不同导致其安息角不同。水分降低会使得摩擦力减小,下落质量增大;聚四氟乙烯材质的流动性折线位置靠前,底部摩擦系数小,同样角度下落质量更多,流动性增强。【结论】水分在原煤流动性中起关键作用,粒径对原煤流动性的影响微弱,粒径只有与水分共同作用才会对其流动性产生较大影响。材质对原煤流动性的影响也较大,但在水分偏低时可忽略其影响。

燃煤电站掺烧污泥热力学与经济性分析

我国污泥产量逐年增加,如何对其进行无害化、资源化处理成为亟待解决的问题,拟将燃煤电站与污泥干燥系统耦合,湿污泥干燥后进行掺烧。以某典型超临界660MW机组为研究对象,在THA工况下,通过对锅炉进行热力计算和对系统整体进行热力学分析及经济性分析,研究掺烧不同含水率(10%、20%、35%、50%、65%)不同掺烧量(2%、4%、6%、8%、10%)的干化污泥对排烟温度、锅炉效率、净发电效率、湿污泥发电折合净效率和干化污泥发电折合净效率等参数的影响。结果表明:当干化污泥含水率超过50%时会导致参数恶化且随掺烧量的增加变化趋势加剧;干化污泥的含水率应控制在50%及以下,若超过此值,掺烧量应小于4%;掺烧污泥导致系统的㶲效率降低,主要原因是锅炉和干燥设备的㶲损失增加;当掺烧含水率为20%,掺烧量为10%的干化污泥时,系统经济性最好,动态回收周期仅为4.02年。

大佛寺煤矿开采区土壤水分变化遥感反演研究

土壤水分是驱动矿区生态环境变化的关键要素。为研究黄土高原煤矿区开采沉陷对土壤水分变化的扰动影响,以彬长矿区大佛寺煤矿为例,采用主动微波和光学遥感影像反演开采沉陷区土壤水分的空间变化,用水云模型消除植被对主动微波影像的后向散射系数影响,通过实地采样数据构建支持向量机回归模型,获取矿区地表土壤水分的分布特征,分析黄土沟壑区地形因子和开采沉陷变形对矿区土壤水分变化的影响。结果表明:SVM构建的回归分析模型可以有效反演黄土高原煤矿开采区土壤水分的空间分布,地形特征对土壤水分的影响最大,沟壑区域土壤含水量更高;在未受开采影响的区域,土壤水分变化受地形坡度影响最大,坡向次之,高程影响最小;在40201工作面开采沉陷变形区域,土壤水分分布的变异系数显著增大,尤其在采动裂缝发育区更为明显。研究结果为揭示黄土高原煤矿开采区土壤水分变化的时空特征及机理提供了技术支持。

干燥温度对磨煤机出力的影响

煤的可磨性指数表征的是破碎煤的难易程度,影响到制粉系统能耗。通过一组干燥试验,研究了干燥强度对大同烟煤和元宝山褐煤的哈氏可磨性指数的影响规律,归集出干燥强度对哈氏可磨性指数影响趋势线。干燥对可磨性指数的影响不仅体现在水分的变化,干燥过程中会使煤的结构变化,也影响着可磨性指数。研究结果可以指导火电厂磨煤机运行中,各干燥介质风量组成及一次风温度等参数的调整。通过煤的干燥强度的调整,可以有效降低制粉系统的能耗。

高水分褐煤流动性离散元数值模拟

【目的】由于火电厂实际运行下使用的均为高水分褐煤,输送煤的过程中经常会发生堵塞以及黏附等问题。因此,利用EDEM软件对该问题进行数值模拟分析。【方法】通过对现场煤样考察分析,模拟过程中主要对煤的粒径、水分以及流动总量进行分析,并探究其对煤的流动性的影响。数值模拟分析后,将流动速度以及颗粒之间作用力进行对比,得到各项因素对煤流动的影响。【结果】造成堵塞的主要原因如下:首先,煤的粒径过大或过小导致在仓体流动过程中其自身颗粒与颗粒之间发生相对作用;其次,煤在仓体流动过程中,随着煤量增加,其流动状态由整体流动转变为中心流动;最后,煤的含水率是最主要的因素,其不仅影响自身黏附性,还会引起自重的增加,所以水分过大会引起流动缓慢,进而发生堵塞。【结论】研究结果可为解决燃煤电厂堵煤问题提供理论支持。