An expanded model for predicting surface coal mine drill respirable dust emissions

Overexposure to airborne respirable crystalline silica dust can cause disabling or fatal respiratory disease, and mine worker exposure to silica dust continues to be an ongoing occupational health concern. Exposures of surface coal mine rock drillers to respirable crystalline silica are of particular concern. On surface coal mine drills, bailing air flushes the cuttings out of the drill hole. Conveyor belting material is typically used to fabricate a shroud around the drill deck in an effort to contain the drill dust so that it can be captured by a collector. Dust leakage from the drill shroud is usually the worst dust source problem on most drills. The focus of this work is drill shroud dust leakage and the relationships of various drill parameters on this leakage. Experimental data were obtained and used in combination with dimensional analysis to establish these relationships. In general, it is found that airborne respirable dust (ARD) concentrations vary in a direct relationship with shroud leakage area and in an inverse relationship with drill deck cross-sectional area and shroud height. This work expands the testing and dimensional analysis previously reported for collector/bailing air flow ratios ranging from 2:1 to 4:1 to include ratios approaching 1:1. A semi-empirical mathematical model has been developed and expanded to describe ARD generation on surface coal mine drills. Geometric parameters included are drill deck height and cross-sectional area, shroud leakage associated with the deck shroud, and the operational parameters of bailing airflow and dust collector airflow. The relationships can be described by logarithmic functions and yield predictive ARD values, which fall in the range measured on operating drills for collector/bailing air flow ratios greater than 2. However, at values of collector/bailing air flow ratios of approximately 1.1, the amount of ARD shows minimal response, if any, to drill deck shroud improvements that do not result in near-perfect seals. This is a condition that can occur in actual operation and is a substantially different result than previously expected and reported. Application of these results should provide mine operators with sufficient information to determine (1) the relative magnitude of their dust emissions, (2) where they should focus their efforts to reduce ARD emissions and (3) the improvement they could reasonably expect to achieve. Given that exposures of surface coal mine rock drillers to respirable crystalline silica are of particular concern, substantial reductions of airborne silica dust during drilling may be estimated and achieved through use of the analysis presented.     

Semi-Empirical Model for Predicting Surface Coal Mine Drill Respirable Dust Emissions

Over exposure to airborne respirable crystalline silica dust can cause serious or fatal respiratory disease and mine worker exposure to silica dust continues to be an ongoing occupational health concern. Exposures of surface coal mine rock drillers to respirable crystalline silica are of particular concern. MSHA dust exposure data from 1985–1992 showed that the percentage of the highwall drill dust samples (Designated Work Position, DWP) having greater than 5 percent silica and exceeding the 100 µg/m 3 silica limit were 81 percent and 77 percent, respectively. Although a recent analysis of the MSHA data from 1996–2000 shows that the percentage of the DWP drill dust samples exceeding the permissible exposure limit has dropped to 31 percent, MSHA data still suggests that over exposure to silica dust is an ongoing surface coal mine dust problem for the highwall drill operator. On surface coal mine drills, bailing airflow flushes out the drill hole by removing the cuttings from the hole. Conveyor belting material is typically used to fabricate a shroud around the drill deck in an effort to contain the drill dust so that it can be captured by a collector. Dust leakage from the drill shroud is usually the worst dust source problem on most drills. The focus of this work is drill shroud dust leakage and the relationships of various drilling parameters on this leakage. Experimental data was obtained and used in combination with dimensional analysis to establish these relationships. In general, it is found that airborne respirable dust concentrations vary in a direct relationship with shroud leakage area and in an inverse relationship with drill deck cross-sectional area and shroud height.     

煤层钻孔孔口除尘装置的设计与实验研究

针对煤矿瓦斯抽放干式钻孔施工过程中产生大量粉尘的问题,提出利用射流泵技术除尘的新思路,即运用有压水流从喷嘴以一定速度喷出引起负压场卷吸煤尘进入除尘器,并与水流混合后排出,进而达到除尘效果。为使除尘效果最优,研究了孔口除尘器的结构组成和工作原理,并设计了水射流除尘器的结构和尺寸;运用均匀设计法对影响水射流除尘器吸气量的相关参数进行研究,实验优化了水射流除尘器的运行参数和结构参数。通过模拟煤矿瓦斯抽放钻孔施工现场打钻情况对孔口除尘装置的除尘效率进行实验,结果表明,孔口除尘装置除尘效率达到95%以上,能够显著降低煤矿干式钻孔过程中产生的粉尘污染。     

Field evaluation of air-blocking shelf for dust control on blasthole drills

In previous studies, an air-blocking shelf has been shown to be successful in reducing respirable dust leakage from the drill shroud in a laboratory setting. Dust reductions of up to 81% were achieved with the shelf under operating conditions consisting of a 1.9:1 collector-to-bailing airflow ratio and a 5.1-cm gap between the shroud and ground. Recent research focused on evaluating the shelf on two actual operating blasthole drills, in much more severe environments. In the field, the shelf reduced dust levels in the areas surrounding one operating blasthole drill by 70%. Dust reductions measured in the immediate vicinity of the shroud were reduced by 66% at one mine and 81% at the other mine. These field tests confirm that the air-blocking shelf is useful for reducing respirable dust generation from blasthole drills.     

Water separator shows potential for reducing respirable dust generated on small-diameter rotary blasthole drills

Drilling with water has the potential to significantly reduce the respirable dust concentrations generated from small-diameter rotary drills when drilling blastholes on surface mining operations. However, water adversely affects tri-cone drill bits commonly used in surface drilling operations, causing excessive wear and premature replacement. Consequently, dry drilling with a dust collector system has the most widespread use in the industry. Tests have been conducted by the National Institute of Occupational Safety and Health (NIOSH), Pittsburgh Research Laboratory (PRL) on a newly designed device for smaller diameter drills that separates the water from the bailing air before it reaches the bit and thus provides the cost benefit of dry drilling while providing the benefit of wet drilling for dust suppression. The water that is delivered to the hole with the bailing air is separated from the air by a proprietary mechanical device that is encased in a drill sub (short section of drill rod/pipe) located immediately behind the cutting bit. A cascade cyclone and a real-time dust monitor were used to sample dust emissions from the holes. Dust concentrations and silica content were measured when drilling dry versus drilling wet. The tests show that drilling with this water separating sub can reduce both measured dust emissions from the boreholes and visible dust around the drill rig.     

Optimization of overburden drill dust control systems on surface coal mines

ABSTRACT

A significant problem at U.S. surface mining operations is complying with more stringent dust standards resulting from high respirable free silica concentrations. In areas where potentially harmful concentrations of silica-bearing dust exist, more stringent dust standards are applied to limit the amount of respirable free silica to which the workers are exposed. According to U.S. Mine Safety and Health Administration (MSHA) data, overburden drilling occupations have the greatest exposure to silica

Worker exposure may be reduced by reducing the amount of dust produced by the drill. This can be accomplished with either dry collection or wet suppression systems. Both of these systems were evaluated in the field, results of this testing are the subject of this paper. This work was performed under a U.S. Bureau of Mines contract by PEI Associates, Inc.

A special study of dry and wet systems was conducted to determine the proper operating parameters for each type of system. Shroud height was evaluated for dry systems and water flow rate was evaluated for wet systems. In the case of dry systems, it was found that a nearly Inverse relationship exists between shroud height and control efficiency. The dry system performed most efficiently when the shroud was positioned 0.23 m or less from the ground. In the case of wet systems, the control efficiency versus water flow rate curve showed a steep Increase in efficiency in the range of 0.09 to 0.11 m³/hr. The highest control efficiency (96%) was at a water flow rate of 0.27 m³/hr. Flow rates this high however, can cause operational problems, such as plugging of the drill bit

In general, the results of the study demonstrated the efficacy of control equipment available in the U.S. for overburden drills. Used In combination, dust control equipment, pressurized cabs, and personal protective equipment should allow U.S. surface mine operators to comply with more stringent dust standards at surface coal mines.     

Study on dust control performance of a hammer drill bit

A computational fluid dynamics (CFD) study was conducted to investigate the effect of several important factors on the dust control performance of a down-the-hole (DTH) air hammer drill bit for reverse circulation drilling in mines. It was shown that an increasing number of suction nozzles or inclination angles of suction nozzles was advantageous to improve dust control performance of the drill bit. Lowering the location of suction nozzles in the drill bit body is another way to increase its ability to control dust. There exists a critical diameter of suction nozzles for dust control performance. A series of experimental tests in the laboratory were carried out to validate the results of CFD modelling. It was shown that the CFD simulation results were in good agreement with experimental data. A prototype of the drill bit was built for testing in laboratory experiments. The same prototype was field-tested by drilling vertically downward exploration boreholes in one of the largest Molybdenum Ore Districts in Luanchuan of Henan Province, China. Field test results indicate that the modified drill bit could control drilling dust effectively. No cuttings escaped from the borehole when it was used for downward drilling. The DTH air hammer drill bit has not been tested for drilling a vertically upward hole, and therefore, future studies are required to improve the suction capacity of the drill bit for drilling vertically upward holes.     

瓦斯抽采钻孔集成除尘系统设计与应用

 本文针对平顶山矿区突出煤矿井下瓦斯抽采钻孔工程量大,钻孔施工过程中产尘量大、除尘难度大的特点,系统分析了当前国内外孔口除尘技术研究现状,在现场实测研究钻孔施工过程中粉尘扩散、流动、沉降规律的基础上,开发设计高效钻孔孔口集成除尘装置,对进一步降低瓦斯抽采钻孔粉尘危害进行了探索。     

孔口除尘系统在李子垭煤矿的应用

通过对钻孔防尘现状及存在问题分析的基础上,介绍了一套新型的孔口降尘系统,该套系统通过在李子垭煤矿的现场应用和考察,有效抑制了干式钻孔的粉尘污染问题,大大改善工人的工作环境,为大力推广干式钻孔奠定了基础。     

YZG7矿用钻孔轨迹仪在朱家店煤矿的应用

以随钻轨迹测量为研究对象,针对传统的回转钻机钻进测量钻孔空间轨迹的方式,造成钻孔实际轨迹与设计出现较大偏差为研究背景,结合矿井现场应用,提出了采用进行钻孔轨迹测量。阐述了YZG7矿用钻孔轨迹记录仪结构与原理以及施工方法,并在朱家店煤矿进行现场应用。实践得出实钻终孔位置和设计终孔位置上下偏差2.28 m,左右偏差7.62 m,掌握了实钻钻孔轨迹钻进情况。     

新型孔口除尘器研究及应用

针对目前矿井干式打钻时粉尘浓度严重超标,严重威胁施工人员职业健康和矿井安全生产问题,研究开发了新型的孔口除尘器。该产品采用水环真空泵做动力,处理气体不受瓦斯浓度的限制,负载能力强,集多种除尘原理于一体,操作简便,易于维护。通过实验室试验研究和现场工业性试验证明,除尘效率在90%以上,大大的减少了打钻时产生的粉尘,对保障煤矿工人的职业健康和矿井安全生产将起到非常积极的作用。     

探究喷雾除尘方式及粉尘粒径分布规律的数值模拟研究

为研究喷雾除尘方式及粉尘粒径分布规律,利用CFD模拟分析除尘器内部粉尘颗粒扩散规律,对其降尘效果进行仿真模拟研究。该设备喷雾所利用的水可循环,无需人工持续供水,且箱体底部增加海绵垫吸收雾滴和粉尘,多余的水经由排水口排出,进水口吸入继续循环工作,环保绿色可持续。结果表明:喷射源设置3处,其中喷射源在①(x=0.3,y=0,z=0.8)、②(x=0,y=0,z=0.8)和③(x=-0.3,y=0,z=0.8)位置处时,风流受到一定阻碍作用,使得前中部粉尘较难继续向除尘器后部扩散,进而形成绕流,致使粉尘颗粒的运动轨迹发生较大偏移,除尘器后半段粉尘浓度偏低,约为0.0008kg/m3;对除尘器出口面设置trap捕捉粉尘颗粒,分析粉尘粒径分布,表明除尘器可以有效降低粉尘浓度,达到理想的除尘效果。     

中心通缆钻杆及其在煤矿井下定向钻进中的应用

针对煤矿井下定向钻技术对钻杆的随钻测量通讯和强度要求,钻杆采用中心通缆方式,可实时传输钻孔随钻测量信号。采用高强度管材、特种螺纹丝扣结构、摩擦焊技术,可提高钻杆抗拉、压、弯、扭强度。并根据现场使用中存在的问题给出了解决方法。大佛寺煤矿随钻测量应用实例说明中心通缆钻杆满足最大孔深1200 m的随钻测量通讯和钻杆强度要求,朱仙庄梳状孔应用实例说明中心通缆钻杆满足最小弯曲半径54 m定向孔施工,哈沙图煤矿定向钻孔应用实例说明中心通缆钻杆满足急倾斜58°煤层定向孔施工。     

ZDY12000全液压煤矿用履带式坑道钻机研制

本文介绍了ZDY12000全液压煤矿用履带车牵引式坑道钻机.从坑道钻机的适用性出发,提出了履带车牵引钻机组合的新思路.     

煤矿风井排风口除尘装置除尘效率的数值模拟

在某矿风井排风口安装了惯性重力除尘装置,安装该装置后,周围的环境得到大大的改善.运用数值模拟的方法计算该除尘装置的除尘效率.结果表明:该惯性重力除尘器的导风口处,从上至下气流速度逐渐减小,增加最下部导风口的面积,可以增大对小粒径颗粒的捕集量;在该惯性重力除尘器中,颗粒浓度最大的地方是在扩散塔外圆弧面附近,在紧连外圆弧面一侧的导流叶片中,最低的导流叶片出口处,颗粒的浓度很大;随着颗粒粒径的增加,惯性重力除尘器的除尘效率显著增加,对于120μm以下的颗粒,该除尘装置的除尘效率低于50%.     

电缆湿接头在小口径定向孔中的应用

小口径地质勘探不断向深部发展,受地层条件、孔内事故和孔斜要求等因素影响,很多钻孔需要定向钻进施工。而小口径钻孔一般采用50、60 mm钻具无法满足随钻仪器的下入要求。通过技术攻关及数次现场试验和改进,研制成功了一套小直径电缆湿接头,较好地解决了小通孔钻杆随钻受控定向钻进的关键技术及难点。具体方案为:把测量探管和传输电缆分开,定向测量探管事先与钻具连接,随钻具下放到预定深度,电缆连接信号上接头由钻杆内腔下入,与探管顶部的信号下接头在钻井液中实现电气连接和信号传输,完成定向作业。该方法在国投新集杨村煤矿DF33断层地面探测及注浆工程和莲塘李井田煤炭勘探中进行了试验并成功应用。具有一定的推广应用价值。     

中国煤矿瓦斯抽采技术装备现状与展望

以旋风除尘器为研究对象,建立几何模型,通过FLUENT数值模拟软件对旋风除尘器粉尘收集率进行分析,得到旋风除尘器的筒体高度、阻力、入口风速与粉尘收集率的关系。以数值模拟的结果为依据,设计旋风除尘器样机,并对其各个参数与过滤效率之间的关系进行验证,最终得到旋风除尘器工艺参数。结果表明：最佳筒体高度为1.5倍的筒体直径,入口风速为15 m/s,此时模拟的粉尘收集率为82.47%,阻力为500.76 Pa。实验旋风除尘器过滤效率为80.22%,阻力为494.6 Pa,与数值模拟的结果相近。

     

矿用湿式螺旋扑尘器的设计及应用

在向煤层内打瓦斯抽放钻孔过程中,从钻孔里会涌出大量的煤尘,这些煤尘如果不及时扑捉,散布到空气中随气体流动,被人体吸收后会给人们的身心健康带来危害,平煤集团技术人员大胆尝试,经过技术研究及实验,设计出了矿用湿式螺旋扑尘器,该设备投入生产使用后,取得了良好的使用效果,值得在全煤系统推广应用。     

螺旋钻杆的有限元分析及运动仿真

以某矿现有旋转钻机为研究对象,运用有限元分析软件ANSYS WorkBench对钻杆进行了受力分析及参数优化,获得了钻杆质量最小时钻杆轴内径和螺旋叶片厚度值。运用ADAMS软件建立了钻杆钻进系统刚-柔体模型,通过对钻进过程的运动仿真,得到了钻杆在钻进工作中的接触及变形情况,并分析了钻杆完全钻进过程中的屈曲行为。研究结果为钻机的改进及钻进效率的提高提供了理论参考。     

矿用气动湿式孔口除尘器的研发及应用

针对煤矿井下干式钻孔粉尘污染问题,研究了集本质安全、轻便、小型于一体的新型矿用气动湿式孔口除尘器。在对影响除尘效果的主要因素进行试验分析研究的基础上,对关键动力元件,即空气引射器进行了系统深入的研究,并对除尘器的主要性能进行实验室和工业性试验,试验结果表明：该除尘器总粉尘除尘效率分别达99.1%和98.6%,呼吸性粉尘除尘效率分别达94.1%和93.2%,有效保障了矿井安全生产。