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.     

Development of a dust collector inlet hood for enhanced surface mine drill dust capture

Surface mine drill operators have the highest frequency of overexposure to quartz dust, and drilling is one of the occupations associated with the highest incidence of silicosis. Previous field assessment studies of drilling machines indicate that they can emit some of the highest airborne respirable quartz dust concentrations found at surface mining operations. Typically, the surface mine drills are equipped with dry dust collector systems to capture the dust being flushed with compressed air from the hole during the drilling process. The overall control effectiveness of the dust collector system is initially dependent on capturing the dust cloud at the source via the collector inlet. To assist the initial capture of the dust being flushed from the drill hole, the bottom of the drill deck is typically shrouded or enclosed on all sides to help contain the dust for the collector inlet plenum located on the underside perimeter of the drill deck. Openings, gaps and breaches in the shroud enclosure permit dust to escape dust collector capture.

The National Institute for Occupational Safety and Health (NIOSH) has developed a collector inlet hood that reconfigures the inlet plenum around the drill steel and above the hole to enhance dust capture. Laboratory development and testing show that this inlet hood improves dust capture by an average of nearly 50% over a wide range of collector flows and shroud leakage areas. This report describes the laboratory and subsequent field testing of this inlet hood concept.     

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.     

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.     

SLB56／75型“三合一”取心钻进系统

论述了将绳索取心、螺杆钻、不提钻换钻头三项技术结合在一起的新型取心钻进系统。介绍了系统的结构、工作原理及其技术性能参数和操作要点。     

碎软煤层干式定向钻孔控尘技术研究

针对目前碎软煤层干式定向钻孔产尘量大、粉尘扩散严重的问题,提出一种钻孔孔口非接触式控尘技术方案,设计并研制出集尘罩样机。对集尘罩与钻杆间隙宽度、密封装置气缝宽度、控尘气幕压力等影响控尘效果的工艺参数进行了试验研究,得到了最佳控尘效果的工艺参数。研究结果表明,当钻杆与集尘罩间隙宽度为2.0 mm、气缝宽度为0.2 mm、排渣气体压力为0.3 MPa、控尘气幕压力为0.5 MPa时,粉尘质量浓度由540 mg/m³降低到15 mg/m³,控尘效率达97.2%。现场应用结果表明,使用集尘罩后控尘效率达到98.3%,取得了较好的控尘效果。     

空气潜孔锤孔底局部反循环封堵工具研究与应用

空气潜孔锤钻进工艺钻进效率是常规钻井工艺的10~20倍,对提高矿产资源勘探开发效率,促进贵州省经济发展具有重大意义。西南(贵州)喀斯特地区是全球最大的喀斯特连片分布区,碳酸盐岩地层分布广泛,溶洞及溶隙、裂隙发育,在使用空气潜孔锤钻进工艺钻进时,容易发生漏风现象,导致返渣困难,甚至发生卡钻、埋钻事故。双壁钻杆空气潜孔锤局部反循环钻进工艺可以有效解决喀斯特地区空气潜孔锤钻进工艺使用困难的问题,但该工艺使用的封堵工具极易磨损,限制了该工艺在深井钻探中的使用。本项目主要以双壁钻杆空气潜孔锤局部反循环封堵工具为对象,通过调整封堵工具结构,增加封堵环旋转性能等手段,对封堵环进行改良和优化设计,增加封堵工具的使用寿命,实现双壁钻杆空气潜孔锤局部反循环钻进工艺在深井钻探中的应用。     

空气动力掏煤工艺之压风排水排渣关键技术

基于谢一矿地面钻井空气动力掏煤压风吹水吹渣工程实践，通过分析环空内气体携水携渣机制、吹水作业单次下钻深度，对压风排水排渣关键技术进行了研究。首次确定了套管段吹水作业单次下钻深度、吹水时间等策略；提出了煤层段是否含水条件下的吹水吹渣技术，包括下钻接单根速度要快，开始下行前须先实现压风洗井循环，并使钻柱保持旋转状态，且下行速度宜缓，以及针对固结干煤粉的定点强吹法等技术要点；理清了环空“架桥”、钻杆“倒吸”堵塞发生机制及处理对策，认为在洞穴内有水条件下，下钻前不实现压风洗井循环，是导致环空“架桥”堵塞的主因，而起钻使钻头位置高于堵塞部位，再压风洗井即可解堵；钻杆“倒吸”堵塞则是由于其在井口放气过快导致的，关闭放气阀，或放气减速，即可预防；探究了空气动力造穴高压放喷排渣机制和技术，认为，高压下放喷，环空中压降大，固气混合流体上返流速快，返排效果好；钻杆下入洞穴内的顶部和中低部相比，后者条件下煤粉上返量更多；对放喷后大块率增加的垮塌煤体可采用旋转钻头碾压破碎、定点强吹实现目标。     

中国现代地质钻探技术

中国幅员辽阔，矿产富饶。中国钻探历史悠久。４０余年来中国地质钻探在矿产、能源与水资源勘查以及工程勘察与建设中作出了卓越贡献。中国现代地质钻探技术正步入世界先进行列，其应用领域日益宽广。     

空气（雾化）钻井气液固多相流模拟与分析研究

在我局承钻的十口空气（雾化）钻井试验的基础上，依据两相流理论模式开发出空气（雾化）钻井计算机模拟软件，研究分析了空气（雾化）钻井气液固流动规律，得出空气流，雾化液，钻屑在井筒中主要处于环雾流，雾状流。但在一些特殊因素影响下还存在段塞流，过渡流。     

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。     

高温硬岩空气潜孔锤钻头设计

干热岩试验性开发井钻井施工,在高温硬岩的地层条件下,如何实现高效钻进仍存在很多技术难点。空气潜孔锤钻进技术是解决硬岩地层钻进的有效方法之一,潜孔锤钻头是空气潜孔锤钻进的关键器具。根据青海共和干热岩GH-01井空气潜孔锤钻进技术应用情况,分析探讨了空气潜孔锤钻头断齿、掉齿、磨损严重、使用寿命短等问题,从钻头结构设计、钻头材料选取、钻头冷压固齿工艺等几个方面对空气潜孔锤钻头进行了优化。固齿优化过程中采用有限元分析方法,对钻头冷压固齿过盈量进行仿真分析计算,根据分析计算结果确定最优固齿过盈量。通过对潜孔锤钻头结构、材料、加工等优化,为适用于高温硬岩的空气潜孔锤钻头研制提供了借鉴。为提高空气潜孔锤钻进综合效率,为干热岩钻探开发提供了技术支持和技术储备。     

气动潜孔锤钻进用孔口密封装置优化设计

气动潜孔锤钻进具有效率高的优点,是矿山地面应急救援孔、煤层气井和水井等施工中重点考虑的工艺方法。其缺点是在钻进过程中,孔口会出现大量粉尘。孔口密封装置的作用是实现孔口的密封净化,并将返出的粉尘导向远离孔口的沉渣池。介绍了气动潜孔锤钻进用孔口密封装置的设计,并通过计算流体力学分析,对设计进行了优化,最后进行了现场试验,证明了孔口密封装置完全满足了气动潜孔锤钻进的需要。     

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.     

液压煤钻的研制

煤电钻打眼粉尘多 ,湿式钻眼难 ,要有专用供电线路和防尘水管路 ,然而电器易失爆 ,电缆易破损 ,严重影响煤矿安全生产。液压煤钻克服了煤电钻的缺点 ,它以液压支柱的乳化液泵站为动力源 ,将液压能以输出转矩的方式转化为机械能 ,实施钻孔 ,有小部分乳化液经空心钻杆到钻头 ,实现湿式打眼 ,降低粉尘浓度 ,改善工作环境。     

珊瑚礁地层钻探取心技术研究及应用

人工吹填珊瑚岛礁地层结构比较特殊,以珊瑚砂和珊瑚碎屑为主,取心和成孔难度较大。以南海某岛礁地质钻探取心工程实践为例,针对地层岩性特点,采用一系列对应技术措施:上部松散或弱胶结砂砾层采取跟管钻进和无水干钻取心技术;礁灰岩全漏失地层设计了一套掏砂钻具进行掏砂,确保井眼干净;软硬互层采用超前侧喷钻头;粉砂质地层采取小口径钻具无水干钻取心技术等。该技术在18个钻孔实施中取得了良好的效果,可为后续珊瑚礁地层钻探取心提供借鉴。     

风管式气举反循环钻具及其在大口径钻井施工中的应用

目前大口径钻井施工中常用的泥浆正循环钻进存在着泥浆流速慢、携渣能力差、重复破碎严重、钻井效率低、钻头磨损快、能源消耗大、钻井事故发生率高等问题,气举反循环钻进工艺可有效解决上述问题。风管式气举反循环钻井工艺简单易实现,能有效减少重复破碎,钻进效率高,能源消耗少,钻头寿命长,成井质量好,对涌水和漏失均有很好的抑制作用。介绍了风管式气举反循环钻井工艺原理、专用钻具及其现场使用情况。     

贯通式空气反循环潜孔锤连续取心锤头改进与试验效果

贯通式空气反循环潜孔锤连续取心技术主要适用于干旱无水或缺水地区的地质钻探工作。为了了解该工艺的普遍适用性,在某大水矿区进行了一系列试验,通过对锤头和钻杆的局部改造,解决了钻探、取心、治水等一系列重大难题,为提高该工艺的普遍适用性和推广性提供了可靠的技术支撑。     

煤层液压钻输出机构的优化设计

相比煤电钻,煤层液压钻由于安全性好,可以实现湿式钻孔正得到越来广泛的应用。以煤层液压钻输出机构的体积为目标函数,建立结构优化设计数学模型。应用MATLAB优化工具箱求解最优设计变量,使其满足输出机构的体积最小,实现产品轻型化,从而减轻工人劳动强度,为进一步推广创造条件。