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Critical Analysis of Longwall Ventilation Systems and Removal of Methane.

机译：长壁通风系统的临界分析和甲烷的去除。

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摘要

Bleeder systems are an important component for ventilation and the control of methane. The bleeder system of a coal mine contains a mixing zone for methane-laden air from the mined-out portions of the seam to mix with fresh air and the methane concentrations in the bleeders can often be elevated. Bleeders also provides a pathway for coalbed methane-laden ventilation air to quickly flow out of the mine through low resistance airways of a mine, such as supported gateroads, along the un-compacted outer perimeter of the gob, etc. Substantial quantities of coalbed methane are typically removed from underground workings. Although it is a relatively simple task to determine the methane quantities exiting the mine through direct measurements, a clear understanding of the exact manner and associated concentrations in which bleeder entries accumulate and transport methane-air mixtures is not known. The benefit of this improved understanding will decrease the likelihood of an explosion due to unknown accumulations of explosive gases in the bleeder entries, thereby improving worker safety.;In order to provide a better understanding of how a bleeder system works in moving methane through the mine, several field monitoring studies have been designed and completed using a tube bundle system and tracer gas releases. The tube bundle system was installed at a bleederless (progressively sealed) underground coal mine. The tube bundles monitoring points were located at different critical locations surrounding the longwall to specifically monitor gas concentrations and barometric pressures on a 30 minute interval for a period of two years. The tracer gas studies, on the other hand, were conducted at an underground coal operation with a traditional bleeder system. The objectives of these tracer tests were to determine transportation pathways and retention times of tracer gasses to better understand the exact gas movements in longwall gobs. The tracer gas was sampled from different headgate and tailgate entries through sample tubes of different lengths using vacutainers. The gas samples were analyzed using gas chromatography for determining concentration measurements for tracer and other gasses, including methane.;The tube bundle system results showed that falling barometric atmospheric pressure can cause the caved material to outgas higher concentrations of contaminants into the bleeder system. During prolonged atmospheric pressure drops, the gas concentrations leaving the caved material via the bleederless system were measured to increase by over two times the average values. These results strongly suggest that to effectively monitor and detect these outgassing events, the bleeder system requires collecting data more often than the once-a-week regulation stated in the 30 CFR Part §75.364.;The tracer gas testing showed locations of high methane in the bleeders, but the practice in multi panel longwall districts of use premixing of the airflow exiting the longwall panels with cleaner airflow to dilute the methane concentrations to below allowable levels before passing through bleeder evaluation points masked the high methane concentrations. Specifically, samples with methane concentration above 4% were collected from the middle entry of the tailgate, but these airflows were diluted to below 2% just before reaching the bleeder evaluation points, and the mine was unaware of the higher methane levels. This result indicates that premixing of explosive airflow as soon possible, as it exits from the tailgate entries in this case, is beneficial to reducing possible explosions, sampling locations need to be closer to the caved material to better monitor and record the actual conditions existing within the inaccessible bleeder locations.;The explosive mixtures of methane in the bleeder are not theoretical but exist and are measurable with direct and indirect methods within both bleeder and bleederless ventilation system. Obtaining measurements of these mixtures is the first step to be able to better engineer longwall ventilation safety.;The conclusions for this research are: 1) Long duration atmospheric pressure drops of a day or more in length are the controlling factor in increased emission from the caved material. 2) The practice of pre-mixing airflows leaving the middle entries between longwall panels with low methane airflow before reaching the bleeder evaluation points, can mask the existence of explosive mixtures of methane at other locations in the bleeders. 3) Without knowledge of the precise locations of high methane in the bleeder entries, the bleeder system cannot be optimized for minimizing explosive methane concentrations and improve miner safety. To solve the atmospheric pressure drop issue it is recommended that a continuous monitoring system should be installed on surface to record these mine-wide changes in total methane emissions. It is also recommended that bleeder evaluation points should be moved closer to the caved material or the sample tubes should be used to monitor critical locations before mixing occurs. Both of these recommendations will improve the understanding of the nature of gas transportation within the bleeder system and thereby lead to improved worker safety.
机译：放气系统是通风和控制甲烷的重要组成部分。煤矿的放气系统包含一个混合区，用于从煤层开采出来的部分中掺入甲烷的空气与新鲜空气混合，放气器中的甲烷浓度通常可以提高。放气机还为含煤层甲烷的通风空气提供了一条途径，使其沿着矿山的低压实外部沿矿山的低阻力气道（例如，支撑的闸门）沿着矿山的紧凑外部区域快速流出矿井。大量的煤层甲烷通常从地下作业中移除。尽管通过直接测量来确定从矿井中排出的甲烷量是一项相对简单的任务，但对透支入口积累和运输甲烷-空气混合物的确切方式和相关浓度的清晰了解尚不清楚。增进了解的好处将减少由于放气口中爆炸性气体的未知积累而引起爆炸的可能性，从而提高了工人的安全性。；以便更好地了解放气系统如何将甲烷输送通过矿井，已经使用管束系统和示踪气体释放装置设计并完成了一些现场监测研究。管束系统安装在无放气（渐进密封）地下煤矿中。管束监测点位于长壁周围的不同关键位置，专门监测气体浓度和大气压力，间隔30分钟，为期两年。另一方面，示踪气体研究是在具有传统放气系统的地下煤炭运营中进行的。这些示踪剂测试的目的是确定示踪气体的运输路径和保留时间，以更好地了解长壁气滴中确切的气体运动。示踪气体使用真空容器通过不同长度的样品管从不同的前门和后门入口采样。使用气相色谱仪分析了这些气体样本，以确定示踪剂和其​​他气体（包括甲烷）的浓度测量结果;管束系统结果表明，大气气压下降会导致溶洞的材料将较高浓度的污染物排泄到泄放系统中。在长时间的大气压下降过程中，经无泄漏系统离开溶洞材料的气体浓度经测量，增加了两倍以上的平均值。这些结果强烈表明，要有效地监视和检测这些放气事件，放气系统需要比30 CFR Part§75.364中规定的每周一次法规更频繁地收集数据。示踪气体测试表明，但是，在多面板长壁区域中，使用长壁面板流出的气流与更干净的气流进行预混合的做法是，将甲烷浓度稀释到允许水平以下，然后再通过泄放评估点，从而掩盖了高甲烷浓度。具体来说，是从后挡板的中间入口处收集甲烷浓度高于4％的样品，但在达到放气评估点之前，这些气流被稀释至2％以下，并且矿井未意识到甲烷含量较高。该结果表明，爆炸性气流在这种情况下从后挡板入口排出时，应尽快进行预混合，这有利于减少可能发生的爆炸，采样位置需要更靠近已陷落的物料，以便更好地监控和记录内部存在的实际条件。泄放器中的甲烷爆炸性混合物不是理论上的，而是存在的，并且可以通过泄放器和无泄放器通风系统中的直接和间接方法进行测量。获得这些混合物的测量值是能够更好地设计长壁通风安全性的第一步。本研究的结论是：1）持续一天或更长的持续时间的大气压降是导致温室气体排放增加的控制因素。洞穴物质。 2）预混合气流在到达放气口评估点之前离开长壁板之间的中间入口且甲烷流量低，可以掩盖放气口其他位置的甲烷爆炸性混合物。 3）不知道放气口中高甲烷的确切位置，无法优化放气系统以最大程度降低爆炸性甲烷浓度并提高矿工安全性。为了解决大气压力下降的问题，建议在地面上安装一个连续的监测系统，以记录矿井范围内甲烷排放总量的变化。还建议在混合发生之前，应将放气孔评估点移至更靠近被陷落材料的位置，或使用样品管监测关键位置。这两项建议将增进对泄放系统内气体运输性质的了解，从而提高工人的安全性。

著录项

  • 作者

    Krog, Robert B.;

  • 作者单位

    West Virginia University.;

  • 授予单位 West Virginia University.;
  • 学科 Mining engineering.;Engineering.
  • 学位 Ph.D.
  • 年度 2016
  • 页码 200 p.
  • 总页数 200
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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