Cooling pathways for deep Australian longwall coal mines of the future

Cooling of coal mines in the Bowen Basin, characterized by steep geothermal gradient, is presently achieved mostly through rental surface bulk air cooling in summer months. This paper argues that future mines will be required to focus their cooling resources more intensively to manage a challenging thermal environment where virgin coal temperatures over 50 °C at a depth of 500 m are expected. Currently, mine cooling systems are employed to maintain the wet bulb temperatures(WBT) to below 27 °C at which point the risks of heat stroke or other heat related issues are manageable. The capacities of these systems are in the range of 6–10 MW refrigeration power. The relationship between high working temperature environment and injury frequency rates is well established. Therefore, provision of appropriate cooling strategies and understanding their optimum performance and suitability are important to Australian coal mines of the future. This paper evaluates the underground temperature profiles of deep, gassy coal mines with propensity for spontaneous combustion and proposes the long term cooling pathways to effectively manage the thermal hazards. Thermodynamic modeling is performed on a longwall face and includes air leakage effects from goaf streams at various locations along the longwall face. The strategy summarizes the application of underground bulk air cooling, chilled water sprays on the shearer and the resulting temperature profiles. Considering the new mining projects planned for the Bowen Basin region, a review of implementable cooling strategies such as mid-gate mobile bulk air coolers(BACs), spot coolers, underground bulk air cooling and the use of chilled water to enhance the positional efficiency of cooling plants,are discussed in this paper. Finally, the comparison of ‘rental' versus ‘ownership' of cooling plants is analysed as part of long-term cooling strategies.     

Application of HEMS cooling technology in deep mine heat hazard control

This paper mainly deals with the present situation, characteristics, and countermeasures of cooling in deep mines. Given existing problems in coal mines, a HEMS cooling technology is proposed and has been successfully applied in some mines. Be-cause of long-term exploitation, shallow buried coal seams have become exhausted and most coal mines have had to exploit deep buried coal seams. With the increase in mining depth, the temperature of the surrounding rock also increases, resulting in ever increasing risks of heat hazard during mining operations. At present, coal mines in China can be divided into three groups, i.e., normal temperature mines, middle-to-high temperature mines and high temperature mines, based on our investigation into high temperature coal mines in four provinces and on in-situ studies of several typical mines. The principle of HEMS is to extract cold energy from mine water inrush. Based on the characteristics of strata temperature field and on differences in the amounts of mine water inrush in the Xuzhou mining area, we proposed three models for controlling heat hazard in deep mines: 1) the Jiahe model with a moderate source of cold energy; 2) the Sanhejian model with a shortage of source of cold energy and a geothermal anomaly and 3) the Zhangshuanglou model with plenty of source of cold energy. The cooling process of HEMS applied in deep coal mine are as follows: 1) extract cold energy from mine water inrush to cool working faces; 2) use the heat extracted by HEMS to supply heat to buildings and bath water to replace the use of a boiler, a useful energy saving and environmental protection measure. HEMS has been applied in the Jiahe and Sanhejian coal mines in Xuzhou, which enabled the temperature and humidity at the working faces to be well controlled.     

Deep mine cooling,a case for Northern Ontario:Part Ⅱ

Cooling energy needs, for mines in Northern Ontario, are mainly driven by the mining cooling technologies available and the cost to implement them in a 2500 m deep underground mine. The cooling technologies reviewed herein include mechanical and natural cooling systems, ranging from mechanical chillers to seasonal thermal storages. The economic and operating parameters for each technology were estimated and evaluated according to the mine's energy loads. Including consideration of any combined heat and power benefits of the technology, cooling tower requirements, etc., the resulting cost of implementation for each technology could be ranked. This showed that the natural thermal storage systems and conventional chillers were the most cost-effective, mainly since the natural systems had very low operating cost and the chillers had relatively low capital costs.     

Principles and technology for stepwise utilization of resources for mitigating deep mine heat hazards

As is well known, deep mines are hot. As mining depth increases, the temperature of the surrounding rock also increases. This seriously affects mine safety and production and has restricted the exploitation of deep coal resources. Therefore, reducing the working face temperature to improve working conditions by controlling these heat hazards is an urgent problem. Considering problems in cooling deep mines both domestically and abroad along with the actual conditions of the Zhangshuanglou coal mine, we propose a HEMS technology that uses heat resources from deep mines in a stepwise manner. HEMS means a high temperature exchange machinery system. Mine inrush-water is used as a source of cooling. Twice the energy is extracted from the mine inrush water. Heat is used for building heating in the winter and cold water is used for cooling buildings in the summer. This opens a new technology for stepwise utilization of heat energy in deep mines. Energy conservation and reduced pollution, an improved environment and sustainable economic development are realized by this technique. The economic and social effects are obvious and illustrate a good prospect for the application and extension of the method.     

Deep mine cooling,a case for Northern Ontario:Part Ⅰ

Cooling energy needs,for mines in Northern Ontario,are mainly driven by the mining depth and its operation.Part I of this research focusses on the thermal energy loads in deep mines as a result of the virgin rock temperature,mining operations and climatic conditions.A breakdown of the various heat sources is outlined,for an underground mine producing 3500 tonnes per day of broken rock,taking into consideration the latent and sensible portions of that heat to properly assess the wet bulb global temperature.The resulting thermal loads indicate that cooling efforts would be needed both at surface and underground to maintain the temperature underground within the legal threshold.In winter the air might also have to be heated at surface and cooled underground,to ensure that icing does not occur in the inlet ventilation shaft-the main reason why cooling cannot be focussed solely at surface.     

Quantitative hazard assessment for Zonguldak Coal Basin underground mines

Underground coal mining is one of the most dangerous occupations throughout the world. The reasons behind an underground occupational accident are too complex to analyze mainly due to many uncertainties which may arise from geological, operational conditions of the mine or individual characteristics of employees. This study proposes implementing a quantitative methodology for the analysis and assessment of hazards associated with occupational accidents. The application of the proposed approach is performed on the mines of Turkish Hard Coal Enterprises(TTK). The accidents in TTK between the years 2000 and 2014 are firstly statistically analyzed with respect to the number, type and location of accidents, age,experience, education level and main duty of the casualties and also injuries resulting from such accidents. The hazards are classified as individual, operational and locational hazards and quantified using contingency tables, conditional and total probability theorems. Lower and upper boundaries of hazards are determined and event trees for each hazard class are prepared. Total hazard evaluation results show that Armutcuk, Karadon and Uzulmez mines have relatively high hazard levels while Amasra and Kozlu mines have relatively lower hazard values.     

深井降温的技术经济分析

本文论述了典型深井降温空调系统的技术特点,提出了我国深井降温系统应用年计算费用法进行技术经济分析的方法.工程实例的技术经济比较表明,深井降温应用冰冷却系统比常规矿井空调系统具有更大的优越性.     

Occurrence,predication,and control of coal burst events in the U.S.

Coal burst represented a major hazard for some U.S. mining operations. This paper provides an historical review of the coal burst hazards,identifies the fundamental geological factors associated with these events,and discusses mechanisms that can be used to avoid their occurrences. Coal burst are not common in most underground mines. Their occurrence almost always has such dramatic consequences to a mining operation that changes in practice are required. Fundamental factors influencing coal burst events include strong strata,abnormal strata caving,elevated stresses,critical size pillars and the lack of sufficiently sized barrier pillars during extraction. These factors interact to produce excessive stress,seismic shock and loss of confinement mechanisms. Over the 90 years of dealing with these hazards,many novel prevention controls have been developed including novel mine designs and extraction sequences,most of which are site specific in their application. Without an accurate assessment of the fundamental factors that influence coal burst and knowledge of their mechanisms of occurrence,control techniques may be misapplied and risk inadequately mitigated.     

海孜煤矿顶板动力冲击水害的成因研究

离层水害是一种罕见而危害严重的灾害形式,本文通过水文地质分析、相似材料模拟、数值模拟和冲击水压试验证实发生在淮北海孜煤矿的顶板次生离层水害的成因。针对灾害原因,采取了采动疏干的防治水方法,取得了满意的效果,确保了类似条件工作面开采的安全。     

Closed-loop bulk air conditioning:A renewable energy-based system for deep mines in arctic regions

With depletion of shallow deposits, the number of underground mines expected to reach more than 3 km depth during their lifetime is growing. Although surface cooling plants are mostly effective in mine airconditioning, usually secondary cooling units are needed below 2 km depth. This need emerges due to the elevated thermal impacts caused by auto-compression of mine air as well as heat emissions from strata and mine machinery. As a result, in cold climates, like Canada, ultra-deep mines need their secondary underground cooling plants running year-round while the intake air must be heated to protect the sensitive machinery and liners from freezing during the winter season. To cool mine air, horizontal bulk-airconditioners with direct spray cooling systems are commonly used due to their high performance.Conventionally, sprayed water in bulk-air-coolers are mechanically circulated and refrigerated in coupled refrigeration plants. This set up can be transformed to a natural cooling/heating process by resurfacing the warm underground bulk-air-cooler spray water for mine air heating on the surface and re-sinking the chilled water for cooling in the underground bulk air coolers. This could significantly cut-down the fossil-fuel consumption in burners for mine air pre-conditioning and refrigeration cost when applicable.This paper presents an anonymous real-life example to study the feasibility of the proposed idea for an ultra-deep Canadian mine.     

Scale of seismic and rock burst hazard in the Silesian companies in Poland

Presently the seismic and rock burst hazard appears still to be important in most of hard coal mines in Poland. Recently, there was a significant increase of seismic activity of the Silesian rock massive, when compared with the previous years. In the period 1999-2008 the hard coal mines experienced 34 rock bursts. The causes of rockburst occurrence are presented based on the analysis of the rockbursts occurring in the Polish hard coal mines. The scale of the rockburst hazard has been characterized with respect to the mining and geological conditions of the existing exploitation. Of the factors influencing the state of rockburst hazard, the most essential one is considered the depth interval ranging from 600 m to 900 m. The basic factors that promote the rockburst occurrence are as follows: seismogenic strata, edges and remnants, goaf, faults, pillars and excessive paneling.     

Geological factors controlling deep geothermal anomalies in the Qianjiaying Mine,China

Here, the geological factors controlling deep geothermal anomalies in mines were studied based on the geotemperature, lithologic thermal conductivity, and related geological data collected from the Qianjiaying Mine, China. A simulation of the change in magma waste heat, conducted using the ANSYS Workbench, revealed the distribution characteristics of geothermal anomalies in this mine and the corresponding geological control factors. The results revealed the following points. (1) First-degree heat hazard level (temperature = 31–37 ℃) occurred in the central and southwestern parts of the mine at an ~600-m depth, while second-degree heat hazard level (temperature ≥ 37 ℃) occurred at an ~800-m depth. The geotemperature and geothermal gradient in the southwestern part of the mine were anomalously high. (2) The geotemperatures measured in the mine generally reflected a standard increase with depth, while the geothermal gradient remained unchanged with depth. The geothermal gradient and its average value in the study area were 0.70–4.23 and 2.12 °C·hm⁻¹, respectively. (3) A combination of stratum characteristics, geological structure, and groundwater characteristics led to geothermal anomalies in mines; additionally, the waste heat from magma had no significant effect on the geothermal field.     

从安全心理学角度探析新型安全矿井的创建

从安全心理学角度分析了煤矿井下安全影响因素：缺乏安全生产技术与经验、不安全行为心理和生理因素及人为失误.提出可采用改变培训考核方式、进行心理辅导、增加视觉和听觉两方面的信号刺激,以及改善井下环境尤其是照明环境等方法,解决出现人的不安全行为的问题,以创建新型安全矿井.     

Review of coal and gas outburst in Australian underground coal mines

Outburst of coal and gas represents a significant risk to the health and safety of mine personnel working in development and longwall production face areas. There have been over 878 outburst events recorded in twenty-two Australian underground coal mines. Most outburst incidents have been associated with abnormal geological conditions.Details of Australian outburst incidents and mining experience in conditions where gas content was above current threshold levels are presented and discussed. Mining experience suggests that for gas content below 9.0 m³/t, mining in carbon dioxide (CO₂) rich seam gas conditions does not pose a greater risk of outburst than mining in CH₄ rich seam gas conditions. Mining experience also suggests that where no abnormal geological structures are present that mining in areas with gas content greater than the current accepted threshold levels can be undertaken with no discernible increase in outburst risk. The current approach to determining gas content threshold limits in Australian mines has been effective in preventing injury from outburst, however operational experience suggests the current method is overly conservative and in some cases the threshold limits are low to the point that they provide no significant reduction in outburst risk. Other factors that affect outburst risk, such as gas pressure, coal toughness and stress and geological structures are presently not incorporated into outburst threshold limits adopted in Australian mines. These factors and the development of an outburst risk index applicable to Australian underground coal mining conditions are the subject of ongoing research.     

A semi-quantitative coal burst risk classification system

Safety is the highest priority in the mining industry as underground mining in particular poses high safety risks to its workers. In underground coal mines, coal bursts are one of the most catastrophic hazards, which involves sudden and violent dynamic coal mass failure with rapid ejection of the broken material into the mine workings. Despite decades of research, the contributing mechanisms of coal bursts are still not completely understood. Hence, it remains challenging to forecast coal bursts and quantify their likelihood of occurrence. However, a range of geological and geotechnical factors are associated with coal bursts and can increase the coal burst proneness. This paper introduces a semi-quantitative coal burst risk classification system, namely, BurstRisk. Based on back-analysis of case histories from Australia, China and the United States, BurstRisk classifies the coal burst risk into three categories:low, medium and high risk. In addition, it allows mining engineers to modify the weighting of the selected factors based on specific conditions. The risk classification charts introduced are for both longwall retreat and development sections of long-wall mining operations. This paper also provides a set of risk management strategies and control measures for effective coal burst mitigation.     

地下流体注采诱发地震综述及对深部高温岩体地热开发的影响

大规模地下流体注采常诱发微地震,甚至是地面破坏性地震的发生。本文系统综述了四类典型的流体注采工程（废水深井注入、二氧化碳地质封存、油气开采、深层地热能开发）诱发地震事件的案例,来探讨多类型流体注采工程诱发地震发育位置、诱震时间和影响范围,以及触发机制。进而专门针对深部地热能开发,总结了诱发最大地震震级的确定方法,以及降低诱发地震风险面临的挑战等。我国的深部地热资源开发潜力巨大,可利用多种观测手段（震法、电法、磁法等）来获取多尺度地球物理信息,并且利用室内实验和数值模拟相结合的方法,来逐渐认识诱发地震主要因素和地震发育位置及大小的对应关系。可利用断层和隐伏断层识别技术或微地震监测技术等来降低深部高温岩体EGS工程中诱发破坏性地震的风险。在注采井的高效连通控制技术方面,可开发复合热储刺激技术,即冷热水交替热刺激-化学腐蚀-水力压裂技术,并充分利用微震的监测解译数据,现场及时调整热储刺激的方案。通过开展一系列示范工程,逐步攻克关键开发技术,循序渐进地推进EGS工程的安全高效实施。     

Proposing a novel comprehensive evaluation model for the coal burst liability in underground coal mines considering uncertainty factors

Coal burst is a severe hazard that can result in fatalities and damage of facilities in underground coal mines. To address this issue, a robust unascertained combination model is proposed to study the coal burst hazard based on an updated database. Four assessment indexes are used in the model, which are the dynamic failure duration(DT), elastic energy index(WET), impact energy index(KE) and uniaxial compressive strength(RC). Four membership functions, including linear(L), parabolic(P), S and Weibull(W)functions, are proposed to measure the uncertainty level of individual index. The corresponding weights are determined through information entropy(EN), analysis hierarchy process(AHP) and synthetic weights(CW). Simultaneously, the classification criteria, including unascertained cluster(UC) and credible identification principle(CIP), are analyzed. The combination algorithm, consisting of P function,CW and CIP(P-CW-CIP), is selected as the optimal classification model in function of theory analysis and to train the samples. Ultimately, the established ensemble model is further validated through test samples with 100% accuracy. The results reveal that the hybrid model has a great potential in the coal burst hazard evaluation in underground coal mines.     

Double-directional control bolt support technology and engineering application at large span Y-type intersections in deep coal mines

Under deep and complex geological conditions,severe deformation occurs at intersection points of Y-type roadways with large cross sections during engineering projects in coal mines,especially at junction arches.Based on in-situ investigations and theoretical studies,we have summarized typical forms of destruction and identified high stress and unrestricted support at both sides of junction arch as its main causes.In this study,we also presented double-directional control bolt support technology for a large Y-type span intersection,applied to deep intersection engineering in the Jiahe Coal Mine,which has proved effective.     

Fundamentals of modern ground control management in Australian underground coal mines

Underground coal mining is inherently hazardous, with uncontrolled ground failure regarded as one of only several critical risks for multiple fatality events. Development, implementation and management of overarching systems and procedures for maintaining strata control is an important step to mitigating the impact of ground failure hazards at a mine site operational level. This paper summarised the typical pro-active ground control management system(PGCMS) implemented in various Australian underground coal mines. Australia produces approximately 100 million tonnes a year of metallurgical and thermal coal from approximately 30 of the world's safest longwall mines operating in New South Wales and Queensland. The increased longwall productivity required to achieve both high levels of safety and profitability, places significant emphasis on the reliability of pro-active ground control management for longwall mining operations. Increased depths, adverse geological conditions, elevated variable stress regimes and weaker ground conditions, coupled with an industry wide need for increased development rates continue to make ground control management challenging. Ground control management is not only about ground support and pillar design though but also a structured process that requires a coordinated effort from all levels of the workforce to both minimise the occurrence of adverse geotechnical events and mitigate the potential risks when they do occur. The PGCMS presented in this paper is proven to provide both a safer and more productive mine environment through minimisation of unplanned delays. The critical elements of the method are presented in detail and demonstrate the utility and value of a ground control management system that has potential for implementation in underground coal mining globally.     

Investigation of factors influencing roof stability at a Western U.S.longwall coal mine

The coal mine roof rating(CMRR) was developed to bridge the gap between geological variation in underground coal mines and engineering design. The CMRR accounts for the compressive strength of the immediate roof, the shear strength and intensity of any discontinuities present, and the moisture sensitivity of the immediate roof. The CMRR has been widely used and validated in Eastern US coal mines, but it has seen limited application in the Western US. This study focuses on roof behavior at a Western coal mine(Mine A). Mine A shows significant lateral geological variation, along with localized faulting and a laterally extensive sandstone channel network. The CMRR is not used to predict roof instability at the mine. It is, therefore, hypothesized that there are other factors that are correlated with roof instability in underground coal mines that could potentially also be considered in conjunction with the CMRR.This hypothesis was tested by collecting 30 CMRR measurements at Mine A. At each measurement location, a binary record of the roof condition(stable or unstable) was made, and other parameters such as depth of cover, presence of faulting, and sandstone channels were also recorded. ANOVA tests showed that the CMRR values and the roof conditions were not strongly correlated, indicating that the CMRR input criteria are not fully predictive of roof stability at this mine. The CMRR values showed statistically significant correlations(p less than 0.05) with faulting as well as with location at an intersection. For areas that had previously experienced roof fall but were currently stable, faulting was correlated with roof condition(p less than 0.05) only when the condition was classified as unstable.