اتوماسیون جبهه کار بلند: ارائه فناوری توانمند برای دستیابی به معادن زیرزمینی ایمن تر و به بهره وری بیشتر

Longwall automation: Delivering enabling technology to achieve safer and more productive underground mining

Abstract

The ongoing need to deliver improved safety, productivity and environmental benefit in coal mining presents an open challenge as well as a powerful incentive to develop new and improved solutions. This paper assesses the critical role that enabling technologies have played in the delivery of remote and automated capability for longwall mining. A brief historical account is given to highlight key technical contributions which have influenced the direction and development of present-day longwall technology. The current state of longwall automation is discussed with particular attention drawn to the technologies that enable automated capability. Outcomes are presented from an independently conducted case study that assessed the impact that CSIRO’s LASC longwall automation research has made to the longwall mining industry in Australia. Importantly, this study reveals how uptake of this innovative technology has significantly benefitted coal mine productivity, improved working conditions for personnel and enhanced environmental outcomes. These benefits have been widely adopted with CSIRO automation technology being used in 60 per cent of all Australian underground operations. International deployment of the technology is also emerging. The paper concludes with future challenges and opportunities to highlight the ongoing scope for longwall automation research and development.

1 Introduction

1-1 CSIRO mining strategy and rationale Industrial

Research Organisation (CSIRO) undertakes missiondirected research to promote transformational change in the Australian mining and resource ecosystems. The vision is to secure a clean energy future in order to sustain long term benefits across environmental, economic and societal sectors. The fundamental approach has been to collaborate with industry, research organisations and government to create cost-competitive, low-emission energy technologies. A vital component of this strategy has been the development of remote and automated mining technologies to achieve safer, more productive and more environmentally sustainable coal mining systems. Coal accounts for around 24% of employment and 27% of total revenue for the Australian mining sector. Longwall coal mining, in particular, accounts for around 90% of Australia’s total underground coal production and thus represents a major interest area for innovative research and development.

1-2 Longwall coal mining process

Longwall coal mining is a full extraction underground mining method that involves the removal of coal in large blocks or panels using a mechanised shearer. The coal panel is typically 200–450 m wide and can be up to five kilometres in length. The mechanical shearer is mounted on a shearer pan and rails which guide the shearer as it moves back and forth along the coal face. Coal cut from the longwall face by the shearer is removed by an Armoured Face Conveyor (AFC) that transports coal to the adjoining gateroad for conveyance to the surface.

The roof over the working area is supported by hydraulic shields that are advanced towards the freshly cut face according to a well-defined motion configuration. As the roof support system advances into the coal panel, the roof behind the shields is no longer supported and is thus allowed to collapse into the void (goaf) behind the shields. For reference, a representation of a small portion of a longwall operation and shearer is shown in Fig. 1. The coal seam is indicated by the hatched layer between the underlying and overlying strata.

رفتار مکانیکی و تکامل نفوذپذیری گاز زغال سنگ در طول استخراج لایه محافظ 

Mechanical behavior and permeability evolution of gas infiltrated coals during protective layer mining

Abstract

This study investigated the stress–strain–permeability relationship of a Chongqing coal under the stress path during the mining process. The abutment stress was first measured at the longwall (LW) face 3211 of Songzao Mine in Chongqing, China. The field monitoring results revealed that the concentration coefficient of the abutment stress was approximately 1.5–2.0 during protective layer mining. Then, triaxial compression tests for the gas-infiltrated coals were conducted under the above stress path and different gas pressures. These tests, with the simultaneous actions of unloading confining stress and loading axial stress, are called SUL tests. The triaxial compression tests revealed that the peak deviatoric stress and the corresponding strain of coal under SUL tests were lower than those under conventional triaxial compression (CTC) tests. Poisson’s ratio was higher, but the elastic modulus was lower in SUL tests. The permeability evolution of coal under the SUL tests underwent four distinct stages: the increasing stage in the process of SUL, decreasing stage, slowly increasing stage beyond the yield point, and sharply increasing stage after the peak stress. With the increased gas pressure, the peak deviatoric stress and corresponding axial strain decreased, Poisson’s ratio increased, and elastic modulus decreased. Further, the permeability of coal increased with increasing gas pressure in the complete deformation process.

1 Introduction

Coal mining induces different stress zones in front of the working face of coal—a relief stress zone, abutment stress zone, and recovered stress zone—from the initial in-situ stress state.1 During this coal mining process, the stress path experiences the loading of axial stress and the simultaneous unloading of confining stress. However, current investigations on the coupling mechanism between the mechanical behavior and permeability of coal are almost all based on conventional triaxial compression (CTC) tests. This CTC path may not represent the coal mining process. It is necessary to validate the applicability of the current investigations to the coal mining process.

The stress evolution of coal seams has been widely investigated. A series of three-dimensional numerical models were developed to examine the effect of the mining depth, in-situ stress and stope geometry as well as the orientation on the overbreak of a stope wall.2 For example, Wang et al. took the cutting face from disaster sites as prototypes to study the effect of the stress distribution on dynamic disasters of coal mines.3 Guo et al. presented a comprehensive study on the longwall in a deep underground coal mine.4 They investigated the mining-induced strata movement, stress changes, fracture openings, and gas flows. Their studies included the field monitoring of overburden displacement, changes of stress and water pressure at the LW face. They concluded that the vertical stress increased and the horizontal stress decreased during mining. All of the above investigations revealed that deeper mining faces a higher risk of mining disasters.

Coal seam gas couples with coal deformation to affect mining safety. In China, coal seams are rich in coal seam gas. There is approximately 10 billion m3 of the recoverable coalbed methane (CBM) in China. The Erlian basin in Inner Mongolia contains 2 billion m3 of recoverable CBM. The Ordos basin and Qinshui basin contain more than 1 billion m3 of recoverable CBM. The gas content gradually increases with coal burial depth. The accumulation of coal seam gas during mining may trigger dynamic disasters, such as gas emission, and even the occurrence of coal and gas outburst in front of the working face. The gas accumulation depends on many parameters, of which the permeability evolution of coal is the most important. Therefore, the investigation of the permeability distribution within coal and the surrounding rocks is the core work of the simultaneous extraction of coal and gas.

تئوری تیر طره ای برشی در استخراج جبهه کار بلند و روش استخراج 110 در چین (سومین نوآوری علوم معدن)

Longwall mining “cutting cantilever beam theory” and 110 mining method in ChinadThe third mining science innovation

Abstract

With the third innovation in science and technology worldwide, China has also experienced this marvelous progress. Concerning the longwall mining in China, the “masonry beam theory” (MBT) was first proposed in the 1960s, illustrating that the transmission and equilibrium method of overburden pressure using reserved coal pillar in mined-out areas can be realized. This forms the so-called “121 mining method”, which lays a solid foundation for development of mining science and technology in China. The “transfer rock beam theory” (TRBT) proposed in the 1980s gives a further understanding for the transmission path of stope overburden pressure and pressure distribution in high-stress areas. In this regard, the advanced 121 mining method was proposed with smaller coal pillar for excavation design, making significant contributions to improvement of the coal recovery rate in that era. In the 21st century, the traditional mining technologies faced great challenges and, under the theoretical developments pioneered by Profs. Minggao Qian and Zhenqi Song, the “cutting cantilever beam theory” (CCBT) was proposed in 2008. After that the 110 mining method is formulated subsequently, namely one stope face, after the first mining cycle, needs one advanced gateway excavation, while the other one is automatically formed during the last mining cycle without coal pillars left in the mining area. This method can be implemented using the CCBT by incorporating the key technologies, including the directional pre-splitting roof cutting, constant resistance and large deformation (CRLD) bolt/anchor supporting system with negative Poisson’s ratio (NPR) effect material, and remote real-time monitoring technology. The CCBT and 110 mining method will provide the theoretical and technical basis for the development of mining industry in China.

1 Introduction

In the 1960s, Prof. Minggao Qian proposed the “masonry beam theory” (MBT) (Qian, 1981, 1982) for the first time in China, and presented a full discussion on the transmission and equilibrium method of overburden pressure in mined-out areas by using reserved coal pillar. On this basis, the “121 mining method” was established, namely one stoping face needs two advanced excavation tunnels and one reserved coal pillar before the next mining cycle. The MBT and mining system based on the 121 mining method laid a sound foundation for the development of mining science in China. The second mining innovation started in the 1980s, which was characterized by the “transfer rock beam theory” (TRBT) (Song, 1979, 1982) proposed by Prof. Zhenqi Song. This illustrated a further transmission path of stope overburden pressure and the pressure distribution in high-stress areas. Then the advanced “121 mining method” was raised with smaller coal pillar in terms of field excavation design, making important contributions to development of the coal recovery rate in that era.

At the beginning of the 21st century, large deformation failure problems in coal mines became more challenging with increasing mining depth, and the accidents in risk-prone gateway and deep gob-side gateway accounted for 80%e90% of total accidents in working face gateways (He, 2004, 2005; He et al., 2005). It is basically considered that the traditional 121 mining method was not suitable for the deep mining purpose (Zhai and Zhou, 1999; Li, 2000; Liu and Shi, 2007; Fei, 2008). In 2008, the theory of “cutting cantilever beam theory” (CCBT) was first put forward. In this theory, it can be noted that the ground pressure was used for the purpose of advanced roof caving by precutting to form a cantilever beam above the gob-side gateway. When the precutting was performed on the roof of gateway, the transmission of overburden pressure was cut off, which mitigated the periodic pressure when using the 121 mining method, and part of roof rock mass was driven down, forming one side of the gateway for the next stope mining cycle. The CCBT provides a new basis for the non-pillar mining, under which the 110 mining method was developed (He et al., 2007; Zhang et al., 2011; Song and Xie, 2012; Wang and Wang, 2012; Liu and Zhang, 2013; Sun et al., 2014), namely one stope face, after the first mining cycle, only needs one advanced gateway excavation; while the other one is automatically formed during the last mining cycle without coal pillars left in the mining area by using this mining technology. The core idea of the 110 mining method is that, first, the natural ground pressure is used to make part of the roof fall down, instead of fully reinforcing it by artificial supporting system and coal pillar; second, the gob roof rock is used to form one side wall of the gob-side gateway; and third, the expansion characteristic of broken gob roof rock is used to reduce the surface subsidence. This mining method will reduce 50% of gateway excavation workload in the stope and fulfill 100% coal pillar recovery, which achieves a significant reduction in mining costs and more importantly, will reduce the accidents in the stope. It may be used to fulfill the “N00 mining method” in the future, which is the optimization and innovation of the 110 mining method. The symbol “N00” means no matter how many mining cycles and working faces are in the district, all the gateways would be formed automatically with CCBT, suggesting no need for gateways to be excavated when using traditional methods. In this paper, China’s three innovations in longwall mining will be reviewed and discussed, including the related theories and the 121 mining method, the CCBT and the 110 mining method, and the key technologies involved. The CCBT and 110 mining method will be considered to be the basis for China’s next-generation mining industry development, from mining giants to mining powers.

تحلیل عملکردهای تولیدی چال تهویه برای گاز حاصل از زائدات معدن زغال سنگ جهت کنترل گاز چینه ها در استخراج معدن با جبهه کار بلند

Analysis of gob gas venthole production performances for strata gas control in longwall mining

Abstract

Longwall mining of coal seams affects a large area of overburden by deforming it and creating stress-relief fractures, as well as bedding plane separations, as the mining face progresses. Stress-relief fractures and bedding plane separations are recognized as major pathways for gas migration from gas-bearing strata into sealed and active areas of the mines. In order for strata gas not to enter and inundate the ventilation system of a mine, gob gas ventholes (GGVs) can be used as a methane control measure. The aim of this paper is to analyze production performances of GGVs drilled over a longwall panel. These boreholes were drilled to control methane emissions from the Pratt group of coals due to stress-relief fracturing and bedding plane separations into a longwall mine operating in the Mary Lee/Blue Creek coal seam of the Upper Pottsville Formation in the Black Warrior Basin, Alabama. During the course of the study, Pratt coal’s reservoir properties were integrated with production data of the GGVs. These data were analyzed by using material balance techniques to estimate radius of influence of GGVs, gas-in-place and coal pressures, as well as their variations during mining.

The results show that the GGVs drilled to extract gas from the stress-relief zone of the Pratt coal interval is highly effective in removing gas from the Upper Pottsville Formation. The radii of influence of the GGVs were in the order of 330–380 m, exceeding the widths of the panels, due to bedding plane separations and stress relieved by fracturing. Material balance analyses indicated that the initial pressure of the Pratt coals, which was around 648 KPa when longwall mining started, decreased to approximately 150 KPa as the result of strata fracturing and production of released gas. Approximately 70% of the initial gas-in-place within the area of influence of the GGVs was captured during a period of one year.

1 Introduction

Longwall mining induces deformation, fracturing, and bedding plane separations within a large volume in the overburden strata. These effects can release a significant amount of gas from overburden strata, which may find its way into sealed and active areas of the mine if not controlled. Therefore, strata gas control, especially in geologies with high gas amount, is an important consideration in support of ventilation to ensure mine safety in addition to its benefits as an unconventional energy source.1–3

In the U.S and elsewhere, gob gas ventholes (GGVs) are the most common borehole type used to control gas from the fractured strata by capturing it before it can enter the mine environment.4–8 Despite the importance of these boreholes in controlling gob gas, it may be hard to predict their performance due to stability issues,9,10 relative importance of different operational parameters on their performance,11 and the effect of surface elevation (overburden thickness) on the rate-decline properties.12 A schematic representation of the various zones of deformation in longwall overburden and a GGV placed to control strata gas is shown in Fig. 1.

While some of the operational constraints, such as suction pressure, casing depth, proximity to tailgate of the longwall panel, can be addressed for optimum performance of GGVs,11 one of the most important aspects of gob gas venthole performance is dynamic subsidence and the geology of the overburden strata that is affected by it. Dynamic subsidence, or surface movement, of a particular location begins as mining face approaches, and continues until maximum displacement occurs after longwall face passes that location to some distance. The magnitude of the displacement and how it progresses are controlled primarily by the thickness of the extraction, the width of the panel, the overburden thickness and the properties of the strata. The properties of the strata not only affect the subsidence and the stress distribution,13 but also where emission potential from the strata surrounding the coal mine can develop and how GGV designs can be optimized to control emissions.

تاثیر استخراج جبهه کار بلند بر روی آبهای زیرزمینی بالای پانل جبهه کار بلند در لایه های کم عمق زغال سنگ

Impact of longwall mining on groundwater above the longwall panel in shallow coal seams

Abstract

Since longwall mining causes subsidence through the overlying strata to the ground surface, the surface water and groundwater above the longwall panels may be affected and drained into the lower levels. Therefore, loss or interruption of streams and overburden aquifers is a common concern in coal industry. This paper analyzed the potential effects of longwall mining on subsurface water system in shallow coal seam. In order to monitor different water level fluctuations throughout the mining period, three water wells were drilled down to the proposed deformation zone above the longwall panel. A GGU-SS-FLOW3D model was used to predict water table contours for the periods of pre- and post-mining conditions. The field data from the three water wells were utilized to calibrate the model. The field test and numerical model can help to better understand the dewatering of shallow aquifers and surface waters related to ground subsidence from longwall mining in shallow coal seam.

1 Introduction

Longwall mining method is a highly productive underground mining method in which a panel or a block of coal is completely extracted (Peng, 2006, 2008; Qian and Shi, 2003; Wang, 2009). When a longwall panel with sufficient width and length is excavated, the overburden roof strata are disturbed in order of severity from the immediate roof toward the surface, or even the aquifers, which can lead to serious mine-flooding accidents and increasing damages to ecological environments (Miao and Qian, 1995; Qian and Miao, 1995; Qian et al., 1996). Thus it is absolutely essential to determine the degree of dewatering for prevention of water inrush and protection of groundwater resources (Li, 2011; Li and Qiu, 2012). In this paper, three water wells drilled in site and a GGU-SS-FLOW3D model are used to monitor different water level fluctuations throughout the mining period. The potential effects of longwall mining on subsurface water system are analyzed in shallow coal seam with the field data measured from the three water wells and the numerical model.

2. Geology and mining conditions of study area

The geology of the study area includes sedimentary rocks of Pennsylvanian and Permian ages (Paleozoic). Alluvial deposits of Quaternary age occupy the valley bottom of the dissected topography. The boundary between the Pennsylvanian and Permian systems is indistinct, but it is generally defined by the sequence of rocks extending from the base of the Waynesburg coal bed to the present topographic surface.

The Dunkard Group consists of the Greene Washington and Waynesburg formations. The lower section of the Dunkard Group resembles that of the Monongahela Group which contains laterally persistent Pittsburgh coal. The top bedrock unit is the Dunkard Group, which belongs to the Permian age.

The longwall panels B5 and B6 studied in this paper are located in the Appalachia Coalfield, United States (Fig. 1). The overburden depth varied from 600 ft to 900 ft (1 ft ¼ 0.3048 m). The average mining height was 7 ft. The length of panels B5 and B6 was 12,000 ft and 5700 ft, respectively. The width of the both panels was 1433 ft. The width of headgate and tailgate entries was 16 ft. The chain pillar system between panels B5 and B6 was 200 ft wide. The average longwall face retreat rate was 30e50 ft/d during the longwall face mining in the study area.