Article

Numerical investigation of CO 2 fringe behaviour on a longwall face and its control

Authors:
  • China Coal Reseach Institute
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Abstract

Gas management at longwall faces has always been a challenging issue to mine operators. Along a longwall face of an Australian colliery where CO2 is the dominant coal seam gas, frequent power trip off occurred due to the high goaf gas (CO2) emission, which significantly affected the normal longwall production and brought about safety threats to the longwall crew. CO2 fringe fluctuation changes close to tailgate (TG) was identified as a major concern. To better understand the CO2 fringe behaviour on the longwall face and develop the corresponding effective control measures, Computational Fluid Dynamics (CFD) model was developed and validated based upon field data collected from the colliery. General gas flow characteristics on the longwall face were obtained based on which parametric studies were then carried out to investigate the impact of ventilation system and gas drainage options on goaf gas fringe behaviour. The use of a back-return ventilation system was demonstrated to be an effective approach to control the CO2 fringe at TG; however, it was not practical due to the restriction of existing panel layout. As a compromise of the back-return system, a new gas drainage option using TG borehole which was more practical and cost effective was proposed and assessed by the CFD models. Model results indicated that goaf gas fringe at TG can be effectively controlled when a suction pressure between − 1500 Pa and − 2000 Pa was applied to the TG borehole. Therefore, it can be concluded from this study that gas drainage conducted through TG borehole can be an effective approach to solve the CO2 accumulation at TG on a longwall face, especially when the back-return system is not applicable on site.

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... Related research studies have shown that under the effect of gravity, the density of a gas mixture will affect its migration trend in the vertical direction in a gob. 17,18 There are many coal-fired power plants in China's major coal-producing regions, and a correspondingly, large amount of low-oxygen flue gas is produced in the production process. Table 1 compares the relevant characteristics of the N 2 , CO 2 , and power plant flue gas for fire prevention in a gob. ...
... Moreover, due to the complexity and inaccessibility of the gob area, onsite observation and measurement of the oxidation and self-heating process of the residual coal are difficult to perform. 27 Based on the computational fluid dynamics (CFD) technique, relevant scholars have studied the evolution process, 28 influencing factors 27,[29][30][31][32] and prevention measures 17,18,[33][34][35][36][37] of coal spontaneous combustion in gobs. Yuan and Smith studied the self-heating process of coal in a longwall gob with 3D numerical simulation and analyzed the influence of the ventilation system and coal properties. ...
... According to the "O"-ring theory and field measurements, the caving of the roof rock strata under the support of coal pillars behaved similarly. 17 Therefore, assuming that the bulking factor of the fractured coal rocks in the middle of the gob conformed to Equation (11), and taking into account the influence of the sustainment of the coal pillars, we defined an equivalent distance from any point in the gob to the side wall as: ...
Article
Full-text available
To effectively prevent and control the spontaneous combustion of residual coal at the bottom of a large fully mechanized gob space, we proposed a targeted inertization technology based on the injection of power plant flue gas. Based on the real onsite conditions of the gob, the three‐dimensional distributions of the overburden fractures, gas emission, and residual coal were added to the multiphysics coupled model of spontaneous coal combustion. The simulation method based on moving coordinates was used to complete the risk evaluation and the locating of the spontaneous combustion in the fully mechanized gob, and the key control factors of the inerted zone and the fire prevention effect of the flue gas injection were analyzed. The results showed that the mismatch between the inerted zone and the spontaneous combustion risk zone was the root cause of the poor fire prevention effect of the inert gas injection. Because the density of the flue gas was greater than that of the leaked air, the flue gas mainly migrated and diffused in the lower part of the gob. At a distance of 100 m from the working face, the flue gas with 3%‐9% oxygen content injected at a rate of 2000 m³/h completely covered the high‐temperature residual coal. This caused the maximum temperature (Tmax) to drop from 334.2 K upon nitrogen injection to below 310 K. Additionally, the effect of the oxygen content fluctuation on Tmax was controlled within 2.6 K. The methods and the results in this study can serve as a reference for efficiently preventing and controlling local spontaneous combustion hazards in large spaces for underground coal mining.
... Brattice curtains or wings are employed in some coal mines in Australia to divert the airflow and reduce the methane concentration in areas of concern. Ren et al. [48] conducted CFD simulations to shed light on the carbon dioxide (CO 2 ) fringe behaviour on a longwall face, and it was observed that the use of brattice in the tailgate could enable CO 2 concentration at the goaf stream of the tailgate end to reduce by 0.5%. A similar study was conducted by Tanguturi et al. who [49] numerically investigated the impact of various curtain configurations on methane mitigation on the longwall face. ...
... In summary, it was noted that the use of curtains at the tailgate end assisted in reducing methane concentration at the intersection of the working face and tailgate end, which was consistent with results from Ren et al. [48] who did not conduct a thorough investigation into the influence of curtain and brattice configuration on methane mitigation at the tailgate end. The analysis of simulation results indicated that the width of curtain A, the distance between curtain C (B) and goaf side rib, and the length of curtain C significantly influence the methane concentration at the tailgate end. ...
Article
Spontaneous heating in the active goaf area during normal mining processes poses increased threats to mine productivity and safety, as evidenced in events induced by spontaneous combustion of coal. To control and mitigate this engineering problem, there is a need to gain critical knowledge of spontaneous combustion in the longwall goaf area, which can be achieved through a combination of field tests and numerical modelling. This paper introduces the spontaneous combustion management system widely used in Australia and presents Computational Fluid Dynamics (CFD) models for the simulation of gas flow dynamics in the goaf area, based on the site conditions of an underground coal mine where coal seam gas is predominantly comprised of carbon dioxide. The models were validated with gas monitoring data and used to conduct parametric studies for proactive goaf inertisation optimization. Qualitative and quantitative analysis of simulation results indicated that better goaf inertisation could be achieved when nitrogen was injected via cut-through at 250 m on the maingate (MG) side and surface boreholes at 100 m and 700 m on the tailgate (TG) side, with a total injection rate greater than 1750 l/s. The oxygen concentration on the MG and TG side dropped below 5% at distances of 120 m and 75 m behind the longwall face, with an oxidation zone area of 35375 m², which was approximately one-third of the oxidation zone area of the scenario without inert gas injection. Simulation results help shed light on improving current goaf inertisation practices to effectively reduce the risk of heating in goaf areas and improve mining process safety based on Australian conditions and practices.
... Brattice curtains or wings are employed in some coal mines in Australia to divert the airflow and reduce the methane concentration in areas of concern. Ren et al. [48] conducted CFD simulations to shed light on the carbon dioxide (CO 2 ) fringe behaviour on a longwall face, and it was observed that the use of brattice in the tailgate could enable CO 2 concentration at the goaf stream of the tailgate end to reduce by 0.5%. A similar study was conducted by Tanguturi et al. who [49] numerically investigated the impact of various curtain configurations on methane mitigation on the longwall face. ...
... In summary, it was noted that the use of curtains at the tailgate end assisted in reducing methane concentration at the intersection of the working face and tailgate end, which was consistent with results from Ren et al. [48] who did not conduct a thorough investigation into the influence of curtain and brattice configuration on methane mitigation at the tailgate end. The analysis of simulation results indicated that the width of curtain A, the distance between curtain C (B) and goaf side rib, and the length of curtain C significantly influence the methane concentration at the tailgate end. ...
... Coal is a heterogeneous material with "dual porosity" characteristics that are typically controlled by a matrix rich in micropores (<2 nm), mesopores (2-50 nm), and macropores (>50 nm) and a multi-scale fracture system. The presence of fractures is crucial for enabling the movement of fluids, and their size can range from 0.5 nm to several millimeters (Karayigit et al., 2017;Nie et al., 2015;Ren et al., 2018;Safaei-Farouji et al., 2023). ...
Article
This study represents the first assessment of CO2 storage potential in Austrian coal seams. Coal samples were taken from Fohnsdorf and Leoben abandoned coal mines, with particular emphasis on the Fohnsdorf coal since Leoben coal reserves were largely mined during previous coal production. Several methods were used to compare coal characteristics, including Rock-Eval pyrolysis (RE), organic petrography, and low-pressure N2 and CO2 sorption measurements. Both Fohnsdorf and Leoben coal samples show low sulfur and ash yields, as well as correspondingly high total organic carbon (TOC) contents. The pyrolysis Tmax and vitrinite reflectance values agree with a low coal rank for both sites. According to the N2 adsorption measurements at 77 K, low-lying mire coals from Fohnsdorf show a higher BET-specific surface area (BET-SSA) and BJH pore volume compared to raised-mire coals from Leoben. However, sapropelic shales and high-ash coals from Leoben show the highest BET-SSA and BJH pore volumes of all investigated samples and considerably exceed the N2 adsorption volumes of pure coals from both locations (N2 uptake up to 16 cm3/g; avg. for all samples 5.4 cm3/g). In contrast, the mean adsorbed CO2 uptake measured at 273 K and ~ 1 bar followed the order of Fohnsdorf low-lying mire coals > Leoben raised-mire coals > Leoben sapropelic coals and shales, ranging at ~0.8 mmol/g, ~0.7 mmol/g, and ~ 0.2 mmol/g, respectively. This shows that BET-SSA and BJH equations did not allow for adequate estimation of CO2 adsorption capacity trends in the investigated sample set. Furthermore, based on the existence of a hysteresis loop between CO2 adsorption and desorption branches for all investigated samples, the occurrence of weak chemisorption phenomena during CO2 adsorption is indicated. This effect helps to increase CO2 uptake and storage safety since the chemisorption process is not fully reversible upon pressure decrease. Ultimately, the theoretical CO2 sequestration potential of the remaining unmined Fohnsdorf coal reserves was estimated at 4.65 million tons, with an additional potential for enhanced coal bed methane production due to the gas-rich nature of Fohnsdorf coals with an estimated 1.2 billion m3 of CH4 in place.
... Coal is a heterogeneous material with "dual porosity" characteristics that are typically controlled by a matrix rich in micro-(<2 nm), meso-(2-50 nm), and macropores (>50 nm; IUPAC classification; Sing, 1985) and a multi-scale fracture system. Those fractures are essential to facilitate fluid flow and can vary in aperture from 0.5 nm to several millimeters (He et al., 2017;Karayigit et al., 2017;Li et al., 2012;Meng et al., 2016;Mitra et al., 2012;Nie et al., 2015;Puskarczyk et al., 2022;Ramandi et al., 2016;Ren et al., 2018;Shi et al., 2014;Sun et al., 2018). ...
Article
Geological formations are suitable locations for CO2 sequestration, and among them, coals are excellent targets because of their nanoporous structure, which leads to a high gas adsorption capacity. The first part of this review summarizes the most important influencing factors on coal pore structure and resulting CO2 storage capacity. In the second part, the most commonly applied methods for pore structural characterization are introduced and discussed in the light of the challenges that arise from the complex and heterogeneous nature of coal microstructures. In general, it is recommended to use an array of complementary methods for microstructural characterization since pores in coals span over a wide size range from <1 nm to >1 mm. Coals furthermore show dual porosity (matrix pores and fractures) in most cases. Numerous factors may influence the occurrence of these pore types as well as the gas adsorption capacity, including formation temperature, coal rank, moisture content, swelling, maceral composition, ash content, stress state, type of gas, and gas pressure. All of these factors must be taken into account in order to optimize planned CO2 storage operations.
... In view of the goaf's concealment characteristics, it is difficult to directly detect the gas flow law when on-site or to do full-scale model experiments in the laboratory (Yuan and Smith 2008). Numerical simulations have therefore become an important means to study the coupling disaster of coal spontaneous combustion and gas in the goaf (Juganda et al. 2020;Ren et al. 2018;Taraba and Michalec 2011;Wang et al. 2017cWang et al. , 2018Wolf and Bruining 2007;Xia et al. 2016). ...
Article
Full-text available
In view of the complexity and concealment of goafs, numerical simulations have become an important means for studying the coupling disasters of spontaneous coal combustion and gas. Porosity is an important parameter in the numerical simulation, but this is difficult to detect directly on site, as the current porosity model does not fully reflect the characteristics of "three horizontal areas" and "three vertical zones" in the goaf. To establish a more accurate porosity model which is based on a theory of overlying strata movement, the Sigmoid function was introduced to reflect the distribution characteristics of the "three horizontal areas" in the goaf, and subsidence models of the main roof and overlying strata were established. A model that measures the porosity of the goaf was formulated, which reflects its O-shaped circle characteristics. The accuracy of the theoretical model was verified by obtaining experimental data. The results showed that the main roof subsidence in the natural accumulation area was approximately zero, there was an exponential decrease in the load-affected area, and the maximum subsidence appeared in the compacted area. The descending displacement was very small around the impacted area along the roadway wall. The movement of overlying strata in the fractured zone was controlled by the main roof, and the subsidence of the strata near the roadway wall and the working face was very small. In the vertical direction, the subsidence of the overlying strata decreased as the distance from the mining coal seam increased. The distribution of porosity in the goaf was shaped like a dustpan. In the horizontal direction, the porosity of the natural accumulation area and the impacted area of the roadway wall was the largest. Deep within the goaf, the porosity gradually decreased. The porosity in the fractured zone decreased in the vertical direction in a logarithmic manner. The porosity model proposed in this paper fully reflects the characteristics of the goaf, and provides a more accurate porosity model for the numerical simulation of spontaneous coal combustion and gas coupling disasters in the goaf.
... The areas of CFD application in studies on ventilation safety in the mining industry The areas of CFD application Identified papers as part of a systematic search according to specific criteria in the Scoopus and WoS databases Dust hazard Arasteh and Saeedi, 2017; Arya and Novak, 2020; Arya et al., 2020; Cai et al., 2019; Cao et al., 2019; Chang et al., 2019; Chen et al., 2018; Du et al., 2020; Geng et al., 2018; Geng et al., 2020; Hu et al., 2015; Hu et al., 2016; Hu et al., 2019; Hu et al., 2020; Liu et al., 2017; Liu t al., 2018; Kurnia et al., 2014b; Kurnia et al., 2015; Morla et al., 2018; Morla et al., 2019; Ren et al., 2014; Ren et al., 2018b Toraño et al., 2011; Xu et al., 2019; Xiu et al., 2019; Yin et al., 2019; Wang et al., 2011b; Wang et al., 2015; Wang et al., 2016b; Wang et al., 2017a; Wang et al., 2017b Wang et al., 2019c; Wang and Ren, 2013; Wang and Tang, 2019; Zhang et al., 2018 Zhang et al., 2019b; Zhang et al., 2020; Zhou et al., 2017; Zhou et al., 2018a; Zhou et al., 2018b; Zhou et al., 2020Gas hazardBrodny, et al., 2018;Brune et al., 2016;Guo et al., 2012;Guo and Yuan, 2015;Hasheminasab et al., 2019;Juganda et al., 2020;Krawczyk, 2020;Kurnia et al., 2014a;Kurnia et al., 2016;Lolon et al., 2020;Mishra et al., 2016;Qin et al., 2019;Ren and Edwards, 2000;Ren et al., 2018a;Saki et al., 2017;Sasmito et a., 2013;Torno et al., 2013;Toraño et al., 2009;Tutak and Brodny, 2018;Walentek et al., 2019;Yueze et al., 2017;Wang et al., 2019b;Zhang et al., 2011 ...
Article
The safety of the coal production process, which in the coming years will continue to be one of the basic energy resources in many countries worldwide, has a significant impact on its efficiency. The random character of many hazardous phenomena accompanying this process requires the application of both modern and safe methods to study these phenomena. Model studies based on the Computational Fluid Dynamics (CFD) method are known to have such features. They enable the analysis of very complex and hazardous phenomena, which are hard or even impossible to investigate with the use of other methods. Therefore, this article focuses on the analysis of the state of the art in terms of the Computational Fluid Dynamics application in research on ventilation safety during underground hard coal mining. It was assumed that CFD-based studies may significantly improve the safety of the mining production process. For this purpose, a systematic literature review was carried out, which – according to the adopted methodology – involved four research questions. The review included scientific publications (articles) contained in the two most prestigious databases, i.e., the Web of Science and the Scopus. In accordance with the adopted search criteria, articles that used the Computational Fluid Dynamics method and focused on ventilation safety during underground coal mining were selected. The meta-analysis of these data made it possible to identify seven thematic areas undertaken in these publications. The following paper presents a list of articles assigned to these groups with selected items being discussed. On the basis of the conducted research, comprehensive answers to the research questions were provided. The results systematize the knowledge of CFD application in research on ventilation safety in mining. Also, they are a valuable source of information for future researchers and engineers concerned with the safety of the mining production process. Moreover, potential directions of further research in the field of possible Computational Fluid Dynamics applications were indicated to improve the safety of the process in question.
... Currently, three main research methods are used to improve the understanding of ventilation in longwall mines: numerical modeling, field studies, and physical modeling. Numerical modeling studies have primarily been conducted using the computational fluid dynamics modeling (CFD) [5][6][7][8][9][10][11][12] and ventilation network simulators [13,14]. CFD provides the advantage to model fluid flow and estimate gas concentration in inaccessible areas of the longwall mines, such as gobs. ...
Article
In longwall mining, ventilation is considered one of the more effective means for controlling gases and dust. In order to study longwall ventilation in a controlled environment, researchers built a unique physical model called the Longwall Instrumented Aerodynamic Model (LIAM) in a laboratory at the National Institute for Occupational Safety and Health (NIOSH) Pittsburgh Mining Research Division (PMRD) campus. LIAM is a 1:30 scale physical model geometrically designed to simulate a single longwall panel with a three-entry headgate and tailgate configuration, along with three back bleeder entries. It consists of a two-part heterogeneous gob that simulates a less compacted unconsolidated zone and more compacted consolidated zone. It has a footprint of 8.94 m (29 ft.) by 4.88 m (16 ft.), with a simulated face length of 220 m (720 ft.) in full scale. LIAM is built with critical details of the face, gob, and mining machinery. It is instrumented with pressure gauges, flow anemometers, temperature probes, a fan, and a data acquisition system. Scaling relationships are derived on the basis of Reynolds and Richardson numbers to preserve the physical and dynamic similitude. This paper discusses the findings from a study conducted in the LIAM to investigate the gob-face interaction, airflow patterns within the gob, and airflow dynamics on the face for varying roof caving characteristics. Results are discussed to show the impact of caving behind the shields on longwall ventilation.
... It is generally acknowledged that coal is a kind of complex organic rock, composed of amorphous carbon based compounds with pores, cracks, defects, i.e., complicated surface structures [12][13][14][15]. The pore system in coals is quite heterogeneous, ranging from micropores, mesopores, and macropores, and the methane or CO 2 adsorption behavior is significantly affected by pore size distribution [16][17][18]. On one hand, the pore characteristics within coal are affected by many factors, such as coal rank, degree of deformation, coal macerals and minerals [19][20][21][22]. ...
Article
Accurate characterization of nanopore structure within coal is of great significance for understanding the mechanism of coalbed methane transportation and accumulation. In order to quantitatively analyze the nanopore characteristics and surface roughness of coal, atomic force microscopy (AFM) experiments were conducted on nine coal samples with different ranks from the Qinshui Basin in Shanxi Province, North Chia in this study. The visible surface three-dimensional topographies of coal were obtained. The nanopore parameters including pore number, mean pore size, areal porosity and form factor were acquired through AFM image processing on the scanning area of 1 μm × 1 μm. Comparison of nanopore distribution determined by AFM and low-pressure nitrogen gas adsorption (LP-N 2 GA) has also been made to validate the reliability of AFM. Based on the experimental data, relationships between these nanopore parameters and the degree of coalification (indicated by vitrinite reflectance, R o = 1.19%–3.15%) were studied. The results show that the pore number and areal porosity of studied samples are 1716–6885 and 0.91%–10.47%, respectively, with the mean pore size of 8.75–24.76 nm. The linearly positive correlation between the form factor and R o suggests the enhancement of coal maturity can make the nanopore shape within coal tend to be more regular. As a response, the values of R a and R q demonstrate a similar nonlinear decreasing trend with the increase of R o . Besides, dramatic changes of nanopore distribution have been observed during coalification jump, resulting in the shift to smaller nanopores. Comparison of nanopore distribution between AFM and LP-N 2 GA was made, indicating that AFM result is closer to the true value than LP-N 2 GA. This study enables us to better understand the surface characteristic of coal at nanoscale.
... where S i stands for the momentum loss for the ith momentum equation, µ represents the viscosity of air, α represents the permeability, v i represents the velocity in the ith direction, and C 2 means the inertial resistance factor (taken as 100th the inverse of α), ρ indicates the air density, and |v| is the velocity magnitude. In this study, goaf permeability varied from 10 −3.5 m 2 to 10 −5.5 m 2 , and a hyperbolic function was used to express the permeability distribution [66][67][68]. ...
Article
Full-text available
Mine ventilation has always been critical for underground mining operations to ensure operational efficiency and compliance with safety and health statutory requirements. To obtain a thorough understanding of the ventilation flow characteristics on a longwall face, innovative three dimensional (3D) models, incorporating key features of the longwall equipment and a zone of immediate goaf area, were developed. Mesh independent studies were conducted to determine the desirable mesh required for a mesh-independent solution. Then the model results were validated using field ventilation survey data. At both intersections of maingate/tailgate (MG/TG) and face where the flow boundary changes sharply, the occurrence of undesirable flow separation which causes additional energy loss was identified, as well as its extent of influence. The recirculation of airflow resulting from separation in the TG will lead to accumulation of high concentrations of mine gas, thus regular inspection or continuous monitoring of gas concentration in that area is highly recommended, especially when high gas emission is expected from the working seam. In addition, we also investigated the influence of shearer position and cutting sequence on longwall ventilation. Overall, the longwall models developed in this study together with the flow characteristics obtained will provide fundamental basis for the investigation of longwall gas and dust issues in the future.
Article
Full-text available
Low-oxygen (oxygen concentration below 18.5%) phenomena often occur in the top coal caving working face of ultrathick coal seams, posing a serious threat to the safety of workers. The characteristics of oxygen consumption and gas production at low-constant temperature and the corresponding functional group evolution of residual coal in goaf were studied by temperature-programmed and infrared spectrum experiments. The influence of different factors on the emission of low-oxygen gases was studied through numerical calculation. The results show that low-temperature oxygen consumption and gas production occurred when the coal was about 40 °C. When the temperature was constant, the oxygen consumption and gas production rate increased with the extension of time. In the early stage of coal oxidation, the aliphatic C–H components were attacked by oxygen molecules and reacted with them. The asymmetric methyl and methylene groups were more likely to oxidize and produce carbonyl compounds. With the increase of nitrogen injection, the overall width of the oxidation zone (oxygen concentration was defined as 10–18%) narrowed, and the range of the oxidation zone moved forward from the depth of the goaf. The oxygen concentration in the air return corner decreased gradually, and the low-oxygen area in the air return corner expanded gradually. The distance between the low-oxygen area of the working face and the air intake corner was gradually shortened. With the increase of air intake, the width of the oxidation zone increased and moved to the depth of goaf, and the degree of low oxygen in the air return corner increased. The research results are of great significance for the understanding and prevention of the low-oxygen phenomenon in ultrathick coal seams.
Article
Spontaneous heating of coal continues to present a health and safety hazard in underground coal mines. The influence of seam gas composition on gas flow dynamics and distribution characteristics in the active longwall goaf has not been studied in-depth, and corresponding effective proactive goaf inertization strategies for preventing potential spontaneous heating from occurring have limited investigation. To advance this knowledge, an 80-m-height goaf model was constructed and developed based on specific conditions of an Australian underground coal mine, and onsite gas monitoring data was collated to verify base model results, which allowed for various scenarios of seam gas composition to be simulated and investigated with confidence. This study involved modeling five different gas composition scenarios for the goaf atmosphere, namely, 100% CO2 (case 1), 80% CO2 and 20% CH4 (case 2), 50% CO2 and 50% CH4 (case 3), 20% CO2 and 80% CH4 (case 4), and 100% CH4 (case 5). Simulation results show that O2 is primarily distributed at the middle and upper part of the CO2-dominant goaf model, while it is mainly layered at the floor level of the CH4-dominant goaf model. N2 is superior to CO2 in the goaf inertization for the CO2-dominant goaf model, whereas CO2 performs better than N2 for the CH4-dominant goaf model. The optimal inert gas flowrates for case 1 to case 5 are 1.5, 1.75, 0.75, 0.5, and 1.0 m3/s, and the oxidation zone area is reduced by 55.76%, 67.21%, 58.04%, 78.17%, and 81.82%, respectively. The simulation results allow for increased insight and understanding of the gas distribution patterns in the active goaf with different seam gas composition and the development of corresponding proactive goaf inertization practices, thus minimizing potential spontaneous-heating-related hazards and improving mining safety.
Article
To define the diffusion behavior of harmful exhaust substances from diesel vehicles and support safety risk assessments of underground coal mines, we performed a multi-species coupling calculation of the emission and diffusion of harmful substances from a trackless rubber-wheel diesel vehicle. A computational fluid dynamics (CFD) model of the diffusion of harmful emissions was hence established and verified. From the perspective of risk analysis, the diffusion behavior and distribution of hazardous substances emitted by the diesel vehicle were studied under 4 different conditions; moreover, we identified areas characterized by hazardous levels of emissions. When the vehicle idled upwind in the roadway, high-risk areas formed behind and to the right of the vehicle: particularly high concentrations of pollutants were measured near the rear floor of the vehicle and within 5 m behind the vehicle. When the vehicle idled downwind, high-risk areas formed in front of it: particularly high concentrations of pollutants were measured near the floor and within 5 m from the front of the vehicle. In the above cases, the driver would not breathe highly polluted air and would be relatively safe. When the vehicle idled into the chamber, however, high-risk areas formed on both sides of the vehicle and near the upper roof. Forward entry of the vehicle caused a greater increase in the concentration of pollutants in the chamber and in the driver’s breathing zone compared with reverse entry.
Article
Three stages of nitrogen (N2) injection enhanced gas drainage through underground in-seam boreholes were carried out in a coal mine located in the southern Sydney basin. Due to the high CO2 content and low permeability, hard-to-drain coals were encountered during the excavation process in this coal mine. Two parallel in-seam boreholes (the length of 36 m, the diameter of 96 mm and the borehole space of 5 m) were drilled on the rib of the gateroad. A total of ten-cylinder packs of nitrogen (approximately 1500 m³) were injected into the coal seam. Different nitrogen injection pressures (150 KPa, 250 KPa, 350 KPa and 450 KPa) and injection methods (continuous injection and cyclic injection) were employed. Gas flow rates and gas compositions from the production borehole were recorded during and after the nitrogen injection process. It was observed that gas breakthrough was tightly related to the nitrogen injection pressure. The higher injection pressure was, the shorter breakthrough time was. Specifically, no gas breakthrough was obtained when the injection pressure was 150 KPa. The minimum of breakthrough time was 35 min when 450 KPa’s injection pressure was employed. Strong post-injection effect was monitored after each stage of injection and it was affected by the volume of the injected nitrogen. Under the current injection conditions, the performances of different injection methods were like each other, which was out of our expectation. After the injections, the results of cores showed that less than 5 % of the total injected nitrogen was remained in the coal seam. The coal seam gas content dropped 0.99–1.65 m³/t after these three stages of injection. All these findings provide implications and guidance not only for laboratory experiment and numerical modelling, but also for the field application of this new technology.
Thesis
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This thesis is primarily concerned with mapping a path for industry to fully automated drill and blast, which despite the progress made with automation in the mining industry remains the hitherto unattainable ‘Holy Grail’ for mining. This would remove personnel from drill and blast zones, but in harmony with fully automated harvesting units like LHDs, would remove personnel from most operational areas in both open cut and underground mines, for hardrock and coal. Fully automated drill and blast will not only improve safety but eliminate many of the safety and health management systems that are presently designed to protect personnel from operational risks. That is not to say that risk assessment and management will not be necessary in development or production areas once they are fully automated but keeping machinery safe from harm invokes a different view of the risks. Reducing the regulatory burdens reduces the overall costs of mining. It would also enable the exploitation of now difficult to mine resources and bring new mining methodologies to bear on existing mining operations. Fully automated drill and blast may see blasting return to underground coal mines to advance production rates above that presently gained with Longwalls and continuous miners – and all at an aggregate lower cost per tonne than now achieved. Fully automating the drill function is conceptually not that difficult. There are many semiautomated drill rigs that can readily be made fully automated with robotics and AI. Fully automating the blast function is a somewhat more complex undertaking. It can be achieved by loading blast holes with prepackaged blast cartridges. Indeed, it can only be achieved in this way. The prepackaged blast cartridges will allow more precise blasting and with a lot less explosive than is now used. The days of loading blast holes with large volumes of expensive bulk explosives may be coming to an end. Conventional blast procedures may be likened to the muskets of old, where black powder is poured into the breach, a ball, and a wad inserted, then rammed home firm with a rod. A cap is then added at the firing end for initiation when the trigger is squeezed. Firing on full-automatic only became possible with the development of cartridge technology. There is no such animal as a musket machine gun!
Article
Computational fluid dynamics (CFD) is an effective methodology that has been widely used for decades to solve engineering problems involving spontaneous combustion and abnormal gas emissions. However, most of the previous CFD modelling focused on qualitative rather than quantitative analysis, and the factors influencing spontaneous combustion control and gas management are numerically under-researched. The onset of spontaneous heating in the goaf area is dictated by many operational and environmental parameters, including mining method, ventilation and geology. Based on field data from a real mine site, extensive CFD modelling was conducted and analyzed qualitatively and quantitatively to investigate the impact of ventilation design and operational measures on the management and control of spontaneous combustion and gas exceedance. Real-time gas monitoring data was utilized for model validation, and a good agreement between simulation results and monitoring data was reached. The tightness of goaf seals described by permeability was quantitatively investigated, revealing that the permeability should be smaller than 10⁻⁹ m² to prevent air leakage effectively. Goaf inertisation parameter optimization is crucial to minimize the risk of spontaneous combustion. The systematic study revealed that the oxidation zone area (OZA) was the largest for nitrogen injection (29706 m²), followed by boiler gas (28396 m²), while it was the smallest for carbon dioxide (11902 m²), which produced the best goaf inertisation performance. Injection flow rate is another significant factor influencing the effectiveness of heating prevention. The simulation results indicated that a critical injection rate of 1750 m³/h was determined, and the ratio of the OZA to the goaf area (GA) fluctuated around 7% once the injection rate was beyond this critical value. The installation location of curtains and brattices both on the longwall face and tailgate end was also simulated and optimized. Noticeable methane reduction at the tailgate end was observed with optimal configurations of brattices and curtains. Results from the modelling will shed light on improving current practices to effectively contain goaf heating in the longwall goaf areas and mitigate methane exceedance on the longwall face.
Article
Goafs are composed of large, irregularly shaped broken rocks. This means in order to calculate the permeability and inertial resistance coefficient of a goaf, the Ergun equation must be modified. The coupling relationships between coefficients A and B, and particle size and porosity are established based on the existing simulation research. Coefficients A and B both have a quadratic polynomial relationship with porosity. The quadratic polynomial's constant term ratio has a good power function relationship with particle size, while the linear term ratio and quadratic term ratio both have good exponential function relationships with particle size. By introducing the shape factor of permeability and inertial resistance coefficient, which are calculated by dividing the experimental value with the theoretical value, the correction model is established for the permeability and inertial resistance coefficient of the goaf. The permeability and inertial resistance coefficient shape factor have good power function relationships with particle size.
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