A new design of foam spray nozzle used for precise dust control in underground coal mines

In order to improve the utilization rate of foam,an arc jet nozzle was designed for precise dust control.Through theoretical analysis,the different demands of foam were compared amongst arc jets,flat jets and full cone jets when the dust source was covered identically by foam.It is proved that foam consumption was least when an arc jet was used.Foam production capability of an arc jet nozzle under different conditions was investigated through experiments.The results show that with the gas liquid ratio(GLR)increasing,the spray state of an arc jet nozzle presents successively water jet,foam jet and mist.Under a reasonable working condition range of foam production and a fixed GLR,foam production quantity increases at first,and then decreases with the increase of liquid supply quantity.When the inner diameter of the nozzle is 14 mm,the best GLR is 30 and the optimum liquid supply quantity is0.375 m~3/h.The results of field experiments show that the total dust and respirable dust suppression efficiency of arc jet nozzles is 85.8%and 82.6%respectively,which are 1.39 and 1.37 times higher than the full cone nozzles and 1.20 and 1.19 times higher than the fiat nozzles.     

A new design of foaming agent mixing device for a pneumatic foaming system used for mine dust suppression

To overcome the drawbacks of the conventional foam technology used for dust suppression,including large pressure loss,high water pressure and low driving pressure,a new pneumatic foaming system is introduced.Then an original design of foaming agent mixing device is proposed,and its performance is investigated and evaluated under different pressure compensations.Experimental results show that the maximum absorption amount increases by 2.9-6.7 times at a pressure compensation of 0.04-0.2 MPa compared with no pressure compensation.The pressure loss and pressure fluctuation both reduce significantly with increasing pressure compensation.The critical outlet pressure increases by30.4-240%.Field application indicates that the proposed mixing device ensures the reliable addition of foaming agent used for foam dust suppression.The effect of foam on dust suppression is remarkable,and the economic cost of foam is low.Therefore,there is reason to believe that the new mixing device will greatly promote foam technology to be widely used for suppressing dust in underground coal mines.     

Application of foam technology for dust control in underground coal mine

In order to effectively control the dust in the underground coal mine, this study proposes and develops a new technology for dust control by foam, and briefly demonstrates the advantage of the foam technology for dust control, such as the good isolation performance, large contact area, high wetting ability, strong adhesion and so on. Besides, the details of the technology are introduced, including the foam agent, foam generator, and foam production process. Then the paper studies the relationship between the foaming agent concentration and liquid surface tension, and explains the principle of the foam generator. The technology is applied in heading face. The application results show that the foam has a remarkable effect on dust control in underground coal mines.     

Mechanism of micro-wetting of highly hydrophobic coal dust in underground mining and new wetting agent development

The internal mechanism of the high hydrophobicity of the coal samples from the Pingdingshan mining area was studied through industrial, element, and surface functional group analysis. Laboratory testing and molecular dynamics simulations were employed to study the impact of three types of surfactants on the surface adsorption properties and wettability of highly hydrophobic bituminous coal. The results show that the surface of highly hydrophobic bituminous coal is compact, rich in inorganic mine...     

Time-depth conversion of transient electromagnetic method used in coal mines

Accuracy of time-depth conversion in data processing of transient electromagnetic prospecting always affects the accurate positioning of water bodies in coal mines. In order to improve the accuracy of time-depth conversion, we established a mathematical model of time-depth conversion for a transient electromagnetic method based on the theory of "double smoke ring effect"of full space transient electromagnetic field transmission. Using a 3-layer as well as a 4-layer geo-electric model for roadway floors,we performed the time-depth conversion of theoretical curves of apparent resistance varying over time. In these curves, the depth corresponding to extreme value points is nearly the same as the depth of a geo-electric model. The position of water body determined by our time-depth conversion method agrees well with the result of borehole drilling, indicating that the established time-depth conversion model can clearly improve the accuracy of spatial positioning of water bodies in coal mines.     

High efficiency dust scrubbers for continuous miner in underground mines

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煤矿井下无火花截割机的研制

煤矿井下地质复杂,条件恶劣,常有事故和故障发生.当紧急排除故障时,需要对被堵地段进行疏通和清理,为此,研制了一种无火花截割机进行快速疏通,该机的主机部分为经过优化设计的曲柄摇块机构.经井下试验表明该机设计合理、简单实用,是煤矿井下尽快排除故障或打开一条救生通道时可选用的一种先进设备.     

煤矿井下无火花截割机的研制

煤矿井下地质复杂 ,条件恶劣 ,常有事故和故障发生 .当紧急排除故障时 ,需要对被堵地段进行疏通和清理 ,为此 ,研制了一种无火花截割机进行快速疏通 ,该机的主机部分为经过优化设计的曲柄摇块机构 .经井下试验表明 :该机设计合理、简单实用 ,是煤矿井下尽快排除故障或打开一条救生通道时可选用的一种先进设备     

Computer simulation of evacuation in underground coal mines

In order to study the evacuation behavior of miners during accidents,we analyzed the rational layout of a safe chamber,and improved evacuation efficiency.A visual model of evacuation was developed and used to simulate the evacuation process of mines,given their special underground environments.In our simulation,the working faces of a coal mine and nearby tunnels were divided into 0.5 m×0.5 m grids to reflect the location of occupants and obstacles.Based on a"flow potential of the occupant",we determined the direction of movement and routes of occupants.In the model,evacuation speed changed as a function of crowd density,with an average speed of 1.30 m/s.The model also takes into account detection time of the disaster and the personnel response time.Evacuation time,exit flow rate and evacuation path were obtained by simulation.The results indicate that using simulation technology can present a more visual evacuation process and show the behavior of occupants.Our establishment of a mine safety evacuation system has merit as reference value.     

Electromagnetic environments in roadways of underground coal mines and a novel testing method

The electromagnetic environment of laneways in underground coal mines is an important area for the design of new electronic products,as well as a fundamental space for mine monitoring,surveillance,communications and control systems.An investigation of electromagnetic interference in coal mines is essential for the enhancement of performances of these systems.In this study,a new field method is provided in which radiated emission tests in coal mine laneways have been carried out.We conclude that:1) the wiring motor vehicles can radiate interference with a bandwidth up to 1 GHz and with an amplitude 10 dBμV/m higher than the background noise;2) the PHS (Personal Handy phone System) mobile communication system can cause interference 40 dBμV/m higher than the background noise;3) an interference 25 dBμV/m higher than the background noise can be generated during the communication at a working bandwidth of 48.8 MHz;and 4) power cables,battery vehicles as well as mechanical and electrical dong rooms have little effect on the electromagnetic radiation environment in coal mine tunnels.     

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 novel coating technology for fast sealing of air leakage in underground coal mines

Air leakage in underground coal mines presents a serious hazard for coal production and the safety of miners. Coating technology is commonly used as an efficient means for preventing air leakage. To address existing problems with high dust concentrations in large operations involving complex processes and the high cost of traditional coating technology, a novel coating technology that ensures intrinsic safety by utilizing water pressure and wind pressure was developed. This new coating technology was designed to suction and spray, and the technical parameters of its spray performance was also studied. The experimental tests and evaluation indicated the optimum working range is 0.3–0.7 MPa of wind pressure,1.2–10.2 L/min of water quantity, and 1.0–3.5 m of spraying distance. Moreover, this novel coating technology was tested in the Dashuitou Coal Mine in Gansu Province of China. Compared with conventional counterparts, the proposed new technology is safe, efficient, and convenient to operate. During spraying,dust concentrations were kept at less than 10 mg/m3, and the average rebound ratio resilient rate of solid materials was below 13%. After spraying, the average leakage every 100 m was 4 m3/min, and the oxygen volume fraction in the adjacent goaf was approximately 4%, demonstrating excellent air leakage prevention.     

Analysis of underground fires in Polish hard coal mines

In the period of the first twenty years after World War II the number of fires in Polish hard coal mines reached annually the value of several thousands of cases. About 80% of fires constituted spontaneous fires. Investigations into the development of new methods of fire hazard prediction and implementation of new methods and means of fire prevention as well as the introduction of prohibition concerning the use of products manufactured of combustible organic materials in underground mine workings re-duced considerably the hazard of underground fire rise. The worked out at the Central Mining Institute (GIG) new method of un-derground fire prediction allows the correct selection of fire prevention means. The introduction into common use of fire-resistant conveyor belts, the main factor giving rise to spontaneous fires, and methods of assessment of their fire resistance eliminated prac-tically the fire hazard. These activities contributed in an efficient way to the reduction of the number of underground fires to a sa-tisfactory level.     

Review of current method to determine outburst threshold limits in Australian underground coal mines

Desorption rate index (DRI) was presented to the Australian underground coal industry in 1995 as a means for determining outburst threshold limits for Australian coal seams. DRI is a measure of the gas volume released from a coal sample in the first 30 s of crushing during the Q3 stage of gas content testing, multiplied by the ratio between measured Q3 and QM. Relationships were identified between QM and DRI for both CO₂ and CH₄ rich coal samples collected from the Bulli Seam at West Cliff Colliery and that identified relationship was referred to as the Bulli Seam Benchmark. The outburst mining gas content threshold limit values specified for the Bulli Seam at that time, when applied to the QM-DRI Bulli Seam benchmark, was shown to closely align with a DRI value of 900 (DRI900), for both CO₂ and CH₄ rich seam gas conditions. The Australian coal industry adopted the DRI900 as the basis for determining outburst gas content TLV for Australian coal seams. Outburst mining experience in Australia has shown that gas content is not the only significant factor that impacts outburst risk, as all significant outburst events have been associated with abnormal geological conditions, such as faults and dykes. Therefore, assessing the potential application of additional outburst risk factors, to accurately define outburst risk zones, set safe mining threshold levels, and determine appropriate mining controls, warrants further investigation. Several Australian coal mines have implemented mining procedures enabling mining to continue in areas with gas content greater than the TLV determined using the DRI900 approach, without inducing an outburst. There is a broad lack of understanding among Australian coal mine operators as to the procedure and calculations used to determine DRI. Also, there has been growing concern regarding the accuracy and validity of the DRI900 method for determining outburst TLV. A comprehensive set of gas data has been collected from Australian coal seams, including the Bulli Seam, and this data has been used to investigate the DRI, Bulli Seam Benchmark, and the applicability of using DRI900 as the basis for assessing outburst risk and determining gas content TLV. The results are presented and discussed.     

Spatial context in the calculation of gas emissions for underground coal mines

The prediction of gas emissions arising from underground coal mining has been the subject of extensive research for several decades, however calculation techniques remain empirically based and are hence limited to the origin of calculation in both application and resolution. Quantification and management of risk associated with sudden gas release during mining(outbursts) and accumulation of noxious or combustible gases within the mining environment is reliant on such predictions, and unexplained variation correctly requires conservative management practices in response to risk. Over 2500 gas core samples from two southern Sydney basin mines producing metallurgical coal from the Bulli seam have been analysed in various geospatial context including relationships to hydrological features and geological structures. The results suggest variability and limitations associated with the present traditional approaches to gas emission prediction and design of gas management practices may be addressed using predictions derived from improved spatial datasets, and analysis techniques incorporating fundamental physical and energy related principles.     

Novel foaming agent used in preparation process of aluminum foams

The performances of a novel foaming agent used in the preparation process of aluminum foams were investigated,and the effects of some factors,such as addition of the foaming agent,foaming temperature on the porosity,and appearance of aluminum foams were also discussed.Experimental results show that the novel foaming agent has a wide decomposition temperature range and a mild decomposed rate; the foaming agent has the ability to enhance the viscosity of aluminum melt,as a result,an extra viscosifier such as Ca or SiCp is unnecessary while using this foaming agent; the bubble-free zone in material decreases and the foaming efficiency increases with the increase of foaming agent; the bubble-free zone disappears and the foaming efficiency is near 100% when the addition of foaming agent is more than 1.4wt% ; the porosity of the aluminum foam increases with the increase of foaming agent when the addition of foaming agent is less than 2.2wt% .     

Experimental research on inorganic solidified foam for sealing air leakage in coal mines

In order to efficiently seal air leakages and control spontaneous combustion of coal, solidified foam was developed by adding a certain compound additive to fly coal ash and cement as the main materials. It was prepared basing on the foaming characteristic through physical and mechanical system. We studied the effects of the different types of foaming agents, the mass ratio of cement to fly ash, and the mass ratio of solid to water and content of cellulose on the performance of solidified foam. The results show that when adding the composite protein, surfactant and cellulose foaming agents. The cement-fly ash ratio of 0.75:1, the water solid ratio as large as 2:1, and the solidified foam with high properties and density of only 516 kg/m³ and compressive strength of up to 12.68 MPa were prepared. But the initial setting time, identity and compressive strength may be changed by varying the water solid ratio and/or the additives. We theoretically analyzed the influence mechanism of foam density, compressive strength and water solid ratio. The solidified foam is especially suitable for sealing surface leakage channels and filling the goaf with a wide application prospects.     

Developing coal burst propensity index method for Australian coal mines

Coal burst is the violent failure of overstressed coal, and it is often accompanied by sound, coal ejection and seismic events. It is subsequently recognized as a serious safety risk of Australia after double fatalities coal burst happened at Austar Coal Mine. Considering the increasing trend of coal burst severity and frequency with mining depth, it is an urgent task to develop the coal burst risk assessment methods for Australia underground coal mines. Coal burst propensity index method is a widely used method of burst risk evaluation of coal as it is summed up from the coal burst research and practice of many countries.This paper presents the experimental and theoretical research of coal burst propensity index method for coal burst risk assessment in Australia. The definition of four indexes including elastic strain energy index(W_(ET)), bursting energy index(K_E), dynamic failure time(DT) and uniaxial compression strength(RC)is introduced in the first part. Then, the standard laboratory test process and test parameter of coal burst propensity index is presented. DT test is conducted with 0.3 mm/min displacement control loading rate while other test is with 0.5 mm/min. Besides, modified data processing and risk classification method of test are proposed. Differentiate analysis of stress-strain curve is adopted in the data processing of DT and KEindex. A four level risk classification form of burst risk is recommended for Australian underground coal mines. Finally, two likely improvement methods of W_(ET) test, including volumetric strain indicator method and theoretical calculation method, are discussed.     

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.