Dynamic behavior of outburst two-phase flow in a coal mine T-shaped roadway:The formation of impact airflow and its disaster-causing effect

The study of the dynamic disaster mechanism of coal and gas outburst two-phase flow is crucial for improving disaster reduction and rescue ability of coal mine outburst accidents.An outburst test in a T-shaped roadway was conducted using a self-developed large-scale outburst dynamic disaster test system.We investigated the release characteristics of main energy sources in coal seam,and obtained the dynamic characteristics of outburst two-phase flow in a roadway.Additionally,we established a formation model for outburst impact flow and a model for its flow in a bifurcated structure.The results indicate that the outburst process exhibits pulse characteristics,and the rapid destruction process of coal seam and the blocking state of gas flow are the main causes of the pulse phenomenon.The outburst energy is released in stages,and the elastic potential energy is released in the vertical direction before the horizontal direction.In a straight roadway,the impact force oscillates along the roadway.With an increase in the solid–gas ratio,the two-phase flow impact force gradually increases,and the disaster range extends from the middle of the roadway to the coal seam.In the area near the coal seam,the disaster caused by the two-phase flow impact is characterized by intermittent recovery.In a bifurcated roadway,the effect of impact airflow on impact dynamic disaster is much higher than that of two-phase flow,and the impact force tends to weaken with increasing solid-gas ratio.The impact force is asymmetrically distributed;it is higher on the left of the bifurcated roadway.With an increase in the solid-gas ratio,the static pressure rapidly decreases,and the bifurcated structure accelerates the attenuation of static pressure.Moreover,secondary acceleration is observed when the shock wave moves along the T-shaped roadway,indicating that the bifurcated structure increases the shock wave velocity.

Evaluation of airlift pump performance for vertical conveying of coal particles

One of the crucial aspects of reducing air consumption when conveying particles with an airlift pump is to know the factors that affect the process of particle motion at an initial velocity of zero.To determine the influence of submer-gence ratio and physical properties of particles(such as size,shape,and mass)on the onset of vertical particle motion,the airlift pump was taken as the research object,and spherical glass together with irregular shaped coal were used as experimental test particles.The results show that unlike the water-solid environment,the start of particle motion in the water-air mixture does not always occur at a certain value of superficial water velocity and this value also increases with increasing submergence level.Among the parameters considered,the role of submergence ratio is much more effective than the dimensions and the shape of the particle,because by increasing submergence from 0.3 to 0.8,it is possible to reduce air consumption by up to 8 times.Based on this study the corresponding theoretical model derived by Fujimoto et al.is optimized,wherein the overall agreement between the modified theory and present experimental data is particularly good.Contrary to Fujimoto,the minimum superficial water velocity for lifting solids in the air-water mixture is not always smaller than water ambient which indicates on optimum submergence ratio higher than 0.7.Finally,a new criterion was introduced to describe the moment of onset of the particle motion as a function of the superficial fluid velocity ratio for each submergence value.

Paste-like self-flowing transportation backfilling technology based on coal gangue

A paste-like self-flowing pipeline transportation backfilling technology with coal gangue as aggregate is proposed to remove the potential damage caused by coal gangue piles.As well,the difficult problems of recovering high quality safety coal pillars and deep mining of the Suncun Coal Mine(SCM),Xinwen Coal Group,Shandong are resolved.The physical-chemical properties of coal gangue,optimized proportion of materials,backfilling system and craft in the SCM were studied in the laboratory and then an industrial test was carried out on high quality coal pillars under a town.The results show that finely crushed kaolinized and fresh gangue with granularity less than 5 mm can be used as aggregate with fly ash to replace part of the cement and a composite water reducer as an additive,accounting for 1.0%-1.5% of the total amount of cement and fly ash.The recommended proportion is 1(cement):4(fly ash):15(coal gangue),with a mass fraction of 72%-75%,rheological paste-like properties and a strength of more than 0.7 MPa at 7 d.The sequence of adding cement,fly ash,water reducer and then coal gangue ensures that the suspended state of the slurry,reducing the wear and jam of pipelines.The working face is advancing continuously by the alternating craft of building block walls with coal gangue and backfilling mined-out gobs with paste-like slurry.The recovery rate is as high as 90% with a backfilling cost of 36.9 Yuan/t,good utilization of coal gangue and no subsidence on the surface.This technology provides a good theoretical basis and application experience for coal mines,cement backfilling with paste-like slurry.

FUZZY CONTROLLED AUTOMATION SYSTEM FOR THE MAIN COAL BUNKER

A fuzzy control scheme is presented according to the coal quantity in the main coal bunker, this method has a good dynamic response characteristic and is suited for complex nonlin-ear systems. The designation of self-adopting fuzzy controller, the working principle and functions of this system are also proposed, with the hardware and the main flow diagram of this system in-troduced in this paper.

Multi-factor dynamic analysis of the deformation of a coal bunker in a coal preparation plant

To assess the deformation of a coal bunker and propose effective preventative measures for such,a real-time monitoring system was designed.Moreover,methods were proposed for monitoring the coal-bunker inclination,settlement,groundwater level,temperature,and material level.By using a vector autoregression model and time-series data for the coal-bunker deformation,a long-term equilibrium relationship was derived between the coal-bunker inclination and settlement and their influencing factors.The dynamic effects of each factor on the coal-bunker inclination and settlement and how the contribution of each factor changes were revealed by using an impulse response function and variance decomposition.The results show that the coal-bunker inclination and settlement vary hysteretically.Groundwater level has constant and small negative effects on the coal-bunker inclination and settlement,and temperature has continuous and significant negative effects;however,material level has constant positive effects on the coal-bunker settlement and slightly influences the eastward inclination while significantly influencing the northward inclination of the coal bunker.Also,unbalanced loading has little influence on the coal-bunker settlement and eastward inclination but significant influence on its northward inclination.Therefore,monitoring of the coal-bunker deformation should be strengthened in summer,and sudden changes in material level and unbalanced loading should be avoided during production.Moreover,the coal-bunker inclination can be adjusted by unbalanced loading in the reverse direction.

Effect of flow rates of gases flowing through a coal bed during coal heating and cooling on concentrations of gases emitted and fire hazard assessment

The flow velocity of gases in gobs directly influences the kinetics and intensity of gaseous components release during heating and cooling of coal.The assessment of fire hazard is performed on the basis of concentrations of particular gases in a mine air.These concentrations differ in coal heating and cooling phase which was proven in the study.This paper presented the results of the experimental study on temperature distribution in a simulated coal bed in heating(50–250°C)and cooling(250–35°C)phases as well as its correlation to variations in concentration of gases released in these phases and flow rates of gases flowing through the coal bed.The research was performed on twenty-two samples of bituminous coals acquired from various coal beds of Polish coal mines.Considerable differences were observed between heating and cooling phases in terms of the concentrations of gases taken into account in calculations of self-combustion index.In the heating phase temperature increase resulted in the decrease of concentrations ratios of ethane,ethylene,propane,propylene and acetylene,while in the cooling phase these ratios increased systemically.The effect of air(in heating phase)and nitrogen(in cooling phase)flow rate on the self-ignition index CO/CO2 was also determined.

Research of the underground coal bunker clearing robot

With the long-term use of coal bunker, a certain amount of sticking objects will beformed on its wall, and coal mine clearing robot can replace man in clearing the bunker wall.Also, since it equip with an explosion-proof camera, the worker can determine the operationby observing the well-head monitor.Moreover, it cannot work unless it is placed in positionand supported stably, and it has three degrees of freedom: rotating, stretching, and shovelcoal.It is driven by the hydraulic and controlled by PLC.The underground coal mine clearingrobot changs the traditional clearing methods, man does not have to enter the bunker toclear it, which ensures the production safety of coal transportation.

Development of coal store and transportation technology using horizontal coal bunker

Discussed the necessity of setting up the coal bunker in mining, introduced the development of coal bunker technology, combining the mining characteristic of the high yield and high-efficient working face in China at present, and point out that the type of horizontal coal bunker, is a kind of security, high-efficient coal store and transportation technology of suiting the modern production need of the colliery, is the developing direc-tion of technology of store and transportation of coal bunker.

Employment of Two-Stage Oxygen Feeding to Control Temperature in a Downdraft Entrained-Flow Coal Gasifier

The traditional practice of employing a two-stage coal-fed gasification process is to feed all of the oxygen to provide a vigorous amount of combustion in the first stage but only feed the coal without oxygen in the second stage to allow the endothermic gasification process to occur downstream of the second stage. One of the merits of this 2-stage practice is to keep the gasifier temperature low downstream from the 2nd stage. This helps to extend the life of refractory bricks, decrease gasifier shut-down frequency for scheduled maintenance, and reduce the maintenance costs. In this traditional 2-stage practice, the temperature reduction in the second stage is achieved at the expense of a higher than normal temperature in the first stage. This study investigates a concept totally opposite to the traditional two-stage coal feeding practices in which the injected oxygen is split between the two stages, while all the coal is fed into the first stage. The hypothesis of this two-stage oxygen injection is that a distributed oxygen injection scheme can also distribute the release of heat to a larger gasifier volume and, thus, reduce the peak temperature distribution in the gasifier. The increased life expectancy and reduced maintenance of the refractory bricks can prevail in the entire gasifier and not just downstream from the second stage. In this study, both experiments and computational simulations have been performed to verify the hypothesis. A series of experiments conducted at 2.5 - 3.0 bars shows that the peak temperature and temperature range in the gasifier do decrease from 600?C - 1550?C with one stage oxygen injection to 950?C - 1230?C with a 60 - 40 oxygen split-injection. The CFD results conducted at 2.5 bars show that 1) the carbon conversion ratio for different oxygen injection schemes are all above 95%;2) H2 (about 70% vol.) dominates the syngas composition at the exit;3) the 80% - 20% case yields the lowest peak temperature and the most uniform temperature distribution along the gasifier;and 4) the 40% - 60% case produces the syngas with the highest HHV. Both experimental data and CFD predictions verify the hypothesis that it is feasible to reduce the peak temperature and achieve more uniform temperature in the gasifier by adequately controlling a two-stage oxygen injection with only minor changes of the composition and heating value of the syngas.

A mathematical model of gas flow during coal outburst initiation

A proposed concept of outburst initiation examines the release of a large amount of gas from coal seams resulted from disintegrating thermodynamically unstable coal organic matter(COM).A coal microstructure is assumed to getting unstable due to shear component appearance triggered by mining operations and tectonic activities considered as the primary factor while COM disintegration under the impact of weak electric fields can be defined as a secondary one.The energy of elastic deformations stored in the coal microstructure activates chemical reactions to tilt the energy balance in a“coal–gas”system.Based on this concept a mathematical model of a gas flow in the coal where porosity and permeability are changed due to chemical reactions has been developed.Using this model we calculated gas pressure changes in the pores initiated by gas release near the working face till satisfying force and energy criteria of outburst.The simulation results demonstrated forming overpressure zone in the area of intensive gas release with enhanced porosity and permeability.The calculated outburst parameters are well combined with those evaluated by field measurements.

A state‑of‑the‑art review on rock seepage mechanism of water inrush disaster in coal mines

Water inrush is one of the most dangerous disasters in coal mining.Due to the large-scale mining and complicated hydrogeological conditions,thousands of deaths and huge economic losses have been caused by water inrush disasters in China.There are two main factors determining the occurrence of water inrush:water source and water-conducting pathway.Research on the formation mechanism of the water-conducting pathway is the main direction to prevent and control the water inrush,and the seepage mechanism of rock mass during the formation of the water-conducting pathway is the key for the research on the water inrush mechanism.This paper provides a state-of-the-art review of seepage mechanisms during water inrush from three aspects,i.e.,mechanisms of stress-seepage coupling,fow regime transformation and rock erosion.Through numerical methods and experimental analysis,the evolution law of stress and seepage felds in the process of water inrush is fully studied;the fuid movement characteristics under diferent fow regimes are clearly summarized;the law of particle initiation and migration in the process of water inrush is explored,and the efect of rock erosion on hydraulic and mechanical properties of the rock media is also studied.Finally,some limitations of current research are analyzed,and the suggestions for future research on water inrush are proposed in this review.

Gasification kinetic modelling of Victorian brown coal chars and validity for entrained flow gasification in CO_(2)

The gasification kinetic modelling of two Victorian brown coal(Yallourn and Maddingley)chars and the validity for entrained flow gasification were investigated in this study.The study was conducted in a thermogravimetric analyzer(TGA)at 750–1100℃,30%–90%CO_(2)concentration using different char particle sizes within 20–106 mm.It was found that random pore model and modified volumetric model are applicable for TGA results,but volumetric model and grain model are not.The effect of particle size under106 mm on gasification rate is very limited.Activation energies of Maddingley char and Yallourn char in CO_(2)gasification are 219–220 and 197–208 k J/mol,respectively.The pre-exponential factors are in the same order of magnitude,and they increased as particle size decreased.A mathematical model was developed to predict carbon conversion over time for entrained flow gasification of Victorian brown coal chars at 1000–1400℃.

Expression of Hsp27 and Hsp70 in Lymphocytes and Plasma in Healthy Workers and Coal Miners with Lung Cancer

In coal mines, main occupational hazard is coal-mine dust, which can cause health problem including coal workers’ pneumoconiosis and lung cancer. Some heat shock proteins (Hsps) have been reported as an acute response to a wide variety of stressful stimuli. Whether Hsps protect against chronic environmental coal-mine dust over years is unknown. It is also interesting to know that whether the expression of Hsp27 and Hsp70 proteins as a marker for exposure is associated risk of lung cancer among coal miners. We investigated the association between levels of Hsp27 and Hsp70 expression in lymphocytes and plasma and levels of coal-mine dust exposure in workplace or risk of lung cancer in 42 cancer-free non-coal miners, 99 cancer-free coal miners and 51 coal miners with lung cancer in Taiyuan city in China. The results showed that plasma Hsp27 levels were increased in coal miners compared to non-coal miners (P<0.01). Except high cumulative coal-mine dust exposure (OR=13.62, 95%CI=6.05—30.69) and amount of smoking higher than 24 pack-year (OR=2.72, 95% CI=1.37—5.42), the elevated levels of plasma Hsp70 (OR=13.00, 95% CI=5.14—32.91) and plasma Hsp27 (OR=2.97, 95% CI=1.40—6.32) and decreased expression of Hsp70 in lymphocytes (OR=2.36, 95% CI=1.05—5.31) were associated with increased risk of lung cancer. These findings suggest that plasma Hsp27 may be a potential marker for coal-mine dust exposure. And the expression of Hsp27 and Hsp70 levels in plasma and lymphocytes may be used as biomarkers for lung cancer induced by occupational coal-mine dust exposure.

Top coal flows in an excavation disturbed zone of high section top coal caving of an extremely steep and thick seam

与轻轻的剧降相比长墙的探穴，在为极其陡峭、厚的缝接的充分使机械化的最高煤的探穴的一张工作的脸的长度是短的，当它的水平节与增加高时生产。但是探穴比率是低的，在一些灾难的力量结果例如房顶下降，在煤气的累积导致的一张工作的脸和危险由最高的煤的本地、大的区域倒塌导致了它。在裂缝的发展以后并且煤身体变弱，极其陡峭的缝接的最高的煤(小粒的媒介) 的高、破节(超过 60 掳) 表演清除非线性的运动的特征。我们彻底地分析了地质的环境，挖掘的采矿条件扰乱了地区。从大规模 3D 为最高的煤鈥搘a ter 鈥揼a s 的模拟建模并且联合的一个物理实验基于结果，我们断定削弱的最高的煤能被认为是间断媒介。我们使用了一个粒子流动代码程序高比较并且分析移植进程和 30 m 的运动节在在 Weihuliang 煤矿极其陡峭的缝接变弱前后随着时间的过去超过煤。我们的模拟，实验和监视表演的结果水的那注射前并且预先切开爆炸改进探穴能力和对称的探穴，为大区域减轻空间动态倒塌超过煤，延长有害气体的迁居时间并且外面免除他们 mined 区域并且那么在采矿完成安全。

Propagation law of shock waves and gas flow in cross roadway caused by coal and gas outburst

In order to study the propagation law of shock waves and gas flow during coal and gas outburst,we analyzed the formation process of outburst shock waves and gas flow and established the numerical simulation models of the roadways with 45°intersection and 135°intersection to simulate the propagation of outburst gas flow and the process of gas transport.Based on the analysis of the simulation results,we obtained the qualitative and quantitative conclusions on the characteristics and patterns of propagation and attenuation of outburst shock waves and gas flow.With the experimental models,we investigated the outburst shock waves and gas flow in the roadways with the similar structures to the simulated ones.According to the simulation results,when the angle between the driving roadway and the adjacent roadway increased,the sudden pressure variation range in adjacent roadway and the influencing scope of gas flow increased and the sudden pressure variation duration decreased.The intersection between the driving roadway and the adjacent roadway has no effect on airflow reversal induced by the shock waves and gas flow.

Forecasting water disaster for a coal mine under the Xiaolangdi reservoir

Xin’an coal mine, Henan Province, faces the risk of water inrush because 40% of the area of the coal mine is under the surface water of the Xiaolangdi reservoir. To forecast water disaster, an effective aquifuge and a limit of water infiltration were determined by rock-phase analysis and long term observations of surface water and groundwater. By field monitoring, as well as physical and numerical simulation experiments, we obtained data reflecting different heights of a water flow fractured zone (WFFZ) under different mining conditions, derived a formula to calculate this height and built a forecasting model with the aid of GIS. On the basis of these activities, the coal mine area was classified into three sub-areas with different potential of water inrush. In the end, our research results have been applied in and verified by industrial mining experiments at three working faces and we were able to present a successful example of coal mining under a large reservoir.

Arch structure effect of the coal gangue flow of the fully mechanized caving in special thick coal seam and its impact on the loss of top coal

Based on the characteristics of the top coal thickness of the fully mechanized caving in special thick coal seam,the long distance of coal gangue caving,as well as the different sizes of the coal gangue broken fragment dimension and spatial variation of drop flow,this paper uses laboratory dispersion simulation experiment and theoretical analysis to study the arch structure effect and its influence rule on the top coal loss in the process of coal gangue flow.Research shows that in the process of coal gangue flow,arch structure can be formed in three types:the lower arch structure,middle arch structure,and upper arch structure.Moreover,the arch structure has the characteristics of dynamic random arch,the formation probability of dynamic random arch with different layers is not the same,dynamic random arch caused the reduction of the top coal fluency;analyzing the dynamic random arch formation mechanism,influencing factors,and the conditions of instability;the formation probability of the lower arch structure is the highest,the whole coal arch and the coal gangue arch structure has the greatest impact on top coal loss.Therefore,to prevent or reduce the formation of lower whole coal arch structure,the lower coal gangue arch structure and the middle whole coal arch structure is the key to reduce the top coal loss.The research conclusion provides theoretical basis for the further improvement of the top coal recovery rate of the fully mechanized caving in extra thick coal seam.

Failure modes of coal containing gas and mechanism of gas outbursts

In order to explain the mechanism for gas outburst, the process of evolving fractures in coal seams is described using system dynamics with variable boundaries. We discuss the failure modes of coal containing gas and then established the flow rules after failure. The condition under which states of deformation convert is presented and the manner in which these convert is proposed. In the end, the process of gas outbursts is explained in detail. It shows that a gas outburst is a process in which the boundaries of coal seams are variable because of coal failure. If the fractures are not connected or even closed owing to coal/rock stress, fractured zones will retain a certain level of carrying capacity because of the self-sealing gas pressure. When the accumulation of gas energy reaches its limit, coal seams will become unstable and gas outbursts take place.

Study on partition of spontaneous combustion danger zone and prediction of self-ignition in coalmine based on numeric simulation

By solving steady model of air flow diffusion and chemical reaction in loose coal, distribution of oxygen concentration and flow velocity magnitude were obtained. Compared the simulating results with critic value as well as duration of spontaneous combustion from large-scale spontaneous combustion experiment, 'three zones' of spontaneous combustion were partitioned and mining conditions to avoid spontaneous combustion were obtained. The above method was employed to partition 'three zones' in gob of fully mechanized top-coal caving long wall face and got fairly good result. Calculation of the above method is much smaller than simulating the whole process of coal spontaneous combustion, but the prediction precision can satisfy the demand of predicting and extinguishing spontaneous combustion in mining.