Prediction of oxygen concentration and temperature distribution in loose coal based on BP neural network

An effective method for preventing spontaneous combustion of coal stockpiles on the ground is to control the air-flow in loose coal. In order to determine and predict accurately oxygen concentrations and temperatures within coal stockpiles, it is vital to obtain information of self-heating conditions and tendencies of spontaneous coal combustion. For laboratory conditions, we designed our own experimental equipment composed of a control-heating system, a coal column and an oxygen concentration and temperature monitoring system, for simulation of spontaneous combustion of block coal （13-25 mm） covered with fine coal （0-3 mm）. A BP artificial neural network （ANN） with 150 training samples was gradually established over the course of our experiment. Heating time, relative position of measuring points, the ratio of fine coal thickness, artificial density, voidage and activation energy were selected as input variables and oxygen concentration and temperature of coal column as output variables. Then our trained network was applied to predict the trend on the untried experimental data. The results show that the oxygen concentration in the coal column could be reduced below the minimum still able to induce spontaneous combustion of coal - 6% by covering the coal pile with fine coal, which would meet the requirement to prevent spontaneous combustion of coal stockpiles. Based on the prediction of this ANN, the average errors of oxygen concentration and temperature were respectively 0.5% and 7 ℃, which meet actual tolerances. The implementation of the method would provide a practical guide in understanding the course of self-heating and spontaneous combustion of coal stockpiles.

Concentration, Distribution, and Occurrence of REEs in Coals from Chongqing,Southwest China

The concentration, distribution, and occurrence of rare earth elements (REEs) in coals as well as stone coalsin different geological periods from Chongqing were studied. The results show that the REE content in coals fromChongqing is much higher than that of the ordinary Chinese coals, the Late Paleozoic coals from North China, UScoals, and the world coals. Although the concentration of light rare earth elements (LREE) is higher than that of heavyrare earth elements (HREE), the ratio of LREE to HREE is as low as 5.11. The REE content decreases with thecoal-formation periods from old to new. The REE content in the Sinian stone coal is the highest, but it is the lowest inEarly Jurassic coals. The similar REE contents in bituminous coals and anthracite show that the metamorphism has alittle influence on REE content in coal. In addition, silicate association dominates the occurrence mode of REEs incoals from Chongqing.

Suction characteristics of a thick material pump at high concentrations of coal slime

A test system was designed to study the parameters affecting the volumetric efficiency of a thick-material pump for coal slime.The parameters studied included solid concentration,the slenderness ratio of the suction cylinder and the running speed of the hydraulic cylinder.In the experiment the concentrations of coal slime were 75.7%,76.3%,74.4%,73.5%,72.1%and 70.63%;the running speeds were 0.23,0.18,0.13,0.10 and 0.08 m/s;and the slenderness ratios of the suction cylinder were 1.63,2.26,2.88,3.50,4.13,4.78 and 5.38.The results show that the suction volumetric efficiency decreases gradually with an increase in material concentration.The critical concentration value is 72%;below 72%the suction volumetric efficiency is above 90%,otherwise it decreases rapidly.When the solid concentration reaches 76.3%,the suction volumetric efficiency is only 40%.When the running speed of the piston is less than or equal to 0.23 m/s,the suction volumetric efficiency increases with an increase in running speed.

The transformation and concentration of environmental hazardous trace elements during coal combustion

Studied the content and distribution of 18 environmental hazardous trace elementsin the lignite, fatty coal, anthracite and its burnt products by combustion simulatingexpriment in the one-dismensinal boiler.The transformations and concentration of 18 traceelements during different coal combustion were discussed.The results show that there aresome content distribution of 18 hazardous trace elements in every burnt product, but thelaw of concentration and dispersion of every trace element during different coal combustionis very different.Experiment results indicate that the transformation and concentrationof trace elements during coal combustion are related to the element contents and occur-rencesof trace elements in raw coal, but are also affected by some man-made factorssuch as the combustion method of boiler, combustion temperature and atmosphere, thetype of precipitators and so on.

Gas concentration monitoring system for small and medium-sized coal mines based on gas-sensing detection and single-chip control

This paper is aimed at the actual conditions of disaster caused by gas in small and medium-sized coal mines. A new gas concentration monitoring system for coal mines is developed on the basis of gas-sensing detection and single-chip control. The monitoring system uses the tin oxide as the main material of N-type semiconductor gas sensors, be- cause it has good sensitive characteristics for the flammable and explosive gas （ such as methane, carbon monoxide）. The QM-N5-semiconductor gas sensor is adopted to detect the output values of the resistance under the different gas con- centrations. The system, designedly, takes the AT89C51 digital chip as the core of the circuit processing hardware structure to analyze and judge the input values of the resistance, and then achieve the control and alarm for going beyond the limit of gas concentration. The gas concentration monitoring system has man）, advantages including simple in struc- ture, fast response time, stable performance and low cost. Thus, it can be widely used to monitor gas concentration and provide early wamings in small and medium-sized coal mines.

Lateral Stress Concentration in Localized Interlayer Rock Stratum and the Impact on Deep Multi-Seam Coal Mining

To explore the impact of lateral stress concentration in interlayer rock stratum on the exploitation of protected coal seam, a field experiment was carried out in a multi-seam mining structure. Lateral stress redistribution and interlayer rock failure behavior were surveyed. Then an assistant numerical investigation was implemented to evolve the effect of liberated seam mining and its influence on stress reconstruction in surrounding rock mass. The cause of lateral stress concentration and its impact were discussed finally. Key findings turn out that a certain lateral stress increases in interlayer rock stratum and concentrates on its lower region. Lateral stress concentration and interlayer rock failure are interactional. The former is an inducing factor of the latter;the latter promotes the increase of concentration degree. Extent of lateral stress concentration increases to the maximum as seam distance is about 50 m. But the efficacy of liberated seam mining decreases as the seam spacing gets larger. Protected seam mining is then classified based upon the impact of lateral stress concentration, which helps to prevent the rock burst hazard and then to achieve a reliable mining in deep mines.

Coupling control on pillar stress concentration and surface cracks in shallow multi-seam mining

In order to ensure safe mining and reduce surface damage in shallow multi-seam mining,the failure characteristics of interburden strata with different coal pillars offset distances between pillars in the upper and lower seams,the distribution characteristics of stress concentration in coal pillars,and the development characteristics of stratum cracks and subsidence were investigated by physical and UDEC2D simulation.Meanwhile,the effect of different coal pillar offset distances on stress concentration of coal pillar and development of stratum cracks were studied.Based on those results,a formula for safe mining and reducing surface damage was established,which provided a theoretical basis for safe and environmentally friendly mining in shallow multi-seam.According to the results,the optimal coal pillar offset distance(the side to side horizontal distance of the upper and lower coal pillars)between the upper and lower coal seams was developed to reduce the stress concentration of coal pillars and surface damage.The results of this study have been applied in Ningtiaota coal mine and have achieved good results in safe and environmentally friendly mining.

High temperature dephosphorization behavior of monazite concentrate with charred coal

Dephosphorization behavior of monazite concentrate with charred coal at high temperature was investigated.It is found that the roast temperature is the main factor for the dephosphorization of the monazite.The high dephosphorization efficiency can be reached at the temperatures ranging from 1 200 to 1 400°C.When the monazite pellets,made by pressing mixture of the monazite,charred coal and water into mould,were roasted at 1 400°C for 2 h,98%of phosphorus was removed from the monazite pellets.The roast time has little effect on the dephosphorization efficiency.Meanwhile,the particle size of the charred coal also has great influence on the dephosphorization efficiency of the monazite,and it is better to control particle size around 150μm,while Fe and Fe2O3 have neglectable effect on the dephosphorization of the monazite.

Effects of the Adjustment of Energy Structure on 24-h Average of NO_2 Concentration in Different Regions of Urumqi City in Winter

[ Objective] The study aimed to discuss the effects of the adjustment of energy structure on daily average concentration of NO2 in different regions of Urumqi city in winter. [ Method] The changes of daily average concentration of NO2 in different areas of Urumqi City from January to February （ NO2 pollution was most serious） before and after the implementation of the project ＂changing coal to gas＂ were analyzed. [ Result] After the implementation of the project, daily average concentration of NO2 in different areas of Urumqi City was increased due to the rapid increase of ve- hicle quantity, but there were certain differences in the increase among various regions. From south to north, daily average concentration of NO2 in winter was decreased gradually, that is, daily average concentration of NO2 was the highest in the south area, while in the north area, it didn＇t change significantly before and after the implementation of the project, but it was still high. Therefore, the local government should pay more attention to pollution NO2 during environmental management process. [ Conclusion] The research could provide scientific references for the control of atmospheric pollution in future.

Features of rare earth elements geochemistry in coals of Central Kazakhstan

This research presents the results of a comprehensive study of mineralogical and geochemical features of REE distribution in coals of Central Kazakhstan deposits—Karaganda coal basin and Shubarkol deposit,which have large hard coal reserves and are industrially important for the coal industry of Kazakhstan;the research is based on 205 samples of clayey interlayers and coal seams.It shows basic patterns of distribution and features of concentration for impurity elements,gives an estimate of the impurity elements concentration,including REE,defines conditions and factors of their accumulation,and studies features of their forms in coal and coal-bearing rocks,which allows estimating the mechanisms of their migration and conditions of accumulation.According to the results of geochemical indicators,the article establishes the factors of REE dislocation,reveals the composition of margin rocks that have influenced REE concentration in coal seams,and the presented latest data on mineralogy allowed to establish the ways of their transportation to the paleobasin during the synand epigenetic periods of formation of the coal deposits of Central Kazakhstan being researched.It was found that the coals are insignificantly enriched with heavy lanthanides from Ho to Lu.The distribution curves of UCC normalized REE values in the coals are similar and coincide,but they are less than the average value for world coal,and amount to only one-third of the UCC.It was found that the highest concentrations of all REE are characteristic of clayey interlayers and oxidized coals.The La/Yb ratio in this case increases upwards along the section,indicating mainly clastogenic mechanism of REE delivery to the coals.In coal and clay samples,the predominant mineral form of REE is light lanthanide phosphates.Identified particles of REE from minerals and their composition peculiarities suppose autigene nature of their formation.The formation of the bulk of autigene minerals occurred during the maturation of brown coals and their transformation into hard ones.

A dynamic ejection coal burst model for coalmine roadway collapse

In this study,we established a dynamic ejection coal burst model for a coalmine roadway subject to stress,and held that the stress concentration zone at the roadway side is the direct energy source of this ejection.The formation and development of such burst undergoes three stages:(1)instability and propagation of the cracks in the stress concentration zone,(2)emerging of a layered energy storage structure in the zone,and(3)ejection of coal mass or coal burst due to instability.Moreover,we figured out the initial strength of periodic cracks is parallel to the maximal dominant stress direction in the stress concentration zone and derived from the damage strain energy within the finite area of the zone based on the Griffith energy theory.In addition,we analyzed the formation process of the layered energy storage structure in the zone,simplified it as a simply supported restraint sheet,and calculated the minimum critical load and the internally accumulated elastic energy at the instable state.Furthermore,we established a criterion for occurrence of the coal burst based on the variational principle,and analyzed the coal mass ejection due to instability and coal burst induced by different intensity disturbances.At last,with the stratum conditions of Junde Coalmine as the model prototype,we numerically simulated the load displacement distribution of the stress concentration zone ahead of the working face disturbed by the main roof-fracture-induced dynamic load during the mining process as well as their varying characteristics,and qualitatively verified the above model.

The distribution and occurrence of mercury in Chinese coals

Mercury is one of the most concerned hazardous elements in coals. 1018 coal samples of different coal-forming periods, coal-accumulating areas and coal ranks all over the country were collected to study the distributions of mercury in Chinese coals. The modes of occurrence of mercury were studied with float-sink experiments of 10 coals from different basins in China and correlation analyses were conducted between concentrations of mercury and maceral and sulfur contents, as well as the ash yield. The theoretic concentrations and affinities of mercury in vitrinite, inertinite, clay and pyrite were then calculated following the methods proposed by Solari. The weighted average concentration of mercury in Chinese coals is 0.154 ~tg/g, which is similar to that in the word coals in general. The mercury concentrations vary largely in the coals of different coal-forming period and coal-accumulating areas as geological settings play key roles in deter- mining the geochemistry of mercury. The concentrations of mercury in coals from south and southwest China and those from North China of C3-P1 are relatively higher while those from North China of Jm-a and Northeast of J3-K1 relatively lower. The general distribution trends of mercury are very similar to that of ash yield, sulfur contents in coals. Pyrite is the dominant carrier of mercury in most coals, especially in some high-sulfur coals with abundant epigenetic pyrite formed during diagenesis and metamorphism. Mercury has higher affinity to vitrinite than to inertinite in most coals, which accords with the geological origin of macerals and geochemistry of mercury.

Effects of coal seam dip angle on the outburst in coal roadway excavation

The prevention and forecast of coal and gas outburst has always been one of the key issues in coal mining safety.By simulating the process of tunneling in coal seam with different dip angle through FLAC3D software,the dangerous zone in which outburst may occur and the probability of outburst near the working face were predicted through the distribution of stress,displacement and plastic zone.Then we discussed the size of unstable area in the surrounding rock through the distribution of stress and the variation curve of the displacement on the roadway wall.The results show that,with an increase of the coal seam dip angle,the risk of outburst in the working face rises gradually.And the dangerous areas in which may outburst occur moves to the upper part of coal seam.The size of unstable area in the surrounding rock increases with the increase of coal seam dip angle.

Characteristics of coal sludge slurry prepared by a wet-grinding process

Coal sludge slurry(CSS) is an alternative fuel and a potential competitive method for sludge reduction.Based on the researches of coal water slurry, we studied CSSs by using a wet-grinding process with different types of regional municipal sludge(sludge) in an orthogonal experiment. The sludge type,sludge mixing proportion, dosage of dispersant, and grinding time were tested in this study. The results show that water content and its occurrence characteristics in the sludge have primary hindering influences on slurry ability. The range of fixed-viscosity concentrations with raw wet sludge is from 50.78%to 44.40%(by weight), while the range is from 53.35% to 51.51%(by weight) with dry sludge. All of the CSSs exhibit shear-thinning behaviors with different variation trends, especially the CSSs with more than 15%(by weight) raw wet sludge in it. Adding the same proportion of raw wet sludge increases the thixotropic properties of CSSs and the highest area of thixotropy loop is 3065 Pa/s, while the highest value of dry sludge is 1798 Pa/s. Hydrophilic group plays an important role in adsorbing water and building three-dimension networks with other particles, which is the main reason for CSS properties.Therefore, the mechanism can be used to find the way for making high quality CSS.

Geophysical criterion of pre-outburst coal outsqueezing from the face space into the working

The initial process of coal and gas sudden outburst is studied in the article when under the influence of rock and gas pressure the part of a coal seam layer(a coal section)is squeezed out from the mouth of the future outburst cavity in a jump-like manner into the working.Geo-mechanical criterion for a part of a coal seam layer outsqueezing in the form of the relation of active(squeezing out)and passive(preventing the outsqueezing)forces is defined in the article.Based on it,the geophysical criterion is defined by expressing basic physical parameters through geo-physical ones:the current stress is defined by spectral-acoustic method through the ratio of high frequency and low-frequency components of an acoustic signal,which is generated into a face working space by the mining equipment operating in the face;in-situ gas pressure is defined by gas analytical method by the concentration of methane in the atmosphere of the working;the strength of the most broken coal layer is defined by a strength measuring device(a device for measuring the depth of a steal cone punched into the coal by a spring mechanism).This paper studies the influence of acoustic,strength and filtrating and collecting properties of a face working space on the limit value of an obtained geophysical criterion of pre-outburst squeezing of a coal‘‘plug”out of the mouth of the future outburst cavity into the working.

Experimental research on flame propagation characteristics of coal dust combustion

The presence of coal dust explosions in coal mining are significant safety hazards.This study mainly explores the flame propagation of coal dust combustion so as to provide a theoretical basis for the prevention and control of coal dust explosions.In the experiment,a dust cloud ignition device was used to experimentally explore the influence of the coal dust concentration on the flame propagation of the coal dust,and high-speed photography was used to record the coal dust flame propagation process.The results show that the flame propagates vertically along the wall of the vertical glass tube,emits a bright yellow light during the propagation process,and forms a mushroom cloud-shaped flame at the upper end of the vertical glass tube.When the concentration of coal dust is 250 g/m^(3),its burning time is much less than those of 500 g/m^(3)and 750 g/m^(3).When the concentrations are 250 g/m^(3),500 g/m^(3)and 750 g/m^(3),respectively,the corresponding maximum propagation velocities of the flame front reach 1.51 m/s,2.00 m/s and 1.61 m/s at 100 ms,353 ms and 310 ms,respectively.The time for the flame front velocity to reach the maximum and the maximum velocity of flame propagation first increase and then decrease with the rising of concentration.

Influence of Ground Stress on Coal Seam Gas Pressure and Gas Content

The influence of ground stress was quantitatively analyzed on coal seam gas pressure and gas content in this paper.Mining activities in coal mine can result in stress concentration in the coal(rock)body around the mining space,but porosity of the coal seam would not change too much.Therefore,gas pressure and gas content in the coal seam are slightly affected.Studies showed that the free gas was gradually transformed into adsorbed gas,and the gas adsorption volume was small,and then gas pressure increases roughly linearly when the porosity decreased because of stress influence.Additionaly,when porosity of coal seam reduced to 40%,the amount of adsorbed gas accounted for no more than 10%of coal seam gas content,and the increase of gas pressure did not exceed 15%of the original gas pressure.

Application of High-pressure Flat Membranes in Coal Chemical Wastewater Treatment

In the process of using high-pressure flat membranes to treat coal chemical wastewater,the effects of high-pressure flat membranes on the concentration of salt ions and the removal of pollutants were studied under the conditions of different concentrations of influent TDS,COD and silicon dioxide.The results showed that when the concentration of influent TDS was 35 000-55 000 mg/L,the economic benefit of high-pressure flat membrane operation was the best,and the concentration ratio of high-pressure flat membranes was stable,varying from 3.3 to 3.6.As the concentration of influent organic matter ranged from 100 to 1 800 mg/L,the removal rate of organic matter ranged from 60% to 79%.In addition,the retention rate of high-pressure flat membranes to silicon dioxide was more than 90%.

Use of coals and wastes in a co-gasification process aimed at producing hydrogen rich gas

The use of low-quality coals and flotoconcentrates is currently severely limited,and the problem of managing municipal waste from anthropogenic activities is currently a challenge.The problems of reducing carbon dioxide emissions,utilizing the energy potential of waste and increasing its recycling have an impact on the costs of electricity production.Considering the abundant streams of unused fuels,they can be considered as attractive energy materials,so environmentally-friendly and cost-effective options for their utilization should be developed.A study was conducted using steam co-gasification technology on selected coals,flotation concentrates and Refuse Derived Fuel(RDF)alternative fuel.Selected low-quality coals were combined with RDF alternative fuel in a process aimed at hydrogen production.The experiments produced gas with hydrogen concentrations ranging from 67%(vol.)to 68%(vol.)with low methane concentrations.It was observed that the addition of alternative fuels helped to increase the hydrogen concentration in syngas.Attention was paid to the catalytic ability of the metal oxides contained in the fuel blend,with particular reference to K_(2)O and Al_(2)O_(3)and TiO_(2).