Modeling behaviors of a coal pillar rib using the progressive S-shaped yield criterion

Spalling of pillar ribs has been a major hazard in the mining industry for decades.In the absence of rib support guidelines,accidents have continued to occur in recent years.Developing effective support guidelines requires a complete understanding of complex pillar damage mechanisms.Continuum models represent a convenient tool for analyzing this problem,but the behavior of such models is dependent of the choice of the constitutive model.In this study,a recently proposed constitutive model was used to simulate the rib fracturing process in a longwall chain pillar at West Cliff mine.After calibration,the model was able to capture the rib displacement profiles for multiple locations of the longwall face and the stress evolution 4 m into the pillar.The rib bolts in the model were found to be yielding over 60% of their length under the headgate loading condition.The model also predicted a steady damage accumulation in the rib for certain face locations,which is consistent with the description of the rib at the site.Damage was localized along the upper part of the pillar and underscored the role that the dirt band played in controlling rib deterioration at the site.The ability of the numerical model to replicate field measurements provides confidence in the capabilities of the new constitutive model.Finally,the need of using multi-point calibration is highlighted by comparing the results of the calibrated model to an alternative model calibrated to a smaller amount of data.

Study on Dynamic Prediction of Two-Phase Pipe Flow in Inclined Wellbore with Middle and High Yield

Gas-liquid two-phase flow is ubiquitous in the process of oil and gas exploitation,gathering and transportation.Flow pattern,liquid holdup and pressure drop are important parameters in the process of gas-liquid two-phase flow,which are closely related to the smooth passage of the two-phase fluid in the pipe section.Although Mukherjee,Barnea and others have studied the conventional viscous gas-liquid two-phase flow for a long time at home and abroad,the overall experimental scope is not comprehensive enough and the early experimental conditions are limited.Therefore,there is still a lack of systematic experimental research and wellbore pressure for gas-liquid two-phase flow under the conditions of middle and high yield and high gas-liquid ratio in conventional viscosity,and the prediction accuracy is low.In view of this,this study carried out targeted systematic research,and from the flow pattern,liquid holdup and pressure drop aspects,established the relevant model,obtained a set of inclined wellbore gas-liquid two-phase pipe flow dynamic prediction method.At the same time,firstly,the model is tested by experimental data,and then the model is compared and verified by a number of field measured wells,which proves that the model is reliable and the prediction accuracy of wellbore pressure is high.

Financing strategies for coal-electricity supply chain under yield uncertainty

The financing strategies for a coal-electricity supply chain in which the coal company has capital constraint and faces yield uncertainty were studied. We propose an advance payment mechanism: in the coal company's initial production period, the electricity company provides advance payment to the coal company, and the coal company pays interest to the electricity company as the risk compensation. The optimal operation strategies for the coal company and the electricity company under the advance payment mechanism are derived and compared with those under the bank loan financing case. We find that,the expected profit functions of the coal company and the electricity company under the advance payment mechanism are the same with those under the case that the coal company has enough capital;under the advance payment mechanism, the profits of the coal company and the electricity company are higher than those under the bank financing case. We also discuss the compensation interest rate of the advance payment and the ordering and production quantities under the advance payment mechanism.

A Study on Final Volatile Yield of Pulverized Coal Pyrolysis with Thermobalance

The final volatile yield of pulverized coal pyrolysis was investigated by means of thermobalance. The experimental conditions are as follows: heating rate, 500℃/min; final temperature, 400 ～1500K; particle diameter, 57～300μm. This paper gives the empirical formula indicating the relation among the final volatile yield, final temperature and coal type.

High Temperature-preventing Cultivation Technology of Single-season Middle Rice for High Yield and High Quality in Jianghuai Area

In recent years,with the global climate change,the frequency and duration of high temperature in summer and autumn have increased,causing high temperature heat damage to summer crops such as rice and maize.From the end of July to early August is the main period of high temperature occurrence,during which the daily average temperature above 30℃is a high probability event,and even the highest temperature is above 38℃,while this period coincides with the booting-blooming-filling stage of the single-season middle rice in Jianghuai,especially the middle-season indica rice,so it often leads to the degradation of rice spikelets,pollen abortion,difficulty in pollen dispersion,and even difficulty in heading,resulting in a serious decline in the seed setting rate and poor filling of grains,which finally affect the yield and quality.Based on the goal of high-yielding high-quality rice cultivation,this paper proposed targeted technical measures for single-season middle rice from the aspects of planting time sequence optimization,selection of high-temperature-resistant varieties,population construction,fertilizer and water management technology,and how to compensate for the occurrence of unexpected disasters to promote plant growth.This study provides technical support for high-yielding high-quality stress-resistant and disaster-reducing rice cultivation technology.

Middle Jurassic vertebrate assemblage of Berezovsk coal mine in western Siberia (Russia)

The Berezovsk coal mine in western Siberia has yielded the most diverse Middle Jurassic limnic and terrestrial vertebrate assemblage of Asia. The vertebrate remains were recovered by screen washing from floodplain deposits on top of a thick coal seam of the Bathonian Itat Formation. A total of 29 vertebrate taxa has been recorded so far,including hybodontiform sharks,acipenseriforms,palaeonisciforms,amiiforms,dipnoans,anurans,caudates,turtles,squamates,choristoderans,crocodyliforms,pterosaurs,dinosaurs,tritylodontids,and a diverse mammaliaform and mammalian assemblage( eleutherodontids,docodontans,? amphilestids,dryolestids,and zatherians). The caudates are among the oldest in the fossil record and the anurans represent the oldest Asian record of this group. Among the mammals,Anthracolestes is the oldest and most basal known member of Dryolestidae and so far the only record from Asia. The vertebrate assemblage from the Berezovsk coal mine is very similar to that from the British Forest Marble Formation( Bathonian) and suggests a limited provincialism in the Middle Jurassic Laurasian landmass.

Whole petroleum system in Jurassic coal measures of Taibei Sag in Tuha Basin,NW China

Based on the latest results of near-source exploration in the Middle and Lower Jurassic of the Tuha Basin,a new understanding of the source rocks,reservoir conditions,and source-reservoir-cap rock combinations of the Jurassic Shuixigou Group in the Taibei Sag is established using the concept of the whole petroleum system,and the coal-measure whole petroleum system is analyzed thoroughly.The results are obtained in three aspects.First,the coal-measure source rocks of the Badaowan Formation and Xishanyao Formation and the argillaceous source rocks of the Sangonghe Formation in the Shuixigou Group exhibit the characteristics of long-term hydrocarbon generation,multiple hydrocarbon generation peaks,and simultaneous oil and gas generation,providing sufficient oil and gas sources for the whole petroleum system in the Jurassic coal-bearing basin.Second,multi-phase shallow braided river delta–shallow lacustrine deposits contribute multiple types of reservoirs,e.g.sandstone,tight sandstone,shale and coal rock,in slope and depression areas,providing effective storage space for the petroleum reservoir formation in coal-measure strata.Third,three phases of hydrocarbon charging and structural evolution,as well as effective configuration of multiple types of reservoirs,result in the sequential accumulation of conventional-unconventional hydrocarbons.From high structural positions to depression,there are conventional structural and structural-lithological reservoirs far from the source,low-saturation structural-lithological reservoirs near the source,and tight sandstone gas,coal rock gas and shale oil accumulations within the source.Typically,the tight sandstone gas and coal rock gas are the key options for further exploration,and the shale oil and gas in the depression area is worth of more attention.The new understanding of the whole petroleum system in the coal measures could further enrich and improve the geological theory of the whole petroleum system,and provide new ideas for the overall exploration of oil and gas resources in the Tuha Basin.

榆家梁薄煤层超长运距刮板输送技术研究

为解决神东榆家梁煤矿1.4 m煤层、350 m宽工作面煤炭开采的运输问题,制定了薄煤层超长工作面成套设备总体配套方案,在对装机功率及链条安全系数进行验算的基础上,确定了刮板输送设备主要技术参数;开发了φ38/86×137宽带链及链传动系统、薄煤层极矮中部槽、下沉式可伸缩机尾、定距端卸一体式机头推移部,满足了薄煤层大功率设备对配套空间的需求;优化了伸缩机尾自动张紧控制流程,配置了刮板输送机智能控制系统,为工作面运输设备无人化管理提供了技术保障。经过井下工业性实践证明,设备使用良好,该工作面已成为薄煤层智能开采的示范工程。

Liberation characteristics of coal middlings comminuted by jaw crusher and ball mill

The associated minerals make coal middlings possess a relatively high ash content.Subsequent liberation through size reduction can cause recovery increase.However,effect of comminution facilities on mineral liberation of middlings was ignored.This paper studied the liberation characteristics of middlings crushed with different kinds of fragmentation forces.Middlings of 3 mm+0.5 mm sampled from a dense medium cyclone were comminuted by a jaw crusher and a ball mill to 0.5 mm with similar size distribution respectively.The generating mechanism of fnes was also analyzed.Full densimetric analyses indicate that mineral liberation of the product crushed by the jaw crusher is better than that by the ball mill at each fraction.For sizes of 0.125 mm+0.074 mm and 0.074 mm,yields of the product with ash content 11%comminuted by jaw crusher are nearly 20%higher than that by the ball mill.Sectional micrographs observed by the scanning electron microscopy(SEM)also show the same law for these two fractions and some intergrowth particles still exist in the fraction of 0.5 mm+0.25 mm.

Mechanical characteristics of intact Middle Pleistocene Epoch loess in northwestern China

In order to research the mechanical characteristics of intact Middle Pleistocene Epoch loess, triaxial shear tests and isotonic compression test of intact Middle Pleistocene Epoch loess were conducted by improved SJ-IA triaxial shear equipment. According to test results, it can be found that the intact Middle Pleistocene Epoch loess has the properties of shear dilatancy and shear shrinkage. With the increase of confining pressure, stress-strain curve develops from softening to hardening. The failure mode of intact Middle Pleistocene Epoch loess is shear failure with the rupture angle between 55° and 61°. And it is better to determine the yield stress （py, qy） of the intact loess under different confining pressures by using the εv-q/p curve. Along with the increase of confining pressure, yield deviatoric stress qy and yield spherical stress py present logarithmic relationship. Besides, the strength parameters, elastic modulus K and G of intact loess, are obtained, which are benefit for loess projects design.

Study on microwave-assisted extraction of coal

The effect of different factors on coal extraction yield-temperature, solvent, coal type and irradiation time were investigated for different China coals under microwave-assisted extraction（MAE）. The results show that the optimum temperature for ethanol, acetone and THF are 393,373 and 373 K respectively and the extraction yield of THF is higher than that of other two solvents under MAE. Extraction with several single organic solvents were conducted for the 5 typical China coals-Shenfu, Tongchuan, Panzhihua, Yitai and Huating coal under microwave-assisted extraction and Soxhlet extraction. Results indicat that extraction yield of ethylenediamine, ethanol, acetone, tetrahydrofuran under MAE are all higher than that of Soxhlet extraction and MAE required less time. Tongchuan coal extracts of ethanol and acetone which were extracted by MAE and Soxhlet extraction were analyzed by GC/MS.

Stability control of surrounding rocks for a coal roadway in a deep tectonic region

In order to effectively control the deformation and failure of surrounding rocks in a coal roadway in a deep tectonic region, the deformation and failure mechanism and stability control mechanism were studied. With such methods as numerical simulation and field testing, the distribution law of the displacement, stress and plastic zone in the surrounding rocks was analyzed. The deformation and failure mechanisms of coal roadways in deep tectonic areas were revealed: under high tectonic stress, two sides will slide along the roof or floor; while the plastic zone of the two sides will extend along the roof or floor,leading to more serious deformation and failure in the corner of two sides and the bolt supporting the corners is readily cut off by the shear force or tension force. Aimed at controlling the large slippage deformation of the two sides, serious deformation and failure in the corners of the two sides and massive bolt breakage, a ‘‘controlling and yielding coupling support'' control technology is proposed. Firstly, bolts which do not pass through the bedding plane should be used in the corners of the roadway, allowing the two sides to have some degree of sliding to achieve the purpose of ‘‘yielding'' support, and which avoid breakage of the bolts in the corner. After yielding support, bolts in the corner of the roadway and which pass through the bedding plane should be used to control the deformation and failure of the coal in the corner. ‘‘Controlling and yielding coupling support'' technology has been successfully applied in engineering practice, and the stability of deep coal roadway has been greatly improved.

The two-factor model of evaluating mining rights of coal resources based on options

MRCR could be regarded as a multi-stage compounding real option,based on option theory,assuming the convenience yield of coal reserves to be constant,built a one-factor model of valuating MRCR with the stochastic value of coal reserves.On the basis of our one-factor model,set up a two-factor model of evaluating MRCR assuming the convenience yield follows the mean-reverting process.When applied to valuate the MRCR of a coalmine,this model gives higher values than the one-factor model and the NPV.This is because the increase of convenience yield can improve the executive oppor- tunity of MRCR.

Design of experiments to optimize the extraction parameters of a power grade Indian coal

Low grade high ash coals with difficult physical washability characteristics require chemical cleaning techniques such as solvent extractio n to obtain super clean coal with lower ash conte nts.Kedla,an In di an low grade coal has ash con tent around 44%-50%and there is a need to maximize its solvent extraction yield so as to make this power grade coal industrially useful.This paper highlights the use of definitive screening design and response surface methodology to extract the maximum organic matter from Kedla coal using ethylenediannnine(EDA)and N-methyl pyrollidone(NMP)as solvents under mild atmospheric pressure conditions.The coal was pre-treated with acetic acid before extractions were carried out.The parameters such as the acid pre-treatment time,acid concenmion,particle size,the co-solvent concentratio n and the solvent concentration were optimized in this paper.With this design of experimenls technique about 40%of the organic matter with minimal ash(less than 2%)content was「endered extractable unlike the already postulated designer solvent system—e,N system(i.e.NMP containing small amount of EDA)that uses coal to solve nt ratio as 1:17(wt/vol)and coal to co-solvent ratio as 1:l(wt/vol)thus only giving 19%extraction yield.Therefore,the present design of experimetechnique helps in conserving the number of experimems for process intensification.

Pillar design and coal burst experience in Utah Book Cliffs longwall operations

Longwall mining has existed in Utah for more than half a century.Much of this mining occurred at depths of cover that significantly exceed those encountered by most other US longwall operations.Deep cover causes high ground stress,which can combine with geology to create a coal burst hazard.Nearly every longwall mine operating within the Utah’s Book Cliffs coalfield has been affected by coal bursts.Pillar design has been a key component in the burst control strategies employed by mines in the Book Cliffs.Historically,most longwall mines employed double-use two-entry yield pillar gates.Double-use signifies that the gate system serves first as the headgate,and then later serves as the tailgate for the adjacent panel.After the 1996 burst fatality at the Aberdeen Mine,the inter-panel barrier design was introduced.In this layout,a wide barrier pillar protects each longwall panel from the previously mined panel,and each gate system is used just once.This paper documents the deep cover longwall mining conducted with each type of pillar design,together with the associated coal burst experience.Each of the six longwall mining complexes in the Book Cliffs having a coal burst history is described on a panel-by-panel basis.The analysis shows that where the mining depth exceeded 450 m,each design has been employed for about 38000 total m of longwall panel extraction.The double-use yield pillar design has been used primarily at depths less than 600 m,however,while the inter-panel barrier design has been used mainly at depths exceeding 600 m.Despite its greater depth of use,the inter-panel barrier gate design has been associated with about one-third as much face region burst activity as the double-use yield pillar design.

Extraction of locked-up coal by strengthening of rib pillars with FRP--A comparative study through numerical modelling

In some of the coalfields in India, coal seams are only developed but no extraction of pillars is possible due to the presence of surface or sub-surface structures and also non-availability of stowing materials which leads to huge amounts of coal being locked-up underground. Spontaneous heating and fire, accumulation of poisonous gases, severe stability issues leading to unsafe workings and environmental hazards are the major problems associated with the developed coal pillars. So, there is a pressing need for a technology for the mining industry to extract the huge amount of coal locked-up under different constraints. In this study, the locked-up coal is proposed to be extracted by artificially strengthening the rib pillars. The detailed comparative study is carried out to know the increase of extraction percentage of locked-up coal by strengthening the rib pillars with FRP. Extraction methodology is designed and studied through numerical modelling for its stability analysis to evaluate its suitability of application in underground.

Coal petrology and genesis of Jurassic coal in the Ordos Basin,China

Multiple sets of thick coal beds characterized by simple structure and shallow burial depth were developed in the Early and Middle Jurassic strata of the Ordos Basin, northwestern China. The huge reserves of this high quality coal have a high commercial value. We studied the coal＇s petrologic characteristics and its maceral distribution to determine the maceral＇s contribution to generation of oil and gas. The results show that the Jurassic coals in the Ordos Basin have special petrological features because of the Basin＇s unique depo- sitional environment which was mainly a series of high-stand swamps in the upper fluvial system. These petro- graphic features are a result of the development of typical inland lakes where some sand bodies were formed by migrating rivers. After burial, the peat continued to undergo oxidizing conditions, this process generated extensive higher inertinite contents in the coals and the vitrinite components were altered to semi-vitrinite. The macroscopic petrographic types of these Jurassic coals are mainly semi-dull coal, dull coal, semilustrous and lustrous coal. The proportions of semi-dull coal and dull coal are higher in the basin margins, especially in the area near the northern margin. The numbers of semilustrous and lustrous coals increase southwards and towards the central basin. This situation indicates that different coal-forming swamp environments have major controlling effects on the coal components. Another observation is that in the Ordos＇ coal sequences, especially in the lower part, some sandstone beds are thick, up to 20 m with a coarse grain size. The higher fusinite content in the macerals accompanies a higher semi-vitrinite content with more complete and regular plant cell structure. The fusinite structure is clear and well preserved. After burial, the lithology of the roof and floor rocks can continue to affect the evolution of coal petrology. The sand bodies in the roof and floor exhibit good physical conditions so that pore water can maintain a long-term state of oxidation, circulation and connection to the coal. So coal components remain in an oxidation environment for a long time. Conversely, in the basin center, lacustrine facies developed and peat was rapidly covered by mudstone after burial and subsequent coal beds rapidly entered a reducing environment. As a result, abundant gelatification occurred and the vitrinite content increased. E^inite often accumulated in a specific position in the coal bed. Although the average exinite content is not high on the whole, it does significantly contribute to the total hydrocarbon generation. The exinite content has been underestimated, especially the amorphous bituminous fluid and its importance is emphasized here. The reason is that the fluid flows easily into fusinite which has strong rigidity, or flows into some fissures, where it is commonly neglected.

Volume and Surface Distribution Heterogeneity of Nano-pore in Coal Samples by CO2 and N2 Adsorption Experiments

In this paper,the heterogeneity of adsorption pores in middle and high rank coal samples were analyzed by using low temperature N2 and CO2 adsorption technology and fractal theory.The following results were achieved.1)According to the results of volume and surface fractal dimension,meso-pores can be classified into Mep-1,Mep-2,and Mep-3,respectively.Micro-pore can be classified into Mip-1,Mip-2,and Mip-3,respectively.2)Pore types play an important role in affecting the heterogeneity of meso-pores.The volume heterogeneity(VHY)of Mep-1 is simpler than that of Mep-2 and Mep-3 in type A samples.However,the VHY of Mep-1 becomes gradually larger than that of Mep-2 and Mep-3 from type A to type B and C.The VHY of open pore in the same diameter is higher than that of semi-open or closed pore.Meanwhile,the surface heterogeneity(SHY)of types A and B samples is significantly larger than that of type C,the SHY of semi-open or closed pores is more complicated than that of open pores.3)Coal rank mainly affects the heterogeneity of micro-pores.The heterogeneity of type A is always smaller than that of type B and C.The VHY of Mip-1 is more complicated than that of Mip-2 and Mip-3 in the same samples,and the sensitivity of the VHY of Mip-1 and Mip-2 to the degree of coal rank is smaller than that of Mip-3.Meanwhile,the SHY of Mip-1 and Mip-2 is simpler than that of Mip-3 in the same sample,the SHY of micro-pores remains stable as the pore size decreases,and the affect of coalification level on SHY decreases with the decrease in pore diameter.Full-scale fractal characterization has enabled quantitative characterization of adsorption pore properties and provided useful information with regards to the similarity of pore features in different coal reservoirs.

中低温煤焦油转化利用技术研究进展

随着煤焦油深加工技术的发展,中低温煤焦油的综合利用受到关注。介绍了国内外中低温煤焦油利用的研究现状,对中低温煤焦油的分离、加氢改质利用,制燃料油、特种油品和高值化学品,煤焦油掺混加氢以及煤沥青利用的研发进行了综述和分析。基于中低温煤焦油馏分的构成特性,提出了中低温煤焦油“分质分级转化利用”技术路线,充分利用其分子特征结构,研究高效催化剂使煤焦油定向转化为目标产品。这为煤焦油高效清洁利用提供了多元化、高值化和精细化的途径。

煤岩显微组分电浮选分离与制氢过程中氢/氧气泡的影响机制

电浮选技术是实现煤岩显微组分高效分离的有效途径,也是一种有显著优势的制氢技术。电浮选中电解气泡既是浮选分离的载体,又是有效的氢气/氧气产物。本文探讨了高惰质组煤电浮选过程中电解气泡对煤岩显微组分分离效果的影响机制,利用诱导时间测定仪、红外光谱、接触角测量仪及气相色谱等考察了氢气泡和氧气泡对煤岩显微组分的选择性以及电化学反应对煤结构和可浮性的影响规律和气体产物组成等。结果表明,电解氢气泡浮选所得的浮物收率及浮物镜质组含量较氧气泡高,相应的镜质组回收率也高于氧气泡;电浮选过程中的电解作用会改善煤岩显微组分的表面结构,引起润湿性的变化,电浮选阴极区对煤具有电化学还原作用,可减少煤中—OH、—COOH与C==O等亲水性官能团,从而增加煤样的接触角,减小氢气泡对煤的诱导时间,从而增加煤的可浮性,而阳极区的作用相反;煤浆电浮选过程中可获得纯度>94%的氢气和>96%的氧气,且镜质组为电解质时的气体产物纯度高于惰质组,但惰质组可获得更高的产气速率;采用两级串联流程进行煤岩显微组分的电浮选分离时,浮选分离的综合效率最高可达到83.7%,此时浮物的镜质组回收率为86.7%,两个沉物产品的回收率分别为41.6%和54.9%,氢气的产率可达到6.49mL/(min∙cm^(2))。