Effects of process parameters on pore structure of semi-coke prepared by solid heat carrier with dry distillation

The semi-coke was prepared by solid heat carrier with dry distillation in single factor method. The pore structures of raw coal and semi-coke were characterized by Brunauer–Emmett–Teller (BET) and scanning electron microscope (SEM). The results show that the adsorption and desorption isotherm of semi-coke are not coincident. There was a wide pore distribution on the semi-coke, in which mesopores and micropores account for a considerable proportion. Also there are many more secondary pores. With the increase of the final temperature of heat carrier and constant temperature, as well as the decrease of volume ratio of coal and hot carrier reactor, specific surface area and pore volume of semi-coke increased rapidly first and then decreased and finally increased, along with the rapidly reduction of average pore size. SEM photos show that the surface of semi-coke becomes increasingly rough and glossy.     

Fractal dimension of coal particles and their CH4 adsorption

We describe the fractal analysis of three differently sized coal samples (0.350–0.833 mm, 0.245–0.350 mm, and 0.198–0.245 mm). The influence of fractal dimension on CH₄ adsorption capacity is investigated. The physical parameters of the samples were determined via the Brunauer–Emmett–Teller (BET) theory. A CH₄ adsorption study over the pressures range from 0 to 5 MPa was carried out with a new volumetric measurement system. The CH₄ adsorption was measured using the differently sized coal. Two fractal dimensions, D₁ and D₂ were determined over the pressure ranges from 0 to 0.5 MPa and from 0.5 to 1 MPa, using the Frenkel-Halsey-Hill (FHH) method. We conclude that the two fractal dimensions correlate with the CH₄ adsorption capacity of the coal: increasing CH₄ adsorption capacity occurs with a corresponding increase in fractal dimension. Furthermore, D₁ and D₂ are positively correlated with surface area, pore volume, and samples size. The size distribution of the samples has fractal characteristics.     

Methane adsorption behavior on coal having different pore structures

The adsorption of methane onto five dry coal samples was measured at 298 K over the pressure range from 0 to 3.5 MPa using a volumetric method. The isotherm data were fitted to the Langmuir and the Freundlich equations. The kinetic data were fitted to a pseudo second order equation, the linear driving force equation (LDF), and an intra-particle diffusion model. These results showed that higher methane adsorption is correlated with larger micro-pore volumes and specific surface areas. The adsorption was related to the narrow micro-pore size distribution when the previous two parameters are large. The kinetics study showed that the kinetics of methane adsorption onto these five dry coal samples followed a pseudo second order model very well. Methane adsorption rates are controlled by intra-particle diffusion. The faster the intra-particle diffusion, the faster the methane adsorption rate will be.     

Deformed coal types and pore characteristics in Hancheng coalmines in Eastern Weibei coalfields

Based on SEM observance, the methods of low-temperature nitrogen and isothermal adsorption were used to test and analyze the coal samples of Hancheng, and pore structure characteristics of tectonic coals were discussed. The results indicate that in the same coal rank, stratification and crack are well developed in cataclastic coal, which is mostly filled by mineral substance in the geohydrologic element abundance, results in pore connectivity variation. Granulated and mylonitic coal being of these characteristics, as develop microstructures and exogenous fractures as well as large quantity of pores resulted from gas generation and strong impermeability, stimulate the recovery of seepage coal, improve coal connectivity and enhance reservoir permeability. Absorption pore (micro-pore) is dominant in coal pore for different coal body structure, the percentage of which pore aperture is from 1 to 100 nm is 71.44% to 88.15%, including large of micro-pore with the 74.56%–94.70%; with the deformation becoming more intense in the same coal rank, mesopore enlarge further, open-end pores become thin-neck-bottle-shaped pores step by step, specific surface area of micro-pore for cataclastic coal is 0.0027 m²/g, while mylonitic coal increases to 7.479 m²/g, micro-pore gradually play a dominant role in effecting pore structural parameters.     

基于液氮吸附实验的煤层夹矸孔隙结构特征研究

煤层夹矸存在孔隙,具有吸附气体的能力。为研究沁水盆地新景矿煤层夹矸孔隙特征,选择8#煤层夹矸和15#煤层夹矸进行液氮静态吸附法实验研究。根据实验结果对新景煤矿8#煤层夹矸和15#煤层夹矸孔隙结构特征中的比表面积、孔径、孔径占比进行分析。结果表明:新景8#煤层夹矸主要以微孔和小孔为主,微孔和小孔占总孔比的92%以上,新景15#煤层夹矸主要由微孔、小孔和中孔为主,微孔、小孔占67%,中孔占到32%左右。微孔、小孔孔径大小与比表面积和吸附量有较强的相关性。     

Numerical simulation of influence of Langmuir adsorption constant on gas drainage radius of drilling in coal seam

To determine reasonable distance of gas pre-drainage drillings in coal seams, a solid–gas coupling model that takes gas adsorption effect into account was constructed. In view of different adsorption constants,the paper conducted the numerical simulation of pre-drainage gas in drillings along coal seam, studied the relationship of adsorption constants and permeability, gas pressure, and effective drainage radius of coal seams, and applied the approach to the layout of pre-drainage gas drillings in coal seams. The results show that the permeability of coal seams is on the gradual increase with time, which is divided into three sections according to the increase rate: the drainage time 0–30 d is the sharp increase section;30–220 d is the gradual increase section; and the time above 200 d is the stable section. The permeability of coal seams is in negative linear and positive exponent relation with volume adsorption constant VLand pressure adsorption constant PL, respectively. The effective drainage radius is in negative linear relation with VLand in positive exponent relation with PL. Compared with the former design scheme, the engineering quantity of drilling could be reduced by 25%.     

Physical properties and ?lter cake structure of ?ne clean coal from flotation简

In order to improve the dewatering rate and the effect of fine clean coal (FCC), the advanced method of fine coal (−0.5 mm) dewatering and the correlated basic theory were investigated in this study. It was found that the dewatering by sleeve type press filter was an efficient way of FCC dewatering. On the other hand, the results also proved that particle size distribution, volatile matter, ash content, pore size distribution and specific surface area of coal particles of FCC samples, as well as viscosity and density of FCC slurry, were important parameters in determining the process of efficient dewatering. Especially, wet mass to dry mass, specific resistance of average mass, compressibility factor and microstructure of filter cake explained the reasons and mechanisms of fine clean coal efficient dewatering.     

Pore characterization of different types of coal from coal and gas outburst disaster sites using low temperature nitrogen adsorption approach

To characterize the pore features of outburst coal samples and investigate whether outburst coal has some unique features or not, one of the authors, working as the member of the State Coal Mine Safety Committee of China, sampled nine outburst coal samples(coal powder and block) from outburst disaster sites in underground coal mines in China, and then analyzed the pore and surface features of these samples using low temperature nitrogen adsorption tests. Test data show that outburst powder and block coal samples have similar properties in both pore size distribution and surface area. With increasing coal rank, the proportion of micropores increases, which results in a higher surface area. The Jiulishan samples are rich in micropores, and other tested samples contain mainly mesopores, macropores and fewer micropores. Both the unclosed hysteresis loop and force closed desorption phenomena are observed in all tested samples. The former can be attributed to the instability of the meniscus condensation in pores,interconnected pore features of coal and the potential existence of ink-bottle pores, and the latter can be attributed to the non-rigid structure of coal and the gas affinity of coal.     

CO2 isothermal adsorption models of coal in the Haishiwan Coalfield

Since the capacity of CO2 adsorption of coal is a key factor in coal and CO2 outbursts,an experimental study was carded out on CO2 isothermal adsorption with high-pressure volumetry with dry coal samples from the No.2 coal seam in the Haishiwan Coalfield.Four different equations (Langmuir,BET,D-R and D-A) were used to fit the experimental data.We discuss adsorption mechanisms.The results show that the amount of CO2 adsorption increases rapidly under low relative pressure,i.e.,the ratio of equilibrium pressure and saturated vapor pressure,which indicates that molecular layer adsorption or micropore filling may occur in coal.No clear equilibrium state was observed on the isothermal adsorption curves under relative pressure (P/P0) ranging from 0 to 0.8.The fitted results show that the accuracy of the D-A equation is highest with n=1.Micropores are more developed in coal by comparing the BET equation with a pressure mercury injection method on the surface area.The D-A equation (n=l) provides the best fit.By comparing the calculated specific surface area of the BET equation and the mercury intrusion method,it is found that micropore adsorption of CO2 occupies a dominant position.     

Constitutive model for methane desorption and diffusion based on pore structure differences between soft and hard coal

This paper aims to improve the accuracy and applicability of gas diffusion mathematical models from coal particles. Firstly, a new constitutive model for gas diffusion from coal particles with tri-disperse pore structure is constructed by considering the difference in characteristics between soft coal and hard coal.The analytical solution is then derived, that is, the quantitative relationship between gas diffusion rate(Qt/Q_∞) and diffusion time(t), The pore structure parameters of soft coal and hard coal from Juji coal mine are determined. Gas diffusion rules are numerically calculated and investigated by physical simulation methods. Lastly, the applicability of this model is verified. The results show that the homogeneous model only applies to the gas diffusion process of hard coal during the initial 10 min. The calculation results from this model and the physical experimental results of soft coal and hard coal are nearly identical during the initial 30 min.     

过渡相煤系泥页岩纳米级孔隙结构非均质性表征及主控因素——以淮南煤田二叠系为例

纳米级孔隙是煤系页岩气赋存的重要场所,具有很强的非均质性。为了研究海陆过渡相煤系泥页岩储层孔隙结构非均质性,对淮南煤田二叠系山西组和下石盒子组泥页岩钻孔岩芯样品进行总有机碳、镜质体反射率、全岩和黏土X射线衍射分析、场发射扫描电镜及低温液氮吸附实验,获得泥页岩有机地球化学、矿物组分、孔隙结构参数,采用孔隙结构相对偏差、FHH分形模型来评价储层孔隙结构非均质性及主控因素。结果表明:储层孔隙类型以黏土矿物片层间的平行板状孔、狭缝状孔及粒间的锥状孔为主,孔隙尺度主要为介孔,其次为微孔和宏孔;孔隙结构具显著分段分形特征,由于与煤储层高度相似而划分为渗透孔隙(r＞7.5 nm)和吸附孔隙(r≤7.5 nm),渗透孔隙复杂程度强于吸附孔隙;微孔越发育,孔容越小,比表面积越大,分形维数越大,孔隙结构越复杂,非均质性越强;过渡相煤系泥页岩储层孔隙结构非均质性主要受控于不同沉积环境及成岩演化下矿物组分差异,随着黏土矿物含量的增加和脆性矿物含量的减小而增大;与下石盒子组相比,山西组黏土矿物含量更低,导致分形维数较低,孔隙结构复杂程度偏弱,比表面积和平均孔径的相对偏差较小,孔隙分布较均匀,非均质性相对弱,对页岩气的储存、解吸和扩散更有利,可考虑优先开采。     

Determining the rational layout parameters of the lateral high drainage roadway serving for two adjacent working faces

To determine the rational layout parameters of the lateral high drainage roadway(LHDR) serving for two adjacent working faces, a mechanical model of the LHDR under mining influence was established, and the overburden fissure, mining-induced stress distribution rules were analyzed. First, the development characteristics of mining-induced overburden fissure and the stress distribution law of the upper section of the working face were analyzed. Second, by analyzing the distribution law of vertical stress at different layers, the lateral distance of the LHDR was determined as 25 m. Third, by analyzing the surrounding rock deformation effect, stress distribution law, and overburden fissure distribution law of the LHDR at the heights of 20, 25, and 30 m away from the roof, the rational horizon of the LHDR was determined to be 25 m. Finally, an example of a LHDR located 25 m above the roof of the No. 2 coal seam and 25 m away from the No. 2-603 working face was presented. Results show that when the No. 2-603 coalface is being mined, the surrounding rocks lag 80 m or even further and the working face tends to be stable. The relative deformations of the roof and floor of the roadway and both of its walls were 583 and 450 mm,respectively. The reduction rate of the roadway section was 21.52%–25.32%. The section of the roadway was sufficient to extract the pressure relief gas in the overburden of the No. 2-605 working face. The average gas concentration and the pure volume at the branch pipeline were 24.8% and 22.3 m~3/min,respectively, showing that the position of high-level boreholes was reasonable.     

Coal and gas outburst dynamic system

Coal and gas outburst is an extremely complex dynamic disaster in coal mine production process which will damage casualties and equipment facilities, and disorder the ventilation system by suddenly ejecting a great amount of coal and gas into roadway or working face. This paper analyzed the interaction among the three essential elements of coal and gas outburst dynamic system. A stress-seepage-damage coupling model was established which can be used to simulate the evolution of the dynamical system, and then the size scale of coal and gas outburst dynamical system was investigated. Results show that the dynamical system is consisted of three essential elements, coal-gas medium(material basis), geology dynamic environment(internal motivation) and mining disturbance(external motivation). On the case of C13 coal seam in Panyi Mine, the dynamical system exists in the range of 8–12 m in front of advancing face. The size scale will be larger where there are large geologic structures. This research plays an important guiding role for developing measures of coal and gas outburst prediction and prevention.     

Surface movement above old coal longwalls after mine closure

Although most subsidence occurs in the months and years after mining by the longwall method, surface movement is still occurring many decades after the mining. The aim of the study is to quantify the long term behavior. Satellite data(radar-interferometry) were analyzed to study an area of about 2 km~2 during the 18 years following the closure of the underground infrastructure and the flooding of the underground workings and rock mass. It was observed that, on average, a residual downward movement took place till 7–12 years after the closure, followed by a clear uplift. However, the first signs of an uplift occurred in certain sub-areas 3–4 years after the closure. Zones within the area studied were identified with either larger or smaller movements. However, the spatial variation of the surface subsidence or uplift could not be directly explained by the characteristics of mining.     

Longwall mining under gateroads and gobs of abandoned small mine

Due to the use of outdated mining technology or room and pillar mining process in small coal mines, the coal recovery ratio is only 10–25%. In many regions of China, the damage area caused by the small coal mines amounted to nearly one hundred square kilometers. Therefore, special mining techniques must be taken to reclaim the wasted resource in disturbed coal areas. This paper focuses on the different mining methods by analyzing the longwall panel layout and abandoned gateroad(AG) distribution in the abandoned area of Cuijiazhai coal mine in northwestern China. On the basis of three-dimensional geological model, FLAC3 D numerical simulation was employed. The abutment pressure distribution was simulated when the panel face passed through the disturbed areas. The proper angle of the inclined face was analyzed when the panel face passed through the abandoned gateroads. The results show that the head end of the face should be 13–20 m ahead of the tail end. The pillars on both sides of abandoned gateroads had not been damaged at the same time, and no large-area stress concentration occured above the main roof.Therefore, the coal reserves of disturbed areas can be successfully recovered by using underground longwall mining.     

Greenhouse gas emissions from shallow uncovered coal seams

This study discusses a method of quantifying emissions from surface coal mining that has been trialled in Australia. The method is based on direct measurement of surface emissions from uncovered coal seams in mine pits, concurrent measurement of residual gas content of blasted coal in mine pits, and measurement of pre-mining gas content of the same seam from cores retrieved from exploration boreholes drilled away from active mining. The results from one of the mines studied are presented in this paper. In this mine, the pre-mining gas content of the target seam was measured using cores from an exploration borehole away from active mining. Gas content varied from 0.7 to 0.8 m³/t and gas composition varied from 16% to 21% CH₄ (84–79% CO₂). In-pit measurements included seam surface emissions and residual gas content of blasted and ripped coal. Residual gas content varied from 0.09 to 0.15 m³/t, less than twofold across the mine pit. Composition of the residual gas was in general 90% CO₂ and 10% CH₄, with slight variation between samples. Coal seam surface emissions varied from 1.03 to 7.50 mL of CO₂-e per minute and per square meter of the coal seam surface, a sevenfold variation across the mine pit.     

Effect of the column height on the performance of liquid–solid fluidized bed for the separation of coarse slime

A liquid–solid fluidized bed separator, used for the separation of coarse slime, was developed. Test particles sized in the range from 0.25 to 0.5, 0.5 to 1.0, and 0.25 to 1.0 mm were separated in the liquid–solid fluidized bed. Beds with column heights of 1200, 1500, and 1800 mm were tried. The clean coal and the tailings were subsequently analyzed by float–sink testing. The results showed that the ash and yield of clean coal both decreased with increasing column height, for all three size fractions, and that the ash of the clean coal obtained from tests on the broader size fraction was less than that from the narrower sized fractions. The separation density decreased with increasing column height. The lowest E value was seen for a column height of 1500 mm, for which conditions the separation density was 1.45 g/cm³. The E value was 0.084 for the 0.25–0.5 mm fraction but the corresponding separation density was 1.48 g/cm³, and the E value 0.089, for the broader 0.25–1.0 mm fraction.     

Determination of consolidation behaviour of clay slurries

The main objective of this study was to determine the consolidation behaviour of clay slurries.A finegrained clay with high consistency limits(W_L = 180%,w_P= 120%) was investigated using conventional oedometer and bench-top centrifuge tests.Results indicated that the slurry had an apparent preconsolidation(due to initial conditions,electrochemical interactions,tortuous drainage,and thixotropic strength) from e = 5.7 to e = 5.5 followed by virgin compression.Likewise,the low hydraulic conductivity(10~(-10)-10~(-12) m/s) was due to low porosity(small pore throats) and high tortuosity(long flow paths).Unlike consolidation of soils,the c_v and m_v decreased with increasing σ' but increased with increasing e and k.The data from the two tests correlated well in the range of σ' = 10-65 kPa,e = 5.5-3.86,k= 1.7 × 10~(-10)-5×10~(-11) m/s,F_c = 1-40 MN.New equations were developed to correlate the consolidation parameters(e,σ',k) with F_c.The deviation of k beyond 40 MN(e = 4.65) was due to deviation from the initial straight line portion of the settlement curve in the centrifuge test.     

方解石去除废水中高浓度磷酸盐机理与影响因素

采用X射线衍射分析（XRD）,透射电镜观测（TEM）,红外光谱分析（FT—IR）,比表面积（BET）与孔径测试（BJH）分析结合理论计算探讨方解石除磷机理;通过实验考察主要影响因素,并对除磷机理加以验证。结果表明：反应时间、反应温度、pH值、投加量对除磷效率影响显著。BET,BJH与TEM测试表明方解石在整个除磷过程中未出现多孔性结构,比表面积均小于16．0m^2／g,孔容低于0．085cm^3／g,其吸附能力很弱,吸附作用不是除磷的主要机制;XRD与FT-IR测试结果显示生成CaHPO4·2H4O（DCPD）沉淀与DCPD转化为非晶态磷酸三钙（ACP）沉淀是除磷的主要机制,DCPD→ACP的转化过程是去除磷酸盐的主要控制步骤．     

Hydration mechanisms of smithsonite from DFT-D calculations and MD simulations

Investigation on the mineral?water interactions is crucial for understanding the subsequent interfacial reactions. Currently, the hydration mechanisms of smithsonite are still obscure. In this paper, the adsorption of H₂O at different coverage rates on smithsonite (1 0 1) surface was innovatively investigated using density-functional theory (DFT) calculations and molecular dynamics (MD) simulations by analyzing adsorption model, interaction energy, atomic distance, density of state, electron density difference, concentration profile, radial distribution function and self-diffusion coefficient. We found that single H₂O preferred to be dissociated on smithsonite (1 0 1) surface via the interaction of surface Zn with the Ow of H₂O and H-bond between Hw of H₂O and surface Os. However, dissociation adsorption and molecular adsorption coexisted on the smithsonite surface at a high coverage rate of H₂O, and dissociation adsorption remained the main adsorption mechanism. Moreover, we found the interaction between smithsonite surface and H₂O was weakened as a function of H₂O coverage, which was because the presence of interlayer H₂O and different layers of H₂O decreased the reactivity of the smithsonite surface. The H₂O is mainly adsorbed on the smithsonite surface by forming three layers of H₂O (about 10–15 Å), with the ordering degree gradually decreasing.