Surface characteristics and wetting mechanism of respirable coal dust

In this study,FTIR and XPS spectroscopy,specific surface area and pore size analyses,wetting and other experimental means have been applied to investigate respirable coal dust surface properties and wetting mechanism.The research shows that coal dust surface structures,chemical and element compositions are changed in the refining process of coal dust.Compared with large particle coal dust,respirable coal dust is a weak hydrophilic and strong hydrophobic substance.The reason:the smaller the particle size of coal dust,the more unsaturated its surface.The absorption of air is strong and it is easy to form an air film on coal dust surfaces.Coal dust contact with water is actually a compound contact of liquid in contact with a solid and gas in contact with a solid.The smaller the particle size,the larger the pore volume and the higher the degree of surface roughness,the larger the area of gas in contact with a solid and the worse the coal dust wettability.Another reason is that the changes in the composition of atoms on the dust surface and structures affect coal dust wettability.The results of this study establish a theoretical basis for the invention of effective reduced-dust technology.     

Application study on complex wetting agent for dust-proof after gas drainage by outburst seams in coal mines

After gas drainage,the outburst seam is dry and,consequently,during subsequent mechanized mining,unwanted dust production is extensive.Because the hard dustfall typically has a small particle size it contains a high percentage of respirable dust.Considering these factors,this paper improved the efficiency of dustfall by reducing the surface tension of the liquid used as a wetting agent,then configuring five kinds of wetting agents by adopting various doses and types of surfactants,neutral inorganic salts and chemical additives,etc.After purchasing DA-85 and SRJ-1 wetting agent,the surface tension and critical micelle concentration of seven kinds of wetting agents were measured using the capillary rise method.Wetting agent A was confirmed to have the best comprehensive effect.The experiments were optimized by measuring and comparatively analyzing contact angles of pure water,SRJ-1 wetting agent and wetting agent A on the surface of different coal samples using a contact angle measurement instrument(HARKESPCA).By comparative analysis,dust-proof effects of seam,dynamic pressure water infusion and highpressure spray in the tunneling face at the Daning coal mine using pure water,wetting agent SRJ-1and A,it was determined that after using wetting agent A,the average dust concentration in the place of the mining machine driver,10 m and 110 m away from the tunneling front is approximately 300 mg/m~3,240 mg/m~3 and 100 mg/m~3,respectively.This practice increased the dust-proof efficiency dramatically and achieved a good comprehensive dust-proof effect.     

表面活性剂润湿煤尘能力的研究

本文通过研究表面活性剂对煤尘的润湿性，提出了性能优良的降尘剂；并讨论了无机电解质及温度对表面活性剂润湿能力的影响。     

Effect of different concentrations of surfactant on the wettability of coal by molecular dynamics simulation

Anionic surfactant sodium dodecyl benzene sulfonate(SDBS) at varying concentrations was selected to investigate the influence on the wettability of Zhaozhuang Coal by molecular dynamics simulation. Six groups of water/surfactant/coal systems with different concentrations were constructed. The influence of surfactant with different concentrations on the wettability of coal was concluded by analyzing various properties from the energetic behaviors to the dynamic characteristics. The results show that the interfacial tension decreases sharply and then rises slowly with the increase of SDBS surfactant concentration,obtaining that surfactants can obviously reduce the interfacial tension. The surfactant molecules could be detected at the water/coal interface through analyzing the system's relative concentration distribution. In addition, the difference in the wettability of surfactants on coal surfaces is caused by the spatial distribution differences of alkyl chains and the benzene ring of the surfactant molecules. And the negative interaction energy between SDBS and the coal surface indicates that adsorption process is spontaneous.Furthermore, it is of great practical significance for improving the dust reduction effect and reducing the disaster of coal dust by exploring the effects of surfactant molecules on the wettability of coal.     

Coupling of anionic wetting agents to dust of sulfide ores by dropping liquid method

By using the experimental approach of dropping liquid, the coupling of three anionic wetting agents with ten dust samples of sulfide ores was studied, and particularly the wetting effects of the wetting agents on the sulfide dust influenced by factors of agent concentration and sulfate additive in the wetting agent solutions were investigated. The results show that when the solution temperature is about 20℃, all the selected wetting agents are effective to most dust samples, but the effect is different. Wetting agents are more effective to the dust which is difficult to be wetted. Wetting agent solution with sodium sulfate can improve the wetting ability of sulfide dust. For sodium dodecyl benzene sulfonate, the suitable concentration of sodium sulfate is 1 - 2 mmol/L. The cost of wetting agents can be reduced because the sodium sulfate is much cheaper than many surfactants. Since the dust of sulfide ores is composed of various minerals and elements, the whole effect of depressing dust should be considered while innovating a wetting agent.     

Application of foam technology for dust control in underground coal mine

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

倒三角形纳米粗糙表面液滴润湿性分子动力学模拟

固体表面纳米结构可以有效地调控界面润湿特性,在材料能源等领域具有重要应用前景。改变纳米结构的几何尺寸能够在一定范围内调节润湿特性,但存在一定的局限性,调节固液间能量系数能够进一步改变界面的润湿特性。然而,纳米粗糙表面液滴在更大区间内的固液相互作用系数下的润湿特性研究甚少。本文采用分子动力学模拟的方法,研究了倒三角形纳米粗糙表面液滴在不同区间能量系数下呈现的润湿行为,并采用渗透率进行表征。结果发现：四个不同的区间内固液间能量系数对渗透率的作用规律不同,呈现出先增后减的趋势,液滴也依次呈现出显著的润湿态,对应润湿状态图中疏水的Cassie态到亲水的Wenzel态,而能量系数越过临界值(~7),Wenzel态再反转回显著的Cassie态;同时,液滴分子空间分布呈现明显的规律性,其底层原子在晶格线或晶面均衡分布,形似壁面原子的外延生长。本文的研究获得了能量系数对润湿性影响规律的全貌性认识,对纳米结构表面润湿性的设计和调控具有一定的指导意义。     

CFD model simulation of bubble surface area flux in flotation column reactor in presence of minerals

Bubble surface area flux(S_b) is one of the main design parameter in flotation column that typically employed to describe the gas dispersion properties, and it has a strong correlation with the flotation rate constant. There is a limited information available in the literature regarding the effect of particle type,density, wettability and concentration on Sb. In this paper, computational fluid dynamics(CFD) simulations are performed to study the gas–liquid–solid three-phase flow dynamics in flotation column by employing the Eulerian–Eulerian formulation with k-e turbulence model. The model is developed by writing Fortran subroutine and incorporating then into the commercial CFD code AVL FIRE, v.2014.This paper studies the effects of superficial gas velocities and particle type, density, wettability and concentration on Sband bubble concentration in the flotation column. The model has been validated against published experimental data. It was found that the CFD model was able to predict, where the response variable as indicated by R-Square value of 0.98. These results suggest that the developed CFD model is reasonable to describe the flotation column reactor. From the CFD results, it is also found that Sb decreased with increasing solid concentration and hydrophobicity, but increased with increasing superficial gas velocity. For example, approximately 28% reduction in the surface area flux is observed when coal concentration is increased from 0 to 10%, by volume. While for the same solid concentration and gas flow rate, the bubble surface area flux is approximately increased by 7% in the presences of sphalerite.A possible explanation for this might be that increasing solid concentration and hydrophobicity promotes the bubble coalescence rate leading to the increase in bubble size. Also, it was found that the bubble concentration would decrease with addition of hydrophobic particle(i.e., coal). For instance, under the same operating conditions, approximately 23% reduction in the bubble concentration is predicted when the system was working with hydrophobic particles. The results presented are useful for understanding flow dynamics of three-phase system and provide a basis for further development of CFD model for flotation column.     

Review of preventive and constructive measures for coal mine explosions: An Indian perspectiveOA

Firedamp and coal dust explosion constitute a lion’s share in mine accidents in a global mining scenario.This paper reports a list of mine explosion disasters since last two decades, a critical review of the different prevention and constructive measures, and its recent development to avoid firedamp and coal dust explosion. Preventive legislation in core coal-producing countries, viz. China, USA, Australia, South Africa, and India related to firedamp and coal dust explosion are critically analys...     

Coal and rock fissure evolution and distribution characteristics of multi-seam mining

Henan Pingdingshan No.10 mine is prone to both coal and gas outbursts. The E_9–10 coal seam is the main coal-producing seam but has poor quality ventilation, thus making it relatively difficult for gas extraction. The F₁₅ coal seam, at its lower section, is not prone to coal and gas outbursts. The average seam separation distance of 150 m is greater than the upper limit for underside protective seam mining. Based on borehole imaging technology for field exploration of coal and rock fracture characteristics and discrete element numerical simulation, we have studied the evolution laws and distribution characteristics of the coal and rock fissure field between these two coal seams. By analysis of the influential effect of group F coal mining on the E_9–10 coal seam, we have shown that a number of small fissures also develop in the area some 150 m above the overlying strata. The width and number of the fissures also increase with the extent of mining activity. Most of the fissures develop at a low angle or even parallel to the strata. The results show that the mining of the F₁₅ coal seam has the effect of improving the permeability of the E_9–10 coal seam.     

Development of 3D top coal caving angle model for fully mechanized extra-thick coal seam miningOA

During high-intensity, fully mechanized mining of extra-thick coal seam, the top coal would cave to a certain 3D form. Based on the data collected during drilling, a 3D model of top coal caving surface space was established to determine the relationship between the location of the stope roof and the caving surface,enabling the mathematical computation of the top caving angle(φ). The drilling method was employed to measure the top caving angle on two extra-thick fully mechanized coal caving faces...     

综采工作面割煤时煤尘污染状况的现场实测研究

在对平沟煤矿综采工作面采煤机割煤时煤尘浓度和分散度现场实测和分析的基础上,得出了综采工作面采煤机割煤时煤尘的污染特征.在一定风速条件下采煤机割煤时,距底板和煤壁较近处煤尘的总粉尘浓度沿程分布曲线出现2个极大值,然后随着煤尘运移距离的增加,煤尘的总粉尘浓度沿程分布曲线趋向于1个稳定值;距顶板和液压支架较近处煤尘的总粉尘浓度沿程分布曲线仅出现1个极大值,然后随着煤尘运移距离的增加,煤尘的总粉尘浓度沿程分布曲线也趋于1个稳定值.     

适用于致密砂岩储层气湿反转剂筛选与评价

通过接触角测试和可注入性实验对非离子型表面活性剂、含氟阳离子型表面活性剂、氟碳纳米液在致密砂岩储层的气润湿性改变能力和注入性进行评价。结果表明,相对于其他化学剂,氟碳纳米液CRS⁃850具有较好的气润湿反转效果,岩心表面接触角从45.6°增加到92.1°,由强水湿转变为气相润湿;处理前岩心自吸盐水量0.360 8 g,处理后自吸量下降至0.020 6 g,岩心自吸量下降幅度达98.85%。最大自吸速率从0.053 g/min下降至0.002 g/min;气润湿反转剂显著提高岩心内部液相渗流能力,增加气驱渗透率,岩心气驱渗透率恢复效果显著,在气驱盐水基础上提高了501.69%~673.91%,表明气润湿反转剂有利于致密砂岩储层解除液相伤害。     

液态水对煤吸附甲烷影响的机理分析

为了研究液态水对煤吸附甲烷影响的机理,进行了不同煤级干燥煤样、平衡水煤样和注水煤样等温吸附实验,基于分子间作用力对液态水影响机理进行分析,并用维里方程拟合等温吸附实验结果来验证.结果表明,煤基质的润湿程度是液态水影响煤吸附甲烷的主要因素.干燥煤样中煤与甲烷分子间作用力远大于甲烷分子间作用力,第二维里系数较低,吸附能力强;平衡水煤样中煤与水分子氢键能高于范德华力,气态水分子竞争吸附,第二维里系数偏高,煤基质吸附能力弱;注水煤样中煤与甲烷分子之间长程作用力和甲烷与水分子之间短程作用力之和较小,与甲烷分子间作用力相当,第二维里系数最高,煤基质吸附能力很低.煤级增高,煤基质表面极性及其润湿程度降低,第二维里系数随之降低.     

改善平沟煤矿16~#煤层润湿性的研究

煤层注水现已成为矿井预防重大事故的综合性安全技术措施.煤层注水是以解决采煤工作面煤尘问题而发展起来的,后来又逐渐应用于预防冲击地压,提高瓦斯抽放效等方面.煤体注水的好处很多,但是不同煤质会对注水造成不同的影响.针对平沟16#煤润湿性差的现象进行了研究,并提出了添加尼诺尔、十二烷基苯磺酸钠和2种表面活性剂改善其煤体的润湿性,以提高煤体注水的效果.     

Influence of wave and current on deep-sea mining transporting system

As a solution to the breaking of pipeline under high axial force, carbon fiber composite pipe with low density and high intensity is applied to deep-sea mining transporting system. Based on the fact that the transporting pipe is under the forces of gravity, inner liquid, buoyancy as well as hydrodynamic force, geometric nonlinear finite element theory has been applied to analyzing the transporting system. Conclusions can be drawn as follows. Under the interaction of waves and currents, node forces F _X and F _Z acted by the transporting pipe on the mining vehicle are less than 2 kN, which indicates that waves and currents have little influence on the spatial shape of the transporting pipe and the mining vehicle movement. On the other hand, the horizontal force acting on the mining ship could be as large as 106 830 N, which has great influence on the mining system.     

Combustion characteristics and synergy behaviors of biomass and coal blending in oxy-fuel conditions: A single particle co-combustion method

Co-combustion biomass and coal can effectively reduce the emission of CO₂. O₂/H₂O combustion is regarded as the next generation of oxy-fuel combustion technology. By co-combustion biomass and coal under oxy-fuel condition, the emission of CO₂ can be minimized. This work investigates the co-combustion characteristics of single particles from pine sawdust (PS) and bituminous coal (BC) in O₂/N₂, O₂/CO₂ and O₂/H₂O atmospheres at different O² mole fractions (21%, 30% and 40%). The experiments were carried out in a drop tube furnace (DTF), and a high speed camera was used to record the combustion process of fuel particles. The combustion temperature was measured by a two-color method. The experiments in O₂/N₂ atmosphere indicate that the particles from pine sawdust and bituminous coal all ignite homogeneously. After replacing H₂O for N₂, the combustion temperature of volatiles of blended fuel particles decreases, while the combustion temperature of char increases. The ignition delay time in O₂/H₂O atmosphere is shorter than that in O₂/N₂ or O₂/CO₂ atmosphere. The combustion temperature of volatiles of blended fuel particles increases as the mass fraction of bituminous coal increases, while the combustion temperature of char of blended fuel particles is higher than that of biomass or bituminous coal. The ignition delay time of blended fuel particles increases with the increasing mass fraction of bituminous coal, and the experimental ignition delay time of blend fuel particles is shorter than the theoretical one. These reveal a synergy during co-combustion process of pine sawdust and bituminous coal.     

Fault tree analysis of dust suppression mechanism in a spray system with wetting agent

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Controlling the coal dust at transshipment point: A study of the foam-sol foaming device

In order to effectively control the dust at the transshipment point with foam-sol, this paper attempted to study the characteristics of dust diffusion at transshipment point and the foam-sol foaming device with diffusion outlet was also designed in this paper. To study the diffusion rules of coal dust, fluent discrete phase model was utilized in the numerical simulation, as the coal dust was thrown down at a horizontal velocity of 2.5 m/s. A foam-sol foaming device was designed, through which foaming agent could be automatically sucked into the Venturi by the negative pressure. The automatic controller was also equipped, which could transform the energy of the compressed air into the constant pressure difference so that the gelling agent could be qualitatively added into the gel container. The diffusion outlet that could spray out foam-sol in a continuous, conical and 3D manner was also designed. Moreover, this paper also carried out the contrast experiments on dust removal efficiency among water, aqueous foam and foam-sol. The results clearly show that the symmetrical whirlpools appeared below the inlet where the largest whirlpool diameter was 0.52 m, and the horizontal distance from swirl range to the inlet was approximately 0.69 m. By using the self-designed foaming device, the foaming was multiplied by 30 times and the volume ratio with water and foaming agent reached 95%:5%. In this context, the gas pressure was controlled at 0.3 MPa, with gas flow at 15 m³/h and water flow at 0.5 m³/h, with water pressure controlled between 0.34 and 0.36 MPa. The foam-sol has the highest dust removal efficiency than other agents.     

The wettability of Fe based alloy on TiO

For developing TiO based imitated gold materials, the wettabilities of Fe and Fe-Cr-Ni-Ti on TiO were studied. The results indicated that the wettabilities of Fe and Fe-Cr on TiO were poor, and their wetting angles were about 90° at melting point. The wetting angles reduced with the increase of wetting temperature, but the influence of temperature was small. Fe and Fe-Cr containing Cr 50% or less could react with TiO on the interface to form Fe₂Ti and Ti₂O₃, but this did not improve the wettability effectively. When Ni-Ti was added into Fe-Cr alloy, Ni₃Ti was formed on the interface, which can reduce the interface energy, improve the wettability, and prevent the formation of Fe₂Ti and Ti₂O₃. The wetting angles could go down to about 40° when 3% Ni-Ti was added to Fe-Cr alloy. Biography of the first author: LI Qing-kui, Dr., senior engineer, born in August 1966, majoring in rare metal materials.