微波激励下煤岩颗粒间电场强化特性研究

Characteristics of electric field strengthening between coal-mineral particles under microwave irradiation

  • 摘要: 微波辐射诱发的热效应与非热效应均会对煤岩产生一系列的影响,微波感应放电属于微波非热效应中的一种现象。煤作为一种非均质性强的多孔、富矿的骨架结构,内部的孔隙、矿物等均会对电场产生影响,不同组分颗粒间的微波放电现象及电场强化特性具有较大差别;而目前相关研究主要围绕在煤体中的煤基质上,忽略了煤体中的矿物及矿物本身形状不规则性带来的影响,导致对真实矿物颗粒间的放电机制以及影响其放电强度的因素仍不清楚。因此,通过绘图软件将电子计算机X射线断层扫描机(XCT)扫描获得的真实煤岩颗粒形状描绘出来,利用COMSOL Multiphyics软件模拟了微波场下真实煤岩颗粒的电场强化特性,并探讨了其产生的原因。结果表明:微波的传播方式及极化特性对颗粒间电场强化有显著影响,颗粒间电场强度在x传播y极化时最大;相对于其他五种颗粒组合,粒径和间距对黄铁矿−黄铁矿组合的电场强化效果最明显,煤岩颗粒组合电场强化的最佳效果出现在大粒径、无间距的情况下;颗粒间夹角的变化对电场强化效果有一定的影响,而且各颗粒形状对应的电场强化最大值均出现在夹角为0°时;规则矿石颗粒(圆、正方形、五边形等)的电场强化效果与颗粒圆度系数直接相关,颗粒间电场强度最大值出现在颗粒尖端角度为60°左右、圆度系数为0.71的正三角形时;而不规则矿石颗粒的电场强度与圆度系数、分形维数并无关系,且随曲率的增大而逐渐增大;此外,碳质材料的石墨化程度会对电场强化效应产生较大的影响,电场强度随着石墨化程度增加而增加。

     

    Abstract: Both thermal and non-thermal effects induced by microwave radiation can produce a series of effects on coal and rock, and microwave induced discharge is one of the phenomena of microwave non-thermal effects. Coal has a porous and ore-rich skeleton structure with strong heterogeneity. Its internal pores and minerals can affect the electric field. The microwave discharge phenomenon and electric field strengthening characteristics between different component particles are quite different. At present, the relevant researches mainly focus on the coal matrix in the coal body, ignoring the influence of the minerals in the coal body and the irregular shape of the minerals themselves. As a result, the discharge mechanism between real mineral particles and the factors affecting its discharge intensity are still unclear. Therefore, the shape of real coal and rock particles scanned by electronic X-ray tomography (XCT) was described by drawing software, and COMSOL Multiphysics software was used by in this work to discuss the electric field strengthening characteristics of real coal and rock particles under a microwave field and the causes. The results show that the propagation mode and polarization characteristics of microwave have a significant effect on the enhancement of the intergranular electric field, and the intensity of the intergranlar electric field is the largest in x propagation and y polarization. Compared with the other five particle combinations, the particle size and spacing have the most obvious effect on the electric field strengthening of the pyrite-pyrite combination, and the best effect of the electric field strengthening of the coal-rock particle combination appears in the case of large particle size and no spacing. The change of the Angle between particles has a certain influence on the effect of electric field strengthening, and the maximum value of electric field strengthening corresponding to each particle shape appears when the Angle is 0°. The electric field strengthening effect of regular ore particles (round, square, pentagon, etc.) is directly related to the roundness coefficient of the particles. The maximum electric field strength between particles occurs when the Angle of particle tip is about 60° and the roundness coefficient is 0.71. However, the electric field intensity of irregular ore particles has no relation with roundness coefficient and fractal dimension, but gradually increases with the increase of curvature. In addition, the degree of graphitization of carbonaceous materials has a great influence on the electric field strengthening effect, and the electric field intensity increases with the increase of graphitization degree.

     

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