Study On Mesostructure And Damage Characteristics For Coal And Gangue Particles Based On X-Ray CT

In coal mining processing, it would met different geological layers and varieties rocks. Coal and gangue are anisotropic heterogeneous particles with different properties. According to the difference of meso-structure, physical-mechanical properties in coal gangue particles, digital image process(DIP) technology has been proposed to study the meso-structure, damage characteristic of coal and gangue particles, which has great significance to improve the separation efficiency and crushing efficiency?reducing energy consumption of coal and gangue particles. In this dissertation, morphological parameters?meso-structure parameters and physical-mechanical parameters of coal and gangue particles are selected as research object based on DIP, the methods of theoretical analysis, numerical simulation experiment and impact experiments are used to study the damage characteristic of coal and gangue particles.CT scanning experiments of coal and gangue particles with different particle size are carried based on different CT scanning technology. Quantitative characterization of spatial location?distribution pattern and content of different mineral phases in the interior particle are realized based on traditional segmentation method and feature-based segmentation method. It provided basic data for numerical experiments of coal and gangue damage characteristics. The CT value distribution of four types coal and gangue particles(coal without inclusion, gangue without inclusion, locked middlings and coal with high density minerals) are studied based on DIP. The results indicated that CT value of coal and gangue particles are followed with normal distribution; the density of coal gangue particles and CT value are followed with linear relationship; the mathematical function between density and CT value of coal and gangue particles are established. It realized non-destructive determination of coal and gangue particles densities.3D reconstruction of coal and gangue particles can be realized based on marching cube and volume rending methods, which can be used to analyze morphology parameters, meso-structure parameters and physical-mechanical parameters of coal and gangue particles. Analysis showed that elongation and zingg index increased with the increasing particle size, but flatness ratio decreases with the increasing particle size. The degree of particle shape irregularity increases with the decrease of sphericity coefficient; meso-structure parameters in each cross section of coal gangue particle are not the same, which indicated that damage degree in each cross section of coal gangue particle are totally different;the intensity of particle inner part with more cracks, and caking place with different mineral phases are relatively weak, and fragmentation will take place more easily.This study provided the way to quantitative analyze of morphology parameters and meso-structure parameters of coal and gangue particles, which is also provide a new method for the study the breakage characteristics for coal and gangue particles.Physical-mechanical parameters of coal and gangue particles can be quantitative characterized and calculated based on finite mixture model and meso-mechanical theory. Analysis results showed that density can be quantitatively calculated for four types coal and gangue particles(coal without inclusion, gangue without inclusion, locked middlings and coal with high density minerals) based on finite mixture model. The calculation results are basically consistent with the traditional drainage method, which has been verified the feasibility of determination of the density of coal gangue particles based on finite mixture model. The equivalent elastic modulus and equivalent Poisson's ratio can be calculated for coal and gangue particles by using the method of mixture rate theory of composite materials. The calculation results showed that physical-mechanical parameters of coal and gangue particles are not the same, which is further verified the heterogeneity of coal and gangue particles. The study provided experimental data for the particle breakage simulation analysis of coal and gangue particles.Numerical simulations of non-spherical agglomerates impacting a target wall are designed, built and analyzed. The agglomerate experiences a large plastic deformation after impact before disintegrating into small debris. Most of the small debris after breakage is primarily near the agglomerate–wall interface, and fragments are created at the top part of the agglomerate. An impact simulation of spherical agglomerate has been performed to examine how the breakage behavior is affected by different impact velocities. The results showed that better breakage performance can be achieved at a higher impact velocity. The collision behavior of non-spherical agglomerates is shown to be more complex than spherical agglomerates. The debris and fragments created by the agglomerate during impact are shown to be independent of the particle shape and impact mode. The maximum wall force and the damage ratio both decrease as the sphericity increases under the face-impact mode, but increase as the sphericity increases under the edge-impact and vertex-impact modes. Detailed examinations of the evolutions of the damage ratio and the wall force show that the contact area size plays an important role in agglomerate's breakage behavior. Most values of the maximum wall force and the final damage ratio tend to decrease under the face-impact, edge-impact and vertex-impact modes, but most of these values are still significantly higher than that of spherical agglomerate. Agglomerates with a smaller sphericity are shown to be significantly influenced by the impact mode. It can also be concluded that minor changes in the sphericity can result in a significant difference in the fracture patterns of non-spherical agglomerates.Numerical model can be established based on the method of DIP-FEM, the dimensionless group of numerical model is also established based on dimensional analysis. Based on the assumption of the impacting wall is infinite quality, the impact force of coal particle is the function of dimensionless E/V2?. The impact force of coal particle increases with the increasing impact velocity; impact force also increases with the increasing particle size for coal and gangue; the gangue impact force is much higher than that coal particle due to the hardness difference between coal and gangue. The research results provide the basis for the selection of impact force for impact crusher.The influence factors of underground coal and gangue separation has been studied by using the orthogonal test method and support vector machine, which is used to determine the best process scheme of coal and gangue separation; fracture rate for coal and gangue particle under different crushing conditions were analyzed based on X-Ray CT technology and digital image processing technology, which is quantitatively analyzed the damage characteristics under different crushing conditions for coal and gangue particles. The research has provided the basis for the selection of parameters for impact crusher.