Research On 3D Reconstruction And Seepage Simulation Of Coal-based Porous Media

Coal-based porou media is a kind of porous material with abundant pores and stable physical and chemical properties,and exhibits excellent comprehensive performance and considerable application prospects in many fields.In the fields of filtration,adsorption and impregnation,pore structure is the most important factor affecting fluid flow and permeability,and the pore structure of porous media has typical heterogeneity and randomness.There are some problems such as poor universality and large error in using the existing model.According to the above problem,this article first uses metallographic scanning electron microscope,scanning electron microscope(SEM),CT scans and other equipment to characterize the two-dimensional pore structure and surface morphology of coal-based porous media,and then through three-dimensional visualization software(AVIOZ)to analyze the three-dimensional porous structure,and through the three-dimensional visualization software(Dragonfly)and mercury intrusion experiment to analyze and verify the three-dimensional reconstruction results,finally export finite element model of the real and seepage simulation under different conditions,the following results are obtained:1)Coal-based porous media,which is produced by mixing and burning coal char particles as aggregate and coal pitch as binder under certain temperature,ratio,pressure and other conditions,has fractal characteristics and can be described by fractal theory.The permeable fractal dimension of No.1-5 coal-based porous media is between 2.941-2.979;the skeleton fractal dimension is:2.734-2.983;the tortuosity fractal dimension is between 1.307-1.866.2)Raman,XRD,IR and other experiments were carried out on the prepared coal-based porous carbon to determine its structure and composition.It was found that samples No.1-3 were all amorphous carbon,and the ratio of the intensity of D peak to G peak of the three 0.19,0.39 and 0.21,respectively,which shows that the disorder of the No.2 sample is the largest,the structural defects are the most obvious,and the graphitization is the lowest.On the contrary,sample No.1 has the lowest degree of disorder,the highest degree of graphitization,and the best structural integrity.3)The porosities of samples No.1-3 are 38.2%,28.54%and 42.25%,respectively,which were measured by mercury intrusion experiments and the accuracy of AVIZO threshold segmentation was further verified by Dragonfly.The porosity after three-dimensional reconstruction using AVIZO are 36.72%,28.78%and 40.57%respectively.The porosity error of the two is within±5%,indicating that the threshold segmentation is reasonable and the three-dimensional pore model reconstruction is reasonable.4)The mercury intrusion test measured the specific surface area of No.1-5coal-based porous media between 2.159-6.157 m~2/g;the true density was between1.893-2.1325 g/cm~3;the bulk density was between 1.2089-1.7526 g/cm~3;The permeability is between 0.1934-2642.065 mD;the tortuosity is between3.5268-9.929;the average pore diameter is between 74.6-253.1 nm.5)The relationship between the cumulative impregnated mercury volume and the pressure of impregnated mercury in No.1-3 coal base porous media No.1-3porous carbon exhibited typical percolation characteristics:a.The volume of mercury intrusion is small,and no interconnected percolation network is formed when the intrusion pressure is less than the percolation pressure;b.The mercury intrusion volume increases rapidly and the mercury liquid are in the pores of the coal-based porous media form an interconnected percolation network when the intrusion pressure is greater than the percolation pressure;c.the cumulative mercury immersion volume of each sample showed a slowly increasing trend,and the curve became stable after the mercury intrusion volume changed into a percolation structure.The threshold pressures of No.1-3 coal-based porous media are:8.49,10.5,and 2.87 psia,respectively.6)After meshing and repairing the three-dimensional reconstructed pore model and importing it into FLUENT for simulation,the following conclusions can be drawn:a.Under different inlet pressures,the seepage of porous media generally shows similar laws,and there are local differences.The greater the inlet pressure,the shorter the stabilization time and the greater the outlet velocity.Under the same conditions,the flow rate of gas in porous media is much greater than that of liquid,and the flow rate of nitrogen in porous media is greater than that of carbon dioxide,which shows that the porous carbon has an adsorption effect on carbon dioxide.b.Different fluid media have different starting pressures and stable pressures when seeping through porous media.The starting pressures of nitrogen,water,and carbon dioxide are:1 MPa,3 Mpa and 0.5 Mpa,respectively;the stable pressures are:7MPa,9 Mpa and 6 Mpa,respectively.c.At different speed inlets,the inlet speed is positively related to the required pressure.When the inlet flow velocity is greater than 3 m/s,the connected pores in the porous carbon are divided into two at the central position,forming a"herringbone"shaped connected pore It shows that under a certain pressure,the pressure will affect the fluid seepage.