Study On The Particle-scale Wear Model Based On Shear Impact Energy And Its Applications

Wear arises frequently in the plants of energy and chemical industry.Meanwhile,coal is very important due to the fact that our country does not have much oil and gas.In the coal industry,various types of equipment undergo severe wear,including the liner wear of coal mill,the erosion of the piping systems,the erosion within fluidized bed and so on.Wear can cause huge time cost and economic loss and is one of the foci in the engineering science field.With the rapid development of the computer technology,an accurate and efficient numerical approach for predicting wear can significantly reduce the time cost of the design of the equipment and guide the maintenance during operation.The main content of the present thesis can be given as follows:(1)A new particle-scale wear model for Discrete Element Method(DEM)– Shear Impact Energy Model(SIEM),is proposed.In DEM,a smaller stiffness coefficient is in general used to reduce the time cost of simulations.The shear impact energy is affected by the stiffness coefficient.Therefore,a new method for calculating the contact point is proposed to exclude the effect of the stiffness coefficient.Comparing the shear impact energy obtained using DEM simulations and the erosion calculated using Finnie’s theory,it can be found that an evident proportional relationship exists between the shear impact energy and wear.After thousands of simulations,it can be concluded that the proportionality coefficient is a constant,and the SIEM is proposed based on the shear impact energy.The SIEM is validated using Finnie’s theory and experimental data.Comparing with Finnie’s model,only the shear impact energy is used for calculating wear,i.e.the impact velocity and impact angle are not necessary.Therefore,the SIEM is also suitable when the particle concentration is large(i.e.large amount of wear is caused by non-direct impacts and sliding,whereas no impact velocity and angle can be obtained).(2)DEM-SIEM is used to investigate the liner wear within tumbling mills.The wear rate and distribution predicted agree with the corresponding experimental data well,which indicates that the approach can accurately predict wear caused by very dense particle phase.The effect of the rotation speed and lifter shape on liner wear is investigated using the current approach.Moreover,a synthetic evaluation of the effect of the rotation speed and lifter shape on wear and energy utilization is conducted.In addition,the effect of ore particle size on liner wear is also investigated using the approach.The results confirm that wear due to small particles is smaller than that due to large particles,though the frequency of the collisions is larger between small particles and liners.The effect of the particle shape on liner wear is also investigated using non-spherical DEM-SIEM.The results show that the particle shape has important influence on liner wear,especially the wear on the top surface of the lifters.(3)CFD-DEM-SIEM is used to predict erosion within piping system and fluidized bed.Firstly,the erosion of elbow due to dilute gas-solid flow is simulated using the approach.The simulation results are validated against corresponding experimental data,which indicates that the current approach can accurately predict erosion due to dilute solid phase.The effect of the coupling method on the erosion of elbow predicted is numerically investigated under different particle concentrations.The results indicate that for the particle concentration in the current work,the oneway coupling method is in general accurate enough for predicting elbow erosion,which can significantely reduce the time cost comparing with two-way coupling method.Secondly,the CFDDEM combined with SIEM is also used to predict erosion of the staggered immersed tubes within a 2D bubbling fluidized bed in this thesis and the simulation results are validated against corresponding experimental data.The characteristics of the tube wear are related to the internal recirculation of the solid phase.Comparing with the simulation results of a 3D fluidized bed,it can be concluded that the erosion of the tubes near the centerline of the fluidized bed is mainly due to the average particle speed(i.e.the ordered motion of the particles),whereas the erosion of the tubes adjacent to the side walls of the fluidized bed is mainly due to the chaos degree of the particle motion(i.e.the fluctuation energy of the particles).