Research On Grinding-Classification Characteristics And Energy Dissipation Mechanism Of ZGM Vertical Spindle Mill

The ZGM-type vertical spindle mill（VSM）equipped with a combination classifier is a comminution and grading integrated device.It adopts a vertical configuration,which has the advantages of compact structure and small footprint.It has been widely and successfully applied in the power industry and is the core equipment for producing qualified pulverized fuel（PF）required for pulverized coal boiler combustion.In order to ensure the stable and safe operation of the pulverized coal boiler,coal-fired power stations usually have detailed specifications for the fineness and particle size distribution,i.e.,spread parameter of the PF.To prepare PF that meets the requirements of pulverized coal boiler combustion,the pulverizing system consumes a large amount of energy.In this study,a corehensive approach combining semi-industrial-scale VSM online sampling,simulation experiments employing a Hardgrove machine,and gas-solid two-phase flow numerical simulation methods was used to investigate the influence of the coordinated action of operating parameters of the ZGM-type VSM with a combination classifier on particle comminution,classification,and energy consumption inside the mill.A irregular non-spherical particle drag coefficient model based on a group of particle shape parameters was established to predict the effect of particle shape parameters on classification performance at the model level.Based on the geometric modeling of the full-size VSM and Open FOAM numerical simulation,the spatial distribution of gas-particle flow and the response mechanism of force field to changes in mill operating parameters were studied to clarify the classification mechanism of particles inside the mill.A predictive model group for comminution,classification,and energy consumption in the VSM system was constructed.The above research provides data support and theoretical basis for the prediction of particle comminution,classification,and energy consumption characteristics in the new type of VSM and the optimization of the VSM.In addition to online sampling of the elutriation zone and classifier of the ZGM-16semi-industrial-scale VSM,this study added a sampling point on the outer side of the grinding zone to investigate the classification phenomenon inside the grinding zone.A modified Rosin-Rammler cumulative particle size distribution and particle volume fraction distribution model based on the 90%,75%,50%,25%,and 10%values of the cumulative particle size distribution curve was proposed.The modified Whiten model clarified the physical meaning of each parameter,which is beneficial for further studying the characteristics of the classification efficiency curve.The relationship between the coordinated action of mill parameters and material particle size distribution and mill energy consumption characteristics was clarified,laying the foundation for subsequent research.A relationship model between the irregular non-spherical particle drag coefficient and the particle Reynolds number and a group of particle shape parameters（sphericity,flatness ratio,and roughness ratio）was constructed based on particle-resolved direct numerical simulation（PR-DNS）.A prediction model for particle flatness ratio based on the maximum,intermediate,and minimum projected area of irregular non-spherical particles was proposed.Based on high-speed dynamic photography and validation with classical model results,it was found that the model has high accuracy in predicting the irregular non-spherical particle drag coefficient.It can be used not only for calculating the drag coefficient of irregular non-spherical particles but also for accurately predicting the drag coefficient of spherical and regular non-spherical particles.The applicable range of the constructed model is as follows:particle Reynolds number Re_p∈[1,3000],sphericity?_p∈[0.71,0.86],flatness ratio_dp^dc∈[0.82,1.44],and particle roughness ratio S_{e f}∈[1,1.24].The synergistic migration of complex gas-solid two-phase flow in the mill was investigated.A calculation model for the irregular non-spherical particle drag coefficient was constructed based on the modified Wenyu/Ergun equation.The MP-PIC algorithm and the sliding mesh technique were used to solve the airflow distribution and particle classification process in the VSM under different operating parameters,revealing the motion mechanism of airflow in the VSM and the classification behavior of particles with different properties.The variation mechanism of dimensionless drag force and dimensionless centrifugal force of particles in the mill under different conditions was analyzed,and a spatial dimension model for particle forces was constructed.The above research reveals the influence mechanism of different mill operating parameters and particle property parameters on the particle classification process inside the mill.The energy consumption of different types of PF was analyzed,revealing the synergistic competitive mechanism of particle size and density on the particle distribution of crushed materials.A relationship model between the characteristic particle size and spread parameter of the material and the energy consumption and properties of the material was constructed.Based on the results of online sampling experiments,models for predicting the comminution of material on the mill disc,the power of the main motor and fan,the particle density on the mill disc,and the particle classification in the mill disc,grinding zone,elutriation zone,and classifier were constructed.Models for predicting comminution,classification,and energy consumption were developed and linked to mill operating parameters and particle property parameters,establishing a direct connection between mill parameters and the comminution-classification model.The above models can accurately predict the comminution-classification and energy consumption characteristics of the mill.Based on the results of sampling experiments,numerical simulations,and mathematical models of the mill operation process,prediction of the mill process control and optimization of the mill structure were achieved.A parameter related to the characteristic particle size and spread parameter was constructed to obtain an optimal operating parameter adjustment scheme for energy consumption.A new type of VSM configuration was proposed,which includes adding a set of adjustable blades at the inlet of the elutriation zone to promote stable airflow and improve the classification efficiency of the elutriation zone.Additionally,the bottom flow outlet of the return cone was designed as a closed structure to prevent particles from bypassing the elutriation zone and entering the classifier directly through the return cone.This structure further expands the range of adjustment for particle size distribution at the mill outlet and transforms the particle classification from being controlled by a single force in the elutriation zone to a composite force mechanism.There are 131 figures,25 tables,168 references.