Analysis Of Twin-roll Granulation Extrusion Process

As a developing country with a population of 1.4 billion,China’s agricultural industry accounts for a huge proportion of the national industry.Most regions require low-cost and efficient use of clean energy in daily life,while redundant biomass resources in agricultural production are only simply utilized.The development of biomass granulation machinery has constrained the process of biomass resource utilization.A dynamic granulation structure design scheme for biomass such as straw,which integrates harvesting and granulation molding,has been proposed in response to the above situation;The analysis of the current material solidification process is limited to the mechanical characteristics of the material and mold.Through theoretical analysis and simulation experiments,the thermal coupling,temperature field and other states during the forming process are comprehensively considered;In response to the problem of excessive volume in the design of the double roller granulation mechanism,volume optimization was carried out on the structural components of the double roller pressure roller.The main work content is summarized as follows:(1)Analysis of biomass compression molding mechanism.Based on the composition and properties of biomass,it is determined that biomass has the possibility of being compressed and compacted.By sorting out the advantages and disadvantages of biomass compression molding technology,the pressing roller molding process in hot pressing molding is selected from wet pressing molding,carbonization molding,hot pressing molding,and other processes.Based on the factors that affect the formation of biomass compressed materials,the biomass compression molding process is divided into four stages to introduce the overall compression process of biomass and explain the mechanism of biomass compression molding.(2)Overall design and analysis of double roll granulator.Based on the functional requirements of the field dynamic real-time granulation of the granulator,the overall design scheme of the dual roll granulator has been determined,which integrates the picking system,material input system,granulation pressure roller to roller system,particle conveying system,screening and conveying lifting system.(3)Structural mechanics analysis of twin roll pelletizing extrusion.Through theoretical analysis of the meshing motion of the pressure roller and the extrusion force analysis of the material in the mold cavity,it is determined that the roller made of 45 steel meets the requirements for strength,stiffness,and other performance.By using finite element theory,the relationship between the strain of the pressure roller and node coordinates,node displacement,as well as the relationship between stress and strain within the pressure roller element can be obtained.The constitutive relationship of materials is characterized by the relationship between stress increment {dσ} and strain increment{dε}.The simulation calculation shows that the particle density ρ颗 after molding is 1.058×10-6kg·mm-3.The industry standard for granular fuel stipulates that the density of formed fuel should be greater than 1×10-6kg·mm-3,indicating that the dual roll granulation scheme is feasible.(4)CAE thermal analysis of the twin-roll granulation extrusion molding process.Based on the finite element analysis theory of temperature field,the relationship between element temperature and node coordinates is obtained through operation and transformation.The thermal conductivity differential equation during the heat transfer process of the temperature field is obtained,and the basic equation of the temperature field finite element is obtained through the weighted residual method.The relationship between stress and strain,the relationship between strain and displacement,the relationship between thermal stress and displacement,and the relationship between initial strain are obtained by applying the pressure roll and material structural mechanics to the thermal stress analysis.Based on the simulation results of the deformation and equivalent stress of the pressure roller and material structure,the coupling deformation and equivalent stress of the pressure roller and material in the thermally coupled state are compared,and it is found that the deformation and stress values of the pressure roller and material in the thermally coupled state have different increases.(5)Optimization of roller design.By analyzing the structure of the pressure roller,a specific volume calculation formula for the pressure roller was proposed as the objective function for volume optimization.Five optimization constraints,including bending fatigue conditions for the pressure roller tooth root,contact fatigue strength conditions for the pressure roller tooth surface,pressure roller root cutting conditions,pressure roller work efficiency,and straw particle forming size,were set up to jointly construct a mathematical model for volume optimization of the pressure roller.Based on the PSO algorithm,an adaptive mutation operation was introduced to construct an algorithm based on adaptive mutation particle swarm optimization.Through this algorithm,the mathematical model for optimizing the volume of the pressure roller was solved and optimized.After iteration,the optimal value of the volume of the roller model was obtained,which reduced by 21.54%compared to the original design scheme.The innovation of the research work is reflected in proposing a dynamic granulator design scheme that combines closed chain transmission and double roller rolling,which is different from static granulators.It is more conducive to achieving the integration of harvesting and granulation of straw and other harvested materials.On the basis of this plan,the coupling analysis of the temperature field and thermal coupling between the granulation process material and the pressure roller was studied based on finite element and thermodynamic theories,further exploring the crop solidification molding technology.