| Salix,as a unique plant that grows in desert areas,has the characteristics of reproducibility,high utilization value,economy and environmental protection,and has become the main target of new energy development.Due to the loose distribution of raw materials of Salix,low energy density,difficult storage and transportation,etc.,it cannot be fully utilized.Therefore,the biomass compacting technology plays a key role,which can transform Salix raw material into high-density,regular-shaped biomass particles,which brings great convenience to people.Aiming at the compact molding process,this paper analyzes the heat transfer mechanism and energy conversion process in the hot pressing process,and studies the evolution law of temperature changes and heat transfer characteristics in detail,which provides a theoretical reference for the promotion and development of biomass compact molding technology.In the process of biomass hot press molding,high temperature is used to soften lignin to reach its melting point,which can improve the molding quality of biomass while reducing the energy consumption of the molding machine.In this paper,the discrete element method is used to simulate the thermo-compression molding of biomass particles.According to the characteristics of temperature rise,the overall change process of biomass particles is divided into three stages:the initial stage,the compression stage,and the pressure-holding stage.Analyze the temperature field gradient changes in each stage;According to the different particle positions,compare its temperature rise changes and temperature differences;Under the same compression conditions,select different particle density,thermal conductivity,specific heat capacity and other related thermodynamic physical properties and change the particle size,shape,compression speed and other controllable physical properties After the model reaches the equilibrium state,the heat transfer effect of the particles is explored during the entire compression process,and the control variable method is used to analyze the significance of the influence of the molding process parameters on the temperature of the biomass particles.The results show that:in the initial stage,the gap between the particles is large,and the temperature does not change significantly;the average particle temperature rises sharply in the compression stage;the temperature change is gentler in the pressure holding stage and finally reaches the thermal equilibrium.Through the research and analysis of single factor variables,it is concluded that when the particle density is 850kg/m~3,the overall temperature of the particles is the highest,the heat transfer rate is accelerated,and the molding quality is the best;the particles with a thermal conductivity of 0.30W/(m·K)are the best.The size of the thermal conductivity determines the speed of temperature heat transfer;the smaller the specific heat capacity of the particles,the greater the temperature rises when the absorbed heat is constant,and the faster the heat transfer rate changes,resulting in a higher overall temperature of the particles after molding,which is conducive to improving the molding quality;When the particle size is equal to 1.0mm,the temperature transfer will show a significant decreasing trend with the increase of the particle size.In the shortest time,the smaller particle size will reach the heat transfer equilibrium point first,and its molding quality will be the best;the particle shape affects the particle transfer The effect of heat speed from large to small is:needle-shaped particles,flake-shaped particles,and spherical particles.The reason is due to the difference in porosity between the particles;under the condition of a certain amount of compression,the molding quality increases with the compression speed.And reduce.Through the analysis of the axial temperature field,the heating rate from fast to slow is:bottom,upper,middle.The above simulation analysis provides reference and reference for the research and production of biomass. |
PDF Full Text Request