Study On The Plunger-Type Pelletizing Mechanism Of Agricultural And Forestry Residues At Room Temperature

As the clean and renewable energy,the development and utilization of biomass energy has become a focus of attention and research in various countries around the world.Because of a large amount of agricultural and forestry resources,China has the potential to develop biomass energy.Biomass pelletizing technology is an effective way to develop biomass energy.Further studying biomass pelletizing mechanism at room temperature is conducive to the maturity of biomass pelletizing technology and can guide the design and optimization of the biomass pelletizing equipment structure.However,the study on the plunger-type pelletizing mechanism of agricultural and forestry residues at room temperature has not been improved,and there are few relevant verification experiments.In this paper,based on the theory of elastoplastic deformation,the biomass pelletizing process with plunger was studied theoretically.The deformation of the material during compression and the stress of the material in the molding sleeve was analyzed.The relationship between the axial stress and radial stress on the material and the exponential distribution of radial stress along the axial direction of the molding sleeve was obtained.ANS YS was used to simulate the plunger-type pelletizing process of the air dried(7% moisture content)corn straw and caragana in molding sleeves with different length-diameter ratios at room temperature.According to simulation results,the flow and deformation laws of the material were analyzed.MATLAB was used to simulate the radial stress on the material and the curve was fitted to obtain the equation of radial stress changing with the position of materials,which was consistent with the theoretical analysis result.Single-factor experiments of the corn straw and caragana at room temperature were carried out under the condition of 7%,11%,15%,19% moisture content and 3.5,4,4.5,5 length-diameter ratio.The results showed that different agricultural and forestry residues had different pelletizing effects under the same experimental condition.The axial stress variation of different pelletizing results was different.However,the radial stress variation of different raw materials in the pelletizing process was the same,and the error between the experimental data and the simulation data was small,which verified the rationality of the theoretical analysis and the reliability of the finite element simulation.In order to further explore the influence of different pelletizing conditions on the pelletizing effect,plunger-type pelletizing tests were carried out at room temperature with the corn straw and caragana as raw materials,the length-diameter ratio of the molding sleeve,the moisture content,the mass fraction of caragana as experimental factors,the pellet izing pressure,the relaxation density,and the surface quality as evaluation indexes.Through response surface analysis,the 2FI model was selected to establish the multivariate quadratic regression equation of experimental factors on each evaluation index.And the order of signif icant influence of experimental factors on each evaluation index was obtained,and combination of the factor level for the best pelletizing effect was determined: the length-diameter ratio of the molding sleeve is 4,the moisture content is 15%,and the mass fraction of caragana is 30%.Through the microscopic observation of the experimental briquettes,it was found that materials of the end face were bonded in the form of overlap,and the combination effect of peripheral materials was better than center materials;materials on the outer surface broke and flowed due to severe friction,and fitted into each other.In addition,the improper moisture content and length-diameter ratio of the molding sleeve will weaken the bonding strength of the material and affect the bonding between materials.