| As one of the sandy shrub species,Salix miltiorrhiza has the advantages of flat stubble and rejuvenated growth,developed root systems,and extremely fast growth rates.It is a typical energy tree species in sandy regions in northwest China.Due to the lack of awareness of this type of resources for a long time,and the shortcomings of such biomass resources being scattered,difficult to store,and high transportation costs,this type of resources cannot be effectively used.Therefore,compacting Shaliu biomass into a biomass pellet fuel with high heating value and convenient storage and transportation can not only make it effectively used,but also alleviate problems such as energy shortage and environmental pollution,and also bring certain economic benefits.This article focuses on the factors that affect the energy consumption and product quality of Salix granules during the compact molding process,focusing on the internal causes of the impact of the geometry of the raw materials on the friction characteristics and energy consumption,and the different effects of the molding die shaft section on the energy consumption.Finally,the compression process parameters are studied and the glass transition temperature of lignin is simulated to explore the deep-seated causes of the bonding mechanism,which provides theoretical guidance for the"high quality and low energy consumption"of dense biomass molding.Biomass compact molding,in addition to the influence of factors such as material type,particle morphology,mold structure,molding pressure,and moisture content,as the temperature increases,the lignin inside the material will change from glass to adhesive,thereby acts as a natural binder;in the molding process at room temperature,this temperature mainly comes from the friction between the particles and the particles and the mold.This paper takes crushed Salix twig particles as the research object,with the help of discrete element method suitable for numerical simulation of bulk materials,and molecular simulation technology suitable for microscopic particle research,the mechanical properties of material particles in the compact molding process,the forming mechanism and the bonding mechanism were studied;the relationship between the friction angle（rest angle）of the particles with various factors was analyzed by the software EDEM,and the influence of the cross-sectional structure of the mold axis on the forming process and fuel quality was studied.The stress and deformation characteristics of individual particles under different conditions,as well as the effects of various parameters on fuel molding quality and power consumption;through the software Material Studio,the effects of pressure,temperature,moisture,etc.on the glass transition temperature（Tg）,diffusion capacity,and intermolecular interaction of Salix lignin molecules were explored,and the glass transition temperature of lignin under different conditions was obtained,also got diffusion characteristics,formation of hydrogen bonds,etc.and their evolutionary laws.The results show that the friction angle of Salix willow particles is between 43.4°and50.7°.The change of this value is mainly affected by the particle shape,particle size,and non-uniformity coefficient.Secondly,the sphere is the smallest;the friction angle also increases with the increase of the particle size,but gradually flattens;within a given particle size range,the friction angle also increases with the increase of the unevenness（Cu）Slowly increased,but the trend gradually flattened and even collapsed smaller.The cross-sectional structure of the mold axis has an impact on the mechanical process,deformation process,fuel quality,and power consumption of the pellets.Among them,the compression force changes more smoothly and the work is minimized under double radians.Contact between them is also good.Through orthogonal analysis,it was found that when the particle diameter is 1-4 mm,the compression speed is 60 mm·min-1,and the holding time is 75 s,the bonding strength and molding density of the molding fuel are high,and the molding energy consumption is small.Molecular dynamics simulations showed that the glass transition temperatures of Salix salicinus lignin at the moisture content of 8%,11%,14%,and 17%were 410,392,381,and 376 K,respectively;second,the diffusion capacity of the lignin molecules It increases with the increase of temperature,and then increases first and then decreases with the increase of pressure and water content,and reaches the highest value when the pressure is 40 MPa and the water content is 14%;when the water content,pressure and temperature are At 14%,40 MPa and 380 K,water molecules can form hydrogen bonds with lignin molecules.The main source is predicted to be the interaction between water molecules and cyclic or non-cyclic hydroxyl groups.Observation of the microscopic morphology of the molded fuel found that the particles in the vertical direction are mainly combined in the form of layered superposition,and the horizontal direction is mainly combined in the form of tile,overlap,and fit.In addition,there are similar to The stent-like mesh structure exists,which effectively enhances the mechanical strength of the particles.The application of discrete element and molecular simulation techniques to the research on dense forming of Salix sibiricum particles can effectively analyze its forming characteristics and bonding mechanism,which can provide reference and reference for the research and production of biomass. |
