Zong Yixiang, Wan Fangxin, Pu Jun, Huang Xiaopeng
Abstract: This paper summarizes the research status of biomass granulation molding mechanism at home and abroad, and elaborates on the three aspects of biomass granulation molding mechanics model, granulation molding compression process and micro forming mechanism, and points out that China's biomass granulation molding The research direction of the mechanism.
Biomass raw materials mainly include crop stalks, firewood, and forestry processing residues, municipal solid waste, livestock manure, and energy crops. Biomass applications involve energy, feed, fertilizers, sewage treatment, powder metallurgy, fuel cells, papermaking, etc. Multiple fields[1].
Biomass granulation molding technology compresses various types of biomass materials with lower density into denser shaped particles by pressurizing [2- 4]Currently, molding processes and forming equipment are the main research directions for biomass granulation molding technology at home and abroad. Wet compression molding, hot press molding and carbonization molding are the main molding technologies; spiral extrusion molding machines, piston stamping Molding machines and roll-type molding machines are widely used molding equipment. The granulation molding equipment is divided into ring molds, flat molds and spiral extrusion molding machines. Now, significant progress has been made in the molding process and molding equipment. However, the research on the mechanism of biomass granulation molding is not enough. The biomass granulation molding mechanism is an important part of the research on biomass granulation molding technology, which can be used for the formulation of biomass granulation molding process and the design of molding equipment. And optimization provides the theoretical basis.
1 Research status of biomass granulation molding mechanism
At present, the research on the mechanism of biomass granulation molding mainly focuses on the three aspects of granulation molding mechanics model, granulation molding compression process and microscopic forming mechanism.
1.1 Research status of granulation molding mechanics model
Holm et al. [5- 7]The mechanical model of the extrusion of the wood powder in the ring mold hole was established. The extrusion force mechanics model was deduced, and the mechanical model was improved to solve the Poisson's ratio, the friction coefficient and the pre-force. Difficult to determine the problem. Osobov [8]The grass particles were used as raw materials for testing and analysis, and the influence of the initial density and compression degree of the material on the magnitude of the compression force was obtained. Rolfe et al. [9]It is proposed that the extrusion force is inversely proportional to the rotational speed of the ring die. Adapa et al. [10]Under the same brewing conditions, the particle quality contrast test between dried and dehydrated valerian was carried out, and the hardness model of alfalfa granules was established.
Cao Kang et al. [11]The process of extrusion granulation is divided into feeding zone, deformation zone, extrusion zone, and the mechanical analysis of the stress state of the extrusion zone. Wu Jinfeng et al. [12]The granulation process simulation experiments were carried out on alfalfa meal with different particle sizes, and a mathematical model for extrusion force and powder particle size and density was established. [13]Orthogonal experimental design was used to establish a mathematical model of granulation density, extrusion force, and material moisture content. [14]Using electrical measurement technology, we obtained the conclusion that the change in radial force and the compression density, the initial density and the compression speed are closely related. [15]The force of the material in the die cylinder was analyzed, the relationship between the material and the pressure was obtained, and the relationship between the axial stress and radial stress was analyzed. Shi Shuijuan et al. [16]An extrusion mechanics model was established, and the finite element software was used to analyze the ring mode. The relationship between the axial mode, circumferential stress, and displacement was obtained. Zhang Wei et al. [17]The finite element software was used for static analysis of the ring mold hole to obtain the distribution law of the axial stress and deformation of the ring mold hole. The effect of the ring mold hole taper angle on the axial stress was determined. Wu Kai et al. [18]By analyzing the forming process and mechanism, a ring model mechanical model and a torque model were established. The influence of material properties and structural parameters on the ring model stress was analyzed.
1.2 Research status of granulation molding compression process
Rehkuglar et al [19]The rheological mechanics model was used to analyze the variation of materials in the forming process. Bock et al. [20]The compressive stress test of the grass material was conducted and the rheological equation of the compression process of the grass material was obtained. The greatest impact on the biomass compression molding is the filling characteristics, rheological properties and compression characteristics of the particles, among which the pressure, the moisture content and the particle size Is the main influencing factor [21]. Bock et al. [22]It was found that during the granulation process of grass particles, the physical force connecting the grass particles determines the particle quality.
Yang Mingzheng et al [23]The rheological properties of straw materials were studied. Zhong Qixin et al. [24]By analyzing the relationship between the interaction forces of the particles in the compression process, the factors influencing the particle quality are obtained. Bai Wei et al. [25]The straw granules were subjected to compression molding simulation experiments. In order to study the compression process more specifically, the forming characteristic curve was divided into four sections, and a mathematical model for the loose, transitional and compaction phases was established. [26]The discrete element method was used to simulate the compaction process of corn stalk powder, and a discrete element analysis model for the compact formation process of corn stalk powder was established. [27]The mechanics model of the compression process was established from the perspective of plasticity theory. The finite element analysis software was used to simulate the extrusion process to obtain the variation law of the material during the extrusion process, revealing the internal stress and strain of the biomass during the molding process. Change process. High reputation [28]Finite element simulation was performed on the temperature field during the molding process, and the distribution law of the temperature field of the biomass during the molding process was obtained. [29]Finite element software was used to analyze the coupled physics of the ring mode, and the distribution of the stress, strain and temperature field of the ring mode was obtained.
1.3 Research status of microscopic forming mechanism
Lindley et al. [30]The type of bonding force and the bonding method inside the molding are divided into the following five categories: 1 bridging or bridging of solid particles; 2 bonding force of a non-freely moving adhesive; 3 surface tension and capillary pressure of a freely moving liquid; 4 particles The molecular attraction or electrostatic attraction; 5 filling or fitting between solid particles. They believe that the biomass combustion characteristics can be used to explain the internal molding mechanism. Kaliyan et al. [31]It was found that the bonding between particles was mainly bridged by solids formed by natural binders (cellulose, proteins).
Guo Kangquan et al [32]The two-way average particle size of the particles under different molding conditions was measured, and the relationship between the two-dimensional average particle diameters of the particles and the molding conditions was obtained. The microscopic binding model of the particles was established by microscopic observation of the particle-to-particle bonding pattern. Xu Guangyin et al. [33]By comparing the changes of the microstructure of the three kinds of straws before and after compression, the micro-combination method of the straw molding particles was obtained, and the optimal compression conditions were proposed. Tian Yuyu et al. [34]The microstructure of straw granules was observed under different forming conditions, and the relationship between the molding conditions and the microstructure was analyzed. The results showed that the combination of straw granules mainly consisted of mechanical inlays and natural binders. Holley et al. [35]By comparing the material micro-morphology and particle binding form of different materials and phases, the micro-mechanism of biomass particle fuel formation is classified into layered compression, which can be divided into central layer, transition layer and surface layer compression. Xing Xianjun et al. [36]The microscopic morphology during the formation of biomass particles was observed and studied, and the combined form of the pellets and the granular areas between the feeding area, compaction area, compaction area, and the forming area of the flat mold forming machine was investigated. [37]The mechanism of microscopic formation of rice hull granules was analyzed from the physical combination form. Studies have shown that ‘pillars’ is the main form of physical binding between rice husk raw materials. Sheng Kuichuan et al. [38]From the macroscopic and microscopic perspectives, the mechanism of biomass formation was studied. The influence of molding conditions on the physical properties of particles was analyzed from the macroscopic perspective. The relationship between particle quality and particle characteristics, biochemical characteristics and potential characteristics was analyzed from a microscopic perspective. Wu Yunyu et al. [39]A geometric contact model of biomass was established to determine the mathematical relationship between the positive pressure of the pressure roller and the surface angle of the biomass. The microscopic mechanism of the molecular electrochemistry and the microscopic mechanism of the energy were analyzed, and the role of the compression temperature in the compression molding process was revealed. And the importance of the reason for the increase in the energy and density of biomass forming fuels.
2 Research and Prospect of Biomass Granulation Molding Mechanism
From the research status, the research on the formation mechanism of biomass granulation has made great progress. In the study of the mechanical model, several mathematical models and torque models for the mechanical properties of the ring mold have been established; in the research of the compression process, The research on the mechanical properties and rheological properties of materials has made great progress. In the study of the micro-mechanism, the micro-molded structure of different materials and the combination of particles have been revealed. The macro-to-micro transitional molding has been initially established. Mechanisms. These research results provide a theoretical basis for the formulation of biomass granulation processes and optimization of molding equipment. In the future, the following aspects should be studied in depth.
(1) Most of the materials used in granulation molding belong to the non-continuous medium of powders and particles. The mechanical properties of discontinuous media are applicable to the mechanical analysis of biomass particles. The current theoretical research on discontinuous media is not enough to deepen people's understanding. To reveal the mechanical properties of materials in the granulation process, the mechanical theory of discontinuous media should be perfected.
(2) Extensive research was conducted on the mechanical model of biomass granulation molding, and many extrusion mechanics models were established, but these mechanical models are based on a single material and under certain compression conditions. Materials used in granulation molding There are many differences, and there are also great differences in the molding and compression conditions. Therefore, it is necessary to establish a more adaptable material extrusion mechanics model and mathematical model.
(3) At present, in the research of biomass granulation molding and compression process, only a single physical field has been numerically simulated, such as pressure field, temperature field or velocity field, etc. Because of the complexity, variability and Systematic, so only a single physical field analysis can not fully reflect the material changes in the granulation molding process, the need for a multi-field coupled physical field analysis. Second, the research on the biomass compression process is mainly focused on rheology In terms of academic characteristics and mechanical properties, deep research is needed on particle characteristics, biochemical characteristics, and electrical properties in the compression process.
(4) The research on the microscopic forming mechanism of biomass granulation mainly focuses on the microscopic characterization of the internal structure of biomass particles before and after compression, and only some qualitative analysis is performed on the binding forms between particles. Combining qualitative and quantitative analysis It is only able to interpret the micro-shaping mechanism more comprehensively. It is more conducive to explore the influence of the microscopic structure of particles and the combination of particles on the granulation quality.
(5) The research on the mechanism of biomass granulation molding is mainly focused on the physical level. The changes in the chemical composition of materials during the molding process and the chemical bonding methods between particles are still in the initial stage. In order to understand the granulation molding mechanism more clearly , The combination of physics and chemistry requires deep research on granulation molding technology.
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