Structural Design And Research Of Wood Pellet Dynamic Screen

As a new kind of biomass energy, wood pellet has following characteristics:moderate density, high calorific value, full combustion, low cost, easy to use and clean. Its main raw materials are three residues of forest, crop stalks and other wooden materials which come from anywhere. These materials have many impurities, high moisture content, and different gradings, so in the preparation stage, we should select the chips and particles of wood or materials similar to wood to prepare for the next process. In the traditional wood pellets production line, people choose the vibrating screen and the classifying screen as the main screening equipment. But the vibrating screen has a fatal weakness which is not suitable for screening wet materials with high moisture content, when using vibrating screen screening wet materials, the materials can easily plug the mesh of the screen, thus the number of the mesh is reduced, the expected goal of screening can not be achieved, and resulting in lower production. The classifying screen also has a fatal weakness:the materials can be sifted out only in the thickness direction. If you want to sift the materials in the length direction, there is no way to complete it.In order to compensate for the deficiencies of the vibrating screen and the classifying screen, we design a new dynamic screen which can screening wet materials with high moisture content and screening the materials in the thickness and length direction. The raw materials need to be sifted always contain dust, sawdust, qualified chips(usually about50mm), oversize chips, so the dynamic screen is divided into three sections, and it has four fractions. The first screening section is used for the removal of the ash and dust in the raw materials, so the rollers in the first screening section adopt the diamond roller which has protruding diamond pattern on its surface. The pattern is smaller and the gap between the two adjacent rollers is smaller too. The second screening section is used for screening the sawdust.In this section, lathing grooves on the main part of the roller, and the depth, width of the scalariform grooves are determined by the gradings of the materials. A roller's circular grooves alternate with the adjacent axis's circular circumferential peaks, all these forming the rectangular discharge gap. The third screening section is used for screening the wood chips. In this section, the roller screening the wood chip is the spline shaft,and the spline belongs to the rectangle spline. The standard sprocket with screw holes is set on the shaft, and the sprocket is settled in the groove of the spline shaft by the bolts. The discharge gate is the space between the two adjacent shafts, which is similar to be rectangular. The wood chips which are within the rectangular size range fall down, but the oversize wood chips out of this size will fall at the edge of the last one axis.The paper also analyzes the screening principle of the wood pellet dynamic screen, and make mechanical analysis of materials' movement on the screening surface, then selects and calculates the main parameters of the dynamic screen. After this the paper uses UG software to do parametric modeling of the screen, and has a interference test of the screen after it has been assembled as the function of the model's late static and dynamic finite element analysis and optimizing design of the structure. At last the paper chooses three basic factors which influences the wood pellet dynamic screen's screening most to do orthogonal experiment, then gains the relationship between primary and secondary of these factors, also gains the optimum process parameters. When the gap between the two adjacent diamond roller is0.8mm, the speed of rollers is125r/min,the inclined angle of the dynamic screen's box is5°, the test proves that the effect of the screen is best.