| In China, the output of maize straw increased year by year, and which has gradually become the first major crop straw in recent years. Utilization of maize straw is related to improve the quality of life and avoid the pollution of environment in the countryside of our country, and involved the increase of soil fertility in agricultural ecosystem security and saving resource as well; it is one of the important factors to realize agriculture sustainable development of our country. With the attention of straw resource, research on straw utilization is also becoming increasingly popular. As maize straw is mainly composed of a certain percentage of rind, pith and leaf, and which are different in chemical composition. Leaf accounts for 45 to 47% in maize straw by mass and is fluffy, but because of its high crude protein, high crude fat and relatively less crude fiber, leaf of maize straw can be used efficiently as animal feed. And its bulking density is so small that it is difficult to storage and transportation leaf of maize straw. Therefore, it is necessary for leaf of maize straw to be condensed into high quality roughage timely.On the basis of test of compression properties of maize straw leaf, and design of the flat mold pelletizer, experiments of pellet properties of maize straw leaf were carried out in the thesis, the main conclusions are as follows:(1)The maize straw leaf was tested to study maximum compression force by Universal Testing Machine and homemade compression device, the maximum compression force was analyzed by three factors——moisture content(%), compression density(g/cm3), loading speed(mm/min). The results indicated that moisture content, density and loading speed had significant effects on the maximum compression force; the influence rules of various factors on the maximum compression force was found: Along with the increase of the moisture content, the maximum compression force decrease obviously; with the increase of compression density, the maximum compression force increase slowly then increase rapidly; With the increase of the loading speed, the maximum compression force increases slowly.(2)On the basis of properties and compression test of maize straw leaf, the flat mold pelletizer was designed. By pre-experiment and theoretical analysis, the following four factor:moisture content(%), mold hole diameter(mm), rotation speed(r/min) and additive proportion(%) have a great influence on pellet quality in this research. Experiments were carried out by the flat mold pelletizer, the suitable parameters were decided as follows: moisture content 19.95%; mold hole diameter 10-12 mm; rotation speed 211 r/min and additive ratio 10.5%, under the condition of the optimized parameters, the pellet productivity is above 98%, crush resistance is higher than 99%, molding rate is greater than 88%, density is greater than 1.28g/cm3.(3)Microstructure of materials and pellet were observed and analyzed by the electronic scanning microscope, results are as follows: original microstructure of maize straw leaf has been changed after compression, new microstructure has been shaped by bulk deformatiom fitting, pellet properties are effected by moisture content, mold hole diameter, rotation speed and additive proportion.(4)On the basis of observation of pelletizing process by high-speed camera and effect analysis of roll, considering properties of maize straw leaf, chute roll is proposed to improve the pelletizing properties. The analog simulation of the working process of chute roll by EDEM software was carried out so as to validate that chute roll play a part on material.The Optimized parameters decided in this thesis can effectively improve the pellet quality and feed quality of maize straw leaf, the productivity can be improved and the wear of mold and roll can be eased for the flat mold pelletizer. |
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