Hot pressing forming experiment of the rice straw and sawdust mixed material

Abstract: The former result of cold pressing forming experiments for rice straw showed that the rice straw cold pellets had poor quality. We found that wood chips had a high content of lignin which can take the function of the binder in high temperature condition. To improve the quality of rice straw pellets, it was proposed to take some wood chips added to the rice straw materials which could form the mixed raw material with the research carried out through the test method. We chose raw straw material which was produced in the south area of Anhui, 2012 and wood processing plant residues - pine sawdust. The equipment of closed compressing molding experiment were design by ourselves. Firstly, pellets' physical properties (loose density, shatter resistance, compressive forces and water resistance) were chosen as judgment criteria, and contrast hot pressing forming experiments was carried out to investigate the effect of different materials(rice straw, wood chips and 1:1 blends of rice straw and wood chips) on pellets. Two hours later after experiment, physical properties were tested, and the date were analyzed by DESIGN EXPERT8.0 with the orthogonal design method of multi-index analysis-comprehensive balance. By analyzing the results of contrast tests, we find that under lower compressive forces, the comprehensive physical (loose density, shatter resistance and compressive forces properties) of 1:1 blend material pellets were better than rice straw pellets and wood chips material pellets, and the results also indicated that added wood chips in the rice straw material can indeed improve the quality of single rice straw material pellets. However, because of the structural feature of wood chips material, the 1:1 blends of rice straw and wood chips material pellets were more weaker than rice straw and wood chips materials pellets in the respects of water resistance physical property. In the actual production, one or more physical properties should be requested high based on the specified use of pellets. Therefore, to further research the effect of blends on the quality of pellets, secondly, we take mixing materials of rice straw and wood chips as research object, a set of orthogonal hot pressing forming experiment with three factors and four levels were used to investigate the effect of compressive forces, mixing ratio and temperature on mixing materials pellets. It aimed to respectively get the most significant effect factors and the reasonable combination of three parameters (compressive forces, mixing ratio and temperature) for each pellets' physical property and the result will testify by test. The orthogonal experiment results indicated that each process parameter had different impact extent to various physical properties. Indexes of loose density, shatter resistance and compressive strength were strongly correlated with compressive force, and the mixing ratio has massive effect on the index of water resistance. The reasonable parameter combination for water resistance and compressive strength: the mixing ratio was 1.5:1 and the temperature was 90℃ and compressive strength was 31.11 MPa. The reasonable parameter combination (mixing ratio，temperature and compressive forces) for loose density was 0.5:1×70℃×31.11 MPa, and for shatter resistance was 2:1×110℃×31.11 MPa. Third, in order to testified the orthogonal experiment results, each reasonable parameter combination of physical property were text contrast with the reference group. The contrast group for physical properties (loose density, shatter resistance, compressive forces and water resistance) were respectively group two, group sixteen, group eleven, group seven. Other parameters of experiment were same as much as possible. Two hours later after experiment, physical properties (loose density, shatter resistance, compressive forces and water resistance) were tested and the date were analyzed. The result showed that each estimated value of treatment group are higher than reference group value, so the orthogonal experiment results were testified. The conclusion can provide technical support for industrialized production of rice straw molding fuel.