Studies On Properties Of Stalk Chopping And Briquetting And Performances Of Equipment

There are abundant resources of crop residues in our country, such as rice straw and cotton stalks. It was estimated that the amount of crop residues is 6.4 X108 t. However, they have not been processed and utilized properly with the development of economic and society in the rural areas. A majority of them are burned on farm and result in serious environmental pollution and biomass resource waste. Therefore, it is important that converting agricultural wastes into solid fuels of high quality by biomass conversion technology for ecological environment and agricultural sustainable development. Now more people become to pay attention to converting agricultural and forestry wastes into briquettes with certain shape and density by mechanical pressing.The main purpose of this paper is to investigate the characteristics of crop stalks like cotton stalk, properties of compression or relaxation of biomass briquettes, and binding mechanism. Moreover, the crop stalk chopper and briequtting machine were designed and their performances were tested. The conclusion as follows:1. The structure of the hard stalks of cotton, mulberry and so on differs distinctly from the rice straw or wheat straw. The major cutting counterforce occurs at the bast of xylem of cotton stalk and mulberry branch .The shearing strength of cotton stalk and mulberry branch is greater than wheat straw. The ash content and sulphur content of cotton stalk and mulberry branch are low. Thus, the cotton stalk and mulberry branch are suitable for solid fuel.2. The straight knife chopper was designed fyr chopping crop stalks. It's feeding mechanism can adjust feeding height by itself with different materials. Results of performance test of prototype indicate that the practical capacity of chopping is close to theoretical capacity, and the chopper has advantage of high productivity of fine particles and low energy consumption. The percentage of 0-2 mm particle size is about 71% from chopped cotton stalks.3. The experimental results show there exists difference of the pressure -displacement relationship in different compression, i.e., loose (p:0-8MPa), transition (p: 8-40MPa) and tight compression (p: >40MPa). By means of regressive analysis, the correlative mathematical models of pressure vs.compressive density are established: P =The effect of specific energy on pressure, particle size distribution and moisture content was studied. The results show that the specific energy increases as the pressure increases under the same initial density, but there is no marketable effect on density of briquette under increasing specific energy in tight compression. The specific energy decreases as the particle size and moisture content decreases under the same condition of the maximum pressure.4. Experiments were carried out to study on the effect of pressure, temperature, particle size distribution and moisture content of chopped materials on relax density. The results show that the relax ratio decreases as the pressure increases under the same condition of temperature and initial density, the value of relax ratio of briquettes with normal temperature compressing is more than that of heating compressing under the same condition of the pressure and initial density, the result also shows that there is no marketable effect on the relax density of briquette under heating compressing from 120癈 to 180癈. The relax ratio increases and durability of briquettes decreases as the moisture content of cotton stalks decreases, over dried materials cannot be briquetted. In addition, the binding mechanism of biomass briquettes was discussed on physical properties and bio-chemical characteristics in this paper.5. The process of pre-heating and briquetting system was presented and operation parameters were determined. At last, the pre-heater and piston press machine were studied and designed.