Research On The Shredding And Efficient Combustion Of Biomass

The shredding technology of biomass can not only overcome such disadvantages as low energy density and large space placement when biomass is in the initial condition but also offer the pretreatment technology for biomass utilization in energy, feedstuff, fertilizer and material fields. Based on the technology, this dissertation presents an efficient energy transformation method by combusting biomass directly in powder, which can help reduce the dependence upon petroleum and has significant environmental benefits.The shredding of agro-residues, such as corn stalk, straw, wood sawdust and other herbaceous biomass, were investigated in this dissertation. According to the machinery mechanics of shredding, the components, shearing strength and pressive strength of the biomass were analysed in theory, which played a critical role during the shredding process. And the powder was examined by Scanning Electron Microscopy. It was founded that shearing,splitting and grinding force were appropriate for shredding biomass. The results also showed that primary shredding was the bulk shredding model, which was mainly affected by shearing and splitting force, therefore the curly knife and the straight knife were useful; while the fine shredding was the surface shredding model, affected by splitting and grinding force, and the straight knife useful. The biomass shredding system was finally achieved through many practices and improvements, including the primary shredder, the fine shredder and the cyclone dust collector used as collecting device. The results indicated that the particle size of the primary shredded biomass was about 10mm with the production of 200kg/h, and that of the fine was between 0.177 mm and 0.125mm on different working parameters with the highest production of 160kg/h.Proximate analysis and ultimate analysis of biomass were studied. And the results of the biomass pyrolysis-combustion research by other scholars were used for reference. Then the three-step combustion model for the powder fuel was assumed, furthermore, based on which the circumfluence furnace especially for biomass powder fuel was designed. A series of experiments were conducted to characterize the powder fuel`s combustion properties by the furnace and other cooperated devices. The results showed that volume characteristic and particle size properties were the most important to powder combustion. It could not be ignited when the particle size above 0.42mm in the furnace. The optimal proportion of biomass powder to wind was 240g/m3. And the amount of powder needed in the furnace in an hour was decided by the main firebox`s volume. Considering combustion efficiency and the shredding cost, the optimal particle size was about 0.177mm. Under the condition of optimal proportion of biomass powder to wind and the particle size about 0.177mm, the powder was suspended in the furnace and formed volume combustion, which was mainly acted in the gas phase. The combustion deposits was fine with little stickiness, fouling and slagging. And the temperature field distributed regularly in the furnace. The highest temperature could reach 1336℃, and the hearth could obtain 900℃. When the total pressure was out of the furnace`s limitation, it would be unsafe. So the possibility of the powder quantity excessing the furnace`s limitation pressure must be noticed .In conclusion, compared with combusting biomass in the initial condition, the method of combustion biomass in powder by the circumfluence furnace can greatly improve the combustion properties and effiency.