The Cold Flow Charateristics Of Agricultural And Forestry Wastes In Fluidized Bed

As one of the most important methods in the recycling use of agriculture and forestry waste, pyrolysis technology was widely followed. The gas-solid exchange between gas and bed material and the mixing mechanism of bed material would influence the efficiency of pyrolysis technology used in fluidized bed. The agriculture and forestry waste is difficult to separate the fluidization in fluidized bed due to its physical properties, which need to mix with the quartz sand or other inert component as fluidization medium, therefore it is of great importance to research the mixed flow characteristics of agriculture and forestry waste with quartz sand in fluidized bed.The dynamics characteristics of two-component mixed flow of biomass with quartz sand in fluidized bed had been researched from the aspect of time domain, frequency domain and phase space structure respectively by means of nonlinear analysis method. On that basis, improving the traditional DEM-CFD to make it is more suitable for simulating the mixed flow of large size biomass particles with small size quartz sand, then simulate the two-component fluidized bed in mesoscopic scale, all the simulation results will be tested by experiments, in addition, the gas flow and particle behavior characteristics of mixed flow would be further analyzed.The forming of different mass ratio of agriculture and forestry waste, wood, rice husk, corn cob and rice straw mixed with quartz sand, as bed material in the mixture flow in fluidized bed, measuring the differential pressure pulsation signal in the bed. The superficial gas velocity in the range of 0.072～2.31m/s. Pressure method is used to measure the bed within the minimum fluidization velocity. In the measurement of the initial fluidization velocity of two-component flow, the initial fluidization velocity of two-component flow had little difference under different mixing ratio when the content of agriculture and forestry waste was less than 8%, which is very close as the initial fluidization velocity of one-component flow of quartz sand.Hilbert-Huang Transform analysis method was used in the frequency-domain analysis, which has the characteristics of adaptive, to research the energy and frequency distribution characteristics of Intrinsic Mode Function. The result showed that the effective frequency range was under 30 Hz, the bubble frequency mainly distributed between 1～5 Hz, and the signal in low frequency area of mixed flow of biomass with quartz sand also distributed between that frequency range.There is no obviously main frequency in the mixed flow of molding biomass with quartz sand, the Energy of each order IMF does not vary with the change of gas velocity obviously in the bubbling bed stage,it is not easy to appear big bubbles in the bed, and the bubble flow and particle behavior is extremely complex. The "slugging" phenomenon would occur when the frequency in bed was concentrated in 0-3 Hz. The recursive diagram theory was introduced to investigate the periodicity and stability of the mixed flow in the bed. The bubbles are of small size and the behavior of particles in the bed were dominant whether it is mixed flow of biomass with quartz sand or one-component flow of quartz sand when the gas velocity is low. The size of bubbles would be larger with the increase of gas velocity in the bed, the mixed flow of quartz sand with molding biomass or corncob showed obvious sine (cosine) periodic. Build a kind of signal processing method which is fused Empirical Mode Decomposition with recursive diagram theory, and then analyze the signal from the aspect of frequency domain and phase space, the flow of molding biomass would not make bubbles appear obvious periodicity, and it would not obviously change with the increase of gas velocity, which is benefit for the heat and mass transfer, and quite wide in operating range.Establish a kind of simulation model which is suitable for the mixed flow of molding cylindrical biomass particles with quartz sand. The ball element superposition method is used to calculate the DEM part, on that basis the cylindrical particles were regard as aggregation of small virtual ball, and particle volume factor concept was introduced to amend the acting force between gas and solid reference the volume-weighted method, Through the calculation the acting force between gas phase and virtual sphere to calculate the force of the cylindrical particles to the gas phase. Coupling the improved DEM-CFD and MPI method to realize the parallel simulation of two-component particle flow by using Fortran. The reliability of simulation was further verified through the experimental results, and then the gas flow and particle behavior characteristics were further analyzed. Spherical particles of small size have little influence on the gas flow, the gas flow direction would change when meeting cylindrical particles, it would flow around the particles and the velocity of gas flow would increase. The trailing vortex of cylindrical particles would disappear because of the dredging effect of particles of small size to the gas flow in fluidized bed. Gas in fluidized bed flow to the centre first, then straight up,finally it would flow around, and the particles showed the same trend. It is easy to form bubbles in the windward direction of cylindrical biomass particles because of the agglomeration of biomass particles or gas velocity, and the cylindrical biomass particles in bubbles would move upward or down influenced by the gas velocity.