| With the growing demand for energy in China,energy problems are becoming more and more prominent.In the proportion of China’s energy consumption structure,traditional fossil fuels still occupy a dominant position.In order to achieve the energy transition and the"double carbon"goal,making full use of biomass energy is an effective way to do so.The application of bubble fluidized bed improves the heat,mass transfer efficiency of biomass in the gasification process and the contact efficiency of biomass particles with gas,thus improving the utilization rate of biomass energy.However,the agglomeration phenomenon of particles inside the fluidized bed and the enlargement of the fluidized bed structure size are two major problems for the industrial application of fluidized bed.Based on this,a three-dimensional model of the gas-solid two-phase fluidization region of the bubbling fluidized bed is established with the help of the computational fluid dynamics simulation software Fluent,and the Eulerian two-fluid model is used to investigate the fluidization characteristics of the gas-solid two-phase with four initial particle filling heights,four inlet gas velocities,four particle sizes and four particle densities.The simulation results show that in this experimental model,the initial filling height H is 0.054 m,the inlet gas velocity V is 0.13 m/s,the particle size d is 215μm,and the particle densityρis 2600 kg/m3 is the best simulation condition,at this time,the volume fraction of particles in the fluidized bed is uniformly distributed,the agglomeration part of particles is small,and the fluidization height is twice as high as itself,and the particles show a better fluidization state.Then,the effect of gas distribution plates with 2 different hole arrangements with an opening ratio of 1.8%on particle fluidization was investigated.The simulation results show that,under suitable simulation parameters,the particles in the fluidized bed under the circumferentially arranged gas distribution plate are uniformly fluidized,the particle velocity fluctuations at four axial heights are smaller,and the particle flow velocity inhomogeneity coefficient is smaller compared to that of the square arranged gas distribution plate,which exhibits better fluidization quality.After determining the gas distribution plate,the size model of the actual bubbling fluidized bed is then determined based on the available experimental equipment.Finally,a laboratory-scale biomass gasification experimental platform was built based on the bubble fluidized bed device for cold and hot state experiments.In the cold state experiment,a high-speed camera can clearly capture the process of bubble generation and rupture in the particle bed,and record the whole process of quartz sand particles in the bubbling fluidized bed from rest to fluidized state.In the thermal state experiment,gasification experiments on biomass were completed.The results of the gasification experiments showed that higher carbon conversion and effective gas yield of 79.30%and 0.64 kg/m~3,respectively,could be obtained with hematite particles as the bed material compared to quartz sand particles.The carbon conversion rate and effective gas yield increased with the increase of reaction temperature,and reached the highest rate of 84.13%and 0.69 kg/m~3 at the reaction temperature of 950°C.The carbon conversion rate and effective gas yield of biomass gasification reached the highest rate of 86.01%and 0.81 kg/m~3 at the water vapor concentration of 15%,respectively. |
