Vibration Fluidization Phenomenon And Dehydration Model Of Hybrid-sized Lignite

With the merits such as high efficiency on drying,fast mass and heat transferring and other advantages,VFB has been widely employed in industry.However,the fluidization state of particles in VFB have seldom been studied.The design and research of VFB at present has seldom considered the divergence in drying effect of particles with different size.Instead,empirical formula and estimations have been adopted,which leading to a poor reliability.Due to the drawbacks mentioned above,coupling computational fluid dynamics(CFD)and discrete element method(DEM),this thesis has applied EDEM and FLUENT software to simulate 3D fluidization behavior.Under the coupled effect of the vibration and fluid,it analyzes the particles movement rule of hybrid-sized particles in VFB.Simultaneously,the experiment has been designed in the thesis to determine the drying curve of the lignite.Combined with the result from the simulation,the dehydration model is built to achieve the optimization calculation of the dehydration rate of lignite in VFB.The main contents and results are as follow:(1)Based on the DEM theory,a proper particle model is created according to the diameter distribution of Wuhai lignite and the VFB structure model is built up.With the actual vibration parameters,the particles movement in vertical and horizontal VFBs is simulated.According to the result,the average fluid velocity of particles in the horizontal VFB is 0.041m/s.And there is a stratification in the particles movement that big particles are in the upper strata and small ones in the lower strata.Besides,there are Pouring Fountain phenomenon and Brazil Nut Effect in the vertical VFB.(2)Taking the influence of vibration and fluid into consideration,the fluid state of particles is simulated in the combination of two fields on the basis of the coupling CFD-DEM theory.The results shows that the particles layer is higher under the effect of fluid.And there is Anti-Brazil Nut Effect that large particles is in the lower strata covered by the small particles which means a more uniform drying.At the same time,a suitable velocity of fluid is determined by 5m/s.(3)The quality of coal sample is measured during the drying experiment every 5minites.lignite samples is of 5 different sizes and the experiment is conducted in 3 different temperature.The analysis manifests that when the diameter is 6 mm or less,the drying velocity is faster than others and the suitable temperature is 100-150℃ the proper time of drying is less than 40 minutes.(4)Drying curve is plotted according to the drying data.Associated with result of particles distribution in the simulation,proper temperature gradient is assumed to solve the drying curve of Hybrid-Sized lignite with 130℃ inlet temperature.