In a gas-solid separation fluidized bed,mixing of fine coal is necessary to achieve a suitable bed density to enable effective separation of low rank coal.On the basis of a variety of mixture models,a gas-solid separa...In a gas-solid separation fluidized bed,mixing of fine coal is necessary to achieve a suitable bed density to enable effective separation of low rank coal.On the basis of a variety of mixture models,a gas-solid separation fluidized bed was judged,where fine coal particles of 0.6-1.0mm were uniformly mixed with magnetite powder.High-speed dynamic camera technology was combined with a slump-sampling method to study the mixing process of the fine coal in the fluidized bed.These results showed that limitations of the fluidized bed structure cause the mixing process to be dominated by lateral diffusion and supplemented by axial diffusion.Axial diffusion was mainly achieved through the ascension of bubbles,whereas lateral diffusion was determined by the bursting action of the gas bubbles at the surface of the bed and the undulating characteristics of the bed.The effective lateral diffusion coefficient increased exponentially with gas velocity but had no strong relationship with the bed height.As the feed point moved toward the center,fine coal began to diffuse to both sides,which shortened the time for the bed density stabilization from 20 to 5 min.The bed density of the layer was stabilized at approximately 1.75 g/cm3.The separation efficiency of the gas-solid separation fluidized bed containing binary mixtures was more obvious for 6-50 mm raw coal,with a probable error E of 0.16.展开更多
A new concept of a supercritical water （SCW） circulating fiuidized bed reactor is proposed to produce hydrogen from coal/biomass gasification. The cyclone is a key component of the reactor system, in this paper, cyc...A new concept of a supercritical water （SCW） circulating fiuidized bed reactor is proposed to produce hydrogen from coal/biomass gasification. The cyclone is a key component of the reactor system, in this paper, cyclones with a single circular inlet （SCI） or a double circular inlet （DCI） were designed to adapt to the supercritical conditions. We evaluated the separation performance of the two cyclones using numerical simulations. A three-dimensional Reynolds stress model was used to simulate the turbulent flow of the fluid, and a stochastic Lagrangian model was used to simulate the particle motion. The flow fields of both cyclones were three-dimensionally unsteady and similar to those of traditional gas-solid cyclones. Secondary circulation phenomena were discovered and their influence on particle separation was estimated. Analyzing the distribution of the turbulence kinetic energy revealed that the most intensive turbulence existed in the zone near the vortex finder while the flow in the central part was relatively stable. The particle concentration distribution was non-uniform because of centrifugal forces. The distribution area can be divided into three parts according to the motion of the particles. In addition, the separation efficiency of both cyclones increased with the inlet SCaN velocity. Because of its perturbance flow, the DCI separator had higher separation efficiency than the SCI separator under comparable simulations. However, this was at the expense of a higher pressure drop across the cyclone.展开更多
Channel confluences are universally present in nature. They can be divided into two types： asymmetrical river confluences and symmetric river confluences. The latter is also called as the Y-shaped confluences. Most o...Channel confluences are universally present in nature. They can be divided into two types： asymmetrical river confluences and symmetric river confluences. The latter is also called as the Y-shaped confluences. Most of previous work has paid more attention to the asymmetrical river confluences, but few studies have been conducted on the Y-shaped confluences. In this article, the effects of bed discordance on the flow patterns at ＂Y＂ shaped open-channel confluences were studied by using a 3-D numerical simulation. It is proved that the model can undertake quantitative assessment of the flow at confluences. The results indicate that there are a lot of differences between the Y-shaped confluence and asymmetrical confluence. The discordant bed height plays an important role at the Y-shaped junction.展开更多
基金the National Natural Science Founda-tion of China(No.51774283,51221462)。
文摘In a gas-solid separation fluidized bed,mixing of fine coal is necessary to achieve a suitable bed density to enable effective separation of low rank coal.On the basis of a variety of mixture models,a gas-solid separation fluidized bed was judged,where fine coal particles of 0.6-1.0mm were uniformly mixed with magnetite powder.High-speed dynamic camera technology was combined with a slump-sampling method to study the mixing process of the fine coal in the fluidized bed.These results showed that limitations of the fluidized bed structure cause the mixing process to be dominated by lateral diffusion and supplemented by axial diffusion.Axial diffusion was mainly achieved through the ascension of bubbles,whereas lateral diffusion was determined by the bursting action of the gas bubbles at the surface of the bed and the undulating characteristics of the bed.The effective lateral diffusion coefficient increased exponentially with gas velocity but had no strong relationship with the bed height.As the feed point moved toward the center,fine coal began to diffuse to both sides,which shortened the time for the bed density stabilization from 20 to 5 min.The bed density of the layer was stabilized at approximately 1.75 g/cm3.The separation efficiency of the gas-solid separation fluidized bed containing binary mixtures was more obvious for 6-50 mm raw coal,with a probable error E of 0.16.
文摘A new concept of a supercritical water （SCW） circulating fiuidized bed reactor is proposed to produce hydrogen from coal/biomass gasification. The cyclone is a key component of the reactor system, in this paper, cyclones with a single circular inlet （SCI） or a double circular inlet （DCI） were designed to adapt to the supercritical conditions. We evaluated the separation performance of the two cyclones using numerical simulations. A three-dimensional Reynolds stress model was used to simulate the turbulent flow of the fluid, and a stochastic Lagrangian model was used to simulate the particle motion. The flow fields of both cyclones were three-dimensionally unsteady and similar to those of traditional gas-solid cyclones. Secondary circulation phenomena were discovered and their influence on particle separation was estimated. Analyzing the distribution of the turbulence kinetic energy revealed that the most intensive turbulence existed in the zone near the vortex finder while the flow in the central part was relatively stable. The particle concentration distribution was non-uniform because of centrifugal forces. The distribution area can be divided into three parts according to the motion of the particles. In addition, the separation efficiency of both cyclones increased with the inlet SCaN velocity. Because of its perturbance flow, the DCI separator had higher separation efficiency than the SCI separator under comparable simulations. However, this was at the expense of a higher pressure drop across the cyclone.
基金supported by the National Natural Science Foundation of China(Grant No. 30490235).
文摘Channel confluences are universally present in nature. They can be divided into two types： asymmetrical river confluences and symmetric river confluences. The latter is also called as the Y-shaped confluences. Most of previous work has paid more attention to the asymmetrical river confluences, but few studies have been conducted on the Y-shaped confluences. In this article, the effects of bed discordance on the flow patterns at ＂Y＂ shaped open-channel confluences were studied by using a 3-D numerical simulation. It is proved that the model can undertake quantitative assessment of the flow at confluences. The results indicate that there are a lot of differences between the Y-shaped confluence and asymmetrical confluence. The discordant bed height plays an important role at the Y-shaped junction.
