Riser has the advantage of high gas-solids contact efficiency,high gas/solids flux and so on.But there is relatively significant gas and solids backmixing.On the ether hand,downer has the great advantage of uniform ga...Riser has the advantage of high gas-solids contact efficiency,high gas/solids flux and so on.But there is relatively significant gas and solids backmixing.On the ether hand,downer has the great advantage of uniform gas and solids residence time, but the entrance structure has great influence on its performance and the solid concentration is much lower than that in riser.A new type of Riser-Downer-Coupling Circulating Fluidized Bed (RDCCFB) is devised in this research, which is a close combination of riser and downer.This new type of CFB takes advantage of both riser and downer.Phosphor particles were used as tracers to study the solid mixing behavior in a cold-model RDCCFB.The results show that the overall Peclet Number is greater than that in a single riser.And the average residence time and the residence time distribution of the particles can be changed according to the requirement.These characteristics make this coupling reactor attractive in many areas.展开更多
It has been acknowledged that a dilute-phase/dense-cluster two-phase micro flow structure exists in the riser. The particle velocity signals from Laser Doppler Velocimeter are analyzed and the velocity and turbulent v...It has been acknowledged that a dilute-phase/dense-cluster two-phase micro flow structure exists in the riser. The particle velocity signals from Laser Doppler Velocimeter are analyzed and the velocity and turbulent velocity of particles in the dilute phase are obtained. The radial velocity distribution of particles in the dilute phase is similar to a parabola. A correlation, similar to the 1/n power law of gas velocity in turbulent state, is given to describe the velocity distribution quantitatively. The cross-sectional average velocity of particles in the dilute phase is nearly equal to the superficial gas velocity, which indicates that the particles in the dilute phase exist in individual particle state. A maximum value exists at the radial position r/R=0.5-0.8 for the turbulent velocity of particles in the dilute phase. This radial position may correspond to the boundary between the dilute phase controlled region and the dense cluster controlled region.展开更多
The velocity, phase fraction and fluctuation velocity of dense clusters are obtained by analysis of transient velocity signals from laser Doppler velocimeter The local velocity of dense clusters increased linearly wit...The velocity, phase fraction and fluctuation velocity of dense clusters are obtained by analysis of transient velocity signals from laser Doppler velocimeter The local velocity of dense clusters increased linearly with superficial gas velocity, while the cross sectional average solids fraction influence the velocity of dense clusters insignificantly A Boltzmann function is used to describe the velocity radial distribution of dense clusters The radial distribution of the phase fraction for dense clusters is described by using an exponential function With the increase of cross sectional average solids fraction, the local phase fraction of dense clusters increases and the area controlled by dense clusters is enlarged The turbulence intensity of dense clusters is highest in the center of the bed while decreases towards the展开更多
文摘Riser has the advantage of high gas-solids contact efficiency,high gas/solids flux and so on.But there is relatively significant gas and solids backmixing.On the ether hand,downer has the great advantage of uniform gas and solids residence time, but the entrance structure has great influence on its performance and the solid concentration is much lower than that in riser.A new type of Riser-Downer-Coupling Circulating Fluidized Bed (RDCCFB) is devised in this research, which is a close combination of riser and downer.This new type of CFB takes advantage of both riser and downer.Phosphor particles were used as tracers to study the solid mixing behavior in a cold-model RDCCFB.The results show that the overall Peclet Number is greater than that in a single riser.And the average residence time and the residence time distribution of the particles can be changed according to the requirement.These characteristics make this coupling reactor attractive in many areas.
文摘It has been acknowledged that a dilute-phase/dense-cluster two-phase micro flow structure exists in the riser. The particle velocity signals from Laser Doppler Velocimeter are analyzed and the velocity and turbulent velocity of particles in the dilute phase are obtained. The radial velocity distribution of particles in the dilute phase is similar to a parabola. A correlation, similar to the 1/n power law of gas velocity in turbulent state, is given to describe the velocity distribution quantitatively. The cross-sectional average velocity of particles in the dilute phase is nearly equal to the superficial gas velocity, which indicates that the particles in the dilute phase exist in individual particle state. A maximum value exists at the radial position r/R=0.5-0.8 for the turbulent velocity of particles in the dilute phase. This radial position may correspond to the boundary between the dilute phase controlled region and the dense cluster controlled region.
文摘The velocity, phase fraction and fluctuation velocity of dense clusters are obtained by analysis of transient velocity signals from laser Doppler velocimeter The local velocity of dense clusters increased linearly with superficial gas velocity, while the cross sectional average solids fraction influence the velocity of dense clusters insignificantly A Boltzmann function is used to describe the velocity radial distribution of dense clusters The radial distribution of the phase fraction for dense clusters is described by using an exponential function With the increase of cross sectional average solids fraction, the local phase fraction of dense clusters increases and the area controlled by dense clusters is enlarged The turbulence intensity of dense clusters is highest in the center of the bed while decreases towards the
