This research focuses on modeling a multi-zone circulating reactor(MZCR)in the polypropylene production process.In these reactors,designed for polyolefin production,small catalyst particles(20–300μm)initiate polymer...This research focuses on modeling a multi-zone circulating reactor(MZCR)in the polypropylene production process.In these reactors,designed for polyolefin production,small catalyst particles(20–300μm)initiate polymerization in the presence of monomer gas.The reactor consists of two main regions:the riser and the downer.The riser operates in the fast fluidization and the downer is in the moving bed regime.Employing the two-fluid model with the Eulerian-Eulerian approach,the dynamics of both solid and gas phases were modeled by applying Newton's laws of motion and assuming spherical particles.The population balance of particles within the reactor was also coupled with the equations of motion.The simultaneous solution of these equations provides valuable insights into particle and fluid behavior,revealing trends such as the growth of polymer particles.Furthermore,the impact of various operating conditions was explored.This study also examined the effects of design parameters(gas inlet velocity,average inlet diameter,and temperature)on the system performance.For instance,it was shown that in the case where the solid circulation flux is 30 kg/(m^(2) s)the velocity of particles in the bed increases from 0.4 at the inlet to 1.1 m/s in the fully developed zone,when it is 43 kg/(m^(2) s)the velocity of particles increases from 0.3 to 1.4 m/s,and when it is 55 kg/(m^(2) s),it is increased from 0.22 to 1.5 m/s.Additionally,trends in particle size distribution based on temperature adjustments were revealed.This study showed that higher temperatures accelerate the polymerization reaction rate,promoting faster growth kinetics and the formation of larger particles.展开更多
In the present work,both computational and experimentalmethods are employed to study the two-phase flow occurring in a model pump sump.The twofluid model of the two-phase flow has been applied to the simulation of the...In the present work,both computational and experimentalmethods are employed to study the two-phase flow occurring in a model pump sump.The twofluid model of the two-phase flow has been applied to the simulation of the threedimensional cavitating flow.The governing equations of the two-phase cavitating flow are derived from the kinetic theory based on the Boltzmann equation.The isotropic RNG k−ε−kca turbulence model of two-phase flows in the form of cavity number instead of the formof cavity phase volume fraction is developed.The RNG k−ε−kca turbulence model,that is the RNG k−εturbulence model for the liquid phase combined with the kca model for the cavity phase,is employed to close the governing turbulent equations of the two-phase flow.The computation of the cavitating flow through a model pump sump has been carried out with this model in three-dimensional spaces.The calculated results have been compared with the data of the PIV experiment.Good qualitative agreement has been achievedwhich exhibits the reliability of the numerical simulation model.展开更多
文摘This research focuses on modeling a multi-zone circulating reactor(MZCR)in the polypropylene production process.In these reactors,designed for polyolefin production,small catalyst particles(20–300μm)initiate polymerization in the presence of monomer gas.The reactor consists of two main regions:the riser and the downer.The riser operates in the fast fluidization and the downer is in the moving bed regime.Employing the two-fluid model with the Eulerian-Eulerian approach,the dynamics of both solid and gas phases were modeled by applying Newton's laws of motion and assuming spherical particles.The population balance of particles within the reactor was also coupled with the equations of motion.The simultaneous solution of these equations provides valuable insights into particle and fluid behavior,revealing trends such as the growth of polymer particles.Furthermore,the impact of various operating conditions was explored.This study also examined the effects of design parameters(gas inlet velocity,average inlet diameter,and temperature)on the system performance.For instance,it was shown that in the case where the solid circulation flux is 30 kg/(m^(2) s)the velocity of particles in the bed increases from 0.4 at the inlet to 1.1 m/s in the fully developed zone,when it is 43 kg/(m^(2) s)the velocity of particles increases from 0.3 to 1.4 m/s,and when it is 55 kg/(m^(2) s),it is increased from 0.22 to 1.5 m/s.Additionally,trends in particle size distribution based on temperature adjustments were revealed.This study showed that higher temperatures accelerate the polymerization reaction rate,promoting faster growth kinetics and the formation of larger particles.
基金This research work was funded by the Chinese National Foundation of Natural Science(Nos.51076077,51176168,51249003 and 51076144)This work is also supported by Science Foundation of Zhejiang Sci-Tech University(ZSTU) under Grant No.11130032241201.
文摘In the present work,both computational and experimentalmethods are employed to study the two-phase flow occurring in a model pump sump.The twofluid model of the two-phase flow has been applied to the simulation of the threedimensional cavitating flow.The governing equations of the two-phase cavitating flow are derived from the kinetic theory based on the Boltzmann equation.The isotropic RNG k−ε−kca turbulence model of two-phase flows in the form of cavity number instead of the formof cavity phase volume fraction is developed.The RNG k−ε−kca turbulence model,that is the RNG k−εturbulence model for the liquid phase combined with the kca model for the cavity phase,is employed to close the governing turbulent equations of the two-phase flow.The computation of the cavitating flow through a model pump sump has been carried out with this model in three-dimensional spaces.The calculated results have been compared with the data of the PIV experiment.Good qualitative agreement has been achievedwhich exhibits the reliability of the numerical simulation model.
