The Effect Of Elevated Pressure On The Fluidiaztion Characteristics In Gas-solid Fluidized Bed

Pressurized oxy-coal combustion technology is one of the CO₂ capture technologies with good application prospects,and it has received extensive attention at home and abroad in recent years.In this paper,the research on gas-solid flow characteristics in pressurized fluidized bed is carried out.The effects of operating pressure and fluidization gas velocity on the minimum fluidization gas velocity?bubble characteristics?gasflow distribution?solid flux and mixing in the pressurized bubbling fluidized bed and pressurized circulating fluidized bed,which can which provides a reference for the design and amplification of pressurized fluidized bed.Firstly,the pressurized bubbling fluidized bed setup was used to study the effects of operating pressure?1bar⁶bar?and fluidization number on gas-solid flow characteristics such as the minimun fluidization gas velocity,bed expansion ratio,bubble size and bubble rising velocity.The experimental results show that as the operating pressure increases,the minimun fluidization gas velocity decreases,but the effect of operating pressure on large size particles is more pronounced than the smaller size particle.As the operating pressure increases,the bed expansion ratio decreases at the same fluidization number conditions,and the average bubble size decreases for large size glass beads as the operating pressure increases.However,for small size glass beads,the operation pressure does not have an significant effect on the bubble diameter,and the difference between the bubble size calculated by the Cai's empirical correlation and experiment results is smaller.As the increase of operation pressure,bubble rise velocity decreases,and the results calculated by the Shen's empirical correlation is close to experiment results.By fitting the average bubble size and the average bubble risie velocity obtained in experiment,the empirical correlations at different operation pressure conditions is gotten,and the proportional coefficient k value in the correlation decreases with the increase of operation pressure.Then,the CFD-DEM model was used to simulate the pressurized bubbling fluidized bed.The effects of operation pressure?1bar,6bar,10bar?and fluidization number on the timing signal of bed pressure drop,the transition gas velocity from bubbling fluidization to turbulent fluidization bubble fraction,bubble size,bubble rise velocity,solid flux and particle mixing were studied and compared with experimental results.The results show that as the operating pressure increases,the gas velocity from bubbling fluidization to turbulent fluidization decreases.As the operating pressure increases,the bubble size decreases but the bubble motion becomes more intense,the bubble risie velocity decreases,bubble fraction decreases slightly.As the operation pressure increases,the volume fraction of the bubble flow increases,but the operation pressure has smaller effect on the flow through the emulsion phase.The volume fraction of the throughflow increases as the number of fluidization increases and decreases as the operation pressure increases.The solid flow rate and particle mixing rate at pressurized conditions are both greater than that at atmospheric conditions,and this difference is more pronounced at smaller fluidization numbers conditions.Finally,a cold-pressure pressurized circulating fluidized bed was used to study the effects of operation pressure,fluidization gas velocity and solid flux on the the distribution of particle cocentration,gas-solid slip velocity,slip factor and the dimensionless gas-solid slip velocity.The effects of slip factors and other aspects were compared and analyzed with literature results.As the operating pressure increases,the fluidization gas velocity is significantly reduced to achieve the same solid flux conditions.At the same solid flux conditions,the particle distribution showed a similar pattern along the axial distribution for different operating pressures.The axial distribution of the particle concentration gradually decreased and the operating pressure had no significant effect on the it.When the particle concentrations at the same axial position is kept at a constant,the gas-solid slip velocity at elevated pressure is significantly reduced.At different operation pressure conditions,the rate of gas-solid slip factor changes with gas-solid slip velocity decreases with increasing operation pressure,and the relationship between slip factor and the dimensionless slip velocity is similar in different conditions.The gas-solid slip velocity increases exponentially with the increase of the dimensionless slip velocity.With the statistical calculation of experimente data,the fitting curves of solid flux and gas-solid slip velocity,particle concentration are obtained.The corresponding solid particle flux can be calculated according to the particle concentration required and the gas-solid slip velocity with the empirical correlation equations in different pressure conditions.