Flow maldistribution and local high velocity in an axial adsorber is numerically studied to investigate the potential occurrence of sorbent pulverization and uneven utility. A considerable maldistribution induced by the entrance effect and local high velocity caused by rapid gas discharge during depressurization is observed. Three types of gas distributors and different depressurization strategies are then proposed and studied to determine their capabilities to create uniform velocity profiles. Results show that locating the predistributor in the dead zone is critical to flow distribution. The maldistribution factor (Mf) can decrease to a minimum of 0.055 when a perforated inlet plenum is used with a conventional distributor. In addition, the internal ring can effectively reduce wall effects. Moreover, both gas expansion and desorption have a significant influence on the evolution of local velocity during depressurization. In this step, local high velocity can possibly exceed incipient fluidization velocity and cause attrition and pulverization of the sorbent. To a certain extent, employing methods to control the depressurization rate is necessary. Applying linear depressurization (p ¼ 101can reduce local high velocity, and thus, improve flow conditions. List of symbols a Thermal diffusion coefficient, m 2 s -1 d p Diameter of adsorbent particle, m D im Mass dispersion rate, m 2 s -1 e f Total fluid energy, kJ kg -1 e p Total solid medium energy, kJ kg -1 F Momentum source term, kg m -2 s -2 DH Heat of adsorption, J mol -1 K i Langmuir parameter, mol kg -1 kPa -1 k 1 Langmuir temperature dependence constant, mol kg -1 kPa -1 k 2 , k 4 Langmuir temperature dependence constant, K k 3 Langmuir temperature dependence constant, kPa -1 k Mass transfer rate coefficient, s -1 k t Turbulent kinetic energy, m 2 s -2 k eff Effective bed thermal conductivity, W m -2 K k p Solid medium thermal conductivity, W m -2 K k f Fluid phase thermal conductivity, W m -2 K Mf Maldistribution factor M i Molar weight of component i, kg mol -1 M w Molar weight of fluid, kg mol -1 q Solid-phase adsorbate concentration, mol kg -1 q * Adsorbate concentration in equilibrium with gas phase, mol kg -1 r Radial coordinate, m R Gas constant, J mol -1 K -1 /radius of bed, m S i Mass source term of the ith component, kg m -3 s -1 S m Total mass source term, kg m -3 s -1 T Temperature, K u i Velocity in the i direction, m s -1 u Velocity vector, m s -1 y Distance from the adsorber side wall, m y i Mass fraction of component i z Axial coordinate, mGreek symbols e Porosity of the fixed bed e t Dissipation rate of turbulence kinetic energy, m 2 s -3 e b Bulk porosity q p Density of adsorbent particle, kg m -3 q f Fluid density, kg m -3
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