Combined wall and thermal effects during non-isothermal packed bed adsorption

Kwapiński, Witold

doi:10.1016/j.cej.2009.05.023

Cited by 23 publications

(9 citation statements)

References 28 publications

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“…It should also be noted that the temperature during adsorption varied across the bed and was higher at the center than at the periphery because of convective heat transfer at the tube wall. In dry conditions, similar observations were made in adsorber bed temperature and HTZ across the adsorber bed in previous modeling and experimental works on activated carbon adsorption of VOCs such as benzene, toluene, acetone, ethanol, and pentane, 22,24,36,56 which gives confidence in the model for simulating heat transfer kinetics.…”

Section: Environmental Science and Technologysupporting

confidence: 74%

Modeling the Effect of Relative Humidity on Adsorption Dynamics of Volatile Organic Compound onto Activated Carbon

Laskar

Hashisho

Phillips

et al. 2019

Environ. Sci. Technol.

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A two-dimensional heterogeneous mathematical model was developed and validated to study the effect of relative humidity on volatile organic compound (VOC) adsorption onto activated carbon. The dynamic adsorption model consists of the macroscopic mass, momentum, and energy conservation equations and includes a multicomponent adsorption isotherm to predict the competitive adsorption equilibria between VOC and water vapor, which is described by an extended Manes method. Experimental verifications show that the model predicted the breakthrough profiles during competitive adsorption of the studied VOCs (2-propanol, acetone, n-butanol, toluene, 1,2,4-trimethylbenzene) at relative humidity range 0− 95% with an overall mean relative absolute error (MRAE) of 11.8% for dry (0% RH) conditions and 17.2% for humid (55 and 95% RH) conditions, and normalized root-mean-square error (NRMSE) of 5.5 and 8.4% for dry and humid conditions, respectively. Sensitivity analysis was also conducted to test the robustness of the model in accounting for the impact of relative humidity on VOC adsorption by varying the adsorption temperature. Good agreement was observed between the experimental and simulated results with an overall MRAE of 12.4 and 7.1% for the breakthrough profiles and adsorption capacity, respectively. The model can be used to quantify the impact of carrier gas relative humidity during adsorption of contaminants from gas streams, which is useful when optimizing adsorber design and operating conditions.

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Section: Environmental Science and Technologysupporting

confidence: 74%

Modeling the Effect of Relative Humidity on Adsorption Dynamics of Volatile Organic Compound onto Activated Carbon

Laskar

Hashisho

Phillips

et al. 2019

Environ. Sci. Technol.

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“…Although the length of the existing maldistribution region is narrow compared with the bed height, local attrition and fluidization frequently indicate the beginning of performance deterioration. Moreover, wall effects typically make the breakthrough in near-wall regions faster than that in the core of the adsorber, thus indicating that the occurrence of such effects reduces bed utilization (Kwapinski 2009;Zheng et al 2010). Hence, employing methods to eliminate maldistribution in the core and near-wall regions is necessary.…”

Section: Itemmentioning

confidence: 99%

Numerical study of flow maldistribution and depressurization strategies in a small-scale axial adsorber

2014

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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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“…In the model the flow velocity distribution is considered as a two-step function and the effect of radial flow velocity distribution is considered only in the near-wall region. Afterward, Tobis and Vortmeyer, Germerdonk and Wang, Bart et al, Mohamadinejad et al, and Kwapinski and co-workers ,− also developed their two-dimensional models for the simulation of trace component removal, part of which consider the heat effect and mass transfer rate. In these researches, Brinkman equation is adopted as the momentum equation for adsorbate gas flow in the adsorbent.…”

Section: Introductionmentioning

confidence: 99%

Two-Dimensional Modeling of the Transport Phenomena in the Adsorber During Pressure Swing Adsorption Process

Zheng¹,

Liu²,

Liu³

2010

Ind. Eng. Chem. Res.

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In this study, a two-dimensional model is established to simulate the pressure swing adsorption process. It is the first time a two-dimensional model has been used to study the transport phenomena occurring inside the adsorber during the PSA process with consideration of the heat effect, gas compressibility, radial porosity, and dead volumes. Parts of the results have been compared with the results either from experiments or from the references, which show the model can give a favorable prediction. The 2D simulation results clearly show the concentration distribution and its propagation with time, and concentration maldistribution induced by a nonuniform packing. The velocity, pressure, and temperature distribution is also presented in the paper. A brief discussion of the effect of maldistribution, pressure drop (resistance of porous media) and sorption heat et al. on the concentration distribution is made. As expected, the results visually show that the maldistribution and sorption heat will reduce the adsorber performance. It is also found that a moderate pressure drop is useful for the performance improvement of an adsorber, because it will help bring evenly distributed flow field. There is independent concentration wave velocity, temperature wave velocity, and gas velocity, and during the adsorption step, the concentration wave velocity is larger than that of temperature wave until they coincide with each other. The gas velocity is much larger than the other two velocities. The two-dimensional simulation is found to be very useful for a better understanding of the dynamic sorption and separation process in an adsorber. The results of further research are capable to guide or optimize the design of adsorber configurations.

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Combined wall and thermal effects during non-isothermal packed bed adsorption

Cited by 23 publications

References 28 publications

Modeling the Effect of Relative Humidity on Adsorption Dynamics of Volatile Organic Compound onto Activated Carbon

Modeling the Effect of Relative Humidity on Adsorption Dynamics of Volatile Organic Compound onto Activated Carbon

Numerical study of flow maldistribution and depressurization strategies in a small-scale axial adsorber

Two-Dimensional Modeling of the Transport Phenomena in the Adsorber During Pressure Swing Adsorption Process

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