Modeling the extra-column volume in a small column setup for bulk gas adsorption
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Modeling the extra-column volume in a small column setup for bulk gas adsorption Lisa Joss · Marco Mazzotti
Received: 6 July 2012 / Accepted: 5 September 2012 / Published online: 20 September 2012 © Springer Science+Business Media, LLC 2012
Abstract This study aims at highlighting the importance of an accurate characterization of the extra-column volume (ECV) and presents an experimental and computational protocol based on the characterization of the extra-column volume in terms of step-response experiments performed under various flow rates and pressures of 1 bar, 5 bar and 10 bar. The experiments are interpreted by describing the extra-column volume with a compartment model that reflects the geometry of the physical setup and that involves a stagnant zone to account for the non-ideal flow behavior through the piping system. The use of a mathematical model combining the description of the adsorption column and of the ECV can successfully predict experimental CO2 – H2 breakthrough profiles performed at different pressures on an activated carbon adsorbent. This work shows how the presence of non-negligible extra-column effects can be accounted for, for the determination of adsorption transport parameters.
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Keywords Breakthrough experiment · Extra-column effects · Heat- and mass transfer coefficients · Mathematical modeling
H hL
c c1 c2 Cads Cg Cgmol Cs Cw Dc De Deff DL dp f
hW k k1
Notation a Parameter for temperature dependent description of qs (J/mol) A Parameter for temperature dependent description of K (J/mol) b Parameter for temperature dependent description of qs (mol/kg)
K KL
L. Joss · M. Mazzotti () Institute of Process Engineering, ETH Zurich, Sonneggstrasse 3, 8092 Zurich, Switzerland e-mail: [email protected]
p Pamb Pin Qamb
k2
Parameter for temperature dependent description of K (1/Pa) Fluid phase concentration (mol/m3 ) Parameter for pressure and flow rate dependent description of f (s/(cm3 bar)) Parameter for pressure and flow rate dependent description of f (–) Heat capacity of the adsorbed phase (J/(K kg)) Heat capacity of the gas (J/(m3 K)) Specific heat capacity of the gas (J/(K mol)) Heat capacity of the solid (J/(K kg)) Lumped heat capacity of the wall (J/(m3 K)) Micro-pore diffusivity (m2 /s) Macro-pore diffusivity (m2 /s) Dispersion coefficient in pipes (m2 /s) Axial dispersion coefficient (m2 /s) Particle diameter (m) Active volume fraction of the tank with stagnant zone (–) Heat of adsorption (J/mol) Heat transfer coefficient (lumping fluid + solid phase) (J/(m2 s K)) Heat transfer coefficient wall (J/(m2 s K)) Overall mass transfer coefficient (1/s) Parameter for velocity dependent description of Deff (m) Parameter for velocity dependent description of Deff (m/s2 ) Sips equilibrium constant (1/Pa) Effective axial thermal conductivity in the fluid phase (J/(m s K)) Fluid pressure (Pa) Pressure in the ECV downstream of the BPR (Pa) Pressure in the ECV upstream of the BPR (Pa) Flow rate in the ECV downstream of the BPR (m3 /s)
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Qin Qtot q q∗ qsat R rin rout s
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