Adsorption equilibrium modelling for different temperature conditions and its influence on adsorption mass transfer / Modeliranje adsorpcijskega ravnotežja v različnih temperaturnih pogojih in njegov vpliv na prenos snovi pri adsorpciji

Teodor Štimec, Matjaž Hriberšek, Jure Ravnik, Sani Bašič, Matej Zadravec

ANALI PAZU, 5 (2015), št. / No. 1-2, strani / pages 26-32
Celotno besedilo / Full text (PDF)

Abstract: The paper deals with numerical modelling of adsorption kinetics in a narrow channel of a honeycomb type adsorber. The mass transfer model consists of solving the diffusion-convection transport equation for adsorbate species in the fluid phase. The adsorbate flux to the wall is computed implicitly by using the Boundary Element Method for the solution of the transport equation. Scalable boundary condition for the adsorbate concentration on the adsorbent walls is used, defined on basis of the ratio of the accumulated adsorbate mass and the equilibrium adsorbate mass for a given system temperature. As the state of equilibrium is dependent also on the system temperature, a sensitivity study of the adsorption process under different system temperatures is performed. Among the studied adsorption equilibria models, including the Freundlich model, Simplified local density (SLD) model and the Dubinin-Radushkevich model, the latter is proved as the best compromise between accuracy and computational cost and applied in mass transfer kinetics computations. The results of computations show, that the increase in system temperature results in a decrease of breakthrough times, as the equilibrium amounts of adsorbate at the adsorbent walls decrease with increasing temperature, therefore making the derived numerical model suitable for further use in detailed mass transfer kinetics computations.
Key words: subdomain boundary element method, laminar viscous fluid flow, mass transfer, adsorption, honeycomb adsorber

Povzetek: V prispevku je predstavljen numerični model za simulacijo adsorpcijskega procesa v kanalu, ki ima na svojih stenah nameščeno plast adsorbenta. V kanalu teče tok nosilnega plina z zelo nizko koncentracijo adsorbata, ki adsorbira v plast adsorbenta. Prenos snovi je simuliran z reševanjem difuzivno-konvektivne prenosne enačbe ohranitve mase adsorbata, diskretizirane z metodo robnih elementov. Adsorpcijski proces je modeliran s prilaganjem vrednosti robne koncentracije, ki je odvisna od razmerja med akumulirano ter ravnotežno množino adsorbata v plasti adsorbenta. Ker se ravnotežno stanje spreminja s temperaturo sistema je v prispevku prikazan vpliv le te na ravnotežno stanje. Ravnotežna množina adsorbata v plasti adsorbenta je določena s Freundlich. SLD in Dubinin-Radushkevich ravnotežnim modelom, kjer se slednji izkaže za najboljšo izbiro glede na natančnost rezultatov in računski čas. Rezultati izvedenih preračunov kažejo, da se s povečevanjem temperature v sistemu zniža čas pri katerem pride do preboja adsorbata, ker se ravnotežna količina adsorbata na stenah adsorbenta zmanjšuje s povečevanjem temperature sistema. Izdelana numerična rutina omogoča natančno simuliranje adsorpcijskih procesov v kanalu ter napovedovanje prebojne koncentracijske krivulje adsorbata.
Ključne besede: podobmočna metoda robnih elementov, laminarni viskozni tok tekočine, prenos snovi, adsorpcija, adsorber s satovjem

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