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Nonideal gas modelling of pressure swing adsorption processes

The influence of the nonideal gas phase

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Abstract

Besides adsorption equilibrium and adsorption kinetics, nonisothermal temperature effects have a high impact on the simulation results and hence on the process design of pressure swing adsorption (PSA) processes. Due to moderate pressures of PSA processes, the gas phase is usually treated as ideal for the ease of solving the underlying model equations. As a consequence, only the ideal gas enthalpy is considered for the energy balance of the gas phase of the adsorber column. Real gas effects like the Joule-Thomson effect or the real gas mixing enthalpy effects are usually neglected. With the simulation package ADLIN, it is possible to model the gas phase in general as real phase in both the material and energy balance while the accuracy is depending on the applied underlying real gas model. The modelling of the adsorbed phase is not subject to this investigation and is modelled in the same manner as usual. On an example of detailed dynamic modelling of high pressure swing adsorption for the purification of hydrogen, the impact of nonideal gas phase vs. ideal gas phase towards the simulation results is shown. Furthermore, additional results of PSA processes are discussed based on the overall material and energy balance of the gas separation process. It turns out that for the simulation of typical hydrogen purification processes by PSA the ideal gas model is usually sufficient to get reasonable results. For high adsorption pressure or methane purification PSA, the nonideal gas simulation results deviate significantly from the ideal gas behavior, and real gas models should be applied for detailed dynamic PSA simulation. Although the capacity of the PSA was generally increased due to the nonideality of the gas phase, the product recovery was generally reduced.

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Abbreviations

c :

Concentration of gas phase (mol/m\(^3\))

\(c_s\) :

Heat capacity of adsorbent solid (mol/m\(^3\))

\(D_{ax}\) :

Axial dispersion coefficient (m\(^2\)/s)

h :

Enthalpy of gas phase (J/mol)

\(f_1\) :

Parameter for laminar pressure drop (m\(^{-2}\))

\(f_2\) :

Parameter for turbulent pressure drop (m\(^{-1}\))

\(h_{id}\) :

Enthalpy of ideal gas (J/mol)

\(h_{a}\) :

Enthalpy of adsorbed phase (J/mol)

\(\Delta h_{st}\) :

Isosteric heat of adsorption (J/mol)

\(Kk_{LDF}\) :

Fluid film LDF mass transfer coefficient (mol/kg bar s)

\(N_c\) :

Number of components

p :

Absolute pressure (bar)

\(p_i^*\) :

Equilibrium partial pressure (bar)

q :

Adsorbent loading or absolutes adsorbed amount per mass of adsorbent (mol/kg)

v :

Superficial gas velocity (m/s)

\({\mathfrak{R}}\) :

Ideal gas constant (J/mol K)

t :

Time (s)

T :

Temperature (K)

x :

Axial distance of adsorbent bed (m)

y :

Molar gas phase fraction (mol/mol)

\(\epsilon\) :

Void fraction of gas phase (m\(^3\)/m\(^3\))

\(\eta\) :

Dynamic viscosity of gas phase (Pa s)

\(\varpi\) :

Reduced spreading pressure (mol/kg)

\(\rho\) :

Density of gas phase (kg/m\(^3\))

\(\rho _b\) :

Bed density (kg/m\(^3\))

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Authors and Affiliations

  1. Linde AG, Linde Engineering Division, Adsorption and Membrane Technology R&D and Process Design, Dr.-Carl-von-Linde-Str. 6-14, 82049, Pullach, Germany

    Matthias Stegmaier

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  1. Matthias Stegmaier
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Correspondence to Matthias Stegmaier.

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Stegmaier, M. Nonideal gas modelling of pressure swing adsorption processes. Adsorption 23, 455–464 (2017). https://doi.org/10.1007/s10450-017-9877-2

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  • DOI: https://doi.org/10.1007/s10450-017-9877-2

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