Adsorption

, Volume 21, Issue 4, pp 283–305 | Cite as

Modelling and optimization of hybrid PSA/membrane separation processes

Article

Abstract

The present work proposes a modelling and optimization framework for hybrid pressure swing adsorption (PSA) and membrane processes for gas separations. The hybrid PSA/membrane scheme has been applied on the process of hydrogen production from steam methane reformer off gas. Three different hybrid separation schemes have been considered and analyzed. Maximum overall hydrogen recovery has been achieved for given minimum requirements in product purity, while optimizing various PSA and membrane operating and design parameters: the number of adsorption columns, PSA cycle configurations, the number of pressure equalizations/co-current depressurization steps, multiple adsorbent layers, PSA and membrane feed pressure, purge-to-feed ratio, bed length, carbon-to zeolite ratio, membrane area, thickness, and support thickness. The optimization results have been compared to the optimization results of the PSA only case and the benefits of hybrid separation systems have been assessed in terms of the improvements in the overall hydrogen recovery (~2 %), reduction of adsorption beds size (up to 46 %), concentration of the carbon dioxide and carbon monoxide captured in a separate stream (up to 76 %), and reduction of the carbon dioxide content in the waste gases (up to 74 %).

Keywords

Hybrid processes Pressure swing adsorption Porous membranes Gas separations Modeling Optimization 

List of symbols

Amembrane

Area of the membrane (m2)

aV

Specific area (m2/m3)

b

Langmuir isotherm parameter (m3/mol)

C

Gas phase molar concentration of species i (mol/m3)

Ciin

Gas phase molar concentration of species i at the membrane inlet (mol/m3)

Cp

Molar concentrations of gas phase in particles (mol/m3)

cp

Heat capacity (J/(kg K))

Cv

Gas valve constant

D

Bed diameter (m)

De

Effective diffusivity coefficient (m2/s)

Dm

Molecular diffusion coefficient (m2/s)

Ds

Surface diffusion coefficient (m2/s)

Dz

Axial dispersion coefficient (m2/s)

\( {-}\!\!\!{D}_{i}\)

Stefan Maxwell diffusivity of species i (m2/s)

\( {-}\!\!\!{D}_{ij}\)

Stefan Maxwell diffusivity (molecule–molecule interactions) (m2/s)

\( {-}\!\!\!{D}_{i}^{s}\)

Stefan Maxwell surface diffusivity of species i (m2/s)

\( {-}\!\!\!{D}_{ij}^{s}\)

Stefan Maxwell surface diffusivity (sorbate–sorbate interactions) (m2/s)

Dz

Axial dispersion coefficient (m2/s)

F

Molar flowrate (mol/s)

ΔHads

Heat of adsorption (J/mol)

L

Bed or membrane unit length (m)

MW

Molecular weight (kg/mol)

Ncomp

Number of components (–)

Ni

Molar flux, mol/(m2 s)

P

Total pressure (Pa)

pi

Partial pressure of species i (Pa)

Q

Adsorbed amount (mol/kg)

Q*

Adsorbed amount in equilibrium state with gas phase (in the mixture) (mol/kg)

Qm

Langmuir isotherm parameter (mol/kg)

qisat

Monolayer saturation capacity of species i (mol/kg)

qi

The amount adsorbed of species i (mol/kg)

r

Radial domain

Rp

Particle diamater (m)

Rbed

Bed radius (m)

R

Ideal gas constant (J/(K mol))

T

Temperature (K)

Tp

Temperature of particles (K)

u

Interstitial velocity (m/s)

uin

Interstitial velocity at the membrane inlet (m/s)

x

Molar fraction in gas phase (–)

z

Axial domain

Z

Compressibility factor (–)

PSA operating steps

PressCC

Counter-current pressurization step

Ads

Adsorption step

PEQ1, PEQ2, PEQ3

Pressure equalization steps

CoCD

Co-current depressurization step

Blow

Counter-current blowdown step

Purge

Counter-current purge step

Greek letters

δm

Membrane thickness (m)

δs

Support layer thickness (m)

ε

Adsorbent porosity (–)

εbed

Adsorbent bed porosity (–)

εp

Porosity of particles (–)

γ

Activity coefficient (–)

Γ

Thermodynamic factor (–)

θ

Fractional coverage (–)

θm

Membrane stage cut (–)

λ

Thermal conductivity (J/(m K))

λp

Thermal conductivity of particles (J/(m K))

μ

Viscosity (Pa s)

μi

Chemical potential of species i (J)

ρ

Density (kg/m3)

ρp

Density of the particles (kg/m3)

τ

Time (s)

τcycle

PSA cycle time (s)

Abbreviations

PSA

Pressure swing adsorption

SMROG

Steam methane reformer off gas

IAS

Ideal adsorption solution theory

RAS

Real adsorption solution theory

CBMC

Configurational-bias Monte-Carlo

Notes

Acknowledgments

Financial support from PRISM EC-funded RTN (Contract number MRTN-CT-2004-512233) is gratefully acknowledged.

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Copyright information

© Springer Science+Business Media New York 2015

Authors and Affiliations

  • Dragan D. Nikolić
    • 1
  • Eustathios S. Kikkinides
    • 1
  1. 1.Department of Mechanical EngineeringUniversity of Western MacedoniaKozaniGreece

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