Adsorption

, Volume 1, Issue 2, pp 133–151 | Cite as

Sensitivity of PSA process performance to input variables

  • D. G. Hartzog
  • S. Sircar
Article

Abstract

Mathematical models for pressure swing adsorption (PSA) processes essentially require the simultaneous solutions of mass, heat and momentum balance equations for each step of the process using appropriate boundary conditions for the steps. The key model input variables needed for estimating the separation performance of the process are the multicomponent adsorption equilibria, kinetics and heats of adsorption for the system of interest. A very detailed model of an adiabatic Skarstrom PSA cycle for production of high purity methane from a ethylene-methane bulk mixture is developed to study the sensitivity of the process performance to the input variables. The adsorption equilibria are described by the heterogeneous Toth model which accounts for variations of isosteric heats of adsorption of the components with adsorbate loading. A linear driving force model is used to describe the kinetics. The study shows that small errors in the heats of adsorption of the components can severely alter the overall performance of the process (methane recovery and productivity). The adsorptive mass transfer coefficients of the components also must be known fairly accurately in order to obtain precise separation performance.

Keywords

PSA process sensitivity equilibria kinetics heats 

Nomenclature

a

Specific heat transfer area from adsorbent in differential kinetic test

bi

Interaction parameter of Toth isotherm equation

bi*

b i atT→∞

Cg

Molar heat capacity of gas

Cs

Heat capacity of adsorbent

dp

Particle diameter

f

Fractional uptake in differential kinetic test

F

Feed gas quantity per cycle in PSA process

h

External heat transfer coefficient in differential kinetic test

k

Parameter of Toth isotherm equation

ki

Adsorptive mass transfer coefficient for componenti

L

Column length

m

Saturation adsorption capacity of Toth isotherm equation

ni

Specific amount of componenti adsorbed

P

Pressure

P/F

Purge to feed gas quantity (actual volume)

PP

Purge gas inlet pressure

PF

Feed gas inlet pressure

PD

Final depressurization pressure

Q

Superficial molar flux through column

qi

Isosteric heat of adsorption of componenti

qi*

Pure gas isosteric heat of adsorption at Henry's Law region

R

Gas constant

t

Time

T

Temperature

T0

Reference temperature

y

Gas phase mole fraction

z

Distance in column

z*

z/L

Greek Letters

α

Parameter in Eq. (13)

β

Parameter in Eq. (13)

λ

Parameter in Eq. (13)

υ

Parameter in Eq. (13)

μ

Gas viscosity

ρg

Gas density (=P/RT)

ρs

Adsorbent bulk density

ϑi

Fractional adsorbate loading for componenti (=n i /g)

ϑ

Total fractional adsorbate loading (= Σϑ i )

ε

Total void fraction in column

\(\frac{\varepsilon }{\varepsilon }\)

Inter-particle void fraction in column

Superscripts and Subscripts

D

Desorption

F

Feed gas entrance conditions

P

Purge gas entrance conditions

i

Componenti

*

Equilibrium conditions

o

Pure gas

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References

  1. Ergun, S., “Fluid Flow Through Packed Columns,”Chem. Engr. Prog.,48(2), 89 (1952).Google Scholar
  2. Hindmarsh, A.C., “ODEPACK, A Systematized Collection of ODE Solvers,”Scientific Computing, R.S. Stepleman et al. (Eds.), North-Holland, Amsterdam, 1983.Google Scholar
  3. Hartzog, D.G., V.G. Fox, R. Kumar, Y.C. Chen, P.A. Houghton, and T. Naheiri, “A Versatile Process Simulator for Adsorptive Separations,” paper presented at AIChE Meeting in Miami, Florida, Nov. 1992.Google Scholar
  4. Jaroniec, M. and J. Toth, “Adsorption of Gas Mixtures on Heterogeneous Solid Surfaces: Extension of Toth Isotherm on Adsorption from Gas Mixtures,”J. Colloid Polym. Sci.,254, 643 (1976).Google Scholar
  5. Sircar, S., “Linear Driving Force Model for Non-Isothermal Gas Adsorption Kinetics,”J. Chem. Soc. Faraday Trans. I.,79, 785 (1983).Google Scholar
  6. Sircar, S., and R. Kumar, “Equilibrium Theory for Adiabatic Desorption of Bulk Binary Gas Mixture by Purge,”I.&E.C. Proc. Des. Dev.,24, 358 (1985).Google Scholar
  7. Sircar, S., “Pressure Swing Adsorption: Research Needs by Industry,”Fundamentals of Adsorption, Proceedings of the Engineering Foundation Conference held at Sonthofen, Germany, A.B. Mersmann et al. (Eds.), 815 (1991a).Google Scholar
  8. Sircar, S., “Isosteric Heats of Multicomponent Gas Adsorption on Heterogeneous Adsorbents,” Langmuir,7, 3065 (1991b).Google Scholar
  9. Skarstrom, C.N., “Method and Apparatus for Fractionating Gaseous Mixtures by Adsorption,” U.S. Patent 2,944,627 (1960).Google Scholar
  10. Szepesy, L. and V. Illes, “Adsorption of Gases and Gas Mixtures, I,”Acta Chim. Hung.,35, 37 (1963a).Google Scholar
  11. Szepesy, L. and V. Illes, “Adsorption of Gases and Gas Mixtures, III,”Acta Chim. Hung.,35, 245 (1963b).Google Scholar
  12. Valenzuela, D., and A.L. Myers, “Gas Adsorption Equilibria,”Separation and Purification Methods,13, 153 (1984).Google Scholar

Copyright information

© Kluwer Academic Publishers 1995

Authors and Affiliations

  • D. G. Hartzog
    • 1
  • S. Sircar
    • 2
  1. 1.Dynamic Matrix Control Corp.Houston
  2. 2.Air Products and Chemicals, Inc.AllentownUSA

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