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.
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Abbreviations
- a :
-
Specific heat transfer area from adsorbent in differential kinetic test
- b i :
-
Interaction parameter of Toth isotherm equation
- b * i :
-
b i atT→∞
- C g :
-
Molar heat capacity of gas
- C s :
-
Heat capacity of adsorbent
- d p :
-
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
- k i :
-
Adsorptive mass transfer coefficient for componenti
- L :
-
Column length
- m :
-
Saturation adsorption capacity of Toth isotherm equation
- n i :
-
Specific amount of componenti adsorbed
- P :
-
Pressure
- P/F :
-
Purge to feed gas quantity (actual volume)
- P P :
-
Purge gas inlet pressure
- P F :
-
Feed gas inlet pressure
- P D :
-
Final depressurization pressure
- Q :
-
Superficial molar flux through column
- q i :
-
Isosteric heat of adsorption of componenti
- q * i :
-
Pure gas isosteric heat of adsorption at Henry's Law region
- R :
-
Gas constant
- t :
-
Time
- T :
-
Temperature
- T 0 :
-
Reference temperature
- y :
-
Gas phase mole fraction
- z :
-
Distance in column
- z*:
-
z/L
- α :
-
Parameter in Eq. (13)
- β :
-
Parameter in Eq. (13)
- λ:
-
Parameter in Eq. (13)
- υ :
-
Parameter in Eq. (13)
- μ :
-
Gas viscosity
- ρ g :
-
Gas density (=P/RT)
- ρ s :
-
Adsorbent bulk density
- ϑ i :
-
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
- D :
-
Desorption
- F :
-
Feed gas entrance conditions
- P :
-
Purge gas entrance conditions
- i :
-
Componenti
- *:
-
Equilibrium conditions
- o :
-
Pure gas
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Hartzog, D.G., Sircar, S. Sensitivity of PSA process performance to input variables. Adsorption 1, 133–151 (1995). https://doi.org/10.1007/BF00705001
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DOI: https://doi.org/10.1007/BF00705001