property methods in aspen plus
DESCRIPTION
Property Methods In Aspen Plus. Ref: Physical Property Methods and Models, Aspen Technology, Inc. , 2006 . Property Methods. A property method is a collection of property calculation routes. Thermodynamic properties: • Phase equilibrium (VLE, LLE, VLLE) • Enthalpy • Entropy - PowerPoint PPT PresentationTRANSCRIPT
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Property Methods In Aspen Plus
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Ref: Physical Property Methods and Models, Aspen Technology, Inc., 2006
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Property MethodsA property method is a collection of property calculation routes.
Thermodynamic properties:• Phase equilibrium (VLE, LLE, VLLE)• Enthalpy• Entropy• Gibbs free energy• Molar volume
Transport properties:• Viscosity• Thermal conductivity• Diffusion coefficient• Surface tension
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Property MethodsIt is important to choose the right property method for an
application to ensure the success of your calculation.
The classes of property methods available are:• IDEAL• Liquid fugacity and K-value correlations• Petroleum tuned equations of state• Equations of state for high pressure hydrocarbon applications• Flexible and predictive equations of state• Liquid activity coefficients• Electrolyte activity coefficients and correlations• Solids processing• Steam tables
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EOS Method1- Vapor-Liquid Equilibrium
At Equilibrium:
Where
Therefore
li
vi ff
tili
liti
vi
vi PxfPyf ,
vi
li
i
ivli x
yk
4
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EOS Method2- Liquid-Liquid Equilibrium
At Equilibrium:
Where
Therefore
21 li
li ff
tli
li
lit
li
li
li PxfPxf 222111 ,
1
2
2
121
li
li
li
lill
i xxk
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EOS Method3- Vapor-Liquid-Liquid Equilibrium
At Equilibrium:
Where
Therefore
vi
li
li fff 21
tivi
vi
tli
li
lit
li
li
li
PyfPxfPxf
222111 ,
vi
li
li
ivliv
i
li
li
ivli x
ykxyk
2
2
21
1
1 , 6
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EOS Method4- Fugacity Coefficient Formula
m
V
nVTii ZdV
VRT
nP
RTj
ln1ln,,
Cubic Equations of State in the Aspen Physical Property SystemRedlich-Kwong(-Soave) based Peng-Robinson basedRedlich-Kwong (RK) Standard Peng-Robinson(PENG-ROB)Standard Redlich-Kwong-Soave(RK-SOAVE ) Peng-Robinson(PR-BM)Redlich-Kwong-Soave (RKS-BM) Peng-Robinson-MHV2Redlich-Kwong-ASPEN(RK-ASPEN) Peng-Robinson-WSSchwartzentruber-RenonRedlich-Kwong-Soave-MHV2Predictive SRK (PSRK)Redlich-Kwong-Soave-WS 7
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EOS Method5- Standard RK-SOAVE
)( bVVa
bVRTP
mmm
Where
i
iii j
ijjiji bxbkaaxxa ,)1()( 5.0
ci
cii
ci
ciii P
RTbPTRa 08664.0,42747.0
22
225.0 176.057.148.0,)]1(1[)( iiiriii mTmT 8
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EOS Method6- Standard PENG-ROB
)()( bVbbVVa
bVRTP
mmmm
Where
i
iii j
ijjiji bxbkaaxxa ,)1()( 5.0
ci
cii
ci
ciii P
RTbPTRa 07780.0,45724.0
22
225.0 26992.054226.137464.0,)]1(1[)( iiiriii mTmT 9
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EOS Method7- Advantages and Disadvantages
Equations of state can be used over wide ranges of temperature and pressure, including subcritical and supercritical regions.
Thermodynamic properties for both the vapor and liquid phases can be computed with a minimum amount of component data.
For the best representation of non-ideal systems, you must obtain binary interaction parameters from regression of experimental VLE data. Binary parameters for many component pairs are available in the Aspen databanks.
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EOS Method7- Advantages and Disadvantages…
Equations of state are suitable for modeling hydrocarbon systems with light gases such as CO2 , N2 and H2 S .
The assumptions in the simpler equations of state (SRK, PR, Lee-Kesler , … ) are not capable of representing highly non-ideal chemical systems, such as alcohol-water systems. Use the activity-coefficient options sets for these systems at low pressures. At high pressures, use the predictive equations of state.
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EOS Method8- Enthalpy calculation
Vapor Enthalpy:
Liquid Enthalpy:
Where:
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Standard enthalpy of formation for ideal gas at 298.15 K and 1 atm
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Activity Coefficient Method 1- Vapor-Liquid Equilibrium
At Equilibrium: Where Therefore
F0r ideal gas and liquid
li
vi ff
liii
liti
vi
vi fxfPyf *,,
tvi
lii
i
ivli P
fxyk
*,
LawsRaoultPP
xyk
t
i
i
ivli
vii '1,1
*
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Activity Coefficient Method 2- Liquid-Liquid Equilibrium
At Equilibrium:
Where
Therefore
21 li
li ff
li
li
li
li
li
li
li
li fxffxf *,*, 222111 ,
1
2
2
121
li
li
li
lill
i xxk
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Activity Coefficient Method 3- Vapor-Liquid-Liquid Equilibrium
At Equilibrium:
Where
Therefore
vi
li
li fff 21
tivi
vi
li
li
li
li
li
li
li
li
Pyffxffxf
*,*, 222111 ,
tvi
li
li
li
ivli
tvi
li
li
li
ivli P
fxyk
Pf
xyk
*,*, 2
2
21
1
1 , 15
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Activity Coefficient Method 4- Liquid Phase Reference Fugacity
For solvents: The reference state for a solvent is defined as pure component in the liquid state, at the temperature and pressure of the system.
i*,v = Fugacity coefficient of pure component i at the system
temperature and vapor pressures, as calculated from the vapor phase equation of state
qi*,l = Poynting factor
)11(,),( *,*,*,*,*, iil
il
il
iv
il
i xasPPTf q
P
P
li
li l
i
dPVRT *,
*,*, 1expq16
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Activity Coefficient Method 4- Liquid Phase Reference Fugacity
For dissolved gases: Light gases (such as O2 and N2 ) are usually supercritical at the temperature and pressure of the solution. In that case pure component vapor pressure is meaningless and therefore it cannot serve as the reference fugacity.
Using an Empirical Correlation: The reference state fugacity is calculated using an empirical correlation. Examples are the Chao-Seader or the Grayson-Streed model.
01** iiiiil
i xasandHxf
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Activity Coefficient Method 5- Multicomponent Mixtures
Multicomponent vapor-liquid equilibria are calculated from binary parameters. These parameters are usually fitted to binary phase equilibrium data (and not multicomponent data) and represent therefore binary information. The prediction of multicomponent phase behavior from binary information is generally good.
Multi-component liquid-liquid equilibria cannot be reliably predicted from binary interaction parameters fitted to binary data only. In general, regression of binary parameters from multi-component data will be necessary.
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Activity Coefficient Method 6- NRTL (Non-Random Two-Liquid)
The NRTL model calculates liquid activity coefficients for the following property methods: NRTL, NRTL-2, NRTL-HOC, NRTL-NTH, and NRTL-RK. It is recommended for highly nonideal chemical systems, and can be used for VLE, LLE and VLLE applications.
jk
kjk
mmjmjm
ij
kkjk
ijj
kkik
jjijij
i Gx
Gx
GxGx
Gx
Gx
ln
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Activity Coefficient Method 6-NRTL (Non-Random Two-Liquid)
Where
The binary parameters aij, bij, cij, dij, eij and fij can be determined from VLE and/or LLE data regression. The Aspen Physical Property System has a large number of built-in binary parameters for the NRTL model.
jk
kjk
mmjmjm
ij
kkjk
ijj
kkik
jjijij
i Gx
Gx
GxGx
Gx
Gx
ln
)15.273(
0,ln
1,)exp(
Tdc
TfTeTba
GG
ijijij
iiijijijijij
iiijijij
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Activity Coefficient Method 7- Advantages and Disadvantages
The activity coefficient method is the best way to represent highly non-ideal liquid mixtures at low pressures.
You must estimate or obtain binary parameters from experimental data, such as phase equilibrium data.
Binary parameters are valid only over the temperature and pressure ranges of the data.
The activity coefficient approach should be used only at low pressures (below 10 atm).
The Wilson model cannot describe liquid-liquid separation at all; UNIQUAC, UNIFAC and NRTL are suitable. 21
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Activity Coefficient Method 8- Enthalpy calculation
Vapor Enthalpy: Vapor enthalpy are computed from the EOS that selected for vapor phase (The same as EOS method).
Liquid Enthalpy:
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1. Choosing the most suitable property method.
2. Comparing the obtained predictions with data from the literature.
3. Estimate or obtain binary parameters from experimental data if necessary.
4. Generation of lab data if necessary to check the property model.
Principle Steps in Selecting the Appropriate Property Method
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Eric Carlson’s Recommendations
E?
R?
P?
Polar
Real
Electrolyte
Pseudo & Real
Vacuum
Non-electrolyte
Braun K-10 or ideal
Chao-Seader,Grayson-Streed or Braun K-10
Peng-Robinson,Redlich-Kwong-Soave,Lee-Kesler-Plocker
Electrolyte NRTLOr Pizer
See Figure 2Figure 1
Polarity
R?Real or pseudocomponents
P? Pressure
E? Electrolytes
All Non-polar
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P?
ij?
ij?
LL?
(See alsoFigure 3)
P < 10 bar
P > 10 bar
PSRKPR or SRK with MHV2
Schwartentruber-RenonPR or SRK with WSPR or SRK with MHV2
UNIFAC and its extensions
UNIFAC LLE
PolarNon-electrolytes
No
Yes
Yes
LL?No
No
Yes
Yes
NoWILSON, NRTL,UNIQUAC and their variances
NRTL, UNIQUACand their variances
LL? Liquid/Liquid
P? Pressure
ij? Interaction Parameters Available
Figure 2
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VAP?
DP?Yes
No Wilson, NRTL,UNIQUAC, or UNIFAC* with ideal Gas or RK EOS
Wilson NRTLUNIQUACUNIFAC
Hexamers
Dimers Wilson, NRTL, UNIQUAC, UNIFAC with Hayden O’Connell or Northnagel EOS
Wilson, NRTL, UNIQUAC, or UNIFAC with special EOS for Hexamers
VAP? Vapor Phase Association
Degrees of PolymerizatiomDP?UNIFAC* and its Extensions
Figure 3
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Eric Carlson’s Recommendationsfor 1-Propanol ,H2O mixture
E?Polar
Non-electrolyteSee Figure 2
Figure 1
Polarity
R?Real or pseudocomponents
P? Pressure
E? Electrolytes27
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P?
ij?
LL?
(See alsoFigure 3)
P < 10 bar
UNIFAC and its extensions
PolarNon-electrolytes
Yes
LL?No
No
NoWILSON, NRTL,UNIQUAC and their variances
LL? Liquid/Liquid
P? Pressure
ij? Interaction Parameters Available
Figure 2
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