Choose your model!

Practical guide to process modeling

choose your Thermodynamic model!

START

Definitions to know

Importance of a good choice

Credits

Definitions to know

What is a property?

What is a thermodynamic model?

What is a parameter?

What do you mean by data?

Why should I choose the right thermodynamic model?

INNOVATION

SAFETY

COST OPTIMIZATION

Just a few questions to define your perfect model!

2° step: Fluid type

1° step: Process type

Individual examples of use

Which data ?

Which model?

Play

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1- Which process?

Separation

Energy system

Reaction

Flow Assurance

Select the type of separation process

LIQUID-SOLID

LIQUID-LIQUID

LIQUID-VAPOR

Crystallization

Flash drum

Liquid-liquid decantation

Solvent absorption

Liquid-liquid extraction

Distillation

Stripping

Supercritical extraction

Select the type of distillation process?

Severe specifications

Extractive Distillation

Close boiling

Severe Specifications

A severe specification consists in not exceeding very low concentration of some impurities in the distillate

Key data to collect for model parameterization / validation:

Inifinite dilution activity coefficient (or Henry constants) of impurities in the main component in the distillate

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Close boiling

Compounds with close boiling point are expected to form an azeotropic mixture

Key data to collect for model parameterization / validation:

Close boiling pure compounds vapour pressures

Azeotrope data (temperature, pressure, composition) Only azeotropes in the cut point region are of interest!

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Extractive distillation

Key data to collect for model parameterization / validation:

Distribution coefficients (Ki) of key compounds in the solvent

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Flash drum

Key data to collect for model parameterization / validation:

Distribution coefficients (Ki) of key compounds

Azeotrope data for close boiling components

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Solvent absorption

Key data to collect for model parameterization / validation:

Low solubility of the solutes:

Henry constant of solutes in the liquid solvent

Low and high solubilities of the solutes:

Solubility (mole fraction) of the solutes in the liquid solvent

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Supercritical extration

Key data to collect for model parameterization / validation:

Distribution coefficients (Ki) of key compounds in the solvent

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Stripping

Key data to collect for model parameterization / validation:

Distribution coefficients (Ki) of key compounds in the solvent

Henry constant of the stripping gas in the solvent

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Liquid-liquid decantation

Key data to collect for model parameterization / validation:

Low solubility of the solutes:

Inifinite dilution activity coefficient of low-concenration components

Low and high solubilities of the solutes:

Liquid-liquid equilibrium data (tie-lines)

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Liquid-liquid extraction

Key data to collect for model parameterization / validation:

Partitioning coefficients of the key components to be extracted

(often, ternary data between solute + solvent 1 + co-solvent)

If low solubility of the solutes:

Inifinite dilution activity coefficient of solutes in the solvent / co-solvent

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Crystallization

Key data to collect for model parameterization / validation:

Pure component : melting temperature and melting enthalpy Mixtures : Solid + Fluid equilibrium data Beware to eutectic points !

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Specify the type of reactor modelling

Thermodynamic control

Kinetic control

Wagner, N., & Pross, A. (2011). The nature of stability in replicating systems. Entropy, 13(2), 518–527. https://doi.org/10.3390/e13020518

Kinetic control

Key data to collect for model parameterization / validation:

Single phase systems

No thermodynamic issues

Multiphase systems

Solubilities of reactants and products in the reacting phase must be known. Focus on the rate limiting species.

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Thermodynamic control

Key data to collect for model parameterization / validation:

All systems:

Equilibrium constant of the reaction(s)

Enthalpies of the reaction(s)

Multiphase systems:

Solubilities of reactants and products in the reacting phase must be known.

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In which phase is the fluid flow?

Two phase flow

Gas flow

Liquid flow

Which is the most likely risk of appearance?

Solid appearance

Vapor appearance

Liquid flow Vapor appearance risk

Key data to collect for model parameterization / validation:

Bubble temperature (or pressure) of the liquid mixture

Focus on data involving the lighest component of the mixture

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Liquid flow Solid appearance risk

Which kind of solid is expected to form ?

ASPHALTENES

SCALES

WAXES

HYDRATES

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Hydrate

Key data to collect for model parameterization / validation:

Hydrate appearance temperature (or pressure) with or without hydrate inhibitor

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Wax

Key data to collect for model parameterization / validation:

Wax appearance temperature (WAT)

Wax amount formed at a given temperature and pressure

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Asphaltene

Key data to collect for model parameterization / validation:

Onset pressures: upper (UOP) and/or lower (LOP)

Fraction of asphaltene precipitated

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Scales

Key data to collect for model parameterization / validation:

Brine analysis

Equilibrium constants of the salt formation reactions

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Which is the most likely risk of appearance?

Solid appearance

Liquid appearance

Gas flow Liquid appearance risk

Key data to collect for model parameterization / validation:

Dew temperature (or pressure) of the vapor mixture

Focus on data involving the heaviest component of the mixture

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Gas flow Solid appearance risk

Which kind of solid is expected to form ?

HYDRATES

DEPOSITION

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Two phase flow

Key data to collect for model parameterization / validation:

Distribution coefficients (Ki) of key compounds

Look also the specific properties for the liquid flow and vapor flow !

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Energy system

Compressor, pump, heat exchangers,...

Key data to collect for model parameterization / validation:

Phase density

Phase enthalpy

Look also the specific risks for the liquid flow and vapor flow !

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2- Model Selection

Select the type of fluid to model

MIXTURE

PURE COMPONENT

Pure component

What is the state of the pure component fluid ?

Vapor - Low pressure ( < 10 bara)

Vapor - High pressure ( > 10 bara)

Liquid (or unknown)

Finally! Here are the models proposed for your process.

IDEAL GAS

Pure component Liquid state

Do I need only properties of the saturated liquid ?

No!

Yes!

Finally! Here are the models proposed for your process.

Specific correlations for pure liquid saturated properties

Pure component

Is there a specific equation of state for your component ?

Yes!

No! (or I don't know!)

Finally! Here are the models proposed for your process.

Specific Equation of State

Select the property type to analyze

Phase equilibrium property

Phase property

Which type of mixture ?

Mixture with polar compounds

Mixture of non polar compounds

Mixture with H2 (large quantity)

Which other components ?

Hydrocarbons < C16

H2

Other molecules

Finally! Here are the models proposed for your process.

Cubic EOS (PR, SRK)with T-dependent kij

GRAYSON - STREED

Finally! Here are the models proposed for your process.

Cubic EOS (PR, SRK)with T-dependent kij

Close boiling point process ?

Yes!

No

Finally! Here are the models proposed for your process.

Cubic EOS (PR, SRK)- Beware to alpha function ! - Adjust kij !

Reminder of data needs

Almost there...

Do you have key experimental data for your process?

Yes, it is available

No, I have no data

Finally! Here are the models proposed for your process.

Cubic EOS (PR, SRK)- Adjust kij !

Finally! Here are the models proposed for your process.

PPR78

Consider this!

Large size asymetry ?

No! (or I don't know)

Yes!

What is the operating pressure?

High pressure P > 10 bara

Low pressure P < 10 bara

Almost there...

Do you have key experimental data for your process?

Yes, it is available

No, I have no data

Finally! Here are the models proposed for your process.

Equations of state

Activity coefficient models

UNIQUAC

SAFT

Finally! Here are the models proposed for your process.

Equations of state

Activity coefficient models

UNIFAC

GC-SAFT

FLORY

Consider this!

Almost there...

Do you have key experimental data for your process?

Yes, it is available

No, I have no data

Finally! Here are the models proposed for your process.

Equations of state

SAFT

Finally! Here are the models proposed for your process.

Equations of state

GC-SAFT

Consider this!

Just in case...

Does your process contain electrolyte species?

No!

Yes!

Almost there...

Do you have key experimental data for your process?

Yes, it is available

No, I have no data

Finally! Here are the models proposed for your process.

Activity coefficient model

LIFAC

Consider this!

Finally! Here are the models proposed for your process.

Equations of state (low and high pressure)

Activity coefficient models (low pressure)

e-NRTL(pure and mixed solvents)

Soreide & Whitson

Global salinity

LIQUAC(pure and mixed solvents)

e-PC-SAFT

Ion-dependant

Pitzer(water)

e-CPA

About operating pressure and temperature

P < 10 bara

AND

T < min(Tc,i)

P > 10 bara

OR

T > min(Tc,i)

Almost there...

Do you have key experimental data for your process?

Yes, it is available

No, I have no data

Finally! Here are the models proposed for your process.

Activity coefficient models

UNIFAC

Consider this!

Finally! Here are the models proposed for your process.

Activity coefficient models

NRTL

UNIQUAC

Almost there...

Do you have key experimental data for your process?

Yes, it is available

No, I have no data

Does your process contain Hydrogen-bonded molecules ?

Yes! (or I don't know!)

No!

Finally! Here are the models proposed for your process.

Equations of state

PPR78

Consider this!

Finally! Here are the models proposed for your process.

Equations of state

PSRK

GC-SAFT

Consider this!

Finally! Here are the models proposed for your process.

Equations of state

Cubic EOS + GE mixing rules(ex: PRH, SRK-MHV2)

CPA

SAFT

Cubic EOS + asymetric kij mixing rules(ex: SRK -Twu)

What is the type of interaction in the system ?

Non polar interactions

Polar interactions

Finally! Here are the models proposed for your process.

LEE-KESLER

Almost there...

Do you have key experimental data for your process?

Yes, it is available

No, I have no data

Finally! Here are the models proposed for your process.

SAFT

Finally! Here are the models proposed for your process.

Equations of state

VTPR

GC-SAFT

Consider this!

3- Process examples

CO2 capture unit

Ethanol to Ethylene Dehydration Unit

Ethanol to Ethylene Dehydration unit

Dryer

Compressor

Reactor

Ethane / Ethylene Splitter

Water washing

Flash drum

Which model?

Ethanol to Ethylene Dehydration unit

Key data to collect for model parameterization / validation:

Equilibrium constant to determine extend of reaction

Monophasic adiabatic reactor, thermodynamic control (main reaction)

Enthalpies of reaction to determine outlet temperature

Reactor

Ethanol to Ethylene Dehydration unit

Key data to collect for model parameterization / validation:

Distribution coefficients (Ki) : water, ethylene, non-converted ethanol, ethane, diethylether, acétaldehyde

To separate water from the ethylene-rich vapour phase

Flash drum

Ethanol to Ethylene Dehydration unit

Key data to collect for model parameterization / validation:

Phase density

Phase enthalpy

Compressor

Ethanol to Ethylene Dehydration unit

Key data to collect for model parameterization / validation:

Henry constant of light solutes (ethylene, ethane, ether) in liquid water

Solubilities (mole fraction) of the soluble solutes (ethanol, acetaldehyde) in liquid water

Water washing

Ethanol to Ethylene Dehydration unit

Key data to collect for model parameterization / validation:

Cool down a wet gas pressurized gas Risk of hydrate formation!

To correctly size the dryer, the data needed are: Hydrate appearance temperature as a function of water content

Dryer and cooler

Ethanol to Ethylene Dehydration unit

Key data to collect for model parameterization / validation:

Pure compounds vapour pressures

Azeotrope data (Possibly)

Close boiling distillation

Ethane - Ethylene splitter

Ethanol to Ethylene Dehydration unit

Model Selection

P > 10 bara

OR

T > min(Tc,i)

No large size asymetry

Data available

Mixture with polar compounds

No electrolytes

Phase equilibrium property

Cubic EOS + GE mixing rules(ex: PRH, SRK-MHV2)

Cubic EOS + asymetric kij mixing rules(ex: SRK -Twu)

CO2 Capture process

Heat exchangers

Reactive Stripper

Reactive Absorber

Which model?

CO2 Capture process

Key data to collect for model parameterization / validation:

Reactive absorber

Henry constant of light solutes (CO2, H2S, COS, ...) in liquid amine solvent

* Gas absorption/desorption * Chemical reactions under thermodynamic control

Equilibrium constants to determine extend of reactions

Enthalpies of reaction to determine duties

Reactive stripper

CO2 Capture process

Key data to collect for model parameterization / validation:

Phase enthalpy

Phase density

CO2 Capture process

Model Selection

No large size asymetry

Mixture with polar compounds

Data available

with electrolytes

Phase equilibrium property

e-NRTL

Activity coefficient models (low pressure) with mixed solvent (aqueous amine)

LIQUAC

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EXEMPLES

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