Excel Peng Robinson Vapor Liquid Ratio

[GaTechTheron]

I need determine the ratio of liquid to gas, of a flashing LNG mixture. I'm using Peng Robinson EOS, and I cannot use HYSYS, refprop, or any external tool to Excel. I have the flash calculation working, so I have all fugacitys and relative composition of liquid and vapor for all components.

My knowns are the feed composition, temp, pressure, feed flow.

Is there a way to get liquid composition (after flash), or should I assume its the same as the feed? In HYSYS they are nearly the same.

Is there a way to get vapor or liquid flow rates ? I'm trying to avoid a huge system of equations, but I'm not against doing this provided its reasonable to build in excel.

Thanks !

 

[georgeverghese]

If this is an adiabatic feed flash, temp will drop after the letdown valve. In this case, you'll have both compositional equilibrium and enthalpy equilibrium problems to converge and it will then be easier to run this on a simulator if you ask me.
If your feed temperature is after the letdown, then you have an isothermal feed flash, and this may be easier to work out the only problem related to compositional equilibrium - see Perry Chem Engg Handbook 7th edn page 13-25 for algorithm for isothermal flash calcs.

 

[pierreick]

Hi,
Let you perform the calculation, and you will get your answers.
A calculator is shared (link)
A set of equations/method is also available, bottom of the page under reference "Che guide", click on it.

CheCalc ‐ Multicomponent Flash Calculation

Multicomponent Flash Calculations like BUBBLE P, DEW P, BUBBLE T, DEW T and PT Flash based on Peng Robinson (PR) Equation of State (EOS).

checalc.com

Pierre

 

[apetri]

in Excel, Python etc. you can easily obtain fugacities, vapor/liquid fraction, mass and volume flows and many other properties with an add-in library, see

Fluid properties, multi phase equilibria, process simulation software for Windows Linux Android

Prode software for properties of fluids and mixtures, gas vapor liquid solid hydrate multi phase equilibria

www.prode.com

it includes many thermodynamic models suitable for LNG including Peng-Robinson, GERG 2008 etc. and a complete set of multiphase flash operations...

Hoping this helps.

 

[GaTechTheron]

If this is an adiabatic feed flash, temp will drop after the letdown valve. In this case, you'll have both compositional equilibrium and enthalpy equilibrium problems to converge and it will then be easier to run this on a simulator if you ask me.
If your feed temperature is after the letdown, then you have an isothermal feed flash, and this may be easier to work out the only problem related to compositional equilibrium - see Perry Chem Engg Handbook 7th edn page 13-25 for algorithm for isothermal flash calcs.

Very helpful, and thank you, this calculation is confirming what I was afraid of. My case is isothermial flash. The solution is both iterative, and a very large number of equations for a mixture of say 10-12 components.

 

[GaTechTheron]

in Excel, Python etc. you can easily obtain fugacities, vapor/liquid fraction, mass and volume flows and many other properties with an add-in library, see

Fluid properties, multi phase equilibria, process simulation software for Windows Linux Android

Prode software for properties of fluids and mixtures, gas vapor liquid solid hydrate multi phase equilibria

www.prode.com

it includes many thermodynamic models suitable for LNG including Peng-Robinson, GERG 2008 etc. and a complete set of multiphase flash operations...

Hoping this helps.

This is helpful, thank you ! I can use this with other somewhat related problems I'm working to solve.