2 replies to this topic

[efwefsef]

Can i use two methods in aspen plus at the same time like NRTL and RK-BM.Is it right to do so or i have to perform simulation using only one method and remove all the other methods in aspen?

 

[twell]

NRTL can predict liquid activity (plus residual enthalpy of liquid phase etc.) 

while SRK (RK-BM has specific alpha function) can predict fugacities, enthalpies, entropies, volumes etc.

in almost all simulators you can select different models to be used on different sections of the plant (for example EOSs for high pressure sections, models  based on liquid activity for complex - low pressure separations etc.) ,

you may also adopt different models for multistage separations such as columns,

the details (as the list of models available) are specific for each software,

for example, my copy of Prode Properties allows to select different models for each state and property (fugacity, enthalpy, entropy, Volume etc.)

I would guess that Aspen offers a similar option.

[Saml]

You can use two or more methods for different equipments if those method are the one that better predicts the properties you are interested in.

In heat exchangers you can use one method on each both sides. Example:

 

If you have an exchanger with Boiler Feed Water on one side and syn gas on the other, you may use an equation of state on the gas side and steam tables or IAPWS on the boiler feed water side.