Iulia,

You can go to the Aspen tech support websitte, http://support.aspentech.com/. There you will find several examples of how to deal with freezing. For example, from solution ID 3222: "How to simulate freezing in an Aspen Plus simulation?"

Problem Statement:

How to simulate freezing in an Aspen Plus simulation?

Solution:

There are two ways to simulate freezing in a simulation:

1.       Use the Reaction Chemistry to handle the formation of the solid as a salt precipitation reaction with appropriate K-Salt.

2.       Use the RGibbs unit operation block to calculate the solid phase equilibrium.

Chemistry Method:

Aspen Plus can handles formation of a solid as a salt precipitation reaction with an appropriate K-Salt.

The Electrolyte Wizard can be used to include ice formation as a reaction by checking the Include ice formation box under Options. Then, the component ICE(S) of component type Solid will be added to the component list, and a Salt reaction with K-Salt parameters will be added to the Chemistry:

Reaction

Type

Stoichiometry

ICE(S)

Salt

ICE(S) H2O

ln (Keq) = -62.705 + 1681.4/T + 10.317 ln (T) + -0.004851 T

T in Kelvin

An example of using Aspen Plus to predict the amount of ice formed at different temperatures for a 18 wt. % Methanol-Water solution is attached. Note that there are no ions in this system.

The freezing point of a 18% methanol-water solution is -11.13 C from the Handbook of Chemistry and Physics, 52nd ed., p. D-198, and the freezing point predicted by Aspen Plus is about -11.8 C.

Ions do not have to be part of the system and any solid can be used instead of the water/ice system with the appropriate equation for the equilibrium constant. This method can also be used to predict solubilities (see Solution 102340 for an example). Note that K-SALT and activity coefficient model parameters are not independent of each other.

The true component approach should be used in order to see the solid in the stream results.

The advantage of this method is that the solid equilibrium is evaluated for every stream and in every unit operation block.

RGibbs Method:

RGibbs can be used to calculate solid phase equilibrium (e.g. ice forming from water). To do this, give the solid a different component ID - this tricks the RGibbs block into thinking it is doing chemical equilibrium instead of phase equilibrium (See Solution 102346 for an example).

RGibbs can even handle solid solutions (alloys). RGibbs can be used for much more complex applications that the Chemistry method discussed above.

NOTE: Phase equilibrium calculations between solids and liquids rely on accurate calculation of the Gibbs Free Energy for both phases. A small difference in Gibbs Free Energy calculations can cause Aspen Plus to predict a melting temperature far from reality. Phase equilibrium should be verified for the components and Physical Property models of interest before relying on the predictive capability of RGibbs.

RGibbs bases its prediction on pure component properties and should not be used to predict solubilities.

The two example files attached supposed show how to use both methods. They come from rather old versions of A+ so I don't know how well they work in newer versions of the program.

 Dear Brian, 

I have checked your examples. However after running the gibbs file in the stream results I see there is no solid formation, i.e. after the reactor the streams remain in liquid form. Maybe I am making a mistake running the file, please let me know. 

Also, I would like to ask why/how di you input the pure components. 

Finally why you did not model the process using a crystallizer? and in that case Do you have an example of how would it be done?

Thank you for your help.

Kind regards.

I have checked your file for ice formation using RGibbs but there is no solid in the outlet after running the simulation . I tried varying everything but nothing seems to work.

I want to frreze out CO2 from natural gas liquid stream.Nothing seems to work for freezing any component (The process is CFZ for CO2 removal patented by ExxonMobil)

Any solution for that ?

Brian Hanley Olivia Maria Morales Gonzalez

simulation of crystallization of Na2CO3 in NaOH and Na2CO3 solution. How to define and simulate crystallization process of Na2CO3 in electrolyte environment by Aspen Plus???

Thanks

hi i am trying to freeze CH2Cl2 using R23