discussion0fs117flash mixing+8.0

8/13/2019 Discussion0fs117Flash Mixing+8.0

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Flash Calculations and

Gibbs Free Energies of Mixingusing

ASPENPLUS

ECH 152B Discussion

January 17, 2014Updated for Aspen 8.0 1/24/14


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Basics of Flash (Reminder)

System is brought into two-phase region

Overall concentration is fixed

Flash is used to separate Vapor fromLiquid (which have different

concentrations)

We need to calculate the concentrations(simple VLE calculation) and the number

of moles (or flow rates) on the Vapor (V)

and Liquid (L) sides


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Using Aspen Plusto calculate

Flash (updated for Aspen 8)

Open AspenTech-

>ProcessModeling8.0-

>AspenPlus->AspenPlus

V8.0


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Fugacity Coefficients

Close Start Page


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Using Aspen Plus8.0 to

calculate Fugacity Coefficients

File->New

Blank Simulation

Create


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Choosing your unit system

Aspen 8.0 Home -> Setup -> Global

Standard: Bar and Celsius (METCBAR)


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Using Aspen Plus 8.0 to

calculate Flash Click on Simulation to obtain open a

Flowsheet


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Flash At bottom select SeparatorsFlash 2

and add it to the open space


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Flash Add Material Streams(bottom left) to

space and connect to Flash Unit (one

input/two output)

Red streams are

mandatory


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Using Aspen Plus 8.0 to

calculate Flash Click on Properties to get back to

component input


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Flash On HomeScreen Go to Components-

>Specifications

Add your component (best to search by

name or formula under component name)

Make Sure your Component ID is not

empty, best you copy the name there


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Using Aspen Plus8.0 to

calculate Flash Close Specifications Window

Go to Methods -> Specification

Choose your Base Method (e.g. Ideal)


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Flash Go to Simulation -> Streams

Check that there are 3 streams

Enter conditions of inlet stream (Streams, Open

Number of Input)

P and T of the

input stream not the

flash


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Flash Go to Simulation -> Blocks (and click on

Number of Block and Specifications)

For Valid Phases Select Vapor-Liquid

Enter conditions you want to flash to

P and T of the

flash


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Flash Home -> Run (will not work if something

missing but will tell you what is missing)

Wait until convergence Ignore economic analysis (for the moment)


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Status after calculation


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Flash Run Status (did run complete)


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Flash Simulation->Results Summary ->

Streams gives you the data

You might have to scroll down for what

you want


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Red: mol fractions in the streams

Purple: flow rate in streams -> fraction of streams from total


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Fraction of phases within streams (here pure vapor and pure liquid)

Reminder: Input at different conditions (p and T)


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Examples to try

Redo Example from Class (1/15):

- 353 K/110 kPa

- Ideal mix- 0.45 acetone / 0.35 acetonitrile / 0.2

nitromethane

This is the one used to generate the screen

shots along the way.


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Property method selection

assistant Which method to use if mixing non-ideal?

Aspen can suggest

Properties -> Home -> Methods Assistant


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assistant


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assistant


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assistant


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Examples to try

Again Example from Class (1/15):

- 353 K/110 kPa

- Now with NRTL (or other methodsuggested by assistant)

- 0.45 acetone / 0.35 acetonitrile / 0.2

nitromethane


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Property changes at mixing

For any property M we define

where Mi is pure system property. It follows

that

For ideal mixing most are zero (like for

ideal gases details next week in class).

=1

=1 ( )

=1

=1


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Gibbs Free Energy of Mixing

Gibbs Free energy of Mixing is difference

between mixed and unmixed system

=1


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Gibbs Free Energy of Mixing Go to Properties -> Components-

>Specifications

Add your components (best to search by

name or formula under component name)

Make Sure your Component ID is not

empty, best you copy the name there

Close Components Window

Go to Properties->Methods-

>Specifications


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Gibbs Free Energy of Mixing Choose your Base Method (e.g. NRTL)


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Gibbs Free Energy of Mixing You might have to confirm parameters

(click and they become blue)

Close Window


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Gibbs Free Energy of Mixing Go to Analysis -> Binary (If you cannot

select it you missed something earlier, e.g.

NRTL parameters)

For Valid Phases Select Vapor-Liquid

Select Analysis Type (Gibbs Energy of

Mixing)

Enter Conditions

(Pressure or Temperature)

Run Analysis


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Examples to try

Benzene Toluene Ideal (300K) -> same as

ANY ideal mixture at 300K

Benzene/Toluene NRTL (300 K)

Ethanol/Water NRTL (300 K)


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Gibbs Free energy of mixing

ideal case at 300K


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Gibbs Free energy of mixing

for ideal case as function of T


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Benzene Toluene (NRTL)


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Ethanol Water (NRTL at 76C)


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You always also get a table

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