1. Aspen Separation Unit Operations
Group 7: Samuel Guo, Marisa Maher, Alex Mitchell, Tanner Pfendner, Vivian Tran

2. Agenda Introduction Separators Columns
Flash
Decanter
Sep/Sep2
Columns
DSTWU
ConSep
RadFrac
Modeling Stripper and Absorption Columns in Aspen
Solid Separators
Gas-Solid
Liquid-Solid
Solid-Solid
Questions?

3. Introduction
The type of separation unit operation is chosen depending on the type of mixture you are trying to separate.
These separators can be found on the Main Flowsheet of Aspen in the Model Pallette.
This presentation will go in detail about several of the separators below.
Separators:
Columns:
Solid Separators:

4. Separators

5. Flash
A one stage process that separates a feed mixture into separate streams, a vapor stream rich in one component and a liquid stream rich in the other component.
Two-outlet flash (Flash2)
Uses rigorous VL (2 phase) or VLL (3 phase) equilibrium.
Can represent equipment such as flashes and evaporators.
Outputs one vapor stream and one liquid stream, may have a water decant stream.
Three-outlet flash (Flash3)
Uses rigorous VLL equilibrium.
Can model flash drums and decanters, especially if you do not know if there is a vapor phase.
Outputs one vapor stream and two liquid streams.
Thermodynamics
For VLL equilibrium, should be (Soave-Redlich-Kwong) SRK and not ideal
Able to specify the fraction of liquid entrained in the vapor stream.

6. Flash Inputs
There are multiple options for Flash Type, and two types must be specified.
If temperature and pressure are specified in the Specifications tab, then they do not need to be specified in the Flash Options tab.
Valid phases can be specified for Flash2.
The key component in the second liquid phase can be specified in Flash3.

7. Decanter Centrifuge for liquid separation
No vapor present- if vapor is present, use flash
In Aspen, separates either Liquid-Liquid, Liquid-FreeWater, or Liquid-DirtyWater
Often used to separate water from a liquid mixture
Separates liquid components based on either fugacity or Gibbs free energy of the system
Fugacity- tendency for liquid to stay as a liquid.
Lower fugacity=lowers Gibbs free energy
Easier to manipulate mathematically in Aspen

8. Decanter- Aspen Inputs
Calculation Options
If fugacity is used, liquid-liquid coefficients can be found from a property method, KLL correlation, or KLL subroutine
KLL=Liquid-liquid distribution coefficients for components in a mixture
Gibbs free energy does not require input of coefficients
Required Specifications
Temperature and Pressure
Duty and Pressure

9. Sep/Sep2
Sep: Representation of a separation technique when column is known, but energy balance is unknown. Splits components into two or more streams
Sep2: offers a wider variety of specifications
In other words, Sep and Sep2 can be used as a “filler” separation unit when the energy balance for a separation is unknown.
Sep Specifications:
Outlet stream and substream can be identified from component ID
Sep2 Specifications:
Offers ability to input additional stream specs such as split fraction

10. Columns

11. Columns
Distillation is used to separate liquids according to boiling point
Helpful for azeotropic swings
Multiple column choices in Aspen
DSTWU
Distl
RadFrac
ConSep
Certain columns are more reliable than others
Distillation columns in Aspen can take on other functions

12. 1. DSTWU Column Winn Underwood Gilliland Method
Calculates Rmin, Nmin, and required number of stages for a set reflux ratio and vice versa
For single feed and two products

13. 2. ConSep Column Determines feasibility of column
Beneficial when working with azeotropes
Interactive design
Change product compositions and reflux ratio
Rectify and Stripping profiles must intersect to be feasible
Can convert ConSep to RadFrac once feasible

14. 3. RadFrac Column Performs “rigorous” calculations
Should be used in final simulation
Can be used to simulate:
Absorption
Stripping
Azeotropic distillation
Reactive distillation

15. 3. RadFrac Column

16. Absorption/Stripping

17. Absorption/Stripping
A RADFRAC column can be used to simulate a stripper or absorber in Aspen.
Strippers use a gaseous stripping agent to separate impurities from liquids while absorbers use a liquid solvent to separate impurities from gases.
Solvents or stripping agents are selected based on the solubility of the impurity in that solvent or stripping agent. Typically, the ideal solvent is chemically similar to the impurity that is to be separated.

18. Modeling an Absorber in Aspen
1. Under the columns tab of the model palette, select a RADFRAC column for your absorber unit.
2. Under the Configuration tab in the RADFRAC properties, select the number of stages and ensure the column has no condenser or reboiler.

19. Modeling an Absorber in Aspen (continued)
3. Under the Streams tab under the RADFRAC properties, ensure the solvent is entering the column at the top (stage 1) and the gas is entering at the bottom of the column (in this case at stage 15).
4. Under product streams, ensure that the liquid product stream is exiting the unit at the bottom of the column (stage 15) and the vapor product is exiting the column at the top of the column (stage 1).

20. Solid Separators

21. Gas-Solid Separation
Cyclone- Separates solids from gas stream using gas vortex centrifugal force
VScrub (Venturi Scrubber)- Removes solid particles from gas stream by contact with atomized liquid stream

22. Liquid-Solid Separation
CFuge- Separates liquid and solids by a rotating basket
Filter- Separates liquid and solids using continuous rotary vacuum filters
Hycyc (Hydrocyclone)- Separates liquids and solids using liquid vortex centrifugal force

23. Solid-Solid Separation
Screen- Separates solids of variable solid particle sizes in a mixture

24. Questions?

25. Literature Consulted
AspenPlus User Guide Volume UCSB ChE. (n.d.). Retrieved January 31, 2018, from
Aspen Tutorial #3: Flash Separation. University of Washington. Retrieved January 31, 2018, from
Aspen Plus V10