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

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?

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:

Separators

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.

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.

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

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

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

Columns

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

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

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

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

3. RadFrac Column

Absorption/Stripping

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.

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.

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).

Solid Separators

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

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

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

Questions?

Literature Consulted AspenPlus User Guide Volume 2 7 - UCSB ChE. (n.d.). Retrieved January 31, 2018, from http://www.chemengr.ucsb.edu/~ceweb/courses/che184b/aspenplus/UserGuideVol1.pdf Aspen Tutorial #3: Flash Separation. University of Washington. Retrieved January 31, 2018, from http://courses.washington.edu/overney/Aspen/Aspen_Tutorial_Unit_3.pdf Aspen Plus V10