1. Aspen Separation Unit Operations
Team 2: Futoon O. Aljirafi, Peter Ho, Neha Kalla, Won Kim, Alexandra Shubina, Rachel Stanoyevitch

2. Outline Introduction 3 Separators 6 Columns 10
Absorption and Stripping 17
Solid Separators 21

3. Introduction

4. General Overview 8
“A separation process is method to achieve any mass transfer phenomenon that converts a mixture of substances (i.e. chemicals) into two or more distinct product mixtures” 1
There are three different classes of separators found in Aspen:
Separators
Columns (distillation, strippers, absorbers)
Solid Separator
The unit operation chosen will depend on the type mixture/solution

5. Available Unit Operations
The following selections can be found in Aspen in the Model Palette bar
Separators:
Columns:
Solid Separators:

6. Separators

7. Flash2 Single stage separator Dependent on components’ volatility
Inputs: T, P, Heat duty, or Molar vapor fraction
Selection of property method
SRK/UNIFAC: azeotrope
IDEAL: no azeotrope
Ensure flash convergence (global flash options)
Useful for more complex simulations

8. Decanter2 Suitable for a liquid-liquid extraction
Separates based on centrifugation
NRTL method should be used because it is better suited for LLE
If any stream were to have a vapor phase then Flash separator is better suited

9. Sep/Sep22
Combine feed streams and create a split depending on user specifications
Useful when details of separation are unknown
Can be used to model flash columns temporarily to make flowsheet work
Sep is good when fractions are known but energy balance is unknown
Sep2 can add specifications like purity and recovery

10. Columns

11. Methanol Synthesis Process: Via Natural Gas Feed3
Feed purification
Natural gas (desulphurization < 1 ppmv)
Water (impurities ppbv)
Reforming (reformer furnace)
Heated by burning natural gas
Methane + Steam → Hydrogen + Carbon Dioxide + Carbon Monoxide
Methanol Synthesis
Gas compressed and sent into synthesis reactor
Produced methanol separated into crude product:
Methanol (~70%)
Water (~30%)
Traces of byproducts
Methanol purification
Distillation Columns

12. Shortcut Distillations2
DSTWU4
Designed for single feed, two product distillation processes
Use the Winn, Underwood, Gilliland methods to calculate the Nmin, Rmin, and reflux ratio given a number of theoretical stages (and vice versa). Must specify reflux ratio, condenser type, condenser and reboiler pressure, and light and heavy key recovery
Assumes constant relative volatilities and constant molar overflows
Distl4
Multicomponent distillation model that separates one inlet stream into two outlet streams. Uses the Edmister method to calculate column compositions for a given number of stages and reflux ratio
Must specify number of theoretical stages, reflux ratio and distillate to feed ratio (works under the same assumptions as the DSTWU column)
Estimates condenser and reboiler duties
SCFrac
Models petroleum refining towers (e.g. crude units and vacuum towers)
Performs calculations for columns with with a single feed, optional stripping stream, and any number of products (does not handle solids)
Estimates: product composition and flows, number of stages per section, heating/cooling duty per section
DSTWU
Used to get a quick idea about a process. The results obtained are then used as input into a more rigorous column, such as the RadFrac.
Results: Rmin and Ractual, Nmin and Nactual, feed stage, reboiler/condenser heat duties, distillate and bottoms temperatures, and distillate to feed fraction

13. Rigorous Distillations2
RadFrac4
Suitable for all types of multistage vapor-liquid separations
Capable of simulating the following operations:
Absorption, reboiled absorption, stripping, reboiled stripping, azeotropic distillation, and extractive distillation
Can model columns with occuring various chemical reaction types:
Equilibrium, rate, electrolytic
MultiFrac4
Models complex configurations including:
Any # of columns with multiple stages per column
Random connections within columns and between columns
Random flow splitting and mixing
Typical applications include:
Heat-integrated columns, stripper/absorber, air separation
PetroFrac
Used for complex vapor-liquid fractionations in petroleum industry
Assumes equilibrium stage calculations (though user can specify murphree/vaporization efficiencies)
RadFrac
Best to start by using DSTWU to get an idea for what inputs to use. Does require iteration for design problems.

14. ConSep and Extract Columns2
Used prior to rigorous simulation using RadFrac
Used for vapor-liquid/vapor-liquid-liquid mixtures
Must specify: reflux or reboil ratio, and column pressure
Extract
Used for liquid-liquid extractions
Accepts specifications for component or stage efficiencies
May include:
Multiple feeds, heater/cooler, side-streams
Must calculate distribution coefficient using the following:
Activity coeff. Model, equation of state, and temperature dependent polynomial

15. Troubleshoot Issue: Cost of cooling utility
Use a partial condenser instead of a total condenser in distillation column
Example:
Want to separate water (bottoms) and vinyl acetate (distillate) from a mixture of water, ethylene, nitrogen, carbon dioxide, acetic acid, and vinyl acetate
Add a partial condenser to minimize the cooling utility cost associated with a total condenser (nitrogen released as vapor)

16. Troubleshoot

17. Absorption & Stripping

18. Absorbers and Strippers
Separation unit used to dissolve solute into solvent by means of direct contact
Objective is to purify a gas component
Stripper
Separation unit used to remove solute from solvent by means of direct contact
Objective is to purify a liquid component

19. Customization Elaborate on: # of stages Reflux Ratio
Distillate Flow Rate
Degree of Freedom
And MORE

20. Troubleshoot
Increase mass flow rate of liquid if bottom flow rate is zero or increase mass flow rate of gas if distillate flow rate is zero
Decrease number of stages

21. Solid Separators

22. Solid Separation in Methanol Synthesis:
Gas-Solid5
Coal gasification:
Left over ash removed from gaseous products
Co-Absorption:
CO and H2 from coke powder
Liquid-Solid6
Catalyst recovery:
Catalyst from wax product
Solid-Solid7
Coal screening:
Suitable feed of fine coal ash
Gas/Solid citation:
liquid/solid citation:
solid/solid citation:

23. Gas-Solid Separators2 ESP: dry electrostatic precipitators
Fabric Filter (FabFl): baghouse fabric filter units
Gas Cyclone (Cyclone): centrifugal force of a gas vortex
Scrubber (VScrub): venturi scrubbers, direct contact with an atomized liquid stream

24. Liquid-Solid Separators2
Hydro Cyclone (HyCyc): centrifugal force of a liquid vortex
Centrifuge (CFuge): centrifugal force of a rotating basket
Liquid Filter (Filter): continuous rotary vacuum filters
Swash (SWash): entrained liquid of a solids stream
CCD: counter-current decanter or multistage washer

25. Solid-Solid Separators2
Screen: separation of various sizes of solid particles in a mixture

26. Questions?

27. Work Cited
Separation process. (accessed Feb 5, 2019).
AspenTech. AspenPlus User Guide Volume 2. (accessed Feb 5, 2019).
Methanol Manufacturing Process. (accessed Feb 5, 2019).
Overney, R. Aspen Tutorial #6: Aspen Distillation. (accessed Feb 5, 2019).
Wang, T.; Wang, J.; Jin, Y. Slurry Reactors for Gas-to-Liquid Processes: A Review. Ind. Eng. Chem. Res. 2007, No. 46, 5824–5847.
Eastland, D. Methanol from Coal; Davy Powergas Inc: Houston, TX.
Lewitt, M. Opportunities for Fine Coal Utilisation. IEA Clean Coal Centre August 2011.
Distillation Equipments - Distillation Column Manufacturer from Mumbai. (accessed Feb 5, 2019).