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

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

Introduction

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

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

Separators

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

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

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

Columns

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

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

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.

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

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)

Troubleshoot

Absorption & Stripping

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

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

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

Solid Separators

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: https://web.anl.gov/PCS/acsfuel/preprint%20archive/Files/20_3_CHICAGO_08-75_0191.pdf liquid/solid citation: https://membrane.ustc.edu.cn/class/ref1/27%20Slurry%20Reactors%20for%20Gas-to-Liquid%20Processes-A%20Review.pdf solid/solid citation: https://www.usea.org/sites/default/files/082011_Opportunities%20for%20fine%20coal%20utilisation_ccc185.pdf

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

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

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

Questions?

Work Cited Separation process. http://research.omicsgroup.org/index.php/Separation_process (accessed Feb 5, 2019). AspenTech. AspenPlus User Guide Volume 2. http://www.chemengr.ucsb.edu/~ceweb/courses/che184b/aspenplus/UserGuideVol1.pdf (accessed Feb 5, 2019). Methanol Manufacturing Process. http://www.southernchemical.com/wp/products/methanol/manufacturing-process (accessed Feb 5, 2019). Overney, R. Aspen Tutorial #6: Aspen Distillation. https://courses.washington.edu/overney/Aspen/Aspen_Tutorial_Unit_6.pdf (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. https://www.indiamart.com/kalina-engineering-mumbai/distillation-equipments.html (accessed Feb 5, 2019).