Introduction to Modelling Air Separation Units

Course Id:  EHY303   |   Duration:  2.00 day(s)   |   CEUs Awarded:  1.4   |   Level:  Advanced

Course Objective

Build, navigate and optimize a steady state simulation of an Air Separation Unit (ASU) using Aspen HYSYS. Utilize a wide variety of unit operation models and calculation tools to model process equipment. Use templates and sub-flowsheets to streamline and organize the different sections of the plant.


  • Leverage the intuitive solving capabilities and other key features of Aspen HYSYS that allow for rapid flowsheet construction
  • Discover how multi-flowsheet integration can streamline and organize simulation efforts
  • Evaluate the performance of existing equipment by leveraging the equipment rating capabilities of Aspen HYSYS
  • Improve the convergence characteristics of columns and flowsheets; troubleshoot common problems
  • Perform Case Studies to determine the optimum operating points for a process


  • New Engineering graduates/technologists in ASU and cryogenic industry who will be using Aspen HYSYS in their daily work
  • Process engineers doing process design and optimization projects and studies of ASU / cryogenic plants
  • Plant engineers checking plant performance under different operating conditions
  • R&D engineers and researchers using Aspen HYSYS for ASU / cryogenic process design



  • Instruction on basic topics
  • An experienced instructor will present modules in an appropriate order for maximum understanding
  • Discussion about the general approach and the key elements for the successful simulation of an ASU
  • Instructor-guided demonstrations of features
  • Hands-on workshops leading to the complete simulation of an ASU
  • Detailed course notes


  • Integrated Crude distillation preheat train overview in HYSYS
  • Convert the HYSYS Simulation to EO Sub-flowsheet
  • Compare performance difference between SM and EO Solvers
  • Use EO configuration group to change flowsheet solution
  • Perform sensitivity analysis


A background in chemical/process engineering (preferably with experience in cryogenic / ASU plant design or operation)

Subsequent Courses

  • EHY101: Aspen HYSYS: Process Modelling
  • EHY121 Building MS Excel User Interfaces for Aspen HYSYS Simulations Using Aspen Simulation Workbook
  • EHY202 Aspen HYSYS: Advanced Process Modeling Topics
  • EHY223 Aspen HYSYS Dynamics: Introduction to Dynamic Modeling

Class Schedule

Class Agenda

EHY303: Introduction to Modelling Air Separation Units

ASU Process Overview

  • Examine the Product requirements for the ASU plant to be simulated
  • Anaylze the proposed process design 
Getting Started
  • Enter necessary elements to fully define a Fluid Package 
  • Understand the relative volatility of components in the system
  • Investigate the phase behavior of typical fluids in the ASU process
Main Air Compressor (MAC)
  • Define the atmospheric air to be used as feedstock
  • Configure a 3-stage air compressor to produce Medium Pressure (MP) Air
Direct Contact After Cooler (DCAC) and Chilled Water Tower (ChWT)
  • Specify two Absorbers to represent the DCAC for MAC discharge air cooling
  • Use a Recycle option to link these two sections
  • Configure an additional column to create ChW for the DCAC, using cold Waste gas from the ASU
  • Use the Column Analysis tool to understand the ChWT hydraulics
Temperature Swing Adsorbers (TSA)
  • Use a component splitter to remove the moisture and carbon dioxide from the coldbox feed air.
Booster Air Compressor (BAC)
  • Split the dry air into process and utility streams
  • Configure a multi-stage compressor producing Intermediate Pressure (IP) Air for expansion and High Pressure (HP) Air for Liquid Air generation
  • Split the HP Air to the HP and Low Pressure (LP) column systems
Main Heat Exchanger (MHE) and Expander
  • Define a multi-stream Plate-Fin heat exchanger to cool the MP, IP and HP Air streams and recover refrigeration from the coldbox. 
  • Use an Expander model to remove energy from the IP Air stream, creating refrigeration.
Column System 
  • Configure a 2-column system (with a side operation, rectifier) to produce streams of the required product flow and composition.
  • Set up a Subcooler and Crude Argon Condenser
  • Fully define all column feed streams (using a Recycle where necessary -for further adjustment)
  • Install a pump to raise the Liquid Oxygen (LOX) pressure to product specification
Heat Integration
  • Integrate Crude Argon condenser (column system) into the Main flowsheet
  • Integrate column product streams into the MHE and Subcooler for refrigeration recovery
  • Link the HP Column condenser to the LP Column reboiler
  • Close heat and mass balance on the waste circuit
Product Compression and Storage
  • Route cryogenic liquid streams to storage
  • Perform ‘heat leak’ calculations on storage tanks
  • Configure a Gaseous Oxygen (GOX) pipeline
  • Use a multi-stage compressor model to compressor Gaseous Nitrogen (GAN) from coldbox to meet product specification
  • Use the HyproTech SQP optimizer to determine the optimum plant conditions to minimize energy usage.

Aspen Technology, Inc. awards Continuing Education Units (CEUs) for training classes conducted by our organization. One CEU is granted for every 10 hours of class participation.