Modeling reboiler configurations in the column
Written by James Holoboff, Process Ecology

In this article we focus on a new feature in HYSYS v7 which will be of interest to many HYSYS users -
support for various reboiler configurations in the column, available from the Input Expert.

The HYSYS release notes outline features and enhancements in a number of different areas,
summarized at the end of this article.

Reboiler Configurations

When a reboiled absorber or distillation column are added using the Input Expert, a new page is
available which provides some options for setting up the reboiler in HYSYS:
Users now have the ability to select a different reboiler type or a different circulation option:

Reboiler Configuration
If the default selection is used – “Once-through” and “Regular Hysys reboiler”, then the reboiler will be
set up exactly as it has been done previously. The column subflowsheet appears as follows:
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Once-through - In this case liquid from the bottom stage
of the column is routed to the reboiler; liquid product is
withdrawn from the reboiler while vapour is returned to the
column (possibly via a sump, as shown).
Circulation without baffle – Liquid from the bottom stage
goes to a sump; liquid product is drawn from the sump
but a portion is also routed to the reboiler; the 2-phase
product from the reboiler is returned to the column sump.
This option could be used for thermosiphon reboilers.
Circulation with baffle – similar to the previous option
except a baffle is included (modeled in HYSYS as a
separator).

Reboiler Type

  • Regular HYSYS reboiler – Applicable to the once-through option – heating and separation are
    accomplished in the reboiler.
  • Heater – The reboiler is modeled using a heater followed by a separator which withdraws the
    liquid product and routes vapour to the column.
  • Heat Exchanger – The reboiler is modeled using a heat exchanger followed by a separator which
    withdraws the liquid product and routes vapour to the column.

The addition of this new functionality to HYSYS should be useful for many engineers. We do have some
cautions, however:
  • We have learned from experience that subflowsheets for Amine columns should in general not
    be manipulated; adding additional equipment to the subflowsheet for amine contactors and
    regenerators may give incorrect results.
  • Adding more equipment to the column subflowsheet can make the column more difficult to solve.
    In some cases it may be preferable to model equipment outside of the column subflowsheet (for
    example, when modeling a heat exchanger instead of the standard reboiler)

If you have any comments on this functionality which you would like to share with us or other HYSYS
users, please e-mail us.

List of new features

The new features in HYSYS v7.0 as per the Aspentech release notes are as follows:

“Aspen HYSYS V7.0 includes the following new features and enhancements in the following areas:
  • Enabling Aspen Properties compounds and property methods for simulations
  • APV70 and NISTV70 compound databases
  • New thermodynamic property models
  • Electrolyte capabilities
  • Process Economic Evaluation
  • Hydrates Utility
  • Process Utilities
  • Improved Input Summary
  • Unit Operation Enhancements
  • Aspen Custom Models (ACM) enhancements HYSYS
  • Additional CapeOpen 1.1 Support
  • PID support vendor specific control algorithms
  • Calculated residence time for every tray of the tray section
  • Level Tap option now available for the Sump Bottom tray of columns
  • Rigorous heat exchanger modeling speed improvements”
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