Process Ecology developed a HYSYS extension to enable a 4-phase flash for detection of mercury in gas processing systems

1. Implementation of a 4-phase flash
for the detection of a third liquid
phase in hydrocarbon process
simulation using HYSYS
Speaker: Howard Wilson, James Holoboff
D. Embry1, H. Wilson1, J. Holoboff2 and M. Khoshkbarchi2
1ConocoPhillips Company
2Process Ecology Inc.

2. Outline
• Background & Industry Applications
• Limitations of HYSYS Flash
• Proposed Solution
• Stability Test Utility
• 4-Phase Flash Unit Operation Extension
• Impact on Simulation Results
• Demonstration

3. Background
• Liquid-liquid equilibrium is a common
phenomenon in hydrocarbon processes
• Possibility for liquid phases to further phase
separate (i.e. – 3 liquid phases)
• 3 liquid phases cannot be handled in HYSYS

4. Industry Applications (1)
• Hydrocarbon systems with heavy fractions
resulting in:
heavy phase (wax / asphaltene)
light hydrocarbon phase
water phase
• Immiscible tracer added to two-liquid phase
system
• Some mixtures with perfluoro compounds

5. Industry Applications (2)
• Solvent/polymer/water mixtures
• Oil and natural gas applications, where
mercury-free product is required
• Cryogenic applications where impurities such
as mercury must be addressed

6. Industry Applications - Mercury (1)
• Natural gas may contain low levels of mercury
• In cryogenic applications (e.g. - LNG, nitrogen
rejection), mercury can concentrate in cryogenic
aluminum heat exchangers
• Any contact of liquid mercury with aluminum can
cause liquid metal embrittlement and lead to
catastrophic failure

7. Industry Applications - Mercury (2)
• For some applications, “mercury-free” gas
product streams are required
• Mercury may need to be removed to prevent
catalyst deactivation and heat exchanger
problems in downstream processing

8. Industry Applications – Simulation
• From a simulation perspective, It would be
useful to determine when / where mercury is
predicted to form a separate phase
• HYSYS can be used to model industry
applications, but may not adequately predict
properties of mercury or formation/separation of
mercury phase

9. Improvements to HYSYS
1. Improve pure component property model
(vapor pressure)
2. Improve predicted solubility of key
components in hydrocarbons and water
(modify interaction parameters)
3. Detect presence of key components as a
separate phase
• This presentation focuses on #3

10. Limitations of HYSYS Flash
• If there are in reality three
liquid phases HYSYS
incorrectly distributes
components resulting in
creation of unstable
phases
• Standard HYSYS flash can check for two
liquid phases and a vapor phase
Maximum Phases in
HYSYS – 3 (VLL)

11. Proposed Solution
• Perform stability calculation on stream:
• Select “test” component
• Calculate Gibbs energy of pure
component (Gibbs1)
• Calculate Gibbs energy of specified
component in stream (Gibbs2)
• If Gibbs1 < Gibbs2 then new phase
with pure component is stable

12. Proposed Solution
• Create additional functionality in HYSYS
to check for additional phases:
• Develop HYSYS unit operation
extension, which includes:
• Compiled code (DLL)
• View file (EDF)
• Report file (RDF)

13. Required skills
• Programming (e.g. Visual Basic, C++)
• Familiarity with HYSYS automation interfaces
• Knowledge of user interfaces and formats (EDF, RDF)
• Understanding of interaction between unit operation
and flowsheet
• General and HYSYS-specific thermodynamics
knowledge (e.g., understanding of HYSYS reference
state)
• Extensions required about 7 weeks development time

14. Adding Unit Operation Extension
in HYSYS
• Register the HYSYS extension
• Operation filtered as “Extension” type

15. Stability Test Utility
• Multiple streams can be selected
• Display status & departure:
Unstable – test component could form a pure phase
Stable – test component will not form a pure phase
Incipient – test results inconclusive based on tolerance value

16. Stability Test Utility
• Any available component can be selected as the
“test component”
• A tolerance is selected

17. Four-Phase Separator
• Connections set up much like conventional 3-phase
separator in HYSYS

18. Four-Phase Separator
• Select test component
• Phase Order – density vs. component
• Settings – stability tolerance, objective function

19. Sample Gas Plant Simulation

20. Effect of changes on estimated
Dehy Inlet Hg concentration
64776252.068245
6477630.21824
76760.0282
Updated with
4-phase Flash
(ppb Hg)
Updated
properties &
BIPs (ppb Hg)
Standard
HYSYS thermo
(ppb Hg)
Feed
(ppb Hg)

21. Demonstration

22. Thank-you!
• Thanks to ConocoPhillips and Process
Ecology management for permitting
discussion of this material