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 Company2Process Ecology Inc.

Outline

• Background & Industry Applications

• Limitations of HYSYS Flash

• Proposed Solution

• Stability Test Utility

• 4-Phase Flash Unit Operation Extension

• Impact on Simulation Results

• Demonstration

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

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

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

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

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

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

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

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)

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

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)

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

Adding Unit Operation Extension

in HYSYS

• Register the HYSYS extension

• Operation filtered as “Extension” type

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

Stability Test Utility• Any available component can be selected as the

“test component”

• A tolerance is selected

Four-Phase Separator

• Connections set up much like conventional 3-phase separator in HYSYS

Four-Phase Separator

• Select test component

• Phase Order – density vs. component

• Settings – stability tolerance, objective function

Sample Gas Plant Simulation

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)

Demonstration

Thank-you!

• Thanks to ConocoPhillips and Process

Ecology management for permitting

discussion of this material