State of the art review and recent development of the glycol dehydration facility modelling and optimization

© 2012 Aspen Technology, Inc. All rights reserved
OPTIMIZETM 2013
STATE OF THE ART REVIEW AND
RECENT DEVELOPMENTS IN
GLYCOL DEHYDRATION FACILITY
MODELLING AND OPTIMIZATION
A. Alva-Argaez and J. Holoboff (Process Ecology)
Doris Weiss (Devon Energy)
Speaker: Alberto Alva-Argaez
Process Ecology
May 2013

© 2013 Aspen Technology, Inc. All rights reserved | 2
Outline
Who we are
Glycol Dehydration Simulation
Review
– TEG systems
– EG Refrigeration plants
– Air Emissions
– Other process issues
Optimization approach
Conclusions and future work

Who We Are: Process Ecology Inc.
Founded 2003, Calgary, AB
Engineering consulting, process
simulation & optimization,
software development
Air emissions estimation and
management
Tracking air emissions since
2007 for approximately 1,000
dehys in Western Canada
3

Glycol dehydration
– Simulation widely used for the design and troubleshooting of TEG
dehydration and EG hydrate formation units.
– Increasingly, simulation is relied upon for air emissions reporting
– Aspen HYSYS must be used with care – the application of the
model must be considered
– Simplified approaches for air emissions such as GlyCalc or emission
factors must be limited to their intended purpose
– Simulation relies on experimental data (VLE, VLLE). There is a lack
of data to improve the predictions and increase trust in the results.
– Optimization of process plants requires the evaluation of trade-offs
between capital expenditures, operating cost and environmental
goals

TEG Dehydration
HYSYS (Peng Robinson), HYSYS (Glycol) and GlyCalc compared to:
• GPA RR 131 “Solubility of Selected Aromatic Hydrocarbons in
TEG” (1991)
• Water removal predictions (GPSA, Arnold & Stewart)

Key findings
All simulators show
reasonable match for
BTEX absorption to
glycol phase at contactor
conditions
At regenerator
conditions GlyCalc
overpredicts BTEX K-
values
Overall BTEX emissions
show reasonable match
Dry gas water content
predictions
– Essential for optimization
of operational parameters
– GlyCalc consistently over-
predicts water removal
– HYSYS-Glycol best fit for
water content

Dehydration performance
Data: Surface Production Operations (Arnold & Stewart)

TEG - remarks
Care must be taken when using simulation tools for air
emissions/optimization tasks
GlyCalc can underpredict dry gas water content (not the
ideal optimization tool)
HYSYS offers flexibility to tune parameters to
experimental/plant data
Automation can also assist when performing sensitivity
analysis (e.g. changes in contactor temperature)
Stripping gas effects also need to be considered

EG Refrigeration
HYSYS (Peng Robinson), HYSYS (Glycol), ProMax (SRK) and GlyCalc
compared to:
• GPA RR 137 (VLE only) “Solubility of Selected Aromatic
Hydrocarbons in MEG” (1994)
• Plant data from selected facilities in Western Canada

Key findings
Low Temp Separator (LTS)
is the essential phase split
– How much BTEX splits into
HC liquid and water/EG
phase?
– Also, losses of EG to vapor
HYSYS PR should not be
used for air emissions-
negligible BTEX is predicted
in aqueous phase, resulting
in no calculated emissions
GlyCalc frequently fails to
predict a HC liquid phase
Trends
– HYSYS-Glycol: highest
BTEX
– Caution at lower
pressures (less than
2,500 kPa)
– GlyCalc: lowest amount
of BTEX (when HC liquid
found)
VLLE data required
– -35C to-10C
(-31F to 14F)
– 2,000–7,000kPa
(290–1,015psi)

Simulation results- benzene in mixed liq. phase

Simulation results- benzene in aqueous phase

EG – further work
– Comparison with facility data: It would be helpful to obtain
more plant data, ensuring a close review of the procedure for
collecting data and samples.
– Comparison with experimental data: Although GPA RR-137 is
very useful, a VLLE study would improve on this work and be
very useful in understanding the solubility of BTEX in the
aqueous and hydrocarbon liquid phases of cold separators.
Acknowledgments :
– Brad Johnston (Cenovus Energy Inc.)
– Ian Cosman (Process Ecology Inc.)

Air Emissions- Regulations
BTEX/ HAPs air quality objectives
Greenhouse gas emissions
– EPA Subpart W
– BC GHG reporting (WCI standards)
– AB GHG program
– Climate Registry
– Carbon Disclosure Project
– etc.

Methane emissions- dehys
3rd largest source

Estimation results- GHGs
Simulated results vs. API emission factor estimates -
emission factor is unreliable for individual facilities

Stripping gas effects
HYSYS can also be used to predict the inlet gas temperature at which
stripping gas would be required, for a given dry gas water content.
However, work needs to be done to improve the predictions.

Key findings/ remarks
Emission factors are too
simplistic, HYSYS better for
individual units
We are planning to compare
HYSYS CO2E emissions
calculations to data
Glycalc also recommended
by regulatory agencies but
isn’t as flexible
Stripping gas use can
introduce large errors in
these estimations
HYSYS provides added
flexibility and automation
opportunities
Remarks:
– Once we have gathered
operating data and
simulated these plants
for regulatory reporting:
perform optimization.
– Inform your energy
optimization and
emissions reduction
strategies
Energy and emissions
management is a process
engineering challenge not
just an accounting
challenge

Emissions controls
Condenser systems
– Air cooled
– Glycol cooled
– Water cooled (not in cold
climates)
– Aboveground tanks and
condensing tanks:
modelling activity in
progress
– Flash tank
beneficial/required.
– Stripping gas: eliminate
Incinerators and Flares
– Destruction efficiencies
high in incineration
99+%
– Fuel gas demand
– Flares: 90% destruction
accepted by ERCB
(Canada)
Zero emissions trend in
Canada
– Condensers with burner
systems (e.g., Jatco
units)
– Vents tied into
compressor suction or
burners

Overall optimization strategy
Leverage regulatory reporting efforts with plant optimization
Optimize for minimum energy demand = minimum air
emissions
– BTEX, GHGs from process vents
– GHGs, CACs from combustion
– Stripping gas review – is it really needed?
Frequent glycol overcirculation
– Replace/modify pumps
– Switch to electric pumps

Focus efforts
Total approximately $700,000/yr

Conclusions
Leverage regulatory reporting efforts with plant optimization
Optimize for minimum energy demand = minimum air
emissions
– BTEX, GHGs from process vents
– GHGs, CACs from combustion
– Stripping gas review- really needed?
Frequent glycol overcirculation
– Replace/modify pumps
– Switch to electric pumps
Consider emissions controls in the exercise

THANK YOU FOR YOUR ATTENTION!
ANY QUESTIONS?
alberto@processecology.com

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