Modeling Advanced Flash Stripper for Carbon Dioxide Capture Using Aqueous Amines

284 Pages·2016·3.95 MB·English

Copyright
by
Yu-Jeng Lin
2016
The Dissertation Committee for Yu-Jeng Lin Certifies that this is the approved
version of the following dissertation:

Modeling Advanced Flash Stripper for Carbon Dioxide Capture Using
Aqueous Amines

Committee:

Gary T. Rochelle, Supervisor
Michael Baldea
Eric Chen
Gyeong S. Hwang
David Miller
Modeling Advanced Flash Stripper for Carbon Dioxide Capture Using
Aqueous Amines

by
Yu-Jeng Lin, B.S., M.S.

Dissertation
Presented to the Faculty of the Graduate School of
The University of Texas at Austin
in Partial Fulfillment
of the Requirements
for the Degree of

DOCTOR OF PHILOSOPHY

THE UNIVERSITY OF TEXAS AT AUSTIN
August 2016
To my parents
Acknowledgements
Most importantly I would like to thank Mom and Dad. Pursuing Ph.D. abroad
could be much tougher without your love and encouragement. You were always there
supporting every decision I made. Thank you for giving us everything you have and make
our life better. I would not be the person I am today without you.
I would like to thank my advisor, Dr. Gary Rochelle for this incredible journey.
This work cannot be done without your consistent advising and encouragement. I am so
lucky to have the best mentor who is brilliant, motivating, patient and thoughtful. The
patience you have and the tremendous amount of time you spend on your everty student
make me want to become a better mentor when it comes to teaching. Your passion and
dedication to the work and the people you love while having a well work-life balance
become a role model I want to follow. Every weekly meeting with you was always
inspiring and motivated me to become a better engineer. I had the best learning
experience of my life.
I also appreciate my advisors in National Tsing Hua University, Dr. Shi-Shang Jang
and Dr. Shan-Hill Wong who encouraged me to step outside the comfort zone and meet
the smartest people in the world. Thank you Maeve for editing all of the progress reports
and helping me improve my writing skill. Those feedback is especially valuable for
international students.
I have learned so much from all of my current and previous groupmates not just
technical knowledge but also the way you approach and solve problems. Joining as the
same class year and the same group, Di is a perfect company to discuss qualifying exam,
course work and inevitably carbon capture. Tarun Madan was a great mentor who set
great examples on modeling work when I came in as a first-year. The previous work by
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David Van Wagener and Babatunde Oyenekan is an essential foundation of this work. It
was always enjoyable to have discussions with my groupmates, Peter Frailie, Lynn Li,
Brent Sherman, Matt Walters, Nathan Fine, Darshan Sachde, Eric Chen, Yang Du, Omkar
Namjoshi, Steven Fulk, Matt Beaudry, Yue Zhang, Kent Fischer, Ye Yuan, and Junyuan
Ding. Thank you for extending my vision and reminding me what I can do better. I am
grateful to have my friends whom I’ve known since college, Jerry, Island, Helen, Kaif, and
Ke-Hsun. Every trip we had always refreshed me and made me able to come back to
work with full of energy and memory. It’s been a memorable journey with all of your
participation.
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Modeling Advanced Flash Stripper for Carbon Dioxide Capture Using
Aqueous Amines

Yu-Jeng Lin, Ph.D.
The University of Texas at Austin, 2016

Supervisor: Gary T. Rochelle

The intensive energy use is the major obstacle to deployment of CO capture.
2
Alternative stripper configurations is one of the most promising ways to reduce the energy
consumption of CO regeneration and compression. The advanced flash stripper (AFS)
2
proposed in this work provides the best energy performance among other alternatives.
A systematic irreversibility analysis was performed instead of examining all the
possible alternatives. The overhead condenser and the cross exchanger were identified
the major sources of lost work that causes process inefficiencies. The AFS reduces the
reboiler duty by 16% and the total equivalent work by 11% compared to the simple stripper
using aqueous piperazine. The AFS was demonstrated in a 0.2 MW equivalent pilot plant
and showed over 25% of heat duty reduction compared to previous campaigns, achieving
2.1 GJ/tonne CO of heat duty and 32 kJ/mol CO of total equivalent work. The proposed
2 2
bypass control strategy was successfully demonstrated and minimized the reboiler duty.
Approximate stripper models (ASM) were developed to generalize the effect of
solvent properties on energy performance and guide solvent selections. High heat of
absorption can increase partial pressure of CO at elevated temperature and has potential
2
to reduce compression work and stripping steam heat. The optimum heat of absorption
was quantified as 70–125 kJ/mol CO at various conditions, which is generally higher than
2
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existing amines with 60–80 kJ/mol. The energy performance of AFS is not sensitive to
the heat of absorption.
A techno-economic analysis with process optimization that minimizes the
annualized regeneration cost was performed to demonstrate the profitability of the AFS.
The AFS reduces the annualized regeneration cost by 13% and the major savings come
from the reduction of the OPEX, which counts for over 70% of the regeneration cost. The
compressor and the cross exchanger are the major components of the CAPEX. The
optimum lean loading is around 0.22 mol CO /mol alkalinity for PZ but is flat between
2
0.18 and 0.24 with less than 1% difference.
The AFS was demonstrated as a flexible system that can be applied to a wide range
of solvent properties and operating conditions while still maintaining remarkable energy
performance. Further improvement of energy efficiency by process modifications is
expected to be marginal. Increasing solvent capacity will give the most energy and cost
reduction in the future.

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Table of Contents
List of Tables .........................................................................................................xv
List of Figures ........................................................................................................xx
Chapter 1: Introduction ............................................................................................1
1.1 CO capture from coal-fired power plants ................................................1
2
1.2 Amine scrubbing process ..........................................................................3
1.3 Energy use for CO regeneration ..............................................................4
2
1.4 Prior work of alternative strippers ............................................................6
1.4.1 Solvent selections..........................................................................8
1.4.2 Quantifying energy performance ..................................................9
1.4.3 Demonstration of operability and profitability ...........................10
1.5 Research scope ........................................................................................11
Chapter 2: Modeling Methods ...............................................................................12
2.1 Stripper modeling in Aspen Plus® ..........................................................12
2.2 Calculating heat exchanger LMTD .........................................................14
2.3 Total equivalent work .............................................................................15
2.4 Heat-to-electricity efficiency ..................................................................16
2.5 Multi-stage compressor ...........................................................................18
2.5.1 Characteristics of CO compression ...........................................19
2
2.5.2 Updated multi-stage compressor configuration ..........................20
2.5.3 Compression work correlation ....................................................24
Chapter 3: Process Irreversibility Analysis............................................................26
3.1 Introduction .............................................................................................26
3.2 Methods...................................................................................................28
3.2.1 Process specifications .................................................................28
3.2.2 Theoretical minimum work and lost work ..................................29
3.3 Process descriptions ................................................................................31
3.3.1 Simple stripper ............................................................................31
3.3.2 Lean vapor compression .............................................................32
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3.4 Results and discussions ...........................................................................33
3.4.1 Inefficiency of simple stripper ....................................................33
3.4.1.1 Minimum work and lost work distribution .....................33
3.4.1.2 Lost work of regeneration ...............................................35
3.4.2 Inefficiency of lean vapor compression ......................................37
3.4.3 Proposed design strategies ..........................................................38
3.4.3.1 Heat and mass transfer in the stripper .............................39
3.4.3.2 Self-contained heat integration using cold rich solvent ..40
3.4.3.3 Temperature pinch of the cross exchanger .....................41
3.4.4 Advanced flash stripper ..............................................................42
3.4.4.1 Proposed stripper configuration ......................................42
3.4.4.2 Lost work of regeneration ...............................................44
3.4.4.3 Cold and warm rich bypass .............................................48
3.4.4.4 Irreversibility of the cross exchanger ..............................50
3.4.4.5 Irreversibility of the reboiler/steam heater ......................53
3.4.5 Thermodynamic efficiency of regeneration ................................53
3.5 Conclusions .............................................................................................55
Chapter 4: Energy Performance of Advanced Stripper Configurations ................57
4.1 Introduction .............................................................................................57
4.2 Simulation methods ................................................................................59
4.2.1 Modeling stripper with updated MEA model .............................59
4.2.2 Stripping steam for PZ and MEA ...............................................61
4.2.3 Process specifications .................................................................62
4.3 Process descriptions ................................................................................64
4.3.1 Simple stripper ............................................................................64
4.3.2 Conventional alternatives............................................................65
4.3.2.1 Lean vapor compression (LVC)......................................65
4.3.2.2 Interheated stripper .........................................................66
4.3.2.3 Cold rich bypass ..............................................................67
4.3.3 Rich exchanger bypass strategy ..................................................68
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