Herraiz (2017) PhD thesis_final

287 Pages·2017·8.88 MB·English

SELECTIVE EXHAUST GAS RECIRCULATION IN
COMBINED CYCLE GAS TURBINE POWER PLANTS
WITH POST-COMBUSTION CARBON CAPTURE

Laura Herraiz Palomino

Ph. D. Thesis
School of Engineering
University of Edinburgh

2016

Lay Summary
Gas-fired power plants with Carbon Capture and Storage (CCS) are expected to play a
significant role to reduce carbon dioxide (CO ) emissions from the power generation sector.
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They can provide dispatchable low-carbon electricity to maintain the flexibility required in
an electricity system with high penetration of renewables.
The low CO concentration and large volumes of flue gas generated in natural gas-fired
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power plants make CO separation with post-combustion capture technologies more
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challenging, compared to coal-fired power plants.
This thesis investigates options for increasing CO concentration upstream of the capture
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system by selectively transferring CO from a flue gas stream into an air stream used for
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natural gas combustion. Other components in the flue gas are not recirculated back to the
inlet of the gas turbine system and a large excess of air is maintained. Strategies to enhance
capture should aim to introduce minimal modification in the gas turbine engine, as current
gas turbine technology presents high efficiency and plays an important role in achieving high
combined cycle net power output.
Process simulations in a linked model of a natural gas combined cycle plant with a carbon
capture and compression system conducted in this thesis show that high CO levels at the
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exhaust of the gas turbine can be achieved maintaining levels of oxygen for efficient
combustion, and that existing class of gas turbine engines can be operated with Selective
Exhaust Gas Recirculation (S-EGR). For capture technologies using amine solvents, a
reduction in equipment size and energy requirements are achieved.
A novel system for selective CO transfer between a flue gas stream and an air stream is
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proposed consisting on rotary physical adsorption. A conceptual design assessment shows
that a step change in the performance of adsorbent materials is necessary before this novel
system can be commercially deployed.
Finally, a novel contribution is made to show that the availability of cooling might not
necessarily constitute a limitation for the full scale deployment of CCS, particularly in
regions with increasingly restricted access to cooling water and limited availability of fresh
or sea water abstraction licences. Process simulations showed that cooling and process water
demand can be drastically reduced in natural gas-fired power plants with carbon capture by
using dry cooling systems consisting of rotary gas/gas heat exchangers with ambient air as
the cooling fluid.

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Abstract
Selective Exhaust Gas Recirculation (S-EGR) consists of selectively transferring CO from
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the exhaust gas stream of a gas-fired power plant into the air stream entering the gas turbine
compressor. Unlike in “non-selective” Exhaust Gas Recirculation (EGR) technology,
recirculation of, principally, nitrogen does not occur, and the gas turbine still operates with a
large excess of air.
Two configurations are proposed: one with the CO transfer system operating in parallel to
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the post-combustion carbon capture (PCC) unit; the other with the CO transfer system
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operating downstream of, and in series to, the PCC unit. S-EGR allows for higher CO
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concentrations in the flue gas of approximately 13-14 vol%, compared to 6.6 vol% with
EGR at 35% recirculation ratio. The oxygen levels in the combustor are approximately 19
vol%, well above the minimum limit of 16 vol% with 35% EGR reported in literature.
At these operating conditions, process model simulations show that the current class of gas
turbine engines can operate without a significant deviation in the compressor and the turbine
performance from the design conditions. Compressor inlet temperature and CO
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concentration in the working fluid are critical parameters in the assessment of the effect on
the gas turbine net power output and efficiency. A higher turbine exhaust temperature allows
the generation of additional steam which results in a marginal increase in the combined cycle
net power output of 5% and 2% in the investigated configurations with S-EGR in parallel
and S-EGR in series, respectively. With aqueous monoethanolamine scrubbing technology,
S-EGR leads to operation and cost benefits. S-EGR in parallel operating at 70%
recirculation, 97% selective CO transfer efficiency and 96% PCC efficiency results in a
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reduction of 46% in packing volume and 5% in specific reboiler duty, compared to air-based
combustion CCGT with PCC, and of 10% in packing volume and 2% in specific reboiler
duty, compared to 35% EGR. S-EGR in series operating at 95% selective CO transfer
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efficiency and 32% PCC efficiency results in a reduction of 64% in packing volume and 7%
in specific reboiler duty, compared to air-based, and of 40% in packing volume and 4% in
specific reboiler duty, compared to 35% EGR.
An analysis of key performance indicators for selective CO transfer proposes physical
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adsorption in rotary wheel systems as an alternative to selective CO membrane systems. A
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conceptual design assessment with two commercially available adsorbent materials,
activated carbon and Zeolite X13, shows that it is possible to regenerate the adsorbent with
air at near ambient temperature and pressure. Yet, a significant step change in adsorbent
materials is necessary to design rotary adsorption systems with dimensions comparable to
the largest rotary gas/gas heat exchanger used in coal-fired power plants, i.e. approximately
24 m diameter and 2 m height. An optimisation study provides guidelines on the equilibrium
parameters for the development of materials.
Finally, a technical feasibility study of configuration options with rotary gas/gas heat
exchangers shows that cooling water demand around the post-combustion CO capture
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system can be drastically reduced using dry cooling systems where gas/gas heat exchangers
use ambient air as the cooling fluid. Hybrid cooling configurations reduce cooling and
process water demand in the direct contact cooler of a wet cooling system by 67% and 35%
respectively, and dry cooling configurations eliminate the use of process and cooling water
and achieve adequate gas temperature entering the absorber.
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Acknowledgment
This thesis is the result of work done after generous opportunity given by Dr. Mathieu
Lucquiaud, Prof. Jon Gibbins and Dr. Hannah Chalmers. Thanks to my supervisor Dr.
Mathieu Lucquiaud for his essential support to get this Ph.D. completed and for keeping me
interested in the “broader picture” of CCS and in the essential role of collaboration between
academy and industry for CCS to happen.
Special tanks to Dr. Eva Sánchez Fernández for her guidance and advice, stimulating
discussions and fruitful exchange of ideas. Thanks to Dr. María Sanchez del Río Sáez and
Ms. Olivia Errey. This Ph.D. would not have been possible without their help.
I also thank my colleagues in the Power Plant Engineering & CCS group at the University of
Edinburgh. In particular, I would like to thank Dr. Bill Bulchle, Dr. Ignacio Trabadela, Dr.
Abigail Gonzalez, Dr. Alasdair Bruce, Dr. Juan Riaza, Mr. Paul Tait, Ms. Erika Palfi, Mr.
Thomas Spitz and Mr. Gordon Paterson for their support and unforgettable time spent
together. Special thanks to Dr. Atul Agarwal and Dr. Siraj Sabihuddin for their support,
encouragement and friendship.
This project has also given me the opportunity to work with excellent people outside of
academia. I would like to thank Mr. Dougal Hogg, Mr. Jim Cooper and Mr. Richard Smith
from Howden UK, Glasgow, for their extremely valuable input and technical advice on
rotary heat exchangers. I would also like to thanks Ms. Meron Reid for giving me the
opportunity to attend the Howden Academy.
Financial support for this research was provided by the Doctoral Training Account of School
of Engineering of the School of Engineering at the University of Edinburgh, funded by
the UK Engineering and Physical Science Research Council (EPSRC) and Howden Group
(Glasgow, Scotland). Support from the GAS-FACTS project funded by the EPSRC
(EP/J020788/1) is gratefully acknowledged. Thanks to the UK Carbon Capture and Storage
Research Centre (UKCCSRC)
I sincerely appreciate the time and efforts of my examination committee members, Dr.
Hannah Chalmers and Dr. Richard Marsh. Thank you for sharing your experience and advice
with me as well as being kind in your assessment of this work.
Finally, I am grateful to my family because they have always encouraged me to pursue this
project and follow my dreams, helping me along the way.

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1. Declaration of originality
The work included in this Ph.D. thesis, except when referenced, is the results of the effort of
years that has been done by the author alone under the guidance of her supervisor Dr.
Mathieu Lucquiaud. The author acknowledges essential contributions by others in the
acknowledgment section of this thesis and in further sections of the work where required.
This Ph.D. thesis has not been submitted for any other degree or professional qualifications
in the UK or elsewhere. The author recommends referencing this thesis as follows:
Herraiz, L. (2016), Selective Exhaust Gas Recirculation in Combined Cycle Gas Turbine
Power Plants with Post-combustion Carbon Capture, Ph.D. Thesis, School of Engineering,

University of Edinburgh, United Kingdom of Great Britain and Northern Ireland (UK).

Laura Herraiz Palomino

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