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Flue gas fired absorption chillers [Elektronische Ressource] / Christoph Kren

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277 Pages
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Published 01 January 2008
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PHYSIK-DEPARTMENT
Flue gas fired absorption chillers

Christoph KREN

Dissertation

TECHNISCHE UNIVERSITÄT
MÜNCHEN Technische Universität München – TUM
Physik Department, Lehrstuhl für Physik E19













Flue gas fired absorption chillers

Dipl.-Phys. (Univ.) Christoph KREN







Vollständiger Abdruck der von der Fakultät für Physik der Technischen Universität München
zur Erlangung des akademischen Grades eines

Doktors der Naturwissenschaften (Dr. rer. nat.)

genehmigten Dissertation.



Vorsitzender: Univ.-Prof. Dr. P. Vogl
Prüfer der Dissertation:
1. Univ.-Prof. Dr. U. Stimming
2. Univ.-Prof. Dr. F. Ziegler (Technische Universität Berlin)



Die Dissertation wurde am 28.11.2006 bei der Technischen Universität München
eingereicht und durch die Fakultät für Physik am 18.02.2008 angenommen.
Executive summary iii
Executive summary
Summary in English
The development of direct-fired and exhaust-fired absorption chillers, with optimized cycles
and multi-stage utilization of the flue gas enthalpy, is a key step towards improved energy
efficiency in absorption refrigeration and in CCHP applications. Fundamental thermodynamic
relations and boundary conditions are discussed with regard to promising cycle concepts and
recent developments. A generally valid approach for the optimization of flue gas heat
exchangers is presented and consequently applied in a numerical parameter study at typical
boundary conditions for regenerators in such absorption chillers. Experimental results from
laboratory tests on a novel regenerator prototype, built as a natural convection boiler with
vertical boiling tubes, are given. The heat transfer and pressure drop at the flue gas side are
discussed, as well as the boiling heat transfer and solution circulation inside the tubes. The
agreement of the experimental results and theoretical predictions is shown.
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Zusammenfassung auf Deutsch
Die Entwicklung direktbefeuerter und abgasbeheizter Absorptionskaltwassersätze mit
optimierten Kreisläufen und mehrstufiger Rauchgaswärmenutzung ist ein wesentlicher Schritt
zu besserer Energieeffizienz in Absorptionskälteanlagen und KWKK-Anwendungen.
Grundlegende thermodynamische Zusammenhänge und Randbedingungen werden im
Hinblick auf aussichtsreiche Kreislaufkonzepte und aktuelle Entwicklungen diskutiert. Ein
allgemeiner Ansatz zur Optimierung von Rauchgaswärmetauschern wird dargestellt und in
einer numerischen Parameterstudie unter typischen Randbedingungen für Austreiber solcher
Kältemaschinen angewandt. Experimentelle Ergebnisse von Labortests am Prototyp eines
neuartigen Naturumlauf-Austreibers mit stehenden Siederohren werden dargestellt.
Wärmeübergang und Druckverlust auf der Rauchgasseite sowie der siedende
Wärmeübergang und der Lösungsumlauf innerhalb der Rohre werden diskutiert. Die
Übereinstimmung von experimentellen Ergebnissen mit theoretischen Berechnungen wird
gezeigt.
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Flue gas fired absorption chillers © 2004-2006 Christoph Kren
Flue gas fired absorption chillers © 2004-2006 Christoph Kren Preface and acknowledgements v
Preface and acknowledgements
The present thesis has been created during my work at the Garching department of the
Bavarian Center for Applied Energy Research (ZAE Bayern - Bayerisches Zentrum für
Angewandte Energieforschung e.V.). The experimental part mainly relies on work that has
been conducted in the course of the joint European research project “LiBrAC” by the project
partners ZAE Bayern e.V. (Germany), Weir ENTROPIE S.A (France), Gas Natural SDG S.A.
(Spain), and BG Technology Ltd. / Advantica (UK) with funding by the European Commission.
This thesis would not have been possible without the continued inspiration and support from
my teacher and supervisor Felix Ziegler, who was always available for many enlightening
discussions, not only during his time as head of the division of the ZAE Bayern in Garching
but also at his later position as full professor at the TU Berlin. I also want to express my
gratitude to Wolfgang Schölkopf, present head of the division, who provided me a lot of
valuable guidance and personal assistance for finalizing my thesis although having not been
involved in the origins of this work. In addition, I really have to acknowledge the patience and
the support of Prof. Stimming, scientific director of the division, who always provided me the
suitable environment for my studies although they were not in the focus of his main area of
research and although they took way too much time to get finished.
I want to say “thank you” to all the partners in the “LiBrAC” project for the good cooperation
and for a lot of personal positive experiences with interational collaboration: Marie-Helene
Fulachier, Christophe Larger, and Jürgen Scharfe from Weir ENTROPIE, Jose Sahun from
Gas Natural, Dave Clark, Aik Lua, Jeff Sadler, and Bob Tucker from BGT. And, of course, my
thanks go to all the members of the “LiBrAC” team at the ZAE Bayern over the years: Tobias
Dantele, Herbert Reithmeier, Christian Keil, Dominik Neidinger, Martin Scholz, Tom Jelinek,
Gerhard Eberl, and to all others that I might have forgotten here. Additionally, I want to
express my thanks to all my former colleages at the ZAE Bayern for the friendship and for
the good times – without mentioning names because any listing would be incomplete.
Finally, I want to to say thank you to my wife for her love and her patience throughout all the
years.
Flue gas fired absorption chillers © 2004-2006 Christoph Kren


Flue gas fired absorption chillers © 2004-2006 Christoph Kren Contents vii
Contents
Flue gas fired absorption chillers ..........................................................i
Executive summary............................................................................................... iii
Preface and acknowledgements ............................................................................v
Contents............................................................................................................... vii
Nomenclature........................................................................................................xi
List of figures...................................................................................................... xvii
List of tables xxi
1 Introduction .....................................................................................1
1.1 Absorption refrigeration ..........................................................................1
1.2 Work outline..............................................................................................2
2 State of the art of absorption refrigeration ...................................4
2.1 Fundamentals and terminology ..............................................................4
2.1.1 Thermodynamic fundamentals ...................................................................4
2.1.2 Basic absorption cycle................................................................................7
2.1.3 Multi-stage absorption cycles11
2.1.4 Solution cycle design13
2.1.5 Commercially available types of absorption chillers .................................15
2.1.6 Reference operating conditions................................................................16
2.2 Thermal efficiency of indirect-fired absorption chillers......................17
2.2.1 Thermal efficiency of an ideal/reversible thermodynamic process for
refrigeration ..............................................................................................17
2.2.2 The endoreversible model for absorption chillers.....................................18
2.2.3 Internal loss mechanisms in single-effect cycles......................................24
2.2.4 Efficiency of indirect-fired double-effect chillers........................................29
2.2.5 Triple-effect and quadruple-effect chillers.................................................31
2.2.6 Integrated multi-stage chillers...................................................................32
2.3 Flue gas fired absorption chillers .........................................................33
2.3.1 Terminology33
2.3.2 Common design .......................................................................................33
2.3.3 Thermal efficiency ....................................................................................34
3 Basic concepts for highly efficient flue gas fired chillers .........37
3.1 General settings .....................................................................................37
3.1.1 Terminal temperature difference for flue gas heat exchangers.................37
3.1.2 Lower temperature limit of flue gas utilization ..........................................37
3.1.3 Upper internal temperature limit for driving heat input..............................38
Flue gas fired absorption chillers © 2004-2006 Christoph Kren viii Contents
3.2 Cycle analysis ........................................................................................ 38
3.2.1 Flow scheme and equilibrium states........................................................ 38
3.2.2 Internal losses and internal heat recovery ............................................... 42
3.3 Multi-stage utilization of flue gas enthalpy.......................................... 46
3.3.1 Basic considerations................................................................................ 46
3.3.2 Technical options for external heat input in absorption chillers................ 50
3.4 Examples of recent developments....................................................... 56
3.4.1 Advanced direct-fired absorption chillers................................................. 56
3.4.2 Novel exhaust-fired absorption chillers.................................................... 58
3.5 Conclusions for chiller design.............................................................. 61
4 Fundamentals - Heat transfer and pressure drop in flue gas
fired regenerators......................................................................... 62
4.1 Basic design considerations on flue gas fired regenerators............. 62
4.1.1 Heat exchanger concepts ........................................................................ 62
4.1.2 Typical heat transfer settings ................................................................... 65
4.2 General definitions for heat transfer and pressure drop
calculations ............................................................................................ 68
4.2.1 Heat transfer coefficients at circular tubes............................................... 68
4.2.2 Dimensionless numbers and property data ............................................. 68
4.2.3 Reversible and non-reversible pressure drops ........................................ 70
4.3 Forced single phase flow inside circular tubes .................................. 71
4.3.1 Definition of the Reynolds number........................................................... 71
4.3.2 Heat transfer 71
4.3.3 Frictional pressure drop ........................................................................... 74
4.4 Forced convection flow across tube bundles ..................................... 76
4.4.1 Definition of dimensionless numbers ....................................................... 76
4.4.2 Heat transfer ............................................................................................ 79
4.4.3 Frictional pressure drop 83
4.5 Boiling heat transfer .............................................................................. 86
4.5.1 Boiling regimes ........................................................................................ 86
4.5.2 Convective heat transfer in two-phase flows inside tubes ....................... 89
4.5.3 Onset of nucleate boiling in saturated and subcooled liquids.................. 91
4.5.4 Nucleate pool boiling of saturated liquids ................................................ 94
4.5.5 Nucleate boiling in upward tube flow ..................................................... 100
4.5.6 Calculation of overall heat transfer in flow boiling.................................. 102
4.5.7 Boiling of aqueous salt solutions............................................................ 104
4.6 Natural-convection boilers with vertical boiling tubes..................... 108
4.6.1 Common fields of application................................................................. 108
4.6.2 General aspects of modeling of natural-convection boilers ................... 108
4.6.3 Steam boilers for power generation ........................................................110
4.6.4 Steam-heated thermosiphon reboilers....................................................111
4.6.5 Laboratory experiments with unconventional designs ............................116
Flue gas fired absorption chillers © 2004-2006 Christoph Kren