Solid-solid recuperation to improve the energy efficiency of tunnel kilns [Elektronische Ressource] / Ping Meng

Meng Zhang

Informations

• Publié par: otto-von-guericke-universitat_magdeburg
• Publié le: 01 janvier 2011
• Nombre de lectures: 24
• Langue: Deutsch
• Poids de l'ouvrage: 7 Mo

Extrait

Solid-Solid Recuperation to Improve the
Energy Efficiency of Tunnel Kilns


Dissertation

zur Erlangung des akademischen Grades

Doktoringenieur
(Dr.-Ing.)


vorgelegt von: M. Sc. Ping Meng
geb. am: 06.09.1979
in: Beijing / China

genehmigt durch die Fakultät für Verfahrens- und Systemtechnik
der Otto-von-Guericke-Universität Magdeburg


Gutachter und Betreuer:
Prof. Dr.-Ing. Eckehard Specht, Universität Magdeburg
Gutachter: Gerd Walter, TU Bergakademie Freiberg
Dr.-Ing. Anne Tretau, Institut für Ziegelforschung Essen
Vorsitzender der Prüfungskommission:
Prof. Dr.-Ing. Dominique Thévenin, Universität Magdeburg


eingereicht am: 01.11.2010
Promotionskolloquium am: 21.02.2011
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Schriftliche Erklärung
Ich erkläre hiermit, dass ich die vorliegende Arbeit ohne unzulässige Hilfe Dritter und ohne
Benutzung anderer als der angegebenen Hilfsmittel angefertigt habe; die aus fremden Quellen
direkt oder indirekt übernommenen Gedanken sind als solche kenntlich gemacht.

Insbesondere habe ich nicht die Hilfe einer kommerziellen Promotionsberatung in Anspruch
genommen. Dritte haben von mir weder unmittelbar noch mittelbar geldwerte Leistungen für
Arbeiten erhalten, die im Zusammenhang mit dem Inhalt der vorgelegten Dissertation stehen.

Die Arbeit wurde bisher weder im Inland noch im Ausland in gleicher oder ähnlicher Form
als Dissertation eingereicht und ist als Ganzes auch noch nicht veröffentlicht.

Magdeburg, den 01.11.2010




Ping Meng



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Acknowledgments
First and foremost, I would like to express my deep and heartfelt gratitude and
appreciation to my supervisor, Prof. Dr.-Ing. Eckehard Specht, who provided me with the
opportunity to work as a Ph.D. student in his research group. His encouragement, guidance,
and financial support from the initial stages through the final phase enabled me to develop the
understanding for this research work. Without his input, this dissertation would not have been
possible. Furthermore, his friendly personality, profound knowledge, and rich experience not
only inspired me for deeper academic pursuit, but will continue to benefit all aspects of my
future life.

I would also like to express my deepest gratitude and condolences for Dr.-Ing. Karsten
Junge, who engaged and guided this research project from the beginning, until the day he
unexpectedly passed away. Now, with this presented dissertation, I hope his soul remains at
peace.

I am deeply grateful to Prof. Dr.-Ing. Gerd Walter for his in-depth review of my
dissertation and his constructive comments.

Further acknowledgment goes to Mrs. Dr.-Ing. Anne Tretau, who provided me with
various, valuable technical data during my research and agreed to review my dissertation.

I wish to thank all my colleagues in the Institute for Fluid Mechanics and
Thermodynamics at Otto von Guericke University Magdeburg for their assistance, friendship
and many happy and enjoyed times. Special thanks go to Dr.-Ing. Hermann Woche, Dr.-Ing.
Ashok Nallathambi, M. Sc. Hassan Fawzy Elattar, Dipl.-Ing. Nadine Lorenz, M. Sc. Duc Hai
Do, and of course, our friendly secretary, Mrs. Christin Hasemann. I also thank Ms. Melissa
Schwenk for the English text correction. It was a pleasure to work with all of them and our
time spent together will never be forgotten.

The continuous encouragement given by my loving parents, who brought me into the
world and raised me, is greatly acknowledged and appreciated. All my friends and relatives
both in Germany and in China, who have loved and supported me, are faithfully
acknowledged.

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Abstract
With the continuous increase of energy price in today’s life, it is of high importance to
invent a novel process for the tunnel kiln. In this work, counter-travelling tunnel kilns with
ventilators have been introduced, which work with higher energy efficiencies compared to
regular kilns. The necessary calculations and preliminary investigations have also been
reported.

The concept of a counter-travelling tunnel kiln was further developed and optimized.
With this kiln type, kiln cars move in the two tracks in opposite directions through the central
separated channel. Middle ventilators are used to keep the kiln gas recirculating between both
kiln sides. Thus, the heat from the hot ware can be transferred to the cold ware on both sides
of the kiln. To describe this complicated process of solid-solid-recuperation, a simplified
mathematical model with analytical equations was built first; a standard clinker brick without
holes were taken as an example. The principle effects and process mechanism were clearly
shown with the model. The influence of all kinds of variables, such as temperature, brick
piles' height, gap thickness of brick piles etc., were investigated. It was evident that the
electrical ventilator power is strongly dependent on the gap thickness of the brick piles, and
the ventilator power would be minimal at a gap thickness of around 10-20 mm. Meanwhile,
an energy balance of the whole kiln process was done, including the sum of fossil and primary
electrical energy, illustrating the optimum temperature difference between the hot and cold
side.

Computational fluid dynamics (CFD) was used to study the gas recirculation in the cross
section. 2D and 3D simulations were carried out with the commercial software package
FLUENT 6.3. 2D simulations for the internal horizontal ventilator were carried out at first to
investigate the flow pressure drop by the turn over and inlet/outlet. Later, 2D simulations
were carried out for vertical ventilator as well, where homogenous flow optimization was
performed and then the influence of the ventilator geometry for the total pressure drop of the
gas recirculation was investigated. The optimum operational conditions for the high heat
transfer with low pressure drop in the cross section were determined. In addition to the 2D
simulations, 3D simulations were performed for investigation of the ventilator pressure drop
and the gas recirculation in the firing zone. The gas velocity inside each gap in the cross
section and the gas velocity along the kiln length were revealed.

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Then, the simplified model was verified with an extended model by modifying the
assumptions of the first by an unsteady state model. The transient temperature changes both
for the solid and the gas were shown. The temperature difference inside the solid was also
investigated. It was revealed that the temperature difference between the top and bottom of
the brick pile was less than 10 K, where as between the core and surface is around 64 K. A
comparison of the simplified and transient models was carried out. It was evident that the
simplified model can explain the process relatively accurately, and the results obtained from
the simplified model are reliable.

Furthermore, simulations for roof tiles were carried out, illustrating optimum gap
thickness. It was shown that the principle effects and process mechanism are the same as
those for the clinker bricks. The energy consumption of the flue gas, the driving out, the heat
loss from the kiln wall, and the primary energy of the ventilators were determined.

As this study demonstrated, because of the solid-solid-recuperation, the energy
consumption of this counter-travelling kiln is only approximately 40% of that of conventional
brick tunnel kiln. The most obvious energy-saving term is that from the flue gas. This is the
effect that by the solid-solid-recuperation process the ballast gas by the solid-gas-recuperation
process is avoided. Therefore, the aim of this research project is fully achieved.

Key words: Ceramic firing, Tunnel kiln, Energy saving
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Zusammenfassung
Auf Grund stetig steigender Energiepreise und durch den Vergleich der aktuellen
Energieeffizienz des Tunnelofenprozesses mit anderen Öfen, gewinnt die langfristige
Einführung von alternativen Brennprozessen mehr und mehr an Bedeutung. Als ersten und
wichtigsten Schritt wurden in dieser Arbeit die für die Einführung des neuen
Brennofenprozesses notwendigen Berechnungen und Voruntersuchungen durchgeführt.

Das Konzept des Gegenlauftunnelofens wurde weiterentwickelt und optimiert. Bei
diesem Ofentyp bewegen sich die Ofenwagen auf zwei Linien entgegengesetzt durch den
mittig getrennten Tunnel. Mittels eines Gebläses wird die Umluftströmung zwischen den
beiden Tunnelseiten realisiert. Dadurch wird Wärme von dem heißen Gut an das kalte Gut
übertragen und umgekehrt. Zur Beschreibung des komplizierten Prozesses der Solid-Solid-
Rekuperation wurde zunächst ein vereinfachtes mathematisches Modell mit analytischen
Gleichungen erstellt. Als Beispiel wurde ein üblicher Ziegelstein verwendet. Die prinzipiellen
Effekte und der Prozessmechanismus wurden mit diesem Modell eindeutig gezeigt. Der
Einfluss aller möglichen Variablen, wie z. B. Temperatur, Höhe des Ziegelstapels sowie die