Steam injection into saturated porous media : process analysis including experimental and numerical investigations
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In this paper, the authors investigated the effect of non-isothermal multi-phase system emerging during steam injection into saturated porous media and developed a numerical model to identify important processes and parameters influencing the system behavior.Abstract:
The extensive use of chemicals in industry coupled with the lack of
understanding their potential threat to the environment and
human health has resulted in substantial soil and groundwater
contamination during the 20th century in many industrialized
areas. Sites contaminated by dense non-aqueous phase liquids
(DNAPL's) turned out to be rather problematic. The fact that DNAPL's
have a higher density than water enables them to migrate below the
ground water table causing extensive contaminations in the saturated
zone. Conventional remediation techniques show major difficulties
in the remediation of DNAPL and induced the development of innovative
remediation techniques for such sites. One of the most promising is
the injection of steam into the subsurface. This technique has been
successfully applied to the remediation of DNAPL contaminations in the
unsaturated zone. Today, the application of steam injection for the
treatment of contaminations in the saturated zone is in the focus of
research interest. Although the physical processes elapsing during
steam injection are basically the same either in the saturated and
unsaturated zone, there are distinct differences in their
relevancy.
This work contributes to increasing the insight into the non-isothermal
multi-phase system emerging during steam injection into saturated
porous media. An essential prerequisite for this is to identify and
understand important processes and parameters influencing the
system behavior. First, experimental investigations are carried out
in a saturated two-dimensional flume. The established understanding of
the system behavior was incorporated into the development of a numerical
model. In this process, special attention was placed on an accurate
description of system behavior and a robust operation of the
model. Instabilities occurring at fully saturated conditions were
analyzed, and appropriate measures were taken to prevent them.
The developed model was subsequently used for simulating steam
injection experiments and later utilized for the verification of the
model code. In order to demonstrate the predictive qualities of the
model, a field scale steam injection was simulated.
The experimental and numerical investigations resulted in an
improved understanding of the non-isothermal multi-phase system
emerging during steam injection into saturated porous media. The
relevant processes and parameters influencing the propagation of the
steam front at saturated conditions could be identified. This provided
the possibility of deriving characteristic typecurves for steam
propagation in saturated porous media.
Der massive Einsatz von synthetischen Chemikalien in der Industrie
fuhrte in der Vergangenheit zu erheblichen Verunreinigungen des
Untergrundes und somit auch des Grundwassers. Besonders problematisch
sind Verunreinigungen mit Schadstoffen aus der Gruppe der DNAPL
(dense non-aqueous phase liquids), da diese schon in geringen
Konzentrationen human-toxisch sind und im Verdacht stehen
krebserregend zu sein. DNAPL's haben eine grosere Dichte als
Wasser und konnen somit zu Verunreinigungen in der mit Grundwasser
gesattigten Bodenzone fuhren. Konventionellen Verfahren wie z.B.
Pump & Treat haben oftmals erhebliche Schwierigkeiten das Sanierungs-
ziel bei DNAPL Schadensfallen zu erreichen. Dies initiierte die
Entwicklung einer Reihe innovativer Technologien fur die Sanierung
solcher Schadensfalle. Ein viel versprechendes Verfahren ist dabei die
thermische Sanierung mittels Dampfinjektion. Das Verfahren der
Dampfinjektion ist bereits erfolgreich fur Schadensfalle in der
ungesattigten Bodenzone oberhalb des Grundwasserspiegels eingesetzt
worden. DNAPL Schadensfalle sind jedoch nicht auf die ungesattigte
Bodenzone beschrankt und deshalb wird momentan die Anwendbarkeit
des Verfahrens zur Sanierung von Kontaminationen in der gesattigten
Bodenzone untersucht. Obwohl die Prozesse der Dampfausbreitung dabei
prinzipiell ahnlich sind, wie in der ungesattigten Bodenzone, so
kann sich dennoch deren Einflus auf das Prozessverhalten stark
unterscheiden.
Mit der vorliegenden Arbeit konnte das Prozessverstandnis fur das
nicht-isotherme Mehrphasensystem, welches sich bei der Dampfinjektion
in ein gesattigtes poroses Medium einstellt, verbessert werden. Eine
essentielle Voraussetzung dafur war die Identifikation der relevanten
Prozesse und Parameter.
Dazu wurden in einem ersten Schritt experimentellen Untersuchungen
zur Dampfinjektion in einer zweidimensionalen Kuvette durchgefuhrt.
Das gewonnene Prozessverstandnis wurde in die Entwicklung eines
numerischen Modells einbezogen. Dabei wurde auf eine moglichst exakte
Wiedergabe des Prozessverhaltens und ein robustes Verhalten des
numerischen Modells Wert gelegt. Probleme, die auftraten wurden
analysiert und geeignete Masnahmen getroffen um diese zu umgehen.
Das numerische Modell wurde im Anschlus zur Simulation der
durchgefuhrten Experimente verwendet und konnte dabei erfolgreich
verifiziert werden. Die Prognosefahigkeit des Modells wurde durch
die Simulation der Dampfausbreitung im Vorfeld einer Pilot-Sanierung
unter Beweis gestellt.
Die Verknupfung von experimentellen und numerischen Untersuchungen
resultierte in einem verbesserten Prozessverstandnis des untersuchten
Mehrphasensystems. Die fur die Dampfausbreitung in einem gesattigten
porosen Medium relevanten Prozesse und Parameter konnten identifiziert
und Planungshilfen zur Abschatzung der Dampfausbreitung entwickelt werden.read more
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