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Article
Non-Isothermal Modeling Of Soil Vapor Extraction System Including Soil Temperature Effect

Authors: Talib R. Abbas --- Rafa'a H. Al-Suhaili
Journal: Journal of Engineering مجلة الهندسة ISSN: 17264073 25203339 Year: 2007 Volume: 13 Issue: 1 Pages: 1253-1265
Publisher: Baghdad University جامعة بغداد

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Abstract

Soil vapor extraction (SVE) is a proven effective in-situ technology for the removal of volatile organic compounds (VOCs) from the subsurface. SVE process is highly sensitive to temperature. Studying annual soil temperature variation with depth declares that there is a considerable temperature variation in the upper few meters that may affect the overall efficiency of SVE process.A numerical model was developed to aid in investigation of field-scale soil vapor extraction process. The model is three-dimensional, time dependent that simulates nonisothermal vapor flow and transport of multicomponent mixtures in soil and keeps track of the distribution of each compound in the other three immobile phases (NAPL, aqueous, and sorbed). Rate limited interphase mass transfer with linear driving force expressions were used to model volatilization of oil into gas phase. A local equilibrium partitioning was assumed between gas, water, and solid phase. The model equations were discretized using a standard Galerkin finite element method and solved using set iterative solution algorithm.Simulation of hypothetical field-scale problems was done. The physical domain described a three-dimensional system with flow to a single extraction well. A hypothetical soil temperature variation with depth was incorporated with the model. The result of these simulations showed that this temperature variation has a considerable effect on system efficiency and may play a role in optimum system configuration.

تعتبر عملية استخلاص بخار التربة تكنولوجيا موضعية مثبتة الكفاءة لازالة المركبات العضوية المتطايرة من المنطقة غير المشبعة من التربة. ان هذه العملية حساسة جدا لدرجة الحرارة. من دراسة التغير السنوي لدرجة حرارة التربة مع العمق تبين بأن هنالك تغير حراري لابأس به في الأمتار القليلة العليا من التربة والذي من الممكن أن يؤثر على الكفاءة الكلية لهذه العملية.تم تطوير نموذج عددي للمساعدة في دراسة عملية استخلاص بخار التربة وضمن الأبعاد الحقلية. وهو نموذج ثلاثي الابعاد و معتمد على الزمن والذي يحاكي الجريان و الانتقال متغير الحرارة لأبخرة مخلوطات المكونات المتعددة في التربة مع متابعة توزيع كل مكون في الاطوارالثلاثة الاخرى غيرالمتحركة (الزيتي والمائي و الممتص). تم استعمال نموذج انتقال الكتلة بين طورين ذو المعدل المحدود مع تعبير خطي للقوة الدافعة لنمذجة تطاير الزيت الى الطور الغازي مع افتراض اتزان موقعي لتوزيع الملوث بين الاطوار الثلاثة الغازي والمائي والصلب. حلت معادلات النموذج عدديا وبثلاثة ابعاد باستعمال طريقة العناصر المحدودة التقليدية standard Galerkin finite element methodوباستعمال خوارزمية set-iterative. تمت محاكاة عمليات استخلاص بخار التربة بابعاد حقلية يصف المدى الفيزيائي فيها منظومة ثلاثية الابعاد ووجود جريان بأتجاه بئر سحب واحد. تم ادماج تغير حراري افتراضي للتربة مع النموذج العددي. أظهرت نتائج المحاكات التأثير المهم للتغير الحراري للتربة على كفاءة المنظومة وبينت انها قد تلعب دورا في تحديد الشكل الامثل والابعاد المثلى للمنظومة.


Article
Theoretical Investigation of Pneumatic Soil Vapor Extraction

Authors: Inmar N.Ghazi --- Muhammad A. Abdul-Majeed --- Talib R. Abbas
Journal: Engineering and Technology Journal مجلة الهندسة والتكنولوجيا ISSN: 16816900 24120758 Year: 2011 Volume: 29 Issue: 1 Pages: 96-109
Publisher: University of Technology الجامعة التكنولوجية

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Abstract

Pneumatic Soil Vapor Extraction (SVE) is a new remediation techniquetargeting to improve removal of Volatile Organic Compounds from low permeableareas in heterogeneous soil settings in unsaturated zone. In contrast to traditional SVE,in which soil vapor is extracted continuously by a vacuum pump, pneumatic SVE isbased on enforcing a sequence of large pressure drops on the system to enhance therecovery from the low-permeable areas to enhance removal from areas subject todiffusion limitation. This technique has been shown to be promising at laboratoryscale.A one-dimensional mathematical model was used to study governing factorsand to clarify and quantify the mechanisms responsible for enhanced contaminantremoval during this process. From analytical solution it is clear that the gas phaseinside low permeable area moves with sinusoidal velocity whose amplitude decreaseswith depth. Two zones can be distinguished. First in which the gas phase can reach thehigh permeability area and continuously mixed with clean air, the enhanced removalmechanism is advection. The depth of this zone may range from .05m to .6m. Secondis in which there is no net contaminant advection, the enhanced removal mechanism ishydrodynamic dispersion. The hydrodynamic dispersion coefficient may reach a valuerange from 7 to 700 times the effective molecular diffusion coefficient. In the absenceof non-aqueous phase liquid in the first zone, it can be considered a clean conductivezone and impose no transport resistance on the second zone (i.e. mathematically, theupper boundary can be lowered just below the first zone).The model was tested by comparing its results with experimental resultspublished by a previous study. Overall, comparisons appear to be reasonably good.Investigation shows that pneumatic SVE is promising at field setting. In order for thistechnique has significant removal enhancement the gas phase permeability in the lowpermeability region should be at least on order of 1*10-12 m2 (1 darcy).

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