lecture11

lecture11 - LECTURE 11 SVE & AIR SPARGING DESIGN,...

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LECTURE 11 SVE & AIR SPARGING DESIGN, PERMEABLE REACTIVE BARRIERS
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Soil Vapor Extraction See image at the Web site of Wayne Perry, Inc., Soil Vapor Extraction Systems, http://www.wpinc.com/remedy/remedy30.html Accessed May 11, 2004. Source: Wayne Perry, Inc., undated. Soil Vapor Extraction Systems. Wayne Perry, Inc., Buena Park, CA. http://www.wpinc.com/remedy/remedy30.html. Accessed November 17, 2002.
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SVE Design Vapor transport in the subsurface q a = airflow per unit area [L/T] (specific discharge) k a = apparent permeability of soil [L 2 ] µ a = air viscosity [M/L/T] = 1.8 x 10 -4 g/cm-s = 0.018 cP P a = pressure gradient [(M/L/T 2 )/L] = [M/L 2 /T 2 ] ρ a = density of air [M/L 3 ] 0.0012 g/cm 3 g = gravitational acceleration [L/T 2 ] a a a a P k q µ =
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SVE Design Vapor transport equation is simply Darcy’s Law: KiA A g P g k A P k A q Q a a a a a a a a a a = ρ µ ρ = µ = = () 2 2 2 3 2 2 2 3 2 L L L T L L T L L M T L M LT M T L L M L = = Units:
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Apparent permeability Apparent permeability of soil is closely related to intrinsic permeability but somewhat greater Porosity is decreased by moisture in soil Gas slippage (non-zero velocity at solid surfaces) increases transport Intrinsic permeability approximates apparent permeability in absence of site-specific data
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Gas pressure Absolute pressure is measured relative to an absolute pressure of zero Atmospheric pressure = 14.7 psia = 1 atmosphere psi = pounds (force) per square inch Absolute pressure cannot be negative Gauge pressure is measured relative to atmospheric pressure Define atmospheric pressure as zero = 0 psig Gauge pressure can be negative P gauge = P abs – 14.7 (in psi units)
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Units for gas calculations Volumetric air flow Equipment is based on standard conditions— need to convert to actual conditions for design CFM = cubic feet per minute SCFM = standard cubic feet per minute ACFM = actual cubic feet per minute temp standard 460 temp actual 460 pressure actual atm 1 SCFM ACFM + + × × =
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Units for gas calculations Concentration Concentration is measured and reported in ppmv (parts per million by volume) Convert to mass per volume with: ppmv 273) (T 0.0821 1000 MW atm in P mg/L + × × × =
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SVE design process Test applicability Estimate vapor concentration Estimate removal rate and time Rough estimate Estimate removal rate and time Estimate vapor flow rate Refined estimate Field permeability testing Design Design
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SVE Applicability Nomograph Vapor Pressure (mm Hg) Success Very Likely High (Gravel, Coarse Sand) Weeks Months Months Years Years Weeks Medium (Fine Sand) Low (Clay) Match Point Success Less Likely Success Somewhat Likely Butane Pentane Benzene Toluene Xylene Phenol Aldicarb Naphthalene
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lecture11 - LECTURE 11 SVE & AIR SPARGING DESIGN,...

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