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<br /> 304 ORDLIEUM CONTAMINATED SOILS ESTIMATES FOUR HYDAoCARBON VAPOR EMISSIONS
<br /> C. = residua! 0 Mcentralion of species i In 9011 (mass-ifmass-soil] The solution to Equation 10,subject to the assumptions discussed above,yry
<br /> Y = depth into contaminated sail pile the following expression for the flux. of volatile species i
<br /> C„ concentration of species I in Vapor phase
<br /> t.� t
<br /> The air-filled void fraction c,t, is a function of the soil moisture content Om, the W 1°a=D.Year C15uQ4 xat
<br /> total residual level of hydrocarbons to soil C.i,(=FSC„ lmass-ifmass-soill), and
<br /> E the total void fraction Er where-
<br /> CDi 1rfi
<br /> E6`r<T $f�ii�6rxPb 11 EA+AsRT(C,, J114,,T) l
<br /> PH,p Fire CA 1
<br /> 1
<br /> where pnA and pNe denote the liquid densities of water and the hydrocarbon As expected, Equation 15 predicts that the emission rate decreases with lir
<br /> mixture The effective porous media vapor diffusion coefficient D„`r' is gener- The average flux, `.f�,i B E, betweent 1=0 and t=r is
<br /> ally calculated by the Millington-Quirk expression t'
<br /> t 31 �ItiiIJ:L Di we('C1•w�- {
<br /> D,1 = a~ (12) %been
<br /> f a
<br /> Equation 16 is expected to provide good eimssions estimates for volatile car
<br /> Again, Q;denotes the molecular vapor diffusion coeflicie,nl for species i in air pounds, until significani depletion of the less volatile gasoline components a
<br /> Without simphf}ing assumptions,Equation 10 must be solved numericatl) be- cur In 5111 Ic einission Pates measured during laboratory experitnents
<br /> cause C„ is dependent on composition, not jusl C, In addition E„ and D,"m will compared with predictions from Equation IG
<br /> change with time due it)the drying process Fortunately, for our purposes(emrs-
<br /> sions from gasohne-contarninated soils) we are typically interested in ectunating �� � Emissions l�Ofi a Soil Venting OpBr trod
<br /> emissions of benzene, which happens to be one of the more volatile compounds
<br /> to gasoline (see Table 1) As a result, bervene volatilizes at a much greater rate Figure 3 depicts a typical soil venlmg operation Vapors are removed Ira
<br /> me components Based an this aahscrvaUon,we can rm+ela:l the soil a[a 'rolumelrlc flowrate 0,,., and then are treated by a vapor#rcalura
<br /> than the majority of gasoline
<br /> this situation as the 3ulatlllzatron of a volatile compound from a relatively tion- unit, which may consist of a vapor incinerator, catalytic oxidizer, carbon ba
<br /> volatile mixture Therefore, we assume that or diffuser stank Of these four options, the greatest emission rate of any call
<br /> pound I occurs when the vapor;.are untreated and discharged through a diffn�
<br /> E„ = constant
<br /> stack at a rate ,omrraci equal to
<br /> D,,df = constant /
<br /> C7, = CAtiStant
<br /> L1 MWeled=QV0.1 C11Lg1 f 1
<br /> Ci, =(C.. M,,.TIC,, M. .) M,,, PI/RT (Equation 4) -'vhere C„,l„denotes the vapor concentration of species i in the extraction uel
<br /> 1 he greatest vapor concentration that can be obtained at any time during kenrnt
<br /> where M,,,T and M., denote the molecular weights of the h)drocarbon nuxture is the equilibrium concentration, C„"�, defined by Equation d When the'rJpnr
<br /> and component I,respeclively We also adopt the following initial and boundary are treated by a process w11h a destriictionfreino%al efficiency -1, then the Cliff
<br /> conditions stun rale will be reduced to
<br /> CrF = Cirs� t 0 81uel1[d=0-11)QYew Cewrm (its
<br /> Ci 1 = 0 y = 0 (13) Typical gasoline-range hydrocarbon destruction efficiencies for Inctneratcirs,tftlI
<br /> y = oo catal}tic oxidizers are >b 95
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