Carbon Filtration for Reducing Emissions from Chemical Agent Incineration (1999) / Chapter Skim
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Appendix D Theoretical Modeling of Adsorption
Appendix D Theoretical Modeling of Adsorption
Pages 72-79
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From page 72... ...
~ Psat ) Mitretek measured adsorption equilibrium data for several compounds and found a useful correlation with the following substitutions: ,B was set equal to the critical temperature, Tc; T/p = reduced temperature, Tr; and W = Vmq, where Vm = liquid molar volume and q = adsorbed phase, mole/kg of carbon.
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From page 73... ...
Although no agent was detected in the trialburn flue gas, they are assumed to be present at the detection limits suggested by Mitretek (see Table D-3~. TABLE D-2 Calculated Partial Pressures for Chlorinated Dioxins Based on 1 ng/m3 Molecular Dioxin Weight p (Pa)
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From page 74... ...
The material balance equation is developed by considering that, at any position in the carbon bed, contaminants are either adsorbed by the carbon or are transported by dispersion and the bulk fluid flow. The governing material balance equation for the fixed-bed adsorption process, excluding fluid phase accumulation, addresses adsorption equilibrium, rate processes for mass transfer and fixed bed dynamics is: Pb at = kfOC(Ci -Ci*
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From page 75... ...
Also, the rate of heat transfer to the adsorbent is assumed to be instantaneous and heat losses to or through the column wall are assumed to be negligible. This simplification of the energy balance was made to permit the simulation of a feed temperature upset and to predict the change in filter temperature due to a change in relative humidity without unduly increasing computation time.
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From page 76... ...
0 + 720 + it oV2 + ~03 Strep /T Psat (E16) where ~ = q/qsat for water q = carbon capacity for water at the relative humidity of the bulk gas, moles of water per unit mass of carbon at the partial pressure, p, of water vapor in the bulk gas phase, moles/kg qsat = carbon capacity for water at 100 percent humidity, moles of water per unit mass of carbon at the saturation vapor pressure Psat of water (100 percent humidity)
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From page 77... ...
Be = Ski, the effective fractional loading of the mixture Bi = fractional loading of the ith component in the mixture, i.e., Bi = qi /qsa~ It is equal to 1 at the saturation vapor pressure of the liquid. The assumption is made that the partial pressure of each adsorbate in the vapor phase is equal to the product of its mole fraction in the adsorbed phase mixture times the vapor pressure it would exert if it were a pure adsorbate and filled the carbon pores to the same extent as the mixture (like Roault's law)
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From page 78... ...
Filter characteristics that need to be specified include the cross sectional area, the filter length, the adsorbent shape factor, carbon particle diameter in millimeters, and bulk density of the carbon in kilograms per cubic meter. Feed stream characteristics that need to be specified include the feed temperature in degrees Fahrenheit, the system pressure in Pascals, the relative humidity, the flow rate in standard cubic feet per minute at 80°F, and the filter operating time in days.
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From page 79... ...
Overall, however, the demonstrated model accuracy is adequate for assessing the fundamental performance issues of dioxin and furan breakthrough times and emission levels relative to detection limits. For a test case based on preliminary ANCDF information, the model has been used to make predictions regarding the capability of the PFS to capture and retain the major chronic risk dnvers, i.e., dioxins and furans, for a reasonable time period and also to determine whether the presence of the PFS could contribute to acute health effects during operational upsets in which the filter would be exposed to high temperatures andlor humidity.
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