THERMAL VENTING TO RECOVER LESS-VOLATILE HYDROCARBONS FROM THE UNSATURATED ZONE .2. MODEL APPLICATIONS

The first part (Kaluarachchi and Islam, this issue) of this two-part s eries of papers developed the theoretical framework of analysis descri bing thermal venting using nonisothermal gas flow, heat energy transpo rt and multicomponent mass transport. The work presented in this paper demonstrated the applicability of thermal venting through a series of numerical simulations in one- and two-dimensional flow domains. In bo th cases, a four-component hydrocarbon mixture consisting of volatile benzene, moderately-volatile n-dodecane, and less-volatile naphthalene and n-hexylbenzene in equal mass fraction was used. The results from the one-dimensional laboratory-scale column simulations showed a total recovery of naphthalene, n-dodecane and n-hexylbenzene by thermal ven ting, where as corresponding removal by normal venting was < 33% for t he same time period. Effect of thermal energy was negligible with vola tile benzene due to high ambient vapor pressure. Similar results were obtained from the two-dimensional field-scale simulations too. The tem perature distribution in the subsurface was affected by simultaneous e vaporation of contaminants and moisture condensation from humid air. T he simulations also considered the parameter sensitivity to overall re covery. The overall results of this theoretical analysis suggested tha t thermal venting may be a powerful remediation technique that is appl icable to the unsaturated zone when normal soil venting fails to recov er the less-volatile fraction of the residual plume. However, the resu lts of this analysis need to be experimentally validated for complete evaluation of the overall technology.