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 series of papers developed the theoretical framework of analysis describing thermal venting using nonisothermal gas flow, heat energy transport 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 both 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 venting, where as corresponding removal by normal venting was < 33% for the same time period. Effect of thermal energy was negligible with volatile benzene due to high ambient vapor pressure. Similar results were obtained from the two-dimensional field-scale simulations too. The temperature distribution in the subsurface was affected by simultaneous evaporation of contaminants and moisture condensation from humid air. The simulations also considered the parameter sensitivity to overall recovery. The overall results of this theoretical analysis suggested that thermal venting may be a powerful remediation technique that is applicable to the unsaturated zone when normal soil venting fails to recover the less-volatile fraction of the residual plume. However, the results of this analysis need to be experimentally validated for complete evaluation of the overall technology.