THERMAL VENTING TO RECOVER LESS-VOLATILE HYDROCARBONS FROM THE UNSATURATED ZONE .1. THEORY

Thermal venting is a remediation technique suitable to the liquid unsa turated zone to enhance recovery of less-volatile residual hydrocarbon contaminants. Thermal venting is different to traditional soil ventin g because heated air instead of air at ambient conditions is applied t o the contaminated zone. The vapor pressure of a less-volatile contami nant is typically increased by temperature causing the gas-phase conce ntrations to increase by three- to five-fold over a temperature increa se of 20-30-degrees-C. The work described in this first paper provides the theoretical framework of analysis related to thermal venting. The analysis included nonisothermal gas flow, thermal energy transport an d multicomponent mass transport in a multiphase porous medium. The tra nsient gas flow analysis included the effect of temperature on fluid p roperties and gas compressibility. The heat energy transport analysis was performed under the thermodynamic equilibrium condition with phase -summed effective thermal properties. Multicomponent mass transport wa s performed under local equilibrium for partitioning between phases. M odel verification was performed to the extend possible using analytica l and available experimental data for different physical processes. Th e second paper of this two-part series will demonstrate the applicabil ity of thermal venting technique through numerical simulations of hypo thetical laboratory and field-scale scenarios.