NUMERICAL MODELING OF PHASE CHANGE DURING BIOVENTING: INFLUENCE OF INJECTION FLOW RATES AND THERMAL CONDUCTIVITY

摘要

This modeling investigation examines the influence of evaporative phase change onrnmoisture content and temperature distributions during a bioventing gas injectionrnoperation for vadose zone remediation. Currently few soil vapor extraction orrnbioventing models incorporate non-isothermal effects when considering systemrnperformance. Laboratory and field measurements suggest, however, that even smallrnchanges in temperature and moisture content can enhance or impair biologicalrnactivity and could thus affect the overall efficiency of a bioventing operation. Thernpresented model is a one-dimensional simulator which describes mass and energyrntransport under steady, gaseous phase flow conditions. The coupled mass andrnenergy equations are solved using a sequential iterative solver with matric potentialrnand temperature as primary variables. A literature-derived relation is used tornquantify the combined effect of moisture content and temperature change onrnbiological growth rates. Radial flow simulations indicate that the injection of gas atrntemperatures and/or water vapor contents different from the initial ambient soilrnconditions can result in microbiologically significant changes in moisture content andrnlocal soil temperature. This investigation identifies that under typical gaseous flowrnconditions up to a 37% reduction in biological activity can occur at the injection wellrnand a 20% reduction can occur up to a radius of 3.5 meters after one year ofrninjection. Sensitivity to thermal parameters is explored, revealing that thernrepresentation of the thermal conductivity strongly influences model predictions.