Steam Stripping of Contaminated Unsaturated Zone of Subsoils: Theoretical Model of Start‐up Phase

Abstract

The present paper addresses the unsteady process of steam stripping of the unsaturated zone of soils contaminated with volatile nonaqueous phase liquids. First, on the basis of Darcy's law and the conservation laws of mass and energy, a one-dimensional model is derived for the propagation of the steam front in the start-up phase. It is shown that this process is governed by one dimensionless group y. Subsequently, the evaporation mechanism behind, the transport to, and the condensation at the front of volatile contaminants are considered, taking the view that nonequilibrium exists between liquid and vapor phases. The model leads to a moving boundary problem which is of special mathematical interest. By a suitable transformation of the governing partial differential equations, the problem is brought into a fixed domain and solved numerically. For a broad range of the governing dimensionless numbers, computation results are presented. The results obtained in this paper make clear the role of the prevailing principal physical phenomena during the start-up phase of the process.

Organic contaminant transport and fate in the subsurface: Evolution of knowledge and understanding

“…The potential for NAPL to move into previously NAPL-free zones, such as sinking of mobilized DNAPL [Grubb and Sitar, 1999;Jin et al, 2007], is a risk associated with these enhanced remediation methods but hydraulic gradient control may be used to limit such movement and enhance NAPL capture [Lunn and Kueper, 1997]. Steam injection has been shown to be effective at mobilizing and vaporizing NAPL [Brouwers and Li, 1995;Falta et al, 1992aFalta et al, , 1992bHunt et al, 1988aHunt et al, , 1988bOchs et al, 2010;van der Ham and Brouwers, 1998]. Alcohol flooding, injection of a mixture of water and alcohol, is used to reduce interfacial tension, mobilize NAPL, and enhance dissolution [Lunn and Kueper, 1997].…”

Steam stripping of the unsaturated zone of contaminated sub-soils: The effect of diffusion/dispersion in the start-up phase

“…where D is the coefficient of diffusion/dispersion. This formulation differs from that of Brouwers and Li (1995) in that it includes diffusion and dispersion.…”

“…In comparison with the analysis of Brouwers and Li (1995) the presented model accounts for diffusion/dispersion and for a non-negligible saturation of vapour phase S v . Conditions ( 17) and ( 19), and therefore ( 18) and ( 20) can also be derived as macroscopic boundary conditions following the treatment of such conditions in (Bear, 1979).…”

“…When moreover e = 0, i.e. saturation in vapour phase is neglected, the system reduces further to precisely that analyzed by Brouwers and Li (1995).…”

“…In improvement on the earlier studies, here the mass of vapour behind the steam front is not neglected, and, diffusion/dispersion of the contaminant in the steam phase is retained. Analogous to Brouwers and Li (1995), a one-dimensional situation is considered. This is useful for interpreting column experiments and for verifying more complicated numerical models.…”