Decontamination of Polyaromatic Hydrocarbons from Soil by Steam Stripping:  Mathematical Modeling of the Mass Transfer and Energy Requirement

Abstract

For cleaning of contaminated soil from polyaromatic hydrocarbons (PAH), a thermal separation process is applied. The process uses superheated steam that is supplied through a nozzle together with a suspension (approximately 40% soil content) of the contaminated soil into a tube reactor. In the reactor, the soil suspension is vaporized, and the PAH are stripped from the soil at temperatures of 140-300 degrees C. In a cyclone, a solid-vapor separation is carried out, and after going through a condenser, a separation of the condensed water and the PAH is obtained. For improvement of the economical performance, a heat recovery is integrated. This is realized by preheating the water/stream supplied to the evaporator by cooling the vapor steam leaving the reactor. For the mathematical description of the process, the removal of the PAH from the soil is considered to take place by a desorption process. Sorption isotherms are measured by batch experiments and can be described by isotherms of Langmuir type. A dispersion model is used to describe the mass transfer of the process. The process is mathematically modeled for instationary and stationary operation. The simulation predicts the lowest energy consumption at a good cleaning performance at a steam-to-suspension ratio of 5.

Microwave-assisted stripping of oil contaminated drill cuttings

“…Few workers have specifically studied the remediation of drill cuttings; however, there has been significantly more research carried out into the treatment of contaminated soils, a system which also contains a mineral phase, water and an organic phase. By far the most common method of soil remediation is gas stripping with a heated gas stream, with Lord (1998) and Braass et al (2003) demonstrating steam stripping for the removal of organic contaminants. Enhanced soil stripping processes have also been reported, with Buettner and Daily (1995) demonstrating an air stripping system which utilised electrical heating of the bulk contaminated soil.…”

Combining steam injection with hydraulic fracturing for the in situ remediation of the unsaturated zone of a fractured soil polluted by jet fuel

“…The main NAPL recovery mechanisms with steam injection are (Davis, 1998): (i) the physical displacement by the hot water formed from the condensation of steam, and by the steam itself; (ii) the decrease of the interfacial tension and capillary pressure at elevated temperatures that reduces the residual NAPL saturation; (iii)the decrease of NAPL viscosity, which increases its mobility and the efficiency of its displacement by condensed water (She and Sleep, 1998;Gudbjerg et al, 2004a,b); (iv) the volatilization and steam distillation (Tzovolou et al, 2010); (v) the transport of contaminant vapor in the steam phase (steam stripping) to a condensation front where accumulated light hydrocarbons assist in the reduction of interfacial tension, capillary pressure, and viscosity with similar effect as noted in mechanisms (ii) and (iii). Enhanced desorption of contaminants from the solid surface at elevated temperatures may also occur (Braass et al, 2003).…”

“…A variety of numerical models of different complexity and accuracy have been suggested to simulate steam injection in soils (Shoda et al, 1998;Kuhlman, 2002;Gudbjerg et al, 2004b;Braass et al, 2003;Tse et al, 2006). Experimental and theoretical studies revealed that steam injection is an efficient method of soil remediation for mixtures of volatile and semi-volatile contaminants with low solubility in water (Sleep and McClure, 2001;Schmidt et al, 2002).…”

Static and dynamic sorption of phenanthrene in mangrove sediment slurry

“…The static sorption behavior of PAHs onto soil/sediment has been described by three models. They are the linear model [6,7], the Freundlich model [8,9] and the Langmuir model [10,11]; and these models were evaluated under different situations [12,13]. Salinity was found to be one of the significant factors affecting the biodegradation of PAHs [14][15][16][17].…”