Salifou K. Ouiminga

Influence of Ambient Pressure on the Evaporation of Volatile Organic Pollutants (VOP) during Soil Decontamination: Case of the Trichloroethylene (TCE)

This article presents the results on the volatilization of the volatile organic pollutants (VOP) during decontamination process from the soil. The choice of TCE as a volatile organic pollutant is explained by the fact that it is relatively highly soluble in water, compared to other compounds, which excludes any possibility of adsorption of its vapors on the walls of the experimental device during testing. Its saturation vapor pressure very high (≈7700 Pa at 20oC and nearly 12,000 Pa at 30oC) facilitates its monitoring using a pressure transducer relatively less accurate and less expensive. The results obtained on the evaporation of TCE show a linear dependence with the pressure. The coefficient of volatilization is 3.2 times greater for an atmospheric pressure of 90 kPa than for a pressure of 100 kPa. This coefficient would be multiplied by 20 when the pressure passes from 100 kPa to 10 kPa.

Impact of pre-treatment by torrefaction and carbonization on temperature field, energy efficiency and tar content during the gasification of cotton stalks

The present study focused on the gasification of raw and pre-treated cotton stalks (CS) by torrefaction and carbonization. Temperature fields, mass balance, energy balance, energy efficiency and tar content of the gas were investigated for the gasification of different types of biomass materials (raw, torrefied and carbonized CS). High temperature and thick reduction zone were obtained during the gasification of pre-treated CS comparatively to the gasification of raw CS. Thus, the thermal and catalytic cracking of the tars may be more pronounced for the gasification of pre-treated biomass particularly for the carbonized biomass. Mass and energy balances have shown a reduction of biomass conversion during the gasification of torrefied and carbonized CS. Indeed, the energy efficiency of 58.7, 46.5 and 38.4% were obtained for raw, carbonized and torrefied CS, respectively. The lowest energetic performances were found during the gasification of torrefied CS due probably to the severe degree of the torrefaction. However, the tar content in gas was drastically decreased by the pre-treatment of the CS. Indeed, the tar contents of 4.41, 2.24 and 0.10 g/Nm3 were obtained for the gasification of raw, torrefied and carbonized CS, respectively. Key words: Biomass gasification, pre-treatment, tar content, energy efficiency.

Highlighting of a local non-equilibrium thermodynamics during the transfer of trichlorethylene (TCE) in the superficial layers of arid soils

In this paper, we analyse and model the mass transfer of trichloroethylene in the surface layer of soil. Our study essentially focuses on arid soils taking into account the phase change liquid–vapour. We have then examined the validity of the assumption of local equilibrium by comparing the values of instantaneous pressure of the trichloroethylene during transfer process and the equilibrium vapour pressure. It appears that the assumption of local equilibrium during the transfer of trichloroethylene cannot be admitted.