Ignition and Self-heating Risk Assessment of Hydrocarbon Polluted Soils

Abstract

Polluted soils not only pose environmental problems, but can also have an impact on site remediation workers due to pollutant toxicity and flammability. Soil samples were extracted from a polluted site and tests were performed in order to determine their minimum ignition temperature (MIT) in cloud and their self-heating behavior. Their water and volatile contents were also determined. Moreover, soil samples were depolluted by thermal treatment (24 h at 400 °C), sieved and mixed with diesel or eicosane at different concentrations, ranging from 2 to 30 wt%. The influence of the mixing procedure was examined, as well as the effects of the particle size distribution and the pollutant content on the MIT in cloud and thermal stability. It appears that the contaminated soil is prone to self-heating and critical temperatures ranging from 215 to 285 °C were obtained for 8000 to 125 cm3 baskets, respectively. Pre-heating to 100 °C for 24 h leads to a slight decrease critical temperatures, e.g. 265 °C for 125 cm3. The thermal conductivity of the powders was measured and the Frank-Kamenetskii model was used to extrapolate their self-heating behavior to larger storages. While their thermal stability is questionable, the likelihood of a dust explosion remains low, as their MIT was above 900 °C. However, by adding hydrocarbons to the depolluted sample, the MIT decreases upon introduction of 5 wt% pollutant and reaches 490 °C for 25 wt%. eicosane. The nature of the mixing process appears to have little impact on the ignition sensitivity of the samples. In contrast, the particle size distribution has a significant impact on the self-ignition temperatures of the soils. Such quantitative assessment should improve the process safety practices related to the operations of soil excavation, transportation, storage and thermal treatment operations. In addition, a better knowledge of the self-heating behavior of such soils may be useful in view of smoldering remediation.