Small-scale forward smouldering experiments for remediation of coal tar in inert media

Abstract

This paper presents a series of experiments conducted to assess the potential of smouldering combustion as a novel technology for remediation of contaminated land by water-immiscible organic compounds. The results from a detailed study of the conditions under which a smouldering reaction propagates in sand embedded with coal tar are presented. The objective of the study is to provide further understanding of the governing mechanisms of smouldering combustion of liquids in porous media. A small-scale apparatus consisting of a 100 mm in diameter quartz cylinder arranged in an upward configuration was used for the experiments. Thermocouple measurements and visible digital imaging served to track and characterize the ignition and propagation of the smouldering reaction. These two diagnostics are combined here to provide valuable information on the development of the reaction front. Post-treatment analyses of the sand were used to assess the amount of coal tar remaining in the soil. Experiments explored a range of inlet airflows and fuel concentrations. The smouldering ignition of coal tar was achieved for all the conditions presented here and self-sustained propagation was established after the igniter was turned off. It was found that the combustion is oxygen limited and peak temperatures in the range 800-1080 °C were observed. The peak temperature increased with the airflow at the lower range of flows but decreased with airflow at the higher range of flows. Higher airflows were found to produce faster propagation. Higher fuel concentrations were found to produce higher peak temperatures and slower propagation. The measured mass removal of coal tar was above 99% for sand obtained from the core and 98% for sand in the periphery of the apparatus

Organic liquid mobility induced by smoldering remediation

“…has been shown [9] and is expected since smoldering is an oxygen-limited reaction. All of the 30 cm column results are consistent with published experiments of organic liquid smoldering at the same scale [4,6,7,13 and with solid fuel smoldering at small and large scales [9,11]. For these reasons, this will be referred to as 'typical' smoldering behavior and is understood to be representative of no organic liquid migration.…”

“…While not participating directly in the reaction, the sand provides important physical characteristics, such as air permeability, as well as thermal properties, such as heat retention [7,8]. This facilitates the smoldering of the liquids embedded in the pores of the matrix, destroying the liquids and leaving clean sand behind [4].…”

Ex-Situ Remediation Technologies for Environmental Pollutants: A Critical Perspective

“…Maintenance of the peak ignition temperature of 1340 °C for about 9 days completely removed the contaminant mass. Similar studies were conducted by Pironi et al ( 2009 ) and Switzer et al ( 2009 ) where the treatment effi cacy of STAR for removing 99.9 % PAHs and TPHs was confi rmed. Pironi ( 2010 ) also recommended smouldering combustion as a suitable incineration approach to treat soils contaminated with NAPLs.…”

Smouldering combustion as a treatment technology for faeces: Exploring the parameter space

“…That work also examined the influence of water content, where water filled-porosity external to the non-aqueous coal tar fuel resulted in lower peak temperatures and front velocities but did not impede self-sustaining smouldering in the 15 cm tall column. Increased oxygen mass flux has been shown to result in an increase in the smoulder spread rate [17,[23][24][25]. Smouldering temperatures and quenching limits were demonstrated to be a complex function of oxygen supply, convective heat transfer and the thermal properties of the porous medium [17].…”