Experimental investigation on the destruction rates of organic waste with high moisture content by means of self-sustained smouldering combustion

Self-sustained smoldering has been identified as an effective and efficient treatment for waste with high moisture content. To create the necessary conditions for the propagation of a smoldering reaction through the material, the waste is mixed with an inert material, such as sand, to create a porous matrix. This work shows the effect of different experimental parameters (moisture content, fuel concentration and airflow) on the fuel consumption rate during smoldering experiments under robust conditions. Fuel composition was the same for all experiments conducted. The main observation of these experiments is that the consumption rate remains invariant with the original moisture content of the waste, while showing a linear relationship with fuel concentration and airflow. An expression that describes the fuel consumption rate as a function of both parameters is presented. Based on the experimental observations, a kinetic mechanism analogous to the Eley–Rideal model for gas reactions on the surface of a solid is proposed. Finally, an expression that describes the smoldering front propagation velocity as proportional to the airflow and to the inverse of the density of the sand is presented. This expression is verified by 80 smoldering experiments under a wide range of operating conditions and four reactor sizes. The equation can be utilized for every reactor size, moisture content, fuel concentration and airflow rate, so long the smoldering reaction is robust

Thermal and oxidative decomposition of bitumen at the Microscale: Kinetic inverse modelling

Understanding the thermal decomposition of fuels and estimating their kinetic parameters are essential for simulating chemical reactions in numerical models. In this work, 2-step, 3-step, 4-step, and 5-step kinetic mechanisms for bitumen combustion were developed. The kinetic parameters were optimized via inverse modelling (genetic algorithm) by coupling thermogravimetry (TG) and differential thermogravimetry (DTG), conducted at 5, 10, 20, and 40 °C min−1 under nitrogen and air atmospheres. A 3-step mechanism that includes competing pyrolysis and oxidation reactions was identified as the simplest mechanism able to appropriately simulate all TG experiments, thus avoiding the need for more complex mechanisms. A unique set of kinetic parameters was found by averaging all the parameters optimized at different heating rates and atmospheres, resulting in an average error of 6% when compared with experimental data. This is the first time that averaged optimized parameters were employed, providing similar results as optimizing against all experiments at once. Differential scanning calorimetry experiments were used to calculate the heat of pyrolysis and oxidation, and showed that char oxidation provided the highest energy release, whereas bitumen and asphaltene oxidation represented a 30–110 times lower heat of reaction. This is the first time that thermogravimetry and differential scanning calorimetry experiments were used to optimize kinetic parameters for bitumen combustion

Using fire to remediate contaminated soils

Remediation technology based on smoldering combustion is an innovative approach that has significant potential for sites contaminated with organic compounds. Many common industrial contaminants present in the soil are flammable. Combustion of an organic phase contained within a porous medium involves an exothermic reaction, during which heat is transmitted from the burning to the pore space and the solid matrix. Contaminant destruction in such applications is largely dominated by smoldering (as opposed to flaming) combustion. The results described in this paper indicate that smoldering remediation is viable across a considerable range of porous media types and subsurface conditions

Self-sustaining treatment as a novel alternative for the stabilization of anaerobic digestate

5 Tablas.-- 5 FigurasSelf-sustaining smouldering combustion (SSS) is a technology based on the flameless oxidation of an organic substrate and limited by the rate at which oxygen is diffused to the surface of the substrate. This work aims to evaluate the SSS combustion as a treatment process for the stabilization of anaerobic digestate, determining the limits of operational conditions, (moisture content (MC), air flux) that allow for a self-sustaining process. Maximum possible MC was found at 82 wt% with Darcy air flux of 50 cm/s. The digestate destruction rate (kg/(h·m2), and the addition of sand as an inert solid, to enhance the oxygen diffusion, were also investigated. A sand/substrate mass ratio of 1 allowed for SSS at 85 wt% MC, but decreased the digestate destruction rate. The average composition of the emitted gases showed ca. 25% CO and 10% H2, whereas the analysis of the ashes showed almost complete digestate inertization.This research work was funded by the University of Queensland through to the projects UQECR1945969 and UQECR1946429.Peer reviewe

Self-sustaining treatment as a novel alternative for the stabilization of anaerobic digestate

Self-sustaining smouldering combustion (SSS) is a technology based on the flameless oxidation of an organic substrate and limited by the rate at which oxygen is diffused to the surface of the substrate. This work aims to evaluate the SSS combustion as a treatment process for the stabilization of anaerobic digestate, determining the limits of operational conditions, (moisture content (MC), air flux) that allow for a self-sustaining process. Maximum possible MC was found at 82 wt% with Darcy air flux of 50 cm/s. The digestate destruction rate (kg/(h·m2), and the addition of sand as an inert solid, to enhance the oxygen diffusion, were also investigated. A sand/substrate mass ratio of 1 allowed for SSS at 85 wt% MC, but decreased the digestate destruction rate. The average composition of the emitted gases showed ca. 25% CO and 10% H, whereas the analysis of the ashes showed almost complete digestate inertization

Dielectric spectroscopy of artificial faeces for smouldering applications

Our objective is to develop an analysis concept in order to measure the in situ estimation of state parameter, such as water content, during smouldering of waste and sand mixtures. High frequency electromagnetic (HF EM) method presents a high potential for the quantitative estimation of state parameter in porous media. However, it provides indirect measurement: the major challenge is to derive robust relationship between the performed measured permittivity and the parameter under interest. Thus, laboratory measurement of dielectric properties of waste and sand mixtures under controlled boundary are urgently needed. In this preliminary study, the relative effective complex permittivity of artificial faeces was studied over the 50°MHz-3°GHz frequency range with network analyzer technique in combination with homemade open ended coaxial method. In a first step, the effect of water content on dielectric properties was investigated. The results have shown an important dispersion for the imaginary part which can be related to interface process and a systematic increase of the permittivity with water content. In a second step, a shrinking test was monitored with the homemade probe. The relative complex permittivity shows a nonlinear evolution with gravimetric water content and show marked transitions during the decrease of water content. The results of combined investigations have shown the potential of HF EM techniques for quantitative monitoring of the hydraulic state of waste and sand mixtures during smouldering combustion