STARx Technology for Waste Oil Sludge Treatment Investigated with Numerical Modelling

Growing stockpiles of industrial liquid waste stored in lagoons are an outstanding problem worldwide. Self-sustaining Treatment for Active Remediation (STAR) is an emerging technology based on smouldering combustion that has been successfully deployed for in situ remediation of field sites (Grant et al., 2016). STAR is currently being developed as an ex situ treatment system (STARx) for industrial wastes by intentionally mixing them with sand. One engineering concept for STARx is the “hotpad”, for which some initial experiments have been conducted. However, a thorough experimental investigation is challenging due to the cost and time associated with each experiment. This work employed a two-dimensional (vertical cross-section) numerical model to systematically explore sensitivity of STARx hotpad performance to system design, operational parameters, and environmental factors. The phenomenological model that was used uniquely combines a multiphase flow code and a front expansion routine (MacPhee et al., 2012; Hasan et al., 2015). First, the model was calibrated and validated against pilot-scale (~ 2 m width) hotpad experiments, providing confidence that the rate and extent of treatment were correctly predicted. Pilot-scale simulations then investigated the sensitivity of system performance to: injected airflow rate, organic liquid concentration, hotpad configuration, system dimensions, heterogeneity of intrinsic permeability, and heterogeneity of organic liquid concentration. The expected performance of two field-scale configurations (~ 10 m width) was also explored. Hotpad performance is predicted to be most sensitive to the injected air flux, with higher air fluxes achieving higher rates of organic liquid destruction and treating larger fractions of the initial mass. The uniformity of the advancing smouldering front was predicted to be highly dependent on the effective permeability ratio between untreated and treated materials. As a result, increased heterogeneity – of intrinsic permeability in particular – is predicted to degrade remedial performance. Full-scale systems were predicted to achieve treatment rates an order of magnitude higher than the pilot-scale for a similar organic liquid concentration and injected air flux. It is anticipated that this work will increase understanding of several key processes that impact STARx performance and help optimize hotpad design and operation

ENV-654: NUMERICAL MODELLING OF SMOULDERING COMBUSTION TO OPTIMIZE EX SITU SOIL TREATMENT SYSTEM DESIGN

There is widespread soil contamination at thousands of cites in Canada resulting from the historical improper storage and disposal of industrial liquids (Story et al., 2014). Large financial resources are allocated to remediation efforts due to the human and environmental health risks associated with exposure to such contamination, with over $582 million CAN spent on remediation in 2014-15 by the Canadian government alone (Treasury Board of Canada, 2016). Our scientific understanding of site remediation has evolved greatly over the past decades and it is now widely accepted that remediation of the contaminant source zone is necessary to achieve a high level of long-term remediation (Kueper et al., 2014). Non-aqueous phase liquids, or NAPLS, are one of the most prevalent contaminants at contaminated sites and are challenging to remediate due to their highly recalcitrant nature (Kueper et al., 2003). Although many remediation technologies have been developed over the past decades, the challenge in source zone remediation of NAPLs persists. The application of smouldering combustion to treat NAPL contaminated soils has been proven as an effective technology with both the laboratory experiments and applied in situ at a field site (Switzer et al., 2009, Pironi et al., 2011, Switzer et al, 2014, Salman et al., 2015, Scholes et al., 2015). This technology, titled “Self-sustaining treatment for active remediation”, or STAR, utilizes the high calorific value of NAPLs to ignite and sustain a smouldering oxidation reaction, effectively destroying the contaminant in the process. A phenomenological model developed by MacPhee et al. (2012) uniquely combined a multiphase flow model, perimeter expansion model, and analytical expression for the forward smouldering front velocity. This model is able to predict the propagation of the reaction front in response to the interplay between a heterogeneous distribution of permeability and the time-dependent distribution of air flux. After subsequent calibration by Hasan et al. (2014), the model was shown to correctly predict the ultimate extent and time of remediation during treatment for 2D lab scale experiments