Master of Engineering Science
Civil and Environmental Engineering
Gerhard, Jason I.
Grant, Gavin P.
Savron Solutions, Canada
Applied smouldering systems harness fixed bed smouldering combustion to remediate contaminated soils and organic wastes. In this technology, contaminants/wastes are embedded or purposefully mixed into a fixed, porous medium, waste treatment bed. Then, a smouldering front is ignited and propagated through the bed, burning away the embedded contaminants/wastes as it travels. At the conclusion of smouldering treatment, only a clean, hot porous bed remains. Ahead of a following treatment cycle, the bed is cooled via air injection and off-loaded from the system to allow for the on-loading of more contaminated material. Due to large system sizes and high temperatures, cleaned bed cooling durations and thermal energy storage can be significant. Therefore, reduced bed cooling durations and stored energy reuse are potential optimizations which can greatly improve system efficiency. In this thesis, novel simulations explore these optimizations for the first time. Increased air fluxes, lower bulk density bed materials, and enhanced wall insulation were identified as practical methods to reduce the bed cooling duration. Also, the stored thermal energy was assessed for reuse in terms of temporal availability, quantity, and quality to provide a preliminary waste heat recovery assessment for these systems. Additionally, new scientific insights are provided which detail how temperature inhomogeneities within a porous bed influences thermally induced air channeling through it, impacting cooling dynamics and heat recovery.
Summary for Lay Audience
Impacted soils (e.g., contaminated with coal tar, PFAS, petroleum hydrocarbon products) can be cleaned by forming them into a pile, then applying heat and injecting air. This causes a smouldering wave (i.e., flameless burning, like on the surface of glowing red charcoals in a barbeque) to move through the pile, burning away all embedded contaminants as it travels and leaving behind only cleaned soil. Similarly, different organic wastes (e.g., biosolids from wastewater treatment plants, sludges from the bottom of oil tanks) can also be disposed of through this method, provided they are first mixed with a porous medium like sand. This approach to waste/contaminant management is highly energy efficient/sustainable as its need for external energy input is relatively minimal. This is because the heat released from the smouldering of wastes/contaminants provides the energy (i.e., heat) input need to keep the smouldering treatment process going.
Ultimately, this process results in a hot pile of clean soil/sand. In commercial smouldering treatment systems, hot cleaned piles are cooled via air injection so that they can be safely unloaded from the system and replaced with more waste/contaminated material in need of treatment. Due to the size of these systems and the high temperatures required for treatment, cooling can take many days as large amounts of heat are held (i.e., stored) in the hot piles. Therefore, the efficiency of these systems can be greatly improved through: (1) reducing the time required for pile cooling, which can increase process efficiency by decreasing overall process cycle times, and (2) reusing the heat held in the piles within the treatment process itself, which reduces system energy consumption and operational costs, making these systems more sustainable.
Through new computer modeling this research identified methods for reducing pile cooling time (e.g., enhancing hot pile-to-air heat transfer rates by increasing the flow rate of air into the pile, using lower bulk density pile materials, enhancing containment wall insulation). In addition, the heat held in these hot piles was assessed for reuse within commercial systems for the first time. Also investigated was how temperature differences within a hot, clean pile can alter the air flow through it and impact cooling. Overall, this research provides important scientific insights and practical findings which can greatly improve this waste/contaminant treatment process as well as other related thermal systems.
Morales, Ryan B., "Engineering Cooling Time and Waste Heat Recovery for Thermal Treatment Beds" (2022). Electronic Thesis and Dissertation Repository. 8381.
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Available for download on Friday, February 10, 2023