Engineering Cooling Time and Waste Heat Recovery for Thermal Treatment Beds
Abstract
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.