Downward water mobility in applied smoldering

Wang, Jiahao; Zanoni, Marco A.B.; Rashwan, Tarek L.; Torero, José L. and Gerhard, Jason I. (2024). Downward water mobility in applied smoldering. Proceedings of the Combustion Institute, 40(1-4), article no. 105234.

DOI: https://doi.org/10.1016/j.proci.2024.105234

Abstract

Applied forward smoldering is used in energy-efficient combustion systems to treat high moisture content waste. However, these systems must be operated in a robust manner far from quenching conditions. Quenching can lead to process failure; therefore, it is critical to accurately resolve water transport in different phases throughout space and time to optimize these smoldering systems. In this work, liquid mobility was integrated into a validated smoldering model that previously only included immobile water. The model was applied to a vertical reactor with an upward propagating forward smoldering reaction. Comparisons between mobility and non-mobility models indicate that the water mobility must be considered to accurately simulate both smoldering ignition and propagation in systems with high water saturations. Water mobility during smoldering can lead to two opposing effects: i) water accumulation at the bottom of the pack, which results in large ignition times or ignition failure; and ii) downward displacement of re-condensed water ahead of the smoldering front, which results in robust propagation with high peak temperatures and front velocities. Finally, a sensitivity analysis revealed the influence of operational parameters on water mobility, which can control the fate of smoldering. Tall fuel pack, high permeability, well-sorted particles, and low capillary-bound saturation were found to significantly accelerate water downward mobility and inhibit ignition. Nevertheless, extending the duration of the initial convective heating process and reducing the packing height favored ignition. These results are highly relevant to current industry applications and address a key knowledge gap in smoldering research.

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