Experimental investigation of natural smoldering of char granules in a packed bed

The natural smoldering of a packed bed of wood char granules was investigated experimentally. Parameters characterized experimentally included two types of ignition heaters (a rod heater and a plate heater), a range of four particle sizes (<1, 1–2, 2–3, and <3 mm), different fuel bed heights, and different ignition temperatures. The temperature inside the fuel bed and the concentration of flue gases were measured. Observations and results showed that upward smoldering is affected by many factors, and operational conditions must be rigidly controlled to achieve repeatability, while downward smoldering is stable, and smoldering time is dominated by fuel mass. This is in agreement with our earlier theoretical prediction that upward smoldering is controlled both kinetically and by mass transport, while downward smoldering is dominated only by mass transport. Experiments also showed that smoldering in the reactor is a quasi-one-dimensional process when a plate heater was utilized. Calculated results based on this case are in qualitative agreement with experiments.

► We perform experiments on natural smoldering of char granules in a packed bed.
► Natural upward smoldering is sensitive to operational and environmental conditions.
► Downward smoldering is principally affected by mass of char.
► Experimental results are in agreement with our earlier theoretical predictions.