Experimental Investigation of Smoldering Combustion of Tropical Peat Layer Under Stratified Moisture Content

Considerable amount of experiments regarding smoldering combustion of peat had been conducted through various methods of experiment, modeling, and field study, with factors affecting the smoldering combustion of peatlands include: moisture content, density, porosity, wind speed, etc. However, it can be seen that some researches that focus on the influence of moisture content did not consider the evaporation and drying stages of the smoldering front; thus, the parameters of the test results were determined based on initial moisture content prior to combustion. This experiment was conducted in order to study the smoldering combustion of the peat layer which resembles the real conditions in the field, which involves the stages of preheating, evaporation, drying, pyrolysis, and char oxidation. Varying values of moisture content, increasing with depth, were prepared by drying the raw peat sample (sampling results) at 105 °C for 4, 8, 12, 16, 20, and 24 h. The resulting samples were then placed inside a reactor measuring 10 cm × 10 cm with depth of 20 cm, with each layer of peat with different moisture content at 2.5 cm thick; thus, obtaining a layered peat configuration with the dry peat layer on the surface (MC ~8.5%) and the wet peat layer (raw peat) at the bottom of the reactor. Measurements of smoldering spread, evaporation rate, and mass loss (including evaporation rate) were gathered through instruments of thermocouple, soil moisture sensor, and weight balance, respectively, in real time. The results from the experiment suggested that the evaporation rate, smoldering propagation, and depth of burn depended on the thickness of the burnable dry peat layer, or equivalent to the available amount of heat, which will be partially transferred (converted) for heating, evaporation, pyrolysis, and combustion processes. Therefore, smoldering cannot propagate on the moist peat layer because it will always start with evaporation and drying process. The smoldering front will always be bordered by dry peat layer up to the point where the heat generated is equal or less than the amount needed for evaporation, which is the critical point of extinction.