Carbon Emissions from Smouldering Peat in Shallow and Strong Fronts

Abstract

A series of experiments of shallow and strong smouldering fronts in boreal peat have been conducted under laboratory conditions to study the CO and CO2 emissions. Peat samples of 100 mm by 100 mm in cross section and 50 mm in depth were smouldered in the cone calorimeter apparatus. Two laboratory variables, moisture content and the external heat flux are varied over a wide range of values to establish different burning rates and front thicknesses. This provides a novel framework to study smouldering dynamics by varying the controlling mechanisms and providing burning conditions that otherwise cannot be obtained. Measurements of the burning rate and gas flow, yield and ratio for CO and CO2 are reported at steady state burning conditions. Average mass flow rates per area of smouldering front are reported here for the first time to be 0.27±0.09 g/s/m^2 for CO and 0.65±0.24 g/s/m^2 for CO2. This CO2 mass flux is about 3,000 times larger that the natural decomposition flux from peatlands. The CO yield in dry base is 17±3% g/g and the CO2 yield 42±13% g/g. The CO and CO2 total yield is of 59±15% g/g, and the CO to CO2 ratio was measured on average 0.43±0.12. The results indicate that peat with high moisture content smoulders producing larger CO2 yield but the same CO yield compared to dryer peat. This suggests that smouldering of biomass at lower moisture contents develops wider pyrolysis fronts that release a larger fraction of other carbon-containing gas species.