Experimental study of moisture content effects on the transient gas and particle emissions from peat fires

Abstract

Peat fires are a global-scale source of carbon emissions and a leading cause of regional air quality deterioration, especially in Southeast Asia. The ignition and spread of peat fires are strongly affected by moisture, which acts as an energy sink. However, moisture effects on peat fire emissions are poorly understood in the literature. Here we present the first experimental work to investigate transient gas and particle emissions for a wide range of peat moisture contents (MCs). We include drying, ignition, smouldering spread, and even flaming stages. Peat samples conditioned to different MCs were burnt in the laboratory where a suite of diagnostics simultaneously measured mass loss rate, temperature profiles, real-time concentration of 20 gas species, and size-fractioned particle mass. It was found that MC affects emissions, in addition to peat burning dynamics. An increase in MC below a smouldering threshold of 160% in dry basis leads to a decrease in NH3 and greenhouse gas emissions, including CO2 and CH4.The burning of wet peat emits more coarse particles (between 1 to 10 m) than dry peat, especially during the ignition stage. In contrast, flaming stage emits mostly soot particles less than 1 m, and released 100% more fully oxidised gas species including CO2, NO2 and SO2 than smouldering. The examination of the resulting modified combustion efficiency (MCE) reveals that it fails to recognise with sufficient accuracy for smouldering combustion, especially for wet peat with MC >120%. MCE confuses drying and flaming, and has significant variations during the ignition stage. As a result, MCE 2 is not valid as a universal fire mode indicator used in the field. This work fills the gap knowledge between moisture and emissions, and provides a better understanding which can help mitigate peat fires.

Laboratory study on the suppression of smouldering peat wildfires: effects of flow rate and wetting agent

“…The ignition protocol consisted of supplying 100 W for 30 min through an 18-cm coil heater mounted on one side of the reactor, which was 5 cm below the free surface. This ignition protocol can initiate self-sustained smouldering in peat with MC , 160% and IC , 10% (Hu et al 2019). Fig.…”

“…Our sample preparation protocol followed that in previous studies (Christensen et al 2019;Hu et al 2019). A commercially available peat was used (Shamrock Irish Moss Peat, Bord na Mona Horticulture Ltd) owing to its homogeneous properties and batch consistency in the long term.…”

Influence of soil conditions on the multidimensional spread of smouldering combustion in shallow layers

“…Lateral spread is known to decrease with moisture [19][20][21][22], owing to the latent heat of water evaporation requiring energy and time to dry the soil. Additionally, in wet peat, lateral spread rates are faster below the surface than at the top.…”

Estimating Greenhouse Gas Emissions From Peat Combustion in Wildfires on Indonesian Peatlands, and Their Uncertainty

“…This study does not take into account the possible variabilities of MCE because the studies used in the meta‐analysis provided a similar MCE, indicating a smoldering combustion. However, a recent study (Hu et al., 2019), found that the moisture content affected the combustion dynamic, flaming or smoldering, and consequently, the fire chemistry.…”