Aerosol and carbon monoxide emissions from low-temperature combustion in a sawdust packed-bed stove

Abstract

Low-temperature combustion in biomass-burning stoves used for cooking results in poor thermal efficiency and high emissions. A sawdust packed-bed stove has been shown to give more stable combustion at higher temperatures than woodstoves. The study examines pollutant emissions from this stove and their dependence on stove dimensions, specifically the vertical port radius and the stove-pot spacing. Emission rates of Particulate Matter (PM) - along with size resolution - and of Carbon Monoxide (CO) were measured during steady-state combustion. The stove power increased with increased spacing and vertical port radius. However, the air-flow rate, combustion temperature, and air-fuel ratio showed complex variations with stove dimensions from the described coupling among the pyrolysis, combustion, induced air flow and mixing. Emission rates of PM (0.21–0.36 gh⁻¹ and CO (3–8 gh⁻¹ and were a factor of ten lower than those previously measured from woodstoves. Emission rates of CO decreased, while PM increased, with increasing combustion temperature. Aerosol size distributions were unimodal with Mass Median Aerodynamic Diameters (MMAD) of 0.24–0.40 μ a factor of two smaller than from woodstoves. Cool combustion at 534–625°C gave lower PM emission rates but particles of larger MMAD, while hot combustion at 625–741°C gave higher PM emission rates with smaller particle MMAD. The OC/EC ratio obtained for cool combustion was higher (1.20) than that for hot combustion (0.96). Greater elemental carbon formation was seen at the higher temperatures. PM and CO emission rates followed opposite trends with combustion temperature and stove configuration, resulting in no single configuration at which both CO and PM emissions were minimized. However, its superior thermal efficiency and significantly lower emissions than wood stoves should motivate further study of this device to optimize thermal and emissions performance.