Analysis of high-temperature oxidation of wood combustion particles using tandem-DMA technique

Abstract

Soot particles from combustion sources are known to have significant environmental effects. One of the major sources of soot particles is small-scale wood combustion, and there is an urgent need to develop methods to abate soot emissions from these appliances. The oxidation of soot particles in the combustion chamber is essential for the control of harmful emissions. Thus, the oxidation characteristics of wood combustion particles were studied in a high-temperature tandem differential mobility analyzer using various types of wood combustion particles. These studied particles were generated with a pellet boiler, operated under normal and deteriorated combustion conditions, and with a wood stove. Electron microscopy and chemical analyses, combined with thermodynamic equilibrium calculations, were carried out for interpreting the effect of ash species on the particle shrinking observed at various temperatures. Finally, kinetic parameters for assessing wood combustion soot oxidation under conditions representing the post-combustion zone of small appliances were derived. Pellet combustion soot particles were fully oxidized at 710 °C while wood stove particles were not fully oxidized at 900 °C. This difference is a result of the high alkali metal content in pellet combustion particles, which presumably leads to catalytically enhanced oxidation of soot particles. However, the wood stove particles with low alkali metal content also had lower oxidation temperatures compared to previously studied diesel combustion particles. According to the fitting parameters, about 70% particle reduction could be achieved with one second residence time at 800 °C. These results can be utilized in the development of strategies and technologies to abate soot emissions from small-scale wood-fired combustion appliances.