PM reduction and flame confinement in biomass combustion using a porous inert material

Abstract

The present study aims to determine the effects caused by the inclusion of a ceramic porous material in an experimental biomass combustor. The burner is an underfed fixed-bed facility that allows air staging wood pellet burning. Air staging determines the proportion of air entering by the primary inlet below the bed and the secondary inlet above it. The value used is 30/70 (%primary/%secondary). Due to the inclusion of a porous inert material (PIM) in a specific place in the combustor, the outlet gas flow from the combustion chamber is unaffected, but the behaviour of the combustion process is remarkably altered. Tests are performed by changing the total air flow from 0.223 kg/m2s, 0.279 kg/m2s and 0.334 kg/m2s and the position of the PIM at heights of 380 and 540 mm above the bed. The results show a significant reduction in particulate matter (PM) emissions, with some quantities reaching a reduction above 50% of the original values. The best results are achieved with the material positioned closest to the bed but always above the secondary air inlet. The concentration and distribution of PM were studied. Preliminary results of analysing the temperature profile along the combustor gas phase suggest that the effect of PIM inclusion is flame confinement. A higher rate of radiation is reflected back to the bed (solid combustion) due to the PIM insertion, increasing the temperature of the whole volume beneath. This temperature increase could slightly improve the combustion process in the gaseous phase, leading to a decrease in pollutant emission formation (especially PM).