Wood gasification at fire level heat fluxes

Abstract

This study was motivated by a need to understand the source of pollutant species emitted by wood burning stoves; the results are relevant also to fire research. The study examines the products generated when wood is heated in controlled conditions, without flaming, in atmospheres of varying oxygen concentration (0–21 % O 2 in N 2). Small wood samples (typically 4 × 4 cm exposed face, 2–4 cm thick; mainly white pine and red oak, but also two tests with yellow pine) were subjected to uniform radiative heat fluxes (2–7.8 W/cm 2) on one face. Sample weight was followed in some tests and sample temperature (5 thermocouples in depth) in others since the two measurements could not be made together. In all tests, all evolved products were either monitored (H 2O, CO, CO 2, total hydrocarbons not condensible at −40°C) or trapped and analyzed (condensible organic species) by gas chromatography and mass spectroscopy. Many of the trends of the major products (CO, CO 2, H 2O, THC, total organic condensible or tar) are qualitatively intelligible in terms of the expected impact of varying temperature or oxygen level, for example. The extent of change in these major products is rather limited (factor of two to four) over the range of variables explored here. The organic condensate was difficult to analyze; it is estimated that only 20% of it would pass through a gas chromatograph. More than 40 species in this analyzable portion were positively or tentatively identified and quantified. Chromatographic fingerprints of the organic condensate indicated that its composition does not vary a great deal for the conditions examined here. The fingerprints from the radiative heating tests bear a strong resemblance to those of the smoke condensate from a wood stove.