Abstract
Biomass (pellets, briquettes, logs) are a key contributor to many countries' strategies for decarbonising heat, particularly in domestic applications. The emissions from these small devices can be high and severely impact air quality, but their levels depend on the design, control, abatement and fuel options. This paper is concerned with the last case. A comparative study shows the emissions from a domestic wood stove for three biomass fuels and their torrefied counterparts. The fuels were burned in a multi-fuel stove along with two reload batches creating continuous combustion cycles: the initial cold start data is presented but not included in averaging and calculation of emission factors. Measurements were made using an FTIR instrument for carbon and nitrogen based gaseous emissions, particulates were measured using a smoke meter with micro-quartz filters as well as a size-selective impactor to obtain the particle size distribution. Particulate emissions were significantly reduced from the torrefied fuels and this is thought to be related to their pyrolysis fingerprint, which was investigated by pyrolysis-GC–MS. NOx was slightly reduced, despite increased fuel-N after torrefaction. In addition, the reduced moisture in the torrefied fuels decreases emissions of CO and CH4 because of increased time of flaming combustion.
Highlights
Biomass utilisation, as with other renewable energy sources, has increased mainly due to global warming concerns
Atiku et al [25] showed that the pyrolysis of wood formed decomposition products, such as furfural, that reacted in diffusion flames and formed fine carbonaceous particles that grew in size and agglomerated into 1 to 2.5 μm diameter particles
This indicated that certain pyrolysis products, such as eugenol, which is typical of lignin decomposition to substituted propylphenols, are highly sooting since they can contribute to the two main routes in soot formation, HACA and via cyclopentadiene formation and reaction
Summary
As with other renewable energy sources, has increased mainly due to global warming concerns. Attention has been given to the domestic use of torrefied biomass, where there have been very few studies [13,14,15], or for the potential use of torrefied biomass in gasification [6,16] In both of these cases there would be significant benefits in improved energy densification, in fuel handling and overall combustion emissions. Further work [26] modelled the mechanism of soot formation This indicated that certain pyrolysis products, such as eugenol, which is typical of lignin decomposition to substituted propylphenols, are highly sooting since they can contribute to the two main routes in soot formation, HACA (hydrogen abstraction, carbon addition) and via cyclopentadiene formation and reaction. Studies of the pyrolysis fingerprints of torrefied biomass versus nontorrefied counter parts [27,28] indicate that some of the more sooting components decrease in concentration after torrefaction and this may partly explain the reduction in fine particulate during combustion of torrefied biomass
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