Biomass blending as a way to reduce NOx emissions during the combustion of biomass residues

The use of biomass as a source of energy through combustion has been subject to growing interest, notably to tackle the issue of climate change. This has caused an increasing demand on woody biomass resources, and led to consider other biomass resources, such as agricultural residues. Among the atmospheric pollutants emitted during biomass combustion are nitrogen oxides (NOx: NO and NO2), mainly originating from biomass N-content in boiler operating conditions. These gaseous compounds notably impact ambient air quality and are involved in the acid rain phenomenon. If NOx emissions are quite low for wood combustion, they can act as a disincentive to the use of agricultural residues, in which nitrogen content is higher than for wood. The aim of this work was to study the effect of biomass blending on the NOx emissions of biomass residues. Grape marc, olive pomace, pine bark, rice husk and wheat and rape straw were used. Pellets of these materials, alone or mixed together, were made and combustion experiments were carried out in a laboratory furnace. O2, CO2, CO and NOx concentrations were monitored at the furnace outlet. A linear correlation was found between NOx emissions and the N-content of biomass residues when burned alone. The NOx emissions of blended pellets, however, could not be linearly correlated to their N-content only. The influence of other biomass constituents than nitrogen on NOx emissions, such as inorganic materials, was thus highlighted and analyzed thanks to several blends and data analyses. (Resume d'auteur)