Biomass fuel characterization for NOx emissions in cofiring applications

This dissertation investigates the impact of various biomass fuels and combustion conditions on the NOx emissions during biomass co-firing. Fossil fuels dominated the energy scenario since the industrial revolution. However, in the last decades, increasing concerns about their availability and environmental risks related with their extensive utilization, together with rising oil prices are favouring the development of renewable energies. Increasing the share of renewable energy sources in the power generation sector is strongly promoted in the EU, and the European Commission has set as goal to double its current global share by 2010. Co-firing biomass and waste fuels with fossil fuels appears as a promising route to introduce renewable fuels in the power sector and reduce CO2 emissions. Biomass co-firing has been implemented at several coal-fired units, generally limited to about 5% of the thermal input. This practice offers several advantages. Besides CO2 emission reduction, it enables flexibility in fuel supply as power operators are not dependent on a constant supply of a particular fuel. Economically, co-firing is encouraged in many countries as fiscal incentives are available for power operators going "green" and emission trading spreads. In order to increase the fired biomass share, an important requirement that has to be met by power operators concerns NOx emissions, as future EU targets tighten. It is therefore crucial to characterize the combustion of biomass and waste fuels with pulverized coal, in order to minimize NOx formation. Experimental and modelling tools have been used to investigate the NOx formation from fuel-bound nitrogen of biomass fuels and coal/biomass mixtures