High temperature volatile yield and nitrogen partitioning during pyrolysis of coal and biomass fuels

Nitrogen oxides (NOx) are atmospheric pollutants specifically targeted by legislation which imposes limits on emissions from large scale plant. During combustion, part of the Nitrogen fuel will be released as a component of the volatile matter compounds and as volatile nitrogen, while part will remain in the char. Thus, the fate of volatile-N and char-N becomes crucial for the formation of NOx and, consequently, for determining the concentrations of NO in solid fuels combustion systems. In pulverized fuel combustion, major routes for conversion of the volatile-N are either NO or N2, while char-N reacts through a set of heterogeneous reactions as the char is oxidized. Measuring high temperature char nitrogen content of the fuels directly reduces the likely uncertainty in NOx emissions from solid fuels on modern power stations using deep furnace air staging High temperature volatile-N and char-N partitioning is investigated by pyrolyzing fuels in a high temperature (1600 °C) wire mesh apparatus (HTWM) and analyzing the resulting char. White wood biomass, olive waste, torrefied wood, two bituminous coals and one anthracite coal were used on this study. The volatile yield at high temperatures has been obtained for each sample. The fate of nitrogen released during the pyrolysis as volatile matter and the nitrogen retained in the char has been evaluated for different biomass samples. The nitrogen in the char was measured using a total nitrogen analyzer. Results show a large change in on the volatile yield compared with proximate analysis values for both coals. Only moderate change was observed on the volatile yield for both of the woody biomass that already have high values on proximate analysis, and just a slight increase was obtained on the volatile yield for the olive waste. Differences were found on the fate of nitrogen retained in the char that would lead to NOx formation. The biomass samples release most of their fuel-nitrogen as volatile (between 80 and 95%) while on the coals the volatile nitrogen is wide more variable depending on the coal sample.