NITROGEN OXIDES BEHAVIOR UNDER OXY-COMBUSTION CONDITIONS

Oxy-combustion is one of the promising technologies to achieve CO2 capture, reducing in this way the emission of this greenhouse gas. In this process the combustion reaction takes place in an oxygen rich environment with CO2 in place of nitrogen. One of the inherent advantages in this technology consists in the reduction of NO emissions given the low N2 coming from the air. However, coal in its structure contains nitrogen which is identified as fuel-N that can have different reactivity under high O2/CO2 partial pressures, as is the case in oxy-fuel combustion. Particularly, N2O emission can be highly affected during fluidized bed oxy-combustion reactions. This study is focused in the evolution of N-complexes to NO, NO2 and N2O (NxOy) from a char with high nitrogen content (PAN-8), obtained by the pyrolysis of polyacrylonitrile at 800 oC. Evolution of CO2, CO, and NxOy species was determined by means of FTIR with a gas cell; spectra were taken every two seconds giving rise to detailed evolution profiles for species of interest. Combustion experiments were carried out at 800 oC under bubbling fluidized bed conditions. In general, it was observed that, mainly NO2 and N2O are significantly affected by the presence of both O2 and CO2 in higher concentrations than in the case of conventional combustion. Increasing in O2 partial pressures promotes the homogeneous oxidation of NO to NO2. Experiments carried out at constant O2 concentration with increments in CO2 partial pressures were evaluated, indicating that CO2 presence affects the net emission of N2O and NO2 by the displacement of gaseous phase equilibriums promoting its formation.