Reburning in Oxy-Fuel Combustion: A Parametric Study of the Combustion Chemistry

Abstract

The present work investigates reburning reduction of nitrogen oxides in oxy-fuel combustion by means of a detailed reaction mechanism applied to a plug-flow reactor. Reburning reactions, which are known to convert NO x into N 2 , are of special interest in oxy-fuel combustion due to extensive recirculation of flue gases, including NO x , to the flame. Furthermore, the high concentration of carbon dioxide in oxy-fuel combustion is known to influence the radical pool (H/O/OH), which is critical to the combustion chemistry. In the present work it is shown how the changes in the radical pool alter the nitrogen chemistry both directly and indirectly by influencing the formation and oxidation of hydrocarbon radicals. It is shown that reburning is more sensitive to the combustion temperature but less affected by the combustion stoichiometry under oxy-fuel compared to air conditions. The main reasons are the impact of increased CO 2 concentration on hydrocarbon oxidation and the increased importance of CH 3 as a reactant in oxy-fuel combustion.

NO reburning in oxy-fuel combustion: A comparison between solid and gaseous fuels

“…3a) and the major nitrogen species (NO and HCN; Fig. 3b) calculated with N 2 and CO 2 as bulk gas (Normann et al, 2010). The oxidation rate of the fuel is lowered by CO 2 ; the peak concentration of hydrocarbon radicals (CH 1-3 ) is lower and the residence time in the reducing zone (Stage I) is longer.…”

“…Furthermore, the reduction of NO by char is enhanced by the presence of CO, and the reduction could, thus, be of special interest in oxy-fuel combustion where the CO concentration is locally increased. The authors of this work have previously performed a series of investigations on the emission of nitrogen oxides from oxy-fuel combustion Kühnemuth et al, 2011;Normann et al, 2008Normann et al, , 2009Normann et al, , 2010. From the results it was concluded that the emission of nitrogen oxides, related to the amount of fuel supplied, is significantly reduced in oxy-fuel combustion compared to air-firing, because of increased reduction of formed and recycled NO x .…”

“…This alters the oxidation of HCN (Reaction (2) and (3)) formed during the reburning reduction (Reaction (1)). The oxidation of HCN to NO and N 2 has been examined by detailed chemistry modelling (Normann et al, 2010;Mendiara and Glarborg, 2009;Giménez-López et al, 2010). The modelling shows that the split between NO and N 2 depends on similar reactants in both atmospheres.…”

A comprehensive experimental and modeling study of sulfur trioxide formation in oxy-fuel combustion

“…Alongside the sulfur chemistry, nitrogen chemistry in oxy-combustion has also been a focus of several studies (Croiset and Thambimuthu, 2001;Gimenez-Lopez et al, 2010;Glarborg et al, 2003;Kimura et al, 1995;Kuhnemuth et al, 2010;Liu et al, 2005;Tree, 2009, 2012;Mendiara and Glarborg, 2009;Normann et al, 2009Normann et al, , 2010Normann et al, , 2011Obras-Loscertales et al, 2015;Okazaki and Ando, 1997;Watanabe and Okazaki, 2011). Experiments revealed the emission of nitrogen oxides (NO x ) to be significantly lowered in oxy-combustion comparing to that of air-combustion (Croiset and Thambimuthu, 2001;Kimura et al, 1995;Liu et al, 2005).…”

Effects of flue gas recirculation on the premixed oxy-methane flames in atmospheric condition

“…7. However, the methane oxidation follows the three major routes through CH 2 O or CH 2 and the recombination of CH 3 [28]. CH 3 may be consumed through R10 (O þ CH 3 ]H þ CH 2 O) with production of CH 2 O or through R97 (OH þ CH 3 ] CH 2 (s) þ H 2 O) with production of CH 2 , and recombined to CH 4 via R52 (H þ CH 3 þ M]CH 4 þ M, M: third body).…”