The Role of Carbon Monoxide in the NO−Carbon Reaction

Abstract

The enhancement of the NO/carbon reduction reactions by carbon monoxide has been demonstrated for carbons of widely varying nature (coal char, phenolic resin-derived char and graphite). The evidence supports enhancement of NO reduction via a carbon-surface-catalyzed reaction such as NO + CO → 1/2N2 + CO2. This reaction appears to be characterized by an activation energy of around 116 kJ/mol, and by zero order with respect to CO, in the range of CO pressures examined here (up to order 500 ppm). This suggests that an oxide stripping reaction, e.g., CO + C(O) → CO2 + C*, cannot be invoked in its usual form, to explain the rate enhancement. The reaction appears to be first order with respect to NO, at high temperatures and at NO concentrations of above roughly 100 ppm, but kinetic analysis is complicated by the fact that the NO−carbon reaction itself does not have a unique order at low temperatures. It is also shown that kinetic analysis can be greatly complicated in the presence of other oxidizing gases or surface oxides deposited by these gases.

Development of 2nd Generation Oxyfuel CFB Technology – Small Scale Combustion Experiments and Model Development Under High Oxygen Concentrations

“…Since significant amounts of precursors HCN and NH 3 were not measured in the experiments, released nitrogen was assumed to form NO. A similar approach is used widely in the literature [11][12][13].According to the literature, NO can be reduced in the gas phase reaction with NH 3 on the char surface, and in the CO catalysed reaction with solids in the reactor [14][15][16][17]. In this study, formed NO is assumed to reduce to N 2 on the char surface.…”

Role of ash on the NO formation during char oxidation of biomass

“…Reactions of NO with pure carbons [10], coal chars [10] and biomass chars [11] have been investigated extensively at low temperatures and at high temperature exceeding 1000°C. Factors influencing the rate of the reaction between NO and char are, for example, the nature and availability of internal surface area [12], presence of catalytic elements [13], and concentration of O 2 and CO in the gas [14]. The char morphology is influenced by the volatile content of the fuel and the heating rate during devolatilization.…”

Analysis of environmental benefits of CFB combustors via one-dimensional model

“…The reactions of nitric oxide with carbons or chars are of current interest with regard to their possible role in reducing NO emissions from combustion systems. They also offer new useful insights into the oxidation reactions of carbons, generally [13]. A large literature concerning these reactions has developed, as evidenced in three reviews [14][15][16] and by the recent publication of many papers in the area [17][18][19][20][21][22][23][24][25].…”

“…There are great differences in the hydrodynamics between the dense bed and the dilute region. However, most of the models in the literature do not completely take account of the performance of the dense bed, consider the dense bed as well-mixed distributed flow with constant voidage, and use generally lumped formulation [1][2][3][4][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28]. Experimental evidence has been reported by Svensson et al [29], and Werther and Wein [30] that, the fluid-dynamical behavior of the dense bed is similar to that of bubbling fluidized beds.…”

“…The reactions of nitric oxide with carbons or chars are of current interest with regard to their possible role in reducing NO emissions from combustion systems. They also offer new useful insights into the oxidation reactions of carbons, generally [13]. In the model, char reduces NO to N 2 according to the reaction given in Table 1.…”