Modeling NO−Char Reaction at High Temperature

Abstract

Five Chinese coal chars were prepared in a flat flame flow reactor that can simulate the conditions of real pulverized coal combustion. The kinetics of the NO-char reaction at 1273, 1373, 1473, and 1573 K was studied in a drop tube furnace. A new model of the high-temperature NO-char reaction that took into account the pore diffusion and thermal annealing of char was proposed. The NO-char reaction was predicted by a combination of the model and computational fluid dynamics. Through the comparison of experimental and predicted results, the kinetic parameters for all chars were determined. The predicted results agree well with experimental results at 1273, 1373, and 1473 K, but the model largely underestimates the experimental data at 1573 K. This behavior is explained by a new mechanism of the high-temperature NO-char reaction. In addition, the model successfully normalizes the reactivity of chars with different ranks at high temperature, which is considered to be valuable in predicting the NO reduction on char surface at high temperature.

Models To Predict Kinetics of NOx Reduction by Chars as a Function of Coal Rank

“…While the heterogeneous pathway of NO reduction has been less investigated than the homogeneous pathway, many investigations explore the kinetics and mechanism of the heterogeneous NO–char reaction. Jensen et al and Zhang et al explored the effects of reaction temperature. , Chambrion et al demonstrated a route to N 2 formation from NO by using isotopic labeling of gases and found that N 2 forms from a combination of a surface nitrogen species and the nitrogen from gaseous NO . Chan et al reported the study of the NO–char reaction and found that the reaction rate is first order in NO concentration in addition to exploring the effects of O 2 on the NO–char reduction reaction .…”

“…Their experimental data indicated that lower-rank coal chars were more reactive than higher-rank coal chars. Zhang et al 12 studied five Chinese coal char samples and developed a kinetic model to describe the NO−char reaction behavior and normalize the reactivity of chars with different ranks at high temperature (1273−1573 K). Cances et al 10 reported that the NO reactivity of different solid fuels largely depends on the fuel rank, and the two pathways of NO reduction are competing and predominant at different residence times.…”

The Effects of Coke Parameters and Circulating Flue Gas Characteristics on NOx Emission during Flue Gas Recirculation Sintering Process

“…The generated NOx diffuses, and some are adsorbed on the surface of coke particles to react with their active groups. Combined with previous experiments [21,35,36] and simulation studies, the reaction of NO with coke particles at high temperature is the first-order reaction of NO. The reaction equation of coke particle with NO is Char-C+NO→N 2 +C(O).…”

Importance of volatile AAEM species to char reactivity during volatile–char interactions

“…The detail information about this experiment setup was presented in elsewhere. 34,35 R-form or H-form coal samples were fed into the drop-tube reactor at 12 g h À1 with pure argon as carrying gas (purity 99.999% in volume). The temperature of the reactor was set at 900 C, and under such condition, the sample particles would be heated at a heating rate of 10 4 K s À1 .…”