NO Formation during Oxy-Fuel Combustion of Coal and Biomass Chars

Abstract

The yields of NO from combustion of bituminous coal, lignite, and biomass chars were investigated in O 2 /N 2 and O 2 /CO 2 atmospheres. The experiments were performed in a laboratory-scale fixed-bed reactor in the temperature range of 850− 1150 °C. To minimize thermal deactivation during char preparation, the chars were generated by in situ pyrolysis at the reaction temperature. The NO yield clearly decreased and the CO yield increased when the atmosphere was altered from O 2 /N 2 to O 2 /CO 2 at 850 °C, but only small differences in NO and CO yields were observed between the two atmospheres at 1050−1150 °C. To examine how CO influences the NO yield, the effect of CO on NO reduction over char as well as NO reduction by CO over ash was investigated in the fixed-bed reactor. Furthermore, the influence of CO on the homogeneous oxidation of HCN, possibly a product of the char-N oxidation, was evaluated using a detailed chemical kinetic model. The results indicate that CO influences the NO yield from char combustion through two paths at 850 °C: (1) CO accelerates NO reduction over char and (2) CO accelerates HCN oxidation, increasing the possibility of NO reduction over char. Both effects were more pronounced at 850 °C than at 1050−1150 °C. The present work indicates that the effect of CO 2 on NO formation in oxy-fuel combustion in fluidized beds can partly be attributed to heterogeneous reactions, whereas for high-temperature pulverized fuel combustion, CO 2 mainly affects the volatile chemistry.

Effect of CO2 on N Distribution in Pyrolysis and Oxidation of Volatile N and Char N in Oxy-Fuel Combustion at High Temperatures

“…20,21 CO produced by gasification (RR5) forms a reductive atmosphere around the char surface, which is beneficial to inhibiting the production of char NO and causes char-NO reduction 9,27,28 via RR6−R8=R1. 29 The char-CO 2 gasification reaction becomes more intensive at temperatures higher than 1300 °C; thus, only a little char NO is released after CO 2 oxidation of char at 1300 °C.…”

“…This means that CO 2 has an inhibiting effect on the conversion of char N to char NO. Because of the presence of CO 2 in the atmosphere, char-CO 2 gasification reaction occurs and becomes intensive at higher temperatures. , CO produced by gasification (R ) forms a reductive atmosphere around the char surface, which is beneficial to inhibiting the production of char NO and causes char-NO reduction ,, via R – . The char-CO 2 gasification reaction becomes more intensive at temperatures higher than 1300 °C; thus, only a little char NO is released after CO 2 oxidation of char at 1300 °C. …”

Effects of Temperature and Circulating Flue Gas Components on Combustion and NO<i>_x</i> Emissions Characteristics of Four Types Quasi-particles in Iron Ore Sintering Process

“…10 were consistent with previous investigation. 32,33) The increasing CO 2 concentration promotes the production of CO through R13. CO could either react with NO directly or react with char indirectly to decrease the conversion of fuel-N to NOx and hence suppressing the NOx yield (R10-R12).…”

Justification of the Energy Use of Cedar Husk Waste as an Environmentally Friendly Additive for Co-Combustion with Coal

“…The main problem with the use of granular mixed fuels in small-or large-scale power engineering, the solution for which is necessary when developing technologies for burning such fuels, is that, as established by the results of research [22], the ignition delay times of droplets and particles of any liquid [23,24], solid [25,26], or slurry [27,28] fuels significantly depend on the size of the particles (or droplets) [29]. The larger the size of these particles, the longer the ignition delay time, respectively [30].…”