Study on the NO_x formation and decomposition mechanism at high temperatures

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In order to suppress the NO_x and N_2O emissions during coal combustion, it is necessary to suppress the formatione of NO_x and N_2O from char nitrogen. The mechanism of HCN formation from pure carbon and gas-phase NO was studied. It was clarified that NO is captured on the char surface and the surface nitrogen species thus formed is converted to HCN and N2. It was also found that the amount of hydrogen is an important factor to determine the HCN formation behavior. In the presence of O_2, HCN formation takes place in a lower temperature region like 600 ℃. This is because the surface nitrogen complexes are activated during the carbon-O_2 reaction.N_2 and NO formation behaviors at a high temperature region between 1000-1300 ℃ were investigated using a specially designed pulse-type reactor. Again it was confirmed that the reaction between the surface nitrogen species with gaseous NO is the main reaction for N_2 formation. N_2/NO ratio in the product gas decreased with increasing char conversion. This indicates the importance of the amount of char for N_2 formation. The temperature increase upon the introduction of O_2 also affects the N_2/NO ratio. This is the first fundamental study on the NO-carbon reaction at a high temperature like 1300 ℃, and the information obtained is useful to understand the NO_x formation in a pulverized fuel combustion system.