Significance of destruction reactions in determining net emission of nitrogen oxides
- Massachusetts Inst. of Tech., Cambridge, MA (United States). Dept. of Chemical Engineering
A system model has been developed by coupling the hydrodynamics with the heterogeneous and homogeneous chemistries for a bubbling fluidized bed combustor in order to explain the observed emission trends of nitric and nitrous oxides as a function of bed temperature, excess air and operating pressure. Reduction of the nitrogen oxides in the bed results in only a small fraction of the nitrogen oxides formed by char oxidation being emitted from the bed. At low temperatures, the concentration of CO in the bed is higher than that at high temperatures. This enhances the NO reduction via the catalytic NO/CO destruction reaction. Increases in N{sub 2}O destruction rates at high temperatures lead to reduction in its emissions. As the excess air is increased, the char loading decreases with a consequent decrease in the reduction of nitrogen oxides over bed char and higher emissions. The destruction of nitric oxide within a single char particle immediately after its formation, however, is enhanced as the oxygen levels increase. At elevated operating pressures both the char loading and the residence time of gases in the bed is high. For these reasons, nitric oxide emissions decrease whereas nitrous oxide emissions pass through a maximum with increases in pressure. This behavior can be explained in terms of a competition between the formation and destruction reactions. Dominance of the destruction reactions in determining the net emissions suggest that the optimal operating conditions should be evaluated in order to maximize destruction within the bed.
- OSTI ID:
- 287948
- Report Number(s):
- CONF-950522--; ISBN 0-7918-1305-3
- Country of Publication:
- United States
- Language:
- English
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