Three-dimensional modeling of N{sub 2}O and NO{sub x} emissions from circulating fluidized bed boilers
- Ahlstrom Pyropower, Inc., San Diego, CA (United States)
- A. Ahlstrom Corp., Karhula (Finland). Hans Ahlstrom Lab.
In order to understand the conversion mechanisms of fuel nitrogen into N{sub 2}O and NOx pollutants in circulating fluidized bed (CFB) boilers, a kinetic model of N{sub 2}O has been developed and integrated with the existing NO{sub x} kinetic model into the Ahlstrom Pyroflow{reg_sign} CFB combustion comprehensive three-dimensional model. The kinetic model developed in this study considers the detailed kinetics for formation and destruction reactions of N{sub 2}O and NO{sub x}. The fuel-bound nitrogen is split into volatile-N and char-N in the model. Volatile-N is released into NH{sub 3} and HCN gas species, which are the precursors of NO{sub x} and N{sub 2}O, respectively. N{sub 2}O is formed through the homogeneous reaction of HCN and the direct oxidation of char-N with NO. In the N{sub 2}O destruction, the reactions of thermal and heterogeneous catalytic decompositions are considered. The kinetics of N{sub 2}O reactions are either obtained from literature or through bench-scale experiments. Simulations of an 85 MW{sub th} Pyroflow CFB combustor burning coal were performed. The comparison of model predictions and experimental measurements of emission levels serves the purpose of model validation. The oxidation of char-N with local NO plays a very important role in the overall N{sub 2}O emissions. The N{sub 2}O formed through the oxidation of fast released HCN is mostly destroyed during the transport path by the reactions of thermal decomposition and destruction with char and CaO. The slow volatile and char combustion in the upper part of the combustor contributes significantly to final N{sub 2}O emission due to a lower likelihood for destruction. With this new enhancement, the comprehensive Pyroflow CFB combustion model can be used to explain the formation and destruction mechanisms of pollutants, such as SO{sub 2}, NO{sub x}, CO, and N{sub 2}O, and furthermore to study the interrelationship between the pollutants emission and the combustion process.
- OSTI ID:
- 287967
- Report Number(s):
- CONF-950522--; ISBN 0-7918-1305-3
- Country of Publication:
- United States
- Language:
- English
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