NO{sub x} formation and reduction with NH{sub 3} in fluidized bed combustion -- The influence of the O{sub 2} concentration on the kinetics
In (circulating) fluidized bed combustors, NO{sub x} and N{sub 2}O emissions originate mainly from nitrogen in the fuel. The formation of NO{sub x} and reduction to N{sub 2} follow complicated reaction paths involving both homogeneous and heterogeneous reactions. In these reaction paths oxygen plays an important role. When air staging is used in a (circulating) fluidized bed combustor, the O{sub 2} concentration in the combustor varies over a broad range. Limestone, used as a sorbent for sulfur retention, is a good catalyst for the formation of NO{sub x}. In this study the influence of the O{sub 2} concentration is investigated on homogeneous reactions and on reactions catalyzed by limestone. In a fixed bed reactor the NO formation and reduction reactions are studied at 850 C. With a kinetic model, rate expressions for the NO formation and reduction reactions are obtained from experimental data. The results show, that the O{sub 2} concentration has an influence on the homogeneous formation and reduction of NO, which differs from most literature that assumes a zero dependency. For the reactions catalyzed by CaO, no influence of the O{sub 2} concentration was found. Rate expressions for the homogeneous reduction and oxidation reactions that are O{sub 2} dependent, give a good description of the O{sub 2} influence on the homogeneous NO formation and reduction. The rate of the reduction reaction was similar to the one reported by Jensen et al. (1995). The rate of the oxidation reaction is found to be 50% lower. For the heterogeneous oxidations, O{sub 2} independent rate expressions are obtained that give a reasonably good description of the NO formation. The O{sub 2} dependency found in the heterogeneous experiments is caused by the homogeneous reactions that are O{sub 2} dependent. The rate constants of the heterogeneous reaction found in this work are significantly higher than the ones found by Johnsson (1990). With the model developed in this work, it is possible to predict the influence of O{sub 2} concentration on the emissions of NO and NH{sub 3}.
- Research Organization:
- Delft Univ. of Technology (NL)
- OSTI ID:
- 20006817
- Report Number(s):
- CONF-990534--
- Country of Publication:
- United States
- Language:
- English
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