The amounts of NO{sub x} and N{sub 2}O formed in a fluidized bed combustor during the burning of coal volatiles and also of char
- Cambridge Univ. (United Kingdom). Dept. of Chemical Engineering
Three quite different coals were burned batchwise in electrically heated beds of sand fluidized with O{sub 2} and N{sub 2} at either 800 or 900 C. The concentrations of NO{sub x}, N{sub 2}O, CO, and CO{sub 2} in the off-gases were measured as functions of time whilst the coal was burning. It proved relatively easy to separate the emission of any one of these gases into that from the initial, devolatilization stage of combustion and that from the subsequent burning of the char. Lower concentrations of O{sub 2} resulted in slightly less N{sub 2}O and NO{sub x} being produced. The rates of production of NO{sub x} and N{sub 2}O during combustion of the volatiles were found to be proportional to one another. This seems to derive from a lack of mixing of the volatiles. The fact that large (>1 cm) coal particles float on top of a fluidized bed during devolatilization is important and, e.g., can result in large particles producing less NO{sub x} and N{sub 2}O during devolatilization than tiny particles. The observations made during devolatilization conform to effectively all the fuel-nitrogen in the volatile matter being converted to HCN. Nitric oxide is then produced most probably heterogeneously on the sand from CN radicals, which alternatively can yield NCO radicals. N{sub 2}O is generated during devolatilization by the reaction NCO + NO {yields} N{sub 2}O + CO occurring, probably in the gas phase. As for the burning of char in a fluidized bed, the particle size (>1 mm) here is large enough for there to be control by mass transfer of oxygen to a particle. Oxidation is thus confined to the exterior of the char. It appears that CO, from burning char, is important in converting NO to N{sub 2}. This is why the yield of NO from char-N is less than that from volatile-N.
- OSTI ID:
- 251075
- Journal Information:
- Combustion and Flame, Journal Name: Combustion and Flame Journal Issue: 3 Vol. 105; ISSN CBFMAO; ISSN 0010-2180
- Country of Publication:
- United States
- Language:
- English
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