A detailed study of the role of halogens in the inhibition of nitrogen oxide formation in fluidized bed incinerators
- Queen`s Univ., Kingston, Ontario (Canada). Dept. of Chemical Engineering
A laboratory-scale, electrically heated bed of fluidized sand was used to study the effect of chlorine on NO{sub x} and N{sub 2}O emissions during incineration processes. Pyridine (C{sub 5}H{sub 5}N) was burnt, as a model compound, at temperatures between 700 and 900 C in mixtures of O{sub 2} and N{sub 2} to produce NO{sub x} and N{sub 2}O. The concentration of pyridine in the fluidizing air was between 500 and 2000 ppm. The concentrations of NO{sub x}, N{sub 2}O, CO and CO{sub 2} were measured continuously in the freeboard. Chlorine was introduced to the bed as HCl at concentrations up to 6000 ppm. At 900 C in 11.6 vol% O{sub 2}, as the pyridine concentration increased from 500 to 1500 ppm, the concentration of NO{sub x} increased from 225 ppm to 450 ppm. Adding 1000 ppm HCl to the fluidized air mixture, as a source of halogens, caused the concentration of NO{sub x} in the freeboard to decrease by {approximately}25% when burning 500 ppm pyridine and by {approximately}60% when burning 1500 ppm pyridine. At 750 C, adding 1000 ppm HCl to the fluidizing gas caused the concentration of NO{sub x} in the outlet to fall by {approximately}60% independent of the amount of pyridine being burnt. Changing the concentration of O{sub 2} in the fluidizing air from 11.6 to 3.2 vol% had little effect on the effect that HCl had on NO{sub x} emissions. The effect of HCl on the concentration of N{sub 2}O in the freeboard was not so straightforward; at 900 C, HCl caused the concentration of N{sub 2}O to increase slightly; at 750 C, HCl caused the concentration of N{sub 2}O to decrease slightly. Measurements were also made of the concentration of CO in the freeboard during the experiments described above. In contrast to NO{sub x}, CO emissions increased by up to a factor of 20, when 2000 ppm HCl was added to the fluidized mixture while burning pyridine. The effect was most significant at higher temperatures. As with the NO{sub x} measurements, the concentration of O{sub 2} in the fluidizing air appeared to have little effect. The most likely explanation for these results is that HCl consumes OH radicals and hence inhibits the oxidation of CO to CO{sub 2} and the oxidation of fuel-N to NCO, a crucial precursor for NO{sub x} and N{sub 2}O. The effect of temperature and oxygen concentration will be discussed in detail along with possible chemical mechanistic implications.
- OSTI ID:
- 357892
- Report Number(s):
- CONF-9705116--; ISBN 0-7918-1557-9
- Country of Publication:
- United States
- Language:
- English
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