The effect of solid CaO on the production of NO{sub x} and N{sub 2}O in fluidized bed combustors: Studies using pyridine as a prototypical nitrogenous fuel

Journal Article · Sat Jun 01 04:00:00 EDT 1996 · Combustion and Flame

DOI:https://doi.org/10.1016/0010-2180(95)00219-7· OSTI ID:251088

Hayhurst, A N; Lawrence, A D ^[1]

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1. Cambridge Univ. (United Kingdom). Dept. of Chemical Engineering

Pyridine is typical of the nitrogenous species found in coal which decompose during devolatilization to yield HCN. Hence, pyridine was burned in an electrically heated bed of sand fluidized by O{sub 2} + N{sub 2}. One product, NO, is found to have a concentration proportional to that of the pyridine in the fluidizing gases. A second, N{sub 2}O, has a concentration proportional to the square of the pyridine concentration. The mechanistic implications of this are discussed; it turns out that the production of NO and N{sub 2}O in this system is different from in a homogeneous gas-phase system. In particular, it appears that CN radicals adsorbed on sand are oxidized relatively rapidly to NO. The presence of 2 wt.% CaO in the bed increases the yield of NO by up to a factor of 20 and decreases that of N{sub 2}O slightly, without changing the dependences of NO and N{sub 2}O on pyridine noted above. The effects of oxygen concentration and temperature are investigated. It appears that CaO promotes a new heterogeneous reaction, whereby species in the pool of HCN and CN radicals are converted relatively rapidly to NO, resulting in a lower yield of N{sub 2}O. Certainly, NH{sub 3} is found to react with CaO to produce NO. Addition of NO to the fluidizing air when burning pyridine establishes that N{sub 2}O is produced by reaction between NO and an intermediate which is most probably the NCO radical. Another effect of the presence of CaO is to reduce emissions of CO. It appears that CO burns catalytically on a CaO surface. Finally, CaO probably catalyzes the reduction of NO and N{sub 2}O.

• OSTI ID: 251088
• Journal Information: Combustion and Flame, Journal Name: Combustion and Flame Journal Issue: 4 Vol. 105; ISSN 0010-2180; ISSN CBFMAO
• Country of Publication: United States
• Language: English

Related Subjects

01 COAL, LIGNITE, AND PEAT
CALCIUM OXIDES
CATALYTIC EFFECTS
CHEMICAL REACTION YIELD
COAL
COMBUSTION KINETICS
CYANIDES
FLUIDIZED-BED COMBUSTION
NITRIC OXIDE
NITROGEN OXIDES
NITROUS OXIDE
PYRIDINE
SORBENT INJECTION PROCESSES