the coking properties of coal at elevated pressures. - Argonne ...

Intrinsic Ratio of Fuel Nitrogen Conversion to Nitric Oxide
The significant magnitude of nitric oxide destruction by char or
other reducing gas suggests that the concentration of nitric oxide
measured at the top of the bed or freeboard did not reflect the intrin-
sic evolution level of nitric oxide from the combustion. Thus the
measured value depended on the relative importance of the rate of "NO"
formation reaction and the rate of "NO" reduction. The experimentally
obtained concentration profiles along the height of the bed and free-
board may verify this mechanism. Information concerning the intrinsic
evolution level of "NO" from char particles is required to describe the
above process quantitatively. The response curve of "NO" formed within
the combustor by the puls input char was measured so that the effect of
the subsequent "NO" reduction by char or other reducing gas could be
minimized. This is shown schematically in Fig.5(a). The response peak
of "NO" formed by the combustion with the reduced intensity of the input
puls tends to a certain value from which the intrinsic ration of fuel
nitrogen conversion to nitric oxide could be evaluated. Typical results
are illustrated in Fig. 5(b). This value seems to be a little smaller
than the value obtained by continuous combustion in a small experimental
facility. This fact suggests that the emission level of nitric oxide is
affected by the intensity of combustion, consequently the steady state
carbon concentration within the bed. However, these results do not
reduce the validity of the experimental results obtained by a small
scale combustion facility concerning the behavior of nitric oxide
emission.
11. KINETICS OF "NO" DESTRUCTION
Rate of "NO" reduction by char')
An isothermal fixed bed tubular reactor of diluted char particles
and activated carbon (char 11, carbon in table 2) was used to measure
the reaction rate over a temperature range which is of practical importance
in fluidized bed combustion. Since the "NO" concentrations
employed in the experiment were of the order of several hundred ppm, the
amount of carbon could be assumed to be constant.
reported elsewhere.
The details were
The reduction of "NO" by char and activated carbon was first order
with respect to "NO" concentration. Figure 6 represents the Arrhenius
plot for char where alpha (a) denotes the ratio of the concentration of
oxygen to the concentration of "NO" at the inlet. Thus the line coresponding
to a=O indicates this rate.
At lower temperature ranges the activation energy for char was
16.3 kcal/mol and coincided with the data reported previously. Above
680T the activation energy was 58.6 kcal/mol. The reason for the
increase in the activation energy has not been explained. In the lower
temperatures the desorption of carbon-oxygen surface complex was considered
to control the overall rate. The gaseous reaction product was
Nz, CO and COz. As the temperature was elevated, the fraction of CO
in the reaction product increased.
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