The objective of this work was to study the effect of major factors
such as mixing time, temperature, O2 concentration and residence
time on the SNCR process in a PFR where the mixing process
plays an important part. Meanwhile, a detailed mechanism has
been proposed to quantitatively predict the dynamics of all N-containing
species including NH3.
The major experimental results are as follows: the mixing process
comes into play only at higher temperatures, i.e., higher than
optimal temperature. At lower temperatures enriched O2 enhanced
NO reduction and N2O yield, with more NH3 being consumed. At
higher temperatures, increasing O2 inhibited NO reduction and
suppressed N2O formation, with the depletion of NH3. NO2 yield
was always enhanced by increasing O2, especially at lower temperatures.
Extending residence time progressively shifts the optimum
temperature for NOx reduction to lower values, but for a
sufficiently long residence time the optimum temperature finally
settled at 1173 K.
The detailed mechanism developed in this work gave qualitative
and quantitative agreement with our experimental data of
all N-containing gases. Evaluation against several independent
works illustrates the mechanism’s capability to predict for cases
with or without mixing process within tolerable uncertainty. However,
evaluations against non-premixed reaction system with short
residence time show the approach adopted to treat mass transfer
overestimates the mixing rate, leading to opposite deviations in
different temperature regions. However, this flaw is barely
observed if a longer residence time is available.