Techniques can improve the chemistry of the total combustion zone to reduce NOx emissions. The key parameters that improve the chemical characteristics of the total combustion zone are: (a) a reaction temperature in a range between 1300 ° F and 1900 ° F or so, ideally in a range between 1400 and 1700 ° F; (B) a carbon monoxide concentration less than about 0.5%; and (c) the presence of reducing nitrogen. By adjusting the stoichiometry associated with reburning to obtain a slightly fuel-rich region in which the reducing agent is selectively injected can be obtained at relatively low temperature reductions close to those obtained by the conventional catalytic reduction.
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