An Advanced Selective Reduction Process for NOx Control.

The combustion of coal and heavy oil produces significant quantities of NOx (NO + NO2), which ultimately participates in photochemical smog and acid rain. Combustion modification schemes, such as staged combustion1 and reburning2, or downstream injection of selective reducing agents, particularlarly ammonia3 and urea4, can significantly reduce NOx emissions, but their effectiveness may be limited by operating constraints. Perry and Siebers5 described a selective reduction process using cyanuric acid, reported to be effective over a broad temperature range. Here we report new data that indicate that the same reductions can be achieved without stainless steel to activate the reaction mechanism, if the process is combined with reburning or staged combustion (or slightly fuel-rich operation in internal combustion) to produce carefully controlled stoichiometry. The NOx reductions that can be achieved with cyanuric acid and other –NH- and –CN-containing compounds at relatively low temperatures exceed those possible with either combustion modifications or selective reduction techniques alone or in normal combination.