Application of selective non-catalytic reduction of NOx in small-scale combustion systems

The selective non-catalytic reduction of NOx has been studied experimentally employing commercial grade urea in a pilot-scale diesel-fired tunnel furnace at 3–4% excess oxygen level and with low ppm of baseline NOx ranging from 65 to 75 ppm within the investigated temperature range. The furnace simulated the thermal behavior of small-scale combustion systems such as small capacity boilers, water heaters, oil heaters, etc., where the operating temperatures remain within the range of 950–1300 K. NOx reductions were studied with the variation of injection temperature, residence time, normalized stoichiometric ratio (NSR) of the reagent, etc. With 5% urea solution, at an NSR of 4, as much as 54% reduction was achieved at 1128 K. The result is quite significant, especially for the investigated level of baseline NOx. The ammonia slip measurements showed that the slip was below 16 ppm at NSR of 4 and optimum temperature of NOx reduction. Finally, the investigations have demonstrated that selective non-catalytic reduction process is quite applicable to the small-scale combustion applications.