Industrial boiler retrofit for NOX control:: Combined selective noncatalytic reduction and selective catalytic reduction

A 590 kW (2 MMBtu/hr), oil-fired, three-pass, fire-tube package boiler was retrofit with a combined selective noncatalytic reduction (SNCR) and selective catalytic reduction (SCR) system and demonstrated 85% nitrogen oxide (NOx) reduction with less than 6 ppm ammonia slip A urea-based SNCR solution was injected in the first pass, reducing NOx and providing ammonia reagent for the SCR. A catalyst housing was designed to fit between the second and third passes, where the access doors of the boiler normally attach. The SCR catalyst volume of 0.04 m(3) (1.5 ft(3)) provided a space velocity of 10,000 hr(-1) at a pressure drop of less than 1.5 cm (0.5 in) of water. Numerous runs demonstrated system repeatability and ease of operation. Continued tests using an on-line ammonia monitor, an on-line reagent flow meter, and a different fuel were conducted to show sustained performance and applicability.