Application of Reburning for NOx Control to a Firetube Package Boiler

Abstract

A 730 kW (2.5 × 106 Btu/hr) firetube package boiler was used to demonstrate the application of reburning for NOx emission control. An overall reduction of 50 percent from an uncontrolled NOx emission of 200 ppm was realized by diverting 15 percent of the total boiler load to a natural-gas-fired second stage burner. Tests indicate that the overall reaction order of destruction with respect to initial NOx is greater than one; thus, larger reductions can be expected from reburning applications to systems with higher initial NOx . Rich zone stoichiometry has been identified as the dominant process variable. Primary zone stoichiometry and rich zone residence time are parameters that can be adjusted to maximize NOx reduction. Reburning applied to firetube package boilers requires minimal facility modification. Natural gas would appear to be an ideal reburning fuel as nitrogen in the reburning fuel has been shown to inhibit NOx reduction.