Reducing Persistently High NO x Emissions and the Risk of Hopper’s Thermal-Fatigue in a 600-MWe low-NO x Down-Fired Boiler Furnace with a Staged Arch-Firing Framework: Effect of the Primary-Burner Location

Abstract

ABSTRACT To address high NO x emissions and the hopper’s overheating environment of a 600-MWe low-NO x down-fired boiler furnace, a staged arch-firing framework (SAF) was implemented. This included an enhanced low-NO x framework, a decreased primary-burner coal/air flux, and a hopper-air arrangement which were regulated for (i) repeated deepening air staging and (ii) decreasing coal/air penetration. To evaluate the primary-burner location effect and confirm the SAF’s viability in resolving these problems, detailed real-furnace measurements and simulations were performed within the original furnace and subsequently within the SAF furnace at primary-burner locations of C b = 0.30, 0.35, 0.40, and 0.45 (C b signifying the dimensionless burner location in the upper-arch depth direction). Increasing C b first improved but then decreased combustion symmetry and the overall low-NO x performance. At C b = 0.40, optimal NO x levels of about 660 mg/m3 at 6% O2 were achieved, along with low carbon levels of about 5% in the fly ash. A comparison before and after the SAF suggests that the SAF effectively shortened the flame penetration and raised both combustion intensity and air utilization for coke combustion downstream. As a result, NO x emissions were reduced by approximately 30% (without affecting burnout). Furthermore, hopper-temperature levels were lowered by about 400 K. These results confirm the viability of the SAF.