Advanced In-Furnace NOx Control for Wall and Cyclone-Fired Boilers
- The Babcock & Wilcox Company, Barberton, OH (United States)
A NOx minimization strategy for coal-burning wall-fired and cyclone boilers was developed that included deep air staging, innovative oxygen use, reburning, and advanced combustion control enhancements. Computational fluid dynamics modeling was applied to refine and select the best arrangements. Pilot-scale tests were conducted by firing an eastern high-volatile bituminous Pittsburgh No.8 coal at 5 million Btu/hr in a facility that was set up with two-level overfire air (OFA) ports. In the wall-fired mode, pulverized coal was burned in a geometrically scaled down version of the B and W DRB-4Z® low-NOx burner. At a fixed overall excess air level of 17%, NOx emissions with single-level OFA ports were around 0.32 lb/million Btu at 0.80 burner stoichiometry. Two-level OFA operation lowered the NOx levels to 0.25 lb/million Btu. Oxygen enrichment in the staged burner reduced the NOx values to 0.21 lb/million Btu. Oxygen enrichment plus reburning and 2-level OFA operation further curbed the NOx emissions to 0.19 lb/million Btu or by 41% from conventional air-staged operation with single-level OFA ports. In the cyclone firing arrangement, oxygen enrichment of the cyclone combustor enabled high-temperature and deeply staged operation while maintaining good slag tapping. Firing the Pittsburgh No.8 coal in the optimum arrangement generated 112 ppmv NOx (0.15 lb/million Btu) and 59 ppmv CO. The optimum emissions results represent 88% NOx reduction from the uncontrolled operation. Levelized costs for additional NOx removal by various in-furnace control methods in reference wall-fired or cyclone-fired units already equipped with single-level OFA ports were estimated and compared with figures for SCR systems achieving 0.1 lb NOx/106 Btu. Two-level OFA ports could offer the most economical approach for moderate NOx control, especially for smaller units. O2 enrichment in combination with 2-level OFA was not cost effective for wall-firing. For cyclone units, NOx removal by two-level OFA plus O2 enrichment but without coal reburning was economically attractive.
- Research Organization:
- The Babcock & Wilcox Company, Barberton, OH (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- FC26-05NT42301
- OSTI ID:
- 1037870
- Country of Publication:
- United States
- Language:
- English
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