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Show reburning technology for NOll control from cyclone boilers. This commercial-scale evaluation is justified via the previous EPRI-sponsored (Project RP-1402-30) engineering feasibility study and pilot-scale evaluation co-sponsored jointly by the Electric Power Research Institute (EPRI RP-2154-II) and the Gas Research Institute (GRI 5087-254-1471). The feasibility study revealed that the majority of cyclone-equipped boilers could successfully apply this technology in order to reduce their NOx emission levels by approximately 50 -70% (1). The major criteron that substantiated this potential was that sufficient furnace residence time does exist within these boilers in order to apply the technology. Thus, based upon this conclusion, the next level of confmnation - pilot-scale evaluation - was justified. The pilot-scale tests evaluated the potential of natural gas, oil, and coal as the reburning fuel in reducing NOll emissions (1). The pilotscale data confmned the results of the feasibility study and showed that reburning is a technically feasible and commercially viable technology for cyclone boiler owners. The (cyclone-equipped) pilot test results showed that using coal as reburning fuel provides acceptable NOx reduction and boiler performance despite its low volatility and high fuel nitrogen content as compared to natural gas and oil. Coal was then selected as the reburn fuel at Wisconsin Power and Light (WP&L) Nelson Dewey station. This paper describes the technical approach for designing a reburning system for the Nelson Dewey Unit No.2 boiler. Supportive information on physical and numerical modeling along with pilot-scale and full-scale testing utilized in the design of the retrofit reburning system are also described. BACKGROUND The cyclone furnace consists of a cyclone burner connected to a horizontal water-cooled cylinder called the cyclone barrel (Figure I). This auxiliary furnace is an attractive alternative to conventional pulverized coal (PC) furnaces because it can burn low-grade coals, significantly reduces fly ash in the flue gas, requires less fuel preparation equipment, and allows a reduction in total boiler size. Crushed coal and air are introduced through the cyclone mer into the cyclone barrel. The larger coal particles e thrust out to the barrel walls where they are captured and burned in the molten slag layer which has formed, while the finer particles burn in suspension. The mineral matter melts, exits the cyclone furnace from a tap at the cyclone throat, and is dropped into a water-filled slag tank. The flue gases and remaining ash leave the cyclone and enter the main furnace. No commercially demonstrated combustion modifications have significantly reduced NOx emissions without adversely affecting cyclone operation. Past tests with combustion air staging achieved 15 - 30% reductions. Cyclone slag tapping and tube corrosion concerns due to the resulting reducing conditions were not fully addressed be- 2 cause of the short duration of those tests. Further investigation of staging for cyclone NOx control was halted due to utility corrosion concern. Additionally, since no mandatory Federal/State NOx emission regulation was enforced, no alternative technologies were pursued. Rgure 1. Cyclone Fumat» COAL PIPECRUSHED COAL (1/4- SCREEN) PLUS PRIMARY AIR TERTlARY AlR INLET The recent emergence of the reburning technology offers a promising alternative to conventional combustion controls and SCR systems. Adapting this technology to the inherent characteristics of cyclone boilers was reviewed! determined during the aforementioned B& W engineering feasibility study (1), and confmned in the pilot-scale proofof -concept testing. Based on the results of these studies, it is estimated that a nominal 50% NOx emissions reduction could be achieved from cyclone boilers with the application of reburning. PILOT-SCALE STUDY Experimental Facility B&W's 6-million Btu/hr small boiler simulator (SBS) was utilized to perform the pilot-scale study (Figure ~ . This facility is described in detail elsewhere (1). A short description of the facility pertinent to scale-up is presented here. The SBS is fIred by a single, scaled-down version of B&W's cyclone furnace. Coarse pulverized coal (44% through 200 mesh), carried by primary air, enters tangentially into the burner. Pulverized coal had to be utilized in the SBS instead of crushed coal to obtain complete combustion in this small cyclone. Preheated combustion air at 600- to 8oo-F enters tangentially into the cyclone furnace. The water-cooled furnace simulates the geometry of B&W's single-cyclone, front-wall fIred cyclone boilers. The inside surface of the furnace is insulated to yield a furnace exit gas temperature (FEGT) of 2250-F at the de- |