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Show 2 A 165E738.T The State of New Jersey has recently proposed NOx emission limits for the different boiler design categories (Le. wall-, tangential-, and cyclone-frred boilers) as a function of fuel type (Le. gas, oil, coal). Coal-frred cyclone boilers, which had been grandfathered under the original Clean Air Act, will need to reduce NOx emissions from current levels. The New Jersey Department of Environmental Protection and Energy (NJDEPE) defmition of RACT under Title I follows an analysis by the Northeast States for Coordinated Air Use Management (NESCAUM) which suggested that cyclones, through reburning technology, could reduce emissions to 0.6 Ib/MMBtu, equivalent to reductions up to 60 %. Projections were also made by the NESCAUM study that suggested that similar reductions were achievable for cyclone boilers using Selective Non-Catalytic Reduction (SNCR) flue gas treatment. Atlantic Electric, in an effort to comply with the promulgated regulations, embarked on a technology review for their two coal-frred cyclone boilers at B.L. England Station. These units, similar in NOx emission levels to those discussed in the NESCAUM study, have baseline emissions on the order of 1.3Ib/MMBtu (950 ppm, dry, 3% O2). Cyclone boilers represent a unique NOx control problem. The very intense combustion in the cyclone, with corresponding high flame temperatures, typically results in high NOx emissions. The air-rich environment in the cyclone leads to high fuel nitrogen conversion (coal/oil-fIring) and thermal NOx formation. Unlike the tangentially-frred and wall-frred dry bottom units which already have several retrofit NOx control options from which to choose (e.g. low NOx burners, overfrre air ports, etc.) the only technology demonstrated on coal-fued cyclones is reburning technology. The limited applicability of conventional NOx control techniques to coal-fued cyclone boilers is primarily due to the need to maintain slag flow within the cyclone. Although reburning tends to minimize this issue, the B. L. England cyclone units do not have the boiler residence time for conventional coal reburning. Natural gas is also not available in the region in the quantities required for natural gas reburning. Thus, in an effort to comply with the promulgated regulation, Atlantic Electric h~s been assessing the long term applicability and cost effectiveness of SNCR technology as an alternate approach to achieving NOx reductions on its coal-fired cyclone boilers. SNCR has been demonstrated to work on lower temperature boilers. However, there were concerns that at the higher operating temperatures of cyclone boilers, the addition of NOx reductants would not be effective at reducing NOx and could actually increase NOx through oxidation of the nitrogen in the reagent. Recent kinetic modeling done by Nalco Fuel Tech and demonstrated on full-scale units indicates NOx reductions are achievable above 2000°F with higher baseline NOx levels. A one month test was done in the spring of 1993 on B. L. England Unit 1. Reductions in NOx of about 30 %, from a baseline of 1.1 Ib/MMBtu, were achieved at full load, at optimized injector configurations under steady state operating conditions. At low load (87 MWe), NOx reductions over 40% at optimized injector configurations were achieved from a baseline of 1.0 Ibs/MMBtu. No increase in air heater pressure drop was observed during these short term tests, and NH3 emissions at the stack were less than 1 ppmv while post economizer slips were maintained at less than 5 ppmv. Higher reductions on NOx can be achieved but at the expense of increased NH3 slip. Subsequently, a longer term test was carried out to determine the minimum outlet NOx emission rate that could be achieved under full dispatch conditions. The results of the latter test, which took place from December 1993 through March 1994, are presented in this paper. |