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Show Both Cold-flow and C F D modeling have shown that the gases concentrations are well mixed at the entrance to the catalyst. Seward Station Cascade Performance Public Service Electric & Gas (PSE&G) and Nalco Fuel Tech concluded an evaluation of combined SNCR/SCR N O x reduction as part of a demonstration of post combustion N Ox control on the Mercer Station pulverized coal, wet bottom utility boiler in 1993. This Hybrid system utilized the urea based N O x O U T ® S N C R process to provide both in furnace N O x reduction and sufficient ammonia to feed a downstream reaction catalyst bed. The Hybrid urea process achieved precatalytic reduction of approximately 50 % firing full load coal and a maximum of 67 % firing gas. These results have shown significant increases in chemical utilization, from 32 % to 63 % for full load firing coal, as compared to stand alone S N C R The Cascade system at Seward Station is expected to provide overall NOx reduction of at least 5 5 % , to 0.35 lb/10A6 Btu, from the 1990 baseline at less than 2 ppmv ammonia slip. The primary injection zone will be significantly cooler and the chemical utilization is expected to increase dramatically from the current S N C R system. Overall chemical flow is not expected to increase. System testing and optimization are currently being completed and results will be presented. Expected performance data is summarized in Table 1. N O x O U T ® S N CR performance was initially designed to achieve 4 2 % reduction with an N S R of 1.3 and a resulting chemical utilization of 3 3 % . Based on preliminary testing, N O x O U T C A S C A D E ® performance is expected to increase to at least 5 5 % reduction with an N S R of 1.2, a decrease in chemical flow, and a resulting overall chemical utilization in excess of 45%. Pending the results of complete testing, which will verify the performance estimates of the catalyst vendors, it will be possible to achieve 6 5 % overall N O x reduction with the addition of catalyst to the reactor vessel. This new design may also require additional convective pass chemical injection, but the total chemical flow rate is not expected to increase significantly. Beyond Phase I Phase II of NOx controls in the United States currently refers to "beyond RACT" controls in ozone nonattainment areas or transport regions, as well as to the statutory acid rain provisions. While the acid rain provisions require that N O x limits be promulgated for remaining utility boilers (from Phase I) by January 1, 2000, other requirements are anticipated by M a y of 1999 for units which must reduce N O x for ozone-related reasons. The "Phase II" requirements will be moderate N O x reductions5 beyond " R A C T " (largely low N O x burners or other combustion modifications), and they will only be required during "ozone season" - five months out of the year. According to the referenced Memorandum of Understanding6, more controls may be required in Phase III in 2003. Such a part-time control requirement, on units already employing primary controls which reduce N O x to 0.38-0.50 lb/106Btu, complicates the consideration of minimizing life cycle control costs. Life-cycle Costs The use of hybrid SNCR/SCR systems permits "tailoring" NOx reduction and life-cycle cost to the potentially complex future requirements of N O x reduction for ozone mitigation. The total life cycle cost of the modified SNCR/SCR N O x reduction process is a function of Page 6 |