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Show chemical utilization and catalyst size and capital requirement. Very high N O x reductions, of perhaps 9 0 % , require a substantial catalyst volume. This system cannot be placed in existing duct dimensions and will always require, at the very least, major modifications. A modified S N C R / S C R system, providing between 50-60% precatalytic reduction, would require between 75-80% further N O x reduction to achieve 9 0 % overall. This would still demand 8 8 % of the original catalyst volume. Similarly, for an overall N O x reduction of 7 5 % , a stand-alone S C R system requires approximately 8 8 % of the original high reduction catalytic volume. (These design computations are graphed in Figure 5.) A modified SNCR/SCR process would conceptually be effective for approximately 75% overall N O x reduction. Precatalytic S N C R reduction of 50-60% requires only 38-50% S C R reduction, and no more than half of the original catalyst volume as designed for 9 0 % reduction. This is also only 5 7 % of the catalyst volume required for stand-alone S C R targeted at 7 5 % overall reduction. A n "in-duct" catalyst m a y be used on a site-specific basis to fulfill this half-sized volume requirement. Prior work at the plant site in development of the commercial-scale SNCR system which exists there indicated that 4 2 % N O x reduction was achieved within the 5 ppmv N H 3 slip constraint. T o achieve this level of reduction with a permanent, commercial system required approximately $14/kW capital. Design N S R for urea reagent is approximately 1.3 for the 4 2 % reduction. Equivalently, this is 3 3 % utilization at full load with substantial improvements at lower load. By contrast, the full-scale SCR installed for the PSE&G demonstration of SCR technology was capable of achieving 9 0 % N O x reduction and more for the several-month investigation. Installed capital cost for the retrofit was reported to be $90/kW.7 The field demonstration of that hybrid SNCR/SCR system verified that on a coal-fired unit, the SNCR-related cost performance can be improved substantially. This installation of induct (existing duct) catalyst on a pulverized coal-fired unit provides a basis of broad applicability to the various types of boilers within this population. Conclusions 1. A Hybrid SNCR/SCR system has been designed and installed for a full scale retrofit of a tangentially fired coal boiler in the Ozone Transport Region. 2. Two types of catalyst have been incorporated into the design to provide insight into the achievable performance of various small in-duct reactors. 3. Extensive CFD and cold flow modeling has been completed to provide the required temperature, velocity, and ash distribution profiles required by the catalyst vendors. 4. Chemical utilization and NOx reduction are expected to increase dramatically as compared to stand-alone SNCR. 5. Hybrid SNCR/SCR is capable of addressing the control requirements for many coal-fired boilers in the Ozone Transport Region with up to 7 5 % N O x reduction. 6. Test results will be presented at this conference. Page 7 |