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Show Ladyzhin boiler; this modification was made independent of the reburn system in order to correct a pre-existing problem by improving the heat transfer in the boiler's convection section. The preliminary reburn design was completed by the U.S. team prior to notification of the nose modification; however, the project team believed that the nose would not have a significant negative impact on reburn system effectiveness. Initial Reburn System Performance Results Detail design, fabrication, and installation of the system at Ladyzhin followed the preliminary design activities completed in February 1990. System installation was begun during a major unit outage beginning in March 1992, and the unit was back on-line on August 28,1992. Reburn system installation, installation of an aerodynamic "nose" in the boiler, and major equipment maintenance were conducted during the outage. During a meeting held at Ladyzhin on September 21,1992, among the U.S., Russian and Ukrainian team members, very promising early emission results were announced. Pre-retrofit N O x averaged 600 p p m at an economizer outlet 0 2 of 4 percent at 300 M W e . With only 3 weeks of reburn operating experience, N O x was reduced to approximately 240 p p m at an economizer outlet O z of 4 percent, again at 300 M W e . These early tests used 15 percent reburn fuel quantity. N O x was monitored using both a German Testo 33 electrochemical analyzer and a U.S. EPA-supplied T E C O Model 10 A R chemilumi-nescent analyzer. The U.S. analyzer was operated in accordance with E P A test protocols and quality control procedures. These very early data were obtained on a blend of approximately 90-95 percent Ukraine Donetz coal and 5-10 percent Siberian coal. Chemical analysis of these individual coals is shown in Table 3. No immediate operational problems were noted with the reburn system in service. In general, unit operators held the opinion that the boiler was more controllable with the reburn system operational than before system installation. Slag tapping was unaffected at any load between 200 and 300 M W e . At 200 M W e (or below), reburn was shut off to maintain slag tapping ability. Gas temperature entering the backpass convective horizontal superheater varied between 1688 and 1760 °F prior to the installation of the reburn system and aerodynamic nose. Post-retrofit (with the reburn system off) temperatures in this same region were in the 1472 to 1508 °F range, indicating that the aerodynamic nose was improving convective section heat transfer characteristics, as anticipated. With the reburn system in operation, superheat steam temperatures were well within the plant's normal operation levels prior to retrofit. Normal desuperheat spray quantities were used with the reburn system in service, with zero reheat spray required. Use of reheat spray can substantially reduce boiler efficiency, so these early results on steam- side performance with reburn are encouraging. During the initial testing, it was noted, as expected, that the reburn fuel/FGR injection nozzles required a specific nominal quantity of F G R flow in order to keep the nozzle tips below a 1472 °F operating metal temperature threshold. The tip material used is a 1-percent chromium, 18-percent molybdenum, and 12-percent titanium alloy. The burnout air nozzles also required a nominal level of cooling air at all times. Thermocouples on the nozzle tips defined the minimum cooling gas flow conditions at both the 11 |
