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Show Ansaldo Energia s.p.a. Tavazzano 5 and 6 Boilers are like La Casella # 3 but, differently from Monfalcone and Casella, gas was available so that the plant arrangement was designed for firing oil and natural gas both at main burners and reburn levels. At present only few tests have been performed firing natural gas in O F A configuration. Figure 19 shows the capability to operate the boiler with the respect of N O x limit (< 200 mg/Nm3 3 % 02) at all loads. The next scheduled optimization of O F A set-up should allow higher N O x reduction while controlling both the C O concentration and the excess air. In any case N O x reduction after L o w N O x burner (TEA # 2) retrofit is about 6 0 % (650 mg/Nm3 3 % 0 2 starting value) and 7 7 % in O F A configuration. Optimization of gas over oil reburn configuration is expected to provide additional margins in respect of oil over oil configuration. Fit It. TAVAZZANO * S . Tam^imt NamwrnJCmt OFA Ctmfifuwmtmm 1 1 .320 MM ,!50«W > ^ t - A ^. |NO. | 1 <=o | isoV 0*0 OH 070 0 75 0*0 0*5 0*0 0J6 l 0O l OS III M l PPCKeratsini Unit 8 This natural circulation boiler, rated 160 MWe, is located in a high populated area (Piraeus) very close to downtown Athens (Greece); for this reason, a "top technology" Low-NOx retrofit has been required by local Authorities as a basic requirement for future Power Plant operation. The original combustion system (20 oil fired barrel burners) has been replaced by a totally new combustion scheme, designed to fulfill the following basic requirements: • 1 0 0 % firing capability both with natural gas (reference fuel) and standard fuel oil (backup fuel) • very Low N O x emission guarantees (160 mg/Nm3 @ 3 % 0 2 for gas firing, 250 mg/Nm3 3 % 0 2 for oil firing) • very low particulate emission at stack (no visible smoke - the plant has no ESP) Apart from technical issues related to gas conversion, the new combustion system has been designed according to the following features (see Fig. 20): • 8 gas/oil fired Low-NOx T E A burners, arranged in 2 rows (front wall) • 6 gas/oil reburn injectors, arranged in a single row and located on the rear wall (orientable nozzles) • 6 O F A injection assemblies, arranged in a single row of 3 on each side wall (each assembly made of 3 orientable nozzles) > .4>...0...«- -e-•©••©••©• < ' 0 0 D -0-4-4-1-4-*. Fig. 20: Keratsini Combustion System Arrangement Additional ducting, upgraded auxiliary machines, new instrumentation and B M S have been also part of the overall supply. The retrofitted boiler has recently come back to service, undergoing a series of tests mainly oriented to combustion system and boiler performance optimization. In gas firing operation (the only operating condition presently allowed by local Authorities), field tests have successfully confirmed the design choices; full load emissions steadily below the target level have been achieved, and a very easy operating philosophy for the L o w - N O x system has been focused, which does not involve any change in the combustion system set-up to follow boiler load variations. -9- |