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Show Ansaldo Energia s.p.a. Reducing power boiler emissions via "In Furnace Control" R De Santisn, G Mainini, M. Sala Ansaldo Energia Legnano - Italy r} Speaker Abstract i The very stringent Italian Environmental Regulations have forced ENEL and Ansaldo to implement advanced technologies to control power boiler emissions (NOx, CO, excess Oxygen and Particulate). These technologies have been applied, both in Italy and abroad, on over than 20.000 M W e both on tangentially and front or opposite fired boilers and for different fuels (coal, oil, gas and ORIMULSION). Taking advantage of: a) innovative Low NOx burners design (TEA MK1 & 2 for oil and gas and TEA C for oil and coal) b) new overfire air ports design characterized by extremely low pressure drop c) optimized air staging and reburning techniques it has been possible to attain NOx reductions up to 85%, with no significant impact on boiler efficiency reliability and - most important - without substantially increasing emission level of other pollutants (CO and particulate) or worsening final excess air. Operational N O x levels as low as 90 ppm firing oil have been guaranteed and obtained. Introduction Table 1 reports the emission standards applicable in Italy and Europe. It is also recent information that E P A is proposing to cap N O x emissions in many U S A regions to a level of < 0,15 lb/mmBTU n with the aim of applying said limit nationwide by 2004. According to the to-day available technology above limits can be complied with via in-furnace N Ox reduction firing oil and gas but, except specific cases, cannot be met firing coal, where use of S CR becomes a must. Even firing oil and gas sophisticated techniques must be applied to get the goal. These techniques include : • reducing the peak temperature in the fuel lean flame, by extracting heat with the use of external flue gases recirculation either through the burners (gas mixing) or through the boiler (hopper gas recirculation); • staging the combustion air, to provide a fuel rich/fuel lean sequencing which favors the conversion of fuel bound nitrogen to N2; • staging the fuel (Reburning) to cause a reaction of the N O formed in the flame with hydrocarbon radicals C H to convert N O x to molecular nitrogen The optimization of the combustion system is a difficult process, implying the best trade-off between the minimization of the N O x emissions compatible with acceptable levels of C O and UBC/particulate matter. (*) 0,15 lb/mmBTU correspond to : 239 mg/Nm3 3% 0 2 firing gas 230 mg/Nm3 3% 0 2 firing oil 184 mg/Nm3 6%02 firing coal -1- |