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Show DESIGNING LOW-NOx COMBUSTION SYSTEMS 1. ABSTRACT G. De Michele* - S. Pasini* - S. Ligasacchi* L. Tognotti** (*)ENEL-DSR-CRT - Via A. Pisano,120 56100 PISA, Italia (**) University of Pisa - Department of Chemical Engineering New Italian environmental legislation requires that, starting from 1997 and within 2001, a limit to 200 mg/Nm3 NOx emissions for new and old power plants with thermal capacity higher than 500 MW is reached, irrespective of the type of fuel used. To achieve these aims, the strategy of ENEL consists in applying, where possible, NOx reduction techniques directly in the boiler and limiting the use of the most expensive SCR technique just to cut down the NOx fraction exceeding the limits of law. An important role is given to the use of burners which permit a considerable limitation of the formation of nitric oxides. The paper reports the approach followed for the design of Low-NOx burners (TEA) on the basis of the coupling of mathematical tnodelling and experimental studies. 2. INTRODUCTION Nowadays, the study of cotnbustion systems is performed considering the flames as networks of chemical reactors in which the reactions between air and fuel can be tuned through an opportune design of burners and be piloted towards the achievement of conditions which favour the reduction of undesired substances. The easiest technique to reduce the nitric oxides directly within the combustion chamber is the staged-combustion technique. By suitably proportioning air and fuel inside the combustion system, it is possible to form a fuel rich zone where pyrolysis processes, generating radical compounds, are able to reduce nitric oxides. A zone follows where the remaining part of the comburent air is injected to complete the combustion. This alternance of rich and poor zones can be achieved within the flame of a burner. This is the conceptual basis for the design of the so-called "Low-NOx" burners. In order to perform this activity, Enel has developed methodologies for designing and customizing combustion system modification to the specific unit considered. For all the fuels, the burner configuration used has been defined by a theoretical-experimental approach based on the use of mathematical modeling, fluid-dynamic characterization of isothermal models and tests on various experimental furnaces to optimize the combustion performances. Advanced softwa~e and hard:v.are tools were e~ployed for theoretical studies while the Enel plants ofLivorno and S.Gtlla were uttlIzed for the expenmental tests. |