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Show PAPER NO.18 APPLICATION OF REBURNING TECHNOLOGIES FOR NOx EMISSIONS CONTROL ON OIL AND PULVERIZED COAL TANGENTIALLY FIRED BOILERS ~ By R. C. LaFlesh, J. L. Marion , D. P . Towle, and C. Q. Maney ABB Combustion Engineering Systems Combustion Engineering, Inc . ~indsor, Connecticut USA G. DeMichele, S. Pasini, S. Bertacchi Ente Nazionale Energia Elettrica (ENEL) (Italian Power Authority) Rome, Italy A. Piantanida , G. Galli, G. Mainini F .T.C. Legnano s . r .l Legnano, Italy ABSTRACT E~EL has initiated a comprehensive program to comply with air qual ity standards for fossil fuel fired . thermal power stations in Italy that limit NOz em i ssions to 200 mg/ Nm3 (corrected to 3% O2 for oil and gas, and 61 O2 for coal) . Both in-furnace (combustion modifications ) and post-combustion (e . g . SCR ) technologies are being examined . This paper focuses on the in-furnace combustion modification technology of reburning as a means of providing substantial NOz emissions reductions for oil and pulverized coal tangentially fired boilers. Results are presented from testing in ENEL's 50 KWt laboratory scale test facility in Pisa . Italy, ABB-CE's 15-30 MWt pilot scale combustion test facility in Windsor. Connecticut, and ENEL 's 35 MW. tangentially fired utility boiler in Sardinia, Italy . Presented data highlights maximum achievable NOz reductions for the varied reburn test parameters of reburn fuel (natural gas ) quantity, reburn flue gas recirculation quantity and separated and close coupled overfire air quantity . Influence of furnace zone stoichiometries (windbox . reburn , and burnout zones ) on optimized reburn effectiveness is reviewed in deta il . Impacts of reburn system operation on boiler performance are also discussed . Results show that reburning technology offers substantial NOz emissions reductions in tangentially fired boiler applications . INTRODUCTION Ente Nazionale Energia Elettrica (ENEL) , Italy's electricity board , must meet new and more restrictive boiler emission limits . In the case of NOz , these are 200 mg/NM3 (corrected to 3% O2 for oil and gas , and 6% O2 for coal ) for new and existing power stations with a capacity greater than 500 MWt . ENEL is conducting a comprehensive research and demonstration program in order to define combustion modification NOz control options for all boiler types currently in use in Italy (1. 2). ENEL's utility boilers are predominantly of two types ; wall fired designs as supplied by Ansaldo under license from Babcock and Wilcox, and tangentially-fired designs as manufactured by F. Tosi under license from Combustion Engineering, Inc . Application of reburning techn~logy for the reduction of NOz emissions from tangentially-fired boilers is currently being evaluated by ENEL and is the subject of the work reported herein . The research work has been performed jointly by ENEL and ABB Combustion Engineering Systems (ABB-CE) researchers under fund ing by ENEL . Reburning reduces emitted NOz levels by injection of a secondary fuel (preferably low or zero nitrogen bearing) downstream of the main burner system within a boiler . The thermochemical and kinetic mechanisms which comprise reburning involve complex reactions between hydrocarbons introduced as reburn fuel , amine radicals generated under reducing (oxygen-deficient ) conditions, and the NO generated by the main burner system . Fundamental investigations have shown that NO is reduced to N2 either by reacting with amines (NH1 ) or by reacting with CH and/or CH2 to produce hydrogen cyanide which first converts to NH3 , and then ultimately N2. The effectiveness of reburning in reducing NOz is a function of a specific boiler's design (furnace geometry, firing system arrangement , furnace gas residence time, temperature, and mixing history ), the reburn fuel type, and the reburn system's design and operational characteristics . Through fundamental studies, computational modeling , pilot scale experiments, and full scale demonstrations, ENEL is thoroughly evaluating key technical aspects of reburn technology with the objective of recommending its implementation on candidate existing and new tangentially fired boilers throughout Italy . This paper will focus on the following four major areas of ENEL's reburn study: 1 . Bench scale experiments on a 50 KUt furnace 2 . Isothermal and numerical modeling of the reburn process 3 . Pilot scale experiments on a 15 KWt -30 MWt ABB-CE tangentially fired Boiler Simulation Facility (BSF) 4 . Reburn system demonstration on the 35 KW. tangentially oil-fired Santa Gilla Unit U2 |
