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Show N O x control technologies under consideration in the paper are in different stages of research and development. The technologies can be applied to a variety of combustion sources and can reduce N O x emissions typically by 60-90% at a cost that is potentially 2-4 times lower than the cost of SCR. Prospective methods for N 2 O removal are also discussed. To demonstrate the limitations of existing methods and the need for new technologies, commercially available N O x control techniques are briefly described. Then the fast chemical reactions removing nitrogen oxides from combustion products are reviewed, including the major chain routes that are responsible for effective N O x removal. The main part of the paper presents a review of developing N 0 X reduction methods, promising techniques for N 0 X oxidation, and effective means for N2O removal. Finally, the current R & D activities are summarized and future research needs in the field of controlling nitrogen oxide emissions are discussed. Technologies under consideration include ultra low-NOx combustors; improvements to the reburning and S N C R processes; synergistic combinations of reburning - N-agent injection and S N C R - SCR; N O adsorption followed by its recycling to the combustor; non-flame low-NOx alternatives, such as flameless oxidation and unmixed combustion; plasma and electromagnetic methods; and N O oxidation followed by removal of the oxidation products. The following is a brief description of the prospective techniques for removal of combustion generated nitrogen oxides. Ultra Low NQv Burners Fossil fuel combustors with improved efficiency and ultra-low NOx emissions are under development in different countries. There are already natural gas burners with N O x emissions lower than 10 ppm. The U.S. Department of Energy has established a goal to develop a new generation of coal fired burners with 0.10 lb/106 Btu N O x emissions from the combustion process itself without post-combustion controls. The ultra-low N O x coal fired systems operate on the principle of deep fuel and air staging. The initial N O formation is reduced via reducing local stoichiometry during coal volatilization. Delayed mixing of fuel with air allows converting some N O formed on the initial stage of combustion to molecular nitrogen. Additionally, the volatile nitrogen-containing compounds from coal tend to form N2 instead of N O in the oxygen-deficient atmosphere. Reburning with Alternative Fuels Natural gas reburning is currently a mature commercial NOx control technology. Current R&D efforts are directed towards utilization of alternative and waste reburning fuels, such as coal, coal fines, biomass, agricultural residues, carbonized municipal solid waste, Orimulsion, etc. Although the efficiency of N O x control with alternative/waste fuels is typically comparable to that of natural gas, the cost of the fuel is much lower, sometimes even negative, and therefore the cost of N O x control is significantly lower. Hybrid SNCR/SCR Combination of SNCR and SCR can be employed for achieving higher levels of NOx control, minimizing ammonia slip, and improving the cost efficiency since only a portion of the catalyst is required in comparison with S C R alone. In the hybrid method, higher concentrations of ammonia or urea can be injected in the S N C R zone without concern about ammonia slip because the unreacted N-agent participates in N O x reduction downstream in the S C R zone. A much smaller 2 |