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Show Enhanced NOx·Reduction in Staged Combustion: Technical Application of Premix Technology in Boilers J. Haumann, A. Knopfli, T. Sattel mayer ASB Corporate Research Centre, Baden, Switzerland This paper describes a new approach to the reduction of the NOx emissions of oil-fired furnaces (oil no.2 and no.6). The potential of air-staged combustion was investigated in an experimental and theoretical research program showing a clear advantage for strong air preheat and the use of a premix burner in the first fuel-rich stage instead of a conventional diffusion burner. Using a premix burner (1 OOkWth), the optimum emissions were less than 60% of those from the best diffusion flame in the presence of fuel bound nitrogen. Optimum residence times under substoichiometric conditions were found to be only 100-lS0ms. Based on the positive results, this novel technique was developed on an industrial scale using a 2-stage-process for medium size boilers, while large scale power plant boilers will require a 3-stage combustion system. In a cooperative project between a power utility and ABB, a pilot plant of lOMWth was built and intensively tested. The influence of air preheat, oil quali-ty, load variations, primary and secondary equivalence ratios were investigated in a parametric study. Optimum emissions of 27-47ppm (3% 02) for oil no.2 and 1 04-119ppmNOx for oil no.6 were measured in a load range of 3- 10.SMWth while CO and UHC emissions were negligible. A residual 02 content of 0.5-1 % in the stack could be established while maintaining low levels of soot emissions. Based on these results, the potential of the large scale 3-stage process could be estimated to be ::;7Sppm NOx for a heavy fuel oil with 0.5%N. |
